JP2010254904A - Rubber composition for inner liner and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for an inner liner, wherein heat deterioration resistance is enhanced, and especially hardening deterioration of rubber is suppressed to have excellent durability (especially durability in low internal pressure run) even when an isoprene-based rubber such as a natural rubber is mixed, and a pneumatic tire using the composition. <P>SOLUTION: The rubber composition for the inner liner contains: a rubber component containing the isoprene-based rubber and a butyl-based rubber, silica and a compound represented by formula (I) and/or formula (II). The formula (I): bis(benzothiazolyl-2)-disulfide wherein hydrogens of the benzene nucleus are substituted with R<SP>1</SP>and R<SP>2</SP>, and the formula (II): 2-mercaptobenzothiazole wherein hydrogens of the benzene nucleus are substituted with R<SP>1</SP>and R<SP>2</SP>, and R<SP>1</SP>and R<SP>2</SP>are identical to or different from each other and each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group, however, a case that R<SP>1</SP>and R<SP>2</SP>are simultaneously hydrogen atoms is excluded. <P>COPYRIGHT: (C)2011,JPO&INPIT

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. As the inner liner rubber, butyl rubber, halogenated butyl rubber or the like having excellent air permeation resistance is generally used.

However, in consideration of cost reduction and efficiency of the tire molding process, blending natural rubber can prevent problems in the process such as joint disengagement and can also reduce the cost. On the other hand, when looking at the tire quality, natural rubber has a poor molecular structure and heat resistance, and there is a problem in durability particularly when running at low internal pressure.

Conventionally, anti-aging agents such as 2,2,4-trimethylquinoline derivative (TMQ) are widely used in rubber compositions used for tires and the like in order to enhance heat deterioration resistance. The demand is further increased, and a longer life is required.

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 deterioration resistance, and application to an inner liner has not been studied.

Japanese Patent Laid-Open No. 10-324779

The present invention solves the above-mentioned problems, and even when blended with isoprene-based rubber such as natural rubber, it improves heat resistance deterioration, particularly suppresses deterioration of rubber curing, and durability (especially durability at low internal pressure running) It is an object to provide a rubber composition for an inner liner excellent in property and a pneumatic tire using the same.

（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 isoprene-based rubber and butyl-based rubber, silica, 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 isoprene rubber is preferably natural rubber and the butyl rubber is preferably halogenated butyl rubber.

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

The content of the silica is 10 to 80 parts by mass, and the content of the compounds represented by the formulas (I) and (II) is 1.0 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component. Preferably there is.

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

According to the present invention, a rubber composition for an inner liner in which a rubber component in which isoprene-based rubber is further blended with butyl rubber is blended with a compound represented by silica and the above formula (I) and / or (II). Therefore, despite the addition of isoprene-based rubber, the heat deterioration resistance can be improved, and in particular, the rubber can be prevented from being cured and deteriorated. For this reason, the durability which was excellent at the time of driving | running | working with a low internal pressure can be provided to the pneumatic tire which applied this rubber composition to the inner liner.

The rubber composition for an inner liner of the present invention includes a rubber component containing isoprene-based rubber and butyl-based rubber, silica, 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 deterioration in addition to butyl rubber is used as the rubber component, but further compounded with silica and compounds represented by the above formulas (I) and (II) Therefore, the heat resistance deterioration can be improved, and in particular, it is possible to suppress the 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 curing deterioration suppressing effect is different from so-called heat fatigue resistance (prevention of blow and chunk generation) and heat sag resistance, and is a butyl rubber, isoprene rubber, silica and formula (I ), Specifically when using three components with the compound of (II).

Furthermore, when these three components are used, the effect of improving the heat deterioration resistance (particularly, the effect of suppressing the deterioration of curing) is generated synergistically. For example, styrene butadiene rubber has silica and formulas (I) and (II). Compared with the case where a compound is blended, a very large curing deterioration suppressing effect is produced.
Therefore, in the present invention, despite the use of isoprene-based rubber such as natural rubber, good heat deterioration resistance (particularly, the effect of suppressing curing deterioration) can be obtained. A tire excellent in durability (such as crack resistance) can be manufactured.

In the present invention, isoprene-based rubber and butyl-based rubber are used as the rubber component. In the present invention, despite blending a rubber having an isoprene skeleton, the heat deterioration resistance (particularly, the effect of suppressing curing deterioration) can be improved, and excellent tire durability (particularly durability during running at low internal pressure) is obtained. It is done.

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. Of these, NR and IR are preferable from the viewpoint of tackiness. 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, isoprene-based rubber is preferably contained in 100% by mass of the rubber component, preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more. If it is less than 5% by mass, the effect of suppressing curing deterioration may not be sufficiently obtained. Further, the content of the isoprene-based rubber is preferably 40% by mass or less, more preferably 30% by mass or less, and still more preferably 25% by mass or less.

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 vulcanization adhesion with adjacent rubber, 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 70% 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 95% by mass or less, more preferably 90% by mass or less, and still more preferably 85% by mass or less. If it exceeds 95 mass%, the adhesiveness of the joint portion may be inferior.

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

In the present invention, silica is used. Thereby, heat resistance deterioration property (especially hardening deterioration inhibitory effect) can be improved and the outstanding tire durability (especially durability at the time of low internal pressure driving | running | working) 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 50 m ² / g or more, more preferably 80 m ² / g or more, and still more preferably 100 m ² / g or more. 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.
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 13 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 70 parts by mass or less. If it exceeds 80 parts by mass, the viscosity of the unvulcanized rubber increases, and there is a risk that burns will occur during processing.

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 7 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, 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.

In the present invention, a compound represented by the following formula (I) and / or (II) is used. Although the compound is a vulcanization accelerator, it can improve the heat resistance deterioration (suppression of curing deterioration) of the vulcanized rubber. Accordingly, excellent tire durability (particularly durability during low internal pressure traveling) 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 1.0 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 1.0 mass part, there exists a possibility that the hardening deterioration inhibitory effect may not fully be acquired. The total content is preferably 5.0 parts by mass or less, more preferably 4.5 parts by mass or less. If it exceeds 5.0 parts by mass, it may be difficult to maintain an appropriate crosslinking density and crosslinking form.

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

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 reinforcement.

Iodine adsorption amount of carbon black (IA), from the viewpoint that sufficient reinforcing property and durability can be obtained, preferably at least _{20mgI 2 / g, 30mgI 2 /} g or more is more preferable. Also, IA of carbon black, from the viewpoint of heat generation during rolling is preferably not more than 80mgI ₂ / g, more preferably at most 50mgI ₂ / g.
The IA 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, more preferably 80 ml / 100 g or more, from the viewpoint of obtaining sufficient reinforcement and durability. The DBP of carbon black is preferably 150 ml / 100 g or less, more preferably 110 ml / 100 g or less, from the viewpoint of bending crack growth resistance.
In addition, DBP of carbon black is calculated | required by the measuring method of JISK6217-4.

The content of carbon black is preferably 30 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 30 parts by mass, a predetermined rubber strength may not be obtained. Moreover, this content becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 80 mass parts or less. If it exceeds 100 parts by mass, the heat generation is too high, and there is a risk of burns during processing.

In the present invention, a tackifier resin may be blended. Thereby, moldability improves.
Examples of the tackifying resin include coumarone resin, phenol resin, terpene resin, petroleum hydrocarbon resin, and rosin derivative. In addition, from the viewpoint of air permeation resistance and moisture permeation resistance, two or more kinds of aromatic hydrocarbon resins such as phenolic adhesive resins and aliphatic hydrocarbon resins such as C ₅ , C _{8 and} C ₉ are used. The selected mixed resin can be suitably used, and among them, a combination of an aromatic hydrocarbon resin and an aliphatic hydrocarbon resin is preferable, and a combination of a polymer aromatic hydrocarbon resin and an aliphatic hydrocarbon resin is more preferable. preferable.

The total content of the tackifying resin is preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, the effect may not be exhibited. The total content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less. If it exceeds 10 parts by mass, the heat of the unvulcanized rubber increases, and there is a risk that burns will occur.

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 with respect to 100 parts by mass of the rubber component. If it is less than 0.3 part by mass, the vulcanization time tends to be long. Moreover, this content becomes like this. Preferably it is 5 mass parts or less, More preferably, it is 2 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 car tires, truck / bus tires and the like, and among them, it can be suitably used for passenger car 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.
Natural rubber: TSR20
Styrene butadiene rubber (SBR): S-SBR HPR355 manufactured by JSR Corporation
Chlorinated butyl rubber: Chlorobutyl HT1066 manufactured by Exxon Chemical
Carbon black: Niteron 55U manufactured by Nippon Steel Chemical Co., Ltd. (IA: 36 mgI ₂ / g, DBP oil absorption: 91 ml / 100 g)
Silica: Silica Z115Gr (N ₂ SA: 110 m ² / g) manufactured by Rhodia Japan
Silane coupling agent: Si266 manufactured by Evonik Degussa
Process oil: Diana process PA32 (mineral oil) manufactured by Idemitsu Kosan Co., Ltd.
Phenolic adhesive resin: SP1068 (thermoplastic phenolic resin-based tackifier) manufactured by Scientific Chemicals
Mixed resin: Stractol 40MS (mixture of aromatic hydrocarbon resin and aliphatic hydrocarbon resin) manufactured by Straktor
Stearic acid: Zinc oxide manufactured by NOF Corporation: Zinc Hua 3 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK200-5 manufactured by Hosoi Chemical Co., Ltd. (5% oil treatment)
Vulcanization accelerator MBTS: Noxeller DM (dibenzothiazolyl disulfide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator 4m-MBTS: Bis (4-methylbenzothiazolyl-2) -disulfide (formula (III)) manufactured by NOCIL

Examples 1-4 and Comparative Examples 1-5
According to the contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes under a condition of 130 ° 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 3 minutes at 60 ° 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 10 to 20 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.

Further, the unvulcanized rubber composition obtained above was molded into an inner liner shape, bonded to another tire member, and vulcanized at 170 ° C. for 30 minutes, so that a test tire (tire size: 215 / 45R17).

Using the obtained new samples and deteriorated samples, the following hardness, swelling rate, and M100 were evaluated. Each test result is shown in Table 1. In the table, the value of the deteriorated sample when the new sample is set to 100 is shown as an index, and the closer to 100, the harder the deterioration by hardness, the swelling rate, and M100 is better than the new sample, which is better. Moreover, the following crack resistance was evaluated using the obtained test tire, and the results are shown in Table 1.

<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.

<Crack resistance>
The prepared test tire was run at a speed of 50 km / h at a speed of 15,000 km under the conditions of low internal pressure (50% of normal internal pressure) and high load (150% of normal load), and the outer surface of the inner liner portion was The number of cracks was confirmed. The smaller the number, the better.

In the examples in which natural rubber, silica, and 4m-MBTS were blended with chlorobutyl rubber, the effect of suppressing curing deterioration (hardness, swelling, M100) was better than in Comparative Examples 1 to 3 in which MBTS was blended. . Moreover, even in the test tire, no cracks were observed, and the crack resistance (durability) was greatly improved. Further, in Comparative Examples 4 and 5 in which SBR and MBTS were blended, even when 4m-MBTS was blended in place of MBTS, the effect of improving hardness, swelling, and M100 was small.

Claims (5)

A rubber composition for an inner liner containing a rubber component containing isoprene-based rubber and butyl-based rubber, silica, 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 an inner liner according to claim 1, wherein the isoprene-based rubber is a natural rubber and the butyl-based rubber is a halogenated butyl 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 content of the silica is 10 to 80 parts by mass, and the content of the compounds represented by the formulas (I) and (II) is 1.0 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for an inner liner according to any one of claims 1 to 3. The pneumatic tire which has an inner liner produced using the rubber composition in any one of Claims 1-4.