A flame-retardant cable insulation layer and a method for preparing the same

Abstract

The application discloses a kind of flame-retardant cable insulation layer and preparation method thereof, belong to wire and cable manufacturing technical field.The insulating layer is by high-density polyethylene, maleic anhydride grafting polyethylene, modified bentonite composite carbon agent, epoxy functionalized ammonium polyphosphate and other raw materials are formed according to specific proportion.The modified bentonite composite carbon agent is modified by lignin twice, bentonite functionalization and high-temperature crosslinking are obtained, and the epoxy functionalized ammonium polyphosphate is obtained by reacting with 3-aminopropyl triethoxysilane after ammonium polyphosphate acetone dispersion of ammonium polyphosphate, and the preparation method includes twice mixing and hot-pressing curing, annealing treatment.The application is modified by raw materials, and process optimization makes cable insulation layer have excellent flame-retardant performance, mechanical toughness, thermal stability and electrical insulation, solves the problem of performance imbalance and insufficient durability of existing materials, and process is easy to control, suitable for large-scale production, and widely used.

Description

Technical Field

[0001] This invention relates to the field of wire and cable manufacturing technology, specifically to a flame-retardant cable insulation layer and its preparation method. Background Technology

[0002] As the core carrier of power transmission and signal transmission, cables are widely used in various fields such as construction, industrial production, and transportation. Their safety performance is directly related to the stable operation of related systems. With the increasing demands for electrical safety in modern society, flame-retardant cables have become the preferred product for high-risk locations due to their ability to suppress flame spread and reduce the release of toxic fumes in fire scenarios. The insulation layer, as a key component of the cable, not only needs to possess excellent electrical insulation performance to ensure safe power transmission, but also needs to consider multiple functions such as flame retardancy and mechanical properties. Its performance directly determines the overall safety level and service life of the cable.

[0003] In existing technologies, flame-retardant cable insulation materials generally face the problem of "poor performance balance." Most materials struggle to simultaneously meet the dual requirements of flame retardancy and mechanical properties. Some materials with high flame retardancy ratings often suffer from insufficient toughness and brittleness, making them prone to insulation damage during cable laying, bending, or long-term use, leading to safety hazards such as short circuits. Materials that prioritize mechanical properties typically have limited flame retardancy, spread rapidly during combustion, and produce large amounts of molten drippings, easily igniting surrounding combustibles and expanding the fire's reach. This performance imbalance severely limits the application of cables in complex environments.

[0004] Furthermore, the thermal stability and durability of existing flame-retardant insulation materials need improvement. Under long-term high-temperature operation, ultraviolet radiation, or humid and hot environments, these materials are prone to thermal oxidative degradation, leading to a significant decrease in mechanical properties such as tensile strength and elongation at break. Simultaneously, electrical insulation performance declines, increasing the risk of breakdown and shortening the cable's service life. In addition, uneven dispersion of some flame-retardant systems within the material results in poor product performance consistency, affecting not only the performance but also potentially causing safety accidents due to localized performance deficiencies. Therefore, there is an urgent need to develop a flame-retardant cable insulation layer and its preparation method. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a flame-retardant cable insulation layer and its preparation method.

[0006] In a first aspect, the present invention provides a flame-retardant cable insulation layer, wherein the flame-retardant cable insulation layer is made of the following raw materials in parts by weight: 80-100 parts of high-density polyethylene, 15-25 parts of maleic anhydride-grafted polyethylene, 5-8 parts of modified bentonite composite charring agent, 20-30 parts of epoxy-functionalized ammonium polyphosphate, 0.8-1.5 parts of antioxidant, 3-6 parts of crosslinking aid and 1.2-2.0 parts of crosslinking initiator.

[0007] Furthermore, the modified bentonite composite charring agent is prepared by the following steps: A1: Add lignin to an aqueous ethanol solution, add 3-aminopropyltriethoxysilane, stir at 50℃-60℃ for 5-7 hours, filter, wash, and dry to obtain aminated lignin. Add the aminated lignin to N,N-dimethylformamide, add γ-glycidyl etheroxypropyltrimethoxysilane, stir at 70℃-80℃ for 5-7 hours under nitrogen protection to obtain double-modified lignin. A2: Calcine bentonite at 520℃-570℃ for 2.5h-3h, cool to room temperature, add to ethanol aqueous solution, add composite silane coupling agent, ultrasonically disperse for 50min-60min, heat to 75℃-88℃ and stir for 5h-11h, filter, wash and dry to obtain functionalized bentonite. A3: Add double-modified lignin and functionalized bentonite to N,N-dimethylformamide, heat to 100℃-105℃ under nitrogen protection, add hexamethylenetetramine, stir and react for 12h-15h, filter, wash and dry to obtain modified bentonite composite char agent.

[0008] Further, the raw materials in the modified bentonite composite charring agent, by weight, are as follows: 8-12 parts lignin, 160-200 parts ethanol aqueous solution in step A1, 4-6 parts 3-aminopropyltriethoxysilane, 130-170 parts N,N-dimethylformamide in step A1, 2-3 parts γ-glycidyl etheroxypropyltrimethoxysilane, 12-18 parts bentonite, 200-240 parts ethanol aqueous solution in step A2, 5-7 parts composite silane coupling agent, 250-310 parts N,N-dimethylformamide in step A3, and 1.8-2.5 parts hexamethylenetetramine.

[0009] Further, the mass fraction of the ethanol aqueous solution in step A1 is 20%-30%; the mass fraction of the ethanol aqueous solution in step A2 is 15%-20%; and the composite silane coupling agent is composed of 3-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane in a mass ratio of 1-2:1.

[0010] Further, the epoxy-functionalized ammonium polyphosphate is prepared by the following steps: B1: Disperse ammonium polyphosphate in acetone and sonicate for 30-50 minutes. Add 3-aminopropyltriethoxysilane and heat to 60-75°C with stirring for 4-6 hours. After the reaction is complete, filter, wash, and dry to obtain aminated ammonium polyphosphate. B2: Aminated ammonium polyphosphate is dispersed in N,N-dimethylformamide, 3-glycidyl etheroxypropyltriethoxysilane is added, the temperature is raised to 80℃-90℃ and the reaction is stirred for 4h-5h. After filtration, washing and drying, epoxy-functionalized ammonium polyphosphate is obtained.

[0011] Furthermore, the raw materials in the epoxy-functionalized ammonium polyphosphate, by weight, are as follows: 45-55 parts of ammonium polyphosphate, 8-12 parts of 3-aminopropyltriethoxysilane, 10-15 parts of 3-glycidyl etheroxypropyltriethoxysilane, 150-200 parts of acetone, and 200-250 parts of N,N-dimethylformamide.

[0012] Furthermore, the antioxidant is composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 1-2:1-3:1.

[0013] Furthermore, the crosslinking aid is composed of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:1.5-2.

[0014] Furthermore, the crosslinking initiator is composed of dicumyl peroxide and tert-butyl peroxide in a mass ratio of 1-1.8:1.

[0015] Secondly, the present invention provides a method for preparing a flame-retardant cable insulation layer, comprising the following preparation steps: S1: High-density polyethylene, maleic anhydride-grafted polyethylene, modified bentonite composite charring agent, epoxy-functionalized polyphosphate ammonium, and antioxidant are added to a mixer for the first mixing, and then crosslinking initiator and crosslinking aid are added for the second mixing to obtain a mixed gel. S2: The mixed gel is placed in a hot press vulcanizing machine for hot pressing and curing. After cooling, it is annealed to obtain a flame-retardant cable insulation layer.

[0016] Furthermore, the temperature of the first mixing is 120℃-135℃, the rotation speed is 200rpm-250rpm, and the time is 15min-25min.

[0017] Furthermore, the temperature of the second mixing is 115℃-130℃, the rotation speed is 180rpm-220rpm, and the time is 8min-15min.

[0018] Furthermore, the specific operation of hot-press curing is as follows: the mixed gel is placed in a hot-press vulcanizing machine, preheated at 80℃-95℃ and pressure of 5MPa-8MPa for 10min-18min to remove air bubbles; then the temperature is raised to 150℃-170℃ and the pressure is raised to 12MPa-16MPa for hot-press curing for 30min-50min.

[0019] Furthermore, the annealing process specifically involves annealing the food in an oven at 100℃-110℃ for 3-4 hours.

[0020] The beneficial effects of this invention are: 1. This invention significantly improves the flame retardant and mechanical properties of the insulation layer through precise modification and synergistic combination of core raw materials. The modified bentonite composite charring agent is prepared through multiple modification and cross-linking treatments, which can form a highly efficient flame retardant system with epoxy-functionalized ammonium polyphosphate. During combustion, it can quickly form a continuous and dense char layer, effectively blocking heat and oxygen transfer. At the same time, it has good compatibility with high-density polyethylene substrate, and gives the cable insulation layer both high strength and good toughness, enabling it to better withstand the mechanical stress during cable use.

[0021] 2. The thermal stability and electrical insulation properties of the material are simultaneously optimized. The compounded antioxidant system can effectively resist thermo-oxidative aging and ultraviolet corrosion. Combined with the stable structure of modified bentonite composite charring agent and epoxy-functionalized ammonium polyphosphate, the performance degradation of the insulation material under long-term use or high-temperature environment is significantly reduced, thus extending its service life. Detailed Implementation

[0022] To make the embodiments of the present invention easier to understand, the present invention will be described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not limited to the application scope of the present invention.

[0023] The specific parameters of the raw materials used in this invention are as follows: The high-density polyethylene used in this invention is grade HD5502GA, purchased from Suzhou Boyihui Plastics Co., Ltd.

[0024] The maleic anhydride-grafted polyethylene used in this invention is grade 18410P, purchased from Dongguan Taotao Plastic Raw Materials Co., Ltd.

[0025] The lignin used in this invention is alkaline lignin, CAS number 8068-05-1, purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0026] The bentonite used in this invention is white calcium-based bentonite with a particle size of 200 mesh, purchased from Shijiazhuang Yonglong Refractory Materials Factory.

[0027] The ammonium polyphosphate used in this invention has the CAS number 68333-79-9 and was purchased from Jinan Xinchen Chemical Co., Ltd.

[0028] The γ-glycidoxypropyltrimethoxysilane used in this invention has the CAS number 2530-83-8 and was purchased from Wuhan Kemic Biomedical Technology Co., Ltd.

[0029] The 3-glycidoxypropyltriethoxysilane used in this invention has the CAS number 2602-34-8 and was purchased from Wuhan Kemic Biomedical Technology Co., Ltd.

[0030] The antioxidant 168 used in this invention has the CAS number 31570-04-4 and was purchased from Nanjing Milan New Materials Co., Ltd.

[0031] The antioxidant 1010 used in this invention has the CAS number 6683-19-8 and was purchased from Jinan City, Shandong Province. Jinan Hongteng Weiye New Materials Co., Ltd.

[0032] The ultraviolet absorber UV-531 used in this invention was purchased from Jinan Xiangfeng Weiye Chemical Co., Ltd.

[0033] The CAS number of the trimethylolpropane triacrylate used in this invention is 15625-89-5, and it was purchased from Donghao Chemical (Shandong) Co., Ltd.

[0034] The pentaerythritol tetraacrylate used in this invention has the CAS number 4986-89-4 and was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.

[0035] Example 1 A method for preparing a flame-retardant cable insulation layer includes the following preparation steps: 1. Preparation of modified bentonite composite charring agent: Raw material usage (by weight): 8 parts lignin, 160 parts ethanol aqueous solution (20% by mass) from step A1, 4 parts 3-aminopropyltriethoxysilane, 130 parts N,N-dimethylformamide from step A1, 2 parts γ-glycidyl etheroxypropyltrimethoxysilane, 12 parts bentonite, 200 parts ethanol aqueous solution (15% by mass) from step A2, 5 parts composite silane coupling agent (composed of 3-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane in a mass ratio of 1:1), 250 parts N,N-dimethylformamide from step A3, and 1.8 parts hexamethylenedialdehyde.

[0036] The specific preparation steps are as follows: A1: Add lignin to an aqueous ethanol solution, add 3-aminopropyltriethoxysilane, stir at 50°C for 5 hours, filter, wash three times with deionized water, and dry at 60°C for 4 hours to obtain aminated lignin. Add the aminated lignin to N,N-dimethylformamide, add γ-glycidoxypropyltrimethoxysilane, and stir at 70°C for 5 hours under nitrogen protection to obtain double-modified lignin. A2: Bentonite was calcined at 520℃ for 2.5h, cooled to room temperature, added to an ethanol aqueous solution, a composite silane coupling agent was added, ultrasonic power was 500W, ultrasonic dispersion was performed for 50min, the temperature was raised to 75℃ and stirred for 5h, filtered, washed twice with deionized water, and dried at 70℃ for 5h to obtain functionalized bentonite. A3: Double-modified lignin and functionalized bentonite were added to N,N-dimethylformamide, heated to 100℃ under nitrogen protection, hexadialdehyde was added, and the mixture was stirred for 12 hours. After filtration, the mixture was washed three times each with ethanol and deionized water, and dried at 65℃ for 6 hours to obtain the modified bentonite composite charcoal agent.

[0037] 2. Preparation of epoxy-functionalized ammonium polyphosphate: Raw material usage (by weight): 45 parts ammonium polyphosphate, 8 parts 3-aminopropyltriethoxysilane, 10 parts 3-glycidyl etheroxypropyltriethoxysilane, 150 parts acetone, and 200 parts N,N-dimethylformamide.

[0038] The specific preparation steps are as follows: B1: Ammonium polyphosphate was dispersed in acetone and ultrasonically dispersed for 30 min at 500 W. 3-Aminopropyltriethoxysilane was added, and the mixture was heated to 60 °C and stirred for 4 h. After filtration, the mixture was washed once with acetone and dried at 55 °C for 12 h to obtain aminated ammonium polyphosphate. B2: Aminated ammonium polyphosphate was dispersed in N,N-dimethylformamide, and 3-glycidyl etheroxypropyltriethoxysilane was added. The mixture was heated to 80°C and stirred for 4 hours. After filtration, the mixture was washed three times with N,N-dimethylformamide and dried under vacuum at 50°C (0.08 MPa) for 6 hours to obtain epoxy-functionalized ammonium polyphosphate.

[0039] 3. Preparation of flame-retardant cable insulation layer: Raw material usage (by weight): 80 parts high-density polyethylene, 15 parts maleic anhydride grafted polyethylene, 5 parts modified bentonite composite charring agent, 20 parts epoxy-functionalized ammonium polyphosphate, 0.8 parts antioxidant (composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 1:1:1), 3 parts crosslinking aid (composed of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:1.5), and 1.2 parts crosslinking initiator (composed of dicumyl peroxide and tert-butyl peroxide in a mass ratio of 1:1).

[0040] The specific preparation steps are as follows: S1: High-density polyethylene, maleic anhydride-grafted polyethylene, modified bentonite composite charcoal agent, epoxy-functionalized ammonium polyphosphate, and antioxidant are added to a mixer for the first mixing at a temperature of 120°C, a speed of 200 rpm, and a time of 15 min. Subsequently, a crosslinking initiator and crosslinking aid are added for the second mixing at a temperature of 115°C, a speed of 180 rpm, and a time of 8 min to obtain a mixed gel. S2: Place the mixed gel in a hot press vulcanizing machine, preheat it at 80℃ and 5MPa for 10 minutes to remove air bubbles; then heat it to 150℃ and press it to 12MPa for 30 minutes to cure it. Let it cool naturally to room temperature, then anneal it in a 100℃ oven for 3 hours and cool it to room temperature to obtain the flame-retardant cable insulation layer.

[0041] Example 2 A method for preparing a flame-retardant cable insulation layer includes the following preparation steps: 1. Preparation of modified bentonite composite charring agent: Raw material usage (by weight): 10 parts lignin, 180 parts ethanol aqueous solution (25% by mass) from step A1, 5 parts 3-aminopropyltriethoxysilane, 150 parts N,N-dimethylformamide from step A1, 2.5 parts γ-glycidyl etheroxypropyltrimethoxysilane, 16 parts bentonite, 220 parts ethanol aqueous solution (17.5% by mass) from step A2, 6 parts composite silane coupling agent (composed of 3-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane in a mass ratio of 1.5:1), 270 parts N,N-dimethylformamide from step A3, and 2.1 parts hexamethylenedialdehyde.

[0042] The specific preparation steps are as follows: A1: Add lignin to an aqueous ethanol solution, add 3-aminopropyltriethoxysilane, stir at 55°C for 6 hours, filter, wash with deionized water 4 times, and dry at 67°C for 5 hours to obtain aminated lignin. Add the aminated lignin to N,N-dimethylformamide, add γ-glycidoxypropyltrimethoxysilane, and stir at 75°C for 6 hours under nitrogen protection to obtain double-modified lignin. A2: Bentonite was calcined at 550℃ for 2.7h, cooled to room temperature, added to an ethanol aqueous solution, a composite silane coupling agent was added, ultrasonic power was 550W, ultrasonic dispersion was performed for 55min, the temperature was raised to 82℃ and stirred for 8h, filtered, washed twice with deionized water, and dried at 78℃ for 6h to obtain functionalized bentonite. A3: Double-modified lignin and functionalized bentonite were added to N,N-dimethylformamide, heated to 102℃ under nitrogen protection, hexadialdehyde was added, and the mixture was stirred for 14 hours. After filtration, the mixture was washed four times each with ethanol and deionized water, and dried at 70℃ for 7 hours to obtain the modified bentonite composite char agent.

[0043] 2. Preparation of epoxy-functionalized ammonium polyphosphate: Raw material usage (by weight): 50 parts ammonium polyphosphate, 10 parts 3-aminopropyltriethoxysilane, 12 parts 3-glycidyl etheroxypropyltriethoxysilane, 180 parts acetone, and 220 parts N,N-dimethylformamide.

[0044] The specific preparation steps are as follows: B1: Ammonium polyphosphate was dispersed in acetone and ultrasonically dispersed for 40 min. 3-Aminopropyltriethoxysilane was added, and the mixture was heated to 68 °C and stirred for 5 h. After filtration, the mixture was washed once with acetone and dried at 60 °C for 15 h to obtain aminated ammonium polyphosphate. B2: Aminated ammonium polyphosphate was dispersed in N,N-dimethylformamide, and 3-glycidyl etheroxypropyltriethoxysilane was added. The mixture was heated to 85°C and stirred for 4.5 h. After filtration, the mixture was washed four times with N,N-dimethylformamide and dried under vacuum at 55°C (0.085 MPa) for 7 h to obtain epoxy-functionalized ammonium polyphosphate.

[0045] 3. Preparation of flame-retardant cable insulation layer: Raw material usage (by weight): 90 parts high-density polyethylene, 20 parts maleic anhydride grafted polyethylene, 6.5 parts modified bentonite composite charring agent, 25 parts epoxy-functionalized ammonium polyphosphate, 1.2 parts antioxidant (composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 1.5:2:1), 5 parts crosslinking aid (composed of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:1.8), and 1.6 parts crosslinking initiator (composed of dicumyl peroxide and tert-butyl peroxide in a mass ratio of 1.4:1).

[0046] The specific preparation steps are as follows: S1: High-density polyethylene, maleic anhydride-grafted polyethylene, modified bentonite composite charcoal agent, epoxy-functionalized polyphosphate ammonium, and antioxidant are added to a mixer for the first mixing at a temperature of 125℃, a speed of 220 rpm, and a time of 20 min. Subsequently, a crosslinking initiator and a crosslinking aid are added for the second mixing at a temperature of 122℃, a speed of 200 rpm, and a time of 11 min to obtain a mixed gel. S2: Place the mixed gel in a hot press vulcanizing machine, preheat it at 88℃ and 6MPa for 15 minutes to remove air bubbles; then raise the temperature to 160℃ and press it at 14MPa for 40 minutes to cure it. After naturally cooling to room temperature, demold the initial product and place it in a 105℃ oven for annealing for 3.5 hours. After cooling to room temperature, the flame-retardant cable insulation layer is obtained.

[0047] Example 3 A method for preparing a flame-retardant cable insulation layer includes the following preparation steps: 1. Preparation of modified bentonite composite charring agent: Raw material usage (by weight): 12 parts lignin, 200 parts ethanol aqueous solution (30% by mass) from step A1, 6 parts 3-aminopropyltriethoxysilane, 170 parts N,N-dimethylformamide from step A1, 3 parts γ-glycidyl etheroxypropyltrimethoxysilane, 18 parts bentonite, 240 parts ethanol aqueous solution (20% by mass) from step A2, 7 parts composite silane coupling agent (composed of 3-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane in a mass ratio of 2:1), 310 parts N,N-dimethylformamide from step A3, and 2.5 parts hexamethylenedialdehyde.

[0048] The specific preparation steps are as follows: A1: Add lignin to an aqueous ethanol solution, add 3-aminopropyltriethoxysilane, stir at 60°C for 7 hours, filter, wash with deionized water 5 times, and dry at 75°C for 6 hours to obtain aminated lignin. Add the aminated lignin to N,N-dimethylformamide, add γ-glycidyl etheroxypropyltrimethoxysilane, and stir at 80°C for 7 hours under nitrogen protection to obtain double-modified lignin. A2: Bentonite was calcined at 570℃ for 3 hours, cooled to room temperature, added to an ethanol aqueous solution, a composite silane coupling agent was added, ultrasonic power was 600W, ultrasonic dispersion was performed for 60 minutes, the temperature was raised to 88℃ and stirred for 11 hours, filtered, washed 3 times with deionized water, and dried at 85℃ for 7 hours to obtain functionalized bentonite. A3: Double-modified lignin and functionalized bentonite were added to N,N-dimethylformamide, heated to 105℃ under nitrogen protection, hexadialdehyde was added, and the mixture was stirred for 15 hours. After filtration, the mixture was washed 5 times each with ethanol and deionized water, and dried at 75℃ for 8 hours to obtain the modified bentonite composite charcoal agent.

[0049] 2. Preparation of epoxy-functionalized ammonium polyphosphate: Raw material usage (by weight): 55 parts ammonium polyphosphate, 12 parts 3-aminopropyltriethoxysilane, 15 parts 3-glycidyl etheroxypropyltriethoxysilane, 200 parts acetone, and 250 parts N,N-dimethylformamide.

[0050] The specific preparation steps are as follows: B1: Ammonium polyphosphate was dispersed in acetone and ultrasonically dispersed for 50 min. 3-Aminopropyltriethoxysilane was added, and the mixture was heated to 75 °C and stirred for 6 h. After filtration, the mixture was washed twice with acetone and dried at 65 °C for 18 h to obtain aminated ammonium polyphosphate. B2: Aminated ammonium polyphosphate was dispersed in N,N-dimethylformamide, and 3-glycidyl etheroxypropyltriethoxysilane was added. The mixture was heated to 80℃-90℃ and stirred for 4-5 hours. After filtration, the mixture was washed 5 times with N,N-dimethylformamide and dried under vacuum at 60℃ (0.09MPa) for 8 hours to obtain epoxy-functionalized ammonium polyphosphate.

[0051] 3. Preparation of flame-retardant cable insulation layer: Raw material usage (by weight): 100 parts high-density polyethylene, 25 parts maleic anhydride grafted polyethylene, 8 parts modified bentonite composite charring agent, 30 parts epoxy-functionalized ammonium polyphosphate, 1.5 parts antioxidant (composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 2:3:1), 6 parts crosslinking aid (composed of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:2), and 2.0 parts crosslinking initiator (composed of dicumyl peroxide and tert-butyl peroxide in a mass ratio of 1.8:1).

[0052] The specific preparation steps are as follows: S1: High-density polyethylene, maleic anhydride-grafted polyethylene, modified bentonite composite charcoal agent, epoxy-functionalized polyphosphate ammonium, and antioxidant are added to a mixer for the first mixing at a temperature of 135℃, a speed of 250 rpm, and a time of 25 min. Subsequently, a crosslinking initiator and crosslinking aid are added for the second mixing at a temperature of 130℃, a speed of 220 rpm, and a time of 15 min to obtain a mixed gel. S2: Place the mixed gel in a hot press vulcanizing machine, preheat it at 95℃ and 8MPa for 18 minutes to remove air bubbles; then heat it to 170℃ and press it to 16MPa for 50 minutes to cure it. After naturally cooling to room temperature, demold the product and place it in a 110℃ oven for annealing for 4 hours. After cooling to room temperature, the flame-retardant cable insulation layer is obtained.

[0053] Comparative Example 1 Compared with Example 1, this comparative example replaces "double-modified lignin" with an equal mass of "aminated lignin". All other steps and parameters are the same, and will not be repeated here. The final result is a flame-retardant cable insulation layer.

[0054] Comparative Example 2 Compared with Example 1, this comparative example replaces "functionalized bentonite" with an equal mass of "bentonite". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a flame-retardant cable insulation layer.

[0055] Comparative Example 3 Compared with Example 1, in step A3, the double-modified lignin, functionalized bentonite and adipaldehyde are directly mixed. The remaining steps and parameters are the same, and will not be repeated in this comparative example. Finally, a flame-retardant cable insulation layer is obtained.

[0056] The specific steps in process A3 are as follows: A3: Add double-modified lignin and functionalized bentonite to N,N-dimethylformamide, then add hexamethylenedialdehyde, stir at room temperature for 12 hours, filter, wash with ethanol and deionized water three times each, and dry at 65°C for 6 hours to obtain modified bentonite composite char agent.

[0057] Comparative Example 4 Compared with Example 1, this comparative example replaces "epoxy-functionalized ammonium polyphosphate" with an equal mass of "ammonium polyphosphate". All other steps and parameters are the same, and will not be repeated in this comparative example. The final result is a flame-retardant cable insulation layer.

[0058] Performance testing The performance of the flame-retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are recorded in Table 1.

[0059] 1. Flame retardant properties: The flame retardant performance was tested in accordance with GB / T 2408-2021. The flame retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples. The self-extinguishing time of the samples was recorded. It was observed whether there were drips during the combustion process of the samples and whether the drips ignited the degreased cotton. The flame retardant level was determined according to the standard.

[0060] 2. Mechanical property testing: Mechanical property tests were conducted according to GB / T 1040.2-2006. A universal testing machine was used to press the flame-retardant cable insulation materials prepared in Examples 1-3 and Comparative Examples 1-4 into flat sheets with a thickness of 2.0 mm using a flat vulcanizing machine. These sheets were then cut into type 1A dumbbell-shaped specimens conforming to GB / T 1040.2 using a standard cutter. The tests were conducted in a standard laboratory environment at 23°C and 50% relative humidity. The specimens were stretched at a constant tensile speed of 50 mm / min using a universal testing machine until fracture. The maximum tensile force (F) at specimen fracture was recorded. m The elongation at break (ΔL) between the markings and the gradation line.

[0061] Tensile strength is calculated using the following formula: , where W is the original width of the narrow portion of the sample, and t is the original thickness of the sample.

[0062] Elongation at break is calculated using the following formula: , where L0 is the original gauge length of the sample.

[0063] 3. Thermal stability test: Thermal stability tests were conducted according to GB / T 2951.12-2017. The flame-retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples. First, the tensile strength and elongation at break before thermal aging were determined according to the aforementioned mechanical property test methods. Then, the samples were placed in a thermal aging chamber and suspended in an air-circulating aging chamber for continuous thermal aging at 135°C for 168 h. After aging, the samples were removed and placed in a standard laboratory environment at 23°C and 60% relative humidity for 16 h to adjust. The tensile strength and elongation at break after thermal aging were then determined, and the tensile strength retention rate and elongation at break retention rate were calculated.

[0064] The samples used in the thermal stability test were the same as those used in the mechanical performance test, namely the flame-retardant cable insulation layer samples prepared in Examples 1-3 and Comparative Examples 1-4. When measuring the tensile strength and elongation at break before and after thermal aging, the method of GB / T 1040.2-2006 standard on which the mechanical performance test was based was uniformly referred to.

[0065] Formula for tensile strength retention rate: .

[0066] Formula for elongation at break: .

[0067] 4. Electrical insulation performance test: Electrical insulation performance was tested according to GB / T 1408.2-2016. The flame-retardant cable insulation layers prepared in Examples 1-3 and Comparative Examples 1-4 were processed into uniform samples with a thickness of 1 mm, ensuring that the sample surface was free of bubbles, impurities, and scratches. The test was conducted using a ball-plate electrode device in a standard laboratory environment with a temperature of 23°C and a relative humidity of 50%. To avoid flashover on the sample surface affecting the test accuracy, the sample was completely immersed in transformer oil. During the test, a DC voltage was applied at a rate of 500 V / s and continuously increased until the sample broke down. The breakdown voltage value at this time was recorded, and the DC breakdown strength was calculated.

[0068] Formula for DC breakdown strength: .

[0069] Table 1: Performance Test Results of Flame-Retardant Cable Insulation Layer As shown in Table 1, the properties of Examples 1-3 all exhibit stable and excellent performance. In terms of flame retardancy, they are rapidly self-extinguishing without dripping; mechanically, they possess high strength and good toughness; their performance degradation after thermal aging is minimal; and they maintain excellent electrical insulation capabilities. This is because the modified bentonite composite charring agent and the epoxy-functionalized ammonium polyphosphate in the raw material system form a synergistic effect, resulting in better compatibility with the high-density polyethylene substrate and a uniform and dense cross-linked network structure. Combined with the compounded antioxidants and optimized preparation process, the insulating layer material achieves a balanced improvement in flame retardancy, mechanical properties, thermal stability, and electrical insulation.

[0070] Comparing Comparative Example 1 with Example 1, it is evident that replacing the dual-modified lignin with aminated lignin significantly degrades the material's performance. This is because the number of active groups on the molecular chain of single aminated modified lignin is limited, resulting in weak chemical bonding with functionalized bentonite and an inability to form a stable cross-linked structure. During combustion, it is difficult to form a continuous and dense char layer, failing to effectively block heat and oxygen transfer. Simultaneously, insufficient internal bonding leads to a decrease in mechanical properties and thermal stability, and the electrical insulation performance is also affected by the increased internal defects. This setup demonstrates the crucial role of dual modification of lignin in improving the overall performance of the material.

[0071] Comparing Comparative Example 2 with Example 1, it can be seen that replacing functionalized bentonite with bentonite weakens various properties of the material to varying degrees. Unmodified bentonite, without calcination and silane coupling agent modification, has low surface activity and poor compatibility with high-density polyethylene substrate and other components. It easily agglomerates within the material, leading to stress concentration. During combustion, it cannot synergistically form an effective char layer with the double-modified lignin, resulting in decreased mechanical properties due to uneven dispersion, reduced thermal aging performance, and decreased electrical insulation properties due to increased internal interface defects. This highlights the significant role of functionalized bentonite modification in improving material structure and performance.

[0072] Comparing Comparative Example 3 with Example 1, it is evident that the simplified preparation process of the modified bentonite composite charring agent, which directly mixes double-modified lignin, functionalized bentonite, and adipaldehyde without a high-temperature cross-linking reaction, results in a significant decline in material performance. Direct mixing fails to establish stable chemical bonds between the double-modified lignin, functionalized bentonite, and adipaldehyde; the components remain in a physically mixed state with loose bonds. During combustion, the char layer easily detaches, making it difficult to sustain flame-retardant effects. Mechanical properties decrease due to insufficient internal bonding. During thermal aging, the components easily separate, leading to accelerated performance degradation. Electrical insulation properties also decrease due to the loose internal structure and increased defects. This setting verifies the necessity of a high-temperature cross-linking process in constructing a stable composite charring agent structure.

[0073] Comparing Comparative Example 4 with Example 1, it is evident that replacing epoxy-functionalized ammonium polyphosphate with ammonium polyphosphate significantly reduces the overall performance of the material. Ammonium polyphosphate lacks epoxy groups on its surface, resulting in poor compatibility with high-density polyethylene substrate and other components. It exhibits uneven dispersion within the material and is prone to agglomeration. During combustion, the release of flame-retardant components is irregular, failing to form a highly efficient synergistic flame-retardant system with the composite charring agent. Mechanical properties decrease due to poor dispersibility, and it is easily migrated and lost during thermal aging, leading to a decline in flame retardancy and thermal stability. Electrical insulation performance is also reduced due to the formation of conductive channels by the agglomeration of internal impurities. This demonstrates the crucial role of epoxy-functionalized modification of ammonium polyphosphate in improving the overall performance of the material.

[0074] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A flame-retardant cable insulation layer, characterized in that, The flame-retardant cable insulation layer is made of the following raw materials in parts by weight: 80-100 parts high-density polyethylene, 15-25 parts maleic anhydride-grafted polyethylene, 5-8 parts modified bentonite composite charring agent, 20-30 parts epoxy-functionalized ammonium polyphosphate, 0.8-1.5 parts antioxidant, 3-6 parts crosslinking aid and 1.2-2.0 parts crosslinking initiator.

2. The flame-retardant cable insulation layer according to claim 1, characterized in that, The modified bentonite composite charring agent is prepared by the following steps: A1: Add lignin to an aqueous ethanol solution, add 3-aminopropyltriethoxysilane, stir at 50℃-60℃ for 5-7 hours, filter, wash, and dry to obtain aminated lignin. Add the aminated lignin to N,N-dimethylformamide, add γ-glycidyl etheroxypropyltrimethoxysilane, stir at 70℃-80℃ for 5-7 hours under nitrogen protection to obtain double-modified lignin. A2: Calcine bentonite at 520℃-570℃ for 2.5h-3h, cool to room temperature, add to ethanol aqueous solution, add composite silane coupling agent, ultrasonically disperse for 50min-60min, heat to 75℃-88℃ and stir for 5h-11h, filter, wash and dry to obtain functionalized bentonite. A3: Add double-modified lignin and functionalized bentonite to N,N-dimethylformamide, heat to 100℃-105℃ under nitrogen protection, add hexamethylenetetramine, stir and react for 12h-15h, filter, wash and dry to obtain modified bentonite composite char agent.

3. The flame-retardant cable insulation layer according to claim 2, characterized in that, The modified bentonite composite charring agent comprises the following raw materials by weight: 8-12 parts lignin, 160-200 parts ethanol aqueous solution from step A1, 4-6 parts 3-aminopropyltriethoxysilane, 130-170 parts N,N-dimethylformamide from step A1, 2-3 parts γ-glycidyl etheroxypropyltrimethoxysilane, 12-18 parts bentonite, 200-240 parts ethanol aqueous solution from step A2, 5-7 parts composite silane coupling agent, 250-310 parts N,N-dimethylformamide from step A3, and 1.8-2.5 parts hexamethylenedialdehyde.

4. The flame-retardant cable insulation layer according to claim 3, characterized in that, The mass fraction of the ethanol aqueous solution in step A1 is 20%-30%; the mass fraction of the ethanol aqueous solution in step A2 is 15%-20%; the composite silane coupling agent is composed of 3-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane in a mass ratio of 1-2:

1.

5. The flame-retardant cable insulation layer according to claim 1, characterized in that, The epoxy-functionalized ammonium polyphosphate is prepared by the following steps: B1: Disperse ammonium polyphosphate in acetone and sonicate for 30-50 minutes. Add 3-aminopropyltriethoxysilane and heat to 60-75°C with stirring for 4-6 hours. After the reaction is complete, filter, wash, and dry to obtain aminated ammonium polyphosphate. B2: Aminated ammonium polyphosphate is dispersed in N,N-dimethylformamide, 3-glycidyl etheroxypropyltriethoxysilane is added, the temperature is raised to 80℃-90℃ and the reaction is stirred for 4h-5h. After filtration, washing and drying, epoxy-functionalized ammonium polyphosphate is obtained.

6. The flame-retardant cable insulation layer according to claim 5, characterized in that, The raw materials in the epoxy-functionalized ammonium polyphosphate, by weight, are as follows: 45-55 parts of ammonium polyphosphate, 8-12 parts of 3-aminopropyltriethoxysilane, 10-15 parts of 3-glycidyl etheroxypropyltriethoxysilane, 150-200 parts of acetone, and 200-250 parts of N,N-dimethylformamide.

7. The flame-retardant cable insulation layer according to claim 1, characterized in that, The antioxidant is composed of antioxidant 1010, antioxidant 168 and ultraviolet absorber UV-531 in a mass ratio of 1-2:1-3:

1.

8. The flame-retardant cable insulation layer according to claim 1, characterized in that, The crosslinking aid is composed of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:1.5-2.

9. The flame-retardant cable insulation layer according to claim 1, characterized in that, The crosslinking initiator is composed of dicumyl peroxide and tert-butyl peroxide in a mass ratio of 1-1.8:

1.

10. A method for preparing a flame-retardant cable insulation layer as described in any one of claims 1-9, characterized in that, The preparation steps include the following: S1: High-density polyethylene, maleic anhydride-grafted polyethylene, modified bentonite composite charring agent, epoxy-functionalized polyphosphate ammonium, and antioxidant are added to a mixer for the first mixing, and then crosslinking initiator and crosslinking aid are added for the second mixing to obtain a mixed gel. S2: The mixed gel is placed in a hot press vulcanizing machine for hot pressing and curing. After cooling, it is annealed to obtain a flame-retardant cable insulation layer.

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