Polyethylene insulating material as well as preparation method and application thereof

Abstract

The invention relates to a polyethylene insulating material as well as a preparation method and application thereof, and belongs to the technical field of insulating materials. The polyethylene insulating material is prepared from the following raw materials in parts by weight: 100 parts of low-density polyethylene, 5 to 8 parts of a grafting monomer, 3 to 5 parts of a styrene-ethylene-butylene-styrene block copolymer, 4 to 6 parts of modified hexagonal boron nitride, 8 to 10 parts of activated laponite, 0.3 to 0.8 part of an initiator and 0.1 to 0.3 part of an antioxidant. The grafting monomer is a fluorine-containing methacrylate monomer; the modified hexagonal boron nitride is hexagonal boron nitride modified by a silane coupling agent. According to the polyethylene insulating material provided by the invention, the space charge density is reduced, the direct-current conductivity is reduced, the direct-current breakdown field strength is improved, the problems of space charge accumulation and conductivity high-temperature sudden rise of a traditional material in a high-voltage direct-current field are solved, and the polyethylene insulating material has very high application value.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, and in particular to a polyethylene insulating material, its preparation method, and its application. Background Technology

[0002] Cross-linked polyethylene (XLPE) is currently the mainstream technology for high-voltage DC cable insulation materials, and its core process relies on chemical cross-linking modification. To meet the insulation requirements of ultra-high-voltage cables (such as ±320kV and above), the industry generally adopts ultra-clean production processes, including multi-stage high-precision filtration, post-absorption under nitrogen protection, and closed-loop mixing systems to control impurity content and suppress pre-cross-linking byproducts. Material modification mainly includes nanoparticle doping, blending with small-molecule additives, and delaying aging by quenching high-energy electrons. Additionally, there is an environmentally friendly approach that uses thermoplastic polyolefins (such as polypropylene and ethylene propylene rubber) to replace traditional XLPE, avoiding the increased energy consumption and recycling difficulties caused by chemical cross-linking. However, this requires blending modification (HDPE / LDPE) to improve low-temperature brittleness.

[0003] Traditional cross-linked polyethylene insulation materials suffer from several defects. At the process level, premature decomposition of the cross-linking agent during extrusion can lead to pre-cross-linked gel clogging of the filter, forcing frequent production line shutdowns for filter replacement, limiting capacity and increasing costs. The degassing process is too time-consuming, not only reducing efficiency but also causing residual small molecule precipitates to form pores or scratches over long-term operation, creating potential insulation problems. At the material performance level, the problem of space charge accumulation remains unresolved, especially under DC high-voltage fields and temperature gradients, leading to local electric field distortion and a significantly increased risk of breakdown when polarity reverses; furthermore, the conductivity is excessively temperature-sensitive, with a sharp increase of 10°C at 70°C. 2 -10 3 This exacerbates high-temperature field distortion and limits the increase in cable transmission capacity. Furthermore, nanofillers are difficult to disperse uniformly, and agglomerates become new defect sources, reducing breakdown strength by more than 10%, while residual surface modifiers may introduce ionic conductivity channels. From an environmental perspective, chemical cross-linking products are not recyclable, and waste recycling requires high-temperature pyrolysis, which contradicts the trend of a low-carbon economy.

[0004] Therefore, there is an urgent need to develop a new type of polyethylene insulation material that can improve upon the shortcomings of traditional materials in terms of process, material performance, and environmental protection, and solve the problems of intrinsic charge trapping and uncontrolled carrier migration that cannot be controlled by ultrapure processes. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a polyethylene insulating material, its preparation method, and its applications. The polyethylene insulating material provided by this invention can effectively reduce the electric field distortion within the material and possesses excellent DC electrical performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a polyethylene insulating material, wherein the raw materials for preparing the polyethylene insulating material comprise the following components in parts by weight: 100 parts low-density polyethylene, 5-8 parts grafted monomer, 3-5 parts styrene-ethylene-butene-styrene block copolymer, 4-6 parts modified hexagonal boron nitride, 8-10 parts activated lithium diatomite, 0.3-0.8 parts initiator, and 0.1-0.3 parts antioxidant;

[0008] The grafting monomer is a fluorinated methacrylate monomer; the modified hexagonal boron nitride is hexagonal boron nitride modified with a silane coupling agent.

[0009] This invention primarily addresses the core defects of traditional XLPE, namely, the accumulation of space charge and the rapid increase in conductivity at high temperatures under high-voltage DC fields. Through molecular design, a method is developed for low-density polyethylene (LDPE, with a density of 0.910-0.925 g / cm³). 3 The main link is grafted with fluorinated methacrylate monomers to form a graft chain. The electron traps constructed by the fluorinated groups suppress charge injection. This can work synergistically with the quantum barrier formed by the modified hexagonal boron nitride sheets and the ion adsorption network of activated lithium diatomite to block carrier transitions, effectively reduce space charge density, reduce and stabilize DC conductivity, completely avoid the risks of local electric field distortion and limited transport capacity, and achieve a significant improvement in DC breakdown field strength.

[0010] The agglomeration of traditional nanofillers leads to a deterioration in DC electrical performance. The modified hexagonal boron nitride (h-BN) used in this invention is a silane coupling agent-modified hexagonal boron nitride. Surface modification improves the dispersibility and interfacial compatibility of h-BN in the material. Combined with the layered silicate nanocomposite structure of activated lithium diatomite, this enhances the breakdown field strength and DC volume resistivity.

[0011] Traditional ultrapure processes have approached the physical limits in optimizing the DC electrical performance of insulating materials—even when ash content is reduced to 5 ppm and micron-sized impurities are close to zero, the intrinsic defects of the polyethylene molecular chain still result in imperfect DC electrical performance. This invention makes a breakthrough by grafting fluorinated methacrylate monomers onto the LDPE chain to construct electron traps, fundamentally solving the problem of intrinsic charge traps and uncontrolled carrier migration that cannot be controlled by ultrapure processes.

[0012] The polyethylene insulation material provided by this invention solves the core defects of traditional XLPE materials. It is suitable for high-voltage DC cable insulation and can cover the insulation application of 320-525kV high-voltage DC cables, which has high practical value.

[0013] Preferably, the grafting monomer is at least one of perfluorohexyl ethyl methacrylate and hexafluoroisopropyl methacrylate.

[0014] More preferably, the grafting monomer is perfluorohexyl ethyl methacrylate (FHEMA).

[0015] FHEMA was used as the graft monomer to form the graft chain, in which -C6F 13 The group has a strong negative charge effect, and the constructed electron trap can better bind to the sheet quantum barrier of h-BN, reduce interface charge scattering loss, and block carrier transitions.

[0016] Preferably, the melt index of the low-density polyethylene is 1.5-2.5 g / 10 min.

[0017] Preferably, the modified hexagonal boron nitride is obtained by surface modification of hexagonal boron nitride using KH-570;

[0018] Preferably, the aspect ratio of the modified hexagonal boron nitride is >200;

[0019] Preferably, the modified hexagonal boron nitride has a sheet diameter of 1-5 μm and a thickness of 5-20 nm.

[0020] More preferably, the modified hexagonal boron nitride is prepared by ultrasonically treating hexagonal boron nitride and silane coupling agent KH-570 in an ethanol solution for 2 hours to achieve surface modification, followed by drying at 120°C.

[0021] The h-BN aspect ratio used in this invention is >200. Under the modification of a specific silane coupling agent, its dispersibility and interfacial compatibility can be significantly improved, which facilitates uniform dispersion of particles during the preparation process and avoids agglomeration that becomes a new source of defects.

[0022] Preferably, the activated lithium diatomite is obtained by activating lithium diatomite at 110-130℃.

[0023] Preferably, the average particle size of the activated lithium diatomite is 25-50 nm.

[0024] More preferably, the activation temperature is 120°C and the activation time is 3.5-4.5 hours.

[0025] Adding activated lithium diatomite can effectively reduce the interlayer crystal water content of lithium diatomite, increase porosity and specific surface area, expand interlayer spacing, reduce particle agglomeration, enhance dispersion efficiency, and further optimize the performance of polyethylene materials.

[0026] Preferably, the initiator is di-tert-butyl peroxide (DTBP), and the antioxidant is antioxidant 300. This invention uses DTBP as an initiator, and its half-life at the grafting reaction processing temperature is suitable for processing requirements.

[0027] Secondly, the present invention provides a method for preparing the above-mentioned polyethylene insulating material, which uses an extruder to carry out the preparation reaction, and includes the following steps:

[0028] Step (1): Low-density polyethylene, styrene-ethylene-butene-styrene block copolymer and antioxidant are added through the main feed port and melted and mixed under the shearing action of the screw;

[0029] Step (2): Grafting monomers and initiators are added through the side feed port to carry out the grafting reaction. Modified hexagonal boron nitride and activated lithium diatomite are added through progressive feeding. The kneading block combination is adjusted and then dispersed under a shear field. The melt is obtained by vacuum devouring.

[0030] Step (3) involves extruding and granulating the melt, refluxing and extracting it in hexafluoroisopropanol, then drying and melting it to form a mold, and cooling it to obtain the polyethylene insulation material.

[0031] Preferably, in step (1), the temperature of the main feed inlet is 65-75℃, the melting temperature is 155-165℃, and the screw shearing rate is 75-85s. -1 ;

[0032] Preferably, in step (2), the grafting reaction temperature is 190-200℃, the initiator residence time is 110-130 seconds, and the vacuum devouring temperature is 195-205℃;

[0033] Preferably, in step (3), the extrusion granulation temperature is 170-180℃ and the reflux extraction time is 6-7 hours.

[0034] More preferably, in step (2), the vacuum degree of vacuum devolatilization is maintained below -0.1 MPa for 40 seconds.

[0035] At the process level, the polyethylene insulation material provided by this invention is produced using a zoned temperature control extruder. The reaction grafting temperature of this invention is precisely matched to the DTBP half-life (25±3 seconds), and combined with dynamic vacuum devolatilization. Compared to the existing factory degassing time of over 72 hours, this significantly reduces energy consumption and improves production efficiency, and can efficiently remove unreacted monomers (unreacted monomer residue <100ppm). By matching the initiator half-life and residence time to achieve precise low-temperature grafting, complete initiator decomposition, sufficient monomer diffusion, and complete chain growth are ensured; a high shear field is applied, and the screw shear rate is increased to enhance interfacial mass transfer.

[0036] Preferably, in step (2), the temperature of the applied shear field is 175-185℃, and the shear rate is ≥200s. -1 ;

[0037] Preferably, in step (2), a 45° staggered kneading disc is used to adjust the kneading block combination.

[0038] As a preferred option, a water cooling system is set up between the reaction grafting zone with a higher temperature and the nano-dispersion zone subjected to high shear to appropriately reduce the material temperature and avoid damage to the nanofiller structure caused by high temperature.

[0039] By adjusting the kneading block combination and applying a high shear field, the modified hexagonal boron nitride sheets are oriented along the extrusion direction (orientation degree > 85%), and the activated lithium diatomite is dispersed in the matrix in an exfoliated state to form an ion adsorption network.

[0040] More preferably, in step (2), progressive feeding is achieved through a quantitative feeding device.

[0041] More preferably, in step (3), a flat vulcanizing machine is used for melt molding, with the temperature set at 175-185℃, the pressure at 12-18MPa, and the time at 15-25min, to produce a 100±5μm film.

[0042] More preferably, in step (3), the cooling is water cooling, and the cooling rate is 5°C / min.

[0043] Thirdly, the present invention provides the application of the above-mentioned polyethylene insulation material in high-voltage DC cables.

[0044] The polyethylene insulation material provided by this invention fundamentally solves the problems of intrinsic charge trapping and uncontrolled carrier migration that cannot be controlled by ultrapure processes, and can meet the insulation requirements of ultra-high voltage cables, and can meet the insulation application of high voltage DC cables at the 320-525kV level.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] 1. The polyethylene insulation material provided by this invention grafts fluorine-containing groups onto the LDPE molecular chain to construct an electron trap structure. Through the formulation combination of fluorine-containing monomers grafted onto the polyethylene matrix, combined with the nanostructure of modified hexagonal boron nitride and activated lithium diatomite, it blocks carrier transitions, effectively reduces space charge density, stabilizes DC conductivity, completely avoids the risks of local electric field distortion and limited transmission capacity, and significantly improves DC breakdown field strength, thus solving the core defects of existing XLPE materials.

[0047] 2. Its preparation process achieves precise low-temperature grafting by matching the initiator's half-life and residence time, and employs a dynamic vacuum devouring system to efficiently remove unreacted monomers. This ensures complete initiator decomposition, full monomer diffusion, and complete chain growth, significantly reducing energy consumption and improving production efficiency. This polyethylene insulation material is suitable for insulation applications in high-voltage DC cables, meeting the requirements of 320-525kV, and has high practical value. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating the preparation process of the polyethylene insulation material provided by the present invention. Detailed Implementation

[0049] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0050] Example 1

[0051] An embodiment of the polyethylene insulation material of the present invention is provided. The raw materials for preparing the polyethylene insulation material of this embodiment are composed of the following components in parts by weight: 100 parts low-density polyethylene (LDPE), 6 parts perfluorohexyl ethyl methacrylate (FHEMA), 4 parts styrene-ethylene-butene-styrene block copolymer (SEBS), 5 parts modified hexagonal boron nitride, 9 parts activated lithium diatomaceous earth, 0.5 parts initiator di-tert-butyl peroxide (DTBP), and 0.2 parts antioxidant 300.

[0052] The density of LDPE is 0.92 g / cm³. 3 The melt index is 2.0 g / 10 min. Before use, place it in a vacuum drying oven and dry it at 80°C for 24 hours.

[0053] The preparation method of activated lithium diatomite is as follows: lithium diatomite (Laponite RD) is activated at 120℃ for 4 hours to remove interlayer crystal water.

[0054] The modified hexagonal boron nitride is prepared by ultrasonically treating hexagonal boron nitride with an aspect ratio > 200 in an ethanol solution with silane coupling agent KH-570 for 2 hours, followed by drying at 120°C.

[0055] FHEMA monomers are dehydrated using molecular sieves and then stored in the dark for later use.

[0056] The preparation method of the polyethylene insulation material described in this embodiment uses a co-rotating twin-screw extruder with zoned temperature control (equipped with a vacuum devouring system). The preparation flow chart is as follows. Figure 1 As shown, the specific steps are as follows:

[0057] (1) Feeding and melting mixing

[0058] The feeding zone is set to 70℃: LDPE granules and SEBS are added through the main feed port, along with antioxidant 300.

[0059] The melting and plasticizing zone is set at 160℃; the screw shear rate is controlled at 80s. -1 This allows the materials to melt and mix together.

[0060] (2) Grafting reaction, nano-dispersion orientation, vacuum devolatilization

[0061] The reaction grafting zone is set at 195°C: FHEMA monomer and initiator DTBP are added through a side feed pump. The half-life (25 seconds) and residence time (120 seconds) of DTBP at 195°C are precisely matched to ensure complete decomposition of the initiator, full diffusion of the monomer, and completion of chain growth. Modified hexagonal boron nitride and activated lithium diatomite are added through a quantitative feeding device in the reaction grafting zone to achieve gradual feeding.

[0062] A water-cooling system is installed between the reaction grafting zone and the nano-dispersion zone to reduce the material temperature; in the nano-dispersion zone, a 45° staggered kneading disc is used to adjust the kneading block assembly, and a high shear field is applied at 180°C with a shear rate ≥200s. -1 This allows the modified hexagonal boron nitride sheets to be oriented along the extrusion direction (orientation degree > 85%), while lithium diatomite is dispersed in the matrix in an exfoliated state to form an ion adsorption network;

[0063] The vacuum devolatilization zone is set to 200℃ and the vacuum level is -0.1MPa: the high vacuum system is turned on to remove unreacted monomers and small molecule byproducts, and the vacuum level is maintained below -0.1MPa for 40 seconds.

[0064] (2) Granulation, purification, melt molding

[0065] The die head temperature is set at 175℃: the melt is extruded into strips through the die head, and cylindrical particles with a diameter of 3mm are obtained by water ring pelletizing;

[0066] The particles were refluxed in hexafluoroisopropanol (HFIP) for 6 hours to remove residual monomers and homopolymers, so that the residual fluorine monomers were <100ppm. The particles were then dried in a vacuum oven at 80℃ for 24 hours to constant weight.

[0067] The dried granules were pressed into a 100±5μm film using a flat vulcanizing machine (temperature 180℃, pressure 15MPa, time 20min), and then cooled with water at a rate of 5℃ / min to obtain the polyethylene insulation material.

[0068] Example 2

[0069] An embodiment of the polyethylene insulation material of the present invention differs from that of Example 1 only in that the weight of FHEMA is adjusted to 5 parts, while the other components remain unchanged.

[0070] The preparation method of the polyethylene insulation material described in this embodiment is the same as that in Embodiment 1.

[0071] Example 3

[0072] An embodiment of the polyethylene insulation material of the present invention differs from that of Example 1 only in that the weight of FHEMA is adjusted to 7 parts, while the other components remain unchanged.

[0073] The preparation method of the polyethylene insulation material described in this embodiment is the same as that in Embodiment 1.

[0074] Example 4

[0075] An embodiment of the polyethylene insulation material of the present invention differs from that of Example 1 only in that FHEMA is replaced with an equal part by weight of hexafluoroisopropyl methacrylate (HFIPMA), while the other components remain unchanged.

[0076] The preparation method of the polyethylene insulation material described in this embodiment is the same as that in Embodiment 1.

[0077] Comparative Example 1

[0078] A polyethylene insulation material, the only difference between the raw material composition of which is the same as that of Example 1 is that activated lithium diatomite is not added, while the other components remain unchanged.

[0079] The preparation method of the polyethylene insulation material is as described in Example 1.

[0080] Comparative Example 2

[0081] A polyethylene insulating material, the only difference between the raw material composition of which is the same as that of Example 1 is that modified hexagonal boron nitride is not added, while the other components remain unchanged.

[0082] The preparation method of the polyethylene insulation material is as described in Example 1.

[0083] Comparative Example 3

[0084] A polyethylene insulation material, the only difference between the raw material composition of which is the same as that of Example 1 is that SEBS is not added, while the other components remain unchanged.

[0085] The preparation method of the polyethylene insulation material is as described in Example 1.

[0086] Comparative Example 4

[0087] A polyethylene insulation material, the only difference between the raw material composition of which is the same as that of Example 1 is that FHEMA monomer is not added, while the other components remain unchanged.

[0088] The preparation method of the polyethylene insulation material is as described in Example 1.

[0089] Comparative Example 5

[0090] A polyethylene insulation material, the only difference between the raw material composition of which is the same as that of Example 1 is that the weight of FHEMA is adjusted to 10 parts, while the other components remain unchanged.

[0091] The preparation method of the polyethylene insulation material is as described in Example 1.

[0092] Comparative Example 6

[0093] Comparative Example 6 is a commercially available cable insulation material made of conventional cross-linked polyethylene.

[0094] The raw material composition for preparing the polyethylene insulation materials in Examples 1-4 and Comparative Examples 1-5 is shown in Table 1.

[0095] Table 1. Raw material composition for the preparation of polyethylene insulation materials in the examples and comparative examples.

[0096]

[0097]

[0098] Example of effect

[0099] To investigate the insulation performance of the polyethylene insulation material provided by the present invention, the polyethylene insulation materials in the above embodiments and comparative examples were subjected to the following tests:

[0100] 1. DC conductivity test: The polarization decay current of the insulating sample over time was measured using a three-electrode system and a Keithley 6517B electrometer. The conductivity was calculated using the stable current after 30 minutes, and the results are shown in Table 2.

[0101] 2. DC Breakdown Field Strength Test: A computer-controlled linear boost test device was used, employing 25mm diameter spherical copper electrodes, to conduct a DC breakdown test in transformer oil. The voltage was continuously increased at a linear boost rate of 1kV / s until the membrane broke down. The voltage at this point was recorded as the breakdown voltage, and the breakdown field strength was calculated. A two-parameter Weibull probability distribution was used to analyze the data, and the results are shown in Table 3 (shape parameter data are in parentheses).

[0102] Table 2. DC conductivity test results of polyethylene insulation materials in the examples and comparative examples.

[0103]

[0104]

[0105] Table 3. DC breakdown field strength test results of polyethylene insulation materials in the examples and comparative examples.

[0106]

[0107] The test results in Tables 2 and 3 show that:

[0108] (1) Comparing Example 1 and Comparative Example 6, it can be seen that under the test conditions of increased temperature, the polyethylene insulation material of the present invention has better electrical properties than the traditional polyethylene insulation material. It has lower DC conductivity and higher DC breakdown field strength. This indicates that the use of specific monomers for fluorination grafting has an inhibitory effect on the injection and migration of space charge inside the insulation material, and can effectively reduce the field strength distortion inside the material, so that the material has good DC electrical performance.

[0109] (2) Comparing Example 1 and other examples and comparative examples, it can be seen that the polyethylene insulation material provided by the present invention has better performance under the preferred raw material composition and ratio. The grafting and amount of grafted monomer FHEMA, as well as the addition of modified hexagonal boron nitride, activated lithium diatomite, and styrene-ethylene-butene-styrene block copolymer, all affect the electrical properties of the polyethylene insulation material. Through reasonable combination of components and ratios, the present invention achieves more effective reduction of space charge density, reduction of DC conductivity, and significant improvement of DC breakdown field strength, and has excellent insulation performance.

[0110] In summary, the polyethylene insulation material provided by this invention, through the construction of an electron trap structure via fluorination grafting and the combination of a hexagonal boron nitride and activated lithium diatomite nanostructure, can block carrier transitions, effectively reduce space charge density, stably reduce DC conductivity, and completely avoid the risks of local electric field distortion and limited transmission capacity, thereby significantly improving DC breakdown field strength. Simultaneously, the material preparation process is optimized, avoiding filler agglomeration problems, and significantly reducing energy consumption and improving production efficiency. The technical solution of this invention solves the core defects of existing XLPE materials and can meet the insulation requirements of high-voltage DC cables ranging from 320kV to 525kV, demonstrating high application value in high-voltage DC cables.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyethylene insulation material, characterized in that, The raw materials for preparing the polyethylene insulation material include the following components in parts by weight: 100 parts low-density polyethylene, 5-8 parts grafted monomer, 3-5 parts styrene-ethylene-butene-styrene block copolymer, 4-6 parts modified hexagonal boron nitride, 8-10 parts activated lithium diatomite, 0.3-0.8 parts initiator, and 0.1-0.3 parts antioxidant. The grafting monomer is a fluorinated methacrylate monomer; the modified hexagonal boron nitride is hexagonal boron nitride modified with a silane coupling agent.

2. The polyethylene insulation material as described in claim 1, characterized in that, The grafting monomer is at least one of perfluorohexyl ethyl methacrylate and hexafluoroisopropyl methacrylate.

3. The polyethylene insulation material as described in claim 1, characterized in that, The melt flow index of the low-density polyethylene is 1.5-2.5 g / 10 min.

4. The polyethylene insulation material as described in claim 1, characterized in that, The modified hexagonal boron nitride was obtained by surface modification of hexagonal boron nitride using KH-570; And / or, the aspect ratio of the modified hexagonal boron nitride is >200; And / or, the modified hexagonal boron nitride has a sheet diameter of 1-5 μm and a thickness of 5-20 nm.

5. The polyethylene insulation material as described in claim 1, characterized in that, The activated lithium diatomite is obtained by activating lithium diatomite at 110-130℃; And / or, the average particle size of the activated lithium diatomite is 25-50 nm.

6. The polyethylene insulation material as described in claim 1, characterized in that, The initiator is di-tert-butyl peroxide, and the antioxidant is antioxidant 300.

7. The method for preparing the polyethylene insulating material as described in claim 6, characterized in that, The preparation reaction is carried out using an extruder, including the following steps: Step (1): Low-density polyethylene, styrene-ethylene-butene-styrene block copolymer and antioxidant are added through the main feed port and melted and mixed under the shearing action of the screw; Step (2): Grafting monomers and initiators are added through the side feed port to carry out the grafting reaction. Modified hexagonal boron nitride and activated lithium diatomite are added through progressive feeding. The kneading block combination is adjusted and then dispersed under a shear field. The melt is obtained by vacuum devouring. Step (3) involves extruding and granulating the melt, refluxing and extracting it in hexafluoroisopropanol, then drying and melting it to form a mold, and cooling it to obtain the polyethylene insulation material.

8. The method for preparing the polyethylene insulating material as described in claim 7, characterized in that, In step (1), the temperature of the main feed inlet is 65-75℃, the melting temperature is 155-165℃, and the screw shearing rate is 75-85s. -1 ; And / or, in step (2), the grafting reaction temperature is 190-200℃, the initiator residence time is 110-130 seconds, and the vacuum devouring temperature is 195-205℃; And / or, in step (3), the extrusion granulation temperature is 170-180℃, and the reflux extraction time is 6-7 hours.

9. The method for preparing the polyethylene insulating material as described in claim 7, characterized in that, In step (2), the temperature of the shear field is 175-185℃, and the shear rate is ≥200s. -1 ; And / or, in step (2), the kneading block combination is adjusted using a 45° staggered kneading disc.

10. The application of the polyethylene insulation material as described in any one of claims 1-6 in high-voltage DC cables.

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