Polyethylene insulation material for ultra-high voltage cable and preparation method thereof

Abstract

The present invention relates to the field of polyethylene insulation materials, and specifically discloses a polyethylene insulation material for ultra-high voltage cables and a preparation method thereof, wherein the polyethylene insulation material comprises the following raw materials in parts by weight: 60 to 100 parts of polyethylene resin, 0.4 to 1.2 parts of antioxidant, 1.5 to 5.5 parts of cross-linking agent, 5 to 15 parts of stabilizer, and 3.5 to 15 parts of composite modifier; wherein the composite modifier is a mixture of nano magnesium oxide and lauryl alcohol. The polyethylene insulation material provided by the present invention has excellent electrical properties, excellent mechanical properties, stable performance, and meets the requirements of insulation materials for ultra-high voltage cables.

Description

Technical Field

[0001] The invention relates to the field of polyethylene insulating materials, and specifically discloses a polyethylene insulating material for an ultra-high voltage cable and a preparation method thereof. Background Art

[0002] The wire and cable industry is an indispensable supporting industry for the power industry and plays an important role in my country's economic development. Among many cable materials, polyethylene material has become one of the widely used cable insulation materials for power transmission and distribution network systems because of its relatively simple manufacturing process, excellent mechanical, electrical and thermal properties, high insulation resistance, good voltage resistance, low dielectric constant and dielectric loss, and little influence by temperature and frequency.

[0003] At present, the annual consumption of ultra-clean cross-linked polyethylene cable materials for high voltage / ultra-high voltage in my country is relatively large. Domestic 110KV high voltage polyethylene insulation materials have partially replaced imports, but 220kV and above still use imported materials. Generally speaking, the normal service life of cross-linked polyethylene cables is 30 years, and their electrical performance will continue to decline over time, and they are very prone to failure when approaching the end of life stage; in addition, in addition to the aging of the cross-linked polyethylene cables themselves, this type of insulation material will undergo a series of physical and chemical reactions when it is affected by many natural environmental factors including natural light, temperature, humidity and radiation for a long time. When the internal structure is damaged, the service life will also be shortened, resulting in failure. Therefore, improving the withstand voltage level so that the insulation material can meet the long-term use of 500KV ultra-high voltage cables is a technical problem that needs to be solved by domestic polyethylene insulation materials.

[0004] The invention patent with application number CN202011287494.8 discloses a weather-resistant low-density polyethylene insulation material and a preparation method thereof. The weather-resistant low-density polyethylene insulation material of the invention comprises the following components by weight: 50-70 parts of high-pressure low-density polyethylene, 10-30 parts of high-density polyethylene, 3-10 parts of ethylene-octene copolymer, 2-7 parts of ethylene-vinyl acetate copolymer, 0.1-1 parts of ultraviolet absorber, 0.5-1 parts of antioxidant, 0.1-0.5 parts of brightener, and 1-2 parts of lubricant. The weather-resistant low-density polyethylene insulation material of the invention has excellent comprehensive performance, good flexibility, and its tensile strength and hardness are much better than ordinary low-density polyethylene cable materials. It is a kind of material that is cold-resistant, UV-resistant, environmental stress crack-resistant, processable, and suitable for overhead A new type of environmentally friendly insulated cable laid in an environment; the invention patent with application number 201610310105.6 discloses a method for preparing a cable insulation material containing nano magnesium oxide / low-density polyethylene / modified bentonite and its application, the cable insulation material includes 10-20 parts of low-density polyethylene / modified bentonite, 5-10 parts of nano magnesium oxide, 80-100 parts of phenolic resin, 10-20 parts of carbon nitride, 20-30 parts of polystyrene, 30-40 parts of epoxy resin, 5-8 parts of antioxidant, 5-10 parts of plasticizer, 10-15 parts of glass fiber, 20-30 parts of chloroprene rubber and 20-30 parts of polyvinyl chloride, which can improve the heat resistance and strength of the insulation material, reduce the aging time of the insulation material, and can maintain long-term non-degradation under high temperature and high pressure.

[0005] Although the insulating materials disclosed in the above-mentioned technologies can meet the performance requirements of ultra-high voltage cable insulation materials, the service life of the insulating materials is often lower than the theoretical value due to electrical aging during long-term use. Therefore, there is still room for improvement in the electrical durability of the insulating materials. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a polyethylene insulation material for ultra-high voltage cables and a preparation method thereof. The polyethylene insulation material provided by the present invention has excellent electrical properties and mechanical properties and meets the requirements of insulation materials for 500kV ultra-high voltage cables.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a polyethylene insulation material for an ultra-high voltage cable, wherein the polyethylene insulation material comprises the following raw materials in parts by weight: 60 to 100 parts of polyethylene resin, 0.4 to 1.2 parts of antioxidant, 1.5 to 5.5 parts of cross-linking agent, 5 to 15 parts of stabilizer, and 3.5 to 15 parts of composite modifier;

[0009] Wherein, the composite modifier is a mixture of nano magnesium oxide and lauryl alcohol.

[0010] In some embodiments of the present invention, the mass ratio of the composite modifier to the stabilizer is (0.5~1):1.

[0011] Preferably, the mass ratio of the composite modifier to the stabilizer is 0.75:1.

[0012] In some embodiments of the present invention, the mass ratio of the nano magnesium oxide to lauryl alcohol is 1:(0.8-1.5).

[0013] Preferably, the mass ratio of the nano magnesium oxide to lauryl alcohol is 1:1.2.

[0014] In some embodiments of the present invention, the preparation steps of the stabilizer are as follows:

[0015] (1) adding an organic solvent, γ-methacryloxypropyltrimethoxysilane and nano-magnesium oxide in sequence, raising the temperature to 60-80°C, stirring for 8-15 hours, and after the reaction is completed, centrifuging to obtain a precipitate, washing and drying the precipitate to obtain pretreated nano-magnesium oxide;

[0016] (2) Add ethanol to the reactor, mix the pretreated nano-magnesium oxide and branched alkane in step (1), add them, disperse them by ultrasonic, then add benzophenone compound and initiator, heat to 80-90° C., react for 1-3 hours, wash and dry, and obtain a modified stabilizer;

[0017] (3) The modified stabilizer of step (2) is mixed with m-aminobenzoic acid to obtain a stabilizer.

[0018] In some embodiments of the present invention, the particle size of the nano magnesium oxide is 20-40 nm.

[0019] In some embodiments of the present invention, the dosage ratio of γ-methacryloxypropyltrimethoxysilane and nano-magnesium oxide in step (1) is (0.5-0.7):1.

[0020] Preferably, in step (1), the usage ratio of γ-methacryloxypropyltrimethoxysilane to nano-magnesium oxide is 0.6:1.

[0021] Preferably, the organic solvent in step (1) is toluene or ethanol.

[0022] In some embodiments of the present invention, the mass ratio of the pretreated nano-magnesium oxide, linear alkane and benzophenone compound in step (2) is (0.3-0.5): (0.1-0.4): 1.

[0023] Preferably, in step (2), the mass ratio of the pretreated nano-magnesium oxide, the linear alkane and the benzophenone compound is 0.4:0.25:1.

[0024] Preferably, the straight chain alkane is 1-octene.

[0025] Preferably, the benzophenone compound is 4-propyleneoxy-2-hydroxybenzophenone.

[0026] Preferably, the initiator is ammonium persulfate.

[0027] Preferably, the mass ratio of the modified stabilizer to m-aminobenzoic acid is (0.5~1):1.

[0028] Further preferably, the mass ratio of the modified stabilizer to m-aminobenzoic acid is 0.7:1.

[0029] In some embodiments of the present invention, the antioxidant is a mixture of a primary antioxidant and a secondary antioxidant.

[0030] Preferably, the primary antioxidant is a hindered phenol antioxidant.

[0031] Preferably, the auxiliary antioxidant is a phosphite antioxidant.

[0032] In some embodiments of the present invention, the crosslinking agent is a peroxide crosslinking agent.

[0033] In the prior art, small molecule aromatic compounds and some polar small molecule substances are often added as voltage stabilizers to solve the space charge problem and improve the withstand voltage level. However, the precipitation phenomenon of the commonly used voltage stabilizers over time reduces its long-term stability effect. The present application prepares a stabilizer with an increased melting point and significantly improved durability. It can play a role in inhibiting the accumulation of space charges for a long time, and effectively improves the withstand voltage level of polyethylene insulation. The possible reason is that the efficiency of the stabilizer is mainly affected by the core structure of benzophenone, and the compatibility of the stabilizer introduced with a flexible alkyl chain segment and the polymer matrix is ​​improved. As long as the addition amount is relatively low, the electric dendrite of cross-linked polyethylene can be effectively inhibited. At the same time, the introduction of the side chain group with the preferred chain length avoids its adverse effect on the melting point and efficiency of the stabilizer. When the stabilizer is mixed with polyethylene insulation, the service life of the polyethylene insulation is effectively improved.

[0034] The applicant also added nano magnesium oxide and lauryl alcohol and adjusted the mass ratio of the two as a composite modifier into the polyethylene insulation material system, and found that its starting voltage was significantly improved. Different from the prior art which requires organic modification of magnesium oxide nanoparticles to solve the easy agglomeration phenomenon caused by high surface energy, the invention can significantly improve the starting voltage of polyethylene insulation material by directly adding physical blend of nano magnesium oxide and lauryl alcohol. The possible reason is that lauryl alcohol entrains nano magnesium oxide and fills the discharge channel of polyethylene matrix dendrites through migration, thereby reducing the electric field strength, improving the electric field distribution, and inhibiting the growth of electric dendrites. On the other hand, the main components of nano magnesium oxide and stabilizer interact with each other. At this time, nano magnesium oxide can be evenly dispersed in the polyethylene insulation material system, and can play a synergistic role on the stabilizer with a small addition amount. At this time, the stabilizer improves the starting voltage of electric dendrites, while the nano particles inhibit the growth of electric dendrites, and jointly improve the electrical resistance of polyethylene insulation material. At the same time, the mechanical properties, especially the toughness, of polyethylene insulation material are improved. The possible reason is that the stress concentration of nano magnesium oxide in the composite modifier is not obvious, which is more conducive to maintaining the toughness of the polyethylene system. After cross-linking occurs, the formation of the cross-linking network makes it difficult for macromolecular chains to have relative slip, and the interaction force between molecular chains is increased, further improving the tensile strength.

[0035] Another aspect of the present invention also provides a method for preparing a polyethylene insulation material for an ultra-high voltage cable, comprising the following steps:

[0036] (1) Add polyethylene resin, antioxidant, stabilizer and composite modifier, stir and mix, knead, filter with high precision, granulate underwater, and then dehydrate and boil to obtain a semi-finished product;

[0037] (2) treating the semi-finished product at 60-100° C. for 3-6 minutes, adding a cross-linking agent, heat-insulating for 8-18 hours, and cooling to room temperature to obtain the polyethylene insulating material.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention provides a polyethylene insulation material for ultra-high voltage cables. The invention prepares a stabilizer with high melting point and high durability and uses it in combination with a specific composite modifier containing nano-magnesium oxide and lauryl alcohol. When the stabilizer is added to the polyethylene insulation material system, the electrical properties and mechanical properties of the polyethylene insulation material are effectively improved, and the requirements for insulation materials for 500kV ultra-high voltage cables are met.

[0040] (2) The present invention prepares a stabilizer containing both a flexible alkyl chain segment and nano magnesium oxide. The stabilizer has an increased melting point and significantly improved durability. It can play a role in reducing space charge accumulation for a long time, effectively improve the electrical resistance of polyethylene insulation materials, and can effectively inhibit the electrical dendrite formation of cross-linked polyethylene at a relatively low addition amount, while avoiding adverse effects on the melting point and efficiency of the stabilizer. When the stabilizer is mixed with polyethylene insulation materials, the service life of the polyethylene insulation materials can be increased.

[0041] (3) The present invention also adds nano magnesium oxide and lauryl alcohol and adjusts the mass ratio of the two to be added as a composite modifier into the polyethylene insulation material system, and synergistically improves the electrical resistance and mechanical toughness of the polyethylene insulation material with the stabilizer. DETAILED DESCRIPTION

[0042] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0043] Unless otherwise specified, the reagents used below can be easily obtained from commercial companies. Polyethylene resin (model LD200BW, melt index of 2.2 g / 10 min measured at 230 °C with a load of 2.16 kg) was purchased from Dongguan Chenghao Plastic Raw Materials Co., Ltd., and nano magnesium oxide (particle size of 30 nm) was purchased from Qinghe County Ruijiang Metal Materials Co., Ltd.

[0044] Preparation Example 1

[0045] The preparation steps of the stabilizer are as follows:

[0046] (1) adding 30 mL of toluene, 0.6 g of γ-methacryloxypropyltrimethoxysilane and 1 g of nano-magnesium oxide in sequence, heating to 70° C., stirring for 12 h, and after the reaction is completed, centrifuging to obtain a precipitate, washing and drying the precipitate to obtain pretreated nano-magnesium oxide;

[0047] (2) Add 50 mL of ethanol to the reactor, add 4 g of the pretreated nano-magnesium oxide prepared in step (1) and 2.5 g of 1-octene, disperse by ultrasonication, add 10 g of 4-propyleneoxy-2-hydroxybenzophenone and 0.03 g of ammonium persulfate, heat to 85° C., react for 2 h, wash, and dry to obtain a modified stabilizer;

[0048] (3) The modified stabilizer prepared in step (2) and m-aminobenzoic acid are uniformly mixed in a mass ratio of 0.7:1 to obtain a stabilizer.

[0049] Preparation Example 2

[0050] The preparation steps of the stabilizer are the same as those of Preparation Example 1, except that 5.5 g of pretreated nano magnesium oxide is added in step (2).

[0051] Preparation Example 3

[0052] The preparation steps of the stabilizer are the same as those in Preparation Example 1, except that 4.5 g of 1-octene is added in step (2).

[0053] Preparation Example 4

[0054] The preparation steps of the stabilizer are as follows:

[0055] (1) Add 50 mL of ethanol to a reactor, add 2.5 g of 1-octene, disperse by ultrasonication, add 10 g of 4-propyleneoxy-2-hydroxybenzophenone and 0.03 g of ammonium persulfate, heat to 85°C, react for 2 h, wash, and dry to obtain a modified stabilizer;

[0056] (2) The modified stabilizer prepared in step (1) and m-aminobenzoic acid are uniformly mixed in a mass ratio of 0.7:1 to obtain a stabilizer.

[0057] Preparation Example 5

[0058] The preparation steps of the stabilizer are the same as those of Preparation Example 1, except that 0.8 g of γ-methacryloxypropyltrimethoxysilane is added in step (1).

[0059] Unless otherwise specified, the antioxidants used in the following examples and comparative examples are a mixture of hindered phenol 1222 and phosphite 168 in a mass ratio of 1:1, and the cross-linking agents are diisopropylbenzene peroxide.

[0060] Example 1

[0061] A polyethylene insulating material for an ultra-high voltage cable comprises the following raw materials in parts by weight: 80 parts of polyethylene resin, 0.8 parts of antioxidant, 3.5 parts of cross-linking agent, 10 parts of stabilizer, 4 parts of nano magnesium oxide, and 4.5 parts of lauryl alcohol;

[0062] The method for preparing the polyethylene insulation material for the ultra-high voltage cable of this embodiment comprises the following steps:

[0063] (1) The polyethylene resin, antioxidant, stabilizer, nano magnesium oxide and lauryl alcohol are mixed and kneaded at 190°C, filtered with high precision, granulated underwater, and then dehydrated and boiled to obtain a semi-finished product;

[0064] (2) Treat the semi-finished product at 80°C for 5 minutes, add a cross-linking agent, keep it warm for 13 hours, and cool it to room temperature to obtain polyethylene insulation material.

[0065] Wherein, the stabilizer is prepared by Preparation Example 1.

[0066] Example 2

[0067] A polyethylene insulating material for an ultra-high voltage cable comprises the following raw materials in parts by weight: 60 parts of polyethylene resin, 0.4 parts of antioxidant, 1.5 parts of cross-linking agent, 5 parts of stabilizer, 2.3 parts of nano magnesium oxide, and 2.7 parts of lauryl alcohol;

[0068] The method for preparing the polyethylene insulation material for the ultra-high voltage cable of this embodiment comprises the following steps:

[0069] (1) The polyethylene resin, antioxidant, stabilizer, nano magnesium oxide and lauryl alcohol are mixed and kneaded at 190°C, filtered with high precision, granulated underwater, and then dehydrated and boiled to obtain a semi-finished product;

[0070] (2) Treat the semi-finished product at 60°C for 6 minutes, add a cross-linking agent, keep it warm for 8 hours, and cool it to room temperature to obtain polyethylene insulation material.

[0071] Wherein, the stabilizer is prepared by Preparation Example 1.

[0072] Example 3

[0073] A polyethylene insulating material for an ultra-high voltage cable comprises the following raw materials in parts by weight: 100 parts of polyethylene resin, 1.2 parts of antioxidant, 5.5 parts of cross-linking agent, 15 parts of stabilizer, 5.6 parts of nano magnesium oxide, and 6.4 parts of lauryl alcohol;

[0074] The method for preparing the polyethylene insulation material for the ultra-high voltage cable of this embodiment comprises the following steps:

[0075] (1) The polyethylene resin, antioxidant, stabilizer, nano magnesium oxide and lauryl alcohol are mixed and kneaded at 190°C, filtered with high precision, granulated underwater, and then dehydrated and boiled to obtain a semi-finished product;

[0076] (2) Treat the semi-finished product at 100°C for 3 minutes, add a cross-linking agent, keep it warm for 18 hours, and cool it to room temperature to obtain polyethylene insulation material.

[0077] Wherein, the stabilizer is prepared by Preparation Example 1.

[0078] Example 4

[0079] A polyethylene insulation material for an ultra-high voltage cable and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the stabilizer is prepared by Preparation Example 2.

[0080] Example 5

[0081] A polyethylene insulation material for an ultra-high voltage cable and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the stabilizer is prepared by Preparation Example 3.

[0082] Example 6

[0083] A polyethylene insulation material for an ultra-high voltage cable and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the stabilizer is prepared by Preparation Example 4.

[0084] Example 7

[0085] A polyethylene insulation material for an ultra-high voltage cable and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the stabilizer is prepared by Preparation Example 5.

[0086] Example 8

[0087] A polyethylene insulation material for ultra-high voltage cables and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that the stabilizer used is m-aminobenzoic acid.

[0088] Example 9

[0089] A polyethylene insulation material for ultra-high voltage cables and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that, in parts by weight, the added amounts of nano magnesium oxide and lauryl alcohol are 3.4 parts and 4.1 parts, respectively.

[0090] Example 10

[0091] A polyethylene insulation material for ultra-high voltage cables and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that, in parts by weight, the added amounts of nano magnesium oxide and lauryl alcohol are 3.1 parts and 5.4 parts, respectively.

[0092] Comparative Example 1

[0093] A polyethylene insulating material for ultra-high voltage cables and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that an equal amount of nano magnesium oxide is used to replace lauryl alcohol.

[0094] Performance Testing

[0095] The polyethylene insulating materials prepared in the above Examples 1-10 and Comparative Example 1 were melted at 125° C. and 310N pressure for 4 minutes, and then cross-linked at 180° C. and 345N pressure for 15 minutes. After hot pressing, the following performance tests were performed. The specific test results are shown in Table 1:

[0096] Table 1

[0097]

[0098] It can be seen from Table 1 that the polyethylene insulating materials provided in Examples 1 to 3 of the present invention have excellent electrical properties and excellent mechanical properties.

[0099] By comparing Examples 4, 5 and 7 with Example 1, it can be seen that when the amounts of pretreated nano-magnesium oxide, 1-octene and γ-methacryloxypropyltrimethoxysilane added are changed when preparing the stabilizer, the effect of the stabilizer in the system will be affected, resulting in different degrees of decrease in the electrical resistance and mechanical tensile properties of the polyethylene insulation material;

[0100] By comparing Example 6 with Example 1, it can be seen that when the pretreated nano magnesium oxide is not added during the preparation of the stabilizer, the voltage stabilization effect of the stabilizer is reduced, thereby affecting the electrical resistance of the polyethylene insulation material, and also having an adverse effect on its mechanical tensile properties;

[0101] By comparing Example 8 with Example 1, it can be seen that when m-aminobenzoic acid is used as a stabilizer, the electrical resistance of the polyethylene insulation material decreases;

[0102] By comparing Example 9 with Example 1, it can be seen that when the ratio of the composite modifier to the stabilizer is at a specific ratio, the performance of the polyethylene insulation material, especially the electrical resistance, is further improved, which may be achieved by the nano magnesium oxide in the composite modifier playing a highly efficient synergistic role on the stabilizer;

[0103] By comparing Example 10 with Example 1, it can be seen that when the ratio of nano-magnesium oxide and lauryl alcohol in the composite modifier is changed, the electrical resistance and mechanical tensile properties of the polyethylene insulation material will decrease to a certain extent;

[0104] By comparing Comparative Example 1 with Example 1, it can be seen that when lauryl alcohol is replaced by an equal amount of nano-magnesium oxide, its dispersion in the polyethylene insulation material is also affected by the high surface energy of the nano-magnesium oxide, resulting in varying degrees of decrease in the electrical resistance and mechanical tensile properties of the polyethylene insulation material.

[0105] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A polyethylene insulation material for ultra-high voltage cables, characterized in that: The polyethylene insulation material comprises the following raw materials in parts by weight: 60-100 parts of polyethylene resin, 0.4-1.2 parts of antioxidant, 1.5-5.5 parts of cross-linking agent, 5-15 parts of stabilizer, and 3.5-15 parts of composite modifier; Wherein, the composite modifier is a mixture of nano magnesium oxide and lauryl alcohol; The mass ratio of the nano magnesium oxide to lauryl alcohol is 1: (0.8-1.5); The preparation steps of the stabilizer are as follows: (1) adding an organic solvent, γ-methacryloxypropyltrimethoxysilane and nano-magnesium oxide in sequence, raising the temperature to 60-80°C, stirring for 8-15 hours, and after the reaction is completed, centrifuging to obtain a precipitate, washing and drying the precipitate to obtain pretreated nano-magnesium oxide; (2) Add ethanol to the reactor, mix the pretreated nano-magnesium oxide and 1-octene in step (1), add them, disperse them by ultrasonication, add 4-propyleneoxy-2-hydroxybenzophenone and an initiator, raise the temperature to 80-90° C., react for 1-3 hours, wash and dry, and obtain a modified stabilizer; (3) mixing the modified stabilizer of step (2) and m-aminobenzoic acid to obtain a stabilizer; In the step (1), the dosage ratio of γ-methacryloxypropyltrimethoxysilane and nano-magnesium oxide is (0.5-0.7):1; In the step (2), the mass ratio of the pretreated nano-magnesium oxide, 1-octene and 4-propyleneoxy-2-hydroxybenzophenone is (0.3-0.5): (0.1-0.4):

1.

2. The polyethylene insulation material for ultra-high voltage cable according to claim 1, characterized in that: The mass ratio of the composite modifier to the stabilizer is (0.5~1):

1.

3. The polyethylene insulation material for ultra-high voltage cable according to claim 1, characterized in that: The particle size of the nano magnesium oxide is 20-40 nm.

4. The polyethylene insulation material for ultra-high voltage cable according to claim 1, characterized in that: The antioxidant is a mixture of a primary antioxidant and an auxiliary antioxidant.

5. The polyethylene insulation material for ultra-high voltage cable according to claim 1, characterized in that: The crosslinking agent is a peroxide crosslinking agent.

6. A method for preparing the polyethylene insulation material for ultra-high voltage cables according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Add polyethylene resin, antioxidant, stabilizer and composite modifier, stir and mix, knead at 160-220°C, filter with high precision, granulate underwater, and then dehydrate and boil and dry to obtain a semi-finished product; (2) treating the semi-finished product at 60-100° C. for 3-6 minutes, adding a cross-linking agent, heat-insulating for 8-18 hours, and cooling to room temperature to obtain the polyethylene insulating material.

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