A fireproof cable for subway

Abstract

The present invention relates to the technical field of cables, and specifically to a fireproof cable for subways, which includes a plurality of cable cores and a PET film layer; a mica tape winding layer, a copper mesh shielding layer and an outer sheath are sequentially coated outside the PET film layer; the outer sheath is made of the following raw materials in parts by weight: 50-60 parts of PVC resin, 8-15 parts of nylon 66 resin, 5-10 parts of aliphatic TPU, 5-8 parts of EVA-G-MAH, 3-5 parts of POE-G-MAH, 1-3 parts of calcium-zinc stabilizer, 10-20 parts of filler, 1-2 parts of polyethylene wax, 0.5-1 part of calcium stearate, 10-20 parts of flame retardant, 10-30 parts of plasticizer, 0.1-0.5 part of antioxidant. The outer sheath prepared by the present invention has excellent mechanical properties and excellent fireproof and flame-retardant properties. It not only has a high flame-retardant grade, but also generates little heat and smoke after combustion, and is an excellent material for preparing fireproof cables for subways.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and particularly to a fireproof cable for subways. Background Art

[0002] With the rapid development of urban rail transit, as a large-capacity public transportation vehicle, the subway can significantly reduce the use of private cars, thereby reducing carbon emissions and air pollution. It can also effectively transport a large number of passengers and reduce traffic congestion on the roads. However, the subway tunnel environment is enclosed and densely populated. Once a fire occurs, it will seriously threaten the lives of passengers. Therefore, laws and regulations have put forward higher requirements for the fireproof performance of subway cables. How to further improve the fireproof grade of subway cables and reduce the heat and smoke generated during combustion has become the current research focus. Summary of the Invention

[0003] Object of the Invention: Aiming at the above technical problems, the present invention proposes a fireproof cable for subways.

[0004] The technical solution adopted is as follows:

[0005] A fireproof cable for subways includes a plurality of cable cores and a PET film layer for fixing the plurality of cable cores;

[0006] The PET film layer is sequentially coated with a mica tape winding layer, a copper mesh shielding layer, and an outer sheath;

[0007] The outer sheath is made of the following raw materials in parts by weight:

[0008] 50 - 60 parts of PVC resin, 8 - 15 parts of nylon 66 resin, 5 - 10 parts of aliphatic TPU, 5 - 8 parts of EVA - G - MAH, 3 - 5 parts of POE - G - MAH, 1 - 3 parts of calcium - zinc stabilizer, 10 - 20 parts of filler, 1 - 2 parts of polyethylene wax, 0.5 - 1 part of calcium stearate, 10 - 20 parts of flame retardant, 10 - 30 parts of plasticizer, 0.1 - 0.5 part of antioxidant;

[0009] The flame retardant consists of a DOPO derivative and zirconium phosphate particles coated with silicone resin.

[0010] Further, the mass ratio of the DOPO derivative to the zirconium phosphate particles coated with silicone resin is 1 - 5:1 - 5.

[0011] Further, the structural formula of the DOPO derivative is as follows:

[0012] .

[0013] Further, the preparation method of the DOPO derivative is as follows:

[0014] The reaction of 4,4',4''-methylidynetriphenol with 2,2-bis(hydroxymethyl)propionic acid gives intermediate 1. Intermediate 1 reacts with epichlorohydrin to obtain intermediate 2, and finally, intermediate 2 reacts with DOPO to obtain the DOPO derivative.

[0015] Further, the preparation method of the organosilicon resin-coated zirconium phosphate particles is as follows:

[0016] Zirconium phosphate is pre-modified with tetramethylammonium hydroxide and KH-550 in sequence. PDMS and n-hexane are mixed, and an organotin catalyst is added to obtain a prepolymer solution. The pre-modified zirconium phosphate is dispersed in the prepolymer solution, ultrasonically dispersed, then heated to reflux, stirred and reacted for 1 - 10 h, and then tetraethyl orthosilicate is added and the reaction continues for 1 - 10 h.

[0017] Further, the preparation method of the organosilicon resin-coated zirconium phosphate particles is as follows:

[0018] Zirconium oxychloride octahydrate and phosphoric acid are mixed, and hydrothermally reacted in a sealed manner at 180 - 200 °C for 12 - 48 h. After the reaction, the precipitate is collected, washed and dried to obtain zirconium phosphate. Zirconium phosphate is dispersed in DMSO, and then tetramethylammonium hydroxide is added. After stirring and reacting for 1 - 10 h, the precipitate is collected, washed and dried, and then dispersed in the KH-550 hydrolysis solution, stirred at 60 - 80 °C for 1 - 5 h, the precipitate is collected, washed and dried to obtain the pre-modified zirconium phosphate. PDMS and n-hexane are mixed, and an organotin catalyst is added to obtain a prepolymer solution. The pre-modified zirconium phosphate is dispersed in the prepolymer solution, ultrasonically dispersed, then heated to reflux, stirred and reacted for 1 - 10 h, and then tetraethyl orthosilicate is added and the reaction continues for 1 - 10 h.

[0019] Further, the filler is composed of calcium carbonate and calcined kaolin with a mass ratio of 1 - 5:1 - 5.

[0020] Further, the plasticizer is at least one of epoxy soybean oil, dioctyl phthalate, and dioctyl terephthalate.

[0021] Further, the antioxidant is antioxidant 1010 and / or antioxidant 168.

[0022] Further, the cable core is composed of a conductor and a cross-linked polyethylene inner sheath.

[0023] It has the following beneficial effects:

[0024] The present invention provides a fire-resistant cable for subways. The PVC resin in the outer sheath is used as the matrix material. Nylon 66 resin has high tensile strength, rigidity and heat resistance. After being added, it can greatly increase the mechanical properties of the PVC resin. However, due to the polarity difference, the compatibility between the two is not good. The present invention forms a gradient compatibilization network by adding an EVA-G-MAH and POE-G-MAH dual grafting system. The maleic anhydride groups contained therein can form chemical bonding with the amino groups of the nylon 66 resin. At the same time, its main chain is compatible with the polar structure of the PVC, and a transition layer can be formed at the interface between the PVC and the nylon, enhancing the interfacial bonding force, reducing phase separation, and improving the mechanical properties. Aliphatic TPU has good compatibility with the PVC resin and is dispersed in the PVC matrix. It can absorb impact energy through the "sea-island structure", prevent crack propagation under external force, improve the mechanical strength of the outer sheath, and also reduce the melt viscosities of the PVC resin and the nylon 66 resin, broaden the processing temperature window, improve the blend fluidity, and reduce the risk of thermal decomposition;

[0025] DOPO derivatives can decompose at high temperatures to generate phosphorus-containing free radicals. These free radicals can capture active free radicals such as H· and HO· generated during the combustion process, thereby interrupting the combustion chain reaction and slowing down the flame spread. The triphenyl structure increases the carbon content, and can decompose to form a denser carbon layer covering the surface of the cable, playing a role in physical isolation and reducing the smoke density. The hyperbranched epoxy group structure improves the dispersibility and compatibility of the DOPO derivatives in the resin matrix, avoiding the deterioration of the mechanical properties caused by the addition of DOPO derivatives. As a typical layered compound, zirconium phosphate can not only play a role in strengthening and toughening, but also its high heat resistance, high barrier property and self-extinguishing property can play the role of an inorganic flame retardant. The coating of silicone resin not only improves the dispersibility of zirconium phosphate and avoids agglomeration, but also the decomposition products of the silicone resin react with the decomposition products of zirconium phosphate to generate a phosphorus-silicon glass body, jointly constructing a ceramic skeleton to form a continuous and dense ceramic layer, isolating oxygen, delaying combustion, reducing heat, smoke or the release of toxic gases;

[0026] The outer sheath pellets prepared by the present invention have excellent mechanical properties and excellent fire resistance and flame retardancy. Not only is the flame retardancy grade high, but also the heat and smoke generation after combustion are small. It is an excellent material for preparing fire-resistant cables for subways. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the fire-resistant cable for subways in Embodiment 1. The reference numerals in the figure respectively represent:

[0028] 1 - copper conductor, 2 - cross-linked polyethylene inner sheath, 3 - PET film layer, 4 - mica tape wrapping layer, 5 - copper mesh shielding layer, 6 - outer sheath.

[0029] Figure 2Synthesis route diagram of the DOPO derivative in Example 1. Detailed implementation mode

[0030] For those without specific conditions noted in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase. Technologies not mentioned in the present invention refer to the prior art. Unless otherwise specified, the following examples and comparative examples are parallel tests and adopt the same treatment steps and parameters.

[0031] PVC resin: TL-1000, Tianjin LG Dagu Chemical Co., Ltd.;

[0032] Nylon 66 resin: 20NSP NC, Invista;

[0033] Aliphatic TPU: WHT-1190, Wanhua Chemical;

[0034] EVA-G-MAH: SG-MAH-1003, Nanjing Julong Technology Co., Ltd.;

[0035] POE-G-MAH: FB521A, Jia Yirong Polymer (Shanghai) Co., Ltd.;

[0036] Calcium-zinc stabilizer: CEZ-T™ 8100, Baerlocher;

[0037] Calcium carbonate: CC-2000, Jiangxi Guangyuan Chemical Industry;

[0038] Calcined kaolin: LK-800, Fujian Longyan Kaolin Co., Ltd.;

[0039] Polyethylene wax: JRF-200, Shanghai Jinhu Rili;

[0040] Calcium stearate: DZ-202, Qingdao Deda Zhicheng Chemical Industry;

[0041] Flame retardant: self-made;

[0042] Plasticizer DOTP: Palatinol® DOTP, BASF;

[0043] Antioxidant 1010: JY-1010, Beijing Jiyi New Materials.

[0044] Example 1:

[0045] A fire-resistant cable for subway, comprising four cable cores and a PET film layer 3 for fixing the four cable cores;

[0046] The cable core is composed of a copper conductor 1 and a cross-linked polyethylene inner sheath 2;

[0047] The PET film layer is successively coated with a mica tape winding layer 4, a copper mesh shielding layer 5 and an outer sheath 6;

[0048] The outer sheath 6 is made of the following raw materials in parts by weight:

[0049] 55 parts of PVC resin, 12 parts of nylon 66 resin, 8 parts of aliphatic TPU, 6 parts of EVA-G-MAH, 4 parts of POE-G-MAH, 2 parts of calcium-zinc stabilizer, 10 parts of calcium carbonate, 10 parts of calcined kaolin, 1.5 parts of polyethylene wax, 0.5 part of calcium stearate, 15 parts of flame retardant, 20 parts of plasticizer DOTP, 0.25 part of antioxidant 1010;

[0050] The flame retardant is composed of a DOPO derivative and organosilicon resin-coated zirconium phosphate particles with a mass ratio of 1:2.

[0051] The structural formula of the DOPO derivative is as follows:

[0052] 。

[0053] The preparation method of the DOPO derivative is as follows:

[0054] Under the condition of nitrogen protection, add 4,4',4''-methylidynetriphenol (0.1 mol), 2,2-bis(hydroxymethyl)propionic acid (0.3 mol) and catalyst p-toluenesulfonic acid (1 g) into a flask, stir and heat up to 140 °C for reaction for 5 h. During the reaction, use a water separator to separate the water generated by the reaction. After the reaction is completed, stop introducing nitrogen, connect a vacuum pump and distill under reduced pressure until no water distillate comes out. Cool to room temperature, dissolve with an appropriate amount of acetone, recrystallize in toluene, filter by suction to obtain intermediate 1. Under the condition of nitrogen protection, add intermediate 1 (0.01 mol) and epichlorohydrin (0.08 mol) into a flask, stir and heat to 110 °C, then add 4.5 g of sodium hydroxide, continue the reaction for 1 h and then cool to room temperature. Add 100 ml of dichloromethane and 100 ml of deionized water, fully stir and then separate the dichloromethane phase. Dry with anhydrous sodium sulfate and then concentrate under reduced pressure to obtain intermediate 2. Under nitrogen protection, add DOPO (15 mmol) into a flask, heat until dissolved and then add intermediate 2 (5 mmol), keep warm and stir for reaction for 10 h, and then discharge at room temperature to obtain the DOPO derivative, ESI-MS(m / z)(M + ) : theoretical value 1625.59, measured value 1625.13. The synthesis route is shown in Figure 2 。

[0055] The preparation method of the organosilicon resin-coated zirconium phosphate particles is as follows:

[0056] 100 g of zirconium oxychloride octahydrate was mixed with 1000 ml of 12 mol / L phosphoric acid, and then poured into a hydrothermal reactor with a polytetrafluoroethylene inner liner. After sealing, the temperature was raised to 200 °C for hydrothermal reaction for 48 h. After the reaction, the precipitate was collected, washed with deionized water until neutral, then dried in vacuum and ground to obtain zirconium phosphate. 30 g of zirconium phosphate was added to 100 ml of DMSO, and after stirring for 30 min under ultrasonic waves to disperse, 15 g of tetramethylammonium hydroxide was added, and stirring was continued at room temperature for 1 h, then filtered. The precipitate was collected, washed with deionized water, and then dried in vacuum. After mixing KH-550, absolute ethanol and deionized water in a mass ratio of 2:7.2:0.8, the mixture was stirred at 50 °C for 30 min to obtain a KH-550 hydrolysis solution. According to a mass ratio of 1:10, the dried zirconium phosphate was added to the KH-550 hydrolysis solution, stirred at 70 °C for 2 h, then cooled to room temperature and filtered. The precipitate was washed with deionized water and then dried in vacuum to obtain pre-modified zirconium phosphate. 50 g of PDMS was mixed with 500 ml of n-hexane, 0.1 g of dibutyltin dilaurate was added as a catalyst, and the mixture was stirred and reacted for 30 min to obtain a prepolymer solution. 25 g of pre-modified zirconium phosphate was added to the prepolymer solution, ultrasonically dispersed for 30 min, then heated to reflux, stirred and reacted for 5 h, then 5 g of tetraethyl orthosilicate was added, and the reaction was continued for 1 h, then the temperature was restored to room temperature, filtered, and the precipitate was collected, washed with deionized water and absolute ethanol, and then dried in vacuum to obtain organosilicon resin-coated zirconium phosphate particles.

[0057] The preparation method of the outer sheath granule is as follows:

[0058] The raw materials were placed in a high-speed mixer, mixed at 65 °C for 10 min, and then transferred to a twin-screw extruder. Extrusion granulation was carried out at a main machine speed of 80 r / min and a temperature of 150 - 170 °C to obtain the outer sheath granule.

[0059] Example 2:

[0060] A fire-resistant cable for subway includes four cable cores and a PET film layer 3 for fixing the four cable cores;

[0061] The cable core is composed of a copper conductor 1 and a cross-linked polyethylene inner sheath 2;

[0062] Outside the PET film layer, there are sequentially coated with a mica tape wrapping layer 4, a copper mesh shielding layer 5 and an outer sheath 6;

[0063] The outer sheath 6 is made of the following raw materials in parts by weight:

[0064] 60 parts of PVC resin, 15 parts of nylon 66 resin, 10 parts of aliphatic TPU, 8 parts of EVA-G-MAH, 5 parts of POE-G-MAH, 3 parts of calcium-zinc stabilizer, 10 parts of calcium carbonate, 10 parts of calcined kaolin, 2 parts of polyethylene wax, 1 part of calcium stearate, 15 parts of flame retardant, 30 parts of plasticizer DOTP, 0.5 part of antioxidant 1010;

[0065] The flame retardant is composed of a DOPO derivative and organosilicon resin-coated zirconium phosphate particles with a mass ratio of 1:2.

[0066] The structure and preparation method of the DOPO derivative are the same as those in Example 1;

[0067] The preparation method of the organosilicon resin-coated zirconium phosphate particles is the same as that in Example 1;

[0068] The preparation method of the outer sheath pellets is as follows:

[0069] Place the raw materials in a high-speed mixer, mix at 65 °C for 10 min, then transfer to a twin-screw extruder and extrude and pelletize at a main machine speed of 80 r / min and a temperature of 150 - 170 °C to obtain the outer sheath pellets.

[0070] Example 3:

[0071] A fire-resistant cable for subway, comprising four cable cores and a PET film layer 3 for fixing the four cable cores;

[0072] The cable core is composed of a copper conductor 1 and a cross-linked polyethylene inner sheath 2;

[0073] Outside the PET film layer, there are successively coated with a mica tape winding layer 4, a copper mesh shielding layer 5 and an outer sheath 6;

[0074] The outer sheath 6 is made of the following raw materials in parts by weight:

[0075] 50 parts of PVC resin, 8 parts of nylon 66 resin, 5 parts of aliphatic TPU, 5 parts of EVA-G-MAH, 3 parts of POE-G-MAH, 1 part of calcium-zinc stabilizer, 10 parts of calcium carbonate, 10 parts of calcined kaolin, 1 part of polyethylene wax, 0.5 part of calcium stearate, 15 parts of flame retardant, 10 parts of plasticizer DOTP, 0.1 part of antioxidant 1010;

[0076] The flame retardant is composed of a DOPO derivative and organosilicon resin-coated zirconium phosphate particles with a mass ratio of 1:2.

[0077] The structure and preparation method of the DOPO derivative are the same as those in Example 1;

[0078] The preparation method of the organosilicon resin-coated zirconium phosphate particles is the same as that in Example 1;

[0079] The preparation method of the outer sheath granule is as follows:

[0080] Place the raw materials in a high-speed mixer, mix them at 65 °C for 10 min, then transfer them to a twin-screw extruder, and extrude and pelletize at a main machine speed of 80 r / min and a temperature of 150 - 170 °C to obtain the outer sheath granule.

[0081] Comparative Example 1:

[0082] It is basically the same as Example 1, except that nylon 66 resin is not added to the raw materials of the outer sheath 6.

[0083] Comparative Example 2:

[0084] It is basically the same as Example 1, except that aliphatic TPU is not added to the raw materials of the outer sheath 6.

[0085] Comparative Example 3:

[0086] It is basically the same as Example 1, except that EVA-G-MAH is not added to the raw materials of the outer sheath 6.

[0087] Comparative Example 4:

[0088] It is basically the same as Example 1, except that POE-G-MAH is not added to the raw materials of the outer sheath 6.

[0089] Comparative Example 5:

[0090] It is basically the same as Example 1, except that DOPO derivatives are not added to the flame retardant.

[0091] Comparative Example 6:

[0092] It is basically the same as Example 1, except that zirconium phosphate particles coated with silicone resin are not added to the flame retardant.

[0093] Comparative Example 7:

[0094] It is basically the same as Example 1, except that commercially available zirconium phosphate (purchased from Fujian Ruisen New Materials Co., Ltd.) is used instead of zirconium phosphate particles coated with silicone resin.

[0095] Performance Test

[0096] Make specimens from the outer sheath granules in Examples 1 - 3 and Comparative Examples 1 - 7 of the present invention for performance testing.

[0097] The tensile strength is carried out according to the provisions of GB / T 1040.3 - 2006 "Determination of Tensile Properties of Plastics - Part 3 Test Conditions for Films and Sheets", the specimen is of Type 5, and the tensile rate is 100 mm / min.

[0098] Limiting Oxygen Index (LOI) test: Tested on an oxygen index measuring instrument according to ASTM D2863-77 standard. The size of the test specimen is 100mm×6.5mm×3mm.

[0099] The changes of heat release and smoke release with time during the combustion of the test specimen were tested according to ISO5660-1 standard. The radiation power was 50kW. The size of the test specimen was 100mm×100mm×3mm. The total heat release (THR) and total smoke release (TSP) were measured.

[0100] The test results are shown in Table 1 below:

[0101] Table 1:

[0102]

[0103] It can be seen from Table 1 above that the outer sheath pellets prepared by the present invention have excellent mechanical properties and excellent fireproof and flame-retardant properties. Not only the flame-retardant grade is high, but also the heat and smoke generated after combustion are small. It is an excellent material for preparing fireproof cables for subways.

[0104] By comparing Example 1 with Comparative Examples 1-4, it can be seen that the addition of nylon 66 resin, aliphatic TPU, EVA-G-MAH and POE-G-MAH plays a positive role in improving the mechanical properties of the outer sheath;

[0105] By comparing Example 1 with Comparative Examples 5-6, it can be seen that the addition of DOPO derivatives and organosilicon resin-coated zirconium phosphate particles plays a positive role in improving the fireproof and flame-retardant properties of the outer sheath;

[0106] By comparing Example 1 with Comparative Example 7, it can be seen that compared with commercially available zirconium phosphate, the organosilicon resin-coated zirconium phosphate particles prepared by the present invention have a greater improvement in the fireproof and flame-retardant properties of the outer sheath.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fireproof cable for subway, characterized in that: It comprises a plurality of cable cores and a PET film layer for fixing the plurality of cable cores; The PET film layer is sequentially coated with a mica tape wrapping layer, a copper mesh shielding layer and an outer sheath; The outer sheath is made of the following raw materials in parts by weight: 50-60 parts of PVC resin, 8-15 parts of nylon 66 resin, 5-10 parts of aliphatic TPU, 5-8 parts of EVA-G-MAH, 3-5 parts of POE-G-MAH, 1-3 parts of calcium zinc stabilizer, 10-20 parts of filler, 1-2 parts of polyethylene wax, 0.5-1 parts of calcium stearate, 10-20 parts of flame retardant, 10-30 parts of plasticizer, 0.1-0.5 parts of antioxidant; The flame retardant is composed of DOPO derivatives and silicone resin-coated zirconium phosphate particles; The structural formula of the DOPO derivative is as follows: 。 2. The fireproof cable for subway according to claim 1, characterized in that: The mass ratio of the DOPO derivative to the silicone resin-coated zirconium phosphate particles is 1-5:1-5.

3. The fireproof cable for subway according to claim 1, characterized in that: The preparation method of the DOPO derivative is as follows: 4,4',4''-methylenetriphenol reacts with 2,2-dihydroxymethylpropionic acid to obtain intermediate 1, intermediate 1 reacts with epichlorohydrin to obtain intermediate 2, and intermediate 2 finally reacts with DOPO to obtain the DOPO derivative.

4. The fireproof cable for subway according to claim 1, characterized in that: The preparation method of the silicone resin-coated zirconium phosphate particles is as follows: Zirconium phosphate is modified with tetramethylammonium hydroxide and KH-550 in sequence to obtain premodified zirconium phosphate, PDMS is mixed with n-hexane, an organic tin catalyst is added to obtain a prepolymer solution, the premodified zirconium phosphate is dispersed in the prepolymer solution, the temperature is raised to reflux after ultrasonic dispersion, the reaction is stirred for 1-10 hours, and then ethyl orthosilicate is added, and the reaction is continued for 1-10 hours.

5. The fireproof cable for subway according to claim 4, characterized in that: The preparation method of the silicone resin-coated zirconium phosphate particles is as follows: Zirconium oxychloride octahydrate is mixed with phosphoric acid, and a sealed hydrothermal reaction is carried out at 180-200°C for 12-48h. After the reaction is completed, the precipitate is collected, washed, and dried to obtain zirconium phosphate. The zirconium phosphate is dispersed in DMSO, and tetramethylammonium hydroxide is added. The precipitate is collected after stirring for 1-10h, washed, dried, and then dispersed in KH-550 hydrolyzate, stirred at 60-80°C for 1-5h, and the precipitate is collected. The precipitate is washed and dried to obtain premodified zirconium phosphate. PDMS is mixed with n-hexane, and an organic tin catalyst is added to obtain a prepolymer solution. The premodified zirconium phosphate is dispersed in the prepolymer solution, and the temperature is raised to reflux after ultrasonic dispersion. After stirring for 1-10h, ethyl orthosilicate is added, and the reaction is continued for 1-10h.

6. The fireproof cable for subway according to claim 1, characterized in that: The filler consists of calcium carbonate and calcined kaolin in a mass ratio of 1-5:1-5.

7. The fireproof cable for subway according to claim 1, characterized in that: The plasticizer is at least one of epoxidized soybean oil, dioctyl phthalate and dioctyl terephthalate.

8. The fireproof cable for subway according to claim 1, characterized in that: The antioxidant is antioxidant 1010 and / or antioxidant 168.

9. The fireproof cable for subway according to claim 1, characterized in that: The cable core consists of a conductor and a cross-linked polyethylene inner sheath.

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