Rubber composition and tire

Abstract

To provide a rubber composition and a tire that are capable of suppressing a decrease in wet grip performance after deterioration.SOLUTION: A rubber composition comprises a rubber component and an ester compound, where the ester compound is a polymer having a repeating unit represented by the general formula in the figure. (In the general formula: R1 represents an optionally substituted vinyl group or an optionally substituted phenyl group; R2 represents a divalent hydrocarbon group; R3 represents a divalent hydrocarbon group; n represents an integer of 1 or more; x, y, z and w are each independently any integer of 0 or more, satisfying x+y+z+w≥1, where the combination of x, y, z and w for each repeating unit enclosed in square brackets may be the same or different; the bonding order of each repeating unit enclosed in parentheses within the square brackets is arbitrary, and any other repeating unit may be bonded between the respective repeating units.)SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Tires are required to have various performance characteristics such as wet grip performance, and for example, Patent Document 1 proposes a technology for improving wet performance by blending silica, a silane coupling agent, a liquid resin, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-186567 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in recent years, there has been a demand for suppressing the deterioration of wet grip performance, particularly after deterioration. An object of the present invention is to solve the above problems and to provide a rubber composition and a tire that can suppress the deterioration of wet grip performance after deterioration. [Means for solving the problem]

[0005] The present invention includes a rubber component and an ester compound, The rubber composition relates to a rubber composition in which the ester compound is a polymer having a repeating unit represented by the following general formula:

[0006] [ka]

[0007] In the above general formula, R 1 represents an optionally substituted vinyl group or an optionally substituted phenyl group; R 2represents a divalent hydrocarbon group; R 3 represents a divalent hydrocarbon group; n represents an integer of 1 or greater; x, y, z, and w are each any integer of 0 or greater, provided that x+y+z+w≧1, and the combinations of x, y, z, and w for each repeating unit enclosed in square brackets may be the same or different, the repeating units enclosed in round brackets within the square brackets may be bonded in any order, and any other repeating unit may be bonded between each repeating unit. [Effects of the Invention]

[0008] The present invention provides a rubber composition that includes a rubber component and an ester compound, and the ester compound is a polymer having a repeating unit represented by the above general formula, and therefore can provide a rubber composition that can suppress deterioration in wet grip performance after deterioration. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Rubber composition> The present invention is a rubber composition comprising a rubber component and an ester compound, wherein the ester compound is a polymer having a repeating unit represented by the above general formula.

[0010] The reason why the above-mentioned effects are obtained is not entirely clear, but it is presumed that the following mechanism is involved. Generally, even if rubber (rubber composition) contains a softener, over time the softener will leak out or migrate to adjacent components, resulting in the loss of the softener and a decrease in flexibility. Here, as is clear from the general formula, in a polymer having repeating units represented by the above general formula, the units having softening action enclosed in square brackets are bonded by ester bonds. Therefore, when compounded into a rubber composition, the softening action is small at the beginning of use, but over time the ester bonds are hydrolyzed and the molecules are reduced, resulting in an increased softening action. Therefore, by compounding a polymer having a repeating unit represented by the above general formula into a rubber composition, it is possible to counteract the hardening of the rubber due to the outflow and migration of the softener and the increase in sulfur crosslinking points, and to suppress changes in hardness, thereby suppressing deterioration over time of the rubber (rubber composition) and maintaining its flexibility. This is thought to make it possible to suppress the deterioration of wet grip performance after deterioration. Therefore, it is presumed that a rubber composition containing a rubber component and an ester compound, in which the ester compound is a polymer having a repeating unit represented by the above general formula, can suppress the deterioration of wet grip performance after deterioration.

[0011] The rubber composition includes a rubber component. Here, the rubber component is a component that contributes to crosslinking, and is generally a polymer with a weight-average molecular weight (Mw) of 10,000 or more, which is not extracted with acetone after crosslinking. The rubber component is in a solid state at room temperature (25°C). Note that, in this specification, ester compounds are not included in the rubber component.

[0012] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and particularly preferably 270,000 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 favorably obtained.

[0013] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) 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).

[0014] The rubber component that can be used in the rubber composition may be either an unmodified rubber or a modified rubber. Examples of modified rubbers include rubbers having functional groups that interact with fillers such as silica. Examples include terminal-modified rubbers (terminal-modified rubbers having the functional groups at the terminals) in which at least one terminal of the rubber has been modified with a compound (modifier) ​​having the functional group, main-chain-modified rubbers having the functional groups in the main chain, main-chain-terminal-modified rubbers having the functional groups in the main chain and at the terminals (for example, main-chain-terminal-modified rubbers having the functional groups in the main chain and at least one terminal modified with the modifier), and terminal-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.

[0015] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imido group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, and an epoxy group. These functional groups may have a substituent. Among these, an amino group (preferably an amino group in which a hydrogen atom of the amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), and an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms) are preferred.

[0016] Examples of the rubber component 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, with SBR being more preferred, from the viewpoint of achieving better effects.

[0017] 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.

[0018] The styrene content of the SBR is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. The styrene content is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less. Within the above range, the effect tends to be more favorable. In this specification, the amount of styrene is 1 It can be measured by H-NMR measurement.

[0019] The mechanism by which a greater effect is obtained when SBR with a styrene content of a specified amount or less, particularly SBR with a styrene content of 20 mass% or less, is included is not clear, but it is thought that the lower the styrene content, the easier the rubber hardens and the more pronounced the softening effect of the ester compound becomes.

[0020] The styrene content of 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 amount of SBR can be calculated by {Σ(content of each SBR × styrene amount of each SBR)} / total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene amount of 40% by mass and 5% by mass of SBR with a styrene amount of 25% by mass, the average styrene amount of the SBR is 39.2% by mass (=(85×40+5×25) / (85+5)).

[0021] The vinyl content of the SBR is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and still more preferably 35% by mass or more. When the vinyl content is within the above range of preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, the effect tends to be more favorable. In this specification, the vinyl content (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

[0022] The vinyl content of SBR (amount of 1,2-bonded butadiene units) is the proportion of vinyl bonds (unit: mass%) when the total mass of the butadiene parts in the SBR is taken as 100, and is calculated as vinyl content [mass%] + cis content [mass%] + trans content [mass%] = 100 [mass%]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types, it means the average vinyl content. The average vinyl content of SBR can be calculated by Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%]) × vinyl content of each SBR [mass%]} / Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%])}. For example, in 100 parts by mass of the rubber component, 75 parts by mass of SBR with a styrene content of 40% by mass and a vinyl content of 30% by mass, 25 parts by mass of styrene and 10 parts by mass of vinyl are used. In the case where 15 parts by mass of SBR with a vinyl content of 20% by mass is used and the remaining 10 parts by mass are 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])}.

[0023] Both unmodified and modified SBR can be used. Modified SBR includes modified SBR with the same functional groups as modified rubber. Hydrogenated styrene-butadiene copolymer (hydrogenated SBR) can also be used as SBR.

[0024] 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.

[0025] The amount of SBR in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and still more preferably 80% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be better obtained.

[0026] The mechanism by which a greater effect is obtained when the SBR content is a specified amount or more, particularly 50% by mass or more, is not clear. However, SBR is known to exhibit hardening and deterioration behavior, and it is thought that the higher the SBR content, the more easily the rubber hardens, and the more pronounced the softening effect of the ester compound becomes.

[0027] Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. NRs such as SIR20, RSS#3, and TSR20 are commonly used in the rubber industry. IRs are not particularly limited, and examples of IRs such as IR2200 are commonly used in the rubber industry. Modified NRs include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Modified NRs include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Modified IRs include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more.

[0028] When the rubber composition contains an isoprene-based rubber, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and even more preferably 30% by mass or more. It is also preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Within the above ranges, the effects tend to be more favorable.

[0029] 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.

[0030] 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)).

[0031] Both unmodified and modified BR can be used. Modified BR includes modified BR with the same functional groups as modified rubber. Hydrogenated butadiene polymer (hydrogenated BR) can also be used.

[0032] As the BR, for example, products from UBE Corporation, JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used.

[0033] When the rubber composition contains BR, the BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and even more preferably 30% by mass or more. Also, the BR content is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Within the above ranges, the effects tend to be more favorable.

[0034] The rubber composition contains an ester compound, which is a polymer having a repeating unit represented by the following general formula:

[0035] [ka]

[0036] In the above general formula, R 1 represents an optionally substituted vinyl group or an optionally substituted phenyl group; R 2 represents a divalent hydrocarbon group; R 3 represents a divalent hydrocarbon group; n represents an integer of 1 or greater; x, y, z, and w are each any integer of 0 or greater, provided that x+y+z+w≧1, and the combinations of x, y, z, and w for each repeating unit enclosed in square brackets may be the same or different, the repeating units enclosed in round brackets within the square brackets may be bonded in any order, and any other repeating unit may be bonded between each repeating unit.

[0037] The ester compound has a plurality of repeating units represented by the above general formula in its structure, and the plurality of repeating units may be the same or different. When the repeating units are different, they may be in any form, such as a block form or a random form.

[0038] In the above general formula, n represents an integer of 1 or more, preferably 1 or more, more preferably 2 or more, and even more preferably 4 or more. Also, n is preferably 100 or less, more preferably 80 or less, and even more preferably 50 or less. When it is within the above range, better effects tend to be obtained.

[0039] In the above general formula, x, y, z, and w are any integers of 0 or greater, and x+y+z+w≧1. The combinations of x, y, z, and w for each repeating unit enclosed in square brackets may be the same or different. The ratio of x, y, z, and w for each repeating unit enclosed in square brackets in the above general formula is not particularly limited. The lower limit of x+y+z+w is preferably 1 or greater, more preferably 2 or greater, and even more preferably 3 or greater. While the upper limit is not particularly limited, it is preferably 80 or less, more preferably 60 or less, and even more preferably 40 or less. Within the above ranges, better effects tend to be obtained.

[0040] The above x is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more. It is also preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. When it is within the above range, better effects tend to be obtained.

[0041] The above y is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more. It is also preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. When it is within the above range, better effects tend to be obtained.

[0042] The above z is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more. It is also preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. When it is within the above range, better effects tend to be obtained.

[0043] The above w is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more. It is also preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. When it is within the above range, better effects tend to be obtained.

[0044] R in the above general formula 1represents a vinyl group which may have a substituent or a phenyl group which may have a substituent, and examples of the substituent include a linear, branched, or cyclic hydrocarbon group having 1 to 15 carbon atoms; a halogen atom such as fluorine, chlorine, bromine, or iodine; an oxo group (═O), a hydroxy group, a carboxyl group, a carbonyl group, an amino group, an acetyl group, an amido group, an imido group, a cyano group, a nitro group, and a carboxy ester group.

[0045] R in the above general formula 2 represents a divalent hydrocarbon group, while R 2 The number of carbon atoms is preferably 1 or more, more preferably 2 or more, even more preferably 5 or more, and even more preferably 10 or more. Also, it is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, and even more preferably 15 or less. When it is within the above range, the effect tends to be better.

[0046] Above R 2 Examples of the divalent hydrocarbon group in R include an alkylene group, an alkenylene group, an alkylidene group, and an arylene group. 2 is preferably a linear or branched alkylene group or a linear or branched alkenylene group, and more preferably a structural unit based on farnesene. When such a structural unit is present, the effect tends to be more favorable.

[0047] Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene is preferred. Having such a structural unit tends to produce better effects.

[0048] R in the above general formula 3 represents a divalent hydrocarbon group, while R 3The number of carbon atoms is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and even more preferably 4 or more. Also, it is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, even more preferably 15 or less, and even more preferably 10 or less. When it is within the above range, the effect tends to be better.

[0049] Above R 3 Examples of the divalent hydrocarbon group in R include an alkylene group, an alkenylene group, an alkylidene group, and an arylene group. 3 is preferably a linear or branched alkylene group or a linear or branched alkenylene group, and more preferably a linear or branched alkylene group. When such a structural unit is contained, the effect tends to be more favorable.

[0050] Furthermore, in the above general formula, the repeating unit represented by the number of repeating units y and the repeating unit represented by the number of repeating units z can be in a cis form or a trans form, and may be either a cis form or a trans form.

[0051] The weight-average molecular weight of the repeating unit enclosed in square brackets in the above general formula is preferably 10,000 or less. The weight-average molecular weight of the repeating unit is more preferably 8,000 or less, even more preferably 5,000 or less, and even more preferably 3,000 or less. Also, it is preferably 500 or more, more preferably 700 or more, and even more preferably 1,000 or more. Within the above range, better effects tend to be obtained.

[0052] When the weight-average molecular weight of the repeating unit enclosed in square brackets in the above general formula is a predetermined value or less, particularly 10,000 or less, a greater effect is obtained, but although the mechanism is not clear, migration is sufficiently suppressed before decomposition, and after decomposition, the decomposition product can exhibit sufficient plasticity. Therefore, it is believed that the deterioration of wet grip performance after deterioration can be suppressed.

[0053] The weight-average molecular weight of the ester compound is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more. Also, it is preferably 500,000 or less, more preferably 300,000 or less, even more preferably 200,000 or less, and even more preferably 150,000 or less. Within the above range, the effect tends to be better.

[0054] When an ester compound is included, which is a polymer having a repeating unit represented by the above general formula and has a predetermined weight-average molecular weight, particularly an ester compound having a weight-average molecular weight of 10,000 to 150,000, the mechanism by which a greater effect is obtained is not clear, but it is thought that if the molecular weight is too small, migration before decomposition cannot be suppressed, and if the molecular weight is too large, the decomposition products after decomposition do not exhibit plasticity, and that an intermediate molecular weight can achieve both suppression of migration before decomposition and plasticity after decomposition. Therefore, it is believed that the deterioration of wet grip performance after deterioration can be suppressed.

[0055] The ester compound is not particularly limited, and can be produced, for example, by known methods or the following method. Specifically, for example, a method of esterifying a dicarboxylic acid or a diester with a diol (e.g., a long-chain hydrocarbon glycol having an average molecular weight of approximately 500 to 8000) in the presence of a suitable catalyst (e.g., dehydration polycondensation reaction) or transesterification can be used. The dicarboxylic acid may be an aliphatic dicarboxylic acid, such as malonic acid, succinic acid, adipic acid, or sebacic acid. The diester may be an ester of an aliphatic dicarboxylic acid, such as diethyl malonate, diethyl succinate, dimethyl adipate, diethyl adipate, dimethyl sebacate, or diethyl sebacate. A solvent may be used in the esterification reaction or transesterification reaction between a dicarboxylic acid or a diester and a diol. The amount of dicarboxylic acid or diester used relative to the diol is, for example, preferably 50 mol% or more, 55 mol% or more, or 60 mol% or more, and preferably 160 mol% or less, 155 mol% or less, or 150 mol% or less. The catalyst is also not particularly limited, but examples thereof include p-toluenesulfonic acid monohydrate, sulfuric acid, hydrochloric acid, boron trifluoride, zinc oxide, zinc acetate, manganese acetate, antimony trioxide, titanium tetraisopropoxide, and titanium tetrabutoxide. The reaction time of the esterification reaction or transesterification reaction is also not particularly limited, but is, for example, preferably 3 hours or more, 4 hours or more, or 5 hours or more, and preferably 10 hours or less, 9 hours or less, or 8 hours or less. The reaction temperature is also not particularly limited, but is, for example, preferably 90°C or more, 100°C or more, or 110°C or more, and preferably 140°C or less, 130°C or less, or 120°C or less. To suppress radical reactions during the reaction of the diol, a hindered phenol radical chain inhibitor (for example, p-methoxyphenol) may be used.

[0056] The content of the ester compound is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even 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. Also, the content 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. Within the above range, the effect tends to be more favorable.

[0057] The mechanism by which a greater effect is obtained when the ester compound is contained in a predetermined amount, particularly 5 to 50 parts by mass per 100 parts by mass of the rubber component, is not clear, but it is thought that if the amount is too small, the plasticizing effect on the hardening of the rubber is too small, and if the amount is too large, the plasticizing effect on the hardening of the rubber is too great, and that an intermediate amount can exhibit an equivalent plasticizing effect on the hardening of the rubber. Therefore, it is believed that the deterioration of wet grip performance after deterioration can be suppressed.

[0058] The rubber composition preferably contains silica as a filler. Usable silica includes dry-process silica (anhydrous silica) and wet-process silica (hydrated silica). Among these, wet-process silica is preferred because it has a large number of silanol groups. Commercially available products include those from Evonik, Rhodia, Tosoh Silica Corporation, Solvay Japan, and Tokuyama Corporation. These may be used alone or in combination of two or more.

[0059] As the silica, plant-derived silica can also be suitably used. Examples of plant-derived silica include silica derived from plants containing silica. Examples of plants containing silica include rice, corn, sugarcane, horsetail, wheat, barley, rye, Job's tears, millet, foxtail millet, barnyard millet, Miscanthus, and Erianthus. Saccharification residues of the above-mentioned plants containing silica can also be used. Among these, rice husks and straw, which have a high silica content, are preferred, with rice husks being even more preferred. Furthermore, the plants containing silica may be those that have been burned to ash or carbonized.

[0060] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 70 m 2 / g or more, more preferably 140m 2 / g or more, more preferably 160m 2 The upper limit of the N2SA of silica is not particularly limited, but is preferably 500 m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 Within the above range, there is a tendency for the effect to be better obtained. The N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0061] In the rubber composition, the content of silica per 100 parts by mass of the rubber component is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, still more preferably 45 parts by mass or more, and even more preferably 50 parts by mass or more. The upper limit is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 170 parts by mass or less, still more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. Within the above range, the effect tends to be more favorably obtained. The content of the plant-derived silica and the content of the rice husk silica are also preferably in the same range.

[0062] The rubber composition may contain a filler other than silica. Such fillers are not particularly limited, and materials known in the rubber field can be used, including inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica, biochar, and poorly dispersible fillers. Among these, carbon-derived fillers (carbon-containing fillers) such as carbon black are preferred from the viewpoint of obtaining better effects. The fillers may be used alone or in combination of two or more.

[0063] The carbon black that can be used in the rubber composition is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon blacks 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., and Columbia Carbon Co., Ltd. These may be used alone or in combination of two or more. In addition to conventional carbon blacks made from mineral oils and the like, carbon blacks made from biomass materials such as lignin may also be used. Furthermore, recycled carbon black obtained by decomposing rubber products containing carbon black, such as tires, or plastic products, may be used as an appropriate substitute for the above carbon black in equal amounts.

[0064] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 / g or more is more preferable. 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 130m 2 Within the above range, the effect tends to be better. The nitrogen adsorption specific surface area of ​​carbon black can be determined according to JIS K6217-2:2001.

[0065] The dibutyl phthalate oil absorption (DBP) of the carbon black is preferably 40 ml / 100 g or more, more preferably 60 ml / 100 g or more, and even more preferably 70 ml / 100 g or more. Furthermore, when the DBP is within the above range, preferably 200 ml / 100 g or less, more preferably 150 ml / 100 g or less, and even more preferably 120 ml / 100 g or less, the effect tends to be more favorable. The DBP of carbon black is determined by the measurement method of JIS K6217-4:2001.

[0066] In the rubber composition, the content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above ranges, better effects tend to be obtained.

[0067] In the rubber composition, it is preferable that the silica content (the silica content (parts by mass) per 100 parts by mass of the rubber component) and the carbon black content (the carbon black content (parts by mass) per 100 parts by mass of the rubber component) satisfy the following formula: Silica content / carbon black content > 1 The lower limit of the above formula is preferably greater than 1.5, more preferably greater than 3.5, and even more preferably greater than 5.0. The upper limit of the above formula is not particularly limited, but is preferably less than 20.0, more preferably less than 15.0, and even more preferably less than 12.0. Within the above range, better effects tend to be obtained.

[0068] When the ratio of the silica content to the carbon black content (silica content / carbon black content) is greater than a predetermined value, particularly greater than 1, it is believed that deterioration of wet grip performance after aging can be suppressed.

[0069] Examples of the hardly dispersible filler include microfibrillated plant fibers, short fiber cellulose, gel compounds, etc. Among these, microfibrillated plant fibers are preferred.

[0070] The microfibrillated plant fiber is preferably cellulose microfibrils, as 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; 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; and 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.

[0071] 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.

[0072] When the rubber composition 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, per 100 parts by mass of the rubber component. The upper limit of the content 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. Within the above range, the effect tends to be more favorably obtained.

[0073] In the rubber composition, the content of the filler (total amount of fillers such as silica and carbon black) is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, even more preferably 50 parts by mass or more, and still more preferably 55 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and still more preferably 80 parts by mass or less. Within the above ranges, better effects tend to be obtained.

[0074] In the rubber composition, the silica content in the filler (100% by mass) is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. There is no particular upper limit and it may be 100% by mass, but it is preferably 99% by mass or less, more preferably 95% by mass or less. Within the above range, the effect tends to be more favorably obtained.

[0075] The rubber composition for a cap tread preferably further contains 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, 3-trimethoxysilylpropyl-N, Examples 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 NXT and NXT-Z manufactured by Momentive; 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 from Evonik, 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.

[0076] In the rubber composition, the content of the silane coupling agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and even more preferably 6 parts by mass or more, per 100 parts by mass of silica. The upper limit of the content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above range, the effect tends to be more favorable.

[0077] The rubber composition may further contain a plasticizer. In this specification, the term "plasticizer" refers to a material that imparts plasticity to a rubber component, a component with a weight-average molecular weight (Mw) of less than 10,000, and a component that is extracted when a rubber composition is subjected to acetone extraction for 24 hours according to a method conforming to JIS K 6229:2015. The plasticizer may be liquid or solid at room temperature (25°C). These may be used alone or in combination of two or more.

[0078] Examples of the plasticizer include oil, liquid polymer, resin, etc. These may be used alone or in combination of two or more.

[0079] The oil is not particularly limited, and conventionally known oils can be used, such as process oils such as paraffinic process oil, aromatic process oil, naphthenic process oil, and mineral process oil; low PCA (polycyclic aromatic) process oils such as TDAE and MES; vegetable oil; and mixtures thereof. These oils may be used alone or in combination of two or more. From the viewpoint of life cycle analysis, lubricating oils and waste cooking oils used in rubber mixing mixers and automobile engines may also be used as appropriate.

[0080] Examples of the vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil.

[0081] As the above oil, for example, products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0082] Examples of the liquid polymer include liquid diene polymers (liquid rubbers) and liquid farnesene polymers at 25°C. Examples of liquid rubber include liquid styrene butadiene copolymers (liquid SBRs), liquid butadiene polymers (liquid BRs), liquid isoprene polymers (liquid IRs), liquid styrene isoprene copolymers (liquid SIRs), 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 compounds can also be used.

[0083] The liquid diene polymer has a weight average molecular weight (Mw) of 1.0×10 in terms of polystyrene as measured by gel permeation chromatography (GPC). 3 ~5.0×10 4 Preferably, it is 3.0 × 10 3 ~1.5×10 4 The lower or upper limit of Mw of the liquid diene polymer may be 4,500 or 8,500. In this specification, the Mw of the liquid diene polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0084] As the liquid diene polymer, for example, products available from Sartomer Co., Ltd., Kuraray Co., Ltd., etc. can be used.

[0085] The resin may be a resin commonly used in tire compounds, 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, and acrylic resins. The resin may also be a hydrogenated resin (hydrogenated resin). 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 from the viewpoint of obtaining better effects.

[0086] When a resin that is solid at room temperature is used, the softening point of the resin 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, the softening point 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, better effects tend to be obtained. When the resin is liquid at room temperature, the softening point is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 0°C or lower. In the case of hydrogenated resins, it is desirable that the softening point is the same as above. The softening point of the resin 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.

[0087] The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it may be a resin obtained by polymerizing α-methylstyrene and / or styrene, and specifically may be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, or a copolymer of styrene and another monomer.

[0088] 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, vinyltoluene, etc.

[0089] The coumarone resin is a resin containing coumarone as a main monomer component constituting the skeleton (main chain) of the resin.

[0090] The indene resin is a resin containing indene as a main monomer component that constitutes the skeleton (main chain) of the resin.

[0091] 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. Of these, those obtained by reacting with an acid catalyst (such as novolac phenolic resin) are preferred.

[0092] Examples of the rosin resin include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0093] Examples of the petroleum resin include C5 resin, C9 resin, C5 / C9 resin, dicyclopentadiene (DCPD) resin, C9 / DCPD resin, and hydrogenated versions of these. Of these, DCPD resin, hydrogenated DCPD resin, C9 / DCPD resin, and C9 / hydrogenated DCPD resin are preferred.

[0094] The terpene resin is a polymer containing terpene as a structural unit, and examples thereof include polyterpene resins obtained by polymerizing a terpene compound and aromatic-modified terpene resins obtained by polymerizing a terpene compound and an aromatic compound. Examples of aromatic-modified terpene resins 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.). Among these, aromatic-modified terpene resins are preferred.

[0095] 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.

[0096] Examples of the 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] From the viewpoint of sustainability, it is desirable to use the above-mentioned plant-derived oils (vegetable oils) and plant-derived plasticizers such as farnesene-based polymers as the plasticizer.

[0098] Farnesene polymers are polymers obtained by polymerizing farnesene and contain structural units based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene, which has the following structure, is preferred. [ka]

[0099] 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. Among these, a copolymer of farnesene and a vinyl monomer is preferred.

[0100] 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-tert-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-tert-butylstyrene, 3-tert-butylstyrene, 4-tert-butylstyrene, vinylxylene, vinylnaphthalene, vinyltoluene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylene, as well as conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among these, butadiene is preferred. That is, the farnesene-vinyl monomer copolymer is preferably a copolymer of farnesene and butadiene (farnesene-butadiene copolymer).

[0101] 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.

[0102] 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.

[0103] The farnesene polymer may be either a liquid or solid at room temperature (25° C.), with liquid farnesene polymers being preferred.

[0104] In the rubber composition, the content of the plasticizer (total amount of plasticizer) 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, per 100 parts by mass of the rubber component. Although there is no particular lower limit, the content is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.075 parts by mass or more. Within the above range, better effects tend to be obtained. The plasticizer content also includes the amount of oil and resin contained in rubber (oil-extended rubber, resin-extended rubber) and sulfur (oil-containing sulfur).

[0105] When the blending amount of the plasticizer is set to a predetermined amount or less, particularly 10 parts by mass or less per 100 parts by mass of the rubber component, it is believed that deterioration of wet grip performance after aging can be suppressed.

[0106] In the rubber composition, the content of the solid plasticizer in a solid state at room temperature (25°C) 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, per 100 parts by mass of the rubber component. Although there is no particular lower limit, the content is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.075 parts by mass or more. Within the above range, better effects tend to be obtained. The content of the resin in a solid state at room temperature (25° C.) and the content of the aromatic vinyl polymer in a solid state at room temperature (25° C.) are also desirably in the same range.

[0107] In the rubber composition, the content of the liquid plasticizer in a liquid state at room temperature (25°C) 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, per 100 parts by mass of the rubber component. Although there is no particular lower limit, the content is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.075 parts by mass or more. Within the above range, better effects tend to be obtained. The content of the liquid plasticizer includes the amount of oil contained in the oil-extended rubber and the amount of liquid resin in the resin-extended rubber extended with the liquid resin. The oil content in a liquid state at room temperature (25°C) (total amount of oil contained in oil-extended rubber) is also preferably in the same range.

[0108] The rubber composition preferably contains an antioxidant from the viewpoints of crack resistance, ozone resistance, and the like.

[0109] 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, N,N'-di-2-naphthyl-p-phenylenediamine, and the like. Examples of suitable antioxidants include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, with polymers of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline being more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis.

[0110] In the rubber composition, the content of the antioxidant 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, per 100 parts by mass of the rubber component, and is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less.

[0111] The rubber composition preferably contains stearic acid. In the rubber composition, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0112] As the stearic acid, conventionally known products can be used, for example, products available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

[0113] The rubber composition preferably contains zinc oxide. In the above rubber composition, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0114] As the zinc oxide, conventionally known products can be used, for example, products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0115] The rubber composition may contain wax. In the rubber composition, the wax content is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 2.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0116] The wax is not particularly limited, and examples thereof include petroleum waxes, natural waxes, etc. Synthetic waxes obtained by refining or chemically treating multiple waxes can also be used. These waxes may be used alone or in combination of two or more types.

[0117] Examples of petroleum-based waxes include paraffin wax and microcrystalline wax. Natural waxes are not particularly limited as long as they are derived from non-petroleum resources, and include, for example, plant-based waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal-based waxes such as beeswax, lanolin, and spermaceti; mineral-based waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

[0118] The rubber composition preferably contains sulfur. In the rubber composition for cap treads, the sulfur content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.2 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less. Within the above range, the effect tends to be more favorably obtained.

[0119] The mechanism by which a greater effect is obtained when the sulfur content is compounded in a specified amount or more, particularly 0.5 parts by mass or more per 100 parts by mass of the rubber component, is not clear; however, the rubber with a higher sulfur content tends to harden due to deterioration, and therefore the effect of the ester compound becomes more pronounced.

[0120] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more.

[0121] The rubber composition preferably contains a vulcanization accelerator. In the rubber composition, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization rate and crosslink density, but is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 3.9 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 6.0 parts by mass or less.

[0122] The type of vulcanization accelerator is not particularly limited, and commonly used ones 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, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. Commercially available products include those from Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., etc. 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.

[0123] In addition to the above components, the rubber composition may also contain compounding agents generally used in the tire industry, such as a mold release agent, as appropriate.

[0124] The rubber composition can be produced, for example, by kneading the above components using a rubber kneading device such as an open roll or a Banbury mixer, followed by vulcanization.

[0125] As for kneading conditions, in the base kneading step in which additives other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator are kneaded, the kneading temperature is preferably 100°C or higher, more preferably 120°C or higher, and preferably 180°C or lower, more preferably 170°C. In the finish kneading step in which the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is preferably 80°C or higher, and preferably 120°C or lower, more preferably 110°C or lower. 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 preferably 140°C or higher, more preferably 150°C or higher, and preferably 190°C or lower, more preferably 185°C or lower.

[0126] The rubber composition can be used for tires, shoe soles, flooring materials, vibration-proof materials, seismic isolation materials, butyl frames, belts, hoses, packings, drug stoppers, and other rubber industrial products, etc. In particular, it is preferable to use the rubber composition as a rubber composition for tires, since it can suppress deterioration in tire performance such as wet grip performance after degradation.

[0127] The tire components to which the rubber composition is applied are not particularly limited, and examples thereof include any tire components such as a tread (also called a cap tread), a sidewall, a base tread, a bead apex, a clinch apex, an inner liner, an undertread, a breaker topping, a bright topping, etc. Among these, the rubber composition is preferably applied to a tread because it can suppress deterioration in wet grip performance after degradation.

[0128] <Tires> The rubber composition can be suitably used for tires. Examples of tires include pneumatic tires and non-pneumatic tires, with pneumatic tires being preferred. In particular, the rubber composition can be suitably used as summer tires, winter tires (studless tires, snow tires, studded tires, etc.), all-season tires, etc. Tires can be used for passenger car tires, tires for large passenger cars, tires for large SUVs, heavy-duty tires for trucks, buses, etc., light truck tires, motorcycle tires, racing tires (high-performance tires), etc. In particular, the rubber composition can be suitably used for passenger car tires and light truck tires.

[0129] 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 tire component such as 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.

[0130] In addition to the description of the preferred range in the mode for carrying out the present invention, the same is applicable to each of the examples described below. [Example]

[0131] The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0132] The various chemicals used in the examples and comparative examples are collectively described below. If necessary, the chemicals are purified according to standard methods.

[0133] SBR: SL553R manufactured by JSR Corporation (solution polymerization SBR, styrene content: 10% by mass, vinyl content: 39% by mass) Silica: Evonik Ultrasil VN3 (N2SA: 175 ml 2 / g) Carbon black: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd.2 / g, DBP oil absorption: 115ml / 100g) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant 2: Nocrac 224 (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: NOF Corporation's "Tsubaki" stearic acid Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur (5% oil content) manufactured by Tsurumi Chemical Industry Co., Ltd. Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Polymers 1 to 7: Polymers produced in the following Production Examples 1 to 7

[0134] (Production Example 1) The raw materials are added to a separable flask. The raw materials consist of hydroxyl-terminated liquid butadiene rubber (KASOL LBH P2000 manufactured by Cray Valley, number average molecular weight (Mn) 2000, R in the above general formula 1 The mixture consisted of 52.51 mass% of a compound having hydroxyl groups at both ends of the square brackets (where n=8, x=3, y=0, z=2, and w=0), 52.51 mass% of adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.92 mass% of p-toluenesulfonic acid monohydrate (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.55 mass% of p-methoxyphenol (manufactured by Kanto Chemical Co., Ltd.), and 45.00 mass% of toluene (manufactured by Kishida Chemical Co., Ltd.). The mixture was heated and stirred at 100 to 120°C for 6 hours, and the toluene and water produced by the esterification reaction were removed under reduced pressure while heating to obtain a polymer of Production Example 1. The weight-average molecular weight (Mw) of the resulting polymer of Production Example 1 was 10,000.

[0135] (Production Example 2) A polymer of Production Example 2 was obtained in the same manner as in Production Example 1, except that the raw materials were 51.62 mass% hydroxyl-terminated liquid butadiene rubber, 2.83 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 2 was 28,000.

[0136] (Production Example 3) A polymer of Production Example 3 was obtained in the same manner as in Production Example 1, except that the raw materials were 50.83 mass% hydroxyl-terminated liquid butadiene rubber, 3.62 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 3 was 75,000.

[0137] (Production Example 4) A polymer of Production Example 4 was obtained in the same manner as in Production Example 1, except that the raw materials were 50.85 mass% hydroxyl-terminated liquid butadiene rubber, 3.60 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 4 was 93,000.

[0138] (Production Example 5) A polymer of Production Example 5 was obtained in the same manner as in Production Example 1, except that the raw materials were 50.92 mass% hydroxyl-terminated liquid butadiene rubber, 3.53 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 5 was 110,000.

[0139] (Production Example 6) A polymer of Production Example 6 was obtained in the same manner as in Production Example 1, except that the raw materials were 50.99 mass% hydroxyl-terminated liquid butadiene rubber, 3.46 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 6 was 128,000.

[0140] (Production Example 7) A polymer of Production Example 7 was obtained in the same manner as in Production Example 1, except that the raw materials were 51.09 mass% hydroxyl-terminated liquid butadiene rubber, 3.36 mass% adipic acid, 0.53 mass% p-toluenesulfonic acid monohydrate, 0.02 mass% p-methoxyphenol, and 45.00 mass% toluene. The weight average molecular weight (Mw) of the obtained polymer of Production Example 7 was 160,000.

[0141] According to the formulation shown in Table 1, 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 product. Next, sulfur and vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. Next, the resulting unvulcanized rubber composition was press-vulcanized at 170°C for 20 minutes to obtain a vulcanized rubber sheet.

[0142] The obtained vulcanized rubber sheets (samples) were evaluated based on the following evaluation method for wet grip performance after deterioration. The results are shown in Table 1.

[0143] <Wet grip performance after deterioration> The dynamic friction coefficient of each test sample (vulcanized rubber sheet) was measured under the following test conditions using a portable friction tester (PFT device) manufactured by Hentschel. Ten consecutive measurements were taken for each test sample, and the average value was calculated. The values ​​were then indexed, with the value for Comparative Example 1 set at 100. The larger the index, the better the wet grip performance after aging, and the more effectively the deterioration of wet grip performance after aging was suppressed. (Test conditions) Road condition: Wet Processing temperature: 23℃ Load: 0.24 MPa Traveling speed: 5km / hour

[0144] [Table 1]

[0145] The present invention (1) comprises a rubber component and an ester compound, The ester compound is a rubber composition that is a polymer having a repeating unit represented by the following general formula:

[0146] [ka]

[0147] In the general formula, R 1 represents an optionally substituted vinyl group or an optionally substituted phenyl group; R 2 represents a divalent hydrocarbon group; R 3 represents a divalent hydrocarbon group; n represents an integer of 1 or greater; x, y, z, and w are each any integer of 0 or greater, provided that x+y+z+w≧1, and the combinations of x, y, z, and w for each repeating unit enclosed in square brackets may be the same or different, the repeating units enclosed in round brackets within the square brackets may be bonded in any order, and any other repeating unit may be bonded between each repeating unit.

[0148] The present invention (2) is the rubber composition according to the present invention (1), in which the weight average molecular weight of the repeating unit enclosed in square brackets in the above general formula is 10,000 or less.

[0149] The present invention (3) is the rubber composition according to the present invention (1) or (2), wherein the weight-average molecular weight of the ester compound is 10,000 to 150,000.

[0150] The present invention (4) is a rubber composition in any combination with any of the present inventions (1) to (3), in which the content of the ester compound is 5 to 50 parts by mass per 100 parts by mass of the rubber component.

[0151] The present invention (5) is directed to a rubber composition comprising: The rubber composition is an arbitrary combination with any of the present inventions (1) to (4), in which the content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more.

[0152] The present invention (6) is the rubber composition according to the present invention (5), wherein the styrene content of the styrene-butadiene rubber is 20% by mass or less.

[0153] The present invention (7) is a rubber composition in any combination with any of the present inventions (1) to (6) that satisfy the following formula: Silica content / carbon black content > 1

[0154] The present invention (8) is a rubber composition in any combination with any of the present inventions (1) to (7), wherein the total amount of plasticizers in the rubber composition is 10 parts by mass or less per 100 parts by mass of the rubber component.

[0155] The present invention (9) is a rubber composition comprising: The rubber composition is an arbitrary combination with any of the present inventions (1) to (8), in which the content of sulfur per 100 parts by mass of the rubber component is 0.5 parts by mass or more.

[0156] The present invention (10) is a rubber composition in any combination with any of the present inventions (1) to (9), in which the rubber composition is a rubber composition for tires.

[0157] The present invention (11) is a tire having a tire component made of a rubber composition in any combination with any of the present inventions (1) to (10).

[0158] The present invention (12) is the tire according to the present invention (11), wherein the tire component is a tread.

Claims

1. The rubber composition contains a rubber component and an ester compound. The ester compound is a rubber composition which is a polymer having a repeating unit represented by the following general formula: 【Chemical 1】 (In the general formula, R １ represents an optionally substituted vinyl group or an optionally substituted phenyl group; R ２ represents a divalent hydrocarbon group; R ３ represents a divalent hydrocarbon group; n represents an integer of 1 or more; x, y, z, and w are any integers of 0 or more, provided that x + y + z + w ≧ 1, and the combinations of x, y, z, and w for each repeating unit enclosed in square brackets may be the same or different, the repeating units enclosed in round brackets within the square brackets may be bonded in any order, and any other repeating unit may be bonded between each repeating unit.

2. 2. The rubber composition according to claim 1, wherein the weight average molecular weight of the repeating unit enclosed in square brackets in said general formula is 10,000 or less.

3. The rubber composition according to claim 1 or 2, wherein the weight average molecular weight of the ester compound is 10,000 to 150,000.

4. 3. The rubber composition according to claim 1, wherein the content of the ester compound is 5 to 50 parts by mass based on 100 parts by mass of the rubber component.

5. the rubber component contains styrene-butadiene rubber, 3. The rubber composition according to claim 1, wherein the content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more.

6. The rubber composition according to claim 5, wherein the styrene-butadiene rubber has a styrene content of 20% by mass or less.

7. The rubber composition according to claim 1 or 2, which satisfies the following formula: Silica content / carbon black content>1

8. 3. The rubber composition according to claim 1, wherein the total amount of the plasticizer in the rubber composition is 10 parts by mass or less per 100 parts by mass of the rubber component.

9. The rubber composition contains sulfur, 3. The rubber composition according to claim 1, wherein the amount of sulfur per 100 parts by mass of the rubber component is 0.5 parts by mass or more.

10. 3. The rubber composition according to claim 1, which is a rubber composition for tires.

11. A tire having tire components made of the rubber composition according to claim 1 or 2.

12. 12. The tire of claim 11, wherein the tire component is a tread.

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