JP2904688B2 - Pneumatic radial tire for heavy loads - Google Patents

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 generally constructed such that a belt layer comprising a plurality of steel cords is arranged on a carcass layer to bear a strong impact or load received during tire running. In particular, the tread of a pneumatic radial tire for heavy loads receives a remarkably large impact force, and thus is liable to be damaged such as cuts. When such damage occurs, external moisture penetrates through the damage, reaches the belt layer, and comes into contact with the steel cord.
This makes the steel cord rust and corrodes easily,
There has been a problem that the adhesive force between the cord and the rubber is deteriorated, separation between the tread and the belt layer occurs, and the durability of the tire is reduced.

Conventionally used steel cords for the belt layer of such a heavy-duty pneumatic radial tire include, for example, six relatively large diameter steel wires and three relatively small diameter wires. A cord having a so-called 3 + 6 cord structure, which is twisted so as to surround the wire, is generally used, but the cord having such a structure has poor impact resistance and rust resistance, and it is particularly necessary to impart impact resistance. In some cases, a structure is used in which the wire of the outermost layer (usually the fourth belt) is replaced by a high elongation wire such as 4 × 4 or 1 × 5.

[0004] 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 required strength of the belt layer, it is necessary to increase the number of driving of the inner belt layer, increase the diameter of the strand, or adopt a structure having a larger number of strands. There is a drawback that the weight increases, and there is also a drawback that the tire cost is increased due to the increase in the amount of wire used and the high elongation wire being expensive.

[0005]

SUMMARY OF THE INVENTION Accordingly, 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 pneumatic radial tire for heavy load in which 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.
f / mm ² or more , Charpy impact absorption / cutting load ratio
A steel cord having a 1 × 6 structure of 0.28d + 0.05 (where d is the element diameter) or more, and
The long diameter direction of the flat steel cord
The average of the absolute values of the cords is 10 ° or more, the ratio of the major axis to the minor axis in the steel cord cross section perpendicular to the longitudinal direction of the steel cord is in the range of 1.2 to 2.0, and when the cord is loaded with 5 kgf Heavy load obtained by using a steel cord having an elongation of 0.30 to 0.85% as the at least second and third belt layers, counting from the carcass layer side.
A pneumatic radial tire is provided.

[0007] If the impact resistance of the entire belt layer can be improved while satisfying the strength and rust resistance required of the belt cord, the need for a high elongation wire is eliminated, and the above-mentioned disadvantages can be improved. The present inventor has found a cord structure that provides rust resistance and greatly improves impact resistance while securing strength performance by improving a 3 + 6 structure that is frequently used as a tire for trucks and buses. We have found a tire structure that can significantly improve the impact resistance of truck and bus tires.

According to the study of the present inventors, 3 + 6 1 ×
Part 3 was found to have a small function against impact. That is, to increase the impact resistance at the same strength, 3 + 6 1 × 3
It was found that the impact resistance was improved by increasing the diameter of the six outer wires to compensate for the strength of 1 × 3. In addition, 1 × 6 has a flat open cord structure, and the flatness and elongation under a 5 kgf load are within a specific range, so that rubber is uniformly introduced into the cord and the tensile strength of the wire is 290 kg.
It was found that increasing the f / mm ² or more greatly improved the impact resistance of the cord structure of 3 + 6.

When the present inventors use this 1 × 6 cord structure for at least the 2nd and 3rd belt layers (2B and 3B) counted from the carcass layer side, they use the conventional 3 + 6 cord structure. It has been found that the impact resistance is greatly improved as compared to More preferably, in a flat open cord structure of 1 × 6 with Charpy impact absorption / cutting load of 0.28 d + 0.05 or more (here, d is the element diameter) as an index of impact resistance per unit strength of the cord, This improvement effect is further enhanced, and the same impact resistance as that obtained by using the high elongation wire for the fourth belt layer (4B) can be obtained.

[0010] The belt layer of the tire is located immediately below the tread layer, and when the tire tread is damaged, water penetrates from it and is easily rusted. In order to prevent this, it is effective to use a cord with good rubber penetration, but the 1 × 6 flat open cord structure is also optimal as a belt cord in this regard.

In the present invention, the 1 × 6 code structure is limited to the 1 × 5 code structure as an alternative to the 3 + 6 code structure, and the strength is insufficient in the 1 × 5 code structure, and the element wire is not used in the 1 × 7 or more code structure. The cord must have a 1 × 6 cord structure because it easily falls into the center of the cord and twisting becomes unstable. If the strand diameter is less than 0.25 mm in the 1 × 6 cord structure, the required strength cannot be secured, and if the strand diameter exceeds 0.40 mm, the fatigue property is reduced. .
It needs to be 40 mm.

If the flatness of the cord (that is, the ratio of the major axis to the minor axis in the cross section of the steel cord perpendicular to the longitudinal direction of the steel cord) is less than 1.2, a thick part and a narrow part are periodically formed in the cord diameter in the longitudinal direction of the cord. When the flatness exceeds 2.0, the flattening must be 1.2 to 2.0 because the excessive flattening also lowers the fatigue. Preferably, the flatness is 1.3 or more. If the elongation of the cord under a 5 kgf load is less than 0.30%, it is difficult to uniformly inject the rubber inside the cord. Conversely, if it exceeds 0.85%, a portion where the filaments are completely separated is likely to be generated. When it is subjected, it is not preferable because the strain becomes non-uniform and the fatigue durability decreases.

In the 1 × 6 flat cord structure of the present invention, the cord has a flatness of 1.2 to 2.0, so that the major axis and the minor axis are different. As shown in FIG. 1, when the flat steel cord 1 is arranged so that the major axis direction (see the one-dot broken line in the figure) coincides with 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 appropriately dispersed in the major axis direction (see the dashed line in the drawing), distortion at the major axis end is alleviated, which is effective in suppressing belt edge separation.
To meet this purpose, the angle between the long axis direction of the cord 1 and the belt width direction in the belt 2 is dispersed in an average of absolute values (meaning whether clockwise or counterclockwise) to 10 ° or more. Is effective.

In order to obtain a strength equivalent to a 3 + 6 cord structure with a 1 × 6 cord structure, it is necessary to increase the strand diameter. However, if the strand diameter is too large, the cord weight increases. The tensile strength of the wire needs to be 290 kgf / mm ² or more. The 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 element wire diameter). This is because when the Charpy impact absorption amount / cutting load is 0.28d + 0.05 (where d is the element diameter) or more, the effect of improving the impact resistance of the tire is remarkable. There is no particular upper limit for this ratio, and the higher the ratio, the better. In addition, 1 × 6 code structure and 3+
The relationship between the Charpy impact absorption / cord cutting load and the wire diameter in the six-cord structure is as shown in the graph of FIG. In FIG. 3, 1 × 6 dots are shown between two dashed lines.
3 + 6 code between two solid lines
The scope of the structure.

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 if the carbon content is less than 0.77% by weight, it is necessary to obtain a predetermined tensile strength. Since it is difficult, the amount of carbon 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 wires become brittle, and industrial production is difficult.

Although the thickness of the coat rubber constituting the belt layer is not limited, it is preferably at least 2.0 times the minor axis and at most 1.8 times the major axis. If the minor axis is less than twice the minor axis, when the major axis of the cord is oriented in the belt thickness direction, the interval between the upper and lower cords becomes small, and separation is likely to occur. If it exceeds 1.8 times the major axis, the distance between the belt layers becomes too large, and the belt stiffness tends to decrease, so that steering stability tends to decrease.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail 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 1-3, Comparative Example 1 and Control Example 1
２2 A steel cord having a cord structure shown in Table 1 was prepared, and a belt layer having a structure shown in the table was used.
A 1000R20 14PR tire having the same size was manufactured in combination with a common carcass layer using a steel cord of 15 × 0.175 + 1 × 0.15 and having 28 shots. With respect to these tires, the breaking of the wire of the No. 4 belt after running 100,000 km on a bad road under a 100% load according to JIS was visually observed, and the results are shown in Table 1. The Charpy impact absorption was measured according to JIS Z2242.

[0019]

[Table 1]

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

In Table 1, Comparative Example 1 has 1B = 16,2
Number of shots of B = 22, 3B = 22, 4B = 20/50
In Comparative Example 2, Comparative Example 1, and Examples 1 to 3, the number of shots of 1B = 16, 2B = 27, 3B = 27, 4B = 20 was set to 50 mm. Comparative Examples 1 and 2 are conventional typical examples, and Comparative Example 1 uses a high elongation wire for the No. 4 belt (4B).

The test results after running on a bad road were as follows: After running on a bad road for 100,000 km, 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 practical problem ×: The number of breaks is very large

Examples 3 to 5 (Charpy impact value / cut load)
Relationship Between Weight and Wire Breakage) In the cord structure of the third embodiment, a rough road running test was performed in the same manner as in the third embodiment using wires having different Charpy impact absorption / cutting load. The results are shown in Table 2.

[0024]

[Table 2]

Examples 6 and 7 and Comparative Example 2 In the cord structure of Example 3, the first belt (1 ×
6 x 0.37, number of shots 16, flatness 1.6), 2
No. 3 belt (1 × 6 × 0.37, number of driving 26, flatness 1.6), No. 3 belt (1 × 6 × 0.37, number of driving 27, flatness 1.6) and No. 4 belt (1 × 6 ×
0.37, the number of shots is 20, the flatness is 1.6)
As shown in Table 3, the average separation was changed to evaluate edge separation. The results are shown in Table 3.

[0026]

[Table 3]

In Table 3, the edge separation was evaluated as follows. After traveling on a bad road for 100,000 km, the tread of the tire was peeled off on the outermost belt layer, the cord ends of the second and third belt layers were exposed, and the length of the crack was measured. A tire equivalent to or more than the conventional tire was rated good, and a tire less than the conventional tire was rated 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 the third belt, high impact resistance can be imparted even when a high elongation wire is not used for the outermost belt layer, and since it is excellent in rubber permeability, rust resistance is improved. Can also be improved. Further, by appropriately dispersing the longitudinal direction of the cord in the belt, belt edge separation can be effectively suppressed.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing an example of an arrangement of flat cords in a 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 ... cord 2 ... belt layer t ... cord interval

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60C 9/00-9/20 D07B 1/06

Claims (1)

(57) [Claims] A wire having a wire diameter of 0.25 to 0.40 mm, a tensile strength of a wire of 290 kgf / mm ² or more , and a Charpy impact absorption
The yield / cutting load ratio is 0.28d + 0.05 (where d is
1 × 6 steel cord with a diameter of
The long diameter direction of the flat steel cord in the belt layer
Is 10 ° or more on average of the absolute value in the belt width direction.
Ri, major and the ratio of the minor axis of the codes in the steel cord cross section perpendicular to the steel cord longitudinal direction 1.2 to 2.0
And the elongation of the cord under a load of 5 kgf is 0.
A pneumatic radial tire for heavy loads, wherein 30 to 0.85% of steel cord is counted from the carcass layer side and used for at least the second and third belt layers.