Heat-resistant flexible three-layer insulated wire and preparation method thereof

Abstract

The invention relates to the field of insulated wires, and discloses a heat-resistant flexible three-layer insulated wire and a preparation method thereof.The heat-resistant flexible three-layer insulated wire comprises a copper core and three insulating layers wrapping the copper core, and the three insulating layers sequentially comprise a thermoplastic elastic layer, an insulating low-density polyethylene layer and a modified polyamide resin protective layer from inside to outside; the modified polyamide resin protective layer comprises polyamide resin, a modified composite filler, maleic anhydride grafted POE and a lubricant, the modified composite filler is prepared by grafting a modifier on the surface of the composite filler, and the modifier is prepared by grafting raw materials including 5-isocyanate isopeptide acyl chloride, p-aminodiphenylamine, dibutyl phosphate, p-phenylenediamine and 3-chloropropyltriethoxysilane; the composite filler is prepared by attaching graphene oxide to the surface of 3-aminopropyltrimethoxysilane grafted glass fiber by using an electrostatic self-assembly method. The added modified composite filler can endow the material with good mechanical properties, high-temperature aging resistance, flame retardance, heat resistance and wear resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulated wires, and particularly relates to a heat-resistant flexible three-layer insulated wire and a preparation method thereof. Background Art

[0002] The three-layer insulated wire is a high-performance insulated wire, which is composed of a metal conductor and three insulating layers coated on the outer surface of the metal conductor. At present, with the development of modern industry, electrical and electronic equipment shows the trends of safety, high efficiency, energy saving and light weight. The application of high-performance insulating materials in the electrical and electronic fields has reduced the volume and raw materials of components by nearly 30%. However, the small and light weight will inevitably lead to an increase in its working temperature. Therefore, a three-layer insulated wire with high temperature resistance is required.

[0003] As an engineering plastic with a large consumption, polyamide resin has excellent comprehensive properties and is easy to process. It is widely used in the electronic and electrical industries. However, the flame retardant performance of polyamide resin is not high, and it needs to be flame retardant modified to broaden its application fields. In addition, the weak bonds on its molecular chain are easily affected by environmental factors such as heat and oxygen, resulting in a series of pyrolysis reactions, breaking the main chain of polyamide resin, and leading to a decline in the physical and chemical properties of the material. In addition, with the development trend of high power and miniaturization of power supplies, higher requirements are put forward for the heat resistance of the materials used, and the materials are required to have good mechanical strength and wear resistance. Summary of the Invention

[0004] To solve the deficiencies mentioned in the above background art, the purpose of the present invention is to provide a heat-resistant flexible three-layer insulated wire and a preparation method thereof. The thermoplastic elastomer layer, insulating low-density polyethylene layer, and modified polyamide resin protective layer are successively extruded and coated on the outer surface of the copper core. The modified polyamide resin protective layer is added with a modified composite filler to endow the material with good mechanical properties, high temperature aging resistance, flame retardant performance, heat resistance and wear resistance.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A heat-resistant flexible three-layer insulated wire, comprising a copper core and three insulating layers coated on the copper core. The three insulating layers are successively a thermoplastic elastomer layer, an insulating low-density polyethylene layer, and a modified polyamide resin protective layer from the inside to the outside. The modified polyamide resin protective layer comprises the following components in parts by weight: 60-70 parts of polyamide resin, 2-5 parts of modified composite filler, 1-2 parts of maleic anhydride grafted POE, and 0.1-0.3 parts of lubricant;

[0007] The modified composite filler is prepared by grafting a modifier onto the surface of the composite filler through a chemical reaction. Among them, the modifier is grafted using 5-isocyanatophthaloyl chloride, p-phenylenediamine, dibutyl phosphate, p-phenylenediamine, and 3-chloropropyltriethoxysilane as raw materials. The structural formula of the modifier is as follows:

[0008]

[0009] The composite filler is prepared by electrostatic self-assembly to attach negatively charged graphene oxide to the surface of positively charged 3-aminopropyltrimethoxysilane-grafted glass fiber.

[0010] Preferably, the polyamide resin is one or a combination of more than one of PA6, PA66, and PA56; the lubricant is one of polyethylene wax and oxidized polyethylene wax.

[0011] Preferably, the thermoplastic elastic layer uses a thermoplastic elastomer as a raw material, and the thermoplastic elastomer is one or a combination of more than one of thermoplastic polyurethane elastomer, polyester thermoplastic elastomer, polyolefin thermoplastic elastomer, and styrene-based thermoplastic elastomer.

[0012] Preferably, the preparation method of the modified composite filler includes the following steps:

[0013] A. Take glass fiber and ultrasonicate it in acetone for 0.5 - 1 h, then soak it for 2 - 3 h to remove the surface sizing agent, and wash it with deionized water to remove surface residues, thus obtaining pretreated glass fiber.

[0014] B. Mix anhydrous ethanol and deionized water evenly, add 3-aminopropyltrimethoxysilane, and stir for 0.5 - 1 h to obtain a silane hydrolysis solution. Then immerse the pretreated glass fiber in the silane hydrolysis solution, soak it for 4 - 6 h, and finally dry it thoroughly to obtain modified glass fiber.

[0015] C. Take graphene oxide and ultrasonically disperse it in deionized water to obtain a suspension. Then add the modified glass fiber, and adjust the pH value of the system to 3 - 4 with concentrated hydrochloric acid. Place it at 75 - 90 °C and stir for 2 - 3 h. After the reaction is completed, wash it with deionized water, and finally heat-treat it in an oven at 155 - 170 °C for 10 - 12 h to obtain the composite filler.

[0016] D. Take the composite filler and ultrasonically disperse it in a mixed solution of anhydrous ethanol and deionized water. Then add the modifier, place it at 80 - 95 °C and stir for 6 - 12 h. After the reaction is completed, filter, wash, and dry it to obtain the modified composite filler.

[0017] Preferably, the preparation method of the modifier in step D includes the following steps:

[0018] D1. Take 5-aminoisophthalic acid, chlorobenzene, oxalyl chloride, and N-methylimidazole in a reactor, place it at 70-85°C and stir for 8-12 h, then heat up to 100-110°C and continue stirring for 2-4 h. After the reaction is completed, distill and recover the excess oxalyl chloride and chlorobenzene, continue to heat up to 135-145°C for distillation using capillary distillation method, collect the distillate, and recrystallize with carbon tetrachloride to prepare 5-isocyanatoisophthaloyl chloride;

[0019] D2. Take 5-isocyanatoisophthaloyl chloride in a reactor, add tetrahydrofuran solvent, then add p-phenylenediamine and triethylamine, place it at 55-70°C and stir for 4-8 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component One;

[0020] D3. Take Component One in a reactor, add toluene solvent and stir evenly, then add dibutyltin dilaurate, heat up to 40-65°C, add dibutyl phosphate and stir for 4-6 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component Two;

[0021] D4. Take Component Two and p-phenylenediamine in a reactor, add tetrahydrofuran solvent, place it at 110-125°C and stir for 8-12 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component Three;

[0022] D5. Take Component Three in a reactor, add N,N-dimethylformamide solvent, then add 3-chloropropyltriethoxysilane and triethylamine, place it at 75-90°C and stir for 6-8 h. After the reaction is completed, filter by suction and rotary evaporate to prepare the modifier.

[0023] Preferably, the molar ratio of 5-isocyanatoisophthaloyl chloride to p-phenylenediamine in step D2 is 1:2-2.3.

[0024] Preferably, the molar ratio of Component One to dibutyl phosphate in step D3 is 1:1-1.2.

[0025] Preferably, the molar ratio of Component Two to p-phenylenediamine in step D4 is 1:2-2.5.

[0026] Preferably, the molar ratio of Component Three to 3-chloropropyltriethoxysilane in step D5 is 1:1-1.7.

[0027] A preparation method of a heat-resistant flexible three-layer insulating wire, comprising the following steps:

[0028] S1. Weigh polyamide resin, modified composite filler, maleic anhydride grafted POE, and lubricant in parts by weight in a high-speed mixer and mix evenly. Then, extrude and blend the evenly mixed materials using a twin-screw extruder, granulate to prepare a modified polyamide resin protective layer;

[0029] S2. Combine copper conductors into the copper core of the insulated wire, then use an extruder to sequentially extrude and coat the thermoplastic elastomer layer and the insulating low-density polyethylene layer on the outer surface of the copper core, and finally use an extruder to extrude and coat the modified polyamide resin protective layer on the outer surface of the insulating low-density polyethylene layer to prepare a heat-resistant flexible three-layer insulated wire.

[0030] Advantages of the present invention:

[0031] The present invention uses the reaction of the acyl chloride group in the 5-isocyanato isophthaloyl chloride structure with the amino group in the p-aminodiphenylamine structure to prepare Component 1. Then, the isocyanate group in the Component 1 structure reacts with the hydroxyl group in the dibutyl phosphate structure to prepare Component 2, and uses a chemical reaction to react the phosphate ester bond in the Component 2 structure with one end amino group in the p-phenylenediamine structure to prepare Component 3. Then, further use 3-chloropropyltriethoxysilane to undergo a substitution reaction with the amino group in the Component 3 structure to prepare a modifier.

[0032] The present invention uses 3-aminopropyltrimethoxysilane grafted pretreated glass fiber to prepare a positively charged modified glass fiber, and then attaches negatively charged graphene oxide to the surface of the modified glass fiber by electrostatic self-assembly method to prepare a composite filler. The introduction of graphene oxide significantly increases the roughness and surface energy of the glass fiber, improves the mechanical interlock in the matrix interface region, is beneficial to improving the interfacial bonding strength of the glass fiber in the polyamide resin matrix, and thus improves the mechanical properties and thermal stability of the material. And the introduction of graphene oxide is beneficial to form a dense and uniform friction layer, thereby improving the wear resistance of the material.

[0033] The present invention uses the condensation reaction of the silicon hydroxyl group in the modifier structure with the hydroxyl group in the composite filler structure to prepare a modified composite filler, thereby grafting the antioxidant intermediate p-aminodiphenylamine and the antioxidant p-phenylenediamine on the surface of the composite filler, and further introducing multiple anti-aging functional groups -NH, endowing the material with good high-temperature aging resistance. And due to the strong bonding of chemical bonds, the antioxidant intermediate and the antioxidant are tightly combined with the composite filler, thus limiting the problem of antioxidant migration and exudation. At the same time, the grafting reaction is beneficial to improving the dispersion uniformity of the composite filler, avoiding performance defects caused by the agglomeration of the composite filler. In addition, the phosphorus element and amide group introduced into the composite filler structure improve the flame retardancy and heat resistance of the material to a certain extent.

[0034] The present invention uses a thermoplastic elastomer layer, an insulating low-density polyethylene layer, and a modified polyamide resin protective layer to be extruded around the outer surface of a copper core in sequence to prepare a three-layer insulated wire. The modified polyamide resin protective layer uses polyamide resin as the base material, maleic anhydride-grafted POE as a toughening agent, and adds a modified composite filler as a functional additive, endowing the material with good mechanical properties, high-temperature aging resistance, flame retardancy, heat resistance, and wear resistance. Detailed implementation manners

[0035] The following will describe clearly and completely the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] Example 1 A preparation method of a modifier includes the following steps:

[0037] D1. Take 20 g of 5-aminoisophthalic acid, 80 mL of chlorobenzene, 100 mL of oxalyl chloride, and 0.75 mL of N-methylimidazole in a reactor, place it at 75 °C and stir for 10 h, then raise the temperature to 110 °C and continue to stir for 2 h. After the reaction is completed, distill and recover the excessive oxalyl chloride and chlorobenzene, continue to raise the temperature to 140 °C for distillation by capillary distillation method, take the distillate, and recrystallize with carbon tetrachloride to prepare 5-isocyanatoisophthaloyl chloride;

[0038] D2. Take 2.4 g of 5-isocyanatoisophthaloyl chloride in a reactor, add 50 mL of tetrahydrofuran solvent, then add 4.1 g of p-phenylenediamine and 2.1 g of triethylamine, place it at 65 °C and stir for 7 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component One;

[0039] D3. Take 5.4 g of Component One (Mr = 539.5) in a reactor, add 80 mL of toluene solvent and stir evenly, then add 0.002 g of dibutyltin dilaurate, raise the temperature to 55 °C, add 2.2 g of dibutyl phosphate and stir for 6 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component Two;

[0040] D4. Take 6.8 g of Component Two (Mr = 749.7) and 2.2 g of p-phenylenediamine in a reactor, add 80 mL of tetrahydrofuran solvent, place it at 120 °C and stir for 10 h. After the reaction is completed, remove the solvent by rotary evaporation to prepare Component Three;

[0041] D5. Take 7.5 g of Component 3 (Mr = 817.9) in a reactor, add 100 mL of N,N-dimethylformamide solvent, then add 2.9 g of 3-chloropropyltriethoxysilane and 0.9 g of triethylamine, and stir and react at 85 °C for 8 h. After the reaction is completed, carry out suction filtration and rotary evaporation to prepare a modifier.

[0042] Example 2. A preparation method of a modified composite filler comprises the following steps:

[0043] A. Take glass fibers and ultrasonicate them in acetone for 1 h, then soak them for 2 h to remove the surface sizing agent, and wash them with deionized water to remove surface residues, thereby preparing pretreated glass fibers.

[0044] B. Mix 180 mL of absolute ethanol and 20 mL of deionized water evenly, add 3 g of 3-aminopropyltrimethoxysilane, and stir for 0.5 h to obtain a silane hydrolysis solution. Then immerse 10 g of pretreated glass fibers in the silane hydrolysis solution and soak for 4 h. Finally, dry them thoroughly to prepare modified glass fibers.

[0045] C. Take 0.5 g of graphene oxide and ultrasonically disperse it in 500 mL of deionized water to obtain a suspension. Then add 10 g of modified glass fibers, and adjust the pH value of the system to 3 with concentrated hydrochloric acid. Stir and react at 80 °C for 2 h. After the reaction is completed, wash with deionized water, and finally heat-treat in an oven at 160 °C for 12 h to prepare a composite filler.

[0046] D. Take 5 g of the composite filler and ultrasonically disperse it in a mixed solution of 90 mL of absolute ethanol and 10 mL of deionized water. Then add 4.7 g of the modifier prepared in Example 1, and stir and react at 85 °C for 10 h. After the reaction is completed, carry out suction filtration, washing, and drying to prepare a modified composite filler.

[0047] Example 3. A heat-resistant flexible three-layer insulating wire comprises the following components in parts by weight:

[0048] 62 parts of polyamide resin PA66, 2 parts of the modified composite filler prepared in Example 2, 1 part of maleic anhydride grafted POE, 0.1 part of lubricant polyethylene wax;

[0049] A preparation method of a heat-resistant flexible three-layer insulating wire comprises the following steps:

[0050] S1. Weigh polyamide resin PA66, the modified composite filler prepared in Example 2, maleic anhydride grafted POE, and lubricant in a high-speed mixer and mix them evenly. Then extrude and blend the uniformly mixed materials using a twin-screw extruder and granulate to prepare a modified polyamide resin protective layer.

[0051] S2. Combine copper conductors into the copper core of the insulated wire, and then use an extruder to successively extrude and coat the thermoplastic elastomer layer and the insulating low-density polyethylene layer on the outer surface of the copper core. The thermoplastic elastomer layer uses thermoplastic polyurethane elastomer as the raw material. Finally, use an extruder to extrude and coat the modified polyamide resin protective layer on the outer surface of the insulating low-density polyethylene layer to prepare a heat-resistant flexible three-layer insulated wire.

[0052] Example 4 A modified polyamide resin protective layer, comprising the following components in parts by weight:

[0053] Polyamide resin PA66 65 parts, the modified composite filler prepared in Example 2 3 parts, maleic anhydride grafted POE 1.4 parts, lubricant oxidized polyethylene wax 0.2 parts;

[0054] The preparation method of a heat-resistant flexible three-layer insulated wire is the same as that in Example 3.

[0055] Example 5 A modified polyamide resin protective layer, comprising the following components in parts by weight:

[0056] Polyamide resin PA66 68 parts, the modified composite filler prepared in Example 2 4 parts, maleic anhydride grafted POE 1.7 parts, lubricant polyethylene wax 0.3 parts;

[0057] The preparation method of a heat-resistant flexible three-layer insulated wire is the same as that in Example 3.

[0058] Comparative Example 1 A preparation method of a composite filler comprises the following steps:

[0059] A. Take glass fiber and ultrasonicate it in acetone for 1 h, then soak it for 2 h to remove the surface sizing agent, and wash it with deionized water to remove the surface residues to prepare pretreated glass fiber;

[0060] B. Take 180 mL of absolute ethanol and 20 mL of deionized water, mix them evenly, add 3 g of 3-aminopropyltrimethoxysilane, stir for 0.5 h to obtain a silane hydrolysis solution, then immerse 10 g of pretreated glass fiber in the silane hydrolysis solution, soak it for 4 h, and finally dry it thoroughly to prepare modified glass fiber;

[0061] C. Take 0.5 g of graphene oxide and ultrasonically disperse it in 500 mL of deionized water to obtain a suspension, then add 10 g of modified glass fiber, and adjust the pH value of the system to 3 with concentrated hydrochloric acid, place it at 80 °C and stir for 2 h. After the reaction is completed, wash it with deionized water, and finally heat-treat it in an oven at 160 °C for 12 h to prepare the composite filler.

[0062] Comparative Example 2 A preparation method of modified glass fiber comprises the following steps:

[0063] A. Take glass fiber and ultrasonically treat it in acetone for 1 h, then soak it for 2 h to remove the surface sizing agent, and wash it with deionized water to remove surface residues, thus obtaining pretreated glass fiber;

[0064] B. Take 5 g of the pretreated glass fiber and ultrasonically disperse it in a mixed solution of 90 mL of absolute ethanol and 10 mL of deionized water, then add 4.7 g of the modifier prepared in Example 1, place it under stirring reaction at 85 °C for 10 h, and after the reaction is completed, carry out suction filtration, washing, and drying to obtain modified glass fiber.

[0065] Comparative Example 3 A modified polyamide resin protective layer, comprising the following components in parts by weight:

[0066] Polyamide resin PA66 68 parts, composite filler prepared in Comparative Example 1 4 parts, maleic anhydride grafted POE 1.7 parts, lubricant polyethylene wax 0.3 parts;

[0067] The preparation method of a heat-resistant flexible three-layer insulated wire is the same as that in Example 3.

[0068] Comparative Example 4 A modified polyamide resin protective layer, comprising the following components in parts by weight:

[0069] Polyamide resin PA66 68 parts, modified glass fiber prepared in Comparative Example 2 4 parts, maleic anhydride grafted POE 1.7 parts, lubricant polyethylene wax 0.3 parts;

[0070] The preparation method of a heat-resistant flexible three-layer insulated wire is the same as that in Example 3.

[0071] Performance testing

[0072] Make the modified polyamide resin protective layers prepared in Examples 3 - 5 and Comparative Examples 3 - 4 into test samples with specifications of 100 mm × 6.5 mm × 3 mm, conduct tensile property tests with reference to GB / T 1040.2 - 2022, and test the tensile property retention rate under high-temperature aging conditions of 135 °C / 168 h; conduct cantilever beam notched impact strength tests with reference to GB / T 1843 - 2008; conduct flexural strength tests with reference to GB / T 9341 - 2008 standard; use a CSM ball-disk type friction and wear testing machine, set the amplitude to 2.5 cm, the load to 5 N, the rate to 10 cm / s, use a 6-mm steel ball as the counter material, and conduct friction tests on the samples; under nitrogen protection, heat the sample to be tested from 50 °C to 600 °C at a rate of 10 °C / min, record the initial thermal decomposition temperature of the material, and evaluate its heat resistance; use an LOI instrument to test the LOI value of the sample with reference to GB / T 2406.2 - 2009, and the data results are shown in Table 1.

[0073] Table 1 Test results of sample performance

[0074]

[0075]

[0076] As can be seen from the data in Table 1, the protective layer materials prepared in Examples 3-5 of the present invention have high tensile strength, good flexibility, and small friction coefficient, showing excellent mechanical properties and wear resistance. Moreover, under the high-temperature aging conditions of 135°C / 168 h, the tensile strength retention rate is high, with excellent high-temperature aging resistance. At the same time, the initial thermal decomposition temperature and limiting oxygen index are relatively high, having good heat resistance and flame retardancy. Among them, in Comparative Example 3, unmodified composite fillers were added, and the measured mechanical properties, tensile strength retention rate, initial thermal decomposition temperature, and LOI value were lower than those in Examples 3-5, indicating that the composite fillers treated with a modifier can improve the mechanical properties, high-temperature aging resistance, heat resistance, and flame retardancy of the materials. In Comparative Example 4, the modified composite fillers were replaced with modified glass fibers in equal amounts. The measured friction coefficient increased significantly compared with Examples 3-5, and the wear resistance performance was poor. At the same time, the mechanical properties were lower than those in Examples 3-5 because graphene oxide was not introduced.

[0077] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0078] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A heat-resistant flexible three-layer insulated wire, characterized in that: The invention relates to a three-layer insulation layer comprising a copper core and a coating of the copper core, wherein the three insulation layers are, from the inside to the outside, a thermoplastic elastic layer, an insulating low-density polyethylene layer, and a modified polyamide resin protective layer, wherein the modified polyamide resin protective layer comprises the following components in parts by weight: 60 to 70 parts of polyamide resin, 2 to 5 parts of modified composite filler, 1 to 2 parts of maleic anhydride grafted POE, and 0.1 to 0.3 parts of lubricant; The modified composite filler is prepared by grafting a modifier onto the surface of the composite filler using a chemical reaction, wherein the modifier is grafted using 5-isocyanate isopeptide chloride, p-aminodiphenylamine, dibutyl phosphate, p-phenylenediamine, and 3-chloropropyltriethoxysilane as raw materials, and the structural formula of the modifier is as follows: The composite filler is prepared by attaching negatively charged graphene oxide to the surface of positively charged 3-aminopropyltrimethoxysilane grafted glass fiber using an electrostatic self-assembly method.

2. The heat-resistant flexible three-layer insulated wire according to claim 1, characterized in that: The polyamide resin is one or more combinations of PA6, PA66, and PA56; the lubricant is one of polyethylene wax and oxidized polyethylene wax.

3. The heat-resistant flexible three-layer insulated wire according to claim 1, characterized in that: The thermoplastic elastic layer uses thermoplastic elastomer as a raw material, and the thermoplastic elastomer is one or a combination of thermoplastic polyurethane elastomer, polyester thermoplastic elastomer, polyolefin thermoplastic elastomer, and styrene thermoplastic elastomer.

4. The heat-resistant flexible three-layer insulated wire according to claim 1, characterized in that: The preparation method of the modified composite filler comprises the following steps: A. Ultrasonicate the glass fiber in acetone for 0.5 to 1 hour, then soak it for 2 to 3 hours to remove the surface slurry, and wash it with deionized water to remove the surface residue to prepare the pretreated glass fiber; B. Take anhydrous ethanol and deionized water and mix them evenly, add 3-aminopropyltrimethoxysilane, stir for 0.5 to 1 hour to obtain a silane hydrolyzate, then immerse the pretreated glass fiber in the silane hydrolyzate for 4 to 6 hours, and finally fully dry it to prepare a modified glass fiber; C. Ultrasonic dispersion of graphene oxide in deionized water to obtain a suspension, then adding modified glass fiber, and adjusting the pH value of the system to 3-4 with concentrated hydrochloric acid, placing it at 75-90° C. and stirring for 2-3 hours, washing with deionized water after the reaction is completed, and finally heat-treating it in an oven at 155-170° C. for 10-12 hours to prepare a composite filler; D. Ultrasonic dispersion of the composite filler in a mixed solution of anhydrous ethanol and deionized water, then adding a modifier, stirring and reacting at 80-95° C. for 6-12 hours, and after the reaction is completed, filtering, washing and drying to prepare a modified composite filler.

5. The heat-resistant flexible three-layer insulated wire according to claim 4, characterized in that: The preparation method of the modifier in step D comprises the following steps: D1. 5-aminoisophthalic acid, chlorobenzene, oxalyl chloride and N-methylimidazole are placed in a reactor, stirred and reacted at 70-85°C for 8-12 hours, then heated to 100-110°C, and stirred and reacted for 2-4 hours. After the reaction is completed, excess oxalyl chloride and chlorobenzene are distilled and recovered, and the temperature is further raised to 135-145°C for distillation by capillary distillation. The fraction is taken and recrystallized with carbon tetrachloride to prepare 5-isocyanate isopeptide chloride; D2, take 5-isocyanate isopeptide chloride in a reactor, add tetrahydrofuran solvent, then add p-aminodiphenylamine and triethylamine, stir and react at 55-70° C. for 4-8 hours, and after the reaction is completed, remove the solvent by rotary evaporation to prepare component 1; D3, take component 1 in a reactor, add toluene solvent and stir evenly, then add dibutyltin dilaurate, raise the temperature to 40-65°C, add dibutyl phosphate and stir to react for 4-6 hours, after the reaction is completed, remove the solvent by rotary evaporation to prepare component 2; D4, taking component 2 and p-phenylenediamine in a reactor, adding tetrahydrofuran solvent, placing at 110-125° C. and stirring to react for 8-12 hours, after the reaction is completed, removing the solvent by rotary evaporation to prepare component 3; D5. Take component three into a reactor, add N,N-dimethylformamide solvent, then add 3-chloropropyltriethoxysilane and triethylamine, place at 75-90°C and stir to react for 6-8h. After the reaction is completed, filter and rotary evaporate to prepare the modifier.

6. The heat-resistant flexible three-layer insulated wire according to claim 5, characterized in that: In the step D2, the molar ratio of 5-isocyanate isopeptide chloride to p-aminodiphenylamine is 1:2-2.

3.

7. The heat-resistant flexible three-layer insulated wire according to claim 5, characterized in that: The molar ratio of component 1 to dibutyl phosphate in step D3 is 1:1-1.

2.

8. The heat-resistant flexible three-layer insulated wire according to claim 5, characterized in that: The molar ratio of component 2 to p-phenylenediamine in step D4 is 1:2 to 2.

5.

9. The heat-resistant flexible three-layer insulated wire according to claim 5, characterized in that: The molar ratio of component three to 3-chloropropyltriethoxysilane in step D5 is 1:1 to 1.

7.

10. A method for preparing a heat-resistant flexible three-layer insulated wire according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, weighing parts by weight of polyamide resin, modified composite filler, maleic anhydride grafted POE, and lubricant, and mixing them evenly in a high-speed mixer, and then using a twin-screw extruder to blend and extrude the mixed materials, granulate, and prepare a modified polyamide resin protective layer; S2. Combine the copper conductors into a copper core of the insulated wire, and then use an extruder to extrude the thermoplastic elastic layer and the insulating low-density polyethylene layer on the outer surface of the copper core in sequence, and finally use an extruder to extrude the modified polyamide resin protective layer on the outer surface of the insulating low-density polyethylene layer to prepare a heat-resistant flexible three-layer insulated wire.

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