JP5575054B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire provided with an inner liner.

  In recent years, tires have been reduced in weight due to the strong social demand for low fuel consumption of vehicles, and among tire members, they are arranged inside the tires to prevent air leakage from the inside of the pneumatic tires to the outside. That is, weight reduction is also demanded for the inner liner that increases the air permeation resistance.

  At present, the rubber composition for an inner liner improves the air permeation resistance of a tire by using a rubber compound mainly composed of butyl rubber including, for example, 70 to 100% by mass of butyl rubber and 30 to 0% by mass of natural rubber. Has been done. In addition to butylene, the rubber compound mainly composed of butyl rubber contains about 1% by mass of isoprene, which, when combined with sulfur, vulcanization accelerator, and zinc white, enables co-crosslinking between adjacent rubber layers. I have to. The butyl rubber usually requires a thickness of about 0.6 to 1.0 mm for passenger car tires and about 1.0 to 2.0 mm for truck and bus tires. Therefore, there has been proposed a polymer that is more excellent in air permeation resistance than butyl rubber and can make the inner liner layer thinner.

  In the prior art, attempts have been made to reduce the weight of the inner liner layer, and it has been proposed to use a thermoplastic elastomer. However, if the thickness is thinner than the butyl rubber inner liner, it is difficult to achieve both air permeation resistance and light weight. Moreover, the strength of the inner liner is reduced by making it thinner, and the inner liner may be broken by the heat and pressure of the bladder during the vulcanization process. Further, a thermoplastic elastomer having a low strength has a problem that cracks are likely to occur in the inner liner particularly in a buttress portion that is subjected to large repeated shear deformation during tire running.

  Patent Document 1 discloses a laminate for improving the adhesion between the inner liner layer and the rubber layer. By providing an adhesive layer on both sides of the inner liner layer, the adhesive layers come into contact with each other at the overlapping portion of the inner liner layer, and are firmly bonded by heating, thereby improving air pressure retention. . However, the adhesive layer for superimposing the inner liner layer comes into contact with the bladder in a heated state in the vulcanization process, and there is a problem that it adheres to and adheres to the bladder.

  Patent Document 2 proposes an inner liner layer having a thickness of 100 μm by preparing a mixture of nylon resin having good air permeation resistance and butyl rubber by dynamic crosslinking. However, nylon resin is hard at room temperature and unsuitable as an inner liner for tires. In addition, the vulcanization adhesion to the rubber layer is not performed only with the mixture obtained by the dynamic crosslinking. Therefore, the adhesion layer for vulcanization is required in addition to the inner liner layer. Therefore, the inner liner member has a complicated structure and many processes. This is disadvantageous from the viewpoint of productivity.

  Prior Document 3 discloses that a flexible gas barrier layer is prepared by dispersing maleic anhydride-modified hydrogenated styrene-ethylene-butadiene-styrene block copolymer in an ethylene-vinyl alcohol copolymer having good air permeation resistance. Yes. In addition, the thermoplastic polyurethane layer has an sandwich sandwich structure, and rubber paste (70/30 of butyl rubber / natural rubber is dissolved in toluene) is applied to the surface to be bonded to the tire rubber to produce an inner liner layer.

  However, the modified ethylene-vinyl alcohol copolymer dispersed in a flexible resin has low adhesive strength and may be peeled off from the thermoplastic polyurethane layer. In the modified ethylene-vinyl alcohol copolymer dispersed with a flexible resin, the flexible resin is dispersed, but the EVOH of the matrix is poor in bending fatigue and breaks during running of the tire. Furthermore, although rubber paste is applied to the surface to be bonded to the tire rubber, a process different from the normal inner liner process is required, resulting in poor productivity.

  Prior literature 4 describes a pneumatic tire having an air permeation preventive layer of a thermoplastic elastomer composition containing a thermoplastic resin or a thermoplastic resin and an elastomer inside a carcass layer. It has been proposed that the average thickness Gs of the air permeation preventive layer in the large region Ts is made thinner than the tire maximum width and the average thickness Gf of the air permeation preventive layer in the bead toe region Tf to improve the bending durability. Yes. However, in such a configuration, peeling between the rubber layer of the carcass ply and the air permeation preventive layer may occur.

JP-A-9-19987 Patent No. 2999188 JP 2008-24219 A JP 2008-174037 A

  An object of the present invention is to improve air permeation resistance, bending fatigue resistance and crack resistance in a pneumatic tire provided with an inner liner.

  The present invention is a pneumatic tire provided with an inner liner on the inner side of the tire, wherein the inner liner is made of a thermoplastic elastomer containing a styrene-isobutylene-styrene triblock copolymer and has a thickness of 0.05 mm to 0 mm. A polymer laminate comprising a .6 mm first layer and a thermoplastic elastomer comprising an epoxidized styrene-butadiene-styrene triblock copolymer, the second layer having a thickness of 0.01 mm to 0.3 mm. And the second layer is disposed so as to be in contact with the rubber layer of the carcass ply, and the inner liner has a belt layer from the tire maximum width position from the average thickness Gb of the bead region Rb extending from the tire maximum width position to the bead toe. Pneumatic tire characterized in that average thickness Gs of buttress region Rs over corresponding position Lu at the end is thin A.

  The ratio (Gs / Gb) of the average thickness Gs of the buttress area of the inner liner to the average thickness Gb of the bead area is preferably 0.3 to 0.75. The average thickness Gs of the buttress area of the inner liner is preferably 0.05 to 0.45 mm.

  In the present invention, the styrene-isobutylene-styrene triblock copolymer preferably has a weight average molecular weight of 50,000 to 400,000 and a styrene component content of 10 to 30% by mass. The epoxidized styrene-butadiene-styrene triblock copolymer has a weight average molecular weight of 100,000 to 400,000, a styrene component content of 10 to 30% by mass, and an epoxy equivalent of 50 or more. 1,000 or less is desirable.

  In the present invention, by using the polymer laminate for an inner liner, the thickness can be reduced while maintaining air permeation resistance. Furthermore, adhesiveness with an adjacent rubber layer can be improved. And the pneumatic tire which used this polymer laminated body for the inner liner improves bending fatigue property. Then, by adjusting the average thicknesses Gb and Gs of the inner liners of the bead region Rb and the buttress region Rs, it is possible to effectively relieve the stress associated with the repeated deformation of the tire during traveling and improve the crack resistance.

It is a schematic sectional drawing which shows the right half of the pneumatic tire in one embodiment of this invention. It is a schematic sectional drawing of the inner liner in the pneumatic tire of the present invention.

  The present invention is a pneumatic tire provided with an inner liner on the inner side of the tire, and the inner liner is formed of at least two polymer laminates. The first layer is made of styrene-isobutylene-styrene triblock copolymer (SIBS) and has a thickness in the range of 0.05 mm to 0.6 mm. The second layer includes an epoxidized styrene-butadiene-styrene triblock copolymer and has a thickness of 0.01 mm to 0.3 mm. The second layer is disposed in contact with the rubber layer of the carcass ply.

  An embodiment of a pneumatic tire according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the right half of a pneumatic tire for passenger cars. The pneumatic tire 1 has a tread portion 2 and sidewall portions 3 and bead portions 4 so as to form a toroid shape from both ends of the tread portion. Further, a bead core 5 is embedded in the bead portion 4. Also, a carcass ply 6 provided from one bead portion 4 to the other bead portion, with both ends folded back and locked around the bead core 5, and at least two sheets on the outer side of the crown portion of the carcass ply 6 A belt layer 7 made of a ply is arranged.

  The belt layer 7 usually intersects two plies made of steel cords or cords such as aramid fibers with respect to the tire circumferential direction so that the cords are usually at an angle of 5 to 30 °. Are arranged as follows. In addition, a topping rubber layer can be provided on both outer sides of the belt layer to reduce peeling at both ends of the belt layer. In the carcass ply, organic fiber cords such as polyester, nylon, and aramid are arranged at approximately 90 ° in the tire circumferential direction. In the region surrounded by the carcass ply and the folded portion, the bead core 5 extends from the upper end to the sidewall direction. An extending bead apex 8 is arranged. Further, an inner liner 9 extending from one bead portion 4 to the other bead portion 4 is disposed inside the carcass ply 6 in the tire radial direction.

  In the present invention, from the average thickness Gb of the inner liner 9 in the bead area Rb extending from the tire maximum width position Le to the bead toe Lt, the inner liner 9 in the buttress area Rs extending from the tire maximum width position Le to the corresponding position Lu at the belt layer end. The average thickness Gs is made thin.

  By reducing the thickness of the inner liner in the buttress region Rs, even when shear deformation occurs due to repeated bending deformation in this region during tire running, the stress can be relieved and cracking can be prevented. can do.

  In order to effectively relieve the stress due to bending deformation, the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs of the inner liner to the average thickness Gb of the bead region Rb is 0.3-0. 75. Further, in order to maintain the air pressure holding performance and also have the effect of relaxing the stress in the buttress region, it is desirable that the average thickness Gs of the buttress region Rs of the inner liner is 0.05 to 0.45 mm.

<Polymer laminate>
In one embodiment of the present invention, the polymer laminate used for the inner liner includes a first layer made of styrene-isobutylene-styrene triblock copolymer (SIBS) having a thickness of 0.05 mm to 0.6 mm, an epoxy The second layer contains a styrene-butadiene-styrene triblock copolymer, and the thickness of the second layer is 0.01 mm to 0.3 mm.

<First layer>
In one embodiment of the invention, the first layer is composed of a thermoplastic elastomer composition comprising a styrene-isobutylene-styrene triblock copolymer (SIBS). Due to the isobutylene block of SIBS, the polymer film made of SIBS has excellent air permeation resistance. Therefore, when a polymer film made of SIBS is used for the inner liner, a pneumatic tire having excellent air permeation resistance can be obtained.

  Furthermore, since the molecular structure other than aromatic is completely saturated, SIBS has excellent durability with suppressed deterioration hardening. Therefore, when SIBS is used for the inner liner, a pneumatic tire having excellent durability can be obtained.

  When a pneumatic tire is manufactured by applying a polymer film made of SIBS to the inner liner, air permeation resistance can be secured. Therefore, it is not necessary to use a halogenated rubber having a high specific gravity, which has been conventionally used for imparting air permeation resistance, such as a halogenated butyl rubber. Even if it is used temporarily, the amount of use can be reduced, and the fuel consumption can be improved by reducing the weight of the tire.

  The molecular weight of SIBS is not particularly limited, but the weight average molecular weight by GPC measurement is preferably 50,000 to 400,000 from the viewpoints of fluidity, molding process, rubber elasticity and the like. If the weight average molecular weight is less than 50,000, the tensile strength and the tensile elongation may be lowered, and if it exceeds 400,000, the extrusion processability may be deteriorated. From the viewpoint of improving air permeation resistance and durability, SIBS has a styrene component content in SIBS of 10 to 30% by mass, preferably 14 to 23% by mass.

  The SIBS is a copolymer in which the degree of polymerization of each block maintains rubber elasticity, and in terms of workability (becomes liquid when the degree of polymerization is less than 10,000), isobutylene is 10,000 to 150,000. The degree is preferably about 5,000 to 30,000 for styrene.

  SIBS can be obtained by a living cationic polymerization method of a general vinyl compound. For example, JP-A-62-48704 and JP-A-64-62308 disclose that living cationic polymerization of isobutylene and other vinyl compounds is possible. By using isobutylene and other compounds as vinyl compounds, It is disclosed that a polyisobutylene-based block copolymer can be produced.

  The thickness of the first layer made of SIBS is 0.05 to 0.6 mm. When the thickness of the first layer is less than 0.05 mm, the first layer is broken by pressing pressure during vulcanization of a green tire in which the polymer laminate is applied to the inner liner, and an air leak phenomenon occurs in the obtained tire. May occur. On the other hand, if the thickness of the first layer exceeds 0.6 mm, the tire weight increases and the fuel efficiency performance decreases. The thickness of the first layer is preferably 0.05 to 0.4 mm. The first layer can be obtained by forming SIBS into a film by an ordinary method of forming a thermoplastic resin or thermoplastic elastomer into a film such as extrusion molding or calendar molding.

<Second layer>
In the present invention, the second layer includes an epoxidized SBS layer made of an epoxidized styrene-butadiene-styrene triblock copolymer (hereinafter also referred to as “epoxidized SBS”).

  Epoxidized styrene-butadiene-styrene triblock copolymer (epoxidized SBS) is a thermoplastic in which the hard segment is a styrene block and the soft segment is a butadiene block, and the unsaturated double bond portion contained in the butadiene block is epoxidized. It is an elastomer.

  Since the epoxidized SBS has a styrene block, the epoxidized SBS is excellent in melt adhesion with SIBS similarly having a styrene block. Accordingly, when the SIBS layer and the epoxidized SBS layer are arranged adjacent to each other and vulcanized, a polymer laminate in which the SIBS layer and the epoxidized SBS layer are well bonded can be obtained.

  Epoxidized SBS has a soft segment composed of a butadiene block, and thus is easily vulcanized and bonded to a rubber component. Therefore, when the SBS layer is disposed adjacent to a rubber layer forming, for example, a carcass or an insulation and vulcanized, when the polymer laminate including the epoxidized SBS layer is used as an inner liner, the polymer laminate and the adjacent rubber are used. Adhesion with the layer can be improved.

  The molecular weight of the epoxidized SBS is not particularly limited, but from the viewpoint of rubber elasticity and moldability, the weight average molecular weight by GPC measurement is preferably 10,000 to 400,000. If the weight average molecular weight is less than 10,000, the tensile strength may be reduced and the dimensions may not be stable. If the weight average molecular weight exceeds 400,000, the extrusion processability deteriorates, which is not preferable. It is preferable that content of the styrene component in epoxidized SBS is 10-30 mass% from a viewpoint of adhesiveness, adhesiveness, and rubber elasticity.

  The epoxidized SBS preferably has a molar ratio of butadiene units to styrene units (butadiene units / styrene units) of 90/10 to 70/30. In the epoxidized SBS, the degree of polymerization of each block is preferably about 500 to 5,000 for a butadiene block and about 50 to 1,500 for a styrene block from the viewpoint of rubber elasticity and processability.

  The epoxy equivalent of epoxidized SBS is preferably 50 or more and 1,000 or less from the viewpoint of improving adhesiveness.

  The epoxidized SBS layer can be obtained by forming the epoxidized SBS into a film by a usual method of forming a thermoplastic resin or a thermoplastic elastomer into a film such as extrusion molding or calender molding.

  The thickness of the second layer containing the epoxidized SBS is 0.01 mm to 0.3 mm. When the thickness of the second layer is less than 0.01 mm, the second layer may be broken by the press pressure during vulcanization of the raw tire in which the polymer laminate is applied to the inner liner, and the vulcanization adhesive force may be reduced. There is. On the other hand, if the thickness of the second layer exceeds 0.3 mm, the tire weight increases and the fuel efficiency performance decreases. The thickness of the second layer is further preferably 0.05 to 0.2 mm.

  In the present invention, the second layer contains other styrene-based thermoplastic elastomer, for example, styrene-isoprene-styrene block copolymer (SIS), styrene--in the range of less than 50% by mass of the thermoplastic elastomer component. An isobutylene block copolymer (SIB) etc. can be mixed.

<Polymer laminate>
Various structures can be adopted as the structure of the polymer laminate used for the inner liner in the present invention. These forms will be described with reference to FIG. 2, which is a schematic sectional view of the inner liner.

  As shown in FIG. 2, the polymer laminate 10 includes a SIBS layer 11 as a first layer and an epoxidized SBS layer 12 as a second layer. When the polymer laminate 10 is applied to an inner liner of a pneumatic tire, if the epoxidized SBS layer 12 is disposed facing the outer side in the tire radial direction so as to be in contact with the carcass ply 6, the epoxidized SBS is formed in the tire vulcanization process. The adhesive strength between the layer 12 and the carcass 6 can be increased. Therefore, the obtained pneumatic tire can have excellent air permeation resistance and durability since the inner liner and the rubber layer of the carcass ply 6 are well bonded.

  The polymer laminate 10 can be obtained, for example, by subjecting a first layer of SIBS and a second layer of epoxidized SBS to laminate extrusion such as laminate extrusion or coextrusion.

<Pneumatic tire manufacturing method>
A general manufacturing method can be used for the pneumatic tire of the present invention. The polymer laminate 10 can be produced by applying it to an inner liner of a raw tire of the pneumatic tire 1 and vulcanizing it together with other members. When the polymer laminate 10 is arranged on the green tire, the epoxidized SBS layer 12 that is the second layer of the polymer laminate 10 is arranged outward in the tire radial direction so as to be in contact with the carcass ply 6.

  In order to adjust the thickness of the inner liner in the bead region Rb and the buttress region Rs, for example, a profile is attached to the extrusion opening of the polymer sheet, and an integrated sheet having a thin buttress region thickness Gs is prepared. This is arranged on the inner surface of the tire as an inner liner.

  The rubber layer of the carcass ply used in the pneumatic tire of the present invention is composed of generally used rubber components such as natural rubber, polyisoprene, styrene-butadiene rubber, polybutadiene rubber, and fillers such as carbon black and silica. Can be used.

  With the specifications shown in Table 1, pneumatic tires of Examples and Comparative Examples were manufactured and performance was evaluated. The SIBS, epoxidized SBS, and compounding components used for the first layer and the second layer are as follows.

<SIBS>
Shibstar SIBSTAR 102T (Shore A hardness 25, styrene component content 25 mass%, weight average molecular weight: 100,000) manufactured by Kaneka Corporation was used.

<Epoxidized SBS>
"Epofriend A1020" (Styrene component content 30 mass%, weight average molecular weight: 100,000, epoxidation equivalent 500) manufactured by Daicel Chemical Industries, Ltd. was used.

<Manufacture of pneumatic tires>
The SIBS and epoxidized SBS were pelletized with a twin screw extruder (screw diameter: φ50 mm, L / D: 30, cylinder temperature: 220 ° C.). Thereafter, co-extrusion was performed using a T-die extruder (screw diameter: φ80 mm, L / D: 50, die lip width: 500 mm, cylinder temperature: 220 ° C.), and the SIBS layer and epoxidized SIBS layer having the thicknesses shown in Table 1 were used. A polymer laminate was prepared.

  As the pneumatic tire, a 195 / 65R15 size raw tire having the basic structure shown in FIG. 1 was produced. Here, the epoxidized SIBS of the polymer laminate was disposed inside the green tire so as to be adjacent to the carcass ply, and was press molded at 170 ° C. for 20 minutes with a vulcanization mold to produce a tire.

  Here, in order to adjust the thickness between the bead region Rb and the buttress region Rs of the inner liner, a tire is formed using a single sheet with a profile attached to the extrusion opening of the polymer sheet and the thickness Gs of the buttress region being reduced. Arranged on the inner surface.

  In Table 1, the total thickness of the first layer and the second layer indicates the average thickness Gb of the bead region Rb. Except for Comparative Example 1, in all Examples and Comparative Examples, the average thickness Gb of the bead region Rb is 0.6 mm.

<Comparative Example 1>
In the inner liner of Comparative Example 1, the following blending components were mixed with a Banbury mixer and formed into a sheet with a calender roll to obtain a polymer film having a thickness of 1.0 mm. The value of Gs / Gb is 1.

Chlorobutyl (Note 1) 90 parts by weight Natural rubber (Note 2) 10 parts by weight Filler (Note 3) 50 parts by weight (Note 1) “Exon Chlorobutyl 1068” manufactured by ExxonMobil Corporation
(Note 2) TSR20
(Note 3) “Seast V” manufactured by Tokai Carbon Co., Ltd. (N660, nitrogen adsorption specific surface area: 27 m ² / g)
<Comparative example 2>
A 0.6 mm thick SIBS layer produced by the above method was used as an inner liner. The value of Gs / Gb is 1.

<Comparative Example 3>
A composite layer of a 0.40 mm SIBS layer and a 0.20 mm epoxidized SBS layer was used as the inner liner. The value of Gs / Gb is 1.

<Examples 1-4>
In Examples 1 to 4, SIBS is used for the first layer and epoxidized SBS is used for the second layer. The value of Gs / Gb is the highest in Example 1 and the lowest in Example 4.

<Performance test>
Pneumatic tires were produced using the polymer laminates of Examples and Comparative Examples and the polymer laminates as inner liners, and the following performance tests were performed.

<Peel test>
A test piece was prepared according to JIS-K-6256 “Vulcanized rubber and thermoplastic rubber—How to determine adhesion”. A test piece of a thermoplastic elastomer composition and a rubber sheet are bonded together and vulcanized. After vulcanization, the peel force is measured at the bonding interface. The larger the inner liner and carcass peeling force, the better.

<Bending fatigue test>
A predetermined test piece having a groove in the center was prepared according to JIS-K-6260 “Testing method for demature bending cracking of vulcanized rubber and thermoplastic rubber”. As the inner liner, a sheet having a thickness of 0.3 mm was attached to rubber and vulcanized to prepare a predetermined test piece. An incision was made in advance at the center of the groove of the test piece, and a test was conducted to measure crack growth by repeatedly bending and deforming. The crack length was measured at an ambient temperature of 23 ° C., a strain of 30%, and a period of 5 Hz, and the number of repetitions of bending deformation required for the crack to grow by 1 mm was calculated. Using the value of Comparative Example 1 as a reference (100), the flexural fatigue properties of the polymer laminates of Examples and Comparative Examples were expressed as indices. It can be said that the larger the numerical value, the better the cracks are less likely to grow. For example, the index of Example 1 is obtained by the following formula.

(Bending fatigue index) = (Number of repetitions of bending deformation of Example 1) / (Number of repetitions of bending deformation of Comparative Example 1) × 100
<Static air pressure drop rate test>
The 195 / 65R15 steel radial PC tire manufactured by the above method was assembled into a JIS standard rim 15 × 6 JJ, sealed with an initial air pressure of 300 Kpa, left at room temperature for 90 days, and the rate of decrease in air pressure was calculated.

<Measurement of average thickness>
A 195 / 65R15 steel radial PC tire was divided into 8 equal parts in the circumferential direction, and 8 cut samples cut along the tire radial direction with a width of 20 mm were created at each location, and each of these 8 cut samples was The thickness of the inner liner layer was measured at five points equally divided into five in the buttress region Rs and the bead region Rb. The arithmetic average values of the total 40 measured values were Gs and Gb.

<Crack resistance>
195 / 65R15 steel radial PC tire is assembled to JIS standard rim 15 × 6JJ, filled with regular air pressure, and the maximum load corresponding to this air pressure is applied from the air pressure-addition capacity correspondence table with JATMYEAR BOOK, speed 80km / The vehicle traveled on the drum at h, and when the damage that could be visually confirmed was generated, the vehicle was stopped and the travel distance was determined. The travel distance of Comparative Example 1 is taken as 100 and is shown as an index. The larger the index, the better the crack resistance.

<Performance evaluation results>
In Table 1, Examples 1 to 4 use a polymer laminate including an SIBS layer (thickness 0.4 mm) as the first layer and an SIS layer (thickness 0.2 mm) as the second layer. Gs / Gb is the largest at 0.75 in Example 1 and the smallest at 0.33 in Example 4.

  In Comparative Examples 1 to 3, Gs / Gb is all 1. In all examples, the crack resistance index is improved as compared with Comparative Example 1.

  The pneumatic tire of the present invention can be used as a pneumatic tire for trucks, buses, heavy machinery, etc. in addition to a pneumatic tire for passenger cars.

  DESCRIPTION OF SYMBOLS 1 Pneumatic tire, 2 tread part, 3 side wall part, 4 bead part, 5 bead core, 6 carcass ply, 7 belt layer, 8 bead apex, 9 inner liner, 10 polymer laminated body, 11 SIBS layer, 12 SIS layer, 13 SIB layer, Rb bead area, Rs buttress area, Le tire maximum width position, Lt bead toe, Lu belt layer edge corresponding position.

Claims (3)

A pneumatic tire provided with an inner liner inside the tire, wherein the inner liner is made of a thermoplastic elastomer composition containing a styrene-isobutylene-styrene triblock copolymer and has a thickness of 0.05 mm to 0.6 mm. It is composed of a polymer laminate composed of a first layer and a second layer made of an epoxidized styrene-butadiene-styrene triblock copolymer and having a thickness of 0.01 mm to 0.3 mm. It is placed in contact with the rubber layer of the carcass ply,
The inner liner, than the average thickness Gb of bead region Rb over the bead toe from the tire maximum width position, the average thickness Gs of buttress region Rs over the corresponding positions Lu of the belt layer end from the tire maximum width position is rather thin,
The ratio (Gs / Gb) of the average thickness Gs of the buttress region of the inner liner to the average thickness Gb of the bead region is 0.33 to 0.75,
The pneumatic tire has an average thickness Gs of a buttress area of the inner liner of 0.20 to 0.45 mm . The pneumatic tire according to claim 1, wherein the styrene-isobutylene-styrene triblock copolymer has a weight average molecular weight of 50,000 to 400,000 and a styrene component content of 10 to 30% by mass. The epoxidized styrene-butadiene-styrene triblock copolymer has a weight average molecular weight of 100,000 to 400,000, a styrene component content of 10 to 30% by mass, an epoxy equivalent of 50 or more, and 1, The pneumatic tire according to claim 1 or 2 , which is 000 or less.

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