A high solid content polyamic acid slurry based on PAA nanoparticles, preparation method and application thereof

Abstract

This invention provides a high-solids-content polyamic acid slurry based on PAA nanoparticles, its preparation method, and its application. The polyamic acid slurry is prepared by high-speed dispersion of a low-viscosity PAA solution and PAA nanoparticles; the mass ratio of PAA nanoparticles to the low-viscosity PAA solution in the slurry is 0.1-1, and the solid content is 20-60%; the low-viscosity PAA solution is obtained by low-temperature homogeneous polycondensation of dianhydride and diamine in a solvent at a molar ratio of 1.01-1.1, and the PAA solution has a solid content of 10-20 wt.% and a viscosity of 100-1000 mPa·s; the PAA nanoparticles are obtained from the PAA solution by precipitation, with an average particle size <500 nm. The PI coating obtained from this slurry has comprehensive properties such as withstand voltage ≥1000V DC, insulation resistance >1GΩ, high temperature resistance of 400℃, adhesion grade 0, no cracking after 30° bending, hardness ≥5H, scratch resistance, and abrasion resistance. This invention is applicable to high-end protective fields where high requirements are placed on the heat resistance, insulation, uniformity, density, and reliability of the coating.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and corrosion-resistant coatings, specifically to a high-solids-content polyamic acid slurry based on PAA nanoparticles, its preparation method, and its application. Background Technology

[0002] Polyimide (PI) materials possess excellent high-temperature resistance, mechanical properties, electrical insulation properties, chemical stability, flame retardancy, and corrosion resistance. Their films, fibers, and resins have wide applications in aerospace, electronics, and new energy fields. However, PI is rarely used in corrosion-resistant coatings, primarily due to its poor solubility. Its precursor, polyamic acid (PAA), typically has a low solids content (usually below 20%) and high viscosity (above 10,000 mPa·s), resulting in poor workability. It is difficult to level and defoam at low temperatures, and prone to sagging during high-temperature curing, with each coat typically only reaching a thickness of 10-30 μm. These problems significantly limit the application of PI materials in corrosion-resistant coatings. The interior of lithium battery aluminum casings is in constant contact with highly corrosive electrolytes, making them prone to corrosion and leakage, which severely impacts battery life and safety, especially in high-voltage battery systems and harsh operating conditions. Therefore, there is an urgent need for a protective coating material that combines voltage resistance, insulation, high-temperature resistance, chemical stability, flame retardancy, and good application performance.

[0003] In existing technologies, methods such as adjusting monomer ratios, controlling polymerization temperature, or introducing chemically modified groups are commonly used to increase the solids content and reduce viscosity of PAA solutions. For example, polyamic acid esters are prepared by partial alcoholysis of dianhydrides and monohydric alcohols, replacing some carboxyl groups with ester groups to weaken intermolecular hydrogen bonding and thus reduce viscosity. However, such chemical modification methods alter the intrinsic chemical structure of PAA, potentially affecting the overall performance of the final PI coating, and the preparation process is complex. Another approach is to increase the solids content by adding inorganic nanofillers, but inorganic fillers suffer from poor compatibility with organic matrices, easy agglomeration, and interfacial defects, making it difficult to simultaneously meet the requirements of high solids content, moderate viscosity, and excellent coating performance. Furthermore, there are no reports in existing technologies of using homogeneous PAA nanoparticles combined with low-viscosity PAA solutions to construct high-solids slurries. Summary of the Invention

[0004] Technical problem to be solved: The present invention aims to provide a high-solids-content polyamic acid slurry based on PAA nanoparticles, its preparation method and application; developing a PAA slurry that maintains the intrinsic chemical structure of PAA, achieves a synergistic effect of high solids content and moderate viscosity, and possesses excellent workability and comprehensive coating protection capabilities is a technical problem that urgently needs to be solved in this field.

[0005] Technical solution: A high-solids polyamic acid slurry based on PAA nanoparticles, wherein the polyamic acid slurry comprises a low-viscosity PAA solution and PAA nanoparticles dispersed in the low-viscosity PAA solution, wherein the mass ratio of the PAA nanoparticles to the low-viscosity PAA solution is 0.1-1, and the solids content of the polyamic acid slurry is 20-60%.

[0006] Preferably, the low-viscosity PAA solution is prepared by the following steps: S1. Under nitrogen positive pressure protection, add solvent to the reactor, then add diamine under stirring, and dissolve the diamine at room temperature or by gradually heating to 35°C until it is clear and transparent, then cool down to 0-10°C; S2. Turn on the reflux cooling device of the reactor. Under the protection of nitrogen positive pressure throughout the process, add the solvent and dianhydride in sequence to another reactor. Under stirring, slowly raise the temperature to 120-140℃. After the reactants are dissolved and clear, slowly lower the temperature to below 50℃. Replace with an ice bath and continue to lower the temperature to below 10℃. S3. Slowly add the diamine solution obtained in step S1 to the reaction system in step S2, and continue the reaction for 6-8 hours to obtain a clear and transparent yellow PAA solution.

[0007] Preferably, the method for preparing the PAA nanopowder includes the following steps: S11. A PAA solution with a concentration of 1-5 wt.% is added dropwise to an acetone solution containing 0.1-1 wt.% polyvinylpyrrolidone to obtain a slightly blue PAA suspension; S12. The PAA suspension was centrifuged to obtain solid powder, which was then washed with acetone and petroleum ether in sequence and dried under vacuum to obtain PAA nanoparticles.

[0008] Preferably, the method for preparing the high-solids polyamic acid slurry based on PAA nanoparticles involves dispersing the PAA nanoparticles at high speed in the low-viscosity PAA at a rotation speed of 2000-8000 r / min to obtain the PAA slurry; then storing the PAA slurry at 0-5°C under nitrogen-sealed conditions for more than 180 days.

[0009] Preferably, the diamine is any one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, or p-phenylenediamine; the dianhydride is any one of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; and the solvent is one or more of N,N-dimethylacetamide and N-methylpyrrolidone.

[0010] Preferably, the molar ratio of the dianhydride to the diamine is 1.01-1.1.

[0011] Preferably, the solid content of the low-viscosity PAA solution is 10-20 wt.%; and the viscosity is 100-1000 mPa.s.

[0012] Preferably, the average particle size of the PAA nanoparticles is less than 500 nm.

[0013] Preferably, the application of the high-solids-content polyamic acid slurry based on PAA nanoparticles in the preparation of PI coatings, wherein the PI coating is prepared by the following steps: Substrate treatment: The substrate is sanded or sandblasted, then cleaned with ethanol and dried; Coating: The PAA slurry is coated onto the treated substrate; Stepwise curing: The coated substrate is sequentially subjected to imidization curing in an 80℃ oven for 30-60 min, an 140℃ oven for 30-60 min, and an 250℃ oven for 30-60 min to obtain a PI coating with a thickness of 20-100 μm.

[0014] Beneficial effects: The high-solids-content polyamic acid slurry based on PAA nanoparticles of this invention has the following advantages: In this invention, when PAA is dispersed in the form of nanoparticles in a low-viscosity PAA continuous phase, the dynamic physical entanglement between the uniminoamic acid groups on the surface of the nanoparticles and the continuous phase can significantly reduce the rapid growth effect of chain entanglement in the traditional PAA system, thereby ensuring that the slurry remains coatable even when the solid content is increased to 20-60 wt.%.

[0015] This invention overcomes the contradiction between high solids content and low viscosity. Compared to traditional PAA solutions, the PAA slurry of this invention has a high solids content and a relatively low viscosity, making it suitable for both flat substrates and the inner walls of complex-shaped battery casings. It is self-leveling, does not easily drip on vertical surfaces, is easy to apply, and can form a uniform and dense coating. A single coating can achieve a thickness greater than 30 micrometers, reducing the problem of uneven coating thickness caused by multiple coatings.

[0016] In this invention, PAA nanoparticles are added, whose molecular structure is the same as that of the original PAA molecule, resulting in good compatibility. In addition, the average particle size is less than 500 nm, which is a suitable particle size, ensuring that the slurry has excellent storage stability even without the addition of any stabilizers.

[0017] The PI coating obtained in this invention has excellent and balanced comprehensive performance, meeting the requirements of high voltage resistance of 1000V DC with leakage current <0.1mA, high temperature resistance at 400℃ for 1-2 hours, high insulation greater than 1 GΩ, adhesion reaching level 0, good flexibility that can be bent at 30° without cracking, hardness ≥5H, scratch resistance that meets the requirements of 2000g load without damage, and wear resistance that meets the requirements of 1000 cycles of friction under 1Kg load without damage.

[0018] This invention significantly reduces the solvent content, making it more environmentally friendly; it also reduces the number of coating passes and improves coating efficiency. Attached Figure Description

[0019] Figure 1 Photograph of a low-viscosity PAA solution; Figure 2 Photograph of PAA suspension; Figure 3 Photo of PAA nanoparticles Figure 4 The image shows the PAA infrared spectrum (ATR). Figure 5 Here is a scanning electron microscope (SEM) image of PAA nanoparticles; Figure 6 Photograph of high-solids PAA slurry; Figure 7 Photograph of PI coating; Figure 8 The infrared spectrum (ATR) of PI; Figure 9 The thermogravimetric analysis (TGA) curves of the PI coating in air atmosphere are shown. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1

[0021] Synthesis of low-viscosity polyamic acid (PAA) solution Under nitrogen protection, 15.37 g of 4,4'-diaminodiphenyl ether (ODA) was added to a reactor at room temperature, followed by 50 g of N-methylpyrrolidone (NMP). The mixture was stirred until the diamine dissolved and became clear. The temperature was then gradually lowered to 5°C. Under positive nitrogen pressure, 22.8 g of solid 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 130 g of NMP were added sequentially to another reactor with a reflux condenser. The mixture was stirred and slowly heated to 120°C until the reactants dissolved and became clear. The temperature was then slowly lowered to below 50°C, and an ice bath was used to further cool the mixture to below 10°C. The ODA solution was then slowly added dropwise, and the reaction was allowed to proceed for 6 hours. The reactants were observed to be clear and transparent. Finally, a deep orange transparent PAA solution with a solid content of 17.5% and a viscosity of approximately 200 mPa·s (rotational viscometer) was obtained. Figure 1 As shown; Example 2

[0022] Synthesis of low-viscosity polyamic acid (PAA) solution Under nitrogen protection, 15.37 g of 4,4'-diaminodiphenyl ether (ODA) was added to a reactor at room temperature, followed by 50 g of N-methylpyrrolidone (NMP). The mixture was stirred until the diamine dissolved and became clear. The temperature was then gradually lowered to 0°C. Under positive nitrogen pressure, 24.98 g of solid 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 246 g of NMP were added sequentially to another reactor with a reflux condenser. The mixture was stirred, and the temperature was slowly raised to 140°C until the reactants dissolved. The temperature was then slowly lowered to below 50°C, and the reactor was placed in an ice bath. The temperature was then lowered to below 10°C. The ODA solution was slowly added dropwise, and the reaction was allowed to proceed for 8 hours. The final product was a yellow PAA solution with a solid content of 12% and a viscosity of approximately 500 mPa·s (rotational viscometer).

[0023] Example 3

[0024] Synthesis of low-viscosity polyamic acid (PAA) solution Under nitrogen protection, 15.37 g of 4,4'-diaminodiphenyl ether (ODA) was added to a reactor at room temperature, followed by 50 g of N,N-dimethylacetamide (DMAC). The mixture was stirred until the diamine dissolved and became clear. The temperature was gradually lowered to 3°C. Under positive nitrogen pressure, 17.08 g of solid pyromellitic dianhydride (PMDA) and 134 g of DMF were added sequentially to another reactor with a reflux condenser. The mixture was stirred, and the temperature was slowly raised to 120°C until the reactants dissolved and became clear. The temperature was then slowly lowered to below 50°C, and an ice bath was used to further cool the mixture to below 10°C. The ODA solution was slowly added dropwise, and the reaction was allowed to proceed for 8 hours. The final product was a yellow, transparent PAA solution with a solid content of 15% and a viscosity of approximately 250 mPa·s (rotational viscometer).

[0025] Example 4

[0026] Preparation of polyamic acid (PAA) nanoparticles Under nitrogen protection, magnetic stirring, and at room temperature, 200g of PAA solution (1%) was added dropwise to 1000g of acetone solution containing a small amount of polyvinylpyrrolidone (PVP) (0.1%). The resulting PAA suspension was as follows: Figure 2 The PAA suspension was then centrifuged to obtain a solid powder sample, which was subsequently washed with acetone and petroleum ether, and then vacuum dried to obtain PAA nanoparticles with an average particle size of less than 200 nm. Figure 5 As shown.

[0027] Example 5

[0028] Preparation of polyamic acid (PAA) nanoparticles Under nitrogen protection, magnetic stirring, and at room temperature, 200g of PAA solution (3%) was added dropwise to 1400g of acetone solution containing a small amount of polyvinylpyrrolidone (PVP) (0.5%) to obtain a PAA suspension. The PAA suspension was then centrifuged to obtain a solid powder sample, which was then washed with acetone and petroleum ether in sequence and vacuum dried to obtain PAA nanoparticles with an average particle size of less than 500nm.

[0029] Example 6

[0030] Preparation of PI coating on aluminum sheet Substrate treatment: Polish the 3003 aluminum sheet with fine sandpaper, clean it with ethanol and dry it; Preparation of coating solution and coating: 6 g of the PAA solution obtained in Example 1 and 1.0 g of the PAA powder obtained in Example 4 were rapidly dispersed and mixed, and after standing for 2 hours, a high-solids PAA slurry (e.g.) was obtained. Figure 6 As shown), the aluminum sheet is coated using a wire rod. Curing: The coated aluminum sheet was sequentially placed in an 80℃ oven for 30 min, an 140℃ oven for 30 min, and a 250℃ oven for 30 min to obtain a uniform PI coating of approximately 30 μm thickness. Figure 7 As shown.

[0031] Example 7

[0032] Preparation of PI coating on aluminum sheet Substrate treatment: Polish the 3003 aluminum sheet with fine sandpaper, clean it with ethanol and dry it; Preparation of coating solution and coating: 6g of PAA solution obtained in Example 3 and 3g of PAA powder obtained in Example 5 were dispersed and mixed at high speed. After standing for 2 hours, a high solids content and low viscosity PAA slurry was obtained and manually coated on the surface of aluminum sheet using a wire rod. Curing: The coated aluminum sheet was placed in an 80℃ oven for 45 min, a 140℃ oven for 45 min, and a 250℃ oven for 45 min in sequence to obtain a uniform PI coating of about 50 μm.

[0033] Comparative Example 1 The main difference between Comparative Example 1 and Example 6 is that: a low-viscosity PAA solution (solid content 17.5%, viscosity 200 mPa·s) was prepared according to the method of Example 1, without adding any PAA nanopowder, and the solution was directly coated onto the treated aluminum sheet according to the method of Example 6, and then cured by gradient heating to obtain a PI coating of about 20 μm.

[0034] Comparative Example 2 The subject difference between Comparative Example 2 and Example 6 is as follows: A low-viscosity PAA solution (solid content 17.5%, viscosity 200 mPa·s) was prepared according to the method of Example 1 without adding any PAA nanopowder. The solution was directly coated onto the treated aluminum sheet according to the method of Example 6. After being placed in an 80°C oven for 30 min, it was removed and cooled. The PAA solution was then coated onto the existing coating, and the sheet was placed in an 80°C oven for 30 min, an 140°C oven for 30 min, and an 250°C oven for 30 min to obtain a PI coating with a thickness of about 40 μm.

[0035] Comparative Example 3 The main difference between Comparative Example 3 and Example 6 is that the low-viscosity PAA solution was prepared according to the process of Example 1, but the molar ratio of dianhydride / diamine was 1.2. Without adding any PAA nanopowder, the solution was directly coated onto the treated aluminum sheet according to the method of Example 6, and then cured to obtain a PI coating of approximately 20 μm.

[0036] Comparative Example 4 The subject difference between Comparative Example 4 and Example 7 is that: 6 g of PAA solution obtained in Example 1 and 3.0 g of PAA powder (particles in block form) were dispersed and mixed at high speed, and after standing for 2 hours, a high solids content PAA slurry was obtained. The slurry was coated onto the surface of an aluminum sheet using a wire rod. The coated aluminum sheet was then placed in an 80°C oven for 30 min, a 140°C oven for 30 min, and a 250°C oven for 30 min in sequence to obtain a PI coating of 30-50 μm.

[0037] Comparative Example 5 The subject difference between Comparative Example 5 and Example 6 is as follows: 6 g of PAA solution and 8 g of PAA nanoparticles obtained in Example 1 were dispersed and mixed at high speed, and after standing for 2 hours, a high solids PAA slurry was obtained, which was then coated onto the surface of an aluminum sheet using a wire rod; Curing: the coated aluminum sheet was placed in an 80℃ oven for 30 min, an 140℃ oven for 30 min, and a 250℃ oven for 30 min in sequence to obtain a PI coating of 30-80 μm.

[0038] Comparative Example 6 The main difference between Comparative Example 6 and Example 7 is that the viscosity of the PAA solution used is 5000 mPa·s. 6 g of this PAA solution and 3.0 g of PAA nanoparticles were dispersed and mixed at high speed, and after standing for 2 hours, a high-solids PAA slurry was obtained. This slurry was then coated onto the surface of an aluminum sheet using a wire rod. The coated aluminum sheet was then sequentially placed in an 80°C oven for 30 min, a 140°C oven for 30 min, and a 250°C oven for 30 min to obtain a PI coating of 30-80 μm.

[0039] Performance testing: Withstand voltage test: The insulation withstand capability of the coating under DC high voltage is evaluated using a safety tester.

[0040] High temperature resistance test: Usually, an oven heat aging test is used to observe whether the coating blisters, peels off or carbonizes at high temperature.

[0041] Insulation resistance test: Use a safety tester to measure the insulation resistance of the coating.

[0042] Adhesion test: The cross-cut test (GB / T 9286) is used. Grade 0 means that the cut edge is completely smooth and no cross-cuts fall off.

[0043] Flexibility test: Commonly used bending test (such as GB / T 1731), no cracks after bending at 30° indicates that the coating has good bending resistance.

[0044] Pencil hardness test: According to GB / T 6739, use pencils of different hardness to scratch the coating surface. ≥5H indicates that the coating has a high hardness.

[0045] Scratch resistance test: Using a scratch tester, a scratch needle is used to scratch the coating surface under a load of 2000g. If there is no scratch, it is considered qualified.

[0046] Wear resistance test: The commonly used Taber wear test (GB / T 1768) is to rotate and rub for 1000 revolutions under a 1Kg load. If there is no wear, it meets the requirements.

[0047] Table 1 Example 6 32 1000 <0.1 pass pass Example 7 55 1000 <0.1 pass pass Comparative Example 1 18 1000 <0.1 pass pass Comparative Example 2 39 1000 <0.1 pass pass Comparative Example 3 21 1000 <0.1 pass pass Comparative Example 4 62 1000 Local > 0.1 pass Partial failure Comparative Example 5 69 1000 Local > 0.1 pass Partial failure Comparative Example 6 55 1000 Local > 0.1 pass Partial failure In Comparative Examples 4-5, the coating surface was uneven, with obvious defects and localized leakage.

[0048] Table 2 Example 6 0 No cracks 5H pass pass Example 7 0 No cracks 5H pass pass Comparative Example 1 0 No cracks 5H pass pass Comparative Example 2 0 No cracks 5H pass pass Comparative Example 3 0 Cracks 5H pass pass Comparative Example 4 - - - - - Comparative Example 5 - - - - - Comparative Example 6 - - - - - In Comparative Examples 4-6, the coating surface was uneven and had obvious defects, making it impossible to conduct overall performance testing. Figure 4 2500-3500cm -1The broad peak is attributed to the complex characteristic peak of carboxylic acid and amino groups in PAA; 1712 cm⁻¹ -1 The absorption peak is due to the stretching vibration of the carbonyl group in the carboxyl group; 1640 cm⁻¹ -1 The peak represents the stretching vibration of the carbonyl group in the amide group. This indicates that PAA has been successfully synthesized. Figure 5 As can be seen, PAA nanoparticles are mainly spherical, elliptical, or peanut-shell shaped, consisting of two spherical particles connected together, with an average particle size of less than 200 nm. Figure 8 This is the total reflectance infrared spectrum of PI. 1775cm -1 and 171 cm -1 The peak at 1368 cm⁻¹ represents the stretching vibration of the carbonyl group (—C=O) on the imide ring. -1 The peak at 730 cm⁻¹ represents the stretching vibration of the imide bond (—C—N). -1 The peak at 2500-3500 cm⁻¹ corresponds to the bending vibration of the carbonyl group (—C=O) on the imide ring. -1 The significantly weakened peak intensity of the broad composite peaks of -NH- and -OH indicates that PAA has been converted to PI; Figure 9 As can be seen, PI exhibits excellent high-temperature resistance with a 9% weight loss temperature of 550℃ in air and a mass retention rate of 77% at 600℃. The approximately 7% weight loss in the 250-360℃ range may originate from the evaporation of the solvent NMP and a small amount of uniminolated cyclization dehydration.

[0049] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-solids-content polyamic acid slurry based on PAA nanoparticles, characterized in that: The polyamic acid slurry comprises a low-viscosity PAA solution and PAA nanopowder dispersed in the low-viscosity PAA solution, wherein the mass ratio of the PAA nanopowder to the low-viscosity PAA solution is 0.1-1, and the solid content of the polyamic acid slurry is 20-60%.

2. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that: The low-viscosity PAA solution is prepared by the following steps: S1. Under nitrogen positive pressure protection, add solvent to the reactor, then add diamine under stirring, and dissolve the diamine at room temperature or by gradually raising the temperature to 35°C until it is clear and transparent, and then cool it down to 0-10°C; S2. Turn on the reflux cooling device of the reactor. Under the protection of nitrogen positive pressure throughout the process, add the solvent and dianhydride in sequence to another reactor. Under stirring, slowly raise the temperature to 120-140℃. After the reactants are dissolved and clear, slowly lower the temperature to below 50℃. Replace with an ice bath and continue to lower the temperature to below 10℃. S3. Slowly add the diamine solution obtained in step S1 to the reaction system in step S2, and continue the reaction for 6-8 hours to obtain a clear and transparent yellow PAA solution.

3. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that, The method for preparing the PAA nanopowder includes the following steps: S11. A PAA solution with a concentration of 1-5 wt.% is added dropwise to an acetone solution containing 0.1-1 wt.% polyvinylpyrrolidone to obtain a slightly blue PAA suspension; S12. The PAA suspension was centrifuged to obtain solid powder, which was then washed with acetone and petroleum ether in sequence and dried under vacuum to obtain PAA nanoparticles.

4. The method for preparing high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that: The PAA nanopowder was dispersed at high speed in the low-viscosity PAA at a rotation speed of 2000-8000 r / min to obtain a PAA slurry; then the PAA slurry was stored at 0-5℃ under nitrogen-sealed conditions for more than 180 days.

5. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that: The diamine is any one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, or p-phenylenediamine; the dianhydride is any one of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the solvent is one or more of N,N-dimethylacetamide and N-methylpyrrolidone.

6. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that: The molar ratio of the dianhydride to the diamine is 1.01-1.

1.

7. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that: The low-viscosity PAA solution has a solid content of 10-20 wt.% and a viscosity of 100-1000 mPa.s.

8. The high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1, characterized in that, The average particle size of the PAA nanopowder is less than 500 nm.

9. The application of the high-solids-content polyamic acid slurry based on PAA nanoparticles according to claim 1 in the preparation of PI coatings, characterized in that, The PI coating is prepared by the following steps: Substrate treatment: The substrate is sanded or sandblasted, then cleaned with ethanol and dried; Coating: The PAA slurry is coated onto the treated substrate; Stepwise curing: The coated substrate is sequentially subjected to imidization curing in an 80℃ oven for 30-60 min, an 140-150℃ oven for 30-60 min, and an 250-300℃ oven for 30-60 min to obtain a PI coating with a thickness of 20-60 μm.

Images