Flame-retardant high-flexibility crosslinked polyethylene insulated power cable and method for producing the same

Abstract

The application discloses a kind of flame-retardant high-flexibility crosslinked polyethylene insulated power cable and preparation method thereof, belong to cable technical field.The inside to outside includes conductor, insulating layer, filling layer, tape layer and sheath layer in proper order.Conductor uses the 5th or 6th soft copper conductor, insulating layer includes polyethylene, ethylene-vinyl acetate copolymer and magnesium hydroxide modified by vinyltriethoxysilane and polybutadiene, filling layer is alkali-free glass fiber rope coated with aluminum hydroxide powder on the surface, prepared by impregnation-extrusion process, sheath layer includes DOPO-PEG and pentaerythritol phosphate ester compounded intumescent halogen-free phosphorus flame-retardant system and organic modified montmorillonite.The application realizes efficient halogen-free flame-retardant by multilayer synergistic flame-retardant design, and has high flexibility and good weather resistance simultaneously.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a flame-retardant, highly flexible cross-linked polyethylene insulated power cable and its preparation method. Background Technology

[0002] In the field of existing power cable technology, cross-linked polyethylene (XLPE) insulated power cables are widely used in power transmission and distribution systems due to their excellent electrical properties and heat resistance. However, traditional XLPE cables still have the following technical shortcomings in practical applications: Firstly, conventional cross-linked polyethylene materials are inherently flammable. To meet increasingly stringent fire safety requirements, it is usually necessary to add a large amount of halogenated flame retardants or high-filling inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide. However, halogenated flame retardants release a large amount of toxic fumes when burning, while high-filling inorganic flame retardants significantly degrade the mechanical properties and flexibility of the cable, making it difficult to bend the cable and install it in confined spaces. Secondly, existing cables often employ a single flame-retardant mechanism when pursuing flame-retardant performance. For example, they may only add flame retardants to the sheath layer or rely solely on filler ropes for isolation. This lacks a multi-layered and synergistic flame-retardant design, resulting in low flame-retardant efficiency and difficulty in simultaneously meeting multiple requirements such as bundled combustion, low smoke, and halogen-free performance. Third, as the material for the internal filling layer of the cable, traditional methods often use ordinary glass fiber rope or polypropylene filling rope. Although the former has a certain fire resistance, it lacks active flame retardant function, while the latter is flammable and melts and drips at high temperatures, making it difficult to effectively prevent flames from spreading along the gaps in the cable core. Even if some solutions attempt to coat the surface of the filling rope with flame retardant, fluidized bed and other processes are often used, which have problems such as uneven coating thickness, difficulty in precise control, and insufficient adhesion of flame retardant, affecting the long-term reliability of the cable. Fourth, the existing flame-retardant cable sheaths mostly use halogenated polyvinyl chloride or polyolefin materials filled with a large amount of inorganic flame retardants. The former has poor environmental performance, while the latter has poor processing fluidity and is prone to cracking of the sheath or a decrease in fatigue resistance. At the same time, small molecule phosphorus-based flame retardants are prone to migration and precipitation in the polyethylene matrix, affecting the durability of the flame retardant effect and the surface quality of the cable.

[0003] Therefore, developing a cross-linked polyethylene insulated power cable that combines high flexibility, high efficiency, halogen-free flame retardancy, good weather resistance, and good synergistic effect of each layer of materials has important practical application value. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a flame-retardant, highly flexible cross-linked polyethylene insulated power cable and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A flame-retardant, highly flexible cross-linked polyethylene insulated power cable comprises, from the inside out: a conductor, an insulation layer, a filler layer, a wrapping layer, and a sheath layer.

[0006] Preferably, the conductor is a Class 5 or Class 6 soft copper conductor.

[0007] Preferably, the insulating layer comprises the following components in parts by weight: 85-95 parts of polyethylene, 8-12 parts of ethylene-vinyl acetate copolymer (vinyl acetate content 28-33%), 10-15 parts of modified magnesium hydroxide, 2.0-2.5 parts of dicumyl peroxide, 0.3-0.5 parts of triallyl isocyanurate, and 0.3-0.5 parts of antioxidant 1010.

[0008] Preferably, the polyethylene has a melt flow index of 0.5-1.5 g / 10 min and a density of 0.915-0.925 g / cm³. 3 The polyethylene used in the sheath layer also meets the above-mentioned melt index and density range.

[0009] Preferably, the preparation method of the modified magnesium hydroxide includes the following steps: dispersing magnesium hydroxide powder in a mixed solvent of anhydrous ethanol and water in a mass ratio of 7:3, adding vinyltriethoxysilane and polybutadiene, stirring at 300-500 rpm for 4-6 hours at 70-80°C, filtering while hot to obtain a filter cake, washing the filter cake 2-3 times with anhydrous ethanol, then washing with deionized water until neutral, placing the washed product in a vacuum drying oven at 50-60°C for 12-14 hours, removing it, grinding it, and passing it through a 200-300 mesh sieve to obtain surface-modified magnesium hydroxide.

[0010] Preferably, the magnesium hydroxide powder has a particle size of 3-5 μm, and the ratio of magnesium hydroxide powder to the mixed solvent of anhydrous ethanol and water is 1 g: 8-10 ml.

[0011] Preferably, the amount of vinyltriethoxysilane used is 2-4% of the mass of magnesium hydroxide powder.

[0012] Preferably, the polybutadiene has a number average molecular weight of 1000-2000 Da, and its amount is 1-2% of the mass of magnesium hydroxide powder.

[0013] Preferably, the filling layer is an alkali-free glass fiber rope coated with aluminum hydroxide powder. The preparation method includes the following steps: mixing aluminum hydroxide powder with ethylene-vinyl acetate emulsion at a mass ratio of 1:2-3, adding deionized water, and stirring with a high-speed disperser at 1000-1500 rpm for 15-20 minutes to prepare a uniformly dispersed suspension slurry. Then, completely immersing the alkali-free glass fiber rope in the suspension slurry for 2-3 minutes, pressing the impregnated fiber rope through a pair of extrusion rollers, adjusting the gap between the rollers to 0.8-0.9 times the rope diameter, and controlling the slurry retention in the extruded fiber rope to be 25-35% of the dry fiber rope mass. The extruded fiber rope is then placed in a hot air circulating oven and dried at 60-80℃ for 45-60 minutes. Finally, talc powder weighing 0.5-1.0% of the rope's mass is sprayed onto the dried fiber rope surface to obtain an alkali-free glass fiber rope coated with aluminum hydroxide powder.

[0014] Preferably, the alkali-free glass fiber rope has a diameter of 2.0-5.0 mm and is made of 10-20 strands of alkali-free glass fiber yarn twisted together, with a twist of 30-50 twists / meter.

[0015] Preferably, the aluminum hydroxide powder has a particle size of 3-5 μm, and the amount of deionized water added is 70-80% of the mass of the aluminum hydroxide powder.

[0016] Preferably, the ethylene-vinyl acetate emulsion has a solid content of 50-55% and a vinyl acetate content of 14-18%.

[0017] Preferably, the wrapping layer is two layers of halogen-free flame-retardant mica tape or one layer of ceramicized silicone rubber tape, with a wrapping overlap rate of 30-35%.

[0018] Preferably, the sheath layer comprises the following components in parts by weight: 50-65 parts polyethylene, 15-25 parts ethylene-octene copolymer (octene content 20-30%), 5-8 parts maleic anhydride grafted polyethylene, 8-12 parts DOPO-PEG, 10-15 parts pentaerythritol phosphate, 3-5 parts organically modified montmorillonite, 1-2 parts ultraviolet stabilizer (UV-531 and hindered amine light stabilizer 292 compounded in a mass ratio of 1:1-2), and 1-3 parts ethylene bis-stearamide.

[0019] Preferably, the preparation method of DOPO-PEG includes the following steps: dissolving DOPO in a mixed solvent of dioxane and N,N-dimethylformamide at a volume ratio of 1:1, then adding maleic anhydride, heating to 110-120℃ under nitrogen protection, stirring at 200-300 rpm for 8-12 hours, cooling to room temperature after the reaction, adding 3-5 times the volume of deionized water, stirring until the product precipitates, filtering to collect the white solid crude product, washing 2-3 times with deionized water, and then vacuum drying at 70-80℃ for 20-20 minutes. After 4 hours, DOPO-MA intermediate was obtained. Then, the obtained DOPO-MA intermediate was mixed with polyethylene glycol, and p-toluenesulfonic acid was added as a catalyst. The mixture was heated to 150-160℃ under nitrogen protection and stirred at 200-300 rpm for 6-8 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, and the product solidified into solid blocks. The solid blocks were removed and pre-crushed using a coarse crusher or hammer mill to obtain coarse particles. The coarse particles were then further ground in a grinder and passed through an 80-100 mesh sieve to finally obtain DOPO-PEG.

[0020] Preferably, the molar ratio of DOPO to the mixed solvent of dioxane and N,N-dimethylformamide is 0.1 mol: 15-30 ml; the molar ratio of DOPO to maleic anhydride is 1: 1.2-1.5.

[0021] Preferably, the number average molecular weight of the polyethylene glycol is 3500-4500 Da, and the mass ratio of DOPO-MA intermediate to polyethylene glycol is 1:2-3.

[0022] Preferably, the amount of p-toluenesulfonic acid used is 1.5-3.0% of the total weight of DOPO-MA intermediate and polyethylene glycol.

[0023] Preferably, the preparation method of the organically modified montmorillonite includes the following steps: dispersing montmorillonite in deionized water to prepare a montmorillonite suspension with a mass fraction of 5-10%, and stirring in a water bath at 70-80℃ for 30-60 minutes to ensure full dispersion; separately dissolving hexadecyltrimethylammonium bromide in deionized water to prepare an intercalating agent solution with a mass fraction of 10-15%; slowly adding the intercalating agent solution dropwise into the montmorillonite suspension under stirring, and after the addition is complete, raising the temperature to 80-90℃ and continuing to stir the reaction at a speed of 300-500 rpm for 4-6 hours; after the reaction is completed, filtering the product to obtain a filter cake, washing the filter cake repeatedly with deionized water 4-5 times, and then drying the filter cake in a vacuum drying oven at 60-80℃ for 12-24 hours, removing it, grinding it, and passing it through a 200-300 mesh sieve to obtain the organically modified montmorillonite.

[0024] Preferably, the amount of hexadecyltrimethylammonium bromide used is 15-25% of the mass of montmorillonite.

[0025] A method for preparing a flame-retardant, highly flexible cross-linked polyethylene insulated power cable includes the following steps: S1. Conductor preparation: After the copper rod is drawn and annealed, it is bundled and re-stranded by a stranding machine to obtain a soft copper conductor with a stranding pitch ratio of 12-16. The conductor surface is smooth, without burrs or oil stains. S2. Insulation layer extrusion: Insulation layer material is extruded onto the conductor in single layer through an extruder to form an insulated wire core. The extrusion temperature is as follows: barrel zone 1 135-145℃, zone 2 145-155℃, zone 3 150-160℃, die head 150-160℃, screw speed 40-50rpm, and insulation layer thickness is 1.8-2.0mm. S3. Crosslinking treatment: The insulated wire core after S2 extrusion is continuously fed into the CCV catenary crosslinking tube. Dry heating crosslinking is carried out under nitrogen protection. The temperature of the heating section of the crosslinking tube is controlled at 250-280℃, the nitrogen pressure inside the tube is maintained at 0.8-1.5MPa, the nitrogen purity is not less than 99.5%, and the time is 2-5 minutes. After the wire core completes the crosslinking reaction under high temperature nitrogen protection, it passes through the precooling section in sequence. Water cooling is used. The precooling water temperature is controlled at 60-80℃ to cool the surface temperature of the wire core to below 100℃. Then it enters the cooling water section, where circulating cooling water at 20-40℃ is used for full cooling to fully crosslink and shape the insulation layer. S4. Cable filling: Three S3 cross-linked insulated wire cores are twisted together and cabled using an untwisting twisting method. The cable pitch ratio is controlled at 20-30 times. At the same time, the gaps are filled with alkali-free glass fiber rope coated with aluminum hydroxide powder to ensure that the cable core is round and dense. S5. Wrapping with tape: Wrap two layers of halogen-free flame-retardant mica tape or one layer of ceramicized silicone rubber tape around the outside of the cable core, with an overlap rate of 30-35% for each layer; S6. Sheath Extrusion: The sheath material is extruded over the outer layer of the tape using an extruder. Extrusion temperatures are: Zone 1 of the barrel 150-160℃, Zone 2 160-165℃, Zone 3 165-170℃, Die head 170-175℃, and screw speed 35-45 rpm. After extrusion, the material undergoes gradient cooling in a 20-26m long cooling water tank: Section 1 70-80℃, length 8-10m; Section 2 50-60℃, length 6-8m; Section 3 25-35℃, length 6-8m. After drying, the material is printed, wound up, and the finished cable is obtained.

[0026] Compared with the prior art, the beneficial effects of the present invention are: 1. By using Category 5 or Category 6 soft copper conductors and optimizing the stranding pitch ratio, while introducing elastomer components such as ethylene-vinyl acetate copolymer and ethylene-octene copolymer into the insulation and sheath layers, and by surface organic modification of magnesium hydroxide, the compatibility between inorganic flame retardants and polymer matrices is significantly improved. This avoids the material stiffness and cracking problems caused by high filler flame retardant content, enabling the cable to maintain high flexibility while possessing excellent flame retardant properties, making it easy to lay and install in confined spaces.

[0027] 2. This invention constructs a multi-layer synergistic flame-retardant system consisting of a filler layer, a wrapping layer, and a sheath layer: the filler layer uses a special impregnation process to firmly coat the surface of alkali-free glass fiber rope with aluminum hydroxide powder, which has the functions of active flame retardancy and preventing flame spread; the wrapping layer uses halogen-free flame-retardant mica tape or ceramicized silicone rubber tape; the sheath layer contains DOPO-PEG macromolecular flame retardant, pentaerythritol phosphate, and organically modified montmorillonite, achieving a synergistic effect of expansion into char and heat and oxygen insulation, resulting in high flame retardant efficiency, overall halogen-free and environmentally friendly properties, and no release of toxic fumes during combustion, which can meet the stringent requirements of bundled combustion, low smoke and halogen-free combustion.

[0028] 3. The self-made DOPO-PEG in the sheath layer links the flame retardant elements to the polyethylene glycol segments by chemical bonds, which effectively solves the problem of easy migration and precipitation of small molecule phosphorus flame retardants in the polyethylene matrix, ensuring the durability of the flame retardant effect and the surface quality of the cable; at the same time, the compounded ultraviolet stabilizer significantly improves the weather resistance.

[0029] 4. The insulation layer adopts a crosslinking system of dicumyl peroxide and triallyl isocyanurate, and is dry crosslinked under high temperature and high pressure nitrogen with CCV catenary crosslinking tube. The crosslinking is sufficient and uniform, with excellent heat resistance. The parameters of each process are precisely controlled, especially the gradient cooling design after sheath extrusion, which effectively reduces internal stress and prevents sheath cracking. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a flame-retardant, highly flexible cross-linked polyethylene insulated power cable proposed in this invention.

[0031] In the diagram: 1. Conductor; 2. Insulating layer; 3. Filler layer; 4. Wrapping tape layer; 5. Sheath layer. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] Preparation Example 1: The preparation method of modified magnesium hydroxide includes the following steps: Take 100g of magnesium hydroxide powder with a particle size of 3μm, disperse it in 1000ml of a mixed solvent of anhydrous ethanol and water (anhydrous ethanol: water = 7:3), add 2g of vinyltriethoxysilane and 1g of polybutadiene with a number average molecular weight of 1000Da, stir at 300rpm for 6h at 75℃, filter while hot after the reaction is completed, wash the filter cake twice with anhydrous ethanol, and then wash it with deionized water until neutral, place the washed product in a vacuum drying oven at 50℃ and dry for 14h, take it out and grind it, pass it through a 200-mesh sieve to obtain modified magnesium hydroxide.

[0034] Preparation Example 2: The preparation method of modified magnesium hydroxide includes the following steps: Take 100g of magnesium hydroxide powder with a particle size of 5μm, disperse it in 800ml of a mixed solvent of anhydrous ethanol and water (anhydrous ethanol: water = 7:3), add 4g of vinyltriethoxysilane and 2g of polybutadiene with a number average molecular weight of 2000Da, stir at 500rpm for 4h at 80℃, filter while hot after the reaction is completed, wash the filter cake 3 times with anhydrous ethanol, and then wash it with deionized water until neutral, place the washed product in a vacuum drying oven at 60℃ and dry for 12h, take it out and grind it, pass it through a 300-mesh sieve to obtain modified magnesium hydroxide.

[0035] Preparation Example 3: The preparation method of alkali-free glass fiber rope with aluminum hydroxide powder coating includes the following steps: Take 100g of aluminum hydroxide powder with a particle size of 3μm, mix it with 200g of ethylene-vinyl acetate emulsion (solid content 50%, vinyl acetate content 14%), add 70g of deionized water, and stir at 1000rpm for 20min with a high-speed disperser to prepare a uniformly dispersed suspension slurry. Immerse the alkali-free glass fiber rope (diameter 2.0mm, made of 10 strands of alkali-free glass fiber yarn twisted together, twist degree 30 twists / meter) completely into the suspension slurry for 3min, and then squeeze it through a pair of squeezing rollers (the gap between the rollers is 0.8 times the rope diameter) to control the slurry retention to 25% of the dry fiber rope mass. Send the squeezed fiber rope into a hot air circulating oven and dry it at 60℃ for 60min. Spray 0.5% of the rope weight of talc powder on the surface of the dried fiber rope to obtain the alkali-free glass fiber rope with aluminum hydroxide powder coating.

[0036] Preparation Example 4: The preparation method of alkali-free glass fiber rope with aluminum hydroxide powder coating includes the following steps: Take 100g of aluminum hydroxide powder with a particle size of 5μm, mix it with 300g of ethylene-vinyl acetate emulsion (solid content 55%, vinyl acetate content 18%), add 80g of deionized water, and stir at 1500rpm for 15min with a high-speed disperser to prepare a uniformly dispersed suspension slurry. Immerse the alkali-free glass fiber rope (diameter 5.0mm, made of 20 strands of alkali-free glass fiber yarn twisted together, twist 50 twists / meter) completely into the suspension slurry for 2min, and then squeeze it through a pair of squeezing rollers (the gap between the rollers is 0.9 times the rope diameter) to control the slurry retention to 35% of the dry fiber rope mass. Send the squeezed fiber rope into a hot air circulating oven and dry it at 80℃ for 45min. Spray 1.0% of the rope weight of talc powder on the surface of the dried fiber rope to obtain the alkali-free glass fiber rope with aluminum hydroxide powder coating.

[0037] Preparation Example 5: The preparation method of DOPO-PEG includes the following steps: 21.6g of DOPO is dissolved in 20ml of a mixed solvent of dioxane and N,N-dimethylformamide (volume ratio 1:1), 11.8g of maleic anhydride is added, the temperature is raised to 110℃ under nitrogen protection, and the reaction is stirred at 200rpm for 12h. After cooling to room temperature, 60ml of deionized water is added, and the mixture is stirred evenly to precipitate. The precipitate is filtered, washed twice with deionized water, and dried under vacuum at 70℃ for 24h to obtain DOPO-MA intermediate. 10g of DOPO-MA intermediate is mixed with 20g of polyethylene glycol with a number average molecular weight of 3500Da, and 0.45g of p-toluenesulfonic acid is added. The mixture is heated to 150℃ under nitrogen protection and stirred at 200rpm for 8h. After naturally cooling to room temperature, the mixture is pulverized, ground, and passed through an 80-mesh sieve to obtain DOPO-PEG.

[0038] Preparation Example 6: The preparation method of DOPO-PEG includes the following steps: 21.6g of DOPO is dissolved in 30 ml of a mixed solvent of dioxane and N,N-dimethylformamide (volume ratio 1:1), 14.7g of maleic anhydride is added, the temperature is raised to 120℃ under nitrogen protection, and the reaction is stirred at 300 rpm for 8 h. After cooling to room temperature, 100 ml of deionized water is added, the mixture is stirred evenly, precipitated, filtered, washed 3 times with deionized water, and dried under vacuum at 80℃ for 20 h to obtain DOPO-MA intermediate. 10g of DOPO-MA intermediate is mixed with 30g of polyethylene glycol with a number average molecular weight of 4500 Da, 1.2g of p-toluenesulfonic acid is added, the temperature is heated to 160℃ under nitrogen protection, and the reaction is stirred at 300 rpm for 6 h. After naturally cooling to room temperature, the mixture is pulverized after solidification, ground, and passed through a 100-mesh sieve to obtain DOPO-PEG.

[0039] Preparation Example 7: The preparation method of organically modified montmorillonite includes the following steps: 10g of montmorillonite is dispersed in 90g of deionized water and stirred in a 70℃ water bath for 60min to prepare a montmorillonite suspension. Separately, 1.5g of hexadecyltrimethylammonium bromide is dissolved in 13.5g of deionized water to prepare an intercalating agent solution. The intercalating agent solution is slowly added dropwise to the montmorillonite suspension under stirring. After the addition is complete, the temperature is raised to 80℃ and the mixture is stirred at 300rpm for 6h. The mixture is then filtered, the filter cake is washed 4 times with deionized water, and dried in a 60℃ vacuum drying oven for 24h. After drying, the cake is ground and passed through a 200-mesh sieve to obtain organically modified montmorillonite.

[0040] Preparation Example 8: The preparation method of organically modified montmorillonite includes the following steps: 10g of montmorillonite is dispersed in 190g of deionized water and stirred in an 80℃ water bath for 30min to prepare a montmorillonite suspension. Separately, 2.5g of hexadecyltrimethylammonium bromide is dissolved in 14.17g of deionized water to prepare an intercalating agent solution. The intercalating agent solution is slowly added dropwise to the montmorillonite suspension under stirring. After the addition is complete, the temperature is raised to 90℃ and stirred at 500rpm for 4h. The mixture is then filtered, the filter cake is washed 5 times with deionized water, placed in an 80℃ vacuum drying oven and dried for 12h. The cake is then removed, ground, and passed through a 300-mesh sieve to obtain organically modified montmorillonite.

[0041] Example 1: Please refer to Figure 1 A flame-retardant, highly flexible cross-linked polyethylene insulated power cable, comprising, from the inside out: conductor 1, insulation layer 2, filler layer 3, wrapping layer 4, and sheath layer 5.

[0042] The conductor is a Class 5 soft copper conductor.

[0043] The insulation layer comprises the following components in parts by weight: polyethylene (melt index 0.5 g / 10 min, density 0.915 g / cm³). 3 85 parts of ethylene-vinyl acetate copolymer (vinyl acetate content 28%), 8 parts of modified magnesium hydroxide of Preparation Example 1, 10 parts of dicumyl peroxide, 2.0 parts of triallyl isocyanurate, and 0.3 parts of antioxidant 1010.

[0044] The filling layer is an alkali-free glass fiber rope with aluminum hydroxide powder coated on the surface, as described in Preparation Example 3.

[0045] The wrapping layer consists of two layers of halogen-free flame-retardant mica tape.

[0046] The sheath layer comprises the following components by weight: polyethylene (melt index 0.5 g / 10 min, density 0.915 g / cm³). 350 parts of ethylene-octene copolymer (octene content 20%), 15 parts of maleic anhydride grafted polyethylene, 8 parts of DOPO-PEG of Preparation Example 5, 10 parts of pentaerythritol phosphate, 3 parts of organic modified montmorillonite of Preparation Example 7, 1 part of ultraviolet stabilizer (UV-531: hindered amine light stabilizer 292 = 1:1), and 1 part of ethylene bis-stearamide.

[0047] A method for preparing a flame-retardant, highly flexible cross-linked polyethylene insulated power cable includes the following steps: S1. Conductor preparation: After the copper rod is drawn and annealed, it is bundled and re-stranded by a stranding machine to obtain a soft copper conductor with a stranding pitch ratio of 12. The conductor surface is smooth, without burrs or oil stains. S2. Insulation layer extrusion: The insulation layer material is extruded onto the conductor in a single layer through an extruder to form an insulated wire core. The extrusion temperature is: 135℃ in zone 1 of the barrel, 145℃ in zone 2, 150℃ in zone 3, 150℃ at the die head, and the screw speed is 40 rpm. The insulation layer thickness is 1.8 mm. S3. Crosslinking treatment: The insulated wire core after S2 extrusion is continuously fed into the CCV catenary crosslinking tube. Dry heating crosslinking is carried out under nitrogen protection. The temperature of the heating section of the crosslinking tube is controlled at 250℃, the nitrogen pressure inside the tube is maintained at 0.8MPa, the nitrogen purity is not less than 99.5%, and the time is 5min. After the wire core completes the crosslinking reaction under high temperature nitrogen protection, it passes through the precooling section in sequence. Water cooling is used. The precooling water temperature is controlled at 80℃ to cool the surface temperature of the wire core to below 100℃. Then it enters the cooling water section and is fully cooled with circulating cooling water at 40℃ to fully crosslink and shape the insulation layer. S4. Cable filling: Three S3 cross-linked insulated wire cores are twisted together and cabled using an untwisting twisting method. The cable pitch ratio is controlled at 30 times. At the same time, the gaps are filled with alkali-free glass fiber rope coated with aluminum hydroxide powder to ensure that the cable core is round and dense. S5. Wrapping with tape: Wrap two layers of halogen-free flame-retardant mica tape around the outside of the cable core, with each layer having an overlap rate of 30%; S6. Sheath Extrusion: The sheath material is extruded from the outer layer of the tape using an extruder. The extrusion temperature is as follows: Zone 1 of the barrel is 150℃, Zone 2 is 160℃, Zone 3 is 165℃, and the die head is 170℃. The screw speed is 35 rpm. After extrusion, the material is subjected to gradient cooling in a 20m long cooling water tank: the first section is 70℃ and 8m in length, the second section is 50℃ and 6m in length, and the third section is 25℃ and 6m in length. After drying, the material is printed, wound up, and the finished cable is obtained.

[0048] Example 2: Please refer to Figure 1 A flame-retardant, highly flexible cross-linked polyethylene insulated power cable, comprising, from the inside out: conductor 1, insulation layer 2, filler layer 3, wrapping layer 4, and sheath layer 5.

[0049] The conductor is a Class 6 soft copper conductor.

[0050] The insulation layer comprises the following components by weight: polyethylene (melt index 1.5 g / 10 min, density 0.920 g / cm³). 3 95 parts of ethylene-vinyl acetate copolymer (vinyl acetate content 33%), 12 parts of modified magnesium hydroxide of Preparation Example 1, 15 parts of dicumyl peroxide, 2.5 parts of triallyl isocyanurate, and 0.5 parts of antioxidant 1010.

[0051] Filler layer: Alkali-free glass fiber rope with aluminum hydroxide powder coated on the surface of Preparation Example 3.

[0052] Wrapping layer: One layer of ceramicized silicone rubber tape.

[0053] The sheath layer comprises the following components by weight: polyethylene (melt index 1.5 g / 10 min, density 0.925 g / cm³). 3 65 parts of ethylene-octene copolymer (octene content 25%), 25 parts of maleic anhydride grafted polyethylene, 8 parts of DOPO-PEG of Preparation Example 5, 12 parts of pentaerythritol phosphate, 5 parts of organic modified montmorillonite of Preparation Example 7, 2 parts of ultraviolet stabilizer (UV-531: hindered amine light stabilizer 292 = 1:2), and 3 parts of ethylene bis-stearamide.

[0054] A method for preparing a flame-retardant, highly flexible cross-linked polyethylene insulated power cable includes the following steps: S1. Conductor preparation: After the copper rod is drawn and annealed, it is bundled and re-stranded by a stranding machine to obtain a soft copper conductor with a stranding pitch ratio of 16. The conductor surface is smooth, without burrs or oil stains. S2. Insulation layer extrusion: The insulation layer material is extruded onto the conductor in single layer through an extruder to form an insulated wire core. The extrusion temperature is: 145℃ in zone 1 of the barrel, 155℃ in zone 2, 160℃ in zone 3, 160℃ at the die head, and the screw speed is 50 rpm. The insulation layer thickness is 2.0 mm. S3. Crosslinking treatment: The insulated wire core after S2 extrusion is continuously fed into the CCV catenary crosslinking tube. Dry heating crosslinking is carried out under nitrogen protection. The temperature of the heating section of the crosslinking tube is controlled at 280℃, the nitrogen pressure inside the tube is maintained at 1.5MPa, the nitrogen purity is not less than 99.5%, and the time is 2min. After the wire core completes the crosslinking reaction under high temperature nitrogen protection, it passes through the precooling section in sequence. Water cooling is used. The precooling water temperature is controlled at 60℃ to cool the surface temperature of the wire core to below 100℃. Then it enters the cooling water section and is fully cooled with circulating cooling water at 20℃ to fully crosslink and shape the insulation layer. S4. Cable filling: Three S3 cross-linked insulated wire cores are twisted together and cabled using an untwisting twisting method. The cable pitch ratio is controlled at 20 times. At the same time, the gaps are filled with alkali-free glass fiber rope coated with aluminum hydroxide powder to ensure that the cable core is round and dense. S5. Wrapping with ceramicized silicone rubber tape: Wrap a layer of ceramicized silicone rubber tape around the outside of the cable core, with an overlap rate of 35% for each layer; S6. Sheath Extrusion: The sheath material is extruded from the outer layer of the tape using an extruder. The extrusion temperature is as follows: Zone 1 of the barrel is 160℃, Zone 2 is 165℃, Zone 3 is 170℃, and the die head is 175℃. The screw speed is 45 rpm. After extrusion, the material is subjected to gradient cooling in a 26m long cooling water tank: the first section is 80℃ and 10m long, the second section is 60℃ and 8m long, and the third section is 35℃ and 8m long. The material is then dried, printed, and wound up to obtain the finished cable.

[0055] Example 3: The only difference between Example 3 and Example 2 is that the modified magnesium hydroxide in the insulating layer is the modified magnesium hydroxide prepared in Example 2.

[0056] Example 4: The only difference between Example 4 and Example 2 is that the filling layer is an alkali-free glass fiber rope with aluminum hydroxide powder coated on the surface prepared in Example 4.

[0057] Example 5: The only difference between Example 5 and Example 2 is that the DOPO-PEG in the sheath layer is the DOPO-PEG prepared in Preparation Example 6.

[0058] Example 6: The only difference between Example 6 and Example 2 is that the organic modified montmorillonite in the sheath layer is the organic modified montmorillonite prepared in Example 8.

[0059] Comparative Example 1: Based on Example 2, the difference is that modified magnesium hydroxide is not used in the insulating layer, but an equal amount of unmodified magnesium hydroxide powder with a particle size of 5μm is used instead, and the rest is the same as in Example 2.

[0060] Comparative Example 2: Based on Example 2, the difference is that the filling layer uses ordinary alkali-free glass fiber rope (without aluminum hydroxide coating and talc spraying), and the rest is the same as Example 2.

[0061] Comparative Example 3: Based on Example 2, the difference is that DOPO-PEG and pentaerythritol phosphate were removed from the sheath layer, the number of polyethylene parts was increased to 92 parts, and the rest was the same as in Example 2.

[0062] Comparative Example 4: Based on Example 2, the difference is that the organic modified montmorillonite and ultraviolet stabilizer are removed from the sheath layer, the number of polyethylene parts is increased to 72 parts, and the rest is the same as in Example 2.

[0063] Cable samples prepared in Examples 1-6 and Comparative Examples 1-4 were selected, with a rated voltage of 0.6 / 1kV and a specification of 3×50mm. 2 Full performance testing was conducted. All tests were performed 24 hours after sample preparation, at an ambient temperature of 23±2℃ and a relative humidity of 50±5%.

[0064] Performance testing: 1. Flame retardant performance test: Bundle cable samples with a length of 3.5±0.5m are installed on a vertical trapezoidal test frame. A 20.5kW strip torch is used to ignite the cable for 20 minutes. After the ignition is stopped and the cable is cooled, the maximum height of the charred part is measured.

[0065] 2. Smoke density test: A cable sample with a length of 1.00±0.05m was placed horizontally in a 3m×3m×3m sealed combustion chamber. After the alcohol cotton burner was ignited, it was kept for about 40s. The smoke produced by the combustion was collected, the change in light transmittance was detected, and the maximum smoke density (Ds,max) and minimum light transmittance (%) were recorded.

[0066] 3. Oxygen Index Test: Take cable sheath material and insulation material respectively, make standard size (80-150mm×10mm×4mm) strip samples, install them vertically in the glass combustion tube, adjust the oxygen and nitrogen mixing ratio, ignite the top of the sample, observe its continuous combustion within 3 minutes, gradually adjust the oxygen concentration and measure the critical oxygen index, and record the oxygen index (LOI, %) of the sheath layer and insulation layer.

[0067] 4. Insulation resistance test: Immerse a 5m long cable sample in water, apply a 1kV DC voltage, and test the insulation resistance value (MΩ·km) of the finished cable using the voltage-current method or DC comparison method.

[0068] 5. Insulation layer tensile properties test: Dumbbell-shaped specimens are cut axially from the cable insulation layer with a clamping distance of 50 mm and a tensile speed of 250 mm / min. The specimens are stretched continuously until they break, and the tensile strength (MPa) and elongation at break (%) of the insulation layer are tested.

[0069] 6. Sheath layer tensile performance test: Peel the outer sheath from the cable sheath layer, prepare dumbbell-shaped specimens, clamp with a spacing of 50 mm, stretch at a speed of 250 mm / min, and stretch continuously until the specimen breaks. Test the tensile strength (MPa) and elongation at break (%) of the sheath layer.

[0070] 7. Cable impact test: The cable sample with a length of 1m is rigidly fixed on the test platform. The impact tester is used, and the impact hammer with an energy of (5±0.5)J is selected. The number of impacts is 3 (the impact points are distributed in different parts). The impact head should be perpendicular to the cable surface. After the impact, the sheath layer is visually inspected for cracks, fissures or defects.

[0071] 8. Thermal aging performance test: The prepared dumbbell-shaped sheath layer sample was placed in a forced ventilation aging chamber at (135±2)℃ for 168h (7 days). After being taken out, it was cooled in an environment of (23±2)℃ for 24h. Then, the tensile strength and elongation at break of the aged sample were tested according to the tensile test method. The tensile strength retention rate and elongation at break retention rate (%) were calculated compared with those before aging.

[0072] Table 1. Test results of flame retardant properties, smoke density, oxygen index and insulation resistance of cables

[0073] As shown in Table 1, the char height of the bundled combustion in Examples 1-6 of the present invention is between 1.15 and 1.25 m, the maximum smoke density is not more than 68, and the minimum light transmittance is not less than 74%, indicating that the cable has excellent low-smoke halogen-free flame retardant performance. The oxygen index of the sheath layer in Examples 1-6 is greater than 33.0%, and the oxygen index of the insulation layer is greater than 29.0%, further illustrating the high efficiency of the multi-layer synergistic flame retardant system.

[0074] Comparative Example 1 showed a significant decrease in flame retardant performance due to the use of unmodified magnesium hydroxide in the insulation layer (char height 2.10m, oxygen index of insulation layer only 24.0%). This was attributed to the uneven dispersion and agglomeration of unmodified magnesium hydroxide in the polyethylene matrix, leading to reduced flame retardant efficiency. Comparative Example 2, using ordinary alkali-free glass fiber rope (without aluminum hydroxide coating), showed that flames easily spread along the gaps in the cable core, resulting in a char height as high as 3.20m and a significantly increased smoke density (Ds,max=112), indicating that the flame retardant coating of the filler layer is crucial for suppressing flame spread. Comparative Example 3, after removing DOPO-PEG and pentaerythritol phosphate, saw its sheath oxygen index drop to 24.5%, char height reach 3.85m, and smoke density severely exceed the standard (Ds,max=158, minimum light transmittance only 41%), indicating that the expanded halogen-free phosphorus flame retardant system in the sheath layer is the core flame retardant barrier. Comparative Example 4, after removing organically modified montmorillonite and ultraviolet stabilizer, showed a slight decrease in flame retardant performance (char height 1.45m), but it was still superior to Comparative Examples 1-3.

[0075] Table 2. Test results of the mechanical properties of the cable

[0076] As can be seen from Table 2, the tensile strength of the insulation layer in Examples 1-6 is 11.4-11.6 MPa, and the elongation at break is 240-245%; the tensile strength of the sheath layer is 13.4-13.7 MPa, and the elongation at break is 171-174%. The high elongation at break reflects the good flexibility of the cable.

[0077] The tensile strength of the insulation layer in Comparative Example 1 decreased to 8.5 MPa, and the elongation at break was only 185%. This was because the unmodified magnesium hydroxide had poor compatibility with polyethylene, forming stress concentration points and severely deteriorating the mechanical properties. The sheath layer in Comparative Example 4 lacked the reinforcing effect of organically modified montmorillonite and the toughening effect of UV stabilizer, resulting in both tensile strength (11.8 MPa) and elongation at break (145%) failing to meet the standards. The tensile strength and elongation at break of the sheath layer in Comparative Example 3 also decreased slightly (12.8 MPa, 155%), indicating that the addition of DOPO-PEG and pentaerythritol phosphate contributed to the mechanical properties.

[0078] Table 3. Test results of thermal aging performance of cable sheath layer

[0079] As shown in Table 3, after heat aging at 135℃ for 168 hours, the sheath layers of Examples 1-6 retained 88-90% of the tensile strength and 85-87% of the elongation at break, both of which are far higher than the standard requirement of 80%, indicating that the cables have excellent heat aging resistance.

[0080] Comparative Examples 1-3 all met the requirements for heat aging retention rates (above 80%), but Comparative Example 4, lacking both organic modified montmorillonite and UV stabilizer, had a tensile strength retention rate of only 72% and an elongation at break retention rate of only 68% after aging, failing to meet the standard requirements. This result indicates that the combination of organic modified montmorillonite and UV stabilizer is crucial for long-term aging resistance: organic modified montmorillonite can form a nano-layered barrier effect, delaying the diffusion of heat and oxygen; the combined UV stabilizer can effectively inhibit the photo-oxidative degradation of cables in outdoor or light-exposed environments, extending their service life.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A flame-retardant, highly flexible cross-linked polyethylene insulated power cable, characterized in that, From the inside out, it includes: conductor, insulating layer, filling layer, wrapping layer and sheath layer; The conductor is a Class 5 or Class 6 soft copper conductor; The insulating layer comprises the following components in parts by weight: 85-95 parts polyethylene, 8-12 parts ethylene-vinyl acetate copolymer, 10-15 parts modified magnesium hydroxide, 2.0-2.5 parts dicumyl peroxide, 0.3-0.5 parts triallyl isocyanurate, and 0.3-0.5 parts antioxidant 1010; The filling layer is an alkali-free glass fiber rope with aluminum hydroxide powder coated on its surface; The wrapping layer is two layers of halogen-free flame-retardant mica tape or one layer of ceramicized silicone rubber tape; The sheath layer comprises the following components by weight: 50-65 parts polyethylene, 15-25 parts ethylene-octene copolymer, 5-8 parts maleic anhydride-grafted polyethylene, 8-12 parts DOPO-PEG, 10-15 parts pentaerythritol phosphate, 3-5 parts organically modified montmorillonite, 1-2 parts ultraviolet stabilizer, and 1-3 parts ethylene bis-stearamide. The polyethylene in the insulation layer and sheath layer has a melt flow index of 0.5-1.5 g / 10 min and a density of 0.915-0.925 g / cm³. 3 .

2. The flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The method for preparing the modified magnesium hydroxide includes the following steps: Magnesium hydroxide powder was dispersed in a mixed solvent of anhydrous ethanol and water in a mass ratio of 7:3; Add vinyltriethoxysilane and polybutadiene, and stir at 300-500 rpm for 4-6 hours at 70-80℃. After the reaction is complete, filter while hot to obtain filter cake. The filter cake is washed 2-3 times with anhydrous ethanol, and then washed with deionized water until neutral. The washed product was dried in a vacuum drying oven at 50-60℃ for 12-14 hours, then ground and passed through a 200-300 mesh sieve to obtain surface-modified magnesium hydroxide.

3. The flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 2, characterized in that, The magnesium hydroxide powder has a particle size of 3-5 μm, and the ratio of magnesium hydroxide powder to anhydrous ethanol and water mixed solvent is 1 g: 8-10 ml; the amount of vinyltriethoxysilane is 2-4% of the mass of magnesium hydroxide powder; the number average molecular weight of polybutadiene is 1000-2000 Da, and its amount is 1-2% of the mass of magnesium hydroxide powder.

4. The flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The method for preparing the alkali-free glass fiber rope with aluminum hydroxide powder coating on the surface Includes the following steps: Aluminum hydroxide powder and ethylene-vinyl acetate emulsion are mixed at a mass ratio of 1:2-3, and deionized water is added. The mixture is stirred for 15-20 minutes at a speed of 1000-1500 rpm using a high-speed disperser to prepare a uniformly dispersed suspension. The alkali-free glass fiber rope is completely immersed in the suspension slurry for 2-3 minutes. The impregnated fiber rope is squeezed through a pair of squeezing rollers, and the gap between the squeezing rollers is adjusted to 0.8-0.9 times the rope diameter. The amount of slurry retained in the fiber rope after extrusion is controlled to be 25-35% of the dry fiber rope mass. The extruded fiber rope is sent into a hot air circulating oven and dried at 60-80℃ for 45-60 minutes. Spray 0.5-1.0% of the rope's weight of talc powder onto the dried fiber rope surface to obtain an alkali-free glass fiber rope with an aluminum hydroxide powder coating.

5. A flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 4, characterized in that, The alkali-free glass fiber rope has a diameter of 2.0-5.0 mm and is made of 10-20 strands of alkali-free glass fiber yarn twisted together, with a twist of 30-50 twists / meter; the aluminum hydroxide powder has a particle size of 3-5 μm, and the amount of deionized water added is 70-80% of the mass of the aluminum hydroxide powder; the ethylene-vinyl acetate emulsion has a solid content of 50-55% and a vinyl acetate content of 14-18%.

6. The flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The preparation method of the DOPO-PEG includes the following steps: DOPO was dissolved in a 1:1 mixture of dioxane and N,N-dimethylformamide, and maleic anhydride was added. The mixture was heated to 110-120°C under nitrogen protection and stirred at 200-300 rpm for 8-12 hours. After the reaction was completed, the mixture was cooled to room temperature, and 3-5 times the volume of deionized water was added. The mixture was stirred until the product precipitated. The white solid crude product was collected by filtration, washed 2-3 times with deionized water, and dried under vacuum at 70-80°C for 20-24 hours to obtain the DOPO-MA intermediate. The DOPO-MA intermediate was mixed with polyethylene glycol, p-toluenesulfonic acid was added as a catalyst, and the mixture was heated to 150-160°C under nitrogen protection. The mixture was stirred at 200-300 rpm for 6-8 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product solidified into a solid block. After removing the solid block, it is first crushed by a coarse crusher or hammer mill to obtain coarse particles. Then, the coarse particles are further ground in a grinder and passed through an 80-100 mesh sieve to obtain DOPO-PEG.

7. A flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 6, characterized in that, The molar ratio of DOPO to the mixed solvent of dioxane and N,N-dimethylformamide is 0.1 mol: 15-30 ml; the molar ratio of DOPO to maleic anhydride is 1:1.2-1.5; the number average molecular weight of the polyethylene glycol is 3500-4500 Da, and the mass ratio of DOPO-MA intermediate to polyethylene glycol is 1:2-3; the amount of p-toluenesulfonic acid used is 1.5-3.0% of the total weight of DOPO-MA intermediate and polyethylene glycol.

8. The flame-retardant, highly flexible cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The preparation method of the organically modified montmorillonite includes the following steps: Montmorillonite was dispersed in deionized water to prepare a montmorillonite suspension with a mass fraction of 5-10%, and stirred in a water bath at 70-80℃ for 30-60 minutes to ensure full dispersion. Dissolve hexadecyltrimethylammonium bromide in deionized water to prepare an intercalating agent solution with a mass fraction of 10-15%, wherein the amount of hexadecyltrimethylammonium bromide is 15-25% of the mass of montmorillonite; The intercalating agent solution was slowly added dropwise to the montmorillonite suspension under stirring. After the addition was complete, the temperature was raised to 80-90℃ and the reaction was continued to be stirred at 300-500 rpm for 4-6 hours. After the reaction was completed, the product was filtered to obtain a filter cake. Wash the filter cake repeatedly with deionized water 4-5 times, then dry it in a vacuum drying oven at 60-80℃ for 12-24 hours. After drying, grind the filter cake and pass it through a 200-300 mesh sieve to obtain organic modified montmorillonite.

9. A method for preparing a flame-retardant, highly flexible cross-linked polyethylene insulated power cable as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Conductor preparation: After drawing and annealing, copper rods are bundled and re-stranded by a stranding machine to obtain soft copper conductors with a stranding pitch ratio of 12-16. S2. Insulation layer extrusion: Insulation layer material is extruded onto the conductor in single layer through an extruder to form an insulated wire core; wherein, the extrusion temperature is: barrel zone 1 135-145℃, zone 2 145-155℃, zone 3 150-160℃, and die head 150-160℃; screw speed is 40-50 rpm; insulation layer thickness is 1.8-2.0 mm; S3. Crosslinking treatment: The insulated wire core after S2 extrusion is continuously fed into the CCV catenary crosslinking tube. Dry heating crosslinking is carried out under nitrogen protection. The temperature of the heating section of the crosslinking tube is controlled at 250-280℃, the nitrogen pressure inside the tube is maintained at 0.8-1.5MPa, the nitrogen purity is not less than 99.5%, and the time is 2-5 minutes. After the wire core completes the crosslinking reaction under high temperature nitrogen protection, it passes through the precooling section in sequence. Water cooling is used. The precooling water temperature is controlled at 60-80℃ to cool the surface temperature of the wire core to below 100℃. Then it enters the cooling water section, where circulating cooling water at 20-40℃ is used for full cooling to fully crosslink and shape the insulation layer. S4. Cable filling: Three S3 cross-linked insulated wire cores are twisted together and cabled using an untwisting twisting method. The cable pitch ratio is controlled at 20-30 times. At the same time, the gaps are filled with alkali-free glass fiber rope coated with aluminum hydroxide powder to ensure that the cable core is round and dense. S5. Wrapping with tape: Wrap two layers of halogen-free flame-retardant mica tape or one layer of ceramicized silicone rubber tape around the outside of the cable core, with an overlap rate of 30-35% for each layer; S6. Sheath Extrusion: The sheath material is extruded over the outer layer of the tape using an extruder. Extrusion temperatures are: Zone 1 of the barrel 150-160℃, Zone 2 160-165℃, Zone 3 165-170℃, Die head 170-175℃, and screw speed 35-45 rpm. After extrusion, the material undergoes gradient cooling in a 20-26m long cooling water tank: Section 1 at 70-80℃ for 8-10m, Section 2 at 50-60℃ for 6-8m, and Section 3 at 25-35℃ for 6-8m. After drying, the material is printed, wound up, and the finished cable is obtained.

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