Enameled flat wire and preparation method thereof

Abstract

The invention relates to an enameled flat wire. The surface of a conductor is sequentially coated with first polyimide paint, second polyamide-imide paint, third polyimide paint and fourth polyimide paint, wherein the second polyamide-imide paint and the third polyimide paint are alternately arranged; wherein the peel strength of the first polyimide paint is not lower than 1.5 N / mm; the relative dielectric constant of the third polyimide paint is not greater than 2.1; nanoscale zirconium dioxide and nanoscale aluminum oxide are added into the fourth polyimide paint. The tensile strength of the enameled flat wire is not lower than 230 MPa; in a measurement standard within 100PC, a partial discharge initial voltage value of 50Hz-20kHz is not less than 2000V; under the condition that the leakage current does not exceed 5mA, the breakdown voltage value is not lower than 11kV; in a corona environment with the temperature being 155 DEG C, the voltage of Vp-p being 4000 V, the rising edge being 100 ns and the frequency being 20 kHz, the corona-resistant service life is 100-400 hours; in an ATF oil resistance test of T / CEEIA415-2019 standard, a partial discharge initial voltage value and a breakdown voltage value are both not lower than 90% of an initial value.

Description

Technical Field

[0001] The invention relates to the technical field of enameled wires, and in particular to an enameled flat wire and a preparation method thereof. Background Art

[0002] With the rapid development of new energy vehicle technology, the performance requirements for drive motors are increasing. Especially in terms of high-speed charging, extended driving range and reduced energy loss, the market demand for automotive drive motors is developing towards high performance, high power and high efficiency. In this context, flat wire motors have gradually become the first choice for new energy vehicle drive motors due to their high slot fill rate and good heat dissipation efficiency.

[0003] The mainstream flat wire motors on the market are flat wire oil-cooled drive motors. The high-voltage platform motors used in these motors have extremely high performance requirements for enameled flat wires. Enameled flat wires need to have high partial discharge inception voltage (PDIV) performance, corona resistance, and oil resistance. Therefore, enameled flat wires are usually designed as a three-composite paint film structure, with a composite structure of a base layer of high-adhesion polyimide (PI), a middle layer of corona-resistant polyimide (PI), and an outer layer of oil-resistant and hydrolysis-resistant polyimide (PI).

[0004] When operating under high voltage platform, enameled flat wire needs strong voltage resistance, and the insulation layer must reach a high PDIV value to avoid partial discharge and ensure the stable operation of the motor. Improving PDIV can be achieved by increasing the thickness of the paint film or using a low dielectric film. However, increasing the thickness of the paint film will reduce the space utilization rate of the motor and hinder heat dissipation. Therefore, it is necessary to use a paint film with a low dielectric constant.

[0005] In order for the enameled flat wire to meet the requirements of the ultra-high voltage platform of 1000V and above, even if the paint with the lowest dielectric constant on the market is used as the intermediate paint layer, the thickness needs to reach more than 60 microns. Adding the thickness of the primer and the outer paint layer, the double-sided paint film thickness of the enameled flat wire will reach more than 360 microns. This is a huge challenge for the adhesion, flexibility and heat dissipation performance of the paint film of the enameled flat wire. At the same time, such a thickness requires the paint film to be painted more than 60 times, which puts forward new improvement requirements for the power system and painting device of the production equipment.

[0006] In terms of process solutions, to meet the requirements of the ultra-high voltage platform, it is necessary to have a certain thickness of low dielectric coating, corona-resistant coating, and oil-resistant coating, and at the same time meet the comprehensive performance requirements such as adhesion and flexibility. However, under the limitation of customer size conditions, such a process structure cannot fully meet all performance requirements.

[0007] In summary, there is an urgent need for an enameled flat wire and a preparation method thereof to meet the high performance requirements of new energy vehicles for drive motors under an ultra-high voltage platform. Summary of the invention

[0008] The object of the present invention is to provide an enameled rectangular wire and a preparation method thereof in view of the deficiencies in the prior art.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] The first aspect of the present invention is to provide an enameled rectangular wire, comprising: a conductor; a surface of the conductor is coated with a first polyimide paint, a second polyamide-imide paint and a third polyimide paint arranged alternately, and a fourth polyimide paint in sequence; wherein:

[0011] The first polyimide paint has a peel strength of not less than 1.5 N / mm, a viscosity of 1800 mPa·s-2200 mPa·s, and a coating pass number of 1-10;

[0012] The viscosity of the second polyamide-imide paint is 2300mPa·s-2700mPa·s, and the number of coating passes is 3-12;

[0013] The third polyimide paint has a relative dielectric constant of no more than 2.1, a viscosity of 17800 mPa·s-18200 mPa·s, and a coating pass number of 6-24;

[0014] The fourth polyimide paint contains nano-scale zirconium dioxide and nano-scale aluminum oxide, has a viscosity of 14800 mPa·s-15200 mPa·s, and is coated 3-15 times.

[0015] In the present invention, the first polyimide paint is further preferably a 240-grade polyimide paint, which has low viscosity and good fluidity, is closely combined with the copper conductor, effectively ensures the adhesion and winding properties of the paint layer, and solves the problem of paint film loosening during processing;

[0016] In the present invention, the second polyamide-imide paint is further preferably a 220-grade polyamide-imide paint, and the second polyamide-imide paint of about 10 μm is interspersed in the third polyimide paint every 20 μm, which effectively solves the problem of cracks that are easy to appear in the third polyimide paint during the bending process, simplifies the processing process, improves the flexibility and winding properties of the overall paint film, and effectively avoids problems such as cracking and warping of the paint film during the processing process;

[0017] In the present invention, the third polyimide paint is further preferably a 240-grade polyimide paint, which has extremely strong resistance to partial discharge. Although the viscosity is relatively high and the fluidity is poor, it is only used as an intermediate paint layer through optimized design, which effectively improves the electrical insulation performance of the overall paint film.

[0018] In the present invention, the fourth polyimide paint is further preferably a 240-grade polyimide paint, which greatly improves the anti-corona performance and mechanical strength of the paint film by adding nano-scale zirconium dioxide and aluminum oxide, and effectively ensures the product's corona resistance and oil resistance.

[0019] Preferably, the solid content of the first polyimide paint is 20%-40%.

[0020] Preferably, the solid content of the second polyamide-imide paint is 20%-45%.

[0021] Preferably, the solid content of the third polyimide paint is 20%-45%.

[0022] Preferably, the solid content of the fourth polyimide paint is 30%-40%, and the particle size of the nano-scale zirconium dioxide and the particle size of the nano-scale aluminum oxide added to the fourth polyimide paint are both less than 100 nanometers.

[0023] Preferably, the thickness of each coating layer on one side is 3 μm-5 μm, so as to meet the requirement that the thickness of the paint film on both sides of the enameled flat wire is 320 μm-440 μm.

[0024] Preferably, the tensile strength of the enameled flat wire is not less than 230MPa; in the measurement standard within 100PC, the partial discharge inception voltage value of 50Hz-20kHz is not less than 2000V; under the condition that the leakage current does not exceed 5mA, the breakdown voltage value is not less than 11kV; in the corona environment of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life is 100-400 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the partial discharge inception voltage value and the breakdown voltage value are not less than 90% of the initial value.

[0025] The second aspect of the present invention is to provide a method for preparing the enameled rectangular wire as described above, the steps comprising:

[0026] S0, provide flat wire core material;

[0027] S1. At a certain temperature, sequentially apply a first amount of first polyimide paint, alternately apply a second polyamide-imide paint and a third polyimide paint, and apply a fourth polyimide paint to the surface of the flat wire core material, and after curing the flat wire core material, the enameled flat wire is obtained.

[0028] Preferably, the step S0 comprises:

[0029] S01, melting the electrolytic copper plate through an upper furnace, cooling and solidifying it to obtain a round rod-shaped conductor;

[0030] S02, forming the round rod-shaped conductor into a flat conductor by a continuous rolling mill, and forming the flat conductor into a flat wire core material by a triple single-mode wire drawing machine;

[0031] S03, cleaning the surface of the flat wire core material by an ultrasonic cleaning water tank, and removing residual stress and residual emulsion and / or oil stains by an annealing furnace.

[0032] Furthermore, the temperature of the annealing furnace is 300° C.-700° C., and the speed at which the flat wire core material passes through the annealing furnace is 2 m / min-30 m / min.

[0033] Preferably, in step S1,

[0034] The flat wire core material is coated by a polycrystalline paint mold, and the flat wire core material is cured by a baking oven;

[0035] Among them, the temperature of the evaporation zone of the oven is 300℃-450℃, the temperature of the curing zone of the oven is 350℃-700℃, the rotation speed of the circulation fan of the oven is 1000r / min-4000r / min, the rotation speed of the exhaust fan of the oven is 1000r / min-4000r / min, and the linear speed of the flat wire core material in the oven is 2m / min-60m / min.

[0036] Preferably, in step S1,

[0037] After the flat wire core material is solidified, the flat wire core material is cooled and lubricated by a lubricating oil coating device, and then wound up by a wire winding machine, and the wire is tightly and evenly wound up on a wire drum, thus obtaining the enameled flat wire.

[0038] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0039] The tensile strength of the enameled flat wire of the present invention is not less than 230MPa; in the measurement standard within 100PC, the partial discharge inception voltage value of 50Hz-20kHz is not less than 2000V; under the condition that the leakage current does not exceed 5mA, the breakdown voltage value is not less than 11kV; in a corona environment of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life is 100-400 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the partial discharge inception voltage value and the breakdown voltage value are not less than 90% of the initial value.

[0040] The enameled flat wire of the present invention not only meets the requirements of the ultra-high voltage platform, but also achieves comprehensive improvement in adhesion, flexibility, corona resistance and oil resistance by optimizing the paint film structure and material selection, thereby providing reliable insulation protection for the stable operation of the drive motor of new energy vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure of the enameled flat wire in the present invention;

[0042] The reference numerals include:

[0043] Conductor 1; first polyimide paint 2; second polyamide-imide paint 3; third polyimide paint 4; fourth polyimide paint 5. DETAILED DESCRIPTION

[0044] The specific embodiments of the present invention will be described in detail below.

[0045] Unless otherwise defined, technical or scientific terms used in the claims and the specification shall have the common meanings understood by persons having ordinary skills in the technical field to which the present invention belongs.

[0046] The words "include" or similar words used in the patent application specification and claims of the present invention mean that the items appearing before "include" include the items listed after "include" or their equivalents, and do not exclude other items.

[0047] The numerical values ​​mentioned in the present invention include all numerical values ​​that increase from low to high by one unit, assuming that there are at least two units between any lower value and the higher value. For example, if a component or a physical quantity is said to be from 1 to 100, 10 to 90 is more preferred, and 20 to 80 is the most preferred, it is intended to express that values ​​such as 5 to 95, 14 to 76, 23 to 67, 32 to 58, 41 to 49 are clearly listed in this specification; for values ​​less than 1, 0.0001, 0.001, 0.01 or 0.1 are considered to be more suitable as a unit. The above examples are for illustrative purposes only. In fact, all numerical combinations between the lowest value and the highest value listed are deemed to be clearly listed in this specification in a similar manner.

[0048] Example 1

[0049] This embodiment provides a method for preparing an enameled rectangular wire, the steps comprising:

[0050] S0. Provide flat wire core materials:

[0051] S01, melting the electrolytic copper plate through an upper furnace, cooling and solidifying it in a cylindrical pipe to obtain a round rod-shaped conductor;

[0052] S02, forming the round rod-shaped conductor into a flat conductor by a continuous rolling mill, and forming the flat conductor into a flat wire core material by a triple single-mode wire drawing machine, wherein the size of the flat wire core material is 1.500 mm×2.400 mm;

[0053] S03, cleaning the surface of the flat wire core material by an ultrasonic cleaning water tank, and removing residual stress and residual emulsion and / or oil stains by an annealing furnace;

[0054] Wherein, the temperature of the annealing furnace is 530°C, and the speed at which the flat wire core material passes through the annealing furnace is 8.5 m / min;

[0055] S1. Use a polycrystalline material coating die to sequentially coat the surface of the flat wire core material:

[0056] 5 coats of the first polyimide paint 2, having a peel strength of 1.8 N / mm, a viscosity of 1900 mPa·s, and a solid content of 32%;

[0057] 3 coats of second polyamide-imide paint 3, with a viscosity of 2400 mPa·s and a solid content of 30%;

[0058] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0059] 3 coats of second polyamide-imide paint 3, with a viscosity of 2300 mPa·s and a solid content of 30%;

[0060] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0061] 3 coats of second polyamide-imide paint 3, with a viscosity of 2400 mPa·s and a solid content of 30%;

[0062] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0063] 13 fourth polyimide paint 5, to which zirconium dioxide with a particle size of less than 100 nanometers and aluminum oxide with a particle size of less than 100 nanometers are added, with a viscosity of 15100 mPa·s and a solid content of 35%;

[0064] The flat wire core material is solidified by a drying furnace: the temperature of the evaporation zone of the drying furnace is 350° C., the temperature of the curing zone of the drying furnace is 400° C., the rotation speed of the circulation fan of the drying furnace is 2700 r / min, the rotation speed of the exhaust fan of the drying furnace is 2200 r / min, and the linear speed of the flat wire core material in the drying furnace is 8.5 m / min;

[0065] After the flat wire core material is naturally cooled and lubricated by a lubricating oil coating device, it is wound up by a wire take-up machine, and the wire is tightly and evenly wound on a wire drum to obtain the enameled flat wire. The size of the enameled flat wire is 1.654 mm×2.545 mm, that is, the thickness of the single-side paint film outside the conductor is 0.145 mm;

[0066] The tensile strength of the enameled flat wire prepared in this embodiment is 242MPa; after 15% stretching, the enameled flat wire was bent 180° with twice the diameter of the narrow side and the wide side, and no cracking or appearance defects occurred; under the test conditions of 100PC, the PDIV peak was 2050V and the BDV was 16kV; under the test conditions of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life was 260 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the PDIV peak was 1910V and the BDV was 15.1kV, which were 93.2% and 94.4% of the initial values, respectively; the oil durability test used Castrol BOT 383 oil, and the reaction was carried out for 2000 hours at a temperature of 150°C in a sealed can, and the paint film did not have appearance problems such as cracking and damage.

[0067] Comparative Example 1

[0068] This comparative example provides another method for preparing an enameled rectangular wire, the steps comprising:

[0069] S0. Provide flat wire core materials:

[0070] S01, melting the electrolytic copper plate through an upper furnace, cooling and solidifying it in a cylindrical pipe to obtain a round rod-shaped conductor;

[0071] S02, forming the round rod-shaped conductor into a flat conductor by a continuous rolling mill, and forming the flat conductor into a flat wire core material by a triple single-mode wire drawing machine, wherein the size of the flat wire core material is 1.500 mm×2.400 mm;

[0072] S03, cleaning the surface of the flat wire core material by an ultrasonic cleaning water tank, and removing residual stress and residual emulsion and / or oil stains by an annealing furnace;

[0073] Wherein, the temperature of the annealing furnace is 530°C, and the speed at which the flat wire core material passes through the annealing furnace is 9.3 m / min;

[0074] S1. Use a polycrystalline material coating die to sequentially coat the surface of the flat wire core material:

[0075] 5 coats of the first polyimide paint 2, having a peel strength of 1.8 N / mm, a viscosity of 1900 mPa·s, and a solid content of 32%;

[0076] 18 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0077] 13 fourth polyimide paint 5, to which zirconium dioxide with a particle size of less than 100 nanometers and aluminum oxide with a particle size of less than 100 nanometers are added, with a viscosity of 15100 mPa·s and a solid content of 35%;

[0078] The flat wire core material is solidified by a drying furnace: the temperature of the evaporation zone of the drying furnace is 350° C., the temperature of the curing zone of the drying furnace is 400° C., the rotation speed of the circulation fan of the drying furnace is 2600 r / min, the rotation speed of the exhaust fan of the drying furnace is 2150 r / min, and the linear speed of the flat wire core material in the drying furnace is 8.5 m / min;

[0079] After the flat wire core material is naturally cooled and lubricated by a lubricating oil coating device, it is wound by a wire take-up machine, and the wire is tightly and evenly wound on the wire drum to obtain the enameled flat wire. The size of the enameled flat wire is 1.594 mm×2.485 mm, that is, the thickness of the single-side paint film outside the conductor is 0.115 mm;

[0080] The tensile strength of the enameled flat wire prepared in this comparative example is 224MPa; after 15% stretching, when the enameled flat wire is bent 180° with twice the diameter of the narrow side and the wide side, the paint film shows slight warping; under the test condition of 100PC, the PDIV peak is 1710V and the BDV is 14.2kV; under the test conditions of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life is 230 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the PDIV peak is 1150V and the BDV is 9.17kV, which are 67.3% and 64.6% of the initial value respectively;

[0081] That is, compared with Comparative Example 1, although the single-side paint film thickness outside the conductor increased by 20.7%, the PDIV peak value in the ATF oil resistance test increased by 66.1% and there was no appearance problem; and the enameled flat wire of Comparative Example 1 showed a significant decline in tensile strength and flexibility.

[0082] Comparative Example 2

[0083] This comparative example provides another method for preparing an enameled rectangular wire, the steps comprising:

[0084] S0. Provide flat wire core materials:

[0085] S01, melting the electrolytic copper plate through an upper furnace, cooling and solidifying it in a cylindrical pipe to obtain a round rod-shaped conductor;

[0086] S02, forming the round rod-shaped conductor into a flat conductor by a continuous rolling mill, and forming the flat conductor into a flat wire core material by a triple single-mode wire drawing machine, wherein the size of the flat wire core material is 1.500 mm×2.400 mm;

[0087] S03, cleaning the surface of the flat wire core material by an ultrasonic cleaning water tank, and removing residual stress and residual emulsion and / or oil stains by an annealing furnace;

[0088] Wherein, the temperature of the annealing furnace is 530°C, and the speed at which the flat wire core material passes through the annealing furnace is 8.5 m / min;

[0089] S1. Use a polycrystalline material coating die to sequentially coat the surface of the flat wire core material:

[0090] 5 coats of the first polyimide paint 2, having a peel strength of 1.8 N / mm, a viscosity of 1900 mPa·s, and a solid content of 32%;

[0091] 3 coats of second polyamide-imide paint 3, with a viscosity of 2400 mPa·s and a solid content of 30%;

[0092] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0093] 3 coats of second polyamide-imide paint 3, with a viscosity of 2300 mPa·s and a solid content of 30%;

[0094] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0095] 3 coats of second polyamide-imide paint 3, with a viscosity of 2400 mPa·s and a solid content of 30%;

[0096] 6 coats of third polyimide paint 4, having a relative dielectric constant of no more than 2.1, a viscosity of 17900 mPa·s, and a solid content of 30%;

[0097] 13 coats of the fourth polyimide paint 5, without the addition of zirconium dioxide with a particle size of less than 100 nanometers and aluminum oxide with a particle size of less than 100 nanometers, with a viscosity of 2500 mPa·s and a solid content of 35%;

[0098] The flat wire core material is solidified by a drying furnace: the temperature of the evaporation zone of the drying furnace is 350° C., the temperature of the curing zone of the drying furnace is 400° C., the rotation speed of the circulation fan of the drying furnace is 2700 r / min, the rotation speed of the exhaust fan of the drying furnace is 2200 r / min, and the linear speed of the flat wire core material in the drying furnace is 8.5 m / min;

[0099] After the flat wire core material is naturally cooled and lubricated by a lubricating oil coating device, it is wound up by a wire take-up machine, and the wire is tightly and evenly wound on a wire drum to obtain the enameled flat wire. The size of the enameled flat wire is 1.652 mm×2.543 mm, that is, the thickness of the paint film on one side of the conductor is 0.144 mm;

[0100] The enameled flat wire prepared in this comparative example has a PDIV peak of 1650V and a BDV of 13.8kV under the test conditions of 100PC; under the test conditions of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life is 80 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the PDIV peak is 1150V and the BDV is 8.98kV, which are 69.7% and 65.1% of the initial values, respectively;

[0101] That is, compared with Comparative Example 2, Example 1 shows that the fourth polyimide paint has a synergistic effect with nano-scale zirconium dioxide and nano-scale aluminum oxide, which greatly improves the corona resistance life.

[0102] In summary, the enameled rectangular wire of the present invention not only meets the requirements of the ultra-high voltage platform, but also achieves comprehensive improvement in adhesion, flexibility, corona resistance and oil resistance by optimizing the paint film structure and material selection, thereby providing reliable insulation protection for the stable operation of the drive motor of new energy vehicles.

[0103] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. An enameled rectangular wire, comprising: Conductor (1); characterized in that the surface of the conductor (1) is coated in sequence with a first polyimide paint (2), a second polyamide-imide paint (3) and a third polyimide paint (4) arranged alternately, and a fourth polyimide paint (5); wherein, The first polyimide paint (2) has a peel strength of not less than 1.5 N / mm, a viscosity of 1800 mPa·s-2200 mPa·s, and a coating pass number of 1-10; The viscosity of the second polyamide-imide paint (3) is 2300 mPa·s-2700 mPa·s, and the number of coating passes is 3-12; The third polyimide paint (4) has a relative dielectric constant of no more than 2.1, a viscosity of 17800 mPa·s-18200 mPa·s, and a coating pass number of 6-24; The fourth polyimide paint (5) contains nano-scale zirconium dioxide and nano-scale aluminum oxide, has a viscosity of 14800 mPa·s-15200 mPa·s, and is coated 3-15 times.

2. The preparation method according to claim 1, characterized in that: The solid content of the first polyimide paint (2) is 20%-40%.

3. The preparation method according to claim 1, characterized in that: The solid content of the second polyamide-imide paint (3) is 20%-45%.

4. The preparation method according to claim 1, characterized in that: The solid content of the third polyimide paint (4) is 20%-45%.

5. The preparation method according to claim 1, characterized in that: The solid content of the fourth polyimide paint (5) is 30%-40%, and the particle size of the nano-scale zirconium dioxide and the particle size of the nano-scale aluminum oxide added to the fourth polyimide paint (5) are both less than 100 nanometers.

6. The enameled rectangular wire according to claim 1, characterized in that: The single-side thickness of each coating pass is 3μm-5μm.

7. The enameled rectangular wire according to claim 1, characterized in that: The tensile strength of the enameled flat wire is not less than 230MPa; in the measurement standard within 100PC, the partial discharge starting voltage value of 50Hz-20kHz is not less than 2000V; under the condition that the leakage current does not exceed 5mA, the breakdown voltage value is not less than 11kV; in the corona environment of 155°C, Vp-p 4000V, rising edge 100ns, and frequency 20kHz, the corona resistance life is 100-400 hours; in the ATF oil resistance test of T / CEEIA415-2019 standard, the partial discharge starting voltage value and the breakdown voltage value are not less than 90% of the initial value.

8. A method for preparing the enameled rectangular wire according to any one of claims 1 to 7, characterized in that the steps include: S0, provide flat wire core material; S1. At a certain temperature, sequentially apply a first amount of first polyimide paint, alternately apply a second polyamide-imide paint and a third polyimide paint, and apply a fourth polyimide paint to the surface of the flat wire core material, and after curing the flat wire core material, the enameled flat wire is obtained.

9. The preparation method according to claim 8, characterized in that: The step S0 comprises: S01, melting the electrolytic copper plate through an upper furnace, cooling and solidifying it to obtain a round rod-shaped conductor; S02, forming the round rod-shaped conductor into a flat conductor by a continuous rolling mill, and forming the flat conductor into a flat wire core material by a triple single-mode wire drawing machine; S03, cleaning the surface of the flat wire core material by an ultrasonic cleaning water tank, and removing residual stress and residual emulsion and / or oil stains by an annealing furnace.

10. The preparation method according to claim 8, characterized in that: In the step S1, The flat wire core material is coated by a polycrystalline paint mold, and the flat wire core material is cured by a baking oven; Among them, the temperature of the evaporation zone of the oven is 300℃-450℃, the temperature of the curing zone of the oven is 350℃-700℃, the rotation speed of the circulation fan of the oven is 1000r / min-4000r / min, the rotation speed of the exhaust fan of the oven is 1000r / min-4000r / min, and the linear speed of the flat wire core material in the oven is 2m / min-60m / min.

11. The preparation method according to claim 8, characterized in that: In the step S1, After the flat wire core material is solidified, the flat wire core material is cooled and lubricated by a lubricating oil coating device, and then wound up by a wire winding machine, and the wire is tightly and evenly wound up on a wire drum, thus obtaining the enameled flat wire.

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