Extrusion insulation low-voltage fire-resistant power cable

Abstract

The invention provides an extruded insulated low-voltage fire-resistant power cable, which belongs to the technical field of crosslinked polyethylene insulated power cables and cable accessories, and comprises a conductor, a fire-resistant layer, an insulating layer, a shielding layer and a sheath layer which are sequentially arranged from inside to outside, the fireproof layer is a mica tape wrapping layer wrapping the conductor, and the mica tape is a composite structure of synthetic mica paper and glass fiber cloth; the insulating layer is made of a cross-linked polyethylene and low-smoke flame-retardant polyolefin mixed material, nanoscale aluminum hydroxide and carbon nanotubes are dispersed in the insulating layer, the length-diameter ratio of the carbon nanotubes is greater than or equal to 100, and the sheath layer is a ceramic silicone rubber sheath extruded outside the shielding layer. The power cable provided by the invention has excellent fire resistance, flame retardance and mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of cross-linked polyethylene insulated power cables and cable accessories, and in particular relates to an extruded insulated low-voltage fire-resistant power cable. Background Art

[0002] Power cables, as essential carriers of electrical energy transmission, 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 life and property. This is especially true in low-voltage power systems, where the fire resistance of cables is directly related to the continuous power supply to critical facilities such as emergency lighting and firefighting equipment. Therefore, higher fire resistance requirements are placed on cables.

[0003] Currently, most fire-resistant cables on the market utilize a mica tape wrapping structure. However, traditional mica tape suffers from low mechanical strength and easy detachment. It also becomes brittle at high temperatures, compromising the cable's long-term reliability. Furthermore, the cable's insulation is typically made of polyolefins. While this material offers excellent electrical properties, it can easily decompose under high temperatures or fire conditions, releasing large amounts of smoke and toxic gases, exacerbating the fire hazard. While some research has explored adding flame retardants to the insulation to improve fire resistance, high levels of conventional flame retardants can affect the material's mechanical properties and processing, while insufficient amounts can hinder the desired flame retardant effect. Furthermore, the cable's outermost layer, the sheath, is crucial for fire resistance, but traditional sheath materials are prone to melting or burning at high temperatures, failing to provide continuous protection. Furthermore, the cable's shielding performance significantly impacts signal transmission stability and interference immunity. Traditional shielding layers, often made of ordinary copper wire, have poor heat and oxidation resistance, making them susceptible to failure in fire environments.

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

[0005] The first purpose of the present invention is to provide an extruded insulated low-voltage fire-resistant power cable. Through the material optimization and structural design of each functional layer, the cable has excellent fire resistance, low smoke flame retardant properties, high mechanical strength and stable electromagnetic shielding performance. It is particularly suitable for low-voltage power transmission scenarios with strict safety performance requirements.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0007] An extruded insulated low-voltage fire-resistant power cable, comprising a conductor, a fire-resistant layer, an insulating layer, a shielding layer and a sheath layer arranged in sequence from the inside to the outside;

[0008] The fire-resistant layer is a mica tape wrapped around 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 mixed material of cross-linked polyethylene and low-smoke flame-retardant polyolefin, and nano-aluminum hydroxide and carbon nanotubes are dispersed in the insulating layer. The particle size of the nano-aluminum hydroxide is 50-100 nm, the aspect ratio of the carbon nanotubes is ≥100, and the mass ratio of the nano-aluminum hydroxide to the carbon nanotubes is (10-15):1;

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

[0011] The present invention mainly provides an extruded insulated low-voltage fire-resistant power cable, which mainly includes a multi-layer structure design of a conductor, a fire-resistant layer, an insulation layer, a shielding layer and a sheath layer arranged in sequence from the inside to the outside, and specifically defines the materials, composition and key parameters of each layer. By optimizing the materials and synergizing the fire-resistant layer, the insulation layer and the sheath layer, the fire resistance, flame retardancy, mechanical strength and high-temperature stability of the cable are significantly improved while maintaining the basic electrical properties of the cable. It is suitable for low-voltage power transmission scenarios with high safety performance requirements.

[0012] First, the present invention defines the fire-resistant layer as a mica tape wrapping layer wrapped around the outside of the conductor, and further clarifies that the specific structure of the mica tape wrapping layer is a composite structure of synthetic mica paper and glass fiber cloth, with a thickness controlled at 0.1-0.3mm, thereby solving the problem of insufficient mechanical strength and easy falling off of the mica tape in traditional fire-resistant cables. The synthetic mica paper has higher high temperature resistance and insulation performance, while the addition of glass fiber cloth enhances the flexibility and tensile strength of the mica tape, making it less likely to break when the cable is bent or subjected to external force. In addition, the optimized thickness of the mica tape avoids the problem of increased cable rigidity or increased processing difficulty due to excessive thickness while ensuring fire resistance. In the event of a fire, the fire-resistant layer of the composite structure can effectively isolate high temperatures, delay the spread of flames to the conductor, and ensure that the cable can still maintain its power transmission function for a certain period of time in a high temperature environment.

[0013] Secondly, the present invention also defines the composition of the insulating layer, which is a mixed material of cross-linked polyethylene and low-smoke flame-retardant polyolefin, and disperses nano-scale aluminum hydroxide and carbon nanotubes in the insulating layer, and specifically stipulates the particle size of aluminum hydroxide, the aspect ratio of carbon nanotubes (≥100) and the mass ratio of the two. This design makes the insulating layer not only have good electrical insulation properties, but also have excellent thermal conductivity and flame retardancy. The mixed insulating layer substrate used in the present invention is composed of cross-linked polyethylene and low-smoke flame-retardant polyolefin materials. Cross-linked polyethylene is used as the base material, which has excellent electrical insulation properties and high temperature resistance. Its three-dimensional network structure It can still maintain stability at high temperatures, and the addition of low-smoke flame-retardant polyolefin further optimizes the flame retardancy and environmental protection of the material, significantly reducing the smoke density and toxic gas release during combustion. The design of this mixed substrate 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; and the nano-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 the combustible gas; at the same time, its nano-particle size enables it to be evenly dispersed in the polyolefin matrix, avoiding negative effects on the mechanical properties of the material.

[0014] At the same time, the sheath layer is extruded from ceramic silicone rubber material. Ceramic silicone rubber has the flexibility and workability of ordinary rubber at room temperature, and can be transformed into a hard ceramic protective layer under high temperature or open flame conditions, effectively isolating the internal structure from damage by flames and high temperatures. Therefore, compared with traditional PVC or ordinary rubber sheaths, ceramic silicone rubber sheaths not only have better fire resistance, but also emit low smoke and no toxic gas when burning, which meets the safety and environmental protection requirements of cables in modern buildings and public facilities.

[0015] The conductor of the present invention is formed by twisting multiple strands of tinned copper wires, the thickness of the tinned layer is 0.5-2 μm, and the twisting pitch is 8-12 times the diameter of the conductor. The tinned layer not only improves the oxidation resistance and welding performance of the conductor, but also enhances the bonding strength between the conductor and the fire-resistant layer; the optimization of the twisting pitch balances the flexibility and conductive efficiency of the conductor, avoiding the problem of increased cable outer diameter due to excessive pitch or loose conductor caused by too small pitch.

[0016] The fire-resistant power cable of the present invention achieves comprehensive improvement in the fire resistance, flame retardancy, mechanical properties and electrical properties of the cable through the coordinated optimization of the multi-layer structure, solves the shortcomings of traditional cables in 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 carboxyl-modified carbon nanotubes with a surface grafting rate of 3-5%, and the carboxyl-modified carbon nanotubes are axially arranged in the insulation layer along the cable to form a continuous heat-conducting network.

[0018] The carbon nanotubes of the present invention are carboxyl 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 heat conduction network. This method not only solves the key problems of poor dispersion of nanomaterials in polymer matrices and weak interface bonding, but also achieves a synergistic improvement in the thermal conductivity and mechanical properties of the insulation layer through precise microstructure control. The carboxyl modification treatment makes the surface of the carbon nanotubes carry polar functional groups, which on the one hand significantly improves the interface compatibility between the carbon nanotubes and the polyolefin matrix, allowing the nanoparticles to be evenly dispersed without agglomeration. On the other hand, the stress transfer efficiency between the filler and the matrix is enhanced through chemical bonding, so that the insulation layer can give full play to the reinforcing effect of the carbon nanotubes when subjected to mechanical loads. A grafting rate that is too low cannot provide sufficient active sites to improve dispersibility, while a grafting rate that is too high may destroy the intrinsic structure of the carbon nanotubes, affecting their thermal and electrical conductivity. At the same time, the present invention also arranges the carbon nanotubes axially in the insulating layer, so that the carbon nanotubes form a continuous heat conduction path along the length of the cable, so that the Joule heat generated during the operation of the conductor can be quickly conducted and dissipated along the longitudinal direction of the cable, avoiding local accumulation of heat and causing insulation aging. In terms of mechanical properties, the directionally arranged carbon nanotubes can more effectively bear axial tensile stress, thereby increasing the tensile strength of the cable by more than 30%; in terms of electrical performance, this arrangement can prevent the carbon nanotubes from forming a conductive network in the radial direction, while improving the longitudinal thermal conductivity and maintaining the excellent radial insulation performance of the insulation layer.

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

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

[0021] 40-60 parts of ceramic filler;

[0022] 15-25 parts of flame retardant;

[0023] 1-2 parts of vulcanizing agent.

[0024] The present invention also makes specific restrictions on the composition of the sheath layer material, which contains 100-120 parts by mass of methyl vinyl silicone rubber, 40-60 parts by mass of ceramic filler, 15-25 parts by mass of flame retardant and 1-2 parts by mass of vulcanizer. This method combines ceramic transformation technology with traditional rubber sheath materials, and realizes the perfect unity of the flexibility of the sheath layer at room temperature and the ceramic protection characteristics at high temperature through the synergistic effect of multiple components, which fundamentally solves the technical problem that traditional cable sheaths are easy to melt in fire and cannot provide continuous protection. Among them, methyl vinyl silicone rubber is used as the matrix material, and its main chain is composed of alternating silicon and oxygen atoms, which gives the material excellent thermal stability and weather resistance. The methyl group of the side chain does not directly participate in the cross-linking reaction, but its small volume and low polarity make the silicone rubber main chain maintain high flexibility, which is convenient for the vinyl to approach and react during the vulcanization process to improve the cross-linking efficiency. The C-H bond energy of the methyl group is relatively high, which can reduce the main chain under vulcanization or high temperature environment. Breaking, protecting the vinyl cross-linking points from being destroyed, thereby providing appropriate cross-linking sites through the joint action of methyl and vinyl groups, so that the material can form a moderate cross-linking network to maintain mechanical strength during the vulcanization process, and can also achieve transformation to a ceramic phase through molecular chain breakage and recombination under high temperature conditions, wherein the addition amount of ceramic filler is controlled at 40-60 parts. This ratio range not only ensures that the filler is sufficient to form a continuous ceramic skeleton structure at high temperature, but also avoids the problem of increased hardness and brittleness of the material at room temperature due to excessive filler. In addition, the present invention also limits the ceramic filler to a composite system of glass powder, kaolin and nano-zirconium dioxide, wherein the glass powder as a low-temperature melting phase can soften and flow first at 500-700°C, kaolin provides an aluminosilicate skeleton structure, and nano-zirconium dioxide 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, so that the sheath layer can 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 performance and mechanical properties of the material. The amount of vulcanizer is controlled at 1-2 parts, which can ensure that the silicone rubber is fully cross-linked to form a three-dimensional network structure during the processing process, and avoid the problem of decreased material elasticity caused by oversulfurization, so that the sheath layer still has good flexibility and installation applicability while maintaining sufficient mechanical strength.

[0026] The ceramic silicone rubber sheath of the present invention constructs a "trinity" protection mechanism: at room temperature, the sheath layer exhibits typical elastomer properties and can withstand various mechanical stresses during cable laying and use; when the ambient temperature rises to 300-500°C, the flame retardant system is first activated and takes effect, delaying the combustion of the material through multiple pathways such as carbonization, glass formation and free radical capture, thereby buying valuable time for personnel evacuation; when the temperature continues to rise to above 600°C, the ceramic filler and the silicone rubber matrix undergo a synergistic reaction, and the silica produced by the decomposition of the 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, can effectively block the external high temperature from being transmitted to the interior of the cable, and maintain the integrity of the cable structure.

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

[0028] The present invention also specifically defines the ceramic filler in the ceramic silicone rubber sheath, clarifying that it is a mixed system composed of glass powder, kaolin and nano zirconium dioxide in a specific mass ratio of (5-7): (3-5): 2. The core of this definition is that through the coordinated cooperation of three inorganic fillers with different functional properties, the efficient transformation of the sheath material from the rubber state to the ceramic state is achieved, while ensuring the structural stability and thermal insulation performance of the ceramic layer in a high-temperature environment. The combination design of the ceramic filler first reflects the precise control of the phase change process of the material. The glass powder, as a low-temperature melting component, softens at high temperature to form a liquid phase, which plays a role in adhesion. The role of the binder is to provide the necessary material migration channel for the ceramicization process. Its content is controlled in the range of 5-7 parts, which not only ensures sufficient liquid phase to promote sintering densification, but also avoids the problem of excessive glass phase leading to 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. The property of its melt viscosity changing with temperature has been carefully selected so that it can flow quickly to fill the pores at the initial stage of a fire, and maintain 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 temperature to generate a new high-temperature resistant crystal phase, further strengthening the structure of the ceramic layer.

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

[0030] The addition ratio of nano zirconium dioxide is only 2 parts, but it has a significant effect on improving the performance of the ceramic layer. From the perspective of thermal performance, the thermal conductivity of zirconium dioxide is significantly lower than that of common metal materials, and its unique phase change toughening properties can absorb the thermal stress in the ceramic layer and prevent the generation and expansion of cracks at high temperatures; from the perspective of structural stability, nano-scale zirconium dioxide particles have an extremely high specific surface area, which can effectively pin the movement of grain boundaries, inhibit the abnormal growth of ceramic grains at high temperatures, and maintain the excellent mechanical properties brought by the fine-grained structure. In addition, the oxygen vacancy defects on the surface of zirconium dioxide have a certain capture effect on the free radicals generated during the combustion process, which provides an additional flame retardant mechanism for the sheath material.

[0031] For the present invention, the mass ratio of the three fillers is crucial. The combination of (5-7) parts of glass powder and (3-5) parts of kaolin forms a reasonable "bonding phase-skeleton phase" ratio, ensuring that there is sufficient liquid phase to promote densification during the ceramicization process and sufficient structural strength to resist the impact of hot air flow. The addition of 2 parts of nano-zirconium dioxide 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 the sintering process; on the other hand, the interfacial reaction between zirconium dioxide and the silicone rubber matrix at high temperature forms a transition layer such as zirconium silicate, which effectively alleviates the internal stress caused by the difference in thermal expansion coefficient between the ceramic layer and the undecomposed rubber layer. It is particularly noteworthy that the particle size distribution of the three fillers in this ratio system presents a multi-graded feature, with micron-sized glass powder and kaolin constituting the main skeleton and nano-zirconium dioxide filling the gap. This "micro-nano composite" structure optimizes the packing density of the fillers, laying an ideal initial state for the subsequent ceramicization process.

[0032] In addition, the filler system can also exhibit a subtle phased response under a temperature gradient. When the ambient temperature rises to 300-400°C, the silicone rubber matrix begins to thermally decompose. At this time, 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°C, the glass powder softens to form a liquid phase, which begins to wrap the kaolin and zirconium dioxide particles. At the same time, the active sites on the surface of nano-zirconium dioxide catalyze the further carbonization of organic residues; when the temperature continues to rise to above 700°C, the liquid phase promotes particle rearrangement and diffusion mass transfer, and the kaolin conversion products react with zirconium dioxide in a solid phase reaction, eventually forming a three-dimensional interlocking ceramic structure with silicate as the matrix and zirconium oxide as the reinforcement phase. This gradual phase change process ensures that the sheath material can provide continuous protection throughout the entire temperature rise range, avoiding the defects of traditional materials where performance suddenly changes at critical temperature points. From the perspective of actual fire protection performance, this filler system enables the sheath layer to exhibit three key protection mechanisms: first, the thermal barrier effect. The thermal conductivity of the formed ceramic layer can be as low as 0.15W / (m·K), effectively blocking the transmission of external high temperatures into the cable; second, mass transfer barrier. The dense ceramic structure prevents the diffusion of oxygen into the undecomposed material and the outward escape of combustible pyrolysis products; and finally, mechanical protection. The high-temperature compressive strength of the ceramic layer can reach over 10MPa, which can withstand the impact of falling objects at the 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] The present invention also specifically defines the flame retardant system in the ceramic silicone rubber sheath, clarifying that it is 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 the synergistic effect of three compounds with different flame retardant mechanisms to construct a multiple protection system covering gas phase, condensed phase and catalytic flame retardancy, realizing the full process protection of the sheath material from suppressing the spread of flames in the early stage of fire to promoting ceramic transformation in the high temperature stage.

[0035] In this composite flame retardant, ammonium polyphosphate, the main component of the intumescent flame retardant, begins to decompose in the early stages of heating to produce polyphosphoric acid and ammonia. This process has a triple flame retardant effect: polyphosphoric acid acts as a strong dehydrating agent, promoting carbonization of the silicone rubber substrate surface to form an intumescent char layer; ammonia, as an inert gas, dilutes the concentration of combustible volatiles; the decomposition reaction itself is a strongly endothermic process, effectively reducing the local temperature of the material. Ammonium polyphosphate accounts for a dominant proportion of 6-7 parts in the system, ensuring that there is a sufficient amount of active ingredients to quickly establish the first line of defense at the initial stage of a fire. The addition of zinc borate brings unique flame retardant synergy to the flame retardant system. When the temperature rises to the range of 300-400°C, the zinc borate dehydrates and decomposes to produce boron oxide. This product softens and flows at higher temperatures (>450°C), reacting with the decomposition products of ammonium polyphosphate and silicon dioxide generated by the thermal decomposition of silicone rubber to form a borosilicate glass layer covering the material surface, blocking oxygen and heat.

[0036] Ferrocene, as a key additive in flame retardant systems, plays an irreplaceable catalytic and regulatory role, even though only one part is added. Under combustion conditions, ferrocene first decomposes to form 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 toxic gas release. More importantly, iron ions can form an iron silicate phase with the pyrolysis products of silicone rubber at high temperatures. This mineral phase with a spinel structure significantly improves the infrared reflectivity of the ceramic layer and enhances its thermal insulation properties. The addition ratio of ferrocene has been carefully optimized. Too little will result in insufficient catalytic effect, while too much may lead to premature crosslinking of the material during processing or a decrease in thermal stability.

[0037] The design of the three flame-retardant components in a ratio of (6-7):(3-5):1 ensures that corresponding flame-retardant mechanisms are effective at different stages of fire development: the initial stage is dominated by the expansion of ammonium polyphosphate; the middle stage is dominated by the melt coverage of zinc borate; and the later stage is controlled by the catalytic effect of ferrocene and high-temperature phase transition. This time-dependent mechanism relay creates seamless protection, avoiding the "time window" problem of traditional single flame retardants.

[0038] Preferably, as a further specific embodiment, the conductor is formed by twisting a plurality of tinned copper wires, the thickness of the tinned layer is 0.5-2 μm, and the twisting pitch is 8-12 times the diameter of the conductor.

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

[0040] At the same time, the design of the multi-strand twisted structure balances the electrical and mechanical properties of the conductor. The twist pitch is set to 8-12 times the diameter of the conductor. From the perspective of conductive efficiency, this pitch range controls the increase in the AC resistance of the twisted conductor to within 3%, effectively suppressing the additional losses caused by the skin effect and proximity effect. From the perspective of mechanical properties, the moderate twisting angle enables the single wires of the conductor to deform in a coordinated manner when bending, avoiding local stress concentration and extending the repeated bending life of the conductor to more than 10,000 times. From the perspective of high-temperature stability, the optimized twisted structure can maintain uniform stress distribution when thermally expanded, preventing deformation or breakage of the conductor due to local looseness. Especially in the application scenario of fire-resistant cables, when the fire-resistant layer of the mica tape shrinks at high temperatures, this twisted structure can relieve stress through moderate self-adjustment and maintain close contact between the conductor and the insulation layer.

[0041] Preferably, as a further specific implementation manner, the shielding layer is a silver-plated copper wire braided layer coated outside the insulating layer, with a coverage rate of ≥90% and a thickness of the silver-plated layer of 1-3 μm.

[0042] The present invention specifically defines the structure of the cable shielding layer, clarifying that it is a silver-plated copper wire braided layer wrapped around the insulating layer, with a coverage requirement of ≥90% and a silver plating thickness of 1-3μm. This method achieves excellent electromagnetic shielding performance through the synergistic optimization of metal plating and braiding processes, while significantly improving the stability of the shielding layer in high-temperature and corrosive environments, providing a key guarantee for the reliable operation of the cable under complex working conditions. Among them, silver is the metal with the best conductivity. Its 1-3μm plating thickness ensures that during high-frequency signal transmission, the current within the skin depth range mainly flows through the low-resistance silver layer, reducing the surface resistance of the shielding layer to below 0.1Ω / sq, which is about 40% lower than that of ordinary copper braided layers. It is particularly noteworthy that the lower limit of the silver plating thickness of 1μm ensures that the local conductivity drop caused by the silver layer breaking when the copper wire is bent during the braiding process will not occur; the upper limit of 3μm avoids the sharp increase in material cost and increased processing difficulty caused by the excessive thickness of the silver layer.

[0043] Preferably, as a further specific embodiment, the method for preparing the extruded insulated low-voltage fire-resistant power cable comprises the following steps: first, twisting a plurality of tinned copper wires into a conductor, cleaning the surface of the conductor with plasma, and then wrapping a mica tape around the conductor to form a fire-resistant layer;

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

[0045] Then, a silver-plated copper wire shielding layer is woven outside the insulating layer to form a shielding layer, and finally a ceramic silicone rubber sheath material is extruded and wrapped around the shielding layer by hot pressing to obtain the product.

[0046] This invention also details a method for preparing extruded insulated low-voltage fire-resistant power cables. Through a multi-step, precision manufacturing process, performance optimization and structural integration of each cable's functional layers are achieved. This method, centered around key technical nodes such as plasma cleaning, nanofiller pre-dispersion, magnetic field-induced orientation, and hot-pressing extrusion, constructs a complete process flow suitable for industrial production, ensuring high consistency in microstructural control and macroscopic performance in the final product. The mica tape wrapping process utilizes a 45° cross-wrap method with tension controlled within a range of 5-8N. This process design enables the composite structure of synthetic mica paper and glass fiber cloth to adhere closely 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 directional alignment of the carbon nanotubes when the insulating layer is extruded, and ultrasonic vibration is applied to eliminate bubbles.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention provides an extruded insulated low-voltage fire-resistant power cable. Through the material optimization and structural design of each functional layer, the cable has excellent fire resistance, low smoke flame retardant properties, high mechanical strength and stable electromagnetic shielding performance. It is particularly suitable for low-voltage power transmission scenarios with stringent safety performance requirements. DETAILED DESCRIPTION

[0050] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, not all of them, 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 ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] In order to more clearly illustrate the technical solutions of the present invention, specific embodiments are provided below for illustration.

[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: tinned copper wire, diameter 0.15mm, tin coating thickness 0.5μm;

[0056] Twisting: 36 strands of tinned copper wire are twisted into a conductor using a high-speed stranding machine. The conductor diameter after twisting is 2.5mm. 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: using an argon plasma cleaning machine with a power of 300W, a frequency of 13.56MHz, and a cleaning time of 5 minutes to remove oxides and organic pollutants on the surface of the conductor to obtain the conductor;

[0058] 2. Refractory layer wrapping

[0059] Materials: The base material is synthetic mica paper (thickness 0.02mm) and glass fiber cloth (thickness 0.08mm). The total thickness after compounding is 0.1mm, the width is 20mm, and the temperature resistance is above 1000℃.

[0060] Wrapping: Use a 45° oblique wrapping machine to wrap two layers of mica tape around the above-mentioned conductor with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a close fit. After wrapping, check that there are no wrinkles or damage.

[0061] 3. Extrusion of insulation layer

[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] Nanofiller: 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 of nano-aluminum hydroxide, 1.2 parts of carboxylated carbon nanotubes (ratio 10:1);

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

[0066] Extrusion molding: A single-screw extruder is then used to extrude the insulation material onto the surface of the refractory layer to form an insulation layer with a thickness of 1.2 mm. The axial magnetic field is applied to the extrusion die to induce alignment of the carbon nanotubes along the axial direction of the cable. Ultrasonic defoaming is then performed, and 40kHz ultrasound is applied during the extrusion process to eliminate bubbles before cooling.

[0067] 4. Shield braid (silver-plated copper wire braid)

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

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

[0070] Hot air leveling: After braiding, hot air leveling (temperature 150℃, time 10 seconds) is used to improve the bonding strength between the shielding layer and the insulation layer;

[0071] 5. Extrusion of sheath layer

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

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

[0074] Extrusion molding: Use hot press extruder (temperature 160℃, pressure 15MPa) to extrude the sheath layer on the surface of the shielding layer with a thickness of 2.0mm;

[0075] Vulcanization: The sheath layer crude product is then vulcanized using a peroxide vulcanizing agent at a vulcanization temperature of 180° C. for 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: tinned copper wire, diameter 0.15mm, tin coating thickness 2μm;

[0080] Twisting: 36 strands of tinned copper wire are twisted into a conductor using a high-speed stranding machine. The conductor diameter after twisting is 2.5mm. 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: using an argon plasma cleaning machine with a power of 300W, a frequency of 13.56MHz, and a cleaning time of 5 minutes to remove oxides and organic pollutants on the surface of the conductor to obtain the conductor;

[0082] 2. Refractory layer wrapping

[0083] Materials: The base material is synthetic mica paper (thickness 0.1mm) and glass fiber cloth (thickness 0.2mm). The total thickness after compounding is 0.3mm, the width is 20mm, and the temperature resistance is above 1000℃.

[0084] Wrapping: Use a 45° oblique wrapping machine to wrap two layers of mica tape around the above-mentioned conductor with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a close fit. After wrapping, check that there are no wrinkles or damage.

[0085] 3. Extrusion of insulation layer

[0086] Materials: The base material is 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] Nanofiller: nano-aluminum hydroxide, particle size 100nm; carboxylated carbon nanotubes with an aspect ratio of 120 and a grafting rate of 5%;

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

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

[0090] Extrusion molding: A single-screw extruder is then used to extrude the insulation material onto the surface of the refractory layer to form an insulation layer with a thickness of 1.2 mm. The axial magnetic field is applied to the extrusion die to induce alignment of the carbon nanotubes along the axial direction of the cable. Ultrasonic defoaming is then performed, and 40kHz ultrasound is applied during the extrusion process to eliminate bubbles before cooling.

[0091] 4. Shield braid (silver-plated copper wire braid)

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

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

[0094] Hot air leveling: After braiding, hot air leveling (temperature 150℃, time 10 seconds) is used to improve the bonding strength between the shielding layer and the insulation layer;

[0095] 5. Extrusion of sheath layer

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

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

[0098] Extrusion molding: Use hot press extruder (temperature 160℃, pressure 15MPa) to extrude the sheath layer on the surface of the shielding layer with a thickness of 2.0mm;

[0099] Vulcanization: The sheath layer crude product is then vulcanized using a peroxide vulcanizing agent at a vulcanization temperature of 180° C. for 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: tinned copper wire, diameter 0.15mm, tin coating thickness 1μm;

[0104] Stranding: 36 strands of tinned copper wire are twisted into a conductor using a high-speed stranding machine. The conductor diameter after twisting is 2.5mm. 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: using an argon plasma cleaning machine with a power of 300W, a frequency of 13.56MHz, and a cleaning time of 5 minutes to remove oxides and organic pollutants on the surface of the conductor to obtain the conductor;

[0106] 2. Refractory layer wrapping

[0107] Materials: The base material is synthetic mica paper (thickness 0.08mm) and glass fiber cloth (thickness 0.12mm). The total thickness after compounding is 0.2mm, the width is 20mm, and the temperature resistance is above 1000℃.

[0108] Wrapping: Use a 45° oblique wrapping machine to wrap two layers of mica tape around the above-mentioned conductor with an overlap rate of 50%, a wrapping tension of 5N, and a wrapping speed of 10m / min to ensure a close fit. After wrapping, check that there are no wrinkles or damage.

[0109] 3. Extrusion of insulation layer

[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] Nanofiller: 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 of nano-aluminum hydroxide and 1 part of carboxylated carbon nanotubes (ratio 10:1);

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

[0114] Extrusion molding: A single-screw extruder is then used to extrude the insulation material onto the surface of the refractory layer to form an insulation layer with a thickness of 1.2 mm. The axial magnetic field is applied to the extrusion die to induce alignment of the carbon nanotubes along the axial direction of the cable. Ultrasonic defoaming is then performed, and 40kHz ultrasound is applied during the extrusion process to eliminate bubbles before cooling.

[0115] 4. Shield braid (silver-plated copper wire braid)

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

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

[0118] Hot air leveling: After braiding, hot air leveling (temperature 150℃, time 10 seconds) is used to improve the bonding strength between the shielding layer and the insulation layer;

[0119] 5. Extrusion of sheath layer

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

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

[0122] Extrusion molding: Use hot press extruder (temperature 160℃, pressure 15MPa) to extrude the sheath layer on the surface of the shielding layer with a thickness of 2.0mm;

[0123] Vulcanization: The sheath layer crude product is then vulcanized using a peroxide vulcanizing agent at a vulcanization temperature of 180° C. for 10 minutes to form a dense sheath layer.

[0124] Comparative Example 1

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

[0126] Comparative Example 2

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

[0128] Comparative Example 3

[0129] The specific implementation method is consistent with Example 3, except that the surface grafting rate of the carboxyl-modified carbon nanotubes in Example 3 is adjusted to 1%.

[0130] Comparative Example 4

[0131] The specific implementation method is consistent with Example 3, except that the surface grafting rate of the carboxyl-modified carbon nanotubes in Example 3 is adjusted to 10%.

[0132] Comparative Example 5

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

[0134] Comparative Example 6

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

[0136] Comparative Example 7

[0137] The specific implementation method is the same as that of Example 3, except that the carbon nanotubes are not carboxylated.

[0138] Experimental Example 1 Performance test of extruded insulation low-voltage fire-resistant power cable

[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 the insulation layer, ceramic effect of the sheath, smoke density (light transmittance), mechanical strength (tensile strength), and volume resistivity;

[0140] 1. Sample fire resistance test

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

[0142] Test steps: Cut 1.5m long power cable samples obtained in Examples 1-3 and Comparative Examples 1-7, strip the sheaths and shielding layers at both ends to expose the conductors, and connect them to a low-voltage power supply;

[0143] Installation and fixation: Hang the sample horizontally in the refractory furnace, aim the flame nozzle at the middle of the sample, and place the thermocouple close to the sample surface to detect the temperature;

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

[0145] 2. Thermal conductivity test of insulation layer

[0146] Test equipment: heat flow thermal conductivity instrument (equipped with constant temperature hot plate, cooling plate, 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 discs with a diameter of 30 mm and a thickness of 1.2 mm from the cable insulation layer, and polish the surface to a flat surface;

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

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

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

[0152] 3. Sheath ceramic effect test

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

[0154] Test steps:

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

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

[0157] Hardness test: Use a Shore D hardness tester, press the needle vertically into the surface of the ceramic layer, hold for 15 seconds and then read the reading;

[0158] Microscopic analysis: Observe the cross section of the ceramic layer using an electron microscope to confirm that there are no cracks;

[0159] 4. Smoke density (light transmittance) test

[0160] Test equipment: Smoke density test box (3m 3 volume), laser light source, optical receiver, data recorder;

[0161] Test steps:

[0162] Sample combustion: 100 g of the cable sheath material of the power cables obtained in Examples 1-3 and Comparative Examples 1-7 were placed in a combustion chamber, ignited, and the chamber door was closed;

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

[0167] Test steps:

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

[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 (mm 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, electrode (diameter 20mm).

[0174] Test steps:

[0175] Sample processing: 50 mm diameter and 1.2 mm thick discs were cut from the insulation layer of the power cables in Examples 1-3 and Comparative Examples 1-7, and the surfaces were coated with conductive silver paste to eliminate contact resistance;

[0176] Test process: Press the electrodes tightly against the two sides of the sample, apply 500V voltage, and read the resistance value (R) after stabilization;

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

[0178] Error control: test environment humidity ≤ 40%, repeat 3 times and take the average value;

[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 above table, Examples 1-3 demonstrate the performance of a series of optimized extruded insulated low-voltage fire-resistant power cables. The gradient changes in these three examples clearly demonstrate 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] From the data in Comparative Examples 1-2, it can be seen that when the mass ratio of nano-aluminum hydroxide to carbon nanotubes is adjusted to 1:1 in Comparative Example 1, this change leads to a significant decline in cable performance. The fire resistance time is reduced to 85 minutes, which is 11 minutes less than that of Example 3, and the thermal conductivity is also reduced to 0.28W / m·K. This performance degradation is mainly due to the excessive content of carbon nanotubes, which destroys the uniform distribution of nanofillers in the insulating layer. Although excessive carbon nanotubes improve conductivity, they reduce the flame retardant properties of the material. At the same time, high-content carbon nanotubes are prone to agglomeration in the matrix, resulting in local electric field concentration, which reduces the volume resistivity to 8.7×10 13 Ω·cm. In terms of mechanical properties, the tensile strength dropped 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, that is, the aluminum hydroxide content was greatly increased. From the above data, it can be seen that although the fire resistance time was improved compared with Comparative Example 1 to 88 minutes, it was still significantly lower than the 96 minutes of Example 3.

[0185] It can be seen from the data in Comparative Examples 3-4 that when the surface grafting rate of carboxylated carbon nanotubes is reduced to 1% in Comparative Example 3, this slight adjustment brings about significant performance changes, resulting in the fire resistance time of the power cable prepared in Comparative Example 3 being reduced to 82 minutes, and the thermal conductivity coefficient being greatly reduced to 0.25 W / m·K, indicating that insufficient grafting rate seriously affects the dispersion and interface bonding of carbon nanotubes. The low grafting rate causes uneven dispersion of carbon nanotubes in the matrix and easily forms agglomerates, which not only reduces the thermal conductivity efficiency but also affects the mechanical strength of the material. At the same time, the volume resistivity is reduced to 7.6×10 13 Ω·cm, indicating that the insulation performance has also declined; while in Comparative Example 4, the surface grafting rate of carboxylated carbon nanotubes was increased to 10%. This excessive modification also brought negative effects, resulting in the fire resistance time of the power cable obtained in Comparative Example 4 being further reduced to 79 minutes, which is the worst among all comparative examples, and the thermal conductivity is only 0.23W / m·K. This shows that although the excessive grafting rate improves the dispersion of carbon nanotubes, the excessive modification destroys the structural integrity of the carbon nanotubes themselves, resulting in a decrease in their thermal conductivity. In addition, the tensile strength is reduced to 10.2MPa, and the volume resistivity is 6.9×10 13 Ω·cm, all performance indicators deteriorated, and the smoke density transmittance dropped to 65.3%;

[0186] It can be seen from the data in Comparative Examples 5-6 that in Comparative Example 5, the particle size of nano-aluminum hydroxide is reduced to 10 nm. This change leads to a decrease in many performance indicators. At this time, the fire resistance time is 75 minutes and the thermal conductivity is 0.15 W / m·K, which is significantly lower than that in Example 3. This is because although the excessively small particle size increases the specific surface area, it also causes the nanoparticles to agglomerate more easily, which reduces the dispersion effect. When the particle size of nano-aluminum hydroxide is increased to 200 nm in Comparative Example 6, it can be seen from the above data that this change is also not conducive to the performance of the cable. The fire resistance time of the cable prepared at this time is 71 minutes and the thermal conductivity is 0.14 W / m·K, which is even worse than that of Comparative Example 5. This is because the excessively large particle size reduces the interface effect of the filler, making it difficult to form an effective barrier network.

[0187] The data in Comparative Example 7 show that in Comparative Example 7, the carbon nanotubes are not carboxylated. The fire resistance time of the power cable prepared at this time is 61 minutes, the thermal conductivity is 0.13 W / m·K, which are much lower than those in Example 3, and the tensile strength is 7.1 MPa and the volume resistivity is 3.5×10 13 Ω·cm, indicating that it is difficult for unmodified carbon nanotubes to form a good bond 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, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 conductor, fire-resistant layer, insulation layer, shielding layer and sheath layer arranged in sequence from the inside to the outside; The fire-resistant layer is a mica tape wrapped around 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-aluminum hydroxide and carbon nanotubes are dispersed in the insulating layer, the particle size of the nano-aluminum hydroxide is 50-100 nm, the aspect ratio of the carbon nanotubes is ≥100, and the mass ratio of the nano-aluminum hydroxide to the carbon nanotubes is (10-15):1; The sheath layer is a ceramic silicone rubber sheath extruded outside the shielding layer.

2. The extruded insulated low-voltage fire-resistant power cable according to claim 1, characterized in that: The carbon nanotubes are carboxyl modified carbon nanotubes with a surface grafting rate of 3-5%. The carboxyl modified carbon nanotubes are arranged in a direction along the axial direction of the cable in the insulating layer to form a continuous heat conduction network.

3. The extruded insulated low-voltage fire-resistant power cable according to claim 1, characterized in that: The ceramic silicone rubber sheath comprises the following components in parts by mass: 100-120 parts of methyl vinyl silicone rubber; 40-60 parts of ceramic filler; 15-25 parts of flame retardant; 1-2 parts of vulcanizing agent.

4. The extruded insulated low-voltage fire-resistant power cable according to claim 3, characterized in that: The ceramic filler is a mixture of glass powder, kaolin and nano zirconium dioxide; the mass ratio of the glass powder, kaolin and nano zirconium dioxide is (5-7): (3-5):

2.

5. The extruded insulated low-voltage fire-resistant power cable according to claim 3, characterized in that: The flame retardant is ammonium polyphosphate, zinc borate and ferrocene, wherein the mass ratio of the ammonium polyphosphate, zinc borate and ferrocene is (6-7): (3-5):

1.

6. The extruded insulated low-voltage fire-resistant power cable according to claim 1, characterized in that: The conductor is formed by twisting multiple strands of tinned copper wires, the thickness of the tinned layer is 0.5-2 μm, and the twisting pitch is 8-12 times the diameter of the conductor.

7. The extruded insulated low-voltage fire-resistant power cable according to claim 1, characterized in that: The shielding layer is a silver-plated copper wire braided layer coated outside the insulating layer, with a coverage rate of ≥90% and a thickness of the silver-plated layer of 1-3 μm.

8. The method for preparing an extruded insulated low-voltage fire-resistant power cable according to any one of claims 1 to 7, characterized in that: The following steps are involved: First, a plurality of tinned copper wires are twisted into a conductor, and the surface of the conductor is cleaned by plasma, and then a mica tape is wrapped around the conductor to form a fire-resistant layer; Subsequently, nano-aluminum hydroxide and carboxylated carbon nanotubes are pre-dispersed in a mixed material of cross-linked polyethylene and low-smoke flame-retardant polyolefin, and then extruded onto the surface of the fire-resistant layer to form an insulating layer; Then, a silver-plated copper wire shielding layer is woven outside the insulating layer to form a shielding layer, and finally a ceramic silicone rubber sheath material is extruded and wrapped around the shielding layer by hot pressing to obtain the product.

9. The preparation method according to claim 8, characterized in that When extruding to form the insulating layer, an axial magnetic field is used to induce the carbon nanotubes to align, and ultrasonic vibration is applied to eliminate bubbles.

Images