A composite cable for electric vehicle charging piles and a preparation method thereof

Abstract

The application provides a composite cable for electric vehicle charging piles and a preparation method thereof, wherein a semi-conductive buffer layer is arranged outside the cable core and is formed by overlapping and wrapping a first semi-conductive buffer water-blocking belt, a semi-conductive buffer belt and a water-blocking and flame-retardant composite belt in sequence, so that the semi-conductive buffer layer has multiple properties of buffering, water-blocking and flame-retardation, can buffer the mechanical extrusion stress generated by the bending, dragging and rolling of the composite cable, effectively prevents the extrusion damage of the insulation shielding layer and the cable core, and has excellent water-proof and flame-retardant properties. Meanwhile, the flame-retardant insulation sheath is prepared from polyether thermoplastic polyurethane, ethylene-vinyl acetate copolymer, a compatibilizer, a flame retardant, a foaming agent and an antioxidant, and a buffer bubble cavity is formed in the flame-retardant insulation sheath, so that the flame-retardant and bending-resistant properties of the composite cable are further enhanced, and the outdoor service life of the cable is significantly prolonged.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a composite cable for electric vehicle charging piles and its preparation method. Background Technology

[0002] With the rapid popularization of high-voltage platforms and high-power fast charging technology for new energy vehicles, the voltage level of vehicle power batteries has generally reached 800V, and high-power charging of 350kW and above has become the mainstream development direction. As the core carrier for power transmission between charging piles and vehicle batteries, the comprehensive performance of charging pile cables directly affects charging safety, power transmission efficiency and cable life.

[0003] Under high-power fast charging conditions, the cable continuously carries a large current, generating a significant amount of Joule heat in the conductor, resulting in a noticeable overall temperature rise in the cable. Conventional charging pile cable sheaths have poor heat resistance and flame retardancy. Under prolonged high-temperature conditions, the polymer materials are prone to thermal decomposition and the release of flammable gases. When the circuit experiences overload or short-circuit arcing, it can easily lead to cable combustion, flame spread, cable damage, or even equipment fires, posing significant fire safety hazards and failing to meet the long-term, high-load flame-retardant requirements of high-power charging piles. Furthermore, outdoor charging piles are constantly exposed to rain and moisture, and ordinary sheaths have poor waterproof sealing, allowing moisture to easily penetrate the cable and cause short circuits and leakage. In addition, charging pile cables are frequently subjected to laying, dragging, and vehicle crushing, which can easily cause sheath cracking and insulation layer damage, further increasing the risk of leakage and fire. This makes it difficult to simultaneously meet the multiple requirements of flame retardancy, heat dissipation, waterproofing, and mechanical shock resistance.

[0004] Therefore, it is necessary to use a special cable for charging piles that is flame-retardant, waterproof, and bend-resistant to meet the long-term outdoor safety requirements of high-voltage, high-power charging piles. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a composite cable for electric vehicle charging stations.

[0006] A composite cable for electric vehicle charging piles includes a cable core and an insulating shielding layer, a semi-conductive buffer layer, a metallic shielding layer, and a flame-retardant insulating sheath sequentially wrapped around the outside of the cable core. The cable core includes a core body and a high-temperature resistant insulating layer wrapped around the core body. The core body includes a temperature-measuring optical cable, three charging wire cores twisted around the temperature-measuring optical cable, and three signal wire cores respectively disposed in the gaps between adjacent charging wire cores. The semi-conductive buffer layer is composed of a first semi-conductive buffer water-blocking tape, a semi-conductive buffer tape, and a water-blocking and flame-retardant composite tape wrapped in an overlapping manner from the inside out. The water-blocking and flame-retardant composite tape is woven from a second semi-conductive buffer water-blocking tape and alkali-free glass fiber tape. The flame-retardant insulating sheath forms a plurality of buffer bubble cavities and is prepared from polyether-type thermoplastic polyurethane, ethylene-vinyl acetate copolymer, compatibilizer, flame retardant, foaming agent, and antioxidant.

[0007] Preferably, the insulating shielding layer is a cross-linked polyethylene insulating shielding layer; the metal shielding layer is a galvanized copper mesh braided shielding layer; and the high-temperature resistant insulating layer is a polyimide insulating layer.

[0008] Preferably, both the first semiconductive buffer water-blocking strip and the second semiconductive buffer water-blocking strip include a semiconductive non-woven fabric layer, a water-blocking powder layer, and a semiconductive fluffy cotton layer arranged from the inside out.

[0009] Preferably, the flame retardant includes aluminum diethylphosphonate, melamine polyphosphate, polysiloxane masterbatch, and zinc borate.

[0010] Preferably, the foaming agent includes azodicarbonamide, zinc oxide, zinc stearate, and a nucleating agent; the antioxidant is a compound of antioxidant 168 and antioxidant 1010 in a mass ratio of 1:1.

[0011] Preferably, the temperature-measuring optical cable includes a multimode optical fiber and a loose tube and a flexible protective sleeve sequentially wrapped around the multimode optical fiber, and water-blocking fiber grease is filled between the multimode optical fiber and the loose tube; the charging core includes a charging conductor and a first insulating layer and an inner sheath layer sequentially wrapped around the charging conductor; the signal core includes a twisted pair and an aluminum foil shielding layer wrapped around the twisted pair, and the twisted pair is composed of two sets of signal conductors wrapped with a second insulating layer twisted together.

[0012] Preferably, the outer surface of the flame-retardant insulating sheath is coated with an anti-ultraviolet coating, and the surface of the flame-retardant insulating sheath is recessed inward to form several annular grooves, and a reflective ring is installed in the annular grooves.

[0013] This invention also provides a method for preparing a composite cable for electric vehicle charging piles, comprising: step S1, selecting raw materials for preparing a flame-retardant insulating sheath; wherein, by weight, the raw material composition is: 80-85 parts of polyether thermoplastic polyurethane, 10-15 parts of ethylene-vinyl acetate copolymer, 2-3 parts of compatibilizer, 18-20 parts of aluminum diethylphosphinate, 10-14 parts of melamine polyphosphate, 2-3 parts of zinc borate, and 1-2 parts of polysiloxane masterbatch. Antioxidant 0.6-1 parts, nucleating agent 1-3 parts, azodicarbonamide 1.5-2.0 parts, zinc oxide 0.7-0.9 parts, zinc stearate 0.3-0.6 parts; Step S2: Add polyether-type thermoplastic polyurethane, ethylene-vinyl acetate copolymer, and compatibilizer to a high-speed mixer, stir at room temperature for 3-5 minutes, mix evenly, and obtain mixture one; Step S3: Add aluminum diethylphosphinate, melamine polyphosphate, zinc borate, and polysiloxane to mixture one in sequence. Alkane masterbatch and antioxidant are stirred for 5-8 minutes; then azodicarbonamide, zinc oxide, zinc stearate and nucleating agent are added, and stirred at low speed until uniform to obtain mixture two; in step S4, mixture two is fed into a twin-screw extruder, the extrusion temperature is set to 160-180℃ and the screw speed is 30-50 r / min. After mixture two is fully melted and plasticized by the extruder, it is extruded from the die head and coated onto the surface of a pre-made cable core material. The azodicarbonamide in mixture two is also coated onto the zinc oxide. Under the activation of zinc stearate and nucleating agent, it rapidly foams, thereby forming a flame-retardant insulating sheath with several buffered bubble cavities inside on the surface of the prefabricated cable core material; Step S5: The prefabricated core material with the flame-retardant insulating sheath is uniformly pulled and first sent to a hot water bath at a temperature of 35℃~38℃ for preliminary cooling; then sent to a warm water bath at 28℃~30℃ for further cooling and shaping; finally sent to a cold water bath at 18℃~20℃ for complete cooling and curing, to obtain the composite cable.

[0014] Preferably, the prefabricated core material includes a cable core and an insulating shielding layer, a semi-conductive buffer layer, and a metal shielding layer sequentially covering the outside of the cable core.

[0015] Preferably, the method further includes: step S6, cleaning the surface of the flame-retardant insulating sheath of the composite cable, then applying an anti-UV coating to its surface, and then curing it at 70±5℃ for 8-9 hours, so that an anti-UV coating is formed on the surface of the composite cable. The anti-UV coating has a thickness of 20-55 μm, and the anti-UV coating is an acrylic coating containing nano-zinc.

[0016] The beneficial effects of this invention are as follows: This invention provides a composite cable for electric vehicle charging piles. By integrating a temperature-measuring optical cable inside the cable core, the internal operating temperature of the cable can be monitored in real time, and the risk of overheating under high-current fast charging conditions can be predicted in a timely manner, thereby improving the safety monitoring capability of high-voltage charging.

[0017] Secondly, the semi-conductive buffer layer is formed by overlapping and wrapping a first semi-conductive buffer water-blocking strip, a semi-conductive buffer strip, and a water-blocking and flame-retardant composite strip in sequence. Through the multi-layer composite buffer structure, the semi-conductive buffer layer has multiple properties of buffering, water blocking, and flame retardancy. It can buffer the mechanical extrusion stress generated by bending, dragging, and crushing of the composite cable, effectively prevent the insulation shielding layer and cable core from being crushed and damaged, and has excellent waterproof and flame-retardant properties.

[0018] Finally, the flame-retardant insulating sheath and the internal buffer bubble chamber further enhance the flame-retardant and bending resistance of the composite cable, thereby significantly extending its service life outdoors and making it suitable for frequent outdoor winding and retraction scenarios of charging piles. Attached Figure Description

[0019] Figure 1 A schematic diagram of the cross-sectional structure of a composite cable for electric vehicle charging piles provided by the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the temperature-measuring optical cable provided by the present invention; Figure 3 A schematic flowchart illustrating a method for preparing a composite cable for an electric vehicle charging pile, provided by the present invention. Attached image labels: 1. Cable core; 2. Insulation shielding layer; 3. Semi-conductive buffer layer; 4. Metallic shielding layer; 5. Flame-retardant insulating sheath; 51. Buffer bubble cavity; 6. High-temperature resistant insulation layer; 7. Temperature measuring optical cable; 71. Multimode optical fiber; 72. Loose tube; 73. Flexible protective sleeve; 74. Water-blocking fiber grease; 8. Charging core; 9. Signal core; 10. UV-resistant coating. Detailed Implementation

[0020] To provide a more detailed description of the present invention, the following description is provided in conjunction with the accompanying drawings. It should be noted that the embodiments described below are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Example 1

[0021] refer to Figure 1 and Figure 2 As shown, a composite cable for electric vehicle charging piles includes a cable core 1 and an insulating shielding layer 2, a semi-conductive buffer layer 3, a metallic shielding layer 4, and a flame-retardant insulating sheath 5 sequentially wrapped around the outside of the cable core 1.

[0022] The cable core 1 includes a core body and a high-temperature resistant insulation layer 6 covering the core body. In this embodiment, the high-temperature resistant insulation layer 6 is a polyimide insulation layer.

[0023] By setting a polyimide insulation layer on the outside of the core, the high temperature resistance, excellent insulation strength, and high temperature resistance of polyimide can be fully utilized to effectively prevent the inner core from being broken down by high temperature during use, thus significantly improving the high temperature insulation stability of cable core 1.

[0024] The core includes a temperature measuring optical cable 7, three charging wire cores 8 twisted outside the temperature measuring optical cable 7, and three signal wire cores 9 respectively disposed in the gaps on the outside of adjacent charging wire cores 8.

[0025] The temperature measuring optical cable 7 includes a multimode optical fiber 71, a loose tube 72 and a flexible protective sleeve 73 wrapped around the multimode optical fiber 71 in sequence, and water-blocking fiber paste 74 is filled between the multimode optical fiber 72 and the loose tube 72.

[0026] The water-blocking fiber grease 74 acts as a lubricant and buffer, protecting the multimode optical fiber 71 from tensile damage. In this embodiment, an optical fiber shielding layer is provided between the loose tube sleeve 72 and the flexible protective sleeve 73.

[0027] When the temperature-measuring optical cable 7 detects the heat generated by the cable core 1, the light pulse propagates in the multimode optical fiber 71 and interacts with the fiber molecules to cause Raman scattering. The Raman scattering propagates along the optical fiber and is reflected back to an optical fiber sensor connected to one end of the temperature-measuring optical cable 7. The optical fiber sensor sends the returned signal to a signal processing module, and then uses the ratio of anti-Stokes light intensity to Stokes light intensity in Raman scattering theory to measure the internal temperature of the cable body. The positioning can be achieved by using the principle of optical time-domain reflectometry.

[0028] By setting up the temperature-measuring optical cable 7, the operating temperature of the cable core can be obtained, and the user can be promptly reminded of the cable temperature, effectively avoiding safety hazards caused by overheating of the cable core 1, and significantly improving the safety of cable use.

[0029] The charging core 8 includes a charging conductor and a first insulating layer and an inner sheath layer sequentially covering the charging conductor; the signal core 9 includes a twisted pair and an aluminum foil shielding layer wrapped around the twisted pair, the twisted pair being composed of two sets of signal conductors covered with a second insulating layer twisted together.

[0030] In this embodiment, both the charging conductor and the signal conductor are aluminum alloy flexible conductors, and the diameter of a single wire in the aluminum alloy flexible conductor is 0.20-0.35mm. The use of aluminum alloy flexible conductors for both the charging conductor and the signal conductor, compared to traditional conductor materials, provides better flexibility while maintaining a certain level of conductivity. This makes the cable more flexible during use, easier to bend and store, and less prone to conductor breakage due to repeated bending, thus improving convenience and reliability.

[0031] The aluminum foil shielding layer can prevent electromagnetic interference between the wire cores and prevent external electromagnetic interference signals from affecting the signal transmission inside the cable core 9, thereby improving the cable's anti-interference performance.

[0032] The insulating shielding layer 2 is a cross-linked polyethylene insulating shielding layer; the cross-linked polyethylene insulating shielding layer has good electrical uniformity, which can evenly disperse the high voltage electric field of the cable core 1, eliminate the phenomenon of local electric field concentration, reduce corona discharge, and reduce the insulation aging rate under long-term high voltage operation.

[0033] The semi-conductive buffer layer 3 is composed of a first semi-conductive buffer water-blocking tape, a semi-conductive buffer tape, and a water-blocking and flame-retardant composite tape, which are overlapped and wrapped from the inside out. The water-blocking and flame-retardant composite tape is woven from a second semi-conductive buffer water-blocking tape and an alkali-free glass fiber tape.

[0034] By setting a semiconductive buffer layer 3 outside the cable core 1, which is composed of a first semiconductive buffer water-blocking tape, a semiconductive buffer tape, and a water-blocking and flame-retardant composite tape wrapped in sequence, the outer second semiconductive buffer water-blocking tape further achieves electric field equalization and water-blocking protection. The alkali-free glass fiber has high temperature resistance and non-flammability, which can form a flame-retardant and heat-insulating barrier. When the cable overheats, it prevents the flame from spreading to the inner cable core, greatly improving the flame-retardant safety performance of the cable. The middle semiconductive buffer tape has stable semiconductive properties and can connect the inner first semiconductive buffer water-blocking tape and the outer water-blocking and flame-retardant composite tape, so that the overall potential of the semiconductive buffer layer 3 is uniform. It can also absorb the squeezing and friction stress generated by cable bending, dragging, and rolling. The cost is significantly reduced compared to the structure of three layers of semiconductive buffer tape directly overlapping and wrapping. The inner first semiconductive buffer water-blocking tape can balance the electric field of the insulation shielding outer surface, eliminate the hidden danger of interface partial discharge, reduce the risk of insulation aging and breakdown during long-term high-voltage operation, and at the same time prevent moisture from penetrating inward, achieving secondary water-blocking protection.

[0035] Through the composite arrangement of each layer, the semi-conductive buffer layer 3 has multiple properties such as semi-conductive voltage equalization, buffering, water blocking, and flame retardancy. It can buffer the mechanical extrusion stress generated by bending, dragging, and rolling of the composite cable, effectively improve the cable's resistance to bending and impact, prevent the insulation shield layer 2 and cable core 1 from being crushed and damaged, and has excellent waterproof and flame retardant properties, thus avoiding the risks that exist in the composite cable under various accidental conditions.

[0036] Both the first and second semi-conductive buffer water-blocking strips comprise, from the inside out, a semi-conductive non-woven fabric layer, a water-blocking powder layer, and a semi-conductive fluffy cotton layer. In this embodiment, the water-blocking powder layer is a polyacrylate water-blocking powder layer.

[0037] The semi-conductive non-woven fabric layer can balance the electric field and eliminate the risk of partial discharge at the interface. The water-blocking powder in the middle expands rapidly when it comes into contact with water to block the water seepage channels. Combined with the fluffy cotton layer, it forms a water storage buffer space. The multi-layer synergy achieves efficient longitudinal and radial water blocking, effectively preventing outdoor moisture from seeping into the cable core 1. At the same time, the semi-conductive fluffy cotton is soft and can further enhance the cushioning and shock absorption effect.

[0038] The metal shielding layer 4 is a galvanized copper mesh braided shielding layer. The galvanized copper mesh braided shielding layer has excellent shielding performance, which can effectively block the electromagnetic radiation generated by high-voltage charging and prevent interference with signal line transmission. At the same time, the galvanized layer can delay the oxidation and corrosion of the copper mesh, extending the outdoor service life of the metal shielding layer 4.

[0039] The flame-retardant insulating sheath 5 forms a plurality of buffer bubble cavities 51, and the flame-retardant insulating sheath 5 is prepared from polyether thermoplastic polyurethane, ethylene-vinyl acetate copolymer, compatibilizer, flame retardant, foaming agent and antioxidant.

[0040] By using a composite of polyether-type thermoplastic polyurethane and ethylene-vinyl acetate copolymer as the resin matrix, along with a compatibilizer, the two resins are tightly bonded at the interface, exhibiting excellent compatibility. The resulting flame-retardant insulating sheath 5 possesses high overall toughness, bend resistance, low-temperature resistance, and is not prone to brittleness, making it suitable for the frequent bending and winding conditions of outdoor charging piles. Furthermore, the addition of flame retardants, foaming agents, and antioxidants not only provides excellent flame-retardant properties but also creates several buffer air bubbles internally, thereby enhancing the sheath's cushioning, shock absorption, and compression resistance. This effectively absorbs the mechanical impact of the charging pile cable during dragging, winding, crushing, and bending, preventing cracking and internal structural damage during use. Consequently, the composite cable's outdoor service life is significantly extended, making it suitable for the frequent winding scenarios of outdoor charging piles.

[0041] The flame retardant includes aluminum diethylphosphonate, melamine polyphosphate, polysiloxane, and zinc borate.

[0042] By employing a composite flame-retardant system of aluminum diethylphosphonate, melamine polyphosphate, polysiloxane masterbatch, and zinc borate, a multi-layered synergistic effect of organophosphorus, nitrogen, boron, and silicon flame-retardant components is achieved. Specifically, aluminum diethylphosphonate and melamine polyphosphate exert phosphorus-nitrogen gas-phase flame-retardant effects, capturing combustion free radicals and releasing inert diluent gases. Zinc borate, upon heating, dehydrates and absorbs heat, generating boron-based glassy substances to assist in solid-phase char formation. Meanwhile, the polysiloxane masterbatch migrates to the surface at high temperatures to construct a high-temperature resistant silicon barrier layer. This allows the flame-retardant insulation sheath 5 to rapidly form a dense borosilicate composite expanded carbon layer when the composite cable catches fire. The carbon layer structure is intact and resistant to cracking, effectively isolating oxygen, inhibiting the generation of combustible gases through substrate decomposition, significantly reducing heat conduction inward, and blocking the continuous spread of flames. This achieves a comprehensive effect of no melting dripping, low smoke release, and a high flame-retardant rating, significantly improving the long-term fire safety performance of the composite cable under fire conditions.

[0043] The foaming agent includes azodicarbonamide, zinc oxide, a nucleating agent, and zinc stearate. In this embodiment, the nucleating agent is an organophosphate, such as sodium 2,2-methylene-bis-(4,6-di-tert-butylphenyl) phosphate.

[0044] The foaming agent uses azodicarbonamide as the main foaming agent, and zinc oxide effectively reduces the foaming decomposition temperature, promotes uniform decomposition and foaming of the main foaming agent, and avoids the problem of cell deformity caused by excessively fast or slow foaming rate. At the same time, zinc stearate is added to improve the dispersion uniformity of each raw material component, reduce material agglomeration, reduce extrusion molding resistance, and avoid sticking to the mold and uneven thickness during the sheath molding process.

[0045] The addition of zinc oxide and zinc stearate can regulate the foaming rate and cell uniformity, resulting in regular bubble formation and stable, uniform pore size, thus avoiding defects such as voids, broken bubbles, and uneven wall thickness. Simultaneously, the nucleating agent provides numerous uniform nucleation sites during the sheath foaming process, effectively reducing the foaming activation energy and promoting uniform, dense bubble formation. This avoids molding defects such as large bubbles, voids, and inconsistent cell size, further refining and standardizing the cell structure, significantly improving foaming uniformity and the density and surface smoothness of the flame-retardant insulating sheath 5.

[0046] In this embodiment, the average pore size of the buffer bubble cavity 51 of the flame-retardant insulating sheath 5 is 90–130 μm, and the pore density is approximately 3.2 × 10⁻⁶. 6 The number of bubbles per cm³ is approximately 32 vol%, and the buffer bubble chambers 51 are closed-cell structures with uniform distribution.

[0047] The antioxidant is a compound of antioxidant 168 and antioxidant 1010 in a mass ratio of 1:1.

[0048] Antioxidant 1010 effectively captures free radicals generated during the thermo-oxidative aging of materials, terminating the chain aging reaction and inhibiting the oxidative degradation of the sheath material at its source. Antioxidant 168 efficiently decomposes hydrogen peroxides generated during high-temperature processing and long-term operation of materials, preventing peroxides from continuously inducing aging reactions and effectively inhibiting high-temperature yellowing of materials. The two antioxidants work synergistically to significantly inhibit the thermo-oxidative aging and yellowing degradation of the flame-retardant insulation sheath material under long-term high-temperature, energized, and outdoor conditions, preventing sheath cracking, powdering, and performance degradation, and greatly improving the long-term stability and aging resistance of the cable.

[0049] The outer surface of the flame-retardant insulating sheath 5 is coated with an anti-ultraviolet coating 10, and the surface of the flame-retardant insulating sheath 5 is recessed inward to form several annular grooves, and a reflective ring is installed in the annular grooves.

[0050] By coating the outer surface of the flame-retardant insulating sheath 5 with an anti-ultraviolet coating 10, ultraviolet rays in outdoor sunlight can be effectively blocked and absorbed, significantly improving the cable's outdoor weather resistance and resistance to ultraviolet aging. This allows the charging pile cable to withstand complex outdoor conditions such as exposure to sunlight and rain for a long time. Simultaneously, by setting a reflective ring on the outside of the flame-retardant insulating sheath 5, the location of the composite cable can be displayed at night, thus serving as a reminder of the cable's position and preventing damage caused by running over the cable due to poor visibility at night. This also prevents new energy vehicles from running over the charging cable when entering the charging pile parking space due to limited visibility at night. Example 2

[0051] refer to Figure 1 and Figure 3 As shown, the present invention also provides a method for preparing a composite cable for electric vehicle charging piles, comprising: Step S1: Select raw materials for preparing flame-retardant insulating sheaths; The raw material composition, by weight, is as follows: 80-85 parts of polyether-type thermoplastic polyurethane, 10-15 parts of ethylene-vinyl acetate copolymer, 2-3 parts of compatibilizer, 18-20 parts of aluminum diethylphosphinate, 10-14 parts of melamine polyphosphate, 2-3 parts of zinc borate, 1-2 parts of polysiloxane masterbatch, 0.6-1 part of antioxidant, 1-3 parts of nucleating agent, 1.5-2.0 parts of azodicarbonamide, 0.7-0.9 parts of zinc oxide, and 0.3-0.6 parts of zinc stearate.

[0052] Step S2: Add polyether-type thermoplastic polyurethane, ethylene-vinyl acetate copolymer and compatibilizer into a high-speed mixer, stir at room temperature for 3-5 minutes until uniformly mixed, and obtain mixture one.

[0053] Step S3: Add aluminum diethylphosphonate, melamine polyphosphate, zinc borate, polysiloxane masterbatch, and antioxidant to mixture one in sequence, and stir for 5-8 minutes; then add azodicarbonamide, zinc oxide, zinc stearate, and nucleating agent, and stir at low speed until uniform to obtain mixture two.

[0054] First, polyether-type thermoplastic polyurethane, ethylene-vinyl acetate copolymer, and compatibilizer are premixed to achieve uniform blending of the base materials. Then, aluminum diethylphosphinate, melamine polyphosphate, zinc borate, polysiloxane masterbatch, and antioxidant are added sequentially and mixed. Finally, azodicarbonamide, zinc oxide, zinc stearate, and nucleating agent are added at a low speed. This effectively avoids powder agglomeration and sedimentation, while preventing premature failure and thermal decomposition of the foaming agent. It maximizes the retention of the activity of each functional component and ensures that all kinds of additives are uniformly dispersed in the resin system. This results in uniform flame retardancy, antioxidant, and foaming cushioning performance after the sheath is molded, eliminating local performance defects.

[0055] Step S4: Feed the mixture into a twin-screw extruder, set the extrusion temperature to 160-180℃ and the screw speed to 30-50 r / min. After the mixture is fully melted and plasticized by the extruder, it is extruded from the die head and coated onto the surface of a precast cable core. The azodicarbonamide in the mixture rapidly foams under the activation of zinc oxide, zinc stearate and nucleating agent, thereby forming a flame-retardant insulating sheath 5 with several buffered bubble cavities inside on the surface of the precast cable core.

[0056] By leveraging the synergistic activation effect of zinc oxide and zinc stearate, the foaming temperature of azodicarbonamide is effectively reduced, and the extrusion processing temperature range is matched. This allows for the stable formation of uniformly sized and regularly distributed buffer bubble cavities inside the sheath, significantly improving the cushioning, shock absorption, and compression resistance of the manufactured flame-retardant insulating sheath 5.

[0057] Step S5: The prefabricated core material with flame-retardant insulating sheath is pulled at a uniform speed and first sent to a hot water bath at a temperature of 35℃~38℃ for initial cooling; then sent to a warm water bath at 28℃~30℃ for further cooling and shaping; and finally sent to a cold water bath at 18℃~20℃ for complete cooling and curing to obtain the composite cable.

[0058] By adopting a gradient segmented cooling and shaping process, which sequentially involves initial shaping with hot water, secondary cooling with warm water, and complete solidification with cold water, compared to the direct low-temperature rapid cooling process, the internal stress of the sheath can be effectively eliminated. This avoids defects such as warping, cracking, surface shrinkage cavities, and uneven wall thickness caused by rapid cooling of the sheath. It also ensures stable shaping of the foam cavity structure, a smooth appearance of the flame-retardant insulating sheath 5, and ensures that the flame-retardant insulating sheath 5 is tightly wrapped and firmly attached to the inner structure, significantly improving the overall structural stability of the cable.

[0059] Step S6: Clean the surface of the flame-retardant insulating sheath of the composite cable, then apply an anti-UV coating to its surface, and cure it at 70±5℃ for 8-9 hours to form an anti-UV coating on the surface of the composite cable. The anti-UV coating has a thickness of 20-55 μm, and the anti-UV coating is an acrylic coating containing nano-zinc.

[0060] By applying an acrylic UV-resistant coating containing nano-zinc and using a constant temperature (70±5℃) long-term curing process, the coating can fully cross-link and form a dense UV-resistant coating with a uniform and stable thickness of 20-55μm. The nano-zinc component can effectively shield and absorb outdoor ultraviolet rays. Combined with the excellent film-forming properties and adhesion of acrylic resin, it firmly adheres to the surface of the flame-retardant insulation sheath 5, avoiding the problems of embrittlement, cracking, and powdering of the flame-retardant insulation sheath 5 caused by outdoor sun exposure and aging, and significantly improving the outdoor weather resistance and service life of the cable.

[0061] Preferably, the prefabricated core material includes a cable core 1 and an insulating shielding layer 2, a semi-conductive buffer layer 3, and a metal shielding layer 4 sequentially covering the outside of the cable core 1.

[0062] Preferably, in this embodiment, the raw materials of the flame-retardant insulating sheath, by weight, consist of: 85 parts of polyether-type thermoplastic polyurethane, 15 parts of ethylene-vinyl acetate copolymer, 3 parts of compatibilizer, 20 parts of aluminum diethylphosphinate, 14 parts of melamine polyphosphate, 3 parts of zinc borate, 2 parts of polysiloxane masterbatch, 1 part of antioxidant, 3 parts of nucleating agent, 2 parts of azodicarbonamide, 0.9 parts of zinc oxide, and 0.6 parts of zinc stearate.

[0063] To clearly verify the role and value of each key raw material in the five components of the flame-retardant insulating sheath of this invention, samples were prepared using the optimal proportions of the components. Five sets of the five components of the flame-retardant insulating sheath with the above-mentioned preferred weight ratios were prepared. The first sample, designated as Test Example 1, retained all components. The following components were removed sequentially from samples 2-5: "aluminum diethylphosphinate, melamine polyphosphate, zinc borate, polysiloxane masterbatch," "azodicarbonamide, zinc oxide, zinc stearate, nucleating agent," "antioxidant," and "aluminum diethylphosphinate, melamine polyphosphate, zinc borate, polysiloxane masterbatch, antioxidant, nucleating agent, azodicarbonamide, zinc oxide, zinc stearate." Samples 2-5 were then designated as: Control Groups 1, 2, and 3, respectively. 4. The raw materials of the specified percentage are mixed and then fully melted and plasticized in an extruder. The mixture is then extruded from the die and applied to the surface of different prefabricated cable cores of the same specification, structure, and material. Samples of the resulting cables are then tested for flame retardancy, anti-aging properties, and bending resistance. The test follows the VW-1 vertical burning test method for single cables in UL1581, using a 500W Bunsen burner with a flame height of 125mm. The flame is applied for 15 seconds, then removed and allowed to stand for 15 seconds, repeated 5 times. The total afterburning time, the charred area of ​​the indicator flag on the upper part of the sample, and whether the burning drips ignite the bottom degreased cotton are recorded to determine whether the VW-1 qualification requirements are met. Failure to meet these requirements results in non-compliance. The mandatory VW-1 qualification criteria are: total afterburning time ≤ 60s over 5 cycles, charred area of ​​the indicator flag not exceeding 25%, and burning drips not igniting the bottom degreased cotton. The thermo-oxidative aging yellowing level test is conducted according to GB / T250 and GB / T7141.2 standards. Samples are placed in an environment of 100℃±2℃ for 48 hours of thermo-oxidative aging. After cooling, the samples are rated using a gray scale for color fastness. The rating rule is that the higher the level, the more severe the yellowing aging. Level 1 indicates no obvious yellowing, and Level 4 indicates severe yellowing and chalking. This accurately characterizes the material's anti-aging and anti-yellowing performance. Repeated bending resistance test: According to GB / T2951.21-2020 standard for mechanical bending test of cable sheaths, a bending radius of 6 times the cable outer diameter is uniformly selected. A constant bending frequency is set to simulate the actual working conditions of charging pile cables. Continuous reciprocating bending tests are performed on the cable sheath, and the number of bends at which the sheath first shows micro-cracks and damage is recorded.

[0064] Finally, the performance test results are shown in Table 1 below: Table 1

[0065] As shown in Table 1, the test data of this invention demonstrates that the rational compounding of flame retardant additives, foaming agents, and antioxidants results in a significant synergistic effect among the components. The complete formulation exhibits optimal overall performance in terms of flame retardancy, resistance to thermo-oxidative aging, bending fatigue resistance, buffer structure stability, and mechanical strength retention. The absence of the flame retardant system alone directly reduces the cable's fire safety rating; the absence of the foaming system results in the loss of the buffer bubble cavity structure, significantly reducing the cable's resistance to compression and bending; the absence of the antioxidant system leads to easy aging and yellowing of the sheath and rapid degradation of mechanical properties; and the absence of all functional additives results in a complete failure of the cable's overall performance.

[0066] Meanwhile, to verify the special role of zinc borate and polysiloxane masterbatch in the flame retardant system of this embodiment, samples were prepared using the optimal proportion of components. Four sets of the above-mentioned preferred weight ratio of the flame-retardant insulating sheath 5-component raw materials were prepared. The first sample was used as a test example, retaining all components. The components "zinc borate, polysiloxane masterbatch," "zinc borate," and "polysiloxane masterbatch" were removed from samples 2-4 in sequence. Samples 2-4 were then designated as control groups 5, 6, and 7, respectively. After mixing these percentage-based components, they were fully melted and plasticized using an extruder, then extruded from the die head and coated onto materials of the same specification and structure. Different prefabricated cable core materials were used to sample the finished cables. After the finished cables cooled and solidified, the prepared flame-retardant insulation sheaths were peeled off. Samples were then uniformly tested for flame retardancy, smoke suppression, and heat release performance according to the corresponding national standards. Flame retardancy rating testing was conducted according to GB / T2408-2021, using the vertical combustion method to test the self-extinguishing performance of the samples after flame removal and the ignition of molten droplets, thus determining the flame retardancy rating. Limiting oxygen index (LOI) was tested according to GB / T2406.2, using an oxygen-nitrogen mixed gas flow to ignite the sample and measure the minimum oxygen concentration required to sustain combustion; a higher value indicates greater ignition difficulty. Smoke density (SDR) was tested according to GB / T8323.2, using a closed smoke box with an open flame to burn the sample, calculating the smoke production level based on light transmittance; a higher value indicates more smoke production. Peak heat release (PHRR) was measured using a cone calorimeter (GB / T16172), baking the sample with constant thermal radiation, calculating the peak heat release based on oxygen consumption; a lower value indicates milder heat release during combustion.

[0067] The test results are shown in Table 2: Table 2

[0068] As can be seen from the test data in Table 2, compared with control group 2, the flame retardant and smoke-suppressing performance and heat release resistance of comparative example 5 showed a sharp decline, with the limiting oxygen index dropping to 28.5%, significantly reducing the difficulty of combustion; the smoke density level was as high as 113, with extremely large smoke production during combustion; the peak heat release rate reached 402kW / m², indicating intense heat release during combustion, and the vertical combustion level was only V-1, with no self-extinguishing advantage, and the fire safety performance was relatively ordinary.

[0069] Comparative Example 6 utilizes the polysiloxane component to form a dense silica-based barrier char layer on the combustion surface, effectively blocking some heat transfer and smoke diffusion. Therefore, its overall performance is superior to Comparative Examples 5 and 7. However, due to the loose structure and insufficient mechanical strength of the pure silica char layer, and the lack of filling, cross-linking, and curing reinforcement from zinc borate, it cannot effectively suppress melt flow during combustion, resulting in the problem of igniting molten droplets. Ultimately, the flame retardant rating cannot reach V-0, indicating certain defects in flame retardant stability.

[0070] In contrast, control group 7 relied on zinc borate to increase melt viscosity and suppress excessive flow. Although the flame retardant rating could reach V-0, it lacked a high-temperature resistant silicon layer to block heat and smoke. Its smoke density and heat release rate were significantly higher than control group 2, highlighting its shortcomings in smoke suppression, heat insulation, and heat resistance.

[0071] Therefore, it can be seen that in the composition of the flame-retardant insulating sheath provided in this application, by compounding a limited amount of zinc borate and polysiloxane masterbatch, the two work together to construct a dense borosilicate composite carbon layer, which, together with aluminum diethylphosphonate and melamine polyphosphate, forms a gas-solid two-phase flame-retardant system. This system can suppress combustion, block heat, reduce smoke generation, and prevent ignition dripping, achieving a comprehensive effect of V-0 flame retardancy, no ignition dripping, and low smoke and low heat release. As a result, the flame-retardant insulating sheath 5 has excellent comprehensive fire protection performance with high oxygen index, low smoke density, and low heat release rate, which greatly improves the safety and flame resistance stability of the cable insulation sheath.

[0072] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention and do not limit the invention to the specific implementations described. Obviously, other modifications and variations can be made based on the content of this specification. The embodiments selected and specifically described in this specification are intended to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. They are not intended to limit the invention, and any simple modifications to the invention fall within the scope of protection of this invention.

Claims

1. A composite cable for electric vehicle charging piles, characterized in that, It includes a cable core and an insulating shielding layer, a semi-conductive buffer layer, a metal shielding layer and a flame-retardant insulating sheath sequentially wrapped around the outside of the cable core; The cable core includes a core body and a high-temperature resistant insulation layer covering the core body; the core body includes a temperature measuring optical cable, three charging wire cores twisted outside the temperature measuring optical cable, and three signal wire cores respectively disposed in the gaps on the outer sides of adjacent charging wire cores. The semi-conductive buffer layer is composed of a first semi-conductive buffer water-blocking tape, a semi-conductive buffer tape, and a water-blocking and flame-retardant composite tape, which are overlapped and wrapped sequentially from the inside to the outside; the water-blocking and flame-retardant composite tape is woven from a second semi-conductive buffer water-blocking tape and an alkali-free glass fiber tape. The flame-retardant insulating sheath forms several buffer bubble cavities, and the flame-retardant insulating sheath is made of polyether thermoplastic polyurethane, ethylene-vinyl acetate copolymer, compatibilizer, flame retardant, foaming agent and antioxidant.

2. The composite cable for electric vehicle charging piles according to claim 1, characterized in that, The insulating shielding layer is a cross-linked polyethylene insulating shielding layer; the metal shielding layer is a galvanized copper mesh braided shielding layer; and the high-temperature resistant insulating layer is a polyimide insulating layer.

3. The composite cable for electric vehicle charging piles according to claim 1, characterized in that, Both the first and second semi-conductive buffer water-blocking strips include a semi-conductive non-woven fabric layer, a water-blocking powder layer, and a semi-conductive fluffy cotton layer arranged from the inside out.

4. The composite cable for electric vehicle charging piles according to claim 1, characterized in that, The flame retardant includes aluminum diethylphosphonate, melamine polyphosphate, polysiloxane masterbatch, and zinc borate.

5. A composite cable for electric vehicle charging piles according to claim 1, characterized in that, The foaming agent includes azodicarbonamide, zinc oxide, zinc stearate, and a nucleating agent; the antioxidant is a compound of antioxidant 168 and antioxidant 1010 in a mass ratio of 1:

1.

6. A composite cable for electric vehicle charging piles according to claim 1, characterized in that, The temperature-measuring optical cable includes a multimode optical fiber and a loose tube and a flexible protective sleeve sequentially wrapped around the multimode optical fiber, with water-blocking fiber grease filling the space between the multimode optical fiber and the loose tube; the charging core includes a charging conductor and a first insulating layer and an inner sheath layer sequentially wrapped around the charging conductor; the signal core includes a twisted pair and an aluminum foil shielding layer wrapped around the twisted pair, the twisted pair being composed of two sets of signal conductors covered with a second insulating layer twisted together.

7. A composite cable for electric vehicle charging piles according to claim 1, characterized in that, The outer surface of the flame-retardant insulating sheath is coated with an anti-ultraviolet coating, and the surface of the flame-retardant insulating sheath is recessed inward to form several annular grooves, and a reflective ring is installed in the annular grooves.

8. A method for preparing a composite cable for electric vehicle charging piles, characterized in that, include: Step S1: Select the raw materials for preparing the flame-retardant insulating sheath; wherein, by weight, the raw material composition is as follows: 80-85 parts of polyether thermoplastic polyurethane, 10-15 parts of ethylene-vinyl acetate copolymer, 2-3 parts of compatibilizer, 18-20 parts of aluminum diethylphosphinate, 10-14 parts of melamine polyphosphate, 2-3 parts of zinc borate, 1-2 parts of polysiloxane masterbatch, 0.6-1 part of antioxidant, 1-3 parts of nucleating agent, 1.5-2.0 parts of azodicarbonamide, 0.7-0.9 parts of zinc oxide, and 0.3-0.6 parts of zinc stearate; Step S2: Add polyether-type thermoplastic polyurethane, ethylene-vinyl acetate copolymer and compatibilizer into a high-speed mixer, stir at room temperature for 3-5 minutes, mix evenly, and obtain mixture one; Step S3: Add aluminum diethylphosphonate, melamine polyphosphate, zinc borate, polysiloxane masterbatch, and antioxidant to mixture one in sequence, and stir for 5-8 minutes; then add azodicarbonamide, zinc oxide, zinc stearate, and nucleating agent, and stir at low speed until uniform to obtain mixture two. Step S4: Feed the mixture 2 into a twin-screw extruder, set the extrusion temperature to 160-180℃ and the screw speed to 30-50 r / min. After the mixture 2 is fully melted and plasticized by the extruder, it is extruded from the die head and coated onto the surface of a pre-made cable core. The azodicarbonamide in the mixture 2 is rapidly foamed under the activation of zinc oxide, zinc stearate and nucleating agent, thereby forming a flame-retardant insulating sheath with several buffer bubble cavities inside on the surface of the pre-made cable core. Step S5: The prefabricated core material with flame-retardant insulating sheath is pulled at a uniform speed and first sent to a hot water bath at a temperature of 35℃~38℃ for initial cooling; then sent to a warm water bath at 28℃~30℃ for further cooling and shaping; and finally sent to a cold water bath at 18℃~20℃ for complete cooling and curing to obtain the composite cable.

9. A method for preparing a composite cable for an electric vehicle charging pile according to claim 8, characterized in that, The prefabricated core material includes a cable core and an insulating shielding layer, a semi-conductive buffer layer, and a metal shielding layer sequentially wrapped around the outside of the cable core.

10. A method for preparing a composite cable for an electric vehicle charging pile according to claim 8, characterized in that, It also includes: step S6, cleaning the surface of the flame-retardant insulation sheath of the composite cable, then applying an anti-UV coating to its surface, and then curing it at 70±5℃ for 8-9 hours, so that an anti-UV coating is formed on the surface of the composite cable. The anti-UV coating has a thickness of 20-55 μm, and the anti-UV coating is an acrylic coating containing nano-zinc.

Images