A crosslinked polyethylene cable and a method for producing the same

Abstract

The application discloses a kind of crosslinked polyethylene cable and preparation method thereof, it is related to the field of polymer materials.The crosslinked polyethylene cable of the application includes copper conductor, insulating layer, copper band shielding layer, steel band armoring layer and high-density polyethylene sheath layer.The insulating layer is made of cable material particles;The cable material particles include the following mass parts of raw materials:acetone 50-60 parts, dicumyl peroxide 12-15 parts, triallyl isocyanurate 8-10 parts, low-density polyethylene 765-955 parts, synergistic nanorod 80-100 parts, modified toughening agent masterbatch 120-150 parts, antioxidant 3-4 parts, dilauryl thiodipropionate 2-3 parts, zinc stearate 10-12 parts.In the application, the introduction of triallyl isocyanurate, synergistic nanorod, modified toughening agent masterbatch and other raw materials simultaneously improves the flame retardancy, smoke suppression, low temperature resistance, water tree aging resistance and heat resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a cross-linked polyethylene cable and its preparation method. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables are widely used in urban power distribution networks, rail transit, new energy power plants, and industrial power distribution due to their excellent electrical insulation properties, good mechanical processing properties, and low dielectric loss. Their insulation layer uses low-density polyethylene as the matrix, forming a three-dimensional network structure through peroxide cross-linking. The long-term allowable operating temperature can reach 90℃, significantly improving the cable's current carrying capacity and service life.

[0003] However, in practical applications, the insulation layer of cross-linked polyethylene (XLPE) cables still has the following performance shortcomings: First, poor flame retardancy and smoke suppression performance, as polyethylene itself is a flammable material that releases a large amount of toxic fumes and heat when burning; second, insufficient resistance to water treeing, as dendritic water tree defects gradually form inside the insulation layer under the combined action of long-term humid environments and alternating electric fields, leading to a decrease in insulation resistance; third, poor low-temperature toughness, as the movement of polyethylene molecular chains is restricted after cross-linking, making it prone to brittleness in extreme low-temperature environments below -40℃; and fourth, limited heat resistance, as ordinary XLPE has a low heat distortion temperature, making it prone to thermal deformation and melting under overload or short-circuit conditions, leading to insulation failure and limiting the short-term overload capacity of the cable. Therefore, the flame retardancy, smoke suppression, low-temperature resistance, water treeing resistance, and heat resistance of the insulation layer of existing XLPE cables still need to be improved simultaneously. Summary of the Invention

[0004] The purpose of this invention is to provide a cross-linked polyethylene cable and its preparation method, thereby solving the following technical problems: Existing cross-linked polyethylene cables still suffer from poor flame retardancy, smoke suppression, low-temperature resistance, water tree aging resistance, and heat resistance.

[0005] The objective of this invention can be achieved through the following technical solutions: A cross-linked polyethylene cable includes a copper conductor, an insulation layer, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer. The insulation layer is made of cable material granules; the cable material granules comprise the following raw materials in parts by weight: 50-60 parts acetone, 12-15 parts dicumyl peroxide, 8-10 parts triallyl isocyanurate, 765-955 parts low-density polyethylene, 80-100 parts synergistic nanorods, 120-150 parts modified toughening agent masterbatch, 3-4 parts antioxidant, 2-3 parts disodium thiopropionate, and 10-12 parts zinc stearate. The enhanced nanorods are prepared by first hydrolyzing hydroxyapatite nanorods with tetraethyl orthosilicate to coat them with silica, then grafting them with vinyltriethoxysilane, then grafting them with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and finally coating them with melamine-formaldehyde-borate resin. The modified toughening agent masterbatch is prepared by first copolymerizing monomethacrylate-terminated polydimethylsiloxane with 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole and an antioxidant to obtain an organosilicon elastomer, and then melt-blending it with low-density polyethylene.

[0006] Preferably, the method for preparing the synergistic nanorods is as follows: A1: Hydroxyapatite nanorods were added to anhydrous ethanol 1 and ultrasonically dispersed for 30 min. Then, tetraethyl orthosilicate, ammonia 1, and deionized water 1 were added while stirring, and the mixture was stirred at 40 °C for 60 min. The mixture was then centrifuged, the precipitate was washed, and the precipitate was redispersed in anhydrous ethanol 2. Subsequently, vinyltriethoxysilane, ammonia 2, and deionized water 2 were added while stirring, and the mixture was stirred at 25 °C for 8 h. Finally, the mixture was centrifuged, the precipitate was washed, and the precipitate was dried to obtain pretreated nanorods. A2: Pretreated nanorods and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to 1,4-dioxane and ultrasonically dispersed for 20 min. Then, high-purity nitrogen was introduced to remove oxygen for 45 min. Dicumyl peroxide was then added and the system was sealed. The mixture was then refluxed at 100 °C for 8 h. After cooling, the mixture was centrifuged, the precipitate was washed, and dried to obtain modified nanorods. A3: Melamine and formaldehyde aqueous solution were added to anhydrous ethanol and the pH was adjusted to 9.0. The mixture was stirred at 75°C for 1 hour. Modified nanorods were then added and ultrasonically dispersed for 30 minutes. The mixture was stirred at 75°C for 1 hour. Boric acid was then added and the pH was adjusted to 9.5-10.0. The mixture was then stirred and refluxed at 75°C for 10 hours. Finally, the mixture was centrifuged, the precipitate was washed, and dried to obtain the enhanced nanorods.

[0007] Preferably, the mass ratio of anhydrous ethanol 1, hydroxyapatite nanorods, tetraethyl orthosilicate, ammonia 1, deionized water 1, anhydrous ethanol 2, vinyltriethoxysilane, ammonia 2, and deionized water 2 in A1 is 450:50-60:30-36:1:20:450:15-18:3:10; The mass fraction of ammonia in A1 is 25%.

[0008] Preferably, the mass ratio of 1,4-dioxane, pretreated nanorods, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and dicumyl peroxide in A2 is 400:60-70:28-32:1.5-1.7.

[0009] Preferably, the mass ratio of anhydrous ethanol, melamine, formaldehyde aqueous solution, modified nanorods, and boric acid in A3 is 150:18:30:70-75:10; The formaldehyde aqueous solution described in A3 has a mass fraction of 37%.

[0010] Preferably, the modified toughening agent masterbatch is prepared as follows: B1: Add monomethacrylate-terminated polydimethylsiloxane, 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, and antioxidant to xylene and stir for 20-30 min. Then, purge with nitrogen for 30 min to remove oxygen. Next, add azobisisobutyronitrile, seal the system, and stir at 70 °C for 5 h. Finally, distill under reduced pressure at 80 °C to recover 89% of the xylene, and obtain the organosilicon elastomer. B2: Mix low-density polyethylene, antioxidant, and silicone elastomer, then melt-blend at 110-120℃ for 5-8 minutes, cool and pulverize to obtain modified toughening agent masterbatch.

[0011] Preferably, the mass ratio of xylene, monomethacrylate-terminated polydimethylsiloxane, 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, antioxidant, and azobisisobutyronitrile in B1 is 200-220:40:8:6:0.3.

[0012] Preferably, the mass ratio of low-density polyethylene, antioxidant, and silicone elastomer in B2 is 100:0.1:75-80.

[0013] A method for preparing a cross-linked polyethylene cable includes the following steps: S1: Add dicumyl peroxide and triallyl isocyanurate to acetone and stir for 30 min to obtain a mixed solution; S2: Mix low-density polyethylene, enhanced nanorods, modified toughening agent masterbatch, antioxidant, dodecyl thiodipropionate, and zinc stearate and stir at 1500 r / min for 15 min. Then, mix and granulate, cool with water, air dry, cut into pellets, and dry. Then, add the mixed solution and stir for 30-50 min. Finally, dry to obtain cable material granules. S3: The copper conductor formed by twisting copper wires is preheated to 110°C. Then, cable material particles are extruded onto the surface of the copper conductor to form an insulation layer. Then, cross-linking treatment is performed, followed by vacuum degassing. After cooling, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer are sequentially coated to obtain a cross-linked polyethylene cable.

[0014] Preferably, the crosslinking process is as follows: a copper conductor covered with an insulating layer is fed into a continuous vulcanization pipeline with a heating section of 170°C, a main crosslinking section of 175°C, and a heat preservation section of 175°C, and then left in a pipeline under a nitrogen atmosphere of 1.5 MPa for 25-35 minutes.

[0015] The beneficial effects of this invention are: This invention provides a cross-linked polyethylene cable and its preparation method. The invention simultaneously improves the tensile strength, impact strength, flame retardancy, smoke suppression, low temperature resistance, water tree aging resistance and heat resistance of the cross-linked polyethylene cable through the following method.

[0016] (1) The enhanced nanorods of the present invention are hydroxyapatite nanorods modified in three steps: silica coating, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide grafting, and melamine-formaldehyde-boric acid resin coating, forming a multi-layered coating structure of "rigid inorganic core-silica intermediate layer-phosphorus nitrogen boron functional shell". The hydroxyapatite nanorods themselves have high modulus and high strength. Their nano-size effect can form a large number of physical cross-linking points in the polyethylene matrix, restricting the slippage of molecular chains and significantly improving the tensile strength and elastic modulus of the material. The organic coating layer on the surface eliminates the interfacial tension between the inorganic filler and the non-polar polyethylene matrix, reduces interfacial defects and stress concentration, and avoids the problem of sudden drop in impact strength caused by the direct addition of pure inorganic fillers. The enhanced nanorods constitute a halogen-free flame-retardant system with synergistic phosphorus-nitrogen-boron ternary structure, possessing both condensed-phase and gas-phase flame-retardant effects. Phosphorus-based flame retardants decompose at high temperatures to generate phosphates, promoting the dehydration and char formation of the polyethylene matrix. Boron combines with the char layer to form a glassy borate protective layer, blocking heat and oxygen transfer. Water vapor generated from the decomposition of hydroxyapatite dilutes combustible gases, while the silica layer enhances the mechanical strength of the char layer, preventing it from cracking. Phosphorus-based flame retardants release phosphorus-oxygen free radicals in the gas phase, which can inhibit the combustion chain reaction by capturing hydroxyl and hydrogen free radicals. The dense char layer acts as a barrier, hindering the escape of smoke particles, while efficient char formation reduces the generation of volatile combustibles, thus significantly reducing smoke density. The high aspect ratio of the nanorods creates a "maze effect" in the matrix, significantly extending the diffusion path of water molecules and ions and reducing the water permeation rate. The hydrophobic organic coating on the surface reduces the adsorption and aggregation of water molecules at the filler-matrix interface, avoiding the formation of water tree initiation points at the interface. The uniform dispersion of the nanorods in the matrix reduces the size and number of structural defects such as micropores, lowering the probability of water tree initiation. The addition of rigid nanofillers increases the glass transition temperature and heat distortion temperature of the matrix, restricting the movement of molecular chains at high temperatures. The char layer formed by the flame-retardant system provides thermal insulation and protection at high temperatures, delaying the thermal decomposition process of the material and improving its thermal stability.

[0017] (2) The modified toughening agent masterbatch of the present invention is prepared by first copolymerizing monomethacrylate-terminated polydimethylsiloxane with 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole and antioxidant GM, and then premixing it with low-density polyethylene. The polydimethylsiloxane elastomer is uniformly dispersed in the polyethylene matrix in a "sea-island structure". When the material is impacted, the elastomer particles act as stress concentration points, inducing a large number of crazes and shear bands, absorbing a large amount of impact energy, thereby significantly improving the impact strength of the material. However, directly adding polydimethylsiloxane will lead to severe phase separation due to poor compatibility, and the toughening effect is limited. Pre-preparing it into a masterbatch can significantly improve the dispersion uniformity of the elastomer in the polyethylene matrix and effectively improve the toughening efficiency. The glass transition temperature of polydimethylsiloxane is extremely low. It can still maintain good elasticity at a low temperature of -40℃, which can effectively prevent the propagation of cracks in the polyethylene matrix at low temperatures and significantly improve the low-temperature toughness of the material.

[0018] (3) The triallyl isocyanurate molecule of this invention contains three double bonds, which can act as crosslinking bridges to connect different polyethylene molecular chains. Dicumyl peroxide decomposes upon heating to generate free radicals, which trigger the formation of macromolecular free radicals in polyethylene molecular chains. When pure peroxide is crosslinked, two macromolecular free radicals directly combine to form crosslinking bonds, resulting in low crosslinking efficiency and easy side reactions such as chain breakage. After adding triallyl isocyanurate, its double bonds can preferentially react with macromolecular free radicals to form active intermediates, and then combine with another macromolecular free radical to form crosslinking bonds, significantly improving crosslinking efficiency and crosslinking density, while reducing the occurrence of side reactions. The addition of a specific amount of triallyl isocyanurate can increase the crosslinking density, optimize the crosslinking network structure, and help improve the tensile strength and elastic modulus of the material. The three-dimensional network structure formed by crosslinking completely changes the thermal behavior of polyethylene, transforming the material from thermoplastic to thermosetting. At high temperatures, the molecular chains cannot move freely or melt, so the heat distortion temperature will be significantly increased, and the thermal stability and high-temperature mechanical properties of the material will also be improved. The dense three-dimensional cross-linked network structure reduces free volume and lowers the diffusion rate of water molecules and ions; cross-linking reduces the ends and defects of polyethylene molecular chains, lowering the probability of water tree initiation; the cross-linked network has higher mechanical strength, which can prevent the propagation of water tree cracks.

[0019] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below 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.

[0021] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: Low-density polyethylene (melt index 2g / 10min), grade: Saudi SABIC HP2023J.

[0022] Example 1: A method for preparing a cross-linked polyethylene cable is as follows: S1: Add 50g of hydroxyapatite nanorods (diameter 20-30nm, length 100-200nm) to 450g of anhydrous ethanol and ultrasonically disperse for 30min. Then, while stirring, add 30g of tetraethyl orthosilicate, 1g of 25% ammonia, and 20g of deionized water and stir at 40℃ for 60min. Then, centrifuge and wash the precipitate three times with anhydrous ethanol. Then, redisperse the precipitate in 450g of anhydrous ethanol. Then, while stirring, add 15g of vinyltriethoxysilane, 3g of 25% ammonia, and 10g of deionized water and stir at 25℃ for 8h. Centrifuge and wash the precipitate three times with anhydrous ethanol. Finally, vacuum dry at 80℃ for 12h to obtain pretreated nanorods. S2: 60g of pretreated nanorods and 28g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to 400g of 1,4-dioxane and ultrasonically dispersed for 20min. Then, high-purity nitrogen was introduced to remove oxygen for 45min. 1.5g of dicumyl peroxide was added and the system was sealed. The mixture was then refluxed at 100℃ for 8h. After cooling, the mixture was centrifuged and the precipitate was washed three times with anhydrous ethanol. Finally, the mixture was vacuum dried at 80℃ for 12h to obtain the modified nanorods. S3: Add 18g of melamine and 30g of 37% formaldehyde aqueous solution to 150g of anhydrous ethanol, and adjust the pH to 9.0 with 0.1mol / L sodium hydroxide aqueous solution. Stir at 75℃ for 1h, then add 70g of modified nanorods and disperse ultrasonically for 30min. Stir at 75℃ for 1h, then add 10g of boric acid and adjust the pH to 9.5 with 0.1mol / L sodium hydroxide aqueous solution. Stir and reflux at 75℃ for 10h, centrifuge, and wash 5 times alternately with 40℃ hot deionized water and anhydrous ethanol. Finally, vacuum dry at 100℃ for 12h to obtain the enhanced nanorods. S4: Add 40g of monomethacrylate-terminated polydimethylsiloxane (viscosity average molecular weight 3000, methacrylate content 0.6mmol / g), 8g of 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, and 6g of antioxidant GM to 200g of xylene and stir for 20min. Then, purge with high-purity nitrogen for 30min to remove oxygen. Next, add 0.3g of azobisisobutyronitrile. Then, seal the system and stir at 70℃ for 5h. Finally, distill under reduced pressure at 80℃ to recover xylene until the system reaches 75g, and obtain the organosilicon elastomer. S5: Mix 100g of low-density polyethylene, 0.1g of antioxidant 1010 and 75g of organosilicon elastomer, then melt-blend at 110℃ for 5min, cool and pulverize to obtain modified toughening agent masterbatch. S6: Add 12g of dicumyl peroxide and 8g of triallyl isocyanurate to 50g of acetone and stir for 30min to obtain a mixed solution; S7: Mix 765g of low-density polyethylene, 80g of enhanced nanorods, 120g of modified toughening agent masterbatch, 3g of antioxidant 1010, 2g of dodecyl thiodipropionate, and 10g of zinc stearate and stir at 1500r / min for 15min. Then, use a co-rotating twin-screw extruder to mix and granulate at zone temperatures of 90℃, 100℃, 110℃, 120℃, die head temperature of 120℃, and screw speed of 200r / min. After water cooling and air drying, the extrudate is granulated and then vacuum dried at 60℃ for 4h. Then, 70g of mixed solution is added and stirred at 80r / min for 30min. Finally, vacuum dry at 40℃ to constant weight to obtain cable material granules. S8: The copper conductor, formed by stranding copper wires, is preheated to 110°C. Then, using a φ90 type cable extruder with a body temperature of 120°C, a die head temperature of 130°C, and a mold temperature of 135°C, the cable material particles are extruded onto the surface of the copper conductor at an extrusion speed of 15 m / min to form a 3.3 mm thick insulation layer. The material is then immediately introduced into a continuous vulcanization pipeline and cross-linked under a 1.5 MPa high-purity nitrogen atmosphere (purity 99.999%). The cross-linking process is carried out with a heating section of 170°C, a main cross-linking section of 175°C, an insulation section of 175°C, and a residence time of 25 min in the pipeline. Finally, the material is vacuum degassed for 7 days at 70°C and 50 Pa absolute pressure. After cooling, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer are sequentially coated to obtain a cross-linked polyethylene cable.

[0023] Example 2: A method for preparing a cross-linked polyethylene cable is as follows: S1: Add 55g of hydroxyapatite nanorods (diameter 20-30nm, length 100-200nm) to 450g of anhydrous ethanol and ultrasonically disperse for 30min. Then, while stirring, add 33g of tetraethyl orthosilicate, 1g of 25% ammonia, and 20g of deionized water and stir at 40℃ for 60min. Then, centrifuge and wash the precipitate 4 times with anhydrous ethanol. Then, redisperse the precipitate in 450g of anhydrous ethanol. Then, while stirring, add 16.5g of vinyltriethoxysilane, 3g of 25% ammonia, and 10g of deionized water and stir at 25℃ for 8h. Centrifuge and wash the precipitate 4 times with anhydrous ethanol. Finally, vacuum dry at 80℃ for 12h to obtain pretreated nanorods. S2: 65g of pretreated nanorods and 30g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to 400g of 1,4-dioxane and ultrasonically dispersed for 20min. Then, high-purity nitrogen was introduced to remove oxygen for 45min. 1.6g of dicumyl peroxide was added and the system was sealed. The mixture was then refluxed at 100℃ for 8h. After cooling, the mixture was centrifuged and the precipitate was washed four times with anhydrous ethanol. Finally, the mixture was vacuum dried at 80℃ for 14h to obtain the modified nanorods. S3: Add 18g of melamine and 30g of 37% formaldehyde aqueous solution to 150g of anhydrous ethanol, and adjust the pH to 9.0 with 0.1mol / L sodium hydroxide aqueous solution. Stir at 75℃ for 1h, then add 73g of modified nanorods and disperse ultrasonically for 30min. Stir at 75℃ for 1h, then add 10g of boric acid and adjust the pH to 9.8 with 0.1mol / L sodium hydroxide aqueous solution. Stir and reflux at 75℃ for 10h, centrifuge, and wash 6 times alternately with 40℃ hot deionized water and anhydrous ethanol. Finally, vacuum dry at 100℃ for 14h to obtain the enhanced nanorods. S4: Add 40g of monomethacrylate-terminated polydimethylsiloxane (viscosity average molecular weight 3000, methacrylate content 0.6mmol / g), 8g of 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, and 6g of antioxidant GM to 210g of xylene and stir for 25min. Then, purge with high-purity nitrogen for 30min to remove oxygen. Next, add 0.3g of azobisisobutyronitrile. Then, seal the system and stir at 70℃ for 5h. Finally, distill under reduced pressure at 80℃ to recover xylene until the system reaches 78g, and obtain the organosilicon elastomer. S5: Mix 100g of low-density polyethylene, 0.1g of antioxidant 1010 and 78g of organosilicon elastomer, then melt-blend at 115℃ for 7min, cool and pulverize to obtain modified toughening agent masterbatch. S6: Add 13.5g dicumyl peroxide and 9g triallyl isocyanurate to 55g acetone and stir for 30min to obtain a mixed solution; S7: Mix 860g of low-density polyethylene, 90g of enhanced nanorods, 135g of modified toughening agent masterbatch, 3.5g of antioxidant 1010, 2.5g of disodium thiopropionate, and 11g of zinc stearate and stir at 1500r / min for 15min. Then, use a co-rotating twin-screw extruder to mix and granulate at zone temperatures of 90℃, 100℃, 110℃, 120℃, die head temperature of 120℃, and screw speed of 200r / min. After water cooling and air drying, the extrudate is granulated and then vacuum dried at 60℃ for 4h. Then, 77.5g of mixed solution is added and stirred at 90r / min for 40min. Finally, vacuum dry at 40℃ to constant weight to obtain cable material granules. S8: The copper conductor, formed by stranding copper wires, is preheated to 110°C. Then, using a φ90 type cable extruder with a body temperature of 125°C, a die head temperature of 130°C, and a mold temperature of 135°C, the cable material particles are extruded onto the surface of the copper conductor at an extrusion speed of 15 m / min to form a 3.4 mm thick insulation layer. The material is then immediately introduced into a continuous vulcanization pipeline and subjected to cross-linking treatment in a 1.5 MPa high-purity nitrogen atmosphere (purity 99.999%). The treatment includes a heating section at 170°C, a main cross-linking section at 175°C, an insulation section at 175°C, and a residence time of 30 min in the pipeline. Finally, the material is vacuum degassed for 7 days at 70°C and 50 Pa absolute pressure. After cooling, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer are sequentially coated to obtain a cross-linked polyethylene cable.

[0024] Example 3: A method for preparing a cross-linked polyethylene cable is as follows: S1: Add 60g of hydroxyapatite nanorods (diameter 20-30nm, length 100-200nm) to 450g of anhydrous ethanol and ultrasonically disperse for 30min. Then, while stirring, add 36g of tetraethyl orthosilicate, 1g of 25% ammonia, and 20g of deionized water and stir at 40℃ for 60min. Then, centrifuge and wash the precipitate 5 times with anhydrous ethanol. Then, redisperse in 450g of anhydrous ethanol. Then, while stirring, add 18g of vinyltriethoxysilane, 3g of 25% ammonia, and 10g of deionized water and stir at 25℃ for 8h. Centrifuge and wash the precipitate 5 times with anhydrous ethanol. Finally, vacuum dry at 80℃ for 12h to obtain pretreated nanorods. S2: 70g of pretreated nanorods and 32g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to 400g of 1,4-dioxane and ultrasonically dispersed for 20min. Then, high-purity nitrogen was introduced to remove oxygen for 45min. 1.7g of dicumyl peroxide was added and the system was sealed. The mixture was then refluxed at 100℃ for 8h. After cooling, the mixture was centrifuged and the precipitate was washed 5 times with anhydrous ethanol. Finally, the mixture was vacuum dried at 80℃ for 16h to obtain the modified nanorods. S3: Add 18g of melamine and 30g of 37% formaldehyde aqueous solution to 150g of anhydrous ethanol, and adjust the pH to 9.0 with 0.1mol / L sodium hydroxide aqueous solution. Stir at 75℃ for 1h, then add 75g of modified nanorods and disperse ultrasonically for 30min, then stir at 75℃ for 1h. Then add 10g of boric acid and adjust the pH to 10.0 with 0.1mol / L sodium hydroxide aqueous solution. Stir and reflux at 75℃ for 10h, centrifuge, and wash alternately with 40℃ hot deionized water and anhydrous ethanol 7 times. Finally, vacuum dry at 100℃ for 16h to obtain the enhanced nanorods. S4: Add 40g of monomethacrylate-terminated polydimethylsiloxane (viscosity-average molecular weight 3000, methacrylate content 0.6mmol / g), 8g of 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, and 6g of antioxidant GM to 220g of xylene and stir for 30min. Then, purge with high-purity nitrogen for 30min to remove oxygen. Next, add 0.3g of azobisisobutyronitrile. Then, seal the system and stir at 70℃ for 5h. Finally, distill under reduced pressure at 80℃ to recover xylene until the system reaches 80g, and obtain the organosilicon elastomer. S5: Mix 100g of low-density polyethylene, 0.1g of antioxidant 1010 and 80g of organosilicon elastomer, then melt-blend at 120℃ for 8min, cool and pulverize to obtain modified toughening agent masterbatch; S6: Add 15g of dicumyl peroxide and 10g of triallyl isocyanurate to 60g of acetone and stir for 30min to obtain a mixed solution; S7: Mix 955g of low-density polyethylene, 100g of enhanced nanorods, 150g of modified toughening agent masterbatch, 4g of antioxidant 1010, 3g of disodium thiopropionate, and 12g of zinc stearate and stir at 1500r / min for 15min. Then, use a co-rotating twin-screw extruder to mix and granulate at zone temperatures of 90℃, 100℃, 110℃, 120℃, die head temperature of 120℃, and screw speed of 200r / min. After water cooling and air drying, the extrudate is granulated and then vacuum dried at 60℃ for 4h. Then, 85g of mixed solution is added and stirred at 100r / min for 50min. Finally, vacuum dry at 40℃ to constant weight to obtain cable material granules. S8: The copper conductor, formed by stranding copper wires, is preheated to 110°C. Then, using a φ90 type cable extruder with a body temperature of 130°C, a die temperature of 130°C, and a die temperature of 135°C, the cable material particles are extruded onto the surface of the copper conductor at an extrusion speed of 15 m / min to form a 3.5 mm thick insulation layer. The material is then immediately introduced into a continuous vulcanization pipeline and subjected to cross-linking treatment in a 1.5 MPa high-purity nitrogen atmosphere (purity 99.999%). The treatment includes a heating section at 170°C, a main cross-linking section at 175°C, an insulation section at 175°C, and a residence time of 35 min in the pipeline. Finally, the material is vacuum degassed for 7 days at 70°C and 50 Pa absolute pressure. After cooling, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer are sequentially coated to obtain a cross-linked polyethylene cable.

[0025] Comparative Example 1: Compared with Example 1, this comparative example only replaces the "pretreated nanorods" added in the preparation process of S2 with "hydroxyapatite nanorods (diameter 20-30nm, length 100-200nm)". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, cross-linked polyethylene cable is obtained.

[0026] Comparative Example 2: Compared with Example 1, this comparative example only replaces the "modified nanorods" added in the preparation process of S3 with the "pretreated nanorods" prepared in S1. All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a cross-linked polyethylene cable is obtained.

[0027] Comparative Example 3: Compared with Example 1, this comparative example only replaces the "enhancing nanorods" added in the preparation process of S7 with the "modified nanorods" prepared in S2. All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a cross-linked polyethylene cable is obtained.

[0028] Comparative Example 4: Compared with Example 1, this comparative example only did not add "enhancing nanorods" in the preparation process of S7. All other steps and parameters were the same, and will not be repeated here. The final product was a cross-linked polyethylene cable.

[0029] Comparative Example 5: Compared with Example 1, this comparative example only replaces the "modified toughening agent masterbatch" added in the preparation process of S7 with the "organosilicon elastomer" prepared in S4. All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a cross-linked polyethylene cable is obtained.

[0030] Comparative Example 6: Compared with Example 1, this comparative example only omits the addition of "modified toughening agent masterbatch" in the preparation process of S7. All other steps and parameters are the same, and will not be repeated here. The final product is a cross-linked polyethylene cable.

[0031] Comparative Example 7: Compared with Example 1, this comparative example only omits the addition of "enhancing nanorods and modified toughening agent masterbatch" in the preparation process of S7. All other steps and parameters are the same, and will not be repeated here. The final result is a cross-linked polyethylene cable.

[0032] Comparative Example 8: Compared with Example 1, this comparative example only omits the addition of "trimethylene isocyanurate" in the preparation process of S6. All other steps and parameters are the same, and will not be repeated here. The final product is a cross-linked polyethylene cable.

[0033] Performance testing: Determination of tensile strength: Referring to GB / T 2951.11-2008 standard, the tensile strength (MPa) of the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention was determined using the dumbbell tensile test method at 25°C and a tensile rate of 250 mm / min. The test results are shown in Table 1.

[0034] Impact strength determination: Referring to GB / T 1043.1-2008 standard, the impact strength (kJ·m) of the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention was determined using the simply supported beam impact method at 25°C and a pendulum energy of 5J. -2 The test results are shown in Table 1.

[0035] Flame retardancy testing: Referring to GB / T 2406.2-2009 standard, at 25℃, the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention were determined by vertical combustion method in an oxygen-nitrogen mixed gas flow. The minimum oxygen volume fraction (%) when the flame spread exceeded the 50mm mark line below the top of the sample after the specimens were made into specimens with a size of 100mm×10mm×4mm were prepared. The test results are shown in Table 1.

[0036] Determination of smoke suppression properties: Referring to GB / T 8323.2-2008 standard, the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention were measured using the optical density method. After preparing 25mm × 25mm specimens, they were tested in a 1m³ test chamber. 3The maximum smoke density when the radiant heat source power is 25kW is shown in Table 1.

[0037] Low temperature resistance test: Referring to GB / T 2951.14-2008 standard, the tensile strength (MPa) of the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention was determined by the dumbbell tensile test method at -40℃ for 16 hours and at a tensile rate of 250 mm / min. The test results are shown in Table 2.

[0038] Determination of the aging properties of water-resistant trees: Referring to GB / T 21224-2007, the average length (mm) of water trees in the cross-linked polyethylene cable insulation materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention was determined using the needle-plate electrode accelerated water tree aging method. The test results are shown in Table 2. The test results are as follows: the specimen thickness is 2 mm, the needle tip curvature radius is 3 μm, the test voltage is 6 kV (50 Hz AC power frequency), the test medium is 0.1 mol / L sodium chloride aqueous solution, the test temperature is 90 ℃, and the test duration is 1000 h.

[0039] Determination of heat resistance: Referring to GB / T 1634.1-2004 standard, the cross-linked polyethylene cable insulation layer materials prepared in Examples 1-3 and Comparative Examples 1-8 of this invention were measured using the three-point bending method. After preparing 80mm×10mm×4mm specimens, the temperature (°C) was measured at a load of 0.45MPa, a heating rate of 2°C / min, and a specimen deformation of 0.21mm. The test results are shown in Table 2.

[0040] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-8

[0041] Table 2: Performance test results of Examples 1-3 and Comparative Examples 1-8

[0042] Data Analysis: As can be seen from Tables 1 and 2, the cross-linked polyethylene cable prepared in the embodiments of the present invention has excellent tensile strength, impact strength, flame retardancy, smoke suppression, low temperature resistance, water tree aging resistance and heat resistance.

[0043] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A crosslinked polyethylene cable, characterized in that, It includes a copper conductor, an insulating layer, a copper strip shielding layer, a steel strip armor layer, and a high-density polyethylene sheath layer; The insulation layer is made of cable material granules; the cable material granules comprise the following raw materials in parts by weight: 50-60 parts acetone, 12-15 parts dicumyl peroxide, 8-10 parts triallyl isocyanurate, 765-955 parts low-density polyethylene, 80-100 parts synergistic nanorods, 120-150 parts modified toughening agent masterbatch, 3-4 parts antioxidant, 2-3 parts disodium thiopropionate, and 10-12 parts zinc stearate. The enhanced nanorods are prepared by first hydrolyzing hydroxyapatite nanorods with tetraethyl orthosilicate to coat them with silica, then grafting them with vinyltriethoxysilane, then grafting them with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and finally coating them with melamine-formaldehyde-borate resin. The modified toughening agent masterbatch is prepared by first copolymerizing monomethacrylate-terminated polydimethylsiloxane with 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole and an antioxidant to obtain an organosilicon elastomer, and then melt-blending it with low-density polyethylene.

2. The crosslinked polyethylene cable of claim 1, wherein, The preparation method of the enhanced nanorods is as follows: A1: Hydroxyapatite nanorods were added to anhydrous ethanol 1 and ultrasonically dispersed for 30 min. Then, tetraethyl orthosilicate, ammonia 1, and deionized water 1 were added while stirring, and the mixture was stirred at 40 °C for 60 min. The mixture was then centrifuged, the precipitate was washed, and the precipitate was redispersed in anhydrous ethanol 2. Subsequently, vinyltriethoxysilane, ammonia 2, and deionized water 2 were added while stirring, and the mixture was stirred at 25 °C for 8 h. Finally, the mixture was centrifuged, the precipitate was washed, and the precipitate was dried to obtain pretreated nanorods. A2: Pretreated nanorods and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to 1,4-dioxane and ultrasonically dispersed for 20 min. Then, high-purity nitrogen was introduced to remove oxygen for 45 min. Dicumyl peroxide was then added and the system was sealed. The mixture was then refluxed at 100 °C for 8 h. After cooling, the mixture was centrifuged, the precipitate was washed, and dried to obtain modified nanorods. A3: Melamine and formaldehyde aqueous solution were added to anhydrous ethanol and the pH was adjusted to 9.

0. The mixture was stirred at 75°C for 1 hour. Modified nanorods were then added and ultrasonically dispersed for 30 minutes. The mixture was stirred at 75°C for 1 hour. Boric acid was then added and the pH was adjusted to 9.5-10.

0. The mixture was then stirred and refluxed at 75°C for 10 hours. Finally, the mixture was centrifuged, the precipitate was washed, and dried to obtain the enhanced nanorods.

3. The cross-linked polyethylene cable according to claim 2, characterized in that, The mass ratio of anhydrous ethanol 1, hydroxyapatite nanorods, tetraethyl orthosilicate, ammonia 1, deionized water 1, anhydrous ethanol 2, vinyltriethoxysilane, ammonia 2, and deionized water 2 in A1 is 450:50-60:30-36:1:20:450:15-18:3:10; The mass fraction of ammonia in A1 is 25%.

4. The cross-linked polyethylene cable according to claim 2, characterized in that, The mass ratio of 1,4-dioxane, pretreated nanorods, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and dicumyl peroxide in A2 is 400:60-70:28-32:1.5-1.

7.

5. The cross-linked polyethylene cable according to claim 2, characterized in that, The mass ratio of anhydrous ethanol, melamine, formaldehyde aqueous solution, modified nanorods, and boric acid in A3 is 150:18:30:70-75:10; The formaldehyde aqueous solution described in A3 has a mass fraction of 37%.

6. The cross-linked polyethylene cable according to claim 1, characterized in that, The preparation method of the modified toughening agent masterbatch is as follows: B1: Add monomethacrylate-terminated polydimethylsiloxane, 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, and antioxidant to xylene and stir for 20-30 min. Then, purge with nitrogen for 30 min to remove oxygen. Next, add azobisisobutyronitrile, seal the system, and stir at 70 °C for 5 h. Finally, distill under reduced pressure at 80 °C to recover 89% of the xylene, and obtain the organosilicon elastomer. B2: Mix low-density polyethylene, antioxidant, and silicone elastomer, then melt-blend at 110-120℃ for 5-8 minutes, cool and pulverize to obtain modified toughening agent masterbatch.

7. The cross-linked polyethylene cable according to claim 6, characterized in that, The mass ratio of xylene, monomethacrylate-terminated polydimethylsiloxane, 2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]-2H-benzotriazole, antioxidant, and azobisisobutyronitrile in B1 is 200-220:40:8:6:0.

3.

8. The cross-linked polyethylene cable according to claim 6, characterized in that, The mass ratio of low-density polyethylene, antioxidant, and silicone elastomer described in B2 is 100:0.1:75-80.

9. A method for preparing a cross-linked polyethylene cable according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Add dicumyl peroxide and triallyl isocyanurate to acetone and stir for 30 min to obtain a mixed solution; S2: Mix low-density polyethylene, enhanced nanorods, modified toughening agent masterbatch, antioxidant, dodecyl thiodipropionate, and zinc stearate and stir at 1500 r / min for 15 min. Then, mix and granulate, cool with water, air dry, cut into pellets, and dry. Then, add the mixed solution and stir for 30-50 min. Finally, dry to obtain cable material granules. S3: The copper conductor formed by twisting copper wires is preheated to 110°C. Then, cable material particles are extruded onto the surface of the copper conductor to form an insulation layer. Then, cross-linking treatment is performed, followed by vacuum degassing. After cooling, a copper tape shielding layer, a steel tape armor layer, and a high-density polyethylene sheath layer are sequentially coated to obtain a cross-linked polyethylene cable.

10. The method for preparing a cross-linked polyethylene cable according to claim 9, characterized in that, The crosslinking process involves sending a copper conductor coated with an insulating layer into a continuous vulcanization pipeline with a heating section at 170°C, a main crosslinking section at 175°C, and a heat preservation section at 175°C, and then keeping it in a pipeline under a 1.5MPa nitrogen atmosphere for 25-35 minutes.

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