Rubber composition and tire

Abstract

The present invention provides a rubber composition and a tire with which it is possible to improve wet grip performance. The present invention is a rubber composition containing a rubber component A and vulcanized rubber particles. 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 following formulas are satisfied. Hardness of domains when dry (kgf / mm2) / hardness of matrix when dry (kgf / mm2) ≥ 1.1 Hardness of domains when wet by water (kgf / mm2) / hardness of matrix when wet by water (kgf / mm2) ≤ 0.98

Description

Rubber composition and tire

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

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

[0003] Special Publication No. 2013-544936

[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.

[0005] The present invention relates to a rubber composition containing a rubber component A and vulcanized rubber particles, wherein domains composed of the vulcanized rubber particles exist in a matrix composed of the rubber component A, the average diameter of the domains is 50 μm or more, and the following formula is satisfied: ２ ) / Dry matrix hardness (kgf / mm ２ ) ≧1.1 Hardness of domain when wetted with water (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２ )≦0.98

[0006] The present invention provides a rubber composition that contains a rubber component A and vulcanized rubber particles, in which domains composed of the vulcanized rubber particles exist 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 enabling improvement in wet grip performance.

[0007] The present embodiment is a rubber composition containing a rubber component A and vulcanized rubber particles, in which domains composed of the vulcanized rubber particles exist 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: dry domain hardness (kgf / mm ２ ) / Dry matrix hardness (kgf / mm ２ ) ≧1.1 Hardness of domain when wetted with water (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２ )≦0.98

[0008] The reason why the rubber composition of this embodiment achieves the above-mentioned effects is presumed to be as follows: When the average domain diameter is within the above range, energy loss in the frequency range that contributes to wet grip performance is likely to occur. Furthermore, when the domain hardness and matrix hardness in the dry state satisfy the above formula, domain-derived energy loss is unlikely to occur in the dry state, and when the domain hardness and matrix hardness in the wet state satisfy the above formula, domain-derived energy loss is likely to occur in the wet state. It is believed that these actions significantly improve 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, i.e., a sea-island structure is formed in which rubber component A forms the sea and vulcanized rubber particles form the islands. The matrix preferably contains a component other than the vulcanized rubber particles (e.g., silica A) in addition to rubber component A. The rubber composition in this state is formed by kneading rubber component A and vulcanized rubber particles under normal conditions. The existence of 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 domain diameter may be 50 μm or more, preferably 80 μm or more, more preferably 95 μm or more, even more preferably 98 μm or more, even more preferably 99 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 range, the effect tends to be better. Furthermore, from the viewpoint of abrasion resistance, it is preferably 99 μm or less, more preferably 98 μm or less, and even more preferably 95 μm or less. The average domain diameter is measured by the method described in the Examples below.

[0011] The rubber composition of the present embodiment satisfies the following formula. The formula 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) / Dry matrix hardness (kgf / mm ２ ) ≧1.1 Hardness of domain when wetted with water (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２ )≦0.98 Note that "dry" refers to a state after the following drying treatment has been carried out, and "water-wet" refers to a state after the following wetting treatment has been carried out. Drying treatment: The sample is left to stand for 24 hours under an ambient temperature of 30°C, a relative humidity of 30%, and 1 atmosphere. Thereafter, the sample is left to stand for 1 hour under an ambient temperature of 120°C, a relative humidity of 30%, and 1 atmosphere. Wetting treatment: The sample after the drying treatment is immersed in water in a water tank whose temperature has been adjusted to 60°C. The water tank is left to stand under an atmosphere of 1 atmosphere. After the sample has been immersed for 24 hours, the water on the surface of the sample is wiped off.

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

[0013] Hardness of the domain when dry (kgf / mm ２ ) / Dry matrix hardness (kgf / mm ２ ) is preferably 1.2 or more, more preferably 1.6 or more, even more preferably 1.8 or more, and is preferably 30 or less, more preferably 20 or less, even more preferably 10 or less, still more preferably 2.6 or less, and even more preferably 2.4 or less. From the viewpoint of abrasion resistance, it is preferably 1.8 or less, more preferably 1.6 or less, and even more preferably 1.2 or less. From the viewpoint of abrasion resistance, it is preferably 2.4 or more, and more preferably 2.6 or more. The hardness of the domain when wetted with water (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２) is preferably 0.92 or less, more preferably 0.90 or less, even more preferably 0.89 or less, still more preferably 0.80 or less, and still more preferably 0.67 or less, and is preferably 0.10 or more, more preferably 0.30 or more, and still more preferably 0.50 or more. From the viewpoint of abrasion resistance, it is preferably 0.67 or more, more preferably 0.80 or more, even more preferably 0.89 or more, even more preferably 0.90 or more, and even more preferably 0.92 or more. When it is within the above range, the effect tends to be better obtained.

[0014] The hardness of the domain when dry may be adjusted as appropriate within the range that satisfies the above relationship, but is preferably 10 kgf / mm ２ More preferably, 15 kgf / mm ２ More preferably, 20 kgf / mm ２ or more, and preferably 50 kgf / mm ２ Less than or equal to 40 kgf / mm ２ More preferably, 35 kgf / mm ２ The hardness of the domain when wetted with water may be adjusted as appropriate within the range that satisfies the above relationship, but is preferably 1 kgf / mm ２ More preferably, 5 kgf / mm ２ More preferably, 8 kgf / mm ２ or more, and preferably 30 kgf / mm ２ Less than 20 kgf / mm, more preferably ２ More preferably, 15 kgf / mm ２ Within the above range, the effect tends to be better.

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

[0016] The object of the present application is to improve wet grip performance, and the above formula for hardness is one of the means for achieving this. In this specification, hardness is a value obtained by performing a hardness test in the Examples described below 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 more favorable. In this specification, the weight average molecular weight (Mw) can be determined in terms of standard polystyrene based on measurements obtained using a gel permeation chromatograph (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 preferably -10°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower, and particularly preferably -35°C or lower. Within the above range, the effect tends to be better. This is presumably because the energy loss in the frequency range that contributes to wet grip performance increases. From the viewpoint of abrasion resistance, the glass transition temperature is preferably -35°C or higher, more preferably -30°C or higher, even more preferably -20°C or higher, and even more preferably -10°C or higher. On the other hand, the glass transition temperature is preferably 10°C or lower, more preferably 5°C or lower, and even more preferably 0°C or lower. 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 Co., Ltd. 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 polar functional groups at terminals) in which at least one terminal of the rubber has been modified with a compound (modifier) ​​having a polar functional group, main chain modified rubbers having polar functional groups in the main chain, main chain terminal modified rubbers having polar functional groups in the main chain and at terminals (for example, main chain terminal modified rubbers having polar functional groups in the main chain and at least one terminal 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 hydroxyl groups or epoxy groups 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. Using these polar functional groups tends to produce better effects. This is presumably because the introduction of the polar functional groups results in a small change in the pH of the raw material (rubber), making side reactions less likely to occur during introduction.

[0022] Examples of 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). Other examples include polymers such as butyl rubber and fluororubber. 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, or the like may also be used. Among these, isoprene rubber, BR, and SBR are preferred.

[0023] Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. NR can be, for example, SIR20, RSS#3, TSR20, or other rubber industry-standard rubber. IR is not particularly limited, and can be, for example, IR2200, or other rubber industry-standard rubber. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber, etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

[0024] The BR is not particularly limited, and examples thereof 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. Of these, 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 content of BR means the cis content of the BR when there is one type of BR, and means the average cis content 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 of Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used.

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

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

[0030] The styrene content of the SBR means the styrene content of the SBR when there is one type of SBR, and means the average styrene content when there are multiple types of SBR. The average styrene content of the SBR can be calculated by {Σ(content of each SBR × styrene content 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 content of 40% by mass and 5% by mass of SBR with a styrene content of 25% by mass, the average styrene content 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 effects tend to be more favorably obtained. In this specification, the vinyl content (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 butadiene parts in the SBR is taken as 100 (unit: mass %), and is calculated as follows: 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 of SBR, 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 [mass %] of each SBR) × vinyl content [mass %] of each SBR} / Σ{content of each SBR × (100 [mass %] - styrene content [mass %] of each SBR)}. For example, when 100 parts by mass of the rubber component contains 75 parts by mass of SBR with a styrene content of 40% by mass and a vinyl content of 30% by mass, and 25 parts by mass of vinyl, the average vinyl content is 100 parts by mass. In the case where the vinyl content is 15 parts by mass of SBR with a vinyl content of 20% by mass and the remaining 10 parts by mass is a component other than SBR, the average vinyl content of the SBR is 28% by mass (= {75 × (100 [% by mass] - 40 [% by mass]) × 30 [% by mass] + 15 × (100 [% by mass] - 25 [% by mass]) × 20 [% by mass])} / {75 × (100 [% by mass] - 40 [% by mass]) + 15 × (100 [% by mass] - 25 [% by mass])}).

[0033] As the SBR, a 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, Nippon Zeon Co., Ltd., etc. can be used. SBR synthesized by a known method can also be used.

[0035] The raw materials (monomers) for 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 examples thereof include recycled butadiene and recycled aromatic vinyl. Examples of butadienes include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyls include, but are not particularly limited to, styrene. Among these, it is preferable to use recycled butadiene (recycled butadiene) and / or recycled styrene (recycled styrene) as raw materials.

[0036] The method for producing the recycled monomer is not particularly limited, and examples thereof include synthesis from recycled naphtha obtained by decomposing rubber products such as tires. The method for producing 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 materials (monomers) of synthetic rubbers such as SBR and BR may be derived from biomass. Examples of biomass-derived monomers (biomass monomers) include, but are not limited to, biomass-derived butadiene and biomass-derived aromatic vinyl. Examples of butadienes include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyl include, but are not limited to, styrene. Furthermore, methods for producing biomass monomers are not particularly limited, and include, for example, biological and / or chemical and / or physical conversion of animals and plants. A typical example of biological conversion is fermentation using microorganisms, while examples of chemical and physical conversion include catalytic, high-temperature, high-pressure, electromagnetic, and critical fluid conversion, as well as combinations thereof. Biomass sources for these monomers include sugar, wood, plant residues after useful components have been extracted, plant-derived ethanol, and biomass naphtha.

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

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

[0040] pMC is the modern standard reference １４ of sample with respect to C concentration １４ This value is used as an index showing the biomass ratio of the compound (rubber). The significance of this value will be described below.

[0041] 1 mole of carbon atoms (6.02 x 10 ２３ ) contains approximately 6.02 × 10 atoms, which is about one trillionth of the number of ordinary carbon atoms. １１ pieces １４ C exists. １４ C is called a radioactive isotope, and its half-life is 5,730 years, and it decreases regularly. It takes 226,000 years for all of it 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 it was first fixed. １４ All C elements have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas contain １４ Therefore, chemical substances produced using these fossil fuels as raw materials also contain no C element. １４ The element C is not contained at all.

[0042] on the other hand, １４C is produced continuously by nuclear reactions in the atmosphere caused by cosmic rays, and this balances with the decrease due to radioactive decay. In the Earth's atmospheric environment, １４ Therefore, the amount of C in the biomass resources currently circulating in the environment is １４ As mentioned above, the C concentration is about 1 × 10 －１２ Therefore, the difference between these values ​​can be used 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 C concentration is the carbon circulating in nature as of 1950. １４ The specific radioactivity of carbon in this oxalic acid (carbon specific activity per gram of carbon) is used as the standard material. １４ C radioactivity intensity) for each carbon isotope, １３ The standard value is the value corrected for decay from 1950 to the measurement date. １４ The ratio of this value to the value of the actually measured 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 fossil fuels such as petroleum, １４When the C concentration is measured, it will be approximately 0 pMC (for example, 0.3 pMC), which corresponds to the biomass ratio of 0% mentioned above.

[0045] From the above, 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, 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 more favorably obtained. From the viewpoint of abrasion resistance, the content is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. On the other hand, the content is preferably 1% by mass or more, and more preferably 3% by mass or more.

[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, 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 more favorably obtained. From the viewpoint of abrasion resistance, the content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 5% by mass or less. On the other hand, the content is preferably 1% by mass or more, and more preferably 3% by mass or more.

[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 more favorably obtained. From the viewpoint of abrasion resistance, the content is preferably 65% ​​by mass or less, more preferably 55% by mass or less, even more preferably 45% by mass or less, and even more preferably 30% by mass or less. On the other hand, the content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more.

[0049] The rubber composition of this embodiment preferably contains silica A. Silica A is not particularly limited, and can be, for example, silica prepared by a dry process (anhydrous silica), silica prepared by a wet process (hydrated silica), or other silica commonly used in the tire industry. The raw material for 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 derived from a biomass material such as rice husk), or silica recycled from a silica-containing product. Among these, hydrated silica prepared by a wet process is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

[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] Silica recycled from silica-containing products can be, for example, silica recovered from products containing silica, such as electronic components such as semiconductors, tires, desiccants, and filtering materials such as diatomaceous earth. The recovery method is not particularly limited, and examples include thermal decomposition and decomposition by electromagnetic waves. Among these, silica recovered from electronic components such as semiconductors or tires is preferred.

[0052] When silica crystallizes, it becomes insoluble in water, and its component, silicic acid, cannot be utilized. By controlling the combustion temperature and duration, it is possible to suppress the crystallization of silica in rice husk ash (see, for example, JP 2009-2594 A and Akita Prefectural University Web Journal B / 2019, vol. 6, pp. 216-222).

[0053] Amorphous silica extracted from rice husks may be commercially available from Wilmar Co., Inc., etc.

[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, relative to 100 parts by mass of rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained. From the viewpoint of abrasion resistance, the content is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 30 parts by mass or less. On the other hand, the content is preferably 10 parts by mass or more, and more preferably 20 parts by mass or more.

[0055] The nitrogen adsorption specific surface area of ​​silica A (N ２ SA) is preferably 50 m ２ / g or more, more preferably 100m ２ / g or more, more preferably 150m ２ / g or more, and even more preferably 170m ２ / g or more, and even more preferably 175m 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, the effect tends to be more favorable. ２ SA 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 compounds include sulfide-based compounds such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane and Momentive's NXT and NXT-Z; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products that can be used include those manufactured by Degussa, Momentive, Shin-Etsu Silicones Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., 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, and even more preferably 8 parts by mass or more, relative to 100 parts by mass of silica A, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. Within the above range, the effect tends to be more favorable.

[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, and mica, biochar, and poorly dispersible fillers. Of these, carbon black is preferred from the viewpoint of obtaining better effects.

[0059] The 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 for carbon black may be a biomass material such as lignin or vegetable oil, or pyrolysis oil obtained by pyrolysis of waste tires. Furthermore, carbon black may be produced by combustion, such as in a furnace process, by hydrothermal carbonization (HTC), or by pyrolysis of methane, such as in a thermal black process. Commercially available products include those 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.

[0060] The nitrogen adsorption specific surface area of ​​carbon black (N ２ SA) is preferably 5 m ２ / g or more, more preferably 50m ２ / g or more, more preferably 90m ２ / g or more, and even more preferably 110m ２ / g or more, and even more preferably 111m ２ / g or more, and preferably 200m２ / g or less, more preferably 150m ２ / g or less, more preferably 130m ２ / g or less. Within the above range, the effect tends to be more favorable. The nitrogen adsorption specific surface area of ​​carbon black is determined in accordance with JIS K6217-2:2001.

[0061] The carbon black content 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, relative to 100 parts by mass of the rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained. From the viewpoint of abrasion resistance, the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less. On the other hand, the content is preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more.

[0062] Examples of the hardly dispersible filler include microfibrillated plant fibers, short fiber cellulose, gel compounds, etc. Among these, microfibrillated plant 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 include those derived from resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, and kenaf, as well as pulp, paper, and cloth obtained from these raw materials, waste biomass such as agricultural waste, food waste, and sewage sludge, unused biomass such as rice straw, wheat straw, and thinned wood, as well as cellulose produced by sea squirts, acetic acid bacteria, and the like. 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 hardly-dispersible filler, the content of the hardly-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, still 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, better effects tend to be obtained.

[0066] The rubber composition of this embodiment preferably contains a softener. A softener is a material that imparts plasticity to a rubber component, and the concept encompasses 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, and ester-based plasticizers. These softeners may be derived from petroleum, biomass, or naphtha recycled from rubber or non-rubber products. Low-molecular-weight hydrocarbon components obtained by pyrolysis and extraction of used tires or products containing various components may also be used as softeners. These softeners may be used alone or in combination of two or more. Polyacrylic acid resins, described below, are also included in the softener category.

[0067] Examples of oils include process oil, vegetable oil, and animal oil. Examples of process oils include paraffinic process oil (mineral oil), naphthenic process oil, and aromatic process oil. Specific examples of process oils include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). Furthermore, as an environmental measure, process oils with a low content of polycyclic aromatic compound (PCA) compounds can also be used. Examples of the low PCA content process oil include MES, TDAE, heavy naphthenic oil, etc. From the viewpoint of life cycle assessment, waste oil used in rubber mixers or engines, or refined waste cooking oil used in restaurants may also 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, tung 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 Japan wax. Further examples of vegetable oils include refined oils (such as salad oil) obtained by refining the above-mentioned oils, interesterified oils obtained by interesterifying 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 recovered from edible oils and the like. 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 this embodiment preferably contains acylglycerol, and more preferably triacylglycerol. In this specification, acylglycerol refers to a compound in which a hydroxy group of glycerin is esterified with a fatty acid. 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 (trimer or higher). Dimer or higher acylglycerols can be obtained by thermal polymerization, oxidative polymerization, or the like. Furthermore, 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: 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, the rubber composition is immersed in deuterated chloroform at room temperature. １ When H-NMR was measured, signals were observed around 5.26 ppm, 4.28 ppm, and 4.15 ppm, assuming that the signal of tetramethylsilane (TMS) was 0.00 ppm. These signals are presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to the oxygen atoms of the ester groups. In this paragraph, "around" refers to a range of ±0.10 ppm.

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

[0072] Among these, it is desirable that the fatty acid contains a fatty acid with few double bonds, i.e., a saturated fatty acid or a monounsaturated fatty acid, and oleic acid is preferred. As a vegetable oil containing such a fatty acid, for example, vegetable oil containing a saturated fatty acid or a monounsaturated fatty acid may be used, or vegetable oil modified by ester exchange or the like may be used. Furthermore, in order to produce vegetable oil containing such a fatty acid, plants may be improved by breeding, genetic modification, 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 Corporation, 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, 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, based on 100 parts by mass of the rubber component A. When the content is within the above range, better effects tend to be obtained.

[0075] Examples of liquid polymers include liquid diene-based polymers (liquid rubbers) and liquid farnesene-based 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 terminals or main chains of these may be modified with polar groups. Hydrogenated versions of these may also be used. Of these, liquid BR is preferred.

[0076] The liquid diene polymer has a weight average molecular weight (Mw) of 1.0×10 in terms of polystyrene measured by gel permeation chromatography (GPC). ３ ~5.0 x 10 ４ It is preferable that the ３~1.5 x 10 ４ The lower or upper limit of the Mw of the liquid diene-based polymer may be 4500 or 8500. 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 manufactured by 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, per 100 parts by mass of the rubber component A. When the content is within the above range, better effects tend to be obtained.

[0079] As the resin component, resins commonly used in tire compounds 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 derived from multiple sources. Among these, aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins thereof are preferred, with petroleum resins being 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, preferably 10°C or lower, and preferably 0°C or lower. In the case of a hydrogenated resin, the softening point is preferably the same as 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] An aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. Examples include resins obtained by polymerizing α-methylstyrene and / or styrene, and specific examples include a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, and a copolymer of styrene and another monomer.

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

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

[0084] An indene resin is a resin containing 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 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 petroleum resins include C5 resins, C9 resins, C5 / C9 resins, dicyclopentadiene (DCPD) resins, C9 / DCPD resins, and hydrogenated versions of these. Among these, C5 / C9 resins, DCPD resins, hydrogenated DCPD resins, C9 / DCPD resins, and C9 / hydrogenated DCPD resins are preferred, with C5 / C9 resins being more preferred.

[0088] Terpene resins are polymers containing terpene as a structural unit, and examples thereof include polyterpene resins obtained by polymerizing terpene compounds and aromatic-modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. Examples of aromatic-modified terpene resins that can be used include 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. Examples of terpene compounds include α-pinene and β-pinene, phenolic compounds include phenol and bisphenol A, and aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.). Of 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 with an acrylic monomer component can be used. Among them, a solvent-free carboxyl-containing styrene-acrylic resin can be preferably used.

[0090] Farnesene polymers are polymers obtained by polymerizing farnesene and contain structural units based on farnesene. Farnesene includes 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.

[0091] The farnesene 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. Of these, 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)dimethylaminoethyl ether, 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; and conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Of 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 to vinyl monomer (farnesene / vinyl monomer) is preferably 40 / 60 to 90 / 10.

[0094] The farnesene polymer preferably has a weight average molecular weight (Mw) of 3,000 or more and 300,000 or less. The Mw of the farnesene polymer is preferably 8,000 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 effects tend to be more favorably obtained.

[0095] The farnesene polymer may be in a liquid state or a solid state at room temperature (25° C.), with liquid farnesene polymers being preferred.

[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, ExxonMobil, KRATON, Nitto 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, relative to 100 parts by mass of the rubber component A, 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. When the content is within the above range, better effects tend to be obtained.

[0098] From the perspective of sustainability, it is desirable to use plant-derived plasticizers such as plant-derived oils and farnesene-based polymers.

[0099] The content of the plasticizer (total amount of 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. When the content is within the above range, better effects tend to be obtained.

[0100] The rubber composition of the present embodiment preferably contains an antioxidant. The antioxidant is not particularly limited, but 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), and N,N'-ditolyl-p-phenylenediamine. 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 polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; 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 these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and polymers of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products that can be used include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry 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, per 100 parts by mass of the rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained.

[0102] The rubber composition of the present embodiment preferably contains stearic acid. As the stearic acid, a conventionally known product can be used, for example, a product manufactured by NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

[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, per 100 parts by mass of rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained.

[0104] The rubber composition of the present embodiment preferably contains zinc oxide. As the zinc oxide, a conventionally known product can be used, for example, a product manufactured by Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

[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, per 100 parts by mass of rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained.

[0106] The rubber composition of this embodiment may contain a wax. The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used. Examples include petroleum-based waxes, mineral-based waxes, synthetic waxes, and plant-derived waxes. Among these, petroleum-based waxes and plant-derived waxes are preferred, and petroleum-based waxes are more preferred. Examples of plant-derived waxes include rice wax, carnauba wax, and candelilla wax. Examples of petroleum-based waxes include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. Examples of commercially available waxes include those available 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.

[0107] When the rubber composition of the present embodiment contains wax, the amount of wax per 100 parts by mass of rubber component A 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. When the amount is within the above range, better effects tend to be obtained.

[0108] The rubber composition of this embodiment preferably contains sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, 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 Kanzushi Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These may be used alone or in combination of two or more.

[0109] The amount of sulfur is preferably 0.1 part by mass or more, more preferably 0.6 part by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of rubber component A, 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. Within the above ranges, the effect tends to be more favorably 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 accelerators can be used. Examples of the vulcanization accelerator include benzothiazole-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, N-t-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-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Of these, 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, and particularly preferably 3.6 parts by mass or more, relative to 100 parts by mass of the rubber component A, 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. Within the above ranges, the effect tends to be more favorably obtained.

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

[0113] The contents of rubber component A and the like described above do not include components in the vulcanized rubber particles. In the entire rubber composition, domains of vulcanized rubber particles exist 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 more favorably obtained. This is presumably because energy loss increases in the frequency range that contributes to wet grip performance.

[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, relative to 100 parts by mass of the rubber component A, 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. Within the above ranges, the effect tends to be better obtained. Furthermore, from the viewpoint of abrasion resistance, it is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. On the other hand, it 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.

[0116] In the rubber composition of this embodiment, the ratio of the content of vulcanized rubber particles to the content of silica A is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and even more preferably 0.4 or more, and is preferably 1.2 or less, more preferably 0.9 or less, and even more preferably 0.6 or less. Within the above ranges, better effects tend to be obtained. This is presumably because, when the amount of vulcanized rubber particles is too large relative to the amount of silica A, the amount of reinforcing component is small and the reinforcing properties during drying cannot be sufficiently maintained. Furthermore, when the amount of silica A is too large, a strong reinforcing network is formed 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 vulcanized rubber particles and the content of silica A are the contents (unit: parts by mass) relative to 100 parts by mass of 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 form is 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 rubber having a polar functional group) and an unmodified 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, 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. 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, even more 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 an 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, 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. When the content is within the above range, better effects tend to be 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. When the content is within the above range, the effect tends to be more favorably obtained.

[0122] In the vulcanized rubber particles, the content of SBR in 100% by mass of the 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, better effects tend to be obtained.

[0123] The vulcanized rubber particles preferably contain silica B. As silica B, the same silica as 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, even more preferably 25% by mass or more, even more preferably 30% 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 more excellent.In addition, from the viewpoint of abrasion resistance, it is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and from the viewpoint of abrasion resistance, it is preferably 40% by mass or more, more preferably 50% by mass or more.

[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 effects of this embodiment are not impaired. The polyacrylic acid resin may be either crosslinked or non-crosslinked, but is preferably crosslinked. The polyacrylic acid resin may be either liquid or solid at room temperature (25°C). Commercially available products include those from Toagosei Co., Ltd. and Fujifilm Wako Pure Chemical Industries, Ltd.

[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, even more preferably 20 parts by mass or more, and 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. Within the above ranges, the effect tends to be better obtained. Furthermore, from the viewpoint of abrasion resistance, the content is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 60 parts by mass or more. On the other hand, the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less.

[0127] In the vulcanized rubber particles, the ratio of the polyacrylic acid resin content to the silica B content 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 1.0 or less, and even more preferably 0.9 or less. Within the above ranges, the effect tends to be better. This is presumably because polyacrylic acid is a water-absorbing resin, and a certain amount is required to fully exert its softening effect when wet with water. In this relationship, the polyacrylic acid resin content and the silica B content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component B.

[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, and 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, and even more preferably 12 parts by mass or less, relative to 100 parts by mass of silica B. Within the above ranges, the effect tends to be more favorable.

[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, per 100 parts by mass of the rubber component B, 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. When the content is within the above range, better effects tend to be obtained.

[0131] When the vulcanized rubber particles contain a hardly-dispersible filler, the content of the hardly-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, better effects tend to be 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, per 100 parts by mass of the rubber component B. When the content is within the above range, better effects tend to be 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, relative to 100 parts by mass of the rubber component B, 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 still more preferably 15 parts by mass or less. When the content is within the above range, better effects tend to be 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, relative to 100 parts by mass of the rubber component B, 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. When the content is within the above range, better effects tend to be obtained.

[0135] When the vulcanized rubber particles contain a plasticizer, the content of the plasticizer (total amount of plasticizer) is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and still more preferably 25 parts by mass or more, relative to 100 parts by mass of the rubber component B, 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. When the content is within the above range, better effects tend to be 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, per 100 parts by mass of the rubber component B, 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. Within the above ranges, the effect tends to be more favorably obtained.

[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, per 100 parts by mass of the rubber component B, 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. When the content is within the above range, better effects tend to be 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, per 100 parts by mass of rubber component B, 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. When the content is within the above range, better effects tend to be 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, better effects tend to be obtained.

[0140] When the vulcanized rubber particles contain sulfur, the sulfur content 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, better effects tend to be 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, better effects tend to be obtained.

[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 also contain compounding agents that are generally used in the tire industry, such as materials such as a mold release agent, as appropriate.

[0143] In this specification, various materials containing carbon atoms (e.g., rubber, oil, resin, vulcanization accelerator, antioxidant, surfactant, etc.) may be derived from atmospheric carbon dioxide. The compound of this embodiment can be obtained from carbon dioxide by directly converting carbon dioxide, or by converting methane obtained through a methanation process in which methane is synthesized from carbon dioxide.

[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 kneading the above-mentioned components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing the components.

[0145] As for kneading conditions, in the base kneading step in which additives other than the vulcanizing agent (sulfur) and 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 vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 80 to 115°C, and more preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and 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 20 minutes.

[0146] The rubber composition of this embodiment can be used (as a rubber composition for a tire) for tire components such as a tread, sidewall, undertread, shoulder, clinch, bead apex, breaker cushion rubber, carcass cord coating rubber, insulation, chafer, inner liner, etc., and a side reinforcing layer of a run-flat tire. It is particularly suitable for a tread. Furthermore, when the tread has a multi-layer structure, it can be used for either a surface layer (cap tread) or an inner layer (base tread), but is particularly suitable for a 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 this embodiment may be a pneumatic tire or a non-pneumatic tire, with pneumatic tires being 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-duty tire for trucks, buses, etc., a light truck tire, a motorcycle tire, or a racing tire (high-performance tire). In particular, it is desirable to use the tire as a passenger car tire.

[0149] A tire is manufactured by a conventional method using the 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 conventional 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 tread component at 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 more favorable.

[0151] The thickness G of the member 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 member on the equatorial plane in a cross section cut along a plane including the rotation axis of the tire.

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

[0153] In the tire of this embodiment, the thickness G (mm) is a value measured in a normal state, which means that the tire is mounted on a normal rim, inflated to a normal internal pressure, and is not under load. Here, a "regular rim" refers to a rim that is determined for each tire by a standard system that includes the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Manufacturers Association), this refers to the standard rim for the applicable size listed in the "JATMA YEAR BOOK," in the case of ETRTO (The European Tyre and Rim Technical Organization), this refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and in the case of TRA (The Tire and Rim Association, Inc.), this refers to the "Design Rim" listed in the "YEAR BOOK." Reference is made to JATMA, ETRTO, and TRA in that order, and if an applicable size is available at the time of reference, that standard will be followed. In the case of tires not specified in a standard, it refers to a rim that can be mounted on a rim and can maintain internal pressure, i.e., a rim with the smallest rim diameter and the next narrowest rim width, among those that do not cause air leakage between the rim and tire. Furthermore, "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. For JATMA, it refers to "maximum air pressure," for ETRTO, it refers to "inflation pressure," and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." JATMA, ETRTO, and TRA are referenced in that order, and if there is an applicable size at the time of reference, that standard is followed. In the case of tires not specified in the standard, it refers to the normal internal pressure (250 KPa or more) of another tire size (defined in the standard) that is listed using the regular rim as the standard rim. Note that if multiple normal internal pressures of 250 KPa or more are listed, it refers to the smallest value among them.

[0154] Below, examples (embodiments) that are considered preferable for implementation 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 explained below. If necessary, the chemicals are purified according to standard methods.

[0156] <Chemicals in Table 1> SBR: SBL0545 (carboxy group-modified SBR, Tg: -30°C) manufactured by ENEOS Material Corporation Polyacrylic acid resin: Junron PW-120 (crosslinked type) manufactured by Toagosei Co., Ltd. Silica: Ultrasil VN3 (N) manufactured by Evonik Degussa ２ SA: 175m 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: RICON131MA10 (liquid BR) manufactured by Cray Valley Corporation Sulfur: 5% oil-treated powdered sulfur (soluble sulfur containing 5% by mass of oil) manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0157] <Chemicals in Table 2> SBR: SBL0545 (carboxy group-modified SBR, Tg: -30°C) manufactured by ENEOS Material Corporation BR: BR150B (vinyl content: 1 mass%, cis content: 97 mass%) manufactured by Ube Industries, Ltd. NR: TSR20 Silica: Ultrasil VN3 (N) manufactured by Evonik Degussa ２ SA: 175m ２ / g) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa Co., Ltd. Carbon black: Showblack N220 (N) manufactured by Cabot Japan Co., Ltd. ２ SA: 111m ２ / g) Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. C5 / C9 resin: Petrotack 100V manufactured by Tosoh Corporation Antioxidant: 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 and Smelting Co., Ltd. Sulfur: 5% oil-treated powdered sulfur (soluble sulfur containing 5% by mass of oil) manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanized rubber particles 1 to 6: Prepared as follows

[0158] <Preparation of vulcanized rubber particles> According to the formulation 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 mixture. Sulfur and vulcanization accelerator are added to the kneaded mixture, and the mixture 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 freezer pulverizer to obtain vulcanized rubber particles.

[0159]

[0160] <Examples and Comparative Examples> According to the formulation shown in Table 2, chemicals other than sulfur and vulcanization accelerator were kneaded for 4 minutes at 160°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture. Sulfur and vulcanization accelerator were added to the kneaded mixture, and the mixture was kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was press-vulcanized at 170°C for 20 minutes to obtain a vulcanized rubber composition. Furthermore, a 10 mm-thick component was prepared using the unvulcanized rubber composition and applied to a 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 were present in a matrix composed of rubber component A. This could be confirmed by the color shading when osmium-stained samples were observed under SEM.

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

[0162] <Average Domain Diameter> The vulcanized rubber composition dyed with osmium is observed under an SEM, and the equivalent circle diameter of the domains is calculated. The average value of the equivalent circle diameters at 50 locations is taken as the average domain diameter.

[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 hardness (Martens hardness) of the domain and matrix of the obtained measurement sample is measured using a nanoindenter (PICODENTOR HM-500 manufactured by Fischer 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 about 6 μm, and the surface area A (μm) is calculated from the diagonal length of the pyramidal depression formed on the surface. ２ ) and divide it by the test load F, i.e., F / A is used to calculate the Martens hardness (kgf / mm ２ The indentation conditions are as follows: 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 formulation. 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 measuring 40 mm in length, 3 mm in width, and 0.5 mm in 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 Corporation under the following conditions: temperature 30°C, initial strain 10%, dynamic strain 1%, frequency 10 Hz, extension mode, and measurement time 30 minutes. The measured value is obtained 30 minutes after the start of measurement.

[0165] <Hardness and E* in Dry State> The above hardness measurement sample and the above viscoelasticity measurement sample are subjected to a drying treatment, and then Martens hardness and E* are measured. Drying treatment: The sample is left to stand for 24 hours under an ambient temperature of 30°C, a relative humidity of 30%, and 1 atmosphere. Thereafter, the sample is left to stand for 1 hour under an ambient temperature of 120°C, a relative humidity of 30%, and 1 atmosphere.

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

[0167] <Hardness ratio in dry state> Calculated by the following formula. The larger the value, the greater the hardness of the domain in dry state. ２ ) / Dry matrix hardness (kgf / mm ２ )

[0168] <Hardness ratio when wetted with water> Calculated using the following formula. The smaller the value, the lower 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 ) / Hardness of the matrix when wetted with water (kgf / mm ２ )

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

[0170] The vulcanized rubber composition of this example is capable of undergoing reversible changes in physical properties when dry and when wetted with water. Therefore, when re-dried (after wetting treatment, the same drying treatment as before is carried out again), the E* is the same as when dry (or within ±1%), and when re-wetted with water (after re-drying treatment, the same wetting treatment as before is carried out again), the E* is the same as when wetted with water (or within ±1%).

[0171]

[0172] The present invention (1) is a rubber composition containing a rubber component A and vulcanized rubber particles, wherein domains composed of the vulcanized rubber particles exist in a matrix composed of the rubber component A, the average diameter of the domains is 50 μm or more, and the hardness of the domains in a dry state (kgf / mm ２) / Dry matrix hardness (kgf / mm ２ ) ≧1.1 Hardness of domain when wetted with water (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２ )≦0.98

[0173] The present invention (2) is the rubber composition according to the present invention (1), wherein the matrix contains silica A, and 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 the rubber composition according to the present invention (1) or (2), wherein the vulcanized rubber particles contain a rubber component B, and 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 silica B in the vulcanized rubber particles is 5% by mass or more.

[0176] The present invention (5) is a rubber composition according to any one of the present inventions (1) to (4), which satisfies the following formula: Domain hardness (kgf / mm ２ ) / Hardness of the matrix 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 the tire radial cross section is 10 mm or less.

[0180] The present invention (9) is a method for manufacturing a tire having a tire-tread structure, comprising: a thickness G (mm) on the equatorial plane of a cross section of the tire in the radial direction of the member; and a domain hardness (kgf / mm ２ ) / Hardness of the matrix when wetted with water (kgf / mm ２ ) is 9 or less.

Claims

1. 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 following formula is satisfied: The hardness of the domains 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. The rubber composition according to claim 1, wherein the matrix contains silica A, and the ratio of the content of the vulcanized rubber particles to the content of the silica A is 1.2 or less.

3. The rubber composition according to claim 1 or 2, wherein the vulcanized rubber particles contain a rubber component B, and the rubber component B contains a diene rubber having a polar functional group.

4. A rubber composition according to any one of claims 1 to 3, wherein the vulcanized rubber particles contain silica B, and the content of silica B in the vulcanized rubber particles is 5 mass % or more.

5. The rubber composition according to any one of claims 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 6. A rubber composition according to any one of claims 1 to 5, which is capable of reversibly changing its physical properties when dry and when wet with water.

7. A tire using a member made of the rubber composition according to any one of claims 1 to 6 in the tread.

8. The tire according to claim 7, wherein the thickness G of said member on the equatorial plane of a radial cross section 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 9. The tire according to claim 7 or 8, wherein the ratio of the axial length of the tire to the radial length of the tyre is 9 or less.

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