Rubber composition and tire

Abstract

To provide a rubber composition and a tire capable of improving wet grip performance.SOLUTION: There is provided a rubber composition which comprises a rubber component A and vulcanized rubber particles and satisfies the following expressions, wherein a domain constituted by the vulcanized rubber particles exists in a matrix constituted by the rubber component A and the average diameter of the domain is 50 μm or more. The hardness (kgf / mm2) of the domain during drying / the hardness (kgf / mm2) of the matrix during drying≥1.1. The hardness (kgf / mm2) of the domain during water wetting / the hardness (kgf / mm2) of the matrix during water wetting≤0.98.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Conventionally, various methods for improving wet grip performance have been studied (for example, see Patent Document 1). However, in recent years, there has been a demand for further improvement in wet grip performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-544936 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a rubber composition and a tire that can solve the above problems and improve wet grip performance. [Means for solving the problem]

[0005] The present invention relates to a rubber composition comprising a rubber component A and vulcanized rubber particles, wherein domains composed of the vulcanized rubber particles are present in a matrix composed of the rubber component A, the average diameter of the domains is 50 μm or more, and the rubber composition satisfies the following formula: Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 ) ≧ 1.1 Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )≦0.98 Effect of the Invention

[0006] The present invention is a rubber composition that contains a rubber component A and vulcanized rubber particles, in which domains composed of the vulcanized rubber particles are present in a matrix composed of the rubber component A, the average diameter of the domains is 50 μm or more, and satisfies the above formula, thereby improving wet grip performance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present embodiment is a rubber composition that contains a rubber component A and vulcanized rubber particles, in which domains composed of the vulcanized rubber particles are present in a matrix composed of the rubber component A, the average diameter of the domains is 50 μm, and the rubber composition satisfies the following formula: Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 ) ≧ 1.1 Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )≦0.98

[0008] The reason why the rubber composition of the present embodiment provides the above-mentioned effects is presumed to be as follows. When the average domain diameter is within the above range, energy loss in a frequency range that contributes to wet grip performance is more likely to occur. Furthermore, when the domain hardness and matrix hardness when dry satisfy the above formula, domain-derived energy loss is unlikely to occur when dry, and when the domain hardness and matrix hardness when wet with water satisfy the above formula, domain-derived energy loss is likely to occur when wet with water. It is believed that these effects result in a significant improvement in wet grip performance.

[0009] In the rubber composition of this embodiment, domains composed of vulcanized rubber particles exist in a matrix composed of rubber component A, that is, a sea-island structure is formed in which the rubber component A is the sea and the vulcanized rubber particles are the islands. The matrix preferably contains, together with the rubber component A, a component other than the vulcanized rubber particles (for example, silica A). The rubber composition in the above state is formed by kneading the rubber component A and the vulcanized rubber particles under normal conditions. The above state can be confirmed from the color shade when an osmium-stained sample is observed under a scanning electron microscope (SEM).

[0010] The average diameter of the domains may be 50 μm or more, but is preferably 80 μm or more, more preferably 95 μm or more, and is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less. Within the above ranges, the effect tends to be better. The average domain size is measured by the method described in the Examples below.

[0011] The rubber composition of the present embodiment satisfies the following formula, which means that the hardness of the domain is 10% or more higher than the hardness of the matrix when dry, and that the hardness of the domain is 2% or more lower than the hardness of the matrix when wet with water. Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 ) ≧ 1.1 Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )≦0.98 Note that "dry" refers to a state in which the drying treatment described below has been carried out, and "wet with water" refers to a state in which the wetting treatment described below has been carried out. Drying treatment: Leave the sample at rest for 24 hours at an atmospheric temperature of 30°C, a relative humidity of 30%, and 1 atmosphere, then leave the sample at rest for 1 hour at an atmospheric temperature of 120°C, a relative humidity of 30%, and 1 atmosphere. Wetting treatment: The sample after drying treatment is immersed in water in a water tank whose temperature is adjusted to 60°C. The water tank is left under an atmosphere of 1 atmosphere. After immersing the sample for 24 hours, the water on the surface of the sample is wiped off.

[0012] In addition, the rubber composition (vulcanized rubber composition) of this embodiment is capable of reversible changes in physical properties when dried and when wetted with water, so that when re-dried (after wetting treatment, the same drying treatment is performed again as before), the E* will be the same as when dry (or within ±1%), and when re-wetted with water (after re-drying treatment, the same wetting treatment is performed again as before), the E* will be the same as when wetted with water (or within ±1%).

[0013] Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 ) is preferably 1.2 or more, more preferably 1.6 or more, and even more preferably 1.8 or more, and is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 ) is preferably 0.90 or less, more preferably 0.89 or less, even more preferably 0.80 or less, and is preferably 0.10 or more, more preferably 0.30 or more, even more preferably 0.50 or more. Within the above range, better effects tend to be obtained.

[0014] The hardness of the domain when dry may be adjusted appropriately within a range that satisfies the above relationship, but is preferably 10 kgf / mm 2 More preferably, 15kgf / mm 2 More preferably, 20 kgf / mm 2 More preferably, it is 50 kgf / mm 2 Less than or equal to 40kgf / mm 2 Less than 35kgf / mm, more preferably 35kgf / mm 2 The following is the result. The hardness of the domain when wetted with water may be appropriately adjusted within a range that satisfies the above relationship, but is preferably 1 kgf / mm 2 More preferably, 5kgf / mm 2 More preferably, 8kgf / mm 2 More preferably, it is 30 kgf / mm 2Less than or equal to 20kgf / mm 2 Less than 15kgf / mm, more preferably 2 The following is the result. Within the above range, better effects tend to be obtained.

[0015] The dry hardness can be adjusted by the type and amount of chemicals (especially rubber components, fillers, softeners such as oils) compounded in the rubber composition; for example, reducing the amount of softener or increasing the amount of filler tends to increase the dry hardness. The hardness when wet can also be adjusted in a similar manner; for example, the hardness when wet tends to be reduced by adding a water-absorbing chemical such as polyacrylic acid resin or by reducing the amount of filler.

[0016] The object of the present application is to improve wet grip performance, and the above formula regarding hardness is one of the means for achieving this. In this specification, the hardness is a value obtained by carrying out a hardness test in the Examples section described later on a rubber composition after vulcanization.

[0017] The rubber composition of the present embodiment contains a rubber component A. Here, the rubber component A is a component that contributes to crosslinking, and generally has a weight average molecular weight (Mw) of 10,000 or more.

[0018] The weight average molecular weight of the rubber component A is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above ranges, the effect tends to be better obtained. In this specification, the weight average molecular weight (Mw) can be determined by converting it into standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0019] The glass transition temperature (Tg) of the rubber component A is preferably -120°C or higher, more preferably -80°C or higher, even more preferably -60°C or higher, particularly preferably -50°C or higher, and is preferably -10°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower, particularly preferably -35°C or lower. Within the above range, the effect tends to be better obtained. This is presumably because the energy loss in the frequency range that contributes to wet grip performance becomes large. In this specification, the glass transition temperature is a value measured in accordance with JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan at a heating rate of 10°C / min.

[0020] The rubber component A may be a non-modified rubber or a modified rubber. Examples of modified rubbers include terminally modified rubbers (terminally modified rubbers having a polar functional group at an end) in which at least one end of the rubber has been modified with a compound (modifying agent) having a polar functional group, main chain modified rubbers having a polar functional group in the main chain, main chain terminal modified rubbers having polar functional groups in the main chain and at least one end (for example, main chain terminal modified rubbers having a polar functional group in the main chain and at least one end modified with the above-mentioned modifier), and terminally modified rubbers modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein.

[0021] Examples of polar functional groups include carboxyl groups, pyridinyl groups, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, nitrile groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, at least one selected from the group consisting of carboxyl groups, pyridinyl groups, amino groups, and imidazole groups is preferred, at least one selected from the group consisting of carboxyl groups and pyridinyl groups is more preferred, and carboxyl groups are even more preferred. By using these polar functional groups, the effect tends to be better. This is presumed to be because the amount of change in pH of the raw material (rubber) due to the introduction of the polar functional group is small, and side reactions are less likely to occur during introduction.

[0022] Examples of the rubber component A include diene rubbers such as isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Polymers such as butyl rubber and fluororubber are also included. These may be used alone or in combination of two or more. These rubber components may be modified or hydrogenated, and extended rubbers extended with oil, resin, liquid rubber components, etc. may be used. Among these, isoprene rubber, BR, and SBR are preferred.

[0023] Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. Examples of NR include SIR20, RSS♯3, TSR20, and other rubber industry-standard rubbers. Examples of IR include IR2200 and other rubber industry-standard rubbers. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and other rubbers. Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more.

[0024] The BR is not particularly limited, and examples of the BR that can be used include high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. In particular, the BR preferably contains high cis BR with a cis content of 90% by mass or more. The cis content is more preferably 95% by mass or more. The cis content can be measured by infrared absorption spectroscopy.

[0025] The cis amount of BR means the cis amount of the BR when there is one type of BR, and means the average cis amount when there are multiple types of BR. The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)} / total content of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis content of 90% by mass and 10% by mass of BR with a cis content of 40% by mass, the average cis content of BR is 73.3% by mass (=(20×90+10×40) / (20+10)).

[0026] As the BR, a hydrogenated butadiene polymer (hydrogenated BR) can also be used.

[0027] As the BR, for example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used.

[0028] The SBR is not particularly limited, and for example, emulsion polymerized styrene butadiene rubber (E-SBR), solution polymerized styrene butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more kinds.

[0029] The styrene content of the SBR is preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 24% by mass or more, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Within the above ranges, the effect tends to be better obtained. In this specification, the amount of styrene is 1 It can be measured by H-NMR measurement.

[0030] The styrene amount of SBR means the styrene amount of the SBR when there is one type of SBR, and means the average styrene amount when there are multiple types of SBR. The average styrene amount of SBR can be calculated by {Σ(content of each SBR × styrene amount of each SBR)} / total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene amount of 40% by mass and 5% by mass of SBR with a styrene amount of 25% by mass, the average styrene amount of the SBR is 39.2% by mass (=(85×40+5×25) / (85+5)).

[0031] The vinyl content of the SBR is preferably 3% by mass or more, more preferably 10% by mass or more, and even more preferably 17% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained. In this specification, the vinyl content (the amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

[0032] The vinyl content of SBR (amount of 1,2-bonded butadiene units) is the proportion of vinyl bonds when the total mass of the butadiene parts in SBR is taken as 100 (unit: mass%), and is calculated as vinyl content [mass%] + cis content [mass%] + trans content [mass%] = 100 [mass%]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types, it means the average vinyl content. The average vinyl content of SBR can be calculated by Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%]) × vinyl content of each SBR [mass%]} / Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%])}. For example, in 100 parts by mass of the rubber component, there are 75 parts by mass of SBR with a styrene content of 40 mass% and a vinyl content of 30 mass%, 25 parts by mass of styrene, and 10 parts by mass of vinyl. In the case where SBR with a vinyl content of 20 mass% is 15 parts by mass and the remaining 10 parts by mass is a component other than SBR, the average vinyl content of the SBR is 28 mass% (={75 × (100 [mass%] - 40 [mass%]) × 30 [mass%] + 15 × (100 [mass%] - 25 [mass%]) × 20 [mass%])} / {75 × (100 [mass%] - 40 [mass%]) + 15 × (100 [mass%] - 25 [mass%])}.

[0033] As SBR, hydrogenated styrene-butadiene copolymer (hydrogenated SBR) can also be used.

[0034] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used. In addition, SBR synthesized by a known method can also be used.

[0035] The raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from petroleum or may be recycled from rubber products such as tires or non-rubber products such as polystyrene. Monomers obtained by recycling (recycled monomers) are not particularly limited, and include recycled butadiene and recycled aromatic vinyl. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. Examples of the aromatic vinyl include, but are not particularly limited, styrene. Among them, it is preferable to use recycled butadiene (recycled butadiene) and / or recycled styrene (recycled styrene) as the raw materials.

[0036] The method for producing the recycled monomer is not particularly limited, and examples thereof include synthesis from recycle-derived naphtha obtained by decomposing rubber products such as tires. The method for producing the recycled naphtha is also not particularly limited, and examples thereof include decomposing rubber products such as tires under high temperature and pressure, decomposing with microwaves, or mechanically crushing and then extracting.

[0037] Furthermore, the raw material (monomer) of synthetic rubber such as SBR and BR may be derived from biomass. Examples of the monomer derived from biomass (biomass monomer) include, but are not limited to, butadiene derived from biomass and aromatic vinyl derived from biomass. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. Examples of the aromatic vinyl include, but are not limited to, styrene. In addition, the method for producing the biomass monomer is not particularly limited, and examples thereof include biological and / or chemical and / or physical conversion of animals and plants. A representative example of biological conversion is fermentation by a microorganism, and examples of chemical and / or physical conversion include those using a catalyst, those using high heat, those using high pressure, those using electromagnetic waves, those using critical liquids, and combinations thereof. Examples of biomass sources for these monomers include sugar, wood, plant residues after useful components are obtained, plant-derived ethanol, biomass naphtha, etc.

[0038] The polymer (biomass polymer) synthesized from a biomass monomer component is not particularly limited, and examples thereof include polybutadiene rubber synthesized from butadiene derived from biomass, aromatic vinyl / butadiene copolymer synthesized from butadiene derived from biomass and / or aromatic vinyl derived from biomass, etc. Examples of the aromatic vinyl / butadiene copolymer include styrene butadiene rubber synthesized from butadiene derived from biomass and / or styrene derived from biomass.

[0039] Whether the raw material for a polymer is biomass-derived can be determined by the percent modern carbon (pMC) measured in accordance with ASTM D6866-10.

[0040] pMC stands for modern standard reference carbon. 14 C concentration vs. sample 14 This is the ratio of the carbon concentration to the biomass concentration of the compound (rubber), and this value is used as an index of the biomass ratio of the compound (rubber). The significance of this value is described below.

[0041] 1 mole of carbon atoms (6.02 × 10 23 ) contains approximately 6.02 × 10 atoms, which is about one trillionth of the size of a normal carbon atom. 11 pcs 14 C exists. 14 C is called a radioisotope, and its half-life is 5,730 years, and it decreases regularly. It takes 226,000 years for all of them to decay. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms more than 226,000 years ago, C was also included in these when they were first fixed. 14 All C elements have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas are 14 There is no C element at all. Therefore, chemical substances produced using these fossil fuels as raw materials also 14 It does not contain any C elements.

[0042] on the other hand, 14 C is produced continuously by nuclear reactions in the atmosphere caused by cosmic rays, and this is balanced by the loss of C due to radioactive decay. In the Earth's atmospheric environment, 14 The amount of C is constant. Therefore, the amount of biomass-derived materials circulating in the current environment is 14 As mentioned above, the C concentration is about 1×10 -12 The value is about mol%. Therefore, by using the difference between these values, it is possible to calculate the ratio (biomass ratio) of compounds derived from natural resources (compounds derived from biomass resources) in a certain compound (rubber).

[0043] this 14 C is typically measured as follows: using accelerator mass spectrometry based on a tandem accelerator, 13 C concentration ( 13 C / 12 C). 14 C concentration ( 14 C / 12 C) is measured. 14 The modern standard reference for the C concentration is the carbon circulating in nature in 1950. 14 The specific standard substance used is the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific radioactivity of carbon in this oxalic acid (per gram of carbon) is 14 C) for each carbon isotope, 13 The standard value is the value corrected for decay from 1950 to the measurement date, with C corrected to a constant value. 14 This is used as the C concentration value (100%). The ratio of this value to the value actually measured for the sample is the pMC value.

[0044] Therefore, if rubber is made from 100% biomass (natural) derived materials, it will show a value of approximately 110 pMC, although there may be regional differences (currently, under normal conditions, it is often not 100). On the other hand, for chemical substances derived from petroleum and other fossil fuels, 14 When the C concentration is measured, it will show approximately 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

[0045] For these reasons, it is preferable in terms of environmental protection to use a material such as rubber having a high pMC value, that is, a material such as rubber having a high biomass ratio, in a rubber composition.

[0046] The content of the isoprene-based rubber in 100% by mass of the rubber component A is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0047] The content of BR in 100% by mass of rubber component A is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0048] The content of SBR in 100% by mass of rubber component A is preferably 30% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, particularly preferably 65% ​​by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0049] The rubber composition of the present embodiment preferably contains silica A. Silica A is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method, or the like, which is common in the tire industry. The raw material of silica is not particularly limited, and can be, for example, a mineral-derived raw material such as quartz, a biological raw material such as rice husk (for example, silica made from a biomass material such as rice husk), or silica recycled from a product containing silica. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. These silicas can be used alone or in combination of two or more types.

[0050] Silica made from biomass materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then reacting the silicate with sulfuric acid in the same manner as conventional wet-process silica to produce a silicon dioxide precipitate, which is then filtered, washed with water, dried, and pulverized.

[0051] The silica recycled from a product containing silica can be, for example, silica recovered from a product containing silica, such as electronic parts such as semiconductors, tires, desiccants, and filtering materials such as diatomaceous earth. The recovery method is not particularly limited, and examples include pyrolysis and decomposition by electromagnetic waves. Among them, silica recovered from electronic parts such as semiconductors or tires is preferred.

[0052] When silica crystallizes, it does not dissolve in water and its component silicic acid cannot be used. By controlling the combustion temperature and combustion time, it is possible to suppress the crystallization of silica in rice husk ash (see JP 2009-2594 A, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.).

[0053] As the amorphous silica extracted from rice husks, commercially available products such as those sold by Wilmar Co. can be used.

[0054] The content of silica A is preferably 30 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 80 parts by mass or more, and is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less, based on 100 parts by mass of rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0055] The nitrogen adsorption specific surface area (N2SA) of silica A is preferably 50 m 2 / g or more, more preferably 100m 2 / g or more, more preferably 150m 2 / g or more, particularly preferably 170m 2 / g or more, and preferably 300m 2 / g or less, more preferably 250m 2 / g or less, more preferably 200m 2 Within the above range, there is a tendency for the effect to be better obtained. The N2SA of Silica A is a value measured by the BET method in accordance with ASTM D3037-93.

[0056] Silica A is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and those known in the rubber field can be used. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N, Examples of such silylsilanes include sulfide-based silylsilanes such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silylsilanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silylsilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silylsilanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silylsilanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silylsilanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silylsilanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those manufactured by Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry, Azumax, and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.

[0057] The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, based on 100 parts by mass of silica A. When the content is within the above range, the effect tends to be better obtained.

[0058] The rubber composition of the present embodiment may contain a filler other than silica A. The filler other than silica A is not particularly limited, and materials known in the rubber field can be used, for example, inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar, poorly dispersible fillers, etc. Among them, carbon black is preferred from the viewpoint of obtaining a greater effect.

[0059] Carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The raw material of carbon black may be a biomass material such as lignin or vegetable oil, or may be pyrolysis oil obtained by pyrolyzing waste tires. The carbon black may be produced by combustion such as a furnace method, hydrothermal carbonization (HTC), or pyrolysis of methane such as a thermal black method. Commercially available products include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more.

[0060] The nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 5 m 2 / g or more, more preferably 50m 2 / g or more, more preferably 90m 2 / g or more, particularly preferably 110m 2 / g or more, and preferably 200m2 / g or less, more preferably 150m 2 / g or less, more preferably 130m 2 Within the above range, there is a tendency for the effect to be better obtained. The nitrogen adsorption specific surface area of ​​carbon black can be determined in accordance with JIS K6217-2:2001.

[0061] The amount of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, based on 100 parts by mass of the rubber component A. When the amount is within the above range, the effect tends to be better obtained.

[0062] Examples of the poorly dispersible filler include microfibrillated vegetable fibers, short fiber cellulose, gel compounds, etc. Among these, microfibrillated vegetable fibers are preferred.

[0063] As the microfibrillated plant fiber, cellulose microfibrils are preferred because they provide good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products, and examples thereof include those derived from resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, and kenaf, and pulp, paper, cloth, agricultural waste, waste biomass such as food waste and sewage sludge obtained from these as raw materials, unused biomass such as rice straw, wheat straw, and thinned wood, as well as cellulose produced by sea squirts, acetic acid bacteria, etc. These microfibrillated plant fibers may be used alone or in combination of two or more.

[0064] In this specification, cellulose microfibrils typically refer to cellulose fibers having an average fiber diameter of 10 μm or less, more typically cellulose fibers having a microstructure formed by the aggregation of cellulose molecules and an average fiber diameter of 500 nm or less. Typical cellulose microfibrils are formed, for example, as an aggregate of cellulose fibers having the above-mentioned average fiber diameter.

[0065] When the rubber composition of the present embodiment contains a poorly dispersible filler, the content of the poorly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, relative to 100 parts by mass of the rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0066] The rubber composition of the present embodiment preferably contains a softener. A softener is a material that imparts plasticity to a rubber component, and is a concept that includes both softeners that are liquid (liquid state) at room temperature (25°C) and softeners that are solid at room temperature (25°C). Examples of softeners include resin components, oils, liquid polymers, ester-based plasticizers, and the like. These softeners may be derived from petroleum, may be derived from biomass, or may be derived from naphtha recycled from rubber products or non-rubber products. In addition, low molecular weight hydrocarbon components obtained by pyrolysis and extraction of used tires or products containing various components may be used as softeners. These softeners may be used alone or in combination of two or more types. The softener also includes polyacrylic acid resin, which will be described later.

[0067] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil (mineral oil), naphthenic process oil, and aromatic process oil. Specific examples of the process oil include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include MES, TDAE, and heavy naphthenic oil. In addition, from the viewpoint of life cycle assessment, waste oil after use in rubber mixers and engines, and refined waste edible oil used in cooking restaurants may be used.

[0068] In this specification, examples of vegetable oils include linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, paulownia oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grapeseed oil, and wood wax. In addition, examples of vegetable oils include refined oils (such as salad oils) obtained by refining the above-mentioned oils, transesterified oils obtained by transesterifying the above-mentioned oils, hardened oils obtained by hydrogenating the above-mentioned oils, thermally polymerized oils obtained by thermally polymerizing the above-mentioned oils, oxidatively polymerized oils obtained by oxidizing the above-mentioned oils, and waste edible oils obtained by recovering oils that have been used as edible oils or the like. The vegetable oils may be liquid or solid at room temperature (25° C.). These vegetable oils may be used alone or in combination of two or more.

[0069] The vegetable oil according to the present embodiment preferably contains acylglycerol, and more preferably contains triacylglycerol. In this specification, acylglycerol refers to a compound in which a hydroxyl group of glycerin and a fatty acid are ester-bonded. The acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol, or triacylglycerol. Furthermore, the acylglycerol may be a monomer, a dimer, or a polymer of trimer or more. Incidentally, dimer or more acylglycerols can be obtained by thermal polymerization, oxidative polymerization, or the like. Moreover, the acylglycerol may be liquid or solid at room temperature (25°C).

[0070] The method for confirming whether the rubber composition contains the acylglycerol is not particularly limited, but may be any of the following methods: 1 For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at room temperature (25°C) for 24 hours, and after removing the rubber composition, 1 When H-NMR was measured, signals were observed at around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm when the signal of tetramethylsilane (TMS) was set at 0.00 ppm, and the signals were presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to oxygen atoms of ester groups. Note that "around" in this paragraph refers to a range of ±0.10 ppm.

[0071] The fatty acid is not particularly limited, and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid. Examples of the saturated fatty acid include butyric acid and lauric acid.

[0072] Among them, the fatty acid is preferably a fatty acid with few double bonds, i.e., a saturated fatty acid or a monounsaturated fatty acid, and oleic acid is preferable. As the vegetable oil containing such a fatty acid, for example, a vegetable oil containing a saturated fatty acid or a monounsaturated fatty acid may be used, or a vegetable oil modified by ester exchange or the like may be used. In addition, in order to produce a vegetable oil containing such a fatty acid, a plant may be improved by breeding, genetic recombination, genome editing, or the like.

[0073] As the vegetable oil, for example, commercially available oils from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Fuji Kosan Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0074] The content of the oil is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, relative to 100 parts by mass of the rubber component A, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above ranges, the effect tends to be better obtained.

[0075] Examples of liquid polymers include liquid diene polymers (liquid rubber) and liquid farnesene polymers at 25°C. Examples of liquid rubbers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), and liquid styrene isoprene styrene block copolymers (liquid SIS block polymers). The ends or main chains of these may be modified with polar groups. Hydrogenated products of these may also be used. Among these, liquid BR is preferred.

[0076] The liquid diene polymer has a weight average molecular weight (Mw) of 1.0×10 based on polystyrene standards, as measured by gel permeation chromatography (GPC). 3 ~5.0×104 Preferably, it is 3.0×10 3 ~1.5×10 4 The lower or upper limit of Mw of the liquid diene polymer may be 4,500 or 8,500. In this specification, the Mw of the liquid diene-based polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0077] As the liquid diene polymer, for example, products available from Cray Valley, Sartomer, Kuraray Co., Ltd., etc. can be used.

[0078] When the rubber composition of the present embodiment contains a liquid polymer, the content of the liquid polymer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less, based on 100 parts by mass of the rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0079] As the resin component, a resin that is usually used as a tire compound can be used, and may be liquid or solid at room temperature (25°C). Examples include aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, acrylic resins, and farnesene polymers. Hydrogenated products (hydrogenated resins) of these may also be used. These may be used alone or in combination of two or more. The resin itself may also be a copolymer of monomer components of multiple origins. Among these, aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins of these are preferred, and petroleum resins are more preferred.

[0080] When a resin that is solid at room temperature is used, the softening point of the resin component is preferably 50° C. or higher, more preferably 55° C. or higher, even more preferably 60° C. or higher, and particularly preferably 85° C. or higher. Also, it is preferably 160° C. or lower, more preferably 150° C. or lower, even more preferably 140° C. or lower, and particularly preferably 100° C. or lower. Within the above range, the effect tends to be better obtained. When the resin component is liquid at room temperature, the softening point is preferably 20° C. or lower, more preferably 10° C. or lower, and even more preferably 0° C. or lower. In the case of hydrogenated resins, it is desirable for the softening point to be similar to that mentioned above. The softening point of the resin component is the temperature at which the ball drops when the softening point specified in JIS K6220-1:2001 is measured using a ring and ball softening point tester.

[0081] The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it can be a resin obtained by polymerizing α-methylstyrene and / or styrene, and specifically, it can be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, a copolymer of styrene and another monomer, etc.

[0082] Coumarone-indene resin is a resin containing coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0083] The coumarone resin is a resin that contains coumarone as the main monomer component that constitutes the skeleton (main chain) of the resin.

[0084] An indene resin is a resin that contains indene as a main monomer component that constitutes the skeleton (main chain) of the resin.

[0085] The phenolic resin may be a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural in the presence of an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

[0086] Examples of rosin resins include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0087] Examples of the petroleum resin include C5 resin, C9 resin, C5 / C9 resin, dicyclopentadiene (DCPD) resin, C9 / DCPD resin, and hydrogenated versions of these resins. Among these, C5 / C9 resin, DCPD resin, hydrogenated DCPD resin, C9 / DCPD resin, and C9 / hydrogenated DCPD resin are preferred, and C5 / C9 resin is more preferred.

[0088] Terpene resins are polymers containing terpene as a structural unit. Examples include polyterpene resins obtained by polymerizing terpene compounds, and aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. As aromatic modified terpene resins, terpene phenol resins made from terpene compounds and phenolic compounds, terpene styrene resins made from terpene compounds and styrene compounds, and terpene phenol styrene resins made from terpene compounds, phenolic compounds, and styrene compounds can also be used. Examples of terpene compounds include α-pinene and β-pinene, examples of phenolic compounds include phenol and bisphenol A, and examples of aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.). Among these, aromatic modified terpene resins are preferred.

[0089] The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, a styrene-acrylic resin having a carboxyl group and obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component, such as a styrene-acrylic resin, can be used. Among them, a solventless carboxyl group-containing styrene-acrylic resin can be preferably used.

[0090] Farnesene polymers are polymers obtained by polymerizing farnesene and have structural units based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene, which has the following structure, is preferred. [ka]

[0091] The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer). These may be used alone or in combination of two or more. Among them, a copolymer of farnesene and a vinyl monomer is preferred.

[0092] Examples of vinyl monomers include aromatic vinyl compounds such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, 5-t-butyl-2-methylstyrene, vinylethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethylether, N,N-dimethylaminoethylstyrene, N,N-dimethylaminomethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-t-butylstyrene, 3-t-butylstyrene, 4-t-butylstyrene, vinylxylene, vinylnaphthalene, vinyltoluene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylene, as well as conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among these, butadiene is preferred. That is, the farnesene-vinyl monomer copolymer is preferably a copolymer of farnesene and butadiene (farnesene-butadiene copolymer).

[0093] In the farnesene-vinyl monomer copolymer, the copolymerization ratio by mass of farnesene and vinyl monomer (farnesene / vinyl monomer) is preferably 40 / 60 to 90 / 10.

[0094] The farnesene-based polymer preferably has a weight average molecular weight (Mw) of 3000 or more and 300,000 or less. The Mw of the farnesene-based polymer is preferably 8000 or more, more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 50,000 or less. Within the above ranges, the effect tends to be more preferably obtained.

[0095] The farnesene-based polymer may be either a liquid or solid polymer at room temperature (25° C.), and is preferably a liquid farnesene-based polymer that is a liquid at room temperature (25° C.).

[0096] Examples of resin components (resin components other than polyacrylic acid resins) that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Exxon Mobil Corporation, KRATON, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

[0097] The content of the resin component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less, based on 100 parts by mass of the rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0098] From the viewpoint of sustainability, it is desirable to use a plasticizer derived from a plant, such as a plant-derived oil or a farnesene-based polymer.

[0099] The content of the plasticizer (total amount of the plasticizer) is preferably 10 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 40 parts by mass or more, relative to 100 parts by mass of the rubber component A, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. Within the above ranges, the effect tends to be better obtained.

[0100] The rubber composition of the present embodiment preferably contains an antioxidant. The antioxidant is not particularly limited, and examples thereof include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine, and the like. p-phenylenediamine-based antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine (DNPD); quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among them, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline polymers are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis, and the like.

[0101] The content of the antioxidant is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the rubber component A. When the content is within the above range, the effect tends to be better.

[0102] The rubber composition of the present embodiment preferably contains stearic acid. As the stearic acid, any known stearic acid can be used, for example, products available from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like.

[0103] The content of stearic acid is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0104] The rubber composition of the present embodiment preferably contains zinc oxide. As the zinc oxide, any known zinc oxide can be used, for example, products available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., and the like.

[0105] The content of zinc oxide is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of rubber component A. When the content is within the above range, the effect tends to be better obtained.

[0106] The rubber composition of the present embodiment may contain wax. The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used. Examples include petroleum wax, mineral wax, synthetic wax, and plant-derived wax. Among them, petroleum wax and plant-derived wax are preferred, and petroleum wax is more preferred. Examples of plant-derived wax include rice wax, carnauba wax, and candelilla wax. Examples of petroleum wax include paraffin wax, microcrystalline wax, and selected special waxes thereof, and paraffin wax is preferred. The wax according to this embodiment does not contain stearic acid. The wax can be, for example, commercially available waxes from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., Ltd., and the like. These waxes may be used alone or in combination of two or more types.

[0107] When the rubber composition of the present embodiment contains a wax, the wax content is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 4 parts by mass or less, based on 100 parts by mass of the rubber component A. When the wax content is within the above range, the effect tends to be better obtained.

[0108] The rubber composition of the present embodiment preferably contains sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0109] The amount of sulfur is preferably 0.1 parts by mass or more, more preferably 0.6 parts by mass or more, and even more preferably 1 part by mass or more, and is preferably 6 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, based on 100 parts by mass of the rubber component A. When the amount is within the above range, the effect tends to be better obtained.

[0110] The rubber composition of the present embodiment preferably contains a vulcanization accelerator. The type of vulcanization accelerator is not particularly limited, and commonly used ones can be used. Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based, guanidine-based and benzothiazole-based vulcanization accelerators are preferred.

[0111] The content of the vulcanization accelerator is preferably 1.5 parts by mass or more, more preferably 2.5 parts by mass or more, even more preferably 3.2 parts by mass or more, particularly preferably 3.6 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the rubber component A. Within the above ranges, the effect tends to be better obtained.

[0112] The rubber composition of the present embodiment contains vulcanized rubber particles. The vulcanized rubber particles can be obtained by vulcanizing an unvulcanized rubber composition and then pulverizing the vulcanized rubber composition. The method of vulcanization and pulverization is not particularly limited, and a conventional method can be used. The vulcanized rubber particles may be used alone or in combination of two or more kinds.

[0113] The above-described content of rubber component A does not include the components in the vulcanized rubber particles. In the entire rubber composition, there are domains of vulcanized rubber particles in the matrix, and rubber component A constituting the matrix does not contain rubber component B constituting the domains of the vulcanized rubber particles, and silica A constituting the matrix does not contain silica B constituting the domains of the vulcanized rubber particles.

[0114] The glass transition temperature (Tg) of the vulcanized rubber particles is preferably -35°C or higher, more preferably -33°C or higher, even more preferably -31°C or higher, particularly preferably -30°C or higher, and is preferably -5°C or lower, more preferably -15°C or lower, even more preferably -20°C or lower, particularly preferably -25°C or lower. Within the above range, the effect tends to be better obtained. This is presumably because the energy loss in the frequency range that contributes to wet grip performance increases.

[0115] The content of the vulcanized rubber particles is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 25 parts by mass or more, particularly preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less, based on 100 parts by mass of the rubber component A. Within the above ranges, the effect tends to be better obtained.

[0116] In the rubber composition of the present embodiment, the content of vulcanized rubber particles / content of silica A is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and also preferably 1.2 or less, more preferably 0.9 or less, even more preferably 0.6 or less. Within the above range, the effect tends to be better obtained. This is presumed to be because, when the amount of vulcanized rubber particles is too large relative to silica A, the reinforcing component is small and the reinforcing property during drying cannot be sufficiently maintained. In addition, when the amount of silica A is too large, a strong reinforcing network is constructed by silica A, and the softening effect of the vulcanized rubber particles does not appear as a physical property of the rubber composition. In this relationship, the content of the vulcanized rubber particles and the content of silica A are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component A.

[0117] The vulcanized rubber particles preferably contain a rubber component B. As the rubber component B, the same rubber as the rubber component A can be used, and the preferred forms are also the same.

[0118] The rubber component B preferably contains a diene rubber having a polar functional group.

[0119] The rubber component B may contain a modified rubber (a diene-based rubber having a polar functional group) and a non-modified rubber. The content of the modified rubber in 100% by mass of the rubber component B is preferably 30% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more. The upper limit is not particularly limited, and may be 100% by mass. The content of the unmodified rubber in 100% by mass of the rubber component B is preferably 70% by mass or less, more preferably 40% by mass or less, further preferably 20% by mass or less, and particularly preferably 10% by mass or less. The lower limit is not particularly limited, and may be 0% by mass.

[0120] When the vulcanized rubber particles contain isoprene-based rubber, the content of the isoprene-based rubber in 100% by mass of rubber component B is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0121] When the vulcanized rubber particles contain BR, the content of BR in 100% by mass of rubber component B is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0122] In the vulcanized rubber particles, the content of SBR in 100% by mass of rubber component B is preferably 30% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The upper limit is not particularly limited and may be 100% by mass. Within the above range, the effect tends to be better obtained.

[0123] The vulcanized rubber particles preferably contain silica B. As the silica B, the same one as the silica A can be used, and the preferred forms are also the same.

[0124] In the vulcanized rubber particles, the content of silica B is preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less. Within the above range, the effect tends to be better obtained.

[0125] The vulcanized rubber particles preferably contain a polyacrylic acid resin. The polyacrylic acid resin is a polymer containing acrylic acid as a constituent monomer. It is usually a homopolymer of acrylic acid, but may contain other monomers as long as the effect of the present embodiment is not impaired. It may be either a crosslinked or non-crosslinked type, but is preferably a crosslinked type. It may be either a liquid or a solid at room temperature (25°C). As a commercially available product, products from Toagosei Co., Ltd., Fujifilm Wako Pure Chemical Co., Ltd., etc. can be used.

[0126] In the vulcanized rubber particles, the content of the polyacrylic acid resin is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0127] In the vulcanized rubber particles, the content of polyacrylic acid resin / the content of silica B is preferably 0.2 or more, more preferably 0.4 or more, even more preferably 0.6 or more, and is preferably 1.5 or less, more preferably 1.2 or less, even more preferably 0.9 or less. Within the above range, the effect tends to be better obtained. This is presumably because polyacrylic acid is a water-absorbing resin, and a certain amount is required to fully exert the softening effect when wet with water. In this relationship, the content of the polyacrylic acid resin and the content of the silica B are the contents relative to 100 parts by mass of the rubber component B (unit: parts by mass).

[0128] The vulcanized rubber particles may contain the materials described in the rubber composition of this embodiment, such as a silane coupling agent. The preferred forms of these materials are the same as those described in the rubber composition of this embodiment.

[0129] In the vulcanized rubber particles, the content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, based on 100 parts by mass of silica B. When the content is within the above range, the effect tends to be better obtained.

[0130] When the vulcanized rubber particles contain carbon black, the content of carbon black is preferably 2 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0131] When the vulcanized rubber particles contain a poorly dispersible filler, the content of the poorly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0132] When the vulcanized rubber particles contain oil, the content of the oil is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0133] When the vulcanized rubber particles contain a liquid polymer, the content of the liquid polymer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0134] When the vulcanized rubber particles contain a resin (a resin other than a polyacrylic acid resin), the content thereof is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0135] When the vulcanized rubber particles contain a plasticizer, the content of the plasticizer (total amount of the plasticizer) is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0136] When the vulcanized rubber particles contain an antioxidant, the content of the antioxidant is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 6 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better.

[0137] When the vulcanized rubber particles contain stearic acid, the content of stearic acid is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 6 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0138] When the vulcanized rubber particles contain zinc oxide, the content of zinc oxide is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 4 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0139] When the vulcanized rubber particles contain wax, the content of the wax is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 4 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0140] When the vulcanized rubber particles contain sulfur, the content of sulfur is preferably 0.1 parts by mass or more, more preferably 0.6 parts by mass or more, and even more preferably 1 part by mass or more, and is preferably 6 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better obtained.

[0141] When the vulcanized rubber particles contain a vulcanization accelerator, the content of the vulcanization accelerator is preferably 1.5 parts by mass or more, more preferably 2.5 parts by mass or more, even more preferably 3.2 parts by mass or more, particularly preferably 3.6 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component B. When the content is within the above range, the effect tends to be better.

[0142] In addition to the above components, the rubber composition of the present embodiment and the vulcanized rubber particles contained in the rubber composition of the present embodiment may appropriately contain compounding agents that are generally used in the tire industry, such as materials such as a release agent.

[0143] In this specification, various materials containing carbon atoms (e.g., rubber, oil, resin, vulcanization accelerator, antioxidant, surfactant, etc.) may be derived from carbon dioxide in the atmosphere. As a method for obtaining the compound of this embodiment from carbon dioxide, carbon dioxide may be directly converted, or methane obtained through a methanation process for synthesizing methane from carbon dioxide may be converted.

[0144] The rubber composition of this embodiment and the vulcanized rubber particles contained in the rubber composition of this embodiment can be produced, for example, by a method in which the above-mentioned components are kneaded using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanized.

[0145] As for the kneading conditions, in the base kneading step in which additives other than the vulcanizing agent (sulfur) and the vulcanization accelerator are kneaded, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish kneading step in which the vulcanizing agent and the vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 80 to 115°C, more preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and the vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

[0146] The rubber composition of the present embodiment can be used for tire components (as a rubber composition for tires) such as treads, sidewalls, undertreads, shoulders, clinches, bead apex, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and the like, and side reinforcing layers of run-flat tires. In particular, it is suitable for treads. In addition, when the tread has a multi-layer structure, it can be used for both the surface layer (cap tread) and the inner layer (base tread), but is particularly suitable for the cap tread.

[0147] The tire of the present embodiment uses the rubber composition of the present embodiment as a tire component, and in particular, a tire using the rubber composition as a tread is preferable.

[0148] The tire of the present embodiment may be a pneumatic tire or a non-pneumatic tire, among which a pneumatic tire is preferred. In particular, the tire can be suitably used as a summer tire (summer tire), a winter tire (studless tire, snow tire, studded tire, etc.), or an all-season tire. The tire can be used as a passenger car tire, a large passenger car tire, a large SUV tire, a heavy load tire such as a truck or a bus, a light truck tire, a two-wheeled vehicle tire, or a racing tire (high performance tire). In particular, the tire is preferably used as a passenger car tire.

[0149] A tire is manufactured by a normal method using the above rubber composition. For example, a rubber composition containing various materials is extruded in an unvulcanized state to match the shape of a tread, and molded together with other tire components in a tire building machine by a normal method to form an unvulcanized tire, which is then heated and pressurized in a vulcanizer to manufacture a tire.

[0150] In the tire of this embodiment, the thickness G (mm) of the member constituting the tread on the equatorial plane of the tire radial cross section is preferably 15.0 mm or less, more preferably 10.0 mm or less, even more preferably 9.0 mm or less, and particularly preferably 8.0 mm or less. The lower limit is preferably 5.0 mm or more, more preferably 5.5 mm or more, even more preferably 6.0 mm or more, and particularly preferably 6.5 mm or more. Within the above range, the effect tends to be better obtained.

[0151] The thickness G of the component constituting the tread, which is made of the rubber composition of this embodiment, on the equatorial plane of the tire radial cross section is the thickness of the component on the equatorial plane in a cross section cut along a plane including the tire axis.

[0152] The tire of the present embodiment is a tire having a thickness G (mm) on the equatorial plane of the tire radial cross section of the member constituting the tread × domain hardness (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 ) is preferably 9 or less, more preferably 8 or less, and even more preferably 7 or less, and is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more. When it is within the above range, the effect tends to be better obtained.

[0153] In the tire of this embodiment, the thickness G (mm) is a value measured in a normal state. The "normal state" refers to a state in which the tire is mounted on a normal rim, inflated to a normal internal pressure, and no load is applied. Here, the "normal rim" refers to a rim that is determined for each tire by a standard system including the standard on which the tire is based, such as the standard rim for the applicable size described in the "JATMA YEAR BOOK" for JATMA (Japan Automobile Tire Manufacturers Association), the "Measuring Rim" described in the "STANDARDS MANUAL" for ETRTO (The European Tyre and Rim Technical Organisation), and the "Design Rim" described in the "YEAR BOOK" for TRA (The Tire and Rim Association, Inc.), and the order of reference is JATMA, ETRTO, and TRA, and if there is an applicable size at the time of reference, the standard is followed. In the case of a tire not specified in the standard, it refers to the rim that can be assembled to a rim and can hold internal pressure, that is, the rim with the smallest rim diameter and the next narrowest rim width among the rims that do not leak air from between the rim and the tire. In addition, "normal internal pressure" refers to the air pressure specified for each tire by each standard in the standard system including the standard on which the tire is based, and refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for JATMA, "maximum air pressure" for ETRTO, and "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and refers to JATMA, ETRTO, and TRA in that order, and follows the standard if there is an applicable size at the time of reference. In the case of a tire not specified in the standard, it refers to the normal internal pressure (250KPa or more) of another tire size (defined in the standard) that is listed with the normal rim as the standard rim. In addition, if multiple normal internal pressures of 250KPa or more are listed, it refers to the minimum value among them. EXAMPLES

[0154] In the following, examples (embodiments) that are considered to be preferable for carrying out the present invention will be shown, but the scope of the present invention is not limited to the examples.

[0155] The various chemicals used in the examples are described below. If necessary, the chemicals are purified according to standard methods.

[0156] <Drugs in Table 1> SBR: SBL0545 (carboxyl-modified SBR, Tg: -30°C) manufactured by ENEOS Materials Co., Ltd. Polyacrylic acid resin: Junron PW-120 (cross-linked type) manufactured by Toagosei Co., Ltd. Silica: Ultrasil VN3 (N2SA: 175m) manufactured by Evonik Degussa 2 / g) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. Liquid polybutadiene: Cray Valley RICON131MA10 (liquid BR) Sulfur: 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (soluble sulfur containing 5% oil by mass) Vulcanization accelerator 1: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0157] <Drugs in Table 2> SBR: SBL0545 (carboxyl-modified SBR, Tg: -30°C) manufactured by ENEOS Materials Co., Ltd. BR: BR150B manufactured by Ube Industries, Ltd. (vinyl content: 1% by mass, cis content: 97% by mass) NR:TSR20 Silica: Ultrasil VN3 (N2SA: 175m) manufactured by Evonik Degussa 2 / g) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa Carbon black: Show Black N220 (N2SA:111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. C5 / C9 resin: Petrotac 100V manufactured by Tosoh Corporation Anti-aging agent: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (soluble sulfur containing 5% oil by mass) Vulcanization accelerator 1: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanized rubber particles 1 to 6: Made as follows

[0158] <Preparation of vulcanized rubber particles> According to the compounding recipe shown in Table 1, chemicals other than sulfur and vulcanization accelerator are kneaded for 4 minutes at 160°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Sulfur and vulcanization accelerator are added to the kneaded product, and the product is kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is press-vulcanized at 170°C for 20 minutes to obtain a vulcanized rubber composition. The vulcanized rubber composition is pulverized using a freezing pulverizer to obtain vulcanized rubber particles.

[0159] [Table 1]

[0160] <Examples and Comparative Examples> According to the compounding recipe shown in Table 2, chemicals other than sulfur and vulcanization accelerator are kneaded for 4 minutes at 160°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Sulfur and vulcanization accelerator are added to the kneaded product, and the product is kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is press-vulcanized at 170°C for 20 minutes to obtain a vulcanized rubber composition. A 10 mm thick member is prepared using the unvulcanized rubber composition and applied to the tread to produce a tire. In Examples 1 to 3 and Comparative Examples 2 to 4, which contain vulcanized rubber particles, domains composed of vulcanized rubber particles exist in a matrix composed of rubber component A. This can be confirmed from the shade of color when osmium-stained samples are observed with an SEM.

[0161] The vulcanized rubber composition was evaluated as follows.

[0162] <Average domain diameter> The vulcanized rubber composition stained with osmium is observed under a SEM, and the equivalent circle diameter of the domains is calculated. The average of the equivalent circle diameters of 50 points is taken as the average diameter of the domains.

[0163] <Hardness test> A hardness measurement sample measuring 40 mm in length, 3 mm in width, and 0.5 mm in thickness is taken from the vulcanized rubber composition, and the domain and matrix hardness (Martens hardness) of the obtained measurement sample is measured using a nanoindenter (PICODENTOR HM-500, manufactured by Fisher Instruments, Inc.). Specifically, the positions of the domain and matrix are confirmed using a microscope attached to the device, and a diamond indenter is brought into contact with the measurement point (estimated contact range: 35 μm) and pressed to a depth of approximately 6 μm, and the surface area A (μm 2 ) and divide it by the test load F, i.e., F / A is the Martens hardness (kgf / mm 2 The compression conditions are: at 30°C, a load of 0 to 100 mgh is applied for 2 seconds, held for 1 second, and then the load is removed from 100 to 0 mgh for 2 seconds. Two samples are prepared for each compound. For each sample, the domain and matrix are measured at 10 points and the average values ​​are calculated.

[0164] <Viscoelasticity test> A viscoelasticity measurement sample of 40 mm length × 3 mm width × 0.5 mm thickness is taken from the vulcanized rubber composition. E* and tan δ of the obtained viscoelasticity measurement sample are measured using an Iplexer manufactured by GABO under the conditions of temperature 30°C, initial strain 10%, dynamic strain 1%, frequency 10 Hz, elongation mode, and measurement time 30 minutes, and the measured value is obtained 30 minutes after the start of the measurement.

[0165] <Dry hardness and E*> The above hardness measurement sample and the above viscoelasticity measurement sample are subjected to a drying treatment, and then the Martens hardness and E* are measured. Drying treatment: Leave the sample at rest for 24 hours at an atmospheric temperature of 30°C, a relative humidity of 30%, and 1 atmosphere, then leave the sample at rest for 1 hour at an atmospheric temperature of 120°C, a relative humidity of 30%, and 1 atmosphere.

[0166] <Hardness when wet with water, E* and tan δ> The hardness measurement sample and the viscoelasticity measurement sample are subjected to a wetting treatment, and then the Martens hardness, E* and tan δ are measured. Wetting treatment: The sample after drying treatment is immersed in water in a water tank whose temperature is adjusted to 60°C. The water tank is left under an atmosphere of 1 atmosphere. After immersing the sample for 24 hours, the water on the surface of the sample is wiped off.

[0167] <Hardness ratio when dry> It is calculated using the following formula. A larger value indicates a higher hardness of the domain when dry. Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 )

[0168] <Hardness ratio when wet> It is calculated by the following formula: The smaller the value, the smaller the hardness of the domain when wetted with water, that is, the more the domain is softened when wetted with water. Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )

[0169] <Wet Index> The tan δ of each formulation when wetted with water is expressed as an index, with the tan δ of Comparative Example 1 when wetted with water being set at 100. A larger value indicates a larger tan δ (energy loss) and better wet grip performance.

[0170] In addition, since the vulcanized rubber composition of this embodiment is capable of undergoing reversible changes in physical properties when dry and when wetted with water, when it is re-dried (after wetting treatment, the same drying treatment as before is performed again), it will have the same E* (or within ±1%) as when it was dry, and when it is re-wetted with water (after re-drying treatment, the same wetting treatment as before is performed again), it will have the same E* (or within ±1%) as when it was wetted with water.

[0171] [Table 2]

[0172] The present invention (1) contains a rubber component A and vulcanized rubber particles, A domain constituted by the vulcanized rubber particles is present in a matrix constituted by the rubber component A, The average diameter of the domains is 50 μm or more, The rubber composition satisfies the following formula: Domain hardness when dry (kgf / mm 2 ) / Matrix hardness when dry (kgf / mm 2 ) ≧ 1.1 Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )≦0.98

[0173] The present invention (2) comprises silica A in the matrix, In the rubber composition according to the present invention (1), the ratio of the content of the vulcanized rubber particles to the content of the silica A is 1.2 or less.

[0174] The present invention (3) is characterized in that the vulcanized rubber particles contain a rubber component B, In the rubber composition according to the present invention (1) or (2), the rubber component B contains a diene rubber having a polar functional group.

[0175] The present invention (4) is the rubber composition according to any one of the present inventions (1) to (3), wherein the vulcanized rubber particles contain silica B, and the content of the silica B in the vulcanized rubber particles is 5 mass % or more.

[0176] The present invention (5) is the rubber composition according to any one of the present inventions (1) to (4), which satisfies the following formula: Domain hardness when wetted with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 )≦0.90

[0177] The present invention (6) is a rubber composition according to any one of the present inventions (1) to (5), which is capable of undergoing reversible changes in physical properties when dry and when wet with water.

[0178] The present invention (7) is a tire using a member made of the rubber composition according to any one of the present inventions (1) to (6) in the tread.

[0179] The present invention (8) is the tire according to the present invention (7), wherein the thickness G of the member on the equatorial plane of a radial cross section of the tire is 10 mm or less.

[0180] The present invention (9) is a method for determining the thickness G (mm) of the member on the equatorial plane of the tire radial cross section × the hardness of the domain when wet with water (kgf / mm 2 ) / Matrix hardness when wetted with water (kgf / mm 2 ) is 9 or less.

Claims

1. Contains rubber component A and vulcanized rubber particles, A domain constituted by the vulcanized rubber particles is present in a matrix constituted by the rubber component A, The average diameter of the domain is 50 μm or more, A rubber composition that satisfies the following formula: Hardness of domain when dry (kgf / mm ２ ) / Dry matrix hardness (kgf / mm ２ ) ≧1.1 Domain hardness when wetted with water (kgf / mm ２ ) / Matrix hardness when wetted with water (kgf / mm ２ )≦0.98

2. Silica A is contained in the matrix, 2. The rubber composition according to claim 1, wherein the ratio of the content of said vulcanized rubber particles to the content of said silica A is 1.2 or less.

3. The vulcanized rubber particles contain a rubber component B, 3. The rubber composition according to claim 1, wherein the rubber component B comprises a diene rubber having a polar functional group.

4. The vulcanized rubber particles contain silica B, 3. The rubber composition according to claim 1, wherein the content of said silica B in said vulcanized rubber particles is 5% by mass or more.

5. The rubber composition according to claim 1 or 2, which satisfies the following formula: Domain hardness when wetted with water (kgf / mm ２ ) / Matrix hardness when wetted with water (kgf / mm ２ )≦0.90

6. 3. The rubber composition according to claim 1, which is capable of undergoing reversible changes in physical properties between when dry and when wet with water.

7. A tire having a tread member made of the rubber composition according to claim 1 or 2.

8. 8. The tire according to claim 7, wherein a thickness G of the member on the equatorial plane of a cross section in the radial direction of the tire is 10 mm or less.

9. Thickness G (mm) of the member on the equatorial plane of the tire radial cross section × domain hardness when wet with water (kgf / mm ２ ) / Matrix hardness when wetted with water (kgf / mm ２ 8. The tire according to claim 7, wherein the ratio of the axial length of the tire to the radial length of the tire is 9 or less.

Images