A flexible mineral insulated fire-resistant cable

Abstract

The present invention discloses a flexible mineral insulated fireproof cable, belonging to the technical field of fireproof cables, which includes four parallel copper conductors. A silicone rubber mineral insulation layer is wrapped around the outer side of the copper conductors. A mica tape wrapping layer is wrapped around the outer side of the silicone rubber mineral insulation layer. A filling layer is provided outside the mica tape wrapping layer. An armor layer is wrapped outside the filling layer. An outer sheath is provided outside the armor layer. In the present invention, the brucite mineral fiber is modified to form a silicone rubber mineral insulation layer, which improves the mechanical properties of the cable, avoids structural damage caused by stress concentration, ensures the structural integrity of the cable, enhances the flexibility of the cable, and is not prone to breakage or internal structural damage during the bending process. Through the physical properties of the modified brucite fiber, it can effectively resist abrasion and extend the service life of the cable. The compatibility of the modified brucite fiber with silicone rubber and fillers is better, and the cable added with the modified brucite fiber has excellent fireproof and flame retardant properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of fire-resistant cables, and particularly relates to a flexible mineral-insulated fire-resistant cable. Background Art

[0002] Mineral-insulated fire-resistant cables, as key materials in the field of power transmission and distribution, play a crucial role in modern buildings, industrial facilities, and various places with strict fire safety requirements. Their main function is to maintain the integrity of the line and the normal power supply ability in extreme situations such as fires, providing reliable power support for personnel evacuation, fire fighting and rescue, and the continuous operation of important equipment.

[0003] Currently, in the preparation process of mineral-insulated fire-resistant cables, the method of directly adding inorganic mineral flame retardants is generally adopted. Due to the large differences in the physical and chemical properties between inorganic mineral flame retardants and cable matrix materials, it is difficult to disperse them evenly in the matrix during processing, and agglomeration is likely to occur. This not only leads to the non-uniformity of the cable internal structure, affects the overall performance of the cable, but also may form weak points in local areas, reducing the fire resistance and service life of the cable. Secondly, inorganic mineral flame retardants will migrate to the outside of the layer where they are located. During the long-term use of the cable, affected by factors such as temperature changes, electric field effects, and mechanical vibrations, inorganic mineral flame retardants will gradually migrate from their original positions to the outer layer of the cable. This migration phenomenon will change the distribution of the flame retardants inside the cable, destroying the originally designed flame retardant structure, thereby weakening the fire resistance of the cable. Summary of the Invention

[0004] In view of the above situation, to overcome the defects of the prior art, the present invention modifies brucite mineral fibers and applies them to the preparation of silicone rubber mineral insulation layers, effectively solving the problems of uneven dispersion and migration of inorganic mineral flame retardants in the cable matrix, and improving the mechanical properties, insulation properties, and fire resistance and flame retardancy of the cable.

[0005] To achieve the above object, the following technical solution is adopted: The present invention provides a flexible mineral-insulated fire-resistant cable, including four parallel copper conductors. A silicone rubber mineral insulation layer is wound around the outside of the copper conductors. A mica tape winding layer is wound around the outside of the silicone rubber mineral insulation layer. A filling layer is provided outside the mica tape winding layer. An armor layer is wrapped outside the filling layer. An outer sheath is provided outside the armor layer.

[0006] Among them, the composition of the silicone rubber mineral insulation layer includes, by mass: 60 - 80 parts of silicone rubber, 2 - 5 parts of vulcanizing agent, 30 - 40 parts of filler, and 8 - 12 parts of modified brucite fibers.

[0007] Among them, the modified brucite fibers are prepared through the following steps:

[0008] S1. Disperse brucite fibers in acetic acid solution with a concentration of 0.1 - 0.5 mol / L, react at 50 °C for 2 h to obtain a brucite fiber dispersion. Dissolve (2,6 - dichlorobenzenesulfonylamino)-acetic acid in DMF to obtain an intercalation modification solution. Slowly drip the intercalation modification solution into the brucite fiber dispersion, stir at 80 °C for 5 - 8 h, and then stir at room temperature for 24 - 48 h. After the reaction is completed, filter, wash the filter cake with DMF three times, then wash the filter cake with deionized water three times, and vacuum dry at 80 °C for 12 - 18 h to obtain intercalation - modified brucite fibers;

[0009] S2. Add 3 - mercaptopropionic acid to absolute ethanol, add intercalation - modified brucite fibers and stir for 15 min, then add a photoinitiator and divinyl - terminated polydimethylsiloxane, irradiate with 365 nm ultraviolet light, and react at room temperature for 3 - 6 h. Filter, wash the filter cake with toluene three times, and vacuum dry at 80 °C for 12 - 18 h to obtain grafted silane intercalation - modified brucite fibers;

[0010] S3. Add grafted silane intercalation - modified brucite fibers to absolute ethanol, stir to disperse them evenly, then slowly add diglycerol borate, continue to stir for 15 min, then drip triethylamine, react at 70 °C for 3 - 5 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake with absolute ethanol three times, and dry in a vacuum drying oven at 50 °C for 24 - 36 h to obtain the modified brucite fiber product.

[0011] Preferably, in step S1, the mass ratio of brucite fibers to acetic acid solution is 1:10 - 15.

[0012] Preferably, in step S1, the mass ratio of (2,6 - dichlorobenzenesulfonylamino)-acetic acid to DMF is 1:8 - 10.

[0013] Preferably, in step S1, the mass ratio of the intercalation modification solution to the brucite fiber dispersion is 1:5 - 8.

[0014] Preferably, in step S2, the mass ratio of 3 - mercaptopropionic acid, absolute ethanol, intercalation - modified brucite fibers, photoinitiator and divinyl - terminated polydimethylsiloxane is 1:20 - 35:5 - 10:0.05 - 0.2:3 - 5.

[0015] Preferably, in step S3, the mass ratio of absolute ethanol, grafted silane intercalation - modified brucite fibers, diglycerol borate and triethylamine is 30:5 - 10:1 - 5:1 - 3.

[0016] Preferably, the photoinitiator is one of Irgacure 2959, Irgacure 184, Irgacure 369, Irgacure 500 and Irgacure 651.

[0017] Preferably, the molecular weight of the silicone rubber is 300,000 - 450,000.

[0018] Preferably, the vulcanizing agent is one or a combination of more than one of tert-butyl perbenzoate, di-tert-butyl peroxide, bis(2,4-dichlorobenzoyl) peroxide, and bis(2,5-dichlorobenzoyl) peroxide.

[0019] Preferably, the filler is a combination of silica white and calcium carbonate in a mass ratio of 5:1 - 3.

[0020] Preferably, the specific surface area of the silica white is 150 - 200 m 2 / g.

[0021] Preferably, the filling layer is refractory mineral wool; the armored layer is galvanized steel strip; the outer sheath is a low-smoke and halogen-free cross-linked polyethylene material.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) In the present invention, the brucite mineral fiber is modified to form a silicone rubber mineral insulation layer, which improves the compressive, flexural, and abrasion resistance strengths of the cable, avoids structural damage caused by stress concentration, thereby ensuring the structural integrity of the cable in a complex environment, enhancing the flexibility of the cable, making it not easy to break or have internal structural damage during the bending process. Through the physical properties of the modified brucite fiber, it can effectively resist abrasion, extend the service life of the cable, and the compatibility of the modified brucite fiber with silicone rubber and filler is better. The cable added with the modified brucite fiber has excellent fire and flame retardancy. The cable can form a stable heat insulation layer at high temperatures, prevent the rapid transfer of heat, and delay the combustion speed;

[0024] (2) Since the reaction between (2,6-dichlorobenzenesulfonylamino)-acetic acid and brucite fiber is difficult, in the present invention, the brucite fiber is first reacted with acetic acid, and then (2,6-dichlorobenzenesulfonylamino)-acetic acid is used to replace acetic acid based on the principle of strong acid displacing weak acid to intercalate the brucite fiber. Through the intercalation treatment, the layer spacing of the brucite is increased, making the internal structure of the brucite fiber more porous, thereby providing more space for the absorption and dispersion of heat;

[0025] (3) In the present invention, divinyl-terminated polydimethylsiloxane is introduced onto the surface of brucite through thiol-ene click reaction, and brucite is connected to diglycerol borate through divinyl-terminated polydimethylsiloxane as a bridge. In the prepared modified brucite fibers, there is a synergistic flame retardant effect of multiple elements such as silicon, nitrogen, sulfur, and boron. Silicon can form a glassy protective film at high temperatures, nitrogen can decompose to produce non-combustible gases, sulfur will generate sulfur-containing compounds during combustion to promote the formation of a carbon layer and enhance the stability of the carbon layer, and boron can melt at a relatively low temperature and cover the surface of the cable to play a role in heat insulation and oxygen isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic structural diagram of a flexible mineral insulated fireproof cable of the present invention;

[0027] Figure 2 is the test result of the mechanical properties of the silicone rubber mineral insulation layer in a flexible mineral insulated fireproof cable of the present invention;

[0028] Figure 3 is the test result of the insulation performance of the silicone rubber mineral insulation layer in a flexible mineral insulated fireproof cable of the present invention;

[0029] Figure 4 is the test result of the fireproof and flame retardant performance of a flexible mineral insulated fireproof cable of the present invention.

[0030] Legend: 1. Copper conductor; 2. Silicone rubber mineral insulation layer; 3. Mica tape wrapping layer; 4. Filling layer; 5. Armor layer; 6. Outer sheath.

[0031] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described herein are only for illustrative purposes and do not limit the content of this application.

[0034] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all purchased from commercial channels unless otherwise specified. Example 1

[0035] A flexible mineral insulated fireproof cable includes four parallel copper conductors. A silicone rubber mineral insulation layer is wound around the outside of the copper conductors. A mica tape winding layer is wound around the outside of the silicone rubber mineral insulation layer. A filling layer is provided outside the mica tape winding layer. An armor layer is wrapped outside the filling layer. An outer sheath is provided outside the armor layer.

[0036] The composition of the silicone rubber mineral insulation layer includes, by mass: 60 parts of silicone rubber, 2 parts of vulcanizing agent, 30 parts of filler, and 8 parts of modified brucite fiber.

[0037] The modified brucite fiber is prepared by the following steps:

[0038] S1. Disperse brucite fiber in 0.1 mol / L acetic acid solution. The mass ratio of brucite fiber to acetic acid solution is 1:10. React at 50 °C for 2 h to obtain a brucite fiber dispersion. Dissolve (2,6-dichlorobenzenesulfonylamino)-acetic acid in DMF. The mass ratio of (2,6-dichlorobenzenesulfonylamino)-acetic acid to DMF is 1:8 to obtain an intercalation modification solution. Slowly drip the intercalation modification solution into the brucite fiber dispersion. The mass ratio of the intercalation modification solution to the brucite fiber dispersion is 1:5. Stir at 80 °C for 5 h, then stir at room temperature for 24 h. After the reaction is completed, filter, wash the filter cake 3 times with DMF, and then wash the filter cake 3 times with deionized water. Vacuum dry at 80 °C for 12 h to obtain intercalation-modified brucite fiber;

[0039] S2. Add 3-mercaptopropionic acid to absolute ethanol. The mass ratio of 3-mercaptopropionic acid, absolute ethanol, intercalation-modified brucite fiber, photoinitiator, and divinyl-terminated polydimethylsiloxane is 1:20:5:0.05:3. Add the intercalation-modified brucite fiber and stir for 15 min, then add photoinitiator Irgacure 2959 and divinyl-terminated polydimethylsiloxane. Irradiate with 365 nm ultraviolet light and react at room temperature for 3 h. Filter, wash the filter cake 3 times with toluene, and vacuum dry at 80 °C for 12 h to obtain grafted silane intercalation-modified brucite fiber;

[0040] S3. Add grafted silane intercalated modified brucite fibers to absolute ethanol. The mass ratio of absolute ethanol, grafted silane intercalated modified brucite fibers, diglycerol borate, and triethylamine is 30:5:1:1. Stir to disperse them evenly, then slowly add diglycerol borate, continue stirring for 15 min, then add triethylamine dropwise, and react at 70 °C for 3 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake with absolute ethanol three times, and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the modified brucite fiber product.

[0041] The molecular weight of the silicone rubber is 300,000, the vulcanizing agent is tert-butyl perbenzoate, the filler is a combination of silica and calcium carbonate in a mass ratio of 5:1, and the specific surface area of the silica is 150 m² / g; the filling layer is refractory mineral wool; the armor layer is galvanized steel strip; the outer sheath is a low-smoke and halogen-free cross-linked polyethylene material. Example 2

[0042] A flexible mineral insulated fire-resistant cable includes four parallel copper conductors. A silicone rubber mineral insulation layer is wrapped around the outside of the copper conductors, a mica tape wrapping layer is wrapped around the outside of the silicone rubber mineral insulation layer, a filling layer is provided outside the mica tape wrapping layer, an armor layer is wrapped outside the filling layer, and an outer sheath is provided outside the armor layer.

[0043] The composition of the silicone rubber mineral insulation layer includes, by mass: 80 parts of silicone rubber, 5 parts of vulcanizing agent, 40 parts of filler, and 12 parts of modified brucite fibers.

[0044] The modified brucite fibers are prepared by the following steps:

[0045] S1. Disperse brucite fibers in a 0.5 mol / L acetic acid solution. The mass ratio of brucite fibers to acetic acid solution is 1:15. React at 50 °C for 2 h to obtain a brucite fiber dispersion. Dissolve (2,6-dichlorobenzenesulfonylamino)-acetic acid in DMF. The mass ratio of (2,6-dichlorobenzenesulfonylamino)-acetic acid to DMF is 1:10 to obtain an intercalation modification solution. Slowly drop the intercalation modification solution into the brucite fiber dispersion. The mass ratio of the intercalation modification solution to the brucite fiber dispersion is 1:8. Stir at 80 °C for 8 h, then stir at room temperature for 48 h. After the reaction is completed, filter, wash the filter cake with DMF three times, then wash the filter cake with deionized water three times, and dry it in a vacuum at 80 °C for 18 h to obtain intercalated modified brucite fibers;

[0046] S2. Add 3-mercaptopropionic acid into absolute ethanol. The mass ratio of 3-mercaptopropionic acid, absolute ethanol, intercalated modified brucite fibers, photoinitiator and divinyl-terminated polydimethylsiloxane is 1:35:10:0.2:5. Add the intercalated modified brucite fibers and stir for 15 min, then add photoinitiator Irgacure 651 and divinyl-terminated polydimethylsiloxane. Irradiate with 365 nm ultraviolet light and react at room temperature for 6 h. Filter, wash the filter cake with toluene three times, and dry it in vacuum at 80 °C for 18 h to obtain grafted silane intercalated modified brucite fibers;

[0047] S3. Add the grafted silane intercalated modified brucite fibers into absolute ethanol. The mass ratio of absolute ethanol, grafted silane intercalated modified brucite fibers, diglycerol borate and triethylamine is 30:10:5:3. Stir to disperse evenly, then slowly add diglycerol borate and continue to stir for 15 min, then dropwise add triethylamine and react at 70 °C for 5 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake with absolute ethanol three times, and dry it in a vacuum drying oven at 50 °C for 36 h to obtain the modified brucite fiber product.

[0048] The molecular weight of the silicone rubber is 450,000; the vulcanizing agent is a combination of di-tert-butyl peroxide, bis(t-butylperoxyisopropyl)benzene and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane in a mass ratio of 1:1:2; the filler is a combination of fumed silica and calcium carbonate in a mass ratio of 5:3, and the specific surface area of the fumed silica is 200 m² / g; the filling layer is refractory mineral wool; the armor layer is galvanized steel strip; the outer sheath is a low-smoke, halogen-free cross-linked polyethylene material. Example 3

[0049] A flexible mineral insulated fire-resistant cable includes four parallel copper conductors. A silicone rubber mineral insulation layer is wound around the outside of the copper conductors. A mica tape winding layer is wound around the outside of the silicone rubber mineral insulation layer. A filling layer is provided outside the mica tape winding layer. An armor layer is wrapped outside the filling layer. An outer sheath is provided outside the armor layer.

[0050] The composition of the silicone rubber mineral insulation layer includes, by mass: 70 parts of silicone rubber, 3.5 parts of vulcanizing agent, 35 parts of filler and 10 parts of modified brucite fibers.

[0051] The modified brucite fibers are prepared by the following steps:

[0052] S1. Disperse brucite fibers in 0.3 mol / L acetic acid solution. The mass ratio of brucite fibers to acetic acid solution is 1:12.5. React at 50 °C for 2 h to obtain a brucite fiber dispersion. Dissolve (2,6-dichlorobenzenesulfonylamino)-acetic acid in DMF. The mass ratio of (2,6-dichlorobenzenesulfonylamino)-acetic acid to DMF is 1:9 to obtain an intercalation modification solution. Slowly add the intercalation modification solution to the brucite fiber dispersion. The mass ratio of the intercalation modification solution to the brucite fiber dispersion is 1:6.5. Stir at 80 °C for 6.5 h, then stir at room temperature for 36 h. After the reaction is completed, filter, wash the filter cake 3 times with DMF, and then wash the filter cake 3 times with deionized water. Vacuum dry at 80 °C for 15 h to obtain intercalation-modified brucite fibers;

[0053] S2. Add 3-mercaptopropionic acid to absolute ethanol. The mass ratio of 3-mercaptopropionic acid, absolute ethanol, intercalation-modified brucite fibers, photoinitiator, and divinyl-terminated polydimethylsiloxane is 1:27.5:7.5:0.125:4. Add intercalation-modified brucite fibers and stir for 15 min, then add photoinitiator Irgacure 369 and divinyl-terminated polydimethylsiloxane. Irradiate with 365 nm ultraviolet light and react at room temperature for 4.5 h. Filter, wash the filter cake 3 times with toluene, and vacuum dry at 80 °C for 15 h to obtain grafted silane intercalation-modified brucite fibers;

[0054] S3. Add grafted silane intercalation-modified brucite fibers to absolute ethanol. The mass ratio of absolute ethanol, grafted silane intercalation-modified brucite fibers, diglycerol borate, and triethylamine is 30:7.5:3:2. Stir to disperse evenly, then slowly add diglycerol borate and continue to stir for 15 min, then dropwise add triethylamine. React at 70 °C for 4 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake 3 times with absolute ethanol, and dry in a vacuum drying oven at 50 °C for 30 h to obtain the modified brucite fiber product.

[0055] The molecular weight of the silicone rubber is 380,000; the vulcanizing agent is a combination of tert-butyl perbenzoate and di-tert-butyl peroxide in a mass ratio of 1:2; the filler is a combination of fumed silica and calcium carbonate in a mass ratio of 5:2, and the specific surface area of the fumed silica is 175 m² / g.

[0056] Comparative Example 1

[0057] In this comparative example, disperse brucite fibers in deionized water equal in amount to acetic acid solution. React at 50 °C for 2 h to obtain a brucite fiber dispersion. The remaining steps are the same as those in Example 3.

[0058] Comparative Example 2

[0059] In this comparative example, equivalent amounts of intercalated modified brucite fibers were used to replace the modified brucite fiber product, and the rest was the same as in Example 3.

[0060] Comparative Example 3

[0061] In this comparative example, equivalent amounts of grafted silane intercalated modified brucite fibers were used to replace the modified brucite fiber product, and the rest was the same as in Example 3.

[0062] Result Analysis

[0063] (1) Cable Performance Testing

[0064] The following tests were conducted on the flexible mineral insulated fire cables prepared in each example and comparative example:

[0065] Mechanical property testing: The tensile strength of the silicone rubber mineral insulation layer before and after aging in each example and comparative example was tested according to the measurement method in GB / T 5013-2008. The aging conditions were: constant temperature at 110°C for 7 days. The results are shown in Figure 2 .

[0066] Insulation property testing: The silicone rubber mineral insulation layers in each example and comparative example were cut into standard specimens, and then the resistivity of the specimens was tested according to the measurement method in GB / T 1692-2008. The test voltage was 1000V. The results are shown in Figure 3 .

[0067] It can be seen from Figure 2 that the tensile strength of the silicone rubber mineral insulation layer before and after aging in Examples 1-3 is high and shows good aging resistance. The brucite fibers modified through multiple steps in the present invention may have better toughness and strength. Its combination with the silicone rubber matrix is closer, forming a more integral structure. When subjected to tensile stress, it can effectively disperse the stress, prevent stress concentration, so that the entire insulation layer shows a higher load-bearing capacity. The modified brucite fibers have better compatibility with silicone rubber and fillers, which makes a more uniform and continuous structure formed in the insulation layer, reducing the weak points that may be generated due to incompatibility between materials. The weak points are prone to become the starting points of cracks when subjected to tension, while good compatibility ensures the integrity of the insulation layer structure, thereby improving the tensile strength.

[0068] It can be seen from Figure 3 that the resistivity of the specimens made of the silicone rubber mineral insulation layer in Examples 1-3 is high, showing excellent insulation properties. The good compatibility of the modified brucite fibers with components such as silicone rubber and fillers in the insulation layer, as well as its special microstructure and chemical composition, make it difficult for charges to conduct therein. Therefore, the insulation properties of the silicone rubber mineral insulation layer in Examples 1-3 are better.

[0069] (2)Cable fire prevention and flame retardancy performance test

[0070] The flexible mineral insulated fireproof cables prepared in each example and comparative example were subjected to cable fire prevention and flame retardancy performance tests:

[0071] Oxygen index determination: The cables prepared in each example and comparative example were subjected to oxygen index determination according to the standard of GB / T 2406.2-2009, and the results are shown in Figure 4 .

[0072] From Figure 4 the results, it can be seen that the oxygen index of the cables in Examples 1-3 is higher than that of the comparative examples, which indicates that the cables prepared by the present invention have better fire prevention and flame retardancy performance. The main reason is that the modified brucite fiber in the examples plays an important role. During the preparation process, the synergistic flame retardancy effect of various elements is introduced through multi-step modification. Silicon elements can form a vitreous protective film at high temperatures, effectively blocking heat and oxygen; nitrogen elements decompose to produce non-combustible gases, which can dilute the oxygen concentration in the combustion environment; sulfur elements promote the formation of a carbon layer and enhance the stability of the carbon layer; boron elements melt at a lower temperature and cover the surface of the cable, playing a role in heat and oxygen insulation.

[0073] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

[0074] The above describes the present invention and its embodiments. This description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual application is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar ways and embodiments without creative efforts without departing from the purpose of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A flexible mineral insulated fire-resistant cable, characterized in that: It comprises four parallel copper conductors, the outer side of the copper conductor is wrapped with a silicone rubber mineral insulation layer, the outer side of the silicone rubber mineral insulation layer is wrapped with a mica tape wrapping layer, the outer side of the mica tape wrapping layer is provided with a filling layer, the outer side of the filling layer is wrapped with an armor layer, and the outer side of the armor layer is provided with an outer sheath; The silicone rubber mineral insulation layer comprises, by weight, 60-80 parts of silicone rubber, 2-5 parts of vulcanizing agent, 30-40 parts of filler and 8-12 parts of modified brucite fiber; The modified brucite fiber is prepared by the following steps: S1. Dispersing brucite fiber in 0.1-0.5 mol / L acetic acid solution, reacting at 50°C for 2h to obtain a brucite fiber dispersion, dissolving (2,6-dichlorobenzenesulfonylamino)-acetic acid in DMF to obtain an intercalation modification solution, slowly dropping the intercalation modification solution into the brucite fiber dispersion, stirring at 80°C for 5-8h, and then stirring at room temperature for 24-48h. After the reaction is completed, filtering, washing the filter cake 3 times with DMF, and then washing the filter cake 3 times with deionized water, and vacuum drying at 80°C for 12-18h to obtain intercalation modified brucite fiber; S2. 3-mercaptopropionic acid was added to anhydrous ethanol, and the intercalated modified brucite fiber was added and stirred for 15 minutes, and then a photoinitiator and divinyl-terminated polydimethylsiloxane were added, and the mixture was irradiated with 365 nm ultraviolet light, and reacted at room temperature for 3-6 hours, filtered, and the filter cake was washed with toluene for 3 times, and vacuum dried at 80° C. for 12-18 hours to obtain the grafted silane intercalated modified brucite fiber; S3. Add the grafted silane intercalation modified brucite fiber to anhydrous ethanol, stir to make it evenly dispersed, then slowly add diglycerol borate, continue stirring for 15 minutes, then dropwise add triethylamine, react at 70° C. for 3-5 hours, after the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake three times with anhydrous ethanol, and dry it in a vacuum drying oven at 50° C. for 24-36 hours to obtain the modified brucite fiber product; In step S1, the mass ratio of brucite fiber to acetic acid solution is 1:10-15; In step S1, the mass ratio of (2,6-dichlorobenzenesulfonylamino)-acetic acid to DMF is 1:8-10; In step S1, the mass ratio of the intercalation modification solution to the brucite fiber dispersion is 1:5-8; In the step S2, the mass ratio of 3-mercaptopropionic acid, anhydrous ethanol, intercalated modified brucite fiber, photoinitiator and divinyl-terminated polydimethylsiloxane is 1:20-35:5-10:0.05-0.2:3-5; In the step S3, the mass ratio of anhydrous ethanol, grafted silane intercalation modified brucite fiber, boric acid diglyceride and triethylamine is 30:5-10:1-5:1-3.

2. A flexible mineral insulated fire resistant cable according to claim 1, characterized in that: The photoinitiator is one of Irgacure 2959, Irgacure 184, Irgacure 369, Irgacure 500 and Irgacure 651.

3. A flexible mineral insulated fire resistant cable according to claim 2, characterized in that: The molecular weight of the silicone rubber is 300,000-450,000.

4. A flexible mineral insulated fire resistant cable according to claim 3, characterized in that: The vulcanizing agent is a combination of one or more of tert-butyl perbenzoate, di-tert-butyl peroxide, bis(2,4-dimethylbenzene) and bis(2,5-dimethylbenzene).

5. A flexible mineral insulated fire resistant cable according to claim 4, characterized in that: The filler is a combination of white carbon black and calcium carbonate in a mass ratio of 5:1-3.

6. A flexible mineral insulated fire resistant cable according to claim 5, characterized in that: The specific surface area of ​​the white carbon black is 150-200m 2 / g.

7. A flexible mineral insulated fire resistant cable according to claim 6, characterized in that: The filling layer is fire-resistant mineral wool; the armor layer is galvanized steel strip; and the outer sheath is low-smoke halogen-free cross-linked polyethylene material.

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