JP7794631B2 - Rubber composition and tire - Google Patents

Description

The present invention relates to a rubber composition and a tire using the same.

Tires are required to achieve both wet grip performance, which is grip performance on wet road surfaces, and rolling resistance performance, which contributes to fuel economy. Therefore, for example, Patent Document 1 proposes compounding a silane coupling agent with polyethylene glycol in its main chain skeleton in a silica-containing rubber composition to improve low electrical resistance, low rolling resistance, wet grip performance, mechanical strength, and processability.

Patent Document 2 describes compounding alkyltriethoxysilane together with a silane coupling agent having a mercapto group in a rubber composition containing silica in order to produce a tire with excellent wet performance and rolling resistance.

Patent Document 3 describes a method for producing a rubber composition by preparing a mixture of two types of rubber containing different silane coupling agents and mixing them together in order to improve processability and low heat buildup.

As such, various proposals have been made to improve wet grip performance and rolling resistance. However, wet grip performance and rolling resistance are mutually exclusive properties; improving one results in a decrease in the other, making it difficult to achieve both.

Patent No. 3908368 Patent No. 4930661 Patent No. 6385655

An embodiment of the present invention aims to provide a rubber composition that can improve the trade-off between wet grip performance and rolling resistance, and a tire using the same.

A rubber composition according to an embodiment of the present invention comprises a diene rubber, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane, and the rubber composition is vulcanized to form a vulcanized rubber. The rubber composition is then vulcanized to form a vulcanized rubber stretched 50%. The vulcanized rubber has a radius of gyration V50 of silica aggregates measured by small-angle X-ray scattering, and the vulcanized rubber is unstretched to form a vulcanized rubber. The ratio of change in inter-aggregate distance, expressed as V50/V0, calculated from the radius of gyration V50 of silica aggregates measured by small-angle X-ray scattering, is 1.30 or greater.

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 50% elongated state and the radius of gyration V0 of silica aggregates obtained by small-angle X-ray scattering measurement of the vulcanized rubber in an unelongated state, of 1.30 or greater.

In the rubber composition, the silica content may be 5 to 150 parts by mass per 100 parts by mass of the diene rubber. The sulfur-containing silane coupling agent content may be 1 to 15 mass % relative to the silica content. The alkylalkoxysilane content may be 10 to 300 mol % relative to the sulfur-containing silane coupling agent content. 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 while the vulcanized rubber is stretched 50% in a direction perpendicular to the silica orientation direction.

A tire according to an embodiment of the present invention is manufactured using the above-described rubber composition for tires.

Embodiments of the present invention can improve the trade-off between wet grip performance and rolling resistance.

FIG. 1 is a diagram showing an example of a two-dimensional scattering image in small-angle X-ray scattering measurement.

The rubber composition according to this embodiment contains a diene rubber as a rubber component, silica, a sulfur-containing silane coupling agent, and an alkylalkoxysilane.

Diene rubber refers to rubber containing repeating units corresponding to diene monomers with conjugated double bonds, with double bonds in the polymer backbone. Specific examples of diene rubber include 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, all of which are commonly used in rubber compositions. These may be used alone or in combination. The concept of diene rubber also includes those whose terminals or backbone have been modified as needed (e.g., terminal-modified SBR) and those modified to impart desired properties (e.g., modified NR).

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 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.

Styrene butadiene rubber may be, for example, solution-polymerized styrene butadiene rubber (SSBR) or emulsion-polymerized styrene butadiene rubber (ESBR). If necessary, modified styrene butadiene rubber, in which the terminals or main chain have been modified, may also be used.

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 preferably 150 to 250 m ² /g, for example. The nitrogen adsorption specific surface area of the silica is more preferably 180 to 220 m ² /g.

The silica content 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, per 100 parts by mass of diene rubber.

A sulfur-containing silane coupling agent is a silane coupling agent that contains a sulfur atom in its molecule, and various sulfur-containing silane coupling agents that are compounded together with silica in rubber compositions can be used.

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;
mercaptosilanes such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane, and "VP Si363" manufactured by Evonik Degussa and represented by the formula: HS-(CH ₂ ) ₃ -Si(OC ₂ H ₅ ) _m (O(C ₂ H ₄ O) _k -C ₁₃ H ₂₇ ) _n (wherein m is 1 on average, n is 2 on average, and k is 5 on average);
and protected mercaptosilanes (i.e., silane compounds having a thiol ester structure in which a 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 either alone or in combination of two or more.

Among these, sulfur-containing silane coupling agents are preferably sulfide silanes containing sulfide groups, and more preferably those containing disulfide groups.

The content of the sulfur-containing silane coupling agent is preferably, for example, 1 to 15 mass% relative to the silica content. In other words, the total amount of sulfur-containing silane coupling agent is preferably 1 to 15 mass parts per 100 mass parts of silica. The content of the sulfur-containing silane coupling agent is more preferably 2 to 10 mass% relative to the silica content, and may be 3 to 7 mass%.

The alkylalkoxysilane may be an alkyldialkoxysilane, but an alkyltrialkoxysilane is preferred. 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), ^R1 represents an alkyl group having 3 to 20 carbon atoms. The number of carbon atoms in the alkyl group is more preferably 6 to 20, and even more preferably 10 to 20.

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

In the rubber composition according to this embodiment, the combined use of a sulfur-containing silane coupling agent and an alkylalkoxysilane as described above improves the deformation compliance of the rubber polymer around the silica when the vulcanized rubber obtained by vulcanizing the rubber composition is deformed. This increases 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, improved deformation compliance makes it easier to achieve both wet grip performance and rolling resistance. Specifically, the alkylalkoxysilane hydrophobizes the silica surface, improving silica dispersibility and improving the rubber's compliance with external stimuli, resulting in improved wet grip performance. Furthermore, friction between silica particles is reduced, reducing energy loss and improving rolling resistance.

In addition to the above components, the rubber composition according to this embodiment can contain various additives commonly used in rubber compositions, such as fillers other than silica, zinc oxide, stearic acid, antioxidants, oils, waxes, vulcanizing agents, and vulcanization accelerators.

In addition to silica, carbon black may be compounded as a filler. That is, the filler may be silica alone or a combination of silica and carbon black. Preferably, the filler is primarily composed of silica, and the carbon black content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of diene rubber.

Sulfur is preferably used as the vulcanizing agent. There are no particular limitations on the amount of vulcanizing agent used, but it 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 diene rubber.

Vulcanization accelerators include, for example, sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators, and any of these may 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 diene rubber.

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

Preferably, in the first mixing stage, a sulfur-containing silane coupling agent is added and mixed with silica to the 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 rubber composition is obtained by mixing an alkylalkoxysilane with a first mixture obtained by mixing silica and a sulfur-containing silane coupling agent with a diene rubber, 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 greater, as shown in the examples described below.

In this case, there are no particular restrictions on the timing of mixing additives other than the alkylalkoxysilane and vulcanization agent, but it is preferable to add and mix them into the diene rubber together with the silica and sulfur-containing silane coupling agent in the first mixing stage.

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 an elongation rate of 0% to 50%. The higher the rate of change, V50/V0, the higher the ability of the rubber polymer around the silica to follow deformation when the vulcanized rubber is deformed, and the trade-off between wet grip performance and rolling resistance can be improved. V50/V0 is preferably 1.32 or more, and more preferably 1.34 or more. There is no particular upper limit for V50/V0, but it is preferably 2.0 or less, and more preferably 1.50 or less.

Here, V50 is the radius of gyration (nm) of silica aggregates obtained by small-angle X-ray scattering (SAXS) measurement of vulcanized rubber 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.

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 exhibit anisotropy in the two-dimensional scattering image), SAXS measurement is performed after 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 after the rubber is stretched 50% in a direction perpendicular to the orientation direction. For vulcanized rubber that does not exhibit anisotropy in the unstretched state, V50 is the radius of gyration of silica aggregates obtained by SAXS measurement after the rubber is stretched 50% in any direction.

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.

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 greater. 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 greater. The vulcanized rubber may constitute a part of a rubber product such as a tire, or may constitute the entire rubber product.

The radius of gyration of silica aggregates can be obtained by irradiating vulcanized rubber with X-rays and performing small-angle X-ray scattering measurements. 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° 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 resulting scattering profile.

Specifically, the radius of gyration can be determined by the method described in Japanese Patent No. 6,578,200. Specifically, by irradiating vulcanized rubber with high-intensity X-rays of 10 ¹⁰ (photons/s/mrad ² /mm ² /0.1% bw) or more and performing small-angle X-ray scattering measurement, a two-dimensional scattering image showing the magnitude of scattering intensity, as shown in Figure 1, is obtained. In Figure 1, white indicates higher scattering intensity, while black indicates lower scattering intensity, and the contour lines are shown as white (dotted) lines. Note that the black part at the scattering center and the black line extending downward from it are the shadow created by the 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 in a predetermined angle range β = 30° (a range of 15° on each side of the elongation direction centered on the elongation direction) in a direction perpendicular to the silica orientation direction (sector portion) of the two-dimensional scattering image. 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 wavelength of the X-ray). 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 an unstretched state, the above circular average is taken over an angle range β=30° centered on the stretching direction when V50 is measured.

As described in Japanese Patent No. 6,578,200, the radius of gyration calculated from the angular range β of the sector portion increases as the elongation rate increases, and the structural factor (spatial structural information of the filler) has a significant influence. Therefore, by using the radius of gyration calculated from the angular range β of the sector portion to observe changes in the radius of gyration due to differences in elongation rate, it 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 rate) and the radius of gyration V50 measured at 50% elongation rate 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 section below.

The rubber composition according to this embodiment can be suitably used as a rubber composition for tires. Examples of tires include pneumatic tires of various sizes and for various uses, such as tires for passenger cars and heavy-duty tires for trucks and buses.

A tire according to one embodiment is a tire made using the above rubber composition. That is, the tire is provided with vulcanized rubber made from the above rubber composition. Examples of tire applications include tread rubber and sidewall rubber, with tread rubber being preferred.

Tire tread rubber can be made of either a two-layer structure consisting of cap rubber and base rubber, or a single-layer structure in which the two are integrated. In the case of a single-layer structure, the tread rubber may be formed from the above-mentioned rubber composition. In the case of a 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 placed inside the cap rubber may be formed from the above-mentioned rubber composition, or both the cap rubber and base rubber may be formed from the above-mentioned rubber composition.

The method for manufacturing a tire is not particularly limited. For example, the rubber composition is molded into a predetermined shape by extrusion processing according to conventional methods, and then combined with other components to produce an unvulcanized tire (green tire). For example, tread rubber is made using the rubber composition, and then combined with other tire components to produce an unvulcanized tire. The tire can then be manufactured by vulcanizing and molding at, for example, 140 to 180°C.

The following examples are provided, but the present invention is not limited to these examples.

A rubber composition was prepared according to the formulation (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 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 1.0 mm thick vulcanized rubber sample.

Details of each component in Tables 1 and 2 are as follows:
S-SBR: "HPR350" manufactured by JSR Corporation, amino group-terminated solution polymerized SBR
Silica: "Nipsil AQ" manufactured by Tosoh Corporation (nitrogen adsorption specific surface area: 205 m ² /g)
Sulfur-containing silane coupling agent: "Si75" manufactured by Evonik Japan Co., Ltd., bis(3-triethoxysilylpropyl) disulfide alkylalkoxysilane 1: manufactured by Tokyo Chemical Industry Co., Ltd., propyltriethoxysilane alkylalkoxysilane 2: manufactured by Tokyo Chemical Industry Co., Ltd., hexyltriethoxysilane alkylalkoxysilane 3: manufactured by Tokyo Chemical Industry Co., Ltd., octadecyltriethoxysilane zinc oxide: "Zinc Oxide No. 3" manufactured by Mitsui Mining & Smelting Co., Ltd.
Stearic acid: "Lunac S-20" manufactured by Kao Corporation
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.

The rate of change in inter-aggregate distance, V50/V0, was calculated for the resulting vulcanized rubber samples. The measurement method was as follows:

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 orientation direction of the silica. 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 in that state, the sample was irradiated with X-rays and SAXS measurements were performed. Next, based on the orientation direction of the silica confirmed by this measurement, the sample was elongated by 50% in the direction perpendicular to the orientation direction and fixed, and in that state, SAXS measurements were performed by irradiating the sample with X-rays.

The SAXS measurement was carried out using the beamline BL08B2 of SPring-8 at the Japan Synchrotron Radiation Research Institute as a synchrotron emitting high-intensity X-rays under the following measurement conditions.
Wavelength of incident X-rays: 0.15 nm
・Camera length: 6m
Exposure time: 1 second q range: 0.015 to 0.8 ^nm
・Detector: PILATUS

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 determined by fitting to the obtained scattering profile. The radius of gyration determined at an elongation rate of 0% was defined as V0, and the radius of gyration determined at an elongation rate of 50% as V50, and the rate of change in inter-aggregate distance, V50/V0, was calculated. Note that if there was no constriction in the two-dimensional scattering image at an elongation rate of 0% (i.e., no anisotropy), V0 was determined by circular averaging over an angle range of β = 30° in any direction, and then V50 was determined by elongating 50% in that direction.

The fitting was performed by the least squares method using the following fitting function (source: G. Beaucage, J. Appl. Cryst. 28, 717-728 (1995)).
where I(q) is the scattering intensity, Gi, Bi, k, Pi are regression coefficients, q is the scattering vector and the independent variable, and Rgi represents the aggregate radius (radius of gyration of silica aggregates).

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

[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, a static strain of 10%, a dynamic strain of 1%, and a 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.

[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, a static strain of 10%, a dynamic strain of 1%, and a temperature of 60° 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 smaller the index, the smaller the tan δ, indicating better rolling resistance performance when made into a tire.

[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 the index being 100. The larger the index, the greater the effect of improving the trade-off between wet grip performance and rolling resistance performance, indicating that these performances are excellent.

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

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, a smaller amount than in the experimental examples shown in Table 1. In this case, too, Examples 7 to 11, in which V50/V0 was 1.30 or higher, had a larger wet/RR index than the benchmark Comparative Example 2, and were able to achieve both high levels of wet grip performance and rolling resistance performance.

The various numerical ranges described in this specification can each be combined with any upper and lower limit, and all such combinations are considered to be preferred numerical ranges and are described in this specification. Furthermore, a numerical range described as "X to Y" means greater than or equal to X and less than or equal to Y.

Claims (5)

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. The rubber composition according to claim 1 , wherein the alkylalkoxysilane has an alkyl group having 3 to 20 carbon atoms. 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. A pneumatic tire made using the rubber composition according to any one of claims 1 to 3 . 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.