Polyimide insulating paint, preparation and application thereof

Abstract

The application provides a polyimide insulating paint, preparation and application thereof. The polyimide insulating paint comprises a polyimide precursor, a crosslinking agent and a phase separation agent, the polyimide precursor is formed by reaction of aromatic diamine and aromatic dianhydride in an organic solvent, the aromatic dianhydride comprises 3,3',4,4'-diphenyl tetracarboxylic dianhydride with a molar content of 10-30%; the phase separation agent is an organic solvent with a boiling point higher than 170 DEG C, and the content of the crosslinking agent and the phase separation agent is respectively 0.1-10wt% and 10-50wt% of the total mass of aromatic dianhydride and aromatic diamine. The application also provides an electromagnetic wire comprising a conductor and an insulating layer coated on the surface of the conductor, the insulating layer is formed by coating and curing of the polyimide insulating paint of the first aspect. The polyimide insulating paint provided by the application has the advantages of low BPDA content, low cost, resistance to ATF oil water and high PDIV.

Description

Technical Field

[0001] This invention relates to the field of insulating materials for electric motors in new energy vehicles, specifically to an oil- and water-resistant, low-dielectric polyimide insulating varnish with low biphenyl anhydride content, its preparation method, and its application. Background Technology

[0002] As new energy vehicle drive systems develop towards higher power density, higher speed, and higher voltage platforms (800V and above), the internal working environment of the motor is becoming increasingly harsh. As the core insulation material of the motor windings, the reliability of the electromagnetic wire directly determines the lifespan and safety of the drive system.

[0003] Currently, most new energy vehicle motors use an oil-cooled structure, with automatic transmission fluid (ATF) directly or indirectly contacting the winding insulation layer. Under long-term high-temperature (150-200℃), high-frequency pulse voltage, and superimposed electric field stress conditions, the insulating varnish film must not only withstand electrothermal aging but also resist the penetration and chemical erosion of polar additives, antioxidants, and trace amounts of moisture in the ATF. Therefore, ATF oil and water resistance has become one of the key indicators of high-end electromagnetic wire materials.

[0004] In existing technologies, ATF oil-water resistance is mainly achieved by increasing the content of biphenyl dianhydride (BPDA) in the polyimide molecule. For example, in the patents CN202011258014.5 and CN202011258010.7 of Sumitomo Technology (Shenzhen) Co., Ltd., the BPDA content is 30% to 90% of the total dianhydride. Due to the high price of BPDA monomers, the cost of ATF oil-water resistant electromagnetic wires remains high.

[0005] Furthermore, new energy vehicle motors generally employ high-frequency inverter drive systems composed of SiC or IGBT devices, making increasing the partial discharge initiation voltage (PDIV) a core technological direction for improving the long-term reliability of the motor. The main way to achieve a high PDIV is by reducing the dielectric constant of the insulating material.

[0006] Existing technologies typically employ multi-layer coating schemes to achieve ATF (Acid-Treated Fluorescent Agent) resistance and low dielectric properties separately, resulting in complex processes and high costs. Shenzhen Juxing New Materials Co., Ltd. (CN202511502879.4) discloses a low-dielectric polyimide resistant to corona and oil / water, but it uses fluorinated monomers to achieve low dielectric properties, leading to high costs. Aerogel Technology Co., Ltd. (US20250270371A1) discloses a hydrophobic polyimide aerogel, using a crosslinking agent to improve hydrophobicity; however, its pore structure is aerogel-type rather than bubble-type, and it is mainly used in thermal insulation materials.

[0007] Therefore, developing a low-cost polyimide insulating varnish that combines excellent ATF oil and water resistance with high PDIV is an urgent need in the field of new energy vehicle drive motor materials. Summary of the Invention

[0008] The purpose of this invention is to overcome the technical defects of existing ATF-resistant polyimide insulating varnishes, which require high BPDA content, resulting in high cost, and the difficulty in simultaneously achieving high PDIV. This invention provides a low-BPDA content, low-cost polyimide insulating varnish that combines ATF resistance and high PDIV, and its preparation method. Furthermore, by applying the polyimide insulating varnish to a conductor, an electromagnetic wire that is resistant to ATF resistance and high PDIV is obtained.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polyimide insulating varnish comprising a polyimide precursor, a crosslinking agent, and a phase separating agent. The polyimide precursor is formed by reacting an aromatic diamine with an aromatic dianhydride in an organic solvent, wherein the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.9 to 1.1:1, and the aromatic dianhydride contains 10-30% molar amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). The crosslinking agent is present in an amount of 0.1-10 wt% of the total mass of the aromatic dianhydride and the aromatic diamine. The phase separating agent is an organic solvent with a boiling point higher than 170°C, and its content is 10-50 wt% of the total mass of the aromatic dianhydride and the aromatic diamine.

[0010] Preferably, the aromatic dianhydrides included in the aromatic dianhydrides, excluding 3,3',4,4'-biphenyltetracarboxylic dianhydride, include, but are not limited to, one or more of the following: pyromellitic dianhydride (PMDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), 4,4'-(hexafluoroisopropyl)diphthalic anhydride (6FDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), bisphenol A type dianhydride (BPADA), and naphthalene tetracarboxylic dianhydride (NTDA).

[0011] Preferably, the aromatic diamine includes, but is not limited to, one or more of 4,4'-diaminodiphenyl ether (ODA), m-phenylenediamine (m-PDA), p-phenylenediamine (p-PDA), 4,4'-diaminodiphenylmethane (DDM), 3,3'-diaminodiphenyl sulfone (3,3'-DDS), 4,4'-diaminodiphenyl sulfone (4,4'-DDS), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), and 4,4'-diaminobiphenyl.

[0012] The polyimide insulating varnish further includes a solvent, which is an organic solvent introduced during the reaction of aromatic diamine and aromatic dianhydride. The organic solvent is a polar aprotic solvent, preferably at least one of N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The amount of organic solvent added is determined based on the solid content of the polyimide precursor, satisfying the following relationship: Organic solvent addition amount = (diamine + dianhydride + crosslinking agent) / solid content of polyimide insulating varnish - (diamine + dianhydride + crosslinking agent + phase separating agent). The solid content of the polyimide insulating varnish is 12-35 wt%, preferably 18-30 wt%, more preferably 25-28 wt%. This invention refers to JB / T 7599.1-2013 Enamelled Wire Insulating Varnish, Part 1: General Provisions to determine the solid content of the insulating varnish, wherein the baking conditions in the oven are: baking at 180°C for 1 hour.

[0013] Preferably, the polyimide insulating varnish has a weight-average molecular weight of 15,000-80,000 and a viscosity of 1,000-30,000 cp (20°C).

[0014] Preferably, the crosslinking agent is selected from at least one of multifunctional crosslinking agents and crosslinking agents containing carbon-carbon double or triple bonds. The multifunctional crosslinking agent is an isocyanate or epoxy resin containing at least two functional groups in the molecule that can react with the polyimide end group. The functional group is selected from at least one of isocyanate group and epoxy group. More preferably, the isocyanate is selected from one or more products with the brand names BIH-1080, Vestanet B1358A, BI7951, PL340BA / SN, BI7963, BL 3175, BL 3300, BL 4825, BL 4190, BL 5100, BL 2200, BL32, BL37, BL201, BLN320, VESTAGON™ BI1401, VESTAGON™ 80, VESTAGON™ NX 153, VESTAGON™ LC 1008, ISONATE™ B135, ISONATE™ B1964, VESTAGON™ TBX 300, and VESTAGON™ R960; the epoxy resin is selected from one or more products with the brand names Araldite MY721, Araldite MY720, DEN 438, and Epon. One or more of the following products: 1031, AralditeMY0510, EPN 1180 Epoxy Novolac, YDPN-638 Epoxy Novolac Resin, and ERISYS GA-240; wherein the crosslinking agent containing carbon-carbon double or triple bonds is selected from one or more of maleic anhydride, norbornene anhydride, 4-phenylethynyl phthalic anhydride (PEPA), and 4-ethynyl aniline.

[0015] Preferably, the phase separating agent is selected from one or more of the following: dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisodecyl phthalate, dinonyl phthalate, diisobutyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol monophenyl ether, triphenyl phosphate, tricresyl phosphate, tributyl phosphate, trioctyl phosphate, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, diisodecyl adipate, tributyl citrate, triethyl citrate, and acetylated tributyl citrate.

[0016] More preferably, the content of the phase separating agent is 30-40 wt% of the total mass of dianhydride and diamine.

[0017] Preferably, the polyimide insulating varnish further comprises a bubble control agent, the content of which accounts for 0.1-1% of the total mass of the polyimide insulating varnish, more preferably 0.3-0.5%.

[0018] More preferably, the bubble control agent is selected from one or more of the following: silicon-based, modified silicon-based, polyether-based, mineral oil-based, organosilicon polyether-based, fatty alcohol-based, and fatty acid ester-based.

[0019] In a second aspect, the present invention provides a method for preparing the polyimide insulating varnish described in the first aspect, comprising the following steps: reacting an aromatic diamine and an aromatic dianhydride in an organic solvent, controlling the molar ratio of the aromatic diamine to the aromatic dianhydride to be 0.9~1.1:1, to prepare a polyimide precursor (i.e., polyamic acid) solution; adding a crosslinking agent to the obtained solution and stirring evenly at room temperature; adding a phase separating agent and stirring evenly at room temperature to obtain the polyimide insulating varnish.

[0020] Preferably, the reaction conditions for the aromatic diamine and aromatic dianhydride are: stirring at room temperature for 10-15 hours.

[0021] Preferably, the preparation method further includes: after adding a phase separating agent and stirring evenly at room temperature, adding a bubble control agent and stirring evenly at room temperature to obtain a polyimide insulating varnish.

[0022] This invention provides a rapid method for evaluating the ATF oil-water resistance of polyimide insulating varnish. The ATF oil-water resistance test method is relatively complex. According to new energy industry standards, it is currently required to add 2000ppm water to the ATF oil, hold it at -40℃ for 8 hours under sealed conditions, then rapidly heat it to 155℃ and hold it for 40 hours, subjecting it to 8 cycles of high and low temperature shock. Testing one product typically takes about 16 days (excluding preparation and testing time). This invention provides a rapid simulation test method by preparing a PI film and then immersing it in 5wt% liquid alkali at 40℃ for 24 hours to simulate screening. Extensive test data shows that after immersion in 5wt% liquid alkali at 40℃ for 24 hours, the film retains over 90% of its mechanical properties (elongation at break), and the corresponding breakdown voltage retention rate in the ATF oil-water resistance test (2000ppm water content) can reach over 80%.

[0023] Thirdly, the present invention also provides an electromagnetic wire comprising a conductor and an insulating layer coated on the surface of the conductor, the insulating layer being formed by coating and curing the polyimide insulating varnish described in the first aspect.

[0024] In some embodiments, the curing is thermosetting. During thermosetting, the polyimide precursor is converted into polyimide through thermal imidization and forms a crosslinked structure through a crosslinking agent, while bubbles are formed in the coating through a phase separating agent. The volume percentage of bubbles in the insulating layer is 20-50%, more preferably 30-40%; the average diameter of the bubbles is 1-8 μm, more preferably 1-5 μm, and most preferably 1-3 μm.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. The polyimide insulating varnish of the present invention reduces the amount of BPDA used from 60-90% in the traditional solution to 10-30%, and maintains excellent oil and water resistance by adding a crosslinking agent, thereby reducing the raw material cost by 30-50%.

[0026] 2. The same coating forms bubbles through a phase separating agent, which can simultaneously achieve oil and water resistance and high PDIV, simplifying the production process and avoiding the complex process of multi-layer coating.

[0027] 3. By adding optional bubble control agents, precise control of bubble size can be achieved. After imidization, the average diameter of the bubbles can be controlled within 1-3 μm, ensuring low dielectric constant and high PDIV while maintaining good mechanical properties. Detailed Implementation

[0028] The present invention will be further illustrated by specific embodiments below, but the present invention is not limited thereto.

[0029] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.

[0030] Example 1: A solution of 0.1 mol 4,4'-diaminodiphenyl ether (ODA) and 1.4 mol N,N-dimethylacetamide (DMAC) was dissolved by stirring in a reactor. Then, 0.067 mol pyromellitic dianhydride (PMDA) and 0.03 mol 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added, and the mixture was stirred at room temperature for 12 h to prepare a polyamic acid solution. Then, 3 wt% (relative to the total mass of diamine and dianhydride) of the multifunctional crosslinking agent BIH-1080 was added, and the mixture was stirred evenly at room temperature for 3 h. 30 wt% (relative to the total mass of diamine and dianhydride) of dibutyl phthalate was added as a phase separating agent, and the mixture was stirred evenly for 2 h. Finally, 0.3 wt% of the bubble control agent BYK-085 was added, and the mixture was stirred evenly at room temperature for 6 h. The product was discharged to obtain a polyimide insulating varnish with a solid content of 25 ± 1.5% and a viscosity of 12000 cp (20℃). Viscosity testing was performed using a Bollerfeld CAP2000+ low-temperature cone-plate viscometer with rotor #4 at 25 rpm. The weight-average molecular weight of the obtained polyamic acid was 45,000.

[0031] Sample Preparation and Evaluation: The above-mentioned polyimide insulating varnish was uniformly coated onto a glass plate using a doctor blade with a 300-micron graduation. It was then placed in a forced-air oven for baking at 80℃ for 20 minutes, followed by a temperature increase to 350℃ at a rate of 3℃ / min, and then held at 350℃ for 20 minutes. After cooling to room temperature, a polyimide film of approximately 50 microns was obtained. The volume of the polyimide film was measured to be 30% by air bubbles. The average diameter of the air bubbles was measured to be 2 microns using SEM.

[0032] The molecular weights were obtained using GPC (with PS as a standard), and the volume fraction of bubbles in the film was obtained using the density method.

[0033] Bubble volume fraction r app Apparent density r ture Intrinsic density.

[0034] Examples 2-8: Following the method described in Example 1, the types and amounts of raw materials are shown in Examples 2-8 of Table 1, and polyimide insulating varnish is obtained.

[0035] Table 1. Types and Dosage of Raw Materials

[0036] Note: The amounts of crosslinking agent, phase separating agent, and bubble control agent added in Table 1 are all calculated as the proportion of their mass to the total mass of aromatic dianhydride and aromatic diamine.

[0037] Comparative Example 1: The method described in Example 1 is different in that the content of BPDA is increased to 60% (i.e., the molar ratio of dianhydride is BPDA:PMDA=0.6:0.4), while the types and amounts of other raw materials are the same as in Example 1, to obtain polyimide insulating varnish.

[0038] Comparative Example 2: The method described in Example 1 is different in that no multifunctional crosslinking agent is added, while the types and amounts of other raw materials are the same as in Example 1, to obtain polyimide insulating varnish.

[0039] Comparative Example 3: The method described in Example 1 is different in that the content of BPDA is increased to 50% (i.e., the molar ratio of dianhydride is BPDA:PMDA=0.5:0.5), and no multifunctional crosslinking agent is added. The types and amounts of other raw materials are the same as in Example 1, and polyimide insulating varnish is obtained.

[0040] Comparative Example 4: The method described in Example 1 is different in that no phase separating agent is added, while the types and amounts of other raw materials are the same as in Example 1, to obtain polyimide insulating varnish.

[0041] Comparative Example 5: The method described in Example 1 is different in that no multifunctional crosslinking agent or phase separating agent is added, while the types and amounts of other raw materials are the same as in Example 1, to obtain polyimide insulating varnish.

[0042] Comparative Example 6: The polyimide insulating varnish was obtained by following the method described in Example 1, except that no bubble control agent was added, while the types and amounts of other raw materials were the same as in Example 1.

[0043] Electromagnetic wire preparation

[0044] The polyimide insulating varnishes prepared in Examples 1-8 and Comparative Examples 1-6 were coated onto 0.9mm copper wires. Excess varnish was scraped off through a mold, and the wires were placed in an oven (front section 280℃, middle section 420℃, outlet 480℃) and rapidly cooled with cold air. The coating was repeated 20 times to obtain the electromagnetic wire.

[0045] Performance testing

[0046] The electromagnetic wires prepared above were subjected to rapid hydrolysis resistance mechanical property retention rate test, ATF oil and water resistance breakdown voltage retention rate test and PDIV test, respectively. The test methods are as follows, and the test results are shown in Table 2.

[0047] 1. Rapid hydrolysis resistance test: The insulating varnish was coated into a thin film (approximately 50 μm thick). Curing conditions: baking at 80℃ for 20 min, followed by baking at 3℃ / min to 350℃ for 20 min. The film was then immersed in a 5% NaOH aqueous solution at 40℃ for 24 h, and the elongation at break retention rate was tested.

[0048] 2. ATF oil and water resistance test: Add 2000ppm water to ATF oil, keep the electromagnetic wire sealed at -40℃ for 8h, then rapidly heat to 155℃ and keep at 155℃ for 40h, and continuously perform 8 cycles of high and low temperature shock to test the breakdown voltage retention rate.

[0049] 3. PDIV test: The partial discharge initiation voltage is tested according to IEC 60851-5 standard, and the peak voltage at a boost rate of 25V / s is taken as PDIV.

[0050] 4. Dielectric constant :according to The dielectric constant is calculated, where V refers to the PDIV peak voltage (partial discharge initiation voltage), tested at a boost rate of 25V / s; t refers to the film thickness. This represents the dielectric constant.

[0051] Table 2 Performance Test Results

[0052] As shown in Table 2, the addition of the crosslinking agent significantly improves the ATF oil and water resistance of the lacquered wire; the addition of the phase separating agent significantly improves the PDIV of the lacquered wire and reduces the dielectric constant; the addition of the bubble control agent reduces the average diameter of the bubbles, thereby improving the PDIV of the lacquered wire and reducing the dielectric constant. The overall performance of the embodiments of the present invention is significantly better than that of the comparative embodiments. While ensuring a low dielectric constant, good appearance and bubble control, it achieves excellent ATF oil and water resistance and has higher application value.

Claims

1. A polyimide insulating varnish, characterized in that: The polyimide insulating varnish comprises a polyimide precursor, a crosslinking agent, and a phase separating agent. The polyimide precursor is formed by reacting an aromatic diamine with an aromatic dianhydride in an organic solvent. The molar ratio of the aromatic diamine to the aromatic dianhydride is 0.9 to 1.1:

1. The aromatic dianhydride contains 10-30% molar amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride. The crosslinking agent content is 0.1-10 wt% of the total mass of the aromatic dianhydride and the aromatic diamine. The phase separating agent is an organic solvent with a boiling point higher than 170°C, and its content is 10-50 wt% of the total mass of the aromatic dianhydride and the aromatic diamine.

2. The polyimide insulating varnish as described in claim 1, characterized in that: The aromatic dianhydrides, excluding 3,3',4,4'-biphenyltetracarboxylic dianhydride, include other aromatic dianhydrides selected from one or more of the following: pyromellitic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyl)diphthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bisphenol A type dianhydride, and naphthalene tetracarboxylic dianhydride. The aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, and 4,4'-diaminobiphenyl.

3. The polyimide insulating varnish as described in claim 1, characterized in that: The polyimide insulating varnish also includes a solvent, which is an organic solvent introduced during the reaction of an aromatic diamine and an aromatic dianhydride. The organic solvent is a polar aprotic solvent selected from at least one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide.

4. The polyimide insulating varnish according to any one of claims 1-3, characterized in that: The solid content of the polyimide insulating varnish is 12-35 wt%.

5. The polyimide insulating varnish according to any one of claims 1-3, characterized in that: The crosslinking agent is selected from at least one of multifunctional crosslinking agents and crosslinking agents containing carbon-carbon double or triple bonds; the multifunctional crosslinking agent is an isocyanate crosslinking agent or an epoxy resin crosslinking agent containing at least two functional groups in the molecule that can react with the polyimide end group, and the functional group is selected from at least one of isocyanate group and epoxy group.

6. The polyimide insulating varnish according to any one of claims 1-3, characterized in that: The phase separating agent is selected from one or more of the following: dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisodecyl phthalate, dinonyl phthalate, diisobutyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol monophenyl ether, triphenyl phosphate, tricresyl phosphate, tributyl phosphate, trioctyl phosphate, polyethylene glycol, polypropylene glycol, polytetrahydrofuran, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, diisodecyl adipate, tributyl citrate, triethyl citrate, and acetylated tributyl citrate.

7. The polyimide insulating varnish according to any one of claims 1-3, characterized in that: The polyimide insulating varnish also contains a bubble control agent, the content of which accounts for 0.1-1% of the total mass of the polyimide insulating varnish.

8. The polyimide insulating varnish as described in claim 7, characterized in that: The bubble control agent is selected from one or more of the following: silicon-based, modified silicon-based, polyether-based, mineral oil-based, organosilicon polyether-based, fatty alcohol-based, and fatty acid ester-based.

9. A method for preparing a polyimide insulating varnish as described in any one of claims 1-8, characterized in that: The preparation method includes the following steps: reacting an aromatic diamine and an aromatic dianhydride in an organic solvent, controlling the molar ratio of the aromatic diamine to the aromatic dianhydride to be 0.9~1.1:1, to prepare a polyimide precursor solution; adding a crosslinking agent to the obtained solution and stirring evenly at room temperature; adding a phase separating agent and stirring evenly at room temperature to obtain a polyimide insulating varnish.

10. The preparation method according to claim 9, characterized in that: The preparation method further includes: after adding a phase separating agent and stirring evenly at room temperature, adding a bubble control agent and stirring evenly at room temperature to obtain a polyimide insulating varnish.

11. An electromagnetic wire comprising a conductor and an insulating layer coated on the surface of the conductor, characterized in that: The insulating layer is formed by coating and curing the polyimide insulating varnish as described in any one of claims 1-8.

12. The electromagnetic wire as described in claim 11, characterized in that: The volume percentage of bubbles in the insulating layer is 20-50%; the average diameter of the bubbles is 1-8 μm.

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