Rubber composition and tire

Abstract

To provide a rubber composition capable of improving conflicting performances of a wet-grip performance and rigidity.SOLUTION: A rubber composition includes diene rubber and silica. In the rubber composition, a value Dm / Rg is 0.20nm-1 or more, the value obtained by using the inertial radius Rg of a silica aggregate obtained by a small angle X-ray scattering measurement through irradiating, with X-rays, vulcanized rubber obtained by vulcanizing the rubber composition and a mass fractal dimension Dm of the silica aggregate obtained by a super-small angle X-ray scattering measurement through irradiating the vulcanized rubber with X-rays, and dividing the mass fractal dimension Dm by the inertial radius Rg.SELECTED DRAWING: None

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 improved wet grip performance, which is the grip performance on wet road surfaces, and therefore, various proposals have been made to improve the wet grip performance of rubber compositions used in tires.

[0003] For example, Patent Document 1 describes that a rubber composition containing a conjugated diene polymer whose terminals have been reacted with an alkoxysilane compound is blended with a special silica having a branched structure, thereby improving fuel economy, wet grip performance, and abrasion resistance.

[0004] Patent Document 2 describes that dry silica treated with silicone oil is compounded into a rubber composition together with a silane coupling agent, thereby improving low rolling resistance, wet performance, and rubber hardness.

[0005] However, wet grip performance and hardness are trade-offs, and it is difficult to achieve both at the same time, since increasing hardness reduces wet grip performance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-105242 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-104840 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 capable of improving the trade-off between wet grip performance and hardness, 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 containing a diene rubber and silica, and the rubber composition is vulcanized. The rubber composition is vulcanized, and the vulcanized rubber is subjected to small-angle X-ray scattering measurement to obtain a radius of gyration Rg of the silica aggregate. The vulcanized rubber is irradiated with X-rays, and the vulcanized rubber is subjected to ultra-small-angle X-ray scattering measurement. The value Dm / Rg obtained by dividing the mass fractal dimension Dm by the radius of gyration Rg is 0.20 nm. -1 That's all.

[0009] A vulcanized rubber according to one embodiment of the present invention is obtained by vulcanizing a rubber composition containing a diene rubber and silica, and the vulcanized rubber is irradiated with X-rays and subjected to small-angle X-ray scattering measurement to obtain a radius of gyration Rg of silica aggregates. The vulcanized rubber is irradiated with X-rays and subjected to ultra-small-angle X-ray scattering measurement to obtain a mass fractal dimension Dm of silica aggregates. The value Dm / Rg obtained by dividing the mass fractal dimension Dm by the radius of gyration Rg is 0.20 nm. -1 That's all.

[0010] The rubber composition may further contain a nitrogen-containing alkoxysilane and an alkylalkoxysilane. The content of the silica may be 5 to 150 parts by mass relative to 100 parts by mass of the diene rubber. The total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane may be 3 to 15 mass% relative to the content of the silica. The content ratio of the nitrogen-containing alkoxysilane in the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane may be 10 to 80 mol%. The nitrogen-containing alkoxysilane may have at least one functional group selected from the group consisting of an amino group, a ureido group, an isocyanate group, a cyano group, an azide group, and an amide group.

[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 hardness. [Brief explanation of the drawings]

[0013] [Figure 1] An example of a two-dimensional scattering image in small-angle X-ray scattering measurement. [Figure 2] An example of a scattering profile in ultra-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 and silica.

[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 rubber composition according to the present embodiment may further contain a nitrogen-containing alkoxysilane and an alkylalkoxysilane. -1The reason for this is thought to be as follows: By using a nitrogen-containing alkoxysilane in combination with an alkylalkoxysilane, it is possible to hydrophobize the silica surface while maintaining a portion of the surface hydrophilic. In other words, the alkylalkoxysilane hydrophobizes the silica surface, improving the dispersibility of the silica, which is thought to reduce the size of the silica aggregate (Rg). In addition, the hydrogen bonding sites in the nitrogen-containing alkoxysilane act as intermediaries between the dispersed silica particles, making it easier to maintain a certain higher-order structure, i.e., the mass fractal dimension (Dm).

[0021] Above-mentioned nitrogen-containing alkoxysilane is the alkoxysilane that contains nitrogen atom in molecule.As nitrogen-containing alkoxysilane, for example, can be selected from the group consisting of amino group, ureido group, isocyanate group, cyano group, azide group and amide group, and the compound that has the alkoxy group that is bonded to silicon atom, and can use the one that contains nitrogen atom in molecule among the ones that are generally called silane coupling agent.

[0022] Specific examples of nitrogen-containing alkoxysilanes include aminoalkoxysilanes such as 3-aminopropylalkoxysilane (e.g., 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane), and 3-(2-aminoethylamino)propylalkoxysilane (e.g., 3-(2-aminoethylamino)propyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane); ureidoalkoxysilanes such as 3-ureidopropylalkoxysilanes (e.g., 3-ureidopropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropylmethyldimethoxysilane, 3-ureidopropylmethyldiethoxysilane), 2-ureidoethylalkoxysilanes (e.g., 2-ureidoethyltrimethoxysilane, 2-ureidoethyltriethoxysilane, 2-ureidoethylmethyldimethoxysilane), and ureidomethylalkoxysilanes (e.g., ureidomethyltrimethoxysilane, ureidomethylmethyldimethoxysilane, ureidomethyltriethoxysilane, ureidomethylmethyldiethoxysilane); Isocyanate alkoxysilanes such as 3-isocyanatepropylalkoxysilane (e.g., 3-isocyanatepropyltriethoxysilane, 3-isocyanatepropyltripropoxysilane), 2-isocyanateethylalkoxysilane (e.g., 2-isocyanateethyltrimethoxysilane, 2-isocyanateethyltriethoxysilane), and isocyanatemethylalkoxysilane (e.g., isocyanatemethyltrimethoxysilane, isocyanatemethyltriethoxysilane); cyanoalkoxysilanes such as 3-cyanopropylalkoxysilane (e.g., 3-cyanopropyltrimethoxysilane, 3-cyanopropyltriethoxysilane); azidoalkoxysilanes such as 3-azidopropylalkoxysilane (e.g., 3-azidopropyltriethoxysilane, 3-azidopropyltrimethoxysilane), and 11-azidoundecylalkoxysilane (e.g., 11-azidoundecyltrimethoxysilane); Examples include amide bond-containing alkoxysilanes such as triethoxysilylpropylmaleamic acid.These can be used alone or in combination of two or more.

[0023] 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 even more preferably has 10 to 20 carbon atoms. [ka]

[0024] The total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane in the rubber composition is preferably, for example, 3 to 15 mass% relative to the silica content. That is, the total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane is preferably 3 to 15 mass parts relative to 100 mass parts of silica. The total content of the nitrogen-containing alkoxysilane and alkylalkoxysilane is more preferably 5 to 12 mass%, and even more preferably 8 to 12 mass%, relative to the silica content.

[0025] The compounding ratio of the nitrogen-containing alkoxysilane to the alkylalkoxysilane is, for example, preferably 10 to 80 mol %, more preferably 20 to 60 mol %, and even more preferably 25 to 50 mol %, of the nitrogen-containing alkoxysilane in the total content of both.

[0026] 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, vulcanization accelerators, etc. Although a sulfur-containing silane coupling agent, which is usually compounded when compounding silica, may be compounded, in one embodiment, it is preferable not to compound a sulfur-containing silane coupling agent.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The rubber composition according to this embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing stage (non-pro kneading step), additives other than the vulcanizing agent and vulcanization accelerator are added to and mixed with the diene rubber along with silica. Then, in the final mixing stage (pro kneading step), the vulcanizing agent and vulcanization accelerator are added to and mixed with the resulting mixture. This allows the preparation of an unvulcanized rubber composition.

[0031] The rubber composition according to the present embodiment has a quotient (Dm / Rg) of 0.20 nm obtained by dividing the mass fractal dimension Dm of the silica aggregate by the radius of gyration Rg (nm) of the silica aggregate. -1 or more. The larger the Dm / Rg, the smaller the Rg and the larger the Dm. A small Rg means that the silica is highly dispersible, and improved silica dispersibility can improve wet grip performance. A large Dm also means that the silica maintains a high-order structure, which enhances the reinforcing effect of silica and improves rubber hardness. Therefore, the larger the Dm / Rg, the easier it is to achieve both wet grip performance and hardness, and a Dm / Rg of 0.20 nm or less is considered to be acceptable. -1 This improves the trade-off between wet grip performance and hardness. Dm / Rg is 0.21 nm. -1 The upper limit of Dm / Rg is not particularly limited, and is, for example, 2.0 nm. -1 Less than 1.0 nm is acceptable. -1 Less than 0.50 nm is acceptable. -1 Less than 0.30 nm is acceptable. -1 Here, the value of Dm / Rg has two significant digits and is rounded off.

[0032] The value of Dm is preferably, for example, 2.0 to 3.5, more preferably 2.5 to 3.5, and may be 2.8 to 3.3. The value of Rg may be, for example, 1.0 to 20 nm, 5.0 to 20 nm, or 10 to 17.5 nm.

[0033] The above Dm and Rg are values ​​obtained by measuring a vulcanized rubber obtained by vulcanizing a rubber composition. -1 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 Dm / Rg of 0.20 nm or more. -1 The vulcanized rubber may be a part of a rubber product such as a tire, or may be the entire rubber product.

[0034] Here, the radius of gyration Rg of the silica aggregate is obtained by irradiating the vulcanized rubber with X-rays and measuring it with small-angle X-ray scattering, and the mass fractal dimension Dm of the silica aggregate is obtained by irradiating the vulcanized rubber with X-rays and measuring it with ultra-small-angle X-ray scattering.

[0035] 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 vulcanized rubber is irradiated with X-rays, the X-rays are scattered, reflecting the electron density of the materials that make up the vulcanized rubber. The radius of gyration Rg of the silica aggregates can be calculated from the scattering profile obtained.

[0036] Specifically, Rg is determined by the method described in Japanese Patent No. 6578200. That is, the vulcanized rubber is stretched by 50% in a direction perpendicular to the silica orientation direction, and in the stretched state, the vulcanized rubber is subjected to 10 10 (photons / s / mrad 2 / mm 2 Small-angle X-ray scattering measurements are performed by irradiating the rubber with high-intensity X-rays (at least 0.1% bw). The orientation direction of silica can be confirmed by performing SAXS measurements on unstretched vulcanized rubber. For vulcanized rubber that does not show anisotropy in the two-dimensional scattering image in the unstretched state, SAXS measurements can be performed after stretching the rubber 50% in any direction.

[0037] This produces a two-dimensional scattering image showing the magnitude of the scattering intensity, as shown in Figure 1. In Figure 1, the whiter the color, the greater the scattering intensity, and the blacker the color, the weaker the scattering intensity. The contour lines are shown as white (dotted) lines. The black portion of the scattering center and the black lines extending downward from it are shadows cast by the beam stopper. The two-dimensional scattering image has constrictions on both sides of the scattering center, and the left-right direction of these constrictions 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 the silica orientation direction (the left and right constrictions) over a predetermined angle range α = 30° (a range of 15° on each side of the orientation direction). 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 Rg of the silica aggregate is calculated by fitting the obtained scattering profile. Details of the measurement conditions are as described in the Examples below.

[0038] Ultra-small angle X-ray scattering (USAXS) is a technique for measuring scattered X-rays at angles smaller than those of small angle X-ray scattering (usually 0.1° or less). In detail, the vulcanized rubber is stretched 50% in the direction perpendicular to the silica orientation direction, and then 10 10 (photons / s / mrad 2 / mm 2 Bonse-Hart USAXS measurement is performed by irradiating high-intensity X-rays (at least 0.1% bw). The orientation direction of silica can be confirmed by performing SAXS measurement on unstretched vulcanized rubber. For vulcanized rubber that does not show anisotropy in the two-dimensional scattering image in the unstretched state, USAXS measurement can be performed after stretching the rubber by 50% in any direction.

[0039] This yields a one-dimensional scattering profile as shown in Figure 2. 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 mass fractal dimension Dm of the silica aggregate is determined by fitting to the obtained scattering profile. Details of the measurement conditions are as described in the Examples below.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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]

[0044] Examples will be shown below, but the present invention is not limited to these examples.

[0045] Rubber compositions were prepared according to the formulations (parts by mass) listed in Tables 1 to 3 below. Specifically, a diene rubber was masticated for 30 seconds using a Daihan Corporation lab mixer (300 cc), and then all ingredients except sulfur and the vulcanization accelerator were added to the lab mixer and mixed for 240 seconds before being discharged. The discharged mixture was again added to the lab mixer and mixed for 180 seconds before being discharged. The discharged mixture was then added to the lab mixer together with sulfur and the vulcanization accelerator, mixed for 60 seconds, and discharged. The resulting unvulcanized rubber composition was sheeted using a two-roll mill to a thickness of 1.0 mm, and then subjected to a vulcanization press at 160°C for 20 minutes to obtain a vulcanized rubber sample having a thickness of 1.0 mm.

[0046] Details of each component in Tables 1 to 3 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: "Si75" manufactured by Evonik Japan Co., Ltd. Alkylalkoxysilane: Octadecyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. Aminoalkoxysilane: 3-aminopropyltriethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. Ureidoalkoxysilane: 1-[3-(Triethoxysilyl)propyl]urea (40-52% in Methanol) manufactured by Tokyo Chemical Industry Co., Ltd., 3-ureidopropyltriethoxysilane Isocyanate alkoxysilane: 3-isocyanate propyl triethoxysilane, 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.

[0047] In Tables 1 to 3, the "molar ratio (%) of nitrogen-containing alkoxysilane" refers to the content (mol %) of nitrogen-containing alkoxysilane in the total content of nitrogen-containing alkoxysilane and alkylalkoxysilane. The blended amount of ureidoalkoxysilane in Table 2 includes the amount of methanol in the product.

[0048] For the obtained vulcanized rubber sample, the radius of gyration Rg and mass fractal dimension Dm of the silica aggregate were determined, and Dm / Rg was calculated. The measurement method is as follows.

[0049] [Radius of inertia Rg] SAXS measurements were performed based on the method described in Japanese Patent No. 6578200. For the measurements, SAXS measurements were performed on an unstretched sample to confirm the silica orientation direction, and then the sample was stretched by 50% in the direction perpendicular to the orientation direction and irradiated with X-rays in the stretched state. SAXS measurements were performed using beamline BL08B2 at 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

[0050] 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 α = 30° at the constrictions on both sides of the scattering center to obtain a one-dimensional scattering profile. The radius of gyration Rg of the silica aggregate was calculated by fitting the obtained scattering profile. The fitting was performed by the least-squares method using the following fitting function (formula source: G. Beaucage, J. Appl. Cryst. 28, 717-728 (1995)).

[0051]

number

[0052] [Mass fractal dimension Dm] USAXS measurements were performed using a Bonse-Hart optical system in the A1 experimental hutch of BL24XU, Spring-8 at the Japan Synchrotron Radiation Research Institute, and a one-dimensional scattering curve was obtained. Prior to the measurements, the orientation of the silica was confirmed using the SAXS measurements described above. The sample was stretched 50% in the direction perpendicular to the orientation, and X-rays were irradiated in this stretched state. The X-rays were reflected four times by a collimator crystal Si(220) before entering the sample, and then four times by an analyzer crystal Si(220) after scattering from the sample. The X-rays were detected using an APD detector and subjected to desmearing processing. The measurement conditions were as follows: Beam size: 0.2mm x 0.3mm ·Incoming X-ray wavelength: 0.124nm q range: 0.001~0.2nm -1

[0053] The mass fractal dimension Dm of the silica aggregates was determined by fitting the obtained one-dimensional scattering curve. Fitting was performed using the least squares method using the following fitting function (Source: Koga, T.; Hashimoto, T.; Takenaka, M.; Aizawa, K.; Amino, N.; Nakamura, M.; Yamaguchi, D.; Koizumi, S.: Macromolecules, 2008, 41, 453 (2008)).

number

[0054] Furthermore, the unvulcanized rubber composition obtained above was vulcanized at 160°C for 20 minutes, and the hardness and wet grip performance of the sample were measured, and the balance between the two (Hs*Wet index) was evaluated. The measurement and evaluation methods were as follows.

[0055] [hardness] The hardness was measured at 23°C using a Type A durometer conforming to JIS K6253-3:2012, and is shown as an index with the value for Comparative Example 1 in Tables 1 and 2 and the value for Comparative Example 10 in Table 3 set to 100. A larger index indicates higher hardness and better steering stability when made into a tire.

[0056] [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. In Tables 1 and 2, the value for Comparative Example 1, and in Table 3, the value for Comparative Example 10, are shown as indexes, with 100 being the index. A larger index indicates a larger tan δ, which means that the tire will have better wet grip performance when made into a tire.

[0057] [Hs*Wet index] The Hs*Wet index was calculated from the hardness index (Hs) and wet grip performance index (Wet) obtained above using the following formula. The larger this index, the greater the improvement effect on the trade-off between wet grip performance and hardness. (Hs*Wet index)=(Hs×Wet) / 100

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] The results are shown in Tables 1 to 3. In Comparative Example 1, a sulfur-containing silane coupling agent was blended into the silica compound, while in Comparative Example 2, the sulfur-containing silane coupling agent was replaced with an aminoalkoxysilane. In Comparative Example 2, Dm / Rg was low at 0.17, and although hardness was improved, wet grip performance was significantly deteriorated. In Comparative Examples 3 and 4, aminoalkoxysilane and alkylalkoxysilane were used in combination, but Dm / Rg was less than 0.20, and the trade-off between hardness and wet grip performance could not be improved. In contrast, in Examples 1 to 4, where Dm / Rg was 0.20 or higher, the trade-off between hardness and wet grip performance was improved compared to Comparative Example 1. In particular, Examples 2 and 3 showed a significant improvement, and Example 2 achieved a high level of balance between hardness and wet grip performance.

[0062] As shown in Table 2, in Examples 5 to 8, in which ureidoalkoxysilane or isocyanatealkoxysilane was used instead of aminoalkoxysilane as the nitrogen-containing alkoxysilane, Dm / Rg was 0.20 or more, and the trade-off between hardness and wet grip performance was improved compared to the benchmark Comparative Example 1. In particular, Examples 5, 6, and 7 showed a well-balanced improvement in hardness and wet grip performance.

[0063] In the experimental example shown in Table 3, the compounding amount of silica was 50 parts by mass per 100 parts by mass of diene rubber, which was a smaller amount than the experimental examples shown in Tables 1 and 2. In this case as well, Example 9, in which Dm / Rg was 0.20 or more, showed an improvement in the trade-off between hardness and wet grip performance compared to Comparative Example 10, which served as the benchmark.

[0064] 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 nitrogen-containing alkoxysilane, and an alkylalkoxysilane having an alkyl group having 6 to 20 carbon atoms, 100 parts by mass of the diene rubber contains 70 parts by mass or more of styrene-butadiene rubber, the content of the silica is 5 to 150 parts by mass per 100 parts by mass of the diene rubber, the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is 3 to 15% by mass based on the content of the silica, and the content ratio of the nitrogen-containing alkoxysilane in the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is 10 to 80 mol %, The radius of gyration Rg of silica aggregates obtained by irradiating X-rays on a vulcanized rubber obtained by vulcanizing the rubber composition and performing small-angle X-ray scattering measurement, and the mass fractal dimension Dm of silica aggregates obtained by irradiating X-rays on the vulcanized rubber and performing ultra-small-angle X-ray scattering measurement, are used to determine whether the value Dm / Rg obtained by dividing the mass fractal dimension Dm by the radius of gyration Rg is 0.20 nm. －１ The rubber composition is as described above.

2. The rubber composition according to claim 1, wherein the nitrogen-containing alkoxysilane has at least one functional group selected from the group consisting of an amino group, a ureido group, an isocyanate group, a cyano group, an azido group, and an amide group.

3. A pneumatic tire made using the rubber composition according to claim 1 or 2.

4. A vulcanized rubber obtained by vulcanizing a rubber composition containing a diene rubber, silica, a nitrogen-containing alkoxysilane, and an alkylalkoxysilane having an alkyl group having 6 to 20 carbon atoms, 100 parts by mass of the diene rubber contains 70 parts by mass or more of styrene-butadiene rubber, the content of the silica is 5 to 150 parts by mass per 100 parts by mass of the diene rubber, the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is 3 to 15% by mass based on the content of the silica, and the content ratio of the nitrogen-containing alkoxysilane in the total content of the nitrogen-containing alkoxysilane and the alkylalkoxysilane is 10 to 80 mol %, The radius of gyration Rg of the silica aggregate obtained by irradiating the vulcanized rubber with X-rays and performing small-angle X-ray scattering measurement, and the mass fractal dimension Dm of the silica aggregate obtained by irradiating the vulcanized rubber with X-rays and performing ultra-small-angle X-ray scattering measurement, are used to determine whether the value Dm / Rg obtained by dividing the mass fractal dimension Dm by the radius of gyration Rg is 0.20 nm. －１ That's it, vulcanized rubber.

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