Rubber composition for tire sidewalls and pneumatic tires

Abstract

To provide a tire sidewall rubber composition that can improve the reinforcing properties of the final vulcanized rubber while reducing the amount of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine used as an anti-aging agent, and a pneumatic tire that has the vulcanized rubber of the tire sidewall rubber composition in at least the sidewall portion. [Solution] A rubber composition for tire sidewalls containing diene rubber, a filler, a vulcanizing agent, an antioxidant, and graphene powder, wherein the antioxidant contains at least an amine-ketone type antioxidant, and the graphene powder content is 1 to 10 parts by mass when the total amount of diene rubber is 100 parts by mass. Preferably, the rubber composition does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine as the antioxidant.

Description

[Technical Field]

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

[0002] The side of a pneumatic tire is called the tire sidewall, and from the perspective of improving durability during tire operation, it is essential to improve the reinforcing properties of the rubber portion (vulcanized rubber) that makes up the tire sidewall. However, since the tire sidewall is constantly exposed to the atmosphere, antioxidants are generally added to the rubber composition used as raw material for tire sidewalls to prevent aging caused by ultraviolet rays and heat.

[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] In Patent Document 2 below, rubber components, sp 2 A rubber composition containing a type carbon material and a metal oxide, sp 2 The following rubber composition is described, in which the carbon material is one or more selected from the group consisting of graphite, graphene, fullerene, and carbon nanohorns. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 7385429 [Patent Document 2] Japanese Patent Publication No. 2015-143298 [Overview of the project] [Problems that the invention aims to solve]

[0006] N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (hereinafter also referred to as "6PPD") is known as an anti-aging agent and has been widely used in the rubber industry. When 6PPD is incorporated, for example, into tire sidewall applications, it reacts with ozone to form 6PPD-quinone. However, since 6PPD-quinone is toxic, it is desirable to reduce the amount of 6PPD used as much as possible. In the technologies described in the above-mentioned Patent Documents 1 and 2, graphenes are incorporated into the rubber composition. However, after diligent research by the present inventors, it was found that there is room for further improvement from the standpoint of reducing the amount of 6PPD used in the rubber composition while improving the reinforcing properties of the final vulcanized rubber.

[0007] The present invention has been made in view of the above circumstances, and its object is to provide a rubber composition for tire sidewalls that can improve the reinforcing properties of the final vulcanized rubber while reducing the amount of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine used as an anti-aging agent, and a pneumatic tire that has the vulcanized rubber of the tire sidewall rubber composition in at least the sidewall portion. [Means for solving the problem]

[0008] The above problems can be solved by the following configuration. That is, the present invention relates to a rubber composition for tire sidewalls (1) containing a diene rubber, a filler, a vulcanizing agent, an antioxidant, and graphene powder, wherein the antioxidant contains at least an amine-ketone type antioxidant, and the content of the graphene powder is 1 to 10 parts by mass when the total amount of the diene rubber is 100 parts by mass.

[0009] In the above-mentioned rubber composition for tire sidewalls (1), a rubber composition for tire sidewalls (2) that does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine as the anti-aging agent is preferred.

[0010] In the above-mentioned rubber composition for tire sidewalls (1) or (2), a preferred rubber composition for tire sidewalls (3) is one in which the diene rubber is selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

[0011] In any of the above tire sidewall rubber compositions (1) to (3), the filler has an iodine adsorption amount of 75 to 100 g / kg and a DBP absorption amount of 95 to 130 cm 3 A rubber composition (4) for tire sidewalls, which is carbon black in an amount of 100g, is preferred.

[0012] In any of the above tire sidewall rubber compositions (1) to (4), the vulcanizing agent contains at least sulfur and a sulfenamide-based vulcanization accelerator, and a tire sidewall rubber composition (5) in which the sulfur content is greater than that of the sulfenamide-based vulcanization accelerator is preferred.

[0013] Of the above tire sidewall rubber compositions (1) to (5), the tire sidewall rubber composition (6) is preferred, in which the amine-ketone-based antioxidant is a 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0014] The present invention also relates to a pneumatic tire (7) having at least one of the tire sidewall rubber compositions (1) to (6) vulcanized rubber in the sidewall portion. [Effects of the Invention]

[0015] N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) can impart a high anti-aging effect to vulcanized rubber, but as mentioned above, when used in tire sidewall applications, it becomes 6PPD-quinone upon ozone exposure, so its usage should be reduced as much as possible. As a result of diligent research, the inventors have found that by using an amine-ketone-based anti-aging agent in combination with graphene, it is possible to reduce the amount of 6PPD blended while improving the reinforcing properties of the resulting vulcanized rubber. The reason for this effect is not clear, but the following reasons can be hypothesized.

[0016] Graphene powder tends to aggregate and disperse easily when mixed in diene-based rubber. On the other hand, amine-ketone antioxidants, such as the 2,2,4-trimethyl-1,2-dihydroquinoline polymer, have a softening point of 80-110°C. This suggests that amine-ketone antioxidants soften during the mixing of the rubber composition. Therefore, when mixing the rubber composition, the graphene powder tends to disperse uniformly due to the softening effect of the amine-ketone antioxidant. As a result, it is estimated that the reinforcing effect of graphene powder can be effectively utilized while reducing the amount of 6PPD, thereby improving the reinforcing properties of the final vulcanized rubber.

[0017] The vulcanized rubber of the rubber composition according to the present invention makes it possible to improve the reinforcing properties of the final vulcanized rubber while reducing the amount of 6PPD blended in. Therefore, the vulcanized rubber of the rubber composition according to the present invention is particularly useful for the sidewall portion of pneumatic tires where durability is required. [Modes for carrying out the invention]

[0018] The rubber composition for tire sidewalls according to the present invention contains diene rubber, a filler, a vulcanizing agent, an anti-aging agent, and graphene powder.

[0019] 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. From the viewpoint of solving the problems, in the rubber composition for a tire sidewall according to the present invention, the diene rubber is preferably at least one selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

[0020] For example, it may contain carbon black, silica, etc. as a filler.

[0021] As the carbon black, for example, in addition to carbon black used in the normal rubber industry such as SAF, ISAF, HAF, FEF, GPF, etc., conductive carbon black such as acetylene black and ketjen black can be used. From the viewpoint of solving the problems, in the rubber composition for a tire sidewall according to the present invention, as the filler, it is preferable to contain carbon black having an iodine adsorption amount of 75 to 100 g / kg and a DBP absorption amount of 95 to 130 cm 3 / 100 g. When the total amount of the diene rubber in the rubber composition for a tire sidewall according to the present invention is 100 parts by mass, the content of the carbon black is preferably 5 to 80 parts by mass.

[0022] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc. used for normal rubber reinforcement are used. Among them, wet silica is preferable. When the total amount of the diene rubber in the rubber composition for a tire sidewall according to the present invention is 100 parts by mass, the content of the silica is preferably 1 to 50 parts by mass.

[0023] When silica is included as a filler, it is also preferable to include a silane coupling agent. 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 rubber compositions 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.

[0024] Preferably, sulfur and a vulcanization accelerator can be used as vulcanizing agents.

[0025] Any ordinary sulfur for rubber can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. The rubber composition for tire sidewalls according to the present invention preferably contains 0.1 to 10 parts by mass of sulfur when the total amount of diene-based rubber is 100 parts by mass.

[0026] 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. However, from the viewpoint of solving the problem, the rubber composition for tire sidewalls according to the present invention preferably contains a sulfenamide-based vulcanization accelerator as the vulcanization accelerator. In the rubber composition for tire sidewalls according to the present invention, when the total amount of diene-based rubber is 100 parts by mass, the content of the vulcanization accelerator, more preferably a sulfenamide-based vulcanization accelerator, is preferably 0.1 to 5 parts by mass.

[0027] From the viewpoint of solving the problem, the rubber composition for tire sidewalls according to the present invention contains at least sulfur and a sulfenamide-based vulcanization accelerator as vulcanizing agents, and it is preferable that the sulfur content is higher than the sulfenamide-based vulcanization accelerator, and it is more preferable that the sulfur content is twice or more the content of the vulcanization accelerator. Furthermore, it is preferable that the sulfur content is four times or less the content of the vulcanization accelerator, and more preferably three times or less.

[0028] Examples of anti-aging agents 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, which are commonly used for rubber. However, the rubber composition for tire sidewalls according to the present invention contains at least an amine-ketone-based anti-aging agent. Examples of amine-ketone-based anti-aging agents include 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, and reaction products of diphenylamine and acetone, with 2,2,4-trimethyl-1,2-dihydroquinoline polymer being particularly preferred. On the other hand, considering environmental factors, the rubber composition for tire sidewalls according to the present invention preferably contains 3 parts by mass or less, more preferably 1 part by mass or less, of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) when the total amount of diene rubber is 100 parts by mass, and it is particularly preferable that the composition does not contain 6PPD as an antioxidant.

[0029] Graphene is a two-dimensional sheet-like material classified as a nanocarbon material, sp 2 It has a structure made up of six-membered rings of carbon. Graphene readily aggregates or bonds with each other through van der Waals forces, and in this invention, graphene powder is used, either alone or in the form of two or more aggregated or bonded graphene particles. From the viewpoint of solving the problem, the graphene used in the rubber composition for tire sidewalls according to the present invention has a BET specific surface area of ​​550 to 850 m² as measured by the BET method. 2 It is preferable that the amount be / g, and 650-750m 2 It is more preferable that the amount is / g. The rubber composition for tire sidewalls according to the present invention preferably contains 1 to 10 parts by mass of graphene powder when the total amount of diene rubber is 100 parts by mass.

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

[0031] The rubber composition for tire sidewalls according to the present invention is obtained by mixing diene rubber, fillers, vulcanizing agents, antioxidants, and graphene powder, in addition to softeners such as zinc oxide, stearic acid, and wax, and processing aids, using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and roll.

[0032] Furthermore, the method of combining the above components is not particularly limited. It may be a method in which the components other than sulfur and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added and kneaded further; a method in which the components are added and kneaded in any order; or a method in which all components are added and kneaded simultaneously.

[0033] The vulcanized rubber of the rubber composition according to the present invention makes it possible to improve the reinforcing properties of the final vulcanized rubber while reducing the amount of 6PPD blended in. Therefore, the vulcanized rubber of the rubber composition according to the present invention is particularly useful for the sidewall portion of pneumatic tires where durability is required. [Examples]

[0034] The present invention will be described in more detail below by illustrating some embodiments.

[0035] (Preparation of rubber composition for tire sidewalls) To 100 parts by mass of rubber components, the tire sidewall rubber compositions of Example 1 and Comparative Example 1 were blended according to the formulations in Table 1, and the mixture was kneaded using a standard Banbury mixer to prepare the tire sidewall rubber compositions. The individual compounding agents listed in Table 1 are shown below.

[0036] (Diene-based rubber) - Butadiene rubber: manufactured by UBE Industries, Ltd., product name "UBEPOL BR150B" - Natural rubber: RSS#3 (Filler) - Carbon black: manufactured by Tokai Carbon Co., Ltd., product name "SEAST KH", iodine adsorption amount 90 g / kg and DBP absorption amount 119 cm 3 / 100 g (Graphene powder) - Graphene powder: manufactured by Fujifilm Wako Pure Chemical Corporation, product name "Graphene Powder", BET specific surface area 650 - 750 m 2 / g (Antioxidant) - Amine-ketone antioxidant (2,2,4-trimethyl-1,2-dihydroquinoline polymer): manufactured by Kawaguchi Chemical Industry Co., Ltd., product name "ANTAGE RD" - 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine): manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "NOCRACK 6C" (Other compounding agents) - Aromatic oil: "PROCESS NC140" manufactured by ENEOS - Zinc oxide: "Zinc Oxide Type 3" manufactured by Mitsui Mining & Smelting Co., Ltd. - Stearic acid: "LUNAC S-20" manufactured by Kao Corporation - Wax: "OZOACE0355" manufactured by Nippon Seiro Co., Ltd. (Vulcanizing agent) - Sulfur: "Powdered Sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. - Vulcanization accelerator (sulfenamide-based vulcanization accelerator): manufactured by Sumitomo Chemical Co., Ltd., product name "SOKCINOL CZ"

[0037] After preparing unvulcanized samples of the rubber compositions for tire sidewalls of Example 1 and Comparative Example 1 obtained above, scorch (processability) was evaluated. Further, vulcanized rubber was produced by vulcanizing at 160 °C for 20 minutes, and the 300% tensile stress and elongation retention rate at break were evaluated under the following conditions.

[0038] (Scorch (processability) of the rubber composition for tire sidewall) Using a Mooney scorch tester (L-type rotor) conforming to JIS K6300-1, the t5 value was determined after preheating for 1 minute and at a temperature of 125°C. The value was then expressed as an index with the value from Example 1 set to 100. A higher value indicates less burning and superior scorching (machinability).

[0039] (300% tensile stress of vulcanized rubber) The 300% tensile stress of vulcanized rubber was determined by performing a tensile test on vulcanized rubber test specimens in accordance with JIS K6251, and expressed as an index with the value of Comparative Example 1 (the standard) set to 100. A higher index indicates superior reinforcing properties of the rubber.

[0040] (Elongation retention rate of vulcanized rubber at the time of cutting) The retention rate of elongation at break of vulcanized rubber was determined by first measuring the elongation at break of a vulcanized rubber test specimen by performing a tensile test in accordance with JIS K6251, and then heating the vulcanized rubber test specimen in a gear oven temperature-controlled to 90°C for 96 hours in accordance with JIS K6257, followed by a similar tensile test to measure the elongation at break. The retention rate of elongation at break after aging compared to elongation at break before aging was determined and expressed as an index with the value of Comparative Example 1 (the standard) set to 100. A higher index indicates a higher retention rate and superior aging resistance.

[0041] [Table 1]

[0042] The results in Table 1 show that the tire sidewall rubber composition according to Example 1 has high scorch resistance and excellent processability. Furthermore, the vulcanized rubber of the tire sidewall rubber composition according to Example 1 shows improved 300% tensile stress of the vulcanized rubber while maintaining elongation retention at break, indicating excellent reinforcing properties of the vulcanized rubber.

Claims

1. A rubber composition for tire sidewalls containing diene rubber, filler, vulcanizing agent, antioxidant and graphene powder, The aforementioned anti-aging agent contains at least an amine-ketone type anti-aging agent, A rubber composition for tire sidewalls, characterized in that when the total amount of the diene-based rubber is 100 parts by mass, the content of the graphene powder is 1 to 10 parts by mass.

2. The rubber composition for tire sidewalls according to claim 1, wherein the aforementioned antioxidant does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

3. The rubber composition for tire sidewalls according to claim 1, wherein the diene rubber is at least one selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

4. The aforementioned filler has an iodine adsorption capacity of 75 to 100 g / kg and a DBP absorption capacity of 95 to 130 cm. ３ The rubber composition for tire sidewalls according to claim 1, wherein the carbon black is / 100g.

5. The rubber composition for tire sidewalls according to claim 1, wherein the vulcanizing agent contains at least sulfur and a sulfenamide-based vulcanization accelerator, and the sulfur content is greater than that of the sulfenamide-based vulcanization accelerator.

6. The rubber composition for tire sidewalls according to claim 1, wherein the amine-ketone-based antioxidant is a 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

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

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