Enameled wire with good corona resistance and flexibility and preparation method thereof

Abstract

The invention provides corona-resistant polyamide-imide insulating paint and a preparation method and application thereof, the polyamide-imide insulating paint is prepared from the following raw materials: aromatic tricarboxylic anhydride, aromatic diisocyanate and alcoholic hydroxyl group modified silicon dioxide nanoparticles, and the three materials are matched to prepare the corona-resistant polyamide-imide insulating paint. The obtained polyamide-imide insulating paint has excellent storage stability before curing, and after curing, silicon dioxide nanoparticles can be uniformly dispersed in a formed insulating paint film and are not easy to agglomerate; and therefore, the enameled wire prepared from the polyamide-imide insulating paint has excellent corona resistance and excellent flexibility, and is suitable for being applied to a high-voltage motor.

Description

[0001] This application is a divisional application. The application number of the parent application is 202311508132.0. The application date is November 13, 2023. The name of the invention is "A corona-resistant polyamide-imide insulating varnish, its preparation method and application". Technical Field

[0002] The invention relates to the technical field of coatings, and in particular to an enameled wire with good corona resistance and flexibility and a preparation method thereof. Background Art

[0003] With the deepening of people's environmental protection concept, the new energy industry has developed rapidly, and the performance requirements for motors have gradually increased. In particular, in order to solve the problem of fast charging of new energy vehicles, a high voltage demand of 800V is also proposed for motors. However, the production of 800V high-voltage motors has put forward more high requirements for enameled wires. It is necessary not only to improve the heat resistance of enameled wires, but also to improve the insulation performance of enameled wires. Corona resistance is an important factor in improving insulation. The corona phenomenon is the failure of coil insulation caused by local discharge. The principle is that the charged particles generated by local discharge collide with the insulating material, which causes the organic polymer chain of the insulating material to break, and partial thermal decomposition occurs with local temperature rise. In addition, local discharge will also produce ozone, which will cause chemical damage to the insulating material. The result of these damages will eventually lead to insulation failure of the electric machinery coil. Therefore, it is very important to improve the corona resistance of enameled wires.

[0004] At present, the common method of improving the corona resistance of enameled wire is to coat the wire by adding inorganic insulating particles to the insulating slurry, and to prepare by dispersing inorganic insulating material nanoparticles such as silicon dioxide, aluminum oxide, titanium oxide, etc. The addition of inorganic particles can not only effectively improve the corona resistance of the insulating paint, but also significantly improve the thermodynamic properties and mechanical properties of the paint layer. The more conventional method of adding inorganic particles to the insulating slurry is to mix the inorganic nanoparticles into the insulating slurry after physical dispersion. However, the insulating slurry obtained by this method has a lower solution stability, because the inorganic particles are physically dispersed in the slurry instead of dissolved, and the electrostatic force and van der Waals force between the inorganic particles cause the particles to further agglomerate or coarse during the storage and access process of the slurry. Moreover, the larger the specific surface area of ​​the nanoparticles, the better the corona resistance. On the contrary, as the particle size increases, the corona resistance effect will decrease. Therefore, the corona resistance of the enameled wire obtained by simply physically blending the inorganic insulating particles into the insulating slurry to coat the wire still needs to be improved.

[0005] In order to reduce the agglomeration or coarsening of inorganic insulating particles added to the insulating slurry and to improve storage and production stability, the sol of dispersed inorganic particles and the insulating resin may also be physically mixed. However, the limitation of this method is that the solvent used to disperse the inorganic sol is relatively special. It must not only disperse the inorganic sol but also have good solubility in the insulating slurry. In addition, the inorganic particles of the insulating slurry obtained in this way will also further agglomerate during the curing process, affecting the improvement of the corona resistance of the final enameled wire. At the same time, the addition of inorganic sol has certain limitations in improving the solid content of the insulating resin.

[0006] Therefore, in order to solve the above technical problems, it is urgent to develop a corona-resistant polyamide-imide insulating varnish with excellent storage stability and uniform dispersion after curing. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a corona-resistant polyamide-imide insulating varnish and a preparation method and application thereof. The polyamide-imide insulating varnish has excellent storage stability before curing, and after curing, the silicon dioxide nanoparticles can be evenly and stably dispersed in the paint film without agglomeration, so that the enameled wire made of the polyamide-imide insulating varnish has excellent corona resistance and excellent flexibility, and is suitable for use in high-voltage (800V) motors.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a corona-resistant polyamide-imide insulating varnish, wherein the raw materials for preparing the polyamide-imide insulating varnish include aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified silica nanoparticles.

[0010] The raw materials for preparing the corona-resistant polyamide-imide insulating varnish provided by the present invention include aromatic tricarboxylic anhydride, aromatic diisocyanate and silica nanoparticles modified with alcohol hydroxyl groups; silica nanoparticles modified with alcohol hydroxyl groups are added to the raw materials for preparation, and the alcohol hydroxyl groups contained in the silica nanoparticles can be used to carry out an esterification reaction with the aromatic tricarboxylic anhydride, and the silica nanoparticles are successfully introduced into the structural formula of the intermediate product obtained by the reaction by chemical bonds; and the intermediate product containing the silica nanoparticles is then reacted with the remaining part of the aromatic tricarboxylic anhydride and the aromatic diisocyanate to obtain a molecular The insulating varnish contains silicon dioxide nanoparticles in the chain, and the various components in the insulating varnish have good compatibility, thereby having excellent storage stability. At the same time, after the insulating varnish is coated on a substrate, it can be imidized at high temperature to form a polyamide-imide insulating varnish film. In the above-mentioned imidization process, the silicon dioxide nanoparticles will lose the chemical bond connection with the insulating varnish due to the high temperature, and will be evenly and stably dispersed in the formed polyamide-imide insulating varnish film, thereby making the enameled wire made of the polyamide-imide insulating varnish have excellent corona resistance and excellent flexibility, and is suitable for use in high-voltage motors.

[0011] From the above content, it can be seen that the insulating paint provided by the present invention does not undergo an imidization reaction before curing, that is, no polyamide-imide structure is formed. However, it is called "polyamide-imide insulating paint" because an imidization reaction will occur during the curing process of coating on the surface of the substrate, thereby forming a polyamide-imide paint film.

[0012] Preferably, the polyamide-imide insulating varnish is obtained by condensation reaction of aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified silica nanoparticles.

[0013] Preferably, the aromatic tricarboxylic anhydride includes any one of trimellitic anhydride (TMA), benzophenone tricarboxylic anhydride or diphenylmethane tricarboxylic anhydride, or a combination of at least two thereof.

[0014] Preferably, the aromatic diisocyanate includes any one or a combination of at least two of 4,4′-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, diphenyl ether diisocyanate or diisocyanate polymers.

[0015] Preferably, the molar ratio of the acidic group to the isocyanate group in the raw material for preparing the polyamide-imide insulating varnish is (0.95-1.05):1, such as 0.97:1, 0.99:1, 1.01:1 or 1.03:1, etc. The above-mentioned acidic groups include but are not limited to anhydride groups, carboxyl groups and other groups that can generate hydrogen ions upon hydrolysis or ionization.

[0016] Preferably, based on the solid content of the polyamide-imide insulating varnish being 100%, the mass of the alcoholic hydroxyl-modified silica nanoparticles is 1 to 40%, for example 5%, 10%, 15%, 20%, 25%, 30% or 35%, etc., more preferably 5 to 30%.

[0017] As a preferred technical solution, the present invention further limits the content of alcoholic hydroxyl-modified silica nanoparticles in the polyamide-imide insulating varnish. If the content of alcoholic hydroxyl-modified silica nanoparticles in the polyamide-imide insulating varnish is too low, it is easy to cause the corona resistance of the product to decrease. If the content of alcoholic hydroxyl-modified silica nanoparticles in the polyamide-imide insulating varnish is too high, it is easy to cause the flexibility of the paint film after the polyamide-imide insulating varnish is cured into a film to deteriorate.

[0018] Preferably, the raw materials for preparing the alcoholic hydroxyl-modified silica nanoparticles include an epoxy silane coupling agent, a secondary amine and silica nanoparticles.

[0019] Preferably, the epoxy silane coupling agent comprises any one or a combination of at least two of the compounds having the structure shown in the following formula I, formula II or formula III;

[0020]

[0021] In Formula I, R' is selected from -Me or -Et, and R" is selected from n=0, 1 or 2, m=1, 2 or 3;

[0022]

[0023] In formula II, R' is selected from -Me or -Et, and n = 0, 1 or 2;

[0024]

[0025] In formula III, R' is selected from -Me or -Et, n=0, 1 or 2, and m=0, 1 or 2.

[0026] Preferably, the epoxy silane coupling agent includes any one of γ-glycidyloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane or a combination of at least two thereof.

[0027] Preferably, based on 100% of the mass of the silica nanoparticles, the mass of the epoxy silane coupling agent is 1 to 20%, for example 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16% or 18%, and more preferably 5 to 15%.

[0028] Preferably, the secondary amine includes any one of dioctadecylamine, diethylamine or dibenzylamine, or a combination of at least two thereof.

[0029] Preferably, the D of the silica nanoparticles 50 The particle size is 10 to 300 nm, for example, 200 nm, 40 nm, 60 nm, 80 nm, 100 nm, 130 nm, 160 nm, 180 nm, 200 nm, 230 nm, 250 nm or 280 nm, and more preferably 10 to 80 nm.

[0030] Preferably, the silica nanoparticles are hydrophilic silica nanoparticles.

[0031] Preferably, the alcoholic hydroxyl-modified silica nanoparticles are prepared by the following method, which comprises the following steps:

[0032] (A1) reacting an epoxy silane coupling agent with silica nanoparticles to obtain epoxy silane-modified silica nanoparticles;

[0033] (A2) reacting the epoxysilane-modified silica nanoparticles obtained in step (A1) with secondary amines to obtain the alcoholic hydroxyl-modified silica nanoparticles.

[0034] The reaction in step (A1) is specifically a coupling grafting reaction. For example, the reaction formula is as follows:

[0035]

[0036] The reaction in step (A2) is specifically a ring-opening reaction. Exemplarily, the reaction formula is as follows:

[0037]

[0038] In the above reaction formula, represents epoxy silane coupling agent, stands for silica nanoparticles.

[0039] Preferably, the raw materials for preparing the polyamide-imide insulating varnish also include aromatic dicarboxylic acid.

[0040] Preferably, the aromatic dicarboxylic acid includes any one of terephthalic acid, isophthalic acid or biphenyl dicarboxylic acid, or a combination of at least two thereof.

[0041] Preferably, the mass ratio of the aromatic tricarboxylic anhydride to the aromatic dicarboxylic acid is not higher than 1:0.4, for example, 1:0.35, 1:0.3, 1:0.25, 1:0.2, 1:0.15, 1:0.1 or 1:0.05.

[0042] In a second aspect, the present invention provides a method for preparing the corona-resistant polyamide-imide insulating varnish, the method comprising the following steps:

[0043] (1) reacting some aromatic tricarboxylic acid anhydrides with silica nanoparticles modified with alcoholic hydroxyl groups to obtain an intermediate product;

[0044] (2) reacting the intermediate product obtained in step (1), the remaining part of the aromatic tricarboxylic anhydride, the aromatic diisocyanate and optionally the aromatic dicarboxylic acid to obtain the corona-resistant polyamide-imide insulating varnish.

[0045] The reaction in step (1) is specifically an esterification reaction. For example, the reaction formula is as follows:

[0046]

[0047] The reaction in step (2) is specifically a polymerization reaction. If no aromatic dicarboxylic acid is added in step (2), the reaction formula is shown below by way of example:

[0048]

[0049] Exemplarily, if an aromatic dicarboxylic acid is added in step (2), the reaction formula is as follows:

[0050]

[0051] In the above reaction formula, represents epoxy silane coupling agent, stands for silica nanoparticles.

[0052] Preferably, the reaction in step (1) is carried out in a mixed solvent.

[0053] Preferably, the mixed solvent includes a first type of solvent and a second type of solvent, the first type of solvent includes any one of dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone (NMP) or γ-butyrolactone or a combination of at least two, and the second type of organic solvent includes any one of toluene, o-xylene, m-xylene or p-xylene or a combination of at least two.

[0054] Preferably, the reaction temperature in step (1) is 40-100°C, such as 50°C, 60°C, 70°C, 80°C or 90°C, and more preferably 60-80°C.

[0055] Preferably, the reaction time of step (1) is 1 to 5 h, such as 1.5 h, 2 h, 2.5 h, 3 h or 3.5 h, and more preferably 2 to 4 h.

[0056] Preferably, the reaction in step (2) is carried out under stepwise heating conditions.

[0057] Preferably, the step (2) of the step-by-step heating method comprises: heating the system to 25-80°C (for example, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or 75°C, etc.), reacting for 1-6h (for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or 5.5h, etc.), then heating to 120-150°C (for example, 125°C, 130°C, 135°C, 140°C or 145°C, etc.), reacting for 5-24h (for example, 7h, 9h, 11h, 13h, 15h, 17h, 19h, 21h or 23h, etc.), to complete the step-by-step heating.

[0058] In a third aspect, the present invention provides a corona-resistant enameled wire, the enameled wire comprising a conductor and the corona-resistant polyamide-imide insulating varnish as described in the first aspect, which is coated on the conductor after curing.

[0059] After the polyamide-imide insulating varnish provided by the first aspect of the present invention is coated on the outside of the conductor and heated and cured, an imidization reaction will occur during the heating and curing process. During the imidization reaction, the silicon dioxide nanoparticles will lose the chemical bond connection with the polyamide-imide and be evenly dispersed in the formed paint film, thereby coating the outside of the conductor with a layer of polyamide-imide insulating varnish with excellent corona resistance.

[0060] Exemplarily, the reaction formula in the above heating and curing process is as follows:

[0061]

[0062] It should be noted that the polyamide-imide insulating varnish provided in the first aspect can be used alone or in combination with other varnishes. For example, the polyamide-imide insulating varnish provided by the present invention can be used together with ordinary polyamide-imide insulating varnish, polyester-imide varnish or polyimide varnish.

[0063] Preferably, the coating has a thickness of 20 to 150 μm, for example, 30 μm, 50 μm, 70 μm, 90 μm, 110 μm or 130 μm.

[0064] Preferably, the drying temperature is not less than 300°C, for example, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C or 500°C, etc.

[0065] In a fourth aspect, the present invention provides a use of the corona-resistant polyamide-imide insulating varnish as described in the first aspect or the corona-resistant enameled wire as described in the third aspect in a motor.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) The raw materials for preparing the corona-resistant polyamide-imide insulating varnish provided by the present invention include aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified silica nanoparticles. The above three raw materials are matched so that the obtained polyamide-imide insulating varnish has excellent storage stability before curing, and the silica nanoparticles have uniform and stable dispersion in the obtained paint film after curing;

[0068] (2) The present invention also provides an enameled wire made of the polyamide-imide insulating varnish. Since the silicon dioxide in the varnish film of the enameled wire is evenly dispersed and not easy to agglomerate, the enameled wire has excellent flexibility and excellent corona resistance, and has no effect on the pinhole performance of the enameled wire. The enameled wire is suitable for use in high-voltage (such as 800V) motors. DETAILED DESCRIPTION

[0069] 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.

[0070] The test methods for solid content and viscosity involved in the specific implementation methods of the present invention are as follows:

[0071] Solid content: Take an aluminum foil disk with a diameter of 60 mm and weigh it 0 ; Take 1±0.1g of paint sample and place it in an aluminum pan, weigh the weight of the aluminum pan plus the paint (m 1 ); Place the aluminum plate containing the paint in a blast oven at 180±5℃, take it out after 1 hour, and weigh the mass of the aluminum plate containing the paint (m 2 ); solid content = (m 2 -m 0 ) / (m 1 -m 0 )×100%;

[0072] Viscosity: The test was conducted using an American Boller cone and plate viscometer at a temperature of 25°C.

[0073] Preparation Example 1

[0074] A dispersion of silica nanoparticles modified with alcoholic hydroxyl groups, the preparation method of which comprises the following steps:

[0075] (1) γ-glycidyloxypropyltrimethoxysilane was dissolved in an ethanol aqueous solution to prepare a solution with a mass fraction of 2%, and then mechanically stirred and dispersed for 10 minutes, the pH was adjusted to 6, and hydrophilic silica nanoparticles (D 50 The silica nanoparticles are 20 nm in diameter, and the mass ratio of the hydrophilic silica nanoparticles to the γ-glycidyloxypropyltrimethoxysilane is 10:1. After being evenly mixed, the mixture is dispersed in an ultrasonic water bath for 30 minutes, and then heated to 50° C. for coupling grafting reaction. After 12 hours of reaction time, the mixture is centrifuged and dried to obtain epoxysilane-modified silica nanoparticles.

[0076] (2) The epoxysilane-modified silica nanoparticles obtained in step (A1) are dispersed in xylene (solid content is 20%), dioctadecylamine is added (the mass ratio of dioctadecylamine to epoxysilane-modified silica nanoparticles is 20:1), and the mixture is heated to 80° C. for reaction for 5 h to obtain a dispersion of alcoholic hydroxyl-modified silica nanoparticles.

[0077] Preparation Example 2

[0078] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that the D of the hydrophilic silica nanoparticles is 50 The other substances, dosages and preparation methods are the same as those in Preparation Example 1.

[0079] Preparation Example 3

[0080] An alcoholic hydroxyl-modified silica nanoparticle dispersion is disclosed, which differs from Preparation Example 1 only in that an equimolar amount of diethylamine is used to replace dioctadecylamine, and other substances, amounts used and preparation methods are the same as those in Preparation Example 1.

[0081] Preparation Example 4

[0082] An alcoholic hydroxyl-modified silica nanoparticle dispersion is disclosed, which differs from Preparation Example 1 only in that an equimolar amount of dibenzylamine is used to replace dioctadecylamine, and other substances, dosages and preparation methods are the same as those in Preparation Example 1.

[0083] Preparation Example 5

[0084] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that an equal mass of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is used to replace γ-glycidyloxypropyltrimethoxysilane, and other substances, amounts and preparation methods are the same as those in Preparation Example 1.

[0085] Preparation Example 6

[0086] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that the D of the hydrophilic silica nanoparticles is 50 The other substances, dosages and preparation methods are the same as those in Preparation Example 1.

[0087] Comparative Preparation Example 1

[0088] A dispersion of epoxysilane-modified silica nanoparticles, the preparation method of which comprises: dissolving γ-glycidyloxypropyltrimethoxysilane in an ethanol aqueous solution to prepare a solution with a mass fraction of 2%, then mechanically stirring and dispersing for 10 minutes, adjusting the pH to 6, adding hydrophilic silica nanoparticles (D 50 The particle size is 20nm, the mass ratio of hydrophilic silica nanoparticles and γ-glycidyloxypropyltrimethoxysilane is 10:1), after being evenly mixed, ultrasonic water bath dispersion treatment is used for 30min, and then heated to 50°C for coupling grafting reaction. After 12h of reaction time, centrifugation, drying, and dispersion in xylene are obtained to obtain a silica nanoparticle dispersion modified with epoxy silane with a solid content of 20%.

[0089] Example 1

[0090] A corona-resistant polyamide-imide insulating varnish, the preparation method of which comprises the following steps:

[0091] (1) Add NMP (1 kg) and the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1 (solid content 20%, 0.79 kg) to a 10 L reactor, then add trimellitic anhydride (110 g), stir and heat to 80° C. for 3 h to obtain an intermediate product;

[0092] (2) NMP (2.42 kg), trimellitic anhydride (790 g) and diphenylmethane diisocyanate (692 g) were added to the reactor, the temperature was raised to 90° C. and the reaction was carried out for 3 h. The system temperature was then raised to 150° C. and the reaction was carried out for 2 h to obtain a polyamide-imide insulating varnish with a viscosity of 1760 cp.

[0093] Example 2

[0094] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 only in that the addition amount of the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1 is 0.395 kg, and other substances, amounts and preparation methods are the same as those in Example 1.

[0095] Example 3

[0096] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 only in that the addition amount of the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1 is 1.185 kg, and other substances, amounts and preparation methods are the same as those in Example 1.

[0097] Example 4

[0098] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 in that the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 2 is used to replace the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 1650cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0099] Example 5

[0100] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 in that the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 3 is used to replace the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 1490cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0101] Example 6

[0102] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 in that the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 4 is used to replace the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 1710cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0103] Example 7

[0104] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 in that the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 5 is used to replace the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 1640cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0105] Example 8

[0106] A corona-resistant polyamide-imide insulating varnish, which differs from Example 1 in that the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 6 is used to replace the alcoholic hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 1960cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0107] Comparative Example 1

[0108] A polyamide-imide insulating varnish, which differs from Example 1 in that the epoxy silane-modified silica nanoparticle dispersion provided in Comparative Preparation Example 1 is used to replace the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1, the viscosity of the polyamide-imide insulating varnish is 840cp, and other substances, amounts and preparation methods are the same as those in Example 1.

[0109] Comparative Example 2

[0110] A polyamide-imide insulating varnish, in particular a commercially available polyamide-imide insulating varnish (BOYA AIP36UN).

[0111] Comparative Example 3

[0112] A polyamide-imide insulating varnish, the preparation method of which comprises: adding NMP (1 kg), a xylene dispersion of silicon dioxide nanoparticles (solid content of 20%, 0.79 kg), trimellitic anhydride (900 g) and diphenylmethane diisocyanate (692 g) into a 10L reactor, stirring and heating to 80°C for reaction for 3 hours to obtain the polyimide insulating varnish.

[0113] Application Example 1

[0114] A corona-resistant enameled wire with an outer diameter of 284 μm, comprising a copper conductor, the outer surface of which is sequentially coated with a primer coating and a topcoat coating;

[0115] The raw material of the primer coating is commercially available polyamide-imide insulating paint (BOYA AIP 36UN);

[0116] The thickness of the topcoat coating is 75 μm, and the raw material is the corona-resistant polyamide-imide insulating varnish provided in Example 1;

[0117] The coating equipment is: Sun H5000-1T-20D enameling machine; the process parameters are: oven inlet: 330°C; oven middle: 370°C; oven outlet: 400°C; production specification: 0.25mm; vehicle speed: 90m / min; paint passes: 1 (commercially available polyamide-imide insulating paint) + 16 (corona-resistant polyamide-imide insulating paint provided in Example 1).

[0118] Application Examples 2 to 8

[0119] A corona-resistant enameled wire, which differs from Application Example 1 only in that the corona-resistant polyamide-imide insulating varnish provided by Examples 2 to 8 is used to replace the corona-resistant polyamide-imide insulating varnish provided by Example 1, and other materials, parameters and processes are the same as those in Application Example 1.

[0120] Comparative Application Examples 1-2

[0121] An enameled wire, which differs from Application Example 1 only in that the polyamide-imide insulating varnishes provided in Comparative Examples 1 to 2 are used to replace the corona-resistant polyamide-imide insulating varnish provided in Example 1, and other materials, parameters and processes are the same as those in Application Example 1.

[0122] Comparative Application Example 3

[0123] An enameled wire is different from Application Example 1 only in that the materials of the topcoat coating and the primer coating are both commercially available polyamide-imide insulating varnish (BOYA AIP 36UN), and other materials, parameters and processes are the same as those of Application Example 1.

[0124] Comparative Application Example 4

[0125] An enameled wire is different from Application Example 1 only in that a conventional commercially available paint 1 is used to replace the corona-resistant polyamide-imide insulating paint provided in Example 1, and other materials, parameters and processes are the same as those in Application Example 1.

[0126] Performance Testing:

[0127] (1) Elongation: Tested in accordance with the test method provided in the national standard GB / T 4074.3-2008;

[0128] (2) Corona damage resistance time: At an ambient temperature of 155°C, a voltage of 1500Vp is applied to the film of the enameled wire at a frequency of 50Hz. The time it takes for the film to break down and cause a short circuit is the corona damage resistance time.

[0129] (3) Salt water pinhole leakage test: The test was conducted according to the test method provided by the national standard "GB / T4074.5-2008", and the test conditions were: 24V, 6M;

[0130] (4) Pressure resistance: The softening breakdown test was carried out according to the method provided in the national standard "GB / T 4074.21-2018" at 220°C for 1 min.

[0131] According to the above test method, the enameled wires provided in Examples 1 to 8 and Comparative Application Examples 1 to 4 were tested, and the test results are shown in Table 1:

[0132] Table 1

[0133]

[0134] From the data in Table 1, we can see that:

[0135] The enameled wire made by coating with the corona-resistant polyamide-imide insulating varnish provided by the present invention has excellent pressure resistance, salt water resistance and corona resistance, and also has high flexibility;

[0136] Specifically, the enameled wires provided in Application Examples 1 to 7 have an elongation of up to 45-47%, a corona resistance time of 55-131 hours, a number of salt water pinholes of 0, and pass the pressure resistance test;

[0137] Compared with Application Example 1, the pressure resistance test of the enameled wire provided in Comparative Application Examples 1 and 4 failed, indicating that the pressure resistance of the polyamide-imide insulating varnish made of silicon dioxide nanoparticles modified with epoxy silane and the conventional commercially available varnish 1 after film formation was poor;

[0138] Compared with Application Example 1, the corona resistance time of the enameled wires provided in Comparative Application Examples 2 to 3 is shorter, indicating that the commercially available polyamide-imide insulating varnish (BOYAAIP 36UN) and the polyamide-imide insulating varnish prepared by adding silica nanoparticles in a physical blending method have poor corona resistance after film formation;

[0139] Finally, by comparing the data of Application Examples 1 to 3 with Application Example 8, it can be found that the smaller the particle size of the alcoholic hydroxyl-modified silica nanoparticles and the greater the amount added, the better the corona resistance of the polyamide-imide insulating varnish after film formation.

[0140] The applicant declares that the present invention illustrates a corona-resistant polyamide-imide insulating varnish and its preparation method and application 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 protection scope and disclosure scope of the present invention.

Claims

1. An enameled wire with good corona resistance and flexibility, It is characterized in that The enameled wire comprises a copper conductor and a primer coating and a topcoat coating sequentially coated on the outside of the copper conductor; The raw material of the topcoat coating is corona-resistant polyamide-imide insulating varnish; The raw materials for preparing the corona-resistant polyamide-imide insulating varnish include aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified silica nanoparticles; The aromatic tricarboxylic anhydride includes any one of trimellitic anhydride, benzophenone tricarboxylic anhydride or diphenylmethane tricarboxylic anhydride or a combination of at least two thereof; The aromatic diisocyanate includes any one or a combination of at least two of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, diphenyl ether diisocyanate or diisocyanate polymers; The raw materials for preparing the alcoholic hydroxyl modified silica nanoparticles include epoxy silane coupling agent, secondary amine and silica nanoparticles; Taking the solid content of the corona-resistant polyamide-imide insulating varnish as 100%, the mass of the alcoholic hydroxyl-modified silicon dioxide nanoparticles is 1-40%.

2. The enameled wire having good corona resistance and flexibility according to claim 1, It is characterized in that The raw material of the primer coating is polyamide-imide insulating paint BOYAAIP 36UN.

3. The enameled wire having good corona resistance and flexibility according to claim 1, It is characterized in that The raw materials for preparing the corona-resistant polyamide-imide insulating varnish also include aromatic dicarboxylic acid; The aromatic dicarboxylic acid includes any one of terephthalic acid, isophthalic acid or biphenyl dicarboxylic acid or a combination of at least two thereof.

4. An enameled wire having good corona resistance and flexibility according to any one of claims 1 to 3, It is characterized in that The preparation method of the corona-resistant polyamide-imide insulating varnish comprises the following steps: (1) reacting some aromatic tricarboxylic acid anhydrides with silica nanoparticles modified with alcoholic hydroxyl groups to obtain an intermediate product; (2) reacting the intermediate product obtained in step (1), the remaining part of the aromatic tricarboxylic anhydride, the aromatic diisocyanate and the optional aromatic dicarboxylic acid to obtain the corona-resistant polyamide-imide insulating varnish.

5. The enameled wire having good corona resistance and flexibility according to claim 1, It is characterized in that The outer diameter of the enameled wire is 284 μm.

6. The enameled wire having good corona resistance and flexibility according to claim 1, It is characterized in that The thickness of the topcoat coating is 75 μm.

7. A method for preparing an enameled wire having good corona resistance and flexibility as claimed in any one of claims 1 to 6, It is characterized in that The following steps are involved: The copper conductor, primer and topcoat are prepared by using a Sun H5000-1T-20D enameling machine to obtain the enameled wire with good corona resistance and flexibility.

8. The preparation method according to claim 7, It is characterized in that The process parameters of the Sun H5000-1T-20D enameling machine are: oven inlet: 330°C; oven middle: 370°C; oven outlet: 400°C; production specification: 0.25mm; vehicle speed: 90m / min; painting passes: 1 primer, 16 topcoats.

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