Tread rubber composition, tire, and heavy load tire

Abstract

Provided is a tread rubber composition having excellent abrasion resistance without any reduction in other physical properties.　The present invention pertains to a rubber composition that contains a rubber component, silica, and an antioxidant, and that is characterized in that the rubber component contains a highly pure natural rubber having a nitrogen content of 0.3 mass% or less, the content of the silica is more than 15 parts by mass with respect to 100 parts by mass of the rubber component, 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.

Description

Tread rubber composition, tire and heavy-duty tire

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

[0002] Conventionally, in the case of heavy-duty pneumatic tires for rough roads, methods for preventing deterioration in heat generation performance, appearance performance, abrasion resistance, etc. have been implemented by selecting the carbon black to be compounded in the tire tread rubber composition and optimizing the amount of carbon black to be added, etc. In recent years, various tread rubbers for heavy-duty pneumatic tires have been proposed in which silica is compounded in addition to carbon black in the tread rubber composition.

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

[0004] JP-A-1-311141, JP-A-3-65406, JP-A-4-226140

[0005] However, the techniques of Patent Documents 1 to 3 were not sufficient for improving the heat generation performance, appearance performance, and abrasion resistance after running and suppressing deterioration of physical properties in rubber compositions for treads of heavy-duty pneumatic tires. In particular, further improvement in abrasion resistance was desired.

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

[0007] The gist of the present invention, which solves the above problems, is as follows: (1) A rubber composition for a tread, comprising a rubber component, silica, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3% by mass or less, the content of the silica exceeds 15 parts by mass per 100 parts by mass of the rubber component, and the content of the antioxidant is 0.4 parts by mass or more per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration has excellent abrasion resistance without deteriorating other physical properties.

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

[0009] (3) The rubber composition for a tread according to (1) or (2), further comprising carbon black, the content of the carbon black being 45 parts by mass or more and 55 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition for a tread having the above configuration has better abrasion resistance.

[0010] (4) The rubber composition for a tread according to any one of (1) to (3), characterized in that the silica has a CTAB specific surface area of ​​200 to 240 ml / 100 g. The rubber composition for a tread having the above configuration has better abrasion resistance.

[0011] (5) A tire comprising the rubber composition for a tread according to any one of (1) to (4) above. The tire having the above configuration has excellent abrasion resistance without deteriorating other physical properties.

[0012] According to the present invention, it is possible to provide a rubber composition for a tread having excellent abrasion resistance without deteriorating other physical properties, and also to provide a tire and a heavy-duty tire having excellent abrasion resistance without deteriorating other physical properties.

[0013] An embodiment of the rubber composition for tread and tire of the present invention will be described below by way of example.

[0014] <Rubber Composition for Tread> The rubber composition for tread of the present invention contains a rubber component, silica, and an antioxidant. Each component constituting the rubber composition for tread of the present invention will be described below. (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, which makes it possible to suppress gelation, thereby achieving excellent wear resistance. 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.

[0015] Here, the high-purity natural rubber is not particularly limited in other requirements, so long as the nitrogen content is 0.3% by mass or less. For example, the high-purity natural rubber may be natural rubber obtained by removing proteins through a centrifugation process. The centrifugation process is a process in which natural rubber latex, the raw material for natural rubber, is deproteinized by centrifugation. The conditions for the centrifugation (e.g., rotation speed, time) are not particularly limited, and can be changed appropriately depending on the protein content to be removed. For example, to reduce the nitrogen content in natural rubber to 0.1% by mass or less, the centrifugation process can be carried out several times at a rotation speed of about 7,500 rpm. After the centrifugation process, the product can be washed and dried to obtain highly purified natural rubber.

[0016] The natural rubber latex used in the centrifugation process is not particularly limited. For example, field latex extracted from rubber trees or concentrated natural rubber latex obtained by processing field latex can be used. The dry rubber content in the natural rubber latex is also not particularly limited. From the viewpoint of obtaining better abrasion resistance, the dry rubber content is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0017] The content of the highly purified natural rubber in the rubber component can be 100%, but other rubbers can also be contained within a range that does not impair the object of the present invention. Furthermore, the natural rubber can be a mixture of not only the highly purified natural rubber but also ordinary natural rubber. In this case, the content of the highly purified natural rubber in the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of further improving abrasion resistance.

[0018] The rubber component may contain other synthetic rubbers in addition to the natural rubbers described above. Examples of synthetic rubbers include diene-based synthetic rubbers such as butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR), and non-diene-based synthetic rubbers such as ethylene propylene diene rubber (EPDM), ethylene propylene rubber (EPM), and butyl rubber (IIR).

[0019] Furthermore, the rubber component preferably contains butadiene rubber and / or styrene-butadiene rubber among the above-mentioned synthetic rubbers, because this allows achieving both low loss properties and abrasion resistance at a higher level.

[0020] The natural rubber and the diene-based synthetic rubber (hereinafter collectively referred to as "diene-based rubber") may be unmodified diene-based rubber (hereinafter sometimes referred to as "unmodified diene-based rubber") or modified diene-based rubber (hereinafter sometimes referred to as "modified diene-based rubber").

[0021] (Silica) The rubber composition for tire treads of the present invention contains silica in addition to the rubber component described above, and the content of the silica exceeds 15 parts by mass per 100 parts by mass of the rubber component. By making the content of the silica exceed 15 parts by mass per 100 parts by mass of the rubber component, the tire reinforcement property can be enhanced and better wear resistance can be achieved. From the same viewpoint, the content of the silica is preferably 18 parts by mass or more per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration of the processability of the rubber composition, the content of the silica is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, per 100 parts by mass of the rubber component.

[0022] Here, the silica preferably has a CTAB specific surface area of ​​200 to 240 ml / 100 g. When the CTAB specific surface area of ​​the silica is 200 ml / 100 g or more, a more excellent effect of improving abrasion resistance can be obtained, and when the CTAB specific surface area of ​​the silica is 240 ml / 100 g or less, poor dispersion and deterioration of processability can be suppressed. The CTAB specific surface area of ​​the silica can be measured, for example, in accordance with JIS K 6430:2008.

[0023] Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred because it contains a large number of silanol groups. These silicas may be used alone or in combination of two or more.

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

[0025] Here, the carbon black has a nitrogen adsorption specific surface area (N ２ SA) is 130-180m ２ / g. ２ SA is 130m ２When the N content of the carbon black is 1 / g or more, better abrasion resistance can be obtained. ２ SA is 180m ２ / g or less, deterioration in productivity and low heat buildup can be suppressed. ２ SA is 140-170m ２ / g. The nitrogen adsorption specific surface area (N ２ SA) can be measured, for example, in accordance with JIS K 6217-7:2013.

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

[0027] Furthermore, the amount of carbon black is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, per 100 parts by mass of the rubber component. When the amount of carbon black is 30 parts by mass or more per 100 parts by mass of the rubber component, reinforcement is enhanced and better abrasion resistance is obtained. On the other hand, the amount of carbon black is preferably 55 parts by mass or less per 100 parts by mass of the rubber component. When the amount of carbon black is 55 parts by mass or less per 100 parts by mass of the rubber component, deterioration of low heat buildup can be suppressed.

[0028] Furthermore, in the rubber composition for tires of the present invention, the compounding ratio of the silica to the carbon black (silica / carbon black) is 0.1 to 0.5, preferably 0.35 to 0.5. When this ratio is 0.1 or more, effects such as suppression of decreases in abrasion resistance and elongation at break (Eb) can be more reliably obtained, while when the silica / carbon black ratio is less than 0.5, poor dispersion and deterioration of low heat buildup can be suppressed.

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

[0030] The content of the antioxidant is also preferably 2 parts by mass or less per 100 parts by mass of the rubber component, because when the content of the antioxidant is 2 parts by mass or less per 100 parts by mass of the rubber component, the reaction between the silica and a silane coupling agent (described later) can be inhibited and deterioration in the kneading quality of the rubber composition can be suppressed.

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

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

[0033] (Other Components) In addition to the above-mentioned components, other components may be appropriately selected and blended into the rubber composition for treads of the present invention, as needed, within the scope of not impairing the effects of the present invention. Examples of other components include additives such as silane coupling agents, inorganic fillers other than silica and carbon black, zinc oxide, softeners, tackifiers, dispersants, crosslinking agents, crosslinking accelerators, crosslinking aids, stearic acid, colorants, antistatic agents, and lubricants, as well as various known compounding chemicals commonly used in the rubber industry. Commercially available products may be used for these.

[0034] Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, Silane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate acrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, 3-octanoylthiopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltri Examples of suitable silane coupling agents include ethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and 3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propanethiol (manufactured by Degussa under the trade name "Si363"). These silane coupling agents may be used alone or in combination of two or more.

[0035] Examples of inorganic fillers other than silica and carbon black include aluminum hydroxide, clay, etc. Among these inorganic fillers, aluminum hydroxide, etc. is preferred because it has a relatively high reinforcing property, and clay, etc. is effective because it makes use of its shape characteristics.

[0036] The rubber composition for treads of the present invention preferably contains zinc oxide (ZnO) as a crosslinking accelerator. This is because the inclusion of ZnO can further improve heat aging resistance and high elastic modulus. However, if the ZnO content is too high, crack growth resistance may deteriorate, so the ZnO content is preferably less than 5 parts by mass per 100 parts by mass of the rubber component.

[0037] Furthermore, the softener is not particularly limited and can be appropriately selected depending on the purpose. Examples include naphthenic base oils, paraffinic base oils, and aromatic base oils. The content of the softener is preferably 2 to 30 parts by mass per 100 parts by mass of the rubber component. If the content of the softener exceeds 30 parts by mass per 100 parts by mass of the rubber component, the softener may bleed onto the surface of the rubber product or the abrasion resistance may be reduced. Furthermore, among the softeners described above, naphthenic base oils or paraffinic base oils are preferred, with naphthenic base oils being most preferred. Aromatic oils are undesirable because they contain a large amount of aromatic components, which increases their affinity with the chemicals, which are aromatic compounds, and further inhibit their reaction with the polymer. On the other hand, naphthenic base oils and paraffinic base oils have the effect of facilitating diffusion and reaction in the polymer, while oils with lower pour points diffuse more easily into the polymer. The classification of naphthenic base oils, paraffinic base oils, and aromatic base oils is determined by their CA, CP, and CN values. For example, naphthenic base oils include TDAE, SRAE, RAE, and black oil. Paraffinic base oils include spindle oil and paraffin oil. Furthermore, a blend of naphthenic base oil and naphthenic asphalt, such as A / O Mix (Sankyo Yuka Kogyo Co., Ltd.), can also provide a more favorable effect. The timing of blending these lubricating oils is not particularly limited. For example, they may be extended during the production of the rubber component, or may be added during kneading of the rubber composition for treads.

[0038] The crosslinking agent is not particularly limited, either. For example, sulfur can be used. The crosslinking accelerator is also not particularly limited, and known ones can be used. Examples include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and dibenzothiazyl disulfide; sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazyl sulfenamide and N-t-butyl-2-benzothiazyl sulfenamide; guanidine-based vulcanization accelerators such as diphenyl guanidine; thiuram-based vulcanization accelerators such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, tetradodecyl thiuram disulfide, tetraoctyl thiuram disulfide, tetrabenzyl thiuram disulfide and dipentamethylene thiuram tetrasulfide; dithiocarbamate-based vulcanization accelerators such as zinc dimethyldithiocarbamate; and zinc dialkyldithiophosphate.

[0039] (Production of Rubber Composition for Tread) The method for producing the rubber composition for tread of the present invention is not particularly limited, but for example, the rubber composition can be produced by blending various components appropriately selected as necessary with the rubber component, and kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0040] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0041] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0042] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0043] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for vulcanization include molding vulcanizers using molds used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0044] <Tire> The tire of the present invention is characterized by including the above-described rubber composition for tread of the present invention. By including the rubber composition for tread of the present invention as a tire material, excellent wear resistance can be achieved without deteriorating other physical properties. Here, the tire of the present invention can be used as, for example, a heavy-duty tire, a truck / bus tire, an aircraft tire, or a passenger car tire, but among these, a heavy-duty tire is preferable. This is because the rubber composition for tread used as a material for the tread portion has excellent wear resistance and is a great advantage when used as a heavy-duty tire.

[0045] When using the rubber composition for a tread of the present invention described above, for example, an unvulcanized rubber composition may be used to mold and then vulcanize the composition, or a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like may be used to mold and then vulcanize the composition. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0046] Furthermore, in the tire of the present invention, the above-described rubber composition for a tread of the present invention must be applied to the tread (base tread, cap tread, undertread), but it can also be applied to various other structural members. For example, it can be used in cushion rubber, shoulders, sidewalls, clinches, bead fillers, carcass coating rubber, insulation, chafers, inner liners, etc., and it can also be used in side reinforcing layers of run-flat tires, etc. Furthermore, the rubber composition for a tread of the present invention can be applied to rubber crawlers, seismic isolation rubber, etc., in addition to tires.

[0047] 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.

[0048] [Manufacturing Examples 1 to 4] Samples of rubber compositions for treads were prepared by compounding rubber compositions according to the formulations shown in Table 1, with each component falling within the ranges shown in Table 1, and kneading the mixture using a Banbury mixer. In addition to the compounds shown in Table 1, the same chemicals such as vulcanization accelerators and sulfur were compounded in the same amounts in all examples. [Examples 1 to 5, Comparative Examples 1 to 4] It is assumed that each component is compounded according to the formulations shown in Table 2 to prepare samples of rubber compositions for treads.

[0049] <Evaluation> Each sample of Production Examples 1 to 4 was extruded into a sheet and then vulcanized for 90 minutes at a temperature of 145° C. to prepare a vulcanized rubber sample. The obtained vulcanized rubber sample was then evaluated as follows.

[0050] (1) Evaluation of Abrasion Resistance Each vulcanized rubber sample of Production Examples 1 to 4 was formed into a tire shape and rolled on a grindstone at a constant speed to measure the abrasion rate. The reciprocal of the abrasion rate was calculated and expressed as an index, with the reciprocal of the abrasion rate of the vulcanized rubber made from the rubber composition of Production Example 1 set at 100. A larger index value indicates a slower abrasion rate and better abrasion resistance. The evaluation results are shown in Table 1.

[0051]

[0052] Furthermore, based on the results of the abrasion resistance due to the compounding differences in Production Examples 1 to 4 described above, the abrasion resistance was predicted for the rubber compositions with the compounding shown in Table 2. The predicted abrasion resistance value is an index value, and the larger the index value, the better the abrasion resistance. The results are shown in Table 2.

[0053]

[0054] *1 TSR20 *2 High-purity natural rubber obtained by centrifugation with a nitrogen content of 0.18% by mass *3 N ２ SA: 126m ２ / g, DBP oil supply amount: 92 ml / 100 g of carbon black *4 N ２ SA: 145m ２ / g, DBP oil supply amount: 99 ml / 100 g of carbon black *5 CTAB specific surface area: 220 m ２ / g *6 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *7 One or more selected from thiazole vulcanization accelerators, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators and dithiocarbamate vulcanization accelerators. The same amount of the same substance was used in all examples and comparative examples.

[0055] Table 1 shows the relationship between the type of natural rubber, the type of carbon black, and the blended amount of antioxidant and abrasion resistance. Tables 1 and 2 also show that each sample of the rubber composition for treads corresponding to the examples exhibits excellent abrasion resistance.

[0056] According to the present invention, it is possible to provide a rubber composition for a tread having excellent abrasion resistance without deteriorating other physical properties, and also to provide a tire and a heavy-duty tire having excellent abrasion resistance without deteriorating other physical properties.

Claims

1. A rubber composition for treads comprising a rubber component, silica, and an antioxidant, wherein the rubber component contains high-purity natural rubber having a nitrogen content of 0.3 mass% or less, the silica content exceeds 15 parts by mass per 100 parts by mass of the rubber component, and the antioxidant content is 0.4 parts by mass or more per 100 parts by mass of the rubber component.

2. The rubber composition for treads according to claim 1, wherein the high purity natural rubber is obtained by removing proteins from natural rubber latex through a centrifugation process.

3. A rubber composition for treads according to claim 1 or 2, further comprising carbon black, the content of said carbon black being 45 parts by mass or more and 55 parts by mass or less per 100 parts by mass of said rubber component.

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

5. A tire comprising the rubber composition for treads according to claim 1 or 2.

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