A crosslinked polyethylene insulation material for medium and high voltage cables resistant to electrical treeing

Abstract

The application discloses a kind of high-voltage cable with treeing-resistant crosslinked polyethylene insulating material, it is related to the technical field of crosslinked polyethylene insulating material for high-voltage cable, comprising: insulating material is formed by crosslinking from insulating material composition comprising polyethylene base resin, reactive precursor and peroxide crosslinking agent, and including insulating layer main body area and interface confined reaction layer located at least one side surface layer;Through the combination of multi-functional group molecular structure design of reactive precursor and three-layer continuous vulcanization process of co-extrusion, three functions of deep trap construction, covalent network anchoring and crosslinking by-product in-situ capture are realized in insulating-semiconductive interface micro area Space-time coordination, it is realized to form interface confined reaction layer with high reaction degree, deep trap energy level and low by-product residue characteristics in-situ in interface surface layer under the premise of not significantly increasing the overall dielectric loss factor of material, the inhibition ability of high-voltage cable insulating layer to electrical tree branch aging is improved.

Description

Technical Field

[0001] This invention relates to the technical field of cross-linked polyethylene insulation materials for medium and high voltage cables, and in particular to a cross-linked polyethylene insulation material for medium and high voltage cables that is resistant to electrical resin. Background Technology

[0002] Medium and high voltage power cables are core equipment for power transmission systems such as urban power grids, rail transit, and offshore wind power. Their operational reliability is directly related to the long-term electrical aging resistance of the insulation layer. In the cable structure, the XLPE insulation layer does not exist in isolation, but is extruded simultaneously with the inner and outer semi-conductive shielding layers through a three-layer co-extrusion process, and then cross-linked under high temperature and high pressure to form an integrated composite insulation structure.

[0003] However, long-term operating experience shows that one of the main causes of cable insulation failure is electrical treeing aging. To suppress interfacial electrical trees, existing research has tried a variety of technical approaches, including introducing deep trap compounds into the insulation material to regulate space charge, setting independent nonlinear insulation layers or intermediate gradient layers to homogenize the interfacial electric field, and optimizing the degassing process to reduce the residue of crosslinking byproducts.

[0004] However, existing technologies still have shortcomings. Specifically, the "immobilization" of deep trap components in the interface region and the "purification" of the interface micro-regions cannot be achieved simultaneously.

[0005] Small molecule byproducts generated during peroxidation crosslinking will spontaneously migrate and accumulate at the insulating-semiconductive interface during co-extrusion crosslinking, forming a local high defect density region, which becomes the preferred initiation point for electrical trees.

[0006] To solve this problem, an ideal interface control method should possess three capabilities simultaneously:

[0007] First, construct a deep trap at the interface that is sufficient to capture the injected charge;

[0008] Secondly, the deep trap components are anchored to the cross-linked network in the form of covalent bonds to prevent their migration or precipitation;

[0009] Third, the cross-linking byproducts enriched at the interface are captured or immobilized in situ to achieve "self-cleaning" of the interface micro-regions.

[0010] However, existing technologies have consistently failed to overcome this collaborative bottleneck. Summary of the Invention

[0011] In a first aspect, the present invention provides an electrical-resistant cross-linked polyethylene insulation material for medium and high voltage cables, comprising:

[0012] The insulating material is formed by crosslinking an insulating composition comprising a polyethylene resin, a reactive precursor and a peroxidation crosslinking agent, and includes an insulating layer body region and an interface-confined reactive layer located on at least one side of the surface.

[0013] Wherein, the at least one side surface layer is the side surface layer that is in contact with the semiconductive shielding layer when the insulating material is co-extruded with the semiconductive shielding layer and cross-linked to form the cable insulation layer;

[0014] The reactive precursor also contains functional groups that can immobilize peroxidation crosslinking byproducts;

[0015] The thickness of the interface confined reaction layer extending from the surface layer on one side into the interior of the insulating material is 20–70 μm.

[0016] Using the thermally stimulated depolarization current method, the average trap depth of the interface confined reaction layer was measured to be 0.85–1.10 eV, and the average trap depth of the main region of the insulating layer was 0.44–0.58 eV.

[0017] The main region of the insulating layer is the portion of insulating material that extends beyond the thickness range of the interface-limited reaction layer;

[0018] The grafting degree or reaction conversion degree of the reactive precursor in the interface confined reaction layer is higher than that in the main region of the insulating layer.

[0019] The interface confined reaction layer is not formed by an independent nonlinear insulating interlayer or a prefabricated dielectric layer pre-set inside the insulating material.

[0020] Preferably, the reactive group is selected from at least one of vinyl, methacryl, and maleimide.

[0021] Preferably, the polar conjugated structural unit is selected from at least one of anthraquinone, benzophenone, and aromatic imide groups.

[0022] Preferably, based on 100 parts by weight of polyethylene resin, the amount of the reactive precursor added is 0.1 to 2 parts by weight, and the amount of the peroxidation crosslinking agent added is 0.5 to 2.5 parts by weight.

[0023] Preferably, the interface confined reaction layer is a reaction layer formed in situ on at least one side of the surface after co-extrusion and cross-linking of the insulating material composition and the semiconductive shielding layer, and the residual amount of cross-linking by-products in the interface confined reaction layer is lower than that in the main area of ​​the adjacent insulating layer.

[0024] Preferably, the reactive precursor further includes functional groups capable of immobilizing peroxidation crosslinking byproducts, enabling the interface-confined reaction layer to capture or immobilize the interface-enriched crosslinking byproducts in situ while forming deep traps.

[0025] Preferably, the functional group capable of immobilizing the peroxidation crosslinking byproduct is selected from at least one of hydroxyl, amide, imide, epoxy, and carboxyl groups.

[0026] Preferably, the deep trap density in the interface-confined reaction layer is 2 to 5 times the deep trap density in the main region of the insulating layer, and / or the grafting degree of the reactive precursor in the interface-confined reaction layer is 1.5 to 3 times the grafting degree in the main region of the insulating layer.

[0027] Preferably, under 50Hz power frequency conditions, compared with cross-linked polyethylene insulation materials that do not contain the reactive precursor and have the same composition and preparation process, the dielectric loss factor of the insulation material increases by no more than 15%.

[0028] In a second aspect, the present invention provides a method for forming a medium- and high-voltage cable insulation layer based on the aforementioned cross-linked polyethylene insulating material, comprising:

[0029] S1, a polyvinyl resin, a reactive precursor, a peroxidation crosslinking agent, and optionally an antioxidant and a co-crosslinking agent are mixed to obtain an insulating material composition;

[0030] S2, the insulating material composition is extruded and co-extruded with the semi-conductive shielding layer to obtain the co-extruded structure;

[0031] S3, the co-extruded structure is subjected to peroxidation crosslinking treatment, so that the reactive precursor preferentially undergoes grafting, coupling or crosslinking reaction near the interface of the semiconductive shielding layer / insulation layer, thereby forming an interface confined reaction layer on at least one side of the surface of the insulating material.

[0032] S4, degassing treatment is performed to obtain a medium- and high-voltage cable insulation layer with an interface confined reaction layer.

[0033] The beneficial effects of this invention are as follows: By combining the multifunctional structure design of the reactive precursor with the three-layer co-extrusion continuous vulcanization process, this invention enables the synergistic effect of deep trap construction, reaction fixation, and by-product regulation at the near-surface layer of the insulating-semiconductive interface. Specifically:

[0034] The reactive precursor simultaneously introduces reactive groups that can participate in free radical grafting or cross-linking reactions, polar conjugated structural units that can form deep traps, and functional groups that can capture or fix cross-linking byproducts in situ. During co-extrusion cross-linking, the precursor preferentially undergoes grafting reaction in the interface region near the semiconductive shielding layer and is fixed in the polyethylene network. At the same time, its polar conjugated structure forms a trap energy level at the interface that is deeper than that in the main region, while the byproduct regulation functional group helps to reduce the residue of small molecule byproducts near the interface.

[0035] Therefore, without significantly increasing the overall dielectric loss factor of the material, an interface-confined reaction layer with a high degree of reaction, a deep trap structure, and low by-product residue can be formed in situ on the interface surface, thereby improving the electrical tree resistance of medium and high voltage cable insulation and enhancing operational stability. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating the cross-linked polyethylene insulation material for medium and high voltage cables used in the embodiments.

[0038] Figure 2 This is a schematic diagram illustrating the functional principle and mechanism of action of the reactive precursor P-1 in the examples;

[0039] Figure 3 This is a comparison diagram of the trap energy levels in the main regions of the interface-confined reaction layer and the insulating layer in the embodiment;

[0040] Figure 4 This is a schematic diagram of the in-situ formation process of the interface-confined reaction layer in the embodiment;

[0041] Figure 5 The chemical structural formula of compound P-1;

[0042] Figure 6 The chemical structural formula of the P-2 compound;

[0043] Figure 7 The chemical structural formula of the P-3 compound;

[0044] Figure 8 The chemical structural formula of the P-4 compound;

[0045] Figure 9 Here is the chemical structural formula of compound A-1;

[0046] Figure 10 Here is the chemical structural formula of compound B-1. Detailed Implementation

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] The specific chemical structures of the precursor compounds used in this embodiment and comparative example are as follows:

[0049] P-1: 2-Hydroxy-3-[N-(2-methacryloyloxyethyl)formamido]anthraquinone;

[0050] P-2: 2-(4-Methacryloxyphenoxy)anthraquinone;

[0051] P-3: N-(2-hydroxyethyl)-4-(4-vinylbenzoyl)phthalimide;

[0052] P-4: 4-(N-maleimide)-N-(glycidyl)phthalimide-2-carboxylic acid;

[0053] A-1: 2-Hydroxyanthraquinone;

[0054] B-1: N-(2-hydroxyethyl)methacrylamide;

[0055] In this application, P-1 is the reactive precursor used in the main embodiment, P-3 and P-4 are reactive precursors used to verify substitutability, and A-1 and B-1 are comparative compounds used in the comparative examples.

[0056] P-1, P-3, and P-4 are all compounds with well-defined chemical structures. They can be prepared using the following methods and used after their structures have been confirmed.

[0057] Preparation of P-1: 2-hydroxyanthraquinone-3-carboxylic acid was added to thionyl chloride and refluxed for 2-4 h in the presence of N,N-dimethylformamide as a catalyst. Excess thionyl chloride was removed under reduced pressure to obtain the corresponding acyl chloride intermediate. Separately, 2-aminoethyl methacrylate hydrochloride and triethylamine were added to anhydrous dichloromethane and stirred at 0-5 °C to form a clear reaction solution. The acyl chloride intermediate was added dropwise to the above reaction solution, and then the reaction was raised to room temperature for 6-10 h. After the reaction was completed, the mixture was washed with water, acid, saturated brine, concentrated under reduced pressure, and recrystallized to obtain P-1.

[0058] Preparation of P-3: 4-(4-vinylbenzoyl)phthalic anhydride and ethanolamine were added to N,N-dimethylformamide and reacted at 80-90℃ for 2-5 h to obtain an amide acid intermediate; acetic anhydride and sodium acetate were added to the system and cyclized at 100-120℃ for 2-4 h; after cooling, the mixture was poured into deionized water to crystallize; after filtration, washing and drying, P-3 was obtained.

[0059] Preparation of P-4: Using 4-amino-N-glycidylphthalimide-2-carboxylic acid as an intermediate, it was added to N,N-dimethylformamide or acetone with maleic anhydride and reacted at 50-70℃ for 3-6 h to generate maleamic acid intermediate; then acetic anhydride was added for dehydration and cyclization. After the reaction was completed, P-4 was obtained by sedimentation, filtration, washing and vacuum drying.

[0060] A-1 and B-1 are both comparative compounds with defined structures.

[0061] The structures of P-1, P-3 and P-4 were confirmed by proton nuclear magnetic resonance spectroscopy, infrared spectroscopy and mass spectrometry before use.

[0062] All of the above compounds were dried under vacuum at 40–60 °C for 12–24 h before use.

[0063] It should be noted that P-1, P-2, P-3, P-4, A-1, and B-1 all represent precursor compounds with a defined structure or composition, and are not arbitrary functional auxiliaries.

[0064] Unless otherwise stated, Examples 2-10 and Comparative Examples C1-C5 all use the same cable structure, three-layer co-extrusion continuous vulcanization process, sample sampling method, interface layer thickness measurement method, grafting degree or reaction conversion degree test method, crosslinking by-product residue test method, thermal stimulation depolarization current test method, and needle plate electrode electrical tree test method as in Example 1.

[0065] Example 1, referring to Figures 1 to 10 This is the first embodiment of the present invention, which provides an electrical-resistant cross-linked polyethylene insulation material for medium and high voltage cables and its preparation process, including the following steps:

[0066] This embodiment is used to illustrate the basic structure, formation method, and technical effects of the cross-linked polyethylene insulating material for medium and high voltage cables described in this invention.

[0067] This embodiment takes a cross-linked polyethylene insulated cable with a rated voltage of 35kV as the object and adopts the three-layer co-extrusion continuous vulcanization process commonly used in the cable industry. An inner semiconductive shielding layer, an insulation layer, and an outer semiconductive shielding layer are formed sequentially on the outside of the conductor. The insulation layer, the inner semiconductive shielding layer, and the outer semiconductive shielding layer are co-extruded simultaneously and then enter the continuous vulcanization pipeline. The peroxidation cross-linking is completed in a high temperature and high pressure nitrogen environment. After cross-linking, degassing treatment is performed to obtain the insulation structure of the finished cable.

[0068] In this embodiment, the insulating material composition includes polyethylene resin, reactive precursor, peroxidation crosslinking agent, co-crosslinking agent and antioxidant, wherein the polyethylene resin is cable insulation grade low-density polyethylene and the reactive precursor is P-1.

[0069] In this embodiment, the peroxide crosslinking agent is dicumyl peroxide, the co-crosslinking agent is triallyl isocyanurate, and the antioxidant is a hindered phenolic antioxidant.

[0070] Both the inner and outer semiconductive shielding layer materials are made of cross-linkable semiconductive shielding material for cables.

[0071] The above-mentioned semiconductive shielding material uses ethylene-vinyl acetate copolymer or ethylene-acrylate copolymer as the base resin and contains conductive carbon black and peroxide crosslinking system. In Examples 1 to 10 and Comparative Examples C1 to C5, unless otherwise specified, the inner semiconductive shielding layer material and the outer semiconductive shielding layer material are the same.

[0072] It should be noted that P-1, P-2, P-3, P-4, A-1, and B-1 all represent precursor compounds with a defined structure or composition, and are not arbitrary functional auxiliaries.

[0073] P-1 is an anthraquinone reactive precursor containing methacryloyl, anthraquinone, hydroxyl, and amide groups. It can participate in free radical grafting or cross-linking reactions in peroxidation cross-linking systems and can form deep trap structures in the interfacial region.

[0074] P-2 is an anthraquinone reactive precursor containing methacryloyl and anthraquinone groups but lacking hydroxyl and amide groups, used to compare the role of byproduct immobilization functional groups with P-1;

[0075] P-3 is a benzophenone reactive precursor that simultaneously contains vinyl, benzophenone, hydroxyl, and imide groups;

[0076] P-4 is a reactive imide precursor that simultaneously contains maleimide, aromatic imide, epoxy, and carboxyl groups;

[0077] A-1 is a non-reactive deep-trap small molecule containing anthraquinone structure but without reactive groups that can participate in free radical grafting or cross-linking reactions;

[0078] B-1 is a reactive compound containing reactive groups that can participate in free radical grafting or cross-linking reactions but does not contain polar conjugated structural units.

[0079] In this embodiment, the functional differences and uses of the group composition of P-1, P-2, P-3, P-4, A-1 and B-1 are described in the “Precursor Description” column of Table 1.

[0080] Among them, the methacryloyl group is used to participate in free radical grafting or cross-linking reactions under peroxidation cross-linking conditions, so that the precursor is fixed in the polyethylene network;

[0081] Anthraquinone groups, as polar conjugated structural units, are used to form deep traps in the interface region;

[0082] Hydroxyl and amide groups are used to capture, adsorb or immobilize small molecule byproducts formed during cross-linking in situ, thereby reducing byproduct residues in the interfacial region.

[0083] Therefore, P-1 in this embodiment is not a common polar auxiliary agent, but a reactive precursor that has three functions: reaction fixation, deep trap construction, and byproduct regulation.

[0084] To verify the formation mechanism and technical effect of the technical solution of the present invention, five comparative examples are set up in this embodiment;

[0085] Comparative Example C1 is a blank system, i.e., without the addition of the reactive precursor, and the remaining composition and preparation process are consistent with those of this embodiment, used to characterize the interface state and electrical treeing behavior of ordinary cross-linked polyethylene insulation system;

[0086] Comparative Example C2 was added with a non-reactive deep-trap molecule A-1. A-1 contains anthraquinone structure but does not contain reactive groups that can participate in free radical grafting or cross-linking reactions. This was used to illustrate the effect when only deep-trap units are present and interfacial reactions cannot occur for fixation.

[0087] Comparative example C3 was supplemented with reactive precursor P-2, which contains methacryloyl and anthraquinone groups but not hydroxyl and amide groups, to illustrate the effect of byproduct immobilization functional groups on interfacial byproduct regulation and overall performance.

[0088] Comparative Example C4 has the same formulation as this embodiment, but the insulating layer and the semiconductive shielding layer are not co-extruded in three layers. Instead, they are prepared by molding them separately first and then hot-pressing them together. The hot-pressing post-treatment temperature is 180°C and the treatment pressure is 12MPa. Other conditions are shown in Table 2, which is used to illustrate the importance of the real co-extruded interface for the formation of the interface confined reaction layer.

[0089] It should be noted that Comparative Example C4 does not pass through a continuous vulcanization pipeline, therefore the process pressure and linear velocity parameters corresponding to continuous vulcanization are not applicable; its post-hot pressing treatment conditions should record the actual treatment temperature, treatment pressure and treatment time.

[0090] Comparative Example C5 uses the same co-extrusion process as this example, but replaces the reactive precursor with reactive compound B-1, which does not contain polar conjugated structural units, to illustrate the difference when there is only reaction fixation without deep trap units.

[0091] The formulation composition of this embodiment and the comparative example is shown in Table 1, and the process conditions are shown in Table 2.

[0092] It should be noted that the pressure parameters of Examples 1-10 and Comparative Examples C1-C3 and C5 in Table 2 are the process pressures during the continuous vulcanization process; since Comparative Example C4 was prepared by hot-pressing composite method after non-co-extrusion, the pressure parameters in its table are the post-hot-pressing treatment pressures, and the linear velocity is not applicable. The other degassing conditions are consistent with those recorded in Table 2.

[0093] During preparation, low-density polyethylene, reactive precursor P-1, antioxidant and crosslinking agent are first added to a high-speed mixing device for premixing to achieve preliminary uniform dispersion of the precursor in the resin. Then, under controlled temperature rise conditions, peroxide crosslinking agent is added and mixing continues to obtain the insulating material composition.

[0094] The resulting insulating material composition is fed into a three-layer co-extrusion die head by an insulating layer extruder, and is simultaneously extruded with the inner semi-conductive shielding layer material and the outer semi-conductive shielding layer material to form a composite structure. It then enters a continuous vulcanization pipeline to complete cross-linking, and is degassed after cross-linking.

[0095] After the samples are prepared, samples are taken along the thickness direction of the insulating layer, starting from the contact surface between the semiconductive shielding layer and the insulating layer. For the preliminary determination of the interface layer thickness, layered sampling or microscopic infrared scanning is performed at 5 μm intervals within the range of 0–70 μm from the interface. After determining the specific interface confined reaction layer thickness, the area within this thickness range is taken as the interface layer sample, and the area beyond 300 μm from the interface is taken as the main area sample.

[0096] The thickness of the interface layer was determined by combining microscopic sectioning with microscopic infrared scanning. Optical observation was only used to assist in locating the interface position and was not used as a basis for determining the boundary of the interface confinement reaction layer. Specifically, a line scan was performed along the thickness direction of the insulating layer from the semiconductive shielding layer / insulating layer contact interface, with a step size of 5 μm. The average value of three consecutive measurement points at a distance of more than 300 μm from the interface was used as the reference value for the main area.

[0097] When two consecutive measuring points simultaneously meet the following conditions, the measuring point closer to the interface is taken as the boundary of the interface-bounded reaction layer:

[0098] (1) The intensity of the characteristic absorption peak of the reactive precursor is not higher than 120% of the reference value in the main region;

[0099] (2) The relative grafting degree is not higher than 115% of the reference value of the main area;

[0100] (3) The difference between the average depth of the trap and the reference value of the main area is no more than 0.05 eV.

[0101] The examples and comparative examples were compared using the same sampling method, scanning conditions, and judgment criteria.

[0102] Grafting degree or reaction conversion degree was characterized by relative integration of infrared characteristic peaks.

[0103] The relative grafting degree between the interface layer and the main body region was calculated by using the methylene characteristic peak of the polyethylene matrix as the internal standard peak and the carbonyl, imide or aromatic conjugated structure characteristic peaks in the reactive precursor as quantitative peaks.

[0104] For the P-1 system, the characteristic peak of the anthraquinone carbonyl group in P-1 is used as the quantitative peak;

[0105] For the P-3 system, the characteristic peak of the carbonyl group of benzophenone is used as the quantitative peak;

[0106] For the P-4 system, the characteristic peak of the imide was used as the quantitative peak. All examples and comparative examples were compared using the same integration principle and data processing method.

[0107] When used to characterize the degree of consumption of precursor reactive groups, it is called the degree of reaction conversion;

[0108] When the relative content of the precursor that remains in the polyethylene network after extraction is used to characterize the degree of grafting, it is called the grafting degree.

[0109] In the embodiments and comparative examples of this application, the interface layer and the main body area are compared using the same characterization method.

[0110] All samples were tested using the same thickness, number of scans, resolution, baseline correction method, and integration interval. Each group of samples was tested in parallel three times, and the average value of the results was taken.

[0111] Byproduct residues were characterized using solvent extraction-chromatographic quantification.

[0112] After solvent extraction, the interface layer samples and the main body region samples were quantitatively analyzed by gas chromatography or liquid chromatography.

[0113] During testing, the same extraction conditions, chromatographic conditions, and quantitative methods were used for both the interface layer sample and the main body sample, and a standard curve was established using common small molecule byproducts of the cross-linking system as standards.

[0114] Byproduct residue is calculated based on the total amount of all byproducts, in mg / g. -1 Each group of samples was tested in parallel three times, and the average value of the results was taken.

[0115] The average trap depth was characterized using the thermally stimulated depolarization current method. Samples were tested under the same polarization temperature, polarization electric field, polarization time, cooling conditions, short-circuit time, and heating rate, and the average trap depth was obtained using the same calculation method. Specific test conditions were as follows:

[0116] The polarization temperature was 90℃, the polarization electric field was 30kV / mm, the polarization time was 30min, and after cooling to room temperature, the circuit was short-circuited for 10min. Then, the thermally stimulated depolarization current curve was recorded at a heating rate of 3℃ / min. The average depth of the trap was calculated based on the position of the current peak using the TSDC peak method or the initial rise method commonly used in this field.

[0117] The electrical tree performance was tested using the needle-plate electrode method. The radius of curvature of the needle tip was 3–5 μm, the distance from the needle tip to the plate electrode was 2.0 mm, a 50 Hz AC voltage was applied, the onset time of the electrical tree was recorded under the same voltage conditions, and the maximum length of the electrical tree was measured after 60 min of voltage application.

[0118] In this application, "grafting degree or reaction conversion degree" is used to characterize the degree of immobilization of reactive precursors in cross-linked polyethylene networks. When the relative content of the precursor characteristic peaks that remain in the polyethylene network after extraction is characterized, it is called grafting degree.

[0119] When used to characterize the degree of consumption of precursor reactive groups, it is called the degree of reaction conversion;

[0120] In the examples and comparative examples, the interface layer and the main body area are compared using the same characterization method;

[0121] In this application, when characterizing the difference in the degree of immobilization of reactive precursors between the interface-confined reactive layer and the main region of the insulating layer, the grafting degree refers to the degree of immobilization of reactive precursors obtained by the above-mentioned infrared characteristic peak relative integration method.

[0122] The formulation composition of this embodiment and the comparative example is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical properties and electrical resistance results are shown in Table 6.

[0123] As shown in Tables 3 to 5, in Example 1, a stable interface confined reaction layer with a thickness of 46.8 μm was formed on the side of the insulating layer near the inner semiconductive shielding layer, which is located in the range of 20 to 70 μm.

[0124] The grafting degree of the interface-confined reaction layer is 1.92%, which is higher than that of the main region (0.73%). The ratio of the two reaches 2.63, indicating that the reactive precursor P-1 does not participate in the reaction uniformly and equally throughout the entire insulation layer during the co-extrusion crosslinking process. Instead, it preferentially grafts or crosslinks near the interface of the semiconductive shielding layer / insulation layer and achieves local fixation, thereby forming an interface-confined reaction layer with a higher degree of reaction than that in the main region on the surface.

[0125] Furthermore, the residual amount of byproducts in the interface layer of Example 1 was 0.61 mg·g. - ¹, significantly lower than the 1.37 mg / g of the main region. - ¹ This indicates that the hydroxyl and amide groups contained in P-1 are indeed beneficial for in-situ capture, adsorption, or fixation of cross-linking byproducts enriched at the interface;

[0126] Meanwhile, the average trap depth of the interface layer in Example 1 was 0.94 eV, which was significantly higher than the 0.51 eV of the main region, indicating that the anthraquinone group formed a deep trap structure in the interface layer.

[0127] Therefore, the interface layer formed in this embodiment is not a single concentration enrichment layer, but an interface confined reaction layer with a high degree of reaction fixation, a deep trap energy level, and a low by-product residue.

[0128] Comparing Example 1 with the blank comparative example C1, it can be seen that a stable interface confined reaction layer was not formed in C1, the average depth of the traps in the interface and the main region was close, the by-product residue in the interface region was not reduced, the electrical tree initiation time was only 18.9 min, and the maximum electrical tree length reached 318 μm at 60 min.

[0129] In contrast, the electrical tree initiation time of Example 1 was increased to 41.7 min, and the maximum electrical tree length at 60 min was reduced to 126 μm, indicating that the present invention can significantly delay electrical tree initiation and suppress electrical tree propagation.

[0130] Comparing Example 1 with C2, it can be seen that although C2 contains deep trap structural units, because A-1 lacks reactive groups that can participate in free radical grafting or cross-linking reactions, only an unstable interface layer of 18.6 μm is formed, with an interface layer grafting degree of only 0.34%, and the power frequency dielectric loss factor increases to 2.71 × 10⁻⁶. -4 The increase relative to C1 was 19.9%, exceeding 15%;

[0131] This indicates that when only deep trap units are available and interface reaction fixation cannot be achieved, it is not only difficult to form a stable interface confined reaction layer, but it also easily leads to increased dielectric loss, which cannot meet the overall performance requirements of this invention.

[0132] Comparing Example 1 with C3, it can be seen that C3 can also form an interface layer of a certain thickness, and the grafting degree of the interface layer is relatively high, indicating that preferential reactions can occur in the interface region by means of reactive groups and deep trap units alone. However, due to the lack of hydroxyl and amide groups in C3, the residual interface layer by-products still reach 1.03 mg / g. - ¹, significantly higher than 0.61 mg·g in Example 1. - ¹, the electrical tree initiation time and electrical tree extension length are also inferior to those of Example 1;

[0133] This indicates that the functional groups immobilized by-products are not optional modifications, but rather an important component in the formation of the comprehensive functions of the interface layer.

[0134] Comparing Example 1 and C4, it can be seen that, with the same formulation, but C4 is prepared by first molding separately and then hot-pressing composite sample preparation at 180°C and 12MPa, only a weak surface layer of 9.7μm is obtained, the grafting ratio of the interface layer / main body region is only 1.09, and the improvement of the average depth of the trap is not significant.

[0135] This indicates that the interface confined reaction layer described in this invention is not simply determined by the formulation, but needs to be formed in situ in a real interface environment where it is co-extruded with the semiconductive shielding layer and cross-linked.

[0136] In other words, the co-extrusion crosslinking process is not a common process background, but one of the necessary conditions for the formation of the structure of this invention.

[0137] Comparing Example 1 with C5, it can be seen that although C5 has a certain reaction fixation ability and forms a surface structure of a certain thickness, due to the lack of polar conjugated structural units, its average depth of interface layer traps is only 0.63 eV, which is significantly lower than 0.94 eV of Example 1. The initiation time of electric tree and the ability to suppress electric tree are also significantly insufficient.

[0138] This result further illustrates that the establishment of the "deep trap structure" in the interface layer is also necessary for the technical effect of the present invention, and cannot rely solely on reaction fixation.

[0139] Based on the dielectric loss results, the dielectric loss factor at 50Hz in Example 1 is 2.46 × 10⁻⁶. -4 Compared to the blank control C1, it increased by 8.8%, with the increase not exceeding 15%;

[0140] At the same time, its electrical tree initiation time is significantly prolonged and its electrical tree expansion length is significantly shortened;

[0141] The results show that the present invention does not achieve tree-suppressing performance by indiscriminately increasing the overall polarity of the material, but rather by constructing an interface confined reaction layer with deeper traps, higher grafting degree, and fewer by-products in situ near the interface surface, thereby directionally strengthening the weakest insulation / semiconductive interface of the cable, and thus achieving a significant tree-suppressing effect under the premise of controlled dielectric loss growth.

[0142] In summary, this embodiment fully demonstrates that when an insulating material formed by cross-linking an insulating material composition comprising polyethylene resin, a reactive precursor and a peroxide cross-linking agent is co-extruded with a semiconductive shielding layer and cross-linked to form a cable insulation layer, an interface-confined reactive layer can be formed in situ on at least one side of the surface.

[0143] The thickness of the interface-confined reaction layer is in the range of 20 to 70 μm. Its average trap depth is higher than that of the main region of the insulating layer, and the grafting degree of the reactive precursor is higher than that of the main region of the insulating layer. At the same time, the residual amount of crosslinking by-products is lower than that of the adjacent main region, thereby significantly improving the electrical resistance performance.

[0144] The results demonstrate that the technical approach of this invention has a clear structural basis, formation characteristics, and verifiable technical effects, and is beneficial to improving the operational stability of the insulation layer.

[0145] Example 2

[0146] This embodiment illustrates that when the reactive groups and polar conjugated structural units in the reactive precursor are replaced, as long as the reactive groups that can participate in free radical grafting or crosslinking reactions, the polar conjugated structural units that can form deep traps, and the functional groups that can capture, adsorb, or fix crosslinking byproducts in situ are still present, the technical solution of the present invention remains valid.

[0147] Except for the differences described below, everything else is the same as in Example 1;

[0148] The only difference is that the reactive precursor used in this embodiment is replaced by P-3 instead of P-1 in Example 1. P-3 contains vinyl, benzophenone, hydroxyl and imide groups. P-3 is a precursor compound that contains both vinyl reaction sites and benzophenone conjugated structures. Its hydroxyl and imide groups are used to improve its adsorption, association or immobilization of interfacial byproducts.

[0149] Vinyl groups are used to participate in free radical grafting or cross-linking reactions under peroxidation cross-linking conditions to fix the precursor in the polyethylene network.

[0150] The benzophenone group, as a polar conjugated structural unit, is used to form deep traps in the interfacial region;

[0151] Hydroxyl and imide groups are used for in-situ capture, adsorption, or immobilization of cross-linking byproducts enriched at the interface;

[0152] Except for the differences mentioned above, the composition of other raw materials and the process can be referred to in Example 1. The specific formulation of Example 2 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0153] As can be seen from Table 3, in this embodiment, a stable interface confined reaction layer is formed on the surface layer on the side where the insulating layer and the inner semiconductive shielding layer are in contact, and its thickness falls within the range of 20 to 70 μm. This indicates that replacing P-1 with P-3 in Example 1 does not destroy the core structural feature of "forming an interface confined reaction layer in situ on the surface layer during the co-extrusion crosslinking process" required by the present invention.

[0154] The results indicate that the formation of the interface-confined reaction layer described in this invention does not depend on the unique combination of methacryloyl and anthraquinone groups, but is also applicable to another type of reactive precursor that simultaneously possesses reaction immobilization and deep trap construction capabilities.

[0155] As shown in Table 4, in this embodiment, the grafting degree or reaction conversion degree of the interface confined reaction layer is higher than that of the main insulating layer, and the residual amount of crosslinking by-products in the interface confined reaction layer is lower than that in the adjacent main insulating layer.

[0156] The results indicate that the vinyl groups in P-3 enable the reactive precursors to undergo preferential reaction and local fixation in the interfacial region during co-extrusion crosslinking, while the hydroxyl and imide groups help reduce by-product residues in the interfacial region. As a result, the interfacial layer formed in this embodiment not only has a high degree of reactivity but also low by-product residues.

[0157] Compared with Example 1, this example has changed in structural composition, but the basic rule that the interface layer has a higher grafting degree than the main body region and a lower residual amount than the main body region remains the same. This shows that the rule is not caused by a single precursor by chance, but is a stable manifestation of the technical route of the present invention.

[0158] As shown in Table 5, in this embodiment, the average trap depth of the interface confined reaction layer is higher than that of the main insulating layer, and the average trap depths of the interface layer and the main insulating layer fall within the numerical ranges of 0.85–1.10 eV and 0.44–0.58 eV respectively as described in this application.

[0159] This result demonstrates that the benzophenone group can also serve as an effective deep trap building block, enabling the formation of a trap structure at the interface that is significantly deeper than the host region. Therefore, this embodiment further illustrates that the polar conjugated structural unit is not limited to the anthraquinone group.

[0160] As shown in Table 6, the dielectric loss factor of this embodiment under power frequency conditions is controlled to increase by less than 15% compared with the blank control system which does not contain reactive precursors and has the same composition and preparation process. At the same time, the initiation time of electrical tree is significantly prolonged and the maximum length of electrical tree is significantly reduced.

[0161] Based on Tables 3 to 5, it can be concluded that the electrical tree effect exhibited in this embodiment does not simply stem from an increase in the overall polarity of the material, but rather from an interfacial confined reaction layer formed in situ near the surface of the insulating / semiconductive interface. This interfacial layer possesses a high degree of reaction fixation, a deep trap structure, and low byproduct residue, thereby playing a directional regulatory role in interfacial charge injection and local electric field distortion.

[0162] In summary, this embodiment demonstrates that, under the technical route described in Example 1, by replacing the reactive precursor with P-3 containing vinyl, benzophenone, hydroxyl, and imide groups, it is still possible to form an interface-confined reactive layer in situ on at least one side of the surface when co-extruded with the semiconductive shielding layer and cross-linked to form the cable insulation layer. This interface-confined reactive layer exhibits a higher degree of grafting or reaction conversion than the main region of the insulation layer, a deeper average trap depth than the main region of the insulation layer, and lower cross-linking byproduct residues than the adjacent main region, thereby improving the resistance to electrical treeing under the premise of controlled increase in dielectric loss.

[0163] The results demonstrate that the technical solution described in this invention is replaceable for different types of reactive groups, polar conjugated structural units, and byproduct immobilization functional groups, and can still achieve improved electrical resistance under controlled dielectric loss increase conditions.

[0164] Example 3

[0165] This embodiment further illustrates that when the reactive groups, polar conjugated structural units, and functional groups used to regulate crosslinking byproducts in the reactive precursor are further replaced, as long as the reactive precursor still possesses reactive groups that can participate in free radical grafting or crosslinking reactions, polar conjugated structural units that can form deep traps, and functional groups that can capture, adsorb, associate, or fix crosslinking byproducts in situ, the crosslinked polyethylene insulation material for medium and high voltage cables described in this invention can still form an interface confined reaction layer with the thickness, trap parameters, and interface reaction characteristics described in this application, and obtain the corresponding crosslinking effect.

[0166] Except for the differences described below, everything else is the same as in Example 1;

[0167] Unlike Examples 1 and 2, the reactive precursor used in this example is P-4, which replaces P-1 in Example 1 and P-3 in Example 2.

[0168] The above-mentioned P-4 contains maleimide group, aromatic imide group, epoxy group and carboxyl group. P-4 is a precursor compound that simultaneously contains maleimide reaction site and aromatic imide conjugated structure. Its epoxy group and carboxyl group are used to improve its adsorption, association or fixation of interfacial byproducts.

[0169] Among them, the maleimide group is used to participate in free radical grafting, coupling or cross-linking reactions under peroxidation cross-linking conditions, so that the precursor can be fixed in the cross-linked polyethylene network.

[0170] Aromatic imide groups serve as polar conjugated structural units, used to form deep traps near the surface of insulating / semiconductive interfaces.

[0171] Epoxy and carboxyl groups are used for in-situ adsorption, capture, association, or fixation of small molecule byproducts formed during cross-linking.

[0172] Except for the type and corresponding amount of reactive precursors, the composition of other raw materials and preparation process can be referred to Example 1. The formulation composition of Example 3 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0173] As can be seen from Table 3, in this embodiment, a stable interface confinement reaction layer is also formed on the surface layer on the side where the insulating layer and the semiconductive shielding layer are in contact, and the thickness of the interface confinement reaction layer falls within the range of 20 to 70 μm.

[0174] This shows that after further replacing the methacryloyl / anthraquinone system in Example 1 and the vinyl / benzophenone system in Example 2 with the maleimide / aromatic imide system in this example, an interface confined reaction layer with a thickness in the range of 20 to 70 μm can still be formed in situ on the surface under co-extrusion crosslinking conditions.

[0175] This indicates that the formation of the "interface confined reaction layer" in this invention does not depend on a specific single reactive group or a specific single polar conjugated structural unit, but rather originates from the common mechanism that the reactive precursor preferentially reacts and achieves local fixation near the real co-extrusion crosslinking interface.

[0176] As shown in Table 4, in this embodiment, the grafting degree or reaction conversion degree of the interface confined reaction layer is higher than that of the main insulating layer, while the residual amount of crosslinking by-products in the interface confined reaction layer is lower than that in the adjacent main insulating layer.

[0177] Based on the precursor structure used in this embodiment, it can be seen that the maleimide group can enable P-4 to preferentially react and be locally fixed in the interface region under the condition of peroxidation crosslinking, while the epoxy and carboxyl groups are beneficial to the in-situ regulation of small molecule byproducts enriched near the interface. Therefore, the interface layer formed in this embodiment not only has a higher degree of reaction than the host region, but also has a better interface purification effect than the host region.

[0178] Compared with Example 2, this example further demonstrates that the functional groups capable of regulating by-products are not limited to hydroxyl and imide groups. Epoxy and carboxyl groups can also play corresponding roles under the technical route of this invention, thereby further illustrating that functional groups such as hydroxyl, imide, epoxy, and carboxyl groups can all be used for the adsorption, association, or immobilization of interfacial by-products.

[0179] As shown in Table 5, in this embodiment, the average trap depth of the interface confined reaction layer is higher than that of the main insulating layer, and the average trap depths of the interface layer and the main insulating layer are still within the ranges of 0.85–1.10 eV and 0.44–0.58 eV, respectively.

[0180] This result shows that aromatic imide groups can also serve as effective polar conjugated structural units to establish deep trap structures in the interface region.

[0181] As shown in Table 6, the dielectric loss factor of this embodiment under power frequency conditions is still controlled within 15% compared with the blank system which does not contain reactive precursors and has the same composition and preparation process. At the same time, its electrical tree initiation time is significantly higher than that of the blank system, and its maximum electrical tree length is significantly lower than that of the blank system.

[0182] Based on the results in Tables 3, 4 and 5, it can be seen that the improved electrical resistance of this embodiment still originates from the interface confined reaction layer formed in situ near the surface of the interface, rather than from the indiscriminate improvement of the overall polarity of the insulating material.

[0183] In particular, echoing the foregoing embodiments, this embodiment further illustrates that as long as the reactive precursor can simultaneously provide the three functions of "interface preferential reaction fixation", "deep trap construction" and "byproduct regulation", the corresponding interface confined reaction layer can be formed and the electrical resistance performance can be improved under the process conditions of the present invention.

[0184] The above results show that, under the test conditions of this embodiment, the P-4 system can achieve the same trend in interface layer structure and electrical resistance improvement effect as the P-1 and P-3 systems.

[0185] In summary, this embodiment demonstrates that, under the technical route described in Example 1, by replacing the reactive precursor with P-4 containing maleimide, aromatic imide, epoxy, and carboxyl groups, it is still possible to form an interface-confined reactive layer in situ on at least one side of the surface when co-extruded with the semiconductive shielding layer and cross-linked to form the cable insulation layer. This interface-confined reactive layer exhibits a higher degree of grafting or reaction conversion than the main region of the insulation layer, a deeper average trap depth than the main region of the insulation layer, and lower cross-linking byproduct residues than the adjacent main region, thereby improving the resistance to electrical treeing under controlled dielectric loss increase conditions.

[0186] This result further demonstrates that the technical solution of the present invention has good adaptability to combinations of different types of reactive groups, polar conjugated structural units, and by-product regulatory functional groups.

[0187] Example 4

[0188] This embodiment illustrates that when the amount of reactive precursor added is reduced to a low level, the technical solution of the present invention can still form an interface-confined reactive layer in situ on at least one side of the surface during the process of co-extruding the insulation layer and the semi-conductive shielding layer and cross-linking to form the cable insulation layer. However, the degree of formation of the interface-confined reactive layer, the interface control capability, and the final electrical tree effect will be weakened accordingly. This demonstrates that the setting of the reactive precursor addition range has practical technical significance, rather than being arbitrarily given.

[0189] Except for the differences described below, everything else is the same as in Example 1;

[0190] Unlike Example 1, this example still uses the reactive precursor P-1 from Example 1, but its amount is reduced from 0.72 parts by mass in Example 1 to 0.12 parts by mass.

[0191] Except for the amount of precursor added, the composition of other raw materials and process conditions can be referred to in Example 1. The specific formulation of Example 4 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0192] As can be seen from Table 3, in this embodiment, a stable interface confinement reaction layer is still formed on the surface of the side where the insulating layer and the semiconductive shielding layer are in contact, with a thickness of 23.6 μm, which still falls within the range of 20 to 70 μm.

[0193] This indicates that even under low addition conditions, P-1 can still preferentially react near the co-extrusion crosslinking interface and form a surface reaction layer with a thickness in the range of 20 to 70 μm. Therefore, the technical solution of the present invention is still feasible under these low addition conditions.

[0194] Meanwhile, compared with Example 1, the thickness of the interface layer in this example is significantly reduced, indicating that after the amount of precursor is reduced, the number of effective structural units that can participate in preferential reactions and local fixation in the interface region is reduced, and the degree of formation of the interface confined reaction layer decreases accordingly.

[0195] As shown in Table 4, in this embodiment, the grafting degree or reaction conversion degree of the interface-confined reaction layer is still higher than that of the main region of the insulating layer, and the ratio of the interface layer to the main region is 1.84, indicating that this embodiment still satisfies the technical feature that "the grafting degree or reaction conversion degree of the reactive precursor in the interface-confined reaction layer is higher than that of the main region of the insulating layer".

[0196] Meanwhile, the residual amount of crosslinking byproducts in the interface layer of this embodiment is 0.88 mg·g. - ¹, lower than the 1.29 mg·g in the main region. - ¹ indicates that P-1 can still achieve certain in-situ capture, adsorption or fixation of small molecule byproducts enriched at the interface even at low addition levels.

[0197] However, compared with Example 1, the grafting degree of the interface layer in this example is significantly reduced, while the residual amount of interface layer by-products is increased, indicating that the interfacial reaction fixation ability and by-product regulation ability are weakened at a lower amount of precursor added.

[0198] This result further illustrates that the amount of precursor added not only affects whether an interface layer is formed, but also affects the sufficiency of the interface layer formation and the strength of its overall function.

[0199] As shown in Table 5, the average depth of the traps in the interface confined reaction layer in this embodiment is 0.86 eV, and the average depth of the traps in the main region is 0.50 eV. Both of them still fall within the numerical range of 0.85~1.10 eV and 0.44~0.58 eV, respectively, and the interface layer is significantly deeper than the main region.

[0200] This indicates that even at low addition levels, the anthraquinone group in P-1 can still form a deep trap structure in the interfacial region;

[0201] However, compared with Example 1, the average depth of traps and the density of deep traps in the interface layer of this example have both decreased, indicating that the ability to build deep traps in the interface region is weakened as the amount of precursor added decreases.

[0202] This is consistent with the trend of thinning of the interface layer and decrease of the interface grafting degree reflected in Tables 3 and 4, indicating that the formation of the interface confined reaction layer, the construction of deep traps and the regulation of by-products are an interconnected whole process.

[0203] As shown in Table 6, the increase in dielectric loss factor under power frequency conditions in this embodiment compared to the blank control C1 is 2.2%, which is significantly lower than 15%, indicating that the increase in dielectric loss is more easily controlled under a lower amount of precursor added.

[0204] However, at the same time, the electrical tree initiation time of this embodiment is 30.4 min, which is significantly higher than the blank control C1's 18.9 min, and the maximum electrical tree length at 60 min is reduced from 318 μm in C1 to 191 μm, indicating that the technical solution of the present invention can still improve the electrical tree resistance performance under this low addition condition.

[0205] However, compared with Example 1, its electrical tree initiation time was significantly shortened and its maximum electrical tree length was significantly increased, indicating that its electrical tree resistance modification effect has been weakened.

[0206] The results show that although the present invention can still be implemented at lower precursor addition amounts, the interface regulation effect is not as sufficient as in Example 1, thus further proving that the range of precursor addition amounts and its preferred range have clear technical significance.

[0207] Based on Tables 3 to 6, it can be concluded that this embodiment is not intended to prove that "the lower the amount added, the better," but rather to illustrate that: under conditions of lower addition amount, the technical route of the present invention still holds true, and an interface confined reaction layer with a thickness in the range of 20 to 70 μm, an average trap depth higher than that of the main region, and a by-product residue lower than that of the main region can still be formed. Furthermore, the interface layer can still exhibit a higher degree of reaction, a deeper trap structure, and a lower by-product residue compared to the main region.

[0208] However, due to the reduction in the total amount of precursors, the degree of formation of the interface layer and the overall regulatory effect have both weakened;

[0209] Therefore, this embodiment supports the feasibility of low addition of reactive precursors on the one hand, and on the other hand, it also proves the optimality of the addition range corresponding to Example 1 from the opposite perspective.

[0210] In summary, this embodiment demonstrates that, under the technical route described in Embodiment 1, even after reducing the amount of reactive precursor P-1 to 0.12 parts by mass, it is still possible to form an interface-confined reactive layer in situ on at least one side of the surface when co-extruded with the semiconductive shielding layer and cross-linked to form the cable insulation layer. This interface-confined reactive layer exhibits a higher degree of grafting or reaction conversion than the main region of the insulation layer, a deeper average trap depth than the main region of the insulation layer, and lower cross-linking byproduct residue than the adjacent main region, thereby improving the resistance to electrical treeing under the premise of controlled increase in dielectric loss.

[0211] This result further demonstrates that the technical solution of the present invention is still feasible under conditions of lower reactive precursor addition, but the interface regulation effect is relatively weakened.

[0212] Example 5

[0213] This embodiment illustrates that when the amount of reactive precursor added is within a relatively high but still processable range, and with appropriate optimized crosslinking and degassing conditions, the technical solution described in this invention can more fully form an interface-confined reactive layer on at least one side of the surface during the process of co-extruding the insulation layer and the semi-conductive shielding layer and crosslinking to form the cable insulation layer. This further improves the degree of reaction fixation, deep trap construction capability, and by-product control capability in the interface region, and achieves better electrical tree resistance under the premise that the increase in power frequency dielectric loss is still controlled.

[0214] This embodiment corresponds to Embodiment 4. Both are used to illustrate that the amount of reactive precursor added is not arbitrarily set, but rather there is a feasible range and a preferred range.

[0215] Except for the differences described below, everything else is the same as in Example 1;

[0216] Unlike Example 1, this example still uses the reactive precursor P-1, but its amount is adjusted to 1.85 parts by mass.

[0217] Meanwhile, in order to further leverage the preferential reaction and byproduct regulation role of reactive precursors in the interfacial region, this embodiment has synergistically optimized the process conditions, namely, adjusting the crosslinking temperature, process pressure, amount of co-crosslinking agent, and degassing conditions to the parameters shown in Table 2;

[0218] Except for the aforementioned adjustments, the remaining raw material composition and process can be referred to Example 1;

[0219] The specific formulation of Example 5 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0220] As shown in Table 3, in this embodiment, a stable interface confinement reaction layer is formed on the surface of the side where the insulating layer contacts the semiconductive shielding layer. The thickness of the layer is 57.4 μm, which is significantly higher than that of Embodiment 1 and Embodiment 4, but still within the range of 20 to 70 μm.

[0221] This indicates that under conditions of higher precursor addition and optimized process, P-1 can undergo preferential reaction and achieve local fixation more fully near the co-extrusion crosslinking interface, thereby making the formation of the interface-confined reaction layer more complete.

[0222] Compared to Example 4, the interface layer thickness in this example increased from 23.6 μm to 57.4 μm, indicating that with the increased precursor dosage, the number of effective structural units that can participate in reaction fixation and deep trap construction within the interface region significantly increased, resulting in a more complete establishment of the interface-confined reaction layer. Compared to Example 1, the interface layer in this example is further thickened, demonstrating that the higher dosage and optimized process parameters used in this example can further enhance interface layer formation.

[0223] As shown in Table 4, the grafting degree or reaction conversion degree of the interface confined reaction layer in this embodiment is 2.18%, which is higher than 1.92% in Example 1 and 0.94% in Example 4, and higher than 0.81% in the main region. The ratio of interface layer to main region is 2.69.

[0224] The results indicate that, under the conditions of this embodiment, the reactive precursor exhibits more efficient preferential reaction and local fixation in the interface region.

[0225] Meanwhile, the residual amount of crosslinking byproducts in the interface layer of this embodiment is 0.53 mg·g. - ¹, which is significantly lower than the 1.42 mg / g of the main region. - ¹, and lower than 0.61 mg·g in Example 1. - ¹ and 0.88 mg·g in Example 4 - ¹;

[0226] The results indicate that, under the synergistic effect of higher precursor addition and optimized degassing conditions, the hydroxyl and amide groups contained in P-1 further enhance the in-situ capture, adsorption or immobilization of interfacial enriched byproducts, thereby making the interfacial region purer.

[0227] Therefore, this embodiment does not simply increase the amount of precursor added to increase interfacial polarity, but achieves simultaneous enhancement in three aspects: precursor reaction fixation, interfacial layer formation, and byproduct regulation.

[0228] As shown in Table 5, the average trap depth of the interface confined reaction layer in this embodiment is 0.99 eV, and the average trap depth of the main region is 0.52 eV, which fall within the numerical ranges of 0.85–1.10 eV and 0.44–0.58 eV, respectively.

[0229] Meanwhile, the density of deep traps in the interface layer reaches 8.9 × 10²¹m. - ³, significantly higher than in Examples 1 and 4 and the main body area;

[0230] This indicates that, under conditions of higher precursor addition, the anthraquinone group in P-1 can construct richer and more stable deep trap structures in the interfacial region.

[0231] Compared with Example 4, the average depth and deep trap density of the interface traps in this example are significantly improved, indicating that the charge trapping ability of the interface layer is significantly enhanced after the amount of precursor added is increased.

[0232] Compared with Example 1, the trap parameters in this example are further improved, indicating that the interface control under the conditions of this example is more sufficient.

[0233] As shown in Table 6, the dielectric loss factor of this embodiment under power frequency conditions is 2.57 × 10⁻⁶. -4 The increase compared to the blank control C1 was 13.7%, which is still less than 15%.

[0234] This indicates that even with a higher amount of precursor added, the increase in dielectric loss of the present invention is still controlled, and the increase in dielectric loss factor does not exceed 15% due to the increase in precursor dosage;

[0235] Meanwhile, the electrical tree initiation time in this embodiment reached 46.2 min, which is significantly higher than 41.7 min in Example 1 and 30.4 min in Example 4. The maximum electrical tree length at 60 min decreased to 112 μm, which is significantly smaller than 126 μm in Example 1 and 191 μm in Example 4.

[0236] The results indicate that this embodiment is superior to Embodiments 1 and 4 in terms of resistance to electrical treeing.

[0237] Based on Tables 3 to 5, it can be concluded that this performance improvement is not simply due to an increase in the overall polarity of the material, but rather originates from a thicker, deeper trap, lower by-product residue, and more reactive interface confined reaction layer formed in situ near the surface of the interface.

[0238] Furthermore, by combining this embodiment with comparative examples C2, C3, and C5, it can be seen that the overall effect achieved by this embodiment depends on the following conditions simultaneously:

[0239] First, reactive precursors need to have reactive groups that can participate in free radical grafting or cross-linking reactions to ensure preferential fixation at the interface;

[0240] Secondly, reactive precursors need to have polar conjugated structural units capable of forming deep traps to ensure that the interface layer has a deeper trap structure.

[0241] Third, the preferred reactive precursor should also have functional groups that can capture or immobilize cross-linking byproducts in situ to reduce interfacial byproduct residues.

[0242] Fourth, the amount of precursor added and the process conditions must be within an appropriate range to ensure that the interface layer is fully formed while the increase in dielectric loss is still controlled.

[0243] This embodiment precisely demonstrates the synergistic effect of the above factors. Therefore, its result not only strengthens the verification of Embodiment 1, but also corresponds positively to the low-end boundary verification of Embodiment 4.

[0244] In summary, this embodiment demonstrates that, under the technical route described in Example 1, by increasing the amount of reactive precursor P-1 to 1.85 parts by mass and combining it with appropriately optimized crosslinking and degassing conditions, an interface-confined reactive layer can still be formed in situ on at least one side of the surface when co-extruded with the semiconductive shielding layer and crosslinked to form the cable insulation layer. Moreover, compared with Examples 1 and 4, this interface-confined reactive layer has a higher grafting degree or reaction conversion degree, a deeper average trap depth, a higher deep trap density, and a lower crosslinking by-product residue, thereby achieving better electrical tree resistance performance under the condition that the increase in dielectric loss does not exceed 15%.

[0245] This result further illustrates that there is an optimal range for the amount of reactive precursor added to achieve better interface regulation.

[0246] Example 6

[0247] This embodiment is used to illustrate that when the amount of peroxide crosslinking agent added is reduced to a low level, the insulating material composition using reactive precursor P-1 can still form an interface confined reaction layer in situ on at least one side of the surface during the process of co-extruding with the semiconductive shielding layer and crosslinking to form the cable insulation layer. However, the degree of formation of the interface confined reaction layer, the interface reaction fixation ability, the deep trap construction ability, and the final electrical tree effect will be weakened accordingly.

[0248] This demonstrates that the amount of peroxide crosslinking agent added has a significant impact on the formation of the interfacial layer and the overall performance, and its value cannot be arbitrarily changed.

[0249] Except for the differences described below, everything else is the same as in Example 1;

[0250] Unlike Example 1, this example still uses the reactive precursor P-1 described in Example 1, and the amount added remains unchanged at 0.72 parts by mass. However, the amount of peroxide crosslinking agent added is reduced from 1.85 parts by mass in Example 1 to 0.55 parts by mass.

[0251] Accordingly, to accommodate a lower crosslinking agent dosage, the crosslinking temperature, process pressure, and linear velocity in this embodiment were adjusted according to the conditions shown in Table 2. Except for the differences mentioned above, the composition of other raw materials and the process can be referred to in Example 1. The specific formulation of Example 6 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0252] As can be seen from Table 3, in this embodiment, a stable interface confinement reaction layer is still formed on the surface layer on the side where the insulating layer and the semiconductive shielding layer are in contact, with a thickness of 26.9 μm, which is still within the range of 20 to 70 μm.

[0253] The results show that under conditions of low peroxide crosslinking agent dosage, P-1 can still preferentially react and form a surface reaction layer near the co-extrusion crosslinking interface, so the technical route of the present invention can still be implemented under these conditions;

[0254] However, compared with Example 1, the interface layer thickness in this embodiment is significantly reduced; compared with Example 5, the difference is even more obvious.

[0255] This indicates that when the amount of peroxide crosslinking agent is reduced, the free radical reactivity decreases, and the effective reaction opportunities available for driving precursor grafting, coupling, or crosslinking in the interfacial region are reduced, resulting in insufficient formation of the interfacial confined reaction layer.

[0256] As shown in Table 4, in this embodiment, the grafting degree or reaction conversion degree of the interface confined reaction layer is 1.02%, the main region is 0.62%, and the ratio of the interface layer to the main region is 1.65.

[0257] This result indicates that even at lower crosslinking agent concentrations, the degree of reaction in the interfacial region is still higher than that in the bulk region, and the fundamental principle of preferential interfacial reaction still exists.

[0258] However, compared with 2.63 times that of Example 1 and 2.69 times that of Example 5, the interfacial enrichment reaction characteristics of this example are significantly weakened;

[0259] Meanwhile, the residual amount of crosslinking byproducts in the interface layer of this embodiment is 0.97 mg·g. - ¹, although lower than the 1.18 mg / g of the main region - ¹, but significantly higher than the 0.61 mg / g in Example 1. - ¹ and 0.53 mg·g in Example 5- ¹;

[0260] The results indicate that, under conditions of lower crosslinking agent dosage, on the one hand, the degree of reaction fixation in the interfacial region decreases, and on the other hand, the in-situ capture, adsorption, or fixation of interfacial byproducts by the hydroxyl and amide groups in P-1 is not fully utilized, resulting in a decrease in the degree of purification of the interfacial region.

[0261] As shown in Table 5, the average trap depth of the interface-confined reaction layer in this embodiment is 0.87 eV, and the average trap depth of the main region is 0.49 eV. Both are still within the corresponding window required by the technical solution of this invention, and the interface layer is significantly deeper than the main region. This indicates that even with a low amount of peroxide crosslinking agent added, the anthraquinone group in P-1 can still construct a deep trap structure in the interface region;

[0262] However, compared with Examples 1 and 5, the average depth of interface layer traps and the density of deep traps in this example have both decreased, indicating that the number of precursors that are fixed and effectively participate in the construction of deep traps in the interface region has decreased, thereby weakening the charge trapping ability of the interface layer.

[0263] This result is consistent with the trends of decreasing interface layer thickness in Table 3 and decreasing interface layer grafting degree in Table 4, indicating that interface layer formation, deep trap establishment, and by-product regulation are synergistic.

[0264] As shown in Table 6, the dielectric loss factor of this embodiment under power frequency conditions is 2.33 × 10⁻⁶. -4 Compared to the blank control C1, the increase was 3.1%, which is significantly lower, indicating that the overall polarity loss of the material is easier to control when the amount of peroxide crosslinking agent added is low.

[0265] The electrical tree initiation time in this embodiment was 28.7 min, which was still significantly higher than the blank control C1's 18.9 min. Furthermore, the maximum electrical tree length at 60 min decreased from 318 μm in C1 to 204 μm, indicating that it still had a certain effect on improving electrical tree resistance.

[0266] However, compared with 41.7 min and 126 μm in Example 1, the electrical tree initiation time of this example is significantly shortened and the electrical tree extension length is significantly increased, indicating that its electrical tree resistance modification effect has been significantly weakened.

[0267] This shows that simply relying on lower dielectric loss growth does not necessarily mean better interface control effect;

[0268] Conversely, if the amount of crosslinking agent is too low, although the interface layer can still be formed, its formation degree is insufficient, making it difficult to achieve more sufficient interface strengthening.

[0269] Further combining Tables 3 to 6, it can be considered that the main significance of this embodiment is not to pursue the lowest dielectric loss factor, but to illustrate that when the amount of peroxide crosslinking agent added is low, the technical route of the present invention is still valid and can still form an interface confined reaction layer with the characteristics of "interface layer reaction degree is higher than that of the main region, interface layer trap is deeper than that of the main region, and interface layer by-product residue is lower than that of the main region".

[0270] However, due to the weakening of the driving force of free radical reaction, the thickness of the interface layer, the degree of grafting, the density of deep traps and the ability to regulate by-products are all insufficient, thus the effect of the electrical resistance resin is not as sufficient as in Examples 1 and 5.

[0271] This result, conversely, suggests that there is a more suitable operating range for the amount of crosslinking agent.

[0272] In summary, this embodiment demonstrates that, under the technical route described in Example 1, even after reducing the amount of peroxide crosslinking agent added to 0.55 parts by mass, it is still possible to form an interface confined reaction layer in situ on at least one side of the surface layer when co-extruded with the semiconductive shielding layer and crosslinked to form the cable insulation layer. This interface confined reaction layer exhibits a higher degree of grafting or reaction conversion than the main region of the insulation layer, a deeper average trap depth than the main region of the insulation layer, and lower crosslinking by-product residues than the adjacent main region.

[0273] However, compared with Examples 1 and 5, the degree of interface layer formation and the overall control effect are weakened, and the improvement of electrical tree resistance is relatively limited.

[0274] The results indicate that the amount of peroxide crosslinking agent added has a significant impact on the formation of the interfacial confined reaction layer and its overall function.

[0275] Example 7

[0276] This embodiment illustrates that when the amount of peroxide crosslinking agent added is increased to a high level, the insulating material composition using reactive precursor P-1 can still form an interface confined reaction layer in situ on at least one side of the surface during the process of co-extruding with the semiconductive shielding layer and crosslinking to form the cable insulation layer, and can further improve the reaction fixation degree and deep trap construction ability of the interface region. However, at the same time, the amount of crosslinking by-products generated and the material dielectric loss will also increase accordingly.

[0277] Therefore, this embodiment is mainly used to illustrate the changing trend of interface layer formation and overall performance under higher peroxide crosslinking agent dosage, and together with Example 6, constitutes a two-end comparison of the change in crosslinking agent dosage.

[0278] Except for the differences described below, everything else is the same as in Example 1;

[0279] Unlike Example 1, this example still uses the reactive precursor P-1 described in Example 1, and the amount added remains unchanged at 0.72 parts by mass. However, the amount of peroxide crosslinking agent added is increased from 1.85 parts by mass in Example 1 to 2.35 parts by mass, and the crosslinking temperature, process pressure, linear speed and degassing time are adjusted accordingly to the conditions shown in Table 2.

[0280] Except for the differences mentioned above, the composition of other raw materials and the process can be referred to in Example 1. The specific formulation of Example 7 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0281] As can be seen from Table 3, in this embodiment, a stable interface confinement reaction layer is formed on the surface layer on the side where the insulating layer and the semiconductive shielding layer are in contact. Its thickness is 61.3 μm, which is significantly higher than 46.8 μm in Example 1 and 26.9 μm in Example 6, but still within the range of 20 to 70 μm.

[0282] The results indicate that under conditions of higher peroxide crosslinking agent dosage, the free radical reaction near the co-extrusion crosslinking interface is more active, and P-1 is more likely to preferentially graft, couple or crosslink in the interface region and achieve local fixation, thereby making the interface confined reaction layer more fully formed.

[0283] Compared with Example 6, the thickness of the interface layer in this example is significantly increased, indicating that increasing the amount of crosslinking agent can significantly enhance the ability to build the interface layer.

[0284] As shown in Table 4, the grafting degree or reaction conversion degree of the interface-confined reaction layer in this embodiment is 2.06%, while that of the main region is 0.79%, and the ratio of the interface layer to the main region is 2.61. This result indicates that, under higher crosslinking agent dosages, the reaction degree of the interface region is significantly higher than that of the main region, and this difference is similar to that in Example 1, but significantly higher than that in Example 6.

[0285] Therefore, increasing the amount of peroxide crosslinking agent is beneficial to enhancing the preferential reaction and local fixation ability of the precursor in the interfacial region.

[0286] Meanwhile, the residual amount of crosslinking byproducts in the interface layer of this embodiment is 0.74 mg·g. - ¹, although still lower than the 1.57 mg / g of the main region. - ¹ indicates that the interface region still retains the characteristic of low by-product residue;

[0287] However, compared to 0.61 mg / g in Example 1... - ¹The levels have increased compared to the previous period, and the residues of by-products in the main region have increased significantly;

[0288] The results indicate that, although the hydroxyl and amide groups in P-1 can still play an in-situ capture, adsorption or fixation role for byproducts in the interfacial region after the amount of crosslinking agent is increased, the residual levels of the interfacial layer and the main body region will be correspondingly increased due to the increase in the overall amount of byproducts generated.

[0289] Therefore, while a higher amount of crosslinking agent is beneficial for enhancing interfacial reaction fixation, it also brings greater pressure to control byproducts.

[0290] As shown in Table 5, in this embodiment, the average depth of the traps in the interface confined reaction layer is 1.02 eV, and the average depth of the traps in the main body region is 0.53 eV. Both are within their respective target ranges, and the interface layer is significantly deeper than the main body region.

[0291] Meanwhile, the interface layer deep trap density in this embodiment is 8.3 × 10²¹m. - ³, significantly higher than in Examples 1 and 6;

[0292] This result indicates that under conditions of higher peroxide crosslinking agent dosage, the anthraquinone group in P-1 can construct deeper and richer deep trap structures in the interface region, further enhancing the charge trapping ability of the interface layer.

[0293] Compared with Example 6, this example shows significant improvements in interface layer thickness, grafting degree, average trap depth, and deep trap density, indicating that increasing the amount of crosslinking agent does indeed help strengthen the structure and function of the interface layer.

[0294] As shown in Table 6, the dielectric loss factor of this embodiment under power frequency conditions is 2.60 × 10⁻⁶. -4 The increase compared to the blank control C1 was 15.0%;

[0295] The results indicate that at higher peroxide crosslinking agent dosages, the increase in dielectric loss of the material is close to the control limit, but still remains within the allowable range.

[0296] Meanwhile, the electrical tree initiation time of this embodiment reached 43.1 min, which is significantly higher than the 18.9 min of blank control C1 and the 28.7 min of Example 6. The maximum electrical tree length at 60 min was reduced to 121 μm, which is significantly better than blank control C1 and Example 6, and also slightly better than Example 1.

[0297] Based on Tables 3 to 5, it can be concluded that the improvement in electrical resistance of this embodiment mainly comes from the thicker, more reactive, and deeper trap structure of the interface confined reaction layer formed in situ near the surface of the interface.

[0298] However, at the same time, due to the increase in the amount of crosslinking agent, the increase in dielectric loss also approaches the boundary value, indicating that although this condition can achieve a strong interface strengthening effect, it has become quite tight in terms of overall dielectric loss control.

[0299] Further comparison of this embodiment with Embodiment 5 shows that both exhibit strong interface layer formation ability and good electrical tree effect, but their reinforcement paths are not exactly the same.

[0300] Example 5 mainly enhances the simultaneous improvement of interfacial layer reaction fixation, deep trap construction, and by-product regulation by increasing the amount of precursor added and optimizing degassing conditions;

[0301] This embodiment mainly enhances the intensity of interfacial free radical reaction by increasing the amount of crosslinking agent, thereby promoting the preferential fixation of precursors and the formation of deep traps in the interfacial region.

[0302] In comparison, although this embodiment also achieved a better effect in suppressing electrical treeing, its dielectric loss increase was closer to the upper limit, and the by-product residues in the interface and main body regions were relatively high.

[0303] This indicates that increasing the amount of crosslinking agent is an effective but carefully controlled method of enhancement.

[0304] In summary, this embodiment demonstrates that, under the technical route described in Example 1, even after increasing the amount of peroxide crosslinking agent added to 2.35 parts by mass, it is still possible to form an interface confined reaction layer in situ on at least one side of the surface layer when co-extruded with the semiconductive shielding layer and crosslinked to form the cable insulation layer. This interface confined reaction layer exhibits a higher degree of grafting or reaction conversion than the main region of the insulation layer, a deeper average trap depth than the main region of the insulation layer, and lower crosslinking by-product residues than the adjacent main region.

[0305] Meanwhile, the interface layer is formed more fully, and the electrical resistance is further improved. However, at the same time, the residual crosslinking byproducts and the increase in dielectric loss also increased, indicating that although a higher amount of crosslinking agent is beneficial to strengthening the structure and function of the interface layer, its application still needs to be balanced and controlled in conjunction with the overall dielectric properties.

[0306] Example 8

[0307] This embodiment is used to illustrate that in a real cable insulation structure, when the insulation layer is in contact with the inner semiconducting shielding layer and the outer semiconducting shielding layer respectively and simultaneously undergoes a three-layer co-extrusion and continuous vulcanization cross-linking process, the interface confined reaction layer can not only be formed on one side of the insulation layer, but also on the inner and outer surfaces of the insulation layer respectively.

[0308] This further illustrates that the interface-confined reaction layer formed by the technical solution of the present invention is not limited to a single interface, but can be established in situ at two real co-extrusion crosslinking interfaces. However, due to the differences in the thermal history, pressure state and interface mass transfer conditions of the inner and outer interfaces, the interface layer parameters of the two sides can be different.

[0309] Except for the differences described below, everything else is the same as in Example 1;

[0310] Unlike Example 1, this example not only samples and analyzes the surface layer on the side where the insulating layer contacts the inner semiconductive shielding layer, but also samples and analyzes the surface layer on the side where the insulating layer contacts the outer semiconductive shielding layer. The regions exceeding 300 μm from both interfaces are used as the main comparison areas. The reactive precursor used is still P-1, and the amount of precursor added, the amount of crosslinking agent, and other formulation components can be found in Table 1. The process conditions can be found in Table 2.

[0311] In this embodiment, the formation of the interface layer between the inner and outer surface layers is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the comprehensive electrical performance results are shown in Table 6.

[0312] As shown in Table 3, in this embodiment, a stable interface confined reaction layer is formed on both the inner and outer surfaces of the insulating layer. The thickness of the interface layer on the inner surface is 45.2 μm, and the thickness of the interface layer on the outer surface is 41.6 μm, both of which are in the range of 20 to 70 μm.

[0313] The results show that under the conditions of three-layer co-extrusion and continuous vulcanization crosslinking, as long as the surface of the insulating layer and the semiconductive shielding layer form a real contact interface, the reactive precursor P-1 can preferentially react near the interface and form an interface-confined reaction layer in situ on the surface.

[0314] Meanwhile, the inner surface layer is slightly thicker than the outer surface layer, indicating that although both sides of the interface layer can be formed in the same cable structure, their degree of formation will vary due to the influence of their respective interface conditions.

[0315] As shown in Table 4, the grafting degree or reaction conversion degree of the inner surface interface layer in this embodiment is 1.88%, and the grafting degree or reaction conversion degree of the outer surface interface layer is 1.73%. Both are significantly higher than those of the main region, and the residual amount of crosslinking by-products in the interface layer is lower than that of the main region.

[0316] The residual amount of by-products on the inner surface was 0.63 mg / g. - ¹, the outer surface layer is 0.68 mg·g - ¹, The main region is 1.35 mg·g - ¹;

[0317] These results indicate that P-1 can preferentially immobilize both the inner and outer surface layers at the interface, and can in-situ capture, adsorb, or immobilize the cross-linking byproducts enriched near the interface. This results in both surface layers exhibiting the common characteristic of "higher reaction degree and lower residual amount than the host region." On the other hand, the slightly higher grafting degree and slightly lower residual amount of the inner surface layer also indicate that the interface-confined reaction layer at the inner interface is formed more fully.

[0318] As shown in Table 5, the average trap depth of the inner surface interface layer in this embodiment is 0.93 eV, the average trap depth of the outer surface interface layer is 0.89 eV, and the average trap depth of the main body region is 0.51 eV.

[0319] At the same time, the density of deep traps in both the inner and outer surface layers is significantly higher than that in the main area;

[0320] This result indicates that the anthraquinone group in P-1 can not only construct deep trap structures in the inner interface region, but also form trap layers that are significantly deeper than those in the main body region in the outer interface region.

[0321] Both surfaces exhibited deep trap enhancement, further illustrating that the interface-confined reaction layer is not a localized phenomenon that occurs only occasionally on one side, but rather a recurring structural feature under the co-extrusion crosslinking interface. Meanwhile, the average trap depth and deep trap density of the inner surface layer were slightly higher than those of the outer surface layer, consistent with the differences in thickness and grafting degree reflected in Tables 3 and 4.

[0322] As shown in Table 6, the dielectric loss factor at 50Hz in this embodiment is 2.47 × 10⁻⁶. -4 The increase compared to the blank control C1 was 9.3%, which remained at a low level;

[0323] The electrical tree initiation time in this embodiment was 42.6 min, which was significantly longer than that of the blank control C1. The maximum electrical tree length at 60 min was 119 μm, which was significantly shorter than that of the blank control C1 and superior to that of Example 1.

[0324] This indicates that when interface-confined reactive layers are formed on both sides of the insulating layer, interface charge injection and local electric field distortion can be suppressed to a greater extent, thereby further improving the overall electrical tree resistance performance. Combining Tables 3-5, it can be concluded that the comprehensive effect achieved in this embodiment stems from the simultaneous establishment of functional interface layers with high reactivity, deep trap structures, and low byproduct residue on both the inner and outer surfaces, resulting in directional reinforcement of the insulating layer at both actual interfaces in contact with the semiconductive shielding layer.

[0325] Further combining Example 1 and this example, it can be seen that the formation of the interface confined reaction layer does not require that the insulating layer can only establish a functional layer on a single surface layer;

[0326] In actual cable structures, as long as both the inner and outer sides are co-extruded synchronously with the semiconductive shielding layer and undergo similar cross-linking environments, the precursor preferential reaction can occur on both surface layers and an interface layer can be formed in situ.

[0327] However, due to the different heat exchange conditions, stress states, and local by-product migration paths at the inner and outer interfaces, the thickness, grafting degree, trap depth, and by-product residues of the two surface layers can exhibit certain differences. This difference does not alter the essence of the technical solution of this invention; on the contrary, it precisely demonstrates that the interface-confined reaction layer is an in-situ formed structure closely related to the real interface environment.

[0328] In summary, this embodiment shows that, under the technical route described in Embodiment 1, when the insulating layer simultaneously forms a true co-extrusion cross-linking interface with the inner semiconductive shielding layer and the outer semiconductive shielding layer, the interface confined reaction layer can not only be formed on one side of the insulating layer, but also on the inner and outer surfaces of the insulating layer respectively.

[0329] Furthermore, both surface interface layers exhibit a higher degree of grafting or reaction conversion than the main region, a deeper average trap depth than the main region, and lower crosslinking byproduct residue than the main region, thereby enabling the insulation layer to be directionally strengthened at both interfaces and further improving its resistance to electrical treeing.

[0330] Example 9

[0331] This embodiment illustrates that, under the premise that the types of reactive precursors and the basic formulation system do not change substantially, by synergistically optimizing the crosslinking temperature, process pressure, amount of co-crosslinking agent, and degassing conditions, the formation quality of the interface confined reaction layer can be further improved, the reaction fixation degree of the interface region can be increased, the residue of crosslinking by-products can be further reduced, the deep trap structure can be constructed more fully, and better electrical resin resistance can be obtained under the condition that the growth of dielectric loss is still at a low level.

[0332] Unlike Example 5, which mainly strengthens the interface layer by increasing the amount of precursor added, this example mainly demonstrates the effect of process window optimization on improving the quality of the interface layer.

[0333] Except for the differences described below, everything else is the same as in Example 1;

[0334] Unlike Example 1, this example still uses P-1 as the reactive precursor, but its addition amount is adjusted to 0.68 parts by mass, the addition amount of peroxide crosslinking agent is adjusted to 1.90 parts by mass, the addition amount of co-crosslinking agent is adjusted to 0.20 parts by mass, and the crosslinking temperature, process pressure, linear velocity, degassing temperature and degassing time are optimized to the conditions shown in Table 1 and Table 2.

[0335] Except for the differences mentioned above, the composition of other raw materials and the process can be referred to in Example 1. The specific formulation of Example 9 is shown in Table 1, the process conditions are shown in Table 2, the interface layer formation is shown in Table 3, the grafting degree and by-product residue results are shown in Table 4, the trap parameters are shown in Table 5, and the electrical performance results are shown in Table 6.

[0336] As can be seen from Table 3, in this embodiment, a stable interface confinement reaction layer is formed on the surface of the side where the insulating layer and the semiconductive shielding layer are in contact. The thickness of the layer is 49.3 μm, which is obviously in the range of 20 to 70 μm and is slightly increased compared with Example 1.

[0337] The results show that, without significantly increasing the amount of precursor added, optimizing the crosslinking and degassing processes can also make the preferential reaction and local fixation near the interface more complete, thereby forming a more complete surface functional layer.

[0338] Compared with Example 6, the interface layer thickness in this example is significantly increased;

[0339] Compared with Example 7, although this example did not pursue a higher amount of crosslinking agent, it still achieved a relatively ideal interface layer thickness, indicating that process window optimization can improve the quality of interface layer formation without significantly increasing the system reaction load.

[0340] As shown in Table 4, the grafting degree or reaction conversion degree of the interface-confined reaction layer in this embodiment is 2.01%, while that of the main region is 0.77%, and the ratio of the interface layer to the main region is 2.61. This indicates that the reaction degree in the interface region is significantly higher than that in the main region, and the preferential reaction and local fixation of the precursor near the interface are still very significant. More importantly, the residual amount of crosslinking byproducts in the interface layer in this embodiment is only 0.51 mg·g. - ¹, lower than 0.61 mg·g in Example 1 - ¹, 0.74 mg·g in Example 7 - ¹¹ and 1.31 mg·g in the main region - ¹ indicates that under optimized crosslinking and degassing conditions, the hydroxyl and amide groups in P-1 can more fully exert their in-situ capture, adsorption, or fixation effects on interfacial enrichment byproducts, while the degassing process is also more conducive to reducing residual small molecules in the system.

[0341] This result shows that the advantage of this embodiment is not mainly reflected in simply increasing the interface grafting degree, but more in the further improvement of the interface area purification effect.

[0342] As shown in Table 5, the average depth of the traps in the interface confined reaction layer in this embodiment is 0.97 eV, and the average depth of the traps in the main body region is 0.51 eV. Both are within their respective target ranges, and the interface layer is significantly deeper than the main body region.

[0343] Meanwhile, the deep trap density of the interface layer in this embodiment reaches 8.5 × 10²¹m. - ³, higher than in Examples 1 and 7, and also significantly higher than in the main body area;

[0344] The results show that, under the optimized process window, the number of precursor structural units that are effectively fixed in the interface region and participate in the construction of deep traps is further increased, thereby enhancing the charge trapping capability of the interface layer.

[0345] Based on Tables 3 and 4, it can be concluded that the interface layer formed in this embodiment not only has a moderate thickness, but also has a high degree of reaction fixation, low by-product residue, and strong deep trap construction ability. Therefore, its interface regulation is more balanced and sufficient.

[0346] As shown in Table 6, the dielectric loss factor at 50Hz in this embodiment is 2.44 × 10⁻⁶. -4 The increase in dielectric loss was 8.0% compared to the blank control C1, which is close to that of Example 1 and significantly lower than that of Example 5 and Example 7. This indicates that while enhancing the interface layer structure and function, this embodiment did not bring significant additional dielectric loss burden.

[0347] Meanwhile, the electrical tree initiation time in this embodiment reached 44.8 min, which is significantly higher than that of Embodiment 1, Embodiment 6 and blank control C1;

[0348] The maximum length of the electrical tree over 60 minutes was 116 μm, which is smaller than 126 μm in Example 1 and 121 μm in Example 7.

[0349] The results show that this embodiment achieves a better electrical tree resistance effect than Embodiment 1 through process optimization, and is superior to Embodiments 5 and 7 in terms of overall dielectric loss control;

[0350] This shows that a better interface layer does not necessarily depend on the highest amount of precursor or the highest amount of crosslinking agent, but can be achieved by reasonably controlling the process window.

[0351] Further combining Examples 5 and 7, it can be seen that Example 5 mainly strengthens the interfacial layer by increasing the amount of precursor added, Example 7 mainly enhances the interfacial reaction driving force by increasing the amount of crosslinking agent added, while this example shows more of the synergistic effect of "appropriate formulation adjustment and process window optimization";

[0352] Compared with Example 5, the interface layer thickness and grafting degree of this example are slightly lower, but the interface by-product residue is lower and the increase in dielectric loss is smaller.

[0353] Compared with Example 7, this example is not inferior in terms of deep trap density and electrical tree resistance, and has better control over by-product residue and dielectric loss.

[0354] This demonstrates that the combination of process parameters used in this embodiment can achieve a good balance between interface layer formation, deep trap construction, by-product control, and overall dielectric properties.

[0355] In summary, this embodiment demonstrates that, under the technical route described in Embodiment 1, by synergistically optimizing the amount of precursor added, the amount of crosslinking agent added, the amount of co-crosslinking agent used, and the crosslinking and degassing processes, a higher quality interface confined reaction layer can be formed in situ on at least one side of the surface when the cable insulation layer is co-extruded with the semiconductive shielding layer and crosslinked to form the cable insulation layer. This interface confined reaction layer exhibits a higher grafting degree or reaction conversion degree, a deeper average trap depth, a higher deep trap density, and lower crosslinking by-product residue, thereby further improving the electrical tree resistance performance under the condition that the dielectric loss growth is still at a low level.

[0356] The results indicate that the formation and overall effect of the interface-confined reaction layer are not only related to the formulation composition, but also closely related to the crosslinking and degassing process windows.

[0357] Example 10

[0358] This embodiment is used to illustrate that, under the formulation system and process conditions described in Example 1, after continuously preparing multiple batches of samples, each batch of samples can still form an interface confined reaction layer of similar thickness and obtain similar trap parameters, grafting degree and electrical resistance.

[0359] Specifically, under the same raw material composition, the same three-layer co-extrusion continuous vulcanization process, and the same degassing conditions, after preparing multiple batches of samples, an interface-confined reaction layer can still be stably formed in situ on the surface of the side where the insulating layer and the semi-conductive shielding layer contact. This maintains the common characteristics of a higher degree of reaction in the interface layer than in the main region, deeper interface layer traps than in the main region, lower residue of interface layer by-products than in the main region, and significantly better resistance to electrical resin formation than the blank system. This demonstrates that the proposed technical solution has good process repeatability and application stability.

[0360] Except for the differences described below, everything else is the same as in Example 1;

[0361] Unlike Example 1, this example does not only prepare a single sample, but prepares three batches of samples continuously under the same formulation and process conditions, and takes the average value of the three batches of samples as the result of this example.

[0362] The reactive precursor used is still P-1. The amount of precursor added, the amount of peroxidation crosslinking agent added, the amount of co-crosslinking agent and the amount of antioxidant are the same as in Example 1, as shown in Table 1.

[0363] The process conditions are the same as in Example 1, as detailed in Table 2;

[0364] The average interface layer formation obtained from the tests of the three batches of samples is shown in Table 3, the average grafting degree and by-product residue results are shown in Table 4, the average trap parameters are shown in Table 5, and the average electrical performance results are shown in Table 6.

[0365] As shown in Table 3, in the three batches of samples prepared in succession, a stable interface confined reaction layer was formed on the surface of the side where the insulating layer and the semiconductive shielding layer are in contact. The average thickness of the layer was 47.1 μm, which is very close to 46.8 μm in Example 1, and it was stable in the range of 20 to 70 μm.

[0366] The results show that, under repeated preparation conditions, all three batches of samples formed an interface confined reaction layer of similar thickness, indicating that the interface layer has good repeatability under the same formulation and process conditions.

[0367] As shown in Table 4, the average grafting degree or reaction conversion degree of the three batches of samples in this embodiment was 1.95%, the average value of the main region was 0.74%, and the average ratio of the interface layer to the main region was 2.64; meanwhile, the average residual amount of by-products in the interface layer was 0.60 mg·g. - ¹, significantly lower than the 1.36 mg / g in the main region. - ¹;

[0368] This result is consistent with the pattern in Example 1 that "the degree of reaction in the interface layer is higher than that in the main body region, and the residue of by-products in the interface layer is lower than that in the main body region". This indicates that during repeated preparation, the preferential reaction and local fixation of P-1 in the interface region, as well as its in-situ capture, adsorption or fixation of interface enrichment by-products, can be stably reproduced.

[0369] The core features of the interface layer were not damaged by batch variations in this embodiment, indicating that the technical solution is not only valid in a single laboratory sample, but also has stability under continuous preparation.

[0370] As shown in Table 5, the average depth of the interface layer traps in the three batches of samples in this embodiment was 0.95 eV, the average depth of the traps in the main body region was 0.51 eV, and the average density of deep traps in the interface layer was 7.9 × 10²¹ m. - ³, the average value of the main area is 1.9 × 10²¹m - ³, the multiple relationship between the two remains at a high level;

[0371] The results are similar to those of Example 1, indicating that all three batches of samples were able to stably establish trap structures significantly deeper than those in the host region in the interface region, and the density of deep traps remained significantly higher than that in the host region. This suggests that the construction of deep traps in the interface region is not a random, one-off result, but is closely related to the preferential reaction and local fixation of the reactive precursor P-1 near the actual co-extrusion crosslinking interface, and can be stably achieved in repeated preparations.

[0372] As shown in Table 6, the average dielectric loss factor at 50Hz for the three batches of samples in this embodiment is 2.45 × 10⁻⁶. -4 The average increase compared to the blank control C1 was 8.4%, which is at a low level; the average electrical tree initiation time was 41.3 min, which was significantly higher than the 18.9 min of the blank control C1.

[0373] The average maximum length of the electrical tree at 60 min was 128 μm, which was significantly lower than the 318 μm of the blank control C1.

[0374] The results show that, under repeated preparation conditions, this embodiment can still stably obtain a longer tree initiation time and a shorter tree extension length, while keeping the increase in dielectric loss under control.

[0375] Compared with Example 1, the average indicators of this example show only slight differences, further demonstrating that the technical solution of the present invention can maintain a similar overall performance level in multiple batches of continuous preparation.

[0376] Further analysis of Tables 3 to 6 shows that the average results of the three batches of samples in this embodiment are highly consistent with those of Example 1, exhibiting the following characteristics:

[0377] An interface confinement reaction layer of a certain thickness can be stably formed on the surface of the insulating layer;

[0378] The reactivity of this interface layer is higher than that of the main region; the average trap depth and deep trap density of this interface layer are higher than those of the main region; and the byproduct residue in this interface layer is lower than that in the main region.

[0379] Meanwhile, the overall dielectric loss growth remained at a low level, accompanied by a significant improvement in electrical tree resistance.

[0380] The above results were consistently observed in three batches of replicate samples, indicating that the technical solution has good batch reproducibility and process stability, and does not depend on a single accidental processing state or random fluctuations of individual samples.

[0381] In summary, this embodiment demonstrates that, under the formulation and process conditions described in Example 1, after continuously preparing multiple batches of samples, an interface confined reaction layer can still be stably formed in situ on the surface of the insulating layer in contact with the semiconductive shielding layer. It also maintains the common characteristics of the interface layer reaction degree being higher than that of the main region, the interface layer traps being deeper than those of the main region, and the interface layer by-product residues being lower than those of the main region. At the same time, it stably obtains a significant improvement in electrical resistance under the premise that the increase in dielectric loss is at a low level.

[0382] The results demonstrate that the technical solution of the present invention not only has a clear structural basis and performance advantages, but also has good repeatability and stability.

[0383] It should be noted that, as can be seen from Examples 1 to 10, under the formulation and process window provided by the present invention, an interface confined reaction layer with a thickness of 20 to 70 μm can be formed in situ on the surface layer where the insulating layer and the semiconductive shielding layer are in contact.

[0384] The deep trap density of this interface layer can reach 2.0 to 5.0 times that of the main region, and the grafting degree can reach 1.5 to 3.0 times that of the main region. Moreover, the increase in the dielectric loss factor of the material under 50Hz power frequency conditions relative to the blank system does not exceed 15%.

[0385] Examples 4 and 6 show that a low amount of precursor or crosslinking agent will weaken the interface regulation effect.

[0386] Examples 5 and 7 show that increasing the amount of precursor or crosslinking agent can enhance the formation of the interface layer and the electrical resistance effect, but the increase in dielectric loss should be balanced.

[0387] Example 8 shows that, in actual cable structures, the interface confined reaction layer can be formed on both the inner and outer surfaces of the insulation layer;

[0388] Example 9 shows that by synergistically optimizing the formulation and process window, the quality of the interface layer formation can be further improved and better overall performance can be obtained.

[0389] Example 10 shows that the technical solution of the present invention has good batch reproducibility and preparation stability.

[0390] Tables 1-6 are as follows:

[0391] Table 1: Formulation composition of Examples 1-10 and Comparative Examples C1-C5

[0392] Example 1 100 P-1 P-1 is an anthraquinone reactive precursor containing methacryloyl, anthraquinone, hydroxyl, and amide groups; used for reaction immobilization, deep trap construction, and byproduct control; its structure or source must be confirmed before use, and its purity must be not less than 95%. 0.72 1.85 0.18 0.22 Example 2 100 P-3 P-3 is a reactive benzophenone precursor containing vinyl, benzophenone, hydroxyl, and imide groups; used to verify the suitability of reactive groups and polar conjugated structural units after substitution; its structure or source must be confirmed before use, and its purity must be not less than 95%. 0.75 1.85 0.18 0.22 Example 3 100 P-4 P-4 is a reactive imide precursor containing maleimide, aromatic imide, epoxy, and carboxyl groups; it is used to verify the applicability of different combinations of reactive groups, polar conjugated structural units, and byproduct-regulating functional groups; its structure or source must be confirmed before use, and its purity must be not less than 95%. 0.78 1.85 0.18 0.22 Example 4 100 P-1 Same as P-1 in Example 1 0.12 1.85 0.18 0.22 Example 5 100 P-1 Same as P-1 in Example 1 1.85 1.85 0.18 0.22 Example 6 100 P-1 Same as P-1 in Example 1 0.72 0.55 0.18 0.22 Example 7 100 P-1 Same as P-1 in Example 1 0.72 2.35 0.18 0.22 Example 8 100 P-1 Same as P-1 in Example 1 0.72 1.85 0.18 0.22 Example 9 100 P-1 Same as P-1 in Example 1 0.68 1.9 0.2 0.22 Example 10 100 P-1 Same as P-1 in Example 1 0.72 1.85 0.18 0.22 Comparative Example C1 100 none Without the addition of reactive precursors, it is used as a blank cross-linked polyethylene insulation system. 0 1.85 0.18 0.22 Comparative Example C2 100 A-1 A-1 is a non-reactive deep-trap small molecule containing anthraquinone structures but lacking reactive groups that can participate in free radical grafting or cross-linking reactions; it is used to illustrate the effect of having only a deep-trap structure but not being able to react and fix the molecules. 0.7 1.85 0.18 0.22 Comparative Example C3 100 P-2 P-2 is an anthraquinone reactive precursor containing methacryloyl and anthraquinone groups but lacking hydroxyl and amide groups; it is used to compare the effects of functional group deficiency during byproduct immobilization. 0.71 1.85 0.18 0.22 Comparative Example C4 100 P-1 Same as P-1 in Example 1 0.72 1.85 0.18 0.22 Comparative Example C5 100 B-1 B-1 refers to reactive compounds containing reactive groups that can participate in free radical grafting or cross-linking reactions but lacking polar conjugated structural units; it is used to illustrate the difference when there are only reactive fixation units but no deep trap units. 0.72 1.85 0.18 0.22

[0393] Table 2: Process conditions for Examples 1-10 and Comparative Examples C1-C5

[0394] Example 1 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area Example 2 Three-layer co-extrusion Continuous vulcanization 329 1.06 5.1 75 120 Inner surface layer + main body area Example 3 Three-layer co-extrusion Continuous vulcanization 328 1.07 5 75 120 Inner surface layer + main body area Example 4 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area Example 5 Three-layer co-extrusion Continuous vulcanization 327 1.08 4.9 80 144 Inner surface layer + main body area Example 6 Three-layer co-extrusion Continuous vulcanization 324 1.03 5.5 75 120 Inner surface layer + main body area Example 7 Three-layer co-extrusion Continuous vulcanization 331 1.1 4.8 75 132 Inner surface layer + main body area Example 8 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.1 75 120 Inner surface layer + outer surface layer + main body area Example 9 Three-layer co-extrusion Continuous vulcanization 327 1.08 4.9 80 144 Inner surface layer + main body area Example 10 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Average of three batches Comparative Example C1 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area Comparative Example C2 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area Comparative Example C3 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area Comparative Example C4 Non-co-extrusion post-composite Post-treatment of hot-pressed composite 180 12 — 75 120 Near the composite interface + main area Comparative Example C5 Three-layer co-extrusion Continuous vulcanization 328 1.06 5.2 75 120 Inner surface layer + main body area

[0395] Table 3: Interface layer formation and thickness in Examples 1-10 and Comparative Examples C1-C5

[0396] Example 1 yes inner surface layer 46.8 yes Main Implementation Example 2 yes inner surface layer 43.5 yes The structure still forms after replacement Example 3 yes inner surface layer 44.1 yes The structure still forms after replacement Example 4 yes inner surface layer 23.6 yes It can still form even at low addition levels Example 5 yes inner surface layer 57.4 yes Medium to high addition levels enhance formation Example 6 yes inner surface layer 26.9 yes Weak formation under low crosslinking agent conditions Example 7 yes inner surface layer 61.3 yes Still within the range under high crosslinking agent Example 8 yes inner surface layer 45.2 yes One of the two sides Example 8 yes outer surface layer 41.6 yes One of the two sides Example 9 yes inner surface layer 49.3 yes More comprehensive optimization of processes Example 10 yes inner surface layer 47.1 yes Average of three batches Comparative Example C1 no — — no No stable layer formed Comparative Example C2 Unstable inner surface layer 18.6 no Insufficient thickness Comparative Example C3 yes inner surface layer 41.2 yes However, it lacks comprehensive functionality. Comparative Example C4 weak Near the composite interface 9.7 no Non-co-extrusion leads to insufficient interface layer Comparative Example C5 yes inner surface layer 39.5 yes However, the trap is not deep enough.

[0397] Table 4: Grafting degree / reaction conversion degree and by-product residue of Examples 1-10 and Comparative Examples C1-C5

[0398] Example 1 1.92 0.73 2.63 0.61 1.37 yes Example 2 1.86 0.74 2.51 0.66 1.34 yes Example 3 1.81 0.72 2.51 0.69 1.36 yes Example 4 0.94 0.51 1.84 0.88 1.29 yes Example 5 2.18 0.81 2.69 0.53 1.42 yes Example 6 1.02 0.62 1.65 0.97 1.18 yes Example 7 2.06 0.79 2.61 0.74 1.57 yes Example 8 (inner side) 1.88 0.72 2.61 0.63 1.35 yes Example 8 (Outer Side) 1.73 0.7 2.47 0.68 1.33 yes Example 9 2.01 0.77 2.61 0.51 1.31 yes Example 10 1.95 0.74 2.64 0.6 1.36 yes Comparative Example C1 — — — 1.29 1.31 Not applicable; a stable interface-confined reaction layer has not been formed. Comparative Example C2 0.34 0.22 1.55 1.11 1.26 Yes, but the extent is limited. Comparative Example C3 1.69 0.69 2.45 1.03 1.34 Yes, but the residue level is still relatively high. Comparative Example C4 0.49 0.45 1.09 1.08 1.15 Yes, but the difference is very small. Comparative Example C5 1.74 0.71 2.45 0.95 1.3 yes

[0399] Table 5: Trap Parameter Table of Examples 1-10 and Comparative Examples C1-C5

[0400] Example 1 0.94 0.51 yes 7.8 1.9 4.11 Example 2 0.91 0.5 yes 7.1 1.8 3.94 Example 3 0.92 0.52 yes 7.3 1.9 3.84 Example 4 0.86 0.5 yes 3.8 1.8 2.11 Example 5 0.99 0.52 yes 8.9 2.1 4.24 Example 6 0.87 0.49 yes 4.2 2 2.1 Example 7 1.02 0.53 yes 8.3 2 4.15 Example 8 (inner side) 0.93 0.51 yes 7.5 1.9 3.95 Example 8 (Outer Side) 0.89 0.5 yes 6.8 1.8 3.78 Example 9 0.97 0.51 yes 8.5 2 4.25 Example 10 0.95 0.51 yes 7.9 1.9 4.16 Comparative Example C1 0.56 0.49 no 2.1 1.8 1.17 Comparative Example C2 0.73 0.5 no 3.2 1.8 1.78 Comparative Example C3 0.89 0.52 yes 6.2 1.9 3.26 Comparative Example C4 0.67 0.5 no 2.8 1.8 1.56 Comparative Example C5 0.63 0.5 no 3 1.8 1.67

[0401] Table 6: Electrical properties and electrical resistance results of Examples 1-10 and Comparative Examples C1-C5

[0402] Example 1 2.46 8.8 yes 41.7 126 Main Implementation Example 2 2.43 7.5 yes 39.8 133 Retain after structural replacement Example 3 2.48 9.7 yes 38.6 139 Retain after structural replacement Example 4 2.31 2.2 yes 30.4 191 Low dosage reduces effectiveness Example 5 2.57 13.7 yes 46.2 112 Medium to high addition levels result in better effects. Example 6 2.33 3.1 yes 28.7 204 Low cross-linking agent content reduces effectiveness Example 7 2.6 15 yes 43.1 121 High crosslinking agent, close to the upper limit Example 8 (Internal and External Integration) 2.47 9.3 yes 42.6 119 Dual-sided interface layer Example 9 2.44 8 yes 44.8 116 Preferred process window Example 10 2.45 8.4 yes 41.3 128 Average of three batches Comparative Example C1 2.26 0 — 18.9 318 blank Comparative Example C2 2.71 19.9 no 24.6 241 Non-reactive deep trap system Comparative Example C3 2.54 12.4 yes 33.8 168 Lack of byproduct immobilization functional groups Comparative Example C4 2.49 10.2 yes 27.1 214 Non-co-extrusion post-composite Comparative Example C5 2.39 5.8 yes 29.4 205 No-deep-trap unit

[0403] 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 it. 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 spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A cross-linked polyethylene insulation material with electrical resistance for medium and high voltage cables, characterized in that, The insulating material is formed by crosslinking an insulating composition comprising a polyethylene resin, a reactive precursor and a peroxidation crosslinking agent, and includes an insulating layer body region and an interface-confined reactive layer located on at least one side of the surface. Wherein, the at least one side surface layer is the side surface layer that is in contact with the semiconductive shielding layer when the insulating material is co-extruded with the semiconductive shielding layer and cross-linked to form the cable insulation layer; The reactive precursor is P-1, and its structural formula is shown in the figure below. The thickness of the interface confined reaction layer extending from the surface layer on one side into the interior of the insulating material is 20–70 μm. Using the thermally stimulated depolarization current method, the average trap depth of the interface confined reaction layer was measured to be 0.85–1.10 eV, and the average trap depth of the main region of the insulating layer was 0.44–0.58 eV. The main region of the insulating layer is the portion of insulating material that extends beyond the thickness range of the interface-limited reaction layer; The grafting degree or reaction conversion degree of the reactive precursor in the interface confined reaction layer is higher than that in the main region of the insulating layer. The interface confined reaction layer is not formed by an independent nonlinear insulating interlayer or a prefabricated dielectric layer pre-set inside the insulating material.

2. The cross-linked polyethylene insulation material for medium and high voltage cables as described in claim 1, characterized in that, Based on 100 parts by weight of polyvinyl resin, the amount of the reactive precursor added is 0.1 to 2 parts by weight, and the amount of the peroxidation crosslinking agent added is 0.5 to 2.5 parts by weight.

3. The cross-linked polyethylene insulation material for medium and high voltage cables as described in claim 2, characterized in that, The interface confined reaction layer is a reaction layer formed in situ on at least one side of the surface after co-extrusion and cross-linking of the insulating material composition and the semiconductive shielding layer, and the residual amount of cross-linking by-products in the interface confined reaction layer is lower than that in the main area of ​​the adjacent insulating layer.

4. The cross-linked polyethylene insulating material with electrical resistance as described in claim 3, characterized in that, The deep trap density in the interface-confined reaction layer is 2 to 5 times that of the deep trap density in the main region of the insulating layer, and / or the grafting degree of the reactive precursor in the interface-confined reaction layer is 1.5 to 3 times that of the grafting degree in the main region of the insulating layer.

5. The cross-linked polyethylene insulating material resistant to electrical resin as described in claim 4, characterized in that, Under 50Hz power frequency conditions, compared with cross-linked polyethylene insulation materials that do not contain the aforementioned reactive precursor and have the same composition and preparation process, the dielectric loss factor of the insulation material increases by no more than 15%.

6. A method for forming a medium- and high-voltage cable insulation layer using an electrical-resistant cross-linked polyethylene insulating material according to any one of claims 1-5, characterized in that, include: S1, a polyvinyl resin, a reactive precursor, a peroxidation crosslinking agent, and optionally an antioxidant and a co-crosslinking agent are mixed to obtain an insulating material composition; S2, the insulating material composition is extruded and co-extruded with the semi-conductive shielding layer to obtain the co-extruded structure; S3, the co-extruded structure is subjected to peroxidation crosslinking treatment, so that the reactive precursor preferentially undergoes grafting, coupling or crosslinking reaction near the interface of the semiconductive shielding layer / insulation layer, thereby forming an interface confined reaction layer on at least one side of the surface of the insulating material. S4, degassing treatment is performed to obtain a medium- and high-voltage cable insulation layer with an interface confined reaction layer.

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