Flame-retardant aerial insulated cable and method for manufacturing the same

Abstract

The application relates to the technical field of electric wire and cable, and discloses a flame-retardant overhead insulated cable and a preparation method thereof. The flame-retardant overhead insulated cable comprises, from inside to outside, a conductor, a shielding layer and an insulation layer. The insulation layer comprises the following raw materials in parts by weight: 100-130 parts of low-density polyethylene, 20-25 parts of a silicon carbide-based composite flame retardant, 5-7 parts of an ethylene-unsaturated carboxylic acid copolymer, 1-2 parts of an antioxidant, 1.5-2 parts of a crosslinking agent, 8-12 parts of calcium carbonate and 3-5 parts of a compatibilizer. The silicon carbide-based composite flame retardant comprises, from inside to outside, a silicon carbide skeleton, a magnesium-aluminum hydrotalcite coating layer and a silicon-boron impregnated modification layer. The raw materials of the silicon-boron impregnated modification layer comprise sodium silicate and sodium borate in a mass ratio of 1-3:1. The above technical scheme solves the problem of insufficient flame-retardant performance of the overhead insulated cable in the related art.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, specifically to a flame-retardant overhead insulated cable and its preparation method. Background Technology

[0002] Overhead insulated cables offer advantages such as convenient overhead conductor installation, economical cost, and reliable insulation protection. They are widely used in urban and rural power distribution networks, industrial parks, residential areas, and complex outdoor environments such as forests and areas with many trees, making them one of the core components of modern power grid construction and renovation. Currently, conventional overhead insulated cables mostly use ordinary polyolefin materials, which generally lack sufficient flame retardant properties. With the continuous expansion of power grid coverage and increasingly stringent outdoor power safety requirements, these cables can no longer meet the stringent safety requirements for cables in high-density power consumption areas and key fire prevention locations. Therefore, it is necessary to develop a flame-retardant overhead insulated cable and its preparation method. Summary of the Invention

[0003] This invention proposes a flame-retardant overhead insulated cable and its preparation method, which solves the problem of insufficient flame-retardant performance of overhead insulated cables in related technologies.

[0004] The technical solution of the present invention is as follows: This invention proposes a flame-retardant overhead insulated cable, which comprises, from the inside out, a conductor, a shielding layer, and an insulation layer; the insulation layer comprises the following raw materials in parts by weight: 100-130 parts of low-density polyethylene, 20-25 parts of silicon carbide-based composite flame retardant, 5-7 parts of ethylene-unsaturated carboxylic acid copolymer, 1-2 parts of antioxidant, 1.5-2 parts of crosslinking agent, 8-12 parts of calcium carbonate, and 3-5 parts of compatibilizer; The silicon carbide-based composite flame retardant comprises, from the inside out, a silicon carbide skeleton, a magnesium aluminum hydrotalcite coating layer, and a silicon boron impregnation modification layer. The raw materials for the silicon-boron impregnation modified layer include sodium silicate and sodium borate in a mass ratio of 1 to 3:1, preferably 2:1.

[0005] As a further technical solution, the magnesium-aluminum hydrotalcite coating layer is prepared by co-precipitation method.

[0006] As a further technical solution, the mass of the silicon boron impregnation modified layer is 5% to 15% of the mass of the magnesium aluminum hydrotalcite coating layer, preferably 10%.

[0007] As a further technical solution, the preparation method of the silicon carbide-based composite flame retardant includes the following steps: A1. After mixing silicon carbide with an aqueous nitric acid solution, the mixture is filtered, washed, and dried to obtain a silicon carbide framework; A2. Disperse magnesium nitrate and aluminum nitrate in water to form a salt solution; disperse sodium hydroxide and sodium carbonate in water to form an alkaline solution; then mix the silicon carbide framework with the salt solution and alkaline solution, adjust the pH to 10-11, and then crystallize, filter, wash and dry to form a magnesium aluminum hydrotalcite coating layer, thus obtaining a silicon carbide framework with a magnesium aluminum hydrotalcite coating layer. A3. Disperse sodium silicate and sodium borate in water, then add the silicon carbide skeleton with magnesium aluminum hydrotalcite coating for impregnation, and then filter, wash, dry and calcine to form a silicon boron impregnation modified layer to obtain the silicon carbide-based composite flame retardant.

[0008] As a further technical solution, in step A1, the concentration of the nitric acid aqueous solution is 1 mol / L; the mass-to-volume ratio of silicon carbide to the nitric acid aqueous solution is 1 g: 13~17 mL, preferably 1 g: 15 mL.

[0009] As a further technical solution, in step A1, the mixing temperature is 75~85℃ and the mixing time is 1.5~2.5h.

[0010] As a further technical solution, the mass ratio of magnesium nitrate to aluminum nitrate is 1.5~2.5:1, preferably 2:1.

[0011] As a further technical solution, the total mass of magnesium nitrate and aluminum nitrate is 20% to 23% of the mass of silicon carbide, preferably 21%; the total mass of sodium hydroxide is 30% to 50% of the total mass of magnesium nitrate and aluminum nitrate, preferably 40%; and the total mass of sodium carbonate is 15% to 25% of the total mass of magnesium nitrate and aluminum nitrate, preferably 20%.

[0012] As a further technical solution, in step A2, the mass ratio of magnesium nitrate and aluminum nitrate to the volume ratio of water in the salt solution is 1g:5~8mL, preferably 1g:6mL.

[0013] As a further technical solution, in step A2, the mass ratio of sodium hydroxide and sodium carbonate to water in the alkaline solution is 1g:8~12mL, preferably 1g:10mL.

[0014] As a further technical solution, in step A2, the crystallization temperature is 90~95℃ and the crystallization time is 7~9h.

[0015] As a further technical solution, in step A3, the ratio of the total mass of sodium silicate and sodium borate to the volume of water is 1g:12~15mL, preferably 1g:15mL.

[0016] As a further technical solution, in step A3, the impregnation temperature is 40~60℃ and the impregnation time is 1~3h; the calcination temperature is 200~300℃ and the calcination time is 1~2h.

[0017] As a further technical solution, the ethylene-unsaturated carboxylic acid copolymer includes an ethylene-methacrylic acid copolymer and an ethylene-methacrylic acid-acrylate terpolymer with a mass ratio of 6~8:5.

[0018] As a further technical solution, the antioxidant includes one or more of antioxidant 1010, antioxidant 168 and antioxidant 1076.

[0019] As a further technical solution, the crosslinking agent includes one or two of triallyl isocyanurate and trimethylolpropane trimethacrylate.

[0020] As a further technical solution, the compatibilizer includes maleic anhydride-grafted polyethylene.

[0021] This invention also proposes a method for preparing a flame-retardant overhead insulated cable, which includes the following steps: weaving a shielding layer material onto the outside of a conductor to obtain the shielding layer; then uniformly mixing the raw materials of the insulation layer and extruding them onto the outside of the shielding layer to form the insulation layer, thereby obtaining the flame-retardant overhead insulated cable.

[0022] As a further technical solution, the conductor is a copper conductor; the shielding layer material is galvanized copper wire.

[0023] The working principle and beneficial effects of this invention are as follows: This invention improves the flame-retardant performance of overhead insulated cables by adding a silicon carbide-based composite flame retardant to the insulation layer. The outermost silicon-boron impregnated modified layer of the silicon carbide-based composite flame retardant forms a glassy or ceramic protective layer during combustion, effectively isolating oxygen and heat. The middle magnesium-aluminum hydrotalcite coating decomposes and absorbs heat when heated, lowering the surrounding temperature and simultaneously generating oxides that cover the material surface, further isolating oxygen from contact with combustibles. The innermost silicon carbide skeleton has high thermal stability, delaying heat transfer. The synergistic effect of these components further enhances the flame-retardant performance of the insulation layer. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In the following examples and comparative examples, the low-density polyethylene is MG70; the silicon carbide has a particle size of 2.5 μm; and the maleic anhydride-grafted polyethylene is ADMER L2100.

[0026] Example 1 A flame-retardant overhead insulated cable comprises, from the inside out, a conductor, a shielding layer, and an insulation layer. The insulation layer comprises the following raw materials in parts by weight: 100 parts low-density polyethylene, 20 parts silicon carbide-based composite flame retardant, 5 parts ethylene-unsaturated carboxylic acid copolymer, 1 part antioxidant 1010, 1.5 parts triallyl isocyanurate, 8 parts calcium carbonate, and 3 parts maleic anhydride-grafted polyethylene; wherein the ethylene-unsaturated carboxylic acid copolymer is ethylene-methacrylic acid copolymer, model 9910. A method for preparing a silicon carbide-based composite flame retardant includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 75℃ for 2.5 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 14 parts magnesium nitrate and 4 parts aluminum nitrate in water to form a salt solution. The ratio of the mass of magnesium nitrate and aluminum nitrate to the volume of water in the salt solution is 1 g: 6 mL. Disperse 8.4 parts of sodium hydroxide and 4.2 parts of sodium carbonate in water to form an alkaline solution; in the alkaline solution, the ratio of the total mass of sodium hydroxide and sodium carbonate to the volume of water is 1 g: 10 mL. Subsequently, the silicon carbide framework was mixed with salt solution and alkaline solution, the pH was adjusted to 10, and crystallized at 90°C for 9 hours. After filtration, washing and drying, a magnesium aluminum hydrotalcite coating layer was formed, and a silicon carbide framework with a magnesium aluminum hydrotalcite coating layer was obtained. A3. Disperse 1.4 parts of sodium silicate and 0.7 parts of sodium borate in water, with the total mass ratio of sodium silicate and sodium borate to the volume of water being 1g:15mL; then add a silicon carbide skeleton with a magnesium aluminum hydrotalcite coating, impregnate at 40℃ for 3h, then filter, wash, dry, and calcine at 200℃ for 2h to form a silicon boron impregnation modified layer, thus obtaining a silicon carbide-based composite flame retardant; A method for preparing a flame-retardant overhead insulated cable includes the following steps: Galvanized copper wire is braided onto the outside of a copper conductor to obtain a shielding layer; then, the raw materials for the insulation layer are mixed evenly and extruded onto the outside of the shielding layer to form an insulation layer, thus obtaining a flame-retardant overhead insulated cable.

[0027] Example 2 A flame-retardant overhead insulated cable comprises, from the inside out, a conductor, a shielding layer, and an insulation layer. The insulation layer comprises the following raw materials in parts by weight: 120 parts low-density polyethylene, 23 parts silicon carbide-based composite flame retardant, 6 parts ethylene-unsaturated carboxylic acid copolymer, 1.5 parts antioxidant 168, 1.8 parts trimethylolpropane trimethacrylate, 10 parts calcium carbonate, and 4 parts maleic anhydride-grafted polyethylene; wherein the ethylene-unsaturated carboxylic acid copolymer is ethylene-methacrylic acid copolymer, model 9910. A method for preparing a silicon carbide-based composite flame retardant includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 80℃ for 2 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 14 parts magnesium nitrate and 4 parts aluminum nitrate in water to form a salt solution. The ratio of the mass of magnesium nitrate and aluminum nitrate to the volume of water in the salt solution is 1 g: 6 mL. Disperse 8.4 parts of sodium hydroxide and 4.2 parts of sodium carbonate in water to form an alkaline solution; in the alkaline solution, the ratio of the total mass of sodium hydroxide and sodium carbonate to the volume of water is 1 g: 10 mL. Subsequently, the silicon carbide framework was mixed with salt solution and alkaline solution, and the pH was adjusted to 10.5. After crystallization at 92°C for 8 hours, the mixture was filtered, washed and dried to form a magnesium aluminum hydrotalcite coating layer, thus obtaining a silicon carbide framework with a magnesium aluminum hydrotalcite coating layer. A3. Disperse 1.4 parts of sodium silicate and 0.7 parts of sodium borate in water, with the total mass ratio of sodium silicate and sodium borate to the volume of water being 1g:15mL; then add a silicon carbide skeleton with a magnesium aluminum hydrotalcite coating, impregnate at 50℃ for 2h, then filter, wash, dry, and calcine at 250℃ for 1.5h to form a silicon boron impregnation modified layer, thus obtaining a silicon carbide-based composite flame retardant; A method for preparing a flame-retardant overhead insulated cable includes the following steps: Galvanized copper wire is braided onto the outside of a copper conductor to obtain a shielding layer; then, the raw materials for the insulation layer are mixed evenly and extruded onto the outside of the shielding layer to form an insulation layer, thus obtaining a flame-retardant overhead insulated cable.

[0028] Example 3 A flame-retardant overhead insulated cable comprises, from the inside out, a conductor, a shielding layer, and an insulation layer. The insulation layer comprises the following raw materials in parts by weight: 130 parts low-density polyethylene, 25 parts silicon carbide-based composite flame retardant, 7 parts ethylene-unsaturated carboxylic acid copolymer, 2 parts antioxidant 1076, 2 parts trimethylolpropane trimethacrylate, 12 parts calcium carbonate, and 5 parts maleic anhydride-grafted polyethylene; wherein the ethylene-unsaturated carboxylic acid copolymer is ethylene-methacrylic acid copolymer, model 9910. A method for preparing a silicon carbide-based composite flame retardant includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 85℃ for 1.5 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 14 parts magnesium nitrate and 4 parts aluminum nitrate in water to form a salt solution. The ratio of the mass of magnesium nitrate and aluminum nitrate to the volume of water in the salt solution is 1 g: 6 mL. Disperse 8.4 parts of sodium hydroxide and 4.2 parts of sodium carbonate in water to form an alkaline solution; in the alkaline solution, the ratio of the total mass of sodium hydroxide and sodium carbonate to the volume of water is 1 g: 10 mL. Subsequently, the silicon carbide framework was mixed with salt solution and alkaline solution, and the pH was adjusted to 11. After crystallization at 95°C for 7 hours, the mixture was filtered, washed and dried to form a magnesium aluminum hydrotalcite coating layer, thus obtaining a silicon carbide framework with a magnesium aluminum hydrotalcite coating layer. A3. Disperse 1.4 parts of sodium silicate and 0.7 parts of sodium borate in water, with the total mass ratio of sodium silicate and sodium borate to the volume of water being 1g:15mL; then add a silicon carbide skeleton with a magnesium aluminum hydrotalcite coating, impregnate at 60℃ for 1h, then filter, wash, dry, and calcine at 300℃ for 1h to form a silicon boron impregnation modified layer, thus obtaining a silicon carbide-based composite flame retardant; A method for preparing a flame-retardant overhead insulated cable includes the following steps: Galvanized copper wire is braided onto the outside of a copper conductor to obtain a shielding layer; then, the raw materials for the insulation layer are mixed evenly and extruded onto the outside of the shielding layer to form an insulation layer, thus obtaining a flame-retardant overhead insulated cable.

[0029] Example 4 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 6:5.

[0030] Example 5 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 7:5.

[0031] Example 6 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 8:5.

[0032] Example 7 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 5:5.

[0033] Example 8 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 9:5.

[0034] Example 9 Compared with Example 1, the only difference in this example is that the ethylene-unsaturated carboxylic acid copolymer in this example is an ethylene-methacrylic acid-acrylate terpolymer, model AX8900.

[0035] Comparative Example 1 Compared with Example 1, the only difference in this comparative example is that the silicon carbide-based composite flame retardant is replaced with an equal amount of silicon carbide.

[0036] Comparative Example 2 Compared with Example 1, the only difference in this comparative example is that the preparation method of the silicon carbide-based composite flame retardant in this comparative example includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 75℃ for 2.5 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 14 parts magnesium nitrate and 4 parts aluminum nitrate in water to form a salt solution. The ratio of the mass of magnesium nitrate and aluminum nitrate to the volume of water in the salt solution is 1 g: 6 mL. Disperse 8.4 parts of sodium hydroxide and 4.2 parts of sodium carbonate in water to form an alkaline solution; in the alkaline solution, the ratio of the total mass of sodium hydroxide and sodium carbonate to the volume of water is 1 g: 10 mL. Subsequently, the silicon carbide framework was mixed with salt and alkali solutions, the pH was adjusted to 10, and the mixture was crystallized at 90°C for 9 hours. After filtration, washing, and drying, a magnesium-aluminum hydrotalcite coating layer was formed, resulting in a silicon carbide-based composite flame retardant.

[0037] Comparative Example 3 Compared with Example 1, the only difference in this comparative example is that the preparation method of the silicon carbide-based composite flame retardant in this comparative example includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 75℃ for 2.5 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 1.4 parts of sodium silicate and 0.7 parts of sodium borate in water, with the total mass ratio of sodium silicate and sodium borate to the volume of water being 1 g: 15 mL; then add a silicon carbide skeleton, impregnate at 40°C for 3 h, then filter, wash, dry, and calcine at 200°C for 2 h to form a silicon boron impregnation modified layer, thus obtaining a silicon carbide-based composite flame retardant.

[0038] Comparative Example 4 Compared with Example 1, the only difference in this comparative example is that the preparation method of the silicon carbide-based composite flame retardant in this comparative example includes the following steps: A1. Mix 100 parts of silicon carbide with 1 mol / L nitric acid aqueous solution at 75℃ for 2.5 h, then filter, wash and dry to obtain a silicon carbide framework; the mass-volume ratio of silicon carbide to nitric acid aqueous solution is 1 g: 15 mL. A2. Disperse 1.4 parts of sodium silicate and 0.7 parts of sodium borate in water, with the total mass of sodium silicate and sodium borate to the volume of water being 1 g: 15 mL; then add a silicon carbide framework, impregnate at 40°C for 3 h, then filter, wash, dry, and calcine at 200°C for 2 h to obtain a silicon carbide framework with a silicon boron impregnation modification layer. A3. Disperse 14 parts magnesium nitrate and 4 parts aluminum nitrate in water to form a salt solution. The ratio of the mass of magnesium nitrate and aluminum nitrate to the volume of water in the salt solution is 1 g: 6 mL. Disperse 8.4 parts of sodium hydroxide and 4.2 parts of sodium carbonate in water to form an alkaline solution; in the alkaline solution, the ratio of the total mass of sodium hydroxide and sodium carbonate to the volume of water is 1 g: 10 mL. Subsequently, the silicon carbide skeleton with the silicon boron impregnation modification layer was mixed with salt solution and alkaline solution, and after adjusting the pH to 10, it was crystallized at 90℃ for 9 hours. After filtration, washing and drying, a magnesium aluminum hydrotalcite coating layer was formed, and a silicon carbide-based composite flame retardant was obtained.

[0039] Experimental Example 1 The insulation layers of the flame-retardant overhead insulated cables prepared in Examples 1-3 and Comparative Examples 1-4 were tested for oxygen index according to standard GB / T2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test"; the sample type was I, the ignition method was Method A, and the average of the results of 3 samples in each group was taken as the final result, and the result was retained to one decimal place; the test results are shown in Table 1: Table 1. Test results of oxygen index of insulation layer of flame-retardant overhead insulated cables

[0040] The results in Table 1 show that the silicon carbide-based composite flame retardant prepared in this invention can improve the flame retardant performance of the insulation layer when added to the insulation layer of overhead insulated cables.

[0041] Experiment Example 2 Following the methods in GB / T 2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods - Thickness and Dimensional Measurement - Mechanical Properties Test", the insulation layer of the flame-retardant overhead insulated cables prepared in Examples 1, 4-9 was made into dumbbell specimens with a thickness of 2 mm for tensile strength testing; the total spacing between the clamps was 34 mm, and the clamp moving speed was 25 mm / min. The test results are shown in Table 2: Table 2. Test results of tensile strength of flame-retardant overhead insulated cables

[0042] The results in Table 2 show that when the ethylene-unsaturated carboxylic acid copolymer is composed of ethylene-methacrylic acid copolymer (model 9910) and ethylene-methacrylic acid-acrylate terpolymer (model AX8900) in a mass ratio of 6~8:5, adding it to the insulation layer of the flame-retardant overhead insulated cable can improve the tensile strength of the overhead insulated cable insulation layer.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flame-retardant overhead insulated cable, characterized in that, From the inside out, it includes a conductor, a shielding layer, and an insulating layer; the insulating layer comprises the following raw materials in parts by weight: 100-130 parts of low-density polyethylene, 20-25 parts of silicon carbide-based composite flame retardant, 5-7 parts of ethylene-unsaturated carboxylic acid copolymer, 1-2 parts of antioxidant, 1.5-2 parts of crosslinking agent, 8-12 parts of calcium carbonate, and 3-5 parts of compatibilizer; The silicon carbide-based composite flame retardant comprises, from the inside out, a silicon carbide skeleton, a magnesium aluminum hydrotalcite coating layer, and a silicon boron impregnation modification layer. The raw materials for the silicon-boron impregnation modified layer include sodium silicate and sodium borate in a mass ratio of 1 to 3:

1.

2. The flame-retardant overhead insulated cable according to claim 1, characterized in that, The magnesium-aluminum hydrotalcite coating was prepared by co-precipitation.

3. The flame-retardant overhead insulated cable according to claim 1, characterized in that, The mass of the silicon boron impregnation modified layer is 5% to 15% of the mass of the magnesium aluminum hydrotalcite coating layer.

4. The flame-retardant overhead insulated cable according to claim 1, characterized in that, The preparation method of the silicon carbide-based composite flame retardant includes the following steps: A1. After mixing silicon carbide with an aqueous nitric acid solution, the mixture is filtered, washed, and dried to obtain a silicon carbide framework; A2. Disperse magnesium nitrate and aluminum nitrate in water to form a salt solution; disperse sodium hydroxide and sodium carbonate in water to form an alkaline solution; then mix the silicon carbide framework with the salt solution and alkaline solution, adjust the pH to 10-11, and then crystallize, filter, wash and dry to form a magnesium aluminum hydrotalcite coating layer, thus obtaining a silicon carbide framework with a magnesium aluminum hydrotalcite coating layer. A3. Disperse sodium silicate and sodium borate in water, then add the silicon carbide skeleton with magnesium aluminum hydrotalcite coating for impregnation, and then filter, wash, dry and calcine to form a silicon boron impregnation modified layer to obtain the silicon carbide-based composite flame retardant.

5. A flame-retardant overhead insulated cable according to claim 4, characterized in that, In step A2, the crystallization temperature is 90~95℃ and the crystallization time is 7~9h.

6. A flame-retardant overhead insulated cable according to claim 1, characterized in that, The ethylene-unsaturated carboxylic acid copolymer includes ethylene-methacrylic acid copolymer and ethylene-methacrylic acid-acrylate terpolymer with a mass ratio of 6~8:

5.

7. A flame-retardant overhead insulated cable according to claim 1, characterized in that, The compatibilizer includes maleic anhydride-grafted polyethylene.

8. A flame-retardant overhead insulated cable according to claim 1, characterized in that, The antioxidant includes one or more of antioxidant 1010, antioxidant 168, and antioxidant 1076.

9. A flame-retardant overhead insulated cable according to claim 1, characterized in that, The crosslinking agent includes one or both of triallyl isocyanurate and trimethylolpropane trimethacrylate.

10. A method for preparing a flame-retardant overhead insulated cable, used to prepare a flame-retardant overhead insulated cable as described in any one of claims 1 to 9, characterized in that, Includes the following steps: The shielding material is woven onto the outside of the conductor to obtain the shielding layer; then the raw materials of the insulation layer are mixed evenly and extruded onto the outside of the shielding layer to form the insulation layer, thus obtaining the flame-retardant overhead insulated cable.

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