Copper wire

Abstract

To provide a copper wire that enables highly reliable laser welding with lower power and shorter duration than before by enhancing fatigue resistance under repeated bending and achieving high laser absorption characteristics, without the need for introducing trace additive elements.SOLUTION: A copper wire 1 is made of oxygen-free copper. When in a cross-sectional view, the length of a line segment drawn from the center position C of a cross section to an outer surface position P on an outer surface contour line O of the copper wire 1 is defined as L, a region that includes the center position C of the copper wire, enclosed by a virtual first boundary enclosing line BL1, which is formed by tracing a path around the center position C at a radial distance equal to 0.9 times the segment length L from the center position C is defined as a first inner region 2, and a surface annular region defined between the outer contour line O and the virtual first boundary enclosing line BL1 is defined as a first outer region 3, then the ratio of the oxygen concentration in the first outer region 3 to the oxygen concentration in the first inner region 2 is 2.00 or more and 5.00 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a copper wire, and more particularly to a copper wire that can be used for electric wires and windings such as coil wires for automobiles, lead wires for electronic components, and audio cables. [Background technology]

[0002] Conductor connections are made by welding for the electrical wires and windings used in automobile coil wires, lead wires for electronic components, audio cables, etc., in order to improve performance and reliability and achieve miniaturization. For this reason, oxygen-free copper is used as the copper wire that makes up the conductor, as it is less likely to develop blowholes such as voids in the welded joints and is highly resistant to hydrogen embrittlement in the welded joints.

[0003] Copper wire made of oxygen-free copper has problems such as weak strength at the welded parts and susceptibility to breakage due to bending or repeated vibration. Therefore, in order to improve the mechanical strength of the welded parts and fatigue properties when repeatedly bent, the concentrations of oxygen, hydrogen, and other impurities contained in the copper wire have been reduced or the metal structure has been controlled for conventional copper wire made of oxygen-free copper.

[0004] For example, Patent Document 1 describes a method for producing low-oxygen copper wire for magnet wire, which includes, in a melting and casting process, providing heating means for a tundish equipped with a pouring nozzle and a trough for guiding molten copper to the tundish, providing porous weirs at the inlet of the trough and the outlet of the tundish, distributing a solid reducing agent in the trough and tundish, covering the interior of the mold extending forward from the tip of the pouring nozzle with a reducing gas to deoxidize it, and performing dehydrogenation treatment in the tundish. This method reduces the oxygen concentration by providing a solid reducing agent and maintaining a reducing atmosphere in the pouring section, reduces the hydrogen concentration by performing dehydrogenation treatment in the tundish, and provides a trough in the molten copper transport path to prevent the intrusion of foreign matter. This method controls the concentrations of oxygen, hydrogen, iron, and sulfur contained in the copper wire, thereby providing a method for producing copper wire made of oxygen-free copper with excellent weldability, bendability, and wiredrawability.

[0005] Patent Document 2 also describes a soft dilute copper alloy material for use in bus bars for solar cells, which contains 4 to 55 massppm of Ti, 2 to 12 massppm of sulfur, more than 2 to 30 massppm of oxygen, the remainder being copper, and has an average crystal grain size of 20 μm or less in a surface layer extending to a depth of 50 μm from the surface of the material. This copper alloy material contains trace additive elements such as titanium, and by controlling the processing process to reduce the average crystal grain size near the surface of the conductor, it is possible to provide rectangular conductors (bus bars) for solar cells that have high conductivity and a long flex life. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4014900 [Patent Document 2] Patent No. 5499330 Summary of the Invention [Problem to be solved by the invention]

[0007] However, there is a limit to how much the oxygen concentration in copper wire can be reduced, and introducing trace amounts of additive elements into copper wire to improve the mechanical properties of the copper wire, or further refining the metal structure of the copper wire by introducing trace amounts of additive elements and controlling the processing process, can cause a decrease in the properties of the copper wire, such as its conductivity. Furthermore, as a welding method for connecting a conductor to a copper wire, laser welding can be cited as a welding method that requires a short welding time and can perform welding efficiently, but because copper wire made of oxygen-free copper has a high reflectivity to lasers, there is room for improvement in terms of further improving the laser absorption properties of the copper wire.

[0008] The present invention aims to provide a copper wire that can be used for highly reliable laser welding at lower output and in a shorter time than conventional methods by improving fatigue characteristics when repeatedly bent while avoiding the introduction of trace additive elements and by providing high absorption characteristics for lasers. [Means for solving the problem]

[0009] The inventors discovered that by optimizing the distribution of oxygen concentration contained in a copper wire made of oxygen-free copper, it is possible to avoid a decrease in conductivity due to the introduction of trace additive elements, while improving the fatigue properties of the copper wire when repeatedly bent, and enhancing the laser absorption properties, and thus completed the present invention.

[0010] In order to achieve the above object, the gist of the present invention is as follows. (1) A copper wire made of oxygen-free copper, wherein, in a cross section of the copper wire, the length of a line segment drawn from a center position C of the cross section to an outer surface position P on an outer surface contour line O of the copper wire is defined as L, and a region including the center position C of the copper wire surrounded by an imaginary first boundary encirclement line BL1 obtained by connecting positions away from the center position C by a length 0.9 times the line segment length L around the center position C is defined as a first inner region, and a surface annular region defined by the outer surface contour line O and the imaginary first boundary encirclement line BL1 is defined as a first outer region, wherein the ratio of the oxygen concentration in the first outer region divided by the oxygen concentration in the first inner region is 2.00 or more and 5.00 or less. (2) When viewed in the cross section, a region including the center position C of the copper wire surrounded by an imaginary second boundary encirclement line BL2 obtained by connecting a position away from the center position C by a length 1 / 6L equivalent to one-sixth of the line segment length L around the center position C is defined as a second inner region, and a surface annular region defined by an imaginary third boundary encirclement line BL3 obtained by connecting a position away from the outer surface contour line O by a length 1 / 3L equivalent to one-third of the line segment length L around the center position C and the outer surface contour line O is defined as a second outer region, The copper wire according to (1) above, wherein the specific gravity of the second inner region is greater than the specific gravity of the second outer region by 0.002 or more and 0.007 or less. (3) The copper wire according to (1) or (2) above, wherein the copper wire is a round wire having a diameter in the range of 0.01 mm to 3.5 mm. (4) The copper wire is a ribbon wire, and the cross-sectional area of ​​the cross section is 70 μm 2 Over 9.5mm 2 The copper wire according to (1) or (2) above, which is within the following range: [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a copper wire that can be used for highly reliable laser welding at lower output and in a shorter time than conventional methods, by improving fatigue characteristics when repeatedly bent and providing high absorption characteristics for lasers, while avoiding the introduction of trace additive elements. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view schematically showing a first inner region and a first outer region in a cross section when the copper wire of the present invention is a round wire. [Figure 2] 1 is a cross-sectional view schematically showing a first inner region and a first outer region in a cross section when the copper wire of the present invention is a ribbon wire. FIG. [Figure 3] FIG. 2 is a cross-sectional view schematically showing a second inner region and a second outer region in a cross section when the copper wire of the present invention is a round wire. [Figure 4] 3 is a cross-sectional view schematically showing the second inner region and the second outer region in a cross section when the copper wire of the present invention is a ribbon wire. FIG. [Figure 5] 1 is a front view schematically showing an example of a copper wire manufacturing apparatus used to manufacture the copper wire of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the copper wire of the present invention will be described in detail.

[0014] The copper wire according to the present invention is a copper wire made of oxygen-free copper, and as shown in FIG. 1 , for example, when viewed in a cross section of copper wire 1, the length of a line segment drawn from the center position C of the cross section to an outer surface position P on the outer surface contour line O of copper wire 1 is defined as L, and the region including the center position C of the copper wire surrounded by an imaginary first boundary encirclement line BL1 obtained by connecting positions 0.9 times the line segment length L from the center position C around the center position C is defined as a first inner region 2, and the surface annular region defined by the outer surface contour line O and the imaginary first boundary encirclement line BL1 is defined as a first outer region 3. When the oxygen concentration in first outer region 3 is divided by the oxygen concentration in first inner region 2, the ratio is 2.00 or more and 5.00 or less.

[0015] In the copper wire of the present invention, for copper wire 1 made of oxygen-free copper, by setting the ratio of the oxygen concentration in first outer region 3 divided by the oxygen concentration in first inner region 2 to a range of 2.00 or more and 5.00 or less, more oxygen is dissolved in first outer region 3 and many ultrafine copper oxide particles are formed in first outer region 3. When copper wire 1 is bent and deformed, stress is applied intensively to first outer region 3, but by bringing about solid solution strengthening and precipitation strengthening in first outer region 3, first outer region 3 becomes less likely to deform, and therefore fatigue properties when copper wire 1 is repeatedly bent can be improved.

[0016] Furthermore, as the dissolved oxygen concentration in the first outer region 3 increases, a large number of extremely fine copper oxide particles having a lower optical reflectivity than the oxygen-free copper parent phase are precipitated and dispersed in the first outer region 3, thereby improving the laser absorption characteristics of the copper wire 1.

[0017] With the copper wire 1 according to the present invention, even without introducing trace additive elements into the copper wire 1, the copper oxide particles formed in large quantities in the first outer region 3 bring about precipitation strengthening in the first outer region 3 and enhance the laser absorption characteristics of the first outer region 3. This makes it possible to improve fatigue characteristics when repeatedly bent and to provide high laser absorption characteristics while avoiding a decrease in electrical conductivity due to the introduction of trace additive elements. As a result, it is possible to provide a copper wire that can be laser welded with high reliability even at a lower output and in a shorter time than conventional copper wires.

[0018] [1] Copper wire material The copper wire according to the present invention is a copper wire made of oxygen-free copper. Here, oxygen-free copper is high-purity copper with alloy number C1020 specified in JIS H3100 and other standards. The composition of oxygen-free copper is 99.96 mass% or more copper (Cu), 10 ppm or less oxygen (O), and unavoidable impurities. Here, oxygen (O) may not be contained, but this is not a limitation. Such oxygen-free copper is distinguished from tough pitch copper with alloy number C1100, which contains a larger amount of oxygen (O), and phosphorus-deoxidized copper with alloy number C1220, which contains a trace amount of phosphorus (P).

[0019] The remainder other than the above elements are inevitable impurities. The inevitable impurities refer to impurities at a level that is inevitably mixed in during the manufacturing process. Depending on the content of the inevitable impurities, they may be a factor that reduces the conductivity of the copper wire, so it is preferable that the content of the inevitable impurities is small.

[0020] Examples of unavoidable impurities contained in copper wire include elements such as aluminum (Al), beryllium (Be), iron (Fe), chromium (Cr), nickel (Ni), magnesium (Mg), phosphorus (P), lead (Pb), cadmium (Cd), silicon (Si), tin (Sn), titanium (Ti), zirconium (Zr), etc. It is preferable that the upper limit of the content of unavoidable impurities is low, and more specifically, the total of the above elements is preferably 30 ppm or less.

[0021] [2] Oxygen concentration distribution in copper wire In the copper wire 1, the ratio of the oxygen concentration in the first outer region 3 divided by the oxygen concentration in the first inner region 2 is 2.00 or more and 5.00 or less. As a result, the oxygen concentration in the first outer region 3 is 2.00 or more and 5.00 or less times the oxygen concentration in the first inner region 2. In such a copper wire 1, oxygen is concentrated in the first outer region 3, resulting in an increase in strength of the first outer region 3 due to the effect of solid solution strengthening. In addition, as the dissolved oxygen concentration in the first outer region 3 increases, extremely fine copper oxide particles precipitate in the first outer region 3, resulting in precipitation strengthening, which also increases the strength of the first outer region 3. Due to such solid solution strengthening and precipitation strengthening in the first outer region 3, when the copper wire 1 is bent and deformed, stress is applied intensively to the first outer region 3, but the solid solution strengthening and precipitation strengthening brought about in the first outer region 3 makes the first outer region 3 less likely to deform, thereby improving the fatigue characteristics when the copper wire 1 is repeatedly bent. At the same time, as the dissolved oxygen concentration in the first outer region 3 increases, many ultrafine copper oxide particles, which have a lower optical reflectivity than the oxygen-free copper parent phase, are precipitated and dispersed in the first outer region 3, thereby improving the laser absorption characteristics of the copper wire 1.

[0022] Here, if the oxygen concentration in the first outer region 3 is less than 2.00 times the oxygen concentration in the first inner region 2, the amount of solid solution and precipitation in the first outer region 3 will be small, making it difficult to improve the fatigue characteristics when the copper wire 1 is repeatedly bent and the laser absorption characteristics of the copper wire 1. This is also undesirable from the viewpoint of the manufacturing efficiency of the copper wire 1 and from the viewpoint of the deterioration of fatigue characteristics when the copper wire 1 is repeatedly bent, which is caused by coarse shrinkage cavities that continue longitudinally in the center of the ingot. On the other hand, if the oxygen concentration in the first outer region 3 is more than 5.00 times the oxygen concentration in the first inner region 2, an excessively large amount of oxygen will be solid-solved in the first outer region 3. This will further strengthen the tendency for the oxygen dissolved in the copper wire 1 to react with hydrogen gas and generate blowholes when the ingot that serves as the base of the copper wire 1 is formed by casting, making metal fatigue more likely to occur when the copper wire 1 is repeatedly bent.

[0023] Therefore, the ratio of the oxygen concentration in the first outer region 3 divided by the oxygen concentration in the first inner region 2 is 2.00 or more and 5.00 or less, and preferably 4.00 or more and 5.00 or less.

[0024] The oxygen concentration in the first inner region 2 is not particularly limited, but can be, for example, in the range of 0.6 ppm to 2 ppm. The oxygen concentration in the first outer region 3 is higher than the oxygen concentration in the first inner region 2, and can be, for example, in the range of 2 ppm to 6 ppm.

[0025] In this specification, the cross section refers to a cross section obtained by cutting along a plane perpendicular to the central axis. If the copper wire is a round wire, the cross section will be circular, and if the copper wire is a ribbon wire, the cross section will be rectangular.

[0026] The first inner region 2 is defined as a region including the center position C of the copper wire 1, surrounded by an imaginary first boundary envelope BL1 obtained by drawing a line segment from the center position C of the cross section of the copper wire 1 to an outer surface position P on the outer surface contour line O of the copper wire 1, where the length of the line segment is L. The imaginary first boundary envelope BL1 is obtained by connecting positions 0.9 times the line segment length L from the center position C around the center position C. In other words, the first inner region 2 is the imaginary first boundary envelope BL1 and the region inside it in the cross section of the copper wire 1. Here, the imaginary first boundary envelope BL1 can be obtained by drawing a locus from the line segment drawn from the center position C of the cross section to the outer surface position P, when the outer surface position P is moved around the outer surface contour line O while keeping the center position C fixed, to a position 0.9 times the line segment length L from the center position C.

[0027] The first outer region 3 is a surface annular region defined by the outer surface contour line O of the copper wire 1 and the above-mentioned imaginary first boundary encirclement line BL1. That is, the first outer region 3 is the region of the cross section of the copper wire 1 that is the imaginary first boundary encirclement line BL1 and beyond.

[0028] For example, when the copper wire is a round wire, as shown in copper wire 1 in Fig. 1, the cross section is circular, and a circle having a center position C as its center and a radius of 0.9 times the length L (9L / 10) can be defined as a first imaginary boundary envelope BL1, and the region including the center position C of the copper wire 1 surrounded by this first imaginary boundary envelope BL1 can be defined as a first inner region 2. Furthermore, a surface annular region defined by the outer surface contour line O and the first imaginary boundary envelope BL1 and having a thickness of 0.1 times the line segment length L (L / 10) can be defined as a first outer region 3.

[0029] The oxygen concentrations in the first inner region 2 and the first outer region 3 of the round copper wire 1 can be measured using a test material prepared by performing a surface removal process on the copper wire 1 after the cold working process [Step 4] described below. The process removes a thickness equivalent to one-tenth of L from the surface of the copper wire 1, where L is the length of a line segment drawn from the center position C of the cross section of the copper wire 1 to the outer surface position P on the outer surface contour line O of the copper wire 1. The oxygen concentrations of the copper wire 1 before and after the surface removal process are measured, and the oxygen concentration of the test material can be used as the oxygen concentration of the first inner region. The mass and oxygen concentration of the copper wire and the test material are measured, respectively, and the mass and oxygen content of the portion removed by the surface removal process are calculated from the difference between these values, thereby calculating the oxygen concentration of the first outer region.

[0030] On the other hand, when the copper wire is a ribbon wire, as shown in copper wire 1A in Figure 2, the cross section is rectangular, and when the length in the long side direction from the center position C of the rectangle to the outer surface contour line O is L1 and the length in the short side direction is L2, a rectangle that passes through a position that is 0.9 times the length L1 (9L1 / 10) away from the center position C in the long side direction and a position that is 0.9 times the length L2 (9L2 / 10) away from the center position C in the short side direction and has four sides that are parallel to the four sides of the rectangle of the cross section can be defined as a first imaginary boundary envelope line BL1, and the area including the center position C of the copper wire 1A surrounded by this first imaginary boundary envelope line BL1 can be defined as a first inner area 2A. In addition, the surface annular region defined by the outer surface contour line O and the imaginary first boundary envelope line BL1, in which the thickness of the portion along the short side in the long side direction is 0.1 times (L1 / 10) the length L1 and the thickness of the portion along the long side in the short side direction is 0.1 times (L2 / 10) the length L2, can be defined as the first outer region 3A.

[0031] The oxygen concentrations in the first inner region 2A and the first outer region 3A of the copper wire 1A, which is a ribbon wire, can be measured using a test material prepared by performing a surface removal process on the copper wire 1A after performing the cold working process [Step 4] described below. The copper wire 1A is removed from the surface of the copper wire 1A by a thickness equivalent to one-tenth of L1 on the long side and a thickness equivalent to one-tenth of L2 on the short side, where L1 is the length in the long side direction from the center position C of the rectangle in a cross section of the copper wire 1A to the outer surface contour line O of the copper wire 1A, and L2 is the length in the short side direction. Here, the oxygen concentrations of the copper wire 1A before and after the surface removal process are measured, and the oxygen concentration of the test material can be determined as the oxygen concentration of the first inner region. In addition, the mass and oxygen concentration of these copper wires and test materials are measured, and the mass and oxygen content of the portion removed by the surface removal process are calculated from the difference between these, thereby allowing the oxygen concentration of the first outer region to be calculated.

[0032] Here, the oxygen concentrations of the copper wires 1, 1A and the test materials can be measured by non-dispersive infrared absorption using, for example, an oxygen analyzer. The surface removal process for the copper wires 1, 1A may be performed by either a mechanical processing method such as polishing or a chemical method such as acid dissolution. The copper wires 1, 1A and the test materials for which the oxygen concentrations are measured are not limited to those described above. For example, the copper wires 1, 1A may be rough wires that have been subjected to the continuous hot rolling process [step 3], and the test materials may be rough wires that have been subjected to the surface removal process.

[0033] [3] Distribution of specific gravity of copper wire When viewed in cross section, the copper wire 1 has a line length L drawn from the center position C of the cross section to an outer surface position P on the outer surface contour line O of the copper wire 1, and the second inner region is a region including the center position C of the copper wire surrounded by an imaginary second boundary line BL2 obtained by drawing around the center position C a position that is a length 1 / 6L, which corresponds to one-sixth of the line length L, from the center position C. The second outer region 5 is a surface annular region defined by the outer surface contour line O and an imaginary third boundary line BL3 obtained by drawing around the center position C a position that is a length 1 / 3L, which corresponds to one-third of the line length L, from the outer surface contour line O. The specific gravity of the second inner region 4 is preferably greater than the specific gravity of the second outer region 5 by a range of 0.002 to 0.007, more preferably greater by a range of 0.004 to 0.007, and even more preferably greater by a range of 0.004 to 0.006.

[0034] Here, by making the specific gravity of the second inner region 4 larger by 0.002 or more than the specific gravity of the second outer region 5, when an ingot serving as the base of the copper wire 1 is formed by casting, blowholes generated by a reaction between oxygen dissolved in the copper wire 1 and hydrogen gas are generated more unevenly in the second outer region 5 than in the second inner region 4. This makes it difficult for defects to propagate from the blowholes to the second inner region 4, thereby improving the fatigue characteristics when the copper wire 1 is repeatedly bent. On the other hand, if the specific gravity of the second inner region 4 is equal to or lower than the specific gravity of the second outer region 5, or if the difference between the specific gravities of the second inner region 4 and the second outer region 5 is less than 0.002, blowholes and shrinkage cavities exist in the second inner region 4, and the fatigue characteristics when the copper wire 1 is repeatedly bent are reduced. On the other hand, if the specific gravity in the second inner region 4 is greater than 0.007 compared to the specific gravity in the second outer region 5, excessive blowholes will be formed in the second outer region 5, significantly reducing the strength near the surface of the copper wire 1, and therefore reducing the fatigue characteristics of the copper wire 1 when repeatedly bent.

[0035] The specific gravity of the second inner region 4 is not particularly limited, but can be, for example, in the range of 8.920 to 8.928, or in the range of 8.922 to 8.928. The specific gravity of the second outer region 5 is smaller than that of the second inner region 4, and can be, for example, in the range of 8.916 to 8.924, or in the range of 8.916 to 8.919.

[0036] Here, the second inner region 4 is defined as a region including the center position C of the copper wire 1, surrounded by an imaginary second boundary envelope line BL2 obtained by drawing a line segment from the center position C of the cross section to an outer surface position P on the outer surface contour line O of the copper wire 1, where L is the length of the line segment. The imaginary second boundary envelope line BL2 is obtained by connecting positions that are a distance 1 / 6L, equivalent to one-sixth of the line segment length L, from the center position C around the center position C. In other words, the second inner region 4 is the imaginary second boundary envelope line BL2 and the region inside it in the cross section of the copper wire 1. Here, the imaginary second boundary envelope line BL2 can be obtained by drawing a locus of positions that are a distance 1 / 6 of the line segment length L from the center position C when the outer surface position P is moved around the outer surface contour line O while keeping the center position C fixed, from the line segment drawn from the center position C of the cross section to the outer surface position P.

[0037] The second outer region 5 is a surface annular region defined by an imaginary third boundary envelope BL3 obtained by connecting a position away from the outer surface contour O by a length 1 / 3L, which corresponds to one-third of the line segment length L, around the center position C, and the outer surface contour O. In other words, the second outer region 5 is the imaginary third boundary envelope BL3 and the region outside it in the cross section of the copper wire 1.

[0038] For example, when the copper wire is a round wire, as shown in copper wire 1 in Fig. 3, the cross section is circular, and a circle having a center position C as its center and a radius of one-sixth (1 / 6L) of the length L can be defined as an imaginary second boundary envelope BL2, and the region including the center position C of the copper wire 1 surrounded by this imaginary second boundary envelope BL2 can be defined as a second inner region 4. Furthermore, a circle having a center position C as its center and a distance of one-third (1 / 3L) of the length L from the outer surface contour line O, i.e., a circle having a radius of two-thirds (2 / 3L) of the length L, can be defined as an imaginary third boundary envelope BL3, and the surface annular region defined by the outer surface contour line O and the imaginary third boundary envelope BL3 and having a thickness of one-third (L / 3) of the line segment length L can be defined as a second outer region 5.

[0039] The specific gravities of the first inner region 2 and the first outer region 3 of the round copper wire 1 can be measured using two specimens: a specimen A prepared by performing a surface removal process in which a thickness equivalent to 5 / 6 of L is removed from the surface of the copper wire after the cold working process [Step 4] described below, where L is the length of a line segment drawn from the center position C of the copper wire cross section to the outer surface position P on the outer surface contour line O of the copper wire; and a specimen B prepared by performing a surface removal process in which a thickness equivalent to 1 / 3 of L is removed from the surface of the copper wire. The specific gravities of the copper wire, specimen A, and specimen B are measured, and the specific gravity of specimen A can be used as the specific gravity of the second inner region. The specific gravity of the copper wire and specimen B can also be calculated by measuring the mass and volume of the copper wire and specimen B, respectively, and then calculating the mass and volume of the portion removed in the surface removal process from the difference between the measured mass and volume.

[0040] On the other hand, when the copper wire is a ribbon wire, as shown in copper wire 1A in Figure 4, the cross section is rectangular, and when the length in the long side direction from the center position C of the rectangle to the outer surface contour line O is L1 and the length in the short side direction is L2, a rectangle that passes through a position that is 1 / 6 of the length L1 (L1 / 6) away from the center position C in the long side direction and a position that is 1 / 6 of the length L2 (L2 / 6) away from the center position C in the short side direction and has four sides that are parallel to the four sides of the rectangle of the cross section can be defined as a virtual second boundary envelope line BL2, and the area including the center position C of the copper wire 1A surrounded by this virtual second boundary envelope line BL2 can be defined as a second inner area 4A. Furthermore, a virtual third boundary envelope BL3 can be defined as a rectangle that passes through a position one-third (L1 / 3) of the length L1 in the long side direction from the outer surface contour line O toward the center position C, and a position one-third (L2 / 3) of the length L2 in the short side direction from the center position C, and has four sides parallel to the four sides of the rectangular cross section.The second outer region 5A can be defined as a surface annular region that is bounded by the outer surface contour line O and the virtual third boundary envelope BL3, and whose part extending in the short side direction has a thickness in the long side direction of one-third (L1 / 3) of the length L1 and a thickness in the short side direction of one-third (L2 / 3) of the length L2.

[0041] The specific gravity of the first inner region 2A and the first outer region 3A of the copper wire 1A, which is a ribbon wire, can be measured using test material A, which is prepared by performing a surface removal process on the copper wire 1A after the cold processing process [process 4] described below, in which a thickness equivalent to 5 / 6 of L1 is removed from the surface of the copper wire 1A on the long side and a thickness equivalent to 5 / 6 of L2 is removed from the surface of the copper wire 1A on the short side, where L1 is the length in the long side direction from the center position C of the rectangle when viewed in cross section of the copper wire 1A to the outer surface contour line O of the copper wire 1A, and L2 is the length in the short side direction. Test material B can also be prepared by performing a surface removal process on the copper wire 1A in which a thickness equivalent to 1 / 3 of L1 is removed from the surface of the copper wire 1A on the long side and a thickness equivalent to 1 / 3 of L2 is removed from the surface of the copper wire 1A on the short side. Here, the specific gravity of the copper wire before the surface removal step and the specimens A and B obtained after the surface removal step are measured, and the specific gravity of specimen A can be used as the specific gravity of the second inner region. In addition, the mass and volume of the copper wire and specimen B are measured, and the difference between these masses and volumes is used to calculate the mass and volume of the portion removed by the surface removal step, thereby calculating the specific gravity of the second outer region.

[0042] Here, the specific gravities of the copper wires 1 and 1A and the test material can be measured by, for example, the Archimedes method using an electronic balance. The surface removal process for the copper wires 1 and 1A may be performed by either a mechanical processing method such as polishing or a chemical method such as acid dissolution. The copper wires 1 and 1A and the test material for which the specific gravities are measured are not limited to those described above. For example, the copper wires 1 and 1A may be rough wires that have been subjected to the continuous hot rolling process [step 3], and the test material may be rough wires that have been subjected to the surface removal process.

[0043] In addition, in the copper wire 1 of this embodiment, in order to make the difference in specific gravity between the second outer region 5 and the second inner region 4 more pronounced and clearly distinguishable, the difference in specific gravity is specified for regions other than the above-mentioned first outer region 3 and first inner region 2.

[0044] [4] Shapes and uses of copper wire The shape of the copper wire can be, for example, a round wire or a ribbon wire, and the size can be selected appropriately depending on the electrical product or electronic component to be wired, the characteristics of the coil to be formed, and the like.

[0045] Here, when the copper wire is a round wire, the diameter of the cross section is preferably in the range of 0.01 mm to 3.5 mm. If the diameter of the cross section exceeds 3.5 mm, it becomes difficult to miniaturize the coil, electrical product, or electronic component when forming a coil using a winding made of copper wire or when wiring an electric wire made of copper wire in the electric product or electronic component. On the other hand, if the diameter of the cross section is less than 0.01 mm, processing when forming the copper wire 1 becomes difficult from the viewpoint of material strength.

[0046] In addition, when the copper wire is a ribbon wire, the cross-sectional area of ​​the cross section is 70 μm 2 Over 9.5mm 2 The cross-sectional area of ​​the cross section is preferably in the range of 9.5 mm 2 If the cross-sectional area of ​​the wire exceeds 70 μm, it becomes difficult to miniaturize the coil, electrical product, or electronic component when forming a coil using a winding made of copper wire or when wiring an electric wire made of copper wire in the coil, electrical product, or electronic component. 2 If the thickness is less than 1000 nm, it becomes difficult to process the copper wire 1 when it is formed, from the viewpoint of material strength.

[0047] The copper wire 1 of this embodiment includes those with large and small cross-sectional areas, but blowholes that may be formed near the surface of the copper wire 1 are not affected by fusion or the like due to cold working, and the oxygen concentration near the surface of the copper wire 1 is also not affected by cold working. Therefore, evaluation of fatigue properties when the copper wire 1 is repeatedly bent may be performed using test materials whose cross-sectional areas are adjusted to any desired area within the above range by changing the presence or absence of cold working or the working rate. For the same reason, the laser absorption properties and specific gravity of the copper wire 1 may also be evaluated using test materials whose cross-sectional areas are adjusted to any desired area by changing the presence or absence of cold working or the working rate.

[0048] The copper wire of the present invention is preferably used for electric wires and windings such as coil wires for automobiles, lead wires for electronic components, and audio cables. Use of the copper wire of the present invention for these applications enables the miniaturization of coils, electrical products, and electronic components that use the copper wire, as well as improving reliability by making metal fatigue less likely to occur when repeatedly bent and enabling laser welding at lower output and in a shorter time than conventional methods. When the copper wire is used for an electric wire, the electric wire may have at least an insulating coating layer formed on the surface of the copper wire.

[0049] [5] An example of copper wire manufacturing method Next, a method for manufacturing the copper wire of the embodiment will be described. The copper wire of the embodiment can be manufactured by a manufacturing method including a melting step (step 1), a casting step (step 2), a continuous hot rolling step (step 3), and a cold working step (step 4) using a manufacturing apparatus 10 schematically shown in Fig. 5, for example.

[0050] In the melting process [Step 1], a continuous melting furnace 11, such as that provided in a manufacturing apparatus 10 shown in FIG. 5, is used to melt a metal such as electrolytic copper to obtain molten copper. The obtained molten copper is supplied to a tundish 13 through a trough 12 extending from the continuous melting furnace 11, and degassing is performed in the trough 12 and the tundish 13. More specifically, a solid reducing agent is placed on the surface of the molten copper flowing through the trough 12, and reacts with the molten copper to reduce the oxygen concentration in the molten copper. In addition to placing the solid reducing agent on the surface of the molten copper inside the tundish 13, an inert gas is also blown into the tundish 13. The reaction between the inert gas and the molten copper deoxidizes and dehydrogenates the molten copper, allowing the oxygen and hydrogen concentrations in the molten copper to be controlled within desired ranges.

[0051] The solid reducing agent used in the melting step (step 1) is not limited in amount, type, size, porosity, etc., but an example of such a method is to cover the surface of the molten copper with charcoal to make it float. Also, the inert gas blown into the tundish 13 is not limited in type or amount, but an example of such a method is to forcibly blow nitrogen gas into the bottom of the tundish 13.

[0052] In the casting process [Step 2], molten copper is supplied from the tundish 13 to the rotary moving mold 20. Here, the rotary moving mold 20 may be one composed of a ring-shaped grooved mold 21 and a belt 22, such as a belt and wheel system. The radius R of the grooved mold 21 may be, for example, in the range of 2500 mm to 3500 mm.

[0053] The pouring section of the tundish 13 that supplies the molten copper to the rotary mold 20 is preferably kept warm by heating with a gas burner and in an inert gas atmosphere in order to keep the temperature of the molten copper constant and to suppress oxidation of the molten copper.

[0054] The temperature of the groove 21 is adjusted so that, when the temperature of the molten copper is in the range of 1085°C to 1100°C, the temperature (A) at a position 10 mm deep from the molten metal surface 20a is in the range of 80°C to 120°C, the temperature (C) at the mold bottom 20b is in the range of 135°C to 175°C, and the temperature (B) at a position intermediate these is in the range of 90°C to 130°C. Furthermore, it is preferable to perform casting so that the temperature difference between temperatures (A) and (B) is at least one-sixth and at most one-third of the temperature difference between temperatures (B) and (C). By controlling the temperature of the groove 21 within these ranges, the center of the ingot formed from the molten copper in the rotating mold 20 solidifies at an appropriate speed and position, thereby suppressing defects in the ingot. At the same time, solidifying the surface of the ingot at an appropriate rate promotes degassing, in which gas components dissolved in the molten copper form bubbles and rise to the surface, allowing the oxygen concentration in the surface of the ingot to be controlled within an appropriate range. Here, if the temperature difference between temperatures (A) and (B) is greater than one-third of the temperature difference between temperatures (B) and (C), the molten copper solidifies rapidly in the surface of the ingot, forcing oxygen and hydrogen into solid solution in the ingot, resulting in the formation of excessive blowholes in the surface, which then become the starting point for fracture. Furthermore, if the temperature difference between temperatures (A) and (B) is less than one-sixth of the temperature difference between temperatures (B) and (C), the solidification of the center of the ingot is extremely slow, causing the center of the ingot to solidify beyond the mold bottom 20b. This reduces the hydrostatic pressure of the molten copper, reducing the ability to supply molten metal to the solidifying area. As a result, large shrinkage cavities extending longitudinally may occur in the center of the ingot, which may cause wire breakage during drawing and bending, and may also cause blisters during heat treatment. In addition, excessive degassing in the surface layer of the ingot reduces the oxygen concentration in the surface layer of the ingot, particularly in the first outer region 3, to a value close to the oxygen concentration in the first inner region 2, making it difficult for solid solution strengthening or precipitation strengthening to occur in the first outer region 3.In particular, from the viewpoint of further reducing the occurrence of large shrinkage cavity defects in the center of the ingot and promoting solid solution strengthening and precipitation strengthening by controlling the oxygen concentration in the surface layer of the ingot, it is more preferable to cast so that the temperature difference between temperatures (A) and (B) is at least one-fourth of the temperature difference between temperatures (B) and (C). Here, temperature (B) is the temperature at a position midway along the flow path of molten copper between the measurement positions of temperature (A) and temperature (C), and is the temperature at a position where the length along the flow path of molten copper to the measurement position of temperature (A) is equal to the length along the flow path of molten copper to the measurement position of temperature (C).

[0055] Methods for controlling the temperature of the groove mold 21 of the rotating moving mold 20 include spraying cooling water from a spray nozzle, or changing the type and amount of release agent applied to the groove mold 21 and the belt 22.

[0056] The ingot obtained in the casting step [Step 2] is directly supplied to a continuous rolling mill 30, where it is formed into a wire rod by a continuous hot rolling step [Step 3]. In this embodiment, when obtaining an ingot by the casting step [Step 2], blowholes may be generated by the reaction between oxygen remaining in the molten copper and hydrogen gas. However, because gas components are removed from the center of the ingot, blowholes are formed unevenly near the surface of the ingot. Such blowholes near the surface of the ingot are fused by the concentrated force applied to the surface of the ingot during hot rolling in the continuous hot rolling step [Step 3]. Therefore, if the number of blowholes near the surface of the wire rod after hot rolling is appropriate, most of the blowholes can be reduced by fusion. As a result, surface defects that can be the initiation points of fracture can be reduced in the obtained copper wire, thereby increasing the tensile strength of the copper wire and improving the fatigue properties of the copper wire when repeatedly bent.

[0057] In the continuous hot rolling process [Step 3], the ingot is hot rolled using rolls that operate in the vertical and horizontal directions and are arranged alternately inside the continuous rolling mill 30, thereby obtaining a roughly drawn wire in a round wire shape.

[0058] In the continuous hot rolling step [step 3], the temperature of the ingot when it is supplied to the continuous rolling mill 30 is not particularly limited, but can be set in the range of 820°C or higher and 920°C or lower, for example.

[0059] After the continuous hot rolling process [Step 3], the roughly drawn wire is subjected to cold working, including wire drawing and rolling, in the cold working process [Step 4], whereby it can be formed into a round wire or ribbon wire of a predetermined shape.

[0060] The wire drawing and rolling processes in the cold working step [Step 4] may be performed in multiple steps, and a stripping step to remove less than 2% of the wire diameter may be performed before the cold working step [Step 4] or between multiple wire drawing and rolling processes. By performing the stripping step, blowholes near the surface of the wirerod can be removed, further reducing surface defects that can be the starting point for breakage in the resulting copper wire. Here, if the stripping amount in the stripping step is 2% or more, the high-oxygen-concentration portions formed near the surface of the wirerod, which contribute to improving fatigue properties when repeatedly bent and laser absorption properties, will be removed, and this is also undesirable from the standpoint of production yield.

[0061] Furthermore, when wire drawing or rolling is performed in multiple steps as the cold working step [step 4], an annealing step may be included between the multiple steps of wire drawing or rolling.

[0062] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. [Example]

[0063] Next, in order to further clarify the effects of the present invention, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples of the present invention.

[0064] (Invention Examples 1 to 7 and Comparative Examples 1 to 4) A melting process [Step 1] was carried out in which electrolytic copper ingot (purity: 99.96% or more) was melted in a shaft furnace, which is a continuous melting furnace 11 of a manufacturing apparatus 10 shown in Figure 5, to obtain molten copper, and this molten copper was supplied to a tundish 13 using a trough 12 extending from the continuous melting furnace 11. At this time, charcoal as a solid reducing agent was suspended inside the trough 12 in an amount sufficient to almost cover the surface of the molten copper flowing through the trough 12. Furthermore, in the tundish 13, in addition to charcoal as a solid reducing agent being suspended in an amount sufficient to almost cover the surface of the molten copper, nitrogen gas as an inert gas was forcibly injected into the bottom of the molten copper at a flow rate of 200 liters / minute.

[0065] The casting process [Step 2] was carried out by supplying the molten copper supplied to the tundish 13 into the rotary mold 20. The rotary mold 20 was comprised of a ring-shaped grooved mold 21 and a belt 22, and the grooved mold 21 had a radius R of 3000 mm. The pouring section of the tundish 13 was maintained at a constant temperature by heating with a gas burner and placed in an inert gas atmosphere. The temperature conditions for the casting process [Step 2] were as follows: the temperature of the molten copper was set to 1090°C; the temperature (A) at a position 10 mm deep from the molten metal surface 20a, the temperature (C) at the mold bottom 20b, and the temperature (B) at a position intermediate between them were set to the temperatures listed in Table 1. The ratio of the temperature difference between temperatures (A) and (B) to the temperature difference between temperatures (B) and (C) is also listed in Table 1.

[0066] The ingot obtained in the casting step [step 2] was directly supplied to a continuous rolling mill 30, and a rough wire was formed by a continuous hot rolling step [step 3]. In the continuous hot rolling step [step 3], the temperature of the ingot when supplied to the continuous rolling mill 30 was set to 900°C.

[0067] After the continuous hot rolling process [Step 3], the rough wire was subjected to cold processing including wire drawing and rolling in the cold processing process [Step 4] (total processing rate: 99.0% to 99.999%) to obtain copper wire for evaluation with the shape shown in Table 1.

[0068] [Various measurement and evaluation methods] The copper wires according to the above-mentioned invention examples and comparative examples were used to carry out the following characteristic evaluations. The evaluation conditions for each characteristic were as follows.

[0069] [1] Measurement of oxygen concentration For the round wire-shaped copper wire after the cold working process [Step 4], where L is the length of a line segment drawn from the center position C of the cross section of the copper wire to the outer surface position P on the outer surface contour line O of the copper wire, a surface removal process was performed to remove a thickness equivalent to one-tenth of L from the surface of the copper wire by polishing to prepare a test material. Here, the oxygen concentrations of the copper wire before and after the surface removal process were measured, and the oxygen concentration of the test material was designated as the oxygen concentration of the first inner region. In addition, the mass and oxygen concentration of the copper wire and the test material were measured, and the mass and oxygen amount of the portion removed by the surface removal process were calculated from the difference between these values ​​to calculate the oxygen concentration of the first outer region.

[0070] In addition, for the ribbon-shaped copper wire after the cold working process [Step 4], where L1 is the length in the long side direction from the center position C of the rectangle in the cross section of the copper wire to the outer surface contour line O of the copper wire and L2 is the length in the short side direction, a surface removal process was performed to remove a thickness equivalent to 1 / 10 of L1 from the surface of the copper wire on the long side and a thickness equivalent to 1 / 10 of L2 from the short side by polishing, to prepare a test material. Here, the oxygen concentrations of the copper wire before and after the surface removal process were measured, and the oxygen concentration of the test material was designated as the oxygen concentration of the first inner region. In addition, the mass and oxygen concentration of the copper wire and the test material were measured, and the mass and oxygen content of the portion removed by the surface removal process were calculated from the difference between these values, thereby calculating the oxygen concentration of the first outer region.

[0071] The oxygen concentrations of the copper wire and the test material were measured by non-dispersive infrared absorption using an oxygen analyzer (manufactured by Leco, model number: EF-400). The measured oxygen concentrations of the first inner region and the first outer region are shown in Table 2.

[0072] [2] Measurement of specific gravity For the round wire-shaped copper wire after the cold working process [Step 4], where L is the length of a line segment drawn from the center position C of the cross section of the copper wire to the outer surface position P on the outer surface contour line O of the copper wire, a surface removal process was performed to remove a thickness equivalent to 5 / 6 of L from the surface of the copper wire by polishing, thereby producing Sample Material A. Additionally, a surface removal process was performed to remove a thickness equivalent to 1 / 3 of L from the surface of the copper wire by polishing, thereby producing Sample Material B. The specific gravities of the copper wire, Sample Material A, and Sample Material B were each measured, and the specific gravity of Sample Material A was used as the specific gravity of the second inner region. The masses and volumes of the copper wire and Sample Material B were also measured, and the difference between these values ​​was used to calculate the mass and volume of the portion removed by the surface removal process, thereby calculating the specific gravity of the second outer region.

[0073] Furthermore, for the ribbon-shaped copper wire after the cold working process [Step 4], where L1 is the length in the long direction from the center position C of the rectangle in the cross section of the copper wire to the outer surface contour line O of the copper wire and L2 is the length in the short direction, a surface removal process was performed to remove a thickness equivalent to 5 / 6 of L1 from the surface of the copper wire on the long side and a thickness equivalent to 5 / 6 of L2 from the short side by polishing, to produce Test Material A. Furthermore, a surface removal process was performed to remove a thickness equivalent to 1 / 3 of L1 from the surface of the copper wire on the long side and a thickness equivalent to 1 / 3 of L2 from the short side by polishing, to produce Test Material B. Here, the specific gravity of the copper wire before the surface removal process and of Test Material A and Test Material B obtained after the surface removal process were measured, and the specific gravity of Test Material A was determined as the specific gravity of the second inner region. In addition, the mass and volume of these copper wires and test material B were measured, and the specific gravity of the second outer region was calculated by calculating the mass and volume of the portion removed by the surface removal process from the difference between these values.

[0074] The specific gravities of the copper wire and the test material were measured by the Archimedes method using an electronic balance. The measured oxygen concentrations in the second inner region and the second outer region are shown in Table 2.

[0075] [3] Evaluation of fatigue characteristics when repeatedly bent For Inventive Examples 1 to 4, 6, and 7 and Comparative Examples 1 to 4, the copper wires for evaluation obtained above were subjected to repeated bending tests in accordance with JIS H 0500 No. 4100. The copper wires were drawn into round wires with a wire diameter of 0.1 mm and used as test materials. The radius R of the jig at the bending fulcrum during bending was 4 mm, and one end of the test material was fixed to a grip, while a 20 g weight was hung from the other end to prevent bending. Repeated bending deformation was performed until fracture. On the other hand, for Inventive Example 5, since the wire diameter was 0.01 mm, the rough wire after the continuous hot rolling process [Step 3] was drawn into a round wire with a wire diameter of 0.1 mm in the cold working process [Step 4], and the same test was performed on the copper wire obtained as the test material. When the number of bending deformations leading to fracture was 3,500 or more but less than 4,000, the fatigue properties when repeatedly flexed were evaluated as "Excellent". When the number of bending deformations leading to fracture was 3,000 or more but less than 3,500, the fatigue properties when repeatedly flexed were evaluated as "Good". On the other hand, when the number of bending deformations leading to fracture was less than 3,000, the fatigue properties when repeatedly flexed were evaluated as "Poor". In the examples of the present invention and the comparative examples, "Excellent" and "Good" were evaluated as pass levels. The results are shown in Table 2.

[0076] [4] Evaluation of laser absorption properties The rough wire after the continuous hot rolling process [Step 3] was subjected to a cold working process [Step 4] to form rectangular test pieces measuring 3.5 mm in width, 2.5 mm in thickness, and 30 mm in length. The test piece was irradiated with a laser on the surface including the width direction of the test piece. The laser irradiation conditions were a 300 W blue laser (wavelength 400 nm) with a 3 mm diameter and a 3-second irradiation time. A thermocouple wire was attached to the back of the test piece to measure the temperature, and the laser absorption characteristics of the test piece were evaluated based on the temperature rise of the thermocouple. A thermocouple temperature rise of 450°C or more was deemed excellent in terms of laser absorption characteristics and rated as "Excellent." A thermocouple temperature rise of 400°C or more but less than 450°C was deemed good in terms of laser absorption characteristics and rated as "Good." On the other hand, when the temperature rise of the thermocouple was less than 400°C, the laser absorption characteristics were deemed poor and the evaluation was "× (fail)." In the present invention examples and comparative examples, "◎" and "◯" were evaluated as pass levels. The results are shown in Table 2.

[0077] [5] Overall rating When both of the evaluation results for fatigue properties after repeated bending and laser absorption properties were rated as "◎," the overall evaluation was rated as "◎," indicating that both the fatigue properties after repeated bending and the laser absorption properties were excellent. When either or both of the evaluation results for fatigue properties after repeated bending and laser absorption properties were rated as "◯," both of these properties were considered to be at least good, and the overall evaluation was rated as "○." On the other hand, when at least one of the evaluation results for fatigue properties after repeated bending and laser absorption properties was rated as "×," the overall evaluation was rated as "×," indicating that at least one of these properties was insufficient. The results are shown in Table 2.

[0078] [Table 1]

[0079] [Table 2]

[0080] As shown in Tables 1 and 2, in Examples 1 to 7 of the present invention, the copper wires were made of oxygen-free copper, and the ratio of the oxygen concentration in the first outer region divided by the oxygen concentration in the first inner region was within the range of 2.00 to 5.00, so that both the fatigue characteristics when repeatedly bent and the laser absorption characteristics were at least good. Therefore, the copper wires of Examples 1 to 7 of the present invention, while avoiding the introduction of trace additive elements, improved fatigue characteristics when repeatedly bent and provided high laser absorption characteristics, enabling reliable laser welding to be performed at lower power and in a shorter time than conventional methods.

[0081] On the other hand, in Comparative Examples 1 to 4, the ratio of the oxygen concentration in the first outer region divided by the oxygen concentration in the first inner region was not controlled within a predetermined range, and therefore, in Comparative Examples 1 to 4, at least one of the two evaluation results regarding fatigue characteristics after repeated bending and laser absorption characteristics was poor. [Explanation of symbols]

[0082] 1, 1A copper wire 2, 2A 1st inner area 3, 3A 1st outer area 4, 4A 2nd inner area 5, 5A 2nd outer area 10 Manufacturing equipment 11 Continuous melting furnace 12 Gutter 13 Tundish 20 Rotating and moving mold 21 groove mold 22 Belt 30 Continuous rolling mill C Center position of cross section L is the length of the line drawn from the center of the cross section to the outer surface on the outer surface contour line. O Outer surface contour of copper wire P outer surface position BL1 Virtual First Boundary Encirclement Line BL2 Virtual Second Boundary Encirclement Line BL3 Virtual Third Boundary Encirclement Line

Claims

1. A copper wire made of oxygen-free copper, When viewed from the cross section of the copper wire, the length of a line segment drawn from the center position C of the cross section to an outer surface position P on the outer surface contour line O of the copper wire is defined as L, and a region including the center position C of the copper wire surrounded by an imaginary first boundary encirclement line BL1 obtained by connecting positions away from the center position C by a length 0.9 times the line segment length L around the center position C is defined as a first inner region, and a surface annular region defined by the outer surface contour line O and the imaginary first boundary encirclement line BL1 is defined as a first outer region, A copper wire, wherein a ratio of the oxygen concentration in the first outer region divided by the oxygen concentration in the first inner region is 2.00 or more and 5.00 or less.

2. When viewed in the cross section, a region including the center position C of the copper wire surrounded by an imaginary second boundary encircling line BL2 obtained by drawing around the center position C a position that is away from the center position C by a length 1 / 6L that corresponds to one-sixth of the line segment length L is defined as a second inner region, and a surface annular region defined by an imaginary third boundary encircling line BL3 obtained by drawing around the center position C a position that is away from the outer surface contour line O by a length 1 / 3L that corresponds to one-third of the line segment length L and the outer surface contour line O is defined as a second outer region, The copper wire according to claim 1 , wherein the specific gravity of the second inner region is greater than the specific gravity of the second outer region by 0.002 to 0.

007.

3. The copper wire is a round wire, 3. The copper wire according to claim 1, having a diameter in the range of 0.01 mm to 3.5 mm.

4. the copper wire is a ribbon wire, The cross-sectional area of ​​the cross section is 70 μm ２ Over 9.5mm ２ 3. The copper wire according to claim 1, wherein the copper wire has a thickness in the range of:

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