JPH0443806B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention provides an air-filled belt cover layer that has greatly improved durability of a belt cover layer made of aromatic polyamide fiber cords arranged on the outermost side of a plurality of steel cord belt layers. Regarding radial tires.

[Conventional technology]

In recent years, with the development of expressway networks and higher performance of passenger cars, the characteristics required for tires have become more sophisticated.
Diversification knows no bounds. for example,
HR tires that can run even faster than SR tires, and can run even faster than this.
There is a demand for VR tires and flat radial tires with even better handling stability. On the other hand, from the vehicle's perspective, radial tires are desirable because of their relationship with the tire house, allowing them to run at high speeds with the conventional aspect ratio, and also have excellent handling stability.

When pneumatic radial tires for passenger cars are driven at high speeds of 100 km/hr or more, the steel cord belt layer, which has a large mass, is lifted up at both ends in the width direction due to centrifugal force, which deteriorates steering stability. . In order to prevent this, it has been proposed that a belt cover layer made of nylon cord with a cord angle of substantially 0° with respect to the tire circumferential direction is placed on the outermost side of the steel cord belt layer to cover both ends thereof. has been done. This is because the nylon cord is heat-shrinkable, so it shrinks when heated during vulcanization, further enhancing the hoop effect and tightening the steel cord belt layer.

However, since nylon cord has a low modulus, when used in tires for ultra-high speed applications as mentioned above, it has a small force to suppress the rise of both ends of the steel cord belt layer during high-speed running. , it has become difficult to sufficiently improve steering stability.

In order to solve these problems, it is conceivable to use an aromatic polyamide fiber cord, which has a significantly higher modulus than a nylon cord, instead of a nylon cord. However, because aromatic polyamide fibers inherently have poor adhesion to coated rubber due to their polymer molecular structure, simply replacing them with conventional nylon cords will cause the aromatic polyamide fiber cords and coated rubber to separate. death,
Satisfactory durability could not be obtained. In particular, the splice part where both ends in the circumferential direction were overlapped was thickened in a step-like manner, so stress was concentrated and separation occurred at this splice part.

As a result of intensive study on measures to prevent the separation of aromatic polyamide fiber cords that have low adhesion to rubber, the present inventors determined that the direction of fiber orientation could be changed from the basic concept of deformation characteristics in composite material mechanics. On the other hand, we thought that it would be best to set the relationship in such a way that the rubber deformation would be the least likely to occur. That is,
In fiber-reinforced rubber composites (FRR) in which rubber is reinforced with fibers, the rubber hardly stretches (does not deform) in the longitudinal direction of the fibers, but the larger the angle to the longitudinal direction, the greater the deformation. , is well known to be largest in the orthogonal direction. Therefore, based on this basic idea, if the deformation of the cord rubber with respect to the aromatic polyamide fiber cord in the belt cover layer can be minimized, it is possible to make separation between the cord and the coat rubber less likely to occur. I thought. It was discovered that the direction of the fibers constituting the cord, that is, the twist angle, as well as the axial direction of the cord, are important factors in minimizing the deformation of the coated rubber.

By the way, aromatic polyamide fiber cords conventionally supplied from tire cord manufacturers to tire manufacturers have a specified twist angle of 27.3 degrees. Therefore, the above-mentioned separation problem has not been essentially solved.

[Purpose of the invention]

An object of the present invention is to provide a pneumatic radial tire that significantly improves tire durability by preventing separation at the splice portion of a belt cover layer made of aromatic polyamide fiber cords arranged on the outermost side of a steel cord belt layer. Our goal is to provide tires.

[Structure of the invention]

An object of the present invention is to provide a belt cover layer having a cord angle of approximately 0° with respect to the tire circumferential direction on the outermost side of a plurality of steel cord belt layers arranged on the tread portion side of the carcass layer. In a pneumatic radial tire spliced so that both ends are overlapped, the belt cover layer is composed of aromatic polyamide fiber cords, and the twist angle of the aromatic polyamide fiber cords is an acute angle with respect to the axis of the cords. Measured from the side
This can be achieved by setting the angle between 31.3° and 39.3°.

In this way, the twist angle measured from the acute angle side with respect to the axis of the aromatic polyamide fiber cord is 31.3°~
By setting the angle in the range of 39.3°, it is possible to minimize the deformation of the coated rubber against the aromatic polyamide fiber cord at the splice part of the belt cover layer, thereby dramatically improving the effect of preventing separation. can be improved.

This will be explained in more detail with reference to FIGS. 3 and 4.

As shown in FIG. 3, from the basic concept of deformation characteristics in FRR, the coat rubber 20 in the belt cover layer is hardly deformed in the axial direction of the cord 10 embedded in the coat rubber 20; The force F in the direction perpendicular to causes the largest deformation. Therefore, if the deformation of the cord rubber 20 in the direction perpendicular to the axial direction of the cord 10 can be suppressed as much as possible, the occurrence of separation can be reduced.

Therefore, based on the idea that the deformation characteristics of FRR are affected not only by the axial direction of the cord 10 itself, but also by the direction of the elementary fibers that make up the cord 10,
We investigated the deformation (shearing deformation) of the coated rubber when a constant force F was applied in the direction orthogonal to the belt cover layer composed of aromatic polyamide fiber cords with various twist angles θ. was found to change depending on the twist angle θ. This indicates that the direction of the elementary fibers constituting the cord 10 (that is, the twist angle θ) is greatly involved in suppressing the deformation of the coat rubber 20. According to the results of experiments with various cord diameters, it was found that this deformation control effect becomes minimum at a twist angle θ=35.3°, and gradually increases as the distance from this angle increases. That is, as shown in FIG. 4a, when the twist angle θ of the cord 10 is less than 31.3 degrees, the cord 10
In response to a force F in a direction perpendicular to the axis of
gradually increases until it reaches its minimum deformation at 35.3°, as shown in Figure 4b. Furthermore, when the twist angle θ of cord 10 is increased to exceed 39.3°, the result shown in Fig. 4c
As shown in FIG. 2, the coat rubber 20 is deformed (shear deformed) into a parallelogram tilted to the right as shown by the two-dot chain line. Therefore, by setting the twist angle θ of the cord 10 in the range of 31.3° to 39.3°, the deformation of the coat rubber 20 with respect to the aromatic polyamide fiber cord 10 of the splice S of the belt cover layer V can be controlled to an almost minimum state, and the splice portion The occurrence of separation can be prevented.

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1a is a partially cutaway perspective explanatory view of a pneumatic radial tire according to an embodiment of the present invention.

In the figure, E denotes a pneumatic radial tire according to an embodiment of the present invention, which includes a pair of left and right bead portions 1,
It is composed of a pair of left and right sidewall parts 2 connected to the beat part 1, and a tread part 3 located between the sidewall parts 2. Furthermore, a carcass layer 4 having a cord angle of substantially 90° with respect to the tire circumferential direction is installed between the bead wires 6 of the pair of left and right bead portions 1, and the carcass layer 4 in the tread portion 3 is , 2 consisting of an upper belt layer 5u and a lower belt layer 5d that intersect with each other at a cord angle of 10° to 35° with respect to the tire circumferential direction.
The steel cord belt layers 5 of the layers are arranged in a laminated manner. Further, on the outermost upper belt layer 5u of the steel cord belt layer 5, a belt cover layer V made of aromatic polyamide fiber cords with a cord angle of approximately 0° with respect to the tire circumferential direction is arranged around the entire tire circumference. has been done. Note that 7 is a bead filler.

The belt cover layer V is composed of an aromatic polyamide fiber cord 10 and a coat rubber 20 covering it, and as shown in FIG. A splice portion S is formed by overlapping them to have a width w.

The aromatic polyamide fiber cord 10 constituting this belt cover layer V has a tensile strength of 150
It is preferable to use a cord made of yarn having properties of Kg/mm ² or more and a tensile modulus of 3000 Kg/mm ² or more. This yarn was twisted according to a conventional method so that the twist angle θ measured from the acute angle side with respect to the axis of the cord was in the range of 31.3° to 39.3°, and then adhesive treatment was applied to the surface. make it what it is.

The number of aromatic polyamide fiber cords 10 implanted in this belt cover layer V is preferably in the range of 40 to 70 cords per 50 mm width, measured perpendicular to the cord direction. More preferably, the range is 45 to 65.

Furthermore, it is preferable to use a coating rubber 20 that covers the aromatic polyamide fiber cord 10 with a 100% modulus in the range of 30 Kg/cm ² to 70 Kg/cm ² . By setting the modulus of this coated rubber 20 to 30 kg/cm ² or more, the difference in modulus with the aromatic polyamide fiber cord is reduced, and the adhesion between the cord 10 and the coated rubber 20 is improved.
Tire durability can be improved. Also,
By keeping it below 70Kg/cm ² , it prevents it from becoming too hard and improves productivity during tire manufacturing.
Cost can be reduced.

〔Example〕

The use and test conditions of the pneumatic radial tire used in the present invention are as follows.

[Carcass layer]

(a) The cord angle with respect to the tire circumferential direction is substantially
Two layers arranged at 90° (b) The carcass cord is 1000d/2 polyester cord.

[Belt layer]

(a) The cord angle with respect to the tire circumferential direction is 20 degrees and the two layers are arranged so that they intersect with each other. (b) Cord 5s is steel cord 1 x 5 (0.22) (c) Perpendicular to the cord direction and per 50 mm The number of cords inserted is 40 (d) The 100% modulus of the coated rubber is 55Kg/cm ² .

[Belt cover layer]

(a) The cord angle to the tire circumferential direction is 0° (b) Cord 10 is an aromatic polyamide fiber cord of 1000d/2 (c) The number of cords inserted per 50 mm is 60 (measured perpendicular to the cord direction) ( d) The 100% modulus of coated rubber is 55Kg/cm ² .

(e) Aromatic polyamide fiber cord has a tensile strength of 150
Kg/mm ² or more, and a cord with a tensile modulus of 3000 Kg/mm ² or more is used.

In the pneumatic radial tire, the twist angle θ of the cords 10 of the belt cover layer V is 23.3°,
The angles of 27.3°, 31.3°, 35.3°, 39.3° and 43.3° were manufactured.

〔Test conditions〕

Rim: 5 1/2JJ×14 Air pressure: 1.9Kg/cm ² Drum diameter: 1707mm Speed: 80Kg/hr, initial load is 525Kg, load is increased to 50Kg every 2 hours
The tires were run in increments of Kg until breakage occurred on the surfaces of the tread, sidewall, etc. of the tire, and the distance traveled at that time was measured. The measurement results are expressed as an index when the measured value of a comparison tire with a cord twist angle θ of 27.3° is set as 100.

At the end of the test, the tire was cut open and it was confirmed whether or not peeling had occurred between the aromatic polyamide fiber cord at the bent portion of the belt layer and the coated rubber over the entire circumference of the tire.

The experimental results are shown in Figure 2.

Figure 2 is a diagram showing the relationship between the twist angle θ of the cords of the belt cover layer V and the tire durability. , the horizontal axis shows the twist angle θ of the cord.

From FIG. 2, it can be seen that the pneumatic radial tire of the present invention in which the aromatic polyamide fiber cords of the belt cover layer V have a twist angle θ in the range of 31.3° to 39.3° is the same as the comparative tire in which the twist angle θ of the cord 10 is 27.3. It can be seen that the tire durability can be significantly improved compared to the above. In particular, the twist angle θ of the cord is
The pneumatic radial tire of the present invention with an angle of 35.3° is
Tire durability is improved by 10% compared to the comparison tires above.

〔Effect of the invention〕

According to the present invention, for a belt cover layer made of aromatic polyamide fiber cords arranged on the outermost side of a plurality of steel cord belt layers, when the twist angle of the aromatic polyamide fiber cords is measured from the acute angle side with respect to the axis. , in the range of 31.3° to 39.3°, the deformation of the coated rubber against the aromatic polyamide fiber cord at the splice part of the belt cover layer is minimized, thereby dramatically improving the effect of preventing separation. can be improved.

[Brief explanation of drawings]

FIG. 1a is a partially cutaway explanatory perspective view showing an embodiment of the pneumatic radial tire of the present invention, FIG. 1b is a plan view of the splice portion S of the belt cover layer V of FIG. 1a, and FIG. The figure shows the relationship between the twist angle θ of the aromatic polyamide fiber cords constituting the belt cover layer and the durability of the tire. Figure 3 is a partially enlarged explanatory diagram of the belt cover layer. 3c is a diagram illustrating the deformation of the belt cover layer when a force F perpendicular to the axis of the aromatic polyamide fiber cord is applied. V...Belt cover layer, S...Splice part,
5u...Outermost (upper) belt layer, 10...Aromatic polyamide fiber cord, 20...Coat rubber.

Claims (1)

[Claims] 1 A belt cover layer with a cord angle of approximately 0° to the tire circumferential direction is spliced to the outermost side of the multiple steel cord belt layers arranged on the tread side of the carcass layer so that both ends of the belt cover layer in the circumferential direction overlap. In the pneumatic radial tire, the belt cover layer is composed of aromatic polyamide fiber cords, and the twist angle of the aromatic polyamide fiber cords is 31.3° to 31.3° as measured from the acute angle side with respect to the axis of the cords. Pneumatic radial tire with 39.3°.