Rubber composition and method for producing the same

Abstract

To utilize glass as a rubber composition and enhance re-utilization rate of waste glass, and more specifically, to provide a rubber composition enabling compatibility of excellent mechanical characteristics with abrasion resistance and processability.SOLUTION: A rubber composition contains glass powder and rubber, the average long diameter of the glass powder as observed by transmission electron microscopy being 5 nm or more and 990 nm or less. In the rubber composition, the median diameter of the glass powder as measured by laser diffraction particle size distribution is 0.1 μm or more and 70 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a method for producing the same. [Background technology]

[0002] Systems have been established around the world for sorting, collecting, and recycling most of the glass from used beverage bottles. On the other hand, plate glass is used in a variety of fields, including window glass, building glass, automotive glass, solar panel glass, and amusement machine glass, but its recycling rate is low and it is usually buried underground as shredder dust.

[0003] Patent Documents 1 and 2 propose a crushing method and crushing device for arranging plate glass into glass particles of an appropriate particle size to facilitate recycling.

[0004] Patent Document 3 proposes a rubber composition that exhibits high steering stability and good fuel economy by incorporating glass particles having an average particle size of 1 to 100 μm into the rubber composition. Patent Document 4 discloses a rubber composition that improves the fuel economy of a tire by controlling the particle size and amount of silica added to the rubber. Patent Document 5 discloses a tire that can achieve both high grip and wear resistance by incorporating a predetermined amount of silica in the rubber tread. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2021 / 192254 [Patent Document 2] International Publication No. 2021 / 161445 [Patent Document 3] Japanese Patent Publication No. 2023-130532 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-014339 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-113604 Summary of the Invention [Problem to be solved by the invention]

[0006] The better the silica is dispersed in the rubber and the higher the loading rate, the better the fuel economy and grip performance. However, highly hydrophilic silica has poor affinity with rubber and forms secondary structures in which primary particles are chemically bonded like grape clusters, making it difficult to finely disperse these secondary structures uniformly. Another problem is that silica hardens the rubber, impairing processability. There is a trade-off between fuel economy and grip performance on the one hand and wear resistance and processability on the other. Improvements in physical properties through silica alone are approaching their limits. Because fuel economy and grip performance are highly correlated with the mechanical properties of a rubber composition, such as tensile strength, tear strength, and dynamic viscoelasticity, the challenge of achieving both these physical properties and wear resistance (durability) and processability is not limited to tire applications, but is also a common challenge for various rubber compositions, such as shoe sole rubber, vibration-isolating rubber, anti-vibration rubber, packing, sealant, hose, rubber belt, etc.

[0007] Furthermore, there has been a growing demand in recent years to replace conventional materials with sustainable materials (materials with less environmental impact, such as naturally derived materials and recycled materials), and the replacement of silica has also begun to be considered, but issues such as cost, supply shortages, and concerns about supply stability are obstacles.

[0008] On the other hand, the biggest issue with utilizing waste glass is the lack of applications that are economically rational and have sufficient demand, and there is a need to create new applications.

[0009] That is, the problem to be solved by the present invention is to utilize glass as a rubber composition to improve the recycling rate of waste glass, and more specifically, to provide a rubber composition that combines excellent mechanical properties with abrasion resistance (durability) and processability.

[0010] Therefore, an object of an embodiment of the present invention is to improve the recycling rate of waste glass, and to achieve a balance between excellent mechanical properties, abrasion resistance (durability), and processability of a rubber composition. [Means for solving the problem]

[0011] Through extensive research, the inventors have found that the above problems can be solved by adding glass powder having an average major axis of 5 nm or more and 990 nm or less, as determined by transmission electron microscope image observation, to rubber.

[0012] That is, the present invention includes the following embodiments [1] to [5]. The embodiments of the present invention are not limited to the following.

[0013] [1] A rubber composition comprising glass powder and rubber, wherein the glass powder has an average major axis of 5 nm or more and 990 nm or less as measured by transmission electron microscope observation.

[0014] [2] The rubber composition according to [1], wherein the glass powder has a median diameter of 0.1 μm or more and 70 μm or less as measured by laser diffraction particle size distribution measurement.

[0015] [3] The rubber composition according to [1] or [2], wherein the content of the glass powder is 30% by mass or more and 300% by mass or less based on the mass of the rubber.

[0016] [4] A method for producing a rubber composition, comprising a kneading step of kneading glass powder with rubber, wherein the glass powder has an average major axis of 5 nm or more and 990 nm or less as measured by transmission electron microscope observation.

[0017] [5] [4] The method for producing a rubber composition according to [4], further comprising, before the kneading step, a step of causing the coarse glass particles to collide with grinding media, and / or the coarse glass particles themselves, in a liquid medium to refine the coarse glass particles, and removing the liquid medium to obtain glass powder. [Effects of the Invention]

[0018] According to an embodiment of the present invention, waste glass is recycled to provide a rubber product having excellent mechanical properties, abrasion resistance (durability) and processability. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below with reference to the following embodiments. The present invention is not limited to the following embodiments, and includes embodiments that are implemented within the scope of the present invention.

[0020] <Rubber composition> The rubber composition of the present invention contains glass powder and rubber. The rubber composition of the present invention can be used for various applications, such as, but not limited to, rubber for tires, rubber for shoe soles, vibration-isolating rubber, vibration-proof rubber, packing, sealing material, hose, rubber belt, etc. In particular, the rubber composition of the present invention can be suitably used for rubber for tires and rubber for shoe soles.

[0021] <Glass powder> The glass powder of the present invention preferably contains a silicon compound, a sodium compound, and a calcium compound, more preferably a silicon compound and a sodium compound, and may contain other components. Examples of other components include compounds containing boron, magnesium, strontium, barium, lithium, potassium, titanium, iron, and antimony, particularly oxides thereof. The silicon compound, sodium compound, and calcium compound are preferably SiO2, Na2O, and CaO, respectively, and their compositions are preferably 50-85% by mass of SiO2, 10-30% by mass of Na2O, and 0-30% by mass of CaO, respectively. When the components of the glass powder are within the above ranges, interaction with rubber is easily achieved. The components of the glass powder can be determined using the fundamental parameter method of X-ray fluorescence analysis.

[0022] The shape of the glass powder may be, but is not limited to, spherical, non-cornered amorphous particulate, or angular amorphous particulate, but spherical or non-cornered amorphous particulate is preferred because it reduces wear on the equipment when kneaded with rubber.

[0023] The average major axis of the glass powder observed under a transmission electron microscope is calculated by measuring the longest cross-sectional length of 100 powder particles and averaging the measured values. The average major axis of the glass powder in the present invention is 5 nm or more, preferably 10 nm or more, and more preferably 15 nm or more. The average major axis of the glass powder is 990 nm or less, preferably 500 nm or less, and more preferably 100 nm or less. When the average major axis of the glass powder is within the above range, the number of silanol groups on the glass surface and the specific gravity of the glass powder are well balanced, and it is possible to advantageously achieve both elastic modulus, abrasion resistance (durability), and processability.

[0024] The median diameter of the glass powder measured by laser diffraction particle size distribution measurement is preferably 0.1 μm or more, more preferably 0.4 μm or more, and even more preferably 0.8 μm or more. Furthermore, the median diameter of the glass powder is preferably 70 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. When the median diameter of the glass powder is within the above range, the number of silanol groups on the glass surface and the specific gravity of the glass powder are well balanced, and it is possible to advantageously achieve both elastic modulus, abrasion resistance (durability), and processability. Specifically, the median diameter of the glass powder can be measured by the method described in the Examples.

[0025] The content of the glass powder in the rubber composition is preferably 30% by mass or more and 300% by mass or less, more preferably 60% by mass or more and 250% by mass or less, and even more preferably 70% by mass or more and 200% by mass or less, based on the mass of the rubber. When the content of the glass powder in the rubber composition is within the above range, an excellent elastic modulus is likely to be obtained.

[0026] Glass powder can be obtained, for example, by crushing plate glass. Crushing plate glass in multiple stages is preferable because it can be efficiently performed while achieving uniform size. For example, in a first step, plate glass is crushed to several centimeters to several millimeters using a known dry crusher (e.g., a roll crusher, hammer mill, attritor, ball mill, etc.) to obtain glass fragments. In a second step, the glass fragments are further crushed to 1 mm to several μm using a known dry crusher (e.g., a dry bead mill, a dry jet mill, etc.) to obtain coarse glass particles. In a third step, the coarse glass particles are further crushed to 1 μm to several nanometers in a liquid medium using a known wet crusher (e.g., a wet bead mill, a wet jet mill, etc.) to obtain glass powder. The particle size can be observed and measured visually, with an optical microscope, a transmission electron microscope, or the like, as appropriate depending on the size. When using a wet crusher, water or a hydrophilic organic solvent is preferably used as the liquid medium from the viewpoints of environmental impact and cost, and water is more preferred. When a wet mill is used, it is preferable to use a milling medium, and the milling medium is preferably zirconia, zircon, alumina, steel, or the like, with zirconia being particularly preferable.

[0027] When a wet grinding machine is used, it is preferable to remove the liquid medium from the glass powder paste containing the liquid medium. Filtration and drying are preferred as a method for removing the liquid medium. As a filtration method, known methods such as natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration can be used, with pressure filtration being preferred from the viewpoint of efficiency, but not limited to these. As a drying method, known methods such as natural drying, hot air drying, vacuum drying, and heat drying under reduced pressure can be used, with hot air drying being preferred from the viewpoint of cost and efficiency, but not limited to these.

[0028] During pulverization, auxiliary agents such as polymer dispersants, surfactants, silane coupling agents, alcohols, etc. may be added to prevent reagglomeration and / or sedimentation, or to improve pulverization efficiency, etc. When using these auxiliary agents, their use is particularly effective in wet pulverization.

[0029] <Rubber> The rubber is not particularly limited, and for example, natural rubber, diene rubber, or non-diene rubber can be used. One type may be used alone, or two or more types may be used in combination.

[0030] As the natural rubber, those with adjusted molecular weight or those with adjusted components may be used.

[0031] Examples of diene rubbers include styrene-butadiene rubber, isoprene rubber, butadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, and hydrogenated versions of these.

[0032] Examples of non-diene rubbers include butyl rubber (isobutene-isoprene rubber), ethylene-propylene rubber, ethylene-propylene-diene rubber, urethane rubber, and silicone rubber.

[0033] <Silane coupling agent> The rubber composition of the present invention preferably contains a silane coupling agent. Known silane coupling agents can be used, such as aminosilane, epoxysilane, vinylsilane, acrylicsilane, chlorosilane, mercaptosilane, and ureidosilane. More specifically, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, ethoxy(3-mercaptopropyl)bis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silane (e.g., "Si363" manufactured by Evonik Degussa, "NXT-Z30", "NXT-Z45", and "NXT-Z60" manufactured by Momentive) "," "NXT Silane" and other mercapto group-containing silane coupling agents, bis-[3-(triethoxysilyl)-propyl]-tetrasulfide, bis-[3-(triethoxysilyl)-propyl]-disulfide, bis-[2-(triethoxysilyl)-ethyl]-tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis-[2-(triethoxysilyl)-ethyl]-tetrasulfide, bis(3-trimethoxysilylpropyl) Tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N ,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, etc. These silane coupling agents may be used alone or in combination of two or more.

[0034] The use of a silane coupling agent bonds the silanol groups on the surface of the glass powder with the rubber, making it easier to obtain an interaction between the glass powder and the rubber. It also improves the dispersion efficiency of the glass powder in the rubber. From the viewpoint of achieving the above effects, the amount of the silane coupling agent blended is preferably 0.1% by mass or more, and more preferably 1% by mass or more, based on the mass of the rubber. Furthermore, the amount of the silane coupling agent blended is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on the mass of the rubber.

[0035] <Other ingredients> The rubber composition of the present invention may contain, as necessary, a reinforcing agent, a vulcanizing agent, a vulcanization accelerator, oil, zinc oxide, stearic acid, an antioxidant, a scorch inhibitor, wax, process oil, etc., and may contain known components used in rubber products.

[0036] Examples of reinforcing agents include inorganic fillers such as carbon black, silica, calcium carbonate, basic magnesium carbonate, clay, Lissajous silica, diatomaceous earth, reclaimed rubber, powdered rubber, etc. Carbon black is particularly preferred, and silica may also be included.

[0037] Examples of the vulcanizing agent include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, etc. The content of the vulcanizing agent is usually 0.1 to 10 parts by mass in terms of sulfur content per 100 parts by mass of rubber.

[0038] Examples of the vulcanization accelerator include vulcanization aids, such as sulfenamide vulcanization accelerators, thiuram vulcanization accelerators, thiazole vulcanization accelerators, thiourea vulcanization accelerators, guanidine vulcanization accelerators, dithiocarbamate vulcanization accelerators, etc. The content of the vulcanization accelerator is usually 0.1 to 7 parts by mass per 100 parts by weight of rubber.

[0039] Examples of the antioxidant include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, thiourea-based antioxidants, etc. Examples of the scorch inhibitor include organic acids, nitroso compounds, N-cyclohexylthiophthalimide, and sulfonamide derivatives.

[0040] Examples of waxes include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more. Of these, petroleum waxes (particularly paraffin wax) are preferred. The content of the wax is usually 0.5 to 5 parts by mass per 100 parts by mass of the rubber component. As the process oil, paraffin-based process oil, aromatic process oil, naphthenic process oil, etc. can be used. Process oil is generally liquid at room temperature (20°C). The content of the process oil is usually about 5 to 60 parts by mass per 100 parts by mass of rubber.

[0041] <Method of manufacturing rubber composition> The rubber composition of the present invention can be obtained by kneading glass powder and rubber. Kneading is preferably performed under temperature conditions that soften the rubber, and is preferably determined appropriately depending on the type of rubber. Known devices can be used to knead the rubber, such as a Banbury mixer, a pressure kneader, or a two-roll mill. When kneading the glass powder, rubber, and other components, any combination and addition order can be used. However, from the viewpoint of thoroughly dispersing the glass powder and obtaining favorable interaction with the rubber, two-stage kneading is preferred, in which the glass powder, rubber, and silane coupling agent are first kneaded, followed by the addition of a vulcanizing agent and a vulcanization accelerator, followed by secondary kneading. The kneading temperature is preferably 30°C or higher and 160°C or lower, more preferably 40°C or higher and 150°C or lower. When kneading in two stages, the temperature during the primary kneading is preferably 30°C or higher and 100°C or lower, more preferably 35°C or higher and 80°C or lower, from the viewpoints of workability and preventing rubber degradation. The temperature during secondary kneading is preferably 80°C or higher and 160°C or lower, more preferably 90°C or higher and 150°C or lower, from the viewpoint of sufficiently promoting vulcanization while suppressing deterioration of the rubber.

[0042] The longer the kneading time, the better the dispersion of the glass powder, but if the kneading stress and time are too long, the rubber is likely to deteriorate, so the kneading time is preferably 10 minutes to 1 hour. In addition, the glass powder is preferably pulverized before use, and may be surface-treated to increase its affinity with rubber. [Example]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0044] [Average long diameter of glass powder] The average major axis of the glass powder was calculated by observing and photographing the glass powder with a transmission electron microscope (TEM), randomly selecting 100 glass powder particles, measuring the maximum length of each particle, and averaging the results.

[0045] <Evaluation of the physical properties of glass powder> [Median diameter of glass powder] The median diameter of the glass powder was calculated as the particle size at an integrated value of 50% in terms of cumulative mass percentage in volume terms, assuming the refractive index of the glass powder to be 1.5, using a laser diffraction particle size distribution analyzer (SALD-2300 manufactured by Shimadzu Corporation).

[0046] <Evaluation of mechanical properties of rubber compositions> [Mooney viscosity (ML 1+4 , 100℃)] Mooney viscosity (ML) of the rubber composition 1+4 , 100°C) was measured using 40 g of the rubber composition at a temperature of 100°C using an L-shaped rotor in accordance with Japanese Industrial Standard JIS K6300-1. The lower the Mooney viscosity, the better the processability of the rubber composition.

[0047] [Tensile strength][Tear strength][Elongation at break] The tensile strength [MPa] and tear strength [kN / m] of the rubber composition were calculated in accordance with JIS K6251 using a dumbbell-shaped No. 3 test specimen at a test speed of 500 mm / min, a grip distance of 60 mm, and a gauge length of 20 mm, from the maximum tensile force until the test specimen broke and the tensile force at break. The length of the test specimen before the test was taken as the reference (i.e., the length of the test specimen before the test was taken as 100%), and the ratio of the length of the test specimen at break to the elongation at break [%] of the rubber composition. The higher the tensile strength, tear strength, and elongation at break, the better the physical properties of the rubber composition.

[0048] [loss tangent tanδ] The loss tangent tanδ of a rubber composition at 50°C (hereinafter sometimes simply referred to as "tanδ") was measured in accordance with JIS K6394 using a viscoelasticity measuring device (ARES-G2, manufactured by TA Instruments) at a temperature of 50°C, an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz. The smaller the tanδ, the more resistant the rubber composition to deformation under stress. For example, a rubber composition with a small tanδ will have higher fuel efficiency when used in tires, and will have higher resilience and be superior when used in shoe soles.

[0049] <Abrasion resistance evaluation of rubber compositions> The abrasion resistance of the rubber composition was measured in accordance with JIS K6264-2 using an Acron abrasion tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) under conditions of a load of 44.1 N and 3,000 revolutions. The abrasion resistance was calculated from the abrasion amounts of each example and comparative example, using the abrasion amount of Reference Example 1 as the standard (i.e., the abrasion amount of Reference Example 1 was set to 1.0). The larger the value, the better the abrasion resistance.

[0050] <Glass powder manufacturing> (Production Example 1) The solar panel was processed using a roll-type glass peeling device (Crystaliner, manufactured by Asahi Co., Ltd.) and crushed while separating the plate glass from other components to obtain glass fragments. The panel was then processed twice using a glass crushing device (Millsizer, manufactured by Asahi Co., Ltd.) to obtain coarse glass particles A with an average major axis of 5.0 μm. A dry bead mill (Drystar SDA, manufactured by Ashizawa Finetech Co., Ltd.) was charged with 8 mm diameter alumina beads as crushing media, and the coarse glass particles A were fed at 3.0 kg / h and processed at a peripheral speed of 5.0 m / s to obtain coarse glass particles B with an average major axis of 1.0 μm and a median diameter of 140 μm. A portion of this coarse glass particles B was used in Comparative Example 1. The remaining coarse glass particles B were further milled in a wet bead mill (Mugen Flow MGF015, manufactured by Ashizawa Finetech Co., Ltd.) using 0.5 mm diameter zirconia beads as milling media. A premix of coarse glass particles B (10 parts by mass), ion-exchanged water (88 parts by mass), and isopropanol (2 parts by mass) was fed at 70 L / min and processed at a peripheral speed of 8 m / s to obtain a glass powder paste containing ion-exchanged water. The glass powder paste was filtered, washed with water, and dried at 80°C for 24 hours to obtain Glass Powder 1. The average major axis of Glass Powder 1 was 15 nm and the median diameter was 9 μm. The major components of Glass Powder 1 were 71.1 mass% SiO2, 13.9 mass% Na2O, and 10.1 mass% CaO. Additionally, 0.02 mass% As2O3 was detected as a trace component.

[0051] (Production Example 2) Glass powder 2 was obtained in the same manner as in Production Example 1, except that a laminated automobile front glass was used instead of a solar panel. The average major axis of glass powder 2 was 24 nm and the median diameter was 30 μm. The main components of glass powder 2 were 72.4 mass% of SiO, 13.1 mass% of NaO, and 11.8 mass% of CaO. 0.1 mass% of FeO was detected as a trace component.

[0052] (Production Example 3) Glass powder 3 was obtained in the same manner as in Production Example 1, except that laminated glass from a pachinko machine was used instead of a solar panel. The average major axis of Glass powder 3 was 20 nm and the median diameter was 18 μm. The main components of Glass powder 3 were 70.0 mass% of SiO, 12.1 mass% of NaO, 9.3 mass% of CaO, and 4.8 mass% of AlO.

[0053] <Preparation of Rubber Composition> Example 1 100.0 g of natural rubber (RSS No. 3), 80.0 g of glass powder 1, 4.0 g of bis[3-(triethoxysilyl)propyl]tetrasulfide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a silane coupling agent, 3.0 g of stearic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), and 10.0 g of TDAE oil (manufactured by ENEOS Corporation) were charged into a 250 mL Banbury mixer, heated to a temperature of 40°C, and kneaded for 1 minute. Next, 2.0 g of sulfur (manufactured by Tokyo Chemical Industry Co., Ltd.), 5.0 g of zinc oxide (manufactured by Tokyo Chemical Industry Co., Ltd.), 2.0 g of 1,3-diphenylguanidine (manufactured by Tokyo Chemical Industry Co., Ltd.), 2.0 g of N-cyclohexyl-2-benzothiazolysulfenamide (manufactured by Tokyo Chemical Industry Co., Ltd.), and 1.0 g of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to the Banbury mixer, heated to 150°C, and kneaded for 5 minutes. The kneaded product was placed in a predetermined mold and pressed at 170°C for 5 minutes, obtaining rubber composition 1.

[0054] (Examples 2 and 3, Comparative Example 1, Reference Example 1) Each rubber composition (rubber compositions 2, 3, comparative rubber composition 1, reference rubber composition 1) was obtained in the same manner as in Example 1, except that glass powder 2, glass powder 3, coarse glass particles B, and reference silica (VN3: Nipsil VN3, precipitated silica manufactured by Tosoh Silica Corporation) were used instead of glass powder 1. The evaluation results of each rubber composition are shown in Table 1.

[0055] [Table 1]

Claims

1. A rubber composition comprising glass powder and rubber, wherein the glass powder has an average major axis of 5 nm or more and 990 nm or less as measured by transmission electron microscope observation.

2. The rubber composition according to claim 1, wherein the glass powder has a median diameter of 0.1 μm or more and 70 μm or less as measured by laser diffraction particle size distribution measurement.

3. The rubber composition according to claim 1 or 2, wherein the content of the glass powder is 30% by mass or more and 300% by mass or less based on the mass of the rubber.

4. A method for producing a rubber composition, comprising a kneading step of kneading glass powder with rubber, wherein the glass powder has an average major axis of 5 nm or more and 990 nm or less as measured by observation under a transmission electron microscope.

5. 5. The method for producing a rubber composition according to claim 4, further comprising, before the kneading step, a step of causing the coarse glass particles to collide with grinding media and / or with each other in a liquid medium to refine the coarse glass particles, and removing the liquid medium to obtain a glass powder.

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