Rubber composition for tires

Abstract

Provided is a tire rubber composition by which snow performance, wet performance, and wear resistant performance can be improved, and these performances can be demonstrated with a high degree of balance. The tire rubber composition is obtained by blending a white filler in an amount of 30 parts by mass or more and less than 100 parts by mass and a thermoplastic resin in an amount of 15-80 parts by mass with respect to 100 parts by mass of a diene rubber containing: 55 mass% or more of a styrene-butadiene copolymer having a glass transition temperature of -55°C or more; and 5 mass% or more of a butadiene copolymer. In a mixture obtained by blending the diene rubber and the thermoplastic resin at a mass ratio of 1:1, the difference Tga-Tgm between a theoretical value Tga of the glass transition temperature of the mixture, which is calculated from the glass transition temperatures of the diene rubber and the thermoplastic resin, and a measured value Tgm of the glass transition temperature of the mixture is 10°C or more.

Description

[Technical field]

[0001] The present invention relates to a rubber composition for tires intended to be used primarily in the tread portions of winter tires and all-season tires. [Background technology]

[0002] Tires (winter tires and all-season tires) intended for use on snowy roads are required to have excellent driving performance (snow performance) on snowy roads. In addition, the basic performance of tires is also required to have excellent driving performance (wet performance) and wear resistance on wet roads. For example, the tire in Patent Document 1 proposes blending silica and various resin components into styrene-butadiene rubber, which has a low glass transition temperature, to improve performance at room temperature, such as wet performance, while suppressing the deterioration of low-temperature performance.

[0003] However, in recent years, the performance required for tires has been increasing, and the above-mentioned measures alone are not necessarily sufficient. Therefore, measures are required for rubber compositions for tires to achieve a better balance of snow performance, wet performance, and abrasion resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent No. 6888948 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a rubber composition for tires which has improved snow performance, wet performance and abrasion resistance, and which enables these performances to be simultaneously achieved in a well-balanced manner to a high degree. [Means for solving the problem]

[0006] The rubber composition for tires according to the present invention, which achieves the above object, comprises 55% by mass or more of a styrene-butadiene copolymer having a glass transition temperature of -55°C or lower and butadiene. Rubber The rubber composition for tires is prepared by blending 100 parts by mass of a diene rubber containing 5% or more of a white filler with 30 parts by mass or more but less than 100 parts by mass and 15 parts by mass or more but less than 80 parts by mass of a thermoplastic resin, and is characterized in that in a mixture in which the diene rubber and the thermoplastic resin are blended in a mass ratio of 1:1, the difference Tga-Tgm between the theoretical glass transition temperature Tga of the mixture calculated from the glass transition temperatures of the diene rubber and the thermoplastic resin and the measured glass transition temperature Tgm of the mixture is 10°C or less. Effect of the Invention

[0007] The rubber composition for tires of the present invention comprises a styrene-butadiene copolymer having a specific glass transition temperature and a predetermined amount of butadiene. Rubber A specific thermoplastic resin and a white filler are blended with a diene rubber containing the above, thereby making it possible to improve snow performance, wet performance, and abrasion resistance.

[0008] In the present invention, the total amount of oil contained in the rubber composition for tires is preferably less than 25 parts by mass per 100 parts by mass of the diene rubber, which is advantageous for improving snow performance.

[0009] In the present invention, the glass transition temperature of the styrene-butadiene copolymer is preferably −64° C. or lower. In addition, at least one end of the styrene-butadiene copolymer is preferably modified with a functional group, which is advantageous for improving snow performance and wet performance.

[0010] In the present invention, the glass transition temperature of the thermoplastic resin is preferably 40° C. to 120° C. In addition, the thermoplastic resin is preferably at least one selected from the group consisting of resins composed of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 components, and C9 components, and resins in which at least a portion of the double bonds of these resins are hydrogenated.

[0011] In the present invention, the amount of oil extension of the styrene-butadiene copolymer is preferably 10 parts by mass or less based on 100 parts by mass of the styrene-butadiene copolymer, which is advantageous for improving the abrasion resistance.

[0012] In the present invention, the maximum value of the loss tangent tanδ of the rubber composition for a tire at -40°C to 60°C is determined in relation to a rubber composition B having the same composition as the rubber composition for a tire except that all of the thermoplastic resin is replaced with oil. MAXA and the maximum value tanδ of the loss tangent of the rubber composition B at -40°C to 60°C. MAXB However, it is preferable that the following formula (1) is satisfied. tan δ MAXA / tanδ MAXB > 0.8 (1)

[0013] The above-mentioned rubber composition for tires can be suitably used in the tread portion of winter tires or all-season tires. A tire having a tread portion made of the above-mentioned rubber composition for tires can exhibit good snow performance, wet performance, and wear resistance due to the excellent physical properties of the above-mentioned rubber composition for tires. The tire in which the rubber composition for tires of the present invention is used is preferably a pneumatic tire, but may be a non-pneumatic tire. In the case of a pneumatic tire, the inside can be filled with air, an inert gas such as nitrogen, or other gases. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The rubber component constituting the rubber composition for tires of the present invention is a diene rubber, and 100% by mass of this diene rubber necessarily contains 55% by mass or more of a styrene-butadiene copolymer having a glass transition temperature (hereinafter sometimes referred to as "Tg") of -55°C or less. By containing a styrene-butadiene copolymer having a Tg of -55°C or less, the dispersibility of silica can be improved, and abrasion resistance and wet performance can be ensured. The styrene-butadiene copolymer having a Tg of -55°C or less is 55% by mass or more, preferably 55% to 80% by mass, and more preferably 60% to 75% by mass, of 100% by mass of the diene rubber. If the styrene-butadiene copolymer is less than 55% by mass, the effect of improving the dispersibility of silica cannot be sufficiently obtained, and wet performance is reduced.

[0015] If the Tg of the styrene-butadiene copolymer is higher than -55°C, the wet performance cannot be sufficiently ensured. The Tg is preferably -64°C or lower, more preferably -65°C or lower, and even more preferably -70°C or lower. The Tg of the styrene-butadiene copolymer can be measured as the midpoint temperature of the transition region from a thermogram obtained by differential scanning calorimetry (DSC) under a heating rate condition of 20°C / min. In addition, when the styrene-butadiene copolymer is an oil-extended product, the Tg of the styrene-butadiene copolymer is measured in a state in which it does not contain an oil-extending component (oil).

[0016] The styrene-butadiene copolymer having a Tg of -55°C or less may have at least one end modified with a functional group. By modifying the styrene-butadiene copolymer having a Tg of -55°C or less, the dispersibility of silica can be improved and the rolling resistance of the tire can be further reduced. Examples of functional groups include epoxy groups, carboxy groups, amino groups, hydroxy groups, alkoxy groups, silyl groups, alkoxysilyl groups, amide groups, oxysilyl groups, silanol groups, isocyanate groups, isothiocyanate groups, carbonyl groups, and aldehyde groups, and among these, those having a polyorganosiloxane structure or an aminosilane structure are preferably mentioned. By having a functional group having a polyorganosiloxane structure or an aminosilane structure, the dispersibility of silica can be improved and wet performance can be improved.

[0017] The styrene content of the styrene-butadiene copolymer is not particularly limited, but is preferably 5% by mass to 30% by mass, more preferably 8% by mass to 25% by mass. By setting the styrene content within such a range, it is preferable that the tire has low rolling resistance. The styrene content of the styrene-butadiene rubber can be measured by 1H-NMR.

[0018] The vinyl content of the styrene-butadiene copolymer is not particularly limited, but is preferably 9 mol% to 45 mol%, more preferably 20 mol% to 45 mol%, further preferably 25 mol% to 45 mol%, and particularly preferably 28 mol% to 42 mol%. By setting the vinyl content within such a range, it is possible to improve the dispersibility of silica, reduce the temperature dependency of rolling resistance, and ensure wear resistance, which is preferable. The vinyl content of the styrene-butadiene rubber can be measured by 1H-NMR.

[0019] The styrene-butadiene copolymer may contain an oil-extended component. The amount of oil-extended component is preferably 10 parts by mass or less per 100 parts by mass of the styrene-butadiene copolymer. By setting the amount of oil-extended component to 10 parts by mass or less, the abrasion resistance can be effectively improved. The amount of oil-extended component is more preferably 8 parts by mass or less, and further preferably 5 parts by mass or less.

[0020] The rubber composition for tires of the present invention contains, in addition to the above-mentioned styrene-butadiene copolymer, butadiene in 100% by mass of diene rubber. Rubber Must contain 5% or more by mass. Butadiene Rubber By including butadiene, in addition to the above-mentioned properties, snow performance can be improved. Rubber The content of butadiene is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the diene rubber. Rubber The butadiene is preferably blended in an amount of 65% by mass or less, more preferably 50% by mass or less, based on 100% by mass of the diene rubber. Rubber If the content is less than 5 mass %, the effect of improving snow performance cannot be sufficiently obtained.

[0021] The rubber composition for tires is a styrene-butadiene copolymer and a butadiene Rubber The diene rubber may contain other diene rubbers other than the above. Examples of the other diene rubbers include styrene butadiene copolymers having a Tg of more than -55°C, natural rubber, isoprene rubber, butyl rubber, emulsion-polymerized styrene butadiene rubber, halogenated butyl rubber, acrylonitrile-butadiene rubber, and modified rubbers obtained by adding functional groups to these rubbers. These other diene rubbers may be used alone or as an arbitrary blend. The content of the other diene rubber is preferably 40% by mass or less, more preferably 0% by mass to 35% by mass, and even more preferably 0% by mass to 25% by mass, based on 100% by mass of the diene rubber.

[0022] The rubber composition for tires is compounded with 30 parts by mass or more and less than 100 parts by mass of a white filler per 100 parts by mass of a diene rubber. By compounding the white filler, wet performance and low rolling resistance can be excellent. If the white filler is less than 30 parts by mass, the wet performance and / or low rolling resistance are insufficient. If the white filler is more than 100 parts by mass, low rolling resistance is rather deteriorated. The white filler is preferably compounded in an amount of 40 parts by mass or more and less than 100 parts by mass, more preferably 45 parts by mass or more and less than 100 parts by mass.

[0023] The type of white filler is not particularly limited, but examples thereof include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These can be used alone or in combination of two or more. Among them, silica is preferable, and can provide better wet performance and low heat generation. As the silica, those usually used in rubber compositions for tires can be used, such as wet-process silica, dry-process silica, or carbon-silica (dual-phase filler) in which silica is supported on the surface of carbon black, and silica surface-treated with a compound that is reactive or compatible with both silica and rubber, such as a silane coupling agent or polysiloxane. Among these, wet-process silica, which is mainly composed of hydrated silicic acid, is preferable.

[0024] The rubber composition for tires can be blended with other fillers than the white filler to increase the strength of the rubber composition and ensure tire durability. Examples of other fillers include inorganic fillers such as carbon black, mica, aluminum oxide, and barium sulfate, and organic fillers such as cellulose, lecithin, lignin, and dendrimers.

[0025] Among them, by blending carbon black, the strength of the rubber composition can be improved. Carbon black such as furnace black, acetylene black, thermal black, channel black, graphite, etc. may be blended. 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, etc. These carbon blacks can be used alone or in combination of two or more kinds. Surface-treated carbon blacks obtained by chemically modifying these carbon blacks with various acid compounds, etc., can also be used.

[0026] When silica is used as a white filler, it is preferable to use a silane coupling agent in combination. By compounding a silane coupling agent, the dispersibility of silica in diene rubber can be improved. The type of silane coupling agent is not particularly limited as long as it can be used in a rubber composition containing silica, and examples thereof include sulfur-containing silane coupling agents such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. Among these, those having a tetrasulfide bond in the molecule can be preferably used. The compounding amount of the silane coupling agent is preferably 3% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the compounding amount of silica. If the compounding amount of the silane coupling agent exceeds 20% by mass of the compounding amount of silica, the silane coupling agents condense with each other, and the desired hardness and strength of the rubber composition cannot be obtained.

[0027] The rubber composition for tires can adjust the temperature dependency of its dynamic viscoelasticity by blending a specific thermoplastic resin. The specific thermoplastic resin is blended in an amount of 15 parts by mass or more and 80 parts by mass or less, preferably 20 parts by mass or more and 75 parts by mass or less, more preferably 25 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of diene rubber. If the amount of the thermoplastic resin is less than 15 parts by mass, the object of the present invention, which is to provide excellent abrasion resistance and wet performance, and to provide good low rolling resistance and reduce its temperature dependency, cannot be achieved. Also, if the amount of the specific thermoplastic resin exceeds 75 parts by mass, there is a risk that the abrasion resistance will decrease.

[0028] The specific thermoplastic resin satisfies the following relationship with the diene rubber. That is, in a mixture in which the diene rubber and thermoplastic resin are blended at a mass ratio of 1:1, the difference Tga-Tgm between the theoretical value Tga of the glass transition temperature of the mixture calculated from the glass transition temperatures of the diene rubber and the thermoplastic resin and the measured value Tgm of the glass transition temperature of the mixture is set to 10°C or less. By making the difference Tga-Tgm 10°C or less, the abrasion resistance and wet performance are excellent, and the rolling resistance can be reduced and its temperature dependency can be reduced. The difference Tga-Tgm is preferably 7°C or less, more preferably 5°C or less. When the difference Tga-Tgm is 10°C or less, the diene rubber and the thermoplastic resin are in a compatible relationship, and it is considered that blending a relatively large amount of the thermoplastic resin increases the tensile break strength of the rubber composition and contributes to improving viscoelastic properties such as tan δ. In the present invention, the theoretical glass transition temperature Tga of the mixture can be calculated as a weighted average value from the glass transition temperatures and mass ratios of the diene rubber and the thermoplastic resin. The glass transition temperatures of the diene rubber and the thermoplastic resin, and the glass transition temperature Tgm of the mixture are measured by measuring a thermogram at a temperature rise rate of 20°C / min by differential scanning calorimetry (DSC) and measuring the temperature at the midpoint of the transition region. When the thermogram has multiple transition regions, the midpoint of the largest transition region is taken as the glass transition temperature Tgm of the mixture.

[0029] Thermoplastic resins are resins that are usually blended into rubber compositions for tires, have a molecular weight of several hundred to several thousand, and have the effect of imparting adhesiveness to rubber compositions for tires. As thermoplastic resins, resins made of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 components, and C9 components are preferred. Examples of such resins include natural resins such as terpene-based resins, modified terpene-based resins, rosin-based resins, and rosin ester-based resins, and synthetic resins such as petroleum-based resins made of C5 components and C9 components, coal-based resins, phenol-based resins, and xylene-based resins.

[0030] Examples of terpene resins include α-pinene resin, β-pinene resin, limonene resin, hydrogenated limonene resin, dipentene resin, terpene phenol resin, terpene styrene resin, aromatic modified terpene resin, hydrogenated terpene resin, etc. Examples of rosin resins include modified rosins such as gum rosin, tall oil rosin, wood rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, maleic rosin, and fumaric rosin, ester derivatives of these rosins such as glycerin ester, pentaerythritol ester, methyl ester, and triethylene glycol ester, and rosin-modified phenol resin.

[0031] Examples of petroleum-based resins include aromatic hydrocarbon resins and saturated or unsaturated aliphatic hydrocarbon resins, such as C5 petroleum resins (aliphatic petroleum resins obtained by polymerizing fractions of isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, pentene, etc.), C9 petroleum resins (aromatic petroleum resins obtained by polymerizing fractions of α-methylstyrene, o-vinyltoluene, m-vinyltoluene, p-vinyltoluene, etc.), and C5C9 copolymer petroleum resins.

[0032] The thermoplastic resin preferably has a glass transition temperature (Tg) of 40° C. to 120° C., preferably 45° C. to 115° C., and more preferably 50° C. to 110° C. By making the Tg of the thermoplastic resin 40° C. or higher, it is possible to improve wet performance. Furthermore, by making the Tg of the thermoplastic resin 120° C. or lower, it is possible to improve abrasion resistance. The glass transition temperature of the thermoplastic resin can be measured by the method described above.

[0033] In the following description, the rubber composition for tires of the present invention is referred to as rubber composition A, and a rubber composition having the same composition as rubber composition A except that all the thermoplastic resins contained in rubber composition A are replaced with oil is referred to as rubber composition B. In addition, the maximum value of the loss tangent of rubber composition A at -40°C to 60°C is tanδ MAXA The maximum loss tangent of rubber composition B at -40°C to 60°C is tanδ MAXB In this case, tan δ MAXA and tan δ MAXB It is preferable that the relationship of the following formula (1) is satisfied. tan δ MAXA / tanδ MAXB > 0.8 (1)

[0034] Ratio of maximum loss tangents tanδ MAXA / tanδ MAXB When tan δ of rubber composition A is larger than 0.8, the tensile break strength of the rubber composition for tires of the present invention (rubber composition A) is large, and the abrasion resistance of the tire when made into a tire is excellent, which is preferable. Rubber composition B tends to have high compatibility with the diene rubber and oil contained therein and has high tensile break strength. MAXA The tan δ of rubber composition B MAXB It is presumed that the viscoelastic behavior of the rubber composition is similar, the compatibility of the diene rubber and the thermoplastic resin is good, and the thermoplastic resin is prevented from becoming the starting point of fracture, resulting in a large tensile strength at break. MAXA / tanδ MAXB is more preferably greater than 0.85, and further preferably greater than 0.9. MAXAand tan δ MAXB The dynamic viscoelasticity of the cured products of rubber compositions A and B was measured using a viscoelasticity spectrometer under conditions of an elongation deformation strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature range of -40°C to 60°C. Viscoelasticity curves were obtained with the measurement temperature on the horizontal axis and loss tangent (tan δ) on the vertical axis. The thickest value (peak value) of tan δ was defined as tan δ. MAXA and tan δ MAXB It can be said that:

[0035] The rubber composition for tires of the present invention may further contain oil. The amount of oil is preferably less than 25 parts by mass, more preferably less than 10 parts by mass, and even more preferably 8 parts by mass, per 100 parts by mass of diene rubber. Restricting the amount of oil in this manner is advantageous for maintaining good snow performance. If the amount of oil is 25 parts by mass or more, the change in snow performance over time becomes large, making it difficult to maintain good snow performance.

[0036] In addition to the above components, various compounding agents generally used in rubber compositions for tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, processing aids, liquid polymers, and thermosetting resins, can be compounded in the rubber composition for tires in a conventional manner. Such compounding agents can be kneaded in a conventional manner to prepare a rubber composition, which can then be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be conventionally used amounts, so long as they do not contradict the object of the present invention. The rubber composition for tires can be prepared by mixing the above components using a known rubber kneading machine, such as a Banbury mixer, kneader, roll, etc.

[0037] The rubber composition for tires is suitable for forming the tread and sidewalls of winter tires and all-season tires that are expected to run on snowy roads, and is particularly suitable for forming the treads of these tires. The winter tires and all-season tires obtained thereby can exhibit excellent snow performance, wet performance, and wear resistance.

[0038] 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

[0039] In preparing 17 kinds of rubber compositions for tires (Standard Example 1, Examples 1-8, Comparative Examples 1-8) having a common additive formulation shown in Table 3 and consisting of the formulations shown in Tables 1 and 2, the components except for sulfur and vulcanization accelerator were weighed and kneaded in a 1.7-liter closed Banbury mixer for 5 minutes, and then the master batch was discharged from the mixer and cooled at room temperature. This master batch was fed to the same Banbury mixer, and sulfur and vulcanization accelerator were added and mixed to obtain a rubber composition for tires. Regarding Comparative Example 8 in Table 1, since SBR4 is an oil-extended product with 25 parts by mass, the compounding amount without the oil-extended component is written in parentheses in the lower row. The additive formulation in Table 3 is written in parts by mass relative to 100 parts by mass of the diene rubber listed in Tables 1 and 2. In addition, the rubber compositions for tires of the above-mentioned Examples 1-8 and Comparative Examples 1-8 were each designated as rubber composition A, and rubber composition B having the same composition as each rubber composition A except that all the thermoplastic resins were replaced with oil was prepared in the same manner as above. Furthermore, for the mixtures of the diene rubber and the thermoplastic resin constituting the rubber composition for tires of each Example and Comparative Example in a mass ratio of 1:1, the glass transition temperature (Tgm) was measured by the above-mentioned method, and the theoretical glass transition temperature Tga was calculated, and the difference Tga-Tgm from the measured glass transition temperature Tgm was calculated and shown in Tables 1 and 2. In addition, Tables 1 and 2 show the tan δ of each rubber composition A. MAXA and tan δ of each rubber composition B MAXB Ratio of tan δ MAXA / tanδ MAXB tan δ MAXA and tan δ MAXB The dynamic viscoelasticity of each of the cured products of rubber compositions A and B was measured using a viscoelasticity spectrometer under conditions of an elongation deformation strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature range of -40°C to 60°C. A viscoelasticity curve was obtained with the measurement temperature on the horizontal axis and the loss tangent (tan δ) on the vertical axis. The thickest value (peak value) of tan δ was calculated as tan δ. MAXA and tan δMAXB was requested as follows.

[0040] The rubber compositions for tires obtained above were vulcanized in a mold of a predetermined shape at 160° C. for 20 minutes to prepare evaluation samples. The obtained evaluation samples were used to measure the abrasion resistance, wet performance, and snow performance by the following methods.

[0041] Abrasion resistance The amount of wear of the obtained evaluation sample of the rubber composition for tires was measured in accordance with JIS K6264 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of a load of 15.0 kg (147.1 N) and a slip ratio of 25%. The reciprocals of the obtained results were calculated and are shown in the "Wear Resistance" column of Tables 1 and 2 as indexes with the reciprocal of the wear amount of Standard Example 1 set to 100. A higher wear resistance index means better wear resistance.

[0042] Wet Performance The above-mentioned 17 kinds of rubber compositions for tires (Standard Example 1, Comparative Examples 1 to 8, Examples 1 to 8) were used for the cap tread to manufacture pneumatic tires (test tires) with a tire size of 195 / 55R15. These test tires were mounted on wheels with a rim size of 15 inches, and the air pressure was set to 230 kPa and mounted on a test vehicle. The braking distance from a running state of 40 km / h to a stop of the vehicle by applying ABS braking on a test course consisting of a wet road surface was measured. The evaluation results are shown in the "Wet Performance" column of Tables 1 and 2 as index values ​​with Standard Example 1 being 100, using the reciprocal of the measured value. The larger the index value, the shorter the braking distance and the better the wet performance.

[0043] Snow Performance The above-mentioned 17 kinds of rubber compositions for tires (Standard Example 1, Comparative Examples 1-8, Examples 1-8) were used for the cap tread to manufacture pneumatic tires (test tires) with a tire size of 195 / 55R15. These test tires were mounted on wheels with a rim size of 15 inches, and the air pressure was set to 230 kPa and mounted on a test vehicle. The braking distance from a running state of 40 km / h to a stop of the vehicle by applying ABS braking on a test course consisting of a packed snow road was measured. The evaluation results are shown in the "Snow performance" column of Tables 1 and 2 as index values ​​using the reciprocal of the measured values, with Standard Example 1 being 100. The higher the index value, the shorter the braking distance and the better the snow performance.

[0044] [Table 1]

[0045] [Table 2]

[0046] The types of raw materials used in Tables 1 and 2 are shown below. NR: Natural rubber, TSR20 (glass transition temperature: -65°C) SBR1: Terminally modified solution polymerized styrene butadiene rubber having a polyorganosiloxane structure, Nipol NS612 manufactured by Zeon Co., Ltd. (glass transition temperature: -61°C, styrene content: 15% by mass, vinyl content: 31% by mole, non-oil extended product) SBR2: Terminally modified solution polymerized styrene butadiene rubber having a polyorganosiloxane structure, Nipol NS616 manufactured by Zeon Co., Ltd. (glass transition temperature: -23°C, styrene content: 22% by mass, vinyl content: 67% by mole, non-oil extended product) SBR3: Unmodified solution-polymerized styrene-butadiene rubber produced by batch polymerization, JSR HPR850 (glass transition temperature: -25°C, styrene content: 27% by mass, vinyl content: 59% by mole, oil-extended product) SBR4: Alkoxysilane-modified solution-polymerized styrene-butadiene rubber produced by continuous polymerization, LG M2520 (glass transition temperature: -48°C, styrene content: 27% by mass, vinyl content: 27% by mole, oil extension amount: 25 parts by mass) BR: Butadiene rubber, Zeon Nipol BR1220 (glass transition temperature: -105°C) CB: Carbon black, Tokai Carbon Co., Ltd. Seast 7HM Silica 1: Solvey Zeosil 1165MP (nitrogen adsorption specific surface area: 159 m 2 / g) Silica 2: Evonic ULTRASIL 9100GR (nitrogen adsorption specific surface area: 220 m 2 / g) Silica 3: Solvey Zeosil 115GR (nitrogen adsorption specific surface area: 110 m 2 / g) Resin 1: Aromatic modified terpene resin, HSR-7 (glass transition temperature: 72°C) manufactured by Yasuhara Chemical Co., Ltd. Resin 2: Aromatic modified terpene resin, YS Resin TO-105 manufactured by Yasuhara Chemical Co., Ltd. (glass transition temperature: 57°C) Resin 3: Indene resin, Mitsui Chemicals FMR0150 (glass transition temperature: 89°C) Resin 4: Phenol-modified terpene resin, Arakawa Chemical Industries, Ltd., Tamanol 803L (glass transition temperature: 95°C) Silane coupling agent 1: Sulfur-containing silane coupling agent, bis(3-triethoxysilylpropyl)tetrasulfide, Si69 from Evonik Silane coupling agent 2: 3-octanoylthio-1-propyltriethoxysilane, NXT silane from Evonik Degussa Oil: Showa Shell Sekiyu Extract No. 4 S

[0047] [Table 3]

[0048] The types of raw materials used in Table 3 are shown below. Anti-aging agent: LANXESS VULANOX 4020 Wax: NIPPON SEIRO OZOACE-0015A Sulfur: Sulfax 5 manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela CZ-G manufactured by Ouchiko Chemical Industry Co., Ltd.

[0049] As is clear from Table 2, the rubber compositions for tires of Examples 1 to 8 were excellent in abrasion resistance, wet performance and snow performance, and these performances were improved in a well-balanced manner.

[0050] On the other hand, as is clear from Table 1, the rubber composition for tires of Comparative Example 1 did not contain butadiene rubber, so the snow performance was reduced. The rubber composition for tires of Comparative Example 2 had a low blending amount of styrene-butadiene rubber, so the wet performance was reduced. The rubber composition for tires of Comparative Example 3 had a difference Tga-Tgm exceeding 10°C, so the abrasion resistance and wet performance were reduced. The rubber composition for tires of Comparative Example 4 had a too large amount of resin, so the abrasion resistance and snow performance were reduced. The rubber composition for tires of Comparative Example 5 had a high blending amount of silica, so the snow performance was reduced. The rubber composition for tires of Comparative Example 6 had a low blending amount of silica, so the wet performance was reduced. The rubber composition for tires of Comparative Example 7 had a high glass transition temperature of styrene-butadiene rubber, so the abrasion resistance and snow performance were reduced. The rubber composition for tires of Comparative Example 8 had a high glass transition temperature of styrene-butadiene rubber, so the abrasion resistance and snow performance were reduced.

Claims

1. A rubber composition for tires is prepared by blending 30 parts by mass or more and less than 100 parts by mass of a white filler and 15 parts by mass or more and 80 parts by mass or less of a thermoplastic resin with 100 parts by mass of a diene rubber containing 55% by mass or more of a styrene-butadiene copolymer having a glass transition temperature of -55°C or less and 5% by mass or more of butadiene rubber, wherein the diene rubber and the thermoplastic resin are blended in a mass ratio of 1:1, and the difference Tga - Tgm between the theoretical value Tga of the glass transition temperature of the mixture calculated from the glass transition temperatures of the diene rubber and the thermoplastic resin and the measured value Tgm of the glass transition temperature of the mixture is 10°C or less.

2. 2. The rubber composition for tires according to claim 1, further comprising less than 25 parts by mass of oil blended with respect to 100 parts by mass of the diene rubber.

3. 3. The rubber composition for tires according to claim 1, wherein the styrene-butadiene copolymer has a glass transition temperature of −64° C. or lower.

4. 3. The rubber composition for a tire according to claim 1, wherein at least one terminal of the styrene-butadiene copolymer is modified with a functional group.

5. 3. The rubber composition for tires according to claim 1, wherein the thermoplastic resin has a glass transition temperature of 40°C to 120°C.

6. 3. The rubber composition for tires according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of resins consisting of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 components, and C9 components, and resins in which at least a portion of the double bonds of these resins are hydrogenated.

7. 3. The rubber composition for tires according to claim 1, wherein the amount of the oil-extended styrene-butadiene copolymer is 10 parts by mass or less based on 100 parts by mass of the styrene-butadiene copolymer.

8. The maximum value tan δ of the loss tangent of the rubber composition for tires at -40°C to 60°C in relation to a rubber composition B having the same composition as the rubber composition for tires except that all of the thermoplastic resin is replaced with oil. MAXA and the maximum value tan δ of the loss tangent of the rubber composition B at −40° C. to 60° C. MAXB The rubber composition for tires according to claim 1 or 2, characterized in that the following formula (1) is satisfied: tanδ MAXA / tanδ MAXB > 0.8 (1)

9. A tire having a tread portion made of the rubber composition for tires according to claim 1 or 2.

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