Rubber compositions and pneumatic tires

Abstract

To provide a rubber composition that serves as a raw material for vulcanized rubber with excellent tear resistance, and a pneumatic tire comprising vulcanized rubber of the rubber composition. [Solution] A rubber composition containing diene rubber, silica, and graphene, wherein the graphene has a specific surface area of ​​200 m². 2 A rubber composition comprising graphene having a particle size of 10 μm or less, an average particle thickness of 10 nm or less, and an oxygen content of 1% by mass or less. Preferably, the graphene content is 1.5 to 10 parts by mass when the total amount of diene rubber is 100 parts by mass. Preferably, the silica content is 60 to 120 parts by mass when the total amount of diene rubber is 100 parts by mass. Furthermore, it is preferable that the rubber composition does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

Description

[Technical Field]

[0001] This invention relates to a rubber composition and a pneumatic tire. [Background technology]

[0002] Pneumatic tires consist of a rubber section formed by vulcanizing a rubber composition. These rubber compositions typically contain fillers such as carbon black and silica to enhance their reinforcing properties. Recently, tires incorporating graphene as a filler have also been reported.

[0003] Patent Document 1 below describes a rubber composition containing diene rubber, graphene oxide, and carbon black, wherein the content of graphene oxide is 0.1 to 10 parts by mass, the content of carbon black is 30 to 80 parts by mass, and the oxygen content of graphene oxide is 45 to 60 atom% per 100 parts by mass of diene rubber.

[0004] The following Patent Document 2 describes a base rubber composition comprising 0.1 to 20% by weight of graphene carbon particles having a bendable 3D shape and an oxygen content of 2 atomic percent or less, and 1 to 50% by weight of filler particles containing silica, which hardens to 10 10 A curable rubber compound having a surface resistivity of less than Ω / sq is described.

[0005] Patent Document 3 below describes at least one elastomer resistant to heating at 100°C for 70 hours, exhibiting at least one of the following properties: (a) a change in durometer hardness of 15 points or less, (b) a change in tensile strength of 40% or less, and (c) a change in ultimate elongation of 40% or less; and at least one graphene-based material present in the amount of the at least one elastomer in the range of 0.01 to 30 phr, selected from reduced graphene oxide, and with a range of 40 to 1600 m 2The document describes an elastomer compound comprising at least one graphene-based material having a BET surface area in the range of / g, and at least one carbon black present in an amount in the range of 15 to 150 phr relative to the at least one elastomer.

[0006] Patent Document 4 below describes a composition comprising a graphene sheet, at least one reinforcing material containing silicon, and at least one type of rubber.

[0007] Patent Document 5 below describes a composition comprising a graphene sheet, at least one reinforcing material containing silicon, and at least one type of rubber, wherein the composition includes 2 to 4 parts by weight of the graphene sheet per 100 parts by weight of the rubber. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7385429 [Patent Document 2] Patent No. 6087424 [Patent Document 3] Patent No. 6802281 [Patent Document 4] Japanese Patent Publication No. 2018-15054 [Patent Document 5] Patent No. 6404121 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] As a result of diligent research by the inventors, it was found that in vulcanized rubber compositions containing graphene and silica as fillers, the tear resistance deteriorates due to the aggregation of graphene within the rubber. Further diligent research to improve the tear resistance of vulcanized rubber revealed that using graphene with specific physical properties in combination with silica significantly improves the tear resistance of the vulcanized rubber.

[0010] The present invention has been made in view of the above circumstances, and its purpose is to provide a rubber composition that serves as a raw material for vulcanized rubber with excellent tear resistance, and a pneumatic tire equipped with vulcanized rubber of the rubber composition. [Means for solving the problem]

[0011] The above problems can be solved by the following configuration. That is, the present invention is a rubber composition containing diene rubber, silica and graphene, wherein the graphene has a specific surface area of ​​200 m². 2 The present invention relates to a rubber composition (1) characterized by being graphene having a particle size of 10 μm or less, an average particle thickness of 10 nm or less, and an oxygen content of 1% by mass or less.

[0012] In the above rubber composition (1), a rubber composition (2) is preferred in which the graphene content is 0.5 to 30 parts by mass when the total amount of the diene-based rubber is 100 parts by mass.

[0013] In the above rubber composition (1) or (2), a rubber composition (3) is preferred in which the silica content is 60 to 120 parts by mass when the total amount of the diene rubber is 100 parts by mass.

[0014] Of the above rubber compositions (1) to (3), rubber composition (4) that does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is preferred.

[0015] The present invention also relates to a pneumatic tire comprising at least one vulcanized rubber from rubber compositions (1) to (4). [Effects of the Invention]

[0016] Generally, graphene is likely to aggregate and difficult to disperse when kneaded in diene rubber. However, the graphene used in the present invention is designed to have a specific specific surface area, particle size, average thickness of particles, and oxygen content. Therefore, when such graphene and silica are kneaded in diene rubber, at least one or both of them exhibit a dispersion-assisting effect on each other, so that they are less likely to aggregate and easier to disperse in diene rubber. As a result, the tear resistance of the vulcanized rubber obtained from the rubber composition as a raw material is significantly improved.

Mode for Carrying Out the Invention

[0017] The rubber composition according to the present invention contains a diene rubber, silica, and graphene.

[0018] The rubber composition according to the present invention contains a diene rubber. The diene rubber is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and the like. These can be used alone or in combination of two or more. In the present invention, it is particularly preferable to use styrene-butadiene rubber (SBR) and / or butadiene rubber (BR).

[0019] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc. that are usually used for rubber reinforcement are used. Among them, wet silica is preferable. In the rubber composition according to the present invention, when the total amount of the diene rubber is 100 parts by mass, the content of silica is preferably 60 to 120 parts by mass, and more preferably 70 to 100 parts by mass.

[0020] The rubber composition according to the present invention may also preferably contain a silane coupling agent in addition to silica. The silane coupling agent is not particularly limited as long as it contains sulfur in its molecule, and various silane coupling agents that are compounded together with silica in the rubber composition can be used. Examples include sulfidosilanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan), bis(3-triethoxysilylpropyl) disulfide (e.g., "Si75" manufactured by Evonik Japan), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triecethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl) disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane. The amount of silane coupling agent is preferably 2 to 20% by mass, when the total amount of silica is considered to be 100% by mass.

[0021] The graphene used in this invention is designed to have a specific specific surface area, particle size, average particle thickness, and oxygen content. Graphene is a two-dimensional sheet-like material classified as a nanocarbon material, and sp 2 It has a structure composed of six-membered rings of carbon. This structure allows for the imparting of anti-aging properties to the final vulcanized rubber. This point will be discussed later.

[0022] The BET specific surface area of ​​the graphene used in this invention is 200 m². 2 Designed to be less than / g. From the perspective of improving dispersibility in diene-based rubber, the BET specific surface area is 80m². 2It is preferable to use graphene with a density of 1 / g or less. In this invention, the BET specific surface area of ​​graphene is measured in accordance with the BET method described in JIS K6430.

[0023] The graphene particle size used in this invention is designed to be 10 μm or less. From the viewpoint of improving dispersibility in diene-based rubber, it is preferable to use graphene with a particle size of 7 μm or less. In this invention, the graphene particle size is defined as the particle size at 50% of the cumulative value of the particle size distribution (volume basis) measured by laser diffraction-scattering method (D50).

[0024] The average thickness of the graphene particles used in this invention is designed to be 10 nm or less. From the viewpoint of improving dispersibility in diene-based rubber, it is preferable to use graphene with an average particle thickness of 3 nm or less. In this invention, the average thickness of the graphene particles is calculated from the thickness measured by transmission electron microscopy (TEM) observation. The average thickness of 100 graphene particles is measured, and the arithmetic mean is taken as the average thickness of the graphene particles.

[0025] The oxygen content of the graphene used in this invention is designed to be 1% by mass or less. From the viewpoint of improving dispersibility in diene-based rubber, it is preferable to use graphene with an oxygen content of 1% by mass or less. In this invention, the oxygen content of graphene is determined using X-ray photoelectron spectroscopy (for example, the method described in DRDreyer et al., Chem. Soc. Rev. 39, 228-240 (2010)).

[0026] Graphene is a two-dimensional sheet-like material classified as a nanocarbon material, and it readily forms a layered structure by aggregating or bonding with other elements through van der Waals forces. However, it is preferable to use graphene with a layered structure of 20 layers or less in this invention.

[0027] From the viewpoint of improving the processability of the rubber composition, when the total amount of diene rubber is 100 parts by mass, the graphene content is preferably 0.5 to 30 parts by mass, and more preferably 1.5 to 10 parts by mass.

[0028] The rubber composition according to the present invention may contain fillers other than graphene and silica. Examples of fillers include carbon black.

[0029] As carbon black, in addition to carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, conductive carbon blacks such as acetylene black and Ketjen black can be used. In the rubber composition according to the present invention, when the total amount of diene rubber is 100 parts by mass, the carbon black content may be 20 to 150 parts by mass, 30 to 100 parts by mass, or 40 to 80 parts by mass. Preferably, it is 40 to 80 parts by mass.

[0030] The rubber composition according to the present invention contains diene rubber, silica, and graphene. In addition to these, the rubber composition according to the present invention may also contain fillers such as carbon black, vulcanizing agents, antioxidants, zinc oxide, stearic acid, softeners such as waxes and oils, processing aids, and the like.

[0031] Preferably, sulfur and a vulcanization accelerator can be used as vulcanizing agents.

[0032] Any ordinary sulfur for rubber can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. The rubber composition according to the present invention preferably contains 0.1 to 5 parts by mass of sulfur, and more preferably 0.5 to 3 parts by mass, when the total amount of diene rubber is 100 parts by mass.

[0033] As the vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used individually or in appropriate mixtures. The rubber composition according to the present invention preferably contains 0.1 to 5 parts by mass of vulcanization accelerator, and more preferably 0.5 to 3 parts by mass, when the total amount of diene rubber is 100 parts by mass.

[0034] Examples of anti-aging agents commonly used for rubber include aromatic amine-based anti-aging agents, amine-ketone-based anti-aging agents, monophenol-based anti-aging agents, bisphenol-based anti-aging agents, polyphenol-based anti-aging agents, dithiocarbamate-based anti-aging agents, and thiourea-based anti-aging agents. However, in recent years, from the perspective of developing environmentally friendly products, there has been a focus on reducing the use of materials derived from fossil fuels or replacing them with other materials. The graphene used in this invention is sp 2 Because it has a structure that is tiled with six-membered rings of carbon, sp 2 The remaining electrons in the hybrid orbitals can capture radicals that cause aging of vulcanized rubber. For this reason, the rubber composition according to the present invention preferably contains diene rubber and graphene, with reduced amount or no N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), taking the environment into consideration. The rubber composition according to the present invention preferably contains 1 to 10 parts by mass of the antioxidant, and more preferably 2 to 5 parts by mass, when the total amount of diene rubber is 100 parts by mass.

[0035] The rubber composition according to the present invention is obtained by mixing diene rubber, silica and graphene, fillers such as carbon black, vulcanizing agents, antioxidants, zinc oxide, stearic acid, softeners such as waxes and oils, and processing aids using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and rolls.

[0036] In addition, the compounding method of each of the above components is not particularly limited, and methods such as pre-kneading compounding components other than vulcanization-based compounding agents such as sulfur and vulcanization accelerators to form a masterbatch, adding the remaining components and further kneading, adding and kneading each component in any order, and adding and kneading all components simultaneously may be used.

[0037] The vulcanized rubber of the rubber composition according to the present invention is excellent in the dispersibility of graphene and silica in the diene-based rubber, and thus the reinforcing effect by graphene is particularly effectively exhibited. Therefore, the vulcanized rubber of the rubber composition according to the present invention is particularly useful for the rubber parts of pneumatic tires.

Examples

[0038] Examples of the present invention will be described below for a more specific explanation.

[0039] (Preparation of rubber composition) For 100 parts by mass of the rubber component, rubber compositions of Examples 1 to 4 and Comparative Examples 1 to 2 were compounded according to the compounding formulations in Table 1, and kneaded using an ordinary Banbury mixer to prepare the rubber compositions. Each compounding agent described in Table 1 is shown below.

[0040] (Diene-based rubber) · Styrene-butadiene rubber: manufactured by JSR Corporation, trade name "SBR1723" · Butadiene rubber: manufactured by UBE Industries, Ltd., trade name "UBEPOL BR150B" (Graphene) · Graphene 1: manufactured by avanzare, trade name "av-PLAT-7", specific surface area 70 m 2 / g, particle size (Lateral size (LD50)) 7.2 μm, average thickness of particles 3 nm, oxygen content (XPS) <1% by mass, 5 to 10-layer layered structure · Graphene 2: manufactured by avanzare, trade name "av-PLAT-2", specific surface area >200 m 2 / g, particle size (Lateral size (LD50)) 2 μm, average thickness of particles <10 nm, oxygen content (XPS) <1% by mass, 20-layer or less layered structure • Graphene 3: Manufactured by Tokyo Chemical Industry Co., Ltd., product name "Graphene Nanoplatelets Aggregates (sub-micron particles, surface area 500m²)" 2 / g)", specific surface area 500m 2 / g, particle size 2μm, average particle thickness 10nm or less, oxygen content 0.5% by mass or less • Graphene 4: Manufactured by Tokyo Chemical Industry Co., Ltd., product name "Graphene Nanoplatelets Aggregates (sub-micron particles, surface area 750m2 / g)", specific surface area 750m 2 / g, particle size 2μm, average particle thickness 10nm or less, oxygen content 0.5% by mass or less (Filler) • Silica: Manufactured by Tosoh Corporation, product name "NipSeal AQ" (Other combination drugs) • Silane coupling agent: Evonik Corporation, product name "Si75" • Zinc oxide: Mitsui Mining & Smelting Co., Ltd.'s "No. 1 Zinc Oxide" • Stearic acid: Kao Corporation's "Lunaq S-20" • Anti-aging agent: Sumitomo Chemical Co., Ltd., product name "Antigen 6C" (Vulcanizing agent) • Sulfur: Manufactured by Tsurumi Chemical Industry Co., Ltd., product name "Powdered Sulfur" • Sulfurization accelerator 1 (sulfenamide-based sulfurization accelerator): Manufactured by Sumitomo Chemical Co., Ltd., product name "Soxinol CZ" • Vulcanization accelerator 2 (thiazole-based vulcanization accelerator): Manufactured by Sanshin Chemical Industry Co., Ltd., product name "Sunceller DM-G"

[0041] Unvulcanized samples of the rubber compositions obtained in Examples 1-4 and Comparative Examples 1-4 were prepared, and the vulcanized rubber, which was molded at 160°C for 20 minutes, was evaluated by the following method.

[0042] (Tear resistance of vulcanized rubber) Samples punched out in a crescent shape according to JIS K6252, with a 0.50 ± 0.08 mm cut in the center of the indentation, were tested using a Shimadzu Corporation tensile testing machine at a tensile speed of 500 mm / min. Comparative Example 1 was set to 100 and expressed as an index. A higher index indicates superior tear resistance.

[0043] [Table 1]

[0044] The results in Table 1 show that the vulcanized rubbers of the rubber compositions in Examples 1 to 4 exhibit excellent tear resistance.

Claims

1. A rubber composition containing diene rubber, silica, and graphene, The graphene has a specific surface area of ​​200 m². ２ A rubber composition characterized by being graphene having a particle size of 10 μm or less per gram, an average particle thickness of 10 nm or less, and an oxygen content of 1% by mass or less.

2. The rubber composition according to claim 1, wherein the graphene content is 0.5 to 30 parts by mass when the total amount of the diene rubber is 100 parts by mass.

3. The rubber composition according to claim 1, wherein the silica content is 60 to 120 parts by mass when the total amount of the diene rubber is 100 parts by mass.

4. The rubber composition according to claim 1, which does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

5. A pneumatic tire comprising at least vulcanized rubber of the rubber composition described in claim 1.

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