Steel cord and tire

Abstract

Provided is a single-wire steel cord having a flat shape with a thickness less than the width in a cross section perpendicular to a longitudinal direction, the thickness being between 0.31 mm and 0.55 mm (both inclusive) and the cross section having a cross-sectional area between 0.155 mm2 and 0.250 mm2 (both inclusive).

Description

Steel cord, tires

[0001] The present disclosure relates to a steel cord and a tire.

[0002] This application claims priority based on Japanese Application No. 2023-138942 filed on August 29, 2023, and incorporates by reference all of the contents of the aforementioned Japanese application.

[0003] In Patent Document 1, a pneumatic radial tire is provided with a side reinforcing layer formed by aligning a plurality of single-wire steel wires and embedding them in rubber in a region from a bead portion to a sidewall portion, in which the single-wire steel wires are flattened, the aspect ratio of the single-wire steel wires is 40% to 70%, the major diameter of the single-wire steel wires is 0.80 mm or less, the average spacing of the single-wire steel wires is 0.60 mm or more, and the product of the buckling load of each single-wire steel wire and the wire mass per unit area of ​​the side reinforcing layer is 400 N kg / m 2 A pneumatic radial tire characterized by the above has been proposed.

[0004] JP 2015-178301 A

[0005] The steel cord of the present disclosure is a single-wire steel cord, and the steel cord has a flat shape in which the thickness is shorter than the width in a cross section perpendicular to the longitudinal direction, the thickness is 0.31 mm or more and 0.55 mm or less, and the cross-sectional area in the cross section is 0.155 mm ２ 0.250mm or more ２ The following is the result.

[0006] FIG. 1A is a cross-sectional view of a steel cord according to one embodiment of the present disclosure, taken along a plane perpendicular to the longitudinal direction. FIG. 1B is an enlarged view of region A in FIG. 1A. FIG. 2 is an explanatory diagram of a rolling mill that can be used when manufacturing a steel cord according to one embodiment of the present disclosure. FIG. 3 is a cross-sectional view of a cord-rubber composite according to one embodiment of the present disclosure. FIG. 4 is a cross-sectional view of a tire according to one embodiment of the present disclosure. FIG. 5 is an explanatory diagram of an evaluation method for a Charpy impact test. FIG. 6 is an explanatory diagram of the relationship between the thickness of the steel cord and Charpy impact test B in Experimental Examples 1 to 11.

[0007] [Problem to be solved by the present disclosure]

[0008] Conventionally, a sheet-like cord-rubber composite, in which a plurality of steel cords are aligned and embedded in rubber, has been used as a tire reinforcing material. With the aim of reducing the tire weight and rolling resistance, the use of a single-wire steel cord with a flat cross section in the cord-rubber composite has been studied.

[0009] By using a single-wire steel cord with a flat cross section, the thickness of the cord-rubber composite can be reduced, thereby reducing the amount of rubber used, thereby enabling the cord-rubber composite and tires using the cord-rubber composite to be lighter.

[0010] However, by using a steel cord with a flat cross section, there have been cases where the punching resistance, which is a property that prevents damage to the tire when an external force is applied to the tire's contact surface, has decreased.

[0011] From the viewpoint of reducing the frequency of tire replacement, there has been a demand for a single-wire steel cord that has excellent punching resistance and a flat cross section when applied to tires or cord-rubber composites used in tires.

[0012] Therefore, an object of the present disclosure is to provide a single-wire steel cord that has excellent punching resistance and a flat cross section when applied to a cord-rubber composite. [Advantages of the present disclosure]

[0013] According to the present disclosure, it is possible to provide a single-wire steel cord that has excellent punching resistance when applied to a cord-rubber composite and has a flat cross section.

[0014] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. In the following description, the same or corresponding elements will be denoted by the same reference numerals, and the same description will not be repeated.

[0015] (1) A steel cord according to one aspect of the present disclosure is a single-wire steel cord, and the steel cord has a flat shape in a cross section perpendicular to the longitudinal direction, the thickness of which is less than the width, the thickness being 0.31 mm or more and 0.55 mm or less, and the cross-sectional area of ​​the cross section being 0.155 mm or less. ２ 0.250mm or more ２ The following is the result.

[0016] Steel cords can be used in tires as a sheet-like cord-rubber composite, in which multiple steel cords are aligned and embedded in rubber. The thickness of the cord-rubber composite can be selected so that the steel cords can be embedded in the rubber. Therefore, by making the cross-sectional shape of the steel cord flat and reducing its thickness, the thickness of the cord-rubber composite can also be reduced. As a result, by using a steel cord with a flat cross-sectional shape, the amount of rubber contained in the cord-rubber composite can be reduced compared to when a steel cord with a circular cross-section having the same cross-sectional area is used. Therefore, by using a steel cord with a flat cross-sectional shape, the weight of the cord-rubber composite can be reduced, and the weight of the tire including the cord-rubber composite can also be reduced.

[0017] By setting the thickness to 0.31 mm or more, when the steel cord according to one embodiment of the present disclosure is used in a cord-rubber composite or a tire, punching resistance and toughness can be improved.

[0018] By setting the thickness to 0.55 mm or less, the thickness of the cord-rubber composite can be reduced, and the cord-rubber composite and the tire can be made lighter in weight.

[0019] The cross-sectional area of ​​the cross section perpendicular to the longitudinal direction is 0.155 mm ２ By setting the above, it is possible to improve the tensile load of the steel cord, and the toughness and punching resistance when the steel cord is used in a cord-rubber composite or a tire.

[0020] The cross-sectional area of ​​the cross section perpendicular to the longitudinal direction is 0.250 mm ２ By setting the thickness of the cord-rubber composite to the following value, the cord-rubber composite and the tire can be made lighter in weight.

[0021] (2) In (1), the flattening ratio, which is the ratio of the thickness to the width in the cross section, may be 45% or more and 60% or less.

[0022] By setting the aspect ratio to 45% or more, the thickness relative to the width can be made sufficiently long, and compared to a case in which a steel cord of the same width is used, punching resistance can be particularly improved when the cord is used in a cord-rubber composite or a tire.

[0023] By setting the aspect ratio to 60% or less, a steel cord can be made into a flat shape with a sufficiently short thickness relative to its width, and when applied to a cord-rubber composite, the thickness of the cord-rubber composite can be made thinner than when a steel cord of the same width is used, thereby enabling the cord-rubber composite and the tire to be made lighter.

[0024] (3) In (1) or (2), the width of the cross section may be 0.50 mm or more and 0.90 mm or less.

[0025] By setting the width to 0.90 mm or less, the amount of processing required to obtain the desired thickness can be reduced, and the decrease in tensile load due to processing can be reduced.

[0026] By making the width of the steel cord 0.50 mm or more, it is possible to particularly improve the punching resistance of a cord-rubber composite or when the cord is used in a tire.

[0027] (4) In any of (1) to (3), the cross section may have a pair of straight line portions arranged opposite each other, and a pair of curved line portions connecting the pair of straight line portions and arranged opposite each other, and a corner between the straight line portion and the curved line portion may have an arc shape.

[0028] By making the corners arc-shaped, when the cord is used in a cord-rubber composite or a tire, cracks and the like can be prevented from occurring in the rubber starting from the corners.

[0029] (5) In (4), the radius of curvature of the corners in the cross section may be equal to or less than half the width.

[0030] By making the radius of curvature of the corners equal to or less than half the width, it is possible to particularly prevent cracks from occurring in the rubber starting from the corners.

[0031] (6) In any of (1) to (5), a brass plating film may be provided on the surface.

[0032] When a steel cord is embedded in rubber to form a cord-rubber composite, the copper contained in the brass plating film reacts with the sulfur (S) contained in the rubber. Then, copper sulfide (Cu), a reaction product, is formed in the rubber near the interface between the steel cord and the rubber. ２ S).

[0033] The resulting adhesive layer can improve the initial adhesive performance between the steel cord and the rubber.

[0034] It is also believed that the zinc contained in the brass plating film promotes and controls the reaction that forms the adhesive layer.

[0035] (7) A tire according to one aspect of the present disclosure includes the steel cord according to any one of (1) to (6).

[0036] According to a tire according to one aspect of the present disclosure, a cord-rubber composite including the steel cord according to one aspect of the present disclosure is used in the belt layer.

[0037] Therefore, the thickness of the belt layer can be reduced, the weight of the belt layer and the tire including the belt layer can be reduced, and the rolling resistance of the tire can be reduced.

[0038] Furthermore, the tire according to one aspect of the present disclosure has excellent punching resistance and toughness.

[0039] [Details of the embodiment of the present disclosure] Specific examples of a steel cord 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. Note that 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.

[0040] [Steel Cord] Hereinafter, the steel cord according to this embodiment will be described with reference to Figs. 1A and 1B.

[0041] Fig. 1A shows a cross-sectional view of a steel cord 10 of this embodiment taken along a plane perpendicular to the longitudinal direction. Fig. 1B is an enlarged view of region A in Fig. 1A. In Fig. 1A, the X-axis is an axis along the width W of the steel cord 10. The Y-axis is an axis along the thickness T of the steel cord 10. The Z-axis is an axis perpendicular to the plane of the paper and is an axis along the longitudinal direction of the steel cord 10.

[0042] The steel cord 10 of the present embodiment is a single wire, i.e., a single-wire steel cord, and may also be called a single-wire steel cord, a steel wire, etc. Furthermore, the steel cord 10 of the present embodiment does not need to be twisted along its length, and may be a straight steel cord.

[0043] 1A , the steel cord 10 of the present embodiment can have a flat shape in a cross section perpendicular to the longitudinal direction, with a thickness T shorter than a width W. Hereinafter, the cross section perpendicular to the longitudinal direction of the steel cord 10 will also be simply referred to as a “cross section.”

[0044] Steel cords can be used in tires as a sheet-like cord-rubber composite, in which multiple steel cords are aligned and embedded in rubber. The thickness of the cord-rubber composite can be selected so that the steel cords can be embedded in the rubber. Therefore, by making the cross-sectional shape of the steel cord flat and reducing the thickness T, the thickness of the cord-rubber composite can also be reduced. As a result, by using a steel cord with a flat cross-sectional shape, the amount of rubber contained in the cord-rubber composite can be reduced compared to when a steel cord with a circular cross-section having the same cross-sectional area is used. Therefore, by using a steel cord with a flat cross-sectional shape, the weight of the cord-rubber composite can be reduced, and the weight of the tire including the cord-rubber composite can also be reduced.

[0045] However, according to the investigations of the present inventors, there have been cases where the punching resistance is insufficient in tires using cord-rubber composites containing steel cords with a flat cross-sectional shape.

[0046] In this specification, "punch resistance" refers to a property that prevents damage to a tire when an external force is applied to the tire's contact surface. Furthermore, in this specification, "external force" refers to a force applied vertically to the tire's contact surface when a foreign object such as a pebble comes into contact with the tire's contact surface. Furthermore, "damage" refers to the formation of a hole penetrating the tire by the foreign object.

[0047] The cord-rubber composite is used as a belt layer disposed along the tread portion of a tire, and is a component that receives external forces applied to the tire's contact surface. Therefore, in the definitions of punching resistance, external force, and breakage, the tire and the tire's contact surface can also be rephrased as the cord-rubber composite and the main surface of the cord-rubber composite, respectively. The cord-rubber composite is formed by aligning multiple steel cords so that they are parallel to each other and embedded in rubber. The main surface of the cord-rubber composite refers to the surface of the cord-rubber composite along the length of the steel cords and the arrangement of the multiple steel cords.

[0048] Therefore, the inventors of the present invention have conducted research into a single-wire steel cord having a flat cross section perpendicular to its longitudinal direction, which has excellent punching resistance when applied to a cord-rubber composite or a tire.

[0049] As a result, they discovered that by setting the thickness and cross-sectional area of ​​a single-filament steel cord in a cross section perpendicular to its longitudinal direction within a predetermined range, a steel cord with excellent punching resistance can be obtained when applied to a cord-rubber composite, etc., and thus completed the present invention. (1) Regarding Shape and Size (1-1) Regarding Thickness and Width As shown in FIG. 1A , the steel cord 10 of this embodiment has a flat shape in a cross section perpendicular to its longitudinal direction, in which the thickness T is shorter than the width W. (Thickness) The thickness T can be set to 0.31 mm or more and 0.55 mm or less. Setting the thickness T to 0.31 mm or more can improve punching resistance and toughness when used in a cord-rubber composite or a tire. Setting the lower limit of the thickness T to 0.36 mm or more can further improve punching resistance and toughness when used in a cord-rubber composite or a tire.

[0050] As used herein, toughness refers to the property of resistance to fracture, i.e., resistance to breakage, when a force is applied to a single steel cord contained in a cord-rubber composite or a tire and the steel cord 10 contained in the cord-rubber composite or a tire is deformed. In this specification, toughness refers to two types of properties: resistance to fracture when force is applied to a flat surface, including the straight portion 11, of the steel cord 10 contained in the cord-rubber composite or the tire, and resistance to fracture when force is applied to a side surface, including the curved portion 12. When toughness is not used in this specification to distinguish between the two, it includes two types of toughness. The resistance to fracture when force is applied to a flat surface, including the straight portion 11, of the steel cord 10 can be evaluated by Charpy impact test A, which will be described in the experimental examples, and is also referred to as first toughness. The resistance to fracture when force is applied to a side surface, including the curved portion 12, of the steel cord 10 can be evaluated by Charpy impact test B, which will be described in the experimental examples, and is also referred to as second toughness.

[0051] By setting the thickness T to 0.55 mm or less, the thickness of the cord-rubber composite can be reduced, and the cord-rubber composite and the tire can be made lighter. The thickness T may be set to 0.50 mm or less, or 0.45 mm or less. By setting the thickness T to 0.50 mm or less, or 0.45 mm or less, the thickness of the cord-rubber composite can be made particularly thin.

[0052] Therefore, the thickness T of the steel cord 10 may be, for example, 0.31 mm or more and 0.55 mm or less, or 0.36 mm or more and 0.55 mm or less.

[0053] From the viewpoint of reducing the thickness of the cord-rubber composite and particularly reducing the weight of the cord-rubber composite and the tire, the thickness T of the steel cord 10 may be 0.31 mm or more and 0.50 mm or less, or 0.31 mm or more and 0.45 mm or less. (Width) The width W of the steel cord 10 of the present embodiment is not particularly limited, but may be, for example, 0.50 mm or more and 0.90 mm or less.

[0054] A steel cord having a flat cross section can be produced, for example, by applying pressure to a steel cord base material having a circular cross section and flattening it. In this case, the thickness T is the length along the axis of pressure applied when forming, for example, the straight section 11 in FIG. 1A , and the width W is the length along the axis of pressure applied when forming, for example, the curved section 12 in FIG. 1A . The width W is approximately the same as the outer diameter of the steel cord having a circular cross section before processing. By setting the width W to 0.90 mm or less, the amount of processing required to achieve the desired thickness T can be reduced, and the decrease in tensile load due to processing can be minimized. In particular, from the viewpoint of reducing the amount of processing and increasing the tensile load of the steel cord 10, the width W may be 0.87 mm or less. That is, for example, the width W may be 0.50 mm or more and 0.87 mm or less.

[0055] By making the width W of the steel cord 10 0.50 mm or more, punching resistance can be particularly improved when the steel cord 10 is used in a cord-rubber composite or a tire. The width W of the steel cord 10 may be 0.52 mm or more. Therefore, the width W of the steel cord 10 may be, for example, 0.52 mm or more and 0.90 mm or less, or 0.52 mm or more and 0.87 mm or less. (1-2) Regarding the aspect ratio The aspect ratio of the steel cord of this embodiment, which is the ratio of the thickness T to the width W in the cross section, is not particularly limited, but can be, for example, 45% or more and 60% or less.

[0056] By setting the aspect ratio to 45% or more, the thickness T relative to the width W can be made sufficiently long, and compared to a case in which a steel cord of the same width is used, punching resistance can be particularly improved when used in a cord-rubber composite or a tire.

[0057] By setting the aspect ratio to 60% or less, a steel cord can be made in a flat shape with a sufficiently short thickness T relative to the width W, and when applied to a cord-rubber composite, the thickness of the cord-rubber composite can be made thinner than when a steel cord of the same width is used, thereby enabling the cord-rubber composite and the tire to be made lighter.

[0058] In particular, from the viewpoint of reducing the thickness of the cord-rubber composite, the aspect ratio may be 58% or less. That is, the aspect ratio of the steel cord of this embodiment may be, for example, 45% or more and 58% or less. (1-3) Cross-sectional Shape As shown in FIG. 1A , the steel cord 10 of this embodiment can have, in its cross section, a pair of straight portions 11 and a pair of curved portions 12 arranged to face each other. Hereinafter, the surfaces of the straight portions 11 will also be referred to as flat surfaces, and the surfaces of the curved portions 12 will also be referred to as side surfaces.

[0059] As shown in FIG. 1A , the straight line portion 11 and the curved line portion 12 are the contour lines of the steel cord 10 .

[0060] The steel cord 10 of this embodiment can have, in cross section, a pair of straight portions 11, that is, a first straight portion 111 and a second straight portion 112 arranged to face each other.

[0061] Furthermore, the steel cord 10 of this embodiment can have, in its cross section, a pair of curved portions 12, namely, a first curved portion 121 and a second curved portion 122 that connect the first straight portion 111 and the second straight portion 112 and are arranged facing each other.

[0062] The shape of the corner 13 between the straight portion 11 and the curved portion 12 is not particularly limited, but may be an arc shape. By making the corner 13 arc-shaped, when the cord is used in a cord-rubber composite or a tire, cracks and the like can be prevented from occurring in the rubber starting from the corner 13.

[0063] 1B shows an enlarged view of region A near corner 131 in FIG. 1A. As shown in FIG. 1B, corner 13 is a portion where the contour shape changes from straight portion 11 to curved portion 12, and is, for example, a curved portion having a constant shape that is directly connected to straight portion 11. As shown in FIG. 1B, corner 13 may also be an arc-shaped portion with a constant radius of curvature R that is directly connected to straight portion 11. In this way, corner 13 is a region where the contour shape transitions from straight portion 11 to curved portion 12, and therefore may be referred to as a transition region or the like.

[0064] When the corner 13 has an arc shape, its radius of curvature R is not particularly limited, but can be, for example, equal to or less than half the width W. By making the radius of curvature of the corner 13 equal to or less than half the width W, it is possible to particularly prevent cracks from occurring in the rubber starting from the corner 13.

[0065] The lower limit of the radius of curvature R is not particularly limited, but can be, for example, 0.2 mm or more.

[0066] The steel cord 10 of this embodiment has, as corners 13, corners 131, 132, 133, and 134 located in four transition regions between the straight portion 11 and the curved portion 12. The above-mentioned effect can be obtained by making at least some of the four corners 13 arc-shaped, but from the viewpoint of particularly enhancing the effect, all of the corners 13 can also be arc-shaped.

[0067] In addition, when a plurality of corners 13 have an arc shape, the radius of curvature R may be the same for all of the corners 13 having an arc shape, or at least some or all of the corners 13 may be different. (1-4) Regarding Cross-Sectional Area The steel cord 10 of this embodiment has a cross-sectional area of ​​0.155 mm ２ 0.250mm or more ２ The cross-sectional area of ​​the cross section perpendicular to the longitudinal direction can be 0.155 mm or less. ２ By making the cross-sectional area 0.155 mm or more, the tensile load of the steel cord can be increased. ２ By setting the above, it is possible to improve the toughness and punching resistance when the steel cord 10 is used in a cord-rubber composite or a tire. ２ It may be more than that.

[0068] The cross-sectional area of ​​the steel cord 10 perpendicular to the longitudinal direction is 0.250 mm ２ By setting the thickness T of the cord-rubber composite to the value below, the thickness T of the cord-rubber composite can be reduced, and the weight of the cord-rubber composite and the tire can be reduced. ２ It may be less than 0.229 mm ２ The following may also be used.

[0069] Therefore, the cross-sectional area of ​​the steel cord 10 is, for example, 0.155 mm ２ 0.250mm or more ２ and can be 0.160 mm or less. ２ 0.250mm or more ２ The following may also be used.

[0070] From the viewpoint of reducing the thickness of the cord-rubber composite and making the cord-rubber composite and the tire particularly light, the cross-sectional area of ​​the steel cord 10 is 0.155 mm ２ More than 0.240 mm ２ It may be less than 0.155 mm ２ 0.229mm or more ２ The following may be used. (2) Regarding the Material of the Steel Cord The steel cord 10 of this embodiment may be composed of only a wire rod 101, or may have a brass plating film 102 on its surface. Specifically, the steel cord 10 may have a wire rod 101 and a brass plating film 102 covering the wire rod 101. (Wire Rod) The wire rod 101 may be, for example, a steel wire, and a high-carbon steel wire may also be used. (Brass Plating Film) The brass plating film 102 may contain copper (Cu) and zinc (Zn). As shown in FIG. 1A , the brass plating film 102 may be disposed so as to cover the side surface of the wire rod 101.

[0071] When the steel cord 10 is embedded in rubber to form a cord-rubber composite, the copper contained in the brass plating film 102 reacts with sulfur (S) contained in the rubber. Then, copper sulfide (Cu), which is a reaction product, is formed in the rubber near the interface between the steel cord 10 and the rubber. ２ S).

[0072] The adhesive layer thus formed can improve the initial adhesive performance between the steel cord 10 and the rubber. The initial adhesive performance means the adhesive performance between the steel cord 10 and the rubber immediately after vulcanization during the production of the cord-rubber composite or the tire including the cord-rubber composite.

[0073] It is believed that the zinc contained in the brass plating film 102 promotes and controls the reaction that forms the adhesive layer.

[0074] The brass plating film 102 may contain elements other than copper and zinc, and may further contain one or more selected from the group consisting of cobalt (Co), nickel (Ni), tin (Sn), iron (Fe), and manganese (Mn).

[0075] The additive elements cobalt, nickel, tin, iron, and manganese have a greater ionization tendency than copper. Therefore, when the brass plating film 102 contains an additive element in addition to copper and zinc, the brass plating film 102 functions as a sacrificial anticorrosion agent or can make the composite potential of copper and zinc more noble. Therefore, when the brass plating film 102 contains an additive element, the corrosion resistance of the steel cord 10 can be improved. (3) Manufacturing Method of Steel Cord The manufacturing method of the steel cord of this embodiment is not particularly limited, and the steel cord can be manufactured so that its cross-sectional shape is a predetermined flat shape.

[0076] The steel cord of this embodiment can be manufactured, for example, by rolling a steel cord base material having a circular cross section perpendicular to the longitudinal direction.

[0077] The method for producing the steel cord of the present embodiment may include, for example, the following steps.

[0078] A steel cord base material preparation process in which a steel cord base material having a circular cross section perpendicular to the longitudinal direction is prepared.

[0079] a first rolling step in which the steel cord base material is supplied between a pair of first rolling rollers having opposing pressure surfaces, and pressed along a first axis parallel to the diameter of the steel cord base material in a cross section perpendicular to the longitudinal direction thereof;

[0080] a second rolling step in which the steel cord base material after the first rolling step is supplied between a pair of second rolling rollers whose pressing surfaces face each other, and pressed along a second axis perpendicular to the first axis in a cross section perpendicular to the longitudinal direction of the steel cord base material;

[0081] The first rolling step and the second rolling step can be carried out by, for example, the rolling mill 20 shown in FIG.

[0082] The rolling mill 20 has a pair of first rolling rollers 221 and 222 with pressure surfaces facing each other. The steel cord base material 21 supplied to the rolling mill 20 is transported along the arrow B in the figure, i.e., the Z axis. The pair of first rolling rollers 221 and 222 can pressurize the steel cord base material 21 being transported along the first axis, for example, along the thickness direction. In the case of the rolling mill 20 shown in FIG. 2 , the first axis corresponds to the Y axis, and the pair of first rolling rollers 221 and 222 can pressurize the steel cord base material 21 from above and below along the Y axis in FIG. 2 to perform the first rolling step.

[0083] In the first rolling step, the steel cord base material 21 is pressed and rolled by a pair of first rolling rollers 221 and 222, thereby forming the straight portion 11 in the cross section of the steel cord 10 shown in Fig. 1A. Therefore, the pair of first rolling rollers 221 and 222 can include flat portions corresponding to the first straight portion 111 and the second straight portion 112 on their respective pressing surfaces, i.e., the surfaces that come into contact with the steel cord base material 21.

[0084] The rolling device 20 can have a pair of first rolling rollers 221 and a pair of second rolling rollers 231 and 232 downstream of the first rolling rollers 222 along the transport path of the steel cord base material 21. The pair of second rolling rollers 231 and 232 can pressurize the steel cord base material 21 after the first rolling step along a second axis, for example, the width W, that is perpendicular to the first axis in the cross section of the steel cord base material 21. The second rolling step can be carried out for the purpose of adjusting the shape of corners 13 between straight portions 11 and curved portions 12, etc.

[0085] In the case of the rolling mill 20 shown in Fig. 2, the second axis corresponds to the X axis, and a pair of second rolling rollers 231 and 232 pressurize the steel cord base material 21 after the first rolling step from the left and right along the X axis in Fig. 2, thereby carrying out the second rolling step. The term "orthogonal" as used here does not mean "orthogonal" in the strict sense, but rather it is sufficient if the orientation is substantially orthogonal, including a certain amount of error.

[0086] In the second rolling step, the steel cord base material 21 after the first rolling step is pressed and rolled by a pair of second rolling rollers 231 and 232, thereby forming the corners 13 and curved portions 12 in the cross section of the steel cord 10 shown in Fig. 1A. Therefore, the pair of second rolling rollers 231 and 232 can have their pressing surfaces, i.e., the surfaces that come into contact with the steel cord base material 21, that have shapes corresponding to the first curved portion 121, the second curved portion 122, and the corners 13. Specifically, the second rolling rollers 231 and 232 can have grooves 231A and grooves 232A, respectively, on the surfaces that come into contact with the steel cord base material 21. The cross-sectional shapes of grooves 231A and 232A on a plane passing through the central axes of second rolling rollers 231 and 232 can be shaped to correspond to first curved portion 121, second curved portion 122, and corner portion 13.

[0087] In the first rolling step and the second rolling step, the degree of pressure and rolling can be adjusted so as to satisfy the cross-sectional shape of the steel cord 10 of this embodiment.

[0088] Although the structural example of the method for producing a steel cord according to the present embodiment has been described above using the first rolling step and the second rolling step as an example, the present invention is not limited to this. For example, if the cross-sectional shape can be formed into a desired shape by the first rolling step alone, the second rolling step does not need to be performed.

[0089] [Cord-Rubber Composite] FIG. 3 shows a cross-sectional view of a cord-rubber composite 30 of this embodiment taken along a plane perpendicular to the longitudinal direction of the steel cord 10. As shown in FIG.

[0090] As shown in FIG. 3, a cord-rubber composite 30 of this embodiment can have rubber 31 and the steel cord 10 of this embodiment embedded in the rubber 31 .

[0091] The thickness of the cord-rubber composite 30 can be selected so that the steel cord 10 can be embedded in the rubber 31. Specifically, the thickness t1 of the rubber disposed below the steel cord 10 and the thickness t2 of the rubber disposed above the steel cord 10 can be selected.

[0092] For this reason, by making the cross-sectional shape of the steel cord 10 flat and reducing the thickness T, the thickness of the cord-rubber composite 30 can also be reduced. As a result, by using a steel cord 10 with a flat cross-sectional shape, the amount of rubber contained in the cord-rubber composite 30 can be reduced, compared to when a steel cord with a circular cross-section having the same cross-sectional area is used, thereby achieving weight reduction. Furthermore, the tire including the cord-rubber composite 30 of this embodiment can also be made lighter.

[0093] Furthermore, the cord-rubber composite 30 including the steel cord 10 according to one aspect of the present disclosure has excellent punching resistance and toughness.

[0094] The components contained in the cord-rubber composite of this embodiment will be described below. (1) Components Included in the Cord-Rubber Composite (1-1) Steel Cord The cord-rubber composite 30 can include a plurality of steel cords 10. The steel cords 10 contained in the cord-rubber composite 30 can be arranged so that the longitudinal direction of each steel cord 10 is along the Z axis in Figure 3. The plurality of steel cords 10 can be arranged along the width of the cord-rubber composite 30, i.e., along the X axis in Figure 3.

[0095] The plurality of steel cords 10 can be arranged in parallel with one another.

[0096] The details of the steel cord 10 have already been explained, so the explanation will be omitted. (1-2) Rubber The rubber 31 of the cord-rubber composite 30 can be produced by molding a rubber composition and vulcanizing it as necessary.

[0097] 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 30 is applied, the required properties, etc. The rubber can contain, for example, a rubber component, sulfur, and a vulcanization accelerator.

[0098] The rubber component may contain 60% by mass or more, 70% by mass or more, or 100% by mass of one or more types selected from, for example, natural rubber (NR) and isoprene rubber (IR).

[0099] This is because by setting the proportion of one or more types of rubber selected from natural rubber and isoprene rubber in the rubber component to 60% by mass or more, the breaking strength of the cord-rubber composite 30 and the tire can be increased.

[0100] Examples of rubber components used in combination with natural rubber or isoprene rubber include 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).

[0101] The sulfur is not particularly limited, but for example, sulfur generally used as a vulcanizing agent in the rubber industry can be used.

[0102] 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.

[0103] This is because, by setting the proportion 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 proportion 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.

[0104] The vulcanization accelerator is not particularly limited, and examples thereof include sulfenamide accelerators such as N,N'-dicyclohexyl-2-benzothiazolylsulfenamide, N-cyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide, and N-oxydiethylene-2-benzothiazolylsulfenamide. If desired, thiazole accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide, and thiuram accelerators such as tetrabenzylthiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, and tetramethylthiuram monosulfide may also be used.

[0105] The rubber composition used in the cord-rubber composite 30 of this embodiment can be produced by kneading raw materials such as rubber components, heating the mixture, and extruding it.

[0106] The rubber of the cord-rubber composite 30 of this embodiment may contain one or more types selected from simple cobalt and compounds containing cobalt.

[0107] Examples of the cobalt-containing compound include organic acid cobalt and inorganic acid cobalt.

[0108] The organic cobalt salt may be, for example, one or more selected from cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, cobalt tallate, etc. The organic cobalt salt may be a composite salt in which part of the organic acid is replaced with boric acid.

[0109] As the inorganic acid cobalt, for example, one or more selected from cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt phosphate, and cobalt chromate can be used.

[0110] In particular, the rubber of the cord-rubber composite 30 of this embodiment may contain cobalt organic acid. By containing cobalt organic acid in the rubber of the cord-rubber composite 30 of this embodiment, the initial adhesive performance between the steel cord and the rubber can be particularly improved.

[0111] Furthermore, according to the research of the inventor of the present invention, by adding cobalt to rubber, copper sulfide (Cu ２ This can increase the proportion of cobalt (S), thereby increasing the adhesive strength between the steel cord and the rubber. This tendency becomes more pronounced when organic acid cobalt is used as the added cobalt. For this reason, the rubber of the cord-rubber composite 30 of this embodiment may contain cobalt, particularly organic acid cobalt, which can result in a cord-rubber composite 30 and tire with particularly excellent durability.

[0112] Furthermore, the rubber may contain optional components in addition to the above-mentioned 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 30 is not particularly limited and can be selected depending on the characteristics required of the cord-rubber composite 30 and a tire including the cord-rubber composite 30. Here, ends refers to the number of steel cords 10 included per 50 mm width of the cord-rubber composite 30 in a cross section perpendicular to the longitudinal direction of the steel cords 10 in the cord-rubber composite 30. Therefore, in this specification, the unit of ends is "pieces / 50 mm." In this case, the cord-rubber composite 30 may contain steel cords 10 such that the number of ends is, for example, 30 cords / 50 mm or more and 60 cords / 50 mm or less. The ends of the cord-rubber composite 30 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.

[0113] By making the ends of the cord-rubber composite 30 30 / 50 mm or more, the gaps between the steel cords 10 included in the cord-rubber composite 30 can be reduced, allowing the steel cords to be arranged at a high density. This particularly improves the punching resistance of the cord-rubber composite 30. Furthermore, the durability of products such as tires that include the cord-rubber composite 30 can be particularly improved.

[0114] By setting the ends of the cord-rubber composite 30 to 60 pieces / 50 mm or less, the number of supply devices for supplying steel cords can be reduced when manufacturing the cord-rubber composite 30, thereby increasing productivity.

[0115] [Tire] Next, the tire according to this embodiment will be described with reference to FIG.

[0116] The tire of this embodiment may include a steel cord 10 according to one aspect of the present disclosure.

[0117] Fig. 4 shows a cross-sectional view of a tire 41 according to this embodiment taken along a plane perpendicular to the outer periphery. Although Fig. 4 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 the axis of symmetry.

[0118] As shown in FIG. 4 , a tire 41 includes a tread portion 42 , a sidewall portion 43 , and a bead portion 44 .

[0119] The tread portion 42 is the portion that comes into contact with the road surface. The bead portions 44 are provided at positions closer to the inner diameter of the tire 41 than the tread portion 42. The bead portions 44 are the portions that come into contact with the rim of a vehicle wheel. The sidewall portions 43 connect the tread portion 42 and the bead portions 44. When the tread portion 42 receives an impact from the road surface, the sidewall portions 43 elastically deform and absorb the impact.

[0120] The tire 41 includes an inner liner 45 , a carcass 46 , a belt layer 47 , and a bead wire 48 .

[0121] The inner liner 45 includes rubber and seals the space between the tire 41 and the wheel.

[0122] The carcass 46 forms the framework of the tire 41. The carcass 46 includes organic fibers such as polyester, nylon, or rayon, or steel cords, and rubber.

[0123] The bead wires 48 are provided in the bead portions 44. The bead wires 48 receive the tensile force acting on the carcass.

[0124] The belt layer 47 tightens the carcass 46 to increase the rigidity of the tread portion 42. In the example shown in Fig. 4, the tire 41 has the cord-rubber composite 30, which is two belt layers 47. The cord-rubber composite 30 has already been described, so its description will be omitted.

[0125] As described above, according to the tire of the present embodiment, the belt layer 47 uses the cord-rubber composite 30 including the steel cord 10 according to one aspect of the present disclosure.

[0126] Therefore, the thickness of the belt layer 47 can be reduced, the weight of the belt layer 47 and the tire 41 including the belt layer 47 can be reduced, and the rolling resistance of the tire can be reduced.

[0127] Furthermore, the tire 41 including the steel cord 10 according to one aspect of the present disclosure has excellent punching resistance and toughness.

[0128] 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.

[0129] Specific examples will be given below for explanation, but the present invention is not limited to these examples. (Evaluation Method) First, the evaluation method for the steel cords produced in the following experimental examples will be explained. (1) Evaluation of the Cross-Sectional Shape of the Steel Cord The steel cord produced in each experimental example was embedded in a transparent resin, and a sample was cut out so that a surface (cross section) perpendicular to the longitudinal direction of the steel cord was exposed.

[0130] Then, the length and distance of each part in the cross section of the steel cord are measured using a projector.

[0131] Specifically, the thickness T, which is the maximum distance between the first straight portion 111 and the second straight portion 112, is measured.

[0132] The width W of the steel cord 10, which is the maximum distance between the first curved portion 121 and the second curved portion 122, is measured.

[0133] Then, the flattening ratio is calculated from the thickness T and width W using the following formula:

[0134] (Flatness (%)) = T / W × 100 The radius of curvature R of the corner 13 was also measured. In each of the following experimental examples, the radius of curvature was the same for the four corners 131, 132, 133, and 134, so only one numerical value is shown.

[0135] The cross-sectional area is calculated from the measured length and angle of each part. (2) Plunger Test The plunger test is conducted in accordance with JIS D 4230 (1998), except that a cord-rubber composite is used instead of a tire. The cord-rubber composite is positioned so that the main surface 30A (see Figure 3) of the cord-rubber composite faces the plunger, and the plunger test is evaluated. In the plunger test, the plunger depression amount and travel distance just before the plunger penetrates the cord-rubber composite are measured, and the fracture energy is calculated.

[0136] In the plunger test, the fracture energy of a reference cord-rubber composite was measured, which was prepared under the same conditions as in the experimental example, except that a steel cord having a 1 x 2 structure in which two wires with a wire diameter of 0.30 mm were twisted together, which is commonly used in passenger car tires, was used. The reference cord-rubber composite had a thickness of 1.5 mm.

[0137] The fracture energy measured for the reference cord-rubber composite is set as the reference, that is, 100, and the fracture energy for each experimental example is normalized to obtain an index value for the plunger test.

[0138] If the plunger test index value is greater than 100, it is rated as A; if the plunger test index value is greater than 90 but not greater than 100, it is rated as B; and if the plunger test index value is 90 or less, it is rated as C.

[0139] When the plunger test evaluation is A, the cord-rubber composite can be said to have excellent punching resistance, and the evaluation decreases in the order of B, C. When the plunger test evaluation is A, the cord-rubber composite has sufficiently excellent punching resistance. (3) Charpy Impact Test (3-1) Charpy Impact Test A In Charpy Impact Test A, a Charpy impact value is measured by the Charpy impact test using the Charpy impact tester shown in Figure 5.

[0140] 5, the Charpy impact test can be carried out by rotating a hammer 51 having a mass m from an initial position S around a rotation axis 52 and swinging it down on a specimen 50 that has been set in advance on the path of movement of the hammer 51. After destroying the specimen 50, the hammer 51 continues to move along the circumference of a circle centered on the rotation axis 52, and reaches a final position E.

[0141] The sample 50 used was a rectangular parallelepiped sample obtained by cutting the cord-rubber composite prepared in each experimental example so that the cross section perpendicular to the longitudinal direction of the steel cord contained therein was 2 mm square. The sample 50 was processed so that the length along the longitudinal direction of the steel cord was sufficient to obtain a surface that would come into contact with the hammer 51. One steel cord was disposed within the sample 50. In the Charpy impact test A, the sample 50 was rotated from the initial position S and positioned so that the main surface 30A of the cord-rubber composite 30, i.e., the surface including the straight portion 11, which is the flat surface of the steel cord, faced the hammer 51 that was swung down.

[0142] Here, the height of the initial position S relative to the position of the sample 50 is defined as the initial height HS, and the height of the arrival position E relative to the position of the sample 50 is defined as the arrival height HE. In this case, mg (HS-HE), which is the difference between the potential energy of the initial position S and the potential energy of the arrival position E, is the absorbed energy when the sample 50 is broken. The absorbed energy is the Charpy impact value, and a larger value indicates a cord-rubber composite with better impact absorption performance, i.e., toughness.

[0143] The Charpy impact value of the same reference cord-rubber composite as in the plunger test is taken as the standard, i.e., 100, and the Charpy impact value measured in each experimental example is normalized to obtain an index value for Charpy impact test A.

[0144] If the index value of the Charpy impact test A is greater than 100, it is evaluated as A; if the index value of the Charpy impact test A is greater than 90 but not greater than 100, it is evaluated as B; and if the index value of the Charpy impact test A is 90 or less, it is evaluated as C.

[0145] When the evaluation in the Charpy impact test A is A, the cord-rubber composite can be said to have excellent first toughness, which is the resistance to fracture when force is applied to a surface including the straight portion 11, which is a flat surface of the steel cord 10, and the evaluation decreases in the order of B, C. When the evaluation in the Charpy impact test A is A, the cord-rubber composite has sufficiently high first toughness. (3-2) Charpy Impact Test B In the Charpy impact test B, the sample 50 is rotated from the initial position S and positioned so that the side of the cord-rubber composite 30, i.e., the surface including the curved portion 12, which is the side of the steel cord, faces the hammer 51 that is swung down.

[0146] Except for the above points, the Charpy impact test is carried out under the same conditions as in the Charpy impact test A.

[0147] The Charpy impact value in Experimental Example 2 was set to 100, and the impact value measured in each Experimental Example was normalized and shown as an index value for Charpy impact test B. (4) Tensile Load The tensile load is measured in accordance with JIS Z 2241 (2022). (5) Rubber Cracking Evaluation Rubber cracking is evaluated by measuring the lengths of cracks contained in the vicinity of the interface between the steel cord and the rubber in a cross section perpendicular to the longitudinal direction of the steel cord contained in the cord-rubber composite after conducting a plunger test, and then calculating the total value.

[0148] Measurements are performed on two steel cords and the rubber surrounding them, starting from the center of the point where the plunger was pressed during the plunger test, along the arrangement of the steel cords, i.e., along the X axis in Figure 3, with the steel cord closest to the point 15 mm away as the starting point.

[0149] The evaluation result for the same reference cord-rubber composite as in the plunger test is taken as the standard, i.e., 100, and the sum of the lengths measured in each experimental example is normalized and used as an index value for evaluating rubber cracking.

[0150] If the index value of the rubber crack evaluation is 90 or less, the rubber crack evaluation is rated as A; if the index value of the rubber crack evaluation is 90 or more but 100 or less, the rubber crack evaluation is rated as B; and if the index value of the rubber crack evaluation is greater than 100, the rubber crack evaluation is rated as C.

[0151] When the rubber cracking evaluation is A, it can be said that rubber cracking originating from the surface of the steel cord has been sufficiently reduced for the cord-rubber composite, with the evaluation decreasing in the order of B and C. When the rubber cracking evaluation is A, it can be said that rubber cracking originating from the surface of the steel cord has been sufficiently reduced. (6) Weight index The cord-rubber composite produced in each experimental example was cut into a 100 mm square size and the weight was measured. The size here is the size as seen from the main surface 30A of the cord-rubber composite 30 shown in Figure 3.

[0152] The evaluation result of the same reference cord-rubber composite as in the plunger test is set as the standard, that is, 100, and the weight measured in each experimental example is normalized and used as the weight index value.

[0153] If the weight index value is 90 or less, it is evaluated as A; if the weight index value is greater than 90 and less than 100, it is evaluated as B; and if the weight index value is greater than 100, it is evaluated as C.

[0154] When the evaluation is A, it can be said that the weight of the cord-rubber composite has been particularly lightened and a reduction in weight has been achieved, with the evaluation decreasing 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 lightened and a reduction in weight has been achieved. (Experimental Examples) Experimental conditions will be explained below. Experimental Examples 1 to 3 are comparative examples, and Experimental Examples 4 to 11 are working examples. [Experimental Example 1] (Steel Cord) A steel cord base material 21 having a circular cross section is prepared (steel cord base material preparation step), and a steel cord is manufactured by rolling according to the following procedure. As the steel cord base material 21, one having an outer diameter slightly smaller than the width of the intended steel cord is used, taking into account that the width will be slightly increased during rolling compared to before processing, so that the steel cord will have the desired shape and size after rolling.

[0155] The steel cord base material 21 is a high-carbon steel wire having a brass plating film made of copper and zinc as metal components disposed on the surface thereof.

[0156] In this experimental example, the steel cord base material is supplied to the rolling mill 20 shown in Fig. 2 and processed so that the cross section has the flat shape shown in Fig. 1A. At this time, the processing is carried out so that the thickness T has the value shown in Table 1, and so that the corners 13 have an arc shape with a radius of curvature of the value shown in Table 1.

[0157] The rolling device 20 has a pair of first rolling rollers 221 and 222 whose pressure surfaces face each other, and the steel cord base material 21 is supplied between the pair of first rolling rollers 221 and 222 .

[0158] In the rolling mill 20, first, a pair of first rolling rollers 221 and 222 pressurize the steel cord base material 21 from above and below along the Y axis in Fig. 2 (first rolling step). Each of the pair of first rolling rollers 221 and 222 has flat portions on its pressing surface that correspond to the first straight portion 111 and the second straight portion 112 to be formed.

[0159] 2 , a pair of second rolling rollers 231 and 232 are arranged downstream of the pair of first rolling rollers 221 and 222 along the transport path of the steel cord base material 21. Therefore, the steel cord base material 21 after the first rolling step is supplied between the pair of second rolling rollers 231 and 232.

[0160] Then, the steel cord base material 21 after the first rolling step is pressed along the X-axis in Figure 2, i.e., from the left and right, by a pair of second rolling rollers 231 and 232 (second rolling step). The pair of second rolling rollers 231 and 232 have grooves 231A and 232A on their pressing surfaces, respectively. The grooves 231A and 232A have cross-sectional shapes on a plane passing through the central axes of the second rolling rollers 231 and 232 that correspond to the first curved portion 121, the second curved portion 122, and the corners 13.

[0161] The steel cord base material 21 was transported along the arrow B in FIG. 2 and subjected to the first rolling step and the second rolling step along the longitudinal direction, thereby producing the steel cord of this experimental example.

[0162] The obtained steel cord was subjected to the evaluations described above. The evaluation results are shown in Table 1. (Cord-Rubber Composite) The steel cord of this experimental example was embedded in rubber so that the ends were 46 cords / 50 mm, and a cord-rubber composite having the structure shown in Figure 3 was produced.

[0163] 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 a vulcanization accelerator, 8 parts by mass of zinc oxide, and 2 parts by mass of cobalt stearate as an organic cobalt acid salt, relative to 100 parts by mass of the rubber component.

[0164] 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.

[0165] The evaluation results for the cord-rubber composite are shown in Table 1. [Experimental Example 2] A steel cord was manufactured using the same procedure as in Experimental Example 1, except that a steel cord base material having a circular cross section was used and processing was carried out so that the thickness and the radius of curvature of the corners 13 had the values ​​shown in Table 1.

[0166] A cord-rubber composite was produced under the same conditions as in Experimental Example 1, except that the steel cord produced in this Experimental Example was used.

[0167] The evaluation results are shown in Table 1. [Experimental Example 3] A steel cord base material having a circular cross section was used, and a steel cord was produced without processing the steel cord base material.

[0168] A cord-rubber composite was produced under the same conditions as in Experimental Example 1, except that the steel cord of this Experimental Example was used.

[0169] The evaluation results are shown in Table 1. [Experimental Examples 4 to 10] Steel cords were manufactured using the same procedure as in Experimental Example 1, except that a steel cord base material having a circular cross section was used and processing was carried out so that the thickness and the radius of curvature of the corners 13 had the values ​​shown in Table 1. Note that in Experimental Example 8, none of the corners 13 had an arc shape.

[0170] A cord-rubber composite was produced under the same conditions as in Experimental Example 1, except that the steel cord produced in this Experimental Example was used.

[0171] The evaluation results are shown in Table 1. [Experimental Example 11] A steel cord base material having a circular cross section was used. In addition, the steel cord base material 21 had a brass plating film made of metal components of copper, zinc, and cobalt disposed on the surface of a high-carbon steel wire.

[0172] The steel cords were manufactured in the same manner as in Experimental Example 1, except that they were processed so that the thickness and the radius of curvature of the corners 13 had the values ​​shown in Table 1.

[0173] A cord-rubber composite was produced under the same conditions as in Experimental Example 1, except that the steel cord produced in this Experimental Example was used.

[0174] The evaluation results are shown in Table 1.

[0175] According to Table 1, the cross section is flat, the thickness is 0.31 mm or more and 0.55 mm or less, and the cross-sectional area is 0.155 mm ２ 0.250mm or more ２ The cord-rubber composites using the steel cords of Experimental Examples 4 to 11 below had a weight index of A or B. Furthermore, the cord-rubber composites using the steel cords of Experimental Examples 4 to 11 were evaluated as having punching resistance of A. In other words, it can be confirmed that the steel cords of Experimental Examples 4 to 11 are single-wire steel cords with a flat cross section that can reduce weight and improve punching resistance when applied to a cord-rubber composite.

[0176] Furthermore, it can be confirmed that the cord-rubber composites using the steel cords of Experimental Examples 4 to 11 are superior to the cord-rubber composites using the steel cords of Experimental Examples 1 and 2, which have a flat cross section, in Charpy impact test A and Charpy impact test B. In other words, it can be confirmed that the steel cords of Experimental Examples 4 to 11 are also superior in toughness when used as a cord-rubber composite.

[0177] In particular, in Charpy impact test B in which the steel cord receives an impact on the side surface, it can be confirmed that the Charpy impact values ​​of the steel cords of Experimental Examples 4 to 11 are sharply higher than those of the steel cords having flat cross sections of Experimental Examples 1 and 2. That is, it can be confirmed that the steel cords of Experimental Examples 4 to 11 are particularly excellent in second toughness, which is the resistance to fracture when force is applied to a surface including the curved portion 12, which is the side surface of the steel cord 10, compared to the steel cords of Experimental Examples 1 and 2.

[0178] Specifically, as shown in FIG. 6, it can be confirmed that the results of the Charpy impact test B for Experimental Examples 1 and 2, which have a thickness of less than 0.31 mm and a flat cross section, lie on a straight line 61.

[0179] In contrast to this, in Experimental Examples 4 to 11, in which the thickness is 0.31 mm or more and 0.55 mm or less, it can be confirmed that the index values ​​of the Charpy impact test B are significantly higher than the straight line 61 and are distributed within a region 63 that is higher than the straight line 62 that is parallel to the straight line 61. It can also be confirmed that the index value of the Charpy impact test B of Experimental Example 3, in which the cross section is circular rather than flat, is distributed within the region 63.

[0180] Therefore, it can be confirmed that by setting the thickness of the steel cord to 0.31 mm or more and 0.55 mm or less, the characteristics in the Charpy impact test B, i.e., the second toughness, are significantly improved compared to when the thickness is less than 0.31 mm, and characteristics equivalent to those in a case where the cross section is circular can be exhibited. For this reason, it can be said that the tires using the steel cords of Experimental Examples 4 to 11 also have excellent durability when subjected to impacts during cornering, etc.

[0181] REFERENCE SIGNS LIST 10 Steel cord 101 Wire rod 102 Brass plating film 11 Straight portion 111 First straight portion 112 Second straight portion 12 Curved portion 121 First curved portion 122 Second curved portion 13 Corner portion 131 Corner portion 132 Corner portion 133 Corner portion 134 Corner portion A Region R Radius of curvature T Thickness W Width 20 Rolling mill 21 Steel cord base material 221 First rolling roller 222 First rolling roller 231 Second rolling roller 232 Second rolling roller 231A Groove 232A Groove B Arrow 30 Cord-rubber composite 31 Rubber 30A Main surface t1 Rubber thickness t2 Rubber thickness 41 Tire 42 Tread portion 43 Sidewall portion 44 Bead portion 45 Inner liner 46 Carcass 47 Belt layer 48 Bead wire CL Center line 50 Sample 51 Hammer 52 Rotation axis S Initial position E End position HS Initial height HE End height 61 Straight line 62 Straight line 63 Area

Claims

1. A single-wire steel cord, the steel cord having a flat shape in a cross section perpendicular to the longitudinal direction, the thickness of which is shorter than the width, the thickness being 0.31 mm or more and 0.55 mm or less, and the cross-sectional area of ​​the cross section being 0.155 mm ２ 0.250mm or more ２ The steel code is as follows:

2. The steel cord according to claim 1, wherein the flattening ratio, which is the ratio of the thickness to the width in the cross section, is 45% or more and 60% or less.

3. A steel cord according to claim 1 or 2, wherein the width in the cross section is 0.50 mm or more and 0.90 mm or less.

4. A steel cord as claimed in any one of claims 1 to 3, having, in the cross section, a pair of straight portions arranged opposite each other, and a pair of curved portions connecting the pair of straight portions and arranged opposite each other, wherein corners between the straight portions and the curved portions have an arc shape.

5. A steel cord as set forth in claim 4, wherein the radius of curvature of the corners in the cross section is equal to or less than half the width.

6. A steel cord according to any one of claims 1 to 5, having a brass plating film on its surface.

7. A tire comprising the steel cord according to any one of claims 1 to 6.

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