Flame-retardant medium-voltage power cable

Abstract

The invention discloses a flame-retardant medium-voltage power cable, which relates to the technical field of cables and comprises a cable core, a shielding layer, a fireproof layer, an armor layer and an outer sheath layer which are sequentially arranged from inside to outside. The cable is characterized in that the cable core is composed of a plurality of insulated wire cores which are twisted with one another, and each insulated wire core is composed of copper wires which are twisted with one another and insulating layers which are sequentially coated outside the copper wires which are twisted with one another; a filling material is filled between the cable core and the shielding layer; the five-layer structure of cable core, shielding, fire resistance, armoring and outer sheath is adopted to form a complete protection system, the strict electrical performance requirement is met, excellent mechanical strength, flame retardant property, heat aging resistance and environmental adaptability are achieved, the service life is effectively prolonged, and the safety and reliability of power transmission are improved.

Description

Technical Field

[0001] The invention relates to the technical field of cables, and in particular to a flame-retardant medium-voltage power cable. Background Art

[0002] Medium voltage power cable refers to a power transmission cable with a rated voltage of 6 to 35 kV. Its typical structure includes multiple functional layers from the inside to the outside, such as conductor, insulation layer, semi-conductive shielding layer, metal shielding layer, filling layer, inner sheath, armor layer and outer sheath. The conductor is usually made of copper or aluminum; the insulation layer mainly uses cross-linked polyethylene (XLPE) or ethylene propylene rubber (EPR) materials, which have excellent insulation performance and heat resistance; the semi-conductive shielding layer is used for uniform electric field distribution; the metal shielding layer provides grounding protection and electromagnetic shielding functions; the armor layer enhances the mechanical strength and resistance to external damage of the cable; the outer sheath protects the internal structure of the cable from environmental damage. Medium voltage power cables are widely used in urban power grid construction, industrial park power distribution, commercial complexes, transportation hubs, data centers and other places, and have strict requirements on insulation performance, mechanical strength, heat aging resistance and flame retardant safety.

[0003] With the rapid development of power system construction, medium voltage power cables, as a key component of power transmission networks, play an irreplaceable role in urban power distribution, industrial power supply and infrastructure construction. Its safety and reliability are directly related to the stable operation of the power system and the safety of people's lives and property. Especially in crowded places, important public buildings and flammable and explosive environments, the flame retardant performance of cables has become a core indicator to measure their safety.

[0004] At present, common flame-retardant medium-voltage power cables mainly adopt three technical routes: one is to add halogen flame retardants, such as bromine and chlorine compounds, to the insulation layer and sheath layer materials; the second is to use inorganic flame retardant fillers, such as aluminum hydroxide and magnesium hydroxide; the third is to use phosphorus-nitrogen flame retardants. However, the existing technology has obvious shortcomings: although halogen flame retardants have high flame retardant efficiency, they will release toxic gases and thick smoke when burned, causing serious harm to the environment and human health; inorganic flame retardant fillers need to be added in large quantities to achieve flame retardant effects, resulting in a decrease in the mechanical properties of the cable and poor processing performance; traditional phosphorus-nitrogen flame retardants have problems such as poor compatibility, easy migration, and poor weather resistance.

[0005] CN109971067A discloses a low-smoke, halogen-free, highly flame-retardant, oxygen-insulating cable material for medium-voltage cables, comprising the following components, the formula ratio being calculated by mass: 20 to 24 parts of ethylene-vinyl acetate resin, 0.4 parts of coupling agent, 20 parts of magnesium hydroxide, 48 to 50 parts of aluminum hydroxide, 1.5 to 2 parts of silicone rubber, 1 to 2 parts of carbon black, 5 to 6 parts of graft copolymer, and 0.2 to 0.3 parts of antioxidant.

[0006] The structural design and material selection of existing flame-retardant medium-voltage power cables often struggle to simultaneously meet comprehensive requirements such as flame retardancy, mechanical properties, electrical properties, and long-term reliability. Especially under extreme conditions, such as high-temperature environments, fire scenarios, mechanical impacts, etc., existing cables are prone to safety hazards such as insulation breakdown, sheath rupture, and flame-retardant failure, and cannot ensure the continuous power supply capacity in emergencies such as fires.

[0007] With the continuous improvement of national electrical fire safety standards and the increasingly strict environmental protection requirements, there is an urgent need to develop new and highly efficient environmentally friendly flame-retardant technologies and develop flame-retardant medium-voltage power cables with excellent comprehensive performance to meet the growing safety and reliability requirements of modern power systems. Summary of the Invention

[0008] To address the deficiencies of the existing technology, the purpose of the present invention is to provide a flame-retardant medium-voltage power cable. The cable adopts a five-layer structure of core - shield - fireproof - armor - outer sheath to form a complete protection system. In particular, the organically modified diatomaceous earth introduced in the outer sheath layer constructs a Si - P - N ternary synergistic flame-retardant system, achieving excellent flame-retardant effects at low addition amounts. This cable not only meets strict electrical performance requirements but also has excellent mechanical strength, heat aging resistance, and environmental adaptability, effectively extending the service life and improving the safety and reliability of power transmission.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions:

[0010] A flame-retardant medium-voltage power cable includes a core, a shielding layer, a fireproof layer, an armor layer, and an outer sheath layer arranged in sequence from the inside to the outside; the core is composed of multiple mutually stranded insulated wire cores, and each insulated wire core is composed of mutually stranded copper conductors and an insulating layer sequentially coated outside the mutually stranded copper conductors; a filler is filled between the core and the shielding layer.

[0011] Preferably, the outer sheath layer is made of the following components in parts by weight: 80 - 100 parts of low-density polyethylene, 30 - 70 parts of EVA, 20 - 35 parts of maleic anhydride-grafted polypropylene, 10 - 25 parts of modified diatomaceous earth, 0.5 - 3 parts of antioxidant, 0.5 - 2 parts of anti-dripping agent, and 2 - 6 parts of zinc stearate.

[0012] Preferably, the preparation method of the modified diatomaceous earth includes the following steps:

[0013] (1) Immerse the diatomaceous earth in a dilute sulfuric acid solution, perform ultrasonic acidification treatment, filter and wash until neutral, then calcine, take out and cool to room temperature, grind and sieve to obtain pretreated diatomaceous earth;

[0014] Diatomite pretreatment: Through ultrasonic acidification treatment with dilute sulfuric acid solution, it mainly dissolves and removes impurities such as carbonates and metal oxides in diatomite, and at the same time partially destroys the surface structure to increase the specific surface area. In the subsequent calcination process, on the one hand, organic impurities are removed by oxidative decomposition at high temperature; on the other hand, the siloxane (Si-O-Si) structure on the surface of diatomite is partially broken and reorganized to form a large number of surface silanol groups (Si-OH). This pretreatment process ultimately maximizes the content of surface silanol groups on diatomite, providing active sites for subsequent grafting reactions.

[0015] Preferably, in step (1), the dosage ratio of diatomite to dilute sulfuric acid solution is 10 g: 40 - 80 mL; the concentration of dilute sulfuric acid is 0.5 - 2 mol / L.

[0016] Preferably, in step (1), the acidification treatment time is 1 - 2 h; the calcination conditions are calcination at 400 - 500 °C for 2 - 5 h; grinding through a 150 - 200 mesh sieve.

[0017] (2) Disperse the pretreated diatomite in THF, add N,N - diisopropylethylamine under nitrogen protection and ice bath, then slowly add spirophosphoryl dichloride, stir and mix under ice bath, and then raise the temperature for reaction. Filter, wash, and dry the product to obtain intermediate diatomite;

[0018] Reaction of silanol group with spirophosphoryl dichloride: The activated surface silanol group (Si-OH) on diatomite acts as a nucleophile, and the lone pair of electrons on its oxygen atom attacks the phosphorus atom in the spirophosphoryl dichloride molecule. Subsequently, the P-Cl bond breaks and chloride ions are released. N,N - diisopropylethylamine acts as a weak base to capture the generated HCl to prevent possible side reactions under acidic conditions. Each spirophosphoryl dichloride molecule contains two chlorine atoms. In this step of the reaction, usually only one chlorine is substituted by the silanol group to form a Si-O-P bond, and the other chlorine atom remains as the active site for the next step of the reaction. Finally, intermediate diatomite with active phosphoryl chloride groups modified on the surface is obtained.

[0019] Preferably, in step (2), the dosage ratio of pretreated diatomite, THF, N,N - diisopropylethylamine, and spirophosphoryl dichloride is 10 g: 80 - 100 mL: 0.5 - 3 mL: 2 - 6 g.

[0020] Preferably, in step (2), stir and mix under ice bath at 0 - 5 °C for 1 - 2 h, and then raise the temperature to room temperature and stir for reaction for 12 - 15 h.

[0021] (3) Disperse the intermediate diatomite in DMF, then add triethylamine, add 2-(4 - aminophenyl)-5 - aminobenzimidazole in batches under nitrogen protection, and then stir for reaction. Filter, wash, and dry the product to obtain modified diatomite.

[0022] Reaction of intermediate diatomite with amino compounds: The nitrogen atom on the amino group in 2-(4-aminophenyl)-5-aminobenzimidazole acts as a nucleophile, attacking the phosphorus atom on the phosphoryl chloride group to form a P-N bond, while releasing chloride ions. Triethylamine acts as an organic base to capture the HCl generated in the reaction. Finally, modified diatomite with a nitrogen-containing heterocyclic compound grafted on its surface is obtained, endowing it with new physical and chemical properties and flame retardancy.

[0023] Preferably, in step (3), the dosage ratio of intermediate diatomite, DMF, triethylamine, and 2-(4-aminophenyl)-5-aminobenzimidazole is 10 g: 100 - 120 mL: 0.5 - 2 mL: 2.4 - 6.0 g.

[0024] Preferably, in step (3), 2-(4-aminophenyl)-5-aminobenzimidazole is added in 3 portions, with an interval of 5 - 10 min between each addition; the stirring reaction conditions are stirring and reacting at 35 - 50 °C for 18 - 24 h.

[0025] Preferably, the insulating layer is extruded from polyvinyl chloride material, with a thickness of 0.7 - 1 mm; the filling material is non-alkali fiberglass rope; the shielding layer is formed by winding copper tape; the fire-resistant layer is formed by winding fire-resistant mica tape; the armor layer is formed by winding non-magnetic stainless steel tape.

[0026] Preferably, the preparation method of the outer sheath layer includes the following steps: placing the components in a high-speed kneader for heating and kneading and stirring to obtain a mixture; placing the mixture in a granulator for extrusion granulation, and then cutting and cooling to obtain the outer sheath material.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The flame-retardant medium-voltage power cable of the present invention adopts a multi-layer structure design, and each layer acts synergistically, significantly improving the comprehensive performance of the cable. The polyvinyl chloride insulating layer has excellent insulation performance and durability, ensuring the safe transmission of electric energy; the non-alkali fiberglass rope filling material is filled between the cable core and the shielding layer, effectively preventing moisture penetration and improving the compressive strength of the cable; the copper tape shielding layer not only shields electromagnetic interference but also evenly distributes the electric field to prevent partial discharge; the fire-resistant mica tape layer has excellent high-temperature resistance and can keep the cable working normally for a certain period of time in case of fire; the non-magnetic stainless steel tape armor layer provides excellent mechanical protection and anti-external force damage ability, while avoiding hysteresis loss; the outer sheath layer provides comprehensive environmental protection and flame retardancy for the entire cable, forming a complete protection system.

[0029] 2. The present invention discloses an outer sheath layer. Low-density polyethylene serves as the matrix resin, providing excellent processability, mechanical strength, and flexibility; EVA enhances the toughness and low-temperature resistance of the material, while improving its compatibility with other components; maleic anhydride grafted polypropylene is used as a compatibilizer to improve the interfacial bonding between organic and inorganic components and enhance the mechanical properties of the material; modified diatomite not only provides a significant flame retardant effect but also enhances the mechanical strength and thermal stability of the material; antioxidants effectively prevent the oxidative degradation of the polymer during processing and use, extending its service life; anti-dripping agents prevent the melting and dripping phenomenon of the material during combustion, improving the flame retardant safety; zinc stearate acts as a lubricant and dispersant, improving the processing fluidity and component dispersibility. These components act synergistically to endow the outer sheath layer with excellent flame retardancy, mechanical properties, aging resistance, and processing performance.

[0030] 3. The present invention provides a modified diatomite. The first-step acidification and calcination pretreatment not only effectively remove impurities but also retain and optimize the unique porous structure of diatomite, increase the surface silanol active sites, and improve the specific surface area, laying a foundation for subsequent modification. The second step involves reacting with spirophosphoryl dichloride to introduce phosphorus-containing groups on the surface of diatomite, which not only serves as a bridge for subsequent grafting but also directly endows diatomite with excellent flame retardant properties. The third step involves reacting with the nitrogen-containing heterocyclic compound 2-(4-aminophenyl)-5-aminobenzimidazole to successfully construct an organic modification layer on the surface of diatomite, while introducing a benzimidazole ring structure, significantly enhancing the anti-aging performance and heat resistance stability of the material.

[0031] Organic modification endows the surface of diatomite with lipophilicity, fundamentally changing the compatibility problem between traditional diatomite and the polymer matrix. The modified diatomite can be uniformly dispersed in the polyolefin matrix, effectively avoiding the agglomeration phenomenon of conventional inorganic fillers and significantly reducing interfacial defects. This excellent dispersibility creates conditions for the modified diatomite to enhance the mechanical properties of the sheath layer: on the one hand, the uniformly dispersed diatomite particles can serve as stress dispersion points, improving the impact strength of the material; on the other hand, the interfacial interaction formed between the organic modification layer and the polymer matrix strengthens the overall rigidity and toughness balance of the filled system. At the same time, the unique porous structure of the modified diatomite increases the mechanical engagement with the matrix, improving the tensile strength and elongation at break of the composite material.

[0032] In terms of flame retardancy, the modified diatomite constructs a unique Si-P-N ternary synergistic flame retardant system. The phosphorus-containing groups decompose during combustion to produce phosphoric acid and polyphosphoric acid, promoting the formation of a dense carbon layer on the material surface; the nitrogen-containing benzimidazole groups release non-combustible gases during thermal decomposition, diluting the concentration of combustible gases and promoting the formation of an expanded carbon layer; while the silicon skeleton structure of diatomite provides carbon layer stability and acts as a heat insulation barrier. In particular, the porous structure of diatomite itself can effectively adsorb and intercept toxic flue gas during combustion, significantly reducing the flue gas release amount and toxicity.

[0033] This multiple modification not only enables diatomite to achieve excellent flame retardant effects at a low addition amount, but also solves problems such as poor dispersibility, low interfacial compatibility, and easy migration and precipitation existing in traditional inorganic flame retardants, ensuring the long-term stability of flame retardant performance. At the same time, the introduction of the benzimidazole ring structure in the organic modification layer endows the material with excellent antioxidant and heat resistance, greatly improving the service life of the cable sheath in harsh environments such as high temperature, humidity, and ultraviolet rays. Generally speaking, this modified diatomite not only meets the flame retardant requirements of power cables, but also takes into account mechanical properties, environmental protection, and long-term reliability, and is a high-performance and multifunctional flame retardant filler. Specific Embodiments

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in conjunction with embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased through market channels or synthesized from raw materials purchased through market channels.

[0036] EVA: VA content is 28 wt%, the melt index under the conditions of 190 °C / 2.16 kg is 3 g / 10 min, the melting point measured by DSC method is 73 °C, grade ELVAX 265, DuPont, USA;

[0037] Low-density polyethylene is purchased from Wuhan Rongchuang Plastic Co., Ltd., grade DFDA-7042;

[0038] Maleic anhydride grafted polypropylene is purchased from Dongguan Zhangmutou Hongji Plasticization Business, model DuPont 50E806;

[0039] Diatomite with a silicon dioxide content of 90 - 92 wt% is purchased from Changbai County Qingshanyuan Diatomite Co., Ltd.;

[0040] Ethylene-vinyl acetate copolymer model is EA19400, purchased from LG Co., Ltd., South Korea;

[0041] Low-density polyethylene model is 7102-0140, purchased from Thermo Fisher Scientific;

[0042] The fire-resistant mica tape was purchased from Yangzhou Shengkai Electrical Insulation Co., Ltd., with the model 65.

[0043] A flame-retardant medium-voltage power cable includes a cable core, a shielding layer, a fire-resistant layer, an armor layer, and an outer sheath layer arranged in sequence from inside to outside; the cable core is composed of a plurality of mutually twisted insulated wire cores, and each insulated wire core is composed of mutually twisted copper conductors and an insulating layer sequentially coated outside the mutually twisted copper conductors; a filler is filled between the cable core and the shielding layer; the insulating layer is extruded from polyvinyl chloride material with a thickness of 0.7 - 1 mm; the filler is an alkali-free fiberglass rope; the shielding layer is formed by winding copper tape; the fire-resistant layer is formed by winding fire-resistant mica tape; the armor layer is formed by winding non-magnetic stainless steel tape.

[0044] A preparation method for the outer sheath layer includes the following steps:

[0045] (1) Immerse 10 g of diatomite in 40 - 80 mL of dilute sulfuric acid solution with a concentration of 0.5 - 2 mol / L, perform ultrasonic acidification treatment for 1 - 2 h, filter and wash until neutral, then calcine at 400 - 500 °C for 2 - 5 h, take out and cool to room temperature, grind through a 150 - 200 mesh sieve to obtain pretreated diatomite;

[0046] (2) Disperse 10 g of pretreated diatomite in 80 - 100 mL of THF, add 0.5 - 3 mL of N,N - diisopropylethylamine under nitrogen protection and ice bath, then slowly add 2 - 6 g of spirophosphoryl dichloride, stir and mix at 0 - 5 °C in ice bath for 1 - 2 h, then raise the temperature to room temperature and stir and react for 12 - 15 h, filter, wash and dry the product to obtain intermediate diatomite;

[0047] (3) Disperse 10 g of intermediate diatomite in 100 - 120 mL of DMF, then add 0.5 - 2 mL of triethylamine, add 2.4 - 6.0 g of 2-(4 - aminophenyl)-5 - aminobenzimidazole in batches under nitrogen protection, add it in 3 times, with an interval of 5 - 10 min each time, then stir and react at 35 - 50 °C for 18 - 24 h, filter, wash and dry the product to obtain modified diatomite;

[0048] (4) Put 80 - 100 parts of low-density polyethylene, 30 - 70 parts of EVA, 20 - 35 parts of maleic anhydride grafted polypropylene, 10 - 25 parts of modified diatomite, 0.5 - 3 parts of antioxidant, 0.5 - 2 parts of anti-dripping agent, and 2 - 6 parts of zinc stearate into a high-speed kneader, heat and knead and stir to obtain a mixture; put the mixture into a granulator for extrusion granulation, and perform cutting and cooling to obtain outer sheath material.

[0049] The following is a further description of the present invention through specific embodiments.

[0050] Example 1

[0051] A preparation method of an outer sheath layer, comprising the following steps:

[0052] (1) Immerse 10 g of diatomite in 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 2 h, filter and wash until neutral, then calcine at 500 °C for 2 h, take out and cool to room temperature, grind through a 200-mesh sieve to obtain pretreated diatomite;

[0053] (2) Disperse 10 g of pretreated diatomite in 100 mL of THF, add 3 mL of N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add 6 g of spirophosphoryl dichloride, stir and mix at 2 °C in ice bath for 2 h, then raise the temperature to room temperature and stir and react for 15 h, filter, wash and dry the product to obtain intermediate diatomite;

[0054] (3) Disperse 10 g of intermediate diatomite in 100 mL of DMF, then add 2 mL of triethylamine, add 6.0 g of 2-(4-aminophenyl)-5-aminobenzimidazole in batches under nitrogen protection, add it in 3 times, with an interval of 10 min each time, then stir and react at 50 °C for 18 h, filter, wash and dry the product to obtain modified diatomite;

[0055] (4) Put 100 g of low-density polyethylene, 70 g of EVA, 35 g of maleic anhydride grafted polypropylene, 25 g of modified diatomite, 3 g of antioxidant 1010, 2 g of anti-dripping agent DF-S10, and 6 g of zinc stearate into a high-speed kneader, heat and knead and stir to obtain a mixture; put the mixture into a granulator for extrusion granulation, and perform cutting and cooling to obtain outer sheath material.

[0056] Example 2

[0057] A preparation method of an outer sheath layer, comprising the following steps:

[0058] (1) Immerse 10 g of diatomite in 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 1.5 h, filter and wash until neutral, then calcine at 480 °C for 3 h, take out and cool to room temperature, grind through a 200-mesh sieve to obtain pretreated diatomite;

[0059] (2) Disperse 10 g of pretreated diatomite in 100 mL of THF, add 2.5 mL of N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add 5 g of spirophosphoryl dichloride, stir and mix at 2 °C in ice bath for 1.5 h, then raise the temperature to room temperature and stir and react for 14 h, filter, wash and dry the product to obtain intermediate diatomite;

[0060] (3) Disperse 10 g of intermediate diatomaceous earth into 100 mL of DMF, then add 1.5 mL of triethylamine, and add 4.8 g of 2-(4-aminophenyl)-5-aminobenzimidazole in batches under nitrogen protection. Add it in 3 times, with an interval of 10 min each time. Then stir and react at 45 °C for 20 h. Filter, wash, and dry the product to obtain modified diatomaceous earth;

[0061] (4) Place 95 g of low-density polyethylene, 60 g of EVA, 30 g of maleic anhydride-grafted polypropylene, 20 g of modified diatomaceous earth, 2 g of antioxidant 1010, 1.5 g of anti-dripping agent DF-S10, and 5 g of zinc stearate in a high-speed kneader, heat and knead and stir to obtain a mixture; Place the mixture in a granulator for extrusion granulation, and perform cutting and cooling to obtain the outer sheath material.

[0062] Example 3

[0063] A preparation method of an outer sheath layer, comprising the following steps:

[0064] (1) Immerse 10 g of diatomaceous earth into 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 1.5 h, filter and wash until neutral, then calcine at 420 °C for 4 h, take out and cool to room temperature, and grind through a 200-mesh sieve to obtain pretreated diatomaceous earth;

[0065] (2) Disperse 10 g of pretreated diatomaceous earth into 100 mL of THF, add 1 mL of N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add 4 g of spirophosphoryl dichloride, stir and mix at 2 °C in ice bath for 1.5 h, then raise the temperature to room temperature and stir and react for 13 h. Filter, wash, and dry the product to obtain intermediate diatomaceous earth;

[0066] (3) Disperse 10 g of intermediate diatomaceous earth into 100 mL of DMF, then add 1 mL of triethylamine, and add 3.6 g of 2-(4-aminophenyl)-5-aminobenzimidazole in batches under nitrogen protection. Add it in 3 times, with an interval of 10 min each time. Then stir and react at 40 °C for 22 h. Filter, wash, and dry the product to obtain modified diatomaceous earth;

[0067] (4) Place 85 g of low-density polyethylene, 40 g of EVA, 25 g of maleic anhydride-grafted polypropylene, 15 g of modified diatomaceous earth, 1 g of antioxidant 1010, 1 g of anti-dripping agent DF-S10, and 3 g of zinc stearate in a high-speed kneader, heat and knead and stir to obtain a mixture; Place the mixture in a granulator for extrusion granulation, and perform cutting and cooling to obtain the outer sheath material.

[0068] Example 4

[0069] A preparation method of an outer sheath layer, comprising the following steps:

[0070] (1) Immerse 10 g of diatomite in 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 1 h, filter and wash until neutral, then calcine at 400 °C for 5 h, take out and cool to room temperature, grind through a 200-mesh sieve to obtain pretreated diatomite;

[0071] (2) Disperse 10 g of pretreated diatomite in 100 mL of THF, add 0.5 mL of N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add 2 g of spirophosphoryl dichloride, stir and mix at 2 °C in ice bath for 1 h, then raise the temperature to room temperature and stir to react for 12 h, filter, wash and dry the product to obtain intermediate diatomite;

[0072] (3) Disperse 10 g of intermediate diatomite in 100 mL of DMF, then add 0.5 mL of triethylamine, add 2.4 g of 2-(4-aminophenyl)-5-aminobenzimidazole in batches under nitrogen protection, add it in 3 times, with an interval of 10 min each time, then stir and react at 35 °C for 24 h, filter, wash and dry the product to obtain modified diatomite;

[0073] (4) Put 80 g of low-density polyethylene, 30 g of EVA, 20 g of maleic anhydride grafted polypropylene, 10 g of modified diatomite, 0.5 g of antioxidant 1010, 0.5 g of anti-dripping agent DF-S10, and 2 g of zinc stearate into a high-speed kneader, heat and knead and stir to obtain a mixture; put the mixture into a granulator for extrusion granulation, and perform cutting and cooling to obtain outer sheath material.

[0074] Comparative Example 1

[0075] A preparation method of an outer sheath layer, comprising the following steps:

[0076] (1) Immerse 10 g of diatomite in 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 2 h, filter and wash until neutral, then calcine at 500 °C for 2 h, take out and cool to room temperature, grind through a 200-mesh sieve to obtain pretreated diatomite;

[0077] (2) Disperse 10 g of pretreated diatomite in 100 mL of THF, add 3 mL of N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add 6 g of spirophosphoryl dichloride, stir and mix at 2 °C in ice bath for 2 h, then raise the temperature to room temperature and stir to react for 15 h, filter, wash and dry the product to obtain intermediate diatomite;

[0078] (3) Put 100 g of low-density polyethylene, 70 g of EVA, 35 g of maleic anhydride-grafted polypropylene, 25 g of intermediate diatomite, 3 g of antioxidant 1010, 2 g of anti-dripping agent DF-S10, and 6 g of zinc stearate into a high-speed kneader, heat and knead and stir to obtain a mixed material; put the mixed material into a granulator for extrusion granulation, and perform cutting and cooling to obtain an outer sheath material.

[0079] Comparative Example 2

[0080] A preparation method of an outer sheath layer includes the following steps:

[0081] (1) Immerse 10 g of diatomite in 80 mL of 1 mol / L dilute sulfuric acid solution, perform ultrasonic acidification treatment for 2 h, filter and wash until neutral, then calcine at 500 °C for 2 h, take out and cool to room temperature, and grind through a 200-mesh sieve to obtain pretreated diatomite;

[0082] (2) Put 100 g of low-density polyethylene, 70 g of EVA, 35 g of maleic anhydride-grafted polypropylene, 25 g of pretreated diatomite, 3 g of antioxidant 1010, 2 g of anti-dripping agent DF-S10, and 6 g of zinc stearate into a high-speed kneader, heat and knead and stir to obtain a mixed material; put the mixed material into a granulator for extrusion granulation, and perform cutting and cooling to obtain an outer sheath material.

[0083] Perform performance tests on the outer sheath materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2. Refer to GB / T 2951.11-2008 "General test methods for insulating and sheathing materials of cables and optical cables - Part 11: General test methods - Measurement of thickness and overall dimensions, Mechanical properties tests" to test the tensile strength and elongation at break; refer to GB / T 2406.2-2009 "Plastics - Determination of burning behavior by the oxygen index method - Part 2: Room temperature test" to test the limiting oxygen index; refer to GB / T 17651.2-2021 "Measurement of smoke density of cables or optical cables when burning under specific conditions - Part 2: Test procedures and requirements" to test the smoke density (light transmittance); refer to GB / T 2951.12-2008 "General test methods for insulating and sheathing materials of cables and optical cables - Part 12: General test methods - Thermal ageing test methods" to perform thermal ageing in an air box at 185 °C for 120 h, and test the change rates of tensile strength and elongation at break after thermal ageing. The specific data are shown in Table 1.

[0084] Table 1 Performance test results of outer sheath materials

[0085]

[0086] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A flame-retardant medium-voltage power cable, comprising a cable core, a shielding layer, a fire-resistant layer, an armor layer, and an outer sheath layer arranged in sequence from inside to outside; characterized in that, The cable core is composed of a plurality of mutually twisted insulated wire cores, and each insulated wire core is composed of mutually twisted copper conductors and an insulating layer sequentially coated outside the mutually twisted copper conductors; a filler is filled between the cable core and the shielding layer.

2. The flame-retardant medium-voltage power cable according to claim 1, wherein The outer sheath layer is made of the following components by weight parts: 80-100 parts of low-density polyethylene, 30-70 parts of EVA, 20-35 parts of maleic anhydride grafted polypropylene, 10-25 parts of modified diatomite, 0.5-3 parts of antioxidant, 0.5-2 parts of anti-dripping agent, and 2-6 parts of zinc stearate.

3. The flame-retardant medium-voltage power cable according to claim 2, wherein, The preparation method of the modified diatomite includes the following steps: (1) Immerse diatomite into a dilute sulfuric acid solution, perform ultrasonic acidification treatment, filter and wash until neutral, then calcine, take out and cool to room temperature, grind and sieve to obtain pretreated diatomite; (2) Disperse the pretreated diatomite into THF, add N,N-diisopropylethylamine under nitrogen protection and ice bath, then slowly add spirophosphoryl dichloride, stir and mix under ice bath, then raise the temperature for reaction, filter, wash and dry the product to obtain intermediate diatomite; (3) Disperse the intermediate diatomite into DMF, then add triethylamine, add 2-(4-aminophenyl)-5-aminobenzimidazole in batches under nitrogen protection, then stir and react, filter, wash and dry the product to obtain modified diatomite.

4. The flame-retardant medium-voltage power cable according to claim 3, wherein In step (1), the dosage ratio of diatomite to the dilute sulfuric acid solution is 10 g: 40-80 mL; the concentration of the dilute sulfuric acid is 0.5-2 mol / L.

5. The flame-retardant medium-voltage power cable according to claim 3, characterized in that, In step (1), the acidification treatment time is 1-2 h; the calcination condition is calcination at 400-500 °C for 2-5 h; grind and sieve through a 150-200 mesh sieve.

6. The flame-retardant medium-voltage power cable according to claim 3, wherein, In step (2), the dosage ratio of pretreated diatomite, THF, N,N-diisopropylethylamine, and spirophosphoryl dichloride is 10 g: 80-100 mL: 0.5-3 mL: 2-6 g.

7. The flame-retardant medium-voltage power cable according to claim 3, wherein In step (2), stir and mix at 0-5 °C under ice bath for 1-2 h, then raise the temperature to room temperature and stir and react for 12-15 h.

8. The flame-retardant medium-voltage power cable according to claim 3, wherein, In step (3), the dosage ratio of intermediate diatomite, DMF, triethylamine, and 2-(4-aminophenyl)-5-aminobenzimidazole is 10 g: 100-120 mL: 0.5-2 mL: 2.4-6.0 g.

9. The flame-retardant medium-voltage power cable according to claim 3, wherein, In step (3), add 2-(4-aminophenyl)-5-aminobenzimidazole in 3 batches, with an interval of 5-10 min each time; the stirring reaction condition is stirring reaction at 35-50 °C for 18-24 h.

10. The flame-retardant medium-voltage power cable according to claim 1, wherein, The insulating layer is extruded from polyvinyl chloride material, with a thickness of 0.7-1 mm; the filler is an alkali-free glass fiber rope; the shielding layer is formed by winding copper tape; the fire-resistant layer is formed by winding fire-resistant mica tape; the armor layer is formed by winding non-magnetic stainless steel tape.

Images