JP2010285513A - Rubber composition for bead apex and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a long-lived (durable) bead apex which is restrained in hardening deterioration. <P>SOLUTION: The rubber composition includes a rubber component including 20 mass% or more of isoprene rubber, and a compound represented by formula (I) and/or formula (II) (wherein R<SP>1</SP>and R<SP>2</SP>, which may be the same or different, are a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a bead apex rubber composition and a pneumatic tire using the same.

In recent years, low fuel consumption and durability of tires have been regarded as important from the viewpoints of resource saving and strengthening regulations for suppressing carbon dioxide emission. Many tire components other than tread rubber contain a large amount of natural rubber. However, the curing phenomenon due to thermal degradation of natural rubber causes a decrease in the mechanical properties of the rubber. Therefore, in order to improve the durability of the tire, it is desired to provide a rubber composition that suppresses the curing phenomenon due to thermal deterioration and has a long life.

Conventionally, anti-aging agents have been widely used in rubber compositions used for tires and the like in order to increase the heat resistance of the rubber composition. Anti-aging agents include amines such as N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD) and N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). Anti-aging agents are widely used.

However, in recent years, the demand for improved heat resistance has further increased, and further life extension has been demanded. Long life can be achieved by increasing the amount of the anti-aging agent, but the anti-aging agent has the property of moving through the rubber and precipitating on the surface, so that 6PPD and IPPD adhere to adjacent members by precipitation on the rubber surface. There are problems such as causing defects and poor appearance of tires. Therefore, it is desired to provide a rubber composition that can improve heat resistance and extend the life without increasing the amount of anti-aging agent.

Patent Document 1 discloses a rubber composition in which N- (1-methylheptyl) -N′-phenyl-p-phenylenediamine as an antiaging agent and a wax are blended with a diene rubber. However, there is still room for improvement in terms of improving heat resistance.

Japanese Patent Laid-Open No. 10-324779

The present invention solves the above-mentioned problems, improves the heat resistance without increasing the amount of anti-aging agent, particularly suppresses the curing deterioration of rubber, and can extend the life (improve durability) rubber composition for bead apex It is an object of the present invention to provide a pneumatic tire using the same and a bead apex of the tire.

The present invention relates to a rubber composition for bead apex containing a rubber component containing 20% by mass or more of isoprene-based rubber and a compound represented by the following formula (I) and / or (II).

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く。）

(In the formula (I), (II), ^{R 1} and ^{R 2} are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group. However, ^{R 1} and ^{R 2} is simultaneously hydrogen atom Except in cases.)

The isoprene-based rubber is preferably at least one selected from the group consisting of isoprene rubber, natural rubber and modified natural rubber.

The compound is preferably a compound represented by the following formula (III).

The rubber component preferably contains butadiene rubber and / or styrene butadiene rubber.

The present invention also relates to a pneumatic tire having a bead apex produced using the rubber composition.

According to the present invention, since the compound represented by the above formula (I) and / or (II) is blended with the rubber component containing the isoprene-based rubber, the heat resistance can be improved, and particularly, the rubber can be cured and deteriorated. Suppression is possible. Therefore, the life of the rubber composition can be extended without increasing the amount of the anti-aging agent such as 6PPD, and can be suitably applied to a bead apex of a tire, and the durability of the tire can be improved.

The rubber composition of the present invention includes a rubber component containing an isoprene-based rubber and a compound represented by the above formula (I) and / or (II). By using isoprene-based rubber as the rubber component and further blending the compounds represented by the above formulas (I) and (II), the heat resistance can be improved, and in particular, the deterioration of the rubber can be suppressed.

Here, the curing deterioration of rubber is a deterioration phenomenon in which the rubber becomes harder than the initial state when heat is applied under the condition where oxygen is present as a deterioration factor. Can be effectively suppressed. Such an effect of suppressing hardening deterioration is an effect different from so-called heat fatigue resistance (prevention of blow and chunk generation) and heat sag resistance.

Further, when these two components are used, a heat resistance improvement effect (particularly, a curing deterioration suppressing effect) is generated synergistically. For example, a compound of formula (I) or (II) is blended with styrene butadiene rubber. Compared with the case where it does, a very big hardening deterioration inhibitory effect arises.
Therefore, in the present invention, since the heat resistance (particularly the effect of suppressing hardening deterioration) can be improved without increasing the amount of anti-aging agent, it can be suitably used for tire bead apex and the like, and the life of the tire can be extended. Become.

In the present invention, isoprene-based rubber is used as the rubber component. In the present invention, the heat resistance (particularly, the effect of suppressing the curing deterioration) can be improved despite using a rubber having an isoprene skeleton. Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. These may be used alone or in combination of two or more. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Of these, NR and IR are preferred from the viewpoint of good breaking strength and workability.

In the present invention, 100% by mass of the rubber component contains 20% by mass or more of isoprene-based rubber, preferably 30% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass or more. If it is less than 20% by mass, the effect of suppressing curing deterioration may not be sufficiently obtained. Further, the content of the isoprene-based rubber is preferably 90% by mass or less, more preferably 80% by mass or less. If it exceeds 90% by mass, the mechanical strength, heat resistance, and fatigue resistance may be inferior, and the initial vulcanization rate is remarkably high, and rubber burning during processing tends to occur.

In addition to isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR) can be used as rubber components. And acrylonitrile butadiene rubber (NBR). A rubber component may be used independently and may use 2 or more types together. Of these, BR and SBR are preferred because of their good heat resistance.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having a high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd. BR containing syndiotactic polybutadiene crystals can be used.

In the present invention, BR is preferably contained in an amount of 10% by mass or more, more preferably 30% by mass or more, and still more preferably 50% by mass or more in 100% by mass of the rubber component. If it is less than 10% by mass, mechanical strength and bending fatigue resistance tend to be inferior.
The BR content is preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90 mass%, there exists a tendency for production workability and heat resistance to be inferior.

It does not specifically limit as SBR, For example, what was obtained by the solution polymerization method and what was obtained by the emulsion polymerization method can be used.

In the present invention, SBR is preferably contained in an amount of 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more in 100% by mass of the rubber component. If it is less than 5% by mass, the heat resistance tends to be inferior.
Further, the SBR content is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 50% by mass or less. If it exceeds 90% by mass, the production processability and mechanical strength tend to be inferior.

In the present invention, a compound represented by the following formula (I) and / or (II) is used. The compound is a vulcanization accelerator, but can improve the heat resistance (suppression of curing deterioration) of the vulcanized rubber.

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く（即ち、同一の環に結合しているＲ^１及びＲ^２がともに水素原子である化合物を除く）。）

(In the formulas (I) and (II), R ¹ and R ² are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, provided that R ¹ and R ² are hydrogen atoms at the same time. Except for the case (that is, excluding compounds in which R ¹ and R ² bonded to the same ring are both hydrogen atoms).

As R ¹ and R ² , the alkyl group preferably has 1 to 10 carbon atoms, the aryl group has 6 to 10 carbon atoms, and the aralkyl group has 7 to 10 carbon atoms. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, Examples include 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Examples of the aralkyl group include a benzyl group and a phenethyl group. The hydrocarbon group of R ^{1 to} R ² may be linear, branched or cyclic. Of the alkyl group, aryl group, and aralkyl group, an alkyl group is preferable, and the alkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. Further, ^{R 1} is an alkyl group, ^{R 2} is preferably a hydrogen atom. In this case, the effect of suppressing curing deterioration can be obtained satisfactorily.

Specific examples of the compound represented by the formula (I) include bis (4-methylbenzothiazolyl-2) -disulfide, bis (4-ethylbenzothiazolyl-2) -disulfide, bis (5- Methylbenzothiazolyl-2) -disulfide, bis (5-ethylbenzothiazolyl-2) -disulfide, bis (6-methylbenzothiazolyl-2) -disulfide, bis (6-ethylbenzothiazolyl) -2) -disulfide, bis (4,5-dimethylbenzothiazolyl-2) -disulfide, bis (4,5-diethylbenzothiazolyl-2) -disulfide, bis (4-phenylbenzothiazolyl-) 2) -disulfide, bis (5-phenylbenzothiazolyl-2) -disulfide, bis (6-phenylbenzothiazolyl-2) -disulfide, etc. That. Specific examples of the compound represented by the above formula (II) include 2-mercapto-4-methylbenzothiazole, 2-mercapto-4-ethylbenzothiazole, 2-mercapto-5-methylbenzothiazole, 2-mercapto- 5-ethylbenzothiazole, 2-mercapto-6-methylbenzothiazole, 2-mercapto-6-ethylbenzothiazole, 2-mercapto-4,5-dimethylbenzothiazole, 2-mercapto-4,5-diethylbenzothiazole, Examples include 2-mercapto-4-phenylbenzothiazole, 2-mercapto-5-phenylbenzothiazole, 2-mercapto-6-phenylbenzothiazole and the like. Of these, bis (4-methylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2) -disulfide, mercapto-4-methylbenzothiazole, and mercapto-5-methylbenzothiazole are preferable. . In the formulas (I) and (II), the compound represented by the formula (I) is preferably used. Furthermore, among the compounds described above, the compound (4m-MBTS) represented by the formula (III) is particularly preferably used. When using the above compounds, the effect of suppressing curing deterioration can be obtained satisfactorily.

式（Ｉ）、（ＩＩ）で表される化合物は、単独で用いてもよく、２種以上を併用してもよい。該化合物の市販品として、例えば、ＮＯＣＩＬ社の製品を使用することができる。

The compounds represented by the formulas (I) and (II) may be used alone or in combination of two or more. As a commercial product of the compound, for example, a product of NOCIL can be used.

The total content of the compounds represented by the above formulas (I) and (II) is preferably 0.8 parts by mass or more, more preferably 1.0 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.8 part by mass, the effect of suppressing the curing deterioration may not be obtained sufficiently. The total content is preferably 5.5 parts by mass or less, more preferably 5.0 parts by mass or less. If it exceeds 5.5 parts by mass, it may be difficult to maintain an appropriate crosslinking density and crosslinking form.

The rubber composition of the present invention preferably contains carbon black. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, it is possible to enhance the reinforcing property and improve the heat resistance (particularly the effect of suppressing the curing deterioration).

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 15 m ² / g or more, and more preferably 25 m ² / g or more. If it is less than 15 m < ² > / g, there exists a tendency for reinforcement | strengthening property to be insufficient and sufficient durability not to be acquired. Further, the nitrogen adsorption specific surface area of the carbon black is preferably at most 220 m ² / g, more preferably not more than ^{210m 2 / g, 100m 2 /} g or less is more preferable. When it exceeds 220 m ² / g, heat generation tends to increase.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When the rubber composition contains carbon black, the carbon black content is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and still more preferably 60 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. If the amount is less than 20 parts by mass, sufficient strength cannot be obtained, and the necessary hardness tends not to be obtained. Further, the carbon black content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less. If it exceeds 100 parts by mass, rubber kneading and extrusion may become difficult.

The rubber composition of the present invention preferably contains silica. Thereby, low exothermic property, post-deterioration physical properties, and heat resistance (particularly an effect of inhibiting curing degradation) can be improved. Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 20 m ² / g or more, more preferably 50 m ² / g or more, still more preferably 60 m ² / g or more, and most preferably 80 m ² / g or more. . If it is less than 20 m ² / g, low heat build-up, post-deterioration physical properties, and heat resistance tend to deteriorate. Further, N ₂ SA of silica is preferably 200 m ² / g or less, more preferably 150 m ² / g or less, and further preferably 130 m ² / g or less. If it exceeds 200 m ² / g, the workability tends to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

When the rubber composition contains silica, the content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, the effect of suppressing curing deterioration may not be sufficiently obtained, and heat generation may not be sufficiently suppressed. The silica content is preferably 80 parts by mass or less, more preferably 50 parts by mass or less. When it exceeds 80 mass parts, workability will worsen and there exists a tendency for fracture strength to fall.

When the rubber composition contains carbon black and silica, the total content of carbon black and silica is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, further preferably 100 parts by mass of the rubber component. Is 50 parts by mass or more. If it is less than 30 parts by mass, the effect of suppressing the curing deterioration may not be obtained satisfactorily, and there is a tendency that the breaking strength reduction, the hardness reduction, and the heat generation suppressing effect are deteriorated. The total content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. When it exceeds 150 parts by mass, the dispersibility of the filler is deteriorated and the workability may be deteriorated.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropylbenzothiazoli And sulfide systems such as tetratetrasulfide and 3-triethoxysilylpropylbenzothiazole tetrasulfide. Moreover, mercapto type, vinyl type, glycidoxy type, nitro type, chloro type and the like can also be mentioned. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferably used from the viewpoint of the reinforcing effect and processability of the silane coupling agent. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 5 parts by mass or more with respect to 100 parts by mass of the silica. If it is less than 2 parts by mass, the fracture strength tends to be greatly reduced. Moreover, 15 mass parts or less are preferable, and, as for content of this silane coupling agent, 10 mass parts or less are more preferable. When the amount exceeds 15 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent tend not to be obtained.

The rubber composition of the present invention preferably contains zinc oxide. When blending zinc oxide, the content of zinc oxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the reinforcing property tends to be inferior. Further, the content of zinc oxide is preferably 6 parts by mass or less, more preferably 5 parts by mass or less. When it exceeds 6 mass parts, it will become hard and there exists a tendency for deterioration performance (curing deterioration inhibitory effect) to deteriorate.

In addition to the above components, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, for example, inorganic and organic fillers such as clay, softeners such as oil, and vulcanization acceleration aids such as stearic acid. Agents, various anti-aging agents, ozone degradation inhibitors, vulcanizing agents such as waxes, sulfur or sulfur compounds, vulcanization accelerators, and the like can be appropriately blended as necessary.

In the present invention, an amine-based anti-aging agent is preferably used as an anti-aging agent because of its excellent destructive properties, and heat resistance (especially an effect of inhibiting curing deterioration) can be improved without increasing the amount used. is there. Examples of amine-based antioxidants include diphenylamine-based and p-phenylenediamine-based amine derivatives. Examples of the diphenylamine derivative include p- (p-toluenesulfonylamide) -diphenylamine, octylated diphenylamine, and the like. Examples of p-phenylenediamine derivatives include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). ), N, N′-di-2-naphthyl-p-phenylenediamine, and the like.

The content of the amine anti-aging agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the fracture characteristics may not be improved. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 6 parts by mass, bloom may be generated on the surface.

In the present invention, sulfur can be suitably used as a vulcanizing agent. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.
The sulfur content is preferably 1 part by mass or more and more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the effect may be small. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 6 parts by mass, the effect of suppressing the curing deterioration may not be sufficiently obtained.

In the present invention, other vulcanization accelerators may be blended together with the compounds represented by the above formulas (I) and (II), and even in this case, the effect of suppressing the curing deterioration can be suitably obtained.
Other vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl- Examples include 2-benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). 0.1 to 2.0 parts by mass may be blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention can be suitably used for each member of a tire such as a bead apex. When the rubber composition of the present invention is used for a bead apex, the heat resistance can be improved without increasing the amount of an anti-aging agent such as 6PPD. Therefore, adhesion failure between adjacent members due to precipitation of the anti-aging agent on the rubber surface In addition, the appearance defect of the tire can be suppressed, the life of the rubber composition can be extended, and the durability of the tire can be improved.

The rubber composition of the present invention is used for a bead apex disposed on the inner side of a tire clinch so as to extend radially outward from the bead core. Specifically, it is used for the members shown in FIGS. 1 to 3 of JP-A-2008-38140, FIG. 1 of JP-A-2004-339287, and the like.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition. That is, at the unvulcanized stage, the rubber composition is extruded according to the shape of the bead apex, molded by a normal method on a tire molding machine, bonded together with other tire members, and unvulcanized. Form a tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

The pneumatic tire of the present invention is preferably used as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, and the like, and particularly preferably used as a tire for passenger cars.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: RSS # 3
SBR: Nipol SBR1502 manufactured by Nippon Zeon Co., Ltd.
BR: BR150B manufactured by Ube Industries, Ltd.
Carbon black: N330T (N ₂ SA: 71 m ² / g) manufactured by Cabot Japan
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Co., Ltd.
Silica: Silica 115Gr (N ₂ SA: 110 m ² / g) manufactured by Rhodia Japan Co., Ltd.
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Zinc oxide: Zinc Hua No. 1 made by Mitsui Mining & Smelting Co., Ltd. Stearic acid: “Kashiwa” made by NOF Corporation
Anti-aging agent: Nocrack 6C (6PPD) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. 1: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator 2: bis (4-methylbenzothiazolyl-2) -disulfide (formula (III)) manufactured by NOCIL

Examples 1-4 and Comparative Examples 1-4
According to the contents shown in Tables 1 and 2, materials other than sulfur and a vulcanization accelerator were kneaded for 3 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 170 ° C. for 15 minutes to obtain a vulcanized rubber composition. The obtained vulcanized rubber composition was used as a new sample.

(Deterioration conditions)
The new sample prepared above was thermally deteriorated in an oven at 100 ° C. for 7 days. The obtained sample was used as a deteriorated sample.

The following evaluation was performed using the obtained new samples and deteriorated samples. The test results are shown in Tables 1 and 2. The hardness, swelling rate, and M100 in the table show the value of the deteriorated sample as an index when the new sample is set to 100. Shows good.

<Hardness>
Using the prepared sample, the hardness of the rubber was measured using a hardness meter at a temperature of 25 ° C. in accordance with JIS K6253 (Shore-A measurement). It shows that it is so hard that a numerical value is large.

<Swelling rate>
The immersion test of the prepared sample was performed according to JIS K6258, and the volume of the sample after being immersed in toluene at 40 ° C. for 24 hours and swollen was measured and calculated from the volume change. The smaller the value, the higher the crosslink density.

<Stress at 100% elongation (M100)>
Using a No. 3 dumbbell-shaped test piece made of the prepared sample, a tensile test was performed at a pulling speed of 500 mm / min in accordance with JIS K6251 “vulcanized rubber and thermoplastic rubber—determining tensile properties”. The stress at 100% elongation at 23 ° C. (M100 (MPa)) was measured. Larger numbers indicate higher modulus and hardness. M100 is also an index of crosslink density.

<Appearance>
A new sample molded in a length of 15 cm, a width of 15 cm, and a thickness of 4 mm was exposed to sunlight for 2 weeks, and the degree of browning was visually evaluated on a five-point scale. Larger values indicate better brown discoloration.

According to Table 1, Examples 1 and 2 in which 4m-MBTS is blended with a rubber component containing NR are more effective in suppressing curing deterioration (hardness, swelling rate, and the like) than Comparative Example 1 in which a conventional accelerator such as TBBS is blended. M100) could be improved. The comparative example 2 which increased the anti-aging agent was inferior in the inhibitory effect (hardness, swelling rate, M100) of hardening deterioration, and especially the external appearance compared with Example 1,2.

According to Table 2, Examples 3 and 4 in which 4 m-MBTS was blended with a rubber component containing NR were more effective in suppressing curing deterioration (hardness, swelling rate, and the like) than Comparative Example 3 in which a conventional accelerator such as TBBS was blended. M100) could be improved. The comparative example 4 which increased the anti-aging agent was inferior in the suppression effect of hardening deterioration (swelling rate, M100) and especially the external appearance compared with the examples 3 and 4.

Claims (5)

A rubber composition for bead apex containing a rubber component containing 20% by mass or more of isoprene-based rubber and a compound represented by the following formula (I) and / or (II).

(In the formula (I), (II), ^{R 1} and ^{R 2} are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group. However, ^{R 1} and ^{R 2} is simultaneously hydrogen atom Except in cases.) The rubber composition for bead apex according to claim 1, wherein the isoprene-based rubber is at least one selected from the group consisting of isoprene rubber, natural rubber and modified natural rubber. The rubber composition for bead apex according to claim 1 or 2, wherein the compound is a compound represented by the following formula (III).

The rubber composition for bead apex according to any one of claims 1 to 3, wherein the rubber component includes butadiene rubber and / or styrene butadiene rubber. The pneumatic tire which has the bead apex produced using the rubber composition in any one of Claims 1-4.