JPH08113017A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To provide a pneumatic radial tire whose appearance has been improved by preventing the lowring of fatigue resistance by tire travel when a polyester monofilament cord is applied to the tire carcass ply, improving tire performance such as maneuvering stability of the tire and rolling resistance, and restraining a recess-projection on a surface of a sidewall part when internal pressure is filled. CONSTITUTION: When the total thickness of a tire is denoted by A and a distance up to a cord of a carcass layer folding-back part from an outer wall of the tire is denoted by B, a shape of a bead part of the carcass layer folding- back part is formed so as to satisfy (B/A>0.5), and a carcass layer is composed of a polyester monofilament cord having intrinsic viscosity not less than 0.75, and fineness of the polyester monofilament cord constituting a carcass is set not less than 1000 denier.

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 using a monofilament code as a cord material for forming a carcass layer, and particularly, the durability is lowered due to the characteristics of the monofilament code. For tires to prevent.

[0002]

2. Description of the Related Art A pneumatic radial tire using as a carcass material an organic fiber cord having both a high elastic modulus and a low heat shrinkage rate is excellent in steering stability and in filling with internal pressure. It is well known that it is advantageous for suppressing unevenness on the surface of the side wall portion. Organic fiber core with such characteristics
As a cord, a radial tire using a rayon cord (however, a so-called multifilament cord in which a large number of filaments are twisted) is provided. However, when using rayon cords, the resource saving problem of raw pulp and cord
There are disadvantages such as environmental conservation problems in the production process and complexity of process control during tire production due to the high hygroscopicity of the rayon cord.

Under the circumstances, development of a rayon-replacement cord has been promoted and various new polymer fiber materials have been proposed. At present, polyester-based synthetic materials are used as a fiber agent having high elastic modulus and low heat shrinkability. Only fibers have been put to practical use as a cord material for tire carcass. Moreover, when it is used for a tire carcass cord, filaments (ultrafine fiber yarns) are bundled to form 3 to 6 denier (denoted by symbol D, fiber 90).
A large number of yarns (grams per 00 m) are bundled to form a lower twisted yarn of a multi-yarn bundle of, for example, 1000D or more, and the two twisted yarns are changed in direction and twisted for 1000D / 2. It has been customary to use a cord or a twist of three lower twisted yarns in different directions to form a cord of 1000D / 3.

On the other hand, a cord made of one filament, a so-called monofilament cord, is intended to improve the production efficiency and reduce the production cost by omitting the step of twisting the filament bundles as described above. Is being developed. This monofilament code is expected to further enhance the characteristics of high elastic modulus and low heat shrinkability as compared with the above-mentioned multifilament code due to the characteristics of the code structure. At first, a nylon monofilament cord having excellent fatigue properties was studied, but the desired high elastic modulus and low heat shrinkability were not obtained, and the polyester material was also used. It was confirmed to be suitable, and for example, Japanese Patent Laid-Open No.
Japanese Patent No. 185111 discloses a polyester monofilament cord applied with a low carboxyl group polyester fiber material, and Japanese Laid-Open Patent Publication No. 4-232102 discloses a polyester monofilament cord obtained by steam heat drawing applied to a tire. Can be seen.

[0005]

However, while the monofilament cord mainly composed of polyester certainly exhibits excellent characteristics of high elastic modulus and low heat shrinkage, on the other hand, in this type of cord, the molecular chain is When the tire cord is subjected to compressive strain due to fibrillation due to the extremely small inter-force, the cord is prone to fatigue fracture and twisting in the case of a multi-filament twist cord While each angled ultrafine filament has the function of absorbing and relaxing the compressive strain input to the tire code due to flexural deformation, such a function cannot be expected due to the code structure. Filament twist
The running fatigue resistance of the monofilament cord is remarkably inferior to that of the cord, so that the tire in which the polyester monofilament cord is applied to the carcass ply has not yet been put to practical use.

Therefore, an object of the present invention is to prevent the deterioration of fatigue resistance due to running of the tire, which is a drawback peculiar to the polyester cord when the polyester monofilament cord is applied to the tire carcass ply, and to control the tire. Improves tire performance such as stability and rolling resistance.
It is an object of the present invention to provide a pneumatic radial tire that improves the tire appearance by suppressing the unevenness on the surface of the inner surface of the inner wall during filling with internal pressure.

[0007]

In order to achieve the above object, in the pneumatic radial tire of the present invention, as described in claim 1, a pair of ring-shaped belts arranged at right and left intervals are provided. -A core, a carcass layer whose both ends are wound around the bead core and folded back, and a central portion of which is formed in an annular shape, and a crown portion of the central portion of the carcass layer on the tire radial outside. As a main reinforcing structure with a plurality of belt-shaped belt layers laminated, a ring-shaped tread rubber is arranged on the outer side in the tire radial direction of the belt-shaped belt layer, and the carcass layer is covered on both sides of the tread rubber. A pneumatic radial tire in which a pair of left and right side rubbers are arranged, and further, the carcass layer is embedded in a coated rubber by arranging a plurality of polyester monofilament cords in a direction substantially perpendicular to the equatorial plane of the tire. And Thus, the shape of the bead portion of the carcass layer turnback portion, which is wound around the bead core and turned back from the inner side to the outer side in the rotation axis direction of the tire, has a total thickness of the tire as A and the tire Where B is the distance from the outer wall to the cord of the carcass layer turnaround portion, B / A> 0.
5, the carcass layer is made of a polyester monofilament cord having an intrinsic viscosity of 0.75 or more. In order to prevent the increase in the number of tire carcass plies and the increase in tire weight in terms of strength, the polyester monofilament cord constituting the carcass has a fineness of 1 or less.
The pneumatic radial tire according to claim 1, which has a denier of 000 or more.

The polyester monofilament cord used for the carcass ply layer may be composed of a single polyester or may have a so-called core-sheath structure having two or more layers. However, as mentioned above,
Since the monofilament code has the characteristics of high modulus and low heat shrinkage, the monofilament code having a high code modulus taken out from the tire is preferable.

Further, in the present invention, the bead portion of the carcass layer folded-back portion means a tire maximum width in a tire mounted on a wheel and filled with standard air pressure set to a standard or the like. The range of the carcass ply from the lower part to the upper part of the bead core. And the lower part of the tire maximum width (100 in FIG. 1) is
Approximately ¼ of the distance from the apex (101) of the flange portion of the wheel to the maximum width (102) of the tire measured with a straight line distance in the direction perpendicular to the tire rotation axis is approximately 1/4 of the maximum tire width (102). The position is taken in the direction of the bead core.

[0010]

The present inventors prototyped a tire having a normal structure using a polyester monofilament cord as a carcass ply cord, and conducted an indoor drum test under severe tire load conditions and a long distance of 100,000 km or more. From the results of detailed measurements of the remaining strength of the carcass ply cord at each part of the tire after running by running the actual vehicle test, the bead portion of the folded portion of the carcass ply layer after running was compared to before running. The code tensile strength is remarkably reduced (cord rupture is observed in some areas), but the rate of decrease in code tensile strength (code strength after running compared to before running) is high in other areas. It was found that it was within 10% and the code strength was hardly reduced. Further, as a result of observing in detail the fracture failure portion of the monofilament code in the bead portion of the carcass ply layer folded-back portion, the degree of the fracture failure is the compressive strain based on the bending deformation of the tire bead portion when the tire touches the ground. It turned out to be dependent on the size of the quantity. In other words, it was found that if the amount of compressive strain applied to the bead portion of the carcass ply layer turnback portion is reduced, the tire life leading to code breakage can be extended.

Based on the above findings, the inventors studied the structure of the bead portion for reducing the compressive strain and obtained the structure described in claim 1. That is, the carcass layer (ply)
When the shape of the bead portion of the folded portion is A and the total thickness of the tire is A, and the distance from the tire outer wall to the cord of the carcass layer folded portion is B, B / A> 0. It is formed so as to satisfy 5.

When the structure of the bead portion is set in this manner, the bead portion of the folded back portion of the carcass ply layer is located at the center position of the wall thickness at each position (that is, 0 .. 5
It is arranged on the inner side in the tire axial direction of the so-called neutral axis corresponding to the line connecting the positions (xA). Therefore, when the tire runs while being filled with the internal pressure, the tire bead portion is repeatedly subjected to bending deformation so as to incline it to the outside in the tire axial direction, and the tire axial direction of the neutral axis of the cross section of the bead portion. Compressive strain is repeatedly generated on the outer part of
As described above, in the bead structure of the present invention, the carcass ply layer is not arranged in this portion, so that it does not suffer from this compressive strain. Therefore, the cord fatigue and the code breakage at the folded portion of the carcass ply layer, which are fatal in the conventional polyester monofilament code tire, are prevented, and the durability of the tire is remarkably improved.

In general, in a polymer material, the higher the material is, the better the fatigue resistance is considered to be in terms of molecular mechanics. Therefore, the value of the intrinsic viscosity [η], which is a measure of the molecular weight, is changed. As a result of investigating a decrease in strength of the carcass cord after running the tire by prototyping several kinds of tires using a polyester monofilament cord as a carcass, it is found that the above-mentioned intrinsic viscosity is less than 0.75. Since it was found that the cord strength after running was remarkably reduced even in the carcass ply layer other than the bead portion of the layer turn-back portion, the intrinsic viscosity of the cord of the carcass ply layer was found in the present invention. Is set to 0.75 or more. In addition, it is preferable to set this value to 0.85 or more in consideration of variations in usage conditions.

The selection of the weaving degree (that is, the number of denier) of the polyester monofilament cord is 100.
If it is less than 0 denier, the carcass ply layer is insufficient in strength (safety factor) against the filling internal pressure with 1 ply, so that an increase in the number of plies is required, resulting in an increase in tire weight and in turn an increase in rolling resistance. This is not preferable because it leads to a decrease in manufacturing efficiency and an increase in cost.

Further, in the pneumatic radial tire according to the present invention, a multifilament twisted cord which is conventionally used in general is used.
In order to have characteristics of extremely high modulus and low heat shrinkage as compared with the pneumatic radial tire of the conventional type, the same number of denier or the same number of denier as the pneumatic radial tire of the conventional multi-filament twisted cord was used. If
It is possible to obtain a tire in which the rigidity of the tire is significantly improved, the steering stability is excellent, and the unevenness on the tire side at the time of filling the internal pressure due to the nonuniform carcass arrangement is suppressed.

On the other hand, in the pneumatic radial tire according to the present invention, the carcass rigidity of this tire is set to be substantially the same as that of the conventional pneumatic radial tire of multifilament twist code, so that The number of driving (the number of cords per unit width) and the number of denier of the cord itself (that is, the thickness of the cord) can be reduced, the tire weight is reduced, and the rolling of the tire Therefore, the resistance can be reduced, and the fuel efficiency of the tire can be improved.

Incidentally, if it is attempted to reduce the driving force and the number of deniers equivalent to these with a conventional radial radial tire having a multifilament twist cord, in order to make up for a decrease in tire rigidity, the filament is reduced. It is necessary to use another type of polymeric fiber material with a higher modulus than polyester as the material, and at the same time the side cut resistance of the tire (the ability to prevent foreign matter on the road surface from trying to penetrate the tire side part) It has been confirmed by another experiment by the inventors that the tendency to decrease is caused, and it is very difficult to put it into practical use due to safety problems of tires.

[0018]

Embodiments of the present invention will be described below. Several tires were manufactured as prototypes for each of the examples of the tire size of the radial tire 195 / 70R14, the basic structure of the tire was one layer of the carcass ply and the two steel belts, and the comparative example. Various tests were conducted.

Table 1 shows the results of the physical property test of the cord. As is clear from the test results, the polyester monofilament cord according to the present invention has a relatively large load load per cord as compared with the polyester multifilament cord which has been conventionally used for tires. The elongation at the so-called intermediate elongation (elongation at a load of 6.75 kg per cord) does not change much, but in the stress range corresponding to the load applied to the tire code when the tire is actually used. The value of the initial modulus is large (143%), and therefore the tire rigidity which affects the deformation of the tire and the steering stability at the time of filling with internal pressure is high, and the heat shrinkage is extremely small.

[0020]

[Table 1]

The tires of the examples of Table 2 and the test tires of Table 3 are all 3,000 denier elliptical cross sections (minor diameter 0.33 mm) having the physical properties shown in the right column of Table 1 as the material of the carcass ply. , Long diameter 0.83 mm) polyester monofilament cord, while the tire of the comparative example in Table 2 is a 1500 denier multi-yarn bundle having the physical properties shown in the left column of Table 1 as the material of the carcass ply. A polyester multi-filament cord is used in which two bodies are twisted with the lower twist and the upper twist at a twist number of 40 times per 10 cm length (that is, 1500 D / 2-twist).

Table 2 shows the physical properties shown in Table 1 and changes in the driving of the carcass ply cord using a polyester monofilament cord having an intrinsic viscosity [η] of 0.83 to improve the steering stability. The tire of Example 1 according to the present invention aiming at improvement and the tire of Example 2 according to the present invention aiming at improvement of fuel consumption characteristics by reducing rolling resistance of the tire were prototyped and separately prototyped conventionally. A tire performance test was carried out and compared with the tire of Comparative Example 1 in which the polyester multifilament cord of No. 1 was used for the carcass ply.

The bead portion 1 of the first and second embodiments
As shown in FIG. 1, the structure of FIG.
Is wound around the bead core 2 and folded back to approach the body side of the carcass layer in the vicinity of the upper surface of the bead core and thereafter extend in the tire radial direction in parallel with the body side of the carcass layer. Has been done. Further, the terminal 4 of the folded-back portion 3 is stopped below the lower portion of the tire maximum width. When the total thickness of the tire is A and the distance from the outer wall 5 of the tire to the cord 6 of the carcass layer folding portion is B, the shape of the bead portion of the folding portion 3 is B, The B / A values are formed to satisfy 0.55 and 0.75, respectively. In the case of the second embodiment, the rigidity of the side portion is lower than that of the first embodiment by the amount of reduced driving, so the value of B / A is set to a large value. The value of B / A is changed by changing the cross-sectional area ratios and shapes of the left and right reinforcing rubbers 7 and 7 ′ sandwiching the carcass layer turn-back portion 3.

As is clear from Table 2, in the tire of Example 1 with a large amount of driving, the side plunger value indicating the side cut resistance is very large, the rigidity of the tire side portion is extremely high, and the steering stability performance is improved. Are better. On the other hand, in the tire of Example 2 in which the number of driving is reduced and the rigidity of the tire side portion (that is, the side plunger value) is comparable to that of the comparative example tire, the steering stability performance is comparable to that of the comparative example tire (that is, the conventional tire). The rolling resistance is reduced and the fuel economy performance is improved while being maintained at. Further, the unevenness of the tire side surface at the time of filling with the internal pressure is suppressed to a level that is almost undetectable by the tires of the examples.

[0025]

[Table 2]

Next, as shown in Table 3, the polyester monofilament cord according to the present invention described in Table 1 was used as the carcass ply code, and the bead portion of the folded portion of the carcass layer was used. A bead endurance drum test was conducted to confirm the degree of influence of the B / A value which defines the shape and the intrinsic viscosity value of the carcass plycode. At the same time, the durability of the bead portions of the tires of Examples 1 and 2 described above was also confirmed. The durability of the bead portion of the conventional tire, that is, the tire of the comparative example shown in Table 2 above, is a level of no failure after running 20,000 km, which is 20,000 km after running in the past market. The level is regarded as a passing level.

From the results shown in Table 3, when the value of B / A which defines the shape of the bead portion of the carcass layer folded-back portion is 0.5 or less, sufficient durability cannot be expected, and the peculiarity is unique. Viscosity is near an intermediate value between 0.70 and 0.83 (that is, about 0.
If it is less than 75), it can be judged that the durability is insufficient. In addition, it was confirmed that the tires of Examples 1 and 2 examined in Table 2 both completed the 20,000 km and had a pass level durability.

[0028]

[Table 3]

Although the carcass ply is one layer and the belt is two layers of the steel belt as the basic structure of the tire in the above embodiment, the present invention is not limited to this.
It is also applicable to those structures that are modified and arranged as necessary.

[0030]

The pneumatic radial tire of the present invention greatly improves the durability against running fatigue of a radial tire in which a polyester monofilament cord is applied to a carcass ply, improves steering stability, and reduces the weight of the tire. As a result, the tire performance can be remarkably improved by reducing the rolling resistance due to the increase in pressure, and further, the unevenness on the tire side at the time of filling with internal pressure is suppressed, and a good appearance can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a tire bead portion showing a structure of a bead portion of an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 bead part 2 bead core 3 carcass layer folded part 4 end of carcass layer folded part 5 tire outer wall 6 cord of carcass layer folded part 7, 7'reinforcement rubber 100 tire maximum width Lower part 101 Top of flange 102 Maximum tire width

Claims (2)

[Claims] 1. A pair of ring-shaped bead cores arranged at right and left intervals, and a carcass having both ends wound around the bead core and folded back to form a central portion in an annular shape. Layer and a plurality of belt-shaped belt layers laminated on the tire radial direction outer side of the top of the center portion of the carcass layer as a main reinforcing structure, and the ring-shaped tread of the belt shaped belt layer on the tire radial direction outer side. A rubber is disposed, and a pair of left and right side rubbers are disposed so as to cover the carcass layer on both sides of the tread rubber, and the carcass layer has a plurality of polyester monofilament cords with respect to the equatorial plane of the tire. A pneumatic radial tire which is juxtaposed in a substantially perpendicular direction and embedded in a coated rubber, wherein a carcass layer is folded back around a bead core from an inner side to an outer side in a rotation axis direction of the tire. Part of When the total thickness of the tire is A and the distance from the outer wall of the tire to the cord of the carcass layer folding portion is B, the shape of the cord portion is B / A> 0.
5. A pneumatic radial tire characterized in that the carcass layer is formed of a polyester monofilament cord having an intrinsic viscosity of 0.75 or more. 2. The pneumatic radial tire according to claim 1, wherein the polyester monofilament cord constituting the carcass has a fineness of 1000 denier or more.