JP2006104636A - Steel cord for reinforcing rubber article and pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord for reinforcing a rubber article; and to provide a pneumatic radial tire having improved durability by using the steel cord for reinforcing the rubber article as a reinforcing material. <P>SOLUTION: The steel cord for reinforcing the rubber article has a 1+6 double twisted structure constituted of one core strand having two- or three-ply layered twist structure, and six sheath strands surrounding the core strand and having two- or three-ply layered twist structures. The whole layered twist directions in the core strand 1 and the twist direction of the sheath strand 4 are the same direction, and the layered twist directions in the sheath strands 4 are the combination of different directions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a steel cord for reinforcing rubber articles and a pneumatic radial tire (hereinafter also simply referred to as “tire”), and more specifically, to a steel cord for reinforcing rubber articles used as a rubber article reinforcing material for a pneumatic radial tire and the like. The present invention relates to a pneumatic radial tire improved in durability by using the steel cord for reinforcing rubber articles as a reinforcing material, and more particularly to a pneumatic radial tire for construction vehicles.

  Steel cords used for reinforcement of construction vehicle tires and conveyor belts are required to have high strength, and steel cords with a double twist structure in which multiple steel filaments are twisted and strands are further twisted are widely used. Many techniques for improving the steel cord having such a double twist structure have been proposed. For example, Patent Document 1 proposes a steel cord with a double twist structure in which a strand having a specific structure with good roundness is selected and the strand is twisted in the same direction as the outermost filament to improve strength. It has been reported that by using this steel cord as a reinforcing material, the weight of the tire can be reduced, the fuel consumption can be reduced, and the transportation cost can be reduced.

Further, in Patent Document 2, sufficient rubber is infiltrated into the steel cord having a double twist structure by setting the diameters of the core strand and the surrounding (sheath) strand within a predetermined range, thereby having the maximum reinforcing effect. It has been proposed to do so.
Japanese Patent No. 3506279 ([Claim 1], [0007], etc.) JP-A-6-240590 ([Claim 1], [0003], etc.)

  However, with the development of vehicles in recent years, the demand for tires is also demanded for durability at higher speeds and higher loads. In particular, mining vehicles are required to improve fatigue resistance against inputs such as bending and compression, cut resistance due to trauma, etc., even for reinforcing steel cords, in order to break rough roads with high loads. However, the current situation is that the conventional code has reached the limit for these requirements.

  Accordingly, an object of the present invention is to provide a steel cord for reinforcing rubber articles having durability capable of satisfying all of these recent requirements for vehicles, and air in which durability is improved by using the steel cord for reinforcing rubber articles as a reinforcing material. The purpose is to provide a radial tire.

  As a result of intensive studies to solve the above problems, the present inventor has found that bending and compression input increases due to high speed and high load, and sometimes the reinforcing steel cord is also locally locally compressed and deformed, resulting in fatigue of the cord. It has been found that it leads to breakage. In addition, the deformation due to the compression is a deformation that approximates a sine wave of half wavelength or one wavelength. If this deformation is an ideal sine wave deformation, the distortion due to the compression is dispersed, and the deformation until the breakage occurs. Although the life was improved, it was found that when the deformation was close to the triangular wave deformation, the strain was concentrated near the apex, and the life until breakage was greatly reduced. Therefore, as a result of further intensive studies to control compression deformation by the cord structure based on such knowledge, the present inventor has found that the life of fatigue fracture can be improved more than ever by adopting the following configuration. The invention has been completed.

  That is, the steel cord for reinforcing rubber articles of the present invention is composed of one core strand having a two-layer or three-layer twist structure and six sheath strands having a two-layer or three-layer twist structure surrounding the core strand. In the steel cord for reinforcing a rubber article having a 1 + 6 double twist structure, all the layer twist directions in the core strand and the twist direction of the sheath strand are the same direction, and the layer twist direction in the sheath strand is It consists of a combination of different directions.

  The pneumatic radial tire of the present invention is a pneumatic radial tire in which a carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and a crown portion of the carcass is reinforced with a belt layer. The carcass and / or the belt The steel cord for reinforcing rubber articles is applied to the layer.

  According to the present invention, since the compression deformation of the steel cord approximates an ideal sine wave deformation, the strain due to the compression is dispersed and the life until breakage is improved. The code is obtained. Therefore, the pneumatic radial tire to which the steel cord for reinforcing rubber articles is applied also has an effect of excellent durability.

Hereinafter, one preferred embodiment of the present invention will be described in detail.
The steel cord for reinforcing rubber articles of the present invention is composed of one core strand having a two-layer or three-layer twist structure and six sheath strands having a two-layer or three-layer twist structure surrounding the core strand. 1 + 6 double twist structure. As a strand having a two-layer twist structure, 3 + 9 and the like are preferable, and as a strand having a three-layer twist structure, 3 + 9 + 15 and the like are preferable. The layer twist structure of each strand may be the same or different, but from the viewpoint of the cord uniformity, the contact area between the filaments, the manufacturing cost, etc., the structure of the six sheath strands of the strands may be the same. preferable.

  In the present invention, it is important that all the layer twist directions in the core strand are the same as the twist direction of the sheath strand, and the layer twist directions in the sheath strand are a combination of different directions. This mechanism will be described in detail below with reference to FIG.

  FIG. 1 shows the twisting direction and compression direction of each layer in a steel cord 10 of a 1 + 6 double twist structure composed of a core strand 1 having a two-layer twist structure and a sheath strand 4 having a two-layer twist structure surrounding the core strand 1. Is schematically shown.

  In order to bring the compression deformation of the steel cord 10 shown in FIG. 1 close to the ideal sine wave deformation, it is effective to reduce the compression rigidity in the cord axis direction indicated by the thick arrow. Therefore, the twist direction of all the layers in the core strand 1 (in the illustrated example, the inner layer 2 and the outer layer 3) and the twist direction of the sheath strand 4 are the same direction. By setting the same direction in this way, the directions of untwisting of the core strand 1 and the sheath strand 4 during compression become the same as shown by thin arrows, and the compression rigidity (thick arrow) in the cord axis direction is reduced. .

  On the other hand, the sheath strand 4 needs to be promoted so that the core strand 1 and the entire cord 10 are uniformly bent and deformed. Therefore, it is desirable that the sheath strand 4 itself be untwisted uniformly with respect to compression in the cord axial direction, and it is necessary to ensure compression rigidity in the axial direction of the sheath strand 4. In order to ensure such rigidity, the twist direction of the layers in the sheath strand 4 needs to be different direction twist. That is, in order to bring the cord 10 close to an ideal sine wave deformation during compression, the twist direction of all the layers (the inner layer 2 and the outer layer 3) in the core strand 1 and the twist direction of the sheath strand 4 are set in the same direction. In addition, the twisting directions of the layers in the sheath strand 4 (in the illustrated example, the inner layer 5 and the outer layer 6) are different directions, and combining these both makes the compression deformation of the steel cord 10 closer to the ideal sin wave deformation. is important.

  Moreover, the wire diameter of the filament which comprises each strand becomes like this. Preferably it is 0.15-0.34 mm. When the wire diameter of the filament is less than 0.15 mm, when the steel cord is applied to a pneumatic radial tire for construction vehicles, the necessary air pressure cannot be maintained, and the applicable range is limited. On the other hand, if it is larger than 0.34 mm, the fatigue property at the time of large bending such as a hump portion is lowered.

  Furthermore, it is preferable that the sheath strand is twisted at a twist angle of 73 degrees or more and less than 86 degrees with respect to the direction perpendicular to the cord center line. If the twist angle is less than 73 degrees, the cord is not broken, but the strength at the time of breaking the cord is lowered, which is not preferable. On the other hand, if it is 86 degrees or more, the bending rigidity becomes high, the workability is remarkably lowered, and it is not suitable for reinforcing rubber articles.

  As described above, the steel cord for reinforcing rubber articles of the present invention has better durability than before because the strain due to compression is dispersed and the life until breakage is improved as compared with the steel cord having the conventional double twist structure. ing. Therefore, for example, instead of a conventional steel cord having a double twist structure, a ply formed by arranging a plurality of cords parallel to each other and embedded in a rubber sheet is not shown, but in a toroidal shape between a pair of bead portions. When used as a carcass ply and / or belt ply of a pneumatic radial tire for construction vehicles in which the extending carcass is a skeleton and the crown of the carcass is reinforced with a belt layer, the durability of high speed and high load is greatly improved. become.

Next, the present invention will be specifically described with reference to examples and comparative examples.
Various steel cords according to the cord structures, twist pitches, and twist directions shown in Tables 1 to 3 below were made as trial products. In addition, among the steel cords shown in Tables 1 to 3, a strand consisting of 3 core filaments and 9 sheath filaments was twisted in a 1 + 6 double twist structure, and 1 × (3 + 9) + 6 × (3 + 9) +1 structure The steel cord is shown in FIG. 2, and a strand composed of 3 core filaments, 9 intermediate sheath filaments and 15 outer sheath filaments is twisted in a 1 + 6 double twisted structure. 1 × (3 + 9 + 15) + 6 × (3 + 9 + 15) The steel codes of the +1 structure are shown in FIG. In the figure, reference numeral 1 denotes a core strand, 2 denotes an inner layer, 3 denotes an outer layer, 4 denotes a sheath strand, 5 denotes an inner layer, 6 denotes an outer layer, and 7 and 8 denote intermediate layers.

The following tests were performed on the obtained cord.
The compression fatigue resistance test cords were applied as ply cords for a construction vehicle radial tire (size: 4000R57), and a sample having a width of 10 cm, a length of 10 cm, and a thickness of 6 cm was cut out from the bead portion. An input of 6% compression strain, 5 Hz, and 1 million repetitions was applied to the sample indoors, and the presence or absence of a cord cut after the test was evaluated. ○ indicates that there is no code breakage, and x indicates that there is a code breakage.
Rotating Bending Fatigue A rotating bending test was carried out on the same sample as above, and the value of the number of unbroken pieces / total number of filaments was determined. In Example 4, Comparative Example 2 was set to 100. Otherwise, Comparative Example 1 was set to 100 The index was displayed. The larger the value, the better the result.
Cord breaking strength Each cord was stretched in the cord axis direction, and the load at the time of breaking was evaluated. In Example 4, the comparative example 2 was set to 100, and other than that, the comparative example 1 was set to 100 and displayed as an index. The larger the value, the better the result.
The presence or absence of productivity problems was evaluated during the preparation of processable tires. ○ indicates good and × indicates poor.
The obtained results are shown in Tables 1 to 3 below.

  From the test results shown in Tables 1 to 3, in a cord having a 1 + 6 double twist structure, a strand composed of two or three layer twist cords, all layer twist directions in the core strand and sheath strand twist directions In the cords of the examples in which the same direction was used and the layer twist in the sheath strand was different, it was confirmed that the local compression fatigue property was improved in all cases.

It is explanatory drawing which shows typically the twist direction of each layer of the steel cord which concerns on suitable embodiment of this invention. It is sectional drawing of the steel cord of a 1x (3 + 9) + 6x (3 + 9) structure. It is sectional drawing of the steel cord of a 1 * (3 + 9 + 15) + 6 * (3 + 9 + 15) structure.

Explanation of symbols

1 Core strand 2, 5 Inner layer 3, 6 Outer layer 4 Sheath strand 7, 8 Intermediate layer

Claims (4)

  Steel for reinforcing rubber articles having a 1 + 6 double twist structure composed of one core strand having a two-layer or three-layer twist structure and six sheath strands having a two-layer or three-layer twist structure surrounding the core strand. In the cord, a rubber article characterized in that all layer twist directions in the core strand and the twist direction of the sheath strand are the same direction, and the layer twist directions in the sheath strand are a combination of different directions. Steel cord for reinforcement.   The steel cord for reinforcing rubber articles according to claim 1, wherein a wire diameter of a filament constituting the core strand and the sheath strand is in a range of 0.15 to 0.34 mm.   The steel cord for reinforcing rubber articles according to claim 1 or 2, wherein the sheath strand is twisted at a twist angle of 73 degrees or more and less than 86 degrees with respect to a direction perpendicular to the cord center line.   A pneumatic radial tire in which a carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and a crown portion of the carcass is reinforced by a belt layer, and the carcass and / or the belt layer is any one of claims 1 to 3. A pneumatic radial tire characterized in that the steel cord for reinforcing rubber articles according to one item is applied.

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