A high heat-resistant polyimide enameled wire and its preparation method

Abstract

This invention discloses a high heat-resistant polyimide enameled wire and its preparation method. The high heat-resistant polyimide enameled wire includes a copper or aluminum conductor and a polyimide insulating varnish layer disposed on the conductor. The insulating varnish layer is formed by immersing the conductor in a polyamic acid solution containing hexadecyltrimethylammonium bromide modified ZrO2 powder for coating, followed by multi-stage heat treatment and curing. This invention uses CTAB-modified zirconium oxide and, for the first time, uses CTAB-modified ZrO2 powder to prepare the polyimide enameled wire insulating varnish layer, effectively improving the tensile strength and heat resistance of the insulating varnish layer in the enameled wire. The thermal decomposition temperature of the polyimide insulating varnish layer can be increased to 520℃, and the tensile strength can be increased to 88MPa. At the same time, the insulation and flame retardant properties of the enameled wire are also improved, expanding the application scenarios of polyimide enameled wire.

Description

Technical Field

[0001] This invention relates to the field of enameled wire technology, and in particular to a high heat-resistant polyimide enameled wire and its preparation method. Background Technology

[0002] Enamelled wire is a type of winding wire, consisting of two parts: a metal conductor and an insulating varnish coated on its surface. It is typically prepared using a coating method, where the varnish is applied to the conductor surface and then dried and cured. Enamelled wire is widely used in motors and electrical appliances, and the quality of the insulating varnish directly affects the operation and lifespan of the electrical equipment. With the continuous and rapid growth of the power industry and the rapid development of household appliances, miniaturization, lightweighting, and high power of components are important trends in the development of electrical products. Small size and high power will cause the coil to generate a large amount of heat during operation. Simultaneously, during motor operation, current flows through the windings, and continuous rotation, along with prolonged energization and friction, generates a significant amount of heat. This places higher demands on the temperature resistance of enamelled wire, and the temperature resistance performance of enamelled wire is mainly affected by the insulating varnish.

[0003] Currently, the main materials for insulating varnishes of enameled wires are concentrated in polyester, polyurethane, and polyesterimide. Among them, polyimide is a high-performance special engineering plastic containing an imide structure in its main chain. It exhibits excellent heat resistance, solvent resistance, and resistance to extreme environments, making it one of the best-performing organic polymer materials. It is now widely used in insulating varnishes. Enameled wires using polyimide insulating varnish have advantages such as high heat resistance, resistance to refrigerants, low dielectric loss, good insulation performance, cold resistance, radiation resistance, high mechanical strength, stable electrical performance, chemical resistance, and strong overload capacity. Although polyimide enameled wires have the highest heat resistance rating, with long-term operating temperatures exceeding 220℃, they still cannot meet the requirements of current more stringent high-temperature environments. Therefore, it is necessary to develop polyimide insulating varnishes with even higher heat resistance. Commonly used methods include adding inorganic reinforcing materials such as silicon dioxide, alumina, and graphene, and adjusting the polymer monomer or polymer polymerization structure. Numerous studies have been conducted on improving heat resistance by adding inorganic reinforcing materials. For example, CN112592653A discloses a method for preparing a high-temperature resistant polyimide enameled wire varnish, which uses a composite system of surface-modified graphene oxide and polyimide. Graphene oxide possesses an ultra-high specific surface area and a two-dimensional planar nanostructure, making it possible to combine with the polyimide system to obtain high heat resistance and mechanical properties. CN115746696A discloses a high-heat-resistant polyimide enameled wire, which uses a polyamic acid solution obtained by in-situ polycondensation of aromatic dianhydride, aromatic diamine, and fluorinated amino graphene as the polyimide varnish, and thus prepares the enameled wire. The resulting enameled wire maintains excellent heat resistance while also exhibiting excellent mechanical properties, high-temperature durability, and low dielectric loss. CN111154100A discloses a method for preparing a high-heat-resistant polyimide. It involves preparing cage-like octameric (γ-aminopropyl)silsesquioxane using γ-aminopropyltriethoxysilane as a raw material, and then preparing a modified polyimide using the cage-like octameric (γ-aminopropyl)silsesquioxane, diamine, dianhydride, and other raw materials. The unique cage-like structure of the cage-like octameric (γ-aminopropyl)silsesquioxane possesses excellent mechanical properties and thermodynamic stability. Introducing it into the raw materials for the synthesis of polyimide precursors can improve the comprehensive mechanical properties, elastic properties, and heat resistance of the polyimide. CN109535713A discloses a hollow microsphere / polyimide composite material, comprising hollow microspheres and a polyimide resin matrix, wherein the hollow microspheres are uniformly dispersed in the polyimide resin matrix. This composite material possesses high heat resistance, excellent mechanical properties, and stable broadband low dielectric properties. However, the following drawbacks still exist. First, the addition of a large amount of powder will affect the performance of polyimide. Second, the introduction of inorganic powder will cause dispersion problems in the polyimide precursor, which may lead to agglomeration, resulting in limited performance improvement of polyimide insulating varnish.To improve dispersion, inorganic oxide particles are currently pretreated with coupling agents or surfactants. However, coupling agent-modified oxide particles are expensive, increasing manufacturing costs. Furthermore, the introduction of coupling agents introduces more impurities into the product, affecting its performance. Removing coupling agents through heat treatment may introduce more porosity into the oxides, affecting long-term stability and durability, potentially leading to performance degradation and shortened lifespan with prolonged use. Research has also been conducted on improving the heat resistance of insulating varnishes by adjusting their organic composition or polymer structure. For example, CN115472332A discloses an enameled wire with a first, second, and third varnish layer sequentially coated on the conductor. By selecting suitable insulating varnish and adjusting process parameters, the performance of each varnish layer is fully utilized, resulting in an enameled wire with high heat resistance, significantly improving the product's heat resistance and meeting the requirements for oil-cooled drive motors on high-voltage platforms above 800V. CN104073155A discloses a polyimide enameled wire varnish, which uses different dianhydrides to prepare different polyamic acid solutions. The different polyamic acid solutions are then blended in proportion as needed to form the varnish, which improves the heat resistance temperature and greatly increases the elongation at break, as well as the toughness, making it less prone to breakage during winding.

[0004] Although the polyimide insulating varnishes currently available have good heat resistance, the emergence of complex operating environments such as high power and high voltage still requires polyimide enameled wires with higher temperature resistance ratings, which is also an important direction for industry development. Summary of the Invention

[0005] The present invention aims to overcome the problems in the prior art and provide a high heat-resistant polyimide enameled wire. This enameled wire meets the mechanical properties and weather resistance of conventional polyimide enameled wires, but has higher heat resistance, which can further improve its high-temperature service life and expand its application fields.

[0006] To achieve the above-mentioned objectives of this invention, a first aspect of this invention provides a high-heat-resistant polyimide enameled wire, comprising a conductor and a polyimide insulating varnish layer disposed on the conductor. The polyimide insulating varnish layer is formed by heating and curing a polyamic acid solution containing hexadecyltrimethylammonium bromide-modified ZrO2 powder. Through extensive experimentation, the applicant unexpectedly discovered that adding hexadecyltrimethylammonium bromide-modified ZrO2 powder to the polyimide insulating varnish effectively improves the tensile strength and heat resistance of the insulating varnish layer in the enameled wire. Compared to polyimide insulating varnish layers with directly added zirconium oxide powder, the insulating varnish layer using the specific additives in this invention achieves a thermal decomposition temperature of 520°C and a tensile strength of 88 MPa. This represents a significant improvement over the 495°C decomposition temperature and 51 MPa tensile strength of directly added, unmodified ZrO2, further expanding the application scenarios of polyimide enameled wires.

[0007] As a preferred technical solution, the conductor is a copper wire or an aluminum wire, and the thickness of the polyimide insulating varnish layer is 0.01~0.1mm.

[0008] As a preferred technical solution, the preparation method of the hexadecyltrimethylammonium bromide modified ZrO2 powder is as follows: 10-20g of ZrOCl2·8H2O solid is dissolved in distilled water to obtain a zirconium oxychloride solution with a concentration of 0.5-1mol / L; 1% by weight of hexadecyltrimethylammonium bromide of ZrOCl2·8H2O solid is weighed and dissolved in distilled water to obtain a CTAB solution with a concentration of 0.01-0.05mol / L; the CTAB solution is slowly added dropwise to the zirconium oxychloride solution under stirring until it is mixed evenly; the evenly mixed solution is transferred to a hydrothermal reactor and reacted at 140-180℃ for 6-12 h; the precipitate is collected by centrifugation and washing, and then dried in an oven at 50-90℃ for 3-9 h to obtain the hexadecyltrimethylammonium bromide modified ZrO2 powder.

[0009] As a preferred technical solution, the method for preparing the polyamic acid solution includes the following steps:

[0010] 1) Weigh 0.99 mol to 1.01 mol of diacid anhydride and dissolve it in 1 L of organic solvent. Stir and continuously pass a protective gas through the solution to obtain solution A.

[0011] 2) Weigh a certain mass of hexadecyltrimethylammonium bromide modified ZrO2 powder, and slowly add it to solution A under stirring and continuous purging of protective gas until it is evenly dispersed to obtain solution B;

[0012] 3) Weigh 0.98 mol to 1 mol of diamine and dissolve it in solution B. Stir and continuously introduce protective gas. After the mixture is evenly dispersed, react at 50 to 80 °C for 4 to 12 hours. Cool to room temperature to obtain the final product.

[0013] As a preferred technical solution, the diacid anhydride is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the diamine is at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, or 4,4'-diaminobenzophenone; and the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0014] As a preferred technical solution, the protective gas is one of nitrogen, helium, and argon, and the amount of the hexadecyltrimethylammonium bromide-modified ZrO2 powder added is 1% to 5% of the mass of the diamine.

[0015] Another aspect of the present invention provides a method for preparing high heat-resistant polyimide enameled wire, comprising the following steps:

[0016] 1) Preparation of hexadecyltrimethylammonium bromide modified ZrO2 powder: Weigh and dissolve 10-20g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 0.5-1mol / L; weigh 1% by weight of hexadecyltrimethylammonium bromide of ZrOCl2·8H2O solid and dissolve it in distilled water to obtain a CTAB solution with a concentration of 0.01-0.05mol / L; slowly add CTAB solution to zirconium oxychloride solution under stirring until it is mixed evenly; transfer the evenly mixed solution to a hydrothermal reactor and react at 140-180℃ for 6-12 h; centrifuge and wash to collect the precipitate, and dry it in an oven at 50-90℃ for 3-9 h before taking it out;

[0017] 2) Preparation of polyamic acid solution: Weigh 0.99 mol to 1.01 mol of diacid anhydride and dissolve it in 1 L of organic solvent. Stir and continuously introduce protective gas to obtain solution A. Weigh a certain mass of hexadecyltrimethylammonium bromide modified ZrO2 powder and slowly add it to solution A under stirring and continuous introduction of protective gas until it is evenly dispersed to obtain solution B. Weigh 0.98 mol to 1 mol of diamine and dissolve it in solution B. Stir and continuously introduce protective gas. After even dispersion, react at 50 to 80 °C for 4 to 12 h and cool to room temperature.

[0018] 3) Immerse the wire in the polyamic acid solution obtained in step 2) for coating, and perform multi-stage heating treatment until the surface of the wire is covered with a polyimide insulating varnish layer of the required thickness.

[0019] As a preferred technical solution, the conductor is a copper wire or an aluminum wire, and the thickness of the polyimide insulating varnish layer is 0.01~0.1mm.

[0020] As a preferred technical solution, the diacid anhydride is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the diamine is at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, or 4,4'-diaminobenzophenone; the organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; and the amount of hexadecyltrimethylammonium bromide-modified ZrO2 powder added is 1% to 5% of the mass of the diamine.

[0021] As a preferred technical solution, step 3) specifically involves: placing the polyamic acid solution into the fixed container of the dip coating machine, immersing the wire at a speed of 40-60 mm / min, then lifting it at a speed of 10-30 mm / min for coating, and placing the coated wire into a tube furnace for sequentially holding at 70-90℃ for 2-4 hours, 140-160℃ for 40-60 minutes, 220-240℃ for 30-40 minutes, and 280-300℃ for 30-40 minutes.

[0022] The present invention also provides the application of high heat-resistant polyimide enameled wire, which is wound into a winding coil for use in motor equipment. The motor equipment using the winding coil can achieve miniaturization and high power, and still has high stability under long-term high temperature conditions. At the same time, the introduction of CTAB-modified zirconium dioxide powder also improves the flame retardant properties of the polyimide insulating varnish layer, further improving the safety of the enameled wire product.

[0023] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0024] This invention is the first to propose using hexadecyltrimethylammonium bromide-modified ZrO2 powder as an additive to prepare the insulating varnish layer of polyimide enameled wire. The CTAB-modified ZrO2 powder obtained through specific treatment, when added to the polyimide insulating varnish, can effectively improve the tensile strength and heat resistance of the insulating varnish layer in the enameled wire. Compared with the polyimide insulating varnish layer with directly added zirconium oxide powder, the thermal decomposition temperature of the insulating varnish layer of this invention can reach 520℃, and the tensile strength can reach 88MPa. At the same time, while improving the heat resistance stability, it also enhances the flame retardant effect of the polyimide insulation layer, expanding the application scenarios of polyimide enameled wire.

[0025] Meanwhile, the preparation method of the enameled wire of the present invention is simple, and the CTAB-modified ZrO2 powder in the polyimide insulating varnish layer is distributed and uniformly, which effectively inhibits the failure of insulating varnish delamination caused by sedimentation and agglomeration of conventional oxide powder in polyamic acid solution, and greatly improves the heat resistance and mechanical strength of polyimide enameled wire. Attached Figure Description

[0026] Figure 1 This is a cross-sectional SEM image of the enameled wire prepared in Comparative Example 1;

[0027] Figure 2 The images show the cross-sectional SEM and EDS spectra of the enameled wire prepared in Comparative Example 1.

[0028] Figure 3 Here is a cross-sectional SEM image of the enameled wire prepared in Example 1;

[0029] Figure 4These are the cross-sectional SEM and EDS energy dispersive spectra of the enameled wire prepared in Example 1;

[0030] Figure 5 These are FT-IR images of ZrO2 powder before and after CTAB modification;

[0031] Figure 6 These are TGA test images of the enameled wires prepared in Example 1 and Comparative Examples 1 and 2;

[0032] Figure 7 This is a comparison diagram of the dielectric constants of the enameled wires prepared in Example 1 and Comparative Examples 1 and 2. Detailed Implementation

[0033] To make the technical problems solved by this invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of this invention will be described in further detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] It should be noted that, in this document, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0036] Example 1

[0037] A high heat-resistant polyimide enameled wire is prepared by the following method:

[0038] 1) Preparation of hexadecyltrimethylammonium bromide modified ZrO2 powder: Weigh and dissolve 10g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 0.5mol / L; weigh 0.1g of hexadecyltrimethylammonium bromide and dissolve it in distilled water to obtain a CTAB solution with a concentration of 0.01mol / L; slowly add CTAB solution to zirconium oxychloride solution under stirring until it is mixed evenly; transfer the evenly mixed solution to a hydrothermal reactor and react at 140℃ for 6 h; centrifuge and wash to collect the precipitate, place it in an oven and dry at 50℃ for 3 h to obtain CTAB-ZrO2;

[0039] 2) Preparation of polyamic acid solution: Weigh 0.99 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride and dissolve it in 1 L of N,N-dimethylformamide. Stir and continuously purge with nitrogen to obtain solution A; weigh 1.96 g of CTAB-ZrO2 powder and slowly add it to solution A under stirring and continuous nitrogen purge until it is evenly dispersed to obtain solution B; weigh 0.98 mol of 4,4'-diaminodiphenyl ether and dissolve it in solution B. Stir and continuously purge with nitrogen. After even dispersion, react at 50 °C for 4 h and cool to room temperature.

[0040] 3) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 40 mm / min, and then lift it at a speed of 10 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 70℃ for 2 hours, 140℃ for 40 minutes, 220℃ for 30 minutes, and 280℃ for 30 minutes until the surface of the conductor is covered with a 0.01 mm polyimide insulating varnish layer.

[0041] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 520℃, a tensile strength of 88MPa, and a dielectric constant of 2.6 at 200KHz.

[0042] Example 2

[0043] A high heat-resistant polyimide enameled wire is prepared by the following method:

[0044] 1) Preparation of hexadecyltrimethylammonium bromide modified ZrO2 powder: Weigh and dissolve 20g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 1mol / L; weigh 0.2g of hexadecyltrimethylammonium bromide and dissolve it in distilled water to obtain a CTAB solution with a concentration of 0.05mol / L; slowly add CTAB solution to zirconium oxychloride solution under stirring until it is mixed evenly; transfer the evenly mixed solution to a hydrothermal reactor and react at 180℃ for 12 h; centrifuge and wash to collect the precipitate, place it in an oven and dry at 90℃ for 9 h to obtain CTAB-ZrO2;

[0045] 2) Preparation of polyamic acid solution: Weigh 1.01 mol of pyromellitic dianhydride and dissolve it in 1 L of N-methylpyrrolidone. Stir and continuously purge with argon gas to obtain solution A; Weigh 9.81 g of CTAB-ZrO2 powder and slowly add it to solution A under stirring and continuous argon gas until it is evenly dispersed to obtain solution B; Weigh 0.98 mol of 4,4'-diaminodiphenyl ether and dissolve it in solution B. Stir and continuously purge with argon gas. After even dispersion, react at 80℃ for 12 h and cool to room temperature;

[0046] 3) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 60 mm / min, and then lift it at a speed of 30 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 90℃ for 4 hours, 160℃ for 60 minutes, 240℃ for 40 minutes, and 300℃ for 40 minutes until the surface of the conductor is covered with a 0.1 mm polyimide insulating varnish layer.

[0047] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 523℃, a tensile strength of 82MPa, and a dielectric constant of 3.2 at 200KHz.

[0048] Example 3

[0049] A high heat-resistant polyimide enameled wire is prepared by the following method:

[0050] 1) Preparation of hexadecyltrimethylammonium bromide modified ZrO2 powder: Weigh and dissolve 20g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 1mol / L; weigh 0.2g of hexadecyltrimethylammonium bromide and dissolve it in distilled water to obtain a CTAB solution with a concentration of 0.05mol / L; slowly add CTAB solution to zirconium oxychloride solution under stirring until it is mixed evenly; transfer the evenly mixed solution to a hydrothermal reactor and react at 150℃ for 8 h; centrifuge and wash to collect the precipitate, place it in an oven and dry at 70℃ for 4 h to obtain CTAB-ZrO2;

[0051] 2) Preparation of polyamic acid solution: Weigh 1.0 mol of pyromellitic dianhydride and dissolve it in 1 L of N-methylpyrrolidone. Stir and continuously purge with argon gas to obtain solution A; Weigh 6.37 g of CTAB-ZrO2 powder and slowly add it to solution A under stirring and continuous argon gas conditions until it is evenly dispersed to obtain solution B; Weigh 1 mol of 4,4'-diaminobenzophenone and dissolve it in solution B. Stir and continuously purge with argon gas. After even dispersion, react at 60℃ for 5 h and cool to room temperature;

[0052] 3) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 50 mm / min, and then lift it at a speed of 10 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 80℃ for 3 hours, 150℃ for 50 minutes, 230℃ for 30 minutes, and 300℃ for 30 minutes until the surface of the conductor is covered with a 0.05 mm polyimide insulating varnish layer.

[0053] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 521℃, a tensile strength of 84MPa, and a dielectric constant of 2.9 at 200KHz.

[0054] Comparative Example 1

[0055] A polyimide enameled wire is prepared by the following method:

[0056] 1) Preparation of ZrO2 powder: Weigh and dissolve 20g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 1mol / L; under stirring conditions, slowly add an ammonia solution with a pH of 12 to the zirconium oxychloride solution until the pH value is 10, and a white precipitate is obtained; wash the white precipitate three times with anhydrous ethanol to remove impurities and obtain zirconium hydroxide precipitate; put the zirconium hydroxide precipitate into a hydrothermal reactor with a filling ratio of 60% and react at 200℃ for 4h. The product is washed alternately with deionized water and anhydrous ethanol, then centrifuged 6 times in a centrifuge at 9000r / min, and finally placed in a drying oven and dried at 80℃ for 38h to obtain zirconium dioxide powder;

[0057] 2) Preparation of polyamic acid solution: Weigh 1.0 mol of pyromellitic dianhydride and dissolve it in 1 L of N-methylpyrrolidone. Stir and continuously introduce argon gas to obtain solution A; weigh 6.37 g of ZrO2 powder and slowly add it to solution A under stirring and continuous argon gas until it is evenly dispersed to obtain solution B; weigh 1 mol of 4,4'-diaminobenzophenone and dissolve it in solution B. Stir and continuously introduce argon gas. After evenly dispersing, react at 60℃ for 5 h and cool to room temperature;

[0058] 3) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 50 mm / min, and then lift it at a speed of 10 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 80℃ for 3 hours, 150℃ for 50 minutes, 230℃ for 30 minutes, and 300℃ for 30 minutes until the surface of the conductor is covered with a 0.05 mm polyimide insulating varnish layer.

[0059] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 495℃, a tensile strength of 51MPa, and a dielectric constant of 1.9 at 200KHz.

[0060] Comparative Example 2

[0061] A polyimide enameled wire is prepared by the following method:

[0062] 1) Preparation of polyamic acid solution: Weigh 1.0 mol of pyromellitic dianhydride and dissolve it in 1 L of N-methylpyrrolidone. Stir and continuously introduce argon gas to obtain solution A; Weigh 1 mol of 4,4'-diaminobenzophenone and dissolve it in solution A. Stir and continuously introduce argon gas. After being evenly dispersed, react at 60℃ for 5 h and cool to room temperature.

[0063] 2) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 50 mm / min, and then lift it at a speed of 10 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 80℃ for 3 hours, 150℃ for 50 minutes, 230℃ for 30 minutes, and 300℃ for 30 minutes until the surface of the conductor is covered with a 0.05 mm polyimide insulating varnish layer.

[0064] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 479℃, a tensile strength of 49.8MPa, and a dielectric constant of 1.5 at 200KHz.

[0065] Comparative Example 3

[0066] A polyimide enameled wire is prepared by the following method:

[0067] 1) Zirconia powder was prepared according to the method in Comparative Example 1;

[0068] 2) First, take 55 mL of distilled water and adjust its pH to 5 with glacial acetic acid. Then, add 150 mg of silane coupling agent KH-550 and stir at room temperature until hydrolysis is achieved to obtain a coupling agent solution. Add zirconium dioxide powder to the coupling agent solution at a mass ratio of 100:3 (zirconia powder to coupling agent). Stir mechanically at 600 r / min for 35 min, then place in a constant temperature drying oven and dry at 120℃ for 45 min. Finally, grind using a mortar and pestle to obtain modified zirconium dioxide powder.

[0069] 3) Preparation of polyamic acid solution: Weigh 1.0 mol of pyromellitic dianhydride and dissolve it in 1 L of N-methylpyrrolidone. Stir and continuously purge with argon gas to obtain solution A; Weigh 6.37 g of modified ZrO2 powder and slowly add it to solution A under stirring and continuous argon gas until it is evenly dispersed to obtain solution B; Weigh 1 mol of 4,4'-diaminobenzophenone and dissolve it in solution B. Stir and continuously purge with argon gas. After even dispersion, react at 60℃ for 5 h and cool to room temperature;

[0070] 3) Place the polyamic acid solution into the fixed container of the dip coating machine, immerse the copper wire at a speed of 50 mm / min, and then lift it at a speed of 10 mm / min for coating. After coating, place the copper wire into a tube furnace and sequentially heat it at 80℃ for 3 hours, 150℃ for 50 minutes, 230℃ for 30 minutes, and 300℃ for 30 minutes until the surface of the conductor is covered with a 0.05 mm polyimide insulating varnish layer.

[0071] The enameled wire was measured to have a weight loss rate of 10%, a thermal decomposition temperature of 484℃, a tensile strength of 57MPa, and a dielectric constant of 1.6 at 200KHz.

[0072] Cross-sectional scanning and energy dispersive spectroscopy (EDS) analyses were performed on the enameled wires prepared in Example 1 and Comparative Example 1. The results are shown in [reference needed]. Figures 1-4 In Example 1, no obvious agglomerated granular objects were observed in the cross-sectional scan image. The CTAB-ZrO2 particles were uniformly dispersed in the insulating varnish layer, indicating that the CTAB-modified nanoparticles had a smaller particle size and could be better dispersed in the PI matrix. In contrast, the cross-section of Comparative Example 1 showed some obvious agglomerated large granular objects attached to the cross-section.

[0073] from Figure 5 The FT-IR infrared spectra of ZrO2 powder before and after CTAB modification show that the wavelength range is 3419~3452 cm⁻¹. -1 The broad vibrational band centered on the OH bond in the H2O molecule is the absorption peak at 503 and 615 cm⁻¹. -1 The presence of Zr-O-Zr bonds in the absorption band confirms the formation of ZrO2 nanostructures. (1357~1386 cm⁻¹) -1 The weak absorption peak centered at 1454 cm⁻¹ is related to the vibration of COH. From the FT-IR spectrum, due to the larger grain size, the ZrO₂ nanopowder sample exhibits a stronger absorption band than the CTAB-modified ZrO₂ sample. -1 The presence of CH bending vibrations in the nearby CTAB molecule indicates that ZrO2 has been successfully modified.

[0074] Figure 6 The thermogravimetric analysis (TGA) charts show the enameled wires prepared in Example 1, Comparative Examples 1 and 2. The thermal decomposition temperatures of the pure PI film, PI / ZrO2 composite film, and PI / CTAB-ZrO2 composite film at a weight loss rate of 10% are 479.4℃, 494.7℃, and 520℃, respectively. The CTAB-modified ZrO2 significantly improves the high-temperature resistance of the PI film, thus enhancing the heat resistance of the enameled wire. This improvement in heat resistance may be due to the positively charged groups carried by CTAB, which significantly reduce the surface tension of the particles, effectively preventing particle aggregation, improving the interfacial bonding between the filler and the polymer matrix, and enhancing the application of the PI composite film in high-temperature environments.

[0075] Figure 7 The figures show the dielectric constant of the enameled wires prepared in Example 1 and Comparative Examples 1 and 2 at 25°C and 1 MHz, changing from low to high frequencies. At 200 kHz, the dielectric constants of pure PI, PI / ZrO2, and PI / CTAB-ZrO2 composite layers are 1.5, 1.9, and 2.6, respectively. Furthermore, the dielectric constant of the PI / CTAB-ZrO2 insulating varnish layer remains high in the higher frequency range, improving the dielectric stability of the composite film.

[0076] The above provides a detailed description of a high heat-resistant polyimide enameled wire and its preparation method. The above content is a further detailed explanation of the invention in conjunction with specific preferred embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, the structure of this invention can be flexibly varied without departing from its concept, and a series of products can be derived. Any simple deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. A method for preparing high heat-resistant polyimide enameled wire, characterized in that, Includes the following steps: Step 1: Preparation of hexadecyltrimethylammonium bromide modified ZrO2 powder: Weigh and dissolve 10-20g of ZrOCl2·8H2O solid in distilled water to obtain a zirconium oxychloride solution with a concentration of 0.5-1mol / L; weigh 1% by weight of hexadecyltrimethylammonium bromide of ZrOCl2·8H2O solid and dissolve it in distilled water to obtain a CTAB solution with a concentration of 0.01-0.05mol / L; slowly add the CTAB solution dropwise to the zirconium oxychloride solution under stirring until it is mixed evenly; transfer the evenly mixed solution to a hydrothermal reactor and react at 140-180℃ for 6-12 h; centrifuge and wash to collect the precipitate, and dry it in an oven at 50-90℃ for 3-9 h before taking it out; Step 2: Preparation of polyamic acid solution: Weigh 0.99 mol to 1.01 mol of diacid anhydride and dissolve it in 1 L of organic solvent. Stir and continuously introduce a protective gas to obtain solution A. Weigh hexadecyltrimethylammonium bromide modified ZrO2 powder and slowly add it to solution A under stirring and continuous introduction of a protective gas until it is evenly dispersed to obtain solution B. Weigh 0.98 mol to 1 mol of diamine and dissolve it in solution B. Stir and continuously introduce a protective gas. After even dispersion, react at 50 to 80 °C for 4 to 12 h and cool to room temperature. Step 3: Immerse the wire in the polyamic acid solution obtained in Step 2 for coating, and perform multi-stage heat treatment until the surface of the wire is covered with a polyimide insulating varnish layer of the required thickness.

2. The method for preparing high heat-resistant polyimide enameled wire according to claim 1, characterized in that, The conductor is a copper or aluminum wire, and the polyimide insulating varnish layer has a thickness of 0.01~0.1mm.

3. The method for preparing high heat-resistant polyimide enameled wire according to claim 1, characterized in that, The diacid anhydride is at least one of pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride; the diamine is at least one of 4,4'-diaminodiphenyl ether or 4,4'-diaminobenzophenone; the organic solvent is selected from at least one of N,N-dimethylformamide or N-methylpyrrolidone; the amount of hexadecyltrimethylammonium bromide-modified ZrO2 powder added is 1% to 5% of the mass of the diamine; and the protective gas is either nitrogen or argon.

4. The method for preparing high heat-resistant polyimide enameled wire according to claim 1, characterized in that, Step 3 specifically involves: placing the polyamic acid solution into the fixed container of the dip coating machine, immersing the wire at a speed of 40-60 mm / min, and then lifting it at a speed of 10-30 mm / min for coating. After coating, the wire is placed in a tube furnace and subjected to the following conditions in sequence: holding at 70-90℃ for 2-4 hours, holding at 140-160℃ for 40-60 minutes, holding at 220-240℃ for 30-40 minutes, and holding at 280-300℃ for 30-40 minutes.

5. A high heat-resistant polyimide enameled wire prepared by the method for preparing high heat-resistant polyimide enameled wire according to any one of claims 1 to 4, characterized in that, The high heat-resistant polyimide enameled wire includes a conductor and a polyimide insulating varnish layer disposed on the conductor. The polyimide insulating varnish layer is formed by heating and curing a polyamic acid solution containing hexadecyltrimethylammonium bromide modified ZrO2 powder.

6. The high heat-resistant polyimide enameled wire according to claim 5, characterized in that, The thickness of the polyimide insulating varnish layer is 0.01~0.1mm.

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