Tread rubber composition and tire

Abstract

The purpose of the present invention is to provide a rubber composition for treads which attains excellent wear resistance, without lowering other physical properties.　This rubber composition comprises a rubber component, silica, carbon black, and an aging inhibitor, and is characterized in that the rubber component includes high-purity natural rubber having a nitrogen content of 0.3 mass% or less, the total content of the silica and the carbon black is 50 parts by mass or higher per 100 parts by mass of the rubber component, the carbon black has a nitrogen-adsorption specific surface area (N2SA) of 135 m2 / g or larger, and the content of the aging inhibitor is 0.4 part by mass or higher per 100 parts by mass of the rubber component.

Description

Tread rubber composition and tire

[0001] The present invention relates to a tread rubber composition 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 the tire tread rubber composition and optimizing the amount of carbon black to be added, etc. 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 the tread rubber composition.

[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] JP-A-1-311141 JP-A-3-65406 JP-A-4-226140

[0005] 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 improvement in abrasion resistance was desired.

[0006] Therefore, an object of the present invention is to provide a rubber composition for a tread having excellent abrasion resistance without deteriorating other physical properties, and to provide a tire having excellent abrasion resistance without deteriorating other physical properties.

[0007] The gist of the present invention for solving the above-mentioned problems is as follows: A rubber composition including a rubber component, silica, carbon black, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less, the total content of the silica and the carbon black is 50 parts by mass or more per 100 parts by mass of the rubber component, and the nitrogen adsorption specific surface area (N ２SA) is 135m ２ / g or more, and the content of the antioxidant is 0.4 parts by mass or more per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration has excellent abrasion resistance without deteriorating other physical properties.

[0008] A tire comprising the above rubber composition for a tread. A tire having the above configuration has excellent abrasion resistance without deteriorating other physical properties.

[0009] According to the present invention, it is possible to provide a rubber composition for a tread having excellent abrasion resistance without deteriorating other physical properties, and it is also possible to provide a tire having excellent abrasion resistance without deteriorating other physical properties.

[0010] An embodiment of the rubber composition for tread and tire of the present invention will be described below by way of example.

[0011] <Rubber Composition for Tread> The rubber composition for tread of the present invention contains a rubber component, silica, carbon black, and an antioxidant. Hereinafter, each component constituting the rubber composition for tread of the present invention will be described.

[0012] (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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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).

[0017] 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.

[0018] 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").

[0019] (Silica) The rubber composition for tire treads of the present invention contains silica in addition to the rubber component described above, and the total content of the silica and the carbon black described below is 50 parts by mass or more per 100 parts by mass of the rubber component. By setting the total content of the silica and the carbon black to 50 parts by mass or more per 100 parts by mass of the rubber component, the tire reinforcement properties can be improved 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, 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 suppressing 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.

[0020] Furthermore, the content of the silica needs to satisfy the above-mentioned total content, but from the viewpoint of realizing fracture resistance, the content of the silica alone is preferably 5 parts by mass or more per 100 parts by mass of the rubber component. By setting the content of the silica to 5 parts by mass or more per 100 parts by mass of the rubber component, the tire reinforcement property can be enhanced 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, the content of the silica is preferably 25 parts by mass or less per 100 parts by mass of the rubber component.

[0021] Here, the silica preferably has a CTAB specific surface area of ​​200 to 240 ml / 100 g. When the CTAB specific surface area of ​​the silica is 200 ml / 100 g or more, the fracture resistance is improved, and when the CTAB specific surface area of ​​the silica is 240 ml / 100 g or less, poor dispersion and deterioration of processability can be suppressed. The CTAB specific surface area of ​​the silica can be measured, for example, in accordance with JIS K 6430:2008.

[0022] 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.

[0023] 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.

[0024] (Carbon Black) The rubber composition of the present invention further contains carbon black in addition to the above-described rubber component and silica, because this enhances the reinforcing properties of the rubber composition and provides better abrasion resistance.

[0025] Here, the carbon black has a nitrogen adsorption specific surface area (N ２ SA) is 135m ２ / g or more. ２ SA is 135m ２ / g or more, better abrasion resistance can be obtained. ２ SA) is 180m ２ / g or less. ２ SA is 180m ２ / g or less, deterioration in productivity and low heat buildup can be suppressed. ２ SA is 140-170m ２ / g. It is more preferable that the nitrogen adsorption specific surface area (N ２ SA) can be measured, for example, in accordance with JIS K 6217-7:2013.

[0026] The carbon black preferably has a dibutyl phthalate (DBP) oil absorption of 80 to 120 ml / 100 g. ２ / g or more, deterioration of low heat buildup and productivity can be suppressed, and the N ２ When the SA is 120 ml / 100 g or less, gelation can be suppressed and better abrasion resistance can be obtained. ２ / g, and 85 to 100m ２ The DBP oil supply amount of the carbon black can be measured in accordance with JIS K 6217-4:2017.

[0027] The total content of the carbon black and the silica must be 50 parts by mass or more per 100 parts by mass of the rubber component. 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 carbon black content 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 carbon black content 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 carbon black content is 60 parts by mass or less per 100 parts by mass of the rubber component, deterioration of low heat buildup can be suppressed.

[0028] The carbon black may also include recycled carbon black. In this specification, "recycled carbon black" refers to carbon black recovered from recycled waste materials. Examples of recycled waste include rubber products (particularly vulcanized rubber products) containing carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum and natural gas, i.e., non-recycled carbon black. Here, "used" refers not only to carbon black that has been discarded after actual use, but also to carbon black that has been produced but discarded without actually being used.

[0029] (Antiaging Agent) The rubber composition for a tread of the present invention contains an antioxidant in addition to the above-mentioned rubber component, silica, and carbon black as an optional component, and the content of the antioxidant is 0.4 parts by mass or more per 100 parts by mass of the rubber component. By containing 0.4 parts by mass or more of the antioxidant per 100 parts by mass of the rubber component in the rubber composition for a tread, the reinforcement properties and abrasion resistance of the rubber composition for a tread can be improved. From the same viewpoint, the content of the antioxidant is preferably 1 part by mass or more per 100 parts by mass of the rubber component.

[0030] The content of the antioxidant is preferably less than 3 parts by mass per 100 parts by mass of the rubber component. This is because better fracture resistance can be obtained when the content of the antioxidant is less than 3 parts by mass per 100 parts by mass of the rubber component. From the same viewpoint, the content of the antioxidant is preferably less than 2 parts by mass per 100 parts by mass of the rubber component.

[0031] The type of the antiaging agent is not particularly limited. For example, an amine-based antiaging agent, a phenol-based antiaging agent, or other antiaging agents can be used. Among these antiaging agents, it is preferable to use at least an amine-based antiaging agent from the viewpoint of obtaining better wear resistance.

[0032] The amine-based antioxidant is preferably at least one selected from the group consisting of N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine, N-isopropyl-N'-p-phenylenediamine, N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Of these, N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine is particularly preferred. The amine-based antioxidants may be used alone or in combination of two or more.

[0033] (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, zinc oxide, softeners, tackifiers, dispersants, crosslinking agents, crosslinking accelerators, 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The crosslinking agent is not particularly limited, either. For example, sulfur can be used. The crosslinking accelerator is also not particularly limited, and known ones can be used. Examples 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.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 molding vulcanizers using molds used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0043] <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 can be achieved without deteriorating other physical properties. Here, the tire of the present invention can be used as, for example, 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 is a great advantage when used as a heavy-duty tire.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] [Examples 1 to 7, Comparative Examples 1 to 3] It is assumed that samples of rubber compositions for treads are prepared by blending the components and kneading them using a Banbury mixer according to the formulation shown in Table 1. Furthermore, although not shown in Table 1, various processing aids, additives, vulcanization chemicals, and vulcanization accelerators are appropriately added during sample preparation within ranges that do not affect the effects of the present invention.

[0048] <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. It is assumed that the obtained vulcanized rubber sample is then subjected to the following evaluations.

[0049] (1) Evaluation of Low Heat Buildup Properties For each vulcanized rubber sample, the loss tangent (tan δ) was measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under the following conditions: temperature 23°C, initial load 1600 mN, dynamic strain 1%, and frequency 52 Hz. 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 loss tangent (tan δ) of the formulations listed in the table was predicted. For evaluation, the reciprocal of the measured tan δ was taken and expressed as an index, with the reciprocal value of tan δ of the sample of Comparative Example 1 being set at 100. The higher the index value, the better the low heat buildup properties. The evaluation results are shown in Table 1. An index value of 90 or higher indicates no impact on tire performance.

[0050] (2) Evaluation of Abrasion Resistance It was assumed that each vulcanized rubber sample was rolled on a grindstone at a constant speed and the abrasion rate was measured. 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 1 set to 100. A larger index value indicates a slower abrasion rate and better abrasion resistance. The evaluation results are shown in Table 1.

[0051] (3) Puncture Resistance It is assumed that the breaking strength of each vulcanized rubber sample is measured after thermal aging at 100°C for 24 hours. 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 of the formulations shown in the table was predicted. The evaluation is expressed as an index value, with the measurement result of Comparative Example 1 set to 100, and the higher the index value, the better the fracture resistance.

[0052]

[0053] *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 supply amount: 99 ml / 100 g of carbon black *5 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *6 "Nipsil KQ" manufactured by Tosoh Silica Corporation

[0054] From Table 1, it can be seen that each sample of the rubber composition for treads corresponding to the Examples exhibits well-balanced and excellent results in terms of low heat buildup, abrasion resistance, and fracture resistance, while each sample of the rubber composition for treads corresponding to the Comparative Examples is inferior to the Examples in any of the evaluation items.

[0055] According to the present invention, it is possible to provide a rubber composition for a tread having excellent abrasion resistance without deteriorating other physical properties, and it is also possible to provide a tire having excellent abrasion resistance without deteriorating other physical properties.

Claims

1. A rubber composition comprising a rubber component, silica, carbon black, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3 mass% or less, the total content of the silica and the carbon black is 50 parts by mass or more per 100 parts by mass of the rubber component, and the nitrogen adsorption specific surface area (N ２ SA) is 135m ２ / g or more, and a content of the antioxidant is 0.4 parts by mass or more per 100 parts by mass of the rubber component.

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 through a centrifugation process.

3. The rubber composition for treads according to claim 1 or 2, characterized in that the content of the antioxidant is 0.7 parts by mass or more and less than 3 parts by mass per 100 parts by mass of the rubber component.

4. The rubber composition for treads according to claim 1 or 2, characterized in that the content of the carbon black is 40 parts by mass or more per 100 parts by mass of the rubber component.

5. A rubber composition for treads as described in claim 1 or 2, characterized in that the content of the silica is 5 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the rubber component.

6. A rubber composition for treads according to claim 1 or 2, characterized in that the CTAB specific surface area of ​​said silica is 200 to 240 ml / 100 g.

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

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