Carbon nanotube-coated electric wire

Abstract

A carbon nanotube coated wire (1) according to the present invention is provided with a conductor, and a compression coating layer (20) which coats the conductor. The conductor is a carbon nanotube stranded wire (10) in which a plurality of carbon nanotube wires (11) are twisted, and a ratio (R1 / R2) of a resistance value R2 (mΩ / m) of the conductor prior to being coated by the compression coding layer (20) to a resistance value R1 (mΩ / m) after being coated by the compression coding layer (20) is less than 0.96.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube-coated wire, and more particularly to a carbon nanotube-coated wire in which a carbon nanotube twisted wire is coated with a coating material exhibiting compressibility.

Background Art

[0002] As power lines or signal lines in various fields such as automobiles and industrial equipment, a coated wire composed of a conductor and an insulating coating covering the conductor is used. As a material for the wire constituting the conductor, usually, a metal wire such as copper or a copper alloy is used from the viewpoint of electrical characteristics.

[0003] On the other hand, with the recent trend of weight reduction of automobiles, expansion of the interior space of vehicles, and increase in signal lines, weight reduction of current wires is required. As one of the methods for reducing the weight of wires, a technique using carbon nanotubes as a conductor is known. Carbon nanotubes are materials having various characteristics and are expected to be applied to many fields. For example, carbon nanotubes are lightweight and excellent in various characteristics such as electrical conductivity, thermal conductivity, and mechanical strength, and thus are regarded as promising as a material for wires.

[0004] When carbon nanotubes are used as a wire material, in order to improve the strength of the wire, usually, a twisted wire obtained by twisting each strand of the carbon nanotube wire material is used. However, since carbon nanotubes are fibrous strands, when each strand of carbon nanotubes is twisted at a long pitch, the adhesion between the strands decreases, and the twist is likely to unwind. In this case, gaps may occur between the strands, which may lead to a decrease in conductivity. On the other hand, if the number of twists is increased to prevent the twist from easily unwinding, tension is applied to the carbon nanotube wire material, and there is a possibility of quality deterioration due to wire breakage. Therefore, it is necessary to fix the carbon nanotube wire material formed into a twisted wire with a small number of twists and suppress a decrease in conductivity.

[0005] Patent Document 1 discloses a carbon nanotube stranded wire including a plurality of carbon nanotube fibers formed only of carbon nanotubes and a pipe, in which the plurality of carbon nanotube fibers are housed in the pipe in a state of being firmly gripped from the outside by the pipe over the entire longitudinal direction. In Patent Document 1, although the carbon nanotube fibers can be held by the pipe, when the outer periphery of the carbon nanotube stranded wire as a conductor is further coated with a cylindrical metal pipe, the weight of the added pipe increases the weight of the electric wire. Therefore, there is a problem that the light weight of the carbon nanotubes cannot be exhibited and the weight reduction of the electric wire cannot be achieved. Further, when the carbon nanotube stranded wire is coated with a resin pipe, the influence of the conductivity due to the use of such a pipe is not mentioned.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a carbon nanotube-coated electric wire with improved conductivity while taking advantage of the light weight of carbon nanotubes.

Means for Solving the Problems

[0008] The carbon nanotube-coated electric wire according to the present embodiment includes a conductor and a compression coating layer that coats the conductor, the conductor is a carbon nanotube stranded wire in which a plurality of carbon nanotube stranded wires are twisted together, and the ratio (R1 / R2) of the resistance value R1 (mΩ / m) of the conductor after the compression coating layer is coated to the resistance value R2 (mΩ / m) of the conductor before the compression coating layer is coated is less than 0.96.

[0009] In one embodiment of the present invention, the ratio (φ1 / φ2) of the conductor diameter φ1 (mm) after the compression coating layer is coated to the conductor diameter φ2 (mm) before the compression coating layer is coated is less than 0.95.

[0010] In one embodiment of the present invention, the wire diameter of the carbon nanotube strand is 150 μm or less, and the number of the carbon nanotube strands is 20 or more.

[0011] In one embodiment of the present invention, the wire diameter of the carbon nanotube strand is 80 μm or less, and the number of the carbon nanotube strands is 50 or more.

[0012] In one embodiment of the present invention, the number of twists of the carbon nanotube twisted wire is 50 T / m or more and 400 T / m or less.

[0013] The carbon nanotube-coated electric wire according to another embodiment of the present invention includes a conductor and a compression coating layer that coats the conductor. The conductor is a carbon nanotube twisted wire in which a plurality of carbon nanotube strands are twisted together. The wire diameter of the carbon nanotube strand is 150 μm or less, and the number of the carbon nanotube strands is 20 or more. The number of twists of the carbon nanotube twisted wire is 80 T / m or more and 300 T / m or less, and the conductor diameter φ1 after the compression coating layer is coated is 1.3 mm or less.

[0014] In one embodiment of the present invention, the wire diameter of the carbon nanotube strand is 50 μm or less, and the number of the carbon nanotube strands is 100 or more.

[0015] In one embodiment of the present invention, the compression coating layer is a heat-shrinkable tube.

[0016] In one embodiment of the present invention, the carbon nanotube twisted wire is held by the compression coating layer having a flexural modulus of 500 MPa or more.

[0017] In one embodiment of the present invention, an insulating resin layer is further provided on the outer periphery of the compression coating layer.

[0018] In one embodiment of the present invention, the carbon nanotube coated wire is used as an automotive wire harness.

Effects of the Invention

[0019] According to the present invention, it is possible to obtain a carbon nanotube coated wire with improved conductivity while taking advantage of the light weight of the carbon nanotubes.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0021] Hereinafter, the carbon nanotube coated wire according to the embodiment of the present invention will be described with reference to the drawings.

[0022] [Carbon Nanotube Coated Wire] As shown in FIG. 1, a carbon nanotube coated wire (hereinafter sometimes referred to as "CNT coated wire") 1 according to an embodiment of the present invention includes a carbon nanotube twisted wire (hereinafter sometimes referred to as "CNT twisted wire") 10 as a conductor and a compression coating layer 20 that coats the CNT twisted wire 10, and the compression coating layer 20 is coated on the outer peripheral surface of the CNT twisted wire 10. That is, the compression coating layer 20 is coated along the longitudinal direction of the CNT twisted wire 10. In the CNT coated wire 1, since the entire outer peripheral surface of the CNT twisted wire 10 is coated with the compression coating layer 20, the compression coating layer 20 is in close contact with the outer peripheral surface of the CNT twisted wire 10.

[0023] [Conductor] The CNT twisted wire 10 is formed from a carbon nanotube aggregate (hereinafter sometimes referred to as a "CNT aggregate"), and the CNT aggregate is used as a carbon nanotube elementary wire (hereinafter sometimes referred to as a "CNT elementary wire") 11. The CNT twisted wire 10 is formed by twisting a plurality of CNT elementary wires 11. By forming the conductor of the CNT into the form of a twisted wire, the conductor can be thickened and the strength is improved. The conductor diameter (equivalent circular diameter) of the CNT twisted wire 10 is not particularly limited, but for example, it is preferably 0.1 mm or more and 10 mm or less. Further, the cross-sectional area of the CNT twisted wire 10 is 0.005 mm 2 or more and 50 mm 2 or less is preferable. The equivalent circular diameter is obtained by calculating the cross-sectional area from the cross-sectional observation in the radial direction of the CNT twisted wire 10 and calculating the diameter of a circle having the same area as this.

[0024] The CNT twisted wire 10 may be doped with a different element. In this case, the CNT twisted wire 10 may be formed by twisting a plurality of carbon nanotube composites in which the CNT elementary wire 11 is doped with a different element. By doping with a different element, the conductivity of the CNT twisted wire 10 can be improved. Examples of the different element include one or more elements or molecules selected from the group consisting of nitric acid, sulfuric acid, iodine, bromine, potassium, sodium, boron, and nitrogen.

[0025] The CNT twisted wire 10 can be formed as a twisted wire by bundling a plurality of CNT elementary wires 11, fixing one end, and then twisting the other end a predetermined number of times. The twist number (twist degree) of the CNT twisted wire 10 is represented by the number of turns per unit length when a plurality of CNT elementary wires 11 are twisted together. That is, the twist number can be represented by a value obtained by dividing the number of twists (T) by the length (m) of the wire (unit: T / m). The twist number (T / m) of the CNT twisted wire 10 is preferably more than 0 T / m and not more than 1000 T / m, and more preferably 50 T / m or more and 400 T / m or less, in order to impart a certain strength to the CNT twisted wire 10. In particular, when the twist number of the CNT twisted wire 10 is 80 T / m or more and 300 T / m or less, the strength is improved and the twisting process can be simplified.

[0026] In the CNT twisted wire 10, the CNT elementary wire 11 is in direct contact with other adjacent CNT elementary wires 11. Also, the CNT elementary wire 11 is excellent in longitudinal conductivity. Since the CNT elementary wire 11 is in direct contact with other adjacent CNT elementary wires 11, the CNT twisted wire 10 exhibits excellent conductivity as a whole.

[0027] Also, when the twist number is large, tension is applied to the CNT elementary wire 11 due to the twisting process, and there is a possibility of quality degradation due to breakage of the CNT elementary wire 11. Therefore, by setting the twist number to be relatively small, such as 80 T / m or more and 300 T / m or less as described above, such a risk can be reduced. Furthermore, as will be described later, by disposing a compression coating layer 20 made of a thermally compressible resin, excellent conductivity can be exhibited while maintaining the contact between the CNT elementary wires 11.

[0028] The CNT elementary wire 11 used in the CNT coated electric wire 1 is composed of a plurality of carbon nanotubes (hereinafter sometimes referred to as "CNT") having a layer structure of one layer or more. Here, the CNT twisted wire 10 means a CNT wire material in which the proportion of CNT is 70% by mass or more. In calculating the CNT proportion in the CNT twisted wire, plating and dopants are excluded. Since the longitudinal direction of the CNT elementary wire 11 forms the longitudinal direction of the CNT twisted wire 10, the CNT elementary wire 11 is linear.

[0029] The CNT strand 11 is a long bundle of CNTs having a layer structure of one or more layers. The longitudinal direction of the CNTs forms the longitudinal direction of the CNT strand 11. The strand diameter (circle equivalent diameter) of the CNT strand 11 is preferably 10 μm or more and 150 μm or less, and the lower limit of the strand diameter is more preferably 20 μm or more. The upper limit of the strand diameter is more preferably 80 μm or less, and more preferably 50 μm or less. The number of CNT strands 11 constituting the CNT strand 10 is preferably 20 to 1000, and the lower limit of the number of CNT strands 11 is more preferably 50 or more, and even more preferably 100 or more. The upper limit of the number of CNT strands 11 is more preferably 800 or less. In particular, by having the wire diameter of the CNT wires 11 be 80 μm or less and the number of CNT wires 11 be 50 or more, the effect of increasing the contact area of ​​each CNT wire 11 by compression coating is improved, and a CNT-coated electric wire 1 with improved conductivity can be obtained. Furthermore, by having the wire diameter of the CNT wires 11 be 50 μm or less and the number of CNT wires 11 be 100 or more, a CNT-coated electric wire 1 in which the above-mentioned effects are prominent can be obtained.

[0030] The CNTs constituting the CNT strand 11 are cylindrical bodies having a single-layer structure or a multi-layer structure, and are called SWNTs (single-walled nanotubes) and MWNTs (multi-walled nanotubes), respectively. The CNT strand 11 may be formed from CNTs having a single-layer structure, CNTs having a two-layer structure, or CNTs having a three-layer or more layer structure, or may be formed using a plurality of CNTs having these layer structures.

[0031] In the CNTs that make up the CNT wire 11, in the case of CNTs having a two-layer structure, a three-dimensional network structure is formed in which two cylindrical bodies having a hexagonal lattice network structure are arranged substantially coaxially, and this is called a DWNT (Double-walled nanotube). The hexagonal lattice that is the structural unit is a six-membered ring with carbon atoms arranged at its vertices, and these are continuously bonded adjacent to other six-membered rings.

[0032] The properties of the CNTs that make up the CNT wire 11 depend on the chirality of the above-mentioned cylindrical bodies. Chirality is roughly classified into armchair type, zigzag type, and chiral type. The armchair type shows metallic behavior, the zigzag type shows semiconductor and semimetal behavior, and the chiral type shows semiconductor and semimetal behavior. Therefore, the conductivity of the CNTs varies greatly depending on which chirality the cylindrical bodies have.

[0033] [Compression coating layer] Next, the compression coating layer 20 that coats the outer peripheral surface of the CNT twisted wire 10 used in the CNT coated wire 1 will be described.

[0034] In the CNT coated wire 1 according to the present embodiment, a heat-shrinkable material is used as the material of the compression coating layer 20. Such a compression coating layer 20 is preferably a cylindrical body into which the CNT twisted wire 10 can be inserted, and more preferably a heat-shrinkable tube available on the market. As a specific example, when the compression coating layer 20 is a heat-shrinkable tube, the CNT twisted wire 10 is inserted into the heat-shrinkable tube and heated, so that the heat-shrinkable tube shrinks and a coating with compressive force is applied to the CNT twisted wire 10. As a result, the adhesion between the CNT wires 11 is improved and the twist of the CNT wires 11 is fixed. As a result, the generation of gaps between the CNT wires 11 is suppressed, and a decrease in the conductivity of the CNT coated wire 1 can be suppressed.

[0035] Examples of the material of the compression coating layer 20 include polytetrafluoroethylene, polyolefin, polyvinyl chloride, ethylene propylene rubber, silicone rubber, etc., and the material before heating is used. These materials may be used alone or may be appropriately mixed and used in two or more kinds.

[0036] In the CNT-coated electric wire 1, the force with which the compression coating layer 20 compresses the CNT twisted wire 10 is not particularly limited, but can be adjusted according to the material of the compression coating layer 20, its combination, heating temperature, heating time, etc. At that time, by adjusting so that the CNT twisted wire 10 is held by the compression coating layer 20 having a bending elastic modulus of 500 MPa or more (after compression), the CNT twisted wire 10 can be appropriately compressed. By the bending elastic modulus being 500 MPa or more, the CNT twisted wire 10 is more reliably held via the compression coating layer 20, and the compression of the compression coating layer 20 can be maintained for a long time. Further, the upper limit of the bending elastic modulus is preferably 4000 MPa or less, more preferably 1000 MPa or less, and still more preferably 600 MPa or less. By the upper limit of the bending elastic modulus being 4000 MPa or less, it is possible to prevent the CNT-coated electric wire 1 from being difficult to bend, and the processing in the subsequent process can be easily performed. The measurement of the bending elastic modulus of the resin can be performed by a method conforming to JIS K7171 (2016). Further, a bending elastic modulus of 500 MPa or more is particularly suitable when the wire diameter of the CNT single wire 11 is 150 μm or less, the number of CNT single wires 11 is 20 or more, and the twist number of the CNT twisted wire 10 is 80 T / m or more and 300 T / m or less, because the effect of increasing the contact area of the CNT single wire 11 can be exhibited. Furthermore, when the wire diameter of the CNT single wire 11 is thinner and the number is larger, the effect can be remarkably exhibited.

[0037] An insulating resin layer may be further provided on the outer periphery of the compression coating layer 20. The material of the insulating resin layer is not particularly limited as long as it is a commonly used insulating resin. Further, the insulating resin layer is formed by a general processing method such as extrusion coating, and a heated insulating resin is used as the coating material. That is, since a heated material is used for the insulating resin layer, the insulating resin layer does not shrink thermally regardless of the resin material. Examples of such materials for the insulating resin layer include polyvinyl chloride, polyvinyl alcohol, polystyrene, polyethylene, polypropylene, polyacetal, polymethyl methacrylate, cellulose acetate, polycarbonate, polyethylene terephthalate, polyamide, polyamideimide, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, enamel, and the like. These may be used alone or two or more of them may be appropriately mixed and used. By further coating the insulating resin layer on the compression coating layer 20, the insulation property, shape retention property, and weather resistance of the compression coating layer 20 can be enhanced. Further, since the insulating resin layer has good compatibility with the adhesion to the compression coating layer 20, the adhesion strength can be higher than that when the insulating resin layer is coated on the CNT twisted wire 10.

[0038] The total thickness of the compression coating layer 20 and the insulating resin layer is not particularly limited, but is preferably 0.002 mm or more and 2 mm or less, and more preferably 0.005 mm or more and 1 mm or less. Further, the thickness of the compression coating layer 20 is not particularly limited, but is preferably 0.001 mm or more and 1.5 mm or less, and more preferably 0.0025 mm or more and 0.5 mm or less. Further, when the compression coating layer 20 is a heat-shrinkable tube, the diameter of the heat-shrinkable tube is preferably 1.05 to 1.5 times the conductor diameter of the CNT twisted wire 10.

[0039] <Ratio of conductor resistance value> In the CNT-coated electric wire 1 according to this embodiment, the ratio R1 / R2 of the resistance value R1 (mΩ / m) of the conductor after the compression coating layer 20 is coated to the resistance value R2 (mΩ / m) of the conductor before the compression coating layer 20 is coated is less than 0.96, preferably 0.9 or less, and more preferably 0.7 or less. By controlling the compression force applied to the CNT twisted wire 10 so that the ratio (R1 / R2) is less than 0.96, the adhesion between the respective CNT strands 11 constituting the CNT twisted wire 10 is increased, and a decrease in conductivity is suppressed. Further, the volume resistivity of the conductor coated with the compression coating layer 20 decreases as compared with the conductor before the compression coating layer 20 is coated. Therefore, the CNT-coated electric wire 1 with improved conductivity can be obtained. Furthermore, the CNT twisted wire 10 can be fixed by the compression coating layer 20 without interposing another member such as a pipe. Also, in order to reduce the variation in the resistance value in the longitudinal direction, the lower limit of the ratio (R1 / R2) is preferably 0.3 or more.

[0040] The range of the resistance value R1 of the conductor is preferably, for example, 0.96 mΩ / m or more and 960 mΩ / m or less, and the range of the resistance value R2 of the conductor is preferably, for example, more than 1 mΩ / m and 1000 mΩ / m or less. Incidentally, the resistance values R1 and R2 of the conductor are measured, for example, by the four-terminal method.

[0041] <Ratio of conductor diameters> In the CNT-coated electric wire 1 according to this embodiment, the ratio (φ1 / φ2) of the conductor diameter φ1 after the compression coating layer 20 is coated to the conductor diameter φ2 before the compression coating layer 20 is coated is preferably less than 0.95, more preferably less than 0.9, and even more preferably less than 0.85. Specifically, as shown in FIG. 1, the conductor diameter φ1 after the CNT twisted wire 10 is coated with the compression coating layer 20 is smaller than the conductor diameter φ2 before the CNT twisted wire 10 is coated with the compression coating layer 20 as shown in FIG. 2 at a predetermined ratio, and thus the ratio (φ1 / φ2) is controlled. Thereby, since the CNT twisted wire 10 is more reliably fixed by the compression coating layer 20, the adhesion between the CNT strands 11 is improved, and a decrease in conductivity due to the generation of gaps between the CNT strands 11 can be suppressed. Further, in order to prevent excessive compressive force from being applied to the CNT twisted wire 10 and breakage of the CNT strands, the lower limit of the ratio (φ1 / φ2) is preferably 0.7 or more.

[0042] The range of the conductor diameter φ1 is preferably, for example, 0.095 mm or more and 9.5 mm or less. The lower limit of the conductor diameter φ1 is preferably 0.3 mm or more, and more preferably 0.5 mm or more. Also, the upper limit of the conductor diameter φ1 is preferably 5.0 mm or less, and more preferably 1.3 mm or less. On the other hand, the range of the conductor diameter φ2 is preferably, for example, 0.1 mm or more and 10 mm or less. The lower limit of the conductor diameter φ2 is preferably 0.3 mm or more, and more preferably 0.5 mm or more. Also, the upper limit of the conductor diameter φ2 is preferably 5.0 mm or less, and more preferably 1.5 mm or less. In particular, when the upper limit of the conductor diameter φ1 is 1.3 mm or less, the strand diameter of the CNT strand 11 is 150 μm or less, the number of CNT strands 11 is 20 or more, and the twist number of the CNT twisted wire 10 is 80 T / m or more and 300 T / m or less, it is suitable because the conductivity can be improved even with a small twist number, and furthermore, the effect can be remarkably exhibited when the strand diameter of the CNT strand 11 is thinner and the number is larger. Note that the conductor diameters φ1 and φ2 can be obtained, for example, by calculating the equivalent circular diameter from the cross-sectional area measured by microscopic observation of the cross-section.

[0043] [Method for manufacturing CNT-coated wire] Next, an example of a method for manufacturing the CNT-coated wire 1 according to an embodiment of the present invention will be described. For the CNT-coated wire 1, first, CNTs are produced, and a CNT strand 11 is produced from the obtained plurality of CNTs. Next, a plurality of the obtained CNT strands 11 are twisted together to produce a CNT twisted wire 10. Then, the CNT-coated wire 1 can be manufactured by coating a compression coating layer 20 on the outer peripheral surface of the CNT twisted wire 10.

[0044] The CNT 11 can be produced, for example, by methods such as the floating catalyst method (Patent No. 5819888) and the substrate method (Patent No. 5590603), and the floating catalyst method is preferred. Also, the CNT strand 11 can be produced, for example, by methods such as dry spinning (Patent Nos. 5819888, 5990202, 5350635), wet spinning (Patent Nos. 5135620, 5131571, 5288359), and liquid crystal spinning (Japanese Patent Publication No. 2014-530964).

[0045] As a method for coating the compression coating layer 20 on the outer peripheral surface of the CNT twisted wire 10, a method of coating using the heat shrinkage of the compression coating layer 20 can be used. For example, the CNT twisted wire 10 is inserted into the heat shrinkable tube which is the material of the compression coating layer 20, and the heat shrinkable tube is shrunk by heating with a dryer or the like, so that the compression coating layer 20 is coated on the CNT twisted wire 10.

[0046] The CNT-coated wire 1 in this embodiment can be used as a power line and a signal line in various fields such as automobiles, electrical equipment, and control equipment. In particular, the CNT-coated wire 1 is suitable for use as an automotive wire harness.

[0047] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, includes all aspects included in the concept of the present invention, and can be variously modified within the scope of the present invention.

Examples

[0048] Next, examples of the present invention will be described, but the present invention is not limited to these examples unless it exceeds the gist thereof.

[0049] [Examples 1 to 4 and Comparative Examples 1 to 2] For Examples 1 to 4 and Comparative Examples 1 to 2, coated electric wires were produced by the following manufacturing process.

[0050] <Production of conductor> First, using CNTs produced by the floating catalyst method, CNT strands having the strand diameters shown in Table 1 were produced by wet spinning. Next, the obtained CNT strands were twisted together at the number of strands and twist number shown in Table 1 to produce CNT twisted wires respectively.

[0051] <Production of CNT coated electric wire> Using heat shrinkable tubes made of polytetrafluoroethylene (PTFE), each CNT twisted wire was inserted into the inside of each heat shrinkable tube having the inner diameter shown in Table 1. Next, by heating at the shrinkage temperature (340°C) of the heat shrinkable tube to compressively coat the heat shrinkable tube, a compressive coating layer with a thickness of 0.05 mm was formed on the outer periphery of the CNT twisted wire. Also, when the flexural modulus of PTFE was measured in accordance with JIS K7171 (2016), it was 550 MPa. Thus, CNT coated electric wires in each example and comparative example were produced.

[0052] The following measurements and evaluations were performed on the CNT coated electric wires produced in this way.

[0053] <Measurement of conductor diameter> Regarding the conductor before being coated with the heat shrinkable tube, it was cut with a cutter to expose the cross section, observed with a microscope, and the cross sectional area of the conductor was obtained. The diameter of a circle (equivalent circle diameter) having the same cross sectional area as this was obtained, and the value was taken as the conductor diameter φ2 (mm). Next, the conductor diameter was also measured in the same manner for the conductor after being coated with the heat shrinkable tube, and the measured value was taken as the conductor diameter φ1 (mm). Based on the obtained conductor diameters φ1 and φ2, the ratio of the conductor diameters (φ1 / φ2) was calculated.

[0054] <Resistance value of conductor> Regarding the conductor before being coated with the heat-shrinkable tube, the resistance value when a current of 100 mA was passed through it using a source meter (manufactured by Keithley Instruments, Inc.) was measured, and the measured value was designated as R2 (mΩ / m). Next, the resistance value of the conductor after being coated with the heat-shrinkable tube was similarly measured, and the measured value was designated as R1 (mΩ / m). Based on the obtained resistance values R1 and R2, the ratio of the resistance values of the conductor (R1 / R2) was calculated.

[0055] <Ratio of volume resistivity> The volume resistivity ρ1 (mΩ·cm) after coating is obtained from the following formula (1). In formula (1), R1 is the resistance value per 1 m of the conductor after coating (mΩ / m), and S1 is the cross-sectional area obtained from the microscopic image of the cross-section of the conductor after coating (cm 2 ). Also, the volume resistivity ρ2 (mΩ·cm) before coating is obtained from the following formula (2). In formula (2), R2 is the resistance value per 1 m of the conductor before coating (mΩ / m), and S2 is the cross-sectional area obtained from the microscopic image of the cross-section of the conductor before coating (cm 2 ). Based on the obtained volume resistivities ρ1 and ρ2, the ratio of the volume resistivities (ρ1 / ρ2) was calculated. If the ratio of the volume resistivities (ρ1 / ρ2) is 0.75 or less, it was evaluated that a CNT-coated electric wire with improved conductivity was obtained.

[0056] ρ1=(R1 / 100)×S1···(1) ρ2=(R2 / 100)×S2···(2)

[0057] The measurement and evaluation results of the CNT-coated electric wires prepared in each example and comparative example are shown in Table 1 below.

[0058]

Table 1

[0059] As shown in Table 1, in the CNT-coated electric wire in which the carbon nanotube twisted wire as a conductor is coated with a heat-shrinkable tube as a compression coating layer, in Examples 1 to 4 where the ratio (R1 / R2) of the resistance value of the conductor is less than 0.96, in all cases, the ratio (ρ1 / ρ2) of the volume resistivity is 0.7 or less, and the obtained CNT-coated electric wire exhibited excellent conductivity. Further, since the CNT twisted wire is directly coated with the heat-shrinkable tube, the CNT strands are firmly fixed to each other by the compression coating layer without using other fixing members. Therefore, in Examples 1 to 4, it was possible to improve the adhesion between the CNT strands while maintaining the weight of the conductor, and it was possible to obtain a CNT-coated electric wire with improved conductivity while taking advantage of the light weight of the CNT. Further, in Examples 1 to 4, the conductivity could be improved even with a small number of twists, and furthermore, when the strand diameter of the CNT strand 11 was thinner and the number was larger, the improvement in conductivity was remarkably exhibited.

[0060] On the other hand, in Comparative Example 1 where the ratio (R1 / R2) of the resistance value of the conductor is 0.98, the ratio of the volume resistivity is 0.78, and the conductivity is inferior compared to Examples 1 to 4. In Comparative Example 1, the heat-shrinkable tube is not coated on the CNT twisted wire with sufficient compressive force, and the adhesion between the respective strands is not sufficient, so it is presumed that gaps are generated between the strands. Therefore, in Comparative Example 1, a CNT-coated electric wire showing excellent conductivity could not be obtained.

[0061] Also in Comparative Example 2 where the ratio (R1 / R2) of the resistance value of the conductor is 0.99, as in Comparative Example 1, the conductivity was inferior compared to Examples 1 to 4. Further, in Comparative Example 2, the ratio (φ1 / φ2) of the conductor diameter is 0.96, and the adhesion between the respective strands is not sufficient compared to Comparative Example 1, so a CNT-coated electric wire showing sufficient conductivity could not be obtained.

[0062] Thus, in the CNT-coated electric wire in which the carbon nanotube twisted wire as a conductor is coated with a heat-shrinkable tube as a compression coating layer, by the ratio (R1 / R2) of the resistance value of the conductor being less than 0.96, it is possible to provide a carbon nanotube-coated electric wire with improved conductivity while taking advantage of the light weight of the CNT.

Explanation of Signs

[0063] 1 Carbon nanotube-coated wire 10 Carbon nanotube stranded wire 11 Carbon nanotube single wire 20 Compression coating layer

Claims

1. comprising a conductor and a compression coating layer covering the conductor, wherein the conductor is a carbon nanotube twisted wire formed by twisting a plurality of carbon nanotube strands, the ratio (R1 / R2) of the resistance value R1 (mΩ / m) of the conductor after being covered with the compression coating layer to the resistance value R2 (mΩ / m) of the conductor before being covered with the compression coating layer is less than 0.96, the ratio of volume resistivity (ρ1 / ρ2) is 0.75 or less, the volume resistivity ρ1 (mΩ·cm) after coating is obtained from the following formula (1), the volume resistivity ρ2 (mΩ·cm) before coating is obtained from the following formula (2), S1 is the cross-sectional area (cm2) obtained from a microscopic image of the cross-section of the conductor after coating, and S2 is the cross-sectional area (cm2) obtained from a microscopic image of the cross-section of the conductor before coating, characterized in that it is a carbon nanotube coated electric wire. ρ1 = (R1 / 100) × S1... (1) ρ2 = (R2 / 100) × S2... (2)

2. The carbon nanotube coated electric wire according to claim 1, wherein the ratio (φ1 / φ2) of the conductor diameter φ1 (mm) after being covered with the compression coating layer to the conductor diameter φ2 (mm) before being covered with the compression coating layer is less than 0.

95.

3. The carbon nanotube coated electric wire according to claim 1 or 2, wherein the strand diameter of the carbon nanotube strand is 150 μm or less, and the number of the carbon nanotube strands is 20 or more.

4. The carbon nanotube coated electric wire according to any one of claims 1 to 3, wherein the strand diameter of the carbon nanotube strand is 80 μm or less, and the number of the carbon nanotube strands is 50 or more.

5. The carbon nanotube-coated electric wire according to any one of claims 1 to 4, wherein the compression coating layer is a heat-shrinkable tube.

6. The carbon nanotube-coated electric wire according to any one of claims 1 to 5, wherein the number of twists of the carbon nanotube stranded wire is 50 T / m or more and 400 T / m or less.

7. The carbon nanotube-coated electric wire according to any one of claims 1 to 6, wherein an insulating resin layer is further provided on the outer periphery of the compression coating layer.

8. The carbon nanotube-coated electric wire according to any one of claims 1 to 7, which is used as an automotive wire harness.

9. A conductor and a compression coating layer covering the conductor, wherein the conductor is a carbon nanotube stranded wire in which a plurality of carbon nanotube strands are twisted together, wherein the strand diameter of the carbon nanotube strand is 150 μm or less, and the number of carbon nanotube strands is 20 or more, wherein the number of twists of the carbon nanotube stranded wire is 80 T / m or more and 300 T / m or less, and a carbon nanotube-coated electric wire, characterized in that the conductor diameter φ1 after the compression coating layer is coated is 1.3 mm or less.

10. The carbon nanotube-coated electric wire according to claim 9, wherein the carbon nanotube stranded wire is held by the compression coating layer having a bending elastic modulus of 500 MPa or more.

11. The carbon nanotube-coated electric wire according to claim 9 or 10, wherein the strand diameter of the carbon nanotube strand is 50 μm or less, and the number of carbon nanotube strands is 100 or more.

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