Flame-retardant medium-voltage power cable

Abstract

The invention relates to the technical field of cables, and provides a flame-retardant medium-voltage power cable and a preparation method thereof. The flame-retardant medium-voltage power cable comprises a conductor and a flame-retardant layer, the flame-retardant layer is prepared from the following raw materials in parts by weight: 65 to 75 parts of ethylene-vinyl acetate copolymer, 25 to 35 parts of polyolefin elastomer, 10 to 12 parts of maleic anhydride grafted polyethylene, 10 to 14 parts of phosphorus-nitrogen modified wollastonite, 8 to 10 parts of polydopamine / silane double-layer modified magnesium hydroxide, 3 to 5 parts of nano zinc borate, 0.6 to 1 part of antioxidant and 0.5 to 0.7 part of calcium stearate. According to the flame-retardant medium-voltage power cable prepared in the invention, the flame-retardant performance is improved, and the flame-retardant stability of the cable is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cables, and in particular to a flame-retardant medium-voltage power cable. Background Art

[0002] With rapid socioeconomic development and accelerating urbanization, electricity demand continues to grow. As key equipment for power transmission and distribution, power cables are playing an increasingly important role in power systems. Medium-voltage power cables are widely used in urban power grids, industrial and mining enterprises, and building power distribution. Across all cable applications, fire hazards remain a significant threat to the safe and stable operation of power systems. Once a fire occurs, ordinary power cables can easily burn and spread rapidly, causing not only power outages but also potentially serious secondary disasters such as casualties, property damage, and environmental pollution.

[0003] While the flame-retardant materials and technologies used in existing flame-retardant medium-voltage power cables can meet basic flame-retardant requirements to a certain extent, some flame-retardant materials easily decompose and become ineffective at high temperatures, making them unable to effectively and continuously prevent the spread of flames. Furthermore, the flame-retardant properties of existing cables can fluctuate under varying environmental conditions (such as high temperature and humidity), affecting their reliability in practical applications. To address these technical issues, the present invention proposes a new flame-retardant medium-voltage power cable. Summary of the Invention

[0004] The present invention provides a flame-retardant medium-voltage power cable and a preparation method thereof, which improves the ability of the flame-retardant material to continuously and effectively prevent the spread of flames at high temperatures and improves the stability of the cable's flame-retardant performance under different environmental conditions.

[0005] The technical solutions of the present invention are as follows: In the first aspect, the present invention proposes a flame-retardant medium-voltage power cable, comprising a conductor and a flame-retardant layer, wherein the flame-retardant layer is composed of the following raw materials in parts by weight: 65-75 parts of ethylene-vinyl acetate copolymer, 25-35 parts of polyolefin elastomer, 10-12 parts of maleic anhydride grafted polyethylene, 10-14 parts of phosphorus-nitrogen modified wollastonite, 8-10 parts of polydopamine / silane double-layer modified magnesium hydroxide, 3-5 parts of nano-zinc borate, 0.6-1 part of antioxidant, and 0.5-0.7 part of calcium stearate.

[0006] As a further technical solution, the preparation method of the phosphorus-nitrogen modified wollastonite includes: immersing the wollastonite in a mixture of ethanol and water for ultrasonic dispersion, adding ethyl orthosilicate, hydrolyzing at a pH of 9.0±0.2, then adding hexachlorocyclotriphosphazene for reaction, centrifuging, washing, and drying to obtain the product.

[0007] As a further technical solution, the hydrolysis temperature is 45-55° C., and the hydrolysis time is 100-140 min; the reaction temperature is 65-75° C., and the reaction time is 3-5 h.

[0008] As a further technical solution, the usage ratio of wollastonite, ethanol, water, ethyl orthosilicate and hexachlorocyclotriphosphazene is 100g:380-420mL:80-120mL:15-18g:8.2-9.8g.

[0009] As a further technical solution, the preparation method of the polydopamine / silane double-layer modified magnesium hydroxide includes: dispersing Mg(OH)2 in Tris-HCl buffer, adding dopamine and stirring to polymerize, dispersing in ethanol after centrifugation, adding a silane coupling agent, refluxing the reaction, filtering and drying after completion.

[0010] As a further technical solution, the polymerization temperature is 25±1° C., and the polymerization time is 11-13 h; the reflux reaction temperature is 75-85° C., and the time is 3-5 h.

[0011] As a further technical solution, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0012] As a further technical solution, the weight ratio of Mg(OH)2, dopamine and silane coupling agent is 10:0.2-0.4:0.1-0.2.

[0013] In a second aspect, the present invention provides a method for preparing a flame-retardant medium-voltage power cable, comprising the following steps: mixing ethylene-vinyl acetate copolymer, polyolefin elastomer and maleic anhydride grafted polyethylene at a temperature of 85-95°C for 2-4 minutes; adding phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide in multiple batches, mixing for 2-3 minutes each time; subsequently adding nano-zinc borate, calcium stearate and an antioxidant and mixing for 3-5 minutes, heating to 100-120°C, continuing to mix for 4-6 minutes, and standing at room temperature for 24 hours after discharging to obtain a flame-retardant layer rubber compound; and melt-extruding the coated conductor through a twin-screw extruder to form the flame-retardant medium-voltage power cable.

[0014] As a further technical solution, the multiple times are 2-4 times, with an interval of 2-3 minutes each time; the temperature of the first zone of the twin-screw extruder is 105-115°C, the temperature of the second zone is 115-125°C, the temperature of the third zone is 125-135°C, and the die head temperature is 130-140°C.

[0015] The working principle and beneficial effects of the present invention are: The present invention utilizes multiple components to cooperate with each other to jointly improve the flame retardant performance of the cable. Different flame retardant ingredients have different flame retardant mechanisms. Phosphorus-nitrogen modified wollastonite combines the flame retardant properties of phosphorus and nitrogen. Phosphorus can promote the formation of a solid carbon layer during combustion, which can isolate oxygen and heat transfer, thereby preventing the spread of flames; nitrogen can produce a gas-phase flame retardant effect, releasing non-combustible gas during combustion, diluting the concentration of combustible gas and oxygen, and reducing the severity of combustion. In the polydopamine / silane double-layer modified magnesium hydroxide, the magnesium hydroxide itself will decompose and absorb heat when heated, while releasing water vapor, which plays a role in cooling and diluting combustible gases; and after the double-layer modification of polydopamine and silane, not only the dispersibility of magnesium hydroxide is improved, but also its interfacial bonding force with the matrix material is enhanced, so that it can better play a flame retardant role. Nano zinc borate also undergoes a series of chemical reactions during combustion, absorbing heat and generating flame retardant substances, further enhancing the flame retardant effect. Multiple flame retardant ingredients work synergistically through different flame retardant mechanisms, greatly improving the cable's ability to continuously and effectively prevent the spread of flames at high temperatures.

[0016] The present invention performs phosphorus-nitrogen synergistic modification on wollastonite to prepare phosphorus-nitrogen modified wollastonite with special properties. The presence of phosphorus and nitrogen elements in the phosphorus-nitrogen modified wollastonite enables the flame retardant layer to have the dual effects of gas-phase flame retardancy and solid-phase carbonization during the combustion process. Phosphorus promotes the formation of a dense carbon layer in the base material at high temperatures. The carbon layer can prevent the transfer of heat and oxygen and slow down the combustion rate; the non-combustible gas released by nitrogen can dilute the concentration of combustible gas and inhibit the progress of the combustion reaction. This phosphorus-nitrogen synergistic effect greatly improves the flame retardant efficiency of the flame retardant layer and can effectively prevent the spread of flames under different environmental conditions.

[0017] This invention uses polydopamine and silane to perform a dual-layer modification on magnesium hydroxide, improving its performance. The polydopamine layer enhances the dispersion of the filler, allowing the flame-retardant filler to be evenly distributed within the flame-retardant layer, preventing filler agglomeration and deterioration of flame retardancy and mechanical properties. The silane layer strengthens the filler-matrix interface, improving the adhesion between the filler and the matrix, preventing filler migration and dislodging, and ensuring the stability of the cable's flame retardancy over long-term use.

[0018] The flame-retardant medium-voltage power cable of the present invention can still maintain good flame retardant properties under different environmental conditions, such as wet-heat cycles. Both phosphorus-nitrogen synergy and double-layer modification can effectively inhibit moisture from eroding the filler interface to a certain extent. In a wet-heat environment, moisture easily enters the interface between the filler and the matrix, resulting in a decrease in interfacial bonding force, affecting the flame retardant properties and mechanical properties of the cable. The special structure of phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide can prevent the intrusion of moisture and maintain good bonding between the filler and the matrix, thereby ensuring the performance stability of the cable under different environmental conditions. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0020] It should be noted that the ethylene-vinyl acetate copolymer in the present invention, CAS No.: 24937-78-8, MDL No.: MFCD00133996, Article No.: P815474, was purchased from Maclean's Reagent; the polyolefin elastomer is POE-8842, produced by Dow Chemical, USA, with the trade name ENGAGE 8842; maleic anhydride grafted polyethylene, CAS No.: 9006-26-2, MDL No.: MFCD00212579, Article No.: P875047, was purchased from Maclean's Reagent; wollastonite, 800 mesh, was purchased from Xinyu Southern Wollastonite Co., Ltd.; Mg(OH)2, CAS No.: 1309-42-8, MDL No.: MFCD00011104, Article No.: M768990, was purchased from Maclean's Reagent.

[0021] Example 1 The present embodiment provides a flame-retardant medium-voltage power cable, comprising a conductor and a flame-retardant layer, wherein the flame-retardant layer is composed of the following raw materials in parts by weight: 70 parts of ethylene-vinyl acetate copolymer, 30 parts of polyolefin elastomer, 11 parts of maleic anhydride grafted polyethylene, 12 parts of phosphorus-nitrogen modified wollastonite, 9 parts of polydopamine / silane double-layer modified magnesium hydroxide, 4 parts of nano-zinc borate, 0.8 parts of antioxidant 1010, and 0.6 parts of calcium stearate.

[0022] The preparation method of phosphorus-nitrogen modified wollastonite includes: immersing 100 g of wollastonite in a mixture of 400 mL of ethanol and 100 mL of water and ultrasonically dispersing the mixture for 30 minutes, adding 16 g of ethyl orthosilicate, adjusting the pH to 9.0 with aqueous ammonia, hydrolyzing the mixture at 50° C. for 120 minutes, then adding 9 g of hexachlorocyclotriphosphazene and reacting the mixture at 70° C. for 4 hours, centrifuging and washing the mixture, and drying the mixture at 120° C. for 6 hours to obtain the obtained product. The preparation method of polydopamine / silane double-layer modified magnesium hydroxide includes: dispersing 10g of Mg(OH)2 in 150mL of Tris-HCl buffer with a pH of 8.5, adding 0.3g of dopamine, stirring and polymerizing at 25°C and 200rpm for 12h, centrifuging and dispersing in 100mL of ethanol, adding 0.15g of γ-aminopropyltriethoxysilane, and reflux reacting at 80°C for 4h. After completion, filtering and vacuum drying at 80°C to constant weight to obtain the obtained product; The method for preparing the flame-retardant medium-voltage power cable comprises the following steps: First, phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are pretreated at 80°C for 6 hours, and then ethylene-vinyl acetate copolymer, polyolefin elastomer and maleic anhydride grafted polyethylene are mixed at 90°C for 3 minutes; phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are added in three times, with an interval of 2.5 minutes each time and mixing for 2.5 minutes each time; then nano zinc borate, calcium stearate and antioxidant are added and mixed for 4 minutes, the temperature is raised to 110°C, and mixing is continued for 5 minutes. After discharging, the material is kept at room temperature for 24 hours to obtain a flame retardant layer compound rubber; the conductor is melt-extruded through a twin-screw extruder to form a flame retardant medium voltage power cable, the temperature of the first zone of the twin-screw extruder is 110°C, the temperature of the second zone is 120°C, the temperature of the third zone is 130°C, and the temperature of the die head is 135°C.

[0023] Example 2 This embodiment provides a flame-retardant medium-voltage power cable, comprising a conductor and a flame-retardant layer, wherein the flame-retardant layer is composed of the following raw materials in parts by weight: 65 parts of ethylene-vinyl acetate copolymer, 25 parts of polyolefin elastomer, 10 parts of maleic anhydride grafted polyethylene, 10 parts of phosphorus-nitrogen modified wollastonite, 8 parts of polydopamine / silane double-layer modified magnesium hydroxide, 3 parts of nano-zinc borate, 0.6 parts of antioxidant 1010, and 0.5 parts of calcium stearate.

[0024] The preparation method of phosphorus-nitrogen modified wollastonite includes: immersing 100 g of wollastonite in a mixture of 380 mL of ethanol and 80 mL of water, ultrasonically dispersing the mixture for 30 minutes, adding 15 g of ethyl orthosilicate, adjusting the pH to 9.0 with aqueous ammonia, hydrolyzing the mixture at 45° C. for 100 minutes, then adding 8.2 g of hexachlorocyclotriphosphazene, reacting the mixture at 65° C. for 3 hours, centrifuging and washing the mixture, and drying the mixture at 120° C. for 6 hours. The preparation method of polydopamine / silane double-layer modified magnesium hydroxide includes: dispersing 10g of Mg(OH)2 in 140mL of Tris-HCl buffer with a pH of 8.5, adding 0.2g of dopamine, stirring and polymerizing at 25°C and 150rpm for 11 hours, centrifuging and dispersing in 95mL of ethanol, adding 0.1g of γ-aminopropyltriethoxysilane, and reflux reacting at 75°C for 3 hours. After completion, filtering and vacuum drying at 80°C to constant weight to obtain the obtained product; The method for preparing the flame-retardant medium-voltage power cable comprises the following steps: First, phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are pretreated at 80°C for 6 hours, and then ethylene-vinyl acetate copolymer, polyolefin elastomer and maleic anhydride grafted polyethylene are mixed at 85°C for 2 minutes; phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are added in two batches, with an interval of 2 minutes each time and mixing for 2 minutes each time; then nano zinc borate, calcium stearate and antioxidant are added and mixed for 3 minutes, the temperature is raised to 100°C, and mixing is continued for 4 minutes. After discharging, the material is kept at room temperature for 24 hours to obtain a flame retardant layer compound rubber; the conductor is melt-extruded through a twin-screw extruder to form a flame retardant medium voltage power cable, the temperature of the first zone of the twin-screw extruder is 105°C, the temperature of the second zone is 115°C, the temperature of the third zone is 125°C, and the temperature of the die head is 130°C.

[0025] Example 3 This embodiment provides a flame-retardant medium-voltage power cable, comprising a conductor and a flame-retardant layer, wherein the flame-retardant layer is composed of the following raw materials in parts by weight: 75 parts of ethylene-vinyl acetate copolymer, 35 parts of polyolefin elastomer, 12 parts of maleic anhydride grafted polyethylene, 14 parts of phosphorus-nitrogen modified wollastonite, 10 parts of polydopamine / silane double-layer modified magnesium hydroxide, 5 parts of nano-zinc borate, 1 part of antioxidant 1010, and 0.7 parts of calcium stearate.

[0026] The preparation method of phosphorus-nitrogen modified wollastonite includes: immersing 100 g of wollastonite in a mixture of 420 mL of ethanol and 120 mL of water, ultrasonically dispersing the mixture for 30 minutes, adding 18 g of ethyl orthosilicate, adjusting the pH to 9.0 with aqueous ammonia, hydrolyzing the mixture at 55° C. for 140 minutes, then adding 9.8 g of hexachlorocyclotriphosphazene, reacting the mixture at 75° C. for 5 hours, centrifuging and washing the mixture, and drying the mixture at 120° C. for 6 hours. The preparation method of polydopamine / silane double-layer modified magnesium hydroxide includes: dispersing 10g of Mg(OH)2 in 160mL of Tris-HCl buffer with a pH of 8.5, adding 0.4g of dopamine, and stirring and polymerizing at 25°C and 250rpm for 13h, dispersing the mixture in 105mL of ethanol after centrifugation, adding 0.2g of γ-aminopropyltriethoxysilane, and reflux reacting at 85°C for 5h. After completion, filtering and vacuum drying at 80°C to constant weight to obtain the obtained product; The method for preparing the flame-retardant medium-voltage power cable comprises the following steps: First, phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are pretreated at 80°C for 6 hours, and then ethylene-vinyl acetate copolymer, polyolefin elastomer and maleic anhydride grafted polyethylene are mixed at 95°C for 4 minutes; phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are added in 4 times, with an interval of 3 minutes each time and mixing for 3 minutes each time; then nano zinc borate, calcium stearate and antioxidant are added and mixed for 5 minutes, the temperature is raised to 120°C, and mixing is continued for 6 minutes. After discharging, the material is kept at room temperature for 24 hours to obtain a flame retardant layer compound rubber; the conductor is melt-extruded through a twin-screw extruder to form a flame retardant medium voltage power cable, the temperature of the first zone of the twin-screw extruder is 115°C, the temperature of the second zone is 125°C, the temperature of the third zone is 135°C, and the temperature of the die head is 140°C.

[0027] Comparative Example 1 In this comparative example, phosphorus-nitrogen modified wollastonite is replaced by nitrogen-modified wollastonite, and the preparation method includes: immersing 100 g of wollastonite in a mixture of 400 mL of ethanol and 100 mL of water and ultrasonically dispersing it for 30 minutes, adding 9 g of hexachlorocyclotriphosphazene and reacting it at a temperature of 70° C. for 4 hours, centrifuging and washing, and drying it at 120° C. for 6 hours. The rest is the same as in Comparative Example 1, and the preparation steps are the same as in Comparative Example 1.

[0028] Comparative Example 2 In this comparative example, the phosphorus-nitrogen modified wollastonite is replaced by phosphorus-modified wollastonite, and the preparation method includes: immersing 100 g of wollastonite in a mixture of 400 mL of ethanol and 100 mL of water and ultrasonically dispersing it for 30 minutes, adding 16 g of ethyl orthosilicate, adjusting the pH to 9.0 with ammonia water, hydrolyzing it at a temperature of 50°C for 120 minutes, centrifuging and washing, and drying it at 120°C for 6 hours. The rest is the same as that of Comparative Example 1, and the preparation steps are the same as those of Comparative Example 1.

[0029] Comparative Example 3 In this comparative example, the phosphorus-nitrogen modified wollastonite was replaced by unmodified wollastonite, and the rest was the same as in comparative example 1, and the preparation steps were the same as in comparative example 1.

[0030] Comparative Example 4 This comparative example does not include phosphorus-nitrogen modified wollastonite, and the rest is the same as that of comparative example 1, and the preparation steps are the same as those of comparative example 1.

[0031] Comparative Example 5 In this comparative example, the polydopamine / silane double-layer modified magnesium hydroxide is replaced by polydopamine-modified magnesium hydroxide, and the preparation method includes: dispersing 10g of Mg(OH)2 in 150mL of Tris-HCl buffer with a pH of 8.5, adding 0.3g of dopamine, and stirring and polymerizing at a temperature of 25°C and 200rpm for 12h. After completion, filtering and vacuum drying at 80°C to constant weight to obtain the obtained product; the rest is the same as that of Comparative Example 1, and the preparation steps are the same as those of Comparative Example 1.

[0032] Comparative Example 6 In this comparative example, the polydopamine / silane double-layer modified magnesium hydroxide is replaced by a silane double-layer modified magnesium hydroxide; the preparation method comprises: dispersing 10 g of Mg(OH)2 in 100 mL of ethanol, adding 0.15 g of γ-aminopropyltriethoxysilane, and refluxing the mixture at 80°C for 4 h. After completion, filtering the mixture and vacuum drying the mixture at 80°C to a constant weight. The rest of the preparation steps are the same as those in comparative example 1.

[0033] Comparative Example 7 In this comparative example, the polydopamine / silane double-layer modified magnesium hydroxide was replaced by unmodified magnesium hydroxide, and the rest was the same as in comparative example 1, and the preparation steps were the same as in comparative example 1.

[0034] Comparative Example 8 This comparative example does not include polydopamine / silane double-layer modified magnesium hydroxide, and the rest is the same as that of comparative example 1, and the preparation steps are the same as those of comparative example 1.

[0035] Test Example 1: The flame-retardant medium-voltage power cables prepared in Examples 1-4 and Comparative Examples 1-8 were subjected to the following tests: Limiting Oxygen Index (LOI): Tested in accordance with GB / T 2406.2-2009, sample size 100 mm × 6.5 mm × 3 mm; Vertical burning grade: tested in accordance with GB / T 18380.12-2008, sample size 125 mm × 13 mm × 3 mm, flame application time 60 s; Peak heat release rate (pHRR): tested according to ISO 5660-1:2015, sample size 100 mm × 100 mm × 3 mm, radiant power 50 kW / m²; Smoke density (Ds): Tested in accordance with GB / T 8323.2-2008, sample size 25 mm × 25 mm × 3 mm, flame power 25.5 W; Tensile strength: Tested in accordance with GB / T1040.2-2006 standard, the specimen is dumbbell-shaped, the tensile speed is 50mm / min; Tensile strength (MPa) = maximum load (N) / specimen cross-sectional area (mm 2 ); Elongation at break (%) = (gauge length at break - original gauge length) / original gauge length × 100%; Thermal aging performance: Tested in accordance with GB / T 2951.12-2008. Hang the specimens in an aging chamber, avoiding contact with the chamber wall or overlap between specimens. Set the temperature to 135°C for 168 hours. Remove the specimens after expiration and cool them in a standard environment (23±2°C, 50±10%RH) for 24 hours. The flame retardant performance test results are shown in Table 1 below: Table 1

[0036] The mechanical and thermal aging performance test results are shown in Table 2 below: Table 2

[0037] The results of the special environmental stability test are shown in Table 3 below: Table 3

[0038] In summary, the indicators of Examples 1-3 are better than those of the comparative examples in all aspects. Comparative Example 1 lacks the phosphorus element, the solid phase carbon layer is insufficiently generated, and the flame retardant efficiency is reduced; Comparative Example 2 lacks the nitrogen element, the gas phase flame retardant fails, and the smoke suppression ability is reduced; Comparative Example 3 has unmodified wollastonite agglomerates, and the flame retardancy / mechanical properties deteriorate simultaneously; Comparative Example 4 completely lacks the wollastonite skeleton, the carbon layer strength is insufficient, and the environmental stability collapses; Comparative Example 5 lacks the silane layer, the interface bonding force is weak, and the filler is easy to migrate and fall off; Comparative Example 6 lacks the polydopamine layer, the filler dispersion is poor, and the flame retardant efficiency is reduced; Comparative Example 7 has unmodified magnesium hydroxide, agglomerates severely, and the smoke suppression / flame retardant function fails; Comparative Example 8 completely lacks magnesium hydroxide, the solid phase flame retardant collapses, and the smoke surges.

[0039] Therefore, Comparative Examples 1-2 demonstrate the essential role of both phosphorus and nitrogen. When only phosphorus or nitrogen is retained, the LOI decreases by >5% and the smoke density increases by >100%, confirming that phosphorus-nitrogen synergy produces both gas-phase flame retardancy and solid-phase charring. Comparative Examples 5-6 demonstrate the essential role of both layers. When modified alone, the mechanical retention rate decreases by >5%, while the pHRR increases by >40%, indicating that the polydopamine layer enhances filler dispersibility and the silane layer strengthens the filler-matrix interface. Furthermore, after wet-heat cycling in Example 1, the LOI remains at 98%, demonstrating that both phosphorus-nitrogen synergy and dual-layer modification can effectively inhibit moisture erosion at the filler interface to a certain extent.

[0040] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flame retardant medium voltage power cable, characterized in that: The invention comprises a conductor and a flame retardant layer, wherein the flame retardant layer is composed of the following raw materials in parts by weight: 65-75 parts of ethylene-vinyl acetate copolymer, 25-35 parts of polyolefin elastomer, 10-12 parts of maleic anhydride grafted polyethylene, 10-14 parts of phosphorus-nitrogen modified wollastonite, 8-10 parts of polydopamine / silane double-layer modified magnesium hydroxide, 3-5 parts of nano zinc borate, 0.6-1 part of antioxidant, and 0.5-0.7 part of calcium stearate.

2. The flame-retardant medium voltage power cable according to claim 1, characterized in that: The preparation method of the phosphorus-nitrogen modified wollastonite comprises: immersing the wollastonite in a mixture of ethanol and water for ultrasonic dispersion, adding ethyl orthosilicate, hydrolyzing at a pH of 9.0±0.2, then adding hexachlorocyclotriphosphazene for reaction, centrifuging, washing, and drying to obtain the product.

3. The flame-retardant medium voltage power cable according to claim 2, characterized in that: The hydrolysis temperature is 45-55° C., and the hydrolysis time is 100-140 min; the reaction temperature is 65-75° C., and the reaction time is 3-5 h.

4. The flame-retardant medium voltage power cable according to claim 2, characterized in that: The usage ratio of wollastonite, ethanol, water, ethyl orthosilicate and hexachlorocyclotriphosphazene is 100g:380-420mL:80-120mL:15-18g:8.2-9.8g.

5. The flame-retardant medium voltage power cable according to claim 1, characterized in that: The preparation method of the polydopamine / silane double-layer modified magnesium hydroxide comprises: dispersing Mg(OH)2 in a Tris-HCl buffer, adding dopamine and stirring to polymerize, dispersing the resultant in ethanol after centrifugation, adding a silane coupling agent, performing a reflux reaction, filtering after completion, and drying to obtain the resultant.

6. The flame-retardant medium voltage power cable according to claim 5, characterized in that: The polymerization temperature is 25±1° C., and the polymerization time is 11-13 h; the reflux reaction temperature is 75-85° C., and the time is 3-5 h.

7. The flame-retardant medium voltage power cable according to claim 5, characterized in that: The silane coupling agent is γ-aminopropyltriethoxysilane.

8. The flame-retardant medium voltage power cable according to claim 6, characterized in that: The weight ratio of the Mg(OH)2, dopamine and silane coupling agent is 10:0.2-0.4:0.1-0.

2.

9. A method for preparing a flame retardant medium voltage power cable according to any one of claims 1 to 8, characterized in that the steps include: Ethylene-vinyl acetate copolymer, polyolefin elastomer and maleic anhydride grafted polyethylene are mixed at a temperature of 85-95°C for 2-4 minutes; phosphorus-nitrogen modified wollastonite and polydopamine / silane double-layer modified magnesium hydroxide are added in multiple times, each time mixing for 2-3 minutes; nano zinc borate, calcium stearate and an antioxidant are then added and mixed for 3-5 minutes, the temperature is raised to 100-120°C, and mixing is continued for 4-6 minutes. After discharging, the material is left at room temperature for 24 hours to obtain a flame retardant layer rubber compound; and the conductor is melt-extruded and coated through a twin-screw extruder to form the flame retardant medium voltage power cable.

10. The method for preparing a flame-retardant medium-voltage power cable according to claim 9, characterized in that: The multiple times are 2-4 times, with an interval of 2-3 minutes each time; the temperature of the first zone of the twin-screw extruder is 105-115°C, the temperature of the second zone is 115-125°C, the temperature of the third zone is 125-135°C, and the die head temperature is 130-140°C.

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