A shielding material for thermoplastic polyethylene power cables and a preparation method and application thereof

Abstract

This invention belongs to the field of polymer materials technology and discloses a thermoplastic polyethylene-based shielding material for power cables, its preparation method, and its application. The thermoplastic polyethylene-based shielding material for power cables of this invention comprises the following components in parts by weight: 64-78 parts of polyethylene resin, 20-30 parts of conductive filler, and 2-6 parts of additives. This invention constructs a highly efficient three-dimensional conductive network through the compounding of specific conductive carbon blacks, where "large-particle-size carbon black forms the primary skeleton, and small-particle-size carbon black fills and bridges." This significantly reduces volume resistivity while effectively suppressing the positive temperature coefficient effect, and also possesses excellent processing fluidity, mechanical toughness, and long-term resistance to thermo-oxidative aging. It solves the technical problem of simultaneously achieving conductive stability and thermomechanical reliability in non-crosslinked shielding materials. Furthermore, the shielding material of this invention has good compatibility with thermoplastic polyethylene insulation layers and has broad application prospects in the field of semi-conductive shielding layers for medium and high voltage power cables.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a thermoplastic polyethylene-based shielding material for power cables, its preparation method, and its application. Background Technology

[0002] Power cables are core equipment in power transmission and distribution networks, and their operational reliability is closely related to the performance of their insulation systems. With increasingly stringent environmental regulations and the deepening of sustainable development concepts, the drawbacks of traditional thermosetting cross-linked polyethylene (XLPE) insulated cables—their difficulty in degradation and non-recyclability—are becoming increasingly prominent. Furthermore, the cross-linking and degassing processes involved in their production are not only energy-intensive and time-consuming, but residual cross-linking byproducts (such as cumyl alcohol and acetophenone) can induce space charge accumulation and a decrease in volume resistivity in the cable insulation medium, thereby deteriorating insulation performance. In recent years, non-cross-linked thermoplastic polyethylene-based insulation materials have received widespread attention from academia and industry due to their advantages such as low processing energy consumption, melt-recyclability, and no need for degassing treatment, and are considered one of the potential alternatives for insulation materials in medium and high voltage power cables. For example, Chinese invention patent CN115216081A discloses a high-performance medium and high voltage non-cross-linked polyethylene cable insulation material, which possesses excellent electrical, mechanical, and anti-aging properties, showing promising potential to replace XLPE materials.

[0003] However, the long-term safe operation of power cables depends not only on the performance of the main insulation material itself, but also to a large extent on the synergistic effect of the accompanying semi-conductive shielding layer. The semi-conductive shielding layer is typically placed between the conductor core and the main insulation layer (inner shielding) and between the main insulation layer and the metal sheath or insulating sheath (outer shielding). Its core function is to improve the contact characteristics of the conductor / insulation interface and the insulation / sheath interface, eliminate interfacial air gaps, homogenize the interlayer electric field distribution, and effectively suppress the initiation and development of partial discharge and electrical treeing, thereby significantly extending the cable's service life.

[0004] Currently, commercially available semiconductive shielding materials are mainly based on polar polymer matrices such as ethylene-vinyl acetate copolymer (EVA) and ethylene-butyl acrylate copolymer (EBA), combined with conductive carbon black and peroxide crosslinking agents to form a crosslinkable system. Their design logic is compatible with the crosslinking process of XLPE insulated cables. However, these crosslinked shielding materials face significant technical drawbacks when applied to non-crosslinked polyethylene insulation systems: Firstly, the processing window and rheological properties of crosslinked shielding materials differ considerably from those of thermoplastic non-crosslinked insulation layers. During co-extrusion, viscosity mismatch can easily cause interfacial fluctuations, and the crosslinked shielding layer cannot be thermoplastically recycled along with the non-crosslinked insulation material, weakening the environmental advantages of green cable systems. Secondly, non-crosslinked shielding materials, lacking a three-dimensional crosslinked network, are prone to softening deformation, creep relaxation, or thermo-oxidative degradation under high-temperature or long-term service conditions, leading to deterioration of the conductive filler dispersion, increased volume resistivity, and significant decreases in mechanical strength and elongation at break.

[0005] Therefore, developing a non-crosslinked thermoplastic semiconductive shielding material that can effectively solve the above problems and has excellent conductivity stability, thermomechanical reliability, and resistance to thermo-oxidative aging is of great practical significance and market value for meeting the demand for core supporting materials in the fields of environmentally friendly manufacturing and long-term safe operation of medium and high voltage power cables, and promoting the closed-loop technology and engineering application of the entire chain of non-crosslinked cable insulation systems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a thermoplastic polyethylene-based shielding material for power cables, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a shielding material for thermoplastic polyethylene-based power cables, comprising the following components in parts by weight: 64-78 parts of polyethylene resin, 20-30 parts of conductive filler, and 2-6 parts of additives; The conductive filler includes a first conductive carbon black and a second conductive carbon black; the oil absorption value of the first conductive carbon black is ≤200cc / 100g, and the oil absorption value of the second conductive carbon black is ≥300cc / 100g. The mass ratio of the first conductive carbon black to the second conductive carbon black is (1~4):1.

[0008] The thermoplastic polyethylene-based shielding material for power cables of the present invention achieves a comprehensive balance of low and stable volume resistivity, excellent processing rheological properties, high elongation at break, and superior resistance to thermo-oxidative aging through the synergistic compounding of two specific conductive carbon blacks and further combined with a matrix resin and additive system. Firstly, the thermoplastic polyethylene-based shielding material for power cables of the present invention employs a two-component conductive carbon black system with a specific oil absorption value. The first conductive carbon black is easily and uniformly dispersed in the polyethylene matrix, which helps to construct a stable primary conductive skeleton and effectively reduces the viscosity of the system, improving processing performance. The second conductive carbon black can significantly improve the conductivity of the composite material at a low addition amount and preferentially fills the gaps in the primary skeleton. Secondly, the introduction of the first and second conductive carbon blacks in a specific ratio in this invention achieves a synergistic conductive mechanism of "coarse skeleton + fine network": the first conductive carbon black forms a continuous primary conductive skeleton, and the second conductive carbon black fills the gaps in the skeleton and bridges isolated conductive points, thereby constructing a dense and stable three-dimensional conductive network with a low total carbon black content. This not only significantly reduces the volume resistivity but also effectively suppresses the breakage of the conductive network when polyethylene expands due to heat, greatly weakens the PTC (positive temperature coefficient) effect, and ensures the stability of the electrical performance of the cable within the operating temperature range. This solves the technical contradiction of high resistivity or strong PTC effect in traditional single-component carbon black filling systems. Furthermore, this invention also avoids excessive carbon black aggregation, maintaining the material's high elongation at break and excellent resistance to thermo-oxidative aging.

[0009] Therefore, through the above-mentioned multi-dimensional synergistic mechanism, this invention successfully prepared a thermoplastic polyethylene-based shielding material with excellent conductivity stability, thermomechanical stability, and resistance to thermo-oxidative aging. This solves the contradiction between conductive network construction and long-term reliability in non-crosslinked shielding materials. Furthermore, the thermoplastic polyethylene-based shielding material for power cables of this invention has good compatibility with thermoplastic polyethylene insulation layers, can be fully recycled, and has broad application prospects in the field of semi-conductive shielding layers for medium and high voltage power cables.

[0010] In a preferred embodiment of the thermoplastic polyethylene-based power cable shielding material of the present invention, the polyethylene resin is linear low-density polyethylene with a density of 0.91 g / cm³. 3 ~0.94g / cm 3 The melt index at 190℃ and 2.16kg load is 0.15g / 10min to 0.25g / 10min.

[0011] In the thermoplastic polyethylene-based power cable shielding material of this invention, the use of linear low-density polyethylene with high crystallinity and excellent mechanical properties allows for more efficient dispersion and network construction of the two-component conductive filler. Simultaneously, it balances material processing fluidity and high-temperature mechanical strength, making it suitable as the matrix resin for non-crosslinked cable shielding layers. Furthermore, it exhibits good compatibility with current mainstream thermoplastic polyethylene insulation materials, facilitating interfacial bonding between the shielding and insulation layers in the three-layer co-extrusion process. This avoids micro-gap or electric field distortion caused by differences in thermal expansion coefficients, thereby achieving a better balance in processability, conductivity, and mechanical reliability. If the melt index is too low, extrusion difficulties, melt fracture, and reduced production efficiency will occur; if it is too high, thermal stability will decrease, and creep deformation under high-temperature service conditions will be exacerbated.

[0012] Preferably, the density of the polyethylene resin is 0.923 g / cm³. 3 The melt index is 0.2 g / 10 min under the conditions of 190℃ and 2.16 kg load.

[0013] As a preferred embodiment of the shielding material for thermoplastic polyethylene-based power cables described in this invention, the first conductive carbon black has an oil absorption value of 120cc / 100g to 200cc / 100g, and the second conductive carbon black has an oil absorption value of 300cc / 100g to 400cc / 100g.

[0014] Through research, the inventors discovered that by controlling the oil absorption values ​​of the first and second conductive carbon blacks within the aforementioned range in the thermoplastic polyethylene-based power cable shielding material of this invention, the complementary advantages of the first and second conductive carbon blacks in terms of dispersibility and conductivity can be more fully utilized, while avoiding agglomeration and processing difficulties caused by excessive high oil absorption carbon black. If the oil absorption value of the first conductive carbon black is too high, its own structure is too low, and it cannot form an effective primary conductive skeleton, resulting in limited improvement in the conductivity of the material and failing to achieve the expected low resistivity effect. If the oil absorption value of the second conductive carbon black is too low, on the one hand, its specific surface area is extremely large and the interparticle forces are too strong, making it prone to agglomeration and leading to a sharp deterioration in dispersibility; on the other hand, it will significantly increase the viscosity of the system, deteriorate the processing performance, and accelerate the thermo-oxidative degradation of the polyethylene matrix due to the presence of a large number of polar surface groups.

[0015] Preferably, the oil absorption value of the first conductive carbon black is 120cc / 100g~180cc / 100g, and the oil absorption value of the second conductive carbon black is 330cc / 100g~350cc / 100g.

[0016] More preferably, the first conductive carbon black has an oil absorption value of 123cc / 100g, and the second conductive carbon black has an oil absorption value of 330cc / 100g.

[0017] In a preferred embodiment of the shielding material for thermoplastic polyethylene-based power cables described in this invention, the particle size of the first conductive carbon black is 30 nm to 60 nm, and the particle size of the second conductive carbon black is 10 nm to 20 nm.

[0018] Preferably, the particle size of the first conductive carbon black is 30nm~45nm, and the particle size of the second conductive carbon black is 12nm~15nm.

[0019] More preferably, the particle size of the first conductive carbon black is 45 nm, and the particle size of the second conductive carbon black is 15 nm.

[0020] In a preferred embodiment of the shielding material for thermoplastic polyethylene-based power cables described in this invention, the mass ratio of the first conductive carbon black to the second conductive carbon black is (1.5~4):1.

[0021] The inventors discovered through research that when the amounts of the first and second conductive carbon blacks are within the aforementioned range, a balance can be achieved between conductivity, processing rheology, and mechanical properties. If the proportion of the first conductive carbon black is too high, the amount of high-structure, small-particle-size carbon black in the system is insufficient, leading to inadequate filling and bridging of the conductive network and an increase in volume resistivity. Conversely, if the proportion of the small-particle-size second conductive carbon black is too high, the strong van der Waals forces between nanoparticles cause severe agglomeration, resulting in localized stress concentration and deterioration of mechanical properties. At the same time, the viscosity of the system increases sharply, and the processing window narrows significantly.

[0022] Preferably, the mass ratio of the first conductive carbon black to the second conductive carbon black is 1.5:1.

[0023] As a preferred embodiment of the shielding material for thermoplastic polyethylene-based power cables of the present invention, the additives include the following components in parts by weight: 0.1 to 1.0 parts of antioxidant and 1 to 4 parts of dispersant.

[0024] The antioxidant of this invention can effectively capture free radicals and decompose hydrogen peroxide, significantly delaying the thermo-oxidative degradation of polyethylene during high-temperature processing and long-term operation, which is key to improving the thermal stability and service life of the material; while the dispersant promotes the uniform dispersion of carbon black in the melt blending process by reducing the van der Waals forces between carbon black particles and improving its interfacial compatibility with the polyethylene matrix, preventing agglomeration, thereby ensuring the integrity of the conductive network and the uniformity of mechanical properties.

[0025] Preferably, the additive comprises the following components in parts by weight: 0.5 parts antioxidant and 3 parts dispersant.

[0026] Preferably, the antioxidant includes at least one of antioxidant 300, antioxidant 1010, and antioxidant 168.

[0027] More preferably, the antioxidant includes antioxidant 300.

[0028] Preferably, the dispersant includes at least one of white oil, ethylene bis-stearamide, and oleamide.

[0029] More preferably, the dispersant comprises white oil.

[0030] This invention uses white oil as a liquid dispersant, which also has a lubricating effect during processing, further reducing melt viscosity and improving extrusion stability. At the same time, it has good compatibility with the polyethylene matrix and will not produce obvious phase separation defects at the interface.

[0031] Secondly, the present invention provides a method for preparing the shielding material for thermoplastic polyethylene-based power cables, comprising the following steps: S1. After drying, polyethylene resin, conductive filler and additives are mixed to obtain a premix; S2. The premix is ​​melt-blended, discharged, and then granulated to obtain granules. S3. Dry the granular material to obtain the shielding material for thermoplastic polyethylene-based power cables.

[0032] In a preferred embodiment of the preparation method of the present invention, in step S1, the drying temperature is 50℃~70℃ and the time is 24h~36h.

[0033] The present invention uses the above-mentioned drying conditions to effectively remove the adsorbed moisture and volatile impurities in the raw materials, avoids bubbles, scorching or uneven dispersion caused by moisture vaporization during the subsequent melt blending process, as well as the agglomeration of base material particles, and avoids premature decomposition of additives or changes in the surface properties of carbon black caused by excessively high temperatures.

[0034] Preferably, in step S1, the drying temperature is 60°C and the drying time is 24 hours.

[0035] In a preferred embodiment of the preparation method of the present invention, in step S2, the temperature of the melt blending is 170℃~190℃, the rotation speed is 50rpm~60rpm, and the particle size of the granules is 3mm~5mm.

[0036] The temperature range of the melt blending described above is higher than the melting point of polyethylene resin but lower than its significant thermal degradation temperature, which can ensure sufficient melt flow and avoid antioxidant decomposition. The screw speed of the melt blending provides sufficient shear force to break up carbon black agglomerates while avoiding excessive shearing that could lead to molecular chain breakage or melt instability, and can also avoid damaging the secondary structure of carbon black.

[0037] Preferably, in step S2, the melt blending temperature is 180°C and the rotation speed is 50 rpm.

[0038] In a preferred embodiment of the preparation method of the present invention, in step S2, the equipment for melt blending is any one of a twin-screw extruder, a Buss extruder, an internal mixer, or a torque rheometer.

[0039] In a preferred embodiment of the preparation method of the present invention, in step S3, the drying temperature is 50℃~70℃ and the time is 24h~36h.

[0040] The drying step of this invention aims to remove trace amounts of moisture or residual volatiles that may be adsorbed during the melt granulation process, prevent the generation of pores, interface defects, or electrical performance fluctuations during cable extrusion, and ensure the density of the shielding layer and its long-term operational reliability.

[0041] Preferably, in step S3, the drying temperature is 60°C and the drying time is 24 hours.

[0042] Thirdly, the present invention provides the application of the aforementioned thermoplastic polyethylene-based shielding material for power cables in a semiconductive shielding layer for medium and high voltage power cables.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention successfully prepares a thermoplastic polyethylene-based shielding material for power cables with excellent comprehensive performance by synergistically compounding two specific conductive carbon blacks and combining them with a matrix resin and additive system. It not only has low and stable volume resistivity and excellent positive temperature coefficient (PTC) suppression ability, effectively avoiding the risk of conductive network failure caused by cable operating temperature fluctuations, but also maintains good processing fluidity and melt strength, ensuring rheological matching with the thermoplastic polyethylene insulation layer in the three-layer co-extrusion process. This significantly improves the long-term thermomechanical reliability and resistance to thermo-oxidative aging of the material, and expands its application range under high temperature and long service life conditions. Secondly, this invention achieves synergistic optimization of conductivity and mechanical properties with a moderate amount of conductive carbon black filling, effectively avoiding the technical contradictions of mechanical degradation due to high filling amounts or poor conductivity due to low filling amounts in traditional single-component carbon black systems. Furthermore, by precisely controlling the temperature and shear rate during the phase transition and melt blending stages, carbon black particles are uniformly dispersed in the amorphous region of polyethylene, maximizing the density of conductive pathways without damaging the matrix's crystalline structure, further enhancing the overall reliability of the material. In addition, the fully thermoplastic system of this invention's thermoplastic polyethylene-based power cable shielding material allows for melt recycling and reuse along with the non-crosslinked polyethylene insulation layer, perfectly aligning with the development direction of green and environmentally friendly cables. Moreover, without relying on crosslinking processes, it achieves an organic unity of high conductivity, low PTC effect, excellent resistance to thermo-oxidative aging, good mechanical properties, and processability, providing a reliable technical solution for environmentally friendly semi-conductive shielding materials for medium and high voltage power cables. Attached Figure Description

[0044] Figure 1 Here is a SEM image of the low-temperature brittle fracture surface of the shielding material for thermoplastic polyethylene-based power cables in Example 1. Figure 2 SEM image of the low-temperature brittle fracture surface of the shielding material for thermoplastic polyethylene-based power cables in Comparative Example 3. Figure 3 The image shows the XRD pattern of the shielding material for thermoplastic polyethylene-based power cables in Example 1. Figure 4 The graph shows the volume resistivity variation of the shielding material for thermoplastic polyethylene-based power cables in Example 1 and Comparative Example 1 at different temperatures. Figure 5 This is a tensile stress-strain curve of the shielding material for thermoplastic polyethylene-based power cables in Example 1 before aging. Figure 6 This is a tensile stress-strain curve of the shielding material for thermoplastic polyethylene-based power cables in Example 1 after aging. Figure 7The tensile stress-strain curve of the shielding material for thermoplastic polyethylene-based power cables in Comparative Example 2 before aging is shown. Figure 8 The tensile stress-strain curve of the shielding material for thermoplastic polyethylene-based power cables in Comparative Example 2 after aging is shown. Detailed Implementation

[0045] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] The following description, in conjunction with specific embodiments, illustrates the practical effects of the present invention.

[0047] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0048] The raw materials used in the following embodiments and comparative examples are described below, but are not limited to these materials: Linear low-density polyethylene (LLDPE) has a density of 0.923 g / cm³. 3 The melt index at 190℃ and 2.16kg load is 0.2g / 10min. It was purchased from Borealis and the model is FB2230. Linear low-density polyethylene (LLDPE) with a density of 0.920 g / cm³ 3 The melt index at 190℃ and 2.16kg load is 0.3g / 10min. It was purchased from PetroChina Lanzhou Petrochemical and the model is 20030BA. High-density polyethylene (HDPE) has a density of 0.945 g / cm³. 3 The melt index at 190℃ and 2.16kg load is 0.75g / 10min. It was purchased from Dow Chemical, USA, model DGDK-3364 NT. Conductive carbon black 1, with a particle size of 45nm, an oil absorption value of 123cc / 100g, and an ash content of 0.1%, was purchased from Cabot Corporation, model VXC68. Conductive carbon black 2, with a particle size of 15nm and an oil absorption value of 330cc / 100g, was purchased from Cabot Corporation, model BP2000. Conductive carbon black 3, with a particle size of 30nm, an oil absorption value of 174cc / 100g, and an ash content of 0.1%, was purchased from Cabot Corporation, model VXC72. Conductive carbon black 4, with a particle size of 40nm, an oil absorption value of 151cc / 100g, and an ash content of 0.1%, was purchased from Cabot Corporation, model VULCAN XC605; Conductive carbon black 5, with a particle size of 30nm, an oil absorption value of 230cc / 100g, and an ash content of <0.1%, was purchased from Tianjin Huayuan Chemical Technology Co., Ltd., and is classified as superconducting P80 powder.

[0049] Antioxidant 300, 4,4'-thiobis(6-tert-butyl-3-methylphenol), purchased from Aladdin, model number T162247; The white oil was purchased from Henan Luying Chemical Co., Ltd., and its grade is No. 46 white oil.

[0050] Example 1: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0051] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0052] Example 2: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 70:30. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0053] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0054] Example 3: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 3 with a particle size of 30 nm, an oil absorption value of 174 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 70:30. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0055] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0056] Example 4: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 3 with a particle size of 30 nm, an oil absorption value of 174 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 80:20. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0057] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0058] Example 5: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 50:50. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0059] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0060] Example 6: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.920 g / cm³. 3 The melt flow index was 0.3 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0061] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0062] Example 7: This embodiment provides a thermoplastic polyethylene-based shielding material for power cables, which comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 4 with a particle size of 40 nm, an oil absorption value of 151 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0063] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0064] Comparative Example 1: This comparative example provides a shielding material for thermoplastic polyethylene-based power cables, which differs from Example 1 only in that it uses only the first conductive carbon black as a conductive filler and does not add the second conductive carbon black. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black, which is conductive carbon black 1 with a particle size of 45nm, an oil absorption value of 123cc / 100g, and an ash content of 0.1%. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0065] The comparative method for preparing shielding material for thermoplastic polyethylene-based power cables includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0066] Comparative Example 2: This comparative example provides a thermoplastic polyethylene-based shielding material for power cables, which differs from Example 1 only in the amount of polyethylene resin and conductive filler used. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 61.5 parts polyethylene resin, 35 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0067] The comparative method for preparing shielding material for thermoplastic polyethylene-based power cables includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0068] Comparative Example 3: This comparative example provides a thermoplastic polyethylene-based shielding material for power cables, which differs from Example 1 only in that the weight ratio of the first conductive carbon black to the second conductive carbon black is different. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 40:60. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0069] The comparative method for preparing the shielding material for thermoplastic polyethylene-based power cables includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly at room temperature in a sealed container to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) Place the granules from step (2) in a 60°C oven and dry for 24 hours to obtain the thermoplastic polyethylene-based shielding material for power cables.

[0070] Comparative Example 4: This comparative example provides a thermoplastic polyethylene-based shielding material for power cables, which differs from Example 1 only in that the weight ratio of the first conductive carbon black to the second conductive carbon black is different. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 90:10. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0071] The comparative method for preparing shielding material for thermoplastic polyethylene-based power cables includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0072] Comparative Example 5: This comparative example provides a thermoplastic polyethylene-based shielding material for power cables, which differs from Example 1 only in that the type of polyethylene resin is different. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is high-density polyethylene with a density of 0.945 g / cm³. 3 The melt flow index was 0.75 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0073] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0074] Comparative Example 6: This comparative example provides a shielding material for thermoplastic polyethylene-based power cables, which differs from Example 1 only in that the type of first conductive carbon black is different. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 5 with a particle size of 30 nm, an oil absorption value of 230 cc / 100 g, and an ash content of <0.1%. The second conductive carbon black is conductive carbon black 2 with a particle size of 15 nm and an oil absorption value of 330 cc / 100 g. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40. The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0075] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0076] Comparative Example 7: This comparative example provides a shielding material for thermoplastic polyethylene-based power cables, which differs from Example 1 only in that the type of the second conductive carbon black is different. The thermoplastic polyethylene-based shielding material for power cables in this comparative example comprises the following components in parts by weight: 71.5 parts polyethylene resin, 25 parts conductive filler, and 3.5 parts additives; The polyethylene resin is linear low-density polyethylene with a density of 0.923 g / cm³. 3 The melt flow index was 0.2 g / 10 min (test conditions: 190℃, 2.16 kg). The conductive filler includes a first conductive carbon black and a second conductive carbon black. The first conductive carbon black is conductive carbon black 1 with a particle size of 45 nm, an oil absorption value of 123 cc / 100 g, and an ash content of 0.1%. The second conductive carbon black is conductive carbon black 5 with a particle size of 30 nm, an oil absorption value of 230 cc / 100 g, and an ash content of <0.1%. The mass ratio of the first conductive carbon black to the second conductive carbon black in the conductive filler is 60:40.

[0077] The additives include 0.5 parts antioxidant and 3 parts dispersant, wherein the antioxidant is antioxidant 300 and the dispersant is white oil.

[0078] The preparation method of the shielding material for thermoplastic polyethylene-based power cables in this embodiment includes the following steps: (1) The above polyethylene resin, conductive filler and additives were placed in an oven at 60°C and dried for 24 hours. Then they were mixed evenly in a sealed container at room temperature to obtain a premix. (2) Add the premix from step (1) into a torque rheometer and melt-blend it at 180°C and 50 rpm. After the mixture is uniform, discharge the material and granulate it by extrusion to obtain granules with a particle size of 3 mm-5 mm. (3) The granules from step (2) are dried in an oven at 60°C for 24 hours to obtain the shielding material for thermoplastic polyethylene power cables.

[0079] Test example: The thermoplastic polyethylene-based power cable shielding material of the above embodiments and comparative examples was hot-pressed at 180°C and 15MPa for 10 minutes to prepare a sheet sample with a thickness of 1mm, and the following performance tests were performed.

[0080] (1) Microscopic morphology characterization test Test method: The sample was cut into strips of 20×5×1mm and immersed in liquid nitrogen for 5min until it reached the glassy state and then fractured brittlely to obtain a flat low-temperature brittle fracture surface. The microstructure of the low-temperature brittle fracture surface and the dispersion state of carbon black were observed using a scanning electron microscope (SEM).

[0081] like Figure 1As shown in the SEM image of the low-temperature brittle section of the shielding material for thermoplastic polyethylene-based power cables in Example 1, the conductive carbon black is uniformly dispersed in the polyethylene matrix resin as fine particles. No obvious carbon black agglomerates or clusters were observed, and the carbon black particle size distribution is relatively uniform. This uniform dispersion is beneficial for constructing a complete conductive network structure and reduces local stress concentration points caused by filler agglomeration, thereby maintaining the mechanical properties of the material while ensuring conductivity. In contrast, as... Figure 2 As shown in the SEM image of the low-temperature brittle section of the shielding material for thermoplastic polyethylene-based power cables in Comparative Example 3, conductive carbon black agglomerates can be clearly observed. This indicates that the present invention effectively suppresses the agglomeration tendency of high-structure, small-particle-size carbon black by reasonably controlling the ratio between different types of conductive carbon black, and achieves the ideal dispersion state of conductive filler in the polymer matrix.

[0082] (2) Crystal structure characterization test Test method: The crystal structure of the sample was analyzed by X-ray diffraction (XRD) with a scanning range of 5° to 60°.

[0083] like Figure 3 As shown in the XRD pattern of the thermoplastic polyethylene-based power cable shielding material of Example 1, two diffraction peaks of polyethylene molecules are clearly observed at 21.4° and 23.8°, representing the (110) and (200) crystal planes of polyethylene, respectively. This indicates that the polyethylene molecular chains of the matrix resin in the thermoplastic polyethylene-based power cable shielding material of the present invention retain their semi-crystalline structure, while the carbon black particles are mainly dispersed in the amorphous regions of polyethylene. This structural feature is of great significance to the comprehensive performance of the shielding material: on the one hand, the presence of the crystalline region of polyethylene provides the material with the necessary mechanical strength and structural stability; on the other hand, the selective distribution of conductive carbon black particles in the amorphous region is beneficial to forming a penetrating conductive path in the amorphous region, while avoiding excessive interference with the crystalline region, thus achieving a balance between conductivity and mechanical properties.

[0084] (3) Volume resistivity test: Test method: A four-electrode system was used to test the volume resistivity of the sample at room temperature (25℃) and at 50℃, 70℃ and 90℃ according to GB / T 1551-2009 standard.

[0085] like Figure 4As shown, in the test temperature range of 25°C to 90°C, the volume resistivity of the thermoplastic polyethylene-based power cable shielding material of Example 1 increases relatively slowly with increasing temperature, and the resistance-temperature curve shows good stability. In contrast, the volume resistivity of Comparative Example 1 increases sharply with increasing temperature, and is significantly higher than that of Example 1 throughout the entire test temperature range, exhibiting a significant positive temperature coefficient effect. This indicates that the present invention constructs a dense and stable three-dimensional conductive network through the compounding of two-component conductive carbon blacks—using large-particle-size, low-structure carbon black to construct the primary conductive framework, and using small-particle-size, high-structure carbon black to fill the gaps in the framework and form bridges—ensuring that the conductive pathways in this network maintain good continuity even when the polyethylene matrix expands due to heat.

[0086] (4) PTC coefficient test: Test method: The PTC coefficient is used to characterize the temperature stability of the volume resistivity of shielding materials, and it is defined as the volume resistivity (ρ) at 90℃. 90 ) and volume resistivity at room temperature and 25℃ (ρ 25 The common logarithm of the ratio; IPTC 90 = log(ρ 90 / ρ 25 ); The smaller the value, the better the thermal stability of the material. The results are shown in Table 1.

[0087] (5) Processing rheological property test Test method: The equilibrium torque of each sample during the melt blending process was measured using a torque rheometer at 180℃ and 50rpm. The higher the torque value, the greater the melt viscosity and the worse the processing performance. The results are shown in Table 1.

[0088] (6) Tensile property test: Test method: According to GB / T 1040.2-2006 standard, the elongation at break of the specimen was tested at a tensile rate of 100 mm / min under room temperature (25±5℃) conditions. The specimen was then vertically suspended in a constant temperature oven at 110℃ for a 10-day accelerated thermal aging test. After aging, the elongation at break of the aged specimen was measured and the change rate of elongation at break before and after aging was calculated. The results are shown in Table 1. Change rate (%) = (Elongation at break before aging - Elongation at break after aging) / Elongation at break before aging × 100%.

[0089] like Figure 5 and Figure 6As shown, the tensile curves of the thermoplastic polyethylene-based power cable shielding material in Example 1 remained largely consistent before and after aging, exhibiting typical ductile fracture characteristics. That is, after yielding, it underwent significant necking and cold drawing stages until final fracture. Although the yield stress and elongation at break of the aged samples decreased slightly, the decrease was very limited. Meanwhile, as... Figure 7 and Figure 8 As shown in the figure, the shielding material for thermoplastic polyethylene power cables in Comparative Example 2, although its tensile curve before aging also showed a certain plastic deformation capacity, the necking stage after yielding was significantly shortened, the cold stretching elongation was significantly less than that in Example 1, the elongation at break was greatly reduced, and the morphology of the tensile curve after aging was essentially deteriorated. This directly indicates that its molecular chains underwent severe degradation or chain breakage during the thermo-oxidative aging process, the original tough matrix of the material was destroyed, and the mechanical properties were poor.

[0090] Table 1: Performance test results of the shielding material for thermoplastic polyethylene-based power cables in the test examples of this invention As can be seen from the results in Table 1, the thermoplastic polyethylene-based power cable shielding material of the present invention achieves a good balance between conductivity, processing performance and mechanical properties, and fully meets the comprehensive requirements of medium and high voltage power cables for shielding materials in terms of conductivity efficiency, thermal stability, processing adaptability and long-term reliability.In contrast, the comparative examples, due to their failure to follow the technical solution of this invention, all exhibited significant deterioration in key performance indicators. Specifically, Comparative Example 1, lacking a high-structure second conductive carbon black, failed to form a complete conductive network, resulting in excessively high volume resistivity and poor temperature stability. Furthermore, its low equilibrium torque indicates excessively low melt viscosity, which could lead to insufficient melt strength and poor extruded shape stability in actual extrusion processing. Additionally, its elongation at break after aging was as high as -27.1%, far inferior to the embodiments, demonstrating poor resistance to heat and oxygen aging. Comparative Example 2, due to its excessively high total conductive filler content, achieved extremely low resistivity, but its elongation at break decreased, and the decrease in elongation at break after aging was also significant. This is because the mechanical weaknesses of the material are mostly concentrated at the junction of carbon black and the matrix resin molecular chains. Increasing the carbon black content increases the number of mechanical weaknesses in the material. At the same time, a high carbon black content also makes carbon black dispersion more difficult, increasing the possibility of carbon black agglomeration. Compared with the other examples, the torque of Comparative Example 2 is significantly increased at the same temperature and speed, indicating that its material has poor extrusion and processing performance, and the carbon black is difficult to disperse evenly in the shielding material. Comparative Example 3 has an excessive proportion of small-particle-size, high-structure carbon black, resulting in severe filler agglomeration and deterioration of dispersibility, leading to a significant decrease in mechanical properties and anti-aging properties. Although its volume resistivity at room temperature is at a low level, its elongation at break after aging is as high as -19.43%, and its PTC coefficient is also higher than most others. Examples show that the temperature stability and aging resistance of the conductive network cannot meet the requirements of practical applications. In Comparative Example 4, due to the excessively high proportion of the first conductive carbon black, the content of the second conductive carbon black, which plays a filling and bridging role in the system, is seriously insufficient. This makes it impossible to effectively fill the gaps in the primary conductive skeleton constructed by large-particle carbon black, resulting in poor integrity of the three-dimensional conductive network, low density of conductive pathways, easy breakage at high temperatures, and poor temperature stability. In Comparative Example 5, high-density polyethylene is used instead of linear low-density polyethylene as the matrix resin. Due to the high crystallinity and low molecular chain branching of high-density polyethylene, its interfacial interaction with conductive carbon black is weak, which is not conducive to the uniform dispersion of carbon black in the matrix. The mechanical toughness and resistance to thermo-oxidative aging are significantly inferior. In the embodiments; the first conductive carbon black used in Comparative Example 6 had an oil absorption value exceeding the range defined by the present invention, making it difficult to achieve uniform primary dispersion in the polyethylene matrix and unable to form a stable and continuous primary conductive skeleton. At the same time, its excessively high structure also led to a significant increase in system viscosity, deterioration of processing performance, and failure to meet the requirements for use in medium and high voltage cable shielding layers in terms of conductivity and temperature stability. The second conductive carbon black used in Comparative Example 7 had an oil absorption value lower than the range defined by the present invention, with poor continuity of its conductive network and many defects. Its conductive pathways were easily broken when the polyethylene matrix was heated and expanded, resulting in extremely poor resistance and temperature stability. At the same time, the interfacial bonding with the matrix resin was weak, which easily induced the propagation of microcracks during thermo-oxidative aging, accelerating the deterioration of mechanical properties.

[0091] In summary, this invention, by carefully selecting two conductive carbon blacks with specific particle sizes and oil absorption values ​​and strictly controlling their ratio, combined with a suitable additive system and preparation process, not only achieves low and stable volume resistivity at room temperature, but also exhibits excellent performance retention under high temperature and thermal aging conditions. It successfully solves the technical problem of the difficulty in simultaneously achieving conductivity, processing performance and mechanical properties in traditional shielding materials. The resulting thermoplastic polyethylene-based shielding material for power cables has excellent comprehensive performance and broad application prospects in the field of power cables.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A shielding material for thermoplastic polyethylene-based power cables, characterized in that, It includes the following components in parts by weight: 64-78 parts of polyethylene resin, 20-30 parts of conductive filler, and 2-6 parts of additives; The conductive filler includes a first conductive carbon black and a second conductive carbon black; the oil absorption value of the first conductive carbon black is ≤200cc / 100g, and the oil absorption value of the second conductive carbon black is ≥300cc / 100g. The mass ratio of the first conductive carbon black to the second conductive carbon black is (1~4):

1.

2. The shielding material for thermoplastic polyethylene-based power cables as described in claim 1, characterized in that, The polyethylene resin is linear low-density polyethylene with a density of 0.91 g / cm³. 3 ~0.94g / cm 3 The melt index at 190℃ and 2.16kg load is 0.15g / 10min to 0.25g / 10min.

3. The shielding material for thermoplastic polyethylene-based power cables as described in claim 1, characterized in that, The first conductive carbon black has an oil absorption value of 120cc / 100g to 200cc / 100g, and the second conductive carbon black has an oil absorption value of 300cc / 100g to 400cc / 100g.

4. The shielding material for thermoplastic polyethylene-based power cables as described in claim 1, characterized in that, The particle size of the first conductive carbon black is 30nm~60nm, and the particle size of the second conductive carbon black is 10nm~20nm.

5. The shielding material for thermoplastic polyethylene-based power cables as described in claim 1, characterized in that, The additives include the following components in parts by weight: 0.1 to 1.0 parts of antioxidant and 1 to 4 parts of dispersant.

6. The shielding material for thermoplastic polyethylene-based power cables as described in claim 5, characterized in that, The antioxidant includes at least one of antioxidant 300, antioxidant 1010, and antioxidant 168.

7. The shielding material for thermoplastic polyethylene-based power cables as described in claim 5, characterized in that, The dispersant includes at least one of white oil, ethylene bis-stearamide, and oleamide.

8. A method for preparing the shielding material for thermoplastic polyethylene-based power cables according to any one of claims 1-7, characterized in that, Includes the following steps: S1. After drying, polyethylene resin, conductive filler and additives are mixed to obtain a premix; S2. The premix is ​​melt-blended, discharged, and then granulated to obtain granules. S3. Dry the granular material to obtain the shielding material for thermoplastic polyethylene-based power cables.

9. The preparation method according to claim 8, characterized in that, In step S1, the drying temperature is 50℃~70℃ and the time is 24h~36h; and / or, in step S2, the melt blending temperature is 170℃~190℃ and the rotation speed is 50rpm~60rpm; the particle size of the granules is 3mm~5mm; and / or, in step S3, the drying temperature is 50℃~70℃ and the time is 24h~36h.

10. The application of the thermoplastic polyethylene-based shielding material for power cables according to any one of claims 1-7 in the semiconductive shielding layer for medium and high voltage power cables.

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