JP2020147870A - Pneumatic radial tire - Google Patents

Abstract

To provide a radial tire, which does not decrease the productivity of the steel cord, and which improves the durability by improving the rubber permeability into the inner portion of the strand.SOLUTION: As the reinforcing cord of the belt layer, the steel cord 20 is used, wherein it comprises 7 strands 10 having the core filament 11 having the N (N=2 to 3) numbers, which are mutually twisted, and the sheath filament 12 having M (M=6 to 9) numbers, which are twisted around the core filament 11. It has the 7×(N+M) structure in which the remaining 6 strands 10 are twisted around the 1 strand 10. The tensile strength T1 (MPa) of the sheath filament 12a having X (X=1 to 3) numbers as contained in each strand 10 complies with the relationship of T1 being equal to and greater than 4000-2000Ds against its strand diameter Ds (mm). The tensile strength T2 (MPa) of other sheath filament 12b as contained in each strand 10 complies with the relationship of T2 being equal to and less than 3800-2000Ds against its strand diameter Ds (mm).SELECTED DRAWING: Figure 2

Description

The present invention relates to a pneumatic radial tire in which a steel cord having a 7 × (N + M) structure is used as a reinforcing cord of a reinforcing layer typified by a belt layer. More specifically, the present invention does not reduce the productivity of the steel cord. With respect to pneumatic radial tires that have made it possible to improve rubber penetration into the strands and improve durability.

In pneumatic radial tires for construction vehicles, N (N = 2-3) core filaments twisted together and M (M = 6) twisted around the core filaments are twisted together as reinforcing cords for the belt layer. A steel cord having a 7 × (N + M) structure containing 7 strands having a sheath filament of ~ 9) and the remaining 6 strands twisted around one of the 7 strands. (See, for example, Patent Documents 1 to 3) are used.

Generally, a steel cord having a 7 × (N + M) structure is a tight cord and has a low rubber penetration rate inside the strand. Therefore, when moisture seeps into the strand, the moisture propagates along the longitudinal direction of the steel cord. However, there is a problem that rust grows in a wide range, and as a result, the durability of the pneumatic radial tire is reduced.

On the other hand, by making the molding ratio of the sheath filament contained in each strand different, a sufficient gap can be formed between the filaments and the rubber permeability can be improved. However, when selective preforming is performed so that the molding rates of the sheath filaments are different, there is a disadvantage that the productivity of the steel cord is lowered.

Japanese Unexamined Patent Publication No. 2013-227698 Japanese Unexamined Patent Publication No. 2013-234412 Japanese Unexamined Patent Publication No. 2016-56456

An object of the present invention is to provide a pneumatic radial tire capable of improving rubber permeability into a strand and improving durability without reducing the productivity of a steel cord.

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 tires (N = 2 to 2) twisted together as the reinforcing cords. 7 strands having the core filament of 3) and M (M = 6-9) sheath filaments twisted around the core filament, and one of the seven strands It has a 7 × (N + M) structure in which the remaining 6 strands are twisted around it, and the tensile strength T ₁ (MPa) of X (X = 1-3) sheath filaments contained in each strand is the element. The relationship of T ₁ ≧ 4000-2000 Ds is satisfied with respect to the wire diameter Ds (mm), and the tensile strength T ₂ (MPa) of the other sheath filament contained in each strand is T with respect to the wire diameter Ds (mm). It is characterized in that a steel cord satisfying the relationship of ₂ ≦ 3800-2000 Ds is used.

As a result of diligent research on a steel cord having a 7 × (N + M) structure, the present inventor selectively increases the tensile strength T ₁ of X (X = 1 to 3) sheath filaments contained in each strand. By lowering the tensile strength T ₂ of the other sheath filaments contained in each strand, the sheath filament of each strand is subjected to a uniform preforming process prior to the stranded wire, so that the tensile strength is high. Since the sheath filament having T ₁ is hard to be habitual, the type ratio of the sheath filament is different due to the difference in the tensile strengths T ₁ and T ₂ , and as a result, a gap is formed between the sheath filaments. The findings led to the present invention.

That is, in the present invention, when a steel cord having a 7 × (N + M) structure is adopted as the reinforcing cord of the reinforcing layer, the tensile strength T ₁ of some of the sheath filaments contained in each strand is selectively increased. By lowering the tensile strength T ₂ of the other sheath filaments contained in each strand, gaps are formed between the sheath filaments, which improves rubber permeability into the strands and improves the durability of pneumatic radial tires. Can be improved.

Moreover, since it is possible to form a gap between the sheath filaments by utilizing the difference in the tensile strengths T ₁ and T ₂ of the sheath filaments, it is not necessary to perform preforming processing to a different degree for each sheath filament, and steel. It does not cause the inconvenience of reducing the productivity of the code.

In the present invention, it is preferable that the wire diameter Dc of the core filament of each strand and the wire diameter Ds of the sheath filament satisfy the relationship of Dc> Ds and Ds / Dc ≧ 0.8. By making the core filament thicker in this way, the rubber permeability can be further improved, and the steel cord is less likely to buckle. As a result, the durability of the pneumatic radial tire can be further improved.

In the steel cord, the tensile strength T ₁ is preferably 4200 MPa or less. As a result, it is possible to prevent the filament from breaking in the stranded wire process of the steel cord and to avoid a decrease in the productivity of the steel cord.

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, a belt protective 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.

The present invention is preferably applied to a pneumatic radial tire for a construction vehicle, but as long as the steel cord as described above is used as a reinforcing cord for a reinforcing layer, the pneumatic radial tire for purposes other than the above is used. It is also applicable to.

FIG. 5 is a meridian half-section view showing a pneumatic radial tire for a construction vehicle according to an embodiment of the present invention. It is sectional drawing which shows an example of the steel cord having a 7 × (N + M) structure used in this invention. (A) to (e) are sectional views showing the steel cord 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 for a construction vehicle 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.

A plurality of belt layers 6a, 6b, 6c, and 6d are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 6a to 6d include a plurality of reinforcing cords 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 layers 6a to 6d, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 15 ° to 40 °, and the cord driving density is set in the range of, for example, 10/50 mm to 25/50 mm. There is.

Further, a plurality of belt protection layers 7a and 7b are embedded on the outer peripheral side of the belt layers 6a to 6d. While the belt layers 6a to 6d support the reinforcement of the tread portion 1, the belt protection layers 7a and 7b are arranged for the purpose of protecting the belt layers 6a to 6d. These belt protective layers 7a and 7b include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords intersect each other between the layers. In the belt protective layers 7a and 7b, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 20 ° to 40 °, and the cord driving density is set in the range of, for example, 10/50 mm to 30/50 mm. ing. As the reinforcing cords of the belt protective layers 7a and 7b, for example, steel cords having a breaking elongation of 4% or more are used.

In the pneumatic radial tire, a steel cord having a 7 × (N + M) structure, which will be described later, is used as a reinforcing cord for the belt layers 6a to 6d. This steel cord can also be used as a reinforcing layer such as a carcass layer 4 in addition to the belt layers 6a to 6d or instead of the belt layers 6a to 6d.

FIG. 2 shows a steel cord having a 7 × (N + M) structure used in the present invention. As shown in FIG. 2, the steel cord 20 has N core filaments 11 (N = 2 to 3) twisted to each other and M core filaments (M = 6 to 9) twisted around the core filament 11. It has a 7 × (N + M) structure including 7 strands 10 having the sheath filament 12 of the above, and the remaining 6 strands 10 twisted around one strand 10 of the 7 strands 10. are doing. The sheath filament 12 contained in each strand 10 is spirally molded prior to the stranded wire. The filaments 11 and 12 in the same layer have the same wire diameter and the same molding pitch. In this embodiment, each strand 10 is composed of three core filaments 11 and nine sheath filaments 12. That is, it has a 7 × (3 + 9) structure. Other examples include, for example, a 7 × (3 + 8) structure and a 7 × (2 + 6) structure.

Of the M sheath filaments 12 contained in each strand 10, the tensile strength T ₁ (MPa) of X (X = 1 to 3) sheath filaments 12a (with diagonal lines) is relative to the wire diameter Ds (mm). T ₁ ≥ 4000-2000 Ds, and the tensile strength T ₂ (MPa) of the other sheath filament 12b contained in each strand 10 is T ₂ ≤ 3800-2000 Ds with respect to its wire diameter Ds (mm). Meet the relationship. Similar to the tensile strength T ₂ of the sheath filament 12b, it is desirable that the tensile strength T ₃ of the core filament 11 satisfies the relationship of T ₃ ≤ 3800-2000 Dc with respect to the wire diameter Dc (mm). The tensile strength of these filaments 11 and 12 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, when the steel cord 20 having a 7 × (N + M) structure is adopted as the reinforcing cord of the belt layers 6a to 6, the tensile strength T of a part of the sheath filament 12a contained in each strand 10 is used. _{Since 1} is selectively increased and the tensile strength T ₂ of the other sheath filaments 12b contained in each strand 10 is decreased, uniform preforming processing is performed on the sheath filaments 12a and 12b prior to the stranded wire. Even when the sheath filament 12a has a high tensile strength T ₁ , it is difficult for the sheath filament 12a to have a habit. Therefore, the molding ratios of the sheath filaments 12a and 12b differ due to the difference in the tensile strengths T ₁ and T _2. , A gap is formed between the sheath filaments 12 of each strand 10. As a result, the rubber permeability into the inside of the strand 10 can be improved, and the durability of the pneumatic radial tire can be improved.

Moreover, since it is possible to form a gap between the filaments 12 of each strand 10 by utilizing the difference in the tensile strengths T ₁ and T ₂ of the sheath filaments 12a and 12b, the degree of difference with respect to the sheath filaments 12a and 12b is high. It is not necessary to perform the preforming process of the steel cord 20, and the productivity of the steel cord 20 is not reduced.

Here, the tensile strength T ₁ (MPa) of X (X = 1-3) sheath filaments 12a contained in each strand 10 has a relationship of T ₁ ≧ 4000-2000 Ds with respect to the wire diameter Ds (mm). However, if the tensile strength T ₁ is smaller than 4000-2000 Ds (MPa), the effect of improving the rubber permeability into the inside of the strand 10 becomes insufficient. The tensile strength T ₁ is preferably 4200 MPa or less. As a result, it is possible to prevent the sheath filament 12a from breaking in the stranded wire process of the steel cord 20 and to avoid a decrease in the productivity of the steel cord 20. On the other hand, the tensile strength T ₂ (MPa) of the other sheath filament 12b contained in each strand 10 needs to satisfy the relationship of T ₂ ≤ 3800-2000 Ds with respect to the wire diameter Ds (mm). If the tensile strength T ₂ is larger than 3800-2000 Ds (MPa), the effect of improving the rubber permeability into the inside of the strand 10 becomes insufficient. The tensile strength T ₂ is preferably 2000 MPa or more in order to secure the reinforcing performance of the steel cord 20.

Further, the number of sheath filaments 12a having a tensile strength T ₁ needs to be X (X = 1 to 3), but when X> 3, the effect of improving rubber permeability is reduced. In particular, it is desirable to satisfy the relationship of 1 ≦ X ≦ M / 3. Further, when X ≧ 2, it is preferable that the sheath filaments 12a having the tensile strength T ₁ are arranged so as not to be adjacent to each other. Thereby, the rubber permeability can be effectively increased.

In the pneumatic radial tire, the wire diameter Dc of the core filament 11 of each strand 10 and the wire diameter Ds of the sheath filament 12 may satisfy the relationship of Dc> Ds and Ds / Dc ≧ 0.8. By making the core filament 11 thick in this way, the rubber permeability can be further improved. Further, when the core filament 11 is made thicker, the steel cord 20 is less likely to buckle. As a result, the durability of the pneumatic radial tire can be further improved. Here, when Ds / Dc <0.8, the sheath filament 12 of each strand 10 is not arranged at an appropriate position, so that the effect of improving durability is reduced. The wire diameter Dc of the core filament 11 and the wire diameter Ds of the sheath filament 12 are not particularly limited, but are 0.15 mm or more in order to obtain a suitable reinforcing effect as a reinforcing cord for the belt layers 6a to 6d. It can be appropriately selected from the range of 0.40 mm. If the wire diameter Dc of the core filament 11 and the wire diameter Ds of the sheath filament 12 are too large, the fatigue resistance will deteriorate.

For the belt layer constituting the pneumatic radial tire for a construction vehicle having a tire size of 2700R49, test samples (conventional example, Comparative Examples 1 to 3 and Examples 1 to 5) in which only the reinforcing cord was different were produced.

In the conventional example, Comparative Examples 1 to 3 and Examples 1 to 5, a steel cord having a 7 × (3 + 9) structure was used as the reinforcing cord of the belt layer. In Conventional Example 1, the steel cord is composed of a standard filament, while in Comparative Examples 1 and 2 and Examples 1 to 5, at least a part of the standard filament is replaced with a high-strength filament, and in Comparative Example 3, at least a part of the standard filament is used. Was replaced with a low-strength filament. Cord driving density, wire diameter Dc, Ds of each filament, wire diameter ratio Ds / Dc, number of high-strength filaments, tensile strength of each filament, arrangement of high-strength filaments [FIGS. 3 (a) to 3 (e) ] Was set as shown in Table 1. In FIGS. 3A to 3E, the shaded filaments are high-strength filaments. However, in Comparative Example 3, the low-strength filament was arranged at the position of the high-strength filament in FIG. 3 (b).

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

Rubber permeability:
After vulcanizing five rolled members (belt layers) including the reinforcing cords, take out eight steel cords from the third layer, remove the rubber on the outside of the steel cords with a utility knife, and sheath the strands. One filament was removed, and the rubber permeability in the strand was visually measured. The average value of the rubber penetration rates of the eight steel cords was calculated and used as the rubber penetration rate.

Tire durability:
Two rolled members (belt layers) including a reinforcing cord are stacked and vulcanized so that the cord angles are 90 °, and then in a pressure vessel, the temperature is 130 ° C. and the humidity is 95% for 96 hours. After deterioration over, the peeling force between layers was measured. The evaluation result is shown by an index of 100 in the conventional example. The larger the index value, the better the peeling resistance, that is, the better the durability as a tire.

As is clear from Table 1, in Examples 1 to 5, in comparison with the conventional examples, as a result of improving the rubber permeability into the inside of the strand, the peeling resistance is excellent and the durability as a tire is improved. Was there. In particular, in Example 3, since the ratio Ds / Dc of the wire diameter was optimized by increasing the diameter of the core filament, the rubber permeability was improved and the effect of improving the tire durability was remarkable. On the other hand, in Example 4, since the ratio Ds / Dc of the wire diameter was small, the effect of improving the tire durability tended to decrease. In Example 5, the productivity of the steel cord tended to decrease due to the high tensile strength of the high-strength filaments arranged in the outermost layer of each strand.

On the other hand, in the tire of Comparative Example 1, since nine high-strength filaments were arranged in the outermost layer of each strand, the effect of improving the rubber permeability could not be obtained. In the tire of Comparative Example 2, since the core filament was a high-strength filament, the effect of improving the rubber permeability could not be obtained. In the tire of Comparative Example 3, since the low-strength filament was arranged in the outermost layer of each strand, the low-strength filament was floated, 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 6a to 6d belt layer 7a, 7b belt protection layer 10 strand 11 core filament 12 sheath filament 20 steel cord

Claims (3)

In a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, N core filaments (N = 2 to 3) twisted to each other and twisted around the core filaments as the reinforcing cords. 7 × (N + M) containing 7 strands with M (M = 6-9) sheath filaments and the remaining 6 strands twisted around one of the 7 strands. ) The tensile strength T ₁ (MPa) of X (X = 1-3) sheath filaments contained in each strand is T ₁ ≧ 4000-2000 Ds with respect to the wire diameter Ds (mm). A steel cord that satisfies the relationship and the tensile strength T ₂ (MPa) of the other sheath filament contained in each strand satisfies the relationship of T ₂ ≤ 3800-2000 Ds with respect to the wire diameter Ds (mm) is used. Featuring pneumatic radial tires. The pneumatic radial according to claim 1, wherein the wire diameter Dc of the core filament of each strand and the wire diameter Ds of the sheath filament satisfy the relationship of Dc> Ds and Ds / Dc ≧ 0.8. tire. The pneumatic radial tire according to claim 1 or 2, wherein the tensile strength T ₁ is 4200 MPa or less.

Images