Rubber composition for tire sidewalls and pneumatic tires

Abstract

To provide a rubber composition for tire sidewalls that can improve the fracture characteristics of the final vulcanized rubber while reducing the amount of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine used as an antioxidant. [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 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and when the total amount of diene rubber is 100 parts by mass, the content of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is X and the content of graphene powder is Y, such that 1.5 ≤ X + Y ≤ 10 and X:Y is 1:3 to 3:1.

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 improving the fracture characteristics (tensile strength) of the rubber (vulcanized rubber) that makes up the tire sidewall is essential from the perspective of improving durability during tire operation. However, since the tire sidewall is constantly exposed to the atmosphere, antioxidants are generally added to the rubber composition used 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.

[0005] Patent Document 3 below describes a method for manufacturing a composite material, which includes the steps of: preparing a first material containing randomly layered graphene; preparing a second material containing rubber; mixing the first material and the second material; and manufacturing a randomly layered graphene-rubber composite material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 7385429 [Patent Document 2] Japanese Patent Publication No. 2015-143298 [Patent Document 3] Special Publication No. 2024-504244 [Overview of the project] [Problems that the invention aims to solve]

[0007] 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 to 3, graphenes are incorporated into the rubber composition, but 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 fracture characteristics of the final vulcanized rubber.

[0008] The present invention has been made in view of the above circumstances, and its purpose is to provide a rubber composition for tire sidewalls that can improve the fracture characteristics 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]

[0009] 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 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and when the total amount of the diene rubber is 100 parts by mass, the content of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is X and the content of the graphene powder is Y, such that 1.5 ≤ X + Y ≤ 10 and X:Y is 1:3 to 3:1.

[0010] In the above-mentioned rubber composition for tire sidewalls (1), a preferred rubber composition for tire sidewalls (2) 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 the above tire sidewall rubber composition (1) or (2), 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 (3) 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 (3), the vulcanizing agent contains at least sulfur and a sulfenamide-based vulcanization accelerator, and a tire sidewall rubber composition (4) 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 (4), the tire sidewall rubber composition (5) 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 having at least one of the tire sidewall rubber compositions (1) to (5) 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 optimizing the blending ratio of 6PPD and graphene powder in the presence of an amine-ketone-based anti-aging agent, specifically, by designing the blend so that 1.5 ≤ X + Y ≤ 10 and X:Y ≤ 1:3 to 3:1, when the total amount of diene rubber is 100 parts by mass, the tensile strength of the resulting vulcanized rubber can be improved while reducing the amount of 6PPD used. 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, 6PPD has a melting point of 46-50°C and is considered to be liquid at the time of mixing the rubber composition. Therefore, when mixing the rubber composition, if the total amount of graphene powder and 6PPD is set within a desired range and in a desired ratio, the graphene powder tends to disperse uniformly due to the liquid effect of 6PPD. 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 fracture properties (tensile strength) of the final vulcanized rubber.

[0017] The vulcanized rubber of the rubber composition according to the present invention can improve the breaking properties (tensile strength) of the finally obtained vulcanized rubber while reducing the compounding amount of 6PPD. Therefore, the vulcanized rubber of the rubber composition according to the present invention is particularly useful for the sidewall portion of a pneumatic tire that requires durability.

Mode for Carrying Out the Invention

[0018] The rubber composition for a tire sidewall according to the present invention contains a diene rubber, a filler, a vulcanizing agent, an antioxidant, 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, it is preferable that the diene rubber is at least one selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

[0020] As the filler, for example, carbon black, silica, or the like may be contained.

[0021] Examples of the carbon black include carbon black used in the normal rubber industry such as SAF, ISAF, HAF, FEF, GPF, etc., and conductive carbon black such as acetylene black and ketjen black can also 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, the iodine adsorption amount is 75 to 100 g / kg and the DBP absorption amount is 95 to 130 cm 3It is preferable to contain carbon black at 100 g. In the rubber composition for a tire sidewall according to the present invention, when the total amount of the diene rubber is 100 parts by mass, the content of 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. that are usually used for rubber reinforcement are used. Among them, wet silica is preferable. In the rubber composition for a tire sidewall according to the present invention, when the total amount of the diene rubber is 100 parts by mass, the content of silica is preferably 1 to 50 parts by mass.

[0023] When containing silica as a filler, it is also preferable to contain a silane coupling agent together. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents blended with silica in the rubber composition can be used. For example, bis(3-triethoxysilylpropyl)tetrasulfide (for example, "Si69" manufactured by Evonik Japan Co., Ltd.), bis(3-triethoxysilylpropyl)disulfide (for example, "Si75" manufactured by Evonik Japan Co., Ltd.), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, sulfide silanes such as bis(2-trimethoxysilylethyl)disulfide, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane, etc. mercapto silanes, 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, etc. protected mercapto silanes can be mentioned. The blending amount of the silane coupling agent is preferably 2 to 20% by mass when the total amount of silica is 100% by mass.

[0024] As the vulcanizing agent, sulfur and a vulcanization accelerator can be suitably used.

[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 and 6PPD as anti-aging agents. 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. The rubber composition for tire sidewalls according to the present invention preferably contains 0.1 to 20 parts by mass of an amine-ketone-based antioxidant, more preferably 2,2,4-trimethyl-1,2-dihydroquinoline polymer, when the total amount of diene rubber is 100 parts by mass. The rubber composition for tire sidewalls according to the present invention preferably contains 0.375 to 7.5 parts by mass of 6PPD when the total amount of diene rubber is 100 parts by mass.

[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 0.375 to 7.5 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 is designed such that, when the total amount of diene-based rubber is 100 parts by mass, the content of 6PPD is X and the content of graphene powder is Y, then 1.5 ≤ X + Y ≤ 10 and X:Y is 1:3 to 3:1. This makes it possible to improve the fracture characteristics of the final vulcanized rubber while reducing the amount of 6PPD blended. From the viewpoint of solving the problem, it is preferable that 1.5 ≤ X + Y ≤ 5. Furthermore, it is preferable that X:Y is 1.5:2.5 to 2.5:1.5.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] The vulcanized rubber of the rubber composition according to the present invention makes it possible to improve the fracture characteristics 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]

[0035] The embodiments of this invention are described below for a more specific explanation.

[0036] (Preparation of Rubber Composition for Tire Sidewall) For 100 parts by mass of the rubber component, according to the formulation in Table 1, the rubber compositions for tire sidewalls of Examples 1 to 3 and Comparative Examples 1 to 2 were blended and kneaded using an ordinary Banbury mixer to prepare the rubber compositions for tire sidewalls. Each compounding agent described in Table 1 is shown below.

[0037] (Diene Rubber) · Butadiene Rubber: Manufactured by UBE Industries, Ltd., trade name "UBEPOL BR150B" · Natural Rubber: RSS#3 (Filler) · Carbon Black: Manufactured by Tokai Carbon Co., Ltd., trade 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, trade name "Graphene", 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., trade name "Antage RD" · 6PPD (N - (1,3 - Dimethylbutyl) - N’ - phenyl - p - phenylenediamine): Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrack 6C" (Other Compounding Agents) · Aromatic Oil: "Process NC140" manufactured by ENEOS · Zinc Oxide: "Zinc Oxide No. 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: Manufactured by Tsurumi Chemical Industry Co., Ltd., trade name "Powder Sulfur" · Vulcanization Accelerator (Sulfenamide - type Vulcanization Accelerator): Manufactured by Sumitomo Chemical Co., Ltd., trade name "Soxinol CZ"

[0038] Unvulcanized samples of the tire sidewall rubber compositions obtained in Examples 1-3 and Comparative Examples 1-2 were prepared, and their scorching (processability) was evaluated. Furthermore, vulcanized rubber was produced by vulcanization at 160°C for 20 minutes, and the tensile strength, bending test (fatigue resistance), and 300% tensile stress retention rate were evaluated under the following conditions.

[0039] (Scorching (processability) of rubber compositions for tire sidewalls) 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 2 set to 100. A higher value indicates less burning and superior scorching (machinability).

[0040] (Tensile strength (breaking characteristics) of vulcanized rubber) The tensile strength of vulcanized rubber was measured in accordance with JIS K-6251 2017. Specifically, a dumbbell-shaped test piece (Type 3) was cut from the vulcanized rubber, and the tensile force of the dumbbell-shaped test piece was measured using a tensile testing machine to determine the tensile strength (breaking characteristics). The tensile strength of Comparative Example 1 is expressed as an index with the tensile strength of Comparative Example 1 set to 100. A larger index indicates greater tensile strength.

[0041] (Flexural test of vulcanized rubber (fatigue resistance)) Fatigue resistance was evaluated according to the JIS K6260 bending crack initiation test, measuring the time until a 10 mm crack in the test specimen. The results are shown as an index with the fatigue resistance of Comparative Example 1 set to 100. A higher index indicates superior fatigue resistance.

[0042] (300% tensile stress retention rate of vulcanized rubber) The retention rate of 300% tensile stress in vulcanized rubber was determined by first conducting a tensile test on a vulcanized rubber specimen in accordance with JIS K6251 to measure the 300% tensile stress. Then, the specimen was heated in a gear oven at a temperature controlled to 90°C for 96 hours in accordance with JIS K6257, and a tensile test was performed again to measure the 300% tensile stress. The retention rate of 300% tensile stress after aging compared to the 300% tensile stress before aging was determined and expressed as an index with the value of Comparative Example 1, which served as the standard, set to 100. Generally, under the above conditions, if the aging resistance is poor, the value of the 300% tensile stress after aging increases, and the retention rate of 300% tensile stress becomes greater than 100. However, if the aging resistance is excellent, the increase in the value of the 300% tensile stress after aging is small, and the retention rate is close to 100. Therefore, a smaller index indicates better aging resistance.

[0043] [Table 1]

[0044] The results in Table 1 show that the rubber compositions for tire sidewalls according to Examples 1 to 3 have high scorch resistance and excellent processability. Furthermore, the vulcanized rubber of the tire sidewall rubber compositions according to Examples 1 to 3 shows improved tensile strength (breaking characteristics) while maintaining flexibility (fatigue resistance) and 300% tensile stress retention rate (anti-aging performance).

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 and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 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 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is X and the content of graphene powder is Y, then 1.5 ≤ X + Y ≤ 10 and X:Y is 1:3 to 3:

1.

2. 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.

3. The aforementioned filler has an iodine adsorption capacity of 75 to 100 g / kg and a DBP absorption capacity of 95 to 130 cm³. ３ The rubber composition for tire sidewalls according to claim 1, wherein the carbon black is / 100g.

4. 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.

5. 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.

6. 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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