Rubber composition for tires

Abstract

To provide a rubber composition for tires capable of securing durability while achieving both wet performance and snow performance at a high level.SOLUTION: A rubber composition for tires contains 100-150 pts.mass of silica and 30 pts.mass or more of a plasticizer component based on 100 pts.mass of a diene rubber containing 10-80 mass% of a styrene-butadiene copolymer and containing a butadiene copolymer. A glass transition temperature of the styrene-butadiene copolymer is in a range of -75 to -50°C. As the plasticizer component, at least a thermoplastic resin and oil and optionally a liquid polymer are used. A difference ΔTg between an average glass transition temperature Tg1 of the plasticizer component and an average glass transition temperature Tg2 of a mixture of the plasticizer component and the diene rubber is set to 10°C or more and 40°C or less. A ratio of mass of bound sulfur to mass of the silica is set to less than 3.30 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires intended to be used for winter tires or all-season tires.

Background Art

[0002] Winter tires and all-season tires assumed to be used in winter are required to have excellent snow performance and wet performance. Among these performances, as a method for improving wet performance, it is known to incorporate a large amount of silica (see, for example, Patent Document 1). However, incorporating a large amount of silica causes an increase in hardness and rigidity, which may affect snow performance. On the other hand, as a method for improving snow performance, it is known to incorporate a large amount of plasticizer components such as oil (see, for example, Patent Document 2). However, when a large amount of plasticizer components are incorporated, there is a problem that oil migration and crosslinking progress occur over time, and there is a risk of an increase in hardness, so it is difficult to maintain snow performance over a long period. Therefore, in the rubber composition for tires, measures for highly achieving both wet performance and snow performance are required. In addition, when either a large amount of silica or a plasticizer component is incorporated, the strength of the rubber composition tends to weaken, and there is a risk of reduced durability compared to summer tires, and there is also room for improvement in this regard.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present invention is to provide a rubber composition for tires that enables a high degree of balance between wet performance and snow performance while ensuring durability. [Means for solving the problem]

[0005] The present invention provides a tire rubber composition for achieving the above objectives, comprising 10% to 80% by mass of styrene-butadiene copolymer, 100 to 150 parts by mass of silica, and 30 parts by mass or more of a plasticizer component, per 100 parts by mass of diene rubber containing the butadiene copolymer, wherein the styrene-butadiene copolymer has a glass transition temperature in the range of -75°C to -50°C, the plasticizer component includes at least a thermoplastic resin and an oil, and optionally a liquid polymer, the difference ΔTg between the average glass transition temperature Tg1 of the plasticizer component and the average glass transition temperature Tg2 of the mixture of the plasticizer component and the diene rubber is 10°C or more and 40°C or less, and the ratio of the mass of bound sulfur to the mass of silica is less than 3.30% by mass. [Effects of the Invention]

[0006] The rubber composition for tires of the present invention, having the above-described formulation and satisfying the above-described conditions, can ensure durability as a tire while achieving a high level of balance between wet performance and snow performance. In particular, as described above, a sufficient amount of plasticizer component is blended, ensuring snow performance. Furthermore, since the difference ΔTg between the average glass transition temperature Tg1 of the plasticizer component and the average glass transition temperature Tg2 of the mixture of the plasticizer component and diene rubber is within an appropriate range, even if changes such as migration occur, changes in the physical properties of the rubber composition can be suppressed, ensuring snow performance and wet performance over the long term. On the other hand, when silica is generally blended, a silane coupling agent is used in combination to improve the dispersion of silica. However, the sulfur component contained in this silane coupling agent may affect the physical properties of the rubber due to the progression of vulcanization over time. Therefore, in the present invention, taking this into consideration, the ratio of the mass of bound sulfur to the mass of silica is specified, thereby suppressing changes in the physical properties of the rubber (increase in hardness, decrease in breaking strength and elongation), and maintaining good snow performance over the long term. Through this collaboration, it is possible to achieve a high level of balance between wet and snow performance while ensuring tire durability.

[0007] In the present invention, it is preferable to include a liquid polymer with a molecular weight of 10,000 or more as a plasticizer component. This makes it possible to suppress the migration rate and maintain good chipping resistance.

[0008] In this invention, it is preferable that the oil content in the plasticizer component is less than 75% by mass. By keeping the oil content low in this way, migration can be suppressed, which is advantageous for improving snow performance and chipping resistance.

[0009] In the present invention, it is preferable that 3-octanoylthio-1-propyltriethoxysilane is used as the silane coupling agent. By using a silane coupling agent with a low sulfur content in this way, the amount of sulfur in the rubber composition can be suppressed while exhibiting good silica dispersibility, which is advantageous for improving chipping resistance while improving wet performance and snow performance.

[0010] In the present invention, it is preferable that the thermoplastic resin is at least one selected from the group consisting of a resin comprising at least one selected from terpenes, modified terpenes, C5 components, C9 components, rosin, and rosin esters, and a resin in which at least a portion of the double bonds of such resins are hydrogenated, and that the glass transition temperature of the thermoplastic resin is 40°C to 120°C. Using a thermoplastic resin that satisfies these conditions is advantageous for improving compatibility with the polymer and enhancing wet performance.

[0011] In the present invention, it is preferable that the average glass transition temperature Tg2 is in the range of -70°C to -50°C. This makes it possible to impart tire performance suitable for winter tires and all-season tires. The tire rubber composition of the present invention that satisfies this condition can be suitably used in the tread portion of winter tires and can improve wet performance and snow performance.

[0012] In this invention, "bound sulfur" refers to sulfur (C-Sx-C) that is cross-linked between two rubber molecules in a bridged manner in a tire rubber composition, and sulfur (C-Sx-) that is only bonded to one rubber molecule in a branched or looped manner and does not contribute to cross-linking. Of these sulfurs, the latter (i.e., sulfur that is not bonded between two rubber molecules in a bridged manner) may cause thermal aging because, for example, heat can promote cross-linking between rubber molecules. Furthermore, the mass of bound sulfur can be determined as the amount of bound sulfur contained in vulcanized rubber by measuring the amount of sulfur dioxide detected by the combustion infrared detection method in accordance with JIS Z2616 from the acetone extraction residue after removing free sulfur by acetone extraction of a rubber sample in accordance with JIS K6229 Method A using a HORIBA carbon-sulfur analyzer (EMIA). [Modes for carrying out the invention]

[0013] The tire rubber composition of the present invention always contains 10% to 80% by mass of styrene-butadiene copolymer having a glass transition temperature (hereinafter sometimes referred to as "Tg") of -75°C to -50°C in 100% by mass of diene rubber. By including styrene-butadiene copolymer with a Tg of -75°C to -50°C, the dispersibility of silica is improved and wet performance can be ensured. The content of styrene-butadiene copolymer with a Tg of -75°C to -50°C is 10% to 80% by mass, preferably 15% to 75% by mass, and more preferably 20% to 70% by mass, in 100% by mass of diene rubber. If the amount of styrene-butadiene copolymer is less than 10% by mass, the effect of improving silica dispersibility is not sufficiently obtained and wet performance decreases. If the amount of styrene-butadiene copolymer exceeds 80% by mass, snow performance decreases.

[0014] If the Tg of the styrene-butadiene copolymer is lower than -75°C, the wet performance will decrease. If the Tg of the styrene-butadiene copolymer is higher than -50°C, sufficient snow performance cannot be ensured. The Tg of the styrene-butadiene copolymer is preferably -65°C to -50°C, more preferably -63°C to -53°C. The Tg of the styrene-butadiene copolymer can be measured as the temperature of the midpoint of the transition region from a thermogram obtained by differential scanning calorimetry (DSC) under a heating rate of 20°C / min. Furthermore, when the styrene-butadiene copolymer is an oil-expanded product, the Tg of the styrene-butadiene copolymer should be measured in a state that does not contain the oil-expanding component (oil).

[0015] The tire rubber composition of the present invention always contains a butadiene copolymer in addition to the styrene-butadiene copolymer described above, in 100% by mass of diene rubber. By including the butadiene copolymer, snow performance can be improved in addition to the performance described above. The content of the butadiene copolymer is 90% to 20% by mass, preferably 50% to 25% by mass, in 100% by mass of diene rubber. If the amount of butadiene copolymer is less than 20% by mass, the effect of improving snow performance cannot be sufficiently obtained. If the amount of butadiene copolymer exceeds 90% by mass, wet performance will decrease.

[0016] The tire rubber composition of the present invention may include styrene-butadiene copolymer and other diene rubbers other than butadiene copolymers. Examples of other diene rubbers include styrene-butadiene copolymers with a Tg outside the range of -75°C to -50°C, natural rubber, isoprene rubber, butyl rubber, halogenated butyl rubber, acrylonitrile-butadiene rubber, and modified rubbers obtained by attaching functional groups to these rubbers. These other diene rubbers can be used alone or in any blend. The content of the other diene rubbers is preferably 0% to 40% by mass, more preferably 0% to 30% by mass, based on 100% by mass of the diene rubber.

[0017] The tire rubber composition of the present invention always contains silica in addition to the diene-based rubber described above. The amount of silica added is 100 to 150 parts by mass, preferably 105 to 145 parts by mass, and more preferably 110 to 140 parts by mass, per 100 parts by mass of diene-based rubber. By adding such a sufficient amount of silica, wet performance can be improved. If the amount of silica added is less than 100 parts by mass, wet performance will be insufficient. If the amount of silica added exceeds 150 parts by mass, hardness and rigidity will increase, making it difficult to ensure snow performance.

[0018] Examples of silica used in the present invention include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, and aluminum silicate. These may be used individually or in combination of two or more. Surface-treated silica, which has been treated with a silane coupling agent, may also be used.

[0019] The silica used in this invention preferably has a nitrogen adsorption specific surface area of ​​80 m². 2 / g~250m 2 / g, comfortable 100m 2 / g~180m 2 It is desirable that the particle size of silica is 80 m² / g. Using silica with an appropriate particle size in this way is advantageous for improving the physical properties of the rubber composition and enhancing its wet performance. The nitrogen adsorption specific surface area of ​​silica is 80 m². 2 If the value is less than / g, durability will decrease. The specific surface area of ​​silica for nitrogen adsorption is 250m². 2 If the amount exceeds / g, the processability deteriorates. The specific surface area of ​​silica for nitrogen adsorption shall be the value measured in accordance with JIS K6217-2.

[0020] When blending silica as described above, it is preferable to use a silane coupling agent in combination. By blending a silane coupling agent, the dispersibility of silica in the diene rubber can be improved. The type of the silane coupling agent is not particularly limited as long as it can be used in the rubber composition containing silica. For example, sulfur-containing silane coupling agents such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthio-1-propyltriethoxysilane can be exemplified. However, since the sulfur component contained in the silane coupling agent may affect the rubber physical properties (snow performance) due to the progress of vulcanization over time, in the present invention, a silane coupling agent with a low sulfur content, such as 3-octanoylthio-1-propyltriethoxysilane, can be preferably used.

[0021] As described above, since the sulfur component in the rubber composition may affect the rubber physical properties (snow performance) due to the progress of vulcanization over time, in the present invention, the ratio of the mass of bound sulfur to the mass of silica is set to less than 3.30% by mass, preferably 1.80% to 3.10% by mass, more preferably 2.00% to 2.80% by mass. Thereby, the change in rubber physical properties over time (increase in hardness, decrease in breaking strength and elongation) caused by the sulfur component can be suppressed, and the snow performance can be maintained well over a long period. When the ratio of the mass of bound sulfur to the mass of silica is 3.30% by mass or more, aging progress is likely to occur, and the snow performance decreases due to an increase in the hardness of the rubber and a decrease in breaking strength and elongation.

[0022] The blending amount of the silane coupling agent is not particularly limited, but it is preferably 3% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the blending amount of the above-mentioned silica. When the blending amount of the silane coupling agent is less than 3% by mass of the silica blending amount, the amount of the silane coupling agent used is too small, so the effect of blending the silane coupling agent cannot be fully expected. When the blending amount of the silane coupling agent exceeds 20% by mass of the silica blending amount, the silane coupling agents condense with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

[0023] By blending other fillers in addition to silica in the rubber composition for tires of the present invention, the strength of the rubber composition can be increased and the tire durability can be ensured. Examples of other fillers include materials generally used in rubber compositions for tires such as carbon black, clay, talc, calcium carbonate, mica, aluminum hydroxide, and the like.

[0024] Among them, by blending carbon black, the strength of the rubber composition can be made excellent. Examples of carbon black include furnace black, acetylene black, thermal black, channel black, graphite, and the like. Among these, furnace black is preferable, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, FEF, and the like. These carbon blacks can be used alone or in combination of two or more. Further, surface-treated carbon black obtained by chemically modifying these carbon blacks with various acid compounds or the like can also be used.

[0025] When blending carbon black, the blending amount is preferably 3 parts by mass to 30 parts by mass, more preferably 5 parts by mass to 20 parts by mass, based on 100 parts by mass of the above-mentioned diene rubber. When the blending amount of carbon black is 3 parts by mass, the electrical conductivity decreases. When the blending amount of carbon black exceeds 30 parts by mass, the rolling resistance deteriorates.

[0026] The rubber composition for tires of the present invention always contains a plasticizer component. In particular, the present invention always contains a thermoplastic resin and an oil as the plasticizer component, and optionally contains a liquid polymer. By incorporating the plasticizer component in this way, snow performance can be improved. The amount of the plasticizer component is 30 parts by mass or more, preferably 35 to 85 parts by mass, and more preferably 40 to 80 parts by mass, per 100 parts by mass of the diene-based rubber described above. If the amount of the plasticizer component is less than 30 parts by mass, snow performance cannot be sufficiently improved.

[0027] When formulating these plasticizer components, it is preferable to keep the oil content in the plasticizer components below 75% by mass, and more preferably between 5% and 70% by mass. Keeping the oil content low in this way suppresses migration, which is advantageous for improving snow performance and chipping resistance. If the oil content in the plasticizer components exceeds 70% by mass, migration is more likely to occur over time, making it difficult to maintain snow performance over the long term. The oil content in the plasticizer components is the ratio of the mass of oil to the total mass of the materials (thermoplastic resin, oil, liquid polymer) formulated as plasticizer components (if liquid polymer, which is an optional component, is not included, it is the ratio of oil to the total of thermoplastic resin and oil). Furthermore, if the styrene-butadiene copolymer described above is an oil-expanding product, the oil-expanding component (oil) contained in the styrene-butadiene copolymer shall also be treated as oil in the plasticizer components.

[0028] The type of thermoplastic resin used as a plasticizer component is not particularly limited, but it is preferable that it be at least one selected from the group consisting of a resin comprising at least one selected from terpenes, modified terpenes, C5 components, C9 components, rosin, rosin esters, and resins in which at least a portion of the double bonds of those resins are hydrogenated. Using such a resin is advantageous in improving compatibility with the polymer and enhancing wet performance.

[0029] Examples of terpene resins include α-pinene resin, β-pinene resin, limonene resin, hydrogenated limonene resin, dipentene resin, terpene phenol resin, terpene styrene resin, aromatically modified terpene resin, and hydrogenated terpene resin. Examples of rosin resins include gum rosin, tall oil rosin, wood rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, maleated rosin, and modified rosin such as fumarated rosin, as well as ester derivatives of these rosins such as glycerin ester, pentaerythritol ester, methyl ester, and triethylene glycol ester, and rosin-modified phenol resin. Examples of C5 petroleum resins include aliphatic petroleum resins obtained by polymerizing fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene. Examples of C9 petroleum resins include aromatic petroleum resins obtained by polymerizing fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, and p-vinyltoluene.

[0030] Among the resins selected from the aforementioned group, it is preferable to use one whose glass transition temperature is preferably 40°C to 120°C, more preferably 45°C to 115°C, and even more preferably 50°C to 110°C. Using a thermoplastic resin that satisfies these conditions is advantageous for improving wet performance. If the glass transition temperature of the thermoplastic resin is below 40°C, the wet performance will decrease. If the glass transition temperature of the thermoplastic resin exceeds 120°C, the snow performance will decrease. The glass transition temperature of the thermoplastic resin can be measured in the same way as the Tg of the styrene-butadiene copolymer described above.

[0031] The type of liquid polymer optionally blended as a plasticizer component is not particularly limited, but examples include liquid polybutene, liquid polyisobutene, liquid polyisoprene, liquid polybutadiene, liquid poly-α-olefin, liquid isobutylene, liquid ethylene-α-olefin copolymer, liquid ethylene propylene copolymer, and liquid ethylene-butylene copolymer. The liquid polymer may also be various modified versions of the above-mentioned liquid polymers (maleic acid modification, terminal isocyanate modification, epoxy modification, etc.). By blending liquid polymers in this way, the rubber hardness at low temperatures can be made more flexible, and the snow performance can be improved. Among these, it is preferable to use a liquid polymer with a molecular weight of 10,000 or more, more preferably 20,000 to 50,000. This can suppress the migration rate, maintain snow performance over a long period of time, and maintain good chipping resistance.

[0032] The content of each material in the plasticizer component is preferably such that the oil content is less than 75% by mass as described above, but the other materials are not particularly limited. Furthermore, if an optional liquid polymer is included, the content of the thermoplastic resin in the plasticizer component is preferably 18% to 70% by mass, more preferably 25% to 60% by mass, and the content of the liquid polymer in the plasticizer component is preferably 10% to 40% by mass, more preferably 20% to 35% by mass.

[0033] The plasticizer components mentioned above generally tend to migrate over time when incorporated into rubber compositions. Therefore, measures are needed to prevent significant changes in rubber properties even if the plasticizer component in the rubber composition decreases due to migration. In this invention, when the average glass transition temperature of the plasticizer component is defined as Tg1 and the average glass transition temperature of the mixture of the plasticizer component and diene rubber is defined as Tg2, the difference between Tg1 and Tg2, ΔTg, is set to 10°C to 40°C, preferably 15°C to 39°C, and more preferably 20°C to 38°C. By setting the difference in glass transition temperatures ΔTg within an appropriate range, changes in the properties of the rubber composition can be suppressed even if changes such as oil migration occur, which is advantageous for ensuring long-term snow performance. If the difference in glass transition temperatures ΔTg is less than 10°C, the deterioration of snow performance due to aging becomes significant. If the difference in glass transition temperatures ΔTg exceeds 40°C, the deterioration of wet performance becomes significant when the plasticizer component decreases due to migration.

[0034] The average glass transition temperature Tg1 of the plasticizer component is a weighted average value based on the glass transition temperature of each material blended as a plasticizer component (thermoplastic resin and oil, and optionally liquid polymer) and the amount of each material blended. Similarly, the average glass transition temperature Tg2 of the mixture of the plasticizer component and diene rubber is a weighted average value based on the glass transition temperature of each material blended as a plasticizer component, and each rubber blended as a diene rubber, and the amount of each material blended. The glass transition temperature of each material can be measured in the same way as the Tg of the styrene-butadiene copolymer described above. The individual values ​​of these glass transition temperatures Tg1 and Tg2 are not particularly limited, but the average glass transition temperature Tg2 is preferably -70°C to -50°C, more preferably -68°C to -52°C. An average glass transition temperature Tg2 within the above range makes it suitable for use in tires intended for winter use (winter tires and all-season tires).

[0035] In addition to the above components, the tire rubber composition may contain various compounding agents commonly used in tire rubber compositions, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, processing aids, and thermosetting resins, according to conventional methods. Such compounding agents can be mixed in a conventional manner to form a rubber composition, which can then be used for vulcanization or crosslinking. The amounts of these compounding agents can be conventional amounts, as long as they do not contradict the purpose of the present invention. The tire rubber composition can be prepared by mixing the above components using a known rubber mixing machine, such as a Banbury mixer, kneader, or roll.

[0036] The rubber composition for tires of the present invention is suitable for forming the tread portion of winter tires and all-season tires that are intended to be driven on snowy roads. Winter tires and all-season tires obtained as a result can exhibit good snow performance, wet performance, and durability (chipping resistance).

[0037] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. [Examples]

[0038] Sixteen tire rubber compositions (Standard Example 1, Comparative Examples 1-7, Examples 1-8) consisting of the formulations shown in Tables 1-2 were prepared. For each composition, the components excluding the vulcanization accelerator and sulfur were weighed and kneaded in a 1.8 L sealed Banbury mixer for 5 minutes. The masterbatch was then released and allowed to cool to room temperature. Subsequently, this masterbatch was placed in a 1.8 L sealed Banbury mixer, the vulcanization accelerator and sulfur were added, and the mixture was mixed for 2 minutes to obtain each tire rubber composition.

[0039] Tables 1 and 2 show, for each tire rubber composition, the oil content (oil ratio) in the plasticizer component, the sulfur content (theoretical value), the ratio of the mass of bound sulfur to the mass of silica (bound sulfur content), the average glass transition temperature Tg2 of the mixture of the plasticizer component and diene rubber, the average glass transition temperature Tg1 of the plasticizer component, and the difference ΔTg between Tg1 and Tg2.

[0040] In this specification, the ratio of the mass of bound sulfur to the mass of silica (amount of bound sulfur) was calculated by measuring the acetone extract residue after removing free sulfur by acetone extraction of each tire rubber composition in accordance with Method A of JIS K6229 using a HORIBA carbon-sulfur analyzer (EMIA), and determining the amount of bound sulfur contained in the vulcanized rubber from the amount of sulfur dioxide detected by the combustion-infrared detection method in accordance with JIS Z2616. Based on this mass of bound sulfur and the mass of silica, the amount of bound sulfur (%) was calculated using the formula: Amount of bound sulfur (%) = Mass of bound sulfur / Mass of silica × 100.

[0041] Test tires (tire size: 205 / 55R16) using each tire rubber composition in the tread were vulcanized and molded. Using the resulting test tires, the wet performance and snow performance when new, and the wet performance, snow performance, and durability performance after aging were evaluated using the method described below.

[0042] Wet performance when new Each test tire was mounted on a 16×6.5JJ rim wheel and fitted to a test vehicle (1.8L engine displacement). The tire pressure was set to 250kPa, and the braking distance was measured on a wet surface at a speed of 100km / h. The evaluation results were shown as an index, with the reciprocal of the measured value set to 100, where standard example 1 is the index value. A higher index value indicates a shorter braking distance and superior wet performance (braking performance on wet surfaces).

[0043] Snow performance when new Each test tire was mounted on a 16×6.5JJ rim wheel and fitted to a test vehicle (1.8L engine displacement). The tire pressure was set to 250kPa, and the braking distance was measured on a compacted snow surface at a speed of 30km / h. The evaluation results were shown as an index, with the reciprocal of the measured value set to 100, where standard example 1 is the index value. A higher index value indicates a shorter braking distance and superior snow performance (braking performance on compacted snow surfaces).

[0044] Wet performance after aging Each test tire underwent an accelerated degradation treatment at 70°C for 336 hours. Afterward, each test tire was mounted on a 16×6.5JJ rim wheel and installed on a test vehicle (1.8L engine). The tire pressure was set to 250kPa, and the braking distance was measured on a wet surface at a speed of 100km / h. The evaluation results were expressed as an index, using the reciprocal of the measured value, with standard example 1 set to 100. A higher index value indicates a shorter braking distance and superior wet performance (braking performance on wet surfaces).

[0045] Snow performance after aging Each test tire underwent an accelerated degradation treatment at 70°C for 336 hours. Afterward, each test tire was mounted on a 16×6.5JJ rim wheel and installed on a test vehicle (1.8L engine). The tire pressure was set to 250kPa, and the braking distance was measured on a compacted snow surface at a speed of 30km / h. The evaluation results were expressed as an index, using the reciprocal of the measured value, with Standard Example 1 set to 100. A higher index value indicates a shorter braking distance and superior snow performance (braking performance on compacted snow surfaces).

[0046] Durability after aging Each test tire underwent an accelerated degradation treatment at 70°C for 336 hours. Afterward, each test tire was mounted on a 16×6.5JJ rim wheel and installed on a test vehicle (1.8L engine). The tire pressure was set to 250kPa, and the vehicle was driven 1000km on an unpaved test track. The number of chips on the tread was then measured. The evaluation results were expressed as an index, using the reciprocal of the measured value, with the value of Conventional Example 1 set to 100. A higher index value indicates fewer chips and superior durability (chipping resistance).

[0047] [Table 1]

[0048] [Table 2]

[0049] The types of raw materials used in Tables 1 and 2 are shown below. • SBR1: Styrene-butadiene rubber, NIPOL NS616 manufactured by Nippon Zeon Corporation (glass transition temperature: -23℃) • SBR2: Styrene-butadiene rubber, manufactured by Nippon Zeon Corporation (NIPOL NS612; glass transition temperature: -61°C) • SBR3: Styrene-butadiene rubber: Asahi Kasei Corporation, Tuffden 1834 (glass transition temperature: -72℃) • SBR4: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, Tuffden L263 (glass transition temperature: -48℃) • BR: Butadiene rubber, manufactured by Nippon Zeon Corporation, Nipol BR1220 (glass transition temperature: -106℃) • Liquid polymer 1: Liquid butadiene rubber, manufactured by Kuraray Co., Ltd., LBR302 (molecular weight: 5000, glass transition temperature: -85℃) • Liquid polymer 2: Liquid butadiene rubber, manufactured by Kuraray Co., Ltd., LBR305 (molecular weight: 30000, glass transition temperature: -95℃) • CB: Carbon Black, manufactured by Cabot Japan, Show Black N339 • Silica: Solvay ZEOSIL1165MP • Thermoplastic resin 1: Aromatic modified terpene resin, manufactured by Yasuhara Chemical Co., Ltd., TO-125 • Thermoplastic resin 2: C5 / C9 resin, Eastman ImperaD1506 • Thermoplastic resin 3: Polyterpene resin, manufactured by Arizona Chemicals, SYL VARESTR-5147 • Silane coupling agent 1: Si69 manufactured by Evonik Degussa. • Silane coupling agent 2: Momentive NXT • Oil 1: TDAE Oil, manufactured by Showa Shell Sekiyu Co., Ltd., Extract No. 4S • Oil 2: Sunflower oil, manufactured by Yokozeki Oil & Fat Industry Co., Ltd. (High-Olec Sunflower Oil) • Anti-aging agent: PILFLEX13 manufactured by NOCIL LIMITED • Wax: OZOACE-0355 manufactured by Nippon Seiro Co., Ltd. • Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. • Stearic acid: Beads-type stearic acid manufactured by NOF Corporation • Sulfur: Fine-grained sulfur containing Kinka oil, manufactured by Tsurumi Chemical Industry Co., Ltd. • Vulcanization accelerator 1: Noxellar CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Vulcanization accelerator 2: Sumitomo Chemical Co., Ltd.'s Soxiel D-G

[0050] As is clear from Tables 1-2, Examples 1-8 showed improved wet performance and snow performance compared to Standard Example 1 when new. Furthermore, even after aging, wet performance, snow performance, and durability were improved, and these performances were maintained well from new to aged.

[0051] On the other hand, Comparative Example 1 had a high amount of bound sulfur (ratio of the mass of bound sulfur to the mass of silica), resulting in poor snow performance when new, snow performance after aging, and durability. Comparative Example 2 had a high amount of silica and a low ΔTg, resulting in poor snow performance when new, snow performance after aging, and durability. Comparative Example 3 did not contain a thermoplastic resin as a plasticizer component, had a high amount of bound sulfur, and a low ΔTg, resulting in poor wet performance when new, wet performance after aging, snow performance, and durability. Comparative Example 4 had a high amount of bound sulfur, resulting in poor snow performance when new, snow performance after aging, and durability. Comparative Example 5 had a high ΔTg, resulting in poor snow performance when new and after aging. Comparative Example 6 contained a large amount of styrene-butadiene copolymer that did not meet the glass transition temperature conditions, resulting in poor wet performance and snow performance when new, as well as poor wet performance and snow performance after aging, and durability. Comparative Example 7 had a large ratio of bonded sulfur mass to silica mass, and a large ΔTg, resulting in poor snow performance when new, snow performance after aging, and durability.

[0052] This disclosure encompasses the following inventions: Invention [1] A tire rubber composition comprising 10% to 80% by mass of styrene-butadiene copolymer and 100 parts by mass of diene rubber containing the butadiene copolymer, with 100 to 150 parts by mass of silica and 30 parts by mass or more of a plasticizer component, wherein the styrene-butadiene copolymer has a glass transition temperature in the range of -75°C to -50°C, the plasticizer component comprises at least a thermoplastic resin and an oil, and optionally a liquid polymer, the difference ΔTg between the average glass transition temperature Tg1 of the plasticizer component and the average glass transition temperature Tg2 of the mixture of the plasticizer component and the diene rubber being 10°C or more and 40°C or less, and the ratio of the mass of bound sulfur to the mass of silica being less than 3.30%. Invention [2] The tire rubber composition according to Invention [1], characterized in that it contains a liquid polymer having a molecular weight of 10,000 or more as the plasticizer component. Invention [3] The tire rubber composition according to Invention [1] or [2], characterized in that the oil content in the plasticizer component is less than 75% by mass. Invention [4] A tire rubber composition according to any one of Inventions [1] to [3], characterized in that it is formulated with 3-octanoylthio-1-propyltriethoxysilane as a silane coupling agent. Invention [5] A rubber composition for tires according to any one of Inventions [1] to [4], characterized in that the thermoplastic resin is at least one selected from the group consisting of a resin comprising at least one selected from terpenes, modified terpenes, C5 components, C9 components, rosin, rosin esters, and resins in which at least a portion of the double bonds of such resins are hydrogenated, and the glass transition temperature thereof is 40°C to 120°C. Invention [6] A rubber composition for tires according to any one of Inventions [1] to [5], characterized in that the glass transition temperature Tg2 is in the range of -70°C to -50°C. Invention [7] A winter tire characterized by using the tire rubber composition described in Inventions [1] to [6] in the tread portion.

Claims

1. A tire rubber composition comprising 10% to 80% by mass of styrene-butadiene copolymer, 100 to 150 parts by mass of silica, and 30 parts by mass or more of a plasticizer component per 100 parts by mass of diene rubber containing the butadiene copolymer, The styrene-butadiene copolymer has a glass transition temperature in the range of -75°C to -50°C. The plasticizer component comprises at least a thermoplastic resin and an oil, and optionally a liquid polymer. The difference ΔTg between the average glass transition temperature Tg1 of the plasticizer component and the average glass transition temperature Tg2 of the mixture of the plasticizer component and the diene rubber is 10°C or more and 40°C or less. The ratio of the mass of bound sulfur to the mass of silica is less than 3.30% by mass. A tire rubber composition characterized by containing 3-octanoylthio-1-propyltriethoxysilane as a silane coupling agent.

2. The tire rubber composition according to claim 1, characterized in that it contains a liquid polymer having a molecular weight of 10,000 or more as the plasticizer component.

3. The tire rubber composition according to claim 1 or 2, characterized in that the oil content in the plasticizer component is less than 75% by mass.

4. The thermoplastic resin is a terpene, a modified terpene, C ５ System component, C ９ The rubber composition for tires according to claim 1 or 2, characterized in that it is at least one selected from the group consisting of a resin comprising at least one selected from a system component, rosin, rosin ester, and a resin in which at least a portion of the double bonds of the resin are hydrogenated, and the glass transition temperature is 40°C to 120°C.

5. The tire rubber composition according to claim 1 or 2, characterized in that the glass transition temperature Tg2 is in the range of -70°C to -50°C.

6. A winter tire characterized by using the tire rubber composition described in claim 5 in the tread portion.

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