Rubber composition and tire

Abstract

To provide a rubber composition capable of suppressing reversion 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 diene rubber, a filler, and a silane coupling agent. The diene rubber contains 40 mass% or more of natural rubber. A content of the filler is 30-200 pts.mass, a content of the silane coupling agent is 5 pts.mass or more, and a content of a metal oxide is less than 0.5 pt.mass based on 100 pts.mass of the diene rubber.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 added 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. Furthermore, Patent Document 3 discloses the addition of a thiazole derivative having two or more thiol groups to a diene rubber together with a vulcanizing agent, with the aim of suppressing reversion even when the zinc atom concentration in the rubber composition is low. [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 [Patent Document 3] Japanese Patent Application Publication No. 2017-088789 Summary of the Invention [Problem to be solved by the invention]

[0005] Metal oxides such as zinc oxide, which are used as essential materials for vulcanization accelerators, are useful for suppressing reversion when a rubber composition is vulcanized at high temperatures. Therefore, reducing the zinc oxide content or eliminating zinc oxide altogether can lead to the problem of reversion occurring easily.

[0006] In view of the above, an object of an embodiment of the present invention is to provide a rubber composition that can suppress reversion while reducing or eliminating the amount of metal oxides such as zinc oxide. [Means for solving the problem]

[0007] A rubber composition according to an embodiment of the present invention comprises a diene rubber, a filler, and a silane coupling agent, wherein the diene rubber comprises 40% by mass or more of natural rubber, and the filler content is 30 to 200 parts by mass, the silane coupling agent content is 5 parts by mass or more, and the metal oxide content is less than 0.5 parts by mass, per 100 parts by mass of the diene rubber. Here, the metal oxide content of less than 0.5 parts by mass also includes a case where the metal oxide content is 0 part by mass, i.e., a case where no metal oxide is contained.

[0008] A tire according to an embodiment of the present invention is produced using the above rubber composition. [Effects of the Invention]

[0009] According to an embodiment of the present invention, reversion can be suppressed while reducing or eliminating the amount of metal oxides such as zinc oxide. DETAILED DESCRIPTION OF THE INVENTION

[0010] A rubber composition according to an embodiment of the present invention includes a diene rubber containing 40% or more by mass of natural rubber, a filler, and a silane coupling agent, and the metal oxide content is less than 0.5 parts by mass per 100 parts by mass of the diene rubber. Metal oxides such as zinc oxide function as vulcanization accelerators, and reducing the amount of metal oxide or eliminating it altogether can lead to reversion, in which bonds formed during vulcanization are broken. In contrast, by incorporating a silane coupling agent into a rubber composition containing 40% or more by mass of natural rubber in the diene rubber, the reversion suppression effect can be enhanced, resulting in a reversion suppression effect equal to or greater than that achieved when a normal amount of metal oxide is incorporated.

[0011] In the rubber composition according to the embodiment, the diene rubber as the rubber component contains 40% by mass or more of natural rubber (NR), i.e., 40 parts by mass or more of natural rubber per 100 parts by mass of diene rubber. The amount of natural rubber relative to the total mass of the diene rubber may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or even 100% by mass.

[0012] Diene rubber refers to rubber having repeating units corresponding to diene monomers having conjugated double bonds, and has double bonds in the polymer backbone. The diene rubber may be natural rubber alone, or natural rubber may be used in combination with other diene rubbers. The other diene rubbers are not particularly limited, and examples include various diene rubbers commonly used in rubber compositions, such as 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 of two or more. Among these, it is preferable to use at least one of butadiene rubber and styrene-butadiene rubber as the other diene 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).

[0013] In one embodiment, 100% by mass of the diene rubber may include 40 to 80% by mass (more preferably 50 to 70% by mass) of natural rubber and 20 to 60% by mass (more preferably 30 to 50% by mass) of styrene-butadiene rubber and / or butadiene rubber. In another embodiment, 100% by mass of the diene rubber may include 40 to 80% by mass (more preferably 50 to 70% by mass) of natural rubber, 10 to 55% by mass (more preferably 15 to 30% by mass) of styrene-butadiene rubber, and 5 to 50% by mass (more preferably 10 to 20% by mass) of butadiene rubber.

[0014] As the filler to be compounded in the rubber composition, it is preferable to use carbon black and / or silica.

[0015] The carbon black is not particularly limited, 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.

[0016] The silica is not particularly limited, and examples thereof include wet silica, dry silica, etc. Preferably, wet silica such as wet precipitation silica or wet gelation silica is used.

[0017] The filler content is preferably 30 to 200 parts by mass per 100 parts by mass of diene rubber, and can be appropriately set depending on the application, etc. The filler content per 100 parts by mass of diene rubber is preferably 40 to 150 parts by mass, more preferably 45 to 120 parts by mass, or may be 50 to 100 parts by mass. The carbon black content may be 5 to 150 parts by mass, 10 to 120 parts by mass, 20 to 100 parts by mass, or 30 to 80 parts by mass per 100 parts by mass of diene rubber. The silica content may be 10 to 150 parts by mass, 20 to 120 parts by mass, or 30 to 100 parts by mass per 100 parts by mass of diene rubber.

[0018] In one embodiment, the filler may be primarily composed of carbon black. That is, the amount of carbon black relative to the total mass of the filler may be more than 50 mass%, 70 mass% or more, or even 100 mass%. In this case, for example, the amount of carbon black may be 30 to 120 mass parts and silica 0 to 30 mass parts, or 40 to 100 mass parts and silica 0 to 20 mass parts, relative to 100 mass parts of diene rubber.

[0019] In one embodiment, the filler may be primarily composed of silica. That is, the amount of silica relative to the total mass of the filler may be more than 50 mass%, 60 mass% or more, 70 mass% or more, or even 100 mass%. In this case, for example, the amount of silica may be 30 to 120 mass parts and carbon black may be 5 to 50 mass parts, or 40 to 100 mass parts and carbon black may be 5 to 20 mass parts, relative to 100 mass parts of diene rubber.

[0020] The rubber composition according to the present embodiment contains a silane coupling agent. As described above, when the amount of metal oxide is reduced or not contained at all, reversion tends to occur, but by containing a silane coupling agent, reversion can be suppressed, and this effect can be further enhanced in a rubber composition containing a large amount of natural rubber.

[0021] 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, as they can further enhance the reversion suppression effect.

[0022] The content of the silane coupling agent is 5 parts by mass or more per 100 parts by mass of diene rubber. By compounding 5 parts by mass or more in this manner, the effect of suppressing reversion can be enhanced, and a decrease in rubber strength due to reversion can be suppressed. The content of the silane coupling agent is more preferably 7 parts by mass or more per 100 parts by mass of diene rubber. From the viewpoint of suppressing reversion, there is no particular upper limit to the content of the silane coupling agent. However, from the viewpoint of suppressing a decrease in strength, the content of the silane coupling agent is preferably 40% by mass or less, and may be 30% by mass or less, relative to the content of the filler. In one embodiment, the content of the silane coupling agent may be 5 to 20 parts by mass per 100 parts by mass of diene rubber.

[0023] Generally, a silane coupling agent is used in combination with silica as a filler, but in this embodiment, a silane coupling agent is blended even when silica is not used as a filler. Even when silica is used as a filler, 5 parts by mass or more of the silane coupling agent is blended per 100 parts by mass of diene rubber, regardless of the silica content. In one embodiment, the silane coupling agent may be included in the rubber composition in an amount of more than 20 parts by mass per 100 parts by mass of silica.

[0024] 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 diene rubber. Here, when multiple types of metal oxides are contained, the metal oxide content refers to the total amount.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 diene rubber.

[0029] 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.

[0030] 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, along with the filler and silane coupling agent, are added to and mixed with the diene rubber. 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.

[0031] 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.

[0032] 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]

[0033] Examples will be shown below, but the present invention is not limited to these examples.

[0034] The components used in the examples and comparative examples are as follows. NR: Natural rubber "RSS#3" BR: Butadiene rubber, "BR150B" manufactured by Ube Industries, Ltd. SBR: Styrene butadiene rubber (terminally modified), JSR Corporation "HPR840" Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Silica: Evonik Industries "Ultrasil VN3" Silane coupling agent 1: Bis(3-triethoxysilylpropyl)tetrasulfide, "Si69" manufactured by Evonik Silane coupling agent 2: Bis(3-triethoxysilylpropyl) disulfide, Evonik "Si75" Silane coupling agent 3: 3-octanoylthio-1-propyltriethoxysilane, Momentive "NXT" 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.

[0035] The evaluation methods used in the examples and comparative examples are as follows. (1) Reversion suppression index For the unvulcanized rubber compositions, the rheometer curve (torque) was measured at 175°C in accordance with the conditions of JIS K6300-2:2013, and the reversion properties were determined using the following formula, and the reciprocal thereof was calculated. The reversion suppression index for each Example and Comparative Example was calculated using the reciprocal of the reversion properties of Comparative Example 1 in Table 1, Comparative Example 4 in Table 2, Comparative Example 7 in Table 3, and Comparative Example 10 in Table 4 as 100. A higher index indicates a better reversion suppression effect. Reversion (%) = [(MH-M15) / (MH-ML)] x 100 In the formula, MH represents the maximum torque, ML represents the minimum torque, and M15 represents the torque value 15 minutes after the start of measurement.

[0036] (2) Tensile strength (M100) The rubber samples used were obtained by vulcanizing an unvulcanized rubber composition by heating at 175°C for 15 minutes. The 100% modulus M100 (MPa) of samples prepared using a JIS No. 3 dumbbell was measured in accordance with JIS K6251. The tensile strength of each Example and Comparative Example was expressed as an index, with the M100 of Comparative Example 1 in Table 1, the M100 of Comparative Example 4 in Table 2, the M100 of Comparative Example 7 in Table 3, and the M100 of Comparative Example 10 in Table 4 all set to 100. The smaller the index, the greater the decrease in rubber strength due to reversion.

[0037] [Examples 1 to 4 and Comparative Examples 1 to 3] Using a Banbury mixer, in the first mixing stage, compounding ingredients except for sulfur and vulcanization accelerator were added to natural rubber and kneaded according to the formulation (parts by mass) shown in Table 1 below (discharge temperature = 150°C). Next, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting kneaded mixture and kneaded (discharge temperature = 90°C). Each rubber composition thus obtained was evaluated for reversion inhibition index and tensile strength (M100). The results are shown in Table 1.

[0038] [Table 1]

[0039] The examples shown in Table 1 use NR alone as the diene rubber and carbon black alone as the filler. In this case, Comparative Example 2, in which zinc oxide was simply omitted, showed greater reversion and a greater decrease in tensile strength than Comparative Example 1, in which zinc oxide was blended. In contrast, Examples 1 to 4, in which a silane coupling agent was blended, showed suppression of reversion to the same level as Comparative Example 1, which contained zinc oxide, despite not containing zinc oxide, and also showed a significant improvement in the decrease in tensile strength seen in Comparative Example 2.

[0040] [Examples 5 to 9 and Comparative Examples 4 to 6] Rubber compositions were prepared in the same manner as in Example 1, with the formulation (parts by mass) shown in Table 2 below. The reversion inhibition index and tensile strength (M100) of each resulting rubber composition were evaluated. The results are shown in Table 2.

[0041] [Table 2]

[0042] The examples shown in Table 2 use a diene rubber with a NR / BR ratio of 50 / 50 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, Examples 5 to 9, which contain a silane coupling agent, suppressed reversion to the same level as Comparative Example 4, which contains zinc oxide, despite not containing zinc oxide, and also significantly improved the decrease in tensile strength observed in Comparative Example 5. Furthermore, when comparing the types of silane coupling agents at the same compounding amounts, those using a sulfide silane coupling agent tended to have a greater effect on suppressing reversion and improving tensile strength.

[0043] [Examples 10 to 13 and Comparative Examples 7 to 9] Rubber compositions were prepared in the same manner as in Example 1, according to the formulations (parts by mass) shown in Table 3 below. The reversion inhibition index and tensile strength (M100) of each obtained rubber composition were evaluated. The results are shown in Table 3.

[0044] [Table 3]

[0045] The examples shown in Table 3 use a diene rubber with a NR / BR / SBR ratio of 60 / 20 / 20 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, in Examples 10 to 13 in which a silane coupling agent was blended, reversion was suppressed to the same level as in Comparative Example 7, which contained zinc oxide, despite the absence of zinc oxide, and the decrease in tensile strength observed in Comparative Example 8 was also significantly improved.

[0046] [Examples 14 to 18 and Comparative Examples 10 to 12] Rubber compositions were prepared in the same manner as in Example 1, according to the formulations (parts by mass) shown in Table 4 below. The reversion inhibition index and tensile strength (M100) of each obtained rubber composition were evaluated. The results are shown in Table 4.

[0047] [Table 4]

[0048] The examples shown in Table 4 use a diene rubber with a NR / BR / SBR ratio of 40 / 10 / 50 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, in Examples 14 to 18, which contain a silane coupling agent, reversion is suppressed to the same level as in Comparative Example 10, which contains zinc oxide, despite the absence of zinc oxide, and the decrease in tensile strength observed in Comparative Example 11 is also significantly improved.

[0049] 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.

[0050] 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 includes a diene rubber, a filler, and a silane coupling agent, The diene rubber contains 40% by mass or more of natural rubber, the content of the filler is 30 to 200 parts by mass, the content of the silane coupling agent is 5 parts by mass or more, and the content of the metal oxide is less than 0.5 parts by mass, relative to 100 parts by mass of the diene rubber; The rubber composition, wherein the filler contains carbon black, and the amount of carbon black relative to the total mass of the filler is 100% by mass.

2. The rubber composition according to claim 1 , wherein the silane coupling agent comprises a sulfide silane coupling agent.

3. The rubber composition according to claim 1 or 2, wherein the content of the silane coupling agent is 40% by mass or less based on the content of the filler.

4. A tire made using the rubber composition according to any one of claims 1 to 3.

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