Rubber composition and tire

Abstract

To provide a rubber composition capable of realizing a wet-grip performance and a rolling resistance performance simultaneously at a high level.SOLUTION: A rubber composition includes diene rubber, silica, a sulfur-containing silane coupling agent and alkylalkoxysilane. A rate of change of a distance between aggregates is 1.30 or more, the rate of change of a distance between aggregates expressed by V50 / V0 calculated with an inertial radius V50 of a silica aggregate obtained by a small angle X-ray scattering measurement with vulcanized rubber obtained by vulcanizing the rubber composition extended by 50% and an inertial radius V0 of the silica aggregate obtained by a small angle X-ray scattering measurement with the vulcanized rubber in an unextended state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a tire using the same. [Background technology]

[0002] Tires are required to have both wet grip performance, which is the grip performance on wet road surfaces, and rolling resistance performance, which contributes to fuel economy. For this reason, for example, Patent Document 1 proposes compounding a silane coupling agent having polyethylene glycol in its main chain skeleton in a rubber composition containing silica in order to improve low electrical resistance, low rolling resistance, wet grip performance, mechanical strength, and processability.

[0003] Patent Document 2 describes that in order to produce a tire with excellent wet performance and rolling resistance, an alkyltriethoxysilane is compounded together with a silane coupling agent having a mercapto group in a rubber composition containing silica.

[0004] Patent Document 3 describes that in order to improve processability and low heat buildup performance, a rubber composition is produced by preparing a mixture of two types of rubber containing different silane coupling agents and mixing the two.

[0005] As described above, various proposals have been made to improve wet grip performance and rolling resistance performance. However, wet grip performance and rolling resistance performance are mutually exclusive properties, meaning that improving one performance results in a decrease in the other. Therefore, it is difficult to achieve both. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3908368 [Patent Document 2] Patent No. 4930661 [Patent Document 3] Patent No. 6385655 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of an embodiment of the present invention is to provide a rubber composition that can improve the trade-off between wet grip performance and rolling resistance performance, and a tire using the same. [Means for solving the problem]

[0008] A rubber composition according to an embodiment of the present invention is a rubber composition comprising a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, and the rubber composition is vulcanized to obtain a vulcanized rubber stretched by 50%. The rubber composition is then subjected to small-angle X-ray scattering measurement to determine the radius of gyration V50 of the silica aggregates, and the vulcanized rubber is subjected to small-angle X-ray scattering measurement in an unstretched state. The rate of change in inter-aggregate distance, expressed as V50 / V0, is 1.30 or more.

[0009] The vulcanized rubber according to one embodiment of the present invention is obtained by vulcanizing a rubber composition containing a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, and has a rate of change in inter-aggregate distance, expressed as V50 / V0, calculated from the radius of gyration V50 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in a state stretched by 50%, and the radius of gyration V0 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in an unstretched state, of 1.30 or more.

[0010] In the rubber composition, the content of the silica may be 5 to 150 parts by mass relative to 100 parts by mass of the diene rubber. The content of the sulfur-containing silane coupling agent may be 1 to 15% by mass relative to the content of the silica. The content of the alkylalkoxysilane may be 10 to 300 mol% relative to the content of the sulfur-containing silane coupling agent. The sulfur-containing silane coupling agent may have a sulfide group. The alkylalkoxysilane may have an alkyl group having 3 to 20 carbon atoms. The vulcanized rubber may have silica orientation in an unstretched state. In this case, the radius of gyration V50 is a value obtained by small-angle X-ray scattering measurement in a state in which the vulcanized rubber is stretched 50% in a direction perpendicular to the silica orientation direction.

[0011] A tire according to an embodiment of the present invention is produced using the rubber composition for a tire. [Effects of the Invention]

[0012] According to an embodiment of the present invention, it is possible to improve the trade-off between wet grip performance and rolling resistance performance. [Brief explanation of the drawings]

[0013] [Figure 1] An example of a two-dimensional scattering image in small-angle X-ray scattering measurement. DETAILED DESCRIPTION OF THE INVENTION

[0014] The rubber composition according to the present embodiment contains a diene rubber as a rubber component, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane.

[0015] Diene rubber refers to rubber having repeating units corresponding to diene monomers with conjugated double bonds, and has double bonds in the polymer backbone. Specific examples of diene rubber include various diene rubbers commonly used in rubber compositions, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These may be used alone or in combination of two or more. The concept of diene rubber also includes those whose terminals or backbone have been modified as necessary (e.g., terminal-modified SBR) and those modified to impart desired properties (e.g., modified NR).

[0016] In one embodiment, the diene rubber preferably includes at least one selected from the group consisting of natural rubber, styrene-butadiene rubber, and butadiene rubber. More preferably, the diene rubber includes styrene-butadiene rubber. For example, 100 parts by mass of the diene rubber preferably includes 50 parts by mass or more of styrene-butadiene rubber, more preferably 70 parts by mass or more of styrene-butadiene rubber, and may include styrene-butadiene rubber alone.

[0017] The styrene butadiene rubber may be, for example, solution polymerized styrene butadiene rubber (SSBR) or emulsion polymerized styrene butadiene rubber (ESBR). As the styrene butadiene rubber, modified styrene butadiene rubber whose terminals or main chain are modified may also be used as necessary.

[0018] As the silica, it is preferable to use wet silica such as wet precipitation silica or wet gelation silica. The nitrogen adsorption specific surface area (BET) of the silica according to JIS K6430:2008 Appendix E (multipoint nitrogen adsorption method: BET method) is, for example, 150 to 250 m 2 The nitrogen adsorption specific surface area of ​​silica is preferably 180 to 220 m / g. 2 / g.

[0019] The content of silica is, for example, preferably 5 to 150 parts by mass, more preferably 30 to 120 parts by mass, and even more preferably 50 to 100 parts by mass, and may be 60 to 90 parts by mass, relative to 100 parts by mass of the diene rubber.

[0020] The sulfur-containing silane coupling agent is a silane coupling agent containing a sulfur atom in the molecule, and various sulfur-containing silane coupling agents that are compounded together with silica in rubber compositions can be used.

[0021] Specific examples of sulfur-containing silane coupling agents include: Sulfide silanes (bis-silane-based sulfide silane coupling agents) such as bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) tetrasulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, and bis(2-trimethoxysilylethyl) disulfide; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane, formula: HS-(CH2)3-Si(OC2H5) m (O(C2H4O) k -C 13 H 27 ) n Mercaptosilanes such as "VP Si363" manufactured by Evonik Degussa (wherein m is an average of 1, n is an average of 2, and k is an average of 5); Examples include protected mercaptosilanes (i.e., silane compounds having a thiol ester structure in which the mercapto group is protected with an acyl group) such as 3-octanoylthio-1-propyltriethoxysilane (formula: CH3(CH2)6C(=O)S-(CH2)3-Si(OC2H5)3) and 3-propionylthiopropyltrimethoxysilane. These sulfur-containing silane coupling agents can be used alone or in combination of two or more.

[0022] Among these, sulfur-containing silane coupling agents are preferably sulfide silanes having a sulfide group, more preferably those having a disulfide group.

[0023] The content of the sulfur-containing silane coupling agent is preferably, for example, 1 to 15 mass% relative to the content of silica. That is, the total amount of the sulfur-containing silane coupling agent is preferably 1 to 15 mass% relative to 100 mass% of silica. The content of the sulfur-containing silane coupling agent is more preferably 2 to 10 mass% relative to the content of silica, and may be 3 to 7 mass%.

[0024] The alkylalkoxysilane may be an alkyldialkoxysilane, but is preferably an alkyltrialkoxysilane. The alkylalkoxysilane preferably has an alkyl group having 3 to 20 carbon atoms, and specifically, an alkyltriethoxysilane represented by the following formula (1) is preferably used. In formula (1), R 1 represents an alkyl group having 3 to 20 carbon atoms. The alkyl group more preferably has 6 to 20 carbon atoms, and further preferably has 10 to 20 carbon atoms. [ka]

[0025] The content of the alkylalkoxysilane is, for example, preferably 10 to 300 mol %, more preferably 10 to 100 mol %, and even more preferably 10 to 50 mol %, relative to the content of the sulfur-containing silane coupling agent.

[0026] In the rubber composition according to this embodiment, the combined use of a sulfur-containing silane coupling agent and an alkylalkoxysilane as described above can improve the deformation compliance of the rubber polymer around the silica when the vulcanized rubber obtained by vulcanizing the rubber composition is deformed. This can increase the change in inter-aggregate distance during rubber deformation, making it easier to achieve a V50 / V0 value of 1.30 or greater, as described below. Furthermore, the improved deformation compliance can more easily achieve both wet grip performance and rolling resistance. Specifically, the alkylalkoxysilane hydrophobizes the silica surface, improving silica dispersibility, improving the rubber's compliance with external stimuli and improving wet grip performance. Furthermore, friction between silica particles is reduced, reducing energy loss and improving rolling resistance.

[0027] In addition to the above components, the rubber composition according to the present embodiment may contain various additives that are generally used in rubber compositions, such as fillers other than silica, zinc oxide, stearic acid, antioxidants, oils, waxes, vulcanizing agents, and vulcanization accelerators.

[0028] Carbon black may be blended as a filler in addition to silica. That is, the filler may be silica alone or a combination of silica and carbon black. Preferably, the filler is mainly composed of silica, and the content of carbon black is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of diene rubber.

[0029] As the vulcanizing agent, sulfur is preferably used. The content of the vulcanizing agent is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and may be 1 to 3 parts by mass, per 100 parts by mass of the diene rubber.

[0030] Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based accelerators, and any one of them can be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and may be 1 to 4 parts by mass, per 100 parts by mass of the diene rubber.

[0031] The rubber composition according to this embodiment can be prepared by kneading in accordance with a conventional method using a commonly used mixer such as a Banbury mixer, kneader, or roll, and an unvulcanized rubber composition can be prepared.

[0032] Preferably, in the first mixing stage, a sulfur-containing silane coupling agent is added and mixed with silica to a diene rubber, and then an alkylalkoxysilane is added and mixed to the resulting mixture in the second mixing stage. Then, in the third mixing stage (final mixing stage), vulcanization-related chemicals such as a vulcanizing agent and a vulcanization accelerator are added and mixed to the resulting mixture. That is, a preferred embodiment of the rubber composition is obtained by mixing a first mixture obtained by mixing silica and a sulfur-containing silane coupling agent with a diene rubber, mixing an alkylalkoxysilane, and then mixing the vulcanization-related chemicals with the second mixture obtained. By premixing the sulfur-containing silane coupling agent with the diene rubber and silica in this way and then adding and mixing the alkylalkoxysilane, the deformation compliance is improved, and the V50 / V0 value can be set to 1.30 or more, as shown in the examples described below.

[0033] In this case, the timing of mixing additives other than alkylalkoxysilane and vulcanization-related agents is not particularly limited, but it is preferable to add and mix them into the diene-based rubber together with silica and sulfur-containing silane coupling agent in the first mixing stage.

[0034] The rubber composition according to this embodiment has a rate of change in inter-aggregate distance, V50 / V0, of 1.30 or more when a vulcanized rubber obtained by vulcanizing the rubber composition is deformed from 0% to 50% elongation. The larger the rate of change, V50 / V0, the higher the ability of the rubber polymer around the silica to follow deformation during deformation of the vulcanized rubber, and the greater the trade-off between wet grip performance and rolling resistance performance can be improved. V50 / V0 is preferably 1.32 or more, more preferably 1.34 or more. The upper limit of V50 / V0 is not particularly limited, but is preferably 2.0 or less, more preferably 1.50 or less.

[0035] Here, V50 is the radius of gyration (nm) of silica aggregates obtained by small-angle X-ray scattering (SAXS) measurement of vulcanized rubber in a state stretched 50% in a direction perpendicular to the silica orientation direction. V0 is the radius of gyration (nm) of silica aggregates obtained by small-angle X-ray scattering measurement of vulcanized rubber in an unstretched state. The rate of change in inter-aggregate distance is the value (quotient) obtained by dividing the radius of gyration V50 at 50% stretch by the radius of gyration V0 at 0% stretch.

[0036] The orientation direction of silica can be confirmed by performing SAXS measurement on unstretched vulcanized rubber. For vulcanized rubber in which silica is not oriented in the unstretched state (i.e., vulcanized rubber that does not show anisotropy in the two-dimensional scattering image), SAXS measurement is performed while the rubber is stretched 50% in any direction. That is, for vulcanized rubber in which silica is oriented (i.e., anisotropic) in the unstretched state, V50 is the radius of gyration of silica aggregates obtained by SAXS measurement while the rubber is stretched 50% in a direction perpendicular to the orientation direction. For vulcanized rubber that does not show anisotropy in the unstretched state, V50 is the radius of gyration of silica aggregates obtained by SAXS measurement while the rubber is stretched 50% in any direction.

[0037] The values ​​of V0 and V50 may be, for example, 1.0 to 100 nm, 5.0 to 50 nm, or 10 to 40 nm.

[0038] V0 and V50 are values ​​obtained by measuring a vulcanized rubber obtained by vulcanizing a rubber composition. Therefore, in this embodiment, the vulcanized rubber may have a V50 / V0 ratio of 1.30 or more. That is, the vulcanized rubber according to one embodiment is obtained by vulcanizing a rubber composition containing a diene rubber and silica, and has a V50 / V0 ratio of 1.30 or more. The vulcanized rubber may constitute a part of a rubber product such as a tire, or may constitute the entire rubber product.

[0039] The radius of gyration of silica aggregates can be obtained by irradiating vulcanized rubber with X-rays and measuring small-angle X-ray scattering. Small-angle X-ray scattering (SAXS) is a technique for measuring scattered X-rays at a scattering angle of a few degrees or less (usually 10 degrees or less). When X-rays are irradiated onto vulcanized rubber, the X-rays are scattered, reflecting the electron density of the substances that make up the vulcanized rubber. The radius of gyration of silica aggregates can be determined from the scattering profile obtained.

[0040] Specifically, the radius of gyration is determined by the method described in Japanese Patent No. 6578200. 10 (photons / s / mrad 2 / mm 2Small-angle X-ray scattering measurements are performed using high-intensity X-rays (e.g., 0.1% bw or higher) to obtain a two-dimensional scattering image showing the magnitude of scattering intensity, as shown in Figure 1. In Figure 1, white indicates higher scattering intensity, while black indicates lower scattering intensity, with the contours shown by white (dotted) lines. The black portion at the scattering center and the black line extending downward from it are shadows cast by a beam stopper. The two-dimensional scattering image has constricted portions on both sides of the scattering center, and the left-right direction of these constricted portions corresponds to the silica orientation direction. A one-dimensional scattering profile is obtained by averaging (circular averaging) the scattering intensity of the two-dimensional scattering image over a predetermined angle range β = 30° (a 15° range on each side of the elongation direction) in the direction perpendicular to the silica orientation direction (fan-shaped portion). The scattering profile is a curve showing the magnitude of the scattering intensity I(q) versus the scattering vector q (= (4π / λ) sin(θ / 2), where θ is the scattering angle and λ is the X-ray wavelength). The radius of gyration of the silica aggregate is determined by fitting to the obtained scattering profile. When V0 is determined for vulcanized rubber that has no anisotropy in the unstretched state, the above circular average is taken over an angle range β = 30° centered on the stretching direction when V50 is measured.

[0041] As described in Japanese Patent No. 6578200, the radius of gyration calculated from the angular range β of the sector portion increases with increasing elongation, and is significantly influenced by the structural factor (spatial structural information of the filler). Therefore, the radius of gyration calculated from the angular range β of the sector portion can be used to measure the change in the radius of gyration due to differences in elongation, and can be used as an indicator of the deformation followability of the rubber polymer around the filler. Therefore, in this embodiment, the radius of gyration V0 measured at unstretched (i.e., 0% elongation) and the radius of gyration V50 measured at 50% elongation are calculated, and the ratio of the two is calculated. This ratio, V50 / V0, is defined as the rate of change in the inter-aggregate distance. Details of the measurement conditions for small-angle X-ray scattering measurement and the method for calculating the radius of gyration are described in the Examples below.

[0042] The rubber composition according to the present embodiment can be suitably used as a rubber composition for tires, such as pneumatic tires of various sizes and for various uses, including tires for passenger cars and heavy-duty tires for trucks and buses.

[0043] A tire according to one embodiment is a tire manufactured using the rubber composition. That is, the tire includes a vulcanized rubber made of the rubber composition. Examples of the application site of the tire include tread rubber and sidewall rubber, and the tread rubber is preferred.

[0044] The tread rubber of a tire may have a two-layer structure of a cap rubber and a base rubber, or a single-layer structure in which the two are integrated. In the single-layer structure, the tread rubber may be formed from the above-mentioned rubber composition. In the two-layer structure, the outer cap rubber that comes into contact with the road surface may be formed from the above-mentioned rubber composition, the base rubber disposed inside the cap rubber may be formed from the above-mentioned rubber composition, or both the cap rubber and the base rubber may be formed from the above-mentioned rubber composition.

[0045] The method for producing a tire is not particularly limited. For example, the rubber composition is extruded into a predetermined shape according to a conventional method, and then combined with other components to produce an unvulcanized tire (green tire). For example, tread rubber is produced using the rubber composition, and then combined with other tire components to produce an unvulcanized tire. Thereafter, a tire can be produced by vulcanizing and molding at, for example, 140 to 180°C. [Example]

[0046] Examples will be shown below, but the present invention is not limited to these examples.

[0047] Rubber compositions were prepared according to the formulations (parts by mass) listed in Tables 1 and 2 below. Specifically, a diene rubber was masticated for 30 seconds using a Daihan Corporation lab mixer (300 cc). All ingredients except the alkylalkoxysilane and vulcanization-related agents (sulfur, vulcanization accelerator) were then added to the lab mixer and mixed for 240 seconds before being discharged. The discharged mixture was then added to the lab mixer together with the alkylalkoxysilane, mixed for 180 seconds, and discharged. The discharged mixture was then added to the lab mixer together with the sulfur and vulcanization accelerator, mixed for 60 seconds, and discharged. The resulting unvulcanized rubber composition was sheeted to a thickness of 1.0 mm using a two-roll mill, and then subjected to a vulcanization press at 160°C for 20 minutes to obtain a vulcanized rubber sample with a thickness of 1.0 mm.

[0048] Details of each component in Tables 1 and 2 are as follows: S-SBR: JSR Corporation "HPR350", amino-terminated solution-polymerized SBR Silica: Tosoh Corporation's "Nipsil AQ" (nitrogen adsorption specific surface area 205 m 2 / g) Sulfur-containing silane coupling agent: Evonik Japan Co., Ltd. "Si75", bis(3-triethoxysilylpropyl) disulfide Alkylalkoxysilane 1: Propyltriethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd. Alkylalkoxysilane 2: Hexyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. Alkylalkoxysilane 3: Octadecyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. Zinc oxide: "Zinc oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. Vulcanization accelerator 2: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0049] The rate of change in inter-aggregate distance, V50 / V0, was calculated for the obtained vulcanized rubber sample. The measurement method is as follows.

[0050] Based on the method described in Japanese Patent No. 6578200, SAXS measurements were performed at elongation rates of 0% and 50%, taking into account the silica orientation direction. Specifically, using a double-ended tensile device that can be fixed at any strain, the sample was first fixed at an elongation rate of 0%, and then irradiated with X-rays to perform SAXS measurements. Next, based on the silica orientation direction confirmed by this measurement, the sample was elongated by 50% in the direction perpendicular to the orientation direction and fixed, and then irradiated with X-rays to perform SAXS measurements.

[0051] The SAXS measurements were performed using the beamline BL08B2 of SPring-8 at the Japan Synchrotron Radiation Research Institute as a synchrotron emitting high-brilliance X-rays under the following measurement conditions. Incident X-ray wavelength: 0.15 nm Camera length: 6m Exposure time: 1 second q range: 0.015~0.8nm -1 Detector: PILATUS

[0052] From the two-dimensional scattering image obtained by small-angle X-ray scattering measurement, the scattering intensity was circularly averaged over an angle range of β = 30° (see Figure 1) in the direction perpendicular to the orientation direction (meridian direction) to obtain a one-dimensional scattering profile. The radius of gyration of the silica aggregate was calculated by fitting to the obtained scattering profile. The radius of gyration calculated at an elongation rate of 0% was defined as V0, and the radius of gyration calculated at an elongation rate of 50% was defined as V50. The rate of change in the inter-aggregate distance, V50 / V0, was calculated. Note that if there is no constriction in the two-dimensional scattering image at an elongation rate of 0% (i.e., no anisotropy), V0 was calculated by circular averaging over an angle range of β = 30° in any direction, and then V50 was calculated by elongating 50% in that direction.

[0053] The fitting was performed by the least squares method using the following fitting function (source: G. Beaucage, J. Appl. Cryst. 28, 717-728 (1995)).

number

[0054] Furthermore, the unvulcanized rubber compositions obtained above were used to measure wet grip performance (wet) and rolling resistance (RR) using samples vulcanized at 160°C for 20 minutes, and the balance between the two (wet / RR index) was evaluated. The measurement and evaluation methods were as follows:

[0055] [Wet grip performance] Using a viscoelasticity tester manufactured by Ueshima Seisakusho Co., Ltd., the loss factor tan δ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 0°C. The values ​​are expressed as an index, with the value for Comparative Example 1 in Table 1 and the value for Comparative Example 3 in Table 2 being set at 100. The larger the index, the larger the tan δ, indicating better wet grip performance when made into a tire.

[0056] [Rolling resistance performance] Using a viscoelasticity tester manufactured by Ueshima Seisakusho Co., Ltd., the loss factor tan δ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 60°C. In Table 1, the value for Comparative Example 1 is set to 100, and in Table 2, the value for Comparative Example 3 is set to 100, and the results are expressed as an index. The smaller the index, the smaller the tan δ, indicating better rolling resistance performance when made into a tire.

[0057] [wet / RR index] The tan δ value at 0°C, which is the wet grip performance (wet) measured above, was divided by the tan δ value at 60°C, which is the rolling resistance performance (RR), and the index of the obtained value (wet / RR index) was taken as the balance performance. In Table 1, the value of Comparative Example 1 and in Table 2, the value of Comparative Example 3 were each expressed as an index, with each index being set to 100. The larger the index, the greater the effect of improving the trade-off between wet grip performance and rolling resistance performance, indicating superiority in these performances.

[0058] [Table 1]

[0059] [Table 2]

[0060] The results are shown in Tables 1 and 2. As shown in Table 1, in Examples 1 to 6, in which V50 / V0 was 1.30 or more, the rubber polymer around the silica had excellent deformation followability when the vulcanized rubber was deformed, and therefore the wet / RR index was larger than in Comparative Example 1, improving the trade-off between wet grip performance and rolling resistance performance and achieving both performances at a high level.

[0061] In the experimental examples shown in Table 2, the amount of silica compounded was 50 parts by mass per 100 parts by mass of diene rubber, which was a smaller amount than in the experimental examples shown in Table 1. In this case as well, Examples 7 to 11, in which V50 / V0 was 1.30 or more, had a larger wet / RR index than the benchmark Comparative Example 2, and were able to achieve both wet grip performance and rolling resistance performance at a high level.

[0062] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

Claims

1. A rubber composition comprising a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, the sulfur-containing silane coupling agent is a bis-silane disulfide silane coupling agent, the content of the silica is 50 to 100 parts by mass based on 100 parts by mass of the diene rubber, the content of the sulfur-containing silane coupling agent is 2 to 10% by mass based on the content of the silica, and the content of the alkylalkoxysilane is 10 to 300 mol % based on the content of the sulfur-containing silane coupling agent, A rubber composition, wherein the rate of change in inter-aggregate distance, expressed as V50 / V0, calculated from the radius of gyration V50 of silica aggregates obtained by small-angle X-ray scattering measurement of a vulcanized rubber obtained by vulcanizing the rubber composition and stretching the vulcanized rubber by 50% and the radius of gyration V0 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in an unstretched state, is 1.30 or more.

2. 2. The rubber composition according to claim 1, wherein the alkylalkoxysilane has an alkyl group having 3 to 20 carbon atoms.

3. 3. The rubber composition according to claim 1, wherein the vulcanized rubber has silica orientation in an unstretched state, and the radius of gyration V50 is a value obtained by small-angle X-ray scattering measurement in a state where the vulcanized rubber is stretched 50% in a direction perpendicular to the silica orientation direction.

4. A pneumatic tire produced using the rubber composition according to any one of claims 1 to 3.

5. A vulcanized rubber obtained by vulcanizing a rubber composition containing a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, the sulfur-containing silane coupling agent is a bis-silane disulfide silane coupling agent, the content of the silica is 50 to 100 parts by mass based on 100 parts by mass of the diene rubber, the content of the sulfur-containing silane coupling agent is 2 to 10% by mass based on the content of the silica, and the content of the alkylalkoxysilane is 10 to 300 mol % based on the content of the sulfur-containing silane coupling agent, A vulcanized rubber in which the rate of change in inter-aggregate distance, expressed as V50 / V0, calculated from the radius of gyration V50 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in a state stretched by 50% and the radius of gyration V0 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in an unstretched state, is 1.30 or more.

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