Flame-retardant and insulating low-voltage power cable and preparation method and application thereof

Abstract

The present application relates to the technical field of crosslinked polyethylene insulated power cable, in particular to a flame-retardant and insulating low-voltage power cable, and a preparation method and application thereof.The flame-retardant and insulating low-voltage power cable comprises, from inside to outside, an inner core layer, a filler layer, a wrapping layer, an inner liner layer, a metal armor layer and an outer sheath layer, the multi-layer arrangement can effectively protect the inner core and endow the cable with good performance.In addition, the present application also adopts low-density polyethylene, furan-modified polyethylene compatibilizer, reactive flame retardant, bismaleimide, dicumyl peroxide and additives to obtain a crosslinked polyethylene material for the outer sheath of the above-mentioned cable, which has excellent insulation, flame retardance, strength, toughness and repair performance.

Description

Technical Field

[0001] This invention relates to the field of cross-linked polyethylene insulated power cable technology, specifically to a flame-retardant and insulated low-voltage power cable, its preparation method, and its application. Background Technology

[0002] Low-voltage power cables (typically referring to those with a rated voltage of 1kV and below) serve as the final "capillaries" of electrical energy transmission, widely used in various buildings, industrial facilities, and public infrastructure. Their complex operating environments and dense installations place stringent demands on cable safety, particularly in terms of flame retardancy, insulation, and resistance to damage. However, existing low-voltage cable technology faces significant challenges in synergistically improving these two core performance characteristics, making it difficult to meet the ever-increasing demands for higher safety standards.

[0003] To improve flame retardancy and insulation performance, a common method is to use large amounts of inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide. Although these additives are environmentally friendly and inexpensive, in order to achieve an effective flame retardant concentration, they severely disrupt the continuity of the polyethylene matrix, leading to a significant increase in material brittleness and a substantial decrease in tensile strength and impact resistance. In addition, polyolefin materials will undergo a certain degree of aging and embrittlement after long-term outdoor exposure, resulting in cracks. Furthermore, surface scratches and micro-cracks caused by construction and installation (such as dragging and collision) or operation (such as external pressure and rock scratches) in polyolefin sheaths can continuously expand through the "environmental stress cracking" mechanism, eventually leading to sheath cracking, loss of protective function, and a chain of failures such as insulation moisture absorption or metal shielding corrosion.

[0004] Therefore, improving the flame retardancy, insulation, and resistance to environmental cracking effects (intelligent repair) of cross-linked polyethylene insulated power cables remains a technical problem that needs to be solved when preparing them. Summary of the Invention

[0005] In view of the technical problems raised in the background art, the present invention provides corresponding solutions to solve such technical problems. The present invention belongs to the field of cross-linked polyethylene insulated power cables, specifically relating to a flame-retardant and insulated low-voltage power cable, its preparation method, and its application.

[0006] This invention provides a flame-retardant and insulated low-voltage power cable, comprising, from the inside out, an inner core layer, a filler layer, a wrapping layer, an inner liner layer, a metal armor layer, and an outer sheath layer. This multi-layered structure effectively protects the inner core, giving the cable superior performance.

[0007] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, the number of inner cores in the inner core layer is not less than two.

[0008] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, each inner core is made up of at least four single wires twisted together.

[0009] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, each inner core is made of seven single wires twisted together.

[0010] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, "single wire" refers to a single conductor, and the conductor material is copper or a copper alloy.

[0011] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, the outer sheath material is cross-linked polyethylene.

[0012] This invention provides a cross-linked polyethylene material. It can be used in the aforementioned cable outer sheath material. The raw materials for its preparation include: 80-120 parts of low-density polyethylene, 7-10 parts of furan-modified polyethylene compatibilizer, 7-15 parts of reactive flame retardant, 2-4 parts of bismaleimide, 1-2.5 parts of dicumyl peroxide, and 2-4 parts of additives. The additives include at least one of carbon black, antioxidant, and zinc stearate.

[0013] The present invention also provides a method for preparing a flame-retardant and insulated low-voltage power cable, comprising the following steps: Step 1: Twist at least three conductors together and extrude insulation to obtain the inner core. Set multiple inner cores and twist them together to form a cable as the inner core layer of the cable. Step 2: Place a filler on the outer surface of the inner core layer to obtain a filler layer; Step 3: Set a wrapping layer on the outer surface of the filler layer, and set an inner liner layer on the outer surface of the wrapping layer; Step 4: Set a metal armor layer on the outer surface of the inner lining layer, and then set an outer sheath layer on the outer surface of the metal armor layer.

[0014] The present invention also provides the application of the flame-retardant and insulated low-voltage power cable in power grid facilities.

[0015] The beneficial effects of this invention are: This invention relates to a cross-linked polyethylene flame-retardant and insulated cable, which comprises, from the inside out, an inner core layer, a filler layer, a wrapping tape layer, an inner liner layer, a metal armor layer, and an outer sheath layer. This multi-layered structure effectively protects the inner core, giving the cable superior performance.

[0016] The invention uses cross-linked polyethylene as the outer sheath material, which can give the cable excellent flame retardancy, insulation, strength, toughness and repairability.

[0017] This invention utilizes reactive flame retardants for chemical grafting to overcome the shortcomings of traditional flame retardants, endowing materials with excellent strength, toughness, insulation, and repair capabilities. This invention also uses bismaleimide in the reaction, effectively enhancing flame retardancy and repair capabilities. In the preparation of cross-linked polyethylene materials, this invention incorporates furan-modified polyethylene compatibilizers and improves the combination of raw materials and processes for preparing furan-modified polyethylene compatibilizers, both of which effectively enhance the material's mechanical properties and its flame retardant, insulation, and repair capabilities. This invention uses glycidyl methacrylate, diallyl chlorophosphate, and other raw materials to prepare reactive flame retardants, which can impart good insulation, strength, toughness, flame retardancy, and repair effects to the materials.

[0018] The flame-retardant and insulated cable prepared by this invention has excellent performance. Combustion experiments show that the cable prepared by this invention can effectively retard flames and has good application prospects. Attached Figure Description

[0019] Figure 1 : Schematic diagram of cable 1.

[0020] Figure 2 This is a diagram of the cable material before combustion.

[0021] Figure 3 This is a diagram of the cables used in the combustion equipment.

[0022] Figure 4 This is a picture of the scene during the combustion process.

[0023] Figure 5 This is a front view of the cable after it has burned.

[0024] Figure 6 This is a reverse view of the cable after it has burned. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] A flame-retardant and insulated low-voltage power cable comprises, from the inside out, an inner core layer, a filler layer, a wrapping layer, an inner liner layer, a metal armor layer, and an outer sheath layer. This multi-layered structure effectively protects the inner core, giving the cable superior performance.

[0027] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, the number of inner cores in the inner core layer is not less than two.

[0028] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, each inner core is made up of at least four single wires twisted together.

[0029] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, each inner core is made of seven single wires twisted together.

[0030] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, "single wire" refers to a single conductor, and the conductor material is copper or a copper alloy.

[0031] Furthermore, in the aforementioned flame-retardant and insulated low-voltage power cables, the outer sheath material is cross-linked polyethylene.

[0032] This invention provides a cross-linked polyethylene material. It can be used in the aforementioned cable outer sheath material. The raw materials for its preparation include: 80-120 parts of low-density polyethylene, 7-10 parts of furan-modified polyethylene compatibilizer, 7-15 parts of reactive flame retardant, 2-4 parts of bismaleimide, 1-2.5 parts of dicumyl peroxide, and 2-4 parts of additives. The additives include at least one of carbon black, antioxidant, and zinc stearate.

[0033] Furthermore, the furan-modified polyethylene compatibilizer is obtained by premixing low-density polyethylene with furan methacrylate, dicumyl peroxide and antioxidant, then heating and melting it before extrusion, cooling and pelletizing.

[0034] Furthermore, in the furan-modified polyethylene compatibilizer, the weight of furan methacrylate is 5-7% of that of low-density polyethylene.

[0035] Furthermore, in the furan-modified polyethylene compatibilizer, the weight of dicumyl peroxide is 0.2-0.45% of that of low-density polyethylene.

[0036] Furthermore, the furan-modified polyethylene compatibilizer is prepared by premixing low-density polyethylene with furan methacrylate, dicumyl peroxide and antioxidant in a high-speed mixer, then heating and melting extrusion at an extrusion temperature of 150-180℃ (for example, the extrusion temperature of different zones is set to 150℃, 165℃, 165℃, 175℃, 170℃, 165℃, and the extrusion speed is 100-200 rpm), and then cooling and pelletizing the product.

[0037] In the preparation of the aforementioned furan-modified polyethylene compatibilizer, during the twin-screw extruder process, dicumyl peroxide decomposes upon heating to generate free radicals. These free radicals abstract tertiary hydrogen atoms from the polyethylene backbone to form macromolecular free radicals. These free radicals then undergo a radical addition reaction with the methacrylate double bond of furan-2-ylmethacrylate, grafting the furan ring-containing side chain onto the polyethylene chain. The furan ring on its side chain is a key functional group (diene) for constructing a dynamic and reversible network, thereby achieving self-repair. As a grafting agent for polyethylene, it can improve the dispersion of subsequently added components such as bismaleimide in the polyethylene matrix, thus improving the material's performance.

[0038] Furthermore, the preparation method of the reactive flame retardant includes: adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and tetrahydrofuran premix to a reaction vessel, adding diallyl chlorophosphate, a mixture of triethylamine and tetrahydrofuran, stirring the reaction, raising the temperature after the reaction is completed, adding 3-aminopropyltriethoxysilane to continue the reaction, then adding glycidyl methacrylate, raising the temperature and stirring the reaction, and the reaction product is post-treated to obtain the reactive flame retardant.

[0039] Furthermore, in the preparation method of the reactive flame retardant, the reaction solvent includes toluene. The weight ratio of diallyl chlorophosphate to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 0.7-0.9:1. Triethylamine is 0.5-1.5% of the weight of diallyl chlorophosphate. The weight ratio of 3-aminopropyltriethoxysilane to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1-1.2:1. The weight ratio of glycidyl methacrylate to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 0.7-0.8:1.

[0040] Furthermore, the preparation method of the reactive flame retardant includes: introducing nitrogen gas into a reaction vessel and adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and tetrahydrofuran, premixing in an ice-water bath, adding dropwise a mixture composed of diallyl chlorophosphate, triethylamine and tetrahydrofuran, stirring and reacting at room temperature for 3-6 hours, raising the temperature to 35-50°C after the reaction, adding 3-aminopropyltriethoxysilane and continuing the reaction for 2-5 hours, then adding glycidyl methacrylate, raising the temperature to 55-65°C and stirring and reacting for 4-7 hours, and post-processing the reaction product to obtain the reactive flame retardant.

[0041] Furthermore, the above post-treatment includes cooling the reaction product to room temperature and removing tetrahydrofuran by vacuum distillation.

[0042] In the preparation of the above-mentioned reactive flame retardant, under the action of alkali (triethylamine), the pH bond of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is deprotonated to generate a nucleophilic phosphine anion, which can attack the phosphorus center of diallyl phosphoryl chloride, undergoing SN2 nucleophilic substitution to form a POP bond, introducing an allyl double bond and the DOPO phosphorus-nitrogen heterocycle. Further addition of the primary amino group of 3-aminopropyltriethoxysilane as a nucleophile allows it to form PN-Si and PO-Si bonds with the phosphorus center of the intermediate, introducing a hydrolyzable triethoxysilane segment and simultaneously providing an amino active group. This introduced amino group can attack the epoxy ring of glycidyl methacrylate, undergoing ring-opening addition, introducing a methacrylate double bond and an epoxy group. Among them, DOPO provides gas-phase free radical quenching (P·, PO·); phosphorus, nitrogen, and silicon synergistically promote the formation of a dense, heat-insulating, and oxidation-resistant "ceramicized" carbon layer; flame retardant elements are covalently bonded to the cross-linked polyethylene network matrix through chemical grafting, avoiding the increase in conductivity caused by interface defects and ionic impurities in physically blended flame retardants (such as hydroxides and phosphates). Furthermore, siloxane units may also bind charge carriers through the "trap" effect, which is beneficial to maintaining high volume resistivity; the reactive flame retardant prepared by this invention participates in the formation of the cross-linked network as a reactive monomer, enhancing the strength of the cross-linked polyethylene material; in addition, the introduced siloxane chains may undergo dynamic siloxane exchange reactions at high temperatures, which can provide a self-healing pathway under certain conditions (such as heating or high temperature).

[0043] The present invention also provides a method for preparing the above-mentioned cross-linked polyethylene material, comprising: mixing a portion of low-density polyethylene, furan-modified polyethylene compatibilizer, bismaleimide and additives in a mixer, then adding a reactive flame retardant and continuing to mix to obtain a mixture; heating a mixer, adding the mixture and mixing, then heating again and continuing to mix, then discharging, and then processing in a two-roll mill to produce sheets and pulverize, then mixing the pulverized material with a dicumyl peroxide-low-density polyethylene premix (i.e., a premix obtained by mixing dicumyl peroxide with the remaining low-density polyethylene) in a mixer, vulcanizing in a flat vulcanizing agent, holding pressure and cooling, and demolding to obtain the cross-linked polyethylene material.

[0044] The present invention also provides a method for preparing a flame-retardant and insulated low-voltage power cable, comprising the following steps: Step 1: Twist at least three single wires together and extrude insulation to obtain the inner core, and set multiple inner cores to form a cable as the inner core layer of the cable; Step 2: Place a filler on the outer surface of the inner core layer to obtain a filler layer; Step 3: Set a wrapping layer on the outer surface of the filler layer, and set an inner liner layer on the outer surface of the wrapping layer; Step 4: Set a metal armor layer on the outer surface of the inner lining layer, and then set an outer sheath layer on the outer surface of the metal armor layer.

[0045] The above-mentioned extrusion insulation process involves applying insulating material to the surface of a stranded conductor and then performing extrusion insulation treatment.

[0046] The present invention also provides the application of the flame-retardant and insulated low-voltage power cable in power grid facilities.

[0047] Low-density polyethylene: ExxonMobil™ LDPE LD 100.BW, ExxonMobil.

[0048] Bismaleimide: N,N'-(4,4'-methylenediphenyl)bismaleimide, CAS: 13676-54-5.

[0049] Furan methacrylate: furan-2-ylmethacrylate.

[0050] Diallyl chlorophosphate: also known as diallylphosphonochloride, CAS No.: 16383-57-6.

[0051] Antioxidant: Antioxidant 1010.

[0052] Carbon black: Insulating carbon black, SPECIAL BLACK 4, Evonik degussa.

[0053] Furan-modified polyethylene compatibilizer: Raw material composition, by weight: 100 parts low-density polyethylene, 6 parts furan methacrylate, 0.35 parts dicumyl peroxide, and 0.2 parts antioxidant; Preparation method: At room temperature, turn on a high-speed mixer at 800 rpm, feed the above raw materials, stir for 10 minutes, discharge, and then feed into a twin-screw extruder, set the temperature of each section to 150℃, 165℃, 165℃, 175℃, 170℃, and 165℃, the extrusion speed to 150 rpm, cool with cooling water after extrusion, and granulate to obtain the product.

[0054] Reactive flame retardants: Nitrogen gas was introduced into the reaction vessel, and 43g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 250g of tetrahydrofuran were added. The mixture was premixed in an ice-water bath. A mixture of 35g diallyl chlorophosphate, 0.35g triethylamine, and 250g tetrahydrofuran was added dropwise over an ice-water bath for about 1 hour. The ice-water bath was then removed, and the temperature was raised to room temperature. The mixture was stirred and reacted for 5 hours. After the reaction was completed, the temperature was raised to 40°C, and 49g of 3-aminopropyltriethoxysilane was added to continue the reaction for 4 hours. Then, 34g of glycidyl methacrylate was added, and the temperature was raised to 60°C and stirred for 5 hours. The reaction product was cooled to room temperature, and tetrahydrofuran was removed by vacuum distillation to obtain a reactive flame retardant.

[0055] Example 1 The specific production method for cross-linked polyethylene materials is as follows.

[0056] Example 1: The raw material composition by weight is as follows: 100 parts low-density polyethylene, 8 parts furan-modified polyethylene compatibilizer, 12 parts reactive flame retardant, 3 parts bismaleimide, 1.8 parts dicumyl peroxide, and 2.5 parts additives; the additives include antioxidant 1010 and carbon black in a weight ratio of 0.1:1.

[0057] Production process: 97 parts of low-density polyethylene, furan-modified polyethylene compatibilizer, bismaleimide and additives are mixed in a mixer at 150 rpm for 5 minutes. The mixture is then heated to 50°C, a reactive flame retardant is added, and the mixture is stirred at 220 rpm for 4 minutes to obtain a compound. The internal mixer is heated to 125°C, the compound is added, and the mixture is stirred at 80 rpm for 5 minutes. The temperature is then raised again to 150°C, and the mixture is stirred for another 12 minutes. The material is discharged and fed into a two-roll mill with a set temperature of 145°C for stirring and sheeting. The sheet is then crushed. The crushed material is mixed with a dicumyl peroxide-low-density polyethylene premix (i.e., a premix obtained by mixing dicumyl peroxide with the remaining 3 parts of low-density polyethylene) in a mixer at room temperature. The mixture is then vulcanized in a flat vulcanizing machine with a set temperature of 175°C and a pressure of 15 MPa for 15 minutes. After holding the pressure and cooling, the material is demolded to obtain cross-linked polyethylene material.

[0058] Example 2: The raw material composition by weight is as follows: 90 parts low-density polyethylene, 7.3 parts furan-modified polyethylene compatibilizer, 10.5 parts reactive flame retardant, 2.8 parts bismaleimide, 1.6 parts dicumyl peroxide, and 2.3 parts additives; the additives include antioxidant 1010 and carbon black in a weight ratio of 0.15:1.

[0059] Production process: 87 parts of low-density polyethylene, furan-modified polyethylene compatibilizer, bismaleimide, dicumyl peroxide, and additives are mixed in a mixer at 120 rpm for 4 minutes. The mixture is then heated to 50°C, a reactive flame retardant is added, and the mixture is stirred at 220 rpm for 5 minutes to obtain a compound. The internal mixer is heated to 127°C, the compound is added, and the mixture is stirred at 90 rpm for 4 minutes. The temperature is then raised again to 152°C, and the mixture is stirred for another 10 minutes. The mixture is then discharged and fed into a two-roll mill at a set temperature of 145°C for stirring and sheeting. The sheet is then crushed. The crushed material and the dicumyl peroxide-low-density polyethylene premix (i.e., the premix obtained by mixing dicumyl peroxide with the remaining 3 parts of low-density polyethylene) are mixed in a mixer at room temperature. The mixture is then vulcanized in a flat vulcanizing machine at a set temperature of 175°C and a pressure of 15 MPa for 15 minutes. The mixture is then held under pressure and cooled, and then demolded to obtain cross-linked polyethylene material.

[0060] Comparative Example 1: Compared to Example 1, the reactive flame retardant was replaced with an equal weight of alumina.

[0061] Comparative Example 2: Compared to Example 1, bismaleimide was not used.

[0062] Comparative Example 3: Compared to Example 1, an equal weight of PE-g-MAH was used to replace the furan-modified polyethylene compatibilizer.

[0063] Comparative Example 4: Compared to Example 1, furan methacrylate, a raw material in the preparation of furan-modified polyethylene compatibilizer, was replaced with an equal weight of methyl methacrylate.

[0064] Comparative Example 5: Compared to Example 1, the step of adding glycidyl methacrylate for reaction in the preparation of reactive flame retardant was omitted.

[0065] Comparative Example 6: Compared to Example 1, diallyl chlorophosphate in the preparation of the reactive flame retardant was replaced with an equal weight of 1,2-propadienephosphochloride.

[0066] Example 2 The performance of the above-mentioned cross-linked polyethylene material was tested using the following methods.

[0067] Tensile strength, elongation at break, volume resistivity and limiting oxygen index: GB / T 32129-2015; each sample was tested in parallel 4 times.

[0068] Retention rate: Standard dumbbell-shaped samples (1.5 mm thick) were made from the cross-linked polyethylene materials of Examples 1-2 and Comparative Examples 1-6 (refer to GB / T 1040-2006). The tensile strength A1 of the material was tested. Then, a 0.6 mm deep incision was made on its surface, and the tensile strength A2 was tested again. The incision was then heat-treated at 125℃ for 150 s for heat repair and allowed to cool naturally to room temperature. The tensile strength A3 was then tested. The repair rate was calculated using the formula: (A3-A2) / (A1-A2) × 100%. Each test was performed in parallel for four times. The test results are shown in Table 1.

[0069] Table 1: Test Results As shown in Table 1, the cross-linked polyethylene material for cable outer sheath prepared by this invention has good strength, elongation at break, insulation and flame retardant properties, and also has good repair properties.

[0070] In Comparative Example 1, alumina was used to replace the reactive flame retardant of this invention, resulting in a significant reduction in tensile strength and elongation, and a volume resistivity two orders of magnitude lower. If physically filled alumina is used as a flame retardant, it severely disrupts the continuous phase and crystalline structure of polyethylene, leading to deterioration of mechanical properties. Conventional inorganic fillers form defects at the interface with the matrix, creating charge traps and conductive pathways, thus impairing insulation. In contrast, this invention uses a reactive flame retardant for chemical grafting to overcome the defects of traditional flame retardants and improve the overall performance of the material.

[0071] In Comparative Example 2, no bismaleimide was added, resulting in severe damage to the flame retardant and self-healing functions of the material. The maleimide group of the bismaleimide (BMI) used in this invention is a dynamically cross-linked "dieneophile". After omission, the furan ring cannot form a reversible Diels-Alder cross-linked network, and the material loses its ability to "soften and dissipate energy at high temperatures and reconnect and repair upon cooling". It also loses its reversible property of plastic flow upon heating, resulting in the loss of the material's self-healing ability and reduced flame retardant performance.

[0072] In Comparative Example 3, the use of PE-g-MAH to replace the furan-modified polyethylene compatibilizer resulted in the loss of the material's self-healing ability. Although maleic anhydride graft (PE-g-MAH) is an excellent physical compatibilizer that can form chemical bonds with fillers to improve dispersion, it does not contain the furan rings that can form reversible reactions in the furan-modified polyethylene compatibilizer of this invention. Therefore, it cannot construct a dynamic network and cannot achieve self-healing, resulting in the loss of the material's self-healing ability.

[0073] Comparative Example 4: Replacing furan methacrylate, a raw material in the preparation of furan-modified polyethylene compatibilizer, with an equal weight of methyl methacrylate significantly reduced the flame retardant properties and self-healing ability. Although methyl methacrylate (MMA) can be grafted, the grafted side chains are inert ester groups, lacking both the dynamic network of furan rings and flame retardant elements, thus leading to a decrease in material performance.

[0074] In Comparative Example 5, the step of adding glycidyl methacrylate during the preparation of the reactive flame retardant was omitted. The flame retardant in Comparative Example 5 lacks epoxy groups, resulting in decreased flame retardant and insulating properties. The epoxy groups provided by glycidyl methacrylate can participate in the ring-opening reaction, more firmly integrating the flame retardant into the cross-linked polyethylene network. Omitting this step worsens the immobilization degree and network compatibility of the flame retardant, affecting its efficiency and insulation properties, thereby reducing the performance of the cross-linked polyethylene material.

[0075] In Comparative Example 6, replacing diallyl chlorophosphate with 1,2-propadienephosphonic chloride significantly reduced flame retardancy and overall performance. In this invention, diallyl chlorophosphate (component 3) contains two allyl ester bonds for subsequent grafting, while 1,2-propadienephosphonic chloride contains an unstable propadienyl group and two P-Cl bonds, exhibiting very high reactivity. This reactivity leads to uncontrollable side reactions when reacting with DOPO, preventing the formation of the desired flame retardant structure and resulting in a significant decrease in material performance.

[0076] This invention achieves a combination of integrated flame-retardant monomers (phosphorus-nitrogen-silicon synergy + graftable / crosslinkable double bonds) and a dynamic reversible network (furan / bismaleimide DA reaction), realizing the characteristics that traditional crosslinked polyethylene cable materials struggle to simultaneously achieve: high insulation, high flame retardancy (V-0), good mechanical properties, and intelligent self-healing. This results in crosslinked polyethylene cable materials possessing excellent flame retardancy, insulation, strength, toughness, and repair performance. In the furan-modified polyethylene compatibilizer of this invention, a "furan ring" is attached to the polyethylene molecular chain, and the "furan ring" is one of the key switches for the subsequent self-healing reaction. The reactive flame retardant contains not only flame-retardant elements (phosphorus, nitrogen, silicon) but also "carbon-carbon double bonds" and "epoxy groups" that can participate in the reaction. During the heated mixing process in the internal mixer, the maleimide groups at both ends of the bismaleimide undergo a Diels-Alder (high-temperature reversible) cycloaddition reaction with the furan ring in the furan-modified polyethylene compatibilizer, initially connecting different polyethylene molecular chains to form an internal network. During the final molding in the flat vulcanizing machine, the furan-maleimide bonds undergo a reverse reaction and break again. Simultaneously, the high temperature in the flat vulcanizing machine activates the peroxide crosslinking agent dicumyl peroxide, initiating free radical polymerization reactions between polyethylene molecular chains and between polyethylene and the reactive flame retardant, forming strong carbon-carbon permanent covalent bonds. This irreversible reaction constitutes a stable, heat-resistant, permanent crosslinked network, serving as the core foundation for the mechanical strength and dimensional stability required for crosslinked polyethylene cable sheaths. During the pressure holding and cooling process after molding, the furan rings and maleimide bonds that were "unlocked" by the high temperature will, driven by molecular thermal motion, re-match and interlock within and around the permanently cross-linked network, forming an intelligent "interpenetrating double network." This results in a multi-network structure (a network composed of carbon-carbon covalent bonds + a network composed of reversible "furan-maleimide" bonds). This reversible furan ring-maleimide structure allows the cable jacket to remain in a locked state under normal conditions. When local high-temperature damage or heat treatment occurs, this high-temperature reversible locking state will break due to heat, absorbing energy, releasing stress, and preventing brittle cracking of the material. The increased mobility of the molecular chain segments due to loosening facilitates heat dissipation. When the temperature drops or returns to normal, these unlocked states return to a re-locked state, pulling together and repairing the damaged area, thereby restoring some performance.

[0077] Example 3 The specific methods for producing flame-retardant and insulated low-voltage power cables are as follows.

[0078] Filler: Alkali-free glass fiber filler rope, Changzhou Hongxing Meike Electrical Materials Co., Ltd.

[0079] Covering layer: Halogen-free, low-smoke, flame-retardant fiberglass cloth tape, Zhejiang Kaicheng Mica Tape Material Co., Ltd.

[0080] Inner lining: Halogen-free low-smoke flame-retardant oxygen barrier material, WDZ-Y-H90, CGN Top (Sichuan) New Materials Co., Ltd.

[0081] Metal armor layer: Steel strip for armored cables, Shenzhen Hezhongfu Metal Materials Co., Ltd.

[0082] Cable 1, the manufacturing process is as follows: Step 1: Twist 7 copper single wires (3mm in diameter) together and extrude insulation (using halogen-free low-smoke flame-retardant fiberglass tape) to obtain the inner core. Twist 3 inner cores together to form a cable to obtain the inner core layer of the cable. Step 2: Place a filler on the outer surface of the inner core layer to obtain a filler layer; Step 3: Set a wrapping layer on the outer surface of the filler layer, and set an inner liner layer on the outer surface of the wrapping layer; Step 4: Set a metal armor layer on the outer surface of the inner lining layer, and then set an outer sheath layer made of cross-linked polyethylene material as described in Example 1 on the outer surface of the metal armor layer.

[0083] manual Figure 1 The diagram shows the structure of cable 1, which consists of the following layers from the inside out: inner core layer (including stranded conductors and extruded insulation material), filler layer, wrapping layer, inner lining layer, metal armor layer, and outer sheath layer.

[0084] Cable 2, the manufacturing process is as follows: Step 1: Twist 7 copper single wires (3.5mm in diameter) together and extrude insulation (using halogen-free low-smoke flame-retardant fiberglass tape) to obtain the inner core. Twist 4 inner cores together to form a cable to obtain the inner core layer of the cable. Step 2: Place a filler on the outer surface of the inner core layer to obtain a filler layer; Step 3: Set a wrapping layer on the outer surface of the filler layer, and set an inner liner layer on the outer surface of the wrapping layer; Step 4: Set a metal armor layer on the outer surface of the inner lining layer, and then set an outer sheath layer made of cross-linked polyethylene material as described in Example 2 on the outer surface of the metal armor layer.

[0085] To verify the overall flame-retardant performance of the cable prepared according to this invention, a combustion test (bundled flame-retardant performance combustion test) was conducted on the finished cable 1. The combustion test conditions were: air flow rate 77.7±4.8 L / min, propane flow rate 13.5±0.5 L / min, and combustion time 40 min. The specific combustion process and results are detailed below. Figures 2 to 6 ;in, Figure 2 Diagram of the cable material before combustion; Figure 3 This is a diagram of the cables used in the combustion equipment. Figure 4 These are photos of the scene during the combustion process; Figure 5 This is a front view of the cable after it has burned. Figure 6This is a reverse view of the cable after combustion. The combustion test results show that the cable prepared according to this invention is effectively flame-retardant and has good fire-resistant properties.

Claims

1. A flame-retardant and insulated low-voltage power cable, characterized in that, From the inside out, it includes an inner core layer, a filler layer, a wrapping layer, an inner liner layer, a metal armor layer, and an outer sheath layer; the outer sheath layer is made of cross-linked polyethylene. According to the weight parts, the raw materials for preparing cross-linked polyethylene materials include: 80-120 parts of low-density polyethylene, 7-10 parts of furan-modified polyethylene compatibilizer, 7-15 parts of reactive flame retardant, 2-4 parts of bismaleimide, 1-2.5 parts of dicumyl peroxide, and 2-4 parts of additives. The furan-modified polyethylene compatibilizer is obtained by premixing low-density polyethylene with furan methacrylate, dicumyl peroxide and antioxidant, then heating and melting it before extrusion, cooling and pelletizing. The preparation method of the reactive flame retardant includes: adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and tetrahydrofuran premix to a reaction vessel, adding diallyl chlorophosphate, a mixture of triethylamine and tetrahydrofuran, stirring the reaction, raising the temperature after the reaction is completed, adding 3-aminopropyltriethoxysilane to continue the reaction, then adding glycidyl methacrylate, raising the temperature and stirring the reaction, and the reaction product is post-treated to obtain the reactive flame retardant.

2. The flame-retardant and insulated low-voltage power cable according to claim 1, characterized in that, The number of inner cores in the inner core layer is no less than two.

3. The flame-retardant and insulated low-voltage power cable according to claim 2, characterized in that, Each core is made up of at least four single wires twisted together.

4. A flame-retardant and insulated low-voltage power cable according to claim 2, characterized in that, Each inner core is made of seven single wires twisted together.

5. A flame-retardant and insulated low-voltage power cable according to claim 3 or 4, characterized in that, The material of the single wire is copper and / or copper alloy.

6. A method for preparing a flame-retardant and insulated low-voltage power cable according to any one of claims 1-5, characterized in that, The steps include the following: Step 1: Twist at least three single wires together and extrude insulation to obtain the inner core, and set multiple inner cores to form a cable as the inner core layer of the cable; Step 2: Place a filler on the outer surface of the inner core layer to obtain a filler layer; Step 3: Set a wrapping layer on the outer surface of the filler layer, and set an inner liner layer on the outer surface of the wrapping layer; Step 4: Set a metal armor layer on the outer surface of the inner lining layer, and then set an outer sheath layer on the outer surface of the metal armor layer.

7. The application of a flame-retardant and insulated low-voltage power cable according to any one of claims 1-5 in power grid facilities.

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