JPH07156606A - Radial tire for passenger car - Google Patents

Abstract

PURPOSE:To provide a passenger car with a radial tire, which is a sort of a radial tire equipped with a cap ply over the outer surface of a belt, is excel lent in tire uniformity, concurrently in productivity, and ensure durability at high speed, which is identical to that of a former tire. CONSTITUTION:This invention is concerned with a radial tire for an automobile, where a great number of organic fiber cords covered with rubber are lined up in parallel in the circumferential direction of the tire over the outer surface of steel belts disposed in the outer side in the radial direction of the crown equivalent section of a carcass, and comprise both the ends of the cords mutually joined together while being formed into a cap ply. As an organic fiber cord, a nylon cord is used, the dimension stability index defined as the sum of the values of elongation (%) and dry heat shrinkage factor (5) at 2.7g/d loading of which is less than 10.5, and the shrinking force of the cord per 25mm wide in cap ply width shall be less than 10.0Kgf.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for passenger cars. More specifically, the reinforcing cord of a cap ply arranged on the outer surface of a steel belt is made of a specific nylon cord having good dimensional stability. The present invention relates to a radial tire for passenger cars which is excellent and has excellent high-speed durability.

[0002]

2. Description of the Related Art A tire mounted on a high-speed vehicle produces a large centrifugal force during traveling, and particularly, a centrifugal force generated on a tread portion and a belt portion of a radial tire having a steel belt is large. Since both ends of the steel belt in the width direction are not constrained at the ends of the steel cord, both ends of the steel belt in the width direction are floated outward in the radial direction when a centrifugal force is applied, which causes belt separation.

Therefore, in order to prevent such a phenomenon,
Conventionally, as a belt reinforcing layer, at least one cap ply formed by arranging a large number of rubber-coated heat-shrinkable organic fiber cords in the tire circumferential direction has been arranged and laminated on the outside of the belt. To form a cap ply on the outer surface of the belt, attach a sheet-like band made by cutting the rubber-topped weave woven tire cord on the front and back sides to a specified length and width on the belt layer. Either a method of polymerizing and joining each other or a method of spirally winding a tape manufactured by rubberizing a plurality of cords arranged in parallel along the tire circumferential direction on the outer surface of the belt is adopted.

However, in the so-called sheet-attaching method for attaching the band to the outer surface of the belt, the both ends thereof are usually overlapped and joined to each other, so that a lap joint consisting of two layers is formed over the entire width. Inevitably, if the reinforcing cord of the cap ply is composed of nylon cords that have large heat shrinkage as in the conventional case, the cord will shrink from the above two layers as the cord shrinks during vulcanization. The outer diameter of the lap joint is smaller than that of other parts, and a tire with good uniformity cannot be obtained. On the other hand, the method of spirally winding the tape on the belt does not produce a lap joint, but requires a special device for manufacturing the tape and spirally winding the tape, and
Since it takes a long time to spirally wind, the productivity of the molding process is low.

Japanese Patent Publication No. 1-15403 proposes a method of improving the uniformity of a radial tire by using a low shrinkage nylon cord as a reinforcing cord of a cap ply formed by attaching a sheet. However, the dry heat shrinkage of the nylon cord used is low,
As a result, the hoop effect of the cap ply on the belt is insufficient, belt separation is likely to occur during running, and there is still room for improvement in high-speed durability of the tire.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a purpose thereof is to provide a tire using an organic fiber cord as a reinforcing cord of a cap ply on a steel belt. The tire uniformity is good and at the same time excellent in productivity,
Another object of the present invention is to provide a radial tire for passenger cars, which has good high-speed running performance.

[0007]

[Means for Solving the Problems] However, as a result of earnest research to achieve the above-mentioned object, a sheet-like band made by cutting a blind-weave tire cord after topping is attached to a belt and a cap ply is attached. It was found that the initial purpose can be achieved by using a nylon cord having low heat shrinkability and good dimensional stability in specifying the shape and specifying the dry heat shrinkage force per unit width of the cap ply. At the outset, the present invention was completed.

That is, according to the present invention, the outer surface of the steel belt arranged radially outside the carcass equivalent to the crown portion,
A radial tire for passenger cars, in which a large number of rubber-coated organic fiber cords are arranged in parallel in the tire circumferential direction and both ends thereof are joined to each other to form a cap ply, and the above-mentioned organic fiber cords have a 2.7 g / d load. Elongation at time
(%) And dry heat shrinkage (%) are defined as the sum of each value, and a nylon cord with a dimensional stability index of 10.5 or less is used to measure the dry heat shrinkage force of the cord per 25 mm width of the cap ply.
The gist of the invention is a radial tire for passenger cars, which is characterized by having a weight of 10.0 kgf or more.

The nylon cord that can be used in the present invention is not particularly limited as long as the dimensional stability index of the treated cord satisfies the above requirements, but a modified nylon 66 cord obtained by the following method is used. Particularly preferred. That is, a 1% solution of a nylon sample in which sulfuric acid having a concentration of 98% was used as a solvent was measured at 25 ° C. using an Ostwald viscometer.
The time (seconds) required to flow down under the constant temperature of is measured, and the flow time (second) of 98% sulfuric acid (solvent) at the same temperature is measured.
With a relative viscosity of 2.5 or higher,
And the yarn was spun at a high speed while stretching so that the birefringence Δn immediately after spinning measured using a polarization microscope with a compensator was in the range of 20 to 40 × 10 ^-3 , and twisted to a predetermined twist coefficient. Then, it can be obtained by RFL adhesive treatment and hot stretching according to a conventional method.

When the relative viscosity is less than 2.5, the dimensional stability index becomes 10.5 or less under conditions other than the above spinning conditions, but sufficient strength to withstand high-speed spinning cannot be obtained, which is not preferable. Also,
If the birefringence Δn is out of the range of 20 to 40 × 10 ^-3 , the physical properties such as dimensional stability and fatigue resistance of the treated cord will be impaired.

The dimensional stability index of the nylon cord in the present invention is the elongation (%) at 2.7 g / d load, which is obtained from the load / elongation curve of the above treated cord, and the same treated cord at 150 ° C. No tension 3 in the dryer held
After heating for 0 minutes, the shrinkage amount is measured, and it is defined as the sum of each numerical value with the dry heat shrinkage ratio (%) expressed as a ratio to the original length. Generally, the elongation at 2.7 g / d load and the dry heat shrinkage ratio are in a trade-off relationship, and the dry heat shrinkage ratio increases even if the elongation at 2.7 g / d load is decreased depending on the heat treatment conditions. , The dimensional stability index obtained as the sum of the two hardly changes. In the present invention, a specific nylon cord having a dimensional stability index of 10.5 is used.

A comparison of the material characteristics and the treated cord characteristics of the modified nylon 66 cord and the commercially available general nylon 66 cord is shown in Table 1.
The dimensional stability index of the modified nylon 66 cord is as small as 10.5 or less, and the tire uniformity when it is used in a tire is improved and excellent as shown in FIG. However, the dry heat shrinkage force per cord is 20% or more lower than that of general nylon 66 cord, and in the cap ply made of such cord, the hoop effect on the belt becomes poor and the belt separation is reduced. There is a problem that the high-speed durability is deteriorated due to easy occurrence.

Therefore, in the present invention, the dry heat shrinkage force of the cord per unit width of 25 mm of the cap ply is set to 10 kgf.
As described above, the above problems have been overcome. That is, since the dry heat shrinkage force of the current tires using general nylon 66 cords is set to around 10.5 kgf, setting the dry heat shrinkage force to 10.0 kgf or more will increase the high-speed durability of the current tires. Based on the above, a tire having a performance at least equal to or higher than this is obtained. A proportional relationship as shown in FIG. 2 is seen between the dry heat shrinkage force per unit width of the cap ply and the high speed durability of the tire, and the higher the dry heat shrinkage force, the better the high speed durability.

That is, the radial tire for passenger cars of the present invention uses a nylon cord having a dimensional stability index of 10.5 or less in order to achieve both the tire uniformity and the improvement in high-speed durability, and at the same time, the unit width of the cap ply is The dry heat shrinkage force of the cord is set to 10.0 kgf or more, which is equal to or more than that of the current tire.

[0015]

[Function] Since the organic fiber cords forming the cap ply are made of nylon cords having low heat shrinkability and good dimensional stability, uneven tires due to the contraction of cords during vulcanization found in conventional cords are used. The phenomenon that the outer diameter of the tire becomes smaller at the lap joint portion when the sheet is stuck, especially when the sheet is pasted, is effectively alleviated, and the tire uniformity is improved. Also, the dry heat shrinkage force per unit width of the cap ply is set to be equal to or more than the dry heat shrinkage force of the conventional cap ply made of heat shrinkable nylon, so high speed running due to the low heat shrinkability of the cord is set. The lack of the taga effect against the centrifugal force at the time is solved,
Good high speed durability is ensured.

[0016]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Table 1 shows the characteristics of the tire cord made of the low-shrinkage nylon 66 fiber used in the present invention in comparison with the characteristics of the tire cord made of the commercially available conventional nylon 66 fiber.

The low shrinkage nylon 66 cords (Sample Nos. 1 and 2) according to the present invention shown in Table 1 were produced by spinning molten nylon 66 having a relative viscosity of 3.18 and having a birefringence of 28 × immediately after spinning. It is obtained by hot drawing to 10 ⁻³ , twisting the obtained yarn with a predetermined twist coefficient, and then subjecting it to RFL adhesive treatment and hot drawing by a conventional method. These cord characteristics are comparable to those of the conventional nylon 66 cord (sample No.
The dimensional stability index is less than 10.5, which is better than that of Nos. 3 to 5). However, the dry heat shrinkage force per cord is reduced by 20% or more.

[0018]

[Table 1]

FIG. 1 shows the dimensional stability indexes of the nylon 66 cords shown in Table 1 and the cords made of these cords and cut into a predetermined size to form a band, which is attached to the outer surface of the steel belt. It is the graph which showed the relation with the radial force variation (RFV) of the tire which formed the cap ply which consisted of one layer. The tire size is 195 / 60R14 85V, the cap ply has a cord structure of 1260 d / 2, and one of the above bands consisting of 25E / 25mm of striking cords is attached to the sheet so that the cord angle is 0 °, and both ends are spliced together. And then joined. As is clear from the figure, when a low shrinkage nylon cord having a dimensional stability index of 10.5 or less is used, the RFV is small and a tire with good tire uniformity can be obtained.

Nylon 6 shown in Table 1 and FIG. 1 above
The characteristics and the tire uniformity (RFV) of the treated cord composed of 6 fibers are obtained by the following methods. Elongation at 2.7 g / d load; For example, in the case of 1260 d / 2 cord, 2.7 × (1260 × 2) = 6.8 kg, that is, at 6.8 kgf load on the stress strain curve according to JIS L-1017 method. This is the value obtained as the elongation (%). Dry heat shrinkage; JIS L-1017 required condition (150 ± 3
It is the shrinkage rate (%) upon heating at ℃ × 30 minutes. Dimensional stability index; displayed as the sum (absolute value) of dry heat shrinkage (%) of treated cord at 150 ° C for 30 minutes and elongation (%) at 2.7 g / d It is a value. Dry heat shrinkage force: Dry heat shrinkage force measured in JIS L-1017 in an atmosphere of 150 ° C. Tire Uniformity: The tire tire radial direction force variation (RFV, unit: kg) was measured according to the Japan Automotive Standards (JASO) uniformity test JASO C607-74, and the control tire (Sample No. No. 3
The tire is provided with an RFV value of 100), which has a cap lie made of a cord having a dimensional stability index of 11.0, and is expressed as an index. The smaller the value, the better.

Table 2 is a radial tire constructed in the same manner as above using the low shrinkage nylon 66 cord shown in sample No. 1 of Table 1, and by changing the number of driving, the unit width of the cap ply is 25 mm. It is a result of making a radial tire having different dry heat shrinkage force and testing the high speed durability of the tire. The tire of the reference example is a control tire for evaluating high-speed durability performance,
The cap ply of this tire is made of the conventional nylon 66 cord shown in sample No. 4 of Table 1.

[0022]

[Table 2]

The high-speed durability of these prototype tires was determined by running the drum under the step speed conditions specified in the European Economic Commission standard ECER30, and after running for a predetermined time to pass the safety standard, the tires were continuously run under the same conditions. It was evaluated by measuring the time until failure. In addition,
The values shown in this table are indexed with the tire of the reference example (conventional tire) as 100, and the larger the value, the better. FIG. 3 is a graph showing the relationship between the high speed durability of these tires and the dry heat shrinkage force of the cap ply.

As can be seen from Table 2 and FIG. 2, the higher the dry heat shrinkage force per 25 mm width of the cap ply, the better the high-speed durability of the tire, and particularly the value of 10.0 kgf or more. In the tire of No. 4, high speed durability equal to or higher than that of the conventional tire given as the reference example can be obtained. For the tires of Comparative Examples No. 1 to No. 3, the number of cords to be driven was small and the dry heat shrinkage force per 25 mm width of the cap ply did not reach 10.0 kgf, and the hoop effect on the steel belt was insufficient. As a result, belt separation is induced and high-speed durability is reduced.

In each of the above examples, a 1260 d / 2 cord is used to form a one-layer cap ply, but it is also possible to use other cord structures, for example, 840 d / 2. However, in this case, in order to set the dry heat shrinkage force of the cap ply to 10.0 kgf or more, there is a limit to the upper limit of the number of driving, so it is necessary to attach two bands. In such a configuration, the lap joint portion of the cap ply is 2 on the tire circumference.
Since it is formed in several places, it can be said that it is a very unfavorable choice for improving the tire uniformity.

[0026]

As can be seen from the above results, in the present invention, a nylon cord having low heat shrinkability and good dimensional stability is used as the cord of the cap ply arranged on the outer surface of the steel belt, and the sheet is used. The dry heat shrinkage force per unit width of the cap ply formed by pasting is 10.0 k
Since the tire is configured to be set to gf or more, a radial tire for passenger cars is provided that has good tire uniformity, excellent productivity, and high-speed durability comparable to that of current tires.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between dimensional stability of a nylon cord constituting a cap ply and tire uniformity.

FIG. 2 is a graph showing the relationship between the dry heat shrinkage force per unit width of the cap ply and the high speed durability of the tire.

Claims (1)

[Claims] 1. A cap in which a large number of organic fiber cords coated with rubber are arranged in parallel in the tire circumferential direction on the outer surface of a steel belt arranged radially outside a portion corresponding to the crown of a carcass, and both ends thereof are mutually joined. In a passenger car radial tire formed with ply, the above-mentioned organic fiber cord has an elongation (%) at a load of 2.7 g / d and a dry heat shrinkage ratio.
The dimensional stability index, defined as the sum of the numerical values of (%), is 1
A radial tire for passenger cars, characterized by using a nylon cord of 0.5 or less and having a dry heat shrinkage force of 10.0 kgf or more per 25 mm width of the cap ply.