Low-smoke halogen-free heat-resistant environment-friendly medium-voltage cable and preparation process thereof

Abstract

The application relates to the technical field of cable preparation, and particularly discloses a low-smoke halogen-free heat-resistant environment-friendly medium-voltage cable and a preparation process thereof. The cable comprises, from inside to outside, a tightly-pressed annealed copper conductor, a ceramicized polyolefin insulation layer and a phase-change flame-retardant sheath. The conductor surface is coated with a high-temperature-resistant self-repairing interface glue, the insulation layer is a ternary ethylene-propylene-diene rubber and modified glass microbead-boron nitride hybrid filler composite system, a chemical bond reinforced phase is constructed through in-situ grafting, and a continuous ceramic shell is generated under heat; the sheath contains microencapsulated phase-change heat storage materials and intumescent flame retardants, the two form a thermal response linkage in the combustion stage, and the structure of the intumescent carbon layer is optimized; and the insulation layer and the sheath generate a chemically-bonded radiation crosslinking interfacial bonding layer through radiation crosslinking. The composite cable structure is formed through chemical bonding, in-situ grafting and thermal response time sequence matching, so that the cable can keep the low-smoke halogen-free environmental protection characteristics, and the heat resistance, mechanical reliability and flame-retardant efficiency are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, and more specifically to a low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cable and its manufacturing process. Background Technology

[0002] Low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cables are key components in modern power transmission systems and are widely used in applications with stringent requirements for fire safety, environmental protection, and long-term operational reliability.

[0003] In existing technologies, such cables typically use EPDM rubber or cross-linked polyethylene as insulation materials, coupled with a polyolefin-based low-smoke halogen-free flame-retardant sheath to meet basic electrical performance and flame-retardant requirements. However, with the continuous increase in the operating load of medium-voltage cables and the increasing complexity of the operating environment, existing technical solutions have gradually revealed systemic defects.

[0004] Regarding the insulation layer, although traditional ceramic fire-resistant cables can form a ceramic shell at high temperatures to maintain the integrity of the line, their ceramic layer is brittle and hard, and lacks effective stress transfer between it and the elastic insulation matrix. Under the periodic electrostrictive stress caused by the medium voltage electric field and the mechanical vibration caused by load fluctuations, micro-cracks or even overall peeling are easily generated, leading to insulation failure. Meanwhile, the interface between the insulation layer and the conductor relies heavily on physical bonding, which can easily lead to gaps under long-term thermal cycling, providing channels for oxygen diffusion and partial discharge. At the sheath level, existing low-smoke halogen-free flame retardant systems mostly use physical blending to add intumescent flame retardants and phase change heat storage materials. After absorbing heat, the phase change materials cannot effectively assist in flame retardant foaming, and the intumescent carbon layer has a loose structure and is prone to dripping, resulting in limited thermal insulation protection efficiency. Furthermore, small-molecule flame retardants are prone to migration and precipitation, leading to stickiness and performance degradation on the sheath surface. Moreover, the insulation layer and sheath of existing cables are mostly simply physically bonded together. The difference in thermal expansion coefficients causes interfacial shear stress between the two layers when the temperature changes, which can easily lead to delamination and separation after long-term operation. This not only weakens the overall mechanical strength but also allows flame retardant components to migrate into the insulation layer, further impairing the long-term stability of electrical performance. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable and its manufacturing process, so as to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, comprising, from the inside out, a compacted annealed copper conductor, a ceramicized polyolefin insulation layer, and a phase-change flame-retardant sheath; The surface of the compacted annealed copper conductor is coated with a high-temperature resistant self-healing interface adhesive, which fills the gap between the single wires of the compacted annealed copper conductor and forms a silicone resin condensation sealing layer. The ceramicized polyolefin insulation layer is coated on the compacted annealed copper conductor. The ceramicized polyolefin insulation layer is a composite system of EPDM rubber matrix and modified glass microsphere-boron nitride hybrid filler. The modified glass microsphere-boron nitride hybrid filler is grafted onto the molecular chain of EPDM rubber matrix by a silane coupling agent to form a chemically bonded reinforcing phase. The ceramicized polyolefin insulation layer forms a continuous ceramic shell through the melting and sintering of the modified glass microsphere-boron nitride hybrid filler under heated conditions. The phase change flame retardant sheath is extruded over the ceramicized polyolefin insulation layer. The phase change flame retardant sheath comprises a polyolefin substrate, a microencapsulated phase change heat storage material, and an intumescent flame retardant. The microencapsulated phase change heat storage material is dispersed in the polyolefin substrate. The microencapsulated phase change heat storage material and the intumescent flame retardant form a thermal response linkage during the combustion stage. The inert gas released by the microencapsulated phase change heat storage material is injected into the foamed melt generated by the intumescent flame retardant. The intumescent carbon layer generated by the intumescent flame retardant encapsulates the unreacted microencapsulated phase change heat storage material. The ceramicized polyolefin insulation layer and the phase change flame-retardant sheath form a chemical bonding interface through radiation cross-linking, and the thickness ratio of the ceramicized polyolefin insulation layer to the phase change flame-retardant sheath is 1:1.2-1:1.8.

[0007] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, the high-temperature self-healing interface adhesive is composed of liquid methylphenyl silicone resin, nano silica sol, and latent curing agent. The nano silica sol adjusts the rheological properties of the high-temperature self-healing interface adhesive so that the high-temperature self-healing interface adhesive maintains thixotropy at room temperature. The latent curing agent is activated when the operating temperature of the compacted annealed copper conductor reaches above 90°C and promotes the liquid methylphenyl silicone resin to undergo a condensation reaction. The condensation reaction transforms the physical contact between the monofilaments of the compacted annealed copper conductor into a chemically bonded elastic sealing structure.

[0008] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, the modified glass microsphere-boron nitride hybrid filler in the ceramicized polyolefin insulation layer adopts a core-shell structure. The core is a hollow glass microsphere, and the shell is a thermally conductive orientation layer formed by the self-polymerization modification of plate-shaped boron nitride nanosheets with dopamine. The core-shell structure is in-situ grafted with vinyltrimethoxysilane and the EPDM rubber matrix during peroxide vulcanization. The plate-shaped boron nitride nanosheets are oriented along the electric field direction in the EPDM rubber matrix. The hollow glass microspheres absorb the periodic mechanical vibration energy generated by the load fluctuation of the compacted annealed copper conductor.

[0009] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, the microencapsulated phase change heat storage material in the phase change flame retardant sheath uses a paraffin-fatty acid eutectic mixture as the core material and melamine-formaldehyde resin as the wall material. The phase change temperature of the core material is 75°C to 85°C. The wall material releases nitrogen and ammonia under thermal decomposition. The nitrogen and ammonia are injected as auxiliary foaming agents into the melt formed by the expanding flame retardant to generate a porous structure.

[0010] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, the intumescent flame retardant is a polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant. The molecular structure of the polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant contains phosphorus, nitrogen and carbon elements simultaneously. The polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant carbonizes to form a primary carbonized skeleton in the early stage of combustion. The primary carbonized skeleton provides nucleation sites for the retention and expansion of the gas released by the microencapsulated phase change heat storage material.

[0011] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, the chemical bonding interface between the ceramicized polyolefin insulation layer and the phase change flame-retardant sheath is generated by online electron beam irradiation treatment after double-layer co-extrusion, with an irradiation dose of 80kGy to 120kGy. The unsaturated double bonds on the outer surface of the ceramicized polyolefin insulation layer undergo free radical copolymerization reaction with the polar groups on the inner surface of the phase change flame-retardant sheath to generate a radiation crosslinking interface bonding layer, the thickness of which is 50μm to 150μm.

[0012] A manufacturing process for low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cables includes the following steps: Conductor pretreatment and coating steps: After the annealed copper conductor is activated by plasma cleaning, a high-temperature resistant self-healing interface adhesive is uniformly coated on the surface of the annealed copper conductor using a precision coating device. Immediately after coating, the conductor is placed in an infrared preheating zone to allow the high-temperature resistant self-healing interface adhesive to pre-cur and form a semi-gel state. In-situ grafting extrusion step of the insulation layer: EPDM rubber, modified glass microsphere-boron nitride hybrid filler, peroxide vulcanizing agent and crosslinking agent are mixed in a multi-stage mixer, and then coated onto the pre-coated annealed copper conductor through a screw extruder. Under the action of high temperature and high pressure extrusion shear field, the in-situ grafting reaction of the modified glass microsphere-boron nitride hybrid filler and the EPDM rubber is completed and vulcanized to form a ceramicized polyolefin insulation layer; Co-extrusion and online irradiation crosslinking steps for the sheath: The phase change flame retardant sheath material is directly extruded onto the ceramicized polyolefin insulation layer that has not yet been completely cooled using a double-layer co-extrusion die. Then, it enters an electron beam irradiation device for online crosslinking treatment, so that a chemically bonded radiation crosslinking interface bonding layer is generated at the interface. Finally, it is shaped by a segmented gradient cooling water tank to generate the phase change flame retardant sheath.

[0013] Preferably, in the above-mentioned manufacturing process of a low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable, in the conductor pretreatment and adhesive coating steps, the plasma cleaning adopts a mixed atmosphere of argon and oxygen with a power density of 2W / cm³. 2 Up to 5W / cm 2 The processing time is 30s to 60s, the temperature of the infrared preheating zone is set to 120℃ to 140℃, and the preheating time is 2min to 5min, so that the latent curing agent in the high temperature resistant self-healing interface adhesive is partially activated.

[0014] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable manufacturing process, in the in-situ grafting extrusion step of the insulation layer, the multi-stage mixing adopts a two-stage process. The mixing temperature of the first stage is controlled at 80°C to 100°C, and the mixing temperature of the second stage is increased to 110°C to 130°C and a vulcanization system is added. The length-to-diameter ratio of the screw extruder is 24:1 to 28:1, the compression ratio is 3.5:1 to 4.5:1, the die head temperature is set to 160°C to 180°C, and the extrusion pressure is maintained at 15MPa to 25MPa.

[0015] Preferably, in the above-mentioned low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable manufacturing process, in the sheath co-extrusion and online irradiation crosslinking steps, the segmented gradient cooling water tank is provided with four temperature zones: the first temperature zone has a water temperature of 60°C to 70°C, the second temperature zone has a water temperature of 40°C to 50°C, the third temperature zone has a water temperature of 20°C to 30°C, and the fourth temperature zone is a room temperature air-cooled section. The length ratio of the first temperature zone, the second temperature zone, the third temperature zone, and the fourth temperature zone is 2:3:3:1. The electron beam irradiation device is located before the first temperature zone, and the irradiation acceleration voltage is 1.5MeV to 2.5MeV.

[0016] The technical effects and advantages of this invention are as follows: The modified glass microsphere-boron nitride hybrid filler in the insulating layer of this invention is chemically grafted into the rubber matrix to form a chemically bonded reinforcing phase that has both elastic buffering and high-temperature ceramicization capabilities. It can absorb electrostriction and mechanical vibration energy under normal conditions and generate a continuous and dense ceramic shell when heated, thus avoiding the brittle cracking of traditional ceramic layers.

[0017] The high-temperature self-healing interface adhesive undergoes a condensation reaction at the conductor's operating temperature, transforming the physical contact between monofilaments into a chemically bonded elastic sealing structure. This blocks the diffusion path of oxygen along the conductor gaps and provides radial support for the insulation layer. The microencapsulated phase-change thermal storage material in the sheath interacts with the intumescent flame retardant in a thermal response linkage. The phase-change endothermic reaction slows the temperature rise, while the gas released from the decomposition of the wall material is injected into the flame-retardant melt to optimize the pore structure. The intumescent carbon layer encapsulates unreacted microcapsules, enhancing thermal insulation and anti-dripping properties, while the hyperbranched topological structure of the flame retardant prevents migration and precipitation issues.

[0018] In this invention, the insulation layer and sheath are cross-linked via radiation to form a radiation-crosslinked interfacial bonding layer, eliminating the risk of delamination caused by thermal expansion mismatch and preventing the migration of flame-retardant components into the insulation layer, thus ensuring long-term stability of electrical performance. The cable layers in this invention are not simply stacked, but rather formed into an integral composite cable structure through chemical bonding, in-situ grafting, and thermal response timing matching. This allows the cable to maintain its low-smoke, halogen-free, and environmentally friendly characteristics while significantly improving its heat resistance, mechanical reliability, and flame-retardant performance. Attached Figure Description

[0019] Figure 1 This is a flowchart of the manufacturing process of a low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cable according to the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The technical solutions involved in the present invention are not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cable, which, from the inside out, comprises a compacted annealed copper conductor, a ceramicized polyolefin insulation layer, and a phase-change flame-retardant sheath. The surface of the compacted annealed copper conductor is coated with a high-temperature self-healing interface adhesive. The high-temperature self-healing interface adhesive fills the gap between the single wires of the compacted annealed copper conductor and forms a silicone resin condensation sealing layer. A ceramicized polyolefin insulation layer is coated on the outside of a compacted annealed copper conductor. The ceramicized polyolefin insulation layer is a composite system of EPDM rubber matrix and modified glass microsphere-boron nitride hybrid filler. The modified glass microsphere-boron nitride hybrid filler is grafted onto the molecular chain of EPDM rubber matrix through a silane coupling agent to form a chemically bonded reinforcing phase. Under heated conditions, the ceramicized polyolefin insulation layer generates a continuous ceramic shell through the melting and sintering of the modified glass microsphere-boron nitride hybrid filler. A phase change flame retardant sheath is extruded over a ceramicized polyolefin insulation layer. The phase change flame retardant sheath includes a polyolefin substrate, a microencapsulated phase change heat storage material, and an intumescent flame retardant. The microencapsulated phase change heat storage material is dispersed in the polyolefin substrate. The microencapsulated phase change heat storage material and the intumescent flame retardant form a thermal response linkage during the combustion stage. The inert gas released by the microencapsulated phase change heat storage material is injected into the foamed melt generated by the intumescent flame retardant. The intumescent carbon layer generated by the intumescent flame retardant wraps the unreacted microencapsulated phase change heat storage material. The ceramicized polyolefin insulation layer and the phase change flame retardant sheath form a chemical bonding interface through radiation cross-linking, and the thickness ratio of the ceramicized polyolefin insulation layer to the phase change flame retardant sheath is 1:1.2-1:1.8.

[0022] To further optimize the above technical solution, the high-temperature self-healing interface adhesive is composed of liquid methylphenyl silicone resin, nano silica sol, and latent curing agent. The nano silica sol adjusts the rheological properties of the high-temperature self-healing interface adhesive so that it maintains thixotropy at room temperature. The latent curing agent is activated when the operating temperature of the compacted annealed copper conductor reaches above 90°C and promotes the condensation reaction of the liquid methylphenyl silicone resin. The condensation reaction transforms the physical contact between the monofilaments of the compacted annealed copper conductor into a chemically bonded elastic sealing structure.

[0023] To further optimize the above technical solution, the modified glass microsphere-boron nitride hybrid filler in the ceramicized polyolefin insulation layer adopts a core-shell structure. The core is a hollow glass microsphere, and the shell is a thermally conductive orientation layer formed by the self-polymerization modification of plate-shaped boron nitride nanosheets with dopamine. The core-shell structure is in-situ grafted with vinyltrimethoxysilane and EPDM rubber matrix during peroxide vulcanization. The plate-shaped boron nitride nanosheets are oriented along the electric field direction in the EPDM rubber matrix. The hollow glass microspheres absorb the periodic mechanical vibration energy generated by load fluctuations in the compacted annealed copper conductor.

[0024] To further optimize the above technical solution, the microencapsulated phase change thermal storage material in the phase change flame retardant sheath uses a paraffin-fatty acid eutectic mixture as the core material and melamine-formaldehyde resin as the wall material. The phase change temperature of the core material is 75°C to 85°C. The wall material releases nitrogen and ammonia under thermal decomposition. Nitrogen and ammonia are injected as auxiliary foaming agents into the melt formed by the expanding flame retardant to generate a porous structure.

[0025] To further optimize the above technical solution, the intumescent flame retardant is a polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant. The molecular structure of the polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant contains phosphorus, nitrogen and carbon elements. In the early stage of combustion, the polyammonium phosphate-pentaerythritol condensation type intumescent flame retardant carbonizes to form a primary carbonized skeleton. The primary carbonized skeleton provides nucleation sites for the retention and expansion of the gas released by the microencapsulated phase change thermal storage material.

[0026] To further optimize the above technical solution, the chemical bonding interface between the ceramicized polyolefin insulation layer and the phase change flame retardant sheath is generated by online electron beam irradiation after double-layer co-extrusion, with an irradiation dose of 80kGy to 120kGy. The unsaturated double bonds on the outer surface of the ceramicized polyolefin insulation layer undergo free radical copolymerization with the polar groups on the inner surface of the phase change flame retardant sheath to generate a radiation crosslinking interface bonding layer with a thickness of 50μm to 150μm.

[0027] A manufacturing process for low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cables includes the following steps: Conductor pretreatment and coating steps: After the annealed copper conductor is activated by plasma cleaning, a high-temperature resistant self-healing interface adhesive is uniformly coated on the surface of the annealed copper conductor using a precision coating device. Immediately after coating, the conductor is placed in an infrared preheating zone to allow the high-temperature resistant self-healing interface adhesive to pre-cur and form a semi-gel state. In-situ grafting extrusion step of insulation layer: EPDM rubber, modified glass microsphere-boron nitride hybrid filler, peroxide vulcanizing agent and crosslinking agent are mixed in a multi-stage mixer, and then coated on the pre-coated annealed copper conductor through a screw extruder. Under the action of high temperature and high pressure extrusion shear field, the in-situ grafting reaction of modified glass microsphere-boron nitride hybrid filler and EPDM rubber is completed and vulcanization is performed to generate ceramic polyolefin insulation layer; Co-extrusion and online irradiation crosslinking steps for the sheath: The phase change flame retardant sheath material is directly extruded onto the ceramicized polyolefin insulation layer that has not been completely cooled using a double-layer co-extrusion die. Then, it enters an electron beam irradiation device for online crosslinking treatment, so that a chemically bonded radiation crosslinking interface bonding layer is generated at the interface. Finally, it is shaped by a segmented gradient cooling water tank to generate the phase change flame retardant sheath.

[0028] To further optimize the above technical solution, in the conductor pretreatment and coating steps, plasma cleaning uses a mixed atmosphere of argon and oxygen with a power density of 2W / cm². 2 Up to 5W / cm 2 The processing time is 30s to 60s, the infrared preheating zone temperature is set to 120℃ to 140℃, and the preheating time is 2min to 5min, so that the latent curing agent in the high-temperature self-healing interface adhesive is partially activated.

[0029] To further optimize the above technical solution, in the in-situ grafting extrusion step of the insulation layer, the multi-stage mixing adopts a two-stage process. The mixing temperature of the first stage is controlled at 80℃ to 100℃, and the mixing temperature of the second stage is increased to 110℃ to 130℃ and a vulcanization system is added. The length-to-diameter ratio of the screw extruder is 24:1 to 28:1, the compression ratio is 3.5:1 to 4.5:1, the die head temperature is set at 160℃ to 180℃, and the extrusion pressure is maintained at 15MPa to 25MPa.

[0030] To further optimize the above technical solution, in the sheath co-extrusion and online irradiation crosslinking steps, the segmented gradient cooling water tank is set with four temperature zones: the first temperature zone has a water temperature of 60℃ to 70℃, the second temperature zone has a water temperature of 40℃ to 50℃, the third temperature zone has a water temperature of 20℃ to 30℃, and the fourth temperature zone is a room temperature air-cooled section. The length ratio of the first, second, third, and fourth temperature zones is 2:3:3:1. The electron beam irradiation device is located before the first temperature zone, and the irradiation acceleration voltage is 1.5MeV to 2.5MeV.

[0031] The technical principle of this invention: The core principle of this invention lies in forming an integral composite cable structure through chemical bonding, in-situ grafting, and thermal response timing matching. In the insulation layer, a silane coupling agent grafts modified glass microspheres-boron nitride hybrid filler onto the EPDM rubber molecular chain, forming a chemically bonded reinforcing phase: the hollow microspheres absorb mechanical vibration energy during compression deformation, the plate-like boron nitride is oriented along the electric field to conduct local heat, and when heated, the hybrid filler melts and sinters to form a continuous ceramic shell, while the elasticity of the rubber matrix buffers the volume shrinkage stress during the ceramicization process.

[0032] The high-temperature self-healing interface adhesive on the conductor surface activates the latent curing agent above 90℃, promoting the condensation of liquid methylphenyl silicone resin and transforming the gaps between monofilaments into a chemically bonded elastic sealing structure, blocking oxygen diffusion and providing radial support. In the sheath, the phase change temperature of the microencapsulated phase change thermal storage material is set at 75℃ to 85℃. Under overload, the core material absorbs heat and melts to buffer the temperature rise. At higher temperatures, the wall material decomposes and releases nitrogen and ammonia, which are injected as auxiliary foaming agents into the melt formed by the polyphosphate-pentaerythritol condensation-type intumescent flame retardant to optimize the pore structure of the intumescent carbon layer. The primary carbonized skeleton generated by the initial carbonization of the hyperbranched flame retardant during the early stage of combustion provides nucleation sites for gas retention, achieving temporal synergy of flame retardant components.

[0033] In this invention, the insulation layer and the sheath are co-extruded in two layers and then irradiated with an online electron beam to cause the unsaturated double bonds and polar groups to undergo free radical copolymerization, generating a radiation crosslinking interface bonding layer. This not only eliminates thermal expansion mismatch stress but also prevents flame retardant migration. Each layer forms an inseparable functional whole through chemical bonding and thermal response linkage.

[0034] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cable, characterized in that: From the inside out, it consists of a compacted annealed copper conductor, a ceramicized polyolefin insulation layer, and a phase change flame-retardant sheath. The surface of the compacted annealed copper conductor is coated with a high-temperature resistant self-healing interface adhesive, which fills the gap between the single wires of the compacted annealed copper conductor and forms a silicone resin condensation sealing layer. The ceramicized polyolefin insulation layer is wrapped around the compacted annealed copper conductor. The ceramicized polyolefin insulation layer is a composite system of EPDM rubber matrix and modified glass microsphere-boron nitride hybrid filler. The phase change flame retardant sheath is extruded over the ceramicized polyolefin insulation layer, and the phase change flame retardant sheath comprises a polyolefin substrate, a microencapsulated phase change heat storage material, and an intumescent flame retardant. The ceramicized polyolefin insulation layer and the phase change flame-retardant sheath form a chemical bonding interface through radiation cross-linking, and the thickness ratio of the ceramicized polyolefin insulation layer to the phase change flame-retardant sheath is 1:1.2-1:1.

8.

2. The low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 1, characterized in that, The high-temperature resistant self-healing interface adhesive is composed of liquid methylphenyl silicone resin, nano silica sol, and latent curing agent.

3. The low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 1, characterized in that, The modified glass microsphere-boron nitride hybrid filler in the ceramicized polyolefin insulation layer adopts a core-shell structure, with the core being hollow glass microspheres and the shell being a thermally conductive orientation layer formed by the self-polymerization modification of sheet-like boron nitride nanosheets with dopamine.

4. The low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 1, characterized in that, The microencapsulated phase change thermal storage material in the phase change flame retardant sheath uses a paraffin-fatty acid eutectic mixture as the core material and melamine-formaldehyde resin as the wall material.

5. The low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 1, characterized in that, The intumescent flame retardant is an ammonium polyphosphate-pentaerythritol condensation type intumescent flame retardant.

6. The low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 1, characterized in that, The chemical bonding interface between the ceramicized polyolefin insulation layer and the phase change flame retardant sheath is generated by online electron beam irradiation after double-layer co-extrusion, with an irradiation dose of 80 kGy to 120 kGy. The unsaturated double bonds on the outer surface of the ceramicized polyolefin insulation layer undergo free radical copolymerization with the polar groups on the inner surface of the phase change flame retardant sheath to generate a radiation crosslinked interface bonding layer with a thickness of 50 μm to 150 μm.

7. A manufacturing process for a low-smoke, halogen-free, heat-resistant, and environmentally friendly medium-voltage cable as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Conductor pretreatment and coating steps: After the annealed copper conductor is activated by plasma cleaning, a high-temperature resistant self-healing interface adhesive is uniformly coated on the surface of the annealed copper conductor using a precision coating device. Immediately after coating, the conductor is placed in an infrared preheating zone to allow the high-temperature resistant self-healing interface adhesive to pre-cur and form a semi-gel state. In-situ grafting extrusion step of the insulation layer: EPDM rubber, modified glass microsphere-boron nitride hybrid filler, peroxide vulcanizing agent and crosslinking agent are mixed in a multi-stage mixer, and then coated onto the pre-coated annealed copper conductor through a screw extruder. Under the action of high temperature and high pressure extrusion shear field, the in-situ grafting reaction of the modified glass microsphere-boron nitride hybrid filler and the EPDM rubber is completed and vulcanized to form a ceramicized polyolefin insulation layer; Co-extrusion and online irradiation crosslinking steps for the sheath: The phase change flame retardant sheath material is directly extruded onto the ceramicized polyolefin insulation layer that has not yet been completely cooled using a double-layer co-extrusion die. Then, it enters an electron beam irradiation device for online crosslinking treatment, so that a chemically bonded radiation crosslinking interface bonding layer is generated at the interface. Finally, it is shaped by a segmented gradient cooling water tank to generate the phase change flame retardant sheath.

8. The manufacturing process of the low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 7, characterized in that, In the conductor pretreatment and coating steps, the plasma cleaning uses a mixed atmosphere of argon and oxygen with a power density of 2 W / cm². 2 Up to 5W / cm 2 The processing time is 30s to 60s, the temperature of the infrared preheating zone is set to 120℃ to 140℃, and the preheating time is 2min to 5min, so that the latent curing agent in the high temperature resistant self-healing interface adhesive is partially activated.

9. The manufacturing process of the low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 7, characterized in that, In the in-situ grafting extrusion step of the insulation layer, the multi-stage mixing adopts a two-stage process. The mixing temperature of the first stage is controlled at 80°C to 100°C, and the mixing temperature of the second stage is increased to 110°C to 130°C and a vulcanization system is added. The length-to-diameter ratio of the screw extruder is 24:1 to 28:1, the compression ratio is 3.5:1 to 4.5:1, the die head temperature is set at 160°C to 180°C, and the extrusion pressure is maintained at 15MPa to 25MPa.

10. The manufacturing process of the low-smoke halogen-free heat-resistant and environmentally friendly medium-voltage cable according to claim 7, characterized in that, In the co-extrusion and online irradiation crosslinking steps of the sheath, the segmented gradient cooling water tank is set with four temperature zones: the first temperature zone has a water temperature of 60°C to 70°C, the second temperature zone has a water temperature of 40°C to 50°C, the third temperature zone has a water temperature of 20°C to 30°C, and the fourth temperature zone is a room temperature air-cooled section. The length ratio of the first temperature zone, the second temperature zone, the third temperature zone, and the fourth temperature zone is 2:3:3:

1. The electron beam irradiation device is located before the first temperature zone, and the irradiation acceleration voltage is 1.5MeV to 2.5MeV.

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