Pneumatic tyres

Abstract: A pneumatic tyre having a sidewall rubber, which has improved weatherability and flexing fatigue resistance and is not discoloured. The pneumatic tyre comprises a pair of bead cores (1), a toroidal carcass fixed by turning up both edges thereof around the bead core (11), a belt layer (3) arranged in the peripheral direction outside of the crown of the carcass, a tread (4) arranged outside of the belt layer (3), and a sidewall rubber (5) arranged outside of the carcass, wherein the sidewall rubber (5) has a two-layer structure comprising an inner layer rubber (6) adjacent to the carcass and an outer layer rubber (7) arranged outside thereof, and the outer layer rubber (7) comprises 40 to 90% by weight of at least one diene rubber selected from a group consisting of a natural rubber, an isoprene rubber, a styrene-butadiene rubber and a butadiene rubber, and 10 to 60% by weight of a rubber obtained by halogenating a copolymer of an iso-monooelfin having 4 to 7 carbon atoms and p-alkylstyrene, as a rubber component.

Description: The present invention relates to a pneumatic tyre having a sidewall rubber, which has improved weatherability and flexing fatigue resistance and is not discoloured even if it is used for a long time. As sidewall rubber for tyres, there has been generally used a rubber (highly unsaturated rubber) with a high content of a double bond, such as a natural rubber, an isoprene rubber and a butadiene rubber. Since these highly unsaturated rubbers have double bonds in the main chain, these are poor in ozone resistance, hear resistance, etc., and thus cracks may be formed during long-term storage and use. Accordingly, an amine antioxidant and a wax have been mixed therewith for the purpose of preventing cracks. However, there is a problem that the surface of the sidewall rubber is bloomed with the amine antioxidant and the wax during long-term storage or use, and then the surface of the sidewall rubber is discoloured. As a means to solve these problems, use of a rubber excellent in weatherability, such as ethylene propylene diene rubber (EPDM) has been proposed (Japanese Examined Patent Publication No 52-1761/1977, Japanese Unexamined Patent Publication No 56-11933/1981, Japanese Unexamined Patent Publication No 1-297307/1989, Japanese Unexamined Patent Publication No 1-231773/1996 etc). However, since EPDM has an ethylene segment, the ethylene segment is crystallised and cracking is formed from the crystalline as an origin, when a tyre made from EPDM is cooled after it is heated to nearly 100°C in a use thereof. Document US-A-5,376,438, which is considered to represent the most relevant state of the art to the subject-matter of independent claim 1, discloses a pneumatic tyre having a multilayered sidewall comprising an axially inner layer rubber adjacent to the carcass and an axially outer layer rubber arranged outside thereof, and the outer layer rubber comprises 10 to 90 phr of at least one diene rubber selected from the group consisting of a natural rubber, an isoprene rubber, a styrene-butadiene rubber and a butadiene rubber, and 10 to 90 phr of a rubber obtained by halogenating a copolymer of an iso-monoolefin having 4 to 7 carbon atoms and p-alkylstyrene, as a rubber component, and wherein the Shore-A hardness of the outer rubber layer after vulcanization is 46. The object of the present invention is to provide a pneumatic tyre having a sidewall rubber which is excellent in weatherability and flexing fatigue resistance, is not discoloured and does not form crack from crystalline. Accordingly the present invention provides a pneumatic tyre comprising a pair of bead cores, a toroidal carcass fixed by turning up both edges thereof at the bead core, a belt layer arranged in the peripheral direction outside of the crown of the carcass, a tread arranged outside of the belt layer, and a sidewall rubber arranged outside of the carcass, wherein the sidewall rubber has a two-layer structure comprising an axially inner layer rubber adjacent to the carcass and an axially outer layer rubber arranged outside thereof, and the outer layer rubber comprises 40 to 90% by weight of a least one diene rubber selected from a group consisting of a natural rubber, an isoprene rubber, a styrene-butadiene rubber and a butadiene rubber, and 10 to 60% by weight of a rubber obtained by halogenating a copolymer of an iso-monoolefin having 4 to 7 carbon atoms and p-alkylstyrene, as a rubber component. In the above-mentioned pneumatic tyre, a softener for a rubber is preferably mixed with the outer layer rubber. The relationship between JIS A hardness (H SO ) of the outer layer rubber and the JIS A hardness (H SI ) of the inner layer rubber preferably satisfied the following equation (1): H SI - 10 ≤ H SO ≤ H SI - 3 Also it is preferable that the diene rubber in the outer layer rubber comprises a natural rubber or an isoprene rubber and a butadiene rubber, and an amount of the butadiene rubber based on the natural rubber or the isoprene rubber is more than 1. The thickness of the outer layer rubber is preferably 0.6 to 2.0 mm. The thickness of the inner layer is preferably 2 to 8 mm. An embodiment of the present invention will now be described, by way of example only, in conjunction with the attached drawing in which:- Figure 1 is a partial sectional view of the pneumatic tyre of the present invention. The pneumatic tyre of the present invention comprises a pair of bead cores 1, a toroidal carcass 2 fixed by turning up both edges thereof around the bead core, a belt layer 3 arranged in the peripheral direction outside of the crown 8 of the carcass, a tread 4 arranged outside of the belt layer, and a sidewall rubber 5 arranged outside of the carcass. The sidewall rubber 5 in the present invention comprises a two-layer structure comprising an axially inner layer rubber 6 adjacent to the carcass 2 and an axially outer layer rubber 7 arranged outside thereof. The outer layer rubber comprises a diene rubber and a halogenated copolymer rubber obtained by halogenating a copolymer of an iso-monoolefin having 4 to 7 carbon atoms and p-alkylstyrene, as a rubber component. The amount of the mixed diene rubber is 40 to 90% by weight, preferably 50 to 80% by weight, more preferably 55 to 80% by weight. If the amount of the mixed diene rubber is less than 40% by weight, adhesion to the inner layer rubber 6 becomes significantly low and simultaneously flexing fatigue resistance becomes also low. On the other hand, if the amount is more than 90% by weight, satisfactory weatherability cannot be achieved. The diene rubber is at least one selected from the group consisting of a natural rubber, an isoprene rubber, a styrene-butadiene rubber and a butadiene rubber. Tensile properties, particularly breaking strength and flexing fatigue resistance are important for the outer layer rubber in the sidewall rubber. These properties can be maintained by incorporating 40 to 90% by weight of at least one of these diene rubbers into the rubber component. As the styrene-butadiene rubber, there can be used a styrene-butadiene rubber obtained by solution polymerisation and a styrene-butadiene rubber obtained by emulsion polymerisation, wherein an amount of the styrene unit is preferably 10 to 40% by weight. From the viewpoint of improvement in properties at a low temperature, the diene rubber is preferably a natural rubber or an isoprene rubber and a butadiene rubber. When the natural rubber and the butadiene rubber are used as the diene rubber, a weight ratio of the butadiene rubber to the natural rubber is preferably more than 1, more preferably above 1 to 1.8, and most preferably above 1 to 1.5. When the ratio of the mixed butadiene rubber is less than 1, the flexing fatigue resistance is lowered. When the ratio is more than 1.8, the strength is significantly lowered. When the isoprene rubber and the butadiene rubber are used as the diene rubber, a weight ratio of the butadiene rubber to the isoprene rubber is preferably 1 to 1.8, more preferably 1 to 1.5. The amount of the halogenated copolymer rubber obtained by halogenising a copolymer of an iso-monoolefin having 4 to 7 carbon atoms and p-alkylstyrene is 10 to 60% by weight, preferably 20 to 50% by weight, more preferably 20 to 45% by weight. When the amount of the halogenated copolymer rubber is less than 10% by weight, weatherability cannot be satisfactorily achieved. When the amount is more than 60% by weight, adhesion to the inner layer rubber 6 is significantly lowered, and simultaneously the breaking strength and flexing fatigue resistance is also lowered. Examples of the above-mentioned iso-monoolefin having 4 to 7 carbon atoms are iso-butylene, 2-methyl-1-butene, 2-methyl-2-butene, 2,3-dimethyl-2-butene and the like. The above-mentioned p-alkylstyrene is preferably the one having 1 to 6, more preferably 1 to 5, carbon atoms of an alkyl group. In the halogenation, a part or all of the hydrogen atoms are replaced by using halogens such as bromine, chlorine and iodine. A content of the halogen in the halogenated copolymer is preferably 0.1 to 5% by weight, more preferably 0.1 to 2% by weight. If the content of halogen is less than 0.1%, the strength thereof tends to be lowered since a vulcanisation degree is too low. If the content is more than 5%, the copolymer tends to be rigid since a vulcanisation degree is high. The halogenated copolymer can be prepared, for example, by mixing isobutylene with p-alkylstyrene in a predetermined ratio, polymerising them to obtain a copolymer by a conventional polymerisation method, and partially replacing hydrogen atoms on the alkyl group in p-alkylstyrene unit by halogens such a chlorine. This process is shown as follows: wherein R represents an alkyl group having 1 to 6 carbon atoms, R' represents an alkyl group having 1 to 6 carbon atoms whose hydrogen atoms are partially replaced by a halogen, and X represents a halogen. The content of a p-alkylstyrene unit in the halogenated copolymer is preferably 3 to 20% by weight. If the content of the p-alkylstyrene unit is less than 3% by weight, adhesion to the inner layer rubber tends to be lowered. If the content is more than 20% by weight, the copolymer tends to be highly rigid and not only tensile properties but also flexing fatigue resistance tend to be low. The weight average molecular weight of the halogenated copolymer is preferably 300,000 to 700,000, and a glass transition temperature thereof is preferably -60 to -40°C. It is thought that the halogenated copolymer is usually cross-linked by eliminating a substituted halogen in the alkyl group of the p-alkylstyrene unit due to mixing metal oxides and sulfur, and by reacting the substituted halogen with a phenyl group in the adjacent p-alkylstyrene unit. The outer layer rubber is preferably mixed with softeners for a rubber such as a softener of petroleum, a softener of paraffin, a softener of aromatics, a softener of naphthene, a softener of aliphatics and a softener of synthetic resin in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the rubber component. It is difficult to mix the halogenated copolymer with diene rubbers such as a natural rubber and a butadiene rubber, this dispersion thereof often becomes insufficient. Accordingly, the softener for a rubber can be mixed in an amount of 0.5 to 5 parts by weight, more preferably 0.7 to 3 parts by weight, so that dispersibility can be improved by raising the compatibility therebetween to improve flexing fatigue resistance and ozone resistance. Among the softeners for a rubber, the softener of aliphatics, the softener of aromatics or a mixture of phenol resin are preferable. Particular, for example, Struktol 40 MS and Struktol 60 MS available from S&S Japan are preferable. The outer layer rubber can be formed into a sheet, for example, by kneading the rubber component with the softener in a Banbury mixer or a kneader and then sheeting with a roll, an extruder or the like. The JIS A hardness of the outer layer rubber after vulcanisation is preferably adjusted to 52 to 59, more preferably 54 to 58. The thickness of the outer layer rubber is 0.6 to 2 mm, preferably 0.7 to 1.8 mm, and more preferably 0.7 to 1.5 mm. If the thickness of the outer layer rubber is less than 0.6 mm, cracking occurs in the tyre. If the thickness is more than 2 mm, the preparation costs become too high. The thickness of the outer layer rubber is preferably at most 60%, more preferably 20 to 50%, of the thickness of the sidewall rubber. As the inner layer rubber, a raw rubber generally used in rubber compositions for sidewall can be used without any particular limitation. Examples of the rubber are a natural rubber, a butadiene rubber, an isoprene rubber, a styrene-butadiene rubber, a butyl rubber, a halogenated butyl rubber, p-methylstyrene-isobutylene brominated rubber, and a terpolymer rubber of ethylene-propylene-diene (EPDM-EPT) and the like. These may be used solely or in a combination use of two or more thereof. The inner layer rubber can also be formed into a sheet after kneading the rubber component in the same manner as in the outer layer rubber. The pneumatic tyre of the present invention has a two-layer structure of a sidewall rubber, and the functions of the sidewall rubbers are shared by the inner layer rubber and the outer layer rubber. Namely, the halogenated copolymer is incorporated into the outer layer rubber, and simultaneously the JIS A hardness (HSO) is adjusted to 52 to 59, and the JIS A hardness (H SI ) of the inner layer rubber satisfied the equation (1): H SI - 10 ≤ H SO ≤ H SI - 3 The rigidity of the sidewall rubber can be maintained and flexing fatigue resistance can be improved by enlarging the hardness of the inner layer rubber within the predetermined range higher than the hardness of the outer layer rubber. Although the thickness of the inner layer rubber is not particularly limited, the thickness is preferably 2 to 8 mm, more preferably 2 to 5 mm. If the thickness of the inner layer rubber is less than 2 mm, function of protecting the carcass tends to be low. If the thickness is more than 8 mm, weight of the tyre merely increases. The inner layer rubber and the outer layer rubber in the present invention can also contain fillers such as carbon black in addition to the above-mentioned rubber component. The amount of carbon black is preferably 30 to 60 parts by weight based on 100 parts by weight of the rubber component contained in the inner layer rubber and the outer layer rubber, respectively. If the amount of carbon black is less than 30 parts by weight, strength tends to be low. If the amount is more than 60 parts by weight, the rubber tends to be rigid. The inner layer rubber and the outer layer rubber in the present invention can be mixed with various additives used generally in the rubber industry, such as various process oils, waxes, antioxidants, metal oxides, stearic acid, zinc oxide, vulcanising agents (sulfur and the like) and vulcanisation accelerators, in addition to the rubber components and fillers. The sidewall rubber of the present invention can be obtained, for example, by laying the inner layer rubber on the outer layer rubber and by vulcanising them. Hereinafter, the present invention is explained in more detail by using Test Examples and Examples, but the present invention is not limited thereto. "Part" and "%" show "part by weight" and "% by weight", respectively, otherwise specified. Components used in Test Examples and Examples below are shown as follows: NR: RSS#3 BR: Nipol 1220 (available from Nippon Zeon Co Ltd) EXXPRO: EXXPRO 90-10 (available from Exxon Chemical Corporation), copolymer of isobutylene-p-methylstyrene with a bromine content of about 2% and a content of P-methylstyrene unit of 7.5% Carbon black: Seast SO (available from Tokai Carbon Co Ltd) Process oil: Diana Process Oil PW32 (available from Idemitsu Kosan Co Ltd) Wax: Sunnoc (Ouchi Shinko Kagaku Kogyo Co Ltd) Antioxidant: Nocrac 6C (N-phenyl-N'-(1,3-dimethyl butyl)-p-phenylene diamine) (Ouchi Shinko Kagaku Kogyo Co Ltd) Softener for rubber: Struktol 40MS (S&S Japan Co Ltd) Zinc oxide: available from Mitsui Mining & Smelting Co Ltd Stearic acid: available from NOF Corporation Sulfur: available from Tsurumi Chemical Co Ltd Vulcanisation accelerator: NOCCELER DM (dibenzothiazyl disulfide) (Ouchi Shinko Kagaku Kogyo Co Ltd) TEST EXAMPLES 1 to 8 (rubber sheet) According to the composition in Table 1, these chemicals other than sulfur and the vulcanisation accelerator were kneaded in an 1.7-L Banbury mixer. Thereto were added sulfur and the vulcanisation accelerator to prepare an unvulcanised rubber sheet, and following tests were carried out. Ozone resistance The above unvulcanised rubber sheet was vulcanised at 170°C for 15 minutes to prepare a vulcanised rubber sheet. The sheet was examined under the conditions of a temperature of 40°C, an ozone concentration of 50 pphm, an elongation degree of 50%, and for 96 hours, according to JIS K6301. Crack state of the test specimen was judged according to JIS K6301. Flexing fatigue resistance (at room temperature The above unvulcanised rubber sheet was vulcanised at 170°C for 15 minutes and was examined in a flexing crack test according to JIS K6301. In the test, after the specimen was bent repeatedly 100,000 times, the specimen was evaluated based on the length (mm) of crack growth. Flexing fatigue resistance (at high temperature) The test specimen was examined in an atmosphere at 80°C in the same manner as in the flex crack test at room temperature, to evaluate the length (mm) of crack growth. Adhesive property The above unvulcanised rubber sheet was laid on the unvulcanised sheet in Test Example 1. These sheets were adhered by vulcanisation at 170°C for 15 minutes, and cut into pieces of 2.5 cm in width to prepare a specimen for adhesion peeling test. The specimen was peeled off at a separation rate of 50 mm/minute to evaluate the peeling strength. Unit of the peeling strength is expressed as "kgf/2.5 cm". A higher value shows higher peeling strength, and a sample showing a value of at least 100 kgf/2.5 cm means practically usable one. Appearance discoloration By using rubber please of 4 mm in thickness vulcanised at 170°C for 15 minutes, these were placed outdoor in such a way that they were not exposed to rain. After the specimens were place outdoor for 30 days, their appearance was visibly observed to determine the degree of discoloration in 5 ranks. A smaller value shows a higher degree of discoloration. Results are shown in Table 1. As can be seen from the results in Table 1, the specimens using a predetermined amount of EXXPRO in Test Examples 3, 4 and 5 have not only suppressed discoloration, but also improved ozone resistance and flexing fatigue resistance as compared with the specimen using no EXXPRO in Test Example 1. The rubber sheet using EPDM in Test Example 2 is excellent in flexing fatigue resistance at a room temperature, but is poor in flexing fatigue resistance at a high temperature. Namely, cracking is easily caused under the actually using condition. On the other hand, the test specimens using EXXPRO in Test Examples 3, 4 and 5 are equivalent or slightly superior to the specimen in Test Example 1 with respect to the degree of crack at a high temperature. However, the specimen using at least 60% by weight of EXXPRO in Test Example 6 did not show sufficient adhesion. Also in the specimens mixed with Struktol 40MS as a softener for a rubber in Test Examples 7 and 8 in an amount of 0.5 to 5 parts, adhesion strength was improved. EXAMPLES 1 to 4 and COMPARATIVE EXAMPLES 1 to 2 (tyre) Then, the inner layer rubber was combined with the outer layer rubber as shown in Table 2, to constitute sidewall rubbers having a two-layer structure. This sidewall rubber was used to make a passenger car steel radial tyre (size 195/65R15). The sidewall rubber was provided with a cut of 0.3 mm in thickness and 5 mm in width and the tyre was tested for durability using a drawn tester. The tyre is an accepted product if it can run 1000 km without bursting. Results are shown in Table 2. As can be seen from Table 2, the specimens in Examples 1 to 3, wherein EXXPRO is used in the outer layer rubber and the relationship between the hardness (H IS ) of the inner layer rubber and the hardness (H SO ) of the outer layer rubber is in the predetermined range, are particularly excellent in durability. TEST EXAMPLES 9 to 17 (rubber sheet) The chemicals were used according to the compositions in Table 3 to prepare an unvulcanised rubber sheet in the same manner as in Test Examples 1 to 8. The sheet was examined in the following tests. Ozone resistance The above unvulcanised rubber sheet was vulcanised at 170°C for 15 minutes to prepare a vulcanised rubber sheet. The sheet was examined under the condition of a temperature of 40°C, an ozone concentration of 50 pphm, an elongation degree of 50%, and for 96 hours according to JIS K6259. Crack state of the test specimen was judged according to JIS K6259. Flexing fatigue resistance The above unvulcanised rubber sheet was vulcanised at 170°C for 15 minutes and was examined in a flexing crack test according to JIS K6260. In the test, after the specimen was bent repeatedly 500,000 times, the crack state thereof was evaluated using six classes. The smaller class number shows higher flexing fatigue resistance. Adhesive property Peeling strength was evaluated in the same manner as in Test Examples 1 to 8. Unit of the peeling strength was expressed as "kgf/2.5 cm". A higher value shows higher peeling strength, and a sample showing a value of at least 100 kgf/2.5 cm indicates that the sample is practically usable. Appearance discoloration The test specimen was examiner outdoor in the same manner as in Test Examples 1 to 8 to evaluate the degree of discoloration. As can be seen from the results in Table 3, the specimens using a predetermined amount of EXXPRO in Test Examples 9 to 15, have not only suppressed discoloration, but also improved ozone resistance and flexing fatigue resistance as compared with the specimen using no EXXPRO in Test Example 16. Further, the specimen using at least 60% by weight of EXXPRO in Test Example 17n shows insufficient adhesive property. TEST EXAMPLES 18 to 33 (inner layer rubber-outer layer rubber According to Table 4, the unvulcanised rubber sheet in Test Example 9 to 15 was laid on the unvulcanised rubber sheet in Test Example 16. These sheets were vulcanised at 170°C for 15 minutes to prepare a sample having a two-layer structure. By using these samples, a flex crack test was carried out in the same manner as for Test Examples 9 to 17. If an amount of BR in the outer layer rubber is smaller than that of NR, the degree of crack formation increases in case that the thickness of the outer layer rubber is less than 0.6 mm. On the other hand, if the amount of BR is higher than that of NR, the degree of crack formation is low even if the thickness of the outer layer rubber is 0.4 mm. Test Ex. No. Outer layer rubber Inner layer rubber Resistance to flexing fatigue Composition Thickness (mm) Composition Thickness (mm) 18 Test Ex. 9 1.8 Test Ex. 16 3.2 First class 19 Test Ex. 9 1.2 Test Ex. 16 3.8 First class 20 Test Ex. 9 0.7 Text Ex. 16 4.3 First class 21 Test Ex. 9 0.5 Text Ex. 16 4.5 Fourth class 22 Test Ex. 11 1.8 Text Ex. 16 3.2 First class 23 Test Ex. 11 1.2 Test Ex. 16 3.8 First class 24 Test Ex. 11 0.7 Text Ex. 16 4.3 First class 25 Test Ex. 11 0.5 Text Ex. 16 4.5 Fourth class 26 Test Ex. 12 0.7 Text Ex. 16 4.3 First class 27 Test Ex. 12 0.5 Test Ex. 16 4.5 Fourth class 28 Test Ex. 13 0.7 Test Ex. 16 4.3 First class 29 Test Ex. 13 0.5 Test Ex. 16 4.5 Fourth class 30 Test Ex. 14 0.7 Test Ex. 16 4.3 First class 31 Test Ex. 14 0.4 Test Ex. 16 4.6 First class 32 Test Ex. 15 0.7 Test Ex. 16 4.3 First class 33 Test Ex. 15 0.4 Test Ex. 16 4.6 First class EXAMPLES 5 to 20 (tyre) Then, according to Table 5, tyres of 215/45ZR17 size were prepared using a sidewall rubber having a two-layer structure wherein the rubber sheet in Test Examples 9 to 15 was used as the outer layer rubber and the rubber sheet in Test Example 16 was used as the inner layer rubber, to examine durability thereof on a drawn tester. A tyre is an accepted product if it can run 30,000 km without visible cracking forming. As shown in Table 5, if the amount of NR was higher than that of BR, the crack formation could be confirmed on the tyre having run up to 30,000 km in case that the thickness of the outer layer was less than 0.6 mm. On the other hand, if the amount of BR was higher than that of NR, the tyre was accepted even if the thickness was 0.4 mm. Ex. No Outer layer rubber Inner layer rubber Durability test Composition Thickness (mm) 5 Test Ex. 9 1.8 Test Ex. 16 good 6 Test Ex. 9 1.2 Test Ex. 16 good 7 Test Ex. 9 0.7 Text Ex. 16 good 8 Test Ex. 9 0.5 Text Ex. 16 Crack formation at 16,000 Km 9 Test Ex. 11 1.8 Text Ex. 16 good 10 Test Ex. 11 1.2 Test Ex. 16 good 11 Test Ex. 11 0.7 Text Ex. 16 good 12 Test Ex. 11 0.5 Text Ex. 16 Crack formation at 23,000 Km 13 Text Ex. 12 0.7 Test Ex. 16 good 14 Test Ex. 12 0.5 Test Ex. 16 Crack formation at 16,000 Km 15 Test Ex. 13 0.7 Test Ex. 16 good 16 Test Ex. 13 0.5 Test Ex. 16 Crack formation at 23,000 Km 17 Test Ex. 14 0.7 Test Ex. 16 good 18 Test Ex. 14 0.7 Test Ex. 16 good 19 Test Ex. 15 0.4 Test Ex. 16 good 20 Test Ex. 15 0.4 Test Ex. 16 good According to the present invention, there is provided a pneumatic tyre have a sidewall rubber, which has improved weatherability and flexing fatigue resistance and, is not discoloured even if it is used for a long time.

Claims: A pneumatic tyre comprising a pair of bead cores (1), a toroidal carcass fixed by turning up both edges thereof around the bead core (1), a belt layer (3) arranged in the peripheral direction outside of the crown of the carcass, a tread (4) arranged outside of the belt layer, and a sidewall rubber (5) arranged outside of the carcass, wherein the sidewall rubber (5) has a two-layer structure comprising an axially inner layer rubber (6) adjacent to the carcass and an axially outer layer rubber (7) arranged outside thereof, and the outer layer rubber comprises 40 to 90% by weight of at least one diene rubber selected from a group consisting of a natural rubber, an isoprene rubber, a styrene-butadiene rubber and a butadiene rubber, and 10 to 60% by weight of a rubber obtained by halogenating a copolymer of an iso-monoolefin having 4 to 7 carbon atoms and p-alkylstyrene, as a rubber component, and wherein the the JIS A hardness (H SO ) of the outer layer rubber after vulcanization is adjusted to 52 to 59. A pneumatic tyre of claim 1, characterised in that the outer layer rubber (7) is mixed with a softener for a rubber. A pneumatic tyre of claim 1 or 2, characterised in that the relationship between the JIS A hardness (H SO ) of the outer layer rubber (7) and the JIS A hardness (H SI ) of the inner layer rubber (6) satisfies the following equation (1): H SI - 10 ≤ H SO ≤ H SI - 3 A pneumatic tyre of claim 1, 2 or 3, characterised in that the diene rubber in the outer layer rubber comprises a natural rubber or an isoprene rubber and a butadiene rubber, and an amount of the butadiene rubber based on the natural rubber or the isoprene rubber is more than 1. A pneumatic tyre of any of claims 1 to 4, characterised in that the thickness of the outer layer rubber (7) is 0.6 to 2.0 mm. A pneumatic tyre of any of claims 1 to 5, characterised in that the thickness of the inner layer rubber (6) is 2 to 8 mm.

Inventors: MINAGAWA YASUHISA, MINAGAWA, YASUHISA, Minagawa, Yasuhisa, c/o Sumitomo Rubber Ind. Ltd.
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES, LTD.
Application year: 2000
Main classification: B60C1
IPC codes: C08L21, B60C1, B60C13, C08L23