Power transmission cable and method of manufacturing a power transmission cable

Abstract

The present invention provides a power cable and a manufacturing method thereof, which suppresses a gap between a sheath layer and an insulation layer and improves a tensile strength on an inner side than the sheath layer. The power cable has: (a) a core having a conductor (2) and an insulation layer (4) on an outer periphery thereof; and (b) a sheath layer (9) formed on an outer periphery of the core, and has the following configuration. The sheath layer is formed of a resin composition containing a base polymer, a silane coupling agent, and a peroxide, the content of the silane coupling agent is 2 parts by mass or more, and the content of the peroxide is 4 parts by mass or more, with respect to 100 parts by mass of the base polymer, and the tensile strength on the inner side than the sheath layer is 10 kgf or more. By adding the silane coupling agent and the peroxide as cross-linking agents within the range, cross-linking can be performed at a lower temperature, a gap between the insulation layer and the sheath layer can be suppressed, and the tensile strength can be ensured even in a case where the insulation layer is thick and the linear expansion coefficient is large and the influence of thermal expansion and contraction is large.

Description

Technical Field

[0001] This invention relates to power transmission cables and methods for manufacturing power transmission cables, and more particularly to power transmission cables using halogen-free flame-retardant resin compositions and methods for manufacturing the same. Background Technology

[0002] To reduce the damage to cables used in railway vehicles and other applications in fires, properties such as flame retardancy and low smoke emission are required. To achieve high flame retardancy, materials containing halogenated flame retardants such as chlorine- or bromine-based agents are used in polyolefins. However, substances containing large amounts of these halogenated flame retardants produce large quantities of toxic and harmful gases during combustion, and depending on the combustion conditions, can sometimes produce highly toxic secondary gases. Therefore, from the perspective of fire safety and reducing environmental impact, cables using halogen-free materials (materials without halogens) in their coating are becoming increasingly popular.

[0003] For example, Patent Document 1 discloses a power transmission cable that, in order to achieve high flame retardancy and low smoke emission, uses a halogen-free flame-retardant resin composition as the sheath layer, which contains a matrix polymer of ethylene-vinyl acetate copolymer with a vinyl acetate content of 50% or more and a total of 100 to 180 parts by weight of metal hydrate and silica relative to 100 parts by weight of the matrix polymer.

[0004] Furthermore, Patent Document 2 discloses a power transmission cable comprising: an inner semiconductive layer formed on the outer periphery of a conductor; an insulating layer formed on the outer periphery of the inner semiconductive layer; an outer semiconductive layer formed on the outer periphery of the insulating layer; a semiconductive strip layer formed by winding a semiconductive strip around the outer periphery of the outer semiconductive layer; a shielding layer formed by winding metal wires around the outer periphery of the semiconductive strip layer; and a sheath layer formed on the outer periphery of the shielding layer. In this power transmission cable, the metal wires constituting the shielding layer suppress depressions in the outer semiconductive layer and the insulating layer.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-100140

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-100148 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] A power transmission cable formed by coating a core having a conductor and an insulating layer formed on the outer periphery of the conductor with a halogen-free flame-retardant resin composition as a sheath layer is formed by heating the resin material after coating with the halogen-free flame-retardant resin composition to crosslink the resin material.

[0011] When the halogen-free flame-retardant resin composition that forms the sheath is heated, the inner insulation layer and sheath layer thermally expand and contract during the cooling process. This difference in shrinkage rates between the insulation and sheath layers causes an excessively large gap between them. This excessive gap can hinder connection reliability at the junctions of the power transmission cable with other components. For example, due to the excessive gap between the core (insulation layer) and sheath layer, either component between the core (insulation layer) and sheath layer may shift along the length of the power transmission cable, resulting in sheath misalignment. Such sheath misalignment hinders the reliable connection of the power transmission cable with other components.

[0012] Here, the object of the present invention is to provide a power transmission cable and a method for manufacturing the power transmission cable that can suppress the formation of excessive gaps between the sheath layer and the insulation layer, improve the pull-out strength inside the sheath layer, and improve the reliability of the connection between the power transmission cable and other components.

[0013] Methods for solving problems

[0014] [1] One aspect of the present invention provides a power transmission cable comprising: (a) a core 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; the insulating layer is thicker than the sheath layer, the coefficient of linear expansion of the insulating layer is greater than the coefficient of linear expansion of the sheath layer, the sheath layer is formed of a halogen-free flame-retardant resin composition containing a matrix polymer, a silane coupling agent and a peroxide, wherein the content of the silane coupling agent is 2 parts by mass or more relative to 100 parts by mass of the matrix polymer, the content of the peroxide is 4 parts by mass or more relative to 100 parts by mass of the matrix polymer, and the pull-out strength on the inner side of the sheath layer is 10 kgf or more.

[0015] [2] In [1], the tensile strength of the sheath layer is 10 MPa or more, and the oil-resistant tensile strength retention rate is 60% or more.

[0016] [3] In [1], the thickness of the insulation layer is more than 3 times the thickness of the sheath layer, and the ratio of the linear expansion coefficients of the sheath layer to the insulation layer, i.e., the linear expansion coefficient of the insulation layer / the linear expansion coefficient of the sheath layer, is more than 1.3.

[0017] [4] In [1], there is a shielding layer between the sheath layer and the insulation layer.

[0018] [5] In [4], there is a pressing band layer between the sheath layer and the shielding layer.

[0019] [6] In [1], the matrix polymer contains an ethylene-vinyl acetate copolymer and contains 100 to 150 parts by mass of a metal hydroxide relative to 100 parts by mass of the matrix polymer.

[0020] [7] In [1], the core is formed of a resin core having a conductor, an inner semiconducting layer, an insulating layer and an outer semiconducting layer.

[0021] [8] A method for manufacturing a power transmission cable according to one aspect of the present invention includes: (a) a step of coating a core having a conductor and an insulation layer formed on the outer periphery of the conductor with a halogen-free flame-retardant resin composition as a sheath layer, and (b) a step of crosslinking the sheath layer by heating; wherein the insulation layer is thicker than the sheath layer, the coefficient of linear expansion of the insulation layer is greater than the coefficient of linear expansion of the sheath layer, the sheath layer is formed from a halogen-free flame-retardant resin composition containing a matrix polymer, a silane coupling agent and a peroxide, wherein the content of the silane coupling agent is 2 parts by mass or more relative to 100 parts by mass of the matrix polymer, and the content of the peroxide is 4 parts by mass or more relative to 100 parts by mass of the matrix polymer.

[0022] [9] In [8], in the above-mentioned step (b), heating is performed while the sheath layer is covered by the covering material.

[0023] Invention Effects

[0024] According to one aspect of the present invention, the power transmission cable can suppress the gap between the sheath layer and the insulation layer (core) and improve the pull-out strength on the inner side of the sheath layer. Attached Figure Description

[0025] Figure 1 It is a cross-sectional view showing the structure of a power transmission cable.

[0026] Figure 2 It is a schematic diagram showing the manufacturing process of power transmission cables.

[0027] Figure 3 It is a schematic diagram showing the manufacturing process of power transmission cables.

[0028] Figure 4 It is a cross-sectional view showing what a pull-out test looks like.

[0029] Symbol Explanation

[0030] 1: Power transmission cable, 2: Conductor, 3: Inner semi-conductive layer (3M material), 4: Insulation layer, 5: Outer semi-conductive layer, 6: Semi-conductive 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 forming device, 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 clamp, 310a: Convex part, C: Resin core. Detailed Implementation

[0031] (Implementation Method)

[0032] (The composition of power transmission cables)

[0033] The power transmission cable of this embodiment will be described below. Figure 1 It is a cross-sectional view showing the structure of a power transmission cable.

[0034] Figure 1 The power transmission cable 1 shown has a conductor 2, an inner semiconducting layer 3 formed on the outer periphery of the conductor 2, an insulation layer 4 formed on the outer periphery of the inner semiconducting layer 3, an outer semiconducting layer 5 formed on the outer periphery of the insulation layer 4, a semiconducting strip layer 6 formed on the outer periphery of the outer semiconducting layer 5, a shielding layer 7 formed on the outer periphery of the semiconducting strip layer 6, a pressing strip layer 8 formed on the outer periphery of the shielding layer 7, and a sheath layer 9 formed on the outer periphery of the pressing strip layer 8.

[0035] The power transmission cable in this embodiment is, for example, an ultra-high voltage power transmission cable for transmitting high voltages of 7000V or higher. The outer diameter (diameter) of the power transmission cable is, for example, 30mm or more and 60mm or less. Such a power transmission cable is, for example, arranged along the roof and sidewalls of a vehicle to connect the pantograph installed on the roof of the railway vehicle and the multi-voltage switch (multi-voltage switch) installed under the floor.

[0036] Conductor 2 is formed by stranding multiple bare wires. For example, conductor wire, copper alloy wire, etc., can be used as the bare wires. Alternatively, a metal plating such as tin plating may be applied to the bare wires. Conductor 2 carries, for example, a high voltage of 7000V or higher as described above. A separator tape may also be wound onto conductor 2.

[0037] The inner semiconducting layer 3 and the outer semiconductor layer 5 are provided to mitigate electric field concentration. For example, they are formed from a material that imparts conductivity by dispersing conductive powder such as carbon in rubbers such as ethylene propylene rubber and butyl rubber. When there are fine gaps between the conductor 2 and the insulating layer 4, or between the insulating layer 4 and the shielding layer 7, electric field concentration is prone to occur. Therefore, the inner semiconducting layer 3 and the outer semiconducting layer 5 are preferably formed to be tightly fitted to the insulating layer 4. By sandwiching the insulating layer 4 between the inner semiconducting layer 3 and the outer semiconducting layer 5, the electric field concentration between the conductor 2 and the insulating layer 4, or between the insulating layer 4 and the shielding layer 7, can be mitigated.

[0038] The insulating layer 4 may be formed of, for example, ethylene propylene rubber, vinyl chloride, cross-linked polyethylene, silicone rubber, fluorine-based materials, etc. Alternatively, the insulating layer 4 may also contain clay.

[0039] Because high insulation properties are required for the insulation layer 4, its thickness is greater than that of the inner semiconductive layer 3, the outer semiconductive layer 5, the shielding layer 7, and the sheath layer 9. The thickness of the insulation layer 4 is, for example, between 8 mm and 16 mm.

[0040] Here, the laminate from the inside out, consisting of conductor 2, inner semiconducting layer 3, insulating layer 4, and extending to outer semiconducting layer 5, is sometimes referred to as resin core C.

[0041] A semi-conductive strip 6, a shielding layer 7, and a pressing strip layer 8 are provided on the outer periphery of the resin core C.

[0042] The semiconductive tape layer 6 on the outer periphery of the outer semiconductive layer 5 (resin core C) is, for example, obtained by winding the semiconductive tape into a spiral shape along the cable axis. As the semiconductive tape, for example, a material formed by impregnating a base fabric or non-woven fabric woven from warp and weft yarns of nylon, rayon, PET, etc., with conductive powder such as carbon dispersed in rubber such as ethylene propylene rubber or butyl rubber can be used. The thickness of the semiconductive tape is, for example, 0.1 mm to 0.4 mm and the width of the semiconductive tape is, for example, 30 mm to 70 mm. The semiconductive tapes can be stacked and wound in an overlapping manner, for example, 1 / 4 to 1 / 2 of the width.

[0043] The shielding layer 7 is obtained by winding a metal wire into a spiral shape around the outer periphery of the semi-conductive strip layer 6, for example, along the direction of the cable shaft. The metal wire is formed of a conductive material such as tin-plated soft copper, and a wire with a diameter of, for example, 0.4 mm to 0.6 mm can be used. This shielding layer 7 is grounded during use.

[0044] The compression tape layer 8 is obtained by spirally winding, for example, compression tape around the outer periphery of the shielding layer 7 along the cable axis. The compression tape can be made of plastic or rayon. Alternatively, polyester nonwoven fabric can also be used. The thickness of the compression tape is, for example, 0.03 mm to 0.2 mm, and the width of the compression tape is, for example, 50 mm to 90 mm.

[0045] It should be noted that the laminate from conductor 2 to pressing layer 8 up to this point is sometimes referred to as the core with shielding layer.

[0046] A sheath layer 9 is provided on the outer periphery of the press-fit layer 8 (the core with the shielding layer). The sheath layer 9 is obtained, for example, by extruding a halogen-free flame-retardant resin composition onto the outer periphery of the press-fit layer 8. The sheath layer 9 is cross-linked. The sheath layer 9 is a protective layer that protects the core with the shielding layer (the laminate from the conductor 2 to the press-fit layer 8). The thickness of the sheath layer 9 is, for example, 2.5 mm or more and 3.0 mm or less.

[0047] The halogen-free flame-retardant resin composition constituting the sheath layer 9 contains a matrix polymer (resin component), flame retardant, crosslinking agent (silane coupling agent and peroxide) and other additives.

[0048] Ethylene-vinyl acetate copolymer (EVA) can be used as the matrix polymer (resin component). Preferably, EVA with a vinyl acetate content of 40% by mass or more is used. When the vinyl acetate content is 40% by mass or more, the resulting combustion residue becomes robust, resulting in good flame retardancy and low smoke production.

[0049] As a matrix polymer (resin component), it can also be used in combination with the above-mentioned EVA and maleic acid modified polyolefins, styrene butadiene rubber, etc.

[0050] Metal hydroxides can be used as flame retardants. Magnesium hydroxide and aluminum hydroxide are suitable metal hydroxides. The amount (content) of the metal hydroxide added relative to 100 parts by weight of the base polymer is preferably 100 parts by weight to 150 parts by weight. A content of 100 parts by weight to 150 parts by weight results in good thermal aging properties and low smoke emission. From the viewpoint of balancing high flame retardancy and low smoke emission, the amount (content) of the metal hydroxide added relative to 100 parts by weight of the base polymer is preferably 100 parts by weight to 125 parts by weight.

[0051] As metal hydroxides, aluminum hydroxide, magnesium hydroxide, etc., are used. High flame retardancy can be achieved by using either magnesium hydroxide or aluminum hydroxide. Furthermore, aluminum hydroxide or magnesium hydroxide with surface coupling via fatty acids or silane compounds is preferred. Using such coupled materials results in good tensile strength and elongation at break in tensile tests.

[0052] Alternatively, aluminum hydroxide and magnesium hydroxide can be used together as metal hydroxides. In this case, it is preferable to adjust the ratio to be within the range of 40:60 to 60:40 by mass. This is because a phased dehydration method is more effective in suppressing the temperature rise of the cable after the start of combustion and in promoting the solidification of the slag. The dehydration start temperatures of aluminum hydroxide and magnesium hydroxide are approximately 210°C and 280°C, respectively. By setting the above mass ratio, phased dehydration can be effectively promoted, the temperature rise of the cable after the start of combustion can be suppressed, and the solidification of the slag can be promoted.

[0053] Peroxides and silane coupling agents are used as crosslinking agents. As peroxides (compounds having the -OO- structural part), tert-butyl peroxycarbonate (2-ethylhexyl) ester, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxycarbonate isopropyl ester, tert-pentyl peroxycarbonate isopropyl ester, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di-tert-butyl peroxide, di-tert-pentyl peroxide, 1,1-di(tert-pentylperoxy)cyclohexene, etc., can be used.

[0054] As a silane coupling agent (R-Si-X3, R: organic group, X: functional group; it should be noted that X can also be different functional groups including H), silane coupling agents with functional groups (X) having vinyl, epoxy, styrene, methacrylate, amino, isocyanurate, mercapto, or anhydride groups can be used. It should be noted that X can also be different functional groups including H. Specifically, as silane coupling agents, vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltri(β-methoxyethoxy)silane; epoxy silane compounds such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, and γ-epoxypropoxypropylmethyldiethoxysilane; styrene silane compounds such as p-styrenetrimethoxysilane; and 3-methacryloyloxypropyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldimethoxysilane, and 3-methacryloyl... Methacrylate silane compounds such as oxypropylmethyldiethoxysilane; aminosilane compounds such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; isocyanurate silane compounds such as tris(trimethoxysilylpropyl)isocyanurate; mercaptosilane compounds such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; and acid anhydride silanes such as 3-trimethoxysilylpropylsuccinic anhydride. Additionally, two or more of these silane compounds may be used in combination.

[0055] The amount (content) of peroxide added is preferably 4 parts by mass or more relative to 100 parts by mass of the matrix polymer, and the amount (content) of silane coupling agent added is preferably 2 parts by mass or more relative to 100 parts by mass of the matrix polymer. By keeping the amounts of peroxide and silane coupling agent added as crosslinking agents within the above ranges, the mechanical strength of the sheath layer can be maintained even when low-temperature crosslinking is performed. In particular, by adding 4 parts by mass or more of peroxide relative to 100 parts by mass of the matrix polymer, the decrease in oil resistance can be suppressed. In addition, the upper limit of the amount (content) of peroxide added is 10 parts by mass. By keeping the amount of peroxide added to 10 parts by mass or less, unnecessary crosslinking can be avoided, and processing (especially extrusion processing) can be performed in a state of good operability. In addition, by adding 2 parts by mass or more of silane coupling agent relative to 100 parts by mass of the matrix polymer, the decrease in tensile strength can be suppressed. In addition, the upper limit of the amount (content) of silane coupling agent added is 6 parts by mass. By keeping the amount of silane coupling agent added to 6 parts by mass or less, the decrease in elongation at break can be suppressed. It should be noted that the amount (content) of silane coupling agent added refers to the amount added when the silane coupling agent itself is added, excluding the amount of silane coupling agent surface treatment that has been applied to the surface of the metal hydroxide.

[0056] Other additives that can be used include crosslinking aids, stabilizers, antioxidants, colorants, and lubricants.

[0057] (Manufacturing method of power transmission cables)

[0058] The manufacturing method of the power transmission cable according to this embodiment will be described below. Figure 2 and Figure 3 It is a schematic diagram showing the manufacturing process of power transmission cables.

[0059] Forming (preparing) the resin core C of the power transmission cable. First, prepare the conductor 2, and extrude an inner semiconducting material as the raw material for the inner semiconducting layer 3, an insulating material as the raw material for the insulating layer 4, and an outer semiconducting material as the raw material for the outer semiconducting layer 5 around the outer periphery of the conductor 2. For example, the inner semiconducting material (3M) is extruded around the outer periphery of the conductor 2 by an extruder (200a), and the insulating material and the outer semiconducting material are extruded separately by another extruder (not shown). In this way, the inner semiconducting layer 3, the insulating layer 4, and the outer semiconducting layer 5 can be extruded together, for example, sequentially around the conductor.

[0060] Alternatively, as a variation, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 can be extruded sequentially. This allows the formation of a resin core C composed of the conductor 2, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5.

[0061] Next, the rubber contained in the layer constituting the resin core C is cross-linked (first cross-linking).

[0062] Such a resin core C, for example, can be used Figure 2 The apparatus shown is used to form it. Figure 2 The single-spindle extruder 200a shown has a screw 220 and a material inlet 221 disposed within a barrel. For example, material 3M of the inner semi-conductive layer 3 is fed into the material inlet (hopper) 221. Another single-spindle extruder (not shown) also has a screw and a material inlet disposed within a barrel, and material of the insulating layer 4 is fed into the material inlet (hopper). Furthermore, yet another single-spindle extruder (not shown) also has a screw and a material inlet disposed within a barrel, and material of the outer semi-conductive layer 5 is fed into the material inlet (hopper). Thus, the conductor 2 passes through the extrusion head 230, and material of the inner semi-conductive layer 3, insulating layer 4, and outer semi-conductive layer 5 is extruded sequentially from the inside out around its outer periphery, and cross-linking (cross-head extrusion) occurs simultaneously as it passes through the cross-linking tube (steam tube) 240. By using this continuous cross-linking device, the inner semi-conductive layer 3, insulating layer 4, and outer semi-conductive layer 5 of the resin core C are heated and cross-linked (cross-linked by passing them through pressurized steam). For example, crosslinking is performed for 30 to 60 minutes in a water vapor atmosphere at a temperature between 150°C and 180°C. This allows the formation of the resin core C.

[0063] It should be noted that, in the above, the materials of the inner semiconductive layer 3, the insulating layer 4 and the outer semiconductive layer 5 are extruded together on the outer periphery of the conductor 2. Furthermore, the three layers of the inner semiconductive layer 3, the insulating layer 4 and the outer semiconductive layer 5, which are extruded sequentially on the outer periphery of the conductor 2, are cross-linked together. Alternatively, one layer can be extruded on the outer periphery of the conductor 2 each time and the three layers can be cross-linked together.

[0064] Next, the cross-linked resin core C is cooled. For example, ... Figure 2 The resin core C (conductor 2, inner semiconductive layer 3, insulating layer 4 and outer semiconductive layer 5) delivered from the middle is continuously supplied to water in a cooling tank (not shown) for cooling (water cooling method).

[0065] Next, a semiconductive strip is spirally wound around the outer periphery of the outer semiconductive layer 5 along the cable axis direction to form a semiconductive strip layer 6. The semiconductive strips can be spirally wound in an overlapping manner, for example, with an overlap bandwidth of more than 1 / 4 and less than 1 / 2. Next, a metal wire is spirally wound around the outer periphery of the semiconductive strip layer 6 along the cable axis direction to form a shielding layer 7. Next, a pressing strip is spirally wound around the outer periphery of the shielding layer 7 along the cable axis direction to form a pressing strip layer 8. This allows the formation of a shielded core (a laminate from conductor 2 to pressing strip layer 8).

[0066] Next, the above-mentioned halogen-free flame-retardant resin composition is extruded and molded around the outer periphery of the pressing tape layer 8 (the core with the shielding layer) to form the sheath layer 9. Then, the sheath layer 9 is cross-linked (second cross-linking).

[0067] For example, by Figure 3 (a) The extruder 100 shown supplies material 51, which is the granular material of the above-mentioned halogen-free flame-retardant resin composition, to the hopper 101. It should be noted that a portion of the components of the above-mentioned halogen-free flame-retardant resin composition (e.g., a crosslinking agent) may also be added from the feed port (not shown) midway through the extruder 100. Then, in the shielded core (the laminate from conductor 2 to the pressing tape layer 8, see reference...) supplied from the upstream side... Figure 3 (b)) The outer periphery is coated with the above-mentioned halogen-free flame-retardant resin composition to form a sheath layer 9.

[0068] Next, the power transmission cable (the laminate from conductor 2 to sheath layer 9) fed from the extruder 100 is supplied to the lead coating forming apparatus 110 located downstream of the extruder 100. The power transmission cable (the laminate from conductor 2 to sheath layer 9, see...) Figure 3 (c) While moving, a lead coating layer 10 is continuously formed on the outer periphery of the power transmission cable (sheath layer 9). Figure 3 (d) Refer to), and wind it onto the take-up spool 120. By providing the lead coating layer 10, steam will not come into contact with the sheath layer 9 during the crosslinking process described later, thereby suppressing the deformation of the surface of the sheath layer 9 due to steam pressure. It should be noted that the material of the coating layer (coating material) is not limited to lead.

[0069] Next, for the power transmission cable (the laminate from conductor 2 to lead coating 10) wound onto the take-up reel 120, refer to... Figure 3 (d) Perform cross-linking treatment. Specifically, a take-up reel 120 with the power transmission cable (a laminate from conductor 2 to lead coating 10) is placed in a cross-linking device (autoclave cross-linking device) 130 to perform cross-linking treatment (heat treatment) on the sheath layer 9. For example, it is left to stand in a steam atmosphere at 90°C for 72 hours (h).

[0070] In terms of heating conditions (crosslinking temperature and crosslinking time), the crosslinking temperature is preferably 70°C to 110°C. If it is below 110°C, the gap between the sheath and the core with the shielding layer can be suppressed; if it is above 70°C, the crosslinking speed will not become extremely slow. Furthermore, as the crosslinking temperature, it is more preferably 85°C to 105°C. Additionally, as the crosslinking time, it is preferably 5 hours to 270 hours, more preferably 24 hours to 72 hours.

[0071] Next, the cross-linked sheath layer 9 is cooled. For example, the power transmission cable (the laminate from conductor 2 to lead coating layer 10) wound on the winding drum 120 is taken out of the cross-linking equipment (autoclave cross-linking equipment) 130, cooled by standing at room temperature (e.g., 25°C), and the lead coating layer 10 is peeled off to manufacture the power transmission cable.

[0072] Thus, in this embodiment, by adding silane coupling agent and peroxide as crosslinking agents within the aforementioned range to the sheath layer, crosslinking can be allowed at a lower temperature while maintaining mechanical strength, thereby suppressing gaps between the insulation layer and the sheath layer that may arise due to the difference in shrinkage rates between them. This, in turn, suppresses the decrease in connection reliability caused by misalignment of the core (insulation layer).

[0073] The effects of this embodiment will now be explained in detail. As a method for crosslinking the sheath layer 9, when the above-described autoclave crosslinking is applied, gaps are generated between the insulating layer 4 and the sheath layer 9, and more specifically, between the outer semiconductive layer 5 and the shielding layer 7. These gaps are believed to be caused by the different shrinkage rates of the layers (especially the insulating layer 4 and the sheath layer 9) formed sequentially in a manner covering the periphery of the conductor 2. In the case of autoclave crosslinking, the crosslinked inner semiconductive layer 3, insulating layer 4, and outer semiconductive layer 5, other than the sheath layer 9 to be crosslinked, are also exposed to high temperatures for an extended period (e.g., exposed at 145°C for 2 hours). As a result, the inner semiconductive layer 3, insulating layer 4, and outer semiconductive layer 5 expand due to heat and shrink during the subsequent cooling process. At this time, due to the different shrinkage rates of each layer, gaps are generated based on these differences in shrinkage rate.

[0074] For example, when ethylene propylene rubber is used for insulation layer 4 and EVA is used for sheath layer 9, the ratio of "insulation layer linear expansion coefficient / sheath layer linear expansion coefficient" is 1.3 or higher.

[0075] Even when the coefficient of linear expansion of insulation layer 4 is greater than that of sheath layer 9, excessive gaps will not occur if the thickness of insulation layer 4 is thin. However, in the case of ultra-high voltage transmission cables, there is a tendency to make the thickness of insulation layer 4 thicker to improve insulation characteristics. The thickness of insulation layer 4 is greater than that of sheath layer 9, preferably more than three times the thickness of sheath layer 9. Thus, with a thicker insulation layer 4, the deformation of insulation layer 4 due to the difference in coefficients of linear expansion will increase, making gaps more likely to occur.

[0076] As described above, when gaps occur between the layers constituting a power transmission cable, the cable's characteristics degrade due to these gaps. In particular, when, as in this embodiment, the conductor 2 is positioned at the center of the sheath layer 9, and the inner semiconductive layer 3, insulation layer 4, outer semiconductive layer 5, and sheath layer 9 are arranged around the conductor 2, sheath misalignment easily occurs between the layers where gaps exist. When this sheath misalignment occurs, connection reliability at the connection points between the power transmission cable and other components can sometimes be hindered. Here, "sheath misalignment" refers to the phenomenon of sheath movement occurring between the layers where gaps exist when the conductor 2 is positioned at the center of the sheath layer 9, and the inner semiconductive layer 3, insulation layer 4, outer semiconductive layer 5, and sheath layer 9 are arranged around the conductor 2. For example, it refers to movement between the pressing tape layer 8 and the shielding layer 7, or between the shielding layer 7 and the semiconductive tape layer 6, or in the core with the shielding layer (the laminate from the conductor 2 to the pressing tape layer 8, see reference 1). Figure 3 (b) The phenomenon that the sheath layer moves along the length of the power transmission cable due to an excessive gap between the sheath layer and the sheath layer 9.

[0077] The gaps between the layers of the power transmission cable as described above are caused by thermal expansion and contraction during the heating (crosslinking) of the sheath layer 9. Therefore, by reducing the heating temperature, the generation of gaps can be suppressed.

[0078] However, there are concerns about a decrease in the degree of crosslinking and mechanical strength of the sheath layer during low-temperature crosslinking. In this embodiment, to increase mechanical strength even during low-temperature crosslinking, the type and amount of crosslinking agent in the halogen-free flame-retardant resin composition constituting the sheath layer are adjusted, thereby successfully suppressing gap formation in the power transmission cable while maintaining mechanical strength. The following is a more detailed description based on examples.

[0079] Example

[0080] The following describes in more detail the halogen-free flame-retardant resin composition used in the power transmission cable of this embodiment, based on examples.

[0081] (Material Name)

[0082] 1) EVA: "Evaflex EV45LX" manufactured by Mitsui-DuPont Chemicals Co., Ltd. (VA content: 46% by mass)

[0083] 2) EVA: "Evaflex V9000" manufactured by Mitsui DuPont Chemicals Co., Ltd. (VA content: 41% by mass)

[0084] 3) Magnesium hydroxide: Kyowa Chemical Industry manufactures "Kisuma 5L"

[0085] 4) Aluminum hydroxide: "BF013STV" (silane 1.0μm) manufactured by Japan Light Metals.

[0086] 5) Silane coupling agent: Shin-Etsu Chemical Co., Ltd., "KBM-503"

[0087] 6) Peroxides: Kayaku Akzo's "Trigonox 22-70E" (1,1-bis(tert-butylperoxide)cyclohexane)

[0088] 7) Triallyl isocyanate: Nippon Chemical Industries' "TAIC"

[0089] 8) Zinc oxide: "Zinc White No. 3" manufactured by Sakai Chemical Co., Ltd.

[0090] 9) 2,2,4-Trimethyl-1,2-dihydroquinoline polymer: Nocrack224, manufactured by Ouchi Emerging Chemicals.

[0091] 10) Carbon: Asahi Carbon's "FT Carbon"

[0092] 11) Lithium hydroxystearate: Nitto Kasei Corporation, "LS-6"

[0093] 12) Zinc stearate: Nitto Kasei Corporation, "EZ-101"

[0094] (Example 1)

[0095] The halogen-free flame-retardant resin composition was prepared according to the component ratios shown in Table 1, and after mixing, it was laminated from conductor 2 to pressing tape layer 8. Figure 3 (b) Referring to) the outer periphery of the halogen-free flame-retardant resin composition (solid extrusion) to form a sheath layer 9. Then, it is covered by a lead coating layer 10 (refer to) Figure 3(d) and wound onto a take-up reel 120, which is then placed in a crosslinking apparatus (autoclave crosslinking apparatus) 130 for crosslinking treatment (heat treatment) of the sheath layer 9. The halogen-free flame-retardant resin composition and treatment conditions (crosslinking temperature, crosslinking time) used in the sheath layer 9 are shown in Table 2. Finally, the sheath layer 9 is cooled to obtain the power transmission cable. As conductor 2, a stranded wire (outer diameter 12.53 mm) formed by re-twisting 19 strands is used, wherein the strands are formed by twisting 27 tin-plated soft copper wires. A separator is provided between conductor 2 and inner semiconductive layer 3, and the separator formed of nylon is wound around the outer periphery of conductor 2 with a 1 / 2 width overlap. The thickness of inner semiconductive layer 3 is 1.000 mm, and it is solidly extruded from carbon-containing conductive ethylene propylene rubber. The outer diameter after forming inner semiconductive layer 3 is 14.97 mm. The insulation layer 4 has a thickness of 15.165 mm and is solidly extruded from clay-containing ethylene propylene rubber. The outer diameter after forming the insulation layer 4 is 45.30 mm. The semi-conductive tape layer 6 has a thickness of 0.500 mm and a width of 40 mm, formed by overlapping and winding carbon-containing nylon tape at a 1 / 2 width. The outer diameter after forming the semi-conductive tape layer 6 is 46.30 mm. As the shielding layer 7, a wrapped shielding element is used, consisting of 30 tin-plated soft copper wires wound at a spacing of 136 mm. The shielding layer 7 has a thickness of 0.800 mm, and the outer diameter after forming the shielding layer 7 is 47.90 mm. The pressing tape layer 8 has a thickness of 0.220 mm and a width of 90 mm, formed by overlapping and winding nylon pressing tape at a 1 / 2 width. The outer diameter after forming the insulation layer 4 is 48.34 mm. The sheath layer 9 has a thickness of 2.5 mm, and the outer diameter after forming the sheath layer 9 is 53.34 mm.

[0096] (Comparative Examples 1-3)

[0097] As shown in Table 1, the composition ratio and processing conditions (crosslinking temperature, crosslinking time) were changed, and the same procedure as in Example 1 was followed to obtain the power transmission cable.

[0098] It should be noted that the proportions of each component shown in Table 1 are expressed as parts by mass relative to a total of 100 parts by mass of the matrix polymer.

[0099] Table 1

[0100]

[0101] (evaluate)

[0102] (Tension test)

[0103] For the resulting power transmission cable, pull out the shielded core (the laminate from conductor 2 to the pressing layer 8, refer to...) Figure 3(b) The sheath layer 9 is stamped into a dumbbell shape to obtain a sample (test piece). The test piece is a No. 6 dumbbell shape with a distance of 20 mm between the marks.

[0104] A tensile test was performed on the specimen. The tensile test was conducted according to IEC 60811-1-1 standard. Specifically, the specimen was stretched at a speed of 200 mm / min using a tensile testing machine, and the tensile strength and elongation at break were determined.

[0105] (Oil resistance test)

[0106] For the resulting power transmission cable, pull out the shielded core (the laminate from conductor 2 to the pressing layer 8, refer to...) Figure 3 (b) The sheath layer 9 is stamped into a dumbbell shape to obtain a sample (test piece). The test piece is a No. 6 dumbbell shape with a distance of 20 mm between the marks.

[0107] After immersing the specimen in IRM902 at 100°C for 72 hours, a tensile test was performed. Specifically, the oil-immersed specimen was stretched at a speed of 200 mm / min using a tensile testing machine, and the tensile strength and elongation at break were measured. The tensile strength after oil immersion relative to the initial (before oil immersion) tensile strength, i.e., the "oil-resistant tensile strength retention rate", and the elongation at break after oil immersion relative to the initial elongation at break, i.e., the "oil-resistant elongation at break retention rate", were measured.

[0108] (Pull-out test)

[0109] The obtained power transmission cable was cut into 20cm lengths as test specimens. In the pull-out test, the core of the shielding layer (the laminate from conductor 2 to the pressing layer 8, see reference) was pressed down from the cut surface of the power transmission cable. Figure 3 (b) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) " ...

[0110] Figure 4 It is a cross-sectional view showing what a pull-out test looks like. Specifically, as shown... Figure 4As shown, a scale 300 and a convex clamp 310 are used for the test. The convex clamp 310 has a protrusion 310a that contacts the shielded core of the power transmission cable. The diameter Rc of the protrusion 310a is greater than or equal to the diameter Ra of the resin core (the laminate from conductor 2 to the outer semiconductive layer 5) and less than the diameter Rb of the shielded core (the laminate from conductor 2 to the pressing strip layer 8). A cylindrical member with a diameter of 3 cm is used here. The convex clamp 310 is set on the scale 300, the shielded core of the power transmission cable is aligned with the protrusion 310a, the power transmission cable is pressed down toward the protrusion 310a, and the maximum value (kgf) of the scale 300 is measured until the shielded core moves relative to the sheath layer 9. If the measured value (pull-out strength) is less than 10 kgf, it is determined that sheath misalignment has occurred and is recorded as unqualified (×).

[0111] Thus, in a power transmission cable, when a force (load) in the opposite direction is applied between the sheath layer and the portion inside the sheath layer, the sheath layer and the portion inside the sheath layer will be misaligned relative to each other. This is called sheath misalignment, and the force (load) at this time is defined as "pull-out strength", which is determined by using the above-mentioned scale and convex clamp test (pull-out test).

[0112] (result)

[0113] As shown in Table 1, the sheath layer of Example 1 achieved good values ​​in both the tensile test and the oil resistance test. Furthermore, the pull-out test result was above 10 kgf, indicating that it could suppress the gap between the shielded core and the sheath layer. It should be noted that, upon observation of the comparative examples, it was found that the gaps were not limited to the area between the sheath layer 9 and the pressing tape layer 8; sometimes gaps also occurred between the pressing tape layer 8 and the shielding layer 7, or between the shielding layer 7 and the semi-conductive tape layer 6.

[0114] In contrast, although the sheath layer of Comparative Example 3 obtained good values ​​in both the tensile test and the oil resistance test, the measured value in the pull-out test was less than 10 kgf, indicating that the gap between the shielded core and the sheath layer was relatively large.

[0115] In addition, the pull-out test values ​​of the sheath layers in Comparative Examples 1 and 2 were less than 10 kgf, indicating that although the gap between the shielded core and the sheath layer was suppressed, the tensile test and oil resistance test characteristics were poor.

[0116] In contrast, according to this embodiment, by adjusting the crosslinking agent as described above, the gap between the shielded core and the sheath can be suppressed while maintaining the mechanical properties of the power transmission cable, even under low-temperature crosslinking conditions.

[0117] (Application Example)

[0118] In the above embodiments, by Figure 1 The multiple laminates shown constitute a power transmission cable, but a power transmission cable can also be constructed by using an insulated wire having a conductor 2 and an insulation layer 4 disposed around it as the core and a sheath layer 9 disposed around it. Alternatively, multiple insulated wires can be used as the core. As the sheath layer of such a power transmission cable, the aforementioned halogen-free flame-retardant resin composition can also be used, and the sheath layer is formed around the core in the same manner as in the above embodiment.

[0119] In addition, in the above embodiments, by Figure 1 The multi-layered laminate shown constitutes a power transmission cable, but for example, conductor 2 and insulation layer 4 can be included as essential components in the resin core C, omitting the inner semi-conductive layer 3 or outer semi-conductive layer 5. Furthermore, the semi-conductive strip 6, shielding layer 7, or compression strip layer 8 on the outer periphery of the resin core C can also be omitted. In this case, it is sufficient to use the portion inside the sheath layer as the core for tensile tests, oil resistance tests, and pull-out tests.

[0120] This invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from its spirit.

Claims

1. A power transmission cable, comprising: (a) A core having a conductor and an insulating layer formed around the outer periphery of the conductor, and (b) A sheath layer formed on the outer periphery of the core; The insulating layer is thicker than the sheath layer. The coefficient of linear expansion of the insulating layer is greater than that of the sheath layer. The sheath layer is formed from a halogen-free flame-retardant resin composition containing a matrix polymer, a silane coupling agent, and a peroxide. The content of the silane coupling agent is more than 2 parts by mass and less than 6 parts by mass relative to 100 parts by mass of the matrix polymer. The content of the peroxide is between 4 and 10 parts by mass relative to 100 parts by mass of the matrix polymer. The pull-out strength of the inner side of the sheath layer is above 10 kgf.

2. The power transmission cable as described in claim 1, wherein, The sheath layer has a tensile strength of 10 MPa or more, and the oil-resistant tensile strength retention rate is 60% or more.

3. The power transmission cable as described in claim 1, wherein, The thickness of the insulating layer is more than three times the thickness of the sheath layer. The ratio of the linear expansion coefficients of the sheath layer to the insulation layer, i.e., the ratio of the linear expansion coefficient of the insulation layer to the linear expansion coefficient of the sheath layer, is 1.3 or higher.

4. The power transmission cable as described in claim 1, wherein, A shielding layer is provided between the sheath layer and the insulating layer.

5. The power transmission cable as described in claim 4, wherein, A pressing band layer is provided between the sheath layer and the shielding layer.

6. The power transmission cable as described in claim 1, wherein, The matrix polymer contains an ethylene-vinyl acetate copolymer. Relative to 100 parts by weight of the matrix polymer, it contains 100 to 150 parts by weight of metal hydroxide.

7. The power transmission cable as described in claim 1, wherein, The core is formed from a resin core having a conductor, an inner semi-conductive layer, an insulating layer, and an outer semi-conductive layer.

8. A method for manufacturing a power transmission cable, comprising: (a) A step of coating a core having a conductor and an insulating layer formed on the outer periphery of the conductor with a halogen-free flame-retardant resin composition as a sheath layer, and (b) A process of cross-linking the sheath layer by heating; The insulating layer is thicker than the sheath layer. The coefficient of linear expansion of the insulating layer is greater than that of the sheath layer. The sheath layer is formed from a halogen-free flame-retardant resin composition containing a matrix polymer, a silane coupling agent, and a peroxide. The content of the silane coupling agent is more than 2 parts by mass and less than 6 parts by mass relative to 100 parts by mass of the matrix polymer. The content of the peroxide is between 4 and 10 parts by mass relative to 100 parts by mass of the matrix polymer.

9. The method for manufacturing a power transmission cable as described in claim 8, wherein, In step (b), heating is performed while the sheath layer is covered by the covering material.

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