Electric wire and manufacturing method thereof

Abstract

To provide an electric wire 2 capable of exhibiting good insulation performance that a fluorine resin has.SOLUTION: An electric wire 2 includes a conductor 6, and a covering layer 8 covering the conductor 6. The covering layer 8 contains a crosslinked fluorine resin that is a crosslinked object of a fluorine resin. A maximum height indicating roughness of the surface of the covering layer 8 is 4 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric wire and a method for manufacturing an electric wire. [Background technology]

[0002] 2. Description of the Related Art Known electric wires used for motor windings include electric wires in which an insulating varnish is applied to the surface of a conductor and then the insulating varnish is baked to form a coating layer (see, for example, Patent Document 1 below).

[0003] Fluorine resins such as polytetrafluoroethylene (PTFE) are known as materials with excellent abrasion resistance and chemical resistance. Fluorine resins have a higher crystalline melting point than polyethylene, which is a common insulating material, and a lower dielectric constant than polyethylene. Fluorine resins are expected to be used as insulating materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 073397 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacture of electric wires with a fluororesin coating, a fluororesin-containing fluorocoating is usually used. The fluorocoating is passed through a coating die together with the conductor to form a coating film on the conductor surface. After the coating film is baked, it is irradiated with ionizing radiation to form the coating layer.

[0006] In this manufacturing process, the coating film, i.e., the surface of the coating layer, is formed by passing through a coating die. Fluorine resins are generally prone to fibrillation. The surface of the coating layer tends to become rough, and it is difficult to form a coating layer with a smooth surface. The presence of dents or pinholes leads to a decrease in the insulating performance of the wire. In order to utilize the good insulating performance of fluororesins, there is a need to establish technology that can form a coating layer with a smooth surface.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electric wire capable of exhibiting the excellent insulating performance of fluororesin, and a method for producing the same. [Means for solving the problem]

[0008] The electric wire according to one aspect of the present invention includes a conductor and a coating layer that coats the conductor. Fluorine resin Includes. The fluororesin in the coating layer is a crosslinked fluororesin. The maximum height representing the roughness of the surface of the coating layer is 4 μm or less.

[0009] A method for producing an electric wire according to one aspect of the present invention is a method for producing an electric wire including a conductor and a coating layer that coats the conductor. The method for producing an electric wire includes the steps of forming a coating film made of a fluororesin-containing ... The fluororesin in the coating film is crosslinked to become a crosslinked fluororesin, The coating layer is formed do. Effect of the Invention

[0010] According to the present invention, it is possible to obtain an electric wire capable of exhibiting the excellent insulating performance inherent to a fluororesin, and a method for producing the same. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an electric wire according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing an example of an electric wire manufacturing apparatus. [Diagram 3] FIG. 3 is a plan view showing an example of a coating die. [Figure 4] FIG. 4 is a plan view showing an example of a shaping die. [Diagram 5] FIG. 5 is a flow diagram showing a flow of the method for producing the electric wire according to the embodiment. [Figure 6] FIG. 6 is a diagram for explaining the action of the shaping die. [Figure 7] FIG. 7 is a diagram for explaining the surface state of the electric wire. [Figure 8] FIG. 8 is a diagram illustrating the surface state of a conventional electric wire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. [1] An electric wire according to one embodiment of the present disclosure includes a conductor and a coating layer that coats the conductor, However, fluororesin Including, The fluororesin in the coating layer is a crosslinked fluororesin, The maximum height representing the roughness of the surface of the coating layer is 4 μm or less.

[0013] In the electric wire configured as described above, the coating layer has a smooth surface. This coating layer does not include dents or pinholes that may be the starting points of dielectric breakdown. The insulating performance of this coating layer is fully achieved due to the characteristics of the material that constitutes this coating layer. This coating layer contains a cross-linked fluororesin, which is a cross-linked product of a fluororesin. In this electric wire, the good insulating performance of the fluororesin is achieved.

[0014] In the present disclosure, the maximum height representing the roughness of the coating layer surface is expressed as the maximum height Sz measured in accordance with ISO 25178-2. The measurement is performed on an area of ​​0.25 mm x 0.25 mm using a surface roughness measuring device (Keyence Corporation's "VKX-1100").

[0015] [2] In the electric wire described in the above-mentioned [1], preferably, the conductor is a rectangular wire, the conductor has four corners, the coating layer has curved portions at portions corresponding to the corners of the conductor, the outer surfaces of the curved portions form the corners of the electric wire, the corners of the conductor and the corners of the electric wire are rounded, and a ratio (Rw / Rc) of a rounding radius Rw of the corners of the electric wire to a rounding radius Rc of the conductor corners is 1 or less.

[0016] In the electric wire configured as described above, the thickness of the coating layer is ensured to be sufficient at the corners where the electric field is likely to concentrate, and the excellent insulating performance of the fluororesin is exhibited in this electric wire.

[0017] [3] In the electric wire according to the above-mentioned [1] or [2], preferably, Crosslinking The fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride. Cross-linked material It is.

[0018] In the electric wire configured as described above, the excellent insulating performance of the fluororesin is exhibited.

[0019] [4] A method for producing an electric wire according to another aspect of the present disclosure is a method for producing an electric wire including a conductor and a coating layer coating the conductor. The method for producing an electric wire includes the steps of forming a coating film made of a fluororesin-containing ... The fluororesin in the coating film is crosslinked to become a crosslinked fluororesin, The coating layer is formed do.

[0020] In the manufacturing method of an electric wire configured as described above, the fluororesin contained in the coating film is plasticized before passing through the shaping die. Since the coating film passes through the heated shaping die, the temperature of the coating film passing through the shaping die is kept stable. The coating film passes through the shaping die with the fluororesin in a plasticized state. The coating film is smoothed by passing through the shaping die. In this manufacturing method, a coating layer having a smooth surface is formed. The formation of dents and pinholes, which are likely to be the starting point of insulation breakdown, is prevented. The insulating performance of this coating layer is fully achieved due to the characteristics of the material constituting this coating layer. This coating layer contains a cross-linked fluororesin, which is a cross-linked product of a fluororesin. In the electric wire obtained by this manufacturing method, the good insulating performance of the fluororesin is achieved.

[0021] [5] In the method for producing an electric wire described in the above item [4], preferably, in the step of baking the coating film, the coating film is baked in an atmosphere adjusted to a temperature equal to or higher than the crystalline melting point of the fluororesin.

[0022] In the electric wire manufacturing method configured as described above, the plasticization of the fluororesin contained in the coating film is promoted. The coating film passes through the shaping die with the fluororesin in a sufficiently plasticized state. In this manufacturing method, a coating layer having a smooth surface is formed. The insulating performance of this coating layer is fully achieved due to the characteristics of the material that constitutes this coating layer. In the electric wire obtained by this manufacturing method, the good insulating performance of the fluororesin is achieved.

[0023] In the present disclosure, the crystalline melting point of a fluororesin is measured by the following method using differential scanning calorimetry. A differential scanning calorimeter (SII NanoTechnology's "X-DSC7000") that has been temperature calibrated in advance using indium and lead as standard samples is used. 3 mg of the fluororesin is placed in an aluminum pan (crimp container) and heated at a rate of 10°C / min in a temperature range of 230 to 380°C under a nitrogen gas flow of 40 ml / min. The minimum point of the melting peak in the aforementioned range is measured and this minimum point is regarded as the crystalline melting point of the aforementioned fluororesin.

[0024] [6] In the method for producing an electric wire according to the above-mentioned [4] or [5], preferably, the shaping die has a temperature equal to or higher than the crystalline melting point of the fluororesin.

[0025] In the electric wire manufacturing method configured as described above, the plasticized state of the fluororesin is stably maintained in the coating film passing through the shaping die. Since the coating film is effectively leveled by the shaping die, this manufacturing method forms a coating layer having a smooth surface. The insulating performance of this coating layer is fully dependent on the characteristics of the material that constitutes this coating layer. In the electric wire obtained by this manufacturing method, the good insulating performance of the fluororesin is exhibited.

[0026] [7] In the method for producing an electric wire according to any one of the above [4] to [6], the conductor is preferably a rectangular wire.

[0027] In the method for producing an electric wire configured as described above, a coating layer with a sufficient thickness is formed at the corners where the electric field is likely to concentrate. The insulating performance of this coating layer is fully achieved due to the characteristics of the material that constitutes this coating layer. In the electric wire obtained by this production method, the excellent insulating performance of the fluororesin is achieved.

[0028] [8] In the method for producing an electric wire according to any one of the above-mentioned [4] to [7], the fluororesin is preferably at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride.

[0029] In the electric wire configured as described above, the excellent insulating performance of the fluororesin is exhibited.

[0030] [Details of the embodiment of the present disclosure] The present disclosure will be described below with reference to the drawings, taking specific examples of the embodiments. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0031] [Electric wire] FIG. 1 shows an example of an electric wire 2 according to an embodiment of the present disclosure. FIG. 1 shows a cross section of the electric wire 2. The electric wire 2 is a rectangular electric wire. The electric wire 2 has four corners 4. These corners 4 are rounded. The cross-sectional shape of the electric wire 2 is approximately rectangular. The electric wire 2 may also be a round electric wire whose cross-sectional shape is circular.

[0032] In this disclosure, approximately rectangular means a rectangle with four rounded corners.

[0033] The electric wire 2 shown in Fig. 1 is an electric wire used for the windings of a motor. From the viewpoint of being able to wind the electric wire 2 at high density, the rectangular electric wire shown in Fig. 1 is preferable as the electric wire 2 used for the windings of a motor.

[0034] The electric wire 2 includes a conductor 6 and a coating layer 8. The conductor 6 is usually a copper wire. The conductor 6 may be a metal wire such as an aluminum wire, an aluminum alloy wire, a nickel-plated copper wire, or a silver-plated copper wire. As described above, the electric wire 2 is a rectangular electric wire. In the electric wire 2, a rectangular wire having a substantially rectangular cross-sectional shape is used as the conductor 6. If the electric wire 2 is a round electric wire, a round wire having a circular cross-sectional shape is used as the conductor 6. In FIG. 1, the arrow Rc indicates the rounding radius of a corner 10 of the conductor 6 (hereinafter, the conductor corner 10).

[0035] The covering layer 8 covers the conductor 6. Since the conductor 6 is a rectangular wire, the covering layer 8 has bends 12 at portions corresponding to the corners 4 of the conductor 6. This covering layer 8 has four bends 12. In this electric wire 2, the outer surfaces of the bends 12 form the corners 4 of the electric wire 2 (hereinafter, referred to as electric wire corners 4). As described above, the electric wire corners 4 are rounded. In FIG. 1, the arrow Rw indicates the rounding radius of the electric wire corners 4.

[0036] In the electric wire 2, the coating layer 8 is formed using a fluororesin paint. As described later, the coating layer is obtained by irradiating a coating film formed by applying a fluororesin paint around the conductor 6 with ionizing radiation under predetermined conditions. Examples of the ionizing radiation include electron beams, gamma rays, X-rays, neutron beams, and high-energy ions.

[0037] The fluororesin includes fluororesin. In the electric wire 2, examples of the fluororesin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), fluoroolefin-vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer. These may be used alone or in combination of two or more.

[0038] In the electric wire 2, from the viewpoint of good electrical properties, heat resistance, and chemical resistance, the fluororesin is preferably at least one selected from the group consisting of PTFE, PFA, FEP, ETFE, PVDF, and PVF, and more preferably PTFE.

[0039] When the fluororesin is PTFE, the PTFE may be homo-PTFE or modified PTFE. Homo-PTFE refers to a homopolymer of tetrafluoroethylene. Modified PTFE refers to a copolymer of tetrafluoroethylene and a monomer other than tetrafluoroethylene (also called a "modified monomer"). The upper limit of the content of the structural unit derived from the modified monomer in the modified PTFE is preferably 1% by mass, more preferably 0.5% by mass. As the modified monomer, a known monomer may be used, and one type may be used alone, or two or more types may be used.

[0040] The fluororesin can be produced by a conventionally known production method. Specifically, in the case of PTFE, it can be produced by emulsion polymerization of tetrafluoroethylene (TFE) in the presence of an aqueous dispersion medium, a surfactant, and a radical polymerization initiator. Here, examples of the surfactant include fluorine-containing surfactants such as perfluoroalkyl carboxylic acids and their salts, and fluorine-containing sulfonic acids and their salts. Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide and tert-butyl hydroperoxide. When synthesizing PTFE, a chain transfer agent may be used to control the molecular weight (melt viscosity) of the resulting PTFE, and further, an emulsion stabilizer such as paraffin wax, a pH adjuster such as ammonium carbonate, and the like may be used. In this electric wire 2, a commercially available fluororesin can also be used as the fluororesin.

[0041] The fluororesin coating is a liquid in which the above-mentioned fluororesin powder is dispersed in a solvent mainly composed of water. In the electric wire 2, for example, a fluororesin powder having an average primary particle size of 0.1 μm or more and 0.5 μm or less is used as the fluororesin. The content of the fluororesin contained in the fluororesin coating is appropriately adjusted, for example, in the range of 10 mass % or more and 60 mass % or less.

[0042] In the present disclosure, the average primary particle diameter of the fluororesin powder is determined as follows. The transmittance per unit length of projected light with a wavelength of 550 nm of an aqueous dispersion of the fluororesin powder, in which the polymer concentration has been adjusted to 0.22% by mass, is measured. The unidirectional diameter of the fluororesin powder in a transmission electron microscope photograph is measured to determine the primary particle diameter. A calibration curve is prepared between the measured transmittance and the determined average primary particle diameter. The transmittance of the aqueous dispersion to be measured is measured, and the average primary particle diameter of the fluororesin particles is determined based on the prepared calibration curve.

[0043] The solvent is not particularly limited as long as it is a liquid whose main component is water. The solvent may be composed of only water. The solvent may contain components other than water. Examples of components other than water include water-soluble organic solvents such as alcohol. "Mainly composed of water" means that the ratio of water in the solvent is 50% by volume or more.

[0044] In addition to the fluororesin and the solvent, the fluorocoating may contain chemicals such as surfactants, thickeners, film-forming agents, antifoaming agents, fillers, pigments, and flame retardants.

[0045] [Manufacturing equipment] Next, a manufacturing apparatus used to manufacture the electric wire 2 will be described. FIG. 2 shows an example of a manufacturing apparatus 22. A conductor 6 is supplied to this manufacturing apparatus 22 from a conductor supplying apparatus (not shown). In this manufacturing apparatus 22, a coating layer 8 is formed around the conductor 6 to manufacture the electric wire 2. The manufactured electric wire 2 is taken up by an electric wire winding apparatus (not shown). In FIG. 2, the conductor 6 moves from left to right. The left side of the page is the upstream side of the manufacturing apparatus 22, and the right side is the downstream side of the manufacturing apparatus 22. The conductor supplying apparatus is located upstream of the manufacturing apparatus 22, and the electric wire winding apparatus is located downstream of the manufacturing apparatus 22.

[0046] The manufacturing apparatus 22 includes, from the upstream side to the downstream side, an alignment device 24, a coating device 26, and a forming device 28. The manufacturing apparatus 22 will be described taking as an example a case in which the electric wire 2 is manufactured by passing the conductor 6 through the alignment device 24, the coating device 26, and the forming device 28 in this order.

[0047] The centering device 24 adjusts the position of the conductor 6 relative to the coating device 26 and the forming device 28. As the centering device 24, a device that is generally used in the manufacture of electric wires is used.

[0048] The coating device 26 is located downstream of the alignment device 24. The coating device 26 forms a coating film made of fluororesin paint around the conductor 6. This coating device 26 is equipped with a coating die 30 for forming the coating film. Although not shown, in this coating device 26, the conductor 6 is passed through a paint tank filled with fluororesin paint. This causes the fluororesin paint to adhere to the periphery of the conductor 6. The conductor 6 together with the adhered fluororesin paint is passed through the coating die 30. This causes a coating film to be formed around the conductor 6.

[0049] FIG. 3 shows a front view of the coating die 30 as seen from the upstream side. The coating die 30 has a through hole 32 in its center. The conductor 6 to which the fluororesin coating material is applied passes through this through hole 32. As described above, the electric wire 2 is a rectangular electric wire. The shape of this through hole 32 is approximately rectangular. In FIG. 3, the double-headed arrow Wb indicates the width of the through hole 32. The double-headed arrow Tb indicates the height of the through hole 32. The arrow Rb indicates the rounding radius of the corners 34 of the through hole 32. The size, length and shape of the through hole 32 in the coating die 30 are appropriately determined according to the specifications of the electric wire 2 to be manufactured.

[0050] The forming device 28 is located downstream of the coating device 26. The forming device 28 bakes the coating film formed around the conductor 6 and irradiates the coating film with ionizing radiation. The forming device 28 includes a baking module 36 that bakes the coating film and an irradiation module 38 that irradiates the coating film with ionizing radiation.

[0051] The firing module 36 has the same configuration as an apparatus generally used in the manufacture of electric wires, except that it is provided with a shaping die, which will be described later. The firing module 36 includes a cylindrical firing furnace 40. The conductor 6 on which the coating film is formed passes through the firing furnace 40. In the firing module 36, the temperature inside the firing furnace 40 is adjusted by a temperature adjustment device (not shown). The coating film is fired in an atmosphere adjusted to a predetermined temperature.

[0052] The firing module 36 further includes a shaping die 42. The shaping die 42 is disposed in the firing furnace 40. In the firing furnace 40, the shaping die 42 is located downstream. The temperature of the shaping die 42 is also regulated by the above-mentioned temperature regulating device. In the firing module 36, the fired coating film, together with the conductor 6, is passed through the shaping die 42, the temperature of which is regulated.

[0053] FIG. 4 shows a front view of the shaping die 42 as seen from the upstream side. The shaping die 42 has a through hole 44 in its center, similar to the coating die 30. The fired coating film passes through this through hole 44 together with the conductor 6. As described above, the electric wire 2 is a rectangular electric wire. The shape of this through hole 44 is approximately rectangular. In FIG. 4, the double-headed arrow Wa indicates the width of the through hole 44. The double-headed arrow Ta indicates the height of the through hole 44. The arrow Ra indicates the rounding radius of the corners 46 of the through hole 44. The size, length and shape of the through hole 44 in the shaping die 42 are determined appropriately according to the specifications of the electric wire 2 to be manufactured.

[0054] In this manufacturing apparatus 22, the coating film that has passed through the baking module 36 is fed into the irradiation module 38 together with the conductor 6. The irradiation module 38 has a configuration similar to that of an apparatus generally used in the manufacture of the electric wire 2. This irradiation module 38 includes an irradiation unit 48 that irradiates ionizing radiation. In this irradiation module 38, the irradiation unit 48 irradiates the coating film that passes through the reactor 50 together with the conductor 6 with ionizing radiation. This causes a crosslinking reaction of the fluororesin contained in the coating film, forming a coating layer 8. This coating layer 8 contains a crosslinked fluororesin that is a crosslinked product of the fluororesin.

[0055] In the irradiation module 38, the inside of the reactor 50 is adjusted to a substantially oxygen-free state. -4 The atmosphere is adjusted to a vacuum state of Torr or less, or to an inert gas atmosphere such as nitrogen with an oxygen concentration of 100 ppm or less. In this irradiation module 38, ionizing radiation is irradiated toward the coating film in a substantially oxygen-free state. This prevents the coating film from being oxidized during irradiation.

[0056] In this irradiation module 38, the temperature inside the reaction furnace 50 is adjusted by a temperature adjustment device (not shown). In this irradiation module 38, ionizing radiation is irradiated toward the coating film in an atmosphere adjusted to a predetermined temperature.

[0057] The forming device 28 further includes a cooling module 52. The temperature of the electric wire 2 discharged from the irradiation module 38 is high. The electric wire 2 in a high temperature state is cooled in the cooling module 52. After cooling, the electric wire 2 is wound by an electric wire winding device.

[0058] [Method of manufacturing electric wire 2] Next, a method for manufacturing the electric wire 2 according to an embodiment of the present disclosure will be described. Fig. 5 shows an example of a flow of this manufacturing method. This manufacturing method is a method for manufacturing the electric wire 2 including the conductor 6 and the covering layer 8 that covers the conductor 6. This manufacturing method includes a forming step S1, a firing step S2, a shaping step S3, and a shaping step S4. It includes a step S3 and an irradiation step S4.

[0059] In this manufacturing method, the forming step S1, the firing step S2, the shaping step S3, and the irradiation step S4 are continuously performed to manufacture the electric wire 2. In this manufacturing method, for example, the forming step S1, the firing step S2, the shaping step S3, and the irradiation step S4 may be performed in a batch manner to manufacture the electric wire 2.

[0060] In the forming step S1, the conductor 6 is passed through a coating die 30 together with the fluororesin in the coating device 26. As a result, a coating film made of the fluororesin is formed around the conductor 6. This coating film contains a fluororesin.

[0061] In this manufacturing method, a method of forming a coating film containing a fluororesin by passing the conductor 6 through the coating die 30 while applying fluororesin paint around the conductor 6 has been shown, but the method of forming the coating film is not limited to the method using the coating die 30. In this manufacturing method, the coating film may be formed by immersing the conductor 6 in the fluororesin paint, or by spraying the fluororesin paint onto the conductor 6. A coating film containing a fluororesin may be formed by applying powder made of fluororesin to the conductor 6 by a powder coating method, or a coating film containing a fluororesin may be formed by covering the conductor 6 with fluororesin by a melt extrusion method.

[0062] In the firing step S2, the coating film formed around the conductor 6 is fired in the firing module 36 of the forming device 28. This causes volatile components such as the solvent contained in the coating film to volatilize, and the coating film hardens.

[0063] In the shaping step S3, the fired coating film is passed through the shaping die 42 together with the conductor 6. As described above, the shaping die 42 is placed in the firing furnace 40. The temperature inside the firing furnace 40 is adjusted to a temperature at which at least volatile components such as the solvent contained in the coating film can volatilize. The shaping die 42 placed in the firing furnace 40 is heated by the atmosphere inside the firing furnace 40. In this shaping step S3, the fired coating film is passed through the heated shaping die 42 together with the conductor 6. This causes the coating film to be shaped.

[0064] In the irradiation step S4, the coating film shaped in the shaping step S3 is irradiated with ionizing radiation in a substantially oxygen-free environment, thereby forming a coating layer 8 containing a cross-linked fluororesin, and the electric wire 2 shown in FIG.

[0065] In the irradiation step S4, the amount of ionizing radiation irradiated to the coating film is preferably 10 kGy or more, and more preferably 30 kGy or less, from the viewpoint of sufficiently proceeding with the crosslinking reaction, and is preferably 2000 kGy or less, and more preferably 200 kGy or less, from the viewpoint of preventing a decrease in productivity and mechanical properties of the coating layer 8.

[0066] In this irradiation step S4, from the viewpoint of effectively progressing the crosslinking reaction, the temperature inside the reaction furnace 50 is preferably set to be equal to or higher than the crystalline melting point of the fluororesin. The crystalline melting point of the fluororesin varies depending on the molecular weight, etc., but is, for example, in the range of 320° C. or higher and lower than 350° C. The temperature inside the reaction furnace 50 is equal to or higher than the crystalline melting point, and is preferably 320° C. or higher and 360° C. or lower.

[0067] The above describes the manufacturing method by taking as an example the case where the conductor 6 passes through the aligning device 24, the coating device 26, and the forming device 28 in this order to manufacture the electric wire 2, that is, the case where the electric wire 2 is manufactured by irradiating the coating film formed on the conductor 6 with ionizing radiation. However, the electric wire 2 may be manufactured by irradiating a laminate of coating films obtained by laminating a plurality of coating films with ionizing radiation. In this case, the forming step S1 is repeated a plurality of times, and then the heating step S2, the shaping step S3, and the irradiation step S4 are performed to manufacture the electric wire 2. In this manufacturing method, the forming step S1 to the irradiation step S4 are regarded as one course, and the electric wire 2 may be formed by repeating this course a plurality of times. In this case, the coating layer 8 of the electric wire 2 is configured as a laminate of a cured layer of the coating film containing a cross-linked fluororesin. In the second and subsequent courses, the forming step S1, the heating step S2, the shaping step S3, and the irradiation step S4 are performed on the conductor 6 coated with the cured layer.

[0068] In this manufacturing method, the coating film containing the fluororesin is baked in the baking step S2. In this baking step S2, the coating film hardens due to the evaporation of the volatile components, while the plasticization of the fluororesin contained in the coating film is promoted. Since the shaping step S3 is performed after the baking step S2, in this manufacturing method, the fluororesin contained in the coating film is plasticized before passing through the shaping die 42. As described above, in the shaping step S3, the coating film passes through the heated shaping die 42. The temperature of the coating film passing through the shaping die 42 is kept stable. In this manufacturing method, the coating film passes through the shaping die 42 in a state in which the fluororesin is plasticized.

[0069] Figure 6 conceptually shows the change in state of the coating film 54 as it passes through the shaping die 42. The lower left side of Figure 6 shows a cross section of the coating film 54 before it passes through the shaping die 42, taken along line bb in the conceptual diagram above, together with a cross section of the conductor 6. The lower right side of Figure 6 shows a cross section of the coating film 54 after it passes through the shaping die 42, taken along line aa in the conceptual diagram above, together with a cross section of the conductor 6.

[0070] As shown in Fig. 6, dents 56 and pinholes 58 that existed in the coating film 54 disappear by passing through the shaping die 42. The uneven thickness of the coating film 54, also called dog bone, is eliminated, and the coating film 54 before passing through the shaping die 42 is corrected to have a substantially uniform thickness. In this way, the coating film 54 is leveled by passing through the shaping die 42. The irradiation step S4 is performed on the leveled coating film 54, and therefore, in this manufacturing method, a coating layer 8 having a smooth surface is formed.

[0071] In this manufacturing method, the through hole 44 of the shaping die 42 is preferably configured to have the same shape as the through hole 32 of the coating die 30. As long as an electric wire 2 having a smooth coating layer 8 is obtained, the through hole 44 of the shaping die 42 may be larger than the through hole 32 of the coating die 30, or the through hole 44 of the shaping die 42 may be smaller than the through hole 32 of the coating die 30.

[0072] Fig. 7 shows an example of the surface state of the electric wire 2 shown in Fig. 1. Fig. 8 shows an example of the surface state of a conventional electric wire manufactured by a conventional manufacturing method that does not include the shaping step S3.

[0073] 7 and 8, the surface of the coating layer 8 of the electric wire 2 is smoother than the surface of the coating layer of the conventional electric wire. Specifically, the maximum height representing the roughness of the surface of the coating layer 8 of the electric wire 2 is 4 μm or less. In the coating layer of the conventional electric wire, the maximum height representing the roughness of the coating layer surface is in the range of 60 μm to 70 μm, so it is clear that the smoothness of the surface of the coating layer 8 of the electric wire 2 is significantly improved compared to that of the conventional electric wire.

[0074] The electric wire 2 manufactured by this manufacturing method has a smooth coating layer 8. The formation of dents 56 and pinholes 58, which are likely to be the starting points of dielectric breakdown, is prevented. This coating layer 8 does not include dents 56 and pinholes 58, which are likely to be the starting points of dielectric breakdown. The insulating performance of this coating layer 8 is fully achieved due to the characteristics of the material constituting this coating layer 8. This coating layer 8 contains a cross-linked fluororesin, which is a cross-linked product of a fluororesin. The electric wire 2 obtained by this manufacturing method achieves the good insulating performance of the fluororesin.

[0075] In this manufacturing method, in the baking step S2, the coating film 54 is preferably baked in an atmosphere adjusted to a temperature equal to or higher than the crystalline melting point of the fluororesin. This promotes plasticization of the fluororesin contained in the coating film 54. The coating film 54 passes through the shaping die 42 in a state in which the fluororesin is sufficiently plasticized. In this manufacturing method, a coating layer 8 having a smooth surface is formed. The insulating performance of this coating layer 8 is fully achieved due to the characteristics of the material constituting this coating layer 8. In the electric wire 2 obtained by this manufacturing method, good insulating performance of the fluororesin is achieved. From the viewpoint of preventing deterioration of the coating film 54 due to baking, the coating film 54 is preferably baked in an atmosphere adjusted to a temperature lower than a temperature 60° C. higher than the crystalline melting point of the fluororesin.

[0076] In this manufacturing method, in the shaping step S3, the shaping die 42 preferably has a temperature equal to or higher than the crystalline melting point of the fluororesin. This allows the fluororesin to be stably maintained in a plasticized state in the coating film 54 passing through the shaping die 42. Since the coating film 54 is effectively leveled by the shaping die 42, a coating layer 8 having a smooth surface is formed in this manufacturing method. The insulating performance of this coating layer 8 is fully exhibited by the characteristics of the material constituting this coating layer 8. In the electric wire 2 obtained by this manufacturing method, the good insulating performance of the fluororesin is exhibited. From the viewpoint of preventing deterioration of the coating film 54 due to passage through the shaping die 42, the shaping die 42 preferably has a temperature lower than a temperature 50° C. higher than the crystalline melting point of the fluororesin.

[0077] From the viewpoint of stably forming the coating layer 8 having a smooth surface, it is more preferable that in the baking step S2, the coating film 54 is baked in an atmosphere adjusted to a temperature equal to or higher than the crystalline melting point of the fluororesin, and that in the shaping step S3, the shaping die 42 has a temperature equal to or higher than the crystalline melting point of the fluororesin. In this case, from the viewpoint of preventing deterioration of the coating film 54, it is more preferable that the coating film 54 is baked in an atmosphere adjusted to a temperature lower than a temperature 60° C. higher than the crystalline melting point of the fluororesin, and that the shaping die 42 has a temperature lower than a temperature 50° C. higher than the crystalline melting point of the fluororesin.

[0078] As described above, the conductor 6 of the electric wire 2 is a rectangular wire. From the viewpoint of securing the conductor area, it is preferable that the conductor corner 10 has a small rounding radius Rc. In this case, it is preferable that the electric wire corner 4 also has a small rounding radius like the conductor corner 10. However, it is difficult to form a coating layer so that the electric wire corner has a small rounding radius. For example, in a conventional electric wire having a coating layer formed by baking an insulating varnish, an electric wire corner having a rounding radius larger than the rounding radius Rc of the conductor corner 10 is formed. In contrast, in this manufacturing method, the coating film 54 is effectively leveled by passing through the shaping die 42, so that the electric wire corner 4 is obtained with a rounding radius Rc equal to or smaller than the rounding radius Rc of the conductor corner 10. Specifically, the ratio (Rw / Rc) of the rounding radius Rw of the electric wire corner 4 to the rounding radius Rc of the conductor corner 10 is 1 or less. In this manufacturing method, an electric wire 2 is obtained in which the coating layer 8 at the electric wire corner 4 is thicker than that of the conventional electric wire.

[0079] In this electric wire 2, from the viewpoint of ensuring the thickness of the coating layer 8 at the electric wire corner 4, the ratio (Rw / Rc) of the rounding radius Rw of the electric wire corner 4 to the rounding radius Rc of the conductor corner 10 is preferably 0.77 or less, and more preferably 0.67 or less.

[0080] As is clear from the above description, the electric wire 2 of the present disclosure can exhibit the excellent insulating performance of the fluororesin. And, according to the manufacturing method of the electric wire of the present disclosure, the electric wire 2 capable of exhibiting the excellent insulating performance of the fluororesin can be obtained. [Explanation of symbols]

[0081] 2 electric wire 4 Corner (electric wire corner) 6 Conductors 8 Covering layer 10 Corner of conductor 6 (conductor corner) 12 Curved portion of coating layer 8 22 Manufacturing equipment 24 Alignment device 26 Coating equipment 28 Forming device 30 Coating Dies 32 Through hole of coating die 30 34 Corner of coating die 30 36 Firing module 38 Irradiation Module 40 Kiln 42 Shaping Dies 44 Through hole of shaping die 42 46 Corner of shaping die 42 48 Irradiation Unit 50 Reactor 52 Cooling module 54 Paint film 56 Dent 58 Pinhole

Claims

1. A conductor and a coating layer that coats the conductor, The coating layer contains a fluororesin, The fluororesin in the coating layer is a crosslinked fluororesin, The maximum height representing the roughness of the coating layer surface is 4 μm or less; Electric wire.

2. The conductor is a rectangular wire, The conductor has four corners, the coating layer has a curved portion at a portion corresponding to a corner of the conductor, The outer surface of the bent portion constitutes a corner of the electric wire, Corners of the conductor and corners of the wire are rounded, The ratio (Rw / Rc) of the rounding radius Rw of the electric wire corner to the rounding radius Rc of the conductor corner is 1 or less. The electric wire according to claim 1.

3. The crosslinked fluororesin is at least one crosslinked material selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride. The electric wire according to claim 1 or 2.

4. A method for manufacturing an electric wire including a conductor and a coating layer coating the conductor, comprising the steps of: forming a coating film made of a fluororesin-containing fluororesin coating material around the conductor; A step of baking the coating film; A step of shaping the baked coating film; irradiating the shaped coating with ionizing radiation; Including, In the step of forming the coating film, the conductor is passed through a coating die together with the fluorine coating material, In the step of shaping the coating, the fired coating is passed through a heated shaping die together with the conductor; In the step of irradiating the coating film with ionizing radiation, the fluororesin in the coating film is crosslinked to become a crosslinked fluororesin, thereby forming the coating layer. A method for manufacturing electric wire.

5. In the step of baking the coating film, the coating film is baked in an atmosphere adjusted to a temperature equal to or higher than the crystalline melting point of the fluororesin. The method for producing the electric wire according to claim 4 .

6. The shaping die has a temperature equal to or higher than the crystalline melting point of the fluororesin. The method for producing an electric wire according to claim 4 or 5.

7. The conductor is a rectangular wire. The method for producing the electric wire according to any one of claims 4 to 6.

8. The fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, and polyvinyl fluoride. The method for producing the electric wire according to any one of claims 4 to 7.

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