JPH09142103A - Rubber reinforcing steel cord and radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the buckling deformation resistance of a steel cord itself for a reinforcing layer when the steel cord is less used by specifying a relationship between the pitch and amplitude of a plane waveform continuously ranging along the longitudinal direction and the strand pitch of each of element wires constituting the steel cord. SOLUTION: A plane waveform given to a steel cord SC in a 1×4 structure with four element wires 1a stranded at the same time continuously ranges along the longitudinal direction at the same cycles. The plane waveform has an amplitude H. The strand pitch of each of element wires 1a constituting the steel cord SC is represented by P and the cycle pitch of the waveform given to the steel cord SC is represented by L, the ratio (L/P) of the pitch L of the waveform to the strand pitch P being 1.20-2.50. The ratio (H/L) of the amplitude H to the pitch L of the waveform is 0.03-0.05.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord used for reinforcing a rubber product such as a radial tire for an automobile or a conveyor belt, and a radial tire which is particularly lightweight by using the steel cord.

[0002]

2. Description of the Related Art A radial tire for an automobile, for example, a tire for a passenger car, has a belt portion 1 as shown in FIG.
First, in the truck / bus tire, as shown in FIG. 5, the belt portion 12 to the carcass portion 13 is provided with a reinforcing layer 10 in which a large number of steel cords are arranged in parallel in rubber.

Reinforcing layer 1 for passenger car tires
In the tire for trucks and buses, 0 is usually provided in a two-layered manner, and in the tire for trucks and buses, the reinforcing layer 10 is usually provided in a four-layered manner in the belt portion 12 and one in the carcass portion 13 is provided as a single layer. . The steel cords used for such a reinforcing layer 10 are incorporated in rubber so as to be arranged very closely.

The steel cord used in the belt portion of a passenger car tire has a structure in which two to five strands are twisted together, for example, four strands 1a as shown in FIG. 6 (A).
7 or a structure in which five strands 1a are twisted as shown in (B) is used, and a steel cord used for the belt portion of a truck / bus tire is as shown in FIG. As shown in Fig. 8, a structure in which six strands 1b are twisted around a core strand formed by twisting three strands 1a is A structure in which eight strands of wire 1b are twisted around a core strand of twisted cores is generally used.

[0005]

By the way, recently, due to the demand for reduction of fuel consumption of automobiles, there has been a strong demand for weight reduction of tires mounted on automobiles. In order to meet this demand, it is necessary to reduce the amount of rubber and reinforcing materials used, especially heavy steel cords.

When the amount of steel cord used in a tire is reduced, it is necessary to increase the strength of the cord in order to compensate for the reduction in strength of the reinforcing layer caused by this. At present, regarding the strength of cords, the tensile strength (Z) of the strand before being twisted into the cord is Z = -200d +
From 365 (kgf / mm ² ), Z = −200d + 385
Practical materials up to about (kgf / mm ² ) have been put into practical use, and research into higher strength is underway.

Thus, the weight reduction of the tire is achieved by further increasing the strength of the steel cord and reducing the usage amount thereof, but even if this is achieved, another big problem remains.

When the number of steel cords embedded in the reinforcing layer is reduced, the distance p1 between the steel cords SC embedded in the rubber R becomes large as shown in the sectional view of the reinforcing layer in FIG. Rubber width between SC p2
Becomes larger. When the tire reinforcement layer is in such a state, the vehicle corners and meanders, and
When a large compressive force is applied to the cord 0 in the longitudinal direction of the cord as indicated by an arrow 0, the cord SC easily escapes to the rubber R side and is easily buckled and deformed.

Further, in the reinforcing layer of the carcass portion, particularly when the air pressure of the tire becomes low, the steel cord is largely bent, and a similar buckling phenomenon occurs. When such a state occurs, steering response and steering stability are deteriorated, the cord is broken early, and durability is deteriorated, which is a serious problem. These problems, of course, remain for tires before weight reduction.

The present invention provides a steel cord which has a large buckling deformation resistance of the cord itself in the reinforcing layer when the amount of the steel cord used is reduced to cope with the weight reduction of the tire, and which is hard to break even if it buckles. It is also an object of the present invention to provide a lightweight radial tire using the steel cord, which has good performance and long life.

[0011]

In order to achieve this object, the present invention is a steel cord in which a plurality of strands are twisted together, and has a planar corrugation continuously along its longitudinal direction. Then, when the pitch length L and the amplitude H of the waveform are P, where the twisting pitch length of the wires forming the cord is P,
1.20 ≦ L / P ≦ 2.50 and 0.03 ≦ H / L
This satisfies ≦ 0.05.

The steel cord is used for reinforcing the belt portion, the carcass portion or a part thereof of the tire. In the steel cord of the present invention, since the planar corrugation is continuously formed along the longitudinal direction on the cord itself, the planar portion of the planar corrugation is formed on the tread surface of the tire or at the carcass portion. By arranging so that they are almost parallel to the peripheral surface and forming a reinforcing layer, when the cord in the tire is compressed in the longitudinal direction, the cord is less likely to buckle and Also, the compressive stress in the longitudinal direction is relaxed, so the amount of cords used is reduced and the buckling resistance is strong even if the cord intervals arranged in the rubber are wide,
The durability can be ensured even when the vehicle is cornering during driving or repeated during meandering.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows an example of a steel cord for rubber reinforcement according to the present invention. The symbol SC shown in the figure is a steel cord having a 1 × 4 structure in which four strands 1a are twisted at the same time. The steel cord SC is corrugated in a planar waveform, and the waveform has the same period. It is continuous along its longitudinal direction. The amplitude of this planar waveform is H.

Therefore, in this steel cord SC, the cross section at right angles to the longitudinal direction of the steel cord SC is repeatedly positioned in the ellipse S of the same direction with H as the major axis at any portion in the longitudinal direction. The structure is occupied.

Each strand 1a constituting the steel cord SC
The pitch length of the twist is P, the pitch length of the period of the waveform applied to the steel cord SC is L, and the pitch length L (L / P) of the waveform with respect to the pitch length P of the twist is 1 The range is from 20 to 2.50. Further, the amplitude H (H / L) of the waveform with respect to the pitch length L of the waveform is 0.0.
It is in the range of 3 to 0.05.

When L / P is less than 1.20, when the steel cord SC formed by twisting the individual strands 1a is subjected to a flat corrugation, the strand 1a is deformed and bulges randomly toward the cord diameter side. The code loses its shape, and the fatigue resistance tends to decrease.

Further, when L / P becomes a large value exceeding 2.50, the effect of increasing the compression resistance of the steel cord SC becomes small. When H / L is less than 0.03, the effect of improving the compression resistance of the steel cord SC is small, and when H / L is greater than 0.05, the cord loses its shape and fatigue resistance increases. When the tire is incorporated into a tire, the steering stability becomes poor due to a decrease in rigidity against compression.

FIG. 2 shows a sectional view of a reinforcing layer using the steel cord SC of the present invention. This reinforcing layer is formed by arranging a plurality of steel cords SC in a rubber R in parallel and at a predetermined interval p1. Then, the rubber R of the reinforcing layer is vulcanized together with the rubber of the tire, and the steel cords SC and the rubber R are integrated by this vulcanization and used as a reinforcing composite.

If the rubber R and the steel cord SC are not sufficiently integrated with each other, the reinforcing function cannot be sufficiently exerted. The rubber R and the steel cord SC are vulcanized and adhered via brass plating on the surface of the cord, but in this case, if the rubber R does not penetrate well into the cord SC, a continuous void inside the cord (center) The department will exist. For this reason, if the tire is damaged to reach the reinforcing layer, moisture penetrates into the reinforcing layer from the outside, the moisture propagates through the voids inside the cord, and rust spreads along the entire length of the steel cord SC. . As a result, the steel cord SC is broken, the adhesive layer between the rubber R and the cord SC is broken, and the integration is impaired, so-called separation phenomenon occurs, and the function of the tire is greatly deteriorated.

The present invention can be applied to any cord as long as it is a steel cord having a structure in which a plurality of strands are twisted together, but rubber penetrates well from the viewpoint of corrosion resistance to the inside of the cord. Thus, for example, in a passenger car tire, a loose open structure in which a plurality of strands 1a are twisted loosely as shown in FIGS. 3 (A) and 3 (B), or as shown in FIGS. It is preferable to employ a tight open structure or the like in which the n strands 1a are bundled substantially parallel to each other and the m strands 1b are twisted together.

[0021]

EXAMPLES Next, specific examples of the present invention will be shown. [Specific Example 1] A wire having a diameter of 0.28 mm (tensile strength = 32
2kgf / mm ² ) 3 wires are used, and about 1
Excessive 25% patterning was performed, and a buncher type twisting machine was used to twist together in the S direction at a pitch of 12.5 mm to form a 1 × 3 loose-open steel cord.
Further, this cord was passed between a pair of upper and lower gears to continuously perform planar corrugation. And by this process,
Various cords having different pitch lengths P and amplitudes H of the waveform by corrugation were manufactured and used as Examples and Comparative Examples. It should be noted that a cord without corrugation is used as a conventional example. The results of testing these are shown in Table 1.

[0022]

[Table 1] [Specific Example 2] A wire having a diameter of 0.25 mm (tensile strength = 32
8 kgf / mm ² ), bundle two of these strands almost in parallel, and use a buncher type twisting machine to wind two more strands around this bundle, and the pitch is 14.0 m.
The steel cord having a tight open structure of 2 + 2 was twisted in the S direction at m to make a steel cord having a tight open structure, and the cord was continuously corrugated in the same manner as in Example 1 to obtain Examples and Comparative Examples. It should be noted that a cord without corrugation is used as a conventional example.
The results of testing these codes are shown in Table 2.

[0023]

[Table 2]

In Tables 1 and 2, the "fatigue resistance index" means that one steel cord was vulcanized in rubber to form a strip sample, and the strip sample was arranged in a zigzag pattern. The cord is stretched over three rolls and a tensile load of 10% of the breaking load is applied to the cord. In this state, the rolls are repeatedly moved to the left and right to repeatedly bend the sample until the cord breaks. It is the result of measuring the number of repetitions and is represented by an index with the conventional example product as 100. However, in the case of the example product and the comparative example product, the cord was fatigued by hanging it so that the flat corrugated plane portion was parallel to the peripheral surface of the roll.

The term "compression durability index" means that a predetermined number of steel cords are linearly arranged at predetermined intervals in rubber to form one test reinforcing layer, and another cord reinforcing layer is also added thereto. After stacking one sheet into two layers, this is vulcanized to form an integral sheet sample, and this sheet sample is hung along the roll having a prescribed diameter on the side of the test reinforcement layer, and the sheet sample is suspended under a prescribed tension. When the reinforcing layer, which is made up of two layers, is bent along the roll, a compressive force is applied to the cord in the inner test reinforcing layer, and therefore the bending is repeated. The cord of the test reinforcement layer was repeatedly compressed, and the relationship between the number of repetitions of this compression and the number of wire breakage points of the cord of the test reinforcement layer was investigated.

The numerical values in each table are the values up to the occurrence of a certain number of wire breakage points in the cord in the test reinforcement layer in which the cords are arranged in the rubber with a width of 1.2 times the width of the conventional cord. Comparison of the number of compression repetitions and the number of compression repetitions until a certain number of wire breakage points occur in the test reinforcement layer in which conventional steel cords are arranged in rubber in the conventional narrow width Is represented by an index when the number of repetitions of compression is 100 for the conventional code and interval width.

The term "rubber penetrability" means that one steel cord is vulcanized in rubber to prepare a sample, the cord in the rubber is taken out, and the strand of the cord is separated and disassembled in the longitudinal direction. Then, the degree of penetration of the rubber into the inside of the cord was visually observed, and the completely penetrated rubber was judged as 100%.

As is clear from Tables 1 and 2, the steel cord of the present invention, that is, L / P is 1.20 to 2.5.
It can be seen that in the steel cord having 0 and H / L of 0.03 to 0.05, the fatigue resistance and the compression durability are superior to those of the comparative example and the conventional example.

In particular, since the compression durability, that is, the buckling resistance due to the compression in the longitudinal direction is excellent, when this steel cord is used for the reinforcing layer of the tire, the automobile performs cornering or meandering running and the longitudinal direction of the cord. Even if a large compressive force is applied to the cord, buckling deformation of the cord can be suppressed, so that it is possible to reliably prevent deterioration of steering response and steering stability, and also to prevent breakage of the cord itself and deterioration of durability. A long-life tire with good performance can be obtained.

Since the buckling deformation of the cord can be prevented, it becomes possible to arrange the cord in the rubber of the reinforcing layer at a wide interval, that is, the amount of the cord used can be reduced, thereby reducing the weight of the tire. Can be achieved. The steel cord of the present invention can be used not only as a reinforcing material for tires but also as a reinforcing material for rubber products such as conveyor belts.

[0031]

As described above, the steel cord of the present invention is excellent in fatigue resistance and buckling resistance. Therefore, when this steel cord is used for the reinforcing layer of the tire, the buckling deformation of the cord is caused. It is possible to maintain good steering response and steering stability by arranging the cords and to arrange the cords at wide intervals in the rubber of the reinforcing layer, thus reducing the amount of cords used and making it a lightweight radial tire. Can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a side surface and a cross section of a steel cord according to an embodiment of the present invention in comparison.

FIG. 2 is a sectional view of a reinforcing layer using the steel cord.

FIG. 3 is a sectional view showing an example of the twisted structure of the steel cord.

FIG. 4 is a sectional view of a passenger car tire.

FIG. 5 is a partially cutaway perspective view of a truck / bus tire.

FIG. 6 is a cross-sectional view showing an example of a twisted structure of a steel cord used in a passenger car tire.

FIG. 7 is a cross-sectional view showing an example of a twisted structure of a steel cord used for a truck / bus tire.

FIG. 8 is a cross-sectional view showing another example of a twisted structure of a steel cord used for a truck / bus tire.

FIG. 9 is a sectional view of a reinforcing layer using a conventional steel cord.

FIG. 10 is an explanatory view schematically showing a state when a compressive force is applied to a reinforcing layer using a conventional steel cord.

[Explanation of symbols]

 SC ... Steel cord R ... Rubber 1a ... Element wire 1b ... Element wire

Claims (2)

[Claims] 1. A cord in which a plurality of strands are twisted together, having a planar corrugation continuously along its longitudinal direction, and the pitch length L and the amplitude H of the corrugation form the cord. When the pitch length of the twist of the constituent wires is P, 1.
20 ≦ L / P ≦ 2.50 and 0.03 ≦ H / L ≦
Steel cord for rubber reinforcement characterized by satisfying 0.05. 2. A radial tire comprising the steel cord according to claim 1 for reinforcing at least a part of a belt portion or a carcass portion of the tire.