High-flame-retardant cable and preparation method thereof

Abstract

The invention provides a high-flame-retardant cable and a preparation method thereof, and belongs to the technical field of cables, and the preparation method comprises the following steps: S1, preparing an insulating layer-conductor material; s2, preparing an insulating layer-conductor filling composite material; and S3, putting an ethylene-vinyl acetate copolymer, an ethylene-octylene copolymer, a flame retardant and montmorillonite into the internal mixer, performing internal mixing and extrusion to obtain a sheath material, and sequentially coating the insulating layer-conductor filling composite material, the semi-conductive layer, the shielding layer and the sheath along the axial direction of the conductor to obtain the high-flame-retardant cable. According to the technical scheme provided by the invention, the purposes of good flame retardance and good smoke suppression performance of the cable are achieved.

Description

Technical Field

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

[0002] With the development of power systems toward higher voltages and larger capacities, and the stringent cable safety requirements in specialized scenarios like rail transit and nuclear power facilities, the flame-retardant properties of traditional cables are no longer sufficient to meet modern engineering needs. According to statistics, the limiting oxygen index of conventional flame-retardant cables under high-temperature, open-flame conditions is often below 28%, with a generally high heat release rate and the production of large amounts of toxic smoke during combustion, posing significant safety risks. Traditional flame-retardant systems rely on the endothermic decomposition of aluminum / magnesium hydroxide or the vapor-phase quenching effect of halogenated flame retardants. While halogenated flame retardants are highly efficient, their combustion releases toxic gases such as HBr and dioxins, causing environmental pollution.

[0003] Patent application publication number CN103093873A discloses a halogen-free, highly flame-retardant cable. The cable's insulation layer comprises an outer insulation layer and an inner insulation layer formed by double-layer co-extrusion. The outer insulation layer has a tensile strength of ≥13.8 MPa and an elongation at break of ≥300%. The inner insulation layer is made of a highly flame-retardant rubber compound. The outer insulation layer comprises 100 parts of an ethylene copolymer and / or EPDM rubber, 60-150 parts of a halogen-free flame retardant, 1-10 parts of a compatibilizer, 0.1-5 parts of an antioxidant, 0.1-5 parts of a lubricant, 0-20 parts of a polymer elastomer, and 0-3 parts of a coupling agent. The inner insulation layer comprises 100 parts of an ethylene copolymer and / or EPDM rubber, 80-250 parts of a halogen-free flame retardant, 1-10 parts of a compatibilizer, 0.1-5 parts of a antioxidant, 0.1-5 parts of a lubricant, 0-20 parts of a polymer elastomer, and 0-3 parts of a coupling agent. This patent only improves the flame retardant performance of the insulation layer, and the overall flame retardant performance of the cable is still insufficient.

[0004] Therefore, it is necessary to provide a highly flame-retardant cable and a preparation method thereof to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a highly flame-retardant cable and a preparation method thereof, so as to achieve the purpose of having good flame retardancy and good smoke suppression properties of the cable.

[0006] The specific solution of the present invention is as follows: a method for preparing a highly flame-retardant cable, comprising the following steps: Step S1. Methyl vinyl silicone rubber and KH-550 (γ-aminopropyltriethoxysilane) are mixed and kneaded, and then boron nitride, aluminum hydroxide, and composite powder are added. The mixture is further kneaded and degassed to obtain a mixed rubber material, which is injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material. Step S2. The sesbania powder is added to deionized water, gelled, and then expanded graphite powder, magnesium hydroxide and azodicarbonamide are added, mixed evenly, and kneaded to obtain a filling material, which is injected into the gap between the insulating layer and the conductor material of the cable core and foamed to obtain an insulating layer-conductor filled composite material; Step S3. Ethylene-vinyl acetate copolymer, ethylene-octene copolymer, flame retardant, and montmorillonite are placed in an internal mixer, mixed, and extruded to obtain a sheath material. The insulating layer-conductor filling composite material, the semiconductive layer, the shielding layer, and the sheath are sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable; The raw materials of the composite powder include sesbania powder and cerium oxide.

[0007] The cable insulation layer is prepared using methyl vinyl silicone rubber as the base material. It has a high Si-O bond energy, which can give the insulation layer high-temperature stability. As an elastomer, it can increase the flexibility of the cable. Boron nitride has a unique two-dimensional layered structure. Through molding, the directional arrangement of boron nitride is promoted to form an efficient heat transfer channel, thereby significantly improving the thermal conductivity of the insulation layer. At the same time, boron nitride also has insulation and stability, which can make the insulation performance and high-temperature stability of the insulation layer better. The cerium oxide in the composite powder can provide thermal stability at high temperatures, and together with boron nitride and aluminum hydroxide, it forms an inorganic skeleton to provide structural support, prevent collapse, and enhance the mechanical properties of the cable. Cerium oxide can also enhance the strength of the carbon layer after the silicone rubber is ceramicized, and promote the improvement of the flame retardant properties of the cable. As a flame retardant, aluminum hydroxide absorbs heat and decomposes into aluminum oxide at high temperatures, which can block oxygen and inhibit combustion.

[0008] At high combustion temperatures, the sulfuric acid molecules between the layers of expanded graphite vaporize, allowing it to expand rapidly and form a porous structure. Simultaneously, the gelation of sesbania powder forms a three-dimensional gel network. This 3D gel network carbonizes to form a porous carbon layer when the cable is exposed to combustion. This synergistic effect with the porous structure of the expanded graphite absorbs smoke particles and suppresses smoke. Magnesium hydroxide decomposes at high temperatures, forming MgO and releasing water vapor. MgO absorbs acidic smoke, reducing smoke density and acting as a flame retardant and smoke suppressant, enhancing the cable's flame retardancy.

[0009] Ethylene-vinyl acetate copolymer has excellent flexibility and impact resistance, providing strong adhesion and helping to strengthen the bond between the sheath and other layers. Ethylene-octene copolymer has excellent flexibility and resilience, significantly improving the cable's bending properties and also contributing to increased abrasion and tear resistance. Montmorillonite has excellent thermal stability, compressive strength, and expansion properties, and when combined with flame retardants, it can enhance the flame retardancy of the sheath.

[0010] The cable's sheath, insulation layer and conductor filling materials are all flame-retardant from the outside to the inside. The carbon layer formed by the sheath can block oxygen, and the composite carbon layer formed by the expanded graphite powder and sesbania powder in the filling layer can seal the gap and absorb smoke. The ceramicized insulation layer further blocks oxygen and can also conduct heat quickly to reduce the temperature. The triple effects synergistically inhibit combustion, achieving the purpose of flame retardancy and smoke suppression.

[0011] Preferably, in step S1, the mixing and kneading time is 5-10 minutes; the mixing temperature is continued at 85-95° C. for 15-20 minutes; and the conductor is formed by twisting the copper core.

[0012] Preferably, the preparation of the composite powder comprises the following steps: adding sesbania powder and cerium oxide into a ball mill, performing ball milling, sieving, and drying to obtain the composite powder.

[0013] Preferably, the ball milling speed is 200-400 rpm and the time is 1.5-3 h.

[0014] Preferably, in step S2, the gelling temperature is 55-65° C. and the gelling time is 20-30 min.

[0015] Sesbania powder is a natural high-molecular-weight polysaccharide whose hydroxyl groups can form hydrogen bonds with the hydroxyl groups on the surface of cerium oxide, promoting its dispersion in the base material and preventing agglomeration. Furthermore, sesbania powder gels to form a three-dimensional gel network, acting as a binder.

[0016] Preferably, in step S3, the montmorillonite is modified montmorillonite, and the modification step is as follows: 30-40 parts of 1,8-cineole and 500-600 parts of montmorillonite are added to a mixer, heated and mixed to obtain modified montmorillonite.

[0017] 1,8-Cineole is non-polar and has strong lipophilicity. It can penetrate the lipid bilayer structure of the cell membrane of microorganisms, interfere with the permeability of the membrane, cause the death of microorganisms, and achieve an antibacterial effect. The introduction of 1,8-Cineole intercalation modified montmorillonite can achieve the slow release of 1,8-Cineole, thereby enhancing the antibacterial and mildew-proof properties of the cable.

[0018] Preferably, the heating and mixing is carried out at a temperature of 50-60° C. and for a time of 30-60 min.

[0019] Preferably, in step S3, the banburying temperature is 135-150° C. and the time is 20-40 min.

[0020] Preferably, in step S3, the semiconductive layer is EPDM rubber; and the shielding layer is a copper wire braided shielding layer.

[0021] To achieve the above object, the present invention also provides a highly flame-retardant cable prepared by the above method for preparing a highly flame-retardant cable.

[0022] Preferably, the highly flame-retardant cable is obtained by sequentially coating an insulation layer-conductor filling composite material, a semi-conductive layer, a shielding layer and a sheath along the axial direction of the conductor.

[0023] Preferably, the insulating layer-conductor filling composite material is obtained by compounding an insulating layer-conductor material and a filling material.

[0024] Preferably, the insulating layer in the insulating layer-conductor material comprises the following raw materials in parts by weight: 50-60 parts of methyl vinyl silicone rubber, 2-4 parts of KH-550, 10-15 parts of boron nitride, 18-23 parts of aluminum hydroxide and 8-12 parts of composite powder.

[0025] Preferably, the filling material comprises the following raw materials in parts by weight: 9-11 parts of sesbania powder, 90-110 parts of deionized water, 28-32 parts of expanded graphite powder, 45-55 parts of magnesium hydroxide and 4-5 parts of azodicarbonamide.

[0026] Preferably, the sheath material comprises the following raw materials in parts by weight: 35-45 parts of ethylene-vinyl acetate copolymer, 35-45 parts of ethylene-octene copolymer, 10-20 parts of flame retardant and 10-15 parts of montmorillonite.

[0027] The present invention adopts the above components in parts by weight to obtain a cable with the best flame retardant performance, thereby achieving the purpose of good flame retardancy and good smoke suppression of the cable.

[0028] The above technical solution of the present invention includes at least the following beneficial effects: (1) Methyl vinyl silicone rubber can impart high-temperature stability to the insulation layer, and as an elastomer, it can increase the flexibility of the cable. Boron nitride has a unique two-dimensional layered structure that can form an efficient heat transfer channel, improving the thermal conductivity of the insulation layer while also improving the insulation performance and high-temperature stability of the insulation layer. Aluminum hydroxide, as a flame retardant, absorbs heat and decomposes into aluminum oxide at high temperatures, which can block oxygen and inhibit combustion.

[0029] (2) Under high combustion temperatures, the porous structure of expanded graphite and the porous carbon layer formed by the sesbania powder produce a synergistic effect, adsorbing smoke particles and playing a role in smoke suppression. Magnesium hydroxide absorbs heat and decomposes at high temperatures, forming MgO and releasing water vapor. MgO can absorb acidic smoke, reduce smoke density, play a flame retardant and smoke suppression role, and improve the flame retardant properties of the cable.

[0030] (3) The carbon layer formed by the cable sheath can block oxygen, the composite carbon layer formed by the filling layer can seal the gap and absorb smoke, and the insulating layer can further block oxygen and conduct heat quickly to reduce the temperature. The triple effects synergistically inhibit combustion and achieve the purpose of flame retardancy and smoke suppression. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0032] In the following embodiments, the semi-conductive layer is made of EPDM rubber, and the shielding layer is made of a copper wire braided shielding layer.

[0033] Example 1 50g of sesbania powder and 40g of cerium oxide were added to a ball mill and ball-milled at 300rpm for 2h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 55g of methyl vinyl silicone rubber and 3g of KH-550 were added to a mixer, heated to 80°C, and mixed for 10min. 12g of boron nitride, 20g of aluminum hydroxide, and 10g of the composite powder were then added, heated to 90°C, mixed for 15min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0034] 10 g of sesbania powder was added to 100 ml of deionized water, heated to 65°C, and stirred at 200 rpm for 20 minutes. 30 g of expanded graphite powder, 50 g of magnesium hydroxide, and 5 g of azodicarbonamide were added and kneaded to obtain a filling material, which was injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0035] 35 g of 1,8-cineole and 500 g of montmorillonite were added to a mixer, heated to 55° C., and mixed at a speed of 700 rpm for 50 min to obtain modified montmorillonite.

[0036] 40g of ethylene-vinyl acetate copolymer, 40g of ethylene-octene copolymer, 15g of flame retardant and 10g of modified montmorillonite were put into an internal mixer, fully stirred, heated to 150°C, and mixed for 20min. The mixture was extruded and granulated to obtain a sheath material. The insulating layer-conductor filling composite material, the semi-conductive layer, the copper wire braided shielding layer and the sheath were sequentially coated along the axial direction of the conductor and cooled to obtain a highly flame-retardant cable.

[0037] Example 2 50g of sesbania powder and 40g of cerium oxide were added to a ball mill, ball-milled at 200rpm for 3h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 50g of methyl vinyl silicone rubber and 4g of KH-550 were added to a mixer, heated to 80°C, and mixed for 5min. 15g of boron nitride, 18g of aluminum hydroxide, and 12g of the composite powder were then added, heated to 90°C, mixed for 15min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0038] 9 g of sesbania powder was added to 90 ml of deionized water, heated to 55°C, and stirred at 200 rpm for 25 min. 30 g of expanded graphite powder, 55 g of magnesium hydroxide, and 4 g of azodicarbonamide were added and kneaded to obtain a filling material, which was injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0039] 30 g of 1,8-cineole and 550 g of montmorillonite were added to a mixer, heated to 60° C., and mixed at a speed of 650 rpm for 60 min to obtain modified montmorillonite.

[0040] 35g of ethylene-vinyl acetate copolymer, 45g of ethylene-octene copolymer, 10g of flame retardant and 10g of modified montmorillonite were put into an internal mixer, fully stirred, heated to 140°C, and mixed for 35 minutes. The mixture was extruded and granulated to obtain a sheath material. The insulating layer-conductor filling composite material, the semi-conductive layer, the copper wire braided shielding layer and the sheath were sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable.

[0041] Example 3 50g of sesbania powder and 40g of cerium oxide were added to a ball mill and ball-milled at 400rpm for 2h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 60g of methyl vinyl silicone rubber and 2g of KH-550 were added to a mixer, heated to 80°C, and mixed for 8min. 10g of boron nitride, 23g of aluminum hydroxide, and 8g of the composite powder were then added, heated to 90°C, mixed for 20min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0042] 11 g of sesbania powder was added to 110 ml of deionized water, heated to 60°C, and stirred at 200 rpm for 25 min. 32 g of expanded graphite powder, 50 g of magnesium hydroxide, and 5 g of azodicarbonamide were added and kneaded to obtain a filling material, which was then injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0043] 40 g of 1,8-cineole and 500 g of montmorillonite were added to a mixer, heated to 50° C., and mixed at a speed of 800 rpm for 30 min to obtain modified montmorillonite.

[0044] 45g of ethylene-vinyl acetate copolymer, 40g of ethylene-octene copolymer, 10g of flame retardant and 15g of modified montmorillonite were put into an internal mixer, fully stirred, heated to 135°C, mixed for 40min, extruded and granulated to obtain a sheath material, and the insulating layer-conductor filling composite material, semi-conductive layer, copper wire braided shielding layer and sheath were sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable.

[0045] Example 4 50g of sesbania powder and 40g of cerium oxide were added to a ball mill, ball-milled at 400rpm for 1.5h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 55g of methyl vinyl silicone rubber and 4g of KH-550 were added to a mixer, heated to 80°C, and mixed for 5min. 10g of boron nitride, 23g of aluminum hydroxide, and 8g of the composite powder were then added, heated to 90°C, mixed for 20min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0046] 10 g of sesbania powder was added to 100 ml of deionized water, heated to 60°C, and stirred at 200 rpm for 20 minutes. 32 g of expanded graphite powder, 45 g of magnesium hydroxide, and 5 g of azodicarbonamide were added and kneaded to obtain a filling material, which was injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0047] 35 g of 1,8-cineole and 600 g of montmorillonite were added to a mixer, heated to 55° C., and mixed at a speed of 750 rpm for 40 min to obtain modified montmorillonite.

[0048] 40g of ethylene-vinyl acetate copolymer, 45g of ethylene-octene copolymer, 15g of flame retardant and 15g of modified montmorillonite were put into an internal mixer, fully stirred, heated to 140°C, mixed for 30min, extruded and granulated to obtain a sheath material, and the insulating layer-conductor filling composite material, semi-conductive layer, copper wire braided shielding layer and sheath were sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable.

[0049] Example 5 50g of sesbania powder and 40g of cerium oxide were added to a ball mill and ball-milled at 350rpm for 2h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 60g of methyl vinyl silicone rubber and 2g of KH-550 were added to a mixer, heated to 80°C, and mixed for 10min. 15g of boron nitride, 18g of aluminum hydroxide, and 12g of the composite powder were then added, heated to 90°C, mixed for 15min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0050] 11 g of sesbania powder was added to 110 ml of deionized water, heated to 55°C, and stirred at 200 rpm for 30 min. 30 g of expanded graphite powder, 45 g of magnesium hydroxide, and 5 g of azodicarbonamide were added and kneaded to obtain a filling material, which was injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0051] 30 g of 1,8-cineole and 600 g of montmorillonite were added to a mixer, heated to 50° C., and mixed at a speed of 700 rpm for 45 minutes to obtain modified montmorillonite.

[0052] 35g of ethylene-vinyl acetate copolymer, 35g of ethylene-octene copolymer, 20g of flame retardant and 15g of modified montmorillonite were put into an internal mixer, fully stirred, heated to 135°C, mixed for 40min, extruded and granulated to obtain a sheath material, and the insulating layer-conductor filling composite material, semi-conductive layer, copper wire braided shielding layer and sheath were sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable.

[0053] Example 6 50g of sesbania powder and 40g of cerium oxide were added to a ball mill, ball-milled at 250rpm for 2.5h, passed through a 200-mesh sieve, and dried to obtain a composite powder. 50g of methyl vinyl silicone rubber and 3g of KH-550 were added to a mixer, heated to 80°C, and mixed for 8min. 15g of boron nitride, 21g of aluminum hydroxide, and 12g of the composite powder were then added, heated to 90°C, mixed for 17min, and degassed to obtain a mixed rubber compound, which was then injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor, thereby obtaining an insulating layer-conductor material.

[0054] 10 g of sesbania powder was added to 100 ml of deionized water, heated to 55°C, and stirred at 200 rpm for 25 minutes. 28 g of expanded graphite powder, 50 g of magnesium hydroxide, and 4 g of azodicarbonamide were added and kneaded to obtain a filling material, which was injected into the cable core gap of the insulation layer-conductor material and foamed to obtain an insulation layer-conductor filling composite material.

[0055] 40g of ethylene-vinyl acetate copolymer, 35g of ethylene-octene copolymer, 15g of flame retardant and 10g of montmorillonite were put into an internal mixer, fully stirred, heated to 150°C, mixed for 30 minutes, extruded and granulated to obtain a sheath material, and the insulating layer-conductor filling composite material, semi-conductive layer, copper wire braided shielding layer and sheath were sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable.

[0056] The present invention also carried out comparative examples and related tests Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the composite powder was not prepared, and the other compositions and preparation methods were the same as those in Example 1, and a highly flame-retardant cable was prepared.

[0057] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no sesbania powder is used in the preparation of the insulating layer-conductor filling composite material. Other compositions and preparation methods are the same as those in Example 1, and a highly flame-retardant cable is prepared.

[0058] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that expanded graphite powder is not used, and other compositions and preparation methods are the same as those of Example 1, and a highly flame-retardant cable is prepared.

[0059] Performance testing The flame retardant properties of the highly flame retardant cables prepared in Examples 1-6 and Comparative Examples 1-3 were tested according to the GB / T 31248-2014 test standard. The results are shown in Table 1.

[0060] Table 1 Flame retardant performance test results

[0061] It can be seen from the results in Table 1 that the flame retardant performance of Comparative Example 1 is significantly different from that of Example 1, which shows that the addition of the composite powder can effectively improve the flame retardant performance of the insulation layer, thereby improving the flame retardancy of the cable; compared with Example 1, the smoke suppression performance of Comparative Example 2 is significantly reduced, indicating that the field sesbania powder helps to improve the density of the carbon layer and promote the improvement of the smoke suppression performance of the cable; compared with Example 1, the flame retardant performance of Comparative Example 3 is reduced to a certain extent, and the difference in smoke suppression performance is the largest, indicating that the expanded graphite powder can improve the flame retardant performance of the cable and can greatly improve the smoke suppression performance of the cable.

[0062] The highly flame-retardant cables prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to toughness tests and antibacterial tests. The toughness performance test was performed according to GB / T 2951-2008, and the antibacterial test was performed according to ISO 22196-2011. The test results are shown in Table 2 below.

[0063] Table 2 Toughness and antibacterial performance test results

[0064] From the test results in Table 2, it can be seen from the comparison of the test results of Comparative Examples 1-3 and Examples 1-6 that the toughness of Comparative Example 2 decreases significantly, indicating that the three-dimensional gel network formed by the sesbania powder has a promoting effect on improving the toughness of the cable; compared with Examples 1-5, the antibacterial rate of Example 6 decreases significantly, which can be said that 1,8-cineole-modified montmorillonite helps to improve the antibacterial properties of the cable.

[0065] The above is a preferred embodiment of the present invention. Those skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly flame-retardant cable, characterized in that: The following steps are involved: Step S1. Methyl vinyl silicone rubber and KH-550 are mixed and kneaded, and then boron nitride, aluminum hydroxide and composite powder are added, and the mixing is continued and degassed to obtain a mixed rubber material, which is injected into a conductor outer layer mold for extrusion molding, vulcanized, and demolded to form an insulating layer covering the conductor to obtain an insulating layer-conductor material; Step S2. The sesbania powder is added to deionized water, gelled, and then expanded graphite powder, magnesium hydroxide and azodicarbonamide are added, mixed evenly, and kneaded to obtain a filling material, which is injected into the gap between the insulating layer and the conductor material of the cable core and foamed to obtain an insulating layer-conductor filled composite material; Step S3. Ethylene-vinyl acetate copolymer, ethylene-octene copolymer, flame retardant, and montmorillonite are placed in an internal mixer, mixed, and extruded to obtain a sheath material. The insulating layer-conductor filling composite material, the semiconductive layer, the shielding layer, and the sheath are sequentially coated along the axial direction of the conductor to obtain a highly flame-retardant cable; The raw materials of the composite powder include sesbania powder and cerium oxide.

2. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: In step S1, the mixing and kneading time is 5-10 minutes; the mixing temperature is continued at 85-95° C. for 15-20 minutes; and the conductor is formed by twisting the copper core.

3. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: The preparation of the composite powder comprises the following steps: adding sesbania powder and cerium oxide into a ball mill, performing ball milling, sieving, and drying to obtain the composite powder.

4. The method for preparing a highly flame-retardant cable according to claim 3, characterized in that: The ball milling speed is 200-400 rpm, and the time is 1.5-3 hours.

5. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: In step S2, the gelling temperature is 55-65° C. and the gelling time is 20-30 minutes.

6. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: In step S3, the montmorillonite is modified montmorillonite, and the modification steps are as follows: 30-40 parts of 1,8-cineole and 500-600 parts of montmorillonite are added into a mixer, heated and mixed to obtain the modified montmorillonite.

7. The method for preparing a highly flame-retardant cable according to claim 6, characterized in that: The heating and mixing is performed at a temperature of 50-60° C. and for a time of 30-60 minutes.

8. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: In step S3, the mixing temperature is 135-150° C. and the mixing time is 20-40 minutes.

9. The method for preparing a highly flame-retardant cable according to claim 1, characterized in that: In step S3, the semi-conductive layer is EPDM rubber; and the shielding layer is a copper wire braided shielding layer.

10. A highly flame-retardant cable, characterized in that: The highly flame-retardant cable is prepared by the method for preparing the highly flame-retardant cable according to any one of claims 1 to 9.

Images