JP6171759B2 - Pneumatic radial tire - Google Patents

Description

  In the present invention, a steel cord having one core filament, an intermediate layer composed of N (N = 5 to 6) filaments, and an outermost layer composed of M (M = 10 to 12) filaments is used as a carcass layer. Regarding pneumatic radial tires used as reinforcement cords for representative reinforcement layers, more specifically, pneumatic radial tires that can improve rubber penetration into the cord without reducing break strength and fatigue resistance Regarding tires.

  In pneumatic radial tires for trucks and buses, steel cords having a multi-layer twisted structure are widely used as reinforcing cords for carcass layers (see, for example, Patent Documents 1 to 3). More specifically, for example, a single core filament, an intermediate layer composed of 6 filaments twisted around the core filament, and an outermost layer composed of 12 filaments twisted around the intermediate layer. And a steel cord having a 1 + 6 + 12 structure having an outer layer.

  A steel cord having such a multi-layer twist structure is preferably used as a reinforcement cord for a carcass layer of a pneumatic radial tire for trucks and buses. However, due to the twist structure, rubber penetration into the cord is prevented. Since it is low, there is a concern about breakage due to fretting. Therefore, in order to improve rubber permeability, it is possible to reduce the number of filaments in the intermediate layer or outermost layer. In this case, if the number of filaments in the intermediate layer or outermost layer is excessively reduced, the breaking strength of the entire cord Will drop. In order to improve rubber permeability, it is conceivable to increase the diameter of the core filament to form a gap between the filaments constituting the intermediate layer and the outermost layer. In this case, the steel cord is bent and deformed. Since the strain generated in the thickened core filament when received is relatively large, the core filament is easily broken and its fatigue resistance is lowered.

JP 2008-290502 A JP 2007-15627 A JP 2005-336664 A

  The object of the present invention is to improve the rubber penetration into the cord without lowering the breaking strength or fatigue resistance when using the steel cord having a multi-layer twist structure as the reinforcing cord of the reinforcing layer. The object is to provide a pneumatic radial tire.

In order to achieve the above object, a pneumatic radial tire according to the present invention is a pneumatic radial tire including a reinforcing layer including a plurality of reinforcing cords, wherein the reinforcing cord includes one core filament, Steel having an intermediate layer composed of N (N = 5 to 6) filaments twisted around and an outermost layer composed of M (M = 10 to 12) filaments twisted around the intermediate layer Using the cord, the core filament diameter d ₁ , the intermediate filament diameter d _2, and the outermost filament diameter d ₃ satisfy the relationship d ₁ > d ₂ > d _3. The tensile strength T ₁ (MPa) of the core filament satisfies the relationship of T ₁ ≧ 4500-2000d _{1 with} respect to the strand diameter d ₁ (mm), and the tension of the filament of the intermediate layer The strength T ₂ (MPa) satisfies the relationship of 4200−2000d ₂ ≦ T ₂ ≦ 4400−2000d ₂ with respect to the wire diameter d ₂ (mm), and the tensile strength T ₃ (MPa) of the outermost layer filament is It satisfies the relationship of T ₃ ≦ 4100−2000d _{3 with} respect to the wire diameter d ₃ (mm).

In the present invention, as the reinforcing cord of the reinforcing layer of the pneumatic tire, one core filament, an intermediate layer composed of N (N = 5 to 6) filaments twisted around the core filament, and the intermediate In constructing a steel cord having M (M = 10 to 12) outermost layers twisted around the layers, the filament diameters d ₁ , d ₂ , and d ₃ of the filaments of each layer are steel cords By gradually increasing the diameter toward the center side, it is possible to form an appropriate gap between the filaments constituting the intermediate layer and the outermost layer, thereby improving the rubber permeability into the inside of the cord. Therefore, breakage due to fretting of the steel cord and diffusion of rust can be prevented.

In addition, the filament diameters d ₁ , d ₂ , and d ₃ of the filaments of each layer are sequentially increased toward the center side of the steel cord, and at the same time, the tensile strengths T ₁ , T ₂ , and T ₃ of the filaments of each layer are increased to the center of the steel cord. By gradually increasing the size toward the side, it is possible to avoid a decrease in fatigue resistance in a relatively thick filament. Furthermore, since the number of filaments in the intermediate layer and the outermost layer is sufficiently secured, it is possible to avoid a decrease in the breaking strength of the entire cord. Thereby, durability of a pneumatic radial tire can be improved.

In the present invention, the strand diameter d ₁ of the core filament is 0.23 mm or less, and the strand diameter d ₁ of the core filament and the strand diameter d ₂ of the filament in the intermediate layer are 1.0 <d ₁ / d ₂ ≦ It is preferable that the relationship 1.1 is satisfied and the filament diameter d ₂ of the intermediate layer filament and the filament diameter d ₃ of the outermost layer filament satisfy the relationship 1.0 <d ₂ / d ₃ ≦ 1.1. . Thereby, the rubber penetration improvement effect can be obtained while maintaining good fatigue resistance under a stable twisted structure.

Further, the core filament has been subjected to spiral typing, it is preferable to satisfy the relationship of H ≦ 1.1d ₁ wave height H of the core filaments for the wire diameter d _1. The effect of improving rubber permeability can be enhanced by applying a spiral mold to the core filament. In addition, by defining the wave height H of the core filament as described above, it is possible to obtain an effect of improving rubber permeability while maintaining good fatigue resistance under a stable twisted structure.

  In the present invention, the reinforcing layer 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 carcass layer. In this case, the durability of the pneumatic radial tire can be effectively improved by improving the rubber penetration into the cord in the carcass layer and maintaining good breaking strength and fatigue resistance.

  The present invention is preferably applied to pneumatic radial tires for trucks and buses. However, as long as the steel cord as described above is used as a reinforcing cord for a carcass layer, a pneumatic radial tire for uses other than the above is used. It is also applicable to.

1 is a meridian half cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is sectional drawing which shows an example of the steel cord which has a multilayer twist structure used by this invention. It is sectional drawing which shows the other example of the steel cord which has a multilayer twist structure used by this invention. It is a side view which extracts and shows the core filament of the steel cord of FIG. It is sectional drawing which shows the steel cord which has the conventional multilayer twist structure.

  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 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 layer 6, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a 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 multilayer twist structure used in the present invention. As shown in FIG. 2, the steel cord 10 is composed of one core filament 11 that has not been typed and N (N = 5 to 6) filaments 12 twisted around the core filament 11. The intermediate layer 12A has an outermost layer 13A composed of M (M = 10 to 12) filaments 13 twisted around the intermediate layer 12A. In the present embodiment, the steel cord 10 includes an intermediate layer 12A composed of one core filament 11 and six filaments 12, and an outermost layer 13A composed of twelve filaments 13. That is, it is a 1 + 6 + 12 structure.

Wire diameter d ₁ and wire diameter d ₃ of wire diameter of the filament 12 of the intermediate layer 12A d ₂ and the outermost layer 13A of the filaments 13 of the core filament 11 satisfies the relation of d _1> d _2> d ₃ . That is, the wire diameters d _{1 to} d ₃ of the filaments 11 to 13 of each layer are gradually increased toward the center side of the steel cord 10.

Further, the tensile strength T ₁ (MPa) of the core filament 11 satisfies the relationship of T ₁ ≧ 4500-2000d _{1 with} respect to its strand diameter d ₁ (mm), and the tensile strength T ₂ ( MPa) satisfies the relationship of 4200−2000d ₂ ≦ T ₂ ≦ 4400−2000d ₂ with respect to the strand diameter d ₂ (mm), and the tensile strength T ₃ (MPa) of the filament 13 of the outermost layer 13A is the strand. The relationship of T ₃ ≦ 4100−2000d ₃ is satisfied with respect to the diameter d ₃ (mm). The tensile strengths of these filaments 11 to 13 can be appropriately adjusted based on the carbon content of steel and the degree of wire drawing.

In the pneumatic radial tire described above, an intermediate layer composed of one core filament 11 and N (N = 5 to 6) filaments 12 twisted around the core filament 11 as a reinforcing cord of the carcass layer 4. In constructing the steel cord 10 having 12A and the outermost layer 13A composed of M (M = 10 to 12) filaments 13 twisted around the intermediate layer 12A, the strands of the filaments 11 to 13 of each layer When the diameters d _{1 to} d ₃ are sequentially increased toward the center side of the steel cord 10, the filaments 21 to 23 having the same strand diameter as in the conventional steel cord 20 are arranged in a tight state (see FIG. 5), an appropriate gap is formed between the filaments 12 and 13 constituting the intermediate layer 12A and the outermost layer 13A. , It is possible to improve the rubber penetration into the inside of the steel cord 10. Therefore, contact between the filaments of the steel cord 10 can be avoided to prevent breakage due to fretting, and diffusion of rust due to moisture that has penetrated into the steel cord 10 can be prevented.

Here, if the relationship of d ₁ > d ₂ > d ₃ is not satisfied for the filament diameters d ₁ to d ₃ of the filaments 11 to 13, the effect of improving rubber permeability cannot be sufficiently obtained. In particular, wire diameter d ₁ of the core filament 11 is equal to or less than 0.23 mm, the wire diameter d ₂ of the wire diameter d ₁ and the filaments 12 of the intermediate layer 12A of the core filament 11 1.0 <d ₁ / d ₂ ≦ 1.1 and the filament diameter d ₂ of the filament 12 of the intermediate layer 12A and the filament diameter d ₃ of the filament 13 of the outermost layer 13A are 1.0 <d ₂ / d ₃ ≦ 1. It is desirable to satisfy the relationship of 1. Thereby, the rubber penetration improvement effect can be obtained while maintaining good fatigue resistance under a stable twisted structure. Or wire diameter d ₁ is too large the core filament 11, when the difference between the wire diameter d ₁ to d ₃ of the adjacent layers is too large, it becomes difficult to place the filaments 11 to 13 in place, stable It becomes difficult to obtain a twisted structure. To ensure the breaking strength of the steel cord 10, the lower limit of the wire diameter d ₁ of the core filament 11 may be set to be 0.15 mm.

Further, in the pneumatic radial tire described above, the filament diameters d _{1 to} d ₃ of the filaments 11 to 13 are sequentially increased toward the center side of the steel cord 10, and at the same time, the tensile strengths T _{1 to} T _{3 of the} filaments 11 to 13 are increased. By gradually increasing the diameter toward the center side of the steel cord 10, it is possible to avoid a decrease in fatigue resistance in the relatively thick filaments 11 and 12. That is, the strain generated in the filaments 11 to 13 when the steel cord 10 is subjected to bending deformation increases as the strand diameters d _{1 to} d ₃ increase, but the strain corresponding to the strand diameters d _{1 to} d ₃ is increased. The fatigue resistance of the steel cord 10 can be improved by making the tensile strengths T _{1 to} T ₃ of the filaments 11 to 13 different from each other.

Here, the tensile strength T ₁ of the core filament 11 (MPa) is required to satisfy a relation of T ₁ ≧ 4500-2000d ₁ for the wire diameter d ₁ (mm), the tensile strength T ₁ Is less than 4500-2000d ₁ (MPa), the fatigue resistance of the core filament 11 becomes insufficient. The upper limit of the tensile strength T ₁ is preferably 4400 MPa in order to maintain good cord productivity and cord toughness. The tensile strength T ₂ (MPa) of the filament 12 of the intermediate layer 12A needs to satisfy the relationship of 4200−2000d ₂ ≦ T ₂ ≦ 4400−2000d ₂ with respect to the strand diameter d ₂ (mm). If the tensile strength T ₂ is smaller than 4200-2000d ₂ (MPa), the fatigue resistance of the filament 12 of the intermediate layer 12A becomes insufficient. Conversely, if the tensile strength T ₂ is larger than 4400-2000d ₂ (MPa), the cord productivity is increased. In addition, it is easy to cause disconnection due to a decrease in cord toughness. Tensile strength T ₃ of the filaments 13 of the outermost layer 13A (MPa) is it is necessary to satisfy the relationship of T ₃ ≦ 4100-2000d ₃ for the wire diameter d ₃ (mm), the tensile strength T ₃ Is larger than 4100-2000d ₃ (MPa), the cord productivity is lowered, and disconnection is liable to occur due to the lowered cord toughness. The lower limit value of the tensile strength T ₃ is preferably 3100 MPa in order to ensure the breaking strength of the steel cord 10.

  Further, in the pneumatic radial tire described above, the number of filaments 12 constituting the intermediate layer 12A is N (N = 5 to 6), and the number of filaments 13 constituting the outermost layer 13A is M (M = 10 to 10). 12), the rubber permeability can be improved while avoiding a decrease in the breaking strength of the steel cord 10. Here, if the number of filaments 12 and 13 is too small, the breaking strength of the steel cord 10 is lowered, and conversely if too large, the rubber permeability into the steel cord 10 is lowered.

3 and 4 show another example of a steel cord having a multilayer twist structure used in the present invention. As shown in FIGS. 3 and 4, the steel cord 10 includes an intermediate layer 12 </ b> A composed of a single core filament 11 and N (N = 5 to 6) filaments 12 twisted around the core filament 11. And an outermost layer 13A composed of M (M = 10 to 12) filaments 13 twisted around the intermediate layer 12A. The core filament 11 has been subjected to spiral typed, wave height H of the core filament 11 satisfies the relationship H ≦ 1.1d ₁ for the wire diameter d _1.

As described above, the effect of improving rubber permeability can be enhanced by providing spiral molding to the core filament 11. Moreover, by setting the wave height H of the core filament 11 to a relationship of H ≦ 1.1d ₁ , it is possible to obtain an effect of improving rubber permeability while maintaining good fatigue resistance under a stable twisted structure. . Here, if the wave height H is larger than 1.1 d ₁ , it becomes difficult to arrange the filaments 11 to 13 at predetermined positions, and it becomes difficult to obtain a stable twisted structure.

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

  In the pneumatic radial tire of tire size 295 / 80R22.5, tires of conventional examples, comparative examples 1 to 3 and examples 1 to 5 in which only the reinforcing cords of the carcass layer were changed were manufactured.

That is, in the conventional example, Comparative Examples 1 to 3 and Examples 1 to 5, as a reinforcing cord of the carcass layer, one core filament and an intermediate layer composed of six filaments twisted around the core filament And a steel cord having an outermost layer composed of 12 filaments twisted around the intermediate layer, and tensile strengths T ₁ , T ₂ , T ₃ , strand diameters d ₁ , d ₂ , As shown in Table 1, d ₃ , ratio d ₁ / d ₂ , ratio d ₂ / d ₃ , and ratio H / d ₁ of wave height H to core filament diameter d ₁ were set.

  In addition, the driving density of the carcass cord at the crown portion at the time of molding the tire was 28/50 mm, and the driving density of the carcass cord at the crown portion after vulcanization was 15.5 / 50 mm. That is, the rate of increase in the circumferential length of the tire crown was about 82%.

  For these test tires, cord productivity, rubber penetration rate and cord 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”.

Rubber penetration rate:
The steel cord of the carcass layer was taken out from each test tire, the rubber adhering to the outside of the steel cord was removed with a cutter knife, one filament was removed from the outermost layer, and the rubber penetration rate in the cord was measured visually. . Next, all the filaments in the outermost layer were removed, the rubber adhering to the outside of the intermediate layer was removed, one filament was removed from the intermediate layer, and the rubber penetration rate in the cord was visually measured. Such measurement is performed on the steel cords arranged at eight locations on the tire circumference, and the average value of the rubber penetration rates in the outermost layer and the intermediate layer of these eight steel cords is obtained. did.

Cord durability:
The steel cord of the carcass layer is taken out from each test tire over the entire length, and the above steel cord is embedded in the center of a rubber block having a width of 10 mm, a thickness of 5 mm and a length of 500 mm under a vulcanization condition of 145 ° C. × 25 minutes. Was made. The test piece was mounted on a three-point roller type rotary bending fatigue tester having a roller diameter of 35 mm, and a fatigue test was performed until the steel cord in the test piece was broken under the condition of a cord tension of 180N. For each test tire, 25 steel cords were subjected to a fatigue test to determine the median number of breaks. The evaluation results are indicated by an index with the conventional example being 100. A larger index value means better cord durability.

As is clear from Table 1, in Examples 1 to 5, the rubber penetration rate was high and the cord durability was good in comparison with the conventional example. On the other hand, in Comparative Example 1, since the strand diameters d ₂ and d ₃ of the filaments in the intermediate layer and the outermost layer are the same, the effect of improving the rubber penetration rate was not obtained. In Comparative Example 2, since the strand diameters d ₁ and d _{2 of} the core filament and the intermediate layer filament were the same, the effect of improving the rubber penetration rate could not be obtained. In Comparative Example 3, since the tensile strengths T ₁ , T ₂ , and T ₃ of all the filaments were uniformly increased, the cord productivity was poor, and the cord durability was lowered due to a decrease in cord toughness.

In Example 2, since the ratios d ₁ / d ₂ and d ₂ / d ₃ were both optimized, the twisted structure of the steel cord was more stable than in Example 1, and the durability of the cord was improved by improving fatigue resistance. Has been improved. In Example 3, since the filament wire diameters d _{1 to} d ₃ were relatively increased, the fatigue resistance improvement effect was lower than that in Example 2. In Example 4, since the core filament was appropriately shaped, rubber permeability, fatigue resistance, and fretting resistance were improved as compared to Example 2. In Example 5, since the core filament was heavily typed, the rubber permeability was further improved as compared to Example 4, but the fatigue resistance improvement effect was reduced.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Belt layer 10 Steel cord 11 Core filament 12 Intermediate layer filament 12A Intermediate layer 13 Outermost layer filament 13A Outermost layer

Claims (4)

In a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, as the reinforcing cord, one core filament and N (N = 5 to 6) filaments twisted around the core filament And a core cord diameter d _{1 of the} core filament and the intermediate layer, and a steel cord having an outermost layer made of M (M = 10 to 12) filaments twisted around the intermediate layer. filled wire diameter d ₃ of the wire diameter d ₂ of the filaments of the layer the outermost layer of filaments the relationship _{d 1> d 2> d 3} , the tensile strength T ₁ (MPa) is the wire of the core filament The relation of T ₁ ≧ 4500-2000d ₁ is satisfied with respect to the diameter d ₁ (mm), and the tensile strength T ₂ (MPa) of the filament of the intermediate layer is 4200 with respect to the strand diameter d ₂ (mm). −2000d ₂ ≦ T ₂ ≦ 4400−2000d ₂ is satisfied, and the tensile strength T ₃ (MPa) of the outermost filament is T ₃ ≦ 4100−2000d _{3 with} respect to the strand diameter d ₃ (mm). A pneumatic radial tire characterized by satisfying the relationship. The core filament diameter d _{1 of the} core filament is 0.23 mm or less, and the core filament diameter d ₁ and the intermediate layer filament diameter d ₂ are 1.0 <d ₁ / d ₂ ≦ 1. .1 and the filament diameter d ₂ of the intermediate layer filament and the filament diameter d ₃ of the outermost layer filament satisfy the relationship of 1.0 <d ₂ / d ₃ ≦ 1.1. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is a pneumatic tire. 3. The core filament is spirally shaped, and the wave height H of the core filament satisfies a relationship of H ≦ 1.1d ₁ with respect to the strand diameter d ₁ . Pneumatic radial tire described in 2.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the reinforcing layer is a carcass layer.

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