An extruded insulated low-voltage fire-resistant power cable

Abstract

This invention provides an extruded insulated low-voltage fire-resistant power cable, belonging to the technical field of cross-linked polyethylene insulated power cables and cable accessories. The power cable comprises, from the inside out, a conductor, a fire-resistant layer, an insulation layer, a shielding layer, and a sheath layer. The fire-resistant layer is a mica tape wrapping around the conductor, the mica tape being a composite structure of synthetic mica paper and fiberglass cloth. The insulation layer is a mixture of cross-linked polyethylene and low-smoke flame-retardant polyolefin, and nano-sized aluminum hydroxide and carbon nanotubes are dispersed within the insulation layer, the carbon nanotubes having an aspect ratio ≥100. The sheath layer is a ceramicized silicone rubber sheath extruded over the shielding layer. The power cable provided by this invention exhibits excellent fire resistance, flame retardancy, and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the technical field of cross-linked polyethylene insulated power cables and cable accessories, specifically relating to an extruded insulated low-voltage fire-resistant power cable. Background Technology

[0002] Power cables, as an important carrier of electrical energy, are widely used in construction, industry, transportation and other fields. However, in extreme environments such as fires, traditional cables often fail due to insufficient fire resistance, leading to power outages and even secondary disasters, seriously threatening the safety of life and property. Especially in low-voltage power systems, the fire resistance of cables is directly related to the continuous power supply of critical facilities such as emergency lighting and fire-fighting equipment, thus placing higher demands on the fire resistance of cables.

[0003] Currently, most fire-resistant cables on the market use mica tape wrapping structures. However, traditional mica tape suffers from low mechanical strength, is prone to detachment, and easily becomes brittle at high temperatures, affecting the long-term reliability of the cable. Furthermore, the cable insulation layer is typically made of polyolefin materials, which, while possessing good electrical properties, are easily decomposed under high temperatures or fire conditions, releasing large amounts of smoke and toxic gases, exacerbating fire hazards. Although some research has attempted to add flame retardants to the insulation layer to improve fire resistance, excessive amounts of conventional flame retardants can affect the material's mechanical properties and processing technology, while insufficient amounts fail to achieve the desired flame-retardant effect. Simultaneously, the sheath layer, as the outermost layer of the cable, is also crucial for fire resistance, but traditional sheath materials are prone to melting or burning at high temperatures, failing to provide continuous protection for the cable. On the other hand, the cable's shielding performance significantly impacts the stability of signal transmission and its anti-interference capabilities. Traditional shielding layers often use ordinary copper wire braiding, which has poor high-temperature resistance and oxidation resistance, making it prone to failure in fire environments.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide an extruded insulated low-voltage fire-resistant power cable. Through material optimization and structural design of each functional layer, the cable simultaneously possesses excellent fire resistance, low smoke flame retardant properties, high mechanical strength, and stable electromagnetic shielding performance, making it particularly suitable for low-voltage power transmission scenarios with stringent safety requirements.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] An extruded insulated low-voltage fire-resistant power cable includes, from the inside out, a conductor, a fire-resistant layer, an insulation layer, a shielding layer, and a sheath layer;

[0008] The refractory layer is a mica tape wrapping layer covering the conductor. The mica tape is a composite structure of synthetic mica paper and glass fiber cloth, and the thickness of the mica tape is 0.1-0.3 mm.

[0009] The insulating layer is a mixture of cross-linked polyethylene and low-smoke flame-retardant polyolefin, and nano-sized aluminum hydroxide and carbon nanotubes are dispersed in the insulating layer. The particle size of the nano-sized aluminum hydroxide is 50-100nm, the aspect ratio of the carbon nanotubes is ≥100, and the mass ratio of the nano-sized aluminum hydroxide to the carbon nanotubes is (10-15):1.

[0010] The sheath layer is a ceramicized silicone rubber sheath extruded outside the shielding layer.

[0011] This invention provides an extruded insulated low-voltage fire-resistant power cable, which mainly includes a multi-layer structure design consisting of a conductor, a fire-resistant layer, an insulation layer, a shielding layer, and a sheath layer arranged sequentially from the inside out. The materials, composition, and key parameters of each layer are specifically defined. Through the optimization of the materials and synergistic effect of the fire-resistant layer, insulation layer, and sheath layer, the fire resistance, flame retardancy, mechanical strength, and high-temperature stability of the cable are significantly improved while maintaining its basic electrical performance. It is suitable for low-voltage power transmission scenarios with high safety requirements.

[0012] First, this invention defines the fire-resistant layer as a mica tape wrapping around the conductor, and further clarifies that the specific structure of the mica tape wrapping is a composite structure of synthetic mica paper and fiberglass cloth, with a thickness controlled between 0.1-0.3 mm. This solves the problems of insufficient mechanical strength and easy detachment of mica tape in traditional fire-resistant cables. The synthetic mica paper has higher high-temperature resistance and insulation performance, while the addition of fiberglass cloth enhances the flexibility and tensile strength of the mica tape, making it less prone to damage when the cable is bent or subjected to external force. Furthermore, the optimized thickness of the mica tape ensures fire resistance while avoiding the problems of increased cable rigidity or increased processing difficulty caused by excessive thickness. In the event of a fire, the fire-resistant layer of this composite structure can effectively insulate against high temperatures, delay the spread of flames to the conductor, and ensure that the cable can maintain its power transmission function for a certain period of time under high-temperature conditions.

[0013] Secondly, this invention also specifies the composition of the insulating layer, namely, a mixture of cross-linked polyethylene and low-smoke flame-retardant polyolefin, with nano-sized aluminum hydroxide and carbon nanotubes dispersed within the insulating layer. The specific particle size of the aluminum hydroxide, the aspect ratio of the carbon nanotubes (≥100), and the mass ratio of the two are defined. This design ensures that the insulating layer not only possesses excellent electrical insulation properties but also exhibits superior thermal conductivity and flame retardancy. The mixed insulating layer substrate used in this invention is composed of cross-linked polyethylene and low-smoke flame-retardant polyolefin. Cross-linked polyethylene, as the base material, possesses excellent electrical insulation properties and high-temperature resistance, and its three-dimensional network structure... It maintains stability at high temperatures, while the addition of low-smoke flame-retardant polyolefins further optimizes the flame retardancy and environmental friendliness of the material, significantly reducing smoke density and toxic gas release during combustion. This hybrid matrix design not only retains the processing convenience of traditional polyolefin materials, but also improves the safety of the material under fire conditions through molecular structure modification. Among them, nano-sized aluminum hydroxide, as a highly efficient flame retardant, decomposes and absorbs heat and releases water vapor when heated, thereby reducing the temperature of the insulation layer and diluting flammable gases. At the same time, its nano-sized particle size allows it to be uniformly dispersed in the polyolefin matrix, avoiding negative impacts on the mechanical properties of the material.

[0014] Meanwhile, the sheath layer is extruded from ceramicized silicone rubber material. Ceramicized silicone rubber has the flexibility and processability of ordinary rubber at room temperature, but it can be transformed into a hard ceramic-like protective layer under high temperature or open flame conditions, effectively isolating the internal structure from damage caused by flames and high temperatures. Therefore, compared with traditional PVC or ordinary rubber sheaths, ceramicized silicone rubber sheaths not only have better fire resistance, but also produce less smoke and release no toxic gases when burning, meeting the safety and environmental protection requirements of modern buildings and public facilities for cables.

[0015] The conductor of this invention is made of multiple strands of tin-plated copper wires twisted together, with a tin plating thickness of 0.5-2μm and a twisting pitch of 8-12 times the conductor diameter. The tin plating not only improves the conductor's oxidation resistance and weldability but also enhances the bonding force between the conductor and the fire-resistant layer. The optimization of the twisting pitch balances the conductor's flexibility and conductivity, avoiding the problem of increased cable outer diameter due to excessive pitch or loose conductor caused by excessively small pitch.

[0016] The fire-resistant power cable of this invention achieves a comprehensive improvement in fire resistance, flame retardancy, mechanical properties and electrical properties through the synergistic optimization of a multi-layer structure. It solves the shortcomings of traditional cables in terms of fire resistance, flame retardancy and high-temperature stability, and has significant technological progress and practical value.

[0017] Preferably, as a further specific embodiment, the carbon nanotubes are carboxylated modified carbon nanotubes with a surface grafting rate of 3-5%, and the carboxylated modified carbon nanotubes are oriented along the cable axis in the insulation layer to form a continuous heat-conducting network.

[0018] The carbon nanotubes of this invention are carboxylated modified carbon nanotubes with a surface grafting rate of 3-5%, and are oriented along the cable axis in the insulation layer to form a continuous thermally conductive network. This approach not only solves key problems such as poor dispersion and weak interfacial bonding of nanomaterials in polymer matrices, but also achieves a synergistic improvement in the thermal conductivity and mechanical properties of the insulation layer through precise microstructure control. The carboxylation modification treatment imparts polar functional groups to the carbon nanotube surface, which significantly improves the interfacial compatibility between the carbon nanotubes and the polyolefin matrix, allowing the nanoparticles to disperse uniformly without agglomeration. Furthermore, it enhances the stress transfer efficiency between the filler and the matrix through chemical bonding, enabling the insulation layer to fully utilize the reinforcing effect of the carbon nanotubes when subjected to mechanical loads. Too low a grafting rate cannot provide enough active sites to improve dispersion, while too high a grafting rate may destroy the intrinsic structure of carbon nanotubes, affecting their thermal and electrical conductivity. Furthermore, this invention axially orients carbon nanotubes in the insulation layer, creating a continuous thermally conductive path along the cable length. This allows for rapid dissipation of Joule heat generated during conductor operation along the longitudinal direction of the cable, preventing localized heat accumulation that could lead to insulation aging. In terms of mechanical properties, the oriented carbon nanotubes can more effectively withstand axial tensile stress, increasing the cable's tensile strength by more than 30%. In terms of electrical properties, this arrangement prevents the formation of a radial conductive network by the carbon nanotubes, maintaining excellent radial insulation performance of the insulation layer while improving longitudinal thermal conductivity.

[0019] Preferably, as a further specific embodiment, the ceramicized silicone rubber sheath comprises the following components in parts by weight:

[0020] 100-120 parts of methyl vinyl silicone rubber;

[0021] 40-60 parts of ceramicized filler;

[0022] 15-25 parts flame retardant;

[0023] 1-2 parts of vulcanizing agent.

[0024] This invention also specifies the composition of the sheath material, comprising 100-120 parts by weight of methyl vinyl silicone rubber, 40-60 parts of ceramicized filler, 15-25 parts of flame retardant, and 1-2 parts of vulcanizing agent. This method combines ceramicization transformation technology with traditional rubber sheath materials, achieving a perfect balance between the flexibility of the sheath layer at room temperature and the ceramicized protective properties at high temperatures through the synergistic effect of multiple components. This fundamentally solves the technical problem of traditional cable sheaths being prone to melting in fires and unable to provide continuous protection. Methyl vinyl silicone rubber, as the matrix material, has a main chain composed of alternating silicon and oxygen atoms, giving the material excellent thermal stability and weather resistance. While the methyl groups in the side chains do not directly participate in the crosslinking reaction, their small size and low polarity allow the silicone rubber main chain to maintain high flexibility, facilitating the vinyl groups to approach and react during vulcanization, thus improving crosslinking efficiency. Furthermore, the high C-H bond energy of the methyl groups reduces the main chain size under vulcanization or high-temperature conditions. The process of breaking down the vinyl crosslinking points protects them from damage, thereby providing appropriate crosslinking sites through the combined action of methyl and vinyl groups. This allows the material to form a moderately crosslinked network during vulcanization to maintain mechanical strength, while also achieving a transformation to the ceramic phase at high temperatures through molecular chain breakage and recombination. The amount of ceramic filler added is controlled at 40-60 parts. This ratio ensures that the filler is sufficient to form a continuous ceramic skeleton structure at high temperatures, while avoiding the problem of increased hardness and brittleness of the material at room temperature due to excessive filler. In addition, this invention also specifies that the ceramic filler is a composite system of glass powder, kaolin, and nano-zirconia. Glass powder, as a low-temperature melting phase, can soften and flow first at 500-700℃. Kaolin provides an aluminosilicate skeleton structure, and nano-zirconia enhances the high-temperature stability of the ceramic body. The three work synergistically at a specific mass ratio to form a gradient melting-ceramic transformation mechanism, enabling the sheath layer to automatically adjust its structural state according to temperature changes.

[0025] The addition of 15-25 parts of flame retardant ensures sufficient flame retardant effect without excessively affecting the processing and mechanical properties of the material. The amount of vulcanizing agent is controlled at 1-2 parts, which ensures that the silicone rubber is fully cross-linked to form a three-dimensional network structure during processing, and avoids the problem of reduced material elasticity caused by over-vulcanization. This allows the sheath layer to maintain sufficient mechanical strength while still having good flexibility and installation applicability.

[0026] The ceramicized silicone rubber sheath of this invention constructs a "three-in-one" protection mechanism: at room temperature, the sheath layer exhibits typical elastomer characteristics, capable of withstanding various mechanical stresses during cable laying and use; when the ambient temperature rises to 300-500℃, the flame retardant system is activated first, delaying material combustion through multiple pathways such as carbonization, glass formation, and free radical capture, thus buying valuable time for personnel evacuation; when the temperature continues to rise above 600℃, the ceramicized filler and the silicone rubber matrix undergo a synergistic reaction, and the silica produced by the decomposition of silicone rubber combines with the active components in the filler to form a porous ceramic skeleton structure. This ceramic body has significant thermal insulation properties, effectively blocking the transmission of external high temperatures to the inside of the cable and maintaining the integrity of the cable structure.

[0027] Preferably, as a further specific embodiment, the ceramicized filler is a mixture of glass powder, kaolin and nano-zirconia; the mass ratio of the glass powder, kaolin and nano-zirconia is (5-7):(3-5):2.

[0028] This invention also specifically defines the ceramic filler in the ceramicized silicone rubber sheath, clarifying that it is a mixed system composed of glass powder, kaolin, and nano-zirconia in a specific mass ratio of (5-7):(3-5):2. The core of this definition lies in the synergistic cooperation of three inorganic fillers with different functional properties, which achieves an efficient transformation of the sheath material from a rubber state to a ceramic state, while ensuring the structural stability and thermal insulation performance of the ceramic layer under high-temperature conditions. The combination design of the ceramicized filler first reflects the precise control of the material phase transformation process. Among them, glass powder, as a low-temperature melting component, softens at high temperatures to form a liquid phase, playing a role in adhesion. The role of the binder is to provide the necessary material migration channels for the ceramization process. Its content is controlled within the range of 5-7 parts, which ensures that there is enough liquid phase to promote sintering and densification, while avoiding the problem of excessive glass phase causing a decrease in the high-temperature strength of the ceramic layer. The chemical composition of the glass powder is usually an alkali metal borosilicate system. Its melt viscosity changes with temperature and is carefully selected so that it can flow rapidly to fill the pores in the early stage of fire, while maintaining an appropriate viscosity at higher temperatures to support the ceramic skeleton. At the same time, the alkali metal ions in the glass component react with other filler components at high temperatures to generate new high-temperature resistant crystalline phases, which further strengthen the ceramic layer structure.

[0029] Furthermore, kaolin, as a representative aluminosilicate mineral, plays multiple roles in the ceramicization process. From a chemical perspective, kaolin undergoes a dehydroxylation reaction at 450-600℃, transforming into highly reactive metakaolin. When the temperature continues to rise above 900℃, metakaolin reacts with components in the glass phase to form high-temperature stable phases such as mullite. From a physical structure perspective, the platy microstructure of kaolin provides skeletal support for the ceramic layer. An addition of 3-5 parts can form a continuous network structure without causing excessive rigidity of the material at room temperature due to over-addition. It is particularly noteworthy that the dehydration process of kaolin is an endothermic reaction, a characteristic that helps reduce the local temperature of the material and slow down the thermal decomposition process in the early stages of a fire. In addition, the hydroxyl functional groups on the surface of kaolin particles can form hydrogen bonds with silicone rubber molecular chains at room temperature, improving the interfacial bonding strength between the filler and the matrix to some extent.

[0030] The addition of nano-zirconia, at a ratio of only 2 parts, significantly improves the performance of the ceramic layer. From a thermal perspective, the thermal conductivity of zirconia is significantly lower than that of common metallic materials, and its unique phase transformation toughening properties can absorb thermal stress in the ceramic layer, preventing the generation and propagation of cracks at high temperatures. From a structural stability perspective, nano-zirconia particles have an extremely high specific surface area, which can effectively pin grain boundary movement, inhibit abnormal growth of ceramic grains at high temperatures, and maintain the excellent mechanical properties brought about by the fine-grained structure. In addition, the oxygen vacancy defects on the surface of zirconia have a certain capturing effect on free radicals generated during combustion, which provides an additional flame-retardant mechanism for the sheath material.

[0031] For this invention, the mass ratio of the three fillers is crucial. The combination of (5-7) parts glass powder and (3-5) parts kaolin forms a reasonable "binder-skeleton phase" ratio, ensuring that there is sufficient liquid phase to promote densification during the ceramicization process, while maintaining sufficient structural strength to resist the impact of hot airflow. The addition of 2 parts nano-zirconia optimizes the performance of the entire system like a "material gene": on the one hand, the nanoparticles fill the gaps between the micron-sized glass powder and kaolin particles, significantly reducing the porosity during sintering; on the other hand, the interfacial reaction between zirconia and the silicone rubber matrix at high temperature generates transition layers such as zirconium silicate, effectively alleviating the internal stress caused by the difference in thermal expansion coefficients between the ceramic layer and the undecomposed rubber layer. Of particular note is that the particle size distribution of the three fillers in this ratio system exhibits a multi-gradation characteristic, with micron-sized glass powder and kaolin forming the main skeleton and nano-sized zirconia filling the gaps. This "micro-nano composite" structure optimizes the packing density of the fillers, laying an ideal initial state for the subsequent ceramicization process.

[0032] Furthermore, this filler system exhibits a sophisticated phased response under temperature gradients. When the ambient temperature rises to 300-400℃, the silicone rubber matrix begins to thermally decompose. At this point, the dehydroxylation reaction of kaolin absorbs a large amount of heat, delaying the overall temperature rise of the material. When the temperature reaches 500-600℃, the glass powder softens to form a liquid phase, which begins to encapsulate kaolin and zirconium dioxide particles. Simultaneously, the active sites on the nano-zirconia surface catalyze the further carbonization of organic residues. When the temperature continues to rise above 700℃, the liquid phase promotes particle rearrangement and diffusion mass transfer. The kaolin conversion products undergo a solid-phase reaction with zirconium dioxide, ultimately forming a three-dimensional interlocking ceramic structure with silicate as the matrix and zirconium oxide as the reinforcing phase. This gradual phase transition process ensures that the sheath material provides continuous protection throughout the entire temperature rise range, avoiding the performance abrupt changes of traditional materials at the critical temperature point. From the perspective of actual fire resistance, this filler system enables the sheath layer to exhibit three key protection mechanisms: First, a thermal barrier effect, with the formed ceramic layer having a thermal conductivity as low as 0.15 W / (m·K), effectively blocking the transfer of external high temperatures into the cable; second, mass transfer barrier, with the dense ceramic structure preventing the diffusion of oxygen into the undecomposed material and the outward escape of combustible pyrolysis products; and finally, mechanical protection, with the high-temperature compressive strength of the ceramic layer reaching over 10 MPa, capable of withstanding the impact of falling objects at a fire scene.

[0033] Preferably, as a further specific embodiment, the flame retardant is ammonium polyphosphate, zinc borate and ferrocene, wherein the mass ratio of ammonium polyphosphate, zinc borate and ferrocene is (6-7):(3-5):1.

[0034] In this invention, the flame retardant system in the ceramicized silicone rubber sheath is specifically defined as a composite flame retardant system composed of ammonium polyphosphate, zinc borate and ferrocene in a mass ratio of (6-7):(3-5):1. Its core is to construct a multi-layer protection system covering the gas phase, condensed phase and catalytic flame retardancy through the synergistic effect of three compounds with different flame retardant mechanisms, thereby realizing the full-process protection of the sheath material from the initial stage of fire to the high-temperature stage to promote the ceramicization transformation.

[0035] In this composite flame retardant, ammonium polyphosphate, as the main component of the intumescent flame retardant, begins to decompose in the early stages of heating, generating polyphosphoric acid and ammonia. This process has a triple flame retardant effect: polyphosphoric acid, as a strong dehydrating agent, promotes the carbonization of the silicone rubber matrix surface, forming an expanded carbon layer; ammonia, as an inert gas, dilutes the concentration of combustible volatiles; at the same time, the decomposition reaction itself is a strongly endothermic process, effectively reducing the local temperature of the material. Ammonium polyphosphate occupies a dominant position of 6-7 parts in the system, which ensures that there is a sufficient amount of active ingredients to quickly establish the first line of defense in the early stages of a fire. The addition of zinc borate brings a unique flame retardant synergy to the flame retardant system. When the temperature rises to the range of 300-400℃, zinc borate decomposes to generate boron oxide. This product softens and flows at higher temperatures (>450℃), reacting with the decomposition products of ammonium polyphosphate and the silica generated by the pyrolysis of silicone rubber to form a borosilicate glass layer covering the surface of the material, blocking oxygen and heat.

[0036] Ferrocene, a key additive in flame retardant systems, plays an irreplaceable catalytic and regulatory role despite being added in a small quantity (only one part). Under combustion conditions, ferrocene first decomposes to generate active iron species. These iron ions have a dual function: on the one hand, they act as free radical scavengers, interrupting the combustion chain reaction; on the other hand, they act as oxidation catalysts, promoting the deep oxidation of incomplete combustion products, thereby significantly reducing smoke density and the release of toxic gases. More importantly, at high temperatures, iron ions can form an iron silicate phase with the pyrolysis products of silicone rubber. This mineral phase with a spinel structure significantly improves the infrared reflectivity of the ceramic layer, enhancing its thermal insulation performance. The proportion of ferrocene added is carefully optimized; too little will result in insufficient catalytic effect, while too much may lead to premature cross-linking or decreased thermal stability of the material during processing.

[0037] Meanwhile, the ratio design of the three flame-retardant components (6-7):(3-5):1 ensures that the corresponding flame-retardant mechanisms play a role at different stages of fire development: in the early stage, it mainly relies on the expansion flame retardancy of ammonium polyphosphate; in the middle stage, it is dominated by the melt coverage of zinc borate; and in the later stage, it is controlled by the catalytic effect of ferrocene and high-temperature phase change. This time-dimensional mechanism relay forms seamless protection, avoiding the "time window" problem of traditional single flame retardants.

[0038] Preferably, as a further specific embodiment, the conductor is made of multiple strands of tin-plated copper wire twisted together, the tin plating layer thickness is 0.5-2μm, and the twisting pitch is 8-12 times the diameter of the conductor.

[0039] This invention also defines the specific structure of the cable conductor, specifying that it is composed of multiple strands of tin-plated copper wire twisted together. The tin plating thickness is specified to be 0.5-2 μm, and the twisting pitch is 8-12 times the conductor diameter. Through surface treatment and structural optimization of the conductor material, the conductor's oxidation resistance and structural stability under high-temperature environments are significantly improved while ensuring conductivity, and the cable's flexibility and durability are also taken into account. The design of the tin-plated copper wire reflects a comprehensive consideration of the conductor's long-term reliability. The tin layer thickness is controlled within the range of 0.5-2 μm, thus ensuring that the impact on overall conductivity within this thickness range is controlled to within 1%, which is almost negligible. From a protective function perspective, the tin layer within this thickness range can form a continuous and dense protective film, effectively blocking the contact between copper and oxygen and sulfides in the air, increasing the conductor's oxidation resistance in harsh environments such as humidity and salt spray by more than 5 times.

[0040] Meanwhile, the multi-strand stranded structure design balances the electrical and mechanical properties of the conductor. The stranding pitch is set at 8-12 times the conductor diameter. From a conductivity perspective, this pitch range keeps the increase in AC resistance of the stranded conductor below 3%, effectively suppressing additional losses caused by the skin effect and proximity effect. From a mechanical performance perspective, the appropriate stranding angle allows each individual wire to deform in a coordinated manner when the conductor is bent, avoiding local stress concentration and enabling the conductor to withstand over 10,000 repeated bending cycles. From a high-temperature stability perspective, the optimized stranding structure maintains a uniform stress distribution during thermal expansion, preventing conductor deformation or breakage due to localized loosening. Especially in fire-resistant cable applications, when the mica tape fire-resistant layer shrinks at high temperatures, this stranding structure can alleviate stress through appropriate self-adjustment, maintaining close contact between the conductor and the insulation layer.

[0041] Preferably, as a further specific embodiment, the shielding layer is a silver-plated copper wire braided layer covering the insulation layer, with a coverage of ≥90% and a silver plating layer thickness of 1-3μm.

[0042] This invention specifically defines the structure of the cable shielding layer as a silver-plated copper wire braided layer covering the insulation layer, requiring a coverage rate of ≥90% and a silver plating thickness of 1-3 μm. This approach, through the synergistic optimization of the metal plating and braiding process, achieves excellent electromagnetic shielding performance while significantly improving the stability of the shielding layer in high-temperature and corrosive environments, providing crucial assurance for the reliable operation of the cable under complex conditions. Silver, as the metal with the best conductivity, ensures that during high-frequency signal transmission, the current within the skin depth range primarily flows through the low-resistance silver layer, reducing the surface resistance of the shielding layer to below 0.1 Ω / sq, approximately 40% lower than that of ordinary copper braided layers. It is particularly noteworthy that the lower limit of the silver plating thickness of 1 μm ensures that the silver layer will not crack during the bending of the copper wires in the braiding process, preventing localized decreases in conductivity; the upper limit of 3 μm avoids a significant increase in material costs and processing difficulty due to excessively thick silver layers.

[0043] Preferably, as a further specific embodiment, the preparation method of the extruded insulated low-voltage fire-resistant power cable includes the following steps: first, multiple strands of tin-plated copper wire are twisted into a conductor, the surface of the conductor is cleaned by plasma, and then mica tape is wrapped around the conductor to form a fire-resistant layer;

[0044] Subsequently, nano-sized aluminum hydroxide and carboxylated carbon nanotubes are pre-dispersed in a mixture of cross-linked polyethylene and low-smoke flame-retardant polyolefin and then extruded onto the surface of the refractory layer to form an insulating layer.

[0045] Subsequently, a silver-plated copper wire shielding layer is woven outside the insulation layer to form a shielding layer. Finally, a ceramicized silicone rubber sheath material is wrapped around the shielding layer by hot pressing and extrusion to obtain the final product.

[0046] This invention also details the preparation method of extruded insulated low-voltage fire-resistant power cables. Through a multi-process collaborative precision manufacturing process, the performance optimization and structural integration of each functional layer of the cable are achieved. This method, with key technologies such as plasma cleaning, nanofiller pre-dispersion, magnetic field-induced orientation, and hot-press extrusion as its core, constructs a complete industrially achievable process flow, ensuring a high degree of consistency in the final product's microstructure control and macroscopic performance. The mica tape wrapping process adopts a 45° cross-over wrapping method, with tension controlled within the range of 5-8N. This process design allows the composite structure of synthetic mica paper and glass fiber cloth to tightly adhere to the conductor surface, with a wrapping gap of less than 0.2mm.

[0047] Preferably, as a further specific embodiment, an axial magnetic field is used to induce the directional alignment of carbon nanotubes during the extrusion forming of the insulating layer, while ultrasonic vibration is applied to eliminate air bubbles.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) This invention provides an extruded insulated low-voltage fire-resistant power cable. Through material optimization and structural design of each functional layer, the cable simultaneously possesses excellent fire resistance, low smoke flame retardant properties, high mechanical strength and stable electromagnetic shielding performance, making it particularly suitable for low-voltage power transmission scenarios with stringent safety requirements. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] To more clearly illustrate the technical solutions in this invention, specific embodiments are described below.

[0052] Example 1

[0053] The preparation process of the extruded insulated low-voltage fire-resistant power cable of the present invention is as follows:

[0054] 1. Conductor preparation

[0055] Material: Tin-plated copper wire, 0.15mm in diameter, with a tin plating thickness of 0.5μm;

[0056] Stranding: A high-speed stranding machine is used to strand 36 strands of tin-plated copper wire into a conductor with a diameter of 2.5mm after stranding. The stranding pitch is set to 20mm, and the stranding tension is controlled at 3-5N to ensure the roundness of the conductor.

[0057] Plasma cleaning: An argon plasma cleaner with a power of 300W and a frequency of 13.56MHz was used for 5 minutes to remove oxides and organic contaminants from the conductor surface.

[0058] 2. Refractory layer wrapping

[0059] Materials: The substrate is synthetic mica paper (thickness 0.02mm) and glass fiber cloth (thickness 0.08mm), with a total thickness of 0.1mm and a width of 20mm after lamination, and a temperature resistance of over 1000℃;

[0060] Wrapping: Use a 45° inclined wrapping machine to wrap two layers of mica tape around the conductor, with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a tight fit. After wrapping, check for wrinkles and damage.

[0061] 3. Insulation layer extrusion

[0062] Materials: The base material is 60 parts of low-smoke halogen-free flame-retardant polyolefin (purchased from Dow Chemical) and 40 parts of cross-linked polyethylene (purchased from Henan Zhuolin Polymer New Materials Co., Ltd.);

[0063] Nanofillers: nano-aluminum hydroxide, particle size 50nm; carboxylated carbon nanotubes with an aspect ratio of 120 and a grafting rate of 3%;

[0064] Mass ratio: 12 parts nano aluminum hydroxide, 1.2 parts carboxylated carbon nanotubes (ratio 10:1);

[0065] Pre-dispersion: Nano-aluminum hydroxide, carboxylated carbon nanotubes, polyolefin and cross-linked polyethylene are pre-mixed in a high-speed mixer for 10 minutes to obtain the insulating layer material;

[0066] Extrusion molding: Subsequently, a single screw extruder is used to extrude the insulating material onto the surface of the refractory layer to form an insulating layer with a thickness of 1.2 mm. Axial magnetic field induces alignment. An axial magnetic field is applied at the extrusion die to orient the carbon nanotubes along the cable axis. Ultrasonic defoaming is then performed. 40 kHz ultrasound is applied during the extrusion process to eliminate bubbles and then the material is cooled.

[0067] 4. Shielding layer braid (silver-plated copper wire braided layer)

[0068] Material: Silver-plated copper wire, single wire diameter is 0.1mm, silver plating thickness is 1μm;

[0069] Weaving: A 16-spindle braiding machine is used, with a braiding angle of 60°, a braiding density of 92%, and the braiding tension is controlled at 2-3N to ensure uniform coverage;

[0070] Hot air leveling: After weaving, the material is leveled with hot air (temperature 150℃, time 10 seconds) to improve the bonding force between the shielding layer and the insulation layer;

[0071] 5. Sheath layer extrusion

[0072] Materials: 100 parts methyl vinyl silicone rubber, 40 parts ceramicized filler (of which glass powder: kaolin: nano zirconium dioxide = 5:3:2), 15 parts flame retardant (of which ammonium polyphosphate: zinc borate: ferrocene = 6:3:1), and 1 part peroxide vulcanizing agent;

[0073] Mixing: Mix methyl vinyl silicone rubber, ceramicized filler and flame retardant in an internal mixer (temperature 120°C) for 15 minutes;

[0074] Extrusion molding: A coarse sheath layer with a thickness of 2.0 mm is extruded onto the surface of the shielding layer using a hot extruder (temperature 160℃, pressure 15MPa);

[0075] Vulcanization: Subsequently, the rough sheath layer is vulcanized with a peroxide vulcanizing agent at a vulcanization temperature of 180℃ and a vulcanization time of 10 minutes to form a dense sheath layer.

[0076] Example 2

[0077] The preparation process of the extruded insulated low-voltage fire-resistant power cable of the present invention is as follows:

[0078] 1. Conductor preparation

[0079] Material: Tin-plated copper wire, 0.15mm in diameter, with a tin plating thickness of 2μm;

[0080] Stranding: A high-speed stranding machine is used to strand 36 strands of tin-plated copper wire into a conductor with a diameter of 2.5mm after stranding. The stranding pitch is set to 30mm and the stranding tension is controlled at 3-5N to ensure the roundness of the conductor.

[0081] Plasma cleaning: An argon plasma cleaner with a power of 300W and a frequency of 13.56MHz was used for 5 minutes to remove oxides and organic contaminants from the conductor surface.

[0082] 2. Refractory layer wrapping

[0083] Materials: The substrate is synthetic mica paper (thickness 0.1mm) and glass fiber cloth (thickness 0.2mm), with a total thickness of 0.3mm and a width of 20mm after lamination, and a temperature resistance of over 1000℃;

[0084] Wrapping: Use a 45° inclined wrapping machine to wrap two layers of mica tape around the conductor, with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a tight fit. After wrapping, check for wrinkles and damage.

[0085] 3. Insulation layer extrusion

[0086] Materials: The base material consists of 70 parts of low-smoke halogen-free flame-retardant polyolefin (purchased from Dow Chemical) and 30 parts of cross-linked polyethylene (purchased from Henan Zhuolin Polymer New Materials Co., Ltd.);

[0087] Nanofillers: nano-aluminum hydroxide, 100nm in size; carboxylated carbon nanotubes with an aspect ratio of 120 and a grafting rate of 5%;

[0088] Mass ratio: 15 parts nano aluminum hydroxide, 1 part carboxylated carbon nanotubes (ratio 15:1);

[0089] Pre-dispersion: Nano-aluminum hydroxide, carboxylated carbon nanotubes, polyolefin and cross-linked polyethylene are pre-mixed in a high-speed mixer for 10 minutes to obtain the insulating layer material;

[0090] Extrusion molding: Subsequently, a single screw extruder is used to extrude the insulating material onto the surface of the refractory layer to form an insulating layer with a thickness of 1.2 mm. Axial magnetic field induces alignment. An axial magnetic field is applied at the extrusion die to orient the carbon nanotubes along the cable axis. Ultrasonic defoaming is then performed. 40 kHz ultrasound is applied during the extrusion process to eliminate bubbles and then the material is cooled.

[0091] 4. Shielding layer braid (silver-plated copper wire braided layer)

[0092] Material: Silver-plated copper wire, single wire diameter is 0.1mm, silver plating thickness is 3μm;

[0093] Weaving: A 16-spindle braiding machine is used, with a braiding angle of 60°, a braiding density of 92%, and the braiding tension is controlled at 2-3N to ensure uniform coverage;

[0094] Hot air leveling: After weaving, the material is leveled with hot air (temperature 150℃, time 10 seconds) to improve the bonding force between the shielding layer and the insulation layer;

[0095] 5. Sheath layer extrusion

[0096] Materials: 120 parts methyl vinyl silicone rubber, 60 parts ceramicized filler (of which glass powder: kaolin: nano zirconium dioxide = 7:5:2), 25 parts flame retardant (of which ammonium polyphosphate: zinc borate: ferrocene = 7:5:1), and 2 parts peroxide vulcanizing agent.

[0097] Mixing: Mix methyl vinyl silicone rubber, ceramicized filler and flame retardant in an internal mixer (temperature 120°C) for 15 minutes;

[0098] Extrusion molding: A coarse sheath layer with a thickness of 2.0 mm is extruded onto the surface of the shielding layer using a hot extruder (temperature 160℃, pressure 15MPa);

[0099] Vulcanization: Subsequently, the rough sheath layer is vulcanized with a peroxide vulcanizing agent at a vulcanization temperature of 180℃ and a vulcanization time of 10 minutes to form a dense sheath layer.

[0100] Example 3

[0101] The preparation process of the extruded insulated low-voltage fire-resistant power cable of the present invention is as follows:

[0102] 1. Conductor preparation

[0103] Material: Tin-plated copper wire, 0.15mm in diameter, with a tin plating thickness of 1μm;

[0104] Stranding: A high-speed stranding machine is used to strand 36 strands of tin-plated copper wire into a conductor with a diameter of 2.5mm after stranding. The stranding pitch is set to 25mm, and the stranding tension is controlled at 3-5N to ensure the roundness of the conductor.

[0105] Plasma cleaning: An argon plasma cleaner with a power of 300W and a frequency of 13.56MHz was used for 5 minutes to remove oxides and organic contaminants from the conductor surface.

[0106] 2. Refractory layer wrapping

[0107] Materials: The substrate is synthetic mica paper (thickness 0.08mm) and glass fiber cloth (thickness 0.12mm), with a total thickness of 0.2mm and a width of 20mm after lamination, and a temperature resistance of over 1000℃;

[0108] Wrapping: Use a 45° inclined wrapping machine to wrap two layers of mica tape around the conductor, with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a tight fit. After wrapping, check for wrinkles and damage.

[0109] 3. Insulation layer extrusion

[0110] Materials: The base material is 60 parts of low-smoke halogen-free flame-retardant polyolefin (purchased from Dow Chemical) and 40 parts of cross-linked polyethylene (purchased from Henan Zhuolin Polymer New Materials Co., Ltd.);

[0111] Nanofillers: nano-aluminum hydroxide, particle size 80nm; carboxylated carbon nanotubes with an aspect ratio of 130 and a grafting rate of 4%;

[0112] Mass ratio: 10 parts nano aluminum hydroxide, 1 part carboxylated carbon nanotubes (ratio 10:1);

[0113] Pre-dispersion: Nano-aluminum hydroxide, carboxylated carbon nanotubes, polyolefin and cross-linked polyethylene are pre-mixed in a high-speed mixer for 10 minutes to obtain the insulating layer material;

[0114] Extrusion molding: Subsequently, a single screw extruder is used to extrude the insulating material onto the surface of the refractory layer to form an insulating layer with a thickness of 1.2 mm. Axial magnetic field induces alignment. An axial magnetic field is applied at the extrusion die to orient the carbon nanotubes along the cable axis. Ultrasonic defoaming is then performed. 40 kHz ultrasound is applied during the extrusion process to eliminate bubbles and then the material is cooled.

[0115] 4. Shielding layer braid (silver-plated copper wire braided layer)

[0116] Material: Silver-plated copper wire, single wire diameter is 0.1mm, silver plating thickness is 2.5μm;

[0117] Weaving: A 16-spindle braiding machine is used, with a braiding angle of 60°, a braiding density of 92%, and the braiding tension is controlled at 2-3N to ensure uniform coverage;

[0118] Hot air leveling: After weaving, the material is leveled with hot air (temperature 150℃, time 10 seconds) to improve the bonding force between the shielding layer and the insulation layer;

[0119] 5. Sheath layer extrusion

[0120] Materials: 100 parts methyl vinyl silicone rubber, 55 parts ceramic filler (of which glass powder: kaolin: nano zirconium dioxide = 7:5:2), 22 parts flame retardant (of which ammonium polyphosphate: zinc borate: ferrocene = 7:5:1), and 1.5 parts peroxide vulcanizing agent;

[0121] Mixing: Mix methyl vinyl silicone rubber, ceramicized filler and flame retardant in an internal mixer (temperature 120°C) for 15 minutes;

[0122] Extrusion molding: A coarse sheath layer with a thickness of 2.0 mm is extruded onto the surface of the shielding layer using a hot extruder (temperature 160℃, pressure 15MPa);

[0123] Vulcanization: Subsequently, the rough sheath layer is vulcanized with a peroxide vulcanizing agent at a vulcanization temperature of 180℃ and a vulcanization time of 10 minutes to form a dense sheath layer.

[0124] Comparative Example 1

[0125] The specific implementation method is the same as in Example 3, except that the mass ratio of nano-sized aluminum hydroxide to carboxylated carbon nanotubes in Example 3 is adjusted to 1:1.

[0126] Comparative Example 2

[0127] The specific implementation method is the same as in Example 3, except that the mass ratio of nano-sized aluminum hydroxide to carboxylated carbon nanotubes in Example 3 is adjusted to 25:1.

[0128] Comparative Example 3

[0129] The specific implementation method is the same as in Example 3, except that the grafting rate of the carboxylated modified carbon nanotube surface in Example 3 is adjusted to 1%.

[0130] Comparative Example 4

[0131] The specific implementation method is the same as in Example 3, except that the grafting rate of the carboxylated modified carbon nanotube surface in Example 3 is adjusted to 10%.

[0132] Comparative Example 5

[0133] The specific implementation method is the same as in Example 3, except that the particle size of the nano-sized aluminum hydroxide in Example 3 is adjusted to 10 nm.

[0134] Comparative Example 6

[0135] The specific implementation method is the same as in Example 3, except that the particle size of the nano-sized aluminum hydroxide in Example 3 is adjusted to 200 nm.

[0136] Comparative Example 7

[0137] The specific implementation method is the same as in Example 3, except that the carbon nanotubes are not modified by carboxylation.

[0138] Experiment Example 1: Performance Testing of Extruded Insulated Low-Voltage Fire-Resistant Power Cables

[0139] The power cables prepared in Examples 1-3 and Comparative Examples 1-7 were used as samples to measure fire resistance, thermal conductivity of insulation layer, ceramicization effect of sheath, smoke density (transmittance), mechanical strength (tensile strength) and volume resistivity.

[0140] 1. Sample fire resistance test

[0141] Testing equipment: fire resistance test furnace, thermocouple temperature sensor, timer, circuit integrity testing device (multimeter);

[0142] Test procedure: Cut a 1.5m long sample of the power cable obtained in Examples 1-3 and Comparative Examples 1-7, remove the sheath and shielding layer from both ends to expose the conductor, and connect it to a low-voltage power supply;

[0143] Installation and fixing: Suspend the sample horizontally inside the refractory furnace, align the flame nozzle with the center of the sample, and place the thermocouple tightly against the sample surface to detect the temperature.

[0144] Combustion test: Start the test furnace, heat up to 950℃ within 30 seconds, keep the flame burning stably, and record whether the conductor is energized every 5 minutes. Continue burning for 90 minutes or record the actual fire resistance time after the circuit is interrupted.

[0145] 2. Thermal conductivity test of insulation layer

[0146] Test equipment: heat flow thermal conductivity meter (equipped with constant temperature hot plate, cooling plate, and heat flow sensor), data acquisition system;

[0147] Test steps:

[0148] Sample preparation: Take the power cables obtained in Examples 1-3 and Comparative Examples 1-7, cut circular pieces with a diameter of 30 mm and a thickness of 1.2 mm from the cable insulation layer, and polish the surface to a smooth surface;

[0149] Test setup: The hot plate temperature was set to 50℃, the cooling plate temperature to 20℃, and the temperature difference ΔT = 30℃. The sample was then placed between the hot plate and the cooling plate, and a pressure of 0.1MPa was applied to ensure tight contact.

[0150] Data acquisition: After the heat flow stabilizes (approximately 10 minutes), record the heat flow sensor reading (Q) and sample thickness (d);

[0151] Thermal conductivity λ = Q × d / ΔT;

[0152] 3. Ceramicization effect test of the sheath

[0153] Testing equipment: muffle furnace (1200℃), Shore D hardness tester, electron microscope;

[0154] Test steps:

[0155] Sample preparation: Sheath layer samples (20mm×20mm) were taken from the samples obtained in Examples 1-3 and Comparative Examples 1-7 and placed in a muffle furnace to burn at 950°C for 30 minutes;

[0156] Ceramic layer formation: After cooling, observe whether a continuous ceramic layer has formed on the surface;

[0157] Hardness test: Using a Shore D hardness tester, the needle is pressed vertically into the surface of the ceramic layer, and the reading is taken after 15 seconds;

[0158] Microscopic analysis: Electron microscope observation of the ceramic layer cross-section confirmed the absence of cracks;

[0159] 4. Smoke density (transmittance) test

[0160] Testing equipment: Smoke density testing chamber (3m) 3 (Volume), laser light source, optical receiver, data logger;

[0161] Test steps:

[0162] Sample combustion: Take 100g of the cable sheath material of the power cables obtained in Examples 1-3 and Comparative Examples 1-7 respectively and place it in a combustion dish. After ignition, close the box door.

[0163] Optical path monitoring: A laser light source (wavelength 635nm) passes through the smoke, and the receiver records the transmittance in real time (initial value is 100%), recording data once every 10 seconds for 10 minutes;

[0164] Result calculation: Take the lowest transmittance value;

[0165] 5. Mechanical strength (tensile) test

[0166] Testing equipment: Electronic tensile testing machine (range 50kN), fixtures, displacement sensor;

[0167] Test steps:

[0168] Sample preparation: Take a 200mm cable segment of the power cable obtained in Examples 1-3 and Comparative Examples 1-7, and fix both ends with clamps (clamping length 50mm);

[0169] Tensile test: Stretch at a rate of 50 mm / min and record the force-displacement curve until fracture;

[0170] Tensile strength = maximum tensile force (N) / cross-sectional area (mm²) 2 );

[0171] Fracture analysis: Observe the fracture morphology;

[0172] 6. Volume resistivity test

[0173] Test equipment: high resistance meter (test voltage 500V DC), shielded test box, electrodes (diameter 20mm).

[0174] Test steps:

[0175] Sample preparation: Cut circular pieces with a diameter of 50 mm and a thickness of 1.2 mm from the insulation layer of the power cables in Examples 1-3 and Comparative Examples 1-7, and coat the surface with conductive silver paste to eliminate contact resistance;

[0176] Test procedure: The electrodes are pressed firmly against both sides of the sample, a voltage of 500V is applied, and the resistance value (R) is read after stabilization;

[0177] Volume resistivity ρ=R×πr 2 / d(r = electrode radius, d = sample thickness);

[0178] Error control: The ambient humidity of the test environment is ≤40%, and the test is repeated 3 times and the average value is taken.

[0179] The final data results are shown in Table 1 below.

[0180] Table 1 Test Results

[0181]

[0182]

[0183] As can be seen from the table above, Examples 1-3 demonstrate a series of optimized performance of extruded insulated low-voltage fire-resistant power cables. The gradient changes in these three examples clearly show the impact of fine-tuning the content of each component on the final performance. In particular, Example 3 achieves excellent thermal conductivity and mechanical properties while maintaining high fire resistance.

[0184] Data from Comparative Examples 1-2 show that when the mass ratio of nano-aluminum hydroxide to carbon nanotubes was adjusted to 1:1 in Comparative Example 1, this change led to a significant decline in cable performance. The fire resistance time decreased to 85 minutes, 11 minutes less than in Example 3, and the thermal conductivity also dropped to 0.28 W / m·K. This performance decline is mainly due to the excessive carbon nanotube content, which disrupts the uniform distribution of nanofillers in the insulation layer. While excessive carbon nanotubes improve conductivity, they reduce the material's flame retardant properties. Simultaneously, the high carbon nanotube content easily leads to agglomeration in the matrix, causing localized electric field concentration and reducing the volume resistivity to 8.7 × 10⁻⁶. 13 In terms of mechanical properties, the tensile strength decreased to 11.3 MPa, indicating that excessive carbon nanotubes would affect the mechanical integrity of the matrix material. In Comparative Example 2, the mass ratio of nano-aluminum hydroxide to carbon nanotubes was adjusted to 25:1, which significantly increased the aluminum hydroxide content. As can be seen from the above data, although the refractory time was improved compared to Comparative Example 1, reaching 88 minutes, it was still significantly lower than the 96 minutes of Example 3.

[0185] The data from Comparative Examples 3-4 show that when the surface grafting rate of carboxylated carbon nanotubes in Comparative Example 3 was reduced to 1%, this subtle adjustment resulted in a significant change in performance. Consequently, the fire resistance time of the power cable prepared in Comparative Example 3 decreased to 82 minutes, and the thermal conductivity dropped sharply to 0.25 W / m·K. This indicates that insufficient grafting rate severely affects the dispersibility and interfacial bonding of carbon nanotubes. A low grafting rate leads to uneven dispersion of carbon nanotubes in the matrix, making them prone to agglomeration. This not only reduces thermal conductivity but also affects the mechanical strength of the material, while the volume resistivity decreases to 7.6 × 10⁻⁶. 13 The Ω·cm indicates a decrease in insulation performance. In Comparative Example 4, the surface grafting rate of carboxylated carbon nanotubes was increased to 10%. This over-modification also had negative effects, resulting in a further reduction in the fire resistance time of the power cable obtained in Comparative Example 4 to 79 minutes, the worst among all comparative examples. The thermal conductivity was also only 0.23 W / m·K. This shows that while an excessively high grafting rate improved the dispersion of carbon nanotubes, over-modification damaged the structural integrity of the carbon nanotubes themselves, leading to a decrease in thermal conductivity. Furthermore, the tensile strength decreased to 10.2 MPa, and the volume resistivity was 6.9 × 10⁻⁶. 13 Ω·cm, all performance indicators deteriorated across the board, and the smoke density transmittance dropped to 65.3%;

[0186] The data from Comparative Examples 5 and 6 show that reducing the particle size of nano-sized aluminum hydroxide to 10 nm in Comparative Example 5 led to a decrease in several performance indicators. The fire resistance time was 75 minutes and the thermal conductivity was 0.15 W / m·K, which was significantly lower than that of Example 3. This is because although the smaller particle size increases the specific surface area, it also makes the nanoparticles more prone to agglomeration, thus reducing the dispersion effect. When the particle size of nano-sized aluminum hydroxide was increased to 200 nm in Comparative Example 6, the data shows that this change was also detrimental to the cable performance. The fire resistance time of the cable prepared in this case was 71 minutes and the thermal conductivity was 0.14 W / m·K, which was even worse than that of Comparative Example 5. This is because the larger particle size reduced the interfacial effect of the filler and made it difficult to form an effective barrier network.

[0187] The data from Comparative Example 7 show that, without carboxylation modification of the carbon nanotubes, the resulting power cable has a fire resistance time of 61 minutes and a thermal conductivity of 0.13 W / m·K, both significantly lower than those in Example 3. Furthermore, its tensile strength is 7.1 MPa and its volume resistivity is 3.5 × 10⁻⁶. 13 The value of Ω·cm indicates that unmodified carbon nanotubes are difficult to bond well with the matrix.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An extruded insulated low-voltage fire-resistant power cable, characterized in that, It includes, from the inside out, a conductor, a fire-resistant layer, an insulating layer, a shielding layer, and a sheath layer; The refractory layer is a mica tape wrapping layer covering the conductor. The mica tape is a composite structure of synthetic mica paper and glass fiber cloth, and the thickness of the mica tape is 0.1-0.3 mm. The insulating layer comprises cross-linked polyethylene and low-smoke flame-retardant polyolefin materials, and nano-sized aluminum hydroxide and carbon nanotubes are dispersed within the insulating layer. The particle size of the nano-sized aluminum hydroxide is 50-100 nm, the aspect ratio of the carbon nanotubes is ≥100, and the mass ratio of the nano-sized aluminum hydroxide to the carbon nanotubes is (10-15):

1. The sheath layer is a ceramicized silicone rubber sheath extruded outside the shielding layer; The carbon nanotubes are carboxylated modified carbon nanotubes with a surface grafting rate of 3-5%, and the carboxylated modified carbon nanotubes are oriented along the cable axis in the insulation layer to form a continuous heat-conducting network. The ceramicized silicone rubber sheath comprises the following components: 100-120 parts of methyl vinyl silicone rubber; 40-60 parts of ceramicized filler; 15-25 parts flame retardant; 1-2 parts of vulcanizing agent; The ceramicized filler is a mixture of glass powder, kaolin and nano-zirconia; the mass ratio of glass powder, kaolin and nano-zirconia is (5-7):(3-5):

2. The flame retardant is ammonium polyphosphate, zinc borate and ferrocene, wherein the mass ratio of ammonium polyphosphate, zinc borate and ferrocene is (6-7):(3-5):1; The shielding layer is a silver-plated copper wire braided layer covering the insulation layer, with a coverage of ≥90% and a silver plating thickness of 1-3μm.

2. The extruded insulated low-voltage fire-resistant power cable according to claim 1, characterized in that, The conductor is made of multiple strands of tin-plated copper wires twisted together, with a tin plating thickness of 0.5-2μm and a twisting pitch of 8-12 times the diameter of the conductor.

3. The method for preparing extruded insulated low-voltage fire-resistant power cable according to any one of claims 1-2, characterized in that, Includes the following steps: First, multiple strands of tin-plated copper wire are twisted together to form a conductor. After plasma cleaning of the conductor surface, mica tape is wrapped around the conductor to form a fire-resistant layer. Subsequently, nano-sized aluminum hydroxide and carboxylated carbon nanotubes are pre-dispersed in a polyolefin material and then extruded onto the surface of the refractory layer to form an insulating layer. Subsequently, a silver-plated copper wire shielding layer is woven outside the insulation layer to form a shielding layer. Finally, a ceramicized silicone rubber sheath material is wrapped around the shielding layer by hot pressing and extrusion to obtain the final product.

4. The preparation method according to claim 3, characterized in that, During the extrusion process to form the insulating layer, an axial magnetic field is used to induce the directional alignment of carbon nanotubes, while ultrasonic vibration is applied to eliminate air bubbles.

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