Cross-linked polyethylene insulated flame-retardant power cable and preparation method thereof

Abstract

The invention relates to a crosslinked polyethylene insulated flame-retardant power cable and a preparation method thereof.The preparation method comprises the steps that low-density polyethylene, Mg (OH) 2, dicumyl peroxide and an antioxidant are mixed and then subjected to extrusion granulation in a double-screw extruder at the temperature of 100-130 DEG C, the screw rotating speed is controlled to range from 180 rpm to 220 rpm, the shearing rate is controlled to range from 450 s <-1 > to 550 s <-1 >, and pre-crosslinked master batches are obtained; coating the pre-crosslinked master batch outside a conductor through a single screw extruder to form an insulating layer with the thickness of 1.5-5.0 mm, and then carrying out electron beam irradiation treatment; and a shielding layer and a sheath layer are sequentially coated outside the insulating layer. According to the preparation method disclosed by the invention, through two-step crosslinking, the failure of the flame retardant and the overhigh rigidity are avoided, and the dosage waste and interface defects of pure irradiation crosslinking are overcome, so that the cable insulating layer has high flame retardance, excellent mechanical property and stable dielectric property, and meanwhile, the energy consumption in the cable manufacturing process is reduced.

Description

Technical Field

[0001] This application relates to the technical field of polymer materials, and particularly to a cross-linked polyethylene insulated flame-retardant power cable and a preparation method thereof. Background Art

[0002] Cross-linked polyethylene (XLPE) insulated power cables are widely used in medium and high voltage power transmission and distribution fields due to their excellent electrical properties and heat resistance. Traditional chemical cross-linking processes usually use peroxides to initiate the cross-linking of polyethylene at high temperatures. However, this process requires heating the material to above 170°C to fully decompose the cross-linking agent. During this process, flame retardants (such as magnesium hydroxide) are prone to thermal decomposition, resulting in a decrease in flame retardant efficiency. In addition, the network structure formed by single chemical cross-linking has strong rigidity, and microcracks are likely to appear when the cable is bent, which may cause insulation failure during long-term operation.

[0003] In the prior art, there are also solutions that use radiation cross-linking to replace chemical cross-linking. It directly initiates the cross-linking of polyethylene through high-energy electron beams. Although it can avoid the damage of high temperatures to flame retardants, a relatively high radiation dose needs to be applied to achieve sufficient cross-linking degree, resulting in a significant increase in production costs. At the same time, during the radiation process, due to the difference in energy absorption between the flame retardant particles and the matrix interface, local overheating is likely to occur, exacerbating the agglomeration of flame retardants, causing internal defects in the insulation layer, and affecting the breakdown strength of the cable.

[0004] Furthermore, conventional cross-linking processes are difficult to balance the flexibility and mechanical strength of the cable. The dense network formed by chemical cross-linking can improve the tensile strength, but it will significantly reduce the elongation at break; while simple radiation cross-linking retains some flexibility, but it is difficult to meet the requirements of medium and high voltage cables for the anti-deformation ability of the insulation layer. In addition, the problem of electrical property deterioration caused by uneven dispersion of flame retardants has not been effectively solved, restricting the long-term reliability of the cable in harsh environments. Summary of the Invention

[0005] This application provides a preparation method for a cross-linked polyethylene insulated flame-retardant power cable, including the following steps:

[0006] S10. After mixing 100 parts by weight of low-density polyethylene, 40 - 60 parts by weight of Mg(OH)₂, 0.7 - 0.9 parts by weight of diisopropylbenzene peroxide, and 0.2 - 0.4 parts by weight of antioxidant, extrude and pelletize in a twin-screw extruder at 100 - 130°C, controlling the screw speed at 180 - 220 rpm and the shear rate at 450 - 550 s -1 , to obtain a pre-cross-linked masterbatch;

[0007] S20. Coating the pre-crosslinked masterbatch on the outside of the conductor through a single-screw extruder to form an insulating layer with a thickness of 1.5 - 5.0 mm, and then performing electron beam irradiation treatment with an electron energy of 2.0 - 3.0 MeV and an irradiation dose of 15 - 25 kGy to obtain an irradiated insulating layer;

[0008] S30. Sequentially coating a semiconductive shielding layer, a metal shielding layer, and a halogen-free flame-retardant sheath layer on the outside of the irradiated insulating layer to obtain a power cable.

[0009] In some embodiments, the antioxidant is pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0010] In some embodiments, the active oxygen content of the dicumyl peroxide ≥ 6.5%.

[0011] In some embodiments, in S10, in the twin-screw extruder, the temperature of the feeding compression zone is 100 - 110 °C, the temperature of the melting and plasticizing zone is 115 - 125 °C, the temperature of the dispersion and mixing zone is 125 - 135 °C, and the temperature of the die head is 120 - 130 °C.

[0012] In some embodiments, the length-diameter ratio L / D of the screw of the twin-screw extruder is 38:1 - 42:1.

[0013] In some embodiments, in S20, in the single-screw extruder, the temperature of the feeding section is 100 - 110 °C, the temperature of the compression section is 120 - 130 °C, the temperature of the metering section is 135 - 140 °C, and the temperature of the die head forming section is 130 - 135 °C.

[0014] In some embodiments, when the thickness of the insulating layer is less than or equal to 3 mm, the irradiation dose is 15 kGy. For each 1 mm increase in the thickness of the insulating layer, the irradiation dose increases by 1.5 - 2.5 kGy, and the irradiation dose does not exceed 25 kGy. The dose rate of the irradiation is 1.8 - 2.2 kGy / min.

[0015] In some embodiments, the scanning width of the irradiation is 180 - 220 mm, and during the irradiation, the transmission speed of the cable is 4 - 6 m / min.

[0016] In some embodiments, after S20 and before S30, the following steps are further included: standing for 18 - 30 h to complete free radical quenching.

[0017] The embodiments of the present application also provide a crosslinked polyethylene insulated flame-retardant power cable prepared by the method described in any one of the foregoing.

[0018] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0019] 1. Through the step-by-step cross-linking process, the flame retardant (magnesium hydroxide) is fixed in the matrix at the pre-cross-linking stage, avoiding secondary decomposition caused by high temperature during irradiation. At the same time, the low-temperature characteristics of electron beam irradiation further protect the activity of the flame retardant, realizing the synergistic optimization of flame retardancy and insulation performance.

[0020] 2. By preparing the pre-cross-linked masterbatch in a low-temperature shear environment using a twin-screw extruder, the magnesium hydroxide particles are wrapped by the cross-linking network, inhibiting decomposition during subsequent high-temperature processing and retaining the flame retardancy.

[0021] 3. Through deep cross-linking of the insulating layer by electron beam irradiation and combining with the pre-cross-linked network to form a gradient structure, the cable has both high tensile strength, heat resistance and flexibility.

[0022] 4. By controlling the addition amount of the antioxidant pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], excessive cross-linking and oxidative degradation are inhibited, ensuring the processing stability of the pre-cross-linked masterbatch and the formation of the gradient network after irradiation.

[0023] 5. Through the optimized ratio of dicumyl peroxide, the pre-cross-linking degree and the melt fluidity are balanced, reserving reaction sites for subsequent irradiation, and synergistically improving the mechanical properties of the insulating layer.

[0024] 6. Through the segmented temperature control and the design of the length-diameter ratio of the twin-screw extruder, the uniform dispersion of magnesium hydroxide and the controllable construction of the cross-linking network are realized, ensuring the dispersibility of the flame retardant and the integrity of the masterbatch structure.

[0025] 7. Through the dynamic matching of the electron beam dose and the thickness of the insulating layer, surface carbonization is avoided and deep cross-linking is ensured to be sufficient, reducing energy consumption while maintaining dielectric stability.

[0026] 8. Through the free radical quenching process of standing for 18 - 30 h after irradiation, internal stress is eliminated and the cross-linking network is stabilized, improving the bending life and anti-aging performance of the cable.

[0027] 9. Through the synergistic effect of pre-cross-linking and irradiation cross-linking, the defects of single chemical or irradiation cross-linking are overcome, realizing the comprehensive optimization of flame retardancy, mechanical properties and processing efficiency. Description of the Drawings

[0028] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present invention, and are used together with the specification to explain the principles of the present invention.

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is a flowchart of a preparation method of a cross-linked polyethylene insulated flame-retardant power cable provided by an embodiment of the present application. Detailed implementation manners

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0032] Figure 1 It is a flowchart of a preparation method of a cross-linked polyethylene insulated flame-retardant power cable provided by an embodiment of the present application.

[0033] As Figure 1 shown, the present application provides a preparation method of a cross-linked polyethylene insulated flame-retardant power cable, including the following steps:

[0034] S10. Mix 100 parts by weight of low-density polyethylene, 40 - 60 parts by weight of magnesium hydroxide, 0.7 - 0.9 parts by weight of diisopropylbenzene peroxide, and 0.2 - 0.4 parts by weight of antioxidant, and then extrude and pelletize at 100 - 130 °C in a twin-screw extruder, controlling the screw speed to be 180 - 220 rpm and the shear rate to be 450 - 550 s -1 , to obtain a pre-crosslinked masterbatch;

[0035] S20. Coat the pre-crosslinked masterbatch outside the conductor through a single-screw extruder to form an insulating layer with a thickness of 1.5 - 5.0 mm, and then perform electron beam irradiation treatment with an electron energy of 2.0 - 3.0 MeV and an irradiation dose of 15 - 25 kGy to obtain an irradiated insulating layer;

[0036] S30. Coat a semiconductive shielding layer, a metal shielding layer, and a halogen-free flame-retardant sheath layer outside the irradiated insulating layer in sequence to obtain a power cable.

[0037] S10 is the pre-crosslinking stage. In the pre-crosslinking stage, in the mixed system of low-density polyethylene (LDPE) and Mg(OH)2, dicumyl peroxide (DCP) and antioxidant, dicumyl peroxide is mechanically sheared (450-550s -1 ) and partially decomposes at low temperatures of 100-130°C to generate isopropylphenoxy radicals (C9H 11 O·). The free radical attacks the CH bond of the polyethylene molecular chain, captures hydrogen atoms to form PE chain free radicals (PE·), and then forms CC cross-linked bonds through the reaction of PE·+PE·→PE-PE. The shear energy provided by the screw speed of 180-220rpm promotes the uniformity of melt mixing. At the same time, the local high temperature generated by mechanical shearing (although the overall temperature is lower than the complete decomposition temperature of diisopropyl peroxide 175°C) can activate diisopropyl peroxide to release an appropriate amount of free radicals to form a pre-cross-linked network with a gel content of 15-20%. The network wraps the Mg(OH)2 particles in the cross-linked polyethylene matrix to form a physical barrier, inhibiting the decomposition of Mg(OH)2 due to high temperature in subsequent processing (Mg(OH)2→MgO+H2O↑), thereby retaining its flame retardant efficiency. At this stage, the antioxidant captures free radicals to prevent the degradation of melt fluidity caused by premature cross-linking, thereby ensuring the processing stability of the pre-cross-linked masterbatch.

[0038] In S10, when the amount of diisopropylbenzene peroxide added is within the range of 0.7-0.9 parts by weight, 0.64-0.82mmol of free radicals are generated for every 100g of low-density polyethylene, which is sufficient to form a pre-crosslinked network with a gel content of 15-20% to encapsulate the Mg(OH)2 particles, thereby avoiding the decomposition of the flame retardant during subsequent high-temperature extrusion, and avoiding the surge in melt viscosity caused by premature crosslinking caused by excessive diisopropylbenzene peroxide. The pre-crosslinked masterbatch maintains moderate fluidity during subsequent single-screw extrusion, thereby improving the elongation at break of the cable insulation layer.

[0039] When the antioxidant is less than 0.2 parts by weight, it cannot effectively inhibit the excessive crosslinking during the processing of dicumyl peroxide, resulting in a pre-crosslinked masterbatch gel content exceeding 20% ​​and affecting subsequent extrusion molding; when it is higher than 0.4 parts by weight, it will excessively quench free radicals, making the pre-crosslinking degree less than 15%, weakening the encapsulation effect on Mg(OH)2. The addition of 0.2-0.4 parts by weight of antioxidant allows the antioxidant to only inhibit non-target oxidation reactions in the pre-crosslinking stage without interfering with the controllable crosslinking initiated by dicumyl peroxide, ultimately ensuring that the insulating layer can form a gradient network structure in the crosslinking stage after irradiation, while maintaining the material processing stability and long-term thermal aging performance.

[0040] S20 is the post-crosslinking stage. In the post-crosslinking stage, the insulating layer formed by the pre-crosslinked masterbatch is deeply crosslinked by electron beam irradiation (2.0 - 3.0 MeV, 15 - 25 kGy). When high-energy electrons penetrate the insulating layer, secondary free radicals (PE·) are generated in the polyethylene molecular chains through ionization. These newly generated free radicals combine with the unreacted active sites in the pre-crosslinked network to form a crosslinked structure with a higher density. The setting of the electron energy of 2.0 - 3.0 MeV makes the electron penetration depth match the thickness of the insulating layer (1.5 - 5.0 mm), so that even at the maximum dose of 25 kGy, the material will not carbonize. The pre-crosslinked region retains some linear segments to provide flexibility, while the irradiated crosslinked region improves the tensile strength and heat resistance through dense crosslinking, so that the cable has flame retardancy, flexibility and heat resistance at the same time.

[0041] Through the innovative combination of a two-step crosslinking process, this application uses low-temperature shear activation of dicumyl peroxide to form a three-dimensional network with a crosslinking degree of 15 - 20% in the pre-crosslinking stage, effectively encapsulating Mg(OH)2 particles and inhibiting their thermal decomposition, while retaining the melt processability; in the post-crosslinking stage, through electron beam irradiation under the dose control of the insulating layer thickness gradient matching, the synergistic effect of the pre-crosslinked network and the irradiated dense crosslinking is realized, avoiding both the problems of flame retardant failure and excessive rigidity caused by single chemical crosslinking, and overcoming the dose waste and interface defects of pure irradiated crosslinking, making the cable insulating layer have high flame retardancy, excellent mechanical properties and stable dielectric properties, while reducing the energy consumption in the cable manufacturing process.

[0042] In some embodiments, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0043] In S10, when part of the dicumyl peroxide in the twin-screw extruder is decomposed by shear heat, the antioxidant provides hydrogen atoms to the cumyloxyl radical (C9H 11 O·) and polyethylene chain radicals generated by the decomposition of dicumyl peroxide through the phenolic hydroxyl group (-OH), forming a stable quinone structure (C9H 11 O-H and PE-H), thereby blocking the extension of the free radical chain reaction in the direction of oxidative degradation; at the same time, the large molecular steric hindrance effect (3,5-di-tert-butyl substituents) of the antioxidant can physically shield the unreacted phenolic hydroxyl groups, avoiding premature consumption of the antioxidant itself.

[0044] In some embodiments, the active oxygen content of the dicumyl peroxide ≥ 6.5%.

[0045] In the pre-crosslinking stage, an active oxygen content ≥ 6.5% ensures that a sufficient amount of active oxygen can be released per unit mass of dicumyl peroxide, while reserving sufficient unreacted sites for electron beam irradiation to initiate secondary crosslinking, improving the tensile strength of the cable insulating layer.

[0046] In some embodiments, in step S10, in the twin-screw extruder, the temperature in the feeding and compressing zone is 100 - 110°C, the temperature in the melting and plasticizing zone is 115 - 125°C, the temperature in the dispersion and mixing zone is 125 - 135°C, and the temperature of the die head is 120 - 130°C.

[0047] In the feeding and compressing zone (100 - 110°C), the low-temperature environment mainly realizes the preliminary melting and densification of the material. The low-density polyethylene particles start to soften but are not completely melted at this temperature. Diisopropylbenzene peroxide remains chemically inert due to its relatively high decomposition temperature, avoiding premature release of free radicals. In this section, axial pressure is generated through the conveying thread design of the twin-screw, enabling the Mg(OH)₂ particles to be preliminarily embedded in the polyethylene matrix. At the same time, the mechanical shearing action (450 - 550 s -1 ) breaks up the low-density polyethylene agglomerates, laying the foundation for subsequent uniform dispersion.

[0048] Entering the melting and plasticizing zone (115 - 125°C), the low-density polyethylene is completely melted to form a continuous phase, and the melt viscosity is reduced to 10³ - 10⁴ Pa·s. Diisopropylbenzene peroxide is activated by the local high temperature generated by the screw shearing in this temperature zone and begins to slowly decompose to generate cumyloxyl radicals (C₉H 11 O·), but the controlled upper temperature limit restricts the free radical generation rate. The newly generated free radicals attack the tertiary carbon sites of the polyethylene molecular chains, causing the C - H bonds to break to form PE chain radicals (PE·). Through the reaction of PE· + PE· → PE - PE, an initial cross-linking network is formed, and the cross-linking degree is about 5 - 8% at this time.

[0049] In the dispersion and mixing zone (125 - 135°C), the increased temperature further reduces the melt viscosity to 10² - 10³ Pa·s. Combined with a high shear rate (550 s -1 ), the dispersion of Mg(OH)₂ is achieved. In this region, the screw adopts a combination of intermeshing blocks and reverse-thread elements to generate a tensile flow field and vortices, breaking up the Mg(OH)₂ agglomerates to 5 - 10 μm and uniformly coating them on the polyethylene matrix. At the same time, the continuous thermo-mechanical action promotes the decomposition degree of diisopropylbenzene peroxide to increase to 30 - 40%, and the cross-linking reaction accelerates. The PE chain radicals recombine to form a three-dimensional network structure, anchoring the Mg(OH)₂ particles around the cross-linking points, and the gel content reaches 12 - 15% at this time.

[0050] In the die head area (120 - 130 °C), the melt rheological behavior is stabilized by reducing the temperature. The decrease in temperature causes the melt viscosity to rise to 10^3 - 10^4 Pa·s, inhibits the die swell effect, and ensures that the particle size of the pre-crosslinked masterbatch is controlled within 2.5 - 3.5 mm. The decomposition of diisopropylbenzene peroxide basically stops at this stage, and the remaining unreacted diisopropylbenzene peroxide is encapsulated within the crosslinked network, providing supplementary crosslinking sites for the subsequent irradiation crosslinking stage. The finally discharged pre-crosslinked masterbatch forms a "semi-open" network structure, which not only has sufficient mechanical strength to maintain the granulation form but also retains sufficient linear segments to ensure the fluidity of secondary processing.

[0051] In some embodiments, the length-to-diameter ratio L / D of the twin-screw extruder is 38:1 - 42:1.

[0052] The length-to-diameter ratio range of 38:1 - 42:1 generates a shear rate (450 - 550 s -1 ) by matching the screw rotation speed (180 - 220 rpm), causing the Mg(OH)2 particles to experience an alternating tensile-compressive flow field in the melt, break to 3 - 7 μm, and be uniformly dispersed in the crosslinked polyethylene matrix. At the same time, excessive shear is avoided to prevent the breakage of the pre-crosslinked network, ensuring both the dispersibility of the flame retardant and the melt strength of the masterbatch, and providing a semi-finished product with a complete structure for the subsequent irradiation crosslinking stage.

[0053] In some embodiments, in S20, in the single-screw extruder, the temperature of the feeding section is 100 - 110 °C, the temperature of the compression section is 120 - 130 °C, the temperature of the metering section is 135 - 140 °C, and the temperature of the die head forming section is 130 - 135 °C.

[0054] In the feeding section (100 - 110 °C), the pre-crosslinked masterbatch is transported to the extruder in the form of solid particles, and the low-temperature environment ensures the structural integrity of the material. This temperature zone reduces the accumulation of shear heat through the deep screw groove design of the screw, avoids premature melting and adhesion of the surface of the pre-crosslinked masterbatch, and at the same time uses the frictional heat generated by the rotation of the screw to slightly soften the surface of the particles, providing a transition condition for subsequent plasticization. The Mg(OH)2 particles maintain their dispersed state in the pre-crosslinked network under low shear, preventing the separation of the interface between the flame retardant and the matrix due to a sudden temperature rise.

[0055] Entering the compression section (120 - 130 °C), the depth of the screw groove gradually decreases, and the axial pressure borne by the material increases. The increase in temperature promotes the melting of the core area of the pre-crosslinked masterbatch, the melt viscosity decreases, and the crosslinked polyethylene network undergoes reversible disentanglement in the shear flow field. At this time, the residue of diisopropylbenzene peroxide is still encapsulated around the crosslinking points and remains chemically inert due to the temperature being lower than its decomposition threshold, ensuring that the pre-crosslinked structure is not damaged during plasticization.

[0056] In the metering section (135 - 140 °C), the melt undergoes homogenization at a high shear rate, and the viscosity further decreases. The shallow screw groove design of the screw generates a pressure boosting effect, forcing the melt to pass through the filter screen and enter the die head. The temperature at this stage is close to the complete melting point of low-density polyethylene (130 - 140 °C), but is precisely controlled within the range of 135 - 140 °C, achieving both sufficient melt flow and avoiding thermal decomposition of antioxidants due to overheating, thus maintaining the antioxidant stability of the material.

[0057] In the die head forming section (130 - 135 °C), the elastic behavior of the melt is regulated by moderate cooling. The temperature gradient gradually decreases from 135 °C to 130 °C, reducing the melt exit swell ratio, and thereby controlling the outer diameter tolerance of the insulating layer. The melt forms a stable laminar flow in the die head channel, and the cross-linked network is oriented along the axial direction of the conductor during tensile flow, forming an anisotropic reinforcement structure. This temperature range also cures the surface morphology of the melt, forming a smooth insulating layer interface, providing a uniform energy absorption substrate for subsequent electron beam irradiation.

[0058] In some embodiments, when the thickness of the insulating layer is less than or equal to 3 mm, the irradiation dose is 15 kGy. For each 1 mm increase in the thickness of the insulating layer, the irradiation dose increases by 1.5 - 2.5 kGy, and the irradiation dose does not exceed 25 kGy. The dose rate of the irradiation is 1.8 - 2.2 kGy / min, the scanning width of the irradiation is 180 - 220 mm, and during the irradiation, the transmission speed of the cable is 4 - 6 m / min.

[0059] When the electron beam energy is 2.0 - 3.0 MeV, its penetration depth in polyethylene is approximately 5 - 8 mm, but the energy deposition shows exponential decay (the surface absorption rate is higher than that of the deep layer). For a thin insulating layer with a thickness ≤ 3 mm, a 15 kGy dose can evenly distribute the electron beam energy during penetration, and the difference in free radical concentration between the surface layer and the bottom layer is not high, forming a homogeneous network with a small cross-linking degree deviation. When the thickness increases, the dose increases in a gradient of 1.5 - 2.5 kGy / mm to compensate for the insufficient free radical generation in the deep layer due to energy attenuation. At the same time, since a carbon content > 0.5% will deteriorate the insulation performance, the upper limit of the irradiation dose of 25 kGy can avoid carbonization caused by excessive dose on the surface layer. With such a setting, combined with the initial network structure of the pre-crosslinked masterbatch, only a slight supplement of cross-linking is required during the irradiation stage, ensuring sufficient cross-linking in the thick cross-section area while reducing the total irradiation dose, improving production efficiency while maintaining the thermal stability of Mg(OH)2.

[0060] The dose rate controls the free radical generation density per unit time (1.8 - 2.2 kGy / min corresponds to the generation of 2.5×10^18 - 3.0×10^18 free radicals per second per m 3), in coordination with a transmission speed of 4 - 6 m / min, ensures that the residence time of each cable segment in the irradiation area is precisely controlled within 0.3 - 0.5 seconds to control the cumulative dose deviation; the scanning width of 180 - 220 mm covers the circumferential surface of the cable through the electron beam magnetic deflection system, combined with the longitudinal movement trajectory formed by the transmission speed, constituting a spiral irradiation path to eliminate the crosslinking stripe effect caused by traditional straight-line scanning. This parameter combination enables the residual diisopropylbenzene peroxide in the pre-crosslinked masterbatch to supplement and release isopropylphenoxy radicals under the excitation of the electron beam, forming a gradient crosslinking network in the cross-thickness direction with polyethylene chain radicals, enhancing the overall voltage withstand strength while maintaining the flexibility of the insulation layer, and improving the irradiation efficiency.

[0061] In some embodiments, after S20 and before S30, the following steps are further included: standing for 18 - 30 h to complete free radical quenching.

[0062] During the standing process, free radicals migrate to adjacent active sites through thermal motion and preferentially undergo quenching reactions with the residual isopropylphenoxy radicals C9H 11 O· and the phenolic hydroxyl groups of the antioxidant. At the same time, the unreacted PE· free radicals combine with each other to form stable crosslinking bonds. The standing time of 18 - 30 h is set by matching the free radical half-life at room temperature of about 8 - 12 h, ensuring the quenching efficiency and avoiding the secondary crosslinking caused by the residual free radicals when heated, which leads to embrittlement of the insulation layer. By standing the irradiated insulation layer, the crosslinking network formed by irradiation is fully relaxed, internal stress is eliminated, the bending life of the cable is improved, and at the same time, premature encapsulation of the sheath layer is avoided, which hinders the slow oxidation degradation caused by the contact of free radicals with oxygen.

[0063] The embodiment of the present application also provides a crosslinked polyethylene insulated flame-retardant power cable prepared by the method described in any one of the foregoing.

[0064] The method of the present invention will be described in detail below in combination with examples, comparative examples, and experimental data.

[0065] Example 1

[0066] This example provides a method for preparing a crosslinked polyethylene insulated flame-retardant power cable, and the method includes the following steps:

[0067] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.8kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1 , extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0068] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0069] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0070] Example 2

[0071] This embodiment provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0072] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.7kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1, extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0073] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0074] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0075] Example 3

[0076] This embodiment provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0077] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.8kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1 , extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0078] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 3mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 3mm, the total dose is adjusted to 15kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0079] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0082] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm and 0.8kg of diisopropyl peroxide with an active oxygen content of 6.8%, and put them into a high-speed mixer for mixing at room temperature for 10 minutes. Add the mixture into a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1 , extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0083] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0084] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0085] Comparative Example 2

[0086] This comparative example provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0087] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.5kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1 , extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0088] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0089] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0090] Comparative Example 3

[0091] This comparative example provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0092] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.8kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1, extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0093] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single screw extruder, set the feeding section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die head molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.0kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy.

[0094] S30: A 0.8 mm thick semi-conductive shielding layer (ethylene-vinyl acetate copolymer with a carbon black content of 30%), a 0.5 mm thick copper tape shielding layer and a 2.0 mm thick halogen-free flame-retardant sheath layer (polyolefin elastomer with an aluminum hydroxide filling amount of 60%) are sequentially coated outside the insulation layer to obtain a power cable.

[0095] Comparative Example 4

[0096] This comparative example provides a method for preparing a cross-linked polyethylene insulated flame-retardant power cable, the method comprising the following steps:

[0097] S10: Prepare pre-crosslinked masterbatch. Take 100kg of low-density polyethylene with a melt index of 2.0g / 10min, 50kg of Mg(OH)2 with an average particle size of 5μm, 0.8kg of diisopropylbenzene peroxide with an active oxygen content of 6.8% and 0.3kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] as an antioxidant, put them into a high-speed mixer and mix them at room temperature for 10 minutes. Add the mixture to a twin-screw extruder with a length-to-diameter ratio of L / D=40:1, set the feed compression zone temperature to 105°C, the melt plasticization zone to 120°C, the dispersion mixing zone to 130°C, the die head temperature to 125°C, the screw speed to 200rpm, and the shear rate to 500s -1 , extrusion granulation was performed to obtain a pre-crosslinked masterbatch with a particle size of 3 mm and a gel content of 18%.

[0098] S20: Extrusion of insulation layer and radiation cross-linking. Add the pre-cross-linked masterbatch to the single-screw extruder, set the feed section to 105°C, the compression section to 125°C, the metering section to 140°C, and the die molding section to 135°C, and extrude and coat it on the surface of the annealed copper conductor with a diameter of 20mm to form an insulation layer with a thickness of 4mm. Use electron beam irradiation equipment, set the electron energy to 2.5MeV, the dose rate to 2.5kGy / min, the scanning width to 200mm, and irradiate at a transmission speed of 5m / min. According to the thickness of 4mm, the total dose is adjusted to 19kGy. After irradiation, the cable is left to stand in an environment of 25°C for 24 hours.

[0099] S30: Over the insulating layer, successively wrap a semiconductive shielding layer (ethylene-vinyl acetate copolymer with 30% carbon black content) with a thickness of 0.8 mm, a copper tape shielding layer with a thickness of 0.5 mm, and a halogen-free flame-retardant sheath layer (polyolefin elastomer filled with 60% aluminum hydroxide) with a thickness of 2.0 mm to obtain a power cable.

[0100] Experimental methods

[0101] 1. Crosslinking degree (%): Place the insulating layer sample (10×10×2 mm 3 ) in boiling xylene for extraction for 24 hours, take it out and dry it in vacuum until constant weight. Calculate using the gel content method: Crosslinking degree = (mass after extraction / mass before extraction) × 100%. The testing instrument is a precision balance (Mettler Toledo ME204E, accuracy 0.1 mg).

[0102] 2. Tensile strength (MPa) and elongation at break (%): Prepare dumbbell-shaped insulating layer samples (thickness 2 mm, gauge section 25 mm) according to ASTM D638 standard, and use a universal material testing machine (Instron 5967) to stretch at a speed of 50 mm / min until fracture, and record the maximum load and the gauge length at fracture. Tensile strength = maximum load / initial cross-sectional area, elongation at break = (gauge length at fracture - initial gauge length) / initial gauge length × 100%.

[0103] 3. Breakdown voltage (kV / mm): Place the insulating layer in an oil bath test tank with an electrode spacing of 10 mm, increase the voltage at a rate of 1 kV / s until breakdown, and record the breakdown voltage value. The testing equipment is a high-voltage breakdown tester (Haefely Hipotronics TCH200), breakdown voltage = breakdown voltage value / insulating layer thickness.

[0104] 4. Flame retardancy rating (UL94): According to the UL94 vertical burning standard, cut a 127×12.7×3 mm3 cable sheath layer specimen, fix it vertically and apply a 20 mm blue flame (methane flow rate 105 mL / min) twice, each time for 10 seconds. Record the self-extinguishing time and whether the cotton pad below is ignited, and determine the rating (V-0: self-extinguishing time ≤ 10 seconds for both times and no ignition; V-1: ≤ 30 seconds; V-2: ≤ 30 seconds but there is ignition).

[0105] 5. Surface defect rate (%): Immerse the insulating layer sample (length 50 cm) in a 0.1% methylene blue aqueous solution for 5 minutes, take it out, rinse it with clean water and dry it. Dye residues at surface cracks or holes form visible blue marks, visually inspect with a 10× magnifying glass, and count the number of surface defects per meter of the cable (linear defects with a length ≥ 1 mm and a width ≥ 0.2 mm or holes with a diameter ≥ 0.5 mm). The calculation formula for the surface defect rate is as follows:

[0106]

[0107] wherein, l i is the length of the i-th linear defect (unit: mm), w is the average width of the linear defect (usually fixed at 0.2 mm), d j is the diameter of the j-th hole defect (unit: mm), D is the outer diameter of the insulating layer (unit: mm), and L is the length of the cable (unit: mm).

[0108] The experimental results are shown in Table 1

[0109] Table 1 Comparison table of key performance indicators between the examples and the comparative examples

[0110]

[0111] Analysis of experimental results

[0112] The crosslinking degree of the insulating layer in Example 1 is stable at 68 - 72%, and the balanced performance of the tensile strength of 18 - 20 MPa and the elongation at break of 350 - 400% indicates that the two-step crosslinking process can produce synergy. The initial crosslinking network of 18% in the pre-crosslinking stage is supplemented to about 70% by electron beam irradiation, which not only retains the flexibility of the polyethylene chain but also improves the mechanical strength through dense crosslinking. The excellent electrical performance of the breakdown voltage of 32 - 35 kV / mm benefits from the uniform dispersion of Mg(OH)2 particles, and the flame retardant grade of V-0 indicates that the continuous carbon layer formed during combustion effectively inhibits the flame spread.

[0113] After the addition amount of dicumyl peroxide in Example 2 was reduced from 0.8 parts by weight to 0.7 parts by weight, the pre-crosslinking degree slightly decreased from 18% to 16%, but through irradiation dose compensation (total crosslinking degree of 65 - 70%), the qualified levels of the tensile strength of 17 - 19 MPa and the breakdown voltage of 30 - 33 kV / mm were still maintained, indicating that the content of dicumyl peroxide has a process tolerance within the range of 0.7 - 0.9 parts by weight.

[0114] After the insulating layer thickness in Example 3 was reduced to 3 mm and an irradiation dose of 15 kGy was used, the crosslinking uniformity was improved (the difference in crosslinking degree between the surface layer and the core was ≤ 3%), and the breakdown voltage further increased to 34 - 36 kV / mm, proving that thin-section cables can achieve equivalent performance by reducing the dose while reducing energy consumption by 20 - 25%.

[0115] In Comparative Example 1, the lack of antioxidant led to out-of-control free radical reactions in the pre-crosslinking stage, fluctuations in the gel content, and 2.5 - 4.0% surface defects caused by melt fracture during extrusion. The breakdown voltage decreased to 25 - 28 kV / mm and the combustion self-extinguishing time extended to 15 - 20 seconds, and the flame retardant grade dropped to V-1.

[0116] In Comparative Example 2, the addition amount of dicumyl peroxide was 0.5 parts by weight, resulting in a pre-crosslinking degree of only 8%. After irradiation, the total crosslinking degree was less than 52%, the tensile strength dropped sharply to 10 - 12 MPa, and the flame retardant grade V-2 indicated that Mg(OH)2 failed to effectively form a protective carbon layer due to the loose crosslinking network.

[0117] In Comparative Example 3, after canceling the standing step, residual free radicals initiated secondary crosslinking during the extrusion of the sheath layer, and the crosslinking degree locally increased to 80%. The elongation at break ≤ 150% indicated embrittlement of the insulating layer, resulting in a decrease in its bending life.

[0118] In Comparative Example 4, after using an excessive dose rate of 2.5 kGy / min, the surface layer was carbonized due to excessive irradiation, the breakdown voltage dropped to 18 - 20 kV / mm, and insufficient crosslinking in the core (50%) led to a tensile strength of only 10 MPa. Moreover, the surface defect rate of 3.0 - 5.0% further deteriorated the insulation reliability.

[0119] The above data show that by controlling the addition amount of 0.7 - 0.9 parts by weight of dicumyl peroxide, the dynamic matching of the irradiation dose of 15 - 25 kGy with the thickness, the stabilization of 0.2 - 0.4 parts by weight of antioxidant, and standing quenching, the comprehensive properties of a crosslinking degree of 65 - 75%, a tensile strength ≥ 17 MPa, an elongation at break ≥ 320%, a breakdown voltage ≥ 30 kV / mm, and a V-0 flame retardant grade can be synergistically achieved, which are significantly superior to the traditional single-step crosslinking process.

[0120] It should be noted that in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant is intended to cover non-exclusively, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0121] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A preparation method of a cross-linked polyethylene insulated flame-retardant power cable, characterized in that, It includes the following steps: S10: After mixing 100 parts by weight of low-density polyethylene, 40 - 60 parts by weight of Mg(OH)₂, 0.7 - 0.9 parts by weight of dicumyl peroxide, and 0.2 - 0.4 parts by weight of antioxidant, extrude and pelletize in a twin-screw extruder at 100 - 130 °C, control the screw speed at 180 - 220 rpm, and the shear rate at 450 - 550 s⁻¹ to obtain a pre-crosslinked masterbatch; S20: Coat the pre-crosslinked masterbatch outside the conductor through a single-screw extruder to form an insulating layer with a thickness of 1.5 - 5.0 mm, and then perform electron beam irradiation treatment with an electron energy of 2.0 - 3.0 MeV and an irradiation dose of 15 - 25 kGy to obtain an irradiated insulating layer; S30: Coat a semiconductive shielding layer, a metal shielding layer, and a halogen-free flame-retardant sheath layer outside the irradiated insulating layer in sequence to obtain a power cable.

2. According to the preparation method described in claim 1, the antioxidant is pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

3. The preparation method according to claim 1, wherein The active oxygen content of the dicumyl peroxide ≥ 6.5%.

4. The preparation method according to claim 1, wherein, In S10, in the twin-screw extruder, the temperature of the feeding compression zone is 100 - 110 °C, the temperature of the melting and plasticizing zone is 115 - 125 °C, the temperature of the dispersion and mixing zone is 125 - 135 °C, and the temperature of the die head is 120 - 130 °C.

5. The preparation method according to claim 4, characterized in that, The length-diameter ratio L / D of the screw of the twin-screw extruder is 38:1 - 42:

1.

6. The preparation method according to claim 1, characterized in that, In S20, in the single-screw extruder, the temperature of the feeding section is 100 - 110 °C, the temperature of the compression section is 120 - 130 °C, the temperature of the metering section is 135 - 140 °C, and the temperature of the die head forming section is 130 - 135 °C.

7. The preparation method according to claim 1, wherein When the thickness of the insulating layer is less than or equal to 3 mm, the irradiation dose is 15 kGy. For each 1 mm increase in the thickness of the insulating layer, the irradiation dose increases by 1.5 - 2.5 kGy, and the irradiation dose does not exceed 25 kGy. The dose rate of the irradiation is 1.8 - 2.2 kGy / min.

8. The preparation method according to claim 1, characterized in that, The scanning width of the irradiation is 180 - 220 mm. During the irradiation, the transmission speed of the cable is 4 - 6 m / min.

9. The preparation method according to claim 1, characterized in that, After S20 and before S30, the following step is also included: standing for 18 - 30 h to complete free radical quenching.

10. A cross-linked polyethylene insulated flame-retardant power cable, characterized in that, Prepared by the method according to any one of claims 1 - 9.

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