JP7458247B2 - Rubber compositions, rubber compositions for tires, rubber compositions for tire treads, crosslinked rubber for tires, tire treads and tires - Google Patents

Description

The present invention relates to a rubber composition, a rubber composition for tires, a rubber composition for tire treads, a crosslinked rubber for tires, a tire tread, and a tire.

In recent years, due to the social demand for energy conservation, tires with low rolling resistance have been required in order to promote fuel efficiency in automobiles, and rubber compositions with superior heat generation (low loss properties) than before have been desired. There is.
On the other hand, it is desired to improve the wear resistance of automobile tires, and a rubber composition with a high storage modulus, particularly a high dynamic storage modulus (G') is desired.

Patent Document 1 discloses that natural rubber or synthetic isoprene rubber is mixed with a specific resin composition and thermoplastic resin in order to provide a rubber composition that has low heat build-up and high elasticity. Rubber compositions formulated in proportions are described.

Japanese Patent Application Publication No. 2012-92179

In Patent Document 1, a rubber composition that has low heat build-up and high elasticity with respect to a specific rubber component was obtained, but the rubber components used were limited. Furthermore, the amounts of the resin composition and thermoplastic resin added were large, and the selectivity of the formulation of the rubber composition was limited.

The object of the present invention is to provide a rubber composition capable of producing a crosslinked rubber having a high dynamic storage modulus; a crosslinked rubber for tires and a tire having a high dynamic storage modulus, and a rubber composition for tires capable of producing these. Another object of the present invention is to provide a tire tread having a high dynamic storage modulus and a rubber composition for a tire tread capable of producing the same, and to solve the above problems.

As a result of extensive investigations, the present inventors have found that the above problems can be solved by blending a compound having a specific structure.
That is, the present invention relates to the following <1> to <9>.
<1> A rubber composition comprising: a rubber component containing a diene rubber; a crosslinking agent; a benzoic acid derivative having one or two methoxy groups, with at least the methoxy group being at a para-position relative to a carboxy group; and 20 to 120 parts by mass of a filler per 100 parts by mass of the rubber component, wherein the content of at least one selected from a thermosetting resin, an imidazole compound, and a methylene acceptor is 0 to 0.1 parts by mass per 100 parts by mass of the rubber component.

<2> The rubber composition for a tire according to <1>, wherein the benzoic acid derivative includes at least one selected from the group consisting of m,p-dimethoxybenzoic acid and p-methoxybenzoic acid.
<3> The rubber composition according to <1> or <2>, wherein the amount of the benzoic acid derivative is 0.05 to 10 parts by mass based on 100 parts by mass of the rubber component.
<4> The rubber composition according to any one of <1> to <3>, wherein the crosslinking agent contains a vulcanizing agent and further contains a vulcanization accelerator, and the mass ratio (a/b) of the content (a) of the vulcanization accelerator to the content (b) of the benzoic acid derivative is 0.2 to 5.0.

<5> A rubber composition for tires comprising the rubber composition according to any one of <1> to <3>.
<6> A rubber composition for a tire tread comprising the rubber composition according to any one of <1> to <3>.

<7> A crosslinked rubber for tires obtained by crosslinking the rubber composition for tires according to <5>.

<8> A tire tread obtained by crosslinking the rubber composition for a tire tread according to <6>.
<9> A tire comprising the crosslinked rubber for tires according to <7>.

According to the present invention, a rubber composition capable of producing a crosslinked rubber having a high dynamic storage modulus; a crosslinked rubber for a tire having a high dynamic storage modulus, a tire, and a rubber composition for a tire capable of producing the same. Also, it is possible to provide a tire tread having a high dynamic storage modulus and a rubber composition for a tire tread capable of producing the same.

EMBODIMENT OF THE INVENTION Below, this invention will be illustrated and explained in detail based on the embodiment. In addition, in the following explanation, the description "A to B" indicating a numerical range represents a numerical range that includes the endpoints A and B, and "A or more and B or less" (in the case of A<B), or " Less than or equal to A and more than or equal to B (in the case of A>B).

<Rubber composition>
The rubber composition of the present invention comprises a rubber component containing a diene rubber, a crosslinking agent, and a benzoic acid derivative having one or two methoxy groups and having at least the methoxy group at the para position with respect to a carboxy group. , 20 to 120 parts by mass of filler per 100 parts by mass of the rubber component, and the content of at least one selected from a thermosetting resin, an imidazole compound, and a methylene acceptor is based on 100 parts by mass of the rubber component. 0 to 0.1 parts by mass.
Hereinafter, a benzoic acid derivative having one or two methoxy groups and having at least the methoxy group at the para position with respect to a carboxy group will be referred to as a benzoic acid derivative in the present invention.
As a result of extensive studies, the present inventors have found that the crosslinked rubber obtained by crosslinking the rubber composition containing the benzoic acid derivative of the present invention has a high dynamic storage modulus (G'). Although the detailed mechanism by which such an effect is obtained is unknown, it is partially assumed as follows.
In the crosslinking process, it is thought that the benzoic acid derivative in the present invention and the rubber component form a pseudo crosslink, and it is presumed that a high dynamic storage modulus (G') was achieved.
The present invention will be explained in detail below.

[Rubber component]
The rubber composition of the present invention contains a rubber component containing a diene rubber.
The rubber component can be appropriately selected from rubber components including diene rubbers used in the rubber industry. The diene rubber may be natural rubber or synthetic rubber, and these may be used alone or in combination.
Examples of diene-based synthetic rubbers include styrene-butadiene copolymer (SBR), polybutadiene (BR), polyisoprene (IR), styrene-isoprene copolymer (SIR), butadiene-isoprene copolymer, butadiene-styrene- Examples include isoprene copolymer, acrylonitrile-butadiene copolymer, chloroprene rubber, butyl rubber (IIR), and halogenated butyl rubber. Further, a part thereof may have a branched structure by using a polyfunctional modifier, for example, a modifier such as tin tetrachloride.
The rubber component is preferably made of diene rubber, and preferably contains a styrene-butadiene copolymer or natural rubber. The rubber components may be used alone or in combination of two or more.

[Benzoic acid derivative]
The rubber composition of the present invention contains a benzoic acid derivative having one or two methoxy groups and having at least the methoxy group at the para position relative to the carboxy group. The benzoic acid derivative in the present invention has at least one methoxy group at the para position, and may further have another methoxy group at either the ortho position or the meta position with respect to the carboxy group. .
The rubber composition of the present invention may contain only one kind of benzoic acid derivative according to the present invention, or may contain two or more kinds.

Among the above, the benzoic acid derivative in the present invention preferably has a methoxy group at each of the meta and para positions, or has a methoxy group only at the para position. Specifically, m,p-dimethoxy Benzoic acid (DMBA) and p-methoxybenzoic acid (pMBA) are preferred. That is, the benzoic acid derivative preferably contains at least one selected from the group consisting of m,p-dimethoxybenzoic acid and p-methoxybenzoic acid.

The benzoic acid derivatives in the present invention may be commercially available or may be synthesized.

The content of the benzoic acid derivative in the present invention in the rubber composition is preferably 0.01 parts by mass or more, more preferably 0.05 to 10 parts by mass, based on 100 parts by mass of the rubber component. . Within this range, the storage modulus (G') of the crosslinked rubber can be further improved and tan δ at 50°C can be lowered. From the same viewpoint, the content of the benzoic acid derivative in the present invention in the rubber composition is more preferably 0.1 parts by mass or more, even more preferably 0.3 parts by mass or more, and even more preferably 0.3 parts by mass or more. It is even more preferably at least 5 parts by mass, even more preferably at most 5 parts by mass, even more preferably at most 3 parts by mass, and even more preferably at most 2.5 parts by mass. More preferred.

[Crosslinking agent]
The rubber composition of the present invention contains a crosslinking agent.
The crosslinking agent is not particularly limited as long as it is a component capable of crosslinking rubber molecules. Examples include vulcanizing agents that cause sulfur crosslinking, organic peroxides that cause peroxide crosslinking, oxidation compounds that cause quinoid crosslinking, and diamine compounds that cause amine crosslinking. A vulcanizing agent is usually used.
Sulfur is usually used as the vulcanizing agent, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.

In the rubber composition, the content of the crosslinking agent is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass, based on 100 parts by mass of the rubber component, from the viewpoint of sufficiently promoting crosslinking between rubber molecules. parts or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and from the viewpoint of improving anti-aging properties, preferably 10 parts by mass or less, more preferably 5 parts by mass or less. , more preferably 3 parts by mass or less.

[Thermosetting resin, imidazole compound, methylene acceptor]
The content of at least one selected from a thermosetting resin, an imidazole compound, and a methylene acceptor in the rubber composition of the present invention is 0 to 0.1 part by mass based on 100 parts by mass of the rubber component. be.
This means that the rubber composition of the present invention is substantially free of thermosetting resin, imidazole compound, and methylene acceptor. Since the rubber composition does not substantially contain a thermosetting resin, an imidazole compound, and a methylene acceptor, it has excellent wear resistance.

Examples of thermosetting resins include unsaturated polyester resins, epoxy resins, vinyl ester resins, phenol resins, polyamide resins, urea resins, melamine resins, polyimide resins, diallyl phthalate resins, and urethane resins. Examples include resins.

Imidazole compounds include imidazole, 4-ethylaminoimidazole, 2-mercapto-1-methylimidazole, 1-methylimidazole, 2,4,5-triphenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptadecylimidazole, etc.

Examples of methylene acceptors include m-substituted phenols such as resorcinol; condensates of aldehydes such as formaldehyde and acetaldehyde with m-substituted phenols; condensates of m-substituted phenols and other mono-substituted phenols with aldehydes, etc.

The content of at least one selected from a thermosetting resin, an imidazole compound, and a methylene acceptor in the rubber composition of the present invention is preferably 0 parts by mass based on 100 parts by mass of the rubber component. That is, it is preferable that the rubber composition of the present invention contains neither a thermosetting resin, an imidazole compound, nor a methylene acceptor.

[Vulcanization accelerator]
When the crosslinking agent contains a vulcanizing agent, the rubber composition of the present invention preferably further contains a vulcanization accelerator.
The vulcanization accelerator is not particularly limited and can be appropriately selected depending on the purpose. Specifically, CBS (N-cyclohexyl-2-benzothiazole sulfenamide), TBBS (N-t-butyl-2-benzothiazole sulfenamide), TBSI (N-t-butyl-2-benzothiazole sulfenamide), sulfenamide-based vulcanization accelerators such as phenimide); guanidine-based vulcanization accelerators such as DPG (diphenylguanidine); thiuram-based vulcanization accelerators such as tetraoctylthiuram disulfide and tetrabenzylthiuram disulfide; MBT ( Examples include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole) and MBTS (di-2-benzothiazolyl disulfide); vulcanization accelerators such as zinc dialkyldithiophosphate; and the like. These may be used alone or in combination of two or more.
Among these, in the presence of the benzoic acid derivative in the present invention, it is preferable to contain at least a sulfenamide-based vulcanization accelerator as a vulcanization accelerator, from the viewpoint of proceeding with appropriate vulcanization, and at least CBS It is more preferable to contain one or both of and TBBS.

The content of the vulcanization accelerator in the rubber composition is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of proceeding with moderate vulcanization at an appropriate vulcanization rate, and is preferably 10 parts by mass or less, more preferably 7.5 parts by mass or less, and even more preferably 5 parts by mass or less.

In addition, in the rubber composition, the mass ratio (a/b) of the content (a) of the vulcanization accelerator to the content (b) of the benzoic acid derivative in the present invention is the vulcanization inhibition of the benzoic acid derivative in the present invention. From the viewpoint of suppressing the effect, promoting appropriate vulcanization, and obtaining a crosslinked rubber composition with low heat build-up, the It is preferably 5.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less.

[Filling material]
The rubber composition of the present invention contains 20 to 120 parts by mass of filler per 100 parts by mass of the rubber component.
When the rubber composition contains a filler in the above range, the reinforcing properties of the crosslinked rubber can be improved and the tan δ at 50° C. can be further reduced.
Generally, when a rubber composition contains a large amount of filler, the crosslinked rubber tends to generate heat due to friction between the fillers, but when the rubber composition contains the benzoic acid derivative of the present invention, the aggregation of the filler is increased, Can suppress fever. That is, it is easy to lower tan δ at 50°C.
From the viewpoint of further improving the reinforcing properties of the crosslinked rubber and further reducing the tan δ at 50°C, the total content of fillers in the rubber composition is preferably 30 parts by mass or more based on 100 parts by mass of the rubber component, It is more preferably 40 parts by mass or more, and preferably 90 parts by mass or less, and more preferably 80 parts by mass or less.

The filler may be an organic filler such as carbon black, an inorganic filler such as silica, or a blend of these two types of fillers. Among these, one or more fillers selected from carbon black and silica are preferably used.
The carbon black is not particularly limited, and any one that has been conventionally used as a filler for rubber can be appropriately selected and used. For example, SRF, GPF, FEF, HAF, ISAF, SAF, etc. are used, and FEF, HAF, ISAF, SAF, etc., which are particularly excellent in bending resistance and fracture resistance, are preferred.
From the viewpoint of reinforcing properties, the carbon black has a nitrogen adsorption specific surface area N ₂ SA (conforming to JIS K 6217-2:2001) of preferably 30 m ² /g or more, more preferably 35 m ² /g or more, and preferably 150 m ² /g or less, more preferably 130 m ² /g or less.
The carbon black may be used alone or in combination of two or more kinds.

On the other hand, examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and among them, wet silica is preferred.
The BET specific surface area (measured based on ISO 5794/1) of this wet silica is preferably 40 m ² /g or more, more preferably 80 m 2 /g or more, and preferably 350 m ² /g or more, from the viewpoint of reinforcing properties. ² /g or less, more preferably 300m ² /g or less. As such silica, commercial products such as "Nipsil AQ" and "Nipsil KQ" manufactured by Tosoh Silica Co., Ltd. and "Ultrasil VN3" manufactured by Degussa Corporation can be used.
One type of silica may be used alone, or two or more types may be used in combination.
Examples of inorganic fillers other than silica include aluminum hydroxide, clay, talc, calcium carbonate, and zeolite.

In the present invention, it is preferable to use carbon black and silica together as a filler. In this case, the content of carbon black in the rubber composition of the present invention is higher than that of the rubber component from the viewpoint of reinforcing properties and low heat build-up. Based on 100 parts by mass, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and preferably 60 parts by mass or less, more preferably 55 parts by mass or less, and Preferably it is 50 parts by mass or less.
Further, when carbon black and silica are used together, the content of silica in the rubber composition of the present invention is preferably 1 part by mass or more based on 100 parts by mass of the rubber component from the viewpoint of reinforcing properties and low heat generation. , more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 35 parts by mass. below.

(Silane coupling agent)
When silica is used as a filler in the rubber composition of the present invention, it is preferable to compound a silane coupling agent for the purpose of further improving the reinforcing properties.
Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,N N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide and the like are included, and among these, bis(3-triethoxysilylpropyl)polysulfide and 3-trimethoxysilylpropylbenzothiazyl tetrasulfide are preferred from the viewpoint of the reinforcement improving effect and the like.
These silane coupling agents may be used alone or in combination of two or more.

In the rubber composition of the present invention, the preferred amount of the silane coupling agent to be blended varies depending on the type of silane coupling agent, but from the viewpoint of improving the dispersibility of silica and suppressing gelation of the rubber component, Based on 100 parts by mass of silica, the amount is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass. The amount is preferably 10 parts by mass or less.

[Other ingredients]
In addition to the above-mentioned components, the rubber composition of the present invention may contain other additives as long as the object of the present invention is not impaired. Other additives may be appropriately selected from various additives normally used in the rubber industry, and specifically include vulcanization accelerators, anti-aging agents, softeners, colorants, flame retardants, lubricants, Examples include blowing agents, plasticizers, processing aids, antioxidants, ultraviolet inhibitors, antistatic agents, coloring inhibitors, and other compounding agents.

(vulcanization accelerator)
The rubber composition of the present invention may contain vulcanization accelerating aids such as zinc white and fatty acids from the viewpoint of accelerating vulcanization. The fatty acid may be saturated or unsaturated, and may be linear or branched. Further, the number of carbon atoms is not particularly limited, and for example, those having 1 to 30 carbon atoms, preferably 15 to 30 carbon atoms can be used.
Specific examples of fatty acids include cyclohexanoic acid (cyclohexanecarboxylic acid), naphthenic acids such as alkylcyclopentane having side chains, hexanoic acid, octanoic acid, decanoic acid (including branched carboxylic acids such as neodecanoic acid), and dodecanoic acid. , saturated fatty acids such as tetradecanoic acid, hexadecanoic acid, and octadecanoic acid (stearic acid), unsaturated fatty acids such as methacrylic acid, oleic acid, linoleic acid, and linolenic acid, and resin acids such as rosin, tall oil acid, and abietic acid. and stearic acid is preferred. These may be used alone or in combination of two or more. In the present invention, stearic acid and zinc white can be suitably used, and it is particularly preferable to use zinc white and stearic acid together.
The total content of these vulcanization accelerators in the rubber composition is not particularly limited, but from the viewpoint of kneading workability and vulcanization acceleration, it is preferably 0.000 parts by mass per 100 parts by mass of the rubber component. The amount is 5 parts by weight or more, more preferably 1 part by weight or more, even more preferably 3 parts by weight or more, and preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 7 parts by weight or less.

(Anti-aging agent)
Examples of anti-aging agents that can be used in the rubber composition of the present invention include 3C(N-isopropyl-N'-phenyl-p-phenylenediamine), 6C[N-(1,3-dimethylbutyl)-N'-phenyl -p-phenylenediamine], TMDQ (2,2,4-trimethyl-1,2-dihydroquinoline polymer), AW (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline), diphenylamine Examples include high-temperature condensates of and acetone.
The anti-aging agents may be used alone or in combination of two or more.
The blending amount of the anti-aging agent in the rubber composition is preferably from the viewpoint of imparting sufficient weather resistance and ozone resistance and suppressing discoloration and deterioration of crack resistance, based on 100 parts by mass of the rubber component. 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 1 part by mass or more, and preferably 6 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 3 parts by mass. It is as follows.

The rubber composition of the present invention can be used for manufacturing various rubber products.
In addition to tires, rubber products include anti-vibration rubber, seismic isolation rubber, belts such as conveyor belts, rubber crawlers, and various hoses.

<Preparation of rubber composition>
The method for producing the rubber composition of the present invention is not particularly limited.
The rubber composition is prepared by blending various compounding agents in addition to the rubber component, crosslinking agent, and benzoic acid derivative of the present invention, and then kneading, heating, and extruding using a Banbury mixer, roll, intensive mixer, twin screw extruder, etc. It can be manufactured by et al.
From the viewpoint of suppressing vulcanization during production of the rubber composition and improving handling properties during production, the components to be included in the rubber composition, excluding the crosslinking agent and vulcanization accelerator, are blended in advance. It is preferable to prepare a rubber composition by mixing (first kneading step) and then blending and mixing a crosslinking agent and a vulcanization accelerator (second kneading step).

By preparing the rubber composition by the above method, vulcanization is unlikely to occur even if the first kneading step is performed under high temperature conditions, so the rubber composition can be manufactured with high productivity.
Regarding the kneading temperature in the first kneading step, from the viewpoint of suppressing thermal decomposition of each component, the maximum temperature is preferably 250°C or less, more preferably 200°C or less, and even more preferably 180°C or less. Further, from the viewpoint of productivity, the kneading temperature in the first kneading step is preferably 100°C or higher, more preferably 120°C or higher, and still more preferably 140°C or higher.
Regarding the kneading temperature in the second kneading step, the maximum temperature is preferably 150°C or less, more preferably 130°C or less, from the viewpoint of suppressing the occurrence of vulcanization during kneading. Further, from the viewpoint of productivity, the kneading temperature in the second kneading step is preferably 80°C or higher, more preferably 100°C or higher.

<Rubber composition for tires, rubber composition for tire treads>
The rubber composition for tires of the present invention consists of the rubber composition of the present invention.
The rubber composition for tire tread of the present invention consists of the rubber composition of the present invention.
The rubber composition of the present invention can produce crosslinked rubber with an excellent balance between high elastic modulus and low tan δ, and is therefore suitable for producing tires, especially tire treads. It is preferable to use it as a rubber composition for tread.

<Crosslinked rubber for tires>
The crosslinked rubber for tires of the present invention is obtained by crosslinking the rubber composition for tires of the present invention.
In the crosslinked rubber for tires, crosslinks are formed between rubber molecules by a crosslinking agent, and in addition, pseudo crosslinks may be formed by the benzoic acid derivative of the present invention.
The crosslinking conditions are not particularly limited and can be appropriately selected depending on the purpose, but it is preferable that the crosslinking temperature is 120 to 200° C. and the crosslinking time is 1 to 900 minutes.

<Tire tread and tires>
The tire tread and tire of the present invention contain the crosslinked rubber for tires of the present invention.
The crosslinked rubber for tires of the present invention is suitably used for manufacturing tires.
The rubber composition for tire treads of the present invention is suitably used for manufacturing tire treads. That is, the tire tread is obtained by crosslinking the rubber composition for tire tread of the present invention. The crosslinked rubber for tires of the present invention may be used for manufacturing tire treads.
There is no particular restriction on the application site of the crosslinked rubber for tires of the present invention, and it can be appropriately selected depending on the purpose. For example, it may be used in the tread portion as described above, or it may be suitably used in at least one of the sidewall portions, bead portions, inner liners, and other reinforcing rubber portions.

Further, the tire of the present invention can be manufactured according to a conventional method without any particular limitation other than using the rubber composition for tires or the rubber composition for tire treads of the present invention. That is, the rubber composition for a tire tread of the present invention is extruded into a tread member at an unvulcanized stage, and is pasted and molded by a conventional method on a tire molding machine to mold a green tire. This raw tire is heated and pressurized in a vulcanizer to produce a tire. Further, as the gas to fill the tire, in addition to normal air or air with adjusted oxygen partial pressure, inert gas such as nitrogen, argon, helium, etc. can be used.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the Examples below.

<Examples 1-2 and Comparative Examples 1-3>
[Preparation and crosslinking of rubber composition]
A rubber composition is prepared by kneading the ingredients in the proportions shown in Table 1 using a Banbury mixer, and then crosslinked (vulcanized) by heating at 145°C for 33 minutes using a pressure-type vulcanizer. (vulcanized rubber) was obtained. The components shown in Table 1 are as follows.
・NR: Natural rubber, RSS #1
・Carbon black: manufactured by Tokai Carbon Co., Ltd., product name "SEAST 3", HAF, N ₂ SA = 79 m ² /g
・Silica: Manufactured by Tosoh Silica Co., Ltd., product name “Nipsil AQ”, BET specific surface area = 205 m ² /g
・Silane coupling agent: Manufactured by Evonik Co., Ltd., product name "Si69", bis[(3-triethoxysilyl)propyl]tetrasulfide ・Anti-aging agent: Manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., product name "Nocrac 6C", N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine/vulcanization accelerator: Manufactured by Sanshin Kagaku Kogyo Co., Ltd., trade name "Suncellar NS-G", N-(t-butyl)- 2-benzothiazolesulfenamide stearic acid: manufactured by Kao Corporation, trade name “Lunac S-70V”,
・Zinc white: Manufactured by Wako Pure Chemical Industries, Ltd. ・Sulfur: Manufactured by Wako Pure Chemical Industries, Ltd.

Compound DMBA: m,p-dimethoxybenzoic acid (Tokyo Chemical Industry Co., Ltd.)
pMBA: p-methoxybenzoic acid (Tokyo Chemical Industry Co., Ltd.)
BA: Benzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd., structure shown below)
pCBA: p-carboxybenzoic acid (Tokyo Chemical Industry Co., Ltd., structure shown below)

〔evaluation〕
The storage modulus (G' (50° C., 5%)) and loss tangent (tan δ (50° C., 5%)) of the obtained crosslinked rubber were measured.
Specifically, the obtained crosslinked rubber was measured at a strain of 5% at 50°C at a frequency of 10Hz using a viscoelasticity measuring device "ARES-G2" (manufactured by TA Instruments). Dynamic storage modulus (tensile dynamic storage modulus, G' (50°C, 5%)) and loss tangent (tan δ (50°C, 5%)) were measured.
Regarding the dynamic storage modulus (G'), the dynamic storage modulus (G') of Comparative Example 1 was set as 100 and expressed as an index. It should be noted that the larger the value of G', the better the steering stability and wear resistance of the vehicle.
Furthermore, regarding the loss tangent (tan δ), the loss tangent (tan δ) of Comparative Example 1 was set as 100, and the loss tangent (tan δ) was expressed as an index. Note that the smaller the value of tan δ, the lower the heat build-up and the lower the rolling resistance when used in tires.

The results in Table 1 show that by adding a compound having a specific structure, a crosslinked rubber having a high dynamic storage modulus (G') can be obtained.

According to the present invention, a rubber composition from which a crosslinked rubber having a high dynamic storage modulus is obtained is provided, and the rubber composition and crosslinked rubber are applicable to the production of tires, and in particular, to the production of tire treads. It is useful for A tire using the rubber composition or crosslinked rubber in its tire tread is expected to have excellent wear resistance, low heat generation, and excellent energy saving properties.

Claims (9)

A rubber component containing diene rubber,
a crosslinking agent;
A benzoic acid derivative having two methoxy groups, each having a methoxy group at a meta position and a para position with respect to a carboxy group;
20 to 120 parts by mass of filler per 100 parts by mass of the rubber component,
A rubber composition in which the content of at least one selected from a thermosetting resin, an imidazole compound, and a methylene acceptor is 0 to 0.1 part by mass based on 100 parts by mass of the rubber component. The rubber composition according to claim 1, wherein the benzoic acid derivative comprises m,p-dimethoxybenzoic acid . The rubber composition according to claim 1 or 2, wherein the content of the benzoic acid derivative is 0.05 to 10 parts by mass per 100 parts by mass of the rubber component. The crosslinking agent contains a vulcanizing agent and further contains a vulcanization accelerator, and the mass ratio (a/b) of the content (a) of the vulcanization accelerator to the content (b) of the benzoic acid derivative. The rubber composition according to any one of claims 1 to 3, wherein 0.2 to 5.0. A rubber composition for tires comprising the rubber composition according to any one of claims 1 to 4. A rubber composition for a tire tread comprising the rubber composition according to any one of claims 1 to 4. A crosslinked rubber for tires obtained by crosslinking the rubber composition for tires according to claim 5. A tire tread obtained by crosslinking the tire tread rubber composition according to claim 6. A tire comprising the crosslinked rubber for tires according to claim 7.