Preparation method of insulated wire

Abstract

The invention discloses a preparation method of an insulated wire. Specifically, the method comprises the following steps: annealing a rolled conductor to obtain an annealed conductor; the periphery of the annealed conductor is coated with insulating paint to form a first prefabricated core wire, the first prefabricated core wire coated with the insulating paint is subjected to high-temperature curing to form an insulating layer, and a second prefabricated core wire is obtained; the outer side of the insulating layer of the second prefabricated core wire is coated with finish paint containing a modified polyamide-imide intermediate to form a third prefabricated core wire, the third prefabricated core wire coated with the finish paint is subjected to high-temperature curing to form a finish paint layer on the outer side of the insulating layer, and the insulated wire is further obtained. The insulated wire provided by the invention improves the wire flexibility, adapts to closer arrangement of complex slot types, and further improves the slot fullness rate of a motor, thereby reducing the size of a stator core under the same power, indirectly reducing the weight of the motor and meeting the requirement of light weight.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of insulated wires, and more particularly to a preparation method of an insulated wire. BACKGROUND

[0002] With the development of motor systems, the heat resistance grade of polyamide-imide is close to the upper limit of use, and it is difficult to independently meet the long-term reliability requirements under higher temperature rise conditions. Therefore, at present, the scheme of compounding polyamide-imide and polyimide paint is usually adopted to cooperatively improve the heat resistance grade and electrical insulation performance of the insulation layer. In addition, the polyamide-imide has strong molecular structure rigidity and high paint film hardness, and the flexibility is insufficient during winding, and stress concentration is easily generated at the bending part, and paint film cracking is generated. In order to avoid paint film cracking, a larger bending radius must be used, which limits the close arrangement of the insulated wire in the complex slot type, resulting in a decrease in motor slot fill rate, and then affecting the power density improvement.

[0003] Under this background, how to modify the structure and material of the polyamide-imide insulated wire without sacrificing the heat resistance and insulation performance to significantly improve the flexibility has become the key to realize the high slot fill rate winding design. By improving the bending performance of the wire, a more compact coil arrangement can be realized, thereby reducing the size of the stator core under the same output power, effectively reducing the volume and weight of the motor, and helping the new energy vehicles to develop in the direction of "high power density, high efficiency and light weight".

[0004] Therefore, it is a technical problem to be solved at present to develop an insulated wire with high heat resistance and high flexibility. SUMMARY

[0005] Therefore, the main purpose of the present application is to provide a preparation method of an insulated wire.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows.

[0007] The first aspect of the present application comprises a preparation method of an insulated wire, comprising the following steps: S1: subjecting a conductor to at least one calendering to a target size to obtain a calendered conductor; S2: annealing the calendered conductor to obtain an annealed conductor; S3: coating an insulating paint on the outer periphery of the annealed conductor to form a first precore wire, and feeding the first precore wire coated with the insulating paint into a varnishing machine, wherein the insulating paint is cured at high temperature to form an insulation layer, and the coating and curing steps are repeated multiple times to obtain a second precore wire with a predetermined thickness of the insulation layer; S4: coating a finish on the outer side of the insulation layer to form a third preformed core wire, and feeding the third preformed core wire coated with the finish into a varnishing machine to form a finish layer on the outer side of the insulation layer by high-temperature curing, and repeating the coating and curing steps multiple times to obtain an insulated wire.

[0008] In the present application, the predetermined thickness insulation layer in the S3 step comprises a bottom layer and optionally an intermediate layer. The varnish forming the bottom layer is optionally a conventional polyamide-imide varnish, such as a conventional commercially available polyamide-imide varnish, such as TONGMID 595 series of ELANTAS or HI406 series of RESONAC, etc. The varnish forming the intermediate layer is optionally a polyimide varnish, preferably a corona-resistant polyimide varnish or a low-dielectric polyimide varnish. The low-dielectric polyimide varnish refers to a polyimide varnish with a dielectric constant less than 3.5, in particular a polyimide varnish with a dielectric constant less than 3. The corona-resistant polyimide varnish is a polyimide varnish with ionization breakdown resistance. For example, commercially available TONGTHERM 537 series of ELANTAS or SI-750D series of RESONAC, etc. The second preformed core wire with a predetermined thickness insulation layer can be obtained by sequentially coating and curing the above-mentioned insulation varnishes in the method.

[0009] The second aspect of the present application provides a method for preparing a finish, wherein the finish is a modified polyamide-imide varnish.

[0010] The modified polyamide-imide varnish is prepared by dissolving a modified polyamide-imide intermediate in a solvent B, wherein the modified polyamide-imide intermediate is obtained by an addition reaction of a diisocyanate with a mixed anhydride, and the mixed anhydride comprises a short-chain anhydride and a long-chain anhydride.

[0011] The short-chain anhydride comprises at least one of the following anhydrides: an aromatic short-chain anhydride, an aliphatic short-chain anhydride, and an alicyclic short-chain anhydride. The aromatic short-chain anhydride refers to an aromatic anhydride with not more than 5 carbon atoms of chain-like aliphatic substituents on the aromatic ring, or an unsubstituted aromatic anhydride. The aliphatic short-chain anhydride refers to an aliphatic anhydride with not more than 5 carbon atoms of chain-like aliphatic structure in the molecule of the anhydride. The alicyclic short-chain anhydride refers to an alicyclic anhydride with not more than 7 carbon atoms of ring-like alicyclic structure. The molecular structure of the short-chain anhydride should at least comprise an anhydride structure and a carboxyl group; or a dianhydride structure.

[0012] In a preferred embodiment of the present application, the short-chain anhydride is an aromatic short-chain anhydride.

[0013] In a preferred embodiment of the present application, the aromatic short-chain anhydride comprises at least one of the following anhydrides: trimellitic anhydride, methyl-substituted trimellitic anhydride, ethyl-substituted trimellitic anhydride, and pyromellitic dianhydride.

[0014] In the present application, the long-chain anhydride comprises at least one of the following: alicyclic anhydride, aromatic anhydride, and bio-based long-chain anhydride. The molecular structure of the long-chain anhydride should at least contain an anhydride structure and a carboxyl group. More specifically, the long-chain anhydride is prepared from a long-chain aliphatic diacid or its derivative and a short-chain carboxylic acid or its derivative.

[0015] In the present application, the long-chain aliphatic diacid or its derivative refers to an aliphatic chain structure with not less than 6 carbon atoms in its molecular structure, or an alicyclic structure with not less than 8 carbon atoms. The short-chain carboxylic acid or its derivative refers to an aliphatic chain structure with not more than 5 carbon atoms in the molecular structure of the carboxylic acid, or an aromatic monocarboxylic acid with not more than 5 carbon atom chain aliphatic substituent or an unsubstituted aromatic monocarboxylic acid or its derivative.

[0016] It should be noted that "not more than" in the present application includes the case of 0.

[0017] In the present application, the modified polyamide-imide intermediate is prepared from a mixed anhydride comprising a long-chain anhydride and a short-chain anhydride and a diisocyanate.

[0018] Among the mixed anhydride, the molar ratio of long-chain anhydride to mixed anhydride is 10% or less, preferably 3-5%.

[0019] In the present application, the diisocyanate is selected from aromatic diisocyanate, preferably at least one of toluene diisocyanate (TDI) and diphenyl methane diisocyanate (MDI).

[0020] The third aspect of the present application is a method for preparing a modified polyamide-imide intermediate.

[0021] The method comprises the following steps: (1) In the S4 step, the long-chain aliphatic dicarboxylic acid and the monocarboxylic acid are fed at a molar ratio of 1:1, a solvent A, an activating agent, and a catalyst are added to react to obtain a long-chain anhydride; (2) Further, in the S4 step, the long-chain anhydride obtained after reaction is mixed with a short-chain anhydride and reacted with a diisocyanate to obtain a modified polyamide-imide intermediate; (3) The modified polyamide-imide intermediate is dissolved in a solvent B to obtain a modified polyamide-imide varnish; the solvent B is at least one of NMP, DMF, or DMAC.

[0022] In the step (1), the activating agent is DCC (dicyclohexyl carbodiimide), and the catalyst is DMAP (4-dimethylaminopyridine); the solvent A includes dichloromethane and ethylbenzene.

[0023] The activated agent DCC is diluted and added dropwise in a reactor with stirring, wherein the concentration of the diluted DCC is not more than 3 mol / L. During the dropwise addition of DCC, the reaction temperature is preferably 0-10°C, more preferably, the reaction temperature is 0-5°C.

[0024] In the present application, the activated agent DCC is preferably added in excess based on the molar amount of the monocarboxylic acid in the mixed carboxylic acid. The molar ratio of DCC to the monocarboxylic acid is 1.05-1.2:1.

[0025] In step (1), the amount of DMAP added is 10%-20% of the molar amount of the monocarboxylic acid.

[0026] In step (2), the feeding ratio of the long-chain acid anhydride is not more than 10% of the mixed acid anhydride, preferably 3-5%. The feeding ratio is based on the molar feeding ratio. In step (2), the diisocyanate is added in excess based on the molar ratio of the acid anhydride to the theoretical amount of diisocyanate added for the reaction with the acid anhydride, wherein the molar ratio of the isocyanate groups in the diisocyanate to the sum of the carboxyl groups and the acid anhydride groups corresponding to the reaction with the acid anhydride is 10-20%. That is, for the present application, when the reactants are diisocyanate and acid anhydride or diacid anhydride containing one acid anhydride and carboxyl group, the molar ratio of diisocyanate to acid anhydride is 1.1-1.2:1.

[0027] The fourth aspect of the present application provides an insulated wire comprising the modified polyamide-imide topcoat layer.

[0028] The obtained modified polyamide-imide intermediate is dissolved in solvent B to obtain a modified polyamide-imide paint, i.e. a topcoat. The modified polyamide-imide paint is coated on the wire and heated to cure to obtain an insulated wire comprising a topcoat layer.

[0029] The insulated wire of the present application comprises a conductor, and a paint layer surrounding the conductor. The paint layer has a multi-layer structure, and comprises, from the inside to the outside, an insulation layer, and a topcoat layer. The insulation layer optionally comprises a base layer and / or an intermediate layer.

[0030] In the present application, the base layer is selected from conventional polyamide-imide paint, such as conventional commercially available polyamide-imide paint of general grade. The intermediate layer is selected from polyimide paint, preferably corona-resistant polyimide paint or low-dielectric polyimide paint. The low-dielectric polyimide paint refers to polyimide paint with a dielectric constant less than 3.5, in particular a dielectric constant less than 3. The corona-resistant polyimide paint is polyimide paint with anti-ionization breakdown performance.

[0031] In the present application, the topcoat layer is formed by coating and curing the modified polyamide-imide paint.

[0032] In a preferred embodiment of the present application, the thickness of the topcoat layer accounts for 10% to 50% of the total thickness of the enameled layer. The total thickness of the enameled layer includes the thickness of the insulating layer disposed on the conductor and the thickness of the topcoat layer formed by curing the modified polyamide-imide paint. That is, the thickness of the topcoat layer accounts for 10% to 50% of the sum of the thicknesses of the insulating layer in the S3 step and the topcoat layer in the S4 step.

[0033] In the present application, the total thickness of the enameled layer is 50 to 500 μm, and preferably, the total thickness of the enameled layer is 50 to 200 μm.

[0034] Compared with the prior art, the present application has the following advantages.

[0035] The modified polyamide-imide intermediate of the present application serves as the main component of the topcoat, and after coating and curing, forms a topcoat layer that covers the surface of the insulated wire, thereby improving the flexibility of the insulated wire. The insulated wire having the insulating layer of the present application can maintain good electrical insulation performance at a relatively high use temperature, is less likely to crack, has good flexibility, and is suitable for complex slot types that are more closely arranged, thereby improving the slot fill rate of the motor, reducing the volume of the stator core at the same power, indirectly reducing the weight of the motor, and achieving the requirement of light weight. DETAILED DESCRIPTION

[0036] Example 1 Step 1) In a 500 mL three-necked flask, dodecanedioic acid (20.2 g, 0.1 mol), benzoic acid (12.2 g, 0.1 mol), DMAP (4-dimethylaminopyridine) (1.22 g, 0.01 mol) were sequentially added, 200 mL of anhydrous dichloromethane was added, and stirring was performed until the solids were completely dissolved. The three-necked flask was placed in an ice bath (0-5°C), and a DCC (dicyclohexyl carbodiimide) dichloromethane solution (DCC 24.7 g, 0.12 mol dissolved in 50 mL of anhydrous dichloromethane) was slowly added dropwise, and the temperature was controlled to be ≤10°C during the dropwise addition. After the dropwise addition was completed, the ice bath was removed, and the reaction was stirred at room temperature (25-30°C) for 12-16 hours. After the reaction was stopped, the filtrate was washed with anhydrous petroleum ether, and rotary evaporation was performed under reduced pressure (vacuum degree 0.08 MPa) to obtain a yellowish oil crude product. Further column chromatography was performed on a silica gel column using ethyl acetate / petroleum ether as the eluent, and the white solid carboxyl-terminated dodecanoyl-benzoic anhydride was obtained after purification, drying, and column chromatography, as shown in formula 1.

[0037] Formula 1.

[0038] In a flask equipped with a reflux condenser, 5 mmol of carboxyl-terminated dodecanoyl-benzoyl anhydride was added, further 95 mmol of trimellitic anhydride (hereinafter referred to as TMA) was added, 500 ml of ethylbenzene was added, 0.12 mol of diphenyl methane diisocyanate (hereinafter referred to as MDI) was added, and the reaction was carried out at 190°C for 2 hours. After the reaction was completed, the reaction product was washed with n-hexane, and the solvent was removed under reduced pressure to obtain a modified polyamide-imide intermediate.

[0039] 2) The modified polyamide-imide intermediate obtained in step 1) was dissolved in NMP (N-methyl pyrrolidone) to prepare a modified polyamide-imide paint (solid content 30%).

[0040] 3) A preformed core wire was coated with a bottom layer of polyamide-imide insulating paint to form an annealed conductor, and the polyamide-imide insulating paint coated preformed core wire was fed into a varnishing machine. The insulating paint was cured at high temperature, and the coating and curing steps were repeated to obtain a polyamide-imide bottom layer having a thickness of 12 μm. An intermediate layer of corona-resistant polyimide paint was further coated on the outside of the bottom layer and cured, and the coating and curing steps were repeated to obtain a corona-resistant polyimide intermediate layer having a thickness of 83 μm. The modified polyamide-imide paint obtained in step 2) was coated on the outside of the intermediate layer, and the modified polyamide-imide paint coated on the outside of the intermediate layer was cured at high temperature to form a modified polyamide-imide paint layer on the outside of the intermediate layer. The coating and curing steps were repeated to obtain a modified polyamide-imide topcoat layer disposed on the outside of the intermediate layer, i.e., an insulated wire coated with a topcoat layer. The topcoat layer obtained by curing the modified polyamide-imide paint had a thickness of 25 μm.

[0041] Example 2 A carboxyl-terminated octadecanoyl-benzoyl anhydride was prepared using octadecanedioic acid according to the method of Example 1, and had the structure shown in Formula 2. Formula 2 In a flask equipped with a reflux condenser, 3 mmol of carboxyl-terminated octadecanoyl-benzoyl anhydride was added, further 97 mmol of TMA was added, 500 ml of ethylbenzene was added, 0.12 mol of MDI was added, and the reaction was carried out at 190°C for 2 hours to prepare a modified polyamide-imide intermediate. A modified polyamide-imide paint was further prepared and coated on a bottom layer of polyamide-imide and an intermediate layer of low-dielectric polyimide insulating layer which had been coated and cured, wherein the bottom layer had a thickness of 12 μm, the intermediate layer had a thickness of 48 μm, and the modified polyamide-imide paint was coated and cured multiple times to obtain a modified polyamide-imide topcoat layer having a thickness of about 60 μm to coat the wire, i.e., to obtain an insulated wire.

[0042] Example 3 A carboxyl-terminated hexadecanoyl-benzoyl anhydride was prepared using hexadecanedioic acid according to the method of Example 1, and had the structure shown in Formula 3. Formula 3; In a flask equipped with a reflux condenser, 10 mmol of carboxyl-terminated hexadecanoyl-benzoyl anhydride was added, further 90 mmol of TMA was added, 500 ml of ethylbenzene was added, 0.12 mol of MDI was added, and the reaction was refluxed at 190°C for 2 hours to prepare a polyamide-imide intermediate. Further, a polyamide-imide paint was prepared by dissolving the polyamide-imide intermediate prepared in the above step in NMP, and the polyamide-imide paint was coated on an insulated conductor on which a cured bottom layer of polyamide-imide and a middle layer of polyimide insulation had been coated, wherein the thickness of the bottom layer was 12 μm and the thickness of the middle layer was 96 μm, and the coated conductor was baked to obtain a modified polyamide-imide top coat layer having a thickness of about 12 μm, thereby obtaining an insulated electric wire.

[0043] Example 4 A modified polyamide-imide paint was prepared by the same method as in Example 1, and coated on an insulated conductor on which a cured bottom layer of polyamide-imide had been coated. The thickness of the polyamide-imide insulation layer was 95 μm, and the coated conductor was baked to obtain a modified polyamide-imide top coat layer having a thickness of about 25 μm, thereby obtaining an insulated electric wire.

[0044] Example 5 A modified polyamide-imide paint was prepared by the same method as in Example 1, and coated on an insulated conductor on which a cured bottom layer of polyamide-imide and a middle layer of corona-resistant polyimide insulation had been coated, wherein the thickness of the bottom layer was 12 μm and the thickness of the middle layer was 83 μm, and the coated conductor was baked to obtain a modified polyamide-imide top coat layer having a thickness of about 25 μm, thereby obtaining an insulated electric wire.

[0045] Comparative Example 1 A polyamide-imide intermediate was prepared by the same method as in Example 1, step 1), except that in a flask equipped with a reflux condenser, 0.1 mol of TMA was added, 500 ml of ethylbenzene was added, and 0.12 mol of MDI was added, and the reaction was refluxed at 190°C for 2 hours. Further, the polyamide-imide intermediate prepared in the above step was dissolved in NMP to obtain a polyamide-imide paint, and the polyamide-imide paint was coated on an insulated conductor on which a cured bottom layer of polyamide-imide and a middle layer of corona-resistant polyimide insulation had been coated, wherein the thickness of the bottom layer was 12 μm and the thickness of the middle layer was 83 μm, and the coated conductor was baked to obtain a polyamide-imide top coat layer having a thickness of about 25 μm, thereby obtaining an insulated electric wire.

[0046] Comparative Example 2 The method of step 1) of Example 1 was used, except that in a flask equipped with a reflux condenser, 20 mmol of carboxyl-terminated dodecanoyl-benzoyl anhydride was added, further 80 mmol of TMA was added, 500 ml of ethylbenzene was added, 0.12 mol of MDI was added, and the reaction was refluxed at 190 °C for 2 hours to prepare the polyamide-imide intermediate. Further, the modified polyamide-imide paint was prepared according to the same method of steps 2) and 3) of Example 1, and coated on the insulated conductor which had been coated with the cured bottom layer of polyamide-imide and the middle layer of corona-resistant polyimide insulating layer, wherein the thickness of the bottom layer was 12 μm, the thickness of the middle layer was 83 μm, and the thickness of the modified polyamide-imide topcoat layer was about 25 μm after baking and curing, to obtain the insulated wire.

[0047] Comparative Example 3 The method of step 1) of Example 1 was used, except that DCC was added dropwise, and the temperature was controlled at 20 °C during the dropwise addition. Further, the modified polyamide-imide paint was prepared according to the same method of steps 2) and 3) of Example 1, and coated on the insulated conductor which had been coated with the cured bottom layer of polyamide-imide and the middle layer of corona-resistant polyimide insulating layer, wherein the thickness of the bottom layer was 12 μm, the thickness of the middle layer was 83 μm, and the thickness of the modified polyamide-imide topcoat layer was about 25 μm after baking and curing, to obtain the insulated wire.

[0048] Comparative Example 4 The method of step 1) of Example 1 was used, except that in a 500 mL three-necked flask, malonic acid (10.4 g, 0.1 mol), benzoic acid (12.2 g, 0.1 mol), DMAP (4-dimethylaminopyridine) (1.22 g, 0.01 mol) were sequentially added, 200 mL of anhydrous dichloromethane was added, and the mixture was stirred until the solids were completely dissolved, to prepare benzoic acid malonic anhydride (PhCO-O-COCH2COOH). Further, 5 mmol of benzoic acid malonic anhydride and 95 mmol of trimellitic anhydride were added to prepare the modified polyamide-imide intermediate. Further, the modified polyamide-imide paint was prepared according to the same method of steps 2) and 3) of Example 1, and coated on the insulated conductor which had been coated with the cured bottom layer of polyamide-imide and the middle layer of corona-resistant polyimide insulating layer, wherein the thickness of the bottom layer was 12 μm, the thickness of the middle layer was 83 μm, and the thickness of the modified polyamide-imide topcoat layer was about 25 μm after baking and curing, to obtain the insulated wire.

[0049] Comparative Example 5 The modified polyamide-imide paint was prepared by the same method as in Example 1 and coated on the insulated conductor which had been coated with a cured bottom layer of polyamide-imide and a middle layer of a corona-resistant polyimide insulating layer, wherein the thickness of the bottom layer was 12 μm and the thickness of the middle layer was 103 μm, to obtain an insulated wire coated with a modified polyamide-imide topcoat layer having a thickness of about 5 μm after baking and curing.

[0050] Comparative Example 6 The modified polyamide-imide paint was prepared by the same method as in Example 1 and coated on the insulated conductor which had been coated with a cured bottom layer of polyamide-imide and a middle layer of a corona-resistant polyimide insulating layer, wherein the thickness of the bottom layer was 12 μm and the thickness of the middle layer was 38 μm, to obtain an insulated wire coated with a modified polyamide-imide topcoat layer having a thickness of about 70 μm after baking and curing.

[0051] The insulated wires of the examples and comparative examples were respectively tested according to the following methods.

[0052] 1. Flexibility test. The flexibility test was carried out according to the flexibility test method provided in IEC 60851-3 2019 test method 8, and the specific steps were as follows.

[0053] Two 500 mm long straight insulated wires were taken, and each of the two insulated wires was bent 180 ± 2° around a polished test core, one was flat wound (core diameter = wire thickness N times, N was 1.0, 1.5 or 2.0), and the other was vertical wound (core diameter = wire width N times). In this test, the surface of the product was smooth without cracking, which was recorded as “qualified”; the surface cracking was recorded as “unqualified”.

[0054] 2. 260℃, 30min heat shock test.

[0055] The test was carried out according to the test method provided in GB / T 4074.6-2024 test method 9.

[0056] The sample was prepared according to the provisions of GB / T 4074.3-2024 6.2.2, and a 400 mm straight sample wire was wound 180 ± 2° around a polished test core, and flat wound (core diameter = wire thickness N times). The sample was placed in a forced air oven and heated for 30 min at a temperature of 260 ± 5℃. The sample was taken out of the oven and cooled to room temperature, and then examined with a 10x magnifying glass to check if the enamel layer had cracks. If there were cracks, it was unqualified, and if there were no cracks, it was qualified.

[0057] 3. Softening breakdown test.

[0058] The softening breakdown tester (model HTC600) is used for the test, the sample is placed in the instrument, and the temperature at the time of breakdown is recorded by using the temperature rising method, and the evaluation is carried out.

[0059] Test conditions: Weight of the weight: 1 kg, i.e. 9.8 N; Temperature rising rate: 2℃ / min; Test voltage: 100 V; Target temperature: 600℃.

[0060] Evaluation criteria: A: above 500℃; B: above 400℃ and less than 500℃; C: less than 400℃.

[0061] The results are shown in the following table.

[0062]

[0063] Note: 2x means that the core diameter of the insulated wire is 2 times the line width or line thickness when bent, 1.5x means that the core diameter is 1.5 times the line width or line thickness when bent, and 1.0x means that the core diameter is 1 times the line width or line thickness.

[0064] From the above test, it can be seen that the insulated wires prepared by examples 1-5 of the present application do not crack during the 2.0x, 1.5x and 1.0x winding group flexibility test, and the qualified rate is 100%; in comparative example 1, because all of them are short-chain anhydride, the flexibility of the prepared insulated wire is insufficient, and the heat shock resistance is also significantly reduced; the conductive wire in comparative example 2 is tested for flexibility, and no cracking is observed, but the winding wire deforms unexpectedly during the 260℃ 30min heat shock test. The wire coated with polyamide-imide obtained by the reaction of comparative example 3 of the present application appears melt casting of the outer layer during the 260℃ 30min heat shock test, and the experiment cannot be carried out. The wire coated with the modified polyamide-imide topcoat layer obtained by the reaction of comparative example 4 of the present application cracks in many samples during the flexibility test at 25℃ and the 260℃ 30min heat shock test. In comparative example 5, due to the insufficient thickness of the modified polyamide-imide paint, the topcoat layer is insufficient, and cracking occurs during the 1.5x and 1.0x winding group flexibility test, and unexpected deformation also occurs during the heat shock test, and the overall flexibility is insufficient; in comparative example 6, due to the excessive thickness of the modified polyamide-imide paint, the topcoat layer exceeds 50% of the total thickness, which reduces the heat shock resistance and heat resistance, and the softening breakdown test result is reduced to B, the overall heat resistance grade is reduced, and the mechanical property is reduced.

[0065] In conclusion, the insulated electric wire provided by the application improves the flexibility of the wire rod, and the insulated electric wire still has good electrical insulation performance at a high use temperature and is not prone to cracking. The insulated electric wire is suitable for complex groove types and is arranged more closely, thereby improving the motor slot filling rate, reducing the volume of the stator core at the same power, indirectly reducing the weight of the motor, and meeting the requirement of light weight.

Claims

1. A method for preparing an insulated wire, characterized in that, Includes the following steps: S1: Roll the conductor to the target size at least once to obtain a rolled conductor; S2: Anneal the rolled conductor to obtain an annealed conductor; S3: Apply insulating varnish to the outer periphery of the annealed conductor to form a first pre-formed core wire. Line the first pre-formed core wire coated with insulating varnish into the enameling machine. The insulating varnish is cured at high temperature to form an insulating layer. Repeat the coating and curing steps multiple times to obtain a second pre-formed core wire with an insulating layer of a predetermined thickness. S4: Apply a topcoat to the outside of the second pre-made core wire insulation layer to form a third pre-made core wire. Line the third pre-made core wire coated with topcoat into an enameling machine. After high temperature curing, a topcoat layer is formed on the outside of the insulation layer. Repeat the coating and curing steps multiple times to obtain an insulated wire. The insulating varnish mentioned in step S3 includes at least one of polyimide varnish and polyamide-imide varnish; The topcoat in step S4 is a modified polyamide-imide paint, and its preparation method further includes the following steps: (1) Long-chain aliphatic dicarboxylic acid and monocarboxylic acid are fed in a 1:1 molar ratio, and solvent A, activator and catalyst are added to react and react to obtain long-chain acid anhydride; (2) The long-chain anhydride obtained after the reaction is mixed with the short-chain anhydride to obtain a mixed anhydride. The mixed anhydride is reacted with diisocyanate to obtain a modified polyamide-imide intermediate. The modified polyamide-imide intermediate is further dissolved in solvent B to obtain a modified polyamide-imide paint.

2. The method for preparing insulated wire according to claim 1, characterized in that, In step S3, the predetermined thickness insulating layer includes a bottom layer and / or an intermediate layer.

3. The method for preparing insulated wire according to claim 1, characterized in that, In step S4, the thickness of the topcoat layer accounts for 10% to 50% of the sum of the thicknesses of the insulating layer in step S3 and the topcoat layer in step S4.

4. The method for preparing insulated wire according to claim 1, characterized in that, In step (1), the activator is dicyclohexylcarbodiimide, and the molar ratio of dicyclohexylcarbodiimide to monocarboxylic acid is 1.05~1.2:

1.

5. The method for preparing insulated wire according to claim 1, characterized in that, In step (1), the activator is added by dropping, and the reaction temperature during the dropping process is 0~10℃.

6. The method for preparing insulated wire according to claim 1, characterized in that, In step (1), the catalyst is 4-dimethylaminopyridine, and the amount of catalyst added is 10% to 20% based on the molar amount of monocarboxylic acid.

7. The method for preparing insulated wire according to claim 1, characterized in that, In step (2), the amount of long-chain anhydride fed shall not exceed 10% of the mixed anhydride.

8. The method for preparing insulated wire according to claim 7, characterized in that, In step (2), the amount of long-chain anhydride fed is 3 to 5% of the mixed anhydride.

9. The method for preparing the insulated wire according to claim 1, characterized in that, In step (2), diisocyanate is added in excess relative to the molar ratio of the mixed anhydride.

10. The method for preparing the insulated wire according to claim 9, characterized in that, In step (2), the molar ratio of diisocyanate to mixed anhydride is 1.1~1.2:1.

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