Rubber composition for tires and tire

Abstract

To provide a rubber composition for tires that can improve wet braking performance, and a tire.SOLUTION: A rubber composition for tires comprises a rubber component containing styrene-butadiene rubber and butadiene rubber, a filler containing silica, and a liquid polymer, where the content of the styrene-butadiene rubber to the content of the butadiene rubber is ≥2, the content of the filler to 100 pts.mass of the rubber component is more than 100 pts.mass, and the content of the silica to the content of the styrene-butadiene rubber is >1.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Various methods for improving wet braking (wet grip) have been studied so far (for example, see Patent Document 1). However, in recent years, further improvements in wet braking have been required. [Prior art documents] [Patent documents]

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

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

[0005] The present invention relates to a rubber composition for tires, which contains a rubber component containing a styrene-butadiene rubber and a butadiene rubber, a filler containing silica, and a liquid polymer, wherein a content of the styrene-butadiene rubber / a content of the butadiene rubber is ≧2, a content of the filler is more than 100 parts by mass per 100 parts by mass of the rubber component, and a content of the silica / a content of the styrene-butadiene rubber is>1. Effect of the Invention

[0006] The present invention relates to a rubber composition for tires which contains a rubber component containing styrene-butadiene rubber and butadiene rubber, a filler containing silica, and a liquid polymer, wherein the styrene-butadiene rubber content / the butadiene rubber content is ≧2, the filler content is more than 100 parts by mass per 100 parts by mass of the rubber component, and the silica content / the styrene-butadiene rubber content is>1, and therefore the wet braking is good. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The rubber composition for tires of the present invention contains a rubber component containing a styrene-butadiene rubber and a butadiene rubber, a filler containing silica, and a liquid polymer, wherein the ratio of the content of the styrene-butadiene rubber to the content of the butadiene rubber is ≧2, the content of the filler is more than 100 parts by mass per 100 parts by mass of the rubber component, and the ratio of the silica content to the content of the styrene-butadiene rubber is >1.

[0008] The reason why the above-mentioned effects are obtained with the above-mentioned rubber composition is presumed to be as follows. By making the amount of styrene butadiene rubber (SBR) / butadiene rubber (BR) ≧2, fine island phases of BR are formed in a sea phase of SBR. In addition, by making the amount of silica greater than the amount of SBR, the silica that cannot be absorbed into the SBR is distributed to the BR. In addition, since liquid polymers can penetrate into the sea / island phase and between the silica particles, the addition of liquid polymers improves the dispersion of silica. It is believed that the above-mentioned effects improve the heat build-up of the rubber composition and the grip of the rubber composition with the road surface, resulting in good wet braking performance.

[0009] The rubber composition contains a rubber component. Here, the rubber component is a component that contributes to crosslinking, and generally has a weight average molecular weight (Mw) of 10,000 or more.

[0010] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above ranges, the effect tends to be better obtained.

[0011] In this specification, the weight average molecular weight (Mw) can be determined by converting it into standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0012] The total styrene content in the rubber component is preferably 5% by mass or more, more preferably 9% by mass or more, and even more preferably 11% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0013] Here, the total amount of styrene in the rubber component is the total content of styrene parts contained in the total amount of rubber component (unit: mass%), and can be calculated by Σ(content of each rubber component × amount of styrene in each rubber component / 100). For example, in a case where 100% by mass of rubber component contains 85% by mass of SBR with styrene content: 40% by mass, 5% by mass of SBR with styrene content: 25% by mass, and 10% by mass of BR with styrene content: 0% by mass, the total amount of styrene in the rubber component is 35.25% by mass (=85×40 / 100+5×25 / 100+10×0 / 100).

[0014] The total vinyl content in the rubber component is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0015] Here, the total vinyl content in the rubber component is the total content (unit: parts by mass) of vinyl bonds in the butadiene part of SBR and BR contained in the rubber component when the total mass of the rubber component is 100, and can be calculated by Σ (content of each rubber component × ratio of vinyl bond amount in the butadiene part of the rubber component to the total mass of each rubber component [% by mass]). For example, in the case where, in 100 parts by mass of the rubber component, there are 85 parts by mass of SBR with 40% by mass of styrene and 30% by mass of vinyl, 5 parts by mass of SBR with 20% by mass of styrene and 20% by mass of vinyl, and 10 parts by mass of BR with 10% by mass of vinyl, the total vinyl content in the rubber component is 17.1 parts by mass (=85×(100[% by mass]-40[% by mass])×30[% by mass]+5×(100[% by mass]-20[% by mass])×20[% by mass]+10×10[% by mass]).

[0016] The styrene amount and vinyl amount in each rubber component can be measured by a nuclear magnetic resonance (NMR) method. In addition, in the examples of this specification, the total styrene amount and the total vinyl amount in the rubber component are calculated according to the above-mentioned formula, but they may also be analyzed from the tire using, for example, a pyrolysis gas chromatograph mass spectrometer (Py-GC / MS) or the like.

[0017] The rubber composition contains styrene-butadiene rubber (SBR) as a rubber component. The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. Commercially available products include those from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc.

[0018] The styrene content of the SBR is preferably 5% by mass or more, more preferably 12% by mass or more, and even more preferably 16% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0019] The vinyl content of the SBR is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0020] The above-mentioned 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 above-mentioned SBR is the proportion of vinyl bonds when the total mass of the butadiene parts in the SBR is taken as 100 (unit: mass %), and is expressed as vinyl content [mass %] + cis content [mass %] + trans content [mass %] = 100 [mass %]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types, it means the average vinyl content. The average vinyl content of SBR can be calculated by Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%]) × vinyl content of each SBR [mass%]} / Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%])}. For example, in 100 parts by mass of the rubber component, there is 75 parts by mass of SBR with a styrene content of 40 mass% and a vinyl content of 30 mass%, and the styrene content is 25 mass%, Vinyl content: In the case where 20% by mass SBR is 15 parts by mass and the remaining 10 parts by mass is something other than SBR, the average vinyl content of the SBR is 28% by mass (={75 x (100[% by mass] - 40[% by mass]) x 30[% by mass] + 15 x (100[% by mass] - 25[% by mass]) x 20[% by mass])} / {75 x (100[% by mass] - 40[% by mass]) + 15 x (100[% by mass] - 25[% by mass])}.

[0022] As the SBR, hydrogenated SBR to which hydrogen has been added can also be used. When the SBR is hydrogenated SBR, the hydrogenation method and reaction conditions are not particularly limited, and hydrogenation may be performed by a known method and under known conditions. Usually, hydrogenation is performed at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. Other production methods and conditions are also not particularly limited, and for example, the contents described in International Publication No. 2016 / 039005 can be applied. Hydrogenated SBR has the same structure as a copolymer of ethylene, butadiene, and styrene as a result of hydrogen being added to the butadiene portion of SBR. Therefore, in this specification, hydrogenated SBR includes not only hydrogenated products of copolymers of butadiene and styrene (SBR), but also copolymers of ethylene, butadiene, and styrene.

[0023] The hydrogenation rate of the hydrogenated SBR is preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and is preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less, based on 100 mol% of all butadiene units before hydrogenation. When it is within the above range, the effect tends to be more favorably obtained. The hydrogenation rate is 1 It can be calculated from the spectral reduction rate of the unsaturated bond part of the spectrum obtained by measuring H-NMR.

[0024] The SBR may be oil-extended rubber, resin-extended rubber, or other plasticizer-extended rubber. These may be used alone or in combination of two or more. Among them, resin-extended rubber (resin-extended SBR) is preferable. The amount of plasticizer in these extended rubbers is not particularly limited, but is usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids. The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. Other plasticizers include liquid polymers, which will be described later.

[0025] SBR may be modified to introduce a functional group that interacts with fillers such as silica. Examples of the functional group include a silicon-containing group (-SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), an amino group, an amide 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 carboxy group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have a substituent. Among them, a silicon-containing group is preferable, and -SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)) or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R is a hydroxyl group) is more preferable.

[0026] Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, and the like.

[0027] In 100% by mass of the rubber component, the content of SBR is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0028] The rubber composition contains a butadiene rubber (BR) as a rubber component. The BR is not particularly limited, and may be, for example, a BR having a high cis content such as BR1220 manufactured by Zeon Corporation, BR150B manufactured by Ube Industries, Ltd., or BR1280 manufactured by LG Chem, a BR containing 1,2-syndiotactic polybutadiene crystals (SPB) such as VCR412 or VCR617 manufactured by Ube Industries, Ltd., or a butadiene rubber synthesized using a rare earth element catalyst (rare earth-based BR), which are generally used in the tire industry. These may be used alone or in combination of two or more. Among them, rare earth-based BR is preferable.

[0029] As the rare earth element-based catalyst used in the synthesis of the rare earth-based BR, known catalysts can be used, but lanthanum series rare earth element compounds are preferred, and neodymium-containing compounds (Nd-based catalysts) are more preferred.

[0030] The BR may be an oil-extended rubber, a resin-extended rubber, or an extended rubber with other plasticizers. These may be used alone or in combination of two or more. The amount of plasticizer in these extended rubbers is not particularly limited, but is usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids. The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. Other plasticizers include liquid polymers, which will be described later.

[0031] The BR may be modified to introduce a functional group that interacts with a filler such as silica. Examples of the functional group include a silicon-containing group (-SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), an amino group, an amide 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 carboxy group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have a substituent. Among them, a silicon-containing group is preferable, and -SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)) or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R is a hydroxyl group) is more preferable.

[0032] Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, and the like.

[0033] As the BR, hydrogenated BR to which hydrogen has been added can also be used. When the BR is hydrogenated BR, the hydrogenation method and reaction conditions are not particularly limited, and hydrogenation may be performed by a known method and under known conditions. Usually, hydrogenation is performed at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. Other production methods and conditions are also not particularly limited, and for example, the contents described in the above-mentioned International Publication No. 2016 / 039005 can be applied. Note that hydrogenated BR has the same structure as an ethylene-butadiene copolymer as a result of hydrogen being added to the butadiene portion of BR, and therefore, in the present specification, hydrogenated BR includes not only hydrogenated BR but also ethylene-butadiene copolymers.

[0034] The hydrogenation rate of the hydrogenated BR is preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and is preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less, based on 100 mol% of all butadiene units before hydrogenation. When it is within the above range, the effect tends to be more favorable. The hydrogenation rate is 1 It can be calculated from the spectral reduction rate of the unsaturated bond part of the spectrum obtained by measuring H-NMR.

[0035] The cis amount (cis content) of BR is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, and is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. Within the above ranges, the effect tends to be better obtained. The cis content of BR can be measured by infrared absorption spectroscopy.

[0036] The above-mentioned cis amount of BR means the cis amount of the BR when there is one type of BR, and means the average cis amount when there are multiple types of BR. The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)} / total content of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis content of 90% by mass and 10% by mass of BR with a cis content of 40% by mass, the average cis content of BR is 73.3% by mass (=(20×90+10×40) / (20+10)).

[0037] In 100% by mass of the rubber component, the content of BR is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0038] In the above rubber composition, the SBR content / BR content is ≥ 2. The SBR content / BR content is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. In this relationship, the SBR content and the BR content are the contents in 100% by mass of the rubber component (unit: mass %).

[0039] Other rubber components include diene rubbers such as isoprene rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more. Among these, isoprene rubber is preferred.

[0040] Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. Examples of NR include SIR20, RSS♯3, TSR20, and other rubbers that are common in the tire industry. Examples of IR include IR2200 and other rubbers that are common in the tire industry. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and other rubbers. Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more. Among these, NR is preferred.

[0041] In 100% by mass of the rubber component, the content of the isoprene-based rubber 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 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0042] In the above rubber composition, it is preferable that (SBR content+isoprene-based rubber content) / BR content is ≥ 4. (SBR content+isoprene-based rubber content) / BR content is more preferably 5 or more, further preferably 6 or more, and is preferably 12 or less, more preferably 10 or less, further preferably 9 or less. In this relationship, the SBR content, the isoprene-based rubber content, and the BR content are the contents in 100% by mass of the rubber component (unit: mass %).

[0043] In the rubber composition, it is preferable that the isoprene rubber content / BR content≧1. In this case, the ratio of the isoprene rubber content to the BR content is preferably 1.2 or more, more preferably 1.6 or more, and even more preferably 2.0 or more, and is preferably 4.5 or less, more preferably 3.5 or less, and even more preferably 2.5 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the content of the isoprene-based rubber and the content of the BR are the contents in 100% by mass of the rubber component (unit: mass %).

[0044] The rubber components other than SBR, BR, and isoprene-based rubber may be oil-extended rubber, resin-extended rubber, or other plasticizer-extended rubber. These may be used alone or in combination of two or more. The amount of plasticizer in these extended rubbers is not particularly limited, but is usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids. The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. Other plasticizers include liquid polymers, which will be described later.

[0045] Rubber components other than SBR, BR and isoprene-based rubber may be modified to introduce functional groups that interact with fillers such as silica. Examples of the functional group include a silicon-containing group (-SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), an amino group, an amide 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 carboxy group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have a substituent. Among them, a silicon-containing group is preferable, and -SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)) or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R is a hydroxyl group) is more preferable.

[0046] Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, and the like.

[0047] The raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from petroleum or from biomass. Whether the raw materials are derived from biomass can be determined by pMC (percent modern carbon) measured in accordance with ASTM D6866-10.

[0048] pMC stands for modern standard reference carbon. 14 C concentration vs. sample 14 This is the ratio of the carbon concentration to the biomass concentration of the compound (rubber), and this value is used as an index of the biomass ratio of the compound (rubber). The significance of this value is described below.

[0049] 1 mole of carbon atoms (6.02 × 10 23 ) contains approximately 6.02 × 10 atoms, which is about one trillionth of the size of a normal carbon atom. 11 pcs 14 C exists. 14 C is called a radioisotope, and its half-life is 5,730 years, and it decreases regularly. It takes 226,000 years for all of them to decay. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms more than 226,000 years ago, C was also included in these when they were first fixed. 14 All C elements have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas are 14 There is no C element at all. Therefore, chemical substances produced using these fossil fuels as raw materials also 14 It does not contain any C elements.

[0050] on the other hand, 14 The production of C by nuclear reactions and the decrease by radioactive decay are balanced, and in the Earth's atmospheric environment, 14 The amount of C is constant. Therefore, the amount of biomass-derived materials circulating in the current environment is 14 As mentioned above, the C concentration is about 1×10 -12The value is about mol%. Therefore, by using the difference between these values, it is possible to calculate the ratio (biomass ratio) of compounds derived from natural resources (compounds derived from biomass resources) in a certain compound (rubber).

[0051] this 14 C is typically measured as follows: using accelerator mass spectrometry based on a tandem accelerator, 13 C concentration ( 13 C / 12 C). 14 C concentration ( 14 C / 12 C) is measured. 14 The modern standard reference for the C concentration is the carbon circulating in nature in 1950. 14 The specific standard substance used is the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific radioactivity of carbon in this oxalic acid (per gram of carbon) is 14 C) for each carbon isotope, 13 The standard value is the value corrected for decay from 1950 to the measurement date, with C corrected to a constant value. 14 This is used as the C concentration value (100%). The ratio of this value to the value actually measured for the sample is the pMC value.

[0052] Therefore, if rubber is made from 100% biomass (natural) derived materials, it will show a value of approximately 110 pMC, although there may be regional differences (currently, under normal conditions, it is often not 100). On the other hand, for chemical substances derived from petroleum and other fossil fuels, 14 When the C concentration is measured, it will show approximately 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

[0053] For these reasons, it is preferable in terms of environmental protection to use a material such as rubber having a high pMC value, that is, a material such as rubber having a high biomass ratio, in a rubber composition.

[0054] The rubber composition may contain a thermoplastic elastomer as an elastomer other than the rubber component. Thermoplastic elastomers are copolymers (block copolymers) composed of hard segments that act as crosslinking points and soft segments that exhibit rubber elasticity, and are usually solid at room temperature (25°C).

[0055] Examples of the hard segment include polystyrene, polypropylene, polyester, polyamide, polyvinyl chloride, polyurethane, etc., and examples of the soft segment include vinyl-polydiene, polyisoprene, polybutadiene, polyethylene, polychloroprene, poly2,3-dimethylbutadiene, etc. These may be one type or two or more types.

[0056] The thermoplastic elastomer may be used alone or in combination of two or more kinds. Commercially available products include those from Kuraray Co., Ltd., Asahi Kasei Co., Ltd., and the like. In this specification, the thermoplastic elastomer is not included in the rubber component.

[0057] The thermoplastic elastomer is preferably a thermoplastic elastomer having a styrene block (a styrene-based thermoplastic elastomer). Specific examples of styrene-based thermoplastic elastomers include styrene-vinylisoprene-styrene triblock copolymer (SIS), styrene-isobutylene diblock copolymer (SIB), styrene-butadiene-styrene triblock copolymer (SBS), styrene-ethylene-butylene-styrene triblock copolymer (SEBS), styrene-ethylene-propylene-styrene triblock copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene triblock copolymer (SEEPS), and styrene-butadiene-butylene-styrene triblock copolymer (SBBS). These may be used alone or in combination of two or more. Among them, copolymers having styrene blocks at both ends are preferred, and styrene-ethylene-propylene-styrene triblock copolymer (SEPS) is more preferred. The SEPS may be a hydrogenated styrene-vinylisoprene-styrene triblock copolymer (SIS) in which hydrogen has been added.

[0058] The amount of styrene in the styrene-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better obtained.

[0059] The content of the thermoplastic elastomer is preferably 1 to 30 parts by mass based on 100 parts by mass of the rubber component.

[0060] The rubber composition contains silica as a filler. Examples of silica include dry-process silica (silicic anhydride) and wet-process silica (hydrated silicic acid), but wet-process silica is preferred because it has a large number of silanol groups. The raw material for silica may be water glass (sodium silicate) or a biomass material such as rice husk. Commercially available products include those from EVONIK, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Co., Ltd., etc. These may be used alone or in combination of two or more types.

[0061] The average particle size of the silica is preferably 24 nm or less, more preferably 17 nm or less, even more preferably 16 nm or less, and particularly preferably 15 nm or less. From the viewpoint of dispersibility, the lower limit is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0062] In this specification, the average particle size of silica is measured by observation with a transmission electron microscope (TEM). Specifically, silica particles are photographed with a transmission electron microscope, and when the particle shape is spherical, the diameter of the sphere is taken as the particle size, when the particle shape is needle-like or rod-like, the short diameter is taken as the particle size, when the particle shape is irregular, the average particle size from the center is taken as the particle size, and the average value of the particle diameters of 100 fine particles is taken as the average particle size.

[0063] The content of silica is preferably 70 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0064] In the rubber composition, the silica content / SBR content is > 1. The silica content / SBR content is preferably 1.1 or more, more preferably 1.3 or more, and even more preferably 1.5 or more, and is preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 1.9 or less. In this relationship, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the SBR content is the content (unit: % by mass) in 100% by mass of the rubber component.

[0065] In the rubber composition, the silica content / (isoprene rubber content+BR content) is preferably ≥ 1. The silica content / (isoprene rubber content+BR content) is preferably 2.8 or more, more preferably 3.2 or more, even more preferably 3.5 or more, and is preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the isoprene-based rubber content and BR content are the contents (unit: mass%) in 100% by mass of the rubber component.

[0066] In the rubber composition, the silica content / (100-total styrene content in the rubber component) is preferably ≥ 1. The silica content / (100-total styrene content in the rubber component) is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.4 or more, and is preferably 3.5 or less, more preferably 2.5 or less, even more preferably 1.8 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total styrene amount in the rubber component is the content (unit: % by mass) in 100% by mass of the rubber component.

[0067] Examples of fillers other than silica include carbon black, vulcanized rubber particles, clay, alumina, talc, calcium compounds, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, titanium oxide, and short fibers. These may be used alone or in combination of two or more. Among these, aluminum hydroxide, carbon black, and vulcanized rubber particles are preferred.

[0068] In this specification, aluminum hydroxide means Al(OH)3 or Al2O3·3H2O. Commercially available products include those from Sumitomo Chemical Co., Ltd., Showa Denko K.K., Nabaltec, etc. These may be used alone or in combination of two or more.

[0069] The average particle size of the aluminum hydroxide is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.8 μm or more, and is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Within the above ranges, the effect tends to be better. The average particle size of aluminum hydroxide is a value measured in the same manner as the average particle size of silica.

[0070] The BET specific surface area (nitrogen adsorption specific surface area, N2SA) of the aluminum hydroxide is preferably 5 m 2 / g or more, more preferably 8m 2 / g or more, more preferably 10m 2 / g or more, and preferably 40m 2 / g or less, more preferably 30m 2 / g or less, more preferably 20m 2 / g or less. The BET specific surface area of ​​aluminum hydroxide is a value measured by the BET method in accordance with ASTM D3037-81.

[0071] The content of aluminum hydroxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0072] Carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The raw material of carbon black may be a biomass material such as lignin or vegetable oil, or may be obtained by recycling tires. The carbon black may be produced by combustion such as a furnace method, or by hydrothermal carbonization (HTC). Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone, or two or more of them may be used in combination.

[0073] The cetyltrimethylammonium bromide (CTAB) specific surface area of ​​the carbon black is preferably 80 m 2 / g or more, more preferably 110m 2 / g or more, more preferably 140m 2 / g or more, and preferably 200m 2 / g or less, more preferably 180m 2 / g or less, more preferably 160m 2 Within the above range, there is a tendency for the effect to be better obtained. The CTAB specific surface area of ​​carbon black is a value measured in accordance with JIS K6217-3:2001.

[0074] The amount of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, based on 100 parts by mass of the rubber component. When the amount is within the above range, the effect tends to be better obtained.

[0075] In the rubber composition, the silica content / carbon black content is preferably 5 or more, more preferably 10 or more, and even more preferably 15 or more, and is preferably 40 or less, more preferably 30 or less, and even more preferably 25 or less. Within the above ranges, the effect tends to be better obtained. In this regard, the silica content and the carbon black content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

[0076] The vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder or the like specified in JIS K 6316:2017 can be used. From the viewpoint of environmental consideration and cost, recycled rubber powder produced from crushed waste tires or the like is preferable. These may be used alone or in combination of two or more types.

[0077] As commercially available vulcanized rubber particles, products available from Lehigh Corporation, Muraoka Rubber Industry Co., Ltd., etc. In this specification, vulcanized rubber particles are not included in the rubber component.

[0078] The average particle size of the vulcanized rubber particles is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more, and is preferably 1000 μm or less, more preferably 900 μm or less, and even more preferably 800 μm or less. The average particle size of the vulcanized rubber particles is a mass-based average particle size calculated from the particle size distribution measured in accordance with JIS Z 8815:1994.

[0079] The content of the vulcanized rubber particles 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 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0080] The average particle size of the talc is preferably 50 μm or less, more preferably 30 μm or less. The lower limit of the average particle size of the talc is not particularly limited, but is preferably 1 μm or more.

[0081] The content of talc is preferably 1 to 50 parts by mass based on 100 parts by mass of the rubber component.

[0082] The calcium compound is a compound containing calcium, and examples thereof include inorganic salts such as calcium oxide, calcium hydroxide, and calcium carbide; and oxoacid salts such as calcium carbonate, calcium nitrate, and calcium sulfate. The oxoacid salts also include fatty acid salts such as calcium acetate and calcium stearate. In addition, examples of compounds containing calcium compounds include eggshells (main component: calcium carbonate) and WB16 (a mixture of fatty acid calcium, fatty acid amide, and fatty acid amide ester) manufactured by Struktol. These may be used alone or in combination of two or more. Among these, oxoacid salts are preferred, and calcium carbonate is more preferred.

[0083] The content of the calcium compound is preferably 1 to 30 parts by mass based on 100 parts by mass of the rubber component.

[0084] Examples of the short fibers include organic short fibers and inorganic short fibers. Specific examples of the organic short fibers include nanocellulose such as cellulose nanofibers (CNF) and cellulose nanocrystals (CNC); chitin nanofibers; and biomass nanomaterials such as chitosan nanofibers. Specific examples of the inorganic short fibers include metal fibers and glass fibers. Commercially available products include products from Nippon Paper Industries Co., Ltd. and Sugino Machine Co., Ltd. These may be used alone or in combination of two or more. Among them, organic short fibers are preferred, and nanocellulose is more preferred.

[0085] The particle size of nanocellulose is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 25 nm or more, particularly preferably 28 nm or more, and is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 35 nm or less, particularly preferably 32 nm or less. Within the above range, the effect tends to be better obtained.

[0086] The particle size of nanocellulose is the average fiber diameter measured by image analysis using a scanning electron microscope, image analysis using a transmission electron microscope, image analysis using an atomic force microscope, analysis of X-ray scattering data, pore electrical resistance method (Coulter principle method), etc. In this specification, the average fiber diameter of nanocellulose (cellulose fiber) is typically the average fiber diameter of an aggregate of cellulose fibers formed by the aggregation of cellulose molecules.

[0087] The content of the short fibers is preferably 1 to 40 parts by mass based on 100 parts by mass of the rubber component.

[0088] The amount of the filler may be more than 100 parts by mass relative to 100 parts by mass of the rubber component, but is preferably at least 110 parts by mass, more preferably at least 120 parts by mass, and is preferably at most 160 parts by mass, more preferably at most 150 parts by mass, and even more preferably at most 140 parts by mass. Within the above ranges, the effect tends to be better.

[0089] The rubber composition preferably contains a resin as a plasticizer. In this specification, the resin may be either solid or liquid at room temperature (25° C.).

[0090] Examples of the resin that can be used include C5 resins, C9 resins, aromatic resins, terpene resins, cyclopentadiene resins, etc. These may be used alone or in combination of two or more, but it is preferable to use two or more, and it is more preferable to use two types in combination. As the resin, a terpene resin is preferable, and a combination of a terpene resin and a C5 resin is more preferable.

[0091] The C5 resin is a polymer containing a C5 fraction as a constituent monomer, and examples thereof include homopolymers obtained by polymerizing one type of C5 fraction alone, copolymers obtained by copolymerizing two or more types of C5 fractions, and copolymers of a C5 fraction and other monomers that can be copolymerized with the C5 fraction.

[0092] Examples of the C5 fraction include olefinic hydrocarbons such as 1-pentene, 2-pentene, and 2-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, and 1,3-pentadiene. These may be used alone or in combination of two or more.

[0093] Examples of other monomers include C9 fractions such as vinyltoluene, indene, methylindene, etc. These may be used alone or in combination of two or more.

[0094] From the viewpoint of wet braking and the like, the C5 resin is preferably a copolymer of a C5 fraction and a C9 fraction (C5 / C9 resin). In this specification, a polymer containing a C5 fraction and an aromatic monomer (C9 fraction) as constituent monomers, such as a C5 / C9 resin, is treated as a C5 resin, not an aromatic resin or a C9 resin.

[0095] The content of the C5 resin is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, and is preferably 40 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. When the content is within the above range, the effect tends to be better obtained.

[0096] The C9 resin is a polymer containing a C9 fraction as a constituent monomer, and examples thereof include polymers obtained by polymerizing a C9 fraction, which is by-produced together with petrochemical basic raw materials such as ethylene and propylene by thermal decomposition of naphtha in the petrochemical industry, using a Friedel-Crafts catalyst such as AlCl3 or BF3. Specific examples of the C9 fraction include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, indene, etc. The C9 resin may be obtained by copolymerizing a mixture of these C8 to C10 fractions as they are using a Friedel-Crafts catalyst, for example, using a C8 fraction such as styrene, a C10 fraction such as methylindene, 1,3-dimethylstyrene, and further such as naphthalene, vinylnaphthalene, vinylanthracene, and p-tert-butylstyrene, in addition to the C9 fraction, as raw materials. In this specification, the C9 resin is treated as a resin different from the aromatic resin.

[0097] The amount of the C9 resin, relative to 100 parts by mass of the rubber component, is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less.

[0098] An aromatic resin is a polymer containing an aromatic monomer as a constituent monomer, and examples of such a resin include a homopolymer obtained by polymerizing one type of aromatic monomer alone, a copolymer obtained by copolymerizing two or more types of aromatic monomers, and a copolymer of an aromatic monomer and another monomer that can be copolymerized with the aromatic monomer.

[0099] Examples of aromatic monomers include styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, and p-chlorostyrene; phenol monomers such as phenol, alkylphenol, and alkoxyphenol; naphthol monomers such as naphthol, alkylnaphthol, and alkoxynaphthol; coumarone, indene, and the like. These may be used alone or in combination of two or more. Among them, styrene monomers are preferred, and styrene and α-methylstyrene are more preferred.

[0100] Examples of the other monomers include non-conjugated olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, etc. These may be used alone or in combination of two or more.

[0101] From the viewpoint of wet braking, etc., the aromatic resin is preferably an α-methylstyrene resin (an α-methylstyrene homopolymer, a copolymer of styrene and α-methylstyrene, etc.), and more preferably a styrene α-methylstyrene resin (a copolymer of styrene and α-methylstyrene).

[0102] The content of the aromatic resin is preferably 1 part by mass or more, more preferably 6 parts by mass or more, and even more preferably 10 parts by mass or more, and is preferably 25 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0103] Terpene resins are polymers that contain a terpene compound (terpene monomer) as a constituent monomer, and examples of such resins include homopolymers in which one type of terpene compound is polymerized alone, copolymers in which two or more types of terpene compounds are copolymerized, and copolymers of a terpene compound and another monomer that can be copolymerized with the terpene compound.

[0104] Terpene compounds are (C5H8) n The hydrocarbons and their oxygen-containing derivatives represented by the composition 10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpenes (C 20 H 32 ), and examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, γ-terpineol, etc. These may be used alone or in combination of two or more.

[0105] The terpene resin is preferably a homopolymer obtained by polymerizing one kind of terpene compound alone, or a copolymer of a terpene compound and an aromatic monomer. Furthermore, when the terpene resin is a homopolymer formed by polymerizing one type of terpene compound alone, β-pinene is preferred, and when the terpene resin is a copolymer of a terpene compound and an aromatic monomer, a copolymer of a terpene compound and styrene (terpene styrene resin) is preferred. In this specification, a polymer containing a terpene compound and an aromatic monomer as constituent monomers, such as a terpene styrene resin, is treated as a terpene resin rather than an aromatic resin.

[0106] The amount of the terpene resin is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, and is preferably 40 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. When the amount is within the above range, the effect tends to be better obtained.

[0107] The cyclopentadiene-based resin is a polymer containing a cyclopentadiene-based monomer as a constituent monomer, and examples thereof include homopolymers obtained by polymerizing one type of cyclopentadiene-based monomer alone, copolymers obtained by copolymerizing two or more types of cyclopentadiene-based monomers, and copolymers of a cyclopentadiene-based monomer and another monomer that can be copolymerized therewith.

[0108] Examples of cyclopentadiene monomers include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. These may be used alone or in combination of two or more. Among them, dicyclopentadiene is preferred. That is, the cyclopentadiene resin is preferably a polymer (DCPD resin) containing dicyclopentadiene (DCPD) as a constituent monomer, and more preferably a hydrogenated DCPD resin.

[0109] The amount of the cyclopentadiene resin is preferably 1 part by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 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 10 parts by mass or less, based on 100 parts by mass of the rubber component. When the amount is within the above range, the effect tends to be better obtained.

[0110] The resin may be a modified resin into which a functional group has been introduced (functionalized resin). The modified resin can be produced by a known method, for example, a slurry method, a metathesis method, etc. Specifically, for example, the modified resin can be produced by reacting a polymer that becomes the polymer backbone of the modified resin with a functional compound that can introduce a functional group by a known method.

[0111] The polymer that becomes the polymer backbone is not particularly limited, and may be, for example, the above-mentioned C5 resin, aromatic resin, terpene resin, or other resin. These may be used alone or in combination of two or more. Among them, aromatic resins are preferred, α-methylstyrene resins are more preferred, and styrene α-methylstyrene resins (copolymers of styrene and α-methylstyrene) are even more preferred.

[0112] The functional group is preferably a functional group containing at least one element selected from the group consisting of oxygen, silicon, and nitrogen, and more preferably a functional group containing silicon.

[0113] The content of the modified resin is preferably 1 part by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 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 10 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0114] Examples of commercially available 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, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

[0115] The amount of the resin is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, based on 100 parts by mass of the rubber component. When the amount is within the above range, the effect tends to be better obtained.

[0116] In the rubber composition, it is preferable that the resin content / total styrene content in the rubber component is > 1. The resin content / total styrene content in the rubber component is preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 2.5 or more, and is preferably 7.0 or less, more preferably 6.0 or less, and even more preferably 5.0 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the resin content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total styrene amount in the rubber component is the content (unit: % by mass) in 100% by mass of the rubber component.

[0117] In the rubber composition, the resin content / silica content is preferably 0.10 or more, more preferably 0.20 or more, and even more preferably 0.25 or more, and is preferably 0.60 or less, more preferably 0.50 or less, and even more preferably 0.40 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the resin content and the silica content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

[0118] The rubber composition contains a liquid polymer as a plasticizer. The liquid polymer is a (co)polymer that is in a liquid state at room temperature (25° C.), and for example, liquid rubber can be used. As the liquid rubber, at least one (co)polymer selected from the group consisting of butadiene, isoprene, styrene, farnesene, and derivatives thereof can be used. Specific examples include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid farnesene polymer, liquid farnesene-butadiene copolymer, etc. The liquid polymer may be modified or hydrogenated. Commercially available products include those from Cray Valley, Kuraray Co., Ltd., etc. These may be used alone or in combination of two or more. The liquid polymer is preferably a liquid resin, more preferably a liquid C5 resin, and even more preferably a liquid C5 / C9 resin. The C5 resin and C5 / C9 resin are the same as those described above in the explanation of the resin.

[0119] The weight average molecular weight (Mw) of the liquid polymer is preferably 8000 or less, more preferably 6000 or less, and even more preferably 4000 or less, and is preferably 100 or more, more preferably 300 or more, and even more preferably 1000 or more. Within the above ranges, the effect tends to be better obtained. In this specification, the liquid polymer is not included in the rubber component.

[0120] The content of the liquid resin is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, and is preferably 40 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. When the content is within the above range, the effect tends to be better obtained.

[0121] In the rubber composition, the liquid resin content / total styrene content in the rubber component is preferably 0.5 or more, more preferably 0.9 or more, and even more preferably 1.4 or more, and is preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 2.0 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the liquid resin content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total styrene amount in the rubber component is the content (unit: % by mass) in 100% by mass of the rubber component.

[0122] In the rubber composition, the liquid resin content / silica content is preferably 0.05 or more, more preferably 0.12 or more, and even more preferably 0.15 or more, and is preferably 0.35 or less, more preferably 0.25 or less, and even more preferably 0.20 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the liquid resin content and the silica content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

[0123] The content of the liquid polymer is preferably 1 part by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0124] In the rubber composition, the liquid polymer content / total styrene content in the rubber component is preferably 0.5 or more, more preferably 0.9 or more, even more preferably 1.4 or more, and is preferably 2.5 or less, more preferably 2.2 or less, even more preferably 2.0 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the resin component content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total styrene amount in the rubber component is the content (unit: % by mass) in 100% by mass of the rubber component.

[0125] In the rubber composition, the liquid polymer content / silica content is preferably 0.05 or more, more preferably 0.12 or more, and even more preferably 0.15 or more, and is preferably 0.35 or less, more preferably 0.25 or less, and even more preferably 0.20 or less. Within the above ranges, the effect tends to be better obtained. In this relationship, the resin component content and the silica content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

[0126] The rubber composition may contain oil as a plasticizer. Examples of the oil include process oil, vegetable oil, and mixtures thereof. These may be used alone or in combination of two or more. Among them, it is preferable to use vegetable oil.

[0127] As the process oil, for example, paraffin-based process oil, aromatic process oil, naphthene-based process oil, etc. can be used.

[0128] In this specification, examples of vegetable oils include linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, paulownia oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grapeseed oil, and wood wax. In addition, examples of vegetable oils include refined oils (such as salad oils) obtained by refining the above oils, transesterified oils obtained by transesterifying the above oils, hardened oils obtained by hydrogenating the above oils, thermally polymerized oils obtained by thermally polymerizing the above oils, oxidatively polymerized oils obtained by oxidizing the above oils, and waste edible oils obtained by recovering oils that have been used as edible oils or the like. The vegetable oils may be liquid or solid at room temperature (25° C.). These may be used alone or in combination of two or more.

[0129] As the vegetable oil, acylglycerol is preferred, and triacylglycerol is more preferred. In this specification, acylglycerol refers to a compound in which a hydroxyl group of glycerin and a carboxylic acid are ester-bonded. The acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol, or triacylglycerol. Furthermore, the acylglycerol may be a monomer, a dimer, or a polymer of trimer or more. Incidentally, dimer or more acylglycerols can be obtained by thermal polymerization, oxidative polymerization, or the like. Moreover, the acylglycerol may be liquid or solid at room temperature (25°C).

[0130] The method for confirming whether the rubber composition contains the acylglycerol is not particularly limited, but may be any of the following methods: 1For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at room temperature (25°C) for 24 hours, and after removing the rubber composition, 1 When H-NMR was measured, signals were observed at around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm when the signal of tetramethylsilane (TMS) was set at 0.00 ppm, and the signals were presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to oxygen atoms of ester groups. Note that "around" in this paragraph refers to a range of ±0.10 ppm.

[0131] The carboxylic acid is not particularly limited, and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid.

[0132] The amount of the vegetable oil is preferably at least 1 part by mass, more preferably at least 5 parts by mass, and even more preferably at least 10 parts by mass, and is preferably at most 30 parts by mass, more preferably at most 20 parts by mass, and even more preferably at most 15 parts by mass, based on 100 parts by mass of the rubber component. Within the above ranges, the effect tends to be better obtained.

[0133] Commercially available oils that can be used include 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., and Nisshin Oillio Group Co., Ltd.

[0134] 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 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0135] Examples of the other plasticizers include ester-based plasticizers, etc. The other plasticizers may be used alone or in combination of two or more kinds.

[0136] The ester plasticizer is not particularly limited as long as it is a compound having an ester group that is in a liquid state at room temperature (25°C), and examples thereof include phthalic acid derivatives, long-chain fatty acid derivatives, phosphoric acid derivatives, sebacic acid derivatives, adipic acid derivatives, etc. These may be used alone or in combination of two or more. Among them, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives are preferred, and sebacic acid derivatives are more preferred. The phthalic acid derivatives include, but are not limited to, phthalic acid esters such as di-2-ethylhexyl phthalate (DOP) and diisodecyl phthalate (DIDP). The long-chain fatty acid derivatives include, but are not limited to, long-chain fatty acid glycerin esters. The phosphoric acid derivatives include, but are not limited to, phosphoric acid esters such as tris(2-ethylhexyl)phosphate (TOP) and tributyl phosphate (TBP). The sebacic acid derivatives include, but are not limited to, sebacic acid esters such as di(2-ethylhexyl)sebacate (DOS) and diisooctylsebacate (DIOS). The adipic acid derivatives include, but are not limited to, adipic acid esters such as di(2-ethylhexyl)adipate (DOA) and diisooctyladipate (DIOA). Among these, phosphate ester, sebacic acid ester, and adipic acid ester are preferred, and sebacic acid ester is more preferred. Specific examples of the compound include TOP, DOS, and DOA, and DOS is more preferred. As the ester-based plasticizer, for example, products available from Daihachi Chemical Industry Co., Ltd., Taoka Chemical Industry Co., Ltd., etc. can be used.

[0137] The glass transition temperature (Tg) of the ester plasticizer is preferably −110° C. or higher, more preferably −100° C. or higher, even more preferably −80° C. or higher, and is preferably −20° C. or lower, more preferably −40° C. or lower, even more preferably −55° C. or lower. By keeping it within the above range, the above-mentioned effects tend to be more suitably obtained. In this specification, the glass transition temperature is a value measured in accordance with JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan at a heating rate of 10°C / min.

[0138] The content of the ester plasticizer is preferably 1 to 20 parts by mass based on 100 parts by mass of the rubber component.

[0139] The rubber composition preferably contains a silane coupling agent. The silane coupling agent is not particularly limited, and examples thereof include 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, mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; 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. As commercially available products, for example, products from Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Toray Dow Corning Co., Ltd., etc. can be used. These may be used alone or in combination of two or more. Among them, mercapto-based products are preferred.

[0140] As the mercapto-based silane coupling agent, in addition to a compound having a mercapto group, a compound having a structure in which the mercapto group is protected by a protecting group (for example, a compound represented by the following formula (S1)) can also be used.

[0141] Particularly suitable mercapto-based silane coupling agents include silane coupling agents represented by the following formula (S1) and silane coupling agents containing a bond unit A represented by the following formula (I) and a bond unit B represented by the following formula (II). [ka] (In the formula, R 1001 -Cl, -Br, -OR 1006 , -O(O=)CR 1006 , -ON=CR 1006 R 1007 , -NR 1006 R 1007 and-(OSiR 1006 R 1007 ) h (OSiR 1006 R 1007 R 1008 ) a monovalent group (R 1006 , R 1007 and R 1008 may be the same or different, each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4; 1002 is R 1001 , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R 1003 is -[O(R 1009 O) j ]-group(R 1009 is an alkylene group having 1 to 18 carbon atoms, and j is an integer of 1 to 4. 1004 is a divalent hydrocarbon group having 1 to 18 carbon atoms, R 1005 represents a monovalent hydrocarbon group having 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationship: x+y+2z=3, 0≦x≦3, 0≦y≦2, 0≦z≦1. [ka] [ka] (In the formula, v is an integer of 0 or more, and w is an integer of 1 or more. R 11 R represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxy group. 12 R represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. 11 and R 12 may form a ring structure.)

[0142] In formula (S1), R 1005 , R 1006 , R 1007 and R 1008 are each preferably independently selected from the group consisting of a linear, cyclic or branched alkyl group, an alkenyl group, an aryl group and an aralkyl group having 1 to 18 carbon atoms. 1002 When R is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of linear, cyclic or branched alkyl groups, alkenyl groups, aryl groups and aralkyl groups. 1009 R is preferably a linear, cyclic or branched alkylene group, and particularly preferably a linear one. 1004 Examples of R include an alkylene group having 1 to 18 carbon atoms, an alkenylene group having 2 to 18 carbon atoms, a cycloalkylene group having 5 to 18 carbon atoms, a cycloalkylalkylene group having 6 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, and an aralkylene group having 7 to 18 carbon atoms. The alkylene group and the alkenylene group may be either linear or branched, and the cycloalkylene group, the cycloalkylalkylene group, the arylene group, and the aralkylene group may have a functional group such as a lower alkyl group on the ring. This R 1004As the alkylene group, an alkylene group having 1 to 6 carbon atoms is preferable, and a linear alkylene group such as a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, or a hexamethylene group is particularly preferable.

[0143] R in formula (S1) 1002 , R 1005 , R 1006 , R 1007 and R 1008 Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group, and a naphthylmethyl group. R in formula (S1) 1009 Examples of the linear alkylene group include a methylene group, an ethylene group, an n-propylene group, an n-butylene group, and a hexylene group, and examples of the branched alkylene group include an isopropylene group, an isobutylene group, and a 2-methylpropylene group.

[0144] Specific examples of the silane coupling agent represented by formula (S1) include 3-hexanoylthiopropyl triethoxysilane, 3-octanoylthiopropyl triethoxysilane, 3-decanoylthiopropyl triethoxysilane, 3-lauroylthiopropyl triethoxysilane, 2-hexanoylthioethyl triethoxysilane, 2-octanoylthioethyl triethoxysilane, 2-decanoylthioethyl triethoxysilane, 2-lauroylthioethyl triethoxysilane, 3-hexanoylthiopropyl trimethoxysilane, 3-octanoylthiopropyl trimethoxysilane, 3-decanoylthiopropyl trimethoxysilane, 3-lauroylthiopropyl trimethoxysilane, 2-hexanoylthioethyl trimethoxysilane, 2-octanoylthioethyl trimethoxysilane, 2-decanoylthioethyl trimethoxysilane, and 2-lauroylthioethyl trimethoxysilane. These may be used alone or in combination of two or more kinds. Among them, 3-octanoylthiopropyltriethoxysilane is particularly preferable.

[0145] In the silane coupling agent containing the bond unit A represented by formula (I) and the bond unit B represented by formula (II), the content of the bond unit A is preferably 30 mol% or more, more preferably 50 mol% or more, and preferably 99 mol% or less, more preferably 90 mol% or less. The content of the bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and preferably 70 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less. The total content of the bond units A and B is preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 100 mol%. The content of the bond units A and B includes the case where the bond units A and B are located at the terminals of the silane coupling agent. When the bond units A and B are located at the terminals of the silane coupling agent, the form is not particularly limited, and it is sufficient that they form units corresponding to the formulas (I) and (II) representing the bond units A and B.

[0146] R in formula (I) and (II)11 With respect to the above, examples of halogen include chlorine, bromine, and fluorine. Examples of branched or unbranched alkyl groups having 1 to 30 carbon atoms include methyl and ethyl groups. Examples of branched or unbranched alkenyl groups having 2 to 30 carbon atoms include vinyl and 1-propenyl groups. Examples of branched or unbranched alkynyl groups having 2 to 30 carbon atoms include ethynyl and propynyl groups.

[0147] R in formula (I) and (II) 12 Regarding the above, examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms include an ethylene group, a propylene group, etc. Examples of the branched or unbranched alkenylene group having 2 to 30 carbon atoms include a vinylene group, a 1-propenylene group, etc. Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms include an ethynylene group, a propynylene group, etc.

[0148] In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the total number of repetitions (v+w) of the bonding unit A and the bonding unit B is preferably in the range of 3 to 300.

[0149] The content of silane coupling agent is preferably 6 parts by mass or more, more preferably 7 parts by mass or more, even more preferably 8 parts by mass or more, and is preferably 13 parts by mass or less, more preferably 11 parts by mass or less, even more preferably 9 parts by mass or less, based on 100 parts by mass of silica.When it is within the above range, the effect tends to be obtained better.

[0150] The rubber composition may contain a processing aid. Examples of processing aids include metal salts (compounds in which the hydrogen atoms of an acid are replaced with metal ions), fatty acid amides, amide esters, fatty acid esters, etc. These may be used alone or in combination of two or more. Among these, metal salts and fatty acid amides are preferred, and metal salts are more preferred.

[0151] Examples of metals used in the metal salt include alkali metals such as potassium and sodium, and alkaline earth metals such as calcium and barium. Magnesium, zinc, nickel, molybdenum, etc. can also be used. Of these, zinc is preferred.

[0152] Examples of acids used in the metal salt include fatty acids such as lauric acid, myristic acid, palmitic acid, etc. In addition, boric acid, carbonic acid, hydrochloric acid, nitric acid, sulfuric acid, etc. can also be used. Among these, fatty acids are preferred.

[0153] As commercially available processing aids, products from Kishida Chemical Co., Ltd., Kenei Pharmaceutical Co., Ltd., Struktol Co., Ltd., Performance Additives Co., Ltd., etc. can be used.

[0154] The content of the processing aid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0155] The rubber composition may contain an antioxidant. Examples of the antioxidant 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, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples of the antioxidant include p-phenylenediamine antioxidants such as quinolinone; 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. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd. These may be used alone or in combination of two or more.

[0156] The content of the antioxidant is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. Within the above ranges, the effect tends to be better.

[0157] The rubber composition may contain a wax. The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0158] The amount of the wax is preferably 1 part by mass or more, 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, based on 100 parts by mass of the rubber component. Within the above ranges, the effect tends to be better obtained.

[0159] The rubber composition may contain stearic acid. As the stearic acid, a conventionally known one can be used, and as a commercially available product, a product from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Corp., Chiba Fatty Acid Corp., etc. can be used. These may be used alone or in combination of two or more kinds.

[0160] The content of stearic acid is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0161] The rubber composition may contain zinc oxide. As the zinc oxide, a conventionally known one can be used, and as a commercially available product, it is possible to use 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. These may be used alone or in combination of two or more kinds.

[0162] The amount of zinc oxide is preferably 1 part by mass or more, 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, based on 100 parts by mass of the rubber component. Within the above ranges, the effect tends to be better obtained.

[0163] The rubber composition may contain sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are generally used as crosslinking agents in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0164] The amount of sulfur is preferably 0.5 parts by mass or more, more preferably 1.2 parts by mass or more, and even more preferably 1.5 parts by mass or more, and is preferably 3.5 parts by mass or less, more preferably 2.8 parts by mass or less, and even more preferably 2.5 parts by mass or less, based on 100 parts by mass of the rubber component. When the amount is within the above range, the effect tends to be better obtained.

[0165] The rubber composition may contain an organic crosslinking agent. The organic crosslinking agent is not particularly limited, and examples thereof include maleimide compounds, alkylphenol-sulfur chloride condensates, organic peroxides, amine organic sulfides, etc. These may be used alone or in combination of two or more kinds.

[0166] The content of the organic crosslinking agent is preferably 1 to 15 parts by mass based on 100 parts by mass of the rubber component.

[0167] The rubber composition may contain a vulcanization accelerator. Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. Commercially available products include products from Sumitomo Chemical Co., Ltd. and Ouchi Shinko Chemical Co., Ltd. These may be used alone or in combination of two or more.

[0168] The content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better.

[0169] In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides, etc. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0170] The rubber composition 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 mixture.

[0171] As for the kneading conditions, in the base kneading step in which additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish kneading step in which the vulcanizing agent and the vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and the vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

[0172] The rubber composition can be used for tire components (as a rubber composition for tires) such as treads, sidewalls, undertreads, shoulders, clinches, bead apex, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and side reinforcing layers of run-flat tires. In particular, it is suitable for treads. In addition, when the tread has a multi-layer structure, it can be used for both the surface layer (cap tread) and the inner layer (base tread), but is particularly suitable for the cap tread.

[0173] The tire of the present invention is produced by a conventional method using the above rubber composition. That is, the rubber composition is extruded in an unvulcanized state to match the shape of the tread, etc., and molded together with other tire components in a tire building machine by a normal method to form an unvulcanized tire. The unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire.

[0174] The above tires (pneumatic tires, etc.) can be used for passenger car tires; truck and bus tires; motorcycle tires; high-performance tires; winter tires such as studless tires; run-flat tires with side reinforcing layers; tires with sound-absorbing material having a sound-absorbing material such as sponge in the tire cavity; tires with sealing material having a sealant inside or in the tire cavity that can seal in the event of a puncture; tires with electronic components having electronic components such as sensors and wireless tags inside or in the tire cavity, etc., and are suitable for passenger car tires.

[0175] The size of the tire is not particularly limited, and can be appropriately selected, for example, from a tire width in the range of 100 to 400 mm, an aspect ratio in the range of 25 to 85%, and a rim diameter in the range of 10 to 25 inches. Specific examples include 105 / 50R16, 115 / 50R17, 125 / 55R20, 135 / 45R21, 145 / 45R21, 155 / 45R18, 165 / 45R22, 175 / 45R23, 185 / 60R20, 195 / 55R14, 205 / 40R16, 215 / 40R16, 225 / 40R17, 235 / 40R17, 245 / 40R16, 255 / 40R17, 265 / 40R17, 275 / 35R18, 285 / 30R19, and 295 / 45R20.

[0176] It is preferable that the tire outer diameter Dt and the tire section width Wt of the tire satisfy the following relational expression.

number

[0177] Specific examples of tires that can satisfy the above formula include 145 / 60R18, 145 / 60R19, 155 / 55R18, 155 / 55R19, 155 / 70R17, 155 / 70R19, 165 / 55R20, 165 / 55R21, 165 / 60R19, 165 / 65R19, 165 / 70R18, 175 / 55R19, 175 / 55R20, 175 / 55R22, 175 / 60R18, 185 / 55R19, 185 / 60R20, 195 / 50R20, 195 / 55R20, and the like.

[0178] A tire satisfying the above formula is preferably applied to a pneumatic tire for a passenger vehicle, because a pneumatic tire for a passenger vehicle satisfying the above formula tends to be more suitable for solving the problem of the present invention. EXAMPLES

[0179] In the following, examples (embodiments) that are considered to be preferable for carrying out the present invention will be shown, but the scope of the present invention is not limited to the examples.

[0180] The various chemicals used in the examples and comparative examples will be described below.

[0181] (Rubber component) NR:TSR20 BR: Buna CB24 manufactured by LANXESS (BR synthesized using a Nd-based catalyst, cis content: 96% by mass, vinyl content: 0.7% by mass) SBR1: HPR840 manufactured by JSR Corporation (styrene content: 10% by mass, vinyl content: 40% by mass) SBR2: Modified SBR synthesized in Production Example 1 below (styrene content: 33% by mass, vinyl content: 31% by mass) SBR3: Tufuden 3830 manufactured by Asahi Kasei Corporation (styrene content: 33% by mass, vinyl content: 31% by mass, contains 37.5 parts by mass of oil per 100 parts by mass of rubber solids) SBR4: SBR1723 manufactured by JSR Corporation (styrene content: 24% by mass, vinyl content: 17% by mass, contains 37.5 parts by mass of oil per 100 parts by mass of rubber solids) SBR5: Resin-extended SBR synthesized in Production Example 2 below (styrene content: 10% by mass, vinyl content: 38% by mass, containing 10 parts by mass of resin per 100 parts by mass of rubber solids)

[0182] (Chemicals other than rubber components) Carbon black 1: Prototype carbon black (CTAB specific surface area: 160 m 2 / g) Carbon black 2: N134 (CTAB specific surface area: 111 m 2 / g) Vulcanized rubber particles: Lehigh's Ekodyne (rubber powder) Silica 1: Ultrasil VN3 manufactured by Evonik Degussa (average particle size: 17 nm) Silica 2: Ultrasil 9100GR (average particle size: 15 nm) manufactured by Evonik Degussa Aluminum hydroxide: APYRAL 120E manufactured by Nabaltec (average particle size: 0.8 μm, BET specific surface area: 11 m 2 / g) Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Silane coupling agent 2: NXT (3-octanoylthiopropyl) manufactured by Momentive Oil 1: PW-380 manufactured by Idemitsu Kosan Co., Ltd. Oil 2: H&R VIVATEC 500 (aromatic process oil) Resin 1: Sylvatraxx 4150 (β-pinene resin) manufactured by Arizona Chemical Company Resin 2: YS Resin TO125 (Terpene-styrene resin (copolymer of styrene and terpene compounds)) manufactured by Yasuhara Chemical Co., Ltd. Resin 3: Sylvatraxx 4401 (styrene α-methylstyrene resin (copolymer of α-methylstyrene and styrene)) manufactured by Arizona Chemical Company Liquid resin: Cray Valley Ricon 340 (C5 / C9 resin, Mw: 1200) 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 RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Processing aid: ULTRA-FLOW 440 (zinc fatty acid) from Performance Additives Stearic acid: NOF Corporation's "Tsubaki" stearic acid Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccela M (2-mercaptobenzothiazole) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 3: Noccelaer D (N,N'-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0183] (Production Example 1) Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene are charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium is added to initiate polymerization. Polymerization is carried out under adiabatic conditions, with the maximum temperature reaching 85°C. When the polymerization conversion rate reaches 99%, 1,3-butadiene is added, and polymerization is continued for another 5 minutes. Then, a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane (monomer) and oligomer components is added as a modifier to carry out the reaction. After the polymerization reaction is completed, 2,6-di-tert-butyl-p-cresol is added. Next, the solvent is removed by steam stripping, and the mixture is dried with a heated roll adjusted to 110°C to obtain SBR2.

[0184] (Production Example 2) Resin 3 and SBR are added to cyclohexane in a given ratio and stirred at a stirring speed of 400 rpm under nitrogen pressure of 0.4 bar with heating for 2 hours. The resulting solution is dried to obtain resin extended SBR (SBR5).

[0185] Examples and Comparative Examples According to the formulations shown in Tables 1 to 3, materials other than sulfur and vulcanization accelerator are kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product, and the mixture is kneaded for 5 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. Next, the unvulcanized rubber composition is molded into the shape of a cap tread, and is laminated together with other tire components to form an unvulcanized tire. The unvulcanized tire is press-vulcanized at 150° C. for 12 minutes to produce a test tire (size: 175 / 60R18). The test tires thus manufactured were examined, and the results calculated based on the following evaluation methods are shown in Tables 1 to 3.

[0186] In Tables 1 to 3, the rubber content in the oil-extended rubber is listed in the rubber column, and the oil content in the oil-extended rubber is added to the Oil 2 column. The rubber content in the resin-extended rubber is listed in the rubber column, and the resin content in the resin-extended rubber is added to the Resin 3 column.

[0187] In the evaluation methods described below, the evaluation criteria for calculating the index are as follows: Table 1: Comparative Example 2 Table 2: Comparative Example 5 Table 3: Comparative Example 6

[0188] (Wet braking (wet grip)) Each test tire is mounted on a vehicle, and the braking distance from an initial speed of 80km / h on a wet asphalt road surface is measured and expressed as an index with the evaluation standard being 100. The higher the index, the shorter the braking distance and the better the wet braking.

[0189] [Table 1]

[0190] [Table 2]

[0191] [Table 3]

[0192] The present invention (1) comprises a rubber component containing a styrene-butadiene rubber and a butadiene rubber, a filler containing silica, and a liquid polymer, The content of the styrene butadiene rubber / the content of the butadiene rubber is ≧2, The content of the filler per 100 parts by mass of the previous rubber component is more than 100 parts by mass, The rubber composition for tires has a ratio of the silica content to the styrene-butadiene rubber content>1.

[0193] The present invention (2) is the rubber composition for tires according to the present invention (1), which contains aluminum hydroxide.

[0194] The present invention (3) is the rubber composition for tires according to the present invention (1) or (2), wherein the rubber component contains an isoprene-based rubber.

[0195] The present invention (4) is the rubber composition for tires according to the present invention (3), wherein (the content of the styrene-butadiene rubber+the content of the isoprene-based rubber) / the content of the butadiene rubber≧4.

[0196] The present invention (5) is a rubber composition for tires according to any one of the present inventions (1) to (4), which contains a resin.

[0197] The present invention (6) is a rubber composition for tires according to the present invention (5), which contains two or more of the above resins.

[0198] The present invention (7) is the rubber composition for tires according to any one of the present inventions (1) to (6), wherein the silica contains silica having an average particle size of 16 nm or less.

[0199] The present invention (8) is a rubber composition for tires according to any one of the present inventions (1) to (7), which contains a mercapto-based silane coupling agent.

[0200] The present invention (9) is the rubber composition for tires according to any one of the present inventions (1) to (8), wherein the filler contains vulcanized rubber particles.

[0201] The present invention (10) is the rubber composition for tires according to any one of the present inventions (1) to (9), wherein the styrene-butadiene rubber contains a resin-extended styrene-butadiene rubber.

[0202] The present invention (11) is a tire having a tread using the rubber composition according to any one of the present inventions (1) to (10).

Claims

1. The rubber composition contains a rubber component including a styrene butadiene rubber and a butadiene rubber, a filler including silica, and a liquid polymer, The content of the styrene butadiene rubber / the content of the butadiene rubber is ≧2, The content of the filler per 100 parts by mass of the rubber component is more than 100 parts by mass, The rubber composition for tires, wherein the silica content / the styrene-butadiene rubber content>1.

2. The rubber composition for tires according to claim 1, which contains aluminum hydroxide.

3. 3. The rubber composition for tires according to claim 1, wherein the rubber component contains an isoprene-based rubber.

4. 4. The rubber composition for tires according to claim 3, wherein (the content of said styrene-butadiene rubber+the content of said isoprene-based rubber) / the content of said butadiene rubber≧4.

5. The rubber composition for tires according to claim 1 or 2, which contains a resin.

6. The rubber composition for tires according to claim 5, comprising two or more of the resins.

7. 3. The rubber composition for tires according to claim 1, wherein the silica contains silica having an average particle size of 16 nm or less.

8. 3. The rubber composition for tires according to claim 1, further comprising a mercapto-based silane coupling agent.

9. 3. The rubber composition for tires according to claim 1, wherein the filler comprises vulcanized rubber particles.

10. 3. The rubber composition for tires according to claim 1, wherein the styrene-butadiene rubber comprises a resin-extended styrene-butadiene rubber.

11. A tire having a tread using the rubber composition according to claim 1 or 2.

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