CN113921171A - Power transmission cable and method for manufacturing power transmission cable - Google Patents

Abstract

The invention provides a power transmission cable and a manufacturing method thereof, which can inhibit the gap between a sheath layer and an insulating layer and improve the drawing strength of the inner side of the sheath layer. A power transmission cable is provided with: (a) a core having a conductor (2) and an insulating layer (4) at its outer periphery; and (b) a sheath layer (9) formed on the outer periphery of the core, and having the following configuration. The sheath layer is formed from a resin composition containing a matrix polymer, a silane coupling agent and a peroxide, and 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 per 100 parts by mass of the matrix polymer, and the pull strength of the sheath layer on the inner side is 10kgf or more. By adding the silane coupling agent and the peroxide as the crosslinking agent in the above-mentioned ranges, crosslinking can be performed at a relatively low temperature, and even when the insulating layer is thick and the linear expansion coefficient is large and the influence of thermal expansion and contraction is large, the occurrence of a gap between the insulating layer and the sheath layer can be suppressed, and the pull strength can be ensured.

Description

Power transmission cable and method for manufacturing power transmission cable

Technical Field

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

Background

In order to reduce the damage of cables used in railway vehicles and the like in fire, characteristics such as flame retardancy and low smoke emission are required. In order to obtain high flame retardancy, a material obtained by adding a halogen flame retardant such as chlorine or bromine to polyolefin is 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 may generate highly toxic gases depending on the combustion conditions

English. Therefore, cables using halogen-free materials (halogen-free materials) containing no halogen substance as the covering material are becoming popular from the viewpoint of safety during fire and reduction of environmental load.

For example, patent document 1 discloses a power transmission cable in which a halogen-free flame retardant resin composition containing a matrix polymer of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 50 wt% or more, and a metal hydrate and silica in a total amount of 100 parts by mass or more and 180 parts by mass or less with respect to 100 parts by mass of the matrix polymer is used as a sheath layer in order to achieve high flame retardancy and low smoke generation.

Further, patent document 2 discloses a power transmission cable having: the shield layer is formed by winding a wire around the outer periphery of the semiconductive layer, and the shield layer is formed by winding a metal wire around the outer periphery of the semiconductive layer. In the power transmission cable, the metal wires constituting the shield layer suppress the sag of the outer semiconductive layer and the insulating layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-100140

Patent document 2: japanese patent laid-open publication No. 2016-100148

Disclosure of Invention

Problems to be solved by the invention

An electric power transmission cable in which a core portion having a conductor and an insulating layer formed on the outer periphery of the conductor is covered with a halogen-free flame-retardant resin composition as a sheath layer is formed by covering the core portion with the halogen-free flame-retardant resin composition and then heating the resultant to crosslink the resin material.

In this case, when the halogen-free flame-retardant resin composition to be the sheath layer is heated, the insulating layer and the sheath layer in the sheath layer are thermally expanded and are respectively contracted in the cooling step. In this case, an excessive gap is formed between the insulating layer and the sheath layer due to a difference in shrinkage rate between the insulating layer and the sheath layer. This excessive clearance becomes a cause of hindering connection reliability at a connection portion between the power transmission cable and another member. For example, an excessive gap is generated between the core (insulating layer) and the sheath layer, and thus any one of the members between the core (insulating layer) and the sheath layer moves in the longitudinal direction of the power transmission cable, and displacement of the sheath occurs. When such a sheath displacement occurs, the reliability of connection between the power transmission cable and another component is impaired.

It is an object of the present invention to provide a power transmission cable and a method for manufacturing the power transmission cable, which can suppress the occurrence of an excessive gap between a sheath layer and an insulating layer, improve the drawing strength on the inner side of the sheath layer, and improve the connection reliability between the power transmission cable and another member.

Means for solving the problems

[1] A power transmission cable according to one embodiment of the present invention includes: (a) a core having a conductor and an insulating layer formed on an outer periphery of the conductor, and (b) a sheath layer formed on an outer periphery of the core; the insulating layer is thicker than the sheath layer, the insulating layer has a coefficient of linear expansion 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 silane coupling agent is contained in an amount of 2 parts by mass or more per 100 parts by mass of the matrix polymer, the peroxide is contained in an amount of 4 parts by mass or more per 100 parts by mass of the matrix polymer, and the drawing strength of the sheath layer is 10kgf or more on the inner side thereof.

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

[3] In the above item [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 coefficients of the sheath layer and the insulating layer, i.e., the insulating layer linear expansion coefficient/sheath layer linear expansion coefficient, is 1.3 or more.

[4] In the above item [1], a shield layer is provided between the sheath layer and the insulating layer.

[5] In item [4], a pressing tape layer is provided between the sheath layer and the shield layer.

[6] In the above item [1], the matrix polymer contains an ethylene-vinyl acetate copolymer, and the metal hydroxide is contained in an amount of 100 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the matrix polymer.

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

[8] A method for manufacturing a power transmission cable according to an embodiment of the present invention includes: (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 halogen-free flame-retardant resin composition to be a sheath layer, and (b) a step of crosslinking the sheath layer by heating; the insulating layer is thicker than the sheath layer, the insulating layer has a coefficient of linear expansion 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 silane coupling agent is contained in an amount of 2 parts by mass or more per 100 parts by mass of the matrix polymer, and the peroxide is contained in an amount of 4 parts by mass or more per 100 parts by mass of the matrix polymer.

[9] In [8], in the step (b), the sheath layer is heated in a state covered with a coating material.

Effects of the invention

According to the power transmission cable of one aspect of the present invention, the gap between the sheath layer and the insulating layer (core) can be suppressed, and the pull strength can be increased on the inner side of the sheath layer.

Drawings

Fig. 1 is a sectional view showing the configuration of a power transmission cable.

Fig. 2 is a schematic view showing a manufacturing process of the power transmission cable.

Fig. 3 is a schematic view showing a manufacturing process of the power transmission cable.

Fig. 4 is a sectional view showing the appearance of a pull-out test.

Description of the symbols

1: power transmission cable, 2: conductor, 3: inner semiconductive layer (3M material), 4: insulating layer, 5: outer 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 device, 120: take-up reel, 130: crosslinking apparatus (kettle crosslinking apparatus), 200 a: extruder, 220: screw, 221: material input port (hopper), 230: extrusion head, 240: steam pipe (cross-linked pipe), 300: scale, 310: convex jig, 310 a: convex portion, C: a resin core.

Detailed Description

(embodiment mode)

(construction of Power Transmission Cable)

Hereinafter, the power transmission cable according to the present embodiment will be described. Fig. 1 is a sectional view showing the configuration of a power transmission cable.

A power transmission cable 1 shown in fig. 1 includes a conductor 2, an inner semiconductive layer 3 formed on an outer periphery of the conductor 2, an insulating layer 4 formed on an outer periphery of the inner semiconductive layer 3, an outer semiconductive layer 5 formed on an outer periphery of the insulating layer 4, a semiconductive belt layer 6 formed on an outer periphery of the outer semiconductive layer 5, a shield layer 7 formed on an outer periphery of the semiconductive belt layer 6, a pressing belt layer 8 formed on an outer periphery of the shield layer 7, and a sheath layer 9 formed on an outer periphery of the pressing belt layer 8.

The power transmission cable according to the present embodiment is, for example, an extra-high voltage power transmission cable that transmits a high voltage of 7000V or more. The outer diameter (diameter) of the power transmission cable is, for example, 30mm to 60 mm. Such a power transmission cable is disposed along, for example, a roof portion or a wall portion of a railway vehicle to connect a pantograph provided on a roof of the railway vehicle and a multi-pressure device (multi-pressure device) provided under a floor.

The conductor 2 is formed by stranding a plurality of bare wires. As the bare wire, for example, a conductive wire, a copper alloy wire, or the like can be used. In addition, metal plating such as tin plating may be applied to the bare wires. The conductor 2 transmits a high voltage of 7000V or more as described above. A separator may be wound in superposition on the conductor 2.

The inner semiconductive layer 3 and the outer semiconductive layer 5 are provided to alleviate electric field concentration, and are formed of a material to which conductivity is imparted by dispersing conductive powder such as carbon in rubber such as ethylene propylene rubber or butyl rubber. When a fine gap is formed between the conductor 2 and the insulating layer 4 or between the insulating layer 4 and the shield layer 7, electric field concentration is likely to occur, and therefore, the inner semiconductive layer 3 and the outer semiconductive layer 5 are preferably formed to be in close contact with the insulating layer 4. By sandwiching the insulating layer 4 between the inner semiconductive layer 3 and the outer 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 shield layer 7 can be alleviated.

The insulating layer 4 is formed of, for example, ethylene propylene rubber, vinyl chloride, cross-linked polyethylene, silicone rubber, fluorine-based material, or the like. The insulating layer 4 may contain clay.

Since the insulating layer 4 is required to have high insulating properties, the thickness of the insulating layer 4 is greater than the respective thicknesses of the inner semiconductive layer 3, the outer semiconductive layer 5, the shield layer 7, and the jacket layer 9. The thickness of the insulating layer 4 is, for example, about 8mm to 16 mm.

Here, a laminate of the conductor 2, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 from the inside may be referred to as a resin core C.

A semiconductive tape 6, a shield layer 7, and a pressing tape layer 8 are provided on the outer periphery of the resin core C.

The semiconductive tape layer 6 on the outer periphery of the outer semiconductive layer 5 (resin core C) is obtained by, for example, winding a semiconductive tape in a spiral shape along the cable axis direction. As the semiconductive belt, for example, a semiconductive belt obtained by impregnating a base fabric or a nonwoven fabric obtained by weaving warp and weft yarns made of nylon, rayon, PET, or the like, with a material in which conductive powder such as carbon is dispersed in rubber such as ethylene propylene rubber or butyl rubber is used. The thickness of the semiconductive tape is, for example, 0.1mm to 0.4mm, and the width of the semiconductive tape is, for example, 30mm to 70 mm. The semiconductive tapes may be wound one on top of the other, for example with an overlap of the tape width of 1/4 up to 1/2 down.

The shield layer 7 is obtained by winding a metal wire spirally around the outer periphery of the semiconductive belt layer 6, for example, in the cable axis direction. The wire is made of a conductive material such as tin-plated soft copper, and for example, a wire rod having a diameter of 0.4mm to 0.6mm can be used. The shield layer 7 is grounded in use.

The pressing tape layer 8 is obtained by spirally winding a pressing tape, for example, on the outer periphery of the shield layer 7 along the cable axis direction. As the pressing belt, a belt formed of plastic or rayon may be used. In addition, a polyester nonwoven fabric may also be used. The pressing belt has a thickness of, for example, 0.03mm to 0.2mm, and a width of, for example, 50mm to 90 mm.

The laminated body up to this point from the conductor 2 to the pressing tape layer 8 may be referred to as a core with a shield layer.

A sheath layer 9 is provided on the outer periphery of the pressing tape layer 8 (core with shield layer). The sheath layer 9 is obtained by, for example, extrusion-molding a halogen-free flame-retardant resin composition on the outer periphery of the tape layer 8. The sheath layer 9 is crosslinked. The sheath layer 9 is a protective layer for protecting the core portion (the laminated body from the conductor 2 to the pressing tape layer 8) of the tape shield layer. The thickness of the sheath layer 9 is, for example, 2.5mm to 3.0 mm.

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

As the matrix polymer (resin component), an ethylene-vinyl acetate copolymer (EVA) can be used. Among them, EVA having a vinyl acetate content of 40 mass% or more is preferably used. When the vinyl acetate content is 40% by mass or more, the resulting fuel residue (pattern of fuel え) becomes firm, and good flame retardancy and low smoke generation can be obtained.

The EVA and maleic acid-modified polyolefin, styrene butadiene rubber, and the like may be used in combination as the matrix polymer (resin component).

As the flame retardant, a metal hydroxide may be used. As the metal hydroxide, magnesium hydroxide or aluminum hydroxide can be used. The 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 matrix polymer. When the amount is 100 to 150 parts by mass, good heat aging characteristics and low smoke generation properties can be obtained. From the viewpoint of achieving both high flame retardancy and low fuming property, the amount (content) of the metal hydroxide to be added is preferably 100 parts by mass or more and 125 parts by mass or less with respect to 100 parts by mass of the matrix polymer.

As the metal hydroxide, the above-mentioned aluminum hydroxide, magnesium hydroxide, and the like are used. By using either magnesium hydroxide or aluminum hydroxide, high flame retardancy can be achieved. As the aluminum hydroxide and the magnesium hydroxide, aluminum hydroxide and magnesium hydroxide whose surfaces are coupled by a fatty acid or a silane compound are preferably used. By using such a coupled material, good tensile strength and elongation at break can be obtained in a tensile test.

Further, as the metal hydroxide, the above aluminum hydroxide and magnesium hydroxide may be used in combination. In this case, it is preferable that the magnesium hydroxide: aluminum hydroxide 40: 60-60: 40, was adjusted within the range of. This is because the stepwise dehydration method is more effective for suppressing the temperature rise of the cable after the start of combustion of the halogen-free flame-retardant resin composition and for curing the slag. The dehydration start temperatures of aluminum hydroxide and magnesium hydroxide are in the vicinity of 210 ℃ and in the vicinity of 280 ℃, respectively, and by setting the mass ratio, it is possible to effectively promote the stepwise dehydration, suppress the temperature rise of the cable after the start of combustion, and promote the solidification of the fuel slag.

As the crosslinking agent, peroxide and silane coupling agent are used. Examples of the peroxide (compound having an-O-moiety) include tert-butyl peroxycarbonate (2-ethylhexyl) ester, 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, and 1, 1-di (tert-amyl peroxy) cyclohexene.

As silane coupling agents (R-Si-X)₃And R: organic group, X: the functional group, X, may be a different functional group including H), and a silane coupling agent having a vinyl group, an epoxy group, a styryl group, a methacrylic group, an amino group, an isocyanurate group, a mercapto group, or an acid anhydride as the functional group (X) can be used. X may be a different functional group including H. Specifically, as the silane coupling agent, a vinyl silane compound such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β -methoxyethoxy) silane, or an epoxy silane compound such as β - (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, γ -glycidoxypropyltrimethoxysilane, or γ -glycidoxypropylmethyldiethoxysilane; styryl silane compounds such as p-styryl trimethoxysilane; methacrylic silane compounds such as 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane and 3-methacryloxypropylmethyldiethoxysilane; gamma-aminopropyl trimethoxy silane, gamma-aminopropyl triethoxy silaneAminosilane compounds such as silane, N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane, beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane, and N-phenyl-gamma-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-trimethoxysilylpropyl succinic anhydride. In addition, 2 or more of these silane compounds may be used in combination.

The amount (content) of the peroxide added is preferably 4 parts by mass or more per 100 parts by mass of the matrix polymer, and the amount (content) of the silane coupling agent added is preferably 2 parts by mass or more per 100 parts by mass of the matrix polymer. By setting the addition amounts of the peroxide and the silane coupling agent as the crosslinking agent in 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 to 100 parts by mass of the matrix polymer, the deterioration of the oil resistance can be suppressed. The upper limit of the amount (content) of the peroxide is 10 parts by mass. By adjusting the amount of the peroxide to 10 parts by mass or less, unnecessary crosslinking can be avoided and processing (particularly extrusion processing) can be performed with good workability. Further, by adding 2 parts by mass or more of the silane coupling agent to 100 parts by mass of the matrix polymer, a decrease in tensile strength can be suppressed. The upper limit of the amount (content) of the silane coupling agent is 6 parts by mass. When the amount of the silane coupling agent added is 6 parts by mass or less, the decrease in elongation at break can be suppressed. The amount (content) of the silane coupling agent is the amount of the silane coupling agent added, and does not include the amount of the silane coupling agent subjected to the surface treatment of the surface of the metal hydroxide.

As other additives, crosslinking aids, stabilizers, antioxidants, colorants, lubricants, and the like can be used.

(method of manufacturing Power Transmission Cable)

The following describes a method for manufacturing a power transmission cable according to the present embodiment. Fig. 2 and 3 are schematic views showing a manufacturing process of the power transmission cable.

A resin core C of the power transmission cable is formed (prepared). First, the conductor 2 is prepared, and an inner semiconductive material as a raw material of the inner semiconductive layer 3, an insulating material as a raw material of the insulating layer 4, and an outer semiconductive material as a raw material of the outer semiconductive layer 5 are extrusion-molded on the outer periphery of the conductor 2. For example, the inner semiconductive material (3M) is extrusion-molded on the outer periphery of the conductor 2 by an extruder (200a), and the insulating material and the outer semiconductive material are extrusion-molded by other extruders (not shown), respectively. In this way, the inner semiconductive layer 3, the insulating layer 4 and the outer semiconductive layer 5 can be extruded together, for example, in a manner to surround the conductor in this order.

As a modification, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 may be extrusion-molded in this order. Thereby, the resin core C formed of the conductor 2, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 can be formed.

Next, the rubber contained in the layer constituting the resin core portion C is crosslinked (first crosslinking).

Such a resin core C can be formed, for example, by using the apparatus shown in fig. 2. The single-screw extruder 200a shown in fig. 2 has a screw 220 and a material inlet 221 disposed in a cylinder. For example, the material 3M of the inner semiconductive layer 3 is charged from a material charging port (hopper) 221. Another single-screw extruder (not shown) also has a screw and a material inlet disposed in the cylinder, and the material of the insulating layer 4 is fed from the material inlet (hopper). Further, another single-screw extruder (not shown) also has a screw and a material inlet disposed in the cylinder, and the material of the outer semiconductive layer 5 is fed from the material inlet (hopper). Thus, the conductor 2 is passed 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 this order from the inside on the outer periphery thereof, and cross-linked while passing through the inside of the cross-linking pipe (steam pipe) 240 (cross-head extrusion). By using this continuous crosslinking apparatus, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 of the resin core C are heated and crosslinked (crosslinked by passing them through pressurized water vapor). For example, crosslinking is carried out in a water vapor atmosphere at 150 ℃ to 180 ℃ for 30 minutes to 60 minutes. Thereby, the resin core C can be formed.

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 on the outer periphery of the conductor 2, and further, the inner semiconductive layer 3, the insulating layer 4 and the 3 layers of the outer semiconductive layer 5 extruded sequentially on the outer periphery of the conductor 2 are crosslinked all at once, but 1 layer may be extruded each time on the outer periphery of the conductor 2 and 3 layers may be crosslinked all at once, or 1 layer may be extruded each time on the outer periphery of the conductor 2 and crosslinked.

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

Next, a semiconductive belt layer 6 is formed by spirally winding a semiconductive belt around the outer circumference of the outer semiconductive layer 5 in the cable axis direction. The semiconductive tapes may be wound in superposed relation, for example, in a width of overlap of 1/4 or more and 1/2 or less. Next, a metal wire is spirally wound around the outer periphery of the semiconductive tape layer 6 in the cable axis direction, thereby forming the shield layer 7. Next, a pressing tape layer 8 is formed by spirally winding a pressing tape on the outer periphery of the shield layer 7 along the cable axis direction. This enables formation of a core portion with a shield layer (a laminated body from the conductor 2 to the pressing tape layer 8).

Next, the sheath layer 9 is formed by extrusion molding the halogen-free flame-retardant resin composition on the outer periphery of the pressing tape layer 8 (core portion with shield layer). Then, the sheath layer 9 is crosslinked (second crosslinking).

The material 51, which is a pellet of the halogen-free flame retardant resin composition, is supplied from a hopper 101 of an extruder 100 shown in fig. 3(a), for example. A part of the components (for example, a crosslinking agent) of the halogen-free flame retardant resin composition may be added from an inlet (not shown) in the middle of the extruder 100. Then, the outer periphery of the core portion with the shield layer (the laminated body from the conductor 2 to the pressing tape layer 8, see fig. 3(b)) supplied from the upstream side is covered with the halogen-free flame retardant resin composition to form the sheath layer 9.

Next, the electric power transmission cable (the laminated body from the conductor 2 to the sheath layer 9) fed from the extruder 100 is supplied to the lead coating layer forming device 110 disposed on the downstream side of the extruder 100. While the electric power cable (the laminated body from the conductor 2 to the sheath layer 9, see fig. 3 c) is moved, the lead coating layer 10 (see fig. 3 d) is continuously formed on the outer periphery of the electric power cable (the sheath layer 9) and wound around the winding drum 120. By providing the lead coating layer 10, the steam does not come into contact with the sheath layer 9 in a crosslinking step described later, and deformation of the surface of the sheath layer 9 due to the pressure of the steam can be suppressed. The material of the coating layer (coating material) is not limited to lead.

Next, the electric power transmission cable (the laminate from the conductor 2 to the lead coating layer 10, see fig. 3(d)) in a state of being wound around the winding drum 120 is subjected to a crosslinking treatment. 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 placed in a crosslinking device (kettle crosslinking device) 130, and the sheath layer 9 is subjected to crosslinking treatment (heat treatment). For example, it is allowed to stand in a steam atmosphere at 90 ℃ for 72 hours (h).

In the heating conditions (crosslinking temperature, crosslinking time), the crosslinking temperature is preferably 70 ℃ to 110 ℃. If the temperature is 110 ℃ or lower, the gap between the sheath and the core with the shield layer can be suppressed, and if the temperature is 70 ℃ or higher, the crosslinking speed does not become extremely slow. Further, the crosslinking temperature is more preferably 85 ℃ to 105 ℃. The crosslinking time is preferably 5 hours to 270 hours, and more preferably 24 hours to 72 hours.

Next, the crosslinked sheath layer 9 is cooled. For example, an electric power transmission cable (a laminate from the conductor 2 to the lead coating layer 10) wound around the winding drum 120 is taken out from the crosslinking device (kettle crosslinking device) 130, and is cooled by leaving it at room temperature (e.g., 25 ℃) to peel off the lead coating layer 10, thereby producing an electric power transmission cable.

In this way, in the present embodiment, since the silane coupling agent and the peroxide are added as the crosslinking agent in the above-described range to the jacket layer, crosslinking can be allowed at a relatively low temperature while maintaining the mechanical strength, and a gap between the insulating layer and the jacket layer, which may be generated due to a difference in shrinkage ratio between the insulating layer and the jacket layer, can be suppressed. This can suppress a decrease in connection reliability due to misalignment of the core (insulating layer).

Hereinafter, the effects of the present embodiment will be described in detail. When the above-described autoclave crosslinking is applied as a method of crosslinking the sheath layer 9, a gap is formed between the insulating layer 4 and the sheath layer 9, more specifically, between the outer semiconductive layer 5 and the shield layer 7. This gap is considered to be caused by the difference in the shrinkage rate of the respective layers (particularly, the insulating layer 4 and the sheath layer 9) formed in this order so as to cover the periphery of the conductor 2. In the case of the pot crosslinking, the crosslinked inner semiconductive layer 3, insulating layer 4 and outer semiconductive layer 5 other than the jacket layer 9 to be crosslinked are also exposed to high temperatures for a long time (for example, exposed to high temperatures of 145 ℃ for 2 hours). As a result, the inner semiconductive layer 3, the insulating layer 4, and the outer semiconductive layer 5 expand by heat and contract in the subsequent cooling step. In this case, since the shrinkage rates of the respective layers are different, gaps are generated depending on the shrinkage rates.

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.

Even when the linear expansion coefficient of the insulating layer 4 is larger than that of the sheath layer 9, an excessive gap is not generated if the thickness of the insulating layer 4 is small. However, in the case of the transmission cable for extra-high voltage, the thickness of the insulating layer 4 tends to be thick in order to improve the insulating property, and 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. When the thickness of the insulating layer 4 is large, the amount of deformation of the insulating layer 4 due to the difference in linear expansion coefficient increases, and a gap is likely to be generated.

As described above, when a gap is generated between the layers constituting the power transmission cable, the characteristics of the power transmission cable are degraded by 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 as in the present embodiment, sheath misalignment is likely to occur between the layers in which the gap exists. When the sheath is displaced, connection reliability may be impaired at a connection portion between the power transmission cable and another member. The "jacket misalignment" referred to herein is a phenomenon of jacket movement occurring between the layers in which a gap exists when the conductor 2 is disposed at the center of the jacket layer 9 and the inner semiconductive layer 3, the insulating layer 4, the outer semiconductive layer 5, and the jacket layer 9 are disposed on the outer periphery of the conductor 2, and is a phenomenon of jacket movement in the longitudinal direction of the power transmission cable due to an excessive gap occurring between the pressing tape layer 8 and the shield layer 7, between the shield layer 7 and the semiconductive tape layer 6, or between the core portion with the shield layer (a laminated body from the conductor 2 to the pressing tape layer 8, see fig. 3(b)) and the jacket layer 9, for example.

The gaps between the layers constituting the above-described power transmission cable are caused by thermal expansion and contraction when the sheath layer 9 is heated (crosslinked), and therefore, by lowering the heating temperature, the occurrence of gaps can be suppressed.

However, crosslinking at low temperatures may decrease the degree of crosslinking of the sheath layer and decrease the mechanical strength. In the present embodiment, in order to increase the mechanical strength even when crosslinked at low temperature, the generation of a gap in the power transmission cable is successfully suppressed while maintaining the mechanical strength by adjusting the type and the amount of the crosslinking agent of the halogen-free flame-retardant resin composition constituting the sheath layer. Hereinafter, the following will be described in more detail with reference to examples.

Examples

Hereinafter, the halogen-free flame-retardant resin composition used for the power transmission cable according to the present embodiment will be described in more detail with reference to examples.

(Material name)

1) EVA: "Evaflex EV45 LX" manufactured by DuPont chemical Co., Ltd. (VA amount: 46% by mass)

2) EVA: "Evaflex V9000" manufactured by DuPont chemical Co., Ltd. (VA amount: 41% by mass)

3) Magnesium hydroxide: kisuma 5L manufactured by Kyoho chemical industry "

4) Aluminum hydroxide: "BF 013 STV" (silane 1.0 μm) made of Japanese light metal

5) Silane coupling agent: KBM-503, manufactured by shin-Yue chemical Co., Ltd "

6) Peroxide: trigonox 22-70E (1, 1-bis (t-butylperoxy) cyclohexane) manufactured by Kayaku Akzo

7) Triallyl isocyanate: "TAIC" made by Japan Kasei Kaisha "

8) Zinc oxide: made by Sakai chemistry "Zinc white No. 3"

9)2,2, 4-trimethyl-1, 2-dihydroquinoline polymer: nocrack224 from Dai Xinxing chemical "

10) Carbon: "FT carbon" manufactured by Asahi carbon Co., Ltd "

11) Lithium hydroxystearate: LS-6 manufactured by Nidong chemical industry Co Ltd "

12) Zinc stearate: EZ-101 manufactured by Nidong chemical industry Co., Ltd "

(example 1)

Halogen-free flame-retardant resin compositions were prepared in the component ratios shown in table 1, and after kneading, the halogen-free flame-retardant resin compositions were coated (solid extruded) on the outer periphery of the laminate (see fig. 3 b) from the conductor 2 to the tape 8, thereby forming the sheath layer 9. Then, the sheath layer 9 is covered with the lead coating layer 10 (see fig. 3 d), wound around the winding drum 120, and disposed in the crosslinking device (kettle crosslinking device) 130 to be subjected to crosslinking treatment (heating treatment) of the sheath layer 120. The halogen-free flame-retardant resin composition and the treatment conditions (crosslinking temperature, crosslinking time) used in the sheath layer 9 are shown in table 2. And finally, cooling the sheath layer 9 to obtain the transmission cable. As the conductor 2, a twisted wire (outer diameter 12.53mm) obtained by twisting 19 twisted wire bundles of 27 tinned annealed copper wires was used. A separator is disposed between the conductor 2 and the inner semiconductive layer 3, and a separator made of nylon is wound around the outer periphery of the conductor 2 in a width of 1/2 mm. The inner semiconductive layer 3 has a thickness of 1.000mm and is produced by solid extrusion of a carbon-containing conductive ethylene propylene rubber. The outer diameter after forming the inner semiconductive layer 3 was 14.97 mm. The insulating layer 4 has a thickness of 15.165mm and is made of clay-containing ethylene propylene rubber by solid extrusion. The outer diameter after the insulating layer 4 was formed was 45.30 mm. The semiconductive tape layer 6 had a thickness of 0.500mm and a width of 40mm, and carbon-containing nylon tape was wound in an overlapping manner with a tape width of 1/2. The outer diameter after formation of the semiconductive tape layer 6 was 46.30 mm. As the shield layer 7, a wrapped shield in which 30 soft copper wires plated with tin were wrapped at a pitch of 136mm was used. The thickness of the shield layer 7 was 0.800mm, and the outer diameter after forming the shield layer 7 was 47.90 mm. The pressing tape layer 8 was 0.220mm in thickness and 90mm in width, and a pressing tape formed of nylon was wound in an overlapping manner with a tape width of 1/2. The outer diameter after the insulating layer 4 was formed was 48.34 mm. The thickness of the sheath layer 9 was 2.5mm, and the outer diameter after forming the sheath layer 9 was 53.34 mm.

Comparative examples 1 to 3

A power transmission cable was obtained in the same manner as in example 1, except that the distribution ratio and the treatment conditions (crosslinking temperature and crosslinking time) were changed as shown in table 1.

The blending amounts of the respective components shown in table 1 are shown as parts by mass with respect to 100 parts by mass of the total matrix polymer.

TABLE 1

(evaluation)

(tensile test)

With respect to the obtained electric power transmission cable, the core portion with the shield layer (the laminated body from the conductor 2 to the tape layer 8, see fig. 3(b)) was pulled out, and the sheath layer 9 was punched into a dumbbell shape to obtain a sample (test piece). The test piece is in a No. 6 dumbbell shape, and the distance between the marked lines is 20 mm.

The test piece was subjected to a tensile test. Tensile testing was performed according to IEC60811-1-1 standard. Specifically, the specimen was subjected to stretching at a speed of 200mm/min using a tensile tester, and the tensile strength and elongation at break were measured.

(oil resistance test)

With respect to the obtained electric power transmission cable, the core portion with the shield layer (the laminated body from the conductor 2 to the tape layer 8, see fig. 3(b)) was pulled out, and the sheath layer 9 was punched into a dumbbell shape to obtain a sample (test piece). The test piece is in a No. 6 dumbbell shape, and the distance between the marked lines is 20 mm.

The test specimens were immersed in IRM902 at 100 ℃ for 72 hours and then subjected to a tensile test. Specifically, the oil-impregnated sample was stretched at a speed of 200mm/min using a tensile tester to measure the tensile strength and elongation at break. The tensile strength after oil immersion was measured with respect to the initial tensile strength (before oil immersion), i.e., "retention of tensile strength in oil", and the elongation at break after oil immersion was measured with respect to the initial elongation at break, i.e., "retention of elongation at break in oil".

(drawing test)

The obtained power transmission cable was cut into a length of 20cm to obtain a sample (test piece). In the pull-out test, the core portion with the shield layer (the laminated body from the conductor 2 to the tape layer 8, see fig. 3(b)) was pressed down from the cut surface of the electric power transmission cable, and the force (kgf) until the core portion with the shield layer moved (displaced or peeled) relative to the sheath layer 9 was measured.

Fig. 4 is a sectional view showing the appearance of a pull-out test. Specifically, as shown in fig. 4, the test was performed using a scale 300 and a convex jig 310. The convex jig 310 has a convex portion 310a that contacts the core portion with the shield layer of the power transmission cable. The diameter Rc of the projection 310a is equal to or larger than the diameter Ra of the resin core (the laminate from the conductor 2 to the outer semiconductive layer 5) and equal to or smaller than the diameter Rb of the core with the shield layer (the laminate from the conductor 2 to the pressing tape layer 8). Here, a cylindrical member having a diameter of 3cm was used. The scale 300 was provided with a projecting jig 310, the shielded core portion of the power transmission cable was aligned with the projecting portion 310a, the power transmission cable was pressed down toward the projecting portion 310a, and the maximum value (kgf) of the scale 300 was measured until the shielded core portion was moved relative to the sheath layer 9. When the measured value (pull strength) was less than 10kgf, it was judged that the sheath was dislocated, and it was judged as fail (x).

In the 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 are displaced relative to each other, which is referred to as "sheath displacement", and the force (load) at this time is defined as "pull-out strength", and is measured by a test (pull-out test) using the scale and the convex jig.

(results)

As shown in table 1, the sheath layer of example 1 was excellent in both the tensile test and the oil resistance test, and the gap between the core portion of the tape shielding layer and the sheath layer was considered to be suppressed when the measured value in the drawing test was 10kgf or more. When the comparative example is observed, the location where the gap is found is not limited to between the jacket layer 9 and the pressing tape layer 8, and a gap may be formed between the pressing tape layer 8 and the shield layer 7 or between the shield layer 7 and the semiconductive tape layer 6.

In contrast, the jacket layer of comparative example 3 was good in both the tensile test and the oil resistance test, but the measured value in the drawing test was less than 10kgf, and it is considered that the gap between the core portion with the shield layer and the jacket layer was large.

It is considered that the sheath layers of comparative examples 1 and 2 have a measurement value of less than 10kgf in the drawing test, and the gap between the core portion of the tape barrier layer and the sheath layer is suppressed, but the properties in both the drawing test and the oil resistance test are poor.

In contrast, according to the present embodiment, by adjusting the crosslinking agent as described above, the gap between the core portion with the shield layer and the sheath layer can be suppressed while maintaining the mechanical properties of the electric power transmission cable even in the case of low-temperature crosslinking.

(application example)

In the above embodiment, the power transmission cable is configured by the plurality of laminated bodies shown in fig. 1, but an insulated wire having the conductor 2 and the insulating layer 4 provided around the conductor may be used as a core and the sheath layer 9 may be provided around the core as a power transmission cable. Further, a plurality of insulated wires may be used as the core. As the sheath layer of the electric power transmission cable configured as described above, the halogen-free flame-retardant resin composition may be used, and the sheath layer may be formed around the core portion in the same manner as in the above embodiment.

In the above embodiment, the power transmission cable is configured by the laminate formed by a plurality of layers as shown in fig. 1, but the inner semiconductive layer 3 or the outer semiconductive layer 5 may be omitted by, for example, making the conductor 2 and the insulating layer 4 essential in the resin core portion C. Further, the semiconductive tape 6, the shield layer 7, or the tape pressing layer 8 on the outer periphery of the resin core C may be omitted. In this case, the portion inside the sheath layer may be subjected to a tensile test, an oil resistance test, and a pull-out test as the core portion.

The present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the scope of the invention.

Claims (9)

1. An electrical transmission cable having:

(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 an outer periphery of the core;

the insulating layer is thicker than the jacket layer,

the insulating layer has a linear expansion coefficient greater than that 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,

the content of the silane coupling agent is 2 parts by mass or more per 100 parts by mass of the matrix polymer,

the content of the peroxide is 4 parts by mass or more per 100 parts by mass of the matrix polymer,

the drawing strength of the inner side of the sheath layer is more than 10 kgf.

2. The electrical transmission cable of claim 1,

the tensile strength of the sheath layer is more than 10MPa, and the retention rate of the oil-resistant tensile strength is more than 60%.

3. The electrical transmission cable of claim 1,

the thickness of the insulating layer is more than 3 times of that of the sheath layer,

the ratio of the linear expansion coefficients of the sheath layer and the insulating layer, namely the linear expansion coefficient of the insulating layer/the linear expansion coefficient of the sheath layer, is more than 1.3.

4. The electrical transmission cable of claim 1,

and a shielding layer is arranged between the sheath layer and the insulating layer.

5. The electrical transmission cable of claim 4,

a pressing tape layer is arranged between the sheath layer and the shielding layer.

6. The electrical transmission cable of claim 1,

the matrix polymer comprises an ethylene-vinyl acetate copolymer,

the metal hydroxide is contained in an amount of 100 to 150 parts by mass per 100 parts by mass of the matrix polymer.

7. The electrical transmission cable of claim 1,

the core is formed of a resin core having a conductor, an inner semiconductive layer, an insulating layer, and an outer semiconductive layer.

8. A method of manufacturing an electrical transmission cable comprising:

(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 halogen-free flame-retardant resin composition as a sheath layer, and

(b) a step of heating the sheath layer to crosslink the sheath layer;

the insulating layer is thicker than the jacket layer,

the insulating layer has a linear expansion coefficient greater than that 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,

the content of the silane coupling agent is 2 parts by mass or more per 100 parts by mass of the matrix polymer,

the content of the peroxide is 4 parts by mass or more per 100 parts by mass of the matrix polymer.

9. The method of manufacturing an electrical transmission cable according to claim 8,

in the step (b), the sheath layer is heated while being covered with a coating material.

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