JP2018188776A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire that allows improvement of durability.SOLUTION: In a pneumatic radial tire, a steel cord 10 is included as a reinforcement cord, which comprises two core filaments 11 lined up without any twist and N (N=1-3) sheath filaments 12 twisted around the core filaments 11. An element wire diameter dc of the core filament 11 and an element wire diameter ds of the sheath filament 12 are in the range from 0.15 mm to 0.40 mm. The tensile strength Tc (MPa) of the core filaments 11 satisfies a relation of 4100-2000dc≤Tc≤4500-2000dc with respect to the element wire diameter dc (mm), and the tensile strength Ts (MPa) of the sheath filaments 12 satisfies a relation of 3700-2000ds≤Ts<4100-2000ds with respect to the element wire diameter ds (mm).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic radial tire in which a steel cord having a 2 + N structure (N = 1 to 3) is used as a reinforcement cord of a reinforcement layer typified by a belt layer, and more specifically, to improve durability. It relates to a pneumatic radial tire that has been made possible.

  In pneumatic radial tires for passenger cars or light trucks, steel cords having a 2 + N structure are widely used as reinforcing cords for belt layers (see, for example, Patent Documents 1 to 3). More specifically, for example, there is a 2 + 1 structure steel cord having two core filaments arranged without twisting and one sheath filament twisted around the core filament.

  A steel cord having such a 2 + N structure is preferably used as a reinforcing cord for a belt layer of a pneumatic radial tire for passenger cars or light trucks. When the tire receives a load, the core filament of the steel cord is used. However, there is a drawback that fatigue fracture is easily caused by compressive stress. If the fatigue resistance of the steel cord is insufficient, the durability of the pneumatic radial tire cannot be sufficiently ensured.

JP 2007-63706 A JP 2012-219389 A JP2015-58900A

  An object of the present invention is to provide a pneumatic radial tire that can improve durability when a steel cord having a 2 + N structure (N = 1 to 3) is used as a reinforcing cord for a reinforcing layer.

  In order to achieve the above object, a pneumatic radial tire according to the present invention is a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords. A steel cord having a filament and N (N = 1 to 3) sheath filaments twisted around the core filament is used, and the core filament strand diameter dc and the sheath filament strand The diameter ds is in the range of 0.15 mm to 0.40 mm, and the tensile strength Tc (MPa) of the core filament satisfies the relationship of 4100−2000 dc ≦ Tc ≦ 4500−2000 dc with respect to the strand diameter dc (mm). The tensile strength Ts (MPa) of the sheath filament is 3700-20 with respect to the strand diameter ds (mm). And it is characterized in satisfying the 0ds ≦ Ts <4100-2000ds relationship.

  The present inventor has intensively studied the fatigue fracture of a steel cord having a 2 + N structure, and since the twist angle of the core filament is smaller than the twist angle of the sheath filament, when the steel cord receives a compressive force in the longitudinal direction, It was found that the core filament is more susceptible to compressive stress than the sheath filament and is subject to fatigue fracture, and further, it is possible to improve fatigue resistance by increasing the tensile strength of the core filament. As a result, they have reached the present invention.

  That is, in the present invention, as the reinforcing cord of the reinforcing layer of the pneumatic tire, there are two core filaments arranged without twisting and N pieces (N = 1 to 3) twisted around the core filament. When using a steel cord having a sheath filament, the core filament strand diameter dc and the sheath filament strand diameter ds are optimized, and the core filament tensile strength Tc is increased so that the core filament can be fatigued. Can be suppressed. On the other hand, by lowering the tensile strength Ts of the sheath filament, it is possible to prevent disconnection due to a decrease in cord toughness. Thereby, the fatigue resistance of the steel cord can be improved, and the durability of the pneumatic radial tire using the steel cord can be improved. Further, when the tensile strength Ts of the sheath filament is lowered, there is also an advantage that the steel cord can be easily twisted and the productivity can be maintained well.

  In this invention, it is preferable that the twist pitch Ps of a sheath filament exists in the range of 10.0 mm-20.0 mm. Thereby, fatigue resistance can be improved, maintaining the elongation characteristic of a steel cord favorably.

  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 characteristics of the steel cord, the reinforcing layer in which the steel cord is used is preferably a belt layer. In this case, the fatigue resistance of the steel cord contained in the belt layer can be improved, and the durability of the pneumatic radial tire can be effectively improved.

  Further, the present invention is preferably applied to pneumatic radial tires for passenger cars or light trucks, but as long as the steel cord as described above is used as a reinforcing cord for the reinforcing layer, It can also be applied to pneumatic radial tires.

1 is a meridian half cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is a side view which shows an example of the steel cord which has a 2 + N structure used by this invention. It is sectional drawing which shows the steel cord of FIG.

  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, where 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, 3, and an end portion of the carcass layer 4 is folded around the bead core 5 from the inside to the outside of the tire. It is. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

  On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 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 layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. For the purpose of improving high-speed durability, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed on the outer peripheral side of the belt layer 7. Yes. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In the pneumatic radial tire, a steel cord having a 2 + N structure, which will be described later, is used as a reinforcement cord for the belt layer 7.

  2 and 3 show an example of a steel cord having a 2 + N structure used in the present invention. As shown in FIGS. 2 and 3, the steel cord 10 is composed of two core filaments 11 arranged without twisting and N pieces (N = 1 to 3) twisted around the core filament 11. And a sheath filament 12. In the present embodiment, the steel cord 10 is composed of two core filaments 11 and one sheath filament 12. That is, it is a 2 + 1 structure. Other examples include a 2 + 2 structure and a 2 + 3 structure.

  In the steel cord 10, the strand diameter dc of the core filament 11 and the strand diameter ds of the sheath filament 12 are set in a range of 0.15 mm to 0.40 mm, respectively. Further, the tensile strength Tc (MPa) of the core filament 11 satisfies the relationship of 4100−2000 dc ≦ Tc ≦ 4500−2000 dc with respect to the strand diameter dc (mm), and the tensile strength Ts (MPa) of the sheath filament 12 is The relationship of 3700−2000ds ≦ Ts <4100−2000ds is satisfied with respect to the strand diameter ds (mm). The tensile strengths Tc and Ts of the filaments 11 and 12 can be appropriately adjusted based on the carbon content of steel and the degree of wire drawing.

  In the pneumatic radial tire described above, as the reinforcing cord of the belt layer 7, two core filaments 11 arranged without twisting and N pieces (N = 1 to 3) twisted around the core filament 11. When the steel cord 10 having the sheath filament 12 is used, the strand diameter dc of the core filament 11 and the strand diameter ds of the sheath filament 12 are optimized, and the tensile strength Tc of the core filament 11 is increased. Fatigue fracture of the core filament 11 can be suppressed. That is, in the steel cord 10 having the twisted structure as described above, the twist angle θc with respect to the cord longitudinal direction of the core filament 11 is smaller than the twist angle θs with respect to the cord longitudinal direction of the sheath filament 12 as shown in FIG. When the steel cord 10 is subjected to a compressive force in the longitudinal direction, the core filament 11 is more susceptible to compressive stress than the sheath filament 12, but fatigue resistance is achieved by increasing the tensile strength Tc of the core filament 11. Can be increased. On the other hand, by lowering the tensile strength Ts of the sheath filament 12, it is possible to prevent disconnection due to a decrease in the toughness of the steel cord 10. Thereby, the fatigue resistance of the steel cord 10 can be improved, and the durability of a pneumatic radial tire using the steel cord 10 can be improved. Further, when the tensile strength Ts of the sheath filament 12 is lowered, there is also an advantage that the steel cord 10 can be easily twisted and the productivity can be maintained well.

  Here, in the steel cord 10, it is necessary to set the strand diameter dc of the core filament 11 and the strand diameter ds of the sheath filament 12 within a range of 0.15 mm to 0.40 mm. By optimizing the diameters dc and ds, good fatigue resistance can be ensured while sufficiently securing the cord strength. If the wire diameters dc and ds are smaller than 0.15 mm, the cord strength becomes insufficient, and conversely if larger than 0.40 mm, the fatigue resistance is lowered. Moreover, it is preferable to satisfy | fill the relationship of dc / ds <= 1.10. In particular, dc = ds is preferable.

  Further, the tensile strength Tc (MPa) of the core filament 11 needs to satisfy the relationship of 4100−2000 dc ≦ Tc ≦ 4500−2000 dc with respect to the strand diameter dc (mm). If it is smaller than −2000 dc (MPa), the fatigue resistance of the core filament 11 becomes insufficient. Conversely, if it is larger than 4500−2000 dc, the cord productivity is lowered, and disconnection is likely to occur due to the lowering of the cord toughness. . In particular, 4200−2000 dc ≦ Tc ≦ 4500−2000 dc is preferable. The tensile strength Ts (MPa) of the sheath filament 12 needs to satisfy the relationship of 3700−2000 ds ≦ Ts <4100−2000 ds with respect to the wire diameter ds (mm), and the tensile strength Ts is 3700−2000 ds. If it is smaller than 1, the strength of the cord cannot be sufficiently secured. On the other hand, if it is larger than 4100-2000 ds, the productivity of the cord is lowered, and the disconnection is likely to occur due to the lowering of the cord toughness.

  In the steel cord 10, the number of the core filaments 11 is two. This is to stabilize the flat structure of the steel cord 10. Moreover, although the number of the sheath filaments 12 is N (N = 1 to 3), when the number is out of the above range, the balance with respect to the core filament 11 is deteriorated and it is difficult to obtain a stable twisted structure. .

  In the pneumatic radial tire, as shown in FIG. 2, the twist pitch Ps of the sheath filament 12 is in the range of 10.0 mm to 20.0 mm, more preferably in the range of 12.0 mm to 20.0 mm. Thereby, fatigue resistance can be improved, maintaining the elongation characteristic of the steel cord 10 favorably. Here, if the twist pitch Ps of the sheath filament 12 is smaller than 10.0 mm, for example, the hoop effect due to the belt layer 7 is reduced, so that the outer diameter grows easily in the tire. As the compression rigidity of the cord 10 increases, the fatigue resistance decreases due to belt folding or belt edge separation.

  In the above-described embodiment, the case where the steel cord 10 having the 2 + N structure is used for the belt layer 7 has been described. However, in the present invention, the steel cord 10 as described above can be applied to another reinforcing layer. .

  In the pneumatic radial tire of tire size 195 / 55R16, tires of Conventional Example 1, Comparative Examples 1-2, and Examples 1-5 in which only the reinforcement cords of the belt layer were changed were manufactured.

  That is, in Conventional Example 1, Comparative Examples 1 and 2 and Examples 1 to 5, two core filaments that are arranged in a non-twisted manner as reinforcing cords for the belt layer, and 2 twisted around the core filament. A steel cord having a sheath filament was used, and the tensile strength Tc, Ts, strand diameter dc, ds of each filament, and the twist pitch Ps of the sheath filament were set as shown in Table 1.

  For these test tires, the cord productivity and tire durability were evaluated by the following evaluation methods, and the results are also shown in Table 1.

Code productivity:
In producing steel cords used for each test tire, the productivity was evaluated. The evaluation results are indicated by “◯” when a stable twisted structure is obtained, indicated by “△” when a slight disturbance occurs in the twisted structure, or when a filament breakage occurs slightly during the twisting process, The case where the twisted structure was greatly disturbed and the cord productivity was lowered, or the case where the filament breakage occurred significantly during the twisting process was indicated by “x”.

Tire durability:
Each test tire is mounted on a test rim having a rim size of 16 inches, and a running test is performed by an indoor drum tester under the conditions of an air pressure of 200 kPa, a speed of 90 km / h, and an initial load of 4.2 kPa. It was increased by 2 kN and the running time until the tire failed was measured. The evaluation results are shown as an index with Conventional Example 1 as 100. The larger the index value, the better the durability.

  As is clear from Table 1, in Examples 1 to 5, compared with Conventional Example 1, the fatigue resistance of the steel cord was improved and the durability of the pneumatic radial tire was improved. On the other hand, in Comparative Example 1, since the tensile strength Tc of the core filament was too high, the cord productivity was reduced, and the effect of improving tire durability was not obtained due to the reduction in cord toughness. In Comparative Example 2, since not only the tensile strength Tc of the core filament but also the tensile strength Ts of the sheath filament is increased, the cord productivity is lowered and the cost is increased due to excessive quality.

  Next, tires of Conventional Example 11, Comparative Examples 11 to 12, and Examples 11 to 15 in which only the reinforcing cords of the belt layer were changed in a pneumatic radial tire having a tire size of 195 / 55R16 were manufactured.

  That is, in Conventional Example 11, Comparative Examples 11-12, and Examples 11-15, two core filaments arranged in a non-twisted manner as a reinforcing cord of the belt layer, and 1 twisted around the core filament A steel cord having a sheath filament was used, and the tensile strength Tc, Ts, strand diameter dc, ds of each filament, and the twist pitch Ps of the sheath filament were set as shown in Table 2.

  About these test tires, code productivity and tire durability were evaluated by the above-described evaluation method, and the results are also shown in Table 2. However, the evaluation results of tire durability are indicated by an index with the conventional example 11 as 100.

  As is apparent from Table 2, when the steel cord having the 2 + 1 structure was used, the same result as that when the steel cord having the 2 + 2 structure was used was obtained.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer 10 Steel cord 11 Core filament 12 Sheath filament

Claims (3)

  In a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, as the reinforcing cord, two core filaments that are arranged in a non-twisted manner and N strands that are twisted around the core filament (N = 1 to 3) is used, and the core filament strand diameter dc and the sheath filament strand diameter ds are in the range of 0.15 mm to 0.40 mm, The tensile strength Tc (MPa) of the core filament satisfies the relationship of 4100-2000 dc ≦ Tc ≦ 4500-2000 dc with respect to the strand diameter dc (mm), and the tensile strength Ts (MPa) of the sheath filament is the strand diameter. satisfying the relationship of 3700−2000ds ≦ Ts <4100−2000ds with respect to ds (mm). A pneumatic radial tire for a butterfly.   The pneumatic radial tire according to claim 1, wherein a twist pitch Ps of the sheath filament is in a range of 10.0 mm to 20.0 mm.   The pneumatic radial tire according to claim 1, wherein the reinforcing layer is a belt layer.

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