A modified polyethylene cable insulation material and a method for its production

Abstract

The application belongs to the technical field of polyethylene high molecular material, and particularly relates to a modified polyethylene cable insulation material and a preparation method thereof. The material comprises a polyethylene base resin, a low-migration anti-water-treeing functional master batch, a crosslinking agent, an anti-oxidation stabilizer, a voltage stabilizer and a processing aid. The functional master batch is prepared from a polyethylene carrier resin, glycidyl methacrylate grafted polyethylene, an amino-terminated polyether, surface-treated nano inorganic particles and an anti-oxidation stabilizing component. In the preparation, the nano inorganic particles are first subjected to silane surface treatment, and then the functional master batch is prepared through melt reaction extrusion, followed by melt blending with the polyethylene base, low-temperature absorption of the crosslinking agent and extrusion crosslinking molding. The application can reduce the migration of anti-water-treeing polar components and the agglomeration of nano particles, and improve the anti-water-treeing, dielectric stability and long-term insulation performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene polymer materials technology, specifically relating to a modified polyethylene cable insulation material and its preparation method. Background Technology

[0002] Polyethylene (PE) is a commonly used polyolefin material for wire and cable insulation due to its low dielectric constant, low dielectric loss, low water absorption, and good processability. For power cables, to improve the heat deformation resistance, creep resistance, and long-term operational stability of PE materials, cross-linked polyethylene insulation materials are typically prepared using methods such as peroxide cross-linking, silane cross-linking, or radiation cross-linking. Cross-linked PE is widely used in medium- and low-voltage cables and some high-voltage cables; however, under the combined effects of long-term damp heat, electric fields, thermo-oxidative stress, and mechanical stress, its insulation performance may still degrade.

[0003] During long-term cable operation, trace amounts of moisture, impurities, micropores, interface defects, or areas of concentrated local electric fields within the insulation layer can induce the development of water trees or electrical trees. Water trees typically form and expand gradually under the combined influence of moisture and electric fields, leading to a decrease in local dielectric properties, reduced breakdown strength, and shortened service life of the insulation layer. To address these issues, existing technologies often improve the aging resistance and water tree resistance of polyethylene insulation materials by adding anti-water treeing agents, voltage stabilizers, antioxidants, or nano-inorganic fillers.

[0004] However, existing modification methods still have certain shortcomings. On the one hand, some anti-water treeing additives contain polar structures such as ether bonds, hydroxyl groups, and amide groups, which can interfere with water accumulation and the development of water tree channels to a certain extent. However, if they are directly added to the polyethylene system in the form of free additives, problems such as insufficient compatibility, long-term migration, and local enrichment are likely to occur, and there may be risks of increased water absorption, increased dielectric loss, or decreased volume resistivity. On the other hand, inorganic particles such as nano-magnesium oxide, nano-silica, and nano-alumina can improve the space charge distribution or improve insulation stability through interfacial interactions. However, nanoparticles have high surface energy and are prone to agglomeration when directly added to a non-polar polyethylene matrix. Agglomeration areas may become local electric field distortion points and sources of insulation defects. In addition, existing technologies often use compatibilizers or masterbatch pre-dispersion methods to improve the distribution of additives and fillers in polyethylene. However, if anti-water treeing additives, nanofillers, compatibilizers, and polyethylene are simply physically mixed, it is still difficult to fully solve the problems of polar component migration, nanoparticle agglomeration, and the difficulty in simultaneously ensuring dielectric stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modified polyethylene cable insulation material and its preparation method. The purpose is to improve upon the problems in existing polyethylene or cross-linked polyethylene cable insulation materials, such as the easy migration of anti-water treeing additives, the potential increase in water absorption and dielectric loss after the addition of polar additives, and the tendency for nanofillers to agglomerate and form localized insulation defects when directly added. The aim is to enable the material to maintain low dielectric loss and high volume resistivity while possessing good anti-water treeing properties and helping to suppress space charge accumulation and electrical tree development.

[0006] The technical effects described in this invention are achieved through the following technical solutions: The first aspect of the present invention is to provide a modified polyethylene cable insulation material, comprising, by weight, the following raw materials: 80-100 parts of polyethylene matrix resin, 5-12 parts of low migration and water-tree resistant functional masterbatch, 1-2.5 parts of crosslinking agent, 0.2-0.8 parts of antioxidant stabilizer, 0.1-0.6 parts of voltage stabilizer, and 0.1-0.5 parts of processing aid.

[0007] Preferably, the polyethylene matrix resin is a blend of cable-grade low-density polyethylene and linear low-density polyethylene; Preferably, the mass ratio of the low-density polyethylene to the linear low-density polyethylene is 70-90:10-30; Preferably, the crosslinking agent is one of dicumyl peroxide or bis-tert-butylperoxide; more preferably, it is dicumyl peroxide. Preferably, the antioxidant stabilizer is one of antioxidant 1010, antioxidant 1076, antioxidant 168, or dilauryl thiodipropionate; Preferably, the voltage stabilizer is one of benzophenone, 4-hydroxybenzophenone, or 2-hydroxy-4-methoxybenzophenone; more preferably, it is 4-hydroxybenzophenone. Preferably, the processing aid is one of polyethylene wax, calcium stearate, or fluoropolymer processing aid; more preferably, it is polyethylene wax. Preferably, the low-migration, water-tree resistant functional masterbatch comprises, by weight, the following raw materials: 30-45 parts of polyethylene carrier resin, 35-55 parts of polyethylene compatible reactive carrier, 12-25 parts of water-tree resistant polar component, 2-6 parts of surface-treated nano-inorganic particles, and 0.1-0.4 parts of antioxidant stabilizing component. Preferably, the polyethylene carrier resin is one of low-density polyethylene or linear low-density polyethylene; Preferably, the polyethylene-compatible reactive carrier is glycidyl methacrylate-grafted low-density polyethylene with a grafting rate of 0.5–2.0 wt%. Preferably, the anti-water-tree polar component is an amino-terminated polyether; the amino-terminated polyether is polyoxypropylene diamine with a number-average molecular weight of 300-1000; the amino groups in the amino-terminated polyether can undergo a ring-opening reaction with the epoxy groups in the low-density polyethylene grafted with glycidyl methacrylate, so that the anti-water-tree polar segments are at least partially reacted and connected to the polyethylene compatible segments, thereby reducing the migration tendency of the anti-water-tree polar component during the long-term service of the cable insulation material; Preferably, the antioxidant stabilizing component is one of antioxidant 1010, antioxidant 1076, antioxidant 168, or dilauryl thiodipropionate. Preferably, in one embodiment of the present invention, the surface-treated nano-inorganic particles are vinyltriethoxysilane-treated nano-magnesium oxide; the average particle size of the nano-magnesium oxide is 50-100 nm, and the amount of vinyltriethoxysilane used is 1.0-2.0% of the mass of the nano-magnesium oxide; the specific preparation steps are as follows: Vinyltriethoxysilane was added to a 90wt% aqueous ethanol solution and stirred for 10–30 min to obtain a silane-treated solution. Nano-magnesium oxide dried at 90–120°C for 2–4 h was added to a high-speed mixer, heated to 70–90°C, and stirred at 800–1500 rpm. While stirring, the silane-treated solution was sprayed into the dried nano-magnesium oxide, and mixing continued for 20–50 min to distribute vinyltriethoxysilane on the surface of the nano-magnesium oxide. The mixture was then vacuum-dried at 80–100°C for 3–6 h, cooled, and passed through a 200-mesh sieve to obtain vinyltriethoxysilane-treated nano-magnesium oxide. Preferably, the amount of vinyltriethoxysilane used is 1.0-2.0% of the mass of nano-magnesium oxide, and the amount of the 90wt% ethanol aqueous solution used is 5-15% of the mass of nano-magnesium oxide; Preferably, in another embodiment of the present invention, the surface-treated nano-inorganic particles are octyltriethoxysilane-treated nano-silica; the average particle size of the nano-silica is 20-80 nm, and the amount of octyltriethoxysilane used is 1.0-3.0% of the mass of the nano-silica; the drying, mixing, vacuum drying and sieving conditions are the same as those for the nano-magnesium oxide surface treatment steps; Preferably, in another embodiment of the present invention, the surface-treated nano-inorganic particles are γ-methacryloxypropyltrimethoxysilane-treated nano-alumina; the average particle size of the nano-alumina is 50-150 nm, and the amount of γ-methacryloxypropyltrimethoxysilane used is 1.0-2.5% of the mass of the nano-alumina; the drying, mixing, vacuum drying and sieving conditions are the same as those for the nano-magnesium oxide surface treatment steps; Preferably, the preparation steps of the low-migration, water-tree resistant functional masterbatch are as follows: S1: Dry the polyethylene carrier resin and polyethylene compatible reactive carrier at 60-70℃ for 2-4 hours; dry the surface-treated nano-inorganic particles at 80-100℃ for 1-3 hours; and vacuum dehydrate the water-tree resistant polar component at 70-90℃ for 1-3 hours. S2: The dried polyethylene carrier resin, polyethylene compatible reactive carrier, surface-treated nano-inorganic particles and antioxidant stabilizing components from step S1 are added to a high-speed mixer and mixed at 500-1000 rpm for 5-15 minutes at 40-60°C to obtain a premix. The premix is ​​added to the main feed port of a twin-screw extruder, and the dehydrated anti-water-tree polar component is added to the twin-screw extruder through a liquid metering pump or a side feed port for extrusion. After air cooling, traction and pelletizing, the extrudate is dried at 50-60°C for 3-6 hours to obtain low-migration anti-water-tree functional masterbatch. Preferably, in step S2, the specific operation of the extrusion process is as follows: the premix is ​​added to the main feed port of the twin-screw extruder, and the dehydrated anti-water tree polar component is added to the twin-screw extruder through a liquid metering pump or a side feed port for melt reaction extrusion; the temperature of each zone of the twin-screw extruder is controlled sequentially as follows: 110-125℃, 125-140℃, 140-155℃, 150-165℃, 155-170℃, 150-165℃, the die head temperature is 145-160℃, the screw speed is 100-220 rpm, the vacuum degree of the vacuum exhaust section is -0.05--0.09 MPa, and the residence time of the material in the extruder is 2-5 minutes; In step S2, during the melt reaction extrusion process, the terminal amino group in polyoxypropylene diamine reacts with the epoxy group in low-density polyethylene grafted with glycidyl methacrylate to undergo a ring-opening reaction, so that the water-resistant polar chain segment is at least partially reacted and connected to the polyethylene compatible chain segment. A second aspect of the present invention is to provide a method for preparing a modified polyethylene cable insulation material, specifically comprising the following steps: S101: Polyethylene matrix resin, low-migration water-tree resistant functional masterbatch, antioxidant stabilizer, voltage stabilizer and processing aid are added to a high-speed mixer and mixed at 300-800 rpm for 5-15 min at 30-50℃ to obtain modified polyethylene premix; the modified polyethylene premix is ​​added to a twin-screw extruder for melt blending and extrusion treatment; the extrudate is air-cooled, drawn, and pelletized, and then dried at 45-60℃ for 3-6 h to obtain modified polyethylene base granules; S102: Add the modified polyethylene base particles to a closed low-speed mixer and heat to 65-85°C. Then, add the crosslinking agent in batches to the modified polyethylene base particles obtained in step S101 and mix at 20-80 rpm for 2-6 hours to ensure that the crosslinking agent is evenly absorbed and distributed in the modified polyethylene base particles. Then, cool down to below 40°C and discharge the material to obtain the modified polyethylene cable insulation material. S103: Add the modified polyethylene cable insulation material obtained in step S102 into the cable extruder for extrusion molding of the outer insulation layer of the conductor; during the extrusion process, the barrel temperature is controlled at 90-125℃ and the die head temperature is controlled at 115-130℃. After extrusion molding, the insulation layer is cross-linked to form a cross-linked network in the polyethylene matrix. Preferably, in step S101, the specific parameters of the extrusion process are as follows: the temperatures of each zone of the twin-screw extruder are controlled sequentially as follows: 95-110℃, 105-120℃, 115-130℃, 120-135℃, 120-135℃, and 115-130℃; the die head temperature is 115-130℃; the screw speed is 80-180 rpm; and the vacuum degree of the vacuum exhaust section is -0.04 to -0.08 MPa. Preferably, in step S102, after discharge, the obtained modified polyethylene cable insulation material is sealed and equilibrated at 20-35°C for 12-24 hours to improve the uniformity of crosslinking agent distribution in the particles. Preferably, in step S103, the specific operation of the crosslinking treatment is as follows: the cable insulation layer is prepared by continuous crosslinking, the temperature of the crosslinking tube is 180-230℃, the crosslinking time is 3-15 min, the crosslinking atmosphere is nitrogen, and the crosslinking pressure is 0.6-1.2 MPa; after crosslinking, the insulation layer is cooled in stages to reduce the temperature of the insulation layer to below 60℃; after the crosslinking is completed, the obtained insulation material is placed at 70-90℃ for degassing treatment for 12-72 h.

[0008] The beneficial effects of this invention are as follows: This invention employs a low-migration, water-tree-resistant functional masterbatch to introduce water-tree-resistant polar components, and uses glycidyl methacrylate-grafted low-density polyethylene as a polyethylene-compatible reactive carrier. The amino groups in the terminal amino polyether can undergo a ring-opening reaction with the epoxy groups in the grafted polyethylene, allowing the water-tree-resistant polar segments to be at least partially linked to the polyethylene-compatible segments. Therefore, the water-tree-resistant polar components are no longer primarily dispersed in a free state within the insulating material, reducing their migration tendency under long-term heat, water, and electric field conditions, and improving the problems of easy migration and rapid performance degradation of traditional water-tree-resistant additives.

[0009] The anti-water-tree polar segments in this invention contain polar structures such as ether bonds, which can interfere with the continuous accumulation of moisture and the development of water-tree channels in the polyethylene insulation layer. Simultaneously, these polar segments achieve compatibility confinement through a polyethylene-compatible reactive carrier, reducing the risk of localized enrichment and excessive water absorption. Therefore, this invention effectively balances low dielectric loss and high volume resistivity while improving anti-water-tree performance, alleviating the problem of balancing anti-water-tree performance and dielectric properties in traditional modification methods.

[0010] This invention further introduces surface-treated nano-inorganic particles, which are then co-dispersed with a polyethylene-compatible reactive carrier and anti-water-tree polar components in a low-migration, water-tree-resistant functional masterbatch. Treatment of nano-magnesium oxide with vinyltriethoxysilane improves the interfacial compatibility between the nanoparticles and the polyethylene system, reduces the risk of agglomeration when the nanoparticles are directly added, and helps form a more stable interfacial region, thereby effectively suppressing the generation of local electric field distortion and insulation defects in the insulating layer.

[0011] This invention employs a method of first preparing a low-migration, water-tree-resistant functional masterbatch, and then melt-blending it with a polyethylene matrix resin. This allows the water-tree-resistant polar components, surface-treated nano-inorganic particles, and polyethylene-compatible reactive carriers to complete pre-dispersion and partial reactive bonding during the masterbatch stage. Compared to simple physical mixing methods, this process significantly improves the dispersion uniformity of functional components in polyethylene insulation materials and the batch stability of industrial production.

[0012] This invention involves adding a crosslinking agent after preparing modified polyethylene base particles using a low-temperature mixing method. This avoids the risk of premature decomposition or scorching of the crosslinking agent during the high-temperature melt blending stage, thus improving the processing stability of the material. Subsequent cable extrusion molding and crosslinking treatment result in a crosslinked network formed in the polyethylene matrix, further enhancing the insulation layer's heat resistance, creep resistance, and long-term dimensional stability.

[0013] The preparation method of this invention mainly includes steps such as nanoparticle surface treatment, functional masterbatch melt reaction extrusion, polyethylene base material melt blending, low-temperature absorption of crosslinking agent and extrusion crosslinking treatment. It does not rely on a large amount of organic solvent reaction or complex multilayer nano-coating process. The overall process route is clear, has good industrial applicability, and is easy to prepare on a large scale using conventional plastic modification and cable material processing equipment. Attached Figure Description

[0014] Figure 1 Fourier transform infrared spectra of the low migration water-resistant functional masterbatch of Example 1, the direct physical mixture extruder of Comparative Example 3, glycidyl methacrylate-grafted low-density polyethylene, and polyoxypropylene diamine. Figure 2This is a comparison chart of the maximum and average lengths of water tree branches in the materials obtained in Examples 1-3 and Comparative Examples 1-5; Figure 3 The graph shows a comparison of the maximum space charge density and residual charge ratio of the materials obtained in Examples 1-3 and Comparative Examples 1-5. Detailed Implementation

[0015] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels. Experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0016] Example 1: This example provides a modified polyethylene cable insulation material, which, by weight, includes the following raw materials: 90 parts of polyethylene matrix resin, 8 parts of low migration and water-tree resistant functional masterbatch, 1.8 parts of dicumyl peroxide, 0.5 parts of antioxidant 1010, 0.3 parts of 4-hydroxybenzophenone, and 0.3 parts of polyethylene wax.

[0017] The polyethylene matrix resin is composed of cable-grade low-density polyethylene and linear low-density polyethylene in a mass ratio of 80:20, i.e., 72 parts of low-density polyethylene and 18 parts of linear low-density polyethylene.

[0018] The low-migration, water-resistant masterbatch comprises, by weight, the following raw materials: 38 parts of low-density polyethylene carrier resin, 45 parts of glycidyl methacrylate-grafted low-density polyethylene, 18 parts of polyoxypropylene diamine, 4 parts of vinyltriethoxysilane-treated nano-magnesium oxide, and 0.25 parts of antioxidant 1010.

[0019] The grafting rate of the glycidyl methacrylate-grafted low-density polyethylene is 1.2 wt%; the number-average molecular weight of the polyoxypropylene diamine is 400; and the average particle size of the nano-magnesium oxide is 80 nm.

[0020] The preparation method in this embodiment is as follows: 1. Place nano-magnesium oxide in a vacuum drying oven and dry at 105℃ for 3 hours to obtain dried nano-magnesium oxide; weigh vinyltriethoxysilane at 1.5% of the mass of nano-magnesium oxide and weigh 90wt% ethanol aqueous solution at 10% of the mass of nano-magnesium oxide. Add vinyltriethoxysilane to the 90wt% ethanol aqueous solution and stir for 20 minutes to obtain silane treatment solution. Dry nano-magnesium oxide was added to a high-speed mixer and heated to 80°C. The mixture was stirred at 1200 rpm. While stirring, the silane treatment solution was sprayed into the dry nano-magnesium oxide and the mixture was stirred for another 35 minutes. The mixture was then vacuum dried at 90°C for 4 hours. After cooling, it was passed through a 200-mesh sieve to obtain vinyltriethoxysilane-treated nano-magnesium oxide.

[0021] 2: Low-density polyethylene carrier resin and glycidyl methacrylate grafted low-density polyethylene were dried at 65°C for 3 hours, vinyltriethoxysilane-treated nano-magnesium oxide was dried at 90°C for 2 hours, and polyoxypropylene diamine was vacuum dehydrated at 80°C for 2 hours. The dried low-density polyethylene carrier resin, glycidyl methacrylate-grafted low-density polyethylene, vinyltriethoxysilane-treated nano-magnesium oxide and antioxidant 1010 were added to a high-speed mixer and mixed at 800 rpm for 10 min at 50°C to obtain a premix. The premix was added to the main feed port of a twin-screw extruder, and the dehydrated polyoxypropylene diamine was added to the twin-screw extruder via a liquid metering pump for melt reaction extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially at 120℃, 135℃, 150℃, 160℃, 165℃, and 160℃, with the die head temperature at 150℃, the screw speed at 160 rpm, the vacuum degree in the vacuum exhaust section at -0.07 MPa, and the residence time of the material in the extruder at 3 min. After air cooling, traction, and pelletizing, the extrudate was dried at 55℃ for 4 h to obtain low-migration, water-tree resistant functional masterbatch.

[0022] 3: Add polyethylene matrix resin, low migration water-tree resistant functional masterbatch, antioxidant 1010, 4-hydroxybenzophenone and polyethylene wax into a high-speed mixer and mix at 500 rpm for 10 min at 40°C to obtain modified polyethylene premix. The modified polyethylene premix was added to a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially at 105℃, 115℃, 125℃, 130℃, 130℃, and 125℃, with the die head temperature at 125℃, the screw speed at 130 rpm, and the vacuum degree in the vacuum exhaust section at -0.06 MPa. After air cooling, traction, and pelletizing, the extrudate was dried at 55℃ for 4 hours to obtain modified polyethylene base granules.

[0023] 4. Add the modified polyethylene base particles to a closed low-speed mixer and heat it to 75°C. Then, add dicumyl peroxide in three batches to the modified polyethylene base particles and mix at 50 rpm for 4 hours to ensure that the dicumyl peroxide is evenly absorbed and distributed in the modified polyethylene base particles. Then, cool it down to below 40°C, discharge the material, and equilibrate it in a closed system at 25°C for 18 hours to obtain the modified polyethylene cable insulation material.

[0024] 5: The obtained modified polyethylene cable insulation material is added to a cable extruder for extrusion molding of the outer insulation layer of the conductor. During the extrusion process, the barrel temperature is controlled at 100℃, 110℃, 120℃, and 125℃, and the die head temperature is controlled at 125℃. After extrusion molding, continuous crosslinking is carried out for crosslinking treatment. The crosslinking tube temperature is 205℃, the crosslinking time is 8min, the crosslinking atmosphere is nitrogen, and the crosslinking pressure is 0.9MPa. After crosslinking, the insulation layer temperature is reduced to below 60℃ through segmented cooling. Subsequently, the obtained insulation material is placed at 80℃ for degassing treatment for 36h.

[0025] Example 2: This example provides a modified polyethylene cable insulation material, which, by weight, includes the following raw materials: 80 parts of polyethylene matrix resin, 5 parts of low migration and water-tree resistant functional masterbatch, 2.5 parts of dicumyl peroxide, 0.8 parts of antioxidant 1010, 0.1 parts of 4-hydroxybenzophenone, and 0.5 parts of polyethylene wax.

[0026] The polyethylene matrix resin is composed of cable-grade low-density polyethylene and linear low-density polyethylene in a mass ratio of 70:30, that is, 56 parts of low-density polyethylene and 24 parts of linear low-density polyethylene.

[0027] The low-migration, water-resistant masterbatch comprises, by weight, the following raw materials: 45 parts linear low-density polyethylene carrier resin, 35 parts glycidyl methacrylate-grafted low-density polyethylene, 12 parts polyoxypropylene diamine, 6 parts octyltriethoxysilane-treated nano-silica, and 0.4 parts antioxidant 1010.

[0028] The grafting rate of the glycidyl methacrylate-grafted low-density polyethylene is 0.5 wt%; the number-average molecular weight of the polyoxypropylene diamine is 300; and the average particle size of the nano-silica is 20 nm.

[0029] The preparation method in this embodiment is as follows: 1: Place nano-silica in a vacuum drying oven and dry at 90℃ for 4 hours to obtain dried nano-silica; Weigh 3.0% of the mass of nano-silica into octyltriethoxysilane, and weigh 15% of the mass of nano-silica into a 90wt% ethanol aqueous solution. Add the octyltriethoxysilane to the 90wt% ethanol aqueous solution and stir for 30 minutes to obtain the silane treatment solution. Dry nano-silica was added to a high-speed mixer and heated to 70°C. The mixture was stirred at 800 rpm. While stirring, the silane treatment solution was sprayed into the dry nano-silica and the mixture was stirred for another 50 minutes. The mixture was then vacuum dried at 80°C for 6 hours. After cooling, it was passed through a 200-mesh sieve to obtain octyltriethoxysilane-treated nano-silica.

[0030] 2: Linear low-density polyethylene carrier resin and glycidyl methacrylate grafted low-density polyethylene were dried at 60°C for 4 hours; octyltriethoxysilane-treated nano-silica was dried at 80°C for 3 hours; polyoxypropylene diamine was vacuum dehydrated at 70°C for 3 hours; The dried linear low-density polyethylene carrier resin, glycidyl methacrylate-grafted low-density polyethylene, octyltriethoxysilane-treated nano-silica and antioxidant 1010 were added to a high-speed mixer and mixed at 500 rpm for 15 min at 40°C to obtain a premix. The premix was added to the main feed port of a twin-screw extruder, and the dehydrated polyoxypropylene diamine was added to the twin-screw extruder through a liquid metering pump for melt reaction extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially at 110℃, 125℃, 140℃, 150℃, 155℃, and 150℃, the die head temperature was 145℃, the screw speed was 100 rpm, the vacuum degree of the vacuum exhaust section was -0.05 MPa, and the residence time of the material in the extruder was 5 min. After air cooling, traction, and pelletizing, the extrudate was dried at 50℃ for 6 h to obtain low migration and water tree resistance functional masterbatch.

[0031] 3: Add polyethylene matrix resin, low migration water-tree resistant functional masterbatch, antioxidant 1010, 4-hydroxybenzophenone and polyethylene wax into a high-speed mixer and mix at 300 rpm for 15 min at 30°C to obtain modified polyethylene premix. The modified polyethylene premix was added to a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially as follows: 95℃, 105℃, 115℃, 120℃, 120℃, and 115℃. The die head temperature was 115℃, the screw speed was 80 rpm, and the vacuum degree of the vacuum exhaust section was -0.04 MPa. After air cooling, traction, and pelletizing, the extrudate was dried at 45℃ for 6 hours to obtain modified polyethylene base granules.

[0032] 4. Add the modified polyethylene base particles to a closed low-speed mixer and heat it to 65°C. Then, add dicumyl peroxide in three batches to the modified polyethylene base particles and mix at 20 rpm for 6 hours to ensure that the dicumyl peroxide is evenly absorbed and distributed in the modified polyethylene base particles. Then, cool it down to below 40°C, discharge the material, and equilibrate it in a closed system at 20°C for 24 hours to obtain the modified polyethylene cable insulation material.

[0033] 5: The obtained modified polyethylene cable insulation material is added to a cable extruder for extrusion molding of the outer insulation layer of the conductor. During the extrusion process, the barrel temperature is controlled at 90℃, 100℃, 110℃, and 115℃, and the die head temperature is controlled at 115℃. After extrusion molding, crosslinking treatment is carried out by continuous crosslinking. The crosslinking tube temperature is 180℃, the crosslinking time is 15min, the crosslinking atmosphere is nitrogen, and the crosslinking pressure is 0.6MPa. After crosslinking, the insulation layer temperature is reduced to below 60℃ by segmented cooling. Subsequently, the obtained insulation material is placed at 70℃ for degassing treatment for 72h.

[0034] Example 3: This example provides a modified polyethylene cable insulation material, which, by weight, includes the following raw materials: 100 parts of polyethylene matrix resin, 12 parts of low migration and water-tree resistant functional masterbatch, 1.0 part of dicumyl peroxide, 0.2 parts of antioxidant 1010, 0.6 parts of 4-hydroxybenzophenone, and 0.1 parts of polyethylene wax.

[0035] The polyethylene matrix resin is composed of cable-grade low-density polyethylene and linear low-density polyethylene in a mass ratio of 90:10, i.e., 90 parts of low-density polyethylene and 10 parts of linear low-density polyethylene.

[0036] The low-migration, water-resistant masterbatch comprises, by weight, the following raw materials: 30 parts of low-density polyethylene carrier resin, 55 parts of glycidyl methacrylate-grafted low-density polyethylene, 25 parts of polyoxypropylene diamine, 2 parts of γ-methacryloyloxypropyltrimethoxysilane-treated nano-alumina, and 0.1 parts of antioxidant 1010.

[0037] The grafting rate of the glycidyl methacrylate-grafted low-density polyethylene is 2.0 wt%; the number-average molecular weight of the polyoxypropylene diamine is 1000; and the average particle size of the nano-alumina is 150 nm.

[0038] The preparation method in this embodiment is as follows: 1: Place nano-alumina in a vacuum drying oven and dry at 120℃ for 2 hours to obtain dried nano-alumina; Weigh 2.5% of the mass of nano-alumina and 5% of the mass of nano-alumina and 90wt% of the aqueous ethanol solution. Add γ-methacryloxypropyltrimethoxysilane to the 90wt% aqueous ethanol solution and stir for 10 min to obtain the silane treatment solution. Dry nano-alumina was added to a high-speed mixer and heated to 90°C. The mixture was stirred at 1500 rpm. While stirring, the silane treatment solution was sprayed into the dry nano-alumina and the mixture was stirred for another 20 minutes. The mixture was then vacuum dried at 100°C for 3 hours. After cooling, the mixture was passed through a 200-mesh sieve to obtain γ-methacryloyloxypropyltrimethoxysilane-treated nano-alumina.

[0039] 2: Graft low-density polyethylene carrier resin and glycidyl methacrylate onto low-density polyethylene and dry at 70°C for 2 hours; treat nano-alumina with γ-methacryloxypropyltrimethoxysilane and dry at 100°C for 1 hour; dehydrate polyoxypropylene diamine under vacuum at 90°C for 1 hour; The dried low-density polyethylene carrier resin, glycidyl methacrylate-grafted low-density polyethylene, γ-methacryloxypropyltrimethoxysilane-treated nano-alumina and antioxidant 1010 were added to a high-speed mixer and mixed at 1000 rpm for 5 min at 60°C to obtain a premix. The premix was added to the main feed port of a twin-screw extruder, and the dehydrated polyoxypropylene diamine was added to the twin-screw extruder through a liquid metering pump for melt reaction extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially at 125℃, 140℃, 155℃, 165℃, 170℃, and 165℃, the die head temperature was 160℃, the screw speed was 220 rpm, the vacuum degree of the vacuum exhaust section was -0.09 MPa, and the residence time of the material in the extruder was 2 minutes. After air cooling, traction, and pelletizing, the extrudate was dried at 60℃ for 3 hours to obtain low-migration, water-tree resistant functional masterbatch.

[0040] 3: Add polyethylene matrix resin, low migration water-tree resistant functional masterbatch, antioxidant 1010, 4-hydroxybenzophenone and polyethylene wax into a high-speed mixer and mix at 800 rpm for 5 min at 50°C to obtain modified polyethylene premix. The modified polyethylene premix was added to a twin-screw extruder for melt blending and extrusion. The temperatures of each zone of the twin-screw extruder were controlled sequentially at 110℃, 120℃, 130℃, 135℃, 135℃, and 130℃, with the die head temperature at 130℃, the screw speed at 180 rpm, and the vacuum degree in the vacuum exhaust section at -0.08 MPa. After air cooling, traction, and pelletizing, the extrudate was dried at 60℃ for 3 hours to obtain modified polyethylene base granules.

[0041] 4. Add the modified polyethylene base particles to a closed low-speed mixer and heat it to 85°C. Then, add dicumyl peroxide in three batches to the modified polyethylene base particles and mix at 80 rpm for 2 hours to ensure that the dicumyl peroxide is evenly absorbed and distributed in the modified polyethylene base particles. Then, cool it down to below 40°C, discharge the material, and equilibrate it in a closed system at 35°C for 12 hours to obtain the modified polyethylene cable insulation material.

[0042] 5: The obtained modified polyethylene cable insulation material is added to a cable extruder for extrusion molding of the outer insulation layer of the conductor. During the extrusion process, the barrel temperature is controlled at 105℃, 115℃, 125℃, and 125℃, and the die head temperature is controlled at 130℃. After extrusion molding, continuous crosslinking is carried out for crosslinking treatment. The crosslinking tube temperature is 230℃, the crosslinking time is 3min, the crosslinking atmosphere is nitrogen, and the crosslinking pressure is 1.2MPa. After crosslinking, the insulation layer temperature is reduced to below 60℃ through segmented cooling. Subsequently, the obtained insulation material is placed at 90℃ for degassing treatment for 12h.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is that polyoxypropylene diamine is not added to the low migration water-tree resistant functional masterbatch, and it is supplemented with an equal mass of low-density polyethylene carrier resin; the other raw materials and preparation process are consistent with Example 1.

[0044] Comparative Example 2: The difference between this comparative example and Example 1 is that: the low migration water-resistant functional masterbatch does not contain glycidyl methacrylate grafted low-density polyethylene, and is supplemented with an equal mass of low-density polyethylene carrier resin; the other raw materials and preparation process are consistent with Example 1.

[0045] Comparative Example 3: The difference between this comparative example and Example 1 is that: instead of preparing the low-migration water-tree resistant functional masterbatch in advance, the raw materials corresponding to the low-migration water-tree resistant functional masterbatch in Example 1 are directly added to the preparation step of the modified polyethylene base particles in a one-time melt blending according to the converted amount; specifically, this comparative example does not add 8 parts of the low-migration water-tree resistant functional masterbatch, but directly adds 2.89 parts of low-density polyethylene carrier resin, 3.42 parts of glycidyl methacrylate-grafted low-density polyethylene, 1.37 parts of polyoxypropylene diamine, 0.30 parts of vinyltriethoxysilane-treated nano magnesium oxide, and 0.02 parts of antioxidant 1010 when preparing the modified polyethylene base particles; the remaining raw materials and preparation process are consistent with Example 1.

[0046] Comparative Example 4: The difference between this comparative example and Example 1 is that: the low migration anti-water tree functional masterbatch does not contain vinyltriethoxysilane-treated nano-magnesium oxide, and is supplemented with an equal mass of low-density polyethylene carrier resin; the other raw materials and preparation process are consistent with Example 1.

[0047] Comparative Example 5: The difference between this comparative example and Example 1 is that untreated nano-magnesium oxide was used instead of vinyltriethoxysilane-treated nano-magnesium oxide in the low-migration anti-water-tree functional masterbatch; the other raw materials and preparation process are the same as in Example 1.

[0048] Performance Testing: To verify the effects of the low-migration, water-tree-resistant functional masterbatch, the reaction fixation of the water-tree-resistant polar components, the surface-treated nano-inorganic particles, and the masterbatch pre-dispersion process on the crosslinking stability, water-tree resistance, low migration, dielectric stability, and space charge suppression performance of the modified polyethylene cable insulation material of this invention, performance tests were conducted on the materials obtained in Examples 1-3 and Comparative Examples 1-5. Unless otherwise specified, all test samples were taken from the cable insulation layer samples obtained in Examples 1-3 and Comparative Examples 1-5 after extrusion molding, continuous crosslinking, segmented cooling, and degassing in step 5, without secondary crosslinking treatment. Before testing, the obtained cable insulation layer was peeled off from the outside of the conductor and prepared into sheet samples of different thicknesses using a slicing machine. Depending on the test item, the sample thickness was controlled to be 0.3±0.02mm, 0.5±0.05mm, or 1.0±0.10mm, respectively. The 0.3±0.02mm sample was used for space charge testing; the 0.5±0.05mm sample was used for dielectric properties, volume resistivity, and AC breakdown strength testing; and the 1.0±0.10mm sample was used for thermal elongation, tensile properties, water tree aging, and hot water immersion testing. The resulting sheet samples were degassed at 80℃ for 48 hours, then conditioned in an environment of 23±2℃ and 50±5% relative humidity for 24 hours before testing. Unless otherwise specified, three parallel samples were set for each test, and numerical results are expressed as mean ± standard deviation.

[0049] For the gel content test, a cross-linked sheet sample with a mass of 0.20–0.30 g was taken and recorded as m0. The sample was placed in a pre-weighed stainless steel mesh bag and refluxed in xylene for 12 h. After extraction, the sample was removed and vacuum dried at 80 °C to constant weight. The mass of insoluble matter after drying was weighed and recorded as m1. The gel content was calculated using the following formula: Gel content / % = m1 / m0 × 100%.

[0050] For the thermal elongation test, the cross-linked sheet was cut into dumbbell-shaped specimens with a thickness of 1.0±0.10 mm. The specimens were placed in a hot air oven at 200±3℃ and held under a load of 0.20 MPa for 15 min. The thermal elongation under the load was then measured. The load was then removed and the specimens were allowed to recover at 200±3℃ for another 5 min. After cooling to room temperature, the permanent deformation rate was measured.

[0051] For tensile property testing, the cross-linked sheet was cut into dumbbell-shaped specimens and subjected to tensile testing at 23±2℃ and a tensile speed of 250 mm / min. The tensile strength and elongation at break were recorded. The test results for gel content, thermal elongation, permanent deformation rate, tensile strength, and elongation at break are shown in Table 1.

[0052] The low-migration, water-tree resistant functional masterbatch obtained in Example 1, the corresponding direct physical mixture extruder in Comparative Example 3, glycidyl methacrylate-grafted low-density polyethylene, and polyoxypropylene diamine were vacuum-dried at 80°C for 12 hours and then subjected to ATR-FTIR testing with a scanning range of 4000–650 cm⁻¹. -1 The resolution is 4cm. -1 The scan count was 32. The tests focused on observing the changes in epoxy-related absorption peaks in glycidyl methacrylate-grafted low-density polyethylene, as well as the retention and changes in characteristic absorption peaks related to ether bonds and amino groups in polyoxypropylene diamine within the masterbatch. This was used to help determine whether the ring-opening reaction between terminal amino groups and epoxy groups occurred during the melt reaction extrusion process. The Fourier transform infrared spectroscopy results are shown below. Figure 1 .

[0053] Cross-linked sheets with a thickness of 1.0 ± 0.10 mm were cut into 30 mm × 30 mm samples. The water needle electrode method was used for testing: a water needle cavity was set on one side of the sample, with a contact area diameter of 2 mm between the water needle cavity and the sample. A 0.1 mol / L sodium chloride aqueous solution was added to the water needle cavity, and a platinum wire electrode was inserted as a high-voltage electrode. A stainless steel plate electrode was attached to the other side of the sample as a grounding electrode. During the test, the contact area between the water needle cavity and the sample was kept consistent. An AC voltage of 3.0 kV and a frequency of 1 kHz were applied, the test temperature was 50 ± 2℃, and the aging time was 168 h. After aging, the sample was sliced ​​along the electric field direction, with a slice thickness controlled to 100–200 μm. The slices were stained in a 0.5 wt% methylene blue aqueous solution for 20 min, rinsed with deionized water, and air-dried. The morphology of the water tree was observed using an optical microscope at 100x magnification. At least five effective observation areas were selected for each sample, and the maximum and average lengths of the water trees were measured. The maximum and average lengths of water trees were used as evaluation indicators for water tree resistance. Shorter water tree lengths indicate a better ability of the material to suppress water tree development. The test results for the maximum and average lengths of water trees are shown below. Figure 2 .

[0054] The cross-linked sheets obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to hot water immersion tests. A cross-linked sheet sample with a thickness of 1.0 ± 0.10 mm and dimensions of 50 mm × 50 mm was taken and vacuum dried at 80 °C to constant weight. The initial mass was recorded as m0. The sample was then completely immersed in deionized water at 90 ± 2 °C for 168 h. After immersion, the sample was removed, and the surface moisture was quickly wiped off with lint-free paper. The wet mass was recorded as mw within 5 min. The sample was then dried in a vacuum drying oven at 60 °C to constant weight. The mass after immersion and drying was recorded as m2. The water absorption rate was calculated using the following formula: Water absorption rate (%) = (mw - m0) / m0 × 100%. The hot water immersion mass loss rate was calculated using the following formula: Hot water immersion mass loss rate (%) = (m0 - m2) / m0 × 100%.

[0055] Furthermore, to evaluate the dielectric stability after hot water immersion, the samples that had been immersed and then re-dried were used to measure the dielectric loss factor tanδ at 23±2℃, and compared with the dielectric loss factor before immersion. The change rate of dielectric loss after hot water immersion was calculated using the following formula: Change rate of dielectric loss / % = (tanδ after immersion - tanδ before immersion) / tanδ before immersion × 100%. The test results of water absorption rate, hot water immersion mass loss rate, and change rate of dielectric loss are shown in Table 2.

[0056] For dielectric property testing, a cross-linked sheet with a thickness of 0.5 ± 0.05 mm was used as the sample, and circular electrodes with a diameter of 25 mm were placed on both sides of the sample. The test temperature was 23 ± 2℃, the test frequency was 50 Hz, and the test electric field strength was 1 kV / mm. The relative permittivity and dielectric loss factor tanδ were recorded. Each test group had no fewer than 3 parallel samples.

[0057] For volume resistivity testing, a cross-linked sheet with a thickness of 0.5±0.05mm was used as the sample. The three-electrode method was used for testing. The test temperature was 23±2℃, the relative humidity was 50±5%, a DC voltage of 500V was applied, and the current value was read after stabilizing for 60s and the volume resistivity was calculated.

[0058] For AC breakdown strength testing, a cross-linked sheet with a thickness of 0.5±0.05 mm was used as the sample. The sample was placed in insulating oil to reduce interference from edge discharge and air breakdown. A ball-to-ball electrode structure with an electrode diameter of 25 mm was used for testing. The test temperature was 23±2℃, and the voltage ramp rate was 2 kV / s until the sample broke down. The breakdown voltage was recorded, and the AC breakdown strength was calculated based on the sample thickness. At least 10 valid breakdown points were tested for each material group, and invalid data caused by edge breakdown or obvious electrode contact abnormalities were discarded. The test results for dielectric loss factor, relative permittivity, volume resistivity, and AC breakdown strength are shown in Table 3.

[0059] A cross-linked sheet with a thickness of 0.3±0.02 mm was used as the sample, and aluminum foil electrodes or vapor-deposited metal electrodes were applied to both sides of the sample. Before testing, the sample was placed at 23±2℃ for 24 hours. During testing, a DC electric field of 40 kV / mm was applied, and the polarization time was 1800 s. The space charge distribution during polarization was recorded; subsequently, a short circuit was applied for 600 s, and the change in residual space charge during depolarization was recorded. The maximum space charge density inside the sample at 1800 s polarization and the proportion of residual charge after 600 s short circuit were used as evaluation indicators. The residual charge proportion was calculated using the following formula: Residual charge proportion / % = (Integral of absolute value of space charge inside the sample after 600 s short circuit / Integral of absolute value of space charge inside the sample at 1800 s polarization) × 100%. The lower the maximum space charge density and the lower the residual charge proportion, the better the material's ability to suppress space charge accumulation and promote charge release. The test results for maximum space charge density and residual charge proportion are shown in [the table below]. Figure 3 .

[0060] Table 1. Test results of crosslinking degree, thermal elongation properties and basic mechanical properties of the examples and comparative samples.

[0061] Table 2. Test results of migration, water absorption rate and media loss rate after hot water immersion of the examples and comparative samples.

[0062] Table 3. Test results of dielectric properties, volume resistivity, and AC breakdown strength of the examples and comparative samples.

[0063] As shown in Table 1, the materials obtained in Examples 1-3 all formed relatively stable cross-linked networks and maintained good basic mechanical properties, indicating that the introduction of the low-migration, water-tree-resistant functional masterbatch did not significantly disrupt the polyethylene cross-linking system. Comparative Example 2 did not include glycidyl methacrylate-grafted low-density polyethylene, and the polyoxypropylene diamine lacked effective reaction fixation and compatibility bridging. Comparative Example 3 did not pre-prepare the functional masterbatch, resulting in insufficient reaction connection and pre-dispersion of the functional components. Comparative Example 5 used untreated nano-magnesium oxide, leading to poor interfacial compatibility and a tendency to form local agglomerates and stress concentrations. These results demonstrate that reactive compatibility carriers, masterbatch pre-dispersion, and nanoparticle surface treatment all contribute to improving the structural stability of the system.

[0064] Depend on Figure 1As can be seen, the epoxy-related characteristic peaks in the low-migration anti-water-tree functional masterbatch obtained in Example 1 were significantly weakened, while the NH / OH region exhibited a wider absorption band; whereas the epoxy characteristics were more clearly retained in the direct physical mixing extruder of Comparative Example 3. These results indicate that during the melt reactive extrusion process, the terminal amino groups in polyoxypropylene diamine undergo a ring-opening reaction or form a strong reactive bond with the epoxy groups in the glycidyl methacrylate-grafted low-density polyethylene, causing the anti-water-tree polar segments to be at least partially connected or confined within the polyethylene compatible segments. Therefore, this invention does not simply involve adding free anti-water-tree additives, but rather reduces the risk of polar component migration through reaction fixation.

[0065] Depend on Figure 2 As can be seen, the water tree lengths in Examples 1-3 are all shorter than those in the comparative examples, indicating that the system of the present invention can effectively delay the development of water trees. Among them, Example 1 performs best, showing that appropriate amounts of polyoxypropylene diamine, glycidyl methacrylate-grafted low-density polyethylene, and surface-treated nano-magnesium oxide can jointly construct a stable anti-water tree interface region. The polar structures such as ether bonds in polyoxypropylene diamine can interfere with the continuous accumulation of water and the formation of water tree channels; glycidyl methacrylate-grafted polyethylene, through reaction fixation and compatibility bridging, allows the anti-water tree polar segments to be stably distributed in the polyethylene phase; surface-treated nano-magnesium oxide further improves interface stability and helps to regulate the local electric field. Comparative Example 1 lacks anti-water tree polar segments, and the water tree development is the most obvious; Comparative Example 2 lacks a reaction fixation carrier, and the anti-water tree polar component is difficult to play a stable role; Comparative Example 3 uses direct physical mixing, which is difficult to achieve the pre-reaction and uniform dispersion effect of Example 1; Comparative Examples 4 and 5 show that the presence of nanoparticles and their surface treatment state both affect the development of water trees.

[0066] As shown in Table 2, Examples 1-3 maintained low water absorption, mass loss, and dielectric loss change rates after hot water immersion, indicating that the anti-water-tree polar component has good low migration stability in the polyethylene insulation system. Example 1 showed a good balance between anti-water-tree effect and dielectric retention. Example 2 had a lower water absorption rate but slightly weaker anti-water-tree effect due to its lower proportion of low-migration anti-water-tree functional masterbatch and its anti-water-tree polar chain segments. Example 3 had a slightly increased water absorption rate and dielectric loss change due to its higher proportion of low-migration anti-water-tree functional masterbatch and its anti-water-tree polar chain segments, but it was still better than Comparative Examples 2 and 3. In Comparative Example 2, the polyoxypropylene diamine was mainly in a free or weakly compatible state, making it more prone to migration or induced water absorption in hot water. Although Comparative Example 3 contained the same functional component, direct physical mixing made it difficult to form a stable reactive bond and uniform interface distribution, thus resulting in insufficient low migration and dielectric retention capabilities.

[0067] As shown in Table 3, Examples 1-3 all maintained low dielectric loss, high volume resistivity, and good AC breakdown strength, indicating that the introduction of the anti-water-tree polar structure did not cause significant degradation in insulation performance. Example 1 showed good overall dielectric stability, indicating a good balance between the content of the anti-water-tree polar component, the degree of reaction fixation, the interface regulation effect of nano-magnesium oxide, and the stability of the cross-linked network. Although Comparative Example 1 had low dielectric loss and high volume resistivity, its anti-water-tree ability was insufficient, indicating that simply having low polarity cannot solve the problem of water-tree aging. Comparative Examples 2 and 3 showed increased dielectric loss and decreased volume resistivity, indicating that free polar components or unevenly dispersed polar regions weaken dielectric stability. Comparative Example 4 lacked nano-magnesium oxide, and Comparative Example 5 used untreated nano-magnesium oxide, resulting in decreased breakdown performance, indicating that nanoparticles and their interfacial compatibility have a significant impact on insulation reliability.

[0068] Depend on Figure 3 It is evident that the maximum space charge density and residual charge ratio of Examples 1-3 are lower than those of most comparative examples, indicating that the low-migration anti-water-tree functional masterbatch and surface-treated nano-inorganic particles help suppress space charge accumulation and promote charge release. In Example 1, the vinyltriethoxysilane-treated nano-magnesium oxide, along with the polyethylene-compatible reactive carrier and polyoxypropylene diamine, are co-dispersed, which facilitates the formation of a more uniform interfacial trap structure, reducing local charge accumulation and electric field distortion.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A modified polyethylene cable insulation material, characterized in that, By weight, it comprises the following raw materials: 80-100 parts of polyethylene matrix resin, 5-12 parts of low migration water-resistant functional masterbatch, 1-2.5 parts of crosslinking agent, 0.2-0.8 parts of antioxidant stabilizer, 0.1-0.6 parts of voltage stabilizer, and 0.1-0.5 parts of processing aid; The low-migration, water-tree resistant functional masterbatch comprises, by weight, the following raw materials: 30-45 parts of polyethylene carrier resin, 35-55 parts of polyethylene compatible reactive carrier, 12-25 parts of water-tree resistant polar component, 2-6 parts of surface-treated nano-inorganic particles, and 0.1-0.4 parts of antioxidant stabilizing component. The polyethylene-compatible reactive carrier is glycidyl methacrylate-grafted polyethylene, and the water-resistant polar component is an amino-terminated polyether.

2. The modified polyethylene cable insulation material according to claim 1, characterized in that, The polyethylene matrix resin is a blend of cable-grade low-density polyethylene and linear low-density polyethylene, with a mass ratio of low-density polyethylene to linear low-density polyethylene of 70-90:10-30.

3. The modified polyethylene cable insulation material according to claim 1, characterized in that, The glycidyl methacrylate-grafted polyethylene is glycidyl methacrylate-grafted low-density polyethylene with a grafting rate of 0.5-2.0 wt%; the terminal amino polyether is polyoxypropylene diamine with a number average molecular weight of 300-1000.

4. The modified polyethylene cable insulation material according to claim 1, characterized in that, The surface-treated nano-inorganic particles are one of vinyltriethoxysilane-treated nano-magnesium oxide, octyltriethoxysilane-treated nano-silica, or γ-methacryloyloxypropyltrimethoxysilane-treated nano-alumina.

5. The modified polyethylene cable insulation material according to claim 4, characterized in that, The average particle size of the magnesium oxide nanoparticles treated with vinyltriethoxysilane is 50–100 nm, and the amount of vinyltriethoxysilane used is 1.0–2.0% of the mass of the magnesium oxide nanoparticles; the average particle size of the silica nanoparticles treated with octyltriethoxysilane is 20–80 nm, and the amount of octyltriethoxysilane used is 1.0–3.0% of the mass of the silica nanoparticles; the average particle size of the alumina nanoparticles treated with γ-methacryloxypropyltrimethoxysilane is 50–150 nm, and the amount of γ-methacryloxypropyltrimethoxysilane used is 1.0–2.5% of the mass of the alumina nanoparticles.

6. The modified polyethylene cable insulation material according to claim 1, characterized in that, The crosslinking agent is one of dicumyl peroxide or bis-tert-butylperoxypropylbenzene; the antioxidant stabilizer and antioxidant stabilizing component are each independently one of antioxidant 1010, antioxidant 1076, antioxidant 168 or dilauryl thiodipropionate; the voltage stabilizer is one of benzophenone, 4-hydroxybenzophenone or 2-hydroxy-4-methoxybenzophenone; the processing aid is one of polyethylene wax, calcium stearate or fluoropolymer processing aid.

7. A method for preparing the modified polyethylene cable insulation material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Preparation of surface-treated nano-inorganic particles; S2: Polyethylene carrier resin, polyethylene compatible reactive carrier, surface-treated nano-inorganic particles and antioxidant stabilizing components are premixed, and anti-water-tree polar components are added to a twin-screw extruder for melt reaction extrusion to obtain low-migration anti-water-tree functional masterbatch. S3: Polyethylene matrix resin, low migration water-tree resistant functional masterbatch, antioxidant stabilizer, voltage stabilizer and processing aid are melt-blended and extruded to obtain modified polyethylene base particles; S4: The crosslinking agent is added to the modified polyethylene base particles at low temperature, so that the crosslinking agent is absorbed and distributed in the modified polyethylene base particles to obtain modified polyethylene cable insulation material. S5: The modified polyethylene cable insulation material is extruded and cross-linked.

8. The method for preparing a modified polyethylene cable insulation material according to claim 7, characterized in that, In step S1, the preparation of the surface-treated inorganic nanoparticles includes: drying the inorganic nanoparticles at 90–120°C for 2–4 h; adding a silane coupling agent to a 90 wt% ethanol aqueous solution and stirring for 10–30 min to obtain a silane treatment solution; heating the dried inorganic nanoparticles to 70–90°C, stirring at 800–1500 rpm, and spraying the silane treatment solution into them, continuing to mix for 20–50 min; then vacuum drying at 80–100°C for 3–6 h, and passing the cooled nanoparticles through a 200-mesh sieve.

9. The preparation method according to claim 7, characterized in that, In step S2, the water-resistant polar component is dehydrated and then fed into a twin-screw extruder via a liquid metering pump or a side feed port for melt reaction extrusion. The temperature of the melt reaction extrusion is 110–170°C, the die head temperature is 145–160°C, the vacuum degree of the vacuum exhaust section is -0.05–-0.09 MPa, and the material residence time is 2–5 min.

10. The preparation method according to claim 7, characterized in that, In step S4, the crosslinking agent is added to the modified polyethylene base particles at 65-85°C and mixed for 2-6 hours. After discharge, the mixture is sealed and equilibrated at 20-35°C for 12-24 hours. In step S5, the crosslinking treatment is carried out at 180-230°C for 3-15 minutes in a nitrogen atmosphere. After crosslinking, the mixture is degassed at 70-90°C for 12-72 hours.

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