Flame-retardant, insulated low-voltage power cable and method for producing same

Abstract

The application provides a kind of flame-retardant insulation low-voltage power cable and its preparation method, belongs to cable technical field, including the following steps: S1, polypropylene, styrene-ethylene-butylene-styrene block copolymer, BN composite flame-retardant filler, auxiliary A melt mixing, granulation is obtained from discharge flame-retardant sheath material;S2, polyethylene, silane modified SiO2, methyl vinyl silicone rubber, auxiliary B, triallyl isocyanurate, continue to mix and grind peroxide diisopropylbenzene, granulation is obtained from discharge crosslinkable polyethylene insulation material;S3, crosslinkable polyethylene insulation material is coated on the outside of conductor, heat crosslinking, cooling and setting form crosslinking polyethylene insulation layer;Again, the flame-retardant sheath material is coated on the outside of crosslinking polyethylene insulation layer, is cooled and set, air-dried, traction and winding, and the flame-retardant insulation low-voltage power cable is prepared.The application can improve the flame-retardant smoke suppression performance of cable while realizing good electrical insulation.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a flame-retardant insulated low-voltage power cable and its preparation method. Background Technology

[0002] With the continuous increase in electricity load and the ever-increasing requirements for power supply safety, low-voltage power cables not only need to have stable conductivity, but also need to maintain good insulation reliability and environmental adaptability during long-term operation. However, existing low-voltage power cables are still susceptible to the effects of thermal aging, electric field effects, mechanical bending, and external fire sources in actual use, leading to the degradation of the electrical properties of the insulation layer and insufficient flame-retardant protection of the sheath layer, thereby affecting the service life and safety of the cable.

[0003] To improve the flame retardant properties of cable materials, existing technologies often employ the method of filling large amounts of inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide. These flame retardants have advantages such as being environmentally friendly and low-cost; however, to achieve a good flame retardant effect, a high dosage is usually required, which can easily disrupt the continuity of the polymer matrix, leading to decreased material flexibility, increased brittleness, and affecting the reliability of the cable during bending, laying, and long-term use. Patent application CN107556681A discloses a high flame retardant cable, which, from the inside out, comprises a conductor, an insulation layer, an inner sheath, and a sheath tube. The raw materials for the sheath tube include acrylonitrile / ethylene / styrene copolymer, tanning sludge, bentonite, graphene, octyltriethoxysilane, stearic acid, zinc oxide, sodium alginate, bisphenol fluorene, and hexaphenoxycyclotriphosphazene, among others. This application primarily aims to improve the strength, light resistance, and flame retardancy of the sheathing tube through the compounding of various organic / inorganic components. However, the hexaphenoxycyclotriphosphazene is mainly added to the sheathing material via physical blending, lacking a stable interfacial bond with the polymer matrix and inorganic fillers. Furthermore, the formulation in this application involves numerous components, including tannery sludge, bentonite, graphene, zinc oxide, sodium alginate, bisphenol fluorene, gum arabic, and silica, making it difficult to control the system's compatibility and dispersion uniformity. In addition, this application mainly focuses on modifying the sheathing tube material, lacking further optimization of the cable's electrical insulation stability, and thus still fails to meet the comprehensive requirements of low-voltage power cables.

[0004] Therefore, there is a need to provide a flame-retardant insulated low-voltage power cable and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0005] In view of this, the present invention provides a flame-retardant insulated low-voltage power cable and its preparation method, which can improve the flame-retardant and smoke-suppressing performance of the cable while achieving good electrical insulation.

[0006] To achieve the above objectives, the present invention provides a method for preparing a flame-retardant insulated low-voltage power cable, comprising the following steps:

[0007] S1. After drying polypropylene, styrene-ethylene-butene-styrene block copolymer, BN composite flame retardant filler, and additive A, the mixture is melt-blended, discharged, and granulated to obtain flame retardant sheath material. S2. Low-density polyethylene, linear low-density polyethylene, silane-modified SiO2, methyl vinyl silicone rubber, additive B and triallyl isocyanurate are mixed and then dicumyl peroxide is added and mixed further. The mixture is discharged and granulated to obtain crosslinkable polyethylene insulation material. S3. Crosslinkable polyethylene insulation material is melt-extruded and coated on the outside of the conductor, thermally crosslinked, and cooled and shaped to form a crosslinked polyethylene insulation layer; then flame-retardant sheath material is melt-extruded and coated on the outside of the crosslinked polyethylene insulation layer, and after cooling, drying, traction and winding, flame-retardant insulated low-voltage power cable is obtained. The BN composite flame retardant filler is prepared by mixing triethylamine and hexachlorocyclotriphosphazene in anhydrous tetrahydrofuran, adding the mixture to a BN-OH suspension and heating it, then adding it to a mixed system containing triethylenetetramine and anhydrous tetrahydrofuran, continuing to stir under an ice-water bath, washing, and drying.

[0008] In this invention, a flame-retardant sheath material is prepared by melt blending polypropylene with styrene-ethylene-butene-styrene block copolymer (SEBS) and introducing BN composite flame-retardant filler. The BN composite flame-retardant filler uses BN-OH as a carrier, and hexachlorocyclotriphosphazene (HCCP) is grafted onto the surface of BN-OH in the presence of triethylamine, introducing phosphorus- and nitrogen-rich active sites to enhance the flame-retardant ability of the material. Subsequently, it forms a continuous PN crosslinked network with polyamine-containing triethylenetetramine (TETA) on the surface of the BN sheets. This PN crosslinked structure is beneficial for improving its interfacial bonding and dispersion stability in the polypropylene / SEBS matrix, enabling the BN composite flame-retardant filler to form a more uniform barrier network in the sheath material. During thermal combustion, the PN crosslinked network is activated and thermally decomposes first, releasing phosphorus- and nitrogen-containing active components. This promotes the dehydrogenation, crosslinking, aromatization, and carbonization of the polypropylene / SEBS matrix pyrolysis products, forming a dense carbonized layer rich in PN structures. The BN sheets, acting as an inorganic framework, work with the carbonized layer to construct a multi-scale layered barrier, hindering the transfer of heat, oxygen, and combustible pyrolysis gases, and reducing the escape of some incomplete combustion products. Simultaneously, the phosphorus-containing structure can capture free radicals such as H· and OH· in the combustion chain reaction, while the inert gases generated by the thermal decomposition of the nitrogen-containing structure can dilute the concentration of combustible gases and oxygen, thus achieving synergistic flame retardancy between the condensed and gas phases, improving the flame retardant and smoke-suppressing properties of the flame-retardant sheathing material. Furthermore, the BN sheets, acting as an inorganic ceramic framework, work with the carbonized layer to construct a multi-scale layered barrier, effectively hindering heat transfer, oxygen entry, and the diffusion of combustible pyrolysis gases, enhancing the integrity of the carbon layer, and inhibiting dripping and flame spread.

[0009] In this invention, low-density polyethylene and linear low-density polyethylene are used as the insulating matrix. A cross-linked polyethylene network is formed under the action of dicumyl peroxide and triallyl isocyanurate, which improves the heat deformation resistance of the insulating material. In addition, silane-modified SiO2, as an inorganic filler for electrical insulation, has high thermal stability and insulation properties. It can improve the volume resistivity, breakdown strength and dielectric stability of the insulating material without significantly reducing the flexibility of the material. Methyl vinyl silicone rubber can be used as a flexible interface regulating component between silane-modified SiO2 and polyethylene matrix. Its siloxane segments are beneficial to improving the affinity for the surface of silane-modified SiO2, and methyl and organic segments are beneficial to reducing the interface difference between inorganic filler and polyethylene matrix. The vinyl structure can participate in the free radical cross-linking reaction initiated by dicumyl peroxide, thereby promoting the uniform dispersion of silane-modified SiO2 in polyethylene insulation material, reducing particle agglomeration, interface voids and local electric field distortion defects, and improving the flexibility, breakdown strength and electrical insulation stability of the insulation layer.

[0010] Optionally, in step S1, polypropylene, styrene-ethylene-butene-styrene block copolymer, BN composite flame retardant filler, and additive A are dried at 70-80°C for 3-5 hours, then melt-blended at 175-185°C for 12-18 minutes, discharged and granulated to obtain flame retardant sheath material; the additive A is 3-5 parts by mass of maleic anhydride-grafted polypropylene and 0.7-1 parts by mass of polyethylene wax.

[0011] In this invention, the addition of maleic anhydride-grafted polypropylene during the preparation of flame-retardant sheath material is beneficial to improving the interfacial bonding and dispersion stability between the matrix and inorganic fillers; the addition of polyethylene wax can improve melt flowability and processing lubricity, reduce filler agglomeration, and improve the processing stability of the sheath material.

[0012] Optionally, in step S2, low-density polyethylene, linear low-density polyethylene, silane-modified SiO2, methyl vinyl silicone rubber, additive B, and triallyl isocyanurate are mixed at 105-113°C for 6-8 minutes, dicumyl peroxide is added, and mixing is continued for 3-5 minutes. The mixture is then discharged and granulated to obtain crosslinkable polyethylene insulation material. Additive B includes 0.3-0.5 parts by weight of antioxidant, 0.3-0.5 parts by weight of polyethylene wax, and 0.1-0.2 parts by weight of zinc stearate. The antioxidant is one of antioxidant 1010 and antioxidant 168.

[0013] Optionally, the silane-modified SiO2 is prepared by mixing 6-8 parts by weight of SiO2 powder, 400-600 parts by weight of anhydrous ethanol and 60-80 parts by weight of 25 wt% ammonia water, adding 12-15 parts by weight of perfluorooctyltriethoxysilane, stirring continuously at 20-30°C for 6-8 hours, centrifuging at 7000 rpm for 25-30 minutes, separating, washing the precipitate 3-5 times with anhydrous ethanol, and drying at 65-75°C for 20-24 hours.

[0014] This invention utilizes the hydrolysis of perfluorooctyltriethoxysilane and its condensation with hydroxyl groups on the surface of SiO2 to form a low surface energy fluorosilane layer, which further improves the hydrophobicity and dispersibility of SiO2, reduces moisture absorption and interface defects, and is beneficial to further improving the electrical insulation performance of the insulating material.

[0015] Optionally, the BN composite flame retardant filler is prepared by adding 30-35 parts by weight of triethylamine and 30-35 parts by weight of hexachlorocyclotriphosphazene to 190-200 parts by weight of anhydrous tetrahydrofuran, mixing and stirring under nitrogen protection for 25-30 minutes, then adding it to a BN-OH suspension, reacting at 50-60°C for 6-8 hours, and then adding it to a mixed system containing 25-30 parts by weight of triethylenetetramine and 450-550 parts by weight of anhydrous tetrahydrofuran. After stirring in an ice-water bath for 5-6 hours, it is washed successively with anhydrous tetrahydrofuran and anhydrous ethanol, and then dried at 75-80°C for 14-16 hours.

[0016] Optionally, the BN-OH suspension is prepared by mixing 9-12 parts by mass of boron nitride with 180-200 parts by mass of 68wt% nitric acid solution, magnetically stirring at 70-80℃ for 4-6 hours, cooling to room temperature, filtering, washing with deionized water 3-5 times, then washing with anhydrous ethanol 2-4 times, and vacuum drying at 75-80℃ for 12-15 hours to obtain BN-OH, which is then added to 450-550 parts by mass of anhydrous tetrahydrofuran and ultrasonically treated for 25-30 minutes.

[0017] Optionally, the BN composite flame retardant filler is further end-capped and modified with AO-Cl. Specifically, after drying, it is added to 300-350 parts by weight of toluene, and then 18-20 parts by weight of triethylamine and 20-25 parts by weight of AO-Cl are added sequentially under continuous stirring. The mixture is then reacted at 45-55°C for 14-16 hours, filtered, washed, and vacuum dried at 55-65°C for 15-18 hours to obtain the BN composite flame retardant filler.

[0018] Optionally, the AO-Cl is obtained by mixing and stirring 25-30 parts by mass of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 350-370 parts by mass of chloroform for 10-20 min, adding 18-20 parts by mass of thionyl chloride, stirring and reacting at 40-50°C for 6-8 h, and then rotary evaporating.

[0019] This invention further employs AO-Cl derived from 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid to amidate-end the residual amino groups on the surface of BN-HCCP-TETA, introducing a hindered phenolic antioxidant structure onto the BN surface. This hindered phenolic structure can capture free radicals generated during the thermo-oxidative degradation of polypropylene and SEBS in high-temperature and oxidative environments, inhibiting the continuous oxidative degradation of the polymer chains. Therefore, the resulting BN composite flame-retardant filler possesses both flame-retardant and antioxidant functions, improving the flame-retardant performance and heat aging stability of the flame-retardant sheath layer.

[0020] Optionally, in step S3, cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 105-140°C, followed by thermal cross-linking at 175-190°C for 8-15 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 165-190°C, and after cooling, shaping, air drying, traction, and winding, a flame-retardant insulated low-voltage power cable is obtained; the conductor is formed by twisting 19 copper wires together with 1-3 bundles of ceramic fiber yarn.

[0021] In this invention, the conductor utilizes a composite conductor structure formed by twisting copper wire and ceramic fiber yarn together. Compared to a single copper conductor, this composite structure offers superior high-temperature resistance, shape retention, and mechanical support. The copper wire serves as the primary conductive unit, ensuring the cable's conductivity. The ceramic fiber yarn, characterized by its high-temperature resistance, non-combustibility, and low thermal shrinkage, forms a fire-resistant support skeleton within the conductor. Under fire conditions, when high temperatures cause the copper wire to anneal, soften, lose strength, or deform, the ceramic fiber yarn provides support, constraint, and positioning, enhancing the conductor's shape retention and structural stability under high-temperature flame conditions. Furthermore, it works synergistically with the cross-linked polyethylene insulation layer and flame-retardant sheath, thereby improving the cable's structural integrity and flame-retardant safety during thermal combustion.

[0022] The present invention also provides a flame-retardant insulated low-voltage power cable, comprising a conductor, a cross-linked polyethylene insulation layer and a flame-retardant sheath layer arranged sequentially from the inside out; The raw material for the cross-linked polyethylene insulation layer is cross-linkable polyethylene insulation material, which comprises the following parts by weight: 75-80 parts low-density polyethylene, 18-22 parts linear low-density polyethylene, 1.2-1.8 parts silane-modified SiO2, 2-4 parts methyl vinyl silicone rubber, 0.7-1.2 parts additive B, 0.2-0.6 parts triallyl isocyanurate, and 1.5-1.8 parts dicumyl peroxide; The raw material for the flame-retardant sheath layer is a flame-retardant sheath material, which includes the following parts by weight: 65-70 parts polypropylene, 30-35 parts styrene-ethylene-butene-styrene block copolymer, 10-15 parts BN composite flame-retardant filler, and 3.7-6 parts additive A.

[0023] This invention, by incorporating a conductor, a cross-linked polyethylene insulation layer, and a flame-retardant sheath layer, and by employing the aforementioned mass ratio, enables synergistic protection among these functional layers. Specifically, the cross-linked polyethylene insulation layer possesses excellent electrical insulation properties and flexibility; the PP / SEBS matrix in the flame-retardant sheath layer combines strength and toughness, while the BN composite flame-retardant filler constructs a flame-retardant and heat-insulating barrier, reducing flame spread and smoke release; the conductor structure enhances shape retention at high temperatures, thus enabling the cable to possess both excellent insulation performance and flame-retardant and smoke-suppressing properties.

[0024] The above-described technical solution of the present invention has at least the following beneficial effects: 1. This invention involves the melt blending of polypropylene and SEBS, and the introduction of BN composite flame-retardant filler to prepare a flame-retardant sheath material. The BN composite flame-retardant filler uses BN-OH as a carrier, and constructs a PN cross-linked network on the surface of the BN sheets via HCCP and TETA, improving the interfacial bonding and dispersion stability between the filler and the polypropylene / SEBS matrix. During combustion, the PN structure promotes the carbonization of the matrix pyrolysis products and forms a dense char layer. The BN sheets act as an inorganic skeleton, constructing a layered barrier to block the transfer of heat, oxygen, and combustible gases. Simultaneously, the phosphorus- and nitrogen-containing structures exert a gas-phase flame-retardant effect, thereby improving the flame-retardant and smoke-suppressing performance of the sheath material.

[0025] 2. This invention uses low-density polyethylene and linear low-density polyethylene as the insulating matrix. A cross-linked polyethylene network is formed under the action of dicumyl peroxide and triallyl isocyanurate, improving the heat deformation resistance of the insulating material. Silane-modified SiO2, as an inorganic filler for electrical insulation, can improve the volume resistivity, breakdown strength, and dielectric stability of the insulating material. Methyl vinyl silicone rubber, as a flexible interface regulating component, improves the compatibility between silane-modified SiO2 and the polyethylene matrix. Through the participation of vinyl groups in the cross-linking reaction, it promotes the uniform dispersion of SiO2, reduces interface defects, and thus improves the flexibility and electrical insulation stability of the insulating layer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0027] Example 1 11 parts of boron nitride (BN) were mixed with 190 parts of 68 wt% nitric acid solution, magnetically stirred at 75 °C for 5 h, cooled to room temperature, filtered, washed 4 times with deionized water, then washed 3 times with anhydrous ethanol, and vacuum dried at 78 °C for 14 h to obtain BN-OH. This was then added to 500 parts of anhydrous tetrahydrofuran and mixed, and sonicated for 28 min to obtain a BN-OH suspension. 28 parts of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (AO) and 360 parts of chloroform were mixed and stirred for 15 min, then 19 parts of thionyl chloride were added. The mixture was stirred at 45 °C for 7 h, and then rotary evaporated to obtain AO-Cl. 32 parts of triethylamine and 32 parts of hexachlorocyclotriphosphazene (H...) were mixed... CCP was added to 195 parts of anhydrous tetrahydrofuran, and after mixing and stirring under nitrogen protection for 28 min, it was added to BN-OH suspension. After reacting at 55℃ for 7 h, it was added to a mixed system containing 28 parts of triethylenetetramine (TETA) and 500 parts of anhydrous tetrahydrofuran. After stirring in an ice-water bath for 6 h, it was washed successively with anhydrous tetrahydrofuran and anhydrous ethanol, and dried at 78℃ for 15 h to obtain BN-HCCP-TETA. Then, it was added to 325 parts of toluene, and after stirring continuously, 19 parts of triethylamine and 23 parts of AO-Cl were added successively. After reacting at 50℃ for 15 h, it was filtered, washed, and vacuum dried at 60℃ for 16 h to obtain BN composite flame retardant filler.

[0028] 68 parts of polypropylene, 32 parts of styrene-ethylene-butene-styrene block copolymer, 14 parts of BN composite flame retardant filler, 4 parts of maleic anhydride grafted polypropylene and 0.8 parts of polyethylene wax were dried at 75°C for 4 hours and then added to an internal mixer. The mixture was melt-mixed at 180°C for 15 minutes, discharged and granulated to obtain the flame retardant sheath material.

[0029] Seven parts of SiO2 powder, 500 parts of anhydrous ethanol, and 70 parts of 25 wt% ammonia were mixed. 14 parts of perfluorooctyltriethoxysilane were added and stirred continuously at 25°C for 7 hours. After centrifugation at 7000 rpm for 28 minutes, the mixture was separated. The precipitate was washed four times with anhydrous ethanol and dried at 70°C for 22 hours to obtain silane-modified SiO2. Seventy-eight parts of low-density polyethylene, 20 parts of linear low-density polyethylene, 1.5 parts of silane-modified SiO2, 3 parts of methyl vinyl silicone rubber, 0.4 parts of antioxidant 1010, 0.4 parts of polyethylene wax, 0.15 parts of zinc stearate, and 0.4 parts of triallyl isocyanurate were added to a mixer and mixed at 109°C for 7 minutes. 1.6 parts of dicumyl peroxide were added and mixing continued for 4 minutes. The mixture was then discharged and granulated to obtain crosslinkable polyethylene insulation material.

[0030] Nineteen copper wires and two bundles of ceramic fiber yarns are twisted together to form a conductor; cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 120°C, followed by thermal cross-linking at 180°C for 10 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 180°C, and after cooling, shaping, air drying, traction, and winding, a flame-retardant insulated low-voltage power cable is obtained.

[0031] Example 2 Nine parts of boron nitride (BN) were mixed with 180 parts of 68 wt% nitric acid solution and magnetically stirred at 70 °C for 4 h. After cooling to room temperature, the mixture was filtered, washed three times with deionized water, and then washed twice with anhydrous ethanol. The mixture was then vacuum dried at 75 °C for 12 h to obtain BN-OH, which was added to 450 parts of anhydrous tetrahydrofuran and sonicated for 25 min to obtain a BN-OH suspension. 25 parts of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (AO) and 350 parts of chloroform were mixed and stirred for 10 min. 18 parts of thionyl chloride were added, and the mixture was stirred and reacted at 40 °C for 6 h. The mixture was then rotary evaporated to obtain AO-Cl. 30 parts of triethylamine and 30 parts of hexachlorocyclotriphosphazene (H...) were then mixed... CCP was added to 190 parts of anhydrous tetrahydrofuran and mixed and stirred for 25 min under nitrogen protection. Then it was added to a BN-OH suspension and reacted at 50 °C for 6 h. Then it was added to a mixed system containing 25 parts of triethylenetetramine (TETA) and 450 parts of anhydrous tetrahydrofuran and stirred for 5 h under an ice-water bath. After washing with anhydrous tetrahydrofuran and anhydrous ethanol, it was dried at 75 °C for 14 h to obtain BN-HCCP-TETA. Then it was added to 300 parts of toluene and 18 parts of triethylamine and 20 parts of AO-Cl were added sequentially under continuous stirring. After reacting at 45 °C for 14 h, it was filtered, washed, and vacuum dried at 55 °C for 15 h to obtain BN composite flame retardant filler.

[0032] 65 parts of polypropylene, 30 parts of styrene-ethylene-butene-styrene block copolymer, 12 parts of BN composite flame retardant filler, 3 parts of maleic anhydride grafted polypropylene and 0.7 parts of polyethylene wax were dried at 70℃ for 3 hours and then added to an internal mixer. The mixture was melt-mixed at 175℃ for 12 minutes, discharged and granulated to obtain the flame retardant sheath material.

[0033] Six parts of SiO2 powder, 400 parts of anhydrous ethanol, and 60 parts of 25wt% ammonia were mixed. 12 parts of perfluorooctyltriethoxysilane were added and stirred continuously at 20°C for 6 hours. After centrifugation at 7000 rpm for 25 minutes, the mixture was separated. The precipitate was washed three times with anhydrous ethanol and dried at 65°C for 20 hours to obtain silane-modified SiO2. 75 parts of low-density polyethylene, 18 parts of linear low-density polyethylene, 1.2 parts of silane-modified SiO2, 2 parts of methyl vinyl silicone rubber, 0.3 parts of antioxidant 1010, 0.3 parts of polyethylene wax, 0.1 parts of zinc stearate, and 0.2 parts of triallyl isocyanurate were added to a mixer and mixed at 105°C for 6 minutes. 1.5 parts of dicumyl peroxide were added and the mixture was further mixed for 3 minutes. The mixture was then discharged and granulated to obtain crosslinkable polyethylene insulation material.

[0034] Nineteen copper wires and a bundle of ceramic fiber yarn are twisted together to form a conductor; cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 105°C, followed by thermal cross-linking at 175°C for 8 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 165°C, and after cooling, shaping, air drying, traction and winding, a flame-retardant insulated low-voltage power cable is obtained.

[0035] Example 3 12 parts of boron nitride (BN) were mixed with 200 parts of 68 wt% nitric acid solution and magnetically stirred at 80 °C for 6 h. After cooling to room temperature, the mixture was filtered, washed 5 times with deionized water, and then washed 4 times with anhydrous ethanol. The mixture was then vacuum dried at 80 °C for 15 h to obtain BN-OH. This BN-OH was added to 550 parts of anhydrous tetrahydrofuran and mixed, and ultrasonicated for 30 min to obtain a BN-OH suspension. 30 parts of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (AO) and 370 parts of chloroform were mixed and stirred for 20 min. 20 parts of thionyl chloride were added, and the mixture was stirred and reacted at 50 °C for 8 h. After rotary evaporation, AO-Cl was obtained. 35 parts of triethylamine and 35 parts of hexachlorocyclotriphosphazene (H) were mixed and stirred for 20 min. CCP was added to 200 parts of anhydrous tetrahydrofuran and mixed and stirred for 30 min under nitrogen protection. Then it was added to BN-OH suspension and reacted at 60℃ for 8 h. Then it was added to a mixed system containing 30 parts of triethylenetetramine (TETA) and 550 parts of anhydrous tetrahydrofuran and stirred for 6 h under an ice-water bath. After washing with anhydrous tetrahydrofuran and anhydrous ethanol, it was dried at 80℃ for 16 h to obtain BN-HCCP-TETA. Then it was added to 350 parts of toluene and 20 parts of triethylamine and 25 parts of AO-Cl were added sequentially under continuous stirring. After reacting at 55℃ for 16 h, it was filtered, washed, and vacuum dried at 65℃ for 18 h to obtain BN composite flame retardant filler.

[0036] 70 parts of polypropylene, 35 parts of styrene-ethylene-butene-styrene block copolymer, 15 parts of BN composite flame retardant filler, 5 parts of maleic anhydride grafted polypropylene and 1 part of polyethylene wax were dried at 80℃ for 5 hours and then added to a mixer. The mixture was melt-mixed at 185℃ for 18 minutes, discharged and granulated to obtain flame retardant sheath material.

[0037] Eight parts of SiO2 powder, 600 parts of anhydrous ethanol, and 80 parts of 25wt% ammonia were mixed. 15 parts of perfluorooctyltriethoxysilane were added and stirred continuously at 30°C for 8 hours. After centrifugation at 7000 rpm for 30 minutes, the mixture was separated. The precipitate was washed five times with anhydrous ethanol and dried at 75°C for 24 hours to obtain silane-modified SiO2. Eighty parts of low-density polyethylene, 22 parts of linear low-density polyethylene, 1.8 parts of silane-modified SiO2, 4 parts of methyl vinyl silicone rubber, 0.5 parts of antioxidant 1010, 0.5 parts of polyethylene wax, 0.2 parts of zinc stearate, and 0.6 parts of triallyl isocyanurate were added to a mixer and mixed at 113°C for 8 minutes. 1.8 parts of dicumyl peroxide were added and the mixture was continued to mix for 5 minutes. The mixture was then discharged and granulated to obtain crosslinkable polyethylene insulation material.

[0038] Nineteen copper wires and three bundles of ceramic fiber yarn are twisted together to form a conductor; cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 140°C, followed by thermal cross-linking at 190°C for 15 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 190°C, and after cooling, shaping, air drying, traction and winding, a flame-retardant insulated low-voltage power cable is obtained.

[0039] Example 4 Ten parts of boron nitride (BN) were mixed with 185 parts of 68 wt% nitric acid solution and magnetically stirred at 72 °C for 4.5 h. After cooling to room temperature, the mixture was filtered, washed four times with deionized water, and then washed three times with anhydrous ethanol. The mixture was then vacuum dried at 76 °C for 13 h to obtain BN-OH. This BN-OH was added to 480 parts of anhydrous tetrahydrofuran and mixed, and ultrasonicated for 26 min to obtain a BN-OH suspension. 26 parts of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (AO) and 355 parts of chloroform were mixed and stirred for 12 min. 18.5 parts of thionyl chloride were added, and the mixture was stirred at 42 °C for 6.5 h. After rotary evaporation, AO-Cl was obtained. 31 parts of triethylamine and 31 parts of hexachlorocyclotriphosphazene (... HCCP was added to 192 parts of anhydrous tetrahydrofuran and mixed and stirred for 26 min under nitrogen protection. Then, it was added to a BN-OH suspension and reacted at 52 °C for 6.5 h. After that, it was added to a mixed system containing 26 parts of triethylenetetramine (TETA) and 480 parts of anhydrous tetrahydrofuran. After stirring for another 5 h in an ice-water bath, it was washed successively with anhydrous tetrahydrofuran and anhydrous ethanol, and dried at 76 °C for 15 h to obtain BN-HCCP-TETA. Then, it was added to 315 parts of toluene, and 18.5 parts of triethylamine and 22 parts of AO-Cl were added successively under continuous stirring. After reacting at 48 °C for 15 h, it was filtered, washed, and vacuum dried at 58 °C for 16 h to obtain BN composite flame retardant filler.

[0040] 66 parts of polypropylene, 31 parts of styrene-ethylene-butene-styrene block copolymer, 13 parts of BN composite flame retardant filler, 3.5 parts of maleic anhydride grafted polypropylene and 0.8 parts of polyethylene wax were dried at 72℃ for 4 hours and then added to an internal mixer. The mixture was melt-mixed at 178℃ for 14 minutes, discharged and granulated to obtain the flame retardant sheath material.

[0041] 6.5 parts of SiO2 powder, 450 parts of anhydrous ethanol, and 65 parts of 25wt% ammonia were mixed. 13 parts of perfluorooctyltriethoxysilane were added and stirred continuously at 22°C for 6.5 h. After centrifugation at 7000 rpm for 26 min, the mixture was separated. The precipitate was washed four times with anhydrous ethanol and dried at 68°C for 21 h to obtain silane-modified SiO2. 76 parts of low-density polyethylene, 19 parts of linear low-density polyethylene, 1.4 parts of silane-modified SiO2, 2.5 parts of methyl vinyl silicone rubber, 0.35 parts of antioxidant 1010, 0.35 parts of polyethylene wax, 0.12 parts of zinc stearate, and 0.3 parts of triallyl isocyanurate were added to a mixer and mixed at 107°C for 7 min. 1.6 parts of dicumyl peroxide were added and the mixture was further mixed for 4 min. The mixture was then discharged and granulated to obtain crosslinkable polyethylene insulation material.

[0042] Nineteen copper wires and two bundles of ceramic fiber yarns are twisted together to form a conductor; cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 115°C, followed by thermal cross-linking at 180°C for 10 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 175°C, and after cooling, shaping, air drying, traction, and winding, a flame-retardant insulated low-voltage power cable is obtained.

[0043] Example 5 11.5 parts of boron nitride (BN) were mixed with 195 parts of 68 wt% nitric acid solution and magnetically stirred at 78 °C for 5.5 h. After cooling to room temperature, the mixture was filtered, washed 5 times with deionized water, and then washed 4 times with anhydrous ethanol. The mixture was then vacuum dried at 79 °C for 15 h to obtain BN-OH, which was added to 530 parts of anhydrous tetrahydrofuran and sonicated for 29 min to obtain a BN-OH suspension. 29 parts of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (AO) and 365 parts of chloroform were mixed and stirred for 18 min. 19.5 parts of thionyl chloride were added, and the mixture was stirred at 48 °C for 7.5 h. After rotary evaporation, AO-Cl was obtained. 34 parts of triethylamine and 34 parts of hexachlorocyclotriphosphazene were mixed... (HCCP) was added to 198 parts of anhydrous tetrahydrofuran and mixed and stirred for 29 min under nitrogen protection. Then it was added to a BN-OH suspension and reacted at 58 °C for 7.5 h. After that, it was added to a mixed system containing 29 parts of triethylenetetramine (TETA) and 530 parts of anhydrous tetrahydrofuran. After stirring in an ice-water bath for 6 h, it was washed successively with anhydrous tetrahydrofuran and anhydrous ethanol, and dried at 79 °C for 16 h to obtain BN-HCCP-TETA. Then it was added to 340 parts of toluene, and 19.5 parts of triethylamine and 24 parts of AO-Cl were added successively under continuous stirring. After reacting at 53 °C for 16 h, it was filtered, washed, and dried under vacuum at 63 °C for 17 h to obtain BN composite flame retardant filler.

[0044] 69 parts of polypropylene, 34 parts of styrene-ethylene-butene-styrene block copolymer, 14.5 parts of BN composite flame retardant filler, 4.5 parts of maleic anhydride grafted polypropylene and 0.9 parts of polyethylene wax were dried at 78℃ for 5 hours and then added to an internal mixer. The mixture was melt-mixed at 183℃ for 16 minutes, discharged and granulated to obtain the flame retardant sheath material.

[0045] 7.5 parts of SiO2 powder, 550 parts of anhydrous ethanol, and 75 parts of 25wt% ammonia water were mixed and then 14.5 parts of perfluorooctyltriethoxysilane were added. The mixture was stirred continuously at 28°C for 7.5 h. After centrifugation at 7000 rpm for 29 min, the mixture was separated. The precipitate was washed five times with anhydrous ethanol and dried at 73°C for 23 h to obtain silane-modified SiO2. 79 parts of low-density polyethylene, 21 parts of linear low-density polyethylene, 1.7 parts of silane-modified SiO2, 3.5 parts of methyl vinyl silicone rubber, 0.45 parts of antioxidant 1010, 0.45 parts of polyethylene wax, 0.18 parts of zinc stearate, and 0.5 parts of triallyl isocyanurate were added to a mixer and mixed at 111°C for 8 min. 1.7 parts of dicumyl peroxide were added and the mixture was mixed for another 5 min. The mixture was then discharged and granulated to obtain crosslinkable polyethylene insulation material.

[0046] Nineteen copper wires and three bundles of ceramic fiber yarns are twisted together to form a conductor; cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 130°C, followed by thermal cross-linking at 185°C for 13 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer; further, flame-retardant sheath material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 185°C, and after cooling, shaping, air drying, traction, and winding, a flame-retardant insulated low-voltage power cable is obtained.

[0047] The present invention also includes comparative examples and related experiments.

[0048] Comparative Example 1 Compared with Example 1, the only difference is that an equal amount of boron nitride and hexachlorocyclotriphosphazene physical mixture is used to replace the BN composite flame retardant filler. The other preparation methods and components are completely consistent, and flame retardant insulated low-voltage power cables are finally obtained.

[0049] Comparative Example 2 Compared with Example 1, the only difference is that SiO2 is used instead of silane-modified SiO2. The other preparation methods and components are completely consistent, and flame-retardant insulated low-voltage power cables are finally obtained.

[0050] Comparative Example 3 Compared with Example 1, the only difference is that methyl vinyl silicone rubber was not added when preparing the crosslinkable polyethylene insulation material. The other preparation methods and components are completely consistent, and flame-retardant insulated low-voltage power cables are finally obtained.

[0051] Performance testing Flame-retardant insulated low-voltage power cables prepared in Examples 1-5 and Comparative Examples 1-3 were tested for flame-retardant performance and mechanical properties. Specifically, the flame-retardant and smoke-suppressing performance of the cables was tested according to GB / T31248-2014, and the flame spread distance, total heat release, 20-minute burning drips, and total smoke production were recorded. The performance test results of the flame-retardant insulated low-voltage power cables prepared in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0052] Table 1

[0053] As shown in Table 1, the flame spread of the flame-retardant insulated low-voltage power cables prepared in Examples 1-5 was 0.47-0.68m, the total heat release was 18.6-23.8MJ, and the total smoke production was 18.5-26.6m. 2 Furthermore, no burning droplets were observed during the 20-minute combustion process, indicating that the flame-retardant insulated low-voltage power cable prepared by this invention has good flame-retardant and smoke-suppressing properties and combustion structural stability.

[0054] Compared to Example 1, Comparative Example 1 used a physical mixture of boron nitride and hexachlorocyclotriphosphazene to replace the BN composite flame retardant filler, resulting in an increased flame spread of 1.06 m, a total heat release of 36.5 MJ, and a total smoke production of 54.8 m³. 2 The presence of a small amount of burning droplets indicates that the BN composite flame-retardant filler plays an important role in improving the flame-retardant and smoke-suppressing performance of the cable. The flame spread, total heat release, and total smoke production of Comparative Examples 2 and 3 were also higher than those of Examples 1-5, indicating that although silane-modified SiO2 and methyl vinyl silicone rubber mainly act on the cross-linked polyethylene insulation layer, they also have a certain impact on the density, flexibility, and structural integrity of the insulation layer during combustion, thus affecting the overall combustion stability of the cable.

[0055] The cross-linked polyethylene insulation layers prepared in Examples 1-5 and Comparative Examples 2-3 of this invention were used as samples. The initial tensile strength and elongation at break were tested according to GB / T1040.2-2022, the volume resistivity was determined according to GB / T31838.2-2019, and the dielectric strength was determined according to GB / T1408.1-2016. The specific test results of the cross-linked polyethylene insulation layer performance are shown in Table 2.

[0056] Table 2

[0057] As shown in Table 2, the volume resistivity of the cross-linked polyethylene insulation layers prepared in Examples 1-5 is 5.2 × 10⁻⁶. 15 ~6.6×10 15The dielectric strength is 32.6~36.8kV / mm, the initial tensile strength is 17.4~18.6MPa, and the elongation at break is 468~512%, indicating that the cross-linked polyethylene insulation layer prepared by this invention has both high electrical insulation performance and good mechanical toughness.

[0058] Compared to Example 1, Comparative Example 2 used unmodified SiO2 instead of silane-modified SiO2, and its volume resistivity decreased to 2.6 × 10⁻⁶. 15 The dielectric strength decreased to 22.5 kV / mm, the initial tensile strength decreased to 16.2 MPa, and the elongation at break decreased to 402%. Comparative Example 3, without the addition of methyl vinyl silicone rubber, showed a volume resistivity decrease to 4.9 × 10⁻⁶. 15 The dielectric strength decreased to 30.2 kV / mm, the initial tensile strength decreased to 15.8 MPa, and the elongation at break decreased to 365%.

[0059] The flame-retardant sheath materials prepared in Examples 1-5 and Comparative Example 1 were molded into samples. The initial tensile strength and elongation at break were tested according to GB / T1040.2-2022. The samples were then aged in a 100℃ hot air aging chamber for 7 days according to GB / T2951.12-2008. After cooling to room temperature, the tensile properties were tested again, and the tensile strength retention rate and elongation at break retention rate were calculated to evaluate the heat aging resistance of the samples. The specific mechanical and heat aging resistance test results are shown in Table 3.

[0060] Table 3

[0061] As shown in Table 3, the initial tensile strength of the flame-retardant sheath materials prepared in Examples 1-5 was 20.6-22.8 MPa, and the initial elongation at break was 386-418%. After aging in hot air at 100°C for 7 days, the tensile strength retention rate was 90.4-93.5%, and the elongation at break retention rate was 86.8-90.2%. This indicates that the flame-retardant sheath materials prepared by the present invention maintain good mechanical properties while also exhibiting good heat aging resistance. Compared with Example 1, Comparative Example 1 used a physical mixture of boron nitride and hexachlorocyclotriphosphazene, and its initial tensile strength decreased to 18.7 MPa, and the initial elongation at break decreased to 368%. After aging, the tensile strength retention rate decreased to 80.6%, and the elongation at break retention rate decreased to 73.4%. This indicates that the BN composite flame-retardant filler can not only improve the flame-retardant and smoke-suppressing performance of the sheath material, but also improve the mechanical strength and heat aging stability of the sheath layer.

[0062] The above are preferred embodiments of the present invention. Those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a flame-retardant insulated low-voltage power cable, characterized in that, Includes the following steps: S1. After drying polypropylene, styrene-ethylene-butene-styrene block copolymer, BN composite flame retardant filler, and additive A, the mixture is melt-blended, discharged, and granulated to obtain flame retardant sheath material. S2. Low-density polyethylene, linear low-density polyethylene, silane-modified SiO2, methyl vinyl silicone rubber, additive B and triallyl isocyanurate are mixed and then dicumyl peroxide is added and mixed further. The mixture is discharged and granulated to obtain crosslinkable polyethylene insulation material. S3. Crosslinkable polyethylene insulation material is melt-extruded and coated onto the outside of the conductor, thermally crosslinked, and cooled to form a crosslinked polyethylene insulation layer. The flame-retardant sheath material is then melt-extruded and coated onto the outside of the cross-linked polyethylene insulation layer. After cooling, shaping, air drying, traction, and winding, a flame-retardant insulated low-voltage power cable is obtained. The BN composite flame retardant filler is prepared by mixing triethylamine and hexachlorocyclotriphosphazene in anhydrous tetrahydrofuran, adding the mixture to a BN-OH suspension and heating it, then adding it to a mixed system containing triethylenetetramine and anhydrous tetrahydrofuran, continuing to stir under an ice-water bath, washing, and drying.

2. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, In step S1, polypropylene, styrene-ethylene-butene-styrene block copolymer, BN composite flame retardant filler, and additive A are dried at 70-80°C for 3-5 hours, then melt-blended at 175-185°C for 12-18 minutes, discharged and granulated to obtain flame retardant sheath material; additive A is 3-5 parts by mass of maleic anhydride-grafted polypropylene and 0.7-1 parts by mass of polyethylene wax.

3. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, In step S2, low-density polyethylene, linear low-density polyethylene, silane-modified SiO2, methyl vinyl silicone rubber, additive B, and triallyl isocyanurate are mixed at 105-113°C for 6-8 minutes, dicumyl peroxide is added, and mixing continues for 3-5 minutes. The mixture is then discharged and granulated to obtain crosslinkable polyethylene insulation material. Additive B includes 0.3-0.5 parts by weight of antioxidant, 0.3-0.5 parts by weight of polyethylene wax, and 0.1-0.2 parts by weight of zinc stearate. The antioxidant is one of antioxidant 1010 and antioxidant 168.

4. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, The silane-modified SiO2 is prepared by mixing 6-8 parts by weight of SiO2 powder, 400-600 parts by weight of anhydrous ethanol and 60-80 parts by weight of 25 wt% ammonia water, adding 12-15 parts by weight of perfluorooctyltriethoxysilane, stirring continuously at 20-30°C for 6-8 hours, centrifuging at 7000 rpm for 25-30 minutes, separating, washing the precipitate 3-5 times with anhydrous ethanol, and drying at 65-75°C for 20-24 hours.

5. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, The BN composite flame retardant filler is prepared by adding 30-35 parts by weight of triethylamine and 30-35 parts by weight of hexachlorocyclotriphosphazene to 190-200 parts by weight of anhydrous tetrahydrofuran. After mixing and stirring under nitrogen protection for 25-30 minutes, the mixture is added to a BN-OH suspension and reacted at 50-60°C for 6-8 hours. Then, the mixture is added to a mixed system containing 25-30 parts by weight of triethylenetetramine and 450-550 parts by weight of anhydrous tetrahydrofuran. After stirring in an ice-water bath for 5-6 hours, the mixture is washed successively with anhydrous tetrahydrofuran and anhydrous ethanol, and then dried at 75-80°C for 14-16 hours.

6. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, The BN-OH suspension was prepared by mixing 9-12 parts by weight of boron nitride with 180-200 parts by weight of 68 wt% nitric acid solution, magnetically stirring at 70-80°C for 4-6 hours, cooling to room temperature, filtering, washing with deionized water 3-5 times, then washing with anhydrous ethanol 2-4 times, and vacuum drying at 75-80°C for 12-15 hours to obtain BN-OH, which was then added to 450-550 parts by weight of anhydrous tetrahydrofuran and ultrasonically treated for 25-30 minutes.

7. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, The BN composite flame retardant filler is further end-capped and modified with AO-Cl. Specifically, after drying, it is added to 300-350 parts by mass of toluene, and then 18-20 parts by mass of triethylamine and 20-25 parts by mass of AO-Cl are added sequentially under continuous stirring. The mixture is then reacted at 45-55℃ for 14-16 hours, filtered, washed, and vacuum dried at 55-65℃ for 15-18 hours to obtain the BN composite flame retardant filler.

8. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 7, characterized in that, The AO-Cl is obtained by mixing 25-30 parts by mass of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 350-370 parts by mass of chloroform and stirring for 10-20 min, adding 18-20 parts by mass of thionyl chloride, stirring and reacting at 40-50 °C for 6-8 h, and then rotary evaporating.

9. The method for preparing a flame-retardant insulated low-voltage power cable according to claim 1, characterized in that, In step S3, cross-linkable polyethylene insulation material is melt-extruded onto the outside of the conductor at an extrusion temperature of 105-140°C, followed by thermal cross-linking at 175-190°C for 8-15 minutes, and then cooled and shaped to form a cross-linked polyethylene insulation layer. Further, flame-retardant sheathing material is melt-extruded onto the outside of the cross-linked polyethylene insulation layer at an extrusion temperature of 165-190°C, and then cooled, shaped, air-dried, drawn, and wound to obtain a flame-retardant insulated low-voltage power cable. The conductor is formed by twisting 19 copper wires together with 1-3 bundles of ceramic fiber yarn.

10. A flame-retardant insulated low-voltage power cable, characterized in that, The flame-retardant insulated low-voltage power cable is prepared using the preparation method of any one of claims 1 to 9, comprising a conductor, a cross-linked polyethylene insulation layer, and a flame-retardant sheath layer arranged sequentially from the inside out. The raw material for the cross-linked polyethylene insulation layer is cross-linkable polyethylene insulation material, which comprises the following parts by weight: 75-80 parts low-density polyethylene, 18-22 parts linear low-density polyethylene, 1.2-1.8 parts silane-modified SiO2, 2-4 parts methyl vinyl silicone rubber, 0.7-1.2 parts additive B, 0.2-0.6 parts triallyl isocyanurate, and 1.5-1.8 parts dicumyl peroxide; The raw material for the flame-retardant sheath layer is a flame-retardant sheath material, which includes the following parts by weight: 65-70 parts polypropylene, 30-35 parts styrene-ethylene-butene-styrene block copolymer, 10-15 parts BN composite flame-retardant filler, and 3.7-6 parts additive A.

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