Rubber composition for tire treads and tires

Abstract

To provide a rubber composition for a tire tread, capable of satisfying wet performance, snow performance and fracture strength.SOLUTION: The rubber composition for the tire tread according to an embodiment contains 90-150 pts.mass of silica, 5-30 pts.mass of an oil, and 10 pts.mass or more and less than 40 pts.mass of a thermoplastic resin having a softening point of 40°C or higher with respect to 100 pts.mass of a diene rubber containing 30-85 pts.mass of a styrene-butadiene rubber and 15-70 pts.mass of a butadiene rubber and having an average glass transition temperature of -57°C or lower. The total content of the oil and the thermoplastic resin is less than 45 pts.mass. The content of the oil is 20 pts.mass or less based on 100 pts.mass of the silica.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 Art

[0002] As a performance required for a tire, there is grip performance (i.e., wet performance) on a wet road surface. In order to improve the wet performance, it is known to blend a large amount of silica as a filler and increase the amounts of resin and oil.

[0003] For example, Patent Document 1 describes a rubber composition containing 100 to 160 parts by mass of an inorganic filler containing silica, 5 to 60 parts by mass of a hydrocarbon resin having a glass transition temperature higher than 20°C, and 5 to 60 parts by mass of a liquid plasticizer with respect to 100 parts by mass of a diene rubber containing SBR having a certain functional group. In the rubber composition, the total content of the hydrocarbon resin and the liquid plasticizer is set to be more than 45 parts by mass. According to Patent Document 1, it is described that low rolling resistance and wet performance can be achieved simultaneously with the above configuration.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, wet performance can be improved by incorporating a large amount of silica and consequently increasing the amounts of resin and oil. However, it has been found that increasing the amounts of silica, resin, and oil reduces the proportion of diene-based rubber in the rubber composition, resulting in a decrease in fracture strength. For example, when applied to winter tires where grip performance on snowy roads (i.e., snow performance) is required, maintaining fracture strength becomes a challenge because winter tires have smaller tread block sizes.

[0006] In view of the above, embodiments of the present invention aim to provide a rubber composition for tire treads that can satisfy wet performance, snow performance, and fracture strength, and a tire using the same. [Means for solving the problem]

[0007] The present invention includes embodiments shown below. [1] A rubber composition for tire treads comprising 30 to 85 parts by mass of styrene-butadiene rubber and 15 to 70 parts by mass of butadiene rubber, with an average glass transition temperature of -57°C or lower, per 100 parts by mass of diene rubber, 90 to 150 parts by mass of silica, 5 to 30 parts by mass of oil, and 10 to less than 40 parts by mass of thermoplastic resin having a softening point of 40°C or higher, wherein the total content of the oil and the thermoplastic resin is less than 45 parts by mass, and the content of the oil is 20 parts by mass or less per 100 parts by mass of silica. [2] The tire tread rubber composition according to [1], further comprising 5 to 20 parts by mass of a thioester group-containing silane coupling agent per 100 parts by mass of the silica. [3] The tire tread rubber composition according to [1] or [2], wherein the styrene-butadiene rubber comprises a modified solution polymerized styrene-butadiene rubber. [4] A tire having a tread made using the rubber composition for tire treads described in any one of the above items [1] to [3]. [Effects of the Invention]

[0008] According to embodiments of the present invention, a rubber composition for tire treads that satisfies wet performance, snow performance, and fracture strength can be provided. [Modes for carrying out the invention]

[0009] The rubber composition for tire treads according to this embodiment (hereinafter also referred to as the rubber composition) comprises (A) diene rubber, (B) silica, (C) oil, and (D) thermoplastic resin.

[0010] [(A) Diene-based rubber] In this embodiment, the diene rubber as a rubber component includes styrene-butadiene rubber (SBR) and butadiene rubber (BR). Here, diene rubber refers to rubber having repeating units corresponding to diene monomers having conjugated double bonds, and having double bonds in the polymer main chain.

[0011] The styrene-butadiene rubber may be solution-polymerized styrene-butadiene rubber (SSBR), emulsion-polymerized styrene-butadiene rubber (ESBR), modified styrene-butadiene rubber (modified SBR) in which the ends or main chain are modified, or unmodified styrene-butadiene rubber. Preferably, the styrene-butadiene rubber includes modified solution-polymerized styrene-butadiene rubber (modified SSBR).

[0012] As modified SBR (preferably modified SSBR), SBR modified by introducing functional groups to the terminals and / or main chain is used. The functional groups are preferably those containing oxygen and / or nitrogen atoms, and examples include at least one selected from the group consisting of amino groups, hydroxyl groups, alkoxy groups, epoxy groups, and carboxyl groups. Using such modified SBR can improve the dispersibility of silica.

[0013] The glass transition temperature (Tg) of styrene-butadiene rubber is not particularly limited and may be, for example, -80 to -10°C or -70 to -50°C. Furthermore, two or more types of styrene-butadiene rubber with different glass transition temperatures may be used in combination.

[0014] In this specification, the glass transition temperature is a value measured by differential scanning calorimetry (DSC) in accordance with JIS K7121:2012, at a heating rate of 20°C / min (measurement temperature range: -150°C to 50°C).

[0015] As the butadiene rubber, various types of butadiene rubber commonly used in tire rubber compositions can be used. Modified butadiene rubber (modified BR), in which the ends or main chain are modified, may be used, as may unmodified butadiene rubber.

[0016] In one embodiment, high-cis BR, which has a cis-1,4 bond content of 90% by mass or more, is preferably used as the butadiene rubber. More preferably, the cis-1,4 bond content of high-cis BR is 96% by mass or more.

[0017] Preferably, as high-cis BR, butadiene rubber polymerized using a neodymium (Nd)-based catalyst may be used. The neodymium-based catalyst may be pure neodymium, a compound of neodymium with other metals, or an organic compound containing neodymium. Specific examples include NdCl3 and Et-NdCl2. Butadiene rubber polymerized using a neodymium-based catalyst has a microstructure with a high cis content and a low vinyl content. For example, it is preferable that the microstructure has a cis-1,4 bond content of 96% by mass or more and a vinyl group (1,2-vinyl bond) content of 1.0% by mass or less.

[0018] In this specification, the cis-1,4 bond content and vinyl group content are defined as follows: 1 This value is calculated from the integration ratio of the H-NMR spectrum.

[0019] In this embodiment, the diene rubber may be composed only of the above styrene-butadiene rubber and butadiene rubber, or may contain other diene rubbers. Specific examples of other diene rubbers include natural rubber (NR), synthetic isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), etc., and any one or two or more of these may be used in combination. These other diene rubbers also include those in which the terminal or main chain, etc. are modified as necessary, and those modified to impart desired properties (for example, modified NR) within the concept thereof.

[0020] In this embodiment, 100 parts by mass of the diene rubber contains 30 to 85 parts by mass of styrene-butadiene rubber and 15 to 70 parts by mass of butadiene rubber. Preferably, 100 parts by mass of the diene rubber contains 50 to 85 parts by mass of styrene-butadiene rubber and 15 to 50 parts by mass of butadiene rubber, more preferably 60 to 85 parts by mass of styrene-butadiene rubber and 15 to 40 parts by mass of butadiene rubber, and still more preferably 70 to 80 parts by mass of styrene-butadiene rubber and 20 to 30 parts by mass of butadiene rubber.

[0021] In one embodiment, 100 parts by mass of the diene rubber may contain 30 to 85 parts by mass, may contain 40 to 80 parts by mass, or may contain 45 to 65 parts by mass of modified SSBR as at least a part of the above styrene-butadiene rubber. At that time, the styrene-butadiene rubber may be composed only of modified SSBR, or may be used in combination with unmodified SBR together with modified SSBR.

[0022] In a preferred embodiment, 100 parts by mass of the diene rubber is composed of 40 to 70 parts by mass (preferably 50 to 60 parts by mass) of modified SSBR having a Tg of -75 to -45°C (preferably -70 to -50°C), 10 to 30 parts by mass (preferably 15 to 25 parts by mass) of unmodified SBR having a Tg of -80 to -50°C (preferably -75 to -60°C), and butadiene rubber (preferably high cis BR) 15 ~40 parts by mass (preferably 20 to 30 parts by mass).

[0023] In another embodiment, 100 parts by mass of diene rubber may consist of 15 to 45 parts by mass (preferably 25 to 35 parts by mass) of modified SSBR with a Tg of -40 to -10°C (preferably -30 to -20°C), 35 to 65 parts by mass (preferably 45 to 55 parts by mass) of modified SSBR with a Tg of -75 to -45°C (preferably -70 to -50°C), and 15 to 35 parts by mass (preferably 15 to 25 parts by mass) of butadiene rubber (preferably high-sys BR).

[0024] In this embodiment, the diene rubber has an average glass transition temperature (hereinafter referred to as average Tg) of -57°C or lower. By having an average Tg of -57°C or lower for the diene rubber, the balance between wet performance and snow performance can be improved. The average Tg of the diene rubber is more preferably -70°C or lower. The lower limit of the average Tg is not particularly limited, but may be, for example, -90°C or higher, or -80°C or higher.

[0025] The average Tg of diene rubber is an average value calculated by weighting the glass transition temperatures of each rubber component that makes up the diene rubber, using the mass ratio of each rubber component in the diene rubber, based on the said mass ratio. Specifically, the average Tg is calculated by Σ{(glass transition temperature of each rubber) × (mass ratio of each rubber)}. Here, the mass ratio of each rubber = (mass of each rubber relative to 100 mass parts of diene rubber) / 100.

[0026] [(B) Silica] The rubber composition according to this embodiment contains silica as a filler. Preferably, wet silica, such as wet sedimentation silica or wet gelation silica, is used.

[0027] The nitrogen adsorption specific surface area (N2SA) of silica is not particularly limited, for example, 100-300 m². 2 / g is also acceptable, 150-250m 2 / g is also acceptable, 180-220m 2 / g is also acceptable. The nitrogen adsorption specific surface area of ​​silica is the BET specific surface area measured according to the BET method described in JIS K6430:2008.

[0028] The silica content is 90 to 150 parts by mass per 100 parts by mass of diene rubber. A silica content of 90 parts by mass or more can improve wet performance. A silica content of 150 parts by mass or less can suppress the decrease in fracture strength. Preferably, the silica content is 100 to 140 parts by mass, and more preferably 110 to 130 parts by mass per 100 parts by mass of diene rubber.

[0029] The filler used in the rubber composition may be silica alone, or it may be silica mixed with carbon black. The filler preferably contains 90% by mass or more silica, and more preferably 95% by mass or more. The carbon black content is not particularly limited and may be 10 parts by mass or less, or 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0030] [(C) Oil] The rubber composition according to this embodiment contains an oil. Examples of oils include mineral oils such as paraffinic oils, naphthenic oils, and aromatic oils, and vegetable oils such as linseed oil, safflower oil, soybean oil, corn oil, castor oil, rapeseed oil, and cottonseed oil. Any one or more of these can be used in combination.

[0031] The oil content is 5 to 30 parts by mass, more preferably 10 to 25 parts by mass, and even more preferably 12 to 20 parts by mass, per 100 parts by mass of diene rubber. Note that, if oil-expandable rubber is used as the diene rubber, the oil content also includes the amount of oil contained in the oil-expandable rubber.

[0032] [(D) Thermoplastic resin] The rubber composition according to this embodiment contains a thermoplastic resin having a softening point of 40°C or higher. Examples of thermoplastic resins include terpene resins, styrene resins, petroleum resins, rosin resins, coumarone resins, etc., and one or more of these may be used in combination.

[0033] Terpene resins are resins produced by polymerizing terpene monomers such as α-pinene, β-pinene, limonene, and dipentene. Examples include polyterpene resins produced using only terpene monomers, as well as terpene phenol resins and aromatically modified terpene resins.

[0034] In one embodiment, the terpene resin is preferably a polyterpene resin containing β-pinene units, and may also be a polyterpene resin containing α-pinene units and β-pinene units. For example, an α-pinene / β-pinene mixed resin obtained by polymerizing a mixture of α-pinene and β-pinene may be used. In the α-pinene / β-pinene mixed resin, the mass ratio of α-pinene units to β-pinene units is not particularly limited, but is preferably 35:65 to 4:96, more preferably 20:80 to 4:96, and even more preferably 10:90 to 4:96. Here, α-pinene units are units derived from α-pinene, and β-pinene units are units derived from β-pinene.

[0035] Examples of styrene-based resins include polystyrene, α-methylstyrene homopolymer, styrene / α-methylstyrene copolymer, styrene monomer / aliphatic monomer copolymer, α-methylstyrene / aliphatic monomer copolymer, and styrene monomer / α-methylstyrene / aliphatic monomer copolymer.

[0036] 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 obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions (C5 fractions) with 4 to 5 carbon atoms, and may be hydrogenated. C9 petroleum resins are obtained by cationic polymerization of monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions (C9 fractions) with 8 to 10 carbon atoms, and may be hydrogenated. C / C9 petroleum resins are obtained by copolymerizing a C5 fraction and a C9 fraction by cationic polymerization, and may be hydrogenated.

[0037] Examples of rosin-based resins include natural rosin resins and rosin-modified resins (e.g., rosin-modified maleic acid resins) obtained by modifying natural rosin resins through processes such as hydrogenation, disproportionation, dimerization, and esterification.

[0038] Coumarone-based resins are resins whose main component is coumarone, and examples include coumarone resin, coumarone-indene resin, and copolymer resins whose main components are coumarone, indene, and styrene.

[0039] As mentioned above, thermoplastic resins with a softening point of 40°C or higher are used. The softening point of the thermoplastic resin is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. The upper limit of the softening point may be, for example, 160°C or lower, or 150°C or lower.

[0040] In this specification, the softening point of thermoplastic resins is a value measured using a ring-type softening point measuring device in accordance with JIS K6220-1:2001.

[0041] The thermoplastic resin content is 10 parts by mass or more and less than 40 parts by mass per 100 parts by mass of diene rubber, more preferably 15 to 35 parts by mass, and even more preferably 20 to 30 parts by mass.

[0042] In the rubber composition according to this embodiment, the total content of the oil and thermoplastic resin is set to less than 45 parts by mass per 100 parts by mass of diene rubber, and the oil content is set to 20 parts by mass or less per 100 parts by mass of silica. As described above, in this embodiment, a large amount of silica is blended in order to improve wet performance. In that case, normally, the amount of oil and thermoplastic resin that act as plasticizers is increased in order to maintain a similar level of rubber hardness and to consider processability, etc. However, increasing the amount of oil and thermoplastic resin reduces the fracture strength. In contrast, in this embodiment, by setting the amount of oil to 20% by mass or less of the silica amount and the total content of oil and thermoplastic resin to less than 45 parts by mass, it is possible to improve fracture strength while maintaining excellent wet performance and snow performance.

[0043] The total content of oil and thermoplastic resin is preferably 30 to 44 parts by mass, more preferably 35 to 44 parts by mass, and even more preferably 40 to 44 parts by mass, per 100 parts by mass of diene rubber.

[0044] The ratio of oil to silica, that is, the oil content per 100 parts by mass of silica, is preferably 5 to 20 parts by mass, more preferably 8 to 18 parts by mass, and even more preferably 10 to 17 parts by mass.

[0045] The ratio of thermoplastic resin to silica, that is, the content of thermoplastic resin per 100 parts by mass of silica, is not particularly limited and may be, for example, 10 to 30 parts by mass, 15 to 28 parts by mass, or 20 to 25 parts by mass.

[0046] [(E) Silane coupling agent] The rubber composition according to this embodiment preferably contains a silane coupling agent. Examples of silane coupling agents include sulfide silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)disulfide, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyl Examples of mercaptosilane coupling agents include pyrtriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane, as well as thioester group-containing silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. These can be used individually or in combination of two or more. Among these, thioester group-containing silane coupling agents are preferred from the viewpoint of enhancing the effects according to this embodiment.

[0047] The content of the silane coupling agent (preferably a silane coupling agent containing a thioester group) is preferably 5 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of silica.

[0048] [Other ingredients] In addition to the above-mentioned components, the rubber composition according to this embodiment may also contain various additives commonly used in rubber compositions, such as zinc oxide, stearic acid, wax, antioxidants, processing aids, vulcanizing agents, and vulcanization accelerators.

[0049] The zinc oxide content is not particularly limited; for example, it may be 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 diene rubber.

[0050] The stearic acid content is not particularly limited; for example, it may be 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 diene rubber.

[0051] The wax content is not particularly limited; for example, it may be 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 diene rubber.

[0052] Examples of antioxidants include amine-ketone, aromatic secondary amine, monophenol, bisphenol, and benzimidazole-based antioxidants, and one or more of these can be used in combination. The amount of antioxidant is not particularly limited and may be 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 diene rubber.

[0053] The amount of processing aid is not particularly limited; for example, it may be 0 to 10 parts by mass or 1 to 5 parts by mass per 100 parts by mass of diene rubber.

[0054] Sulfur is preferably used as the vulcanizing agent. The amount of 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 diene rubber.

[0055] Examples of vulcanization accelerators include sulfenamide-based, guanidine-based, thiuram-based, and thiazole-based vulcanization accelerators, which can be used individually 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 or 1 to 5 parts by mass per 100 parts by mass of diene rubber.

[0056] [Method for preparing rubber composition] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing stage (non-progressive kneading stage), additives other than the vulcanizing agent and vulcanization accelerator are added and mixed with silica, oil, and thermoplastic resin to the diene rubber. Then, in the final mixing stage (progressive kneading stage), the vulcanizing agent and vulcanization accelerator are added and mixed to the resulting mixture. This makes it possible to prepare an unvulcanized rubber composition.

[0057] [Uses of rubber compositions] The rubber composition according to this embodiment can be used as a rubber composition for tire treads. Examples of tires include passenger car tires, heavy-duty tires for trucks and buses, and pneumatic tires of various sizes and applications.

[0058] In one embodiment, the rubber composition is preferably used in the tread rubber that constitutes the contact surface of an all-season tire or a winter tire. Compared to summer tires, these tires have more sipes in the tread blocks, and the rubber blocks remain flexible even under icy or snowy conditions.

[0059] A tire according to one embodiment is a tire having a tread made using the above-mentioned rubber composition. That is, a tire according to one embodiment is equipped with a tread rubber made of the above-mentioned rubber composition.

[0060] The tread rubber of a tire may have a two-layer structure consisting of a cap rubber and a base rubber, or a single-layer structure in which both are integrated. In the case of a single-layer structure, the tread rubber may be formed from the above-mentioned rubber composition. In the case of a two-layer structure, the outer cap rubber that contacts the road surface may be formed from the above-mentioned rubber composition, the base rubber placed inside the cap rubber may be formed from the above-mentioned rubber composition, or both the cap rubber and the base rubber may be formed from the above-mentioned rubber composition.

[0061] The method for manufacturing the tire is not particularly limited. For example, the rubber composition described above can be molded into a predetermined shape by extrusion according to a conventional method to obtain an unvulcanized tread rubber member. By combining this tread rubber member with other tire members, an unvulcanized tire (green tire) can be produced. Subsequently, the tire can be manufactured by vulcanization molding at, for example, 140 to 180°C. [Examples]

[0062] The following are examples, but the present invention is not limited to these examples.

[0063] The components used in the examples and comparative examples are as follows: • SBR1: Modified SSBR, Tg = -60℃, manufactured by JSR Corporation, "HPR840" • SBR2: Modified SSBR, Tg = -24℃, manufactured by JSR Corporation, "HPR850" • SBR3: Unmodified SSBR, Tg=-70℃, 37.5 parts by mass of oil per 100 parts by mass of rubber, manufactured by Asahi Kasei Corporation as "Toughden 1834". • BR: High-cis BR polymerized using an Nd-based catalyst, Tg = -102°C, cis-1,4 bond content = 97% by mass, vinyl group content = 0.9% by mass, manufactured by JSR Corporation as "BR730".

[0064] • Carbon Black: N339, manufactured by Tokai Carbon Co., Ltd. "Seast KH" • Silica: N2SA = 205m 2 / g, "Nip Seal AQ" manufactured by Tosoh Silica Co., Ltd. • Silane coupling agent 1: Bis(3-triethoxysilylpropyl) disulfide, Evonik "Si75" • Silane coupling agent 2:3-octanoylthio-1-propyltriethoxysilane, manufactured by Momentive Performance Materials, Inc. "NXT"

[0065] • Oil: ENEOS Corporation's "Process NC140" • Terpene resin: α-pinene / β-pinene mixed resin, Kraton Corporation "SYLVATRAXX4150" (α-pinene units: 5% by mass, β-pinene units: 95% by mass, softening point = 115°C) • Styrene resin: Kraton's "SYLVATRAXX 4401", softening point = 85°C • Petroleum resin: "Petrotac 90" manufactured by Tosoh Corporation, softening point = 100℃

[0066] • Wax: "OZOACE0355" manufactured by Nippon Seiro Co., Ltd. • Stearic acid: "Bead Stearic Acid" manufactured by NOF Corporation • Zinc oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. • Anti-aging agent 1: Aromatic secondary amine (6PPD), "Nocrack 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Anti-aging agent 2: Amine-ketone type (TMQ), manufactured by Kawaguchi Chemical Industry Co., Ltd., "Antage RD" • Processing aid: Lanxess "Aflax 16"

[0067] • Vulcanization accelerator 1: Guanidine-based (DPG), "Noxellar D" manufactured by Ouchi Shinko Chemical Co., Ltd. • Vulcanization accelerator 2: Sulfenamide type (CBS), "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. • Sulfur: Tsurumi Chemical Industries Co., Ltd. "Powdered Sulfur"

[0068] The evaluation methods in the examples and comparative examples are as follows.

[0069] (1) Wet performance A prototype tire was fitted to a vehicle, and under conditions of 25°C temperature, the braking distance was measured from a speed of 100 km / h on a road surface with a water depth of 1 mm until the vehicle came to a complete stop with the ABS activated. The reciprocal of the measured value was calculated, and the results are shown as indices, with the calculated values ​​for Comparative Example 1 (Table 1), Comparative Example 3 (Table 2), Comparative Example 4 (Table 3), and Comparative Example 5 (Table 4) set to 100. A larger index indicates a shorter braking distance and superior wet performance.

[0070] (2) Snow performance A prototype tire was fitted to a vehicle, and under conditions of -10°C temperature, the vehicle was driven on a snowy road at 60 km / h. The braking distance was measured when the ABS was activated and the vehicle decelerated to 20 km / h. The reciprocal of the measured value was calculated, and the results are shown as indices, with the calculated values ​​for Comparative Example 1 (Table 1), Comparative Example 3 (Table 2), Comparative Example 4 (Table 3), and Comparative Example 5 (Table 4) set to 100. A larger index indicates a shorter braking distance and superior snow performance.

[0071] (3) Breaking strength Tensile strength was measured using test specimens in accordance with JIS K6251:2017 by performing a tensile test (dumbbell-shaped, type 3). Table 1 shows the measured values ​​for Comparative Example 1, Table 2 for Comparative Example 3, Table 3 for Comparative Example 4, and Table 4 for Comparative Example 5, all of which are expressed as indices with the measured values ​​set to 100. A higher index indicates greater breaking strength and superior reinforcing properties.

[0072] [First Experimental Example] Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first mixing stage, compounding agents excluding sulfur and vulcanization accelerator were added to the diene rubber and kneaded (discharge temperature = 155°C). Next, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting knead and kneaded (discharge temperature = 90°C) to prepare the rubber composition.

[0073] In the table, the amounts in parentheses for SBR3 represent the amount as rubber. In the table, "Oil / Silica" is the ratio of parts by mass of oil to parts by mass of silica, and this includes the amount of oil contained in the SBR3. In the table, "Resin / Silica" is the ratio of parts by mass of thermoplastic resin (terpene resin, styrene resin, petroleum resin) to parts by mass of silica.

[0074] The obtained unvulcanized rubber composition was vulcanized at 170°C for 15 minutes to prepare test specimens, and their fracture strength was evaluated. Furthermore, a winter pneumatic radial tire (tire size: 205 / 55R16) was manufactured by using the unvulcanized rubber composition as the tread rubber and vulcanizing it according to a conventional method. The wet and snow performance of the resulting prototype tire was evaluated.

[0075] [Table 1]

[0076] The results are shown in Table 1. In Comparative Example 1, where the silica content was increased compared to Comparative Example 2, the wet performance improved, but the tensile strength decreased. In contrast, in Examples 1 to 3, where the total amount of oil and thermoplastic resin, and the ratio of oil to silica were set within a specific range, it was possible to maintain or improve the excellent wet performance resulting from the increased silica content, while maintaining excellent snow performance and improving tensile strength compared to Comparative Example 1.

[0077] [Second Experimental Example] A rubber composition was prepared according to the formulation (parts by mass) shown in Table 2 below, with the rest being the same as in the first experimental example. Using the obtained rubber composition, test specimens and prototype tires were prepared in the same manner as in the first experimental example, and the wet performance, snow performance, and tensile strength were evaluated. The results are shown in Table 2.

[0078] [Table 2]

[0079] [Third experimental example] A rubber composition was prepared according to the formulation (parts by mass) shown in Table 3 below, with the rest being the same as in the first experimental example. Using the obtained rubber composition, test specimens and prototype tires were prepared in the same manner as in the first experimental example, and the wet performance, snow performance, and tensile strength were evaluated. The results are shown in Table 3.

[0080] [Table 3]

[0081] [Fourth experimental example] A rubber composition was prepared according to the formulation (parts by mass) shown in Table 4 below, with the rest of the preparation being the same as in the first experimental example. Using the obtained rubber composition, test specimens and prototype tires were prepared in the same manner as in the first experimental example, and the wet performance, snow performance, and tensile strength were evaluated. The results are shown in Table 4.

[0082] [Table 4]

[0083] As shown in Tables 1 to 4, in Examples 1 to 11 according to this embodiment, the wet performance, snow performance, and tensile strength were satisfied by the above-mentioned specific combination of formulations.

[0084] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0085] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. A diene rubber comprising 30 to 85 parts by mass of styrene-butadiene rubber and 15 to 70 parts by mass of butadiene rubber, with an average glass transition temperature of -57°C or lower, is used in a 100-part diene rubber. Silica 90 to 150 parts by mass, 5 to 30 parts by mass of oil, and A thermoplastic resin having a softening point of 40°C or higher, selected from the group consisting of terpene resins, styrene resins, petroleum resins, rosin resins, and coumarone resins, in an amount of 10 to less than 40 parts by mass, The oil and thermoplastic resin content are less than 45 parts by mass, and the oil content is 20 parts by mass or less per 100 parts by mass of silica. The 100 parts by mass of the diene rubber includes 40 to 70 parts by mass of modified solution polymerized styrene-butadiene rubber having a glass transition temperature of -75 to -45°C and 10 to 30 parts by mass of unmodified styrene-butadiene rubber having a glass transition temperature of -80 to -50°C, as well as 15 to 40 parts by mass of the butadiene rubber. Rubber composition for tire treads.

2. A diene rubber comprising 30 to 85 parts by mass of styrene-butadiene rubber and 15 to 70 parts by mass of butadiene rubber, wherein the average glass transition temperature is -57°C or lower, is present in 100 parts by mass. Silica 90 to 150 parts by mass, 5 to 30 parts by mass of oil, and A thermoplastic resin having a softening point of 40°C or higher, and selected from the group consisting of terpene resins, styrene resins, petroleum resins, rosin resins, and coumarone resins, in an amount of 10 to less than 40 parts by mass, The oil and thermoplastic resin content are less than 45 parts by mass, and the oil content is 20 parts by mass or less per 100 parts by mass of silica. The 100 parts by mass of the diene rubber includes 15 to 45 parts by mass of modified solution polymerized styrene-butadiene rubber having a glass transition temperature of -40 to -10°C and 35 to 65 parts by mass of modified solution polymerized styrene-butadiene rubber having a glass transition temperature of -75 to -45°C, and also includes 15 to 35 parts by mass of the butadiene rubber. Rubber composition for tire treads.

3. The tire tread rubber composition according to claim 1 or 2, further comprising 5 to 20 parts by mass of a thioester group-containing silane coupling agent per 100 parts by mass of the silica.

4. A tire having a tread made using the rubber composition for tire treads described in claim 1 or 2.

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