Power transmission cable and method for manufacturing the same

Abstract

To provide a power transmission cable and a method for manufacturing a power transmission cable which suppress a gap between a sheath layer and an insulation layer, improve tensile strength inside the sheath layer, and have high tensile strength of the sheath layer.SOLUTION: A power transmission cable 1 has (a) a core part having a conductor 2 and an insulation layer 4 formed on the outer periphery of the conductor 2, and (b) a sheath layer 9 formed on the outer periphery of the core part, where the insulation layer 4 is thicker than the sheath layer 9, a coefficient of linear expansion of the insulation layer is larger than a coefficient of linear expansion of the sheath layer 9, tensile strength of the sheath layer 9 is larger than 12.0 MPa, and tensile strength inside the sheath layer 9 is equal to or more than 10 kgf.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power transmission cable, a method for manufacturing the power transmission cable, and more particularly to a power transmission cable using a non-halogen flame-retardant resin composition and a method for manufacturing the same.

Background Art

[0002] Cables used in railway vehicles and the like are required to have properties such as flame retardancy and low smoke generation to reduce damage in the event of a fire. To obtain high flame retardancy, materials in which halogen-based flame retardants such as chlorine-based and bromine-based are added to polyolefins are used. However, substances containing a large amount of these halogen-based flame retardants generate a large amount of toxic and harmful gases during combustion, and generate highly toxic dioxins depending on the incineration conditions. For this reason, cables using non-halogen materials (halogen-free materials) that do not contain halogen substances as coating materials have become widespread from the viewpoints of safety during a fire and reduction of environmental load.

[0003] For example, Patent Document 1 discloses a power transmission cable that uses, as a sheath layer, a base polymer containing an ethylene-vinyl acetate copolymer having a vinyl acetate content of 50% by weight or more, and a non-halogen flame-retardant resin composition containing a total of 100 parts by mass or more and 180 parts by mass or less of a metal hydrate and silica with respect to 100 parts by mass of the base polymer, in order to achieve high flame retardancy and low smoke generation.

[0004] Further, Patent Document 2 discloses a power transmission cable including an internal semiconductive layer formed on the outer periphery of a conductor, an insulating layer formed on the outer periphery of the internal semiconductive layer, an external semiconductive layer formed on the outer periphery of the insulating layer, a semiconductive tape layer formed by winding a semiconductive tape around the outer periphery of the external semiconductive layer, a shielding layer formed by winding a wire around the outer periphery of the semiconductive tape layer, and a sheath layer formed on the outer peripheral side of the shielding layer. In this power transmission cable, the wire constituting the shielding layer suppresses the depression of the external semiconductive layer and the insulating layer.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2016-100140 Patent Document 2 Japanese Patent Application Laid-Open No. 2016-100148 Summary of the Invention Problems to be Solved by the Invention

[0006] A power transmission cable formed by coating a core portion having a conductor and an insulating layer formed on the outer periphery of the conductor with a non-halogen flame-retardant resin composition serving as a sheath layer is formed by crosslinking the resin material by heating after the coating of the non-halogen flame-retardant resin composition.

[0007] Here, when heating the non-halogen flame-retardant resin composition serving as the sheath layer, the internal insulating layer and the sheath layer each thermally expand and contract in the cooling process. At this time, an excessive gap may occur between the insulating layer and the sheath layer due to the difference in the shrinkage rates of the insulating layer and the sheath layer. This excessive gap becomes a factor that inhibits the connection reliability at the connection portion between the power transmission cable and other components. For example, due to the occurrence of an excessive gap between the insulating layer and the sheath layer, any one of the members between the insulating layer and the sheath layer moves in the longitudinal direction of the power transmission cable, resulting in sheath displacement. When such sheath displacement occurs, the connection reliability between the power transmission cable and other components may be inhibited.

[0008] In addition, when the physical strength such as the tensile strength of the sheath layer is high, the risk of damage to the power transmission cable and the like is reduced, and the product life can be extended and improved.

[0009] Therefore, an object of the present invention is to provide a power transmission cable and a method for manufacturing the power transmission cable, which suppress the gap between the sheath layer and the insulating layer, improve the withdrawal strength inside the sheath layer, and have a high tensile strength of the sheath layer. Means for Solving the Problems

[0010] The power transmission cable of the present invention has: (a) a core portion having a conductor and an insulating layer formed on the outer periphery of the conductor; and (b) a sheath layer formed on the outer periphery of the core portion. The insulating layer is thicker than the sheath layer, the linear expansion coefficient of the insulating layer is larger than that of the sheath layer, the tensile strength of the sheath layer is greater than 12.0 MPa, and the withdrawal strength inside the sheath layer is 10 kgf or more.

[0011] The manufacturing method of the power transmission cable of the present invention has: (a) a step of coating a core portion having a conductor and an insulating layer formed on the outer periphery of the conductor with a non-halogen flame-retardant resin composition to be a sheath layer; (b) a step of crosslinking by heating the sheath layer. The insulating layer is thicker than the sheath layer, the linear expansion coefficient of the insulating layer is larger than that of the sheath layer, the tensile strength of the sheath layer is greater than 12.0 MPa, and the withdrawal strength inside the sheath layer is 10 kgf or more.

Advantages of the Invention

[0012] According to the power transmission cable and the manufacturing method of the power transmission cable of one aspect of the present invention, the gap between the sheath layer and the insulating layer can be suppressed, and the withdrawal strength inside the sheath layer can be improved. Furthermore, the tensile strength of the sheath layer can be improved, and both characteristics of the withdrawal strength and the tensile strength can be made good.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0014] (Embodiment) (Configuration of Power Transmission Cable) The power transmission cable of the present embodiment will be described below. FIG. 1 is a cross-sectional view showing the configuration of the power transmission cable.

[0015] The power transmission cable 1 shown in FIG. 1 includes a conductor 2, an internal semiconductive layer 3 formed on the outer periphery of the conductor 2, an insulating layer 4 formed on the outer periphery of the internal semiconductive layer 3, an external semiconductive layer 5 formed on the outer periphery of the insulating layer 4, a semiconductive tape layer 6 formed on the outer periphery of the external semiconductive layer 5, a shielding layer 7 formed on the outer periphery of the semiconductive tape layer 6, a press tape layer 8 formed on the outer periphery of the shielding layer 7, and a sheath layer 9 formed on the outer periphery of the press tape layer 8.

[0016] The power transmission cable of the present embodiment is suitable for a special high-voltage power transmission cable that transmits a high voltage of, for example, 7000V or more. The outer diameter (diameter) of the power transmission cable is, for example, 30 mm or more and 60 mm or less. Such a power transmission cable is arranged along a roof portion or a wall portion so as to connect, for example, a pantograph arranged on the roof of a railway vehicle and a multi-voltage device arranged under the floor.

[0017] The conductor 2 is formed by twisting a plurality of strands. As the strands, for example, a wire, a copper alloy wire, etc. can be used. Further, the strands may be subjected to a metal plating such as tin plating. The conductor 2 transmits a high voltage of, for example, 7000V or more as described above. A separator tape can also be wound on the conductor 2.

[0018] The internal semiconductive layer 3 and the external semiconductor layer 5 are provided to mitigate electric field concentration, and are made of, for example, a material obtained by dispersing conductive powder such as carbon in a rubber such as ethylene propylene rubber or butyl rubber to render conductivity. If a minute gap occurs between the conductor 2 and the insulating layer 4, or between the insulating layer 4 and the shielding layer 7, electric field concentration is likely to occur. Therefore, each of the internal semiconductive layer 3 and the external semiconductive layer 5 is preferably formed so as to be in close contact with the insulating layer 4. By sandwiching the insulating layer 4 with the internal semiconductive layer 3 and the external semiconductive layer 5, electric field concentration between the conductor 2 and the insulating layer 4, or electric field concentration between the insulating layer 4 and the shielding layer 7 can be mitigated.

[0019] The insulating layer 4 is made of, for example, a material such as ethylene propylene rubber, vinyl chloride, crosslinked polyethylene, silicone rubber, or a fluorine-based material. Further, the insulating layer 4 may contain clay.

[0020] Since high insulating properties are required for the insulating layer 4, the thickness of the insulating layer 4 is greater than the thicknesses of each of the internal semiconductive layer 3, the external semiconductive layer 5, the shielding layer 7, and the sheath layer 9. The thickness of the insulating layer 4 is, for example, about 8 mm or more and 16 mm or less.

[0021] Here, the laminate from the conductor 2 to the external semiconductive layer 5 from the inside may be referred to as a resin core part C.

[0022] A semiconductive tape 6, a shielding layer 7, and a pressing tape layer 8 are provided on the outer periphery of the resin core part C.

[0023] The semiconductive tape layer 6 on the outer periphery of the external semiconductive layer 5 (resin core part C) is, for example, formed by spirally winding a semiconductive tape along the cable axis direction. As the semiconductive tape, for example, a base fabric or non-woven fabric woven with warp and weft made of nylon, rayon, PET, etc., impregnated with a rubber such as ethylene propylene rubber or butyl rubber in which conductive powder such as carbon is dispersed can be used. The thickness of the semiconductive tape is, for example, 0.1 mm or more and 0.4 mm or less, and the width of the semiconductive tape is, for example, 30 mm or more and 70 mm or less. The semiconductive tape may be wound in an overlapping manner such that, for example, 1 / 4 or more and 1 / 2 or less of the tape width overlaps.

[0024] The shielding layer 7 is formed by spirally winding a wire along the cable axis direction, for example, on the outer periphery of the semiconductive tape layer 6. The wire is made of a conductive material such as tinned soft copper, and for example, a wire having a diameter of 0.4 mm or more and 0.6 mm or less can be used. This shielding layer 7 is connected to the ground during use.

[0025] The presser tape layer 8 is formed by spirally winding a presser tape along the cable axis direction, for example, on the outer periphery of the shielding layer 7. As the presser tape, a tape made of plastic or rayon can be used. Also, a polyester non-woven fabric can be used. The thickness of the presser tape is, for example, 0.03 mm or more and 0.2 mm or less, and the width of the presser tape is, for example, 50 mm or more and 90 mm or less.

[0026] Note that the laminate from the conductor 2 to the presser tape layer 8 may be referred to as a core part with a shielding layer in some cases.

[0027] A sheath layer 9 is provided on the outer periphery of the presser tape layer 8 (core part with a shielding layer). The sheath layer 9 is formed by extruding a non-halogen flame-retardant resin composition on the outer periphery of the presser tape layer 8, for example. This sheath layer 9 is crosslinked. The sheath layer 9 is a protective layer that protects the core part with a shielding layer (the laminate from the conductor 2 to the presser tape layer 8). The thickness of the sheath layer 9 is, for example, 2.5 mm or more and 3.0 mm or less.

[0028] The non-halogen flame-retardant resin composition constituting the sheath layer 9 contains a base polymer (resin component), a flame retardant, a crosslinking agent (silane coupling agent and peroxide), and other additives.

[0029] As the base polymer (resin component), for example, ethylene vinyl acetate copolymer (EVA) can be used. Among them, it is preferable to use EVA having a vinyl acetate content (VA amount) of 40% by mass or more. When the vinyl acetate content is 40% by mass or more, the resulting char layer becomes strong, and good flame retardancy and low smoke generation can be obtained.

[0030] As the base polymer (resin component), the above EVA may be used in combination with maleic acid-modified polyolefin, styrene-butadiene rubber, etc.

[0031] As the flame retardant, metal hydroxides can be used. As the metal hydroxides, magnesium hydroxide, aluminum hydroxide, etc. can be used. The addition amount (content) of the metal hydroxide is preferably 100 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the base polymer. When it is 100 parts by mass or more and 150 parts by mass or less, good heat aging characteristics and low smoke generation can be obtained. From the viewpoint of achieving both high flame retardancy and low smoke generation, the addition amount (content) of the metal hydroxide is more preferably 100 parts by mass or more and 125 parts by mass or less with respect to 100 parts by mass of the base polymer.

[0032] As the metal hydroxides, the aforementioned aluminum hydroxide, magnesium hydroxide, etc. are used. By using either magnesium hydroxide or aluminum hydroxide, high flame retardancy can be achieved. Also, as aluminum hydroxide and magnesium hydroxide, those having a surface coupled with a fatty acid or a silane compound are preferably used. By using such coupled ones, good tensile strength and elongation at break can be obtained in the tensile test.

[0033] Further, as the metal hydroxide, aluminum hydroxide and magnesium hydroxide described above may be used in combination. In this case, it is preferable to adjust the mass ratio in the range of magnesium hydroxide:aluminum hydroxide = 40:60 to 60:40. This is because a stepwise dehydration method is more effective for suppressing the temperature rise of the cable after the start of combustion and solidifying the char in the non-halogen flame-retardant resin composition. The dehydration start temperatures of aluminum hydroxide and magnesium hydroxide are around 210°C and around 280°C, respectively. By setting the above mass ratio, stepwise dehydration can proceed effectively, suppressing the temperature rise of the cable after the start of combustion and promoting the solidification of the char.

[0034] As the crosslinking agent, a peroxide and a silane coupling agent can be used. Here, the silane coupling agent is grafted onto the base polymer by a peroxide and then used for crosslinking the base polymer by silane crosslinking. As the peroxide (a compound having a -O-O- structural part), tert-butyl peroxy (2-ethylhexyl) carbonate, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxyisopropyl carbonate, tert-amyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di-tert-butyl peroxide, di-tert-amyl peroxide, 1,1-di(tert-amylperoxy)cyclohexene, etc. can be used.

[0035] As the silane coupling agent (R-Si-X3, where R is an organic group, X is a functional group, and X may be different functional groups including H), those having vinyl, epoxy, styryl, methacryl, amino, isocyanurate, mercapto, or acid anhydride in the functional group (X) can be used. Note that X may be different functional groups including H. Specifically, as the silane coupling agent, vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, epoxy silane compounds such as β-(3,4 epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, styryl silane compounds such as p-styryltrimethoxysilane, methacryl silane compounds such as 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, amino silane compounds such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, β-(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, isocyanurate silane compounds such as tris-(trimethoxysilylpropyl)isocyanurate, mercapto silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, acid anhydride silane compounds such as 3-trimethoxysilylpropyl succinic anhydride, etc. can be used. Also, two or more of these silane compounds can be used in combination.

[0036] The addition amount (content) of the peroxide is preferably 4 parts by mass or more with respect to 100 parts by mass of the base polymer, and the addition amount (content) of the silane coupling agent is preferably 2 parts by mass or more with respect to 100 parts by mass of the base polymer. By setting the addition amounts of the peroxide, which is a crosslinking agent, and the silane coupling agent within the above ranges, the mechanical strength of the sheath layer can be maintained even when low-temperature crosslinking is performed. Further, the upper limit of the addition amount (content) of the peroxide is 10 parts by mass. By setting the addition amount of the peroxide to 10 parts by mass or less, processing (particularly extrusion processing) can be performed in a state with good handleability without unnecessary progress of crosslinking. Also, by adding 2 parts by mass or more of the silane coupling agent with respect to 100 parts by mass of the base polymer, a decrease in tensile strength can be suppressed. Further, the upper limit of the addition amount (content) of the silane coupling agent is 6 parts by mass. By setting the addition amount of the silane coupling agent to 6 parts by mass or less, a decrease in elongation at break can be suppressed. Note that the addition amount (content) of the silane coupling agent means the addition amount when adding the silane coupling agent itself, and does not include the surface treatment amount of the silane coupling agent surface-treated on the surface of the metal hydroxide.

[0037] As other additives, crosslinking aids, stabilizers, antioxidants, colorants, lubricants, etc. can be used.

[0038] (Manufacturing Method of Power Transmission Cable) Hereinafter, the manufacturing method of the power transmission cable of the present embodiment will be described. FIGS. 2 and 3 are schematic diagrams showing the manufacturing process of the power transmission cable.

[0039] Form (prepare) the resin core part C of the power transmission cable. First, prepare the conductor 2, and extrude the inner semiconductive material which is the raw material of the inner semiconductive layer 3, the insulating material which is the raw material of the insulating layer 4, and the outer semiconductive material which is the raw material of the outer semiconductive layer 5 onto the outer periphery of the conductor 2. For example, extrude the inner semiconductive material (3M) from an extruder (200a) onto the outer periphery of the conductor 2, and extrude the insulating material and the outer semiconductive material from other extruders (not shown), respectively. In this way, each of the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 can be extruded all at once so as to sequentially surround the periphery of the conductor, for example.

[0040] Also, as a modification, each of the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 may be extruded sequentially. Thereby, the resin core part C composed of the conductor 2, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 can be formed. Next, crosslink the rubber contained in the layers constituting the resin core part C (first crosslinking).

[0041] Such a resin core part C can be formed, for example, using the apparatus shown in FIG. 2. The single-screw extruder 200a shown in FIG. 2 includes a screw 220 disposed within a cylinder and a material inlet 221. For example, the material 3M of the inner semiconductive layer 3 is introduced from the material inlet (hopper) 221. Also, another single-screw extruder (not shown) also includes a screw disposed within a cylinder and a material inlet, and the material of the insulating layer 4 is introduced from the material inlet (hopper). Further, another single-screw extruder (not shown) also includes a screw disposed within a cylinder and a material inlet, and the material of the outer semiconductive layer 5 is introduced from the material inlet (hopper). In this way, the conductor 2 passes through the extrusion head 230, and the materials of the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 are extruded in order from the inside onto its outer periphery and crosslinked while passing through the crosslinking tube (steam tube) 240 (crosshead extrusion). Using such a continuous crosslinking apparatus, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 of the resin core part C are heated and crosslinked (crosslinked by passing through pressurized steam). For example, crosslinking is performed for 30 minutes or more and 60 minutes or less in a steam atmosphere of 150°C or higher and 180°C or lower. In this way, the resin core part C can be formed.

[0042] In the above, the materials of the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 are extruded all at once onto the outer periphery of the conductor 2, and further, the three layers of the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 extruded in order onto the outer periphery of the conductor 2 are crosslinked all at once. However, extrusion may be performed layer by layer onto the outer periphery of the conductor 2, and the three layers may be crosslinked all at once, or extrusion and crosslinking may be performed layer by layer onto the outer periphery of the conductor 2.

[0043] Next, the crosslinked resin core part C is cooled. For example, the resin core part C (conductor 2, inner semiconductive layer 3, insulating layer 4, and outer semiconductive layer 5) fed out in FIG. 2 is continuously supplied and immersed in water in a cooling tank (not shown) for cooling (water cooling method).

[0044] Next, a semiconductive tape is spirally wound around the outer periphery of the external semiconductive layer 5 along the cable axis direction to form a semiconductive tape layer 6. The semiconductive tape may be wound in a manner such that, for example, 1 / 4 or more and 1 / 2 or less of the tape width overlaps.

[0045] Next, a wire is spirally wound around the outer periphery of the semiconductive tape layer 6 along the cable axis direction to form a shielding layer 7. The diameter of the wire used here is, for example, about 0.6 to 0.8 mm. Next, a holding tape is wound spirally along the cable axis direction around the outer periphery of the shielding layer 7 to form a holding tape layer 8. In this way, a core portion with a shielding layer (a laminate from the conductor 2 to the holding tape layer 8) can be formed.

[0046] Next, a sheath layer 9 is formed by extruding the above-described non-halogen flame-retardant resin composition onto the outer periphery of the holding tape layer 8 (core portion with a shielding layer). Thereafter, crosslinking (second crosslinking) of the sheath layer 9 is performed.

[0047] For example, a material 51 which is pellets of the above-described non-halogen flame-retardant resin composition is supplied from the hopper 101 of the extruder 100 shown in Fig. 3(a). Note that a part of the components of the above-described non-halogen flame-retardant resin composition (for example, a crosslinking agent) may be added from an inlet (not shown) in the middle of the extruder 100. Then, the above-described non-halogen flame-retardant resin composition is coated on the outer periphery of the core portion with a shielding layer (a laminate from the conductor 2 to the holding tape layer 8, see Fig. 3(b)) supplied from the upstream side to form a sheath layer 9.

[0048] In this embodiment, at this time, the addition of the silane coupling agent can be carried out, for example, by the integral blending method. The integral blending method is a method of adding the silane coupling agent without using it for the pretreatment of other materials. At this time, the silane coupling agent and other materials may be added simultaneously, or the addition timing of the silane coupling agent and other materials may be shifted. For example, it is preferable to add the silane coupling agent after adding the resin component serving as the base polymer, and it is more preferable to add it immediately after adding the base polymer. At this time, it is not carried out immediately after adding an inorganic filler such as a flame retardant.

[0049] By adding in this way, the silane coupling agent is well dispersed and mixed in the base polymer. Therefore, the sheath layer 9 formed of the non-halogen flame-retardant resin composition mixed in this way can have improved tensile strength.

[0050] Next, the power transmission cable (the laminate from the conductor 2 to the sheath layer 9) sent out from the extruder 100 is supplied to a lead coating layer forming device 110 disposed on the downstream side of the extruder 100. While moving the power transmission cable (the laminate from the conductor 2 to the sheath layer 9, see Fig. 3(c)), a lead coating layer 10 is continuously formed on the outer periphery of the power transmission cable (the sheath layer 9) (see Fig. 3(d)), and it is wound around a winding drum 120. By providing the lead coating layer 10, in the crosslinking process described later, since steam does not contact the sheath layer 9, it is possible to suppress the surface of the sheath layer 9 from being deformed by the pressure of the steam. Note that the material of the coating layer (coating material) is not limited to lead.

[0051] Next, a crosslinking treatment is performed on the power transmission cable (the laminate from the conductor 2 to the lead coating layer 10, see Fig. 3(d)) wound around the winding drum 120. Specifically, the winding drum 120 around which the power transmission cable (the laminate from the conductor 2 to the lead coating layer 10) is wound is disposed in a crosslinking facility (autoclave crosslinking facility) 130, and a crosslinking treatment (heat treatment) of the sheath layer 9 is performed. For example, it is left standing for 72 hours (h) in a steam atmosphere of 90°C.

[0052] Among the heating conditions (crosslinking temperature, crosslinking time), the crosslinking temperature is preferably 90°C or higher and less than 105°C. This is because when it is less than 105°C, the formation of a gap between the sheath and the core portion with the shielding layer can be suppressed, and when it is 90°C or higher, the crosslinking speed will not become extremely slow. Furthermore, it is more preferable that the crosslinking temperature is 90°C or higher and 100°C or lower. Also, as the crosslinking time, it is preferably 5 hours or longer and 270 hours or shorter, and more preferably 24 hours or longer and 72 hours or shorter.

[0053] Next, the crosslinked sheath layer 9 is cooled. For example, the power transmission cable (the laminate from the conductor 2 to the lead sheath layer 10) wound around the take-up drum 120 is taken out from the crosslinking equipment (autoclave crosslinking equipment) 130 and cooled by standing at room temperature (for example, 25°C), the lead sheath layer 10 is peeled off, and the power transmission cable is manufactured.

[0054] Thus, in this embodiment, since the silane coupling agent and the peroxide are added as crosslinking agents to the sheath layer within the above ranges, while maintaining the mechanical strength, crosslinking at a relatively low temperature is allowed, and the gap between the insulating layer and the sheath layer that may occur due to the difference in shrinkage rates of the insulating layer and the sheath layer can be suppressed. Thereby, the decrease in connection reliability due to the displacement of the core portion (insulating layer) can be suppressed.

[0055] The effects of the present embodiment will be described in detail below. When applying kettle crosslinking, which has been commonly used in the past, as a method of crosslinking the sheath layer 9, a gap may occur between the insulating layer 4 and the sheath layer 9, more specifically, between the external semiconductive layer 5 and the shielding layer 7. This gap is considered to be caused by the difference in the shrinkage rates of the respective layers (especially the insulating layer 4 and the sheath layer 9) formed in sequence so as to cover the periphery of the conductor 2. In the case of kettle crosslinking, the already crosslinked internal semiconductive layer 3, insulating layer 4, and external semiconductive layer 5 other than the sheath layer 9 to be crosslinked are also exposed to high temperature for a long time (for example, exposed to a high temperature of 145°C for 2 hours). As a result, the internal semiconductive layer 3, insulating layer 4, and external semiconductive layer 5 each expand due to heat and then contract in the subsequent cooling process. At this time, since the shrinkage rates of the respective layers are different, a gap is generated according to the difference in the shrinkage rates.

[0056] For example, when ethylene propylene rubber is used for the insulating layer 4 and EVA is used for the sheath layer 9, the "insulating layer linear expansion coefficient / sheath layer linear expansion coefficient", which is the ratio of the linear expansion coefficients, is 1.3 or more.

[0057] Even when the linear expansion coefficient of the insulating layer 4 is larger than that of the sheath layer 9, if the thickness of the insulating layer 4 is thin, excessive gaps will not occur. However, in the case of a power transmission cable for extra-high voltage, in order to improve the insulation characteristics, the thickness of the insulating layer 4 tends to be relatively thick. The thickness of the insulating layer 4 is thicker than the thickness of the sheath layer 9, and the thickness of the insulating layer 4 is preferably 3 times or more the thickness of the sheath layer 9. Thus, when the thickness of the insulating layer 4 is thick, the amount of deformation of the insulating layer 4 due to the difference in the linear expansion coefficients becomes large, so that gaps are likely to occur.

[0058] When a gap occurs between the layers constituting the power transmission cable in this way, the characteristics of the power transmission cable deteriorate due to the gap. In particular, when the conductor 2 is disposed at the center of the sheath layer 9, and the inner semiconductive layer 3, the insulating layer 4, the outer semiconductive layer 5, and the sheath layer 9 are disposed on the outer periphery of the conductor 2, sheath displacement is likely to occur between the layers with a gap therebetween. When this sheath displacement occurs, the connection reliability may be inhibited at the connection portion between the power transmission cable and other components. Herein, the "sheath displacement" refers to a phenomenon in which the sheath moves between the layers with a gap therebetween when the conductor 2 is disposed at the center of the sheath layer 9, and the inner semiconductive layer 3, the insulating layer 4, the outer semiconductive layer 5, and the sheath layer 9 are disposed on the outer periphery of the conductor 2. For example, it refers to a phenomenon in which the sheath layer moves in the longitudinal direction of the power transmission cable due to the occurrence of an excessive gap between the press tape layer 8 and the shielding layer 7, or between the shielding layer 7 and the semiconductive tape layer 6, or between the shielded core portion (a laminate from the conductor 2 to the press tape layer 8, see Fig. 3(b)) and the sheath layer 9.

[0059] The gap between the layers constituting the power transmission cable as described above is caused by the thermal expansion and contraction during the heating (crosslinking) of the sheath layer 9. Therefore, by lowering the heating temperature, the generation of the gap can be suppressed. However, in the crosslinking at a low temperature, the crosslinking degree of the sheath layer may decrease, and the mechanical strength may decrease.

[0060] Therefore, in the present embodiment, in order to increase the mechanical strength even in the crosslinking at a low temperature, the type and addition amount of the crosslinking agent of the non-halogen flame-retardant resin composition constituting the sheath layer are adjusted, and further, by setting the addition order of each component to a predetermined one, the generation of the gap occurring in the power transmission cable is successfully suppressed, and the mechanical strength can be improved. This will be described more specifically based on examples below.

[0061] [Examples] Hereinafter, the non-halogen flame-retardant resin composition used for the power transmission cable of the present embodiment will be described more specifically based on examples.

[0062] (Material name) <Base polymer> EVA1: "Evaflex EV45LX" manufactured by Mitsui DuPont Polychemical Co., Ltd. (VA content: 46% by mass) EVA2: "Evaflex V9000" manufactured by Mitsui DuPont Polychemical Co., Ltd. (VA content: 41% by mass) <Crosslinking agent> Silane coupling agent: "KBM-503" (3-methacryloxypropyltrimethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. Peroxide: "Trigonox 22-70E" (1,1-bis(tert-butylperoxy)cyclohexane) manufactured by Chemische Fabrik Stockhausen GmbH

[0063] <Crosslinking aid> Triallyl isocyanate: "TAIC" manufactured by Nippon Kasei Co., Ltd. <Stabilizer> Zinc oxide: "Zinc white No. 3" manufactured by Sakai Chemical Co., Ltd. <Antioxidant> 2,2,4-Trimethyl-1,2-dihydroquinoline polymer: "No Crack 224" manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. <Flame retardant> Magnesium hydroxide: "Kisuma 5L" manufactured by Kyowa Chemical Industry Co., Ltd. Aluminum hydroxide: "BF-013STV" (silane 1.0μm) manufactured by Nippon Light Metal Co., Ltd.

[0064] <Colorant> Carbon: "FT Carbon" manufactured by Asahi Carbon Co., Ltd. <Lubricant> Lithium hydroxystearate: "LS-6" manufactured by Nitto Kasei Kogyo Co., Ltd. Zinc stearate: "EZ-101" manufactured by Nitto Kasei Kogyo Co., Ltd.

[0065] (Examples 1 to 3) A non-halogen flame-retardant resin composition was prepared with the component formulation shown in Table 1 and kneaded. After that, the non-halogen flame-retardant resin composition was coated (fully extruded) on the outer periphery of the laminate from the conductor 2 to the press tape layer 8 (see Fig. 3(b)) to form a sheath layer 9. After that, it was covered with a lead coating layer 10 (see Fig. 3(d)), wound around a winding drum 120, and the winding drum 120 was placed in a cross-linking facility (autoclave cross-linking facility) 130 to perform a cross-linking treatment (heat treatment) on the sheath layer 9. The non-halogen flame-retardant resin composition used for the sheath layer 9 and the treatment conditions (cross-linking temperature, cross-linking time) are as shown in Table 1. Finally, the sheath layer 9 was cooled to obtain a power transmission cable.

[0066] In the extrusion of the non-halogen flame-retardant resin composition, first, a flame retardant (metal hydroxide) was charged into a kneader, and then additives other than the silane coupling agent, the base polymer, and the silane coupling agent were charged in this order. After all the materials were charged, they were kneaded sufficiently and extruded.

[0067] As the conductor 2, a stranded wire (outer diameter 12.53 mm) obtained by collectively stranding 19 strands of 27 soft copper wires plated with tin was used. A separator tape was placed between the conductor 2 and the internal semiconductive layer 3, and a separator tape made of nylon was wound around the outer circumference of the conductor 2 in a 1 / 2 lap. The internal semiconductive layer 3 had a thickness of 1.000 mm and was formed by solid extrusion of a conductive ethylene propylene rubber containing carbon. The outer diameter after forming the internal semiconductive layer 3 was 14.97 mm. The insulating layer 4 had a thickness of 15.165 mm and was formed by solid extrusion of an ethylene propylene rubber containing clay. The outer diameter after forming the insulating layer 4 was 45.30 mm. The semiconductive tape layer 6 had a thickness of 0.500 mm and a width of 40 mm, and a nylon tape containing carbon was wound around it in a 1 / 2 lap. The outer diameter after forming the semiconductive tape layer 6 was 46.30 mm. As the shielding layer 7, a helical shield obtained by helically winding 30 soft copper wires plated with tin at a pitch of 136 mm was used. The thickness of the shielding layer 7 was 0.800 mm, and the outer diameter after forming the shielding layer 7 was 47.90 mm. The pressing tape layer 8 had a thickness of 0.220 mm and a width of 90 mm, and a pressing tape made of nylon was wound around it in a 1 / 2 lap. The outer diameter after forming the insulating layer 4 was 48.34 mm. The sheath layer 9 had a thickness of 2.5 mm, and the outer diameter after forming the sheath layer 9 was 53.34 mm.

[0068] (Comparative Examples 1 to 7) As shown in Table 1 for the component formulation and processing conditions (crosslinking temperature, crosslinking time), power transmission cables were obtained in the same manner as in the examples.

[0069] In the comparative examples, when extruding the non-halogen flame-retardant resin composition, a flame retardant (metal hydroxide) was first charged into the kneader, and then a silane coupling agent, additives other than the silane coupling agent, and a base polymer were charged in that order. After all the materials were charged, they were thoroughly kneaded and extruded.

[0070] Note that the blending amounts of the respective components shown in Table 1 are shown in parts by mass based on a total of 100 parts by mass of the base polymer.

[0071]

Table 1

[0072] (Evaluation) (Tensile test) For the obtained power transmission cable, the core part with a shielding layer (the laminate from conductor 2 to the press tape layer 8, see Fig. 3(b)) was extracted, and the sheath layer 9 was punched out with a dumbbell to obtain a sample (test piece). The test piece was of dumbbell shape No. 6, and the distance between the gauge marks was 20 mm.

[0073] A tensile test was performed on this sample. The tensile test was carried out based on the IEC60811-1-1 standard. Specifically, the sample was pulled at a speed of 200 mm / min using a tensile testing machine, and the tensile strength, elongation at break, and 100% modulus were measured. Note that the tensile strength is the stress corresponding to the maximum force applied during the test. The elongation at break is the value obtained by expressing the permanent elongation after break as a percentage of the original length. The 100% modulus is the stress at the point when the test piece has elongated by 100%.

[0074] (Pull-out test) The obtained power transmission cable was cut into a 20-cm length as a sample (test piece). In the pull-out test, the core portion with a shielding layer (a laminate from conductor 2 to the press tape layer 8, see Fig. 3(b)) was pushed in from the cut surface of the power transmission cable, and the force (kgf) until the core portion with the shielding layer moved (shifted, peeled off) from the sheath layer 9 was measured. Fig. 4 is a cross-sectional view showing the state of the pull-out test. Specifically, as shown in Fig. 4, the test was conducted using a scale 300 and a convex-shaped jig 310. The convex-shaped jig 310 has a convex portion 310a that contacts the core portion with the shielding layer of the power transmission cable. The diameter Rc of the convex portion 310a is equal to or greater than the diameter Ra of the resin core portion (a laminate from conductor 2 to the outer semiconductor layer 5) and equal to or less than the diameter Rb of the core portion with the shielding layer (a laminate from conductor 2 to the press tape layer 8). Here, a cylindrical member with a diameter of 3 cm was used. The convex-shaped jig 310 was placed on the scale 300, the core portion with the shielding layer of the power transmission cable was aligned with the convex portion 310a, the power transmission cable was pushed into the convex portion 310a, and the maximum value (kgf) of the scale 300 until the core portion with the shielding layer moved relative to the sheath layer 9 was measured. When the measured value (pull-out strength) was greater than 10 kgf, it was determined that sheath shift could not occur and the test was passed (〇); when it was less than 10 kgf, it was determined that sheath shift could occur and the test was failed (×).

[0075] Thus, when an opposite-direction force (load) is applied between the sheath layer and the portion inside the sheath layer in the power transmission cable, the relative displacement between the sheath layer and the portion inside the sheath layer is called sheath shift, and the force (load) at this time is defined as the "pull-out strength" and is measured by the test (pull-out test) using the above-mentioned scale and convex-shaped jig.

[0076] (Results) As shown in Table 1, the sheath layers of Examples 1 to 3 have obtained good values in both the tensile test and the 100% modulus test. Also, the measured value of the pull-out test is 10 kgf or more, and it is considered that the gap between the core part with a shielding layer and the sheath layer is suppressed. When observing the comparative examples, the location where the gap occurs is not limited to between the sheath layer 9 and the presser tape layer 8, and gaps may also occur between the presser tape layer 8 and the shielding layer 7, or between the shielding layer 7 and the semiconductive tape layer 6.

[0077] On the other hand, for the sheath layers of Comparative Examples 1 to 4, the addition of the silane coupling agent is immediately after the addition of the flame retardant. Although the measured value of the pull-out test is 10 kgf or more and sheath displacement can be suppressed, the tensile strength is 12.0 MPa or less, and the required characteristics are not achieved.

[0078] Also, for the sheath layers of Comparative Examples 5 to 6, although the measured value of the pull-out test is 10 kgf or more and sheath displacement can be suppressed, the crosslinking temperature is low and the tensile strength is not sufficient.

[0079] In Comparative Example 7, although the tensile strength was sufficient, due to the high crosslinking temperature, the measured value of the pull-out test decreased to less than 10 kgf.

[0080] On the other hand, according to the present embodiment, by adjusting the addition amount and addition timing of the crosslinking agent as described above, even in the case of low-temperature crosslinking, while maintaining the mechanical properties of the power transmission cable, the gap between the core part with a shielding layer and the sheath layer can be suppressed.

[0081] Note that Fig. 5 shows a graph plotting the relationship between the crosslinking temperature on the horizontal axis and the tensile strength and pull-out strength obtained by the examples and comparative examples. From this Fig. 5, it was found that in the low-temperature crosslinking region, by adding the silane coupling agent after the addition of the base polymer, the tensile strength of the sheath layer can be improved, and the pull-out strength can also be made good. Note that when the crosslinking temperature is the same regardless of the addition timing of the silane coupling agent, the pull-out strength is the same value.

[0082] (Application Example) In the above embodiment, a power transmission cable is configured by a plurality of laminated bodies shown in FIG. 1. However, it may also be a power transmission cable in which an insulated wire having a conductor 2 and an insulating layer 4 provided around the conductor 2 as a core portion and a sheath layer 9 is provided around the core portion. Further, a plurality of insulated wires may be used as the core portion. As the sheath layer of the power transmission cable having such a configuration, the above non-halogen flame-retardant resin composition may be used, and in the same manner as in the above embodiment, a sheath layer may be formed around the core portion.

[0083] Also, in the above embodiment, a power transmission cable is configured by a laminated body composed of a plurality of layers shown in FIG. 1. However, for example, in the resin core portion C, the conductor 2 and the insulating layer 4 may be essential components, and the internal semiconductive layer 3 or the external semiconductive layer 5 may be omitted. Further, the semiconductive tape 6, the shielding layer 7, or the pressing tape layer 8 on the outer periphery of the resin core portion C may be omitted. In such a case, a tensile test, a 100% modulus, and a pull-out test may be performed with the portion inside the sheath layer as the core portion.

[0084] The present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the gist thereof.

Explanation of Reference Numerals

[0085] 1 Power transmission cable 2 Conductor 3 Internal semiconductive layer 3M Material 4 Insulating layer 5 External semiconductive layer 6 Semiconductive tape layer 7 Shielding layer 8 Pressing tape layer 9 Sheath layer 10 Lead coating layer 51 Material 100 Extruder 101 Hopper 110 Lead coating layer forming apparatus 120 Take-up drum 130 Crosslinking equipment (autoclave crosslinking equipment) 200a Extruder 220 Screw 221 Material inlet (hopper) 230 Extrusion head 240 Steam pipe (crosslinking pipe) 300 Scale 310 Convex jig 310a Convex part C Resin core part

Claims

1. (a)A core part having a conductor and an insulating layer formed on the outer periphery of the conductor; (b)A sheath layer formed on the outer periphery of the core part, wherein the insulating layer is thicker than the sheath layer, the linear expansion coefficient of the insulating layer is larger than that of the sheath layer, the tensile strength of the sheath layer is greater than 12.0 MPa, and the pulling strength inside the sheath layer is 10 kgf or more. A power transmission cable.

2. In the power transmission cable according to Claim 1, the sheath layer is made of a non-halogen flame-retardant resin composition containing a base polymer, a silane coupling agent, a peroxide, and a flame retardant containing a metal hydroxide, the content of the silane coupling agent is 2 parts by mass or more with respect to 100 parts by mass of the base polymer, and the content of the peroxide is 4 parts by mass or more with respect to 100 parts by mass of the base polymer. A power transmission cable.

3. In the power transmission cable according to Claim 1, the thickness of the insulating layer is 3 times or more the thickness of the sheath layer, and the ratio of the linear expansion coefficient of the insulating layer to that of the sheath layer, i.e., insulating layer linear expansion coefficient / sheath layer linear expansion coefficient, is 1.3 or more. A power transmission cable.

4. In the power transmission cable according to Claim 1, a shielding layer is provided between the sheath layer and the insulating layer. A power transmission cable.

5. In the power transmission cable according to Claim 4, a pressing tape layer is provided between the sheath layer and the shielding layer. A power transmission cable.

6. In the power transmission cable according to Claim 2, the base polymer includes an ethylene vinyl acetate copolymer, and contains 100 parts by mass to 150 parts by mass of a metal hydroxide with respect to 100 parts by mass of the base polymer. A power transmission cable.

7. In the power transmission cable according to Claim 1, the core part is composed of a resin core part including a conductor, an internal semiconductive layer, an insulating layer, and an external semiconductive layer. A power transmission cable.

8. (a)A step of coating a non-halogen flame-retardant resin composition serving as a sheath layer on a core part having a conductor and an insulating layer formed on the outer periphery of the conductor; (b)A step of crosslinking the sheath layer by heating, wherein the insulating layer is thicker than the sheath layer, the linear expansion coefficient of the insulating layer is larger than that of the sheath layer, the tensile strength of the sheath layer is greater than 12.0 MPa, and the pulling strength inside the sheath layer is 10 kgf or more. A method for manufacturing a power transmission cable.

9. ​ In the method for manufacturing a power transmission cable according to claim 8, the sheath layer is made of a non-halogen flame-retardant resin composition containing a base polymer, a silane coupling agent, a peroxide, and a flame retardant containing a metal hydroxide, the content of the silane coupling agent is 2 parts by mass or more with respect to 100 parts by mass of the base polymer, the content of the peroxide is 4 parts by mass or more with respect to 100 parts by mass of the base polymer, the content of the metal hydroxide is 100 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the base polymer, A method for manufacturing a power transmission cable.

10. In the method for manufacturing a power transmission cable according to claim 9, the non-halogen resin composition is obtained by adding and kneading the silane coupling agent by an integral blending method. A method for manufacturing a power transmission cable.

11. In the method for manufacturing a power transmission cable according to claim 8, the step (b) is heating at a temperature of 90°C or higher and lower than 105°C. A method for manufacturing a power transmission cable.

12. In the method for manufacturing a power transmission cable according to claim 8, the step (b) is heating in a state where the sheath layer is covered with a covering material. A method for manufacturing a power transmission cable.

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