JP2016056457A - Steel cord and pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel cord excellent in durability and a pneumatic radial tire that is for a construction vehicle and is excellent in durability.SOLUTION: The steel cord comprises: a core strand comprising a core of three core filaments, an interlayer composed of 8-9 sheath filaments, and an outermost layer of 13-15 sheath filaments; 5-6 sheath strands having the same structure as that of the core strand and inter-twisted on the core strand; and a wrapping wire wound around the periphery. Each of the filaments of the core strand has a tensile strength satisfying the relation of 3700-2000dc≤Tc(MPa)<4500-2000dc. The core filament of the sheath strand has a tensile strength satisfying the relation of 3700-2000dsc≤Tsc(MPa)≤4100-2000dsc. The sheath filament has a tensile strength satisfying the relation of 3200-2000dss<Tss(MPa)≤3600-2000dss. Element wire diameters (mm) of the filaments are denoted by dc, dsc and dss.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic radial tire using a steel cord as a reinforcing cord of a steel cord and a reinforcing layer, and more particularly to a steel cord and a pneumatic radial tire excellent in durability.

Since pneumatic radial tires for construction vehicles are often used in situations where high loads are applied, steel cords are used as reinforcement cords for reinforcing the carcass layer and the belt layer. This steel cord is required to have high strength, and a steel cord having a double twist structure is widely used.
On the other hand, in order to increase the strength of the cord without increasing the cross-sectional area of the steel cord, in order to achieve reduction of the tire weight, lower fuel consumption and reduction of the transportation cost, the material, particularly the carbon content or processing method, for example, A device has been devised to increase the cord strength by changing the area reduction rate to increase the tensile strength of the filament.

Patent Document 1 describes a steel cord for reinforcing rubber articles having a double twist structure in which a sheath strand having a layer twist structure of two or more layers is twisted around a core strand having a layer twist structure of two or more layers. Yes. The steel cord for reinforcement of rubber articles is the outermost layer sheath tensile strength 2500~2810N / mm ² of the filament constituting the core strand, and, among the filaments constituting the cord, tensile strength of all the filaments, excluding the outermost layer sheath filaments Is 3150 N / mm ² or more.

Japanese Patent No. 5036294

  As in Patent Document 1, in the case of a double strand structure in which a sheath strand having a layer twist structure of two or more layers is twisted around a core strand having a layer twist structure of two or more layers, one core strand is Since it is located at the center of the cord, there is a problem that when the steel cord is subjected to compressive stress, the core strand is easily bent and the core strand is likely to be fatigued. When the steel cord of Patent Document 1 is applied to the carcass layer, sufficient durability cannot be obtained for the pneumatic radial tire.

  An object of the present invention is to provide a pneumatic radial tire for a construction vehicle or the like that has solved the problems based on the above-described prior art and has excellent durability and a steel cord and durability.

  In order to achieve the above object, the present invention provides a core composed of three core filaments, an intermediate layer composed of 8-9 sheath filaments, and an outermost layer composed of 13-15 sheath filaments. A sheath strand comprising a core composed of three core filaments, an intermediate layer composed of 8 to 9 sheath filaments, and an outermost layer composed of 13 to 15 sheath filaments And 5-6 sheath strands are twisted around one core strand, and the wrapping wire is wound around the twisted sheath strand, and the core The strand diameter of each filament of the strand is dc (mm), and the strand of the core filament of the sheath strand When the diameter is dsc (mm) and the strand diameter of the sheath filament of the outermost layer of the sheath strand is dss (mm), the tensile strength Tc (MPa) of each filament of the core strand is 3700− The tensile strength Tsc (MPa) of at least the core filament of the core filament of the sheath strand and the sheath filament of the intermediate layer satisfies the relationship of 2000 dc ≦ Tc <4500-2000 dc, and is 3700−2000 dsc ≦ Tsc ≦ 4100−. The steel cord is characterized in that the relationship of 2000 dsc is satisfied, and the tensile strength Tss (MPa) of the sheath filament of the sheath strand satisfies the relationship of 3200−2000 dss <Tss ≦ 3600−2000 dss. .

  When the strand diameter of the core filament of the core strand is dcc (mm) and the strand diameters of the sheath filament of the intermediate layer and the sheath filament of the outermost layer are dst (mm), the core The tensile strength Tcc (MPa) of the core filament of the strand satisfies the relationship of 4200−2000 dcc ≦ Tcc <4500−2000 dcc, and the tensile strength Tst of the sheath filament of the intermediate layer and the outermost sheath filament of the sheath strand (MPa) preferably satisfies the relationship of 3700−2000 dst ≦ Tst ≦ 4100−2000 dst.

  The strand diameter of the core filament of the core strand is dcc (mm), the strand diameter of the sheath filament of the outermost layer of the core strand is dcs (mm), and the sheath of the intermediate layer of the core strand is the sheath When the filament diameter of the filament is dcm (mm) and the filament diameter of each filament of the sheath strand is ds (mm), the filament diameter of each filament is 0.15 mm <ds ≦ dcs ≦ dcm <dcc It is preferable to satisfy <0.40 mm and satisfy 1.0 ≦ dcm / dcs ≦ 1.05 and 1.0 <dcc / dcm <1.10.

  The present invention is a pneumatic radial tire provided with a reinforcing layer including a plurality of reinforcing cords, wherein the reinforcing cords are constituted by a core constituted by three core filaments and 8-9 sheath filaments. A core strand comprising an intermediate layer and an outermost layer comprised of 13 to 15 sheath filaments; a core comprised of three core filaments; and an intermediate layer comprised of 8 to 9 sheath filaments and 13 A sheath strand having an outermost layer composed of -15 sheath filaments and a wrapping wire, and 5-6 sheath strands were twisted and twisted around one core strand The wrapping wire is wound around the sheath strand, and the filament diameter of each filament of the core strand is d The core strand of the sheath strand is dsc (mm), and the sheath filament of the outermost layer of the sheath strand is dss (mm). The tensile strength Tc (MPa) of each of the filaments satisfies the relationship of 3700-2000 dc ≦ Tc <4500-2000 dc, and the tensile strength of at least the core filament of the core filament of the sheath strand and the sheath filament of the intermediate layer The strength Tsc (MPa) satisfies the relationship of 3700−2000 dsc ≦ Tsc ≦ 4100−2000 dsc, and the tensile strength Tss (MPa) of the sheath filament of the sheath strand is 3200−2000 dss <Tss ≦ 3600−2000 dss. There is provided a pneumatic radial tire characterized by satisfying the relationship.

  When the strand diameter of the core filament of the core strand is dcc (mm) and the strand diameters of the sheath filament of the intermediate layer and the sheath filament of the outermost layer are dst (mm), the core The tensile strength Tcc (MPa) of the core filament of the strand satisfies the relationship of 4200−2000 dcc ≦ Tcc <4500−2000 dcc, and the tensile strength Tst of the sheath filament of the intermediate layer and the outermost sheath filament of the sheath strand (MPa) preferably satisfies the relationship of 3700−2000 dst ≦ Tst ≦ 4100−2000 dst.

  The strand diameter of the core filament of the core strand is dcc (mm), the strand diameter of the sheath filament of the outermost layer of the core strand is dcs (mm), and the sheath of the intermediate layer of the core strand is the sheath When the filament diameter of the filament is dcm (mm) and the filament diameter of each filament of the sheath strand is ds (mm), the filament diameter of each filament is 0.15 mm <ds ≦ dcs ≦ dcm <dcc It is preferable to satisfy <0.40 mm and satisfy 1.0 ≦ dcm / dcs ≦ 1.05 and 1.0 <dcc / dcm <1.10. For example, the reinforcing layer is a carcass layer.

  ADVANTAGE OF THE INVENTION According to this invention, durability of a steel cord can be made high and durability can be made high also about a pneumatic radial tire.

It is a mimetic diagram showing the steel cord of the embodiment of the present invention. It is a typical sectional view showing a rubber composite which has a steel cord of an embodiment of the present invention. It is a meridian half section view showing a pneumatic radial tire using a steel cord of an embodiment of the present invention.

Hereinafter, a steel cord and a pneumatic radial tire of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a schematic diagram showing a steel cord according to an embodiment of the present invention.

The steel cord 10 shown in FIG. 1 is composed of, for example, a core 20c composed of three core filaments 13c, an intermediate layer 20m composed of nine sheath filaments 13s, and 15 sheath filaments 13s. The core strand 12 including the outermost layer 20s, the core 22c including three core filaments 15c, the intermediate layer 22m including nine sheath filaments 15m, and the 15 sheath filaments 15s. The sheath strand 14 including the outermost layer 22s and the wrapping wire 16 are included. The core strand 12 and the sheath strand 14 have the same structure. The steel cord 10 has a double twist structure.
In the steel cord 10, for example, six sheath strands 14 are arranged around one core strand 12 and twisted together. A wrapping wire 16 is wound around, for example, a spiral around the twisted sheath strand 14. The wrapping wire 16 is effective in improving the binding property of the steel cord 10 having a double twist structure.

  In the steel cord 10, the number of sheath strands 14 is m (m = 5 to 6), the sheath filaments 13m of the intermediate layers 20m and 22m, and the number of 15m is n (n = 8 to 9), and the outermost layers 20s and 22s. When the number of the sheath filaments 13s and 15s is p (p = 13 to 15), a 1 + m × (3 + n + p) +1 structure is taken. In FIG. 1, the steel cord 10 has a 7 × (3 + 9 + 15) +1 structure. The sheath strand 14 may be five. In this case, the steel cord 10 has a 6 × (3 + 9 + 15) +1 structure. Further, as described above, the sheath filament 13m of the intermediate layer 20m and the sheath filament 15m of the intermediate layer 22m may be eight, and the sheath filament 13s of the outermost layer 20s and the sheath filament 15s of the outermost layer 22s may be 13 or 14. Good.

In the steel cord 10, the strand diameter of the core filament 13c constituting the core strand 12 is dcc (mm), the strand diameter of the sheath filament 13m of the intermediate layer 20m constituting the core strand 12 is dcm (mm), and the core The strand diameter of the sheath filament 13s of the outermost layer 20s constituting the strand 12 is defined as dcs (mm).
The wire diameters of the core filament 13c, the sheath filament 13m of the intermediate layer 20m, and the sheath filament 13s of the outermost layer 20s are collectively referred to as dc (mm).

The strand diameter of the core filament 15c constituting the sheath strand 14 is dsc (mm), the strand diameter of the sheath filament 15m of the intermediate layer 22m constituting the sheath strand 14 is dsm (mm), and the sheath strand 14 is constituted. The strand diameter of the sheath filament 15s of the outermost layer 22s is dss (mm).
The wire diameters of the core filament 15c, the sheath filament 15m of the intermediate layer 22m, and the sheath filament 15s of the outermost layer 22s are collectively referred to as ds (mm).
The strand diameters of the sheath filament 15m of the intermediate layer 22m of the sheath strand 14 and the sheath filament 15s of the outermost layer 22s are collectively referred to as dst (mm).

  The core filament 13c of the core strand 12, the sheath filament 13m of the intermediate layer 20m and the sheath filament 13s of the outermost layer 20s, and the core filament 15c of the sheath strand 14, the sheath filament 15m of the intermediate layer 22m and the sheath filament 15s of the outermost layer 22s are collected. Also simply called each filament.

The tensile strengths Tc (MPa) of the core filament 13c of the core strand 12, the sheath filament 13m of the intermediate layer 20m, and the sheath filament 13s of the outermost layer 20s are the core filament 13c, the sheath filament 13m of the intermediate layer 20m, and the outermost layer 20s. The relationship of 3700−2000 dc ≦ Tc <4500−2000 dc is satisfied with respect to the strand diameter dc (mm) of the sheath filament 13 s of the outer layer 20 s.
When the tensile strength Tc is 4500-2000 dc (MPa) or more, the strength of the filament is too high, and breakage is likely to occur when the filament is twisted. On the other hand, if the tensile strength Tc is less than 3700-2000 dc (MPa), the fatigue resistance of the core filament 13c deteriorates, and a significant improvement in durability cannot be obtained.

Of the core filament 15c of the sheath strand 14 and the sheath filament 15m of the intermediate layer 22m, at least the core filament 15c of the sheath strand 14 has a tensile strength Tsc (MPa) of the core filament 15c with respect to the wire diameter dsc (mm). Satisfies the relationship of 3700−2000 dsc ≦ Tsc ≦ 4100−2000 dsc.
When the tensile strength Tsc exceeds 4100-2000 dsc (MPa), the filament strength is too high, and breakage is likely to occur when the filament is stranded. On the other hand, if the tensile strength Tsc is less than 3700-2000 dsc (MPa), a significant improvement in durability cannot be obtained.

The tensile strength Tss (MPa) of the sheath filament 15 s of the outermost layer 22 s of the sheath strand 14 is 3200−2000 dss <Tss ≦ 3600−2000 dss with respect to the strand diameter dss (mm) of the sheath filament 15 s of the sheath strand 14. Meet.
If the tensile strength Tss exceeds 3600-2000 dsc (MPa), the strength of the filament is too high, and when the sheath strand 14 is manufactured, breakage is likely to occur when the sheath filament 15s is stranded. On the other hand, when the tensile strength Tss is 3200-2000 dsc (MPa) or less, the sheath filament 15 s of the outermost layer 22 s is easily broken.

The tensile strength Tcc (MPa) of the core filament 13c of the core strand 12 satisfies the relationship of 4200−2000dc ≦ Tcc <4500−2000dc with respect to the strand diameter dcc (mm) of the core filament 13c of the core strand 12. preferable. Since the core filament 13c extends linearly at the center position of the steel cord 10, the steel cord 10 is particularly easily bent when subjected to a compressive stress, and easily causes fatigue fracture. By selectively increasing the tensile strength Tcc of the core filament 13c of the core strand 12, the fatigue resistance of the steel cord 10 is further improved.
When the tensile strength Tcc is 4500-2000 dc (MPa) or higher, the strength of the filament is too high, and breakage is likely to occur when the filament is stranded. On the other hand, if the tensile strength Tcc is less than 4200-2000 dc (MPa), the fatigue resistance of the core filament 13c may deteriorate.

The tensile strength Tst (MPa) of the sheath filament 15m of the intermediate layer 22m of the sheath strand 14 and the sheath filament 15s of the outermost layer 22 is determined by the sheath filament 15m of the intermediate layer 22m of the sheath strand 14 and the sheath filament 15s of the outermost layer 22s. It is preferable that the relationship of 3700−2000 dst ≦ Tst ≦ 4100−2000 dst is satisfied with respect to the strand diameter dst (mm). Thereby, fatigue resistance is further improved by increasing the strength of the sheath filament 15m of the intermediate layer 22m of the sheath strand 14 and the sheath filament 15s of the outermost layer 22s.
When the tensile strength Tst exceeds 4100-2000 dst (MPa), if the strength of the filament is too high, breakage is likely to occur when the filament is stranded. On the other hand, if the tensile strength Tcc is less than 3700-2000 dc (MPa), the fatigue resistance of the sheath filaments 15m, 15s of the sheath strand 14 may deteriorate.

The filament diameter of each filament satisfies 0.15 mm <ds ≦ dcs ≦ dcm <dcc <0.40 mm, and 1.0 ≦ dcm / dcs ≦ 1.05, and 1.0 <dcc / dcm <1. .10 is preferable.
If the strand diameter is 0.15 mm or less, the breaking strength of the steel cord 10 may not be ensured. On the other hand, if the strand diameter is 0.40 mm or more, the fatigue resistance of the steel cord 10 decreases. Moreover, when dcm / dcs exceeds 1.05, it becomes difficult to arrange each filament at a predetermined position, and fatigue resistance is lowered.
Moreover, even if dcc / dcm is 1.10 or more, it becomes difficult to dispose each filament at a predetermined position, and fatigue resistance is lowered.

As described above, by defining the magnitude relationship between the filament diameters of the filaments, rubber penetration into the steel cord 10 can be improved while maintaining good fatigue resistance. As a result, contact between the filaments of the steel cord 10 can be avoided to prevent fracturing due to fretting, and diffusion of rust due to moisture penetrating into the steel cord 10 can be prevented.
Each filament may be plated with brass or zinc.
The steel cord 10 of the present embodiment has improved fatigue resistance while maintaining strength, and can obtain high durability. Moreover, since the occurrence of filament breakage can be suppressed during formation, the productivity is also high. Thus, the steel cord 10 has high durability and high production efficiency.

The steel cord 10 can be used for a tire reinforcing layer or the like by coating with rubber, for example. In this case, for example, the steel cord rubber composite 30 shown in FIG. 2 is obtained. In the steel cord rubber composite 30, for example, a plurality of, in the example shown in FIG. 2, five steel cords 10 are covered with a rubber layer 32 in a state in which they are aligned and arranged in parallel.
As described above, the steel cord 10 can improve fatigue resistance while maintaining strength. For this reason, the steel cord rubber composite 30 has excellent durability. Moreover, since the steel cord 10 can improve fatigue resistance while maintaining strength as described above, the steel cord rubber composite 30 can be reduced in weight. Furthermore, since the steel cord 10 has good productivity such as the occurrence of breakage when the filament is twisted, the productivity of the steel cord rubber composite 30 can be increased.

Next, a method for forming the steel cord rubber composite 30 will be described.
When forming the steel cord rubber composite 30, first, a plurality of steel cords 10 are prepared, the plurality of steel cords 10 are aligned in parallel, and the unvulcanized rubber is coated on the top and bottom of the plurality of steel cords 10, Form a molded body. Such a rubber coating method includes, for example, a calendar system in which a plurality of steel cords 10 are arranged in parallel and passed between a pair of processing rolls to cover unvulcanized rubber, and a large number of insertion holes are arranged in a row. There is a CFRE method (Cold Feed Rubber Extruder) in which a plurality of parallelly arranged steel cords 10 are inserted into this die and the unvulcanized rubber is covered by an extruder while being inserted.
Then, the molded body is pressurized at a predetermined pressure while being heated at a predetermined temperature in the vulcanization step, thereby vulcanizing the unvulcanized rubber. Thereby, the steel cord rubber composite 30 can be formed.
The above-mentioned CFRE method is suitable for small-lot production because the equipment can be made smaller and less expensive than the calendar method, and even a small amount of members can be produced.

  As the rubber composition of the rubber layer 32, for example, a diene rubber can be used. As the diene rubber, for example, butyl rubber, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, or the like can be used. The butyl rubber includes halogenated butyl rubber. Halogenated butyl rubber is obtained by halogenating butyl rubber with bromine or chlorine.

The above-described steel cord 10 shown in FIG. 1 can be used, for example, for a casing constituting a skeleton of a pneumatic radial tire for a construction vehicle. FIG. 3 shows a pneumatic radial tire 40 for construction vehicles (hereinafter simply referred to as tire 40). In FIG. 3, only the right half of the meridian line CL of the tire 40 is illustrated.
The tire 40 shown in FIG. 3 has a tread portion 42, a sidewall portion 44, and a bead portion 46 as main components. The tire left half not shown in FIG. 3 has the same configuration.

  In the following description, as indicated by an arrow in FIG. 3, the tire width direction means a direction parallel to the tire rotation axis (not shown), and the tire radial direction is orthogonal to the rotation axis. The direction. Further, the tire circumferential direction refers to the direction of rotation with the rotation axis as the axis serving as the center of rotation. Further, the tire inner side refers to the lower side of the tire in FIG. 3 in the tire radial direction, that is, the tire inner surface side facing the hollow region that applies a predetermined internal pressure to the tire, and the tire outer side refers to the upper side of the tire in FIG. That is, it refers to the tire outer surface side that can be visually recognized by the user on the side opposite to the tire inner peripheral surface.

  The tread portion 42 is provided with a land portion 42b constituting a tread surface 42a outside the tire and a tread groove 42c formed in the tread surface 42a. The land portion 42b is partitioned by the tread groove 42c. The tread groove 42c has a main groove formed continuously in the tire circumferential direction and a plurality of lug grooves (not shown) extending in the tire width direction. A tread pattern is formed on the tread surface 42a by the tread groove 42c and the land portion 42b.

In the tire 40, a carcass layer 48 including a plurality of reinforcing cords extending in the tire radial direction is mounted between a pair of left and right bead portions 46, and an end portion of the carcass layer 48 is arranged around the bead core 50 from the inside of the tire to the outside. It is folded back. The bead core 50 has a function of folding the carcass layer 48 and fixing the tire 40 to the wheel.
A steel cord 10 shown in FIG. 1 is used as a reinforcing cord for the carcass layer 48. An inner liner layer 52 is provided inside the carcass layer 48. The inner liner layer 52 is for preventing air filled in the tire from leaking outside the tire.
A plurality of belt layers 54 a, 54 b, 54 c and 54 d are embedded on the outer peripheral side of the carcass layer 48 in the tread portion 42. These belt layers 54a to 54d 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 layers 54a to 54d, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of 15 ° to 40 °, for example, and the cord driving density thereof is in a range of 10/50 mm to 25/50 mm, for example. Is set. For example, various known steel cords are used as the reinforcing cords for the belt layers 54a to 54d.

  Furthermore, a plurality of belt protective layers 56a and 56b are embedded on the outer peripheral side of the belt layers 54a to 54d. The belt layers 54a to 54d carry the reinforcement of the tread portion 42, whereas the belt protective layers 56a and 56b are provided for the purpose of protecting the belt layers 54a to 54d. These belt protective layers 56a and 56b include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and are disposed so that the reinforcing cords intersect each other between the layers. In the belt protective layers 56a and 56b, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set, for example, in the range of 20 ° to 40 °, and the cord driving density thereof is in the range of, for example, 10/50 mm to 30/50 mm. Is set. As the reinforcing cords for the belt protective layers 56a and 56b, for example, steel cords (HE cords) having a breaking elongation of 4% or more are used so that the protective functions for the belt layers 54a to 54d are sufficiently exhibited. .

The tire 40 can be manufactured, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.
By using the steel cord 10 for the reinforcing cord of the carcass layer 38 of the tire 40, the durability of the carcass layer 38 can be improved, and the durability of the tire 40 can be improved. Furthermore, since the steel cord 10 has good productivity, such as the occurrence of breakage during the twisting of the filament is suppressed, the productivity of the tire 40 can be increased.
Since the steel cord 10 has higher strength than the conventional one, the carcass layer 38 can be reduced in weight, and the tire 40 can be reduced in weight.

  In the above-described embodiment, the example in which the steel cord 10 is used as the reinforcing cord of the carcass layer 48 in the tire 40 has been described. However, the present invention is not limited to this. The steel cord 10 can also be applied to other reinforcing layers of the tire 40. For example, the steel cord 10 can also be used as a reinforcing cord for the belt layers 54a to 54d. The steel cord 10 has improved fatigue resistance as described above, and the durability of the tire 40 can be improved. Even in this case, since the steel cord 10 has higher strength than the conventional one, the belt layers 54a to 54d can be reduced in weight, and the tire 40 can be reduced in weight.

  The present invention is basically configured as described above. Although the steel cord and the pneumatic radial tire of the present invention have been described in detail above, the present invention is not limited to the above-described embodiment, and various improvements or changes may be made without departing from the gist of the present invention. Of course.

Examples of the pneumatic radial tire of the present invention will be specifically described below.
In this example, pneumatic radial tires of Examples 1 to 6 shown in Table 1 below and Comparative Examples 1 to 11 shown in Table 2 below were produced. Each pneumatic radial tire was evaluated for cord productivity and tire durability. The results of cord productivity and tire durability performance are shown in Tables 1 and 2 below.
The tire size of each pneumatic radial tire is 2700R49. The structure of the pneumatic radial tire is the structure shown in FIG. 3, and four belt layers are arranged on the outer peripheral side of the carcass layer in the tread portion, and two belt protective layers are arranged on the outer peripheral side of the belt layer. HE cords were used for the two belt protective layers. The carcass layer was a single layer, and a steel cord was used as a reinforcing cord for the carcass layer. The pneumatic radial tires of Examples 1 to 6 and Comparative Examples 1 to 11 differ only in the configuration of the reinforcing cord of the carcass layer. As the wrapping wire, a steel wire having a wire diameter of 0.15 mm was used, and in Examples 1 to 6 and Comparative Examples 1 to 11, all of the same strength were used.

  In this embodiment, six sheath strands having the same structure as the core strand are arranged around one core strand composed of three core filaments and nine sheath filaments as a reinforcing cord for the carcass layer. A steel cord having a structure of 7 × (3 + 9 + 15) +1 in which one wrapping wire is wound around six sheath strands was used. Tensile strength Tc (Tcc, Tcm, Tcs) of each filament constituting the core strand, tensile strength Ts (Tsc, Tsm, Tss) of each filament constituting the sheath strand, strand diameter dc of each filament constituting the core strand (Dcc, dcm, dcs) and the filament diameter ds (dsc, dsm, dss) of each filament constituting the sheath strand were set as shown in Tables 1 and 2. In all the steel cords, a wrapping wire having a wire diameter of 0.15 mm and having the same strength was commonly used.

Next, a method for evaluating cord productivity and tire durability will be described.
The code productivity was evaluated as follows.
In producing steel cords used for each pneumatic radial tire, the productivity was evaluated. The evaluation result is “◯” when a stable twisted structure is obtained, and “△” when a slight disturbance occurs in the twisted structure or when filament breakage occurs slightly during the twisting process. Was significantly disturbed, resulting in a decrease in cord productivity, or a case where filament breakage occurred significantly during the twisting process. In addition, the evaluation of the tire durability performance was not performed for the case where the evaluation of the code productivity was “x”.

The tire durability performance was evaluated as follows.
Each pneumatic radial tire is mounted on a test rim having a rim size of 19.50, and the air pressure is set to 700 kPa using nitrogen gas as a filling gas. Then, a running test was carried out using an indoor drum tester equipped with a rotating drum provided with a cleat having a height of 200 mm on the outer peripheral surface under conditions of a speed of 10 km / hour and an initial load of 183 kN. In the running test, the load was increased by 52 kN every 10 hours, and the running time until the tire broke down was measured. The results of tire durability performance are indicated by an index with Comparative Example 1 as 100. The larger the value of this index, the better the durability.
In the traveling test described above, the failure of the tire means that traveling is impossible. Specific examples of the tire failure include a burst in which the tread portion ruptures and a separation in which the belt portion is peeled off.

As shown in Table 1 above, in Examples 1 to 6, good results were obtained with respect to cord productivity and tire durability performance. In Example 3, the tensile strength Tcc of the core filament of the core strand is in a preferable range, the fatigue resistance is improved, and the tire durability performance is more excellent. In Example 4, the tensile strength Tcc of the core filament of the core strand is in the preferred range, the strand diameter dcc of the core filament of the core strand is large, and the ratio of the strand diameter (dcc / dcm) is also in the preferred range. The tire durability performance is better. In addition, rubber permeability was improved and fretting resistance was improved.
In Example 5, the tensile strength Tcc of the core filament of the core strand is in the preferred range, and the strand diameter dcc of the core filament of the core strand is large, but the strand diameter ratio (dcc / dcm) is out of the preferred range. The filament is not arranged at a predetermined position, and the degree of improvement in tire durability is small.
In Example 6, the tensile strength Tcc of the core filament of the core strand is in a preferable range, and the strand diameter dcc of the core filament of the core strand and the strand diameter dcm of the sheath filament of the intermediate layer are large. The ratio (dcm / dcs) is out of the preferred range, the filament is not disposed at a predetermined position, and the degree of improvement in tire durability is small.

On the other hand, Comparative Example 1 to Comparative Example 11 shown in Table 2 did not give good results for either cord productivity or tire durability performance.
Comparative Example 1 is a reference for evaluation of tire durability performance. The core strand and the sheath strand have the same tensile strength and the same wire diameter.
In Comparative Example 2, the tensile strength Tss exceeded the upper limit, the steel cord productivity was poor, and the wire was easily disconnected, so the tire durability performance evaluation test was not performed.
In Comparative Example 3, the tensile strength Tc was less than the lower limit, and a significant durability improvement effect was not obtained.
In Comparative Example 4, the tensile strength Tss was less than the lower limit, the preceding break occurred in the sheath strand, and the tire durability performance was low.

In Comparative Example 5, although the strand diameter dcc of the core filament of the core strand is large, the tensile strength Tc is less than the lower limit value, and the fatigue resistance of the core filament is poor.
In Comparative Example 6, the strand diameter dcc of the core filament of the core strand is large, the tensile strength Tc exceeds the upper limit value, the toughness is excessively increased, and the steel cord cannot be manufactured easily due to disconnection. For this reason, the tire durability performance evaluation test was not performed.
In Comparative Example 7, the strand diameter dcc of the core filament of the core strand was large, but the tensile strength Tsc was less than the lower limit, and the core strand was liable to break earlier, and a significant durability improvement effect was not obtained.

In Comparative Example 8, the strand diameter dcc of the core filament of the core strand is large, but the tensile strength Tsc exceeds the upper limit value, the toughness is excessively increased, and the steel cord cannot be manufactured easily due to disconnection. For this reason, the tire durability performance evaluation test was not performed.
In Comparative Example 9, the strand diameter dcc of the core filament of the core strand was large, the tensile strength Tss was less than the lower limit value, the outermost sheath filament was preliminarily broken, and the tire durability performance was low.
In Comparative Example 10, since the strand diameter dcc of the core filament of the core strand is large and the tensile strength Tss exceeds the upper limit value, the toughness is excessively increased, and the steel cord cannot be manufactured easily due to disconnection. For this reason, the tire durability performance evaluation test was not performed.
In Comparative Example 11, the tensile strength Tc exceeds the upper limit, the toughness is excessively increased, and the steel cord cannot be manufactured easily due to disconnection. For this reason, the tire durability performance evaluation test was not performed.

DESCRIPTION OF SYMBOLS 10 Steel cord 12 Core strand 13c, 15c Core filament 13s, 15s Sheath filament 14 Sheath strand 16 Wrapping wire 20c, 22c Core 20s, 22s Outermost layer 30 Steel cord rubber composite 32 Rubber layer 40 Pneumatic radial tire (tire)
42 Tread portion 44 Side wall portion 46 Bead portion 48 Carcass layer 50 Bead core 52 Inner liner layer 54a, 54b, 54c, 54d Belt layer 56a, 56b Belt protective layer

Claims (7)

A core strand comprising a core composed of three core filaments, an intermediate layer composed of 8-9 sheath filaments, and an outermost layer composed of 13-15 sheath filaments, and three core filaments A sheath strand comprising a core composed of 8 to 9 sheath filaments and an outermost layer composed of 13 to 15 sheath filaments, and a wrapping wire,
5-6 sheath strands are twisted around one core strand, and the wrapping wire is wound around the twisted sheath strand,
The strand diameter of each filament of the core strand is dc (mm), the strand diameter of the core filament of the sheath strand is dsc (mm), and the strand diameter of the sheath filament of the outermost layer of the sheath strand is Is dss (mm),
The tensile strength Tc (MPa) of each filament of the core strand satisfies the relationship of 3700−2000 dc ≦ Tc <4500−2000 dc,
Among the core filaments of the sheath strand and the sheath filaments of the intermediate layer, at least the tensile strength Tsc (MPa) of the core filament satisfies the relationship of 3700−2000 dsc ≦ Tsc ≦ 4100−2000 dsc,
The steel cord characterized by the tensile strength Tss (MPa) of the sheath filament of the sheath strand satisfying a relationship of 3200-2000dss <Tss ≦ 3600-2000dss. When the strand diameter of the core filament of the core strand is dcc (mm), and the strand diameter of the sheath filament of the intermediate layer and the sheath filament of the outermost layer is dst (mm),
Tensile strength Tcc (MPa) of the core filament of the core strand satisfies a relationship of 4200−2000 dcc ≦ Tcc <4500−2000 dcc,
2. The steel cord according to claim 1, wherein a tensile strength Tst (MPa) of a sheath filament of the intermediate layer and a sheath filament of the outermost layer of the sheath strand satisfies a relationship of 3700−2000 dst ≦ Tst ≦ 4100−2000 dst. The strand diameter of the core filament of the core strand is dcc (mm), the strand diameter of the sheath filament of the outermost layer of the core strand is dcs (mm), and the sheath of the intermediate layer of the core strand is the sheath When the filament diameter of the filament is dcm (mm) and the filament diameter of each filament of the sheath strand is ds (mm),
The filament diameter of each filament satisfies 0.15 mm <ds ≦ dcs ≦ dcm <dcc <0.40 mm, and 1.0 ≦ dcm / dcs ≦ 1.05, and 1.0 <dcc / dcm <1. The steel cord according to claim 1, wherein the steel cord satisfies 10. A pneumatic radial tire having a reinforcing layer including a plurality of reinforcing cords,
The reinforcing cord includes a core strand including a core composed of three core filaments, an intermediate layer composed of 8 to 9 sheath filaments, and an outermost layer composed of 13 to 15 sheath filaments; A sheath strand having a core composed of three core filaments, an intermediate layer composed of 8-9 sheath filaments, and an outermost layer composed of 13-15 sheath filaments, and a wrapping wire And
5-6 sheath strands are twisted around one core strand, and the wrapping wire is wound around the twisted sheath strand,
The strand diameter of each filament of the core strand is dc (mm), the strand diameter of the core filament of the sheath strand is dsc (mm), and the strand diameter of the sheath filament of the outermost layer of the sheath strand is Is dss (mm),
The tensile strength Tc (MPa) of each filament of the core strand satisfies the relationship of 3700−2000 dc ≦ Tc <4500−2000 dc,
Among the core filaments of the sheath strand and the sheath filaments of the intermediate layer, at least the tensile strength Tsc (MPa) of the core filament satisfies the relationship of 3700−2000 dsc ≦ Tsc ≦ 4100−2000 dsc,
A pneumatic radial tire characterized in that a tensile strength Tss (MPa) of the sheath filament of the sheath strand satisfies a relationship of 3200−2000 dss <Tss ≦ 3600−2000 dss. When the strand diameter of the core filament of the core strand is dcc (mm), and the strand diameter of the sheath filament of the intermediate layer and the sheath filament of the outermost layer is dst (mm),
Tensile strength Tcc (MPa) of the core filament of the core strand satisfies a relationship of 4200−2000 dcc ≦ Tcc <4500−2000 dcc,
The pneumatic radial tire according to claim 4, wherein the tensile strength Tst (MPa) of the sheath filament of the intermediate layer of the sheath strand and the sheath filament of the outermost layer satisfies a relationship of 3700-2000dst≤Tst≤4100-2000dst. . The strand diameter of the core filament of the core strand is dcc (mm), the strand diameter of the sheath filament of the outermost layer of the core strand is dcs (mm), and the sheath of the intermediate layer of the core strand is the sheath When the filament diameter of the filament is dcm (mm) and the filament diameter of each filament of the sheath strand is ds (mm),
The filament diameter of each filament satisfies 0.15 mm <ds ≦ dcs ≦ dcm <dcc <0.40 mm, and 1.0 ≦ dcm / dcs ≦ 1.05, and 1.0 <dcc / dcm <1. The pneumatic radial tire according to claim 4, wherein the pneumatic radial tire satisfies 10.   The pneumatic radial tire according to any one of claims 4 to 6, wherein the reinforcing layer is a carcass layer.