Tread rubber composition, tire, and heavy-load tire

Abstract

The purpose of the present invention is to provide a tread rubber composition that has exceptional abrasion resistance and low heat generation properties without compromising other physical properties. In order to solve the aforementioned problem, the present invention is a rubber composition containing a rubber component, carbon black, and an antioxidant, wherein the rubber composition is characterized in that the rubber component contains a high-purity natural rubber having a nitrogen content of 0.3 mass% or lower, and the mass ratio of the content of the carbon black to the total content of the carbon black and the silica is 0.80 or greater.

Description

Tread rubber composition, tire and heavy-duty tire

[0001] The present invention relates to a tread rubber composition, a tire, and a heavy-duty 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 heat buildup 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 the balance between low heat buildup and abrasion resistance was desired.

[0006] Therefore, an object of the present invention is to provide a rubber composition for a tread that is excellent in abrasion resistance and low heat buildup without deteriorating other physical properties, and to provide a tire and a heavy-duty tire that are excellent in abrasion resistance and low heat buildup without deteriorating other physical properties.

[0007] The gist of the present invention, which solves the above problems, is as follows: (1) A rubber composition for a tread, comprising a rubber component, carbon black, and silica, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less, and the mass ratio of the content of the carbon black to the total content of the carbon black and the silica is 0.80 or more. The rubber composition for a tread having the above configuration has excellent abrasion resistance and low heat buildup without deteriorating other physical properties.

[0008] (2) The rubber composition for a tread according to (1), wherein the high-purity natural rubber is obtained by removing proteins from natural rubber latex through a centrifugation process. The rubber composition for a tread having the above configuration has better abrasion resistance.

[0009] (3) The rubber composition for a tread according to (1) or (2), characterized in that the content of the antioxidant is 0.4 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration has better abrasion resistance without causing a deterioration in kneading quality.

[0010] (4) The rubber composition for a tread according to any one of (1) to (3), characterized in that the total content of the carbon black and the silica is 55 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration is excellent in low heat buildup property.

[0011] (5) The rubber composition for a tread according to any one of (1) to (4), characterized in that the content of the carbon black is less than 45 parts by mass per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration is excellent in low heat buildup property.

[0012] (6) The CTAB specific surface area of ​​the silica is 200 to 240 m ２ The rubber composition for a tread according to any one of (1) to (5), characterized in that the tread viscosity is 1 / g. The rubber composition for a tread having the above configuration is more excellent in abrasion resistance.

[0013] (7) A tire comprising the rubber composition for a tread according to any one of (1) to (6). The tire having the above configuration has excellent wear resistance and low heat buildup without deteriorating other physical properties.

[0014] According to the present invention, it is possible to provide a rubber composition for a tread that is excellent in abrasion resistance and low heat buildup without deteriorating other physical properties. Furthermore, according to the present invention, it is possible to provide a tire and a heavy-duty tire that are excellent in abrasion resistance and low heat buildup without deteriorating other physical properties.

[0015] An embodiment of the rubber composition for tread and tire of the present invention will be described below by way of example.

[0016] <Rubber Composition for Tread> The rubber composition for tread of the present invention contains a rubber component, carbon black, and an antioxidant. Hereinafter, each component constituting the rubber composition for tread of the present invention will be described.

[0017] (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, thereby achieving excellent wear resistance without reducing low heat buildup. 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] 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 heat buildup and abrasion resistance at a higher level.

[0023] 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").

[0024] (Carbon Black) The rubber composition of the present invention further contains carbon black in addition to the rubber component described above. By containing carbon black, the reinforcing properties of the rubber composition are enhanced and excellent abrasion resistance can be obtained.

[0025] 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 must be 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 be 0.80 or more, excellent wear resistance can be achieved. From the viewpoint of maintaining good low heat buildup, 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, and more preferably 0.85 or less.

[0026] Furthermore, in the rubber composition for a tire of the present invention, the total content of the carbon black and the silica is preferably 55 parts by mass or less per 100 parts by mass of the rubber component, because this can more reliably prevent deterioration of low heat buildup properties.

[0027] In addition, in the rubber composition of the present invention, the mass ratio of the carbon black content to the silica content described below is preferably 3.5 or more, more preferably 4.0 or more. By setting the mass ratio of the carbon black content to the silica content described below to 3.5 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 silica content described below is preferably 19 or less, more preferably 10 or less.

[0028] Furthermore, the content of the carbon black is preferably less than 45 parts by mass per 100 parts by mass of the rubber component. Although the inclusion of the carbon black improves the abrasion resistance of the rubber composition, it may also lead to a deterioration in low heat buildup. Therefore, by setting the content of the carbon black to less than 45 parts by mass per 100 parts by mass of the rubber component, deterioration in low heat buildup can be more reliably prevented. From the same viewpoint, the content of the carbon black is more preferably 42 parts by mass or less per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of obtaining better abrasion resistance, the content of the carbon black is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, per 100 parts by mass of the rubber component.

[0029] The carbon black has a nitrogen adsorption specific surface area (N ２ SA) is 130-180m ２ / g. ２ SA is 130m ２ When the N content of the carbon black is 1 / g or more, better abrasion resistance can be obtained. 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. The nitrogen adsorption specific surface area (N ２ SA) can be measured, for example, in accordance with JIS K 6217-7:2013.

[0030] 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.

[0031] (Silica) The rubber composition for tire treads of the present invention preferably contains silica in addition to the rubber component and carbon black described above. By containing an appropriate amount of silica, the abrasion resistance and low heat buildup of the rubber composition can be improved.

[0032] Here, the content of the silica is preferably 5 parts by mass or more per 100 parts by mass of the rubber component. By setting the content of the silica within the above range, the tire reinforcement property can be enhanced and better wear resistance can be achieved. From the same viewpoint, the content of the silica is preferably 8 parts by mass or more per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration in processability and heat generation of the rubber composition, the content of the silica is preferably 30 parts by mass or less per 100 parts by mass of the rubber component, more preferably 20 parts by mass or less, and even more preferably 14 parts by mass or less.

[0033] 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, a more excellent effect of improving abrasion resistance can be obtained, 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.

[0034] 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.

[0035] (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 in the rubber composition for a tread per 100 parts by mass of the rubber component, 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 0.7 parts by mass or more per 100 parts by mass of the rubber component.

[0036] The content of the antioxidant is also preferably 2 parts by mass or less per 100 parts by mass of the rubber component, because when the content of the antioxidant is 2 parts by mass or less per 100 parts by mass of the rubber component, the reaction between the silica and a silane coupling agent (described later) can be inhibited and deterioration in the kneading quality of the rubber composition can be suppressed.

[0037] 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.

[0038] 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.

[0039] (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.

[0040] 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.

[0041] 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.

[0042] The rubber composition for treads of the present invention preferably contains zinc oxide (ZnO) as a crosslinking accelerator. This is because the inclusion of ZnO can further improve heat aging resistance and high elastic modulus. However, if the ZnO content is too high, crack growth resistance may deteriorate, so the ZnO content is preferably less than 5 parts by mass per 100 parts by mass of the rubber component.

[0043] 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 2 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 facilitating diffusion and reaction in the polymer, 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.

[0044] 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.

[0045] (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.

[0046] 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.

[0047] 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 roller typically used for heat-in of a rubber composition.

[0048] 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.

[0049] 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.

[0050] <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 low heat buildup 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 is a great advantage when used as a heavy-duty tire.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Examples 1 to 3, Comparative Examples 1 to 4 According to the formulation shown in Table 1, the components were blended and kneaded using a Banbury mixer to prepare samples of rubber compositions for treads.

[0055] <Evaluation> Each sample of the rubber composition for tread obtained was 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 was then evaluated as follows.

[0056] (1) Evaluation of Low Heat Buildup Property 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. The reciprocal of the measured tan δ was taken and expressed as an index relative to the reciprocal value of tan δ of the sample of Comparative Example 1, which was set to 100. The larger the index value, the better the low heat buildup property. The evaluation results are shown in Table 1. A value of 95 or higher was evaluated as excellent in low heat buildup property.

[0057] (2) Evaluation of Abrasion Resistance Each vulcanized rubber sample was rolled on a grindstone at a constant speed, and the abrasion rate was measured. The abrasion rate of Example 3 was estimated from the measurement results of Comparative Examples 3 and 4 and Example 1, taking into account the amounts of compounded chemicals. 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.

[0058] (3) Evaluation of Puncture Resistance and Puncture Resistance after Aging For each vulcanized rubber sample, the breaking strength and the breaking strength after thermal aging at 100°C for 24 hours (breaking strength after aging) were measured. The breaking strength after aging for Example 3 was estimated from the breaking strength measurement results, taking into account the amounts of compounded chemicals. The evaluation was expressed as an index value, with the measurement result for Comparative Example 1 set to 100, and a larger index value indicates better fracture resistance and post-aging fracture resistance. The evaluation results are shown in Table 1.

[0059]

[0060] *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 absorption: 92 ml / 100 g carbon black *4 N ２ SA: 145m ２ / g, DBP oil absorption: 99 ml / 100 g carbon black *5 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *6 Select one or more from thiazole vulcanization accelerators, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators and dithiocarbamate vulcanization accelerators so that the total amount is the amount listed in Table 1. *7 CTAB specific surface area: 220 m ２ / g *8 "ABC856" manufactured by Shin-Etsu Chemical Co., Ltd.

[0061] From Table 1, it can be seen that each sample of the rubber composition for tread corresponding to the Examples exhibits well-balanced and excellent results in terms of low heat buildup, abrasion resistance, fracture resistance, and fracture resistance after aging. On the other hand, it can be seen that each sample of the rubber composition for tread corresponding to the Comparative Examples is inferior to the Examples in any of the evaluation items.

[0062] According to the present invention, it is possible to provide a rubber composition for a tread that is excellent in abrasion resistance and low heat buildup without deteriorating other physical properties. Furthermore, according to the present invention, it is possible to provide a tire and a heavy-duty tire that are excellent in abrasion resistance and low heat buildup without deteriorating other physical properties.

Claims

1. A rubber composition for treads comprising a rubber component, carbon black, and silica, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3 mass% or less, and the mass ratio of the carbon black content to the total content of the carbon black and the silica is 0.80 or more.

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 0.4 parts by mass or more and less than 2 parts by mass 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 total content of said carbon black and said silica is 55 parts by mass or less per 100 parts by mass of said rubber component.

5. The rubber composition for treads according to claim 1 or 2, characterized in that the content of the carbon black is less than 45 parts by mass per 100 parts by mass of the rubber component.

6. 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 viscosity of the rubber composition for a tread is 100%.

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

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