Rubber composition for tire sidewalls and pneumatic tires

Abstract

To provide a tire sidewall rubber composition that can improve the tensile stress and tear resistance 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 a diene rubber, a filler, a vulcanizing agent, an antioxidant, and laminated micro-graphene, wherein the antioxidant contains at least an amine-ketone type antioxidant, and the content of laminated micro-graphene 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 tensile strength and tear resistance 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 pneumatic tire comprising a tread portion, the tread portion comprising a tread cap layer and a tread base layer, the tread cap layer having a contact surface, the tread portion comprising sipes having an open end and a closed end, the sipes extending radially inward from the contact surface of the tread portion to at least the tread base layer, the tread cap layer comprising a tread cap composition, the tread cap composition comprising at least 100 parts by weight of elastomer The present invention describes a pneumatic tire comprising one diene elastomer and less than 0.5 parts by weight of talc, wherein the tread base layer is located below the tread cap layer, and the tread base layer consists of a tread base composition, the tread base composition comprising 100 parts of at least one diene elastomer and a plate-type filler, and the plate-type filler in the tread base composition is present in an amount ranging from 0.5 to 20 parts by weight, based on the elastomer in 100 parts by weight of the tread base composition.

[0004] Patent Document 2 below describes a pneumatic rubber tire having a circumferential tread with a cap / base configuration including an outer tread cap rubber layer and an inner tread rubber layer, wherein the rubber composition of the inner tread rubber layer comprises (A) rubber containing the following based on parts by weight (phr) per 100 parts by weight of rubber: (1) 10 to 80 phr of syndiotactic-1,2-polybutadiene, and (2) 90 to 20 phr of at least one additional diene elastomer, where the additional diene elastomer is at least one polymer and copolymer of isoprene and 1,3-butadiene, and a copolymer of styrene and at least one of isoprene and 1,3-butadiene. (B) A filler / reinforcement up to 40 phr containing one of the following: (1) carbon black, or (2) precipitated silica, or (3) a combination of carbon black and precipitated silica, or (4) a platter of exfoliated montmorillonite clay up to 10 phr and a non-exfoliated kaolinite clay up to 40 phr; where the filler / reinforcement containing at least one carbon black and precipitated silica may optionally additionally contain at least one of the platter of exfoliated clay up to 10 phr and the non-exfoliated clay up to 40 phr; where the carbon black filler is (5) in amounts of 5 to 40 phr, with a DBP value in the range of 62 to 150 cc / 100 g and 20 to 205 m 2 The invention describes a pneumatic rubber tire comprising: (6) rubber-reinforced carbon black having an iodine value in the range of / g; (7) conductive carbon black in an amount of 5 to 20 phr having a DBP value in the range of 175 to 570 cc / 100g and an iodine value in the range of 180 to 650 m2 / g; (8) graphene plates containing at least partially exfoliated graphite in an amount of up to 15 phr; and (9) at least one of carbon nanotubes in an amount of up to 10 phr. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2019-528207 [Patent Document 2] Japanese Patent Publication No. 2013-136745 [Overview of the Initiative] [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 compounded, for example, for 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 compounded 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 tensile stress and tear resistance of the final vulcanized rubber.

[0007] 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 tensile stress and tear resistance 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) comprising a diene rubber, a filler, a vulcanizing agent, an antioxidant, and laminated micrographene, wherein the antioxidant contains at least an amine-ketone type antioxidant, and the amount of laminated micrographene 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), the laminated micrographene plates have a specific surface area of ​​300 to 600 m² by the BET method. 2 A rubber composition (2) for tire sidewalls with a weight of / g is preferred.

[0010] In the above-mentioned rubber composition for tire sidewalls (1) or (2), a rubber composition for tire sidewalls (3) that does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine as the anti-aging agent is preferred.

[0011] In any of the above tire sidewall rubber compositions (1) to (3), a preferred tire sidewall rubber composition (4) is one in which the diene rubber is selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

[0012] In any of the above tire sidewall rubber compositions (1) to (4), 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 (5) for tire sidewalls, which is carbon black in an amount of 100g, is preferred.

[0013] In any of the above tire sidewall rubber compositions (1) to (5), the vulcanizing agent contains at least sulfur and a sulfenamide-based vulcanization accelerator, and a tire sidewall rubber composition (6) in which the sulfur content is greater than that of the sulfenamide-based vulcanization accelerator is preferred.

[0014] Of the above tire sidewall rubber compositions (1) to (6), the tire sidewall rubber composition (7) is preferred, in which the amine-ketone-based antioxidant is a 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0015] The present invention also relates to a pneumatic tire (8) having at least one of the tire sidewall rubber compositions (1) to (7) vulcanized rubber in the sidewall portion. [Effects of the Invention]

[0016] 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 laminated micro-graphene, the amount of 6PPD can be reduced while improving the tensile stress and tear resistance of the resulting vulcanized rubber. The reason for this effect is not clear, but the following reasons can be hypothesized.

[0017] Graphene tends to aggregate and disperse easily when mixed in diene-based rubber. On the other hand, amine-ketone antioxidants, such as 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, graphene tends to disperse uniformly due to the softening effect of the amine-ketone antioxidant. Laminated micro-graphene, in particular, tends to disperse more easily than regular graphene, and as a result, it is estimated that the reinforcing effect of laminated micro-graphene can be effectively utilized while reducing the amount of 6PPD, thereby improving the tensile stress and tear resistance of the final vulcanized rubber.

[0018] The vulcanized rubber of the rubber composition according to the present invention makes it possible to improve the tensile stress and tear resistance 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]

[0019] The rubber composition for a tire sidewall according to the present invention contains a diene rubber, a filler, a vulcanizing agent, an antioxidant, and laminated platelet graphene.

[0020] 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.

[0021] As the filler, for example, carbon black, silica, etc. may be contained.

[0022] Examples of 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, 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 carbon black is preferably 5 to 80 parts by mass.

[0023] As silica, wet silica, dry silica, sol-gel silica, and surface-treated silica, which are commonly used for rubber reinforcement, can be used. Among these, wet silica is preferred. The rubber composition for tire sidewalls according to the present invention preferably contains 1 to 50 parts by mass of silica when the total amount of diene-based rubber is 100 parts by mass.

[0024] 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.

[0025] Preferably, sulfur and a vulcanization accelerator can be used as vulcanizing agents.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Stacked micrographene is a two-dimensional sheet-like material classified as a nanocarbon material, sp 2 It has a structure tiled with six-membered rings of carbon. Laminated micrographene plates readily aggregate or bond to each other by van der Waals forces, and in this invention, powdered laminated micrographene plates, in which two or more laminated micrographene plates have aggregated or bonded together, are used. From the viewpoint of solving the problem, the laminated micrographene plates used in the rubber composition for tire sidewalls according to the present invention have a BET specific surface area of ​​300 to 600 m² as measured by the BET method. 2 It is preferable that the amount be / g, and 400-550m 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 laminated micrographene when the total amount of diene rubber is 100 parts by mass.

[0031] In the market, the BET specific surface area measured by the BET method is 50-200 m². 2 There are microscopic graphene plates with a density of / g. While laminated microscopic graphene plates form a shape close to particles, microscopic graphene plates are thought to form a plate-like shape. For this reason, for example, if microscopic graphene plates are present on the surface of a pneumatic tire, there is a concern that the plate-like microscopic graphene plates may catch on the road surface or other surfaces, becoming the starting point for fracture and thus worsening tear resistance. On the other hand, since laminated microscopic graphene plates form a shape close to particles, even if they are present on the tire surface, they are less likely to catch on the road surface or other surfaces, and as a result, tear resistance is presumed to improve. As described above, laminated microscopic graphene plates and microscopic graphene plates can be differentiated by their BET specific surface area measured by the BET method.

[0032] The rubber composition for tire sidewalls according to the present invention contains diene rubber, fillers, vulcanizing agents, antioxidants, and laminated micro-graphene. 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.

[0033] The rubber composition for tire sidewalls according to the present invention is obtained by mixing diene rubber, fillers, vulcanizing agents, antioxidants, and laminated micro-graphene, 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.

[0034] 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.

[0035] The vulcanized rubber of the rubber composition according to the present invention can improve the tensile stress and tear resistance 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 part of a pneumatic tire that requires durability.

Examples

[0036] The examples of this invention are described below for a more specific explanation.

[0037] (Preparation of Rubber Composition for Tire Sidewall) Based on 100 parts by mass of the rubber component, according to the compounding formula in Table 1, the rubber compositions for the tire sidewall of Example 1 and Comparative Examples 1 to 2 were compounded and kneaded using an ordinary Banbury mixer to prepare the rubber compositions for the tire sidewall. Each compounding agent described in Table 1 is shown below.

[0038] (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 / 100g (Graphene Powder) · Microplate Graphene: Manufactured by Tokyo Chemical Industry Co., Ltd., trade name "Graphene nanoplatelets 6 - 8nm (thick), 5μm (wide)", BET specific surface area 120 - 150 m 2 / g · Stacked Microplate (Sub - micron Particle) Graphene: Manufactured by Tokyo Chemical Industry Co., Ltd., trade name "Graphene Nanoplatelets Aggregates (sub - micron particles, surface area 500m 2 / g)", BET specific surface area 500 m 2 / g​​​• Amine-ketone-based 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 "Nocrac 6C" (Other combination drugs) • Aroma oil: ENEOS "Process NC140" • Zinc oxide: Mitsui Mining & Smelting Co., Ltd.'s "3 types of zinc oxide" • Stearic acid: Kao Corporation's "Lunaq S-20" • Wax: Nippon Seiro "OZOACE0355" (Vulcanizing agent) • Sulfur: Manufactured by Tsurumi Chemical Industry Co., Ltd., product name "Powdered Sulfur" • Sulfurization accelerator (sulfenamide-based sulfurization accelerator): Manufactured by Sumitomo Chemical Co., Ltd., product name "Soxinol CZ"

[0039] Unvulcanized samples of the tire sidewall rubber compositions obtained in Example 1 and Comparative Examples 1-2 were prepared, and their scorching (processability) was evaluated. Further vulcanized rubber was produced by vulcanization at 160°C for 20 minutes, and its tear resistance, 300% tensile stress, and 300% tensile stress retention rate were evaluated under the following conditions.

[0040] (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 1 set to 100. A higher value indicates less burning and superior scorching (machinability).

[0041] (Tear resistance of vulcanized rubber) Tear resistance was evaluated by punching out the vulcanized rubber obtained above using the crescent shape specified in JIS K6252, and making a 0.50 ± 0.08 mm cut in the center of the indentation to obtain a sample. The tear strength was measured using a Shimadzu Corporation tensile testing machine at a tensile speed of 500 mm / min. The value is expressed as an index with the value of Comparative Example 1 set to 100. A higher index indicates better tear resistance (cut resistance).

[0042] (300% tensile stress of vulcanized rubber) The 300% tensile stress of vulcanized rubber was measured by performing a tensile test on vulcanized rubber test pieces 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 a higher 300% tensile stress and superior reinforcing properties of the rubber. A higher numerical value indicates less burning and better scorching (machinability).

[0043] (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.

[0044] [Table 1]

[0045] From the results in Table 1, it can be seen that the tire sidewall rubber composition according to Example 1 does not contain 6PPD and therefore does not have 6PPD-quinone toxicity. Furthermore, it can be seen that the vulcanized rubber of the tire sidewall rubber composition according to Example 1 has improved tear resistance while maintaining a 300% tensile stress and a 300% tensile stress retention rate (anti-aging performance).

Claims

1. A rubber composition for tire sidewalls containing diene rubber, filler, vulcanizing agent, antioxidant and laminated micro-graphene, 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 laminated micro-plate graphene is 1 to 10 parts by mass.

2. The aforementioned laminated micrographene plates have a specific surface area of ​​300 to 600 m² as measured by the BET method. ２ The rubber composition for tire sidewalls according to claim 1, wherein the amount is / g.

3. 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.

4. 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.

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

6. 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.

7. 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.

8. 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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