JPH11217778A - Steel cord for reinforcing rubber product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel cord for reinforcing a rubber product, constructed by twisting 4 wires, having a stabilized twisting structure, also improving the penetrating property of the rubber, reducing the generation of a buckling and a fretting abrasion even by repeated bending stresses, and excellent in fatigue property. SOLUTION: This steel cord for reinforcing a rubber product, obtained by twisting 2 wires in the center, arranging one each wire at the both sides thereof and twisting in a same direction at a same pitch, is obtained by setting that a circumcircle drawn by the wires at the both sides is an approximately elliptic shape having D1 =2.5-4.0d major axis and D2 =2.1-2.8d minor axis (d: a diameter of the wire).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel cord for reinforcing rubber products used as a reinforcing material for rubber products such as automobile tires and conveyor belts.

[0002]

2. Description of the Related Art Generally, a steel cord of this type has a structure in which a plurality of strands are twisted, and a plurality of the steel cords are covered with a rubber material in a state where the steel cords are aligned in parallel. Used as reinforcement for products. Therefore, the essential conditions for steel cord are:
Not only is it excellent in mechanical properties, but also good chemical adhesion to the rubber material and good penetration of the rubber material into the steel cord. That is, in order for the steel cord to sufficiently serve as a reinforcing material for a rubber product, it is necessary to form a complete composite with the rubber material.

[0003] Conventionally, a steel cord has a so-called closed twist structure in which four to five strands of a wire are closely adhered to each other and twisted. This kind of steel cord has a hollow part in the center of the cord, so when forming a composite sheet using a steel cord and two rubber sheets, the rubber material does not penetrate to the above-mentioned hollow part, Simply covering the outer periphery of the cord could not form a complete composite with the rubber material.

Accordingly, in the case of rubber products using the above-mentioned steel cord, for example, tires for automobiles, the adhesion between the rubber material and the steel cord is not sufficient, and when the automobile is running,
The rubber material and the steel cord are peeled off, causing a so-called separation phenomenon, which significantly impairs the function of the tire,
The water in the rubber material or the water entering from the cuts of the tires reaches the cavity inside the cord, propagates in the longitudinal direction of the cord, corrodes the steel cord, and greatly reduces the mechanical strength.

For this reason, recently, a steel cord in which a rubber material penetrates into the inside of the steel cord and is adhered to the entire circumference of each strand has been considered. This steel cord has a so-called open twist structure in which wires are twisted while providing a gap between the wires.

However, in a steel cord having an open twist structure, in order for the rubber material to adhere to the entire circumference of each strand and to sufficiently penetrate into the cord, the gap between the strands must be rubber. It is necessary to make the gap sufficient for the material to enter, that is, 0.02 mm or more. However, if such a gap is provided between the wires, the free space in which the wires can move is too large, and the elongation under a low load increases,
Due to the low tension applied to the steel cord at the time of rubber vulcanization, the gap is reduced, and there is a problem that the rubber material does not sufficiently penetrate.

Therefore, as shown in FIG. 2, two strands 5, 5 are closely attached to the center and twisted, and one strand 6, 6 is arranged on both sides thereof. There has been proposed a steel cord 4 in which the strands 6 and 6 have a slight clearance with the respective strands 5 and 5 at the center, which are twisted, and are twisted in the same direction and at the same pitch. 393). In the steel cord 4, since the two central wires 5 and 5 are in contact with each other in the longitudinal direction of the cord, the elongation under a low load is small, and the wires 6 on both sides are small.
6 is completely covered with rubber.

However, in the steel cord 4, the wires arranged on both sides do not come into contact with the two wires at the center.
Since the wires are twisted so as to have a small gap, the two wires located at the center have a large degree of freedom, the wires at the center jump out or move at the center, and the stability of twist is very low. Also, since the rubber material does not penetrate into the contact portion between the two central wires 5, 5, not only is the corrosion resistance inferior, but also when the steel cord is repeatedly subjected to compressive stress, fretting wear is likely to occur, There is a problem that the fatigue life is reduced.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. Two wires are twisted in the center, and one wire is arranged on each side. In a steel cord twisted in the same direction and at the same pitch, the twist structure is stable, the penetration of rubber material is improved, and the occurrence of buckling and fretting wear is reduced by repeated bending stress. An object of the present invention is to provide a steel cord for reinforcing rubber products having excellent properties.

[0010]

In order to solve the above-mentioned problems, the steel cord of the present invention is characterized in that the circumscribed circle drawn by the wires on both sides is defined as a major axis D ₁ = 2.5d to 4.0d, and a minor axis. D ₂
= 2.1 to 2.8d (d: wire diameter).

According to the steel cord of the present invention, the two central wires (hereinafter referred to as central wires) or the central wire and both side wires (hereinafter referred to as side wires) are cords. Since the contact is made in the longitudinal direction, the elongation under low load is small, and when the side strand is located near the major axis of the ellipse, it is enough for the rubber material to penetrate with the central strand. Can be provided, and when the side strand is located near the minor axis, the side strand pushes the central strand open and cuts in between, so the central strand is separated, and in this gap, The rubber material that has penetrated flows in through a gap generated when the side element wire is positioned on the longer diameter side.

The reason why the major diameter D _{1 of the} circumscribed circle is set to 2.5 to 4.0 times the wire diameter d is that if the diameter is less than 2.5 times, a sufficient gap is provided for the rubber material to enter. When the ratio exceeds 4.0 times, the stability of twist decreases. Also, the short diameter D ₂ was 2.1 to 2.8 times the wire diameter exceeds 2.8 times, it is impossible to open the gap just rubber material can penetrate into between the central wire , Less than 2.1 times, the side strands are almost in contact with each other, and the rubber penetration is reduced.

Further, when the steel cord of the present invention is used for an automobile tire, if the long diameter sides are arranged in the same direction, the thickness of the tire can be reduced, and the weight of the tire can be reduced. It also leads to the energy saving effect of the car.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a steel cord for reinforcing rubber products.
Twenty 25 mm center wires 2a, 2b are twisted, and one side wire 3a, 3b is arranged on both sides thereof, and twisted in the same direction and at the same pitch. The structure is as follows. 1 (a) to 1 (e) show partial cross sections within a half-twisted pitch in the longitudinal direction. FIGS. 1 (a) and 1 (e) show when the side strands 3a and 3b are located on the long diameter side, and the
a, 2b are in contact with each other, and the center strands 2a, 2b and the side strands 3a, 3b have a small gap C. Also,
(C) is when the side strands 3a, 3b are located on the minor diameter side, the side strands 3a, 3b interrupt between the central strands 2a, 2b, and rubber material can enter between the central strands. Gap S is generated. At this time, the center strand and the side strand are in contact with each other. Further, (b) and (d) show the case where the side strands 3a, 3b are located substantially in the middle between the long diameter side and the short diameter side, and the center strand 2a,
2b are in contact with each other, and the central strands 2a, 2b and the side strands 3a, 3b are substantially in contact with each other.

By the way, in the above embodiment, if the wire diameter is less than 0.15 mm, the strength of the steel cord is insufficient, and if it exceeds 0.40 mm, the flexibility is poor. It is preferable that it is within a range of 0.40 mm.

Next, in order to confirm the performance characteristics of the steel cord of the present invention, a comparative test was conducted between the present invention and the steel cords of the conventional example and the comparative example. When the properties, handling workability and shape stability were evaluated, the results shown in Table 1 below were obtained.

[0017]

[Table 1]

At the time of this evaluation, the RP of rubber material
Is 100 when a 5 kg tensile load is applied to each cord.
% Modulus is embedded in rubber material of 35 kg / cm ² (normal rubber material used for a breaker of a tire in which a steel cord is embedded), and after vulcanization, the steel cord is taken out, the cord is disassembled, and each element wire is disassembled. The constant length was observed, and the ratio of the length with the trace in contact with the rubber material to the observed length was determined as a percentage, and the average value was displayed. This value needs to be 60 or more.

The elongation SL under a load of 5 kg indicates the elongation of each cord, and must be 0.40% or less from the viewpoint of workability.

For the fatigue RF, a plurality of steel cords are used.
A composite sheet was formed by embedding in a rubber material having a 100% modulus of 35 kg / cm ² , and this composite sheet was used to form a composite sheet.
Fretting wear,
The number of repetitions until rupture of the cord after buckling or the like was determined, and the number of the cord of the conventional example was set to 100 and displayed as an index.

The handling workability HW is an evaluation of the complexity of work and the handling of the cord during the production of the steel cord and the forming of the composite sheet. ×, very inferior compared to
A little inferior was evaluated as △, and a no difference was evaluated as ○.

The shape stability SS is an evaluation of the finished state of the cord. Based on the occurrence rate of defects such as twisting and the like, x is very poor compared to the cord of the conventional example 1; When there was no, it was evaluated as ○.

In Table 1, Conventional Example 1 is 1 × 4 × 0.2
5 Closed twisted steel cord, very stable twist, elongation at 5 kg load, good handling workability, but poor rubber material infiltration.

In Conventional Example 2, the average shaping ratio (cord diameter when twisted with a gap between each strand / cord diameter when each strand is densely twisted × 100) is 1 × 130%. 4x
It is a steel cord with a 0.25 open twist structure and has excellent penetration and fatigue properties of rubber material, but has large elongation under a load of 5 kg and is inferior in handling workability.

Conventional Example 3 is a steel cord having a 2 + 1 + 1 structure in which circumscribed circles drawn by both strands are substantially perfect. Although the elongation under a load of 5 kg is small, it is inferior in shape stability and has two strands twisted in the center. No infiltration of the rubber material between the strands was observed, the amount of fretting wear was large, and the fatigue property was poor.

Comparative Examples 1 to 4 are steel cords whose circumscribed circles drawn by the wires on both sides are substantially elliptical. However, the major axis and the minor axis of the elliptical shape are different from those of the present invention, and all the evaluation items are satisfied. Can not.

On the other hand, the steel cords of the present invention 1 to 6 have rubber infiltration properties, elongation under 5 kg load, fatigue properties,
It was found that both the handling workability and the shape stability were satisfied, and that it was optimal as a reinforcing material for rubber products.

[0028]

EFFECT OF THE INVENTION The steel cord for reinforcing rubber products of the present invention has a small elongation under extremely low load, has good handling workability,
The shape is also stable. Further, when the steel cord is covered with a rubber material, the rubber material extends over substantially the entire area between the wires constituting the steel cord, so that a complete complex with the rubber material is obtained, and the corrosion of the cord can be prevented. Also,
When the steel cord of the present invention is used for a tire, for example, the separation phenomenon between the rubber material and the cord can be prevented, the life of the tire can be extended, and the circumcircle of the steel cord is elliptical. By arranging them on the belt portion of the tire so that the major diameter sides are oriented in the same direction, it is possible to reduce the thickness of the tire. .

[Brief description of the drawings]

FIG. 1 shows an embodiment of a steel cord according to the present invention,
(A)-(e) is an outline partial sectional view in a half pitch of a cord longitudinal direction.

FIG. 2 is a schematic sectional view of a conventional steel cord.

[Explanation of symbols]

 1 ... steel cord 2a, 2b ... central strand 3a, 3b ... side strand

Claims (1)

[Claims] 1. A steel cord in which two strands are twisted in the center and one strand is arranged on both sides thereof and twisted in the same direction and at the same pitch. The circumscribed circle drawn by is the major axis D ₁ = 2.5d to 4.0d,
Minor D ₂ = 2.1d~2.8d (d: wire diameter) rubber products for reinforcing steel cord, characterized in that substantially an elliptical shape.