Cable

Abstract

This cable comprises: a conductor; a first semiconductive layer that covers the outer periphery of the conductor; an insulating layer that covers the outer periphery of the first semiconductive layer; and a second semiconductive layer that covers the outer periphery of the insulating layer. The first semiconductive layer is formed of a first crosslinked body of a first composition that contains an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler. The insulating layer is formed of a second crosslinked body of a second composition that contains an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride. The second semiconductive layer is formed of a third crosslinked body of a third composition that contains an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler.

Description

cable

[0001] The present disclosure relates to cables.

[0002] Cables, especially those used on aircraft, are required to be durable at high temperatures. One of the reasons for the end of their lifespan is that the insulation layer covering the conductor deteriorates due to partial discharges that occur during use.

[0003] Patent Document 1 discloses a technique of using a fluoropolymer electrical insulating layer as an insulating layer in order to suppress partial discharge.

[0004] EP 2765581

[0005] The cable of the present disclosure comprises: a conductor; a first semiconductive layer covering the outer periphery of the conductor; an insulating layer covering the outer periphery of the first semiconductive layer; and a second semiconductive layer covering the outer periphery of the insulating layer, wherein the first semiconductive layer is made of a first crosslinked body of a first composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and a conductive filler; the insulating layer is made of a second crosslinked body of a second composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride; and the second semiconductive layer is made of a third crosslinked body of a third composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and a conductive filler.

[0006] Fig. 1 is a cross-sectional view of an example of a cable according to embodiment 1. Fig. 2 is a cross-sectional view of another example of a cable according to embodiment 1. Fig. 3 is a view showing a first cross-section of the cable for explaining a gap length. Fig. 4 is a view showing a second cross-section of the cable for explaining a gap length.

[0007] [Problem to be Solved by the Present Disclosure] When a cable used for power supply is energized in an aircraft or space environment, the cable is exposed to high temperatures. The fluoropolymer electrical insulation layer used in the insulation layer of Patent Document 1 is a non-crosslinked layer, so that under high-temperature conditions, for example, of 320°C or higher, the polymer melts, reducing the strength and shortening the life of the cable. Therefore, there is a demand for a cable whose insulation layer does not melt even when used under high-temperature conditions such as those on an aircraft or in space.

[0008] Therefore, an object of the present disclosure is to provide a cable whose insulating layer does not melt even when used under high-temperature conditions.

[0009] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a cable whose insulating layer does not melt even when used under high temperature conditions.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A cable of the present disclosure is a cable comprising: a conductor; a first semiconductive layer covering the outer periphery of the conductor; an insulating layer covering the outer periphery of the first semiconductive layer; and a second semiconductive layer covering the outer periphery of the insulating layer, wherein the first semiconductive layer is made of a first crosslinked body of a first composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler, the insulating layer is made of a second crosslinked body of a second composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and the second semiconductive layer is made of a third crosslinked body of a third composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler.

[0011] According to the present disclosure, it is possible to provide a cable whose insulation layer does not melt even when used under high temperature conditions.

[0012] (2) In the above (1), the insulating layer may have an average thickness of 0.10 mm or more and 2.0 mm or less, which facilitates extrusion molding during cable fabrication, provides flexibility to the cable, and makes it easier to handle.

[0013] (3) In the above (1) or (2), the average thickness of the insulating layer may be greater than 0.70 mm. This allows the gap length capable of suppressing partial discharge to be increased. Details of the gap length will be described later.

[0014] (4) In any one of (1) to (3) above, the first semiconductive layer may have an average thickness of 0.10 mm or more and 0.5 mm or less, which facilitates extrusion molding during cable fabrication, and also provides flexibility and ease of handling of the cable.

[0015] (5) In any one of (1) to (4) above, the second semiconductive layer may have an average thickness of 0.10 mm or more and 0.5 mm or less, which facilitates extrusion molding during cable fabrication, and also provides flexibility and ease of handling of the cable.

[0016] (6) In any of (1) to (5) above, the cable may further include a shielding layer covering the outer periphery of the second semiconducting layer and a jacket covering the outer periphery of the shielding layer, and the jacket may be made of a fourth crosslinked body of a fourth composition containing ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride.

[0017] The presence of the shielding layer allows the cable to achieve excellent noise shielding effects. The jacket mechanically protects the conductor, first semiconducting layer, insulating layer, second semiconducting layer, and shielding layer, and can also provide the cable with properties such as flame retardancy and oil resistance.

[0018] (7) In any one of (1) to (6) above, the first semiconductive layer may have an elastic modulus of 0.1 MPa or more at 330°C.

[0019] (8) In any one of the above (1) to (7), the insulating layer may have an elastic modulus of 0.1 MPa or more at 330°C.

[0020] (9) In any one of the above (1) to (8), the second semiconducting layer may have an elastic modulus of 0.1 MPa or more at 330°C.

[0021] [Details of the embodiment of the present disclosure] Specific examples of the cable of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0022] In the present disclosure, the notation in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the units of A and B are the same.

[0023] In the present disclosure, when one or more numerical values ​​are recited as the lower limit and the upper limit of a numerical range, a combination of any one numerical value recited as the lower limit and any one numerical value recited as the upper limit is also considered to be disclosed. For example, when a1 or more, b1 or more, and c1 or more are recited as the lower limit and a2 or less, b2 or less, and c2 or less are recited as the upper limit, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are considered to be disclosed.

[0024] [Embodiment 1: Cable] A cable 10 according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figure 1. As shown in Figure 1, cable 10 according to Embodiment 1 includes: a conductor 1; a first semiconductive layer 2 covering the outer periphery of conductor 1; an insulating layer 3 covering the outer periphery of first semiconductive layer 2; and a second semiconductive layer 4 covering the outer periphery of insulating layer 3, wherein first semiconductive layer 2 is made of a first crosslinked body of a first composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler, insulating layer 3 is made of a second crosslinked body of a second composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and second semiconductive layer 4 is made of a third crosslinked body of a third composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler.

[0025] 1 and 2 , the cable 10 of the first embodiment includes a conductor 1, a first semiconductive layer 2 covering the outer periphery of the conductor 1, an insulating layer 3 covering the outer periphery of the first semiconductive layer 2, and a second semiconductive layer 4 covering the outer periphery of the insulating layer 3. The entire outer periphery of the first semiconductive layer 2 can be covered in contact with the inner periphery of the insulating layer 3. As long as the effects of the present disclosure are not impaired, the outer periphery of the first semiconductive layer 2 and the inner periphery of the insulating layer 3 do not have to be partially in contact with each other. The entire outer periphery of the insulating layer 3 can be covered in contact with the inner periphery of the second semiconductive layer 4. As long as the effects of the present disclosure are not impaired, the outer periphery of the insulating layer 3 and the inner periphery of the second semiconductive layer 4 do not have to be partially in contact with each other.

[0026] The cable 10 of embodiment 1 may further include a shielding layer 5 that covers the outer periphery of the second semiconductive layer 4, and a jacket 6 that covers the outer periphery of the shielding layer 5. The entire outer periphery of the second semiconductive layer 4 may be covered with the shielding layer 5. As long as the effects of the present disclosure are not impaired, a portion of the second semiconductive layer 4 may not be covered with the shielding layer 5. The entire outer periphery of the shielding layer 5 may be covered with the jacket 6. As long as the effects of the present disclosure are not impaired, a portion of the shielding layer 5 may not be covered with the jacket 6.

[0027] <Conductor> In the cable 10 of the first embodiment, the material of the conductor 1 is preferably a metal material with high electrical conductivity and high mechanical strength. Examples of such metal materials include copper, copper alloys, aluminum, aluminum alloys, nickel, silver, mild steel, steel, and stainless steel. The conductor 1 may also have a multilayer structure in which a wire is coated with another metal by a technique such as plating. Examples of the conductor 1 having a multilayer structure include tin-plated copper wire, nickel-plated copper wire, silver-plated copper wire, copper-plated aluminum wire, and copper-plated steel wire.

[0028] The shape of the conductor 1 is not particularly limited, and any conventionally known shape can be used. For example, the conductor 1 can be a wire formed from a single metal material. Examples of the shape of the wire include a round wire with a circular cross section, a rectangular wire with a square cross section, and a rectangular wire. The conductor 1 can be a twisted wire formed by twisting together multiple wires. As shown in FIG. 1, the conductor 1 may consist of a single wire or a twisted wire. As shown in FIG. 2, the conductor 1 may consist of multiple wires or multiple twisted wires.

[0029] The average cross-sectional area of ​​the conductor 1 is not particularly limited and can be appropriately selected depending on the application. ２ Over 120mm ２ Less than 13mm is also acceptable. ２ 110mm or more ２ or less. In the present disclosure, the method for measuring the average cross-sectional area of ​​the conductor 1 is as follows. One cable 10 is stretched in a straight line, and the cable 10 is cut along a plane normal to a first direction connecting one end of the cable 10 to the other end, the cross section is exposed, and the cross-sectional area of ​​the conductor 1 is measured. For one cable 10, the cable 10 is cut along a plane normal to the first direction at five arbitrary locations to measure the cross-sectional areas of the conductor 1, and the average value of the cross-sectional areas of the conductor 1 at the five locations is calculated. The average value corresponds to the average cross-sectional area of ​​the conductor 1.

[0030] <First Semiconductive Layer> In the cable 10 of the first embodiment, the first semiconductive layer 2 is provided so as to cover the outer periphery of the conductor 1. The first semiconductive layer 2 has semiconductivity, and can suppress the occurrence of partial discharge by reducing the potential difference in the space between the conductor 1 and the first semiconductive layer 2.

[0031] The first semiconductive layer 2 is made of a first crosslinked body of a first composition containing an ethylene-tetrafluoroethylene copolymer (hereinafter also referred to as "ETFE") or polyvinylidene fluoride (hereinafter also referred to as "PVdF") and a conductive filler.

[0032] Ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride can be crosslinked by irradiation with radiation. Crosslinked ethylene-tetrafluoroethylene copolymer and crosslinked polyvinylidene fluoride do not melt even under high-temperature conditions, for example, at 320°C or higher. The first crosslinked body constituting the first semiconductive layer 2 of embodiment 1 is a crosslinked body of the first composition containing ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and therefore the first crosslinked body also does not melt under high-temperature conditions. Therefore, the first semiconductive layer 2 can maintain its strength even under high-temperature conditions.

[0033] The fact that the first semiconducting layer 2 contains an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride can be confirmed by an infrared spectrophotometer (IR), nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), etc. The same methods can be used to confirm that the insulating layer 3 and second semiconducting layer 4 described below also contain an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride.

[0034] The elastic modulus of the first semiconductive layer 2 at 330°C may be 0.1 MPa or more. This allows the first semiconductive layer 2 to have high strength without melting even under high-temperature conditions such as 330°C. The lower limit of the elastic modulus of the first semiconductive layer 2 at 330°C may be 0.5 MPa or more, 1.0 MPa or more, 1.5 MPa or more, or 1.8 MPa or more. The upper limit of the elastic modulus of the first semiconductive layer 2 at 330°C is not particularly limited, but may be, for example, 10 MPa or less or 5 MPa or less from the viewpoint of handleability at high temperatures. The elastic modulus of the first semiconductive layer 2 at 330°C may be 0.1 MPa or more and 10 MPa or less, or 0.5 MPa or more and 10 MPa or less.

[0035] The elastic modulus of the first semiconductive layer 2 at 330°C is measured as follows. A test piece is prepared by separating the first semiconductive layer 2 from the cable 10. The storage modulus of the test piece is measured using a viscoelasticity measuring device ("DVA-220" (trademark) manufactured by IT Measurement & Control Co., Ltd.) in accordance with the dynamic mechanical property testing method described in JIS K7244-4:1999 (corresponding to ISO6721-4:1994). The measurement conditions are tension mode, temperature range from -50°C to 350°C, heating rate of 10°C / min, frequency of 10 Hz, and strain of 0.08%. The elastic modulus of the test piece at 330°C is calculated from the storage modulus of the test piece measured under the above conditions. The elastic modulus at 330°C of the insulating layer 3 and the elastic modulus at 330°C of the second semiconductive layer 4 described below are measured using a test piece obtained by separating the insulating layer 3 or the second semiconductive layer 4 from the cable 10, using the same measurement method as above.

[0036] Examples of the conductive filler that can be used include carbon black, carbon nanotubes, and various conductive metal particles. One type of these conductive fillers may be used, or two or more types may be used. The presence of a conductive filler in the first semiconductive layer 2 can be confirmed by elemental analysis such as scanning electron microscope observation (SEM) or energy dispersive X-ray analysis (EDX). The presence of a conductive filler in the second semiconductive layer 4 (described below) can also be confirmed by the same method.

[0037] When carbon black is used as the conductive filler, the lower limit of the carbon black content of the first semiconductive layer 2 may be 5% by mass or more, 10% by mass or more, or 15% by mass or more from the viewpoint of ensuring conductivity. The upper limit of the carbon black content of the first semiconductive layer 2 may be 50% by mass or less, 45% by mass or less, or 40% by mass or less from the viewpoint of extrusion moldability. The carbon black content of the first semiconductive layer 2 may be 5% by mass or more and 50% by mass or less, 10% by mass or more and 45% by mass or less, or 15% by mass or more and 40% by mass or less. The carbon black content of the first semiconductive layer 2 can be measured by scanning electron microscope (SEM), specific gravity measurement, volume resistivity measurement, etc.

[0038] In the cable 10 of the first embodiment, the first composition may contain components other than the ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and conductive filler, such as a crosslinking aid, an antioxidant, a lubricant, a colorant, a processing aid, and a flame retardant.

[0039] Examples of the crosslinking aid that can be used include triallyl isocyanurate and trimethylolpropane trimethacrylate. Examples of the antioxidant that can be used include phenol-based antioxidants, sulfur-based antioxidants, and amine-based antioxidants.

[0040] The content of the cross-linking aid in the first composition can be appropriately adjusted depending on the type of cross-linking aid, and may be, for example, 0.5% by mass or more and 10% by mass or less, or 1% by mass or more and 7% by mass or less.

[0041] The content of the antioxidant in the first composition can be appropriately adjusted depending on the type of antioxidant, and may be, for example, 0.01% by mass or more and 5% by mass or less, or 0.03% by mass or more and 3% by mass or less.

[0042] The lower limit of the volume resistivity of the first semiconducting layer 2 at room temperature may be 1 Ω·cm or more, 5 Ω·cm or more, or 10 Ω·cm or more. The upper limit of the volume resistivity of the first semiconducting layer 2 at room temperature may be 100,000 Ω·cm or less, 50,000 Ω·cm or less, 10,000 Ω·cm or less, or 1,000 Ω·cm or less. The volume resistivity of the first semiconducting layer 2 at room temperature may be 1 Ω·cm or more and 100,000 Ω·cm or less, 5 Ω·cm or more and 50,000 Ω·cm or less, or 10 Ω·cm or more and 10,000 Ω·cm or less. In the present disclosure, room temperature means 25°C.

[0043] In the first embodiment, the first semiconductive layer 2 has a smaller volume expansion coefficient under high temperature conditions than an uncrosslinked body of the first composition having the same raw material composition as the first semiconductive layer 2. Therefore, the volume resistivity of the first semiconductive layer 2 at 100°C can be smaller than the volume resistivity of an uncrosslinked body of the first composition having the same raw material composition as the first semiconductive layer 2 at 100°C.

[0044] The lower limit of the volume resistivity of the first semiconducting layer 2 at 100°C may be 2 Ω·cm or more, 10 Ω·cm or more, or 20 Ω·cm or more. The upper limit of the volume resistivity of the first semiconducting layer 2 at 100°C may be 200,000 Ω·cm or less, 100,000 Ω·cm or less, 20,000 Ω·cm or less, 10,000 Ω·cm or less, 5,000 Ω·cm or less, or 2,000 Ω·cm or less. The volume resistivity of the first semiconducting layer 2 at 100°C may be 2 Ω·cm or more and 200,000 Ω·cm or less, 10 Ω·cm or more and 100,000 Ω·cm or less, or 20 Ω·cm or more and 20,000 Ω·cm or less.

[0045] The ratio ρ2 / ρ1 of the volume resistivity ρ2 at 100°C to the volume resistivity ρ1 at room temperature of the first semiconducting layer 2 may be 1.5 or more and 2.5 or less, 1.5 or more and 2.3 or less, 1.5 or more and 2.1 or less, or 1.5 or more and 1.9 or less.

[0046] The volume resistivity of the first semiconductive layer 2 at room temperature and 100°C is measured as follows: A test specimen is prepared by separating the first semiconductive layer 2 from the cable 10. The storage modulus of the test specimen is measured using a resistivity meter (Loresta-GP (trademark) manufactured by Mitsubishi Chemical Corporation) in accordance with the resistivity test method for conductive plastics using the four-probe method described in JIS K7194-1994.

[0047] The average thickness of the first semiconductive layer 2 can be adjusted as appropriate depending on the application of the cable 10. The lower limit of the average thickness of the first semiconductive layer 2 may be 0.10 mm or more, or 0.15 mm or more, from the viewpoint of ease of extrusion molding during production of the cable 10. The upper limit of the average thickness of the first semiconductive layer 2 may be 0.50 mm or less, or 0.40 mm or less, from the viewpoint of flexibility and ease of handling of the cable. The average thickness of the first semiconductive layer 2 may be 0.10 mm or more and 0.50 mm or less, or 0.10 mm or more and 0.40 mm or less.

[0048] In the present disclosure, the average thickness of the first semiconductive layer 2 is measured as follows. A cable 10 is stretched linearly, and the conductor 1 is cut along a plane normal to the first direction connecting one end of the cable 10 to the other, exposing a cross section. The thickness of the first semiconductive layer 2 is measured at three locations on the cross section, and the average value A is calculated. A Keyence VHX-8000 digital microscope is used as the measuring device. For a single cable 10, the conductor 1 is cut along a plane normal to the first direction at five arbitrary locations, and the average value A of the thickness of the first semiconductive layer 2 is calculated at each of the five locations. The average value B of the average values ​​A at the five locations is calculated. This average value B corresponds to the average thickness of the first semiconductive layer 2. The average thickness of the insulating layer 3 and the average thickness of the second semiconductive layer 4, described below, are also measured in a similar manner. The boundaries between the first semiconductive layer 2 and the insulating layer 3, and the boundaries between the insulating layer 3 and the second semiconductive layer 4, can be clearly confirmed by observation with the above-mentioned measuring device.

[0049] <Insulating Layer> In the cable 10 of the first embodiment, the insulating layer 3 is provided so as to cover the outer periphery of the first semiconducting layer 2 .

[0050] The insulating layer 3 is made of a second crosslinked body of a second composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride. The insulating layer 3 may contain impurities in addition to the second crosslinked body, as long as the effects of the present disclosure are not impaired.

[0051] Ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride can be crosslinked by irradiation with radiation. Crosslinked ethylene-tetrafluoroethylene copolymer and crosslinked polyvinylidene fluoride do not melt even under high-temperature conditions, for example, at 300°C or higher. The second crosslinked body constituting the insulating layer 3 of embodiment 1 is a crosslinked body of the second composition containing ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and therefore the second crosslinked body also does not melt under high-temperature conditions. Therefore, the insulating layer 3 can maintain its strength even under high-temperature conditions.

[0052] The elastic modulus of the insulating layer 3 at 330°C may be 0.1 MPa or more. This allows the second semiconducting layer 4 to have high strength without melting even under high-temperature conditions such as 330°C. The lower limit of the elastic modulus of the insulating layer 3 at 330°C may be 0.5 MPa or more, 1.0 MPa or more, or 1.3 MPa or more. The upper limit of the elastic modulus of the insulating layer 3 at 330°C is not particularly limited, but may be, for example, 10 MPa or less or 5 MPa or less from the viewpoint of handleability at high temperatures. The elastic modulus of the insulating layer 3 at 330°C may be 0.1 MPa or more and 10 MPa or less, or 0.5 MPa or more and 10 MPa or less.

[0053] In the cable 10 of the first embodiment, the second composition may contain components other than the ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride, such as a crosslinking aid, an antioxidant, a lubricant, a colorant, a processing aid, and a flame retardant.

[0054] Examples of the crosslinking aid that can be used include triallyl isocyanurate and trimethylolpropane trimethacrylate. Examples of the antioxidant that can be used include phenol-based antioxidants, sulfur-based antioxidants, and amine-based antioxidants.

[0055] The content of the cross-linking aid in the second composition can be appropriately adjusted depending on the type of cross-linking aid, and may be, for example, 0.5% by mass or more and 10% by mass or less, or 1% by mass or more and 7% by mass or less.

[0056] The content of the antioxidant in the second composition can be appropriately adjusted depending on the type of antioxidant, and may be, for example, 0.01% by mass or more and 5% by mass or less, or 0.03% by mass or more and 3% by mass or less.

[0057] The average thickness of the insulating layer 3 can be adjusted as appropriate depending on the application of the cable 10. The lower limit of the average thickness of the insulating layer 3 may be 0.10 mm or more, 0.15 mm or more, or 0.2 mm or more, from the viewpoint of ease of extrusion molding during production of the cable 10. The upper limit of the average thickness of the insulating layer 3 may be 2.00 mm or less, 1.75 mm or less, or 1.50 mm or less, from the viewpoint of flexibility and ease of handling of the cable. The average thickness of the first semiconducting layer 2 may be 0.10 mm or more and 2.00 mm or less, 0.10 mm or more and 1.75 mm or less, 0.15 mm or more and 1.75 mm or less, or 0.2 mm or more and 1.50 mm or less.

[0058] The average thickness of the insulating layer 3 may be greater than 0.70 mm. This allows for a longer gap length where partial discharge does not occur. The gap length in this disclosure will be described with reference to FIGS. 3 and 4 . FIG. 3 is a diagram showing a first cross section of the cable 10 obtained by cutting the cable 10 along a plane normal to a first direction connecting one end of the cable 10 to the other. FIG. 4 is a diagram showing a second cross section of the cable 10 obtained by cutting the cable 10 along a plane along the first direction. As shown in FIG. 3 , a gap that exists between the outer surface of the second semiconductive layer 4 and the inner surface of the shielding layer 5 in a specific first cross section, and that forms a state in which the second semiconductive layer 4 and the shielding layer 5 do not contact each other over the entire circumference of the second semiconductive layer 4, is referred to as a "circumferential gap." In FIG. 3 , the circumferential gap is indicated by the symbol G. As shown in FIG. 4 , the continuous length of the circumferential gap G along the first direction of the cable 10 is referred to as the "gap length." In FIG. 3 , the gap length is indicated by the symbol L. If the gap length L is large, partial discharge is more likely to occur when a potential difference occurs between the conductor 1 and the shield layer 5. If the average thickness of the insulating layer 3 exceeds 0.70 mm, the gap length L at which partial discharge can be suppressed can be increased.

[0059] From the viewpoint of increasing the gap length L at which partial discharge can be suppressed, the average thickness of the insulating layer 3 may be more than 0.70 mm, 0.71 mm or more, or 0.75 mm or more. The average thickness of the insulating layer 3 may be more than 0.70 mm and 3.0 mm or less, more than 0.70 mm and 2.0 mm or less, 0.71 mm or more and 3.0 mm or less, or 0.75 mm or more and 3.0 mm or less.

[0060] <Second Semiconductive Layer> In the cable 10 of the first embodiment, the second semiconductive layer 4 is provided so as to cover the outer periphery of the insulating layer 3. The second semiconductive layer 4 has semiconductivity. When the cable 10 includes a shielding layer 5 that covers the outer periphery of the second semiconductive layer 4, the presence of the second semiconductive layer 4 reduces the potential difference between the second semiconductive layer 4 and the shielding layer 5, thereby making it possible to suppress the occurrence of partial discharge.

[0061] The second semiconductive layer 4 is made of a third crosslinked body of a third composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler.

[0062] Ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride can be crosslinked by irradiation with radiation. Crosslinked ethylene-tetrafluoroethylene copolymer and crosslinked polyvinylidene fluoride do not melt even under high-temperature conditions, for example, at 320°C or higher. The third crosslinked body constituting the second semiconductive layer 4 of embodiment 1 is a crosslinked body of a third composition containing ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and therefore the third crosslinked body also does not melt under high-temperature conditions. Therefore, the second semiconductive layer 4 can maintain its strength even under high-temperature conditions.

[0063] The elastic modulus of the second semiconductive layer 4 at 330°C may be 0.1 MPa or more. This allows the second semiconductive layer 4 to have high strength without melting even under high-temperature conditions such as 330°C. The lower limit of the elastic modulus of the second semiconductive layer 4 at 330°C may be 0.5 MPa or more, 1.0 MPa or more, 1.5 MPa or more, or 1.8 MPa or more. The upper limit of the elastic modulus of the second semiconductive layer 4 at 330°C is not particularly limited, but may be, for example, 10 MPa or less or 5 MPa or less from the viewpoint of handleability at high temperatures. The elastic modulus of the second semiconductive layer 4 at 330°C may be 0.1 MPa or more and 10 MPa or less, or 0.5 MPa or more and 10 MPa or less.

[0064] The type and content of the conductive filler contained in the second semiconductive layer 4 can be the same as those of the conductive filler contained in the first semiconductive layer 2. The type and content of the conductive filler contained in the second semiconductive layer 4 may be the same as or different from those of the conductive filler contained in the first semiconductive layer 2.

[0065] In the cable 10 of the first embodiment, the third composition may contain other components in addition to the ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and conductive filler. Examples of the other components include a cross-linking aid, an antioxidant, a lubricant, a colorant, a processing aid, and a flame retardant. The types and contents of the other components may be similar to those of the other components contained in the first composition. The types and contents of the other components contained in the third composition may be the same as or different from those of the other components contained in the first composition.

[0066] In cable 10 of embodiment 1, the first composition and the third composition may be the same composition or different compositions. In cable 10 of embodiment 1, the first crosslinked body and the third crosslinked body may be the same crosslinked body or different crosslinked bodies.

[0067] The volume resistivity of the second semiconductive layer 4 at room temperature and at 100°C can be in the same range as the volume resistivity of the first semiconductive layer 2 at room temperature and at 100°C, respectively. The volume resistivity of the second semiconductive layer 4 at room temperature and at 100°C may be the same as or different from the volume resistivity of the first semiconductive layer 2 at room temperature and at 100°C, respectively.

[0068] The average thickness of the second semiconductive layer 4 can be adjusted as appropriate depending on the application of the cable 10. The lower limit of the average thickness of the second semiconductive layer 4 may be 0.10 mm or more, or 0.15 mm or more, from the viewpoint of ease of extrusion molding during production of the cable 10. The upper limit of the average thickness of the second semiconductive layer 4 may be 0.50 mm or less, or 0.40 mm or less, from the viewpoint of flexibility and ease of handling of the cable. The average thickness of the second semiconductive layer 4 may be 0.10 mm or more and 0.50 mm or less, or 0.10 mm or more and 0.40 mm or less.

[0069] As described above, in the cable 10 of the first embodiment, the first semiconductive layer 2, the insulating layer 3, and the second semiconductive layer 4 all do not melt and maintain their strength even under high-temperature conditions. Therefore, the cable 10 of the first embodiment can have a long life even when used under high-temperature conditions.

[0070] <Shielding Layer> In the cable 10 of the first embodiment, the shielding layer 5 is provided so as to cover the outer periphery of the second semiconducting layer 4. The presence of the shielding layer 5 allows the cable 10 to obtain an excellent noise shielding effect. To enhance the shielding effect, the shielding layer 5 may be grounded.

[0071] A metal tape, a braided shield, or the like can be used for the shield layer 5. A metal material having high conductivity and high mechanical strength is preferred for the material of the shield layer 5. Examples of such metal materials include copper, copper alloys, aluminum, aluminum alloys, nickel, silver, mild steel, steel, and stainless steel.

[0072] A braided shield is formed by braiding a braided wire made of metal wires. There are no particular restrictions on the metal braid, and any conventionally known metal braid can be used. The metal braid can be a tubular braid made by braiding a wire made of a single metal material. A multilayer structure in which the wire is further coated with another metal can also be used.

[0073] <Jacket> In the cable 10 of the first embodiment, the jacket 6 is provided to cover the outer periphery of the shielding layer 5. The jacket 6 mechanically protects the conductor 1, the first semiconducting layer 2, the insulating layer 3, the second semiconducting layer 4, and the shielding layer 5, and can impart functions such as flame retardancy and oil resistance to the cable 10.

[0074] The jacket 6 may be made of a fourth crosslinked body of a fourth composition including ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride.

[0075] Ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride can be crosslinked by irradiation with radiation. Crosslinked ethylene-tetrafluoroethylene copolymer and crosslinked polyvinylidene fluoride do not melt even under high-temperature conditions, for example, at 300°C or higher. The fourth crosslinked body constituting the jacket 6 of embodiment 1 is a crosslinked body of a fourth composition containing ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and therefore the fourth crosslinked body also does not melt under high-temperature conditions. Therefore, the jacket 6 can maintain its strength even under high-temperature conditions.

[0076] The elastic modulus of the jacket 6 at 330°C may be 0.1 MPa or more. This allows the jacket 6 to have high strength without melting even under high-temperature conditions such as 330°C. The lower limit of the elastic modulus of the jacket 6 at 330°C may be 0.5 MPa or more, 1.0 MPa or more, 1.5 MPa or more, or 1.8 MPa or more. The upper limit of the elastic modulus of the jacket 6 at 330°C is not particularly limited, but may be, for example, 10 MPa or less or 5 MPa or less from the viewpoint of handleability at high temperatures. The elastic modulus of the jacket 6 at 330°C may be 0.1 MPa or more and 10 MPa or less, or 0.5 MPa or more and 10 MPa or less.

[0077] In the cable 10 of the first embodiment, the fourth composition may contain other components in addition to the ethylene-tetrafluoroethylene copolymer and polyvinylidene fluoride. The types and contents of the other components may be similar to those of the other components contained in the second composition. The types and contents of the other components contained in the fourth composition may be the same as or different from those of the other components contained in the second composition.

[0078] The average thickness of the jacket 6 can be adjusted as appropriate depending on the application of the cable 10. From the viewpoint of ease of extrusion molding during production of the cable 10, the lower limit of the average thickness of the jacket 6 may be 0.10 mm or more, 0.15 mm or more, or 0.2 mm or more. From the viewpoint of flexibility and ease of handling of the cable, the upper limit of the average thickness of the jacket 6 may be 3.0 mm or less, 2.0 mm or less, or 1.5 mm or less. The average thickness of the jacket 6 may be 0.10 mm or more and 3.00 mm or less, 0.10 mm or more and 2.00 mm or less, 0.15 mm or more and 2.0 mm or less, or 0.2 mm or more and 1.5 mm or less.

[0079] <Manufacturing Method> A manufacturing method for the cable 10 of the first embodiment will be described.

[0080] A conductor 1 is prepared.

[0081] A first composition is obtained by mixing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, a conductive filler, and optionally other components such as a cross-linking aid. A second composition is obtained by mixing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and optionally other components such as a cross-linking aid. A third composition is obtained by mixing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, a conductive filler, and optionally other components such as a cross-linking aid.

[0082] A three-layer co-extruder is prepared. The three-layer co-extruder includes extruder A, extruder B, and extruder C. A first composition, which is a raw material for the first semiconductive layer, is charged into extruder A. A second composition, which is a raw material for insulating layer 3, is charged into extruder B. A third composition, which is a raw material for second semiconductive layer 4, is charged into extruder C.

[0083] Next, the extrudates from extruder A, extruder B, and extruder C are guided to a common head, and the first composition, second composition, and third composition are simultaneously extruded from the inside to the outside around the outer periphery of conductor 1, thereby obtaining a first coated conductor in which conductor 1 is coated with a layer made of the first composition, a layer made of the second composition, and a layer made of the third composition.

[0084] Next, the first coated conductor is irradiated with an electron beam to crosslink the first composition, the second composition, and the third composition, thereby obtaining a cable having, from the inside to the outside, a first semiconductive layer made of the first crosslinked body, an insulating layer 3 made of the second crosslinked body, and a second semiconductive layer 4 made of the third crosslinked body on the outer periphery of the conductor 1.

[0085] When the cable 10 includes a shielding layer 5 and a jacket 6, the following steps are further performed: The shielding layer 5 can be formed by providing, for example, a metal braid around the outer periphery of the second semiconductive layer 4.

[0086] Next, a fourth composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, which is a raw material of the jacket 6, is charged into the extruder, and the fourth composition is extruded onto the outer periphery of the shielding layer 5 to coat the shielding layer 5 with a layer made of the fourth composition, thereby obtaining a first coated conductor.

[0087] Next, the first coated conductor is irradiated with radiation to crosslink the fourth composition, thereby obtaining cable 10 of embodiment 1, in which a first semiconductive layer made of the first crosslinked body, an insulating layer 3 made of the second crosslinked body, a second semiconductive layer 4 made of the third crosslinked body, a shielding layer 5, and a jacket 6 made of the fourth crosslinked body are provided in the above order around the outer periphery of conductor 1 from the inside to the outside.

[0088] The radiation may be an electron beam, α-ray, γ-ray, or the like. The energy amount of the radiation is an amount that can crosslink the first composition, the second composition, the third composition, and the fourth composition. The energy amount of the radiation may be, for example, an amount that can allow the first coated conductor to receive an energy amount of 10 kGy or more and 480 kGy or less.

[0089] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0090] [Cable Fabrication] The conductor for each sample was prepared by twisting together 19 strands of a stranded wire made up of seven nickel-plated copper wires each having an outer diameter of 0.35 mm.

[0091] A first composition, a second composition, and a third composition were prepared for each sample. The content of each raw material in the first composition, the second composition, and the third composition is as shown in Tables 1 and 2. In Tables 1 and 2, "ETFE" refers to an ethylene-tetrafluoroethylene copolymer. In Tables 1 and 2, "conductive filler" refers to carbon black. In Tables 1 and 2, "other components" refers to antioxidants and colorants. For example, the first composition of Sample 1 contains 80 mass % ETFE, 5 mass % other components, and 15 mass % conductive filler.

[0092] A three-layer co-extruder equipped with extruder A, extruder B, and extruder C was prepared. The first composition was fed into extruder A, the second composition was fed into extruder B, and the third composition was fed into extruder C. Next, the extrudates from extruder A, extruder B, and extruder C were guided to a common head, and the first composition, the second composition, and the third composition were simultaneously extruded from the inside to the outside around the conductor, thereby coating the conductor with a layer made of the first composition, a layer made of the second composition, and a layer made of the third composition, to obtain a first coated conductor. The thicknesses of the layer made of the first composition, the layer made of the second composition, and the layer made of the third composition are as shown in Tables 1 and 2.

[0093] Next, for samples marked "Yes" in the "Electron beam irradiation" column of Table 2, the first coated conductor was irradiated with an electron beam to crosslink the first composition, the second composition, and the third composition, thereby obtaining a cable in which a first semiconductive layer made of the first crosslinked body, an insulating layer made of the second crosslinked body, and a second semiconductive layer made of the third crosslinked body were provided in this order around the outer periphery of the conductor from the inside to the outside. The energy amount of the electron beam was set to an amount that would allow the first coated conductor to receive an energy amount of 180 kGy. For samples marked "No" in the "Electron beam irradiation" column of Table 2, electron beam irradiation was not performed.

[0094]

[0095]

[0096] [Evaluation] <Elastic modulus of first semiconductive layer, insulating layer, and second semiconductive layer at 330°C> The elastic modulus of the first semiconductive layer, insulating layer, and second semiconductive layer of each sample cable at 330°C is shown in the "Elastic modulus 330°C" column of Tables 3 and 4. The specific measurement method is as described in embodiment 1. For samples with the results listed as "Not measurable" in the "Elastic modulus 330°C" column of Tables 3 and 4, this indicates that the test piece melted before the measurement temperature reached 330°C, making measurement impossible.

[0097] <Volume Resistivity of First Semiconductive Layer and Second Semiconductive Layer at Room Temperature and 100°C> The volume resistivity of the first semiconductive layer and the second semiconductive layer of each sample cable at room temperature and 100°C is shown in the "Volume Resistivity Room Temperature" and "Volume Resistivity 100°C" columns in Tables 3 and 4. The specific measurement method is as described in embodiment 1.

[0098] <Thickness of First Semiconductive Layer, Insulating Layer, and Second Semiconductive Layer> The thicknesses of the first semiconductive layer, insulating layer, and second semiconductive layer of each sample cable are shown in the "Thickness" column in Tables 3 and 4. The specific measurement method is as described in Embodiment 1. In all samples, the thicknesses of the first semiconductive layer, insulating layer, and second semiconductive layer in the cable are the same as the thicknesses of the layer made of the first composition, the layer made of the second composition, and the layer made of the third composition in the first coated conductor, respectively.

[0099] <Gap Length> The gap length was measured for each sample cable. The specific measurement method is as follows. A measurement sample was prepared by further covering each sample cable with a shielding layer. For each sample, multiple measurement samples with different circumferential gap lengths between the cable and the shielding layer were prepared. For each sample, an AC voltage was applied between the cable conductor and the shielding layer, starting with the measurement sample with the smallest circumferential gap length. A slight change in current was measured, and when a discharge of 100 pC or more was detected, it was determined that a partial discharge had occurred. The maximum circumferential gap length at which a partial discharge occurred at a voltage of 4000 V or more was defined as the gap length. The results are shown in Table 4.

[0100]

[0101] [Discussion] The cables of Samples 1 to 16 correspond to Examples, and the cables of Samples 1-1 to 1-16 correspond to Comparative Examples.

[0102] In the cables of samples 1 to 16, the first semiconductive layer, insulating layer, and second semiconductive layer had an elastic modulus of 0.1 MPa or more at 330°C, and it was confirmed that the first semiconductive layer, insulating layer, and second semiconductive layer did not melt even when used under high-temperature conditions.

[0103] In the cables of Samples 1-1 to 1-16, the first semiconductive layer, the insulating layer, and the second semiconductive layer melt at temperatures lower than 330°C, and it was confirmed that the first semiconductive layer, the insulating layer, and the second semiconductive layer melt when used under high-temperature conditions.

[0104] The cables of Samples 1, 4, 6, 9, 10, 11, and 12 have the same configuration except for the thickness of the insulation layer. Comparing these samples, it was confirmed that the thicker the insulation layer, the longer the gap length.

[0105] The cables of Samples 3, 5, 7, and 8 have the same configuration except for the thickness of the insulation layer. Comparing these samples, it was confirmed that the thicker the insulation layer, the longer the gap length.

[0106] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0107] 1 Conductor, 2 First semiconductive layer, 3 Insulating layer, 4 Second semiconductive layer, 5 Shield layer, 6 Jacket, 10 Cable, G Total circumferential gap, L Gap length

Claims

1. A conductor; a first semiconductive layer covering the outer periphery of the conductor; an insulating layer covering the outer periphery of the first semiconductive layer; a second semiconductive layer covering the outer periphery of the insulating layer; the first semiconductive layer is made of a first crosslinked body of a first composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride and a conductive filler; the insulating layer is made of a second crosslinked body of a second composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride; The cable, wherein the second semiconductive layer is made of a third crosslinked body of a third composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride, and a conductive filler.

2. 2. The cable according to claim 1, wherein the average thickness of the insulating layer is 0.10 mm or more and 2.0 mm or less.

3. 3. The cable of claim 1 or claim 2, wherein the average thickness of the insulation layer is greater than 0.70 mm.

4. 3. The cable according to claim 1, wherein the first semiconductive layer has an average thickness of 0.10 mm or more and 0.5 mm or less.

5. 3. The cable according to claim 1, wherein the second semiconductive layer has an average thickness of 0.10 mm or more and 0.5 mm or less.

6. the cable further includes a shielding layer covering an outer periphery of the second semiconductive layer, and a jacket covering an outer periphery of the shielding layer, 3. The cable according to claim 1, wherein the jacket is made of a fourth crosslinked product of a fourth composition containing an ethylene-tetrafluoroethylene copolymer or polyvinylidene fluoride.

7. 3. The cable according to claim 1, wherein the first semiconductive layer has an elastic modulus of 0.1 MPa or more at 330°C.

8. 3. The cable according to claim 1, wherein the insulating layer has a modulus of elasticity at 330°C of 0.1 MPa or more.

9. 3. The cable according to claim 1, wherein the second semiconductive layer has an elastic modulus of 0.1 MPa or more at 330°C.