Rubber composition for tire treads and pneumatic tires

Abstract

To provide a tire tread rubber composition that can improve the 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 at least the vulcanized rubber of the tire tread rubber composition in the tread portion. [Solution] A rubber composition for tire treads 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 for tire treads does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine as an antioxidant.

Description

Technical Field

[0001] The present invention relates to a rubber composition for a tire tread and a pneumatic tire.

Background Art

[0002] The surface portion of a pneumatic tire is called a tire tread. From the viewpoint of improving durability, it is essential to improve the tear resistance during tire running. However, since the tire tread is always exposed to the atmosphere, an anti-aging agent is generally blended in the rubber composition for the tire tread as a raw material from the viewpoint of preventing aging caused by ultraviolet rays, heat, etc.

[0003] In Patent Document 1 below, there is described a pneumatic tire including a tread portion, the tread portion including a tread cap layer and a tread base layer, the tread cap layer having a ground contact surface, the tread portion including sipes having open ends and closed ends, the sipes extending radially inwardly from the ground contact surface of the tread portion at least to the tread base layer, the tread cap layer being made of a tread cap composition, the tread cap composition including 100 parts of at least one diene elastomer and less than 0.5 part of talc based on 100 parts by weight of an elastomer, the tread base layer being under the tread cap layer and the tread base layer being made of a tread base composition, the tread base composition including 100 parts of at least one diene elastomer and a small plate-shaped filler, the small plate-shaped filler in the tread base composition being present in a range of 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 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 compounded, for example, in tire tread 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 tear resistance 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 treads that can improve the 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 tread rubber composition in at least the tread 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 treads (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 treads (1), a rubber composition for tire treads (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 treads (1) or (2), a preferred rubber composition for tire treads (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 tread rubber compositions (1) to (3), the filler has an iodine adsorption amount of 105 to 135 g / kg and a DBP absorption amount of 115 to 135 cm 3 A rubber composition (4) for tire treads, which is carbon black in an amount of 100g, is preferred.

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

[0013] Of the above tire tread rubber compositions (1) to (5), tire tread 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 vulcanized rubber from the tire tread rubber compositions (1) to (6) in the tread portion.

[0015] The present invention also relates to a pneumatic tire (8) having a vulcanized rubber from any of the tire tread rubber compositions (1) to (6) on at least the surface of the tread 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 tread 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 added while improving the tear resistance of the final vulcanized rubber. The reason for this effect is not clear, but the following reasons can be hypothesized.

[0017] 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 tear resistance of the final vulcanized rubber can be improved by effectively utilizing the reinforcing effect of graphene powder while reducing the amount of 6PPD added.

[0018] The vulcanized rubber of the rubber composition according to the present invention makes it possible to improve the 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 applications in the tread portion of pneumatic tires where durability is required. [Modes for carrying out the invention]

[0019] The rubber composition for tire treads according to the present invention contains diene rubber, a filler, a vulcanizing agent, an anti-aging agent, and graphene powder.

[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 tread 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.

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

[0022] 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 tread according to the present invention, as the filler, it is preferable to contain carbon black having an iodine adsorption amount of 105 to 135 g / kg and a DBP absorption amount of 115 to 135 cm 3 / 100 g. When the total amount of the diene rubber in the rubber composition for a tire tread according to the present invention is 100 parts by mass, the content of the carbon black is preferably 5 to 80 parts by mass.

[0023] 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 tread according to the present invention is 100 parts by mass, the content of the silica is preferably 0 to 80 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 treads according to the present invention preferably contains 0.5 to 5 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 treads according to the present invention preferably contains a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator as vulcanization accelerators. In the rubber composition for tire treads according to the present invention, when the total amount of diene-based rubber is 100 parts by mass, the total content of the vulcanization accelerator, more preferably a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator, is preferably 0.1 to 4.5 parts by mass.

[0028] From the viewpoint of solving the problem, the rubber composition for tire treads according to the present invention contains at least sulfur, a sulfenamide-based vulcanization accelerator, and a guanidine-based vulcanization accelerator as vulcanizing agents, and it is preferable that the sulfur content is greater than the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator, and it is more preferable that the sulfur content is 1.1 times or more the total content of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator. Furthermore, it is preferable that the sulfur content is 3 times or less the content of the vulcanization accelerator, and more preferable that it is 2 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 treads 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 treads 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] 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 tire tread rubber composition 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 treads 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.

[0031] The rubber composition for tire treads according to the present invention contains diene rubber, fillers, vulcanizing agents, antioxidants, and graphene powder. In addition to these, the rubber composition for tire treads 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 treads 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 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 applications in the tread portion of pneumatic tires where durability is required. [Examples]

[0035] The present invention will be described in more detail below by illustrating some embodiments.

[0036] (Preparation of rubber composition for tire treads) To 100 parts by mass of rubber components, the tire tread 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 tread rubber compositions. The individual compounding agents listed in Table 1 are shown below.

[0037] (Diene-based rubber) • Styrene-butadiene rubber: Manufactured by ENEOS Material Co., Ltd., product name "ESBR1502" • Butadiene rubber: Manufactured by UBE, product name "UBEPOL BR150B" • Natural rubber: RSS#3 (Filler) • Carbon black: Manufactured by Tokai Carbon Co., Ltd., product name "Seas 7HM", iodine adsorption capacity 120g / kg and DBP absorption capacity 125cm 3 / 100g (Graphene powder) • Graphene powder: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "Graphene Powder", BET specific surface area 650-750 m² 2 / g (Anti-aging agent) • 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 1 (guanidine-based sulfurization accelerator): Manufactured by Sumitomo Chemical Co., Ltd., product name "Soccinol D" • Sulfurization accelerator 2 (sulfenamide-based sulfurization accelerator): Manufactured by Sumitomo Chemical Co., Ltd., product name "Soxinol CZ"

[0038] Unvulcanized samples of the tire tread rubber compositions obtained in Example 1 and Comparative Example 1 were prepared, and their scorching (processability) was evaluated. Further vulcanized rubber was produced by vulcanizing at 160°C for 20 minutes, and its tear resistance and 300% tensile stress retention rate were evaluated under the following conditions.

[0039] (Scorching (processability) of rubber compositions for tire treads) 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).

[0040] (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. Example 1 is expressed as an index with the value of Comparative Example 1 set to 100. A higher index indicates superior tear resistance.

[0041] (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 a higher retention rate and superior aging resistance.

[0042] [Table 1]

[0043] The results in Table 1 show that the tire tread rubber composition according to Example 1 has high scorch resistance and excellent processability. Furthermore, the vulcanized rubber of the tire tread rubber composition according to Example 1 shows improved tear resistance while maintaining a 300% tensile stress retention rate (anti-aging performance).

Claims

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

3. The tire tread rubber composition 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 105 to 135 g / kg and a DBP absorption capacity of 115 to 135 cm ３ The tire tread rubber composition according to claim 1, wherein the carbon black is / 100g.

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

6. The rubber composition for tire treads 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 tread rubber composition described in claim 1 in the tread portion.

8. A pneumatic tire comprising the vulcanized rubber of the tire tread rubber composition described in claim 1 on at least the surface of the tread portion.

Images