Recyclable non-crosslinked insulated cable

Abstract

The utility model relates to the technical field of wires and cables, in particular to a recyclable non-crosslinked insulated cable. The utility model discloses a recoverable non-crosslinked insulated cable, which comprises a conductor and a semi-conductive band, and a non-crosslinked inner shielding layer, a non-crosslinked polyvinyl insulating layer and a non-crosslinked outer shielding layer are sequentially coated outside the semi-conductive band. The non-crosslinked inner shielding layer is prepared by extruding an ultra-smooth non-crosslinked semi-conductive shielding material consisting of polyethylene resin, carbon black and an antioxidant; the non-crosslinked polyethylene-based insulating layer is prepared by extruding an ultra-clean polyethylene-based non-crosslinked insulating material consisting of one or more of high-density polyethylene and medium-density polyethylene, linear low-density polyethylene and an antioxidant; and the non-crosslinked outer shielding layer is prepared by extruding an ultra-smooth non-crosslinked semi-conductive shielding material consisting of polyethylene resin, carbon black and an antioxidant. The technical problem to be solved by the utility model is to develop a non-crosslinked insulated cable which is lower in carbon, more environment-friendly and recoverable.

Description

Technical Field

[0001] The utility model relates to the technical field of wires and cables, in particular to a recyclable non-cross-linked insulated cable. Background Art

[0002] Since the 1960s, cross-linked polyethylene (XLPE) insulated cables have gradually replaced oil-filled cables with their superior mechanical and electrical properties, becoming the absolute mainstream in the power cable industry. With the deepening implementation of the dual-carbon strategy, the cable industry is accelerating its green and low-carbon transformation and upgrading. A series of problems with cross-linked polyethylene insulation, such as high energy consumption, high emissions, and low production efficiency, are becoming increasingly prominent:

[0003] a) The cross-linking process requires high temperature heating, which consumes huge amounts of electricity;

[0004] b) The residual by-products produced after cross-linking increase the dielectric loss of the insulation and reduce the electrical performance. The insulation core needs to be heated and degassed for 5 to 7 days before the gas is gradually discharged, which prolongs the delivery cycle.

[0005] c) The cross-linking agent is easy to decompose prematurely during the extrusion process to produce pre-cross-linked products. Scorching is easy to occur during long-term extrusion, requiring frequent shutdowns for cleaning;

[0006] d) Cross-linked polyethylene is a thermosetting material and is difficult to recycle after retirement. Traditional disposal methods such as landfill, incineration, and thermal cracking will cause serious environmental pollution and carbon emissions.

[0007] Therefore, those skilled in the art are committed to developing a more low-carbon, environmentally friendly, and recyclable non-cross-linked insulated cable. Utility Model Content

[0008] In view of the above-mentioned defects of the prior art, the utility model discloses a recyclable non-cross-linked insulated cable, and the technical problem to be solved is to provide a more low-carbon and environmentally friendly, recyclable non-cross-linked insulated cable.

[0009] To achieve the above objectives, the present invention provides a recyclable non-cross-linked insulated cable, comprising a conductor coated with a semi-conductive tape, which is sequentially coated with a non-cross-linked inner shielding layer, a non-cross-linked polyethylene-based insulation layer, and a non-cross-linked outer shielding layer. The non-cross-linked inner shielding layer is extruded from an ultra-smooth, non-cross-linked, semi-conductive shielding material composed of polyethylene resin, carbon black, and an antioxidant, without a cross-linking agent. The non-cross-linked polyethylene-based insulation layer is extruded from an ultra-clean, non-cross-linked polyethylene-based non-cross-linked insulation material composed of one or more of high-density polyethylene and medium-density polyethylene, linear low-density polyethylene, and an antioxidant, without a cross-linking agent. The non-cross-linked outer shielding layer is extruded from an ultra-smooth, non-cross-linked, semi-conductive shielding material composed of polyethylene resin, carbon black, and an antioxidant, without a cross-linking agent. Common insulation and semi-conductive shielding materials containing cross-linking agents, such as the cross-linking agent dicumyl peroxide (DCP), are easily decomposed during the extrusion process to produce trace amounts of pre-cross-linked products. Over long extrusion processes, the pre-cross-linked products accumulate, causing scorching of the insulation and requiring frequent machine downtime for cleaning. In addition, the cross-linking agent DCP decomposes under the high temperature conditions of 200-300℃ in the vulcanized pipe, causing the cross-linked polyethylene to form a cross-linked network molecular structure, which consumes huge amounts of electricity. After the cross-linking agent DCP decomposes, it will produce by-products such as acetophenone, methane, and α-methylstyrene, which remain inside the insulation, causing increased insulation dielectric loss and decreased electrical performance. The insulated wire core needs to be heated and degassed for 5 to 7 days before it can be gradually discharged, resulting in an extension of the delivery cycle. Insulation and semi-conductive shielding materials containing cross-linking agents are difficult to degrade after forming a cross-linked network molecular structure. Repeated recycling is difficult, energy-intensive, and inefficient. Traditional treatment methods such as landfill, incineration, and thermal cracking will cause serious environmental pollution and carbon emissions.

[0010] The high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) in the non-cross-linked polyethylene (PE) insulation layer inherently have high crystallinity and poor toughness. However, when blended with linear low-density polyethylene (LLDPE), which has regular molecular chains, low branching, and good low-temperature flexibility, the crystallinity and flexibility are improved. Furthermore, the folding and entanglement between the different molecular chains, and the resulting lamellar structure, act similarly to physical crosslinking, enhancing mechanical and electrical properties. Compared to thermosetting cross-linked polyethylene (XLPE) using chemical crosslinkers, thermoplastic non-cross-linked polyethylene insulation can be repeatedly molded after heating and melting, making it easy to recycle.

[0011] Preferably, the thickness of the non-cross-linked inner shielding layer is 1.5 to 2.0 mm, the thickness of the non-cross-linked polyethylene-based insulation layer is 16.0 to 27.0 mm, and the thickness of the non-cross-linked outer shielding layer is 1.0 to 1.5 mm. After the conductors are twisted, there are gaps between the copper wires. Setting a non-cross-linked inner shielding layer with a thickness of 1.5 to 2.0 mm can eliminate the increase in the electric field strength on the conductor surface caused by the uneven surface of the conductor, making the inner surface of the insulation layer more round and smooth, and having better electrical contact with the cable conductor, making the electric field distribution more uniform. The thickness of the non-cross-linked polyethylene-based insulation layer is set to 16.0 to 27.0 mm to ensure that the cable has a high electrical insulation strength and can withstand high voltages of more than 110 kV. Setting a non-cross-linked outer shielding layer with a thickness of 1.0 to 1.5 mm can make the outer surface of the insulation layer round and smooth, play a role in uniform electric field, and at the same time prevent insulation damage caused by external scratches.

[0012] Preferably, the size of the protrusions penetrating the non-cross-linked polyethylene-based insulation layer at the interface between the non-cross-linked inner shielding layer and the non-cross-linked polyethylene-based insulation layer is less than 75 μm; the size of the opaque impurities in the non-cross-linked polyethylene-based insulation layer is less than 125 μm; and the size of the protrusions penetrating the non-cross-linked polyethylene-based insulation layer at the interface between the non-cross-linked outer shielding layer and the non-cross-linked polyethylene-based insulation layer is less than 75 μm. The non-cross-linked semi-conductive inner and outer shielding layers ensure that both the inner and outer surfaces of the non-cross-linked polyethylene-based insulation layer are rounded and smooth, resulting in a uniform electric field distribution. However, if the protrusions are too large, they will damage the smoothness of the insulation surface, causing the electric field distribution to concentrate at the location of the protrusions, reducing the withstand voltage of the cable insulation. In severe cases, the local electric field strength may be too high, leading to breakdown. Therefore, the above size restrictions are imposed on the protrusions.

[0013] Preferably, the density of the high-density polyethylene is 0.941 to 0.965 g / gm 3 The density of the medium density polyethylene is 0.926-0.940 g / cm 3 .

[0014] Preferably, the conductor is a compressed circular stranded conductor, a segmented conductor, or a profiled stranded conductor.

[0015] Preferably, the semi-conductive tape is formed by wrapping 1-2 layers of semi-conductive nylon tape with a thickness of 0.10-0.14 mm. This has the following advantages: firstly, it prevents the electric field concentration of burrs in the conductor from causing shield breakdown; secondly, it reduces the shielding material from sinking into the gaps in the conductor, reducing material loss.

[0016] Preferably, the non-cross-linked outer shielding layer is sequentially coated with a buffer layer, a metal wire cloth tape, a metal protective layer, a non-metallic sheath and a semi-conductive layer.

[0017] Preferably, the buffer layer is made of 2 to 3 layers of semi-conductive buffer water-blocking tape with a thickness of 1.5 to 2.5 mm, which are formed by overlapping or gap wrapping; and water-blocking powder is provided on the semi-conductive buffer water-blocking tape.

[0018] Preferably, the metal wire cloth tape is formed by regularly interlacing tinned copper wires with a diameter of 0.18 to 0.22 mm on a semi-conductive nylon tape or a semi-conductive polyester fiber tape, and the thickness of the semi-conductive nylon tape or the semi-conductive polyester fiber tape is 0.4 to 0.5 mm.

[0019] Because water-blocking powder is added to the semi-conductive buffer water-blocking tape, the presence of trace moisture in the air causes the water-blocking powder to come into contact with the external aluminum material, resulting in a metal electrochemical reaction, which can corrode the aluminum and, in severe cases, cause cable breakdown. The structural design of the metal wire cloth tape has the following effects: First, the semi-conductive nylon tape or semi-conductive polyester fiber tape can physically isolate the buffer layer from the metal sheath, preventing ionization and ablation of the metal sheath caused by direct contact between the water-blocking powder in the semi-conductive buffer water-blocking tape and the metal sheath, thereby avoiding cable breakdown accidents caused by metal ablation; second, the addition of tinned copper wire to the cloth tape can put the buffer layer and the metal sheath at the same potential, improving electrical contact performance; third, the copper wire in the cloth tape is also tinned to prevent electrochemical corrosion of the copper wire by the water-blocking powder.

[0020] Preferably, the metal sheath is a corrugated aluminum sheath or a smooth aluminum sheath with a thickness of 1.0 to 3.0 mm. The non-metallic sheath is an extruded polyethylene sheath or a polyvinyl chloride sheath, including sheaths with flame retardant, rodent-proof, and termite-proof properties. The semiconductive layer is an extruded plastic semiconductive layer or a coated graphite layer with a thickness of approximately 0.5 mm.

[0021] The beneficial effects of the utility model are:

[0022] By providing a non-cross-linked inner shielding layer, a non-cross-linked polyethylene-based insulation layer, and a non-cross-linked outer shielding layer, and using non-cross-linked semi-conductive shielding material and polyethylene-based non-cross-linked insulation material as the inner shielding layer, insulation layer, and outer shielding layer of the high-voltage cable, the production process does not require cross-linking or degassing, greatly improving production efficiency and reducing production energy consumption. At the same time, the cables with the above structure are easy to recycle after retirement, solving the problems of high emissions, high energy consumption, and low production efficiency of traditional cross-linked insulated power cables. It is suitable for high-voltage and ultra-high-voltage power cables of 110 kV and above, and can also be promoted and applied in medium and low voltage power cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural diagram of a specific implementation method of the utility model.

[0024] In the above drawings: 11, conductor; 12, semi-conductive tape; 21, non-cross-linked inner shielding layer; 22, non-cross-linked polyethylene-based insulation layer; 23, non-cross-linked outer shielding layer; 31, buffer layer; 32, wire cloth tape; 33, metal sheath; 34, non-metallic sheath; 35, semi-conductive layer. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, in the description of the present invention, the terms "upper," "lower," "left," "right," "inner," "outer," and the like, indicating directions or positions, are based on the directions or positions shown in the accompanying drawings and are intended solely for the purpose of facilitating and simplifying the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific manner. Therefore, they should not be construed as limiting the present invention. The terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] like Figure 1 As shown, the utility model provides a recyclable non-cross-linked insulated cable, including a conductor 11, which is a compressed round stranded conductor, a split conductor, or a shaped stranded conductor. The conductor 11 is coated with a semi-conductive tape 12, which is formed by wrapping 1 to 2 layers of semi-conductive nylon tape with a thickness of 0.10 to 0.14 mm. Its advantages are: first, it prevents the electric field concentration of burrs in the conductor 11 from causing shield breakdown, and second, it reduces the shielding material from sinking into the gaps in the conductor 11, thereby reducing material loss. The semi-conductive tape 12 is coated with a non-cross-linked inner shielding layer 21, a non-cross-linked polyethylene-based insulation layer 22, and a non-cross-linked outer shielding layer 23 in sequence. The non-cross-linked inner shielding layer 21 is made of an ultra-smooth non-cross-linked semi-conductive shielding material composed of polyethylene resin, carbon black, and an antioxidant, and is extruded without a cross-linking agent. The non-cross-linked polyethylene-based insulation layer 22 is made of one or more of high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, and an antioxidant, and is made by extruding an ultra-clean polyethylene-based non-cross-linked insulation material without a cross-linking agent. The density of the high-density polyethylene is 0.941 to 0.965 g / gm. 3 The density of medium density polyethylene is 0.926~0.940g / cm 3 The non-cross-linked outer shielding layer 23 is made of an ultra-smooth non-cross-linked semi-conductive shielding material composed of polyethylene resin, carbon black, and antioxidant and does not contain a cross-linking agent, and is extruded.

[0027] Common insulation and semi-conductive shielding materials containing crosslinkers, such as dicumyl peroxide (DCP), are prone to decomposition during the extrusion process, producing trace amounts of pre-crosslinked products. These products accumulate over long extrusion cycles, leading to scorching of the insulation and requiring frequent downtime for cleaning. Furthermore, DCP decomposes under the high temperatures of 200-300°C in vulcanized pipes, forming a cross-linked network of cross-linked polyethylene molecules, which consumes significant amounts of electricity. Decomposition of DCP produces byproducts such as acetophenone, methane, and α-methylstyrene, which remain within the insulation, increasing dielectric loss and degrading electrical performance. The insulation core requires five to seven days of heating and degassing to gradually remove the gases, extending lead times. Once these crosslinked networks are formed, insulation and semi-conductive shielding materials containing crosslinkers are difficult to degrade, making recycling difficult, energy-intensive, and inefficient. Traditional disposal methods such as landfill, incineration, and thermal cracking result in significant environmental pollution and carbon emissions.

[0028] In the above embodiment, by providing a non-crosslinked inner shielding layer 21, a non-crosslinked polyethylene-based insulation layer 22, and a non-crosslinked outer shielding layer 23, a non-crosslinked semi-conductive shielding material and a polyethylene-based non-crosslinked insulation material are used as the inner shielding layer, insulation layer, and outer shielding layer of the high-voltage cable. The production process does not require crosslinking or degassing, greatly improving production efficiency and reducing production energy consumption. Furthermore, the cable structure is easy to recycle after retirement, solving the problems of high emissions, high energy consumption, and low production efficiency associated with traditional cross-linked insulated power cables. It is suitable for high-voltage and ultra-high-voltage power cables of 110 kV and above, and can also be promoted and applied to medium- and low-voltage power cables.

[0029] More specifically, the thickness of the non-cross-linked inner shielding layer 21 is 1.5 to 2.0 mm, the thickness of the non-cross-linked polyethylene-based insulation layer 22 is 16.0 to 27.0 mm, and the thickness of the non-cross-linked outer shielding layer 23 is 1.0 to 1.5 mm. After the conductor 11 is twisted, gaps exist between the copper wires. Providing a non-cross-linked inner shielding layer 21 with a thickness of 1.5 to 2.0 mm can eliminate the increase in the electric field strength on the surface of the conductor 11 caused by the uneven surface of the conductor 11, making the inner surface of the insulation layer more rounded and smooth, and providing better electrical contact with the cable conductor 11, making the electric field distribution more uniform. The thickness of the non-cross-linked polyethylene-based insulation layer 22 is set to 16.0 to 27.0 mm, ensuring that the cable has high electrical insulation strength and can withstand high voltages of more than 110 kV. Providing a non-cross-linked outer shielding layer 23 with a thickness of 1.0 to 1.5 mm can make the outer surface of the insulation layer round and smooth, play a role in uniform electric field, and at the same time prevent insulation damage caused by external scratches. At the same time, the size of protrusions penetrating the non-cross-linked polyethylene-based insulation layer 22 at the interface between the non-cross-linked inner shielding layer 21 and the non-cross-linked polyethylene-based insulation layer 22 is less than 75 μm; the size of opaque impurities in the non-cross-linked polyethylene-based insulation layer 22 is less than 125 μm; and the size of protrusions penetrating the non-cross-linked polyethylene-based insulation layer 22 at the interface between the non-cross-linked outer shielding layer 23 and the non-cross-linked polyethylene-based insulation layer 22 is less than 75 μm. The non-cross-linked semi-conductive inner and outer shielding layers ensure that both the inner and outer surfaces of the non-cross-linked polyethylene-based insulation layer 22 are rounded and smooth, resulting in a uniform electric field distribution. However, if the protrusions are too large, they will damage the smoothness of the insulation surface, causing the electric field distribution to concentrate at the protrusions, reducing the withstand voltage of the cable insulation. In severe cases, the local electric field intensity may be too high, leading to breakdown. Therefore, the above size limits are imposed on the protrusions.

[0030] In addition, the non-cross-linked outer shielding layer 23 is sequentially coated with a buffer layer 31, a wire cloth tape 32, a metal sheath 33, a non-metallic sheath 34, and a semi-conductive layer 35. Specifically, the buffer layer 31 is made of two to three layers of 1.5-2.5mm thick semi-conductive buffer water-blocking tape, wrapped in overlapping or intermittent layers; the semi-conductive buffer water-blocking tape is provided with water-blocking powder. The wire cloth tape 32 is made of tinned copper wire with a diameter of 0.18-0.22mm, regularly interlaced on a semi-conductive nylon tape or semi-conductive polyester tape, the thickness of which is 0.4-0.5mm. Because the water-blocking powder is added to the semi-conductive buffer water-blocking tape, the presence of trace moisture in the air causes a metal electrochemical reaction between the water-blocking powder and the external aluminum material, causing aluminum corrosion and, in severe cases, cable breakdown. The structural design of the wire tape 32 serves the following functions: First, the semi-conductive nylon or polyester tape physically isolates the buffer layer 31 from the metal sheath 33, preventing ionization and ablation of the metal sheath 33 caused by direct contact between the water-blocking powder in the semi-conductive buffer tape and the metal sheath 33, thereby avoiding cable breakdown accidents caused by metal ablation. Second, the addition of tinned copper wire to the tape equilibrates the buffer layer 31 and the metal sheath 33, improving electrical contact performance. Third, the copper wire in the tape is also tinned to prevent electrochemical corrosion from the water-blocking powder. The metal sheath 33 is a corrugated or smooth aluminum sheath with a thickness of 1.0 to 3.0 mm. The non-metallic sheath 34 is an extruded polyethylene or polyvinyl chloride sheath, including those with flame retardant, rodent-proof, and termite-proof properties. The semiconductive layer 35 is a plastic extruded semiconductive layer 35 or a coated graphite layer with a thickness of about 0.5 mm.

[0031] A specific embodiment is listed below:

[0032] A recyclable 110kV rated voltage non-cross-linked polyethylene insulated high-voltage power cable. The conductor is a split conductor consisting of five split strands twisted together with a central core. The nominal cross-sectional area of the conductor is 1000mm 2The semi-conductive tape is made of two layers of 0.12mm thick semi-conductive nylon tape wrapped around each other. The non-cross-linked inner shielding layer is 1.7mm thick and is extruded from an ultra-smooth, non-cross-linked semi-conductive shielding material composed of polyethylene resin, carbon black, and antioxidants. It contains no chemical cross-linking agents. Protrusions that penetrate the insulation at the interface between the non-cross-linked inner shielding layer and the insulation layer do not exceed 75μm. The polyethylene-based non-cross-linked insulation layer is 16.0mm thick and is extruded from an ultra-clean, non-cross-linked polyethylene insulation material composed of high-density polyethylene, linear low-density polyethylene, and antioxidants. Opaque impurities in the polyethylene-based non-cross-linked insulation layer do not exceed 125μm. The non-cross-linked outer shielding layer is 1.0mm thick and is extruded from an ultra-smooth, non-cross-linked semi-conductive shielding material composed of polyethylene resin, carbon black, and antioxidants. Protrusions that penetrate the insulation at the interface between the non-cross-linked outer shielding layer and the insulation layer do not exceed 75μm. The buffer layer consists of three layers of 2.0mm thick semi-conductive buffer water-blocking tape, wrapped in an overlapping pattern. The wire cloth tape is a semi-conductive nylon tape with 0.2mm tinned copper wires arranged in a regular pattern, 0.45mm thick. The metal sheath is a 2.3mm thick corrugated aluminum sheath, the non-metallic sheath is a 4.5mm thick extruded flame-retardant polyethylene sheath, and the semi-conductive layer is a 0.5mm thick extruded plastic semi-conductive layer.

[0033] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present invention through logical analysis, reasoning, or limited experimentation based on the existing technology should be within the scope of protection defined by the claims.

Claims

1. A recyclable non-cross-linked insulated cable, characterized by: The invention comprises a conductor (11), wherein the conductor (11) is coated with a semi-conductive tape (12), and the semi-conductive tape (12) is coated with a non-cross-linked inner shielding layer (21), a non-cross-linked polyethylene-based insulating layer (22), and a non-cross-linked outer shielding layer (23) in sequence. The non-cross-linked outer shielding layer (23) is sequentially coated with a buffer layer (31), a metal wire cloth tape (32), a metal sheath (33), a non-metallic sheath (34) and a semi-conductive layer (35); The thickness of the non-crosslinked inner shielding layer (21) is 1.5 to 2.0 mm, the thickness of the non-crosslinked polyethylene-based insulating layer (22) is 16.0 to 27.0 mm, and the thickness of the non-crosslinked outer shielding layer (23) is 1.0 to 1.5 mm.

2. The recyclable non-cross-linked insulated cable according to claim 1, characterized in that: The size of the protrusions penetrating the non-cross-linked polyethylene-based insulating layer (22) at the interface between the non-cross-linked inner shielding layer (21) and the non-cross-linked polyethylene-based insulating layer (22) is less than 75 μm; the size of the opaque impurities in the non-cross-linked polyethylene-based insulating layer (22) is less than 125 μm; and the size of the protrusions penetrating the non-cross-linked polyethylene-based insulating layer (22) at the interface between the non-cross-linked outer shielding layer (23) and the non-cross-linked polyethylene-based insulating layer (22) is less than 75 μm.

3. The recyclable non-cross-linked insulated cable according to claim 1, characterized in that: The conductor (11) is a compressed circular stranded conductor, a split conductor, or a profiled stranded conductor.

4. The recyclable non-cross-linked insulated cable according to claim 1, wherein: The semi-conductive tape (12) is formed by wrapping 1 to 2 layers of semi-conductive nylon tape with a thickness of 0.10 to 0.14 mm.

5. The recyclable non-cross-linked insulated cable according to claim 1, wherein: The buffer layer (31) is made of 2 to 3 layers of semi-conductive buffer water-blocking tape with a thickness of 1.5 to 2.5 mm, which are made by overlapping or gap wrapping; the semi-conductive buffer water-blocking tape is provided with water-blocking powder.

6. The recyclable non-cross-linked insulated cable according to claim 5, characterized in that: The metal wire cloth tape (32) is formed by regularly interlacing tinned copper wires with a diameter of 0.18 to 0.22 mm on a semi-conductive nylon tape or a semi-conductive polyester fiber tape, and the thickness of the semi-conductive nylon tape or the semi-conductive polyester fiber tape is 0.4 to 0.5 mm.

7. The recyclable non-cross-linked insulated cable according to claim 1, wherein: The metal sheath (33) is a corrugated aluminum sheath or a smooth aluminum sheath with a thickness of 1.0 to 3.0 mm; the non-metallic sheath (34) is an extruded polyethylene sheath or a polyvinyl chloride sheath; and the semiconductive layer (35) is a plastic extruded semiconductive layer or a coated graphite layer with a thickness of about 0.5 mm.

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