Tread rubber composition, tire, and heavy-load tire

Abstract

To provide a tread rubber composition that has exceptional abrasion resistance and low heat generation properties without compromising other physical properties.SOLUTION: The present invention provides a rubber composition containing a rubber component, carbon black, and an antioxidant, wherein 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.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a tread rubber composition, a tire, and a heavy duty tire. [Background technology]

[0002] Conventionally, in the case of heavy-duty pneumatic tires for rough roads, the selection of carbon black to be blended in the tire tread rubber composition and the optimization of the amount of carbon black to be blended therein have been carried out as a method for preventing deterioration in heat generation performance, appearance performance, abrasion resistance, etc. In recent years, the tread rubber of heavy-duty pneumatic tires blended with silica in addition to blending carbon black in the tread rubber composition has been used. Various proposals have also been made.

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

[0004] [Patent Document 1] Japanese Patent Application Publication No. 1-311141 [Patent Document 2] Japanese Patent Application Publication No. 3-65406 [Patent Document 3] Japanese Patent Application Publication No. 4-226140 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the techniques of Patent Documents 1 to 3 were not sufficient for improving heat generation performance, appearance performance, and abrasion resistance after driving 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 generation and abrasion resistance was desired.

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

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

[0008] (2) The rubber composition for treads 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 treads 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-mentioned configuration is more excellent in abrasion resistance without causing a deterioration in the kneading quality.

[0010] (4) The rubber composition for treads according to any one of (1) to (3), wherein a 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-mentioned configuration is excellent in low heat build-up property.

[0011] (5) The rubber composition for treads according to any one of (1) to (4), wherein the amount 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-mentioned configuration is excellent in low heat build-up 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), wherein the viscosity is 0.05 to 1.0 MPa. The rubber composition for a tread having the above configuration has better abrasion resistance.

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

[0014] According to the present invention, it is possible to provide a rubber composition for a tread which is excellent in abrasion resistance and low heat build-up 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 wear resistance and low heat build-up without deteriorating other physical properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 a 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 tread of the present invention contains high purity natural rubber having a nitrogen content of 0.3% by mass or less. By containing the high purity natural rubber, the natural rubber does not contain an excessive amount of protein, and gelation can be suppressed, resulting in excellent abrasion resistance without reducing low heat build-up. From the same viewpoint, 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 respects so long as the nitrogen content is 0.3% by mass or less. For example, the high purity natural rubber may be natural rubber from which proteins have been removed by a centrifugation process. The centrifugation process is a process for deproteinizing natural rubber latex, which is the raw material of natural rubber, by centrifugation. The conditions for the centrifugation (rotation speed, time, etc.) are not particularly limited, and the conditions can be appropriately changed depending on the protein content to be removed. For example, when the nitrogen content in natural rubber is to be 0.1 mass% or less, the centrifugation process can be carried out several times at a rotation speed of about 7500 rpm. After the centrifugation process, washing and drying processes are carried out 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 the field latex can be used. The dry rubber content in the natural rubber latex is also not particularly limited, and from the viewpoint of obtaining better abrasion resistance, it 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 may be 100%, but other rubbers may also be contained within a range that does not impair the object of the present invention. Furthermore, the natural rubber may be not only the highly purified natural rubber, but also a mixture with 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 above-mentioned natural rubbers. 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] Moreover, 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 build-up 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 either an unmodified diene-based rubber (hereinafter sometimes referred to as "unmodified diene-based rubber") or a 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 above-mentioned rubber component. By including carbon black, the reinforcing properties of the rubber composition are increased, 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 below 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 0.80 or more, excellent abrasion resistance can be achieved. From the viewpoint of maintaining good low heat generation properties, the mass ratio of the content of the carbon black to the total content of the carbon black and silica described below is preferably 0.95 or less, and more preferably 0.85 or less.

[0026] Furthermore, in the rubber composition for tires 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 build-up properties.

[0027] 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, and 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 abrasion resistance can be achieved. From the viewpoint of maintaining good low heat generation properties, the mass ratio of the content of the carbon black to the content of the silica described below is preferably 19 or less, and more preferably 10 or less.

[0028] Furthermore, the amount of the carbon black is preferably less than 45 parts by mass based on 100 parts by mass of the rubber component. By including the carbon black, the wear resistance of the rubber composition is increased, but there is a risk of this causing a deterioration in the low heat build-up properties. 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, the deterioration in the low heat build-up properties can be more reliably prevented. From the same viewpoint, the amount of the carbon black is more preferably 42 parts by mass or less based on 100 parts by mass of the rubber component. On the other hand, from the viewpoint of obtaining better abrasion resistance, the amount of the carbon black is preferably 30 parts by mass or more, and 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 (N2SA) of 130 to 180 m 2 It is preferable that the N2SA of the carbon black is 130m 2 When the N2SA of the carbon black is 180m / g or more, better abrasion resistance is obtained. 2 / g or less, deterioration in productivity and low heat build-up can be suppressed. From the same viewpoint, the N2SA of the carbon black is 140 to 170 m 2 It is preferred that the molecular weight is / g. The nitrogen adsorption specific surface area (N2SA) of the carbon black can be measured in accordance with, for example, 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 When the N2SA of the carbon black is 120 ml / 100 g or less, gelation can be suppressed and better abrasion resistance can be obtained. From the same viewpoint, the DBP oil absorption of the carbon black is 85 to 110 m 2 / g, and 85 to 100m 2 It is more preferable that the molecular weight is / g. The DBP oil content 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 above-mentioned rubber component and carbon black. By containing an appropriate amount of the silica, the wear resistance and low heat build-up property 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 in the above range, the tire reinforcement can be enhanced and better wear resistance can be realized. 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 of 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 in accordance with, for example, JIS K 6430:2008.

[0034] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and among these, wet silica is preferred because it has a large number of silanol groups. These silicas may be used alone or in combination of two or more.

[0035] (Anti-aging agent) The rubber composition for treads 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 including 0.4 parts by mass or more of the antioxidant in the rubber composition for tread with respect to 100 parts by mass of the rubber component, the reinforcement property and abrasion resistance of the rubber composition for tread can be improved. From the same viewpoint, the content of the antioxidant is preferably 0.7 parts by mass or more with respect to 100 parts by mass of the rubber component.

[0036] The content of the antiaging agent is also preferably 2 parts by mass or less per 100 parts by mass of the rubber component. When the content of the antiaging agent 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 of the kneading quality of the rubber composition can be suppressed.

[0037] The type of the antioxidant is not particularly limited. For example, an amine-based antioxidant, a phenol-based antioxidant, or other antioxidants can be used. Among these antioxidants, it is preferable to use at least an amine-based antioxidant from the viewpoint of obtaining better abrasion 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. Among these, N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine is particularly preferred. The amine-based antiaging agent may be used alone or in combination of two or more kinds.

[0039] (Other Ingredients) In addition to the above-mentioned components, the rubber composition for treads of the present invention can be blended with other components as appropriate, as long as the effects of the present invention are not impaired. 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 assistants, stearic acid, colorants, antistatic agents, and lubricants, as well as various known compounding chemicals that are commonly used in the rubber industry. Commercially available products can be used.

[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-mercaptoethyltrimethoxy ... 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 the silane coupling agent include ethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, 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. are preferred because they have a relatively high reinforcing property, and clay, etc. are effective because they can take advantage of their shape characteristics.

[0042] The rubber composition for treads of the present invention preferably contains zinc oxide (ZnO) as a crosslinking promoter. This is because the inclusion of ZnO can further improve heat aging resistance and high elastic modulus. However, if the content of ZnO is too high, crack growth properties may deteriorate, so the 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. For example, naphthenic base oil, paraffinic base oil, aromatic base oil, etc. can be mentioned. Here, 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 decrease. Furthermore, among the above-mentioned softeners, it is preferable to use naphthenic base oil or paraffinic base oil, and it is most preferable to use naphthenic base oil. Aromatic oil is undesirable because it contains a lot of aromatic components, has a high affinity with the chemical, which is an aromatic compound, and inhibits the reaction with the polymer more. On the other hand, naphthenic base oil and paraffinic base oil have the effect of diffusing into the polymer and helping it to react, and oils with low pour points diffuse into the polymer better. The classification of naphthenic base oil, paraffinic base oil, and aromatic base oil is determined by CA value, CP value, and CN value. For example, naphthenic base oil includes TDAE, SRAE, RAE, and black oil. Also, paraffinic base oil includes spindle oil and paraffin oil. Furthermore, a more preferable effect can be obtained by using a mixed oil such as A / O Mix (Sankyo Yuka Kogyo Co., Ltd.) in which the naphthenic base oil and the naphthenic asphalt are mixed. There is no particular limitation on the timing of adding these lubricating oils. For example, the lubricating oils may be added by oil extension during the production of the rubber component, or may be added when the rubber composition for tread is kneaded.

[0044] The crosslinking agent is not particularly limited, and may be, for example, sulfur. The crosslinking accelerator may be any known one and is not particularly limited. For example, thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and dibenzothiazyl disulfide; sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazyl sulfenamide and Nt-butyl-2-benzothiazyl sulfenamide; guanidine-based vulcanization accelerators such as diphenyl guanidine; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetradodecylthiuram disulfide, tetraoctylthiuram disulfide, tetrabenzylthiuram disulfide, and dipentamethylenethiuram 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 treads of the present invention is not particularly limited. For example, the rubber composition can be produced by blending various components appropriately selected as necessary with the rubber component, kneading, heating, extruding, etc. Furthermore, the resulting 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 the 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 of the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, heat-in equipment, etc. can be appropriately selected depending on the purpose. Examples of the heat-in equipment include a heat-in roller machine usually 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 that is usually used for extruding a rubber composition. The extrusion temperature can be appropriately determined.

[0049] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected according to the purpose. As the vulcanization apparatus, a molding vulcanizer using a mold used for vulcanizing a rubber composition can be mentioned. As the vulcanization condition, the temperature is, for example, about 100 to 190°C.

[0050] <Tires> The tire of the present invention is characterized by including the above-mentioned 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 generation can be achieved without deteriorating other physical properties. Here, the tire of the present invention can be used as, for example, a heavy load tire, a truck / bus tire, an aircraft tire, or a passenger car tire, and among these, it is preferable to use it as a heavy load tire, because the rubber composition for tread used as the material of the tread portion has excellent abrasion resistance and is advantageous when used as a heavy load tire.

[0051] In addition, when using the above-mentioned rubber composition for tread of the present invention, for example, it may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or it may be obtained by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization process, etc., and then further vulcanizing it. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled in 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] In addition, in the tire of the present invention, the above-mentioned rubber composition for tread of the present invention must be applied to the tread (base tread, cap tread, under tread), but it can also be applied to various other components. For example, it can be used for cushion rubber, shoulder, sidewall, clinch, bead filler, carcass coating rubber, insulation, chafer, inner liner, etc., and it can also be used for side reinforcing layers of run-flat tires, etc. In addition to tires, the rubber composition for tread of the present invention can also be applied to rubber crawlers, seismic isolation rubber, etc. EXAMPLES

[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, each component was blended and kneaded using a Banbury mixer to prepare a sample of a rubber composition for tread.

[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 evaluated as follows.

[0056] (1) Low heat generation evaluation 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 evaluation was carried out by taking the reciprocal of the measured tan δ and expressing it as an index with the reciprocal of tan δ of the sample of Comparative Example 1 taken as 100, with a larger index value indicating better low heat build-up properties. The evaluation results are shown in Table 1. A value of 95 or higher was evaluated as excellent in low heat build-up properties.

[0057] (2) Abrasion resistance evaluation Each vulcanized rubber sample was rolled on a grindstone at a constant speed to measure the wear rate. The wear 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 evaluation was carried out by calculating the reciprocal of the wear rate and expressing it as an index when the reciprocal of the wear rate of the vulcanized rubber made of the rubber composition of Comparative Example 1 was set to 100. The larger the index value, the slower the wear rate and the better the wear resistance. The evaluation results are shown in Table 1.

[0058] (3) Evaluation of fracture resistance and fracture resistance after deterioration 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 in 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 of Comparative Example 1 taken as 100, and a larger index value indicates better fracture resistance and post-deterioration fracture resistance. The evaluation results are shown in Table 1.

[0059] [Table 1]

[0060] *1 TSR20 *2 High-purity natural rubber with a nitrogen content of 0.18% by mass obtained by centrifugation *3 N2SA: 126m 2 / g, DBP oil absorption: 92ml / 100g carbon black *4 N2SA: 145m 2 / g, DBP oil absorption: 99ml / 100g 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 of the following vulcanization accelerators so that the total amount is the amount listed in Table 1: thiazole vulcanization accelerators, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. *7 CTAB specific surface area: 220m 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 treads corresponding to the Examples shows well-balanced and excellent results in terms of low heat build-up, abrasion resistance, fracture resistance, and fracture resistance after aging. On the other hand, each sample of the rubber composition for treads corresponding to the Comparative Examples is inferior to the Examples in any of the evaluation items. [Industrial Applicability]

[0062] According to the present invention, it is possible to provide a rubber composition for a tread which is excellent in abrasion resistance and low heat build-up 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 wear resistance and low heat build-up without deteriorating other physical properties.

Claims

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

2. 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 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. 3. The rubber composition for a tread according to claim 1, wherein a 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 a tread according to claim 1 or 2, wherein the content of the carbon black is less than 45 parts by mass based on 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 a tread according to claim 1 or 2.

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