Rubber compositions, vulcanized rubber for tire treads, tires, and rubber tracks

Abstract

The objective is to provide a rubber composition that maintains ozone resistance without the need for the antioxidant 6PPD, while using environmentally friendly chemicals. [Solution] 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)

Description

[Technical Field]

[0001] The present invention relates to rubber compositions, vulcanized rubber for tire treads, tires, and rubber tracks. [Background technology]

[0002] Generally, the various rubber components that make up tires and the like can deteriorate under the influence of external environmental factors such as the presence of ozone, and as this deterioration progresses, cracks and other damage may occur. To address this problem, rubber compositions containing anti-aging agents are often applied to the various rubber components that make up tires and the like. For example, Patent Document 1 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 constituting the surface of a tire, cracks and discoloration of the tire surface can be suppressed. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056384 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (anti-aging agent 6PPD) used in the above-mentioned Patent Document 1 may have environmental impacts, and considering the possibility of future regulations under European law, it is desirable to use an anti-aging agent that has a lower environmental impact. Therefore, it is conceivable not to use the anti-aging agent 6PPD in the rubber composition, but 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 chemicals that have a low impact on the environment. 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. [Means for solving the problem]

[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, The aforementioned vulcanization accelerator includes a thiram-based vulcanization accelerator. The aforementioned antioxidant is a rubber composition that 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 anti-aging agent, B represents the descriptor MinAbsEStateIndex of the anti-aging agent, C represents the descriptor SlogP_VSA7 for the anti-aging agent, D represents the descriptor FractionCSP3 of the anti-aging agent, E represents the NumRotatableBonds descriptor for anti-aging agents. The rubber composition described in [1] above can maintain ozone resistance without the use of the antioxidant 6PPD, while using environmentally friendly chemicals.

[0008] [2] The rubber composition according to [1], wherein the vulcanization accelerator does not contain diphenylguanidine. The rubber composition described in [2] above is less environmentally invasive.

[0009] [3] The rubber composition according to [1] or [2], wherein the content of the thiuram vulcanization accelerator is 3 to 30 parts by mass with respect to 100 parts by mass of the sulfur. The rubber composition according to [3] above can maintain ozone resistance without using the antioxidant 6PPD while using chemicals with low environmental impact.

[0010] [4] The rubber composition according to any one of [1] to [3], wherein the vulcanization accelerator further contains a sulfenamide vulcanization accelerator. The rubber composition according to [4] above can maintain ozone resistance without using the antioxidant 6PPD.

[0011] [5] The rubber composition according to [4], wherein the content of the sulfenamide vulcanization accelerator is 50 to 120 parts by mass with respect to 100 parts by mass of the sulfur. The rubber composition according to [5] above can maintain ozone resistance without using the antioxidant 6PPD.

[0012] [6] The rubber composition according to any one of [1] to [5], wherein the content of the antioxidant is less than 5 parts by mass with respect to 100 parts by mass of the diene rubber. The rubber composition according to [6] above can maintain ozone resistance without using the antioxidant 6PPD.

[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).

Chemical formula

[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. The rubber composition described in [8] above not only maintains ozone resistance but also exhibits excellent strength.

[0015] [9] The rubber composition according to [8], wherein the carbon black is recycled carbon black. The rubber compositions described in [9] above are less environmentally invasive.

[0016]

[10] The rubber composition according to [8], wherein the silica is silica derived from rice husks. The rubber compositions described above

[10] are less environmentally invasive.

[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. The rubber compositions described above

[11] not only maintain ozone resistance but also exhibit superior fracture resistance.

[0018]

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

[11] . The vulcanized rubber for tire treads described above

[12] is environmentally friendly while maintaining ozone resistance.

[0019]

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

[12] in the tread portion. The tires described in

[13] above are environmentally friendly while maintaining ozone resistance.

[0020]

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

[11] . The rubber tracks described in

[14] above have a low environmental impact while maintaining ozone resistance. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a rubber composition that can maintain ozone resistance without using the antioxidant 6PPD, while using chemicals that have a low impact on the environment. 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 the vulcanized rubber for tire treads, and a rubber crawler equipped with the rubber composition. [Modes for carrying out the invention]

[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 anti-aging agent, sulfur, and a vulcanization accelerator, The aforementioned vulcanization accelerator includes a thiram-based vulcanization accelerator. The aforementioned anti-aging agent 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 anti-aging agent, B represents the descriptor MinAbsEStateIndex of the anti-aging agent, C represents the descriptor SlogP_VSA7 for the anti-aging agent, D represents the descriptor FractionCSP3 of the anti-aging agent, E represents the NumRotatableBonds descriptor for anti-aging agents. In the rubber composition of this embodiment, ozone resistance can be maintained by using a thiram-based vulcanization accelerator in combination with an anti-aging agent 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 without using the antioxidant 6PPD. Furthermore, the absence of the antioxidant 6PPD results in a low environmental impact.

[0025] (Diene-based rubber) The rubber composition of this embodiment contains a diene rubber, which provides rubber elasticity to the composition. Preferred diene rubbers include 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 includes natural rubber (NR), synthetic isoprene rubber (IR), etc. When the diene 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 rubbers such as isoprene-backed rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber in the diene 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] (Anti-aging agent) The rubber composition of this embodiment contains an anti-aging agent. The anti-aging agent has the effect of preventing the aging of the rubber composition and rubber products using it. The aging inhibitor included in the rubber composition of this embodiment is not limited as long as it 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 anti-aging agent, B represents the descriptor MinAbsEStateIndex of the anti-aging agent, C represents the descriptor SlogP_VSA7 for the anti-aging agent, D represents the descriptor FractionCSP3 of the anti-aging agent, E represents the NumRotatableBonds descriptor for anti-aging agents.

[0027] In this invention, the descriptors for the anti-aging agents were obtained from the molecular structures of each anti-aging agent, expressed in SMILES notation, using the cheminformatics tool RDKit in a Python environment.

[0028] Examples of anti-aging agents that satisfy the condition that X, calculated by the above formula (I), is between -3.4 and -2.7 include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD, X=-3.3) and N,N'-bis(sec-butyl)-p-phenylenediamine (44PD, X=-2.8).

[0029] The aforementioned descriptors are numerical representations of characteristic quantities such as molecular properties.

[0030] The descriptor MinEStateIndex represents the lowest EStateIndex among all atoms in a molecule. EStateIndex is calculated based on a predefined set of atomic parameters, such as electronegativity, atomic polarizability, and resonance effects.

[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 system. In other words, LogP is an index value indicating the degree of hydrophobicity or hydrophilicity of an antioxidant. The descriptor SLogP is calculated using CCG's calculation method.

[0033] The descriptor FractionCSP3 represents sp at all carbon atoms in the molecule. 3 This represents the proportion of carbon.

[0034] The descriptor NumRotatableBonds represents the number of rotatable bonds in a molecule.

[0035] In the rubber composition of this embodiment, the content of the antioxidant is preferably less than 5 parts by mass per 100 parts by mass of diene rubber. A content of less than 5 parts by mass of the antioxidant per 100 parts by mass of diene rubber makes it less likely for the product to discolor and also makes it easier to control the vulcanization rate. The content of the antioxidant is more preferably 4.8 parts by mass or less, and even more preferably 4.3 parts by mass or less, per 100 parts by mass of diene rubber. Furthermore, the content of the antioxidant is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 3.5 parts by mass or more, per 100 parts by mass of diene rubber.

[0036] [Amine-based antioxidants] The antioxidant is preferably an amine-based antioxidant that satisfies the condition that X, determined by the above formula (I), is between -3.4 and -2.7. More preferably, the amine-based antioxidant is represented by the following general formula (1). That is, it is even more preferable that the antioxidant satisfies the condition that X, determined by the above formula (I), is between -3.4 and -2.7, and is an amine-based antioxidant represented by the following general formula (1). [ka] (In general formula (1), R 1 and R 2 These are each independently monovalent saturated hydrocarbon groups. 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. Further, 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 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 are preferably the same from the viewpoint of synthesis.

[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 antioxidant effect increases and the ozone resistance of the rubber composition is improved. R 1 and R 2 in the above general formula (1) 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 an alkyl group and a cycloalkyl group. The alkyl group may be linear or branched, and the cycloalkyl group may further have an alkyl group or the like bonded thereto as a substituent. 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, among which the cyclohexyl group is preferred.

[0040] Specific examples of 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 the adverse effects on rubber properties other than ozone resistance (such as heat generation) will increase. 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, thereby improving the durability of the rubber composition. Various types of sulfur can be used as the aforementioned 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 polymeric 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 promoting vulcanization 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 thiuram-based vulcanization accelerators include tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrapropylthiuram disulfide, tetraisopropylthiuram disulfide, tetrabutylthiuram disulfide, tetrapentylthiuram disulfide, tetrahexylthiuram disulfide, tetraheptylthiuram disulfide, tetraoctylthiuram disulfide, tetranonylthiuram disulfide, tetradecylthiuram disulfide, tetradodecylthiuram disulfide, tetrastearylthiuram disulfide, and tetrabenzylthiuram disulfide. Examples include tetramethylthiuram monosulfide (TBzTD), tetraethylthiuram monosulfide, tetrapropylthiuram monosulfide, tetraisopropylthiuram monosulfide, tetrabutylthiuram monosulfide, tetrapentylthiuram monosulfide, tetrahexylthiuram monosulfide, tetraheptylthiuram monosulfide, tetraoctylthiuram monosulfide, tetranonylthiuram monosulfide, tetradecylthiuram monosulfide, tetradodecylthiuram monosulfide, tetrastearylthiuram monosulfide, tetrabenzylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide. Among these, tetrabenzylthiuram disulfide (TBzTD) is preferred as a thiuram-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 sulfenamide-based vulcanization accelerator content of 50 to 120 parts by mass 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-benzothiazolyl sulfenamide, N-tert-butyl-2-benzothiazolyl sulfenamide, N-oxydiethylene-2-benzothiazolyl sulfenamide, N-methyl-2-benzothiazolyl sulfenamide, N-ethyl-2-benzothiazolyl sulfenamide, 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 Rylsulfenamide, N-stearyl-2-benzothiazolylsulfenamide, N,N-dimethyl-2-benzothiazolylsulfenamide, N,N-diethyl-2-benzothiazolylsulfenamide, N,N-dipropyl-2-benzothiazolylsulfenamide, N,N-dibutyl-2-benzothiazolylsulfenamide, N,N-dipentyl-2-benzothiazolylsulfenamide, N,N-dihexyl-2-benzothiazolylsulfenamide, 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] The rubber composition of this embodiment may contain, in addition to the sulfenamide-based and thiuram-based vulcanization accelerators mentioned above, 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-- The carbon black is preferably recycled carbon black. Using recycled carbon black reduces the environmental impact. In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials submitted for recycling. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only rubber generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated, for example, in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Furthermore, waste rubber includes not only cross-linked rubber but also unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may include, for example, tires that have been retreaded, tires generated from tire replacement or vehicle scrapping, and End-of-Life Tires (ELTs) that have reached the end of their lifespan, or any other type of tire that has been discarded for any reason. Waste oil is not limited to that generated when plastics and rubber are broken down, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oil that does not contain any non-organic components, such as those derived from silicone rubber or polyvinyl chloride, is preferable. Furthermore, waste oil that contains carbon black or rubber containing carbon black is preferable. "Recycled carbon black" is different from carbon black that is not recycled, which is manufactured directly using hydrocarbons such as petroleum, natural gas, and coal as raw materials. Furthermore, "used" here includes not only carbon black that has been discarded after actual use, but also carbon black that was 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 products containing carbon black exist 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. Furthermore, when recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for carbon black production and use it to produce carbon black using existing carbon black production methods (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residues, there are advantages such as the absence of impurities and the absence of mixtures of different grades. In addition, in the production of low-environmental-impact carbon black, there are various options other than using oil obtained by recovering volatile components from the aforementioned rubber pyrolysis, 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 also used for other purposes such as horizontal recycling of plastics, so supply issues are also likely to arise. On the other hand, when using vulcanized rubber products, particularly volatile components (oils) produced by the thermal decomposition of tires, the tire industry has a system in place to continue using existing materials. This allows for the continued use of existing materials, reducing the consumption of new materials in new tire manufacturing and contributing to a reduction in the industry's environmental impact. The grades of carbon black mentioned above are not particularly limited, but include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc.

[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, referring to "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 usually lacks functional groups on its surface, as referred to 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. In addition, it may be possible to group by tire type and by 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 aforementioned recycled carbon black has a nitrogen adsorption specific surface area of ​​40-100 m² as determined by the BET method. 2 It is preferable that the amount be / g, and 50-90m 2 It is more preferable that the amount be / g, which is 55-75m 2 It is particularly preferable that the value be / g. Herein, 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 recycled carbon black is determined according to ASTM D1512.

[0066] The recycled carbon black preferably has a toluene color transmission rate 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. Herein, in this specification, the heating loss of 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 residue of 20 ppm by mass or less after sieving with a 35 mesh, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Herein, in this specification, the 35-mesh sieve residue of recycled carbon black is determined according to ASTM D1514.

[0070] The recycled carbon black preferably has a residue of 1,000 ppm by mass or less after sieving with a 325 mesh (44 μm), more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Herein, in this specification, the 325-mesh (44 μm) sieve residue of 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. Herein, in this specification, the pellet hardness of recycled carbon black is determined according to ASTM D5230.

[0072] The recycled carbon black preferably has a pelletized fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, in this specification, the amount of recycled carbon black pellets 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. In this specification, the particle size (D97) of recycled carbon black is determined using a laser diffraction particle size analyzer, with a refractive index of 1.33 for water and 1.75 for the filler.

[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 rubber products to which the rubber composition is applied can be improved. Herein, in this specification, the ash content of recycled carbon black is determined according to ASTM D8474·D1506.

[0076] The recycled carbon black preferably has a dibutyl phthalate (DBP) 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 DBP absorption amount of recycled carbon black is determined according to ASTM D2414.

[0077] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, in this specification, the 24M4DBP absorption amount of 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 according to the BET method. 2 It is [value] / 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 significant effect in improving the proportion of sustainable materials in the rubber product 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, and aluminum silicate. Among these, wet silica is preferred because it contains a large number 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., and Tokuyama Corporation.

[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 a sufficient 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 method 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. Furthermore, from the viewpoint of reducing environmental impact, it is also preferable to use silica that has been recycled and used in manufacturing by extracting silicic acid components from silicon wafer scraps, which are raw materials for semiconductors, or from glass bottles, etc., as the silica.

[0082] The silica has a nitrogen adsorption specific surface area (N2SA) of 50 m². 2 It is preferable that it be 100m or more per gram. 2 It is more preferable that it be 150m or more per gram. 2 It is even more preferable that it be 350m or more 2It is preferable that it be less than or equal to / g, and 250m 2 It is more preferable that it be less than or equal to / g, and 230m 2 It is even more preferable that it be less than / g, and 200m 2 It is even more preferable that the value be less than or equal to / g. In this specification, the nitrogen adsorption specific surface area (N2SA) of silica is the 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-trimethoxysilylpropylbenzothiazyl 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 aforementioned waxes include paraffin wax and microcrystalline wax. The wax content is preferably 0.1 to 5 parts by mass per 100 parts by mass of the diene rubber. If the wax content 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 wax content 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 wax content 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] (others) 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 manufacturing rubber composition) The method for producing the rubber composition is not particularly limited, but for example, it can be produced by mixing the aforementioned diene rubber, antioxidant, vulcanization accelerator, and sulfur with various components 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. Typical vulcanization apparatuses include molding vulcanizers using molds, which are commonly used for vulcanizing rubber compositions. The vulcanization temperature is typically around 100-190°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] <Tires> 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 track of this embodiment is characterized by using the rubber composition described above. Because the rubber track of this embodiment 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. [Examples]

[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 composition) The rubber compositions of the examples and comparative examples were manufactured according to the formulations shown in Table 1. The following evaluations were performed on the manufactured rubber composition.

[0099] (descriptor) 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 In accordance with ISO 1431 (JIS K 6259), a dynamic ozone degradation test (a test involving repeated strain) was conducted to evaluate ozone resistance. Samples where cracks could not be seen with the naked eye were rated A, and those where cracks could be seen with the naked eye were rated B.

[0101] [Table 1]

[0102] *1 Diene rubber: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, product 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 The amine-based antioxidant, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), manufactured by Eastman, with a saturated hydrocarbon group (1,4-dimethylpentyl group), has X = -3.3. *4 Anti-aging agent (3): R in general formula (1) 1 and R 2 N,N'-bis(sec-butyl)-p-phenylenediamine (44PD), an amine-based antioxidant in which the saturated hydrocarbon group (sec-butyl group) is present, manufactured by Kanto Chemical Co., Ltd., X=-2.8 *5 Anti-aging agent (4): Quinoline-based anti-aging agent, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac AW", X=-3.7 *6 Anti-aging agent (5): Phosphorus-based anti-aging agent, Tris(nonylphenyl) phosphite (TNP), manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrack TNP", X = -3.9 *7 Anti-aging agent (6): Sulfur-based anti-aging agent, dilauryl thiodipropionate, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product 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 impact.

[0104] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of this invention is considered to be a technology that can contribute to "No. 12: Responsible Consumption and Production" and "No. 13: Climate Action," among others.

Claims

1. A rubber composition comprising diene rubber, an anti-aging agent, sulfur, and a vulcanization accelerator, The aforementioned vulcanization accelerator includes a thiram-based vulcanization accelerator. The aforementioned anti-aging agent is a rubber composition that 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 anti-aging agent, B represents the descriptor MinAbsEStateIndex of the anti-aging agent, C represents the descriptor SlogP_VSA7 for the anti-aging agent, D represents the descriptor FractionCSP3 of the anti-aging agent, E represents the NumRotatableBonds descriptor for anti-aging agents.

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 amount 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 aforementioned antioxidant is an amine-based antioxidant represented by the following general formula (1). 【Chemistry 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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