JP5437690B2 - Rubber composition for inner liner and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for an inner liner and a pneumatic tire using the same.

Conventionally, in a pneumatic tire, particularly a tubeless tire, an inner liner rubber made of rubber having a low air permeability is formed on the tire lumen surface for the purpose of maintaining the tire internal pressure. For the inner liner rubber, butyl rubber, halogenated butyl rubber, etc., which have excellent air permeation resistance, are generally used, but they have excellent raw rubber strength (green strength) compared to synthetic rubber and excellent workability. As a vulcanized rubber, natural rubber is often used because of its high mechanical strength and excellent low heat build-up.

Since the inner liner part is likely to generate heat as the car travels, the aging of N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine (6PPD), etc. is prevented to increase the heat resistance of the rubber. Agents are widely used.

However, the demand for improving heat resistance is further increased, and further life extension is required. Although it is possible to extend the service life by increasing the amount of the anti-aging agent, the anti-aging agent in the inner liner rubber may be deposited on the surface under high temperature conditions caused by heat generation. Concerned. Therefore, it is desired to improve the heat resistance of rubber 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 improvement in heat resistance, and application to an inner liner has not been studied.

Japanese Patent Laid-Open No. 10-324779

The present invention provides a rubber composition for an inner liner, which solves the above-mentioned problems, improves the heat resistance of rubber, suppresses deterioration of curing of rubber, and is excellent in durability, and a pneumatic tire using the same. For the purpose.

（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。） The present invention relates to a rubber composition for an inner liner 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 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 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).

In the rubber composition, 0.5 to 10 parts by mass of the compound represented by the formulas (I) and (II) and 0.5 to 6 parts by mass of zinc oxide are contained with respect to 100 parts by mass of the rubber component. It is preferable to do.
The rubber composition is preferably used for competition tires.

The present invention also relates to a pneumatic tire having an inner liner produced using the rubber composition.

According to the present invention, since it is a rubber composition for an inner liner in which a compound represented by the above formula (I) and / or (II) is blended with a rubber component containing a predetermined amount of isoprene-based rubber, the rubber It is possible to improve the heat resistance of the rubber, and in particular, it is possible to suppress the curing deterioration of rubber. For this reason, excellent durability can be imparted to a pneumatic tire in which the rubber composition is applied to the inner liner, and the life can be extended.

The rubber composition for an inner liner of the present invention includes a rubber component containing isoprene-based rubber and a compound represented by the above formula (I) and / or (II). Isoprene-based rubber such as natural rubber that is inferior in heat resistance is used as a rubber component, but since the compound represented by the above formulas (I) and (II) is blended in the rubber component, heat resistance In particular, it is possible to suppress curing deterioration of rubber.

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. The effect of suppressing the curing deterioration is very large as compared with the case where the compounds of the formulas (I) and (II) are blended with styrene butadiene rubber (for example, SBR 100 mass%) as the main component of the rubber component.

Therefore, in the present invention, despite the use of isoprene-based rubber such as natural rubber, good heat resistance (particularly an effect of suppressing curing deterioration) is obtained, so that the tire has excellent durability and has a long life. Can provide.

In the present invention, isoprene-based rubber is used as the rubber component. In the present invention, although the rubber having an isoprene skeleton is blended, the heat resistance (particularly, the effect of suppressing curing deterioration) can be improved, and excellent tire durability can be obtained.

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. Among these, NR is preferable from the viewpoint of low heat generation. As the NR, for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20 and the like can be used.

In the present invention, 100% by mass of the rubber component contains 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more of isoprene-based rubber. 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 85% by mass or less, and still more preferably 80% by mass or less. If it exceeds 90% by mass, the effect of suppressing curing deterioration may be reduced.

In addition to isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), butyl rubber, ethylene propylene diene rubber (EPDM), chloroprene can be used as rubber components. Examples thereof include rubber (CR) and acrylonitrile butadiene rubber (NBR). Of these, butyl rubber is preferred from the viewpoint of air permeability. A rubber component may be used independently and may use 2 or more types together.

The butadiene rubber (BR) that can be used in the present invention is not particularly limited, and for example, BR having a high cis content, BR containing syndiotactic polybutadiene crystals, and the like can be used.

The content of BR is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 25% by mass or more, in 100% by mass of the rubber component. If it is less than 10% by mass, durability (cracking performance) tends to decrease. Further, the BR content is preferably 90% by mass or less, more preferably 85% by mass or less, and still more preferably 80% by mass or less. If it exceeds 90% by mass, air permeability may be deteriorated.

In the present invention, good air permeation resistance can be obtained by using butyl rubber. Examples of the butyl rubber include butyl rubber (IIR); halogenated butyl rubber such as brominated butyl rubber (Br-IIR), chlorinated butyl rubber (Cl-IIR), and fluorinated butyl rubber (F-IIR). Of these, halogenated butyl rubber is preferable from the viewpoint of air permeability, and brominated butyl rubber and chlorinated butyl rubber are more preferable.

The content of butyl rubber in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 65% by mass or more. If it is less than 50% by mass, sufficient air permeation resistance may not be obtained. The content of the butyl rubber is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 75% by mass or less. If it exceeds 90% by mass, durability (cracking performance) may be deteriorated.

In the present invention, the rigidity can be increased by using SBR. Examples of the styrene butadiene rubber (SBR) include emulsion polymerization styrene butadiene rubber (E-SBR) and solution polymerization styrene butadiene rubber (S-SBR).

The amount of styrene unit in SBR is preferably 20% by mass or more, more preferably 30% by mass or more. If the styrene unit amount is less than 20% by mass, the rigidity may not be increased effectively. The styrene unit amount is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60 mass%, low temperature cracks may occur (embrittlement problem).

The content of SBR is preferably 30% by mass or more, more preferably 40% by mass or more, in 100% by mass of the rubber component. If it is less than 30% by mass, the rigidity may not be increased effectively. Further, the content of the SBR is preferably 70% by mass or less, more preferably 60% by mass or less. When it exceeds 70% by mass, the heat generation tends to increase.

The rubber composition of the present invention preferably contains carbon black. Thereby, reinforcement property is improved and heat resistance (especially hardening deterioration inhibitory effect) can be improved. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 30 m ² / g or more, from the viewpoint of obtaining sufficient reinforcement and durability. Also, _N 2 SA of carbon black is preferably not more than 100 m ² / g, more preferably at most ^{60 m} 2 / g. When it exceeds 100 m ² / g, heat generation tends to increase.
The N ₂ SA of carbon black is determined by the A method of JIS K6217.

The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100 g or more, and more preferably 90 ml / 100 g or more, from the viewpoint of obtaining sufficient reinforcement and durability. Further, the DBP of carbon black is preferably 160 ml / 100 g or less, more preferably 120 ml / 100 g or less, from the viewpoint of durability (cracking performance).
In addition, DBP of carbon black is calculated | required by the measuring method of JISK6217-4.

The content of carbon black is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 mass parts, there exists a possibility that desired reinforcement and durability may not be obtained. Moreover, this content becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 95 mass parts or less, More preferably, it is 90 mass parts or less. When it exceeds 100 parts by mass, the heat generation tends to increase.

In the present invention, a compound represented by the following formula (I) and / or (II) is used. The compound acts as a vulcanization accelerator and can improve the heat resistance (suppression of curing deterioration) of the vulcanized rubber. Accordingly, excellent tire durability can be obtained.

（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, a compound (4m-MBTS) represented by the following 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 0.5 parts by mass or more, more preferably 1 part by mass or more, further preferably 1 with respect to 100 parts by mass of the rubber component. .5 parts by mass or more. If it is less than 0.5 part by mass, the effect of suppressing curing deterioration may not be sufficiently obtained. The total content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less. If it exceeds 10 parts by mass, it may be difficult to maintain an appropriate crosslinking density and crosslinking form.

In the present invention, silica may be blended. Thereby, heat resistance (especially hardening deterioration inhibitory effect) can be improved and the outstanding tire durability is obtained. 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 80 m ² / g or more, more preferably 150 m ² / g or more, and further preferably 170 m ² / g or more. If it is less than 80 m ² / g, the desired reinforcement and durability may not be obtained. Further, N ₂ SA of silica is preferably 300 m ² / g or less, more preferably 250 m ² / g or less, and further preferably 220 m ² / g or less. When it exceeds 300 m ² / g, dispersion tends to be poor and durability tends to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, the effect of suppressing the curing deterioration may not be sufficiently obtained. The silica content is preferably 80 parts by mass or less, more preferably 50 parts by mass or less. When it exceeds 80 parts by mass, dispersion tends to be poor and durability tends to deteriorate.

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 3 parts by mass or more and more preferably 10 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 3 mass parts, there exists a tendency for a fracture strength to fall large. Moreover, 30 mass parts or less are preferable and, as for content of this silane coupling agent, 20 mass parts or less are more preferable. When it exceeds 30 parts by mass, there is a tendency that effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent cannot be obtained.

In addition to the components described above, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, such as other fillers, stearic acid, zinc oxide, various anti-aging agents, waxes, sulfur or sulfur compounds, etc. These vulcanizing agents, vulcanization accelerators, and the like can be appropriately blended as necessary.

Examples of zinc oxide include those conventionally used in the rubber industry, and specific examples include zinc oxide No. 1 and No. 2 manufactured by Mitsui Metal Mining Co., Ltd. Zinc oxide acts as a vulcanization acceleration aid.

The content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 parts by mass, the vulcanization is weak and the durability may be deteriorated. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 5 mass parts or less. If it exceeds 6 parts by mass, the dispersion is poor and the durability may be deteriorated.

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 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 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 0.3 parts by mass or more, more preferably 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.3 mass part, there is little bridge | crosslinking and there exists a possibility that durability may deteriorate. Moreover, this content becomes like this. Preferably it is 5 mass parts or less, More preferably, it is 2.5 mass parts or less. If it exceeds 5 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).
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).

The rubber composition for an inner liner 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 is used for an inner liner formed so as to form a tire lumen surface. With this member, the air permeation amount can be reduced and the tire internal pressure can be maintained. Specifically, it is used for the members shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2008-291091, FIGS. 1-2 of Japanese Patent Application Laid-Open No. 2007-160980, and the like.

The rubber composition can be used for passenger cars, trucks and buses, competition (race) tires, and the like, and above all, it can be suitably used for competition tires.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded according to the shape of the inner liner of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine, Bonding together with other tire members forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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
BR: BR150B manufactured by Ube Industries, Ltd.
Chlorobutyl rubber: HT-1068 manufactured by ExxonMobil Corporation
SBR: Toughden 4350 manufactured by Asahi Kasei Co., Ltd. (oil-containing SBR, 50 parts by mass of oil with respect to 100 parts by mass of SBR solid content, 40% by mass of styrene unit)
Carbon black: N550 (N ₂ SA: 42 m ² / g, DBP oil absorption: 113 ml / 100 g) from Cabot Japan
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 210 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Oil: Aroma Process Oil X-140 manufactured by Japan Energy Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Anti-aging agent: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Zinc stearate manufactured by NOF Corporation: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. MBTS: Ouchi Shinsei Chemical Industry ( Noxeller DM (dibenzothiazolyl disulfide)
Vulcanization accelerator 4m-MBTS: bis (4-methylbenzothiazolyl-2) -disulfide (formula (III)) manufactured by NOCIL

Examples 1-6 and Comparative Examples 1-5
According to the contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded at about 150 ° C. for 5 minutes using a Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded at about 80 ° C. for 5 minutes using a biaxial open roll to obtain an unvulcanized rubber composition.
A rubber sheet was prepared using the obtained unvulcanized rubber composition, and vulcanized under conditions of 150 ° C., 35 minutes, and 25 kgf 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.

<Stress at 100% elongation (M100)>
Using the No. 3 dumbbell-shaped test piece consisting of a new sample and a deteriorated sample, a tensile test was conducted at a pulling speed of 500 mm / min in accordance with JIS K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. did. The stress at 100% elongation at 23 ° C. (M100 (MPa)) was measured. Larger numbers indicate higher modulus and hardness.

In Examples 1-2, 3-5, and 6 in which 4m-MBTS was blended with NR and BR, NR and chlorobutyl rubber, NR and SBR, M100 increased in comparison with Comparative Examples 1 to 3 blended with MBTS. It was sufficiently suppressed and a very large effect of suppressing curing deterioration was obtained. Therefore, it can be suitably used as an inner liner for a racing tire or the like. Moreover, when the result of the comparative example 4 which mix | blended MBTS with SBR and the result of the comparative example 5 which mix | blended 4m-MBTS with SBR was compared, there was little improvement effect by 4m-MBTS in a SBR type | system | group.

Claims (8)

A rubber composition for an inner liner 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 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 in cases.) The rubber composition for an inner liner 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 an inner liner according to claim 1 or 2, wherein the compound is a compound represented by the following formula (III).

The compound represented by said Formula (I) and (II) 0.5-10 mass part and 0.5-6 mass part of zinc oxide are contained with respect to 100 mass parts of said rubber components. The rubber composition for an inner liner according to any one of the above. Furthermore, the nitrogen adsorption specific surface area is 20-60 m. ² The rubber composition for an inner liner according to any one of claims 1 to 4, comprising carbon black which is / g. Furthermore, the nitrogen adsorption specific surface area is 20 to 100 m. ² The rubber composition for an inner liner according to any one of claims 1 to 4, further comprising carbon black having a dibutyl phthalate oil absorption of 50 to 120 ml / 100 g. The rubber composition for an inner liner according to any one of claims 1 to 6 , which is used for a tire for competition. A pneumatic tire having an inner liner produced using the rubber composition according to any one of claims 1-7.