Rubber composition and tire

Abstract

To provide a rubber composition capable of maintaining sufficient crosslinking density while containing a reduced amount of a metal oxide such as zinc oxide or not containing the metal oxide.SOLUTION: A rubber composition according to an embodiment contains 100 pts.mass of a diene rubber component containing styrene-butadiene rubber and / or butadiene rubber, 40-150 pts.mass of silica, 0.1-5.0 pts.mass of sulfur, and 0.01-5.0 pts.mass of an organic peroxide. In the diene rubber component, an amount of a vinyl bond unit derived from butadiene is 10 mass% or less in the total amount of the diene rubber component. A content of a metal oxide is less than 0.5 pt.mass based on 100 pts.mass of the diene rubber component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a tire using the same. [Background technology]

[0002] Rubber compositions used in tires, anti-vibration rubber, conveyor belts, etc. generally contain diene rubber as the rubber component, and contain a vulcanizing agent such as sulfur, a vulcanization accelerator, and a metal oxide such as zinc oxide. Vulcanized rubber is formed by vulcanizing the rubber composition. In this vulcanization mechanism, metal oxides such as zinc oxide function as vulcanization accelerators and are used as essential components. However, in recent years, there has been a demand to reduce the amount of metal oxides such as zinc oxide used in order to prevent environmental pollution.

[0003] Incidentally, Patent Document 1 discloses that by compounding a diene-based rubber composition containing silica with polysiloxane, an organic peroxide, and sulfur, productivity and processability are improved while maintaining mechanical properties.

[0004] Patent Document 2 discloses that by compounding sulfur, an organic peroxide, and a tackifier with a diene rubber, the deterioration of grip performance is reduced while maintaining abrasion resistance and handling stability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-257164 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-240704 Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have found that in rubber compositions containing a diene rubber component with a small amount of vinyl bond units derived from butadiene and no metal oxide, the crosslink density of the vulcanized rubber decreases. Therefore, in order to maintain sufficient crosslink density in rubber compositions containing such diene rubber components, they have considered using an organic peroxide in combination with sulfur as a crosslinking agent.

[0007] As mentioned above, Patent Documents 1 and 2 disclose the combined use of organic peroxides and sulfur, but in Patent Document 1, a styrene-butadiene rubber with a high vinyl bond unit content is specifically used as the diene rubber in the examples. Patent Document 1 does not disclose the combined use of organic peroxides and sulfur for a diene rubber component with a low vinyl bond unit content. Furthermore, Patent Document 2 uses carbon black as a reinforcing agent, and does not disclose the combined use of organic peroxides and sulfur in a rubber composition containing silica.

[0008] In view of the above, an embodiment of the present invention aims to provide a rubber composition that can maintain a sufficient crosslink density while reducing or eliminating the amount of metal oxides such as zinc oxide. [Means for solving the problem]

[0009] The rubber composition according to the present embodiment contains 100 parts by mass of a diene rubber component containing a styrene-butadiene rubber and / or a butadiene rubber, 40 to 150 parts by mass of silica, 0.1 to 5.0 parts by mass of sulfur, and 0.01 to 5.0 parts by mass of an organic peroxide. The diene rubber component contains 10% by mass or less of vinyl bond units derived from butadiene in the total amount of the diene rubber component, and the content of a metal oxide per 100 parts by mass of the diene rubber component is less than 0.5 parts by mass. Here, the phrase "less than 0.5 parts by mass of metal oxide" includes a case where the content of metal oxide is 0 part by mass, i.e., a case where no metal oxide is contained.

[0010] A tire according to an embodiment of the present invention is produced using the above rubber composition. [Effects of the Invention]

[0011] According to an embodiment of the present invention, it is possible to maintain a sufficient crosslink density while reducing or eliminating the amount of metal oxides such as zinc oxide. DETAILED DESCRIPTION OF THE INVENTION

[0012] A rubber composition according to an embodiment of the present invention comprises a diene rubber component having a butadiene-derived vinyl bond unit content of 10% by mass or less, silica, sulfur, and an organic peroxide. The silica content is 40 to 150 parts by mass, and the metal oxide content is less than 0.5 parts by mass, per 100 parts by mass of the diene rubber component. Metal oxides such as zinc oxide function as vulcanization accelerators. When the butadiene-derived vinyl bond unit content is 10% by mass or less and the amount of metal oxide is reduced or eliminated, vulcanization typically proceeds slowly and crosslink density decreases. In contrast, by using sulfur and an organic peroxide in combination with a silica content of 40 parts by mass or more, crosslinking via a radical mechanism proceeds even without the metal oxide, maintaining sufficient crosslink density. Furthermore, when a metal oxide is incorporated, most of it remains unreacted. However, by reducing or eliminating the amount of metal oxide, the vulcanized rubber is less likely to generate heat, improving its low heat buildup properties.

[0013] In the rubber composition according to the embodiment, the diene rubber component contains a styrene butadiene rubber (SBR) and / or a butadiene rubber (BR), i.e., the diene rubber component contains SBR, BR, or both SBR and BR.

[0014] The styrene butadiene rubber may be, for example, solution polymerized styrene butadiene rubber (SSBR) or emulsion polymerized styrene butadiene rubber (ESBR). As the styrene butadiene rubber, a modified styrene butadiene rubber in which the terminals or main chain have been modified may be used as necessary. The microstructure of the styrene butadiene rubber is not particularly limited, but one having a low amount of vinyl bond units derived from butadiene is preferably used so that the amount of vinyl bond units derived from butadiene in the diene rubber component is 10% by mass or less.

[0015] The butadiene rubber may be, for example, a high-cis butadiene rubber synthesized using a transition metal catalyst such as a cobalt catalyst, a nickel catalyst, or a neodymium catalyst, or a low-cis butadiene rubber synthesized using an organolithium catalyst. The butadiene rubber may be a modified butadiene rubber whose terminals or main chain have been modified, as needed. The microstructure of the butadiene rubber is not particularly limited, but one with a low vinyl bond unit content is preferably used so that the amount of butadiene-derived vinyl bond units in the diene rubber component is 10% by mass or less.

[0016] The diene rubber component may contain other diene rubbers in addition to the styrene-butadiene rubber and / or butadiene rubber. The diene rubber refers to a rubber having repeating units corresponding to a diene monomer having a conjugated double bond, and has a double bond in the polymer backbone. Specific examples of the other diene rubbers include various diene rubbers commonly used in rubber compositions, such as natural rubber (NR), isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination of two or more. Among these, natural rubber is preferred as the other diene rubber. These other diene rubbers also include those whose terminals have been modified as necessary (e.g., terminal-modified SBR) or those whose properties have been modified to impart desired properties (e.g., modified NR).

[0017] In one embodiment, the diene rubber component preferably contains 40% by mass or more (i.e., 40 to 100% by mass) of styrene-butadiene rubber, more preferably 50% by mass or more, and even more preferably 60% by mass or more of styrene-butadiene rubber.

[0018] In one embodiment, the diene rubber component may contain 40 to 90% by mass of styrene-butadiene rubber and 10 to 60% by mass of butadiene rubber and / or natural rubber (preferably butadiene rubber), or 50 to 80% by mass of styrene-butadiene rubber and 20 to 50% by mass of butadiene rubber and / or natural rubber (preferably butadiene rubber), or alternatively, 60 to 80% by mass of styrene-butadiene rubber and 20 to 40% by mass of butadiene rubber and / or natural rubber (preferably butadiene rubber).

[0019] In this embodiment, the diene rubber component has a butadiene-derived vinyl bond unit content of 10% by mass or less based on the total amount of the diene rubber component. The vinyl bond unit content may be 9.9% by mass or less. The lower limit of the vinyl bond unit content is not particularly limited, but may be, for example, 3% by mass or more.

[0020] The amount of butadiene-derived vinyl bond units is the content of butadiene-derived vinyl bond units contained in all structural units (repeating units of polymer) of the diene rubber constituting the diene rubber component, and is expressed as mass% of the amount of said vinyl bond units relative to 100 mass% of the total amount of the diene rubber component. The butadiene-derived vinyl bond units refer to structural units of vinyl-1,2 bonds among structural units formed by butadiene.

[0021] The microstructure of diene rubber can be measured by FT-IR (Fourier transform infrared spectroscopy). More specifically, BR, NR, and IR are determined by the Morello method, and SBR by the Hampton-Morello method. When a blend of multiple diene rubbers is used, the amount of butadiene-derived vinyl bond units (mass%) in the diene rubber component can be calculated proportionally based on the blending amount from the content of butadiene-derived vinyl bond units measured for each diene rubber (i.e., the content (mass%) of butadiene-derived vinyl bond units contained in all structural units constituting the rubber polymer in each diene rubber).

[0022] The rubber composition according to the embodiment contains silica as a filler. The silica is not particularly limited, and examples thereof include wet silica and dry silica. Preferably, wet silica such as wet precipitation silica or wet gelation silica is used.

[0023] In this embodiment, silica is blended in an amount of 40 to 150 parts by mass per 100 parts by mass of the rubber component. When the silica content is 40 parts by mass or more, sufficient crosslink density can be maintained and low heat buildup can be improved. The silica content is preferably 50 to 140 parts by mass, more preferably 60 to 130 parts by mass, and even more preferably 70 to 120 parts by mass per 100 parts by mass of the diene rubber component.

[0024] The filler to be compounded in the rubber composition may be silica alone, or silica may be compounded together with carbon black. There are no particular limitations on the carbon black, and various known types can be used. Specific examples include SAF grade (N100 series), ISAF grade (N200 series), HAF grade (N300 series), FEF grade (N500 series), and GPF grade (N600 series) (all ASTM grades). These grades of carbon black can be used alone or in combination of two or more.

[0025] The amount of carbon black is not particularly limited, and may be 30 parts by mass or less, 1 to 20 parts by mass, or 2 to 15 parts by mass per 100 parts by mass of the diene rubber component. The filler preferably contains silica as a main component, and therefore, preferably 50% by mass or more of the filler is silica, more preferably 70% by mass or more (even more preferably 80% by mass or more) of the filler is silica.

[0026] The rubber composition according to the embodiment contains sulfur as a crosslinking agent. The sulfur is not particularly limited, and examples thereof include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. The sulfur content is 0.1 to 5.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, and even more preferably 1.0 to 2.5 parts by mass, per 100 parts by mass of the diene rubber component.

[0027] The rubber composition according to the embodiment contains an organic peroxide as a crosslinking agent together with sulfur. By adding the organic peroxide, radicals are generated in the polymer main chain of the diene rubber, accelerating the addition reaction to the double bonds. In this case, the presence of sulfur is thought to accelerate crosslinking between polymers by radicals, thereby improving the crosslink density.

[0028] The organic peroxide is not particularly limited, but an organic peroxide having a one-minute half-life temperature of 130 to 200° C. can be suitably used. Examples of organic peroxides having a one-minute half-life temperature of 130 to 200° C. include disuccinic acid peroxide, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-2-ethylhexanate, a mixture of di(3-methylbenzoyl) peroxide / benzoyl(3-methylbenzoyl) peroxide / dibenzoyl peroxide, dibenzoyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, 1,1 -Di(t-butylperoxy)-2-methylcyclohexane, 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butyl Peroxy-3,5,5-trimethylhexanate, t-butyl peroxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, 2,2-di(t-butylperoxy)butane, t-butyl peroxybenzoate, n butyl-4,4-di-(t-butylperoxy)valerate, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-butyl peroxide, p-menthane hydroperoxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3. These can be used alone or in combination of two or more.

[0029] Among these, organic peroxides include those having a one-minute half-life temperature of 150 to 180°C, such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexanate, t-butylperoxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2-methyl ... Preferably, the organic peroxide is at least one selected from the group consisting of 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, 2,2-di(t-butylperoxy)butane, t-butyl peroxybenzoate, n-butyl-4,4-di(t-butylperoxy)valerate, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, di-t-hexyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and t-butylcumyl peroxide. More preferably, the organic peroxide is dicumyl peroxide and / or 1,1-di(t-butylperoxy)cyclohexane.

[0030] The content of the organic peroxide is 0.01 to 5.0 parts by mass, more preferably 0.05 to 1.0 part by mass, and even more preferably 0.10 to 0.50 parts by mass, based on 100 parts by mass of the diene rubber component.

[0031] The ratio of the sulfur content to the organic peroxide content is not particularly limited, but from the viewpoint of enhancing the effects of the present embodiment, the mass ratio (A) / (B) of the sulfur content (A) to the organic peroxide content (B) is preferably 3.0 to 30.0, and more preferably 5.0 to 25.0.

[0032] The rubber composition according to the embodiment preferably further contains a styrene-based resin, which can improve wet grip performance while maintaining the effects of crosslink density and low heat buildup achieved by a crosslinking system that uses sulfur and an organic peroxide in combination.

[0033] Examples of styrene-based resins include polymers of styrene-based monomers and copolymers of styrene-based monomers and aliphatic monomers. Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, and p-chlorostyrene, and these may be used alone or in combination of two or more. Examples of aliphatic monomers include acrylonitrile, methacrylonitrile, acrylics, methacrylic acid, methyl acrylate, methyl methacrylate, 1-butene, and 1-pentene, and these may be used alone or in combination of two or more.

[0034] Specific examples of preferred styrene-based resins include α-methylstyrene homopolymers, styrene / α-methylstyrene copolymers, α-methylstyrene / aliphatic monomer copolymers, and styrene / α-methylstyrene / aliphatic monomer copolymers.

[0035] The content of the styrene resin is preferably 1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of the diene rubber component.

[0036] The rubber composition according to the embodiment may further contain a silane coupling agent. Examples of the silane coupling agent include sulfide silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; 3-mercaptopropyltrimethoxysilane; Examples of suitable silane coupling agents include mercaptosilane coupling agents such as mercaptotriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and thioester group-containing silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. These can be used alone or in combination of two or more. Among these, sulfide silane coupling agents are preferred as silane coupling agents.

[0037] The content of the silane coupling agent is not particularly limited, but is preferably 2 to 25 mass % of the silica amount, that is, 2 to 25 mass parts per 100 mass parts of silica, more preferably 5 to 20 mass parts.

[0038] In the rubber composition according to the present embodiment, from the viewpoint of preventing environmental pollution, the metal oxide content is less than 0.5 parts by mass, more preferably less than 0.2 parts by mass, and even more preferably 0 parts by mass, i.e., no metal oxide is contained, per 100 parts by mass of the diene rubber component. Here, the metal oxide content refers to the total amount when multiple types of metal oxides are contained. Most of the metal oxide remains unreacted after vulcanization of the rubber composition, but since it is in the form of powder, it can deteriorate the low heat buildup properties. In this embodiment, by substantially not incorporating metal oxide, it is possible to improve the low heat buildup properties and suppress deterioration of rolling resistance.

[0039] Metal oxides are oxides of metal elements, but do not include oxides containing metalloid elements. Here, metal elements are elements (excluding hydrogen) located to the left of the line connecting boron, silicon, germanium, antimony, and bismuth (which are metalloid elements) in the periodic table. A representative example of metal oxides is zinc oxide, but other examples include magnesium oxide and calcium oxide.

[0040] In addition to the above components, the rubber composition according to the embodiment may contain various additives that are generally used in rubber compositions, such as oil, stearic acid, an antioxidant, wax, and a vulcanization accelerator.

[0041] Examples of antioxidants include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants. These can be used alone or in combination of two or more. The content of the antioxidant is not particularly limited and may be, for example, 0.5 to 10 parts by mass per 100 parts by mass of the diene rubber component.

[0042] Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based accelerators, and any one of them can be used alone or in combination of two or more. The amount of the vulcanization accelerator to be added is not particularly limited, and may be, for example, 0.1 to 10 parts by mass or 0.5 to 5 parts by mass per 100 parts by mass of the diene rubber component.

[0043] The rubber composition according to the embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, or roll. For example, in the first mixing stage (non-pro kneading step), additives other than the crosslinking agent (sulfur, organic peroxide) and the vulcanization accelerator are added to and mixed with the diene rubber component along with silica. Then, in the final mixing stage (pro kneading step), the crosslinking agent and the vulcanization accelerator are added to and mixed with the resulting mixture to prepare an unvulcanized rubber composition.

[0044] The rubber composition according to the present embodiment can be used for various rubber members such as tires, anti-vibration rubber, conveyor belts, etc. Preferably, it is for tires, and can be applied to various portions of tires such as treads, sidewalls, and bead portions of pneumatic tires of various sizes for various uses such as tires for passenger cars and large tires for trucks and buses. Preferably, it is used in tire treads.

[0045] In one embodiment, a tire including a rubber portion (e.g., tread rubber, sidewall rubber, etc.) made of the rubber composition is manufactured as follows. The rubber composition is molded into a predetermined shape by a conventional method, for example, extrusion processing. A green tire is manufactured by combining the obtained molded product with other parts. A pneumatic tire can be manufactured by vulcanizing the green tire at, for example, 140 to 180°C. [Example]

[0046] Examples will be shown below, but the present invention is not limited to these examples.

[0047] The components used in the examples and comparative examples are as follows. SBR1: Solution polymerization styrene butadiene rubber (terminally modified), JSR Corporation "HPR350" (styrene content 20.5% by mass, butadiene microstructure; vinyl content 55.5% by mass, butadiene-derived vinyl bond unit content 44.1% by mass) SBR2: Emulsion-polymerized styrene-butadiene rubber, "SBR1502" manufactured by JSR Corporation (styrene content 23.5% by mass, butadiene microstructure; vinyl content 18% by mass, butadiene-derived vinyl bond unit content 13.8% by mass) SBR3: Solution-polymerized styrene-butadiene rubber, "Tufden 1834" manufactured by Asahi Kasei Corporation (styrene content 17% by mass, butadiene microstructure; vinyl content 9% by mass, butadiene-derived vinyl bond unit content 7.5% by mass, 37.5 phr oil-extended) BR: Butadiene rubber, "BR150B" manufactured by Ube Industries, Ltd. (vinyl bond unit content 1% by mass) NR: Natural rubber "RSS#3"

[0048] Carbon black: "Seast KH (N339)" manufactured by Tokai Carbon Co., Ltd. Silica: "Nipsil AQ" manufactured by Tosoh Silica Corporation Silane coupling agent: Bis(3-triethoxysilylpropyl)tetrasulfide, Evonik "Si69" Oil: JXTG Nippon Oil & Energy Corporation "Process NC-140" Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Anti-aging agent: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd.

[0049] Organic peroxide 1:1,1-di(t-butylperoxy)cyclohexane, NOF Corporation "Perhexa C-40" (purity 40% by mass, diluent: inert filler, 1-minute half-life temperature 153.8°C) Organic peroxide 2: Dicumyl peroxide, NOF Corporation "Percumyl D-40" (purity 40% by mass, diluent: inert filler, 1-minute half-life temperature 175.2°C) Sulfur: 5% oil-filled powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. Vulcanization accelerator 2: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0050] The evaluation methods used in the examples and comparative examples are as follows. (1) Vulcanization characteristics (MH) The maximum torque MH was determined in a test to measure the vulcanization behavior of the unvulcanized rubber composition at 170°C using a rheometer. The MH of Comparative Example 2 in Table 1, Comparative Example 5 in Table 2, Comparative Example 7 in Table 3, and Comparative Example 10 in Table 4 was set at 100, and the results were evaluated using an index. The smaller the index, the less sufficient the crosslinking and the lower the crosslink density.

[0051] (2) Low heat generation A rubber sample was used, obtained by vulcanizing an unvulcanized rubber composition by heating at 170°C for 15 minutes. In accordance with JIS K6394, a viscoelasticity tester manufactured by Toyo Seiki Seisakusho, Ltd. was used to measure the loss tangent (tanδ) under conditions of a static strain (initial strain) of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a temperature of 60°C. The tanδ of Comparative Example 2 in Table 1, Comparative Example 5 in Table 2, Comparative Example 7 in Table 3, and Comparative Example 10 in Table 4 was set to 100, and the results were evaluated using an index. The smaller the index, the smaller the tanδ, and therefore the less likely the tire is to generate heat, the better its low heat buildup properties are, and the better its fuel economy performance as a tire is.

[0052] (3) Wet grip performance A rubber sample was used, obtained by vulcanizing an unvulcanized rubber composition by heating at 170°C for 15 minutes. In accordance with JIS K6394, a viscoelasticity tester manufactured by Toyo Seiki Seisakusho, Ltd. was used to measure the loss tangent tanδ under conditions of a static strain (initial strain) of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and a temperature of 0°C. In Table 4, the tanδ of Comparative Example 10 was set to 100, and the results were evaluated using an index. The larger the index, the larger the tanδ, indicating superior wet grip performance as a tire.

[0053] [First Experimental Example] Using a Banbury mixer, in the first mixing stage, compounding ingredients excluding the crosslinking agent and vulcanization accelerator were added to the diene rubber component and kneaded according to the formulation (parts by mass) shown in Table 1 below (discharge temperature = 150°C). Next, in the final mixing stage, the crosslinking agent and vulcanization accelerator were added to the resulting kneaded mixture and kneaded (discharge temperature = 90°C). Each rubber composition thus obtained was evaluated for vulcanization characteristics and low heat buildup. The results are shown in Table 1.

[0054] In Table 1, "vinyl bond unit content" indicates the amount of vinyl bond units derived from butadiene in the total amount of diene rubber components, and was calculated by proportional calculation according to the compounding amount from the content of vinyl bond units derived from butadiene for each diene rubber (same in Tables 2 to 4). "Sulfur / organic peroxide" indicates the mass ratio of sulfur content / organic peroxide content (content as pure content excluding diluent) (same in Tables 2 to 4). For the compounding amount of SBR3, the value in parentheses indicates the amount as rubber polymer excluding oil-extended content. For the compounding amounts of organic peroxides 1 and 2, the value in parentheses indicates the amount of pure organic peroxide excluding diluent (same in Tables 2 to 4).

[0055] [Table 1]

[0056] [Second Experimental Example] Rubber compositions were prepared in the same manner as in Experimental Example 1, according to the formulations (parts by mass) shown in Table 2 below. Each rubber composition obtained was evaluated for vulcanization characteristics and low heat buildup. The results are shown in Table 2.

[0057] [Table 2]

[0058] [Third Experimental Example] Rubber compositions were prepared in the same manner as in Experimental Example 1, according to the formulations (parts by mass) shown in Table 3 below. Each rubber composition obtained was evaluated for vulcanization characteristics and low heat buildup. The results are shown in Table 3.

[0059] [Table 3]

[0060] [Fourth Experimental Example] Rubber compositions were prepared in the same manner as in Experimental Example 1, according to the formulations (parts by mass) shown in Table 4 below. Each rubber composition obtained was evaluated for vulcanization characteristics, low heat buildup, and wet grip performance. The results are shown in Table 4.

[0061] [Table 4]

[0062] In Table 1, Comparative Example 2 is a control compound in which the vinyl bond unit content of the diene rubber component is 10% by mass or less, zinc oxide is contained, and sufficient crosslink density is achieved. In contrast, when the vinyl bond unit content is greater than 10% by mass, sufficient crosslink density is maintained even without zinc oxide, as shown in Comparative Example 1. On the other hand, when the vinyl bond unit content is 10% by mass or less and zinc oxide is not contained, the MH decreases and the crosslink density decreases, as shown in Comparative Examples 3 and 4. This is thought to be because, in a rubber composition with a low vinyl bond unit content, crosslinking between polymers due to sulfur radicals is reduced, and sulfur crosslinking chains due to zinc oxide are not formed, making it impossible to obtain a sufficient crosslinked product.

[0063] In contrast, even when the vinyl bond unit content was 10% by mass or less and zinc oxide was not blended, when sulfur and an organic peroxide were used in combination, a crosslink density equivalent to that of Comparative Example 2 was maintained, as shown in Examples 1 to 5. This is thought to be because blending an organic peroxide together with sulfur generated radicals in the polymer main chain, accelerating the addition reaction to the double bonds. Examples 1 to 5 also generated less heat than Comparative Example 2 and were excellent in low heat buildup.

[0064] The amount of silica was changed in Experimental Examples 2 and 3. Even when the amount of silica was increased from 70 parts by mass to 120 parts by mass, Example 6 maintained the same crosslink density and improved low heat buildup compared to Comparative Example 5 (the control), as shown in Table 2. In contrast, when the amount of silica was 35 parts by mass, Comparative Example 9, which used sulfur and an organic peroxide in combination, was inferior to the control Comparative Example 7 in terms of the effect of maintaining crosslink density and no improvement in low heat buildup was obtained, as shown in Table 3.

[0065] In the fourth experimental example, a styrene-based resin was added. In Examples 7 to 9, an organic peroxide was added instead of zinc oxide, and a styrene-based resin was also blended, in comparison with Comparative Example 10, which serves as a control. As shown in Table 4, in Examples 7 to 9, the addition of a styrene-based resin improved wet grip performance while maintaining the crosslink density and low heat buildup effects of the crosslinking system that uses sulfur and an organic peroxide in combination. In other words, the balance between low heat buildup and wet grip performance was improved while maintaining crosslink density.

[0066] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0067] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. The composition comprises 100 parts by mass of a diene rubber component containing a styrene-butadiene rubber and / or a butadiene rubber, 60 to 150 parts by mass of silica, 1.0 to 5.0 parts by mass of sulfur, and 0.05 to 1.0 part by mass of an organic peroxide, the diene rubber component has a butadiene-derived vinyl bond unit content of 10% by mass or less based on the total amount of the diene rubber component, a content of the metal oxide per 100 parts by mass of the diene rubber component is less than 0.5 parts by mass, The sulfur content / organic peroxide content is 3.0 to 30.0 in mass ratio. Rubber composition.

2. The rubber composition according to claim 1, further comprising 1 to 30 parts by mass of a styrene-based resin per 100 parts by mass of the diene-based rubber component.

3. A tire made using the rubber composition according to claim 1 or 2.

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