Heat-resistant polyurethane insulating varnish and preparation method thereof

Abstract

The present invention belongs to the field of insulating material preparation, and relates to a heat-resistant polyurethane insulating varnish and a preparation method thereof. The heat-resistant polyurethane insulating varnish, calculated by mass fraction, comprises 60-70 parts of a water-based resin matrix, 10-15 parts of water, 5-15 parts of a curing agent, 0-15 parts of a leveling agent, and 0.05-0.5 parts of an organosilane; the water-based resin matrix is ​​composed of a water-based epoxy resin and a water-based polyurethane resin. The preparation method of the insulating varnish selects suitable organosilane and water-based resin components, first heats and mixes the organosilane with the polyurethane resin, so that it is fully physically entangled and hydrolyzed and cross-linked with the polyurethane, and then acts as a film-forming component of the insulating varnish together with other components, effectively improving the temperature resistance of the insulating varnish, and also improving the flexibility of the film layer. The preparation method of the present invention is simple and efficient, avoids complex chemical reaction conditions, and the use of other chemical reagents, and ensures the green environmental protection of the water-based insulating varnish.

Description

Technical Field

[0001] The invention belongs to the field of insulating material preparation, and in particular relates to a heat-resistant polyurethane insulating varnish and a preparation method thereof. Background Art

[0002] Waterborne polyurethane is a common insulating varnish for electromagnetic wires and electronic coils. It has good effects in terms of pressure breakdown, firmness, flexibility, etc., and the product has excellent safety and environmental protection performance. However, it also has problems such as long baking time, poor temperature resistance, and low mechanical strength. For example, CN115011203A discloses an epoxy-modified polyurethane low cross-linking temperature waterborne insulating varnish and a preparation method thereof, which gives full play to the advantages of waterborne epoxy resin and waterborne polyurethane resin, and can perfectly combine the advantages of epoxy resin in terms of salt spray resistance, chemical resistance, good adhesion, and good flexibility, and the advantages of polyurethane in terms of good weather resistance, good flexibility, high hardness, strong cross-linking density, and low cross-linking temperature.

[0003] CN105017958A discloses a composite insulating varnish and a preparation method thereof, which comprises a polyurethane insulating varnish and a silicate-silicon dioxide hybrid, wherein the silicate-silicon dioxide hybrid is a silicate sheet with silicon dioxide particles loaded on its surface, and the obtained insulating varnish has a higher initial decomposition temperature and thermal stability.

[0004] In addition to using silicate-silicon dioxide hybrids, polysiloxanes can also improve certain properties of traditional polyurethanes, such as hydrophobicity, weather resistance, and low temperature resistance. There are two common methods for introducing polysiloxane into polyurethane systems. One is to use polysiloxane as a soft segment to synthesize polysiloxane-polyurethane; the other is to mix polysiloxane with traditional terminal hydroxyl polyether to synthesize polysiloxane-modified polyurethane. CN116200025A discloses a new three-component blended polyurethane thermoplastic elastomer and a preparation method thereof, that is, a compound is reacted with a terminal hydroxyl hydrocarbon polysiloxane to obtain a polysiloxane-polyurethane polymer. In addition, CN116547332A discloses an epoxy resin polysiloxane coating composition having a curing system based on polyurethane-metal or organic matter, comprising polysiloxane, non-aromatic epoxy resin and a curing system. However, this system is designed to solve the problem that the curing rate is easily affected by relative humidity, and the process is complicated. Summary of the invention

[0005] In view of the problem that the existing epoxy-modified polyurethane water-based insulating varnish has insufficient heat resistance, the purpose of the present invention is to propose a method for improving the heat resistance, chemical resistance and mechanical properties of polyurethane insulating varnish by adding organic silane, and to make full use of the coupling reaction between organic silane and polyurethane to obtain a modified insulating coating material.

[0006] The specific technical solutions of the present invention are as follows:

[0007] In a first aspect of the present invention, a method for preparing a heat-resistant polyurethane insulating varnish is provided. The raw materials of the heat-resistant polyurethane insulating varnish include 60-70 parts of a water-based resin matrix, 10-15 parts of water, 5-15 parts of a curing agent, 0-15 parts of a leveling agent, and 0.05-0.5 parts of an organic silane, calculated by weight; the water-based resin matrix is ​​composed of a water-based epoxy resin and a water-based polyurethane resin; the method for preparing the heat-resistant polyurethane insulating varnish includes the following steps:

[0008] (1) Mix the organosilane, waterborne polyurethane resin and part of water, heat to 50-80°C and stir evenly.

[0009] (2) Add water-based epoxy resin and curing agent to the solution obtained in step (1) and stir evenly.

[0010] (3) Add the leveling agent and the remaining water to the solution obtained in step (2) and stir evenly, then filter and degas by pressure filtration.

[0011] By adding organosilane to polyurethane insulating varnish and combining it with process improvements, the organosilane and polyurethane resin are first heated and mixed to allow the organosilane and polyurethane to be fully physically entangled and hydrolyzed and cross-linked, and then used together with other components as a film-forming component of the insulating varnish, the heat resistance and flexibility of the film layer can be significantly improved.

[0012] Preferably, the mass ratio of the waterborne epoxy resin to the waterborne polyurethane resin is 1:1-2, and the paint film performance is better.

[0013] Preferably, the curing agent is a water-based amino resin. Further preferably, the water-based amino resin is selected from a combination of one or more of methyl etherified amino resin, butanol etherified amino resin and isobutanol etherified amino resin.

[0014] Preferably, the organosilane is selected from methylsilane, ethylsilane and propylsilane.

[0015] Preferably, in step (1), the stirring time is 20-120 min and the stirring speed is 200-1000 rpm.

[0016] Preferably, in step (2), the stirring time is 5-60 min and the stirring speed is 2000-8000 rpm.

[0017] Preferably, in step (3), the stirring time is 5-60 min and the stirring speed is 2000-8000 rpm.

[0018] The second aspect of the present invention also provides a heat-resistant polyurethane insulating varnish obtained by the above preparation method.

[0019] The beneficial effects of the present invention are:

[0020] Compared with the prior art, the present invention adds a very small amount of organosilane (less than 0.5 by mass) to the polyurethane insulating varnish under simple and convenient conditions, so that it is physically entangled and hydrolyzed and cross-linked with the polyurethane, and together with the water-based resin, it serves as a film-forming component of the insulating varnish, which effectively improves the temperature resistance of the insulating varnish and the flexibility of the film layer. At the same time, the preparation method of the present invention is simple and efficient, avoiding complex chemical reaction conditions and the use of other chemical reagents, ensuring the green and environmental protection of the water-based insulating varnish. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the infrared spectra of the sample of comparative example 4 and the sample of embodiment 3 of the present invention;

[0022] Figure 2 It is the DSC graph of the sample of comparative example 4 and the sample of embodiment 3 of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0024] Example 1

[0025] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 5 parts of a methyl etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 20 parts of a water-based epoxy resin and 50 parts of a water-based polyurethane resin.

[0026] The preparation method is as follows:

[0027] (1) Mix 0.2 parts of hexamethyldisiloxane, 50 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 50°C, stir for 120 minutes and stir at 1000 rpm.

[0028] (2) Add 20 parts of waterborne epoxy resin and 5 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 30 minutes at a stirring speed of 6000 rpm.

[0029] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred for 30 min at a speed of 6000 rpm, and then filtered for degassing.

[0030] Example 2

[0031] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 60 parts of a water-based resin matrix, 10 parts of water, 10 parts of methyl etherified amino resin, 5 parts of a leveling agent, and 0.05 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 30 parts of a water-based polyurethane resin.

[0032] The preparation method is as follows:

[0033] (1) Mix 0.05 parts of hexamethyldisiloxane, 30 parts of waterborne polyurethane resin and 5 parts of water, heat and stir at 60°C, stir for 80 minutes and at a speed of 800 rpm.

[0034] (2) Add 30 parts of waterborne epoxy resin and 10 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 30 minutes at a stirring speed of 6000 rpm.

[0035] (3) Add 5 parts of leveling agent and the remaining 5 parts of water to the solution obtained in step (2) and stir evenly for 20 min at a stirring speed of 6000 rpm, and then filter press to degas.

[0036] Example 3

[0037] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a methyl etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0038] The preparation method is as follows:

[0039] (1) Mix 0.2 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 80°C, stir for 30 minutes and at a speed of 600 rpm.

[0040] (2) Add 30 parts of waterborne epoxy resin and 15 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 60 minutes at a stirring speed of 3000 rpm.

[0041] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0042] Example 4

[0043] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 5 parts of a butanol-etherified amino resin, 10 parts of a leveling agent, and 0.1 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 40 parts of a water-based epoxy resin and 30 parts of a water-based polyurethane resin.

[0044] The preparation method is as follows:

[0045] (1) Mix 0.1 parts of hexamethyldisiloxane, 30 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 80°C, stir for 5 minutes and at a speed of 1000 rpm.

[0046] (2) Add 40 parts of waterborne epoxy resin and 5 parts of butanol etherified amino resin to the solution obtained in step (1), and stir evenly for 60 minutes at a stirring speed of 4000 rpm.

[0047] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0048] Example 5

[0049] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 10 parts of a butanol-etherified amino resin, 5 parts of a leveling agent, and 0.05 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 20 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0050] The preparation method is as follows:

[0051] (1) Mix 0.05 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 50°C, stir for 20 minutes and at a speed of 1000 rpm.

[0052] (2) Add 20 parts of waterborne epoxy resin and 10 parts of butanol etherified amino resin to the solution obtained in step (1), and stir evenly for 5 minutes at a stirring speed of 8000 rpm.

[0053] (3) Add 5 parts of leveling agent and the remaining 5 parts of water to the solution obtained in step (2) and stir evenly for 50 min at a stirring speed of 2000 rpm, and then filter press to degas.

[0054] Example 6

[0055] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a butanol-etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of methyltrimethoxysilane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0056] The preparation method is as follows:

[0057] (1) Mix 0.2 parts of methyltrimethoxysilane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 70°C, stir for 30 minutes and at a speed of 1000 rpm.

[0058] (2) Add 30 parts of waterborne epoxy resin and 15 parts of butanol etherified amino resin to the solution obtained in step (1), and stir evenly for 30 minutes at a stirring speed of 3000 rpm.

[0059] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred for 5 min at a speed of 5000 rpm, and then filtered for degassing.

[0060] Example 7

[0061] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of isobutyl alcohol etherified amino resin, 10 parts of a leveling agent, and 0.15 parts of methyltrimethoxysilane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0062] The preparation method is as follows:

[0063] (1) 0.15 parts of methyltrimethoxysilane, 40 parts of waterborne polyurethane resin and 10 parts of water were mixed, heated and stirred at 80°C, stirring time of 80 minutes and stirring speed of 200 rpm.

[0064] (2) Add 30 parts of waterborne epoxy resin and 15 parts of isobutyl alcohol etherified amino resin to the solution obtained in step (1), stir evenly for 15 minutes at a stirring speed of 6000 rpm.

[0065] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0066] Example 8

[0067] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by weight, include 70 parts of a water-based resin matrix, 15 parts of water, 10 parts of isobutyl alcohol etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of methyltrimethoxysilane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0068] The preparation method is as follows:

[0069] (1) Mix 0.2 parts of methyltrimethoxysilane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 70°C, stir for 50 minutes and at a speed of 600 rpm.

[0070] (2) Add 30 parts of waterborne epoxy resin and 15 parts of isobutyl alcohol etherified amino resin to the solution obtained in step (1), stir evenly for 40 minutes at a stirring speed of 6000 rpm.

[0071] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0072] Example 9

[0073] A heat-resistant polyurethane insulating varnish, whose raw materials, calculated by weight, include 70 parts of a water-based resin matrix, 15 parts of water, 5 parts of isobutyl alcohol etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0074] The preparation method is as follows:

[0075] (1) Mix 0.2 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 80°C, stir for 50 minutes and at a speed of 600 rpm.

[0076] (2) Add 30 parts of waterborne epoxy resin and 5 parts of isobutyl alcohol etherified amino resin to the solution obtained in step (1), and stir evenly for 30 minutes at a stirring speed of 5000 rpm.

[0077] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 10 min at a stirring speed of 6000 rpm, and then filtered for degassing.

[0078] Comparative Example 1

[0079] A polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a methyl etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0080] The preparation method is as follows:

[0081] (1) Mix 0.2 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin, 10 parts of water, 30 parts of waterborne epoxy resin, and 15 parts of methyl etherified amino resin, and stir them evenly for 60 minutes at a stirring speed of 3000 rpm.

[0082] (2) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0083] The difference from Example 3 is that the process is different, silane is directly mixed with the resin, etc., and the rest is the same.

[0084] Comparative Example 2

[0085] A polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a methyl etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0086] The preparation method is as follows:

[0087] (1) Mix 0.2 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 30°C, stir for 30 minutes and stir at 600 rpm.

[0088] (2) Add 30 parts of waterborne epoxy resin and 15 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 60 minutes at a stirring speed of 3000 rpm.

[0089] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0090] The difference from Example 3 is that in step (1) of the preparation method, the heating temperature is 30° C., and the rest is the same.

[0091] Comparative Example 3

[0092] A polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a methyl etherified amino resin, 10 parts of a leveling agent, and 0.2 parts of hexamethyldisiloxane; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0093] The preparation method is as follows:

[0094] (1) Mix 0.2 parts of hexamethyldisiloxane, 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 90°C, stir for 30 minutes and at a speed of 600 rpm.

[0095] (2) Add 30 parts of waterborne epoxy resin and 15 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 60 minutes at a stirring speed of 3000 rpm.

[0096] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0097] The difference from Example 3 is that in step (1) of the preparation method, the heating temperature is 90° C., and the rest is the same.

[0098] Comparative Example 4

[0099] A polyurethane insulating varnish, whose raw materials, calculated by mass, include 70 parts of a water-based resin matrix, 15 parts of water, 15 parts of a methyl etherified amino resin, and 10 parts of a leveling agent; the water-based resin matrix is ​​composed of 30 parts of a water-based epoxy resin and 40 parts of a water-based polyurethane resin.

[0100] The preparation method is as follows:

[0101] (1) Mix 40 parts of waterborne polyurethane resin and 10 parts of water, heat and stir at 80°C, stir for 30 minutes, and stir at 600 rpm.

[0102] (2) Add 30 parts of waterborne epoxy resin and 15 parts of methyl etherified amino resin to the solution obtained in step (1), and stir evenly for 60 minutes at a stirring speed of 3000 rpm.

[0103] (3) 10 parts of leveling agent and the remaining 5 parts of water were added to the solution obtained in step (2) and stirred evenly for 30 min at a stirring speed of 4000 rpm, and then filtered for degassing.

[0104] The difference from Example 3 is that no organosilane is added.

[0105] Performance Test:

[0106] The insulating paint samples obtained in the examples and comparative examples were subjected to general performance tests in the industry, and the results are shown in Table 1.

[0107] Table 1 Performance test

[0108]

[0109] As can be seen from Table 1, adding a very small amount of organosilane (mass fraction less than 0.5) can improve the heat resistance of the insulating paint. The samples obtained in Examples 2 to 7 and 9 can all remain in a state of no cracking and no powdering at above 200°C, which is significantly improved by 30-60°C compared with Comparative Examples 1-3. Especially when the mass ratio of waterborne epoxy resin to waterborne polyurethane resin is 1:1-2, the improvement is more obvious. It should be noted that, considering the existence of amino groups in the curing agent, the organosilane in the present invention cannot contain amino groups, and only methylsilane, ethylsilane, and propylsilane with simple structures need to be selected.

[0110] The samples of Example 3 and Comparative Example 4 were further subjected to chemical structure analysis test, and the results were as follows: Figure 1 As shown in the figure, it can be seen that the technology of the present invention does not affect the chemical structure of conventional polyurethane insulating paint, ensuring the chemical group characteristic requirements of existing polyurethane insulating paint. Figure 2 It can be seen from the DSC analysis diagrams of the samples (Example 3 and Comparative Example 4) that after the introduction of the silane system, the heat resistance of the insulating varnish is significantly improved, indicating that the structure of the sample prepared by the present invention has good stability at higher temperatures. The heat resistance test results of the samples in Examples 1-9 also verify this point.

[0111] In addition, the comparison between Example 3 and Comparative Examples 1-3 also shows that the process also has an impact on heat resistance. If the organosilane is not fully dispersed with the polyurethane resin in advance to allow it to be physically entangled and hydrolyzed and cross-linked with the polyurethane, but the organosilane is directly mixed, the heat resistance cannot be improved well, and the heat resistance is equivalent to that of the polyurethane insulating paint without the addition of the organosilane. Moreover, the results of Comparative Examples 2-3 show that the appropriate dispersion temperature is also a key factor in obtaining good flexibility of the paint film.

[0112] In addition, the performance test in Table 1 also shows that the elongation of the insulating paint of the present invention is improved to a certain extent after coating, and no cracks occur on the surface, indicating that the flexibility is improved.

[0113] In summary, it can be seen that the polyurethane water-based insulating paint of the present invention greatly improves the heat resistance temperature of the insulating paint after using organic silane, while the basic chemical structure of the original insulating paint is not changed, and the flexibility of the obtained coating is also significantly improved.

[0114] The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a heat-resistant polyurethane insulating varnish, characterized in that: Calculated by weight, the raw materials of the heat-resistant polyurethane insulating paint include 60-70 parts of a water-based resin matrix, 10-15 parts of water, 5-15 parts of a curing agent, 0-15 parts of a leveling agent, and 0.05-0.5 parts of an organic silane; the water-based resin matrix is ​​composed of a water-based epoxy resin and a water-based polyurethane resin; the organic silane is selected from one of methyl silane, ethyl silane, and propyl silane; the curing agent is a combination of one or more selected from methyl etherified amino resin and butanol etherified amino resin; The preparation method of the heat-resistant polyurethane insulating varnish comprises the following steps: (1) Mix the organosilane, waterborne polyurethane resin and part of water, heat to 50-80°C and stir evenly. (2) Add water-based epoxy resin and curing agent to the solution obtained in step (1) and stir evenly. (3) Add the leveling agent and the remaining water to the solution obtained in step (2) and stir evenly, then filter and degas by pressure filtration.

2. The method for preparing the heat-resistant polyurethane insulating varnish according to claim 1, characterized in that: The butanol etherified amino resin includes isobutanol etherified amino resin.

3. The method for preparing the heat-resistant polyurethane insulating varnish according to claim 1, characterized in that: The mass ratio of the waterborne epoxy resin to the waterborne polyurethane resin is 1:1-2.

4. The method for preparing the heat-resistant polyurethane insulating varnish according to claim 1, characterized in that: In the step (1), the stirring time is 20-120 min, and the stirring speed is 200-1000 rpm.

5. The method for preparing the heat-resistant polyurethane insulating varnish according to claim 1, characterized in that: In the step (2), the stirring time is 5-60 min, and the stirring speed is 2000-8000 rpm.

6. The method for preparing the heat-resistant polyurethane insulating varnish according to claim 1, characterized in that: In the step (3), the stirring time is 5-60 min, and the stirring speed is 2000-8000 rpm.

7. A heat-resistant polyurethane insulating varnish, characterized in that: The heat-resistant polyurethane insulating varnish is obtained by the preparation method described in any one of claims 1-6.

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