Steel cord and pneumatic radial tire using same

Abstract

To provide a steel cord capable of improving rubber permeability, and a pneumatic radial tire using the same.SOLUTION: In a pneumatic radial tire having a carcass layer 4 as a reinforcing layer including a plurality of reinforcing cords, there is used a steel cord 10 having a 3 / 9 structure including a first layer L1 composed of three filaments 11, and a second layer L2 composed of nine filaments 12 as a reinforcing cord of the carcass layer 4, the first layer L1 and the second layer L2 are formed by a process of twisting one time, and two-dimensional waving processing is applied to a filament 12B at at least one non-apex position P2 of three non-apex positions P2 defined between mutual three apex positions P1 of the second layer L2.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steel cord having a 3 / 9 structure and a pneumatic radial tire using the steel cord as a reinforcing cord in a reinforcing layer represented by a carcass layer, and more specifically, to a steel cord which enables improved rubber permeability and a pneumatic radial tire using the same. [Background technology]

[0002] In pneumatic radial tires for trucks and buses, steel cords having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments are generally used as reinforcing cords for the carcass layer (see, for example, Patent Document 1).

[0003] While a steel cord with the above-mentioned 3 / 9 structure has the advantage of being able to twist two layers in one go, reducing production costs, it has the disadvantage of poor rubber permeability into the cord due to the narrow filament spacing. Therefore, if moisture seeps into the cord, it will propagate along the length of the steel cord, causing rust to grow over a wide area, resulting in a problem of reduced durability of the pneumatic radial tire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-64688 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a steel cord which enables improvement in rubber permeability, and a pneumatic radial tire using the same. [Means for solving the problem]

[0006] In order to achieve the above object, the steel cord of the present invention is a steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments, the first layer and the second layer being formed by twisting together in a single twisting step, and a filament at at least one non-apex position among three non-apex positions defined between three apex positions of the second layer is two-dimensionally corrugated. The corrugated filaments are arranged so that the amplitude direction of the corrugated filaments coincides with the radial direction of the cord. It is characterized by the above.

[0007] In order to achieve the above object, the pneumatic radial tire of the present invention is a pneumatic radial tire having a reinforcing layer including a plurality of reinforcing cords, the reinforcing cords being a steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments, the first layer and the second layer being formed by twisting together in a single twisting step, and a filament at at least one non-apex position among three non-apex positions defined between three apex positions of the second layer being two-dimensionally corrugated. The corrugated filaments are arranged so that the amplitude direction of the corrugated filaments coincides with the radial direction of the cord. It is characterized by the above. Effect of the Invention

[0008] As a result of extensive research into steel cords having a 3 / 9 structure, which has low production costs, the inventors discovered that rubber permeability can be effectively improved by providing two-dimensional corrugation to filaments located at non-apex positions in the second layer, and thus arrived at the present invention.

[0009] That is, in the present invention, when a steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments is adopted as the reinforcing cord of the reinforcing layer of a pneumatic radial tire, the first and second layers are formed by twisting together in a single twisting process, and the filaments located at at least one of the three non-apex positions defined between the three apex positions of the second layer are two-dimensionally corrugated, thereby forming sufficient gaps between the filaments, thereby improving rubber permeability into the cord and improving the durability of the pneumatic radial tire.

[0010] In the above steel cord, it is preferable that the filament diameter Ds of the second layer and the corrugation height Dh satisfy the relationship 1.07≦Dh / Ds≦2.0. By specifying the corrugation height Dh in this manner, it is possible to effectively prevent the cord ends from coming apart while improving the permeability of rubber into the cord interior.

[0011] In the above steel cord, it is preferable that all of the filaments at the three non-vertex positions are two-dimensionally corrugated, which can effectively improve the permeability of rubber into the inside of the cord.

[0012] In the steel cord, the corrugated filaments are preferably arranged so that the amplitude direction of the corrugated filaments coincides with the radial direction of the cord, thereby stabilizing the shape of the steel cord and effectively preventing the ends of the cord from becoming loose.

[0013] In the present invention, the reinforcing layer of the pneumatic radial tire in which the steel cord is used is not particularly limited, and examples thereof include a carcass layer, a belt layer, and a side reinforcing layer. However, in consideration of the properties of the steel cord, the reinforcing layer in which the steel cord is used is preferably a carcass layer.

[0014] The present invention is preferably applied to pneumatic radial tires for trucks and buses, but can also be applied to pneumatic radial tires for other uses as long as the above-mentioned steel cords are used as reinforcing cords in the reinforcing layer. [Brief description of the drawings]

[0015] [Figure 1] 1 is a meridian half cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view showing an example of a steel cord having a 3 / 9 structure used in the present invention. [Diagram 3] FIG. 2 is a cross-sectional view showing extracted filaments of a second layer that is two-dimensionally corrugated in a steel cord having a 3 / 9 structure used in the present invention. [Figure 4] FIG. 2 is a side view showing extracted filaments of a second layer that is two-dimensionally corrugated in a steel cord having a 3 / 9 structure used in the present invention. [Diagram 5] FIG. 1 is a cross-sectional view showing a steel cord having a conventional 3 / 9 structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The configuration of the present invention will be described in detail below with reference to the attached drawings. Fig. 1 shows a pneumatic radial tire according to an embodiment of the present invention, with 1 being a tread portion, 2 being a sidewall portion, and 3 being a bead portion. A carcass layer 4 including a plurality of reinforcing cords extending in the tire radial direction is mounted between a pair of left and right bead portions 3, 3, and an end portion of the carcass layer 4 is folded back around a bead core 5 from the inside to the outside of the tire.

[0017] In addition, a plurality of belt layers 6 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 6 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layers 6, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of 20° to 60°, for example.

[0018] In the above pneumatic radial tire, a steel cord having a 3 / 9 structure, which will be described later, is used as the reinforcing cord of the carcass layer 4.

[0019] FIG. 2 shows a steel cord having a 3 / 9 structure used in the present invention, and FIGS. 3 and 4 show extracted filaments of the second layer in the steel cord which are two-dimensionally corrugated.

[0020] As shown in Fig. 2, the steel cord 10 has a 3 / 9 structure including a first layer L1 consisting of three filaments 11 and a second layer L2 consisting of nine filaments 12. The steel cord 10 having this 3 / 9 structure is formed by twisting together the first layer L1 consisting of three filaments 11 and the second layer L2 consisting of nine filaments 12 in a single step while the first layer L1 consisting of three filaments 11 and the second layer L2 consisting of nine filaments 12 are bundled together. This has the advantage that the production costs of the steel cord 10 can be reduced.

[0021] In the steel cord 10, the second layer L2 has three vertex positions P1. The vertex positions P1 are positions where the centers of the filaments 11 in the first layer L1 are located relative to the cross-sectional center position of the steel cord 10. Three non-vertex positions P2 are defined between the three vertex positions P1. In the second layer L2, the filament 12 located closest to the vertex position P1 is defined as a filament 12A, and the filament 12 located at the non-vertex position P2 is defined as a filament 12B. The filament 12B located at at least one of the three non-vertex positions P2, and more preferably, all of the filaments 12B located at the three non-vertex positions P2, are two-dimensionally corrugated as shown in Figs. 2 to 4. In contrast, the filament 12A located closest to the three vertex positions P1 is not two-dimensionally corrugated.

[0022] In the above-mentioned pneumatic radial tire, when a steel cord 10 having a 3 / 9 structure including a first layer L1 consisting of three filaments 11 and a second layer L2 consisting of nine filaments 12 is adopted as the reinforcing cord of the carcass layer 4, the filament 12B at at least one of three non-vertex positions P2 defined between three vertex positions P1 of the second layer L2 is two-dimensionally corrugated, so that a sufficient gap is formed between the filaments 11, 12. This improves the rubber permeability into the steel cord 10, and improves the durability of the pneumatic radial tire.

[0023] Fig. 5 shows a conventional steel cord having a 3 / 9 structure. In Fig. 5, the steel cord 20 has a 3 / 9 structure including a first layer L1 consisting of three filaments 21 and a second layer L2 consisting of nine filaments 22. In the steel cord 20, the filament 22A located closest to the three apex positions P1 and the filaments 22B located at the three non-apex positions P2 are not two-dimensionally corrugated. Therefore, the filament 22B located at the non-apex position P2 and the filaments 22A, 22A located on both sides of it are linearly aligned, and the cross-sectional shape of the steel cord 20 is generally triangular. In this case, the filament 22B located at the non-apex position P2 in the second layer L2 is arranged so as to close the gap between the filaments 21, 21 of the first layer L1, resulting in poor rubber permeability.

[0024] In contrast, in the above-mentioned steel cord 10, the filaments 12B at the non-vertex position P2 in the second layer L2 are two-dimensionally corrugated, and this significantly improves the rubber permeability. This makes it possible to improve the rubber permeability of the steel cord 10 having the 3 / 9 structure while taking advantage of the low production cost. However, in the steel cord 10 having the 3 / 9 structure, even if the filaments 12A at the vertex position P1 in the second layer L2 are two-dimensionally corrugated, the rubber permeability is hardly improved.

[0025] In the above steel cord 10, it is preferable that the wire diameter Ds and the corrugation height Dh of the filaments 12 (12B) in the second layer L2 satisfy the relationship 1.07≦Dh / Ds≦2.0. By specifying the corrugation height Dh in this manner, it is possible to prevent the steel cord 10 from coming apart while improving the rubber permeability into the inside of the steel cord 10. Here, if Dh / Ds<1.07, the effect of improving the rubber permeability decreases, and if Dh / Ds>2.0, the cord shape becomes unstable and the cord ends are more likely to come apart.

[0026] In the above steel cord 10, the strand diameter Dc of the filaments 11 constituting the first layer L1 and the strand diameter Ds of the filaments 12 constituting the second layer L2 may be the same or different from each other, but it is preferable that the strand diameters Dc, Ds are set in the range of, for example, 0.15 mm to 0.25 mm.

[0027] In the above-mentioned steel cord 10, it is preferable that the corrugated filaments 12B are arranged so that their amplitude direction coincides with the radial direction of the cord, as shown in Fig. 2. This stabilizes the shape of the steel cord 10 and effectively prevents the cord ends from becoming loose. In other words, by aligning the amplitude direction of the corrugated filaments 12B with the radial direction of the cord, the filaments 12B at the non-apex position P2 do not displace the filaments 12A at the apex position P1, and a stable arrangement structure as shown in the figure can be realized. EXAMPLES

[0028] Steel cords of the conventional example, comparative example 1, and examples 1 to 6 were produced as reinforcing cords constituting the carcass layer of a pneumatic radial tire having a tire size of 11R22.5.

[0029] That is, in the conventional example, comparative example 1, and examples 1 to 6, a steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments was used as the reinforcing cord of the carcass layer. The number of corrugated filaments in the second layer (corrugation number) and the ratio Dh / Ds of the wire diameter and the corrugation height of the filaments in the second layer were set as shown in Table 1. The wire diameter Dc of the filaments in the first layer was 0.20 mm, and the wire diameter Ds of the filaments in the second layer was 0.20 mm.

[0030] The steel cords were evaluated for rubber attachment rate, end breakage, and fatigue resistance by the following evaluation methods. The results are shown in Table 1.

[0031] Steel cord rubber attachment rate: A test specimen was prepared by embedding the steel cord used in the carcass layer in rubber and vulcanizing it, then cutting the test specimen so that the cut end of the steel cord was exposed, and the cut end of the steel cord of the test specimen was immersed in salt water with a concentration of 25% and a temperature of 25°C and left for 14 days. The steel cord was then pulled out of the test specimen, and the rubber attachment rate (%) on the cord surface was measured. A higher rubber attachment rate means better rubber penetration into the cord interior.

[0032] Steel cord end breakage: The steel cords used in the carcass layer were cut with pliers while being held at a position 70 cm away from the cut end, and the filament breakage at the cut end was observed. The evaluation results were indicated as "A" when no breakage occurred after cutting, "B" when the breakage length was 50 mm or less, and "C" when the breakage length was more than 50 mm.

[0033] Fatigue resistance of steel cord: A test specimen was prepared by embedding the steel cords used in the carcass layer in rubber and vulcanizing it, and then the test specimen was attached to a three-point roller type rotary bending fatigue tester with a roller diameter of 35 mm, and the logarithmic value of the number of times the steel cords in the test specimen were bent until they broke under a cord tension of 180 N was recorded. The evaluation results were shown as an index with the conventional example being set at 100. The higher the index value, the better the fatigue resistance of the steel cord.

[0034] [Table 1]

[0035] As is clear from Table 1, in comparison with the conventional examples, in Examples 1 to 6, the rubber attachment rate of the steel cord constituting the carcass layer was high, i.e., the rubber permeability into the inside of the cord was good. However, in Example 3, the ratio Dh / Ds of the wire diameter to the corrugation height of the filaments in the second layer was small, so the improvement effect of the rubber permeability was small. In Example 6, the ratio Dh / Ds of the wire diameter to the corrugation height of the filaments in the second layer was large, so the improvement effect of the rubber permeability was large, but the ends of the steel cord were prone to coming undone.

[0036] On the other hand, in Comparative Example 1, although the filaments at the apex positions of the second layer were corrugated, the filaments at non-apex positions of the second layer were not corrugated, and therefore the rubber penetration into the inside of the cord was insufficient. [Explanation of symbols]

[0037] 1 Tread section 2 Sidewall 3 Bead section 4 Carcass layer 5 Bead Core 6 Belt Layer 10 Steel Cord 11 First layer filament 12 Second layer filament 12A Filament in apex position 12B Filament in non-apical position

Claims

1. A steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments, the first layer and the second layer being formed by twisting together in a single twisting step, and a filament located at at least one non-apex position among three non-apex positions defined between three apex positions of the second layer is two-dimensionally corrugated, and the corrugated filament is arranged such that its amplitude direction coincides with the cord radial direction.

2. 2. The steel cord according to claim 1, wherein a filament diameter Ds of the filaments in the second layer and a corrugation height Dh satisfy the relationship 1.07≦Dh / Ds≦2.

0.

3. 3. The steel cord according to claim 1, wherein all of the filaments at the three non-apex positions are two-dimensionally corrugated.

4. A pneumatic radial tire having a reinforcing layer including a plurality of reinforcing cords, wherein a steel cord having a 3 / 9 structure including a first layer consisting of three filaments and a second layer consisting of nine filaments is used as the reinforcing cord, the first layer and the second layer are formed by twisting together in a single twisting process, and a filament located at at least one non-apex position among three non-apex positions defined between three apex positions of the second layer is two-dimensionally corrugated, and the corrugated filament is arranged so that its amplitude direction coincides with the cord radial direction.

5. 5. The pneumatic radial tire according to claim 4, wherein a filament diameter Ds of the second layer filaments and a corrugation height Dh satisfy the relationship 1.07≦Dh / Ds≦2.

0.

6. 6. The pneumatic radial tire according to claim 4, wherein all of the filaments at the three non-apex positions are two-dimensionally corrugated.

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