Rubber composition and rubber product

Abstract

The present invention addresses the problem of providing a rubber composition with which it is possible to suppress the occurrence of cracks while also improving fuel efficiency. As a means for solving said problem, this rubber composition is characterized by including: a diene rubber (A); a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring; and an anti-aging agent (C). The rubber composition is also characterized in that the anti-aging agent (C) includes a triphenylamine-based anti-aging agent (C1) represented by a specific structural formula.

Description

Rubber composition and rubber product

[0001] The present invention relates to a rubber composition and a rubber product.

[0002] In response to the recent trend toward global carbon dioxide emission regulations due to growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. To meet these demands, tire performance also requires reduced rolling resistance. Generally, applying a low-heat-generating rubber composition to tires reduces tire rolling resistance, thereby achieving improved fuel efficiency for automobiles. Furthermore, applying a low-heat-generating rubber composition to rubber products other than tires, such as rubber crawlers and seismic isolation rubber, can also reduce hysteresis loss and achieve improved fuel efficiency. For example, Patent Documents 1 and 2 listed below disclose rubber compositions containing a diene rubber, a filler such as carbon black or silica, and a tetrazine compound. The tetrazine compound is introduced into the main chain of the diene rubber to improve the dispersibility of the filler, thereby improving the fuel efficiency of the rubber composition.

[0003] In general, various rubber components constituting rubber products such as tires, rubber crawlers, and seismic isolation rubber may deteriorate due to the influence of external environments such as the presence of ozone, and as this deterioration progresses, cracks may occur. To address this problem, rubber compositions containing antioxidants are often applied to the various rubber components constituting rubber products. For example, Patent Document 3 below discloses that cracks and discoloration on the tire surface can be suppressed by applying a rubber composition containing a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) to the rubber constituting the tire surface.

[0004] JP 2021-107506 A JP 2020-176229 A International Publication No. 2018 / 056384

[0005] However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) used in the above-mentioned Patent Document 3 may have an impact on the environment, and it is desirable to use an antioxidant that has a lower environmental impact, taking into account the possibility of future restrictions under European regulations. Conversely, it may be possible to use no or very little antioxidant 6PPD in the rubber that constitutes the surface of a rubber product. However, the inventors' investigations have revealed that when no or very little antioxidant 6PPD is used, the ozone resistance of the rubber that constitutes the surface of a rubber product decreases, making it more susceptible to cracking.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a rubber composition that can suppress the occurrence of cracks while improving fuel economy.A further object of the present invention is to provide a rubber product that suppresses the occurrence of cracks while improving fuel economy.

[0007] The rubber composition and rubber product of the present invention that solve the above problems are summarized as follows.

[0008] [1] A rubber composition comprising: a diene rubber (A); a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring; and an antioxidant (C), wherein the antioxidant (C) is represented by the following general formula (1): [In the formula, R １１ and R １２ each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms; R １３ represents hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ and each independently represent a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms.].

[0009] [2] The rubber composition according to [1], further comprising a metal salt (D) and sulfur (E), wherein the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is 0.1 to 10.

[0010] [3] The rubber composition according to [1] or [2], wherein the heterocyclic compound (B) has a triazine ring or a tetrazine ring.

[0011] [4] The heterocyclic compound (B) is represented by the following general formula (2): [In the formula, X ２１ and X ２２ are each independently a pyridyl group or a pyrimidinyl group, and Y ２１ and Y ２２ are each independently a single bond or a divalent hydrocarbon group.

[0012] [5] The rubber composition according to any one of [2] to [4], wherein the metal salt (D) contains at least one metal selected from the group consisting of transition metals and zinc.

[0013] [6] The rubber composition according to any one of [2] to [5], wherein the metal salt (D) is at least one selected from the group consisting of metal halide salts, metal acrylate salts, metal methacrylate salts, and metal acetate salts.

[0014] [7] The rubber composition according to any one of [2] to [6], wherein the metal salt (D) is a metal salt other than zinc oxide and further contains zinc oxide (F).

[0015] [8] The rubber composition according to any one of [1] to [7], further comprising an organic peroxide (G).

[0016] [9] The rubber composition according to any one of [1] to [8], wherein the diene rubber (A) is modified with the heterocyclic compound (B).

[0017]

[10] The rubber composition according to any one of [2] to [7], wherein the bond dissociation energy between the metal salt (D) and the heterocyclic compound (B) is 100 kJ / mol or more.

[0018]

[11] R in the above general formula (1) １１ and R １２ is an alkyl group selected from the group consisting of an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, and a 1,4-dimethylpentyl group.

[0019]

[12] R in the above general formula (1) １１ and R １２ The rubber composition according to any one of [1] to

[11] , wherein the number of carbon atoms is 2 to 8.

[0020]

[13] The rubber composition according to any one of [2] to [7] and

[10] , wherein the mass ratio (D / C) of the metal salt (D) to the antioxidant (C) is 0.05 to 2.

[0021]

[14] The rubber composition according to any one of [1] to

[13] , wherein the mass ratio (B / C) of the heterocyclic compound (B) to the antioxidant (C) is 0.05 to 2.

[0022]

[15] The rubber composition according to any one of [1] to

[14] , wherein the content of the antioxidant (C) is 0.5 to 10 parts by mass per 100 parts by mass of the diene rubber (A), the antioxidant (C) further contains a quinoline-based antioxidant (C2), and a proportion of the quinoline-based antioxidant (C2) in the antioxidant (C) is 5 to 50% by mass.

[0023]

[16] The antioxidant (C) further comprises a compound represented by the following general formula (3): [In the formula, R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group.], and a proportion of the amine-based antioxidant (C3) in the antioxidant (C) is 0.1 to 80 mass %.

[0024]

[17] The antioxidant (C) further comprises a compound represented by the following general formula (4): [In the formula, R ４１ and R ４２represents a phenyl group, and m4 represents an integer of 7 or greater.], and a proportion of the amine-based antioxidant (C4) in the antioxidant (C) is 0.1 to 80 mass %.

[0025]

[18] The rubber composition according to any one of [1] to

[17] , which is for use in a tire tread.

[0026]

[19] A rubber product selected from the group consisting of a tire, a rubber crawler, and a seismic isolation rubber, characterized in that it contains the rubber composition according to any one of [1] to

[17] .

[0027] According to the present invention, it is possible to provide a rubber composition that can suppress the occurrence of cracks while improving fuel economy. Also, according to the present invention, it is possible to provide a rubber product that suppresses the occurrence of cracks while improving fuel economy.

[0028] The rubber composition and rubber product of the present invention will be described in detail below by way of example based on embodiments thereof.

[0029] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0030] <Rubber Composition> The rubber composition of this embodiment includes a diene rubber (A), a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring, and an antioxidant (C). In the rubber composition of this embodiment, the antioxidant (C) is a compound represented by the following general formula (1): [In the formula, R １１ and R １２ each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms; R １３represents hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ and each independently represent a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms.

[0031] In the rubber composition of this embodiment, a heterocyclic compound (B) is added to the main chain of a diene rubber (A). The diene rubber (A) to which the heterocyclic compound (B) is added has high affinity with compounding agents such as fillers generally compounded in rubber compositions, and can improve the dispersibility of compounding agents such as fillers, thereby reducing the hysteresis loss of the rubber composition and improving the fuel economy of the rubber composition. In addition, the rubber composition of this embodiment contains a triphenylamine-based antioxidant (C1) represented by the above general formula (1), thereby ensuring sufficient ozone resistance and suppressing the occurrence of cracks. Therefore, the rubber composition of this embodiment can suppress the occurrence of cracks while improving fuel economy.

[0032] —Diene-Based Rubber (A)— The rubber composition of this embodiment contains a diene-based rubber (A), which provides rubber elasticity to the composition.

[0033] The diene rubber (A) is a rubber containing units derived from a diene monomer (diene units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene monomer enable crosslinking (vulcanization) of the diene rubber and also enable it to exhibit rubber-like elongation and strength. In the crosslinked rubber, the diene rubber (A) is usually present in a crosslinked state, but a portion of it may not be crosslinked. Specific examples of diene monomers (diene compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds. Specific examples of the aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene. Examples of the diene rubber (A) include natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), etc. These diene rubbers (A) may be used alone or as a blend of two or more.

[0034] In the rubber composition of this embodiment, the diene rubber (A) preferably has a weight average molecular weight (Mw) of 10,000 to 3,000,000. When the weight average molecular weight (Mw) of the diene rubber (A) is 10,000 or more, the fuel economy of the rubber composition is improved, and when it is 3,000,000 or less, the workability in kneading the rubber composition is improved. From the viewpoint of the fuel economy of the rubber composition, the weight average molecular weight (Mw) of the diene rubber (A) is more preferably 100,000 or more, and even more preferably 120,000 or more. Furthermore, from the viewpoint of the workability in kneading the rubber composition, it is more preferably 2,000,000 or less, and even more preferably 1,800,000 or less.

[0035] Heterocyclic Compound (B) The rubber composition of this embodiment contains a heterocyclic compound (B) having at least one heterocyclic ring selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring. The heterocyclic compound (B) is added to the diene rubber (A) to improve the dispersibility of compounding ingredients such as fillers, thereby contributing to improved fuel economy of the rubber composition.

[0036] The heterocyclic compound (B) preferably has a triazine ring or a tetrazine ring. Compounds having a triazine ring or a tetrazine ring have high reactivity with the main chain of the diene rubber (A), and can further improve the fuel economy of the rubber composition. In addition, in a preferred embodiment containing a metal salt (D) described below, the compound having a triazine ring or a tetrazine ring is likely to form a crosslink by a coordinate bond in combination with the metal salt (D).

[0037] Here, it is preferable that a pyridyl group or a pyrimidinyl group be bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups be bonded. When a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, the heterocyclic compound (B) and the metal salt (D) are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with even higher strength can be formed. Furthermore, when two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, the heterocyclic compound (B) and the metal salt (D) are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with even higher strength can be formed. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, but a 2-pyridyl group is preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0038] The heterocyclic compound (B) is represented by the following general formula (2): [In the formula, X ２１ and X ２２ are each independently a pyridyl group or a pyrimidinyl group, and Y ２１ and Y２２ are each independently a single bond or a divalent hydrocarbon group. ] is preferably represented by the formula (2). The compound represented by the formula (2) easily undergoes a Diels-Alder reaction with the main chain of the diene rubber (A), thereby further improving the fuel economy of the rubber composition. In addition, in a preferred embodiment containing a metal salt (D) described below, the compound represented by the formula (2) is more likely to form a crosslink by a coordinate bond in combination with the metal salt (D). In addition, the compound represented by the formula (2) and the metal salt (D) are particularly likely to complex with each other, and the bond dissociation energy is particularly likely to be high, thereby forming a crosslinked structure with even greater strength.

[0039] In the above general formula (2), X ２１ and X ２２ are each independently a pyridyl group or a pyrimidinyl group. ２１ and X ２２ is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0040] In the above general formula (2), Y ２１ and Y ２２ are each independently a single bond or a divalent hydrocarbon group. Here, examples of the divalent hydrocarbon group include an alkylene group, an alkenylene group, and an arylene group. More specifically, examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Examples of the alkenylene group include a vinylene group, a propenylene group, and a butenylene group. Examples of the arylene group include a phenylene group, a tolylene group, and a naphthylene group. From the viewpoint of ease of synthesis, Y ２１ and Y ２２ is preferably a single bond (i.e., X is not attached to the tetrazine ring). ２１ and X ２２ is preferably directly bonded).

[0041] Here, X in the general formula (2) ２１ and X ２２is a pyridyl group, and Y ２１ and Y ２２ is preferably a single bond. In this case, the compound of formula (2) is easily available, and is particularly likely to form a complex with the metal salt (D), so that the bond dissociation energy is particularly likely to be high, and a crosslinked structure with even higher strength can be formed.

[0042] Examples of the compound represented by the general formula (2) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, 3,6-di(3-pyridyl)-1,2,4,5-tetrazine, 3,6-di(4-pyridyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridyl)-1,2,4,5-tetrazine, lysylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine, and the like. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0043] The content of the heterocyclic compound (B) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, and even more preferably 5.0 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the heterocyclic compound (B) is 0.1 parts by mass or more per 100 parts by mass of the diene rubber (A), the hysteresis loss of the rubber composition is further reduced, and the fuel economy of the rubber composition is further improved. Furthermore, when the content of the heterocyclic compound (B) is 10 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomeric properties is easily obtained, even in a preferred embodiment containing a metal salt (D) described later.

[0044] The diene rubber (A) is preferably modified with the heterocyclic compound (B). By modifying the diene rubber (A) with the heterocyclic compound (B), the affinity with compounding agents such as fillers generally compounded in rubber compositions is more reliably improved, and the dispersibility of compounding agents such as fillers can be more reliably improved, thereby more reliably improving the fuel economy of the rubber composition. In addition, in a preferred embodiment containing a metal salt (D) described below, when the diene rubber (A) is modified with the heterocyclic compound (B), multiple heterocyclic compound (B) moieties can be complexed with the metal salt (D) described below to form coordinate bonds, thereby crosslinking the main chains of multiple diene rubbers (A). Here, the modification of the diene rubber (A) with the heterocyclic compound (B) may be performed at the compounding stage of the rubber composition. Alternatively, prior to compounding the rubber composition, the diene rubber (A) may be modified with the heterocyclic compound (B) in advance, and the diene rubber (A) modified with the heterocyclic compound (B) may then be compounded with a metal salt (D) or the like at the compounding stage of the rubber composition to crosslink the main chains of multiple diene rubbers (A).

[0045] When the diene rubber (A) is modified with the heterocyclic compound (B), the heterocyclic compound (B) is preferably bonded in an amount of 0.01 to 10 mol%, more preferably 0.02 to 8 mol%, even more preferably 0.03 to 5 mol%, and particularly preferably 0.03 to 3 mol%, relative to the monomer units in the main chain of the diene rubber (A). When the heterocyclic compound (B) is bonded in an amount of 0.01 mol% or more relative to the monomer units in the main chain of the diene rubber (A), the hysteresis loss of the rubber composition is further reduced, and the fuel economy of the rubber composition is improved. Furthermore, when the heterocyclic compound (B) is bonded in an amount of 10 mol% or less relative to the monomer units in the main chain of the diene rubber (A), a crosslinked rubber with sufficient elastomeric properties is easily obtained, even in a preferred embodiment containing a metal salt (D) described below.

[0046] —Antiaging Agent (C)—The rubber composition of this embodiment contains an antioxidant (C), which has the effect of preventing aging of the rubber composition and rubber products using the same.

[0047] The content of the antioxidant (C) is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass, per 100 parts by mass of the diene rubber (A). When the content of the antioxidant (C) is 0.5 parts by mass or more per 100 parts by mass of the diene rubber (A), the ozone resistance of the rubber composition can be sufficiently ensured. Furthermore, when the content of the antioxidant (C) is 10 parts by mass or less per 100 parts by mass of the diene rubber (A), adverse effects on rubber properties other than ozone resistance (such as heat buildup) are reduced, making the rubber suitable for use as a tire tread rubber.

[0048] The mass ratio (B / C) of the heterocyclic compound (B) to the antioxidant (C) is preferably 0.05 to 2, and more preferably 0.08 to 1.5. When the mass ratio (B / C) of the heterocyclic compound (B) to the antioxidant (C) is 0.05 to 2, an excellent balance is achieved between the effect of improving the fuel economy of the rubber composition and the effect of suppressing the occurrence of cracks.

[0049] --Triphenylamine-based antioxidant (C1) of formula (1)-- The antioxidant (C) is a triphenylamine-based antioxidant represented by the following general formula (1): [In the formula, R １１ and R １２ each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms; R １３ represents hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ each independently represent a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms. The triphenylamine-based antioxidant (C1) represented by general formula (1) has the effect of improving the ozone resistance of the rubber composition and can suppress the occurrence of cracks in rubber products using the rubber composition. Furthermore, the triphenylamine-based antioxidant (C1) represented by general formula (1) has a low environmental impact.

[0050] R in the above general formula (1) １１ and R １２ R each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms. １１ and R １２ As the alkyl group, a linear or branched alkyl group having 2 to 8 carbon atoms and a cycloalkyl group having 5 to 8 carbon atoms are preferred.

[0051] R in the above general formula (1) １３ represents hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ R each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms. １３ is hydrogen, a linear or branched alkyl group having 1 to 10 carbon atoms, -NH-R １３１ , and -O-R １３２ is preferable. １３１ As R, a linear or branched alkyl group having 2 to 8 carbon atoms and a cycloalkyl group having 5 to 8 carbon atoms are preferred. １３２ As the alkyl group, a linear or branched alkyl group having 1 to 10 carbon atoms is preferred.

[0052] R １１ , R １２ and R １３１ With regard to the above, examples of the linear or branched alkyl group having 2 to 8 carbon atoms include an ethyl group, a propyl group (i.e., an n-propyl group, an isopropyl group), a butyl group (i.e., an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group), a pentyl group, a hexyl group, a heptyl group, and an octyl group.

[0053] R １３ and R １３２With regard to (1), examples of the linear or branched alkyl group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group (i.e., an n-propyl group, an isopropyl group), a butyl group (i.e., an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group), a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Among these, a methyl group, an ethyl group, and a propyl group (i.e., an n-propyl group, an isopropyl group) are preferred, a methyl group and an ethyl group are more preferred, and a methyl group is particularly preferred.

[0054] Also, R １１ , R １２ , R １３ , R １３１ and R １３２ Regarding the above, examples of the cycloalkyl group having 5 to 8 carbon atoms include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group, and among these, a cyclohexyl group is preferred.

[0055] The synthesis method of the triphenylamine antioxidant (C1) represented by the above general formula (1) is described in French Patent No. 1,354,536 and US Pat. No. 3,277,174. For example, (i) an aromatic amine compound such as aniline, p-toluidine, or p-anisidine is reacted with a halogenated nitrobenzene such as 4-fluoronitrobenzene or 4-chloronitrobenzene to obtain a dinitrotriphenylamine compound such as 4,4'-dinitrotriphenylamine, 4,4'-dinitro-4''-methyltriphenylamine, or 4,4'-dinitro-4''-methoxytriphenylamine, and the dinitrotriphenylamine compound is reduced to obtain a diaminotriphenylamine compound such as 4,4'-diaminotriphenylamine, 4,4'-diamino-4''-methyltriphenylamine, or 4,4'-diamino-4''-methoxytriphenylamine, and the diaminotriphenylamine compound is reacted with a ketone such as acetone, methyl isobutyl ketone, or 2-octanone, or (ii) tris(p-aminophenyl)amine is reacted with a ketone such as acetone, methyl isobutyl ketone, or 2-octanone, The triphenylamine antioxidant represented by the above general formula (1) can be synthesized.

[0056] R in the above general formula (1) １１ and R １２ is preferably an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, or a 1,4-dimethylpentyl group. １１ and R １２ A triphenylamine-based antioxidant in which R is an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, or a 1,4-dimethylpentyl group can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products to which the rubber composition is applied.

[0057] R in the above general formula (1) １３ is preferably a hydrogen atom, an isopropylamino group, a 1,3-dimethylbutylamino group, a 1,4-dimethylpentylamino group, or a methoxy group. １３A triphenylamine-based antioxidant in which R is hydrogen, an isopropylamino group, a 1,3-dimethylbutylamino group, a 1,4-dimethylpentylamino group, or a methoxy group can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products to which the rubber composition is applied.

[0058] R in the above general formula (1) １１ and R １２ Preferably, R in general formula (1) has 2 to 8 carbon atoms. １１ and R １２ The triphenylamine antioxidant having 2 to 8 carbon atoms can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products using the rubber composition.

[0059] The triphenylamine-based antioxidant (C1) is preferably a compound represented by the following general formula (1-1) or (1-2): [In the formula, R １１ , R １２ and R １３１ each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms.] [In the formula, R １１ and R １２ each independently represent a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms.] is preferred. The compound represented by general formula (1-1) or (1-2) can further improve the ozone resistance of the rubber composition, and can further suppress the occurrence of cracks in rubber products using the rubber composition.

[0060] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １１ and R １２are each independently a linear or branched alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms, and are preferably a linear or branched alkyl group having 2 to 8 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms. Examples of the linear or branched alkyl group having 2 to 8 carbon atoms include an ethyl group, a propyl group (i.e., an n-propyl group, an isopropyl group), a butyl group (i.e., an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group), a pentyl group, a hexyl group, a heptyl group, and an octyl group. Examples of the cycloalkyl group having 5 to 8 carbon atoms include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group, and among these, a cyclohexyl group is preferred.

[0061] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １１ and R １２ is preferably an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, or a 1,4-dimethylpentyl group. １１ , R １２ and R １３１ is an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, or a 1,4-dimethylpentyl group, and a triphenylamine-based antioxidant represented by the general formula (1-2): １１ and R １２ A triphenylamine-based antioxidant in which R is an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, or a 1,4-dimethylpentyl group can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products to which the rubber composition is applied.

[0062] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １１ and R １２ Preferably, R in the general formula (1-1) has 2 to 8 carbon atoms. １１ , R１２ and R １３１ and a triphenylamine-based antioxidant having 2 to 8 carbon atoms, １１ and R １２ The triphenylamine antioxidant having 2 to 8 carbon atoms can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products using the rubber composition.

[0063] The triphenylamine-based antioxidant (C1) is preferably a compound represented by the following general formula (1-3): The compound represented by general formula (1-3) can also further improve the ozone resistance of the rubber composition, and can further suppress the occurrence of cracks in rubber products using the rubber composition.

[0064] In the above general formula (1-3), R １１１ , R １１２ , R １２１ and R １２２ are each independently an alkyl group, provided that R １１１ and R １１２ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. １２１ and R １２２ The total number of carbon atoms in R in the general formula (1-3) is 2 to 11, and preferably 2 to 7. １３ represents R in the general formula (1). １３ and is synonymous with hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ are each independently a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms. １３ With respect to -NH-R １３１ Examples of the group include —NH—CHR １３１１ R １３１２ is preferred, where R １３１１ and R １３１２are each independently an alkyl group, provided that R １３１１ and R １３１２ The total number of carbon atoms is 2 to 11, preferably 2 to 7.

[0065] The triphenylamine-based antioxidant (C1) is preferably a compound represented by the following general formula (1-1-1) or (1-2-1): In the above general formula (1-1-1), a compound represented by R １１１ , R １１２ , R １２１ , R １２２ , R １３１１ and R １３１２ are each independently an alkyl group, provided that R １１１ and R １１２ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. １２１ and R １２２ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. １３１１ and R １３１２ The total number of carbon atoms in R is 2 to 11, and preferably 2 to 7. １１１ , R １１２ , R １２１ and R １２２ are each independently an alkyl group, provided that R １１１ and R １１２ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. １２１ and R １２２ The total number of carbon atoms is 2 to 11, preferably 2 to 7.

[0066] Specific examples of the triphenylamine-based antioxidants represented by the general formula (1) include 4,4'-bis(isopropylamino)triphenylamine, 4,4'-bis(1,3-dimethylbutylamino)triphenylamine, 4,4'-bis(2-octylamino)triphenylamine, 4,4'-bis(1,4-dimethylpentylamino)triphenylamine, 4,4'-bis(isopropylamino)-4''-methyltriphenylamine, 4,4'-bis(1,3-dimethylbutylamino)-4''-methyltriphenylamine, 4,4'-bis(2-octylamino)-4''-methyltriphenylamine, 4,4'-bis(1,4-dimethylpentylamino)-4''-methyltriphenylamine, Preferred are 4,4',4''-tris(isopropylamino)triphenylamine, 4,4',4''-tris(1,3-dimethylbutylamino)triphenylamine, 4,4',4''-tris(2-octylamino)triphenylamine, 4,4',4''-tris(1,4-dimethylpentylamino)triphenylamine, 4,4'-bis(isopropylamino)-4''-methoxytriphenylamine, 4,4'-bis(1,3-dimethylbutylamino)-4''-methoxytriphenylamine, 4,4'-bis(2-octylamino)-4''-methoxytriphenylamine, and 4,4'-bis(1,4-dimethylpentylamino)-4''-methoxytriphenylamine. These triphenylamine-based antioxidants (C1) may be used alone or in combination of two or more.

[0067] The proportion of the triphenylamine-based antioxidant (C1) represented by the general formula (1) in the antioxidant (C) is preferably 10 to 100 mass%, more preferably 20 to 100 mass%. When the proportion of the triphenylamine-based antioxidant (C1) represented by the general formula (1) in the antioxidant (C) is 10 to 100 mass%, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0068] Quinoline-Based Antiaging Agent (C2) The antioxidant (C) preferably further contains a quinoline-based antioxidant (C2). The quinoline-based antioxidant (C2) is an antioxidant having a quinoline moiety or a derivative thereof (e.g., a dihydroquinoline moiety, a tetrahydroquinoline moiety, etc.). The quinoline-based antioxidant (C2) has the effect of improving the ozone resistance of the rubber composition. A rubber composition containing both the triphenylamine-based antioxidant (C1) represented by the general formula (1) above and the quinoline-based antioxidant (C2) can further suppress the occurrence of cracks in rubber products.

[0069] The quinoline-based antioxidant (C2) preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the quinoline-based antioxidant (C2) include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ) and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. The quinoline-based antioxidant (C2) preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ). Quinoline-based antioxidants (C2) containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline are highly effective in improving the ozone resistance of rubber compositions and also have the advantage of being less likely to discolor the rubber composition. Therefore, a rubber composition containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline can further suppress the occurrence of cracks in rubber products and is also less susceptible to discoloration. Examples of the polymer of 2,2,4-trimethyl-1,2-dihydroquinoline include a dimer, trimer, and tetramer of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0070] The proportion of the quinoline-based antioxidant (C2) in the antioxidant (C) is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. When the proportion of the quinoline-based antioxidant (C2) in the antioxidant (C) is 5 to 50% by mass, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0071] --Amine-based antioxidant (C3) of formula (3)-- The antioxidant (C) is further represented by the following general formula (3): [In the formula, R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group. It is preferable to include an amine-based antioxidant (C3) represented by the following general formula (3): The amine-based antioxidant (C3) represented by the following general formula (3) contains a phenylenediamine moiety, just like the general-purpose antioxidant N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD), but differs from antioxidant 6PPD in that it does not contain a double bond outside of the phenylenediamine moiety. The amine-based antioxidant (C3) represented by the general formula (3) has the effect of improving the ozone resistance of the rubber composition.

[0072] In the above general formula (3), R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group. ３１ and R ３２ may be the same or different, but from the viewpoint of synthesis, they are preferably the same.

[0073] The number of carbon atoms in the monovalent saturated hydrocarbon group is preferably 1 to 20, more preferably 3 to 10, and particularly preferably 6 or 7. When the number of carbon atoms in the saturated hydrocarbon group is 20 or less, the number of moles per unit mass increases, which enhances the anti-aging effect and further improves the ozone resistance of the rubber composition. ３１ and R ３２ From the viewpoint of further improving the ozone resistance of the rubber composition, it is preferable that each of the groups independently represents a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms.

[0074] 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 group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,2-dimethylpentyl group, a 1,3-dimethylpentyl group, a 1,4-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,4-dimethylpentyl group, an n-hexyl group, a 1-methylhexyl group, a 2-methylhexyl group, various octyl groups, various decyl groups, and various dodecyl groups. Of these, a 1,4-dimethylpentyl group is preferred. Examples of the cycloalkyl group include a cyclopentyl group, a methylcyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, a cycloheptyl group, and a cyclooctyl group. Of these, a cyclohexyl group is preferred.

[0075] Specific examples of the amine-based antioxidant (C3) represented by the general formula (3) include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD), N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, and N,N'-dicyclohexyl-p-phenylenediamine (antiaging agent CCPD). Of these, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD) and N,N'-dicyclohexyl-p-phenylenediamine (antiaging agent CCPD) are preferred, with N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD) being particularly preferred. The amine-based antioxidant (C3) represented by the formula (3) may be used alone or in combination of two or more.

[0076] The proportion of the amine-based antioxidant (C3) represented by the general formula (3) in the antioxidant (C) is preferably 0.1 to 80 mass%, more preferably 1 to 70 mass%. When the proportion of the amine-based antioxidant (C3) of formula (3) in the antioxidant (C) is 0.1 to 80 mass%, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0077] --Amine-based antioxidant (C4) of formula (4)-- The antioxidant (C) can further be an amine-based antioxidant represented by the following general formula (4): [In the formula, R ４１ and R ４２ represents a phenyl group, and m4 represents an integer of 7 or more. The amine-based antioxidant (C4) represented by the above general formula (4) has a higher molecular weight than conventional antioxidants, and as shown in the above formula (4), it has a bridge moiety having a unique and relatively long chain length, i.e., "-NH-CH(CH ３ )-(CH ２ ) ｍ４ -CH(CH ３ )-NH-". It is believed that the high molecular weight and the presence of a specific bridge moiety of the amine-based antioxidant (C4) reduce the diffusion rate in the rubber composition, further suppressing migration to the rubber surface. Furthermore, the amine-based antioxidant (C4) has a moiety composed of "-CH(CH ３ )-(CH ２ ) ｍ４ -CH(CH ３ One hydrogen atom is bonded to each of the two nitrogen atoms present at both ends of "(2-amino-2-methyl-2-methyl-2-propanol)-" (forming a so-called secondary amino group), and the presence of this bond in the structure represented by formula (4) is thought to contribute to the specific effect of improving ozone resistance (weather resistance).

[0078] In the above general formula (4), R ４１ and R ４２ is a phenyl group. ４１ and R ４２When is a phenyl group, the ozone resistance of the rubber composition can be further improved, and discoloration of the rubber composition can be more reliably prevented.

[0079] In the general formula (4), m4 is an integer of 7 or more, and from the viewpoint of improving the ozone resistance of the rubber composition and preventing discoloration, it is preferably an integer of 8 to 16, and more preferably an integer of 10 to 14.

[0080] Examples of the amine-based antioxidant (C4) of the above formula (4) include N,N'-bis(4-anilinophenyl)dodecane-2,11-diamine, N,N'-bis(4-anilinophenyl)tetradecane-2,13-diamine, N,N'-bis(4-anilinophenyl)hexadecane-2,15-diamine, N,N'-bis(4-anilinophenyl)octadecane-2,17-diamine, etc. Among these, N,N'-bis(4-anilinophenyl)tetradecane-2,13-diamine and N,N'-bis(4-anilinophenyl)octadecane-2,17-diamine are particularly preferred.

[0081] The proportion of the amine-based antioxidant (C4) represented by the general formula (4) in the antioxidant (C) is preferably 0.1 to 80 mass%, more preferably 1 to 70 mass%. When the proportion of the amine-based antioxidant (C4) of formula (4) in the antioxidant (C) is 0.1 to 80 mass%, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0082] --Other Antiaging Agents (C5)-- The rubber composition of this embodiment may or may not contain an antioxidant (C5) other than the triphenylamine-based antioxidant (C1) of formula (1-1) or (1-2), the quinoline-based antioxidant (C2), the amine-based antioxidant (C3) of formula (3), and the amine-based antioxidant (C4) of formula (4). Examples of the other antioxidant (C5) include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and N,N'-diphenyl-p-phenylenediamine (DPPD). However, it is preferable to exclude N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). Commercially available antioxidants can be used as the antioxidants, and examples of commercially available antioxidants that can be used include products from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis, and the like. These antioxidants (C5) may be used alone or in combination of two or more. The proportion of the other antioxidants (C5) in the antioxidant (C) is preferably 0 to 20% by mass, more preferably 0 to 10% by mass.

[0083] (Preferred embodiment) The rubber composition of this embodiment further contains a metal salt (D) and sulfur (E), and it is preferable that the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is 0.1 to 10.

[0084] Conventionally, rubber compositions with excellent durability, such as crack propagation resistance, have been required to improve the durability of rubber products such as tires, rubber crawlers, and seismic isolation rubber. However, in rubber compositions, fuel economy and durability are usually in a trade-off relationship. For example, when sulfur is compounded into a rubber composition to crosslink it and the network density of the sulfur crosslinks is reduced, durability, such as crack propagation resistance, improves, but fuel economy decreases. The present inventors conducted extensive research to resolve this trade-off and found that controlling the strain dependency in the development of hysteresis loss is important. In a rubber composition containing the diene rubber (A) and heterocyclic compound (B) described above, as well as a metal salt (D) and sulfur (E), the heterocyclic compound (B) is attached to the main chain of the diene rubber (A), and the metal salt (D) is coordinately bonded to the heterocyclic compound (B) portion attached to the main chain of the diene rubber (A) to form a complex. The metal salt (D) forms multiple coordinate bonds, thereby crosslinking multiple diene rubbers (A). Furthermore, in a rubber composition containing the metal salt (D) and sulfur (E), crosslinks due to coordinate bonds of the metal salt (D) and sulfur crosslinks are present in the rubber composition after crosslinking (dual crosslink: DCL). Here, the crosslinks due to coordinate bonds are reversible crosslinks in which bonding (crosslinking) and dissociation (cleavage) are reversible, and although they are weaker than sulfur crosslinks, they have sufficient strength in a low strain region even when the rubber composition is subjected to strain. Furthermore, in a rubber composition containing the metal salt (D) and sulfur (E), the network density is maintained high in a low strain region by both crosslinks due to coordinate bonds and sulfur crosslinks, thereby reducing hysteresis loss and further improving fuel economy. On the other hand, in a rubber composition containing a metal salt (D) and sulfur (E), in a high strain region, crosslinks due to coordination bonds are cleaved, resulting in high hysteresis loss, and durability such as crack propagation resistance can be improved by energy dissipation due to the cleavage of the crosslinks (i.e., sacrificial fracture of the crosslinks due to coordination bonds). Furthermore, in a rubber composition containing a metal salt (D) and sulfur (E), the presence of sulfur crosslinks in a high strain region improves the strength of the rubber composition, further improving durability.Furthermore, in a rubber composition containing a metal salt (D) and sulfur (E), the balance between fuel economy and durability of the rubber composition is improved by having a mass ratio (E / D) of sulfur (E) to metal salt (D) in the range of 0.1 to 10. Therefore, a rubber composition containing a metal salt (D) and sulfur (E) and having a mass ratio (E / D) of the sulfur (E) to the metal salt (D) of 0.1 to 10 can achieve a high degree of both fuel economy and durability, which cannot be achieved by conventional crosslinking using only sulfur.

[0085] Metal Salt (D) The rubber composition of this embodiment preferably contains a metal salt (D). The metal salt (D) forms coordinate bonds with the plurality of heterocyclic compounds (B), thereby crosslinking the plurality of diene rubbers (A). Here, the crosslinking by coordinate bonds is a reversible crosslink in which bonding (crosslinking) and dissociation (cleavage) are reversible, and the bond dissociation energy is relatively low. Therefore, even if the crosslinking is broken by an external stimulus, it can be reversibly regenerated.

[0086] The metal salt (D) preferably contains at least one metal selected from the group consisting of transition metals and zinc. Metal salts containing a transition metal and / or zinc are easily complexed with the heterocyclic compound (B), further improving the fuel economy and durability of the rubber composition. Examples of transition metals include elements in Groups 7 to 11 of the periodic table. Specific examples of elements in Group 7 of the periodic table include manganese and rhenium. Examples of elements in Group 8 of the periodic table include iron, ruthenium, and osmium. Examples of elements in Group 9 of the periodic table include cobalt, rhodium, and iridium. Examples of elements in Group 10 of the periodic table include nickel, palladium, and platinum. Examples of elements in Group 11 of the periodic table include copper. Elements in Groups 7 to 11 of the periodic table tend to form stronger bonds with the heterocyclic compound (B). Furthermore, when the metal salt (D) contains an element in Group 8 of the periodic table, the bond with the heterocyclic compound (B) tends to be even stronger. The valence of the metal ions in the metal salt (D) is not particularly limited and may be any valence that each element can have, but is preferably divalent or greater.

[0087] The metal salt (D) particularly preferably contains iron, zinc, copper, or nickel. Iron ions, zinc ions, copper ions, and nickel ions are likely to form particularly strong bonds with the heterocyclic compound (D), and can form a stronger crosslinked structure. The valence of the iron ions is preferably divalent (Fe ２＋ ) or trivalent (Fe ３＋ ) is preferred.

[0088] Examples of the metal salt (D) include metal halides, metal sulfates, metal nitrates, metal acrylates, metal methacrylates, and metal acetates. Among these, metal halides, metal acrylates, metal methacrylates, and metal acetates are preferred. Metal halides, metal acrylates, metal methacrylates, and metal acetates are easy to handle and easily form bonds with the heterocyclic compound (B), further improving the fuel economy and durability of the rubber composition. The form of the metal salt (D) is not particularly limited, and may be, for example, a hydrate.

[0089] Examples of the metal halide salt include metal fluorides, metal chlorides, metal bromides, and metal iodides, and among these, metal chlorides are preferred because they are easy to handle and can easily form a bond with the heterocyclic compound (B).

[0090] Specific examples of the metal salt (D) include FeCl ２ , FeCl ２ ・4H ２ O, FeCl ３ , FeCl ３ ・6H ２ O, ZnCl ２ , CuCl, CuCl ２ , CuBr, zinc diacrylate, zinc dimethacrylate, Ni(CH ３ COO) ２ ・4H ２ O. The metal salt (D) may be a single type or a combination of two or more types.

[0091] The metal salt (D) is preferably a salt other than a metal oxide, a metal carbonate, or a metal salt of a fatty acid having 10 or more carbon atoms. Metal salts (D) other than metal oxides, metal carbonates, and metal salts of a fatty acid having 10 or more carbon atoms are more likely to form a coordinate bond (complex) with the heterocyclic compound (B) moiety added to the diene rubber (A) chain. Therefore, using a metal salt (D) other than these salts makes it easier to form crosslinks by coordinate bonds.

[0092] The content of the metal salt (D) is preferably in the range of 0.1 to 30 parts by mass, more preferably 0.1 to 15 parts by mass, even more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass, per 100 parts by mass of the diene rubber (A). When the content of the metal salt (D) is 0.1 part by mass or more per 100 parts by mass of the diene rubber (A), the network density of the coordinate bond crosslinks is increased, the hysteresis loss in the low strain region is further reduced, and the fuel economy of the rubber composition is further improved. Furthermore, when the content of the metal salt (D) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomeric properties is easily obtained.

[0093] In a rubber composition containing the metal salt (D), the bond dissociation energy between the metal salt (D) and the heterocyclic compound (B) is preferably 100 kJ / mol or more, more preferably 200 kJ / mol or more, even more preferably 240 kJ / mol or more, and preferably 500 kJ / mol or less. When the bond dissociation energy is 100 kJ / mol or more, sufficient strength is obtained in a low strain region, and the fuel economy of the rubber composition can be sufficiently improved. Furthermore, when the bond dissociation energy is 500 kJ / mol or less, crosslinks formed by coordinate bonds between the metal salt (D) and the heterocyclic compound (B) are easily cleaved in a high strain region, and energy dissipation due to the cleavage of the crosslinks can further improve the durability of the rubber composition, such as crack propagation resistance.

[0094] Herein, the bond dissociation energy between the metal salt (D) and the heterocyclic compound (B) is a value calculated in vacuum at the M06 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) level or the M06 / 6-31G(d,p) level, and is a calculated value for a structure in which the heterocyclic compound (B) is bonded to the diene rubber (A). It is believed that the metal salt (D) and the heterocyclic compound (B) form ionic aggregates. Gaussian 09 or GRRM14 can be used to calculate the bond dissociation energy.

[0095] For example, crosslinking by coordinate bonds can be formed by mixing (kneading) the diene rubber (A), the heterocyclic compound (B), and the metal salt (D). Here, it is preferable that the conditions for kneading, such as temperature and time, be appropriately selected depending on the types and reactivities of the diene rubber (A), heterocyclic compound (B), and metal salt (D) used.

[0096] As an example, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as the heterocyclic compound (B), and zinc chloride (ZnCl ２ The reaction scheme of the modification of the diene rubber (A) and the coordination bond crosslinking (complexation) of the modified diene rubber when the diene rubber (A) is used is shown below. Note that the structure of the modified diene rubber shown here is one assumed example, and is not limited thereto. For example, the modified diene rubber may be an isomer due to tautomerism, an oxidized form, or the like.

[0097] As shown in the upper part of the reaction scheme, in one preferred embodiment, a modified diene rubber is produced by a Diels-Alder reaction between the main chain of the diene rubber (A) and the heterocyclic compound (B). In this preferred embodiment, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the modification reaction.

[0098] Furthermore, as shown in the lower part of the above reaction scheme, in the preferred embodiment, the modified diene rubber and the metal salt (D) are complexed to produce a diene rubber crosslinked by a coordinate bond (complexed diene rubber). Note that, although the above reaction scheme shows a mode in which a nitrogen atom in the tetrazine residue, a nitrogen atom of a pyridyl group bonded to the tetrazine residue, and a zinc ion are complexed, the diene rubber crosslinked by a coordinate bond can take various crosslinking modes.

[0099] The mass ratio (D / C) of the metal salt (D) to the antioxidant (C) is preferably 0.05 to 2. When the mass ratio (D / C) of the metal salt (D) to the antioxidant (C) is 0.05 to 2, an excellent balance is achieved between the effect of improving the fuel economy and durability of the rubber composition and the effect of suppressing the occurrence of cracks.

[0100] - Sulfur (E) - The rubber composition of this embodiment preferably contains sulfur (E). When the rubber composition contains sulfur (E) together with the metal salt (D), the rubber composition after crosslinking contains crosslinks due to coordinate bonds with the metal salt (D) and sulfur crosslinks (Dual Cross Link: DCL). In the low strain region, the network density is maintained higher by both the crosslinks due to coordinate bonds and the sulfur crosslinks, thereby further reducing hysteresis loss and further improving fuel economy. On the other hand, in the high strain region, in addition to energy dissipation due to cleavage of crosslinks due to coordinate bonds, the presence of sulfur crosslinks improves the strength of the rubber composition (also referred to as a "crosslinked rubber composition" or "crosslinked rubber"), further improving durability such as crack propagation resistance.

[0101] The content of the sulfur (E) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 30 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of sulfur (E) is 0.1 parts by mass or more per 100 parts by mass of the diene rubber (A), the network density due to sulfur is improved, and fuel economy is further improved. Furthermore, when the content of sulfur (E) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomeric properties is easily obtained.

[0102] In the rubber composition containing the metal salt (D) and sulfur (E), the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is preferably 0.1 to 10. When the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is 0.1 to 10, the balance between fuel economy and durability of the rubber composition is improved. From the viewpoint of the balance between fuel economy and durability of the rubber composition, the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is more preferably in the range of 0.1 to 8, and even more preferably in the range of 0.1 to 6. Note that, in the rubber composition containing the metal salt (D) and sulfur (E), the mass ratio (E / D') of the sulfur (E) to the metal salt (D') other than zinc oxide is preferably 0.1 to 10. Therefore, a preferred embodiment of the rubber composition comprises a diene rubber (A), a heterocyclic compound (B), an antioxidant (C), a metal salt other than zinc oxide (D'), and sulfur (E), and the mass ratio (E / D') of the sulfur (E) to the metal salt other than zinc oxide (D') is 0.1 to 10.

[0103] —Zinc Oxide (F)— In a rubber composition containing the metal salt (D), when the metal salt (D) is a metal salt (D′) other than zinc oxide, the rubber composition preferably further contains zinc oxide (F). When the rubber composition contains zinc oxide (F) together with the metal salt (D′) other than zinc oxide, the fuel economy and durability of the rubber composition are further improved.

[0104] The content of the zinc oxide (F) in the rubber composition is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of zinc oxide (F) is in the range of 0.1 part by mass or more to 30 parts by mass or less, per 100 parts by mass of the diene rubber (A), the fuel economy and durability of the rubber composition are further improved. The mass ratio (F / D') of zinc oxide (F) to metal salt (D') other than zinc oxide is preferably in the range of 0.1 to 50, more preferably 1 to 20.

[0105] -Organic Peroxide (G)- The rubber composition of this embodiment preferably further contains an organic peroxide (G). The rubber composition containing the organic peroxide (G) further improves the durability of the rubber composition. Furthermore, the rubber composition containing the organic peroxide (G) together with the metal salt (D) and sulfur (E) results in the presence of crosslinks due to coordinate bonds of the metal salt (D), sulfur crosslinks, and crosslinked structures (C-C bonds, etc.) resulting from the organic peroxide (G) in the crosslinked rubber composition. In the low strain region, the crosslinks due to coordinate bonds, sulfur crosslinks, and crosslinked structures resulting from the organic peroxide (G) maintain a high network density, thereby further reducing hysteresis loss and further improving fuel economy. Meanwhile, in the high strain region, in addition to energy dissipation due to the cleavage of crosslinks due to coordinate bonds, the presence of sulfur crosslinks and crosslinked structures resulting from the organic peroxide (G) further improves durability, such as crack propagation resistance.

[0106] The organic peroxide (G) is not particularly limited, but examples thereof include tert-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, di(2-tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, perbenzoic acid, benzoyl peroxide, 1,1-bis(1,1-dimethylethylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-hexylperoxy)cyclohexane, 2,2-bis(4,4-di-(tert-butylperoxy)cyclohexyl)propane, n-butyl-4,4-di-(tert-butylperoxy)valerate, tert-butylperoxylaurate, tert-butylperoxy-2-ethylhexanate, 1,1, Examples of the organic peroxide (G) include 3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyacetate, cyclohexanone peroxide, acetylacetone peroxide, diisopropyl peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate, etc. These organic peroxides (G) may be used alone or in combination of two or more.

[0107] The content of the organic peroxide (G) in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of the organic peroxide (G) is 0.1 parts by mass or more per 100 parts by mass of the diene rubber (A), the network density of the crosslinked structure resulting from the organic peroxide (G) is improved, further improving fuel economy. Furthermore, when the content of the organic peroxide (G) is 30 parts by mass or less per 100 parts by mass of the diene rubber (A), a crosslinked rubber having sufficient elastomeric properties is easily obtained. The mass ratio (E / G) of sulfur (E) to organic peroxide (G) is preferably in the range of 0.003 to 300, more preferably 0.01 to 100.

[0108] Carbon Black (H) The rubber composition of this embodiment preferably further contains carbon black (H). The carbon black (H) reinforces the rubber composition and can improve the abrasion resistance of the rubber composition. As the carbon black (H), plant-derived carbon black and recycled carbon black (also referred to as "recycled carbon black" or "recycled carbon black") are preferred. Here, examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0109] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of carbon black (H) in the rubber composition (total of recycled carbon black and carbon black other than recycled carbon black) is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the diene rubber (A). Also, from the viewpoint of workability of the rubber composition, the content of carbon black (H) in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the diene rubber (A).

[0110] --Recycled Carbon Black-- In this specification, "recycled carbon black" refers to carbon black recovered from recycled waste raw materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only that generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process, for example, in tire retreading, where the tread portion remaining on the base tire is scraped off. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0111] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixing of different grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0112] Solid residues obtained by pyrolysis of waste materials such as used rubber and used tires contain ash in addition to carbon black. The ash is derived from non-volatile components contained in the rubber and tires. Therefore, recycled carbon black obtained from the solid residues has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content of the recycled carbon black, the better. The carbon content of the recycled carbon black is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content of the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed moisture.

[0113] Specific examples of the ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, and magnesium oxide. In the case of recycled carbon black produced from solid residue obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0114] The recycled carbon black can also be obtained from a pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

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

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

[0115] The recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained by a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained by a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0116] Furthermore, examples of thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0117] The crosslinked rubber products used for the decomposition may be grouped by the type of rubber component previously compounded, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be performed for each group. Furthermore, the crosslinked rubber products may be grouped by both type of rubber component and type of filler, and then the decomposition step may be performed for each group. When the decomposition step is performed for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when the recycled carbon black is compounded again into a rubber component, a rubber composition with better performance can be obtained.

[0118] Furthermore, when the crosslinked rubber product used in the degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and the degradation step may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and the degradation step may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and the degradation step may be carried out for each group. When the degradation step is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and therefore, when the recycled carbon black is blended again into a rubber component, a rubber composition with better performance can be obtained.

[0119] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m as measured by the BET method. ２ / g, and 50 to 90m ２ / g, and more preferably 55 to 75m ２ In this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black measured by the BET method is a statistical thickness specific surface area (STSA) determined in accordance with ASTM D6556.

[0120] The pH of the recycled carbon black is preferably 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. In this specification, the pH of the recycled carbon black is determined in accordance with ASTM D1512.

[0121] The recycled carbon black preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, the toluene color transmittance of recycled carbon black is determined in accordance with ASTM D1618.

[0122] The recycled carbon black preferably has a heat loss of 3% by mass or less, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less at 125°C. Herein, the heat loss of recycled carbon black at 125°C is determined in accordance with ASTM D1509.

[0123] 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.

[0124] The recycled carbon black preferably has a 35 mesh sieve residue of 20 mass ppm or less, more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less. Herein, the 35 mesh sieve residue of recycled carbon black is determined in accordance with ASTM D1514.

[0125] The recycled carbon black preferably has a 325 mesh (44 μm) sieve residue of 1000 mass ppm or less, more preferably 700 mass ppm or less, and particularly preferably 300 mass ppm or less. Herein, the 325 mesh (44 μm) sieve residue of the recycled carbon black is determined in accordance with ASTM D1514.

[0126] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, the pellet hardness of recycled carbon black is determined in accordance with ASTM D5230.

[0127] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, the pellet fine powder content of recycled carbon black is determined in accordance with ASTM D1508.

[0128] The particle size (D97) of the recycled carbon black is preferably 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size distribution analyzer, assuming a refractive index of 1.33 for water and a refractive index of 1.75 for the filler.

[0129] The recycled carbon black preferably contains particles of 5 μm or less in a proportion of 50% by volume or more, more preferably 70% by volume or more, and particularly preferably 80% by volume or more.

[0130] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, the ash content of the recycled carbon black is determined in accordance with ASTM D8474 and D1506.

[0131] The recycled carbon black preferably has an oil absorption number (OAN) of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the OAN of recycled carbon black is determined in accordance with ASTM D2414.

[0132] The recycled carbon black preferably has an oil absorption (COAN) of a compressed sample of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the COAN of the recycled carbon black is determined in accordance with ASTM D3493.

[0133] Commercially available recycled carbon black can be used. For example, Enrestec's product name "PB365" can be mentioned as such a commercially available product. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m2 as measured by the BET method. ２ / g and contains about 17% by mass of ash.

[0134] The content of the recycled carbon black is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the diene rubber (A). When the content of recycled carbon black is 5 parts by mass or more per 100 parts by mass of the diene rubber (A), the effect of improving the proportion of sustainable materials in rubber products to which the rubber composition is applied is significant, and when the content is 50 parts by mass or less, the fracture resistance of the rubber composition can be more reliably maintained.

[0135] —Silica (I)— The rubber composition of this embodiment preferably further contains silica (I). When the rubber composition contains silica (I), the reinforcement properties of the rubber composition are improved, and durability is further improved.

[0136] Examples of the silica (I) include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These silicas (I) may be used alone or in combination of two or more.

[0137] The content of the silica (I) in the rubber composition is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and preferably 100 parts by mass or less, more preferably 90 parts by mass or less, per 100 parts by mass of the diene rubber (A). When the content of silica (I) is 2 parts by mass or more per 100 parts by mass of the diene rubber (A), the reinforcement of the rubber composition is further improved, and durability is further improved. When the content of silica (I) is 100 parts by mass or less per 100 parts by mass of the diene rubber (A), the fuel economy of the rubber composition is further improved. The mass ratio (H / I) of carbon black (H) to silica (I) is preferably in the range of 0.02 to 50, more preferably 0.05 to 20.

[0138] Others—The rubber composition of this embodiment may contain, in addition to the diene rubber (A), heterocyclic compound (B), antioxidant (C), metal salt (D), sulfur (E), zinc oxide (F), organic peroxide (G), carbon black (H), and silica (I), compounding agents commonly used in the rubber industry, such as softeners, stearic acid, wax, silane coupling agents, adhesion inhibitors (fatty acid metal salts), and vulcanization accelerators, which may be appropriately selected and blended within a range that does not impair the objects of the present invention. Commercially available products can be suitably used as these compounding agents.

[0139] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. Among these, sulfenamide vulcanization accelerators are preferred. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, per 100 parts by mass of the diene rubber (A).

[0140] -Method for Producing Rubber Composition- The method for producing the rubber composition is not particularly limited, but the rubber composition can be produced, for example, by blending various components appropriately selected as necessary with the diene rubber (A), heterocyclic compound (B), and antioxidant (C) described above, and kneading, heating, extruding, etc.

[0141] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0142] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0143] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0144] Furthermore, the rubber composition containing the metal salt (D) and sulfur (E) can be prepared, for example, by blending and kneading in a first stage of kneading a diene rubber (A), a heterocyclic compound (B), and various other components appropriately selected as necessary to form a mixture containing a modified diene rubber in which the heterocyclic compound (B) is bonded to the main chain of the diene rubber (A), and then blending and kneading in a second or subsequent stage of kneading a mixture containing the metal salt (D), sulfur (E), and various other components appropriately selected as necessary to complex the diene rubber (A) modified with the heterocyclic compound (B), thereby forming a crosslinked structure by coordinate bonding and also forming sulfur crosslinks. This method for producing a rubber composition is excellent in productivity because it can form a crosslinked structure by coordinate bonding and sulfur crosslinks during the production of the rubber composition (kneading of the rubber composition).

[0145] Alternatively, for example, a modified diene rubber having a heterocyclic compound (B) bonded to the main chain of a diene rubber (A) may be prepared in advance, and the modified diene rubber may be kneaded with optional compounding ingredients in a first stage of kneading. In a second or subsequent stage of kneading, a metal salt (D), sulfur (E), and various other components appropriately selected as necessary may be blended and kneaded to complex the diene rubber (A) modified with the heterocyclic compound (B), thereby forming a crosslinked structure via a coordinate bond and sulfur crosslinks. This method for producing a rubber composition also makes it possible to easily form a crosslinked structure via a coordinate bond and sulfur crosslinks, and is also excellent in productivity.

[0146] -Applications- The rubber composition of this embodiment can be applied to various rubber products such as tires, rubber crawlers, and seismic isolation rubber. Among these rubber products, the rubber composition of this embodiment is suitable for tires, and particularly suitable for tire treads. By using the rubber composition of this embodiment in tire treads, it is possible to improve the fuel economy of the tire while suppressing the occurrence of cracks on the tread surface.

[0147] <Rubber Product> The rubber product of this embodiment is a rubber product selected from the group consisting of a tire, a rubber crawler, and a seismic isolation rubber, and is characterized by including the rubber composition described above. Because the rubber product of this embodiment includes the rubber composition described above, fuel economy is improved and the occurrence of cracks is suppressed.

[0148] - Tire - When the rubber product of this embodiment is a tire, the application portion of the above-described rubber composition in the tire is not particularly limited and can be appropriately selected depending on the purpose. Examples include the tread, base tread, sidewall, side reinforcing rubber, bead filler, etc., with the tread being preferred. Conventional methods can be used to manufacture the tire. For example, components typically used in tire manufacturing, such as a carcass layer, belt layer, and tread layer, each composed of an unvulcanized rubber composition and / or cords, are laminated on a tire building drum, and the drum is removed to form a green tire. The green tire is then heated and vulcanized according to a conventional method to manufacture a desired tire (e.g., a pneumatic tire).

[0149] - Rubber Track - When the rubber product of this embodiment is a rubber track, in one embodiment, the rubber track comprises steel cords, an intermediate rubber layer covering the steel cords, a core bar arranged on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core bar, and further has a plurality of lugs on the ground contact surface side of the main rubber layer. Here, the above-mentioned rubber composition may be used in any part of the rubber track, but is preferably used in the main rubber layer, particularly the lugs, due to its excellent durability.

[0150] -Seismic isolation rubber- When the rubber product of the present embodiment is a seismic isolation rubber, in one embodiment, the seismic isolation rubber includes a laminate in which soft layers and hard layers are alternately laminated, and a plug that is press-fitted into a hollow portion formed in the center of the laminate. In one embodiment, the above-described rubber composition can be used for at least one of the soft layer and the plug.

[0151] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0152] <Method for Measuring Weight-Average Molecular Weight (Mw) of Diene Rubber> The weight-average molecular weight was determined as a value converted into standard polystyrene by gel permeation chromatography (GPC) under the following conditions: GPC: HLC-8320GPC manufactured by Tosoh Corporation, Column: TSKgel G4000HXL x 2 manufactured by Tosoh Corporation (column temperature: 40°C), Mobile phase: Tetrahydrofuran (flow rate: 1 ml / min), Detector: Differential refractometer (further connected with a multi-wavelength detector (detection wavelength: 254 nm)), Standard substance: TSK standard polystyrene manufactured by Tosoh Corporation.

[0153] Comparative Examples 1 to 19: Each rubber composition was produced using a conventional Banbury mixer according to the formulation shown in Tables 1 to 8. The resulting rubber compositions were evaluated for fuel economy and durability by the following methods. The bond dissociation energy between the compounded metal salt (C) and heterocyclic compound (B) was also measured by the following method. The ozone resistance of each rubber composition was also evaluated by the following method.

[0154] (1) Method for evaluating fuel economy Test pieces were prepared from the rubber compositions, and a viscoelasticity test was performed using an "ARES-G2" manufactured by TA Instruments under conditions of a frequency of 15 Hz, a shear strain of 3%, and a temperature of 30°C, to measure the loss tangent (tan δ) of the rubber compositions. The evaluation results are shown in Table 1, where the compounding data of Comparative Example 1 is set as the control (index value 100) and normalized by the reciprocal of the compounding data of each example. In Table 2, the compounding data of Comparative Example 6 is set as the control (index value 100) and normalized by the reciprocal of the compounding data of each example. In Table 3, the compounding data of Comparative Example 7 is set as the control (index value 100) and normalized by the reciprocal of the compounding data of each example. In Table 4, the compounding data of Comparative Example 8 is set as the control (index value 100) and normalized by the reciprocal of the compounding data of each example. In Table 5, the blending data of Comparative Example 13 was set as the control (index value 100) and normalized by the reciprocal of the blending data of each example; in Table 6, the blending data of Comparative Example 14 was set as the control (index value 100) and normalized by the reciprocal of the blending data of each example; in Table 7, the blending data of Comparative Example 17 was set as the control (index value 100) and normalized by the reciprocal of the blending data of each example; and in Table 8, the blending data of Comparative Example 19 was set as the control (index value 100) and normalized by the reciprocal of the blending data of each example. The larger the index value, the smaller the tan δ and the better the fuel economy. The index values ​​were classified according to the following criteria, and the evaluation results of each example are shown in Tables 1 to 8. A: Index value exceeds 110 B: Index value exceeds 100 and is 110 or less C: Index value is 100 or less

[0155] (2) Durability Evaluation Method 1 The durability of the rubber compositions shown in Table 1 was evaluated by the following method. A rectangular test piece with a hole drilled in the center was prepared from the rubber composition, and the tear energy [J / m] after 1,950 repetitions was measured in a dc / dn test using the test piece (measured at a frequency of 5 Hz, 40°C, and at two or more stress levels for each formulation using a Shimadzu Servo Pulser). ２The crack growth rate was calculated when the common logarithm of [(log(√{square root over ( ...

[0156] (3) Durability Evaluation Method 2 The durability of the rubber compositions shown in Table 2 was evaluated by the following method. Ring test pieces with an inner diameter of 8 mm and an outer diameter of 12 mm were prepared from the rubber compositions, and were stretched to 100% at a rate of 100 mm / min using an Instron tensile tester, and then returned to their initial length at the same rate. The area of ​​the loop drawn in the strain-stress curve at this time was taken as the hysteresis loss at 100% elongation. The larger this value, the more energy can be dissipated and the more difficult crack propagation becomes, and therefore it was used as an index of durability (crack propagation resistance). The compounding data of Comparative Example 6 was taken as the control (index value 100) and normalized by the compounding data of each example. The larger the index value, the larger the area of ​​the loop drawn in the strain-stress curve and the more excellent the durability (crack propagation resistance). The index values ​​were classified according to the following criteria, and the evaluation results for each example are shown in Table 2. A: Index value greater than 200 B: Index value greater than 100 but not greater than 200 C: Index value not greater than 100

[0157] (4) Durability Evaluation Method 3 The durability of the rubber compositions shown in Table 3 was evaluated by the following method. Ring test pieces with an inner diameter of 8 mm and an outer diameter of 12 mm were prepared from the rubber composition and elongated to 100% at a rate of 100 mm / min using an Instron tensile tester, and then returned to the initial length at the same rate. This measurement was performed twice consecutively, and the area of ​​the loop drawn in the strain-stress curve obtained in the second measurement was taken as the hysteresis loss at 100% elongation. The larger this value, the more energy can be dissipated and the more difficult crack propagation, so it was used as an index of durability (crack propagation resistance). The compounding data of Comparative Example 7 was used as the control (index value 100) and normalized by the compounding data of each example. The larger the index value, the larger the loop area drawn in the strain-stress curve and the more excellent the durability (crack propagation resistance). The index values ​​were classified according to the following criteria, and the evaluation results for each example are shown in Table 3. A: Index value exceeds 200 B: Index value exceeds 100 and is 200 or less C: Index value is 100 or less

[0158] (5) Durability Evaluation Method 4 The durability of the rubber compositions shown in Tables 4 to 8 was evaluated by the following method. Ring test pieces with an inner diameter of 8 mm and an outer diameter of 12 mm were prepared from the rubber compositions, and using an Instron tensile tester, they were elongated at a rate of 100 mm / min until the strain energy reached 1 MPa, and then returned to their initial length at the same rate. The area of ​​the loop drawn on the strain-stress curve at this time was taken as the hysteresis loss when elongated with a strain energy of 1 MPa. The larger this value, the more energy can be dissipated and the more difficult crack propagation becomes, so this was used as an index of durability (crack propagation resistance). In Table 4, the formulation data of Comparative Example 8 is set as a control (index value 100) and normalized by the formulation data of each example; in Table 5, the formulation data of Comparative Example 13 is set as a control (index value 100) and normalized by the formulation data of each example; in Table 6, the formulation data of Comparative Example 14 is set as a control (index value 100) and normalized by the formulation data of each example; in Table 7, the formulation data of Comparative Example 17 is set as a control (index value 100) and normalized by the formulation data of each example; and in Table 8, the formulation data of Comparative Example 19 is set as a control (index value 100) and normalized by the formulation data of each example. The larger the index value, the larger the area of ​​the loop drawn in the strain-stress curve, and the more excellent the durability (crack growth resistance). The index values ​​are classified according to the following criteria, and the evaluation results of each example are shown in Tables 4 to 8. A: Index value exceeds 200 B: Index value exceeds 100 and is 200 or less C: Index value is 100 or less

[0159] (6) Calculation Method of Bond Dissociation Energy The bond dissociation energy between the metal salt (C) (specifically, the metal ion of the metal salt (C)) and the heterocyclic compound (B) (specifically, the functional group of the heterocyclic compound (B)) is a value calculated in vacuum at the M06 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) level or the M06 / 6-31G(d,p) level, and is a calculated value for a structure in which the heterocyclic compound (B) is bonded to the diene rubber (A). Note that the metal ion and the functional group are considered to form ionic aggregates. Gaussian09 or GRRM14 can be used to calculate the bond dissociation energy. Here, the dissociation energy of the coordinate bond between the central metal and the tetrazine derivative was determined under the M06 / 6-31G(d,p) level of theory, gas phase conditions.

[0160] For the rubber compositions produced in Examples 1, 3, and 5, the metal salt (C) [ZnCl ２ The bond dissociation energy between the metal salt (C) [zinc dimethacrylate] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 172.0 kJ / mol. For the rubber compositions produced in Examples 2, 4, 6, 12 to 29, and 32 to 40, the bond dissociation energy between the metal salt (C) [zinc dimethacrylate] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 111.9 kJ / mol. For the rubber compositions produced in Examples 7 to 11, 30, and 31, the bond dissociation energy between the metal salt (C) [Ni(CH ３ COO) ２ ・4H ２ The bond dissociation energy between the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] and the heterocyclic compound (B) [3,6-di(2-pyridyl)-1,2,4,5-tetrazine] is 244.1 kJ / mol.

[0161] (7) Ozone Resistance A dynamic ozone degradation test (a test in which repeated strain is applied) is conducted in accordance with ISO 1431 (JIS K 6259), and the sample is observed at 20x magnification using a microscope. The observed samples are ranked according to the size and depth of cracks and classified according to the following criteria (1 to 5), with smaller numbers indicating better results. (Ranking by crack size and depth) 1: Not visible to the naked eye but visible with a 10x magnifying glass. 2: Visible to the naked eye. 3: Deep and relatively large cracks (less than 1 mm). 4: Deep and large cracks (1 mm or more but less than 3 mm). 5: Cracks of 3 mm or more or likely to cause breakage.

[0162] Examples 1 to 40 Each rubber composition was produced using a conventional Banbury mixer according to the compounding recipes shown in Tables 1 to 8. Each rubber composition was evaluated for fuel economy, durability, and ozone resistance using the methods described above.

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[0170]

[0171] * 1 SBR: Styrene-butadiene rubber with a bound styrene content of 10%, a 1,2 vinyl bond content of 42%, and a weight average molecular weight (Mw) of 386,982 * 2 Carbon black-1: ISAF grade, manufactured by Asahi Carbon Co., Ltd., trade name "Asahi #78" * 3 Heterocyclic compound: 3,6-di (2-pyridyl) -1,2,4,5-tetrazine, manufactured by Tokyo Chemical Industry Co., Ltd. * 4 Anti-adhesion agent: fatty acid metal salt * 5 Sulfur-1: manufactured by Hosoi Chemical Industry Co., Ltd., trade name "HK200-5" * 6 Vulcanization accelerator-1: The total amount of thiazole-based and sulfenamide-based vulcanization accelerators, and in the comparative examples and examples in Tables 1, 2, 4, 5, and 6, all are compounded in the same mass ratio for each table. * 7 Zinc oxide * 8 Zinc chloride: ZnCl ２ , manufactured by Tokyo Chemical Industry Co., Ltd. *9 ZDMA: zinc dimethacrylate, manufactured by CRAY VALLEY, trade name "DYMALINK 708" *10 Antioxidant-1: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), manufactured by Ouchi Shinko Chemical Industry Co., Ltd. "Nocrac (registered trademark) 6C" *11 Antioxidant-2: 4,4'-bis(2-octylamino)triphenylamine, a triphenylamine-based antioxidant represented by the following structural formula (1-a) *12 Antioxidant-3: 4,4'-bis(2-octylamino)-4''-methoxytriphenylamine, a triphenylamine-based antioxidant represented by the following structural formula (1-b) *13 Antioxidant-4: 4,4',4''-tris(1,3-dimethylbutylamino)triphenylamine, a triphenylamine-based antioxidant represented by the following structural formula (1-c) *14 Other-1: The total amount of stearic acid and wax. The same amount of each component is blended in Comparative Examples 1 to 6 and Examples 1 to 11. *15 Nickel acetate tetrahydrate: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0172] * 16 IR: Isoprene rubber, manufactured by ENEOS Materials, trade name "IR2200" * 17 EPDM: Ethylene-propylene-diene rubber, manufactured by Mitsui Chemicals, trade name "PX-006M" * 18 Carbon black-2: Manufactured by Tokai Carbon Co., Ltd., trade name "Seast 300" * 19 Sulfur-2: Manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sunfel EX" * 20 Vulcanization accelerator-2: The total amount of thiuram-based and sulfenamide-based vulcanization accelerators, and Comparative Example 7 and Examples 12 to 14 are compounded in the same ratio. * 21 Other-2: Retarder

[0173] *22 NR: Natural rubber *23 BR-1: Butadiene rubber, manufactured by Ube Industries, Ltd., product name "UBEPOL BR150L" *24 Carbon black-3: SAF grade *25 Resin: DCPD resin, manufactured by Nippon Petrochemical Co., Ltd., product name "Nippon Oil Neoresin B-100" *26 Other-3: The total amount of stearic acid, wax and retarder. Comparative Examples 8 to 16 and Examples 15 to 31 contain the same proportions of each component. *27 BR-2: Prepared modified butadiene rubber (HMI-BR), the preparation method is shown below.

[0174] <BR-2 (*27): Preparation of Modified Butadiene Rubber (HMI-BR)> 283 g of cyclohexane, 50 g of 1,3-butadiene, 0.0057 mmol of 2,2-ditetrahydrofurylpropane, and 0.513 mmol of hexamethyleneimine (HMI-BR) were added to a dried, nitrogen-purged, approximately 900 mL pressure-resistant glass vessel. 0.57 mmol of n-butyllithium (BuLi) was then added, and polymerization was carried out for 4.5 hours in a 50°C warm water bath equipped with a stirrer. The polymerization conversion rate during this period was nearly 100%. Next, 0.100 mmol of tin tetrachloride was quickly added to this polymerization reaction system as a modifier (coupling agent), and the modification reaction was carried out with stirring for an additional 30 minutes at 50°C. Thereafter, 0.5 mL of an isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) (BHT concentration: 5% by mass) was added to the polymerization reaction system to terminate the reaction, and the mixture was further dried in a conventional manner to obtain a modified butadiene rubber having tin atoms (HMI-BR). １The amount of vinyl bonds in the butadiene moiety was measured from the integral ratio of the H-NMR spectrum and was found to be 14%. The glass transition temperature (Tg) was calculated from the inflection point of the DSC curve and was found to be −95° C. The coupling rate was calculated from the ratio of the peak area on the highest molecular weight side to the entire area of ​​the molecular weight distribution curve by gel permeation chromatography (GPC) and was found to be 65%.

[0175] *28 Silica: Tosoh Silica Corporation, trade name "Nipsil AQ" *29 Vulcanization accelerator-3: The total amount of guanidine, thiazole, and sulfenamide vulcanization accelerators, Comparative Examples 17 and 18 are guanidine / thiazole / sulfenamide = 1 / 1.43 / 0.5, Examples 32 to 35 are guanidine / thiazole / sulfenamide = 1 / 1.21 / 0.43, Examples 36 and 37 are guanidine / thiazole / sulfenamide = 1 / 1 / 0.35 by mass ratio. *30 Silane coupling agent: Shin-Etsu Chemical Co., Ltd., trade name "ABC-856" *31 Other-4: The total amount of stearic acid and wax, Comparative Examples 17 to 19 and Examples 32 to 40 are each compounded in the same ratio. *32 Vulcanization accelerator-4: The total amount of thiazole-based and sulfenamide-based vulcanization accelerators. In Comparative Example 19 and Examples 38 to 40, each component was blended in the same ratio.

[0176] Tables 1 to 8 show that when a rubber composition containing a diene rubber (A), a heterocyclic compound (B), and a triphenylamine-based antioxidant (C1) of formula (1) is applied to a rubber product, the rubber product can be improved in fuel economy while suppressing the occurrence of cracks.

[0177] The rubber composition of the present invention can be used for rubber products such as tires, rubber crawlers, and seismic isolation rubber.

Claims

1. A rubber composition comprising: a diene rubber (A); a heterocyclic compound (B) having at least one heterocycle selected from the group consisting of a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, and a tetrazine ring; and an antioxidant (C), wherein the antioxidant (C) is represented by the following general formula (1): [In the formula, R １１ and R １２ each independently represents a linear or branched alkyl group having 1 to 12 carbon atoms or a cycloalkyl group having 5 to 8 carbon atoms; R １３ represents hydrogen, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 8 carbon atoms, -NH-R １３１ , or -O-R １３２ where R １３１ and R １３２ and each independently represent a linear or branched alkyl group having 1 to 12 carbon atoms, or a cycloalkyl group having 5 to 8 carbon atoms.].

2. The rubber composition according to claim 1, further comprising a metal salt (D) and sulfur (E), wherein the mass ratio (E / D) of the sulfur (E) to the metal salt (D) is 0.1 to 10.

3. The rubber composition according to claim 1, wherein the heterocyclic compound (B) has a triazine ring or a tetrazine ring.

4. The heterocyclic compound (B) is represented by the following general formula (2): [In the formula, X ２１ and X ２２ are each independently a pyridyl group or a pyrimidinyl group, and Y ２１ and Y ２２ and each independently represents a single bond or a divalent hydrocarbon group.

5. The rubber composition according to claim 2, wherein the metal salt (D) contains at least one metal selected from the group consisting of transition metals and zinc.

6. The rubber composition according to claim 2, wherein the metal salt (D) is at least one selected from the group consisting of metal halide salts, metal acrylate salts, metal methacrylate salts, and metal acetate salts.

7. The rubber composition according to claim 2, wherein the metal salt (D) is a metal salt other than zinc oxide and further contains zinc oxide (F).

8. The rubber composition according to claim 1, further comprising an organic peroxide (G).

9. The rubber composition according to claim 1, wherein the diene rubber (A) is modified with the heterocyclic compound (B).

10. The rubber composition according to claim 2, wherein the bond dissociation energy between the metal salt (D) and the heterocyclic compound (B) is 100 kJ / mol or more.

11. R in the above general formula (1) １１ and R １２ The rubber composition according to claim 1, wherein is an alkyl group selected from the group consisting of an isopropyl group, a 1,3-dimethylbutyl group, a 2-octyl group, and a 1,4-dimethylpentyl group.

12. R in the above general formula (1) １１ and R １２ The rubber composition according to claim 1, wherein has 2 to 8 carbon atoms.

13. The rubber composition according to claim 2, wherein the mass ratio (D / C) of the metal salt (D) to the antioxidant (C) is 0.05 to 2.

14. The rubber composition according to claim 1, wherein the mass ratio (B / C) of the heterocyclic compound (B) to the antioxidant (C) is 0.05 to 2.

15. The rubber composition according to claim 1, wherein the content of the antioxidant (C) is 0.5 to 10 parts by mass per 100 parts by mass of the diene rubber (A), the antioxidant (C) further contains a quinoline-based antioxidant (C2), and the proportion of the quinoline-based antioxidant (C2) in the antioxidant (C) is 5 to 50% by mass.

16. The antioxidant (C) further comprises a compound represented by the following general formula (3): [In the formula, R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group.], and a proportion of the amine-based antioxidant (C3) in the antioxidant (C) is 0.1 to 80 mass %.

17. The antioxidant (C) further comprises a compound represented by the following general formula (4): [In the formula, R ４１ and R ４２ represents a phenyl group, and m4 represents an integer of 7 or greater.], and a proportion of the amine-based antioxidant (C4) in the antioxidant (C) is 0.1 to 80 mass %.

18. The rubber composition of claim 1, which is for use in a tire tread.

19. A rubber product selected from the group consisting of tires, rubber crawlers, and seismic isolation rubber, characterized in that it contains the rubber composition according to claim 1.

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