JPH08118906A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE: To improve durability and steering stability around a bead part by forming a carcass ply cord so as to be a polyester monofilament whose loop strength/strength ratio, intrinsic viscosity and fineness per one piece are specific values respectively. CONSTITUTION: A pneumatic radial tire is provided with a bead part 3 formed on the inner periphery of a side part 2 in both sides of a tread part 1 and reinforced by a carcass ply 4 in which a carcass ply cord 4a is arranged and formed in a tire radial direction and a belt layer 5 buried inside the tread part 1. This carcass ply cord 4a is formed by polyester monofilament with 0.5 or less of loop strength/strength ratio, 0.8 or more of intrinsic viscosity(IV) and 1000 denier or more of fineness per one piece. Therefore, durability around the bead part 3 can be improved, while maintaining high steering stability.

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 having excellent durability around a bead portion and excellent steering stability.

[0002]

2. Description of the Related Art Conventional pneumatic radial tires usually have a rim with a carcass layer fixed to a sidewall portion reinforced with a carcass layer including cords arranged in a direction substantially perpendicular to the tire circumferential direction. And a crown portion reinforced by a belt layer having extremely high rigidity along the tire circumferential direction.

Conventionally, a large number of filaments having a very small denier, for example, 4 to 6 denier / filament, have been used as a cord constituting a carcass layer, and further, in order to improve the yarn converging property and fatigue resistance, Twisted yarn consisting of ply-twisted and ply-twisted fine denier filaments is used.

On the other hand, with the intention of omitting the twisting step in the bundle, it has been attempted to apply a cord composed of one filament, that is, a so-called monofilament cord to a tire, for example, Japanese Unexamined Patent Publication No. 52-1987. -110918 discloses a method for producing a nylon monofilament cord, and is disclosed in U.S. Pat. No. 4,360,360.
No. 050 discloses applying a polyester thick denier monofilament cord to a tire. Further, in the above-mentioned publications and specifications, there is a description about a monofilament cord having an oval cross section or a rectangular cross section, and it can be seen from this that fatigue resistance of the monofilament cord was also taken into consideration. That is, since the monofilament cord cannot disperse the force with respect to the external force input, unlike the twisted cord, it has a defect that the fatigue resistance of the twisted cord is poor. In the case of multi-filament twisted cords, even if compressive strain stress acts, each extra-fine filament with twist angle bends and deforms, so it works in a direction to absorb and absorb the compressive strain input, resulting in excellent fatigue resistance. On the other hand, in the case of a monofilament cord, it receives a compressive strain input directly.

Further, regarding the nylon monofilament cords in the latter half of the 1980s, various cords surface-modified with steam by steam, as can be seen from the disclosures of JP-A-2-99610 and JP-A-2-127507. It can be seen that an attempt was made to apply it to tires. However, the production of monofilament cords by the steam heating method is disclosed in Japanese Patent Laid-Open No. 52-110918, and it is not so novel. Nylon monofilament cords are more commonly used than the polyester multifilament cords currently used. Compared to filament twisted cord, it cannot be said that both elastic modulus and heat shrinkage ratio are excellent.
No superiority to the steering stability of the tire exerted based on these characteristics can be found.

Although nylon is superior to polyester in terms of fatigue resistance in the tire,
It has the basic characteristics of even lower elastic modulus and higher heat shrinkability, and all of these characteristics have a disadvantageous effect on the steering stability of the tire, and the above basic characteristics cannot be resolved even as a monofilament cord. This is because it does not reach the polyester multifilament twisted cord. After all, as long as nylon monofilament cords are used, it is not possible to satisfy the high elastic modulus and low heat shrinkage rate as a carcass ply cord, which is indispensable for realizing tires that are required to have excellent steering stability in recent years. .

In order to improve this point, it has been proposed to use polyester monofilament cords for tires. Japanese Unexamined Patent Publication (Kokai) No. 3-185111 discloses that a monofilament cord to which a low carboxyl group polyester fiber material is applied is used for a tire carcass. However, the low-carboxylated polyester is expected to be improved against deterioration due to an amine that migrates from the rubber composition, but has insufficient fatigue resistance to physical fatigue in the tire, and the cord portion during running may fail. There is a concern that it may occur and there is a difficulty in practicality.

Further, JP-A-4-232102 discloses that a polyester monofilament cord obtained by steam heating is applied to a tire. Technology to reduce the birefringence of the outer layer of the yarn cross section by steam heating in comparison with the inner layer and to make the cross section elliptical to improve flexibility against bending, that is, to improve loop strength as a measure and improve fatigue resistance However, even with these ideas, when applying actual tires,
When the tire strain increases due to a high load, there is a problem that cord breakage around the bead portion occurs at a relatively early stage, and it has not been put into practical use at present.

If the monofilament cord is made of the same material, it can have a significantly higher elastic modulus than conventional twisted cords, not only can impart high steering stability to the tire, but also do not require a twisting process, Even in the productivity of tire cords, the merits are immeasurable.

However, as described above, the monofilament cord mainly composed of nylon has a limitation in increasing its elastic modulus, and has a drawback that it cannot exhibit an elastic modulus higher than that of the conventional polyester twisted cord. On the other hand, a monofilament cord mainly composed of polyester has an advantage that it can exhibit a higher elastic modulus than a conventional polyester twisted cord, but it has a difficulty in fatigue resistance, and how to improve this fatigue resistance. This is a big obstacle.

[0011]

SUMMARY OF THE INVENTION The present invention was created in order to solve the above-mentioned problems of the prior art. The object of the present invention is to provide a polyester monofilament cord excellent in fatigue resistance. By using it, it is intended to provide a pneumatic radial tire having excellent durability around the bead portion and excellent steering stability.

[0012]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has achieved the above object by using a polyester monofilament cord having a specific structure in a carcass layer of a pneumatic radial tire. It succeeded in obtaining a pneumatic radial tire capable of achieving the above, and completed the present invention.

That is, the pneumatic radial tire of the present invention comprises a tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions formed on the inner circumference of the side portion, A carcass ply having carcass ply cords arranged in the radial direction of the tire and a belt layer buried around the carcass ply and buried inside the tread portion are reinforced, and the carcass ply cord has a loop strength / strength ratio of 0. 0.5 or less, intrinsic viscosity (IV)
A polyester monofilament having a fineness of 1,000 denier or more per 0.80 or more is characterized.

The details of the present invention will be described below. The ratio (loop strength / strength ratio) obtained by dividing the loop strength of the polyester monofilament constituting the carcass ply cord in the present invention by the strength is 0.50 or less, preferably 0.4.
It is preferably 5 or less, more preferably 0.40 or less. In the conventional monofilament technology, it is said that increasing the flexibility by reducing the orientation of the outer layer of the yarn cross section is good for fatigue resistance, and the loop strength is used as a measure of the flexibility. A lot of ingenuity is being made to raise it. However, according to the inventor's test, the opposite result was obtained in which the yarn having a lower loop strength shows a better fatigue property in the tire fatigue test or the belt bending fatigue test.

The dip-treated polyester monofilament was embedded in rubber, vulcanized, and then
When a general adhesion test is performed by pulling the cord out of the rubber with a tensile tester, it is observed that the outer layer portion of the monofilament having a high loop strength peels off and remains in the rubber. However, the sample with low loop strength has a clearly reduced amount of peeling, or peeling does not occur at all. This means that peeling is likely to occur when there is a portion where the orientation of the outer layer of the yarn cross section is lower than that of the inner layer of the yarn cross section, and the higher the molecular orientation, the better the peeling resistance.

On the other hand, in terms of fracture morphology, the polyester monofilament cord undergoes a marked increase in diameter at the stress concentration point immediately before fracture in the fatigue test. When the rubber and adhesive are removed, it is also observed that the threads are whitened. From these, it is considered that the monofilament cord undergoes interfacial fracture inside the filament and generally called fibrillation due to repeated compressive stress, leading to destruction from the inside to the whole. Therefore, it can be concluded from the above that the yarn having a lower loop strength has a better fatigue resistance because it has an excellent fibril peeling resistance inside.

Generally, a polyester monofilament is required to have a high loop strength not only in terms of fatigue resistance but also because knots between yarns must be formed during the actual manufacturing process or work, and the strength at that time is required. Is. However, even if the loop strength is low, the present inventor has confirmed that it does not cause any problem at the tire manufacturing process or at the time of using the tire, only by making a special knot. Therefore, the loop strength / strength ratio of the polyester monofilament is 0.50 or less, preferably 0.45 or less, and more preferably 0.40 or less.

The intrinsic viscosity of the polyester monofilament is 0.80 or more, preferably 0.85 or more, more preferably 0.90 or more. Regarding the intrinsic viscosity, the higher the value within the range where the spinnability in the yarn manufacturing process is satisfactory and the required strength and initial elastic modulus are obtained, the more the fatigue resistance is improved, which is not preferable. Regarding this intrinsic viscosity as well, a monofilament having a higher intrinsic viscosity of 0.80 or more shows higher peel resistance in the rubber pull-out adhesion test, which is also considered to be the reason why the fatigue resistance is improved.

The fineness of the polyester monofilament is
Although it depends on the size and structure of the tire, it is 1000 denier or more, preferably 1500 denier or more, more preferably 2000 denier or more. Fineness is 1000
If it is smaller than denier, sufficient case strength cannot be obtained with the same number of plies even if the number of carcass cords is increased. Although it is possible to increase the number of plies in order to secure the strength of the case, it is not preferable because the total weight of the carcass becomes heavy and the rolling resistance becomes large.

Polyethylene terephthalate is the most preferable tire material as the material for the polyester monofilament. However, a polyethylene terephthalate component of 80% or more, to which 10% or less of additives such as a softener and a stabilizer are added, or 10% or less of a copolymerization component, or 20% or less of It may be a blend of polymers such as polybutylene terephthalate and polyethylene naphthalate.

The cross-sectional shape of the polyester monofilament is also not particularly limited, but usually a circular shape or a shape close to a circular shape is preferable in terms of handling. However, when the number of cords to be driven into the carcass is reduced, the cross-sectional shape may be elliptical in order to prevent the cord-cord distance from increasing. As a result of a test conducted by the present inventor, whether the cross-sectional shape was circular or elliptic, the fatigue property was not significantly changed.

[0022]

As described above, the polyester monofilament in the specified range, that is, the loop strength / strength ratio of 0.5
Hereinafter, by using a polyester monofilament having an intrinsic viscosity (IV) of 0.80 or more and a fineness of 1000 denier or more per one as a carcass cord, the durability around the bead portion is compared with a tire using a conventional polyester monofilament, It can be significantly improved. This is an effect of improving the fibril peeling property inside the cord. Due to this effect, we succeeded in producing a tire capable of completing 20,000 km, which is empirically considered to be a practically no problem area in a high load drum durability test as described later.

[0023]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Examples 1 to 5, Comparative Examples 1 to 6) Table 1 below
Each trial tire was manufactured by using the cords obtained under the various manufacturing conditions shown in FIG. The test results of the respective trial tires are shown in Table 1 and FIG. 1 below. The numerical value in FIG. 1 indicates the drum travel distance.

The production of trial tires, cord tensile test, intrinsic viscosity measurement, cord peeling resistance test, high load drum durability test and steering stability test were carried out by the following methods. (1) Production of Prototype Tire As shown in FIG. 2, the trial tire was formed on a tread portion 1, a pair of side portions 2 continuous on both sides of the tread portion 1, and an inner circumference of the side portion 2, respectively. A pair of beads 3
And a carcass ply cord 4 in the radial direction of the tire.
Is a pneumatic radial tire A reinforced by a carcass ply 4a formed by arranging the carcass ply 4a and a belt layer 5 that surrounds the carcass ply 4a and is buried inside the tread portion 1, and the size thereof is 165 / 70R13. . The material of the polyester monofilament constituting the carcass ply cord is polyethylene terephthalate, and the amount of carboxyl group is 25 to 30 mol / 10 ⁶ g. The filament fineness is 3000 denier in each example. Further, the number of carcass cords driven and the tire structure are all the same in each embodiment.

(2) Cord Tensile Test According to JIS L1017, an autograph manufactured by Shimadzu Corporation was used to pull the monofilament cord before dipping at a constant speed under room temperature conditions of 25 ° C. ± 2 ° C., and at the time of cutting the cord. The cord strength was determined by determining the load of and dividing by the cord denier. Regarding the loop strength, grip both ends of the monofilament cord before dipping, which was cut into a certain length, on one side of the chuck, pass the cord that was also cut into a certain length into the loop, and then put both ends on the other chuck. It was grasped and pulled in the same manner as above. The load at the time of cutting the cord was obtained, and this was divided by a value twice the cord denier to obtain the loop strength.

(3) Intrinsic viscosity measurement A p-chlorophenol / tetrachloroethane (3: 1) mixed solvent was used as a solvent, and a dip treatment was carried out at 30 ° C. using an automatic IV measuring device manufactured by SCHOTT. The intrinsic viscosity of the previous monofilament cord was measured.

(4) Cord peeling resistance test The cord was treated with epoxy, then immersed in RFL resin, dried at 160 ° C. for 60 seconds, and further heat treated at 240 ° C. for 60 seconds to treat the adhesive composition. I made a code. This adhesive composition treatment cord was embedded in an unvulcanized compounded rubber composition, and 170 ° C. × 30 minutes, 20 kg / c
Vulcanization was performed under a pressure of m ² , and the cord was pulled out from the obtained vulcanized product at a constant speed. At that time, the amount of the peeled product of the cord remaining in the vulcanized rubber was visually evaluated as follows. . In addition, ◯ and Δ are practically preferable. ○: None or almost none △: Somewhat ×: Yes or broken due to peeling

(5) High load drum durability test After adjusting the trial tire to the maximum air pressure of JIS standard in the room of 25 ° C ± 2 ° C, after leaving it for 24 hours, the air pressure was readjusted to the maximum of JIS standard. A load twice as much as the load was applied to the tire, and the tire was run on a drum having a diameter of about 1.7 m at a speed of 60 km / hour, and the running distance until the occurrence of a failure was measured. Originally, the target is 20,000 km, but in order to confirm the durability of 20,000 km or more in this test, 30,000 km
I calculated the mileage up to.

(6) Steering stability test Each prototype tire was mounted on a passenger car, and a feeling test of steering stability and vibration riding comfort was conducted by a professional driver. The evaluation is generally used polyester twisted cord (1500 denier / 2 strands, 40 × 4 twists)
(0/10 cm) was used as a control tire and the relative evaluation was carried out by a 10-point method using a control tire as 5. 0: No change ± 2: Slightly good (somewhat bad) ± 4: Good (bad)

[0031]

[Table 1]

(Consideration of Table 1 and FIG. 1) Above Table 1 and FIG.
From the above, the following was confirmed. In Comparative Examples 1 and 2, the intrinsic viscosity is low, the cord peeling resistance is poor because the loop strength is high, and the high load drum durability level is low. In Comparative Example 3, the loop strength is low, but the drum endurance level does not reach the target because the intrinsic viscosity is low. In Comparative Examples 4 and 5, the intrinsic viscosity is high, but the loop strength is high, and therefore the target value level of the drum durability level is not reached. All of these drum test failures were due to cord breakage at the bead turnup portion.

On the other hand, Examples 1 to 5 satisfy the conditions of the present invention. The lower the loop strength, the more
It can be seen that the higher the intrinsic viscosity, the higher the peel resistance. As a result, the durability of the heavy duty drum has reached the target level in each of the examples. In Example 5,
Even after traveling 30,000 km, it was judged that it would not be out of order and that it could withstand practical use.

Comparative Example 6 is a control tire in which a commonly used polyester twisted cord is used as a carcass cord. Compared with the tire of Comparative Example 6,
It is recognized that the steering stability of each of the tires of the respective examples using the monofilament as the carcass cord is improved. Further, it can be seen that even if the loop strength and the intrinsic viscosity are increased as in the present invention, the steering stability as compared with the comparative examples is not affected.

[0035]

Since the present invention is configured as described above, it has the following effects. That is, in the pneumatic radial tire of the present invention, the carcass ply cord has a loop strength / strength ratio of 0.5 or less,
Intrinsic viscosity (IV) 0.80 or more, fineness 100 per one
By using a polyester monofilament having a denier of 0 or more, it is possible to improve durability around the bead portion while maintaining high steering stability.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between filament characteristics and high load drum durability.

FIG. 2 is a partial cross-sectional view showing an example of a trial tire used in Examples and the like.

[Explanation of symbols]

 A Prototype tire (pneumatic radial tire) 1 Tread part 2 Side part 3 Bead part 4a Carcass ply cord 4 Carcass ply 5 Belt layer

Claims (1)

[Claims] 1. A carcass ply cord is provided in a radial direction of a tire, comprising a tread portion, a pair of side portions continuous on both sides of the tread portion, and a pair of bead portions each formed on an inner circumference of the side portion. A pneumatic radial tire reinforced by an arrayed carcass ply and a belt layer that surrounds the carcass ply and is buried inside a tread portion, wherein the carcass ply cord has a loop strength / strength ratio of 0.5.
Hereinafter, a pneumatic radial tire characterized by being a polyester monofilament having an intrinsic viscosity (IV) of 0.80 or more and a fineness of 1000 denier or more per filament.