A fire-resistant power cable and its preparation method and application

Abstract

The present invention relates to a fire-resistant cable and its preparation method and application. The fire-resistant power cable includes a conductor core layer, a silicone rubber insulation layer, a fire-resistant mica filling layer, a shielding layer and a fire-resistant flame-retardant sheath layer. When preparing a magnesium hydroxide flame retardant, the present invention adds phytic acid piperazine so that it is adsorbed on the surface of the magnesium hydroxide, forming electrostatic repulsion or steric hindrance, thereby constructing a protective layer on the surface of the particles to prevent particle agglomeration. In addition, after the phytic acid piperazine modified magnesium hydroxide is compounded with expanded graphite and zinc stannate, it exhibits a significant synergistic flame retardant effect, achieving efficient flame retardant and fire-resistant properties of the cable material. The present invention also adds a refractory filler to the polypropylene cable sheath layer, further improving the flame retardancy and fire resistance of the cable, and ensuring that the cable does not drip during the combustion process; this allows the cable to maintain safe and reliable performance under extreme conditions such as fire, providing strong protection for personnel safety and fire rescue.

Description

Technical Field

[0001] The present invention belongs to the technical field of cables, and more particularly, relates to a fire-resistant cable and a preparation method and application thereof. Background Art

[0002] Fire-resistant cables are specially designed to maintain normal operation for a limited period during a fire incident, even if external flames are still burning, ensuring line integrity and the proper functioning of equipment. Due to their exceptional fire resistance and reliability, these cables are widely used in critical locations such as high-rise buildings, railways, airports, large power stations, and important industrial and mining enterprises. These areas are closely related to fire safety and lifesaving, and therefore, fire-resistant cables play a vital role in ensuring personnel safety, maintaining system operations, and minimizing fire losses.

[0003] Currently, the fire-resistant, flame-retardant sheathing of common power cables is primarily composed of flame-retardant polyolefins, achieved by adding organic or inorganic flame retardants to the polyolefin material. Organic flame retardants, such as phosphate esters, ammonium polyphosphate, and melamine, are characterized by their low dosage, high price, and limited smoke suppression. In contrast, inorganic flame retardants are widely used in cable sheathing materials due to their advantages, such as good thermal stability, environmental friendliness, and low production costs. Commonly used inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, antimony compounds, and zinc stannate. Aluminum hydroxide and magnesium hydroxide have the advantages of being non-toxic and low-cost, but they require a large addition amount and can significantly affect the mechanical strength of the material. Zinc stannate, as an inorganic flame retardant, is considered a highly effective, green flame retardant due to its environmental friendliness, non-toxicity, excellent smoke suppression, and high flame retardant efficiency. Furthermore, phytic acid (PA), a renewable biomass resource found widely in plant seeds, is also used as a renewable, environmentally friendly flame retardant due to its wide availability and environmental friendliness. In the research of cable flame retardants, compounding or modification is often used to further improve the flame retardant efficiency. For example, by compounding different types of flame retardants or modifying the surface of flame retardants, the flame retardant and mechanical properties of the material can be significantly improved.

[0004] To address the challenges of current flame retardants, such as poor flame retardancy, high dosage, and severe environmental pollution, the inventors have developed a green, low-toxic, and highly effective functional flame retardant specifically for fire-resistant cable sheathing. This new flame retardant ensures safe cable operation while minimizing the emission of toxic components and smoke during a fire, thereby reducing environmental pollution and harm to human health. In the event of a fire, the cable combustion releases only a small amount of smoke, effectively reducing smoke density and toxic gas emissions, significantly improving fire safety. By optimizing the formulation and production process, this flame retardant reduces the dosage of traditional flame retardants while improving the flame retardancy of the cable sheathing material and the fire resistance of the cable. Furthermore, the new flame retardant utilizes the environmentally friendly material magnesium hydroxide, which is not only non-toxic and environmentally friendly but also forms a protective layer during combustion, further reducing smoke generation. This innovative flame retardant technology not only meets modern environmental and safety standards but also provides an efficient and sustainable solution for the cable industry, helping to promote the development of low-smoke, halogen-free, fire-resistant, and environmentally friendly cable materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a green and environmentally friendly functional flame retardant for the sheath layer of fire-resistant power cables. The sheath layer prepared by the flame retardant is used for fire-resistant cable materials. It not only has low smoke, high flame retardancy and excellent fire resistance, but also does not drip during the combustion process. This enables the cable to maintain safe and reliable performance under extreme conditions such as fire, providing strong protection for personnel safety and fire rescue.

[0006] The invention provides a fire-resistant power cable, comprising a conductor core layer, a silicone rubber insulation layer, a fire-resistant mica filling layer, a shielding layer, and a fire-resistant flame-retardant sheath layer.

[0007] The fire-resistant and flame-retardant sheath layer comprises the following raw materials: 80-100 parts of polypropylene, 20-35 parts of functional flame retardant, 10-20 parts of compatibilizer, 15-25 parts of fire-resistant filler, 1-3 parts of silane coupling agent, 1-5 parts of antioxidant, and 1-5 parts of lubricant.

[0008] The preparation method of the functional flame retardant comprises the following steps:

[0009] Step S1, dissolving 5-10 parts of phytic acid in 20-50 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 0.5-5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 6-8 with ammonia water, heating to react, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0010] Step S2, dissolving 20-30 parts of a soluble magnesium salt in deionized water to prepare a 1-5 mol / L magnesium salt solution, adding 2-5 parts of the phytic acid piperazine of step S1, slowly adding an alkaline solution dropwise to the magnesium salt solution under stirring, stirring to react, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of the soluble magnesium salt to the alkaline solution is 1:2.1-3.5;

[0011] Step S3: melt-extrude 30-50 parts of the modified magnesium hydroxide obtained in step S2, 8-10 parts of expanded graphite, 5-8 parts of zinc stannate, and 60-100 parts of polypropylene through a screw, and granulate to obtain a functional flame retardant.

[0012] The soluble magnesium salt is any one or more of magnesium chloride, magnesium sulfate, and magnesium nitrate; the alkaline solution is any one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0013] The refractory filler includes at least one of mica powder, zirconium oxide, aluminum oxide, expanded perlite, and silicon nitride.

[0014] The D50 particle size of the refractory filler is 50-100 μm.

[0015] The heating reaction temperature in step S1 is 50-80° C., and the reaction time is 3-6 hours.

[0016] The stirring reaction temperature in step S2 is 40-80° C., and the reaction time is 1-5 h.

[0017] The melt extrusion temperature in step S3 is 180-230° C., the screw speed is 300-450 r / min, and the screw aspect ratio is 48:1.

[0018] The polypropylene is homopolymerized polypropylene or propylene-ethylene copolymer, and the melt index of the polypropylene resin under the test conditions of 230° C. and 2.16 kg is 10 to 150 g / 10 min.

[0019] The compatibilizer is at least one of maleic anhydride grafted polypropylene and maleic anhydride grafted polyethylene.

[0020] The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0021] The antioxidant is at least one of antioxidant 1010 and antioxidant 168.

[0022] The lubricant is at least one of stearate, PE wax and oleamide.

[0023] The present invention utilizes the reaction of aminopiperazine with phytic acid based on the ionic reaction between the amino group (-NH2) in aminopiperazine and the phosphate group (-PO3H2) in phytic acid. Phytic acid (PA) is a polyphosphate compound containing multiple phosphate groups. Aminopiperazine, with its basic amino group, reacts with the acidic phosphate groups in phytic acid to form phytic acid piperazine (PA-Pi). During the reaction, the phosphate groups of phytic acid and the amino groups of aminopiperazine form ionic bonds, creating a bio-based flame retardant containing nitrogen and phosphorus. The resulting phytic acid piperazine exhibits excellent thermal stability and flame retardancy, forming a protective char layer during combustion to suppress the release of heat and smoke. Furthermore, as a bio-based flame retardant, phytic acid piperazine offers advantages such as environmental friendliness, low toxicity, and high flame retardancy.

[0024] The present invention adds phytic acid piperazine during the preparation of the magnesium hydroxide flame retardant, and the phytic acid piperazine is adsorbed on the surface of the magnesium hydroxide to form electrostatic repulsion or steric hindrance, thereby forming a protective layer on the surface of the particles, preventing the particles from contacting each other and preventing the magnesium hydroxide particles from agglomerating. The phytic acid piperazine can be used as a stabilizer for the magnesium hydroxide, thereby improving the compatibility of the magnesium hydroxide with a polypropylene matrix, and improving the dispersibility and flame retardant efficiency, thereby improving the comprehensive performance of the fire-resistant cable.

[0025] The functional flame retardant of the present invention also includes expanded graphite and zinc stannate, which exhibit a significant synergistic flame retardant effect with modified magnesium hydroxide in the composite material. Expanded graphite expands rapidly when heated, forming a dense carbon layer that covers the surface of the material, acting as a heat and oxygen barrier. Magnesium hydroxide reduces the material temperature and delays combustion through a dehydration endothermic reaction. When zinc stannate and magnesium hydroxide are used in combination, they can significantly improve the material's flame retardant efficiency and smoke suppression effect. Zinc stannate promotes the dehydration endothermic reaction of magnesium hydroxide by catalyzing the carbonization of the polymer surface, thereby enhancing the flame retardant effect. The addition of expanded graphite can significantly improve the flame retardant properties and mechanical properties of the composite material while reducing the amount of magnesium hydroxide used. When expanded graphite, zinc stannate, and magnesium hydroxide are used together, a denser, continuous carbon layer can be formed, further improving the material's flame retardant properties. A better flame retardant effect can be achieved at a lower flame retardant dosage while reducing the impact on the material's mechanical properties.

[0026] The present invention uses high-quality refractory fillers such as mica powder, zirconium oxide, aluminum oxide, expanded perlite and silicon nitride to fill the polypropylene cable sheath layer. On the one hand, refractory materials such as mica powder and aluminum oxide can significantly improve the charring and crusting properties of the cable sheath, so that there is no dripping during the combustion process, thereby reducing the risk of fire spread and increasing the anti-dripping performance of the cable material. When burned, these materials will form a strong ceramic structure, enhance the fire resistance of the sheath, and effectively reduce the heat release rate. On the other hand, materials such as mica powder, zirconium oxide and aluminum oxide can also significantly improve the mechanical strength and toughness of the cable sheath and reduce wear. Therefore, using these refractory materials to fill polypropylene as the cable sheath layer can significantly improve the flame retardancy, fire resistance, smoke density and anti-dripping performance of the cable, so that it can still maintain safe and reliable performance under extreme conditions such as fire.

[0027] The present invention also provides a method for preparing a fire-resistant power cable, comprising the following steps:

[0028] (1) Preparation of conductor core layer: The conductor material is drawn to obtain a wire to prepare the conductor core layer;

[0029] (2) preparing a silicone rubber insulation layer: using an extrusion die to coat the silicone rubber insulation layer on the surface of the conductor core in step (1) to obtain a silicone rubber insulation layer;

[0030] (3) preparing a fire-resistant mica filling layer: wrapping the fire-resistant mica filling layer on the surface of the silicone rubber insulation layer in step (2) to obtain a fire-resistant mica filling layer;

[0031] (4) preparing a shielding layer: coating the surface of the refractory mica filling layer in step (3) with a shielding layer to obtain a shielding layer;

[0032] (5) Preparation of a fire-resistant flame-retardant sheath layer: Extruding a fire-resistant flame-retardant sheath layer on the surface of the shielding layer in step (4) to obtain a fire-resistant cable.

[0033] The present invention also provides an application of the fire-resistant power cable in the fields of high-rise buildings, subways and airports.

[0034] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0035] 1) In the preparation of the magnesium hydroxide flame retardant, the present invention adds piperazine phytate as a stabilizer. Piperazine phytate can adsorb on the surface of magnesium hydroxide particles, forming a protective film on the particle surface through electrostatic repulsion or steric hindrance. This protective film effectively prevents contact between magnesium hydroxide particles, thereby preventing particle agglomeration. Therefore, piperazine phytate not only serves as a stabilizer for magnesium hydroxide but also significantly improves its compatibility with the polypropylene matrix, improving its dispersibility in the matrix and thus enhancing its flame retardant efficiency. This modification method can significantly enhance the overall performance of fire-resistant cables.

[0036] 2) This invention utilizes a flame retardant compounded with phytic acid-piperazine-modified magnesium hydroxide, expanded graphite, and zinc stannate to achieve highly effective flame retardancy and fire resistance in cable materials. The phytic acid-piperazine-modified magnesium hydroxide contains phytic acid and piperazine, which serve as an acid source. During combustion, the phytic acid decomposes and promotes the formation of a char layer within the composite flame retardant. Simultaneously, the zinc stannate forms a glass-like substance at high temperatures, coating the surface of the char layer, sealing pores and forming a dense layer that effectively prevents the escape of internal combustible gases and the ingress of external oxygen. Expanded graphite rapidly expands upon heating, forming a dense char layer that covers the surface of the material, providing both thermal and oxygen insulation. These three flame retardants work synergistically, significantly enhancing the flame retardancy and fire resistance of the cable material. Testing has shown that the oxygen index of the fire-resistant cable sheath material can reach 41%. Furthermore, the fire-resistant cable line withstands a 1400°C fire temperature for 180 minutes without significant damage, demonstrating excellent fire resistance.

[0037] 3) By adding fire-resistant fillers to the polypropylene cable sheath layer, the present invention significantly improves the flame retardancy and fire resistance of the cable compared to fillers such as talc and glass fiber, so that it can still maintain safe and reliable performance under extreme conditions such as fire. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be further described below by way of specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention, which shall be subject to the claims.

[0039] Experimental Materials:

[0040] Homopolymer polypropylene resin 1#: PPH-Y26, having a melt flow rate of 30 g / 10 min at 230° C. and a load of 2.16 kg, purchased from Sinopec Sales Co., Ltd., East China Branch.

[0041] Homopolymer polypropylene resin 2#: PP M60T, having a melt flow rate of 56 g / 10 min at 230° C. and a load of 2.16 kg, purchased from the East China Branch of Sinopec Chemical Sales Co., Ltd.

[0042] Copolymer polypropylene resin 3#: PP K9930H, having a melt flow rate of 30 g / 10 min at 230° C. and a load of 2.16 kg, and an ethylene propylene rubber content of 29.1 wt %, purchased from Maoming Petrochemical.

[0043] Copolymer polypropylene resin 4#: PP SP179 (Zhenhai), having a melt flow rate of 10 g / 10 min at 230° C. and a load of 2.16 kg, and an ethylene propylene rubber content of 25 wt %, was purchased from Sinopec Zhenhai Petrochemical.

[0044] Compatibilizer 1#: maleic anhydride grafted polypropylene, commercially available.

[0045] Compatibilizer 2#: maleic anhydride grafted polyethylene, commercially available.

[0046] Refractory fillers, coupling agents, antioxidant 1010, antioxidant 168, lubricants, 2-aminopiperazine, phytic acid, expanded graphite, zinc stannate, etc. are all commercially available. Unless otherwise specified, a component (e.g., lubricant) in parallel examples and comparative examples of the present invention is the same commercially available product; the parts per million of each component in the examples of the present invention are equivalent to grams or kilograms under the same conditions.

[0047] 1. The preparation example of functional flame retardant is as follows:

[0048] Example 1 Preparation of functional flame retardant 1#

[0049] Step S1, dissolving 5 parts of phytic acid in 30 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 0.5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 7 with ammonia water, heating to 50° C. for 6 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0050] Step S2, dissolving 20 parts of magnesium chloride in deionized water to prepare a 2 mol / L magnesium salt solution, adding 2 parts of phytic acid piperazine prepared in step S1, slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium chloride solution under stirring, stirring and reacting at 40° C. for 5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.5;

[0051] Step S3, 30 parts of the modified magnesium hydroxide of step S2, 8 parts of expanded graphite, 6 parts of zinc stannate, and 70 parts of polypropylene are melt-extruded with a screw at 190°C and granulated to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0052] Example 2 Preparation of functional flame retardant 2#

[0053] Step S1, dissolving 10 parts of phytic acid in 50 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 4 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 8 with ammonia water, heating to 70° C. for 3 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0054] Step S2, dissolving 25 parts of magnesium nitrate in deionized water to prepare a 5 mol / L magnesium salt solution, adding 5 parts of phytic acid piperazine prepared in step S1, and slowly adding 2 mol / L potassium hydroxide dropwise to the magnesium nitrate solution under stirring, stirring and reacting at 60° C. for 2.5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium nitrate to potassium hydroxide solution is 1:3;

[0055] Step S3: melt-extrude 50 parts of the modified magnesium hydroxide obtained in step S2, 10 parts of expanded graphite, 5 parts of zinc stannate, and 100 parts of polypropylene through a screw, and granulate to obtain a functional flame retardant; the screw speed is 350 r / min, the screw melting temperature is 210° C., and the screw aspect ratio is 48:1.

[0056] Example 3 Preparation of functional flame retardant 3#

[0057] Step S1, dissolving 8 parts of phytic acid in 40 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 4 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 7 with ammonia water, heating to 60° C. for 3.5 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0058] Step S2, dissolving 20 parts of magnesium sulfate in deionized water to prepare a 3 mol / L magnesium salt solution, adding 4 parts of phytic acid piperazine prepared in step S1, and slowly adding 1 mol / L potassium hydroxide dropwise to the magnesium salt solution under stirring, stirring and reacting at 70° C. for 2 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium sulfate to potassium hydroxide solution is 1:2.4;

[0059] Step S3: 40 parts of the modified magnesium hydroxide obtained in step S2, 8 parts of expanded graphite, 8 parts of zinc stannate, and 70 parts of polypropylene are melt-extruded through a screw and granulated to obtain a functional flame retardant; the screw speed is 400 r / min, the screw melting temperature is 220° C., and the screw aspect ratio is 48:1.

[0060] Example 4 Preparation of functional flame retardant 4#

[0061] Step S1, dissolving 10 parts of phytic acid in 35 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 3.5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 6 with ammonia water, heating to 80° C. for 3 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0062] Step S2, dissolving 35 parts of magnesium sulfate in deionized water to prepare a 2 mol / L magnesium salt solution, adding 5 parts of phytic acid piperazine prepared in step S1, slowly adding 1.5 mol / L sodium hydroxide dropwise to the magnesium salt solution under stirring, stirring and reacting at 80° C. for 1.5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium sulfate to potassium hydroxide solution is 1:2.5;

[0063] Step S3: 35 parts of the modified magnesium hydroxide of step S2, 9 parts of expanded graphite, 7 parts of zinc stannate, and 60 parts of polypropylene are melt-extruded through a screw and granulated to obtain a functional flame retardant; the screw speed is 450 r / min, the screw melting temperature is 200° C., and the screw aspect ratio is 48:1.

[0064] Example 5 Preparation of functional flame retardant 5#

[0065] Step S1, dissolving 7 parts of phytic acid in 35 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 2 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 7 with ammonia water, heating to 50° C. for 4 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0066] Step S2, dissolving 25 parts of magnesium chloride in deionized water to prepare a 1.5 mol / L magnesium salt solution, adding 3 parts of phytic acid piperazine prepared in step S1, and slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium salt solution under stirring, stirring and reacting at 50° C. for 4.5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.3;

[0067] Step S3, 40 parts of the modified magnesium hydroxide of step S2, 10 parts of expanded graphite, 7 parts of zinc stannate, and 90 parts of polypropylene are melt-extruded with a screw at 220°C and granulated to obtain a functional flame retardant; the screw speed is 380 r / min, and the screw aspect ratio is 48:1.

[0068] Example 6 Preparation of functional flame retardant 6#

[0069] Step S1, dissolving 20 parts of magnesium chloride in deionized water to prepare a 2 mol / L magnesium salt solution, slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium chloride solution under stirring, stirring at 40° C. for 5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.5;

[0070] Step S2, 30 parts of the modified magnesium hydroxide of step S2, 8 parts of expanded graphite, 6 parts of zinc stannate, and 70 parts of polypropylene are melt-extruded with a screw at 190°C and granulated to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0071] Example 7 Preparation of functional flame retardant 7#

[0072] Step S1, dissolving 20 parts of magnesium chloride in deionized water to prepare a 2 mol / L magnesium salt solution, adding 2 parts of phytic acid, slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium chloride solution under stirring, stirring and reacting at 40° C. for 5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.5;

[0073] Step S2: 30 parts of the modified magnesium hydroxide prepared in step S1, 8 parts of expanded graphite, 6 parts of zinc stannate, and 70 parts of polypropylene are melt-extruded with a screw at 190° C. and granulated to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0074] Example 8 Preparation of functional flame retardant 8#

[0075] Step S1, dissolving 5 parts of phytic acid in 30 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 0.5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 7 with ammonia water, heating to 50° C. for 6 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0076] Step S2, dissolving 20 parts of magnesium chloride in deionized water to prepare a 2 mol / L magnesium salt solution, adding 2 parts of phytic acid piperazine prepared in step S1, slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium salt solution under stirring, stirring and reacting at 40° C. for 5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.5;

[0077] Step S3, 30 parts of the modified magnesium hydroxide of step S2, 6 parts of zinc stannate, and 78 parts of polypropylene are melt-extruded with a screw at 190°C and granulated to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0078] Example 9 Preparation of functional flame retardant 9#

[0079] Step S1, dissolving 5 parts of phytic acid in 30 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 0.5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 7 with ammonia water, heating to 50° C. for 6 hours, cooling to room temperature, and filtering to obtain phytic acid piperazine;

[0080] Step S2, dissolving 20 parts of magnesium chloride in deionized water to prepare a 2 mol / L magnesium salt solution, adding 2 parts of phytic acid piperazine prepared in step S1, slowly adding 1 mol / L sodium hydroxide dropwise to the magnesium chloride solution under stirring, stirring and reacting at 40° C. for 5 hours, filtering, and washing to obtain modified magnesium hydroxide; the molar ratio of magnesium chloride to sodium hydroxide is 1:2.5;

[0081] Step S3: melt-extrude 30 parts of the modified magnesium hydroxide obtained in step S2, 8 parts of expanded graphite, and 76 parts of polypropylene through a screw at 190° C. and granulate to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0082] Example 10 Preparation of functional flame retardant 10#

[0083] 30 parts of magnesium hydroxide, 8 parts of expanded graphite, 6 parts of zinc stannate, and 70 parts of polypropylene are melt-extruded through a screw at 190° C. and granulated to obtain a functional flame retardant; the screw speed is 300 r / min, and the screw aspect ratio is 48:1.

[0084] 2. The present invention also includes a fire-resistant power cable prepared by using functional flame retardants 1#-10# for a fire-resistant flame-retardant sheath layer, comprising the following steps:

[0085] (1) Preparation of conductor core layer: The conductor material is drawn to obtain a wire to prepare the conductor core layer;

[0086] (2) preparing a silicone rubber insulation layer: using an extrusion die to coat the silicone rubber insulation layer on the surface of the conductor core in step (1) to obtain a silicone rubber insulation layer;

[0087] (3) preparing a fire-resistant mica filling layer: wrapping the fire-resistant mica filling layer on the surface of the silicone rubber insulation layer in step (2) to obtain a fire-resistant mica filling layer;

[0088] (4) preparing a shielding layer: coating the surface of the refractory mica filling layer in step (3) with a shielding layer to obtain a shielding layer;

[0089] (5) Preparation of a fire-resistant flame-retardant sheath layer: Extruding a fire-resistant flame-retardant sheath layer on the surface of the shielding layer in step (4) to obtain a fire-resistant cable.

[0090] The conductor core layer diameter of the fire-resistant cable in the application example and the comparative application example is 1.5 cm, the thickness of the silicone rubber insulation layer is 2.0 mm, the thickness of the fire-resistant mica filling layer is 1.5 mm, the thickness of the shielding layer is 1.5 mm, and the thickness of the fire-resistant flame-retardant sheath layer is 3.5 mm.

[0091] The difference between Application Example 1-10 and Comparative Application Example 1-10 is that the fire-resistant and flame-retardant sheath layers are different, as shown in Table 1 and Table 2.

[0092] Table 1 Distribution ratio of each group in application examples 1-10 (parts by weight)

[0093]

[0094] Table 2 Comparative Examples 1-10 Distribution Ratios of Each Group (Parts by Weight)

[0095]

[0096] Performance Testing

[0097] The fire-resistant power cables prepared in Application Examples 1-10 and Comparative Application Examples 1-10 were subjected to relevant performance tests. The specific test methods are as follows:

[0098] (1) Fire resistance: Refer to GBT19216.21-2003 "Line integrity of electrical or optical cables under fire conditions" to test the cable's fire resistance. Fire temperatures are 1200°C and 1400°C for 180 minutes to detect line damage. The results are classified into different levels: A - no obvious line damage; B - obvious line loss; C - line break.

[0099] (2) Smoke density (minimum transmittance): The smoke density of the cable is tested according to the standard "GB / T 17651.2-2021 Determination of smoke density of electric cables or optical cables burning under specific conditions".

[0100] (3) Oxygen index: The oxygen index of the sample is determined according to the method of GB / T 2406.2-2009 "Determination of combustion behavior of plastics using oxygen index method".

[0101] (4) Dripping performance: Take a 10 cm long cable material and burn it with a blowtorch with a heat power of 500 W for 20 seconds. The flame height is 150 mm, and then stop for 15 seconds. Repeat the burning five times. Calculate the content of dripping material during the burning process to measure the degree of cable burn damage. Dripping rate = (weight before burning - weight after burning) / weight before burning × 100%. The test results are shown in Table 3.

[0102] (5) Flame retardancy: UL94 vertical burning grade, tested according to GB / T 2408-2008 for the UL94 vertical burning grade of shielded cables.

[0103] The test results are shown in Table 3.

[0104] Table 3

[0105]

[0106] The test results in Table 3 show that the fire-resistant cable of the present invention exhibits excellent flame retardancy. Its oxygen index exceeds 41%, achieving the UL94 vertical combustion rating of V0. Furthermore, the cable's smoke density (minimum light transmittance) exceeds 80%, meaning it produces less smoke during combustion, facilitating safety and firefighting efforts. Regarding fire resistance, the cable survived a fire temperature of 1200°C for 180 minutes without significant damage, and also survived a fire temperature of 1400°C for 180 minutes without significant damage. Furthermore, its drip rate (burning rate) was less than 2.65%, further demonstrating its excellent fire resistance.

[0107] By comparing the results of application example 1 with comparative application examples 1 and 2, it can be seen that the addition of phytic acid piperazine as a stabilizer for magnesium hydroxide flame retardant can significantly improve the performance of fire-resistant cables. Phytic acid piperazine is adsorbed on the surface of magnesium hydroxide, forming electrostatic repulsion or steric hindrance, thereby building a protective layer on the surface of the particles, effectively preventing particle agglomeration. This not only improves the compatibility of magnesium hydroxide with the polypropylene matrix, but also improves its dispersibility and flame retardant efficiency, thereby significantly enhancing the flame retardancy, fire resistance and smoke density performance of the fire-resistant cable. In addition, phytic acid piperazine itself has good thermal stability and flame retardant properties, can form a protective carbon layer during combustion, suppress the release of heat and smoke, and further improve the flame retardancy and fire resistance of the cable. In contrast, comparative application example 1 does not add phytic acid piperazine as a magnesium hydroxide stabilizer, while comparative application example 2 only uses phytic acid as a stabilizer, and the prepared cable is not as good as application example 1 in terms of flame retardancy and fire resistance.

[0108] By comparing the results of Application Example 1 with Comparative Application Examples 3-5, it can be found that the flame retardant compounded with phytic acid piperazine-modified magnesium hydroxide, expanded graphite, and zinc stannate in Application Example 1 has a significant synergistic effect, achieving efficient flame retardancy and fire resistance of the cable material. The phytic acid piperazine-modified magnesium hydroxide contains phytic acid and piperazine, which can serve as an acid source. During combustion, the phytic acid decomposes and promotes the formation of a carbon layer by the composite flame retardant. At the same time, the zinc stannate forms a glass-like substance at high temperatures, coating the surface of the carbon layer, sealing the pores and forming a dense layer, effectively preventing the escape of internal combustible gases and the entry of external oxygen. When heated, the expanded graphite expands rapidly, forming a dense carbon layer that covers the surface of the material, providing heat and oxygen insulation. These three flame retardants work synergistically to significantly improve the flame retardancy and fire resistance of the cable material. Testing showed that the oxygen index of the fire-resistant cable sheath material in Application Example 1 reached over 41%. The fire-resistant cable line withstood a fire temperature of 1400°C for 180 minutes without significant damage, exhibited a smoke density greater than 80%, and a drip rate less than 3%, demonstrating excellent flame retardancy and fire resistance. In contrast, the flame retardancy and fire resistance of Comparative Application Example 3, which lacked expanded graphite, the zinc stannate in Comparative Application Example 4, and the phytic acid piperazine modification of the magnesium hydroxide in Comparative Application Example 5 were significantly lower than those of Application Example 1.

[0109] Comparison of Application Example 1 with Comparative Application Examples 6-9 reveals that the absence of a functional flame retardant in Comparative Application Example 6 resulted in a significant decrease in the flame retardancy, smoke density, and fire resistance of the fire-resistant cable produced. Comparative Application Examples 7-9, on the other hand, used talc, calcium carbonate, and glass fiber as fillers, respectively, and the fire resistance of the cable materials produced therefrom was significantly lower than the mica powder fire-resistant filler used in Application Example 1. This demonstrates that the present invention significantly enhances the flame retardancy and fire resistance of the cable by selecting mica powder as a filler, a material with excellent fire resistance, enabling it to maintain safe and reliable performance even under extreme conditions such as fire.

[0110] Comparing Application Examples 1 and 10 reveals that the silane coupling agent used in this invention contains two distinct groups: one is a hydrolyzable inorganic group (such as methoxy and ethoxy groups), which reacts with hydroxyl groups on the surface of inorganic fillers to form strong chemical bonds; the other is an organic functional group (such as amino, epoxy, and vinyl groups), which interacts with organic polymers such as polypropylene. When the silane coupling agent is applied to the refractory filler, its inorganic groups react with the hydroxyl groups on the filler surface, reducing the polarity and enhancing the hydrophobicity of the filler surface. This significantly improves the compatibility of the filler with polypropylene, reduces agglomeration of filler particles, and improves the dispersion of the filler in the polypropylene matrix. This improved dispersion ultimately enhances the cable's overall properties, including flame retardancy, fire resistance, and smoke density.

[0111] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, and any modifications, equivalent substitutions, or improvements made within the basic principles and scope of the present invention are deemed to be within the scope of the present invention.

Claims

1. A fire-resistant power cable, characterized in that: It includes conductor core layer, silicone rubber insulation layer, fire-resistant mica filling layer, shielding layer and fire-resistant flame-retardant sheath layer; The fire-resistant flame-retardant sheath layer comprises the following raw materials: 80-100 parts of polypropylene, 20-35 parts of functional flame retardant, 10-20 parts of compatibilizer, 15-25 parts of fire-resistant filler, 1-3 parts of silane coupling agent, 1-5 parts of antioxidant, and 1-5 parts of lubricant; The preparation method of the functional flame retardant comprises the following steps: Step S1, dissolving 5-10 parts of phytic acid in 20-50 parts of deionized water, stirring until completely dissolved to form a transparent solution, then adding 0.5-5 parts of 2-aminopiperazine to the above solution, stirring until completely dissolved, adjusting the pH of the solution system to 6-8 with ammonia water, heating to react, cooling to room temperature, and filtering to obtain phytic acid piperazine; Step S2, dissolving 20-30 parts of a soluble magnesium salt in deionized water to prepare a 1-5 mol / L magnesium salt solution, adding 2-5 parts of the piperazine phytate prepared in step S1, slowly adding the alkaline solution dropwise to the magnesium salt solution under stirring, stirring to react, filtering, and washing to obtain modified magnesium hydroxide; Step S3, melt-extrude 30-50 parts of the modified magnesium hydroxide prepared in step S2, 8-10 parts of expanded graphite, 5-8 parts of zinc stannate, and 60-100 parts of polypropylene through a screw, and granulate to obtain a functional flame retardant; The refractory filler includes at least one of mica powder, zirconium oxide, aluminum oxide, expanded perlite, and silicon nitride.

2. The fire-resistant power cable according to claim 1, characterized in that: In step S2, the soluble magnesium salt is any one or more of magnesium chloride, magnesium sulfate, and magnesium nitrate; the alkaline solution is any one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide; and the molar ratio of the soluble magnesium salt to the alkaline solution is 1:2.1-3.

5.

3. The fire-resistant power cable according to claim 1, characterized in that: The D50 particle size of the refractory filler is 50-100 μm.

4. The fire-resistant power cable according to claim 1, characterized in that: The temperature of the heating reaction in step S1 is 50-80° C., and the reaction time is 3-6 hours; the temperature of the stirring reaction in step S2 is 40-80° C., and the reaction time is 1-5 hours.

5. The fire-resistant power cable according to claim 1, characterized in that: The melt extrusion temperature in step S3 is 180-230° C., the screw speed is 300-450 r / min, and the screw aspect ratio is 48:

1.

6. The fire-resistant power cable according to claim 1, characterized in that: The polypropylene is homopolymerized polypropylene or propylene-ethylene copolymer, and the melt index of the polypropylene resin under the test conditions of 230° C. and 2.16 kg is 10-150 g / 10 min.

7. The fire-resistant power cable according to claim 1, characterized in that: The compatibilizer is at least one of maleic anhydride grafted polypropylene and maleic anhydride grafted polyethylene; the antioxidant is at least one of antioxidant 1010 and antioxidant 168; and the lubricant is at least one of stearate, PE wax and oleamide.

8. The fire-resistant power cable according to claim 1, characterized in that: The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

9. A method for preparing the fire-resistant power cable according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) Preparation of conductor core layer: The conductor material is drawn to obtain a wire to prepare the conductor core layer; (2) preparing a silicone rubber insulation layer: using an extrusion die to coat the silicone rubber insulation layer on the surface of the conductor core in step (1) to obtain a silicone rubber insulation layer; (3) preparing a fire-resistant mica filling layer: wrapping the fire-resistant mica filling layer on the surface of the silicone rubber insulation layer in step (2) to obtain a fire-resistant mica filling layer; (4) preparing a shielding layer: coating the surface of the refractory mica filling layer in step (3) with a shielding layer to obtain a shielding layer; (5) Preparation of a fire-resistant flame-retardant sheath layer: Extruding a fire-resistant flame-retardant sheath layer on the surface of the shielding layer in step (4) to obtain a fire-resistant power cable.

10. Use of the fire-resistant power cable according to any one of claims 1 to 8 in the fields of high-rise buildings, subways, and airports.

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