JP2003237308A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the steering stability, and to reduce the rolling resistance while maintaining the excellent ride quality. <P>SOLUTION: A carcass cord is formed of polyethylene-2,6 naphthalate fiber cord of the cord thickness of 2,500 to 3,600 d, and of the strand number of 30 to 40/10 cm. The polyethylener-2,6 naphthalate fiber cord has the initial modulus of 50 to 65 gf/d at 25°C, the loss tangent (tanδ) of 0.06 to 0.09, and of the dynamic modulus of elasticity (E*) of 2,800 to 4,000 N/cord. In addition, the rates of change of the initial modulus, the loss tangent (tanδ), and the dynamic modulus of elasticity (E*) at a temperature between 25°C and 70°C are ≤±20%, respectively. <P>COPYRIGHT: (C)2003,JPO

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 steering stability, riding comfort and rolling resistance.

[0002]

2. Description of the Related Art Generally, as performance required for radial tires for passenger cars,
Maneuvering stability, riding comfort, fuel economy, durability, etc.
In order to improve these performances, polyethylene terephthalate fiber (PET) cords have been widely used in the carcass layer of passenger car radial tires.

However, with the recent advancement of vehicles, there is a demand for further improvement in performance. Therefore, it has been proposed to use a carcass cord having a higher modulus at initial tension. But in this case,
There is a problem that the riding comfort is rather adversely affected because the rigidity of the sidewall portion is increased. It is also important to reduce rolling resistance and improve fuel economy in the environment.

Under these circumstances, as a result of research conducted by the present inventor, polyethylene 2,6 naphthalate fiber cord having specific physical properties was used as the carcass cord, and the variation of the physical property values in the internal temperature range of the tire during running was obtained. It has been clarified that it is possible to improve the steering stability and reduce the rolling resistance while keeping the ride comfort high by suppressing as much as possible.

That is, the present invention uses a polyethylene 2,6 naphthalate fiber cord as a carcass cord, and the cord thickness, the number of twists, the initial modulus, the loss tangent, and the initial modulus, loss tangent, and dynamic elastic modulus of 25. The object of the present invention is to provide a pneumatic radial tire that can improve steering stability and reduce rolling resistance while maintaining high riding comfort based on specifying the rate of change in the temperature range of 70 ° C to 70 ° C.

[0006]

In order to achieve the above object, the invention of claim 1 of the present application is to provide at least one of a bead core of a bead portion from a tread portion to a sidewall portion.
A pneumatic radial tire comprising a carcass composed of one carcass ply and a belt layer composed of at least two belt plies arranged inside a tread portion and radially outside of the carcass, the carcass ply comprising: Has a cord thickness of 2500 to 3600d and a twist number of 30
A polyethylene 2,6 naphthalate fiber cord of -40 times / 10 cm is used as a carcass cord, and the polyethylene 2,6 naphthalate fiber cord has an initial modulus of 50 to 65 gf / d and a loss tangent (tan δ) of 0 at 25 ° C. 0.06 to 0.09, dynamic elastic modulus (E *)
Is 2800 N / code to 4000 N / code, and the change rate of the initial modulus, the change rate of the loss tangent (tan δ), and the change rate of the dynamic elastic modulus (E *) between 25 ° C. and 70 ° C. are respectively, It is characterized in that it is ± 20% or less.

In the invention of claim 2, the polyethylene 2,6 naphthalate fiber cord has a load of 2.0 gf / d.
The elongation of the cord is 0.5 to 2.5%.

In the invention of claim 3, the polyethylene 2,6 naphthalate fiber cord has a filament number of 4
The feature is that the number is from 00 to 600.

Further, in the invention of claim 4, the tread portion is at least one band in which a band cord is spirally wound outside the belt layer at an angle of 5 degrees or less with respect to a tire circumferential direction. It is characterized in that a band layer made of ply is provided and the polyethylene 2,6 naphthalate fiber cord is used as the band cord.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below.
This will be described together with the illustrated example. FIG. 1 shows a meridional section in the case where the pneumatic radial tire of the present invention is a passenger vehicle tire.

In FIG. 1, a pneumatic radial tire 1
Is a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the tread portion 2
Belt layer 7 disposed inside the carcass and outside the carcass 6
It is equipped with

The carcass 6 is formed by one or more carcass plies 6A in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction, in this example, one carcass ply 6A. The carcass ply 6A has the bead cores 5, 5
On both sides of the ply body portion 6a that straddles the space, there are provided folded-back portions 6b that are folded back around the bead core 5. Between the ply body portion 6a and the folded-back portion 6b, a taper extends radially outward from the bead core 5. A bead apex rubber 8 for bead reinforcement is arranged.

In the present embodiment, a polyethylene 2,6 naphthalate fiber cord having a cord thickness of 2500 to 3600 d and a twist number of 30 to 40 turns / 10 cm is used as the carcass cord. The twist number is 30 to
40 times / 10 cm means that both the number of lower twists and the number of upper twists are 3
It means 0 to 40 times / 10 cm, and a twin-twisted structure having the same number of lower twists and upper twists can be preferably used.

Here, in order to obtain a proper balance between strength, elongation, and fatigue resistance of the polyethylene 2,6 naphthalate fiber cord, the twist number of the cord is 30 to 40 times / 1.
It is important to set it to 0 cm, and if it is less than 30 times / 10 cm, elongation and fatigue resistance become insufficient, and it becomes impossible to obtain required cord durability. The number of twists is 40
When the number of turns exceeds 10 cm, the elongation of the cord becomes excessive and it becomes difficult to maintain the tire dimensions.

In order to secure the rigidity and strength of the tire, it is important that the polyethylene 2,6 naphthalate fiber cord has a thickness of 2500 to 3600 d.
If it is less than 2500d, the cord is too thin and the number of carcass plies needs to be increased. If it exceeds 3600d, the carcass ply 6A becomes unnecessarily thick, which is disadvantageous for weight reduction in any case.

The polyethylene 2,6 naphthalate fiber is not only a homopolymer but also a copolymer comprising 85 mol% or more of polyethylene 2,6 naphthalate and less than 15 mol% of a copolymerizable third component. It may be. Examples of the third component include naphthalenedicarboxylic acid other than 2,6 naphthalenedicarboxylic acid, terephthalic acid, isophthalic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, and the like.

Since such polyethylene 2,6 naphthalate fiber has a high elasticity, it is possible to maintain a proper balance between the strength based on the twist number, the elongation and the fatigue resistance.
The initial modulus at 25 ° C is 50 to 65 gf / d,
The dynamic elastic modulus (E *) can be increased in the range of 2800 to 4000 N / code.

The carcass cord has a stretch of about 1 to 3% and is embedded in the tire due to the stretch during vulcanization molding. The modulus in elongation, the initial modulus M, is important. When the initial modulus M is in the range of 50 to 65 gf / d and the dynamic elastic modulus E * is in the range of 2800 to 4000 N / cord, both steering stability and riding comfort are balanced. Excellent performance can be achieved. If the initial modulus M and the dynamic elastic modulus E * are below the lower limits of the above ranges, the steering stability is impaired, and if they are above the upper limits, the riding comfort is impaired.

In addition, it is necessary to suppress variations of these physical properties as much as possible in the internal temperature range of the tire during running so as to maintain the physical properties of the tire uniformly, and to obtain excellent steering stability and riding comfort.
It is necessary for high and stable performance.

Therefore, in this embodiment, 25
The rate of change of the initial modulus M and the rate of change of the dynamic elastic modulus E * between 0 ° C and 70 ° C are regulated to ± 20% or less. That is, the maximum and minimum values of the initial modulus in the temperature range of 25 ° C. to 70 ° C. are Mmax and Mmi.
When n, the differences Mmax-M and M-Mmin from the initial modulus M at 25 ° C. are respectively 20% or less of the initial modulus M at 25 ° C., and 2
The maximum value of the dynamic elastic modulus in the temperature range of 5 ° C to 70 ° C,
When the minimum values are E * max and E * min, the difference from the dynamic elastic modulus E * at 25 ° C E * max-E *, and E
* -E * min is set to 20% or less of the dynamic elastic modulus E * at 25 ° C., respectively.

In particular, in order to improve the above-mentioned steering stability and riding comfort, the change rate of the initial modulus and the change rate of the dynamic elastic modulus E * are ± 15% or less, and further ± 10%.
The following are preferred.

The polyethylene 2,6 naphthalate fiber cord contains 90% or more of ethylene 2,6 naphthalate unit, DSC peak is 280 ° C. or more, intrinsic viscosity is 0.7 or more, and birefringence is 0. By setting it to be not less than 30, the rate of change as described above can be low and the thermal stability can be good. Further, it is possible that the rate of change can be controlled also by the processing conditions at the time of RFL processing, the number of twists of the polyethylene 2,6 naphthalate fiber cord, the fineness, the number of filaments, and the like.

In order to improve steering stability and riding comfort, it is also preferable that the number of filaments constituting the polyethylene 2,6 naphthalate fiber cord is 400 to 600, and if it is less than 400, If the filament per filament becomes too thick, the riding comfort tends to decrease, and if it exceeds 600 filaments, the filament becomes too thin and the steering stability tends to decrease.

From the viewpoint of rolling resistance, it is necessary to reduce the loss tangent (tan δ) of the carcass cord and to suppress the variation in the tire internal temperature range during running as much as possible. Therefore, in this embodiment, as the polyethylene 2,6 naphthalate fiber cord, 2
Loss tangent (tan δ) at 5 ° C is 0.06-0.09
The rate of change of the loss tangent (tan δ) between 25 ° C. and 70 ° C. is regulated to 20% or less, preferably 15% or less, and more preferably 10% or less.

This rate of change is also polyethylene 2,6.
The naphthalate fiber cord contains 90% or more of ethylene 2,6 naphthalate unit and 2 peaks of DSC.
80 ℃ or more, intrinsic viscosity 0.7 or more, birefringence 0.3
By setting it to 0 or more, it becomes possible to regulate within the above range. Further, it is possible that the rate of change can be controlled also by the processing conditions at the time of RFL processing, the number of twists of the polyethylene 2,6 naphthalate fiber cord, the fineness, the number of filaments, and the like.

Here, the initial modulus M is JI.
It means the slope at the origin in the "load-elongation" curve of the cord obtained in accordance with the chemical fiber tire cord test method of SL1017. The loss tangent (tan δ) and the dynamic elastic modulus (E *) of the cord were measured using a viscoelasticity measuring device manufactured by Iwamoto Manufacturing Co., Ltd. at a frequency (10 Hz) and an initial load (1000 g).
/ Code), sample length (30 mm), dynamic strain (0.01 m
It is the value measured in m).

In the carcass cord, from the viewpoint of tire dimensional stability, it is also preferable that the cord elongation at a load of 2.0 gf / d is in the range of 0.5 to 2.5%. However, the dimensional stability of the product tends to be impaired, which is disadvantageous to the uniformity.

Next, the belt layer 7 is composed of two or more high-strength belt cords, such as steel cords, which are inclinedly arranged at an angle of 10 ° to 35 ° with respect to the tire circumferential direction, as in a conventional tire. , Two belt plies 7A and 7B in this example
Formed from. The belt plies 7A and 7B are stacked in different directions so that the belt cords cross each other, thereby increasing the belt rigidity and increasing the tread portion 2
Reinforces almost the entire width of the product with a hoop effect. The ply width of the belt ply 7A on the inner side in the radial direction is formed wider than that of the outer belt ply 7B, and this ply width constitutes the belt width WB of the belt layer 7.

Further, in this example, a belt layer 9 is provided outside the belt layer 7 in order to suppress lifting of the belt layer 7 and enhance high-speed durability. The band layer 9 is formed by one or more, in this example, one band ply 9A formed by spirally winding a band cord at an angle of 5 degrees or less with respect to the tire circumferential direction.

In this example, the band ply 9A is illustrated as a so-called full band that covers substantially the entire width of the belt layer 7, but as a so-called edge band on both sides that covers only both ends of the belt layer 7. It can also be formed. Regarding the full band, “covering substantially the entire width” of the belt layer 7 means covering 95% or more of the belt width WB, and in this example, the width W of the band ply is the belt width WB.
The case is substantially equal to.

The band ply 9A is a tape-shaped band ply obtained by burying one band cord or a plurality of band cord aligners in a topping rubber, and the band ply is arranged along the tire circumferential direction. It is formed by spiral winding.

At this time, a polyethylene 2,6 naphthalate fiber cord having the same structure as the carcass cord can be used as the band cord. The same configuration means that the cord thickness, the number of twists, the initial modulus, the loss tangent, and the dynamic elastic modulus, and the change rate of the initial modulus, the loss tangent, and the dynamic elastic modulus between 25 ° C. and 70 ° C. Each of them is meant to be included within the above-mentioned range, and therefore, a code other than the code completely identical to the carcass code is also included.

When such a cord is adopted, the restraining force on the belt layer 7 is increased, and the hoop effect is improved. As a result, the circumferential rigidity of the tread portion 2 becomes large and uniform, and the vibration of the road surface during tire running is reduced. Since it is difficult to pick up, road noise is reduced.

Although a particularly preferred embodiment of the present invention has been described above in detail, the present invention is not limited to the illustrated embodiment and can be modified into various modes.

[0035]

EXAMPLES Tire size 195 having the structure shown in FIG.
A / 65R15 tire was prototyped based on the specifications in Table 1, and the test stability, riding comfort, rolling resistance, and road noise of each sample tire were tested, and the results are shown in Table 1.

The carcass is formed of one carcass ply having a cord angle (90 degrees) and a cord density (50 cords / 5 cm) using the carcass cords shown in Table 1, respectively. The belt layer consists of the number of plies (2), cord (steel; 1)
× 3 / 0.27), cord angle (+ 20 ° / −20 °), and cord density (40 cords / 5 cm) have the same specifications. In addition, the band layer is formed by a single band ply of a full band in which a band-shaped ply with a band cord having a width of 10 mm and a cord density (49 lines / 5 cm) is spirally wound. The same PEN code (1500d / 2) as the code is used, and other tires (including the comparative example) have nylon 66 code (12
60d / 2) is used.

(1) Steering stability: Test tires were mounted on all wheels of a passenger car (1800 cc) under an internal pressure (200 kPa), and a tire test on a dry asphalt road surface was conducted to check straightness, turning ability, etc. A sensory evaluation of the driver was performed on the characteristics, and a 10-point method with Comparative Example 1 as 5 points was evaluated. The larger the value, the better the steering stability.

(2) Riding comfort: Using the above-mentioned vehicle, a test course for evaluating riding comfort was run, and a sensory evaluation of the driver was performed with respect to lumpiness, push-up feeling, damping feeling, and the like, and Comparative Example 1 was given 5 points. It was evaluated by the 10-point method. The higher the value, the better the riding comfort.

(3) Rolling resistance: Using the above vehicle, after running for 30 minutes at a speed of 80 km / h, release the brake of the vehicle from 6 m on a slope with a slope of 10 ° and stop after running naturally. Measure the distance. The measurement result is 100 for Comparative Example 1.
The rolling resistance is smaller as the value is larger.

(4) Road noise: Using the above vehicle, a smooth road test course for road noise evaluation was run at a speed of 80 km / h, and a 250 Hz band of a 250 Hz band was used using a sound collecting microphone attached to the driver's seat. Noise level (d
B) was measured. The measurement results are shown as an index with Comparative Example 1 being 100, and the smaller the value, the lower the road noise and the better.

[0041]

[Table 1]

In the examples, it can be confirmed that the steering stability, the riding comfort and the rolling resistance are improved in a well-balanced manner.

[0043]

As described above, the pneumatic tire of the present invention uses polyethylene 2,6 naphthalate fiber cord as the carcass cord, and further, the cord thickness, the number of twists, the initial modulus, the loss tangent, and the initial modulus, Since the loss tangent and the rate of change of the dynamic elastic modulus in the temperature range of 25 ° C. to 70 ° C. are specified, the steering stability can be improved and the rolling resistance can be reduced while maintaining high riding comfort.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a tire showing an embodiment of the invention.

[Explanation of symbols]

2 tread section 3 Side wall part 4 bead section 5 bead core 6 carcass 6A carcass ply 7 Belt layer 7A, 7B Belt ply 9 band layers 9A band ply

Claims (4)

[Claims] 1. A carcass consisting of at least one carcass ply extending from a tread portion to a side wall portion to a bead core of a bead portion, and at least two carcass arranged inside the tread portion and radially outside the carcass. A pneumatic radial tire having a belt layer made of a belt ply according to claim 1, wherein the carcass ply has a cord thickness of 2500 to 360.
A polyethylene 2,6 naphthalate fiber cord having a twist number of 30 to 40 turns / 10 cm was used as a carcass cord, and the polyethylene 2,6 naphthalate fiber cord was 25
At 50 ° C., the initial modulus is 50 to 65 gf / d, the loss tangent (tan δ) is 0.06 to 0.09, the dynamic elastic modulus (E *) is 2800 N / code to 4000 N / code, and 25 ° C. to 70 ° C. Rate of change of initial modulus, loss tangent (tan δ), dynamic modulus of elasticity (E *)
Pneumatic radial tires characterized in that the rate of change is ± 20% or less. 2. The pneumatic radial tire according to claim 1, wherein the polyethylene 2,6 naphthalate fiber cord has a cord elongation of 0.5 to 2.5% at a load of 2.0 gf / d. . 3. The pneumatic radial tire according to claim 1, wherein the polyethylene 2,6 naphthalate fiber cord has a filament number of 400 to 600 filaments. 4. The tread portion has a band layer formed on the outside of the belt layer, the band cord including at least one band ply in which a band cord is spirally wound at an angle of 5 degrees or less with respect to a tire circumferential direction. The pneumatic radial tire according to any one of claims 1 to 3, wherein the band cord comprises the polyethylene 2,6 naphthalate fiber cord.