A halogen-free, low-smoke flame-retardant power cable and its preparation method

Abstract

The present invention discloses a halogen-free, low-smoke flame-retardant power cable and a preparation method thereof, belonging to the field of cable material processing technology. The invention is used to solve the technical problems in the prior art that a large amount of halogen-free flame retardant is added during the processing of the sheath layer of a halogen-free flame-retardant power cable, and the mechanical strength and smoke suppression effect of the cable sheath layer need to be further improved. A halogen-free, low-smoke flame-retardant power cable comprises a plurality of cable cores, a wrapping layer, and a sheath layer arranged in sequence from the inside out; the wrapping layer is obtained by wrapping a wrapping tape around the outside of the plurality of cable cores. The present invention promotes the mutual fusion and uniform dispersion of modified polysiloxane, loaded diatomaceous earth, and low-density polyethylene by using anhydride-modified EVA, and then promotes intermolecular crosslinking under the action of an initiator and high temperature, thereby improving the mechanical strength of the cable sheath layer. At the same time, by optimizing the combination of halogen-free flame retardant additives, the flame retardant properties of the power cable material are improved and the generation of smoke during combustion is suppressed.

Description

Technical Field

[0001] The present invention relates to the technical field of cable material processing, and in particular to a halogen-free and low-smoke flame-retardant power cable and a preparation method thereof. Background Art

[0002] With the increasing safety requirements for power cables in modern construction, transportation, communications, and other industries, flame-retardant cables, as key safety components, have a direct impact on the stable operation of power systems and the safety of life and property. Traditional flame-retardant cables, which often use halogenated flame retardants, have a certain flame-retardant effect, but they release large amounts of toxic smoke and corrosive gases when burned, significantly hindering evacuation and fire fighting, while also causing serious environmental pollution.

[0003] Halogen-free, low-smoke, flame-retardant power cables utilize halogen-free flame-retardant materials. Through a special formulation and preparation process, they achieve flame retardancy while significantly reducing the amount of smoke generated and toxicity during combustion. Currently, the insulation and sheathing materials for halogen-free, low-smoke, flame-retardant power cables primarily utilize low-smoke, halogen-free, flame-retardant polyolefin materials. These materials impart excellent flame-retardant and low-smoke properties to the cables by adding additives such as flame retardants and smoke suppressants. However, current halogen-free flame-retardant systems primarily rely on metal oxides (such as Al2O3 and MgO), phosphorus-based flame retardants, or intumescent flame retardants. These materials are often added in high amounts, requiring approximately 50% to meet flame retardant standards. This significantly reduces the mechanical properties of the cable sheath (such as tensile strength and elongation at break). Furthermore, traditional halogen-free flame retardants have limited smoke suppression effects, making it difficult to meet stringent low-smoke requirements.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a halogen-free, low-smoke flame-retardant power cable and a preparation method thereof, so as to solve the technical problems in the prior art that a large amount of halogen-free flame retardant is added during the processing of the sheath layer of the halogen-free flame-retardant power cable, and the mechanical strength and smoke suppression effect of the cable sheath layer need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A halogen-free, low-smoke flame-retardant power cable, comprising a plurality of cable cores, a wrapping layer and a sheath layer arranged sequentially from the inside to the outside;

[0008] The wrapping layer is obtained by wrapping a wrapping tape around the outside of a plurality of cable cores;

[0009] The sheath layer comprises the following components in parts by weight: 70-80 parts of low-density polyethylene, 10-15 parts of anhydride-modified EVA, 20-28 parts of modified polysiloxane, 25-40 parts of supported diatomaceous earth, 0.8-1.2 parts of dicumyl peroxide and 2-3 parts of additives.

[0010] Furthermore, the preparation method of the anhydride-modified EVA is as follows: EVA and maleic anhydride are added to a torque rheometer at a temperature of 160-170° C. and kneaded for 3 minutes, an initiator is added to the torque rheometer in batches, the mixture is kept warm and mixed for 8-12 minutes, and post-processed to obtain the anhydride-modified EVA.

[0011] Furthermore, the amount ratio of the EVA, maleic anhydride and initiator is 80g:1.2-1.5g:0.2-0.4g, the initiator is diisopropylbenzene peroxide, and the post-treatment includes: crushing the grafted material and mixing it with toluene at 1g:8mL, raising the temperature of the reaction system to 85-95°C, stirring while keeping warm until the system is dissolved, removing the heating, adding acetone to the reaction system, a large amount of solid precipitated, filtering, washing the filter cake with acetone twice and then drying it, transferring the filter cake to a drying oven at a temperature of 50-60°C, and vacuum drying to constant weight to obtain anhydride-modified EVA.

[0012] Furthermore, the modified polysiloxane is obtained by processing the following steps:

[0013] A1. Under an inert atmosphere, melamine and N,N-dimethylformamide were mixed and stirred until the system was dissolved. The temperature of the reaction system was raised to 50-60°C, and 1-dimethoxy(methyl)silylmethyl isocyanate solution was added dropwise to the reaction system. After the addition was complete, the reaction was kept warm for 80-110 minutes and post-treated to obtain a modified triazine.

[0014] The synthetic reaction formula of modified triazine is:

[0015]

[0016] The synthetic reaction mechanism of modified triazine is:

[0017] During the reaction, the amino group on the melamine molecule condenses with the isocyanate group on the 1-dimethoxy(methyl)silylmethyl isocyanate molecule to form a modified triazine modified with dimethoxymethylsilane on the triazine molecule.

[0018] A2, the modified triazine, D4, tetramethyltetravinylcyclotetrasiloxane were mixed and stirred, the reaction system temperature was raised to 120-130 ° C, a catalyst was added to the reaction system, the reaction was kept warm for 4-6 hours, a blocking agent was added, the reaction was kept warm for 2-3 hours, and post-processed to obtain a cross-linked polysiloxane;

[0019] The synthetic reaction formula of cross-linked polysiloxane is:

[0020]

[0021] Where:

[0022]

[0023] The synthetic reaction mechanism of cross-linked polysiloxane is:

[0024] During the reaction, under the action of a catalyst, D4 and tetramethyltetravinylcyclotetrasiloxane molecules undergo ring opening and undergo condensation reaction with silanol groups formed by hydrolysis of siloxane bonds on modified triazine molecules, thereby forming a long polysiloxane cross-linked network with triazine as a connecting axis. The end-capping agent serves as a chain-terminating end-capping modification, which is hydrolyzed under the conditions of a catalyst to form n-propylamine with a silanol modification at one end, forming an amino modification on the long polysiloxane cross-linked network, thereby preparing a cross-linked polysiloxane.

[0025] A3. Under inert atmosphere, polyethylene oxide and N,N-dimethylformamide were mixed, the reaction system temperature was raised to 70-80°C, and the mixture was stirred until the system was dissolved. Isophorone diisocyanate was added to the reaction system and the mixture was kept warm for 40-60 minutes. Cross-linked polysiloxane was added to the reaction system and the mixture was kept warm for 80-100 minutes. After post-treatment, modified polysiloxane was obtained.

[0026] The synthetic reaction formula of modified polysiloxane is:

[0027]

[0028] Where:

[0029] ;

[0030] .

[0031] The synthetic reaction mechanism of modified polysiloxane is:

[0032] During the reaction, the hydroxyl group on the polyethylene oxide molecule undergoes a condensation reaction with an isocyanate group on the isophorone diisocyanate molecule to form an isocyanate-modified polyethylene oxide intermediate. The isocyanate group on the intermediate molecule then undergoes a condensation reaction with the amino group on the cross-linked polysiloxane molecule to form a modified polysiloxane of the polyethylene oxide-modified cross-linked polysiloxane.

[0033] Furthermore, in step A1, the amount ratio of melamine and N,N-dimethylformamide is 1g:3mL, the 1-dimethoxy(methyl)silylmethylisocyanate solution is composed of 1-dimethoxy(methyl)silylmethylisocyanate and N,N-dimethylformamide at 1g:1mL, and the amount ratio of melamine and 1-dimethoxy(methyl)silylmethylisocyanate is 1mol:3mol. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, anhydrous ethanol is added to the reaction system, and filtered. The filter cake is washed three times with anhydrous ethanol and then dried. The filter cake is transferred to a drying oven at a temperature of 50-60°C and vacuum dried to constant weight to obtain a modified triazine.

[0034] Furthermore, in step A2, the amount ratio of the modified triazine, D4, tetramethyltetravinylcyclotetrasiloxane, catalyst and end-capping agent is 1-2g:5-7g:3-4g:0.3g:0.5-0.8g, the catalyst is 90-98wt% sulfuric acid, and the end-capping agent is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, 0.1mol / L sodium carbonate aqueous solution is added to the reaction system, the pH of the system is adjusted to 7, the liquid is allowed to stand and separate, the upper liquid is washed 3 times with purified water and then transferred to a rotary evaporator at a temperature of 80-90°C, and the low-boiling substances are removed under reduced pressure to obtain a cross-linked polysiloxane.

[0035] Furthermore, in step A3, the amount ratio of the polyethylene oxide, N,N-dimethylformamide and cross-linked polysiloxane is 1g:7mL:3g, the molar amount of the isophorone diisocyanate is the same as the molar amount of hydroxyl groups in the polyethylene oxide, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is raised to 110-120°C, and the low-boiling substances are removed under reduced pressure to obtain a modified polysiloxane.

[0036] Furthermore, the preparation method of the loaded diatomite is as follows: biochar-modified diatomite and the loading liquid are mixed, ultrasonically dispersed at room temperature for 30-50 minutes, sodium hydroxide solution is added to the reaction system, the pH of the system is adjusted to 9-10, the temperature of the reaction system is increased to 50-60°C, 5-hexenyltriethoxysilane solution is added to the reaction system, the reaction is kept warm for 60-80 minutes, and post-processed to obtain the loaded diatomite.

[0037] The synthetic reaction mechanism of supported diatomite is:

[0038] The metal nitrate in the loading liquid is hydrolyzed to form metal ions. The metal ions are uniformly dispersed in the biochar-modified diatomaceous earth through ultrasonic dispersion. The metal ions are hydrolyzed to form hydroxide precipitates through the pH condition of the reaction system. The porous structure of the biochar-modified diatomaceous earth provides a good carrier for the precipitation of metal hydroxides. The siloxane bonds on the 5-hexenyltriethoxysilane molecules are hydrolyzed to form silanols, which react with the active functional groups on the surface of the biochar-modified diatomaceous earth to form chemical bonds, thereby preparing olefin double-bond-modified biochar-modified diatomaceous earth loaded with metal hydroxides.

[0039] Furthermore, the amount ratio of the biochar-modified diatomaceous earth, the loading liquid and the 5-hexenyltriethoxysilane solution is 3g:10mL:15mL, the loading liquid is composed of bismuth nitrate, magnesium nitrate, aluminum nitrate and deionized water in a ratio of 1g:2g:2g:20mL, and the 5-hexenyltriethoxysilane solution is composed of 5-hexenyltriethoxysilane and tetrahydrofuran in a ratio of 1g:10mL. The post-treatment includes: after the reaction is completed, filtering, transferring the filter cake to a drying oven at a temperature of 70-80°C, and drying to constant weight to obtain loaded diatomaceous earth.

[0040] Furthermore, the biochar-modified diatomaceous earth is processed by the following steps:

[0041] B1. Place the plant powder in a sodium hydroxide solution, stir, boil for 30-50 minutes, and post-treat to obtain a pretreated powder;

[0042] B2. Mix the pretreated powder, diatomaceous earth, and modified solution, perform ultrasonic dispersion for 60-80 min, and perform post-treatment to obtain a modified mixed powder;

[0043] B3. The modified mixed powder is calcined and then post-processed to obtain biochar-modified diatomaceous earth.

[0044] The synthetic reaction mechanism of biochar-modified diatomaceous earth is:

[0045] During the reaction, the plant powder is treated with alkali to promote the hydrolysis of the ester bonds and hemicellulose of lignin in the plant powder and destroy its cross-linking structure. In addition, the high-temperature boiling of the sodium hydroxide solution accelerates the reaction, removes low-molecular organic matter and impurities in the plant powder, and forms a porous skeleton structure, providing active sites for the subsequent loading of metal ions. The hydrophilic chain segments of polyethylene glycol form hydrogen bonds with the surface hydroxyl groups of diatomaceous earth and pretreated powder to prevent particle agglomeration, and form a micellar structure during ultrasonic dispersion, guiding the uniform loading of zinc chloride on the diatomaceous earth and pretreated powder. Under a high-temperature environment of an inert gas atmosphere, the plant powder in the modified mixed powder undergoes a pyrolysis and carbonization reaction, the zinc chloride melts and reacts with the carbon skeleton, and a rich microporous-mesoporous composite structure is formed through dehydration and condensation. The biochar fills the pores of the diatomaceous earth to form a "carbon-silicon" double network structure, and then the residual metal compounds are removed by acid washing to form a porous biochar-modified diatomaceous earth.

[0046] Furthermore, in step B1, the amount ratio of the plant powder and the sodium hydroxide solution is 1g:10mL, the plant powder is one or more of coconut shell powder, apricot shell powder, and straw powder, the particle size of the plant powder is 5-15mm, and the concentration of the sodium hydroxide solution is 6-8mol / L. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 60-70°C, and vacuum dried to constant weight to obtain a pretreated powder.

[0047] Furthermore, in step B2, the amount ratio of the pretreated powder, diatomaceous earth, and modifying liquid is 0.6-0.8g:1g:10mL, the modifying liquid is composed of zinc chloride, PEG-800 and deionized water at a ratio of 1g:0.1g:10mL, and the post-treatment includes: after the reaction is completed, filtering, transferring the filter cake to a drying oven at a temperature of 60-70°C, and drying to constant weight to obtain a modified mixed powder.

[0048] Furthermore, in step B3, the calcination temperature is 680-750°C, and the post-treatment includes: after the calcination is completed, washing the calcined powder with 1-2 mol / L hydrochloric acid three times and then washing it with purified water until it is neutral, placing the solid in a drying oven at a temperature of 60-70°C and drying it to constant weight to obtain biochar-modified diatomaceous earth.

[0049] A method for preparing a halogen-free, low-smoke flame-retardant power cable comprises the following steps:

[0050] S1. Place several cable cores in parallel and use wrapping tape to wrap and fix the cable cores together to form a wrapping layer on the outside of the cable cores;

[0051] S2. Low-density polyethylene, anhydride-modified EVA, modified polysiloxane, supported diatomaceous earth, dicumyl peroxide and additives are added to an extruder, melt-mixed for 6-9 minutes, and then extruded and coated on the outside of the wrapping layer. The material is cooled and solidified to form a sheath layer on the outside of the wrapping layer to obtain a power cable.

[0052] Furthermore, the additives are composed of a dispersant, a lubricant, a plasticizer, an antioxidant and a stabilizer in a ratio of 5:2:4:2:1, the dispersant is stearate, the lubricant is any one of butyl stearate, oleamide, and ethylene bisstearamide, the plasticizer is a phthalate, the antioxidant is any one of antioxidant AW, antioxidant DNP, and antioxidant CPPD, the stabilizer is a calcium zinc stabilizer, and the temperatures of the five temperature zones of the extruder from the feed end to the discharge end are 170°C, 175°C, 180°C, 180°C, and 185°C, respectively.

[0053] The present invention has the following beneficial effects:

[0054] 1. The halogen-free, low-smoke flame-retardant power cable of the present invention promotes the mutual fusion and uniform dispersion of modified polysiloxane, loaded diatomaceous earth, and low-density polyethylene by using anhydride-modified EVA. Then, under the action of an initiator and high temperature, intermolecular cross-linking is promoted to improve the mechanical strength of the cable sheath layer. When preparing the loaded diatomaceous earth, the diatomaceous earth is modified by biochar, and the porous structures of the diatomaceous earth and biochar are utilized to provide loading sites for metal ions. In addition, the porous and rigid diatomaceous earth and biochar are dispersed in the LDPE matrix as rigid fillers to form physical cross-linking points, which restrict the slippage of polyethylene molecular chains, thereby improving the tensile strength. By modifying the olefin double bonds on its surface, the long-chain olefin ends are combined with the low-density polyethylene molecular chains through entanglement or co-crystallization, thereby improving the compatibility between the filler and the matrix, reducing interface defects, and improving the mechanical strength of the sheath layer material. At the same time, the porous structure of diatomaceous earth and the layered carbon structure of biochar form a dense carbon layer during combustion, isolating oxygen and heat transfer. The loaded metal compounds catalyze the oxidation and decomposition of the sheath layer at high temperature to form a carbon layer, reducing smoke generation. The dense porous carbon layer formed by diatomaceous earth and biochar can reduce the release of organic volatiles, reduce smoke particles generated by incomplete combustion, improve its flame retardant properties, and reduce the concentration of smoke.

[0055] 2. The halogen-free, low-smoke flame-retardant power cable of the present invention uses modified triazine as a matrix to cooperate with D4 and tetramethyltetravinylcyclotetrasiloxane to construct a three-dimensional cross-linked network. This cross-linked network acts as a physical reinforcement phase in the polyethylene matrix, limiting the slippage of polyethylene molecular chains, thereby improving tensile strength. Polyethylene oxide is then modified on the cross-linked polysiloxane molecules so that it can bind to the polyethylene molecular chains through hydrogen bonds or van der Waals forces, thereby enhancing the interfacial bonding between the two phases, reducing stress concentration, and promoting uniform dispersion of the polyoxyethane in the low-density polyethylene, further improving the tensile strength of the material. The flexibility of the polysiloxane main chain and the elasticity of the polyethylene oxide chain segments can absorb part of the energy during the stretching process, thereby improving the elongation at break of the material. The triazine in the modified polysiloxane molecules decomposes at high temperatures to release nitrogen, diluting the concentration of combustible gases and inhibiting the combustion chain reaction. At the same time, the cross-linked polysiloxane decomposes to generate silicon dioxide during combustion, which cooperates with the supported diatomaceous earth to inhibit the release of organic volatiles, reduce smoke particles, further reducing the amount of smoke released and improving the flame retardant properties of the material.

[0056] 3. The halogen-free, low-smoke flame-retardant power cable of the present invention modifies EVA with acid anhydride, modifies a highly polar acid anhydride matrix on the EVA molecule, and uses the acid anhydride-modified EVA as a bridge to improve the compatibility of low-density polyethylene with modified polysiloxane and loaded diatomaceous earth, thereby improving the overall tensile strength. In addition, the high reactivity of the maleic anhydride group can promote the branching and entanglement of the low-density polyethylene molecular chain to form a denser molecular network. The acid anhydride modified on the EVA decomposes at high temperature to generate carboxylic acid groups, which cooperate with the metal compounds loaded on the loaded diatomaceous earth to further catalyze the carbonization of the sheath layer to form a dense protective layer, isolate oxygen and heat, and improve the flame retardant properties of the material. When preparing the sheath layer, its molecules are promoted to cross-link by a free radical initiator, thereby reducing melt dripping during combustion, extending the protection time of the carbon layer, and improving the flame retardant properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0058] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention.

[0059] In the figure: 1. Cable core; 2. Wrapping layer; 3. Sheath layer. DETAILED DESCRIPTION

[0060] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] In this application, D4 is octamethylcyclotetrasiloxane, CAS number 556-67-2;

[0062] In this application, polyethylene oxide was selected from Hubei Langbowan Biopharmaceutical Co., Ltd., with a CAS number of 8441-17-8 and a molecular weight of 1000;

[0063] In this application, PEG-800 is polyethylene glycol 800, selected from Jining Fangyu Chemical Co., Ltd., with CAS number 25322-68-3;

[0064] In this application, EVA is ethylene-vinyl acetate copolymer, wherein the content of vinyl acetate is 12-16%, and the CAS number is 24937-78-8;

[0065] In this application, the calcium zinc stabilizer is selected from Shijiazhuang Zhongdao Chemical Technology Co., Ltd., model 808;

[0066] In this application, the low-density polyethylene brand is Sinopec Yanshan, brand LD605, melt flow rate is 6g / 10min, density is 0.922g / cm 3 .

[0067] Example 1

[0068] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant modified polysiloxane for power cables, comprising the following steps:

[0069] A1. Preparation of modified triazine

[0070] 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide were mixed to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0071] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide were added to a 250 mL reaction flask protected by argon and stirred. The temperature of the reaction flask was raised to 50 ° C. and stirred until the system was dissolved. The above-configured 1-dimethoxy (methyl) silyl methyl isocyanate solution was added dropwise to the reaction flask. After the addition was complete, the reaction was kept warm for 80 minutes. The temperature of the reaction flask was lowered to room temperature, 200 mL of anhydrous ethanol was added to the reaction flask, filtered, and the filter cake was washed three times with anhydrous ethanol and then dried. The filter cake was transferred to a drying oven at a temperature of 50 ° C. and evacuated to a negative pressure of 0.1 MPa. It was vacuum dried to constant weight to obtain a modified triazine.

[0072] A2. Preparation of cross-linked polysiloxane

[0073] Weigh: 10 g of modified triazine, 50 g of D4, and 30 g of tetramethyltetravinylcyclotetrasiloxane are added to a 250 mL reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 120 ° C. 3 g of 90 wt% sulfuric acid is added to the reaction flask, and the reaction is kept warm for 4 h. 5 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added and the reaction is kept warm for 2 h. The temperature of the reaction flask is lowered to room temperature. 0.1 mol / L sodium carbonate aqueous solution is added to the reaction flask, and the pH of the system is adjusted to 7. The liquid is allowed to stand and separated. The upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at a temperature of 80 ° C. The vacuum is evacuated to a negative pressure of 0.1 MPa, and the low-boiling point is removed under reduced pressure to obtain a cross-linked polysiloxane.

[0074] A3. Preparation of modified polysiloxane

[0075] Weigh: 20g of polyethylene oxide and 140mL of N,N-dimethylformamide were added to a 250mL reaction bottle protected by argon and stirred. The temperature of the reaction bottle was raised to 70℃ and stirred until the system was dissolved. 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2 was added to the reaction flask, and the reaction was kept warm for 40 minutes. 30 g of cross-linked polysiloxane was added to the reaction flask, and the reaction was kept warm for 80 minutes. The temperature of the reaction flask was raised to 110°C, and the vacuum was evacuated to a negative pressure of 0.1 MPa. The low-boiling substances were removed under reduced pressure to obtain modified polysiloxane.

[0076] Example 2

[0077] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant modified polysiloxane for power cables, comprising the following steps:

[0078] A1. Preparation of modified triazine

[0079] 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide were mixed to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0080] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide were added to a 250 mL reaction flask protected by argon and stirred. The temperature of the reaction flask was raised to 55 ° C. and stirred until the system was dissolved. The above-configured 1-dimethoxy (methyl) silyl methyl isocyanate solution was added dropwise to the reaction flask. After the addition was complete, the reaction was kept warm for 95 minutes. The temperature of the reaction flask was lowered to room temperature, 200 mL of anhydrous ethanol was added to the reaction flask, filtered, and the filter cake was washed three times with anhydrous ethanol and then dried. The filter cake was transferred to a drying oven at a temperature of 55 ° C. and evacuated to a negative pressure of 0.1 MPa. It was vacuum dried to constant weight to obtain a modified triazine.

[0081] A2. Preparation of cross-linked polysiloxane

[0082] Weigh: 15 g of modified triazine, 60 g of D4, and 35 g of tetramethyltetravinylcyclotetrasiloxane are added to a 250 mL reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 125 ° C. 3 g of 94 wt% sulfuric acid is added to the reaction flask, and the reaction is kept warm for 5 h. 7 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added and the reaction is kept warm for 2.5 h. The temperature of the reaction flask is lowered to room temperature. 0.1 mol / L sodium carbonate aqueous solution is added to the reaction flask, and the pH of the system is adjusted to 7. The liquid is allowed to stand and separated. The upper layer liquid is washed three times with purified water and then transferred to a rotary evaporator at a temperature of 85 ° C. The vacuum is evacuated to a negative pressure of 0.1 MPa, and the low-boiling point is removed under reduced pressure to obtain a cross-linked polysiloxane.

[0083] A3. Preparation of modified polysiloxane

[0084] Weigh: 20g of polyethylene oxide and 140mL of N,N-dimethylformamide were added to a 250mL reaction bottle protected by argon and stirred. The temperature of the reaction bottle was raised to 75℃ and stirred until the system was dissolved. 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2 was added to the reaction flask, and the reaction was kept warm for 50 minutes. 30 g of cross-linked polysiloxane was added to the reaction flask, and the reaction was kept warm for 9 minutes. The temperature of the reaction flask was raised to 115°C, and the vacuum was evacuated to a negative pressure of 0.1 MPa. The low-boiling substances were removed under reduced pressure to obtain modified polysiloxane.

[0085] Example 3

[0086] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant modified polysiloxane for power cables, comprising the following steps:

[0087] A1. Preparation of modified triazine

[0088] 48.4 g of 1-dimethoxy(methyl)silylmethyl isocyanate and 48.4 mL of N,N-dimethylformamide were mixed to obtain a 1-dimethoxy(methyl)silylmethyl isocyanate solution;

[0089] Weigh: 12.6 g of melamine and 37.8 mL of N,N-dimethylformamide were added to a 250 mL reaction flask protected by argon and stirred. The temperature of the reaction flask was raised to 60 ° C. and stirred until the system was dissolved. The above-configured 1-dimethoxy (methyl) silyl methyl isocyanate solution was added dropwise to the reaction flask. After the addition was complete, the reaction was kept warm for 110 minutes. The temperature of the reaction flask was lowered to room temperature, 200 mL of anhydrous ethanol was added to the reaction flask, filtered, and the filter cake was washed three times with anhydrous ethanol and then dried. The filter cake was transferred to a drying oven at a temperature of 60 ° C. and evacuated to a negative pressure of 0.1 MPa. It was vacuum dried to constant weight to obtain a modified triazine.

[0090] A2. Preparation of cross-linked polysiloxane

[0091] Weigh: 20 g of modified triazine, 70 g of D4, and 40 g of tetramethyltetravinylcyclotetrasiloxane are added to a 250 mL reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 130 ° C. 3 g of 98 wt% sulfuric acid is added to the reaction flask, and the reaction is kept warm for 6 hours. 8 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added and the reaction is kept warm for 3 hours. The temperature of the reaction flask is lowered to room temperature. 0.1 mol / L sodium carbonate aqueous solution is added to the reaction flask, and the pH of the system is adjusted to 7. The liquid is allowed to stand and separated. The upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at a temperature of 90 ° C. The vacuum is evacuated to a negative pressure of 0.1 MPa, and the low-boiling point is removed under reduced pressure to obtain a cross-linked polysiloxane.

[0092] A3. Preparation of modified polysiloxane

[0093] Weigh: 20g of polyethylene oxide and 140mL of N,N-dimethylformamide were added to a 250mL reaction bottle protected by argon and stirred. The temperature of the reaction bottle was raised to 80℃ and stirred until the system was dissolved. 聚氧化乙烯-OH / N 异佛尔酮二异氰酸酯-NCO =1:2 was added to the reaction flask, and the reaction was kept warm for 60 minutes. 30 g of cross-linked polysiloxane was added to the reaction flask, and the reaction was kept warm for 100 minutes. The temperature of the reaction flask was raised to 120°C, and the vacuum was evacuated to a negative pressure of 0.1 MPa. The low-boiling substances were removed under reduced pressure to obtain modified polysiloxane.

[0094] Example 4

[0095] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant supported diatomaceous earth for power cables, comprising the following steps:

[0096] B1. Preparation of pre-treated powder

[0097] Weigh: 100 g of coconut shell powder with a particle size of 5-15 mm and 1000 mL of 6 mol / L sodium hydroxide solution are added to a 3 L reaction flask and stirred. The temperature of the reaction flask is increased to the reflux state of the system and kept in a boiling state for 30 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 60° C., evacuated to a negative pressure of 0.1 MPa, and vacuum dried to constant weight to obtain a pretreated powder.

[0098] B2. Preparation of modified mixed powder

[0099] Mix zinc chloride, PEG-800, and deionized water in a ratio of 1 g:0.1 g:10 mL to obtain a modified solution for later use.

[0100] Weigh: 60 g of pretreated powder, 100 g of diatomaceous earth, and 1000 mL of modified liquid are added to a 3 L reaction bottle and mixed, ultrasonically dispersed for 60 min, filtered, and the filter cake is transferred to a drying oven at a temperature of 60°C and dried to constant weight to obtain a modified mixed powder.

[0101] B3. Preparation of biochar-modified diatomaceous earth

[0102] The modified mixed powder was transferred to a tubular furnace in a nitrogen atmosphere, the temperature of the tubular furnace was increased to 680°C, and calcined for 3 hours. The temperature of the tubular furnace was then lowered to room temperature. The calcined powder was washed three times with 1 mol / L hydrochloric acid and then washed with purified water until it was neutral. The solid was placed in a drying oven at 60°C and dried to constant weight to obtain biochar-modified diatomaceous earth.

[0103] B4. Preparation of supported diatomaceous earth

[0104] Bismuth nitrate, magnesium nitrate, aluminum nitrate, and deionized water were mixed in a ratio of 1 g: 2 g: 2 g: 20 mL to obtain a loading solution;

[0105] 5-Hexenyltriethoxysilane and tetrahydrofuran were mixed at a ratio of 1 g:10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0106] Weigh: 90 g of biochar-modified diatomaceous earth and 300 mL of loading liquid are added to a 3 L reaction flask and mixed, ultrasonically dispersed at room temperature for 30 min, 1 mol / L sodium hydroxide solution is added to the reaction flask, the pH of the system is adjusted to 9, the temperature of the reaction flask is raised to 50 ° C, 450 mL of 5-hexenyltriethoxysilane solution is added to the reaction flask, and the reaction is kept warm for 60 min. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is transferred to a drying oven at a temperature of 70 ° C and dried to constant weight to obtain loaded diatomaceous earth.

[0107] Example 5

[0108] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant supported diatomaceous earth for power cables, comprising the following steps:

[0109] B1. Preparation of pre-treated powder

[0110] Weigh: 100 g of apricot shell powder with a particle size of 5-15 mm and 1000 mL of 7 mol / L sodium hydroxide solution are added to a 3 L reaction flask and stirred. The temperature of the reaction flask is raised to the reflux of the system and kept in a boiling state for 40 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 65 ° C, evacuated to a negative pressure of 0.1 MPa, and vacuum dried to constant weight to obtain a pretreated powder.

[0111] B2. Preparation of modified mixed powder

[0112] Mix zinc chloride, PEG-800, and deionized water in a ratio of 1 g:0.1 g:10 mL to obtain a modified solution for later use.

[0113] Weigh: 70 g of pretreated powder, 100 g of diatomaceous earth, and 1000 mL of modified liquid are added to a 3 L reaction bottle and mixed. Ultrasonic dispersion is performed for 70 min. The filter cake is transferred to a drying oven at 65°C and dried to constant weight to obtain a modified mixed powder.

[0114] B3. Preparation of biochar-modified diatomaceous earth

[0115] The modified mixed powder was transferred to a tubular furnace in a nitrogen atmosphere, the temperature of the tubular furnace was increased to 715°C, and calcined for 4 hours. The temperature of the tubular furnace was then lowered to room temperature. The calcined powder was washed three times with 1.5 mol / L hydrochloric acid and then washed with purified water until it was neutral. The solid was placed in a drying oven at a temperature of 65°C and dried to constant weight to obtain biochar-modified diatomaceous earth.

[0116] B4. Preparation of supported diatomaceous earth

[0117] Bismuth nitrate, magnesium nitrate, aluminum nitrate, and deionized water were mixed in a ratio of 1 g: 2 g: 2 g: 20 mL to obtain a loading solution;

[0118] 5-Hexenyltriethoxysilane and tetrahydrofuran were mixed at a ratio of 1 g:10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0119] Weigh: 90 g of biochar-modified diatomaceous earth and 300 mL of loading liquid are added to a 3 L reaction flask and mixed, ultrasonically dispersed at room temperature for 40 min, 1 mol / L sodium hydroxide solution is added to the reaction flask, the pH of the system is adjusted to 9.5, the temperature of the reaction flask is raised to 55 ° C, 450 mL of 5-hexenyltriethoxysilane solution is added to the reaction flask, and the reaction is kept warm for 70 min. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is transferred to a drying oven at a temperature of 75 ° C and dried to constant weight to obtain loaded diatomaceous earth.

[0120] Example 6

[0121] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant supported diatomaceous earth for power cables, comprising the following steps:

[0122] B1. Preparation of pre-treated powder

[0123] Weigh: 100 g of straw powder with a particle size of 5-15 mm and 1000 mL of 8 mol / L sodium hydroxide solution are added to a 3 L reaction flask and stirred. The temperature of the reaction flask is raised to the reflux of the system and kept in a boiling state for 50 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 70° C., evacuated to a negative pressure of 0.1 MPa, and vacuum dried to constant weight to obtain a pretreated powder.

[0124] B2. Preparation of modified mixed powder

[0125] Mix zinc chloride, PEG-800, and deionized water in a ratio of 1 g:0.1 g:10 mL to obtain a modified solution for later use.

[0126] Weigh: 80 g of pretreated powder, 100 g of diatomaceous earth, and 1000 mL of modified liquid are added to a 3 L reaction bottle and mixed, ultrasonically dispersed for 80 min, filtered, and the filter cake is transferred to a drying oven at a temperature of 70°C and dried to constant weight to obtain a modified mixed powder.

[0127] B3. Preparation of biochar-modified diatomaceous earth

[0128] The modified mixed powder was transferred to a tubular furnace in a nitrogen atmosphere, the temperature of the tubular furnace was increased to 750°C, and calcined for 5 hours. The temperature of the tubular furnace was then lowered to room temperature. The calcined powder was washed three times with 2 mol / L hydrochloric acid and then washed with purified water until it was neutral. The solid was placed in a drying oven at a temperature of 70°C and dried to constant weight to obtain biochar-modified diatomaceous earth.

[0129] B4. Preparation of supported diatomaceous earth

[0130] Bismuth nitrate, magnesium nitrate, aluminum nitrate, and deionized water were mixed in a ratio of 1 g: 2 g: 2 g: 20 mL to obtain a loading solution;

[0131] 5-Hexenyltriethoxysilane and tetrahydrofuran were mixed at a ratio of 1 g:10 mL to obtain a 5-hexenyltriethoxysilane solution;

[0132] Weigh: 90 g of biochar-modified diatomaceous earth and 300 mL of loading liquid are added to a 3 L reaction flask and mixed, ultrasonically dispersed at room temperature for 50 min, 1 mol / L sodium hydroxide solution is added to the reaction flask, the pH of the system is adjusted to 10, the temperature of the reaction flask is raised to 60 ° C, 450 mL of 5-hexenyltriethoxysilane solution is added to the reaction flask, and the reaction is kept warm for 80 min. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is transferred to a drying oven at a temperature of 80 ° C and dried to constant weight to obtain loaded diatomaceous earth.

[0133] Example 7

[0134] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant power cable, comprising the following steps:

[0135] Step 1: Preparation of anhydride-modified EVA

[0136] Weigh: 800g of EVA and 12g of maleic anhydride are added to a torque rheometer at a temperature of 160°C and mixed for 3min. 2g of diisopropylbenzene peroxide is added to the torque rheometer in batches and mixed for 8min. The grafted product is crushed and added to the reaction flask with toluene at a ratio of 1g:8mL and mixed. The temperature of the reaction flask is raised to 85°C and stirred until the system is dissolved. The heating is removed and acetone is added to the reaction system at a ratio of acetone / toluene = 3:1. A large amount of solid precipitates and is filtered. The filter cake is washed twice with acetone and then dried. The filter cake is transferred to a drying oven at a temperature of 50°C and vacuum dried to constant weight to obtain anhydride-modified EVA.

[0137] Step 2: Cable core wrapping

[0138] A copper core cable coated with insulating rubber is selected as the cable core 1;

[0139] Several cable cores 1 are placed together in parallel, and a polyester wrapping tape is used to wrap and fix the several cable cores 1 together to form a wrapping layer 2 on the outside of the cable core 1.

[0140] Step 3: Prepare power cables

[0141] Zinc stearate, butyl stearate, dibutyl phthalate, antioxidant AW and calcium zinc stabilizer are mixed in a ratio of 5:2:4:2:1 to obtain an additive;

[0142] The following components were weighed in parts by weight: 70 parts of low-density polyethylene, 10 parts of anhydride-modified EVA, 20 parts of the modified polysiloxane prepared in Example 1, 25 parts of the supported diatomaceous earth prepared in Example 4, 0.8 parts of dicumyl peroxide, and 2 parts of additives, and added to a twin-screw extruder. The temperatures of the five temperature zones of the extruder from the feed end to the discharge end were 170° C., 175° C., 180° C., 180° C., and 185° C., respectively. After melt mixing in the twin-screw extruder for 6 minutes, the resulting mixture was extruded and coated on the outside of the wrapping layer 2, cooled and solidified, and a sheath layer 3 was formed on the outside of the wrapping layer 2 to obtain a power cable.

[0143] Example 8

[0144] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant power cable, comprising the following steps:

[0145] Step 1: Preparation of anhydride-modified EVA

[0146] Weigh: 800g EVA and 13.5g maleic anhydride are added to a torque rheometer at a temperature of 165°C and mixed for 3min. 3g diisopropylbenzene peroxide is added to the torque rheometer in batches and mixed for 10min. The grafted product is crushed and added to the reaction flask with toluene at a ratio of 1g:8mL and mixed. The temperature of the reaction flask is raised to 90°C and stirred until the system is dissolved. The heating is removed and acetone is added to the reaction system at a ratio of acetone / toluene = 3:1. A large amount of solid precipitates and is filtered. The filter cake is washed twice with acetone and then dried. The filter cake is transferred to a drying oven at a temperature of 55°C and vacuum dried to constant weight to obtain anhydride-modified EVA.

[0147] Step 2: Cable core wrapping

[0148] A copper core cable coated with insulating rubber is selected as the cable core 1;

[0149] Several cable cores 1 are placed together in parallel, and a polyester wrapping tape is used to wrap and fix the several cable cores 1 together to form a wrapping layer 2 on the outside of the cable core 1.

[0150] Step 3: Prepare power cables

[0151] Calcium stearate, oleamide, diisobutyl phthalate, antioxidant DNP, and calcium zinc stabilizer are mixed in a ratio of 5:2:4:2:1 to obtain an additive;

[0152] The following components were weighed in parts by weight: 75 parts of low-density polyethylene, 13 parts of anhydride-modified EVA, 24 parts of the modified polysiloxane prepared in Example 2, 27 parts of the supported diatomaceous earth prepared in Example 5, 1.0 part of dicumyl peroxide, and 2.5 parts of additives, and added to a twin-screw extruder. The temperatures of the five temperature zones of the extruder from the feed end to the discharge end were 170° C., 175° C., 180° C., 180° C., and 185° C., respectively. After melt mixing in the twin-screw extruder for 7.5 minutes, the resulting components were extruded and coated on the outside of the wrapping layer 2, cooled and solidified, and a sheath layer 3 was formed on the outside of the wrapping layer 2 to obtain a power cable.

[0153] Example 9

[0154] This embodiment provides a method for preparing a halogen-free, low-smoke flame-retardant power cable, comprising the following steps:

[0155] Step 1: Preparation of anhydride-modified EVA

[0156] Weigh: 800g EVA and 15g maleic anhydride are added to a torque rheometer at a temperature of 170°C and mixed for 3min. 4g diisopropylbenzene peroxide is added to the torque rheometer in batches and mixed for 12min. The grafted product is crushed and added to the reaction flask with toluene at a ratio of 1g:8mL and mixed. The temperature of the reaction flask is raised to 95°C and stirred until the system is dissolved. The heating is removed and acetone is added to the reaction system at a ratio of acetone / toluene = 3:1. A large amount of solid precipitates and is filtered. The filter cake is washed with acetone twice and then dried. The filter cake is transferred to a drying oven at a temperature of 60°C and vacuum dried to constant weight to obtain anhydride-modified EVA.

[0157] Step 2: Cable core wrapping

[0158] A copper core cable coated with insulating rubber is selected as the cable core 1;

[0159] Several cable cores 1 are placed together in parallel, and a polyester wrapping tape is used to wrap and fix the several cable cores 1 together to form a wrapping layer 2 on the outside of the cable core 1.

[0160] Step 3: Prepare power cables

[0161] Magnesium stearate, ethylene bisstearamide, diisooctyl phthalate, antioxidant CPPD and calcium zinc stabilizer are mixed in a ratio of 5:2:4:2:1 to obtain an additive;

[0162] The following components were weighed in parts by weight: 80 parts of low-density polyethylene, 15 parts of anhydride-modified EVA, 28 parts of the modified polysiloxane prepared in Example 3, 40 parts of the supported diatomaceous earth prepared in Example 6, 1.2 parts of dicumyl peroxide, and 3 parts of additives, and added to a twin-screw extruder. The temperatures of the five temperature zones of the extruder from the feed end to the discharge end were 170° C., 175° C., 180° C., 180° C., and 185° C., respectively. After melt mixing in the twin-screw extruder for 9 minutes, the resulting components were extruded and coated on the outside of the wrapping layer 2, cooled and solidified, and a sheath layer 3 was formed on the outside of the wrapping layer 2 to obtain a power cable.

[0163] Comparative Example 1

[0164] The difference between this comparative example and Example 9 is that, during the preparation of the modified polysiloxane used, step A1 is omitted, and modified triazine is not added in step A2.

[0165] Comparative Example 2

[0166] The difference between this comparative example and Example 9 is that, when preparing the modified polysiloxane used, step A3 is omitted, and the modified polysiloxane in step A2 is substituted for the cross-linked polysiloxane in step A3.

[0167] Comparative Example 3

[0168] The difference between this comparative example and Example 9 is that, during the preparation of the supported diatomaceous earth used, step B1 is omitted, and no pre-treated powder is added in step B2.

[0169] Comparative Example 4

[0170] The difference between this comparative example and Example 9 is that step one is eliminated, and the anhydride-modified EVA in step three is replaced by the EVA in step one.

[0171] Performance testing:

[0172] The tensile strength, elongation at break, oxygen index, and smoke density of the sheath layer of the power cable samples prepared in Examples 7-9 and Comparative Examples 1-4 were measured with reference to the standard GB / T 32129-2015 “Halogen-free and low-smoke flame-retardant cable materials for wires and cables”.

[0173] The specific test results are shown in Table 1 below.

[0174] Table 1-Performance test data of the sample

[0175]

[0176] Data Analysis:

[0177] A comparative analysis of the data in Table 1 above shows that the tensile strength of the sheath layer of the power cable sample prepared by the present invention reaches 15.2 MPa, the elongation at break reaches 330%, the oxygen index reaches 37%, the smoke density during flaming combustion is reduced to 118, and the smoke density during flameless smoldering is reduced to 48. All performance parameters are better than those of the comparative example, indicating that the present invention promotes the mutual fusion and uniform dispersion of modified polysiloxane, supported diatomaceous earth and low-density polyethylene by modifying EVA with anhydride, and then promotes intermolecular crosslinking under the action of an initiator and high temperature, thereby improving the mechanical strength of the cable sheath layer while improving the flame retardant properties of the power cable material and suppressing the generation of smoke during combustion.

[0178] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0179] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0180] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A halogen-free, low-smoke flame-retardant power cable, characterized in that: It comprises a plurality of cable cores (1), a wrapping layer (2) and a sheath layer (3) arranged in sequence from the inside out; The wrapping layer (2) is obtained by wrapping a wrapping tape around the outside of a plurality of cable cores (1); The sheath layer (3) comprises the following components in parts by weight: 70-80 parts of low-density polyethylene, 10-15 parts of anhydride-modified EVA, 20-28 parts of modified polysiloxane, 25-40 parts of supported diatomaceous earth, 0.8-1.2 parts of dicumyl peroxide, and 2-3 parts of additives; The modified polysiloxane is processed by the following steps: A1. Under an inert atmosphere, melamine and N,N-dimethylformamide were mixed and stirred until the system was dissolved. The temperature of the reaction system was raised to 50-60°C, and 1-dimethoxy(methyl)silylmethyl isocyanate solution was added dropwise to the reaction system. After the addition was complete, the reaction was kept warm for 80-110 minutes and post-treated to obtain a modified triazine. A2. Modified triazine, octamethylcyclotetrasiloxane, and tetramethyltetravinylcyclotetrasiloxane are mixed and stirred, the reaction system temperature is raised to 120-130° C., a catalyst is added to the reaction system, and the reaction is kept warm for 4-6 hours. A blocking agent is added, and the reaction is kept warm for 2-3 hours. Post-treatment is performed to obtain a cross-linked polysiloxane; A3. Under inert atmosphere, polyethylene oxide and N,N-dimethylformamide were mixed, the reaction system temperature was raised to 70-80°C, and the mixture was stirred until the system was dissolved. Isophorone diisocyanate was added to the reaction system and the mixture was kept warm for 40-60 minutes. A cross-linked polysiloxane was added to the reaction system and the mixture was kept warm for 80-100 minutes. After post-treatment, a modified polysiloxane was obtained. The preparation method of the supported diatomite is as follows: biochar-modified diatomite and a loading liquid are mixed, ultrasonically dispersed at room temperature for 30-50 minutes, sodium hydroxide solution is added to the reaction system, the pH of the system is adjusted to 9-10, the temperature of the reaction system is increased to 50-60° C., 5-hexenyltriethoxysilane solution is added to the reaction system, the reaction is kept warm for 60-80 minutes, and post-processed to obtain the supported diatomite, wherein the loading liquid is composed of bismuth nitrate, magnesium nitrate, aluminum nitrate and deionized water in a ratio of 1 g:2 g:2 g:20 mL.

2. The halogen-free, low-smoke flame-retardant power cable according to claim 1, characterized in that: The preparation method of the anhydride-modified EVA comprises: adding EVA and maleic anhydride into a torque rheometer at a temperature of 160-170° C. and mixing for 3 minutes; adding an initiator into the torque rheometer in batches; keeping the mixture warm for 8-12 minutes; and performing post-treatment to obtain the anhydride-modified EVA.

3. The halogen-free, low-smoke flame-retardant power cable according to claim 2, characterized in that: The usage ratio of the EVA, maleic anhydride and initiator is 80g:1.2-1.5g:0.2-0.4g, and the initiator is dicumyl peroxide.

4. The halogen-free, low-smoke flame-retardant power cable according to claim 1, characterized in that: In step A1, the amount ratio of melamine and N,N-dimethylformamide is 1g:3mL, the 1-dimethoxy(methyl)silylmethylisocyanate solution is composed of 1-dimethoxy(methyl)silylmethylisocyanate and N,N-dimethylformamide at 1g:1mL, and the amount ratio of melamine and 1-dimethoxy(methyl)silylmethylisocyanate is 1mol:3mol; in step A2, the modified triazine, octamethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, catalytic The amount ratio of the catalyst and the end-capping agent is 1-2g:5-7g:3-4g:0.3g:0.5-0.8g, the catalyst is 90-98wt% sulfuric acid, and the end-capping agent is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane; in step A3, the amount ratio of the polyethylene oxide, N,N-dimethylformamide and cross-linked polysiloxane is 1g:7mL:3g, and the molar amount of the isophorone diisocyanate is the same as the molar amount of the hydroxyl group in the polyethylene oxide.

5. The halogen-free, low-smoke flame-retardant power cable according to claim 1, characterized in that: The amount ratio of the biochar-modified diatomaceous earth, the loading liquid and the 5-hexenyltriethoxysilane solution is 3 g:10 mL:15 mL, and the 5-hexenyltriethoxysilane solution is composed of 5-hexenyltriethoxysilane and tetrahydrofuran at a ratio of 1 g:10 mL.

6. The halogen-free, low-smoke flame-retardant power cable according to claim 1, characterized in that: Biochar modified diatomaceous earth is processed by the following steps: B1. Place the plant powder in a sodium hydroxide solution, stir, boil for 30-50 minutes, and post-treat to obtain a pretreated powder; B2. Mix the pretreated powder, diatomaceous earth, and modified solution, perform ultrasonic dispersion for 60-80 min, and perform post-treatment to obtain a modified mixed powder; B3. The modified mixed powder is calcined and then post-processed to obtain biochar-modified diatomaceous earth.

7. The halogen-free, low-smoke flame-retardant power cable according to claim 6, characterized in that: In step B1, the amount ratio of the plant powder and the sodium hydroxide solution is 1g:10mL, the plant powder is one or more of coconut shell powder, apricot shell powder, and straw powder, the particle size of the plant powder is 5-15mm, and the concentration of the sodium hydroxide solution is 6-8mol / L; in step B2, the amount ratio of the pretreated powder, diatomaceous earth, and modifying liquid is 0.6-0.8g:1g:10mL, and the modifying liquid is composed of zinc chloride, PEG-800 and deionized water at 1g:0.1g:10mL; in step B3, the roasting temperature is 680-750°C.

8. A method for preparing a halogen-free, low-smoke flame-retardant power cable according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. placing a plurality of cable cores (1) in parallel, wrapping and fixing the plurality of cable cores (1) together using a wrapping tape, and forming a wrapping layer (2) on the outside of the cable core (1); S2. Low-density polyethylene, anhydride-modified EVA, modified polysiloxane, loaded diatomaceous earth, diisopropylbenzene peroxide and additives are added to an extruder, melt-mixed for 6-9 minutes, and then extruded and coated on the outside of the wrapping layer (2). The mixture is cooled and solidified to form a sheath layer (3) on the outside of the wrapping layer (2) to obtain a power cable.

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