JP6870451B2 - Steel cord and pneumatic radial tire using it - Google Patents

Description

The present invention relates to a steel cord having a two-layer structure composed of N core filaments (N = 1 to 3) and M sheath filaments twisted around the core filaments (M = 5 to 9). Regarding a pneumatic radial tire using the steel cord as a reinforcing cord of a reinforcing layer, more specifically, a steel cord capable of improving rubber permeability and durability and a pneumatic radial tire using the same. Regarding tires.

In pneumatic radial tires for trucks and buses, a two-layer steel cord consisting of N core filaments and M sheath filaments twisted around the core filaments is used as a reinforcing cord for the belt layer. (See, for example, Patent Documents 1 to 3). More specifically, for example, a steel cord having a 2 + 7 structure including two core filaments and seven sheath filaments, and a steel cord having a 3 + 8 structure including three core filaments and eight sheath filaments can be mentioned. Be done.

The steel cord as described above is generally a tight cord, but in order to improve the rubber permeability, the filament constituting the steel cord may be habituated. However, when the filament is habituated, the elongation characteristics of the steel cord change, and the initial elongation (elongation rate in the low load range) tends to become excessive. If the initial elongation of the steel cord is excessive, there is a concern that the durability of the pneumatic radial tire will decrease due to this.

Japanese Unexamined Patent Publication No. 2000-273778 Japanese Unexamined Patent Publication No. 2001-11783 Japanese Unexamined Patent Publication No. 2001-288685

An object of the present invention is to provide a steel cord capable of improving rubber permeability and durability, and a pneumatic radial tire using the steel cord.

The steel cord of the present invention for achieving the above object includes N core filaments (N = 1 to 3) and M sheath filaments twisted around the core filaments (M = 5 to 9). In a steel cord having a two-layer structure composed of, two (M-2) sheath filaments of the sheath filaments are habituated, and all of the habituated sheath filaments are around the core filament. It is characterized in that it is arranged so as to be lined up continuously.

The pneumatic radial tire of the present invention for achieving the above object is a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, and N cores (N = 1 to 3) are used as the reinforcing cords. A steel cord having a two-layer structure composed of a filament and M (M = 5-9) sheath filaments twisted around the core filament is used, and 2 to (M) of the sheath filaments are used. -2) A book sheath filament is habituated, and all of the habituated sheath filaments are arranged so as to be continuously arranged around the core filament.

The present inventor has diligently studied a steel cord having a two-layer structure, and found that when the sheath filament is habituated to improve rubber permeability, the number of habituated sheath filaments and the arrangement thereof are specified to make steel. It was found that the initial elongation of the cord can be suppressed and the durability can be effectively improved, and the present invention was reached.

That is, in the present invention, as the reinforcing cord of the reinforcing layer of the pneumatic radial tire, N core filaments (N = 1 to 3) and M threads (M = 5 to 9) twisted around the core filaments are used. When using a steel cord having a two-layer structure composed of the sheath filaments of the above, it is possible to improve the rubber permeability into the inside of the steel cord by habituating 2 (M-2) sheath filaments. Moreover, by arranging all of the habitual sheath filaments in a continuous line around the core filament, the initial elongation of the steel cord can be suppressed, and the durability of the pneumatic radial tire can be improved. It can be effectively improved.

In the present invention, it is preferable that the core filament and the sheath filament are twisted in the same direction and at the same pitch. As a result, the core filament and the sheath filament can be twisted together, so that the productivity of the steel cord can be increased, and sufficient rubber permeability can be ensured even in such a twisted structure. ..

Further, it is preferable that the wire diameter dc of the core filament and the wire diameter ds of the sheath filament satisfy the relationship of 0.8 ≦ ds / dc <1.0. By making the core filament thicker than the sheath filament in this way, the rubber permeability into the inside of the steel cord can be improved. Further, when the core filament is thicker than the sheath filament, the steel cord is less likely to buckle, which is preferable from the viewpoint of durability.

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, considering the characteristics of the steel cord, the reinforcing layer in which the steel cord is used is preferably a belt layer. In this case, the rubber permeability of the steel cord contained in the belt layer can be improved, and the durability of the pneumatic radial tire can be effectively improved. The steel cord can also be used as a reinforcing cord for reinforcing rubber products other than tires.

Further, the present invention is preferably applied to a pneumatic radial tire for trucks and buses, but as long as the steel cord as described above is used as a reinforcing cord for a reinforcing layer, the present invention is pneumatically used for purposes other than the above. It can also be applied to radial tires.

It is a meridian semi-cross-sectional view which shows the pneumatic radial tire which concerns on embodiment of this invention. It is sectional drawing which shows an example of the steel cord which has a two-layer structure used in this invention. It is a side view which shows another example of the steel cord which has a two-layer structure used in this invention. It is a side view which shows an example of the steel cord which does not satisfy the requirement of this invention. 2 is a graph showing the elongation characteristics of the steel cords of FIGS. 2 and 4. It is a side view which shows by extracting the sheath filament which was habituated in the steel cord of FIG. 2 and FIG. 2 is a side view showing extracted core filaments and sheath filaments that are not habituated in the steel cords of FIGS. 2 and 3. (A) to (f) are cross-sectional views showing the arrangement of filaments of various steel cords used in the test.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a pneumatic radial tire according to an embodiment of the present invention, in which 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 including a plurality of reinforcing cords extending in the tire radial direction is mounted between the pair of left and right bead portions 3 and 3, and the end portion of the carcass layer 4 is folded back from the inside to the outside of the tire around the bead core 5. It has been.

Further, 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 that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In the belt layer 6, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 20 ° to 60 °.

In the pneumatic radial tire, a steel cord having a two-layer structure, which will be described later, is used as a reinforcing cord for the belt layer 6.

FIG. 2 shows an example of a steel cord having a two-layer structure used in the present invention. As shown in FIG. 2, the steel cord 10 includes N core filaments (N = 1 to 3) and M sheath filaments 12 (M = 5 to 9) twisted around the core filaments 11. It has a two-layer structure consisting of. In this embodiment, the steel cord 10 is composed of two core filaments 11 and seven sheath filaments 12. That is, it has a 2 + 7 structure. As another example, for example, as shown in FIG. 3, a 3 + 8 structure can be mentioned. When the steel cord 10 has a plurality of core filaments 11, it is desirable that the core filaments 11 are twisted together.

In the steel cord 10 described above, of the M sheath filaments 12, 2 (M-2) sheath filaments 12A are habituated, and the remaining sheath filaments 12B are habituated. Not. In FIGS. 2 and 3, each of the four sheath filaments 12A is habituated. Then, while all of the habituated sheath filaments 12A are arranged so as to be continuously arranged around the core filament 11, all of the unhabited sheath filaments 12B are continuously arranged around the core filament 11. They are arranged side by side. That is, as shown in FIGS. 2 and 3, the M sheath filaments 12 are arranged so as to surround the core filament 11, but all of the habitualized sheath filaments 12A are arranged so as to be adjacent to each other. All of the unhabited sheath filaments 12B are arranged adjacent to each other.

In the above-mentioned pneumatic radial tire, N core filaments 11 (N = 1 to 3) and M threads (M = 5 to 9) twisted around the core filaments 11 are used as reinforcing cords for the belt layer 7. When using the steel cord 10 having a two-layer structure composed of the sheath filament 12 of the above, by habituating the 2 (M-2) sheath filaments 12A, the rubber permeability into the inside of the steel cord 10 is improved. Can be improved. Moreover, by arranging all of the habituated sheath filaments 12A so as to be continuously arranged around the core filament 11, the sheath filaments 12A are arranged at predetermined positions in a state where the habituation phases are aligned. Therefore, the initial elongation of the steel cord 10 can be suppressed, and the durability of the pneumatic radial tire can be effectively improved.

Here, the difference between the physical properties of the steel cord 10 (FIG. 2) included in the present invention and the physical properties of the steel cord 10 (FIG. 4) not included in the present invention will be described. In the steel cord 10'shown in FIG. 4, the sheath filament 12A is habituated and the sheath filament 12B is not habituated, which is the same as the example of FIG. 2, but FIG. Unlike the examples, all of the habituated sheath filaments 12A are not arranged to line up continuously around the core filament 11. Then, when the elongation rate (%) of the steel cord 10 shown in FIG. 2 and the steel cord 10'shown in FIG. 4 was measured while changing the tensile load (N), the results shown in FIG. 5 were obtained. As shown in FIG. 5, the steel cord 10'of FIG. 4 in which not all of the habituated sheath filaments 12A are arranged so as to be continuously arranged around the core filament 11 is the habituated sheath filament 12A. The initial elongation is larger than that of the steel cord 10 of FIG. 2, in which all of them are arranged so as to be continuously arranged around the core filament 11. Such an increase in initial elongation is due to the arrangement of the habitual sheath filament 12A.

In the steel cord 10 described above, the number of core filaments 11 is N (N = 1-3) and the number of sheath filaments 12 is M (M = 5-9), which are rubber permeability and shape. This is to ensure stability. If the number of core filaments 11 and sheath filaments 12 is too large, the rubber permeability is lowered, and if the number of sheath filaments 12 is too small, it becomes difficult to obtain a stable twisted structure. Further, the 2 (M-2) sheath filaments 12A are habituated in order to suppress the initial elongation while ensuring the rubber permeability. If the number of habituated sheath filaments 12A is too small, the rubber permeability is lowered, and conversely, if the number is too large, the initial elongation becomes excessive.

As shown in FIG. 6, the sheath filament 12A of the steel cord 10 is habituated to meander along its longitudinal direction. The form of habituation may be wavy or spiral. The wave height H of the sheath filament 12A is preferably in the range of 1.3 ≦ H / ds ≦ 2.0 with respect to the wire diameter ds of the sheath filament 12A. If this ratio H / ds is too small, the effect of improving rubber permeability is reduced, and conversely, if it is too large, the effect of suppressing initial elongation is reduced. Further, the habituation pitch L of the sheath filament 12A is preferably in the range of 10 ≦ L / H ≦ 30 with respect to the wave height H of the sheath filament 12A. If this ratio L / H is too small, the effect of suppressing initial elongation is reduced, and conversely, if it is too large, the effect of improving rubber permeability is reduced.

As shown in FIG. 7, in the steel cord 10, the core filament 11 is twisted in one direction (for example, S twist) by the pitch Pc, and the sheath filament 12 is twisted in one direction (for example, S twist) by the pitch Ps. There is. Further, the pitch Pc and the pitch Ps are set to the same value. As described above, the core filament 11 and the sheath filament 12 are preferably twisted in the same direction and at the same pitch. As a result, the core filament 11 and the sheath filament 12 can be twisted together, so that the productivity of the steel cord 10 can be increased. Moreover, even when such a twisted structure is adopted, sufficient rubber permeability can be ensured.

In the steel cord 10, it is preferable that the wire diameter dc of the core filament 11 and the wire diameter ds of the sheath filament 12 satisfy the relationship of 0.8 ≦ ds / dc <1.0. By making the core filament 11 thicker than the sheath filament 12 in this way, the rubber permeability into the inside of the steel cord 10 can be improved. Further, when the core filament 11 is made thicker than the sheath filament 12, the steel cord 10 is less likely to buckle, which is preferable from the viewpoint of durability. However, if the ratio ds / dc is too small, the strong balance between the core filament 11 and the sheath filament 12 becomes poor, and inconveniences such as disconnection are likely to occur.

In the steel cord 10, the wire diameter dc of the core filament 11 and the wire diameter ds of the sheath filament 12 are preferably set in the range of 0.15 mm to 0.40 mm. By optimizing the wire diameters dc and ds in this way, it is possible to secure good fatigue resistance while sufficiently ensuring the strength of the cord. If the wire diameters dc and ds are smaller than 0.15 mm, the cord strength becomes insufficient, and conversely, if it is larger than 0.40 mm, the fatigue resistance is lowered.

In the above-described embodiment, the case where the steel cord 10 having a two-layer structure is used for the belt layer 6 has been described, but in the present invention, the steel cord 10 as described above can be applied to another reinforcing layer. is there.

In the pneumatic radial tire having a tire size of 295 / 80R22.5, the tires of the conventional example, Comparative Examples 1 to 3 and Examples 1 to 5 in which only the reinforcing cord of the belt layer was different were manufactured.

That is, in the conventional example, Comparative Examples 1 to 3 and Examples 1 to 5, as the reinforcing cord of the belt layer, a steel cord or two cores having a 3 + 8 structure composed of three core filaments and eight sheath filaments. Using a steel cord having a 2 + 7 structure consisting of a filament and seven sheath filaments, the wire diameter dc of the core filament, the wire diameter ds of the sheath filament, the ratio ds / dc, the number of habituated sheath filaments, The arrangement of the habituated sheath filaments was set as shown in Table 1. The arrangement of the habituated sheath filaments is as shown in FIGS. 8 (a) to 8 (f), but in order to facilitate understanding, the habituated sheath filaments in FIGS. 8 (a) to 8 (f). Is shaded. Further, in each steel cord, the core filament and the sheath filament were twisted in the same direction and at the same pitch.

The rubber penetration rate and tire durability of these test tires were evaluated by the following evaluation methods, and the results are also shown in Table 1.

Rubber penetration:
Take out the steel cord of the belt layer from each test tire, remove the rubber adhering to the outside of the steel cord with a cutter knife, and determine the rubber penetration rate in the cord when one sheath strand and one core filament are removed. It was measured visually. Such a measurement was performed on steel cords arranged at eight locations on the tire circumference, and the average value of the rubber penetration rates of these eight steel cords was obtained and used as the rubber penetration rate.

Tire durability:
Each test tire was attached to a test rim with a rim size of 22.5 x 7.50, and a running test was conducted with an indoor drum tester under the conditions of an air pressure of 800 kPa, an initial speed of 160 km / h, and a load of 30 kN, and every 10 minutes. The speed was increased by 10 km / h, and the running time until the tire failed was measured. The evaluation result is shown by an index of 100 in the conventional example. The larger the index value, the better the durability.

As is clear from Table 1, in Examples 1 to 5, the rubber penetration rate of the steel cord was high and the tire durability was excellent as compared with the conventional examples. In particular, as can be seen from Examples 3 to 5, when the wire diameter dc of the core filament is made appropriately thicker than the wire diameter ds of the sheath filament, the effect of improving the tire durability is remarkably exhibited. On the other hand, in Comparative Examples 1 and 2, although the number of habituated sheath filaments is the same as that of Example 1, all the habituated sheath filaments are continuously arranged around the core filament. Since it was not arranged in, the effect of improving tire durability could not be obtained due to the increase in initial elongation. Further, in Comparative Example 3, since the number of habituated sheath filaments was too small, the rubber permeability was insufficient, and the effect of improving the tire durability could not be obtained.

1 Tread part 2 sidewall part 3 bead part 4 carcass layer 5 bead core 6 belt layer 10 steel cord 11 core filament 12 sheath filament 12A habitual sheath filament 12B unhabited sheath filament

Claims (7)

The sheath filament in a steel cord having a two-layer structure composed of N core filaments (N = 1 to 3) and M sheath filaments twisted around the core filament (M = 5 to 9). Two (M-2) of these sheath filaments are habituated, and all of the habituated sheath filaments are arranged so as to be continuously arranged around the core filament. Steel cord. The steel cord according to claim 1, wherein the core filament and the sheath filament are twisted in the same direction and at the same pitch. The steel cord according to claim 1 or 2, wherein the wire diameter dc of the core filament and the wire diameter ds of the sheath filament satisfy the relationship of 0.8 ≦ ds / dc <1.0. In a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, N core filaments (N = 1 to 3) and M (M) twisted around the core filaments are used as the reinforcing cords. A steel cord having a two-layer structure composed of sheath filaments of = 5-9) is used, and 2 (M-2) sheath filaments of the sheath filaments are habituated. A pneumatic radial tire characterized in that all of the attached sheath filaments are arranged so as to be continuously arranged around the core filament. The pneumatic radial tire according to claim 4, wherein the core filament and the sheath filament are twisted in the same direction and at the same pitch. The pneumatic radial according to claim 4 or 5, wherein the wire diameter dc of the core filament and the wire diameter ds of the sheath filament satisfy the relationship of 0.8 ≦ ds / dc <1.0. tire. The pneumatic radial tire according to any one of claims 4 to 6, wherein the reinforcing layer is a belt layer.

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