rubber composition

Abstract

Provided is a rubber composition constituted so as to achieve a balance between abrasion resistance, low rolling resistance and wet grip performance. This rubber composition contains 20-150 parts by mass of a white filler and a total of not less than 20 parts by mass and less than 50 parts by mass of a thermoplastic resin and, optionally, a plasticizer relative to 100 parts by mass of a diene-based rubber including a styrene-butadiene rubber. The thermoplastic resin accounts for 75 mass% or more of the total amount. The relationships |σbf-σaf| ≥ 4 and |tanδbf-tanδaf| ≤ 0.02 are satisfied when: the half value width of a tanδ temperature dependency curve of the rubber composition is denoted by σbf (ºC); the tanδ value at a temperature that is 90°C higher than the peak temperature at a maximum tanδ value of the rubber composition is denoted by tanδbf; the half value width of a tanδ temperature dependency curve of the rubber composition after the rubber composition is treated by being immersed in toluene and then dried is denoted by σaf (ºC); and the tanδ value at a temperature that is 90°C higher than the peak temperature at a maximum tanδ value of the treated rubber composition is denoted by tanδaf.

Description

Technical Field

[0001] The present invention relates to a rubber composition that achieves both abrasion resistance, low rolling resistance, and wet performance.

Background Art

[0002] Tires are required to have high levels of abrasion resistance, low rolling resistance, and wet performance. As a rubber composition for a tire tread that improves abrasion resistance, low rolling resistance, and wet performance, it has been proposed to blend an aromatic-modified terpene resin and an oil into the rubber composition (see, for example, Patent Document 1).

[0003] However, in recent years, it has been required to achieve a higher level of balance among abrasion resistance, low rolling resistance, and wet performance than the level described in Patent Document 1.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a rubber composition that achieves abrasion resistance, low rolling resistance, and wet performance at a higher level than the conventional level.

Means for Solving the Problems

[0006] The rubber composition of the present invention for achieving the above object is a rubber composition containing 20 to 150 parts by mass of a white filler in 100 parts by mass of a diene rubber containing at least one styrene-butadiene rubber, and a total of 20 parts by mass or more and less than 50 parts by mass of a thermoplastic resin and an optional plasticizer, wherein the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more. Let the half-value width in the temperature dependence curve of tanδ of the rubber composition be σbf (°C), the value of tanδ at a temperature 90 °C higher than the peak temperature at which tanδ is maximum be tanδbf, the half-value width in the temperature dependence curve of tanδ of the rubber composition after being immersed in toluene and dried be σaf (°C), and the value of tanδ at a temperature 90 °C higher than the peak temperature at which tanδ is maximum be tanδaf. It is characterized by satisfying the following relational expressions (1) and (2). |σbf - σaf| ≥ 4 (1) |tanδbf - tanδaf| ≤ 0.02 (2) [[Effect of the Invention]]

[0007] The rubber composition of the present invention contains a thermoplastic resin and a plasticizer in specific blending ratios in a styrene-butadiene rubber and a white filler, and the half-value width σ of the temperature dependence curve of tanδ and tanδ at a temperature 90 °C higher than the peak temperature at which tanδ is maximum satisfy a specific relationship with the rubber composition after being immersed in toluene and dried. Therefore, abrasion resistance, low rolling resistance, and wet performance can be achieved at a higher level than the conventional level and can be made compatible at a higher level.

[0008] It is preferable that the difference Tgr - Tgp between the lowest glass transition temperature Tgp (°C) of the glass transition temperatures of the at least one styrene-butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin is 100 °C or more, so that the abrasion resistance can be made more excellent.

[0009] The diene rubber preferably contains 70 to 100% by mass of the at least one styrene-butadiene rubber and 0 to 30% by mass of an isoprene rubber, and at least one of the terminals of the at least one styrene-butadiene rubber is preferably modified with a functional group.

[0010] The thermoplastic resin has a glass transition temperature Tgr of 40°C to 120°C, and the thermoplastic resin is preferably at least one selected from the group consisting of a resin composed of at least one selected from terpenes, modified terpenes, rosins, rosin esters, C5 components, and C9 components, and a resin in which at least a part of the double bonds of these resins is hydrogenated.

Embodiments for Carrying Out the Invention

[0011] The rubber composition of the present invention contains at least one styrene-butadiene rubber as a diene rubber. The styrene-butadiene rubber may be contained alone or as a blend of two or more types. By including the styrene-butadiene rubber, the tensile breaking strength can be increased and the abrasion resistance can be improved, and by improving the dispersibility of silica, the tanδ at 0°C can be increased and the wet performance can be made excellent.

[0012] The glass transition temperature (hereinafter sometimes referred to as "Tg") of the styrene-butadiene rubber is preferably -55°C or lower, more preferably -80°C to -58°C, and even more preferably -75°C to -60°C. By setting the Tg of the styrene-butadiene rubber to -55°C or lower, the abrasion resistance can be improved, which is preferable. The Tg of the styrene-butadiene rubber can be measured as the temperature at the midpoint of the transition region from the thermogram obtained under the condition of a heating rate of 20°C / min by differential scanning calorimetry (DSC). Also, when the styrene-butadiene rubber is an oil-extended product, it is the Tg of the styrene-butadiene rubber in a state not containing the oil-extended component (oil).

[0013] Styrene-butadiene rubber has a styrene content that is not particularly limited, but is preferably 5 to 45% by mass, more preferably 8 to 42% by mass. By setting the styrene content within such a range, the abrasion resistance is improved, which is preferable.

[0014] Also, the vinyl content of the styrene-butadiene rubber is not particularly limited, but is preferably 5 to 60%, more preferably 10 to 55%. By setting the vinyl content within such a range, the dry grip performance can be made excellent, which is preferable. The styrene content and vinyl content in the styrene-butadiene rubber 1 can be measured by 1H-NMR.

[0015] It is preferable that at least one end of the styrene-butadiene rubber is modified with a functional group, which can improve the dispersibility of silica and make the rolling resistance of the tire smaller. Examples of the functional group include an epoxy group, a carboxy group, an amino group, a hydroxy group, an alkoxy group, a silyl group, an alkoxysilyl group, an amide group, an oxysilyl group, a silanol group, an isocyanate group, an isothiocyanate group, a carbonyl group, an aldehyde group, etc. Among them, 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 the abrasion resistance, low rolling resistance and wet performance can be made excellent.

[0016] The content of styrene-butadiene rubber is preferably 55% by mass or more, more preferably 70 to 100% by mass, still more preferably 75 to 90% by mass in 100% by mass of the diene rubber. When one type is contained alone, it is the content of that styrene-butadiene rubber, and when contained as a blend of two or more types, it is the total amount of those styrene-butadiene rubbers. By containing 55% by mass or more of styrene-butadiene rubber, the dispersibility of silica can be improved, and the abrasion resistance and wet performance can be enhanced.

[0017] The rubber composition can optionally contain other diene rubbers other than styrene-butadiene rubber. Examples of other diene rubbers include natural rubber, isoprene rubber, butadiene rubber, butyl rubber, halogenated butyl rubber, acrylonitrile-butadiene rubber, and modified rubbers obtained by attaching functional groups to these rubbers. In the present invention, it is preferably free of butadiene rubber, which can improve wet performance and abrasion resistance. These other diene rubbers can be used alone or as any blend. The content of other diene rubbers is preferably 45% by mass or less, more preferably 0 to 30% by mass, and still more preferably 10 to 25% by mass in 100% by mass of the diene rubber.

[0018] The rubber composition is preferably blended with isoprene rubbers such as natural rubber and isoprene rubber, which can improve abrasion resistance. The isoprene rubber is preferably 0 to 30% by mass, more preferably 10 to 25% by mass in 100% by mass of the diene rubber. As the isoprene rubber, natural rubber or the like usually used in rubber compositions may be used.

[0019] The wet performance of the rubber composition can be improved by blending a white filler with the diene rubber. Examples of the white filler include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These may be used alone or in combination of two or more. Among them, silica is preferred, which can make the wet performance and low heat generation more excellent. The white filler is preferably blended in an amount of 20 to 150 parts by mass, more preferably 40 to 150 parts by mass, and still more preferably 60 to 140 parts by mass per 100 parts by mass of the diene rubber. By blending 20 parts by mass or more of the white filler, the wet performance and abrasion resistance can be made more excellent. Also, by blending 150 parts by mass or less, the abrasion resistance and low rolling resistance can be made excellent.

[0020] As the silica, those commonly used in rubber compositions may be used, for example, wet-process silica, dry-process silica, or silica surface-treated with a compound reactive or compatible with both silica and rubber such as carbon-silica (dual-phase filler) obtained by supporting silica on the surface of carbon black, a silane coupling agent, or polysiloxane. Among these, wet-process silica mainly composed of hydrous silicic acid is preferable.

[0021] Also, by blending a silane coupling agent together with silica, the dispersibility of silica is improved, and the wet performance and low heat generation property are further improved, which is preferable. The type of the silane coupling agent is not particularly limited, but a sulfur-containing silane coupling agent is preferable. For example, bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyldimethoxymethylsilane, 3-mercaptopropyldimethylmethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyltriethoxysilane, and VP Si363 manufactured by Evonik Industries AG, mercaptosilane compounds exemplified in Japanese Patent Application Laid-Open No. 2006-249069, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropylbenzothiazolyl tetrasulfide, 3-octanoylthiopropyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, β-(3,Examples thereof include (4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, and the like.,

[0022] The silane coupling agent is preferably compounded in an amount of 3 to 20% by mass, more preferably 5 to 15% by mass, based on the mass of the silica. When the silane coupling agent is 3% by mass or more of the silica mass, it is advantageous for improving the dispersibility of the silica. Also, when the silane coupling agent is 20% by mass or less, gelation of the diene rubber component can be suppressed to obtain the desired effect.,

[0023] By compounding other fillers in addition to the white filler, the strength of the rubber composition can be increased and tire durability can be ensured. Examples of other fillers include inorganic fillers such as carbon black, mica, aluminum oxide, barium sulfate, and organic fillers such as cellulose, lecithin, lignin, dendrimer.,

[0024] Among them, by compounding carbon black, the strength of the rubber composition can be made excellent. As the carbon black, carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite may be compounded. 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. Also, surface-treated carbon blacks obtained by chemically modifying these carbon blacks with various acid compounds and the like can also be used.,

[0025] The rubber composition can adjust the temperature dependence of its dynamic viscoelasticity by blending a specific thermoplastic resin and optionally a plasticizer. The total amount of the thermoplastic resin and the plasticizer is 20 parts by mass or more and less than 50 parts by mass with respect to 100 parts by mass of the diene rubber. That is, the thermoplastic resin may be blended in an amount of 20 parts by mass or more and less than 50 parts by mass without containing a plasticizer, or the plasticizer may be contained and the total amount of the thermoplastic resin and the plasticizer may be blended in an amount of 20 parts by mass or more and less than 50 parts by mass. By blending the thermoplastic resin and the plasticizer within such a range, both wear resistance and low rolling resistance can be achieved. The total amount of the thermoplastic resin and the plasticizer is preferably 25 parts by mass or more and 48 parts by mass or less, more preferably 30 parts by mass or more and 45 parts by mass or less.

[0026] In the rubber composition, the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more. By setting the thermoplastic resin to 75% by mass or more, the wear resistance can be improved. The ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is preferably 80% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less.

[0027] The thermoplastic resin is a resin usually blended into the rubber composition and has an action of imparting adhesiveness to the rubber composition. The thermoplastic resin is preferably at least one selected from the group consisting of at least one resin selected from terpene, modified terpene, rosin, rosin ester, C5 component, C9 component, and a resin in which at least a part of the double bonds of these resins is hydrogenated. For example, natural resins such as terpene resins, modified terpene resins, rosin resins, rosin ester resins, petroleum resins composed of C5 components and C9 components, synthetic resins such as coal-based resins, phenolic resins, and xylene resins can be mentioned. Also, a resin in which at least a part of the double bonds of these resins is hydrogenated may be used.

[0028] Examples of terpene resins include α-pinene resin, β-pinene resin, limonene resin, hydrogenated limonene resin, dipentene 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, maleated rosin, and fumarated rosin, ester derivatives of these rosins such as glycerin esters, pentaerythritol esters, methyl esters, and triethylene glycol esters, and rosin-modified phenolic resins, etc.

[0029] Examples of petroleum resins include aromatic hydrocarbon resins or saturated or unsaturated aliphatic hydrocarbon resins. For example, C5 petroleum resins (aliphatic petroleum resins polymerized from fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene), C9 petroleum resins (aromatic petroleum resins polymerized from fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, and p-vinyltoluene), C5C9 copolymer petroleum resins, etc. are exemplified.

[0030] The glass transition temperature Tgr (°C) of the thermoplastic resin is preferably 40°C to 120°C, preferably 45°C to 115°C, and more preferably 50°C to 110°C. By setting the glass transition temperature Tgr of the thermoplastic resin to 40°C or higher, the dry grip performance is improved, which is preferable. Also, by setting it to 120°C or lower, the wear resistance is improved, which is preferable.

[0031] The difference (Tgr - Tgp) between the glass transition temperature (Tgr) of the thermoplastic resin and the lowest glass transition temperature (Tgp) (°C) of the at least one styrene-butadiene rubber described above is preferably 100°C or higher, thereby providing excellent abrasion resistance. The difference (Tgr - Tgp) in glass transition temperatures is more preferably 105°C or higher, and even more preferably 110°C or higher. In this specification, the glass transition temperatures of diene rubbers and thermoplastic resins are measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min, and are taken as the midpoint temperature of the transition region.

[0032] In this specification, the plasticizer refers to the oil component and liquid rubber contained in the rubber composition. The oil component refers to the sum of the oil blended during preparation of the rubber composition and the oil contained as an oil extender in the diene rubber. The oil component may be either a natural oil or a synthetic oil.

[0033] Liquid rubber refers to rubber that is liquid at 23°C. Therefore, it is distinguished from the above-mentioned diene rubber, which is solid at 23°C. Examples of liquid rubber include liquid polybutadiene, liquid polystyrene butadiene, and liquid polyisoprene. The number average molecular weight (Mn) of the liquid rubber is preferably 1,000 or more and less than 50,000, more preferably 5,000 to 40,000, and even more preferably 10,000 to 30,000.

[0034] The rubber composition of the present invention has a specific relationship in the temperature dependency curve of tan δ (tangent loss) between it and a treated rubber composition obtained by immersing the rubber composition in toluene and drying it. That is, when the half-width in the temperature dependency curve of tan δ of the rubber composition is σbf (°C), the value of tan δ at a temperature 90°C higher than the peak temperature at which tan δ is maximized is tan δbf, the half-width in the temperature dependency curve of tan δ of the treated rubber composition obtained by immersing the rubber composition in toluene and drying is σaf (°C), and the value of tan δ at a temperature 90°C higher than the peak temperature at which tan δ is maximized is tan δaf, the following relationship formulas (1) and (2) are satisfied. |σbf-σaf|≧4 (1) |tanδbf-tanδaf|≦0.02 (2)

[0035] The temperature dependence curve of tan δ of a rubber composition can be determined by measuring the dynamic viscoelasticity of a cured product of a given shape (a 2-mm-thick sheet obtained by vulcanization at 160°C for 25 minutes) using a viscoelasticity spectrometer under conditions of an extensional deformation strain rate of 10±2%, a frequency of 20 Hz, and temperatures from -80°C to 100°C. The viscoelasticity curve is then calculated, with the measurement temperature on the horizontal axis and the loss tangent (tan δ) on the vertical axis. From the temperature dependence curve of tan δ obtained, the maximum value (peak value) of tan δ and the temperature at which this occurs (peak temperature) are determined. The half-width of tan δ, σbf, is calculated as the difference between the higher and lower temperatures at which tan δ is half its peak value. Furthermore, the value of tan δ at a temperature 90°C higher than the peak temperature is calculated as tan δbf.

[0036] The treated rubber composition, in which the rubber composition was immersed in toluene and dried, was prepared by immersing the cured rubber composition in toluene and drying it. Specifically, the rubber composition was vulcanized at 160°C for 25 minutes to obtain a 2 mm-thick sheet (approximately 30 g). This sheet was immersed in 200 ml of toluene and allowed to stand at room temperature (23°C) for 48 hours to dissolve and remove the thermoplastic resin and plasticizer. The removed sheet was then immersed in 200 ml of acetone and allowed to stand at room temperature (23°C) for 48 hours to replace the toluene with acetone. The removed sheet was then dried at room temperature (23°C) for 48 hours to remove the acetone, yielding the treated rubber composition immersed in toluene and dried.

[0037] The temperature dependence curve of tan δ of the treated rubber composition can be determined by measuring the dynamic viscoelasticity of the cured product obtained above using a viscoelasticity spectrometer under conditions of an elongational deformation strain rate of 10±2%, a frequency of 20 Hz, and a temperature range of -80°C to 100°C, and then plotting the curve as a viscoelasticity curve with the measurement temperature on the horizontal axis and the loss tangent (tan δ) on the vertical axis. From the temperature dependence curve of tan δ of the treated rubber composition obtained, the maximum value (peak value) of tan δ and the temperature at that time (peak temperature) are determined. The half-width σaf of tan δ is determined as the difference between the higher and lower temperatures at which tan δ is half its peak value. Furthermore, the value of tan δ at a temperature 90°C higher than the peak temperature is determined as tan δaf.

[0038] The difference |σbf - σaf| between the full width at half maximum of tan δ of the rubber composition σbf and the full width at half maximum of tan δ of the treated rubber composition σaf is 4°C or more, preferably 6°C to 15°C, and more preferably 6°C to 10°C. By keeping the difference |σbf - σaf| within this range, it is possible to improve abrasion resistance without deteriorating wet performance. A rubber composition satisfying the difference |σbf - σaf| of 4°C or more can be prepared by blending a diene rubber containing styrene-butadiene rubber, which has a low glass transition temperature and a large difference from the glass transition temperature of the thermoplastic resin, with a thermoplastic resin and, optionally, a plasticizer in a specific mass ratio.

[0039] The difference |tanδbf - tanδaf| between the value of tanδ of the rubber composition at a temperature 90°C higher than the peak temperature at which tanδ is maximized and the value of tanδ of the treated rubber composition at a temperature 90°C higher than the peak temperature at which tanδ is maximized is 0.02 or less, preferably 0.015 or less. By keeping the difference |tanδbf - tanδaf| within this range, wear resistance can be improved without compromising low rolling resistance. A rubber composition satisfying the difference |tanδbf - tanδaf| of 0.02 or less can be prepared by incorporating a diene rubber and a thermoplastic resin that have good affinity with each other. For example, a rubber composition containing a thermoplastic resin that has low compatibility with the diene rubber will have a large tanδbf, resulting in a difference |tanδbf - tanδaf| exceeding 0.02. As a result, the tanδ at 60°C, an indicator of rolling resistance, will be large.

[0040] In addition to the above components, various compounding agents commonly used in rubber compositions for tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, processing aids, and thermosetting resins, can be compounded into the rubber composition in accordance with conventional methods. These compounding agents can be kneaded in a conventional manner to form a rubber composition, which can then be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be conventional amounts, as long as they do not deviate from the objectives of the present invention. The rubber composition can be prepared by mixing the above components using a known rubber kneading machine, such as a Banbury mixer, kneader, or roll.

[0041] The rubber composition is suitable for forming the tread and sidewalls of tires, particularly the tread, of tires, which can achieve higher levels of wear resistance, low rolling resistance, and wet performance than conventional levels.

[0042] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0043] In preparing 15 types of rubber compositions (standard example, Examples 1 to 8, Comparative Examples 1 to 6) having the common additive formulations shown in Table 3 and consisting of the formulations shown in Tables 1 to 2, the components excluding sulfur and vulcanization accelerators were weighed respectively, kneaded for 5 minutes in a 1.7-liter closed Banbury mixer, and then the masterbatch was discharged outside the mixer and cooled to room temperature. This masterbatch was fed into the same Banbury mixer, sulfur and vulcanization accelerators were added and mixed to obtain a rubber composition. The additive formulations in Table 3 are described in parts by mass based on 100 parts by mass of the diene rubber described in Tables 1 to 2.

[0044] Also, in Tables 1 to 2, the total amount of the thermoplastic resin and plasticizers (oil and liquid rubber) was calculated and described in the column of "resin + plasticizer", and the mass ratio of the thermoplastic resin to the total of the thermoplastic resin and plasticizers was calculated and described in the column of "resin mass ratio". Further, for the rubber compositions of the above-described Examples and Comparative Examples, the difference Tgr - Tgp between the lowest glass transition temperature Tgp (°C) of the styrene-butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin was calculated and described in the column of "difference Tgr - Tgp" in Tables 1 to 2.

[0045] Measurement of the tanδ temperature dependence curve, half-value width σbf, and tanδbf of the rubber composition The rubber compositions obtained above were each vulcanized in a mold of a predetermined shape at 160°C for 25 minutes to prepare samples (2 mm thick sheets) for evaluation of dynamic viscoelasticity (loss tangent tanδ). Using the obtained evaluation samples, tanδ was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of an elongation deformation strain rate of 10±2%, a frequency of 20 Hz, and temperatures from -80°C to 100°C. A temperature dependence curve of tanδ from -80°C to 100°C was plotted, with the measurement temperature on the horizontal axis and the loss tangent (tanδ) on the vertical axis. From the temperature dependence curve of tanδ obtained, the maximum value (peak value) of tanδ and the temperature at which this occurred (peak temperature) were determined. The half-width of tanδ, σbf, was calculated as the difference between the higher and lower temperatures at which tanδ was half its peak value. Furthermore, the value of tanδ at a temperature 90°C higher than the peak temperature at which tanδ reached its peak value was calculated as tanδbf.

[0046] Measurement of tanδ temperature dependence curve and half-width σaf and tanδaf of rubber composition after toluene treatment The rubber compositions shown in Tables 1 and 2 were vulcanized at 160°C for 25 minutes to obtain a 2 mm-thick sheet (approximately 30 g). The sheet was immersed in 200 ml of toluene and allowed to stand at room temperature (23°C) for 48 hours to dissolve and remove the thermoplastic resin and plasticizer. The sheet was then immersed in 200 ml of acetone and allowed to stand at room temperature (23°C) for 48 hours to replace the toluene with acetone. The sheet was then dried at room temperature (23°C) for 48 hours to remove the acetone, and a sample of the treated rubber composition was obtained for evaluation after immersion in toluene and drying.

[0047] Using the evaluation sample of the treated rubber composition obtained above, tan δ was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of an elongation deformation strain rate of 10±2%, a frequency of 20 Hz, and temperatures from -80°C to 100°C. A temperature dependence curve of tan δ from -80°C to 100°C was created with the measurement temperature on the horizontal axis and the loss tangent (tan δ) on the vertical axis. From the obtained temperature dependence curve of tan δ, the maximum value (peak value) of tan δ and the temperature at that time (peak temperature) were determined. The half-width σaf of tan δ of the treated rubber composition was calculated as the difference between the higher and lower temperatures at which tan δ was half its peak value. In addition, the value of tan δ at a temperature 90°C higher than the peak temperature at which tan δ of the treated rubber composition reached its peak value was calculated as tan δaf.

[0048] |σbf-σaf| was calculated from the half width σbf of tanδ of the rubber composition obtained above and the half width σaf of tanδ of the treated rubber composition, and is shown in the "Difference |σbf-σaf|" column in Tables 1 and 2. In addition, |tanδbf-tanδaf| was calculated from the value of tanδbf, which was the value of tanδ at a temperature 90°C higher than the peak temperature of tanδ of the rubber composition, and the value of tanδaf, which was the value of tanδ at a temperature 90°C higher than the peak temperature of tanδ of the treated rubber composition, and is shown in the "Difference |tanδbf-tanδaf|" column in Tables 1 and 2.

[0049] The rubber composition obtained above was used for tire treads to vulcanize and mold pneumatic tires of size 205 / 55R16, and the abrasion resistance, wet performance, and rolling resistance were measured by the following methods.

[0050] Abrasion resistance The obtained tire was assembled onto a wheel of a standard rim size and mounted on a rolling resistance tester equipped with a drum having a radius of 854 mm. After a preliminary running for 30 minutes under the conditions of an air pressure of 210 kPa, a load of 100 N, a speed of 80 km / h, and a surface temperature of the drum of 20°C, a running test of 20,000 km was carried out at a speed of 100 km / h, and then the wear amount of the tread land portion was measured. The evaluation result was calculated as the reciprocal of the measured value and shown as an index with the standard example being 100 in the column of "Abrasion resistance" in Tables 1 to 2. The larger this index, the smaller the wear amount and the better the abrasion resistance, and 110 or more is preferable.

[0051] Wet performance The obtained tire was attached to a standard rim and mounted on a test vehicle equipped with an ABS with a displacement of 2000 cc. The air pressures of the front tire and the rear tire were set to 220 kPa. The test vehicle was run on an asphalt road surface sprinkled with water to a depth of 2.0 to 3.0 mm, and the braking stopping distance from a speed of 100 km / h was measured. The obtained results were calculated as the reciprocals respectively and shown as an index with the value of the standard example being 100 in the column of "Wet performance" in Tables 1 to 2. The larger this index, the shorter the braking stopping distance and the better the wet performance, and 110 or more is preferable.

[0052] Rolling resistance The obtained tire was assembled onto a wheel of a standard rim size and mounted on a rolling resistance tester equipped with a drum having a radius of 854 mm. After a preliminary running for 30 minutes under the conditions of an air pressure of 210 kPa, a load of 100 N, a speed of 80 km / h, and a surface temperature of the drum of 20°C, the rolling resistance was measured under the same conditions. The evaluation result was shown as an index using the reciprocal of the measured value with the standard example being 100 in the column of "Rolling resistance" in Tables 1 to 2. The larger this index, the smaller the rolling resistance and the better, and 95 or more is preferable.

[0053] [Table 1]

[0054] [Table 2]

[0055] The types of raw materials used in Tables 1 to 2 are shown below. · NR: Natural rubber, TSR20, glass transition temperature of -65°C · SBR-1: Terminally modified styrene-butadiene rubber having a polyorganosiloxane structure, Nipol NS612 manufactured by Zeon Corporation, glass transition temperature of -61°C, styrene content of 15% by mass, vinyl content of 31%, non-oil product · SBR-2: Terminally modified styrene-butadiene rubber having a polyorganosiloxane structure, Nipol NS616 manufactured by Zeon Corporation, glass transition temperature of -23°C, styrene content of 22% by mass, vinyl content of 67%, non-oil product · SBR-3: Terminally modified styrene-butadiene rubber having a polyorganosiloxane structure, prototype SBR manufactured by Yokohama Rubber Co., Ltd., glass transition temperature of -80°C, styrene content of 6% by mass, vinyl content of 15%, non-oil product · Carbon black: Seast 7HM manufactured by Tokai Carbon Co., Ltd. · Silica: Zeosil 1165MP manufactured by Solvey, nitrogen adsorption specific surface area of 159 m 2 / g · Coupling agent: Silane coupling agent, Si69 manufactured by Evonik Degussa · Resin-1: C9-based petroleum resin, Neopolymer S100 manufactured by ENEOS, glass transition temperature of 58°C · Resin-2: Aromatic-modified terpene resin, YS Resin TO-105 manufactured by Yasuhara Chemical Co., Ltd., glass transition temperature of 57°C · Resin-3: Indene resin, FMR0150 manufactured by Mitsui Chemicals, glass transition temperature of 89°C · Resin-4: Phenol-modified terpene resin, Tamanol 803L manufactured by Arakawa Chemical Industries, glass transition temperature of 95°C · Liquid rubber: Liquid styrene-butadiene rubber, Ricon100 manufactured by Cray Valley · Oil: Extract No. 4S manufactured by Shell Lubricants Japan

[0056]

Table 3

[0057] 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.

[0058] As is clear from Tables 1 and 2, it was confirmed that the rubber compositions of Examples 1 to 8 were excellent in abrasion resistance, wet performance, and low rolling resistance.

[0059] As is clear from Table 1, the rubber composition of Comparative Example 1 has a ratio of thermoplastic resin to the total of thermoplastic resin and plasticizer of less than 75 mass % and the difference |σbf-σaf| is less than 4°C, so it is not possible to improve the wear resistance and wet performance to a suitable level. In the rubber composition of Comparative Example 2, the total amount of thermoplastic resin and plasticizer is less than 20 parts by mass, and the difference |σbf-σaf| is less than 4°C, so the abrasion resistance and wet performance cannot be improved to a suitable level. The rubber composition of Comparative Example 3 has a difference |tan δbf−tan δaf| of more than 0.02, and therefore the wet performance and rolling resistance are deteriorated. In the rubber composition of Comparative Example 4, the difference |tan δbf−tan δaf| exceeds 0.02, and therefore the rolling resistance deteriorates. In the rubber composition of Comparative Example 5, the total amount of the thermoplastic resin and the plasticizer is 50 parts by mass or more, and therefore the rolling resistance is deteriorated. In the rubber composition of Comparative Example 6, the proportion of the thermoplastic resin relative to the total of the thermoplastic resin and the plasticizer is less than 75 mass %, so the abrasion resistance and wet performance cannot be improved to a suitable level.

[0060] The present disclosure includes the following inventions. Invention [1] A rubber composition comprising 100 parts by mass of a diene rubber containing at least one styrene-butadiene rubber, 20 to 150 parts by mass of a white filler, and a total of 20 parts by mass or more and less than 50 parts by mass of a thermoplastic resin and an optional plasticizer, wherein the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more. In the temperature-dependence curve of tanδ of the rubber composition, the half-value width is σbf (°C), the value of tanδ at a temperature 90 °C higher than the peak temperature at which tanδ is maximum is tanδbf, in the temperature-dependence curve of tanδ of the rubber composition after being immersed in toluene and dried, the half-value width is σaf (°C), and the value of tanδ at a temperature 90 °C higher than the peak temperature at which tanδ is maximum is tanδaf. A rubber composition characterized by satisfying the following relational expressions (1) and (2). |σbf - σaf| ≥ 4 (1) |tanδbf - tanδaf| ≤ 0.02 (2) Invention [2] The rubber composition according to Invention [1], wherein the difference Tgr - Tgp between the lowest glass transition temperature Tgp (°C) of the glass transition temperatures of the at least one styrene-butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin is 100 °C or more. Invention [3] The rubber composition according to Invention [1] or [2], wherein the diene rubber contains 70 to 100% by mass of the at least one styrene-butadiene rubber and 0 to 30% by mass of an isoprene rubber. Invention [4] The rubber composition according to any one of Inventions [1] to [3], wherein at least one of the terminals of the at least one styrene-butadiene rubber is modified with a functional group. Invention [5] The glass transition temperature Tgr of the thermoplastic resin is 40 to 120 °C, and the thermoplastic resin is at least one selected from the group consisting of a resin composed of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 component, C9 component, and a resin in which at least a part of the double bonds of these resins is hydrogenated. The rubber composition according to any one of Inventions [1] to [4].

Claims

Claim 1: A rubber composition comprising 100 parts by mass of a diene rubber containing a terminal-modified styrene-butadiene rubber in which at least one terminal of the styrene-butadiene rubber is modified with a functional group having a polyorganosiloxane structure or an aminosilane structure, 20 to 150 parts by mass of a white filler, and a total of 20 parts by mass or more and less than 50 parts by mass of a thermoplastic resin and an optional plasticizer, wherein the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more. Let the half-width of the temperature dependence curve of tanδ measured under the conditions of an elongation deformation strain rate of 10 ± 2%, a vibration frequency of 20 Hz, and a temperature of -80°C to 100°C of the rubber composition be σbf (°C), and the value of tanδ at a temperature 90°C higher than the peak temperature at which tanδ is maximum be tanδbf. Let the half-width of the temperature dependence curve of tanδ of the rubber composition after the treatment of immersing and drying the rubber composition in toluene be σaf (°C), and the value of tanδ at a temperature 90°C higher than the peak temperature at which tanδ is maximum be tanδaf. A rubber composition characterized by satisfying the following relational expressions (1) and (2). |σbf - σaf| ≥ 4 (1) |tanδbf - tanδaf| ≤ 0.02 (2) Claim 2 The rubber composition according to claim 1, wherein the difference Tgr - Tgp between the lowest glass transition temperature Tgp (°C) of the glass transition temperatures of the at least one styrene-butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin is 100°C or more. Claim 3 The rubber composition according to claim 1 or 2, wherein the diene rubber contains 70 to 100% by mass of the at least one styrene-butadiene rubber and 0 to 30% by mass of an isoprene rubber. Claim 4 The rubber composition according to claim 1 or 2, wherein the glass transition temperature Tgr of the thermoplastic resin is 40 to 120°C, and the thermoplastic resin is at least one selected from the group consisting of a resin composed of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 component, C9 component, and a resin in which at least a part of the double bonds of these resins is hydrogenated.

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