Insulated wire with high PDIV value and preparation method thereof

Abstract

The invention provides an insulated wire with a high PDIV value and a preparation method thereof, the insulated wire comprises a copper conductor, a first insulating layer and polyamide acid slurry, the surface of the copper conductor is coated with the first insulating layer, and preparation raw materials of the polyamide acid slurry comprise a dianhydride monomer, a diamine monomer and an end-capping reagent; the end-capping reagent comprises amino group end-capped polyalkylene oxide and / or anhydride group end-capped polyalkylene oxide; the amino-terminated polyalkylene oxide and / or anhydride-terminated polyalkylene oxide are / is selected as the end-capping reagent, so that the storage stability of the obtained polyamide acid slurry is remarkably improved, and the dielectric constant of a polyimide coating obtained by molding the polyamide acid slurry is effectively reduced; furthermore, an insulated wire prepared from the polyamide acid slurry has a relatively high PDIV value and is suitable for being applied to a high-voltage motor winding.

Description

[0001] This application is a divisional application. The application number of the parent application is 202310889225.6. The application date is July 19, 2023. The name of the invention is “A polyamic acid slurry, its preparation method and application”. Technical Field

[0002] The invention belongs to the technical field of polyamide, and particularly relates to an insulating wire with a high PDIV value and a preparation method thereof. Background Art

[0003] With the continuous advancement of technology, new energy electric vehicles are developing rapidly, and the 800V high-voltage platform is the only way to go in the future. However, the 800V high-voltage platform brings not only faster charging efficiency and longer driving range, but also more severe insulation and safety challenges compared to the 400V system. For motors used in new energy vehicles, high voltage poses a higher voltage resistance challenge to the insulation of the motor windings. Improper handling will reach the breakdown field strength in the local area of ​​the insulation, especially near the tip of the charged body, forming local discharge. Strong local discharge will destroy the insulation performance of the winding wire, causing the motor to short-circuit and cause the motor to fail.

[0004] At present, in order to accurately measure and evaluate the insulation performance of winding wires, PDIV (partial discharge inception voltage) is often used as an insulation evaluation parameter. The higher the PDIV, the better the insulation of the winding wire. The PDIV value of the winding wire can be estimated according to the following empirical formula:

[0005]

[0006] Where V represents the PDIV value (Vrms), t represents the thickness of the insulating material, and ε γ Represents the relative dielectric constant of the insulating material. It can be found that the PDIV value is proportional to the thickness of the insulating material and inversely proportional to the relative dielectric constant of the insulating material. Therefore, if you want to improve the PDIV value of the winding wire, you can also increase the thickness of the insulating paint or use a material with a low dielectric constant as the insulating paint. However, in order to maximize the utilization efficiency of the winding wire, the current technical direction is to increase its PDIV value without increasing the thickness of the paint film as much as possible. Therefore, reducing the low dielectric constant of the insulating paint material has become the most effective solution to improve the PDIV value of the winding.

[0007] Polyimide material is a commonly used winding wire insulation film material. However, the dielectric constant of ordinary aromatic polyimide material is usually between 3.2 and 4.0C. 2 / (N·M 2)(1KHz), which cannot meet the requirements of the microelectronics industry for the continuous reduction of the dielectric properties of dielectric materials. In addition, the conventional method for preparing polyimide film is to first prepare a polyamic acid slurry, and then dehydrate the polyamic acid slurry at high temperature to achieve imidization. However, the reaction of polyamic acid is a reversible reaction. Therefore, in order to maintain the viscosity stability of polyamic acid, the polyamic acid must be kept at a low temperature.

[0008] The commonly used method is to reduce the dielectric constant of polyimide by introducing low dielectric substances or reducing the concentration of imide groups. CN111844976A discloses a preparation method, preparation method and application of a polyimide / fluoropolymer insulation composite material, the method comprising the following steps: 1) the surface of the polyimide film is treated by a corona process, and then a fluoropolymer emulsion is coated, and a fluoropolymer bonding layer is prepared after high-temperature drying and sintering; 2) the surface of the composite material formed in step 1) is hot-pressed with a fluoropolymer insulation outer layer by a bimetallic roller to prepare a polyimide / fluoropolymer insulation composite material with a composite structure, the composite material comprising: a polyimide insulation base layer, a fluoropolymer bonding layer and a fluoropolymer insulation outer layer, and at least one side surface of the polyimide insulation base layer is connected to the fluoropolymer insulation outer layer by a fluoropolymer bonding layer. Through the above-mentioned method, the present invention can integrate excellent heat resistance, mechanical properties, electrical properties, waterproof, oil-proof, scratch-resistant, chemical corrosion-resistant and other characteristics, and the prepared composite system has strong adhesion. Although this method can effectively reduce the dielectric parameters of the composite material, the process is too complicated to be applied to the coating process of enameled wire.

[0009] JP2013253124A discloses a polyimide resin varnish capable of forming an insulating layer with a low dielectric constant, and provides an insulated wire capable of improving corona discharge initiation, wherein the polyimide resin varnish has a polyimide precursor resin as a main component, the polyimide precursor resin being obtained by reacting an aromatic diamine with an aromatic tetracarboxylic anhydride, wherein the imide group concentration of the polyimide precursor resin after imidization is >35.0% and <36.0%, but this method results in the enameled wire having a heat resistance that is difficult to meet the use requirements.

[0010] In summary, developing a polyamic acid slurry with a low dielectric constant after molding to meet the requirements of new energy motors for withstanding high partial discharge starting voltages during operation is still a technical problem that needs to be urgently solved in this field. Summary of the invention

[0011] In view of the shortcomings of the prior art, the object of the present invention is to provide an insulated wire with a high PDIV value and a preparation method thereof. The polyamic acid slurry has excellent storage stability, and the polyimide coating obtained after molding has a low dielectric constant, so that the further prepared insulated wire has a high PDIV value, which is suitable for use in high-voltage motor windings, especially new energy high-voltage motor windings.

[0012] To achieve this object, the present invention adopts the following technical solutions:

[0013] In a first aspect, the present invention provides a polyamic acid slurry, wherein the raw materials for preparing the polyimide slurry include a dianhydride monomer, a diamine monomer and a capping agent;

[0014] The end-capping agent includes amino-end-capped polyalkylene oxide and / or anhydride-end-capped polyalkylene oxide.

[0015] The raw materials for preparing the polyamic acid slurry provided by the present invention include dianhydride monomers, diamine monomers and end-capping agents, and the end-capping agents are limited to amino-terminated polyalkylene oxides and / or anhydride-terminated polyalkylene oxides. On the one hand, the addition of the specific end-capping agents can significantly improve the storage stability of the polyamic acid slurry. On the other hand, during the process of coating the polyamic acid slurry on the surface of a substrate and heating and molding, the polyalkylene oxide will decompose to form uniform nanopores, thereby effectively reducing the dielectric constant of the polyimide coating obtained after molding, so that the further prepared insulating wire has a higher PDIV value.

[0016] Preferably, the dianhydride monomer comprises aromatic tetracarboxylic dianhydride.

[0017] Preferably, the aromatic tetracarboxylic dianhydride includes 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, (4-phthalic anhydride)formyloxy-4-phthalate, bis[(3,4-dianhydride)phenyl]terephthalate, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, p-phenylene-diphenyltrimethic acid Any one of ester dianhydride, 4,4'-terephthalic anhydride, pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxybenzoyloxy)phenyl)hexafluoropropane dianhydride or 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride or a combination of at least two thereof.

[0018] Preferably, the diamine monomer includes any one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzanilide, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 4,4'-diaminodiphenyl sulfone, 2-(4-aminophenyl)-5-aminobenzimidazole, 2,2-bis(4-hydroxy-3-aminophenyl)propane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-biphenyl or 9,9-bis(4-aminophenyl)fluorene, or a combination of at least two thereof.

[0019] Preferably, the amino-terminated polyalkylene oxide has a structure as shown in the following formula I:

[0020]

[0021] In formula I, A is a benzene ring, R1 and R2 are each independently selected from H, halogen, methyl or ethyl, and n is selected from an integer between 2 and 20 (e.g., 4, 6, 8, 10, 12, 14, 16 or 18, etc.).

[0022] It should be noted that the amino-terminated polyalkylene oxide having the structure shown in Formula I can be prepared by the following method: reacting the polyalkylene oxide with the corresponding nitrobenzoyl chloride derivative at low temperature to obtain the corresponding intermediate, and then dehydrating or reducing the intermediate to obtain the amino-terminated polyalkylene oxide having the structure shown in Formula I.

[0023] Preferably, the anhydride-terminated polyalkylene oxide has a structure as shown in the following formula II:

[0024]

[0025] In formula II, A is a benzene ring, R1 and R2 are each independently selected from H, halogen, methyl or ethyl, and n is selected from an integer between 2 and 20 (e.g., 4, 6, 8, 10, 12, 14, 16 or 18, etc.).

[0026] It should be noted that the anhydride-terminated polyalkylene oxide having the structure shown in Formula II can be prepared according to the following method: at low temperature, the polyalkylene oxide is reacted with the corresponding benzoyl chloride derivative substituted with phthalic anhydride to prepare the corresponding ester intermediate, and then the above ester intermediate is dehydrated or reduced to obtain the anhydride-terminated polyalkylene oxide having the structure shown in Formula II.

[0027] Preferably, the number average molecular weight of the amino-terminated polyalkylene oxide and the anhydride-terminated polyalkylene oxide is independently 100 to 2000, for example, 200, 400, 600, 800, 1000, 1200, 1400, 1600 or 1800, and more preferably 300 to 1200.

[0028] Preferably, the total molar ratio of the amino group to the anhydride group in the dianhydride monomer, the diamine monomer and the end-capping agent is 1:1.

[0029] Preferably, based on the total molar number of the dianhydride monomer, the diamine monomer and the capping agent as 100%, the added amount of the capping agent is 0.1 to 0.5 mol, for example, 0.02 mol, 0.04 mol, 0.06 mol, 0.08 mol, 0.1 mol, 0.12 mol, 0.14 mol, 0.16 mol or 0.18 mol, etc., and more preferably 0.01 to 0.15 mol.

[0030] As a preferred technical solution of the present invention, if the amount of the end-capping agent added is relatively large, the viscosity of the polyamic acid slurry will be relatively low under the same solid content conditions, and the porosity will be too high after curing, resulting in a significant reduction in mechanical properties. If the amount of the end-capping agent added is relatively low, the viscosity of the polyamic acid slurry will be relatively high under the same solid content conditions, and the porosity will be too high after curing, resulting in a high dielectric constant, and the dielectric properties cannot meet the use requirements.

[0031] Preferably, the solid content of the polyamic acid slurry is 15-35%, for example, 17%, 19%, 21%, 23%, 25%, 27%, 29%, 31% or 33%, etc.

[0032] Preferably, the viscosity of the polyamic acid is 2000-20000 cp, for example, 4000 cp, 6000 cp, 8000 cp, 10000 cp, 12000 cp, 14000 cp, 16000 cp or 18000 cp.

[0033] In a second aspect, the present invention provides a method for preparing the polyamic acid slurry as described in the first aspect, the preparation method comprising: reacting a diamine monomer and a dianhydride monomer in a polar solvent, adding a capping agent to continue the reaction, and obtaining the polyamic acid slurry.

[0034] In the present invention, the mechanism diagram of the reaction of the amino-terminated polyalkylene oxide as a capping agent with the diamine monomer and the dianhydride monomer is shown in the following formula:

[0035]

[0036] In the present invention, the mechanism diagram of the reaction of anhydride-terminated polyalkylene oxide as a capping agent with a diamine monomer and a dianhydride monomer is shown in the following formula:

[0037]

[0038] Preferably, the polar solvent includes any one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), γ-butyrolactone, propylene glycol monomethyl ether, cyclopentanone, cyclohexanone, ethyl acetate, toluene or methyl ethyl ketone, or a combination of at least two thereof, and more preferably N,N-dimethylformamide and / or N,N-dimethylacetamide.

[0039] In a third aspect, the present invention provides an insulated wire, the insulated wire comprising a conductor, the conductor being sequentially coated with an insulating layer;

[0040] The raw material for preparing the insulating layer includes the polyamic acid slurry as described in the first aspect.

[0041] Preferably, the conductor comprises a copper conductor.

[0042] In a fourth aspect, the present invention provides a method for preparing the insulated wire as described in the third aspect, the preparation method comprising: coating the polyamic acid slurry as described in the first aspect on the surface of a conductor, and heat treating the conductor to obtain the insulated wire.

[0043] Preferably, the temperature of the heat treatment is 80-500°C, for example, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C or 450°C.

[0044] In a fifth aspect, the present invention provides a use of the insulating wire as described in the fourth aspect as a motor winding wire.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The polyamic acid slurry provided by the present invention comprises a dianhydride monomer, a diamine monomer and a capping agent; the capping agent comprises an amino-terminated polyalkylene oxide and / or an anhydride-terminated polyalkylene oxide; by selecting the amino-terminated polyalkylene oxide and / or the anhydride-terminated polyalkylene oxide as the capping agent, on the one hand, the storage stability of the polyamic acid slurry is significantly improved, and on the other hand, the dielectric constant of the polyimide coating formed after the polyamic acid slurry is formed is effectively reduced, so that the insulated wire prepared by using the polyamic acid slurry provided by the present invention has a higher PDIV value and is suitable for use in high-voltage motor windings of 800V or even higher. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Preparation Example 1

[0049] An amino-terminated polyalkylene oxide M1, whose number average molecular weight is 720, and whose specific structure is as follows:

[0050]

[0051] The preparation method thereof comprises the following steps:

[0052] (1) Weigh 60 g (0.1 mol) of polyethylene glycol (molecular weight 600) and add it to a 1 L three-necked reaction flask, add 500 mL of anhydrous 1,4-dioxane (1,4-Dioxane) and 0.15 mol of pyridine (Py); then dissolve 27.75 g (0.15 mol) of p-nitrobenzoyl chloride in 200 mL of anhydrous dichloromethane, and then add it dropwise to the above three-necked flask through a constant pressure dropping funnel, and react at 0° C. overnight; pour the obtained reaction solution into a large amount of petroleum ether, a large amount of white solid precipitates, and filter the filter cake; separate and purify the filter cake by GPC, spin dry the solvent and vacuum dry to obtain 68.6 g of a white intermediate (yield = 91.4%);

[0053] (2) 68.6 g (0.92 mol) of the intermediate was added to ethanol, palladium carbon was added and reacted at room temperature for 24 h, the palladium carbon was filtered off, the ethanol was spin-dried to obtain a crude product, and then the crude product was separated and purified by GPC to obtain 62.4 g of a white solid (yield = 94.6%), which was amino-terminated polyalkylene oxide M1;

[0054] The specific reaction chemical formula of the above preparation method is as follows:

[0055]

[0056] Preparation Example 2

[0057] An amino-terminated polyalkylene oxide M2, whose number average molecular weight is 1120, and whose specific structure is as follows:

[0058]

[0059] The preparation method comprises the following steps:

[0060] (1) 100 g (0.16 mol) of polyethylene glycol (molecular weight 600) was weighed and added to a 1 L three-necked reaction flask, and 600 mL of anhydrous 1,4-dioxane and 0.15 mol of pyridine (Py) were added; 27.75 g (0.15 mol) of p-nitrobenzoyl chloride was then dissolved in 200 mL of anhydrous dichloromethane, and then added dropwise to the above three-necked flask through a constant pressure dropping funnel, and reacted at 0° C. overnight; the obtained reaction solution was poured into a large amount of petroleum ether, a large amount of white solid precipitated, and the filter cake was collected by filtration; the filter cake was separated and purified by GPC, the solvent was spin-dried and vacuum dried to obtain 106.1 g of a white intermediate (yield = 92.3%);

[0061] (2) 106.1 g (0.92 mol) of the intermediate was added to ethanol, palladium carbon was added and reacted at room temperature for 24 h, the palladium carbon was filtered off, the ethanol was dried to obtain a crude product, and then the crude product was separated and purified by GPC to obtain 96.8 g (yield = 93.7%) of a white solid, i.e., amino-terminated polyalkylene oxide M2;

[0062] The specific reaction chemical formula of the above preparation method is as follows:

[0063]

[0064] Preparation Example 3

[0065] An anhydride-terminated polyalkylene oxide M3, whose number average molecular weight is 775, has a specific structure as shown below:

[0066]

[0067] The preparation method comprises the following steps:

[0068] (1) Weigh 60 g (0.1 mol) of polyethylene glycol (molecular weight 600) and add it to a 1 L three-necked reaction flask, add 500 mL of anhydrous 1,4-dioxane and 0.15 mol of pyridine (Py); then dissolve 31.58 g (0.15 mol) of 1,2,4-trimellitic anhydride chloride in 200 mL of anhydrous dichloromethane, then add it dropwise to the three-necked flask through a constant pressure dropping funnel, and react overnight at 0° C.; pour the obtained reaction solution into a large amount of petroleum ether, a large amount of white solid precipitates, and filter the filter cake; separate and purify the filter cake by GPC, spin dry the solvent and vacuum dry to obtain 70.6 g of a white intermediate (yield = 90.3%);

[0069] (2) 70.6 g (0.90 mol) of the intermediate was added to 200 g of acetic anhydride, and the mixture was refluxed for 12 hours. The acetic anhydride was evaporated to obtain a crude product, which was then separated and purified by GPC to obtain 68.7 g of a white solid (yield = 97.3%), i.e., anhydride-terminated polyalkylene oxide M3.

[0070] The specific reaction chemical formula of the above preparation method is as follows:

[0071]

[0072] Example 1

[0073] A polyamic acid slurry, the preparation method of which comprises: under nitrogen protection, adding DMAc (35.9 kg) into a 100 L reactor, then adding 4,4'-diaminodiphenyl ether (5.767 kg, 29 mol), adding pyromellitic dianhydride (6.544 kg, 30 mol) in batches at 50° C., reacting for 18 hours, adding amino-terminated polyalkylene oxide M1 (Preparation Example 1, 1.44 kg, 2 mol), continuing to react at 50° C. for 6 hours, and obtaining a polyamic acid slurry with a solid content of 26% and a viscosity of 13700 cp.

[0074] Example 2

[0075] A preparation method of a polyamic acid slurry comprises: under nitrogen protection, adding DMAc (35.8 kg) into a 100 L reactor, then adding 4,4'-diaminodiphenyl ether (5.887 kg, 29.4 mol), adding pyromellitic dianhydride (6.544 kg, 30 mol) in batches at 50° C., reacting for 18 hours, adding amino-terminated polyalkylene oxide M2 ​​(Preparation Example 2, 1.344 kg, 1.2 mol), and continuing to react at 50° C. for 6 hours to obtain a polyamic acid slurry with a solid content of 26% and a viscosity of 17200 cp.

[0076] Example 3

[0077] A preparation method of a polyamic acid slurry comprises: under nitrogen protection, adding DMAc (37.4 kg) into a 100 L reactor, then adding 4,4'-diaminodiphenyl ether (6.007 kg, 30 mol), adding pyromellitic dianhydride (6.413 kg, 29.4 mol) in batches at 0°C, reacting for 18 hours, adding anhydride-terminated polyalkylene oxide M3 (Preparation Example 3, 0.93 kg, 1.2 mol), and continuing to react at 0°C for 6 hours to obtain a polyamic acid slurry with a solid content of 15% and a viscosity of 14300 cp.

[0078] Example 4

[0079] A preparation method of a polyamic acid slurry comprises: under nitrogen protection, adding DMAc (36.2 kg) into a 100 L reactor, then adding 4,4'-diaminodiphenyl ether (5.887 kg, 29.4 mol), adding pyromellitic dianhydride (6.544 kg, 30 mol) in batches at 50° C., reacting for 18 hours, adding amino-terminated polyalkylene oxide M1 (Preparation Example 1, 0.86 kg, 1.2 mol), and continuing to react at 50° C. for 6 hours to obtain a polyamic acid slurry with a solid content of 26% and a viscosity of 17900 cp.

[0080] Example 5

[0081] A polyamic acid slurry is provided, which differs from Example 1 only in that the addition amount of the amino-terminated polyalkylene oxide M1 provided in Preparation Example 1 is 0.4 mol, and the addition amount of 4,4'-diaminodiphenyl ether is 29.8 mol, to obtain a polyamic acid slurry with a solid content of 26% and a viscosity of 38400 cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0082] Example 6

[0083] A polyamic acid slurry is provided, which differs from Example 1 only in that the addition amount of the amino-terminated polyalkylene oxide M1 provided in Preparation Example 1 is 10 mol, and the addition amount of 4,4'-diaminodiphenyl ether is 25 mol, to obtain a polyamic acid slurry with a solid content of 26% and a viscosity of 8600 cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0084] Comparative Example 1

[0085] A polyamic acid slurry is different from Example 1 only in that amino-terminated polyalkylene oxide M1 is not added, the added amount of 4,4'-diaminodiphenyl ether is 30 mol, and other substances, amounts and preparation methods are the same as those in Example 1.

[0086] Comparative Example 2

[0087] A polyamic acid slurry, which is different from Example 2 only in that amino-terminated polyalkylene oxide M2 ​​is not added, the added amount of 4,4'-diaminodiphenyl ether is 30 mol, and other substances, amounts and preparation methods are the same as those in Example 2.

[0088] Comparative Example 3

[0089] A polyamic acid slurry, which is different from Example 3 only in that no anhydride-terminated polyalkylene oxide M3 is added, the added amount of pyromellitic dianhydride is 30 mol, and other substances, amounts and preparation methods are the same as those in Example 3.

[0090] Comparative Example 4

[0091] A polyamic acid slurry, which is different from Example 1 only in that an equal mole of phthalic anhydride is used to replace the amino-terminated polyalkylene oxide M1 obtained in Preparation Example 1, and other substances, amounts and preparation methods are the same as those in Example 3.

[0092] Application Example 1

[0093] An insulated wire, comprising a copper conductor with a circular cross section and a diameter of 1 mm, wherein the surface of the copper conductor is sequentially coated with a first insulating layer with a thickness of 25 μm (the raw material is a polyamic acid slurry of POYAPIP 30UN (Ningbo Boya Juli New Material Technology Co., Ltd.)), a second insulating layer with a thickness of 25 μm (the raw material is the polyamic acid slurry obtained in Example 1), and a third insulating layer with a thickness of 25 μm (the raw material is the polyamic acid slurry of POYAPIP 30UN);

[0094] The preparation method of the insulated wire provided in this application example comprises: coating POYAPIP 30UN polyamic acid, the polyamic acid slurry obtained in Example 1 and POYAPIP30UN polyamic acid on a copper conductor with a circular cross-section and a diameter of 1 mm in sequence, with the coating line speed being 4.0 m / min, and then repeatedly heating at a hot furnace inlet temperature of 250° C. and a heating furnace outlet temperature of 350° C. to obtain the insulated wire.

[0095] Application Examples 2 to 6

[0096] An insulated wire, which differs from Application Example 1 only in that the polyamic acid slurries obtained in Examples 2 to 6 are used to replace the polyamic acid slurry obtained in Example 1 as the raw material for preparing the second insulating layer, and other structures, materials and preparation methods are the same as those in Application Example 1.

[0097] Application Example 7

[0098] An insulated wire, comprising a copper conductor with a circular cross section and a diameter of 1 mm, wherein the surface of the copper conductor is sequentially coated with a first insulating layer with a thickness of 25 μm (the raw material is a polyamic acid slurry of POYAPIP 30UN) and a second insulating layer with a thickness of 50 μm (the raw material is the polyamic acid slurry obtained in Example 1);

[0099] The preparation method of the insulated wire provided in this application example includes: coating POYAPIP 30UN polyamic acid slurry and the polyamic acid slurry obtained in Example 1 on a copper conductor with a circular cross-section and a diameter of 1 mm in sequence, with the coating line speed being 4.0 m / min, and then repeatedly heating at a hot furnace inlet temperature of 250° C. and a heating furnace outlet temperature of 350° C. to obtain the insulated wire.

[0100] Comparative application example 1

[0101] An insulated wire, comprising a copper conductor with a circular cross section and a diameter of 1 mm, the surface of the copper conductor being sequentially coated with an insulating layer with a thickness of 75 μm (the raw material being the polyamic acid slurry obtained in Example 1);

[0102] The preparation method of the insulated wire provided in this application example includes: coating POYA PIP 30UN polyamic acid slurry on a copper conductor, the coating line speed is 4.0 m / min, and then repeatedly heating under the conditions of a hot furnace inlet temperature of 250°C and a heating furnace outlet temperature of 350°C to obtain the insulated wire.

[0103] Comparative Application Examples 2 to 5

[0104] An insulated wire, which differs from Application Example 1 only in that the polyamic acid slurries obtained in Comparative Examples 1 to 4 are used to replace the polyamic acid slurry obtained in Example 1 as the raw material for preparing the second insulating layer, and other structures, materials and preparation methods are the same as those in Application Example 1.

[0105] Performance Test:

[0106] (1) Storage stability: The polyamic acid slurry was packaged into 2 mL sample bottles, 20 bottles were packaged in each batch, and 15 bottles were sealed and stored in a constant temperature and humidity chamber at 15°C. One bottle was taken out for testing every 2 days; 5 bottles were placed in a constant temperature and humidity chamber at 30°C, and one bottle was taken out for testing viscosity every day; viscosity change rate = (viscosity on the nth day - viscosity on the first day) / viscosity on the first day × 100%.

[0107] The polyamic acid slurries obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were tested according to the above test scheme. The viscosity change rates after storage at 30°C for 3 days and at 15°C for 30 days are shown in Table 1:

[0108] Table 1

[0109]

[0110] According to the data in Table 1, we can see that:

[0111] The viscosity change rate of the polyamic acid slurry obtained in Examples 1 to 6 after being stored at 15° C. for 30 days is only +1 to +6.5%, and the viscosity change rate after being stored at 30° C. for 3 days is only -1.6 to -7.6%, and the viscosity change is relatively low.

[0112] The viscosity change rate of the polyamic acid slurry prepared in Comparative Examples 1 to 3 without adding a capping agent and in Comparative Example 4 using a conventional capping agent (phthalic anhydride) is relatively high, especially the viscosity change rate after storage at 15°C for 30 days, indicating that the use of the capping agent defined in the present invention can effectively improve the storage stability of the polyamic acid slurry.

[0113] (2) Bubble ratio: The bubble occupancy rate per unit area is measured by scanning electron microscopy;

[0114] (3) Average bubble size: The average bubble size per unit area is measured by scanning electron microscopy;

[0115] (4) PDIV value: The test was conducted in accordance with GB / T7354-2018. When the partial discharge was greater than 100 pC, the partial discharge inception voltage of the copper flat wire was recorded, and the Upeak value was calculated. The average of the five Upeak values ​​was taken as the experimental result.

[0116] According to the above test methods (2) to (4), the insulated wires provided by Examples 1 to 7 and Comparative Application Examples 1 to 5 were tested. The test results are shown in Table 2:

[0117] Table 2

[0118]

[0119] According to the data in Table 2, we can see that:

[0120] The bubble content on the surface of the insulating wire provided in Application Examples 1 to 7 is 8 to 64%, the average bubble particle size is 900 to 1500 nm, and the PDIV value is 950 to 1530 Vp, which indicates that the polyamic acid slurry prepared by the specific end-capping agent provided by the present invention can produce nanobubbles after heating treatment, and the bubble content and bubble particle size are adjustable, thereby effectively improving the PDIV value of the insulating paint.

[0121] However, the insulated wires coated with the polyamic acid slurry provided in Comparative Examples 1 to 4 and the commercially available POYA PIP 30UN polyamic acid slurry alone cannot generate bubbles on the surface, and thus have a low PDIV value and poor insulation.

[0122] The applicant declares that the present invention illustrates an insulated wire with a high PDIV value and a method for preparing the same through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims

1. An insulated wire with a high PDIV value, characterized in that: The insulated wire comprises a copper conductor or an aluminum conductor, a first insulating layer and a polyamic acid slurry sequentially coated on the surface of the copper conductor; The preparation method of the polyamic acid slurry is: under nitrogen protection, dimethylacetamide and 4,4'-diaminodiphenyl ether are reacted in pyromellitic dianhydride, and then amino-terminated polyalkylene oxide M1 is added for secondary reaction to obtain polyamic acid slurry; The number average molecular weight of the amino-terminated polyalkylene oxide M1 is 720, and the structural formula is:

2. The insulated wire with a high PDIV value according to claim 1, characterized in that: The mass ratio of dimethylacetamide, 4,4'-diaminodiphenyl ether, pyromellitic acid dianhydride and amino-terminated polyalkylene oxide M1 is 35.9:5.767:6.544:1.

44.

3. The insulated wire with a high PDIV value according to claim 2, characterized in that: The reaction temperature is 50° C. and the reaction time is 18 h.

4. The insulated wire with a high PDIV value according to claim 2 or 3, characterized in that: The temperature of the secondary reaction is 50° C., and the time of the secondary reaction is 6 hours.

5. The insulated wire with a high PDIV value according to claim 4, characterized in that: The polyamic acid slurry has a solid content of 26% and a viscosity of 13700cp; The first insulating layer is made of polyamic acid slurry whose raw material is POYAPIP 30UN.

6. A method for preparing an insulated wire with a high PDIV value according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: coating a first insulating layer and polyamic acid slurry on the surface of a copper conductor in sequence and then performing heat treatment to obtain an insulated wire.

7. The method for preparing an insulated wire with a high PDIV value according to claim 6, characterized in that: The thickness of the coated polyamic acid slurry is 50 μm.

8. The method for preparing an insulated wire with a high PDIV value according to claim 7, characterized in that: The coating line speed is independently 4.0 m / min.

9. The method for preparing an insulated wire with a high PDIV value according to claim 8, characterized in that: The temperature of the heat treatment is 250-350°C.

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