JP6930187B2 - Pneumatic radial tire - Google Patents

Description

In the present invention, as a reinforcing cord of a reinforcing layer represented by a carcass layer, a core composed of three filaments, an intermediate layer composed of N (N = 8 to 9) filaments, and M (M = 13 to 15) A pneumatic radial tire in which a steel cord having an outermost layer made of a filament is used, and more particularly, a pneumatic radial tire capable of improving durability.

In pneumatic radial tires for trucks and buses, steel cords having a multi-layer twisted structure are widely used as reinforcing cords for the carcass layer (see, for example, Patent Documents 1 to 3). More specifically, for example, a core composed of three filaments twisted to each other, an intermediate layer composed of nine filaments twisted around the core filament, and an intermediate layer twisted around the intermediate layer15. Examples thereof include a steel cord having a 3 + 9 + 15 structure having an outermost layer made of a book filament.

A steel cord having such a multi-layer twisted structure is preferably used as a reinforcing cord for the carcass layer of a pneumatic radial tire for trucks and buses, and when the tire is loaded, the core filament of the steel cord is used. Is subject to compressive stress and is prone to fatigue fracture. If the fatigue resistance of the steel cord is insufficient, the durability of the pneumatic radial tire cannot be sufficiently ensured.

Japanese Unexamined Patent Publication No. 2008-290502 Japanese Unexamined Patent Publication No. 2007-15627 Japanese Unexamined Patent Publication No. 2005-336664

An object of the present invention is to provide a pneumatic radial tire capable of improving durability when a steel cord having a multi-layer twisted structure is used as a reinforcing cord of a reinforcing layer.

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, wherein the reinforcing cord is a core composed of three filaments twisted to each other. And the most composed of an intermediate layer consisting of N filaments (N = 8-9) twisted around the core and M filaments (M = 13-15) twisted around the intermediate layer. A steel cord having an outer layer is used, and the filament of the core and the filament of the intermediate layer are twisted in the same direction and at the same pitch, and the tensile strength Tc (MPa) of the filament of the core is the wire diameter thereof. The relationship of 4100-2000 dc ≦ Tc ≦ 4500-2000 dc is satisfied with respect to dc (mm), and the tensile strength Tm (MPa) of the filament of the intermediate layer is 2000 ≦ Tm <4100 with respect to the wire diameter dm (mm). satisfy the relationship of -2000Dm, the meet the relationship of 2000 ≦ Ts <4100-2000ds relative tensile strength of the outermost layer filaments Ts (MPa) is the wire diameter ds (mm), containing the filaments of the core The wire diameter dc, the wire diameter dm of the filament of the intermediate layer, and the wire diameter ds of the filament of the outermost layer satisfy the relationship of 0.15 mm ≦ ds ≦ dm <dc ≦ 0.25 mm. Is.

The present inventor has diligently studied the fatigue fracture of a steel cord having a multi-layer twisted structure, and found that when the filaments of the core and the filaments of the intermediate layer are twisted in the same direction and at the same pitch, the steel cord is compressed in the longitudinal direction. It was found that when a force is applied, the filament of the core is more susceptible to compressive stress and fracture due to fatigue than the filament of the intermediate layer, and further, by increasing the tensile strength of the filament of the core, It was discovered that the fatigue resistance can be improved, and the present invention was reached.

That is, in the present invention, as a reinforcing cord of the reinforcing layer of a pneumatic tire, a core composed of three filaments twisted to each other and N filaments (N = 8 to 9) twisted around the core are used. In using a steel cord having an intermediate layer and an outermost layer composed of M filaments (M = 13 to 15) twisted around the intermediate layer, the filaments of the core and the filaments of the intermediate layer are arranged in the same direction. By twisting at the same pitch and increasing the tensile strength Tc of each filament constituting the core, fatigue fracture of each filament constituting the core can be suppressed. On the other hand, by lowering the tensile strength Tm of each filament constituting the intermediate layer and the tensile strength Ts of each filament constituting the outermost layer, it is possible to prevent disconnection due to a decrease in cord toughness. As a result, 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 Tm of each filament constituting the intermediate layer and the tensile strength Ts of each filament constituting the outermost layer are lowered, the twisting of the steel cords can be facilitated and the productivity thereof can be maintained satisfactorily. There is also an advantage.

In the present invention, the relationship between the wire diameter dc of the filament of the core, the wire diameter dm of the filament of the intermediate layer, and the wire diameter ds of the filament of the outermost layer is 0.15 mm ≦ ds ≦ dm <dc ≦ 0.25 mm. It is preferable to satisfy the relationship of 1.0 ≦ dm / ds ≦ 1.05 and 1.0 <dc / dm ≦ 1.10. As a result, it is possible to improve the rubber permeability into the inside of the steel cord while maintaining good fatigue resistance.

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 carcass layer. In this case, the fatigue resistance of the steel cord contained in the carcass 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 trucks and buses, but as long as the above-mentioned steel cord 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 the multi-layer twist structure used in this invention. It is a side view which shows by extracting each filament of the core, the intermediate layer and the outermost layer of 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, 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 multi-layer twisted structure, which will be described later, is used as a reinforcing cord for the carcass layer 4.

FIG. 2 shows an example of a steel cord having a multi-layer twisted structure used in the present invention, and FIG. 3 shows an extraction of each filament of the core, the intermediate layer and the outermost layer of the steel cord. As shown in FIG. 2, the steel cord 10 is composed of a core 11A composed of three filaments 11 twisted to each other and N filaments 12 (N = 8 to 9) twisted around the core 11A. It has an intermediate layer 12A and an outermost layer 13A composed of M filaments 13 (M = 13 to 15) twisted around the intermediate layer 12A. In the present embodiment, the steel cord 10 is composed of a core 11A composed of three filaments 11, an intermediate layer 12A composed of nine filaments 12, and an outermost layer 13A composed of 15 filaments 13. That is, it has a 3 + 9 + 15 structure. As another example, for example, a 3 + 8 + 13 structure can be mentioned.

In the steel cord 10, as shown in FIG. 3, the filaments 11 constituting the core 11A are twisted in one direction (for example, S twist) by the pitch Pc, and the filaments 12 constituting the intermediate layer 12A are twisted in one direction (for example, S twist) by the pitch Pm. For example, the filament 13 which is twisted in the S twist) and constitutes the outermost layer 13A is twisted in the other direction (for example, the Z twist) by the pitch Ps. Further, at least the pitch Pc and the pitch Pm are set to the same value. That is, the filament 11 of the core 11A and the filament 12 of the intermediate layer 12A are twisted in the same direction and at the same pitch.

In the steel cord 10, the tensile strength Tc (MPa) of each filament 11 constituting the core 11A satisfies the relationship of 4100-2000 dc ≦ Tc ≦ 4500-2000 dc with respect to the wire diameter dc (mm), and the intermediate layer 12A is formed. The tensile strength Tm (MPa) of each of the constituent filaments 12 satisfies the relationship of 2000 ≦ Tm <4100-2000 dm with respect to the wire diameter dm (mm), and the tensile strength Ts of each filament 13 constituting the outermost layer 13A ( MPa) satisfies the relationship of 2000 ≦ Ts <4100-2000 ds with respect to the wire diameter ds (mm). The tensile strengths Tc, Tm, and Ts of these filaments 11, 12, and 13 can be appropriately adjusted based on the carbon content of the steel and the degree of wire drawing.

In the above-mentioned pneumatic radial tire, as the reinforcing cord of the carcass layer 4, the core 11A composed of three filaments 11 twisted to each other and the N cores (N = 8 to 9) twisted around the core 11A are used. In using the steel cord 10 having an intermediate layer 12A made of filament 12 and an outermost layer 13A made of M filaments 13 (M = 13 to 15) twisted around the intermediate layer 12A, the filament of the core 11A is used. By twisting the filaments 12 of 11 and the intermediate layer 12A in the same direction and at the same pitch and increasing the tensile strength Tc of each filament 11 constituting the core 11A, fatigue fracture of each filament 11 constituting the core 11A is suppressed. can do. On the other hand, by lowering the tensile strength Tm of each filament 12 constituting the intermediate layer 12A and the tensile strength Ts of each filament 13 constituting the outermost layer 13A, disconnection due to a decrease in the toughness of the steel cord 10 is prevented. Can be done. As a result, the fatigue resistance of the steel cord 10 can be improved, and the durability of the pneumatic radial tire using the steel cord 10 can be improved. Further, when the tensile strength Tm of each filament 12 constituting the intermediate layer 12A and the tensile strength Ts of each filament 13 constituting the outermost layer 13A are lowered, the steel cord 10 can be easily twisted and the productivity thereof is improved. It also has the advantage of being able to be maintained.

Here, the tensile strength Tc (MPa) of each filament 11 constituting the core 11A needs to satisfy the relationship of 4100-2000 dc ≤ Tc ≤ 4500-2000 dc with respect to the wire diameter dc (mm). If the tensile strength Tc is smaller than 4200-2000 dc (MPa), the fatigue resistance of the filament 11 constituting the core 11A becomes insufficient, and conversely, if it is larger than 4500-2000 dc, the cord productivity decreases. Due to the decrease in cord toughness, disconnection is likely to occur. The tensile strength Tm (MPa) of each filament 12 constituting the intermediate layer 12A needs to satisfy the relationship of 2000 ≦ Tm <4100-2000 dm with respect to the wire diameter dm (mm). If is smaller than 2000, the cord strength cannot be sufficiently secured, and conversely, if it is larger than 4100-2000 dm, the cord productivity is lowered and the cord toughness is lowered, so that disconnection is likely to occur. The tensile strength Ts (MPa) of each filament 13 constituting the outermost layer 13A needs to satisfy the relationship of 2000≤Ts <4100-2000ds with respect to the wire diameter ds (mm). If is smaller than 2000, the cord strength cannot be sufficiently secured, and conversely, if it is larger than 4100-2000 ds, the cord productivity is lowered and the cord toughness is lowered, so that disconnection is likely to occur.

In the steel cord 10, the number of filaments 11 constituting the core 11A is set to 3, in order to stabilize the twisted structure of the intermediate layer 12A and the outermost layer 13A arranged around the steel cord 10. Further, the number of filaments 12 constituting the intermediate layer 12A is N (N = 8 to 9), but when the number is out of the above range, the filaments 12 constituting the intermediate layer 12A are arranged at a predetermined position. It becomes difficult to obtain a stable twisted structure. Similarly, the number of filaments 13 constituting the outermost layer 13A is M (M = 13 to 15), but when the number is out of the above range, the filaments 13 constituting the outermost layer 13A are arranged at a predetermined position. It becomes difficult to obtain a stable twisted structure.

In the steel cord 10, the wire diameter dc of the filament 11 of the core 11A, the wire diameter dm of the filament 12 of the intermediate layer 12A, and the wire diameter ds of the filament 13 of the outermost layer 13A are 0.15 mm ≦ ds ≦ dm <dc. It is preferable to satisfy the relationship of ≦ 0.25 mm and the relationships of 1.0 ≦ dm / ds ≦ 1.05 and 1.0 <dc / dm ≦ 1.10. By defining the magnitude relationship of the wire diameters dc, dm, and ds in this way, it is possible to improve the rubber permeability into the inside of the steel cord 10 while maintaining good fatigue resistance. As a result, it is possible to prevent the filaments of the steel cord 10 from coming into contact with each other to prevent breakage due to fretting, and it is possible to prevent the diffusion of rust due to the moisture that has permeated into the steel cord 10.

The rubber permeability can be improved by increasing the diameter of the filament 11 constituting the core 11A, but if the wire diameter dc exceeds 0.25 mm, the effect of improving the fatigue resistance is reduced. On the other hand, if the wire diameter dm of the filament 12 constituting the intermediate layer 12A and the wire diameter ds of the filament 13 forming the outermost layer 13A are smaller than 0.15 mm, the breaking strength of the steel cord 10 will decrease. .. Further, when the ratio dm / ds and the ratio dc / dm deviate from the above ranges, it becomes difficult to arrange the filaments 11 to 13 at predetermined positions, and the fatigue resistance is lowered.

In the above-described embodiment, the case where the steel cord 10 having a predetermined multi-layer twisted structure is used for the carcass layer 4 has been described, but in the present invention, the steel cord 10 as described above is applied to another reinforcing layer. Is possible.

In the pneumatic radial tire having a tire size of 295 / 80R22.5, the tires of Conventional Example 1, Comparative Examples 1 and 2 and Examples 1 to 6 in which only the reinforcing cord of the carcass layer was different were manufactured. However, in the present specification, Examples 1 to 3 are reference examples.

That is, in Conventional Example 1, Comparative Examples 1 and 2, and Examples 1 to 6, as the reinforcing cord of the carcass layer, a core composed of three filaments twisted to each other and nine cores twisted around the core. Using a steel cord having an intermediate layer made of filaments and an outermost layer made of 15 filaments twisted around the intermediate layer, the tensile strengths Tc, Tm, Ts, and wire diameters dc, dm of each filament are used. , Ds, ratio dc / dm, and ratio dm / ds were set as shown in Table 1.

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

Code productivity:
In producing the steel cord used for each test tire, its productivity was evaluated. The evaluation results are indicated by "○" when a stable twisted structure is obtained, and "△" when a slight disorder occurs in the twisted structure or a slight filament breakage occurs during the twisting process. The case where the twisted structure is significantly disturbed and the cord productivity is lowered, or the case where the filament disconnection occurs remarkably during the twisting process is indicated by "x".

Tire durability:
Each test tire was mounted on 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, a speed of 80 km / h, and an initial load of 30 kN, and every 24 hours. The load was increased by 6 kN, and the running time until the tire failed was measured. The evaluation result is shown by 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 6, the fatigue resistance of the steel cord could be improved and the durability of the pneumatic radial tire could be improved in comparison with the conventional example 1. On the other hand, in Comparative Example 1, since the tensile strength Tc of each filament constituting the core was too high, the cord productivity was lowered, and the effect of improving the tire durability was not obtained due to the lowered cord toughness. Further, in Comparative Example 2, not only the tensile strength Tc of each filament constituting the core but also the tensile strengths Tm and Ts of each filament constituting the intermediate layer and the outermost layer are increased, so that the cord productivity is lowered. Moreover, the effect of improving the tire durability could not be obtained due to the decrease in cord toughness.

Further, in Example 4, since both the ratio dc / dm and the ratio dm / ds were optimized, the rubber permeability into the inside of the steel cord was improved as compared with Example 1, and the effect of improving the tire durability was increased. rice field. In Example 5, since the ratio dc / dm was too large, the twisted structure of the steel cord became unstable, and the effect of improving the tire durability was reduced. In Example 6, since the ratio dm / ds was too large, the steel cord twisted structure became unstable, and the effect of improving the tire durability was reduced.

Next, in the pneumatic radial tire having a tire size of 295 / 80R22.5, the tires of Conventional Example 11, Comparative Examples 11 to 12 and Examples 11 to 16 in which only the reinforcing cord of the carcass layer was different were manufactured. However, in the present specification, Examples 11 to 13 are reference examples.

That is, in Conventional Example 11, Comparative Examples 11 to 12, and Examples 11 to 16, as the reinforcing cord of the carcass layer, a core composed of three filaments twisted to each other and eight cores twisted around the core. Using a steel cord having an intermediate layer made of filaments and an outermost layer made of 13 filaments twisted around the intermediate layer, the tensile strengths Tc, Tm, Ts, and wire diameters dc, dm of each filament are used. , Ds, ratio dc / dm, and ratio dm / ds were set as shown in Table 2.

Code productivity and tire durability were evaluated for these test tires by the above-mentioned evaluation method, and the results are also shown in Table 2. However, the evaluation result of the tire durability is shown by an index with the conventional example 11 as 100.

As is clear from Table 2, even when the steel cord having a 3 + 8 + 13 structure was used, the same result as when the steel cord having a 3 + 9 + 15 structure was used was 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 11A core 12 intermediate layer filament 12A intermediate layer 13 outermost filament 13A outermost layer

Claims (3)

In a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, the reinforcing cords include a core composed of three filaments twisted to each other and N wires (N = 8) twisted around the core. A steel cord having an intermediate layer made of filaments of to 9) and an outermost layer made of M filaments (M = 13 to 15) twisted around the intermediate layer is used, and the filament of the core is used. And the filaments of the intermediate layer are twisted in the same direction and at the same pitch, and the tensile strength Tc (MPa) of the filament of the core is 4100-2000 dc ≤ Tc ≤ 4500-2000 dc with respect to the wire diameter dc (mm). The tensile strength Tm (MPa) of the filament of the intermediate layer satisfies the relationship of 2000 ≦ Tm <4100-2000 dm with respect to the wire diameter dm (mm), and the tensile strength Ts of the filament of the outermost layer is satisfied. (MPa) is satisfied a relationship of 2000 ≦ Ts <4100-2000ds for the wire diameter ds (mm), the a wire diameter dc of filaments of said core and wire diameter dm of filaments of the intermediate layer A pneumatic radial tire characterized in that the wire diameter ds of the filament of the outermost layer satisfies the relationship of 0.15 mm ≦ ds ≦ dm <dc ≦ 0.25 mm. The wire diameter dc of the filament of the core, the wire diameter dm of the filament of the intermediate layer, and the wire diameter ds of the filament of the outermost layer are 1.0 ≦ dm / ds ≦ 1.05 , 1.0 <dc. The pneumatic radial tire according to claim 1, wherein the relationship of / dm ≤ 1.10 is satisfied. The pneumatic radial tire according to claim 1 or 2, wherein the reinforcing layer is a carcass layer.

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