Rubber composition for tread, and tire

Abstract

To provide a rubber composition for a tread which is excellent in wear resistance and fracture resistance without deteriorating other physical properties.SOLUTION: A rubber composition of the present invention contains a rubber component, carbon black, silica, and a resin. The rubber component contains a high-purity natural rubber having a nitrogen content of 0.3 mass% or less. The resin has a softening point of 130°C or higher, and the content of the resin is 1 pt.mass or more based on 100 pts.mass of the rubber component. The total content of the carbon black and the silica is 50 pts.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 rubber composition for treads 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 rubber composition for tire treads, optimization of its filling amount, etc. have been carried out. In recent years, tread rubbers for pneumatic tires for heavy loads containing silica in addition to carbon black in the rubber composition for treads 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 rubber composition for treads of 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 rubber composition for treads 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 has been desired for wear resistance and fracture resistance.

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

Means for Solving the Problems

[0007] The gist configuration of the present invention for solving the above problems is as follows. (1) A rubber composition containing a rubber component, carbon black, silica, and a resin, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less, the resin has a softening point of 130°C or higher and a content of 1 part by mass or more with respect to 100 parts by mass of the rubber component, and a total content of the carbon black and the silica is 50 parts by mass or more with respect to 100 parts by mass of the rubber component, a tread rubber composition. The tread rubber composition having the above configuration is excellent in abrasion resistance and fracture resistance without degrading other physical properties.

[0008] (2) The tread rubber composition according to (1), wherein a content of the antioxidant is 0.7 part by mass or more and less than 3 parts by mass 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 without causing a decrease in kneading quality.

[0009] (3) The tread rubber composition according to (1) or (2), wherein a content of the resin is 10 parts by mass or less with respect to 100 parts by mass of the rubber component. The tread rubber composition having the above configuration can maintain good low heat build-up properties.

[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 to 25 parts by mass with respect to 100 parts by mass of the rubber component. The tread rubber composition having the above configuration can achieve both good workability and excellent fracture resistance.

[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 abrasion resistance.

[0013] (7) The vulcanization accelerator contains at least a sulfenamide-based vulcanization accelerator, and the content of the sulfenamide-based vulcanization accelerator is 1 part by mass or more with respect to 100 parts by mass of the rubber component. The tread rubber composition according to any one of (1) to (6). The tread rubber composition having the above configuration can further improve various physical properties such as the durability of the rubber composition while suppressing rubber scorching.

[0014] (8) The tread rubber composition according to any one of (1) to (7), characterized in that the mass ratio of the content of the resin to the content of the vulcanization accelerator is 9 or less (resin content / vulcanization accelerator content ≤ 9). The tread rubber composition having the above configuration can achieve more excellent fracture resistance while suppressing rubber scorching.

[0015] (10) A tire comprising the tread rubber composition according to any one of (1) to (9) above. The tire having the above configuration is excellent in abrasion resistance and fracture resistance without degrading other physical properties.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a tread rubber composition excellent in abrasion resistance and fracture resistance without degrading other physical properties. Further, according to the present invention, it is possible to provide a tire excellent in abrasion resistance and fracture resistance without degrading other physical properties.

Modes for Carrying Out the Invention

[0017] Hereinafter, an exemplary description will be given of an embodiment of the tread rubber composition and the tire of the present invention. <Definition> The compounds described in this specification may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. Further, it may be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources.

[0018] <Tread Rubber Composition> The tread rubber composition of the present invention contains a rubber component, carbon black, silica, and a resin. Hereinafter, each component constituting the tread rubber composition of the present invention will be described.

[0019] (Rubber Component) The rubber component contained in the tread rubber composition 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 realized. 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.

[0020] Here, for the high-purity natural rubber, as long as the nitrogen content is 0.3% by mass or less, there are no particular limitations on other requirements. 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 of protein removal by centrifugation from natural rubber latex, which is a raw material of natural rubber. There are no particular limitations on the conditions (rotation speed, time, etc.) of the centrifugation, and the conditions can be appropriately changed according to the protein content to be removed. For example, when the nitrogen content in natural rubber is to be 0.1% by mass or less, the centrifugation process can be performed several times at a rotation speed of about 7500 rpm. Note that after the centrifugation process, high-purity natural rubber can be obtained by performing washing and drying treatments.

[0021] Note that there are no particular limitations on the natural rubber latex used in the centrifugation process. For example, field latex collected from rubber trees or concentrated natural rubber latex obtained by processing this can be used. Also, there are no particular limitations on the dry rubber content in the natural rubber latex, 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.

[0022] Also, the content of the high-purity 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 a mixture not only of the high-purity natural rubber but also of ordinary natural rubber. In that case, from the viewpoint of further improving abrasion resistance, the content of the high-purity 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.

[0023] 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), etc., and non-diene-based synthetic rubbers such as ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), butyl rubber (IIR), etc.

[0024] Also, regarding the rubber component, among the synthetic rubbers described above, it is preferable to contain butadiene rubber and / or styrene-butadiene rubber. This is because high levels of low-loss properties and abrasion resistance can be achieved simultaneously.

[0025] Note that regarding the natural rubber and the diene-based synthetic rubbers (hereinafter collectively referred to as "diene-based rubbers"), they may be unmodified diene-based rubbers (hereinafter sometimes referred to as "unmodified diene-based rubbers") or modified diene-based rubbers (hereinafter sometimes referred to as "modified diene-based rubbers").

[0026] (Carbon black) The rubber composition of the present invention further contains carbon black in addition to the rubber component described above. This is because the reinforcement of the rubber composition is enhanced, and excellent abrasion resistance and fracture resistance can be obtained.

[0027] Here, as the carbon black, the nitrogen adsorption specific surface area (N2SA) is preferably 135 to 180 m 2 / g. When the N2SA of the carbon black is 135 m 2 / g or more, more excellent abrasion resistance can be obtained. When the N2SA of the carbon black is 180 m 2 / g or less, deterioration of productivity and low heat generation can be suppressed. From the same perspective, the N2SA of the carbon black is 140 to 170 m 2It is preferably / g. Regarding the nitrogen adsorption specific surface area (N2SA) of the carbon black, it can be measured in accordance with, for example, JIS K 6217-7:2013.

[0028] Also, 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, it is possible to suppress low heat generation and deterioration of productivity. 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. Regarding the DBP oil absorption amount of the carbon black, it can be measured in accordance with JIS K 6217-4:2017.

[0029] And in the rubber composition for a tire tread of the present invention, the total content of the carbon black and silica described later needs to be 50 parts by mass or more with respect to 100 parts by mass of the rubber component. By setting the total content of the carbon black and the silica to 50 parts by mass or more with respect to 100 parts by mass of the rubber component, 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, and more preferably 65 parts by mass or more, with respect to 100 parts by mass of the rubber component. 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 even more preferably 70 parts by mass or less, with respect to 100 parts by mass of the rubber component.

[0030] 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, and even more preferably 55 parts by mass or less with respect to 100 parts by mass of the rubber component. This is because 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, the deterioration of low heat generation property can be suppressed.

[0031] Also, 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.

[0032] (Silica) The rubber composition for a tire tread of the present invention contains silica in addition to the rubber component and carbon black described above. By including the silica, the reinforcing property and fracture resistance of the tire can be enhanced.

[0033] The content of the silica needs to satisfy the total content with the carbon black described above. However, from the viewpoint of realizing more excellent fracture resistance, the content of the silica alone is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the rubber component. By setting the content of the silica to 5 parts by mass or more with respect to 100 parts by mass of the rubber component, the reinforcement of the tire can be enhanced, and more excellent abrasion resistance and fracture resistance can be realized. From the same perspective, the content of the silica is preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. On the other hand, from the perspective of suppressing the deterioration of the processability of the rubber composition, the content of the silica is set to 25 parts by mass or less with respect to 100 parts by mass of the rubber component, so that while improving the abrasion resistance and fracture resistance, the deterioration of the processability and workability can be suppressed. From the same perspective, the content of the silica is preferably 20 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0034] Here, for the silica, the CTAB specific surface area is preferably 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 fracture resistance improvement effect and abrasion resistance improvement effect can be obtained. 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.

[0035] 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 preferred in terms of having many silanol groups. These silicas may be used alone or in combination of two or more.

[0036] Also, from the perspective of reducing environmental impact, silica derived from silicate plants is also preferable as the silica. Such silicate plants exist, for example, in mosses, ferns, toxics, cucurbitaceae, urticaceae, gramineous plants, etc. Among these plants, gramineous plants are preferable. Examples of the gramineous plants include rice, bamboo, sugarcane, etc., and among them, rice is preferable. Since rice is widely cultivated for food, it can be procured locally in a wide area. Also, since a large amount of rice husks are generated as industrial waste, it is easy to secure the quantity. Therefore, from the perspective of easy availability, as the silica, silica derived from rice husks (hereinafter, also referred to as "rice husk silica") is particularly preferable. By using the rice husk silica, rice husks that would otherwise be industrial waste can be effectively utilized. Also, since the raw material can be procured locally near the tire manufacturing factory, the energy and cost of 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 pyrolyzing rice husks by steaming them using a kiln. The rice husk charcoal thus obtained can be pulverized using a known pulverizer (for example, a 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, etc.

[0037] (Resin) The rubber composition for a tread of the present invention contains a resin in addition to the rubber component, silica, and carbon black described above. And the resin has a softening point of 130°C or higher. By the resin having a softening point of 130°C or higher, the fracture resistance can be improved. Also, from the same perspective, 140°C or higher is preferable, and 145°C or higher is more preferable. In this specification, the softening point of the resin is the temperature at which the sphere descends when measured with a ring and ball softening point measuring device in accordance with the softening point defined in JIS K 6220-1:2015 (ISO 28641:2010).

[0038] Here, regarding the resin type, the softening point may be 130°C or higher, and there is no particular limitation. For example, terpene resins, rosin resins, C5 resins, C5-C9 resins, C9 resins, dicyclopentadiene resins, aromatic resins, coumarone resins, indene resins, coumarone-indene resins, olefin resins, polyurethane resins, acrylic resins, etc. may be mentioned. These resins may be used alone or in combination of two or more. Among the above-mentioned resins, the resin is preferably a cyclopentadiene resin, and more preferably a dicyclopentadiene resin. This is because more excellent fracture resistance can be achieved. The dicyclopentadiene resin refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts type catalyst such as AlCl3 or BF3. Examples of the dicyclopentadiene resin include a homopolymer of dicyclopentadiene, a copolymer of dicyclopentadiene and an aromatic monomer, a copolymer of dicyclopentadiene and a C9 fraction (vinyltoluene, indene, etc.).

[0039] Furthermore, regarding the content of the resin, it is 1 part by mass or more, and more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. This is because the above-mentioned effect of improving fracture resistance can be more effectively exerted. Note that from the viewpoint of suppressing the deterioration of low heat generation, the content of the resin is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0040] (Antioxidant) The rubber composition for a tread of the present invention preferably contains an anti-aging agent in addition to the rubber component, silica, carbon black, and resin described above. By including an anti-aging agent in the rubber composition for a tread, the reinforcing property and abrasion resistance of the rubber composition for a tread can be enhanced.

[0041] Here, the content of the anti-aging agent is preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. This is because the effect of improving the reinforcing property and abrasion resistance of the rubber composition for a tread by the anti-aging agent can be more effectively exerted. On the other hand, 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.

[0042] 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.

[0043] 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.

[0044] (Sulfur, vulcanization accelerator) In addition, the rubber composition for a tread of the present invention preferably contains sulfur as a crosslinking agent in addition to the above-described respective components. This is because various physical properties such as the durability of the rubber composition for a tread of the present invention can be improved.

[0045] Furthermore, from the same viewpoint, the rubber composition for a tread of the present invention preferably contains a vulcanization accelerator in addition to the above-described respective components. Here, the type of the vulcanization accelerator 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 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 can be used.

[0046] Furthermore, among the above-described vulcanization accelerators, it is preferable to use at least a sulfenamide-based vulcanization accelerator, and more preferably N-cyclohexyl-2-benzothiazyl sulfenamide, from the viewpoint of controlling the vulcanization rate and the degree of vulcanization and improving the fracture resistance.

[0047] In addition, the content of the vulcanization accelerator is preferably 1 part by mass or more, and more preferably 1.4 parts by mass or more with respect to 100 parts by mass of the rubber component. This is because various physical properties such as the durability of the tire can be improved while appropriately controlling the vulcanization rate.

[0048] Furthermore, the mass ratio of the content of the resin to the content of the vulcanization accelerator is 9 or less (preferably, the content of the resin / the content of the vulcanization accelerator ≤ 9). This is because the vulcanization rate and the degree of vulcanization can be controlled, and various physical properties such as the durability of the tire can be improved. From the same perspective, the mass ratio of the content of the resin to the content of the vulcanization accelerator is more preferably 2 or less (the content of the resin / the content of the vulcanization accelerator ≤ 2).

[0049] (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, for example, silane coupling agents, inorganic fillers other than silica and carbon black, softening agents, tackifiers, dispersants, 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.

[0050] 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.

[0051] In addition, bioethanol can also be used as a raw material for the silane coupling agent. The bioethanol is mainly produced using saccharides and / or celluloses as biological resources, and other biological resources such as proteins, lipids, and amino acids cannot be effectively utilized. Furthermore, saccharides compete with food, and excessive use of celluloses leads to deforestation. Therefore, in addition to the supply situations of various biological resources, according to the supply situations of renewable resources, fossil resources, and market requirements (for example, the demand for biomass resources as food), as the monomer components derived from biological resources, it is preferable to use multiple types of monomer components derived from biological resources, or to use a combination of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources. Thereby, without relying on a single type of biological resource, a wide range of biological resources such as sugars, proteins, and lipids, as well as renewable resources, can be effectively utilized, and environmental considerations can also be made according to the situation during manufacturing.

[0052] Examples of the inorganic filler other than the silica and carbon black include aluminum hydroxide, clay, and the like. Among these inorganic fillers, aluminum hydroxide and the like are preferable in terms of relatively high reinforcing properties, and clay and the like are effective in terms of obtaining effects by taking advantage of their shape characteristics.

[0053] Furthermore, the softening agent is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include naphthene-based base oil, paraffin-based base oil, and aroma-based base oil. 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 may ooze out to the surface of the rubber product, or the abrasion resistance may decrease. Furthermore, among the softeners described above, 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 aroma oil has a high affinity with the chemical, 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 an effect of assisting in diffusing and reacting in the polymer, and an oil with a lower pour point diffuses better into the polymer. Note that the classification of 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, those classified as the naphthenic base oil are TDAE, SRAE, RAE, Black Oil, etc. Also, those classified as the paraffinic base oil are spindle oil and paraffin oil. Furthermore, a mixed oil such as A / O Mix (Sankyo Yuka Kogyo Co., Ltd.), which is a mixture of the naphthenic base oil and the naphthenic asphalt, also provides more preferable effects. There is no particular limitation 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.

[0054] (Manufacture of the tread rubber composition) The method for manufacturing the tread rubber composition of the present invention is not particularly limited. For example, various components appropriately selected as necessary are blended with the rubber component, and the rubber composition can be manufactured by kneading, heat treatment, extrusion, etc. Also, the obtained rubber composition can be made into a vulcanized rubber by vulcanizing it.

[0055] The kneading conditions are not particularly limited, and various conditions such as the input volume of the kneading device, the rotational speed of the rotor, the ram pressure, etc., as well as the kneading temperature, kneading time, type of kneading device, etc. can be appropriately selected according to the purpose. As the kneading device, usually, a Banbury mixer, an intermix, a kneader, a roll, etc. used for kneading rubber compositions can be mentioned.

[0056] Regarding the heat treatment conditions, there are also no particular limitations, and various conditions such as the heat treatment temperature, heat treatment time, heat treatment device, etc. can be appropriately selected according to the purpose. As the heat treatment device, usually, a heat treatment roll machine used for heat treatment of rubber compositions can be mentioned.

[0057] Regarding the extrusion conditions, there are also no particular limitations, and various conditions such as the extrusion time, extrusion speed, extrusion device, extrusion temperature, etc. can be appropriately selected according to the purpose. As the extrusion device, usually, an extruder used for extrusion of rubber compositions can be mentioned. The extrusion temperature can be determined appropriately.

[0058] Regarding the device, method, conditions, etc. for vulcanization, there are also no particular limitations, and they can be appropriately selected according to the purpose. As the device for vulcanization, usually, a molding vulcanizer using a mold used for vulcanization of rubber compositions can be mentioned. As the vulcanization conditions, the temperature is, for example, about 100 to 190 °C.

[0059] <Tire> The tire of the present invention is characterized by including the rubber composition for tread of the present invention described above. By including the rubber composition for tread of the present invention as a tire material, excellent abrasion resistance and fracture resistance can be realized 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, a passenger car tire, etc. Among these, it is preferably a heavy-duty tire. This is because the rubber composition for tread used as the material of the tread part is excellent in abrasion resistance and fracture resistance, and the merits are great when used as a heavy-duty tire.

[0060] 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 full vulcanization 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 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.

[0061] Also, in the tire of the present invention, it is necessary to apply the rubber composition for tread of the present invention described above to the tread (base tread, cap tread, undertread), but 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 the side reinforcement layer of a run-flat tire. 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

[0062] 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.

[0063] [Examples 1-1 to 2-4, Comparative Examples 1-1 to 2-3] Assume that samples of the rubber composition for tread are prepared by blending each component according to the formulations shown in Tables 1 and 2 and kneading using a Banbury mixer. Although not shown in Tables 1 and 2, various processing aids, additives, and vulcanizing chemicals are appropriately added within a range that does not affect the effects of the present invention during sample preparation.

[0064] <Evaluation> For samples of the rubber composition for each tread, after extruding into a sheet shape, it is assumed that a vulcanized rubber sample is prepared by vulcanizing at a temperature of 145°C for 90 minutes. And it is assumed that the following evaluations are performed on the obtained vulcanized rubber samples.

[0065] (1) Low heat build-up evaluation For each vulcanized rubber sample, it is assumed that a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) is used to measure the loss tangent (tanδ) 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 loss tangent (tanδ) of the formulations not shown in the table, a simulation of the performance impact due to formulation changes was performed to predict the loss tangent (tanδ) of the formulations described in the table. For the evaluation, the reciprocal of the measured value of tanδ is taken, and it is shown as an index when the reciprocal values of tanδ of the samples of Comparative Example 1-1 and Comparative Example 2-1 are set to 100. The larger the index value, the better the low heat build-up property. The evaluation results are shown in Table 1 and Table 2. Also, if it is 95 or more, it is evaluated as having excellent low heat build-up property, and if it is 90 or more, it is evaluated as having no impact on the performance as a tire.

[0066] (2) Abrasion resistance evaluation For each vulcanized rubber sample, it is assumed that it is rolled on a grindstone at a constant speed to measure the abrasion rate. Using the measurement results of the formulations not shown in the table, a simulation of the performance impact due to formulation changes was performed to predict the abrasion rate of the formulations described in the table. The evaluation was shown as an index when the reciprocal of the abrasion rate was calculated, and the reciprocal of the abrasion rate of the vulcanized rubber composed of the rubber compositions of Comparative Example 1-1 and Comparative Example 2-1 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 and Table 2.

[0067] (3) Evaluation of fracture resistance and fracture resistance after deterioration For each vulcanized rubber sample, it is assumed that the breaking strength and the breaking strength after heat deterioration at 100°C for 24 hours (breaking strength after deterioration) are measured. Using the measurement results of formulations not shown in the table, the performance impact due to formulation changes was simulated, and the burst resistance and post-deterioration burst resistance of the formulations described in the table were predicted. For the evaluation, the index values were shown when the measurement results of Comparative Example 1-1 and Comparative Example 2-1 were set to 100 respectively. The larger the index value, the better the burst resistance and post-deterioration burst resistance. The evaluation results are shown in Table 1 and Table 2.

[0068]

Table 1

Table 2

[0069] *1 TSR20 *2 High-purity natural rubber with a nitrogen content of 0.18% by mass obtained by centrifugation *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 "Nip Seal KQ" manufactured by Tosoh Silica Corporation *6 Dicyclopentadiene resin, softening point 140°C *7 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrack 6C" manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. *8 One or more selected from thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiuram-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators.

[0070] From Table 1, it can be seen that each sample of the tread rubber composition corresponding to the examples shows excellent results in terms of fracture resistance and fracture resistance after deterioration due to the addition of the resin. Also, from Table 2, it can be seen that each sample of the tread rubber composition corresponding to the examples shows well-balanced excellent results 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

[0071] According to the present invention, it is possible to provide a tread rubber composition excellent in abrasion resistance and fracture resistance without deteriorating other physical properties. Also, according to the present invention, it is possible to provide a tire excellent in abrasion resistance and fracture resistance without deteriorating other physical properties.

Claims

1. A rubber composition comprising a rubber component, carbon black, silica, and a resin, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less, the resin has a softening point of 130°C or higher and a content of 1 part by mass or more with respect to 100 parts by mass of the rubber component, and a total content of the carbon black and the silica is 50 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 a content of the antioxidant is 0.7 part by mass or more and less than 3 parts by mass with respect to 100 parts by mass of the rubber component.

3. The rubber composition for a tread according to claim 1 or 2, wherein a content of the resin is 10 parts by mass or less 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 a 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 a content of the silica is 5 to 25 parts by mass 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 a CTAB specific surface area of the silica is 200 to 240 ml / 100 g.

7. The rubber composition for a tread according to claim 1 or 2, wherein the vulcanization accelerator contains at least a sulfenamide-based vulcanization accelerator, and a content of the sulfenamide-based vulcanization accelerator is 1 part by mass or more with respect to 100 parts by mass of the rubber component.

8. The rubber composition for a tread according to claim 1 or 2, characterized in that the mass ratio of the content of the resin to the content of the vulcanization accelerator is 9 or less (content of resin / content of vulcanization accelerator ≦ 9).

9. A tire, characterized by comprising the rubber composition for a tread according to claim 1 or 2.

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