Conductive wire, coil, and method for manufacturing conductive wire

Abstract

An embodiment provides a conductive wire comprising a conductive base material having a linear shape, and an insulating coating film covering the base material. At least a part of a portion of the insulating film on the outer surface thereof is composed of a nanostructure region composed of nanofibers or nanoparticles.

Description

Conductor, coil, and method for manufacturing conductor

[0001] Embodiments of the present invention relate to a conductor, a coil, and a method for manufacturing a conductor.

[0002] A coil obtained by winding a conductive wire is used, for example, in a driving part of an electric motor. Also, a coil using a superconducting wire as the wire is used, for example, as a superconducting coil that generates a strong magnetic field in a nuclear magnetic resonance apparatus (NMR), a magnetic resonance imaging apparatus (MRI), or the like. In such a coil, for example, an insulating member such as an insulating tape is sandwiched between the wires to prevent a short circuit between the turns of the wound coil. However, due to the misalignment and interlayer pressure of the wires and the insulating member, a short circuit between the turns may occur.

[0003] Instead of sandwiching an independent insulating member such as an insulating tape between the wires, the wires may be coated with an insulating film. Although a solvent at the time of film formation may remain in the insulating film, the insulating film containing the residual solvent exhibits adhesiveness between the films. Therefore, the conductors with insulating films may fuse to each other. As a result, for example, when stress is applied to the coil, a phenomenon of peeling between the layers inside the wire, that is, interlayer peeling occurs, and the current-carrying performance may deteriorate.

[0004] Japanese Patent Application Laid-Open No. 2013-254563

[0005] An object is to provide a conductor capable of suppressing a short circuit in a coil, having high durability, a coil including this conductor, and a method for manufacturing this conductor.

[0006] According to an embodiment, a conductor including a linear conductive base material and an insulating film covering the base material is provided. At least a part of the portion on the outer surface of the insulating film is composed of a nanostructure region made of nanofibers or nanoparticles.

[0007] According to still another embodiment, a coil including a winding and a resin on the winding is provided. The winding includes the conductor according to the above embodiment. A part of the resin is impregnated inside the insulating film.

[0008] In yet another embodiment, a method for manufacturing a conductor is provided, which includes forming a first coating on a substrate, forming a second coating on the first coating, and forming an insulating coating by fusing the first coating and the second coating together. The first coating is formed by depositing a charged raw material solution on the substrate. The second coating is formed by depositing a charged raw material solution on the first coating in the form of nanofibers or nanoparticles. The first coating and the second coating are fused together after the formation of the second coating.

[0009] Figure 1 is a schematic perspective view showing an example of a coil. Figure 2 is a schematic enlarged cross-sectional view showing part A in Figure 1. Figure 3 is a schematic enlarged cross-sectional view showing an example of part B in Figure 2. Figure 4 is a schematic enlarged cross-sectional view showing another example of part B in Figure 2. Figure 5 is a schematic cross-sectional view showing an example of a conductor according to the embodiment. Figure 6 is a schematic cross-sectional view showing another example of a conductor according to the embodiment. Figure 7 is a schematic cross-sectional view showing another example of a conductor according to the embodiment. Figure 8 is a schematic cross-sectional view showing another example of a conductor according to the embodiment. Figure 9 is a schematic cross-sectional view showing another example of a conductor according to the embodiment. Figure 10 is a schematic diagram showing an example of the manufacturing of a conductor according to the embodiment. Embodiment

[0010] Forming an insulating coating on the surface of a conductor is known as a means of reducing defects such as short circuits in coil conductors and improving reliability. The insulating coating should have durability properties such as resistance to degradation and peeling, which help prevent deterioration of the conductor. Naturally, a low-cost insulating coating formation method is preferred.

[0011] As a means of improving peel resistance and preventing delamination, it is known that an electrodeposited coating of block copolymer polyimide containing siloxane bonds in the main chain of polyimide and having anionic groups in the molecule can be applied as an insulating coating. Because this electrodeposited coating has excellent flexibility, it exhibits the function of removing stress concentration areas by plastically deforming. It is also known that forming a release layer on the surface of the insulating coating reduces the adhesion between insulating coatings and suppresses delamination. Examples of materials for the release layer include fluororesins such as Teflon (registered trademark). However, the former electrodeposited coating tends to be expensive because it uses a special polyimide, and the latter uses fluorine-based materials which have a high environmental impact.

[0012] The conductor according to the embodiment includes a conductive substrate having a linear shape and an insulating coating covering the substrate. That is, the conductor is an insulating coated conductor. In the conductor, at least a portion of the insulating coating on the outer surface is composed of nanostructure regions made of nanofibers or nanoparticles.

[0013] The insulating coating on the conductor can be formed using general-purpose raw materials and has a nanostructure region on its surface that has high drying and release properties. The surface of the insulating coating exhibits low adhesion due to the nanostructure region consisting of nanofibers or nanoparticles. This prevents the coating from fusing together. Therefore, although the conductor does not use specially designed insulating polymers or environmentally harmful substances such as fluorine-based materials, delamination between layers can be suppressed in the conductor. In other words, the durability of the conductor is high because the insulating coating has a nanostructure region on its surface. Of course, in a coil using the conductor, the insulating coating can suppress short circuits between the conductors.

[0014] The linear substrate containing the conductor, and consequently the conductor itself, can be a superconducting wire. Furthermore, the substrate and the conductor can be high-temperature superconducting wires with a critical temperature of 25 K or higher, exhibiting superconductivity even at temperatures above 25 K (Kelvin). A coil using a superconducting wire can be a superconducting coil.

[0015] Examples of coils are shown in Figures 1 to 4. Figure 2 is an enlarged cross-sectional view of part A of the coil 30 shown in Figure 1. Figures 3 and 4 are both schematic enlarged cross-sections of part B in Figure 2, but each figure shows an example of a different coil. Figure 3 is an enlarged cross-sectional view of part B when the nanostructure region 23 of the insulating coating of the conductor 1 shown in Figure 2 is made of nanofibers. Figure 4 is an enlarged cross-sectional view of part B when the nanostructure region 23 of the insulating coating of the conductor 1 shown in Figure 2 is made of nanoparticles.

[0016] The illustrated coil 30 includes a conductor 1 and a resin 31. Specifically, the flat rectangular shaped conductor 1 is wound and stacked to form a winding, and the periphery of this winding and the spaces between the stacked conductor 1 are fixed by the resin 31. The coil 30 may have the shape of a pancake coil, as shown in the illustrated example. The z-direction shown in Figures 1 and 2 is along the thickness direction of the pancake coil and intersects the stacking direction of the conductor 1 as shown in Figure 2.

[0017] In the illustrated example, the conductor 1 includes a flat rectangular wire as the base material 10 and is a wire material having a flat rectangular wire shape, but is not limited to this. Although not illustrated, for example, the base material 10 may be a wire material having other cross-sectional shapes such as a round wire. Although also omitted from the illustration, the coil 30 may further include a winding frame on which the conductor 1 is wound around its outer circumference. In the illustrated example of the coil 30, the winding is a wound body formed by winding the conductor 1 in a circular shape, but the shape of the winding is not limited to a circular wound body, and may be a polygonal wound body such as a triangle or a square, for example.

[0018] Although not shown in the diagram, the base material 10 may include, for example, a metal substrate and a superconducting layer provided thereon. In other words, the conductor 1 can be a superconducting wire. Furthermore, the coil 30 using such a conductor 1 can be a superconducting coil.

[0019] The conductor 1 includes a base material 10 having a wire shape and an insulating coating 20 covering the base material 10. The base material 10 is conductive, but the insulating coating 20 is electrically insulating. Therefore, since the conductor 1, which is made of a base material 10 covered with an insulating coating 20, is used as the wire material, even though the conductor 1 is wound in such a way that the wires are in contact with each other in the coil 30, no short circuits occur between turns.

[0020] The insulating coating 20 is broadly composed of a substrate-side portion 21 that is in contact with the substrate 10 and a nanostructure region 23 located on the surface side of the conductor 1. In Figure 2, the substrate-side portion 21 and the nanostructure region 23 are clearly distinguished and shown, but the boundary line between the substrate-side portion 21 and the nanostructure region 23 in the insulating coating 20 is not always clearly visible. For example, as shown in the examples in Figures 3 and 4, the boundary portion 22, where the components of both are fused, can be passed from the substrate-side portion 21 toward the nanostructure region 23. That is, the substrate-side portion 21 and the nanostructure region 23 can be integrated to form the insulating coating 20. In other words, the insulating coating 20 may further include, in addition to the nanostructure region 23, a substrate-side portion 21 located on the back side of the nanostructure region 23, and a boundary portion 22 located between the nanostructure region 23 and the substrate-side portion 21. The boundary portion 22 may include a fused body of the components of the nanostructure region 23 and the components of the substrate-side portion 21.

[0021] In the illustrated example, the insulating coating 20 contains resin lumps 24, and as shown in Figures 3 and 4, at least the substrate-side portion 21 of the insulating coating 20 consists of an aggregate of resin lumps 24, with voids 25 formed between the resin lumps 24 that are connected to each other and constitute the substrate-side portion 21. Although the resin 31 is omitted in Figures 3 and 4, the resin 31 partially penetrates the voids 25 of the insulating coating 20 and is integrated with the conductor 1. As a result, the vibration resistance and thermal conductivity of the coil 30 are improved, and the coil 30 can exhibit high durability. It is desirable that the voids 25 are continuous pores rather than independent spaces. If the voids 25 are continuous, the resin 31 can easily impregnate the voids 25 when constructing the coil 30, and a coil 30 can be obtained in which the resin 31 penetrates even into the interior of the substrate-side portion 21 of the insulating coating 20.

[0022] In the example shown in Figures 3 and 4, in an insulating film 20 containing resin lumps 24 in the substrate-side portion 21, the proportion of resin lumps 24 within the insulating film 20 is highest at the interface between the substrate 10 and the insulating film 20. If the nanostructure region 23 does not contain resin lumps 24, and there is a boundary portion 22 between the substrate-side portion 21 and the nanostructure region 23, then, for example, the proportion of resin lumps 24 within the insulating film 20 decreases from the interface side toward the outer surface of the insulating film 20.

[0023] The structure of the substrate-side portion 21 of the insulating coating 20 is not limited to the structure shown in Figures 3 and 4. Specifically, in the illustrated examples, the substrate-side portion 21 is an aggregate of resin lumps 24 and includes voids 25, but the substrate-side portion of the insulating coating may be, for example, a solid structure without voids. Alternatively, the substrate-side portion of the insulating coating may be composed of, for example, resin fibers on the order of microns with a diameter of about 10 μm to 20 μm instead of resin lumps 24. From the viewpoint of improving the electrical insulation properties of the insulating coating 20, it is desirable that the substrate-side portion 21 be an aggregate of resin lumps 24 or a solid structure.

[0024] The nanostructure region 23 is a portion made up of nanofibers or nanoparticles and constitutes at least a part of the outer surface of the insulating coating 20. Figure 3 shows an example in which the nanostructure region 23 is made up of nanofibers 26. Figure 4 shows an example in which the nanostructure region 23 is made up of nanoparticles 27. Because the nanostructure region 23 is made up of nanofibers 26 or nanoparticles 27, it has low tackiness and can exhibit high release properties. Therefore, since the surfaces made up of the nanostructure region 23 are less likely to bond to each other, fusion between the laminated conductors 1 is suppressed. For example, when stress is applied to the coil 30, the laminated conductors 1 can shift or separate from each other to release or absorb the stress, thus suppressing delamination between the substrate 10 and the insulating coating 20.

[0025] The substrate-side portion 21 may be omitted, and the nanostructure region 23 may be used alone as the insulating coating 20. Compared to the nanofibers 26 and nanoparticles 27 that constitute the nanostructure region 23, coatings composed of resin blocks 24 or micron-order resin fibers and solid-structure coatings have higher adhesion to the substrate 10. Therefore, an insulating coating 20 that includes the substrate-side portion 21 in contact with the substrate 10 in addition to the nanostructure region 23 is preferred.

[0026] With reference to Figures 5 and 6, other examples of the conductor according to the embodiment will be described. The conductors illustrated in each figure correspond to a different configuration from the conductor 1 included in the coil 30 shown in Figures 1 to 4. Figures 5 and 6 are schematic cross-sectional views showing a cross-section intersecting the longitudinal direction of the conductor. Furthermore, each example is an example of a conductor having a flat rectangular wire shape.

[0027] Each conductor 1 includes a flat rectangular wire 11 and an insulating coating as a base material. The insulating coating covers the outer circumference of the flat rectangular wire 11. In the conductors 1 shown in Figures 5 and 6, the proportion of the outer surface of the insulating coating occupied by nanostructure regions 23 is larger compared to the conductor 1 in Figure 2. In Figure 2, at both ends in the width direction (z direction) of the flat rectangular base material 10, there are portions where the outer surface in the thickness direction of the insulating coating (top and bottom surfaces in the figure) is not composed of nanostructure regions 23. In the example shown in Figure 5, the outer surface in the thickness direction of the insulating coating is composed of nanostructure regions 23 over the entire width direction (horizontal direction in the figure) of the flat rectangular wire 11. In the example shown in Figure 6, not only the outer surface in the thickness direction of the insulating coating, but also the portions of the outer surface of the insulating coating corresponding to the sides of the conductor 1 located at both ends in the width direction of the flat rectangular wire 11 are partially composed of nanostructure regions 23.

[0028] The proportion of the outer surface of the insulating film occupied by the nanostructured region 23 may differ between one main surface and the other. Furthermore, the distribution of the nanostructured region 23 on the same main surface does not need to be symmetrical in the width direction.

[0029] With reference to Figures 7 to 9, other examples of the conductor according to the embodiment will be described. The conductors illustrated in each figure correspond to further different embodiments from conductor 1 shown in Figures 5 and 6. Figures 7 to 9 are schematic cross-sectional views showing a cross-section intersecting the longitudinal direction of the conductor. In addition, each example is an example of a conductor having a flat rectangular wire shape.

[0030] In these examples, the thickness of the insulating coating covering the outer circumference of the rectangular wire 11, excluding the nanofibers and nanoparticles, i.e., the thickness of the substrate-side portion 21, is thicker at both ends than at the central portion along the width direction of the rectangular wire 11 in the transverse direction as shown in Figures 7 to 9. Here, the thickness of the insulating coating and the substrate-side portion 21 refers to the thickness in the thickness direction of the rectangular wire 11, for example, the thickness along the vertical direction in each figure. The thickness of the substrate-side portion 21 of the insulating coating at each end may refer to the thickness along the width direction of the rectangular wire 11, for example, the thickness along the transverse direction in each figure (illustrations are omitted).

[0031] Regarding the thickness in the thickness direction, the thickness of the base material-side portion 21 at each location of the insulating coating on one main surface may differ from the thickness of the base material-side portion 21 at each corresponding location on the other main surface. Furthermore, the relationship that the thickness of the base material-side portion 21 at the ends of the insulating coating is greater than the thickness of the base material-side portion 21 at the center of the flat wire 11 in the width direction only needs to be satisfied for each side of the conductor 1. For example, the portion of the base material-side portion 21 of the insulating coating that covers the central part of one side of the flat wire 11 may be thicker than the portion that covers one or both ends of the other side (back side) of the flat wire 11. Also, the thickness of the respective end portions of the insulating coating on the same side may differ from each other.

[0032] Similarly, with respect to the thickness in the width direction at both ends, the thickness of the substrate-side portion 21 of the insulating coating covering the side surface of the rectangular wire 11 at one end and the thickness of the substrate-side portion 21 of the insulating coating covering the side surface at the other end may be different from each other.

[0033] The conductors 1 shown in Figures 7 to 9 have different proportions of the outer surface of the insulating coating occupied by nanostructure regions 23. In the example of Figure 7, as with Figure 2, there are portions at both ends in the width direction of the rectangular wire 11 where the outer surface in the thickness direction of the insulating coating is not composed of nanostructure regions 23. In the example of Figure 8, as with Figure 5, the outer surface in the thickness direction of the insulating coating is composed of nanostructure regions 23 over the entire width direction of the rectangular wire 11. In the example of Figure 9, as with Figure 6, not only the outer surface in the thickness direction of the insulating coating, but also portions of the outer surface of the insulating coating corresponding to the sides of the conductor 1 located at both ends in the width direction of the rectangular wire 11 are partially composed of nanostructure regions 23.

[0034] As shown in the examples from Figures 7 to 9, when the thickness of the insulating coating at both ends in the width direction of the rectangular wire 11 is greater than the thickness in the center, or when both are the same thickness, the insulating coatings of the laminated conductors 1 in the coil tend to come into contact with each other in the portions covering the ends in the width direction. Therefore, in order to prevent fusion of the insulating coatings in the portions covering the ends, it is desirable that the outer surface of the insulating coating, which is thicker at the ends, be composed of nanostructure regions 23 over at least the entire width direction. In other words, among the examples shown in Figures 7 to 9, the examples shown in Figures 8 and 9 are more desirable.

[0035] If the thickness of the insulating coating covering both ends of the flat wire 11 in the width direction is thinner than the thickness covering the central part, the resin 31 can be filled into the gap between the ends of the laminated conductors 1 when constructing the coil 30. Since the resin 31 makes it difficult for the ends of the conductors 1 to come into contact with each other, in this case the outer surface of the insulating coating does not need to be composed of nanostructure regions 23 over the entire width direction. For example, in the example shown in Figure 2, the portion of the insulating coating 20 that covers the ends of the base material 10 in the width direction is thin because it is composed only of the base material side portion 21. In the central portion of the insulating coating 20 in the width direction, nanostructure regions 23 are further provided on top of the base material side portion 21, so the resin 31 is filled between the base material side portions 21 of the ends of the laminated conductors 1. Since the space is filled with resin 31, the end portions of the insulating coating 20 do not come into contact between the conductors 1, so the end portions do not need to be composed of nanostructure regions 23.

[0036] The resin aggregate 24 can be micron-scale particles. For example, the side length of the circumscribing quadrilateral of the resin aggregate may be between 3 μm and 10 μm. The insulating coating 20, in which the substrate-side portion 21 is composed of fine-particle resin aggregate 24, can be made thin while containing voids 25.

[0037] The nanofibers 26 contained within the nanostructure region 23 are nanoscale resin fibers. Here, nanofibers 26 refer to materials whose radial cross-section has a shape symmetrical along an axis intersecting the thickness direction of the nanostructure region 23. The radial cross-section of the nanofibers 26 may be, for example, circular, or elliptical with its short axis aligned with the thickness direction of the nanostructure region 23. The boundary portion 22 contains a fused body of the constituent members of the nanostructure region 23 and the constituent members of the substrate portion 21, but the constituent members of the nanostructure region 23 in this fused body are, for example, nanofibers 26 that have partially dissolved and lost their symmetrical cross-sectional shape. Even if a string-like material with an asymmetrical radial cross-section contained within the fused body constitutes the outermost surface of the insulating film 20, the release properties obtained by the nanofibers 26 constituting the outer surface cannot be obtained. The nanofibers 26 may have a diameter of, for example, 30 nm to 3000 nm. For nanofibers 26 with an elliptical cross-sectional shape, the average diameter in the short axis direction and the long axis direction may be between 10 nm and 3000 nm.

[0038] Similarly, the nanoparticles 27 contained in the nanostructure region 23 are nanoscale resin particles. Here, nanoparticles 27 refer to particles whose radial cross-section has a shape symmetrical along an axis intersecting the thickness direction of the nanostructure region 23. The cross-section of the nanoparticles 27 may be, for example, circular, or elliptical with its short axis direction aligned with the thickness direction of the nanostructure region 23. The fused material contained in the boundary portion 22 is, for example, a material in which the nanoparticles 27 have partially dissolved and lost their symmetrical cross-sectional shape. Even if the granular material contained in the fused material, whose radial cross-section is not symmetrical, constitutes the outermost surface of the insulating film 20, the release properties obtained by the nanoparticles 27 constituting the outer surface cannot be obtained. The nanoparticles 27 may have a diameter of, for example, 100 nm or more and less than 3000 nm. For nanoparticles 27 with an elliptical cross-sectional shape, the average of the diameters in the short axis direction and the long axis direction may be 10 nm or more and 800 nm or less.

[0039] It is preferable that the average thickness of the insulating coating is 10 μm or less. In cases where the thickness of the insulating coating differs depending on the position on the rectangular wire substrate, as shown in the examples from Figures 7 to 9, it is even more preferable that the thickness of the insulating coating is 10 μm or less in all parts. By using a conductor with such a thin insulating coating, the coil can be made high-density. In the case where the insulating coating is thicker on the ends in the width direction of the rectangular wire, it is preferable that the thickness of the insulating coating excluding nanofibers and nanoparticles in the part covering the ends of the rectangular wire is greater than 1 and less than or equal to 2 times the thickness of the part covering the central part of the rectangular wire excluding nanofibers and nanoparticles. In other words, it is preferable that the thickness of the substrate side part is greater than 1 and less than or equal to 2 times the thickness of the end part compared to the central part. By setting the relationship of the insulating coating thickness to this ratio, it is possible to effectively improve short-circuit prevention while keeping the thickness of the end part to a level that allows for the construction of a high-density coil.

[0040] The insulating film can be observed as follows. Ring illumination is applied to the surface of the conductive wire to be observed, and it is observed with a digital microscope. As the digital microscope, for example, the digital microscope VHX-5000 manufactured by Keyence Corporation is used. By observation, it can be confirmed whether the outer surface of the insulating film 20 is composed of nanofibers or nanoparticles. When the outer surface has a structure of nanofibers or nanoparticles, the contours of the nanofibers or nanoparticles can be confirmed by magnified observation of 500 times or more. At this time, a high-luminance image can be obtained due to the phenomenon of irregular reflection of light by the voids. On the other hand, in the case of a structure that has dissolved and does not have a structure of nanofibers or nanoparticles, that is, a structure with few voids, the contours of the nanofibers or nanoparticles cannot be confirmed by magnified observation. Since the light is transmitted, an image with a low luminance is obtained.

[0041] Furthermore, the cross-section of the insulating film can be observed as follows. The conductive wire to be observed is embedded in resin, and polishing is performed by ion milling to expose a cross-section intersecting the longitudinal direction of the conductive wire. The cross-section of the obtained sample is observed with a scanning electron microscope.

[0042] The observed cross-section can be similar to the examples shown in FIGS. 5 to 9, for example. By cross-section observation, it can be confirmed whether the outer surface of the insulating film 20 is composed of nanofibers or nanoparticles. With the thickness direction of the insulating film 20 as the vertical direction, a fibrous member having a shape that is line-symmetric in the vertical direction in the radial cross-section is determined as a nanofiber. A member whose cross-section is not vertically symmetric is not regarded as a nanofiber. Also, a particle member having a shape that is line-symmetric in the vertical direction in the cross-section is determined as a nanoparticle. A member whose cross-section is not vertically symmetric is not regarded as a nanoparticle.

[0043] The thickness of the insulating film 20 covering both ends and the central portion along the width direction (the horizontal direction in each figure) of the flat wire 11 can be measured on both the front and back surfaces (both the upper and lower surfaces in each figure) of the flat wire 11. Here, the flat wire 11 is divided into 15 equal parts in the width direction, and the central area is taken as the central portion of the flat wire 11. The thickness T excluding nanofibers and nanoparticles in the insulating film 20 above this central portion ＣMeasure it. Of the 15 regions, the ones at both ends are each taken as the ends of the straight angle line 11. The thickness T of the insulating film 20 on this end, excluding the nanofibers and nanoparticles, Ｅ is measured. In FIGS. 5 to 9, the thickness T on the upper center Ｃ and the thicknesses T of the upper left and lower right surfaces Ｅ are only indicated, but the thickness on the lower center (T Ｃ ), the thicknesses of the lower left and upper right surfaces (T Ｅ ), and the thicknesses of the end side surfaces are also measured, for a total of 8 thicknesses.

[0044] The conducting wire may include, for example, a straight angle line as a base material. The straight angle line may include, for example, a metal substrate and a stabilization layer provided thereon. The straight angle line may include, for example, a metal substrate and a superconducting layer provided thereon.

[0045] For example, a strip-shaped superconducting layer may be provided on one side of a strip-shaped metal substrate, or strip-shaped superconducting layers may be provided on both sides of the strip-shaped metal substrate, respectively. Note that the metal substrate typically has a thickness on the order of several tens of microns, and the superconducting layer is typically a thin film with a thickness on the order of several microns. The base material may further include an intermediate layer provided between the metal substrate and the superconducting layer. The intermediate layer is, for example, a thin film such as magnesium oxide (MgO) with a thickness on the order of one tenth of a micron, and is sometimes called a buffer layer. The base material may further include, for example, a protective layer made of silver. The protective layer is, for example, provided on the superconducting layer. Also, in a base material where the superconducting layer is provided only on one side of the metal substrate, in addition to the superconducting layer, a protective layer may also be provided on the surface of the metal substrate where the superconducting layer is not provided on the back side. The protective layer typically has a thickness on the order of several microns.

[0046] The metal substrate of the straight angle line included in the conducting wire as the base material may have, for example, a strip shape, more specifically a straight angle line shape. The metal substrate is formed of, for example, a high-strength metal material such as a nickel-based alloy, stainless steel, or copper.

[0047] The superconducting layer of the substrate consists of a superconducting material, including, for example, NbTi alloy, niobium compounds such as Nb3Sn, magnesium diboride (MgB2), iron-based superconductors, bismuth-based oxide superconductors, and rare-earth oxide superconductors. The rare-earth elements may include at least one from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holomium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0048] The stabilization layer is formed, for example, from copper and typically has a thickness on the order of several microns to tens of microns. The stabilization layer may be omitted.

[0049] Alternatively, the conductor may include, for example, a round wire as the base material. The round wire may include, for example, a core wire made of metal or alloy instead of a metal substrate. The round wire may include, for example, a core wire and a stabilizing layer covering its surface. The round wire may include, for example, a core wire and a superconducting layer covering its surface. The number of core wires contained in a single round wire may be one or more. Also, when the base material is a round wire, it may include intermediate layers and protective layers similar to those of a rectangular wire.

[0050] The constituent materials of the insulating coating are, for example, one or more organic materials selected from the group consisting of polyolefins, polyetherimides, polyimides, Nomex®, polyesters, nylons, polyethersulfones, polyvinylpyrrolidones, polystyrene, polycarbonates, styrene-butadiene-styrene block copolymers (SBS), polyurethanes, polyacrylonitriles, polyacrylates, polymethyl methacrylates, polyethylene terephthalates, polylactic acid, silk, chitin, chitosan, polypeptides, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyvinyl butyrate, polyhydroxybutyrate, polyamides, polyamideimides, and polyvinylidene fluoride (PVdF). The constituent materials of both the substrate-side portion and the nanostructure region of the insulating coating are selected from organic materials. The constituent materials of the substrate-side portion and the nanostructure region may be the same or different. It is desirable that the constituent components of both are at least of the same type of material. For example, a derivative of one constituent component may be included as a constituent component of the other. As a specific example, two polyamide-imides that differ in molecular weight, skeleton, or terminal groups may have one component constituting the substrate portion and the other component constituting the nanostructure region. It is more preferable that both contain the same constituent components.

[0051] Examples of resins that are present on the winding containing the conductor in the coil and are partially impregnated into the insulating coating include thermosetting resins such as epoxy resins and thermoplastic resins.

[0052] The method for manufacturing a conductor according to this embodiment includes forming a first coating on a substrate by depositing a charged raw material solution onto the substrate, and forming a second coating on the first coating by depositing a charged raw material solution onto the first coating. In other words, such a conductor can be manufactured by an electrostatic coating method. At least a portion of the first coating becomes the substrate-side portion of the insulating coating. The second coating is formed by depositing the raw material solution in the form of nanofibers or nanoparticles, and at least a portion of it becomes the nanostructure region of the insulating coating. After forming the second coating, the insulating coating is formed by fusing the first coating and the second coating together. The electrostatic coating method can be used for both the formation of the first coating and the formation of the second coating, and an insulating conductor can be manufactured without requiring complicated processes.

[0053] To form an insulating coating, as shown in Figures 3 and 4, in which the substrate side portion is composed of resin clumps, by electrostatic coating, manufacturing conditions are used in which the raw material solution is deposited as droplets on a rectangular wire. When the deposited droplets dry, they become resin clumps, and an aggregate film of resin clumps can be obtained as the first coating. The conditions for the raw material solution to be deposited as droplets on a rectangular wire can be appropriately controlled by the concentration and viscosity of the raw material solution and the molecular weight of the organic material contained in the raw material solution. Lower concentrations of the raw material solution tend to form droplets and deposit as resin clumps on the rectangular wire. Conversely, high concentrations of the raw material solution tend to deposit as fibers and form a fibrous film. Lower viscosity raw material solutions tend to form droplets and deposit as resin clumps, while higher viscosity raw material solutions tend to form a fibrous film. Solutions containing raw materials with low molecular weight tend to form droplets and deposit as resin clumps. Conversely, solutions containing high molecular weight raw materials tend to form a fibrous film. Lower pipe pressures tend to form droplets and deposit resin clumps, while higher pressures tend to form a fibrous film. After forming a resin aggregate film or fiber film, a solid first coating can be obtained by performing a baking process.

[0054] In forming the second coating, whether nanofibers or nanoparticles are deposited on the first coating can be controlled by appropriately selecting conditions such as the raw material solution itself and the supply pressure of the raw material solution, similar to the difference between conditions that facilitate the formation of a resin aggregate film and conditions that facilitate the formation of a fiber film. Since the first and second coatings can be produced separately within the same electrostatic coating apparatus simply by adjusting the composition and flow rate of the raw material solution, the manufacturing cost of the conductive wires can be reduced.

[0055] After the formation of the second coating, the first and second coatings are fused together to obtain an insulating coating that includes a substrate-side portion and a nanostructure region. At least a portion of each of the first and second coatings becomes the substrate-side portion and the nanostructure region. For example, nanofibers or nanoparticles that will become the second coating are deposited on the first coating without drying it. The solvent remaining on the first coating dissolves the nanofibers or nanoparticles in contact with the first coating, forming a fused body of the components of the first coating and the nanofibers or nanoparticles. Note that the vertical line symmetry in the cross-section is lost for the nanofibers or nanoparticles dissolved here. Nanofibers or nanoparticles deposited further on top of the dissolved and fused organic material member do not dissolve and maintain the vertical line symmetry in the cross-section. Alternatively, pressing after the formation of the second coating may be performed to promote the fusion of the first and second coatings. When pressed, for example, in the case of nanofibers or nanoparticles with a circular radial cross-section, the cross-sectional shape may deform into an elliptical shape after pressing, but the elliptical cross-section will be symmetrical in the vertical direction.

[0056] In one example, the formation of the first coating and the formation of the second coating are carried out consecutively. For example, the first coating is formed on a transported substrate, and the formation of the second coating is carried out as the next step downstream in the transport path. A specific example will be described later with reference to Figure 10. Another method for the consecutive formation of the first and second coatings is to deposit the raw material solution of the first coating onto the substrate to form the first coating, and then switch to the formation of the second coating by changing the composition of the raw material solution or changing the conditions for depositing the raw material solution. The formation of the first coating and the formation of the second coating do not have to be consecutive; for example, after forming the first coating, the substrate with the first coating may be collected, and then the formation of the second coating may be carried out again.

[0057] Figure 10 shows an example of the manufacturing of the conductor. Figure 10 is a schematic diagram showing an example of a conductor manufacturing apparatus. As shown in the figure, the manufacturing apparatus 100 includes a winding machine 120, a coating mechanism 130, a dryer 150, and a winding machine 160. A transport line 180 is also formed in the manufacturing apparatus 100. In the manufacturing apparatus 100, the transport line 180 transports the wire-shaped substrate 10 from the winding machine 120 to the winding machine 160, passing sequentially through the coating mechanism 130 and the dryer 150.

[0058] The unwinding machine 120 is equipped with a reel 121. The base material 10 is wound onto the reel 121 in a roll shape. In the unwinding machine 120, the reel 121 rotates in the direction of arrow R1 by driving a drive member (not shown), such as an electric motor. As a result, the base material 10 wound on the reel 121 is unwound. The unwound base material 10 is then fed out to the conveyor line 180.

[0059] The winding machine 160 is equipped with a reel 161. In the winding machine 160, the reel 161 rotates in the direction of arrow R2 by driving a drive member (not shown), such as an electric motor. As a result, the base material 10 conveyed by the conveying line 180 is wound into a roll shape by the reel 161.

[0060] In the manufacturing apparatus 100, the base material 10 is transported from the unwinding machine 120 to the winding machine 160 via the transport line 180 by rotating the reel 121 in the direction of arrow R1 and the reel 161 in the direction of arrow R2. The transport line 180 may be provided with one or more guide rollers (not shown) to guide the base material 10 from the unwinding machine 120 to the winding machine 160. In this case, the guide roller is placed in at least one of the following locations on the transport line 180: between the unwinding machine 120 and the coating mechanism 130, between the coating mechanism 130 and the dryer 150, and between the dryer 150 and the winding machine 160. Alternatively, the guide roller may be placed inside either the coating mechanism 130 or the dryer 150.

[0061] Furthermore, the extension of the conveyor line 180 from the unwinding machine 120 to the winding machine 160 is not particularly limited. In one example, the conveyor line 180 is extended horizontally, and in another example, it is extended vertically. Also, one or more bends or folds in the conveyor line 180 may be provided between the unwinding machine 120 and the winding machine 160, and the extension direction of the conveyor line 180 may be changed at the bends or folds. In one example, a fold in the conveyor line 180 is provided between the coating mechanism 130 and the dryer 150, and in another example, a fold in the conveyor line 180 is provided either inside the coating mechanism 130 or inside the dryer 150.

[0062] The coating mechanism 130 includes one or more nozzle heads, and in the example shown in Figure 10, it includes six nozzle heads. For example, of the six nozzle heads, the four preceding the transport path of the substrate 10 may be nozzle heads 131 used for first film formation. Each nozzle head 131 includes a head body 132 and a nozzle 133 protruding from the head body 132. Each nozzle head 131 may have only one nozzle 133 or multiple nozzles 133. Each nozzle head 131 can store a raw material solution in which an organic material is dissolved in a solvent inside the head body 132. The remaining two subsequent nozzle heads may be nozzle heads 134 used for second film formation. Each nozzle head 134 includes a head body 135 and a nozzle 136 protruding from the head body 135. Each nozzle head 134 may have only one nozzle 136 or multiple nozzles 136. Each of the nozzle heads 134 can store a raw material solution in which an organic material is dissolved in a solvent inside the head body 135.

[0063] In the coating mechanism 130, the substrate 10 unwound from the reel 121 is conveyed toward the winding machine 160. The coating mechanism 130 is also equipped with a power supply (not shown), which allows voltage to be applied between the unwound substrate 10 and each nozzle 133 of the nozzle head 131, and between the substrate 10 and each nozzle 136 of the nozzle head 134.

[0064] With the raw material solution contained inside each head body 132 of the nozzle head 131, the raw material solution inside the nozzle head 131 is charged by applying a voltage between the substrate 10 and the nozzle head 131. The charged raw material solution is ejected from the nozzle 133 toward the surface of the substrate 10 that has been unwound by the unwinding machine 120. The ejected raw material solution accumulates, forming a first coating 201 on the surface of the substrate 10.

[0065] Similarly, when the raw material solution is stored inside the head body 135 of each nozzle head 134, the raw material solution inside the nozzle head 134 is charged by applying a voltage between the substrate 10 and the nozzle head 134. The charged raw material solution is ejected from the nozzle 136 toward the surface of the first coating 201 formed on the substrate 10. As the ejected raw material solution accumulates, a second coating 202 is formed on the surface of the first coating 201. In the illustrated example, the ejection form of the raw material solution for the second coating 202 is depicted as fibers, but the raw material for the second coating 202 can also be ejected as minute droplets.

[0066] By forming the second film 202 immediately following the formation of the first film 201, a portion of the components of the second film 202 dissolves in the solvent remaining in the first film 201. As a result, the first film 201 and the second film 202 fuse together, forming the insulating film 20. In this manner, the coating mechanism 130 forms the insulating film 20 by electrostatic coating.

[0067] Examples of organic materials used in the raw material solution include polyolefins, polyetherimides, polyimides, Nomex®, polyesters, polyethersulfones, polyvinylpyrrolidones, polystyrene, polycarbonates, styrene-butadiene-styrene block copolymers (SBS), polyurethanes, polyacrylonitriles, polyacrylates, polymethyl methacrylates, polyethylene terephthalate, polylactic acid, silk, chitin, chitosan, polypeptides, cellulose, cellulose derivatives, polyvinyl alcohol (PVA), polyvinyl butyrate, polyhydroxybutyrate, polyamide, polyamideimide, and polyvinylidene fluoride (PVdF). Examples of polyolefins include polypropylene (PP), polyethylene (PE), cyclic olefin copolymers, and polymethylpentene. The organic materials contained in the raw material solution serve as raw materials for insulating coatings and the resin blocks that constitute them.

[0068] Furthermore, inside nozzle head 131 and nozzle head 134, the organic material is dissolved in the solvent. Suitable solvents for dissolving the organic material in the raw material solution include cyclohexane, hexane, cyclohexadiene, bicyclopentene, N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), gamma-butyrolactone, acetone, dimethoxyethylene, toluene, tetrahydrofuran, water, methanol, ethanol, acetic acid, formic acid, and alkanes, ketones, esters, alcohols, ethers, etc. For organic materials with low solubility, the sheet-like organic material may be dissolved by a laser or the like. Additionally, multiple types of solvents may be mixed and used in the raw material solution. Here, it is preferable that one or more of the solvents used in the raw material solution are organic solvents with a boiling point of 100°C or higher. Examples of organic solvents with a boiling point of 100°C or higher include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, gamma-butyrolactone, dimethyl sulfoxide, and toluene.

[0069] The voltage between each nozzle 133 of nozzle head 131 and the substrate 10, and the voltage between each nozzle 136 of nozzle head 134 and the substrate 10, are appropriately determined in accordance with the types of solvent and solute in the raw material solution, the boiling point and vapor pressure curve of the solvent in the raw material solution, the concentration and temperature of the raw material solution, the shape of the nozzles, and the distance between the substrate 10 and the nozzles. Furthermore, as described above, the shape of the raw material solution discharged from nozzles 133 and 136 changes depending on the concentration and viscosity of the raw material solution, the molecular weight of the organic material contained in the raw material solution, and the piping pressure in supplying the raw material solution to nozzle heads 131 and 134.

[0070] In the example shown in Figure 10, an insulating coating is formed on the surface of the substrate 10 in the coating mechanism 130 between the unwinding machine 120 and the winding machine 160, as described above. Therefore, in the winding machine 160, the insulating coated conductor is wound onto the reel 161.

[0071] The dryer 150 is positioned in the conveying line 180 between the coating mechanism 130 and the winding machine 160. The substrate 10, on which the first coating 201 and the second coating 202 are sequentially formed on its surface, is conveyed to the dryer 150 from the coating mechanism 130. The dryer 150 dries the coatings formed on the surface of the substrate 10 before the insulated wire is wound onto the reel 161 of the winding machine 160.

[0072] In the illustrated example, the dryer 150 is equipped with an infrared heater 151. The infrared heater 151 generates infrared rays. The infrared heater 151 then radiates the generated infrared rays onto the first coating 201 and the second coating 202 formed on the surface of the substrate 10. Functional groups contained in the organic material and solvent in each coating absorb the infrared rays emitted from the infrared heater 151, causing the coating to heat up and the solvent contained in the coating to evaporate. As a result, the amount of solvent contained in the coating decreases and the coating dries.

[0073] Furthermore, drying the coating in the dryer 150 is not limited to drying using infrared rays emitted from the infrared heater 151. In one example, the coating may be dried in the dryer 150 using hot air instead of infrared rays emitted from the infrared heater 151.

[0074] Although not shown in the diagram, a press mechanism may be provided between the coating mechanism 130 and the dryer 150. By performing a press treatment after the formation of the second coating 202, the fusion of the first coating 201 and the second coating 202 can be promoted.

[0075] Examples are described below, but the examples are not limited to those described below.

[0076] (Example 1) An insulating wire was fabricated as follows. A flat, rectangular superconducting wire was prepared, with an oxide-based high-temperature superconducting material layer on a metal substrate and its outer periphery covered with copper. An insulating coating was formed by sequentially depositing insulating resin lumps and nanofibers onto the superconducting wire using a two-step electrostatic coating method.

[0077] The raw material solution for the resin film constituting the insulating coating was prepared by dissolving polyamide-imide (PAI) in N,N-dimethylacetamide (DMAC). The raw material solution for the resin lumps deposited directly onto the superconducting wire was prepared so that the solid content concentration in the raw material solution was 22% by mass. For the PAI used as the raw material for the resin lumps, imidized PAI was used. The raw material solution for the nanofibers to be further deposited on top of the first coating formed by depositing the resin lumps was prepared by dissolving polyamide-imide (PAI) in N,N-dimethylacetamide (DMAC). For the PAI used as the raw material for the nanofibers, imidized PAI was used.

[0078] (Comparative Examples 1 to 4) By adjusting the type of conductor and the amount of nanofiber deposited, various conductors and second coatings of various thicknesses were formed, and multiple insulated conductors were manufactured, each having an insulating coating with nanostructure regions spanning various thicknesses.

[0079] Each of the obtained insulated wires was observed using the method described above. The details of the observations are summarized in Table 1 below. Furthermore, within the insulating coating, the regions that had dissolved and no longer maintained the shape of the nanofibers and the nanostructure regions that did not dissolve and maintained the shape of the nanofibers were separated by brightness, and the proportion of the latter nanostructure regions was calculated using image processing software.

[0080]

[0081] The adhesive properties of each insulated conductor obtained were evaluated. Specifically, a finger tack test (adhesion test by touch) was performed, in which a finger was pressed against the surface of the insulating coating for 3 seconds, and if a peeling force was detected when the finger was released, adhesion was determined. The results are summarized in Table 2 below.

[0082]

[0083] According to one or more embodiments and examples described above, a conductor is provided. The conductor includes a conductive substrate having a linear shape and an insulating coating covering it. At least a portion of the outer surface of the insulating coating is composed of nanostructure regions made of nanofibers or nanoparticles. Such a conductor can provide a coil with high durability and suppressed short circuits.

[0084] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0085] Several embodiments of the present invention are described below. [1] A conductor comprising a conductive substrate having a linear shape and an insulating film covering the substrate, wherein at least a portion of the outer surface portion of the insulating film is composed of a nanostructure region made of nanofibers or nanoparticles. [2] The conductor according to [1], wherein the insulating film further comprises a substrate-side portion located on the back side of the nanostructure region and a boundary portion located between the nanostructure region and the substrate-side portion, wherein the boundary portion comprises a fused body of the constituent members of the nanostructure region and the constituent members of the substrate-side portion. [3] The conductor according to [2], wherein the nanostructure region and the substrate-side portion contain the same constituent components, or the other contains a derivative of a constituent component of one as a constituent component. [4] The conductor according to [1], wherein the insulating film further comprises resin lumps, the proportion of the resin lumps in the insulating film is highest at the interface between the substrate and the insulating film, and decreases toward the outer surface of the insulating film. [5] The conductor according to [4], wherein the nanostructure region and the resin mass contain the same constituent components, or the other contains a derivative of a constituent component of one of them as a constituent component. [6] The conductor according to any one of [1] to [5], wherein the substrate is a flat wire, and at least the outermost portion of the insulating coating in the thickness direction of the flat wire is composed of the nanostructure region. [7] The conductor according to [6], wherein the average thickness of the insulating coating is 10 μm or less, and the thickness of the portion of the insulating coating that covers the ends in the width direction of the flat wire, excluding the nanofibers and nanoparticles, is greater than 1 and less than or equal to 2 times the thickness of the portion that covers the central part of the flat wire in the width direction, excluding the nanofibers and nanoparticles. [8] The conductor according to any one of [1] to [7], wherein the substrate is a superconducting wire. [9] A coil comprising a winding containing a conductor as described in any one of [1] to [7], and a resin located on the winding, with a portion of it impregnated into the interior of the insulating coating.

[10] A method for manufacturing a wire, comprising: depositing a charged raw material solution onto a substrate to form a first coating on the substrate; depositing the charged raw material solution onto the first coating in the form of nanofibers or nanoparticles to form a second coating on the first coating; and forming an insulating coating by fusing the first coating and the second coating together after forming the second coating.

[11] The manufacturing method according to

[10] , wherein the formation of the first coating and the formation of the second coating are performed in succession.

[0086] 1...Conducting wire, 10...Substrate, 11...Flat wire, 20...Insulating coating, 21...Substrate side portion, 22...Boundary portion, 23...Nanostructure region, 24...Resin mass, 25...Void, 26...Nanofiber, 27...Nanoparticle, 30...Coil, 31...Resin, 100...Manufacturing equipment, 120...Unwinding machine, 130...Coating mechanism, 131...Nozzle head, 132...Head body, 133...Nozzle, 134...Nozzle head, 135...Head body, 136...Nozzle, 150...Dryer, 151...Infrared heater, 160...Winding machine, 201...First coating, 202...Second coating.

Claims

1. A conductive wire comprising a conductive substrate having a linear shape and an insulating coating covering the substrate, wherein at least a portion of the outer surface portion of the insulating coating is composed of nanostructure regions made of nanofibers or nanoparticles.

2. The conductor according to claim 1, wherein the insulating coating further includes a substrate-side portion located on the back side of the nanostructure region and a boundary portion located between the nanostructure region and the substrate-side portion, and the boundary portion includes a fused body of the constituent members of the nanostructure region and the constituent members of the substrate-side portion.

3. The conductive wire according to claim 2, wherein the nanostructure region and the substrate-side portion contain the same constituent components, or the other contains a derivative of a constituent component contained in one of them as a constituent component.

4. The conductor according to claim 1, wherein the insulating film further contains resin lumps, the proportion of resin lumps in the insulating film is highest at the interface between the substrate and the insulating film, and decreases toward the outer surface of the insulating film.

5. The conductive wire according to claim 4, wherein the nanostructure region and the resin mass contain the same constituent components, or the other contains a derivative of a constituent component of one of them as a constituent component.

6. The conductor according to claim 1, wherein the substrate is a flat rectangular wire, and at least the outermost portion of the insulating coating in the thickness direction of the flat rectangular wire is composed of the nanostructure region.

7. The conductor according to claim 6, wherein the average thickness of the insulating coating is 10 μm or less, and the thickness of the portion of the insulating coating that covers the ends of the rectangular wire in the width direction, excluding the nanofibers and nanoparticles, is greater than 1 and less than or equal to 2 times the thickness of the portion that covers the central part of the rectangular wire in the width direction, excluding the nanofibers and nanoparticles.

8. The conductor according to any one of claims 1 to 7, wherein the base material is a superconducting wire.

9. A coil comprising a winding containing a conductor according to any one of claims 1 to 7, and a resin located on the winding and partially impregnated into the interior of the insulating coating.

10. A method for manufacturing a conductor, comprising: forming a first coating on a substrate by depositing a charged raw material solution onto the substrate; forming a second coating on the first coating by depositing the charged raw material solution on the first coating in the form of nanofibers or nanoparticles; and forming an insulating coating by fusing the first coating and the second coating together after forming the second coating.

11. The manufacturing method according to claim 10, wherein the formation of the first coating and the formation of the second coating are carried out in succession.

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