Method for manufacturing a power transmission cable using a non-halogen flame-retardant resin composition

Abstract

To provide a method for manufacturing a power transmission cable with a non-halogen flame-retardant resin composition that maintains good thermal aging characteristics, even with steam crosslinking.SOLUTION: A method includes a steps of: coating a core part having a conductor 2 and an insulating layer 4 formed on an outer periphery of the conductor, with a non-halogen flame-retardant resin composition to be a sheath layer 9; and crosslinking the sheath layer by being brought into contact with steam. The sheath layer is composed of a non-halogen flame-retardant resin composition containing a base polymer and a flame retardant. The flame retardant comprises a combination of magnesium hydroxide and aluminum hydroxide, excluding a combination of magnesium hydroxide and silica. A content of the flame retardant is 50 pts.mass or more and 150 pts.mass or less with respect to 100 pts.mass of the base polymer.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Cables used in railway vehicles and the like are required to have properties such as flame retardancy and low smoke generation in order to reduce damage in the event of a fire. In order to obtain high flame retardancy, materials in which a halogen-based flame retardant such as a chlorine-based or bromine-based flame retardant is added to a polyolefin 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 a non-halogen material (halogen-free material) that does not contain halogen substances as a coating material have been spreading from the viewpoints of safety during a fire and reduction of environmental load.

[0003] For example, Patent Document 1 discloses a power transmission cable using, 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 this base polymer in order to achieve high flame retardancy and low smoke generation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventor is engaged in research and development of a coating material for a power transmission cable, and is examining a resin composition that is a non-halogen material and has good properties as a coating material.

[0006] In particular, for power transmission cables, it is required that good flexibility be maintained over a long period of time. As an evaluation of the flexibility life of a power transmission cable, a heat aging characteristic of satisfying a predetermined standard in the "heat aging elongation retention rate" based on a heat aging test is required.

[0007] Also, as a method of crosslinking the sheath layer which is the outermost covering material of a power transmission cable, when performing crosslinking by heat, the heat of steam may be used. In such a crosslinking method using the heat of steam, in order to prevent deterioration due to direct contact of steam with the power transmission cable, a protective layer having good thermal conductivity may be provided on the outside for crosslinking. In such a crosslinking method, before and after crosslinking, a step of providing a protective layer on the outside of the sheath layer and a step of removing the protective layer on the outside of the sheath layer are required.

[0008] Therefore, if steam can be directly brought into contact with the sheath layer for crosslinking, the step of providing a protective layer on the outside of the sheath layer and the step of removing the protective layer on the outside of the sheath layer become unnecessary, and the production efficiency is improved.

[0009] However, when performing crosslinking by directly bringing steam into contact with the sheath layer, as deterioration due to direct contact of steam, there is a problem that the heat aging characteristic deteriorates due to undesired products, that is, the "heat aging elongation retention rate" cannot satisfy a predetermined standard.

[0010] Therefore, an object of the present invention is to provide a method for manufacturing a power transmission cable using a non-halogen flame-retardant resin composition having good heat aging characteristics even when a crosslinking method in which steam directly contacts is used.

Means for Solving the Problems

[0011] [1] The manufacturing method of a power transmission cable using the non-halogen flame-retardant resin composition according to one aspect of the present invention includes: (a) a step of coating a core part 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 the sheath layer by bringing it into contact with water vapor. And the sheath layer is composed of a non-halogen flame-retardant resin composition containing a base polymer and a flame retardant. The flame retardant is any one of magnesium hydroxide alone, aluminum hydroxide alone, silica alone, a combination of magnesium hydroxide and aluminum hydroxide, and a combination of aluminum hydroxide and silica. The content of the flame retardant is 50 parts by mass or more with respect to 100 parts by mass of the base polymer.

[0012] [2] In [1], the base polymer includes an ethylene-vinyl acetate copolymer.

[0013] [3] In [1], the content of the flame retardant 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.

[0014] [4] In [1], the sheath layer has a tensile elongation residual rate of 75% or more after a heat aging test at 120 °C for 168 hours.

[0015] [5] The manufacturing method of a power transmission cable using the non-halogen flame-retardant resin composition according to one aspect of the present invention includes a step of forming an internal semiconductive layer, an insulating layer, and an external semiconductive layer in order from the inside on the outer periphery of a conductor, a step of forming a shielding layer by winding a wire around the outer periphery of the external semiconductive layer, a step of forming a pressing tape layer by winding a pressing tape around the outer periphery of the shielding layer, and a step of forming a sheath layer on the outer periphery of the pressing tape layer. The step of forming the sheath layer includes (a) a step of coating the outer periphery of the pressing tape layer with the non-halogen flame-retardant resin composition that will form the sheath layer, and (b) a step of cross-linking by bringing the sheath layer into contact with water vapor. The sheath layer is made of a non-halogen flame-retardant resin composition containing a base polymer and a flame retardant. The flame retardant is any one of magnesium hydroxide alone, aluminum hydroxide alone, silica alone, a combination of magnesium hydroxide and aluminum hydroxide, and a combination of aluminum hydroxide and silica. The content of the flame retardant is 50 parts by mass or more with respect to 100 parts by mass of the base polymer.

Advantages of the Invention

[0016] According to the manufacturing method of a power transmission cable using the non-halogen flame-retardant resin composition according to one aspect of the present invention, even when a cross-linking method in which steam directly contacts is used, a power transmission cable with good heat aging characteristics can be manufactured.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] (Embodiment) Hereinafter, the manufacturing method of the power transmission cable of the present embodiment will be described. FIG. 1 is a cross-sectional view showing the configuration of a power transmission cable. In the present embodiment, the manufacturing method of the power transmission cable shown in FIG. 1 will be described as an example.

[0019] The power transmission cable shown in FIG. 1 includes a conductor 2 made of stranded wires, 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 pressing 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 pressing tape layer 8.

[0020] First, the internal semiconductive layer 3, the insulating layer 4, and the external semiconductive layer 5 are simultaneously extrusion-molded on the outer periphery of the conductor 2. Note that the internal semiconductive layer 3, the insulating layer 4, and the external semiconductive layer 5 may be extrusion-molded sequentially.

[0021] The conductor 2 is formed by twisting strands made of a plurality of metal wires. The strands may be metallized, and for example, wire materials such as tinned soft copper wires can be used. The conductor 2 transmits a high voltage of, for example, 7000V or more.

[0022] The internal semiconductive layer 3 and the external semiconductive layer 5 are made of, for example, a material obtained by dispersing conductive powder such as carbon in rubber such as ethylene propylene rubber or butyl rubber to make it conductive. The internal semiconductive layer 3 and the external semiconductive layer 5 are provided to mitigate the concentration of the electric field between the insulating layer 4 and the conductor 2 and between the insulating layer 4 and the shielding layer 7.

[0023] The insulating layer 4 is made of, for example, a material such as ethylene propylene rubber, vinyl chloride, crosslinked polyethylene, silicone rubber, or fluorine-based material.

[0024] Next, a semiconductive tape is spirally wound along the cable axis around the outer periphery of the external semiconductive layer 5 to form a semiconductive tape layer 6. As the semiconductive tape, for example, a base fabric or non-woven fabric woven with warp and weft made of nylon, rayon, PET, etc., and impregnated with a rubber such as ethylene propylene rubber or butyl rubber in which conductive powder such as carbon is dispersed can be used. As the semiconductive tape, for example, those having a thickness of 0.1 mm or more and 0.4 mm or less and a width of 30 mm or more and 70 mm or less can be used. The semiconductive tape may be wound in a superimposed manner such that, for example, 1 / 4 or more and 1 / 2 or less of the tape width overlaps.

[0025] Next, a wire is spirally wound along the cable axis around the outer periphery of the semiconductive tape layer 6 to form a shielding layer 7. 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.

[0026] Next, a presser tape is wound in a superimposed manner along the cable axis around the outer periphery of the shielding layer 7 to form a presser tape layer 8. As the presser tape, for example, a tape made of plastic or rayon having a thickness of 0.03 mm or more and 0.2 mm or less and a width of 50 mm or more and 90 mm or less can be used.

[0027] The laminate from the conductor 2 up to the presser tape layer 8 so far is referred to as the core part C.

[0028] Next, a sheath layer 9 is formed by extruding a non-halogen flame-retardant resin composition around the outer periphery of the core part C (presser tape layer 8). Then, crosslinking of the sheath layer 9 is performed.

[0029] The non-halogen flame-retardant resin composition constituting the sheath layer 9 contains a base polymer (resin component) and a flame retardant (metal hydroxide, silica).

[0030] The base polymer contains, for example, an ethylene vinyl acetate copolymer (EVA) and an ethylene-α-olefin copolymer modified with maleic anhydride (hereinafter also simply referred to as "maleic acid-modified ethylene copolymer").

[0031] As the ethylene vinyl acetate copolymer (EVA) in the base polymer, those having a vinyl acetate content of 40% by mass or more can be used. By setting the vinyl acetate content to 40% by mass or more, the char layer becomes stronger, and good flame retardancy and low smoke generation can be obtained.

[0032] In the ethylene-α-olefin copolymer modified with maleic anhydride in the base polymer, as the α-olefin, an α-olefin having 3 to 8 carbon atoms can be used in consideration of the flexibility of the cable. Examples of such α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, etc., and isomers can also be applied. Further, the α-olefin may be used alone or in combination of two or more.

[0033] Note that styrene butadiene rubber may be added to the ethylene vinyl acetate copolymer (EVA) and the ethylene-α-olefin copolymer modified with maleic anhydride as the base polymer.

[0034] As the flame retardant, a metal hydroxide or silica can be used.

[0035] As the metal hydroxide, magnesium hydroxide or aluminum hydroxide can be used. As such a metal hydroxide, those surface-treated with silane may be used. For example, magnesium hydroxide surface-treated with a silane coupling agent or aluminum hydroxide surface-treated with a silane coupling agent can be used. By using a surface-treated product with a silane coupling agent, the mechanical properties (tensile strength, elongation) are improved.

[0036] Silica may be either amorphous silica or crystalline silica. This silica is used for solidifying the combustion residue during combustion and improving mechanical properties. Also, the shape of this silica is spherical, and the average particle size is 0.05 μm or more and 1.0 μm or less. A more preferable average particle size is 0.15 μm or more and 0.3 μm or less. By using such silica in combination with a metal hydroxide, a balance of flame retardancy, low smoke generation property, and mechanical properties can be achieved. In particular, by making it spherical, the silica can penetrate between the metal hydroxides, improving the dispersibility of the metal hydroxide. Also, by setting the average particle size of the silica to 0.05 μm or more and 1.0 μm or less, the interaction with the polymer becomes appropriate and the mechanical properties are improved. The average particle size of the silica can be the value of the particle size D50 median diameter (μm) at which the cumulative frequency is exactly 50%. Note that the shape of the silica (whether it is spherical or not) can be confirmed by an electron microscope.

[0037] Here, in the present embodiment, as the flame retardant, any one of (a1) magnesium hydroxide alone, (a2) aluminum hydroxide alone, (a3) silica alone, (a4) a combination of magnesium hydroxide and aluminum hydroxide, and (a5) a combination of aluminum hydroxide and silica is used. And the addition amount of the flame retardant is 50 parts by mass or more, more 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.

[0038] In this way, by selecting the flame retardant from the above (a1) to (a5) and avoiding the combination of magnesium hydroxide and silica, even if the steam crosslinking described later is performed, a decrease in the elongation retention rate after heat aging can be suppressed. That is, a decrease in the mechanical properties after the heat aging test can be suppressed. The heat aging test can be regarded as a kind of accelerated test, and the good properties after the heat aging test are an index for being able to maintain the mechanical properties (for example, flexibility) for a long time.

[0039] (a4) When magnesium hydroxide and aluminum hydroxide are used in combination, it is preferable that the mass ratio is aluminum hydroxide:magnesium hydroxide = 40:60 to 60:40. This is because a stepwise dehydration method is more effective for suppressing temperature rise and solidifying the char layer during the combustion of the non-halogen flame-retardant resin composition. Since the dehydration start temperature of aluminum hydroxide is around 210 °C and that of magnesium hydroxide is around 280 °C, stepwise dehydration occurs in the order of aluminum hydroxide and magnesium hydroxide, effectively suppressing the temperature rise of the sheath layer and solidifying the char layer.

[0040] Among the above flame retardants, magnesium hydroxide, aluminum hydroxide, and silica all contribute to flame retardancy and low smoke generation. Magnesium hydroxide and aluminum hydroxide contribute to flame retardancy, and silica contributes to low smoke generation by solidifying the char layer.

[0041] In addition, other polymers (such as other EVA, polyolefins modified with other maleic acids, unmodified polyolefins, etc.), crosslinking agents, crosslinking aids, colorants, lubricants, antioxidants, etc. can also be blended into the non-halogen flame-retardant resin composition used for the above power transmission cable as needed.

[0042] For example, a peroxide may be used as the crosslinking agent. Also, carbon may be used as the colorant. Also, a stearate compound may be used as the lubricant. By blending a lubricant, the processability during extrusion can be improved.

[0043] FIG. 2 is a schematic diagram showing a manufacturing apparatus for a power transmission cable. The single-screw extruder 200 shown in FIG. 2 includes a screw 220 disposed in a cylinder and a material inlet 221. From the material inlet (hopper) 221, the non-halogen flame-retardant resin composition is introduced as the material for the sheath layer 9. The non-halogen flame-retardant resin composition melts, is extruded from the extruder 200, passes through the extrusion head 230, and is coated on the core portion C sent out from the feeder. Next, the core portion C and the sheath layer 9 on its outer periphery are crosslinked while passing through a steam pipe (crosslinking pipe) 240. Using such a continuous crosslinking apparatus, the sheath layer 9 is directly brought into contact with steam for crosslinking (crosslinking is performed by passing through steam). For example, crosslinking is performed for 5 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 power transmission cable 1 can be manufactured.

[0044] Thus, according to the manufacturing method of the power transmission cable 1 of the present embodiment, since a composite of magnesium hydroxide and silica is not used as the flame retardant and is selected from the above (a1) to (a5), the generation of magnesium silicate, which is an undesired reactant between magnesium hydroxide and silica generated during steam crosslinking, can be avoided, and a decrease in the elongation retention rate (%) after heat aging can be suppressed.

[0045] As described above, according to the manufacturing method of the power transmission cable of the present embodiment, a power transmission cable using a non-halogen flame-retardant resin composition excellent in heat aging characteristics can be manufactured. Further, according to the manufacturing method of the power transmission cable of the present embodiment, a power transmission cable can be efficiently manufactured without using a protective layer for suppressing the generation of undesired reactants.

[0046] Here, in the power transmission cable according to the present embodiment, the outer diameter (diameter) is, for example, 30 mm or more and 60 mm or less, and the thickness of the sheath layer is, for example, 2 mm or more and 4 mm or less.

[0047] In addition, the power transmission cable according to this embodiment can be used, for example, as a special high-voltage cable (hereinafter referred to as a special high-voltage cable for railway vehicles) installed in a railway vehicle. The special high-voltage cable for railway vehicles is installed along the roof or wall, for example, to connect a pantograph arranged on the roof of the railway vehicle and a multi-voltage device arranged under the floor. Here, the special high voltage means a voltage of 7000 V or higher.

[0048] [Examples] Hereinafter, the non-halogen flame-retardant resin composition used in the power transmission cable of this embodiment will be described in more detail based on examples. (Material name) 1) EVA: "Levapren 600HV" manufactured by LANXESS (VA content: 60% by mass) 2) Acid-modified polyolefin: Acid-modified ethylene-α-olefin copolymer, "Tafmer MH5040" manufactured by Mitsui Chemicals, Inc. 3) Magnesium hydroxide: "Magnifin H10A" manufactured by Huber (vinyl silane 0.8 - 1.1 μm) 4) Aluminum hydroxide: "BF013STV" manufactured by Nippon Light Metal Co., Ltd. (silane 1.0 μm) 5) Silica: "Sydisther T120U" manufactured by Elkem (spherical, average particle size 0.15 μm) 6) t-Butyl peroxy 2-ethylhexyl carbonate: "Trigonox 117" manufactured by Nouryon 7) Triallyl isocyanate: "TAIC" manufactured by Nippon Kasei Co., Ltd. 8) Zinc oxide: "Zinc white No. 3" manufactured by Sakai Chemical Industry Co., Ltd. 9) Blend-type antioxidant: "AO-18 (AO20 / 412S = 6 / 4)" manufactured by Adeka 10) Carbon: "FT Carbon" manufactured by Asahi Carbon Co., Ltd. 11) Lithium hydroxystearate: "LS-6" manufactured by Nitto Kasei Kogyo Co., Ltd. 12) Zinc stearate: "EZ-101" manufactured by Nitto Kasei Kogyo Co., Ltd. [Examples 1 - 5] A non-halogen flame-retardant resin composition was adjusted with the component formulation shown in Table 1, kneaded using a roll, and then formed into a sheet with a thickness of 1 mm. The formed sheet was subjected to steam crosslinking using a crosslinking tube. Specifically, steam (water vapor) with a saturated water vapor pressure of 1 MPa was brought into direct contact with the sheet (kneaded non-halogen flame-retardant resin composition), and crosslinking was carried out at 180 °C for 10 minutes to obtain a steam-crosslinked sheet.

[0049] (Comparative Examples 1 to 3) The component formulation was changed as shown in Table 1, and in the same manner as in Examples 1 to 5, a steam-crosslinked sheet was obtained.

[0050] Note that the blending amounts of the respective components shown in Table 1 are indicated in parts by mass based on a total of 100 parts by mass of the base polymer.

[0051]

Table 1

[0052] For the obtained sheets, the mechanical properties before and after the heat aging test were evaluated by a tensile test in accordance with the ICE60811-1-1 standard and the ICE60811-1-2 standard as follows.

[0053] The obtained sheet was punched out into a dumbbell No. 6 shape to prepare a test piece with a gauge length of 20 mm. This test piece was pulled at a tensile speed of 200 mm / min, and the gauge length after fracture was measured. The gauge length after fracture was obtained by joining the test piece after fracture and measuring the gauge length between the marks. The elongation before heat aging (%) was determined from the following formula.

[0054] Elongation before heat aging (%) = 100 × Gauge length after fracture (mm) / 20 (mm) The obtained sheet was exposed in an oven at 120 °C for 168 hours, then punched out into a dumbbell No. 6 shape to prepare a test piece with a gauge length of 20 mm. This test piece was pulled at a tensile speed of 200 mm / min, and the elongation at the breaking point was measured. The elongation after heat aging (%) was determined from the following formula.

[0055] Elongation after thermal aging (%) = 100 × distance between gauge marks after rupture (mm) / 20 (mm) Furthermore, the elongation retention rate after thermal aging (%) was determined from the following formula.

[0056] Elongation retention rate after thermal aging (%) = 100 × elongation after thermal aging (%) / elongation before thermal aging (%) The elongation before thermal aging (%) and the elongation retention rate after thermal aging (%) are shown in Table 1.

[0057] Those with an elongation retention rate after thermal aging (%) of 75% or more were rated as "qualified", and those with less than 75% were rated as "unqualified".

[0058] As shown in Table 1, for the sheets of Examples 1 to 5, in each case, the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0059] Specifically, in Example 1, a composite of (a5) aluminum hydroxide and silica was used as the flame retardant, and the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0060] Also, in Example 2, a composite of (a4) magnesium hydroxide and aluminum hydroxide was used as the flame retardant, and the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0061] Also, in Example 3, (a3) silica was used alone as the flame retardant, and the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0062] Also, in Example 4, (a1) magnesium hydroxide was used alone as the flame retardant, and the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0063] Also, in Example 5, (a2) aluminum hydroxide was used alone as the flame retardant, and the elongation retention rate after thermal aging (%) was 75% or more, indicating good thermal aging characteristics.

[0064] Furthermore, in Examples 1 to 5 above, the addition amount of the flame retardant was 50 parts by mass or more with respect to 100 parts by mass of the base polymer. In Examples 1, 2, 4, and 5 where the addition amount of the flame retardant was large, 100 parts by mass or more with respect to 100 parts by mass of the base polymer, the elongation retention rate (%) after heat aging was 90% or more, and the heat aging characteristics were better.

[0065] On the other hand, in Comparative Examples 1 to 3, a composite of magnesium hydroxide and silica was used as the flame retardant. In all cases, the elongation retention rate (%) after heat aging was less than 75%, and the heat aging characteristics were poor. In these comparative examples, although the addition amount of the flame retardant was 100 parts by mass or more with respect to 100 parts by mass of the base polymer, the elongation retention rate (%) after heat aging was low.

[0066] Such a decrease in the elongation retention rate (%) after heat aging is due to the formation of magnesium silicate, which is an undesired reaction product of magnesium hydroxide and silica during steam crosslinking.

[0067] Therefore, as shown in (a1) to (a5) above, by avoiding the combined use of magnesium hydroxide and silica and compounding the flame retardant, the elongation retention rate (%) after heat aging can be improved and the heat aging characteristics can be made better.

[0068] Here, when performing the above steam crosslinking, in order to suppress the generation of undesired reaction products by steam, as described above, it is also possible to cover the sheath layer with a protective layer, perform steam crosslinking, and then peel off the protective layer. However, in this case, a protective layer formation step and a peeling step are required, resulting in a decrease in production efficiency.

[0069] On the other hand, according to the present embodiment, by adjusting the combination of the flame retardant as described above, even when steam crosslinking is performed, no undesired reaction product (magnesium silicate) is generated, and while improving the production efficiency, it is possible to suppress a decrease in the heat aging elongation retention rate.

[0070] Note that the test piece used in this embodiment or the like corresponds to, for example, a piece obtained by peeling the sheath layer of a power transmission cable and punching it out with the above dumbbell.

[0071] (Application Example) In the above embodiment, the power transmission cable is constituted by a plurality of laminates shown in FIG. 1. However, a power transmission cable may be used in which an insulated wire having a conductor 2 and an insulating layer 4 provided around the conductor 2 is used as a core layer and a sheath layer 9 is provided around the core layer. Further, a plurality of insulated wires may be used as the core layer. 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 a sheath layer may be formed around the core layer in the same manner as in the above embodiment.

[0072] 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

[0073] 1 Power transmission cable 2 Conductor 3 Inner semiconductive layer 4 Insulating layer 5 Outer semiconductive layer 6 Semiconductive tape layer 7 Shielding layer 8 Pressing tape layer 9 Sheath layer 200 Extruder 220 Screw 221 Material inlet (hopper) 230 Extrusion head 240 Steam pipe (crosslinking pipe) C Core part

Claims

1. A method for manufacturing a special high-voltage cable for railway vehicles with an outer diameter of 30 mm or more and 60 mm or less, comprising: forming an internal semiconductive layer, an insulating layer, and an external semiconductive layer in sequence from the inside on the outer periphery of a conductor; forming a shielding layer by winding a wire around the outer periphery of the external semiconductive layer; forming a pressing tape layer by winding a pressing tape around the outer periphery of the shielding layer; forming a sheath layer on the outer periphery of the pressing tape layer, wherein the step of forming the sheath layer (a) coating a non-halogen flame-retardant resin composition to be the sheath layer on the outer periphery of the pressing tape layer; (b) crosslinking by bringing the sheath layer into contact with steam; includes the step (b) is carried out for crosslinking for 5 minutes or more and 60 minutes or less in a steam atmosphere of 150° or more and 180° or less; the sheath layer is made of a non-halogen flame-retardant resin composition containing a base polymer and a flame retardant; the flame retardant is a combined use of magnesium hydroxide and aluminum hydroxide (excluding the combined use of magnesium hydroxide, aluminum hydroxide, and silica); the content of the flame retardant is 100 parts by mass with respect to 100 parts by mass of the base polymer; A method for manufacturing a special high-voltage cable using a non-halogen flame-retardant resin composition, wherein the sheath layer has a tensile elongation retention rate of 75% or more after a heat aging test at 120° C. for 168 hours.

2. In the method for manufacturing a power transmission cable using the non-halogen flame-retardant resin composition according to Claim 1, A method for manufacturing a special high-voltage cable using a non-halogen flame-retardant resin composition, wherein the mass ratio of the magnesium hydroxide to the aluminum hydroxide is 60:40.

Images