Rubber composition

Abstract

Provided is a rubber composition having wear resistance, low rolling resistance, and wet land performance at a level higher than or equal to conventional levels, the rubber composition containing a white filler, a thermoplastic resin, and an arbitrarily contained plasticizer in a diene rubber containing a styrene butadiene rubber, the content of the white filler being less than or equal to 100 parts by mass of the diene rubber, and the content of the thermoplastic resin being less than or equal to 10 parts by mass of the plasticizer being less than or equal to 100 parts by mass of the diene rubber. The amount of the white filler is 20-150 parts by mass, the total amount of the thermoplastic resin and the plasticizer is 20 parts by mass or more but less than 50 parts by mass, the thermoplastic resin is 75% by mass or more relative to the total amount, and sigma bf (DEG C) is the half-peak width in the tan [delta] temperature dependence curve of the rubber composition, and sigma bf (DEG C) is the half-peak width in the tan [delta] temperature dependence curve of the rubber composition, and sigma bf (DEG C) is the half-peak width in the tan [delta] temperature dependence curve of the rubber composition. The value of tan [sigma] bf at a temperature 90 DEG C higher than the peak temperature at which tan [delta] is the maximum is defined as tan [sigma] bf, and the half-peak width in a temperature-dependent curve of tan [delta] of a treated rubber composition obtained by immersing the rubber composition in toluene and drying the rubber composition is defined as [sigma] af (DEG C). When tan [sigma] af is the value of tan [delta] at a temperature 90 DEG C higher than the peak temperature at which tan [delta] is the maximum, [sigma] bf-[sigma] af > = 4 and tan [delta] bf-tan [delta] af < = 0.02 are satisfied.

Description

Technical Field

[0001] The present invention relates to a rubber composition having a combination of wear resistance, low rolling resistance and wet performance. Background Art

[0002] Tires are required to have high levels of wear resistance, low rolling resistance, and wet performance. As a rubber composition for tire treads that improves wear resistance, low rolling resistance, and wet performance, a solution has been proposed in which an aromatic modified terpene resin and oil are added to the rubber composition (for example, see Patent Document 1).

[0003] However, in recent years, there has been a demand for a balance among wear resistance, low rolling resistance, and wet performance at a higher level than that described in Patent Document 1.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-166864 Summary of the invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a rubber composition capable of achieving a combination of wear resistance, low rolling resistance, and wet performance at a level higher than the conventional levels.

[0009] Means of solving problems

[0010] The rubber composition of the present invention for achieving the above-mentioned object is a rubber composition comprising a white filler, a thermoplastic resin and an optionally contained plasticizer in a diene rubber containing at least one styrene-butadiene rubber, wherein the white filler is 20 to 150 parts by mass relative to 100 parts by mass of the diene rubber, and the total amount of the thermoplastic resin and the plasticizer is 20 parts by mass or more and less than 50 parts by mass, and characterized in that:

[0011] The ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more, and

[0012] When the half-peak width in the temperature dependence 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 when tan δ is maximum is tanσbf, the half-peak width in the temperature dependence curve of tan δ of the rubber composition after treatment 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 when tan δ is maximum is tanσaf, the following relational expressions (1) and (2) are satisfied,

[0013] |σbf-σaf|≥4 (1)

[0014] |tanδbf-tanδaf|≤0.02 (2).

[0015] Effects of the Invention

[0016] The rubber composition of the present invention can simultaneously have higher levels than conventional levels of wear resistance, low rolling resistance and wet performance by containing a thermoplastic resin and a plasticizer in a specific blending ratio in a styrene-butadiene rubber and a white filler, and by making the half-peak width σ of a curve of temperature dependence of tan δ between the rubber composition and a treated rubber composition obtained by immersing the rubber composition in toluene and drying, and tan δ at a temperature 90° C. higher than the peak temperature at which tan δ is maximum satisfy specific relationships.

[0017] The difference between the lowest glass transition temperature Tgp (°C) of the at least one styrene butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin, namely Tgr-Tgp, is preferably 100°C or more, which can further improve the wear resistance.

[0018] 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 the isoprene rubber. In addition, at least one of the terminals of the at least one styrene butadiene rubber is modified with a functional group.

[0019] The glass transition temperature Tgr of the thermoplastic resin is 40 to 120°C, and the thermoplastic resin is preferably at least one selected from the following resins and resins in which at least a portion of the double bonds of these resins are hydrogenated, and the resin is a resin formed by at least one of terpene, modified terpene, rosin, rosin ester, C5 component, and C9 component. DETAILED DESCRIPTION

[0020] 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 in a blend of two or more. By containing the styrene-butadiene rubber, the tensile strength at break can be increased, the wear resistance can be improved, and by improving the dispersibility of silica, the tanδ at 0°C can be increased, thereby achieving excellent wet performance.

[0021] The glass transition temperature (hereinafter sometimes referred to as "Tg") of the styrene butadiene rubber may be preferably -55°C or less, more preferably -80°C to -58°C, and further preferably -75°C to -60°C. By setting the Tg of the styrene butadiene rubber to -55°C or less, wear resistance can be improved, so it is preferred. The Tg of the styrene butadiene rubber can be measured as the temperature of the midpoint of the transition region based on a thermogram obtained by differential scanning calorimetry (DSC) at a heating rate of 20°C / min. In addition, when the styrene butadiene rubber is an oil-extended product, the Tg of the styrene butadiene rubber in a state without the oil-extending component (oil) is taken.

[0022] The styrene content of the styrene-butadiene rubber is not particularly limited, but is preferably 5 to 45% by mass, more preferably 8 to 42% by mass. The styrene content within such a range is preferred because good abrasion resistance is achieved.

[0023] The vinyl content of the styrene butadiene rubber is not particularly limited, but is preferably 5 to 60%, and more preferably 10 to 55%. By making the vinyl content within such a range, excellent dry grip performance can be achieved, so it is preferred. The styrene content and the vinyl content in the styrene butadiene rubber can be adjusted by 1 H-NMR was used for determination.

[0024] At least one end of the styrene-butadiene rubber is modified by a functional group, so that the dispersibility of the silicon dioxide can be improved, and the rolling resistance of the tire can be further reduced. As the functional group, for example, epoxy, carboxyl, amino, hydroxyl, alkoxy, silyl, alkoxysilyl, amide, oxysilyl, silanol, isocyanate, isothiocyanate, carbonyl, aldehyde etc. can be listed, wherein preferably there is a functional group of polyorganosiloxane structure or aminosilane structure. By containing a functional group with polyorganosiloxane structure or aminosilane structure, the dispersibility of the silicon dioxide can be improved, and the wear resistance, low rolling resistance and wet performance are excellent.

[0025] The content of styrene butadiene rubber is preferably 55% by mass or more, more preferably 70 to 100% by mass, and further preferably 75 to 90% by mass in 100% by mass of the diene rubber. The content of styrene butadiene rubber is the content of the styrene butadiene rubber when one type is contained alone, and the total amount of these styrene butadiene rubbers when contained as a blend of two or more types. By containing 55% by mass or more of styrene butadiene rubber, the dispersibility of silica can be improved, and the wear resistance and wet performance can be improved.

[0026] The rubber composition may arbitrarily 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 giving functional groups to these rubbers. In addition, in the present invention, it is preferred that butadiene rubber is not contained, so that wet performance and wear resistance can be improved. These other diene rubbers can be used alone or as any mixture. The content of other diene rubbers is preferably 45% by mass or less in 100% by mass of the diene rubber, more preferably 0 to 30% by mass, and further preferably 10 to 25% by mass.

[0027] The rubber composition is preferably prepared by mixing isoprene rubber such as natural rubber and isoprene rubber, because the wear resistance is good. The isoprene rubber may preferably be 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 commonly used in rubber compositions may be used.

[0028] The rubber composition can improve wet performance by adding a white filler to the diene rubber. Examples of the white filler include silicon dioxide, calcium carbonate, magnesium carbonate, talc, clay, aluminum oxide, aluminum hydroxide, titanium oxide, and calcium sulfate. These can be used alone or in combination of two or more. Among them, silicon dioxide is preferred, which can make the wet performance and low heat generation more excellent. The white filler can be added in an amount of 20 to 150 parts by mass, preferably 40 to 150 parts by mass, and more preferably 60 to 140 parts by mass to 100 parts by mass of the diene rubber. By adding 20 parts by mass or more of the white filler, the wet performance and wear resistance can be made better. In addition, by adding 150 parts by mass or less, the wear resistance and low rolling resistance can be made excellent.

[0029] As silica, silica commonly used in rubber compositions can be used, for example, wet silica, dry silica, carbon-silica (dual phase filler) in which silica is supported on the surface of carbon black, silica surface treated with a compound reactive or compatible with both silica and rubber, such as a silane coupling agent or polysiloxane, etc. Among them, wet silica having hydrous silicic acid as a main component is preferred.

[0030] In addition, by adding a silane coupling agent together with silica, the dispersibility of silica can be improved, and the wet performance and low heat generation can be further improved, which is preferred. The type of silane coupling agent is not particularly limited, but sulfur-containing silane coupling agents are preferred, and examples thereof include 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, and 3-mercaptopropyldimethoxymethylsilane. Silane compounds exemplified in Japanese Patent Application Publication No. 2006-249069, such as 3-mercaptopropyldimethylmethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyltriethoxysilane, and VPSi363 produced by Evonick Co., Ltd., as well as 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylmethacrylate monosulfide, 3-trimethoxysilylpropylmethacrylate 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-octanoylthiopropyltrisulfide Ethoxysilane, 3-propionylthiopropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, 3-(glycidoxy)propyltrimethoxysilane, 3-(glycidoxy)propylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, etc.

[0031] The silane coupling agent can be preferably mixed with 3 to 20% by mass, more preferably 5 to 15% by mass relative to the mass of silica. When the silane coupling agent is 3% by mass or more of the mass of silica, it is beneficial to improve the dispersibility of silica. In addition, when the silane coupling agent is 20% by mass or less, the gelation of the diene rubber component can be suppressed, and the desired effect can be obtained.

[0032] The rubber composition can be enhanced in strength and tire durability by adding fillers other than the white filler. Examples of other fillers include inorganic fillers such as carbon black, mica, alumina, and barium sulfate, and organic fillers such as cellulose, lecithin, lignin, and dendrimers.

[0033] Among them, by mixing carbon black, the strength of the rubber composition can be made excellent. As carbon black, furnace black, acetylene black, thermal black, channel black, graphite and other carbon blacks can also be mixed. Among them, furnace black is preferred, and as its specific example, SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, FEF and the like can be listed. These carbon blacks can be used alone, or two or more can be used in combination. In addition, surface treated carbon blacks formed by chemically modifying these carbon blacks with various acid compounds etc. can also be used.

[0034] The rubber composition can adjust the temperature dependence of its dynamic viscoelasticity by matching a specific thermoplastic resin and an arbitrary plasticizer. Relative to 100 parts by mass of diene rubber, the total of the thermoplastic resin and the plasticizer is more than 20 parts by mass and less than 50 parts by mass. That is, it is possible to match more than 20 parts by mass and less than 50 parts by mass of thermoplastic resin but without containing a plasticizer, or it is possible to contain a plasticizer and the total of the thermoplastic resin and the plasticizer is more than 20 parts by mass and less than 50 parts by mass. By matching a thermoplastic resin and a plasticizer within such a range, it is possible to take into account both wear resistance and low rolling resistance. The total of the thermoplastic resin and the plasticizer is preferably more than 25 parts by mass and less than 48 parts by mass, more preferably more than 30 parts by mass and less than 45 parts by mass.

[0035] 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 making the thermoplastic resin 75% by mass or more, 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, and more preferably 85% by mass or more and 100% by mass or less.

[0036] Thermoplastic resin is a resin usually added to the rubber composition, and has the function of imparting adhesiveness to the rubber composition. As the thermoplastic resin, it is preferably at least one selected from the following resins and resins in which at least a part of the double bonds of these resins are hydrogenated, wherein the resin is a resin formed by at least one selected from terpene, modified terpene, rosin, rosin ester, C5 component and C9 component. Examples of the thermoplastic resin include natural resins such as terpene resins, modified terpene resins, rosin resins, rosin ester resins, and synthetic resins such as petroleum resins formed by C5 components and C9 components, coal resins, phenolic resins, and xylene resins. In addition, the thermoplastic resin may be a resin in which at least a part of the double bonds of these resins are hydrogenated.

[0037] Examples of the terpene resins include α-pinene resins, β-pinene resins, limonene resins, hydrogenated limonene resins, dipentene resins, terpene styrene resins, aromatic modified terpene resins, hydrogenated terpene resins, etc. Examples of the rosin resins include gum rosin, tall oil rosin, wood rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, modified rosins such as maleated rosin and fumarated rosin, ester derivatives of these rosins such as glycerol esters, pentaerythritol esters, methyl esters and triethylene glycol esters, and rosin-modified phenolic resins.

[0038] Examples of petroleum-based resins include aromatic hydrocarbon resins or 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.

[0039] The glass transition temperature Tgr (°C) of the thermoplastic resin is preferably 40°C to 120°C, more preferably 45°C to 115°C, and more preferably 50°C to 110°C. The glass transition temperature Tgr of the thermoplastic resin is preferably 40°C or higher because dry grip performance can be improved. The glass transition temperature Tgr of the thermoplastic resin is preferably 120°C or lower because wear resistance can be improved.

[0040] The difference between the glass transition temperature Tgr of the thermoplastic resin and the lowest glass transition temperature Tgp (°C) among the glass transition temperatures of the at least one styrene-butadiene rubber, i.e., Tgr-Tgp, is preferably 100°C or more, which can provide excellent wear resistance. The difference in glass transition temperature Tgr-Tgp may be more preferably 105°C or more, and further preferably 110°C or more. In this specification, the glass transition temperature of the diene rubber and the thermoplastic resin is a value obtained by measuring the thermogram at a temperature increase rate of 20°C / min by differential scanning calorimetry (DSC) as the temperature at the midpoint of the transition region.

[0041] In this specification, the plasticizer refers to the oil component and liquid rubber contained in the rubber composition. The oil component refers to the total of the oil blended when preparing the rubber composition and the oil contained as an oil extension component in the diene rubber. The oil component may be any of natural oil and synthetic oil.

[0042] Liquid rubber refers to a rubber that is liquid at 23°C. Therefore, it is distinguished from the above-mentioned diene rubber that 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 may preferably be 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.

[0043] The rubber composition of the present invention and the treated rubber composition obtained by immersing the rubber composition in toluene and drying have a specific relationship in the temperature dependence curves of tan δ (loss tangent). That is, when the half-peak width in the temperature dependence 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 when tan δ is maximum is tan δbf, and the half-peak width in the temperature dependence 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 when tan δ is maximum is tan δaf, the following relationship equations (1) and (2) are satisfied.

[0044] |σbf-σaf|≥4 (1)

[0045] |tanδbf-tanδaf|≤0.02 (2)

[0046] The temperature dependence curve of tanδ of the rubber composition can be obtained by using a viscoelasticity spectrometer to measure the dynamic viscoelasticity of a cured product of a specified shape (a sheet with a thickness of 2 mm obtained by vulcanization at 160°C for 25 minutes) under the conditions of a tensile deformation strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature of -80°C to 100°C, and to obtain a viscoelasticity curve with the measured temperature as the horizontal axis and the loss tangent (tanδ) as the vertical axis. Based on the obtained temperature dependence curve of tanδ, the maximum value (peak value) of tanδ and the temperature at this time (peak temperature) are obtained. The half-peak width σbf of tanδ is obtained as the difference between the temperature on the high temperature side and the temperature on the low temperature side when tanδ becomes half of the peak value. Furthermore, the value of tanδ at a temperature 90°C higher than the peak temperature is obtained as tanδbf.

[0047] The treated rubber composition obtained by immersing the rubber composition in toluene and drying is prepared by immersing the cured product of the rubber composition in toluene and drying. That is, a sheet (about 30 g) having a thickness of 2 mm obtained by vulcanizing the rubber composition at 160° C. for 25 minutes is immersed in 200 ml of toluene and left to stand at room temperature (23° C.) for 48 hours, thereby dissolving and removing the thermoplastic resin and the plasticizer. Next, the removed sheet is immersed in 200 ml of acetone and left to stand at room temperature (23° C.) for 48 hours, thereby replacing toluene with acetone. Then, the removed sheet is dried at room temperature (23° C.) for 48 hours to remove the acetone, thereby obtaining a treated rubber composition immersed in toluene and dried.

[0048] The temperature dependence curve of tanδ of the treated rubber composition is obtained by measuring the dynamic viscoelasticity of the cured product of the specified shape obtained above under the conditions of tensile deformation strain rate of 10±2%, vibration frequency of 20Hz, and temperature of -80℃~100℃ using a viscoelasticity spectrometer, and the viscoelasticity curve is obtained with the measured temperature as the horizontal axis and the loss tangent (tanδ) as the vertical axis. Based on the obtained temperature dependence curve of tanδ of the treated rubber composition, the maximum value (peak value) of tanδ and the temperature at this time (peak temperature) are obtained. The half-peak width σaf of tanδ is obtained as the difference between the temperature on the high temperature side and the temperature on the low temperature side when tanδ becomes half of the peak value. Furthermore, the value of tanδ at a temperature 90℃ higher than the peak temperature is obtained as tanδaf.

[0049] The difference |σbf-σaf| between the half-peak width σbf of tan δ of the rubber composition and the half-peak width σaf of tan δ of the treated rubber composition is 4°C or more, preferably 6 to 15°C, and more preferably 6 to 10°C. By making the difference |σbf-σaf| within such a range, the wear resistance can be improved without reducing the wet performance. The rubber composition satisfying the difference |σbf-σaf| of 4°C or more can be prepared by mixing a thermoplastic resin and an optional plasticizer in a specific mass ratio with respect to a diene rubber containing styrene-butadiene rubber having a large difference in glass transition temperature from the thermoplastic resin and a low glass transition temperature.

[0050] The difference between the value of tanδ of the rubber composition at a temperature 90°C higher than the peak temperature when tanδ is maximum, tanδbf, and the value of tanδ of the rubber composition after treatment at a temperature 90°C higher than the peak temperature when tanδ is maximum, |tanδbf-tanδaf|, is 0.02 or less, preferably 0.015 or less. By setting the difference |tanδbf-tanδaf| within such a range, the wear resistance can be improved without deteriorating the low rolling resistance. The rubber composition satisfying the difference |tanδbf-tanδaf| of 0.02 or less can be prepared by containing a diene rubber and a thermoplastic resin having good affinity with each other. For example, in a rubber composition containing a thermoplastic resin having low compatibility with the diene rubber, tanδbf becomes larger, and the difference |tanδbf-tanδaf| exceeds 0.02. As a result, tanδ at 60°C, which is an indicator of rolling resistance, becomes larger.

[0051] In the rubber composition, in addition to the above-mentioned components, various compounding agents commonly used in tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, processing aids, and thermosetting resins can be used in accordance with conventional methods. Such compounding agents can be mixed and formed into rubber compositions by a general method for vulcanization or crosslinking. The amount of these compounding agents can be the general amount in the past as long as it does not violate the purpose of the present invention. The rubber composition can be prepared by mixing the above-mentioned components using a known rubber mixing machine, such as a Banbury mixer, a kneading machine, a roller, etc.

[0052] The rubber composition can be well formed into a tread portion or a sidewall portion of a tire, and is particularly suitable for forming a tread portion of a tire. The tire thus obtained can have a higher level of wear resistance, low rolling resistance and wet performance than the existing level.

[0053] Hereinafter, the present invention will be further described by way of examples, but the scope of the present invention is not limited to these examples.

[0054] Example

[0055] When preparing 15 rubber compositions (standard examples, examples 1 to 8, comparative examples 1 to 6) having the common additive formula shown in Table 3 and formed with the compositions shown in Tables 1 to 2, the components other than sulfur and vulcanization accelerator were weighed separately, and kneaded for 5 minutes using a 1.7-liter closed Banbury mixer, and then the masterbatch was released outside the mixer and cooled to room temperature. The masterbatch was added to the aforementioned Banbury mixer, sulfur and vulcanization accelerator were added and mixed to obtain a rubber composition. In addition, the additive formula in Table 3 is recorded in mass parts relative to 100 mass parts of diene rubber recorded in Tables 1 to 2.

[0056] In addition, in Tables 1 and 2, the total amount of the thermoplastic resin and the plasticizer (oil and liquid rubber) is calculated and recorded in the column of "Resin + Plasticizer", and the mass ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is calculated and recorded in the column of "Resin Mass Ratio". Furthermore, for the rubber compositions of the above-mentioned 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 is calculated and recorded in the column of "Difference Tgr-Tgp" in Tables 1 and 2.

[0057] Temperature dependence curve of tanδ of rubber composition and measurement of half peak width σbf and tanδbf

[0058] The rubber compositions obtained above were vulcanized at 160°C for 25 minutes in a mold of a specified shape to prepare a sample (a sheet with a thickness of 2 mm) for evaluation of dynamic viscoelasticity (loss tangent tanδ). Using the obtained evaluation sample, tanδ was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the conditions of a tensile strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature of -80°C to 100°C, and a tanδ temperature dependence curve of -80°C to 100°C was prepared with the measured temperature as the horizontal axis and the loss tangent (tanδ) as the vertical axis. Based on the obtained tanδ temperature dependence curve, the maximum value (peak value) of tanδ and the temperature (peak temperature) at this time were determined. The half-peak width σbf of tanδ was determined as the difference between the temperature on the high temperature side and the temperature on the low temperature side when tanδ becomes half of the peak value. In addition, the value of tanδ at a temperature 90°C higher than the peak temperature when tanδ shows a peak value was determined as tanδbf.

[0059] Temperature dependence curve of tan δ and measurement of half-peak width σaf and tan δaf of rubber composition after toluene treatment

[0060] The rubber composition described in Tables 1 and 2 was vulcanized at 160°C for 25 minutes to obtain a sheet (about 30 g) with a thickness of 2 mm, which was immersed in 200 ml of toluene and left to stand at room temperature (23°C) for 48 hours to dissolve and remove the thermoplastic resin and plasticizer. Next, the removed sheet was immersed in 200 ml of acetone and left to stand at room temperature (23°C) for 48 hours to replace the toluene with acetone. Then, the removed sheet was dried at room temperature (23°C) for 48 hours to remove the acetone, and a sample for evaluation of the treated rubber composition obtained by being immersed in toluene and dried was obtained.

[0061] Using the evaluation sample of the treated rubber composition obtained above, a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. was used to measure tanδ under the conditions of a tensile strain rate of 10±2%, a vibration frequency of 20 Hz, and a temperature of -80°C to 100°C, and a tanδ temperature dependence curve of -80°C to 100°C was prepared with the measured temperature as the horizontal axis and the loss tangent (tanδ) as the vertical axis. Based on the obtained tanδ temperature dependence curve, the maximum value (peak value) of tanδ and the temperature (peak temperature) at this time were determined. The half-peak width σaf of tanδ of the treated rubber composition is determined as the difference between the temperature on the high temperature side and the temperature on the low temperature side when tanδ becomes half of the peak value. In addition, the value of tanδ of the treated rubber composition at a temperature 90°C higher than the peak temperature when tanδ shows a peak value was determined as tanδaf.

[0062] |σbf-σaf| was calculated from the half-peak width σbf of tanδ of the rubber composition obtained above and the half-peak width σaf of tanδ of the rubber composition after treatment, and the result is recorded in the column of "Difference |σbf-σaf|" in Tables 1 to 2. In addition, |tanδbf-tanδaf| was calculated from the value tanδbf of tanδ of the rubber composition at a temperature 90°C higher than the peak temperature of tanδ and the value tanδaf of tanδ of the rubber composition after treatment at a temperature 90°C higher than the peak temperature of tanδ, and the result is recorded in the column of "Difference |tanδbf-tanδaf|" in Tables 1 to 2.

[0063] The rubber composition obtained above was used for a tire tread, and a pneumatic tire of size 205 / 55R16 was vulcanized and molded. The wear resistance, wet performance and rolling resistance were measured by the following methods.

[0064] Wear resistance

[0065] The obtained tire was assembled on a wheel of standard size and mounted on a rolling resistance tester with a roller of radius 854 mm. Under the conditions of air pressure 210 kPa, load 100 N, speed 80 km / h, and roller surface temperature 20°C, after 30 minutes of preliminary running, a running test of 20,000 kilometers was carried out at a speed of 100 km / h, and then the wear amount of the tread land part was measured. Regarding the evaluation results, the reciprocal of the measured value was calculated, and the index when the standard example was set to 100 was taken, and it was shown in the "wear resistance" column of Tables 1 to 2. The larger the index, the less the wear amount and the better the wear resistance. Preferably, the index is 110 or more.

[0066] Wetland performance

[0067] The obtained tires were mounted on standard rims and installed on a test vehicle with an ABS displacement of 2000cc, with the air pressure of the front and rear tires being 220kPa. The test vehicle was driven on an asphalt road surface sprinkled with water to a depth of 2.0 to 3.0mm, and the braking stop distance from a speed of 100km / h to the braking stop was measured. The reciprocals of the results obtained were calculated, and the index was taken as 100 with the value of the standard example as the index, and was shown in the "Wetland Performance" column of Tables 1 to 2. The larger the index, the shorter the braking stop distance and the better the wetland performance. Preferably, the index is 110 or more.

[0068] Rolling resistance

[0069] The obtained tire was mounted on a wheel of standard size and installed on a rolling resistance tester with a roller of radius 854 mm. After 30 minutes of preliminary running under the conditions of air pressure 210 kPa, load 100 N, speed 80 km / h, and roller surface temperature 20°C, the rolling resistance was measured under the same conditions. The evaluation results were obtained by taking the index when the standard example was 100 as the reciprocal of the measured value and showing it in the column of "rolling resistance" in Tables 1 to 2. The larger the index, the smaller the rolling resistance and the better it is. The index is preferably 95 or more.

[0070] [Table 1]

[0071]

[0072] [Table 2]

[0073]

[0074] The types of raw materials used in Tables 1 and 2 are as follows.

[0075] NR: Natural rubber, TSR20, glass transition temperature is -65°C

[0076] SBR-1: terminal-modified styrene butadiene rubber with polyorganosiloxane structure, Nipol NS612 produced by Zeon Co., Ltd., Japan, glass transition temperature of -61°C, styrene content of 15% by mass, vinyl content of 31%, non-oil-filled

[0077] SBR-2: terminal modified styrene butadiene rubber with polyorganosiloxane structure, Nipol NS616 produced by Zeon Co., Ltd., Japan, glass transition temperature of -23°C, styrene content of 22% by mass, vinyl content of 67%, non-oil-filled

[0078] · SBR-3: terminal-modified styrene butadiene rubber with a polyorganosiloxane structure, trial-produced SBR by Yokohama Rubber Co., Ltd., glass transition temperature -80°C, styrene content 6% by mass, vinyl content 15%, non-oil-extended

[0079] Carbon black: Seastar 7HM manufactured by Tokai Carbon Co., Ltd.

[0080] Silica: Zeosil 1165MP produced by Solvey, nitrogen adsorption specific surface area 159m 2 / g

[0081] Coupling agent: silane coupling agent, Si69 produced by EvonikDegussa

[0082] Resin-1: C9 petroleum resin, ENEOS Neopolymer S100, glass transition temperature 58°C

[0083] Resin-2: Aromatic modified terpene resin, YS resin TO-105 produced by Yashara Chemical Co., Ltd., glass transition temperature is 57°C

[0084] Resin-3: Indene resin, FMR0150 produced by Mitsui Chemicals, glass transition temperature: 89°C

[0085] Resin-4: Phenol-modified terpene resin, Tamanol 803L produced by Arakawa Chemical Industries, Ltd., glass transition temperature: 95°C

[0086] Liquid rubber: Liquid styrene butadiene rubber, Ricon100 produced by Cray Valley

[0087] ・Oil: Securitol No. 4 S produced by Seiko Reliance Co., Ltd.

[0088] [Table 3]

[0089]

[0090] The types of raw materials used in Table 3 are as follows.

[0091] Anti-aging agent: VULANOX4020 produced by LANXESS

[0092] Wax: OZOACE-0015A manufactured by NIPPON SEIRO

[0093] Sulfur: Tsurumi Chemical Industry Co., Ltd., Sulfux 5

[0094] · Vulcanization accelerator: Noxela CZ-G produced by Ouchi Shinko Chemical Industry Co., Ltd.

[0095] As can be clearly confirmed from Tables 1 to 2, the rubber compositions of Examples 1 to 8 are excellent in wear resistance, wet performance and low rolling resistance.

[0096] As is clear from Table 1, the rubber composition of Comparative Example 1 cannot improve the wear resistance and wet performance to appropriate levels because the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is less than 75% by mass and the difference |σbf-σaf| is less than 4°C.

[0097] In the rubber composition of Comparative Example 2, since the total amount of the thermoplastic resin and the plasticizer was less than 20 parts by mass and the difference |σbf-σaf| was less than 4° C., the wear resistance and wet performance could not be improved to appropriate levels.

[0098] The rubber composition of Comparative Example 3 had poor wet performance and rolling resistance because the difference |tan δbf-tan δaf| was larger than 0.02.

[0099] The rubber composition of Comparative Example 4 had poor rolling resistance because the difference |tan δbf-tan δaf| was larger than 0.02.

[0100] In the rubber composition of Comparative Example 5, since the total amount of the thermoplastic resin and the plasticizer is 50 parts by mass or more, the rolling resistance is poor.

[0101] In the rubber composition of Comparative Example 6, since the ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is less than 75 mass %, the wear resistance and wet performance cannot be improved to a suitable level.

[0102] The present disclosure includes the following inventions.

[0103] Invention [1]. A rubber composition comprising a diene rubber containing at least one styrene butadiene rubber, a white filler, a thermoplastic resin, and an optionally contained plasticizer, wherein the white filler is present in an amount of 20 to 150 parts by mass relative to 100 parts by mass of the diene rubber, and the total amount of the thermoplastic resin and the plasticizer is not less than 20 parts by mass and less than 50 parts by mass, wherein:

[0104] The ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more, and

[0105] When the half-peak width in the temperature dependence 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 when tan δ is maximum is tanσbf, the half-peak width in the temperature dependence curve of tan δ of the rubber composition after treatment 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 when tan δ is maximum is tanσaf, the following relational expressions (1) and (2) are satisfied,

[0106] |σbf-σaf|≥4 (1)

[0107] |tanδbf-tanδaf|≤0.02 (2).

[0108] Invention [2]. The rubber composition according to Invention [1], characterized in that the difference between the lowest glass transition temperature Tgp (°C) of the at least one styrene butadiene rubber and the glass transition temperature Tgr (°C) of the thermoplastic resin, i.e. Tgr-Tgp, is 100°C or more.

[0109] Invention [3]. The rubber composition according to invention [1] or [2], characterized in that the diene rubber contains 70 to 100% by mass of the at least one styrene butadiene rubber and 0 to 30% by mass of the isoprene rubber.

[0110] 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.

[0111] Invention [5]. The rubber composition according to any one of Inventions [1] to [4], 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 following resins and resins in which at least a portion of the double bonds of these resins are hydrogenated:

[0112] The resin is a resin formed of at least one of terpene, modified terpene, rosin, rosin ester, C5 component, and C9 component.

Claims

1. A rubber composition comprising a diene rubber containing at least one styrene butadiene rubber, a white filler, a thermoplastic resin, and an optionally contained plasticizer, wherein the white filler is 20 to 150 parts by mass based on 100 parts by mass of the diene rubber, and the total amount of the thermoplastic resin and the plasticizer is 20 parts by mass or more and less than 50 parts by mass, wherein: The ratio of the thermoplastic resin to the total of the thermoplastic resin and the plasticizer is 75% by mass or more, and When the half-peak width in the temperature dependence curve of tan δ of the rubber composition is σbf, the value of tan δ at a temperature 90°C higher than the peak temperature when tan δ is maximum is tanσbf, the half-peak width in the temperature dependence curve of tan δ of the treated rubber composition obtained by immersing the rubber composition in toluene and drying is σaf, and the value of tan δ at a temperature 90°C higher than the peak temperature when tan δ is maximum is tanσaf, the following relations (1) and (2) are satisfied, wherein the units of σbf and σaf are both °C, |σbf-σaf|≥4 (1) |tanδbf-tanδaf|≤0.02 (2).

2. The rubber composition according to claim 1, characterized in that The difference between the lowest glass transition temperature Tgp of the at least one styrene butadiene rubber and the glass transition temperature Tgr of the thermoplastic resin, that is, Tgr-Tgp, is 100° C. or more, and the units of Tgp and Tgr are both degrees Celsius.

3. The rubber composition according to claim 1 or 2, characterized in that The diene rubber contains 70 to 100% by mass of the at least one styrene-butadiene rubber and 0 to 30% by mass of the isoprene rubber.

4. The rubber composition according to claim 1 or 2, characterized in that: At least one of the terminals of the at least one styrene butadiene rubber is modified with a functional group.

5. The rubber composition according to claim 1 or 2, characterized in that: 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 following resins and resins in which at least a part of the double bonds of these resins are hydrogenated, The resin is a resin formed of at least one of terpene, modified terpene, rosin, rosin ester, C5 component, and C9 component.

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