Cable with co-extruded self-foaming ceramic fireproof layer and preparation method thereof

Abstract

The invention discloses a cable with a co-extrusion self-foaming ceramic fireproof layer and a preparation method of the cable, and belongs to the technical field of polyolefin cables. The cable comprises a conductor, an insulating layer and a fireproof layer from inside to outside, comprising the following raw materials: 40-60 parts of an ethylene-vinyl acetate copolymer, 20-40 parts of a polyolefin elastomer, 20-30 parts of a ceramic precursor filler, 5-10 parts of a compatilizer, 5-10 parts of a cosolvent, 3-5 parts of a flexibilizer, 2-4 parts of a main foaming agent, 1-2 parts of an auxiliary foaming agent, 1-3 parts of a lubricant and 0.5-1.5 parts of an antioxidant. The compatilizer is siloxane containing sulfydryl and phosphaphenanthrene groups, and the flexibilizer is silane coupling agent modified quartz fibers containing double bonds. In a matrix of the ethylene-vinyl acetate copolymer and the polyolefin elastomer, the compatilizer and the flexibilizer are added, so that the fireproof layer is endowed with better impact resistance and flame retardance.

Description

Technical Field

[0001] This invention belongs to the field of polyolefin cable technology, specifically relating to a cable with a co-extruded self-foaming ceramic fireproof layer and its preparation method. Background Technology

[0002] Wires and cables are wire products used to transmit electrical energy, transmit information, and realize electromagnetic energy conversion. Most existing cables have defects such as poor fire resistance and high temperature resistance and insufficient flame retardancy. In the event of a fire, short circuits may occur, and even the fire may spread.

[0003] Ceramic polymer materials possess excellent fire resistance properties. They are high-performance materials made by adding ceramic precursor fillers, fluxes, flame retardants, and other additives to polymers as the base material. Ceramic polymer materials have been widely used in fire-resistant wires and cables.

[0004] Ceramified polymer materials retain the basic properties of polymer materials under normal conditions. When exposed to fire or high temperatures, they can rapidly "ceramize," transforming into a hard, ceramic-like shell that can withstand flames for a long time and prevent the diffusion of internal gases. Simultaneously, due to the structural change, numerous micropores are left on their surface, providing excellent thermal insulation. This prevents external high temperatures from transferring to the interior and avoids the decomposition of internal materials after high-temperature burning, thus fulfilling the thermal insulation function.

[0005] However, existing ceramicized materials used as insulation or fireproofing layers suffer from the problem of difficulty in precisely controlling the foaming process of polymer decomposition, leading to insufficient strength and susceptibility to cracking in the ceramic body, as well as decreased toughness after ceramicization. Furthermore, ceramicized polymer materials, being a combination of inorganic and organic materials, have poor compatibility, and their flexibility, impact resistance, and bending resistance are inferior to traditional polymer materials, making them prone to cracking or breakage. This increases the risk of damage to the cable protection structure after mechanical impact or long-term aging. Summary of the Invention

[0006] This invention provides a cable with a co-extruded self-foaming ceramic fireproof layer and its preparation method, which can solve the problem of poor impact resistance of cables using ceramic polymer materials in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions: A cable having a co-extruded self-foaming ceramicized fire-resistant layer, the cable comprising, from the inside out, a conductor, an insulation layer and a fire-resistant layer; The fireproof layer comprises the following raw materials by weight: 40-60 parts of ethylene-vinyl acetate copolymer, 20-40 parts of polyolefin elastomer, 20-30 parts of ceramic precursor filler, 5-10 parts of compatibilizer, 5-10 parts of cosolvent, 3-5 parts of toughening agent, 2-4 parts of main foaming agent, 1-2 parts of auxiliary foaming agent, 1-3 parts of lubricant, and 0.5-1.5 parts of antioxidant; The compatibilizer is a siloxane containing mercapto and phosphenanthrene groups; The toughening agent is a silane coupling agent modified with double bonds to form quartz fiber.

[0008] The ceramicized polyolefin material of the fireproof layer uses a mixture of EVA (ethylene-vinyl acetate copolymer) and polyolefin elastomer as the main matrix, with ceramic precursor fillers added. When exposed to fire or high temperatures, the polymer matrix decomposes, and the ceramic precursor fillers react with a co-solvent to sinter into a ceramic phase, forming a supporting skeleton that effectively protects the internal structure and prevents cable collapse and short circuits. The compatibilizer possesses multiple functional groups; the phosphaphenanthrene groups in the compatibilizer are highly efficient flame retardants that can capture combustion free radicals. The highly active thiol groups in the compatibilizer form hydrogen bonds with EVA or inorganic materials (ceramic precursor fillers), while the siloxane groups form strong chemical bonds or physical entanglements with the cross-linked polyethylene or fillers in the insulation layer during processing. This greatly enhances the adhesion between the insulation layer and the fireproof layer, preventing failure due to interlayer delamination during use. This improves the compatibility of the polymer and fillers in the fireproof layer and enhances the mechanical properties of the material.

[0009] The toughening agent is modified quartz fiber, which has high high temperature resistance and is interwoven in the polymer system to form an interwoven fiber network structure. This improves the toughness, crack resistance and tensile strength of the fireproof layer at room temperature, making the cable less susceptible to damage during installation and laying. In addition, it can play a role in limiting and physical connection during the ceramization process, preventing cracking after ceramization.

[0010] This invention adds a foaming agent to the microbubble structure generated by polymer decomposition. The foaming agent decomposes to generate gas, which forms a porous foam ceramic layer during the ceramization process, forming an excellent thermal insulation structure that can effectively block the transmission of high flame temperature to the internal insulation layer and conductor.

[0011] Furthermore, the insulating layer is made of cross-linked polyethylene.

[0012] Furthermore, the ceramic precursor filler is at least one selected from kaolin, talc, wollastonite, mica, and quartz powder.

[0013] Furthermore, the method for preparing the compatibilizer includes the following steps: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask, stir until completely dissolved, add terephthalaldehyde, heat to 50-65℃ and stir to react for 6-10 hours. S2. Under a nitrogen atmosphere, heat to 80-90℃ and add DOPO. Reflux and stir for 4-7 hours. Remove the solvent by rotary evaporation and dry under vacuum to obtain a siloxane containing phosphenanthrene groups. S3. Add siloxane containing phosphenanthrene groups to anhydrous ethanol, then add 1,2-ethylenedithiol and a photoinitiator. After uniform mixing, irradiate with ultraviolet light for 1-2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

[0014] One aldehyde group of terephthalaldehyde undergoes nucleophilic addition with a secondary amine of a silane to form an enamine, creating a long-chain molecule with terephthalaldehyde at the center and allyl-containing siloxane groups at both ends. The PH bond in the DOPO molecule is highly reactive; under heating conditions, it undergoes nucleophilic addition to the carbon-carbon double bond of the enamine in the intermediate formed in S1, introducing a phosphaphenanthrene group. Finally, it reacts with the thiol group of 1,2-ethylenedithiol via the double bond on the siloxane, with one thiol group attached and the other exposed.

[0015] Furthermore, the molar ratio of 3-(N-allylamino)propyltrimethoxysilane to terephthalaldehyde is 2.0-2.1:1.

[0016] Furthermore, the molar ratio of DOPO to terephthalaldehyde is 1.9-2.1:1.

[0017] Furthermore, the mass ratio of the 1,2-ethylenedithiol to the siloxane containing the phosphenanthrene group is (0.8-1):5.

[0018] Furthermore, the photoinitiator is one of benzoin ethyl ether and benzoin dimethyl ether; The amount of photoinitiator added is 0.2-0.5% of the mass of the siloxane containing phosphenanthrene groups.

[0019] Furthermore, the co-solvent is at least one of low-temperature glass powder and zinc borate. The co-solvent helps lower the formation temperature of the ceramic phase, ensuring rapid formation of a dense ceramic body whose melting point matches the polymer decomposition temperature.

[0020] Furthermore, the method for preparing the toughening agent includes the following steps: Step 1: Dissolve the silane coupling agent containing double bonds in a solvent, adjust the pH to 4-5 with acetic acid, and obtain the impregnation solution; Step 2: Immerse the quartz fiber in the impregnation solution and heat to 30-40℃ for 8-12 hours; Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry to obtain the toughening agent.

[0021] The silane coupling agent is hydrolyzed under acidic conditions and modified by condensation reaction between silanol and silanol on the surface of quartz fiber. The surface of quartz fiber is covered by a layer of organic molecules with unsaturated double bonds at the ends, which are covalently bonded and can be uniformly dispersed in the polymer matrix.

[0022] Furthermore, the silane coupling agent containing double bonds is at least one of KH570 and KH172.

[0023] Furthermore, the solvent is an aqueous solution of ethanol, with a volume ratio of ethanol to water of (8-9):(1-2).

[0024] Furthermore, the mass concentration of the silane coupling agent in the impregnation solution is 2-5%.

[0025] Furthermore, the main foaming agent is azodicarbonamide; The auxiliary foaming agent is 4,4'-oxobisbenzenesulfonylhydrazine.

[0026] The primary and secondary foaming agents have different decomposition temperature ranges, which broadens the foaming window, makes the foaming process more controllable, and forms a uniform and fine cell structure.

[0027] Furthermore, the lubricant is at least one selected from polyethylene wax, stearic acid, and zinc stearate; The antioxidant is at least one of antioxidant 1010 and antioxidant 168.

[0028] This invention also provides a method for preparing a cable with a co-extruded self-foamed ceramic fire-resistant layer, for preparing the cable with the co-extruded self-foamed ceramic fire-resistant layer as described above, comprising the following steps: Step 1: Weigh the raw materials for the fireproof layer according to the specified proportions, put them into an internal mixer for mixing, and then feed the mixture into a screw extruder for extrusion granulation to obtain the fireproof layer masterbatch. Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0029] The beneficial effects of this invention are: (1) In this invention, ethylene-vinyl acetate copolymer and polyolefin elastomer work together to form a matrix material with good flexibility and processability. Through the multifunctional group effect of compatibilizer, the compatibility between ceramic precursor filler and matrix is ​​enhanced, while giving the fireproof layer better mechanical properties and flame retardant properties.

[0030] (2) In this invention, modified quartz fiber is added to the polyolefin system as a toughening agent. High-temperature resistant quartz fiber is used as a physical crosslinking point to enhance the mechanical properties of the fireproof layer material at room temperature. After being exposed to fire or ceramicized at high temperature, it forms a fiber network in the ceramic phase. Modified quartz fiber is embedded in the ceramic body as a "skeleton" to prevent the fireproof layer from cracking. It greatly improves the mechanical strength of the ceramic body, enhances the impact resistance, and ensures the stability of the fireproof effect.

[0031] (3) The thiol groups on the compatibilizer and the double bonds on the toughening agent of the present invention react to form covalent bonds during processing, which tightly connects the toughening agent and the matrix in the fireproof layer. The network structure of the fiber controls the decomposition of the polymer to form a microbubble pore structure, avoiding cracking caused by stress concentration due to excessively large local pores. The compatibilizer and the toughening agent work together to construct a stable and tough composite material system, ensuring that the cable fireproof layer has excellent performance at room temperature and can successfully transform into a strong ceramic foam at high temperature.

[0032] (4) Add a foaming agent to the fireproof layer to assist in controlling the foaming process. The fireproof layer forms a uniform and dense cell structure during the ceramicization process, thereby improving the fireproof performance.

[0033] (5) The insulation layer and fireproof layer of the cable are coated on the conductor in one step by co-extrusion process, which simplifies the production process. The siloxane groups in the compatibilizer enhance the adhesion between the insulation layer and the fireproof layer, prevent failure due to interlayer peeling during use, and improve the mechanical properties of the material. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1 Preparation of compatibilizer: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask. The concentration of silane is 0.25 mol / L. Stir until completely dissolved. Add terephthalaldehyde at a molar ratio of silane to terephthalaldehyde of 2:1. Heat to 60°C and stir for 8 hours.

[0036] S2. Under a nitrogen atmosphere, the temperature was raised to 90°C and DOPO was added. The molar ratio of DOPO to terephthalaldehyde was 2:1. The mixture was refluxed and stirred for 6 hours. The solvent was removed by rotary evaporation and the product was dried under vacuum to obtain a siloxane containing phosphorus phenanthrene groups.

[0037] S3. Add a siloxane containing phosphenanthrene groups at a concentration of 0.2 mol / L to anhydrous ethanol, then add 1,2-ethanedithiol and benzoin dimethyl ether. The mass ratio of 1,2-ethanedithiol to the siloxane containing phosphenanthrene groups is 0.9:5, and the benzoin dimethyl ether is 0.4% of the mass of the siloxane containing phosphenanthrene groups. After uniform mixing, irradiate the mixture with ultraviolet light at a power of 300W for 2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

[0038] Preparation of toughening agent: Step 1: Dissolve silane coupling agent KH570 in an ethanol-water solution (ethanol to water volume ratio of 9:1), adjust the pH to 4.5 with acetic acid to obtain an impregnation solution with a mass concentration of 3% of silane coupling agent in the impregnation solution.

[0039] Step 2: Immerse the quartz fiber in the impregnation solution and heat it to 35°C for 10 hours.

[0040] Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry at 80°C for 6 hours to obtain the toughening agent.

[0041] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 8 parts compatibilizer, 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 4 parts toughening agent, 3 parts azodicarbonamide, 1.5 parts 4,4'-oxobisbenzenesulfonyl hydrazine, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, 135°C in zone 3, and 140°C in zone 4 to finally obtain the fireproof layer masterbatch.

[0042] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0043] Example 2 The only difference from Example 1 is that the mass fraction of the compatibilizer in the fireproof layer is increased to 10 parts, while the other steps and conditions are the same as in Example 1.

[0044] Example 3 The only difference from Example 1 is that the mass fraction of the compatibilizer in the fireproof layer is reduced to 5 parts, while the other steps and conditions are the same as in Example 1.

[0045] Example 4 The only difference from Example 1 is that the mass concentration of the silane coupling agent in the impregnation solution is increased to 5% when preparing the toughening agent; the other steps and conditions are the same as in Example 1.

[0046] Example 5 The only difference from Example 1 is that the mass concentration of the silane coupling agent in the impregnation solution is reduced to 2% when preparing the toughening agent; the other steps and conditions are the same as in Example 1.

[0047] Example 6 The only difference from Example 1 is that the toughening agent in the raw materials of the fireproof layer is increased to 5 parts by mass, while the other steps and conditions are the same as in Example 1.

[0048] Example 7 The only difference from Example 1 is that the toughening agent in the raw materials of the fireproof layer is reduced to 3 parts by mass, while the other steps and conditions are the same as in Example 1.

[0049] Example 8 The only difference from Example 1 is that the mass fraction of the main foaming agent in the fireproof layer raw material is adjusted to 4 parts, and the mass fraction of the auxiliary foaming agent is adjusted to 2 parts. The other steps and conditions are the same as in Example 1.

[0050] Example 9 The only difference from Example 1 is that the mass fraction of the main foaming agent in the fireproof layer raw material is adjusted to 2 parts, and the mass fraction of the auxiliary foaming agent is adjusted to 1 part. The other steps and conditions are the same as in Example 1.

[0051] Comparative Example 1 The only difference from Example 1 is that no compatibilizer is added to the fireproof layer material.

[0052] Preparation of toughening agent: Step 1: Dissolve silane coupling agent KH570 in an ethanol-water solution (ethanol to water volume ratio of 9:1), adjust the pH to 4.5 with acetic acid to obtain an impregnation solution with a mass concentration of 3% of silane coupling agent in the impregnation solution.

[0053] Step 2: Immerse the quartz fiber in the impregnation solution and heat it to 35°C for 10 hours.

[0054] Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry at 80°C for 6 hours to obtain the toughening agent.

[0055] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 4 parts toughening agent, 3 parts azodicarbonamide, 1.5 parts 4,4'-oxobisbenzenesulfonyl hydrazine, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, and 135°C in zone 3 to finally obtain the fireproof layer masterbatch.

[0056] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0057] Comparative Example 2 The only difference from Example 1 is that the compatibilizer in the fireproof layer does not introduce mercapto groups.

[0058] Preparation of compatibilizer: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask. The concentration of silane is 0.25 mol / L. Stir until completely dissolved. Add terephthalaldehyde at a molar ratio of silane to terephthalaldehyde of 2:1. Heat to 60°C and stir for 8 hours.

[0059] S2. Under a nitrogen atmosphere, heat to 90°C and add DOPO. The molar ratio of DOPO to terephthalaldehyde is 2:1. Reflux and stir for 6 hours. Remove the solvent by rotary evaporation and vacuum drying to obtain a siloxane containing phosphorus phenanthrene groups, which is the compatibilizer.

[0060] Preparation of toughening agent: Step 1: Dissolve silane coupling agent KH570 in an ethanol-water solution (ethanol to water volume ratio of 9:1), adjust the pH to 4.5 with acetic acid to obtain an impregnation solution with a mass concentration of 3% of silane coupling agent in the impregnation solution.

[0061] Step 2: Immerse the quartz fiber in the impregnation solution and heat it to 35°C for 10 hours.

[0062] Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry at 80°C for 6 hours to obtain the toughening agent.

[0063] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 8 parts compatibilizer, 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 4 parts toughening agent, 3 parts azodicarbonamide, 1.5 parts 4,4'-oxobisbenzenesulfonyl hydrazine, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, and 135°C in zone 3 to finally obtain the fireproof layer masterbatch.

[0064] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0065] Comparative Example 3 The only difference from Example 1 is that no toughening agent is added to the fireproof layer material.

[0066] Preparation of compatibilizer: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask. The concentration of silane is 0.25 mol / L. Stir until completely dissolved. Add terephthalaldehyde at a molar ratio of silane to terephthalaldehyde of 2:1. Heat to 60°C and stir for 8 hours.

[0067] S2. Under a nitrogen atmosphere, the temperature was raised to 90°C and DOPO was added. The molar ratio of DOPO to terephthalaldehyde was 2:1. The mixture was refluxed and stirred for 6 hours. The solvent was removed by rotary evaporation and the product was dried under vacuum to obtain a siloxane containing phosphorus phenanthrene groups.

[0068] S3. Add a siloxane containing phosphenanthrene groups at a concentration of 0.2 mol / L to anhydrous ethanol, then add 1,2-ethanedithiol and benzoin dimethyl ether. The mass ratio of 1,2-ethanedithiol to the siloxane containing phosphenanthrene groups is 0.9:5, and the benzoin dimethyl ether is 0.4% of the mass of the siloxane containing phosphenanthrene groups. After uniform mixing, irradiate the mixture with ultraviolet light at a power of 300W for 2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

[0069] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 8 parts compatibilizer, 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 3 parts azodicarbonamide, 1.5 parts 4,4'-oxobisbenzenesulfonyl hydrazine, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, and 135°C in zone 3 to finally obtain the fireproof layer masterbatch.

[0070] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0071] Comparative Example 4 The only difference from Example 1 is that the toughening agent in the fireproof layer material is directly replaced by quartz fiber.

[0072] Preparation of compatibilizer: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask. The concentration of silane is 0.25 mol / L. Stir until completely dissolved. Add terephthalaldehyde at a molar ratio of silane to terephthalaldehyde of 2:1. Heat to 60°C and stir for 8 hours.

[0073] S2. Under a nitrogen atmosphere, the temperature was raised to 90°C and DOPO was added. The molar ratio of DOPO to terephthalaldehyde was 2:1. The mixture was refluxed and stirred for 6 hours. The solvent was removed by rotary evaporation and the product was dried under vacuum to obtain a siloxane containing phosphorus phenanthrene groups.

[0074] S3. Add a siloxane containing phosphenanthrene groups at a concentration of 0.2 mol / L to anhydrous ethanol, then add 1,2-ethanedithiol and benzoin dimethyl ether. The mass ratio of 1,2-ethanedithiol to the siloxane containing phosphenanthrene groups is 0.9:5, and the benzoin dimethyl ether is 0.4% of the mass of the siloxane containing phosphenanthrene groups. After uniform mixing, irradiate the mixture with ultraviolet light at a power of 300W for 2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

[0075] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 8 parts compatibilizer, 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 4 parts quartz fiber, 3 parts azodicarbonamide, 1.5 parts 4,4'-oxobisbenzenesulfonyl hydrazine, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, and 135°C in zone 3 to finally obtain the fireproof layer masterbatch.

[0076] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0077] Comparative Example 5 The only difference from Example 1 is that no main foaming agent and auxiliary foaming agent are added to the fireproof layer raw material.

[0078] Preparation of compatibilizer: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask. The concentration of silane is 0.25 mol / L. Stir until completely dissolved. Add terephthalaldehyde at a molar ratio of silane to terephthalaldehyde of 2:1. Heat to 60°C and stir for 8 hours.

[0079] S2. Under a nitrogen atmosphere, the temperature was raised to 90°C and DOPO was added. The molar ratio of DOPO to terephthalaldehyde was 2:1. The mixture was refluxed and stirred for 6 hours. The solvent was removed by rotary evaporation and the product was dried under vacuum to obtain a siloxane containing phosphorus phenanthrene groups.

[0080] S3. Add a siloxane containing phosphenanthrene groups at a concentration of 0.2 mol / L to anhydrous ethanol, then add 1,2-ethanedithiol and benzoin dimethyl ether. The mass ratio of 1,2-ethanedithiol to the siloxane containing phosphenanthrene groups is 0.9:5, and the benzoin dimethyl ether is 0.4% of the mass of the siloxane containing phosphenanthrene groups. After uniform mixing, irradiate the mixture with ultraviolet light at a power of 300W for 2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

[0081] Preparation of toughening agent: Step 1: Dissolve silane coupling agent KH570 in an ethanol-water solution (ethanol to water volume ratio of 9:1), adjust the pH to 4.5 with acetic acid to obtain an impregnation solution with a mass concentration of 3% of silane coupling agent in the impregnation solution.

[0082] Step 2: Immerse the quartz fiber in the impregnation solution and heat it to 35°C for 10 hours.

[0083] Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry at 80°C for 6 hours to obtain the toughening agent.

[0084] Cable manufacturing: Step 1: Weigh the raw materials for the fireproof layer according to the following mass proportions: 50 parts ethylene-vinyl acetate copolymer, 30 parts polyolefin elastomer, 25 parts ceramic precursor filler (kaolin and talc in a mass ratio of 1:1), 8 parts compatibilizer, 7 parts co-solvent (low-temperature glass powder and zinc borate in a mass ratio of 2:1), 4 parts toughening agent, 2 parts polyethylene wax, and 1.0 part antioxidant (antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1). Put all raw materials into a mixer and mix them at 140°C. The mixture is then fed into a screw extruder for extrusion granulation. The extruder temperature is set to 110°C in zone 1, 120°C in zone 2, and 135°C in zone 3 to finally obtain the fireproof layer masterbatch.

[0085] Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

[0086] The performance of the fireproof layer of the cables prepared in Examples 1-9 and Comparative Examples 1-5 was tested, and the results are shown in Table 1.

[0087] Mechanical properties were tested in accordance with the standard GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets".

[0088] The oxygen index was tested in accordance with the standard GB / T 2406.1-2008 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 1: Guidelines".

[0089] The aging performance was tested in accordance with the standard GB / T 2951.12-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 12: General Test Methods - Thermal Aging Test Method", with aging conditions of 100℃ and 168h.

[0090] The cable was subjected to a fire resistance test in accordance with the standard GB / T 19216.21-2003 "Line Integrity Tests for Cables or Optical Fibers under Flame Conditions - Part 21: Test Procedures and Requirements for Cables with Rated Voltage of 0.6 / 1.0 kV and Below", and the state of the fireproof layer after ceramization was observed.

[0091] Table 1 As can be seen from Table 1, the fireproof cable layers prepared in Examples 1-9 of this invention have excellent mechanical properties, low mechanical property degradation after aging, are suitable for use in high-temperature environments, have good impact resistance, and their oxygen index can reach up to 36%, exhibiting good flame retardant properties. When exposed to fire or high temperatures, the ceramic protective structure of the fireproof layer is hard, the surface is intact without obvious cracks, and the interior exhibits a uniform porous structure, with excellent heat insulation, cooling, and fire resistance effects, and passes the fire resistance test.

[0092] Compared with Examples 1-5, the mechanical properties and flame retardant properties of the Comparative Examples were significantly reduced, and the impact resistance was not as good as that of Example 1. It can be seen that the synergistic effect of the compatibilizer and toughening agent is conducive to building a tight bond between the polymer matrix and the filler of the fireproof layer, which helps to improve the impact resistance and fire resistance of the fireproof layer and the ceramic body. After the fireproof layer is ceramicized, the structure is more complete and the heat insulation and fireproof effect is better.

[0093] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0094] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cable having a co-extruded self-foamed ceramicized fireproof layer, characterized in that, The cable comprises, from the inside out, a conductor, an insulation layer, and a fire-resistant layer; The fireproof layer comprises the following raw materials by weight: 40-60 parts of ethylene-vinyl acetate copolymer, 20-40 parts of polyolefin elastomer, 20-30 parts of ceramic precursor filler, 5-10 parts of compatibilizer, 5-10 parts of cosolvent, 3-5 parts of toughening agent, 2-4 parts of main foaming agent, 1-2 parts of auxiliary foaming agent, 1-3 parts of lubricant, and 0.5-1.5 parts of antioxidant; The compatibilizer is a siloxane containing mercapto and phosphenanthrene groups; The toughening agent is a silane coupling agent modified with double bonds to form quartz fiber.

2. The cable with a co-extruded self-foamed ceramic fireproof layer according to claim 1, characterized in that, The insulating layer is made of cross-linked polyethylene.

3. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 1, characterized in that, The ceramic precursor filler is at least one selected from kaolin, talc, wollastonite, mica, and quartz powder; the flux is at least one selected from low-temperature glass powder and zinc borate. The primary foaming agent is azodicarbonamide; the secondary foaming agent is 4,4'-oxobisbenzenesulfonylhydrazine.

4. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 1, characterized in that, The method for preparing the compatibilizer includes the following steps: S1. Add 3-(N-allylamino)propyltrimethoxysilane and anhydrous ethanol to a flask, stir until completely dissolved, add terephthalaldehyde, heat to 50-65℃ and stir to react for 6-10 hours. S2. Under a nitrogen atmosphere, heat to 80-90℃ and add DOPO. Reflux and stir for 4-7 hours. Remove the solvent by rotary evaporation and dry under vacuum to obtain a siloxane containing phosphenanthrene groups. S3. Add siloxane containing phosphenanthrene groups to anhydrous ethanol, then add 1,2-ethylenedithiol and a photoinitiator. After uniform mixing, irradiate with ultraviolet light for 1-2 hours. Remove the solvent by rotary evaporation, wash with water, and then distill under reduced pressure to obtain the compatibilizer.

5. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 4, characterized in that, The molar ratio of 3-(N-allylamino)propyltrimethoxysilane to terephthalaldehyde is 2.0-2.1:1; the molar ratio of DOPO to terephthalaldehyde is 1.9-2.1:

1.

6. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 4, characterized in that, The mass ratio of the 1,2-ethylenedithiol to the siloxane containing the phosphenanthrene group is (0.8-1):

5.

7. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 4, characterized in that, The photoinitiator is one of benzoin ethyl ether and benzoin dimethyl ether; The amount of photoinitiator added is 0.2-0.5% of the mass of the siloxane containing phosphenanthrene groups.

8. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 1, characterized in that, The toughening agent is prepared by the following steps: Step 1: Dissolve the silane coupling agent containing double bonds in a solvent, adjust the pH to 4-5 with acetic acid, and obtain the impregnation solution; Step 2: Immerse the quartz fiber in the impregnation solution and heat to 30-40℃ for 8-12 hours; Step 3: After the reaction is complete, filter the solution, wash with deionized water, and dry to obtain the toughening agent.

9. A cable with a co-extruded self-foamed ceramic fireproof layer according to claim 8, characterized in that, The silane coupling agent containing double bonds is at least one of KH570 and KH172; The mass concentration of the silane coupling agent in the impregnation solution is 2-5%.

10. A method for preparing a cable with a co-extruded self-foamed ceramicized fire-resistant layer, characterized in that, The method for preparing a cable having a co-extruded self-foamed ceramicized fire-resistant layer as described in any one of claims 1-9 comprises the following steps: Step 1: Weigh the raw materials for the fireproof layer according to the specified proportions, put them into an internal mixer for mixing, and then feed the mixture into a screw extruder for extrusion granulation to obtain the fireproof layer masterbatch. Step 2: The cross-linked polyethylene material and the fireproof layer masterbatch are fed into a double-layer co-extrusion extruder according to the insulation layer and fireproof layer structure, respectively. They are co-extruded onto the conductor surface, with the inner layer being a cross-linked polyethylene insulation layer and the outer layer being a fireproof layer, to obtain the cable product.

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