JPH09143890A - Steel cord for reinforcing tire and pneumatic tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel cord used for reinforcing the carcass part of a tire and improved in weight reduction and durability, and to obtain a pneumatic tire for a large vehicle. SOLUTION: This steel cord is produced from steel element wires having a carbon content of >=0.70wt.%, a diameter of 0.15-0.25mm and a tensile strength of 3,400-3,900N/mm<2> . Therein, an average distance between adjacent steel element wires constituting a sheath is >=0.02mm and <=1.5 times of the diameter of the steel element wire. The molding rate of the steel wire element constituting the sheath is 80-110%. Thus, a wrapping wire is not placed on the outer periphery of the sheath. The spiral curvature radius R0 of the spirally molded steel element wire obtained by loosing the twisting of a steel cord, and the spiral curvature radius R1 of the steel element wire, when the surface layer on the spiral inner side of the steel element wire is dissolved off, have a [(R1 /R0 )×100] ratio of <100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire reinforcing steel cord and a pneumatic tire using the same.
More specifically, the present invention relates to a steel cord used for reinforcement of a carcass portion of a tire and having improved durability while being lightweight, and a pneumatic tire for large vehicles.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of protecting the global environment, it has been a goal to reduce fuel consumption of vehicles, and tires have been reduced in weight, and a steel cord, which is a reinforcing material for tires, has a large strength. Attempts have been made to reduce the usage while maintaining tire reinforcement. On the other hand, however,
It is widely known that the fatigue resistance decreases as the tensile strength per unit cross-sectional area of the steel wire forming the cord is increased.

For this reason, in wet continuous wire drawing, the number of wire drawing dies is increased, and the area reduction rate of each die is reduced to suppress heat generation during wire drawing, thereby providing high strength and high ductility thin steel wire. A method of manufacturing the above is proposed in Japanese Patent Laid-Open No. 3-104821. Further, the carbon content is 0.90 to 0.
95% by weight and chromium content 0.10 to 0.40% by weight
Japanese Patent Application Laid-Open No. 4-126605 proposes a method of maintaining the durability of a tire and reducing its weight by using a steel cord made of carbon steel as a raw material for reinforcing a tire. However, it is possible to reduce the weight of the tire by reducing the amount of members used, but it cannot be denied that there is a risk that the strength will decrease and the durability will decrease.

In the above-mentioned prior art, the method of increasing the number of stages of the wire drawing die for wire drawing has a problem that the workability of wire drawing is deteriorated, while the carbon steel used as a raw material for the steel cord. Special ingredients make expensive steel cords impractical.

[0005]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention
The tensile strength is 2 at the carcass part of the pneumatic tire for buses.
3 + 9 with steel strands of about 750-3150 N / mm ²
x0.23 + 1 two-layer twist structure or 3 + 9 + 15x
A steel cord having a three-layer twist structure of 0.175 + 1 is mainly used, but if the steel cord diameter is reduced to 3 + 9x0.21 structure to reduce the weight of the tire, the tire strength is secured. In order to achieve this, it is necessary to increase the number of driven steel cords, and as a result, the spacing between adjacent steel cords of the carcass becomes too narrow, resulting in an increase in the number of failures at the folded back end of the carcass ply. There is.

In the steel cord having the 3 + 9 + 1 structure described above, since the steel wires are in close contact with each other, the relative movement between the steel wires forming the steel cord due to the rolling of the tire. The movement causes the steel wire to wear and the strength of the steel cord to decrease. Further, if the wrapping wire surrounds the outer circumference of the steel cord, the tendency of the strength of the steel cord to decrease is increased.

The tire may sometimes be damaged by road surface projections or side wall projections reaching the vicinity of the steel cord, and water penetrates from these scratches to corrode the steel strands. It may reduce the durability of the tire. On the other hand, a method of reducing the corrosion of the steel strands by reducing the number of steel strands forming the outer layer and providing a gap between the strands so that the rubber can enter the inside of the steel cord. However, there is a problem that a satisfactory effect cannot be obtained unless the rubber has sufficiently penetrated into the gap. Further, even if the infiltration of the rubber is sufficient, there is a problem that the corrosion fatigue resistance of the steel wire is not always sufficient due to the moisture contained in the rubber.

[0008]

The steel cord for tire reinforcement according to the first aspect of the present invention has a carbon content of 0.70% by weight or more, a diameter of 0.15 to 0.25 mm, and a tensile strength. Of steel wire in the range of 3400 to 3900 N / mm ² ,
The number M of steel wires forming the core is 1 to 4, and the number N of steel wires forming the sheath surrounding the core is M + (2 to 5).
2-layer twisted steel cord with M + N structure, or
A three-layer twist steel cord having a M + N + P structure in which P steel wires are further wound around the outer periphery of the above two-layer twist steel cord, and P is N + (2 to 5). The average value of the gap between the adjacent steel wire constituting the steel is 0.02 mm or more and 1.5 times or less of the diameter of the steel wire, and the die forming ratio of the steel wire forming the sheath is 80 to 110. By setting the percentage
The structure is such that the wrapping wire is not positioned on the outer circumference of the steel wire, and the spiral curvature radius R _{0 of the} steel wire having a spiral shape obtained by untwisting the steel cord and the steel wire The ratio of the radius of curvature R ₁ of the spiral when the surface layer in the inner part of the spiral is removed by dissolution, (R ₁ / R ₀ ) × 100 is 100.
Steel reinforcement for tire reinforcement characterized by being less than
Provide

And, preferably, the surface layer is in a range from the surface of the steel wire to a depth from the surface corresponding to 5% of the diameter of the steel wire, and particularly preferably, the surface layer is from the surface of the steel wire. The present invention relates to a steel cord for reinforcing a tire, which is a range from the surface to a depth corresponding to 10% of the diameter of a steel strand. Further, the carbon content of the steel wire is 0.7 to 0.
It is preferably 85% by weight.

In the tire reinforcing steel cord of the present invention, the diameter d of the steel cord is 50 mm of the rubberized steel cord / rubber composite before being molded into a tire.
For composite strength per width, (50x code strength) /
Composite strength = 1.1 ≤ d (mm) ≤ (50x code strength) / composite strength -0.4, preferably (50x code strength) / composite strength. −0.9 ≦
d (mm) ≤ (50 x code strength) / composite strength -0.
It is a steel cord in which the diameter of the steel wire and the number of steel wires forming the steel cord are selected so as to fall within the range of 6.

In the pneumatic tire according to the second aspect of the present invention, the reinforcing material has a carbon content of 0.70% by weight or more, a diameter of 0.15 to 0.25 mm, and a tensile strength of 3.
In the steel strands in the range of 400 to 3900 N / mm ² , the number M of steel strands constituting the core is 1 to 4, and the number N of steel strands constituting the sheath surrounding the core is M + (2 -5) A two-layer twist steel cord having an M + N structure, or P steel wires are further wound around the outer circumference of the above two-layer twist steel cord, and P is N + (2-5). ), A three-layer twist steel cord having a structure of M + N + P, in which the average value of the gap between the adjacent steel wire constituting the sheath is 0.02 mm or more and 1.5 times or less of the diameter of the steel wire. The steel wire forming the sheath has a die-casting ratio of 80 to 110% so that the wrapping wire is not positioned on the outer periphery of the sheath, and the twist of the steel cord is unwound. And the spiral radius of curvature R _{0 of the} steel wire having a spiral shape and the inside of the spiral of the steel wire. The invention relates to a pneumatic tire using a steel cord having a ratio of (R ₁ / R ₀ ) × 100 to the radius of curvature R ₁ of the spiral when the surface layer is dissolved and removed, and particularly, air It is used to reinforce the carcass portion of the filled tire.

With regard to the structure of the steel cord used, the surface layer has a diameter of 5 mm from the surface of the steel wire.
%, Preferably 10%, to a pneumatic tire using a steel cord having a depth from the surface corresponding to 10%. . Further, a steel cord having a carbon content of the steel wire of 0.7 to 0.85% by weight is used.

Further, regarding the structure of the steel cord, the rubber strength of the rubberized steel cord / rubber composite before the diameter d is molded into a tire is as follows: 50x code strength) / composite strength-1.
1 ≤ d (mm) ≤ (50x code strength) / composite strength-
0.4, preferably (50x code strength) / composite strength-0.9 ≤ d (mm) ≤ (50
x cord strength) / composite strength-0.6, a steel cord is used in which the diameter of the steel wire and the number of steel wires constituting the steel cord are selected. It is a thing.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in more detail with a steel cord for reinforcing a tire.
The carbon content of the carbon steel used as the raw material for the steel cord is set to 0.
The limit of 70% by weight or more is that the tensile strength of the steel wire is 3
This is for 400 to 3900 N / mm ^2, and preferably the carbon content is 0.85 wt% or less to suppress the formation of first-order cementite during patenting and ensure the ductility of the steel wire. Will be easier. The carbon steel used in the present invention is preferably a plain carbon in order to suppress an increase in price.

The diameter of the steel wire is 0.15-0.25 m.
The reason for limiting to m is less than 0.15 mm, but the tensile strength of the steel wire increases, but productivity in wire drawing decreases and it is not economical. If it exceeds 0.25 mm, repeated bending fatigue property deteriorates. At the same time, the bending rigidity of the steel cord becomes too large, which makes it difficult to process the tire at the time of tire molding, especially at the bead portion. Further, the tensile strength of the steel wire is limited. If it is less than 3400 N / mm ² , it is difficult to maintain the strength of the steel cord, and it is not possible to maintain the tire strength and reduce the weight. Also, the tensile strength of the steel wire is 3900N
If it exceeds / mm ² , the wire drawing productivity may decrease or the ductility of the obtained steel wire may become poor, and there is a concern that the number of tire rehabilitation may decrease.

Although it is not necessary that the diameters of the core and the steel wire of the sheath used in the present invention are the same, productivity can be improved by making them the same. And stillco
1 to 4 of the number M of steel wires that form the core
A two-layer twisted steel cord in which the number N of steel strands constituting the sheath is M + (2 to 5), or the two-layer twisted steel
The 3-layer twisted steel cord in which N + (2 to 5) steel wires are arranged on the outer periphery of the rucode has a twisted form that does not adversely affect fatigue resistance while satisfying rubber penetration. This is to improve the wire filling rate in the steel cord cross section and obtain the required cord strength with a steel cord diameter as small as possible. Therefore, it is preferable that the number of steel wires forming the core is one or two having no space inside or three having a small internal space.

The average value d (see FIG. 14) of the gaps between the adjacent steel wire constituting the steel sheath (all sheaths wound around the outer periphery except the core) is defined as 0.02
The range of (mm) ≤ d ≤ strand diameter x 1.5 (mm) is set so that the average value of the gap between adjacent sheath strands is 0.02 m.
If it is less than m, it is difficult to penetrate the rubber into the vicinity of the core during tire vulcanization, and if the gap exceeds the strand diameter x 1.5, the arrangement of the sheath strands is disturbed and fatigue resistance is reduced. The steel cord / rubber composite has a low filling rate of the wire in the circular section of the steel cord circumscribed and the steel cord has insufficient strength or the steel cord diameter is large. This increases the thickness of the tire and adversely affects the weight reduction of the tire.

When the steel cord is untwisted, a plurality of helically shaped steel strands are obtained, which is used in the twisting process in which a straight steel strand is used as the steel cord. This is because plastic deformation is applied to the steel wire, so even if the surface tensile residual stress of the steel wire is reduced in the wire drawing process, the maximum tensile residual stress is generated inside the spiral of the steel wire in the twisting process and corrosion fatigue resistance It was found that the corrosion resistance of the steel cord can be improved by reducing the tensile residual stress in the surface layer inside the spiral of the steel wire made into steel cord. Is.

In the steel cord for tire reinforcement,
When the tire is mounted on a vehicle and travels, the tire is repeatedly bent to cause fretting in which the steel wires forming the steel cord are frictionally worn with each other, which further facilitates corrosion fatigue. Therefore, it is preferable to reduce the tensile residual stress in the range of the depth from the surface of the steel wire to 5% of the wire diameter,
More preferably, the tensile residual stress from the surface of the steel wire to a depth of 10% of the wire diameter is reduced.

According to the present invention, since the one wrapping wire wound around the outermost layer of the steel cord is not positioned, fretting between the sheath wire and the wrapping wire can be prevented, so that the tire can be used for a long period of time. Even if it is used, the reduction in the strength of the steel cord can be remarkably reduced, and the diameter of the steel cord becomes small, which is advantageous for the weight reduction of the tire.

50 m near the bead portion of the tire carcass
The steel cord diameter per m width of the composite is (50 x code strength) / composite strength-1.1 ≤ code
Code diameter (mm) ≤ (50x cord strength) / composite strength-
The reason for setting 0.4 is to keep the steel cord distance D (see FIG. 13) in the vicinity of the bead portion of the tire within the range of 0.4 to 1.1 mm. The durability of the carcass part can be improved.

That is, the steel coils arranged substantially in parallel.
If the length of the rubber between the cords is less than 0.4 mm, the shearing stress of the rubber becomes too large with respect to the stress applied to the carcass when the tire is running, and the rubber between the steel cords is likely to crack. In addition, the adhesive failure between the steel cord and the rubber easily occurs. On the other hand, when the thickness exceeds 1.1 mm, when the tire is filled with air, swelling of the rubber between the steel cords occurs and the load on the rubber increases, and the heat generated by the rubber during tire running increases, resulting in high speed. Durability decreases.
More preferably, a steel cord near the bead portion of the tire
In order to keep the distance between the dots in the range of 0.6 to 0.9 mm,
The diameter d of the steel cord is represented by [(50x cord strength) /
Composite strength] −0.9 ≦ d (mm) ≦ [(50 × code strength) / composite strength] −0.6 is preferable.

[0023]

The present invention will be described in more detail with reference to the following examples. C: 0.81%, Si: 0.23% in weight%,
Mn: 0.49%, P: 0.006%, S: 0.008
% Of plain carbon steel with a content of 5.5% and a diameter of 5.5 m
m steel cord wire rod was dry-drawn to a desired diameter, then subjected to patenting treatment and brass plating, and subjected to wet drawing to obtain a true strain of 3.8 and a diameter of 0.2.
A steel wire having a tensile strength of 1695 and a tensile strength of 3695 N / mm ² was manufactured. At this time, it is preferable to repeatedly bend the steel wire after drawing while applying tension to reduce the residual tensile stress in the surface layer of the steel wire.

The stranded wire is made into a steel cord by a usual method by a tuber stranded wire machine. In the present invention, however, the steel cord is passed when the steel cord is passed through the straightening roller. Tension is applied to the cord, for example, a 3 + 8 × 0.21 mm coil
In the cord, a tension of 450 N / cord was applied to reduce the tensile residual stress inside the spiral of the steel wire constituting the steel cord. The twisting machine is not limited to the tuber type, but a buncher twisting machine can be used.

Further, a tire using the steel cord as a carcass ply was manufactured as a prototype. FIG. 15 is a sectional view of a pneumatic tire, in which a is a belt, b is a carcass, and c is a bead. The tire size is 11R22.5.14
PR, the number of cords to be coded is 3
It is 1.5 lines / 5 cm. The characteristics of the manufactured steel cords and the prototype tires are summarized in Tables 1, 2 and 3. In Table 1, each of the steel cords has the structure shown in FIG. 4 for Conventional Example 1, the structure of 3 + 9 + 15 for Comparative Example 1, and the structures shown in FIGS. 7-12 for Examples 1-6, respectively. Is.
Further, in Table 2, each structure of the steel cords is as follows: Conventional Example 2 has the structure of FIG. 3, Comparative Example 2 has the structure of 3 + 9, Examples 7 to 7
Reference numeral 12 has the structure shown in FIGS. 6 to 11, respectively. Further, in Table 3, each structure of the steel cords is as shown in FIG. 3 for the conventional example 3, the structure as shown in FIG. 3 for the comparative example 3, and FIGS. It has the structure shown in FIG.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

The distance between the steel cords is measured at the carcass folding portion near the bead portion of the tire, and the steel cord spacing is also measured.
The weight of the rucod is 100% for the conventional example and the weight of the tire is
The weight of the steel cord embedded in the residue is displayed as an index, and the smaller the value, the better the weight reduction.

The change in curvature at a depth of 3% from the surface was obtained by removing one of the cords in the tire and untwisting the steel cord to obtain a steel wire having a spiral shape. The steel wire constituting the outer layer is cut to a length of 100 mm, the enamel is applied to the semicircle in the longitudinal direction, and the wire is then immersed in a 50% aqueous nitric acid solution to apply the enamel to the semicircular side. It melted to a depth of 3% of the diameter, and the movement of the wire at that time was measured. The measurement is as shown in FIGS. 1 and 2, in which R ₀ is the radius of spiral curvature (mm) before the removal of the surface layer inside the spiral, and R ₁ is the radius of curvature of the spiral after removal of the surface inside the spiral (( m
m).

The rubber penetrability is the cursor code 1 in the tire.
Take a book and observe the degree of rubber covering the surface of the core over the entire length of the steel cord.
If it is 80, 89% is good, and 79% or less is x.
Was evaluated. If it is 80% or more, there is no practical problem.

The strength retention is determined by running each test tire by a drum test under the condition of JIS regular internal pressure load for 200,000 Km, collecting a carcass cord from the tire, and measuring its strength. It is shown as a ratio to the previous steel code.

The corrosion fatigue resistance is determined by placing a tube inside the inner liner of the tire when the rim of each test tire is assembled.
300 m1 of water was filled between the inner liner and the tube, and each test tire was subjected to JIS C internal pressure and normal load until a car scoring break (CBU) failure in a drum test. It was evaluated by the life (running distance) of. In addition, the traveling distance of the conventional example is represented as an index, and the larger the index, the more excellent the corrosion fatigue resistance.

[0034]

INDUSTRIAL APPLICABILITY As described above, a steel cord having a two-layer twist or a three-layer twist made of a steel wire having a high tensile strength, and a gap is provided between the steel wires of the sheath. In addition, it reduces the tensile residual stress in the surface layer inside the spiral of the steel wire,
Since no rubbing wire was applied to the rucode, it became a steel code with improved code strength retention after repeated bending and improved corrosion fatigue resistance. A vehicle tire using this steel code can improve its durability and improve the fuel efficiency of the vehicle by reducing the weight of the tire. Therefore, it is possible to save resources and protect the natural environment. A very useful pneumatic tire for a vehicle can be provided.

[Brief description of the drawings]

FIG. 1 shows a spiral of a steel wire in which a steel cord is untwisted, and is a state diagram in which the twist is untwisted.

FIG. 2 shows a helix of a steel wire in which the steel cord is untwisted, and is a state diagram after untwisting and melting the inner surface layer of the helix.

FIG. 3 is a cross-sectional view of a conventional steel cord having a 3 + 9 + 1 structure.

FIG. 4 is a cross-sectional view of a conventional steel cord having a 3 + 9 + 15 + 1 structure.

FIG. 5 is a sectional view of a steel cord having a 1 + 5 structure according to the present invention.

FIG. 6 is a sectional view of a steel cord having a 2 + 7 structure according to the present invention.

FIG. 7 is a sectional view of a steel cord having a 3 + 8 structure according to the present invention.

FIG. 8 is a cross-sectional view of a steel cord having a 4 + 9 structure according to the present invention.

FIG. 9 is a sectional view of a steel cord having a 1 + 5 + 10 structure according to the present invention.

FIG. 10 is a schematic view of the 2 + 7 + 12 structure of the present invention.
It is sectional drawing of a rucod.

FIG. 11 is a schematic view of the 3 + 8 + 13 structure of the present invention.
It is sectional drawing of a rucod.

FIG. 12 is a schematic view of the 4 + 9 + 14 structure of the present invention.
It is sectional drawing of a rucod.

FIG. 13 is a cross-sectional view showing a steel cord interval.

FIG. 14 is a cross-sectional view showing a gap between the sheath strands.

FIG. 15 is a cross-sectional view of a pneumatic tire.

Claims (13)

[Claims] 1. A carbon content of 0.70% by weight or more, a diameter of 0.15 to 0.25 mm, and a tensile strength of 3400 to 390.
In the steel wire in the range of 0 N / mm ² , the number M of steel wires forming the core is 1 to 4, and the number N of steel wires forming the sheath surrounding the core is M + (2 to 5). ) A two-layer twist steel cord having an M + N structure, or P steel wires are further wound around the outer periphery of the above two-layer twist steel cord, and P
Is a three-layer twisted steel cord having a structure of M + N + P with N = (2 to 5), wherein the average value of the gaps between adjacent steel wire constituting the sheath is 0.02 mm or more and the steel wire diameter. 1.
It is 5 times or less, and the die forming rate of the steel wire forming the sheath is 8
By setting it to 0 to 110%, the lapping wire is not positioned on the outer periphery of the sheath, and the steel coil
And the radius of curvature R _{0 of} the spirally shaped steel wire obtained by untwisting the cord, and the radius of curvature R ₁ of the spiral when the surface layer in the inner part of the spiral of the steel wire is dissolved and removed. Ratio of
A steel cord for tire reinforcement, wherein (R ₁ / R ₀ ) × 100 is less than 100. 2. The tire reinforcing steel coke according to claim 1, wherein the surface layer has a range from the surface of the steel wire to a depth from the surface corresponding to 5% of the diameter of the steel wire. −
De. 3. The tire reinforcing steel coke according to claim 1, wherein the surface layer has a range from the surface of the steel wire to a depth from the surface corresponding to 10% of the diameter of the steel wire. −
De. 4. The carbon content of the steel wire is 0.7 to 0.85.
The steel cord for tire reinforcement according to claim 1, which is in a weight percentage. 5. A rubberized steel cord-rubber composite having a diameter d of the steel cord of 50 m before being molded into a tire.
Compared to the composite strength per m width (50x code strength)
/ Composite strength-1.1 ≤ d (mm) ≤ (50x code strength) / composite strength -0.4, the diameter of the steel wire and the steel cord are configured. The steel cord for reinforcing a tire according to any one of claims 1 to 4, wherein the number of steel wires to be selected is selected. 6. A rubberized steel cord / rubber composite having a diameter d of the steel cord of 50 m before being molded into a tire.
Compared to the composite strength per m width (50x code strength)
The diameter of the steel wire and the steel cord are configured to be in the range of / composite strength-0.9≤d (mm) ≤ (50x cord strength) / composite strength-0.6. The steel cord for reinforcing a tire according to any one of claims 1 to 4, wherein the number of steel wires to be selected is selected. 7. A carbon content of 0.70% by weight or more, a diameter of 0.15 to 0.25 mm, and a tensile strength of 3400 to 390.
In the steel wire in the range of 0 N / mm ² , the number M of steel wires forming the core is 1 to 4, and the number N of steel wires forming the sheath surrounding the core is M + (2 to 5). ) A two-layer twist steel cord having an M + N structure, or P steel wires are further wound around the outer periphery of the above two-layer twist steel cord, and P
Is a three-layer twisted steel cord having a structure of M + N + P with N = (2 to 5), wherein the average value of the gaps between adjacent steel wire constituting the sheath is 0.02 mm or more and the steel wire diameter. 1.
It is 5 times or less, and the die forming rate of the steel wire forming the sheath is 8
By setting it to 0 to 110%, the lapping wire is not positioned on the outer periphery of the sheath, and the steel coil
And the radius of curvature R _{0 of} the spirally shaped steel wire obtained by untwisting the cord, and the radius of curvature R ₁ of the spiral when the surface layer in the inner part of the spiral of the steel wire is dissolved and removed. Ratio of
(R ₁ / R ₀ ) × 100 is less than 100. A pneumatic tire using a steel cord as a reinforcing steel cord. 8. The pneumatic tire according to claim 7, wherein the steel cord is used for reinforcing a carcass portion. 9. The steel cord according to claim 7, wherein the surface layer uses a steel cord in a range from the surface of the steel wire to a depth corresponding to 5% of the diameter of the steel wire. Pneumatic tires. 10. The steel cord according to claim 7, wherein the surface layer uses a steel cord having a range from the surface of the steel wire to a depth corresponding to 10% of the diameter of the steel wire. Pneumatic tires. 11. The carbon content of the steel wire is 0.7 to 0.8.
The pneumatic tire according to claim 7, wherein a steel cord containing 5% by weight is used. 12. A rubberized steel cord / rubber composite having a diameter d of the steel cord before being molded into a tire is 50.
(50x code strength) / composite strength-1.1 ≤ d (mm) ≤ (50x code-
Strength) / composite strength-0.4,
The pneumatic tire according to claim 7, wherein a steel cord is used in which the diameter of the steel strand and the number of steel strands constituting the steel cord are selected. 13. A rubberized steel cord / rubber composite having a diameter d of the steel cord before being molded into a tire.
(50x code strength) / composite strength-0.9 ≤ d (mm) ≤ (50x code-
(D strength) / composite strength-0.6,
The pneumatic tire according to claim 7, wherein a steel cord is used in which the diameter of the steel strand and the number of steel strands constituting the steel cord are selected.