Rubber composition for tires

Abstract

Provided is a rubber composition for tires which is excellent in wear resistance and wet performance, and which is configured to reduce rolling resistance and temperature dependency. The rubber composition for tires is obtained by blending, in 100 parts by mass of a diene rubber comprising a 55 mass% or more solution-polymerized styrene-butadiene rubber having a glass transition temperature of -50°C, at least 30 parts by mass but less than 100 parts by mass of a white filling agent, at least 15 parts by mass of a thermoplastic resin, and, with respect to the mass of the white filling agent, a 3-20 mass% silane coupling agent represented by a specific average composition formula. The rubber composition is characterized in that, with respect to a mixture of the diene rubber and the thermoplastic resin at a mass ratio of 1:1, a difference, Tga-Tgm, is 10°C or less, said difference being between: a 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 a measured value Tgm of the glass transition temperature of the mixture.

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires, which has excellent abrasion resistance and wet performance, and can obtain good low rolling resistance in a wide temperature range.

Background Art

[0002] Summer tires are required to have high levels of abrasion resistance, wet performance, and low rolling resistance. As a rubber composition for tires that improves wet performance and low rolling resistance, it has been proposed to blend modified styrene-butadiene rubber with silica and various resin components (see, for example, Patent Documents 1 and 2).

[0003] However, in recent years, it has been required to make the low rolling resistance excellent in a wider temperature range. For this reason, in the inventions described in Patent Documents 1, 2, etc. mentioned above, it was not always sufficient to reduce the temperature dependence of the rolling resistance and obtain low rolling resistance in a wider temperature range.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a rubber composition for tires that is excellent in abrasion resistance and wet performance, and reduces rolling resistance and its temperature dependence.

Means for Solving the Problems

[0006] The rubber composition for tires of the present invention that achieves the above object is obtained by blending 100 parts by mass of a diene rubber containing 55% by mass or more of a solution-polymerized styrene-butadiene rubber having a glass transition temperature of -50°C or lower with 30 parts by mass or more and less than 100 parts by mass of a white filler and 15 parts by mass or more of a thermoplastic resin, and further blending 3 to 20% by mass of a silane coupling agent represented by the following average composition formula (1) with respect to the mass of the white filler. In a mixture in which the diene rubber and the 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 10°C or lower. and the thermoplastic resin is 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 It is characterized by the following. (A) a (B) b (C) c (D) d (R 1 ) e SiO (4-2a-b-c-d-e) / 2 ···(1) (In formula (1), A represents a divalent organic group containing a sulfide group, B represents a monovalent hydrocarbon group having 5 to 10 carbon atoms, C represents a hydrolyzable group, D represents an organic group containing a mercapto group, R 1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a to e satisfy the relational expressions of 0 ≦ a < 1, 0 < b < 1, 0 < c < 3, 0 < d < 1, 0 ≦ e < 2, and 0 < 2a + b + c + d + e < 4.) [Effect of the Invention]

[0007] The rubber composition for tires of the present invention is prepared by blending a diene rubber containing a specific solution-polymerized styrene-butadiene rubber with a specific thermoplastic resin, silica, and a specific silane coupling agent. Therefore, it has excellent abrasion resistance and wet performance, and can reduce the rolling resistance in a wide temperature range.

[0008] 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, the maximum value tanδ of the loss tangent of the rubber composition for tires at -40°C to 60°C MAXAand the maximum value of the loss tangent tanδ of the rubber composition B at -40°C to 60°C MAXB is preferably satisfied by the following formula (2). tanδ MAXA / tanδ MAXB > 0.8 (2)

[0009] At least one end of the solution-polymerized styrene-butadiene rubber is preferably modified with a functional group, and the oil extension amount of the solution-polymerized styrene-butadiene rubber is preferably 10 parts by mass or less with respect to 100 parts by mass of the solution-polymerized styrene-butadiene rubber.

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

[0011] A tire having a tread portion made of the above-described rubber composition for tires is particularly suitable as a summer tire, has excellent abrasion resistance and wet performance, and can reduce the rolling resistance in a wide temperature range.

Mode for Carrying Out the Invention

[0012] The rubber composition for tires of the present invention has a rubber component composed of a diene rubber, and contains 55% by mass or more of a solution-polymerized styrene-butadiene rubber having a glass transition temperature (hereinafter sometimes referred to as "Tg") of -50°C or lower in 100% by mass of the diene rubber. By including a solution-polymerized styrene-butadiene rubber having a Tg of -50°C or lower, the dispersibility of silica is improved, abrasion resistance and low rolling resistance are ensured, and the temperature dependence of rolling resistance is reduced. The solution-polymerized styrene-butadiene rubber having a Tg of -50°C or lower is 55% by mass or more, preferably 55 to 80% by mass, more preferably 60 to 75% by mass in 100% by mass of the diene rubber. When the solution-polymerized styrene-butadiene rubber is less than 55% by mass, the effect of improving the dispersibility of silica cannot be sufficiently obtained, and the temperature dependence of rolling resistance cannot be reduced.

[0013] When the Tg of the solution-polymerized styrene-butadiene rubber is higher than -50°C, the temperature dependence of rolling resistance cannot be reduced. The Tg is preferably -50°C to -65°C, more preferably -50°C to -60°C. The Tg of the solution-polymerized 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 temperature increase rate of 20°C / min by differential scanning calorimetry (DSC). Further, when the diene rubber is an oil-extended product, it is the Tg of the diene rubber in a state not containing an oil-extended component (oil).

[0014] Solution-polymerized styrene-butadiene rubber having a Tg of -50°C or lower is preferably such that at least one of its terminals is modified with a functional group, which can improve the dispersibility of silica and further reduce the rolling resistance of a tire. 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, functional groups 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 wet performance and low rolling resistance can be made excellent.

[0015] The styrene content of the solution-polymerized styrene-butadiene rubber is not particularly limited, but is preferably 5 to 30% by mass, more preferably 8 to 25% by mass. By setting the styrene content within such a range, it is possible to make the tire have low rolling resistance, which is preferable. The styrene content of the solution-polymerized styrene-butadiene rubber can be 1 measured by 1H-NMR.

[0016] The vinyl content of the solution-polymerized styrene-butadiene rubber is not particularly limited, but is preferably 9 to 45 mol%, more preferably 20 to 45 mol%, still more preferably 25 to 45 mol%, and particularly preferably 28 to 42 mol%. By setting the vinyl content within such a range, the dispersibility of silica can be improved, the temperature dependence of the rolling resistance can be reduced, and the abrasion resistance can be ensured, which is preferable. The vinyl content of the solution-polymerized styrene-butadiene rubber can be 1 measured by 1H-NMR.

[0017] Solution-polymerized styrene-butadiene rubber can contain an extender oil component. The amount of the extender oil is preferably 10 parts by mass or less with respect to 100 parts by mass of the solution-polymerized styrene-butadiene rubber. By setting the amount of the extender oil to 10 parts by mass or less, it is possible to suppress a decrease in grip performance after the tire has aged. The amount of the extender oil is more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less.

[0018] The rubber composition for a tire can contain, as the rubber component, other diene rubbers other than solution-polymerized styrene-butadiene rubber. Examples of the other diene rubbers include solution-polymerized styrene-butadiene rubber having a Tg of more than -50°C, natural rubber, isoprene rubber, butadiene rubber, butyl rubber, emulsion-polymerized styrene-butadiene rubber, halogenated butyl rubber, acrylonitrile-butadiene rubber, and modified rubbers obtained by attaching a functional group to these rubbers. These other diene rubbers can be used alone or as an arbitrary blend. The content of the other diene rubbers is preferably 45% by mass or less, more preferably 20 to 45% by mass, and even more preferably 25 to 40% by mass in 100% by mass of the diene rubbers.

[0019] The rubber composition for a tire is preferably blended with solution-polymerized styrene-butadiene rubber having a Tg of more than -50°C, as the wet performance is improved. The solution-polymerized styrene-butadiene rubber having a Tg of more than -50°C is preferably 10 to 25% by mass, more preferably 10 to 15% by mass in 100% by mass of the diene rubbers. As the solution-polymerized styrene-butadiene rubber having a Tg of more than -50°C, those usually used in the rubber composition for a tire may be used.

[0020] The rubber composition for a tire can reduce the temperature dependence of rolling resistance by blending natural rubber. The natural rubber is preferably 5 to 40% by mass, more preferably 15 to 30% by mass in 100% by mass of the diene rubbers. As the natural rubber, those usually used in the rubber composition for a tire may be used.

[0021] In addition, it is preferable to compound butadiene rubber because it improves abrasion resistance. The butadiene rubber is preferably 5 to 20% by mass, more preferably 5 to 15% by mass, in 100% by mass of the diene rubber. As the butadiene rubber, those usually used in rubber compositions for tires may be used.

[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 the diene rubber. By compounding the white filler, wet performance and low rolling resistance can be made excellent. 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 preferable, and wet performance and low heat build-up can be made more excellent. If the white filler is less than 30 parts by mass, wet performance and / or low rolling resistance will be insufficient. If the white filler is 100 parts by mass or more, the low rolling resistance will deteriorate instead. 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. As the silica, those usually used in rubber compositions for tires may be used, for example, wet-process silica, dry-process silica, or carbon-silica (dual-phase filler) in which silica is supported on the surface of carbon black, silica treated with a silane coupling agent or a polysiloxane or other compound reactive or compatible with both silica and rubber. Among these, wet-process silica mainly composed of hydrous silicic acid is preferable.

[0023] In addition, it is preferable to compound a silane coupling agent represented by the following average composition formula (1) together with silica because it improves the dispersibility of silica and further improves wet performance and low rolling resistance. (A) a (B) b (C) c (D) d (R 1 ) e SiO(4-2a-b-c-d-e) / 2 ···(1) (In formula (1), A represents a divalent organic group containing a sulfide group, B represents a monovalent hydrocarbon group having 5 to 10 carbon atoms, C represents a hydrolyzable group, D represents an organic group containing a mercapto group, and R 1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a to e satisfy the relational expressions: 0 ≦ a < 1, 0 < b < 1, 0 < c < 3, 0 < d < 1, 0 ≦ e < 2, and 0 < 2a + b + c + d + e < 4.)

[0024] The silane coupling agent represented by the above formula (1) preferably has a polysiloxane skeleton. The polysiloxane skeleton can be linear, branched, three-dimensional, or a combination thereof.)

[0025] In the above formula (1), the hydrocarbon group B is a monovalent hydrocarbon group having 5 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 6 to 10 carbon atoms, more preferably a monovalent hydrocarbon group having 8 to 10 carbon atoms. For example, hexyl group, octyl group, decyl group, etc. can be mentioned. Thereby, the mercapto group can be protected, the Mooney scorch time can be lengthened, and the processability (scorch resistance) can be made more excellent, and the low rolling resistance can be made more excellent. The subscript b of the hydrocarbon group B is greater than 0, and preferably 0.10 ≦ b ≦ 0.89.)

[0026] Also, in the above formula (1), the organic group A represents a divalent organic group containing a sulfide group (hereinafter also referred to as "sulfide group-containing organic group"). By having the sulfide group-containing organic group A, the low heat generation property and processability (especially maintaining and lengthening the Mooney scorch time) can be made more excellent. Therefore, the subscript a of the sulfide group-containing organic group A is preferably greater than 0, and more preferably 0 < a ≦ 0.50. The sulfide group-containing organic group A may have a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom.)

[0027] Among them, the sulfide group-containing organic group A is preferably a group represented by the following formula (3). *-(CH2) n -Sx-(CH2) n-* ···(3) (In the above formula (3), n represents an integer from 1 to 10, x represents an integer from 1 to 6, and * indicates the bonding position.) Specific examples of the sulfide group-containing organic group A represented by the general formula (3) include, for example, *-CH2-S2-CH2-*, *-C2H4-S2-C2H4-*, *-C3H6-S2-C3H6-*, *-C4H8-S2-C4H8-*, *-CH2-S4-CH2-*, *-C2H4-S4-C2H4-*, *-C3H6-S4-C3H6-*, *-C4H8-S4-C4H8-*, etc.

[0028] The silane coupling agent composed of polysiloxane represented by the average composition formula of the general formula (1) has a hydrolyzable group C, thereby making it excellent in affinity and / or reactivity with silica. The subscript c of the hydrolyzable group C in the general formula (1) is preferably 1.2 ≦ c ≦ 2.0 for the reasons that it has lower heat generation, better processability (scorch resistance), and better dispersibility of silica. Specific examples of the hydrolyzable group C include, for example, an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, etc. From the viewpoint of improving the dispersibility of silica and making the processability (scorch resistance) better, the hydrolyzable group C is preferably a group represented by the following general formula (4). *-OR 2 ···(4) In the above general formula (4), * indicates the bonding position. Also, R 2 represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group (arylalkyl group) having 6 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms, and among them, an alkyl group having 1 to 5 carbon atoms is preferable.

[0029] Specific examples of the alkyl group having 1 to 20 carbon atoms include, for example, methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, decyl group, octadecyl group and the like. Specific examples of the aryl group having 6 to 10 carbon atoms include, for example, phenyl group, tolyl group and the like. Specific examples of the aralkyl group having 6 to 10 carbon atoms include, for example, benzyl group, phenylethyl group and the like. Specific examples of the alkenyl group having 2 to 10 carbon atoms include, for example, vinyl group, propenyl group, pentenyl group and the like.

[0030] The silane coupling agent composed of polysiloxane represented by the average composition formula of the general formula (1) can interact and / or react with a diene rubber by having an organic group D containing a mercapto group, and can have excellent low heat build-up property. The subscript d of the organic group D containing a mercapto group is preferably 0.1 ≦ d ≦ 0.8. From the viewpoint of improving the dispersibility of silica and making the processability (scorch resistance) more excellent, the organic group D containing a mercapto group is preferably a group represented by the following general formula (5). *-(CH2) m -SH ···(5) In the general formula (5), m represents an integer of 1 to 10, and preferably an integer of 1 to 5. In the formula, * indicates the bonding position.

[0031] Specific examples of the group represented by the general formula (5) include *-CH2SH, *-C2H4SH, *-C3H6SH, *-C4H8SH, *-C5H 10 SH, *-C6H 12 SH, *-C7H 14 SH, *-C8H 16 SH, *-C9H 18 SH, *-C 10 H 20 SH.

[0032] In the general formula (1), R 1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms. The hydrocarbon group R 1Examples include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0033] The silane coupling agent may be blended in an amount of 3 to 20% by mass, preferably 5 to 15% by mass, based on the mass of the silica. When the blending amount of the silane coupling agent is less than 3% by mass of the silica mass, the effect of improving the dispersibility of the silica cannot be sufficiently obtained. On the other hand, when the silane coupling agent exceeds 20% by mass, the diene rubber component tends to gel, and thus the desired effect cannot be obtained.

[0034] By blending other fillers in addition to the white filler, the strength of the rubber composition for tires can be increased and the tire durability can be ensured. 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 dendrimer.

[0035] Among them, by blending carbon black, the strength of the rubber composition can be made excellent. As the carbon black, carbon black such as furnace black, acetylene black, thermal black, channel black, and graphite 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, and FEF. These carbon blacks can be used alone or in combination of two or more. Further, surface-treated carbon black obtained by chemically modifying these carbon blacks with various acid compounds or the like can also be used.

[0036] The rubber composition for tires can adjust the temperature dependence 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, preferably 20 parts by mass or more, more preferably 25 parts by mass or more, based on 100 parts by mass of the diene rubber. If the amount of the thermoplastic resin is less than 15 parts by mass, the object of the present invention, which is excellent in abrasion resistance and wet performance and reduces rolling resistance and its temperature dependence, cannot be achieved. Also, the specific thermoplastic resin is preferably 75 parts by mass or less, more preferably 60 parts by mass or less, based on 100 parts by mass of the diene rubber. If the amount of the specific thermoplastic resin exceeds 75 parts by mass, there is a risk of deterioration in abrasion resistance.

[0037] The specific thermoplastic resin shall satisfy the following relationship with the diene rubber. That is, in a mixture in which the above-mentioned 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 10°C or less. By making the difference Tga - Tgm 10°C or less, it is possible to achieve excellent abrasion resistance and wet performance, reduce rolling resistance, and reduce its temperature dependence. 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 by blending a relatively large amount of the thermoplastic resin, it is considered to increase the tensile breaking strength of the rubber composition and contribute to the improvement of viscoelastic properties such as tanδ. In this specification, the theoretical value Tga of the glass transition temperature of the mixture can be calculated as a weighted average value from the glass transition temperatures and mass ratio of the diene rubber and the thermoplastic resin. Also, the glass transition temperatures of the diene rubber and the thermoplastic resin, and the glass transition temperature Tgm of the mixture are measured by differential scanning calorimetry (DSC) under the condition of a heating rate of 20°C / min, and measured as the temperature at the midpoint of the transition region. When there are a plurality of transition regions in the thermogram, the midpoint in the largest transition region is taken as the glass transition temperature Tgm of the mixture.

[0038] A thermoplastic resin is a resin that is usually compounded into a rubber composition for tires. It has a molecular weight of several hundred to several thousand and has the effect of imparting adhesiveness to the rubber composition for tires. As the thermoplastic resin, a resin composed of at least one selected from the group consisting of terpenes, modified terpenes, rosins, rosin esters, C5 components, C9 components, and a resin in which at least a part of the double bonds of these resins is hydrogenated is preferred. 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, coal-based resins, phenolic resins, xylene-based resins, etc., and hydrogenated resins obtained by hydrogenating at least a part of the double bonds of these natural resins and synthetic resins can be mentioned.

[0039] 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, maleated rosin, and fumarated rosin, ester derivatives such as glycerin esters, pentaerythritol esters, methyl esters, and triethylene glycol esters of these rosins, and rosin-modified phenolic resins, etc.

[0040] 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, pentene, etc.), C9 petroleum resins (aromatic petroleum resins polymerized from fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, p-vinyltoluene, etc.), C5C9 copolymer petroleum resins, and resins obtained by hydrogenating these resins can be exemplified.

[0041] The glass transition temperature (Tg) of the thermoplastic resin is preferably 40°C to 120°C, more preferably 45°C to 115°C, and even more preferably 50°C to 110°C. By setting the Tg of the thermoplastic resin to 40°C or higher, the wet performance is improved, which is preferable. Also, by setting it to 120°C or lower, the abrasion resistance is improved, which is preferable. The Tg of the thermoplastic resin can be measured by the method described above.

[0042] In the following description, the rubber composition for tires of the present invention is designated as rubber composition A, and a composition having the same composition as rubber composition A except that all the thermoplastic resin contained in rubber composition A is replaced with oil is designated as rubber composition B. Also, the maximum value of the loss tangent of rubber composition A at -40°C to 60°C is tanδ MAXA and the maximum value of the loss tangent of rubber composition B at -40°C to 60°C is tanδ MAXB At this time, it is preferable that tanδ MAXA and tanδ MAXB satisfy the relationship of the following formula (2). tanδ MAXA / tanδ MAXB > 0.8 (2)

[0043] When the ratio of the maximum values of the loss tangent, tanδ MAXA / tanδ MAXB is greater than 0.8, the tensile breaking strength of the rubber composition for tires of the present invention (rubber composition A) increases, and the abrasion resistance when made into a tire becomes more excellent, which is preferable. Rubber composition B has a high compatibility of the contained diene rubber and oil and tends to have a high tensile breaking strength. That tanδ MAXA of rubber composition A is close to tanδ MAXB of rubber composition B suggests that the viscoelastic behavior of the rubber compositions is similar, the compatibility of the diene rubber and the thermoplastic resin is good, and the thermoplastic resin is suppressed from becoming the starting point of fracture, resulting in an increase in the tensile breaking strength. The ratio tanδ MAXA / tanδ MAXB is more preferably greater than 0.85, and even more preferably greater than 0.9. In this specification, tanδ MAXA and tanδ MAXBThe dynamic viscoelasticity of the cured products of rubber compositions A and B was measured using a viscoelastic spectrometer under the conditions of a tensile deformation strain rate of 10 ± 2%, a frequency of 20 Hz, and a temperature range of -40°C to 60°C. A viscoelastic curve with the measurement temperature on the horizontal axis and the loss tangent (tanδ) on the vertical axis was obtained, and the maximum value (peak value) of tanδ was designated as tanδ MAXA and tanδ MAXB respectively.

[0044] In addition to the above components, various compounding agents commonly used in rubber compositions for tire treads, such as vulcanizing or crosslinking agents, vulcanization accelerators, anti-aging agents, processing aids, plasticizers, liquid polymers, and thermosetting resins, can be compounded into the rubber composition for tires according to conventional methods. Such compounding agents can be kneaded by a general method to form a rubber composition and used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be set to conventional general compounding amounts as long as they do not contravene the object of the present invention. The rubber composition for tires can be prepared by mixing the above components using known rubber kneading machines, such as Banbury mixers, kneaders, rolls, etc.

[0045] The rubber composition for tires is suitable for forming the tread and sidewall portions of summer tires, and is particularly suitable for forming the tread portion of summer tires. The summer tires obtained thereby are excellent in abrasion resistance and wet performance, and can reduce the rolling resistance and its temperature dependence to levels lower than the conventional levels.

[0046] 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.

Examples

[0047] In preparing 21 types of rubber compositions for tires (standard example, Examples 1 to 11, Comparative Examples 1 to 9) having the common additive formulation shown in Table 3 and consisting of the formulations shown in Tables 1 and 2, the components excluding sulfur and vulcanization accelerators were weighed respectively, kneaded in a 1.7-liter closed Banbury mixer for 5 minutes, 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 for tires. Regarding Comparative Example 9 in Table 1, since SBR-4 is an oil-extended product with 25 parts by mass, the compounding amount without the oil-extended component is described in the parentheses below. The additive formulation in Table 3 is described in parts by mass based on 100 parts by mass of the diene rubber described in Tables 1 and 2. Further, the rubber compositions for tires of Examples 1 to 11 and Comparative Examples 1 to 9 described above were respectively designated as Rubber Composition A, and those having the same composition as each Rubber Composition A except that all thermoplastic resins were replaced with oil were designated as Rubber Composition B and prepared in the same manner as above. Furthermore, a mixture was prepared by blending the diene rubber and thermoplastic resin constituting the rubber composition for tires of each example and comparative example at a mass ratio of 1:1, the glass transition temperature (Tgm) of the mixture was measured by the method described above, the theoretical value Tga of the glass transition temperature was calculated, and the difference Tga - Tgm from the measured value Tgm of the glass transition temperature was calculated and described in Tables 1 and 2.

[0048] The rubber compositions for tires obtained above were vulcanized in molds of predetermined shapes at 160 °C for 20 minutes to prepare evaluation samples. Using the obtained evaluation samples, the dynamic viscoelasticity (loss tangent tanδ), abrasion resistance, wet performance, rolling resistance, and temperature dependence of rolling resistance were measured by the following methods.

[0049] Dynamic viscoelasticity (loss tangent tanδ) The dynamic viscoelasticity of the evaluation samples of the obtained rubber compositions for tires (Rubber Composition A) and Rubber Composition B was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the conditions of an elongation deformation strain rate of 10 ± 2%, a frequency of 20 Hz, and a temperature range of -40 °C to 60 °C. A viscoelasticity curve from -40 °C to 60 °C was created, and the maximum value (peak value) of tanδ of Rubber Composition A and Rubber Composition B was defined as tanδ MAXA and tanδMAXB and calculated tanδ MAXA / tanδ MAXB The obtained results were listed in Tables 1 and 2. Also, as an index of wet performance, the measured value of tanδ at 0°C of the rubber composition for tires (rubber composition A) was used, and it was described in the column of "Wet Performance" in Tables 1 and 2 as an index that makes the tanδ at 0°C of the standard example 100. The larger this index, the better the wet performance.

[0050] Abrasion resistance Evaluation samples of the obtained rubber composition for tires were prepared in accordance with JIS K6264, and using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.), the abrasion amount was measured under the conditions of a load of 15.0 kg (147.1 N) and a slip ratio of 25%. The reciprocal of each of the obtained results was calculated, and it was described in the column of "Abrasion resistance" in Tables 1 and 2 as an index that makes the reciprocal of the abrasion amount of the standard example 100. The larger the abrasion resistance index, the better the abrasion resistance.

[0051] Rolling resistance A 17-inch pneumatic tire using the rubber composition for tires obtained above as the tread rubber was vulcanized and molded. Each test tire was assembled on a wheel of the standard rim size and mounted on a rolling resistance tester equipped with a drum with 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 results were described in the column of "Low rolling resistance" in Tables 1 and 2 as an index using the reciprocal of the measured value with the standard example being 100. The larger the index value of the rolling resistance, the smaller and better the rolling resistance.

[0052] Temperature dependence of rolling resistance Under the same conditions as the measurement conditions of the rolling resistance, the rolling resistance at a tire surface temperature of 20°C and the rolling resistance at 40°C were evaluated. The measured rolling resistance was plotted against the temperature, and the slope of the difference in rolling resistance at each temperature was evaluated as the temperature dependence of the rolling resistance. Here, the smaller the slope of the rolling resistance, the lower the temperature dependence of the rolling resistance. The evaluation results were described in the column of "Temperature Dependence of Low Rolling Resistance" in Tables 1 and 2 as an index with the standard example being 100, using the reciprocal of the temperature dependence (slope) of the rolling resistance. A larger index value of the temperature dependence of the rolling resistance means that the temperature dependence of the rolling resistance is smaller and better.

[0053]

Table 1

[0054]

Table 2

[0055] The types of raw materials used in Tables 1 and 2 are shown below. · NR: Natural rubber, TSR20, glass transition temperature of -65°C · SBR-1: Terminally modified solution-polymerized styrene-butadiene rubber having a polyorganosiloxane structure, Nipol NS612 manufactured by Zeon Corporation, Japan, glass transition temperature of -61°C, styrene content of 15% by mass, vinyl content of 31 mol%, non-oil product · SBR-2: Terminally modified solution-polymerized styrene-butadiene rubber having a polyorganosiloxane structure, Nipol NS616 manufactured by Zeon Corporation, Japan, glass transition temperature of -23°C, styrene content of 22% by mass, vinyl content of 67 mol%, non-oil product · SBR-3: Unmodified solution-polymerized styrene-butadiene rubber manufactured by batch polymerization, HPR850 manufactured by JSR Corporation, glass transition temperature of -25°C, styrene content of 27% by mass, vinyl content of 59 mol%, non-oil product · SBR-4: An alkoxysilane-modified solution-polymerized styrene-butadiene rubber produced by continuous polymerization, M2520 manufactured by LG Corporation, with a glass transition temperature of -48 °C, a styrene content of 27% by mass, a vinyl content of 27 mol%, and an oil extension amount of 25 parts by mass · BR: Butadiene rubber, Nipol BR1220 manufactured by Zeon Corporation, with a glass transition temperature of -105 °C · Carbon black: Seast 7HM manufactured by Tokai Carbon Co., Ltd. · Silica-1: Zeosil 1165MP manufactured by Solvay, with a nitrogen adsorption specific surface area of 159 m 2 / g · Silica-2: ULTRASIL 5000GR manufactured by Evonik, with a nitrogen adsorption specific surface area of 126 m 2 / g · Coupling agent-1: A silane coupling agent containing a polysiloxane represented by the average composition formula of general formula (1), adjusted by the production method described in the pamphlet of WO2014 / 002750, with an average composition formula of (-C3H6-S4-C3H6-) 0.083 (-C8H 17 ) 0.667 (-OC2H5) 1.50 (-C3H6SH) 0.167 SiO 0.75 A polysiloxane represented by, with an average molecular weight of 860 · Coupling agent-2: A silane coupling agent, Si69 manufactured by Evonik Degussa · Resin-1: An aromatic-modified terpene resin, HSR-7 manufactured by Yasuhara Chemical Co., Ltd., with a glass transition temperature of 72 °C · Resin-2: An aromatic-modified terpene resin, YS resin TO-105 manufactured by Yasuhara Chemical Co., Ltd., with a glass transition temperature of 57 °C · Resin-3: An indene resin, FMR0150 manufactured by Mitsui Chemicals, Inc., with a glass transition temperature of 89 °C · Resin-4: A phenol-modified terpene resin, Tamanol 803L manufactured by Arakawa Chemical Industries, Ltd., with a glass transition temperature of 95 °C · Resin-5: A polyterpene resin, Sylvatraxx8115 manufactured by Kraton, with a glass transition temperature of 67 °C · 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. · Antioxidant: VULANOX 4020 manufactured by LANXESS · Wax: OZOACE-0015A manufactured by NIPPON SEIRO · Sulfur: Sulfax 5 manufactured by Tsurumi Chemical Industry Co., Ltd. · Vulcanization accelerator: Nocceler TOT-N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0058] As is clear from Table 2, the rubber compositions for tires of Examples 1 to 11 were confirmed to be excellent in abrasion resistance, wet performance, and low rolling resistance, and to reduce the temperature dependence of rolling resistance.

[0059] As is clear from Table 1, since the difference Tga - Tgm of the rubber composition for tires of Comparative Example 1 exceeds 10°C, its abrasion resistance is inferior, and it is impossible to reduce the rolling resistance and its temperature dependence. For the rubber composition for tires of Comparative Example 2, since a silane coupling agent (Coupling agent - 2) not represented by the average composition formula of formula (1) was used, the rolling resistance increases. For the rubber composition for tires of Comparative Example 3, since the solution-polymerized styrene-butadiene rubber (SBR-1) having a Tg of -50°C or lower is less than 55% by mass, it is impossible to improve the abrasion resistance, rolling resistance, and its temperature dependence. For the rubber composition for tires of Comparative Example 4, since the compounding amount of silica is less than 30 parts by mass, it is impossible to improve the abrasion resistance and wet performance. For the rubber composition for tires of Comparative Example 5, since the compounding amount of silica exceeds 100 parts by mass, the rolling resistance and its temperature dependence are inferior. The rubber composition for the tire of Comparative Example 6 has less than 3% by mass of the silane coupling agent (Coupling Agent-1) represented by the average composition formula of Formula (1) with respect to the mass of silica, and thus has inferior abrasion resistance, wet performance, low rolling resistance, and temperature dependence of rolling resistance. Since the difference Tga - Tgm of the rubber composition for the tire of Comparative Example 7 exceeds 10°C, the abrasion resistance is inferior, and the rolling resistance and its temperature dependence cannot be reduced. Since the Tg of the solution-polymerized styrene-butadiene rubber (SBR-3) in the rubber composition for the tire of Comparative Example 8 is higher than -50°C, the abrasion resistance, rolling resistance, and its temperature dependence are inferior. Since the Tg of the solution-polymerized styrene-butadiene rubber (SBR-4) in the rubber composition for the tire of Comparative Example 9 is higher than -50°C, the rolling resistance and its temperature dependence are inferior.

Claims

1. 100 parts by mass of a diene rubber containing 55% by mass or more of a solution-polymerized styrene-butadiene rubber having a glass transition temperature of -50°C or lower is compounded with 30 parts by mass or more and less than 100 parts by mass of a white filler and 15 parts by mass or more of a thermoplastic resin, and 3 to 20% by mass of a silane coupling agent represented by the following average composition formula (1) is compounded based on the mass of the white filler. The rubber composition for tires is such that in a mixture of the diene rubber and the thermoplastic resin compounded 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 10°C or lower, and the thermoplastic resin is at least one selected from the group consisting of resins composed of at least one selected from terpene, modified terpene, rosin, rosin ester, C5 component, C9 component, and resins in which at least a part of the double bonds of these resins are hydrogenated. A rubber composition for tires characterized by this. (A) ａ (B) ｂ (C) ｃ (D) ｄ (R １ ) ｅ SiO （４－２ａ－ｂ－ｃ－ｄ－ｅ）／２ ...(1) (In formula (1), A represents a divalent organic group containing a sulfide group, B represents a monovalent hydrocarbon group having 5 to 10 carbon atoms, C represents a hydrolyzable group, D represents an organic group containing a mercapto group, and R １ represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a to e satisfy the relational expressions: 0 ≦ a < 1, 0 < b < 1, 0 < c < 3, 0 < d < 1, 0 ≦ e < 2, and 0 < 2a + b + c + d + e < 4.)

2. In relation to rubber composition B having the same composition as the rubber composition for tires except that all of the thermoplastic resin is replaced with oil, the maximum value tanδ of the loss tangent of the rubber composition for tires at -40°C to 60°C ＭＡＸＡ and the maximum value tanδ 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, characterized in that it satisfies the following formula (2). tanδ ＭＡＸＡ / tanδ ＭＡＸＢ > 0.8 (2)

3. The rubber composition for tires according to claim 1 or 2, characterized in that at least one end of the solution-polymerized styrene-butadiene rubber is modified with a functional group.

4. The rubber composition for tires according to claim 1 or 2, characterized in that the glass transition temperature of the thermoplastic resin is 40°C to 120°C.

5. The rubber composition for tires according to claim 1 or 2, characterized in that the oil extension amount of the solution-polymerized styrene-butadiene rubber is 10 parts by mass or less per 100 parts by mass of the solution-polymerized styrene-butadiene rubber.

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

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