Rubber composition for crawler and rubber crawler

Abstract

To provide a rubber composition for crawlers that can improve crack resistance under high-temperature conditions, and to provide a crawler.SOLUTION: A rubber composition for crawlers contains a rubber component containing an isoprene rubber and a styrene-butadiene rubber, and carbon black, with a carbon black content / a styrene-butadiene rubber content>2.0, and a polymer amount×styrene-butadiene rubber content in the rubber component>an acetone extraction amount.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a rubber composition for a crawler and a rubber crawler.

Background Art

[0002] Various methods for improving the durability of rubber crawlers have been studied (see, for example, Patent Document 1). However, in recent years, further improvement in durability has been demanded.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a rubber composition for a crawler and a rubber crawler that solve the above problems and can improve crack resistance performance under high temperature conditions.

Means for Solving the Problems

[0005] The present disclosure relates to a rubber composition for a crawler containing a rubber component including an isoprene rubber and a styrene-butadiene rubber, and carbon black, wherein the content of the carbon black / the content of the styrene-butadiene rubber > 2.0, and the polymer amount × the content of the styrene-butadiene rubber in the rubber component > the acetone extraction amount.

Effects of the Invention

[0006] This disclosure provides a rubber composition for crawlers containing isoprene rubber and styrene-butadiene rubber, and carbon black, wherein the carbon black content / styrene-butadiene rubber content > 2.0, and the polymer amount × styrene-butadiene rubber content in the rubber component > acetone extraction amount. As such, the main body exhibits good crack resistance under high-temperature conditions. [Modes for carrying out the invention]

[0007] The crawler rubber composition of this disclosure contains a rubber component comprising isoprene rubber and styrene-butadiene rubber, and carbon black, wherein the carbon black content / styrene-butadiene rubber content > 2.0, and the polymer amount × styrene-butadiene rubber content in the rubber component > acetone extraction amount.

[0008] The reason why the above rubber composition produces the aforementioned effects is presumed to be as follows. The presence of isoprene-based rubber and styrene-butadiene rubber in the rubber components is thought to create an interface between these rubber phases, as well as micro-domains formed by the styrene portion of the styrene-butadiene rubber. Since each molecular chain, including the styrene portion, exhibits high mobility at high temperatures, it is thought that it absorbs external inputs within the molecule and also facilitates input absorption at the interface. Furthermore, by ensuring a sufficiently large amount of carbon black compared to the styrene-butadiene rubber, it is thought that the interfaces between each rubber phase will be more easily reinforced by the carbon black. On the other hand, by using a higher proportion of styrene-butadiene rubber than acetone-extracted components such as plasticizers, excessive softening of each rubber phase can be suppressed, allowing each rubber phase and interface to absorb external inputs while providing sufficient reinforcement at the interface. The above effects are thought to result in improved crack resistance under high-temperature conditions.

[0009] In the above rubber composition, the amount of acetone extract (AE) is preferably 4% by mass or more, more preferably 6% by mass or more, even more preferably 8% by mass or more, and also preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the amount is within the above range, a better effect tends to be obtained.

[0010] In the above rubber composition, the polymer content (PC) is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and also preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. When the content is within the above range, the effect tends to be better obtained.

[0011] In the above rubber composition, the amount of carbon black (BC) is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and also preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the amount is within the above range, the effect tends to be better obtained.

[0012] In the above rubber composition, the ash content is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and also preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. When the ash content is within the above range, the effect tends to be better.

[0013] The acetone extract amount (AE), polymer amount (PC), carbon black amount (BC), and ash amount (Ash) are measured by the following methods. First, the amount of acetone extracted (AE) is measured for the above rubber composition (sample) according to the acetone extraction method in accordance with JIS K 6229:2015 (unit: mass %) of the above rubber composition (sample). The polymer content (PC) is calculated from the amount of weight lost (by mass) when the organic matter in the sample remaining after the acetone extraction is thermally decomposed and vaporized by heating in nitrogen (raising the temperature from room temperature to 750°C), in accordance with JIS K6226-1:2003 (unit: mass %) of the above rubber composition (sample). The amount of carbon black (BC) is calculated from the amount of weight (mass) lost when the sample, after the above thermal decomposition and vaporization, is oxidized and burned by heating in air (unit: mass %) of the above rubber composition (sample). The ash content is calculated from the mass of components (ash) that do not burn in the above-mentioned oxidative combustion (unit: mass %) of the above-mentioned rubber composition (sample). Based on the above definitions, the sum of AE, PC, BC, and Ash is 100% by mass.

[0014] Methods known to those skilled in the art can be used to adjust AE, PC, BC, and Ash. For example, AE tends to increase as the amount of plasticizers such as oil in the rubber composition increases. PC tends to increase as the amount of rubber components in the rubber composition increases. BC tends to increase as the amount of carbon black in the rubber composition increases. Ash tends to increase as the amount of components that do not burn by oxidative combustion, such as silica, in the rubber composition increases.

[0015] The above rubber composition contains rubber components. 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.

[0016] The weight-average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and also preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within this range, a better effect tends to be obtained.

[0017] In this specification, the weight-average molecular weight (Mw) can be determined by converting the measured values ​​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) to standard polystyrene equivalents.

[0018] The total styrene content in the rubber component is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, and also preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably less than 8% by mass. Within the above range, it is thought that microscopic styrene domains are more easily formed within the rubber layer, making it easier to absorb external inputs.

[0019] Here, the total amount of styrene in the rubber component is the total amount of styrene contained in the entire rubber component (unit: mass%), and can be calculated using the formula Σ(content of each rubber component × amount of styrene in each rubber component / 100). For example, if 85 mass% of SBR with a styrene content of 40 mass% is out of 100 mass% of the rubber component, 5 mass% of SBR with a styrene content of 25 mass% is out of 5 mass%, and 10 mass% of BR with a styrene content of 0 mass%, then the total amount of styrene in the rubber component is 35.25 mass% (= 85 × 40 / 100 + 5 × 25 / 100 + 10 × 0 / 100).

[0020] The total vinyl content in the rubber component is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and also preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. Within the above range, a better effect tends to be obtained.

[0021] Here, the total amount of vinyl in the rubber component is the total amount of vinyl bonds in the butadiene portion of SBR and BR contained in the rubber component (unit: parts by mass), when the total mass of the rubber component is set to 100, and can be calculated as Σ(content of each rubber component × ratio of the amount of vinyl bonds in the butadiene portion of the rubber component to the total mass of each rubber component [mass%]). For example, if in 100 parts by mass of rubber component, there are 85 parts by mass of SBR with a styrene content of 40% by mass and a vinyl content of 30% by mass, 5 parts by mass of SBR with a styrene content of 20% by mass and a vinyl content of 20% by mass, and 10 parts by mass of BR with a vinyl content of 10% by mass, then the total amount of vinyl in the rubber component is 17.1 parts by mass (= 85 × (100 [mass%] - 40 [mass%]) × 30 [mass%] + 5 × (100 [mass%] - 20 [mass%]) × 20 [mass%] + 10 × 10 [mass%]).

[0022] The amounts of styrene and vinyl in each rubber component can be measured by nuclear magnetic resonance (NMR) spectroscopy. Furthermore, while the total amount of styrene and vinyl in the rubber component is calculated in accordance with the above-described formula in the examples of this specification, it may also be analyzed from the crawler using, for example, a pyrolysis gas chromatograph-mass spectrometer (Py-GC / MS).

[0023] The above rubber composition contains isoprene-based rubber as a rubber component. Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. For NR, for example, SIR20, RSS#3, TSR20, etc., which are commonly used in the manufacture of rubber tracks, can be used. For IR, there are no particular limitations, and for example, IR2200, etc., which are commonly used in the manufacture of rubber tracks, can be used. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). 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 individually or in combination of two or more. Among these, NR is preferred.

[0024] The isoprene-based rubber content in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and also preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Within the above range, it is easier to form a phase structure within the rubber matrix and easier to obtain high strength due to the isoprene-based rubber.

[0025] The above rubber composition contains styrene-butadiene rubber (SBR) as a rubber component. SBR is not particularly limited; for example, emulsion polymerized styrene-butadiene rubber (E-SBR) and solution polymerized styrene-butadiene rubber (S-SBR) can be used. Commercially available products include those from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Corporation.

[0026] SBR may be oil-stretched rubber or resin-stretched rubber. These may be used individually or in combination of two or more types. The oil used in oil-extracted rubber and the resin used in resin-extracted rubber are the same as those described later. Furthermore, the oil content in oil-extracted rubber and the resin content in resin-extracted rubber are not particularly limited, but are typically around 5 to 50 parts by mass per 100 parts by mass of rubber solids.

[0027] SBR may have functional groups that interact with fillers such as silica introduced through modification. Examples of the above functional groups include silicon-containing groups (-SiR3 (where R is the same or different and can be hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, etc. These functional groups may have substituents. Among these, silicon-containing groups are preferred, and -SiR3 (where R is the same or different and can be 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)), with at least one of R being a hydroxyl group) is more preferred.

[0028] Specific examples of compounds (modifiers) that introduce the above functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

[0029] Hydrogenated SBRs, which have hydrogen added to them, can also be used as SBRs. When SBR is hydrogenated SBR, there are no particular limitations on the hydrogenation method or reaction conditions; hydrogenation can be carried out using known methods and conditions. Typically, this is done at 20-150°C, under a hydrogen pressure of 0.1-10 MPa, and in the presence of a hydrogenation catalyst. Other manufacturing methods and conditions are also not particularly limited; for example, the contents described in International Publication No. 2016 / 039005 can be applied. Furthermore, 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 butadiene-styrene copolymers (SBR) but also copolymers of ethylene, butadiene, and styrene.

[0030] The hydrogenation rate of hydrogenated SBR is preferably 65 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, with the total butadiene units before hydrogenation being 100 mol%, and also preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less. Within the above range, better effects tend to be obtained. The hydrogenation rate is 1 It can be calculated from the spectral reduction rate of the unsaturated bond region of the spectrum obtained by measuring 1H-NMR.

[0031] The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and also preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. Within the above range, it is thought that domains formed by the styrene portion are more easily formed in the rubber phase, improving durability at high temperatures.

[0032] The vinyl content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and also preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0033] The styrene content of SBR mentioned above refers to the styrene content of a single type of SBR if that type is used, and to the average styrene content if there are multiple types of SBR. The average styrene content of SBR can be calculated using the formula {Σ(content of each SBR × styrene content of each SBR)} / total content of all SBR. For example, if 85% of the rubber component is SBR with a styrene content of 40% by mass and 5% is SBR with a styrene content of 25% by mass, the average styrene content of the SBR is 39.2% by mass (=(85 × 40 + 5 × 25) / (85 + 5)).

[0034] Furthermore, the vinyl content of SBR mentioned above is the ratio of vinyl bonds when the total mass of the butadiene portion in the SBR is set to 100 (unit: mass%), and is calculated as: vinyl content [mass%] + cis content [mass%] + trans content [mass%] = 100 [mass%]. If there is only one type of SBR, it refers to the vinyl content of that SBR; if there are multiple types, it refers to the average vinyl content. The average vinyl content of SBR can be calculated using the formula: 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, if 100 parts by mass of rubber component, 75 parts by mass of SBR contain 40% styrene and 30% vinyl, and 25% styrene, If 15 parts by mass of SBR have a vinyl content of 20% by mass, and the remaining 10 parts by mass are other than SBR, the average vinyl content of SBR is 28% by mass (= {75 × (100 [mass%] - 40 [mass%]) × 30 [mass%] + 15 × (100 [mass%] - 25 [mass%]) × 20 [mass%])} / {75 × (100 [mass%] - 40 [mass%]) + 15 × (100 [mass%] - 25 [mass%])}.

[0035] The SBR content in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and also preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Within the above range, it is thought that a phase structure can be easily formed within the rubber matrix, improving durability at high temperatures.

[0036] In the above rubber composition, the PC×SBR content is >AE. The value of (left side) / (right side) is preferably 1.1 or greater, more preferably 1.3 or greater, even more preferably 1.5 or greater, and also preferably 2.6 or less, more preferably 2.1 or less, and even more preferably 1.6 or less. When the value is within the above range, a better effect tends to be obtained. In this relationship, PC and AE are values ​​measured by the method described above (unit: mass%), and the SBR content is the value obtained by dividing the content in 100% by mass of rubber components (unit: mass%) by 100.

[0037] The above rubber composition preferably contains butadiene rubber (BR) as a rubber component. The type of rubber (BR) used is not particularly limited. For example, high-cis content BRs such as BR1220 from Nippon Zeon Co., Ltd., BR150B from Ube Industries, Ltd., and BR1280 from LG Chem, BRs containing 1,2-syndiotactic polybutadiene crystals (SPBs) such as VCR412 and VCR617 from Ube Industries, Ltd., and butadiene rubber synthesized using rare earth element catalysts (rare earth BRs) can be used. These can be used individually or in combination of two or more types.

[0038] BR may be oil-stretched rubber or resin-stretched rubber. These may be used individually or in combination of two or more types. The oil used in oil-extracted rubber and the resin used in resin-extracted rubber are the same as those described later. Furthermore, the oil content in oil-extracted rubber and the resin content in resin-extracted rubber are not particularly limited, but are typically around 5 to 50 parts by mass per 100 parts by mass of rubber solids.

[0039] BR may have functional groups that interact with packing materials such as silica introduced through modification. Examples of the above functional groups include silicon-containing groups (-SiR3 (where R is the same or different and can be hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, etc. These functional groups may have substituents. Among these, silicon-containing groups are preferred, and -SiR3 (where R is the same or different and can be 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)), with at least one of R being a hydroxyl group) is more preferred.

[0040] Specific examples of compounds (modifiers) that introduce the above functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

[0041] For BR, hydrogenated BR, which has hydrogen added to it, can also be used. When BR is hydrogenated BR, there are no particular limitations on the hydrogenation method or reaction conditions; hydrogenation can be carried out using known methods and conditions. Typically, this is done at 20-150°C, under a hydrogen pressure of 0.1-10 MPa, and in the presence of a hydrogenation catalyst. Other manufacturing methods and conditions are also not particularly limited; for example, the contents described in International Publication No. 2016 / 039005 can be applied. Furthermore, hydrogenated BR has the same structure as an ethylene-butadiene copolymer as a result of hydrogen being added to the butadiene portion of BR. Therefore, in this specification, hydrogenated BR includes not only hydrogenated BR but also an ethylene-butadiene copolymer.

[0042] The hydrogenation rate of hydrogenated BR is preferably 65 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, with the total butadiene units before hydrogenation being 100 mol%, and also preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less. When the rate is within the above range, better effects tend to be obtained. The hydrogenation rate is 1 It can be calculated from the spectral reduction rate of the unsaturated bond region of the spectrum obtained by measuring 1H-NMR.

[0043] The cis content of BR is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and also preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. When it is within the above range, the effect tends to be better obtained. The cis amount of BR can be measured by infrared absorption spectroscopy.

[0044] The cis amount of BR mentioned above refers to the cis amount of a single type of BR if there is only one type, and to the average cis amount if there are multiple types. The average cis content of BR can be calculated using the formula {Σ(content of each BR × cis content of each BR)} / total BR content. For example, if 20% of BR has a cis content of 90% and 10% has a cis content of 40% out of 100% of rubber components, the average cis content of BR is 73.3% (=(20 × 90 + 10 × 40) / (20 + 10)).

[0045] The BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and also preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0046] Other rubber components include diene rubbers such as acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used individually or in combination of two or more.

[0047] Other rubber components may include oil-stretched rubber or resin-stretched rubber. These may be used individually or in combination of two or more types. The oil used in oil-extracted rubber and the resin used in resin-extracted rubber are the same as those described later. Furthermore, the oil content in oil-extracted rubber and the resin content in resin-extracted rubber are not particularly limited, but are typically around 5 to 50 parts by mass per 100 parts by mass of rubber solids.

[0048] Other rubber components may be modified to introduce functional groups that interact with fillers such as silica. Examples of the above functional groups include silicon-containing groups (-SiR3 (where R is the same or different and can be hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, etc. These functional groups may have substituents. Among these, silicon-containing groups are preferred, and -SiR3 (where R is the same or different and can be 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)), with at least one of R being a hydroxyl group) is more preferred.

[0049] Specific examples of compounds (modifiers) that introduce the above functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

[0050] The raw materials (monomers) for synthetic rubbers such as SBR and BR may be derived from petroleum or biomass. Whether the raw materials are biomass-derived can be determined by measuring pMC (percent Modern Carbon) in accordance with ASTMD6866-10.

[0051] pMC stands for Modern Standard Reference Carbon. 14 Sample relative to C concentration 14It is the ratio of the C concentration, and this value is used as an index indicating the biomass ratio of the compound (rubber). The significance of this value will be described below.

[0052] In one mole (6.02×10 23 atoms) of carbon atoms, there are approximately 6.02×10 11 which is about one trillionth of ordinary carbon atoms. 14 C atoms exist. 14 14C is called a radioactive isotope, and its half-life is 5730 years and it decreases regularly. It takes 226,000 years for all of these to decay. Therefore, after carbon dioxide in the atmosphere and the like are taken up and fixed by plants and the like, in fossil fuels such as coal, oil, and natural gas where more than 226,000 years are considered to have passed, all of the 14 14C element has decayed. Therefore, at present in the 21st century, fossil fuels such as coal, oil, and natural gas do not contain 14 14C element at all. Therefore, chemical substances produced from these fossil fuels also do not contain 14 14C element at all. ​​​​​​​​​​​​​​​​​​​​​​​​​​​12 Perform measurement C). In the measurement, 14 As a modern standard reference for the concentration of C, the amount of cyclic carbon in nature as of 1950 14 The C concentration will be used. The specific standard material will be 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) will be used. 14 The radioactivity intensity of C is separated by carbon isotope, 13 The standard value is obtained by correcting C to a constant value and applying decay correction from 1950 AD to the measurement date. 14 This value is used as the C concentration value (100%). The ratio of this value to the value of the sample actually measured is the pMC value.

[0055] Therefore, if rubber is made from 100% biomass (natural) materials, it will have a value of approximately 110 pMC, although there are regional differences (currently, under normal conditions, it is often not 100). On the other hand, regarding chemical substances derived from fossil fuels such as petroleum, 14 When the C concentration is measured, it will show approximately 0 pMC (for example, 0.3 pMC). This value corresponds to a biomass ratio of 0% as mentioned above.

[0056] Based on the above, using materials such as rubber with a high pMC value, that is, materials such as rubber with a high biomass ratio, in rubber compositions is preferable from an environmental protection standpoint.

[0057] The above rubber composition may also 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).

[0058] Examples of hard segments include polystyrene, polypropylene, polyester, polyamide, polyvinyl chloride, and polyurethane, while examples of soft segments include vinyl-polydiene, polyisoprene, polybutadiene, polyethylene, polychloroprene, and poly2,3-dimethylbutadiene. These may be one type or two or more types.

[0059] Thermoplastic elastomers may be used alone or in combination of two or more types. Commercially available products include those from Kuraray Co., Ltd., Asahi Kasei Corporation, and others. In this specification, thermoplastic elastomers are not included in the rubber component.

[0060] The thermoplastic elastomer is preferably a thermoplastic elastomer having a styrene block (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 individually or in combination of two or more. Among these, copolymers having styrene blocks at both ends are preferred, and styrene-ethylene-propylene-styrene triblock copolymer (SEPS) is more preferred. Furthermore, SEPS may also be hydrogenated SIS obtained by adding hydrogen to styrene-vinylisoprene-styrene triblock copolymer (SIS).

[0061] The styrene content of the styrene-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and also 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 range, better effects tend to be obtained.

[0062] The thermoplastic elastomer content is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component.

[0063] The above rubber composition contains carbon black. The carbon black used is not particularly limited and includes N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. The raw materials for carbon black may be biomass materials such as lignin and vegetable oil, or they may be obtained by recycling tires. The manufacturing method for carbon black may be combustion such as the furnace process, or 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-Nippon Chemical Carbon Co., Ltd., and Columbia Carbon Corporation. These may be used individually or in combination of two or more types.

[0064] The specific surface area of ​​cetyltrimethylammonium bromide (CTAB) in carbon black is preferably 100 m². 2 / g or more, comfortably within 110m 2 / g or more, more preferably 130m 2 It is 180m or more / g, and preferably 180m 2 / g or less, more preferably 170m 2 / g or less, more preferably 160m 2 It is less than or equal to / g. Within the above range, there is a tendency for better results to be obtained. The CTAB specific surface area of ​​carbon black is measured according to JIS K6217-3:2001.

[0065] The carbon black content is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more, per 100 parts by mass of rubber component, and also preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less. Within the above range, the interface between rubber phases is more easily reinforced, and it is believed that durability at high temperatures is improved.

[0066] In the above rubber composition, the ratio of carbon black content to SBR content is > 2.0. The value on the left side is preferably 2.1 or higher, more preferably 2.2 or higher, even more preferably 2.3 or higher, and also preferably 2.7 or lower, more preferably 2.6 or lower, and even more preferably 2.5 or lower. When the value is within the above range, a better effect tends to be obtained. In this relationship, the carbon black content is expressed as the content per 100 parts by mass of the rubber component (unit: parts by mass), and the SBR content is expressed as the content in 100% by mass of the rubber component (unit: mass%).

[0067] The above rubber composition preferably contains silica. Examples of silica include dry-process silica (anhydrous silicic acid) and wet-process silica (hydrated silicic acid), but wet-process silica is preferred because it contains a large number of silanol groups. The raw material for silica may be water glass (sodium silicate) or biomass material such as rice husks. Commercially available products include those from Evonik Degussa, Tosoh Silica Co., Ltd., Solvay Japan Ltd., and Tokuyama Corporation. These may be used individually or in combination of two or more types.

[0068] The average particle size of silica is preferably 20 nm or less, more preferably 19 nm or less, even more preferably 17 nm or less, and preferably 9 nm or more, more preferably 11 nm or more, and even more preferably 13 nm or more. Within this range, better effects tend to be obtained.

[0069] In this specification, the method for measuring the average particle diameter of silica is transmission electron microscopy (TEM) observation. Specifically, silica particles are photographed with a transmission electron microscope, and if the particle shape is spherical, the diameter of the sphere is defined as the particle diameter; if it is needle-shaped or rod-shaped, the shorter axis is defined as the particle diameter; if it is irregularly shaped, the average particle diameter from the center is defined as the particle diameter; and the average value of the particle diameters of 100 fine particles is defined as the average particle diameter.

[0070] The silica content is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the rubber component, and also 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. Because the rubber is more easily stretched, it is thought that it will absorb external inputs while also gaining sufficient strength against deformation.

[0071] In the above rubber composition, the silica content / SBR content is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and also preferably 1.0 or less, more preferably 0.7 or less, and even more preferably 0.4 or less. Within the above range, it is thought that silica can suppress excessive restraint of the rubber component, making it easier to obtain the effect of absorbing external inputs within the rubber phase and at the interface. In this relationship, the silica content is the content per 100 parts by mass of the rubber component (unit: parts by mass), and the SBR content is the content in 100% by mass of the rubber component (unit: mass%).

[0072] The above rubber composition may contain a silane coupling agent. The silane coupling agent is not particularly limited and includes, for example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-trimethoxysilylbutyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl Examples include sulfide-based compounds such as ropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; 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. Commercially available products include those from companies such as Evonik Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Toray Dow Corning Co., Ltd. These can be used individually or in combination of two or more types.

[0073] In addition to compounds containing a mercapto group, compounds in which the mercapto group is protected by a protecting group (for example, compounds represented by the following formula (S1)) can also be used as mercapto-silane coupling agents.

[0074] Particularly suitable mercapto-silane coupling agents include silane coupling agents represented by the following formula (S1), and silane coupling agents containing a bonding unit A shown in the following formula (I) and a bonding unit B shown in 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) selected from ) 1006 , R 1007 and R 1008 They may be the same or different, and each is a hydrogen atom or a monovalent hydrocarbon group with 1 to 18 carbon atoms, and the average value of h is 1 to 4. 1002 is R 1001 , hydrogen atom or monovalent hydrocarbon group having 1 to 18 carbon atoms, R 1003 is -[O(R 1009 O) j ]-group(R 1009 is an alkylene group with 1 to 18 carbon atoms, and j is an integer from 1 to 4. ), R 1004 R is a divalent hydrocarbon group having 1 to 18 carbon atoms. 1005 (where represents a monovalent hydrocarbon group with 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationships x + y + 2z = 3, 0 ≤ x ≤ 3, 0 ≤ y ≤ 2, and 0 ≤ z ≤ 1.) [ka] [ka] (In the formula, v is a non-negative integer and w is a non-negative integer. 11 R represents hydrogen, halogen, branched or unbranched C1-C30 alkyl group, branched or unbranched C2-C30 alkenyl group, branched or unbranched C2-C30 alkynyl group, or an alkyl group in which the terminal hydrogen is substituted with a hydroxyl group or a carboxyl 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 (They may form a ring structure.)

[0075] In equation (S1), R 1005 , R 1006 , R 1007 and R 1008 Each of these is preferably independently selected from the group consisting of linear, cyclic, or branched alkyl groups, alkenyl groups, aryl groups, and aralkyl groups having 1 to 18 carbon atoms. 1002 If 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 The alkylene group is preferably linear, cyclic, or branched, and is particularly preferred to be linear. 1004 Examples of these include alkylene groups having 1 to 18 carbon atoms, alkenylene groups having 2 to 18 carbon atoms, cycloalkylene groups having 5 to 18 carbon atoms, cycloalkylalkylene groups having 6 to 18 carbon atoms, arylene groups having 6 to 18 carbon atoms, and aralkylene groups having 7 to 18 carbon atoms. The alkylene groups and alkenylene groups may be linear or branched, and the cycloalkylene groups, cycloalkylalkylene groups, arylene groups, and aralkylene groups may have functional groups such as lower alkyl groups on their rings. 1004Preferably, the alkylene group has 1 to 6 carbon atoms, and in particular, linear alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, and hexamethylene groups are preferred.

[0076] R in equation (S1) 1002 , R 1005 , R 1006 , R 1007 and R 1008 Specific examples include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, octyl group, decyl group, dodecyl group, cyclopentyl group, cyclohexyl group, vinyl group, propenyl group, allyl group, hexenyl group, octenyl group, cyclopentenyl group, cyclohexenyl group, phenyl group, tolyl group, xylyl group, naphthyl group, benzyl group, phenethyl group, naphthylmethyl group, and the like. R in equation (S1) 1009 Examples of linear alkylene groups include methylene, ethylene, n-propylene, n-butylene, and hexylene groups, while examples of branched alkylene groups include isopropylene, isobutylene, and 2-methylpropylene groups.

[0077] Specific examples of silane coupling agents represented by formula (S1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, and 2-lauroylthioethyltrimethoxysilane. These may be used individually or in combination of two or more. Among them, 3-octanoylthiopropyltriethoxysilane is particularly preferred.

[0078] In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the content of bonding unit A is preferably 30 mol% or more, more preferably 50 mol% or more, preferably 99 mol% or less, and more preferably 90 mol% or less. The content of bonding unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 55 mol% or less. The total content of bonding units A and B is preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 100 mol%. The content of bonding units A and B includes the amount when bonding units A and B are located at the ends of the silane coupling agent. The form of bonding units A and B when they are located at the ends of the silane coupling agent is not particularly limited, as long as they form units corresponding to formulas (I) and (II) that represent bonding units A and B.

[0079] R in equations (I) and (II)11 Examples of halogens include chlorine, bromine, and fluorine. Examples of branched or unbranched alkyl groups with 1 to 30 carbon atoms include methyl and ethyl groups. Examples of branched or unbranched alkenyl groups with 2 to 30 carbon atoms include vinyl and 1-propenyl groups. Examples of branched or unbranched alkynyl groups with 2 to 30 carbon atoms include ethynyl and propynyl groups.

[0080] R in equations (I) and (II) 12 Regarding branched or unbranched alkylene groups with 1 to 30 carbon atoms, examples include ethylene and propylene groups. Regarding branched or unbranched alkenylene groups with 2 to 30 carbon atoms, examples include vinylene and 1-propenylene groups. Regarding branched or unbranched alkylene groups with 2 to 30 carbon atoms, examples include ethynylene and propynylene groups.

[0081] In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the sum of the number of repeats of bonding unit A (v) and the number of repeats of bonding unit B (w), (v+w), is preferably in the range of 3 to 300.

[0082] The content of the silane coupling agent is preferably 1 to 20 parts by mass per 100 parts by mass of silica.

[0083] The above rubber composition preferably contains vulcanized rubber particles. Vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder as specified in JIS K 6316:2017 can be used. From the viewpoint of environmental considerations and cost, recycled rubber powder produced from crushed waste tires is preferred. These may be used individually or in combination of two or more types.

[0084] Commercially available vulcanized rubber particles can be used, including those from Lehigh, Muraoka Rubber Industries, and others. Note that, in this specification, vulcanized rubber particles are not included in the rubber component.

[0085] The average particle size of the vulcanized rubber particles is preferably 50 μm or more, more preferably 100 μm or more, even more preferably 200 μm or more, and also preferably 1000 μm or less, more preferably 900 μm or less, and even more preferably 800 μm or less. The average particle size of vulcanized rubber particles is the mass-based average particle size calculated from the particle size distribution measured in accordance with JIS Z 8815:1994.

[0086] The content of vulcanized rubber particles is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of rubber component, and also preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0087] In the above rubber composition, the ratio of the content of vulcanized rubber particles to the total amount of styrene in the rubber component is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and also preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. Within this range, it is believed that domains of vulcanized rubber particles are appropriately formed within the rubber matrix, and that the interface therefor is more easily able to absorb external inputs. In this relationship, the content of vulcanized rubber particles is the content per 100 parts by mass of rubber component (unit: parts by mass), and the total amount of styrene in the rubber component is the content per 100% by mass of the rubber component (unit: mass%).

[0088] The above rubber composition may contain talc. The average particle size of talc is preferably 50 μm or less, more preferably 30 μm or less. The lower limit of the average particle size of talc is not particularly limited, but is preferably 1 μm or more.

[0089] The talc content is preferably 1 to 50 parts by mass per 100 parts by mass of rubber component.

[0090] The above rubber composition may also contain aluminum hydroxide. 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, and others. These may be used individually or in combination of two or more types.

[0091] The average particle size of aluminum hydroxide is preferably 0.1 μm or larger, more preferably 0.5 μm or larger, even more preferably 0.8 μm or larger, and also preferably 5 μm or smaller, more preferably 3 μm or smaller, and even more preferably 1 μm or smaller. Within this range, a better effect tends to be obtained. The average particle size of aluminum hydroxide is measured using the same method as the average particle size of silica.

[0092] The BET specific surface area (nitrogen adsorption specific surface area, N2SA) of aluminum hydroxide is preferably 5 m². 2 / g or more, more preferably 8m 2 / g or more, more preferably 10m 2 It is 1 / g or more, and preferably 40m 2 / g or less, more preferably 30m 2 / g or less, more preferably 20m 2 It is less than / g. The BET specific surface area of ​​aluminum hydroxide is a value measured by the BET method in accordance with ASTM D3037-81.

[0093] The aluminum hydroxide content is preferably 1 to 25 parts by mass per 100 parts by mass of the rubber component.

[0094] The above rubber composition may contain a calcium compound. Calcium compounds are compounds containing calcium, such as inorganic salts like calcium oxide, calcium hydroxide, and calcium carbide; and oxo salts like calcium carbonate, calcium nitrate, and calcium sulfate. Oxo salts also include fatty acid salts such as calcium acetate and calcium stearate. Other examples of substances containing calcium compounds include eggshells (main component: calcium carbonate) and WB16 manufactured by Structol (a mixture of calcium fatty acid, fatty acid amide, and fatty acid amide ester). These may be used individually or in combination of two or more. Among these, oxo salts are preferred, and calcium carbonate is more preferred.

[0095] The calcium compound content is preferably 1 to 25 parts by mass per 100 parts by mass of the rubber component.

[0096] The above rubber composition may contain short fibers. Examples of short fibers that can be used include organic short fibers and inorganic short fibers. Specific examples of organic short fibers include nanocellulose such as cellulose nanofibers (CNF) and cellulose nanocrystals (CNC); biomass nanomaterials such as chitin nanofibers and chitosan nanofibers; and specific examples of inorganic short fibers include metal fibers and glass fiber systems. Commercially available products include those from Nippon Paper Industries Co., Ltd. and Sugino Machine Co., Ltd. These may be used individually or in mixtures of two or more. Among these, organic short fibers are preferred, and nanocellulose is more preferred.

[0097] The particle size of the nanocellulose is preferably 10 nm or larger, more preferably 20 nm or larger, even more preferably 25 nm or larger, and particularly preferably 28 nm or larger. It is also preferably 50 nm or smaller, more preferably 40 nm or smaller, even more preferably 35 nm or smaller, and particularly preferably 32 nm or smaller. When the particle size is within the above range, a better effect tends to be obtained.

[0098] The particle size of nanocellulose is the average fiber diameter measured by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray scattering data analysis, and pore electrical resistance method (Culter principle method). 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.

[0099] The short fiber content is preferably 1 to 40 parts by mass per 100 parts by mass of rubber component.

[0100] The above rubber composition preferably contains a plasticizer. As plasticizers, resins, oils, liquid polymers, ester-based plasticizers, etc., can be used. These may be used individually or in combination of two or more.

[0101] Examples of resins that can be used include C5 resins, C5 / C9 resins, C9 resins, cyclopentadiene resins, and aromatic resins. These may be used individually or in combination of two or more, but it is preferable to use two or more in combination, and more preferably two or more in combination. The combination of two or more resins may consist of resins from different systems (e.g., cyclopentadiene resins and aromatic resins) or resins from the same system (e.g., a homopolymer of styrene and a homopolymer of α-methylstyrene).

[0102] C5 resins are polymers that contain a C5 fraction as a constituent monomer. Examples include polymers obtained by polymerizing a C5 fraction, which is obtained by the thermal decomposition of naphtha in the petrochemical industry, using a Friedel-Crafts type catalyst such as AlCl3 or BF3. The C5 fraction typically includes olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene; and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene.

[0103] The content of C5 resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of rubber component. It is also preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less.

[0104] C5 / C9 resins are polymers containing C5 and C9 fractions as constituent monomers. Examples include polymers obtained by polymerizing petroleum-derived C5 and C9 fractions using Friedel-Crafts type catalysts such as AlCl3 and BF3. Specifically, examples include copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. In this specification, C5 / C9 resins are treated as separate resins from aromatic resins, C5 resins, and C9 resins.

[0105] The content of C5 / C9 resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of rubber component. It is also preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less.

[0106] C9 resins are polymers that contain a C9 fraction as a constituent monomer. For example, they can be obtained by polymerizing the C9 fraction, which is produced as a by-product along with basic petrochemical raw materials such as ethylene and propylene during the thermal decomposition of naphtha in the petrochemical industry, using a Friedel-Crafts type catalyst such as AlCl3 or BF3. Specific examples of C9 fractions include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, and indene. C9 resins may also be obtained by copolymerizing a mixture of these C8-C10 fractions, for example, using a Friedel-Crafts type catalyst, along with the C9 fraction, including C8 fractions such as styrene, C10 fractions such as methylindene and 1,3-dimethylstyrene, and even naphthalene, vinylnaphthalene, vinylanthracene, and p-tert-butylstyrene. In this specification, C9 resins are treated as a separate type of resin from aromatic resins.

[0107] The content of C9 resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of rubber component. It is also preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less.

[0108] Cyclopentadiene resins are polymers that contain cyclopentadiene monomers as constituent monomers. Examples include homopolymers obtained by polymerizing one type of cyclopentadiene monomer alone, copolymers obtained by copolymerizing two or more types of cyclopentadiene monomers, and copolymers of cyclopentadiene monomers with other monomers that can copolymerize with it.

[0109] Examples of cyclopentadiene monomers include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. These may be used individually or in combination of two or more. Dicyclopentadiene is particularly preferred.

[0110] Other monomers include, for example, C9 fractions such as vinyltoluene, indene, and methylindene. These may be used individually or in combination of two or more.

[0111] From the viewpoint of obtaining better effects, the cyclopentadiene-based resin is preferably a polymer (DCPD-based resin) that contains dicyclopentadiene (DCPD) as a constituent monomer.

[0112] The content of the cyclopentadiene resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component, and also preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less. When the content is within the above range, the effect tends to be better obtained.

[0113] Aromatic resins are polymers that contain aromatic monomers as constituent monomers. Examples include homopolymers obtained by polymerizing one type of aromatic monomer alone, copolymers obtained by copolymerizing two or more types of aromatic monomers, and copolymers of aromatic monomers with other monomers that can copolymerize with them.

[0114] 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 individually or in combination of two or more. Among these, phenol monomers are preferred, and alkylphenols are more preferred.

[0115] Other monomers include, for example, non-conjugated olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. These may be used individually or in combination of two or more.

[0116] The aromatic resin content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. It is also preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less. When the content is within the above range, the effect tends to be better obtained.

[0117] Commercially available resins from companies such as 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., JXTG Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Industries, Ltd. can be used.

[0118] The resin content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 4 parts by mass or more, per 100 parts by mass of the rubber component, and also 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. Within the above range, a better effect tends to be obtained.

[0119] In the above rubber composition, the silica content / resin content is preferably 1 or more, more preferably 1.3 or more, even more preferably 1.7 or more, and also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. When the ratio is within the above range, a better effect tends to be obtained. In this relationship, the silica content and resin content are expressed as the content per 100 parts by mass of rubber component (unit: parts by mass).

[0120] In the above rubber composition, the carbon black content / resin content is preferably 10 or more, more preferably 13 or more, even more preferably 17 or more, and also preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less. When the ratio is within the above range, a better effect tends to be obtained. In this relationship, the carbon black content and resin content are expressed as the content per 100 parts by mass of rubber component (unit: parts by mass).

[0121] Examples of oils include process oils, vegetable oils, or mixtures thereof. Examples of process oils include paraffinic process oils, aromatic process oils, naphthenic process oils, etc. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, etc. Waste oil recovered from vegetable oils used as cooking oil, etc. Commercial products that can be used include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., JXTG Energy Corporation, Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., etc. These may be used individually or in combination of two or more types.

[0122] The oil content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of rubber component, and also preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. Within the above range, a better effect tends to be obtained.

[0123] Liquid polymers are (co)polymers that are in a liquid state at room temperature (25°C). For example, at least one (co)polymer selected from the group consisting of butadiene, isoprene, styrene, farnesene, and their derivatives 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, and liquid farnesene-butadiene copolymer. Liquid polymers may also undergo modification or hydrogenation treatments. Commercially available products include those from Cray Valley and Kuraray Co., Ltd. These may be used individually or in combination of two or more.

[0124] The weight-average molecular weight (Mw) of the liquid polymer is preferably 9000 or less, more preferably 6000 or less, even more preferably 4500 or less, and also preferably 100 or more, more preferably 1000 or more, and even more preferably 2000 or more. Within this range, better effects tend to be obtained. In this specification, liquid polymers are not included in the rubber component.

[0125] The liquid polymer content is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component.

[0126] The ester-based 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), but examples include phthalic acid derivatives, long-chain fatty acid derivatives, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives. These may be used individually or in combination of two or more. Among these, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives are preferred, with sebacic acid derivatives being more preferred. The above phthalic acid derivatives are not particularly limited, but examples include phthalic acid esters such as di-2-ethylhexyl phthalate (DOP) and diisodecyl phthalate (DIDP). The above long-chain fatty acid derivatives are not particularly limited, but examples include long-chain fatty acid glycerol esters. The above phosphate derivatives are not particularly limited, but examples include phosphate esters such as tris(2-ethylhexyl) phosphate (TOP) and tributyl phosphate (TBP). The above sebaciate derivatives are not particularly limited, but examples include sebaciate esters such as di(2-ethylhexyl) sebacate (DOS) and diisooctyl sebacate (DIOS). The above adipic acid derivatives are not particularly limited, but examples include adipic acid esters such as di(2-ethylhexyl) adipate (DOA) and diisooctyl adipate (DIOA). Among these, phosphate esters, sebacate esters, and adipic esters are preferred, with sebacate esters being more preferred. Furthermore, as for specific compounds, TOP, DOS, and DOA are preferred, with DOS being more preferred. As ester-based plasticizers, products from companies such as Daihachi Chemical Industry Co., Ltd. and Taoka Chemical Industry Co., Ltd. can be used.

[0127] The glass transition temperature (Tg) of the ester-based plasticizer is preferably -110°C or higher, more preferably -100°C or higher, even more preferably -80°C or higher, preferably -20°C or lower, more preferably -40°C or lower, and even more preferably -55°C or lower. The aforementioned effects tend to be more favorably obtained within this range. In this specification, the glass transition temperature is the value measured in accordance with JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by T.A. Instruments Japan Co., Ltd., under a heating rate of 10°C / min.

[0128] The content of the ester-based plasticizer is preferably 1 to 20 parts by mass per 100 parts by mass of the rubber component.

[0129] In the above rubber composition, the content of plasticizer (total content of resin and oil, etc.) is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, even more preferably 6 parts by mass or more, and also 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, per 100 parts by mass of rubber component. Within this range, it is believed that appropriate mobility is imparted to the rubber molecules without impairing strength, and durability at high temperatures is improved.

[0130] The above rubber composition may contain processing aids. Examples of processing aids include metal salts (compounds in which the hydrogen atoms of an acid are replaced by metal ions), fatty acid amides, amide esters, and fatty acid esters. These may be used individually or in combination of two or more. Among these, metal salts and fatty acid amides are preferred, and metal salts are more preferred.

[0131] Examples of metals used in metal salts include alkali metals such as potassium and sodium, and alkaline earth metals such as calcium and barium. Magnesium, zinc, nickel, and molybdenum can also be used. Among these, alkali metals are preferred.

[0132] Acids used in metal salts include fatty acids such as lauric acid, myristic acid, and palmitic acid. Boric acid, carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid can also be used.

[0133] Commercially available processing aids include products from companies such as Kishida Chemical Co., Ltd., Ken-ei Pharmaceutical Co., Ltd., Structol, and Performance Additives.

[0134] 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, per 100 parts by mass of the rubber component, and also preferably 12 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 6 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0135] The above rubber composition may contain an anti-aging agent. Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents 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 include p-phenylenediamine-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and other quinoline-based antioxidants; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane. 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 individually or in combination of two or more.

[0136] The amount of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component, and also 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. When the amount is within the above range, a better effect tends to be obtained.

[0137] The above rubber composition may contain wax. The wax is not particularly limited and can be any petroleum-based wax such as paraffin wax or microcrystalline wax; a natural wax such as plant-based wax or animal-based wax; or a synthetic wax such as polymers of ethylene or propylene. Commercially available products from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd. can be used. These can be used individually or in combination of two or more types.

[0138] The wax content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of rubber component. Within this range, a better effect tends to be obtained.

[0139] The above rubber composition may contain stearic acid. Conventional known stearic acid can be used, and commercially available products from companies such as NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries Ltd., and Chiba Fatty Acid Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0140] The stearic acid content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0141] The above rubber composition preferably contains zinc oxide. Conventional known zinc oxides can be used, and commercially available products from companies such as Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., and Sakai Chemical Industry Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0142] The zinc oxide content 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, per 100 parts by mass of the rubber component, and also 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. Within the above range, a better effect tends to be obtained.

[0143] In the above rubber composition, it is preferable that the carbon black content / zinc oxide content < 30. The value on the left side is preferably 28 or less, more preferably 26 or less, even more preferably 24 or less, and also preferably 15 or more, more preferably 18 or more, and even more preferably 21 or more. When the value is within the above range, a better effect tends to be obtained. In this context, the carbon black content and zinc oxide content are expressed as the content per 100 parts by mass of rubber component (unit: parts by mass).

[0144] The above rubber composition may contain sulfur. Examples of sulfur commonly used as a crosslinking agent in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Commercially available products from companies such as Tsurumi Chemical Industries, Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Co., Ltd., Flexis Co., Ltd., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Industry Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0145] The sulfur content is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 2.1 parts by mass or more, per 100 parts by mass of the rubber component, and also preferably 4.5 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less. Within the above range, a better effect tends to be obtained.

[0146] In the above rubber composition, the zinc oxide content / sulfur content is preferably 0.9 or more, more preferably 1.2 or more, even more preferably 1.5 or more, and also preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. It is believed that being within this range makes it easier to suppress the breaking of sulfur bonds due to excessive heat during vulcanization, and thus easier to obtain good durability. In this relationship, the zinc oxide content and sulfur content are expressed as the content per 100 parts by mass of rubber component (unit: parts by mass).

[0147] The above rubber composition may contain an organic crosslinking agent. The organic crosslinking agent is not particularly limited and includes maleimide compounds, alkylphenol-sulfur chloride condensates, organic peroxides, amine organic sulfides, and the like. These may be used individually or in combination of two or more.

[0148] The content of the organic crosslinking agent is preferably 1 to 15 parts by mass per 100 parts by mass of the rubber component.

[0149] The above rubber composition may contain a vulcanization accelerator. Examples of vulcanization accelerators 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-benzothiadylsulfenamide (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, dioltotolylguanidine, and orthotolylbiguanidine. Commercially available products include those from Sumitomo Chemical Co., Ltd. and Ouchi Shinko Chemical Co., Ltd. These may be used individually or in combination of two or more.

[0150] The content of the vulcanization accelerator is preferably 0.3 parts by mass or more, more preferably 0.6 parts by mass or more, even more preferably 0.9 parts by mass or more, and preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of the rubber component. When the content is within the above range, a better effect tends to be obtained.

[0151] In addition to the above components, the above rubber composition may further contain commonly used additives, such as organic peroxides. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0152] The above rubber composition can be produced, for example, by kneading each of the above components using a rubber kneading device such as an open roll or Banbury mixer, and then vulcanizing it.

[0153] Regarding the mixing conditions, in the base mixing step where additives other than the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish mixing step where the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 120°C or lower, preferably 85 to 110°C. The composition mixed with the vulcanizing agent and vulcanization accelerator is then subjected to vulcanization treatment. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

[0154] The above rubber composition can be used in crawler tracks. In particular, it is suitable for the crawler track body. The crawler body refers to the rubber material that forms the vehicle side (inner surface) of the crawler, and is, for example, the material shown as 2(2i, 2a, 2o) in Figure 1 of Patent Document 1.

[0155] The rubber crawler of this disclosure is manufactured by a conventional method using the rubber composition for crawlers of this disclosure. Specifically, the rubber composition for crawlers of this disclosure is extruded to match the shape of the crawler body or the like at an unvulcanized stage, bonded with other crawler components, and an unvulcanized rubber crawler is formed on a rubber crawler molding machine. The rubber crawler of this disclosure can be manufactured by heating and pressurizing this unvulcanized rubber crawler in a vulcanizing machine.

[0156] The rubber crawler of this disclosure is used in crawler vehicles for construction, agriculture, and other purposes, and is particularly suitable for use in crawler vehicles that experience severe wear on rubber crawlers, such as those having a sprocket-type drive unit with sharp, roughly triangular teeth on its outer surface. [Examples]

[0157] The present disclosure will be described in detail based on examples, but the present disclosure is not limited to these examples.

[0158] The various chemicals used in the examples and comparative examples are described below.

[0159] (Rubber component) NR:TSR20 SBR1: JSR1502 manufactured by JSR Corporation (styrene content: 23.5% by mass, vinyl content: 16% by mass) SBR2: HPR840 manufactured by JSR Corporation (styrene content: 10% by mass, vinyl content: 42% by mass) BR: BR150B manufactured by Ube Industries, Ltd. (Vinyl content: 1% by mass, Citric acid content: 97% by mass)

[0160] (Chemicals other than rubber components) Carbon Black 1:N134 (CTAB specific surface area: 142m²) 2 / g) Carbon Black 2: N220 (CTAB specific surface area: 111 m²) 2 / g) Silica: UltraSil VN3 manufactured by Evonik DeGussa (average particle size: 17nm) Oil: VIVATEC500 (aromatherapy process oil) by H&R. Resin 1: Quinton 1325 (dicyclopentadiene resin) manufactured by Nippon Zeon Co., Ltd. Resin 2: SP1068 (alkylphenol-formaldehyde condensation resin) manufactured by Nippon Shokubai Co., Ltd. Vulcanized rubber particles: Ekodyne from Lehigh Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation Processing aid: ULTRA-FLOW 440 (zinc fatty acid) manufactured by Performance Additives. Anti-aging agent: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Vulcanization accelerator: Noxellar NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: M95 (insoluble sulfur) manufactured by Nippon Kanryu Kogyo Co., Ltd.

[0161] (Examples and Comparative Examples) According to the formulations shown in Tables 1 and 2, the materials other than sulfur and vulcanization accelerator were kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a mixture. Next, sulfur and vulcanization accelerator were added to the mixture and kneaded for 5 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was molded into the shape of a crawler body and bonded together with other crawler components to form an unvulcanized crawler. This was vulcanized for 12 minutes at 170°C to produce a test rubber crawler (size: 400-90×42 / WZ). The obtained test crawler was used for the following evaluation, and the results are shown in Tables 1 and 2.

[0162] Furthermore, in the evaluation described below, the evaluation criteria for calculating the index of crack resistance performance in the main body under high-temperature conditions are as follows: Table 1: Comparative Example 3 Table 2: Comparative Example 4

[0163] (Amount of acetone extracted (AE)) For rubber test pieces (samples) cut from the crawler body of the above-mentioned test rubber crawler, the amount of substance extracted by acetone contained in the rubber test piece was measured in accordance with the method for measuring acetone extraction amount compliant with JIS K 6229:2015. Acetone extraction volume (mass %) = (mass of sample before extraction - mass of sample after extraction) / mass of sample before extraction × 100

[0164] (Polymer content (PC)) For the samples after acetone extraction at the above acetone extraction rate (AE), the amount of organic matter was thermally decomposed and vaporized by heating in nitrogen (raising the temperature from room temperature to 750°C) to measure the loss in mass, in accordance with JIS K6226-1:2003, and PC (mass%) was calculated based on this.

[0165] (Carbon black content (BC)) For the samples obtained after thermal decomposition and vaporization of the above polymer amount (PC), the loss in mass was measured when oxidative combustion occurred by heating in air, and the BC (mass%) was calculated based on this.

[0166] (Ash content (Ash)) The mass of the components that do not burn in oxidative combustion (ash) in the above amount of carbon black (BC) was measured, and the Ash (mass%) was calculated based on that.

[0167] (Crack resistance performance of the main body under high-temperature conditions) A sheet measuring 100mm wide x 30mm long x 2mm thick, cut from the crawler body of the above-mentioned test rubber crawler, was chucked across its entire width, leaving a 10mm length unattended. At 70°C, the 10mm section was repeatedly subjected to fatigue at 0-100% strain, and the growth rate of a 20mm crack pre-introduced at one end (da / dN: crack growth length per number of fatigue cycles) was measured. Values ​​were obtained for each strain, and the average value was used to express the results as an index with a baseline of 100. A higher index value indicates superior crack resistance.

[0168] [Table 1]

[0169] [Table 2]

[0170] Tables 1 and 2 show that the example demonstrated superior crack resistance in the main body under the target high-temperature conditions compared to the comparative example.

[0171] The present disclosure (1) is a rubber composition for crawlers that contains a rubber component comprising isoprene rubber and styrene-butadiene rubber, and carbon black, wherein the carbon black content / styrene-butadiene rubber content > 2.0, and the polymer amount × styrene-butadiene rubber content in the rubber component > acetone extraction amount.

[0172] Disclosure (2) is a crawler rubber composition according to Disclosure (1) that contains zinc oxide, wherein the carbon black content / zinc oxide content < 30.

[0173] Disclosure (3) is a crawler rubber composition according to Disclosure (1) or (2) that contains a resin.

[0174] Disclosure (4) is a crawler rubber composition in any combination of any of Disclosures (1) to (3), wherein the total amount of styrene in the rubber component is less than 8% by mass.

[0175] This disclosure (5) states that the specific surface area of ​​the carbon black with cetyltrimethylammonium bromide is 130 m². 2 A crawler rubber composition in any combination of any of (1) to (4) of the present disclosure, wherein the amount is 1 / g or more.

[0176] Disclosure (6) is a crawler rubber composition in which the rubber component is any combination of any of Disclosures (1) to (5) containing butadiene rubber.

[0177] Disclosure (7) is a crawler rubber composition containing silica in any combination of any of Disclosures (1) to (6).

[0178] Disclosure (8) is a crawler rubber composition containing two or more resins in any combination of any of Disclosures (1) to (7).

[0179] Disclosure (9) is a crawler rubber composition containing vulcanized rubber particles in any combination of any of Disclosures (1) to (8).

[0180] Disclosure (10) is a rubber crawler using a rubber composition in any combination of any of Disclosures (1) to (9).

Claims

1. It contains rubber components including isoprene-based rubber and styrene-butadiene rubber, and carbon black. The content of the styrene-butadiene rubber in the rubber component is 30% by mass or more. The carbon black content / styrene-butadiene rubber content > 2.0, The amount of polymer × the amount of styrene-butadiene rubber in the rubber component > the amount extracted with acetone. The amount of acetone extracted from the rubber composition was measured according to the method for measuring the amount of acetone extracted in accordance with JIS K 6229:2015 (unit: mass %) of the rubber composition. The amount of polymer is calculated from the amount of organic matter lost (by mass) when the sample remaining after acetone extraction is thermally decomposed and vaporized by heating in nitrogen (raising the temperature from room temperature to 750°C) in accordance with JIS K6226-1:2003 (unit: mass %) of the rubber composition for crawlers.

2. It contains zinc oxide, The rubber composition for crawlers according to claim 1, wherein the carbon black content / zinc oxide content < 30.

3. The crawler rubber composition according to claim 1 or 2, wherein the total amount of styrene in the rubber component is less than 8% by mass.

4. The specific surface area of ​​the carbon black containing cetyltrimethylammonium bromide is 130 m². ２ A rubber composition for crawlers according to any one of claims 1 to 3, wherein the composition is 1 / g or more.

5. The rubber composition for crawlers according to any one of claims 1 to 4, wherein the rubber component comprises butadiene rubber.

6. A rubber composition for crawlers according to any one of claims 1 to 5, containing silica.

7. A rubber composition for crawlers according to any one of claims 1 to 6, containing vulcanized rubber particles.

8. A rubber crawler using the rubber composition described in any one of claims 1 to 7.

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