Special fire-fighting double-flame-retardant power cable and preparation method thereof

Abstract

The invention relates to the technical field of power cables, in particular to a fire-fighting special double-flame-retardant power cable and a preparation method thereof, and the fire-fighting special double-flame-retardant power cable comprises a circular conductor, an insulation shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath which are sequentially arranged from inside to outside; the polyethylene flame-retardant outer protective layer is prepared by mixing a P / N / S / S i quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating, melting and extruding; the preparation of the flame retardant comprises the following steps: carrying out substitution reaction on three flame-retardant element modified DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) containing amino groups, namely P / N / S, and bis (chloropropyl) tetramethyldisiloxane to prepare a P / N / S / S i quaternary flame-retardant material; carrying out substitution reaction on the C < l > group of the P / N / S / S quaternary flame-retardant material and hydroxylated boron nitride to obtain a P / N / S / S quaternary modified boron nitride flame retardant; according to the invention, the power cable can maintain good flame retardance under the condition of long-time damp-heat aging.

Description

Technical Field

[0001] The present invention relates to the technical field of power cables, and in particular to a double flame-retardant power cable special for fire fighting and a preparation method thereof. Background Art

[0002] Power cables are cables used to transmit and distribute electrical energy. They are commonly used in urban underground power grids, power station lead-out lines, internal power supply for industrial and mining enterprises, and underwater transmission lines across rivers and seas.

[0003] Traditional cables mostly use a single flame retardant system (such as halogen or phosphorus flame retardants). Although they can delay combustion to a certain extent, they have the following problems: a single organic flame retardant has low flame retardant efficiency, and the interface bonding between inorganic flame retardants and polymer matrices is poor, which will also affect the uniformity of the flame retardant material; and some flame retardants are easily hydrolyzed in hot and humid environments, which will in turn affect the overall flame retardant performance of power cables. Summary of the Invention

[0004] The purpose of the present invention is to provide a double flame-retardant power cable for fire protection and a preparation method thereof. The technical problems solved by the present invention are: a single organic flame retardant has low flame retardant efficiency, poor interface bonding between inorganic flame retardants and polymer matrices, which will also affect the uniformity of the flame retardant material; and some flame retardants are easily hydrolyzed in a hot and humid environment.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A double flame-retardant power cable specially designed for fire protection, comprising a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath arranged in sequence from the inside to the outside;

[0007] The polyethylene flame retardant outer protective layer is prepared by mixing P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating and melting, and extruding.

[0008] As a further solution of the present invention: the preparation of the polyethylene flame retardant outer protective layer by using the P / N / S / Si quaternary modified boron nitride flame retardant comprises:

[0009] The quaternary flame retardant material P / N / S / Si was prepared by reacting DOPO modified with three flame retardant elements containing amino groups with bis(chloropropyl)tetramethyldisiloxane through substitution reaction.

[0010] The Cl group of the P / N / S / Si quaternary flame retardant material is reacted with hydroxylated boron nitride through substitution reaction to obtain a P / N / S / Si quaternary modified boron nitride flame retardant.

[0011] As a further solution of the present invention: the specific preparation process of the P / N / S / Si quaternary flame retardant material is:

[0012] The three flame retardant elements P / N / S containing amino groups, modified DOPO, bis(chloropropyl)tetramethyldisiloxane and chloroform are mixed, and nitrogen is introduced for protection. The mixture is stirred for 20-40 minutes at a temperature of 0-5°C to obtain a quaternary flame retardant material of P / N / S / Si.

[0013] As a further solution of the present invention: the usage ratio of DOPO modified by three flame retardant elements P / N / S containing amino groups, bis(chloropropyl)tetramethyldisiloxane and chloroform is 0.1 mol:0.10 mol:150-250 mL.

[0014] As a further solution of the present invention: the preparation process of DOPO modified with three flame retardant elements P / N / S containing amino groups is as follows:

[0015] In an ice bath, DOPO was mixed and dissolved with dichloromethane, and triethylamine and 2-aminobenzothiazole were added and stirred. Carbon tetrachloride was then added dropwise to the reaction system. The reaction temperature was controlled at 10-15°C and the reaction was carried out for 12-15 hours to obtain DOPO modified with three flame retardant elements P / N / S containing amino groups.

[0016] As a further embodiment of the present invention, the mass ratio of DOPO, dichloromethane, triethylamine, 2-aminobenzothiazole and carbon tetrachloride is 22.68:100-150:9-11:15.20:15-17.

[0017] As a further solution of the present invention: a specific preparation process of the P / N / S / Si quaternary modified boron nitride flame retardant includes:

[0018] Hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide are added into a reactor, and the reaction is carried out at a temperature of 70-75°C for 5-8 hours. After the reaction is completed, a P / N / S / Si quaternary modified boron nitride flame retardant is obtained.

[0019] As a further solution of the present invention: the molar ratio of hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide is 0.1 mol: 0.1 mol: 6-10 g: 200-400 mL.

[0020] As a further solution of the present invention: the mass ratio of the P / N / S / Si quaternary modified boron nitride flame retardant to the linear low-density polyethylene is 100:5-12.

[0021] A method for preparing a double flame-retardant power cable for fire protection, the method is used to prepare the above-mentioned power cable, the method comprising:

[0022] From the inside to the outside, a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath prepared by the above-mentioned P / N / S / Si quaternary modified boron nitride flame retardant are arranged in sequence; thereby obtaining a double flame-retardant power cable specially used for fire protection.

[0023] Beneficial effects of the present invention:

[0024] The present invention combines the four elements of P / N / S / Si with hydroxylated boron nitride, that is, combines organic flame retardant materials with inorganic flame retardant materials to form a multi-dimensional flame retardant system. Specifically, the flame retardant properties are as follows: phosphorus (P) promotes the formation of a carbon layer, isolating heat and oxygen; nitrogen (N) releases inert gas to dilute combustible gases; sulfur (S) catalyzes the densification of the carbon layer and inhibits free radical chain reactions; silicon (Si) enhances the thermal stability of the carbon layer; boron nitride (BN) improves thermal conductivity and delays thermal degradation. The synergistic effect of each element can effectively improve the flame retardant properties of the cable outer sheath; and the four-element flame retardant material of P / N / S / Si can also effectively solve the problem that DOPO has high molecular polarity, poor compatibility with polyethylene, and is easy to migrate or precipitate during long-term use.

[0025] Furthermore, boron nitride can induce polyethylene crystallization, refine polyethylene grains, and increase the crystallinity of the composite material, making the molecules of the polyethylene outer sheath more densely packed and less likely to penetrate oxygen, thus promoting the flame retardant properties of polyethylene. Boron nitride can also quickly disperse heat, inhibiting local overheating and maintaining the structural integrity of the outer sheath at high temperatures. Through the substitution reaction of Cl groups and hydroxyl groups, chemical bonding between the P / N / S / Si flame retardant and boron nitride is achieved, avoiding interface defects caused by physical blending. The modified boron nitride is evenly dispersed in the polyethylene matrix, which not only improves the tensile strength of the outer sheath but also makes the flame retardancy more uniform.

[0026] It also includes: combining the four elements of P / N / S / Si with hydroxylated boron nitride to give it good hydrolysis resistance, making the flame retardant stable in humid environments, and promoting the water resistance of the outer sheath of the polyethylene cable, so that the power cable can maintain good flame retardancy under long-term wet and hot aging conditions. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0028] Example 1

[0029] The embodiment of the present invention provides a double flame-retardant power cable for fire protection, comprising a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath arranged in sequence from the inside to the outside;

[0030] The preparation process of the polyethylene flame retardant outer protective layer comprises the following steps:

[0031] Step 1: DOPO modified with three flame retardant elements P / N / S containing amino groups is reacted with bis(chloropropyl)tetramethyldisiloxane to prepare a quaternary flame retardant material of P / N / S / Si;

[0032] In step 1, the specific preparation process of the P / N / S / Si quaternary flame retardant material includes:

[0033] The three flame retardant elements P / N / S containing amino groups, modified DOPO, bis(chloropropyl)tetramethyldisiloxane, and chloroform were mixed and nitrogen was introduced for protection. After stirring at a speed of 200 r / min and a temperature of 0°C for 20 minutes, the chloroform was removed by reduced pressure distillation at 38°C using a rotary evaporator to obtain a P / N / S / Si quaternary flame retardant material;

[0034] Among them, the usage ratio of DOPO modified by three flame retardant elements P / N / S containing amino groups, bis(chloropropyl)tetramethyldisiloxane and chloroform is 0.1mol:0.10mol:150mL;

[0035] More specifically, the preparation process of DOPO modified with three flame retardant elements P / N / S containing amino groups is as follows:

[0036] In an ice bath, DOPO was dissolved in dichloromethane, triethylamine and 2-aminobenzothiazole were added and stirred, carbon tetrachloride was added dropwise to the reaction system, the reaction temperature was controlled at 10°C, and the reaction was carried out for 12-15 hours. The filtrate was collected by filtration. The filtrate was evaporated on a rotary evaporator at 80°C until the solution became viscous. Saturated NaHCO3 solution and acetone reagent were added, and the mixture was stirred until solid particles precipitated. The mixture was filtered and washed with deionized water and ethanol until the filter cake became white. The mixture was dried at 120°C for 12 hours to obtain DOPO modified with three flame retardant elements P / N / S containing amino groups.

[0037] The mass ratio of DOPO, dichloromethane, triethylamine, 2-aminobenzothiazole, and carbon tetrachloride is 22.68:100:9:15.20:15;

[0038] Step 2: The Cl group of the P / N / S / Si quaternary flame retardant material is reacted with hydroxylated boron nitride through a substitution reaction to obtain a P / N / S / Si quaternary modified boron nitride flame retardant;

[0039] In step 2, the specific preparation process of the P / N / S / Si quaternary modified boron nitride flame retardant includes:

[0040] Hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide were added to a reactor and reacted at 70°C for 5 hours. After the reaction was completed, the mixture was cooled to room temperature, transferred to a centrifuge tube, and centrifuged at 8000 rpm for 15 minutes to collect the solid product; the solid product was washed with anhydrous ethanol and deionized water three times in sequence to obtain a P / N / S / Si quaternary modified boron nitride flame retardant;

[0041] The molar ratio of hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide is 0.1 mol: 0.1 mol: 6 g: 200 mL;

[0042] Step 3: mixing the P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating and melting, and extruding to obtain a polyethylene flame-retardant outer protective layer;

[0043] The mass ratio of P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene is 100:5.

[0044] The embodiment of the present invention also provides a method for preparing a double flame-retardant power cable for fire protection, comprising the following steps:

[0045] From the inside to the outside, a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath prepared by the above-mentioned P / N / S / Si quaternary modified boron nitride flame retardant are arranged in sequence; thereby obtaining a double flame-retardant power cable specially used for fire protection.

[0046] Example 2

[0047] The embodiment of the present invention provides a double flame-retardant power cable for fire protection, comprising a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath arranged in sequence from the inside to the outside;

[0048] The preparation process of the polyethylene flame retardant outer protective layer comprises the following steps:

[0049] Step 1: DOPO modified with three flame retardant elements P / N / S containing amino groups is reacted with bis(chloropropyl)tetramethyldisiloxane to prepare a quaternary flame retardant material of P / N / S / Si;

[0050] In step 1, the specific preparation process of the P / N / S / Si quaternary flame retardant material includes:

[0051] The three flame retardant elements P / N / S containing amino groups, modified DOPO, bis(chloropropyl)tetramethyldisiloxane, and chloroform were mixed and nitrogen was introduced for protection. After stirring at a speed of 250 r / min and a temperature of 2°C for 30 minutes, the chloroform was removed by reduced pressure distillation at 38°C using a rotary evaporator to obtain a P / N / S / Si quaternary flame retardant material;

[0052] Among them, the usage ratio of DOPO modified with three flame retardant elements P / N / S containing amino groups, bis(chloropropyl)tetramethyldisiloxane and chloroform is 0.1mol:0.10mol:200mL;

[0053] More specifically, the preparation process of DOPO modified with three flame retardant elements P / N / S containing amino groups is as follows:

[0054] DOPO was dissolved in dichloromethane in an ice bath, and triethylamine and 2-aminobenzothiazole were added and stirred. Carbon tetrachloride was then added dropwise to the reaction system. The reaction temperature was controlled at 12°C and the reaction was carried out for 13 hours. The filtrate was collected by filtration. The filtrate was evaporated on a rotary evaporator at 80°C until the solution became viscous. Saturated NaHCO3 solution and acetone reagent were then added. The mixture was stirred until solid particles precipitated and filtered. The filter cake was washed with deionized water and ethanol until it turned white. The filter cake was dried at 120°C for 12 hours to obtain DOPO modified with three flame retardant elements P / N / S containing amino groups.

[0055] The mass ratio of DOPO, dichloromethane, triethylamine, 2-aminobenzothiazole, and carbon tetrachloride is 22.68:120:10:15.20:16;

[0056] Step 2: The Cl group of the P / N / S / Si quaternary flame retardant material is reacted with hydroxylated boron nitride through a substitution reaction to obtain a P / N / S / Si quaternary modified boron nitride flame retardant;

[0057] In step 2, the specific preparation process of the P / N / S / Si quaternary modified boron nitride flame retardant includes:

[0058] Hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide were added to a reactor and reacted at 72°C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature and transferred to a centrifuge tube. The solid product was centrifuged at 9000 rpm for 18 minutes to collect the solid product. The solid product was washed with anhydrous ethanol and deionized water three times in sequence to obtain a P / N / S / Si quaternary modified boron nitride flame retardant.

[0059] The molar ratio of hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide is 0.1 mol: 0.1 mol: 8 g: 300 mL;

[0060] Step 3: mixing the P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating and melting, and extruding to obtain a polyethylene flame-retardant outer protective layer;

[0061] The mass ratio of P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene is 100:8.

[0062] The embodiment of the present invention also provides a method for preparing a double flame-retardant power cable for fire protection, comprising the following steps:

[0063] From the inside to the outside, a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath prepared by the above-mentioned P / N / S / Si quaternary modified boron nitride flame retardant are arranged in sequence; thereby obtaining a double flame-retardant power cable specially used for fire protection.

[0064] Example 3

[0065] The embodiment of the present invention provides a double flame-retardant power cable for fire protection, comprising a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath arranged in sequence from the inside to the outside;

[0066] The preparation process of the polyethylene flame retardant outer protective layer comprises the following steps:

[0067] Step 1: DOPO modified with three flame retardant elements P / N / S containing amino groups is reacted with bis(chloropropyl)tetramethyldisiloxane to prepare a quaternary flame retardant material of P / N / S / Si;

[0068] In step 1, the specific preparation process of the P / N / S / Si quaternary flame retardant material includes:

[0069] The three flame retardant elements P / N / S containing amino groups, modified DOPO, bis(chloropropyl)tetramethyldisiloxane, and chloroform were mixed and nitrogen was introduced for protection. After stirring at a speed of 300 r / min and a temperature of 5°C for 40 minutes, the chloroform was removed by reduced pressure distillation at 38°C using a rotary evaporator to obtain a P / N / S / Si quaternary flame retardant material;

[0070] Among them, the usage ratio of DOPO modified by three flame retardant elements P / N / S containing amino groups, bis(chloropropyl)tetramethyldisiloxane and chloroform is 0.1mol:0.10mol:250mL;

[0071] More specifically, the preparation process of DOPO modified with three flame retardant elements P / N / S containing amino groups is as follows:

[0072] DOPO was dissolved in dichloromethane under ice bath conditions, and triethylamine and 2-aminobenzothiazole were added and stirred. Carbon tetrachloride was then added dropwise to the reaction system. The reaction temperature was controlled at 15°C and the reaction was carried out for 15 hours. The filtrate was collected by filtration. The filtrate was evaporated on a rotary evaporator at 80°C until the solution became viscous. Saturated NaHCO3 solution and acetone reagent were then added. The mixture was stirred until solid particles precipitated and filtered. The filter cake was washed with deionized water and ethanol until it turned white. The filter cake was dried at 120°C for 12 hours to obtain DOPO modified with three flame retardant elements P / N / S containing amino groups.

[0073] The mass ratio of DOPO, dichloromethane, triethylamine, 2-aminobenzothiazole, and carbon tetrachloride is 22.68:150:11:15.20:17;

[0074] Step 2: The Cl group of the P / N / S / Si quaternary flame retardant material is reacted with hydroxylated boron nitride through a substitution reaction to obtain a P / N / S / Si quaternary modified boron nitride flame retardant;

[0075] In step 2, the specific preparation process of the P / N / S / Si quaternary modified boron nitride flame retardant includes:

[0076] Hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide were added to a reactor and reacted at 75°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature and transferred to a centrifuge tube. The solid product was centrifuged at 10,000 rpm for 20 minutes to collect the solid product. The solid product was washed with anhydrous ethanol and deionized water three times in sequence to obtain a P / N / S / Si quaternary modified boron nitride flame retardant.

[0077] The molar ratio of hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide is 0.1 mol: 0.1 mol: 10 g: 400 mL;

[0078] Step 3: mixing the P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating and melting, and extruding to obtain a polyethylene flame-retardant outer protective layer;

[0079] The mass ratio of P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene is 100:12.

[0080] The embodiment of the present invention also provides a method for preparing a double flame-retardant power cable for fire protection, comprising the following steps:

[0081] From the inside to the outside, a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath prepared by the above-mentioned P / N / S / Si quaternary modified boron nitride flame retardant are arranged in sequence; thereby obtaining a double flame-retardant power cable specially used for fire protection.

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is that the pure linear low-density polyethylene (LLDPE) outer sheath cable is not added with the P / N / S / Si quaternary modified boron nitride flame retardant.

[0084] Comparative Example 2

[0085] Comparative Example 2 uses the polyethylene insulated power cable disclosed in Example 1 of Chinese Patent Publication No. CN 108417301 B.

[0086] The outer protective layers of Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the test results are shown in the table below: The performance tests included limiting oxygen index LO I (test standard GB / T 2408-2021), tensile strength (test standard GB / T 1040-2018), and resistance to wet heat aging test (test standard GB / T2951.12-2008);

[0087]

[0088] It can be seen from the above table that the cable outer sheath prepared by the P / N / S / Si quaternary modified boron nitride flame retardant of the present invention has the advantages of good flame retardancy, resistance to wet and hot aging and tensile strength.

[0089] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A double flame retardant power cable for fire protection, characterized in that: It includes a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame retardant outer sheath arranged in sequence from the inside to the outside; The polyethylene flame retardant outer protective layer is prepared by mixing P / N / S / Si quaternary modified boron nitride flame retardant and linear low-density polyethylene in an internal mixer, heating and melting, and extruding.

2. A fire-fighting double flame-retardant power cable according to claim 1, characterized in that: The polyethylene flame retardant outer sheath is prepared by using a P / N / S / Si quaternary modified boron nitride flame retardant, including: The quaternary flame retardant material P / N / S / Si was prepared by reacting DOPO modified with three flame retardant elements containing amino groups with bis(chloropropyl)tetramethyldisiloxane through substitution reaction. The Cl group of the P / N / S / Si quaternary flame retardant material is reacted with hydroxylated boron nitride through substitution reaction to obtain a P / N / S / Si quaternary modified boron nitride flame retardant.

3. A double flame-retardant power cable for fire protection according to claim 2, characterized in that: The specific preparation process of the quaternary flame retardant material of P / N / S / Si is as follows: The three flame retardant elements P / N / S containing amino groups, modified DOPO, bis(chloropropyl)tetramethyldisiloxane and chloroform are mixed, and nitrogen is introduced for protection. The mixture is stirred for 20-40 minutes at a temperature of 0-5°C to obtain a quaternary flame retardant material of P / N / S / Si.

4. A double flame-retardant power cable for fire protection according to claim 3, characterized in that: The usage ratio of DOPO modified by three flame retardant elements P / N / S containing amino groups, bis(chloropropyl)tetramethyldisiloxane and chloroform is 0.1 mol:0.10 mol:150-250 mL.

5. A double flame-retardant power cable for fire protection according to claim 2, characterized in that: The preparation process of DOPO modified with three flame retardant elements P / N / S containing amino groups is as follows: In an ice bath, DOPO was mixed and dissolved with dichloromethane, and triethylamine and 2-aminobenzothiazole were added and stirred. Carbon tetrachloride was then added dropwise to the reaction system. The reaction temperature was controlled at 10-15°C and the reaction was carried out for 12-15 hours to obtain DOPO modified with three flame retardant elements P / N / S containing amino groups.

6. A double flame-retardant power cable for fire protection according to claim 5, characterized in that: The mass ratio of DOPO, dichloromethane, triethylamine, 2-aminobenzothiazole and carbon tetrachloride is 22.68:100-150:9-11:15.20:15-17.

7. A double flame-retardant power cable for fire protection according to claim 2, characterized in that: The specific preparation process of the P / N / S / Si quaternary modified boron nitride flame retardant includes: Hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide are added into a reactor, and the reaction is carried out at a temperature of 70-75°C for 5-8 hours. After the reaction is completed, a P / N / S / Si quaternary modified boron nitride flame retardant is obtained.

8. A double flame-retardant power cable for fire protection according to claim 7, characterized in that: The molar ratio of hydroxylated boron nitride, P / N / S / Si quaternary flame retardant material, potassium hydroxide and N,N-dimethylformamide is 0.1 mol: 0.1 mol: 6-10 g: 200-400 mL.

9. A double flame-retardant power cable for fire protection according to claim 1, characterized in that: The mass ratio of the P / N / S / Si quaternary modified boron nitride flame retardant to the linear low-density polyethylene is 100:5-12.

10. A method for preparing a double flame-retardant power cable for fire protection, characterized in that: The method is used to prepare the power cable according to any one of claims 1 to 9, and the method comprises: From the inside to the outside, a circular conductor, an insulating shielding layer, a metal layer, a metal armor layer and a polyethylene flame-retardant outer sheath prepared by the above-mentioned P / N / S / Si quaternary modified boron nitride flame retardant are arranged in sequence; thereby obtaining a double flame-retardant power cable specially used for fire protection.

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