Steel cord, cord-rubber composite, and tire

Abstract

A single-wire steel cord having a brass plating film on a surface thereof, and a cord diameter D of 0.20 mm or more and 0.42 mm or less, having alternately repeated bent portions and non-bent portions along a longitudinal axis, wherein three consecutive bent portions are designated, in order along the longitudinal axis, as a first bent portion, a second bent portion, and a third bent portion, and wherein, when a bent height H is defined as the distance between an apex of the second bent portion and a straight line tangent to the apex of the first bent portion and the apex of the third bent portion, the bent height H and the cord diameter D satisfy the relationship: 2.2≦H / D≦2.8.

Description

[Technical field]

[0001] The present disclosure relates to steel cords, cord-rubber composites, and tires. This application claims priority to Japanese Application No. 2023-027700, filed on February 24, 2023, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 discloses a pneumatic tire. A belt layer is embedded in the tread portion of the pneumatic tire near the outer periphery of a carcass layer. The belt layer includes a plurality of single-filament steel wires that are aligned. The single-filament steel wires have a flat cross-sectional shape. The thickness of the rubber under the grooves in the tread portion is 1.0 mm to 2.0 mm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-058515 A Summary of the Invention

[0004] The steel cord of the present disclosure is a single-wire steel cord having a brass plating film on its surface and a cord diameter D of 0.20 mm or more and 0.42 mm or less, and having alternately repeated bent portions and non-bent portions along the longitudinal axis, wherein three consecutive bent portions are designated, in order along the longitudinal axis, as a first bent portion, a second bent portion, and a third bent portion, and wherein the distance between an apex of the second bent portion and a straight line tangent to the apex of the first bent portion and the apex of the third bent portion is defined as a bent height H, and the bent height H and the cord diameter D satisfy the relationship 2.2≦H / D≦2.8. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view of a steel cord according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is an explanatory diagram of a bent portion, a non-bent portion, a bent height, and a pitch in a steel cord according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 is an explanatory diagram of the coil diameter of a steel cord according to one embodiment of the present disclosure. [Figure 4] FIG. 4 is an explanatory diagram of a method for producing a steel cord according to one embodiment of the present disclosure. [Diagram 5] FIG. 5 is an explanatory diagram of a method for producing a steel cord according to one embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic cross-sectional view of a cord-rubber composite according to one embodiment of the present disclosure. [Figure 7] FIG. 7 is a schematic cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is an explanatory diagram of a method for producing a cord-rubber composite according to one embodiment of the present disclosure. [Figure 9A] FIG. 9A is an explanatory diagram of a configuration example of a leveling device. [Figure 9B] FIG. 9B is an explanatory diagram of a configuration example of a leveling device. [Figure 9C] FIG. 9C is an explanatory diagram of a configuration example of a leveling device. [Figure 10] FIG. 10 is a schematic cross-sectional view of a tire according to one embodiment of the present disclosure. [Figure 11] FIG. 11 is an explanatory diagram of the evaluation method of the Charpy impact test. [Figure 12] FIG. 12 is an explanatory diagram of the evaluation method for the curvature evaluation. [Figure 13] FIG. 13 is an explanatory diagram of a method for evaluating position accuracy. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] In order to improve fuel efficiency of automobiles, there is a demand for lighter tires and reduced rolling resistance. One possible method for reducing the weight of tires is to reduce the thickness of the tire belt layer. Therefore, studies are being conducted on reducing the cord diameter of the steel cord used in the tire belt layer to reduce the diameter of the steel cord.

[0007] However, if the cord diameter of the steel cord is reduced, the steel cord may become more susceptible to breakage when an external force is applied to the steel cord.

[0008] An object of the present disclosure is to provide a steel cord that is less likely to break when an external force is applied.

[0009] [Effects of this disclosure] According to the present disclosure, it is possible to provide a steel cord that is less likely to be damaged when an external force is applied.

[0010] [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.

[0011] (1) A steel cord according to one embodiment of the present disclosure is a single-wire steel cord having a brass plating film on a surface thereof, and a cord diameter D of 0.20 mm or more and 0.42 mm or less. The steel cord has bent portions and non-bent portions alternately repeated along a longitudinal axis, wherein three consecutive bent portions are a first bent portion, a second bent portion, and a third bent portion, respectively, along the longitudinal axis, and wherein a bent height H is defined as the distance between an apex of the second bent portion and a straight line tangent to the apex of the first bent portion and the apex of the third bent portion, and the bent height H and the cord diameter D satisfy the relationship 2.2≦H / D≦2.8.

[0012] The apex of the second bend is the point of the second bend that is farthest from a line tangent to the apex of the first bend and the apex of the third bend. The distance between the apex of the second bend and this straight line is the shortest distance from the apex of the second bend to this straight line. This shortest distance is equal to the length of the perpendicular line from the apex of the second bend to this straight line. In other words, in a triangle connecting the apexes of the first bend, the second bend, and the third bend, when the line segment connecting the apexes of the first bend and the third bend is set as the base of the triangle, the height of the triangle is the distance between the apex of the second bend and this straight line. When the steel cord is placed on a plane such that the surface including the first bent portion, the second bent portion, and the third bent portion is perpendicular to the plane and the first bent portion and the third bent portion are tangent to the plane, the point of the first bent portion that is tangent to the plane is the vertex of the first bent portion, and the point of the third bent portion that is tangent to the plane is the vertex of the third bent portion. The cord diameter D is the average value of two perpendicular diameters in a cross section of a straight portion (eg, a non-bent portion) of the steel cord, the cross section being perpendicular to the straight line.

[0013] When a steel cord is embedded in rubber to create a cord-rubber composite, the copper in the brass plating reacts with the sulfur (S) in the rubber. An adhesive layer containing the reaction product copper sulfide (Cu2S) is produced in the rubber near the interface between the steel cord and the rubber.

[0014] The adhesive layer can improve the initial adhesive performance between the steel cord and the rubber.

[0015] It is believed that the zinc contained in the brass plating film promotes and controls the reaction that forms the adhesive layer.

[0016] By making the cord diameter of the steel cord 0.42 mm or less, when the steel cord is applied to a cord-rubber composite, the thickness of the cord-rubber composite can be made thin. This allows the tire containing the cord-rubber composite to be made lighter. In addition, by making the cord diameter 0.42 mm or less, the shock absorption performance of the tire can be improved, and the ride comfort of the automobile equipped with this tire can be improved.

[0017] A cord diameter of 0.20 mm or more can increase the breaking strength of the steel cord. This reduces the number of steel cords required to satisfy the required properties, such as bending rigidity, when manufacturing a cord-rubber composite or a tire, thereby improving the productivity of the cord-rubber composite or the tire. A cord diameter of 0.20 mm or more can reduce the number of steel cords required to manufacture a cord-rubber composite. This allows the steel cords to be spaced sufficiently apart, allowing a sufficient amount of rubber to be disposed between the steel cords. In addition, the adhesion between the steel cords and the rubber can be improved, improving the durability of the cord-rubber composite or the tire.

[0018] The steel cord has bent and non-bent portions alternately repeated along the longitudinal axis, so that when an external force is applied to the steel cord, the steel cord deforms and can absorb shock. Therefore, when an external force is applied to the steel cord, the steel cord is less likely to break. When the steel cord according to one embodiment of the present disclosure is used in a tire, the shock absorption performance can be improved and the rough road driving performance can be improved.

[0019] By providing bent and non-bent sections so that the ratio of bend height H to cord diameter D (H / D) is 2.2 or more, the durability and shock absorption performance when an external force is applied to the steel cord can be improved. By keeping H / D at 2.8 or less, it is possible to prevent a decrease in breaking strength even when bent sections are provided.

[0020] (2) In the above (1), the coil diameter may be 500 mm or more and 600 mm or less.

[0021] By making the coil diameter 500 mm or more, when the steel cord is applied to a cord-rubber composite, the cord-rubber composite is less likely to bend, which increases the productivity when manufacturing products such as tires that use the cord-rubber composite.

[0022] By having a coil diameter of 600 mm or less, the steel cord is less likely to twist. When the steel cord is applied to a cord-rubber composite, the positioning accuracy of the steel cord within the cord-rubber composite can be improved. This allows the thickness of the rubber required to embed the steel cord, i.e., the rubber to be placed around the steel cord, to be thinner, making the cord-rubber composite or tire lighter.

[0023] (3) In the above (1) or (2), the brass plating film may contain one or more elements selected from cobalt, nickel, tin, iron, and manganese.

[0024] The ionization tendency of cobalt, nickel, tin, iron, and manganese is greater than that of copper. When the brass plating film contains additive elements (one or more elements selected from cobalt, nickel, tin, iron, and manganese) in addition to copper and zinc, the brass plating film can function as a sacrificial anticorrosive film or the composite potential of copper and zinc can be made more noble. When the brass plating film contains additive elements, the corrosion resistance of the steel cord can be improved.

[0025] (4) In any of the above (1) to (3), an average value Hav of the bend heights H for all sets of three consecutive bends and the cord diameter D may satisfy the relationship 2.2≦Hav / D≦2.8.

[0026] This makes it possible to further improve the durability and shock absorbing performance when an external force is applied to the steel cord, and makes it even more difficult for the breaking strength to decrease even when a bent portion is provided.

[0027] (5) A cord-rubber composite according to one embodiment of the present disclosure includes a first belt layer. The first belt layer has rubber and a steel cord according to any one of (1) to (4) above, and the steel cord is embedded in the rubber.

[0028] The steel cord in the first belt layer of the cord-rubber composite according to one embodiment of the present disclosure has a small diameter and is not easily broken when an external force is applied.

[0029] In the first belt layer, the thickness of the rubber required for embedding the steel cords can be reduced, and therefore the thickness of the first belt layer and the cord-rubber composite including the first belt layer can be reduced, making the first belt layer and the cord-rubber composite lighter.

[0030] The first belt layer and the cord-rubber composite including the first belt layer are excellent in durability and shock absorbing performance when an external force is applied.

[0031] (6) In the above (5), the number of ends of the first belt layer may be 30 / 50 mm or more and 60 / 50 mm or less.

[0032] By having the ends of the first belt layer be 30 / 50 mm or more, the gaps between the steel cords are small, allowing the steel cords to be arranged at a high density. This improves the punching resistance of the cord-rubber composite, and particularly improves the durability of products such as tires that contain the cord-rubber composite. The punching resistance of the cord-rubber composite is a property that prevents a foreign object from penetrating the cord-rubber composite if the foreign object pierces the cord-rubber composite.

[0033] By setting the ends of the first belt layer to 60 cords / 50 mm or less, the number of supply devices for supplying steel cords during production of the first belt layer or the cord-rubber composite can be reduced, thereby improving productivity.

[0034] (7) The cord-rubber composite according to (5) or (6) above may have a plurality of laminated belt layers, and the first belt layer may be disposed on at least one surface of the cord-rubber composite.

[0035] By disposing the first belt layer on at least one surface of the cord-rubber composite, it is possible to improve durability and impact absorption performance when an external force is applied to the surface of the cord-rubber composite.

[0036] (8) The cord-rubber composite according to any one of (5) to (7) above may have a plurality of laminated belt layers, and the belt layers other than the first belt layer may include a straight steel cord.

[0037] Since the belt layers other than the first belt layer have straight steel cords, i.e., steel cords without bends, the steel cords embedded in the first belt layer are unlikely to deform beyond the elastic deformation region, and therefore the cord-rubber composite can be configured to be repeatedly deformed.

[0038] (9) A tire according to one embodiment of the present disclosure includes the steel cord according to any one of (1) to (4) above, or the cord-rubber composite according to any one of (5) to (8) above.

[0039] The steel cord included in the tire according to the embodiment of the present disclosure has a small diameter and is not easily broken when an external force is applied. The cord-rubber composite included in the tire according to the embodiment of the present disclosure has excellent durability and impact absorption performance when an external force is applied.

[0040] For this reason, the tire according to one embodiment of the present disclosure can be made lighter, and has excellent durability and shock absorbing performance when traveling on rough roads.

[0041] [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. 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.

[0042] In this specification, the names of the members may be described with the numbers 1, 2, 3, etc. added to them. For example, the names are the first belt layer, the second belt layer, the first roll, the second roll, and the third roll. The numbers 1, 2, and 3 added to the belt layers and rolls are merely used to distinguish the members and to prevent confusion during the description, and do not indicate the arrangement or priority. When there is no risk of confusion or when referring to them collectively, they may be referred to as belt layers or rolls.

[0043] [Steel cord] Hereinafter, the steel cord according to the present embodiment will be described with reference to Figs. 1, 2 and 3. <1> Steel cord structure FIG. 1 is a schematic cross-sectional view of a straight portion of a steel cord 10, taken perpendicular to the longitudinal axis (axis parallel to the straight line).

[0044] As shown in Fig. 1, the steel cord 10 is a single-wire steel cord. A single-wire steel cord is not a twisted wire in which multiple wires are twisted together, but is composed of only one wire. The steel cord 10 does not need to be twisted along the longitudinal axis. That is, the steel cord 10 may be a straight steel cord.

[0045] The cross section of the steel cord 10 may be circular. The circular shape may be a perfect circle, but is not limited to a perfect circle, and may be a shape similar to a perfect circle. The cross section of the steel cord 10 may be an ellipse, a shape similar to an ellipse, or a racetrack shape.

[0046] The steel cord 10 has a surface with a brass plating film 12. Specifically, the steel cord 10 has a wire 11 and the brass plating film 12 covering the wire 11. (wire rod) The wire 11 is, for example, a steel wire. The wire 11 may be a high carbon steel wire. (Brass plating film) The brass plating film 12 contains copper (Cu) and zinc (Zn). As shown in FIG.

[0047] When the steel cord 10 is embedded in rubber to form a cord-rubber composite, the copper contained in the brass plating film 12 reacts with the sulfur (S) contained in the rubber. The reaction product in this reaction is copper sulfide (CuS), and an adhesive layer containing copper sulfide is generated in the rubber near the interface between the steel cord 10 and the rubber.

[0048] The adhesive layer can improve the initial adhesive performance between the steel cord 10 and rubber. The initial adhesive performance between the steel cord 10 and rubber means the adhesive performance between the steel cord 10 and rubber immediately after vulcanization during the production of a cord-rubber composite or a tire including the cord-rubber composite.

[0049] It is believed that the zinc contained in the brass plating film 12 promotes and controls the reaction that forms the adhesive layer.

[0050] The brass plating film 12 may contain elements other than copper and zinc. The brass plating film 12 may contain one or more elements selected from cobalt (Co), nickel (Ni), tin (Sn), iron (Fe), and manganese (Mn).

[0051] The ionization tendency of cobalt, nickel, tin, iron, and manganese is greater than that of copper. When the brass plating film 12 contains an additive element (one or more elements selected from cobalt, nickel, tin, iron, and manganese) in addition to copper and zinc, the brass plating film 12 can function as a sacrificial anticorrosive film or can make the composite potential of copper and zinc more noble. Therefore, when the brass plating film 12 contains an additive element, the corrosion resistance of the steel cord 10 can be improved.

[0052] (Bending and non-bending) FIG. 2 is a view of the steel cord 10 viewed from a direction perpendicular to a plane including three consecutive bent portions 21. That is, FIG. 2 is a side view of the steel cord 10. In FIG. 2, the Y axis is the longitudinal axis of the steel cord 10. The bent portion 21A is the first bent portion, the bent portion 21B is the second bent portion, and the bent portion 21C is the third bent portion. The apex of the bent portion 21A (first bent portion) and the apex of the bent portion 21C (third bent portion) are in contact with the straight line 20. In FIG. 2, of the other three consecutive bent portions 21 shown, the apex of every other bent portion 21 is also in contact with the straight line 20. The non-bent portion may be linear. A part of the non-bent portion does not have to be linear. The steel cord 10 has bent portions 21 and non-bent portions 22 alternately and repeatedly along the longitudinal axis. Since the steel cord 10 has bent portions 21 and non-bent portions 22 alternately and repeatedly along the longitudinal axis, the steel cord 10 deforms when an external force is applied to the steel cord 10, and can absorb shock. Therefore, the steel cord 10 is less likely to break when an external force is applied. Furthermore, when the steel cord 10 is used in a tire, it is possible to improve shock absorption performance and improve rough road driving performance.

[0053] The distance between the straight line 20 and the apex of the bent portion 21 (second bent portion) away from the straight line 20 is defined as the bent height H. For example, in FIG. 2, the distance between the straight line 20 and the apex of the bent portion 21B is the bent height H.

[0054] The distance between the straight line 20 and the apex of the second bend is measured using a vernier caliper. In the steel cord 10, the bend height H may be constant.

[0055] The bent height H and the cord diameter D satisfy the relationship 2.2≦H / D≦2.8.

[0056] By providing the bent portions 21 and the non-bent portions 22 so that H / D is 2.2 or more, it is possible to improve the impact absorption performance when an external force is applied to the steel cord 10. By keeping H / D at 2.8 or less, even if the bent portions 21 are provided, it is possible to prevent a decrease in breaking strength.

[0057] The bent height H and the cord diameter D may satisfy the relationship of 2.3≦H / D≦2.75, or may satisfy the relationship of 2.4≦H / D≦2.74. The average value Hav of the bend heights H for all sets of three consecutive bends and the cord diameter D may satisfy 2.2≦Hav / D≦2.8, 2.3≦Hav / D≦2.75, or 2.4≦Hav / D≦2.74. This can further improve the impact absorption performance when an external force is applied to the steel cord 10, and can make it more difficult to reduce the breaking strength even when bends 21 are provided. Furthermore, the bend height H and the cord diameter D for all sets of three consecutive bends may satisfy 2.2≦H / D≦2.8, 2.3≦H / D≦2.75, or 2.4≦H / D≦2.74. This further improves the impact absorption performance when an external force is applied to the steel cord 10, and makes it even more difficult to reduce the breaking strength even when bends 21 are provided.

[0058] The pitch P is the interval at which the bent portions 21 are provided. The pitch P can be selected according to the cord diameter D of the steel cord 10 and the required impact absorption performance, and is not particularly limited. The pitch P may be 2.0 mm or more and 10.0 mm or less, or 4.0 mm or more and 5.5 mm or less. When the pitch P is 10.0 mm or less, a sufficient number of bent portions 21 can be formed per unit length, and the impact absorption performance of the steel cord 10 can be improved. When the pitch P is 2.0 mm or more, the number of bent portions 21 per unit length does not become excessively large, and productivity can be improved. The pitch P is the distance between bent portions 21 of the same shape. In other words, the pitch P is the length from a bent portion to the next adjacent bent portion along the longitudinal axis of the steel cord 10. More specifically, the pitch P is the length from the apex of a bent portion to the apex of the next adjacent bent portion along the longitudinal axis of the steel cord 10. For example, in FIG. 2, the pitch P is the length from the apex of bent portion 21A to the apex of bent portion 21C. When the length from a bent portion to the next adjacent bent portion along the longitudinal axis of the steel cord 10 is not constant, the lengths between all bent portions and the next adjacent bent portion are measured, and the average value of these lengths is the pitch P. The pitch P is measured using a vernier caliper.

[0059] <2> Steel Cord Properties <2-1> Cord diameter The steel cord 10 has a cord diameter D of 0.20 mm or more and 0.42 mm or less. The cord diameter D may be 0.21 mm or more and 0.40 mm or less, 0.22 mm or more and 0.38 mm or less, or 0.22 mm or more and 0.37 mm or less.

[0060] By having the cord diameter D be 0.42 mm or less, when the steel cord is used in a cord-rubber composite, the thickness of the cord-rubber composite can be made thin. This allows the tire containing the cord-rubber composite to be made lighter. By having the cord diameter D be 0.42 mm or less, when the steel cord is used in a tire, the impact absorption performance of the tire can be improved, improving the ride comfort of a car equipped with this tire.

[0061] The cord diameter D of 0.20 mm or more increases the breaking strength of the steel cord 10. This allows the number of steel cords required to satisfy the required properties such as bending rigidity when manufacturing a cord-rubber composite or a tire to be reduced, thereby increasing productivity. The cord diameter D of 0.20 mm or more reduces the number of steel cords required when manufacturing a cord-rubber composite or a tire. Since there is sufficient space between the steel cords, a sufficient amount of rubber can be disposed between the steel cords. This increases the adhesion between the steel cords and the rubber, thereby increasing the durability of the cord-rubber composite or the tire. Diameters D10A and D10B, which are perpendicular to each other, are measured in any cross section perpendicular to a straight portion (e.g., a non-bent portion) of the steel cord 10. The average value of diameters D10A and D10B is the cord diameter D. Diameters D10A and D10B are measured with a micrometer.

[0062] <2-2> Coil diameter The steel cord 10 has a cord diameter D of 0.42 mm or less. When a sheet-shaped cord-rubber composite is formed using such a small-diameter steel cord, the cord-rubber composite may be curved. When forming a sheet-shaped cord-rubber composite, a plurality of steel cords are aligned under a certain tension and embedded in rubber. Before the rubber is sufficiently cured, the position of the steel cord may shift, causing the position of the steel cord to vary within the cord-rubber composite. For this reason, in order to sufficiently embed the steel cord in the rubber, it is necessary to thicken the rubber disposed above and below the steel cord. Therefore, even if the steel cord has a small diameter, it may not be possible to thin the cord-rubber composite.

[0063] As described above, when the steel cord has a small diameter, the cord-rubber composite is curved, and the positional accuracy of the steel cord in the cord-rubber composite in the rubber thickness direction may decrease. Conventionally, the coil diameter has not been noted as a cause of the curvature of the cord-rubber composite and the decrease in the positional accuracy of the steel cord. However, the inventors of the present invention conducted an investigation and found that the coil diameter affects the curvature of the cord-rubber composite and the decrease in the positional accuracy of the steel cord in the rubber thickness direction.

[0064] The steel cord 10 may have a coil diameter of 500 mm or more and 600 mm or less.

[0065] By making the coil diameter 500 mm or more, when the steel cord 10 is applied to a cord-rubber composite, the cord-rubber composite can be made less likely to bend. Use of this cord-rubber composite can increase productivity in manufacturing products such as tires.

[0066] A coil diameter of 600 mm or less makes the steel cord 10 less likely to twist. When the steel cord 10 is applied to a cord-rubber composite, the positioning accuracy of the steel cord 10 in the cord-rubber composite is improved. The thickness of the rubber required to embed the steel cord 10, i.e., the rubber to be placed around the steel cord 10, is reduced, making it possible to make the cord-rubber composite or tire lighter.

[0067] As shown in FIG. 3, the coil diameter D31 is the diameter of the annular portion 31. In FIG. 3, the annular portion 31 is formed naturally when the steel cord 10 is cut, without applying any force to the steel cord 10. When measuring the coil diameter D31, the cut steel cord 10 is placed on a horizontal test stand 30. When the annular portion 31 is formed on the test stand 30, diameters D31A and D31B that are perpendicular to each other are measured with a vernier caliper. The average value of the diameters D31A and D31B is the coil diameter D31. When measuring the coil diameter D31, cut pieces of the steel cord 10 are repeatedly formed until the annular portion 31 that contacts the horizontal test stand 30 is formed.

[0068] <2-3> Breaking strength The breaking strength of the steel cord 10 may be 2500 MPa or more and 4500 MPa or less, or may be 2900 MPa or more and 4200 MPa or less.

[0069] The higher the breaking strength of the steel cord 10, the less likely the steel cord 10 is to break when pulled. When the steel cord 10 has a breaking strength of 2500 MPa or more, the number of steel cords required to satisfy the characteristics required of the cord-rubber composite, such as bending rigidity, can be reduced when the steel cord 10 is applied to a cord-rubber composite. This allows the cord-rubber composite or products such as tires to be made lighter. When the steel cord 10 has a breaking strength of 4500 MPa or less, the productivity of manufacturing the steel cord 10 can be increased.

[0070] <3> Steel cord manufacturing method The method for producing the steel cord is not particularly limited. For example, a steel cord can be produced by drawing a cord base material having a brass plating film on its surface using a die and a roll, and then forming a bent portion.

[0071] For example, as shown in Fig. 4, cord base material 40 being transported along the block arrow is passed through dies 411 and dies 412 and wire-drawn. Next, cord base material 40 that has been wire-drawn by the dies is pressed by rolls 42, whereby the cord diameter is further drawn to a desired cord diameter.

[0072] The rolls 42 may be arranged as shown in Fig. 4. In Fig. 4, an upper roll 421A, an upper roll 421B, and an upper roll 421C are arranged above the cord base material 40 to be drawn, and a lower roll 422A and a lower roll 422B are arranged below the cord base material 40. The upper roll 421A, the upper roll 421B, and the upper roll 421C press the cord base material 40 from above, and the lower roll 422A and the lower roll 422B press the cord base material 40 from below.

[0073] The number and arrangement of the dies are not particularly limited. The shape, number and arrangement of the rolls constituting the roll 42 are not particularly limited. A preliminary test may be performed, and the number and arrangement of the dies may be selected according to the cord diameter and coil diameter of the steel cord produced in the preliminary test, or the shape, number and arrangement of the rolls may be selected. In addition, processing conditions such as the pressure applied to the cord base material may be selected according to the cord diameter and coil diameter of the steel cord produced in the preliminary test. For example, a preliminary test may be performed to determine processing conditions for wire drawing. In addition, by performing a preliminary test, the relationship between the cord diameter and coil diameter of a steel cord having a desired bending height and pitch after wire drawing can be obtained. Based on the results of the preliminary test, processing conditions for wire drawing can be selected so that the cord diameter and coil diameter of the steel cord having a bent portion are the desired values.

[0074] The wire drawing conditions may be changed depending on the shape of the groove of the roll, for example, the shape of the groove of the roll having a constant curvature in a cross section perpendicular to the longitudinal axis of the groove. The upper roll and the lower roll may be disposed adjacent to each other along the transport path of the cord base material 40. The shape of the grooves of the upper roll and the lower roll may have a constant curvature in a cross section perpendicular to the longitudinal axis of the groove, and the radius of curvature of the grooves of the upper roll and the lower roll may be different. The upper limit of the difference between these radii of curvature may be 30% of the cord diameter of the steel cord. By appropriately selecting the shape of the grooves of the upper roll and the lower roll, it is possible to improve the controllability of parameters such as the coil diameter of the steel cord.

[0075] For example, multiple preforms 51 are arranged as shown in Fig. 5. A steel cord 50 after wire drawing is transported along the block arrows and passed between the preforms 51 to form a bent portion. The shape of the bent portion and the length of the non-bent portion can be changed by changing the arrangement, size, or shape of the preforms 51. The preforms 51 have, for example, a pin shape (cylindrical shape) or a gear shape. After the bent portions are formed, the steel cord 50 may be transported while being sandwiched between transport rolls so that the orientation (inclination) of the surface including the three consecutive bent portions of the steel cord 50 does not change, and then wound onto a reel. The steel cord 50 may be wound onto a reel so that this surface is aligned with the surface of a reel body. The reel body is the shaft portion around which the steel cord 50 is wound. The steel cord may be wound while moving the reel along the central axis of the body and changing the position on the reel body around which the steel cord 50 is wound.

[0076] [Cord-rubber composite] FIG. 6 shows a side view of the cord-rubber composite 60. FIG. 7 shows a schematic cross-sectional view taken along line VII-VII in FIG. 6. In FIG. 7, the cord diameter of the steel cord 10 is made smaller than that in FIG. 6 in order to make the bent portion 21 easier to understand. In FIGS. 6 and 7, the X-axis is an axis along the width direction of the cord-rubber composite 60 and the belt layer. The Y-axis is the longitudinal axis of the cord-rubber composite 60 and the belt layer (the longitudinal axis of the steel cord 10). The Z-axis is an axis along the thickness direction of the cord-rubber composite 60 and the belt layer. The XZ plane is perpendicular to the longitudinal axis of the steel cord 10.

[0077] 6, the cord-rubber composite 60 includes a first belt layer 601. The first belt layer 601 has a rubber 61 and a steel cord 10 embedded in the rubber 61.

[0078] The steel cord 10 included in the first belt layer 601 has a small diameter and is not easily damaged when an external force is applied. In the first belt layer 601, the thickness of the rubber required to embed the steel cord 10 can be made thin. Therefore, the thickness of the first belt layer 601 and the cord-rubber composite 60 including the first belt layer 601 can be made thin, and the cord-rubber composite 60 can be made lighter. The first belt layer 601 and the cord-rubber composite 60 including the first belt layer 601 are excellent in durability and shock absorbing performance when an external force is applied.

[0079] [1] Materials contained in the first belt layer [1-1] Steel cord The first belt layer 601 may include a plurality of steel cords 10. Each steel cord 10 may be arranged such that its longitudinal axis is parallel to the Y axis in Fig. 6. In Fig. 6, the plurality of steel cords 10 are arranged along the X axis.

[0080] The steel cords 10 may be arranged in parallel.

[0081] 7, the steel cords 10 may be arranged so that a plane including three consecutive bent portions 21 is aligned along the width direction of the first belt layer 601. By arranging the steel cords 10 in this manner, the thickness of the cord-rubber composite 60 and the thickness T60 of the first belt layer 601 can be reduced.

[0082] Since the steel cord 10 has a bent portion 21 and a non-bent portion 22, the distance between the steel cords 10 may be set in consideration of the bent height H so that adjacent steel cords 10 do not come into contact with each other. Details of the steel cord 10 have already been described, so a description thereof will be omitted here.

[0083] [1-2] Rubber The rubber 61 of the cord-rubber composite 60 can be produced by molding a rubber composition and vulcanizing it as necessary.

[0084] The composition of the rubber 61 is not particularly limited. The composition of the rubber 61 can be selected depending on the application and required properties of a product, such as a tire, to which the cord-rubber composite 60 is applied. The rubber 61 may contain a rubber component, sulfur, and a vulcanization accelerator.

[0085] The rubber component may contain 60% by mass or more, 70% by mass or more, or 100% by mass of one or more rubbers selected from natural rubber (NR) and isoprene rubber (IR).

[0086] When the proportion of one or more rubbers selected from natural rubber and isoprene rubber in the rubber component is 60% by mass or more, the breaking strength of the cord-rubber composite 60 or the tire can be increased.

[0087] The rubber component used together with one or more rubbers selected from natural rubber and isoprene rubber is, for example, one or more rubbers 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).

[0088] There is no particular limitation on the method for impregnating the rubber 61 with sulfur. For example, the rubber 61 can be impregnated with sulfur using a vulcanizing agent commonly used in the rubber industry.

[0089] There is no particular limitation on the sulfur content of the rubber 61. The sulfur content may be 5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0090] When the sulfur content is 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 10 and the rubber 61 can be increased. When the sulfur content is 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 61, and blooming can be made less likely to occur.

[0091] The vulcanization accelerator is not particularly limited. For example, the vulcanization accelerator is a sulfenamide accelerator such as N,N'-dicyclohexyl-2-benzothiazolylsulfenamide. The vulcanization accelerator may be a thiazole accelerator such as 2-mercaptobenzothiazole, or a thiuram accelerator such as tetrabenzylthiuram disulfide.

[0092] The rubber composition used in the cord-rubber composite 60 can be produced by kneading raw materials such as rubber components, and then heating and extruding the mixture.

[0093] The rubber 61 may contain at least one of elemental cobalt and a compound containing cobalt.

[0094] The cobalt-containing compound is, for example, an organic cobalt acid and an inorganic cobalt acid.

[0095] The organic acid cobalt is, for example, one or more selected from cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, and cobalt tall oil acid. The organic acid cobalt may be a composite salt in which a part of the organic acid is replaced with boric acid.

[0096] The inorganic acid cobalt is, for example, one or more selected from cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt phosphate, and cobalt chromate.

[0097] The rubber 61 may contain cobalt organic acid. When the rubber 61 contains cobalt organic acid, the initial adhesive performance between the steel cord and the rubber can be particularly improved.

[0098] According to the study of the present inventors, by adding cobalt to rubber, the proportion of copper sulfide (CuS) in the adhesive layer can be increased, and the adhesive strength between the steel cord and rubber can be increased. This tendency is more pronounced when cobalt is added using an organic acid cobalt. For this reason, the rubber 61 may contain cobalt, particularly an organic acid cobalt. In this case, a cord-rubber composite 60 or a tire having excellent durability can be obtained. The rubber 61 may contain any optional components other than the above-mentioned rubber component, sulfur, vulcanization accelerator, and cobalt. The rubber 61 may contain well-known rubber additives such as reinforcing agents such as carbon black and silica, wax, or antioxidants.

[0099] [2] Characteristics of the first belt layer The number of steel cords 10 included in the first belt layer 601 is not particularly limited. The number of steel cords 10 can be selected according to the properties required for the cord-rubber composite 60 or the tire including the cord-rubber composite 60. The number of steel cords per 50 mm width of the first belt layer 601 in a cross section perpendicular to the longitudinal axis of the steel cord of the first belt layer 601 is defined as the ends. That is, the ends are the number of steel cords counted in a cross section perpendicular to the longitudinal axis of the steel cord of the first belt layer 60 and converted into the number of steel cords per 50 mm width. In this specification, the unit of ends is "pieces / 50 mm". The ends of the first belt layer 601 may be 30 pieces / 50 mm or more and 60 pieces / 50 mm or less. The ends of the first belt layer 601 may be 36 pieces / 50 mm or more and 60 pieces / 50 mm or less, or 40 pieces / 50 mm or more and 60 pieces / 50 mm or less.

[0100] By having the ends of the first belt layer 601 be 30 pieces / 50 mm or more, the gaps between the steel cords 10 included in the first belt layer 601 become small, and the steel cords can be arranged at high density. This improves the punching resistance of the cord-rubber composite 60. In addition, the durability of products such as tires including the cord-rubber composite 60 can be particularly improved.

[0101] By setting the ends of the first belt layer 601 to 60 / 50 mm or less, the number of supplying devices for supplying steel cords during production of the first belt layer 601 and the cord-rubber composite body 60 can be reduced, thereby improving productivity. When the cord-rubber composite 60 has a plurality of belt layers, the ends of each belt layer other than the first belt layer 601 may be within the above range.

[0102] [3] Structure of cord-rubber composite The cord-rubber composite 60 may be composed of only the first belt layer 601. The belt layer may be only the first belt layer 601, which is one layer.

[0103] The cord-rubber composite 60 may include multiple belt layers. In Fig. 6, the cord-rubber composite 60 includes a second belt layer 602 in addition to a first belt layer 601. The belt layer is a layer including rubber and multiple steel cords embedded in the rubber, similar to the first belt layer 601.

[0104] When the cord-rubber composite 60 has a plurality of belt layers, the plurality of belt layers may be laminated.

[0105] A belt layer other than the first belt layer 601, for example the second belt layer 602, may have a rubber 63 and a steel cord 62 embedded in the rubber 63. In the belt layer other than the first belt layer 601, the steel cord 62 may be a steel cord without a bent portion, that is, a straight steel cord. By having the straight steel cord in the second belt layer 602 (a belt layer other than the first belt layer 601), the steel cord 10 embedded in the first belt layer 601 is unlikely to deform beyond the elastic deformation region. Therefore, the cord-rubber composite 60 can be configured to be repeatedly deformed. Except for the point that the steel cord 62 is a straight steel cord, the steel cord 10 and the rubber 61 used in the first belt layer 601 can be used in the second belt layer 602. Therefore, the description of the steel cord 62 and the rubber 63 of the second belt layer 602 will be omitted. The first belt layer 601 and the second belt layer 602 may be the same or different in cord diameter of the steel cord, material of the steel cord, end and rubber composition. The cord-rubber composite 60 may have one second belt layer 602 or a plurality of second belt layers 602.

[0106] When the cord-rubber composite 60 has a plurality of laminated belt layers, the first belt layer 601 may be disposed on at least one surface of the cord-rubber composite 60. That is, the first belt layer 601 may be disposed on the outermost surface of the cord-rubber composite 60. In FIG. 6, the first belt layer 601 is exposed on a surface 60A of the cord-rubber composite 60.

[0107] The first belt layer 601 includes steel cords 10 including bent portions and non-bent portions. The steel cords 10 are bent so as to turn back at each bent portion. When the steel cords 10 are viewed along the Z axis (along the thickness direction of the belt layer), the steel cords 10 have a zigzag shape (see, for example, FIG. 7). The steel cords 10 included in the first belt layer 601 deform when an external force is applied, and can absorb shock. The first belt layer 601 is excellent in durability and shock absorption performance when an external force is applied. Therefore, by disposing the first belt layer 601 on at least one surface of the cord-rubber composite 60, it is possible to improve the durability and shock absorption performance when an external force is applied to that surface.

[0108] [4] Manufacturing method of cord-rubber composite The manufacturing method of the cord-rubber composite 60 may include a reel setting step, a drawing step, an arrangement step, and an embedding step. The manufacturing method of the cord-rubber composite 60 will be described with reference to Figures 8, 9A, 9B, and 9C. (Reel installation process) In the reel setting process, multiple reels 82 are set on a steel cord supplying device 81 (see FIG. 8). The number of reels 82 can be set based on the number of steel cords 10 to be embedded in the rubber of the belt layer of the cord-rubber composite 60. A steel cord 10 is wound on each reel 82. The steel cord supplying device 81 controls the rotation of each reel 82 and supplies the steel cord 10 from each reel 82. The steel cord supplying device 81 is sometimes called a reel supply. Since FIG. 8 is a schematic diagram, only two reels 82 are shown. The number of reels 82 may be equal to the number of steel cords 10 to be embedded in the belt layer of the cord-rubber composite 60. (Pulling out process) In the unwinding process, the steel cord 10 is unwound from each reel 82 by a steel cord supplying device 81 and transported to a position where the arrangement process is carried out.

[0109] (Arrangement process) In the arranging step, a plurality of steel cords 10 unwound from a reel 82 are arranged in a line in a cross section perpendicular to the longitudinal axis of the steel cords 10. In the arranging step, for example, the plurality of steel cords 10 are arranged in a line by an arranging device 83.

[0110] There is no particular limitation on the configuration of the arranging device 83. In order to arrange the steel cords 10 in a line, the arranging device 83 may have a guide plate 831. The guide plate 831 is provided with a groove through which the steel cords 10 pass.

[0111] In the arranging step, the multiple steel cords 10 may be arranged so that a surface including three consecutive bent portions of each steel cord 10 is aligned along the width direction of the cord-rubber composite body 60.

[0112] There is no particular limitation on the method of arranging the steel cords 10 so that the surface including the three consecutive bent portions is aligned along the width direction of the cord-rubber composite 60. The arranging device 83 may have a leveling device 832, for example, as shown in Fig. 8. The leveling device 832 can arrange the steel cords 10 on the conveying path so that the above-mentioned surface is aligned along the width direction of the cord-rubber composite 60.

[0113] The configuration of the leveling device 832 is not particularly limited. The leveling device 832 may have an arrangement roll 90 including three rolls, as shown in FIG. 9A. In FIG. 9A, the three rolls are a first roll 91, a second roll 92, and a third roll 93. By hanging and passing the steel cord 10 on the first roll 91, the second roll 92, and the third roll 93, the surface including three consecutive bent portions can be made horizontal. In FIG. 9A, the steel cord 10 is transported along the block arrow. The location where the arrangement roll 90 is arranged is not particularly limited. The arrangement roll 90 may be arranged downstream of the guide plate 831 on the transport path of the steel cord 10.

[0114] The leveling device 832 is not limited to the form of the arrangement roll 90 shown in FIG. 9A. The leveling device 832 may have a leveling roll 94 as shown in FIG. 9B. The leveling roll 94 has an upper roll 941 and a lower roll 942. In FIG. 9B, the steel cord 10 is transported in the direction of the block arrow. The upper roll 941 and the lower roll 942 may be arranged at a position along the transport path of the steel cord 10 so as to sandwich the steel cord 10 from above and below. By sandwiching the steel cord 10 between the upper roll 941 and the lower roll 942, the steel cord 10 can be arranged so that the surface including the three continuous bent portions is along the width direction of the cord-rubber composite 60. The upper roll 941 and the lower roll 942 may sandwich the steel cord 10 to an extent that the steel cord 10 is not plastically deformed. Multiple pairs of the upper roll 941 and the lower roll 942 may be arranged along the transport path of the steel cord 10.

[0115] The leveling device 832 may have a die 95 as shown in FIG. 9C. The die 95 is provided with a through hole 951 through which the steel cord 10 passes. The through hole 951 allows the steel cord 10 to be arranged so that a surface including three consecutive bends is aligned along the width direction of the cord-rubber composite 60. The shape and size of the through hole 951 can be selected so that the steel cord 10 is not damaged. The height H951 of the through hole 951 may be constant along the conveying path. The height H951 may vary along the conveying path of the steel cord 10. In FIG. 9C, the height H951 is smaller downstream than upstream along the conveying path of the steel cord 10.

[0116] Although several configuration examples are shown for the leveling device 832, the leveling device 832 is not limited to these configurations. The leveling device 832 may include multiple devices, such as an alignment roll 90 (FIG. 9A) and a leveling roll 94 (FIG. 9B).

[0117] 8, the arranging device 83 may have a grooved roll 833 as necessary. When the arranging device 83 has the grooved roll 833, the grooved roll 833 can further correct the position of the steel cord 10 in the arranging step to align the steel cord 10.

[0118] (burying process) In the embedding step, a plurality of steel cords 10 are embedded in rubber. For example, a plurality of steel cords 10 are placed in rubber 84 by a calendar roll 85, and a calendaring process is performed to produce a cord-rubber composite 60. When the cord-rubber composite 60 has a plurality of belt layers, the steps from the reel installation step to the embedding step may be performed for each belt layer.

[0119] 〔tire〕 A tire 100 according to the present embodiment will be described with reference to FIG.

[0120] The tire 100 includes a steel cord 10 .

[0121] Fig. 10 is a schematic cross-sectional view perpendicular to the outer periphery of tire 100 (schematic cross-sectional view perpendicular to the rotational direction of tire 100). Fig. 10 shows only the left side of the center line (CL) of tire 100. Tire 100 has the same structure on the right side of the center line, with the center line as the axis of symmetry.

[0122] In FIG. 10, a tire 100 includes a tread portion 101, a sidewall portion 102, and a bead portion 103.

[0123] The tread portion 101 is a portion that comes into contact with the road surface. The bead portions 103 are provided at positions closer to the axis of rotation of the tire 100 than the tread portion 101. The bead portions 103 are portions that come into contact with the rim of a vehicle wheel. The sidewall portions 102 connect the tread portion 101 and the bead portions 103. When the tread portion 101 receives an impact from the road surface, the sidewall portions 102 elastically deform to absorb the impact.

[0124] In FIG. 10, the tire 100 includes an inner liner 104, a carcass 105, a first belt layer 106, a second belt layer 107, and bead wires 108.

[0125] The inner liner 104 is made of rubber and seals the space between the tire 100 and the wheel.

[0126] The carcass 105 forms the framework of the tire 100. The carcass 105 is made of organic fibers or steel cords, and rubber. The organic fibers are, for example, polyester, nylon, or rayon.

[0127] The bead wire 108 is provided in the bead portion 103. The bead wire 108 receives a tensile force acting on the carcass 105.

[0128] The tire 100 may include multiple belt layers. In Fig. 10, the tire 100 has two belt layers (a first belt layer 106 and a second belt layer 107). The belt layer 106 and the belt layer 107 tighten the carcass 105 to increase the rigidity of the tread portion 101.

[0129] Each of the first belt layer 106 and the second belt layer 107 has a plurality of steel cords and rubber. The plurality of steel cords are arranged in parallel. The plurality of steel cords are arranged in a row in a cross section perpendicular to the longitudinal axis of the first belt layer 106 or the second belt layer 107. The first belt layer 106 may be the same as the first belt layer 601 in FIG. 6. The second belt layer 107 may be the same as the second belt layer 602 in FIG. 6. In FIG. 10, the first belt layer 106 and the second belt layer 107 form a cord-rubber composite.

[0130] When the tire 100 includes multiple belt layers, the first belt layer 106 may be disposed on at least one surface of the cord-rubber composite. That is, the first belt layer 106 may be disposed on the outermost surface of the cord-rubber composite. Here, the first belt layer 106 is the same as the first belt layer 601. When the tire 100 includes a plurality of belt layers, the first belt layer 106 may be disposed closer to the tread portion 101 than the other belt layers. By disposing the first belt layer 106 closer to the tread portion 101 than the other belt layers, the durability and shock absorbing performance of the tire 100 can be improved. Here, the first belt layer 106 is the same as the first belt layer 601. The other belt layers are the same as the second belt layer 602.

[0131] The steel cords included in the tire 100 are thin and not easily damaged when subjected to an external force, so the tire 100 is lightweight and has excellent durability and shock absorption performance when traveling on rough roads.

[0132] [Example] The present invention will be described below with reference to specific examples, but is not limited to these examples. (Evaluation method) <1> Steel cord evaluation method The evaluation method of the steel cord will be described. 1-1 Cord diameter The steel cord 10 is embedded in a transparent resin, and a sample is cut out so that a cross section perpendicular to the straight line of a straight portion (for example, a non-bent portion) of the steel cord 10 is exposed. Diameters D10A and D10B that are perpendicular to each other are measured in a cross section perpendicular to the straight line of a straight portion of the steel cord 10 (see FIG. 1). The average value of diameters D10A and D10B is the cord diameter D of the steel cord 10.

[0133] 1-2 Charpy Index The Charpy impact value is measured by a Charpy impact test using the Charpy impact tester shown in Figure 11. The Charpy index is calculated from the Charpy impact value.

[0134] 11, in the Charpy impact test, a hammer 111 having a mass m is rotated from an initial position S about a rotation axis 112, and is swung down on a specimen 110 that has been set in advance on the moving path of the hammer 111. After destroying the specimen 110, the hammer 111 continues to move in the direction of rotation and reaches a final position E.

[0135] The height of the initial position S based on the position of the sample 110 is the initial height HS, and the height of the destination position E based on the position of the sample 110 is the destination height HE. In this case, the difference mg(HS-HE) between the potential energy of the initial position S and the potential energy of the destination position E is the absorbed energy when the sample 110 is broken. This absorbed energy is the Charpy impact value. The higher the Charpy impact value, the more excellent the impact absorbing performance of the steel cord.

[0136] The Charpy index is expressed with the Charpy impact value of the reference steel cord set to 100. The reference steel cord is a straight steel cord and has no bends. The constituent materials and cord diameter D of the reference steel cord are the same as those of the steel cords used in the Charpy impact test. For example, in the case of Experimental Examples 1 to 11, the Charpy index is shown with the Charpy impact value of a reference steel cord under the same environment as the experimental examples taken as 100. The cord diameter D of this reference steel cord is 0.37 mm, and the material constituting the reference steel cord is the same as the material constituting the steel cords of Experimental Examples 1 to 11.

[0137] 1-3 Breaking strength, strength reduction rate A load is applied along the longitudinal axis of the steel cord using an autograph (Shimadzu Corporation, model: AGS-H 10kN). The breaking strength is calculated from the load applied to the steel cord at the time of breakage and the cross-sectional area of ​​the steel cord calculated from the cord diameter. The calculated breaking strength is compared with the breaking strength of a standard steel cord, and the rate of decrease in breaking strength is the strength decrease rate.

[0138] When the breaking strength of the reference steel cord is SA and the breaking strength of the steel cord of each experimental example is SB, the strength reduction rate is calculated by the following formula (1). Strength reduction rate (%)=(SA-SB)÷SA×100 (1)

[0139] Verdict: 1-4 If the Charpy index is 102 or more and the strength reduction rate is 4.6% or less, the steel code is rated as A. If the Charpy index is greater than 100 and the strength reduction rate is 5% or less, and the steel code does not meet the requirements of A, the steel code is rated as B. If the Charpy index is 100 or less or the strength reduction rate exceeds 5%, the steel code is rated as C. When the rating is A, the steel cord is particularly resistant to breakage when an external force is applied. The resistance of the steel cord decreases in the order of ratings B, C. When the rating is A or B, the steel cord is judged to be resistant to breakage when an external force is applied.

[0140] 1-5 Coil diameter As shown in Fig. 3, the cut steel cord 10 is placed on a horizontal test stand 30. When the annular portion 31 is formed on the test stand 30, the diameters D31A and D31B of the annular portion 31 that are perpendicular to each other are measured. The average value of the diameters D31A and D31B is the coil diameter D31. When measuring the coil diameter D31, cut pieces of the steel cord 10 are repeatedly formed until the annular portion 31 that is in contact with the horizontal test stand 30 is formed.

[0141] 2. Evaluation method for cord-rubber composites 2-1. Bendability evaluation The cord-rubber composite 60 produced in the experimental example is cut to a size of 1 m x 1 m.

[0142] As shown in Fig. 12, the first belt layer 601, which is the cord-rubber composite 60 cut to the above size, is placed on the upper surface 120A of the test stand 120. The maximum height H60 is measured with a ruler in a state where no external force is applied to the first belt layer 601. The maximum height H is the distance between the upper surface 120A and the point of the cord-rubber composite 60 that is the furthest from the upper surface 120A.

[0143] If the maximum height H60 is less than 5 mm, the flexibility of the cord-rubber composite is rated as A; if it is 5 mm or more but less than 20 mm, the flexibility of the cord-rubber composite is rated as B; and if it is 20 mm or more, the flexibility of the cord-rubber composite is rated as C. When the evaluation is A, the cord-rubber composite is particularly resistant to bending. The resistance to bending decreases in the order of B, C. When the evaluation is A or B, the cord-rubber composite is judged to be resistant to bending.

[0144] 《2-2》Position accuracy As shown in Fig. 13, the first belt layer 601, which is the cord-rubber composite 60, is placed on a flat test stand 130. The steel cords 10A, 10B, 10C, 10D, and 10E are arranged in succession, and the first belt layer 601 is placed so that the cross section where these steel cords are exposed is the measurement area. This cross section is perpendicular to the longitudinal axis of the steel cords 10.

[0145] Next, a weight (not shown) is placed on the surface 131 of the cord-rubber composite 60 opposite to the surface in contact with the test stand 130. The cord-rubber composite 60 is subjected to a load of 0.05 kg / mm 2 The weight is pressed against the test stand 130 with a load of 0.15 MPa. The weight is plate-shaped, and the area of ​​the face of the weight facing the cord-rubber composite 60 is the same as the area of ​​the face 131 of the cord-rubber composite 60.

[0146] The cord-rubber composite 60 is cut so that the surface in contact with the test stand 130 and the surface 131 in contact with the weight are both square.

[0147] Of the steel cords 10 included in the cord-rubber composite 60, the steel cord 10A is disposed at an end of the cord-rubber composite 60. A reference line L parallel to the upper surface of the test stand 130 is set so as to pass through the center of the steel cord 10A.

[0148] Next, for each of the steel cords 10B, 10C, 10D, and 10E, the variation width along the thickness direction of the cord-rubber composite body 60 is measured with a vernier caliper.

[0149] The variation width of each steel cord 10 is the distance between the reference line L and the center of each steel cord 10 along the thickness direction of the cord-rubber composite 60. In Fig. 13, the center of each steel cord 10 is indicated by a black dot. The variation width of steel cord 10B is L10B, the variation width of steel cord 10C is L10C, the variation width of steel cord 10D is L10D, and the variation width of steel cord 10E is L10E.

[0150] The average value of the variation width L10B, the variation width L10C, the variation width L10D, and the variation width L10E is the variation width of the position of the steel cord 10.

[0151] If the variation in the position of the steel cord 10 is less than 0.3 mm, the position accuracy is evaluated as A; if it is 0.3 mm or more and less than 0.5 mm, the position accuracy is evaluated as B; and if it is 0.5 mm or more, the position accuracy is evaluated as C.

[0152] When the evaluation is A, the variation in the position of the steel cord 10 is small and the positional accuracy is the highest. The variation in the position increases and the positional accuracy decreases in the order of evaluations B, C. When the evaluation is A or B, it is determined that the positional accuracy of the steel cord 10 in the cord-rubber composite is sufficiently high.

[0153] The manufacturing conditions of the steel cord in each experimental example are explained below. Experimental Examples 2, 3, 4, 6 to 11, 13, 14, and 15 are working examples. Experimental Examples 1, 5, 12, 16, 17, and 18 are comparative examples. [Experimental Example 1] (Steel cord manufacturing) The steel cord 50 is manufactured by the apparatus shown in FIGS.

[0154] A steel cord base material 40 is prepared. A brass plating layer is formed on the surface of the cord base material 40. The cord base material 40 is subjected to wire drawing to manufacture a steel cord 50.

[0155] As shown in Fig. 4, in the wire drawing process, the cord base material 40 is first passed through dies 411 and dies 412 to gradually reduce the cord diameter. The surface of the roll 42 that comes into contact with the steel cord 50 is provided with grooves, and the cord base material 40 is processed by passing between the rolls 42. In this manner, the steel cord 50 is manufactured from the cord base material 40.

[0156] The number of rolls 42, the shape of the grooves, and the pressure are selected so that after the bend is formed in the steel cord 50, the steel cord 50 has the cord diameter D and coil diameter shown in Table 1. Here, the grooves provided in the rolls 42 have a shape with a constant curvature in a cross section perpendicular to the longitudinal axis of the groove.

[0157] 5, the bent portion is formed by passing the drawn steel cord 50 between a plurality of preforms 51. The shape, size, and arrangement of the plurality of preforms 51 are selected so that the bent height H and pitch P of the steel cord 50 are the values ​​shown in Table 1.

[0158] In all experimental examples, including this one, the bending height H and pitch P of the steel cord 10 were constant within the steel cord 10 and coincided with the values ​​shown in Table 1. Table 1 shows the evaluation results for the steel cords.

[0159] (Manufacturing of cord-rubber composites) A plurality of steel cords 10 are embedded in rubber so as to obtain the ends shown in Table 1, to produce a cord-rubber composite 60.

[0160] Specifically, the cord-rubber composite manufacturing apparatus shown in FIG. 8 is used for manufacturing.

[0161] The cord-rubber composite is manufactured by carrying out the following reel setting step, drawing step, arranging step, and embedding step.

[0162] In the reel setting process, a plurality of reels 82 are set in a steel cord supplying device 81. The number of reels 82 is set according to the number of steel cords 10 to be embedded in the rubber of the belt layer. Each reel 82 has a steel cord 10 wound thereon.

[0163] In the unwinding process, the steel cord 10 is unwound from each reel 82 by a steel cord supplying device 81 and conveyed to an arrangement device 83 .

[0164] In the arranging step, a plurality of steel cords 10 unwound from a reel 82 are arranged in a line in a cross section perpendicular to the longitudinal axis of the steel cords 10.

[0165] In the arranging step, a plurality of steel cords 10 are arranged in a line by a guide plate 831 having a groove through which the steel cords 10 pass.

[0166] In the arranging step, the steel cords 10 are arranged so that a plane including three consecutive bent portions of each steel cord 10 is horizontal.

[0167] As shown in Fig. 9A, a leveling device 832 is disposed on the transport path of the steel cord 10. The leveling device 832 is an arrangement roll 90 including three rolls. In Fig. 9A, the three rolls are a first roll 91, a second roll 92, and a third roll 93. The steel cord 10 is wound around and passed through the first roll 91, the second roll 92, and the third roll 93.

[0168] In the arranging step, the position of the steel cord 10 is further corrected and arranged by a grooved roll 833 .

[0169] In the embedding step, a plurality of steel cords 10 are placed in rubber 84 by a calender roll 85, and calendering is performed to embed the plurality of steel cords 10 in the rubber.

[0170] The rubber is produced from a rubber composition. The rubber composition includes a rubber component and additives. The rubber composition includes 100 parts by mass of natural rubber as the rubber component. The rubber composition includes, 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 acid cobalt, relative to 100 parts by mass of the rubber component.

[0171] A cord-rubber composite 60 is produced in advance using the steel cord 10 of this experimental example, and the variation in the position of the steel cord 10 is measured. A preset constant may be added to the variation in the position of the steel cord 10 to determine the rubber thickness. By setting the rubber thickness in this way, the steel cord 10 can be embedded in the rubber.

[0172] When manufacturing the cord-rubber composite 60 of this experimental example, the manufacturing conditions are selected so that the thickness of the rubber placed above and below the steel cord 10 will be a rubber thickness that has been determined in advance.

[0173] The thickness of the rubber placed above the steel cord 10 corresponds to thickness T611 in Figure 6, and the thickness of the rubber placed below the steel cord 10 corresponds to thickness T612 in Figure 6. The evaluation results for the cord-rubber composite 60 are shown in Table 1.

[0174] [Experimental Examples 2 to 8] When manufacturing the steel cord, in each experimental example, processing is performed so that the cord diameter D, coil diameter, bending height H, and pitch P become the values ​​shown in Table 1. The cord diameter D and coil diameter are adjusted by the size of the dies 411 and 412 and the pressure of the roll 42. The bending height H and pitch P are adjusted by the shape, size, and arrangement of the preform 51. Except for the above points, in Experimental Examples 2 to 8, the steel cords and cord-rubber composites were produced under the same conditions as in Experimental Example 1. The evaluation results are shown in Table 1.

[0175] [Experimental Example 9] A steel cord base material 40 is used. The surface of the cord base material 40 is plated with copper, cobalt, and zinc to form a brass plating layer. When manufacturing the steel cord, the cord is processed in each experimental example so that the cord diameter D, coil diameter, bending height H, and pitch P have the values ​​shown in Table 1. The cord diameter D, coil diameter, bending height H, and pitch P are adjusted in the same manner as in experimental examples 2 to 8. Other than the above, in Experimental Example 9, the steel cord and the cord-rubber composite were produced under the same conditions as in Experimental Example 1. The evaluation results are shown in Table 1.

[0176] [Experimental Examples 10 and 11] When manufacturing the steel cord, in each experimental example, processing is performed so that the cord diameter D, coil diameter, bending height H, and pitch P have the values ​​shown in Table 1. The cord diameter D, coil diameter, bending height H, and pitch P are adjusted in the same manner as in experimental examples 2 to 8. In Experimental Examples 10 and 11, except for the above points, steel cords and cord-rubber composites were produced and evaluated under the same conditions as in Experimental Example 1. The evaluation results are shown in Table 1.

[0177] [Experimental Examples 12 to 18] When manufacturing the steel cord, in each experimental example, the cord diameter D, coil diameter, bending height H, and pitch P are processed so as to have the values ​​shown in Table 1. The cord diameter D, coil diameter, bending height H, and pitch P are adjusted in the same manner as in experimental examples 2 to 8.

[0178] Except for the above points, in Experimental Examples 12 to 18, the steel cords and cord-rubber composites were produced under the same conditions as in Experimental Example 1. The evaluation results are shown in Table 1.

[0179] [Table 1] According to Table 1, the steel cords of Experimental Examples 2, 3, 4, 6 to 11, and 13 to 15 have a cord diameter of 0.20 mm or more and 0.42 mm or less, and a ratio of bend height H to cord diameter D (H / D) of 2.2 or more and 2.8 or less. The steel cords of these Experimental Examples have a Charpy index exceeding 100 and a strength reduction rate of 5% or less. The steel cords of these Experimental Examples are less likely to break when an external force is applied. [Explanation of symbols]

[0180] 10 Steel Cord 11 Wire rod 11A side 12 Brass plating film D10 Cord diameter D10A, D10B diameter 20 straight line 21, 21A, 21B, 21C bent part 22 Non-bending part H bending height Pitch 30 Test bench 31 Circular section D31 Coil diameter D31A, D31B diameter 40 Cord Base Material 411, 412 Dice 42 rolls 421A, 421B, 421C Upper Roll 422A, 422B Lower Roll 50 Steel Cord 51 Preform 60 Cord-rubber composite 60A Surface 601 First belt layer 602 Second Belt Layer 61, 63 Rubber 62 Steel Cord T611, T612 Thickness T60 Thickness 81 Steel cord supply device 82 Reels 83 Array device 831 Guide plate 832 Leveling device 833 Grooved Roll 84 Rubber 85 Calendar Roll 90 Array Roll 91 Roll 1 92 Roll 2 93 3rd Roll 94 Leveling Roll 941 Upper Roll 942 Lower Roll 95 Dice 951 Through hole H951 Height CL Center Line 100 Tires 101 Tread 102 Sidewall 103 Bead part 104 Inner Liner 105 Carcass 106 First Belt Layer 107 Second Belt Layer 108 Bead wire 110 Samples 111 Hammer 112 Rotational Axis S initial position E Arrived position HS Initial height HE Reach height 120 Test bench 120A top H120 Maximum height 130 Test bench 10A, 10B, 10C, 10D, 10E Steel cord 131 sides L reference line L10B, L10C, L10D, L10E Variation range

Claims

1. A single-wire steel cord, It has a brass plating film on the surface, The cord diameter D is 0.20 mm or more and 0.42 mm or less, The flexible member has alternating bent and non-bent portions along a longitudinal axis, The three consecutive bent portions are successively designated as a first bent portion, a second bent portion, and a third bent portion along the longitudinal axis; When the distance between the apex of the second bent portion and a straight line tangent to the apex of the first bent portion and the apex of the third bent portion is defined as a bent height H, the bend height H and the cord diameter D satisfy the relationship 2.2≦H / D≦2.8, A steel cord having a coil diameter of 500 mm or more and 600 mm or less.

2. 2. The steel cord according to claim 1, wherein the brass plating film contains one or more elements selected from cobalt, nickel, tin, iron, and manganese.

3. 3. The steel cord according to claim 1, wherein an average value Hav of the bend heights H for all sets of three consecutive bends and the cord diameter D satisfy a relationship of 2.2≦Hav / D≦2.

8.

4. A first belt layer is included. The first belt layer includes rubber and the steel cord according to claim 1 or 2, The steel cord is embedded in the rubber to form a cord-rubber composite.

5. The cord-rubber composite material according to claim 4, wherein the number of ends of the first belt layer is 30 / 50 mm or more and 60 / 50 mm or less.

6. The belt has a plurality of laminated belt layers, The cord-rubber composite according to claim 4, wherein the first belt layer is disposed on at least one surface of the cord-rubber composite.

7. The belt has a plurality of laminated belt layers, The cord-rubber composite body according to claim 4, wherein the belt layers other than the first belt layer include straight steel cords.

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

Images