Fireproof leaky cable and preparation method thereof

Abstract

The invention provides a fireproof leaky cable and a preparation method thereof, and relates to the technical field of cables. The fire-resistant leaky cable sequentially comprises a conductor wire core, an insulating layer, an outer conductor layer, a fire-resistant layer and a sheath layer from inside to outside, the fire-resistant layer is a mica tape, the mica tape comprises an adhesive, and the adhesive is organic silicon resin. The sheath layer is of a double-layer structure and comprises a ceramic polyolefin layer and a flame-retardant polyolefin layer, the ceramic polyolefin layer wraps the outer side of the fireproof layer, and the flame-retardant polyolefin layer wraps the outer side of the ceramic polyolefin layer. According to the technical scheme, the fire-resistant layer, the ceramic polyolefin layer and the flame-retardant polyolefin layer are sequentially coated outside the outer conductor layer to construct an echelon synergistic fire-resistant system, so that the fire-resistant leaky cable has excellent mechanical performance and relatively high fire-resistant capability.

Description

A fire-resistant leaky cable and its preparation method Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a fire-resistant leaky cable and its preparation method. Background Technology

[0002] Leaky cables function as both signal transmission lines and transmitting antennas, serving as the core carrier for wireless communication coverage in enclosed or semi-enclosed spaces such as subway tunnels, mine roadways, underground utility tunnels, and high-rise buildings. Given that these application scenarios typically involve confined spaces, dense populations, and limited ventilation, high requirements are placed on the fire resistance and safety performance of leaky cable materials. Ideally, the sheath material of a leaky cable must not only possess excellent flame-retardant properties to inhibit the spread of fire but also maintain line integrity under sustained high temperatures during a fire, ensuring that the communication system can continue to operate normally for a certain period in emergency situations, thus providing crucial communication support for personnel evacuation and fire rescue.

[0003] In existing fire-resistant protection technologies for leaky cables, halogen-free flame-retardant polyolefin materials or ceramicized polyolefin technology are mainly used. However, the existing halogen-free flame-retardant polyolefin materials are limited by the metal hydroxide flame-retardant mechanism and are easily rendered ineffective under high fire temperatures due to pyrolysis, melting, dripping, and pulverization. While ceramicized polyolefin technology can provide thermal insulation through a high-temperature ceramicization mechanism, the ceramic powder filling amount in existing technologies exceeds 200 parts per cubic centimeter. This excessive filling amount severely impairs the flexibility and processing rheological properties of the leaky cable. The resulting ceramic layer structure after exposure to fire is loose and porous, lacking sufficient mechanical strength to withstand airflow impact, and its flame-retardant rating cannot independently meet the GB 31247 standard B1 requirement. Therefore, it is impossible to simultaneously achieve excellent construction and processing performance and reliable fire communication capabilities. Summary of the Invention

[0004] One objective of the first aspect of this invention is to provide a fire-resistant leaky cable that solves the technical problems of poor fire resistance and poor mechanical properties of cables in the prior art.

[0005] Another objective of this invention is to improve the reliability of fire-resistant leaky cables during fire resistance.

[0006] A second aspect of the present invention is to provide a method for preparing a fire-resistant leaky cable.

[0007] According to a first aspect of the present invention, the present invention provides a fire-resistant leaky cable, the fire-resistant leaky cable comprising, from the inside out, a conductor core, an insulation layer, an outer conductor layer, a fire-resistant layer, and a sheath layer, wherein the fire-resistant layer is mica tape, the mica tape includes an adhesive, the adhesive being an organosilicon resin; the sheath layer has a double-layer structure and includes a ceramicized polyolefin layer and a flame-retardant polyolefin layer, the ceramicized polyolefin layer covering the outside of the fire-resistant layer, and the flame-retardant polyolefin layer covering the outside of the ceramicized polyolefin layer.

[0008] Optionally, the ceramicized polyolefin layer comprises, by weight, 45-65 parts of a first halogen-free polyolefin resin matrix; 12-22 parts of a first halogen-free flame retardant; 70-110 parts of ceramic powder; and 3-8 parts of a first additive.

[0009] Optionally, the first halogen-free polyolefin resin matrix includes ethylene-vinyl acetate copolymer and at least one selected from polyolefin elastomer, ethylene propylene diene monomer (EPDM) rubber, and polyethylene; the first additive is selected from one or more of coupling agent, compatibilizer, lubricant, and antioxidant.

[0010] Optionally, the first halogen-free flame retardant includes a phosphorus-based flame retardant and an inorganic synergist, wherein the mass ratio of the phosphorus-based flame retardant to the inorganic synergist is any value between 1.5:1 and 3:1; the phosphorus-based flame retardant is selected from at least one of aluminum hypophosphite, magnesium hypophosphite, and calcium hypophosphite, and the inorganic synergist is selected from at least one of zinc borate, zinc stannate, and zinc molybdate.

[0011] Optionally, the flame-retardant polyolefin layer comprises, by weight, 60-80 parts of a second halogen-free polyolefin resin matrix; 20-40 parts of a second halogen-free flame retardant; 5-15 parts of a halogen-free flame retardant synergist; 2-5 parts of a charring agent; and 2-8 parts of a second additive.

[0012] Optionally, the second halogen-free polyolefin resin matrix includes ethylene-vinyl acetate copolymer, and one or more selected from polyethylene, polyolefin elastomer, and polypropylene; the second halogen-free flame retardant includes at least one selected from magnesium hydroxide and aluminum hydroxide; the halogen-free flame retardant synergist includes at least one selected from zinc borate, zinc stannate, and aluminum diethylphosphite; and the second additive includes one or more selected from UV stabilizers, antioxidants, lubricants, coupling agents, and compatibilizers.

[0013] Optionally, the mica tape is a double-sided synthetic mica tape and is wound around the outer conductor, wherein the width of the overlapping of the mica tapes is not less than 50% of the bandwidth of the mica tape.

[0014] According to a second aspect of the present invention, the present invention also provides a method for preparing the fire-resistant leaky cable according to the above, comprising the following steps: providing a cable core, the cable core comprising a conductor core, an insulation layer, an outer conductor layer and a fire-resistant layer arranged sequentially from the inside to the outside; preparing a first melt and a second melt; controlling a double-layer co-extrusion die head to coat the first melt onto the surface of the fire-resistant layer to form a ceramicized polyolefin layer; controlling the double-layer co-extrusion die head to coat the second melt onto the surface of the ceramicized polyolefin layer to form a flame-retardant polyolefin layer, wherein the ceramicized polyolefin layer and the flame-retardant polyolefin layer achieve interfacial fusion in a molten state, thereby obtaining a fire-resistant leaky cable to be cooled; and sequentially cooling and drying the fire-resistant leaky cable to be cooled to obtain the fire-resistant leaky cable.

[0015] Optionally, the steps for preparing the first melt and the second melt specifically include the following steps: premixing a first halogen-free polyolefin resin matrix, a first halogen-free flame retardant, ceramic powder, and a first additive, and then performing melt blending and granulation to obtain a first compound; premixing a second halogen-free polyolefin resin matrix, a second halogen-free flame retardant, a halogen-free flame retardant synergist, a charring agent, and a second additive, and then performing melt blending and granulation to obtain a second compound; controlling a first extruder to plasticize the first compound to obtain the first melt, wherein the plasticizing temperature of the first extruder is set to any value between 140℃ and 150℃; controlling a second extruder to plasticize the second compound to obtain the second melt, wherein the plasticizing temperature of the second extruder is set to any value between 140℃ and 175℃.

[0016] Optionally, the step of sequentially cooling and drying the fire-resistant leaky cable to obtain the fire-resistant leaky cable includes the following steps: cooling the fire-resistant leaky cable with atomized spray, or immersing the fire-resistant leaky cable to be cooled in warm water, wherein the water temperature is any value between 40℃ and 60℃; immersing the fire-resistant leaky cable to be cooled after atomized spray or warm water cooling in cold water until the fire-resistant leaky cable to be cooled to room temperature, wherein the cold water temperature is any value between 15℃ and 25℃; and obtaining the fire-resistant leaky cable after drying.

[0017] According to this invention, the fire-resistant cable constructs a tiered synergistic fire-resistant system. The flame-retardant polyolefin layer forms an expanded carbon layer in the early stages of a fire, preventing flame spread. The ceramicized polyolefin layer rapidly sinterstalizes at high temperatures to form a dense and hard composite ceramic shell. The organosilicon resin in the fire-resistant layer transforms into silicon dioxide at high temperatures, not only enhancing the tight bond between the mica tapes but also ensuring a tight bond between the composite ceramic shell and the mica tapes in the fire-resistant layer. This improves the electrical insulation integrity of the fire-resistant leaky cable under extreme fire conditions. When the sheath layer is eroded, the mica tapes, acting as a non-combustible, heat-insulating, and electrically insulating rigid barrier, are directly exposed, effectively blocking the direct impact of high temperatures on the conductor core, protecting the outer conductor layer and insulation layer, significantly extending the integrity maintenance time of the fire-resistant leaky cable line, and ensuring uninterrupted communication. Furthermore, it effectively resolves the contradiction between cable processing performance and fire resistance performance. The ceramicized polyolefin layer has good flexibility and is configured as the inner layer, while the flame-retardant polyolefin layer, with excellent rheological properties and high elongation at break, serves as the outer layer to provide strong mechanical support, effectively ensuring the cable's excellent flexibility and mechanical strength. In summary, this fire-resistant leaky cable can simultaneously meet the B1 flame retardant requirements of GB 31247 standard and the higher fire integrity requirements of GB / T 19216.21 standard, and has both excellent mechanical strength for construction and laying and fire safety assurance capabilities.

[0018] Furthermore, the mica tape is a double-sided synthetic mica tape, wound around the outer conductor, with the overlap width of the mica tapes not less than 50% of the width of the mica tape. This technical solution, employing double-sided synthetic mica tape with an overlap rate of not less than 50%, ensures that the fire-resistant layer of the fire-resistant leaky cable is seamlessly exposed during bending installation or high-temperature expansion in a fire, thereby preventing electrical breakdown and improving the reliability of the fire-resistant leaky cable during fire protection.

[0019] Furthermore, the present invention also provides a method for preparing a fire-resistant leaky cable. This method uses a double-layer co-extrusion technology to achieve simultaneous molding of the ceramicized polyolefin layer and the flame-retardant polyolefin layer in one step, eliminating interface defects, ensuring the integrity of the sheath layer structure, and improving the fire resistance of the fire-resistant leaky cable.

[0020] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0021] The following description will use the accompanying drawings to illustrate some specific embodiments of the invention in an exemplary and non-limiting manner. The same reference numerals in the drawings denote the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 is a schematic structural diagram of a fire-resistant leaky cable according to an embodiment of the invention; Figure 2 is a schematic flowchart of a method for preparing a fire-resistant leaky cable according to an embodiment of the invention; Figure 3 is a schematic flowchart of preparing a first melt and a second melt according to an embodiment of the invention; Figure 4 is a schematic flowchart of sequentially cooling and drying a fire-resistant leaky cable according to an embodiment of the invention.

[0022] Attached reference numerals: 100-fire-resistant leaky cable, 1-conductor core, 2-insulation layer, 3-outer conductor layer, 4-fire-resistant layer, 5-sheath layer. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] In the description of this invention, it should be understood that the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature, that is, include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. When a feature "includes or contains" one or more of the features it encompasses, unless otherwise specifically described, this indicates that other features are not excluded and may be further included.

[0026] Unless otherwise expressly specified and limited, the terms "connection," "installation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art should be able to understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] Unless otherwise specified, all terms (including technical and scientific terms) used in the description of this embodiment have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0028] Figure 1 is a schematic structural diagram of a fire-resistant leaky cable according to an embodiment of the present invention.

[0029] As shown in Figure 1, in a specific embodiment, the fire-resistant leaky cable 100 comprises, from the inside out, a conductor core 1, an insulation layer 2, an outer conductor layer 3, a fire-resistant layer 4, and a sheath layer 5. The fire-resistant layer 4 is mica tape, which includes an adhesive, namely silicone resin. The sheath layer 5 has a double-layer structure and includes a ceramicized polyolefin layer and a flame-retardant polyolefin layer. The ceramicized polyolefin layer covers the outside of the fire-resistant layer 4, and the flame-retardant polyolefin layer covers the outside of the ceramicized polyolefin layer. Specifically, the conductor core 1, as the central conductor for signal propagation in the fire-resistant leaky cable 100, is preferably made of smooth or annealed copper tape, wound into a cylindrical shape using a precision longitudinal wrapping process. Its joints can be secured using laser welding, overlapping, or hook locking to ensure electrical continuity and structural stability. The insulation layer 2 tightly covers the outside of the conductor core 1 and is mainly composed of irradiated physically foamed polyethylene to reduce transmission loss. The outer conductor layer 3 is coaxially disposed on the outside of the insulation layer 2 and adopts a spiral corrugated copper tube structure with multiple inclined slots or holes. This structure not only serves as a conductor for the transmission circuit, but also uses the inclined slots or holes to enable electromagnetic waves to radiate outward or receive external signals in a controlled manner, thereby giving the fire-resistant leaky cable 100 a wireless coverage function similar to an antenna. At the same time, the spiral corrugated morphology also gives the fire-resistant leaky cable 100 excellent compressive strength and bending flexibility.

[0030] In this embodiment, a tiered and synergistic fire-resistant system is constructed. The flame-retardant polyolefin layer forms an expanded carbon layer in the early stages of a fire, preventing the spread of flames. The ceramicized polyolefin layer rapidly sinterstalizes at high temperatures to form a dense and hard composite ceramic shell. The organosilicon resin in the fire-resistant layer 4 transforms into silicon dioxide at high temperatures, which not only enhances the tight bond between the mica tapes but also ensures a tight bond between the composite ceramic shell and the mica tapes in the fire-resistant layer, thereby improving the electrical insulation integrity of the fire-resistant leaky cable 100 under extreme fire conditions. When the sheath layer 5 is eroded, the mica tape, as a non-combustible, heat-insulating, and electrically insulating rigid barrier, is directly exposed, effectively blocking the direct impact of high temperatures on the conductor core, protecting the outer conductor layer 3 and the insulation layer 2, significantly extending the line integrity maintenance time of the fire-resistant leaky cable 100, and ensuring uninterrupted communication. On the other hand, it effectively resolves the contradiction between cable processing performance and fire resistance performance. The ceramicized polyolefin layer has good flexibility and is configured in the inner layer, while the flame-retardant polyolefin layer with excellent rheological properties and high elongation at break is used as the outer layer to provide strong mechanical support, effectively ensuring the excellent flexibility and mechanical strength of the fire-resistant leaky cable 100. In summary, this fire-resistant leaky cable 100 can simultaneously meet the B1 flame retardant requirements in GB 31247 standard and the high fire integrity requirements in GB / T 19216.21 standard, possessing both excellent mechanical strength for construction and laying and fire safety assurance capabilities.

[0031] In some embodiments, the ceramicized polyolefin layer comprises, by weight, 45-65 parts of a first halogen-free polyolefin resin matrix, 12-22 parts of a first halogen-free flame retardant, 70-110 parts of ceramic powder, and 3-8 parts of a first additive. Specifically, the ceramicized polyolefin layer uses halogen-free materials, avoiding the problem of releasing large amounts of dense black smoke and corrosive acidic gases when traditional halogen-containing materials burn. The first halogen-free polyolefin resin matrix can be, for example, 45, 50, 55, or 65 parts; the first halogen-free flame retardant can be, for example, 12, 18, 20, or 22 parts; the ceramic powder can be, for example, 70, 80, 100, or 110 parts; and the first additive can be, for example, 3, 5, or 8 parts. The ceramic powder preferably includes graphite, glass powder, and layered silicates, such as montmorillonite or nano-clay. The low-melting-point glass powder, at high temperatures, generates a viscous liquid that wets and penetrates the mica tape of the refractory layer 4, and undergoes an interfacial eutectic reaction with the silica generated by the thermal decomposition of the organosilicon resin, resulting in a tight bond between the composite ceramic shell and the mica tape. Graphite expands in volume when heated, rapidly filling the microscopic voids left after the vaporization of the first halogen-free polyolefin resin matrix. The low-melting-point glass powder softens and melts at a lower temperature to form a high-viscosity liquid phase. This liquid phase can coat the expanded layered silicates, enabling the ceramicized polyolefin layer to rapidly form a continuous, dense, and rigid integral ceramic shell under high-temperature fire conditions. This embodiment reduces the amount of ceramic powder filling while ensuring excellent processing performance, and also provides a thermal barrier and mechanical support for the conductor core 1, insulation layer 2, and outer conductor layer 3.

[0032] In some embodiments, the first halogen-free polyolefin resin matrix includes an ethylene-vinyl acetate copolymer and at least one selected from polyolefin elastomers, ethylene propylene diene monomer (EPDM) rubber, and polyethylene. The first additive is selected from one or more of coupling agents, compatibilizers, lubricants, and antioxidants. In this embodiment, the excellent polarity and containment capacity of the ethylene-vinyl acetate copolymer are utilized, enabling it to effectively carry a large amount of ceramic powder like an adhesive, preventing the ceramic powder from falling off. The polyolefin elastomer, EPDM rubber, and polyethylene are used to impart excellent flexibility and impact resistance to the ceramicized polyolefin layer, ensuring that the fire-resistant leaky cable 100 will not experience brittle cracking during complex laying and bending processes. The coupling agent is used to enhance the interfacial bonding strength between the ceramic powder and the first halogen-free polyolefin resin matrix. The compatibilizer is responsible for promoting the microscopic fusion and stability between the components. The lubricant improves processing rheology by reducing friction. The antioxidant prevents the first halogen-free polyolefin resin matrix from undergoing thermal oxidative degradation during processing and use, thereby ensuring the aging resistance and service life of the fire-resistant leaky cable 100.

[0033] In some embodiments, the first halogen-free flame retardant comprises a phosphorus-based flame retardant and an inorganic synergist, wherein the mass ratio of the phosphorus-based flame retardant to the inorganic synergist is any value between 1.5:1 and 3:1. The phosphorus-based flame retardant is selected from at least one of aluminum hypophosphite, magnesium hypophosphite, and calcium hypophosphite, and the inorganic synergist is selected from at least one of zinc borate, zinc stannate, and zinc molybdate. In this embodiment, the phosphorus-based flame retardant selected from aluminum hypophosphite, magnesium hypophosphite, or calcium hypophosphite is used as the main flame retardant component. Upon heating at high temperatures, it rapidly decomposes to generate phosphorus-containing free radicals to capture active free radicals in the combustion reaction, thereby interrupting the combustion chain reaction. The inorganic synergist, zinc borate, zinc stannate, or zinc molybdate, is used to catalyze char formation and suppress smoke. The mass ratio of phosphorus-based flame retardant to inorganic synergist is, for example, 1.5:1, 2:1, 2.5:1 or 3:1. The mass ratio of phosphorus-based flame retardant to inorganic synergist is set between 1.5:1 and 3:1 to maximize the formation of a dense carbon layer while ensuring quenching.

[0034] In some embodiments, the flame-retardant polyolefin layer comprises, by weight, 60-80 parts of a second halogen-free polyolefin resin matrix, 20-40 parts of a second halogen-free flame retardant, 5-15 parts of a halogen-free flame retardant synergist, 2-5 parts of a charring agent, and 2-8 parts of a second additive. In this embodiment, the flame-retardant polyolefin layer uses a halogen-free material to eliminate the toxic and corrosive gases and dense black smoke released during the combustion of traditional halogen-containing materials, significantly reducing the toxicity of smoke in a fire environment, thereby maximizing the safety of personnel escape and the integrity of precision electronic equipment. For example, the second halogen-free polyolefin resin matrix can be 60, 65, 70, or 80 parts; the second halogen-free flame retardant can be 20, 30, 35, or 40 parts; the halogen-free combustion synergist can be 5, 10, 12, or 15 parts; the charring agent can be 2, 4, or 5 parts; and the second additive can be 2, 5, 7, or 8 parts.

[0035] In some embodiments, the second halogen-free polyolefin resin matrix comprises an ethylene-vinyl acetate copolymer, and one or more selected from polyethylene, polyolefin elastomers, and polypropylene; the second halogen-free flame retardant comprises at least one selected from magnesium hydroxide and aluminum hydroxide; the halogen-free flame retardant synergist comprises at least one selected from zinc borate, zinc stannate, and aluminum diethylphosphite; and the second additive comprises one or more selected from UV stabilizers, antioxidants, lubricants, coupling agents, and compatibilizers. In this embodiment, the second halogen-free polyolefin resin matrix ensures the wear resistance and crack resistance of the flame-retardant polyolefin layer. The second halogen-free flame retardant utilizes its physical mechanism of absorbing a large amount of heat and releasing water of crystallization upon thermal decomposition to effectively reduce the temperature of the combustion zone and dilute the concentration of combustible gases. The halogen-free flame retardant synergist not only catalyzes the formation of a dense char layer to isolate oxygen but also further inhibits smoke release. In addition, UV stabilizers and antioxidants prevent photo-oxidative aging, and coupling agents, compatibilizers and lubricants are combined to improve the dispersion uniformity and interfacial bonding of the second halogen-free flame retardant and halogen-free flame retardant synergist, thereby ensuring that the flame-retardant polyolefin layer has a smooth and defect-free surface and long-term service stability.

[0036] In some embodiments, the mica tape is a double-sided synthetic mica tape, wound around the outer conductor, with the overlap width of the mica tapes not less than 50% of the bandwidth of the mica tapes. In this embodiment, the fire-resistant layer 4 preferably uses double-sided synthetic mica tape, and is tightly wrapped around the outside of the outer conductor layer 3 with an overlap rate of not less than 50% of the bandwidth. Compared with natural mica, double-sided synthetic mica tape has a higher heat resistance and better flexibility, and the reinforcing structure on both sides significantly improves the tensile strength of the fire-resistant layer 4, preventing damage during high-speed production and subsequent bending. The 50% high overlap wrapping process not only significantly increases the path length for flames and high-temperature hot air to penetrate inward, but also effectively reserves mechanical displacement margin for the fire-resistant leaky cable 100 during complex laying bends or fire thermal expansion, ensuring that the fire-resistant leaky cable 100 can still maintain high electrical insulation strength and physical isolation integrity even under extreme conditions where the sheath layer 5 is completely carbonized and detached.

[0037] Figure 2 is a schematic flowchart of a method for preparing a fire-resistant leaky cable according to an embodiment of the present invention.

[0038] As shown in Figure 2, the present invention also provides a method for preparing the fire-resistant leaky cable 100 according to the above, comprising the following steps: Step S100, providing a cable core, the cable core comprising a conductor core 1, an insulation layer 2, an outer conductor layer 3 and a fire-resistant layer 4 arranged sequentially from the inside to the outside; Step S200, preparing a first melt and a second melt; Step S300, controlling the double-layer co-extrusion die head to coat the first melt onto the surface of the fire-resistant layer 4 to form a ceramicized polyolefin layer; Step S400, controlling the double-layer co-extrusion die head to coat the second melt onto the surface of the ceramicized polyolefin layer to form a flame-retardant polyolefin layer, wherein the ceramicized polyolefin layer and the flame-retardant polyolefin layer achieve interfacial fusion in the molten state, thereby obtaining a fire-resistant leaky cable to be cooled; Step S500, sequentially cooling and drying the fire-resistant leaky cable to be cooled to obtain the fire-resistant leaky cable 100.

[0039] In step S100, the conductor core 1 is used as the central conductive carrier. An insulation layer 2 and an outer conductor layer 3 are sequentially constructed on its surface through conventional foaming or wrapping processes. Subsequently, a fire-resistant layer 4 is wrapped around the outermost side of the outer conductor layer 3, thereby obtaining a structurally stable cable core, which provides a solid foundation for the subsequent extrusion of the ceramicized polyolefin layer and the flame-retardant polyolefin layer.

[0040] In step S300, the double-layer co-extrusion die head is controlled to extrude the first melt in the molten and plasticized state to form a continuous and uniform ceramicized polyolefin layer. The ceramicized polyolefin layer is in the molten state and covers the outer surface of the refractory layer 4. During this process, the high-viscosity first melt can fully fill the micro gaps on the surface of the refractory layer 4.

[0041] In step S400, when the molten ceramicized polyolefin layer covers the outer surface of the refractory layer 4, almost simultaneously, the double-layer co-extrusion die head is controlled to directly and tightly coat the outer surface of the ceramicized polyolefin layer with the second melt. Utilizing the molecular thermal motion of the ceramicized polyolefin layer and the flame-retardant polyolefin layer under high-temperature conditions, the molecular chains at the contact interface undergo cross-phase diffusion and physical entanglement, thereby achieving interfacial fusion at the microscale. After the ceramicized polyolefin layer and the flame-retardant polyolefin layer complete interfacial fusion, the fire-resistant leaky cable to be cooled is shaped through precision processing, ultimately producing a dense fire-resistant leaky cable to be cooled.

[0042] Figure 3 is a schematic flowchart of the preparation of a first melt and a second melt according to an embodiment of the present invention. As shown in Figure 3, in some embodiments, step S200 specifically includes the following steps: Step S210, premixing a first halogen-free polyolefin resin matrix, a first halogen-free flame retardant, ceramic powder and a first additive, and then performing melt blending and granulation to obtain a first rubber compound; Step S220, premixing a second halogen-free polyolefin resin matrix, a second halogen-free flame retardant, a halogen-free combustion enhancer, a charring agent and a second additive, and then performing melt blending and granulation to obtain a second rubber compound; Step S230, controlling a first extruder to plasticize the first rubber compound to obtain a first melt, wherein the plasticizing temperature of the first extruder is set to any value between 140℃ and 150℃; Step S240, controlling a second extruder to plasticize the second rubber compound to obtain a second melt, wherein the plasticizing temperature of the second extruder is set to any value between 140℃ and 175℃.

[0043] In step S210, a high-speed mixer is controlled to premix the first halogen-free polyolefin resin matrix, the first halogen-free flame retardant, ceramic powder and the first additive. Then, a twin-screw extruder is controlled to melt-blend and granulate the mixture. The blending and granulation temperature is any value between 150℃ and 170℃, for example, 150℃, 160℃ or 170℃, thereby preparing the first rubber compound.

[0044] In step S220, a high-speed mixer is controlled to premix the second halogen-free polyolefin resin matrix, the second halogen-free flame retardant, the halogen-free flame retardant synergist, the charring agent, and the second additive. Then, a twin-screw extruder is controlled to melt-blend and granulate the mixture to obtain the second rubber compound.

[0045] In step S230, the first extruder is controlled to plasticize the first rubber compound, ensuring that the first melt is fully plasticized but not decomposed at a melt temperature of 140℃-150℃. The plasticizing temperature of the first extruder is, for example, 140℃, 145℃ or 150℃.

[0046] In step S240, the second extruder is controlled to plasticize the second rubber compound, ensuring that the second melt is well plasticized but does not decompose at a melt temperature of 140℃-175℃. The plasticizing temperature of the second extruder is, for example, 140℃, 160℃ or 175℃.

[0047] Figure 4 is a schematic flowchart illustrating the sequential cooling and drying processes of a fire-resistant leaky cable according to an embodiment of the present invention. As shown in Figure 4, in some embodiments, step S500 specifically includes the following steps: Step S510, cooling the fire-resistant leaky cable to be cooled by atomized spraying, or immersing the fire-resistant leaky cable to be cooled in warm water, the temperature of which is any value between 40℃ and 60℃; Step S520, immersing the fire-resistant leaky cable to be cooled after atomized spraying or warm water cooling in cold water until the fire-resistant leaky cable to be cooled is cooled to room temperature, the temperature of which is any value between 15℃ and 25℃; Step S530, after drying, a fire-resistant leaky cable 100 is obtained.

[0048] In step S510, atomized spraying or immersion in warm water at 40°C to 60°C is used to avoid direct contact between the fire-resistant leaky cable and cold water, which could cause severe thermal shock. The gentle heat exchange conditions provided by the warm water or atomized environment ensure that the final fire-resistant leaky cable 100 has a round appearance, no dents, and uniform physical properties. Furthermore, the water temperature can be, for example, 40°C, 45°C, 50°C, or 60°C.

[0049] In step S520, the cold water treatment can quickly remove the remaining heat from the fire-resistant leaky cable to be cooled using a lower water temperature, until the fire-resistant leaky cable is cooled to room temperature. The water temperature can be, for example, 15°C, 20°C, or 25°C.

[0050] The fire-resistant layer 4 and sheath layer 5 described in this embodiment of the invention can be applied not only to leaky cables 100, but also to power cables, communication optical cables or other cables.

[0051] The following detailed description uses specific embodiments and comparative examples.

[0052] Example 1: This example provides a method for preparing a fire-resistant leaky cable 100. The method includes: step S111, providing a cable core, the cable core including a conductor core 1, an insulation layer 2, an outer conductor layer 3, and a fire-resistant layer 4 arranged sequentially from the inside to the outside; step S121, premixing 55 parts of a first halogen-free polyolefin resin matrix, 25 parts of a first halogen-free flame retardant, 90 parts of ceramic powder, and 5.5 parts of a first additive, and then performing melt blending and granulation to obtain a first adhesive compound; step S122, premixing 70 parts of a second halogen-free polyolefin resin matrix, 40 parts of a second halogen-free flame retardant, 10 parts of a halogen-free flame retardant synergist, 5 parts of a charring agent, and 3 parts of a second additive, and then performing melt blending and granulation to obtain a second adhesive compound; step S123, controlling the first extrusion... The extruder plasticizes the first rubber compound to obtain a first melt, wherein the plasticizing temperature of the first extruder is set to 145℃; in step S124, the second extruder is controlled to plasticize the second rubber compound to obtain a second melt, wherein the plasticizing temperature of the second extruder is set to 175℃; in step S131, the double-layer co-extrusion die head is controlled to coat the first melt onto the surface of the refractory layer 4 to form a ceramicized polyolefin layer, wherein the traction speed of the double-layer co-extrusion die head is 10m / min; in step S141, the double-layer co-extrusion die head is controlled to coat the second melt onto the surface of the ceramicized polyolefin layer to form the flame-retardant polyolefin layer, wherein the ceramicized polyolefin layer and the flame-retardant polyolefin layer achieve interfacial fusion in the molten state, thereby obtaining the fire-resistant leaky cable to be cooled. The traction speed of the double-layer co-extrusion die head is 10m / min.

[0053] Step S151: Cool the fire-resistant leaky cable to be cooled by atomized spraying; Step S152: Immerse the fire-resistant leaky cable to be cooled after atomized spraying into cold water until the fire-resistant leaky cable to be cooled to room temperature, the water temperature of the cold water is 25℃; Step S153: After drying treatment, fire-resistant leaky cable 100 is obtained.

[0054] In step S111, physically foamed polyethylene material is extruded onto the outer surface of the 18mm diameter copper inner conductor core 1 to form an insulation layer 2. Copper strip is then wrapped around the outer surface of the insulation layer 2 and subjected to welding, corrugating, and grooving processes to form a corrugated copper tube outer conductor layer 3 with slots. The fire-resistant layer 4 is made by wrapping synthetic mica tape, with a thickness of 0.1mm, using methyl silicone resin as the adhesive, and an overlap rate of 55%.

[0055] In step S121, the first halogen-free polyolefin resin matrix comprises 35 parts of ethylene-vinyl acetate copolymer (EVA) and 20 parts of polyolefin elastomer (POE), with the EVA containing 28% vinyl acetate (VA) by mass. The ceramic powder comprises 30 parts of ammonium polyphosphate (APP)-coated expandable graphite, 40 parts of phosphate glass powder, and 20 parts of organo-modified montmorillonite, with the APP-coated expandable graphite having a particle size of 80 mesh and the phosphate glass powder having a softening point of 380°C. The first halogen-free flame retardant comprises 20 parts of aluminum hypophosphite and 5 parts of zinc borate. The first additive comprises 3 parts of vinylsilane coupling agent, 2 parts of carbon black, and 0.5 parts of antioxidant.

[0056] In step S122, the second halogen-free polyolefin resin matrix comprises 45 parts of EVA and 25 parts of metallocene linear low-density polyethylene (mLLDPE), with the VA mass fraction in the EVA being 18%. The second halogen-free flame retardant comprises 25 parts of aluminum hydroxide and 15 parts of magnesium hydroxide, with the aluminum hydroxide having a particle size of 1 μm and the magnesium hydroxide having a particle size of 1.5 μm. The halogen-free flame retardant synergist comprises 10 parts of zinc borate. The charring agent comprises 5 parts of silicate. The second auxiliary agent comprises 0.5 parts of antioxidant 1010, 0.5 parts of ultraviolet absorber UV-531, and 2 parts of calcium stearate.

[0057] Example 2: The difference between this example and Example 1 is that step S121 is replaced with the following steps: Step S125, 50 parts of the first halogen-free polyolefin resin matrix, 18 parts of the first halogen-free flame retardant, 85 parts of ceramic powder, and 3 parts of the first additive are premixed, melt-blended, and granulated to obtain the first adhesive; In step S125, the first halogen-free polyolefin resin matrix includes 30 parts of EVA and 20 parts of POE, and the mass fraction of vinyl acetate (VA) in the EVA is 28%. The ceramic powder includes 35 parts of expandable graphite, 35 parts of glass powder, and 15 parts of nano-clay. The first halogen-free flame retardant includes 12 parts of aluminum hypophosphite and 6 parts of zinc borate. The first additive includes 2 parts of vinyl silane coupling agent and 1 part of stearic acid.

[0058] Example 3: The difference between this example and Example 1 is that step S122 is replaced with the following step: Step S126, 65 parts of the second halogen-free polyolefin resin matrix, 40 parts of the second halogen-free flame retardant, 8 parts of the halogen-free flame retardant synergist, 5 parts of the charring agent, and 3 parts of the second additive are premixed, melt-blended, and granulated to obtain the second adhesive. In step S126, the second halogen-free polyolefin resin matrix includes 40 parts of EVA and 25 parts of mLLDPE, and the mass fraction of VA in EVA is 18%. The second halogen-free flame retardant includes 30 parts of aluminum hydroxide and 10 parts of magnesium hydroxide, with the aluminum hydroxide having a particle size of 1 μm and the magnesium hydroxide having a particle size of 1.5 μm. The halogen-free flame retardant synergist includes 8 parts of diethylaluminum hypophosphite. The charring agent includes 5 parts of modified montmorillonite. The second additive is the same as the first additive in Example 1.

[0059] Comparative Example 1: The difference between this comparative example and Example 1 is that the cable core does not include a fire-resistant layer, and the double-layer co-extrusion die head is controlled to coat the first melt onto the outer surface of the outer conductor layer. The other steps are the same as in Example 1.

[0060] Comparative Example 2: The difference between this comparative example and Example 1 is that the sheath layer of the fire-resistant leaky cable only includes a flame-retardant polyolefin layer, and the thickness of the sheath layer in this comparative example is the same as the thickness of the sheath layer 5 in Example 1.

[0061] Comparative Example 3: The difference between this comparative example and Example 1 is that the sheath layer of the fire-resistant leaky cable only includes a ceramicized polyolefin layer, and the thickness of the sheath layer in this comparative example is the same as the thickness of the sheath layer 5 in Example 1.

[0062] Comparative Example 4: The difference between this comparative example and Example 1 is that the ceramic powder in step S121 is replaced with an equal amount of conventional ceramic filler, which includes 50 parts of untreated mica powder and 40 parts of wollastonite. The other steps are the same as those in Example 1.

[0063] Table 1 below shows the comprehensive performance comparison results of the fire-resistant leaky cables prepared in the examples and the comparative examples.

[0064] In the vertical burning test, according to the GB / T 18380.12 standard, the flame retardant rating is divided into three levels from high to low: V-0, V-1 and V-2, based on the cable's self-extinguishing speed and anti-dripping performance.

[0065] As shown in Table 1, the fire-resistant leaky cables 100 prepared in Examples 1 to 3 all exhibited excellent fire resistance limits exceeding 180 minutes, and the vertical burning test results were all V-0. They passed the B1 level flame retardant and fire resistance tests. When the flame-retardant polyolefin layer was eroded, the ceramicized polyolefin layer fused with the fire-resistant layer to form a hard, complete, and dense gray-white ceramic shell with a crisp sound when tapped. The conductor core 1, insulation layer 2, and outer conductor layer 3 remained intact, fully verifying the synergistic effectiveness of the fire-resistant layer 4 and sheath layer 5 of the present invention.

[0066] In contrast, the fire resistance times of Comparative Example 1 (lacking a fire-resistant layer) and Comparative Example 2 (lacking a ceramicized polyolefin layer) were 120 min and 32 min, respectively. In Comparative Example 1, when the flame-retardant polyolefin layer was eroded, the ceramicized polyolefin layer fused with the fire-resistant layer to form a grayish-white ceramic shell, but the ceramicization effect was weak. In Comparative Example 2, when the flame-retardant polyolefin layer was burned through, the mica tape of the fire-resistant layer powdered and loosened. This demonstrates that the mica tape of the fire-resistant layer and the ceramicized polyolefin layer have an irreplaceable complementary effect. The fire resistance times of Comparative Example 3 (lacking a flame-retardant polyolefin layer) and Comparative Example 4 (using traditional ceramicized filler) were only 95 min and 120 min, respectively, and both failed the B1-level flame retardancy and fire resistance tests. When the fire-resistant leaky cable obtained in Comparative Example 3 burned, the ceramicized polyolefin layer formed a loose, porous, and cracked ceramic shell, and part of the mica tape in the fire-resistant layer was exposed and carbonized. When the fire-resistant leaky cable obtained in Comparative Example 4 burned, the ceramicized polyolefin layer formed a brittle and easily peeled ceramic shell, with poor bonding to the mica tape in the fire-resistant layer, and some conductor cores, insulation layers, and outer conductor layers were overheated and deformed. All of the above indicate that the fire-resistant performance of the fire-resistant leaky cables obtained in Comparative Examples 1 to 4 is worse than that of the fire-resistant leaky cables obtained in Examples 1 to 3.

[0067] In summary, the technical effect of the fire-resistant leaky cable prepared by this invention is not a simple superposition of the functions of each component, but rather a significant synergistic effect produced by the coordinated design of the fire-resistant layer 4, the ceramicized polyolefin layer and the flame-retardant polyolefin layer. While having ultra-long fire resistance, it has also achieved outstanding and substantial progress in fire resistance rating, ceramic quality and safety performance.

[0068] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A fire-resistant leaky cable, characterized in that... The fire-resistant leaky cable comprises, from the inside out, a conductor core, an insulation layer, an outer conductor layer, a fire-resistant layer, and a sheath layer. The fire-resistant layer is mica tape, which includes an adhesive, which is silicone resin. The sheath layer has a double-layer structure and includes a ceramicized polyolefin layer and a flame-retardant polyolefin layer. The ceramicized polyolefin layer covers the outside of the fire-resistant layer, and the flame-retardant polyolefin layer covers the outside of the ceramicized polyolefin layer.

2. The fire-resistant leaky cable according to claim 1, characterized in that... The ceramicized polyolefin layer comprises, by weight, 45-65 parts of a first halogen-free polyolefin resin matrix; 12-22 parts of a first halogen-free flame retardant; 70-110 parts of ceramic powder; and 3-8 parts of a first additive.

3. The fire-resistant leaky cable according to claim 2, characterized in that... The first halogen-free polyolefin resin matrix includes ethylene-vinyl acetate copolymer and at least one selected from polyolefin elastomer, ethylene propylene diene monomer (EPDM) rubber, and polyethylene; the first additive is selected from one or more of coupling agent, compatibilizer, lubricant, and antioxidant.

4. The fire-resistant leaky cable according to claim 3, characterized in that... The first halogen-free flame retardant includes a phosphorus-based flame retardant and an inorganic synergist, wherein the mass ratio of the phosphorus-based flame retardant to the inorganic synergist is any value between 1.5:1 and 3:1; the phosphorus-based flame retardant is selected from at least one of aluminum hypophosphite, magnesium hypophosphite, and calcium hypophosphite, and the inorganic synergist is selected from at least one of zinc borate, zinc stannate, and zinc molybdate.

5. The fire-resistant leaky cable according to claim 1, characterized in that... The flame-retardant polyolefin layer comprises, by weight, 60-80 parts of a second halogen-free polyolefin resin matrix; 20-40 parts of a second halogen-free flame retardant; 5-15 parts of a halogen-free flame retardant synergist; 2-5 parts of a charring agent; and 2-8 parts of a second additive.

6. The fire-resistant leaky cable according to claim 5, characterized in that... The second halogen-free polyolefin resin matrix includes ethylene-vinyl acetate copolymer, and one or more selected from polyethylene, polyolefin elastomer, and polypropylene; the second halogen-free flame retardant includes at least one of magnesium hydroxide and aluminum hydroxide; the halogen-free flame retardant synergist includes at least one of zinc borate, zinc stannate, and aluminum diethylphosphite; the second additive includes one or more of UV stabilizers, antioxidants, lubricants, coupling agents, and compatibilizers.

7. The fire-resistant leaky cable according to claim 6, characterized in that... The mica tape is a double-sided synthetic mica tape and is wound around the outer conductor. The width of the overlap between the mica tapes is not less than 50% of the bandwidth of the mica tape.

8. A method for preparing a fire-resistant leaky cable according to any one of claims 1-7, characterized in that... The process includes the following steps: providing a cable core, the cable core comprising, from the inside out, a conductor core, an insulation layer, an outer conductor layer, and a fire-resistant layer; preparing a first melt and a second melt; controlling a double-layer co-extrusion die head to coat the first melt onto the surface of the fire-resistant layer to form a ceramicized polyolefin layer; controlling the double-layer co-extrusion die head to coat the second melt onto the surface of the ceramicized polyolefin layer to form a flame-retardant polyolefin layer; the ceramicized polyolefin layer and the flame-retardant polyolefin layer achieve interfacial fusion in a molten state, thereby obtaining a fire-resistant leaky cable to be cooled; and sequentially cooling and drying the fire-resistant leaky cable to be cooled to obtain the fire-resistant leaky cable.

9. The preparation method according to claim 8, characterized in that... The steps for preparing the first melt and the second melt specifically include the following steps: premixing a first halogen-free polyolefin resin matrix, a first halogen-free flame retardant, ceramic powder and a first additive, and then performing melt blending and granulation to obtain a first rubber compound; premixing a second halogen-free polyolefin resin matrix, a second halogen-free flame retardant, a halogen-free flame retardant synergist, a charring agent and a second additive, and then performing melt blending and granulation to obtain a second rubber compound; controlling a first extruder to plasticize the first rubber compound to obtain the first melt, wherein the plasticizing temperature of the first extruder is set to any value between 140℃ and 150℃; controlling a second extruder to plasticize the second rubber compound to obtain the second melt, wherein the plasticizing temperature of the second extruder is set to any value between 140℃ and 175℃.

10. The preparation method according to claim 9, characterized in that... The process of sequentially cooling and drying the fire-resistant leaky cable to obtain the fire-resistant leaky cable specifically includes the following steps: cooling the fire-resistant leaky cable with atomized spray or immersing the fire-resistant leaky cable to be cooled in warm water, wherein the temperature of the warm water is any value between 40℃ and 60℃; immersing the fire-resistant leaky cable to be cooled after atomized spray or warm water cooling in cold water until the fire-resistant leaky cable to be cooled to room temperature, wherein the temperature of the cold water is any value between 15℃ and 25℃; and drying the cable to obtain the fire-resistant leaky cable.

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