JPH11198617A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity, and to improve a rim slipping-out characteristic and operational stability by covering bead cores arranged in a pair of left/ right bead parts with a thermoplastic resin or a thermoplastic elastomer composition having a Young's modulus not less than a specific value. SOLUTION: In a pneumatic tire by rolling up the tire width directional both end parts of this carcass layer to the outside from the tire inside of a bead core 3 by mounting the carcass layer between a pair of left/right bead parts, the bead core 3 is constituted by winding at least a single stranded wire 6 by plural rounds in the tire circumferential direction. In this case, a covering layer 7 composed of a thermoplastic resin or a thermoplastic elastomer composition having a Young's modulus not less than 50 MPa is arranged around the bead core 3. This covering layer 7 is thermally fused by heat treatment by being arranged around the bead core 3 so as to cover the whole bead core 3 after bundling the stranded wire 6. Therefore, the stranded wire 6 can be firmly bound while reducing weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a bead portion in which a bead core formed by bundling strands of steel wire or the like is arranged. The present invention relates to a pneumatic tire that binds, improves uniformity, increases bead unseating value, and also improves steering stability.

[0002]

2. Description of the Related Art Generally, a bead core of a tire is formed by covering a plurality of high-strength and high-modulus element wires, such as steel wires and aramid fiber cords, arranged in a horizontal line with a rubber, and continuously covering the wires with a circle. It is formed by winding up annularly to form a laminated structure, or by covering one element wire with rubber and winding it up continuously in an annular shape.

[0003] Conventionally, in order to prevent the dispersion of wires (so-called irregularity) at the winding end of the bead core, the entire bead core has been wrapped with a bead cover made of a rubberized plain weave layer of an organic fiber cord. However, with the recent demand for reduction in tire weight, it is necessary to remove the bead cover made of the rubberized plain weave layer described above.

[0004] However, when the bead cover is removed from the periphery of the bead core, the wire becomes uneven at the winding end of the bead core, thereby deteriorating the uniformity of the tire and lowering the bead unseating value and causing the rim to be disengaged. However, there is a problem that the steering stability is deteriorated due to the deformation of the bead core.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the uniformity of a bead core while firmly binding the element wires of the bead while reducing the weight, and to increase the bead unseating value to improve the detachability of the rim. Another object of the present invention is to provide a pneumatic tire with improved steering stability.

[0006]

According to the present invention, there is provided a pneumatic tire having a bead core formed by winding at least one element wire a plurality of times around a pair of left and right bead portions in the tire circumferential direction. In the arranged pneumatic tire, the bead core is coated with a thermoplastic resin or a thermoplastic elastomer composition having a Young's modulus of 50 MPa or more.

[0007] By coating the bead core with a lightweight and high-rigidity thermoplastic resin or thermoplastic elastomer composition, the strands of the bead core can be firmly bound while reducing the weight. Therefore, since the ends of the strands of the bead core do not disperse, uniformity can be improved, and the amount of deformation of the bead core is reduced, so that the bead unseating value is increased, the rim detachability is improved, and the bead core is improved. Deformation is suppressed,
Driving stability can be improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 illustrates a pneumatic tire according to an embodiment of the present invention, and FIGS. 2 and 3 are enlarged views of the bead core. In the figure, a carcass layer 2 is mounted between a pair of right and left bead portions 1, 1, and both end portions of the carcass layer 2 in the tire width direction are wound up from the inside of the bead core 3 to the outside of the tire. Outside the carcass layer 2 in the tread portion 4, a plurality of belt layers 5 in which reinforcing cords are inclined with respect to the tire circumferential direction are arranged so that the cords cross each other between the layers.

As shown in FIGS. 2 and 3, the bead core 3 is configured by winding at least one strand 6 a plurality of times in the tire circumferential direction. This wire 6 has a high strength
A steel wire or an aramid fiber cord having a high elastic modulus can be used. And bead core 3
A plurality of strands 6 arranged in a row are continuously wound in a ring shape to form a laminated structure, or one strand 6
Are continuously wound in an annular shape.

Around the bead core 3, the Young's modulus is 50
A coating layer 7 made of a thermoplastic resin or a thermoplastic elastomer composition having a MPa or higher is provided. This coating layer 7
Are arranged around the bead core 3 so as to cover the entire bead core 3 after the strands 6 are bundled, and are thermally fused by a heat treatment. The thickness of the coating layer 7 is not particularly limited, but is preferably 0.05 to 0.5 mm. However, the form of coating of the coating layer 7 on the bead core 3 is not particularly limited, and the following forms are also possible.

In FIG. 4, a strip-shaped coating layer 7 is spirally wound around the bead core 3. in this case,
In order to increase the binding power of the bead core 3, 10
It is preferable to wind with a tension of １００100 N.
Further, as shown in FIG. 5, one or more of the strands 6 covered with a thermoplastic resin or a thermoplastic elastomer composition are wound into an annular shape and then heat-sealed, thereby forming a periphery of the bead core 3. In addition, the coating layer 7 may be arranged between the strands 6.

Examples of the above-mentioned thermoplastic resin include polyamide resins [eg, nylon 6 (N6), nylon 66 (N
66), nylon 46 (N46), nylon 11 (N1
1), nylon 12 (N12), nylon 610 (N6
10), nylon 612 (N612), nylon 6/6
6 copolymer (N6 / 66), nylon 6/66/610
Copolymer (N6 / 66/610), nylon MXD6
(MXD6), nylon 6T, nylon 6 / 6T copolymer, nylon 66 / PP copolymer, nylon 66 / PP
S copolymer], and N-alkoxyalkylated products thereof (for example, methoxymethylated product of 6-nylon, 6-
610-nylon methoxymethylated product, 612-nylon methoxymethylated product], polyester resin [for example, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), PET / PEI copolymer, Polyarylate (PAR), polybutylene naphthalate (PB
N), liquid crystal polyesters, aromatic polyesters such as polyoxyalkylenediimidic acid / polybutylate terephthalate copolymers), polynitrile resins [eg, polyacrylonitrile (PAN), polymethacrylonitrile, acrylonitrile / styrene copolymers (AS) ), Methacrylonitrile / styrene copolymer, methacrylonitrile / styrene / butadiene copolymer], polymethacrylate-based resins [for example, polymethyl methacrylate (PMM
A), polyethyl methacrylate], polyvinyl resin [for example, vinyl acetate, polyvinyl alcohol (PV
A), vinyl alcohol / ethylene copolymer (EVO
H), polyvinylidene chloride (PDVC), polyvinyl chloride (PVC), vinyl chloride / vinylidene chloride copolymer,
Vinylidene chloride / methyl acrylate copolymer, vinylidene chloride / acrylonitrile copolymer], cellulose resin [for example, cellulose acetate, cellulose acetate butyrate], fluorinated resin [for example, polyvinylidene fluoride (PVD)
F), polyvinyl fluoride (PVF), polychlorofluoroethylene (PCTFE), tetrafluoroethylene / ethylene copolymer], imide resin (for example, aromatic polyimide (PI)), and the like. In particular, it is preferable to use a heat-shrinkable polyimide-based thermoplastic resin in order to enhance the binding force of the bead core 3. Further, in order to avoid plasticization of the coating layer 7 due to temperature rise during running of the tire, it is preferable that the plasticizing temperature of the thermoplastic resin is 100 ° C. or more.

[0013] The thermoplastic elastomer composition is
It is a blend of a thermoplastic resin component and an elastomer component. In this thermoplastic elastomer composition, the content of the thermoplastic resin component is preferably 30% by weight or more. Examples of the elastomer component of the thermoplastic elastomer composition include diene rubbers and hydrogenated products thereof (eg, NR, IR, epoxidized natural rubber, SBR, BR).
(High cis BR and low cis BR), NBR, hydrogenated NB
R, hydrogenated SBR], olefin rubber [eg, ethylene propylene rubber (EPDM, EPM), maleic acid-modified ethylene propylene rubber (M-EPM), IIR, isobutylene and aromatic vinyl or diene monomer copolymer, acrylic rubber (ACM), ionomer], halogen-containing rubber [for example, bromide of Br-IIR, Cl-IIR, isobutylene paramethylstyrene copolymer (Br-
IPMS), chloroprene rubber (CR), hydrin rubber (CHR), chlorosulfonated polyethylene (CM
S), chlorinated polyethylene (CM), maleic acid-modified chlorinated polyethylene (M-CM)], silicone rubber [for example, methyl vinyl silicone rubber, dimethyl silicone rubber,
Methylphenylvinyl silicone rubber], sulfur-containing rubber (for example, polysulfide rubber), fluorine rubber (for example, vinylidene fluoride rubber, fluorinated vinyl ether rubber, tetrafluoroethylene-propylene rubber, fluorine-containing silicon rubber, fluorine-containing phosphazene rubber Rubber) and thermoplastic elastomers [for example, styrene-based elastomers, olefin-based elastomers, ester-based elastomers, urethane-based elastomers, and polyamide-based elastomers].

The method for producing a thermoplastic elastomer composition is as follows: a thermoplastic resin component and an elastomer component (unvulcanized product in the case of rubber) are melt-kneaded in advance by a twin-screw kneading extruder or the like;
By dispersing an elastomer component as a dispersed phase (domain) in a thermoplastic resin forming a continuous phase (matrix). When vulcanizing the elastomer component, a vulcanizing agent may be added under kneading to dynamically vulcanize the elastomer component. The various additives (excluding the vulcanizing agent) to the thermoplastic resin or the elastomer component may be added during the kneading, but it is preferable to mix them before kneading. The kneader used for kneading the thermoplastic resin and the elastomer component is not particularly limited, and a screw extruder, a kneader, a Banbury mixer, a twin-screw kneader or the like can be used. Above all, it is preferable to use a twin-screw kneading extruder for kneading the thermoplastic resin and the elastomer component and for dynamic vulcanization of the elastomer component. Further, two or more kinds of kneaders may be used and the kneading may be performed sequentially. As the conditions for the melt-kneading, the temperature may be at least the temperature at which the thermoplastic resin melts. The shear rate during kneading is 1000 to 7500 Sec.
It is preferably ^-1 . The total kneading time is preferably 30 seconds to 10 minutes, and when a vulcanizing agent is added, the vulcanization time after the addition is preferably 15 seconds to 5 minutes.

When the compatibility between the specific thermoplastic resin and the elastomer component is different from each other, it is preferable to compatibilize the two components by using an appropriate compatibilizer as the third component.
By mixing the compatibilizer into the system, the interfacial tension between the thermoplastic resin and the elastomer component is reduced, and as a result, the rubber particles forming the dispersion layer become finer, so that the properties of both components are more improved. It will be effectively expressed. Such a compatibilizer is generally a copolymer having a structure of both or one of a thermoplastic resin and an elastomer component, or an epoxy group, a carbonyl group, a halogen group, an amino group capable of reacting with the thermoplastic resin or the elastomer component. It can be a copolymer having a group, an oxazoline group, a hydroxyl group and the like. These may be selected according to the type of thermoplastic resin and elastomer component to be mixed,
Commonly used ones are styrene / ethylene / butylene block copolymer (SEBS) and its maleic acid-modified product, EPDM, EPDM / styrene or EPDM / acrylonitrile graft copolymer and its maleic acid-modified product, styrene / maleic acid Copolymers, reactive phenoxines and the like can be mentioned. The amount of the compatibilizer is not particularly limited, but is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the polymer component (total of the thermoplastic resin and the elastomer component).

When the thermoplastic resin and the elastomer are blended, the composition ratio of the specific thermoplastic resin component (A) to the elastomer component (B) is not particularly limited, and may be appropriately determined according to the Young's modulus and the thickness of the molded article. A preferred range is 90/10 to 30/70 by weight. In the polymer composition according to the present invention, in addition to the essential polymer component, other polymers such as the above-described compatibilizer polymer may be mixed as long as the necessary properties of the polymer composition for a tire of the present invention are not impaired. it can. The purpose of mixing other polymers is to improve the compatibility between the thermoplastic resin and the elastomer component, to improve the moldability of the molded material, to improve the heat resistance, to reduce the cost, etc. ,
As a material used for this, for example, polyethylene (PE), polypropylene (PP), polystyrene (P
S), ABS, SBS, polycarbonate (PC), and the like. The polymer composition according to the present invention further includes a filler (calcium carbonate, titanium oxide, alumina, etc.), a reinforcing agent such as carbon black and white carbon, a softener, a plasticizer, which are generally added to the polymer compound. Processing aids, pigments, dyes, antioxidants and the like can be arbitrarily compounded as long as the requirements for the air permeability and Young's modulus are not impaired.

The elastomer component can be dynamically vulcanized at the time of mixing with the thermoplastic resin. The vulcanizing agent, vulcanization aid, vulcanization conditions (temperature, time) and the like for dynamically vulcanizing the elastomer component may be appropriately determined depending on the composition of the elastomer component to be added, and are particularly limited. Not something. As the vulcanizing agent, a general rubber vulcanizing agent (crosslinking agent) can be used. Specifically, as the ionic vulcanizing agent, powdered sulfur, precipitated sulfur, highly dispersible sulfur, surface-treated sulfur, insoluble sulfur, dimorpholine disulfide, alkylphenol disulfide, and the like can be exemplified. 4ph
r [Parts per 100 parts by weight of rubber component (polymer)] can be used.

The organic peroxide-based vulcanizing agents include:
Benzoyl peroxide, t-butyl hydroperoxide, 2,4-bichlorobenzoyl peroxide,
Examples thereof include 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and 2,5-dimethylhexane-2,5-di (peroxylbenzoate).
About 1 to 20 phr can be used.

Further, as a phenol resin-based vulcanizing agent, bromide of alkylphenol resin, tin chloride,
A mixed crosslinking system containing a halogen donor such as chloroprene and an alkylphenol resin can be exemplified.
About 20 phr can be used. In addition, zinc white (about 5 phr), magnesium oxide (about 4 phr), litharge (about 10 to 20 phr), p-quinone dioxime, p-dibenzoylquinone dioxime, tetrachloro-p-benzoquinone, poly-p- Dinitrosobenzene (about 2 to 10 phr), methylene dianiline (0.
About 2 to 10 phr).

[0020] If necessary, a vulcanization accelerator may be added. Examples of the vulcanization accelerator include general vulcanization accelerators such as aldehyde / ammonia, guanidine, thiazole, sulfenamide, thiuram, dithioate, and thiourea, for example, About 2 phr can be used. Specifically, hexamethylenetetramine or the like is used as the aldehyde / ammonia vulcanization accelerator, diphenylguanidine is used as the guanidine vulcanization accelerator, and dibenzothiazyl disulfide is used as the thiazole vulcanization accelerator. DM), 2-mercaptobenzothiazole and its Zn salt, cyclohexylamine salt, etc., as sulfenamide-based vulcanization accelerators, cyclohexylbenzothiazylsulfenamide (CBS), N-oxydiethylenebenzothiazyl-2- Examples of thiuram-based vulcanization accelerators such as sulfenamide, Nt-butyl-2-benzothiazolesulfenamide, 2- (thymopolynyldithio) benzothiazole and the like include tetramethylthiuram disulfide (TMTD), tetraethyl Thiuram disulfide, tetrame Le monosulfide (TMTM), dipentamethylenethiuram tetrasulfide and the like, as the dithio acid salt-based vulcanization accelerator,
Zn-dimethyldithiocarbamate, Zn-diethyldithiocarbamate, Zn-di-n-butyldithiocarbamate, Zn-ethylphenyldithiocarbamate, T
e-diethyldithiocarbamate, Cu-dimethyldithiocarbamate, Fe-dimethyldithiocarbamate,
Examples of thiourea-based vulcanization accelerators such as pipecoline pipecolyl dithiocarbamate include ethylene thiourea and diethyl thiourea.

As the vulcanization accelerating auxiliary, a general rubber auxiliary can be used in combination. For example, zinc white (about 5 phr), stearic acid, oleic acid and their Zn salts (2 to 2 phr) can be used. About 4 phr) can be used. The film thus obtained has a structure in which an elastomer is dispersed as a discontinuous phase in a matrix of a thermoplastic resin. By adopting such a structure, it is possible to impart sufficient flexibility to the film and sufficient low air permeability due to the effect of the resin layer of the continuous phase, and to mold the thermoplastic resin regardless of the amount of the elastomer. Sex can be obtained.

According to the present invention, by coating the bead core 3 with a lightweight and high-rigidity thermoplastic resin or a thermoplastic elastomer composition as described above, the bead core 3 can be removed from the rubber-coated plain weave layer of the organic fiber cord in the conventional manner. The element wires 6 of the bead core 3 can be firmly bound while reducing the weight as compared with the case where a bead cover is used. Therefore, since the strands 6 are not dispersed at the winding end of the bead core 3, the uniformity of the tire can be improved.

Further, since the amount of deformation of the bead core 3 is reduced by increasing the frictional force between the strands 6, 6, the bead unseating value can be increased. The bead unseating value is a value obtained when a radial force is applied to the tire mounted on the rim to cause the rim to come off. If the value is small, the movement of the bead portion 1 during traveling becomes large. Become. Therefore, when the bead unseating value is increased as described above, since the movement of the bead portion 1 is suppressed, the steering stability can be improved.

In the present invention, the coating layer 7 made of a thermoplastic resin or a thermoplastic elastomer composition has a Young's modulus of 5
It is necessary to be 0 MPa or more. If the Young's modulus of the coating layer 7 is less than 50 MPa, a sufficient binding force to the strand 6 cannot be obtained. The upper limit of the Young's modulus of the coating layer 7 is preferably set to 2000 MPa. If the Young's modulus of the coating layer 7 exceeds 2000 MPa, cracks tend to occur in the coating layer 7 due to deformation of the bead wire 3.

In the above embodiment, the case where the thermoplastic resin or the thermoplastic elastomer composition is directly coated around the bead core 3 or the wire 6 has been described. However, the rubber around the bead core 3 or the wire 6 is described. May be coated, and the outside thereof may be coated with a thermoplastic resin or a thermoplastic elastomer composition. However, if rubber coating is not performed, it is advantageous in weight reduction. Also, in order to enhance the adhesiveness with the rubber disposed around the bead core 3,
An adhesive layer may be arranged outside the coating layer 7.
In this case, a laminate of a film made of a thermoplastic resin or a thermoplastic elastomer composition and an adhesive layer film may be wound around the bead core 3.

The adhesive used in the present invention has a critical surface tension difference (Δγc) of 6 mN / m between the thermoplastic resin or the thermoplastic elastomer component and the rubber component of the tire member.
Hereafter, an adhesive composition containing a polymer component of preferably 3 mN / m or less is desirable, and the polymer serving as a main component of the adhesive is a general unvulcanized rubber, an acrylate copolymer, a polyether and a polyester polyol, Styrene copolymer, modified styrene copolymer, polyolefin, etc., specifically, natural rubber, SBR, BR, IR, EP
Unvulcanized rubber such as DM, butyl acrylate, acrylic acid 2
Polymers obtained by polymerizing monomers such as ethylhexyl and ethyl acrylate, and copolymers thereof with ethylene, polypropylene glycol, polyethylene glycol, polytetramethylene glycol, and ethylene which is a condensate of adipic acid with glycol and triol Examples include adipate, butylene adipate, diethylene adipate, styrene ethylene butylene copolymer, styrene ethylene propylene copolymer, and modified products obtained by imparting an epoxy group, a carboxyl group, an amino group, a maleic anhydride group, or the like thereto.

As the cross-linking agent, an isocyanate-based cross-linking agent, an amine-based cross-linking agent and the like can be freely selected according to the type of the polymer, in addition to a general vulcanizing agent for rubber. Specifically, the sulfur type includes powdered sulfur, precipitated sulfur, highly dispersible sulfur, surface-treated sulfur, insoluble sulfur, and dimorpholine.
Disulfide, alkyl-phenol-disulfide, etc., for example, about 1 to 4 phr (parts by weight per 100 parts by weight of rubber, hereinafter the same), as peroxides, for example, benzoyl peroxide, t-butyl hydroperoxide Oxide, 2,4-dichlorodibenzoyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethylhexane-
2,5-di (peroxyl benzoate) is, for example, 1 to
About 15 phr, others are zinc white (about 5 phr),
Magnesium oxide (about 4 phr), litharge (10-2
0 phr), p-quinone dioxime, p-dibenzoyl quinone dioxime, tetrachloro-p-benzoquinone, poly-p-dinitrosobenzene (about 2 to 10 phr) and the like.

The adhesive of the present invention is dissolved in a solvent or the like in advance and applied to the adhesive surface with a brush, a spray, a roller, or the like, or adhered to a thermoplastic film with a dip roll coater, a kiss roll coater, a knife coater, or the like. An adhesive layer can be easily formed by a method in which a two-layer film is prepared by co-extrusion or lamination at the time of preparing a thermoplastic film as a method without using a solvent or a method using no solvent.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pneumatic tire having a tire size of 185 / 70R14 88S and a steel wire wound a plurality of times in the circumferential direction of the tire to form a bead core. A conventional tire 2 in which a steel wire covering material is made rubber and a bead cover made of a rubberized plain weave layer of nylon cord is wound around a bead core;
Comparative tires and the present invention tires 1 and 2 were prepared by winding a bead core using a thermoplastic elastomer or a thermoplastic resin having various Young's moduli as a coating material of a steel wire and then performing heat fusion. The following materials were used as the thermoplastic elastomer and the thermoplastic resin.

Thermoplastic elastomer 1 Nylon 11 (Atochem Rilsan BMNO) was added to 30
Part, Br- (polyisobutylene-p-methylstyrene)
(EXXPRO89-4, Exxon Chemical) 70 parts were kneaded with a biaxial kneader to disperse the rubber in the resin component, and then ZnO, zinc stearate, and stearic acid were 0.42 parts and 1.68, respectively. Parts and 0.84 parts, and dynamic vulcanization was performed.

Thermoplastic elastomer 2 nylon 6.66 copolymer (Toray Amilan CM604)
1) 15 parts, nylon 11 (Atochem Rilsan BM)
NO), and 50 parts of Br- (polyisobutylene-p-methylstyrene) (EXPRO89-4, Exxon Chemical) were kneaded with a twin-screw kneader to disperse the rubber in the resin component. 0.3 parts, 1.2 parts, and 0.6 parts of zinc stearate and stearic acid were added, respectively, and dynamic vulcanization was performed.

A thermoplastic resin nylon 6/66 copolymer (Amilan CM6021, Toray) was used.

When a thermoplastic elastomer and a thermoplastic resin were used as the coating material, a material shown in Table 1 below was applied to the thermoplastic resin as an adhesive to a rubber member to produce a tire.

[0034]

[Table 1]

In the above composition, the composition of EEA, Quinton A-100, and FEF black is mixed by a kneader, and the mixture is homogenized (to a rotational speed of 80) in a mixed solvent of toluene or less.
(00 rpm) to form an adhesive. Finally, dicumyl peroxide was added and stirred.

For these test tires, radial force variation, bead unseating value, presence / absence of unevenness in the bead core, steering stability and weight of the bead core were evaluated by the following test methods.
It was shown to. Radial force variation (RF
V): Radial force variation was measured by the test conditions and method based on JASO C607. The evaluation results are shown as indices with the measured value of the conventional tire 1 being 100. The smaller the index value, the smaller the RFV and the better the uniformity.

Bead unseating value (BUS value):
The bead unseating value was measured based on the test conditions and method specified in JIS D4230. The evaluation results are shown as indices with the measured value of the conventional tire 1 being 100. The larger the index value, the larger the bead unseating value. Presence / absence of irregularity: Before forming each test tire, it was examined whether or not irregularities occurred in the strand at the winding end of the bead core.

Driving stability: Each test tire was mounted on a JATMA standard rim, the air pressure was set to 200 kPa, and the tire was mounted on a 2000 cc passenger car, and a feeling test of the driving stability was performed by five panelists. The results were evaluated by the 10-point method, and the average value of five panelists was shown. The larger this value, the better the steering stability.

Weight of bead core: The weight of the bead core (including the bead cover) was measured for each test tire.
The evaluation results are shown as indices with the measured value of the conventional tire 1 being 100. The smaller the index value, the lighter the weight.

[0040]

[Table 2]

As is clear from Table 2, each of the tires 1 and 2 of the present invention can reduce the weight of the tire 2 compared with the conventional tire 2 and can prevent the variation of the wire at the winding end portion of the bead core. As a result, the uniformity was improved as compared with the conventional tire 1, the bead unseating value was increased, and the steering stability was excellent.
On the other hand, in the comparative tire, the effect as the tires 1 and 2 of the present invention could not be obtained because the Young's modulus of the coating layer made of the thermoplastic resin was low.

[0042]

As described above, according to the present invention, there is provided a pneumatic tire in which a bead core formed by winding at least one element wire a plurality of times around the pair of left and right bead portions in the tire circumferential direction is arranged. By coating the bead core with a thermoplastic resin or a thermoplastic elastomer composition having a Young's modulus of 50 MPa or more, the strands of the bead core are firmly bound while reducing the weight, the uniformity is improved, and the bead unseating value is increased. As it increases, the steering stability can be improved.

[Brief description of the drawings]

FIG. 1 is a meridian sectional view illustrating a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a bead core in FIG. 1;

FIG. 3 is an enlarged perspective view showing a bead core in FIG. 1;

FIG. 4 is a perspective view showing a modified example of the bead core according to the present invention.

FIG. 5 is a sectional view showing another modified example of the bead core according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead part 3 Bead core 6 Element wire 7 Coating layer

Claims (4)

[Claims] 1. A pneumatic tire in which a bead core formed by winding at least one element wire around a pair of left and right bead portions in the circumferential direction of the tire is arranged, wherein the bead core has a Young's modulus of 50 MPa or more. Alternatively, a pneumatic tire coated with a thermoplastic elastomer composition. 2. The pneumatic tire according to claim 1, wherein the strand is covered with the thermoplastic resin or the thermoplastic elastomer composition. 3. The pneumatic tire according to claim 1, wherein the strand is a steel wire. 4. The pneumatic tire according to claim 1, wherein the strand is an aramid fiber cord.