Steel cord, cord-rubber composite, tires

Abstract

A steel cord having a 1×4 structure in which four wires are twisted together, The wire diameter is 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 0.099 mm 2 More than 0.224mm 2 The steel code is as follows:

Description

[Technical field]

[0001] The present disclosure relates to steel cords, cord-rubber composites, and tires.

[0002] 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. [Background technology]

[0003] Patent Document 1 discloses a steel cord for tire reinforcement, which is formed by twisting together 2 to 13 steel wires having a wire diameter of 0.23 to 0.50 mm, and is characterized in that the cord has an elongation rate of 1.5 to 3.0% when a tensile load of 10% of the breaking load is applied, and the value A shown in the following formula is 50 to 100 N / %.

[0004] (Formula) A={(L 50 -L 10 ) / n} / (E 50 -E 10 ) Here, L 50 : 50% of breaking load (N) L 10 : 10% of breaking load (N) E 50 : Cord elongation rate (%) when loaded with 50% of the breaking load E 10 : Cord elongation rate (%) when 10% of the breaking load is applied n: Number of steel wires (pieces) [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-275772 A Summary of the Invention

[0006] 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 diameter is 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 0.099 mm 2 More than 0.224mm 2 The following is the result. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view of a steel cord according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view taken along 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. [Diagram 3] FIG. 3 is an explanatory diagram of a corrugated wire. [Figure 4] FIG. 4 is a cross-sectional view of a cord-rubber composite according to one embodiment of the present disclosure. [Diagram 5] FIG. 5 is a cross-sectional view of a tire according to one embodiment of the present disclosure. [Figure 6] FIG. 6 is an explanatory diagram of a method for evaluating bending rigidity. [Figure 7] FIG. 7 is an explanatory diagram of a method for evaluating durability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Problem that this disclosure aims to solve]

[0009] Conventionally, a sheet-shaped cord-rubber composite, in which a plurality of steel cords are aligned and embedded in rubber, has been used as a reinforcing material for tires.

[0010] In order to reduce the rolling resistance of tires, there is a demand for reducing the weight of the cord-rubber composite.

[0011] The thickness of the rubber in the cord-rubber composite is selected so that the steel cord can be embedded. Therefore, one possible method for reducing the weight of the cord-rubber composite 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 of the wires is reduced, the cord-rubber composite may be more susceptible to breakage when repeatedly bent, which may reduce durability.

[0012] Therefore, an object of the present disclosure is 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.

[0013] [Effects of this disclosure]

[0014] According to the present disclosure, it is possible 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.

[0015] [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.

[0016] (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 diameter is 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 0.099 mm 2 More than 0.224mm 2 The following is the result.

[0017] 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 a tire including the cord-rubber composite can be made lighter.

[0018] By setting the wire diameter to 0.15 mm or more, the number of steel cords required to achieve a desired bending rigidity in a cord-rubber composite including the steel cord according to one embodiment of the present disclosure can be reduced, thereby reducing the weight of the cord-rubber composite and tires including the cord-rubber composite.

[0019] Effective area is 0.099 mm 2 More than 0.224mm 2 By making the thickness of the cord-rubber composite body to be within the range below, the bending rigidity of the cord-rubber composite can be kept within an appropriate range, and durability can be improved.

[0020] (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.

[0021] 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 formed. Also, 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 formed. As a result, the durability of the cord-rubber composite can be particularly increased.

[0022] (3) In the configuration (1) or (2), at least one of the wires is a first corrugated wire having first bent portions and first non-bent portions repeatedly along a longitudinal direction, The three first bent portions successive along the length of the first corrugated wire are designated 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.

[0023] By setting D / H1, which is 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 the 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.

[0024] By making D / H1 1.029 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. Therefore, when a cord-rubber composite is formed, the adhesion between the steel cord 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.

[0025] (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.

[0026] 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 penetration of rubber is increased when the steel cord is embedded in rubber to form a cord-rubber composite. As a result, when the cord-rubber composite is formed, the adhesion between the steel cord and rubber is increased, and the bending rigidity of the cord-rubber composite is particularly increased.

[0027] By setting the ratio of the first corrugated 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. Therefore, when the cord-rubber composite is formed, the adhesion between the steel cord 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.

[0028] (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 designated as a fourth point, a fifth point, and a sixth point, When the shortest distance between the straight line passing through the end of the second corrugated wire closest to the fifth point among the fourth point and the sixth point and the fifth 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 the twist pitch of the steel cord may be 0.50 or more and 1.50 or less.

[0029] 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 the 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.

[0030] By making D / H2 1.029 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. Therefore, when a cord-rubber composite is formed, the adhesion between the steel cord 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.

[0031] By setting the ratio of the second corrugated 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, thereby increasing the effective cross-sectional area.

[0032] Furthermore, by making P2 / Psc 0.50 or more, it is possible to prevent the distance between the wires constituting the steel cord from becoming excessively large when the steel cord is embedded in rubber to form a cord-rubber composite, which 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.

[0033] (6) In any one of (1) to (5), the initial elongation may be 0.20% or more and 0.50% or less.

[0034] By setting the initial elongation to be 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 to the steel cord.

[0035] Furthermore, by setting the initial elongation to 0.50% or less, it is possible to prevent the wires from being pulled together by the tension applied during molding and vulcanization of the rubber when producing a cord-rubber composite, and thus to prevent the gaps between the wires from becoming smaller, thereby preventing a decrease in the degree of rubber penetration when producing a cord-rubber composite, etc.

[0036] (7) In any one of (1) to (6), the rubber penetration rate into the steel cord may be 60% or more.

[0037] By making the rubber penetration rate 60% or more, when a cord-rubber composite is formed, the adhesion between the steel cord and the rubber can be increased, and the bending rigidity of the cord-rubber composite can be increased.

[0038] (8) A cord-rubber composite according to one embodiment of the present disclosure comprises: rubber; and a steel cord according to any one of (1) to (7) embedded in the rubber.

[0039] The cord-rubber composite according to one embodiment of the present disclosure can reduce the thickness and thus the weight of the cord-rubber composite or a tire using the cord-rubber composite. Furthermore, the cord-rubber composite according to one embodiment of the present disclosure can improve the durability of the cord-rubber composite or a tire using the cord-rubber composite.

[0040] (9) A tire according to one embodiment of the present disclosure includes the steel cord according to any one of (1) to (7).

[0041] According to the tire according to one aspect of the present disclosure, the thickness of the belt layer can be reduced, making it possible to reduce the weight of the tire including the belt layer, and thus reducing the rolling resistance of the tire.

[0042] Furthermore, according to a tire according to one aspect of the present disclosure, it is possible to provide a tire with excellent durability.

[0043] [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.

[0044] In this specification, there are cases where the names of members or parts are described with 1st, 2nd, etc. added to them, such as the first corrugated wire, the second corrugated wire, the first bent portion, the second bent portion, the first non-bent portion, and the second non-bent portion. The names 1st, 2nd, etc. are written merely to distinguish each member, 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 be simply written as the corrugated wire, the bent portion, and the non-bent portion.

[0045] 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 body, 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.

[0046] 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 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.

[0047] The steel cord 10 of the present embodiment can 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, in a cross section perpendicular to the longitudinal direction of the steel cord 10, the element wires 11 are arranged in a single row along the circumference of a circle. (2) About the wire (2-1) Wire diameter The wire diameter D (see FIG. 2) of the wires 11 of the steel cord 10 of this embodiment can be set to 0.15 mm or more and 0.20 mm or less.

[0048] 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 of this embodiment, the thickness of the cord-rubber composite using the steel cord 10 can also be reduced, and the cord-rubber composite and the tire including the cord-rubber composite can be made lighter.

[0049] 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) Wire material The wire 11 of the steel cord 10 of this embodiment may be composed of only a wire material 111, or may have a brass plating film 112 on its surface (see FIG. 2). Specifically, the wire 11 may have a wire material 111 and a brass plating film 112 covering the wire material 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 contain 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.

[0050] 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 (CuS), which is a reaction product, is formed in the rubber 21 near the interface between the wire 11 and the rubber 21.

[0051] The produced adhesive layer can improve the initial adhesive performance between the steel cord 10 and the rubber 21. The initial adhesive performance means the adhesive performance between the steel cord 10 and the rubber 21 immediately after vulcanization during the production of the cord-rubber composite or a tire including the cord-rubber composite.

[0052] It is believed that the zinc contained in the brass plating film 112 promotes and controls the reaction that forms the adhesive layer.

[0053] The brass plating film 112 may contain elements other than copper and zinc. The brass plating film 112 may further contain one or more selected from the group consisting of cobalt (Co), nickel (Ni), tin (Sn), iron (Fe), and manganese (Mn).

[0054] 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 the composite potential of copper and zinc can be made 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) About 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.

[0055] When the steel cord 10 of the present embodiment has corrugated wires, the shape and size of the corrugations can be selected according to the properties to be adjusted by the corrugated wires, and are not particularly limited. (First corrugated wire) For example, in the steel cord 10 of the present embodiment, at least one wire 11 may be a first corrugated wire having first bent portions and first unbent portions alternately along the longitudinal direction.

[0056] An example of the configuration of a first corrugated wire 300, which is the corrugated wire 30, will be described with reference to FIG.

[0057] FIG. 3 is a diagram showing a 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, which is the bent portion 31, and the first non-bent portion, which is the non-bent portion 32.

[0058] Here, the first bends, which are three consecutive bends 31 along the length of the first corrugated wire 300, are referred to as a first point, a second point, and a 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.

[0059] 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 said to be the distance between the straight line LA and a straight line LB that is parallel to the straight line LA passing through the end 30B of the first corrugated wire 300 that is closest to the first and third points among the second points.

[0060] In the case where the first bends are on the same plane, as shown in Fig. 3, when the first corrugated wire 300 is arranged 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 bend 31A and the bend 31B, for example.

[0061] The first corrugated wire 300 may have a ratio D / H1 of the wire diameter D (see FIG. 2) to the first corrugation height H1, which is equal to or greater than 1.029 and equal to or less than 1.818, for example.

[0062] By setting D / H1 to 1.818 or less, the distance between adjacent wires 11 in the steel cord 10 is increased and the steel cord is embedded in rubber to increase the degree of rubber penetration when a cord-rubber composite is formed. Therefore, when a cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber is increased, and the bending rigidity of the cord-rubber composite is increased.

[0063] By making D / H1 1.029 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.

[0064] 3, the distance between the bent portion 31A, which is the first point, and the bent portion 31C, which is the third point, of the first corrugated wire 300 is defined as the first corrugation pitch P1. Note that the distance between the first bent portions, which are adjacent bent portions 31 along the plane S when the first corrugated wire 300 is placed on the plane S, can also be defined as the first corrugation pitch P1. In other words, the distance between the first bent portions, which is the distance between the bent portion 31A, which is the first point, and the bent portion 31C, which is the third point, along the plane S, can be defined as the first corrugation pitch P1.

[0065] In this case, the ratio P1 / Psc of the first corrugated 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.

[0066] By setting P1 / Psc to 0.35 or less, the distance between adjacent wires 11 in the steel cord 10 is increased, and the degree of rubber penetration is increased when the steel cord 10 is embedded in rubber to form a cord-rubber composite. As a result, when the cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber is improved, and the bending rigidity of the cord-rubber composite is increased.

[0067] 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.

[0068] 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.

[0069] That is, 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 longitudinal direction.

[0070] The second corrugated wire 310 can have the same configuration as the first corrugated wire 300 except for the corrugation conditions, so an example configuration will be described with reference to FIG.

[0071] In this case, Figure 3 shows the second corrugated wire 310 placed on a plane S such that the plane S is perpendicular to a plane passing through the second bent portion, which is the bent portion 31, and the second non-bent portion, which is the non-bent portion 32.

[0072] 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, the fifth point, and the 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.

[0073] The shortest distance between the fifth point and a 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 a 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.

[0074] In the case where the second bends are on the same plane, as shown in Fig. 3, when the second corrugated wire 310 is arranged on the 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 second corrugation height H2. That is, for example, the shortest length along the vertical direction of the plane S between the bend 31A, which is the fourth point, or the bend 31C, which is the sixth point, and the bend 31B, which is the fifth point, 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 parts of the second corrugated wire 310 at the bends 31A and 31B, for example.

[0075] The second corrugated wire 310 may have a ratio D / H2 of the wire diameter D (see FIG. 2) to the second corrugation height H2 of 1.029 or more and 1.818 or less.

[0076] By setting D / H2 to 1.818 or less, the distance between adjacent wires 11 in the steel cord 10 is increased, and the degree of rubber penetration is increased when the steel cord 10 is embedded in rubber to form a cord-rubber composite. As a result, when the cord-rubber composite is formed, the adhesion between the steel cord 10 and the rubber is improved, and the bending rigidity of the cord-rubber composite is increased.

[0077] By making D / H2 1.029 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.

[0078] The distance between the bent portion 31A, which is the fourth point, and the bent portion 31C, which is the sixth point, of the second corrugated wire 310 is defined as the second corrugating pitch P2. The distance between the second bent portions, which are adjacent bent portions 31 along the plane S of the second corrugated wire 310, can also be defined as the second corrugating pitch P2. In other words, the distance between the bent portion 31A, which is the fourth point, and the bent portion 31C, which is the sixth point, which is the distance between the second bent portions along the plane S, can be defined as the second corrugating pitch P2.

[0079] In this case, the ratio P2 / Psc of the second corrugated 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.

[0080] 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 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 the steel cord embedded in rubber".

[0081] Furthermore, by making P2 / Psc 0.50 or more, when the steel cord is embedded in rubber to form a cord-rubber composite, the distance between the wires constituting the steel cord 10 can be prevented 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 area and effective cross-sectional area The present inventors have conducted research into 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.

[0082] In this specification, durability means the property of preventing the cord-rubber composite from breaking when the cord-rubber composite is repeatedly bent, and can be evaluated by the number of times the cord-rubber composite is repeatedly bent before breaking.

[0083] As a result, it was found that by controlling the bending rigidity within an appropriate range when the cord-rubber composite is embedded in rubber, the cord-rubber composite can follow deformation and prevent breakage even when the cord-rubber composite is repeatedly bent. It was also found that when a cord-rubber composite with bending rigidity controlled within an appropriate range is used in a tire, both durability and ride comfort can be achieved. In other words, it was found that by controlling the bending rigidity of the cord-rubber composite within an appropriate range, the durability of the cord-rubber composite can be increased, and the ride comfort can be improved when the cord-rubber composite is applied to a tire. This is thought to be because, by setting the bending rigidity of the cord-rubber composite within a predetermined range, when the cord-rubber composite is repeatedly bent, the cord-rubber composite can appropriately deform in response to the force applied to bend the cord-rubber composite.

[0084] As shown in Fig. 2, when a 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, and the gaps 12 between the wires 11 of the steel cord 10 change compared to before embedding. According to studies by the inventors of the present invention, in a cross section perpendicular to the longitudinal direction of the steel cord 10 when embedded in rubber 21, 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 improved by setting the effective cross-sectional area, which is the area of ​​the composite region 13, within a predetermined range, and the present invention was completed based on this finding.

[0085] The composite region 13 is defined as the region surrounded by common tangent LO1, common tangent LO2, common tangent LO3, common tangent LO4, 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 rubber 21.

[0086] 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 means the surface of the steel cord 10 that is exposed to the outside.

[0087] Specifically, tangent line LO1 is a common tangent line between wires 11A and 11B. Tangent line LO2 is a common tangent line between wires 11B and 11C. Tangent line LO3 is a common tangent line between wires 11C and 11D. Tangent line LO4 is a common tangent line between wires 11D and 11A.

[0088] 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.

[0089] Specifically, line segment LI1 is a line segment that connects center OA of wire 11A to center OB of wire 11B. Line segment LI2 is a line segment that connects center OB of wire 11B to center OC of wire 11C. Line segment LI3 is a line segment that connects center OC of wire 11C to center OD of wire 11D. Line segment LI4 is a line segment that connects center OD of wire 11D to center OA of wire 11A.

[0090] The composite region 13 is a region where 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 where 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.

[0091] The steel cord 10 of this embodiment has an effective cross-sectional area of ​​0.099 mm 2 More than 0.224mm 2 The effective cross-sectional area can be set to 0.099 mm 2 More than 0.224mm 2By setting the effective cross-sectional area to 0.100 mm or less, the bending stiffness of the cord-rubber composite can be set in an appropriate range, and durability can be improved. 2 More than 0.222mm 2 It may be less than 0.100 mm 2 More than 0.220mm 2 It may be less than 0.100 mm 2 More than 0.210mm 2 It may be the following. (3-2) Area of ​​steel distribution 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.

[0092] The region 14 where steel is distributed 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 region 14 where steel is distributed is the region where the wire 11 is arranged. Since the brass plating film 112 is usually very thin, the region 14 where steel is distributed may be the region where the wire 11 is arranged even if the wire 11 has the brass plating film 112.

[0093] 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.

[0094] By making the area ratio of the steel region 30% or more, the bending rigidity of the cord-rubber composite can be increased when the cord-rubber composite is made. 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 the cord-rubber composite is made. As a result, the durability of the cord-rubber composite can be particularly increased.

[0095] 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.

[0096] By setting the initial elongation to 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 to the steel cord 10, can be improved.

[0097] Furthermore, 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 rubber, for example, when producing 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, for example, when producing a cord-rubber composite.

[0098] 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 The steel cord of the present embodiment may have a rubber penetration rate of 60% or more.

[0099] By making the rubber penetration rate 60% or more, when a cord-rubber composite is formed, the adhesion between the steel cord and the rubber can be increased, and the bending rigidity of the cord-rubber composite can be increased.

[0100] The rubber penetration rate of the steel cord of the present 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.

[0101] The initial elongation and the rubber penetration rate 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, and the like.

[0102] [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.

[0103] As shown in FIG. 4, a cord-rubber composite 40 of this embodiment can have rubber 41 and the steel cord 10 of this embodiment embedded in the rubber 41.

[0104] 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 thickness t1 of the rubber to be disposed below the steel cord 10 and the thickness t2 of the rubber to be disposed above the steel cord 10 can be selected.

[0105] For the steel cord 10, the outer diameter can be reduced by setting the wire diameter D of the wires 11 (see FIG. 1) within a predetermined range. By reducing the outer diameter of the steel cord 10, the thickness of the cord-rubber composite 40 can also be reduced. 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, resulting in a reduction in weight. Furthermore, the weight of a tire including the cord-rubber composite 40 of this embodiment can also be reduced.

[0106] Moreover, according to the cord-rubber composite 40 including the steel cord 10 according to one embodiment of the present disclosure, the bending stiffness can be set within an appropriate range, and durability can be improved.

[0107] 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 include 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.

[0108] The steel cords 10 may be arranged in parallel to each other.

[0109] The details of the steel cord 10 have already been explained, so the explanation will be omitted. (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.

[0110] The specific composition of the rubber is not particularly limited and can be selected depending on the application of various products such as tires to which the cord-rubber composite 40 is applied, the required characteristics, etc. The rubber can contain, for example, a rubber component, sulfur, and a vulcanization accelerator.

[0111] The rubber component may contain 60% by mass or more, 70% by mass or more, or even 100% by mass of one or more types selected from, for example, natural rubber (NR) and isoprene rubber (IR).

[0112] 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.

[0113] Examples of rubber components that may be used in combination with natural rubber or isoprene rubber include one or more selected from the group consisting of styrene-butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), butyl rubber (IIR), and acrylonitrile-butadiene rubber (NBR).

[0114] The sulfur is not particularly limited, but for example, sulfur that is generally used as a vulcanizing agent in the rubber industry can be used.

[0115] The sulfur content of 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.

[0116] 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 obtained rubber can be increased, and in particular, the adhesive strength between the steel cord and the rubber can be increased, and, 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 in the rubber, and blooming can be prevented from occurring.

[0117] The vulcanization accelerator is not particularly limited, and 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.

[0118] 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, and extruding.

[0119] 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.

[0120] Examples of the cobalt-containing compound include organic acid cobalt and inorganic acid cobalt.

[0121] The organic acid cobalt may be, for example, one or more selected from cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, cobalt tall oil acid, etc. The organic acid cobalt may be a composite salt in which a part of the organic acid is replaced with boric acid.

[0122] As the inorganic acid cobalt, for example, one or more selected from cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt phosphate, and cobalt chromate may be used.

[0123] The rubber may also contain any other components in addition to 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 the 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 according to 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 in the cord-rubber composite 40. For this reason, in this specification, the unit of ends is "pieces / 50 mm".

[0124] The cord-rubber composite 40 of the present embodiment may include the steel cord 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 may be 40 cords / 50 mm or more and 60 cords / 50 mm or less.

[0125] By making the ends of the cord-rubber composite 40 30 pieces / 50 mm or more, the gaps between the steel cords 10 included in the cord-rubber composite 40 can be reduced, and the steel cords can be arranged at a high density. This improves punching resistance, which is 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.

[0126] By setting the ends of the cord-rubber composite 40 to 60 pieces / 50 mm or less, the number of supply devices for supplying steel cords during production of the cord-rubber composite 40 can be reduced, thereby improving productivity.

[0127] 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, thereby reducing 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.

[0128] [tire] Next, the tire according to this embodiment will be described with reference to FIG.

[0129] The tire of this embodiment may include a steel cord 10 according to one aspect of the present disclosure.

[0130] 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 a portion to the left of the center line (CL), the same structure extends to the right of the center line (CL) with the CL as an axis of symmetry.

[0131] As shown in FIG. 5, a tire 50 includes a tread portion 51, a sidewall portion 52, and a bead portion 53.

[0132] The tread portion 51 is a portion that comes into contact with the road surface. The bead portions 53 are provided at positions closer to the inner diameter of the tire 50 than the tread portion 51. The bead portions 53 are portions that come into contact with the rim of a vehicle wheel. The sidewall portions 52 connect the tread portion 51 and the bead portions 53. When the tread portion 51 receives an impact from the road surface, the sidewall portions 52 elastically deform to absorb the impact.

[0133] The tire 50 includes an inner liner 54 , a carcass 55 , a belt layer 56 , and a bead wire 57 .

[0134] The inner liner 54 is made of rubber and seals the space between the tire 50 and the wheel.

[0135] 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.

[0136] The bead wire 57 is provided in the bead portion 53. The bead wire 57 receives a tensile force acting on the carcass 55.

[0137] 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.

[0138] As described above, in the tire of the present embodiment, the belt layer 56 uses the cord-rubber composite 40 including the steel cord 10 according to one aspect of the present disclosure.

[0139] Therefore, according to the tire 50 of the present embodiment, the thickness of the belt layer 56 can be reduced, and the tire 50 including the belt layer 56 can be made lighter, and the rolling resistance of the tire can be reduced.

[0140] Moreover, the tire 50 of the present embodiment can be made to have excellent durability.

[0141] Although the embodiments have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the claims. EXAMPLES

[0142] 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, first, 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 divided 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 area and area ratio of steel area The cross-sectional area of ​​the wire is calculated from the wire diameter D, and multiplied by 4 to obtain the area of ​​the wire portion of the steel cord, 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) Bending rigidity As shown in FIG. 6, the bending stiffness of the cord-rubber composite is evaluated by a three-point bending test.

[0143] For the bending stiffness test, the cord-rubber composite prepared in each experiment 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 along the longitudinal direction of the steel cord included in the test piece.

[0144] Specifically, a first end 601 and a second end 602, which are ends in the width of the test piece 60, are supported from below by support jigs 611 and 612. Next, the midpoint between the support jigs 611 and 612 is pressed downward as indicated by block arrow 62 by a pressing jig 613.

[0145] 6 is equal to the distance L601. The distance L601 means the distance between the point where the test piece 60 contacts the support jig 611 and the point where the test piece 60 contacts the pressing jig 613. The distance L602 means the distance between the point where the test piece 60 contacts the support jig 612 and the point where the test piece 60 contacts the pressing jig 613.

[0146] Then, the bending rigidity is obtained by measuring the reaction force when the portion pressed by the pressing jig 613 is displaced 1 mm along the block arrow 62 .

[0147] The test specimen 60 is arranged so that the longitudinal direction of the steel cord contained in the test specimen 60 is aligned along 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.

[0148] The test specimen 60 is arranged so that its long side, 50 mm in length, is aligned with the arrangement of the support jigs 611 and 612, i.e., the Y-axis in FIG. 6, and its short side, 30 mm in length, is aligned with the X-axis perpendicular to the paper surface in FIG. (6) Rubber penetration The steel cord was removed from the cord-rubber composite produced in each experimental example with a cutter knife.

[0149] Then, two adjacent wires are removed from the steel cord that has been taken out. 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.

[0150] A higher rubber penetration value indicates better rubber penetration, and a rubber penetration value of 60% or more indicates sufficient performance for practical use.

[0151] (7) Initial elongation The initial elongation is the percentage of elongation when a load of 50 N is applied to the steel cord, and is evaluated using a tensile tester.

[0152] First, the first distance L0, which is the distance between the chucks of the tensile tester, 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 defined as the second distance L1.

[0153] In this case, the initial elongation of the steel cord is calculated by the following formula (B).

[0154] (Initial elongation (%))=[(L1-L0)÷L0]×100 ···(B) (8) Durability evaluation First, a test specimen was cut out from the cord-rubber composite prepared in each experimental example so as to have a string-like shape with a width of 10 mm in a cross section perpendicular to the longitudinal direction of the steel cord included in the cord-rubber composite. The width is the length along the X-axis in Fig. 4, and is the length along the arrangement of the steel cords 10.

[0155] As shown in FIG. 7, the obtained 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 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 specimen 70. When the specimen 70 is placed on the three rollers, the positions of the rollers are adjusted so that the specimen 70 located between the first roller 71 and the second roller 72 and the 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 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 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 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 specimen is counted until the specimen 70 breaks.

[0156] The evaluation result of the cord-rubber composite of Experimental Example 11 was set as the standard, i.e., 100, and the evaluation results measured on the cord-rubber composites of each Experimental Example were normalized and used as an index value of durability.

[0157] If the durability index value is 110 or more, it is rated as A; if the durability index value is greater than 100 and less than 110, it is rated as B; and if the durability index value is 100 or less, it is rated as C.

[0158] When the rating is A, the cord-rubber composite is said to have particularly excellent durability, with the ratings decreasing in the order of B and C. When the rating is A or B, the cord-rubber composite has high durability. (9) Lightweightness evaluation 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.

[0159] The evaluation result of the cord-rubber composite of Experimental Example 11 was set as the standard, i.e., 100, and the weight measured in each Experimental Example was normalized and used as an index value for lightness.

[0160] If the lightness index value is less than 90, it is rated as A; if the lightness index value is 90 or more but less than 100, it is rated as B; and if the lightness index value is 100 or more, it is rated as C.

[0161] When the rating is A, it can be said that the weight of the cord-rubber composite has been particularly reduced and lightweight, and the ratings decrease in the order of B and C. When the rating is A or B, it can be said that the weight of the cord-rubber composite has been particularly reduced and lightweight. (Experimental Example) The experimental conditions are described below: Experimental Examples 1 to 9 are working 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.

[0162] 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 are steel wires, and a brass plating film 112 containing copper and zinc is disposed on the surface of the wire material 111. The four wires are then twisted together to produce a stranded steel cord having a 1×4 structure.

[0163] 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.

[0164] 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 contains 60 parts by mass of carbon black, 7 parts by mass of sulfur, 0.5 parts by mass of a vulcanization accelerator, 8 parts by mass of zinc oxide, and 2 parts by mass of cobalt stearate as an organic acid cobalt, as additives, relative to 100 parts by mass of the rubber component.

[0165] The cord-rubber composite was produced in advance as a prototype using the steel cord of this experimental example, and the thickness of the rubber was selected so that the steel cord 10 could be embedded, taking into account the variation in the position of the steel cord.

[0166] 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.

[0167] Other than the above, the steel cord and the cord-rubber composite were produced and evaluated using the same procedures and conditions as in Experimental Example 1.

[0168] The evaluation results are shown in Tables 1 and 2.

[0169] [Table 1]

[0170] [Table 2] According to Tables 1 and 2, the wire diameter is 0.15 mm or more and 0.20 mm or less, and the effective cross-sectional area is 0.099 mm 2 More than 0.224mm 2 It can be confirmed that the steel cords of Experimental Examples 1 to 9 below were both evaluated as A or B in terms of durability and light weight. That is, 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. [Explanation of symbols]

[0171] 10 Steel Cord 100 outer surface 11 Wire 11A bare wire 11B Bare wire 11C bare wire 11D bare wire OA center OB center OC-centered 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 rod 112 Brass plating film 12 Gap 13 Multidisciplinary 14 Steel distribution area D Wire diameter 20 Cord-rubber composite 21 Rubber XX axis YY axis ZZ axis 30 Corrugated wire 300 First corrugated wire 310 Second wave wire 30A end 31 Bend 31A Bent part (1st point, 4th point) 31B Bent part (2nd point, 5th point) 31C Bend part (3rd point, 6th point) LA straight line 32 Non-bending part H Corrugation height H1 First corrugation height H2 Second corrugation height P Corrugation pitch P1 First corrugation pitch P2 Second corrugation pitch S plane 40 Cord-rubber composite 400 Top 41 Rubber t1 Rubber thickness t2 Rubber thickness 50 Tires 51 Tread 52 Sidewall 53 Bead section 54 Inner Liner 55 Carcass 56 Belt layer 57 Bead wire CL Center Line 60 Test specimen 601 First end 602 Second end 611 Support jig 612 Support jig 613 Pressing tool 62 Block Arrow L601 distance L602 Distance 70 Test specimen 71 First Roller 72 2nd Roller 73 3rd Roller 74 Arrow

Claims

1. 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 0.099 mm ２ More than 0.224 mm ２ The steel code is as follows:

2. 2. The steel cord according to claim 1, wherein a ratio of an area of ​​a region in which steel is distributed to an effective cross-sectional area in the cross section is 30% or more and 128% or less.

3. 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.

4. 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.

5. 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, 4. 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.

6. 3. The steel cord according to claim 1, having an initial elongation of 0.20% or more and 0.50% or less.

7. 3. The steel cord according to claim 1 or 2, having a rubber penetration rate of 60% or more.

8. Rubber and A cord-rubber composite comprising: the steel cord according to claim 1 or 2 embedded in the rubber.

9. A tire comprising the steel cord according to claim 1 or 2.

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