JP2000301910A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain unevenness from being generated in a side wall part caused by a splice part of a carcass layer even when the number of the carcass layers is reduced, so as to reduce weight of a tire and to enhance productivity for the tire thereby. SOLUTION: In this pneumatic radial tire, a carcass layer 11 is laid between a pair of left and right bead cores 10, 10, one end part in a tire-circumferential direction of the carcass layer 11 is overlapped onto the other end to form a splice part, and a polyester code of very low shrinkage having 3000 D-8000 D of total denier number is used as a code for the carcass layer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention can suppress unevenness generated in a sidewall portion due to a splice portion of a carcass layer even when the number of carcass layers is reduced.
The present invention relates to a pneumatic radial tire capable of reducing the weight of a tire and improving productivity.

[0002]

2. Description of the Related Art Conventionally, in a pneumatic bias tire having a carcass layer made of a nylon cord, in order to reduce the weight and improve the productivity of the tire, the cord is made thicker (a larger diameter cord) to form the carcass layer. A technique to reduce the number was used.

On the other hand, with a pneumatic radial tire, it has been difficult to reduce the number of carcass layers (the number of plies) due to the following reasons. Since the number of plies is originally smaller than that of the bias tire, the reduction in the number of plies results in an increase in the unevenness of the sidewall portion of the tire after vulcanization.

When manufacturing a pneumatic radial tire,
A splice portion is formed by winding a belt-shaped carcass material composed of a carcass cord and coat rubber around an outer peripheral surface of a tire forming drum and overlapping a winding start end and a winding end end. Therefore, the carcass layer is provided with a splice portion extending in the tire width direction.

However, when the splice portion is provided in this manner, the number of ends (50 m in the direction perpendicular to the cord) of the splice portion is smaller than that of the other portion (main body portion) of the carcass layer.
The number of cords per m) is large, so that the rigidity is large, and the splice portion hardly expands when the tire is expanded during molding, and the number of ends hardly changes. Conversely, stress concentrates near the carcass splice and greatly expands, so that the number of ends other than the vicinity of the carcass splice is even smaller.

When the tire is filled with air, the carcass splice has a larger number of ends than the other parts and the carcass cord is less likely to expand, so that the surface of the tire side is depressed, whereas the end near the carcass splice is reversed. Since the number is small and the carcass cord is elongated, the surface of the tire side part is convex, and since this irregularity is adjacent,
The unevenness on the surface of the sidewall portion having a small rubber thickness becomes conspicuous. Generally, the unevenness increases as the number of plies decreases.

[0007] In the case of pneumatic radial tires, in order to improve steering stability and riding comfort during high-speed running,
A polyester cord is used as a cord for the carcass layer. However, polyester cords generally have poorer fatigue resistance than nylon cords, so if the polyester cord is made thicker, the fatigue resistance of the cord, which is not a problem with nylon cords, will decrease, and the tire's load durability will decrease. Will get worse.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic radial tire having a carcass layer made of a polyester cord, and to reduce the number of carcass layers due to spliced portions even when the number of carcass layers is reduced. An object of the present invention is to provide a pneumatic radial tire capable of suppressing unevenness generated in a wall portion, thereby making it possible to reduce the weight and improve productivity of the tire.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided a pneumatic device in which a carcass layer is mounted between a pair of right and left bead cores, and one end and the other end of the carcass layer in the tire circumferential direction are overlapped to form a splice portion. In the radial tire, the total denier number of the carcass layer code is 3000D or more.
8000D ultra-low shrinkage polyester cord is used.

[0010] The ultra-low shrinkage polyester cord is difficult to elongate and has excellent fatigue resistance. Since the ultra-low-shrinkage polyester cord that is difficult to stretch is used as the cord of the carcass layer, the difference in elongation between the carcass splice part and the carcass layer body part in the sidewall part can be reduced, so that irregularities generated in the sidewall part are suppressed. be able to.

Further, by using the ultra-low shrinkage polyester cord as a cord for the carcass layer as described above, it is possible to suppress unevenness generated in the sidewall portion, and the ultra-low shrinkage polyester cord is excellent in fatigue resistance. Thus, by making the ultra-low shrinkage polyester cord used thicker (3000D to 8000D), the number of carcass layers can be reduced, thereby making it possible to reduce the weight of tires and improve productivity (conventional carcass layers). Polyester cord has a total denier of 1000D
~ 3000D).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a pneumatic radial tire according to the present invention has a pair of right and left bead cores 1.
A single carcass layer 11 is mounted between 0 and 10, and two belt layers 13 and 13 are arranged on the tread 12 in the tire circumferential direction over one circumference of the tire.

In the carcass layer 11, as shown in FIG. 2A, a splice portion 15 extending in the tire width direction is formed by overlapping one end and the other end in the tire circumferential direction EE '. Generally, when the carcass layer 11 is a single layer as shown in FIG. 2 (A), the elongation ratio (carcass layer main body portion / splice portion 15) = 1/1/2, as shown in FIG. 2 (B). When the carcass layer 11 is composed of two layers, the elongation ratio (carcass layer main body / splice 15) = 1/2/3,
As shown in FIG. 2C, when the carcass layer 11 has three layers, the elongation ratio (carcass layer main body portion / splice portion 1)
5) = 1/3/4, so that the smaller the number of carcass layers, the larger the irregularities on the surface of the sidewall portion.

On the other hand, in the present invention, the carcass layer 1
Since an ultra-low-shrinkage polyester cord that is difficult to stretch is used as the cord 1, the elongation ratio (carcass layer main body portion / splice portion 15) ≒ 1 even when the carcass layer 11 is a single layer.
/ 1, the side unevenness can be made smaller than before. In the present invention, the number of carcass layers 11 is not particularly limited, but is preferably one (single layer).

The total denier of this ultra-low shrinkage polyester cord is 3000D to 8000D. 3000D
If it is less than 1, the cord is too thin and the strength of the carcass layer cannot be sufficiently increased, so that it is difficult to reduce the number of carcass layers. On the other hand, if it exceeds 8000D, the thickness of the carcass layer becomes too large, and tire moldability deteriorates.

The ultra-low shrinkage polyester cord used here has a dimensional stability index by improving the crystallinity in the fiber and randomizing the molecular chain length and the degree of orientation of the amorphous part as compared with the conventional polyester cord. This is a cord of a polyester fiber in which is reduced. In general, fiber fatigue refers to a phenomenon in which compressive stress applied in the fiber axis direction accumulates and generates heat in a rigid crystal part, thereby promoting deterioration. Normally, stress concentration can be avoided by reducing the restraining force (increase in the degree of randomness) of the amorphous portion, and the life of the fiber can be extended. Therefore, the ultra-low shrinkage polyester cord having a loose amorphous portion has better fatigue resistance than the conventional polyester cord. Here, the dimensional stability index refers to an intermediate elongation plus a heat shrinkage rate, and is one of indexes indicating fibers. The smaller this value is, the more stable the behavior is against heat.

This ultra-low shrinkage polyester cord has a twist coefficient K of 1500 to 2500 (K = T√D, T is the number of twists per 10 cm of cord, D is the denier of cord), and has an intermediate elongation of 2 to 5%. , Heat shrinkage at 150 ° C. is 1.0% or more
4.5% and a dimensional stability index of 2.5% to 6.5%
It is.

If the twist coefficient K is less than 1500, the twist coefficient of the cord has a great influence on the fatigue properties of the cord, so that even the ultra-low shrinkage polyester cord deteriorates to the extent that the fatigue resistance is not suitable for practical use. On the other hand, when the twist coefficient K exceeds 2,500, the cord elongation increases as the twist coefficient increases, so the intermediate elongation increases, and the side unevenness is sufficiently suppressed even when an ultra-low shrinkage polyester cord that is originally difficult to stretch is used. You can't do that.

The intermediate elongation is the cord elongation when a load of 2.25 g per denier is applied (2.25 g / cord).
D). If the intermediate elongation is less than 2%, the fatigue resistance is deteriorated if the intermediate elongation, that is, the elongation of the cord is large, so that even if an ultra-low shrinkage polyester cord originally having good fatigue resistance is not suitable for practical use. Up to the fatigue resistance. If it exceeds 5%, the elongation of the cord is too large, and the side irregularities cannot be sufficiently suppressed.

If the heat shrinkage at 150 ° C. is less than 1.0%, a force against the centrifugal force applied to the carcass layer during running of the tire does not sufficiently occur, and the outer diameter of the tire tends to increase, If it exceeds 4.5%, the shape of the finished tire changes due to heat shrinkage of the polyester cord in the vulcanization step during tire production, and sufficient tire performance cannot be exhibited.

If the dimensional stability index is less than 2.5%, the strength is reduced due to the production constraints of the polyester fiber, so that it becomes difficult to obtain a fiber strength suitable for practical use. If it exceeds 6.5%, the intermediate elongation is reduced. Even if it is set low, the heat shrinkage cannot be made sufficiently low, so it receives heat history during vulcanization, the cord shrinks, the shape of the finished tire changes, and it becomes impossible to exhibit sufficient tire performance .

The above-mentioned ultra-low-shrinkage polyester cord used in the present invention is, for example, an ultra-low-shrinkage polyethylene terephthalate cord (ultra-low-shrinkage PET cord).

[0023]

EXAMPLES A pneumatic radial tire having a tire size of 265 / 70R16 and a carcass layer having the specifications shown in Table 1 was produced (Conventional Example 1, Comparative Examples 1 to 5, and Example 1). Here, the number of ends of the carcass layer is 50 / 5c
m.

The carcass layer weight, side unevenness appearance (bumpy side), and load durability of these tires were evaluated as follows. Table 1 shows the results.

Carcass layer weight : Since one ply is naturally lighter than two plies, a two-ply product is designated as heavy "x" and a one-ply product is designated as light "o".

Side unevenness appearance : When a tire product was assembled on a rim and air pressure was applied, the height difference between the carcass layer splice portion and the vicinity of the splice portion at the side portion was measured and evaluated visually. Large irregularities were evaluated as "No", small irregularities as "Good", and almost no irregularities as "OK".

Load durability : The tire is mounted on a standard rim 16 × 8J according to the method of JIS D4230, and the load applied to the tire is increased stepwise while running at a constant speed on a metal drum in a room. The vehicle was driven until the tire was destroyed, and the total mileage was measured. Conventional example 1 is 10
It is indicated by an index of 0. The larger the index value, the better the load durability.

[0028]

[Table 1]

In Table 1, Conventional Example 1 uses the current low-shrinkage PET code and has a total code denier of 20.
This is the case of 00D (1000D / 2), and the carcass layer weight is large (2 plies) although the side unevenness appearance is good. Comparative Example 1 is a case where the ultra-low shrinkage PET code is used but the total denier number of the code is 2000D (1000D).
/ 2) excellent in load durability, but the weight of the carcass layer is large (2 plies), and the side unevenness appearance is not so much. Comparative Examples 2 and 3 have a total denier number of 4000D within the range of the present invention (2000D / 2), but use the current low shrinkage PET cord, and have a small carcass layer weight (1). Ply), side unevenness appearance is poor. Comparative Example 4 uses an ultra-low shrinkage PET code and has a total code denier of 4000D (2000D /
2) The case where the middle elongation of the cord is as high as 5.4% and the heat shrinkage is as low as 0.7%, which is excellent in load durability and the carcass layer weight is small (1 ply), Bad uneven appearance. On the other hand, in the case of the present invention (Example 1), it can be seen that the carcass layer weight, the side unevenness appearance, and the load durability are all excellent.

[0030]

As described above, the pneumatic radial tire of the present invention uses an ultra-low shrinkage polyester cord having a total denier of 3000D to 8000D as a cord of the carcass layer, so that even if the number of carcass layers is reduced. The unevenness generated in the sidewall portion due to the splice portion of the carcass layer can be suppressed, and therefore, the weight of the coated rubber which contributes most to the carcass layer weight can be reduced by reducing the number of carcass layers, thereby reducing the weight of the tire. , And by reducing the number of carcass layers, tire productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a half sectional view in the meridian direction of an example of a pneumatic radial tire of the present invention.

FIGS. 2A and 2B are cross-sectional views illustrating an example of a splice portion of a carcass layer. FIG.
Indicates a case where two carcass layers are provided, and FIG.
Each case is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Bead core 11 Carcass layer 12 Tread 13 Belt layer 15 Splice part

Claims (4)

[Claims] 1. A pneumatic radial tire in which a carcass layer is mounted between a pair of left and right bead cores, and one end and the other end of the carcass layer in the tire circumferential direction overlap each other to form a splice portion. A pneumatic radial tire using an ultra-low shrinkage polyester cord having a total denier of 3000D to 8000D as the cord. 2. The ultra-low shrinkage polyester cord has a twist coefficient K of 1500 to 2500 (K = T√D, T is the number of twists per 10 cm of cord, D is the denier of cord),
Intermediate elongation is 2-5%, heat shrinkage at 150 ° C is 1.0%
４4.5%, and a dimensional stability index of 2.5% 〜6.5.
%. The pneumatic radial tire according to claim 1, wherein 3. The carcass layer is a single layer.
Or the pneumatic radial tire according to 2. 4. The pneumatic radial tire according to claim 1, wherein the ultra-low shrinkage polyester cord is an ultra-low shrinkage polyethylene terephthalate cord.