Flexible fireproof cable and its preparation method

Abstract

The application discloses a kind of flexible fireproof cable and preparation method thereof, belong to cable technical field.The cable includes conductor, mica insulation layer, copper protection layer, buffer layer and cable sheath layer;The buffer layer is polyurethane foaming material;The preparation raw material of the cable sheath layer includes the following components: by weight fraction, 80-100 parts methyl vinyl silicone rubber, 18-20 parts modified carbon black, 5-8 parts titanium dioxide, 1-2 parts platinum gold catalyst, 3-6 parts hydroxyl silicone oil, 0.5-1 parts zinc stearate, 0.8-1 parts dicumyl peroxide.The application adds modified carbon black in the raw material of sheath layer, effectively improves the compatibility of carbon black and silicone rubber matrix, interface bonding force and flame retardant performance, so as to significantly enhance the mechanical property, wear resistance and fireproof performance of cable sheath layer.

Description

Technical Field

[0001] This invention belongs to the field of cable technology, specifically relating to a flexible fire-resistant cable and its preparation method. Background Technology

[0002] Currently, the demand for flexible fire-resistant cables is increasing in fields such as rail transit, high-rise buildings, and new energy, placing higher demands on their flame retardancy, flexibility, and mechanical strength. Commonly used cable sheath materials, such as ordinary silicone rubber, while possessing certain flexibility and heat resistance, often have insufficient flame retardant properties, requiring the addition of large amounts of flame retardants, which can easily lead to a decline in the material's mechanical properties. Carbon black, as a commonly used reinforcing filler, can improve strength, but its high surface energy and tendency to agglomerate result in poor compatibility with silicone rubber, potentially leading to stress defects, reducing the material's tensile strength and abrasion resistance, and affecting processing fluidity and the reliability of the final product. Furthermore, traditional flame-retardant systems are mostly physical blends, resulting in weak bonding between the flame retardant and the matrix, easy migration and precipitation, and poor durability, making it difficult to maintain a stable and effective flame-retardant effect under high-flux or high-temperature conditions.

[0003] Therefore, developing a flexible fireproof cable that combines good dispersibility, high strength and toughness, excellent wear resistance and efficient and durable flame retardant properties has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a flexible fireproof cable and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A flexible fireproof cable includes a conductor, a mica insulation layer, a copper protective layer, a buffer layer, and a cable sheath layer; the buffer layer is a polyurethane foam material; the raw materials for preparing the cable sheath layer include the following components: by weight, 80-100 parts methyl vinyl silicone rubber, 18-20 parts modified carbon black, 5-8 parts titanium dioxide, 1-2 parts platinum catalyst, 3-6 parts hydroxyl silicone oil, 0.5-1 parts zinc stearate, and 0.8-1 parts dicumyl peroxide.

[0007] In a more optimized manner, the preparation process of the modified carbon black is as follows:

[0008] A1: Under a protective atmosphere, polysilazane and flame-retardant monomers were added to dimethylformamide and stirred until homogeneous. Then, Karstedt catalyst was added, the temperature was raised to 80°C, and the mixture was stirred for 48 hours to obtain modified polysilazane.

[0009] A2: Mix the modified polysilazane with acetone, stir until homogeneous, and slowly add to the carbon black dispersion. After the addition is complete, raise the temperature to 50°C and react for 10-12 hours. After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain the modified carbon black.

[0010] In this scheme, flame-retardant functional groups are first grafted onto polysilazane via a platinum-catalyzed hydrosilylation reaction, and then the modified polysilazane is coated onto the surface of carbon black to obtain modified carbon black.

[0011] In a more optimized manner, the raw materials for preparing the modified polysilazane include the following components: by weight, 80-100 parts of polysilazane, 30-40 parts of flame retardant monomer, 200-300 parts of dimethylformamide, and 1-2 parts of Karstedt catalyst.

[0012] More preferably, the raw materials for preparing the modified carbon black include the following components: 20-30 parts by weight of modified polysilazane, 100-120 parts by weight of acetone, and 200-250 parts by weight of carbon black dispersion; wherein the solid content of carbon black in the carbon black dispersion is 10-30 wt%.

[0013] In a more optimized manner, the preparation process of the flame-retardant monomer is as follows:

[0014] S1: Mix 3,5-diamino-1,2,4-triazole, p-aldehyde phenylboronic acid, and anhydrous ethanol, raise the temperature to 85°C, reflux and stir for 3-4 hours, then add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and continue the reaction at 85°C for 3-4 hours. After the reaction is complete, filter, wash, and dry to obtain intermediate A.

[0015] S2: Mix intermediate A, triethylamine, and anhydrous tetrahydrofuran, stir well, and slowly add acryloyl chloride solution dropwise under ice bath. After the addition is complete, continue stirring at room temperature for 2-3 hours. Then, perform post-treatment to obtain the flame retardant monomer.

[0016] In the scheme, the aldehyde group of p-aldehyde phenylboronic acid undergoes a condensation reaction with an amino group on 3,5-diamino-1,2,4-triazole to form an imine bond. Subsequently, the PH bond of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) attacks the imine bond, undergoing a nucleophilic addition reaction to give intermediate A.

[0017] The amino group retained in intermediate A then reacts with acryloyl chloride to yield the flame-retardant monomer; the specific synthesis process is shown below:

[0018]

[0019] In a more optimized manner, the raw materials for preparing intermediate A include the following components: by weight, 10-15 parts of 3,5-diamino-1,2,4-triazole, 15-20 parts of p-aldehyde phenylboronic acid, 200-250 parts of anhydrous ethanol, and 20-25 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0020] In a more optimized manner, the raw materials for preparing the flame retardant monomer include the following components: by weight, 30-40 parts of intermediate A, 10-15 parts of triethylamine, 80-100 parts of anhydrous tetrahydrofuran, and 10-20 parts of acryloyl chloride solution; wherein the concentration of the acryloyl chloride solution is 12 wt%.

[0021] A more optimized method for preparing a flexible fire-resistant cable includes the following steps:

[0022] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0023] Step 2: Methyl vinyl silicone rubber is plasticized on a two-roll mill. Modified carbon black, titanium dioxide, platinum catalyst, hydroxyl silicone oil and zinc stearate are added in sequence and mixed evenly. Then dicumyl peroxide is added and mixed evenly again. The mixture is discharged to obtain the compound.

[0024] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0025] The beneficial effects of this invention are:

[0026] This invention, by modifying the surface of carbon black and introducing it into the cable sheath layer, effectively solves the defects of traditional flexible fire-resistant cables, which suffer from insufficient mechanical properties, abrasion resistance, and long-lasting flame retardant performance due to poor compatibility between carbon black and the matrix, and the single and easily migrating nature of flame retardants. It achieves a synergistic improvement in fire resistance, abrasion resistance, flexibility, and tensile strength. Specifically:

[0027] First, the cable structure described in this invention constructs multiple synergistic fire barriers between the cable's interior and exterior through the inherent fire-resistant properties of the mica insulation layer, the melt protection of the copper protective layer, and the highly efficient flame-retardant and ceramic-carbonizing ability of the modified carbon black-reinforced sheath layer. When encountering an external fire source, the sheath layer first exerts its highly efficient and long-lasting flame-retardant and ablation-resistant effects, delaying the spread of flames; even if the outer sheath is partially damaged, the internal mica insulation layer can still maintain its insulation performance for a period of time, while the copper protective layer can form a supporting skeleton at extremely high temperatures to prevent the cable core from collapsing, jointly ensuring the cable's emergency power supply function under fire conditions.

[0028] The high-efficiency and durable fire-resistant and ablation-resistant capability of the cable sheath in this invention is achieved by chemically grafting flame-retardant units containing phosphorus (DOPO structure), nitrogen (triazole structure), and boron (derived from p-aldehyde phenylboronic acid) into the modified layer, constructing a multiple flame-retardant mechanism with synergistic effects of the gas phase and condensed phase. At high temperatures, the phosphorus-containing component can effectively capture free radicals to interrupt the combustion reaction; the nitrogen-containing component and polysilazane synergistically promote the formation of a dense and stable ceramicized carbon layer; and the introduced boron element can generate borate glass at high temperatures, which can cover and strengthen the ceramicized carbon layer, further isolating heat and oxygen, significantly improving the density, stability, and ablation resistance of the carbon layer, and forming a stronger condensed phase barrier.

[0029] Second, this invention coats the surface of carbon black particles with modified polysilazane. The main chain of the polysilazane molecule contains -Si-N- bonds similar to those in silicone rubber, and its organic side groups (such as methyl and vinyl groups) have excellent affinity with the silicone rubber matrix, thereby effectively enhancing the interfacial bonding force, preventing the agglomeration of carbon black particles, and ensuring that they are uniformly dispersed and firmly embedded in the matrix. This uniformly transmits stress and significantly improves the wear resistance and overall mechanical properties of the sheathing material. Furthermore, the excellent dispersibility and interfacial compatibility prevent stress defects caused by filler agglomeration, ensuring that the material maintains good flexibility and torsional fatigue resistance during polymer chain segment movement. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: A method for preparing a flexible fire-resistant cable, comprising the following steps:

[0032] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0033] Step 2: Plasticize 80 parts of methyl vinyl silicone rubber on a two-roll mill, then add 18 parts of modified carbon black, 5 parts of titanium dioxide, 1 part of platinum catalyst, 3 parts of hydroxyl silicone oil, and 0.5 parts of zinc stearate and mix evenly. Then add 0.8 parts of dicumyl peroxide and mix evenly again. Discharge the mixture to obtain the compound.

[0034] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0035] The preparation process of modified carbon black is as follows:

[0036] A1: Under a protective atmosphere, 80 parts of polysilazane and 30 parts of flame retardant monomer were added to 200 parts of dimethylformamide and stirred evenly. Then, 1 part of Karstedt catalyst was added, the temperature was raised to 80°C, and the mixture was stirred for 48 hours to obtain modified polysilazane.

[0037] A2: Mix 20 parts of modified polysilazane with 100 parts of acetone, stir evenly, and slowly add dropwise to 200 parts of carbon black dispersion (solid content is 10wt%). After the addition is complete, raise the temperature to 50℃ and react for 10h. After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain modified carbon black.

[0038] The preparation process of the flame-retardant monomer is as follows:

[0039] S1: Mix 10 parts of 3,5-diamino-1,2,4-triazole, 15 parts of p-aldehyde phenylboronic acid, and 200 parts of anhydrous ethanol, raise the temperature to 85°C, reflux and stir for 3 hours, then add 20 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and continue the reaction at 85°C for 3 hours. After the reaction is completed, filter, wash, and dry to obtain intermediate A;

[0040] S2: Mix 30 parts of intermediate A, 10 parts of triethylamine, and 80 parts of anhydrous tetrahydrofuran, stir well, and slowly add 10 parts of acryloyl chloride solution (concentration of 12wt%) dropwise under ice bath. After the addition is complete, continue stirring at room temperature for 2 hours. After post-treatment, the flame retardant monomer is obtained.

[0041] Example 2: A method for preparing a flexible fire-resistant cable, comprising the following steps:

[0042] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0043] Step 2: Plasticize 100 parts of methyl vinyl silicone rubber on a two-roll mill, then add 20 parts of modified carbon black, 8 parts of titanium dioxide, 2 parts of platinum catalyst, 6 parts of hydroxyl silicone oil, and 1 part of zinc stearate and mix evenly. Then add 1 part of dicumyl peroxide and mix evenly again. Discharge the mixture to obtain the compound.

[0044] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0045] The preparation process of modified carbon black is as follows:

[0046] A1: Under a protective atmosphere, 100 parts of polysilazane and 40 parts of flame retardant monomer were added to 300 parts of dimethylformamide and stirred evenly. Then, 2 parts of Karstedt catalyst were added, the temperature was raised to 80°C, and the mixture was stirred for 48 hours to obtain modified polysilazane.

[0047] A2: Mix 30 parts of modified polysilazane with 120 parts of acetone, stir evenly, and slowly add dropwise to 250 parts of carbon black dispersion (solid content is 30wt%). After the addition is complete, raise the temperature to 50℃ and react for 12h. After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain modified carbon black.

[0048] The preparation process of the flame-retardant monomer is as follows:

[0049] S1: Mix 15 parts of 3,5-diamino-1,2,4-triazole, 20 parts of p-aldehyde phenylboronic acid, and 250 parts of anhydrous ethanol, raise the temperature to 85°C, reflux and stir for 4 hours, then add 25 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and continue the reaction at 85°C for 4 hours. After the reaction is completed, filter, wash, and dry to obtain intermediate A;

[0050] S2: Mix 40 parts of intermediate A, 15 parts of triethylamine, and 100 parts of anhydrous tetrahydrofuran, stir well, and slowly add 20 parts of acryloyl chloride solution (concentration of 12wt%) dropwise under ice bath. After the addition is complete, continue stirring at room temperature for 3 hours. After post-treatment, the flame retardant monomer is obtained.

[0051] Example 3: A method for preparing a flexible fire-resistant cable, comprising the following steps:

[0052] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0053] Step 2: Plasticize 90 parts of methyl vinyl silicone rubber on a two-roll mill, then add 19 parts of modified carbon black, 6.5 parts of titanium dioxide, 1.5 parts of platinum catalyst, 4.5 parts of hydroxyl silicone oil, and 0.75 parts of zinc stearate in sequence and mix evenly. Then add 0.9 parts of dicumyl peroxide and mix evenly again. Discharge the material to obtain the compound.

[0054] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0055] The preparation process of modified carbon black is as follows:

[0056] A1: Under a protective atmosphere, 90 parts of polysilazane and 35 parts of flame retardant monomer were added to 250 parts of dimethylformamide and stirred evenly. Then, 1.5 parts of Karstedt catalyst were added, the temperature was raised to 80℃, and the reaction was stirred for 48 hours to obtain modified polysilazane.

[0057] A2: Mix 25 parts of modified polysilazane with 110 parts of acetone, stir evenly, and slowly add dropwise to 225 parts of carbon black dispersion (solid content is 20wt%). After the addition is complete, raise the temperature to 50℃ and react for 11 hours. After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain modified carbon black.

[0058] The preparation process of the flame-retardant monomer is as follows:

[0059] S1: 12.5 parts of 3,5-diamino-1,2,4-triazole, 17.5 parts of p-aldehyde phenylboronic acid, and 225 parts of anhydrous ethanol were mixed, the temperature was raised to 85°C, and the mixture was refluxed and stirred for 3.5 h. Then 22.5 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the reaction was continued at 85°C for 3.5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain intermediate A.

[0060] S2: Mix 35 parts of intermediate A, 12.5 parts of triethylamine, and 90 parts of anhydrous tetrahydrofuran, stir well, and slowly add 15 parts of acryloyl chloride solution (concentration of 12wt%) dropwise under ice bath. After the addition is complete, continue stirring at room temperature for 2.5 hours. After post-treatment, the flame retardant monomer is obtained.

[0061] Comparative Example 1: No modification was performed on the carbon black, as follows:

[0062] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0063] Step 2: Plasticize 90 parts of methyl vinyl silicone rubber on a two-roll mill, then add 19 parts of carbon black, 6.5 parts of titanium dioxide, 1.5 parts of platinum catalyst, 4.5 parts of hydroxyl silicone oil, and 0.75 parts of zinc stearate in sequence and mix evenly. Then add 0.9 parts of dicumyl peroxide and mix evenly again. Discharge the material to obtain the compound.

[0064] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0065] Comparative Example 2: No modification was made to the polysilazane, as follows:

[0066] Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; then, wrap a seamless copper protective layer outside the mica insulation layer to obtain a composite core, which is then twisted into a cable core; and then cover the cable core with a layer of polyurethane foam material as a buffer layer.

[0067] Step 2: Plasticize 90 parts of methyl vinyl silicone rubber on a two-roll mill, then add 19 parts of modified carbon black, 6.5 parts of titanium dioxide, 1.5 parts of platinum catalyst, 4.5 parts of hydroxyl silicone oil, and 0.75 parts of zinc stearate in sequence and mix evenly. Then add 0.9 parts of dicumyl peroxide and mix evenly again. Discharge the material to obtain the compound.

[0068] Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

[0069] The preparation process of modified carbon black is as follows:

[0070] 25 parts of polysilazane and 110 parts of acetone were mixed and stirred evenly. The mixture was then slowly added dropwise to 225 parts of carbon black dispersion (solid content of 20 wt%). After the addition was complete, the temperature was raised to 50°C and the reaction was carried out for 11 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed, and dried to obtain modified carbon black.

[0071] Testing and experimentation:

[0072] (1) At room temperature, fix one end of the cable of the example and the comparative example on the fixed clamp of the testing machine and the other end on the rotating clamp. Set the torsion angle (±180°), the speed (30 times / min), and the target number of times (100,000 times). Start the testing machine to ensure that the cable axis coincides with the torsion axis. During the test, stop the machine every 10,000 times to check: observe whether there is cracking in the appearance; evaluate whether it passes after the test. Evaluation criteria: no cracks or twisting on the surface of the sample.

[0073] (2) The tensile strength of the cable sheath layer of the embodiments and comparative examples was tested in accordance with the standard GB / T 1040-2006;

[0074] (3) According to standard GB / T 9867-2008, the relative volumetric wear of the cable sheath in the examples and comparative examples were tested respectively;

[0075] (4) The oxygen index of the cable sheaths of the examples and comparative examples was determined by high temperature test according to standard GB / T 2406.3-2022;

[0076] (5) The integrity of the fire-resistant cable circuit was tested according to BS 6387:2013 "Fire resistance test method for cable to maintain circuit integrity under flame conditions". Under the test environment of 950±40℃, the test voltage is 0.6 / 1KV and the fire is supplied for 180min. If the fuse does not break or the bulb goes out during the test, it means that the test is passed;

[0077] The obtained data is shown in the table below:

[0078]

[0079] Conclusion: The flexible fire-resistant cable prepared by this invention exhibits excellent performance in terms of tensile strength, abrasion resistance, oxygen index, and fire resistance. The tensile strength of the cable sheath layer in Examples 1 to 3 reaches 11.5-12.1 MPa, and the relative volumetric abrasion loss is 75-85 mm. 3 The oxygen index of all samples was higher than 33%, and all samples passed the room temperature torsion test and fire resistance test, indicating that the cable of the present invention has good mechanical properties, wear resistance, flexibility and long-lasting flame retardant properties.

[0080] Comparative Example 1 used unmodified carbon black. Due to the poor compatibility of carbon black with the silicone rubber matrix and its tendency to agglomerate, the tensile strength was only 7.2 MPa, and the abrasion loss was as high as 135 mm. 3The oxygen index of the unmodified carbon black was only 28.5%, and it failed the fire resistance test, indicating that the unmodified carbon black is prone to stress defects and has insufficient flame retardant effect. Comparative Example 2 used polysilazane-coated carbon black without a grafted flame-retardant structure. Although its tensile strength and abrasion resistance were better than Comparative Example 1, they were still lower than those of the present invention. Its oxygen index was 30.8%, indicating a lack of a phosphorus-nitrogen-boron synergistic flame-retardant structure, and its flame-retardant performance and interfacial bonding were still insufficient.

[0081] In summary, this invention effectively improves the dispersibility and interfacial bonding of carbon black in silicone rubber by introducing modified carbon black, and achieves synergistic flame retardancy of the gas phase and condensed phase by utilizing the grafted phosphorus-nitrogen flame retardant structure, thereby significantly enhancing the overall performance of the cable sheath layer.

[0082] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above 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 one or more embodiments or examples.

[0083] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A flexible fire-resistant cable, characterized in that, The cable includes a conductor, a mica insulation layer, a copper protective layer, a buffer layer, and a cable sheath layer; the buffer layer is a polyurethane foam material; the raw materials for preparing the cable sheath layer include the following components: by weight, 80-100 parts methyl vinyl silicone rubber, 18-20 parts modified carbon black, 5-8 parts titanium dioxide, 1-2 parts platinum catalyst, 3-6 parts hydroxyl silicone oil, 0.5-1 part zinc stearate, and 0.8-1 part dicumyl peroxide; The preparation process of the modified carbon black is as follows: A1: Under a protective atmosphere, polysilazane and flame-retardant monomers were added to dimethylformamide and stirred until homogeneous. Then, Karstedt catalyst was added, the temperature was raised to 80°C, and the mixture was stirred for 48 hours to obtain modified polysilazane. A2: By weight, mix 20-30 parts of modified polysilazane with 100-120 parts of acetone, stir until homogeneous, and then slowly add the mixture to 200-250 parts of carbon black dispersion. After the addition is complete, raise the temperature to 50°C and react for 10-12 hours. After the reaction is complete, cool to room temperature, filter, wash, and dry to obtain modified carbon black; wherein the solid content of carbon black in the carbon black dispersion is 10-30 wt%. The preparation process of the flame-retardant monomer is as follows: S1: Mix 3,5-diamino-1,2,4-triazole, p-aldehyde phenylboronic acid, and anhydrous ethanol, raise the temperature to 85°C, reflux and stir for 3-4 hours, then add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and continue the reaction at 85°C for 3-4 hours. After the reaction is complete, filter, wash, and dry to obtain intermediate A. S2: Mix intermediate A, triethylamine, and anhydrous tetrahydrofuran, stir well, and slowly add acryloyl chloride solution dropwise under ice bath. After the addition is complete, continue stirring at room temperature for 2-3 hours. Then, perform post-treatment to obtain the flame retardant monomer.

2. The flexible fire-resistant cable according to claim 1, characterized in that, The raw materials for preparing the modified polysilazane include the following components: by weight, 80-100 parts polysilazane, 30-40 parts flame retardant monomer, 200-300 parts dimethylformamide, and 1-2 parts Karstedt catalyst.

3. The flexible fire-resistant cable according to claim 1, characterized in that, The raw materials for preparing intermediate A include the following components: by weight, 10-15 parts of 3,5-diamino-1,2,4-triazole, 15-20 parts of p-aldehyde phenylboronic acid, 200-250 parts of anhydrous ethanol, and 20-25 parts of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

4. A flexible fire-resistant cable according to claim 1, characterized in that, The raw materials for preparing the flame retardant monomer include the following components: by weight, 30-40 parts intermediate A, 10-15 parts triethylamine, 80-100 parts anhydrous tetrahydrofuran, and 10-20 parts acryloyl chloride solution; wherein the concentration of the acryloyl chloride solution is 12 wt%.

5. A method for preparing a flexible fire-resistant cable according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Twist multiple strands of soft copper wire to form a conductor, and continuously wrap mica tape around the surface of the conductor to form a mica insulation layer; Subsequently, a seamless copper protective layer is wrapped around the mica insulation layer to obtain a composite core, which is then stranded into a cable core; and a layer of polyurethane foam material is wrapped around the cable core as a buffer layer. Step 2: Methyl vinyl silicone rubber is plasticized on a two-roll mill. Modified carbon black, titanium dioxide, platinum catalyst, hydroxyl silicone oil and zinc stearate are added in sequence and mixed evenly. Then dicumyl peroxide is added and mixed evenly again. The mixture is discharged to obtain the compound. Step 3: The compounded rubber is extruded onto the surface of the buffer layer through an extruder, followed by a first-stage vulcanization and a second-stage vulcanization. After discharge, the cable sheath layer is obtained, cooled, and the final cable is obtained.

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