Rubber composition and tire

Abstract

To provide a rubber composition which allows vulcanization to proceed 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 a rubber component and silica. In the rubber component, an amount of a vinyl bond unit derived from butadiene is 10 mass% or more in a total amount of the rubber component, and a content of a solution-polymerized styrene-butadiene rubber is less than 50 mass%. A content of the silica is 90-200 pts.mass and a content of a metal oxide is less than 0.5 pt.mass based on 100 pts.mass of the 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 act as vulcanization accelerators and are used as essential components.

[0003] However, in recent years, there has been a demand to reduce the amount of metal oxides such as zinc oxide blended in order to prevent environmental pollution. Therefore, for example, Patent Document 1 discloses a rubber composition in which 50% by mass or more of the rubber component is solution-polymerized styrene-butadiene rubber. Patent Document 2 discloses a rubber composition in which 50% by mass or more of the rubber component is solution-polymerized styrene-butadiene rubber with modified molecular ends. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-099709 [Patent Document 2] Japanese Patent Application Publication No. 2019-099708 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, an embodiment of the present invention aims to provide a rubber composition that can be vulcanized while containing a reduced amount of metal oxide such as zinc oxide or no metal oxide at all. [Means for solving the problem]

[0006] The rubber composition according to the present embodiment includes a rubber component and silica. The rubber component contains 10% by mass or more of vinyl bond units derived from butadiene in the total amount of the rubber component, and the content of solution-polymerized styrene-butadiene rubber is less than 50% by mass. The content of silica is 90 to 200 parts by mass, and the content of metal oxide is less than 0.5 parts by mass, per 100 parts by mass of the rubber component. Here, the content of solution-polymerized styrene-butadiene rubber being less than 50% by mass also includes a case where the content of solution-polymerized styrene-butadiene rubber is 0% by mass, i.e., a case where no solution-polymerized styrene-butadiene rubber is included. Furthermore, the content of metal oxide being less than 0.5 parts by mass also includes a case where the content of metal oxide is 0 parts by mass, i.e., a case where no metal oxide is included.

[0007] A tire according to an embodiment of the present invention is produced using the above rubber composition. [Effects of the Invention]

[0008] According to an embodiment of the present invention, vulcanization can be promoted while reducing or eliminating the amount of metal oxides such as zinc oxide. DETAILED DESCRIPTION OF THE INVENTION

[0009] The rubber composition according to the present embodiment includes a rubber component having 10% by mass or more of vinyl bond units derived from butadiene, and silica. The silica content is 90 to 200 parts by mass, and the metal oxide content is less than 0.5 parts by mass, per 100 parts by mass of the rubber component. Metal oxides, such as zinc oxide, function as vulcanization accelerators, so reducing the amount of metal oxide or eliminating it generally slows down vulcanization. In contrast, according to the present embodiment, in which the vinyl bond unit content is 10% by mass or more, vulcanization proceeds via a radical mechanism even without the inclusion of a metal oxide, thereby preventing a decrease in strength of the vulcanized rubber. Furthermore, selective crosslinking of the vinyl bond units improves the abrasion resistance of the vulcanized rubber.

[0010] In the rubber composition according to the embodiment, a diene rubber is used as the rubber component. 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 main chain. Specific examples of the diene rubber include various diene rubbers commonly used in rubber compositions, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination. Among these, the rubber component preferably contains at least one selected from the group consisting of natural rubber, styrene-butadiene rubber, and butadiene rubber. The diene rubbers mentioned above also include those whose terminals have been modified as necessary (for example, terminally modified SBR) and those whose properties have been modified to impart desired characteristics (for example, modified NR).

[0011] The rubber component may or may not contain solution-polymerized styrene-butadiene rubber (SSBR), but the content thereof is less than 50% by mass. That is, the content of solution-polymerized styrene-butadiene rubber is less than 50 parts by mass per 100 parts by mass of the rubber component. According to this embodiment, even though the content of solution-polymerized styrene-butadiene rubber is less than 50% by mass, vulcanization can be progressed while reducing or eliminating the amount of metal oxide. The content of solution-polymerized styrene-butadiene rubber may be 45% by mass or less, 35% by mass or less, 30% by mass or less, 20% by mass or less, or 0% by mass, relative to 100% by mass of the rubber component.

[0012] The rubber component according to this embodiment contains a diene rubber having a structural unit derived from butadiene. Examples of such diene rubbers include butadiene rubber, styrene-butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber, and one or more of these may be used. More preferably, the rubber component contains at least styrene-butadiene rubber and / or butadiene rubber, and may optionally contain other diene rubbers such as natural rubber.

[0013] In one embodiment, the rubber component may contain emulsion-polymerized styrene-butadiene rubber (ESBR), and may contain 30% by mass or more of emulsion-polymerized styrene-butadiene rubber relative to 100% by mass of the rubber component. The content of the emulsion-polymerized styrene-butadiene rubber may be 40% by mass or more, 50% by mass or more, and 80% by mass or less, or 70% by mass or less, relative to 100% by mass of the rubber component.

[0014] In another embodiment, the rubber component may contain emulsion-polymerized styrene-butadiene rubber, solution-polymerized styrene-butadiene rubber, and optionally natural rubber, and may, for example, contain 30% to 80% by mass of emulsion-polymerized styrene-butadiene rubber, 10% to less than 50% by mass of solution-polymerized styrene-butadiene rubber, and 0% to 40% by mass of natural rubber. More preferably, the rubber component may contain 40% to 70% by mass of emulsion-polymerized styrene-butadiene rubber, 15% to 45% by mass of solution-polymerized styrene-butadiene rubber, and 10% to 30% by mass of natural rubber.

[0015] In yet another embodiment, the rubber component may contain emulsion-polymerized styrene-butadiene rubber, natural rubber, and optionally butadiene rubber, for example, 20 to 60 mass% emulsion-polymerized styrene-butadiene rubber, 10 to 60 mass% natural rubber, and 0 to 60 mass% butadiene rubber. More preferably, the rubber component may contain 30 to 50 mass% emulsion-polymerized styrene-butadiene rubber, 10 to 40 mass% natural rubber, and 30 to 60 mass% butadiene rubber.

[0016] In this embodiment, the rubber component has a butadiene-derived vinyl bond unit content of 10% by mass or more based on the total amount of the rubber component. The butadiene-derived vinyl bond unit content is the content of butadiene-derived vinyl bond units contained in all structural units (polymer repeating units) of the diene rubber constituting the rubber component, and is expressed as mass % of the vinyl bond unit content relative to 100% by mass of the total amount of the rubber component. The butadiene-derived vinyl bond unit refers to a vinyl-1,2 bond structural unit among structural units formed by butadiene.

[0017] 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 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).

[0018] The amount of vinyl bond units derived from butadiene in the total amount of the rubber component is more preferably 15% by mass or more, even more preferably 18% by mass or more, and may be 20% by mass or more. The upper limit of the amount of vinyl bond units derived from butadiene is preferably 80% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and may be 40% by mass or less, or may be 30% by mass or less.

[0019] 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.

[0020] In this embodiment, silica is blended in an amount of 90 to 200 parts by mass per 100 parts by mass of the rubber component. By blending a large amount of silica in this manner, it is possible to suppress a decrease in the degree of vulcanization. The content of silica is preferably 90 to 150 parts by mass, more preferably 90 to 120 parts by mass, per 100 parts by mass of the rubber component.

[0021] 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.

[0022] The amount of carbon black is not particularly limited, and may be 50 parts by mass or less, 1 to 30 parts by mass, or 2 to 10 parts by mass per 100 parts by mass of the rubber component.

[0023] The rubber composition may 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 the silane coupling agent.

[0024] 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.

[0025] 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, per 100 parts by mass of the rubber component. Here, when multiple types of metal oxides are contained, the metal oxide content refers to the total amount thereof.

[0026] 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.

[0027] In addition to the above components, the rubber composition according to the present embodiment may contain various additives that are generally used in rubber compositions, such as oil, stearic acid, an antioxidant, wax, a vulcanizing agent, and a vulcanization accelerator.

[0028] 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 rubber component.

[0029] As the vulcanizing agent, sulfur is preferably used, and examples thereof include powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc. The content of the vulcanizing agent 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 rubber component.

[0030] 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 rubber component.

[0031] The rubber composition according to the present 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 vulcanizing agent and vulcanization accelerator are added to and mixed with the rubber component along with silica. Then, in the final mixing stage (pro kneading step), the vulcanizing agent and vulcanization accelerator are added to and mixed with the resulting mixture to prepare an unvulcanized rubber composition.

[0032] 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 purposes such as tires for passenger cars and large tires for trucks and buses.

[0033] 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]

[0034] Examples will be shown below, but the present invention is not limited to these examples.

[0035] 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, JSR Corporation "SBR1723" (styrene content 23.5% by mass, butadiene microstructure; vinyl content 19% by mass, butadiene-derived vinyl bond unit content 14.5% by mass, 37.5 phr oil-extended) BR1: Butadiene rubber, "EUROPRENE BR HV80" manufactured by Versalis (vinyl bond unit content 77% by mass) BR2: Butadiene rubber, "BR150B" manufactured by Ube Industries, Ltd. (vinyl bond unit content 1% by mass) NR: Natural rubber "RSS#3"

[0036] Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Silica: Evonik Industries "Ultrasil VN3" 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. Sulfur: 5% oil-filled powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator CBS: "Noccela CZ-G (CZ)" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator DPG: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0037] The evaluation methods used in the examples and comparative examples are as follows. (1) Vulcanization characteristics (MH-ML) In a test to measure the vulcanization behavior of unvulcanized rubber compositions at 160°C using a rheometer, the maximum torque was defined as MH and the minimum torque as ML, and the (MH-ML) was calculated. The (MH-ML) values ​​of Comparative Example 1 in Table 1, Comparative Example 3 in Table 2, Comparative Example 4 in Table 3, Comparative Example 5 in Table 4, Comparative Example 6 in Table 5, and Comparative Example 7 in Table 6 were all set to 100, and the results were evaluated as an index. The smaller the index, the less sufficient the sulfur vulcanization progressed.

[0038] (2) Breaking strength The rubber samples used were obtained by vulcanizing an unvulcanized rubber composition by heating at 175°C for 15 minutes. The breaking strength (MPa) of samples prepared using JIS No. 3 dumbbells was measured in accordance with JIS K6251. The breaking strengths of Comparative Example 1 in Table 1, Comparative Example 3 in Table 2, Comparative Example 4 in Table 3, Comparative Example 5 in Table 4, Comparative Example 6 in Table 5, and Comparative Example 7 in Table 6 were each set at 100, and the results were evaluated using an index. The larger the value, the higher the breaking strength.

[0039] (3) Abrasion resistance The rubber samples used were obtained by vulcanizing an unvulcanized rubber composition by heating at 175°C for 15 minutes. Abrasion loss was measured using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. in accordance with JIS K6264 under conditions of a load of 40N and a slip ratio of 30%, and the reciprocal of the abrasion loss for Comparative Example 1 in Table 1, Comparative Example 3 in Table 2, Comparative Example 4 in Table 3, Comparative Example 5 in Table 4, Comparative Example 6 in Table 5, and Comparative Example 7 in Table 6 was set to 100 and evaluated as an index. The larger the index, the smaller the abrasion loss and the better the abrasion resistance.

[0040] [Comparative Examples 1 and 2] Using a Banbury mixer, compounding ingredients excluding sulfur and vulcanization accelerator were first added to the rubber component in the first mixing stage (discharge temperature = 150°C) according to the formulation (parts by mass) shown in Table 1 below, and kneaded (discharge temperature = 150°C). Next, sulfur and vulcanization accelerator were added to the resulting kneaded mixture in the final mixing stage (discharge temperature = 90°C). Each rubber composition thus obtained was evaluated for vulcanization characteristics, breaking strength, and abrasion resistance. The results are shown in Table 1. The "amount of vinyl bond units" in Table 1 indicates the amount of butadiene-derived vinyl bond units in the total amount of rubber component, calculated by proportional calculation according to the content of butadiene-derived vinyl bond units for each diene rubber (the same applies to Tables 2 to 6). Regarding the amount of SBR2, the value in parentheses indicates the amount as rubber polymer excluding oil-extended components (the same applies to Tables 2 to 5).

[0041] [Table 1]

[0042] [Examples 1 and 2, Comparative Example 3] Rubber compositions were prepared according to the formulations (parts by mass) shown in Table 2 below, except for the procedures in Comparative Example 1. Each rubber composition obtained was evaluated for vulcanization characteristics, breaking strength, and abrasion resistance. The results are shown in Table 2.

[0043] [Table 2]

[0044] [Examples 3 and 4 and Comparative Example 4] Rubber compositions were prepared according to the formulations (parts by mass) shown in Table 3 below, except for the procedures in Comparative Example 1. Each rubber composition obtained was evaluated for vulcanization characteristics, breaking strength, and abrasion resistance. The results are shown in Table 3.

[0045] [Table 3]

[0046] [Examples 5 and 6 and Comparative Example 5] Rubber compositions were prepared according to the formulations (parts by mass) shown in Table 4 below, except for the procedures in Comparative Example 1. The vulcanization characteristics, breaking strength, and abrasion resistance of each resulting rubber composition were evaluated. The results are shown in Table 4.

[0047] [Table 4]

[0048] [Examples 7 and 8 and Comparative Example 6] Rubber compositions were prepared according to the formulations (parts by mass) shown in Table 5 below, except for the procedures in Comparative Example 1. The vulcanization characteristics, breaking strength, and abrasion resistance of each resulting rubber composition were evaluated. The results are shown in Table 5.

[0049] [Table 5]

[0050] [Examples 9 and 10 and Comparative Example 7] Rubber compositions were prepared according to the formulations (parts by mass) shown in Table 6 below, except for the procedures in Comparative Example 1. Each rubber composition was evaluated for vulcanization characteristics, breaking strength, and abrasion resistance. The results are shown in Table 6.

[0051] [Table 6]

[0052] As shown in Table 1, in Comparative Example 2, which did not contain zinc oxide, vulcanization did not proceed sufficiently and breaking strength was significantly worse than in Comparative Example 1, which contained zinc oxide. As described above, when the amount of vinyl bond units derived from butadiene was less than 10% by mass, the absence of zinc oxide resulted in a decrease in crosslink density, improving abrasion resistance but worsening breaking strength.

[0053] In contrast, as shown in Tables 2 to 6, when the amount of vinyl bond units derived from butadiene was 10% by mass or more, in Examples 1 to 10, in which the amount of zinc oxide was reduced or no zinc oxide was added, vulcanization progressed to the same extent as in Comparative Examples 3 to 7, in which zinc oxide was added, and the decrease in breaking strength was suppressed. Furthermore, Examples 1 to 10 were superior in abrasion resistance to Comparative Examples 3 to 7.

[0054] 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.

[0055] 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. Contains a rubber component and silica, the rubber component contains emulsion-polymerized styrene-butadiene rubber, and the amount of vinyl bond units derived from butadiene in the total amount of the rubber component is 16.0% by mass or more, and the content of solution-polymerized styrene-butadiene rubber is less than 50% by mass, The rubber composition has a silica content of 90 to 200 parts by mass and a metal oxide content of less than 0.5 parts by mass relative to 100 parts by mass of the rubber component.

2. The rubber composition according to claim 1, wherein the amount of vinyl bond units derived from butadiene in the total amount of the rubber component is 80% by mass or less.

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

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