WO2024252735A1 - Steel cord, cord-rubber composite, and tire - Google Patents

Abstract

Provided is a steel cord having a 1 × 4 structure in which four element wires are twisted, wherein the element wires have an element wire diameter between 0.15 mm and 0.20 mm both inclusive, and, when, in a cross section perpendicular to the longitudinal direction of the steel cord embedded in rubber, a region surrounded by common tangent lines between the element wires adjacent to each other, the common tangent lines being in contact with an outer surface of the steel cord, and line segments connecting the centers of the element wires that are adjacent along the outer surface of the steel cord is defined as a composite region, and the area of the composite region is defined as an effective cross-sectional area, the effective cross-sectional area is between 0.099 mm² and 0.224 mm² both inclusive.

Description

Steel cord, cord-rubber composite, tire

This disclosure relates to steel cords, cord-rubber composites, and tires.

This application claims priority to Japanese Application No. 2023-094993, filed on June 8, 2023, and incorporates by reference all of the contents of said Japanese application.

Patent Document 1 discloses a steel cord for reinforcing tires, which is formed by twisting together 2 to 13 steel wires having a wire diameter of 0.23 to 0.50 mm, and which is characterized in that the cord has an elongation rate of 1.5 to 3.0% when subjected to a tensile load of 10% of the breaking load, and the value A shown in the following formula is 50 to 100 N/%.

(Formula) A={(L ₅₀ -L ₁₀ )/n}/(E ₅₀ -E ₁₀ )
Where _L50 : 50% load of breaking load (N)
_L10 : 10% load of breaking load (N)
_E50 : Cord elongation (%) when loaded with 50% of the breaking load
_E10 : Cord elongation (%) when loaded with a load of 10% of the breaking load
n: Number of steel wires (pieces)

JP 2002-275772 A

The steel cord of the present disclosure is a steel cord having a 1×4 structure in which four wires are twisted together,
The wire has a diameter of 0.15 mm or more and 0.20 mm or less,
When embedded in rubber, in a cross section perpendicular to the longitudinal direction of the steel cord,
When a region surrounded by a common tangent line between adjacent wires that is in contact with the outer surface of the steel cord and a line segment that connects centers of adjacent wires along the outer surface of the steel cord is defined as a composite region, and an area of the composite region is defined as an effective cross-sectional area,
The effective cross-sectional area is equal to or greater than 0.099 mm ² and equal to or less than 0.224 mm ² .

FIG. 1 is a perspective view of a steel cord according to one embodiment of the present disclosure. FIG. 2 is a cross-sectional view of a plane perpendicular to the longitudinal direction of a steel cord according to one embodiment of the present disclosure, in a state in which the steel cord is embedded in rubber to form a cord-rubber composite. FIG. 3 is an explanatory diagram of a corrugated wire. FIG. 4 is a cross-sectional view of a cord-rubber composite according to one embodiment of the present disclosure. FIG. 5 is a cross-sectional view of a tire according to one aspect of the disclosure. FIG. 6 is an explanatory diagram of a method for evaluating bending rigidity. FIG. 7 is an explanatory diagram of a method for evaluating durability.

[Problem that this disclosure aims to solve]

　Traditionally, sheet-shaped cord-rubber composites, made by stretching multiple steel cords together and embedding them in rubber, have been used as tire reinforcement materials.

In order to reduce the rolling resistance of tires, there is a demand for lighter cord-rubber composites.

The thickness of the rubber in the cord-rubber composite is selected so that the steel cord can be embedded. For this reason, one possible way to make the cord-rubber composite lighter is to reduce the wire diameter of the wires that make up the steel cord, thereby reducing the outer diameter of the steel cord (cord diameter) and thus the thickness of the cord-rubber composite. However, if the wire diameter is reduced, the cord-rubber composite may be more susceptible to breakage when repeatedly bent, which could reduce its durability.

Therefore, the present disclosure aims to provide a stranded steel cord that, when applied to a cord-rubber composite, can reduce the weight of the cord-rubber composite while increasing its durability.

[Effects of this disclosure]

This disclosure provides a stranded steel cord that, when applied to a cord-rubber composite, can reduce the weight of the cord-rubber composite while increasing its durability.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description thereof will not be repeated.

(1) A steel cord according to one embodiment of the present disclosure is a steel cord having a 1×4 structure in which four wires are twisted together,
The wire has a diameter of 0.15 mm or more and 0.20 mm or less,
When embedded in rubber, in a cross section perpendicular to the longitudinal direction of the steel cord,
When a region surrounded by a common tangent line between adjacent wires that is in contact with the outer surface of the steel cord and a line segment that connects centers of adjacent wires along the outer surface of the steel cord is defined as a composite region, and an area of the composite region is defined as an effective cross-sectional area,
The effective cross-sectional area is equal to or greater than 0.099 mm ² and equal to or less than 0.224 mm ² .

By setting the wire diameter to 0.20 mm or less, the outer diameter of the steel cord can be reduced. The thickness of the cord-rubber composite is selected so that the steel cord contained therein can be embedded. Therefore, by reducing the outer diameter of the steel cord according to one embodiment of the present disclosure, the thickness of the cord-rubber composite can also be reduced, and the cord-rubber composite and tires including the cord-rubber composite can be made lighter.

By setting the wire diameter to 0.15 mm or more, the number of steel cords required to achieve the desired bending rigidity can be reduced for a cord-rubber composite including a steel cord according to one embodiment of the present disclosure. This allows for weight reduction of the cord-rubber composite and tires including the cord-rubber composite.

By setting the effective cross-sectional area to be 0.099 ^mm2 or more and 0.224 ^mm2 or less, the bending rigidity of the cord-rubber composite body can be set within an appropriate range, and durability can be improved.

(2) In (1), the ratio of the area of the region in which steel is distributed to the effective cross-sectional area in the cross section may be 30% or more and 128% or less.

By setting the area ratio of the steel region, which is the ratio of the area of the region where steel is distributed to the effective cross-sectional area, to 30% or more, the bending rigidity of the cord-rubber composite can be increased when the cord-rubber composite is made. Furthermore, by setting the area ratio of the steel region to 128% or less, the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high when the cord-rubber composite is made. As a result, the durability of the cord-rubber composite can be particularly increased.

(3) In the above (1) or (2), at least one of the wires is a first corrugated wire having a first bent portion and a first non-bent portion repeatedly along a longitudinal direction,
The three first bent portions successive along the length of the first corrugated wire are defined as a first point, a second point, and a third point,
When the shortest distance between a straight line passing through an end of the first corrugated wire that is closest to the second point among the first point and the third point and the second point is defined as a first corrugation height,
The first corrugated wire may have a ratio of the wire diameter to the first corrugation height of 1.029 or more and 1.818 or less.

By setting D/H1, the ratio of wire diameter D to first corrugation height H1, to 1.818 or less, the distance between adjacent wires in the steel cord is increased and the rubber penetration rate is increased when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and rubber is improved, and the bending rigidity of the cord-rubber composite is increased.

By making D/H1 1.029 or more, it is possible to prevent the rubber penetration rate from becoming excessively high when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and the rubber can be set in a particularly preferable range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.

(4) In (3), when the distance between the first point and the third point of the first corrugated wire is defined as a first corrugation pitch,
A ratio of the first corrugation pitch of the first corrugated wire to a twist pitch of the steel cord may be 0.09 or more and 0.35 or less.

By setting the ratio of the first corrugated pitch of the first corrugated wire to the twist pitch of the steel cord to 0.35 or less, the distance between adjacent wires in the steel cord is increased, and the rubber penetration rate is increased when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and rubber is improved, and the bending rigidity of the cord-rubber composite is particularly increased.

By setting the ratio of the first corrugation pitch of the first corrugated wire to the twist pitch of the steel cord to 0.09 or more, it is possible to prevent the rubber penetration degree from becoming excessively high when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and the rubber can be set to a particularly preferable range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.

(5) In the configuration of (3) or (4), at least one of the four wires, excluding the first corrugated wire, is a second corrugated wire having second bent portions and second non-bent portions repeatedly along a longitudinal direction,
The three second bent portions successive along the length of the second corrugated wire are a fourth point, a fifth point, and a sixth point,
When the shortest distance between the fifth point and a straight line passing through an end of the second corrugated wire that is closest to the fifth point among the fourth point and the sixth point is defined as a second corrugation height, and the distance between the fourth point and the sixth point of the second corrugated wire is defined as a second corrugation pitch,
The second corrugated wire has a ratio of the wire diameter to the second corrugation height of 1.029 or more and 1.818 or less,
A ratio of the second corrugation pitch of the second corrugated wire to a twist pitch of the steel cord may be 0.50 or more and 1.50 or less.

By setting D/H2, the ratio of wire diameter D to second corrugation height H2, to 1.818 or less, the distance between adjacent wires in the steel cord is increased, and the rubber penetration rate is increased when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and rubber is improved, and the bending rigidity of the cord-rubber composite is increased.

By making D/H2 1.029 or more, it is possible to prevent the rubber penetration rate from becoming excessively high when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord and the rubber can be set in a particularly preferable range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.

By setting the ratio of the second corrugation pitch of the second corrugated wire to the twist pitch of the steel cord (P2/Psc) to 1.50 or less, the distance between adjacent wires in the steel cord can be increased, and the rubber penetration rate can be increased when the steel cord is embedded in rubber to form a cord-rubber composite. This allows the effective cross-sectional area to be increased.

In addition, by making P2/Psc 0.50 or more, it is possible to prevent the distance between the wires that make up the steel cord from becoming excessively large when the steel cord is embedded in rubber to form a cord-rubber composite. This makes it possible to reduce the thickness of the rubber required to embed the steel cord when forming the cord-rubber composite, and thus the weight of the cord-rubber composite.

(6) In any of (1) to (5), the initial elongation may be 0.20% or more and 0.50% or less.

By making the initial elongation 0.20% or more, it is possible to improve the impact resistance, which is the ability to prevent the steel cord from breaking when a force perpendicular to the longitudinal direction of the steel cord is applied.

In addition, by keeping the initial elongation at 0.50% or less, it is possible to prevent the wires from being pulled together by the tension applied during rubber molding and vulcanization, such as when manufacturing a cord-rubber composite, and to prevent the gaps between the wires from becoming smaller. This makes it possible to prevent a decrease in the degree of rubber penetration, such as when manufacturing a cord-rubber composite.

(7) In any of (1) to (6), the rubber penetration rate of the steel cord may be 60% or more.

By increasing the rubber penetration rate to 60% or more, the adhesion between the steel cord and the rubber can be improved when a cord-rubber composite is made, and the bending rigidity of the cord-rubber composite can be increased.

(8) A cord-rubber composite according to one embodiment of the present disclosure comprises a rubber,
and a steel cord according to any one of (1) to (7) embedded in the rubber.

The cord-rubber composite according to one aspect of the present disclosure can reduce the thickness and weight of the cord-rubber composite or a tire using the cord-rubber composite. Furthermore, the cord-rubber composite according to one aspect of the present disclosure can increase the durability of the cord-rubber composite or a tire using the cord-rubber composite.

(9) A tire according to one embodiment of the present disclosure includes a steel cord according to any one of (1) to (7).

In a tire according to one embodiment of the present disclosure, the thickness of the belt layer can be reduced, making the tire including the belt layer lighter, and reducing the rolling resistance of the tire.

Furthermore, a tire according to one aspect of the present disclosure can be made to have excellent durability.

[Details of the embodiment of the present disclosure]
Specific examples of a steel cord, a cord-rubber composite, and a tire according to one embodiment of the present disclosure (hereinafter referred to as the present embodiment) will be described below with reference to the drawings. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

In this specification, there are cases where the names of components or parts are described with '1st', '2nd', etc. added to them, such as 'first corrugated wire', 'second corrugated wire', 'first bent portion', 'second bent portion', 'first non-bent portion', 'second non-bent portion'. '1st', '2nd', etc. are written merely to distinguish between the components, etc., and to prevent confusion during description, and do not represent placement, priority, etc. For this reason, when there is no particular risk of confusion, they can simply be written as 'corrugated wire', 'bent portion', 'non-bent portion', etc.

Moreover, the drawings used in the description are schematic views for explaining configuration examples, such as the steel cord according to one embodiment of the present disclosure, the cord-rubber composite, and the arrangement of members included in the tire, and do not accurately show the length of each part, the length ratio, and the like.
[Steel cord]
Hereinafter, the steel cord according to the present embodiment will be described with reference to the drawings.

Fig. 1 is a perspective view of a steel cord 10 of this embodiment. Fig. 2 is a cross-sectional view of a plane perpendicular to the longitudinal direction of the steel cord 10 in a state in which the steel cord 10 of this embodiment is embedded in rubber 21 to form a cord-rubber composite 20. The Y axis in Figs. 1 and 2 is an axis along the longitudinal direction of the steel cord 10. The XZ plane in Figs. 1 and 2 is a plane perpendicular to the longitudinal direction of the steel cord 10.
(1) Structure of the steel cord The steel cord 10 of this embodiment is a stranded steel cord formed by stranding together four wires 11, that is, wires 11A, 11B, 11C, and 11D (see FIG. 2 ). The four wires 11 are twisted together in a spiral shape along the longitudinal direction of the steel cord 10, as shown in FIG.

The steel cord 10 of the present embodiment may have a 1×4 structure, which is a single-twist structure. A single-twist structure, such as a 1×N structure, means a structure in which N element wires 11 are twisted together to form a single layer (one layer). The single layer means a structure in which the element wires 11 are arranged in a row along the circumference of a circle in a cross section perpendicular to the longitudinal direction of the steel cord 10.
(2) Regarding the Wire (2-1) Regarding the Wire Diameter The wire diameter D (see FIG. 2) of the wire 11 of the steel cord 10 of the present embodiment can be set to 0.15 mm or more and 0.20 mm or less.

By setting the wire diameter D to 0.20 mm or less, the outer diameter of the steel cord 10 can be reduced. The thickness of the cord-rubber composite is selected so that the steel cord 10 contained therein can be embedded. Therefore, by reducing the outer diameter of the steel cord 10 in this embodiment, the thickness of the cord-rubber composite using the steel cord 10 can also be reduced, making it possible to reduce the weight of the cord-rubber composite and tires including the cord-rubber composite.

By setting the wire diameter D to 0.15 mm or more, it is possible to reduce the number of steel cords 10 required to achieve a desired bending rigidity in the cord-rubber composite including the steel cord 10 of this embodiment, and therefore it is possible to reduce the weight of the cord-rubber composite and the tire including the cord-rubber composite.
(2-2) Material of Wire The wire 11 of the steel cord 10 of this embodiment may be composed of only a wire rod 111, or may have a brass plating film 112 on its surface (see FIG. 2). Specifically, the wire 11 may have the wire rod 111 and the brass plating film 112 covering the wire rod 111.
(Wire rod)
The wire 111 may be, for example, a steel wire, and a high carbon steel wire may also be used.
(Brass plating film)
The brass plating film 112 may include copper (Cu) and zinc (Zn). As shown in FIG. 2, the brass plating film 112 may be disposed so as to cover the side surface of the wire 111.

When the steel cord 10 is embedded in the rubber 21 to form the cord-rubber composite 20, the copper contained in the brass plating film 112 reacts with the sulfur (S) contained in the rubber 21. Then, an adhesive layer containing copper sulfide (Cu ₂ S), which is a reaction product, is generated in the rubber 21 near the interface between the wire 11 and the rubber 21.

The adhesive layer thus produced can improve the initial adhesive performance between the steel cord 10 and the rubber 21. Initial adhesive performance refers to the adhesive performance between the steel cord 10 and the rubber 21 immediately after vulcanization during the manufacture of the cord-rubber composite or a tire that includes the cord-rubber composite.

The zinc contained in the brass plating film 112 is thought to promote and control the reaction that forms the adhesive layer.

The brass plating film 112 may contain elements other than copper and zinc. The brass plating film 112 may further contain one or more elements selected from cobalt (Co), nickel (Ni), tin (Sn), iron (Fe), and manganese (Mn).

The additive elements cobalt, nickel, tin, iron, and manganese have a greater tendency to ionize than copper. Therefore, when the brass plating film 112 contains an additive element in addition to copper and zinc, the brass plating film 112 functions as a sacrificial anticorrosion agent or can make the composite potential of copper and zinc more noble. Therefore, when the brass plating film 112 contains an additive element, the corrosion resistance of the steel cord 10 can be improved.
(2-3) Corrugated Wire Some or all of the wires 11 contained in the steel cord 10 of this embodiment may be corrugated wires 30 having bent portions 31 and non-bent portions 32 repeatedly along the length as shown in Fig. 3. By making some or all of the wires 11 corrugated, the penetration degree of rubber into the steel cord 10, the elongation characteristics of the steel cord 10, etc. can be adjusted and selected.

When the steel cord 10 of the present embodiment has a corrugated wire, the shape and size of the corrugation can be selected according to the characteristics to be adjusted by the corrugated wire, and are not particularly limited.
(First corrugated wire)
For example, in the steel cord 10 of the present embodiment, at least one of the wires 11 may be a first corrugated wire having first bent portions and first non-bent portions alternately along the longitudinal direction.

Using Figure 3, an example of the configuration of the first corrugated wire 300, which is the corrugated wire 30, will be described.

FIG. 3 shows the first corrugated wire 300 placed on a plane S such that the plane S is perpendicular to a plane passing through the first bent portion 31, which is the bent portion, and the first non-bent portion 32, which is the non-bent portion.

Here, the first bends, which are three consecutive bends 31 along the length of the first corrugated wire 300, are referred to as the first point, second point, and third point. For example, in FIG. 3, the first point is bend 31A, the second point is bend 31B, and the third point is bend 31C.

The shortest distance between the second point and a straight line LA passing through the end 30A of the first corrugated wire 300 that is closest to the second point among the first and third points is defined as the first corrugation height H1. The first corrugation height H1 can also be defined as the distance between the straight line LA and a straight line LB that is parallel to the straight line LA that passes through the end 30B of the first corrugated wire 300 that is closest to the first and third points among the second points.

When the first bends are on the same plane, as shown in FIG. 3, when the first corrugated wire 300 is placed on a plane S, the shortest distance between the first bends, which are the bends 31, along the vertical direction of the plane S can also be defined as the first corrugation height H1. That is, for example, the shortest length along the vertical direction of the plane S between the bend 31A, which is the first point, or the bend 31C, which is the third point, and the bend 31B, which is the second point, can also be defined as the first corrugation height H1. Therefore, in FIG. 3, the first corrugation height H1 is the distance along the vertical direction of the plane S between the opposing parts of the first corrugated wire 300 at the bends 31A and 31B, for example.

The first corrugated wire 300 can have a ratio D/H1, which is the ratio of the wire diameter D (see Figure 2) to the first corrugation height H1, of 1.029 or more and 1.818 or less.

By setting D/H1 to 1.818 or less, the distance between adjacent wires 11 in the steel cord 10 can be increased, and the degree of rubber penetration can be increased when the steel cord 10 is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be improved, and the bending rigidity of the cord-rubber composite can be increased.

By making D/H1 1.029 or more, it is possible to prevent the rubber penetration rate from becoming excessively high when the steel cord 10 is embedded in rubber to form a cord-rubber composite. Therefore, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be set in a particularly preferable range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.

As shown in FIG. 3, the distance between the first bend 31A, which is the first point, and the third bend 31C, which is the third point, of the first corrugated wire 300 is defined as the first corrugated pitch P1. Note that the distance between the first bends, which are adjacent bends 31 along the plane S when the first corrugated wire 300 is placed on the plane S, can also be defined as the first corrugated pitch P1. In other words, the distance between the first bends, which is the distance along the plane S, between the first bend 31A, which is the first point, and the third bend 31C, which is the distance between the first bends, can be defined as the first corrugated pitch P1.

In this case, P1/Psc, which is the ratio of the first corrugation pitch P1 of the first corrugated wire 300 to the twist pitch Psc of the steel cord, may be 0.09 or more and 0.35 or less, 0.10 or more and 0.34 or less, 0.11 or more and 0.33 or less, or 0.15 or more and 0.33 or less.

By setting P1/Psc to 0.35 or less, the distance between adjacent wires 11 in the steel cord 10 can be increased, and the rubber penetration can be increased when the steel cord 10 is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be improved, and the bending rigidity of the cord-rubber composite can be increased.

By making P1/Psc 0.09 or more, it is possible to prevent the rubber penetration degree from becoming excessively high when the steel cord 10 is embedded in rubber to form a cord-rubber composite. Therefore, when the cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be set within a particularly preferred range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.
(Second corrugated wire)
The steel cord 10 of the present embodiment may have, as the corrugated wires 30, in addition to the first corrugated wires 300, a second corrugated wire 310 having different corrugation conditions.

When the steel cord 10 of this embodiment includes the first corrugated wire 300 and the second corrugated wire 310, the number of each corrugated wire is not particularly limited, and the number of the first corrugated wires 300 and the number of the second corrugated wires 310 may be the same. The steel cord 10 of this embodiment may contain more first corrugated wires 300 than the number of the second corrugated wires 310. The steel cord 10 of this embodiment may contain more second corrugated wires 310 than the number of the first corrugated wires 300.

In other words, in the steel cord 10 of this embodiment, at least one of the four wires 11, excluding the first corrugated wire 300, can be a second corrugated wire 310 having second bent portions and second non-bent portions repeatedly along the length.

The second corrugated wire 310 can be configured in the same way as the first corrugated wire 300, except for the different corrugation conditions, so an example configuration will be explained using Figure 3.

In this case, FIG. 3 shows the second corrugated wire 310 placed on plane S such that plane S is perpendicular to a plane passing through the second bent portion, which is bent portion 31, and the second non-bent portion, which is non-bent portion 32.

Here, the second bends, which are three consecutive bends 31 along the length of the second corrugated wire 310, are designated as the fourth point, fifth point, and sixth point. For example, in FIG. 3, the fourth point is bend 31A, the fifth point is bend 31B, and the sixth point is bend 31C.

The shortest distance between the fifth point and the straight line LA passing through the end of the second corrugated wire 310 closest to the fifth point among the fourth and sixth points is defined as the second corrugation height H2. The second corrugation height H2 can also be defined as the distance between the straight line LA and the straight line LB parallel to the straight line LA passing through the end 30B of the second corrugated wire 310 closest to the fourth and sixth points among the fifth points.

When the second bends are on the same plane, as shown in FIG. 3, when the second corrugated wire 310 is placed on the plane S, the shortest distance along the vertical direction of the plane S between the first bends, which are the bends 31, can also be defined as the second corrugation height H2. That is, for example, the shortest length along the vertical direction of the plane S between the fourth point, bend 31A, or the sixth point, bend 31C, and the fifth point, bend 31B, can also be defined as the second corrugation height H2. Therefore, in FIG. 3, the second corrugation height H2 is the distance along the vertical direction of the plane S between the opposing portions of the second corrugated wire 310 at the bends 31A and 31B, for example.

The second corrugated wire 310 can have a ratio D/H2, which is the ratio of the wire diameter D (see Figure 2) to the second corrugation height H2, of 1.029 or more and 1.818 or less.

By setting D/H2 to 1.818 or less, the distance between adjacent wires 11 in the steel cord 10 can be increased, and the degree of rubber penetration can be increased when the steel cord 10 is embedded in rubber to form a cord-rubber composite. As a result, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be improved, and the bending rigidity of the cord-rubber composite can be increased.

By making D/H2 1.029 or more, it is possible to prevent the rubber penetration rate from becoming excessively high when the steel cord 10 is embedded in rubber to form a cord-rubber composite. Therefore, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber can be set in a particularly preferable range, and the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high. As a result, the durability of the cord-rubber composite can be particularly improved.

The distance between the bend 31A, which is the fourth point of the second corrugated wire 310, and the bend 31C, which is the sixth point, is defined as the second corrugation pitch P2. The distance between the second bends, which are adjacent bends 31 along the plane S of the second corrugated wire 310, can also be defined as the second corrugation pitch P2. In other words, the distance between the bend 31A, which is the fourth point, and the bend 31C, which is the sixth point, which is the distance between the second bends along the plane S, can be defined as the second corrugation pitch P2.

In this case, P2/Psc, which is the ratio of the second corrugation pitch P2 of the second corrugated wire 310 to the twist pitch Psc of the steel cord, may be, for example, 0.50 or more and 1.50 or less, 0.52 or more and 1.48 or less, or 0.53 or more and 1.47 or less.

By setting P2/Psc to 1.50 or less, the distance between adjacent wires 11 in the steel cord 10 can be increased, and the rubber penetration rate can be increased when the steel cord is embedded in rubber to form a cord-rubber composite. This allows the effective cross-sectional area to be increased. The effective cross-sectional area will be explained in "(3) Structure of steel cord embedded in rubber".

Furthermore, by making P2/Psc 0.50 or more, when the steel cord is embedded in rubber to form a cord-rubber composite, it is possible to prevent the distance between the wires constituting the steel cord 10 from becoming excessively large. This makes it possible to reduce the thickness of the rubber required to embed the steel cord in the cord-rubber composite and reduce the weight of the cord-rubber composite.
(3) Structure of Steel Cord Embedded in Rubber (3-1) Composite Region and Effective Cross-Sectional Area The inventors of the present invention have investigated a stranded steel cord that, when applied to a cord-rubber composite, can reduce the weight of the cord-rubber composite while increasing its durability.

In this specification, durability refers to the ability to prevent the cord-rubber composite from breaking when it is repeatedly bent, and can be evaluated based on the number of times the cord-rubber composite can be repeatedly bent before breaking.

As a result, they found that by controlling the bending stiffness within an appropriate range when embedded in rubber to form a cord-rubber composite, the cord-rubber composite can follow deformation and prevent breakage even when the cord-rubber composite is repeatedly bent. They also found that when a cord-rubber composite with bending stiffness controlled within an appropriate range is used in a tire, it is possible to achieve both durability and ride comfort. In other words, they found that by controlling the bending stiffness of the cord-rubber composite within an appropriate range, it is possible to increase the durability of the cord-rubber composite and also improve the ride comfort when used in a tire. This is thought to be because, by keeping the bending stiffness of the cord-rubber composite within a specified range, when the cord-rubber composite is repeatedly bent, the cord-rubber composite can deform appropriately to follow the force applied to bend the cord-rubber composite.

As shown in Figure 2, when the steel cord 10 is embedded in rubber 21 to form a cord-rubber composite 20, the rubber 21 penetrates into the gaps 12 between the wires 11, causing the gaps 12 between the wires 11 of the steel cord 10 to change compared to before embedding. According to studies by the inventors of the present invention, when the steel cord 10 is embedded in rubber 21, in a cross section perpendicular to the longitudinal direction, the area of the composite region 13 correlates with the bending rigidity of the cord-rubber composite 20. For this reason, it was found that the durability of the cord-rubber composite 20 can be increased by setting the effective cross-sectional area, which is the area of the composite region 13, within a predetermined range, and this led to the completion of the present invention.

The composite region 13 is defined as the region surrounded by the common tangent LO1, the common tangent LO2, the common tangent LO3, the common tangent LO4, the line segments LI1, LI2, LI3, and LI4 in a cross section perpendicular to the longitudinal direction of the steel cord 10 when the steel cord 10 is embedded in the rubber 21.

The common tangent LO1, the common tangent LO2, the common tangent LO3, and the common tangent LO4 are all common tangents between adjacent wires 11 that are in contact with the outer surface 100 of the steel cord 10. The outer surface 100 of the steel cord 10 refers to the surface exposed to the outside of the steel cord 10.

Specifically, tangent LO1 is a common tangent between wire 11A and wire 11B. Tangent LO2 is a common tangent between wire 11B and wire 11C. Tangent LO3 is a common tangent between wire 11C and wire 11D. Tangent LO4 is a common tangent between wire 11D and wire 11A.

As shown in FIG. 2, line segments LI1, LI2, LI3, and LI4 are all line segments that connect the centers of adjacent wires 11 along the outer surface 100 of the steel cord 10.

Specifically, line segment LI1 is a line segment connecting center OA of wire 11A and center OB of wire 11B. Line segment LI2 is a line segment connecting center OB of wire 11B and center OC of wire 11C. Line segment LI3 is a line segment connecting center OC of wire 11C and center OD of wire 11D. Line segment LI4 is a line segment connecting center OD of wire 11D and center OA of wire 11A.

The composite region 13 is the region in which the wires 11 of the steel cord 10 and the rubber 21 are arranged when the steel cord 10 is embedded in the rubber 21. For this reason, the composite region 13 is considered to be a region in which the steel cord 10 and the rubber are evaluated as being integrated, and the effective cross-sectional area, which is the area of the composite region 13, correlates with the bending rigidity of the cord-rubber composite 20.

The steel cord 10 of this embodiment can have an effective cross-sectional area of 0.099 ^mm2 or more and 0.224 ^mm2 or less. By setting the effective cross-sectional area to 0.099 ^mm2 or more and 0.224 ^mm2 or less, the bending rigidity of the cord-rubber composite can be set in an appropriate range, and durability can be improved. From the viewpoint of setting the bending rigidity of the cord-rubber composite in a particularly appropriate range and improving durability, the effective cross-sectional area may be 0.100 ^mm2 or more and 0.222 ^mm2 or less, 0.100 ^mm2 or more and 0.220 ^mm2 or less, or 0.100 ^mm2 or more and 0.210 ^mm2 or less.
(3-2) Area of Region Where Steel is Distributed In the steel cord of the present embodiment, when the steel cord 10 is embedded in rubber 21, the ratio of the area of the region where steel is distributed to the effective cross-sectional area in a cross section perpendicular to the longitudinal direction of the steel cord 10, i.e., the area ratio of the steel region, may be 30% or more and 128% or less.

The steel-distributed region 14 is the region where the wire 111 of the wire 11 is arranged. If the wire 11 does not have the brass plating film 112, the steel-distributed region 14 is the region where the wire 11 is arranged. Since the brass plating film 112 is usually very thin, the steel-distributed region 14 may be the region where the wire 11 is arranged even if the wire 11 has the brass plating film 112.

Therefore, the area ratio of the steel region (steel distribution area ratio) can also be said to be the ratio of the cross-sectional area of the wire 111 or the cross-sectional area of the strand 11 to the effective cross-sectional area, which is the area of the composite region 13.

By making the area ratio of the steel region 30% or more, the bending rigidity of the cord-rubber composite can be increased when it is made into a cord-rubber composite. Also, by making the area ratio of the steel region 128% or less, the bending rigidity of the cord-rubber composite can be prevented from becoming excessively high when it is made into a cord-rubber composite. As a result, the durability of the cord-rubber composite can be particularly increased.

From the viewpoint of particularly increasing the durability of the cord-rubber composite, the area ratio of the steel region may be 33% or more and 126% or less.
(4) Characteristics of Steel Cord (4-1) Initial Elongation The steel cord 10 of the present embodiment may have an initial elongation of 0.20% or more and 0.50% or less.

By making the initial elongation 0.20% or more, the impact resistance, which is the ability to prevent the steel cord 10 from breaking when a force perpendicular to the longitudinal direction of the steel cord 10 is applied, can be improved.

In addition, by setting the initial elongation to 0.50% or less, it is possible to prevent the wires 11 from being pulled together by the tension applied during molding and vulcanization of the rubber, such as when manufacturing a cord-rubber composite, and to prevent the gaps 12 between the wires 11 from becoming smaller. This makes it possible to prevent a decrease in the degree of rubber penetration, such as when manufacturing a cord-rubber composite.

The initial elongation of the steel cord of the present embodiment may be 0.21% or more and 0.49% or less, from the viewpoint of further increasing the impact resistance performance and the rubber penetration rate.
(4-2) Rubber Penetration Degree The steel cord of the present embodiment may have a rubber penetration degree of 60% or more.

By increasing the rubber penetration rate to 60% or more, the adhesion between the steel cord and the rubber can be improved when a cord-rubber composite is made, and the bending rigidity of the cord-rubber composite can be increased.

The rubber penetration rate of the steel cord of this embodiment may be 60% or more and 100% or less, or 65% or more and 95% or less, from the viewpoint of setting the bending rigidity of the cord-rubber composite in a particularly optimal range when applied to the cord-rubber composite.

The initial elongation and rubber penetration can be adjusted by selecting the number of corrugated wires in the steel cord 10, the corrugation height H of the corrugated wires 30, the corrugation pitch P, the twist pitch of the steel cord 10, etc.

[Cord-rubber composite]
FIG. 4 shows a cross-sectional view of a cord-rubber composite 40 of this embodiment taken along a plane perpendicular to the longitudinal direction of the steel cord 10.

As shown in FIG. 4, the cord-rubber composite 40 of this embodiment can have rubber 41 and the steel cord 10 of this embodiment embedded in the rubber 41.

The thickness of the cord-rubber composite 40 can be selected so that the steel cord 10 can be embedded in the rubber 41. Specifically, the rubber thickness t1 to be placed under the steel cord 10 and the rubber thickness t2 to be placed on the top of the steel cord 10 can be selected.

The outer diameter of the steel cord 10 can be reduced by setting the wire diameter D (see FIG. 1) of the wires 11 within a predetermined range. Reducing the outer diameter of the steel cord 10 also reduces the thickness of the cord-rubber composite 40. As a result, by using the steel cord 10 according to one aspect of the present disclosure, the amount of rubber contained in the cord-rubber composite 40 of this embodiment can be reduced, making it possible to reduce the weight. Furthermore, the tire including the cord-rubber composite 40 of this embodiment can also be reduced in weight.

Furthermore, the cord-rubber composite 40 including the steel cord 10 according to one embodiment of the present disclosure can achieve bending rigidity within an appropriate range, thereby improving durability.

Hereinafter, the components contained in the cord-rubber composite body of the present embodiment will be described.
(1) Components Contained in the Cord-Rubber Composite (1-1) Steel Cord The cord-rubber composite 40 can contain a plurality of steel cords 10. The steel cords 10 contained in the cord-rubber composite 40 can be arranged such that the longitudinal direction of each steel cord 10 is aligned along the Y axis in Fig. 4. The plurality of steel cords 10 can be arranged along the width of the cord-rubber composite 40, i.e., along the X axis in Fig. 4.

Multiple steel cords 10 may be arranged in parallel with each other.

The details of the steel cord 10 have already been described, and therefore will not be described again.
(1-2) Rubber The rubber 41 of the cord-rubber composite 40 can be produced by molding a rubber composition and vulcanizing it as necessary.

The specific composition of the rubber is not particularly limited and can be selected according to the application of various products, such as tires, to which the cord-rubber composite 40 is applied, and the required characteristics. The rubber can contain, for example, a rubber component, sulfur, and a vulcanization accelerator.

The rubber component may contain at least one type selected from, for example, natural rubber (NR) and isoprene rubber (IR) in an amount of 60% by mass or more, 70% by mass or more, or even 100% by mass.

This is because by making the proportion of one or more types of rubber selected from natural rubber and isoprene rubber in the rubber component 60 mass % or more, the breaking strength of the cord-rubber composite 40 and the tire can be increased.

The rubber components used in combination with natural rubber or isoprene rubber may be, for example, one or more selected from styrene-butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), butyl rubber (IIR), and acrylonitrile-butadiene rubber (NBR).

There are no particular limitations on the type of sulfur used, but for example, sulfur commonly used as a vulcanizing agent in the rubber industry can be used.

The amount of sulfur in the rubber is not particularly limited, but may be, for example, 5 parts by mass or more and 8 parts by mass or less per 100 parts by mass of the rubber component.

This is because by setting the ratio of sulfur to 5 parts by mass or more per 100 parts by mass of the rubber component, the crosslink density of the resulting rubber can be increased, and in particular the adhesive strength between the steel cord and the rubber can be increased. Also, by setting the ratio of sulfur to 8 parts by mass or less per 100 parts by mass of the rubber component, the sulfur can be dispersed particularly uniformly within the rubber, and blooming can be prevented from occurring.

The vulcanization accelerator is not particularly limited, but may be, for example, a sulfenamide accelerator such as N,N'-dicyclohexyl-2-benzothiazolylsulfenamide, N-cyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide, or N-oxydiethylene-2-benzothiazolylsulfenamide. If desired, a thiazole accelerator such as 2-mercaptobenzothiazole or di-2-benzothiazolyl disulfide, or a thiuram accelerator such as tetrabenzylthiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, or tetramethylthiuram monosulfide may be used.

The rubber composition used in the cord-rubber composite 40 of this embodiment can be produced by kneading raw materials such as rubber components, heating them, and extruding them.

The rubber of the cord-rubber composite 40 of this embodiment may contain one or more types selected from simple cobalt and compounds containing cobalt.

Compounds containing cobalt include organic cobalt acids and inorganic cobalt acids.

As the organic cobalt acid salt, for example, one or more selected from cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, cobalt tall oil acid, etc. can be used. The organic cobalt acid salt may be a composite salt in which part of the organic acid is replaced with boric acid.

The inorganic cobalt acid may be, for example, one or more selected from cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt phosphate, and cobalt chromate.

The rubber may also contain any optional components other than the above rubber components, sulfur, vulcanization accelerator, cobalt, etc. The rubber may also contain well-known rubber additives such as reinforcing agents (carbon black, silica, etc.), wax, and antioxidants.
(2) Ends of Cord-Rubber Composite The number of steel cords 10 in the cord-rubber composite 40 of this embodiment is not particularly limited, and can be selected depending on the properties required for the cord-rubber composite 40 and a tire including the cord-rubber composite 40. Here, ends refers to the number of steel cords 10 arranged per 50 mm width of the cord-rubber composite 40 in a cross section perpendicular to the longitudinal direction of the steel cords 10 of the cord-rubber composite 40. For this reason, in this specification, the unit of ends is "pieces/50 mm".

The cord-rubber composite 40 of this embodiment may include steel cords 10 so that the ends are, for example, 30 cords/50 mm or more and 60 cords/50 mm or less. The ends of the cord-rubber composite 40 may be 36 cords/50 mm or more and 60 cords/50 mm or less, or 40 cords/50 mm or more and 60 cords/50 mm or less.

By making the ends of the cord-rubber composite 40 30 pieces/50 mm or more, the gaps between the steel cords 10 contained in the cord-rubber composite 40 can be reduced, allowing the steel cords to be arranged at a high density. This improves punching resistance, a property that prevents foreign objects from penetrating the cord-rubber composite 40. In addition, the bending rigidity of the cord-rubber composite 40 can be easily controlled within a desired range.

By setting the ends of the cord-rubber composite 40 to 60 pieces/50 mm or less, the number of supply devices that supply steel cords during the production of the cord-rubber composite 40 can be reduced, thereby increasing productivity.

The cord-rubber composite 40 of this embodiment uses the steel cord 10 according to one aspect of the present disclosure. This allows the thickness of the cord-rubber composite 40 to be reduced, making it possible to reduce the weight of the cord-rubber composite or a tire using the cord-rubber composite. Furthermore, the cord-rubber composite 40 of this embodiment allows the durability of the cord-rubber composite 40 or a tire using the cord-rubber composite 40 to be improved.

[tire]
Next, the tire according to this embodiment will be described with reference to FIG.

The tire of this embodiment may include a steel cord 10 according to one aspect of the present disclosure.

FIG. 5 shows a cross-sectional view of a tire 50 according to this embodiment taken along a plane perpendicular to the circumferential direction. Although FIG. 5 shows only the portion to the left of the center line (CL), the same structure continues to the right of the center line (CL) with the CL as an axis of symmetry.

As shown in FIG. 5, the tire 50 has a tread portion 51, a sidewall portion 52, and a bead portion 53.

The tread portion 51 is the portion that comes into contact with the road surface. The bead portion 53 is located closer to the inner diameter of the tire 50 than the tread portion 51. The bead portion 53 is the portion that comes into contact with the rim of the vehicle's wheel. The sidewall portion 52 connects the tread portion 51 and the bead portion 53. When the tread portion 51 receives an impact from the road surface, the sidewall portion 52 elastically deforms and absorbs the impact.

The tire 50 includes an inner liner 54, a carcass 55, a belt layer 56, and a bead wire 57.

The inner liner 54 is made of rubber and seals the space between the tire 50 and the wheel.

The carcass 55 forms the framework of the tire 50. The carcass 55 is made of organic fibers such as polyester, nylon, or rayon, or steel cords, and rubber.

The bead wire 57 is provided in the bead portion 53. The bead wire 57 receives the tensile force acting on the carcass 55.

The belt layer 56 tightens the carcass 55 to increase the rigidity of the tread portion 51. In the example shown in FIG. 5, the tire 50 has two belt layers 56. The cord-rubber composite 40 according to one embodiment of the present disclosure can be used as the belt layer 56. The cord-rubber composite 40 has already been described, so a description thereof will be omitted.

In this manner, in the tire of this embodiment, the belt layer 56 uses a cord-rubber composite 40 that includes a steel cord 10 according to one aspect of the present disclosure.

As a result, with the tire 50 of this embodiment, the thickness of the belt layer 56 can be reduced, making the tire 50 including the belt layer 56 lighter, and reducing the rolling resistance of the tire.

Furthermore, the tire 50 of this embodiment can be made to have excellent durability.

Although the embodiments have been described in detail above, the invention is not limited to specific embodiments, and various modifications and variations are possible within the scope of the claims.

The present invention will be described below with reference to specific examples, but is not limited to these examples.
(Evaluation Method)
First, the evaluation methods for the steel cords and cord-rubber composites produced in the following experimental examples will be described.
(1) Wire Diameter The wire diameter D is measured in accordance with JIS G 3510 (1992).
(2) Twist pitch The twist pitch Psc of the steel cord produced in each experimental example is measured by the tracing method of JIS G 3510 (1992). Specifically, a traceable thin paper is placed on the outer surface of the produced steel cord, and the paper is rubbed with a pencil to copy the twist traces of the four wires 11. Then, from the obtained twist traces of the wires 11, the length of five pitches is measured with a ruler, and the value obtained by dividing by 5 is taken as the twist pitch Psc.
(3) Effective Cross-Sectional Area A cross section of the cord-rubber composite produced in each experimental example was photographed, and the effective cross-sectional area was measured using the obtained image.
(4) Area of steel region, area ratio of steel region The cross-sectional area of the wire is calculated from the wire diameter D, and multiplied by 4 to calculate the area of the wire part of the steel cord, that is, the area of the steel region, which is the area of the region where steel is distributed. Each wire has a brass plating film 112, but because the thickness of the brass plating film 112 is very thin, the cross-sectional area of the wire is used as the area of the region where steel is distributed. Also, as shown in the following formula (A), the area ratio of the steel region is calculated from the area of the steel region and the effective cross-sectional area.
(Area ratio of steel region) = (Area of steel region) ÷ (Effective cross-sectional area) × 100 (A)
(5) Flexural Rigidity As shown in FIG. 6, the flexural rigidity of the cord-rubber composite is evaluated by a three-point bending test.

For the bending stiffness test, the cord-rubber composite prepared in each experimental example was cut into a 30 mm x 50 mm test piece. The long side of the test piece, which is 50 mm long, was the side that ran along the length of the steel cord contained in the test piece.

Specifically, the first end 601 and the second end 602, which are the ends of the width of the test piece 60, are supported from the underside by support jigs 611 and 612. Next, the midpoint between support jigs 611 and 612 is pressed downward by pressing jig 613, as shown by block arrow 62.

For this reason, distance L601 and distance L602 in FIG. 6 are equal. Distance L601 refers to the distance between the point where test body 60 contacts support jig 611 and the point where test body 60 contacts pressing jig 613. Distance L602 refers to the distance between the point where test body 60 contacts support jig 612 and the point where test body 60 contacts pressing jig 613.

Then, the bending rigidity is calculated by measuring the reaction force when the point pressed by the pressing tool 613 is displaced 1 mm along the block arrow 62.

The test specimen 60 is arranged so that the longitudinal direction of the steel cord contained within the test specimen 60 is aligned with the Y axis in FIG. 6, that is, along the arrangement of the support jig 611, the pressing jig 613, and the support jig 612. The distance between the support jig 611 and the support jig 612 is 30 mm.

The test specimen 60 is arranged so that its long side, which is 50 mm long, is aligned with the arrangement of the support jigs 611 and 612, i.e., the Y-axis in FIG. 6, and its short side, which is 30 mm long, is aligned with the X-axis perpendicular to the paper surface in FIG.
(6) Rubber Penetration Degree From the cord-rubber composite produced in each experimental example, the steel cord was removed with a cutter knife.

Then, remove two adjacent wires from the steel cord that was removed. The ratio of the length of the rubber-covered portion to the 100 mm observation length along the center line of the exposed area that was left by removing the two adjacent wires is calculated as a percentage, and this is the rubber penetration rate. The center line is a line drawn along the length of the exposed area, passing through the center of the width perpendicular to the length of the exposed area.

The higher the rubber penetration value, the better the rubber penetration, and a rubber penetration value of 60% or more means that the material has sufficient performance for practical use.

(7) Initial Elongation The initial elongation is the percentage elongation when a load of 50 N is applied to a steel cord, and is evaluated using a tensile tester.

First, the first distance L0, which is the distance between the chucks of the tensile testing machine, is set to 500 mm, and the steel cord manufactured in each experimental example is placed in the chuck. Next, a load is applied to the steel cord to change the distance between the chucks, and the distance between the chucks when the load applied to the steel cord reaches 50 N is set as the second distance L1.

In this case, the initial elongation of the steel cord is calculated using the following formula (B).

(Initial elongation (%))=[(L1-L0)÷L0]×100...(B)
(8) Durability Evaluation First, from the cord-rubber composites produced in each experimental example, a test specimen in the form of a cord having a width of 10 mm was cut in a cross section perpendicular to the longitudinal direction of the steel cord contained in the cord-rubber composite. The width is the length along the X-axis in FIG.

As shown in FIG. 7, the obtained test specimen 70 is placed on a first roller 71, a second roller 72, and a third roller 73, each having a roller diameter of 25 mm. When the test specimen 70 is placed on the first roller 71, the second roller 72, and the third roller 73, the first roller 71, the second roller 72, and the third roller 73 are arranged along the longitudinal direction of the steel cord included in the test specimen 70. When the test specimen 70 is placed on the three rollers, the position of each roller is adjusted so that the test specimen 70 located between the first roller 71 and the second roller 72 and the test specimen 70 located between the second roller 72 and the third roller 73 are parallel to each other, as shown in FIG. 7. In addition, a load of 29.4 N is applied along the longitudinal direction to the test specimen 70 placed on the first roller 71, the second roller 72, and the third roller 73. Then, the first roller 71, the second roller 72, and the third roller 73 are rotated to move the test specimen 70 in the direction indicated by the arrow 74 in FIG. 7. Next, the first roller 71, the second roller 72, and the third roller 73 are rotated in the reverse direction to move the test specimen 70 in the opposite direction to the arrow 74 in the figure. The above operations constitute one set, and this set of operations is repeated. The rotation speed of each roller is set so that the above reciprocating movement can be performed 100 times per minute. Then, the number of sets of the above reciprocating movement of the test specimen until the test specimen 70 breaks is counted.

The evaluation result for the cord-rubber composite of Experimental Example 11 is set as the standard, i.e., 100, and the evaluation results measured for the cord-rubber composites of each Experimental Example are normalized and used as the durability index value.

If the durability index value is 110 or more, it is rated as A; if the durability index value is greater than 100 but less than 110, it is rated as B; and if the durability index value is 100 or less, it is rated as C.

When the rating is A, the cord-rubber composite is said to have particularly excellent durability, and the ratings decrease in the order of B and C. When the rating is A or B, the cord-rubber composite has high durability.
(9) Evaluation of Light Weight The cord-rubber composite produced in each experimental example was cut into a 100 mm square and the weight was measured. The size here is the size as seen from the top surface 400 of the cord-rubber composite 40 shown in FIG. 4.

Then, the evaluation result of the cord-rubber composite in Experimental Example 11 is set as the standard, i.e., 100, and the weight measured in each experimental example is normalized and used as the index value for lightness.

If the lightness index value is less than 90, it is rated as A; if the lightness index value is between 90 and 100, it is rated as B; and if the lightness index value is 100 or more, it is rated as C.

When the evaluation is A, it can be said that the weight of the cord-rubber composite has been particularly reduced and the weight has been reduced, and the evaluation decreases in the order of B and C. When the evaluation is A or B, it can be said that the weight of the cord-rubber composite has been particularly reduced and the weight has been reduced.
(Experimental Example)
The experimental conditions are described below. Experimental Examples 1 to 9 are examples, and Experimental Examples 10 to 13 are comparative examples.
[Experimental Example 1]
(Steel cord)
In this experimental example, a steel cord having the structure shown in Figs. 1 and 2 was manufactured.

As the wires 11, one first corrugated wire and three second corrugated wires corrugated as shown in Table 1 are prepared. All four wires have the same wire diameter D, which is the value shown in Table 1. Furthermore, all four wires 11 have a brass plating film 112 containing copper and zinc disposed on the surface of the wire material 111, which is a steel wire. The four wires are then twisted together to produce a stranded steel cord having a 1 x 4 structure.

The evaluation results of the obtained steel cord are shown in Table 1.
(Cord-rubber composite)
The steel cord of this experimental example is embedded in rubber so that the ends are 46 cords/50 mm, and a cord-rubber composite 40 having the structure shown in FIG. 4 is produced.

The rubber is manufactured using a rubber composition containing a rubber component and additives. The rubber composition contains 100 parts by mass of natural rubber as the rubber component. The rubber composition also contains, as additives, 60 parts by mass of carbon black, 7 parts by mass of sulfur, 0.5 parts by mass of vulcanization accelerator, 8 parts by mass of zinc oxide, and 2 parts by mass of cobalt stearate as an organic cobalt acid per 100 parts by mass of the rubber component.

The cord-rubber composite was prototyped in advance using the steel cord of this experimental example, and the thickness of the rubber was selected to allow for the variation in the position of the steel cord so that the steel cord 10 could be embedded.

The evaluation results for the cord-rubber composite are shown in Table 1.
[Experimental Examples 2 to 13]
The wire diameters and corrugation conditions of the first corrugated wire and the second corrugated wire prepared were changed to the values shown in Tables 1 and 2. In addition, the twist pitch when twisting the four wires was changed.

Other than the above, steel cords and cord-rubber composites were manufactured and evaluated using the same procedures and conditions as in Experimental Example 1.

The evaluation results are shown in Tables 1 and 2.

　表１、表２によると、素線径が０．１５ｍｍ以上０．２０ｍｍ以下、かつ有効断面積が０．０９９ｍｍ^２以上０．２２４ｍｍ^２以下である、実験例１から実験例９のスチールコードについて、耐久性評価、軽量性評価が共にＡまたはＢになることを確認できる。すなわち、実験例１から実験例９のスチールコードは、コード－ゴム複合体に適用した場合に、コード－ゴム複合体を軽量化しつつ、耐久性を高めることができる、撚線のスチールコードであることを確認できる。

According to Tables 1 and 2, it can be confirmed that the steel cords of Experimental Examples 1 to 9, which have a wire diameter of 0.15 mm or more and 0.20 mm or less and an effective cross-sectional area of 0.099 ^mm2 or more and 0.224 ^mm2 or less, are evaluated as A or B in terms of durability and light weight. In other words, it can be confirmed that the steel cords of Experimental Examples 1 to 9 are stranded steel cords that, when applied to a cord-rubber composite, can reduce the weight of the cord-rubber composite while increasing its durability.

10 Steel cord 100 Outer surface 11 Wire 11A Wire 11B Wire 11C Wire 11D Wire OA Center OB Center OC Center OD Center LO1 Common tangent LO2 Common tangent LO3 Common tangent LO4 Common tangent LI1 Line segment LI2 Line segment LI3 Line segment LI4 Line segment 111 Wire 112 Brass plating film 12 Gap 13 Composite region 14 Steel-distributed region D Wire diameter 20 Cord-rubber composite 21 Rubber X X-axis Y Y-axis Z Z-axis 30 Corrugated wire 300 First corrugated wire 310 Second corrugated wire 30A End 31 Bend 31A Bend (first point, fourth point)
31B Bent part (2nd point, 5th point)
31C Bend part (3rd point, 6th point)
LA Straight line 32 Non-bent portion H Corrugation height H1 First corrugation height H2 Second corrugation height P Corrugation pitch P1 First corrugation pitch P2 Second corrugation pitch S Flat surface 40 Cord-rubber composite 400 Upper surface 41 Rubber t1 Rubber thickness t2 Rubber thickness 50 Tire 51 Tread portion 52 Sidewall portion 53 Bead portion 54 Inner liner 55 Carcass 56 Belt layer 57 Bead wire CL Center line 60 Test piece 601 First end portion 602 Second end portion 611 Support jig 612 Support jig 613 Pressing jig 62 Block arrow L 601 Distance L 602 Distance 70 Test piece 71 First roller 72 Second roller 73 Third roller 74 Arrow

Claims (9)

A steel cord having a 1×4 structure in which four wires are twisted together,
The wire has a diameter of 0.15 mm or more and 0.20 mm or less,
When embedded in rubber, in a cross section perpendicular to the longitudinal direction of the steel cord,
When a region surrounded by a common tangent line between adjacent wires that is in contact with the outer surface of the steel cord and a line segment that connects centers of adjacent wires along the outer surface of the steel cord is defined as a composite region, and an area of the composite region is defined as an effective cross-sectional area,
The effective cross-sectional area of the steel cord is 0.099 ^mm2 or more and 0.224 ^mm2 or less. The steel cord according to claim 1, wherein the ratio of the area of the region in which steel is distributed to the effective cross-sectional area in the cross section is 30% or more and 128% or less. At least one of the wires is a first corrugated wire having a first bent portion and a first non-bent portion repeatedly along a longitudinal direction thereof,
The three first bent portions successive along the length of the first corrugated wire are defined as a first point, a second point, and a third point,
When the shortest distance between a straight line passing through an end of the first corrugated wire that is closest to the second point among the first point and the third point and the second point is defined as a first corrugation height,
3. The steel cord according to claim 1, wherein a ratio of the wire diameter to the first corrugation height is 1.029 or greater and 1.818 or less. When the distance between the first point and the third point of the first corrugated wire is defined as a first corrugation pitch,
4. The steel cord according to claim 3, wherein a ratio of the first corrugation pitch of the first corrugated wire to a twist pitch of the steel cord is 0.09 or more and 0.35 or less. Among the four wires, at least one of the wires excluding the first corrugated wire is a second corrugated wire having second bent portions and second non-bent portions repeatedly along a longitudinal direction thereof,
The three second bent portions successive along the length of the second corrugated wire are a fourth point, a fifth point, and a sixth point,
When the shortest distance between the fifth point and a straight line passing through an end of the second corrugated wire that is closest to the fifth point among the fourth point and the sixth point is defined as a second corrugation height, and the distance between the fourth point and the sixth point of the second corrugated wire is defined as a second corrugation pitch,
The second corrugated wire has a ratio of the wire diameter to the second corrugation height of 1.029 or more and 1.818 or less,
5. The steel cord according to claim 3, wherein a ratio of the second corrugation pitch of the second corrugated wire to a twist pitch of the steel cord is 0.50 or more and 1.50 or less. A steel cord according to any one of claims 1 to 5, having an initial elongation of 0.20% or more and 0.50% or less. A steel cord according to any one of claims 1 to 6, having a rubber penetration rate of 60% or more. Rubber and
A cord-rubber composite comprising: the steel cord according to any one of claims 1 to 7 embedded in the rubber. A tire comprising the steel cord according to any one of claims 1 to 7.

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