JP3345083B2 - Pneumatic radial tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire which satisfies a significant reduction in the weight of a bead portion, satisfies ease of disposal of the tire, and has both bead breaking safety.

[0002]

2. Description of the Related Art Conventionally, a bead portion in a general pneumatic radial tire is formed of a bead having a bead reinforcing member. As the bead reinforcing member, a plurality of hard steel wires (steel wires) coated with rubber are extruded in parallel, and are laminated and wound so as to have a predetermined diameter and an appropriate total bead strength. Things, so-called steel strand beads, are known. The cross-sectional shape of the bead reinforcing member has a polygonal shape such as a square shape and a hexagonal shape. As another bead reinforcing member, a so-called cable bead having a circular cross section in which a hard steel wire is spirally wound around an annular core wire is also known. On the other hand, in recent years, from the viewpoints of resource saving and global warming due to an increase in atmospheric carbon dioxide, lightweight and fuel-efficient tires have been desired.

However, a conventional bead reinforcing member is:
In each case, a hard steel wire (steel wire) having a specific gravity of about 7, 8 is used as the material, and the tensile strength per steel wire weight is as low as 2.9 (g / d). In pneumatic radial tires designed with a sufficient safety factor, it is difficult to reduce the bead weight. Further, in recent years, in view of the environmental problem of treating waste tires, there has been a demand for a material which is easy to be cut in place of a steel material and which can be easily incinerated.

Incidentally, specific strength as a bead reinforcing member,
When using a fiber bundle such as aromatic polyamide fiber or carbon fiber with a high specific modulus, or the twisted cord itself, these fibers are composed of a bundle of very thin filaments, so the cord is flexible and Since the bend and torsion hardness of steel wire is not high enough and the bead cord is wound and used as a bead reinforcing member, it does not maintain a sufficient perfect circular shape. When the ply is folded, it is difficult to keep the roundness high, and there is a problem that the uniformity of the tire is impaired.

Accordingly, the present applicant has filed an application for a bead reinforcing member made of a fiber-resin composite material cord obtained by impregnating a carbon fiber with a thermosetting resin matrix and solidifying the carbon fiber in a perfect circular shape. No. 16901). However, in the bead reinforcing member made of the fiber-resin composite material cord, the composite material cord is damaged when the rim is assembled and the rim is unraveled, and the tensile strength is reduced. There is a slight problem in that strength cannot be obtained. Further, in the fiber-resin composite cord, there is a slight problem in that in the process of treating the adhesive with rubber, the cord is strongly reduced when passing through rollers in the processing machine.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems. In a pneumatic radial tire having a bead portion having a bead reinforcing member, the present invention relates to a pneumatic radial tire having a bead reinforcing member. By using a fiber-resin composite cord composed of organic fibers with a large specific strength and specific elastic modulus, the bead portion can be significantly reduced in weight, and strong even in the adhesive processing process of the fiber-resin composite cord. An object of the present invention is to provide a pneumatic radial tire that does not lower and has a sufficiently high bead rupture strength that is sufficiently safe even when the rim is assembled and released.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned conventional problems, and as a result, in a pneumatic radial tire provided with a bead portion having a bead reinforcing member, the bead reinforcing member was used. A fiber-resin composite cord formed by embedding a fiber cord composed of a specific fiber in a resin, and a twist coefficient of the fiber cord, a degree of resin impregnation in the fiber cord, and coating around the fiber cord. By specifying the thickness and the like of the resin layer, a pneumatic radial tire having both light weight and safety in bead breaking resistance was successfully obtained, and the present invention was completed.

That is, the present invention relates to a pneumatic radial tire having a bead portion having a bead reinforcing member, wherein the bead reinforcing member is made of an aromatic polyamide fiber, a carbon fiber, a high-strength high-elasticity polyvinyl alcohol fiber and a polyparaphenylene benzo. The fiber cord is composed of a fiber-resin composite cord obtained by embedding a fiber cord composed of fibers selected from bisoxazole fibers with a resin, and the twist coefficient Nt of the fiber cord is represented by the following formula: 0 ≦ Nt ≦ 0.22 And the resin is not present in the fiber cord within a radius of 60% from the center of the cross section of the composite cord,
The thickness d (mm) of the coating resin layer around the fiber cord is characterized by the following expression: 0.01 <d <1.0. (However, twist coefficient Nt is Nt = T × (0.139 × ^1/2 × D / ρ) ^1/2 × 10
Represented by ^-3, T is a twisting number (times / 10 cm), D is the total denier of the fibers, [rho represents the density of the fibers. It is preferable that the fiber cord is composed of an aromatic polyamide fiber, a thermoplastic resin is preferably used as the resin, and a monostrand structure is preferable as the bead structure.

Hereinafter, the contents of the present invention will be described in detail. The fibers constituting the fiber cord used in the present invention are selected from aromatic polyamide fibers (aramid fibers), high-strength high-modulus polyvinyl alcohol fibers, carbon fibers, and polyparaphenylenebenzobisoxazole fibers. These fibers are particularly excellent in specific strength and specific elastic modulus.
Further, the fiber cord used in the present invention is composed of the above-mentioned fibers, and specifically, is composed of a fiber filament bundle of the above-mentioned fibers. In addition, nylon, rayon, conventionally known as general organic reinforcing fibers,
Polyester and the like are not sufficient in terms of strength and elastic modulus for the purpose of the present invention. Glass fiber has a specific gravity of 25.
Heavy and not preferred. Further, fibers having the same high strength and high elasticity, for example, ceramic fibers, Tyranno fibers, etc.
It is not preferable because it is weak against external force from the lateral direction of the fiber axis and is easily broken.

The aromatic polyamide fibers used in the present invention include, for example, poly (1,4-phenyleneterephthalamide) fiber, poly-1,4-phenyleneterephthalamide-3,4'-diaminodiphenylether copolymer fiber, Poly (1,4-benzamide) fiber, poly (1,4-benzamide) fiber
3-phenylene isophthalamide) fiber and the like,
Further, these fibers are subjected to post-heat stretching to further increase the modulus of elasticity, for example, the product name “Kevlar 4” manufactured by DuPont.
9, Kevlar 149 "and the like.

The high-strength and high-elasticity polyvinyl alcohol fiber used in the present invention is, for example, spun from an organic solvent-based spinning solution such as dimethyl sulfoxide (DMSO), ethylene glycol, glycerin or the like by a semi-dry semi-wet spinning method and stretched. High-strength, high-elasticity polyvinyl alcohol fibers having a fiber strength of 15 g / d or more and distinguishable from conventional vinylon. Those obtained by subjecting a part of the hydroxyl groups in the molecule to dehydration or hydroxyl group blocking treatment are excellent in fatigue resistance and are preferably used.

The carbon fibers used in the present invention include, for example, carbonized fibers obtained by firing polyacrylic fibers, and carbonized fibers obtained from pitches of petroleum, coal and the like. Preferably, the former carbonized fiber has a breaking elongation of 1.0% or more.
Those having 3% or more are preferable. In addition, in the present invention, the polyparaphenylene benzobisoxazole fiber (hereinafter referred to as P
BO fiber) can also be used. The PBO fiber has the following general formula (I)

Embedded image Or the following general formula (II)

Embedded image And preferably a fiber represented by the above general formula (I)
A cis-structured PBO fiber represented by

The yarn group used in the present invention has a yarn strength Ty of at least 15 g / d, preferably at least 18 g / d, more preferably at least 20 g / d. is there. If the yarn strength Ty is less than 15 g / d, a lightweight and sufficiently safe bead breaking strength cannot be obtained.

The tensile modulus My of the fiber is 250 g.
/ D or more, and if it is lower than this value, sufficient bead rigidity cannot be obtained, so that sufficient rim slip resistance and rim detachment cannot be achieved. Preferably, My> 500 g / d, more preferably, My> 8.
00 g / d.

The total denier number D used for one bead reinforcing member cord of the fiber is 2,000 <D <100,0.
00, preferably 3,000 <D <25,000
0, more preferably 5,000 <D <15,000
It is. When the total denier D is less than 2,000, the denier per strand is too thin and the beat strand configuration becomes bulky, which is not preferable. On the other hand, when the total denier is 100,000 or more, the denier per strand is too thick, and This is not preferable because the surface distortion at the time of heating increases.

Before embedding in a resin, the fiber cord composed of the above-mentioned fiber is used without twist or with slight twist (single twist or double twist). The twist coefficient Nt at this time is 0 ≦ Nt ≦ 0.22, preferably 0 ≦ Nt ≦
0.17, more preferably 0.04 ≦ Nt ≦ 0.1
4. The twist coefficient Nt is obtained from the following equation. Nt = T × (0.139 × ^1/2 × D / ρ) ^1/2 × 10
^-3 (where T is the number of twists (twice / cm), D is the total denier of the fiber, and ρ represents the density of the fiber).
If it exceeds 2, the cord strength and elastic modulus after twisting are undesirably reduced due to twisting loss.

Further, it is more preferable to have a slight twist than a non-twist in terms of alignment. Before embedding the resin further,
An oil agent or the like may be attached to the fiber cord in order to reduce the friction between the fiber filaments constituting the fiber cord, or a substance such as a silane coupling agent or the like that increases the affinity with the resin may be attached. Further, for the purpose of improving the packing of the twisted fiber cord, improving the convergence, or improving the elastic modulus, the fiber cord may be subjected to a tension heat treatment before being embedded in the resin.

As the resin used to embed the fiber cord, any of a thermoplastic resin and a thermosetting resin can be used. When the resin-fiber cord of the present invention is produced, the inside of the resin is used. Thermoplastic resins are more preferred for producing low impregnation.

Examples of the thermoplastic resin include polyamides such as 66-nylon, 6-nylon, 46-nylon and 610-nylon, polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polyether ether ketone, polycarbonate and polyacetal. Acrylic resin and the like can be mentioned. Further, as the thermosetting resin, for example, an epoxy resin, an unsaturated polyester resin, a phenol resin,
Melamine resins, vinyl ester resins, polyimides, bismaleimide resins, Friedel Crafts resins, furan resins, silicone resins, allyl resins, and the like.

A blend of two or more of these resins,
Copolymers may be used. If the resin is too rigid or too brittle, for example, a resin modified with an elastomer may be used to impart toughness. Such a resin is preferably a resin having a specific gravity of 1.5 or less, more preferably a resin having a specific gravity of 1.2 or less, for the purpose of reducing the weight of the present invention.

The volume ratio Rv (%) of the resin when the fiber cord is embedded in the resin is preferably 30 ≦ Rv ≦ 70 (%). The volume ratio Rv (%) of the resin is Rv
= [(Resin volume / fiber volume) + resin volume] x 100
(%)]. When the volume ratio Rv of the resin is Rv> 7
A value of 0 is not preferable because the resin is too large and the bulk increases, and sufficient weight reduction cannot be achieved. On the other hand, if Rv <30, there is not enough resin to cover the fiber cord, and the bending rigidity for maintaining sufficient roundness during tire molding is insufficient, which is not preferable.

As shown in FIG. 1, the resin-fiber composite material cord A of the present invention comprises a fiber cord 1 composed of a fiber filament bundle and a resin layer 2 covering the fiber cord 1. The resin layer 2 exists only on the surface layer of the fiber cord 1, and the cross section of the composite material cord is within 60% in radius from the center point C (center of gravity) of the cross section of the fiber filament bundle, preferably 80%.
%, More preferably within 90% (the range between C and E, where E is a 60% subdivision point when C is connected to an arbitrary point D on the outermost layer of the fiber filament bundle). Must be absent. When the resin is impregnated into the fiber cord within a radius of 60% or less, the fiber cord is excessively restrained by the resin, so that the stress concentration due to bending is large, and the rim is assembled and unraveled as a bead reinforcing member. When the fiber cord is subjected to a bending input at a time, the fiber cord is damaged and the strength is reduced, which is not preferable. Conversely, if the resin does not penetrate into the area within a radius of 60% and the fiber cord is free at that part and is not restrained by the resin, the strength of the fiber cord will not decrease even if it is bent during rim assembly. Does not happen. In this case, within the range of the radius of 60%, there is no substantial space between the fiber filaments constituting the fiber cord and packing is performed, or even if there is a space, it is sufficient that the resin does not enter. Further, within this range, a low-elasticity elastomer other than the oil agent or the resin may be attached or filled between the fiber filaments.

Further, as shown in FIG.
Is completely covered on the circumference of the fiber cord 1, and the distance d (d between the outermost fiber filament 1a and the outermost resin layer)
Are dmin and dmax), and d (mm) is 0.01 <d <1.0, preferably 0.02 <d <0.5. Yes, and more preferably 0.04 <d <0.3. d is 0.01 (mm)
If it is less than the above range, surface resin cracks occur during the adhesive dip treatment, and the strength is undesirably reduced. on the other hand,
If d exceeds 1.0 (mm), the surface resin is too thick, and stress is concentrated during the adhesive dip processing, so that it is not preferable. Further, regarding the variation of d on the circumference, dmax / dmin <20, preferably dmax / dmin
<10.

In the case where the resin is thermoplastic, the following production method may be used for producing the fiber-resin composite material cord used in the present invention. (1) While heating and melting the polymer chip and extruding it with a screw, the fiber cord continuously passes through the melt,
There is a method in which the fiber cord is embedded in the resin, and then the resin is solidified by cooling using a water bath or the like. (2) A method of blending the reinforcing fiber of the present invention with a thermoplastic resin fiber and then heating and melting the latter thermoplastic resin fiber (blending method) is exemplified.

In the case of the production method (1), the degree of penetration of the resin into the fiber cord is controlled by controlling the viscosity of the heated melt, the residence time of the fiber melt, the time until pressure cooling, and the like. can do. Also,
In the case of the production method (2), the degree of penetration of the resin into the fiber cord can be controlled by controlling the degree of fiber mixing, the method of coating the polymer, and the melting conditions. In addition, after wrapping a film-like thermoplastic resin around the reinforcing fiber, or covering it with a tubular thermoplastic resin,
The coated resin-fiber composite cord used in the present invention can also be obtained by a method of heating and melting. When the fiber cord is composed of aromatic polyamide fiber, carbon fiber or polyparaphenylene benzobisoxazole fiber,
There is no problem because the heat resistance of the fiber is sufficiently high. However, in the case of a high-strength high-elasticity polyvinyl alcohol fiber, attention must be paid to the heating and melting conditions.

In the case where the resin is thermosetting, a method for producing the fiber-resin composite material cord used in the present invention includes, for example, the following production method. Using the liquid material before curing as a liquid bath, a fiber filament bundle which is a fiber cord continuously drawn out is passed through the liquid bath to impregnate the liquid material into the fiber filament bundle, and then the impregnated filament bundle Is passed through a mold having a die having an appropriate (usually circular) cross-section to shape the body, remove excess uncured resin liquid and air bubbles trapped inside, and finally heat through a tubular mold. This is a method of obtaining a cured (or uncured) resin-fiber composite cord. In the case of thermosetting resin, the resin easily penetrates into the fiber cord (fiber filament bundle). In this case, the viscosity of the bath solution is controlled, the tension in the bath solution is increased, or pre-heat stretching is performed. Control the degree of penetration of the resin into the fiber cord by increasing the packing or spraying the liquid in the form of a shower instead of dipping it into the liquid bath, or applying it to the surface of the fiber cord with a brush or the like. It is possible.

Next, the resin-fiber composite material cord is usually immersed in an RFL (resorcin, formalin, latex) aqueous solution and dried and heat-treated for adhesion to rubber. Good. When sufficient adhesion cannot be obtained only by RFL adhesive treatment, pretreatment with an aqueous epoxy solution, isocyanates, or the like may be performed before RFL adhesive treatment, or plasma treatment, corona discharge treatment, or acid treatment For example, surface adhesion activity may be imparted. It is advisable to increase the diameter of the rollers that pass during the bonding process as much as possible to prevent breakage. Further, a plurality of the resin-fiber composite cords may be further twisted and used.

The resin-fiber composite material cord is subjected to an adhesive processing, then subjected to rubber insulation, and further surrounded to be used as a bead. In this case, a normal strand structure may be employed in which a plurality of one-stage insulation is wound in parallel and then wound, or a mono-strand structure in which the insulation is wound after being wound in one stage and forms a continuous row. (See FIG. 2). The monostrand structure is preferable because the rigidity step on the periphery is small and the uniformity is high. In addition, the cable may be wound in a hexagonal cross section or the like (other polygons) or a so-called cable structure in which the cord is spirally wound around an annular core wire. In addition, the bead member may be wrapped around with a wrapping tape or the like, such as a canvas, or wound in a spiral shape in order to control looseness or rubber flow during vulcanization.

[0029]

Next, the present invention will be described more specifically and in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Examples 1 to 7, Comparative Examples 1 to 7, and Conventional Examples) The following Tables 1 to 4 show the fiber type, yarn extension strength, yarn extension modulus, and resin type of the resin-fiber composite material cord. , Resin infiltration range, resin volume ratio, resin coating layer thickness,
Weight of the beads (g / one bead) for Examples and Comparative Examples in which the twist coefficient, bead cord strength, and bead structure were changed
And the results of measuring the tire breaking pressure (kg / cm ² ).

Pneumatic radial tires used in Examples and Comparative Examples were produced as follows. Yarn tensile strength Ty
A total of 600 yarns obtained by combining four 1500D fibers of aramid fiber (poly-1,4-phenylene terephthalamide fiber) having a yarn tensile modulus of 22 g / d and a yarn tensile modulus of My550 g / d.
OD was twisted in a single twist at a twist number T = 4 (twist / 10 cm) → Nt = 0.07, and a nylon resin melted by heating was continuously coated and embedded to prepare a resin-fiber composite material cord.
At this time, resin-fiber composite material cords of Examples 1 to 3 and Comparative Examples 1 to 4 were prepared in which the degree of penetration of resin and the coating thickness were controlled in the radially outward direction from the center of the cord. These composite cords were subjected to a dip heat treatment with an RFL solution, and then insulation-insulated with a single piece of rubber, and wound into a mono-strand structure of 4 rows × 5 rows to produce beads. Further, each pair of beads is used, and as a carcass, a one-ply structure belt of polyester cord 1500d / 2 is used. As a belt, a two-ply structure of aramid 1500d / 2 is used.
A 5 / 70R13 radial tire for passenger cars was manufactured and subjected to a test. Hereinafter, similarly, by changing the twist coefficient, the fiber type, the resin type, the impregnation method, and the like, beads of Examples 4 to 7 and Comparative Examples 5 to 7 having the same size using the beads were produced.

The characteristics of the pneumatic radial tires of the examples and comparative examples were evaluated as follows. (1) Measuring method of yarn tensile strength Ty (g / d), yarn tensile modulus My (g / d) and strength S (kg) of one bead cord of fiber-resin composite cord: JIS L10
The strength was determined by an Instron tester according to the method for measuring the strength and elongation of No. 17.

(2) Method for measuring resin volume ratio Rv (%):
The weight ratio was determined from the fiber before resin coating and the weight per unit length after coating, and recalculated to the volume ratio from each specific gravity.

(3) From the center of the cord to the radially outward direction, a range V (%) where no resin has entered, and a resin coating layer thickness d (m)
Measurement method of m): A fiber-resin composite material cord was embedded in an epoxy resin, and a section of the cured product was cut with a diamond cutter and polished. The cross section of this sample was observed and determined with a reflection-type fluorescence microscope.

(4) Method of measuring tire breaking pressure (kg / cm ² ): Repeat the rim assembly and release the rim so that the test tire is damaged 10 times each time with a regular rim at the same position on the circumference. . After that, the test tire is assembled on a JIS regular rim, water is injected from a valve opening, an injection needle is inserted into a tire side portion, the inside air is removed, and the water is completely replaced. Further, the water pressure was increased, and the pressure was indicated by the pressure when the tire was broken. The test tires were carcass,
The total belt strength was sufficiently high, and all were broken by bead breakage.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

As is clear from the results of Tables 1 to 4, the weight of the conventional bead using a general steel wire was 170 g for one piece and 340 g for one pair (for one tire) according to the present invention. In the embodiment of the present invention, the weight of one pair is 100 g or less, which can be reduced to 1/3 or less of the conventional one. Further, in the tire of this embodiment, since the belt is also made of non-steel, no metal is used at all, so that it is easy to cut, and even if it is incinerated, there is no residue.

In Examples 1 to 3, since the range V in which the resin does not penetrate is 60% or more, the stress is hardly concentrated on the bending input, so that the tire breaking pressure after the rim is assembled and the rim is released is sufficiently high. On the other hand, in Comparative Examples 1 and 2, since the range V in which the resin did not penetrate was less than 60%, the restraint on the resin fibers was too large, and the filament damage upon bending input was large. For this reason, the tire breaking pressure at the time of the rim assembling and rim unraveling test is low, and the rim is broken at the damaged portion when the rim is unraveled.

Comparative Examples 3 and 4 are cases where the resin coating layer thickness d is not included in the range of the present invention (0.01 <d <1.0). That is, in Comparative Example 3, since the resin coating layer thickness is as thin as dmin = 0.01 mm, which is the largest on the circumference, surface resin cracks occur during the dipping treatment, and the bead cord strength after the dipping is low. Therefore, the tire breaking pressure is low. In Comparative Example 4, since dmax = 1.00 mm, it is easily broken during the dipping process, and the bead cord strength after the dipping is also low.

In Comparative Example 5, the twist coefficient Nt was too large than the range of the present invention (Nt ≦ 0.22).
Since t is 0.25, the bead cord strength is low, which is not preferable. In Comparative Example 6, the above-mentioned fiber blending method was used at the time of production, and 6-nylon resin was completely impregnated into the inside, and V =
However, since the resin completely restrains the fiber, stress is easily concentrated on the bending input, so that the tire breaking pressure value after the rim is assembled and the rim is released is low. Example 4,
In Comparative Example 7, the degree of impregnation was changed by using a thermosetting epoxy resin, and V was changed. In Comparative Example 7, the epoxy resin was completely impregnated into the interior and V = 0. Therefore, since the resin completely constrains the fiber, stress is easily concentrated on the bending input, so that the tire breaking pressure value after the rim is assembled and the rim is released is low.

Example 5 uses carbon fiber 9000d and 66
-Nylon resin, 3x4 monostrand bead structure. Example 6 has a high strength and high elasticity PVA fiber of 24000.
d, 6 nylon resin, 2 × 3 monostrand bead structure. In Example 7, as shown in FIG. 3, a single bead structure was formed by winding aramid fiber 6 around one annular resin core 5 and then coating the surface with 66-nylon resin 7. It is. Example 5 of these
In Nos. 7 to 7, since the range V in which the resin does not penetrate is 60% or more, stress is not easily concentrated on the bending input, and thus the tire breaking pressure after the rim is assembled and the rim is released is sufficiently high.

[0045]

According to the present invention, it is possible to provide a pneumatic radial tire that satisfies both a significant reduction in the weight of the bead portion and the ease of disposing of the tire, and also achieves a bead breaking safety.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an example of a fiber-resin composite material cord serving as a bead reinforcing member in a pneumatic radial tire of the present invention.

FIG. 2 is a partial end view showing an example of a bead portion in the pneumatic radial tire of the present invention.

FIG. 3 is a cross-sectional view illustrating a bead structure according to a seventh embodiment.

[Explanation of symbols]

 A Fiber-resin composite material cord 1 Fiber cord 2 Resin layer 3 Bead part

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B60C 1/00-19/12 B29D 30/00-30/72 D02G 1/00-3/48

Claims (4)

(57) [Claims] 1. A pneumatic radial tire having a bead portion having a bead reinforcing member, wherein the bead reinforcing member is made of an aromatic polyamide fiber, a carbon fiber, a high-strength high-elasticity polyvinyl alcohol fiber and a polyparaphenylene benzobisoxazole fiber. A fiber-resin composite material cord obtained by embedding a fiber cord composed of a selected fiber with a resin, wherein a twist coefficient Nt of the fiber cord is as follows: 0 ≦ Nt ≦ 0.22; The resin is not present in the fiber cord within 60% of the radius from the center of the cross section of the composite cord,
A pneumatic radial tire characterized in that a thickness d (mm) of a coating resin layer around the fiber cord satisfies the following expression: 0.01 <d <1.0. (However, twist coefficient Nt is Nt = T × (0.139 × ^1/2 × D / ρ) ^1/2 × 10
Represented by ^-3, T is a twisting number (times / 10 cm), D is the total denier of the fibers, [rho represents the density of the fibers. ) 2. The pneumatic radial tire according to claim 1, wherein the fiber cord is made of an aromatic polyamide fiber. 3. The pneumatic radial tire according to claim 1, wherein a thermoplastic resin is used as the resin. 4. The pneumatic radial tire according to claim 1, wherein the bead structure is a mono-strand structure.