Steel cord for tire belt ply reinforcement

Abstract

The present invention relates to a steel cord for reinforcing a tire belt ply, and includes a cord formed by periodically twisting n wires, the n wires being crimped by rolling, at least one of the n wires being compressed into a non-circular shape, and when n is an odd number, the cross section of one of the n wires is made circular and the cross section of (n-1) wires is made non-circular by rolling, and when n is an even number, the cross sections of two of the n wires are made circular and the cross section of (n-2) wires is made non-circular by rolling.

Description

[Technical Field]

[0001] The present invention relates to a steel cord for reinforcing a tire belt ply, and more specifically to a steel cord for reinforcing a tire belt ply, which is obtained by rolling a cord formed by periodically twisting n wires to produce wires having circular cross sections and non-circular cross sections, but the number of wires having circular cross sections varies depending on the number of wires. [Background technology]

[0002] Among various types of reinforcing materials used to reinforce various rubber products, including vehicle tires and industrial belts, steel cords for tire reinforcement have excellent properties such as strength, modulus, heat resistance, fatigue resistance, and rubber adhesion. Due to these properties, steel cords are widely used as tire reinforcing materials, as components suitable for satisfying the functionality required of tires, and their usage is increasing day by day.

[0003] In addition, due to the drastically tightened regulations on CO2 emissions worldwide, the shift to electric vehicles has been accelerating recently. In the case of electric vehicles, the rolling resistance of tires consumes a large amount of energy, so there is a need to develop a steel cord that can reduce the rolling resistance of tires.

[0004] Furthermore, in order to reduce CO2 emissions, tire life must be improved, and as a result, there is a demand for steel cords that can improve tire durability, fatigue properties, etc. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above-mentioned problems, and more specifically, an object of the present invention is to provide a steel cord for reinforcing a tire belt ply, which is produced by rolling a cord formed by periodically twisting n element wires to produce element wires having circular cross sections and non-circular cross sections, and in which the number of element wires having circular cross sections varies depending on the number of element wires. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the steel cord for tire belt ply reinforcement of the present invention includes a cord formed by periodically twisting n wires, wherein the n wires are crimped by rolling, and at least one of the n wires is compressed into a non-circular shape by rolling, and when n is an odd number, the cross section of one of the n wires becomes circular and the cross sections of (n-1) wires become non-circular by rolling, and when n is an even number, the cross sections of two of the n wires become circular and the cross sections of (n-2) wires become non-circular by rolling.

[0007] In the steel cord for tire belt ply reinforcement of the present invention for solving the above-mentioned problems, when a wire that can be rolled to have a circular cross section is used as a first wire and a wire that can be rolled to have a non-circular cross section is used as a second wire, the ratio of the minor axis of the second wire to the diameter of the first wire is 0.70 to 0.98.

[0008] The number (n) of wires in the steel cord for reinforcing a tire belt ply of the present invention, which solves the above-mentioned problems, is 3 to 9.

[0009] In order to solve the above-mentioned problems, the diameter of the first wire of the steel cord for reinforcing a tire belt ply of the present invention is 0.1 mm to 0.6 mm.

[0010] In the steel cord for reinforcing a tire belt ply of the present invention for solving the above-mentioned problems, when the diameter of the wire before being rolled is d (mm), a first strength (NT: normal tensile) is defined as 3,200-2,000 x d (mm) ± 200 (MPa), a second strength (HT: high tensile) is defined as 3,500-2,000 x d (mm) ± 200 (MPa), a third strength (ST: super tensile) is defined as 3,850-2,000 x d (mm) ± 200 (MPa), a fourth strength (UT: ultra tensile) is defined as 4,200-2,000 x d (mm) ± 200 (MPa), and a fifth strength (MT: mega tensile) is defined as 5,000-5,000 x d (mm) ± 200 (MPa). The tensile strength of the wire before rolling may be any one of the second strength, the third strength, the fourth strength, and the fifth strength.

[0011] In the steel cord for reinforcing a tire belt ply of the present invention, which solves the above-mentioned problems, the wires having a tensile strength of the nth strength before rolling can be processed to have a tensile strength of the (n-1)th strength by rolling. [Effects of the Invention]

[0012] The present invention relates to a steel cord for reinforcing a tire belt ply, and has the advantage that by manufacturing the steel cord through rolling processing, it is possible to increase the rigidity in the axial direction of the tire rotation, thereby improving the durability and fatigue properties of the steel cord.

[0013] In addition, the present invention has the advantage that the durability of the steel cord can be prevented from being reduced due to the penetration of moisture or salt by improving the permeability of the rubber through the rolling process, and the present invention has the advantage that the initial adhesive strength of the steel cord can be improved by improving the permeability of the rubber.

[0014] In addition, the present invention has the advantage that by manufacturing the steel cord through rolling, the thickness of the rubber can be made thin when the steel cord is embedded in the rubber sheet. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram showing a steel cord having two circular cross sections that is rolled according to an embodiment of the present invention, where n is an even number. [Figure 2] FIG. 1 shows a steel cord having a circular cross section and being rolled according to an embodiment of the present invention, where n is an odd number. [Figure 3] FIG. 10 is a diagram showing a minor axis according to an embodiment of the present invention. [Figure 4] 10 is a diagram showing a first strand and a second strand when n is 6 according to an embodiment of the present invention. [Figure 5] This figure shows the conditions for Examples 1, 2, and 3 according to the present invention, where n is an odd number, under which the value of the minor axis (d2) of the second wire relative to the diameter (d1) of the first wire is within the range of 0.70 to 0.98, and the conditions for Comparative Examples 1, 2, and 3 under which the value of the minor axis (d2) of the second wire relative to the diameter (d1) of the first wire is outside the range of 0.70 to 0.98. [Figure 6] FIG. 6 is a diagram showing a comparison of the initial adhesive strength between Comparative Examples 1, 2, and 3 in FIG. 5 and Examples 1, 2, and 3. [Figure 7] FIG. 6 is a diagram showing a comparison of fatigue cycles between Comparative Examples 1, 2, and 3 in FIG. 5 and Examples 1, 2, and 3. [Figure 8] This figure shows the conditions for Examples 1, 2, and 3 according to the present invention, where n is an even number, under which the value of the minor axis (d2) of the second wire relative to the diameter (d1) of the first wire is within the range of 0.70 to 0.98, and the conditions for Comparative Examples 1, 2, and 3 under which the value of the minor axis (d2) of the second wire relative to the diameter (d1) of the first wire is outside the range of 0.70 to 0.98. [Figure 9] FIG. 9 is a diagram showing a comparison of the initial adhesive strength between Comparative Examples 1, 2, and 3 and Examples 1, 2, and 3 of FIG. 8. [Figure 10] 9 is a diagram showing a comparison of fatigue cycles between Comparative Examples 1, 2, and 3 of FIG. 8 and Examples 1, 2, and 3. [Figure 11] This figure shows the linearity quality of Examples 1 and 2, in which the ratio of the minor diameter (d2) of the second wire to the diameter (d1) of the first wire is within the range of 0.70 to 0.98, and the linearity quality of Comparative Examples 1 and 2, in which the ratio of the minor diameter (d2) of the second wire to the diameter (d1) of the first wire is outside the range of 0.70 to 0.98, according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] This specification explains the principles of the present invention and discloses embodiments so as to clarify the scope of the present invention and enable those skilled in the art to practice the invention. The disclosed embodiments may be embodied in various forms.

[0017] The terms "comprise" or "also comprise" as used in various embodiments of the present invention indicate the presence of the disclosed feature, operation, or component, etc., and do not limit the presence of one or more additional features, operations, or components, etc. Furthermore, in various embodiments of the present invention, the terms "comprise" or "have" as specifying the presence of a specified feature, number, step, operation, component, part, or combination thereof, and should not be understood as precluding the possible presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0018] When a component is referred to as being "connected" or "coupled" to another component, it should be understood that the component may be directly connected or coupled to the other component, but that there may be other components between the component and the other component. On the other hand, when a component is referred to as being "directly connected" or "directly coupled" to another component, it should be understood that there are no other components between the component and the other component.

[0019] As used herein, terms such as "first" and "second" may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another.

[0020] The present invention relates to a steel cord for reinforcing a tire belt ply, which is obtained by rolling a cord formed by periodically twisting n wires to produce wires having circular cross sections and non-circular cross sections, and the number of wires having circular cross sections varies depending on the number of wires.

[0021] The steel cord according to the embodiment of the present invention is used for reinforcing the belt ply of an automobile tire, and may also be used for other parts as needed. Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0022] 1 and 2, a steel cord for reinforcing a tire belt ply according to an embodiment of the present invention includes a cord 110 formed by periodically twisting n wires 120.

[0023] The cord 110 is formed by periodically twisting n wires 120, and the number (n) of the wires 120 is preferably 3 to 9. The steel cord for reinforcing a tire belt ply according to an embodiment of the present invention may be manufactured by rolling the cord 110 formed by periodically twisting n wires 120.

[0024] Before being rolled, the n strands 120 may be arranged inside a virtual first circle 130 where the n strands 120 are in contact with each other. As shown in Figures 1 and 2, after the n strands 120 are arranged inside the virtual first circle 130 where the n strands 120 are in contact with each other, the rolling process is carried out.

[0025] When the n number of wires 120 are crimped by rolling, the wires 120 are crimped by the rolling, and at least one of the n number of wires 120 is compressed into a non-circular shape.

[0026] As shown in Figure 1, when n is an even number (n = 4, 6, 8, 10), two of the n wires 120 may have circular cross sections and (n-2) of the n wires may have non-circular cross sections as a result of rolling. As shown in Figure 2, when n is an odd number (n = 3, 5, 7, 9, 11), one of the n wires 120 may have a circular cross section and (n-1) of the n wires may have a non-circular cross section as a result of rolling. Here, a non-circular cross section also refers to a symmetrical or asymmetrical elliptical shape.

[0027] Steel cords for reinforcing the belt ply of automobile tires must be uniformly spaced and free of overlapping cords in order to reduce tire rolling resistance, and it is therefore desirable for the cords to extend uniformly in one direction.

[0028] As described above, before being rolled, the n strands 120 may be arranged inside the imaginary first circle 130, but there may be various directions in which they can be rolled from outside the imaginary first circle 130. However, if the rolling is performed in the wrong direction during the rolling process, there is a risk that the direction of the cord may be shifted and the cord may not be uniformly elongated in a certain direction.

[0029] In the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention, when the cord 110 formed by periodically twisting n wires 120 is rolled, the direction of the rolling is set to a specified direction, so that the cord 110 can be made to extend uniformly in a certain direction.

[0030] Specifically, according to an embodiment of the present invention, when n is an even number (n=4, 6, 8, 10), the rolling direction is determined so that two of the n wires 120 maintain a circular cross section while the other wires have non-circular cross sections; when n is an odd number (n=3, 5, 7, 9, 11), the rolling direction is determined so that one of the n wires 120 maintains a circular cross section while the other wires have non-circular cross sections.

[0031] If the rolling direction is determined by such a method, it becomes possible to produce cords that extend uniformly in a certain direction, and the cords can be spaced uniformly while preventing overlapping of the cords.

[0032] According to an embodiment of the present invention, the rolling strength during rolling can be adjusted by the ratio of the diameter of the wire with a circular cross section to the minor axis of the non-circular cross section. When a wire whose cross section becomes circular through rolling is defined as the first wire 121 and a wire whose cross section becomes non-circular through rolling is defined as the second wire 122, the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is preferably 0.70 to 0.98 (0.70≦d2 / d1≦0.98).

[0033] Here, the minor axis (d2) of the second strand 122 is also the length shown in Figures 1 and 2. However, if the non-circular cross section is not elliptical as shown in Figure 3, the minor axis (d2) of the second strand 122 may be defined as the shortest distance among the lengths extending from one side to the other side passing through the center of a circle having the major axis (d3) of the non-circular cross section as its diameter.

[0034] If the ratio of the minor axis (d2) of the second strands 122 to the diameter (d1) of the first strands 121 is too small (if the d2 / d1 ratio is less than 0.70), the rolling strength will be excessively strong, which may result in wire breakage. Also, if the second strands 122 are compressed too much, there will be insufficient space for the rubber to penetrate, which may reduce the rubber penetration rate and result in reduced fatigue properties.

[0035] On the other hand, if the ratio of the minor axis (d2) of the second strands 122 to the diameter (d1) of the first strands 121 is too large (if the d2 / d1 value is greater than 0.98), the rolling effect cannot be expected, the gaps between the strands become larger, the possibility of moisture penetration increases, and there is a concern that durability and fatigue characteristics will be reduced.

[0036] 4 is a photograph showing that in an embodiment of the present invention, when n is an even number and the value of n is 6, two wires have circular cross sections and four wires have non-circular cross sections. Below, the effects of the present invention on initial adhesive strength and fatigue cycles will be explained by comparing an embodiment of the present invention with a comparative example.

[0037] Figures 5 to 10 compare the initial adhesive strength and fatigue cycle between the examples of the present invention and the comparative examples based on the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121.

[0038] Figure 5 shows the conditions for Comparative Examples 1, 2, and 3 where the value of the minor axis (d2) of the second wire 122 relative to the diameter (d1) of the first wire 121 is outside the range of 0.70 to 0.98 when n is an odd number, and the conditions for Examples 1, 2, and 3 where the value of the minor axis (d2) of the second wire 122 relative to the diameter (d1) of the first wire 121 is within the range of 0.70 to 0.98.

[0039] FIG. 6 is a diagram showing a comparison of the initial adhesive strength between Comparative Examples 1, 2, and 3 in FIG. 5 and Examples 1, 2, and 3, and FIG. 7 is a diagram showing a comparison of the fatigue cycle between Comparative Examples 1, 2, and 3 in FIG. 5 and Examples 1, 2, and 3.

[0040] FIG. 8 shows the conditions for Comparative Examples 1, 2, and 3 where the minor axis (d2) value of the second wire 122 relative to the diameter (d1) of the first wire 121 is outside the range of 0.70 to 0.98 when n is an even number, and the conditions for Examples 1, 2, and 3 where the minor axis (d2) value of the second wire 122 relative to the diameter (d1) of the first wire 121 is within the range of 0.70 to 0.98.

[0041] FIG. 9 is a diagram showing a comparison of the initial adhesive strength between Comparative Examples 1, 2, and 3 in FIG. 8 and Examples 1, 2, and 3, and FIG. 10 is a diagram showing a comparison of the fatigue cycle between Comparative Examples 1, 2, and 3 in FIG. 8 and Examples 1, 2, and 3.

[0042] 5 to 10, in Comparative Example 2, the ratio of the minor axis (d2) of the second strands 122 to the diameter (d1) of the first strands 121 is less than 0.70, which reduces the initial adhesive strength and fatigue characteristics. This indicates that if the second strands 122 are compressed too much, there is a lack of space for the rubber to penetrate, which reduces the rubber permeability and may reduce fatigue characteristics.

[0043] Furthermore, in Figures 5 to 10, when the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is less than 0.70, as in Comparative Example 2, there is a problem that wire breakage may occur during the manufacturing process.

[0044] Referring to Figures 5 to 10, regarding Comparative Examples 1 and 3, it can be seen that the value of the minor axis (d2) of the second strand 122 relative to the diameter (d1) of the first strand 121 is greater than 0.98, so that the initial adhesive strength and fatigue characteristics are reduced, and the rigidity coefficient of the major axis (d3) does not increase.

[0045] If the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is greater than 0.98, the effect of rolling cannot be expected, and if the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is greater than 0.98, it becomes impossible to increase rigidity in the direction of the rotation axis, and it becomes impossible to improve durability either.

[0046] In addition, if the ratio of the minor axis (d2) of the second wires 122 to the diameter (d1) of the first wires 121 is greater than 0.98, the gaps between the wires become wider, increasing the possibility of moisture penetration and reducing durability and fatigue characteristics. Also, if the ratio of the minor axis (d2) of the second wires 122 to the diameter (d1) of the first wires 121 is greater than 0.98, it becomes difficult to expect the effect of reducing the rubber thickness when embedding a steel cord in a rubber sheet.

[0047] Referring to Figures 5 to 10, according to an embodiment of the present invention, if the rolling process is carried out so that the ratio of the minor diameter (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is 0.70 to 0.98, the initial adhesive strength is improved, fatigue properties are improved, and the rigidity coefficient of the major diameter (d3) is also increased compared to Comparative Examples 1, 2, and 3.

[0048] According to an embodiment of the present invention, if the rolling process is performed so that the ratio of the minor axis (d2) of the second wires 122 to the diameter (d1) of the first wires 121 is 0.70 to 0.98, the initial adhesive strength of the steel cord can be improved while preventing a decrease in durability of the steel cord due to the penetration of moisture or salt by improving the permeability of rubber.

[0049] Furthermore, according to an embodiment of the present invention, if the rolling process is carried out so that the ratio of the minor axis (d2) of the second wires 122 to the diameter (d1) of the first wires 121 is 0.70 to 0.98, the durability and fatigue characteristics of the steel cord can be improved by increasing the rigidity in the direction of the tire's rotation axis (increasing the major axis (d3) rigidity coefficient), and when the steel cord is embedded in a rubber sheet, the rubber thickness can be made thinner without reducing strength compared to a circular steel cord.

[0050] Therefore, according to an embodiment of the present invention, it is preferable that the ratio of the minor axis (d2) of the second strands 122 to the diameter (d1) of the first strands 121 is 0.70 to 0.98.

[0051] According to an embodiment of the present invention, the rolling process may be performed so that the tensile strength of the wire 120 is changed before and after the rolling process. When the diameter of the wire 120 before rolling is d (mm), the first strength (NT: normal tensile) can be defined as 3,200-2,000xd (mm) ±200 (MPa), the second strength (HT: high tensile) can be defined as 3,500-2,000xd (mm) ±200 (MPa), the third strength (ST: super tensile) can be defined as 3,850-2,000xd (mm) ±200 (MPa), the fourth strength (UT: ultra tensile) can be defined as 4,200-2,000xd (mm) ±200 (MPa), and the fifth strength (MT: mega tensile) can be defined as 4,600-2,000xd (mm) ±200 (MPa). Here, the diameter (d) of the wire 120 is the diameter of the wire before being rolled, and is the same as the diameter (d1) of the first wire 121.

[0052] The tensile strength of the wires 120 before being rolled may be any one of the first strength (NT), the second strength (HT), the third strength (ST), the fourth strength (UT), and the fifth strength (MT). The tensile strength of the wires 120 before being rolled may be changed depending on the tensile strength required for the steel cord.

[0053] According to an embodiment of the present invention, the rolling process may be performed to change the tensile strength of the wire 120. Specifically, the rolling process may be performed to reduce the tensile strength of the wire 120, and the wire 120 having an n-th tensile strength before the rolling process may be processed to have an (n-1)-th tensile strength through the rolling process (where n=2, 3, 4, or 5).

[0054] Specifically, if the tensile strength of the wire 120 is the fifth strength (MT) before rolling, the tensile strength of the wire 120 will become the fourth strength (UT) after rolling, and if the tensile strength of the wire 120 is the fourth strength (UT) before rolling, the tensile strength of the wire 120 will become the third strength (ST) after rolling.

[0055] As such, the rolling process according to the embodiment of the present invention may be performed in a direction that changes the tensile strength of the strands 120. When the rolling process is performed, the strands are crimped, and the physical properties of the strands may change. If the rolling process is performed without taking this into consideration, it is difficult to accurately determine the tensile strength of the final steel cord, which is a problem.

[0056] In order to solve such problems, the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention changes the physical property (tensile strength) that is changed by rolling processing to a specified value.

[0057] In the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention, the wires 120 having a tensile strength of nth strength before rolling are rolled to have a tensile strength of (n-1)th strength by rolling. By proceeding with the rolling process so that the tensile strength is changed to a predetermined value, the tensile strength of the final steel cord can be accurately determined.

[0058] At this time, since the degree to which the tensile strength of the wire 120 is changed may vary depending on the diameter of the wire 120, the first strength (NT), the second strength (HT), the third strength (ST), the fourth strength (UT), and the fifth strength (MT) may be determined according to the ratio related to the diameter (d) of the wire 120.

[0059] Here, the wires 120 whose tensile strength changes due to the rolling process are also the second wires 122 that are crimped by the rolling process. However, without being limited thereto, the wires 120 whose tensile strength changes due to the rolling process can also be the first wires 121 and the second wires 122, as necessary.

[0060] The diameter of the first wire 121 of the steel cord for reinforcing a tire belt ply according to the embodiment of the present invention is 0.1 mm to 0.6 mm, but is not limited thereto and may be changed as necessary.

[0061] The steel cord for reinforcing a tire belt ply according to the embodiment of the present invention is manufactured through a rolling process, and therefore has excellent straightness quality.

[0062] Generally, a steel cord used as a tire reinforcement material requires several months to be used in a tire. That is, the steel cord is wound around a spool having a certain inner diameter and then used several months later. In view of the characteristics of the steel cord that are used several months after being wound, the straightness of the steel cord is an important characteristic of the steel cord used as a tire reinforcement material.

[0063] Poor linearity can affect the workability of tire manufacturing processes, causing buckling and tip rising, which can lead to problems during rolling and cutting processes.

[0064] Excellent straightness quality means that when a steel cord is wound on a spool for two months to one year, one end of the steel cord is fixed at one point, and the steel cord is lowered vertically by 400 mm, the narrower the distance between the first axis forming a vertical line from the one point and the other end of the steel cord, the better the straightness quality.

[0065] The steel cord for reinforcing a tire belt ply according to an embodiment of the present invention can have excellent straightness quality because it is manufactured through a rolling process.

[0066] Specifically, when a steel cord manufactured according to an embodiment of the present invention is wound on a spool for two months to one year, and the steel cord is fixed at one point on one end and lowered vertically by 400 mm, the distance between a first axis forming a vertical line from the one point and the other end of the steel cord may be 40 mm or less.

[0067] FIG. 11 compares the linearity of an embodiment of the present invention with that of a comparative example based on the ratio of the minor axis (d2) of the second wires 122 to the diameter (d1) of the first wires 121. FIG. 11 shows the distance between the first axis, which forms a vertical line from the point, and the other end of the steel cord when the steel cord is fixed at one point and lowered vertically 400 mm after the steel cord has been wound on a spool for two months to one year.

[0068] Figure 11 shows the linearity quality for Comparative Examples 1 and 2, in which the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is outside the range of 0.70 to 0.98, and for Examples 1 and 2, in which the ratio of the minor axis (d2) of the second wire 122 to the diameter (d1) of the first wire 121 is within the range of 0.70 to 0.98.

[0069] Referring to FIG. 11, it can be seen that when a steel cord is manufactured through rolling according to an embodiment of the present invention, residual stress in the steel cord is removed, thereby maintaining excellent linearity over time.

[0070] The steel cord for reinforcing a tire belt ply according to the embodiment of the present invention described above has the following effects.

[0071] The steel cord for reinforcing a tire belt ply according to an embodiment of the present invention is manufactured by rolling, which has the advantage of increasing the rigidity in the axial direction of the tire, thereby improving the durability and fatigue properties of the steel cord.

[0072] In addition, the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention has an advantage in that it can prevent a decrease in durability of the steel cord due to the penetration of moisture or salt by improving the permeability of rubber, and the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention has an advantage in that it can improve the initial adhesion strength and fatigue characteristics of the steel cord by improving the permeability of rubber.

[0073] In addition, the steel cord for reinforcing a tire belt ply according to the embodiment of the present invention has an advantage that the thickness of the rubber can be reduced when the steel cord is embedded in a rubber sheet by manufacturing the steel cord through a rolling process, and the steel cord for reinforcing a tire belt ply according to the embodiment of the present invention has an advantage that the straightness quality can be improved through the rolling process.

[0074] In particular, when the tensile strength after rolling is the nth strength, the steel cord for reinforcing a tire belt ply according to the embodiment of the present invention has a tensile strength before rolling that is the (n+1)th strength. This has the advantage that, compared to a circular steel cord, the thickness of the rubber can be made thinner when the steel cord is embedded in a rubber sheet without a decrease in strength.

[0075] Furthermore, the steel cord for reinforcing a tire belt ply according to an embodiment of the present invention is advantageous in that it can be manufactured by carrying out a rolling process while specifying the ratio of the minor axis (d2) of the second wire to the diameter (d1) of the first wire to be in the range of 0.70 to 0.98, thereby preventing breakage, a decrease in the penetration power of rubber, and a decrease in the durability and fatigue properties of the steel cord due to the penetration of moisture or salt.

[0076] Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely illustrative, and those skilled in the art will appreciate that various modifications and variations of the embodiments are possible therefrom. Therefore, the true technical scope of protection of the present invention is defined by the technical spirit of the appended claims.

Claims

1. A method for manufacturing a steel cord for reinforcing a tire belt ply of an automobile, comprising: A cord is formed by periodically twisting n wires, The n element wires are crimped by rolling, and at least one of the n element wires is compressed into a non-circular shape by rolling, When n is an odd number, the cross section of one of the n element wires becomes circular by the rolling process, and the cross sections of (n-1) element wires become non-circular, A method for producing a steel cord for reinforcing a tire belt ply, wherein, when n is an even number, two of the n element wires have circular cross sections and (n-2) element wires have non-circular cross sections by rolling, a rolling process in which a wire having a circular cross section by rolling is defined as a first wire, and a wire having a non-circular cross section by rolling is defined as a second wire, and a value of a minor axis of the second wire relative to a diameter of the first wire is 0.70 to 0.98; When the diameter of the wire before rolling is d (mm), the first strength (NT: normal tensile) is defined as 3,200-2,000 x d (mm) ± 200 (MPa), the second strength (HT: high tensile) is defined as 3,500-2,000 x d (mm) ± 200 (MPa), the third strength (ST: super tensile) is defined as 3,850-2,000 x d (mm) ± 200 (MPa), the fourth strength (UT: ultra tensile) is defined as 4,200-2,000 x d (mm) ± 200 (MPa), and the fifth strength (MT: mega tensile) is defined as 5,000-5,000 x d (mm) ± 200 (MPa). the tensile strength of the wire before being rolled is any one of the second strength, the third strength, the fourth strength, and the fifth strength; a rolling step in which the wire, which has a tensile strength of n-th strength before rolling, is rolled to have a tensile strength of (n-1)-th strength.

2. 2. The method for manufacturing a steel cord for reinforcing a tire belt ply according to claim 1, wherein the number (n) of wires is 3 to 9.

3. 2. The method for manufacturing a steel cord for reinforcing a tire belt ply according to claim 1, wherein the diameter of the first wire is 0.1 mm to 0.6 mm.

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