Tread rubber composition and tire

Abstract

To provide a rubber composition for a tread which is excellent in wear resistance without deteriorating other physical properties.SOLUTION: A rubber composition of the present invention contains a rubber component, silica, carbon black, and an antioxidant. The rubber component contains a 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 pts.mass or more based on 100 pts.mass of the rubber component. The carbon black has a nitrogen adsorption specific surface area (N2SA) of 135 m2 / g or more. The content of the antioxidant is 0.4 pt.mass or more based on 100 pts.mass of the rubber component.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, in pneumatic tires for heavy loads on rough roads, as a method for preventing deterioration in heat generation performance, appearance performance, wear resistance, etc., selection of carbon black to be compounded in the tire tread rubber composition, optimization of its filling amount, etc. have been carried out. In recent years, there have also been various proposals for tread rubber of pneumatic tires for heavy loads in which silica is compounded together with carbon black in the tread rubber composition. have also been variously proposed.

[0003] For example, Patent Documents 1 to 3 disclose technologies in which silica is compounded together with carbon black in a tread rubber composition for pneumatic tires for heavy loads such as construction vehicles, aiming to improve wear resistance, cut resistance, heat generation performance, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, with respect to the technologies of Patent Documents 1 to 3, in the tread rubber composition of pneumatic tires for heavy loads, none of them were sufficient in improving the heat generation performance, appearance performance, and wear resistance after running, and further suppressing the deterioration of physical properties. In particular, further improvement in wear resistance has been desired.

[0006] Therefore, an object of the present invention is to provide a rubber composition for treads that has excellent abrasion resistance without degrading other physical properties. Another object of the present invention is to provide a tire that has excellent abrasion resistance without degrading other physical properties.

Means for Solving the Problems

[0007] The gist of the present invention for solving the above problems is as follows. (1) A rubber composition comprising a rubber component, silica, carbon black, and an anti-aging agent, 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 with respect to 100 parts by mass of the rubber component, the nitrogen adsorption specific surface area (N2SA) of the carbon black is 135 m 2 / g or more, and the content of the anti-aging agent is 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component, a rubber composition for treads. The rubber composition for treads having the above configuration is excellent in abrasion resistance without degrading other physical properties.

[0008] (2) The rubber composition for treads according to (1), wherein the high-purity natural rubber is obtained by removing protein from natural rubber latex by a centrifugation process. The rubber composition for treads having the above configuration is more excellent in abrasion resistance.

[0009] (3) The rubber composition for treads according to (1) or (2), wherein the content of the anti-aging agent is 0.7 parts by mass or more and less than 3 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for treads having the above configuration is more excellent in abrasion resistance without causing a decrease in kneading quality.

[0010] (4) The tread rubber composition according to any one of (1) to (3), characterized in that the content of the carbon black is 40 parts by mass or more with respect to 100 parts by mass of the rubber component. The tread rubber composition having the above configuration is more excellent in abrasion resistance.

[0011] (5) The tread rubber composition according to any one of (1) to (4), characterized in that the content of the silica is 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the rubber component. The tread rubber composition having the above configuration is excellent in fracture resistance and processability.

[0012] (6) The tread rubber composition according to any one of (1) to (5), characterized in that the CTAB specific surface area of the silica is 200 to 240 ml / 100 g. The tread rubber composition having the above configuration is more excellent in fracture resistance.

[0013] (7) A tire comprising the tread rubber composition according to any one of (1) to (6) above. The tire having the above configuration is excellent in abrasion resistance without deteriorating other physical properties.

Effects of the Invention

[0014] According to the present invention, it is possible to provide a tread rubber composition excellent in abrasion resistance without deteriorating other physical properties. Further, according to the present invention, it is possible to provide a tire excellent in abrasion resistance without deteriorating other physical properties.

Modes for Carrying Out the Invention

[0015] Hereinafter, an exemplary embodiment of the tread rubber composition and tire of the present invention will be illustrated and described.

[0016] <Tread rubber composition> The rubber composition for a tread of the present invention contains a rubber component, silica, carbon black, and an anti-aging agent. Hereinafter, each component constituting the rubber composition for a tread of the present invention will be described.

[0017] (Rubber component) The rubber component contained in the rubber composition for a 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, an excessive amount of protein is not contained in the natural rubber, gelation can be suppressed, and as a result, excellent abrasion resistance can be achieved. 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, for the high-purity natural rubber, as long as the nitrogen content is 0.3% by mass or less, other requirements are not particularly limited. For example, the high-purity natural rubber includes natural rubber from which protein has been removed by a centrifugation process. The centrifugation process is a process of performing a protein removal treatment by centrifugation from natural rubber latex, which is a raw material of natural rubber. The conditions of the centrifugation (rotation speed, time, etc.) are not particularly limited, and the conditions can be appropriately changed according to the protein content to be removed. For example, when the nitrogen content in the natural rubber is 0.1% by mass or less, the centrifugation process can be performed several times at a rotation speed of about 7500 rpm. In addition, after the centrifugation process, a high-purity natural rubber can be obtained by performing a washing and drying treatment.

[0019] Note that the natural rubber latex used in the centrifugation process is not particularly limited. For example, field latex collected from rubber trees or concentrated natural rubber latex obtained by processing the same can be used. Also, the dry rubber content in the natural rubber latex is 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, and even more preferably 40% by mass or more.

[0020] In addition, the content of the highly purified natural rubber in the rubber component can be 100%, but other rubbers can also be contained as long as the object of the present invention is not impaired. Furthermore, the natural rubber can be not only the highly purified natural rubber but also a mixture with ordinary natural rubber. In that case, from the viewpoint of further improving abrasion resistance, 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.

[0021] Regarding the rubber component, in addition to the natural rubber described above, other synthetic rubbers can also be contained. 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), 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] Also, among the synthetic rubbers described above, it is preferable for the rubber component to contain butadiene rubber and / or styrene-butadiene rubber. This is because high-level low-loss properties and abrasion resistance can be achieved simultaneously.

[0023] Note that for the natural rubber and the diene synthetic rubber (hereinafter collectively referred to as "diene rubber"), it may be an unmodified diene rubber (hereinafter sometimes referred to as "unmodified diene rubber") or a modified diene rubber (hereinafter sometimes referred to as "modified diene rubber").

[0024] (Silica) The rubber composition for a tire tread of the present invention contains silica in addition to the rubber components described above, and the content of the silica is such that the total content with carbon black described below is 50 parts by mass or more with respect to 100 parts by mass of the rubber components. By setting the total content of the silica and the carbon black to 50 parts by mass or more with respect to 100 parts by mass of the rubber components, the reinforcement of the tire can be enhanced and more excellent abrasion resistance can be realized. From the same viewpoint, the content of 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 with respect to 100 parts by mass of the rubber components. On the other hand, from the viewpoint of suppressing deterioration of the processability and low heat generation 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 further preferably 70 parts by mass or less with respect to 100 parts by mass of the rubber components.

[0025] In addition, although it is necessary for the content of the silica to satisfy the total content described above, from the viewpoint of realizing fracture resistance, the content of the silica alone is preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber components. By setting the content of the silica to 5 parts by mass or more with respect to 100 parts by mass of the rubber components, the reinforcement of the tire 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 with respect to 100 parts by mass of the rubber components. 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 with respect to 100 parts by mass of the rubber components.

[0026] Here, for the silica, it is preferable that the CTAB specific surface area is 200 to 240 ml / 100 g. When the CTAB specific surface area of the silica is 200 ml / 100 g or more, an effect of improving the fracture resistance can be obtained, and when the CTAB specific surface area of the silica is 240 ml / 100 g or less, poor dispersion and a decrease in processability can be suppressed. In addition, the CTAB specific surface area of the silica can be measured, for example, in accordance with JIS K 6430:2008.

[0027] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among these, wet silica is preferable in terms of having many silanol groups. These silicas may be used alone or in combination of two or more.

[0028] In addition, from the perspective of reducing environmental impact, silica derived from silicate plants is also preferable as the silica. Such silicate plants are present, for example, in mosses, ferns, thistles, cucurbitaceae, nettle family, and gramineous plants. Among these plants, gramineous plants are preferable. Examples of the gramineous plants include rice, bamboo, and sugarcane, and among these, rice is particularly preferable. Since rice is widely cultivated for food, it can be locally procured in a wide area. Also, since a large amount of rice husks are generated as industrial waste, it is easy to secure a sufficient quantity. Therefore, from the perspective of easy availability, rice husk-derived silica (hereinafter also referred to as "rice husk silica") is particularly preferable as the silica. By using the rice husk silica, rice husks that would otherwise become industrial waste can be effectively utilized. Also, since the raw material can be locally procured near a tire manufacturing factory, the energy and costs for transportation and storage can be reduced, which is environmentally preferable from various perspectives. The rice husk silica may be powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet method using an aqueous alkali silicate solution prepared by extracting rice husk ash generated when rice husks are burned in a biomass boiler using rice husks as fuel 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 thermally decomposing rice husks by steaming them using a kiln. The rice husk charcoal thus obtained can be pulverized using a known pulverizer (e.g., ball mill) and sorted and classified into a predetermined particle size range to obtain powder of rice husk charcoal. Also, the precipitated silica derived from rice husks can be produced by the method described in JP-A-2019-38728 and the like.

[0029] (Carbon black) The rubber composition of the present invention further contains carbon black in addition to the rubber component and silica described above. This is because the reinforcing property of the rubber composition is enhanced, and more excellent abrasion resistance can be obtained.

[0030] Here, the carbon black has a nitrogen adsorption specific surface area (N2SA) of 135 m 2 / g or more. When the N2SA of the carbon black is 135 m 2When it is / g or more, it is because more excellent abrasion resistance can be obtained. Further, the nitrogen adsorption specific surface area (N2SA) of the carbon black is 180 m 2 / g or less is preferable. When the N2SA of the carbon black is 180 m 2 / g or less, it is because deterioration of productivity and low heat generation can be suppressed. From the same viewpoint, the N2SA of the carbon black is more preferably 140 to 170 m 2 / g. Note that the nitrogen adsorption specific surface area (N2SA) of the carbon black can be measured in accordance with, for example, JIS K 6217-7:2013.

[0031] Further, the carbon black preferably has a dibutyl phthalate (DBP) oil absorption of 80 to 120 ml / 100 g. When the DBP oil absorption of the carbon black is 80 m 2 / g or more, deterioration of low heat generation and productivity can be suppressed, and when the N2SA of the carbon black is 120 ml / 100 g or less, gelation can be suppressed and more excellent abrasion resistance can be obtained. From the same viewpoint, the DBP of the carbon black is preferably 85 to 110 m 2 / g, and more preferably 85 to 100 m 2 / g. Note that the DBP oil supply amount of the carbon black can be measured in accordance with JIS K 6217-4:2017.

[0032] The content of the carbon black requires that the total content with the above-described silica is 50 parts by mass or more with respect to 100 parts by mass of the rubber component. Also, 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 with respect to 100 parts by mass of the rubber component. When the content of the carbon black is 40 parts by mass or more with respect to 100 parts by mass of the rubber component, the reinforcing property is enhanced and more excellent abrasion resistance can be obtained. On the other hand, the content of the carbon black is preferably 60 parts by mass or less, more preferably 55 parts by mass or less with respect to 100 parts by mass of the rubber component. When the content of the carbon black is 60 parts by mass or less with respect to 100 parts by mass of the rubber component, it is because the deterioration of low heat generation property can be suppressed.

[0033] Further, the carbon black may include recycled carbon black. In the present specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials subjected to recycling. Examples of the waste materials subjected to the above recycling include rubber products containing carbon black (particularly vulcanized rubber products) typified by used rubber and used tires, waste oil, and the like. "Recycled carbon black" is different from carbon black directly produced from raw materials such as hydrocarbons such as petroleum and natural gas, that is, carbon black that is not a recycled product. Here, "used" includes not only those discarded after actual use but also those discarded without being actually used among the manufactured ones.

[0034] (Antioxidant) The rubber composition for a tread of the present invention contains an antioxidant in addition to the rubber component, silica, and carbon black as an optional component described above, and the content of the antioxidant is 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component. By including an antioxidant in the rubber composition for a tread in an amount of 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component, the reinforcing property and abrasion resistance of the rubber composition for a tread can be enhanced. From the same viewpoint, the content of the antioxidant is preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component.

[0035] Also, the content of the anti-aging agent is preferably less than 3 parts by mass with respect to 100 parts by mass of the rubber component. When the content of the anti-aging agent is less than 3 parts by mass with respect to 100 parts by mass of the rubber component, more excellent fracture resistance can be obtained. From the same viewpoint, the content of the anti-aging agent is preferably less than 2 parts by mass with respect to 100 parts by mass of the rubber component.

[0036] Here, the type of the anti-aging agent is not particularly limited. For example, amine-based anti-aging agents, phenol-based anti-aging agents, and other anti-aging agents can be used. Among these anti-aging agents, from the viewpoint of obtaining more excellent abrasion resistance, it is preferable to use at least an amine-based anti-aging agent.

[0037] The amine-based anti-aging agent is preferably at least one selected from the group consisting of N-(1,3-dimethylbutyl)-N'-phenyl-p-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-p-phenylenediamine is particularly preferable. The amine-based anti-aging agent may be used alone or in combination of two or more.

[0038] (Other components) In addition to the above-described components, the rubber composition for a tread of the present invention can appropriately select and blend other components as needed or for the purpose within a range not impairing the effects of the present invention. Examples of the other components include 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, lubricants, and other additives, as well as various known compounding chemicals commonly used in the rubber industry. Commercially available products can be used for these.

[0039] 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, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropylbenzothiazolyl tetrasulfide, 3-octanoylthiopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 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 (trade name "Si363" manufactured by Degussa), and the like. These silane coupling agents may be used alone or in combination of two or more.

[0040] Examples of the inorganic filler other than the silica and carbon black include aluminum hydroxide, clay, etc. Among these inorganic fillers, aluminum hydroxide, etc. are preferable in that they have relatively high reinforcing properties, and clay, etc. are effective in that the effects of their shape characteristics can be obtained.

[0041] Furthermore, there is no particular limitation on the softening agent, and it can be appropriately selected according to the purpose. For example, naphthenic base oil, paraffinic base oil, aromatic base oil, etc. may be mentioned. Here, the content of the softening agent is preferably blended in an amount of 0 to 30 parts by mass with respect to 100 parts by mass of the rubber component. When the content of the softening agent exceeds 30 parts by mass with respect to 100 parts by mass of the rubber component, there is a risk that the softening agent will ooze out to the surface of the rubber product, or the abrasion resistance may decrease. Furthermore, among the above-mentioned softening agents, it is preferable to use naphthenic base oil or paraffinic base oil, and it is most preferable to use naphthenic base oil. This is because aromatic oil has a high affinity for the drug, which is an aromatic compound, due to its high aromatic component content, and is not preferable because it more inhibits the reaction with the polymer. On the other hand, naphthenic base oil and paraffinic base oil have the effect of assisting in diffusing and reacting in the polymer, and an oil with a lower pour point diffuses better into the polymer. The classification into the naphthenic base oil, the paraffinic base oil, and the aromatic base oil is determined by the CA value, the CP value, and the CN value. For example, the naphthenic base oil is classified as TDAE, SRAE, RAE, Black Oil, etc. Also, the paraffinic base oil is classified as spindle oil and paraffin oil. Furthermore, a mixed oil such as A / O Mix (Sankyo Yuka Kogyo Co., Ltd.) obtained by mixing the naphthenic base oil and the naphthenic asphalt also gives more preferable effects. There are no particular limitations on the timing of blending these lubricating oils. For example, they may be extended with oil at the stage of manufacturing the rubber component, or added when kneading the tread rubber composition.

[0042] There are also no particular restrictions on the crosslinking agent. For example, sulfur may be mentioned. As for the crosslinking accelerator, known ones can be used and there are no particular restrictions. 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 N-t-butyl-2-benzothiazyl sulfenamide; guanidine-based vulcanization accelerators such as diphenylguanidine; 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, etc. can be mentioned.

[0043] (Manufacture of the tread rubber composition) The manufacturing method of the tread rubber composition of the present invention is not particularly limited. For example, by blending various components appropriately selected as necessary with the rubber component, kneading, heating, extrusion, etc., the rubber composition can be manufactured. Also, by vulcanizing the obtained rubber composition, a vulcanized rubber can be obtained.

[0044] There are no particular restrictions on the kneading conditions, and various conditions such as the input volume of the kneading apparatus, the rotation speed of the rotor, the ram pressure, etc., and the kneading temperature, kneading time, and type of kneading apparatus can be appropriately selected according to the purpose. Examples of the kneading apparatus usually include a Banbury mixer, an internal mixer, a kneader, a roll, etc. used for kneading rubber compositions.

[0045] There are also no particular restrictions on the heat treatment conditions, and various conditions such as the heat treatment temperature, heat treatment time, and heat treatment apparatus can be appropriately selected according to the purpose. Examples of the heat treatment apparatus usually include a heat treatment roll machine used for heat treatment of rubber compositions.

[0046] There are also no particular restrictions on the extrusion conditions, and various conditions such as the extrusion time, extrusion speed, extrusion apparatus, and extrusion temperature can be appropriately selected according to the purpose. Examples of the extrusion apparatus usually include an extruder used for extrusion of rubber compositions. The extrusion temperature can be determined as appropriate.

[0047] There are also no particular restrictions on the apparatus, method, conditions, etc. for vulcanization, and they can be appropriately selected according to the purpose. Examples of the apparatus for vulcanization usually include a molding vulcanizer using a mold used for vulcanization of rubber compositions. As the vulcanization conditions, the temperature is, for example, about 100 to 190 °C.

[0048] <Tire> The tire of the present invention is characterized by including the tread rubber composition of the present invention described above. By including the tread rubber composition of the present invention as a tire material, excellent abrasion resistance can be achieved without degrading 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. Among these, it is preferably a heavy-duty tire. This is because the tread rubber composition used as the material for the tread part is excellent in abrasion resistance and has great advantages when used as a heavy-duty tire.

[0049] When using the rubber composition for tread of the present invention described above, for example, it may be obtained by vulcanizing after molding using an unvulcanized rubber composition, or it may be obtained by further vulcanizing after molding using a semi-vulcanized rubber that has undergone a pre-vulcanization process or the like. The tire of the present embodiment is preferably a pneumatic tire. As the gas to be filled in the pneumatic tire, in addition to normal air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used.

[0050] In addition, in the tire of the present invention, although it is necessary to apply the rubber composition for tread of the present invention described above to the tread (base tread, cap tread, under tread), it can also be applied to various other constituent members. For example, it can be used for cushion rubber, shoulder, sidewall, clinch, bead filler, coating rubber for carcass, insulation, chafer, inner liner, etc., and can also be used for side reinforcement layers of run-flat tires. Further, the rubber composition for tread of the present invention can be applied not only to tires but also to rubber crawlers, seismic isolation rubbers, etc.

Examples

[0051] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples at all.

[0052] [Examples 1 to 7, Comparative Examples 1 to 3] Assume that samples of the rubber composition for tread are prepared by blending each component according to the formulation shown in Table 1 and kneading using a Banbury mixer. Although not shown in Table 1, various processing aids, additives, vulcanizing chemicals, and vulcanization accelerators are appropriately added within a range that does not affect the effects of the present invention during sample preparation.

[0053] <Evaluation> Assume that for each sample of the rubber composition for tread, after extruding it into a sheet shape, it is vulcanized at a temperature of 145°C for 90 minutes to prepare a vulcanized rubber sample. And assume that the following evaluations are performed on the obtained vulcanized rubber samples.

[0054] (1) Low heat generation evaluation For each vulcanized rubber sample, it is assumed that the loss tangent (tanδ) is measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under the conditions of a temperature of 23°C, an initial load of 1600 mN, a dynamic strain of 1%, and a frequency of 52 Hz. Using the measurement results of the formulations not shown in the table, the performance impact due to formulation changes was simulated, and the loss tangent (tanδ) of the formulations described in the table was predicted. For the evaluation, the reciprocal of the measured value of tanδ was taken, and it was shown as an index when the reciprocal value of tanδ of the sample in Comparative Example 1 was set to 100. The larger the index value, the better the low heat generation performance. The evaluation results are shown in Table 1. If the index value is 90 or more, there is no impact on the performance as a tire.

[0055] (2) Abrasion resistance evaluation For each vulcanized rubber sample, it is assumed that it is rolled on a grindstone at a constant speed and the abrasion rate is measured. Using the measurement results of the formulations not shown in the table, the performance impact due to formulation changes was simulated, and the abrasion rate of the formulations described in the table was predicted. The evaluation was expressed as an index when the reciprocal of the abrasion rate of the vulcanized rubber composed of the rubber composition in Comparative Example 1 was set to 100. The larger the index value, the slower the abrasion rate and the better the abrasion resistance. The evaluation results are shown in Table 1.

[0056] (3) Fracture resistance For each vulcanized rubber sample, it is assumed that the breaking strength after heat deterioration at 100°C for 24 hours is measured. Using the measurement results of the formulations not shown in the table, the performance impact due to formulation changes was simulated, and the fracture resistance of the formulations described in the table was predicted. For the evaluation, it was shown as an index value when the measurement result of Comparative Example 1 was set to 100. The larger the index value, the better the fracture resistance.

[0057]

Table 1

[0058] *1 TSR20 *2 High-purity natural rubber obtained by centrifugation with a nitrogen content of 0.18% by mass *3 N2SA: 126 m 2 / g, carbon black with a DBP oil absorption of 92 ml / 100 g *4 N2SA: 145 m 2 / g, carbon black with a DBP oil absorption of 99 ml / 100 g *5 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., "No Crack 6C" *6 "Nipsil KQ" manufactured by Tosoh Silica Corporation

[0059] From Table 1, it can be seen that each sample of the tread rubber composition corresponding to the examples shows excellent results with a good balance in terms of low heat build-up, abrasion resistance, and fracture resistance. On the other hand, it can be seen that each sample of the tread rubber composition corresponding to the comparative examples is inferior in any of the evaluation items compared to the examples.

Industrial Applicability

[0060] According to the present invention, a tread rubber composition excellent in abrasion resistance can be provided without degrading other physical properties. Also, according to the present invention, a tire excellent in abrasion resistance can be provided without degrading other physical properties.

Claims

1. A rubber composition comprising a rubber component, silica, carbon black, and an anti-aging agent, 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 with respect to 100 parts by mass of the rubber component, the nitrogen adsorption specific surface area (N ２ SA) of the carbon black is 135 m ２ / g or more, and the content of the anti-aging agent is 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component, a rubber composition for a tread.

2. The rubber composition for a tread 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 a tread according to claim 1 or 2, wherein the content of the anti-aging agent is 0.7 parts by mass or more and less than 3 parts by mass with respect to 100 parts by mass of the rubber component.

4. The rubber composition for a tread according to claim 1 or 2, wherein the content of the carbon black is 40 parts by mass or more with respect to 100 parts by mass of the rubber component.

5. The rubber composition for a tread according to claim 1 or 2, wherein the content of the silica is 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the rubber component.

6. The rubber composition for a tread according to claim 1 or 2, wherein the CTAB specific surface area of the silica is 200 to 240 ml / 100 g.

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

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