Patent Publication Number: US-2022230777-A1

Title: Resin coated superconducting wire, superconducting coil, and shield coil

Description:
TECHNICAL FIELD 
     The present disclosure relates to a resin coated superconducting wire, a superconducting coil, and a shield coil. 
     BACKGROUND ART 
     In the conventional art, a superconducting material is used as a shield coil in applications, such as nuclear magnetic resonance (NMR) systems and systems for magnetic resonance imaging (MRI) inspection. In such applications, the shield coil is used to shield the magnetic field applied from outside to inside so that proper analysis results are obtained, and is used to shield the magnetic field applied from inside to outside so that the human body and the electronic equipment are protected from the effect of the magnetic field. 
     Referring to  FIG. 6 , such a superconducting material is, for example, a resin coated superconducting wire  2  including a superconducting wire  22  such as a NbTi wire, a copper stabilizer  21  called a copper channel coating the superconducting wire  22 , and a braided resin  23  such as polyester around the copper stabilizer  21 . In such a resin coated superconducting wire  2 , by coating the superconducting wire  22  with the copper stabilizer  21 , the heat generated from the superconducting wire  22  is released to the outside to suppress an increase in temperature, for example, with immersing the resin coated superconducting wire  2  into a liquid helium. 
     Moreover, in order to increase a heat generating efficiency of a superconducting material, Patent Document 1 discloses a superconducting wire which includes multiple superconducting wires, a copper stabilizer in which the superconducting wires are embedded, a resin coating the copper stabilizer, and an additional copper stabilizer coating the resin.
     Patent Document 1: Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2017-533579   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     Unfortunately, the conventional superconducting materials mentioned above, which include high-purity metal such as copper stabilizer around the superconducting wire, are relatively expensive and heavy and have low handleability because they tend to have a bending habit. 
     The present disclosure has been provided in view of the circumstances mentioned above, and it is an object of the present disclosure to provide a resin coated superconducting wire that is lightweight, highly flexible, and inexpensive as compared to conventional ones. 
     Means for Solving the Problems 
     [1] A resin coated superconducting wire including: a matrix resin including a synthetic resin material; and a superconducting wire in the matrix resin, in which, in a transverse cross section of the resin coated superconducting wire, a cross section area of the matrix resin is equal to or larger than that of the superconducting wire. 
     [2] The resin coated superconducting wire according to [1], in which the superconducting wire includes one or more selected from the group consisting of a composite of metal and niobium-titanium, a composite of metal and niobium-3 tin (Nb 3 Sn), a composite of metal and magnesium diboride, a rare earth-based superconducting material, and a bismuth-based superconducting material. 
     [3] The resin coated superconducting wire according to [1] or [2], in which the synthetic resin material is a thermoplastic resin. 
     [4] The resin coated superconducting wire according to [3], in which the thermoplastic resin has a melting point of 290° C. or less. 
     [5] The resin coated superconducting wire according to [3] or [4], in which the thermoplastic resin has a melting point of 210° C. or less. 
     [6] The resin coated superconducting wire according to any one of [1] to [5], in which the synthetic resin material is a polyamide or a polyolefin. 
     [7] The resin coated superconducting wire according to [6], in which the polyamide is nylon. 
     [8] The resin coated superconducting wire according to any one of [1] to [7], in which the synthetic resin material is nylon 11, nylon 12, or polyethylene. 
     [9] The resin coated superconducting wire according to any one of [1] to [5], in which the synthetic resin material is an amorphous resin having a glass transition point of 250° C. or less. 
     [10] The resin coated superconducting wire according to any one of [1] to [9], in which the resin coated superconducting wire is a multilayer coated wire, and the matrix resin includes two or more matrix resin layers including an inner matrix resin layer covering an outer circumference of the superconducting wire and at least one outer matrix resin layer covering an outer circumference of the inner matrix resin layer. 
     [11] The resin coated superconducting wire according to [10], in which the inner matrix resin layer includes an olefin-based resin having at least one functional group selected from the group consisting of an epoxy group, an oxazolyl group, an amino group, and a maleic anhydride residue, or includes a copolymer of the olefin-based resin. 
     [12] The resin coated superconducting wire according to [10], in which the inner matrix resin layer includes an olefin-based copolymer containing a carboxylic acid metal salt. 
     [13] The resin coated superconducting wire according to any one of [1] to [12], in which the superconducting wire is a single wire. 
     [14] The resin coated superconducting wire according to any one of [1] to [12], in which the superconducting wire is a stranded wire. 
     [15] The resin coated superconducting wire according to any one of [1] to [14], in which a transverse section of the resin coated superconducting wire has a rectangular shape. 
     [16] The resin coated superconducting wire according to any one of [1] to [14], in which a transverse section of the resin coated superconducting wire has a circular shape. 
     [17] The resin coated superconducting wire according to any one of [1] to [16], in which the resin coated superconducting wire has a dimensional accuracy of ±0.10 mm or less in width and a dimensional accuracy of ±0.10 mm or less in thickness. 
     [18] The resin coated superconducting wire according to any one of [1] to [17], in which the resin coated superconducting wire has a dimensional accuracy of ±0.05 mm or less in width and a dimensional accuracy of ±0.05 mm or less in thickness. 
     [19] A superconducting coil including the resin coated superconducting wire according to any one of [1] to [18]. 
     [20] A shield coil including the resin coated superconducting wire according to any one of [1] to [18]. 
     Effects of the Invention 
     The present disclosure makes it possible to provide a resin coated superconducting wire that is lightweight, highly flexible, and inexpensive as compared to conventional ones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a transverse cross sectional view of a resin coated superconducting wire (rectangular) according to an embodiment of the present disclosure. 
         FIG. 2  is a transverse cross sectional view of a resin coated superconducting wire (circular) according to an embodiment of the present disclosure. 
         FIG. 3  is a transverse cross sectional view of a resin coated superconducting wire (rectangular) according to an embodiment of the present disclosure. 
         FIG. 4  is a transverse cross sectional view of a resin coated superconducting wire (circular) according to an embodiment of the present disclosure. 
         FIGS. 5A to 5F  are transverse cross sectional views showing different modifications of a resin coated superconducting wire (rectangular). 
         FIG. 6  is a transverse cross sectional view of a conventional resin coated superconducting wire. 
     
    
    
     PREFERRED MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail, which are not intended to limit the present disclosure. 
     The present inventors have completed the present disclosure based on findings that designing a resin coated superconducting wire including a matrix resin including a synthetic resin material, and a superconducting wire in the matrix resin, in which, in a transverse cross section of the resin coated superconducting wire, a cross section area of the matrix resin is equal to or larger than that of the superconducting wire makes it possible to provide a resin coated superconducting wire that is lightweight, highly flexible, and inexpensive as compared to a conventional resin coated superconducting wire. 
     1. Resin Coated Superconducting Wire 
     The resin coated superconducting wire according to the present disclosure includes a matrix resin including a synthetic resin material, and a superconducting wire in the matrix resin. In the resin coated superconducting wire, when seen a transverse cross section of the resin coated superconducting wire, a cross section area of the matrix resin is equal to or larger than the cross section area of the superconducting wire. 
       FIG. 1  is a transverse cross sectional view of a resin coated superconducting wire according to an embodiment of the present disclosure, and  FIG. 2  is a transverse cross sectional view of a resin coated superconducting wire according to another embodiment of the present disclosure. As shown in  FIGS. 1 to 2 , the resin coated superconducting wire  1  includes a matrix resin  11  including a synthetic resin material, and a superconducting wire  12  in the matrix resin  11 . According to the embodiment, in the transverse cross section of the resin coated superconducting wire  1 , the cross section area of the matrix resin  11  is equal to or larger than the cross section area of the superconducting wire  12 . The resin coated superconducting wire  1  shown in  FIG. 1  has a rectangular transverse cross section, while the resin coated superconducting wire  1  shown in  FIG. 2  has a circular transverse cross section. The resin coated superconducting wires  1  shown in  FIGS. 1 to 2  are each a monolayer coated wire in which the matrix resin  11  includes a single matrix resin layer covering the outer circumference of the superconducting wire  12 . 
     In shield coil applications, a relatively small current is allowed to flow through the superconducting wire  12  of the resin coated superconducting wire  1 . In such applications, therefore, the superconducting wire  12  is less likely to be quenched. Even in case of quench, the superconducting wire  12  does not need to be combined with a large amount of copper stabilizer since the current in the superconducting wire  12  is small. On the other hand, to provide a shield coil with reliable magnetic field shielding performance, the resin coated superconducting wire  1  should be coiled such that adjacent portions of the coiled superconducting wire  12  are apart from each other at a constant distance. Therefore, the superconducting wire  12  is provided to extend (preferably embedded) in the matrix resin  11  having the transverse cross section area equal to or larger than the transverse cross section area of the superconducting wire  12 . This feature allows the matrix resin  11  to serve as what is called a spacer in the resin coated superconducting wire, so that the superconducting wire  12  can be coiled with its adjacent portions kept apart from each other at a constant distance. 
     [Matrix Resin] 
     The matrix resin  11  includes a synthetic resin material. The matrix resin  11  provides reliable insulation between portions of the superconducting wire  12  and serves as what is called a spacer as mentioned above so that adjacent portions of the superconducting wire  12  can be kept apart from each other at a constant distance. It should be noted that the matrix resin is solid, which is intended to exclude fiber knitting. 
     The matrix resin  11  is preferably a thermoplastic resin which can be subjected to extrusion molding. The extrusion molding is an effective method for forming a thick coating such that the cross section area of the matrix resin  11  is equal to or larger than that of the superconducting wire  12  in the transverse cross section of the resin coated superconducting wire  1 . The matrix resin  11  is more preferably a polyamide or a polyolefin. The polyamide is preferably nylon. The thermoplastic resin is preferably, for example, polyethylene, polypropylene, polystyrene, nylon 11, nylon 12, nylon 6, nylon 66, nylon 610, nylon MXD6 (a polycondensate of m-xylylenediamine and adipic acid), polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-ethylene copolymer resin (ETFE), polycarbonate, polyphenylene ether, polyetherimide, or polyether sulfone. These resins may be used alone, or a mixture of two or more of these resins may be used. 
     The synthetic resin material included in the matrix resin  11  is not only that the matrix resin  11  consists of a synthetic resin material but also that the matrix resin  11  is a resin composition based on a synthetic resin material. Such a resin composition may contain various additives for use in common resin compositions, such as various fillers, antioxidants, and other additives for improving mechanical or chemical durability. For example, the matrix resin  11  may contain a filler so that the matrix resin  11  has a lower heat shrinkage percentage close to the heat shrinkage percentage of the superconducting wire  12  and thus the resin coated superconducting wire  1  has increased heat cycle resistance. 
     When the matrix resin  11  is a crystalline resin, the matrix resin  11  preferably has a melting point of, for example, 290° C. or less, more preferably 280° C. or less, even more preferably 270° C. or less. When the matrix resin  11  is produced by thermoforming a raw material, the raw material with a lower melting point can be molded at a lower temperature, and thus the superconducting wire  12  can be prevented from suffering from performance degradation due to heating during the molding. 
     The crystalline resin, which may constitute the matrix resin  11 , is preferably, for example, polyethylene, polypropylene, nylon 11, nylon 12, nylon 6, nylon 66, nylon 610, nylon MXD6, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), or tetrafluoroethylene-ethylene copolymer resin (ETFE). 
     For the purpose of further preventing the heating-induced degradation of the performance of the superconducting wire  12  during the molding, the matrix resin  11  preferably has a melting point of 210° C. or less, more preferably 200° C. or less, even more preferably 190° C. or less. Among the crystalline resins for forming the matrix resin  11 , polyethylene, polypropylene, nylon 11, and nylon 12 are preferred. 
     The matrix resin  11  is preferably nylon or a polyolefin. In particular, the matrix resin  11  is more preferably nylon 11, nylon 12, nylon 6, nylon 66, nylon 610, nylon MXD6, polyethylene, or polypropylene, and even more preferably nylon 11, nylon 12, polyethylene, or polypropylene since they have particularly low melting points, low heat shrinkage percentages, excellent water absorption resistance (low water absorption rates), excellent flexibility, and excellent mechanical properties. 
     When the matrix resin  11  is an amorphous resin, the synthetic resin material of the matrix resin  11  preferably has a glass transition point of, for example, 250° C. or less, more preferably 240° C. or less, even more preferably 230° C. or less. For example, when the matrix resin  11  is produced by thermoforming a raw material, the lower glass transition point of the raw material allows the resin coating and molding process to be performed at a lower temperature, so that changes in the performance of the superconducting wire  12  due to heating during the thermoforming can be prevented. 
     The amorphous resin, which may constitute the matrix resin  11 , is preferably, for example, polycarbonate, polyphenylene ether, polyetherimide, or polyether sulfone. 
       FIG. 3  is a transverse cross sectional view of another resin coated superconducting wire (rectangular), and  FIG. 4  is a transverse cross sectional view of a further resin coated superconducting wire (circular). The resin coated superconducting wires  1  shown in  FIGS. 3 and 4  are each a multilayer coated wire including a superconducting wire  12 , and a matrix resin  11  including multiple matrix resin layers and covering the outer circumference of the superconducting wire  12 . Specifically, the matrix resin  11  shown in  FIGS. 3 and 4  differs from the matrix resin  11  shown in  FIGS. 1 and 2  in that the matrix resin  11  shown in  FIGS. 3 and 4  includes an annular inner matrix resin layer  11   a  covering the outer circumference of the superconducting wire  12 , and at least one outer matrix resin layer  11   b  covering the outer circumference of the inner matrix resin layer  11   a .  FIGS. 3 to 4  show that the matrix resin  11  has a two-layer structure composed of a single inner matrix resin layer  11   a  and a single outer matrix resin layer  11   b.    
     As shown in  FIGS. 3 and 4 , the resin coated superconducting wire  1  is preferably a multilayer coated wire having two or more matrix resin layers, such as the inner matrix resin layer  11   a  and the outer matrix resin layer  11   b , and is more preferably a multilayer coated wire having two or more and four or less matrix resin layers. When the resin coated superconducting wire  1  is produced in the form of a multilayer coated wire, the resin may be used in a smaller amount per single extrusion coating process, so that the resulting extrusion coated wire is expected to have a higher dimensional accuracy. Moreover, different resins may be used to form the respective matrix resin layers, so that the resin coated superconducting wire  1  can have higher functionality. 
     Specifically, when the matrix resin includes a polyolefin resin, such as polyethylene or polypropylene, which has low adhesion to the superconducting wire  12 , the inner matrix resin layer  11   a , which is the first layer from the conductor side, may include an olefin-based resin having at least one functional group selected from the group consisting of an epoxy group, an oxazolyl group, an amino group, and a maleic anhydride residue, or include a copolymer of the olefin-based resin (also referred to as copolymer (A)). In such a multilayer coated wire, the inner matrix resin layer  11   a  enhances the adhesion between the superconducting wire  12  and the outer polyolefin resin  11   b . Alternatively, the inner matrix resin layer  11   a  may include an olefin-based copolymer containing a carboxylic acid metal salt (also referred to as olefin-based copolymer (B)). In such a multilayer coated wire, the inner matrix resin layer  11   a  is also expected to enhance the adhesion as mentioned above. 
     The olefin component used to form the copolymer (A) is preferably ethylene, propylene, butene-1, pentene-1, 4-methylpentene-1, isobutylene, hexene-1, decene-1, octene-1, 1,4-hexadiene, or dicyclopentadiene, and more preferably ethylene, propylene, or butene-1. These components may be used alone, or two or more of these components may be used. 
     The copolymer component used other than the olefin to form the copolymer (A) may be at least one component of an acrylic component and a vinyl component. 
     The acrylic component is preferably acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, or butyl methacrylate. The vinyl component is preferably vinyl acetate, vinyl propionate, vinyl butyrate, vinyl chloride, vinyl alcohol, or styrene. Among them, methyl acrylate and methyl methacrylate are more preferred. These components may be used alone, or two or more of these components may be used. Typical preferred examples of the copolymer (A) include maleic anhydride-grafted polyethylene or polypropylene, ethylene-glycidyl methacrylate copolymers, and commercially available resins such as Admer (trade name, manufactured by Mitsui Chemicals, Inc.), Bond Fast (trade name, manufactured by Sumitomo Chemical Co., Ltd.), and Lotader (trade name, manufactured by Atofina). 
     Preferred examples of the carboxylic acid used to form the olefin-based copolymer (B) include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and phthalic acid. Examples of the metal salt include Zn salts, Na salts, K salts, and Mg salts. The olefin-based copolymer (B) is preferably a resin generally called an ionomer, such as Himilan (trade mane, manufactured by Mitsui Polychemicals), in which some parts of the carboxylic acid in the ethylene-methacrylic acid copolymer is a metal salt. 
     The matrix resin  11  preferably has a heat shrinkage percentage of 5° or less, more preferably 2° or less, even more preferably 1% or less as calculated using the method shown below. This feature makes the matrix resin  11  less vulnerable to damage or degradation when the matrix resin  11  is immersed in a cooling medium such as liquid helium. 
     (Method of Calculating Heat Shrinkage Percentage) 
     The resin coated superconducting wire  1  is cut along the longitudinal direction of the resin coated superconducting wire  1  into 0.2 g pieces, each of which is immersed in 500 mL liquid helium for several minutes and then measured for size. The heat shrinkage percentage of the resin coated superconducting wire  1  is calculated from the formula (1) below. 
       Heat shrinkage percentage (%)={(the size of the resin coated superconducting wire before the immersion−the size of the resin coated superconducting wire after the immersion)/the size of the resin coated superconducting wire before the immersion}×100  Formula (1)
 
     The matrix resin  11  more preferably has a water absorption rate of 1.0% or less, even more preferably 0.7% or less as calculated using the method shown below. The lower the water absorption rate, the less likely the surface of the matrix resin  11  is to expand. This feature makes the matrix resin  11  less vulnerable to a reduction in mechanical strength, which is caused by damage, degradation, deterioration, or cracking that occurs when the matrix resin  11  absorbs water. The calculation method shown below is one of the methods for determining the water absorption rate of plastics according to JIS K 7209. 
     (Method of Calculating Water Absorption Rate) 
     The resin coated superconducting wire  1  is cut along the longitudinal direction of the resin coated superconducting wire  1  into 1.0 g pieces, each of which is immersed in 500 mL water at 23° C. for 24 hours, then wiped to remove water from the surface, and then measured for weight. The water absorption rate of the resin coated superconducting wire  1  is calculated from the formula (2) below. 
       Water absorption rate (%)={(the weight of the resin coated superconducting wire before the immersion−the weight of the resin coated superconducting wire after the immersion)/the weight of the resin coated superconducting wire before the immersion}×100  Formula (2)
 
     [Superconducting Wire] 
     The superconducting wire  12  is a wire in the matrix resin  11  described above and has superconducting property. 
     As a size of the transverse cross section of the superconducting wire  12 , when the transverse cross section is a circular shape, the size is preferably 0.05 to 2.00 mmφ, more preferably 0.07 to 1.50 mmφ, even more preferably 0.1 to 1.0 mmφ. When the transverse cross section of the superconducting wire  12  is a rectangular shape, the long side of the rectangular shape is preferably 0.8 mm to 2.5 mm, more preferably 1.5 mm to 2.0 mm, and the short side of the rectangular shape is preferably 0.5 mm to 1.5 mm, more preferably 0.9 mm to 1.2 mm. 
     The superconducting wire  12  preferably includes, for example, at least one superconducting material selected from the group consisting of a composite of metal and niobium-titanium, a composite of metal and niobium-3 tin (Nb 3 Sn), a composite of metal and magnesium diboride, a rare earth-based superconducting material, and a bismuth-based superconducting material. In this regard, the composite of metal and niobium-titanium, the composite of metal and niobium-3 tin, or the composite of metal and magnesium diboride refer to a composite in which the metal such as copper or iron covers the surrounding of the niobium-titanium, the niobium-3 tin, or the magnesium diboride. 
     Examples of the rare earth-based material include YBa 2 Cu 3 O 7-δ  and GdBa 2 Cu 3 O 7-δ . Examples of the bismuth-based material include Bi 2 Sr 2 Ca 2 Cu 3 O 10+δ  and Bi 2 Sr 2 CaCu 2 O 8+δ . 
     The superconducting wire  12  may be a single wire or a stranded wire including multiple strands twisted together. 
     [Relationship Between Matrix Resin and Superconducting Wire] 
     As described above, in the resin coated superconducting wire  1 , when seen the transverse cross section of the resin coated superconducting wire  1 , the cross section area of the matrix resin  11  is equal to or larger than the cross section area of the superconducting wire  12 . 
     In the transverse cross section of the resin coated superconducting wire  1 , the ratio of the cross section area of the matrix resin  11  to the cross section area of the superconducting wire  12  (the cross section area of the matrix resin  11 /the cross section area of the superconducting wire  12 ) is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, further more preferably 20 or more, most preferably 40 or more. The ratio of the cross section area preferably has an upper limit of 1000 from practical points of view such as coil material suitability and handleability for coiling operation. 
       FIGS. 1 and 2  show a case in which the superconducting wire  12  is located at the center (gravity center) of the matrix resin  11  in the transverse cross section of the resin coated superconducting wire  1 . However, the superconducting wire  12  may be located at any position in the matrix resin  11  as long as the superconducting wire  12  remains not exposed from the surface of the resin coated superconducting wire  1  (as long as at least a small amount of the resin component of the matrix resin  11  is present over the surface of the resin coated superconducting wire  1 ). For example,  FIGS. 5A to 5F  show modified examples illustrating the transverse cross sections of the resin coated superconducting wires  1 A to  1 F, which have a rectangular cross section and respectively include the superconducting wires  12 A to  12 F located at different positions in the transverse cross sections of the matrix resins  11 A to  11 F. 
     The resin coated superconducting wire has one superconducting wire  12  in the form of a single wire or a stranded wire, which is located in one matrix resin  11 . 
     The resin coated superconducting wire may have any transverse cross section shape such as a circular shape including an elliptic shape, a triangular shape, a square shape, or a rectangular shape. For ease of coiling, the resin coated superconducting wire preferably has a rectangular transverse cross section shape. When the transverse cross section of the resin coated superconducting wire is a rectangular shape, the rectangular transverse cross section shape of the resin coated superconducting wire may have a round corner or corners with an R value of 1 mm or less. 
     When the resin coated superconducting wire has a rectangular shape, the transverse cross section of the resin coated superconducting wire preferably has a long side of, for example, 0.5 mm to 10 mm, more preferably 1 mm to 7 mm. The transverse cross section of the resin coated superconducting wire preferably has a short side of, for example, 0.1 mm to 5 mm, more preferably 0.5 mm to 3 mm. 
     The resin coated superconducting wire preferably has a dimensional accuracy of ±0.10 mm or less in width and a dimensional accuracy of ±0.10 mm or less in thickness, and more preferably has a dimensional accuracy of ±0.05 mm or less in width and a dimensional accuracy of ±0.05 mm or less in thickness. As used herein, the dimensional accuracy refers to the range of difference between the maximum and minimum of a dimension of a piece of the resin coated superconducting wire. The resin coated superconducting wire with such a dimensional accuracy as mentioned above provides higher electromagnetic shielding performance. Such a dimensional accuracy may be achieved by a method of cutting the outer surface of a product resulting from resin extrusion process. Alternatively, such a dimensional accuracy may be achieved by a method of coating the surface of the matrix resin with, for example, a UV-curable resin material. 
     The resin coated superconducting wire described above may be used to form a superconducting coil, specifically, a shield coil for use in NMR systems and MRI inspection systems. 
     As a voltage applied to the above resin coated superconducting wire, the voltage, but is not limited, is preferably 0 to 50 V, more preferably 0 to 20 V, even more preferably 0 to 10 V. 
     As compared to conventional superconducting wires including copper stabilizer, the resin coated superconducting wire is lightweight, inexpensive, improved in flexibility, and less likely to have a bending habit, and is easy to coil because it has high flexibility or bendability and good handleability. 
     2. Method for Producing Resin Coated Superconducting Wire 
     The resin coated superconducting wire according to the embodiment described above may be produced, for example, using an extrusion process similar to a common process for forming an extruded resin material, which inserts a superconducting wire into a synthetic resin raw material for forming a matrix resin and then extrudes the raw material. The heating temperature, the extrusion rate, and other conditions may be appropriately adjusted depending on the kind of the synthetic resin raw material and the size and shape of the product to be formed. 
     A conventional technique includes two steps including covering a superconducting strand with a resin and then embedding the strand in a copper channel. On the other hand, the resin coated superconducting wire according to the embodiment can be completed using a single step instead of the conventional two steps because the matrix resin can be shaped into the same form as that of the copper channel. 
     EXAMPLES 
     Next, examples will be described to make clearer the advantageous effects of the present disclosure. It will be understood that the examples are not intended to limit the present disclosure. 
     Examples 1 to 40 
     The synthetic resin raw materials used were nylon 11 (BESN Noir TN manufactured by Arkema), nylon 12 (UBESTA 3030LUX manufactured by Ube Industries, Ltd.), nylon 6 (UBESTA 1024JI manufactured by Ube Industries, Ltd.), nylon 66 (Leona® 1300S manufactured by Asahi Kasei Corporation), and high-density polyethylene (Suntech®-HD B891 manufactured by Asahi Kasei Corporation). A superconducting wire with 0.3 mmφ of a composite of copper and niobium-titanium was inserted into the synthetic resin raw material and then subjected to an extrusion process at a temperature equal to or more than a temperature that is obtained by adding the melting point of each resin raw material and 20° C. and equal to or less than a temperature that is obtained by adding the melting point of each resin raw material and 80° C. using a die for forming a rectangular product (Examples 1 to 20) or a circular product (Examples 21 to 40) having the dimensions shown in Table 2 or 3 below. As shown in  FIGS. 1 and 2 , the superconducting wire was placed at the center of the synthetic resin material. A resin coated superconducting wire having a rectangular transverse cross section was produced in each of Examples 1 to 20. A resin coated superconducting wire having a circular transverse cross section was produced in each of Examples 21 to 40. 
     Example 41 
     The synthetic resin raw material used was high-density polyethylene (Suntech®-HD B891 manufactured by Asahi Kasei Corporation). A superconducting wire with 0.3 mmφ of a composite of copper and niobium-titanium coated with 20 μm-thick modified low-density polyethylene having a graft-copolymerized maleic anhydride moiety (Admer NB508 manufactured by Mitsui Chemicals, Inc.) was inserted into the synthetic resin raw material and then subjected to an extrusion process at a temperature equal to or more than a temperature that is obtained by adding the melting point of each resin raw material and 20° C. and equal to or less than a temperature that is obtained by adding the melting point of each resin raw material and 80° C. using a die for forming a rectangular product having the dimensions shown in Table 4 below. As shown in  FIG. 3 , the superconducting wire was placed at the center of the synthetic resin material. 
     Example 42 
     A resin coated superconducting wire was obtained as in Example 41 except that a superconducting wire with 0.3 mmφ of a composite of copper and niobium-titanium coated with 20 μm-thick ethylene-methacrylic acid copolymer in which some parts of the carboxylic acid was a metal salt (Himilan 1855 manufactured by Mitsui Polychemicals) was used instead. 
     Example 43 
     The synthetic resin raw material used was high-density polyethylene (Suntech®-HD B891 manufactured by Asahi Kasei Corporation). A superconducting wire with 0.3 mmφ of a composite of copper and niobium-titanium coated with 20 μm-thick modified low-density polyethylene having a graft-copolymerized maleic anhydride moiety (Admer NB508 manufactured by Mitsui Chemicals, Inc.) was inserted into the synthetic resin raw material and then subjected to an extrusion process at a temperature equal to or more than a temperature that is obtained by adding the melting point of each resin raw material and 20° C. and equal to or less than a temperature that is obtained by adding the melting point of each resin raw material and 80° C. using a die for forming a circular product having the dimensions shown in Table 5 below. As shown in  FIG. 4 , the superconducting wire was placed at the center of the synthetic resin material. 
     The cross section area of the matrix resin was calculated by determining, in the transverse cross section of the resin coated superconducting wire, the cross section area of the resin coated superconducting wire from the external dimensions of the resin coated superconducting wire and then subtracting the cross section area of the superconducting wire from the determined cross section area. The calculated cross section area of the matrix resin was used to calculate the weight and cost of the resin per 1000 m length of the resin coated superconducting wire and the cost relative to those of copper. The results are shown in Tables 2 to 5 below. In Tables 2 to 5, the parenthesized values indicate the values calculated in terms of copper. 
     Table 1 shows the melting point, the glass transition point, the heat shrinkage percentage, and the water absorption rate of each of the synthetic resin materials used in Examples 1 to 43. The heat shrinkage percentage and the water absorption rate were determined by the methods described above. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Glass 
                 Heat 
                 Water 
               
               
                   
                 Melting 
                 transition 
                 shrinkage 
                 absorption 
               
               
                   
                 point 
                 point 
                 percentage 
                 rate 
               
               
                 Resin 
                 [° C.] 
                 [° C.] 
                 [%] 
                 [%] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Nylon 11 
                 186 
                 46 
                 &lt;5 
                 0.4 
               
               
                 Nylon 12 
                 180 
                 37 
                 &lt;5 
                 0.4 
               
               
                 Nylon 6 
                 221 
                 45 
                 &lt;5 
                 1.7 
               
               
                 Nylon 66 
                 258 
                 47 
                 &lt;5 
                 1.7 
               
               
                 Polyethylene 
                 141 
                 −45 
                 &lt;5 
                 0.04 
               
               
                 Modified low- 
                 120 
                 &lt;0 
                 &lt;5 
                 &lt;0.5 
               
               
                 density 
               
               
                 polyethylene 
               
               
                 Ethylene- 
                 86 
                 &lt;0 
                 &lt;5 
                 &lt;0.5 
               
               
                 methacrylic 
               
               
                 acid copolymer 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Resin coated superconducting wire 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Cross section 
                 Cross section 
                   
                 Material cost 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 External dimensions [mm] 
                 Cross section 
                 area of 
                 area ratio 
                 Resin 
                 ratio per 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Curvature 
                 area of 
                 superconducting 
                 (matrix resin/ 
                 weight per 
                 unit length 
               
               
                   
                   
                   
                   
                 radius R of 
                 matrix resin 
                 wire 
                 superconducting 
                 1000 m 
                 (cost ratio of 
               
               
                   
                 Resin 
                 Width 
                 Thickness 
                 corner 
                 [mm 2 ] 
                 [mm 2 ] 
                 wire) 
                 [kg] 
                 resin/copper) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 Nylon 11 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/3 
               
               
                 Example 2 
                 Nylon 11 
                 3.5 
                 2.1 
                 0.3 
                 7.1 
                 0.071 
                 100 
                 8 
                 (64) 
                 About 1/3 
               
               
                 Example 3 
                 Nylon 11 
                 5 
                 3 
                 0.3 
                 15 
                 0.071 
                 210 
                 16 
                 (133) 
                 About 1/3 
               
               
                 Example 4 
                 Nylon 11 
                 10.9 
                 6.5 
                 0.3 
                 71 
                 0.071 
                 1000 
                 73 
                 (630) 
                 About 1/3 
               
               
                 Example 5 
                 Nylon 12 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/3 
               
               
                 Example 6 
                 Nylon 12 
                 3.5 
                 2.1 
                 0.3 
                 7.1 
                 0.071 
                 100 
                 8 
                 (64) 
                 About 1/3 
               
               
                 Example 7 
                 Nylon 12 
                 5 
                 3 
                 0.3 
                 15 
                 0.071 
                 210 
                 16 
                 (133) 
                 About 1/3 
               
               
                 Example 8 
                 Nylon 12 
                 10.9 
                 6.5 
                 0.3 
                 71 
                 0.071 
                 1000 
                 73 
                 (630) 
                 About 1/3 
               
               
                 Example 9 
                 Nylon 6 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 5 
                 (33) 
                 About 1/8 
               
               
                 Example 10 
                 Nylon 6 
                 3.5 
                 2.1 
                 0.3 
                 7.1 
                 0.071 
                 100 
                 9 
                 (64) 
                 About 1/8 
               
               
                 Example 11 
                 Nylon 6 
                 5 
                 3 
                 0.3 
                 15 
                 0.071 
                 210 
                 17 
                 (133) 
                 About 1/8 
               
               
                 Example 12 
                 Nylon 6 
                 10.9 
                 6.5 
                 0.3 
                 71 
                 0.071 
                 1000 
                 80 
                 (630) 
                 About 1/8 
               
               
                 Example 13 
                 Nylon 66 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 5 
                 (33) 
                 About 1/6 
               
               
                 Example 14 
                 Nylon 66 
                 3.5 
                 2.1 
                 0.3 
                 7.1 
                 0.071 
                 100 
                 9 
                 (64) 
                 About 1/6 
               
               
                 Example 15 
                 Nylon 66 
                 5 
                 3 
                 0.3 
                 15 
                 0.071 
                 210 
                 17 
                 (133) 
                 About 1/6 
               
               
                 Example 16 
                 Nylon 66 
                 10.9 
                 6.5 
                 0.3 
                 71 
                 0.071 
                 1000 
                 81 
                 (630) 
                 About 1/6 
               
               
                 Example 17 
                 Polyethylene 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/39 
               
               
                 Example 18 
                 Polyethylene 
                 3.5 
                 2.1 
                 0.3 
                 7.1 
                 0.071 
                 100 
                 7 
                 (64) 
                 About 1/39 
               
               
                 Example 19 
                 Polyethylene 
                 5 
                 3 
                 0.3 
                 15 
                 0.071 
                 210 
                 15 
                 (133) 
                 About 1/39 
               
               
                 Example 20 
                 Polyethylene 
                 10.9 
                 6.5 
                 0.3 
                 71 
                 0.071 
                 1000 
                 68 
                 (630) 
                 About 1/39 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Resin coated superconducting wire 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Cross section 
                 Cross section 
                   
                 Material cost 
               
               
                   
                   
                   
                 Cross section 
                 area of 
                 area ratio 
                 Resin 
                 ratio per 
               
               
                   
                   
                 External 
                 area of 
                 superconducting 
                 (matrix resin/ 
                 weight per 
                 unit length 
               
               
                   
                   
                 diameter 
                 matrix resin 
                 wire 
                 superconducting 
                 1000 m 
                 (cost ratio of 
               
               
                   
                 Resin 
                 [mm] 
                 [mm 2 ] 
                 [mm 2 ] 
                 wire) 
                 [kg] 
                 resin/coppcr) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Example 21 
                 Nylon 11 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/3 
               
               
                 Example 22 
                 Nylon 11 
                 3.04 
                 7.1 
                 0.071 
                 100 
                 8 
                 (64) 
                 About 1/3 
               
               
                 Example 23 
                 Nylon 11 
                 4.36 
                 15 
                 0.071 
                 210 
                 16 
                 (133) 
                 About 1/3 
               
               
                 Example 24 
                 Nylon 11 
                 9.49 
                 71 
                 0.071 
                 1000 
                 73 
                 (630) 
                 About 1/3 
               
               
                 Example 25 
                 Nylon 12 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/3 
               
               
                 Example 26 
                 Nylon 12 
                 3.04 
                 7.1 
                 0.071 
                 100 
                 8 
                 (64) 
                 About 1/3 
               
               
                 Example 27 
                 Nylon 12 
                 4.36 
                 15 
                 0.071 
                 210 
                 16 
                 (133) 
                 About 1/3 
               
               
                 Example 28 
                 Nylon 12 
                 9.49 
                 71 
                 0.071 
                 1000 
                 73 
                 (630) 
                 About 1/3 
               
               
                 Example 29 
                 Nylon 6 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 5 
                 (33) 
                 About 1/8 
               
               
                 Example 30 
                 Nylon 6 
                 3.04 
                 7.1 
                 0.071 
                 100 
                 9 
                 (64) 
                 About 1/8 
               
               
                 Example 31 
                 Nylon 6 
                 4.36 
                 15 
                 0.071 
                 210 
                 17 
                 (133) 
                 About 1/8 
               
               
                 Example 32 
                 Nylon 6 
                 9.49 
                 71 
                 0.071 
                 1000 
                 80 
                 (630) 
                 About 1/8 
               
               
                 Example 33 
                 Nylon 66 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 5 
                 (33) 
                 About 1/6 
               
               
                 Example 34 
                 Nylon 66 
                 3.04 
                 7.1 
                 0.071 
                 100 
                 9 
                 (64) 
                 About 1/6 
               
               
                 Example 35 
                 Nylon 66 
                 4.36 
                 15 
                 0.071 
                 210 
                 17 
                 (133) 
                 About 1/6 
               
               
                 Example 36 
                 Nylon 66 
                 9.49 
                 71 
                 0.071 
                 1000 
                 81 
                 (630) 
                 About 1/6 
               
               
                 Example 37 
                 Polyethylene 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 4 
                 (33) 
                 About 1/39 
               
               
                 Example 38 
                 Polyethylene 
                 3.04 
                 7.1 
                 0.071 
                 100 
                 7 
                 (64) 
                 About 1/39 
               
               
                 Example 39 
                 Polyethylene 
                 4.36 
                 15 
                 0.071 
                 210 
                 15 
                 (133) 
                 About 1/39 
               
               
                 Example 40 
                 Polyethylene 
                 9.49 
                 71 
                 0.071 
                 1000 
                 68 
                 (630) 
                 About 1/39 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Resin coated superconducting wire 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Cross section 
                 Cross section 
                   
                 Material cost 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 External dimensions [mm] 
                 Cross section 
                 area of 
                 area ratio 
                 Resin 
                 ratio per 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Curvature 
                 area of 
                 superconducting 
                 (matrix resin/ 
                 weight per 
                 unit length 
               
               
                   
                   
                   
                   
                 radius R of 
                 matrix resin 
                 wire 
                 superconducting 
                 1000 m 
                 (cost ratio of 
               
               
                   
                 Resin 
                 Width 
                 Thickness 
                 corner 
                 [mm 2 ] 
                 [mm 2 ] 
                 wire) 
                 [kg] 
                 resin/copper) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Example 41 
                 Modified low- 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 4 (33) 
                 About 1/39 
               
               
                   
                 density 
               
               
                   
                 polyethylene/ 
               
               
                   
                 polyethylene 
               
               
                 Example 42 
                 Ethylene- 
                 2.5 
                 1.5 
                 0.3 
                 3.6 
                 0.071 
                 51 
                 4 (33) 
                 About 1/39 
               
               
                   
                 methacrylic acid 
               
               
                   
                 copolymer/ 
               
               
                   
                 polyethylene 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Resin coated superconducting wire 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Cross section 
                 Crosssection 
                   
                 Material cost 
               
               
                   
                   
                   
                 Cross section 
                 area of 
                 area ratio 
                 Resin 
                 ratio per unit 
               
               
                   
                   
                 External 
                 area of 
                 superconducting 
                 (matrix resin/ 
                 weight per 
                 length 
               
               
                   
                   
                 diameter 
                 matrix resin 
                 wire 
                 superconducting 
                 1000 m 
                 (cost ratio of 
               
               
                   
                 Resin 
                 [mm] 
                 [mm 2 ] 
                 [mm 2 ] 
                 wire) 
                 [kg] 
                 resin/copper) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 43 
                 Modified low- 
                 2.16 
                 3.6 
                 0.071 
                 51 
                 4 (33) 
                 About 1/39 
               
               
                   
                 density 
               
               
                   
                 polyethylene/ 
               
               
                   
                 polyethylene 
               
               
                   
               
            
           
         
       
     
     It has been demonstrated that the resulting resin coated superconducting wires of Examples 1 to 43 have dimensions substantially the same as that of conventional superconducting wire including a copper channel and provide magnetic shielding performance substantially the same as that of conventional superconducting wire including a copper channel. 
     Tables 2 to 5 also show that the resin coated superconducting wires of Examples 1 to 43 can attain a significantly reduced weight and a reduced material cost as compared to copper coated superconducting wire. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               1 ,  1 A,  1 B,  1 C,  1 D,  1 E,  1 F,  2 : Resin coated superconducting wire 
               11 ,  11 A,  11 B,  11 C,  11 D,  11 E,  11 F: Matrix resin 
               11   a : Inner matrix resin layer 
               11   b : Outer matrix resin layer 
               12 ,  12 A,  12 B,  12 C,  12 D,  12 E,  12 F,  22 : Superconducting wire 
               21 : Copper stabilizer