Compression-resistant insulating power cable material, preparation method and power cable

Abstract

The invention relates to the technical field of power cable insulating materials, and discloses a compression-resistant insulating power cable material, a preparation method and a power cable, the insulating material comprises the following raw materials: low density polyethylene, ethylene propylene diene monomer, N, N '-m-phenylenedimaleimide, 2-mercaptobenzimidazole, zinc stearate, zinc methacrylate and dicumyl peroxide. In the preparation process, N, N '-m-phenylenedimaleimide and 2-sulfydryl benzimidazole are subjected to an in-situ addition reaction to generate a macromolecular crosslinking precursor, and free sulfydryl masking is realized. The precursor and zinc methacrylate are subjected to coordination to form polar nodes, and a homogeneous cross-linked network containing electron deep traps and dynamic sacrificial bonds is constructed after cross-linking and curing. Under the condition that no inorganic filler is added, irreversible slippage and space charge accumulation of macromolecular chain segments in an insulator are effectively inhibited, so that the cable material has high compression resistance, low creep deformation, high electrical strength and long-acting thermo-oxidative aging resistance.

Description

Technical Field

[0001] This invention relates to the field of power cable insulation materials, specifically to a pressure-resistant insulating power cable material, its preparation method, and the power cable itself. Background Technology

[0002] Cross-linked polyethylene (XLPE) is widely used in the insulation layer of power cables due to its excellent electrical insulation and processing properties. With the continuous increase in power grid transmission capacity, the heat generated in the cable core during operation increases, placing higher demands on the mechanical load-bearing capacity and creep resistance of insulation materials in high-temperature environments.

[0003] To improve the compressive strength of cross-linked polyethylene (XLPE) insulation materials, traditional processes typically add inorganic rigid particles as fillers to the polymer matrix. However, there is a significant difference in the coefficient of thermal expansion between these inorganic particles and the non-polar polymer matrix. During the cooling phase after cable cross-linking, microscopic interfacial air gaps easily form within the material. These air gaps become centers for space charge accumulation and induce partial discharge, thereby reducing the breakdown field strength of the insulation layer. When the cable is under high-temperature, heavy-load conditions, microscopic disadhesion easily occurs between the inorganic particles and the matrix resin, causing the filler to lose its stress-transfer capacity, ultimately leading to creep deformation and mechanical failure of the insulation material.

[0004] In long-term, high-temperature operating environments, insulating materials also need to possess stable resistance to thermo-oxidative aging. Existing modification methods often employ direct blending of small-molecule antioxidants to delay material aging. However, traditional small-molecule antioxidants are prone to volatilization during high-temperature crosslinking and long-term service, or they may become free in the amorphous regions of the polymer and gradually migrate and precipitate to the material surface, leading to a decrease in the long-term thermo-oxidative stability of the insulation layer. While some antioxidants containing active groups such as thiol groups have high free radical scavenging efficiency, during the high-temperature crosslinking stage of the insulation material, these active protons can react with primary free radicals generated by the decomposition of peroxide initiators, resulting in chain termination reactions. This indiscriminate consumption disrupts the normal coupling process between polymer macromolecular chains, leading to a decrease in the degree of crosslinking and making it difficult to simultaneously meet the requirements of high-temperature mechanical properties and processing crosslinking stability for cable materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a pressure-resistant insulated power cable material, its preparation method, and a power cable. This invention solves the problems that existing power cable insulation materials, when improving their high-temperature pressure resistance, are prone to interface defects caused by the addition of inorganic fillers, leading to a decrease in electrical strength and creep resistance. At the same time, small molecule antioxidants are prone to migrate and precipitate, interfering with the material's cross-linking and curing process.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a pressure-resistant insulating power cable material, made from raw materials comprising the following parts by weight: 70-90 parts of low-density polyethylene; 10-30 parts of ethylene propylene diene monomer (EPDM) rubber; 1.0-2.5 parts of N,N'-m-phenylenebismaleimide; 0.5-1.5 parts of 2-mercaptobenzimidazole; 0.5-1.5 parts of zinc stearate; 2.0-5.0 parts of zinc methacrylate; and 1.0-2.0 parts of dicumyl peroxide.

[0007] By adopting the above technical solution, the present invention constructs multi-dimensional structural nodes within the homogeneous cross-linked network of polymers through in-situ chemical reactions between formulation components, thereby achieving a comprehensive effect of high-temperature pressure resistance, inhibition of electric field degradation, and anti-oxidation.

[0008] In-situ masking reaction and anchoring of macromolecular antioxidant structure. During the compounding process of the insulating material, the maleimide groups at both ends of N,N'-m-phenylenebismaleimide contain electron-deficient double bonds, while 2-mercaptobenzimidazole contains electron-rich, active thiol functional groups. Under heating and mechanical shearing, the thiol groups undergo a Michael addition reaction with the maleimide double bonds. This addition reaction covalently bonds the benzimidazole ring, which has free radical scavenging activity, to the rigid molecular backbone of m-phenylenebismaleimide, forming a macromolecular antioxidant structural unit in situ. This process avoids the migration and volatilization loss of free small-molecule antioxidants during subsequent high-temperature processing and long-term operation, achieving long-term resistance to thermo-oxidative aging of the insulating medium.

[0009] Construction of a dual crosslinking network and generation of coordination nodes. During the crosslinking and curing stage, dicumyl peroxide decomposes upon heating to generate primary free radicals, which abstract hydrogen atoms from the macromolecular chains of low-density polyethylene and EPDM rubber to form carbon free radicals. At this time, zinc methacrylate undergoes in-situ polymerization within the system and grafts onto the polymer backbone, aggregating into ionic clusters containing zinc ions. Simultaneously, the incompletely reacted residual double bonds at the ends of the macromolecular structural units generated in step one also participate in the free radical crosslinking reaction. Ultimately, a dual crosslinking network composed of carbon-carbon covalent bonds and zinc ion coordination bonds is formed within the matrix. The introduction of ionic coordination bonds increases the slip resistance of polymer molecular chain segments, significantly improving the compressive modulus and creep resistance of the insulation material under high-temperature conditions.

[0010] The aforementioned stages generate specific polar groups in situ within the polymer matrix. The rigid benzene ring structure provided by m-phenylenebismaleimide, the nitrogen-containing heterocyclic structure introduced by 2-mercaptobenzimidazole, and the ionic clusters formed by the polymerization of zinc methacrylate constitute a high-density electron deep trap distribution region within the all-organic homogeneous cross-linked network. When the cable is in a high-voltage electric field environment, the physical and chemical deep traps can effectively capture high-energy initiation electrons injected from the electrodes, reduce the macroscopic mobility of charge carriers, block the acceleration process of electrons under the action of the electric field, inhibit the accumulation of space charge inside the insulation layer, reduce the degree of local electric field distortion, thereby improving the dielectric strength and breakdown life of the cable material.

[0011] Preferably, the reference density of low-density polyethylene at 20°C is 0.922 g / cm³. 3 The melt flow rate at 190℃ and 2.16kg standard load is 2.0g / 10min.

[0012] By adopting the above technical solution, the low-density polyethylene within this parameter range provides suitable initial crystallinity and melt viscosity, ensuring its two-phase compatibility with EPDM rubber during the mixing process, and maintaining the material dimensional stability and extrusion surface smoothness during the extrusion process.

[0013] Preferably, the ethylene structural unit in the main chain of the EPDM rubber has a mass fraction of 70%, the third monomer 5-ethylidene-2-norbornene structural unit has a mass fraction of 4.5%, and its Mooney viscosity ML(1+4) at 125°C is 65.

[0014] By adopting the above technical solution, macroscopic phase separation is less likely to occur when ethylene-containing EPDM rubber is blended with low-density polyethylene matrix; the 5-ethylidene-2-norbornene structural unit provides easy-to-graft double bond crosslinking sites for free radical reactions, improving the overall system's curing and crosslinking efficiency; the specific Mooney viscosity keeps the shear heat generation of the system within a reasonable range during the mixing process, which is beneficial to the dispersion of powder additives and the in-situ addition reaction in step one.

[0015] Preferably, N,N'-m-phenylenebismaleimide has a melting point range of 198°C to 201°C and a purity greater than 98.0%; dicumyl peroxide has an active oxygen mass fraction greater than 5.8% and a half-life of 10 hours at 115°C; and 2-mercaptobenzimidazole has a weight loss upon heating of less than 0.3%.

[0016] By adopting the above technical solutions, high-purity N,N'-m-phenylenebismaleimide with a specific melting point ensures the stable existence of the rigid bridging framework in the matrix; dicumyl peroxide with a defined half-life matches the temperature window of the crosslinking extrusion process, avoiding early scorching and pre-crosslinking of the material in the extruder barrel; and 2-mercaptobenzimidazole with low heating loss ensures that the effective components are not lost under the heated environment of the mixing process, ensuring the conversion rate of the in-situ addition masking reaction.

[0017] By adopting the above technical solution, this invention employs a segmented temperature control and multi-stage feeding mixing process to precisely control the physical dispersion and chemical reaction process of various additives at different processing stages. The specific working principle and steps are as follows: In step S1, under the combined action of high shear force and thermal field in the internal mixer, low-density polyethylene and EPDM rubber undergo melt blending to form a homogeneous polymer matrix. Simultaneously, N,N'-m-phenylenebismaleimide and 2-mercaptobenzimidazole undergo a Michael addition reaction in a constant-temperature, high-shear environment. This process pre-anchors antioxidant molecules to the maleimide backbone, forming a macromolecular precursor. Zinc stearate acts as a lubricant, improving the dispersion of the powder in the melt. Controlling the discharge temperature and the constant-temperature mixing process in this stage provides the activation energy required for the reaction, ensuring the conversion rate of the in-situ addition masking reaction.

[0018] In step S2, zinc methacrylate is added without shutting down the machine, and the melt temperature is appropriately lowered. This step prevents zinc methacrylate from self-polymerizing at excessively high temperatures, while utilizing the established polymer melt flow field to uniformly disperse it into the matrix. At this stage, zinc methacrylate molecules blend with the macromolecular precursor, laying a physical dispersion foundation for the subsequent construction of uniform ion coordination cluster nodes within the matrix.

[0019] In step S3, the rotor speed is reduced to lower the melt temperature below the initiation temperature of dicumyl peroxide, followed by the addition of dicumyl peroxide for low-shear mixing. This temperature reduction treatment effectively prevents premature decomposition of the peroxide within the mixing chamber, thus preventing scorching of the insulating material. The low shear force ensures a macroscopically uniform distribution of the crosslinking agent in the melt without disrupting the already formed polymer aggregate structure.

[0020] In step S4, the uniformly mixed material is extruded and pelletized by a single screw within a safe temperature range to obtain crosslinkable insulation material particles with smooth surfaces and uniform crosslinking agent distribution, providing structurally uniform raw materials for subsequent cable extrusion processes.

[0021] Preferably, in step S1, the internal mixer rotor speed is set to 50 to 70 r / min, and the circulating cooling water system with a set water temperature of 20 to 30°C is turned on to control the material discharge temperature.

[0022] By employing the above technical solution, a specific rotor speed provides the mechanical shear force required for polymer chain breakage and additive dispersion. Combined with a circulating cooling water system at a set temperature, excess frictional heat generated by strong shear can be promptly dissipated, achieving a dynamic balance between heat gain and loss within the mixing chamber. This control prevents thermal degradation of the polymer matrix caused by localized hot spots.

[0023] Preferably, in step S1, the high-shear constant-temperature mixing time is 5 to 8 minutes, and the discharge temperature is 125 to 135°C.

[0024] By employing the above technical solution, a temperature range of 125 to 135°C exceeds the melting point of low-density polyethylene and satisfies the thermodynamic conditions for the Michael addition reaction. The isothermal mixing time of 5 to 8 minutes provides sufficient kinetic reaction time for the in-situ masking reaction of N,N'-m-phenylenebismaleimide and 2-mercaptobenzimidazole, ensuring that the reaction system proceeds in the positive direction towards the formation of a large molecular antioxidant structure.

[0025] Preferably, in step S2, the mixing time after adding zinc methacrylate is 3 to 5 minutes, and the temperature is reduced to and maintained at 115 to 125°C.

[0026] By employing the above technical solution, the temperature is reduced to the range of 115 to 125°C, preserving the good melt flowability of the polymer matrix while suppressing the early thermal polymerization of double bonds in zinc methacrylate. Continuous mixing for 3 to 5 minutes enables the zinc-containing monomers to achieve molecular-level dispersion between polymer segments, avoiding macroscopic aggregation defects of ionic aggregates.

[0027] Preferably, in step S3, the low-shear mixing time is 2 to 3 minutes, and the material temperature is reduced to 90 to 110°C.

[0028] By adopting the above technical solution, 90 to 110°C is within the safe processing temperature range of dicumyl peroxide. By reducing the speed of the internal mixer to reduce internal frictional heat generation, the temperature is controlled within this range, and mixing is carried out for 2 to 3 minutes, allowing the crosslinking agent to be uniformly dissolved in the matrix, eliminating local concentration gradients, and completely eliminating the risk of early pre-crosslinking of the insulation material from the process end.

[0029] A power cable includes a metal conductor and an inner semiconductive shielding layer, an insulation layer, an outer semiconductive shielding layer, and an outer sheath sequentially covering the metal conductor. The insulation layer is formed by extruding the aforementioned pressure-resistant insulated power cable material and then in-situ grafting and vulcanization cross-linking curing in a high-temperature and high-pressure nitrogen environment.

[0030] By adopting the above technical solution, the cable undergoes the final curing and molding stage in the high-temperature, high-pressure nitrogen vulcanization pipe of the production line. Dicumyl peroxide in the insulation material rapidly decomposes at a high temperature of 180 to 200°C, generating free radicals that initiate three-dimensional cross-linking and in-situ polymerization of the low-density polyethylene main chain, the double bonds on the side groups of EPDM rubber, and zinc methacrylate. The cured insulation layer forms a deep trap network structure interwoven with macromolecular antioxidant networks and zinc ion coordination aggregates. This dense cross-linking morphology and trap energy level distribution endow the cable insulation layer with excellent resistance to compressive creep and the ability to suppress space charge injection, significantly extending the insulation life of power cables under high-temperature and high-field-strength operating conditions.

[0031] This invention provides a pressure-resistant insulated power cable material, a preparation method, and a power cable. It has the following beneficial effects: 1. This invention improves the high-temperature compressive strength and creep resistance of cable materials through the meta-benzene ring structure of N,N'-m-phenylenebismaleimide and the dynamic sacrificial bond formed by its coordination with zinc methacrylate. When the insulating material experiences internal stress concentration under high-temperature and heavy-load conditions, the secondary coordination bonds in the material can dissociate before the polymer covalent backbone. The mechanical strain energy is converted into heat energy dissipation through conformational adjustment of the confined macromolecular segments, and recombination is completed at a new equilibrium position. This structural design avoids the irreversible slippage of cross-linked network polymer segments, effectively reducing the creep strain rate of the material.

[0032] 2. This invention utilizes the coordination interaction between the benzimidazole ring grafted with 2-mercaptobenzimidazole and zinc ions to construct charge-transfer complex nodes within the insulating matrix, thereby improving the electrical insulation strength of the material. These polar nodes introduce deep trap levels into the polymer band gap, preferentially capturing hot electrons injected by the electrode and forming a negative space charge layer, thus weakening the effective field strength on the electrode surface. The energy carried by the trapped electrons is dissipated through lattice vibrations, interrupting the energy cascade accumulation path of impact ionization, thereby suppressing space charge accumulation and increasing the macroscopic breakdown field strength.

[0033] 3. This invention covalently grafts thiol-containing antioxidants onto the macromolecular crosslinking precursor backbone via an in-situ Michael addition reaction, balancing the stability of the crosslinking process with long-term resistance to thermo-oxidative aging. The grafting reaction pre-consumes the reactive free thiol groups during the mixing stage, eliminating their interference with chain termination of peroxide crosslinking radicals. Simultaneously, the antioxidant active groups are directly fixed to the nodes of the three-dimensional crosslinking network by chemical bonds, restricting the free sliding and outward precipitation of small-molecule antioxidants within the polymer amorphous region, thus ensuring the free radical scavenging capability of the cable insulation layer under long-term high-temperature service conditions. Attached Figure Description

[0034] Figure 1This is a comparison chart of the gel content of the samples in this invention; Figure 2 This is a comparison diagram of the thermal elongation properties of the samples of this invention; Figure 3 The electrical performance evaluation curves of the present invention are shown in the figure. Subplot (a) shows the trend of charge injection threshold field strength variation of each group of samples, and subplot (b) shows the comparison of deep trap energy level depth of each group of samples. Figure 4 This is a high-temperature mechanical property evaluation diagram of the present invention, wherein sub-figure (a) shows the high-temperature compressive modulus test results of each group of samples, and sub-figure (b) shows the high-temperature constant load creep strain rate test results of each group of samples. Figure 5 The following is a comparison of the insulation performance of the present invention under extreme electric field conditions. Sub-figure (a) shows the characteristic AC breakdown field strength distribution of each group of samples, and sub-figure (b) shows the comparison of the dielectric loss tangent at 90°C of each group of samples. Figure 6 This is a comparison chart of the long-term thermo-oxidative aging performance of the present invention. Sub-figure (a) shows the comparison of the tensile strength retention rate of each group of samples after aging, and sub-figure (b) shows the comparison of the elongation at break retention rate of each group of samples after aging. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To achieve the above objectives, the present invention provides the following technical solution: The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0037] The CAS number for low-density polyethylene is 9002-88-4, and its standard density at 20°C is 0.922 g / cm³. 3 The melt flow rate at 190℃ and 2.16kg standard load is 2.0g / 10min.

[0038] The CAS number of EPDM rubber is 25038-36-2. The mass fraction of ethylene structural units in the main chain is 70%, and the mass fraction of the third monomer 5-ethylidene-2-norbornene structural units is 4.5%. Its Mooney viscosity ML(1+4) at 125℃ is 65.

[0039] The CAS number of dicumyl peroxide is 80-43-3, the active oxygen mass fraction is greater than 5.8%, and the half-life is 10 hours at 115°C.

[0040] The CAS number for N,N'-m-phenylenebismaleimide is 3006-93-7, and its molecular formula is C2. 14 H8N2O4 has a rigid bridging structure with two maleimide active end groups and a middle meta-benzene ring, with a melting point range of 198℃ to 201℃ and a purity greater than 98.0%.

[0041] Zinc methacrylate has the CAS number 13189-00-9 and the molecular formula C8H. 10 O4Zn contains 27.5% zinc by mass and less than 1.5% moisture by mass.

[0042] 2-Mercaptobenzimidazole has the CAS number 583-39-1 and the molecular formula C7H6N2S. Its structure contains a benzimidazole heterocycle and an active thiol functional group. Its melting point range is 298℃ to 303℃, and its weight loss upon heating is less than 0.3%.

[0043] The CAS number for zinc stearate is 557-05-1, and its molecular formula is C. 36 H70O4Zn has a melting point range of 120℃ to 125℃ and a free fatty acid mass fraction of less than 1.0%.

[0044] The CAS number for calcined kaolin is 92704-41-1, and the average particle size is D. 50 The thickness is 1.5 μm, and the surface is treated with vinyltrimethoxysilane coupling.

[0045] Preparation Example 1: This preparation example provides a method for preparing crosslinkable insulating particles, including the following steps: 80 parts by weight of low-density polyethylene, 20 parts by weight of ethylene propylene diene monomer (EPDM) rubber, 1.8 parts by weight of N,N'-m-phenylenebismaleimide, 1.0 part by weight of 2-mercaptobenzimidazole, and 1.0 part by weight of zinc stearate were added to a rotor mixer. The rotor speed of the mixer was set to 60 r / min, and the circulating cooling water system with a set water temperature of 25°C was turned on to control the discharge temperature of the material at 130°C. High-shear constant-temperature mixing was maintained for 6 minutes. Without stopping the mixer, 3.5 parts by weight of zinc methacrylate were added directly to the mixing chamber. The cooling parameters were adjusted to lower the material temperature to 120°C and maintained. Mixing was continued for 4 minutes. The speed of the mixer was reduced to lower the material temperature to 105°C, and 1.5 parts by weight of dicumyl peroxide was added. Low-shear mixing was carried out for 2 minutes. After discharge, the material was fed into a single-screw extruder. The barrel temperature was set to 95°C. After extrusion, the material was pelletized by a water ring and dried by a forced-air drying process to obtain crosslinkable insulating material granules.

[0046] Preparation Example 2: This preparation example provides a method for preparing crosslinkable insulating particles, including the following steps: 90 parts by weight of low-density polyethylene, 10 parts by weight of ethylene propylene diene monomer (EPDM) rubber, 1.0 part by weight of N,N'-m-phenylenebismaleimide, 0.5 parts by weight of 2-mercaptobenzimidazole, and 0.5 parts by weight of zinc stearate were added to a rotary mixer. The rotor speed of the mixer was set to 60 r / min, and the circulating cooling water system with a set water temperature of 25°C was turned on to control the discharge temperature of the material at 125°C. High-shear constant-temperature mixing was maintained for 5 minutes. Without stopping the mixer, 2.0 parts by weight of zinc methacrylate were added directly to the mixing chamber. The cooling parameters were adjusted to lower the material temperature to 115°C and maintained. Mixing was continued for 3 minutes. The speed of the mixer was reduced to lower the material temperature to 90°C, and 1.0 part by weight of dicumyl peroxide was added. Low-shear mixing was carried out for 2 minutes. After discharge, the material was fed into a single-screw extruder. The barrel temperature was set to 90°C. After extrusion, the material was pelletized by a water ring and dried by a forced-air drying process to obtain crosslinkable insulating material granules.

[0047] Preparation Example 3: This preparation example provides a method for preparing crosslinkable insulating particles, including the following steps: 70 parts by weight of low-density polyethylene, 30 parts by weight of ethylene propylene diene monomer (EPDM) rubber, 2.5 parts by weight of N,N'-m-phenylenebismaleimide, 1.5 parts by weight of 2-mercaptobenzimidazole, and 1.5 parts by weight of zinc stearate were added to a rotor mixer. The rotor speed of the mixer was set to 60 r / min, and the circulating cooling water system with a set water temperature of 25°C was turned on to control the discharge temperature of the material at 135°C. High-shear constant-temperature mixing was maintained for 8 minutes. Without stopping the mixer, 5.0 parts by weight of zinc methacrylate were added directly to the mixing chamber. The cooling parameters were adjusted to lower the material temperature to 125°C and maintained. Mixing was continued for 5 minutes. The speed of the mixer was reduced to lower the material temperature to 110°C, and 2.0 parts by weight of dicumyl peroxide were added. Low-shear mixing was carried out for 3 minutes. After discharge, the material was fed into a single-screw extruder. The barrel temperature was set to 105°C. After extrusion, the material was pelletized by a water ring and dried by a forced-air drying process to obtain crosslinkable insulating material granules.

[0048] Preparation Example 4: This preparation example provides a method for preparing crosslinkable insulating particles, including the following steps: 85 parts by weight of low-density polyethylene, 15 parts by weight of ethylene propylene diene monomer (EPDM) rubber, 2.0 parts by weight of N,N'-m-phenylenebismaleimide, 0.8 parts by weight of 2-mercaptobenzimidazole, and 0.8 parts by weight of zinc stearate were added to a rotor mixer. The rotor speed of the mixer was set to 60 r / min, and the circulating cooling water system with a set water temperature of 25°C was turned on to control the discharge temperature of the material at 128°C. High-shear constant-temperature mixing was maintained for 7 minutes. Without stopping the mixer, 4.0 parts by weight of zinc methacrylate were added directly to the mixing chamber. The cooling parameters were adjusted to lower the material temperature to 118°C and maintained. Mixing was continued for 4 minutes. The speed of the mixer was reduced to lower the material temperature to 100°C, and 1.2 parts by weight of dicumyl peroxide were added. Low-shear mixing was carried out for 2 minutes. After discharge, the material was fed into a single-screw extruder. The barrel temperature was set to 100°C. After extrusion, the material was pelletized by a water ring and dried by a forced-air drying process to obtain crosslinkable insulating material granules.

[0049] Example 1: This embodiment provides a method for preparing a pressure-resistant insulated power cable, including the following steps: Step 1: Add the crosslinkable insulating material particles obtained in Preparation Example 1 into the insulation layer hopper of the cable extruder.

[0050] Step 2: Pass the metal conductor through the inner semiconductive layer extruder and the insulation layer extruder in sequence. The barrel temperature of the insulation layer extruder is distributed in four gradient zones, set to 100℃, 105℃, 115℃ and 120℃ respectively. The crosslinkable insulating material is melted and uniformly extruded onto the inner semiconductive shielding layer on the outside of the metal conductor.

[0051] Step 3: The cable core with the insulation layer is directly fed into the continuous vulcanization tube, and in-situ grafting and vulcanization cross-linking curing are carried out in a high temperature and high pressure nitrogen environment with the temperature set at 190℃.

[0052] Step 4: After the cross-linked and cured cable core is cooled by a water-cooling section, an outer semi-conductive shielding layer and an outer sheath are extruded sequentially on the outside of the compression-resistant insulation layer, and then wound up to obtain a compression-resistant insulated power cable.

[0053] Example 2: This embodiment provides a method for preparing a pressure-resistant insulated power cable, including the following steps: Step 1: Add the crosslinkable insulating material particles obtained in Preparation Example 2 into the insulation layer hopper of the cable extruder.

[0054] Step 2: Pass the metal conductor through the inner semiconductive layer extruder and the insulation layer extruder in sequence. The barrel temperature of the insulation layer extruder is distributed in four gradient zones, set to 100℃, 105℃, 110℃ and 115℃ respectively. The crosslinkable insulating material is melted and uniformly extruded onto the inner semiconductive shielding layer on the outside of the metal conductor.

[0055] Step 3: The cable core with the insulation layer is directly fed into the continuous vulcanization tube, and in-situ grafting and vulcanization cross-linking curing are carried out in a high temperature and high pressure nitrogen environment with the temperature set at 180℃.

[0056] Step 4: After the cross-linked and cured cable core is cooled by a water-cooling section, an outer semi-conductive shielding layer and an outer sheath are extruded sequentially on the outside of the compression-resistant insulation layer, and then wound up to obtain a compression-resistant insulated power cable.

[0057] Example 3: This embodiment provides a method for preparing a pressure-resistant insulated power cable, including the following steps: Step 1: Add the crosslinkable insulating material particles obtained in Preparation Example 3 into the insulation layer hopper of the cable extruder.

[0058] Step 2: Pass the metal conductor through the inner semiconductive layer extruder and the insulation layer extruder in sequence. The barrel temperature of the insulation layer extruder is distributed in four gradient zones, set at 105℃, 110℃, 115℃ and 120℃ respectively. The crosslinkable insulating material is melted and uniformly extruded onto the inner semiconductive shielding layer on the outside of the metal conductor.

[0059] Step 3: The cable core with the insulation layer is directly fed into the continuous vulcanization tube, and in-situ grafting and vulcanization cross-linking curing are carried out in a high temperature and high pressure nitrogen environment with the temperature set at 200℃.

[0060] Step 4: After the cross-linked and cured cable core is cooled by a water-cooling section, an outer semi-conductive shielding layer and an outer sheath are extruded sequentially on the outside of the compression-resistant insulation layer, and then wound up to obtain a compression-resistant insulated power cable.

[0061] Example 4: This embodiment provides a method for preparing a pressure-resistant insulated power cable, including the following steps: Step 1: Add the crosslinkable insulating material particles obtained in Preparation Example 4 into the insulation layer hopper of the cable extruder.

[0062] Step 2: Pass the metal conductor through the inner semiconductive layer extruder and the insulation layer extruder in sequence. The barrel temperature of the insulation layer extruder is distributed in four gradient zones, set at 102℃, 108℃, 112℃ and 118℃ respectively. The crosslinkable insulating material is melted and uniformly extruded onto the inner semiconductive shielding layer on the outside of the metal conductor.

[0063] Step 3: The cable core with the insulation layer is directly fed into the continuous vulcanization tube, and in-situ grafting and vulcanization cross-linking curing are carried out in a high temperature and high pressure nitrogen environment with the temperature set at 195℃.

[0064] Step 4: After the cross-linked and cured cable core is cooled by a water-cooling section, an outer semi-conductive shielding layer and an outer sheath are extruded sequentially on the outside of the compression-resistant insulation layer, and then wound up to obtain a compression-resistant insulated power cable.

[0065] Comparative Example 1: Compared with Example 1, the difference is that the insulating material formulation used does not contain N,N'-m-phenylenebismaleimide, zinc methacrylate, 2-mercaptobenzimidazole and zinc stearate, but instead adds 30 parts by weight of calcined kaolin with a surface coupled with vinyltrimethoxysilane, all other parts are the same.

[0066] Comparative Example 2: Compared with Example 1, the difference is that the in-situ reactive mixing process with multi-stage temperature control was not used in the preparation method of insulating material particles. Instead, all raw materials, including dicumyl peroxide, were simultaneously fed into a rotor mixer at one time. The discharge temperature was controlled at 105°C. After constant temperature mixing for 8 minutes, the discharge was directly discharged and sent to a single screw extruder for granulation. All other aspects were the same.

[0067] Comparative Example 3: The difference from Example 1 is that zinc stearate was not added to the insulation material formulation used, but all other aspects are the same.

[0068] Comparative Example 4: Compared with Example 1, the difference is that the insulation material formula used does not contain zinc methacrylate, and the corresponding mixing step of adding zinc methacrylate is removed in the preparation method. After mixing, the temperature is directly lowered to 105°C and dicumyl peroxide is added. All other aspects are the same.

[0069] Comparative Example 5: Compared with Example 1, the difference is that N,N'-m-phenylenebismaleimide and 2-mercaptobenzimidazole were not added to the insulation material formulation used. In the preparation method, the corresponding mixing step was removed. Low-density polyethylene, EPDM rubber, zinc methacrylate and zinc stearate were directly mixed at 120°C for 4 minutes and then cooled before adding dicumyl peroxide. All other steps were the same.

[0070] Test Example 1: This test aims to verify the actual cross-linking network construction of the premixed system under different process and component conditions. The test subjects are the cross-linkable insulating particles prepared in Examples 1 to 4, Comparative Example 2, and Comparative Example 3.

[0071] Sample preparation: The crosslinkable insulating material particles of each group were pre-pressed into sheets with thicknesses of 1 mm and 2 mm at 115℃ using a flat vulcanizing machine. Then, the temperature was raised to 190℃ and held at 15 MPa pressure for 15 minutes to simulate the crosslinking process in a continuous vulcanizing tube. After cooling, the samples were cut into dumbbell-shaped specimens and square test pieces that meet the national standard size requirements.

[0072] Gel content determination: Accurately weigh 0.2 g to 0.3 g of square cross-linked test pieces and place them in a 120-mesh stainless steel mesh bag. Extract by continuous reflux in boiling xylene solvent for 12 hours. After extraction, remove the mesh bag and dry it in a vacuum oven at 150°C to constant weight. Calculate the percentage of the dried sample mass before and after extraction; this is the gel content.

[0073] High-temperature thermal elongation test: Conducted according to GB / T 2951.21 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers Part 21: Test Methods for Elastomer Compounds—Ozone Resistance Test—Thermal Elongation Test—Mineral Oil Immersion Test". The temperature was set and stabilized at 200℃ in a tubular aging test chamber. A dumbbell-shaped specimen was suspended inside the chamber, and an application of 20 N / cm² was applied to the lower end. 2 A constant mechanical load was applied. The specimen was placed under load at a constant temperature for 15 minutes, and the elongation between the gauge lengths was measured. The load was then removed from the chamber, and the specimen was placed for another 5 minutes before being removed and cooled to room temperature. After cooling, the permanent deformation between the gauge lengths was measured. If the specimen fractured within 15 minutes, it was recorded as fracture failure.

[0074] The experimental data are shown in Table 1: Table 1. Data on the crosslinking network and thermal elongation properties of crosslinkable insulating materials. in conclusion: According to Table 1, Figure 1 and Figure 2 The data showed significant differences in physical state in terms of the degree of crosslinking network formation among the samples. The gel content in Examples 1 to 4 remained consistently above 78%, and the corresponding high-temperature load elongation was controlled within a reasonable range of 54% to 82%. This is common in conventional inorganic filler systems, but often difficult to achieve directly in pure polymer systems containing active thiol antioxidants. Due to the inherent free radical scavenging properties of thiol compounds, when we turn our attention to Comparative Example 2, which did not employ a multi-stage mixing sequence, we find that its gel content sharply decreased to 12.4%, and the sample rapidly underwent melt fracture under a 200°C stress field. The underlying reason for this macroscopic failure is that, in the initial stage of mixing, the thiol groups and the primary free radicals generated by the cracking of dicumyl peroxide underwent an indiscriminate chain termination reaction, blocking the coupling process between polyethylene macromolecular chains. This is precisely the long-standing compatibility taboo in the industry.

[0075] Comparative Example 3 in the comparative test system also underwent pre-high-temperature mixing, but the gel content remained at a meager level of only 35.7%. This phenomenon reflects that in the high-viscosity nonpolar resin matrix at 130℃, the mass transfer resistance between molecular chains greatly hindered the progress of the Michael addition reaction. Without zinc stearate as a key lubricant and catalytic medium, an effective local low-viscosity flow field could not be formed within the system, and the maleimide carbonyl group and thiol protons lost their directional activation by Lewis acid-base pairs. The lag in addition conversion rate meant that the residual thiol groups continued to release destructive effects in the subsequent crosslinking stage. Under the combined effect of the formulation and process of the examples, the combination of in-situ reaction timing and the dual-effect catalysis of metal soap forced the covalent masking of thiol groups, eliminating the interference of free thiol groups on crosslinking activity. This resulted in the final material not only retaining the thermo-oxidative stability of the benzimidazole ring but also successfully completing the substantial construction of the macromolecular three-dimensional crosslinked network.

[0076] Test Example 2: This test aims to verify the deep trap energy level distribution introduced in the band gap by the macromolecular coordination-crosslinking precursor and zinc ion cluster constructed by the in-situ coordination reaction of the present invention, and its ability to suppress charge migration. The test objects are crosslinkable insulating material particles prepared in Examples 1 to 4, Comparative Examples 1, 4 and 5, after crosslinking molding.

[0077] Sample preparation: Using a flat vulcanizing machine, the insulating material granules of each group were pre-pressed into circular film specimens with a diameter of 100 mm and a thickness of 0.1 mm at 115 °C. The temperature was then raised to 190 °C, and a pressure of 15 MPa was applied and maintained for 15 minutes to complete the crosslinking. After removal, the specimens were heat-treated in a vacuum drying oven at 60 °C for 24 hours to eliminate internal residual stress and interference from crosslinking byproducts on the electrical test results.

[0078] Space charge injection threshold field strength test: The electroacoustic pulse method (PEA) was used for measurement. At 25℃, a stepped DC voltage was applied to the specimen, with the field strength gradually increasing from 5 kV / mm to 60 kV / mm. A high-frequency piezoelectric sensor was used to collect the charge distribution signal inside the specimen under different field strengths. By analyzing the curve of charge density versus field strength, a clear inflection point of nonlinear charge injection was extracted; the field strength corresponding to this point is the charge injection threshold field strength (…). ).

[0079] Calculation of deep trap energy level depth: Indirect evaluation was performed using the isothermal surface potential decay method (ISPD). The sample surface was charged to its rated potential using a needle-grid corona discharge device, and the decay curve of the surface potential over time was recorded. Based on the thermal stimulation current theory and charge trapping kinetics equation, the potential decay curve was transformed into a trap energy level distribution function. By identifying the energy peak in the distribution curve, the apparent deep trap energy level depth of the material was determined. ).

[0080] The experimental data are shown in Table 2: Table 2 Test data of charge trapping and trap parameters in conclusion: According to Table 2 and Figure 3 The data clearly demonstrate the significant regulatory effect of different network structures on the charge transport properties of the material. The charge injection threshold field strengths of Examples 1 to 4 were all maintained above 21 kV / mm, significantly better than the 11 to 15 kV / mm levels in the comparative examples. This leap in electrical performance can be attributed at the microscopic physical level to the successful introduction of extremely high-density deep trap centers into the polymer matrix in this invention. (From Table 2...) The measured values ​​show that the trap depth of Example 3 reached 1.25 eV, while that of Comparative Example 1 with added conventional calcined kaolin was only 0.76 eV. This indicates that the electron binding capacity provided by a single inorganic interfacial electric bilayer is limited.

[0081] The formation mechanism of these deep traps is closely related to the macromolecular coordination network designed in this scheme. After the Michael addition of N,N'-m-phenylenebismaleimide and 2-mercaptobenzimidazole, the lone pair electrons on the benzimidazole ring undergo strong coordination interactions with the zinc ions in zinc methacrylate, constructing a large number of charge transfer complexes (CTCs) between the polyolefin molecular chains. These polar nodes, as highly localized electron trapping points, form deep traps in the band gap, preferentially trapping hot electrons injected from the electrode. The trapped electrons form a stable negative charge layer in the traps, which, according to the Poisson equation, weakens the effective electric field strength on the electrode surface, thereby significantly increasing the threshold for further charge injection.

[0082] A longitudinal comparison of the data from Comparative Examples 4 and 5 reveals that the absence of either the zinc methacrylate or benzimidazole rings causes the trap depth of the material to drop back to the shallow trap range of approximately 0.8 eV. This experimental phenomenon confirms that the formation of deep traps is not a simple summation of components, but rather stems from the synergistic coordination effect between organic heterocycles and metal ion clusters. Furthermore, the extremely low DC conductivity data in the examples further illustrate that these uniformly distributed deep trap nodes effectively reduce the average carrier mobility. By sacrificing a minimal portion of local charge polarization, they achieve significant stability in macroscopic insulation performance, successfully solving the engineering problem of insulation breakdown caused by space charge accumulation in medium- and high-voltage cables under high-temperature and high-field conditions.

[0083] Test Example 3: This test aims to verify the actual impact of the multi-network structure formed by the premixed system after cross-linking and curing on its macroscopic mechanical load-bearing capacity and stress dissipation capability. The test subjects are standard specimens of cross-linkable insulating materials prepared in Examples 1 to 4, Comparative Examples 1, 4, and 5 after full cross-linking and curing.

[0084] Experimental specimen preparation. Each group of crosslinkable insulating material particles was placed in a flat vulcanizing machine and crosslinked under compression at 190℃ and 15MPa for 15 minutes to prepare a 2mm thick crosslinked homogeneous board. After cooling to room temperature, the boards were cut into cylindrical specimens with a diameter of 12mm and long dumbbell-shaped specimens conforming to national standards using a standard punching machine. These specimens were then placed in a standard laboratory environment for 24 hours to allow for the elimination of internal residual stress.

[0085] High-Temperature Compression Modulus Determination. A cylindrical specimen is placed in the center of the pressure plate of a universal testing machine equipped with a high- and low-temperature environmental chamber. The chamber temperature is set to 90℃ and maintained at this temperature for 30 minutes to allow the specimen's internal temperature to reach thermal equilibrium. The testing machine is started, applying an axial compressive load to the specimen at a constant rate of 1 mm / min, while simultaneously recording displacement and load data. The slope data of the strain in the 1% to 5% linear range of the stress-strain curve is extracted, and the high-temperature compression modulus of the material is calculated. Five parallel specimens are tested in each group, and the average effective value is recorded.

[0086] Creep strain rate testing under extreme thermal loads. Using a self-built high-temperature constant-load creep testing platform, a long strip specimen was vertically suspended in a thermodynamic aging chamber set at 130℃. A counterweight was suspended at the lower end of the specimen to subject it to an initial static load of 0.2 MPa. The initial gauge length of the specimen was recorded at the moment of loading. After 24 hours of continuous loading, the gauge length was measured again using a non-contact optical extensometer. The creep strain rate of the specimen under this high-temperature heavy-load environment was obtained by calculating the ratio of deformation to the initial gauge length.

[0087] The experimental data are shown in Table 3: Table 3. Data on high-temperature compressive strength and creep resistance. in conclusion: According to Table 3 and Figure 4The data shows that the all-organic system, which completely eliminates inorganic fillers, exhibits mechanical characteristics that surpass those of conventional physical blends in terms of high-temperature pressure resistance and dimensional stability. In the actual operation of buried cables, the insulation layer not only needs to withstand the thermal expansion and compression of the conductor, but also faces the continuous heavy pressure from the external soil and protective layer, requiring the material to have extremely high creep resistance. The compressive modulus of Examples 1 to 4 at 90°C remained stable in the range of 14.89 to 16.73 MPa, a value equivalent to that of Comparative Example 1 (16.05 MPa), which was filled with a large amount of calcined kaolin. Filling with inorganic rigid particles to increase the modulus is a common method in polymer processing, but under high-temperature static load at 130°C, the creep rate of Comparative Example 1 rose sharply to 8.74%, exposing the interfacial defects of the inorganic filler in the non-polar resin matrix. The continuous thermodynamic coupling effect leads to microscopic disadhesion between inorganic particles and polymer matrix, and irreversible slippage of macromolecular chain segments that have lost their stress transmission ability. Since the system in the example does not contain micron-sized particles at the macroscopic phase interface, it avoids creep failure caused by interface peeling from a physical structure perspective, reducing the strain rate to about 4%.

[0088] This macroscopic balance of rigidity and flexibility stems from the energy dissipation division of different chemical bonds within the cross-linked network. Analysis of Comparative Example 4 shows that after removing zinc methacrylate, the high-temperature compressive modulus of the material drops to 10.24 MPa, while the creep rate surges. This indicates that relying solely on polyethylene-based cross-linking cannot provide sufficient high-temperature structural support; the absence of zinc ion clusters deprives the network of dynamic sacrificial bonds. In the initial stage of compression, the rigid covalent bridging nodes formed by the meta-benzene rings of bismaleimide bear the main compressive load. When local stress concentration reaches the yield threshold, the secondary coordination bonds composed of zinc ions and polydentate imidazole ligands spontaneously dissociate. The confined macromolecular chain segments dissipate mechanical strain energy into thermal energy through minute conformational adjustments and slippage. Subsequently, the ions and ligands at the new equilibrium positions recombine and recoordinate. In Comparative Example 5, after the rigid framework precursor is removed, the internal network completely degenerates into a loose, conventional cross-linked state, completely losing its load-bearing capacity under thermal stress. This solution, through a molecular-scale dissociation-reconstruction mechanism, endows the insulation layer with the ability to adaptively dissipate external forces under dynamic heavy loads, enabling the final cable product to still possess excellent deep-buried compressive reliability even without the elimination of high-density inorganic fillers.

[0089] Test Example 4: This test aims to evaluate the effect of the homogeneous cross-linked network constructed in situ in this invention on improving macroscopic electrical strength, and to verify the practical engineering value of multipolar nodes in suppressing charge transport and reducing high-frequency polarization loss. The test subjects were cross-linkable insulating material particles prepared in Examples 1 to 4, Comparative Examples 1, 4, and 5, after hot-pressing cross-linking.

[0090] Standardized preparation of experimental specimens. The insulating material particles of each group were pre-melted at 115℃ using a flat vulcanizing machine, then heated to 190℃ and held at 15MPa pressure for 15 minutes for cross-linking and curing. Based on testing requirements, circular specimens with a thickness of 1.0 mm were molded for breakdown testing, and specimens with a thickness of 0.5 mm were molded for dielectric loss testing. The prepared specimens were treated in a vacuum environment at 60℃ for 24 hours to eliminate interference from trace amounts of moisture and cross-linking byproducts such as dodecylbenzene or acetophenone.

[0091] The AC breakdown field strength test was conducted at room temperature (25℃) using a continuous voltage ramp method. A 1.0 mm thick specimen was placed in a column-plate asymmetric brass electrode system, with the entire electrode test unit completely immersed in clean 25# transformer oil to prevent edge flashover. The AC power supply frequency was set to 50 Hz, and the voltage was continuously increased at a constant rate of 1.0 kV / s until the specimen underwent through-breakdown. The instantaneous breakdown voltage value was recorded. Fifteen valid parallel specimens were tested for each formulation. The data were processed using a two-parameter Weibull statistical distribution model, and the characteristic breakdown field strength at a cumulative failure probability of 63.2% was extracted as the final evaluation index.

[0092] The high-temperature dielectric loss tangent was determined using a high-voltage Schering bridge and a matching three-terminal isothermal electrode testing system. A 0.5 mm thick test piece was placed between the test electrodes, and the electrode cavity temperature was set to the limit temperature of 90°C for full-load operation of the cable and maintained at this temperature for 1 hour. A 1 kV AC measurement voltage was applied to the sample at a 50 Hz power frequency. After the bridge reached complete equilibrium, the capacitance and dielectric loss tangent values ​​were recorded. The arithmetic mean of three test samples was taken for each group.

[0093] The experimental data are shown in Table 4: Table 4. Test data of breakdown field strength and dielectric loss in conclusion: According to Table 4 and Figure 5 The data from Examples 1 to 4 show that the characteristic AC breakdown field strength is stably distributed in the range of 128.7 kV / mm to 135.2 kV / mm, while the dielectric loss tangent at 90°C remains at 5.1 × 10⁻⁶. -4The following is a summary of previous research on pressure-resistant cable insulation formulations, where researchers typically favored adding high-density inorganic rigid particles to provide basic mechanical support. The electrical data in Comparative Example 1 directly reflects the weakening effect of this conventional physical modification scheme on insulation strength. The incorporation of a large amount of calcined kaolin into the non-polar polyethylene matrix inevitably introduces a massive number of micro-phase interfaces. Due to the intrinsic difference in the thermal expansion coefficients between the matrix and the inorganic phase, submicron-level micro-gaps easily form at these interfaces during the cooling stage after cross-linking. These defect regions with significantly different polarizabilities induce severe local field strength distortion under strong alternating electric fields, thereby inducing partial discharge and continuously eroding macromolecular chain segments. Ultimately, this leads to a sharp deterioration in the breakdown field strength of this comparative example to 85.6 kV / mm, and the dielectric loss tangent caused by Maxwell-Wagner interface polarization climbs to 32.1 × 10⁻⁶. -4 The all-organic homogeneous crosslinked network in this scheme avoids the introduction of macroscopic inorganic phase interfaces through purely chemical means. The density of the polymer melt after solidification eliminates the physical morphological hazards that could induce early electrical breakdown from the root.

[0094] A single matrix homogenization treatment is insufficient to support a breakdown field strength exceeding 130 kV / mm. Observations of the test results of Comparative Examples 4 and 5 show that when specific coordination nodes or covalent bridging groups are missing from the formulation, the breakdown field strength of the pure polymer matrix remains within the conventional threshold range of 100 to 110 kV / mm. Tracing the physical origins in conjunction with the actual operating conditions of high-voltage cables, the core process of dielectric breakdown is the collision of high-energy hot electrons injected from the electrodes with the polymer backbone under continuous acceleration in an electric field, thereby inducing molecular chain breakage and avalanche-like collisional ionization. In the example samples, the nitrogen-containing heterocyclic network generated by the in-situ reaction of N,N'-m-phenylenebismaleimide and 2-mercaptobenzimidazole, and the ionic coordination clusters constructed by the polymerization of zinc methacrylate, densely and uniformly distributed electron deep trap centers within the insulating matrix. In a high-voltage testing environment, these deep traps can capture primary electrons with a high probability before they undergo long-free-path acceleration. The locally anchored electrons safely dissipate their energy in the form of microscopic lattice phonon vibrations, directly cutting off the energy cascade accumulation path of collisional ionization. Relying on this in-situ control design based on the band structure, the insulating material achieves a substantial improvement in macroscopic withstand voltage without relying on an inorganic phase barrier layer, providing a clear structural design basis for resolving the engineering contradiction between high withstand voltage and low dielectric loss in direct-buried cable insulation layers.

[0095] Test Example 5: This test aims to verify the actual effectiveness of the macromolecular antioxidant structure generated in situ within the insulating material in inhibiting thermo-oxidative degradation and preventing migration and loss over a long period. The test subjects were specimens of crosslinkable insulating material particles prepared in Examples 1 to 4, Comparative Examples 1, 4, and 5, which were then cured by hot-pressing crosslinking.

[0096] Initial performance testing and specimen preparation. Each group of insulating material granules was placed in a flat vulcanizing machine and pressed into a 1 mm thick homogeneous cross-linked sheet at 190℃ and 15 MPa. After cooling, the sheet was punched into test specimens using a standard dumbbell-shaped cutter. Tensile failure tests were performed on five parallel unaged specimens from each group at a tensile rate of 250 mm / min using a universal testing machine at room temperature (25℃). The arithmetic mean of the initial tensile strength and initial elongation at break of the specimens was recorded.

[0097] Forced thermo-oxidative aging treatment involved suspending the remaining dumbbell-shaped cross-linked specimens in a forced-ventilation thermal aging test chamber. The chamber temperature was kept constant at 135°C, and the air inside the chamber was continuously circulated at a specified air exchange rate. The specimens underwent high-temperature thermodynamic and oxygen coupling erosion for 168 hours inside the chamber to simulate the long-term thermal aging process of cables under extreme overload operating conditions.

[0098] For the mechanical property evaluation after aging, after the thermal aging cycle, all specimens were removed from the test chamber and placed on a test bench at room temperature, away from direct sunlight, for at least 16 hours to allow them to settle. Then, using the exact same instrument parameters and environmental conditions as the initial performance test, tensile failure tests were performed on the aged specimens, and the tensile strength and elongation at break were recorded. The tensile strength retention rate and elongation at break retention rate were calculated by dividing the aged test data by the corresponding initial performance data.

[0099] The experimental data are shown in Table 5: Table 5. Retention rate of mechanical properties after thermo-oxidative aging at 135℃ for 168 hours in conclusion: According to Table 5 and Figure 6The data shows that the mechanical degradation characteristics of the samples under extreme thermo-oxidative aging conditions significantly reflect the differences in long-term performance among different antioxidant systems. In actual service, the coupling effect of the heat load generated by conductor current flow and external oxygen permeation is the main degradation mechanism inducing embrittlement and cracking of the insulation layer in polyolefin insulated cables. The tensile strength and elongation at break retention rates of Examples 1 to 4 remained stable within the range of 86.8% to 93.4%, and the cross-linked matrix maintained good structural integrity and mechanical flexibility after 168 hours of high-temperature aging. In contrast, Comparative Example 5, lacking the antioxidant component, showed a significant decrease in tensile strength retention rate to 24.3%, and obvious cracks appeared on the surface of the specimen after aging. This macroscopic failure phenomenon directly confirms the severe degradation effect of free radical chain oxidation reaction on the carbon-carbon backbone of polyethylene under high-temperature conditions.

[0100] Traditional small-molecule antioxidant systems often face severe volatilization and migration issues in working environments of 135℃, which far exceeds the crystallization melting temperature of polyethylene. As the temperature rises, thermodynamic spontaneous diffusion leads to a rapid decrease in the concentration of effective antioxidants within the matrix, causing the insulation layer to gradually lose its ability to decompose hydrogen peroxide. The test results of Comparative Example 1 reflect this limitation; its strength retention rate after aging is only 68.5%, and the debonding phenomenon at the inorganic filler interface under thermodynamic expansion further accelerates the degradation of macroscopic mechanical properties. The effective inhibition of small-molecule migration in the example samples is mainly due to the in-situ grafting masking mechanism implemented in the micro-preparation stage. During the Michael addition reaction, 2-mercaptobenzimidazole not only achieves interference shielding against crosslinking active components but also covalently links its thermo-oxidative-resistant benzimidazole ring to the N,N'-m-phenylenebismaleimide backbone. In the subsequent high-temperature crosslinking stage, this macromolecular precursor backbone directly participates in the construction of the polyethylene three-dimensional crosslinked network through a free radical addition reaction. This chemical anchoring strategy, which transforms small-molecule antioxidants into intrinsic groups within a macromolecular crosslinked network, restricts the slippage of antioxidant groups within the free volume of the polymer's amorphous region and their diffusion to the material surface at the molecular kinetic level. The benzimidazole rings solidified on the crosslinked network nodes can then continuously exert their chemical efficacy in situ during thermo-oxidative oxidation, scavenging reactive free radicals. This antioxidant design based on in-situ solidification of the macromolecular network significantly improves the high-temperature, long-term stability of insulating materials, providing a reliable materials science basis for solving the engineering challenge of limited long-term service life in high-voltage direct-buried cables.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pressure-resistant insulating power cable material, characterized in that, Made from the following ingredients in parts by weight: 70-90 parts of low-density polyethylene; 10-30 parts of EPDM rubber; 1.0-2.5 parts of N,N'-m-phenylenebismaleimide; 0.5-1.5 parts of 2-mercaptobenzimidazole; 0.5-1.5 parts of zinc stearate; Zinc methacrylate 2.0-5.0 parts; 1.0-2.0 parts of dicumyl peroxide.

2. The compression-resistant insulating power cable material according to claim 1, characterized in that, The low-density polyethylene has a reference density of 0.922 g / cm³ at 20°C. 3 The melt flow rate at 190℃ and 2.16kg standard load is 2.0g / 10min.

3. The compression-resistant insulating power cable material according to claim 1, characterized in that, The ethylene structural unit in the main chain of the EPDM rubber has a mass fraction of 70%, the third monomer 5-ethylidene-2-norbornene structural unit has a mass fraction of 4.5%, and its Mooney viscosity ML(1+4) at 125°C is 65.

4. The compression-resistant insulating power cable material according to claim 1, characterized in that, The N,N'-m-phenylenebismaleimide has a melting point range of 198°C to 201°C and a purity greater than 98.0%; the dicumyl peroxide has an active oxygen mass fraction greater than 5.8% and a half-life of 10 hours at 115°C; and the 2-mercaptobenzimidazole has a weight loss upon heating of less than 0.3%.

5. A method for preparing a compression-resistant insulated power cable material, used to prepare a compression-resistant insulated power cable material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Low-density polyethylene, ethylene propylene diene monomer (EPDM) rubber, N,N'-m-phenylenebismaleimide, 2-mercaptobenzimidazole and zinc stearate are put into an internal mixer. The internal mixer rotor speed is set and the circulating cooling water system is turned on. The discharge temperature is controlled to maintain high-shear constant temperature mixing and promote in-situ masking reaction of the system. S2. Add zinc methacrylate directly into the mixing chamber without stopping the machine, adjust and maintain the temperature, and continue mixing to promote the in-situ construction of coordination nodes in the system; S3. Reduce the speed of the internal mixer to lower the material temperature, add dicumyl peroxide, and discharge the rubber after low-shear mixing. S4. The material obtained in S3 is fed into a single screw extruder and extruded at a barrel temperature of 90-105°C. After pelleting and drying, crosslinkable insulating material granules are obtained.

6. The method for preparing a compression-resistant insulating power cable material according to claim 5, characterized in that, In step S1, the internal mixer rotor speed is set to 50-70 r / min, and the circulating cooling water system with a set water temperature of 20-30℃ is turned on to control the material discharge temperature.

7. The method for preparing a compression-resistant insulating power cable material according to claim 5, characterized in that, In step S1, the high-shear constant-temperature mixing time is 5-8 minutes, and the glue discharge temperature is 125-135℃.

8. The method for preparing a compression-resistant insulating power cable material according to claim 5, characterized in that, In step S2, after adding zinc methacrylate, the mixing time is 3-5 minutes, and the temperature is reduced to and maintained at 115-125°C.

9. The method for preparing a compression-resistant insulating power cable material according to claim 5, characterized in that, In step S3, the low-shear mixing time is 2-3 minutes, and the material temperature is reduced to 90-110℃.

10. A power cable, characterized in that, It includes a metal conductor and an inner semiconductive shielding layer, an insulating layer, an outer semiconductive shielding layer, and an outer sheath sequentially covering the metal conductor. The insulating layer is formed by extruding a pressure-resistant insulated power cable material as described in any one of claims 1-4, followed by in-situ grafting and vulcanization crosslinking curing in a high-temperature and high-pressure nitrogen environment.

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