A corona-resistant polyamide-imide insulating paint, a preparation method and application thereof

Abstract

The application provides a corona-resistant polyamide-imide insulating paint and a preparation method and application thereof. The preparation raw material of the polyamide-imide insulating paint comprises aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol-hydroxyl modified silicon dioxide nanoparticles. The three materials are matched to make the obtained polyamide-imide insulating paint have excellent storage stability before curing, and the silicon dioxide nanoparticles can be uniformly dispersed in the formed insulating paint film and are not prone to agglomeration after curing. Therefore, the enameled wire made of the polyamide-imide insulating paint has excellent corona resistance and excellent flexibility, and is suitable for application in high-voltage motors.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of paint, and particularly relates to a corona-resistant polyamide-imide insulating paint as well as a preparation method and application thereof. BACKGROUND

[0002] With the deepening of people's environmental protection concept, the new energy industry has developed rapidly, and the performance requirements for electric machines have gradually increased. In particular, in order to solve the problem of fast charging of new energy vehicles, a high voltage demand of 800V for electric machines is proposed. However, the production of 800V high voltage electric machines puts forward higher requirements for enameled wires. Not only the heat resistance of enameled wires needs to be improved, but also the insulation performance of enameled wires must be improved. Corona resistance is an important factor to improve insulation. Corona is caused by partial discharge leading to coil insulation failure. The principle is that the charged particles generated by partial discharge collide with the insulation material, which causes the organic polymer chain of the insulation material to break and partially thermally decompose due to local heating. In addition, partial discharge also produces ozone, which causes chemical damage to the insulation material. These damages will eventually lead to the insulation failure of the electric machine coil. Therefore, it is very important to improve the corona resistance of enameled wires.

[0003] At present, the common method to improve the corona resistance of enameled wires is to add inorganic insulating particles to the insulation slurry to coat the wire. Inorganic insulating material nanoparticles such as silicon dioxide, aluminum oxide, titanium oxide are dispersed to prepare the inorganic particles. The addition of inorganic particles can effectively improve the corona resistance of the insulation paint, and also significantly improve the thermodynamic and mechanical properties of the paint layer. The common method to add inorganic particles to the insulation slurry is to physically disperse the inorganic nanoparticles and then mix them into the insulation slurry. However, the insulation slurry obtained by this method has low solution stability. Because the inorganic particles are physically dispersed in the slurry rather than dissolved, the particles further agglomerate or coarsen during the storage process due to the electrostatic force and van der Waals force between the inorganic particles. Moreover, the larger the specific surface area of the nanoparticles, the better the corona resistance. Conversely, as the particle size increases, the corona resistance decreases. Therefore, the corona resistance of the enameled wire obtained by simply physically blending inorganic insulating particles into the insulation slurry to coat the wire still needs to be improved.

[0004] To reduce the agglomeration or coarsening of inorganic insulating particles added to insulating slurry and to improve storage and production stability, the dispersed inorganic particle sol and insulating resin can be physically mixed. However, this method has limitations: the solvent used to disperse the inorganic sol is quite special, requiring both dispersion of the inorganic sol and good solubility in the insulating slurry. Furthermore, the inorganic particles in the insulating slurry obtained in this way will further agglomerate during the curing process, affecting the improvement of the corona resistance of the final enameled wire. In addition, the addition of inorganic sol has certain limitations in increasing the solid content of the insulating resin.

[0005] 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

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a corona-resistant polyamide-imide insulating varnish, its preparation method, and its application. The polyamide-imide insulating varnish exhibits excellent storage stability before curing, and after curing, silica nanoparticles can be uniformly and stably dispersed in the varnish film without agglomeration. Consequently, enameled wires made with the polyamide-imide insulating varnish possess excellent corona resistance and superior flexibility, making them suitable for use in high-voltage (800V) motors.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] 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 hydroxyl-modified silica nanoparticles.

[0009] The corona-resistant polyamide-imide insulating varnish provided by this invention comprises aromatic tricarboxylic anhydride, aromatic diisocyanate, and hydroxyl-modified silica nanoparticles. By adding hydroxyl-modified silica nanoparticles to the raw materials, the hydroxyl groups can undergo esterification with the aromatic tricarboxylic anhydride, successfully introducing the silica nanoparticles into the structure of the intermediate product obtained through chemical bonds. The intermediate product containing silica nanoparticles is then reacted with the remaining aromatic tricarboxylic anhydride and aromatic diisocyanate to obtain the molecular... The insulating varnish containing silica nanoparticles has good compatibility among its components, resulting in excellent storage stability. Furthermore, after coating the substrate with this varnish, it undergoes imidization at high temperature to form a polyamide-imide insulating varnish film. During this imidization process, the silica nanoparticles lose their chemical bonds with the varnish due to the high temperature, becoming uniformly and stably dispersed within the formed polyamide-imide insulating varnish film. Consequently, enameled wires made with this polyamide-imide insulating varnish exhibit excellent corona resistance and superior flexibility, making them suitable for use in high-voltage motors.

[0010] As can be seen from the above, the insulating varnish provided by the present invention does not undergo an imidization reaction before curing, that is, it does not form a polyamide-imide structure. However, it is called "polyamide-imide insulating varnish" because an imidization reaction will occur during the curing process on the substrate surface, thereby forming a polyamide-imide varnish film.

[0011] Preferably, the polyamide-imide insulating varnish is obtained by a condensation reaction of aromatic tricarboxylic anhydride, aromatic diisocyanate and hydroxyl-modified silica nanoparticles.

[0012] Preferably, the aromatic tricarboxylic anhydride includes any one or a combination of at least two of trimellitic anhydride (TMA), benzophenone tricarboxylic anhydride, or diphenylmethane tricarboxylic anhydride.

[0013] Preferably, the aromatic diisocyanate includes any one or a combination of at least two of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, phenyl dimethylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, diphenyl ether diisocyanate, or diisocyanate polymers.

[0014] Preferably, the molar ratio of acidic groups to isocyanate groups in the raw materials for preparing the polyamide-imide insulating varnish is (0.95-1.05):1, for example, 0.97:1, 0.99:1, 1.01:1 or 1.03:1, etc. The acidic groups include, but are not limited to, anhydride groups, carboxyl groups and other groups that can generate hydrogen ions by hydrolysis or ionization.

[0015] Preferably, based on the solid content of the polyamide-imide insulating varnish being 100%, the mass of the alcohol-hydroxyl-modified silica nanoparticles is 1-40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, or 35%, and more preferably 5-30%.

[0016] As a preferred technical solution, the present invention further limits the content of hydroxyl-modified silica nanoparticles in polyamide-imide insulating varnish. If the content of hydroxyl-modified silica nanoparticles in polyamide-imide insulating varnish is too low, it will easily lead to a decrease in the corona resistance of the product. If the content of hydroxyl-modified silica nanoparticles in polyamide-imide insulating varnish is too high, it will easily lead to a decrease in the flexibility of the varnish film after the polyamide-imide insulating varnish is cured.

[0017] Preferably, the raw materials for preparing the hydroxyl-modified silica nanoparticles include an epoxy silane coupling agent, a secondary amine, and silica nanoparticles.

[0018] Preferably, the epoxy silane coupling agent comprises any one or a combination of at least two compounds having the structure shown in Formula I, Formula II or Formula III;

[0019]

[0020] 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;

[0021]

[0022] In Equation II, R' is selected from -Me or -Et, and n = 0, 1 or 2;

[0023]

[0024] In Formula III, R' is selected from -Me or -Et, n = 0, 1 or 2, and m = 0, 1 or 2.

[0025] Preferably, the epoxy silane coupling agent comprises any one or a combination of at least two of γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0026] Preferably, based on the mass of the silica nanoparticles as 100%, the mass of the epoxy silane coupling agent is 1-20%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, or 18%, and more preferably 5-15%.

[0027] Preferably, the secondary amine includes any one or a combination of at least two of bis(octadecylamine), diethylamine, or dibenzylamine.

[0028] Preferably, the D of the silica nanoparticles 50 The particle size is 10–300 nm, such as 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 10–80 nm.

[0029] Preferably, the silica nanoparticles are hydrophilic silica nanoparticles.

[0030] Preferably, the hydroxyl-modified silica nanoparticles are prepared by the following method, which includes the following steps:

[0031] (A1) Reaction of epoxy silane coupling agent and silica nanoparticles yields epoxy silane-modified silica nanoparticles.

[0032] (A2) The epoxy silane-modified silica nanoparticles obtained in step (A1) are reacted with a secondary amine to obtain the alcohol hydroxyl-modified silica nanoparticles.

[0033] The reaction that occurs in step (A1) above is specifically a coupling grafting reaction, and exemplarily, the reaction formula is shown below:

[0034]

[0035] The reaction that occurs in step (A2) above is specifically a ring-opening reaction, and for example, the reaction formula is shown below:

[0036]

[0037] In the above reaction formula, Represents epoxy silane coupling agents, Represents silicon dioxide nanoparticles.

[0038] Preferably, the raw materials for preparing the polyamide-imide insulating varnish also include aromatic dicarboxylic acids.

[0039] Preferably, the aromatic dicarboxylic acid includes any one or a combination of at least two of terephthalic acid, isophthalic acid, or biphenyl acid.

[0040] 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, etc.

[0041] Secondly, the present invention provides a method for preparing the corona-resistant polyamide-imide insulating varnish as described above, the method comprising the following steps:

[0042] (1) A portion of aromatic tricarboxylic acid anhydrides and alcohol hydroxyl-modified silica nanoparticles were reacted to obtain an intermediate product;

[0043] (2) The intermediate product obtained in step (1), the remaining aromatic tricarboxylic anhydride, the aromatic diisocyanate and optionally the aromatic dicarboxylic acid are reacted to obtain the corona-resistant polyamide-imide insulating varnish.

[0044] The reaction that occurs in step (1) above is specifically an esterification reaction, and exemplarily, the reaction formula is shown below:

[0045]

[0046] The reaction that occurs in step (2) above is specifically a polymerization reaction. If an aromatic dicarboxylic acid is not added in step (2), the reaction formula is exemplarily shown below:

[0047]

[0048] For example, if an aromatic dicarboxylic acid is added in step (2), the reaction formula is as follows:

[0049]

[0050] In the above reaction formula, Represents epoxy silane coupling agents, Represents silicon dioxide nanoparticles.

[0051] Preferably, the reaction in step (1) is carried out in a mixed solvent.

[0052] Preferably, the mixed solvent includes a first type of solvent and a second type of solvent. The first type of solvent includes any one or a combination of at least two of dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone (NMP), or γ-butyrolactone. The second type of organic solvent includes any one or a combination of at least two of toluene, o-xylene, m-xylene, or p-xylene.

[0053] Preferably, the temperature of the reaction in step (1) is 40 to 100°C, such as 50°C, 60°C, 70°C, 80°C or 90°C, and more preferably 60 to 80°C.

[0054] Preferably, the reaction time in step (1) is 1 to 5 hours, such as 1.5 hours, 2 hours, 2.5 hours, 3 hours or 3.5 hours, and more preferably 2 to 4 hours.

[0055] Preferably, the reaction in step (2) is carried out under a stepped heating condition.

[0056] Preferably, the staged heating method in step (2) includes: heating the system to 25-80℃ (e.g., 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃ or 75℃, etc.), reacting for 1-6 hours (e.g., 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours or 5.5 hours, etc.), then heating to 120-150℃ (e.g., 125℃, 130℃, 135℃, 140℃ or 145℃, etc.), reacting for 5-24 hours (e.g., 7 hours, 9 hours, 11 hours, 13 hours, 15 hours, 17 hours, 19 hours, 21 hours or 23 hours, etc.), to complete the staged heating.

[0057] Thirdly, the present invention provides a corona-resistant enameled wire, the enameled wire comprising a conductor and a cured polyamide-imide insulating varnish as described in the first aspect, which is then wrapped around the conductor.

[0058] After the polyamide-imide insulating varnish provided in 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 silica nanoparticles will lose their chemical bond connection with the polyamide-imide and be uniformly dispersed in the formed varnish film, thereby coating the outside of the conductor with a polyamide-imide insulating varnish film with excellent corona resistance.

[0059] For example, the reaction formula in the above-mentioned heat curing process is as follows:

[0060]

[0061] 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 this invention can be used simultaneously with ordinary polyamide-imide insulating varnishes, polyesterimide varnishes, or polyimide varnishes.

[0062] Preferably, the thickness of the coating is 20 to 150 μm, such as 30 μm, 50 μm, 70 μm, 90 μm, 110 μm or 130 μm.

[0063] Preferably, the drying temperature is not lower than 300°C, such as 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C, or 500°C.

[0064] Fourthly, the present invention provides the application of a corona-resistant polyamide-imide insulating varnish as described in the first aspect or a corona-resistant enameled wire as described in the third aspect in an electric motor.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (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 hydroxyl-modified silica nanoparticles. The above three raw materials are combined to make the polyamide-imide insulating varnish have excellent storage stability before curing, and the silica nanoparticles have uniform and stable dispersion in the obtained varnish film after curing.

[0067] (2) The present invention also provides an enameled wire made of the polyamide-imide insulating varnish. Since the silica in the varnish film of the enameled wire is uniformly dispersed and does not easily agglomerate, it has excellent flexibility and excellent corona resistance, and does not affect the pinhole performance of the enameled wire, making it suitable for use in high voltage (e.g., 800V) motors. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] The specific embodiments of this invention involve the following testing methods for solid content and viscosity:

[0070] Solid content: Take an aluminum foil tray with a diameter of 60 mm and weigh it as m0; take a paint sample of 1 ± 0.1 g and place it in the aluminum tray, weigh the aluminum tray plus the paint (m1); place the aluminum tray containing the paint in a forced-air drying oven at 180 ± 5℃ for 1 hour, then take it out and weigh the aluminum tray containing the paint (m2); Solid content = (m2 - m0) / (m1 - m0) × 100%;

[0071] Viscosity: Tested using a Boller Feinberg cone-plate viscometer at a temperature of 25°C.

[0072] Preparation Example 1

[0073] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, the preparation method of which includes the following steps:

[0074] (1) Dissolve γ-glycidoxypropyltrimethoxysilane in an aqueous ethanol solution to prepare a 2% (w / w) solution, then disperse by mechanical stirring for 10 min, adjust the pH to 6, and add hydrophilic silica nanoparticles (D... 50The 20 nm hydrophilic silica nanoparticles and γ-glycidoxypropyltrimethoxysilane (mass ratio 10:1) were mixed evenly and then dispersed in an ultrasonic water bath for 30 min. After that, they were heated to 50 °C for coupling and grafting reaction. After 12 h of reaction time, they were centrifuged and dried to obtain epoxysilane modified silica nanoparticles.

[0075] (2) The epoxy silane-modified silica nanoparticles obtained in step (A1) are dispersed in xylene (solid content is 20%), and bis(octadecylamine) (mass ratio of bis(octadecylamine) and epoxy silane-modified silica nanoparticles is 20:1) are added. The mixture is heated to 80°C and reacted for 5 hours to obtain a dispersion of hydroxyl-modified silica nanoparticles.

[0076] Preparation Example 2

[0077] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, differing from Preparation Example 1 only in that the D of the hydrophilic silica nanoparticles... 50 The wavelength was 80 nm. Other substances, amounts, and preparation methods were the same as in Preparation Example 1.

[0078] Preparation Example 3

[0079] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that diethylamine is used instead of dioctadecylamine in equimolar amounts, while the other substances, amounts and preparation methods are the same as those in Preparation Example 1.

[0080] Preparation Example 4

[0081] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that an equimolar amount of dibenzylamine is used instead of dioctadecylamine, while the other substances, amounts and preparation methods are the same as in Preparation Example 1.

[0082] Preparation Example 5

[0083] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, which differs from Preparation Example 1 only in that γ-glycidoxypropyltrimethoxysilane is replaced with an equal mass of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. All other substances, amounts and preparation methods are the same as in Preparation Example 1.

[0084] Preparation Example 6

[0085] A dispersion of silica nanoparticles modified with alcohol hydroxyl groups, differing from Preparation Example 1 only in that the D of the hydrophilic silica nanoparticles... 50 The wavelength was 300 nm. Other substances, amounts, and preparation methods were the same as in Preparation Example 1.

[0086] Comparative Preparation Example 1

[0087] A dispersion of epoxy silane-modified silica nanoparticles is prepared by means of: dissolving γ-glycidoxypropyltrimethoxysilane in an aqueous ethanol solution to prepare a 2% (w / w) solution, then mechanically stirring and dispersing for 10 min, adjusting the pH to 6, and adding hydrophilic silica nanoparticles (D...) at room temperature. 50 Hydrophilic silica nanoparticles with a particle size of 20 nm and a mass ratio of 10:1 to γ-glycidoxypropyltrimethoxysilane were mixed evenly and then dispersed in an ultrasonic water bath for 30 min. The mixture was then heated to 50 °C for coupling grafting reaction. After a reaction time of 12 h, the mixture was centrifuged, dried, and dispersed in xylene to obtain a silica nanoparticle dispersion with a solid content of 20%.

[0088] Example 1

[0089] A corona-resistant polyamide-imide insulating varnish, the preparation method of which includes the following steps:

[0090] (1) Add NMP (1 kg) and the dispersion of hydroxyl-modified silica nanoparticles provided in 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 intermediate product;

[0091] (2) Add NMP (2.42 kg), trimellitic anhydride (790 g) and diphenylmethane diisocyanate (692 g) to the reactor, heat to 90 °C and react for 3 h, then heat the system to 150 °C and react for 2 h to obtain a polyamide-imide insulating varnish with a viscosity of 1760 cp.

[0092] Example 2

[0093] A corona-resistant polyamide-imide insulating varnish differs from Example 1 only in that the amount of the alcohol-hydroxyl-modified silica nanoparticle dispersion provided in Example 1 is 0.395 kg, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0094] Example 3

[0095] A corona-resistant polyamide-imide insulating varnish differs from Example 1 only in that the amount of the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Example 1 is 1.185 kg, while the other substances, amounts, and preparation methods are the same as in Example 1.

[0096] Example 4

[0097] A corona-resistant polyamide-imide insulating varnish differs from Example 1 in that the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 2 is used instead of the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 1650 cp, and the other substances, amounts, and preparation methods are the same as in Example 1.

[0098] Example 5

[0099] A corona-resistant polyamide-imide insulating varnish differs from Example 1 in that the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 3 is used instead of the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 1490 cp, and the other substances, amounts, and preparation methods are the same as in Example 1.

[0100] Example 6

[0101] A corona-resistant polyamide-imide insulating varnish differs from Example 1 in that the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 4 is used instead of the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 1710 cp, and the other substances, amounts, and preparation methods are the same as in Example 1.

[0102] Example 7

[0103] A corona-resistant polyamide-imide insulating varnish differs from Example 1 in that the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 5 is used instead of the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 1640 cp, and the other substances, amounts, and preparation methods are the same as in Example 1.

[0104] Example 8

[0105] A corona-resistant polyamide-imide insulating varnish differs from Example 1 in that the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 6 is used instead of the hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 1960 cp, and the other substances, amounts, and preparation methods are the same as in Example 1.

[0106] Comparative Example 1

[0107] 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 instead of the alcohol hydroxyl-modified silica nanoparticle dispersion provided in Preparation Example 1. The viscosity of the polyamide-imide insulating varnish is 840 cp, and the other substances, amounts and preparation methods are the same as in Example 1.

[0108] Comparative Example 2

[0109] A polyamide-imide insulating varnish, specifically a commercially available polyamide-imide insulating varnish (BOYA AIP36UN).

[0110] Comparative Example 3

[0111] A polyamide-imide insulating varnish is prepared by adding NMP (1 kg), xylene dispersion of silica nanoparticles (solid content 20%, 0.79 kg), trimellitic anhydride (900 g), and diphenylmethane diisocyanate (692 g) to a 10 L reactor, stirring and heating to 80 °C for 3 h to obtain the polyamide insulating varnish.

[0112] Application Example 1

[0113] A corona-resistant enameled wire with an outer diameter of 284 μm includes a copper conductor, and the copper conductor is successively coated with a primer coating and a topcoat coating.

[0114] The raw material for the primer coating is commercially available polyamide-imide insulating varnish (BOYA AIP 36UN);

[0115] The thickness of the topcoat is 75 μm, and the raw material is the corona-resistant polyamide-imide insulating varnish provided in Example 1;

[0116] The coating equipment is a Sun H5000-1T-20D enameling machine; the process parameters are: oven inlet: 330℃; oven middle: 370℃; oven outlet: 400℃; production specification: 0.25mm; machine speed: 90m / min; coating passes: 1 (commercially available polyamide-imide insulating varnish) + 16 (corona-resistant polyamide-imide insulating varnish provided in Example 1) passes.

[0117] Application Examples 2-8

[0118] A corona-resistant enameled wire differs from Application Example 1 only in that the corona-resistant polyamide-imide insulating varnish provided in Examples 2-8 is used instead of the corona-resistant polyamide-imide insulating varnish provided in Example 1. All other materials, parameters, and processes are the same as in Application Example 1.

[0119] Comparative application examples 1-2

[0120] An enameled wire differs from Application Example 1 only in that the polyamide-imide insulating varnish provided in Comparative Examples 1 and 2 is used instead of the corona-resistant polyamide-imide insulating varnish provided in Example 1. All other materials, parameters, and processes are the same as in Application Example 1.

[0121] Comparative Application Example 3

[0122] An enameled wire differs from Application Example 1 only in that the materials for both the topcoat and primer coatings are commercially available polyamide-imide insulating varnish (BOYA AIP 36UN), while the other materials, parameters, and processes are the same as in Application Example 1.

[0123] Comparative Application Example 4

[0124] An enameled wire differs from Application Example 1 only in that a commercially available varnish 1 is used instead of the corona-resistant polyamide-imide insulating varnish provided in Example 1; all other materials, parameters, and processes are the same as in Application Example 1.

[0125] Performance testing:

[0126] (1) Elongation: The test shall be conducted in accordance with the test method provided in the national standard GB / T 4074.3-2008;

[0127] (2) Corona resistance time: When a voltage of 1500Vp is applied to the enameled wire at a frequency of 50Hz under an ambient temperature of 155℃, the time it takes for the enameled wire to break down and cause a short circuit is the corona resistance time.

[0128] (3) Salt water pinhole leakage test: The test shall be conducted in accordance with the test method provided in the national standard GB / T4074.5-2008. The test conditions are: 24V, 6M.

[0129] (4) Pressure resistance: The softening breakdown test was conducted according to the method provided in the national standard GB / T 4074.21-2018. The test conditions were 220℃ and 1min.

[0130] The enameled wires provided in Test Cases 1-8 and Comparative Application Examples 1-4 were tested according to the above test methods. The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] According to the data in Table 1:

[0135] The enameled wire made by coating with the corona-resistant polyamide-imide insulating varnish provided by the present invention has excellent voltage 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 rate of up to 45% to 47%, a corona resistance time of 55 to 131 hours, zero salt water pinholes, and pass the pressure resistance test.

[0137] Compared with Application Example 1, the withstand voltage test of the enameled wires provided in Application Examples 1 and 4 failed, indicating that the withstand voltage of the polyamide-imide insulating varnish made of epoxy silane-modified silica nanoparticles and the conventional commercially available varnish 1 after film formation were both poor.

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

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

[0140] The applicant declares that this invention illustrates a corona-resistant polyamide-imide insulating varnish, its preparation method, and its application through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection and disclosure scope of this invention.

Claims

1. A corona-resistant polyamide-imide insulating varnish, characterized in that, The raw materials for preparing the polyamide-imide insulating varnish include aromatic tricarboxylic anhydride, aromatic diisocyanate, and hydroxyl-modified silica nanoparticles. The polyamide-imide insulating varnish is obtained by a condensation reaction of aromatic tricarboxylic anhydride, aromatic diisocyanate and alcohol hydroxyl-modified silica nanoparticles; The raw materials for preparing the hydroxyl-modified silica nanoparticles include epoxy silane coupling agents, secondary amines, and silica nanoparticles. Based on a solid content of 100% for the polyamide-imide insulating varnish, the mass of the alcohol-hydroxyl-modified silica nanoparticles is 1-40%. The hydroxyl-modified silica nanoparticles were prepared by the following method, which includes the following steps: (A1) Reaction of epoxy silane coupling agent and silica nanoparticles yields epoxy silane-modified silica nanoparticles. (A2) React the epoxy silane-modified silica nanoparticles obtained in step (A1) with a secondary amine to obtain the alcohol hydroxyl-modified silica nanoparticles. The corona-resistant polyamide-imide insulating varnish is prepared by the following method, which includes the following steps: (1) A portion of aromatic tricarboxylic acid anhydrides and alcohol hydroxyl-modified silica nanoparticles were reacted to obtain an intermediate product; (2) The intermediate product obtained in step (1), the remaining aromatic tricarboxylic anhydride, aromatic diisocyanate and optionally aromatic dicarboxylic acid are reacted to obtain the corona-resistant polyamide-imide insulating varnish.

2. The polyamide-imide insulating varnish according to claim 1, characterized in that, The aromatic tricarboxylic anhydrides include trimellitic anhydride.

3. The polyamide-imide insulating varnish according to claim 1, characterized in that, The aromatic diisocyanate includes any one or a combination of at least two of the following: 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, phenyl dimethylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate, diphenyl ether diisocyanate, or diisocyanate polymers.

4. The polyamide-imide insulating varnish according to claim 1, characterized in that, The molar ratio of acidic groups to isocyanate groups in the raw materials for preparing the polyamide-imide insulating varnish is (0.95~1.05):

1.

5. The polyamide-imide insulating varnish according to claim 1, characterized in that, Based on a solid content of 100% for the polyamide-imide insulating varnish, the mass of the alcohol-hydroxyl-modified silica nanoparticles is 5-30%.

6. The polyamide-imide insulating varnish according to claim 1, characterized in that, The epoxy silane coupling agent includes any one or a combination of at least two compounds having the structure shown in Formula I, Formula II or Formula III; ； Formula I; In Equation I, R' is selected from -Me or -Et, and R'' is selected from... n = 0, 1, or 2, m = 1, 2, or 3; ； Formula II; In Equation II, R' is selected from -Me or -Et, and n = 0, 1 or 2; ； Formula III; In Equation III, R' is selected from -Me or -Et, n=0, 1 or 2, and m=0, 1 or 2.

7. The polyamide-imide insulating varnish according to claim 6, characterized in that, The epoxy silane coupling agent includes any one or a combination of at least two of γ-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

8. The polyamide-imide insulating varnish according to claim 1, characterized in that, Based on the mass of the silica nanoparticles being 100%, the mass of the epoxy silane coupling agent is 1~20%.

9. The polyamide-imide insulating varnish according to claim 8, characterized in that, Based on the mass of the silica nanoparticles being 100%, the mass of the epoxy silane coupling agent is 5-15%.

10. The polyamide-imide insulating varnish according to claim 1, characterized in that, The secondary amine includes any one or a combination of at least two of octadecylamine, diethylamine, or dibenzylamine.

11. The polyamide-imide insulating varnish according to claim 1, characterized in that, The D of the silica nanoparticles 50 The particle size is 10~300 nm.

12. The polyamide-imide insulating varnish according to claim 11, characterized in that, The D of the silica nanoparticles 50 The particle size is 10~80 nm.

13. The polyamide-imide insulating varnish according to claim 1, characterized in that, The silica nanoparticles are hydrophilic silica nanoparticles.

14. The polyamide-imide insulating varnish according to claim 1, characterized in that, The raw materials for preparing the polyamide-imide insulating varnish also include aromatic dicarboxylic acids.

15. The polyamide-imide insulating varnish according to claim 14, characterized in that, The aromatic dicarboxylic acid includes any one or a combination of at least two of terephthalic acid, isophthalic acid, or biphenyl acid.

16. The polyamide-imide insulating varnish according to claim 14, characterized in that... The mass ratio of the aromatic tricarboxylic anhydride to the aromatic dicarboxylic acid is not higher than 1:0.

4.

17. A method for preparing a corona-resistant polyamide-imide insulating varnish as described in any one of claims 1 to 16, characterized in that, The preparation method includes the following steps: (1) A portion of aromatic tricarboxylic acid anhydrides and alcohol hydroxyl-modified silica nanoparticles were reacted to obtain an intermediate product; (2) The intermediate product obtained in step (1), the remaining aromatic tricarboxylic anhydride, aromatic diisocyanate and optionally aromatic dicarboxylic acid are reacted to obtain the corona-resistant polyamide-imide insulating varnish.

18. The preparation method according to claim 17, characterized in that, The reaction described in step (1) is carried out in a mixed solvent.

19. The preparation method according to claim 18, characterized in that, The mixed solvent includes a first type of solvent and a second type of solvent; The first type of solvent includes any one or a combination of at least two of dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone or γ-butyrolactone; The second type of solvent includes any one or a combination of at least two of toluene, o-xylene, m-xylene, or p-xylene.

20. The preparation method according to claim 17, characterized in that, The reaction temperature in step (1) is 40~100℃.

21. The preparation method according to claim 20, characterized in that, The reaction temperature in step (1) is 60~80℃.

22. The preparation method according to claim 17, characterized in that, The reaction time in step (1) is 1 to 5 hours.

23. The preparation method according to claim 22, characterized in that, The reaction time in step (1) is 2 to 4 hours.

24. The preparation method according to claim 17, characterized in that, The reaction described in step (2) is carried out under a stepped heating condition.

25. The preparation method according to claim 24, characterized in that, The step (2) method of staged heating includes: heating the system to 25~80℃, reacting for 1~6 h, then heating to 120~150℃, reacting for 5~24 h, and completing the staged heating.

26. A corona-resistant enameled wire, characterized in that, The enameled wire includes a conductor and a corona-resistant polyamide-imide insulating varnish as described in any one of claims 1 to 16, which is cured and then covers the conductor.

27. The corona-resistant enameled wire according to claim 26, characterized in that, The thickness of the coating is 20~150 μm.

28. The corona-resistant enameled wire according to claim 26, characterized in that, The curing temperature is not lower than 300℃.

29. The application of a corona-resistant polyamide-imide insulating varnish as described in any one of claims 1 to 16 or a corona-resistant enameled wire as described in any one of claims 26 to 28 in an electric motor.

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