JPH07117406A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PURPOSE:To provide a pneumatic radial tire for heavy loads, having high impact resistance even when no highly ductile wire is used in its outermost belt layer, having improved rust resistance, and restraining the separation of its belt edge. CONSTITUTION:A pneumatic radial tire has steel cords 1 used at least in its second and third belt layers as counted from its carcass layer, the steel cords of 1X6 construction each having a diameter of 0.25 to 0 40mm and a tensile strength of 290Kgf/mm<2> or more, with the ratio of the major to minor axes of each steel cord 1 on its cross section perpendicular to its longitudinal direction being in the range of 1.2 to 2.0, and the elongation of each cord under a load of 5Kgf being 0.30 to 0.85%.

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 for heavy loads such as trucks and buses, and more particularly to a heavy load capable of obtaining high impact resistance even when a high elongation wire is not used for the outermost belt layer. The present invention relates to a heavy duty pneumatic radial tire.

[0002]

2. Description of the Related Art A heavy-duty pneumatic radial tire is usually constructed by arranging a belt layer made of a plurality of steel cords on a carcass layer so as to bear a strong impact and a load received while the tire is running. In particular, the tread of a pneumatic radial tire for heavy loads is subjected to a remarkably large impact force, so that damage such as cut scratches is likely to occur. When such damage occurs, external moisture permeates inside through the damage, reaches the belt layer, and contacts the steel cord.
For this reason, the steel cord easily rusts and corrodes,
There has been a problem that the adhesive force between the cord and the rubber is deteriorated, separation of the tread and the belt layer occurs, and the durability of the tire is reduced.

Steel cords conventionally used for the belt layer of such a pneumatic radial tire for heavy loads include, for example, six relatively thick steel wire strands and three relatively thin strands. A cord having a so-called 3 + 6 cord structure, which is twisted so as to surround the circumference of the cord, is generally used. However, the cord having such a structure is poor in impact resistance and rust resistance, and it is particularly necessary to impart impact resistance. In some cases, a structure in which the wire of the outermost layer (usually the No. 4 belt) is replaced with a high elongation wire such as 4 × 4 or 1 × 5 is used.

However, such a belt structure is
Due to the twist structure of the high elongation wire, the strength sharing ratio is extremely low,
In order to satisfy the strength required for the belt layers, it is necessary to increase the number of inner layer belt layers to be driven in, to increase the diameter of the wire strands, and to make the structure with a larger number of wire strands. There is also a drawback that the weight is increased, and that the tire cost is increased because the amount of wire used is increased and the high elongation wire is expensive.

[0005]

Therefore, the present invention solves the above-mentioned problems of the prior art, and has high impact resistance and rust resistance even when a high elongation wire is not used for the outermost belt layer. It is an object of the present invention to provide a heavy-duty pneumatic radial tire in which the belt edge separation is suppressed and the belt edge separation is suppressed.

[0006]

According to the present invention, the wire diameter is 0.25 to 0.40 mm, and the tensile strength of the wire is 290 kg.
In the steel cord of 1 × 6 structure of f / mm ² or more, the ratio of the major axis to the minor axis of the cord in the steel cord cross section orthogonal to the steel cord longitudinal direction is in the range of 1.2 to 2.0, and Elongation under load of 5 Kgf is 0.30
There is provided a pneumatic radial tire which is used for at least the second and third belt layers by counting a code of 0.85% from the carcass layer side.

[0007] If the impact resistance of the entire belt layer can be improved while satisfying the strength and rust resistance required for the belt cord, the need for high elongation wire is eliminated and the above-mentioned drawbacks can be improved. The present inventor has found a cord structure which is improved in the 3 + 6 structure, which is often used as a tire for trucks and buses, and which is provided with rust resistance and greatly improved impact resistance while ensuring strength performance. We have found a tire structure that can greatly improve the impact resistance of truck and bus tires.

According to the research by the present inventors, 3 + 6 1 ×
It was found that the portion 3 had a small impact resistance. That is, in order to improve impact resistance with the same strength, 3 + 6 of 1 × 3
It has been found that the impact resistance is improved by removing 6 and increasing the diameters of the 6 outer wires to supplement the strength of 1 × 3. Furthermore, 1 × 6 has a flat open cord structure, and the flatness and elongation under load of 5 Kgf are within a specific range so that rubber is evenly inserted inside the cord and the tensile strength of the wire is 290 Kg.
It was found that increasing the f / mm ² or more significantly improved the impact resistance with respect to the 3 + 6 cord structure.

The present inventors have used the conventional 3 + 6 cord structure when this 1 × 6 cord structure is used for at least the second and third belt layers (2B and 3B) counted from the carcass layer side. It was found that the impact resistance was greatly improved as compared with. More preferably, in a 1 × 6 flat open cord structure in which Charpy impact absorption amount / cutting load is 0.28d + 0.05 (where d is the wire diameter) or more as an index of impact resistance per unit strength of the cord, This improvement effect is further increased, and the same impact resistance as that using the high elongation wire in the No. 4 belt layer (4B) can be obtained.

The belt layer of the tire is immediately below the tread layer, and when the tire tread is damaged, water will intrude from it, and thus it easily rusts. In order to prevent this, it is effective to use a cord having a good rubber penetration, but the 1 × 6 flat open cord structure is also optimal as a belt cord in this respect.

In the present invention, the limitation to the 1 × 6 cord structure is that, as an alternative to the 3 + 6 cord structure, the 1 × 5 cord structure lacks strength, and the 1 × 7 or more cord structure has a bare wire. The cord structure must be 1x6 because it tends to fall into the center of the cord and the twisting becomes unstable. With a 1 × 6 cord structure, the required strength cannot be ensured if the wire diameter is less than 0.25 mm, and the fatigue resistance decreases if the wire diameter exceeds 0.40 mm. ．
Must be 40 mm.

If the flatness of the cord (that is, the ratio of the major diameter to the minor diameter of the cord in the steel cord cross section orthogonal to the longitudinal direction of the steel cord) is less than 1.2, thick and thin portions are periodic in the cord diameter in the longitudinal direction of the cord. Therefore, the flatness must be 1.2 to 2.0 because if the flatness exceeds 2.0, the flatness becomes excessively flat and the fatigue also lowers. Preferably, the oblateness is preferably 1.3 or more. If the elongation of the cord under a load of 5 Kgf is less than 0.30%, it is difficult to put rubber evenly inside the cord. On the other hand, if it exceeds 0.85%, the filaments are likely to become completely dispersed and compression occurs. When it is received, the strain becomes non-uniform and the fatigue durability decreases, which is not preferable.

In the 1 × 6 flat cord structure of the present invention, the flatness of the cord is 1.2 to 2.0, and therefore the major diameter and the minor diameter are different. As shown in FIG. 1, when the flat steel cord 1 is arranged so that the major axis direction (see the dashed line in the figure) matches the width direction of the belt 2 as shown in FIG.
In some cases, the cord interval t becomes small and belt edge separation is likely to occur. Therefore, as shown in FIG.
When the cord 1 in the belt 2 is dispersed in the major axis direction (see the one-dot chain line in the figure) appropriately, the strain at the major axis end is alleviated, and the belt edge separation is effectively suppressed.
In order to meet this purpose, the angle formed by the major axis direction of the cord 1 and the belt width direction in the belt 2 is dispersed by 10 ° or more as an average of absolute values (meaning clockwise or counterclockwise). Is effective.

In order to obtain strength equivalent to that of the 3 + 6 cord structure in the 1 × 6 cord structure, it is necessary to thicken the wire diameter. However, if the wire diameter is made too thick, the cord weight increases. The tensile strength of the wire must be 290 Kgf / mm ² or more. A radial tire according to the present invention has a Charpy impact absorption / cutting load of 0.28d + 0.05 (where d
Is preferably not less than the wire diameter). This is because when the Charpy impact absorption / cutting load is 0.28d + 0.05 (where d is the wire diameter) or more, the effect of improving the impact resistance of the tire is remarkable. There is no particular upper limit to this ratio, and the higher the better. 1x6 code structure and 3+
The relationship between the Charpy impact absorption amount / cord cutting load and the wire diameter in the 6-cord structure is shown in the graph of FIG.

The material of the wire material of the steel wire of the cord used in the pneumatic radial tire according to the present invention is not particularly limited, but when the carbon content is less than 0.77% by weight, a predetermined tensile strength is obtained. Since it is difficult, the carbon content is preferably 0.77% by weight or more, more preferably 0.80% by weight or more. If the carbon content exceeds 1% by weight, the strand becomes brittle and industrial production is difficult.

Although the thickness of the coat rubber constituting the belt layer is not limited, it is preferably 2.0 times the minor axis or more and 1.8 times the major axis or less. If it is less than twice the minor axis, the upper and lower cord intervals are small and the separation is likely to occur when the major axis of the cord is oriented in the belt thickness direction. If it exceeds 1.8 times the major axis, the distance between the belt layers becomes too large, the belt rigidity tends to decrease, and the steering stability tends to decrease, such being undesirable.

[0017]

The present invention will be described in more detail below with reference to Examples and Comparative Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples.

Examples 1 to 3 and Comparative Example 1 and Comparative Example 1
~ 2 A steel cord having a cord structure shown in Table 1 was prepared, and a belt layer having a constitution as shown in the table was used to form a cord structure 3 + 9 +
A 1000R20 14PR tire of the same size was manufactured in combination with a common carcass layer using a steel cord of 15 × 0.175 + 1 × 0.15 and a driving number of 28. For these tires, the wire breakage of the No. 4 belt after traveling 100,000 km on a rough road under JIS 100% load was visually observed, and the results are shown in Table 1. The amount of Charpy impact absorption was measured according to JIS Z2242.

[0019]

[Table 1]

In Table 1, the tensile strength of a 1 × 6 × 0.37 element wire is 29.5 Kgf / mm ² , and the cord has a tensile strength of 5 Kgf.
The elongation under load is 0.40%.

In Table 1, Comparative Example 1 has 1B = 16,2
B = 22, 3B = 22, 4B = 20 implantation number / 50
mm, and in Comparative Example 2, Comparative Example 1 and Examples 1 to 3, 1B = 16, 2B = 27, 3B = 27, 4B = 20, and the number of implants / 50 mm. Comparative Examples 1 and 2 are conventional typical examples, and Comparative Example 1 is a No. 4 belt (4B) using a high elongation wire.

The test results after running on a bad road were as follows. After running 100,000 km on a bad road, the tire was disassembled and the breakage of the 4B wire was visually observed according to the following criteria. ⊚: No breaks ○: Some breaks are observed, but there is no problem in practice P: Very many breaks

Examples 3 to 5 (Charpy impact value / cut load)
Relationship between weight and wire breakage) In the cord structure of the third embodiment, a bad road running test was conducted in the same manner as in the third embodiment using wires having different Charpy impact absorption amounts / cutting loads. The results are shown in Table 2.

[0024]

[Table 2]

Examples 6 to 7 and Comparative Example 2 In the cord structure of Example 3, the 1st belt (1 ×
6 × 0.37, number of driving 16, flatness 1.6), 2
No. belt (1 x 6 x 0.37, 26 driving counts, flatness 1.6), 3rd belt (1 x 6 x 0.37, 27 driving counts, flatness 1.6) and 4th belt (1 X6x
0.37, the number of shots 20, the flatness ratio 1.6),
As shown in Table 3, the average degree of orientation was changed and the edge separation was evaluated. The results are shown in Table 3.

[0026]

[Table 3]

In Table 3, the edge separation was evaluated as follows. After running 100,000 km on a rough road, the tread of the tire was peeled off on the outermost belt layer, and the cord ends of the 2nd and 3rd belt layers were exposed, and the cracked length was measured. A tire equal to or more than the conventional tire was evaluated as good, and a tire equal to or less than the conventional tire was evaluated as bad.

[0028]

As described above, according to the present invention, at least two 1 × 6 flat cord structures having excellent impact resistance are provided.
By using it for the No. 3 belt, it is possible to impart high impact resistance even when not using a high elongation wire for the outermost belt layer, and it is also excellent in rubber penetration so that it has rust resistance. Can be improved. Furthermore, the belt edge separation can be effectively suppressed by appropriately dispersing the cords in the long axis direction in the belt.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an arrangement of flat cords on a belt layer in a conventional example.

FIG. 2 is an explanatory diagram showing an example of the arrangement of flat cords in the belt layer according to the present invention.

FIG. 3 is a graph showing a relationship between a Charpy impact absorption amount / cord cutting load and a wire diameter in a 1 × 6 cord structure and a 3 + 6 cord structure.

[Explanation of symbols]

 1 ... Code 2 ... Belt layer t ... Code interval

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[Procedure amendment]

[Submission date] November 18, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

In order to obtain strength equivalent to that of the 3 + 6 cord structure in the 1 × 6 cord structure, it is necessary to thicken the wire diameter. However, if the wire diameter is made too thick, the cord weight increases. The tensile strength of the wire must be 290 Kgf / mm ² or more. A radial tire according to the present invention has a Charpy impact absorption / cutting load of 0.28d + 0.05 (where d
Is preferably not less than the wire diameter). This is because when the Charpy impact absorption / cutting load is 0.28d + 0.05 (where d is the wire diameter) or more, the effect of improving the impact resistance of the tire is remarkable. There is no particular upper limit to this ratio, and the higher the better. 1x6 code structure and 3+
The relationship between the Charpy impact absorption amount / cord cutting load and the wire diameter in the 6-cord structure is shown in the graph of FIG. In Fig. 3, the area between the two dashed lines is 1x6
The range of the card structure, and the 3 + 6 code between the two solid lines
It is the range of structure.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

In Table 1, the tensile strength of a 1 × 6 × 0.37 strand is 295 Kgf / mm ² , and the elongation of the cord under a load of 5 Kgf is 0.40%.

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (3)

[Claims] 1. A steel cord having a 1 × 6 structure with a wire diameter of 0.25 to 0.40 mm and a tensile strength of the wire of 290 Kgf / mm ² or more, in a steel cord cross section orthogonal to the steel cord longitudinal direction. A cord having a ratio of the major axis to the minor axis of the cord of 1.2 to 2.0 and an elongation of the cord of 0.30 to 0.85% under a load of 5 Kgf is counted from the carcass layer side, and at least Pneumatic radial tires used for the second and third belt layers. 2. The pneumatic radial tire according to claim 1, wherein the Charpy impact absorption amount / cutting load ratio of the steel cord is 0.28d + 0.05 (where d is the strand diameter) or more. 3. The flat steel cord in the belt layer has a major axis direction of 10 as an average of absolute values in the belt width direction.
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is at least °.