High strength fire resistant flame retardant wire cable

Abstract

The application relates to the technical field of cables and discloses a high-strength fireproof flame-retardant cable. The high-strength fireproof flame-retardant cable comprises a conductor and a sheath layer, and the sheath layer comprises the following raw materials in parts by weight: low-density polyethylene, ethylene-vinyl acetate copolymer, polyethylene-vinyl acetate, porous silicon dioxide coated calcium carbonate, microencapsulated intumescent flame retardant, antioxidant, zinc stearate and sodium dodecyl sulfonate; the microencapsulated intumescent flame retardant is a microcapsule particle with polyphosphoric acid ammonium and pentaerythritol as core materials and hydrolyzed polycondensed organic silicon resin as shell materials. The high-strength fireproof flame-retardant cable prepared in the application solves the problems of poor and unstable flame-retardant performance, poor mechanical performance, insufficient thermal stability and difficult balance between flame retardation and mechanical performance of traditional cable materials, and overcomes the adverse effects of key process defects in the preparation of the microencapsulated flame retardant and the porous silicon dioxide coated calcium carbonate on the material performance.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a high-strength fire-resistant and flame-retardant wire and cable. Background Technology

[0002] Traditional electrical wires and cables have numerous shortcomings in terms of fire resistance and flame retardancy. Many ordinary electrical wires and cables use sheath materials with low flame retardancy ratings, making them prone to rapid combustion upon contact with an ignition source. During combustion, they release large amounts of toxic and harmful gases and dense smoke, posing a serious threat to human safety and exacerbating the spread of fire. While some electrical wires and cables contain added flame retardants, these are often traditional inorganic flame retardants or non-microencapsulated intumescent flame retardants. Although inorganic flame retardants have some flame-retardant effect, large dosages are often required to achieve the desired flame retardancy rating. This leads to a significant decrease in the cable's mechanical properties, such as reduced tensile strength and decreased flexibility, affecting the cable's normal installation and use. Non-microencapsulated intumescent flame retardants, such as a simple mixture of ammonium polyphosphate and pentaerythritol, can form an expanded char layer when heated, thus providing some flame retardancy. However, due to the hygroscopic migration of ammonium polyphosphate and its poor compatibility with the polymer matrix, the flame retardant tends to leach out of the material during long-term use, leading to a decrease in flame retardant efficiency. This makes it impossible to continuously and effectively exert its flame retardant effect and meet the high requirements of fire safety standards.

[0003] In practical applications, wires and cables need to possess both good fire-retardant properties and excellent mechanical properties; however, existing technologies struggle to achieve a balance between these two. Some cables with high flame-retardant properties often have poor mechanical properties, while cables with good mechanical properties often fail to meet high standards of fire-retardant performance. Furthermore, cables also suffer from insufficient thermal stability; during long-term thermal aging, the material's performance is prone to decline, leading to a shortened cable lifespan. To address these technical problems, this invention proposes a novel high-strength fire-retardant wire and cable. Summary of the Invention

[0004] This invention proposes a high-strength fire-retardant wire and cable, which solves the problems of poor and unstable flame retardant performance, poor mechanical properties, insufficient thermal stability, and difficulty in balancing flame retardancy and mechanical properties in traditional wire and cable materials. At the same time, it overcomes the adverse effects of key process defects in the preparation of microencapsulated flame retardants and porous silica-coated calcium carbonate microspheres on material performance.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention proposes a high-strength fire-resistant and flame-retardant wire and cable, comprising a conductor and a sheath layer, wherein the sheath layer comprises the following raw materials in parts by weight: 20-35 parts of low-density polyethylene, 15-25 parts of ethylene-vinyl acetate copolymer, 10-15 parts of polyethylene-vinyl acetate, 15-20 parts of porous silica-coated calcium carbonate microspheres, 15-25 parts of microencapsulated intumescent flame retardant, 1-1.5 parts of antioxidant, 0.5-1 part of zinc stearate, and 2-3 parts of sodium dodecyl sulfonate; The microencapsulated intumescent flame retardant is a microcapsule made of ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed organosilicon resin as the shell material.

[0006] As a further technical solution, the preparation method of the microencapsulated intumescent flame retardant includes the following steps: Ammonium polyphosphate and pentaerythritol were added sequentially to deionized water, and the mixture was heated in a water bath to 40±2℃ and stirred continuously at this temperature for 60±10 minutes to form a slurry. An aqueous acetic acid solution was added dropwise to control the pH of the system to 4.0. Methyltrimethoxysilane and anhydrous ethanol were mixed and diluted to obtain a diluted solution. Under the conditions of 40±2℃ and 500±50 rpm stirring, the diluted solution was slowly added dropwise to the slurry at a rate of 2 drops / second. After the addition was completed, the temperature was maintained at 40±2℃ and the stirring speed at 500±50 rpm, and the reaction was continued for 2±0.5 hours. Subsequently, a curing polycondensation reaction was carried out for 5±1 hours. After the reaction was completed, the slurry was naturally cooled to room temperature, filtered, washed, dried, and ground through a 200-mesh sieve to obtain the final product.

[0007] As a further technical solution, the weight ratio of deionized water, ammonium polyphosphate, pentaerythritol, methyltrimethoxysilane and anhydrous ethanol is 240-260:75-85:15-25:10-14:18-22.

[0008] As a further technical solution, the curing polycondensation reaction step includes: slowly raising the temperature of the reaction system to 75±5℃ at a heating rate of 1℃ / min, and carrying out the curing polycondensation reaction by stirring at 500±50 rpm at 75±5℃.

[0009] During this stage, dehydration condensation occurs between silanols and between silanols and the hydroxyl groups on the filler surface, forming a dense cross-linked silicone resin shell that completely coats the ammonium polyphosphate / pentaerythritol particles.

[0010] As a further technical solution, the preparation method of the porous silica-coated calcium carbonate microspheres includes: using hexadecyltrimethylammonium bromide as a template agent, performing a sol-gel reaction on the surface of calcium carbonate microspheres with tetraethyl orthosilicate to form a porous silica shell, and then removing the template agent by calcination to obtain the porous silica-coated calcium carbonate microspheres.

[0011] As a further technical solution, the preparation steps of the porous silica shell include: anhydrous ethanol, deionized water, and hexadecyltrimethylammonium bromide are stirred in a water bath at 35±2℃ at a speed of 400±50 rpm until the hexadecyltrimethylammonium bromide is completely dissolved; calcium carbonate microspheres are added, and stirring is continued for 30±5 minutes to allow the hexadecyltrimethylammonium bromide molecules to be fully adsorbed on the calcium carbonate surface; concentrated ammonia is added to the above system in one go, and the system is stirred to alkalize it; then tetraethyl orthosilicate is added to the reaction system; after the addition is complete, the temperature is maintained at 35±5℃ and the stirring speed is 400±50 rpm, and the reaction is continued for 24±2 hours; after the reaction is completed, the product is obtained by centrifugation, washing, and drying.

[0012] As a further technical solution, the mass concentration of the concentrated ammonia solution is 25%~28%.

[0013] As a further technical solution, the calcination step includes: placing the dried porous silica shell powder into a muffle furnace, heating it from room temperature to 550±50℃ at a heating rate of 2℃ / min under an air atmosphere, calcining it at this temperature for 4±1 hours, and then naturally cooling it to room temperature to obtain porous silica-coated calcium carbonate microspheres.

[0014] As a further technical solution, the antioxidant includes antioxidant 1010 and antioxidant 168 with a weight ratio of 1:2-3.

[0015] Secondly, this invention proposes a method for preparing high-strength fire-resistant and flame-retardant wires and cables. The steps include: preparing raw materials according to the formula; then placing the raw materials in a high-speed mixer and premixing them for 5-10 minutes at a speed of 900-1000 rpm to obtain a premix; transferring the premix from the high-speed mixer to an internal mixer for internal mixing at a temperature of 130-140℃ for 15-20 minutes; and after the internal mixing is completed, extruding the premix into a twin-screw extruder to coat the outer layer of the conductor, thereby obtaining the high-strength fire-resistant and flame-retardant wire and cable.

[0016] As a further technical solution, during the extrusion process, the twin-screw extruder has an extrusion temperature of 160-200℃ and a screw speed of 200-400rpm.

[0017] The working principle and beneficial effects of this invention are as follows: This invention employs a microencapsulated intumescent flame retardant with ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed silicone resin as the shell material. This design achieves highly efficient and durable V-0 flame retardant performance. In principle, ammonium polyphosphate and pentaerythritol, as a traditional combination of intumescent flame retardants, form an expanded char layer upon heating, effectively isolating heat and oxygen. However, unencapsulated ammonium polyphosphate is prone to moisture absorption and migration, and has poor compatibility with the polymer matrix, leading to decreased flame retardant efficiency and poor long-term thermal stability. The silicone resin shell formed by hydrolysis and condensation encapsulates the core material, effectively solving these problems. The silicone resin shell not only prevents the moisture migration of ammonium polyphosphate but also enhances its compatibility with the polymer matrix, allowing the flame retardant to be uniformly dispersed in the material and function better upon heating, forming a complete and dense expanded char layer, thus achieving highly efficient and durable flame retardant performance. Simultaneously, the microencapsulation structure protects the core material from damage during processing, further ensuring the stability of the flame retardant performance.

[0018] The porous silica-coated calcium carbonate microspheres prepared in this invention primarily contribute to excellent mechanical properties and thermal stability. They synergistically work with the polymer matrix to enhance the overall performance of the cable sheath material. Ordinary calcium carbonate, as an inert filler, exhibits weak interfacial bonding with the polymer matrix and easily becomes a stress concentration point under stress, leading to a decline in the material's mechanical properties. This invention, however, utilizes hexadecyltrimethylammonium bromide as a template agent and tetraethyl orthosilicate to induce a sol-gel reaction on the surface of the calcium carbonate microspheres, forming a porous silica shell. This porous silica shell possesses a large specific surface area and abundant pore structure, providing superior interfacial bonding conditions for the polymer matrix. On one hand, the porous structure enhances the physical entanglement with the polymer molecular chains, improving interfacial bonding; on the other hand, the potential nano-reinforcing effect allows the material to better disperse stress under load, thereby improving mechanical properties such as tensile strength and elongation at break. In terms of thermal stability, the porous silica shell can play a role in heat insulation and protection, reducing the transfer of heat to the calcium carbonate core. At the same time, after calcination to remove the template agent, the material structure is more stable and can resist degradation during long-term thermal aging, thus ensuring the thermal stability of the material.

[0019] In this invention, the microencapsulated intumescent flame retardant and porous silica-coated calcium carbonate microspheres work synergistically to achieve a balance between strength and flame retardancy in cable sheath materials. From a flame retardant perspective, the microencapsulated intumescent flame retardant is the primary source of the system's flame-retardant function. In a flame, it forms an expanded char layer, isolating heat and oxygen and preventing combustion. While the porous silica-coated calcium carbonate microspheres themselves do not possess flame retardancy, their presence improves the internal structure of the material, resulting in a more uniform distribution of the microencapsulated intumescent flame retardant. When the expanded char layer forms upon heating, the porous silica-coated calcium carbonate supports and stabilizes the char layer, preventing it from cracking and thus enhancing the flame-retardant effect. From a mechanical performance perspective, the porous silica-coated calcium carbonate microspheres play a crucial reinforcing role, improving the material's strength and toughness. Microencapsulated intumescent flame retardants, uniformly dispersed within the material, do not become stress concentration points like ordinary flame retardants. Instead, they fill the material's voids to some extent, further optimizing the material's structure. Working synergistically with porous silica-coated calcium carbonate, this results in a material that possesses excellent mechanical properties in addition to good flame retardancy. Furthermore, the two mutually enhance each other's thermal stability. The organosilicon shell of the microencapsulated intumescent flame retardant and the porous silica-coated calcium carbonate structure together improve the material's resistance to thermal shock and long-term thermal aging, ensuring stable performance under various environmental conditions. Detailed Implementation

[0020] 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.

[0021] It should be noted that the low-density polyethylene in this invention is LDPE 2421H; the ethylene-vinyl acetate copolymer is EV360; and the polyethylene-vinyl acetate is V6110M, all purchased from Yangzi Petrochemical-BASF Co., Ltd.

[0022] Example 1 A high-strength fire-retardant wire and cable includes a conductor and a sheath layer. The sheath layer comprises the following raw materials in parts by weight: 30 parts of low-density polyethylene, 20 parts of ethylene-vinyl acetate copolymer, 12 parts of polyethylene-vinyl acetate, 18 parts of porous silica-coated calcium carbonate microspheres, 20 parts of microencapsulated intumescent flame retardant, 1.2 parts of antioxidant, 0.8 parts of zinc stearate, and 2.5 parts of sodium dodecyl sulfonate. The antioxidants include antioxidant 1010 and antioxidant 168 in a weight ratio of 1:2; Microencapsulated intumescent flame retardants are microcapsule particles using ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed organosilicon resin as the shell material; the preparation method includes: Take 250 parts of deionized water, add 80 parts of ammonium polyphosphate and 20 parts of pentaerythritol in sequence while stirring at 300 rpm, heat the mixture in a water bath to 40°C, and continue stirring at this temperature for 60 minutes to form a slurry; slowly add a 10% acetic acid aqueous solution at a rate of 2 drops / second until the pH of the system stabilizes at 4.0. 12 parts of methyltrimethoxysilane were mixed and diluted with 20 parts of anhydrous ethanol to obtain a diluted solution. Under the conditions of 40°C and 500 rpm stirring, the diluted solution was slowly added dropwise to the slurry at a rate of 2 drops / second. After the addition was completed, the temperature was maintained at 40°C and the stirring speed at 500 rpm, and the reaction was continued for 2 hours. The temperature of the reaction system was slowly increased to 75°C at a heating rate of 1°C / min. At 75°C, the system was stirred at 500 rpm for 5 hours to carry out the curing polycondensation reaction. After the reaction was completed, the slurry was naturally cooled to room temperature, filtered, and the filter cake was washed with a large amount of deionized water until the filtrate was neutral to remove the byproduct methanol and unreacted acetic acid. Then it was dried at 80°C for 12 hours and ground through a 200-mesh sieve to obtain the microencapsulated intumescent flame retardant. The preparation method of porous silica-coated calcium carbonate microspheres includes: using hexadecyltrimethylammonium bromide as a template agent, a sol-gel reaction is carried out on the surface of calcium carbonate microspheres via tetraethyl orthosilicate to form a porous silica shell, and then the template agent is removed by calcination; Specifically, the process involves: mixing 150 parts of anhydrous ethanol, 30 parts of deionized water, and 2 parts of hexadecyltrimethylammonium bromide in a 35°C water bath at 400 rpm until the hexadecyltrimethylammonium bromide is completely dissolved; then adding 10 parts of calcium carbonate microspheres and continuing to stir for 30 minutes to allow the hexadecyltrimethylammonium bromide molecules to be fully adsorbed onto the calcium carbonate surface. Add 3 parts of concentrated ammonia solution with a mass concentration of 26% to the above system at once, and stir for 10 minutes to alkalize the system; then slowly and evenly add 6 parts of tetraethyl orthosilicate dropwise to the reaction system over 60 minutes; after the dropwise addition is complete, maintain the temperature at 35°C and the stirring speed at 400 rpm, and continue the reaction for 24 hours; after the reaction is completed, collect the solid product by centrifugation (8000 rpm, 10 min), wash the product with anhydrous ethanol and deionized water three times each, and place the washed product in an 80°C forced-air drying oven to dry for 6 hours; The dried powder was placed in a muffle furnace and heated from room temperature to 550°C at a rate of 2°C / min in air atmosphere. The powder was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature to obtain porous silica-coated calcium carbonate microspheres. The preparation method of this high-strength fire-retardant wire and cable includes the following steps: preparing raw materials according to the formula; then placing the raw materials in a high-speed mixer and premixing them for 8 minutes at a speed of 950 rpm to obtain a premix; transferring the premix from the high-speed mixer to an internal mixer for internal mixing at a temperature of 135°C for 18 minutes; after internal mixing, extruding the premix into a twin-screw extruder to coat the outer layer of the conductor at a temperature of 180°C and a screw speed of 300 rpm to obtain the high-strength fire-retardant wire and cable.

[0023] Example 2 A high-strength fire-resistant and flame-retardant wire and cable includes a conductor and a sheath layer. The sheath layer comprises the following raw materials in parts by weight: 20 parts of low-density polyethylene, 15 parts of ethylene-vinyl acetate copolymer, 10 parts of polyethylene-vinyl acetate, 15 parts of porous silica-coated calcium carbonate microspheres, 15 parts of microencapsulated intumescent flame retardant, 1 part of antioxidant, 0.5 parts of zinc stearate, and 2 parts of sodium dodecyl sulfonate. The antioxidants include antioxidant 1010 and antioxidant 168 in a weight ratio of 1:2; Microencapsulated intumescent flame retardants are microcapsule particles using ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed organosilicon resin as the shell material; the preparation method includes: Take 240 parts of deionized water, add 75 parts of ammonium polyphosphate and 15 parts of pentaerythritol in sequence while stirring at 300 rpm, heat the mixture in a water bath to 40°C, and continue stirring at this temperature for 60 minutes to form a slurry; slowly add a 10% acetic acid aqueous solution at a rate of 2 drops / second until the pH of the system stabilizes at 4.0. 10 parts of methyltrimethoxysilane were mixed and diluted with 18 parts of anhydrous ethanol to obtain a diluted solution. Under the conditions of 40°C and 500 rpm stirring, the diluted solution was slowly added dropwise to the slurry at a rate of 2 drops / second. After the addition was completed, the temperature was maintained at 40°C and the stirring speed at 500 rpm, and the reaction was continued for 2 hours. The temperature of the reaction system was slowly increased to 75°C at a heating rate of 1°C / min. At 75°C, the system was stirred at 500 rpm for 5 hours to carry out the curing polycondensation reaction. After the reaction was completed, the slurry was naturally cooled to room temperature, filtered, and the filter cake was washed with a large amount of deionized water until the filtrate was neutral to remove the byproduct methanol and unreacted acetic acid. Then it was dried at 80°C for 12 hours and ground through a 200-mesh sieve to obtain the microencapsulated intumescent flame retardant. The preparation method of porous silica-coated calcium carbonate microspheres includes: using hexadecyltrimethylammonium bromide as a template agent, a sol-gel reaction is carried out on the surface of calcium carbonate microspheres via tetraethyl orthosilicate to form a porous silica shell, and then the template agent is removed by calcination; Specifically, the process involves: mixing 150 parts of anhydrous ethanol, 30 parts of deionized water, and 2 parts of hexadecyltrimethylammonium bromide in a 35°C water bath at 400 rpm until the hexadecyltrimethylammonium bromide is completely dissolved; then adding 10 parts of calcium carbonate microspheres and continuing to stir for 30 minutes to allow the hexadecyltrimethylammonium bromide molecules to be fully adsorbed onto the calcium carbonate surface. Add 3 parts of 25% concentrated ammonia solution to the above system at once and stir for 10 minutes to alkalize the system; then slowly and evenly add 6 parts of tetraethyl orthosilicate dropwise to the reaction system over 60 minutes; after the addition is complete, maintain the temperature at 35°C and the stirring speed at 400 rpm and continue the reaction for 24 hours; after the reaction is completed, collect the solid product by centrifugation (8000 rpm, 10 min), wash the product with anhydrous ethanol and deionized water three times each, and dry the washed product in an 80°C forced-air drying oven for 6 hours; The dried powder was placed in a muffle furnace and heated from room temperature to 550°C at a rate of 2°C / min in air atmosphere. The powder was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature to obtain porous silica-coated calcium carbonate microspheres. The preparation method of this high-strength fire-retardant wire and cable includes the following steps: preparing raw materials according to the formula; then placing the raw materials in a high-speed mixer and premixing them for 5 minutes at a speed of 900 rpm to obtain a premix; transferring the premix from the high-speed mixer to an internal mixer for internal mixing at a temperature of 130°C for 15 minutes; after internal mixing, extruding the premix into a twin-screw extruder to coat the outer layer of the conductor at a temperature of 160°C and a screw speed of 200 rpm to obtain the high-strength fire-retardant wire and cable.

[0024] Example 3 A high-strength fire-resistant and flame-retardant wire and cable includes a conductor and a sheath layer. The sheath layer comprises the following raw materials in parts by weight: 35 parts of low-density polyethylene, 25 parts of ethylene-vinyl acetate copolymer, 15 parts of polyethylene-vinyl acetate, 20 parts of porous silica-coated calcium carbonate microspheres, 25 parts of microencapsulated intumescent flame retardant, 1.5 parts of antioxidant, 1 part of zinc stearate, and 3 parts of sodium dodecyl sulfonate. The antioxidants include antioxidant 1010 and antioxidant 168 in a weight ratio of 1:3; Microencapsulated intumescent flame retardants are microcapsule particles using ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed organosilicon resin as the shell material; the preparation method includes: Take 260 parts of deionized water, add 85 parts of ammonium polyphosphate and 25 parts of pentaerythritol in sequence while stirring at 300 rpm, heat the mixture in a water bath to 40°C, and continue stirring at this temperature for 60 minutes to form a slurry; slowly add a 10% acetic acid aqueous solution at a rate of 2 drops / second until the pH of the system stabilizes at 4.0. 14 parts of methyltrimethoxysilane were mixed and diluted with 22 parts of anhydrous ethanol to obtain a diluted solution. Under the conditions of 40°C and 500 rpm stirring, the diluted solution was slowly added dropwise to the slurry at a rate of 2 drops / second. After the addition was completed, the temperature was maintained at 40°C and the stirring speed at 500 rpm, and the reaction was continued for 2 hours. The temperature of the reaction system was slowly increased to 75°C at a heating rate of 1°C / min. At 75°C, the system was stirred at 500 rpm for 5 hours to carry out the curing polycondensation reaction. After the reaction is complete, the slurry is naturally cooled to room temperature, filtered, and the filter cake is washed with a large amount of deionized water until the filtrate is neutral to remove the byproduct methanol and unreacted acetic acid. Then it is dried at 80°C for 12 hours and ground through a 200-mesh sieve to obtain the final product.

[0025] The preparation method of porous silica-coated calcium carbonate microspheres includes: using hexadecyltrimethylammonium bromide as a template agent, a sol-gel reaction is carried out on the surface of calcium carbonate microspheres via tetraethyl orthosilicate to form a porous silica shell, and then the template agent is removed by calcination; Specifically, the process involves: mixing 150 parts of anhydrous ethanol, 30 parts of deionized water, and 2 parts of hexadecyltrimethylammonium bromide in a 35°C water bath at 400 rpm until the hexadecyltrimethylammonium bromide is completely dissolved; then adding 10 parts of calcium carbonate microspheres and continuing to stir for 30 minutes to allow the hexadecyltrimethylammonium bromide molecules to be fully adsorbed onto the surface of the calcium carbonate. Add 3 parts of concentrated ammonia solution with a mass concentration of 28% to the above system at once, and stir for 10 minutes to alkalize the system; then slowly and evenly add 6 parts of tetraethyl orthosilicate dropwise to the reaction system over 60 minutes; after the dropwise addition is complete, maintain the temperature at 35°C and the stirring speed at 400 rpm, and continue the reaction for 24 hours; after the reaction is completed, collect the solid product by centrifugation (8000 rpm, 10 min), wash the product with anhydrous ethanol and deionized water three times each, and place the washed product in an 80°C forced-air drying oven to dry for 6 hours; The dried powder was placed in a muffle furnace and heated from room temperature to 550°C at a rate of 2°C / min in air atmosphere. The powder was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature to obtain porous silica-coated calcium carbonate microspheres. The preparation method of this high-strength fire-retardant wire and cable includes the following steps: preparing raw materials according to the formula; then placing the raw materials in a high-speed mixer and premixing them for 10 minutes at a speed of 1000 rpm to obtain a premix; transferring the premix from the high-speed mixer to an internal mixer for internal mixing at a temperature of 140°C for 20 minutes; after internal mixing, extruding the premix into a twin-screw extruder to coat the outer layer of the conductor at a temperature of 200°C and a screw speed of 400 rpm to obtain the high-strength fire-retardant wire and cable.

[0026] Example 4 This embodiment is an adjustment based on Example 1. The difference from Example 1 is that in the preparation of the microencapsulated intumescent flame retardant, the amount of methyltrimethoxysilane is reduced from 12 parts to 4 parts.

[0027] Example 5 This embodiment is an adjustment based on Embodiment 1. The difference from Embodiment 1 is that the muffle furnace calcination step is omitted in the preparation of porous silica-coated calcium carbonate microspheres. That is, the porous silica-coated calcium carbonate microspheres used are uncalcined porous silica-coated calcium carbonate.

[0028] Comparative Example 1 Based on Example 1, the following adjustment was made: the 20 parts of microencapsulated intumescent flame retardant were replaced with an equal amount of a physical mixture of unmicroencapsulated ammonium polyphosphate and pentaerythritol in a mass ratio of 4:1. The sheath layer comprises the following raw materials in parts by weight: 30 parts low-density polyethylene, 20 parts ethylene-vinyl acetate copolymer, 12 parts polyethylene-vinyl acetate, 18 parts porous silica-coated calcium carbonate microspheres, 20 parts a physical mixture of ammonium polyphosphate and pentaerythritol, 1.2 parts antioxidant, 0.8 parts zinc stearate, and 2.5 parts sodium dodecyl sulfonate; the mass ratio of ammonium polyphosphate to pentaerythritol in the physical mixture of ammonium polyphosphate and pentaerythritol is 4:1.

[0029] Comparative Example 2 This comparative example is an adjustment based on Example 1. The difference from Example 1 is that 18 parts of porous silica-coated calcium carbonate microspheres were replaced with an equal amount of ordinary heavy calcium carbonate.

[0030] Comparative Example 3 This comparative example is an adjustment based on Example 1, except that the amount of microencapsulated intumescent flame retardant is reduced from 20 parts to 10 parts.

[0031] Comparative Example 4 This comparative example is an adjustment based on Example 1, except that no microencapsulated intumescent flame retardant was added.

[0032] Comparative Example 5 This comparative example is an adjustment based on Example 1. The difference from Example 1 is that porous silica-coated calcium carbonate microspheres were not added.

[0033] Test Example 1: The sheath samples of high-strength fire-resistant and flame-retardant wires and cables prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to the following tests: Tensile strength: Tested according to GB / T2951.11-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 11: General Test Methods - Thickness and Dimensional Measurements - Mechanical Properties Tests", using a universal testing machine with a clamp spacing of 50 mm and a tensile speed of 300 mm / min. The maximum tensile force at specimen breakage was recorded. Tensile strength (MPa) = maximum tensile force (N) / specimen cross-sectional area (mm²) 2 Elongation at break (%) = [(gauge length at break - original gauge length) / original gauge length] × 100%; Flame retardant performance: UL94 vertical burning test was conducted in accordance with GB / T 2408-2008 "Determination of flammability of plastics - Horizontal and Vertical Methods"; Thermal shock resistance: The test was conducted in accordance with GB / T 32129-2015 "Halogen-free Low-smoke Flame-retardant Cable Material for Wires and Cables" and was performed after being kept at 100℃ for 1 hour. Heat aging resistance: The test was conducted according to GB / T 2951.12-2008 "General Test Methods for Insulation and Sheath Materials of Cables and Optical Fibers - Part 12: Heat Aging Test". The sample was placed in an oven at 135℃ for 168 hours and then conditioned at 23±2℃ for 24 hours. The tensile strength after aging was tested, and the tensile strength retention rate (%) was calculated as (tensile strength after aging / tensile strength before aging) × 100%. The test results are shown in Table 1 below: Table 1

[0034] Based on the above data, it can be seen that Examples 1-3 exhibit superior performance compared to the comparative examples. The microencapsulated intumescent flame retardant achieves efficient and long-lasting V-0 flame retardant performance; the porous silica-coated calcium carbonate microspheres mainly contribute to the excellent mechanical properties and thermal stability. Together with the polymer matrix, they achieve a balance between the strength and flame retardancy of the cable sheath material.

[0035] Furthermore, compared with Examples 4-5, Example 1 showed improved tensile strength, impact resistance, and heat aging resistance, indicating that the complete organosilicon shell of the microencapsulated flame retardant and the thorough calcination of the porous silica-coated calcium carbonate microspheres are key process steps to ensure the final performance of the material. For the microencapsulated flame retardant, a sufficient amount of methyltrimethoxysilane can form a complete and appropriately thick organosilicon resin shell. This complete shell provides good protection for the core material, preventing mechanical damage during processing and resisting high temperature and oxygen erosion under thermal shock, ensuring that the core material can normally expand and retard when heated. If the shell is incomplete or too thin, the core material is prone to premature decomposition or damage under processing or thermal shock, leading to a decrease in flame retardant efficiency and a deterioration in the local thermal stability of the composite material. For porous silica-coated calcium carbonate, thorough calcination to remove the template agent (CTAB) is crucial. Uncalcined template agent will decompose and generate gas at high temperatures, causing the material to bubble during thermal shock, affecting the material's appearance and performance. Meanwhile, residual organic matter can affect the interfacial stability between the filler and the matrix, accelerating material degradation during long-term thermal aging. However, after complete calcination, the internal structure of the material becomes purer and more stable. The porous silica-coated calcium carbonate can better synergize with the polymer matrix, playing a reinforcing and stabilizing role in thermal properties, thus ensuring the material ultimately possesses excellent overall performance.

[0036] Comparative Example 1 used a common ammonium polyphosphate / pentaerythritol physical mixture. Compared with Example 1, the flame retardant rating decreased to V-1, and the heat aging resistance was reduced. Unencapsulated ammonium polyphosphate is prone to moisture absorption and migration, and has poor compatibility with the matrix, resulting in decreased flame retardant efficiency and poor long-term thermal stability. The microcapsule shell effectively solves the migration and compatibility problems of APP.

[0037] Comparative Example 2 used ordinary heavy calcium carbonate, and compared with Example 1, the mechanical properties (tensile strength and elongation at break) were significantly reduced. Ordinary calcium carbonate, as an inert filler, has weak interfacial bonding with the polymer matrix and is prone to becoming a stress concentration point under stress. The porous silica coating provides superior interfacial bonding and potential nano-reinforcing effects, thereby improving the mechanical properties.

[0038] In Comparative Example 3, the amount of microencapsulated flame retardant was halved, resulting in a significant drop in the flame retardant rating to V-2 compared to Example 1. Insufficient flame retardant content prevented the formation of a sufficiently thick and strong expanded char layer on the material surface, leading to inadequate heat and oxygen insulation and failing to meet flame retardant performance standards.

[0039] In Example 4, the reduced amount of microcapsule shell precursor resulted in a decrease in flame retardancy rating to V-1 compared to Example 1, and defects in thermal shock resistance (minor cracking) were observed. Insufficient methyltrimethoxysilane content led to an incomplete or excessively thin silicone resin shell. This reduced the shell's protective effect on the core material, making it more susceptible to premature decomposition or damage during processing or thermal shock, thus affecting flame retardancy efficiency and the local thermal stability of the composite material.

[0040] Example 5 omits the calcination step of porous silica-coated calcium carbonate, resulting in significantly worse thermal shock resistance and thermal aging resistance compared to Example 1. The unremoved template agent (CTAB) decomposes at high temperatures, generating gas and causing blistering during thermal shock. Simultaneously, residual organic matter affects the interfacial stability between the filler and the matrix, accelerating material degradation during long-term thermal aging.

[0041] Comparative Example 4, without the addition of microencapsulated intumescent flame retardant, produced a material that was completely non-flame retardant and failed the UL94 test. The intumescent flame retardant is the primary source of the system's flame-retardant function. Without it, the material cannot form an expanded char layer in a flame and will continue to burn.

[0042] Comparative Example 5, without porous silica-coated calcium carbonate, exhibited the worst mechanical properties and heat aging resistance compared to Example 1. Porous silica-coated calcium carbonate plays a crucial reinforcing and thermal stabilizing role in the system. Its absence significantly reduced the matrix strength, toughness, and long-term thermal stability, demonstrating that this modified filler is indispensable for achieving high strength and excellent aging resistance.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength fire-resistant and flame-retardant wire and cable, characterized in that, The product includes a conductor and a sheath layer, wherein the sheath layer comprises the following raw materials in parts by weight: 20-35 parts of low-density polyethylene, 15-25 parts of ethylene-vinyl acetate copolymer, 10-15 parts of polyethylene-vinyl acetate, 15-20 parts of porous silica-coated calcium carbonate microspheres, 15-25 parts of microencapsulated intumescent flame retardant, 1-1.5 parts of antioxidant, 0.5-1 part of zinc stearate, and 2-3 parts of sodium dodecyl sulfonate; The microencapsulated intumescent flame retardant is a microcapsule made of ammonium polyphosphate and pentaerythritol as the core material and hydrolyzed condensed organosilicon resin as the shell material.

2. The high-strength fire-resistant and flame-retardant wire and cable according to claim 1, characterized in that, The preparation method of the microencapsulated intumescent flame retardant includes the following steps: Ammonium polyphosphate and pentaerythritol were added sequentially to deionized water, and the mixture was heated in a water bath to 40±2℃ and stirred continuously at this temperature for 60±10 minutes to form a slurry. An aqueous acetic acid solution was added dropwise to control the pH of the system to 4.

0. Methyltrimethoxysilane and anhydrous ethanol were mixed and diluted to obtain a diluted solution. Under the conditions of 40±2℃ and 500±50 rpm stirring, the diluted solution was slowly added dropwise to the slurry at a rate of 2 drops / second. After the addition was completed, the temperature was maintained at 40±2℃ and the stirring speed at 500±50 rpm, and the reaction was continued for 2±0.5 hours. Subsequently, a curing polycondensation reaction was carried out for 5±1 hours. After the reaction was completed, the slurry was naturally cooled to room temperature, filtered, washed, dried, and ground through a 200-mesh sieve to obtain the final product.

3. The high-strength fire-resistant and flame-retardant wire and cable according to claim 2, characterized in that, The weight ratio of deionized water, ammonium polyphosphate, pentaerythritol, methyltrimethoxysilane and anhydrous ethanol is 240-260:75-85:15-25:10-14:18-22.

4. A high-strength fire-resistant and flame-retardant wire and cable according to claim 2, characterized in that, The curing polycondensation reaction step includes: raising the temperature of the reaction system to 75±5℃ at a heating rate of 1℃ / min, and carrying out the curing polycondensation reaction by stirring at 500±50 rpm at 75±5℃.

5. A high-strength fire-resistant and flame-retardant wire and cable according to claim 1, characterized in that, The method for preparing the porous silica-coated calcium carbonate microspheres includes: using hexadecyltrimethylammonium bromide as a template agent, performing a sol-gel reaction on the surface of the calcium carbonate microspheres with tetraethyl orthosilicate to form a porous silica shell, and then removing the template agent by calcination to obtain the porous silica-coated calcium carbonate microspheres.

6. A high-strength fire-resistant and flame-retardant wire and cable according to claim 5, characterized in that, The preparation steps of the porous silica shell include: anhydrous ethanol, deionized water, and hexadecyltrimethylammonium bromide are stirred at 400±50 rpm in a water bath at 35±2℃ until the hexadecyltrimethylammonium bromide is completely dissolved; calcium carbonate microspheres are added and stirring is continued for 30±5 minutes; concentrated ammonia is added to the above system at once and stirred to alkalize the system; then tetraethyl orthosilicate is added to the reaction system; after the addition is complete, the temperature is maintained at 35±5℃ and the stirring speed is 400±50 rpm, and the reaction is continued for 24±2 hours. After the reaction is completed, the product is obtained by centrifugation, washing, and drying.

7. A high-strength fire-resistant and flame-retardant wire and cable according to claim 5, characterized in that, The calcination step includes: placing the dried porous silica shell powder into a muffle furnace, heating it from room temperature to 550±50℃ at a heating rate of 2℃ / min under an air atmosphere, calcining it at this temperature for 4±1 hours, and then naturally cooling it to room temperature to obtain porous silica-coated calcium carbonate microspheres.

8. A high-strength fire-resistant and flame-retardant wire and cable according to claim 1, characterized in that, The antioxidants include antioxidant 1010 and antioxidant 168 in a weight ratio of 1:2-3.

9. A method for preparing a high-strength fire-resistant and flame-retardant wire and cable as described in any one of claims 1-8, characterized in that, step... include: Prepare the raw materials of each component according to the formula, premix them at a speed of 900-1000 rpm for 5-10 minutes to obtain a premix. Then, perform intensive mixing on the premix at a temperature of 130-140℃ for 15-20 minutes. After intensive mixing, extrude the mixture onto the outer layer of the conductor to obtain the high-strength fire-retardant wire and cable.

10. The method for preparing high-strength fire-resistant and flame-retardant wires and cables according to claim 9, characterized in that, During the extrusion process, the temperature is 160-200℃ and the screw speed is 200-400rpm.

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