JPH1143878A - Rubber material-reinforcing steel cord and pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel cord of multi-twisted structure in which covering rubber penetrates to inside of the cord while keeping breaking elongation bearing to instantaneous large input force, and to provide a pneumatic radial tire standing together resistance to corrosion propagation with resistance to belt flexing. SOLUTION: This rubber material-reinforcing steel cord is composed of twisting plural layer-plying structured strands in which a core comprising 1-3 steel filaments is twisted with one- or two-layered sheath comprising plural steel filaments arranged around the core, and at least one layer of the core and the sheath has the closest packed structure and at least one filament in the layer having the closest packed structure has partially thinned cross section diameter extending in the length direction of the cord, preferably a distance from the one thinned part to another thinned part is <=10 cm. The objective pneumatic radial tire is obtained by applying the steel cord at the most outside layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel cord for reinforcing a rubber article and a pneumatic radial tire using the steel cord for reinforcing a rubber article as a reinforcing material for a belt layer.

[0002]

2. Description of the Related Art Off-the-road radial tires, such as construction vehicles and large dump trucks, are forced to travel on a road surface where crushed rocks are scattered, thereby promoting belt cutting failure. The problem that the cut directly leads to the failure of the tire, or that water penetrates from the cut and corrodes the steel cord, which causes a separation failure, or one of the failures, shortening the tire life Has occurred. As a countermeasure against such a cutting problem, the outermost layer of the belt has a multi-twisted steel cord with a relatively large elongation at break (cut elongation), or a multi-twisted structure with rubber penetrating into the cord to provide a rust-proof effect. Steel cord is widely used.

[0003] As such a steel cord having a multi-twist structure, for example, three strands obtained by twisting a sheath made of six steel filaments having the same wire diameter around a core made of one steel filament are twisted.
× (1 + 6) structure or 4 × (1 + 6) structure in which four strands are twisted together, and a sheath consisting of nine steel filaments of the same diameter twisted around a core consisting of three steel filaments 3 × (3 + 9), 4 × (3 + 9) structures, etc., in which twisted strands are similarly twisted. These cords having a close-packed structure have a large elongation at break (cut elongation), but the coating rubber does not sufficiently penetrate inside the strands, and voids exist in the longitudinal direction inside the cords.

Further, for example, a 3 × (1 + 5) structure in which three strands each formed by twisting a sheath made of five steel filaments having the same diameter around a core made of one steel filament are twisted, 4 strands
Also known are steel cords having a 4 × (1 + 5) structure, etc., in which there is a gap between sheath filaments, rubber penetrates into the strands, and a gap is formed in the cord in the longitudinal direction. Although there are no portions, the filaments are mutually restrained by the infiltrated rubber, and the elongation at break of the cord (cut elongation) is not so large.

[0005]

When the steel cord formed of the strands having the close-packed structure as described above is applied to, for example, a belt of an off-the-road radial tire, there are the following problems. In other words, when the vehicle is traveling on rough roads, if the tire tread is cut or damaged by stones,
Moisture that has penetrated from the cut damaged portion propagates in the voids inside the cord strands, deteriorating the adhesion between the cord and the covering rubber, often leading to belt separation failure.

Further, when a steel cord whose strand is not a close-packed structure such as a (1 + 5) structure is applied to, for example, a belt of an off-the-road radial tire, the following problem occurs. That is, when a vehicle travels on a rough road, when a momentary large bending input and a tensile input are applied to the outermost belt cord when stepping over a projecting object such as a stone, the strand is not a close-packed structure. Because of the small code,
At the time of such an input, the code is likely to be cut, and a cut-through failure is likely to occur.

[0007] In the conventional double twisted steel cord, it was not possible to achieve both the elongation that can withstand a momentary large input and the prevention of water propagation inside the cord.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel cord having a multi-twist structure in which a coating rubber penetrates into the inside of the cord while keeping the elongation capable of withstanding a large instantaneous input. It is another object of the present invention to provide a pneumatic radial tire that achieves both corrosion propagation resistance and belt break resistance by using the steel cord.

[0009]

Means for Solving the Problems As a result of diligent studies to solve the above problems, the present inventor has found that in a steel cord having a multi-twist structure, in order to suppress belt separation failure due to water intrusion, the steel cord extends in the longitudinal direction. It is not necessary that the rubber penetrates almost completely inside the strand, and if the rubber partially penetrates into the strand at a certain interval, the propagation of moisture entering from the damaged tread cut can be suppressed. I found that it is possible. Based on this knowledge, in a strand having a layer with a close-packed structure, a multiple twist structure in which a plurality of strands that can partially penetrate the rubber into the interior is used to achieve a cutting elongation that can withstand large input It has been found that it is possible to suppress the propagation of moisture from the cut damage portion and to remarkably improve the life of the tire while ensuring the above, and have completed the present invention.

That is, the steel cord for reinforcing a rubber article of the present invention comprises a core composed of one to three steel filaments, and a one or two-layer sheath composed of a plurality of steel filaments arranged around the core. In a rubber cord for reinforcing a rubber article obtained by twisting a plurality of strands having a layer twist structure, at least one of the core and the sheath has a close-packed structure, and a filament of a layer having the close-packed structure has a close-packed structure. At least one of the cords is characterized in that the cross-sectional diameter is partially reduced in the longitudinal direction of the cord.

[0011] In the filament having a partially reduced cross-sectional diameter, the distance from one reduced portion to the next reduced portion is preferably 10 cm or less. It is preferable that the shape of the portion having a small cross-sectional diameter is a flat shape.

Further, the present invention is a pneumatic radial tire, wherein the steel cord for reinforcing a rubber article is applied to an outermost layer of a belt.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described specifically. The steel cord for reinforcing a rubber article of the present invention is a layer obtained by twisting a core made of one to three steel filaments and one or two sheaths made of a plurality of steel filaments arranged around the core. It has a multiple twist structure in which a plurality of twisted strands are twisted, and at least one layer of the core and the sheath has a close-packed structure.
Here, the close-packed structure refers to a structure in which the filaments of the core or the sheath are adjacent to each other so as to substantially contact each other. As strands having such a structure, for example, 1 + 6 (closest structure of the sheath), 3 + 9 (closest structure of the core and the sheath), 3 + 9 + 15 (closest structure of the core and the sheath of the two layers), 3 + 7 to 8 (closest structure of the core) Structure) 1 + 6 + 11
(The inner sheath has a close-packed structure).

In the steel cord of the present invention, at least one of the filaments in the layer having the close-packed structure has a partially reduced cross-sectional diameter in the longitudinal direction of the cord. The distance from one narrowed portion to the next narrowed portion is preferably 10 cm or less. In this way, a gap is partially provided between adjacent filaments to achieve partial rubber permeation, and the gap between the narrowed portions is set to 10 cm or less to sufficiently improve corrosion propagation resistance. can do.

The shape of the portion where the cross-sectional diameter is small is
In view of its production, it is preferable that the filament has a flat shape.For example, the filament can be obtained by passing it through a gear-shaped roller before twisting the filaments. Other shapes are acceptable as long as they can penetrate.

The steel cord formed by twisting a plurality of strands each having a layer having a close-packed structure through which rubber can only partially penetrate has a double twisted structure in which, for example, 2 to 6 strands are twisted, thereby increasing the 5% The above elongation can be realized, and when such a steel cord is applied to the outermost layer of the belt of the tire, the belt breaking resistance against distortion at the time of large input is improved, and the life of the tire can be extended.

In the steel cord of the present invention, it is preferable to omit the wrap filament around the outermost sheath strand in order to secure the elongation of the cord. However, the wrap filament is spirally wound to strengthen the cord bundle. May be. In the present invention, the filament diameter, the twist direction of the core and sheath filament of each strand, the twist direction of the sheath strand, the twist pitch, and the like are not particularly limited, and conditions conventionally used are adopted. be able to.

The steel cord for reinforcing rubber articles of the present invention is suitably used as a reinforcing material for the outermost layer of a belt of a large off-the-road radial tire. The number of cords to be driven into the belt is preferably 10.0 to 13.5 cords / 5.
It is within the range of 0 mm. The number of shots is 10.0 / 50
If it is less than mm, the cord interval is too wide, so that the rubber between the cords is likely to be cut when going over the protrusion, causing a failure. On the other hand, the number of cords inserted is 13.5
If it exceeds 0 mm, the cord interval is too narrow, so that separation from the belt end is likely to occur. In the pneumatic radial tire of the present invention, the structure and material other than the belt portion may be those conventionally used, and are not particularly limited.

[0019]

Next, the present invention will be specifically described with reference to Examples and Comparative Examples. Examples 1 and 2, Conventional Examples 1 and 2, and Comparative Examples Various steel cords according to the cord structure shown in Table 1 below were prototyped. In the steel cords shown in Table 1, four strands each composed of one core filament and six sheath filaments (one of which is partially flat) of Examples 1, 2 and Comparative Example were twisted. 4 × (1+
6) FIG. 1 shows a steel cord having a structure, and FIG. 2 shows a steel cord having a 4 × (1 + 5) structure obtained by twisting four strands composed of one core filament and five sheath filaments of Conventional Example 1. Furthermore, 4 × (1+
6) Steel cords having the structure are shown in FIG.

FIG. 4 shows the relationship between elongation and stress for each of the cords of Example 1, Conventional Example 1 and Conventional Example 2. As is clear from this figure, 5%
The above elongation is obtained.

A prototype steel cord was sized as shown in FIG. 6 to have a size 3 having a belt layer 3 having a separation structure of six sheets.
This was applied to the outermost two belt layers 3a and 3b of the 6.00R51 off-the-road radial tire at a cord angle of 64 ° with respect to the circumferential direction of the tire at a number of hits of 13.0 / 50mm. In the drawing, 1 is a bead core, 2 is a carcass, and 4 is a tread.

For these prototype tires, the outermost layer belt was evaluated for corrosion propagation resistance and belt break resistance.
The evaluation method is as follows. (1) Corrosion propagation resistance After mounting the prototype tire on a vehicle and traveling 20,000 km on the road, dissect the tire, examine the location of the outermost belt cord where rust has occurred, and develop the most rust The reciprocal number of the length of the portion where the image is formed is represented by an index with the value of Conventional Example 2 being 100. The higher the value, the better the result. (2) Belt resistance The same test as above was performed and the cord 4
Zero filaments were taken out, the percentage of unbroken filaments was calculated, and the value of Conventional Example 1 was set to 100 and displayed as an index. The higher the value, the better the result. The results obtained are shown in Table 1 below.

[0023]

[Table 1]

[0024]

As described above, in the steel cord for reinforcing a rubber article according to the present invention, in a strand having a layer having a close-packed structure, rubber can be partially penetrated into the inside. This allows the rubber to penetrate into the cord while maintaining the elongation that can withstand a momentary large input, and provides an effect excellent in corrosion propagation resistance. Further, in a pneumatic radial tire for heavy loads using this cord as the outermost layer of the belt, the corrosion propagation resistance and the belt breaking resistance are compatible, and the tire life can be greatly extended.

[Brief description of the drawings]

FIG. 1 is a sectional view of a steel cord having a 4 × (1 + 6) twisted structure of Examples 1 and 2 and Comparative Example.

FIG. 2 is a cross-sectional view of a 4 × (1 + 5) twisted steel cord of Conventional Example 1.

FIG. 3 is a cross-sectional view of a 4 × (1 + 6) twisted steel cord of Conventional Example 2.

FIG. 4 is a graph showing the relationship between elongation and stress of each cord of Example 1, Conventional Example 1 and Conventional Example 2.

FIG. 5 is a cross-sectional view of an example pneumatic tire of the present invention.

[Explanation of symbols]

 1 bead core 2 carcass 3 belt 3a outermost layer of belt 4 tread

Claims (4)

[Claims] A plurality of strands having a layer-twisted structure in which a core composed of one to three steel filaments and one or two sheaths composed of a plurality of steel filaments arranged around the core are twisted. In the twisted rubber cord for reinforcing a rubber article, at least one layer of the core and the sheath has a close-packed structure, and at least one filament of the layer having the close-packed structure has a portion extending in a longitudinal direction of the cord. A steel cord for reinforcing rubber articles, characterized in that the cross-sectional diameter is narrower. 2. The rubber article according to claim 1, wherein in the filament having a partially reduced cross-sectional diameter, a distance from one reduced portion to the next reduced portion is 10 cm or less. Steel cord for reinforcement. 3. The steel cord for reinforcing rubber articles according to claim 1, wherein the shape of the portion having a partially reduced cross-sectional diameter is a flat shape. 4. A pneumatic radial tire, wherein the steel cord for reinforcing a rubber article according to claim 1 is applied to an outermost layer of a belt.