Rubber composition for tires

Abstract

To provide a rubber composition for tires which is excellent in fatigue characteristics while containing a natural rubber as a main component.SOLUTION: The rubber composition for tires is obtained by blending 100 pts.mass of a diene rubber containing 60 mass% or more of a natural rubber with 20-55 pts.mass of a filler containing silica and 3.0 pts.mass or more of an amine-based antioxidant. The content of the silica is 50 mass% or more in the filler. The content of the amine-based antioxidant is 5.0 mass% or more based on the mass of the natural rubber.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition for tires that contains natural rubber as a main component and has excellent fatigue properties. [Background technology]

[0002] In recent years, as the conservation of global resources and environmental protection have been attracting attention, there is a demand for product development that aims for a circular economy by using sustainable natural and recycled raw materials instead of petroleum-based products, which are of concern for depletion, for the materials that make up tires. One such material is generally recycled raw materials, but there is a problem that most mechanical properties are reduced in rubber compositions that contain a large amount of recycled raw materials, and it must be said that the scope of application and amount of recycled raw materials are effectively limited.

[0003] In this situation, it would be extremely effective to replace the main rubber in tire materials from petroleum-derived synthetic rubber to natural rubber. However, while natural rubber has excellent mechanical properties, it has the problem of being prone to cracking when subjected to repeated strain, and there is currently no effective way to solve this problem. For this reason, it is difficult to incorporate a large amount of natural rubber into tire components such as sidewalls and rim cushions, which require strict fatigue properties, and this has hindered progress in product development aimed at a circular economy.

[0004] Patent Document 1 describes the incorporation of a specific antioxidant into the rubber component in order to suppress cracking and discoloration of the tire surface due to ozone. However, the invention described in Patent Document 1 could not improve the fatigue properties of a rubber composition for tires that contains natural rubber as the main component. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 056384 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a rubber composition for tires which contains natural rubber as a main component and has excellent fatigue properties. [Means for solving the problem]

[0007] The rubber composition for tires of the present invention that achieves the above-mentioned object comprises 100 parts by mass of diene rubber containing 60% by mass or more of natural rubber, 20 to 55 parts by mass of a filler containing silica, and 3.0 parts by mass or more of an amine-based antioxidant, wherein the silica accounts for 50% by mass or more of the filler, and the amine-based antioxidant accounts for 5.0% by mass or more of the mass of the natural rubber. Effect of the Invention

[0008] The rubber composition for tires of the present invention contains a large amount of silica as a filler and at the same time a large amount of an amine-based anti-aging agent, so even though it is a rubber composition whose main component is natural rubber, it has excellent fatigue properties and can maintain or improve mechanical properties at levels higher than those of conventional rubber.

[0009] The silica may be silica derived from rice husks obtained from a process of burning rice husks, which are agricultural waste. The natural rubber may be modified natural rubber having an epoxy group. This allows the ratio of naturally derived components in the rubber composition to be higher.

[0010] A tire having a sidewall and / or a rim cushion made of the above-mentioned rubber composition for a tire has excellent fatigue properties against repeated strain and can suppress the occurrence of cracks.

[0011] In a tire having a sidewall made of the above-mentioned rubber composition for tires, the difference between the content of the amine-based antioxidant in the sidewall and the content of the amine-based antioxidant in the tire member adjacent to the sidewall may be 6% by mass or less. Also, in a tire having a rim cushion made of the rubber composition for tires, the difference between the content of the amine-based antioxidant in the rim cushion and the content of the amine-based antioxidant in the tire member adjacent to the rim cushion may be 6% by mass or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The rubber composition for tires of the present invention contains 60% by mass or more of natural rubber as a rubber component in 100% by mass of diene rubber. By containing natural rubber, the mechanical properties of the rubber composition can be improved, and at the same time, the ratio of naturally derived components in the rubber composition can be increased, and the product can be closer to the product aimed for by the circular economy. The natural rubber is 60% by mass or more in 100% by mass of diene rubber, preferably more than 60% by mass and 100% by mass or less, more preferably 62% by mass or more and 95% by mass or less, and even more preferably 65% ​​by mass or more and 90% by mass or less. If the natural rubber is less than 60% by mass, the mechanical properties such as tensile break strength become insufficient.

[0013] The natural rubber is preferably modified natural rubber having an epoxy group. A rubber composition containing modified natural rubber having an epoxy group is excellent in strength, fatigue properties, and heat resistance, and is preferable because modified natural rubber having an epoxy group has an affinity with silica due to its polarity, making it easy to disperse. The natural rubber may be entirely modified natural rubber, or unmodified natural rubber and modified natural rubber may be used in combination. The total amount of unmodified natural rubber and / or modified natural rubber having an epoxy group should be within the above-mentioned range.

[0014] The rubber composition for tires may contain other diene rubbers other than natural rubber as a rubber component. Examples of other diene rubbers include synthetic rubbers such as isoprene rubber, styrene butadiene rubber, butadiene rubber, butyl rubber, halogenated butyl rubber, and acrylonitrile-butadiene rubber, and modified rubbers obtained by adding functional groups to these synthetic rubbers. These other diene rubbers may be used alone or as an arbitrary blend. The content of the other diene rubber is preferably 40% by mass or less, more preferably 0% by mass or more and less than 40% by mass, even more preferably 5% by mass or more and 38% by mass or less, and even more preferably 10% by mass or more and 35% by mass or less, based on 100% by mass of the diene rubber.

[0015] The rubber composition for tires is prepared by compounding 20 to 55 parts by mass of a filler containing silica with 100 parts by mass of diene rubber. By compounding the filler containing silica, it is possible to improve the fatigue properties, tensile strength at break, and tensile elongation at break. The filler containing silica is preferably compounded in an amount of 25 to 55 parts by mass, more preferably 30 to 54 parts by mass. If the filler containing silica is less than 20 parts by mass, the tensile strength at break deteriorates. If the filler containing silica is more than 55 parts by mass, the fatigue properties, tensile strength at break, and tensile elongation at break deteriorate.

[0016] The rubber composition for tires may contain 50% by mass or more of silica, preferably more than 60% by mass and 100% by mass or less, and more preferably 65 to 95% by mass, based on 100% by mass of the filler. If the ratio of silica is less than 50% by mass, the effect of improving the fatigue properties of the rubber composition cannot be sufficiently obtained.

[0017] As the silica, it is preferable to use one that is usually used in rubber compositions for tires, such as wet-process silica, dry-process silica, carbon-silica (dual-phase filler) in which silica is supported on the surface of carbon black, and silica surface-treated with a compound that is reactive or compatible with both silica and rubber, such as a silane coupling agent or polysiloxane. Among these, wet-process silica containing hydrated silicic acid as the main component is preferred. Furthermore, the nitrogen adsorption specific surface area of ​​the silica is not particularly limited, but is preferably 100 to 190 m. 2 / g. In addition, silica derived from rice husks obtained from a process of burning rice husks, which are agricultural waste, can be used as the silica. By compounding such silica derived from rice husks, the ratio of naturally derived components in the rubber composition can be increased.

[0018] The rubber composition for tires is preferably blended with 3 to 20 mass % of the silane coupling agent, more preferably 5 to 15 mass %, based on the mass of silica. By blending 3 mass % or more of the silane coupling agent based on the mass of silica, it is preferable to obtain an effect of improving the dispersibility of silica. In addition, by making the silane coupling agent 20 mass % or less, it is possible to suppress gelation of the diene rubber component.

[0019] The filler may contain other fillers than silica. As the other fillers, for example, inorganic fillers such as carbon black, calcium carbonate, magnesium carbonate, talc, clay, mica, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, etc., and organic fillers such as cellulose, lecithin, lignin, and dendrimers, etc., may be arbitrarily blended. These other fillers may be used alone or in combination of two or more. The other fillers are preferably 50% by mass or less, more preferably 0 to less than 40% by mass, and even more preferably 5 to 35% by mass, based on 100% by mass of the filler.

[0020] Among them, by blending carbon black, the strength of the rubber composition can be improved. As the carbon black, furnace black, acetylene black, thermal black, channel black, graphite, and other carbon blacks may be blended. Among these, furnace black is preferable, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, and FEF. Furthermore, the nitrogen adsorption specific surface area of ​​the carbon black is not particularly limited, but is preferably 30 to 80 m 2 / g. These carbon blacks can be used alone or in combination of two or more. Surface-treated carbon blacks obtained by chemically modifying these carbon blacks with various acid compounds or the like can also be used.

[0021] The rubber composition for tires contains 3.0 parts by mass or more of an amine-based antiaging agent per 100 parts by mass of diene rubber. By compounding the amine-based antiaging agent, the fatigue properties of the rubber composition can be improved. The amine-based antiaging agent is preferably 3.0 to 10.0 parts by mass, more preferably 3.5 to 7.5 parts by mass, per 100 parts by mass of diene rubber. If the amine-based antiaging agent is less than 3.0 parts by mass per 100 parts by mass of diene rubber, the effect of improving the fatigue properties of the rubber composition cannot be sufficiently obtained.

[0022] The rubber composition for tires is blended with an amine-based antioxidant in an amount of 5.0% by mass or more relative to the mass of natural rubber. By blending 5.0% by mass or more relative to the mass of natural rubber, the fatigue properties of the rubber composition mainly composed of natural rubber can be improved. The amine-based antioxidant is preferably blended in an amount of 5.0 to 15.0% by mass, more preferably 6.0 to 10.5% by mass, relative to the mass of natural rubber. If the amount of the amine-based antioxidant is less than 5.0 parts by mass relative to the mass of natural rubber, the effect of improving the fatigue properties of the rubber composition cannot be sufficiently obtained.

[0023] Examples of the amine-based antioxidant include naphthylamine-based antioxidants, diphenylamine-based antioxidants, phenylenediamine-based antioxidants, and quinoline-based antioxidants. Specifically, alkylated diphenylamines, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-diphenyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-phenyl-N'-(1-methylheptyl ... )-p-phenylenediamine, p-(p-toluenesulfonylamide)diphenylamine, N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, poly(2,2,4-trimethyl-1,2-dihydroquinoline), N,N-bis(1,4-dimethylpentyl)-p-phenylenediamine, N-cyclohexyl-N-phenyl-p-phenylenediamine, N,N'-dicyclohexyl-p-phenylenediamine, etc. Among them, phenylenediamine-based antiaging agents having an aromatic ring with two secondary amines as substituents in the molecular structure are preferred, and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) is particularly preferred, because the effects of the present invention are more excellent.

[0024] The rubber composition for tires may contain other antioxidants besides the amine-based antioxidants. Examples of other antioxidants include hydroquinone-based antioxidants, phenol-based antioxidants, quinoline-based antioxidants, sulfur-based antioxidants (thioether-based antioxidants), imidazole-based antioxidants, phosphorus-based antioxidants (phosphite-based antioxidants), and the like.

[0025] Examples of the phenol-based antiaging agent include monophenol-based antiaging agents, alkylene bisphenol-based antiaging agents, polyphenol-based antiaging agents, thiobisphenol-based antiaging agents, and hydroquinone-based antiaging agents.

[0026] Examples of phosphorus-based anti-aging agents include tris(nonylphenyl)phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite, cyclic neopentanetetraylbis(octadecylphosphite), distearyl pentaerythritol diphosphite, and pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenol)propionate].

[0027] Examples of sulfur-based anti-aging agents include pentaerythritol-tetrakis-(β-lauryl-thiopropionate), bis[2-methyl-4-{3-n-alkylthiopropionyloxy}-5-t-butylphenyl]sulfide, dilauryl-3,3′-thiodipropionate, dimyristil-3,3′-thiodipropionate, and distearyl-3,3′-thiodipropionate.

[0028] In addition to the above components, various compounding agents generally used in rubber compositions for tire treads, such as vulcanizing or crosslinking agents, vulcanization accelerators, processing aids, plasticizers, liquid polymers, thermosetting resins, and thermoplastic resins, can be compounded in the rubber composition for tires in a conventional manner. Such compounding agents can be kneaded in a conventional manner to prepare a rubber composition, which can then be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be conventionally used amounts, so long as they do not contradict the object of the present invention. The rubber composition for tires can be prepared by mixing the above components using a known rubber kneading machine, such as a Banbury mixer, kneader, roll, etc.

[0029] The rubber composition for tires is suitable for forming a sidewall and / or a rim cushion of a tire. A tire having a sidewall and / or a rim cushion made of the rubber composition for tires of the present invention has excellent fatigue properties against repeated strain and can suppress the occurrence of cracks.

[0030] In a tire having a sidewall made of a rubber composition for tires, the difference between the content of the amine-based antioxidant in the sidewall and the content of the amine-based antioxidant in the tire components adjacent to the sidewall should be 6% by mass or less. By making the difference between the content of the amine-based antioxidant in the sidewall and the tire components adjacent thereto 6% by mass or less, the content of the amine-based antioxidant in the sidewall can be ensured and fatigue properties against repeated strain can be maintained and improved. The tire components adjacent to the sidewall refer to the carcass layer, belt layer, belt cushion, bead filler (including underbead filler), and rim cushion.

[0031] In a tire having a rim cushion made of a rubber composition for tires, the difference between the content of the amine-based antioxidant in the rim cushion and the content of the amine-based antioxidant in the tire components adjacent to the rim cushion should be 6% by mass or less. By making the difference between the content of the amine-based antioxidant in the rim cushion and the tire components adjacent to it 6% by mass or less, the content of the amine-based antioxidant in the rim cushion can be ensured and fatigue properties against repeated strain can be maintained and improved. The tire components adjacent to the rim cushion refer to the carcass layer, belt layer, belt cushion, bead filler (including underbead filler), and sidewall.

[0032] The content of the amine-based antioxidant in the sidewall, the rim cushion, and the tire components adjacent thereto means the mass (unit: mass%) of the amine-based antioxidant relative to the mass of the rubber component in the sidewall, the rim cushion, and the tire components adjacent thereto.

[0033] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. EXAMPLES

[0034] In preparing 21 kinds of rubber compositions for tires (Reference Example 1, Examples 1-12, Comparative Examples 1-8) having a common additive formulation shown in Table 4 and composed of the formulations shown in Tables 1-3, the components except for sulfur and vulcanization accelerator were weighed and mixed in a 1.7-liter closed Banbury mixer for 5 minutes, and then the master batch was discharged outside the mixer and cooled at room temperature. This master batch was fed to the Banbury mixer, and sulfur and vulcanization accelerator were added and mixed to obtain a rubber composition for tires. The additive formulations in Table 4 are shown in parts by mass relative to 100 parts by mass of the diene rubbers shown in Tables 1-3.

[0035] As a rubber composition for tire members adjacent to the sidewall and rim cushion made of the rubber composition for tires of the present invention, a rubber composition for adjacent members was prepared by blending 100 parts by mass of natural rubber with 58 parts by mass of carbon black, 1.0 part by mass of amine-based antioxidant-1, 5.0 parts by mass of zinc oxide, 1.0 part by mass of stearic acid, 5.0 parts by mass of sulfur, and 1.0 part by mass of vulcanization accelerator in the same manner as described above. The types of natural rubber, carbon black, amine-based antioxidant-1, zinc oxide, stearic acid, sulfur, and vulcanization accelerator are the same as those described in Tables 1 to 4.

[0036] The rubber composition for tires and the rubber composition for adjacent components obtained above were molded into sheets and stacked to form an unvulcanized sample, which was then left to stand and stored in an oven at 35°C and 85% humidity for 48 hours.The sample was then vulcanized in a mold of a specified shape at 160°C for 20 minutes to prepare a vulcanized sample for evaluation.The vulcanized sample obtained was sliced ​​and subjected to tensile tests (tensile strength at break and tensile elongation at break) and fatigue properties were measured by the following methods.

[0037] Tensile test (tensile strength at break and tensile elongation at break) The vulcanized sample was punched out into a JIS No. 3 dumbbell shape and subjected to a tensile test at 23°C at a tensile speed of 500 mm / min in accordance with the measurement method specified in JIS K6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties" to measure the tensile strength at break (MPa) and the tensile elongation at break (%). The obtained tensile strength at break and tensile elongation at break results are shown in the "tensile strength at break" and "tensile elongation at break" columns of Tables 1 to 3 as indexes with the value of Reference Example 1 set at 100. The larger the respective indexes, the higher and more excellent the measured values ​​of the tensile strength at break and the tensile elongation at break are.

[0038] Fatigue properties The vulcanized sample was punched into a JIS No. 3 dumbbell shape in accordance with JIS K6251 to prepare a test specimen. The obtained test specimen was subjected to a tensile constant strain fatigue test under the conditions of 20°C, strain 70%, and test frequency 6.67Hz (rotation speed 400rpm) with reference to JIS K6270, and the number of repeated deformations until destruction was measured. The upper limit of the number of repeated deformations was set to 3 million times. The obtained results are shown in the "Constant strain fatigue test" column of Tables 1 to 3 as an index with 3 million times being 100. If this index is 80 or more, it means that the measured value of the constant strain fatigue test is high and the fatigue properties are excellent.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] The types of raw materials used in Tables 1 to 3 are shown below. NR: Natural rubber, SIR20 made by PT.KIRANA SAPTA ENR: Modified natural rubber with epoxy groups, EPOXYPREN manufactured by Muang Mai Guthrie Public Company Limited BR: Butadiene rubber, ZS Elastomers Nipol BR1220 Carbon black: HAF grade carbon black, VULCAN KS manufactured by Cabot Japan Silica-1: Solvey Zeosil 1165MP Silica-2: Silica derived from rice husk, Wilmar K160 Coupling agent: Silane coupling agent, EVONIK Si69 Antioxidant-1: Amine-based antioxidant, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, 6PPD manufactured by EASTMAN Anti-aging agent-2: Hydroquinone-based anti-aging agent, VULANOX HS / LG manufactured by LANXESS Antioxidant-3: Amine-based antioxidant, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, Santoflex 77PD manufactured by Eastman Antioxidant-4: Amine-based antioxidant, N,N'-dicyclohexyl-p-phenylenediamine, Vulkanox 4060 (CCPD) manufactured by LANXESS Vulcanization accelerator-1: Vulcanization accelerator CBS, Sansera NS-G manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator-2: Vulcanization accelerator DPG, Sancerer DG manufactured by Sanshin Chemical Industry Co., Ltd.

[0043] [Table 4]

[0044] The types of raw materials used in Table 4 are shown below. Wax: NIPPON SEIRO HI-MIC-800 Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Stearic acid: NOF Corporation beads stearic acid YR Oil: Shell Lubricants Japan Extract No. 4 S Sulfur: Shikoku Chemical Industry Co., Ltd.'s Myucron OT-20

[0045] As is clear from Tables 2 and 3, it was confirmed that the rubber compositions for tires of Examples 1 to 12 were excellent in tensile strength at break, tensile elongation at break and fatigue properties.

[0046] As is clear from Table 1, the tire rubber composition of Comparative Example 1 has inferior fatigue properties because the amine-based antioxidant is less than 5.0% by mass relative to the natural rubber and no silica is blended. The rubber composition for tires of Comparative Example 2 has inferior fatigue properties since the ratio of silica in the filler is less than 50 mass %. The rubber composition for tires of Comparative Example 3 has a natural rubber content of less than 60% by mass in the diene rubber, and therefore has poor tensile strength at break. The rubber composition for tires in Comparative Example 4 has inferior fatigue properties because the amount of the amine-based antioxidant is less than 3.0 parts by mass relative to the diene rubber and less than 5.0% by mass relative to the natural rubber. In the tire rubber composition of Comparative Example 5, the amine-based antioxidant was less than 5.0% by mass relative to the natural rubber, and therefore the tensile strength at break and fatigue properties were poor. The tire rubber composition of Comparative Example 6 has poor tensile strength at break because the diene rubber contains less than 60% by mass of natural rubber and the amine antioxidant is less than 3.0 parts by mass relative to the diene rubber. The tire rubber composition of Comparative Example 7 has a silica-containing filler content of less than 20 parts by mass, and therefore has poor tensile strength at break. In the tire rubber composition of Comparative Example 8, the amount of the silica-containing filler exceeds 55 parts by mass, and therefore the tensile strength at break is rather inferior.

[0047] The present disclosure includes the following inventions. Invention [1] A rubber composition for tires, comprising 100 parts by mass of diene rubber containing 60% or more by mass of natural rubber, 20 to 55 parts by mass of a filler containing silica, and 3.0 parts by mass or more of an amine-based antioxidant, wherein the silica accounts for 50% by mass or more of the filler, and the amine-based antioxidant accounts for 5.0% by mass or more of the natural rubber. Invention [2] The rubber composition for tires according to invention [1], characterized in that the silica is derived from rice husks. Invention [3] The rubber composition for tires according to invention [1] or [2], wherein the natural rubber is a modified natural rubber having an epoxy group. Invention [4] A tire having a sidewall and / or a rim cushion made of the rubber composition for tires according to any one of inventions [1] to [3]. Invention [5] The tire according to invention [4], characterized in that a difference between a content of the amine-based anti-aging agent in the sidewall and a content of the amine-based anti-aging agent in a tire component adjacent to the sidewall is 6% by mass or less. Invention [6] The tire according to invention [4] or [5], characterized in that the difference between the content of the amine-based anti-aging agent in the rim cushion and the content of the amine-based anti-aging agent in the tire component adjacent to the rim cushion is 6% by mass or less.

Claims

1. A rubber composition for tires is characterized in that 100 parts by mass of diene rubber containing 60% by mass or more of natural rubber is blended with 20 to 55 parts by mass of a filler containing silica and 3.0 parts by mass or more of an amine-based antiaging agent, wherein the silica accounts for 50% by mass or more of the filler and the amine-based antiaging agent accounts for 5.0% by mass or more of the mass of the natural rubber.

2. 2. The rubber composition for tires according to claim 1, wherein the silica is derived from rice husks.

3. 3. The rubber composition for tires according to claim 1, wherein the natural rubber is a modified natural rubber having an epoxy group.

4. A tire having a sidewall and / or a rim cushion made of the rubber composition for tires according to claim 1 or 2.

5. 5. The tire according to claim 4, wherein a difference between a content of the amine-based antiaging agent in the sidewall and a content of the amine-based antiaging agent in a tire member adjacent to the sidewall is 6% by mass or less.

6. 6. The tire according to claim 4, wherein a difference between a content of the amine-based anti-aging agent in the rim cushion and a content of the amine-based anti-aging agent in a tire component adjacent to the rim cushion is 6% by mass or less.

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