Tread rubber composition and tire

Abstract

The present invention provides a tread rubber composition with which it is possible to improve ozone resistance while also having excellent wear resistance and fracture resistance.　The present invention is a rubber composition including a rubber component, carbon black, silica, and an anti-aging agent, said rubber composition characterized in that the rubber component contains a high-purity natural rubber having a nitrogen content of 0.3 mass% or less, and the anti-aging agent contains at least one from among aminoquinoline-based anti-aging agents represented by general formula (1) and phenylenediamine-based anti-aging agents represented by general formula (2).

Description

Rubber composition for tread and tire

[0001] The present invention relates to a rubber composition for a tread and a tire.

[0002] Conventionally, in the case of heavy-duty pneumatic tires for rough roads, methods for preventing deterioration in heat generation performance, appearance performance, abrasion resistance, etc. have been implemented by selecting the carbon black to be compounded in a rubber composition for a tire tread and optimizing the amount of carbon black to be filled. In recent years, various tread rubbers for heavy-duty pneumatic tires have been proposed in which silica is compounded in addition to carbon black in a rubber composition for a tread.

[0003] For example, Patent Documents 1 to 3 disclose techniques in which silica is blended together with carbon black into a rubber composition for treads of heavy-duty pneumatic tires for construction vehicles and the like, thereby improving abrasion resistance, cut resistance, heat generation performance, and the like.

[0004] However, the techniques of Patent Documents 1 to 3 were not sufficient for improving the heat generation performance, appearance performance, and abrasion resistance after running and suppressing deterioration of physical properties in rubber compositions for treads of heavy-duty pneumatic tires. In particular, further improvements in abrasion resistance and fracture resistance were desired.

[0005] Furthermore, tire treads can deteriorate due to the influence of external environments such as the presence of ozone, and as this deterioration progresses, cracks and other defects can occur. To address this problem, rubber compositions containing antioxidants are often applied to the various rubber components that make up tires. For example, Patent Document 4 below discloses that cracks and discoloration on the tire surface can be suppressed by applying a rubber composition containing a selected blend of a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) to the rubber that makes up the tire surface.

[0006] JP-A-1-311141 JP-A-3-65406 JP-A-4-226140 International Publication No. 2018 / 056384

[0007] However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) used in Patent Document 4 may have an impact on the environment, and in consideration of the possibility of future restrictions under European regulations, it has been desired to use an antioxidant that has a lower environmental impact and excellent ozone resistance.

[0008] Therefore, an object of the present invention is to provide a rubber composition for a tread that can improve ozone resistance while having excellent abrasion resistance and puncture resistance, and to provide a tire that has improved ozone resistance while having excellent abrasion resistance and puncture resistance.

[0009] The gist of the present invention for solving the above problems is as follows: [1] A rubber composition including a rubber component, carbon black, silica, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3 mass % or less, and the antioxidant is a compound represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ , R １９ and R １１０ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.], and an aminoquinoline antioxidant represented by the following general formula (2): [In the formula, R ２１ and R ２２ are each independently an alkyl group or an aryl group having 7 or more carbon atoms, and R ２１ and R ２２wherein at least one of the groups is an alkyl group having 7 or more carbon atoms. By having the above-mentioned constitution, it is possible to improve ozone resistance while also achieving excellent abrasion resistance and fracture resistance.

[0010] [2] A tire comprising the above rubber composition for a tread. The tire having the above configuration has excellent abrasion resistance and puncture resistance, and also has improved ozone resistance.

[0011] According to the present invention, it is possible to provide a rubber composition for a tread that can improve ozone resistance while having excellent abrasion resistance and puncture resistance. Also, according to the present invention, it is possible to provide a tire that has improved ozone resistance while having excellent abrasion resistance and puncture resistance.

[0012] An embodiment of the rubber composition for tread and tire of the present invention will be described below by way of example. <Definitions> The compounds described in this specification may be derived in part or entirely from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0013] <Rubber composition for tread> The rubber composition for tread of the present invention (hereinafter sometimes simply referred to as "rubber composition") contains a rubber component, carbon black, silica, and an antioxidant. Hereinafter, each component constituting the rubber composition for tread of the present invention will be described.

[0014] (Rubber Component) The rubber component contained in the rubber composition for treads of the present invention contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less. By containing this high-purity natural rubber, the natural rubber does not contain excessive amounts of protein, which can suppress gelation, resulting in excellent wear resistance. From the same perspective, the nitrogen content in the natural rubber is preferably 0.25% by mass or less, and more preferably 0.2% by mass or less.

[0015] Here, the high-purity natural rubber is not particularly limited in other requirements, so long as the nitrogen content is 0.3% by mass or less. For example, the high-purity natural rubber may be natural rubber obtained by removing proteins through a centrifugation process. The centrifugation process is a process in which natural rubber latex, the raw material for natural rubber, is deproteinized by centrifugation. The conditions for the centrifugation (e.g., rotation speed, time) are not particularly limited, and can be changed appropriately depending on the protein content to be removed. For example, to reduce the nitrogen content in natural rubber to 0.1% by mass or less, the centrifugation process can be carried out several times at a rotation speed of about 7,500 rpm. After the centrifugation process, the product can be washed and dried to obtain highly purified natural rubber.

[0016] The natural rubber latex used in the centrifugation process is not particularly limited. For example, field latex extracted from rubber trees or concentrated natural rubber latex obtained by processing field latex can be used. The dry rubber content in the natural rubber latex is also not particularly limited. From the viewpoint of obtaining better abrasion resistance, the dry rubber content is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0017] The content of the highly purified natural rubber in the rubber component can be 100%, but other rubbers can also be contained within a range that does not impair the object of the present invention. Furthermore, the natural rubber can be a mixture of not only the highly purified natural rubber but also ordinary natural rubber. In this case, the content of the highly purified natural rubber in the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of further improving abrasion resistance.

[0018] The rubber component may contain other synthetic rubbers in addition to the natural rubbers described above. Examples of synthetic rubbers include diene-based synthetic rubbers such as butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR), and non-diene-based synthetic rubbers such as ethylene propylene diene rubber (EPDM), ethylene propylene rubber (EPM), and butyl rubber (IIR).

[0019] Furthermore, the rubber component preferably contains butadiene rubber and / or styrene-butadiene rubber among the above-mentioned synthetic rubbers, because this allows achieving both low loss properties and abrasion resistance at a higher level.

[0020] The natural rubber and the diene-based synthetic rubber (hereinafter collectively referred to as "diene-based rubber") may be unmodified diene-based rubber (hereinafter sometimes referred to as "unmodified diene-based rubber") or modified diene-based rubber (hereinafter sometimes referred to as "modified diene-based rubber").

[0021] (Carbon Black) The rubber composition for tread of the present invention further contains carbon black in addition to the above-mentioned rubber component, because this increases the reinforcing properties of the rubber composition and allows for excellent abrasion resistance and fracture resistance to be obtained.

[0022] In the rubber composition for tire treads of the present invention, the total content of the carbon black and silica, which will be described later, is preferably 50 parts by mass or more per 100 parts by mass of the rubber component. By making the total content of the carbon black and silica 50 parts by mass or more per 100 parts by mass of the rubber component, the tire reinforcement properties can be enhanced and better wear resistance can be achieved. From the same viewpoint, the total content of the silica and the carbon black is preferably 60 parts by mass or more, and more preferably 65 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of preventing deterioration of the processability and low heat buildup properties of the rubber composition, the total content of the silica and the carbon black is preferably 80 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the rubber component.

[0023] The content of the carbon black alone is preferably 40 parts by mass or more, more preferably 46 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. When the content of the carbon black is 40 parts by mass or more per 100 parts by mass of the rubber component, reinforcement is enhanced and better abrasion resistance is obtained. On the other hand, the content of the carbon black is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, per 100 parts by mass of the rubber component. When the content of the carbon black is 60 parts by mass or less per 100 parts by mass of the rubber component, deterioration of low heat buildup can be suppressed.

[0024] Furthermore, in the rubber composition of the present invention, the mass ratio of the carbon black content to the total content of the carbon black and silica described later is preferably 0.70 or more, more preferably 0.80 or more. By setting the mass ratio of the carbon black content to the total content of the carbon black and silica to 0.70 or more, excellent wear resistance can be achieved. Note that, from the viewpoint of maintaining good low heat buildup properties, the mass ratio of the carbon black content to the total content of the carbon black and silica described later is preferably 0.95 or less, more preferably 0.85 or less.

[0025] The carbon black preferably includes plant-derived carbon black and recycled carbon black (also called "recycled carbon black"). Examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0026] As used herein, "recycled carbon black" refers to carbon black recovered from recycled waste materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only waste generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping the tread portion remaining on the base tire during tire retreading, for example. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0027] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixing of different grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0028] Solid residues obtained by pyrolysis of waste materials such as used rubber and used tires contain ash in addition to carbon black. The ash is derived from non-volatile components contained in the rubber and tires. Therefore, recycled carbon black obtained from the solid residues has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content of the recycled carbon black, the better. The carbon content of the recycled carbon black is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content of the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed moisture.

[0029] Specific examples of the ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, and magnesium oxide. In the case of recycled carbon black produced from solid residue obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0030] The recycled carbon black can also be obtained from a pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in paragraph

[0004] of Japanese Patent Publication No. 6,856,781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0031] The recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained by a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained by a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0032] Furthermore, examples of thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0033] The crosslinked rubber products used for the decomposition may be grouped by the type of rubber component previously compounded, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be performed for each group. Furthermore, the crosslinked rubber products may be grouped by both type of rubber component and type of filler, and then the decomposition step may be performed for each group. When the decomposition step is performed for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when the recycled carbon black is compounded again into a rubber component, a rubber composition with better performance can be obtained.

[0034] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m as measured by the BET method. ２ / g, and 50 to 90m ２ / g, and more preferably 55 to 75m ２ In this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black measured by the BET method is a statistical thickness specific surface area (STSA) determined in accordance with ASTM D6556.

[0035] The pH of the recycled carbon black is preferably 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. In this specification, the pH of the recycled carbon black is determined in accordance with ASTM D1512.

[0036] The recycled carbon black preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, the toluene color transmittance of recycled carbon black is determined in accordance with ASTM D1618.

[0037] The recycled carbon black preferably has a heat loss of 3% by mass or less, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less at 125°C. Herein, the heat loss of recycled carbon black at 125°C is determined in accordance with ASTM D1509.

[0038] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0039] The recycled carbon black preferably has a 35 mesh sieve residue of 20 mass ppm or less, more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less. Herein, the 35 mesh sieve residue of recycled carbon black is determined in accordance with ASTM D1514.

[0040] The recycled carbon black preferably has a 325 mesh (44 μm) sieve residue of 1000 mass ppm or less, more preferably 700 mass ppm or less, and particularly preferably 300 mass ppm or less. Herein, the 325 mesh (44 μm) sieve residue of the recycled carbon black is determined in accordance with ASTM D1514.

[0041] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, the pellet hardness of recycled carbon black is determined in accordance with ASTM D5230.

[0042] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, the pellet fine powder content of recycled carbon black is determined in accordance with ASTM D1508.

[0043] The particle size (D97) of the recycled carbon black is preferably 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size distribution analyzer, assuming a refractive index of 1.33 for water and a refractive index of 1.75 for the filler.

[0044] The recycled carbon black preferably contains particles of 5 μm or less in a proportion of 50% by volume or more, more preferably 70% by volume or more, and particularly preferably 80% by volume or more.

[0045] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, the ash content of the recycled carbon black is determined in accordance with ASTM D8474 and D1506.

[0046] The recycled carbon black preferably has a dibutyl phthalate (DBP) absorption of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the DBP absorption of recycled carbon black is determined in accordance with ASTM D2414.

[0047] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the 24M4DBP absorption capacity of the recycled carbon black is determined in accordance with ASTM D3493.

[0048] Commercially available recycled carbon black can be used. For example, Enrestec's product name "PB365" can be mentioned as such a commercially available product. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m2 as measured by the BET method. ２ / g and contains about 17% by mass of ash.

[0049] The amount of recycled carbon black is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, still more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component. When the amount of recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component, the effect of improving the proportion of sustainable materials in rubber products to which the rubber composition is applied is significant, and when the amount is 50 parts by mass or less, the fracture resistance of the rubber composition can be more reliably maintained.

[0050] (Silica) The rubber composition for a tire tread of the present invention contains silica in addition to the rubber component and carbon black described above. By including the silica, the reinforcement property and fracture resistance of the tire can be improved.

[0051] The content of the silica needs to satisfy the above-mentioned total content with the carbon black. However, from the viewpoint of realizing better fracture resistance, the content of the silica alone is preferably 5 to 25 parts by mass per 100 parts by mass of the rubber component. By making the content of the silica 5 parts by mass or more per 100 parts by mass of the rubber component, the tire reinforcement can be enhanced and better wear resistance and fracture resistance can be realized. From the same viewpoint, the content of the silica is preferably 10 parts by mass or more per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration of the processability of the rubber composition, by making the content of the silica 25 parts by mass or less per 100 parts by mass of the rubber component, it is possible to improve wear resistance and fracture resistance while suppressing deterioration of processability and workability. From the same viewpoint, the content of the silica is preferably 20 parts by mass or less per 100 parts by mass of the rubber component.

[0052] Here, the silica has a CTAB specific surface area of ​​200 to 240 m ２ / g. The CTAB specific surface area of ​​the silica is preferably 200 m ２ When the CTAB specific surface area of ​​the silica is 240 m / g or more, a more excellent effect of improving fracture resistance and fracture resistance can be obtained. ２ When the CTAB specific surface area of ​​the silica is 1 / g or less, poor dispersion and deterioration of processability can be suppressed. The CTAB specific surface area of ​​the silica can be measured in accordance with, for example, JIS K 6430:2008.

[0053] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred because it contains a large number of silanol groups. These silicas may be used alone or in combination of two or more.

[0054] Furthermore, from the viewpoint of reducing environmental impact, silica derived from siliceous plants is also preferred as the silica. Such siliceous plants are found, for example, in mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Poaceae plants. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo, and sugarcane, among which rice is preferred. Rice is widely cultivated for food and can be procured locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient supply. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs of transportation and storage, which is environmentally preferable from various viewpoints. The rice husk silica may be a powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet process using an alkali silicate aqueous solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be pulverized using a known pulverizer (e.g., a ball mill), and then sorted and classified into a predetermined particle size range to obtain rice husk charcoal powder. The rice husk-derived precipitated silica can be produced by the method described in JP 2019-38728 A, for example.

[0055] (Resin) The rubber composition for a tread of the present invention preferably contains a resin in addition to the rubber component, silica, and carbon black described above. The resin preferably has a softening point of 130°C or higher. A softening point of 130°C or higher of the resin can improve fracture resistance. From the same viewpoint, the softening point of the resin is more preferably 140°C or higher, and even more preferably 145°C or higher. In this specification, the softening point of the resin is the temperature at which the ball drops when the softening point defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0056] The type of resin is not particularly limited. For example, terpene resin, rosin resin, C ５ based resin, C ５ -C ９ based resin, C ９ Examples of the resins include cyclopentadiene-based resins, dicyclopentadiene-based resins, aromatic resins, coumarone resins, indene resins, coumarone-indene-based resins, olefin-based resins, polyurethane resins, and acrylic resins. These resins may be used alone or in combination of two or more. Among the above-mentioned resins, the resin is preferably a cyclopentadiene-based resin, and more preferably a dicyclopentadiene-based resin. This is because better fracture resistance can be achieved. The dicyclopentadiene-based resin is, for example, AlCl ３ or BF ３ The term "dicyclopentadiene-based resin" refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as Benzene, etc. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, copolymers of dicyclopentadiene and C ９ Examples include copolymers with distillates (vinyl toluene, indene, etc.).

[0057] Furthermore, the content of the resin is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, per 100 parts by mass of the rubber component, because this can further enhance the effect of improving the fracture resistance described above. From the viewpoint of preventing deterioration of low heat buildup, the content of the resin is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0058] (Antiaging Agent) The rubber composition of the present invention contains an antioxidant, which has the effect of preventing aging of the rubber composition and rubber products using the same.

[0059] The content of the antioxidant is preferably 0.5 to 10 parts by mass per 100 parts by mass of the rubber component. When the content of the antioxidant is 0.5 parts by mass or more per 100 parts by mass of the rubber component, better ozone resistance is obtained and decreases in the elongation at break (EB) and tensile strength (TB) of the rubber composition after aging can be sufficiently suppressed. When the content of the antioxidant is 10 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber physical properties other than ozone resistance (heat buildup, etc.) can be suppressed. From the same viewpoint, the content of the antioxidant is preferably 1 to 8 parts by mass per 100 parts by mass of the rubber component.

[0060] The rubber composition of the present invention contains an antioxidant selected from the group consisting of an aminoquinoline-based antioxidant represented by the general formula (1) and a phenylenediamine-based antioxidant represented by the general formula (2), which will be described later. This allows for improved ozone resistance while reducing the environmental impact.

[0061] The aminoquinoline antioxidant represented by the general formula (1) is represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R１６ , R １７ , R １８ , R １９ and R １１０ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.] The aminoquinoline antioxidant represented by the above general formula (1) has the effect of improving ozone resistance and can suppress cracking in the radially outer cap tread layer and the radially inner cap tread layer. In addition, the aminoquinoline antioxidant represented by the above general formula (1) has a small environmental impact.

[0062] In the above general formula (1), is a single bond or a double bond, preferably a double bond; R １１ and R １２ are each independently hydrogen, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group, and are preferably hydrogen or a phenyl group; １３ , R １４ , R １５ , R １６ , R １７ , R １８ , R １９ and R １１０ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms, and are preferably hydrogen or a methyl group. １１ , R １２ , R １３ , R １４ , R １５ , R １６ , R １７ , R １８ , R １９ and R １１０With regard to the above, the alkyl group having 1 to 12 carbon atoms may be linear or branched. Examples of the alkyl group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. The number of carbon atoms in the alkyl group is preferably in the range of 1 to 8, more preferably in the range of 1 to 6, even more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3. R in the above general formula (1) １１ and R １２ Regarding the above, examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 1-methylcyclopentyl group, a 2-methylcyclopentyl group, and a 3-methylcyclopentyl group.

[0063] Specific examples of the aminoquinoline antioxidants represented by the general formula (1) include those represented by the following structural formulas (1-1) to (1-94): Among these, from the viewpoint of suppressing cracking, the compound represented by structural formula (1-1) is particularly preferred. A rubber composition containing the compound represented by structural formula (1-1) has excellent ozone resistance.

[0064] There are no particular limitations on the method for producing the aminoquinoline antioxidant represented by the above general formula (1). For example, when an aromatic amine compound is used as a starting material, the method comprises the steps of: (i) reacting the aromatic amine compound with sodium nitrite in the presence of an acid to produce an aromatic amine compound having a nitroso group; (ii) reducing the produced nitroso group with sodium borohydride or the like to produce an aromatic diamine compound; and (iii) reacting the produced aromatic diamine compound with a ketone compound such as acetone to form a condensed ring, thereby producing a compound having a 6-amino-1,2-dihydroquinoline skeleton, i.e., the compound represented by the above general formula (1), In addition, if desired, (iv) the compound having a 6-amino-1,2-dihydroquinoline skeleton thus produced can be reduced with hydrogen in the presence of a palladium-supported carbon catalyst to produce a compound having a 6-amino-1,2,3,4-tetrahydroquinoline skeleton, i.e., a compound represented by the above general formula (1), Compounds can be prepared in which is a single bond.

[0065] The proportion of the aminoquinoline antioxidant represented by the general formula (1) in the antioxidant (more specifically, in the total amount of antioxidant in each of the radially outer cap tread layer and the radially inner cap tread layer) is preferably 10 to 100 mass%, more preferably 20 to 100 mass%, and even more preferably 30 to 100 mass%. When the proportion of the aminoquinoline antioxidant represented by the general formula (1) in the antioxidant is 10 to 100 mass%, ozone resistance can be further improved.

[0066] The rubber composition for a tread of the present invention is characterized in that the antioxidant is a phenylenediamine-based antioxidant represented by the following general formula (2): [In the formula, R ２１ and R ２２ are each independently an alkyl group or an aryl group having 7 or more carbon atoms, and R ２１ and R ２２ wherein at least one of the groups is an alkyl group having 7 or more carbon atoms. By including the phenylenediamine-based antioxidant represented by the general formula (2), the rubber composition for a tread of the present invention can improve ozone resistance while reducing the burden on the environment.

[0067] In the above general formula (2), R ２１ and R ２２ are each independently an alkyl group or an aryl group having 7 or more carbon atoms, and R ２１ and R ２２At least one of the groups is an alkyl group having 7 or more carbon atoms. Examples of the alkyl group having 7 or more carbon atoms include a 1,2-dimethylpentyl group, a 1,3-dimethylpentyl group, a 1,4-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,4-dimethylpentyl group, a 1-methylhexyl group, a 2-methylhexyl group, an n-heptyl group, a 1,2-dimethylhexyl group, a 1,3-dimethylhexyl group, a 1,4-dimethylhexyl group, a 1,5-dimethylhexyl group, a 2,3-dimethylhexyl group, a 2,4-dimethylhexyl group, a 2,5-dimethylhexyl group, a 3,4-dimethylhexyl group, a 3,5-dimethylhexyl group, a 1-methylheptyl group, a 2-methylheptyl group, an n-octyl group, various decyl groups, and various dodecyl groups. Of these, a 1,4-dimethylpentyl group and a 1-methylheptyl group are preferred. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesyl group, an α-naphthyl group, a β-naphthyl group, an ethylphenyl group, an n-propylphenyl group, an isopropylphenyl group, an n-butylphenyl group, a t-butylphenyl group, various dimethylphenyl groups, various diethylphenyl groups, various methylethylphenyl groups, various trimethylphenyl groups, various dimethylethylphenyl groups, various methyldiethylphenyl groups, and various triethylphenyl groups, and among these, a phenyl group is preferred.

[0068] R in the above general formula (2) ２１ and R ２２ At least one of R is an alkyl group having 7 or more carbon atoms. ２１ and R ２２ The other of R is preferably a phenyl group. ２１ and R ２２ one of R is an alkyl group having 7 or more carbon atoms, ２１ and R ２２ A phenylenediamine-based antioxidant in which the other radical is a phenyl group can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products to which the rubber composition is applied.

[0069] R in the above general formula (2) ２１ and R ２２At least one of R preferably has 7 or 8 carbon atoms. ２１ and R ２２ The phenylenediamine-based antioxidant, at least one of which has 7 or 8 carbon atoms, can further improve the ozone resistance of the rubber composition and can further suppress the occurrence of cracks in rubber products to which the rubber composition is applied.

[0070] Specific examples of the phenylenediamine-based antiaging agent represented by the general formula (2) include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine (8PPD), N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine (7PPD), etc. These phenylenediamine-based antiaging agents may be used alone or in combination of two or more.

[0071] The proportion of the phenylenediamine-based antioxidant represented by general formula (2) in the antioxidant is preferably 0.5 to 10 mass%, more preferably 1 to 8 mass%. When the proportion of the phenylenediamine-based antioxidant represented by general formula (2) in the antioxidant is 0.5 to 10 mass%, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0072] Quinoline-Based Antiaging Agent: The antiaging agent preferably further contains a quinoline-based antiaging agent. The quinoline-based antiaging agent is an antiaging agent having a quinoline moiety or a derivative thereof (such as a dihydroquinoline moiety or a tetrahydroquinoline moiety). The quinoline-based antiaging agent has the effect of improving the ozone resistance of the rubber composition, and a rubber composition containing both the phenylenediamine-based antiaging agent represented by the general formula (1) and a quinoline-based antiaging agent can further suppress the occurrence of cracks in rubber products.

[0073] The quinoline-based antioxidant preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the quinoline-based antioxidant include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ) and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. The quinoline-based antioxidant preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ). Quinoline-based antioxidants containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline are highly effective in improving the ozone resistance of rubber compositions, and also have the advantage of being less likely to discolor the rubber composition. Therefore, a rubber composition containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline can further suppress the occurrence of cracks in rubber products and is also less susceptible to discoloration. Examples of the polymer of 2,2,4-trimethyl-1,2-dihydroquinoline include a dimer, trimer, and tetramer of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0074] The proportion of the quinoline-based antioxidant in the antioxidant is preferably 10 to 50% by mass, and more preferably 15 to 40% by mass. When the proportion of the quinoline-based antioxidant in the antioxidant is 10 to 50% by mass, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0075] Amine-based antioxidant represented by formula (3) The antioxidant may further be an amine-based antioxidant represented by the following general formula (3): [In the formula, R ３１ and R ３２are each independently a monovalent saturated hydrocarbon group. It is preferable to include an amine-based antioxidant represented by the formula (3) (excluding the phenylenediamine-based antioxidant represented by the general formula (1) above). The amine-based antioxidant represented by the formula (3) contains a phenylenediamine moiety like the general-purpose antioxidant N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD), but differs from the antiaging agent 6PPD in that it does not contain a double bond other than the phenylenediamine moiety. The amine-based antioxidant represented by the formula (3) has the effect of improving the ozone resistance of the rubber composition.

[0076] In the above general formula (3), R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group. ３１ and R ３２ may be the same or different, but from the viewpoint of synthesis, they are preferably the same.

[0077] The number of carbon atoms in the monovalent saturated hydrocarbon group is preferably 1 to 20, more preferably 3 to 10, and particularly preferably 6 or 7. When the number of carbon atoms in the saturated hydrocarbon group is 20 or less, the number of moles per unit mass increases, which enhances the anti-aging effect and further improves the ozone resistance of the rubber composition. ３１ and R ３２ From the viewpoint of further improving the ozone resistance of the rubber composition, it is preferable that each of the groups independently represents a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms.

[0078] Examples of the monovalent saturated hydrocarbon group include an alkyl group and a cycloalkyl group. The alkyl group may be linear or branched, and the cycloalkyl group may further have an alkyl group or the like bonded thereto as a substituent. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,2-dimethylpentyl group, a 1,3-dimethylpentyl group, a 1,4-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,4-dimethylpentyl group, an n-hexyl group, a 1-methylhexyl group, a 2-methylhexyl group, various octyl groups, various decyl groups, and various dodecyl groups. Of these, a 1,4-dimethylpentyl group is preferred. Examples of the cycloalkyl group include a cyclopentyl group, a methylcyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, a cycloheptyl group, and a cyclooctyl group. Of these, a cyclohexyl group is preferred.

[0079] Specific examples of the amine-based antiaging agent represented by the general formula (3) include N,N'-dicyclohexyl-p-phenylenediamine, etc. The amine-based antiaging agents represented by the formula (3) may be used alone or in combination of two or more.

[0080] The proportion of the amine-based antioxidant in the antioxidant is preferably 0.1 to 80% by mass, and more preferably 1 to 70% by mass. When the proportion of the amine-based antioxidant in the antioxidant is 0.1 to 80% by mass, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0081] Amine-based antiaging agent of formula (4) Furthermore, the antiaging agent may be an amine-based antiaging agent represented by the following general formula (4): [In the formula, R４１ and R ４２ represents a phenyl group, and m4 represents an integer of 7 or more.]. The amine-based antioxidant represented by the general formula (4) has a higher molecular weight than conventional antioxidants, and as shown in the formula (4), it has a bridge moiety having a unique and relatively long chain length, i.e., "-NH-CH(CH ３ )-(CH ２ ) ｍ４ -CH(CH ３ )-NH-". It is believed that the high molecular weight and the presence of specific bridge moieties of such amine-based antioxidants reduce the diffusion rate in the rubber composition, further suppressing migration to the rubber surface. Furthermore, the amine-based antioxidant (C4) has a moiety composed of "-CH(CH ３ )-(CH ２ ) ｍ４ -CH(CH ３ One hydrogen atom is bonded to each of the two nitrogen atoms present at both ends of "(2-amino-2-methyl-2-methyl-2-propanol)-" (forming a so-called secondary amino group), and the presence of this bond in the structure represented by formula (4) is thought to contribute to the specific effect of improving ozone resistance (weather resistance).

[0082] In the above general formula (4), R ４１ and R ４２ is a phenyl group. ４１ and R ４２ When is a phenyl group, the weather resistance of the rubber composition can be further improved, and discoloration of the rubber composition can be more reliably prevented.

[0083] In the general formula (4), m4 is an integer of 7 or more, and from the viewpoint of improving the weather resistance of the rubber composition and preventing discoloration, it is more preferably an integer of 8 to 16, and even more preferably an integer of 10 to 14.

[0084] Examples of the amine-based antiaging agent of the above formula (4) include N,N'-bis(4-anilinophenyl)dodecane-2,11-diamine, N,N'-bis(4-anilinophenyl)tetradecane-2,13-diamine, N,N'-bis(4-anilinophenyl)hexadecane-2,15-diamine, N,N'-bis(4-anilinophenyl)octadecane-2,17-diamine, etc. Among these, N,N'-bis(4-anilinophenyl)tetradecane-2,13-diamine and N,N'-bis(4-anilinophenyl)octadecane-2,17-diamine are particularly preferred.

[0085] The proportion of the amine-based antioxidant represented by general formula (4) in the antioxidant is preferably 0.1 to 80 mass%, more preferably 1 to 70 mass%. When the proportion of the amine-based antioxidant represented by general formula (4) in the antioxidant is 0.1 to 80 mass%, the ozone resistance of the rubber composition can be further improved, and the occurrence of cracks in rubber products using the rubber composition can be further suppressed.

[0086] Other Antiaging Agents: The rubber composition of the present invention may or may not contain an antioxidant (other antioxidant) other than the phenylenediamine-based antioxidant of formula (1), the quinoline-based antioxidant, the amine-based antioxidant of formula (3), and the amine-based antioxidant of formula (4). Examples of other antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and N,N'-diphenyl-p-phenylenediamine (DPPD). However, it is preferable to exclude N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). Commercially available antioxidants can be used, including those from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., and Flexis. These antioxidants may be used alone or in combination of two or more. The content of the other antioxidant in the antioxidant is preferably 0 to 20% by mass, and more preferably 0 to 10% by mass.

[0087] (Sulfur, Vulcanization Accelerator) Furthermore, the rubber composition for a tread of the present invention preferably contains sulfur as a crosslinking agent in addition to the above-mentioned components, because this can improve various physical properties such as durability of the rubber composition for a tread of the present invention.

[0088] Further, from the same viewpoint, the rubber composition for a tread of the present invention preferably contains a vulcanization accelerator in addition to the above-mentioned components. Here, the type of vulcanization accelerator is not particularly limited, and examples that can be used include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and dibenzothiazyl disulfide; sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazyl sulfenamide and N-t-butyl-2-benzothiazyl sulfenamide; guanidine-based vulcanization accelerators such as diphenyl guanidine; thiuram-based vulcanization accelerators such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, tetradodecyl thiuram disulfide, tetraoctyl thiuram disulfide, tetrabenzyl thiuram disulfide and dipentamethylene thiuram tetrasulfide; dithiocarbamate-based vulcanization accelerators such as zinc dimethyldithiocarbamate; and zinc dialkyldithiophosphate.

[0089] Furthermore, among the above-mentioned vulcanization accelerators, it is preferable to use at least a sulfenamide vulcanization accelerator, and it is more preferable to use N-cyclohexyl-2-benzothiazylsulfenamide, from the viewpoint of being able to control the vulcanization rate and degree of vulcanization and improve the fracture resistance.

[0090] The content of the vulcanization accelerator is preferably 1 part by mass or more, and more preferably 1.4 parts by mass or more, per 100 parts by mass of the rubber component, because this allows for the improvement of various physical properties such as tire durability while appropriately controlling the vulcanization rate.

[0091] Furthermore, the mass ratio of the content of the resin to the content of the vulcanization accelerator is preferably 9 or less (content of resin / content of vulcanization accelerator≦9). This is because the vulcanization rate and the degree of vulcanization can be controlled and various physical properties such as tire durability can be improved. From the same viewpoint, the mass ratio of the content of the resin to the content of the vulcanization accelerator is more preferably 2 or less (content of resin / content of vulcanization accelerator≦2).

[0092] (Other Components) In addition to the above-mentioned components, other components may be appropriately selected and blended into the rubber composition for treads of the present invention, as needed, within the scope of not impairing the effects of the present invention. Examples of other components include additives such as silane coupling agents, inorganic fillers other than silica and carbon black, softeners, tackifiers, dispersants, crosslinking aids, stearic acid, colorants, antistatic agents, and lubricants, as well as various known compounding chemicals commonly used in the rubber industry. Commercially available products may be used for these.

[0093] Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, Silane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate acrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, 3-octanoylthiopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltri Examples of suitable silane coupling agents include ethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and 3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propanethiol (manufactured by Degussa under the trade name "Si363"). These silane coupling agents may be used alone or in combination of two or more.

[0094] Bioethanol can also be used as a raw material for silane coupling agents. Bioethanol is produced primarily using sugars and / or cellulose as biological resources, preventing the effective use of other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of a monomer component derived from a biological resource, a monomer component derived from a renewable resource, and a monomer component derived from a fossil resource. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0095] Examples of inorganic fillers other than silica and carbon black include aluminum hydroxide, clay, etc. Among these inorganic fillers, aluminum hydroxide, etc. is preferred because it has a relatively high reinforcing property, and clay, etc. is effective because it makes use of its shape characteristics.

[0096] Furthermore, the softener is not particularly limited and can be appropriately selected depending on the purpose. Examples include naphthenic base oils, paraffinic base oils, and aromatic base oils. The content of the softener is preferably 0 to 30 parts by mass per 100 parts by mass of the rubber component. If the content of the softener exceeds 30 parts by mass per 100 parts by mass of the rubber component, the softener may bleed onto the surface of the rubber product or the abrasion resistance may be reduced. Furthermore, among the softeners described above, naphthenic base oils or paraffinic base oils are preferred, with naphthenic base oils being most preferred. Aromatic oils are undesirable because they contain a large amount of aromatic components, which increases their affinity with the chemicals, which are aromatic compounds, and further inhibit their reaction with the polymer. On the other hand, naphthenic base oils and paraffinic base oils have the effect of diffusing into the polymer and promoting the reaction, while oils with lower pour points diffuse more easily into the polymer. The classification of naphthenic base oils, paraffinic base oils, and aromatic base oils is determined by their CA, CP, and CN values. For example, naphthenic base oils include TDAE, SRAE, RAE, and black oil. Paraffinic base oils include spindle oil and paraffin oil. Furthermore, a blend of naphthenic base oil and naphthenic asphalt, such as A / O Mix (Sankyo Yuka Kogyo Co., Ltd.), can also provide a more favorable effect. The timing of blending these lubricating oils is not particularly limited. For example, they may be extended during the production of the rubber component, or may be added during kneading of the rubber composition for treads.

[0097] (Production of Rubber Composition for Tread) The method for producing the rubber composition for tread of the present invention is not particularly limited, but for example, the rubber composition can be produced by blending various components appropriately selected as necessary with the rubber component, and kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0098] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0099] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0100] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0101] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for vulcanization include mold vulcanizers that use molds to vulcanize rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0102] <Tire> The tire of the present invention is characterized by including the above-described rubber composition for tread of the present invention. By including the rubber composition for tread of the present invention as a tire material, excellent wear resistance and puncture resistance can be achieved without deteriorating other physical properties. Here, the tire of the present invention can be used, for example, as a heavy-duty tire, a truck / bus tire, an aircraft tire, or a passenger car tire, but among these, a heavy-duty tire is preferable. This is because the rubber composition for tread used as a material for the tread portion has excellent wear resistance and puncture resistance, and is therefore a great advantage when used as a heavy-duty tire.

[0103] When using the rubber composition for a tread of the present invention described above, for example, an unvulcanized rubber composition may be used to mold and then vulcanize the composition, or a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like may be used to mold and then vulcanize the composition. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0104] Furthermore, in the tire of the present invention, the above-described rubber composition for a tread of the present invention must be applied to the tread (base tread, cap tread, undertread), but it can also be applied to various other structural members. For example, it can be used in cushion rubber, shoulders, sidewalls, clinches, bead fillers, carcass coating rubber, insulation, chafers, inner liners, etc., and it can also be used in side reinforcing layers of run-flat tires, etc. Furthermore, the rubber composition for a tread of the present invention can be applied to rubber crawlers, seismic isolation rubber, etc., in addition to tires.

[0105] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0106] [Examples 1-1 to 2-4, Comparative Examples 1-1 to 2-3] Each component was blended according to the formulation shown in Tables 1 and 2, and kneaded using a Banbury mixer to prepare a sample of a rubber composition for a tread. Although not shown in Tables 1 and 2, various processing aids, additives, and vulcanization chemicals were added appropriately when preparing the sample within a range that does not affect the effects of the present invention.

[0107] <Evaluation> It is assumed that a sample of each rubber composition for tread is extruded into a sheet and then vulcanized for 90 minutes at a temperature of 145° C. to prepare a vulcanized rubber sample. The obtained vulcanized rubber sample is then evaluated as follows.

[0108] (1) Evaluation of Low Heat Buildup: For each vulcanized rubber sample, the loss tangent (tan δ) was measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under conditions of a temperature of 23°C, an initial load of 1600 mN, a dynamic strain of 1%, and a frequency of 52 Hz. Using the measurement results of the loss tangent (tan δ) for formulations not shown in the table, a simulation was conducted to determine the performance impact of formulation changes, and the loss tangent (tan δ) for the formulations listed in the table was predicted. The reciprocal of the measured tan δ was taken, and the result was expressed as an index, with the reciprocal value of tan δ for the samples of Comparative Example 1-1 and Comparative Example 2-1 set to 100. The higher the index value, the better the low heat buildup. The index value was rated A for values ​​over 100, B for values ​​over 90 but not exceeding 100, and C for values ​​not exceeding 90. The results are shown in Tables 1 and 2.

[0109] (2) Abrasion Resistance Evaluation Each vulcanized rubber sample was rolled on a grindstone at a constant speed to measure the abrasion rate. Using the measurement results of formulations not shown in the table, a simulation was conducted to determine the effect of formulation changes on performance, and the abrasion rate of the formulations listed in the table was predicted. The reciprocal of the abrasion rate was calculated and expressed as an index, with the reciprocal of the abrasion rate of the vulcanized rubber made from the rubber composition of Comparative Example 2-1 set to 100. The larger the index value, the slower the abrasion rate and the better the abrasion resistance. The results are shown in Table 2, with an index value of over 120 being A, an index value of 120 or less but over 100 being B, and an index value of 100 or less being C.

[0110] (3) Evaluation of Puncture Resistance and Post-Aging Puncture Resistance: For each vulcanized rubber sample, the breaking strength and the breaking strength after thermal aging at 100°C for 24 hours (post-aging breaking strength) were measured. Using the measurement results of formulations not shown in the table, a simulation was conducted to determine the performance impact of formulation changes, and the fracture resistance and post-aging fracture resistance of the formulations listed in the table were predicted. The evaluation was expressed as an index value, with the measurement results of Comparative Example 1-1 and Comparative Example 2-1 set to 100, and the higher the index value, the better the fracture resistance and post-aging fracture resistance. The evaluation results are shown in Tables 1 and 2, with an index value of over 110 being A, an index value of 110 or more but less than 100 being B, and an index value of 100 or less being C.

[0111] (4) Ozone Resistance: Each vulcanized rubber sample was subjected to a dynamic ozone degradation test (a test in which repeated strain was applied) in accordance with ISO 1431 (JIS K 6259), and the sample was observed at 20x magnification using a microscope. The observed samples were ranked according to the size and depth of cracks and classified according to the following criteria (1 to 5), with the results shown in Tables 1 and 2. The smaller the criteria value, the better the result. (Ranking by crack size and depth) 1: Not visible to the naked eye but visible with a 10x magnifying glass. 2: Visible to the naked eye. 3: Deep and relatively large cracks (less than 1 mm). 4: Deep and large cracks (1 mm or more but less than 3 mm). 5: Cracks of 3 mm or more or likely to cause breakage.

[0112]

[0113] *1 TSR20 *2 High-purity natural rubber obtained by centrifugation with a nitrogen content of 0.18% by mass *3 N ２ SA: 126m ２ / g, DBP oil supply amount: 92 ml / 100 g of carbon black *4 N ２ SA: 145m ２ / g, DBP oil amount: 99 ml / 100 g carbon black *5 "Nipsil KQ" manufactured by Tosoh Silica Corporation *6 Dicyclopentadiene resin softening point 140 ° C *7 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *8 Select one or more from thiazole vulcanization accelerators, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators and dithiocarbamate vulcanization accelerators. *9 N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) *10 N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine (8PPD) *11 Aminoquinoline antioxidant represented by the following formula (1-1)

[0114] From Table 1, it can be seen that each sample of the rubber composition for a tread corresponding to the Examples exhibits well-balanced and excellent results in all evaluation items, while each sample of the rubber composition for a tread corresponding to the Comparative Examples is inferior to the Examples in any of the evaluation items.

[0115] According to the present invention, it is possible to provide a rubber composition for a tread that can improve ozone resistance while having excellent abrasion resistance and puncture resistance. Also, according to the present invention, it is possible to provide a tire that has improved ozone resistance while having excellent abrasion resistance and puncture resistance.

Claims

1. A rubber composition comprising a rubber component, carbon black, silica, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3 mass% or less, and the antioxidant is a compound represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ , R １９ and R １１０ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.], and an aminoquinoline antioxidant represented by the following general formula (2): [In the formula, R ２１ and R ２２ are each independently an alkyl group or an aryl group having 7 or more carbon atoms, and R ２１ and R ２２ wherein at least one of the groups is an alkyl group having 7 or more carbon atoms.

2. The rubber composition for treads according to claim 1, wherein the high-purity natural rubber is obtained by removing proteins from natural rubber latex by a centrifugation process.

3. The rubber composition for treads according to claim 1 or 2, wherein the total content of the carbon black and the silica is 50 parts by mass or more per 100 parts by mass of the rubber component.

4. A rubber composition for treads according to claim 1 or 2, characterized in that the mass ratio of the content of said carbon black to the total content of said carbon black and said silica is 0.70 or more.

5. The CTAB specific surface area of ​​the silica is 200 to 240 m ２ The rubber composition for a tread according to claim 1 or 2, wherein the tensile strength is 1 / g.

6. The rubber composition for treads according to claim 1 or 2, wherein the content of said silica is 5 to 25 parts by mass per 100 parts by mass of said rubber component.

7. The nitrogen adsorption specific surface area (N ２ SA) is 135m ２ The rubber composition for a tread according to claim 1 or 2, wherein the modulus of elasticity is 1 / g or more.

8. The rubber composition for a tread according to claim 1 or 2, further comprising a resin.

9. A rubber composition for treads according to claim 8, characterized in that the softening point of the resin is 130°C or higher.

10. A rubber composition for treads according to claim 1 or 2, further comprising a vulcanization accelerator containing at least a sulfenamide vulcanization accelerator, the content of the sulfenamide vulcanization accelerator being 1 part by mass or more per 100 parts by mass of the rubber component.

11. The rubber composition for treads according to claim 10, characterized in that the mass ratio of the resin content to the vulcanization accelerator content is 9 or less (resin content / vulcanization accelerator content≦9).

12. R in the above general formula (2) １１ and R １２ The rubber composition for a tread according to claim 1 or 2, wherein the other of the groups is a phenyl group.

13. R in the above general formula (2) １１ and R １２ 2. The rubber composition for a tread according to claim 1, wherein at least one of the above has 7 or 8 carbon atoms.

14. The rubber composition for treads according to claim 1 or 2, characterized in that the content of the antioxidant is 0.5 to 10 parts by mass per 100 parts by mass of the rubber component, the antioxidant further contains a quinoline-based antioxidant, and the proportion of the quinoline-based antioxidant in the antioxidant is 10 to 50% by mass.

15. The antioxidant is represented by the following general formula (3): [In the formula, R ３１ and R ３２ are each independently a monovalent saturated hydrocarbon group. (However, excluding the phenylenediamine-based antioxidants represented by the general formula (1) above.), and the proportion of the amine-based antioxidant represented by the general formula (3) above in the antioxidants is 0.1 to 80 mass %.

16. The antioxidant is represented by the following general formula (4): [In the formula, R ４１ and R ４２ represents a phenyl group, and m4 represents an integer of 7 or more. ], and a ratio of the amine-based antioxidant represented by general formula (4) in the antioxidants is 0.1 to 80 mass %.

17. A tire comprising the rubber composition for tread according to claim 1 or 2.

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