Rubber composition for tire tread and tire

Abstract

To provide a rubber composition for a tire tread having good chipping resistance, tear resistance, low rolling resistance and wet grip performance.SOLUTION: A rubber composition for a tire tread according to an embodiment contains a rubber component containing natural rubber, silica, a thermoplastic resin, a mercapto-based silane coupling agent, and oil as an optional component. The amount of the natural rubber in 100 parts by mass of the rubber component is not less than 50 parts by mass. The rubber composition comprises 100 pts.mass of a rubber component, 50-150 pts.mass of silica, 3 pts.mass or more of a thermoplastic resin, and 3 pts.mass or more and less than 60 pts.mass in total of the thermoplastic resin and oil. The mass ratio of mercapto-based silane coupling agent / silica is 0.1 or more and less than 0.2.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, in order to improve the low rolling resistance performance (fuel economy) and wet grip performance of tires, it has been known to use silica as a filler compounded in rubber compositions, and to compound a silane coupling agent to improve the dispersibility of the silica.

[0003] For example, Patent Document 1 discloses that fuel economy performance at normal and low temperatures is improved by compounding silica, a mercapto-silane coupling agent, and carbon black with a rubber component containing styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber, and limiting the amount of carbon black.

[0004] Patent Document 2 discloses that abrasion resistance is improved while maintaining low rolling resistance and wet performance by compounding a diene rubber containing a specified modified styrene-butadiene rubber and natural rubber with a tackifying resin, a filler containing silica and carbon black, and a silane coupling agent.

[0005] Patent Document 3 discloses that a rubber composition containing silica and an amine surfactant and having an acetone extractable amount of less than 16% by mass has excellent handling stability, and that adding a mercapto silane coupling agent to the rubber composition improves fuel economy. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-021503 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-047295 [Patent Document 3] Japanese Patent Publication No. 2023-070525 Summary of the Invention [Problem to be solved by the invention]

[0007] For example, off-road tires require chipping resistance and tear resistance. However, it has been difficult to maintain low rolling resistance and wet grip performance while ensuring chipping resistance and tear resistance. Here, chipping refers to the occurrence of chips on the land of blocks or the like provided on the tread surface, and chipping resistance refers to the ability to suppress such chipping.

[0008] In view of the above, an object of an embodiment of the present invention is to provide a rubber composition for a tire tread that has good chipping resistance, tear resistance, low rolling resistance, and wet grip performance, and a tire using the same. [Means for solving the problem]

[0009] The present invention includes the embodiments shown below. [1] A rubber composition for a tire tread, comprising: a rubber component containing natural rubber, silica, a thermoplastic resin, a mercapto-silane coupling agent, and an optional oil; wherein the amount of the natural rubber per 100 parts by mass of the rubber component is 50 parts by mass or more; the content of the silica is 50 to 150 parts by mass, and the content of the thermoplastic resin is 3 parts by mass or more, relative to 100 parts by mass of the rubber component; the total content of the thermoplastic resin and the oil is 3 parts by mass or more and less than 60 parts by mass; and the mass ratio of the mercapto-silane coupling agent to the silica (mercapto-silane coupling agent / silica) is 0.1 or more and less than 0.2. [2] The rubber composition for a tire tread according to [1], wherein 100 parts by mass of the rubber component further contains 10 to 50 parts by mass of styrene-butadiene rubber. [3] The rubber composition for a tire tread according to [2], wherein the styrene-butadiene rubber contains a modified styrene-butadiene rubber. [4] The rubber composition for a tire tread according to any one of [1] to [3], wherein the thermoplastic resin comprises at least one selected from the group consisting of petroleum resins, terpene resins, and styrene resins. [5] A tire having a tread formed from the rubber composition for a tire tread according to any one of [1] to [4]. [Effects of the Invention]

[0010] According to an embodiment of the present invention, it is possible to provide a rubber composition for a tire tread that has good chipping resistance, tear resistance, low rolling resistance, and wet grip performance, and a tire using the same. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the rubber composition for a tire tread according to this embodiment (hereinafter also simply referred to as "rubber composition"), the rubber component contains natural rubber (NR).

[0012] The natural rubber is not particularly limited and examples thereof include ribbed smoked sheet (RSS), technically graded rubber (TSR), and natural rubber latex. Modified versions of these, such as epoxidized natural rubber, may also be used. Modified and unmodified natural rubbers may also be used in combination.

[0013] The rubber component contains 50% by mass or more of natural rubber. That is, the amount of natural rubber per 100 parts by mass of the rubber component is 50 parts by mass or more. When the rubber component contains 50% by mass or more of natural rubber as the main component, chipping resistance and tear resistance can be improved. The rubber component may be natural rubber alone, but in one embodiment, the amount of natural rubber per 100 parts by mass of the rubber component is preferably 50 to 85 parts by mass, more preferably 55 to 80 parts by mass, and even more preferably 60 to 75 parts by mass.

[0014] The rubber component preferably contains styrene-butadiene rubber (SBR) together with natural rubber. By containing styrene-butadiene rubber, the effect of improving low rolling resistance performance can be enhanced. The amount of styrene-butadiene rubber per 100 parts by mass of the rubber component is preferably 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, and even more preferably 20 to 40 parts by mass. In one embodiment, the total amount of natural rubber and styrene-butadiene rubber per 100 parts by mass of the rubber component is preferably 70 parts by mass or more, more preferably 80 parts by mass or more.

[0015] The styrene butadiene rubber may be solution-polymerized styrene butadiene rubber (SSBR) or emulsion-polymerized styrene butadiene rubber (ESBR). The styrene butadiene rubber may be modified styrene butadiene rubber (modified SBR) whose ends or main chain have been modified, unmodified styrene butadiene rubber (unmodified SBR), or a combination of modified SBR and unmodified SBR.

[0016] The styrene-butadiene rubber preferably contains modified SBR, more preferably modified solution-polymerized styrene-butadiene rubber (modified SSBR). In this case, the modified SBR (preferably modified SSBR) is preferably contained in 100% by mass of SBR at 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, and may be 100% by mass.

[0017] The modified SBR can be one modified with a functional group introduced into the terminal and / or main chain. The functional group preferably contains an oxygen atom and / or a nitrogen atom, and examples thereof include at least one selected from the group consisting of an amino group, a hydroxy group, an alkoxy group, an alkoxysilyl group, an epoxy group, and a carboxy group. The use of a modified SBR containing such a functional group can enhance the effect of improving the dispersibility of silica.

[0018] The styrene content (bound styrene content) of the styrene-butadiene rubber is not particularly limited, and may be, for example, 5 to 40% by mass, or 10 to 25% by mass. Here, the styrene content (mass%) is 1 Determined by H-NMR.

[0019] The rubber component may be composed of natural rubber alone, or natural rubber and styrene-butadiene rubber alone, or may further contain other diene rubbers. Diene rubber refers to rubber having repeating units corresponding to diene monomers having conjugated double bonds, and containing carbon-carbon double bonds in the polymer main chain.

[0020] Specific examples of other diene rubbers include synthetic isoprene rubber (IR), butadiene rubber (BR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, and butadiene-isoprene copolymer rubber. Among these, butadiene rubber is preferred as the other diene rubber, and therefore the rubber component may contain natural rubber, styrene-butadiene rubber, and butadiene rubber. The amount of butadiene rubber per 100 parts by mass of the rubber component may be 0 to 30 parts by mass, 0 to 20 parts by mass, or 5 to 20 parts by mass.

[0021] In one embodiment, 100 parts by mass of the rubber component may include 50 to 85 parts by mass of natural rubber, 10 to 50 parts by mass of styrene-butadiene rubber, and 0 to 30 parts by mass of butadiene rubber. Here, butadiene rubber is an optional component. More preferably, 100 parts by mass of the rubber component may include 55 to 80 parts by mass of natural rubber, 15 to 45 parts by mass of styrene-butadiene rubber, and 0 to 20 parts by mass of butadiene rubber. In one embodiment, 100 parts by mass of the rubber component may include 60 to 75 parts by mass of natural rubber, 15 to 35 parts by mass of styrene-butadiene rubber, and 5 to 20 parts by mass of butadiene rubber.

[0022] The rubber composition according to the present embodiment contains silica as a filler. Examples of silica include wet silica and dry silica, and it is preferable to use wet silica such as wet precipitation silica or wet gelation silica.

[0023] The CTAB adsorption specific surface area of ​​silica is not particularly limited, but is preferably 100 to 200 m 2 / g, and more preferably 120 to 190m 2 / g, and more preferably 150 to 180m 2 The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of ​​silica is measured in accordance with JIS K6430:2008, Appendix G.

[0024] The content of silica in the rubber composition is 50 to 150 parts by mass per 100 parts by mass of the rubber component. When the content of silica is 50 parts by mass or more, wet grip performance and tear resistance can be improved. The content of silica is preferably 60 to 120 parts by mass, more preferably 70 to 110 parts by mass per 100 parts by mass of the rubber component.

[0025] In the rubber composition according to the present embodiment, the filler may be silica alone, or other fillers may be blended together with silica. Carbon black is preferably used as the other filler. The proportion of silica in the filler is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0026] When the rubber composition contains carbon black, the content of carbon black is not particularly limited, but is preferably 30 parts by mass or less per 100 parts by mass of the rubber component, and may be, for example, 3 to 20 parts by mass, 3 to 15 parts by mass, or 4 to 10 parts by mass.

[0027] The rubber composition according to the present embodiment includes a mercapto-based silane coupling agent. In this specification, the mercapto-based silane coupling agent includes not only a silane coupling agent having a mercapto group (—SH), but also a silane coupling agent having a structure in which the mercapto group is protected by a protecting group (protected mercaptosilane coupling agent).

[0028] Specific examples of mercapto-based silane coupling agents include those having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane.

[0029] Specific examples of mercapto-based silane coupling agents include protected mercaptosilane coupling agents, such as thioester group-containing silane coupling agents having a thioester group (-S-CO-). Examples of thioester group-containing silane coupling agents include those represented by the following general formula (1): (R 1 ) m (R 2 ) n Si-R 3 -S-CO-R 4 (1)

[0030] In formula (1), R 1 represents an alkoxy group having 1 to 3 carbon atoms, and R 2 represents an alkyl group having 1 to 20 carbon atoms, and R 3 represents an alkanediyl group having 1 to 5 carbon atoms, and R 4 represents an alkyl group having 1 to 18 carbon atoms, m=1 to 3, and m+n=3.

[0031] R in formula (1) 1 is preferably a methoxy group or an ethoxy group. 2 is preferably an alkyl group having 1 to 4 carbon atoms. 1 and R 2 When a plurality of R are present in one molecule, they may be the same or different. Preferably, m and n are 3 and 0, respectively. 3 is preferably an alkanediyl group having 2 to 4 carbon atoms. 4 is preferably an alkyl group having 3 to 15 carbon atoms, and more preferably an alkyl group having 6 to 12 carbon atoms.

[0032] Specific examples of thioester group-containing silane coupling agents include 3-propionylthiopropyltrimethoxysilane, 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, and 2-decanoylthioethyltriethoxysilane. , 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, and the like.

[0033] The above-listed mercapto-based silane coupling agents can be used alone or in combination of two or more.

[0034] The content of the mercapto silane coupling agent is 10 parts by mass or more and less than 20 parts by mass per 100 parts by mass of silica. That is, the mass ratio of the mercapto silane coupling agent to silica (mercapto silane coupling agent / silica) is 0.1 or more and less than 0.2. When the mass ratio is 0.1 or more, chipping resistance, tear resistance, low rolling resistance, and wet grip performance can be improved. When the mass ratio is less than 0.2, chipping resistance can be improved. The mass ratio of the mercapto silane coupling agent / silica is preferably 0.11 to 0.18, more preferably 0.13 to 0.17.

[0035] As the silane coupling agent, it is preferable to use only a mercapto-based silane coupling agent, but other silane coupling agents such as a sulfide-based silane coupling agent may also be blended.

[0036] The rubber composition according to the present embodiment contains a thermoplastic resin. The thermoplastic resin blended into the rubber composition is also called a tackifying resin, and can improve chipping resistance and tear resistance. The thermoplastic resin is not particularly limited, but preferably has a softening point of 50 to 150°C, more preferably 70 to 120°C. The softening point of the resin is measured using a ring and ball softening point tester in accordance with JIS K6220-1:2015.

[0037] Specific examples of thermoplastic resins include petroleum resins, terpene resins, styrene resins, coumarone resins, and rosin resins.

[0038] Examples of petroleum resins include aliphatic petroleum resins (C5 petroleum resins), aromatic petroleum resins (C9 petroleum resins), and aliphatic / aromatic copolymer petroleum resins (C5 / C9 petroleum resins). C5 petroleum resins are resins obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions having 4 to 5 carbon atoms (C5 fractions), and may be hydrogenated. C9 petroleum resins are resins obtained by cationic polymerization of monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions having 8 to 10 carbon atoms (C9 fractions), and may be hydrogenated. C5 / C9 petroleum resins are resins obtained by copolymerizing a C5 fraction and a C9 fraction by cationic polymerization, and may be hydrogenated.

[0039] Terpene resins are resins obtained by polymerizing terpene compounds such as α-pinene, β-pinene, limonene, and dipentene, and contain units derived from terpene compounds. The terpene resin may be a polyterpene resin obtained by polymerizing only terpene monomers, or a modified terpene resin (e.g., terpene phenol resin) obtained by polymerizing a terpene compound with a monomer other than terpene. Examples of modified terpene resins include aromatic modified terpene resins obtained by polymerizing a terpene compound with an aromatic compound. The terpene resin is preferably a pinene resin containing α-pinene and / or β-pinene as a constituent monomer, or may be polypinene obtained by polymerizing only α-pinene and / or β-pinene.

[0040] The styrene-based resin is a resin containing styrene and / or α-methylstyrene as a constituent monomer, and examples thereof include homopolymers obtained by polymerizing styrene or α-methylstyrene alone, copolymers obtained by copolymerizing styrene and α-methylstyrene, and copolymers of styrene and / or α-methylstyrene with other monomers.

[0041] The coumarone resin is a resin containing coumarone as a constituent monomer, and examples thereof include coumarone resin and coumarone-indene resin.

[0042] Examples of rosin-based resins include natural resin rosin and rosin-modified resins obtained by modifying rosin through hydrogenation, disproportionation, dimerization, esterification, etc. (for example, hydrogenated rosin ester, rosin-modified maleic acid resin).

[0043] The thermoplastic resins listed above can be used alone or in combination of two or more. Among these, it is preferable to use at least one thermoplastic resin selected from the group consisting of petroleum resins, terpene resins, and styrene resins.

[0044] The content of the thermoplastic resin is 3 parts by mass or more per 100 parts by mass of the rubber component. When the content of the thermoplastic resin is 3 parts by mass or more, wet grip performance and tear resistance can be improved. The content of the thermoplastic resin is preferably 3 to 50 parts by mass, more preferably 4 to 40 parts by mass, more preferably 4 to 30 parts by mass, and even more preferably 5 to 25 parts by mass per 100 parts by mass of the rubber component.

[0045] The rubber composition according to the present embodiment may or may not contain oil. In other words, oil is an optional component. Mineral oils such as paraffinic oil, naphthenic oil, and aromatic oil are preferably used as the oil. These may be used alone or in combination of two or more.

[0046] The oil content is set so that the total content of the thermoplastic resin and the oil is 3 parts by mass or more and less than 60 parts by mass per 100 parts by mass of the rubber component. When the total content of the thermoplastic resin and the oil is 3 parts by mass or more, wet grip performance can be improved. When the total content of the thermoplastic resin and the oil is less than 60 parts by mass, low rolling resistance, chipping resistance, and tear resistance can be improved. The total content of the thermoplastic resin and the oil is preferably 10 to 57 parts by mass, more preferably 20 to 55 parts by mass, and even more preferably 25 to 55 parts by mass per 100 parts by mass of the rubber component.

[0047] The amount of oil per 100 parts by mass of the rubber component is not particularly limited, but is preferably 0 to 50 parts by mass, more preferably 10 to 40 parts by mass, and even more preferably 20 to 35 parts by mass.

[0048] In addition to the above components, the rubber composition according to the present embodiment may contain various additives that are generally used in rubber compositions, such as zinc oxide, stearic acid, an antioxidant, wax, a vulcanizing agent, and a vulcanization accelerator.

[0049] The content of zinc oxide is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass relative to 100 parts by mass of the rubber component.

[0050] The content of stearic acid is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass relative to 100 parts by mass of the rubber component.

[0051] Examples of the antioxidant include various antioxidants such as amine-ketone, aromatic secondary amine, monophenol, bisphenol, and benzimidazole antioxidants, and any one of them can be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of the rubber component.

[0052] The content of the wax is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of the rubber component.

[0053] As the vulcanizing agent, sulfur is preferably used. The content of the vulcanizing agent is not particularly limited, and may be 0.1 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 3 parts by mass per 100 parts by mass of the rubber component.

[0054] Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, guanidine-based, thiuram-based, and thiazole-based accelerators, and any one of them can be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and may be 0.1 to 10 parts by mass, 1 to 7 parts by mass, or 2 to 5 parts by mass per 100 parts by mass of the rubber component.

[0055] The rubber composition according to the present embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, roll, etc. That is, for example, in a first mixing stage, additives other than the vulcanizing agent and vulcanization accelerator are added and mixed with the rubber component, and then in a final mixing stage, the vulcanizing agent and vulcanization accelerator are added and mixed with the resulting mixture to prepare the rubber composition.

[0056] The rubber composition according to the present embodiment can be used in tire treads. Examples of tires include pneumatic tires of various sizes and for various uses, such as tires for passenger cars and large tires for trucks and buses. The rubber composition is preferably used in the treads of off-road tires such as mud-terrain (M / T) and all-terrain (A / T) tires.

[0057] A tire according to one embodiment includes a tread made using the rubber composition. That is, the tire according to one embodiment includes a tread rubber formed from the rubber composition. The tread rubber of the tire may have a two-layer structure of a cap rubber and a base rubber, or a single-layer structure in which the two are integrated. In the single-layer structure, the tread rubber may be formed from the rubber composition. In the two-layer structure, the outer cap rubber that comes into contact with the road surface is preferably formed from the rubber composition, but the base rubber disposed inside the cap rubber may also be formed from the rubber composition, or both the cap rubber and the base rubber may be formed from the rubber composition.

[0058] The method for manufacturing a tire is not particularly limited. For example, the rubber composition is extruded into a predetermined shape according to a conventional method to obtain an unvulcanized tread rubber component. The tread rubber component is combined with other tire components to produce an unvulcanized tire (green tire). Thereafter, the tire can be manufactured by vulcanizing and molding at, for example, 140°C to 180°C. [Example]

[0059] Examples of the present invention will be shown below, but the present invention is not limited to these examples.

[0060] The components used in the examples and comparative examples are as follows. ·NR:RSS#3 SBR-1: Unmodified ESBR, styrene content = 23.5% by mass, "SBR1502" manufactured by ENEOS Material Corporation SBR-2: Terminally modified SSBR, styrene content = 20.5% by mass, "HPR350" manufactured by ENEOS Material Corporation SBR-3: Terminally modified SSBR, styrene content = 10% by mass, "HPR840" manufactured by ENEOS Material Corporation BR: UBE Corporation "BR150B"

[0061] Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Silica: Evonik Industries "Ultrasil VN3", CTAB=167m 2 / g Silane coupling agent-1: Sulfide type, Evonik Industries "Si69" Silane coupling agent - 2:3-octanoylthiopropyltriethoxysilane, Momentive "NXT"

[0062] Oil: ENEOS Corporation "Process NC-140" Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Wax: Nippon Seiro Co., Ltd. "OZOACE0355"

[0063] Resin-1: C5 / C9 petroleum resin (aliphatic / aromatic copolymer hydrocarbon resin), "Petrotack 90" manufactured by Tosoh Corporation, softening point = 95°C ·Resin-2: α-pinene / β-pinene mixed resin, “SYLVATRAXX4150” manufactured by Clayton, softening point = 115℃, weight average molecular weight = 2110 Resin-3: Styrene-based resin, Kraton "SYLVATRAXX 4401", softening point = 85°C, weight average molecular weight = 1200

[0064] Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator CZ: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. Vulcanization accelerator DPG: "Noccela D" manufactured by Ouchi Shinko Chemical Co., Ltd.

[0065] The evaluation methods used in the examples and comparative examples are as follows. [Low rolling resistance performance] Using the rubber composition as tread rubber, a test pneumatic radial tire (tire size: 215 / 45ZR17) was produced by vulcanization molding according to a conventional method. The rolling resistance of the resulting test tire was measured using a rolling resistance measurement drum tester under conditions of an air pressure of 230 kPa, a load of 450 kgf (4.4 kN), a temperature of 23°C, and a speed of 80 km / h. The reciprocal of the rolling resistance is expressed as an index, with the value for Comparative Example 1 in Table 1 and the value for Comparative Example 5 in Table 2 both set to 100. A larger index indicates lower rolling resistance and better low rolling resistance performance (fuel economy).

[0066] [Wet grip performance] Four test pneumatic radial tires (tire size: 215 / 45ZR17) were mounted on a vehicle. The vehicle was driven on a road surface sprinkled with 2 to 3 mm of water at an ambient temperature of 25°C, and the ABS was activated to decelerate from 90 km / h to 20 km / h, measuring the braking distance (average value of n=10). The reciprocal of the braking distance is expressed as an index, with the value for Comparative Example 1 in Table 1 and the value for Comparative Example 5 in Table 2 set to 100. A larger index indicates a shorter braking distance and better wet grip performance.

[0067] [Chipping resistance] A tensile test was conducted in accordance with JIS K6251:2017 to determine the tensile product. Specifically, the rubber composition was vulcanized at 160°C for 30 minutes to prepare a rubber sample (dumbbell-shaped No. 3, thickness 2.0 mm). A tensile test (speed: 500 mm / min) was conducted on the rubber sample to measure the elongation at break Eb (%) and tensile strength T (MPa). The tensile product, which is the product of the elongation at break and the tensile strength (Eb x T), was determined, and the value for Comparative Example 1 in Table 1 and the value for Comparative Example 5 in Table 2 were expressed as an index, with 100. A larger index indicates a larger tensile product and better chipping resistance.

[0068] [Tear resistance] Tear strength was measured in accordance with JIS K6252-1:2015. Specifically, the rubber composition was vulcanized at 160°C for 30 minutes to prepare a rubber sample (crescent shape, thickness 2.0 mm). A tensile test (speed: 500 mm / min) was conducted on the rubber sample to determine tear strength, and the values ​​for Comparative Example 1 in Table 1 and Comparative Example 5 in Table 2 were expressed as an index, with each index being set to 100. A larger index indicates greater tear strength and better tear resistance.

[0069] [First Experimental Example] Using a Banbury mixer, rubber compositions were prepared according to the formulation (parts by mass) shown in Table 1 below. Specifically, in the first mixing stage, compounding ingredients excluding sulfur and vulcanization accelerator were added to the rubber component and kneaded (discharge temperature = 155°C). Next, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting kneaded mixture and kneaded (discharge temperature = 90°C), thereby preparing a rubber composition. In Table 1, "resin + oil (mass ratio)" represents the total content of thermoplastic resin and oil per 100 parts by mass of the rubber component, and "silane / silica" represents the mass ratio of silane coupling agent to silica (the same applies to Table 2).

[0070] Each of the rubber compositions thus obtained was evaluated for low rolling resistance, wet grip performance, chipping resistance, and tear resistance.

[0071] [Table 1]

[0072] The results are shown in Table 1. Comparative Example 1 is an example in which a sulfide-based silane coupling agent was blended as the silane coupling agent. Compared to Comparative Example 1, Example 1, in which a mercapto-based silane coupling agent was used as the silane coupling agent, showed improved effects in all of low rolling resistance performance, wet grip performance, chipping resistance, and tear resistance. Examples 2 and 3, in which the composition of the diene-based rubber component other than natural rubber was changed, also showed improved effects in each performance compared to Comparative Example 1.

[0073] In Example 4, the total content of oil and thermoplastic resin was increased to 55 parts by mass compared to Example 3, and a tendency for a decrease in chipping resistance and tear resistance was observed, but an improvement in each performance was observed compared to Comparative Example 1, similar to Examples 1 to 3. In Examples 5 to 7, the amount of natural rubber was increased compared to Example 4, and chipping resistance and tear resistance were further improved.

[0074] In Comparative Example 2, the total content of oil and thermoplastic resin was increased to 60 parts by mass, which is higher than the specified amount, compared to Example 1. Comparative Example 2 was inferior to Comparative Example 1 in low rolling resistance, chipping resistance, and tear resistance.

[0075] In Comparative Example 3, the content of the thermoplastic resin was reduced to 2 parts by mass, which is less than the specified amount, compared to Example 1. In Comparative Example 3, the wet grip performance and tear resistance were inferior to those of Comparative Example 1.

[0076] In Comparative Example 4, the amount of natural rubber was reduced to 45 parts by mass, which is less than the specified amount, compared to Example 4. Comparative Example 4 was inferior to Comparative Example 1 in chipping resistance and tear resistance.

[0077] [Second Experimental Example] Using a Banbury mixer, rubber compositions were prepared in the same manner as in Experimental Example 1 according to the formulations (parts by mass) shown in Table 2. Each of the resulting rubber compositions was evaluated for low rolling resistance, wet grip performance, chipping resistance, and tear resistance.

[0078] [Table 2]

[0079] The results are shown in Table 2. Comparative Example 5 is an example in which the mass ratio of the mercapto silane coupling agent to silica was smaller than the specified amount. Compared to Comparative Example 5, Examples 8 to 10, in which the mass ratio of the mercapto silane coupling agent to silica was set to the specified amount of 0.1 or more but less than 0.2, showed improvements in all of low rolling resistance, wet grip performance, chipping resistance, and tear resistance. On the other hand, Comparative Example 6, in which the mass ratio was set to 0.2, which is higher than the specified amount, showed inferior chipping resistance compared to Comparative Example 5.

[0080] Examples 11 to 13 are examples in which the composition of the diene rubber component other than natural rubber was changed compared to Example 8, and improvements in each performance were observed that were equal to or greater than those of Example 8. Example 14 is an example in which the content of thermoplastic resin was increased compared to Example 13, and further improvements in wet grip performance were observed.

[0081] Examples 15 to 17 are examples in which the silica content was changed within the specified range compared to Example 8, and a tendency was observed in which wet grip performance and tear resistance were improved by increasing the silica content. In contrast, Comparative Example 7 is an example in which the silica content was changed to 40 parts by mass, which is less than the specified amount compared to Example 8, and the wet grip performance and tear resistance were inferior to Comparative Example 5.

[0082] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

Claims

1. The rubber composition comprises a rubber component containing natural rubber, silica, a thermoplastic resin, a mercapto-silane coupling agent, and an oil as an optional component, the amount of the natural rubber is 50 parts by mass or more based on 100 parts by mass of the rubber component, a content of the silica is 50 to 150 parts by mass, a content of the thermoplastic resin is 3 parts by mass or more, and a total content of the thermoplastic resin and the oil is 3 parts by mass or more and less than 60 parts by mass, relative to 100 parts by mass of the rubber component; a mass ratio of the mercapto silane coupling agent to the silica (mercapto silane coupling agent / silica) of 0.1 or more and less than 0.2; A rubber composition for tire treads.

2. 2. The rubber composition for a tire tread according to claim 1, wherein 100 parts by mass of the rubber component further contains 10 to 50 parts by mass of styrene-butadiene rubber.

3. The rubber composition for a tire tread according to claim 2 , wherein the styrene-butadiene rubber comprises a modified styrene-butadiene rubber.

4. 2. The rubber composition for a tire tread according to claim 1, wherein the thermoplastic resin comprises at least one selected from the group consisting of petroleum resins, terpene resins, and styrene resins.

5. A tire having a tread formed from the rubber composition for a tire tread according to any one of claims 1 to 4.

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