JP2008255509A - Steel cord for reinforcing rubber article and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord for reinforcing a rubber article, having improved cord strength obtained by heightening a utilization factor of the cord by preventing the occurrence of preceding breakage of the outmost filament in the steel cord in a double-twisted structure, and to provide a pneumatic tire using the steel cord as the reinforcing material. <P>SOLUTION: The steel cord for reinforcing the rubber article in the double twisted structure is obtained by arranging and twisting six sheath strands 2 having three or more-layered layer-twisted structure comprising filaments having the same wire diameter around one core strand 1 having three or more-layered layer-twisted structure comprising the filaments having the same wire diameter. The twisting angle α<SB>c</SB>of the core filament 11, the twisting angle α<SB>is</SB>of the inner layer sheath filament 12, and the twisting angle α<SB>os</SB>of the outermost layer sheath filament 13, constituting each strand satisfy the relation represented by the expression (1): α<SB>c</SB>≈α<SB>is</SB>>α<SB>os</SB>(1). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steel cord for reinforcing rubber articles and a pneumatic tire using the same (hereinafter, also simply referred to as “steel cord” and “tire”), and more specifically, is suitably used for reinforcing rubber articles such as tires. The present invention relates to a steel cord for reinforcing rubber articles and a pneumatic tire using the same as a reinforcing material.

  Steel cords used to reinforce carcass plies, belt plies, or conveyor belts in construction vehicle tires require high strength, so twist a strand of multiple steel filaments together. A steel cord with a double twist structure is widely used. For such steel cords, cord materials (especially carbon as a means to increase cord strength without increasing the cross-sectional area of the steel cord) in order to achieve reduction of tire weight, lower fuel consumption, and reduction of transportation costs. The content is improved and the tensile strength of the filament is increased by changing the processing method (for example, the area reduction rate at the time of wire drawing) to increase the cord strength.

  However, although the conventional method of increasing the tensile strength of the filament and increasing the cord strength is effective for steel cords having a single twist structure or a normal layer twist structure, a double twist with a large diameter using a layer twist structure as a strand. In the steel cord of the structure, there is a problem that the cord strength does not increase by the increase in the tensile strength of the filament, and various improvements have been made conventionally.

  Regarding the improvement of the steel cord having a double twist structure, for example, Patent Document 1 discloses a steel cord having a structure of 7 × 19 made of (1 + 6 + 12) + 6 × (1 + 6 + 12), and an outermost filament in the sheath strand and an adjacent inner layer. A technique for obtaining high cord strength by specifying the tensile strength of a filament by a ratio is disclosed.

Patent Document 2 discloses that the tensile strength of the outermost sheath filament constituting the strand is 3040 N / mm ² or less, and the tensile strength of all inner filaments excluding the outermost sheath filament is 3140 N / mm ² or more. A technique for obtaining a high code strength is disclosed.

Furthermore, the outermost layer filament constituting the strand has a larger diameter than the inner filament, and a technique for obtaining high cord strength by avoiding the preceding break (Patent Document 3), and the tensile strength of the filament constituting the strand “Filament tensile strength of the layer near the center of the strand ≧ filament tensile strength of the layer far from the center of the strand” and the average tensile strength of the strand “average tensile strength of the strand near the center of the cord <layer far from the center of the cord” It is also known to obtain a high cord strength by preventing the preceding breakage of the filament by defining the “average tensile strength of the strands” (Patent Document 4).
Japanese Patent No. 3439329 Japanese Patent No. 3709551 International Publication WO01 / 034900 Pamphlet JP 2005-248373 A

  According to the technique disclosed in Patent Document 2 among the above, although high cord strength can be obtained, the inner filament tensile strength is increased to further increase the cord strength, and the difference from the tensile strength of the outermost sheath filament is increased. If it was too large, part of the filament would also cause a pre-break, and the strength of the cord might not rise as expected.

As described above, the conventional method for increasing the tensile strength of the filament to increase the cord strength is effective for a steel cord having a single twist structure or a normal layer twist structure, and has a large diameter in which a layer twist structure is used as a strand. Even in a steel cord having a double twist structure, the tensile strength of the filament is effective when it is 3040 N / mm ² or less. However, when the tensile strength is higher than that, the increase in the cord strength cannot be obtained by the increase in the tensile strength of the filament.

  In addition, the steel cord disclosed in Patent Document 3 is sufficiently effective immediately after production, and a high cord strength is obtained. However, depending on the thermal history during long-term storage and tire production, the cord strength may be increased. There was a case where it is considerably lowered immediately after production.

  Therefore, in the conventional technology, in the steel cord having the double twist structure, the problem of the preceding breakage of the outermost layer filament that occurs when the cord strength is further improved cannot be sufficiently solved, and more excellent improvement technology can be realized. It was sought after.

  Accordingly, an object of the present invention is to prevent the occurrence of preceding breakage of the outermost layer filament in a steel cord having a double twist structure, and to increase the cord utilization rate, thereby improving the strength of the rubber article, and the steel cord for reinforcing rubber articles It is providing the pneumatic tire which used as a reinforcing material.

In order to solve the above-mentioned problems, the inventor has intensively studied a steel cord having a large-diameter double twist structure. As a result, the twist angle α _c of the core filament constituting the strand, the twist angle α _is of the inner sheath filament, and the outermost layer By making the relationship of the twist angle α _os of the sheath filament satisfy α _c ≈α _is ≧ α _os , the tension burden of the outermost layer filament of the core strand that breaks earlier can be reduced, thereby It has been found that the cord strength can be improved by suppressing breakage, and the present invention has been completed.

That is, the steel cord for reinforcing rubber articles of the present invention has three or more layers composed of filaments having the same wire diameter around one core strand having a three-layer twisted structure composed of filaments having the same wire diameter. In a steel cord for reinforcing rubber articles having a double twist structure in which six sheath strands having a twist structure are arranged and twisted together,
The twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament are _expressed by the following formula (1),
α _c ≈α _is > α _os (1)
It is characterized by satisfying the relationship indicated by.

In the present invention, the twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament are represented by the following formulas (2) and (3),
0.98 ≦ α _is / α _c <1.00 (2)
α _os / α _c <0.96 (3)
Is preferably satisfied. Further, the tensile strength of all the filaments constituting each strand is preferably 3040 N / mm ² or more, and the carbon content of all the filaments constituting each strand is also preferably 0.80 wt% or more.

  The pneumatic tire of the present invention is characterized in that the steel cord for reinforcing rubber articles of the present invention is used as a reinforcing material.

  According to the present invention, by adopting the above-described configuration, it is possible to suppress a preceding break at the contact portion between the strands of the outermost filaments, and realize a steel cord for reinforcing rubber articles that has improved cord strength as compared with the conventional one. It became possible to do. Therefore, by using the steel cord for reinforcing rubber articles of the present invention as a reinforcing material for a pneumatic tire, a pneumatic tire can be obtained that can realize weight reduction, fuel consumption reduction, and transportation cost suppression. .

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional view of a steel cord for reinforcing rubber articles according to a preferred embodiment of the present invention. As shown in the figure, the steel cord for reinforcing rubber articles according to the present invention is composed of 3 filaments having the same wire diameter around one core strand 1 having a layer twist structure of three or more layers made of filaments having the same wire diameter. It has a 1 + 6 double twist structure in which six sheath strands 2 having a layer twist structure equal to or more than one layer are arranged and twisted. Moreover, the code | symbol 3 shows the outermost layer filament of a strand.

As described above, in a steel cord having a relatively small diameter such as a single twist structure or a normal layer twist structure, the cord strength is determined by the tensile strength of each filament. However, in the case of the cord strength of the steel cord having a strand of 1 + 6 as described above, in addition to the tensile strength of the individual filaments, the core strand and the sheath strand are in strong contact with each other by the cord tension, and the contact point In this case, stress concentrates on each outermost layer filament to cause a prior shear failure of the outermost layer filament, and the cord strength may not be improved by an increase in the tensile strength of each filament. In particular, such a pre-breaking phenomenon often appears in filaments with high tensile strength that are easily sheared. Especially for filaments with a tensile strength of 3040 N / mm ² or more, the improvement in cord strength is suppressed as the tensile strength of the filament increases, and long-term storage is achieved. Or even due to the thermal history during tire manufacture. From this point of view, the present invention is directed to the steel cord having the above-mentioned double twist structure in which such a phenomenon has conventionally occurred.

  As a preferred example of the steel cord having a double twist structure according to the present invention, as shown in the figure, seven strands of three core filaments 11, nine inner sheath filaments 12, and fifteen outer sheath filaments 13 are twisted. In addition, a steel cord having a 7 × (3 + 9 + 15) +1 structure in which one spiral filament 4 is wound around a spiral winding can be given. The spiral filament 4 is wound to strengthen the cord bundle, but is not essential in the present invention and can be omitted.

In the present invention, in the steel cord having the above-mentioned double twist structure, the twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament are _expressed by the following formula ( 1),
α _c ≈α _is > α _os (1)
Satisfy the relationship indicated by. By making the twist angle of the core filament and the twist angle of the inner layer sheath filament equal and larger than the twist angle of the outermost layer sheath filament, the tension load of the core filament and inner layer sheath filament is increased and it is easy to break ahead It is possible to reduce the tension load on the outermost sheath filament of the strand, thereby suppressing the shear fracture at the time of pulling and reflecting the increase in the tensile strength of these filaments directly in the improvement of the cord strength.

In the present invention, the relationship among the twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament _is in addition to the condition of the above formula (1). , The following formulas (2) and (3),
0.98 ≦ α _is / α _c <1.00 (2)
α _os / α _c <0.96 (3)
Is preferably satisfied, whereby the code strength can be further improved.

Particularly in the present invention, in the steel cord having the above-mentioned double twist structure, the tensile strength of all the filaments constituting each strand is 3040 N / mm ² or more. When the tensile strength of the filament is less than 3040 N / mm ^2, there is no occurrence of preceding breakage, so that it is not necessary to apply the present invention. In addition, as a material of a filament, it is preferable that carbon content is 0.80 weight% or more.

  In the steel cord for reinforcing rubber articles according to the present invention, as described above, the cord strength is improved as compared with the steel cord having a conventional double twist structure. Therefore, for example, for a construction vehicle in which a steel cord of the present invention is used in place of a steel cord having a conventional double twist structure, and a ply formed by arranging a plurality of the cords in parallel and buried in a rubber sheet is applied to a belt or a carcass. In this pneumatic radial tire, it is possible to reduce weight, reduce fuel consumption, and reduce transportation costs.

  As a preferred example of the pneumatic tire of the present invention, for example, a large off-road radial tire having a tire size of about 40.00R57 as shown in FIG. 2 can be cited. The illustrated tire has a carcass ply 22 that extends in a toroidal manner between bead cores 21 embedded in a pair of left and right bead portions, and six layers that are disposed outside the tread portion 23 in the tire radial direction. A belt 24 is provided, and the steel cord of the present invention can be suitably applied as a reinforcing material for the carcass ply 22 in such a tire. In this case, the number of cords to be driven into the carcass ply 22 can be set to about 8.0 / 50 mm, for example.

  The pneumatic tire of the present invention only needs to use the steel cord of the present invention as a reinforcing material for a carcass ply or a belt, and other details of the tire structure and materials of each member are commonly used. Can be adopted as appropriate, and should not be particularly limited.

Hereinafter, the present invention will be described in more detail with reference to examples.
In accordance with the conditions shown in Tables 1 and 2 below, a steel for reinforcing rubber articles having a multi-twist structure comprising one core strand having a three-layer twist structure and six sheath strands having a three-layer twist structure A cord was made. The cord structures of the steel cords other than Comparative Example 6 are all the same in a 7 × (3 + 9 + 15) +1 structure (see FIG. 1), and only the steel cord of Comparative Example 6 has a 7 × (3 + 9 + 12) +1 structure. As shown in the drawing, each steel cord is formed by twisting six sheath strands 2 around a core strand 1 and winding one spiral filament 4 around a spiral winding. Each strand is formed by twisting nine inner sheath filaments 12 and fifteen (or twelve) outermost sheath filaments 13 around three core filaments 11.

About the steel cord of each Example and the comparative example, the cord breaking strength and the strength exertion rate were evaluated both immediately after the production and after the heating, and the rate of change in strength before and after that was determined. The results are shown together with the values of the twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, the twist angles α _os , α _is / α _c and α _os / α _c of the outermost sheath filament. These are shown in Tables 1 and 2 below. Here, the strength exhibiting rate (%) is the percentage of the ratio of the cord breaking strength to the total breaking strength of the filaments constituting the cord. Immediately after production-the rate of change after heating (%) is immediately after production. It is a change rate of the cord breaking strength after heating with respect to the cord breaking strength.

  As shown in Tables 1 and 2, in the steel cords for reinforcing rubber articles having a predetermined double twist structure, in Examples 1 and 2 that satisfy predetermined conditions for the twist angle of the filaments constituting each strand, It has been confirmed that the code utilization rate can be improved to achieve a high code strength, and that there is little decrease in the code strength even after heating.

It is sectional drawing which shows the steel cord for rubber article reinforcement of one suitable example of this invention. It is an expanded partial sectional view showing a pneumatic tire of one suitable example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core strand 2 Sheath strand 3 Outermost layer filament 4 Spiral filament 11 Core filament 12 Inner layer sheath filament 13 Outer layer sheath filament 21 Bead core 22 Carcass ply 23 Tread part 24 Belt

Claims (5)

Six sheath strands having a twisted structure of three or more layers made of filaments having the same wire diameter are arranged around one core strand having a twisted structure of three or more layers made of filaments of the same wire diameter. In steel cords for reinforcing rubber articles with a twisted double twist structure,
The twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament are _expressed by the following formula (1),
α _c ≈α _is > α _os (1)
A steel cord for reinforcing rubber articles characterized by satisfying the relationship indicated by The twist angle α _c of the core filament constituting each strand, the twist angle α _is of the inner sheath filament, and the twist angle α _os of the outermost sheath filament are _expressed by the following formulas (2) and (3),
0.98 ≦ α _is / α _c <1.00 (2)
α _os / α _c <0.96 (3)
The steel cord for reinforcing rubber articles according to claim 1, satisfying a relationship represented by: The steel cord for reinforcing rubber articles according to claim 1 or 2, wherein the tensile strength of all filaments constituting each strand is 3040 N / mm ² or more.   The steel cord for reinforcing rubber articles according to any one of claims 1 to 3, wherein the carbon content of all filaments constituting each strand is 0.80% by weight or more.   A pneumatic tire using the steel cord for reinforcing rubber articles according to any one of claims 1 to 4 as a reinforcing material.

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