JPH10278508A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a balance between the high-speed performance and comfortableness of riding by spirally winding a band-like ply provided with a compound cord, which is obtained by twisting aramid strand and nylon strand and of which dynamic elastic modulus is restricted in a specified range, in nearly parallel with a tire equator so as to form a band layer. SOLUTION: As a cord 9 of a band layer, a compound cord obtained by twisting an aramid strand 9A, which is formed by twisting an aramid filament, and a nylon strand 9B, which is formed by twisting a nylon filament, is used. This compound cord has a viscoelasticity characteristic that dynamic elastic modulus E* thereof per each one cord at 80 deg.C is 340 kgf or more and that dynamic elastic modulus E* per each one cord at 120 deg.C is 290 kgf or less. Since the dynamic elastic modulus E* in the high temperature condition is set low, this cord is soft in a practical traveling speed area corresponding to a low frequency, and comfortableness of riding is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire capable of achieving both high speed performance and ride comfort by regulating a dynamic elastic modulus E ^* of a cord used for a band layer.

[0002]

2. Description of the Related Art Conventionally, a jointless ply is formed by spirally winding a narrow band ply having a cord embedded in topping rubber so that the cord is substantially parallel to the tire equator. Pneumatic tires having the following band layer have been proposed. Particularly in motorcycle tires suitable for high-speed running, the band layer has a high penetration rate, and aramid cord is generally used as a material for the cord of the band layer.

Aramid cord has a high dynamic elastic modulus E ^* among the textile cords, and therefore has the advantage of being small in elongation even when a centrifugal force is applied during high-speed running and excellent in high-speed performance. However, there is a problem that the ride comfort of the vehicle is hardened.

The present invention has been devised in view of such a problem, and regulates the dynamic elastic modulus E ^* of a cord used for a jointless band layer, thereby achieving high speed performance and ride comfort. It is intended to provide a pneumatic tire capable of balancing the above.

[0005]

According to the first aspect of the present invention, an aramid strand and a nylon strand are twisted and have a dynamic elastic modulus E ^* per strand at 80 ° C. of 340 kgf or more and 120 ° C. A pneumatic tire having a band layer formed by spirally winding a belt-like ply in which one or more composite cords each having a dynamic elastic modulus E ^* per one of 290 kgf or less are spirally wound substantially parallel to the tire equator.

According to a second aspect of the present invention, there is provided the pneumatic tire according to the first aspect, wherein the band layer is formed on a radially outer side of a carcass and is a tire for a motorcycle.

Further, in the invention according to claim 3, the composite cord has a loss tangent (tan δ) at 100 ° C. of 0.08 to less than 0.08.
The pneumatic tire according to claim 1 or 2, wherein the value is 0.09, which is smaller than the aramid cord.

Further, in the invention according to claim 4, the composite cord preferably has a twist of 20 t / 10 cm or less, and the aramid strand has a positive fineness of 1670 dtex or less and a twist of 20 or less.
The pneumatic tire according to claim 1, 2 or 3, wherein the diameter is set to t / 10 cm or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking a pneumatic radial tire for a motorcycle as an example. As shown in FIG. 1, in the pneumatic radial tire for a motorcycle according to the present embodiment, the tread width TW, which is the width in the tire axial direction between the outer ends E of the tread portion 2, forms the tire maximum width, and 2 has an outer surface which is convexly curved outward, and a tread portion 2 to a sidewall portion 3
And a carcass 6 locked by the bead core 5 of the bead portion 4 through the band, and a band layer 7 formed on the outside in the radial direction of the carcass.

The carcass 6 has a cord connected to the tire equator C.
One or more radial structures arranged at an angle of 75 ° to 90 ° with respect to the carcass ply 6A in this example are exemplified. Although the carcass 6 employs a nylon cord in the present embodiment, an organic fiber cord such as polyester or rayon may be employed as appropriate.

The band layer 7 is disposed radially outward of the carcass 6, and is formed over substantially the entire tread width TW in this embodiment. The band layer 7 has, for example, a small width in which one or more cords 9 are aligned in the topping rubber G in parallel with the longitudinal direction, for example, 3 to 15 as shown in FIG.
A belt-shaped ply P having a width of mm is spirally wound so that the tire cord 9 is substantially parallel to the equator C, and has a single-layer structure in which the number of cords per 5 cm is about 50, for example. An example is shown.

[0012] Further, as shown in FIG.
A single cord 9 covered with a topping rubber G and having a circular cross section may be used. In this embodiment, there is no cross belt in which two layers of plies are overlapped so that the so-called cords cross.

Since such a band layer 7 has no seams in the tire circumferential direction, the uniformity of the tire is improved, so that the vibration at the time of high-speed running is small. Therefore, the band layer 7 can be preferably used particularly for a motorcycle tire.

In the present invention, as shown in FIGS. 2 and 3, the cord 9 of the band layer 7 is formed by twisting an aramid strand 9A in which an aramid filament is twisted and a nylon strand 9B in which a nylon filament is twisted. The combined code is combined. The composite cord of this example illustrates one formed by twisting one aramid strand and one nylon strand.

[0015] Then, the composite code is heated at 80 ° C.
Dynamic elastic modulus E per cord ^*(Hereinafter E^*(8
0 ° C) is 340 kgf or more and 120 ° C
Dynamic modulus E per cord^*(Hereinafter E
^*(Referred to as 120 ° C) is less than 290kgf
It is characterized by having.

FIG. 4 shows the viscoelastic properties of typical textile cords for tires.
The vertical axis represents the log (E ^* ) of the dynamic elastic modulus (kgf / code). As is clear from the figure,
The aramid cord conventionally used for the band layer has a high elasticity and a substantially constant dynamic elastic modulus E ^* regardless of the temperature change, compared to other rayon, nylon, vinylon, etc. textile cords. .

Further, from the graph of FIG.
Is the dynamic elasticity per cord at 80 ° C.
Rate E^*Is about 340 kgf, dynamic elasticity at 120 ° C
Rate E ^*Is about 350 kgf.
^*Is high.

In the present invention, E of the composite code of the band layer 7 is used.
^* (80 ° C.) is limited to 340 kgf / cord or more because, when E ^* (80 ° C.) is less than 340 kgf / cord, the band layer 7 is not used at high speed running when the tire internal temperature becomes about 80 ° C. This is because the tightening force of the tread portion 2 is reduced, and the high speed performance is reduced as compared with the conventional tire. Therefore, E ^* (80 ° C.) is 34
Ensuring a sufficient tightening force on the tread portion 2 at 0 kgf / cord or more, more preferably 345 kgf / cord or more, even more preferably 350 kgf / cord or more is desirable from the viewpoint of further improving the high speed performance. The upper limit of E ^* (80 ° C.) can be, for example, 380 kgf / cord.

The aramid cord used in the conventional band layer has a dynamic modulus of elasticity E ^* per cord at 120 ° C. of about 350 kgf, whereas the composite cord of the present invention has an E ^* (120 ° C.) Must be set to 290 kgf / code or less. This is because changing the frequency has the same effect as changing the temperature of the substance, based on the temperature conversion rule of Ferry et al. Observing the viscoelastic properties of the cord at low frequencies, It is supported by the theory that it is equal to the characteristic.

That is, when the dynamic elastic modulus E ^* of the cord at a high temperature is small, the cord is soft in a practical traveling speed range corresponding to a low frequency (for example, a speed of about 50 km / h), and good ride comfort can be obtained. It will be. Thus, for example, the condition for constant traveling at a speed of 50 km / h is determined by a temperature conversion rule of about 120 ° C. according to the WLF equation of the temperature conversion rule (for example, Shin-ichi Tanaya, “Easy Rheological Engineering” published by the Industrial Research Institute, pages 73 to 80). It has been found as a result of analysis that this applies. Under these circumstances, as a result of various experiments, in the present invention, E
^* The upper limit of (120 ° C) is set to 290 kgf / cord, which is lower than conventional aramid.

Preferably, E ^* (1
20 ° C) is 290 kgf / cord or less, more preferably 2 kgf / cord.
85 kgf / cord or less, more preferably 280 kgf /
It is desirable to be less than the code. Note that the composite code E
^* The lower limit of (120 ° C.) can be, for example, 250 kgf / cord.

In this embodiment, the composite code is
The loss tangent (tan δ) at 100 ° C. is 0.08-0.
09 is illustrated. FIG. 5 is a graph showing temperature (° C.) on the horizontal axis and log (tan δ) of loss tangent on the vertical axis as viscoelastic properties of typical textile cords for tires.

As is apparent from the figure, the composite cord of the present embodiment at 100 ° C. is smaller than the loss tangent of the aramid cord. Therefore, the hysteresis loss of the cord of the band layer 7 can be made smaller than before in the actual use temperature range of the tire, which is preferable in that the rolling resistance of the pneumatic tire can be reduced.

The viscoelastic properties were measured by using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd.
g / code, frequency 10 Hz, dynamic strain ± 0.03%,
In a temperature range of 10 ° C. to 150 ° C. at a temperature rising rate of 2 ° C./min, a dynamic elastic modulus E ^* per cord (kg)
f / code] and the loss tangent tan δ.

In the composite cord, when the aramid strand 9A is too thin, the dynamic elastic modulus is reduced and high speed performance is reduced.
It tends to make the ride harder. Preferably, the aramid strand 9A has a positive fineness of about 1670 dtex, and more preferably a thickness of 1670 dtex or less. Note that various types of nylon strands 9B can be adopted. In this example, a nylon strand 9B having a thickness of 940 dtex is used.

As the composite cord, it is conceivable that another textile strand, for example, vinylon, can be used in place of the nylon strand.
It tends to be difficult to set E ^* (120 ° C.) to 290 kgf / cord or less.

Further, in the present embodiment, it is preferable to use a low twist yarn having a lower twist of 20 t / 10 cm or less in the aramid strand 9A in the present embodiment. If the ply twist of the aramid strand is more than 20 t / 10 cm, the dynamic elastic modulus tends to be small, and the high speed performance may be reduced. Preferably, the number of twists of the aramid strand is 5 to 20/10 cm.

The number of ply twists of the nylon strand 9B does not need to be a low twist yarn such as the aramid strand 9A, but can be ply twisted at, for example, about 30 to 60/10 cm, and is 50 t / 10 cm in this example.

When the composite cord is bundled into a single strand and then twisted, it is preferable that the strand length be 20 t / 10 cm or less. When the number of twists exceeds 20 times per 10 cm, the dynamic elastic modulus of the composite cord tends to decrease. Particularly, at a temperature of 80 ° C., E ^* (80 ° C.)
Tends to be difficult to set to 340 kgf or more. Preferably, the number of twists is set to 5 to 20/10 cm.

In the viscoelastic properties of the composite cord, E ^* (80 ° C.) is 350 kgf or more and E ^* (12
(0 ° C.) of 280 kgf or less can be expected to improve high speed performance and ride comfort. As described above, since the cord of the band layer has viscoelastic properties that cannot be achieved by the conventional aramid cord, a pneumatic tire capable of improving ride comfort while maintaining or improving high-speed performance, particularly for motorcycles. Pneumatic tire is obtained.

The band layer 7 can also be used for a tire for a four-wheeled vehicle such as a passenger car. At this time, the band layer 7 is disposed radially outside a belt layer having a cord inclined at 15 to 35 degrees with respect to the tire circumferential direction. sell.

[0032]

EXAMPLES A pneumatic tire for a motorcycle having a tire size of 190/50 ZR17 and shown in Table 1 was prototyped (Examples, Conventional Examples, Comparative Examples 1 to 5), and a domestic motorcycle (displacement: 900 cc). The standard tires were mounted on the front wheels and the test tires were mounted on the rear wheels. Handling, stability, and riding comfort were absolutely evaluated by the 5-point method based on the driver's feeling, and the performance was compared.

A high-speed test was conducted in which the test tire was run on the drum at the same speed for 10 minutes under the conditions of a load of 178 kgf and an internal pressure of 290 kPa, and the speed was stepped up by 10 km / H to 270 km / H. Was. Passed the finish and rejected the one that burst in the middle.

Further, the test tire was tested on a rolling resistance tester manufactured by Kobe Machinery Co., Ltd., with a load of 365 kgf and an internal pressure of 290 kPa.
The vehicle was run at a speed of 80 km / H, and the rolling resistance was measured. Table 1 shows the test results.

[0035]

[Table 1]

As a result of the test, it was confirmed that the tires of the examples greatly improved the riding comfort while maintaining the high speed performance as compared with those of the conventional example and the comparative example. Also, it was confirmed that the durability was sufficiently satisfactory.

[0037]

As described above, according to the first aspect of the present invention,
By using a composite cord having a viscoelastic property, which cannot be realized by a conventional cord for a tire, as a cord of a band layer, it is possible to improve riding comfort performance while maintaining high speed performance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a motorcycle tire showing one embodiment of the present invention.

FIG. 2 is a perspective view of a belt-like ply.

FIG. 3 is a perspective view showing another embodiment of the belt-like ply.

FIG. 4 is a graph showing viscoelastic properties.

FIG. 5 is a graph showing viscoelastic properties.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Band layer P Band ply

Claims (4)

[Claims] An aramid strand and a nylon strand are twisted and have a dynamic elastic modulus E ^* per strand at 80 ° C of 340 kgf or more and a dynamic elastic modulus E ^* per strand at 120 ° C of 290 kgf or less. A pneumatic tire having a band layer formed by spirally winding a belt-like ply in which one or more composite cords are arranged substantially parallel to the tire equator. 2. The pneumatic tire according to claim 1, wherein the band layer is formed on a radially outer side of a carcass and is a tire for a motorcycle. 3. The composite cord according to claim 1, wherein a loss tangent (tan δ) at 100 ° C. is 0.08 to 0.09, which is smaller than that of the aramid cord. Pneumatic tire. 4. The composite cord has a twist of 20 t / 10.
cm or less, and the aramid strand has a positive fineness of 16
The pneumatic tire according to claim 1, 2 or 3, wherein the primary twist is 20 t / 10 cm or less at 70 dtex or less.