JP2011037979A - 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 capable of improving rolling resistance characteristics and endurance with a good balance thereof, and a pneumatic tire having an inner liner produced using the same. <P>SOLUTION: The rubber composition for an inner liner includes 5-45 pts.mass of a coal pitch-based carbon fiber based on 100 pts.mass of a rubber component. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

In a pneumatic tire, in particular, a tubeless tire, an inner liner made of rubber having low air permeability is formed on the tire lumen surface for the purpose of maintaining the tire internal pressure. In recent years, from the viewpoints of environmental issues and economics, there has been a demand for reduction in rolling resistance of tires and improvement in durability during long-term driving, and inner liners also have reduced rolling resistance and improved durability. It has been demanded.

However, it has been difficult to simultaneously realize reduction of rolling resistance and improvement of durability. For example, the hardness can be increased by increasing the blending amount of a filler such as carbon black or silica, or a thermosetting resin such as a phenolic resin, or by miniaturizing the filler. Tended to increase and the rolling resistance increased. Moreover, there also existed a tendency for elongation at break to fall and rubber strength (durability) to fall.

Patent Document 1 discloses a rubber composition for an inner liner containing a deproteinized natural rubber, but carbon fibers have not been studied in detail. There is also room for improvement in the above performance.

JP 2009-13197 A

An object of the present invention is to solve the above problems and provide a rubber composition for an inner liner that can improve the rolling resistance characteristics and durability in a well-balanced manner, and a pneumatic tire having an inner liner produced using the rubber composition. To do.

The present invention relates to a rubber composition for an inner liner containing 5 to 45 parts by mass of coal pitch-based carbon fiber with respect to 100 parts by mass of a rubber component.

The rubber composition has a total content of at least one selected from the group consisting of natural rubber, isoprene rubber and butadiene rubber, in which 100% by mass of the rubber component has a butyl rubber content of 30 to 80% by mass. The amount is preferably 20 to 70% by mass.
The coal pitch-based carbon fiber preferably has an average fiber diameter of 1 to 80 μm and an average fiber length of 0.1 to 30 mm.

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 in which a coal pitch-based carbon fiber is blended with a rubber component, a pneumatic tire excellent in rolling resistance characteristics and durability can be obtained by applying the rubber composition to an inner liner. Can be provided.

Since the rubber composition for an inner liner of the present invention contains a rubber component and coal pitch-based carbon fiber, high hardness and rubber strength can be obtained while maintaining low tan δ and high elongation at break. Therefore, by using the rubber composition for the inner liner, a pneumatic tire excellent in rolling resistance characteristics and durability can be produced.

As the rubber component, it is preferable to use butyl rubber from the viewpoint of air permeability resistance. Examples of the butyl rubber include halogenated butyl rubber (X-IIR) such as brominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR), and butyl rubber (IIR). These butyl rubbers may be used alone or in combination of two or more. Especially, it is preferable to use IIR from the point of having high heat resistance.

When butyl rubber is blended as the rubber component, the content of butyl rubber in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more. . When the content of butyl rubber is less than 30% by mass, the air permeation resistance tends to be low. The butyl rubber content is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. When the content of the butyl rubber exceeds 80% by mass, the rolling resistance tends to increase or the breaking strength of the rubber tends to decrease remarkably.

Examples of rubber components that can be used other than butyl rubber include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and acrylonitrile butadiene rubber. Examples thereof include diene rubbers such as (NBR), chloroprene rubber (CR), styrene isoprene butadiene rubber (SIBR), styrene isoprene rubber, and isoprene butadiene rubber. These may be used alone or in combination of two or more. From the viewpoint that the air permeation resistance and rolling resistance characteristics can be improved in a balanced manner, and the workability and rolling resistance characteristics can be improved in a balanced manner, it is preferable to use NR, IR or BR together with butyl rubber, Or it is more preferable to use IR, BR, and butyl rubber.

NR, IR and BR are not particularly limited, and those commonly used in the tire industry can be used. For example, SIR20, RSS # 3, TSR20, etc. can be used as NR. Further, as IR, JSR IR2200 manufactured by JSR Corporation, NIPOL IR2200 manufactured by Nippon Zeon Corporation, and the like can be used. Moreover, as BR, high cis content BR such as BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd. and BR150B, and syndiotactic such as VCR412, VCR617 manufactured by Ube Industries, Ltd. BR or the like containing polybutadiene (SPB) crystals can be used. Among them, BR containing SPB crystals is preferable, and VCR 617 having a high SPB crystal amount is more preferable.

The total content of NR and IR is preferably 20% by mass or more, more preferably 30% by mass or more, in 100% by mass of the rubber component. If it is less than 20% by mass, the tensile strength of the rubber tends to decrease. The total content of NR and IR is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less. When it exceeds 60% by mass, the air permeation resistance tends to be low.

The content of BR is preferably 5% by mass or more, more preferably 10% by mass or more, in 100% by mass of the rubber component. If it is less than 5% by mass, there is a tendency that it does not sufficiently contribute to rubber reinforcement. The BR content is preferably 40% by mass or less, more preferably 35% by mass or less. If it exceeds 40% by mass, the hardness of the rubber tends to be too high.

The total content of NR, IR and BR is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more, in 100% by mass of the rubber component. When the total content is less than 20% by mass, rolling resistance tends to increase. The total content is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less. When the total content exceeds 70% by mass, the air permeation resistance tends to decrease.

In the present invention, coal pitch-based carbon fiber is used. By blending the coal pitch-based carbon fiber, it is possible to increase rigidity and improve low heat generation without decreasing elongation at break. For this reason, high hardness and rubber strength can be obtained while maintaining low tan δ and high elongation at break. Therefore, by using the rubber composition for the inner liner, it is possible to achieve both a low rolling resistance and a high durability, and to manufacture a pneumatic tire excellent in balance of both performances.

The coal pitch-based carbon fiber preferably has an average fiber diameter of 1 to 80 μm from the viewpoint of dispersion in rubber and improvement in low heat build-up. The lower limit of the average fiber diameter is more preferably 3 μm or more, and further preferably 5 μm or more. Further, the upper limit of the average fiber diameter is more preferably 30 μm or less, and still more preferably 20 μm or less.

Moreover, it is preferable that an average fiber length is 0.1-30 mm from a viewpoint of the dispersion | distribution in rubber | gum, and a low exothermic improvement, as for a coal pitch-type carbon fiber. The lower limit of the average fiber length is more preferably 1 mm or more, and further preferably 4 mm or more. Moreover, the upper limit of average fiber length becomes like this. More preferably, it is 15 mm or less, More preferably, it is 10 mm or less.
In addition, the said average fiber diameter and average fiber length can be measured by observing with an electron microscope, for example.

Although it does not specifically limit as a coal pitch-type carbon fiber in this invention, For example, what is obtained by the manufacturing method as described in Unexamined-Japanese-Patent No. 7-331536 is used suitably. Specifically, the pitch fiber is infusible according to a conventional method, and carbonized and / or graphitized at a desired temperature to obtain “carbon fiber as a raw material”. A coal pitch-based carbon fiber can be produced by placing it in a graphite crucible together with the graphitized packing coke and performing a graphitization treatment.

In addition, as pitch fiber (spinning pitch) used by the said manufacturing method, carbonaceous raw materials (40% or more, preferably 70% or more, more preferably 90%) such as coal-based coal tar, coal tar pitch, and coal liquefaction. And those obtained by spinning using an optically anisotropic structure of at least%). Moreover, a sizing agent (such as an epoxy compound or a water-soluble polyamide compound) may be attached to the “carbon fiber as a raw material”.

According to the manufacturing method, the thermal conductivity in the fiber axis direction is 500 to 1500 W / m · K, the tensile elastic modulus is 85 ton / mm ² or more, the compressive strength is 35 kg / mm ² or more, and the graphite crystal lamination thickness Lc is 30 to 50 nm. Coal pitch-based carbon fibers having a ratio (La / Lc) with a spread La in the layer surface direction of the graphite crystal of 1.5 times or more and a domain size in a cross section in the fiber axis direction of 500 nm or less can be produced. Can be suitably used. The thermal conductivity, tensile elastic modulus, compressive strength, Lc, La, domain size, and optically anisotropic texture ratio can be measured by the method described in the above publication.

The coal pitch-based carbon fiber produced by the above production method uses a liquid crystal (mesophase) whose molecular orientation is regulated in one direction as a raw material, and therefore has a very high degree of crystallinity, a high elastic modulus and a high thermal conductivity.
The coal pitch-based carbon fiber in the present invention preferably has a structure in which polycyclic aromatic molecular skeletons are stacked in layers. As a commercial product of coal pitch-based carbon fiber, “K6331T” manufactured by Mitsubishi Plastics, Inc., and the like can be given.

Content of the said coal pitch-type carbon fiber is 5 mass parts or more with respect to 100 mass parts of rubber components, Preferably it is 10 mass parts or more. Moreover, this content is 45 mass parts or less, Preferably it is 40 mass parts or less. If the amount is less than 5 parts by mass, reduction in rolling resistance and improvement in durability cannot be expected, and if it exceeds 45 parts by mass, the strength of the rubber is lowered and the cost is also increased, which is not preferable.

The rubber composition of the present invention preferably contains a reinforcing filler. Thereby, a reinforcement effect is acquired and rigidity can be improved. As the reinforcing filler, those generally used in the tire industry can be used without particular limitation, and examples thereof include carbon black, silica, clay, talc, and magnesium carbonate. Of these, carbon black is preferably used.

The carbon black is not particularly limited, and for example, FEF, GPF, SRF, HAF, ISAF, SAF and the like can be used. By using carbon black, the strength of the rubber can be improved. Moreover, since the balance between rubber strength and rolling resistance can be improved by using it in combination with coal pitch-based carbon fibers, excellent durability and rolling resistance characteristics can be obtained in a well-balanced manner.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, and more preferably 25 m ² / g or more. If it is less than 20 m ² / g, the reinforcing property of the rubber tends to deteriorate. Also, _N 2 SA of carbon black is preferably not more than 100 m ² / g, more preferably at most ^{80 m} 2 / g. When it exceeds 100 m ² / g, rolling resistance tends to be disadvantageous.
The N ₂ SA of carbon black is determined by the A method of JIS K6217.

The content of carbon black is preferably 8 parts by mass or more and 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 8 parts by mass, the reinforcing property of the rubber tends to deteriorate. The content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 50 parts by mass or less. When it exceeds 70 mass parts, there exists a tendency for rolling resistance to deteriorate.

The rubber composition of the present invention preferably contains mica (mica). Thereby, the air permeation resistance can be improved. As the mica, those generally used in the tire industry can be used without particular limitation, and examples thereof include mascobite (muscovite), phlogopite (phlogopite), biotite (biotite) and the like. These may be used alone or in combination of two or more. Among these, it is preferable to use a phlogopite from the viewpoint that the effect of improving the air permeation resistance is higher than other mica.

The average particle diameter of mica is 40 μm or more, preferably 45 μm or more. If the average particle diameter is less than 40 μm, the effect of improving the air permeation resistance tends to be insufficient. The average particle diameter of mica is 100 μm or less, preferably 70 μm or less. When the average particle diameter exceeds 100 μm, mica becomes a starting point of cracking and the inner liner tends to be easily cracked due to bending fatigue.

The aspect ratio (flatness) of mica is 50 or more, preferably 55 or more. If the aspect ratio is less than 50, the effect of improving the air permeation resistance tends to be insufficient. Further, the aspect ratio of mica is preferably 100 or less, and more preferably 70 or less. When the aspect ratio exceeds 100, the strength of mica tends to decrease, and the mica tends to crack.
Here, the aspect ratio refers to the ratio of the major axis to the thickness in mica.

In the present invention, the average particle diameter and thickness of mica were measured using an electron microscope. The average particle diameter means the major axis, and the major axis is the longest length when mica is projected onto the projection plane while changing the direction of the mica relative to the projection plane. The length of the side, the diameter if it is a disc shape.

The mica used in the present invention can be obtained by a grinding method such as wet grinding or dry grinding. Wet pulverization produces a clean surface, has a slightly high effect of improving air permeation resistance, and dry pulverization is characterized by a simple manufacturing process and low cost, and is preferably used depending on the case.

The mica content is 20 parts by mass or more, preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the mica content is less than 20 parts by mass, the effect of improving the air permeation resistance tends to be insufficient. The mica content is 50 parts by mass or less, preferably 45 parts by mass or less, and more preferably 40 parts by mass or less with respect to 100 parts by mass of the rubber component. When the content of mica exceeds 50 parts by mass, the tear strength of the rubber composition tends to decrease, and cracks tend to occur.

You may mix | blend a thermosetting resin with the rubber composition of this invention. Examples of the thermosetting resin include phenolic resins and cresol resins. Of these, phenolic resins are preferred from the viewpoint of obtaining high hardness.

Examples of phenolic resins include phenolic resins obtained by reacting phenols with aldehydes such as formaldehyde, acetaldehyde, furfural and the like with an acid or alkali catalyst; cashew oil, tall oil, linseed oil, various animal and vegetable oils, Examples thereof include a modified phenolic resin modified with unsaturated fatty acid, rosin, alkylbenzene resin, aniline, melamine and the like. Among the phenol-based resins, a modified phenol resin is preferable and a cashew oil-modified phenol resin or a rosin-modified phenol resin is preferable because the hardness (Hs) can be improved.

You may mix | blend the alkylphenol and sulfur chloride condensate with the rubber composition of this invention. Thereby, a rubber composition with high hardness can be obtained. Examples of the alkylphenol / sulfur chloride condensate include those represented by the following formula.

（式中、ｎは０又は１〜１０の整数であり、ｘは２〜４の整数であり、Ｒは炭素数５〜１２のアルキル基である。）

(In the formula, n is 0 or an integer of 1 to 10, x is an integer of 2 to 4, and R is an alkyl group having 5 to 12 carbon atoms.)

From the viewpoint of good dispersibility of the alkylphenol / sulfur chloride condensate in rubber, n is preferably an integer of 1 to 9. Moreover, x is preferably an integer of 2 to 4 and more preferably 2 from the viewpoint that high hardness can be efficiently obtained. When x exceeds 4, it tends to become thermally unstable, and when x is 1, the sulfur content (sulfur mass) in the alkylphenol-sulfur chloride condensate decreases. From the viewpoint of good dispersibility in rubber, R is preferably an alkyl group having 5 to 12 carbon atoms, more preferably an alkyl group having 6 to 9 carbon atoms. Specific examples of the alkylphenol / sulfur chloride condensate include Tackol V200 (Taoka Chemical Co., Ltd.) having an alkyl group of n = 0 to 10, x = 2, R = C ₈ H ₁₇ and a sulfur content of 24% by mass. Manufactured).

In addition to the above components, the rubber composition of the present invention includes compounding agents, softeners (oils such as paraffinic, aroma-based and naphthenic process oils, plasticizers, etc.), stearic acid Zinc oxide, various anti-aging agents, waxes, vulcanizing agents such as sulfur or sulfur compounds, vulcanization accelerators, vulcanization acceleration aids, and the like can be appropriately blended as necessary.

When sulfur is used as the vulcanizing agent, the sulfur content is preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 3.0 mass parts or less, More preferably, it is 2.7 mass parts or less. If it is less than 0.3 parts by mass, the vulcanization rate tends to be slow and vulcanization tends to be insufficient, and if it exceeds 3.0 parts by mass, the vulcanization rate tends to be high and scorching tends to occur.

Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). Among these, sulfenamide-based vulcanization accelerators such as TBBS and CBS are preferable because an appropriate vulcanization rate can be obtained.

The compounding amount of the vulcanization accelerator is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this compounding quantity becomes like this. Preferably it is 3.0 mass parts or less, More preferably, it is 2.0 mass parts or less. If the amount is less than 0.5 parts by mass, the vulcanization rate tends to be slow and vulcanization tends to be insufficient. If the amount exceeds 3.0 parts by mass, the vulcanization rate tends to increase and scorching tends to occur.

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 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 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.

A tire having a rubber composition for an inner liner produced by using the rubber composition for an inner liner of the present invention can be particularly preferably used for a tire for passenger cars and a tire for trucks and buses.

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.
Butyl rubber: Butyl 268 manufactured by Nippon Butyl Co., Ltd.
Natural rubber (NR): RSS # 3
Butadiene rubber containing 1,2-syndiotactic polybutadiene crystals (SPB-containing BR): VCR412 manufactured by Ube Industries, Ltd. (1,2-syndiotactic polybutadiene crystal content: 12% by mass)
Isoprene rubber (IR): NIPOL IR2200 manufactured by Nippon Zeon Co., Ltd.
Mica: Lepco Mica (Mica) S-200HG (Frogbite, average particle size: 50 μm, aspect ratio: 55)
Coal pitch-based carbon fiber (1): K6331T manufactured by Mitsubishi Chemical Corporation (chopped fiber, average fiber diameter: 11 μm, average fiber length: 6.3 mm)
Coal pitch-based carbon fiber (2): GRANOC XN-80 manufactured by Nippon Graphite Fiber Co., Ltd. (chopped fiber, average fiber diameter: 10 μm, average fiber length: 3.6 mm)
Petroleum pitch-based carbon fiber: Kureha Co., Ltd. Kurekamildo M101T (average fiber diameter 18 μm, average fiber length 100 μm)
Carbon black: Seast V (N660, N ₂ SA: 27 m ² / g) manufactured by Tokai Carbon Co., Ltd.
Mineral oil: Diana Process PA32 manufactured by Idemitsu Kosan Co., Ltd.
Stearic acid: Zinc oxide made by NOF Corporation: Ginseng R made by Toho Zinc Co., Ltd.
Sulfur: 5% oil-treated powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller DM (di-2-benzothiazolyl disulfide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
V200: Tachiroll V200 manufactured by Taoka Chemical Industry Co., Ltd.

Examples 1-6 and Comparative Examples 1-4
According to the formulation shown in Table 1, materials other than sulfur, a vulcanization accelerator, and V200 were kneaded using a Banbury mixer to obtain a kneaded product. Next, using an open roll, sulfur, a vulcanization accelerator, and V200 were added and kneaded with the obtained kneaded material, to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 12 minutes to prepare each vulcanized rubber composition.

The obtained unvulcanized rubber composition was molded into an inner liner shape on a tire molding machine, and an unvulcanized tire obtained by laminating with another tire member was 170 ° C. and 25 kgf / cm ² . Test tires of Examples 1 to 6 and Comparative Examples 1 to 4 were manufactured by press vulcanization for 12 minutes under the conditions (tire size: 195 / 65R15).

The following tests were performed using the vulcanized rubber composition and the test tire produced under the above conditions.

(Air permeation resistance)
The air permeation amount of the vulcanized rubber composition (vulcanized rubber sheet) was measured in accordance with ASTM D-1434-75M method. The air permeation resistance index of Comparative Example 1 was set to 100, and the air permeation amount of each formulation was indicated by an index according to the following formula. In addition, it shows that the larger the air permeation resistance index, the smaller the air permeation amount of the vulcanized rubber sheet, and the better the air permeation resistance.
(Air permeation resistance index) = (Air permeation amount of Comparative Example 1) / (Air permeation amount of each formulation) × 100

(Viscoelasticity test)
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho, the loss tangent (tan δ) of the vulcanized rubber composition was measured under the conditions of a measurement temperature of 80 ° C., an initial strain of 10%, a dynamic strain of ± 2%, and a frequency of 10 Hz. It was measured. It shows that rolling resistance is so small that tan-delta is small, and it is excellent in low heat generating property.

(Tensile test)
In accordance with JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Tensile Properties”, a tensile test was conducted using a No. 3 dumbbell-shaped test piece made of the vulcanized rubber composition, and elongation at break (EB ) And breaking strength (TB). Each unit is EB (%) and TB (MPa). The larger EB and TB, the higher the rubber strength and the better the durability.

(Machine durability index)
A test tire placed in an oven at a temperature of 80 ° C. for one week was run without filling the air pressure during running under conditions of an internal pressure of 200 kPa, a load of 340 kgf (333.261 N), and a speed of 80 km / h, and a crack occurred. Then, the mileage until the air began to leak from the tire was obtained. The measurement was performed with a detection accuracy of 5 kPa or less, and when the internal pressure of the tire reached 95% (190 kPa) of the initial state, the occurrence of air leakage was determined. When the internal pressure of the tire decreases, the durability of the tire also decreases. In Comparative Example 1, the running distance until air leakage occurred was set to 100, and the machine durability of each formulation was displayed as an index according to the following formula. In addition, it shows that durability of an inner liner is excellent, so that a machine durability index | exponent is large.
(Machine durability index)
= (Travel distance until air leakage occurs in each formulation) / (travel distance until air leak occurs in Comparative Example 1) × 100

From Table 1, in Examples 1-6 using coal pitch system carbon fiber which has an average fiber diameter and average fiber length, compared with comparative example 1 (coal pitch system and petroleum pitch system carbon fiber are not added). While maintaining elongation at break and breaking strength, air permeation resistance, low heat build-up, and machine durability were improved. Further, in Comparative Examples 2 to 4 using petroleum pitch-based carbon fibers, the improvement in performance as in Examples 1 to 6 was not observed, and the characteristics deteriorated as the content of petroleum pitch-based carbon fibers increased. There was a tendency to.

Claims (4)

A rubber composition for an inner liner containing 5 to 45 parts by mass of a coal pitch-based carbon fiber with respect to 100 parts by mass of a rubber component. In 100% by mass of the rubber component, the content of butyl rubber is 30 to 80% by mass, and the total content of at least one selected from the group consisting of natural rubber, isoprene rubber and butadiene rubber is 20 to 70% by mass. The rubber composition for an inner liner according to claim 1, wherein the rubber composition is%. The rubber composition for an inner liner according to claim 1 or 2, wherein the coal pitch-based carbon fiber has an average fiber diameter of 1 to 80 µm and an average fiber length of 0.1 to 30 mm. The pneumatic tire which has an inner liner produced using the rubber composition in any one of Claims 1-3.