Shielding material and method for producing same, semiconductive shielding layer and cable

Abstract

The application provides a shielding material and a preparation method thereof, a semi-conductive shielding layer and a cable. The shielding material comprises a base resin, carbon black, an antioxidant and a crosslinking agent. The base resin comprises an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin different from the ethylene-butyl acrylate copolymer. The first polyolefin has a melt index MFR1 of 1 g / 10 min-8 g / 10 min under a load of 2.16 kg at 190 ℃, and the second polyolefin has a melt index MFR2 of 12 g / 10 min-30 g / 10 min under a load of 2.16 kg at 190 ℃, and 8 g / 10 min≤MFR2-MFR1≤29 g / 10 min. After the semi-conductive shielding layer is used in the cable, the space charge injection of the semi-conductive shielding layer to the insulating layer is low, and the insulating layer has excellent polarity reversal resistance.

Description

Technical Field

[0001] This application relates to the field of high voltage DC cable materials technology, and in particular to shielding materials and their preparation methods, semiconductive shielding layers, and cables. Background Technology

[0002] With the rapid development of the Global Energy Interconnection, ultra-high voltage direct current (UHVDC) transmission has become a core technology for transnational energy interconnection due to its advantages such as long transmission distance, large capacity, low loss, and no AC synchronization issues. 500kV and above cross-linked polyethylene (XLPE) insulated power cables, as key equipment in UHVDC transmission systems, have been widely used in submarine cables, urban underground power transmission corridors, and other applications.

[0003] The semiconductive shielding layer is a crucial component of the DC cable insulation system, and its performance directly determines the long-term operational reliability of the cable. Compared to AC cables, DC cables require lower space charge injection and superior polarity reversal tolerance. In related technologies, carbon black is typically used as the conductive agent in the shielding material of the semiconductive shielding layer. When used in cables, semiconductive shielding layers prepared with this material result in higher space charge injection into the insulation layer and poorer polarity reversal tolerance of the insulation layer. Summary of the Invention

[0004] Based on this, this application provides a shielding material and its preparation method, a semiconductive shielding layer, and a cable, so that when the prepared semiconductive shielding layer is used in the cable, the space charge injection of the semiconductive shielding layer to the insulation layer is low, and the insulation layer has excellent polarity reversal tolerance.

[0005] The first aspect of this application provides a shielding material comprising a matrix resin, carbon black, an antioxidant, and a crosslinking agent. The matrix resin comprises an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin different from the ethylene-butyl acrylate copolymer. The first polyolefin has a melt flow index (MFR1) of 1 g / 10 min to 8 g / 10 min at 190°C and a load of 2.16 kg, and the second polyolefin has a melt flow index (MFR2) of 12 g / 10 min to 30 g / 10 min at 190°C and a load of 2.16 kg, wherein 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

[0006] In some embodiments, the mass ratio of the first polyolefin to the second polyolefin is (1-9):3.

[0007] In some embodiments, the mass ratio of the first polyolefin to the second polyolefin is (1.5-6):3.

[0008] In some embodiments, the first polyolefin and the second polyolefin are each independently a polyolefin elastomer.

[0009] In some embodiments, the first polyolefin and the second polyolefin are each independently an ethylene-α-olefin random copolymer.

[0010] In some embodiments, the butyl acrylate unit in the ethylene-butyl acrylate copolymer accounts for 16wt%-18wt% of the total mass.

[0011] In some embodiments, the melt index of the ethylene-butyl acrylate copolymer at 190°C and a load of 2.16 kg is 5 g / 10 min to 15 g / 10 min.

[0012] In some embodiments, the melt index of the ethylene-butyl acrylate copolymer at 190°C and a load of 2.16 kg is 6 g / 10 min to 14 g / 10 min.

[0013] In some embodiments, the carbon black is acetylene black.

[0014] In some embodiments, the total content of impurity elements in the acetylene black is <50ppm.

[0015] In some embodiments, the iodine absorption value of the acetylene black is 70 mg / g-100 mg / g.

[0016] In some embodiments, the iodine absorption value of the acetylene black is 70 mg / g-90 mg / g.

[0017] In some embodiments, the acetylene black has a DBP absorption value of 180 cm⁻¹. 3 / 100g-250 cm 3 / 100g.

[0018] In some embodiments, the Dv50 of the acetylene black is 20nm-50nm.

[0019] In some embodiments, the shielding material comprises, by weight parts: 64-68.5 parts of the matrix resin, 30-35 parts of the carbon black, 0.5-1 part of the antioxidant, and 0.5-2 parts of the crosslinking agent.

[0020] In some embodiments, the shielding material comprises, by weight parts: 64-66 parts of the matrix resin, 32-34.5 parts of the carbon black, 0.5-1 part of the antioxidant, and 0.5-2 parts of the crosslinking agent.

[0021] In some embodiments, the mass fraction of the ethylene-butyl acrylate copolymer in the shielding material is 2 to 10 parts.

[0022] In some embodiments, the mass fraction of the ethylene-butyl acrylate copolymer in the shielding material is 4 to 6 parts.

[0023] In some embodiments, the antioxidant comprises one or more of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and antioxidant 300; and / or,

[0024] The crosslinking agent includes one or more of di-tert-butyl peroxide and diisopropylbenzene peroxide.

[0025] A second aspect of this application provides a method for preparing a shielding material, comprising the following steps:

[0026] A premix is ​​prepared by extruding and granulating a melt containing a matrix resin, carbon black, and antioxidant.

[0027] The premix is ​​mixed with a crosslinking agent to prepare the shielding material;

[0028] The matrix resin includes an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin that are different from the ethylene-butyl acrylate copolymer; the first polyolefin has a melt index (MFR1) of 1 g / 10 min to 8 g / 10 min at 190 °C and 2.16 kg load, and the second polyolefin has a melt index (MFR2) of 12 g / 10 min to 30 g / 10 min at 190 °C and 2.16 kg load, where 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

[0029] In some embodiments, the method for preparing the melt includes: adding the matrix resin, the carbon black and the antioxidant into a reciprocating mixer for mixing to prepare the melt.

[0030] In some embodiments, the reciprocating mixer is a reciprocating single-screw extruder.

[0031] In some embodiments, the mixing temperature is 150℃-230℃ and the screw speed is 150rpm-300rpm.

[0032] In some embodiments, a melt pump is used for extrusion.

[0033] In some embodiments, the speed of the melt pump is 20 rpm to 50 rpm.

[0034] In some embodiments, an underwater pelletizing system is used for pelletizing.

[0035] In some embodiments, the melt is filtered using a screen changer before extrusion; optionally, the screen changer has a screen mesh size of 300-500 mesh.

[0036] In some embodiments, the step of mixing the premix with the crosslinking agent includes: placing the premix in a mixer, atomizing the crosslinking agent and spraying it into the mixer, and allowing the crosslinking agent to be fully absorbed into the premix under rotary heating conditions.

[0037] In some embodiments, the temperature of the mixer is 60°C-70°C, and the mixing speed is 3 rpm-10 rpm.

[0038] The third aspect of this application provides a semiconductive shielding layer, the raw materials for which include the shielding material of the first aspect of this application or the shielding material prepared by the preparation method of the second aspect of this application.

[0039] In some embodiments, the surface of the semiconductive shielding layer contains ≤3 protrusions with a height of 30μm-50μm per 100cm. 2 .

[0040] In some embodiments, the surface of the semiconductive shielding layer contains 0 protrusions with a height ≥ 50 μm.

[0041] The fourth aspect of this application provides a cable comprising a conductor, an inner semiconductive shielding layer, an insulating layer, and an outer semiconductive shielding layer, wherein at least one of the inner semiconductive shielding layer and the outer semiconductive shielding layer is prepared using a shielding material prepared by the method of the first aspect of this application or a shielding material prepared by the method of the second aspect of this application.

[0042] In some embodiments, the cable is a DC cable, and the cable carries a voltage ≥500kV.

[0043] The aforementioned shielding materials have at least the following beneficial effects:

[0044] (1) The shielding material of this application can achieve the goal of not adding processing aids such as zinc stearate and polyethylene wax by optimizing the composition of the matrix resin, thereby fundamentally avoiding the interface pollution and space charge accumulation problems between the semiconductive shielding layer and the insulation layer caused by the precipitation of low molecular weight additives, and significantly improving the long-term DC operation reliability of the cable.

[0045] (2) The shielding material of this application adopts a composite matrix including polyolefins and ethylene-butyl acrylate copolymers with specific melt index combinations. On the one hand, the two polyolefins within the melt index range have excellent two-phase compatibility, forming a continuous two-phase rheological system. The high-viscosity long chains are responsible for "tearing apart carbon black agglomerates", while the low-viscosity short chains are responsible for "penetrating, wetting, and transporting dispersed particles", which greatly improves the carbon black dispersion efficiency at the purely physical rheological level. On the other hand, a small amount of ethylene-butyl acrylate copolymer (EBA) resin is introduced. Due to its polar characteristics, it can form bonds with the oxygen-containing functional groups of carbon black, preventing secondary agglomeration of carbon black from a chemical level. The two aspects work together to fully disperse carbon black. The volume resistivity of the shielding material is much lower than that of traditional DC shielding materials, and the positive temperature coefficient effect (PTC effect) is extremely small, resulting in extremely stable conductivity.

[0046] (3) The excellent carbon black dispersibility and absence of processing aid precipitation of the shielding material of this application result in an extremely smooth surface of the semiconductive shielding layer prepared using this shielding material. In some embodiments, the surface of the semiconductive shielding layer has no protrusions with a height greater than 50 μm, and the number of protrusions with a height of 30 μm-50 μm is only 1-3 per 100 cm. 2 It is far superior to the 500kV DC cable standard requirements and can effectively eliminate the concentration of the interface electric field.

[0047] (4) The shielding material of this application uses two polyolefins with specific melt indexes as a compound, and ethylene-butyl acrylate copolymer is added as a matrix resin. This makes the carbon black in the semiconductive shielding layer of the shielding material uniformly dispersed. After the semiconductive shielding layer is used in the cable, the interface between the semiconductive shielding layer and the insulation layer is clean. The uniform carbon black distribution and clean interface make the electric field on the surface of the semiconductive shielding layer highly uniform, which significantly reduces the interface trap density, thereby significantly reducing the space charge injection into the insulation layer and improving the polarity reversal tolerance of the insulation layer.

[0048] (5) The shielding material of this application significantly reduces the melt viscosity of the shielding material while ensuring sufficient conductivity by optimizing the melt index ratio of the matrix resin. In some embodiments, compared with traditional DC shielding materials, the extrusion torque is significantly reduced (by approximately 20%-75%), and the processing temperature window is significantly widened (by approximately 15°C-20°C), enabling it to adapt to higher extrusion speeds. Simultaneously, the shielding material exhibits excellent melt flow properties, effectively reducing or even avoiding the formation of visible adhesive seams during cable extrusion. Detailed Implementation

[0049] To facilitate understanding of this application, a more complete description of the application will be provided below with reference to relevant embodiments. Preferred embodiments of the application are given below. However, the application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0051] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0052] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0053] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0054] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0055] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0056] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0057] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0058] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0059] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0061] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0062] The semiconductive shielding layer is one of the most critical components in the insulation system of DC cables, and its performance directly determines the long-term operational reliability of the cable. Compared to AC cables, DC cables place more stringent requirements on semiconductive shielding materials: 1. Extremely low space charge injection characteristics: Under a DC electric field, charge continuously injects from the semiconductive shielding layer into the insulation layer and accumulates, leading to distortion of the electric field inside the insulation layer. In severe cases, this can cause electrical treeing aging and insulation breakdown. 2. Excellent polarity reversal tolerance: DC cables may experience polarity reversal during operation. At this time, the electric field at the interface between the semiconductive shielding layer and the insulation layer will instantly double, placing extremely high demands on the interface performance and charge response characteristics of the shielding material. 3. Ultra-smooth surface quality: Tiny protrusions on the surface of the semiconductive shielding layer can cause severe electric field concentration under a DC electric field, becoming the source of space charge injection and the starting point of insulation breakdown. 4. Stable conductivity: The shielding material is required to have stable and low volume resistivity over a wide temperature range (20-90℃) and a small positive temperature coefficient (PTC) effect. 5. No low-molecular-weight precipitation: The precipitation of any low-molecular-weight additives will contaminate the insulation layer interface, introduce deep traps, promote space charge accumulation, and seriously affect the long-term DC performance of the cable.

[0063] In related technologies, carbon black is commonly used as a conductive agent in shielding materials. However, because carbon black is difficult to disperse uniformly in shielding materials, the semiconductive shielding layer using this material results in a high space charge injection into the insulation layer, and the insulation layer exhibits poor polarity reversal tolerance. Furthermore, shielding materials using carbon black as a conductive agent also suffer from high volume resistivity and the presence of micro-protrusions on the surface, which urgently need to be addressed.

[0064] To address the aforementioned issues, the shielding material of this application employs a blend of two polyolefins with specific melt flow index ranges, along with ethylene-butyl acrylate copolymer as the matrix resin. This achieves nanoscale uniform dispersion of carbon black, resulting in a shielding material with extremely low volume resistivity and a smooth surface quality. When the semiconductive shielding layer prepared from this material is used in cables, the space charge injection of the semiconductive shielding layer into the insulation layer is extremely low, and the insulation layer exhibits excellent polarity reversal tolerance. Furthermore, this shielding material also possesses excellent processing performance, improving upon the bonding seam problem and processing aid precipitation problem present in traditional DC shielding materials. It fully meets the usage requirements for DC cables with a carrying voltage of 500kV and above.

[0065] The first aspect of this application provides a shielding material comprising a matrix resin, carbon black, an antioxidant, and a crosslinking agent. The matrix resin comprises an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin, which are different from the ethylene-butyl acrylate copolymer. The first polyolefin has a melt flow index (MFR1) of 1 g / 10 min to 8 g / 10 min at 190 °C and a load of 2.16 kg, and the second polyolefin has a melt flow index (MFR2) of 12 g / 10 min to 30 g / 10 min at 190 °C and a load of 2.16 kg, wherein 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

[0066] It should be noted that the "first polyolefin and second polyolefin different from ethylene-butyl acrylate copolymer" mentioned in the context refers to the fact that the types of the first polyolefin and second polyolefin are different from those of ethylene-butyl acrylate copolymer.

[0067] As an example, the melt flow index (MFR1) of the first polyolefin at 190°C and a load of 2.16 kg can be, but is not limited to, 1 g / 10 min, 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, or any range between two of the above melt flow indices. This is beneficial for ensuring that the shielding material possesses good mechanical properties and thermal stability.

[0068] The melt flow index (MFR2) of the second polyolefin at 190°C and 2.16 kg load can be, but is not limited to, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, 15 g / 10 min, 16 g / 10 min, 17 g / 10 min, 18 g / 10 min, 19 g / 10 min, 20 g / 10 min, 21 g / 10 min, 22 g / 10 min, 23 g / 10 min, 24 g / 10 min, 25 g / 10 min, 26 g / 10 min, 27 g / 10 min, 28 g / 10 min, 29 g / 10 min, 30 g / 10 min, or any range between two of the above melt flow indices. This is beneficial for giving the shielding material excellent melt flowability and processability.

[0069] The difference between the melt index of the second polyolefin and the first olefin, MFR2-MFR1, can be, but is not limited to, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, 15 g / 10 min, 16 g / 10 min, 17 g / 10 min, 18 g / 10 min, 19 g / 10 min, 20 g / 10 min, 21 g / 10 min, 22 g / 10 min, 23 g / 10 min, 24 g / 10 min, 25 g / 10 min, 26 g / 10 min, 27 g / 10 min, 28 g / 10 min, 29 g / 10 min, or any range between any two of the above melt indices. Therefore, when the difference in melt index between the second polyolefin and the first olefin, MFR2-MFR1, is within the above range, it is beneficial to give the matrix resin a wider processing window and viscosity difference, and to make the carbon black more uniformly dispersed, thereby giving the shielding material better surface smoothness and conductivity.

[0070] Understandably, the shielding material of this application has at least the following beneficial effects:

[0071] (1) The shielding material of this application can achieve the goal of not adding processing aids such as zinc stearate and polyethylene wax by optimizing the composition of the matrix resin, thereby fundamentally avoiding the interface pollution and space charge accumulation problems between the semiconductive shielding layer and the insulation layer caused by the precipitation of low molecular weight additives, and significantly improving the long-term DC operation reliability of the cable.

[0072] (2) The shielding material of this application adopts a composite matrix including polyolefins and ethylene-butyl acrylate copolymers with specific melt index combinations. On the one hand, the two polyolefins within the melt index range have excellent two-phase compatibility, forming a continuous two-phase rheological system. The high-viscosity long chains are responsible for "tearing apart carbon black agglomerates", while the low-viscosity short chains are responsible for "penetrating, wetting, and transporting dispersed particles", which greatly improves the carbon black dispersion efficiency at the purely physical rheological level. On the other hand, a small amount of ethylene-butyl acrylate copolymer (EBA) resin is introduced. Due to its polar characteristics, it can form bonds with the oxygen-containing functional groups of carbon black, preventing secondary agglomeration of carbon black from a chemical level. The two aspects work together to fully disperse carbon black. The volume resistivity of the shielding material is much lower than that of traditional DC shielding materials, and the positive temperature coefficient effect (PTC effect) is extremely small, resulting in extremely stable conductivity.

[0073] (3) The excellent carbon black dispersibility and absence of processing aid precipitation of the shielding material of this application result in an extremely smooth surface of the semiconductive shielding layer prepared using this shielding material. In some embodiments, the surface of the semiconductive shielding layer has no protrusions with a height greater than 50 μm, and the number of protrusions with a height of 30 μm-50 μm is only 1-3 per 100 cm. 2It is far superior to the 500kV DC cable standard requirements and can effectively eliminate the concentration of the interface electric field.

[0074] (4) The shielding material of this application uses two polyolefins with specific melt indexes as a compound, and ethylene-butyl acrylate copolymer is added as a matrix resin. This makes the carbon black in the semiconductive shielding layer of the shielding material uniformly dispersed. After the semiconductive shielding layer is used in the cable, the interface between the semiconductive shielding layer and the insulation layer is clean. The uniform carbon black distribution and clean interface make the electric field on the surface of the semiconductive shielding layer highly uniform, which significantly reduces the interface trap density, thereby significantly reducing the space charge injection into the insulation layer and improving the polarity reversal tolerance of the insulation layer.

[0075] (5) The shielding material of this application significantly reduces the melt viscosity of the shielding material while ensuring sufficient conductivity by optimizing the melt index ratio of the matrix resin. In some embodiments, compared with traditional DC shielding materials, the extrusion torque is significantly reduced (by approximately 20%-75%), and the processing temperature window is significantly widened (by approximately 15°C-20°C), enabling it to adapt to higher extrusion speeds. Simultaneously, the shielding material exhibits excellent melt flow properties, effectively reducing or even avoiding the formation of visible adhesive seams during cable extrusion.

[0076] It should be noted that in this application, terms such as "first polyolefin" and "second polyolefin" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first" and "second" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0077] In some embodiments, the mass ratio of the first polyolefin and the second polyolefin is (1-9):3; for example, it can be, but is not limited to, 1:3, 2:3, 3:3, 4:3, 5:3, 6:3, 7:3, 8:3, 9:3, or any range between the above two mass ratios. The first olefin is beneficial for giving the shielding material good mechanical properties and thermal stability, while the second olefin is beneficial for giving the shielding material excellent melt flowability and processability. When the first olefin and the second olefin are compounded and used in the above mass ratio, an optimal balance can be achieved between mechanical properties and processability.

[0078] In some alternative embodiments, the mass ratio of the first polyolefin to the second polyolefin is (1.5-6):3.

[0079] In one possible implementation, the first polyolefin and the second polyolefin are each independently a polyolefin elastomer. This provides excellent melt flowability and processability for the shielding material, while improving carbon black dispersion and reducing space charge generation.

[0080] In some alternative embodiments, the first polyolefin and the second polyolefin are each independently an ethylene-α-olefin random copolymer (POE).

[0081] In some embodiments, the butyl acrylate units in the ethylene-butyl acrylate copolymer (EBA) account for 16wt%-18wt% by mass; for example, it can be, but is not limited to, 16wt%, 17wt%, 18wt%, or any range between the above two mass percentages. The polar butyl acrylate segments in the EBA molecule can form hydrogen bonds with the oxygen-containing functional groups on the carbon black surface. When the mass percentage of butyl acrylate units in the EBA is within the above range, it can significantly improve the interfacial properties between carbon black and the matrix resin and promote carbon black dispersion.

[0082] In some embodiments, the melt index of the ethylene-butyl acrylate copolymer at 190°C and a load of 2.16 kg is 5 g / 10 min to 15 g / 10 min. For example, it can be, but is not limited to, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, 11 g / 10 min, 12 g / 10 min, 13 g / 10 min, 14 g / 10 min, 15 g / 10 min, or any range between two of the above melt indices. Therefore, when EBA at this melt index is compounded with the aforementioned polyolefins with specific melt indices, it can provide optimal melt viscosity and flowability, promoting carbon black dispersion.

[0083] In some alternative embodiments, the ethylene-butyl acrylate copolymer has a melt index of 6 g / 10 min to 14 g / 10 min at 190 °C and a load of 2.16 kg.

[0084] In some implementations, the carbon black is acetylene black.

[0085] As one possible implementation method, the total content of impurity elements in acetylene black is <50ppm; this helps to reduce interface protrusions and suppress space charge generation.

[0086] In some embodiments, the iodine absorption value of acetylene black is 70 mg / g-100 mg / g; for example, it can be, but is not limited to, 70 mg / g, 80 mg / g, 90 mg / g, 100 mg / g, or any range between two of the above iodine absorption values. In some optional embodiments, the iodine absorption value of acetylene black is 70 mg / g-90 mg / g.

[0087] As one possible implementation, the DBP absorption value of acetylene black is 180 cm⁻¹. 3 / 100g-250 cm3 / 100g; for example, it can be, but is not limited to, 180cm. 3 / 100g, 190cm 3 / 100g, 200cm 3 / 100g, 210cm 3 / 100g, 220cm 3 / 100g, 230cm 3 / 100g, 240cm 3 / 100g, 250cm 3 / 100g or the range between any two of the above DBP absorption values, etc.

[0088] Therefore, when the iodine absorption value and DBP absorption value of acetylene black are within the above ranges, acetylene black not only has a certain degree of structure, but also good processing and dispersibility, which is more conducive to imparting good electrical conductivity to shielding materials and promoting carbon black dispersion.

[0089] In some embodiments, the Dv50 of acetylene black is 20nm-50nm; for example, it can be, but is not limited to, 20nm, 30nm, 40nm, 50nm or any two of the above particle sizes.

[0090] In some embodiments, the shielding material comprises, by weight parts: 64-68.5 parts of matrix resin, 30-35 parts of carbon black, 0.5-1 part of antioxidant, and 0.5-2 parts of crosslinking agent. Therefore, the shielding material prepared under this formulation exhibits good conductivity and excellent surface smoothness. When the semiconductive shielding layer prepared from this material is used in a cable, the space charge injection of the semiconductive shielding layer into the insulation layer is extremely low, and the insulation layer exhibits excellent polarity reversal tolerance. Furthermore, this shielding material also possesses excellent processing performance, which can improve the bonding seam problem and processing aid precipitation problem existing in traditional DC shielding materials.

[0091] As an example, the mass fraction of the matrix resin contained in the shielding material, by mass fraction, can be, but is not limited to, 64 parts, 64.5 parts, 65 parts, 65.5 parts, 66 parts, 66.5 parts, 67 parts, 67.5 parts, 68 parts, 68.5 parts, or any range between any two of the above mass fractions.

[0092] The mass fraction of carbon black contained in the shielding material can be, but is not limited to, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, or any range between two of the above mass fractions, in parts by weight.

[0093] The number of parts by weight of antioxidant contained in the shielding material can be, but is not limited to, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, or any range between any two of the above numbers.

[0094] The mass fraction of crosslinking agent contained in the shielding material can be, but is not limited to, 0.5 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts, or any range between any two of the above mass fractions, in parts by weight.

[0095] In some alternative embodiments, the shielding material comprises, by weight parts: 64-66 parts of the matrix resin, 32-34.5 parts of the carbon black, 0.5-1 part of the antioxidant, and 0.5-2 parts of the crosslinking agent.

[0096] In some embodiments, the shielding material contains 2 to 10 parts by weight of ethylene-butyl acrylate copolymer; for example, but not limited to 2, 3, 4, 5, 6, 7, 8, 9, 10 parts, or any range between two of the above. This provides sufficient polarity to reduce carbon black agglomeration without affecting the dispersion of carbon black in the polyolefin main resin matrix.

[0097] In some alternative embodiments, the shielding material contains 4 to 6 parts by weight of ethylene-butyl acrylate copolymer.

[0098] As one possible implementation, the total mass fraction of the matrix resin, carbon black, antioxidant, and crosslinking agent in the shielding material is 100 parts.

[0099] In some exemplary embodiments, the antioxidant includes one or more of 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMQ) and antioxidant 300.

[0100] As one possible implementation, the crosslinking agent includes one or more of bis-tert-butyl peroxide diisopropylbenzene (BIPB) and diisopropylbenzene peroxide (DCP).

[0101] The second aspect of this application provides a method for preparing a shielding material, which can be used to prepare the shielding material of the first aspect of this application. The preparation method includes the following steps: extruding and granulating a melt containing a matrix resin, carbon black, and an antioxidant to prepare a premix; mixing the premix with a crosslinking agent to prepare the shielding material; wherein the matrix resin includes an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin different from the ethylene-butyl acrylate copolymer; the melt index (MFR1) of the first polyolefin at 190°C and a load of 2.16 kg is 1 g / 10 min to 8 g / 10 min, and the melt index (MFR2) of the second polyolefin at 190°C and a load of 2.16 kg is 12 g / 10 min to 30 g / 10 min, where 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

[0102] Understandably, the method for preparing the shielding material of this application has at least the following beneficial effects:

[0103] (1) The preparation method of the shielding material, by optimizing the composition of the matrix resin, can achieve the goal of not adding processing aids such as zinc stearate and polyethylene wax, thereby fundamentally avoiding the interface pollution and space charge accumulation problems between the semiconductive shielding layer and the insulation layer caused by the precipitation of low molecular weight additives, and significantly improving the long-term DC operation reliability of the cable.

[0104] (2) The preparation method of this shielding material uses a composite matrix including polyolefins and ethylene-butyl acrylate copolymers with specific melt index combinations. On the one hand, the two polyolefins within the melt index range have excellent two-phase compatibility, forming a continuous two-phase rheological system. The high-viscosity long chains are responsible for "tearing apart carbon black agglomerates", while the low-viscosity short chains are responsible for "penetrating, wetting, and transporting dispersed particles", which greatly improves the carbon black dispersion efficiency at the purely physical rheological level. On the other hand, a small amount of ethylene-butyl acrylate copolymer (EBA) resin is introduced. Due to its polar characteristics, it can form bonds with the oxygen-containing functional groups of carbon black, preventing secondary agglomeration of carbon black from a chemical level. The two aspects work together to fully disperse carbon black. The resulting shielding material has a volume resistivity much lower than that of traditional DC shielding materials, and the positive temperature coefficient effect (PTC effect) is extremely small, resulting in extremely stable conductivity.

[0105] (3) The shielding material prepared by this method has excellent carbon black dispersibility and no processing aid precipitation, resulting in an extremely smooth surface of the semiconductive shielding layer prepared using this material. In some embodiments, the surface of the semiconductive shielding layer has no protrusions with a height greater than 50 μm, and the number of protrusions with a height of 30 μm-50 μm is only 1-3 per 100 cm. 2 It is far superior to the 500kV DC cable standard requirements and can effectively eliminate the concentration of the interface electric field.

[0106] (4) The method for preparing the shielding material involves using two polyolefins with specific melt indices, and simultaneously adding ethylene-butyl acrylate copolymer as the matrix resin. When the shielding material is used to prepare a semiconductive shielding layer, the carbon black in the prepared semiconductive shielding layer is uniformly dispersed. After the semiconductive shielding layer is used in the cable, the interface between the semiconductive shielding layer and the insulation layer is clean. The uniform carbon black distribution and clean interface make the electric field on the surface of the semiconductive shielding layer highly uniform, significantly reducing the interface trap density, thereby significantly reducing the space charge injection into the insulation layer and improving the polarity reversal tolerance of the insulation layer.

[0107] (5) The method for preparing this shielding material, by optimizing the melt index ratio of the matrix resin, results in a shielding material with significantly reduced melt viscosity while maintaining sufficient conductivity. In some embodiments, compared with traditional DC shielding materials, the extrusion torque is significantly reduced (by approximately 20%-75%), and the processing temperature window is significantly widened (by approximately 15°C-20°C), enabling it to adapt to higher extrusion speeds. Simultaneously, the shielding material exhibits excellent melt flow properties, effectively reducing or even preventing the formation of visible adhesive seams during cable extrusion.

[0108] (6) The preparation method of this shielding material ensures high product quality stability through continuous production process and precise metering control system. In some embodiments, the batch-to-batch volume resistivity fluctuation is less than ±5%, which is far better than the batch-to-batch volume resistivity fluctuation of traditional mixing process, and can meet the requirements of large-scale production of 500kV DC cables.

[0109] It should be noted that the shielding material prepared by this method has similar technical solutions and beneficial effects to the shielding materials mentioned above, and will not be elaborated further here.

[0110] In some embodiments, the method for preparing the melt includes: adding a matrix resin, carbon black, and an antioxidant into a reciprocating mixer for mixing to prepare the melt.

[0111] In some alternative implementations, the reciprocating mixer is a reciprocating single-screw extruder. The reciprocating single-screw extruder, through the rotation and axial reciprocating motion of the screw, generates shearing, stretching, and folding forces 3-5 times stronger than those of a traditional twin-screw extruder, enabling the uniform nanoscale dispersion of carbon black without the addition of any processing aids.

[0112] As one possible implementation, the mixing temperature is 150℃-230℃; for example, it can be, but is not limited to, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃ or any range between two of the above temperatures.

[0113] In some alternative embodiments, the screw speed for mixing is 150 rpm to 300 rpm; for example, it can be, but is not limited to, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, or any range between two of the above screw speeds.

[0114] When the mixing temperature and screw speed are within the above ranges, it can promote the uniform dispersion of carbon black.

[0115] It should be noted that the mixing temperature and screw speed can be combined in any suitable way, and both can be selected from any mixing temperature and screw speed described in this article.

[0116] In some implementations, a melt pump is used for extrusion.

[0117] As one possible implementation, a melt pump is used for extrusion, with the pump rotating at a speed of 20-50 rpm; for example, but not limited to 20 rpm, 30 rpm, 40 rpm, 50 rpm, or any range between two of the above speeds. Thus, the melt pump can provide stable extrusion pressure and flow rate, ensuring the uniformity of underwater pelletizing and the stability of product quality.

[0118] In some embodiments, an underwater pelletizing system is used for pelletizing.

[0119] In some implementations, a screen changer is used to filter the melt before extrusion.

[0120] In some alternative implementations, the melt is filtered using a screen changer with a screen mesh size of 300-500 mesh before extrusion.

[0121] In some embodiments, the step of mixing the premix with the crosslinking agent includes: placing the premix in a mixer, atomizing the crosslinking agent and spraying it into the mixer, and then allowing the crosslinking agent to be fully absorbed into the premix under rotary heating conditions. The atomization spraying technology enables the crosslinking agent to be uniformly distributed on the surface of the premix in the form of tiny droplets of 10μm-50μm, and then gradually penetrates into the interior of the premix under heating conditions, avoiding the problem of localized over-crosslinking or under-crosslinking caused by uneven dispersion of the crosslinking agent in traditional processes.

[0122] In some alternative implementations, the temperature of the mixer is 60°C-70°C; for example, it can be, but is not limited to, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, or any range between two of the above temperatures.

[0123] In some alternative implementations, the mixing speed of the mixer is 3 rpm to 10 rpm; for example, it can be, but is not limited to, 3 rpm, 4 rpm, 5 rpm, 6 rpm, 7 rpm, 8 rpm, 9 rpm, 10 rpm, or any range between two of the above speeds.

[0124] When the temperature and mixing speed of the mixer are within the above ranges, it can promote the uniform dispersion of carbon black while ensuring that the resin does not degrade.

[0125] The third aspect of this application provides a semiconductive shielding layer, the raw materials for which the semiconductive shielding layer is prepared include the shielding material of the first aspect of this application or the shielding material prepared by the preparation method of the second aspect of this application.

[0126] In some embodiments, the surface of the semiconductive shielding layer contains ≤3 protrusions with a height of 30μm-50μm per 100cm. 2 .

[0127] In some embodiments, the surface of the semiconductive shielding layer contains 0 protrusions with a height ≥ 50 μm.

[0128] As an example, the method for preparing a semi-conductive shielding layer includes: preparing a cable using a three-layer co-extrusion extruder, extruding the shielding material using a single-screw extruder, and forming a semi-conductive shielding layer by a three-layer co-extrusion die head, wherein both the insulating shielding layer and the conductor shielding layer are semi-conductive shielding layers.

[0129] The fourth aspect of this application provides a cable comprising a conductor, an inner semiconductive shielding layer, an insulating layer, and an outer semiconductive shielding layer, wherein at least one of the inner and outer semiconductive shielding layers is prepared using a shielding material prepared by the shielding material of the first aspect of this application or the preparation method of the second aspect of this application.

[0130] In some implementations, the cable is a DC cable with a carrying voltage ≥500kV.

[0131] The technical solutions of this application will be described in detail below with reference to specific embodiments. It should be understood that these embodiments are only for illustrating this application and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application first, or follow experimental manuals or conventional conditions in the field, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the field.

[0132] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0133] Unless otherwise specified, all raw materials in the following examples and comparative examples are commercially available or prepared using conventional methods.

[0134] The sources of materials and instruments used in the following embodiments and comparative examples are as follows:

[0135] Reciprocating mixer: Swiss BUSS AG, model: MX-58;

[0136] POE-1: Wanhua Chemical, POE 5039, melt index 3g / 10min, 190℃ / 2.16kg;

[0137] POE-2: Wanhua Chemical, POE 9147, melt index 14g / 10min, 190℃ / 2.16kg;

[0138] POE-3: Dow Chemical, ENGAGE 8440, melt index 1 g / 10 min, 190℃ / 2.16 kg;

[0139] POE-4: Wanhua Chemical, POE 5069, melt index 6g / 10min, 190℃ / 2.16kg;

[0140] POE-5: Dow Chemical, ENGAGE 8402, melt index 30 g / 10 min, 190 °C / 2.16 kg;

[0141] POE-6: Dow Chemical, ENGAGE 8400, melt index 8 g / 10 min, 190℃ / 2.16 kg;

[0142] POE-7: Dow Chemical, ENGAGE 39001, melt index 4 g / 10 min, 190℃ / 2.16 kg;

[0143] POE-8: ExxonMobil, Exact 5061, melt flow index 12g / 10min, 190℃ / 2.16kg;

[0144] POE-9: ExxonMobil, POE0210, melt index 10g / 10min, 190℃ / 2.16kg;

[0145] POE-10: Wanhua Chemical, POE5136, melt index 13.5g / 10min, 190℃ / 2.16kg;

[0146] POE-11: Wanhua Chemical, POE5007, melt index 0.5g / 10min, 190℃ / 2.16kg;

[0147] EBA: Dow Chemical, 3717, melt index 7 g / 10 min, 190℃ / 2.16 kg; butyl acrylate content 16 wt%

[0148] EBA: Lucobi, 1400MN, melt index 7g / 10min, 190℃ / 2.16kg; butyl acrylate content 17wt%;

[0149] EBA: LyondellBasell, 2700M, melt index 6g / 10min, 190℃ / 2.16kg; butyl acrylate content 18wt%

[0150] EBA: Lucobi, 1400PN, melt index 14g / 10min, 190℃ / 2.16kg; butyl acrylate content 17wt%;

[0151] Carbon black: DENKA acetylene black (Nippon Denka).

[0152] Crosslinking agent: bis(tert-butylperoxyisopropylbenzene) (BIPB), 99% purity, Akoma;

[0153] Antioxidant: Antioxidant TMQ.

[0154] In the following examples and comparative examples, "parts" refers to parts by mass, where each part by mass represents 1000g.

[0155] I. Preparation of Shielding Materials

[0156] 1. Component Composition

[0157] The component compositions of Examples 1-6 are shown in Table 1. The component compositions of Comparative Examples 1-6 are shown in Table 2.

[0158] Table 1

[0159]

[0160] Table 2

[0161]

[0162] 2. Preparation process

[0163] The preparation steps for the above embodiments and comparative examples are as follows:

[0164] Step 1: The matrix resin, acetylene black and antioxidant are precisely metered through a loss-in-weight feeding system and continuously added to a reciprocating single screw extruder for mixing. The mixing temperature is 190℃, the screw speed is 220rpm, and the material residence time is 7 minutes.

[0165] Step 2: The mixed melt is filtered through a 400-mesh screen changer and then extruded under pressure by a melt pump. The melt pump speed is 35 rpm and the extrusion pressure is 5 MPa.

[0166] Step 3: The extruded melt is granulated by an underwater pelletizing system, and then centrifugally dried and fluidized bed dried to obtain premixed pellets;

[0167] Step 4: Feed the premixed granules into a low-speed mixer. Spray the crosslinking agent BIPB evenly into the mixer through an atomizing nozzle. The mixer temperature is 65℃, the mixing speed is 6 rpm, and the mixing time is 10 minutes.

[0168] Step 5: Cool to room temperature to obtain the shielding material.

[0169] II. Performance Testing

[0170] The shielding materials prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0171] 1. Mechanical property testing: The testing methods are in accordance with ISO 527, ISO 178 and ISO 180 standards, using the INSTRON 5966 tensile tester.

[0172] 2. Heat extension: It shall be performed in accordance with GB / T 2951.5, and the sample preparation shall be performed in accordance with GB / T 1040.2.

[0173] 3. Volume resistivity: The volume resistivity at 23 ℃ shall be determined in accordance with GB / T 3048.3, and the sample shall be acclimated in an environment with a temperature of 23±3 ℃ and a relative humidity of 50±5% for no less than 24 h. The volume resistivity at 90 ℃ shall be determined in accordance with Appendix A of GB / T 3048.3. The volume resistivity at 90 ℃ after 7 days of heat aging at 135 ℃ shall be determined in accordance with Appendix A of GB / T 3048.3, and the heat aging shall be performed in accordance with GB / T 2951.12.

[0174] 4. Surface protrusions: The testing shall be conducted in accordance with Appendix A of Q / GDW 11883.2—2018 standard. The resolution of protrusion height by the detector should be better than 10 μm. Sampling and testing standards: Class 1000 cleanroom.

[0175] 5. Maximum extrusion torque: Record the torque displayed by the surface protrusion detector.

[0176] 6. Space Charge: The space charge was measured using the pulse electroacoustic (PEA) method, employing a solid dielectric space charge testing system built by Shanghai Jiao Tong University. The semiconductive electrodes used the shielding materials from the examples and comparative studies, and the insulating layer was Borealis LS4258DCE. The FEF parameter was introduced to characterize the space charge. ,in It is the peak height (mV) of the ground electrode signal voltage when a high voltage U = 30kV is applied; At low voltages where there is no space charge The peak height of the ground electrode signal voltage (mV) during calibration measurements at (kV). When stray charges are near the ground electrode, the electric field will be higher than the calculated field assuming no space charge, i.e., FEF > 1. Conversely, when like charges are present, the field is lower, i.e., FEF < 1. The optimal value is FEF = 1, indicating that space charge has no effect on the ground electrode electric field. The closer the FEF value is to 1, the less space charge is generated. The FEF test after polarity reversal is the same as above, only the electrode is reversed.

[0177] 7. Joint Height - Interface Protrusion: Joint problems can be quantitatively assessed by measuring the interface protrusion height at the interface between the insulation shield and the insulation layer. According to Appendix E of the 500kV cable national standard GB / T 22078.1, "Impurities, Micropores, and Micropores and Protrusions at the Interface between Semiconductor Shielding Layer and Insulation Layer," the standard requires that there should be no protrusion at the interface greater than or equal to 0.05mm.

[0178] The test results of the above embodiments are shown in Table 3, and the test results of the comparative examples are shown in Table 4.

[0179] Table 3

[0180]

[0181] Table 4

[0182]

[0183] As shown in Tables 3 and 4, the basic properties of the shielding materials in Examples 1-6 all met the specifications specified in GB / T31489—2020. Compared with Comparative Examples 1-6, the shielding materials in Examples 1-6 have superior mechanical properties, lower volume resistivity, significantly reduced surface protrusions, smaller extrusion torque during processing, no glue seam issues, and the protrusion height at the interface between the outer screen and the insulation layer meets the standard. Furthermore, the amount of space charge injected, both before and after polarity reversal, is also less. This application demonstrates that by using two polyolefins with specific melt indices and a melt index difference within a specific range, nanoscale uniform dispersion of carbon black is achieved. The shielding material exhibits extremely low volume resistivity and a smooth surface quality. When the semiconductive shielding layer prepared from the shielding material is used in cables, the space charge injection of the semiconductive shielding layer into the insulation layer is extremely low, and the insulation layer exhibits excellent polarity reversal tolerance. The shielding material also possesses excellent processing performance, improving upon the bonding seam problem and processing aid precipitation problem existing in traditional DC shielding materials, and fully meeting the usage requirements of DC cables with a carrying voltage of 500kV and above.

[0184] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0185] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A shielding material, characterized in that, The product comprises a matrix resin, carbon black, antioxidants, and crosslinking agents. The matrix resin comprises an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin, which are different from the ethylene-butyl acrylate copolymer. The first polyolefin has a melt flow index (MFR1) of 1 g / 10 min to 8 g / 10 min at 190 °C and a load of 2.16 kg, and the second polyolefin has a melt flow index (MFR2) of 12 g / 10 min to 30 g / 10 min at 190 °C and a load of 2.16 kg, wherein 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

2. The shielding material as described in claim 1, characterized in that, The mass ratio of the first polyolefin to the second polyolefin is (1-9):3, optionally (1.5-6):3; and / or, The first polyolefin and the second polyolefin are each independently a polyolefin elastomer; Optionally, the first polyolefin and the second polyolefin are each independently an ethylene-α-olefin random copolymer.

3. The shielding material as described in claim 1, characterized in that, The ethylene-butyl acrylate copolymer contains 16wt%-18wt% butyl acrylate units by mass; and / or, The ethylene-butyl acrylate copolymer has a melt index of 5 g / 10 min to 15 g / 10 min at 190 °C and 2.16 kg load, and can be optionally 6 g / 10 min to 14 g / 10 min.

4. The shielding material as described in claim 1, characterized in that, The carbon black is acetylene black; Optionally, the total content of impurity elements in the acetylene black is <50ppm; Optionally, the iodine absorption value of the acetylene black is 70 mg / g-100 mg / g, and can be optionally 70 mg / g-90 mg / g; Optionally, the acetylene black has a DBP absorption value of 180 cm⁻¹. 3 / 100g-250 cm 3 / 100g; Optionally, the Dv50 of the acetylene black is 20nm-50nm.

5. The shielding material according to any one of claims 1 to 4, characterized in that, The shielding material comprises, by weight parts: 64-68.5 parts of the matrix resin, 30-35 parts of the carbon black, 0.5-1 part of the antioxidant, and 0.5-2 parts of the crosslinking agent; Optionally, by weight, the shielding material comprises: 64-66 parts of the matrix resin, 32-34.5 parts of the carbon black, 0.5-1 part of the antioxidant, and 0.5-2 parts of the crosslinking agent; Optionally, the ethylene-butyl acrylate copolymer in the shielding material comprises 2-10 parts by mass, optionally 4-6 parts; and / or, The antioxidant includes one or more of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and antioxidant 300; and / or, The crosslinking agent includes one or more of di-tert-butyl peroxide and diisopropylbenzene peroxide.

6. A method for preparing a shielding material, characterized in that, Includes the following steps: A premix is ​​prepared by extruding and granulating a melt containing a matrix resin, carbon black, and antioxidant. The premix is ​​mixed with a crosslinking agent to prepare the shielding material; The matrix resin includes an ethylene-butyl acrylate copolymer and a first polyolefin and a second polyolefin that are different from the ethylene-butyl acrylate copolymer; the first polyolefin has a melt index (MFR1) of 1 g / 10 min to 8 g / 10 min at 190 °C and 2.16 kg load, and the second polyolefin has a melt index (MFR2) of 12 g / 10 min to 30 g / 10 min at 190 °C and 2.16 kg load, where 8 g / 10 min ≤ MFR2 - MFR1 ≤ 29 g / 10 min.

7. The method for preparing the shielding material as described in claim 6, characterized in that, The method for preparing the melt includes: adding the matrix resin, the carbon black, and the antioxidant to a reciprocating mixer for mixing to prepare the melt; optionally, the reciprocating mixer is a reciprocating single-screw extruder; optionally, the mixing temperature is 150℃-230℃, and the screw speed is 150rpm-300rpm; and / or, Extrusion is performed using a melt pump; optionally, the melt pump rotates at a speed of 20 rpm to 50 rpm; and / or, Granulation is performed using an underwater pelletizing system; and / or, Before extrusion, the melt is filtered using a screen changer; optionally, the screen size of the screen changer is 300-500 mesh.

8. The method for preparing the shielding material as described in claim 6 or 7, characterized in that, The step of mixing the premix with the crosslinking agent includes: placing the premix in a mixer, atomizing the crosslinking agent and spraying it into the mixer, and allowing the crosslinking agent to be fully absorbed into the premix under rotary heating conditions; optionally, the temperature of the mixer is 60℃-70℃, the mixing speed is 3rpm-10rpm, and the mixing time is 5 minutes-15 minutes.

9. A semiconductive shielding layer, characterized in that, The raw materials for preparing the semiconductive shielding layer include the shielding material according to any one of claims 1 to 5 or the shielding material prepared by the preparation method according to any one of claims 6 to 8; Optionally, the surface of the semiconductive shielding layer contains ≤3 protrusions with a height of 30μm-50μm per 100cm. 2 ; Optionally, the surface of the semiconductive shielding layer contains zero protrusions with a height ≥ 50 μm.

10. A cable, characterized in that, It includes a conductor, an inner semiconducting shielding layer, an insulating layer, and an outer semiconducting shielding layer, wherein at least one of the inner semiconducting shielding layer and the outer semiconducting shielding layer is prepared using a shielding material prepared by any one of claims 1 to 5 or by any one of claims 6 to 8; Optionally, the cable is a DC cable, and the cable carries a voltage ≥500kV.

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