Rubber composition and rubber product

Abstract

The present invention addresses the problem of providing a rubber composition having excellent wear resistance, mechanical strength before and after thermal degradation, and ozone resistance. As a means for solving said problem, this rubber composition is characterized by including a rubber component (A), syndiotactic 1,2-polybutadiene (B), and an anti-aging agent (C), wherein the anti-aging agent (C) includes a triphenylamine-based anti-aging agent (C1) represented by general formula (1).

Description

Rubber composition and rubber product

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

[0002] Generally, rubber compositions used in the manufacture of rubber articles such as tires are required to have high durability, such as crack growth resistance, etc. As a technique for improving the durability of rubber, for example, Patent Document 1 describes a technique for increasing the crack growth resistance of rubber by blending syndiotactic 1,2-polybutadiene into the rubber composition.

[0003] Furthermore, 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 in the presence of ozone, and as this deterioration progresses, cracks may occur. To address this problem, rubber compositions containing antioxidants are often used in various rubber components constituting rubber products. For example, Patent Document 2 below discloses that cracks and discoloration on the tire surface can be suppressed by applying a rubber composition containing a selected blend of a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) to the rubber constituting the tire surface.

[0004] International Publication No. WO 2019 / 163869 International Publication No. WO 2018 / 056384

[0005] However, it has been found that rubber compositions containing syndiotactic 1,2-polybutadiene, such as those described in Patent Document 1, have room for improvement in terms of mechanical strength after thermal aging. Furthermore, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) used in Patent Document 2 may have an environmental impact. Considering the possibility of future European regulations, it has been desirable to use an antioxidant with a lower environmental impact. Therefore, while technology that does not use the antiaging agent 6PPD in rubber compositions has been considered, the inventors' investigations have revealed that using only a quinoline-based antiaging agent without the antiaging agent 6PPD reduces the ozone resistance of the rubber composition and reduces the durability of the rubber composition after aging (particularly elongation at break (EB) and tensile strength (TB)). Furthermore, rubber compositions used in rubber products are required to have abrasion resistance in addition to mechanical strength and ozone resistance after thermal aging.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional art and to provide a rubber composition excellent in abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance, and to provide a rubber product excellent in abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance.

[0007] The gist and configuration of the present invention to solve the above problems is as follows.

[0008] [1] A rubber composition comprising: a rubber component (A); a syndiotactic 1,2-polybutadiene (B); 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 R１３２ 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], wherein the rubber component (A) contains an isoprene-based rubber.

[0010] [3] The rubber composition according to [1] or [2], wherein the syndiotactic 1,2-polybutadiene (B) has a 1,2-bond content of 80% by mass or more.

[0011] [4] The rubber composition according to any one of [1] to [3], wherein the syndiotactic 1,2-polybutadiene (B) has a syndiotacticity in 1,2-bonds of 60% or more and 95% or less.

[0012] [5] The rubber composition according to any one of [1] to [4], wherein the syndiotactic 1,2-polybutadiene (B) has a crystallinity of 25 to 50%.

[0013] [6] The rubber composition according to any one of [1] to [5], wherein the syndiotactic 1,2-polybutadiene (B) has a melting point of 100 to 150°C.

[0014] [7] The rubber composition according to any one of [1] to [6], wherein the content of the syndiotactic 1,2-polybutadiene (B) is 5 to 40 parts by mass per 100 parts by mass of the rubber component (A).

[0015] [8] The rubber composition according to any one of [1] to [7], wherein the ratio of the 1,2-bond content of the syndiotactic 1,2-polybutadiene (B) to the content of the antioxidant (C) is 8 to 200.

[0016] [9] The rubber composition according to any one of [1] to [8], wherein the ratio of the amount of crystals of the syndiotactic 1,2-polybutadiene (B) to the amount of the antioxidant (C) is 3 to 100.

[0017]

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

[0018]

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

[10] , wherein each independently has 2 to 8 carbon atoms.

[0019]

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

[11] , wherein the content of the antioxidant (C) is 0.5 to 10 parts by mass per 100 parts by mass of the rubber component (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.

[0020]

[13] The antioxidant (C) further comprises a compound represented by the following general formula (2): [In the formula, R ２１ and R ２２ 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 %.

[0021]

[14] The antioxidant (C) further comprises a compound represented by the following general formula (3): [In the formula, R ３１ and R ３２ represents a phenyl group, and m3 represents an integer of 7 or more.], and a proportion of the amine-based antioxidant (C4) in the antioxidant (C) is 0.1 to 80 mass %.

[0022]

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

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

[0023]

[16] 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

[15] .

[0024] According to the present invention, it is possible to provide a rubber composition having excellent abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance. Also, according to the present invention, it is possible to provide a rubber product having excellent abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance.

[0025] The rubber composition and rubber product of the present invention will be described in detail below by way of example based on embodiments thereof.

[0026] <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.

[0027] <Rubber Composition> The rubber composition of the present embodiment includes a rubber component (A), a syndiotactic 1,2-polybutadiene (B), and an antioxidant (C), wherein 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 １３ represents a hydrogen atom, 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.]. By definition, the syndiotactic 1,2-polybutadiene (B) is not included in the rubber component (A).

[0028] As described above, the rubber composition of this embodiment contains at least the rubber component (A) and the syndiotactic 1,2-polybutadiene (B). Without intending to be bound by theory, the syndiotactic 1,2-polybutadiene (B) is a crystalline polymer, and its crystals undergo sacrificial fracture under high strain, thereby dissipating input energy. Furthermore, the syndiotactic 1,2-polybutadiene (B) has the property of being compatible with the rubber component (A), and therefore can be partially immobilized in the rubber component (A). Therefore, the rubber composition of this embodiment can be preferably vulcanized to form a mesh-like three-dimensional network in the matrix of the rubber component (A), the network having a portion consisting of crystals of the syndiotactic 1,2-polybutadiene (B) (crystalline portion) and a portion in which the rubber component (A) and the syndiotactic 1,2-polybutadiene (B) are compatible with each other (compatible portion).

[0029] In the rubber composition of the present embodiment, the above-mentioned three-dimensional network provides a high energy dissipation effect due to the crystalline portion and flexibility due to the compatible portion, so that a tire using such a rubber composition can achieve excellent wear resistance and mechanical strength.

[0030] Furthermore, the rubber composition of the present embodiment contains the triphenylamine-based antioxidant (C1) represented by the above general formula (1) as the antioxidant (C), and thus can sufficiently ensure ozone resistance in addition to abrasion resistance and mechanical properties before and after thermal degradation.

[0031] Therefore, the rubber composition of the present embodiment is excellent in abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance.

[0032] Whether or not the above-described three-dimensional mesh-like network is formed in the rubber composition can be determined, for example, by confirming that the syndiotactic 1,2-polybutadiene (B) forms a co-continuous network structure in the rubber component (A) from an elastic modulus image obtained by an atomic force microscope (AFM). Furthermore, the presence or absence of a three-dimensional network can also be inferred from the composition of the rubber composition before vulcanization.

[0033] (Rubber Component (A)) The rubber composition contains a rubber component (A), which provides rubber elasticity to the composition. The rubber component (A) is preferably a diene-based rubber. Examples of the diene-based rubber include isoprene-based rubber, styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Cl-IIR, Br-IIR, etc.), ethylene-propylene-diene terpolymer rubber (EPDM), ethylene-butadiene copolymer rubber, and propylene-butadiene copolymer rubber. Among these rubber components (A), isoprene-based rubber is preferred. That is, the rubber component (A) preferably contains an isoprene-based rubber. When the rubber component (A) contains an isoprene-based rubber, the mechanical strength of the rubber composition before and after thermal degradation is further improved. Here, the isoprene-based rubber may be natural or synthetic, i.e., it includes natural rubber (NR) and synthetic polyisoprene rubber (IR), and from the viewpoint of mechanical strength before and after thermal degradation, natural rubber is preferred.

[0034] From the viewpoint of mechanical strength before and after thermal degradation, the rubber component (A) preferably contains 50% by mass or more of an isoprene-based rubber, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. It is particularly preferable that the rubber component (A) consists of 100% by mass of an isoprene-based rubber, and it is particularly preferable that the rubber component (A) consists of 100% by mass of a natural rubber. The rubber component (A) may be a single type or a blend of two or more types. Furthermore, the rubber component (A) may contain a non-diene-based rubber as long as the effects of the present invention are not impaired.

[0035] (Syndiotactic 1,2-polybutadiene (B)) The rubber composition contains syndiotactic 1,2-polybutadiene (B) (hereinafter, sometimes referred to as "sPB"). The syndiotactic 1,2-polybutadiene (B) is a crystalline polymer (resin) and is not included in the rubber component (A). The syndiotactic 1,2-polybutadiene (B) forms the above-mentioned double network in the rubber composition together with the rubber component (A), and provides excellent mechanical strength after thermal aging.

[0036] The syndiotactic 1,2-polybutadiene (B) preferably has a weight average molecular weight (Mw) of 100,000 to 750,000. When the weight average molecular weight of the syndiotactic 1,2-polybutadiene (B) is 100,000 to 750,000, double network formation is facilitated, and the mechanical strength of the rubber composition after thermal aging is further improved. From the viewpoint of mechanical strength, the weight average molecular weight of the syndiotactic 1,2-polybutadiene (B) is more preferably 120,000 to 750,000, even more preferably 140,000 to 750,000, even more preferably 160,000 to 750,000, and particularly preferably 160,000 to 600,000. The weight average molecular weight (Mw) of the syndiotactic 1,2-polybutadiene (B) can be determined by gel permeation chromatography in terms of polystyrene using monodisperse polystyrene as the standard.

[0037] The syndiotactic 1,2-polybutadiene (B) preferably has a syndiotacticity in the 1,2-bonds of 60% or more and 95% or less. When the syndiotacticity in the 1,2-bonds of the syndiotactic 1,2-polybutadiene (B) is 60% or more, the formation of a double network becomes easy. From the viewpoint of the ease of forming a double network, the syndiotacticity in the 1,2-bonds of the syndiotactic 1,2-polybutadiene (B) is more preferably 65% ​​or more, even more preferably 70% or more, and even more preferably 80% or more. In one embodiment, the syndiotacticity in the 1,2-bonds of the syndiotactic 1,2-polybutadiene (B) may be 80% or less, or 70% or less. The syndiotacticity in the 1,2-bonds is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis. The syndiotacticity represents the content of syndiotactic structures in 1,2-bonds.

[0038] Furthermore, the syndiotactic 1,2-polybutadiene (B) preferably has a crystallinity of 7 to 40 J / g. By making the crystallinity of the syndiotactic 1,2-polybutadiene (B) 7 J / g or more, the double network described above can be more reliably formed in the rubber composition after vulcanization, and the abrasion resistance and other properties of the rubber composition when applied to a tire can be further improved. From the same viewpoint, the crystallinity of the syndiotactic 1,2-polybutadiene (B) is more preferably 15 J / g or more, and even more preferably 17 J / g or more. On the other hand, if the crystalline amount of syndiotactic 1,2-polybutadiene (B) is too large, the melting point of the syndiotactic 1,2-polybutadiene (B) may become too high, making it difficult to achieve a vulcanization temperature sufficient to form a double network. Alternatively, if the crystalline amount is too large, the crystals may act as fracture nuclei, resulting in a tendency for the elongation at break of the rubber to decrease. From this perspective, the crystalline amount is preferably 40 J / g or less, more preferably 36 J / g or less, and even more preferably 31 J / g or less. The crystalline amount of syndiotactic 1,2-polybutadiene (B) refers to the heat of fusion and is an index indicating the proportion of syndiotactic 1,2-polybutadiene (B) that has crystallized. The crystalline amount of syndiotactic 1,2-polybutadiene (B) can be derived from the melting peak measured with a differential scanning calorimeter.

[0039] The syndiotactic 1,2-polybutadiene (B) preferably has a crystallinity of 25 to 80%. When the syndiotactic 1,2-polybutadiene (B) has a crystallinity of 25 to 80%, double network formation becomes easier, and the mechanical strength of the rubber composition is further improved. From the viewpoint of mechanical strength, the crystallinity of the syndiotactic 1,2-polybutadiene (B) is more preferably 25 to 70%, even more preferably 25 to 60%, and even more preferably 25 to 50%. The crystallinity of the syndiotactic 1,2-polybutadiene (B) can be determined by the method described in the Examples.

[0040] The syndiotactic 1,2-polybutadiene (B) preferably has a melting point of 100 to 180°C. When the melting point of the syndiotactic 1,2-polybutadiene (B) is 100°C or higher, the network of the syndiotactic 1,2-polybutadiene (B) in the resulting rubber composition is not too soft, and the mechanical strength of the rubber composition is improved. Furthermore, when the melting point of the syndiotactic 1,2-polybutadiene (B) is 180°C or lower, the occurrence of rubber scorching (rubber deterioration, molecular cleavage, gel generation, etc.) during kneading of the rubber composition can be suppressed, even if the kneading temperature is a temperature equal to or higher than the melting point of the syndiotactic 1,2-polybutadiene (B), and the physical properties of the rubber composition are improved. Furthermore, when the melting point of the syndiotactic 1,2-polybutadiene (B) is 100 to 180° C., a network of the syndiotactic 1,2-polybutadiene (B) is easily and suitably formed. From the viewpoint of ease of forming a network of the syndiotactic 1,2-polybutadiene (B), the melting point of the syndiotactic 1,2-polybutadiene (B) is more preferably 100 to 170° C., even more preferably 100 to 160° C., and particularly preferably 100 to 150° C. The melting point of the syndiotactic 1,2-polybutadiene (B) can be derived as the melting peak temperature measured with a differential scanning calorimeter.

[0041] The number average molecular weight of the syndiotactic 1,2-polybutadiene is 6.5 × 10 from the viewpoint of being able to more reliably form the double network in the rubber composition after vulcanization and to further improve fuel economy, abrasion resistance, and cut resistance when applied to a tire. ４ From the same viewpoint, the number average molecular weight of the sPB is preferably 8.9 × 10 or more. ４ That's it, 10.0 x 10 ４ That's it, 11.0 x 10 ４ That's it, 12.0 x 10 ４ That's it, 13.0 x 10 ４ That's it, 14.0 x 10 ４ That's it, 15.0 x 10 ４ That's it, 16.0 x 10 ４ That's it, 17.0 x 10 ４ That's it, 17.9 x 10４ That's it, 18.0 x 10 ４ That's it, 19.0 x 10 ４ That's it, 20.0 x 10 ４ On the other hand, the number average molecular weight of the sPB can be 50.0 × 10 or more from the viewpoint of preventing a decrease in crack growth resistance and ride comfort when applied to a tire. ４ From the same viewpoint, the number average molecular weight of the sPB is preferably 40.0 × 10 or less. ４ Below, 39.0 x 10 ４ Below, 38.0 x 10 ４ Below, 37.0 x 10 ４ Below, 36.0 x 10 ４ Below, 35.0 x 10 ４ Below, 34.7 x 10 ４ Below, 34.0 x 10 ４ Below, 33.0 x 10 ４ Below, 32.0 x 10 ４ Below, 31.0 x 10 ４ Below, 30.0 x 10 ４ It can be as follows:

[0042] The syndiotactic 1,2-polybutadiene (B) preferably has a 1,2-bond content of 80% by mass or more. When the syndiotactic 1,2-polybutadiene (B) has a 1,2-bond content of 80% by mass or more, the formation of a double network becomes easy, and after the syndiotactic 1,2-polybutadiene (B) forms a network structure, it selectively bears stress in response to input (deformation) and can dissipate energy more efficiently, thereby further improving the mechanical strength of the rubber composition. The 1,2-bond content of the syndiotactic 1,2-polybutadiene (B) is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0043] The content of the syndiotactic 1,2-polybutadiene (B) in the rubber composition is preferably 5 to 40 parts by mass per 100 parts by mass of the rubber component. When the content of the syndiotactic 1,2-polybutadiene (B) is 5 parts by mass or more per 100 parts by mass of the rubber component, a double network of the rubber component (A) and the syndiotactic 1,2-polybutadiene (B) can be suitably formed. Furthermore, when the content of the syndiotactic 1,2-polybutadiene (B) is 40 parts by mass or less per 100 parts by mass of the rubber component, the syndiotactic 1,2-polybutadiene (B) can be prevented from becoming a foreign matter and becoming a fracture nucleus in the rubber composition. Therefore, when the content of the syndiotactic 1,2-polybutadiene (B) is 5 to 40 parts by mass per 100 parts by mass of the rubber component, the mechanical strength of the rubber composition is further improved. From the viewpoint of mechanical strength, the content of the syndiotactic 1,2-polybutadiene (B) is more preferably 5 to 35 parts by mass, particularly preferably 15 to 35 parts by mass, per 100 parts by mass of the rubber component.

[0044] The syndiotactic 1,2-polybutadiene (B) can be obtained, for example, by polymerizing a 1,3-butadiene monomer in an organic solvent containing an aliphatic solvent using an iron-based catalyst composition, a chromium-based catalyst composition, a cobalt-based catalyst composition, or the like. For example, the syndiotactic 1,2-polybutadiene (B) is disclosed in JP-A-2000-119324, JP-A-2000-119325, JP-A-2000-119326, It can be obtained by the polymerization methods described in JP-T-2004-528410, JP-T-2005-518467, JP-T-2005-527641, JP-A-2009-108330, JP-A-7-25212, JP-A-6-306207, JP-A-6-199103, JP-A-6-92108, JP-A-6-87975, etc. Furthermore, commercially available products can also be used as the syndiotactic 1,2-polybutadiene (B). Examples of commercially available products include RB840 and RB830 manufactured by JSR Corporation.

[0045] Examples of the iron-based catalyst composition include a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, and (c) an organoaluminum compound; a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, (c) an organoaluminum compound, and another organometallic compound or a Lewis base; and a catalyst composition comprising (a) an iron-containing compound, (b) a dihydrocarbyl hydrogen phosphite, and (c) an organoaluminum compound. The (a) iron-containing compound is not particularly limited, but suitable examples include iron carboxylate, organic iron phosphate, organic iron phosphonate, organic iron phosphinate, iron carbamate, iron dithiocarbamate, iron xanthate, iron α-diketonate, iron alkoxide or aryloxide, and organic iron compounds. Among these compounds, compounds having an sPB crystallinity of 7 to 40 J / g and a number-average molecular weight of 6.5 × 10 are also suitable. ４ From the viewpoint of being able to more reliably control the content within the above range, it is more preferable that the iron-based catalyst composition contains iron(III) tris(2-ethylhexanoate), bis(2-ethylhexyl) phosphite, triisobutylaluminum, tri-n-butylaluminum, and tri-n-octylaluminum.

[0046] An example of the chromium-based catalyst composition is a three-component catalyst system comprising (a) a chromium-containing compound, (b) an alkylaluminum hydride compound, and (c) a hydrogen phosphite. Various chromium-containing compounds can be used as component (a) of the chromium-based catalyst composition. Generally, it is advantageous to use a chromium-containing compound soluble in a hydrocarbon solvent such as an aromatic hydrocarbon, an aliphatic hydrocarbon, or an alicyclic hydrocarbon. However, it is also possible for an insoluble chromium-containing compound simply dispersed in the polymerization medium to generate catalytically active species. Therefore, no limitations should be placed on the chromium-containing compound in order to ensure solubility. Examples of chromium in (a) the chromium-containing compound include, but are not limited to, chromium carboxylates, chromium β-diketonates, chromium alkoxides or aryloxides, chromium halides, pseudochromium halides, and organic chromium compounds.

[0047] Examples of the cobalt-based catalyst composition include a catalyst system comprising soluble cobalt such as cobalt octoate, cobalt 1-naphthate, or cobalt benzoate, an organoaluminum compound such as trimethylaluminum, triethylaluminum, tributylaluminum, or triphenylaluminum, and carbon disulfide.

[0048] (Antiaging Agent (C)) The rubber composition of this embodiment contains an antioxidant (C). The antioxidant (C) has the effect of preventing aging of the rubber composition and rubber products using the same. The antioxidant (C) contains the following triphenylamine-based antioxidant (C1), and may further contain at least one of the following quinoline-based antioxidant (C2), an amine-based antioxidant (C3) represented by the following general formula (2), an amine-based antioxidant (C4) represented by the following general formula (3), and other antioxidants (C5).

[0049] The content of the antioxidant (C) is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass, and even more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the antioxidant (C) is within the above range, an excellent balance of abrasion resistance, mechanical strength before and after heat degradation, and ozone resistance is achieved.

[0050] In the rubber composition of this embodiment, the ratio of the 1,2-bond content of the syndiotactic 1,2-polybutadiene (B) to the content of the antioxidant (C) is preferably 8 to 200. When this ratio is within the above range, an excellent balance of abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance is achieved. Furthermore, the ratio of the 1,2-bond content of the syndiotactic 1,2-polybutadiene (B) to the content of the antioxidant (C) is more preferably 7 to 200. In this ratio, the content of the antioxidant (C) refers to the content (parts by mass) per 100 parts by mass of the rubber component (A). That is, the ratio of the 1,2-bond content of the syndiotactic 1,2-polybutadiene (B) to the content of the antioxidant (C) refers to "the 1,2-bond content (% by mass) of the syndiotactic 1,2-polybutadiene (B) / the content (parts by mass) of the antioxidant (C)."

[0051] In the rubber composition of this embodiment, the ratio of the crystalline amount of syndiotactic 1,2-polybutadiene (B) to the content of antioxidant (C) is preferably 3 to 100. When this ratio is within the above range, an excellent balance of abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance is achieved. Furthermore, the ratio of the crystalline amount of syndiotactic 1,2-polybutadiene (B) to the content of antioxidant (C) is more preferably 3 to 80. In this ratio, the content of antioxidant (C) refers to the amount (parts by mass) per 100 parts by mass of the rubber component (A). In other words, the ratio of the crystalline amount of syndiotactic 1,2-polybutadiene (B) to the content of antioxidant (C) refers to "crystalline amount of syndiotactic 1,2-polybutadiene (B) (J / g) / content (parts by mass) of antioxidant (C)."

[0052] [Triphenylamine-based antioxidant (C1) represented by general formula (1)] The triphenylamine-based antioxidant (C1) 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 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 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.] The triphenylamine-based antiaging agent represented by the above general formula (1) has the effect of improving ozone resistance. In addition, the triphenylamine-based antiaging agent represented by the above general formula (1) has a small environmental impact.

[0053] 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.

[0054] 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.

[0055] R １１ , R １２ and R１３１ 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 (e.g., an n-octyl group, a 2-octyl group).

[0056] R in the above general formula (1) １１ and R １２ are preferably each independently an alkyl group selected from the group consisting of an isopropyl group, a 1,3-dimethylbutyl group, a 1,4-dimethylpentyl group, and a 2-octyl group. １１ and R １２ Preferably, each independently has 2 to 8 carbon atoms.

[0057] R １３ and R １３２ With 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.

[0058] 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.

[0059] Specific examples of the triphenylamine-based antioxidants represented by the general formula (1) include 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)triphenylamine, 4,4'-bis(1,3-dimethylbutylamino)triphenylamine, 4,4'-bis(1,4- Preferred are 4,4'-bis(dimethylpentylamino)triphenylamine, 4,4'-bis(2-octylamino)triphenylamine, 4,4'-bis(isopropylamino)-4''-methoxytriphenylamine, 4,4'-bis(1,3-dimethylbutylamino)-4''-methoxytriphenylamine, 4,4'-bis(2-octylamino)-4''-methoxytriphenylamine, 4,4'-bis(1,4-dimethylpentylamino)-4''-methoxytriphenylamine, and 4,4'-bis(1-methylheptylamino)-4''-methoxytriphenylamine. These triphenylamine-based antioxidants (C1) may be used alone or in combination of two or more.

[0060] The triphenylamine-based antioxidant (C1) is 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 １４ and R １５ 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.] The triphenylamine-based antioxidant represented by general formula (1-1) or (1-2) has the effect of improving the ozone resistance of the rubber composition.

[0061] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １４ and R １５ 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, 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.

[0062] 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 １３２ and R １３３ are each independently an alkyl group, provided that R １３２ and R １３３ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. 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, and preferably 2 to 7. １４１ , R １４２ , R １５１ and R １５２ are each independently an alkyl group, provided that R １４１ and R１４２ The total number of carbon atoms in R is 2 to 11, preferably 2 to 7. １５１ and R １５２ The total number of carbon atoms is 2 to 11, preferably 2 to 7.

[0063] The synthesis method of the triphenylamine-based antioxidant (C1) represented by the above general formula (1-1) or (1-2) is described in French Patent No. 1,354,536 and US Pat. No. 3,277,174.

[0064] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １４ and R １５ are preferably each independently an isopropyl group, a 1,3-dimethylbutyl group, a 1,4-dimethylpentyl group, or a 2-octyl group. １１ , R １２ and R １３ is an isopropyl group, a 1,3-dimethylbutyl group, a 1,4-dimethylpentyl group, or a 2-octyl group, and a triphenylamine-based antioxidant represented by the general formula (1-2): １４ and R １５ A triphenylamine-based antioxidant in which R is an isopropyl group, a 1,3-dimethylbutyl group, a 1,4-dimethylpentyl group, or a 2-octyl group can further improve the ozone resistance of the rubber composition.

[0065] R in the above general formula (1-1) １１ , R １２ and R １３１ and R in the general formula (1-2) １４ and R １５ Each of R in the general formula (1-1) preferably has 2 to 8 carbon atoms. １１ , R １２ and R １３１ and a triphenylamine-based antioxidant having 2 to 8 carbon atoms, １４ and R １５The triphenylamine antioxidant having 2 to 8 carbon atoms can further improve the ozone resistance of the rubber composition.

[0066] The proportion of the triphenylamine-based antioxidant (C1) represented by the general formula (1-1) or (1-2) 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 (1-1) or (1-2) in the antioxidant (C) is 10 to 100 mass%, the ozone resistance of the rubber composition can be further improved.

[0067] The triphenylamine-based antioxidant (C1) may be a compound represented by the following general formula (1-3): In the above general formula (1-3), a compound represented by 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 １３１２ are each independently an alkyl group, provided that R １３１１and R １３１２ The total number of carbon atoms is 2 to 11, preferably 2 to 7.

[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 a rubber composition. A rubber composition containing both the triphenylamine-based antioxidant (C1) represented by the above general formula (1-1) or (1-2) and the quinoline-based antioxidant (C2) can further improve the ozone resistance of a rubber product.

[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 improve the ozone resistance of rubber products and is less likely to discolor. 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 mass%, more preferably 10 to 50 mass%. When the proportion of the quinoline-based antioxidant (C2) in the antioxidant (C) is 5 to 50 mass%, the ozone resistance of the rubber composition can be further improved.

[0071] In one embodiment, the rubber composition of the present embodiment preferably contains the antioxidant (C) in an amount of 0.5 to 10 parts by mass relative to 100 parts by mass of the rubber component (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.

[0072] [Amine-based antioxidant (C3) represented by general formula (2)] In the rubber composition of the present embodiment, the antioxidant (C) may further be an amine-based antioxidant represented by the following general formula (2): [In the formula, R ２１ and R ２２ are each independently a monovalent saturated hydrocarbon group. The amine-based antioxidant represented by general formula (2) (hereinafter sometimes simply referred to as "amine-based antioxidant (C3)") is similar to, for example, the conventionally known antioxidant N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) in that it contains a phenylenediamine moiety, but differs in that it does not contain a double bond other than the phenylenediamine moiety. Furthermore, when blended in a predetermined amount with a rubber composition containing the above-mentioned rubber component (A) and the above-mentioned syndiotactic 1,2-polybutadiene (B), the amine-based antioxidant has the effect of significantly maintaining the mechanical strength of the rubber composition even after thermal aging.

[0073] In the above general formula (2), R ２１ and R ２２ are each independently a monovalent saturated hydrocarbon group. ２１ and R ２２ may be the same or different, but from the viewpoint of synthesis, it is preferable that they are the same.

[0074] The number of carbon atoms in the monovalent saturated hydrocarbon group is preferably 1 to 20, more preferably 3 to 10, and even more 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, resulting in a greater anti-aging effect and further improving the mechanical strength of the rubber composition after thermal aging.

[0075] R in the above general formula (2) ２１ and R ２２ and each independently represent a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms, from the viewpoint of further improving the mechanical strength of the rubber composition, particularly the mechanical strength after thermal aging.

[0076] 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.

[0077] Specific examples of the amine-based antioxidant (C3) represented by the general formula (2) 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 (CCPD) are preferred, with N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD) being particularly preferred. The amine-based antioxidant (C3) may be used alone or in combination of two or more.

[0078] The content of the amine-based antioxidant (C3) represented by the general formula (2) is preferably 0.1 to 11 parts by mass per 100 parts by mass of the rubber component. If the content of the amine-based antioxidant (C3) represented by the general formula (2) is less than 0.1 part by mass per 100 parts by mass of the rubber component, the mechanical strength of the rubber composition, particularly the effect of retaining the mechanical strength after heat aging, cannot be sufficiently obtained. On the other hand, if the content of the amine-based antioxidant (C3) represented by the general formula (2) is more than 11 parts by mass per 100 parts by mass of the rubber component (A), adverse effects on rubber physical properties other than mechanical strength (heat buildup, hardness, etc.) become significant, making the rubber unsuitable for tire applications. The content of the amine-based antioxidant (C3) represented by the general formula (2) per 100 parts by mass of the rubber component (A) is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of mechanical strength, and is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, from the viewpoint of influence on other physical properties of the rubber.

[0079] The amine-based antiaging agent (C3) represented by the general formula (2) may be supported on any carrier. For example, the amine-based antiaging agent (C3) represented by the general formula (2) may be supported on a filler such as silica, which will be described later. The amine-based antiaging agent (C3) represented by the general formula (2) may also constitute a masterbatch together with the rubber component (A). The amine-based antiaging agent (C3) represented by the general formula (2) may also be in the form of a salt with an organic acid. The organic acid used to form the salt is not particularly limited, but examples thereof include stearic acid.

[0080] The proportion of the amine-based antioxidant (C3) represented by the general formula (2) 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) represented by the general formula (2) is in the above range, the ozone resistance of the rubber composition can be further improved.

[0081] [Amine-based Antiaging Agent (C4) Represented by General Formula (3)] The antiaging agent (C) may further be an amine-based antiaging agent represented by the following general formula (3): [In the formula, R ３１ and R ３２ represents a phenyl group, and m3 represents an integer of 7 or more. ] (hereinafter, may be simply referred to as "amine-based antioxidant (C4)"). The amine-based antioxidant (C4) represented by the above general formula (3) has a higher molecular weight than conventional antioxidants, and, as shown in the above general formula (3), has a bridge moiety having a unique and relatively long chain length, i.e., "-NH-CH(CH ３ )-(CH ２ ) ｍ３ -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 )ｍ３ -CH(CH ３ One hydrogen atom is bonded to each of the two nitrogen atoms present at both ends of "-" (forming a so-called secondary amino group), and the presence of this bond in the structure represented by general formula (3) is thought to contribute to the specific effect of improving ozone resistance (weather resistance).

[0082] In the above general formula (3), R ３１ and R ３２ is a phenyl group. ３１ and R ３２ When 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.

[0083] In the general formula (3), m3 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.

[0084] Examples of the amine-based antioxidant (C4) of the general formula (3) 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.

[0085] The proportion of the amine-based antioxidant (C4) 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 (C4) represented by the general formula (3) in the antioxidant (C) is 0.1 to 80 mass%, the ozone resistance of the rubber composition can be further improved.

[0086] [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) represented by the general formula (1), the quinoline-based antioxidant (C2), the amine-based antioxidant (C3) represented by the general formula (2), and the amine-based antioxidant (C4) represented by the general formula (3). Examples of the other antioxidant (C5) include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and N,N'-diphenyl-p-phenylenediamine (DPPD). Among these, it is preferable not to include 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.

[0087] (Organic Peroxide (D)) The rubber composition preferably further contains an organic peroxide (D). The organic peroxide (D) acts as a crosslinking agent to crosslink the rubber composition. The organic peroxide (D) has high reactivity with the vinyl bond (1,2-bond) of the syndiotactic 1,2-polybutadiene (B). Therefore, crosslinking with the organic peroxide (D) is thought to improve mechanical strength compared to crosslinking (vulcanization) using general sulfur.

[0088] The organic peroxide 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-trimethyl ... , 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, 1,1,3 , 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. The organic peroxide (D) is preferably dicumyl peroxide. These organic peroxides (D) may be used alone or in combination of two or more.

[0089] The content of the organic peroxide (D) in the rubber composition is preferably 1 to 10 parts by mass per 100 parts by mass of the rubber component (A). When the content of the organic peroxide (D) is 1 part by mass or more per 100 parts by mass of the rubber component (A), the rubber composition can be sufficiently crosslinked, and when the content is 10 parts by mass or less, the rubber composition can sufficiently ensure rubber elasticity.

[0090] In the rubber composition of this embodiment, the mass ratio (D / C) of the organic peroxide (D) to the antioxidant (C) is preferably 0.05 to 4. When the mass ratio is within this range, an excellent balance of abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance is achieved. From the same viewpoint, the mass ratio (D / C) of the organic peroxide (D) to the antioxidant (C) is more preferably 0.06 to 4.

[0091] (Co-crosslinking agent) The rubber composition may contain a co-crosslinking agent. Examples of the co-crosslinking agent include ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, zinc methacrylate, and magnesium methacrylate. The content of the co-crosslinking agent is preferably 1 to 10 parts by mass per 100 parts by mass of the rubber component (A).

[0092] (Filler) The rubber composition may further contain a filler. By including a filler, the strength of the rubber composition is improved. Examples of the filler include carbon black and inorganic fillers. The fillers may be used alone or in combination of two or more. The content of the filler in the rubber composition is preferably 10 to 160 parts by mass, more preferably 15 to 140 parts by mass, even more preferably 15 to 120 parts by mass, and particularly preferably 20 to 120 parts by mass, per 100 parts by mass of the rubber component (A).

[0093] Carbon Black Carbon black reinforces the rubber composition and can improve the abrasion resistance of the rubber composition. As the carbon black, plant-derived carbon black and recycled carbon black (also called "recycled carbon black") are preferred. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0094] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of carbon black (total of recycled carbon black and carbon black other than recycled carbon black) in the rubber composition 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 rubber component (A). Also, from the viewpoint of workability of the rubber composition, the content of carbon black in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of rubber component (A).

[0095] --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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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).

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] The recycled carbon black preferably has a dibutyl phthalate (DBP) absorption of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the DBP absorption of recycled carbon black is determined in accordance with ASTM D2414.

[0117] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the 24M4DBP absorption capacity of the recycled carbon black is determined in accordance with ASTM D3493.

[0118] 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.

[0119] 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, still more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component (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.

[0120] -Inorganic Filler- Silica is preferred as the inorganic filler. Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate, with wet silica being preferred. Inorganic fillers other than silica include aluminum hydroxide and clay. The BET specific surface area of ​​the wet silica (measured in accordance with ISO 5794 / 1) is 40 to 350 m ２ / g is preferred, and 80 to 300m ２ / g is more preferable. Silica having a BET specific surface area in this range can achieve both rubber reinforcement and dispersibility in the rubber component. Silica may be used alone or in combination of two or more types.

[0121] (Silane Coupling Agent) When silica is used as the filler, a silane coupling agent such as bis(3-triethoxysilylpropyl) polysulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl benzothiazyl tetrasulfide, etc. is preferably used. The amount of the silane coupling agent is selected in the range of preferably 2 to 20 parts by mass per 100 parts by mass of silica.

[0122] (Vulcanizing Agent) The rubber composition preferably does not contain a vulcanizing agent (i.e., 0 part by mass), or the content of the vulcanizing agent is preferably 1 part by mass or less per 100 parts by mass of the rubber component (A). Here, the vulcanizing agent is a cross-linking agent that has the effect of sulfur-crosslinking the rubber component (A). Examples of the vulcanizing agent include sulfur (powdered sulfur, etc.), morpholine disulfide, and polymeric polysulfides.

[0123] (Other Components) In addition to the above-mentioned rubber component (A), syndiotactic 1,2-polybutadiene (B), antioxidant (C), organic peroxide (D), co-crosslinking agent, filler, silane coupling agent, and vulcanizing agent, the rubber composition may contain, if desired, compounding agents commonly used in the rubber industry, such as softeners, zinc oxide, stearic acid, etc. The contents of these can be appropriately selected within ranges that do not impair the object of the present invention.

[0124] (Method for Producing Rubber Composition) The method for producing the rubber composition of the present embodiment is not particularly limited, but the rubber composition can be produced, for example, by adding the above-mentioned rubber component (A), syndiotactic 1,2-polybutadiene (B), and antioxidant (C), as well as various components appropriately selected as necessary, simultaneously or in any order, and kneading, heating, extruding, etc.

[0125] 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 internal mixer, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0126] From the viewpoint of more reliably forming the above-mentioned three-dimensional network in the rubber composition, particularly in the rubber composition after vulcanization, it is preferable to provide a step (masterbatch kneading step) of kneading the rubber component (A) and the syndiotactic 1,2-polybutadiene (B) in the absence of a vulcanizing agent or a vulcanization accelerator, and to knead the components at a temperature 10 to 100° C. higher, particularly 10 to 50° C. higher, and particularly 12 to 50° C. higher than the melting point of the syndiotactic 1,2-polybutadiene (B). By setting the kneading temperature at a temperature 10° C. higher or higher than the melting point of the syndiotactic 1,2-polybutadiene (B), the syndiotactic 1,2-polybutadiene (B) can be effectively made compatible with the rubber component (A). Furthermore, by setting the temperature to be 100°C higher than the melting point of the syndiotactic 1,2-polybutadiene (B) or lower, thermal degradation of the rubber component and the syndiotactic 1,2-polybutadiene (B) can be suitably prevented, which can contribute to improving the mechanical strength of the obtained rubber composition, and ultimately the vulcanized rubber composition.

[0127] The temperature during kneading refers to the temperature of the masterbatch at the time when the masterbatch of the unvulcanized rubber composition is discharged from the kneading device, and specifically refers to the temperature measured with a temperature sensor or the like during masterbatch kneading, where the internal temperature of the masterbatch is measured immediately after being discharged from the kneading device. However, if the kneading device is equipped with a means for measuring the temperature of the unvulcanized rubber composition, the temperature of the masterbatch at the time of discharge may be measured. Here, the masterbatch refers to a rubber composition obtained at least at the stage of kneading the rubber component (A) and the syndiotactic 1,2-polybutadiene (B) without blending a vulcanizing agent and a vulcanization accelerator.

[0128] (Applications) The rubber composition of the present 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 the present embodiment is suitable for tires, and particularly suitable for tire treads. By using the rubber composition of the present embodiment in tire treads, tires can be made that are excellent in abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance.

[0129] <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, it has excellent abrasion resistance, mechanical strength before and after thermal degradation, and ozone resistance.

[0130] - 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).

[0131] - 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.

[0132] -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.

[0133] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples in any way.

[0134] <Examples 1-1 to 1-3 and Comparative Example 1-1> For Examples 1-1 to 1-3, rubber compositions for each example were produced according to the compounding recipes shown in Table 1. The rubber compositions obtained for each example were evaluated as follows. For Comparative Example 1-1, a rubber composition was obtained in the same manner as for Examples 1-1 to 1-3, and the following evaluations were carried out.

[0135] <Evaluation Method> (Strength Evaluation) The rubber compositions of Examples 1-1 to 1-3 were subjected to a vulcanization treatment and then processed into JIS No. 3 test pieces. Tensile tests were conducted at room temperature (25°C) to measure the area value (undegraded) of the stress-strain curve. The area value (undegraded) in each example was indexed, with the area value (undegraded) of Comparative Example 1-1 set to 100. The index values ​​were classified according to the following criteria, and the results are shown in Table 1. A higher index value indicates higher strength in the undegraded state. The rubber composition of Comparative Example 1-1 was subjected to the same measurements as the rubber compositions of Examples 1-1 to 1-3, and the results were indexed and classified according to the following criteria. The results are shown in Table 1. A: Calculated value is 100 or more and 110 or less B: Calculated value is 90 or more and less than 100 C: Calculated value is less than 90 Furthermore, the test pieces of Examples 1-1 to 1-3 were left in an air environment at 100°C for 24 hours to cause thermal degradation. Then, for the test specimens after thermal aging, the area value (after thermal aging) of the stress-strain curve is measured in the same manner as above. For the area value (after thermal aging) of each example, the retention rate (%) relative to the area value (unaged) is calculated. The calculated values ​​are classified according to the following criteria, and the results are shown in Table 1. A larger calculated value indicates that the strength is retained to a higher degree even after thermal aging. For the test specimen of Comparative Example 1-1, the same measurements as in Examples 1-1 to 1-3 were carried out, and the results were indexed and classified according to the following criteria. The results are shown in Table 1. A: Index value is 100 or more and 110 or less B: Index value is 90 or more and less than 100 C: Index value is less than 90

[0136] (Evaluation of hardness (M300)) The rubber compositions of Examples 1-1 to 1-3 obtained were subjected to a vulcanization treatment and then processed into JIS No. 3 test pieces, which were then subjected to a tensile test at room temperature (25°C) to measure the stress at 300% strain (M300). The M300 in each example was indexed, with the M300 of Comparative Example 1-1 set to 100. The index values ​​were classified according to the following criteria, and the results are shown in Table 1. An index value of 75 or more is considered to be good for tire applications. The rubber composition of Comparative Example 1-1 was measured in the same manner as Examples 1-1 to 1-3, and the rubber composition was indexed and classified according to the following criteria. The results are shown in Table 1. A: Index value of 75 or more and 100 or less B: Index value less than 75

[0137]

[0138] * 11 Natural rubber: RSS # 1 * 12 Carbon black: HAF grade carbon black * 13 Syndiotactic 1,2-polybutadiene: ENEOS Material Corporation, trade name "JSR RB (registered trademark) 830" * 14 Sulfur: Hosoi Chemical Industry Co., Ltd., trade name "HK200-5" * 15 Vulcanization accelerator: Sanshin Chemical Industry Co., Ltd., trade name "Suncerer NS-G" * 16 Antioxidant-1: 6C, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, Sumitomo Chemical Co., Ltd., trade name "Antigen 6C" * 17 Antioxidant-2: 4,4'-bis(2-octylamino)triphenylamine, a triphenylamine-based antioxidant represented by the following formula (a) *18 Antioxidant-3: 4,4'-bis(2-octylamino)-4''-methoxytriphenylamine, a triphenylamine-based antioxidant represented by the following formula (b) *19 Antioxidant-4: 4,4',4''-tris(1,3-dimethylbutylamino)triphenylamine, a triphenylamine-based antioxidant represented by the following formula (c)

[0139] It can be seen from Table 1 that the rubber compositions of Examples 1-1 to 1-3 are excellent in strength after heat degradation and also in hardness.

[0140] <Preparation of syndiotactic 1,2-polybutadiene> Syndiotactic 1,2-polybutadiene-1 (hereinafter referred to as " Ｓ PB-1) to syndiotactic 1,2-polybutadiene-8 (hereinafter referred to as " Ｓ The following materials were used for the "PB-8" (sometimes abbreviated as "PB-8").

[0141] (sPB-1, sPB-2) For sPB-1, "JSR RB (registered trademark) 840" manufactured by ENEOS Materials Co., Ltd. was used. The 1,2-bond content of sPB-1 was 84% ​​by mass, the melting point was 122°C, and the number average molecular weight was 6.6 × 10 ４ The crystallinity was 21 J / g. For sPB-2, "JSR RB (registered trademark) 820" manufactured by ENEOS Materials Corporation was used. The 1,2-bond content of sPB-2 was 86% by mass, the melting point was 95°C, and the number average molecular weight was 8.9 × 10 ４ The crystal amount was 15 J / g.

[0142] (Preparation of sPB-3 to sPB-7) An oven-dried 1 L (1000 cc) glass bottle was stoppered with a sealing rubber liner and a perforated metal cap. After thoroughly purging the bottle with a stream of dry nitrogen gas, 94 g of hexanes and 206 g of a 1,3-butadiene / hexanes mixture containing 21.8% by weight of 1,3-butadiene were added to the bottle. Next, catalyst components were added to the bottle under the conditions shown in Table 2. The bottle was stirred for 4 hours in a water bath maintained at the reaction temperature shown in Table 2. The resulting polymerization reaction mixture was a fluid, slightly cloudy solution. Immediately after cooling to room temperature, the solution lost its fluidity due to the precipitation of syndiotactic 1,2-polybutadiene. The polymerization reaction mixture was coagulated with 3 liters of isopropanol containing 2,6-di-tert-butyl-4-methylphenol as an antioxidant. The resulting solid was isolated by filtration and dried under reduced pressure at 60° C. to a constant weight to yield syndiotactic 1,2-polybutadiene.

[0143] (Production of sPB-8) 9,764 g of hexanes and 26,423 g of a 1,3-butadiene / hexanes mixture containing 20.6% by mass of 1,3-butadiene were added to a 76 L (760,000 cc) stainless steel reactor that had been thoroughly purged with a stream of dry nitrogen gas, and the temperature inside the reactor was set to 52°C. Next, the catalyst components were added to the reactor under the conditions shown in Table 2. The reactor was set to the reaction temperature shown in Table 2 and stirred for 1 hour. The resulting polymerization reaction mixture was a fluid, slightly cloudy solution. Immediately after cooling to room temperature, the solution lost its fluidity due to the precipitation of syndiotactic 1,2-polybutadiene. The polymerization reaction mixture was coagulated with 9.5 L of isopropanol containing 2,6-di-tert-butyl-4-methylphenol as an antioxidant. The resulting solid was isolated by filtration and dried under reduced pressure at 60° C. to a constant weight to yield syndiotactic 1,2-polybutadiene.

[0144] The melting points, number average molecular weights (Mn) and crystal amounts of sPB-1 to sPB-8 were measured by the following methods, and the measurement results are shown in Table 2.

[0145] (Melting Point of Syndiotactic 1,2-Polybutadiene) A sample of syndiotactic 1,2-polybutadiene was placed in a differential scanning calorimetry (DSC) device, and the melting point was determined by measuring the melting peak temperature on the DSC curve when the temperature was increased at a rate of 10° C. / min.

[0146] (Number average molecular weight (Mn)) This was measured by gel permeation chromatography [GPC: HLC-8220 / HT, manufactured by Tosoh Corporation] using a differential refractometer as a detector, and is shown in terms of polystyrene equivalents with monodisperse polystyrene as the standard. The column was GMHHR-H(S)HT [manufactured by Tosoh Corporation], the eluent was trichlorobenzene, and the measurement temperature was 140°C.

[0147] (Crystal Amount) The crystal amount (J / g) was obtained by calculating the area of ​​the melting peak observed from −100° C. to 200° C. during melting point measurement using a differential scanning calorimetry (manufactured by TA Instruments).

[0148]

[0149] <Comparative Examples 2-1 and 2-2, and Examples 2-1 to 2-9> For Comparative Examples 2-1 and 2-2, a non-production kneading step was carried out using the formulations shown in Table 3. The maximum temperature during kneading was 150°C. Next, the components shown in Table 3 were added to the masterbatch obtained from the non-production kneading step, and a production vulcanization step was carried out to obtain vulcanized rubber compositions. The temperature during vulcanization was 160°C. The resulting vulcanized rubber compositions of each example were evaluated for the balance of abrasion resistance and cut resistance relative to fuel economy using the method described below. The resulting vulcanized rubber compositions of each example were also evaluated for ozone resistance. The results are shown in Table 3. For Examples 2-1 to 2-9, vulcanized rubber compositions were prepared and evaluated in the same manner as for Comparative Examples 2-1 and 2-2.

[0150] <Evaluation Method> (1) Balance between fuel economy and cut resistance For the vulcanized rubber compositions of Comparative Example 2-1 and Comparative Example 2-2, the loss tangent tanδ was measured using a viscoelasticity measuring device (manufactured by Ueshima Seisakusho) under conditions of a frequency of 15 Hz, a tensile strain of 2%, and a temperature of 50°C. This tanδ was divided by the 0.4 power of the stress (M50) at room temperature and 50% strain obtained from a tensile test (JIS 7 test piece) (tanδ / M50 ０．４) to calculate an evaluation value for fuel economy. The evaluation of fuel economy was carried out by taking the reciprocal of the calculated value and expressing it as an index value when the reciprocal of the evaluation value of the vulcanized rubber composition of Comparative Example 2-1 was set to 100. The index values ​​were classified according to the following criteria, and the results are shown in Table 3. The larger the value, the better the performance. For the vulcanized rubber compositions of Examples 2-1 to 2-9, measurements were carried out in the same way as for the vulcanized rubber compositions of Comparative Examples 2-1 and 2-2, and index values ​​were calculated and classified according to the following criteria. The results are shown in Table 3. (Evaluation Criteria for Fuel Efficiency) A: Index value greater than 120 B: Index value greater than 100 but not greater than 120 C: Index value not greater than 100 For the vulcanized rubber compositions of Comparative Examples 2-1 and 2-2, cut resistance was measured using a tensile testing machine (Shimadzu Corporation) in which a pure shear test piece was stretched and an incision was made in the test piece to observe the crack propagation. The crack propagation rate was measured when the common logarithm of the energy release rate was 4.8. The cut resistance was evaluated as an index value, with the crack propagation rate for the vulcanized rubber composition of Comparative Example 2-1 taken as 100. The index values ​​were classified according to the following criteria, and the results are shown in Table 3. A higher index value indicates better cut resistance. For the vulcanized rubber compositions of Examples 2-1 to 2-9, cut resistance was measured in the same manner as for the vulcanized rubber compositions of Comparative Examples 2-1 and 2-2, and index values ​​were calculated and classified according to the following criteria. The results are shown in Table 3. (Cut Resistance Evaluation Criteria) A: Index value greater than 120 B: Index value greater than 100 but not greater than 120 C: Index value less than 100 Regarding the balance between fuel economy and cut resistance, the horizontal axis represents the evaluation value of fuel economy and the vertical axis represents the transfer energy of cut resistance. The values ​​on the line connecting the plotted points of the results of Comparative Examples 2-1 and 2-2 were set to 100. The results of each example were then plotted, and the degree of improvement or decrease from the line was used as an index. The index values ​​were classified according to the following criteria, and the results are shown in Table 3. A higher index value indicates better cut resistance relative to fuel economy. Regarding the vulcanized rubber compositions of Examples 2-1 to 2-9, the balance between fuel economy and cut resistance was indexed in the same way as in Comparative Examples 2-1 and 2-2, and classified according to the following criteria. The results are shown in Table 3.(Evaluation criteria for the balance between fuel efficiency and cut resistance) A: Index value exceeds 160 B: Index value exceeds 140 and is 160 or less C: Index value is 140 or less.

[0151] (2) Ozone Resistance A dynamic ozone degradation test (a test in which repeated strain is applied) was conducted on the vulcanized rubber compositions of Comparative Examples 2-1 to 2-2 and Examples 2-1 to 2-9 in accordance with ISO 1431 (JIS K 6259), and the samples were observed at 20x magnification using a microscope. The observed samples were ranked according to the size and depth of cracks and classified according to the following criteria (1 to 5), with smaller numbers indicating better results. (Ranking by crack size and depth) 1: Not visible to the naked eye but visible with a 10x magnifying glass. 2: Visible to the naked eye. 3: Deep and relatively large cracks (less than 1 mm). 4: Deep and large cracks (1 mm or more but less than 3 mm). 5: Cracks of 3 mm or more or likely to cause breakage.

[0152]

[0153] * 21 Carbon black: ISAF grade carbon black, Asahi Carbon Co., Ltd. "Asahi # 80" * 22 Wax: Microcrystalline wax, Seiko Chemical Co., Ltd. * 23 Vulcanization accelerator: N-(cyclohexyl)-2-benzothiazole sulfenamide, Ouchi Shinko Chemical Industry Co., Ltd. "Noccela (registered trademark) CZ"

[0154] From Table 3, it can be seen that the vulcanized rubber compositions of the examples are excellent in ozone resistance.

[0155] 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 rubber component (A); a syndiotactic 1,2-polybutadiene (B); 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 a hydrogen atom, 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, wherein the rubber component (A) contains an isoprene-based rubber.

3. The rubber composition according to claim 1, wherein the syndiotactic 1,2-polybutadiene (B) has a 1,2-bond content of 80% by mass or more.

4. The rubber composition according to claim 1, wherein the syndiotactic 1,2-polybutadiene (B) has a syndiotacticity in 1,2-bonds of 60% or more and 95% or less.

5. The rubber composition according to claim 1, wherein the syndiotactic 1,2-polybutadiene (B) has a crystallinity of 25 to 50%.

6. The rubber composition according to claim 1, wherein the syndiotactic 1,2-polybutadiene (B) has a melting point of 100 to 150°C.

7. The rubber composition according to claim 1, wherein the content of said syndiotactic 1,2-polybutadiene (B) is 5 to 40 parts by mass per 100 parts by mass of said rubber component (A).

8. The rubber composition according to claim 1, wherein the ratio of the 1,2-bond content of said syndiotactic 1,2-polybutadiene (B) to the content of said antioxidant (C) is 8 to 200.

9. The rubber composition according to claim 1, wherein the ratio of the amount of crystals of said syndiotactic 1,2-polybutadiene (B) to the amount of said antioxidant (C) is 3 to 100.

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

11. R in the above general formula (1) １１ and R １２ and each independently have 2 to 8 carbon atoms.

12. The rubber composition according to claim 1, wherein the content of the antioxidant (C) is 0.5 to 50 parts by mass per 100 parts by mass of the rubber component (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.

13. The antioxidant (C) further comprises a compound represented by the following general formula (2): [In the formula, R ２１ and R ２２ 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 %.

14. The antioxidant (C) further comprises a compound represented by the following general formula (3): [In the formula, R ３１ and R ３２ represents a phenyl group, and m3 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 %.

15. The rubber composition of claim 1, which is for use in tire treads.

16. 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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