JP2013001184A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire provided with an inner liner which improves air permeation resistance, bending fatigue and crack resistance.SOLUTION: The pneumatic tire 1 is provided with the inner liner 9 inside the tire. The inner liner 9 is constituted with a polymer sheet comprising a polymer mixture containing a styrene-isobutylene-styrene triblock copolymer of 99.5 to 60 mass% and styrene-maleic anhydride copolymer of 0.5 to 40 mass% and the ratio (Gs/Gb) is 0.3 to 0.75 where Gs is an average thickness of a buttress area Rs ranging over a corresponding position Lu of the belt layer end from a tire maximum width position, and Gb is an average thickness of a bead area Rb ranging over a bead toe from the tire maximum width position.

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 a strong social demand for lower fuel consumption of vehicles. Among the tire members, an inner liner that is arranged on the inner side in the tire radial direction and has the function of improving the air permeation resistance by reducing the amount of air leakage (air permeation amount) from the inside to the outside of the pneumatic tire. However, weight reduction has come to be performed.

  Currently, the use of butyl rubber containing 70-100% by weight of butyl rubber and 30-0% by weight of natural rubber as the rubber composition for the inner liner is used to improve the air permeation resistance of the tire. . The butyl rubber contains about 1% by mass of isoprene in addition to butylene, and this isoprene, together with sulfur, vulcanization accelerator, and zinc white, enables co-crosslinking with adjacent rubber. 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, in order to reduce the weight of the tire, it has been proposed to use a thermoplastic elastomer, which is superior in air permeation resistance as compared to butyl rubber, and can reduce the thickness of the inner liner, for the inner liner. However, if the inner liner using thermoplastic elastomer is thinner than butyl rubber, it will not be possible to achieve both air permeability and weight reduction, and the strength of the inner liner will be reduced, and the vulcanization process will be reduced. The inner liner may break due to the heat and pressure of the Prader. Furthermore, the thermoplastic elastomer having a relatively low strength has a problem that cracks are likely to occur in the inner liner in a buttress portion that is subjected to repeated large shear deformation during running of the tire.

  Patent Document 1 discloses a laminate for improving the adhesion between the inner liner and the rubber layer. By providing adhesive layers on both sides of the inner liner, the adhesive layers come into contact with each other at the overlapping portion of the inner liner and are firmly bonded by heating, so that the air pressure retention is improved. However, this adhesive layer for overlapping the inner liner 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.

  In Patent Document 2, a mixture of a nylon resin having good air permeability and butyl rubber is prepared by dynamic crosslinking to produce an inner liner having a thickness of 100 μm. 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, an adhesive layer for vulcanization is required in addition to the inner liner. Therefore, the structure of the inner liner member is complicated and the number of processes is increased. , Disadvantageous in terms of productivity.

  In Patent Document 3, 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 barrier properties. . Further, the thermoplastic polyurethane layer is sandwiched sandwiched, and further, rubber glue (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. 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.

  In Patent Document 4, as a pneumatic tire capable of simultaneously suppressing a decrease in air pressure, improving durability, and improving fuel efficiency, 100 parts by mass of a rubber component made of natural rubber and / or synthetic rubber is used. , The following general formula (I),

  (Wherein m and n are each independently 1 to 100 and x is 1 to 1000). The ethylene-vinyl alcohol copolymer represented by the formula is at least within a range of 15 to 30 parts by mass. There has been proposed a pneumatic tire using the contained rubber composition for an inner liner as an inner liner layer. However, in the technique of Patent Document 4, the thickness of the rubber sheet using the rubber composition is 1 mm, and there is room for improvement in terms of weight reduction of the tire.

  Patent Document 5 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 this 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 2007-291256 A JP 2008-174037 A

  An object of the present invention is to provide a pneumatic tire including an inner liner that improves air permeation resistance, bending fatigue resistance, and crack resistance.

  The pneumatic tire of the present invention is provided with an inner liner inside the tire, and the inner liner is composed of 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer and a styrene-maleic anhydride copolymer. An average thickness Gs of a buttress region Rs extending from a tire maximum width position to a corresponding position Lu at the belt layer end, and a tire outermost diameter, the polymer sheet comprising a polymer mixture containing 0.5 to 40% by mass of a polymer. The ratio (Gs / Gb) to the average thickness Gb of the bead region Rb from the large position to the bead toe is 0.3 to 0.75.

  The styrene-isobutylene-styrene triblock copolymer preferably contains a styrene component in the range of 10 to 30% by mass and has a weight average molecular weight of 50,000 to 400,000. The styrene-maleic anhydride copolymer has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10, a weight average molecular weight of 4,000 to 20,000, and a maleic anhydride component. It is preferable to include a styrene-maleic anhydride copolymer base resin having an acid value of 50 to 600.

  The styrene-maleic anhydride copolymer is an ester resin of a styrene-maleic anhydride copolymer having a monoester group and a monocarboxylic acid group, which is obtained by esterifying a styrene-maleic anhydride copolymer base resin. It is preferable to contain.

  The styrene-maleic anhydride copolymer preferably includes an aqueous styrene-maleic anhydride copolymer ammonium salt solution in which a styrene-maleic anhydride copolymer base resin is dissolved in an ammonium salt.

  The average thickness Gs of the buttress region of the inner liner is preferably 0.05 to 0.45 mm.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire provided with the inner liner which improves air permeation resistance, bending fatigue resistance, and crack resistance can be provided.

It is typical sectional drawing which shows the right half of the pneumatic tire in one embodiment of this invention.

<Pneumatic tire>
The present invention is a pneumatic tire provided with an inner liner on the inside of the tire, and the inner liner is 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer (hereinafter also referred to as “SIBS”). And a polymer sheet comprising a polymer mixture containing 0.5 to 40% by mass of a styrene-maleic anhydride copolymer (hereinafter also referred to as SMA). The polymer composition comprising SIBS is inferior in vulcanization adhesion to rubber, but has excellent air barrier properties due to the SIBS isobutylene block. On the other hand, the styrene-maleic anhydride copolymer is inferior in air barrier properties, but is very excellent in vulcanization adhesion with rubber. Therefore, when a polymer film containing SIBS and SMA is used for the inner liner, a pneumatic tire excellent in air permeation resistance and vulcanization adhesion can be obtained.

  The pneumatic tire 1 of the present invention can be used for passenger cars, trucks / buses, heavy machinery and the like. An embodiment of a pneumatic tire according to the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a right half of a pneumatic tire according to an embodiment of the present invention. 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 °. To be arranged. 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. The carcass ply has an organic fiber cord made of polyester, nylon, aramid or the like arranged at approximately 90 ° in the tire circumferential direction. The region surrounded by the carcass ply and its folded portion has a sidewall extending from the upper end of the bead core 5 A bead apex 8 extending in the direction is arranged. Further, an inner liner 9 extending from one bead portion 4 to the other bead portion 4 is disposed on the inner side in the tire radial direction of the carcass ply 6.

  In the present invention, the average thickness Gs of the inner liner 9 in the buttress region Rs from the tire maximum width position Le to the corresponding position Lu at the belt layer end, and the inner liner 9 in the bead region Rb from the tire maximum width position Le to the bead toe Lt. The ratio (Gs / Gb) to the average thickness Gb is 0.3 to 0.75.

  By reducing the thickness of the inner liner in the buttress region Rs in this way, even when shear deformation occurs due to repeated bending deformation in this region during tire running, the stress can be relieved and cracks can be generated. Can be prevented. Furthermore, by setting the average thickness of the inner liner as described above, it is possible to effectively relieve 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 preferably 0.5 to 0.7. Further, in order to maintain the air pressure holding performance and also have the effect of relaxing the stress in the buttress area, it is desirable that the average thickness Gs of the buttress area Rs of the inner liner is 0.05 to 0.45 mm.

<Polymer sheet>
In one embodiment of the present invention, the inner liner contains 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer and 0.5 to 40% by mass of a styrene-maleic anhydride copolymer. A polymer sheet made of a polymer mixture.

  Further, SIBS has excellent durability because its molecular structure other than aromatic is completely saturated, thereby preventing deterioration and hardening.

  In one embodiment of the present invention, when an unvulcanized polymer sheet made of the polymer mixture is used for an inner liner, in order to ensure air permeation resistance by including SIBS, for example, a conventional halogenated butyl rubber, etc. Even when the high specific gravity halogenated rubber which has been used for imparting air permeation resistance is not used or used, the amount of use can be reduced. As a result, the weight of the tire can be reduced, and the effect of improving fuel consumption can be obtained. Further, the halogenated rubber has a problem that the adhesion between the ply cord of the pneumatic tire and the rubber is deteriorated due to the halogen in the rubber. In the present invention, the amount of the halogenated rubber is used. Therefore, the durability of the pneumatic tire can be improved by improving the adhesion between the ply cord and the polymer mixture.

  The thickness of the polymer sheet is preferably 0.05 to 0.6 mm. When the thickness of the polymer sheet is less than 0.05 mm, the polymer sheet may be broken by the press pressure during vulcanization of the raw tire in which the polymer sheet is applied to the inner liner, and an air leak phenomenon may occur in the obtained tire. There is. On the other hand, when the thickness of the polymer sheet exceeds 0.6 mm, the tire weight increases and the fuel efficiency performance decreases. The thickness of the polymer sheet is further preferably 0.05 to 0.4 mm. The polymer sheet can be obtained by forming SIBS into a film by an ordinary method of forming a thermoplastic resin or a thermoplastic elastomer into a film, such as extrusion molding or calendar molding.

<Styrene-isobutylene-styrene triblock copolymer (SIBS)>
In the polymer composition according to one embodiment of the present invention, the content of SIBS in the polymer mixture is 99.5 to 60% by mass. When the SIBS content is 60% by mass or more, an inner liner having excellent air permeation resistance and durability can be obtained. Moreover, when the content of SIBS is 99.5% by mass or less, an inner liner excellent in adhesiveness with adjacent rubber can be obtained. The content is preferably 98 to 70% by mass in terms of better air permeation resistance and durability.

  SIBS generally contains 10-40% by weight of styrene. It is preferable that the content of styrene in SIBS is 10 to 30% by mass in terms of better air permeation resistance and durability.

  SIBS preferably has a molar ratio of isobutylene to styrene (isobutylene / styrene) of 40/60 to 95/5 from the viewpoint of rubber elasticity of the copolymer. In SIBS, the degree of polymerization of each block is about 10,000-150,000 for isobutylene and 10,000-30,000 for styrene in terms of rubber elasticity and handling (becomes liquid when the degree of polymerization is less than 10,000). It is preferably about 000.

  The molecular weight of the SIBS is not particularly limited, but it is preferable that the weight average molecular weight by GPC measurement is 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.

  SIBS can be obtained by a general vinyl compound polymerization method, for example, a living cationic polymerization method.

  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. In addition, methods for producing vinyl compound polymers by the living cationic polymerization method are disclosed in, for example, U.S. Pat. No. 4,946,899, U.S. Pat. No. 5,219,948, and JP-A-3-174403. Are listed.

  Since SIBS does not have double bonds other than aromatics in the molecule, it is more stable to ultraviolet light than polymers having double bonds in the molecule such as polybutadiene, and therefore weather resistance is high. It is good. Furthermore, although it has no double bond in the molecule and is a saturated rubber-like polymer, the refractive index (nD) at 20 ° C. of light with a wavelength of 589 nm is the Polymer Handbook (1989: Wiley). (Polymer Handbook, Willy, 1989)) is 1.506. This is significantly higher than other saturated rubbery polymers such as ethylene-butene copolymers.

<Styrene-maleic anhydride copolymer>
In this specification, a styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer base resin (hereinafter also referred to as “SMA base resin”), and a styrene-maleic anhydride copolymer base resin is an ester. The ester resin of a styrene-maleic anhydride copolymer having a monoester group and a monocarboxylic acid group (hereinafter also referred to as SMA ester resin) and a styrene-maleic anhydride copolymer base resin, which are obtained by conversion into ammonium, are ammonium. It describes as a concept containing the aqueous solution of ammonium salt of styrene-maleic anhydride copolymer (hereinafter also referred to as SMA resin ammonium salt aqueous solution) dissolved in a salt.

  The styrene-maleic anhydride copolymer is used as a polymer surfactant and a highly functional cross-linking agent in dispersion and emulsification, and has excellent vulcanization adhesiveness with rubber. Moreover, since the wettability is given to rubber, the adhesive effect is also excellent.

  In one embodiment of the present invention, the polymer composition for an inner liner can improve vulcanization adhesion with rubber while maintaining air barrier properties by blending SMA with SIBS.

  In the polymer component of the polymer composition for the inner liner, the SMA content is 0.5 to 40% by mass. When the content of SMA is 0.5% by mass or more, an inner liner excellent in adhesiveness with adjacent rubber can be obtained. Moreover, when the SMA content is 40% by mass or less, an inner liner having excellent air permeation resistance and durability can be obtained. The content of SMA in the polymer component is more preferably 2 to 30% by mass.

(Styrene-maleic anhydride copolymer-based resin)
In one embodiment of the present invention, the SMA preferably contains an SMA base resin from the viewpoints of unvulcanized tackiness and post-vulcanized adhesion.

  The SMA base resin preferably has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 from the viewpoints of a high softening point and high thermal stability.

  The SMA base resin preferably has a weight average molecular weight of 4,000 to 20,000 from the viewpoint of adhesion after vulcanization and fluidity. Furthermore, the weight average molecular weight is more preferably 5,000 to 15,000.

  In the SMA base resin, the maleic anhydride component in the styrene-maleic anhydride copolymer preferably has an acid value of 50 to 600 from the viewpoint of unvulcanized adhesiveness. Furthermore, the acid value of the maleic anhydride component is more preferably 95 to 500.

(Ester resin of styrene-maleic anhydride copolymer)
In one embodiment of the present invention, the styrene-maleic anhydride copolymer is obtained by esterifying a styrene-maleic anhydride copolymer-based resin and having a monoester group and a monocarboxylic acid group. It preferably contains an ester resin of maleic anhydride copolymer (hereinafter also referred to as SMA ester resin).

  The SMA ester resin has the property of being excellent in vulcanization adhesion. Therefore, the polymer composition for inner liners excellent in vulcanization adhesiveness with the rubber layer can be obtained by blending SMA ester resin with SIBS.

  The SMA ester resin preferably has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 from the viewpoint of vulcanization adhesion.

  The SMA ester resin preferably has a weight average molecular weight of 5,000 to 12,000 from the viewpoint of adhesion after vulcanization and fluidity. Furthermore, the weight average molecular weight is more preferably 6,000 to 11,000.

  In the SMA ester resin, the maleic anhydride component preferably has an acid value of 50 to 400 from the viewpoint of adhesion to unvulcanized rubber. Furthermore, the acid value of the maleic anhydride component is more preferably 95 to 290.

  The SMA ester resin can be produced, for example, by introducing a base resin and alcohol into a reaction vessel and heating and stirring in an inert gas atmosphere.

(Styrene-maleic anhydride copolymer ammonium salt aqueous solution)
In one embodiment of the present invention, the styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer aqueous ammonium salt solution (hereinafter also referred to as an SMA ammonium salt aqueous solution) in which an SMA base resin is dissolved in an ammonium salt. It is preferable to contain.

  The SMA ammonium salt aqueous solution has a property of excellent wettability. Therefore, the polymer composition for inner liners excellent in adhesiveness can be obtained by mix | blending SMA ammonium salt aqueous solution with SIBS.

  The SMA ammonium salt aqueous solution preferably has a solid content of 10.0 to 45.0% from the viewpoint of adhesion to unvulcanized rubber and molding processability.

  The aqueous SMA ammonium salt solution preferably has a pH of 8.0 to 9.5 from the viewpoint of tackiness.

  An aqueous SMA ammonium salt solution causes exothermic reaction when water is added to a reaction vessel, base resin is added with vigorous stirring, and ammonium hydroxide is gradually added. Then, it can manufacture by heating to predetermined temperature and continuing stirring until melt | dissolution is completed.

<Additive of polymer composition>
The polymer composition in one embodiment of the present invention includes other reinforcing agents, vulcanizing agents, vulcanization accelerators, various oils, anti-aging agents, softeners, plasticizers, coupling agents, etc. Various compounding agents and additives blended in the polymer composition can be blended. Examples of these additives include stearic acid, zinc oxide, anti-aging agent, and vulcanization accelerator.

<Pneumatic tire manufacturing method>
The polymer composition used for the inner liner contained in the pneumatic tire can be produced by a conventionally known method. For example, after weighing each of the above materials to a predetermined blending ratio, an open roll, a Banbury mixer, etc. And kneading at 100 to 250 ° C. for 5 to 60 minutes.

  Specifically, SIBS, SMA, SMA base resin, SMA ester resin, SMA ammonium salt aqueous solution, and various additives as necessary are fed into a twin screw extruder at a temperature of about 100 to 250 ° C. and 50 to 300 rpm. By kneading below, pellets of a polymer composition in which each of these components is dynamically crosslinked are obtained.

  In the twin-screw extruder, SIBS, which is a thermoplastic elastomer composition, becomes a matrix phase and the rubber component becomes an island phase and is dispersed. Further, in the twin-screw extruder, the rubber component and the additive component react, and the rubber component that is an island phase undergoes a crosslinking reaction. This is called dynamic crosslinking because the rubber component is dynamically crosslinked in a twin screw extruder. Even if the rubber component is cross-linked in a twin-screw extruder, the matrix phase of the system is composed of a thermoplastic elastomer component, so that the shear viscosity of the entire system is low and extrusion is possible.

  The pellets of the dynamically cross-linked polymer composition obtained in the twin-screw extruder have the rubber component cross-linked but the matrix phase thermoplastic elastomer component retains plasticity, creating the overall plasticity of the system. Playing a role. For this reason, since plasticity is exhibited even in T-die extrusion, it can be formed into a sheet shape.

  Furthermore, since the rubber component of the dynamically cross-linked polymer composition pellets is cross-linked, the polymer laminate manufactured using the pellets is applied to the inner liner to produce a pneumatic tire. Even if the tire is heated, the polymer composition of the inner liner can be prevented from entering the carcass layer.

  The polymer composition produced above can be produced by applying it to the inner liner of the green tire 1 and vulcanizing it together with other members. The obtained pneumatic tire has excellent air permeation resistance and durability because the inner liner and the rubber layer of the carcass ply are well bonded.

  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.

  Next, the raw tire is mounted on a mold, and heated with pressure from 150 to 180 ° C. for 3 to 50 minutes to obtain a vulcanized tire. Next, it is preferable to cool the obtained vulcanized tire at 50 to 120 ° C. for 10 to 300 seconds.

  A pneumatic tire is produced using the polymer film according to the present invention as an inner liner. Since SIBS, SMA, and the like constituting the polymer film are thermoplastic elastomers, when heated to, for example, 150 to 180 ° C. in the step of obtaining a vulcanized tire, the polymer film is softened in the mold. Here, the softened state means that the molecular mobility is improved and is in an intermediate state between a solid and a liquid. Since the thermoplastic elastomer in the softened state is more reactive than the solid state, it is fused to the adjacent member.

  That is, the inner liner in contact with the outer surface of the expanded bladder is softened by heating and fused to the bladder. If an attempt is made to remove the vulcanized tire from the mold while the inner liner and the outer surface of the bladder are fused, the inner liner peels off from the adjacent insulation or carcass, resulting in an air-in phenomenon. In addition, the tire shape itself may be deformed.

  Therefore, the thermoplastic elastomer used for the inner liner can be solidified by immediately cooling the obtained vulcanized tire at 120 ° C. or lower for 10 seconds or longer. When the thermoplastic elastomer is solidified, the fusion between the inner liner and the bladder is eliminated, and the releasability when the vulcanized tire is taken out from the mold is improved.

  The cooling temperature is preferably 50 to 120 ° C. When the cooling temperature is lower than 50 ° C., it is necessary to prepare a special cooling medium, which may deteriorate productivity. When the cooling temperature exceeds 120 ° C., the thermoplastic elastomer is not sufficiently cooled, and the inner liner remains fused to the bladder when the mold is opened, which may cause an air-in phenomenon. The cooling temperature is more preferably 70 to 100 ° C.

  The cooling time is preferably 10 to 300 seconds. If the cooling time is shorter than 10 seconds, the thermoplastic elastomer is not sufficiently cooled, and the inner liner remains fused to the bladder when the mold is opened, which may cause an air-in phenomenon. When the cooling time exceeds 300 seconds, the productivity is deteriorated. The cooling time is more preferably 30 to 180 seconds.

  The step of cooling the vulcanized tire is preferably performed by cooling the inside of the bladder. Since the inside of the bladder is hollow, a cooling medium adjusted to the cooling temperature can be introduced into the bladder after the vulcanization process is completed.

  The process of cooling the vulcanized tire can be performed by cooling the inside of the bladder and installing a cooling structure in the mold.

  As the cooling medium, it is preferable to use one or more selected from the group consisting of air, water vapor, water, and oil. Among these, it is preferable to use water that is excellent in cooling efficiency.

<Examples 1-18 and Comparative Examples 1-16>
(Production of polymer sheet)
Each compounding agent was put into a twin screw extruder (screw diameter: φ50 mm, L / D: 30, cylinder temperature: 220 ° C.) according to the compounding formulation shown in Tables 1 and 2, and pelletized. From the polymer sheet, the obtained pellets were obtained with a T-die extruder (screw diameter: φ80 mm, L / D: 50, die lip width: 500 mm, cylinder temperature: 220 ° C., film gauge: 0.3 mm) or an inflation co-extruder. An inner liner was prepared.

(Production of pneumatic tires)
The obtained polymer sheet was applied to the inner liner portion of the tire to prepare a raw tire. The green tire was press-molded in a mold at 170 ° C. for 20 minutes to produce a 195 / 65R15 size vulcanized tire.

  Here, in order to adjust the thickness in the bead region Rb and the buttress region Rs of the inner liner, a profile is attached to the extrusion port of the polymer sheet, and an integrated sheet in which the thickness Gs of the buttress region is reduced is prepared. This was disposed on the inner surface of the tire as an inner liner.

  In Examples 1 to 6, Gs / Gb was set to 0.75, and a polymer component containing an SMA ester resin or an aqueous SMA ammonium salt solution was used. In Examples 7-10, SMA base resin was blended with SIBS, and the value of Gs / Gb was adjusted to 0.75-0.33. In Examples 11 to 14, SMA base resin and SMA ester resin were blended with SIBS, and the value of Gs / Gb was adjusted to 0.75 to 0.33. In Examples 15-18, SMA base resin and SMA ammonium salt aqueous solution were blended with SIBS, and the value of Gs / Gb was adjusted to 0.75-0.33.

  In Comparative Example 1, 80 parts by mass of chlorobutyl (IIR), 20 parts by mass of NR, and 20 parts by mass of filler were mixed with a Banbury mixer, respectively, and a polymer film having a thickness of 0.1 mm was formed with a calender roll. Obtained. The value of Gs / Gb of this polymer film was 1.

  In Comparative Examples 2 to 16, a polymer film having the composition shown in Table 2 was used as the inner liner. The value of Gs / Gb of this polymer film is as shown in Table 2.

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

<Peel test>
The inner liner (polymer sheet), a 2 mm thick carcass rubber sheet (compounding: NR / BR / SBR = 40/30/30) and a reinforced canvas fabric are stacked in this order for 12 minutes at 170 ° C. A test specimen for peeling was prepared by heating under pressure. Using the obtained test piece, in accordance with JIS K 6256 “How to determine adhesion of vulcanized rubber and thermoplastic rubber”, a peel test is performed at room temperature of 23 ° C., and a polymer sheet for an inner liner and a rubber sheet The adhesive strength of was measured. The peel strength index was calculated by the following calculation formula using the obtained numerical value as a reference (100) as Comparative Example 1. The larger the value of the inner liner and carcass peeling force, the better the adhesion.
(Peeling strength index) = (Adhesive strength of each formulation) / (Adhesive strength of Comparative Example 1) × 100
<Bending fatigue test>
A predetermined test piece having a groove at the center was prepared in accordance with JIS K 6260 “Demach flex cracking test method for 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 in which bending growth was repeatedly applied and crack growth was measured. 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 bending fatigue properties of the polymer laminates of each Example and each Comparative Example were shown as an index. 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: tire air leak test>
The 195 / 65R15 steel radial PC tire manufactured by the above-described method was assembled into a JIS standard rim 15 × 6JJ, sealed with an initial air pressure of 300 kPa, and left at room temperature for 90 days, and the rate of decrease in air pressure was calculated. It can be said that the smaller the decrease in air pressure, the better the air pressure is less likely to decrease.

<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 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 JATMA YEAR 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.

(Evaluation results)
The test results are shown in Tables 1 and 2.

(Note 1) SIBS: “Sibstar SIBSTAR 102T” manufactured by Kaneka Corporation (Shore A hardness 25, styrene content 25% by mass).
(Note 2) SMA base resin: “SMA1000” manufactured by Sartomer (styrene component / maleic anhydride component: 50/50, weight average molecular weight: 5,500, acid value of maleic anhydride: 490).
(Note 3) SMA ester resin: “SMA1440” manufactured by Sartomer (styrene component / maleic anhydride component: 80/20, weight average molecular weight: 7,000, acid value of maleic anhydride: 200).
(Note 4) SMA ammonium salt aqueous solution: “SMA1000H” (pH 9.0) manufactured by Sartomer.
(Note 5) Chlorobutyl: “Exon Chlorobutyl 1068” manufactured by ExxonMobil Corporation.
(Note 6) NR (natural rubber): TSR20.
(Note 7) Filler: “Seast V” manufactured by Tokai Carbon Co., Ltd. (N660, N ₂ SA: 2)
7 m ² / g).

  The thickness of the “SIBS / SMA layer” in Tables 1 and 2 indicates the thickness of the region other than Gs, and the Gb of each example and each comparative example (excluding Comparative Example 1) is 0.6 mm. Is the thickness.

(Consideration of evaluation results)
<Contrast with Examples 1-6 and Comparative Examples 1-13>
In the pneumatic tires of Examples 1 to 6, the inner liner has a styrene-isobutylene-styrene triblock copolymer of 99.5 to 60% by mass and a styrene-maleic anhydride copolymer of 0.5 to 40% by mass. The ratio of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb (Gs / Gb) was 0.3 to 0.75. . For this reason, the pneumatic tires of Examples 1 to 6 were provided with an inner liner that improved air permeation resistance, bending fatigue resistance and crack resistance.

  On the other hand, since the pneumatic tires of Comparative Examples 1, 3, and 4 were inner liners having a SIBS content of less than 60% by mass, the air permeation resistance, bending fatigue resistance, and crack resistance could not be improved. . Moreover, since the pneumatic tire of Comparative Example 2 was an inner liner having a SIBS content exceeding 99.5% by mass, the air permeability resistance, the bending fatigue resistance and the crack resistance could not be improved. In the pneumatic tires of Comparative Examples 5 to 13, the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb exceeds 0.75 (1.0 Therefore, the air permeation resistance, bending fatigue resistance and crack resistance could not be improved.

<Contrast with Examples 7 to 10 and Comparative Example 14>
The pneumatic tires of Examples 7 to 10 are inner liners in which the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb is 0.3 to 0.75. In contrast, in the pneumatic tire of Comparative Example 14, the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb is less than 0.3 (0.25). )Met. For this reason, the pneumatic tires of Examples 7 to 10 were superior to those of Comparative Example 14 in air permeation resistance, bending fatigue resistance and crack resistance.

<Contrast with Examples 11-14 and Comparative Example 15>
The pneumatic tires of Examples 11 to 14 are inner liners in which the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb is 0.3 to 0.75. In contrast, in the pneumatic tire of Comparative Example 15, the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb was less than 0.3 (0.25). )Met. For this reason, the pneumatic tires of Examples 11 to 14 were superior to those of Comparative Example 15 in air permeation resistance, bending fatigue resistance and crack resistance.

<Contrast with Examples 15 to 18 and Comparative Example 16>
The pneumatic tires of Examples 15 to 18 are inner liners in which the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb is 0.3 to 0.75. In contrast, in the pneumatic tire of Comparative Example 16, the ratio (Gs / Gb) of the average thickness Gs of the buttress region Rs to the average thickness Gb of the bead region Rb was less than 0.3 (0.25). )Met. For this reason, the pneumatic tires of Examples 15 to 18 were superior to those of Comparative Example 16 in air permeation resistance, bending fatigue resistance and crack resistance.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  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, Rb bead area, Rs buttress area, Le tire maximum width position , Lt Bead toe, Lu Corresponding position of belt layer end.

Claims (6)

A pneumatic tire with an inner liner on the inside of the tire,
The inner liner is a polymer sheet made of a polymer mixture containing 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer and 0.5 to 40% by mass of a styrene-maleic anhydride copolymer. The ratio of the average thickness Gs of the buttress region Rs extending from the tire maximum width position to the corresponding position Lu of the belt layer end and the average thickness Gb of the bead region Rb extending from the tire maximum width position to the bead toe (Gs / A pneumatic tire in which Gb) is 0.3 to 0.75.   The pneumatic tire according to claim 1, wherein the styrene-isobutylene-styrene triblock copolymer contains a styrene component in a range of 10 to 30% by mass and has a weight average molecular weight of 50,000 to 400,000.   The styrene-maleic anhydride copolymer has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10, a weight average molecular weight of 4,000 to 20,000, and maleic anhydride. The pneumatic tire according to claim 1 or 2, comprising a styrene-maleic anhydride copolymer base resin having an acid value of 50 to 600 as a component.   The styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer having a monoester group and a monocarboxylic acid group obtained by esterifying the styrene-maleic anhydride copolymer base resin. The pneumatic tire according to claim 1, comprising an ester resin.   The styrene-maleic anhydride copolymer includes an aqueous styrene-maleic anhydride copolymer ammonium salt solution in which the styrene-maleic anhydride copolymer base resin is dissolved in an ammonium salt. The pneumatic tire according to Crab.   The pneumatic tire according to any one of claims 1 to 5, wherein an average thickness Gs of a buttress region of the inner liner is 0.05 to 0.45 mm.

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