Super strong aramid nanocomposite insulation paper, and preparation method and application thereof

Abstract

The application discloses super-strong aramid nanocomposite insulation paper and a preparation method and application thereof, and belongs to the technical field of aramid paper-based insulation materials. The method comprises the following steps: performing suction filtration and drying on a p-aramid nanofiber water dispersion liquid to obtain p-aramid nanometer paper; immersing the p-aramid nanometer paper in a polyamide acid solution, taking out the p-aramid nanometer paper, performing gradient temperature drying, thermal imidization and hot pressing to obtain super-strong aramid nanocomposite insulation paper. The application can solve the technical problem of weak combination of aramid fibers and polyimide in the prior art.

Description

Technical Field

[0001] This application belongs to the technical field of aramid paper-based insulating materials, specifically relating to a super-strong aramid nanocomposite insulating paper, its preparation method, and its application. Background Technology

[0002] Para-aramid (poly(p-phenylene terephthalamide)) chopped fibers are widely used in the field of specialty paper-based insulation materials due to their excellent thermal stability, high strength, and high modulus. However, traditional aramid insulating paper is usually made by mixing meta-aramid chopped fibers and precipitated fibers. It contains a large number of micron-sized pores, and the bonding between fibers mainly relies on physical entanglement and hydrogen bonds, which have limited force. As a result, its tensile strength, tear strength, and dielectric properties are difficult to meet the stringent requirements of next-generation highly lightweight and integrated electrical equipment for ultra-thin insulation materials.

[0003] To improve the performance of aramid paper, existing technologies attempt to introduce polyimide (PI) for composite reinforcement. For example, Chinese patent application CN121110437A uses aramid paper laminated onto both sides of a PI film to prepare high-resistance polyimide aramid insulating paper. While this method can improve performance to some extent, it has significant drawbacks: 1) In the loose network composed of micron-sized fibers, PI is difficult to uniformly and deeply fill the pores, easily accumulating between fiber bundles and causing stress concentration; 2) The relationship between PI and aramid fibers is mainly physical coating and weak interfacial bonding, lacking strong chemical or physical anchoring, resulting in low stress transfer efficiency and the interface easily becoming a performance bottleneck; 3) On a macroscopic scale, PI and fibers are prone to phase separation, making it difficult to form a stable and uniform "skeleton-matrix" composite structure. In recent years, the emergence of aramid nanofibers (ANFs) has provided a new approach for preparing high-performance nanopaper materials. ANFs possess a large specific surface area and abundant surface functional groups, enabling them to form dense nanopapers through strong hydrogen bonds and other interactions, exhibiting significantly superior mechanical properties compared to traditional aramid paper. However, pure ANF nanopapers still have shortcomings in flexibility, tear resistance, stress transfer efficiency, and long-term reliability under certain extreme electrical environments.

[0004] Therefore, how to achieve deep integration and interface strengthening of ANFs and PI at the nanoscale, and construct an ideal composite structure with high strength, high toughness, excellent insulation and thermal stability, remains a technical bottleneck that needs to be overcome in this field. Summary of the Invention

[0005] This application addresses the technical problem of weak bonding between aramid fibers and polyimide in the prior art by providing a super-strong aramid nanocomposite insulating paper, its preparation method, and its application.

[0006] To achieve the above objectives, this application adopts the following technical solution: The first aspect of this application discloses a method for preparing a super-strong aramid nanocomposite insulating paper, comprising the following steps: The aqueous dispersion of para-aramid nanofibers was filtered and dried to obtain para-aramid nanopaper. After impregnating para-aramid nanopaper with a polyamic acid solution, the paper is removed and then subjected to gradient temperature drying, thermal imidization, and hot pressing to obtain ultra-strong aramid nanocomposite insulating paper.

[0007] In some embodiments, the para-aramid nanofiber aqueous dispersion is prepared by the following steps: Para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water were mixed to obtain a para-aramid nanofiber dispersion. After high-pressure injection of deionized water into the para-aramid nanofiber dispersion, the mixture is washed with water under vacuum filtration until it becomes gel-like, thus obtaining an aqueous dispersion of para-aramid nanofibers.

[0008] In some embodiments, the polyamic acid solution is prepared by the following steps: A polyamic acid solution is obtained by mixing polyamic acid resin and N,N-dimethylacetamide.

[0009] In some embodiments, the immersion time is 10-30 min, and the gradient temperature drying includes: first maintaining at 30-40 °C for 10-20 min, then raising the temperature to 40-60 °C and maintaining for 30-40 min, and finally raising the temperature to 60-80 °C and maintaining for 30-40 min.

[0010] In some embodiments, the thermal imidization includes heating to 230-255 °C in a vacuum environment and holding for 30-60 min.

[0011] In some embodiments, the hot pressing temperature is 100~200 ℃, the pressure is 10~15 MPa, and the time is 5~10 min.

[0012] In some embodiments, the concentration of the para-aramid nanofiber aqueous dispersion is 0.05~0.6 mg / mL, the concentration of the polyamic acid solution is 10~60 mg / mL, and the viscosity of the polyamic acid resin is 8000~13000 cp.

[0013] In some embodiments, the concentration of the para-aramid nanofiber dispersion is 2-20 mg / mL.

[0014] In a second aspect of this application, a super-strong aramid nanocomposite insulating paper, obtained based on the aforementioned preparation method, has a tensile strength of 148~248 MPa and a toughness of 1040~2340 MJ / m. 3Its dielectric strength is 90.2~180 kV / mm.

[0015] A third aspect of this application concerns the application of a super-strong aramid nanocomposite insulating paper, as described above, in the preparation of electrical insulation layers.

[0016] Compared with the prior art, this application has the following beneficial effects: This application provides a method for preparing ultra-strong aramid nanocomposite insulating paper. First, para-aramid nanopaper is used as a porous framework. A low-viscosity polyamic acid solution is impregnated to fully penetrate the nanoscale pores, solving the problem of uneven resin filling in traditional micron-scale fiber networks. Second, gradient heating and drying can remove the solvent gradually, avoiding bubbles and stress cracking. Thermal imidization converts the polyamic acid solution into polyimide in situ, which forms a strong interfacial bond with the aramid nanofibers through hydrogen bonds and molecular chain entanglement, constructing a synergistic reinforcing structure of aramid nanofiber framework and polyimide matrix. Finally, hot pressing further densifies the material and eliminates internal defects. The resulting insulating paper has high strength, high modulus, and high dielectric strength, overcoming the shortcomings of traditional aramid paper in terms of mechanical and dielectric properties.

[0017] Furthermore, this application utilizes high-pressure injection of deionized water to efficiently disrupt the solvation layer of aramid nanofibers, promoting their uniform coagulation. Subsequent extensive water washing thoroughly removes residual DMSO and KOH from the reaction system, yielding a pure aqueous dispersion of aramid nanofibers. This avoids the adverse effects of impurities on the dielectric and mechanical properties of the insulating paper during subsequent papermaking processes, ensuring the cleanliness of the functional groups on the nanofiber surface and laying the foundation for the subsequent formation of strong hydrogen bonds with polyamic acid.

[0018] Furthermore, the impregnation time in this application is 10-30 min, which ensures that the polyamic acid solution fully wets and penetrates the aramid nanopaper. Holding the temperature at 30-40 °C for 10-20 min, then raising the temperature to 40-60 °C and holding it for 30-40 min, and finally raising the temperature to 60-80 °C and holding it for 30-40 min, allows for a gradual increase in temperature from the lower temperature. This facilitates the smooth and complete evaporation of the N,N-dimethylacetamide solvent, effectively preventing the formation of bubbles or stress cracking inside the composite paper due to rapid solvent vaporization. This ensures the integrity and density of the composite structure and provides a process guarantee for obtaining defect-free high-performance insulating paper.

[0019] Furthermore, the thermal imidization conditions are as follows: heating to 230-255 °C in a vacuum environment and holding for 30-60 min. Thermal imidization under vacuum can reduce the oxygen and moisture content in the reaction environment, preventing oxidative degradation of polyamic acid during the high-temperature cyclization to form polyimide. The temperature range of 230-255 °C ensures that polyamic acid is fully and completely converted into polyimide. During this process, the generated polyimide molecular chains come into close contact with the surface of aramid nanofibers, forming a strong interfacial bond through hydrogen bonds and physical entanglement of molecular chains. This transforms the soft polyamic acid resin into a high-strength and tough polyimide matrix, thereby significantly improving the mechanical properties and heat resistance of the composite paper.

[0020] Furthermore, the hot-pressing temperature is 100~200 ℃, the pressure is 10~15 MPa, and the time is 5~10 min. Applying moderate hot-pressing after thermal imidization can eliminate residual micropores and defects inside the composite paper without damaging the polyimide matrix and aramid skeleton structure. This increases the contact area and bonding tightness between the aramid nanofibers and the polyimide matrix, making the material structure more compact. This significantly improves the tensile strength, modulus, and dielectric strength of the insulating paper, while ensuring that the paper has a flat surface and stable dimensions, meeting the application requirements of ultra-thin insulation layers.

[0021] Furthermore, the concentration of the para-aramid nanofiber aqueous dispersion is 0.05–0.6 mg / mL, which is beneficial for forming a thin, uniform nanopaper skeleton with controllable pore structure. The concentration of the polyamic acid solution is 10–60 mg / mL, which determines the polyimide content filled in the skeleton after impregnation. By adjusting this concentration, the basis weight, thickness, and properties of the final composite paper can be flexibly controlled. Finally, the resin viscosity is limited to ensure that the solution has suitable fluidity, which can fully wet the nanopores without excessive flow, thereby precisely constructing the reinforcing structure. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This application provides a process flow diagram for the preparation of a super-strong aramid nanocomposite insulating paper; Figure 2 This is a scanning electron microscope image of the surface of the aramid nanocomposite insulating paper in Example 5 of this application; Figure 3This is a scanning electron microscope (SEM) image of the cross-section of the aramid nanocomposite insulating paper in Example 5 of this application; Figure 4(a) is a scanning electron microscope image of the breakdown point of the aramid nanocomposite insulating paper in Example 5 of this application, and Figure 4(b) is a magnified scanning electron microscope image of a portion of the breakdown point of the aramid nanocomposite insulating paper in Example 5 of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Polyimide (PI) is another class of top-performing polymers, renowned for its excellent high-temperature resistance, superior dielectric properties, and mechanical strength. Currently, how to effectively combine ANFs with PI to prepare a composite insulating paper that combines high strength, high toughness, excellent insulation properties, and thermal stability remains a technical challenge that those skilled in the art are striving to solve.

[0026] Therefore, this embodiment describes a method for preparing a super-strong aramid nanocomposite insulating paper, see [link to relevant documentation]. Figure 1 The specific steps include the following: (1) Preparation of para-aramid nanofiber dispersion: Para-aramid short-cut fibers were placed in a system containing dimethyl sulfoxide (DMSO), potassium hydroxide (KOH) and deionized water and stirred to de-fibrillate and obtain stable aramid nanofiber dispersion A; (2) Preparation of para-aramid nanofiber aqueous dispersion: Deionized water was injected into aramid nanofiber dispersion A under high pressure to destroy its solvation layer and cause ANFs to condense. Then, it was washed with a large amount of deionized water under vacuum filtration until it became gel-like to completely remove DMSO and KOH and obtain pure para-aramid nanofiber aqueous dispersion B. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative value of 5~40 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 8000~13000 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 10~60 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 10-30 min to allow the PAA solution to fully penetrate into the ANFs framework. After removal, it is placed in an oven for gradient heating to evaporate the solvent, and then transferred to a vacuum drying oven for thermal imidization to convert PAA into polyimide (PI) to obtain para-aramid nanocomposite paper; the basis weight of the para-aramid nanocomposite paper is 15-60 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 100~200 ℃ and 10~15 MPa for 5~10 min to further densify the material, eliminate internal defects, and obtain the final super-strong aramid nanocomposite insulating paper. Preferably, in step (1), para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water are mixed and sealed, and then stirred at a speed of 1000~3000 r / min for 4~6 h to obtain a para-aramid nanofiber dispersion A with a concentration of 2~20 mg / mL; Preferably, the concentration of the para-aramid nanofiber aqueous dispersion B obtained in (2) is 0.05~0.6 mg / mL; Preferably, the concentration of the polyamic acid solution C obtained in (4) is 10~60 mg / mL; Preferably, the immersion time in step (5) is 10-30 min; Preferably, the solvent evaporation in step (5) includes: first maintaining the temperature at 30-40 °C for 10-20 min, then raising the temperature to 40-60 °C and maintaining it for 30-40 min, and then raising the temperature to 60-80 °C and maintaining it for 30-40 min. This gradient heating process helps to remove the solvent gradually and thoroughly, avoiding the generation of bubbles and stress cracking; Preferably, the thermal imidization in (5) specifically involves: placing the aramid nanocomposite paper in a vacuum drying oven, heating it to 230~255 ℃ in a vacuum environment and maintaining it for 30~60 min to complete the chemical imidization reaction of PAA to PI, and then closing the vacuum drying oven and allowing it to cool naturally. Preferably, the hot pressing temperature in (6) is 100~200 ℃, the hot pressing pressure is 10~15 MPa, and the hot pressing time is 5~10 min; Preferably, in (1), the mass ratio of para-aramid short-cut fiber to potassium hydroxide is 2:3, and the mass ratio of dimethyl sulfoxide to deionized water is 1:25.

[0027] A super-strong aramid nanocomposite insulating paper is obtained based on the preparation method of the super-strong aramid nanocomposite insulating paper according to any one of the preceding claims; preferably, the tensile strength of the insulating paper is not less than 148 MPa, and the dielectric strength is not less than 90 kV / mm.

[0028] An application of the aforementioned ultra-strong aramid nanocomposite insulating paper as an ultra-thin insulating layer in the field of next-generation highly lightweight and integrated special electrical equipment.

[0029] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0030] Example 1: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 1000 r / min for 4 h to obtain a para-aramid nanofiber dispersion A with a concentration of 2 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.05 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative value of 10 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 8000 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 10 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 10 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 30 ℃ for 10 min, then heated to 40 ℃ and kept for 30 min, and then heated to 60 ℃ and kept for 30 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 230 ℃ and kept for 30 min to perform thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 15 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 100 °C and 10 MPa for 5 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 148.0 MPa and its toughness is 1040 MJ / m. 3 The dielectric strength is 90.2 kV / mm.

[0031] Example 2: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 2000 r / min for 4.5 h to obtain a para-aramid nanofiber dispersion A with a concentration of 5 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.1 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 20 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve a polyamic acid resin with a viscosity of 9000 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 20 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 10 min to allow the PAA solution to fully penetrate into the ANFs framework. After removal, it is placed in an oven and kept at 35 °C for 10 min, then heated to 50 °C and kept for 30 min, and then heated to 70 °C and kept for 30 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 235 °C and kept for 30 min for thermal imidization to convert PAA into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 25 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 130 °C and 11 MPa for 5 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 163.4 MPa and its toughness is 1200 MJ / m. 3 The dielectric strength is 102.6 kV / mm.

[0032] Example 3: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 2500 r / min for 5 h to obtain a para-aramid nanofiber dispersion A with a concentration of 8 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.3 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 30 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve a polyamic acid resin with a viscosity of 9500 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 30 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 15 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 30 ℃ for 15 min, then heated to 50 ℃ and kept for 40 min, and then heated to 70 ℃ and kept for 40 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 240 ℃ and kept for 40 min to perform thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 30 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 150 °C and 13 MPa for 10 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 180.5 MPa and its toughness is 1320 MJ / m. 3 The dielectric strength is 124.3 kV / mm.

[0033] Example 4: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 3000 r / min for 6 h to obtain a para-aramid nanofiber dispersion A with a concentration of 15 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.5 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 30 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 13000 cp in N,N-dimethylacetamide (DMAc) to obtain polyamic acid solution C with a concentration of 35 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 30 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 30 ℃ for 20 min, then heated to 55 ℃ and kept for 40 min, and then heated to 75 ℃ and kept for 40 min to evaporate the solvent by gradient heating. Then it is transferred to a vacuum drying oven and heated to 250 ℃ and kept for 60 min for thermal imidization to convert PAA into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 50 g / m². (6) The para-aramid nanocomposite paper obtained in (5) was hot-pressed at 180℃ and 13 MPa for 8 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength was 209.3 MPa and its toughness was 1547 MJ / m. 3 The dielectric strength is 151.5 kV / mm.

[0034] Example 5: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 2500 r / min for 4 h to obtain a para-aramid nanofiber dispersion A with a concentration of 5 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.2 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative value of 28 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 11500 cp in N,N-dimethylacetamide (DMAc) to obtain polyamic acid solution C with a concentration of 30 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 20 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 30 ℃ for 20 min, then heated to 50 ℃ and kept for 40 min, and then heated to 70 ℃ and kept for 40 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 255 ℃ and kept for 60 min to perform thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 43 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 170 °C and 15 MPa for 5 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 192.5 MPa and its toughness is 1500 MJ / m. 3 The dielectric strength is 138.3 kV / mm.

[0035] Taking Example 5 as an example, the surface of the ultra-strong aramid nanocomposite insulating paper prepared by the present invention was first observed. Figure 2 The image shows a scanning electron microscope (SEM) image of the aramid nanocomposite insulating paper obtained in Example 5 of this invention. From the image, we can clearly see that the surface of the aramid nanocomposite insulating paper is smooth and dense. The aramid nanofibers are tightly bonded to the polyimide, and the polyimide completely encapsulates the aramid nanopaper, forming a dense aramid nano-polyimide network. This results in a smooth paper surface, increased bonding force between fibers, and improved tensile strength. The cross-section of the aramid nano-insulating paper was also observed. Figure 3 As shown, the paper has obvious layered and dense structures, indicating that polyimide has entered the interior of the aramid nanofiber paper. After hot pressing, the structure between polyimide and aramid nanofiber becomes dense. Finally, in order to verify its excellent dielectric properties, the aramid nanocomposite insulating paper was subjected to electrical breakdown test and its SEM image was observed. Figure 4(a) is a scanning electron microscope image of the breakdown point of the aramid nanocomposite insulating paper obtained in Example 5 of the present invention, and Figure 4(b) is a locally magnified scanning electron microscope image of the breakdown point of the aramid nanocomposite insulating paper obtained in Example 5 of the present invention. It can be observed that dense carbon particles are generated around the breakdown site, and the structure is compact. Even after breakdown, other parts of the insulating paper do not become loose.

[0036] Taking Example 5 as an example, the super-strong aramid nanocomposite insulating paper prepared by the present invention was tested, and the quantitative analysis result was 43 g / m³. 2 With an average thickness of 0.03 mm, a tensile strength of 192.5 MPa, and a dielectric strength of 138.3 kV / mm, this ultra-strong aramid nanocomposite insulating paper exhibits excellent tensile and dielectric strength. This means it possesses superior mechanical and electrical properties, making it potentially valuable for applications in large electrical equipment such as high-power dry-type transformers, oil-immersed transformers, special mining motors, high-speed train traction motors, wind turbines, and ultra-high voltage transformers.

[0037] Example 6: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water were mixed and sealed, and the mixture was stirred rapidly at 3000 r / min for 5.5 h to obtain a para-aramid nanofiber dispersion A with a concentration of 18 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.6 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 35 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 13000 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 60 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 25 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 30 ℃ for 15 min, then heated to 50 ℃ and kept for 40 min, and then heated to 70 ℃ and kept for 40 min to evaporate the solvent by gradient heating. Then it is transferred to a vacuum drying oven and heated to 250 ℃ and kept for 60 min to perform thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 60 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 170 °C and 15 MPa for 10 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 248.0 MPa and its toughness is 2430 MJ / m. 3 The dielectric strength is 180.0 kV / mm.

[0038] Example 7: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 1800 r / min for 6 h to obtain a para-aramid nanofiber dispersion A with a concentration of 14 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.12 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative value of 40 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 9800 cp in N,N-dimethylacetamide (DMAc) to obtain polyamic acid solution C with a concentration of 40 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 30 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 40 ℃ for 20 min, then heated to 55 ℃ and kept for 35 min, and then heated to 75 ℃ and kept for 35 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 240 ℃ and kept for 60 min for thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 58 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 175 °C and 15 MPa for 10 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 234.2 MPa and its toughness is 2249 MJ / m. 3 The dielectric strength is 171.0 kV / mm.

[0039] Example 8: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 1800 r / min for 4.5 h to obtain a para-aramid nanofiber dispersion A with a concentration of 16 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.3 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 25 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 10500 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 30 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 15 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 38 ℃ for 18 min, then heated to 55 ℃ and kept for 35 min, and then heated to 75 ℃ and kept for 35 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 240 ℃ and kept for 40 min for thermal imidization, so that PAA is converted into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 50 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 175 °C and 15 MPa for 8 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 207.8 MPa and its toughness is 1500 MJ / m. 3 The dielectric strength is 152.3 kV / mm.

[0040] Example 9: The preparation method of the ultra-strong aramid nanocomposite insulating paper in this embodiment specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 1900 r / min for 4.5 h to obtain a para-aramid nanofiber dispersion A with a concentration of 19 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.4 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 30 g / m². This nanopaper was used as a porous framework for subsequent composites. (4) Dissolve polyamic acid resin with a viscosity of 12500 cp in N,N-dimethylacetamide (DMAc) to obtain a polyamic acid solution C with a concentration of 25 mg / mL; (5) The para-aramid nanopaper obtained in (3) is immersed in the polyamic acid solution C obtained in (4) for 20 min, so that the PAA solution can fully penetrate into the ANFs skeleton. After taking it out, it is placed in an oven and first kept at 35 ℃ for 18 min, then heated to 60 ℃ and kept for 35 min, and then heated to 80 ℃ and kept for 35 min to evaporate the solvent. Then it is transferred to a vacuum drying oven and heated to 250 ℃ and kept for 50 min for thermal imidization to convert PAA into polyimide (PI) to obtain para-aramid nanocomposite paper; the quantitative amount of the para-aramid nanocomposite paper is 49 g / m². (6) The para-aramid nanocomposite paper obtained in (5) is hot-pressed at 200 °C and 15 MPa for 8 min to further densify the material and eliminate internal defects, thus obtaining the final ultra-strong aramid nanocomposite insulating paper; its tensile strength is 204.5 MPa and its toughness is 1450 MJ / m. 3 The dielectric strength is 150.5 kV / mm.

[0041] Comparative Example 1: The preparation method of the aramid nano-insulating paper in this comparative example specifically includes the following steps: (1) Mix para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water and seal them. Stir rapidly at 2500 r / min for 6 h to obtain a para-aramid nanofiber dispersion A with a concentration of 20 mg / mL. (2) High pressure injection of deionized water into aramid nanofiber dispersion A to destroy its solvation layer and cause ANFs to condense. Then, under vacuum filtration, it is washed with a large amount of deionized water until it becomes colloidal to completely remove DMSO and KOH, and a pure para-aramid nanofiber aqueous dispersion B with a concentration of 0.2 mg / mL is obtained. (3) The para-aramid nanofiber aqueous dispersion B obtained in (2) was filtered and dried to obtain para-aramid nanopaper with a quantitative amount of 30 g / m². (4) The para-aramid nanopaper obtained in (3) was hot-pressed at 175 °C and 15 MPa for 10 min to obtain aramid nano insulating paper.

[0042] The aramid nano-insulating paper prepared in Comparative Example 1 has a tensile strength of 70 MPa and a dielectric strength of 81.2 kV / mm. The aramid nano-insulating papers prepared through Examples 1-9 of the present invention have tensile strengths of 150-250 MPa and toughnesses of 1000-2500 MJ / m. 3 The dielectric strength is 90~180 kV / mm, which is 2~4 times higher than that of Comparative Example 1 in terms of tensile strength, 4~5 times higher in toughness, and 2~3 times higher in dielectric strength.

[0043] This embodiment provides a method for preparing ultra-strong aramid nanocomposite insulating paper. It creatively uses a three-dimensional network of para-aramid nanofibers (ANFs) as a framework, and fills the pores of the AFA with polyamic acid (PAA) through an impregnation-iminolation process. During the impregnation stage, polyamic acid, rich in amide bonds and carboxyl groups, is a highly polar molecule. The surface of the aramid nanofibers also contains a large number of amide bonds. In-situ thermal iminolation allows the two to form a very extensive and strong hydrogen bond network through "C=O…HN". This not only enhances the bonding force between the fibers but also produces a synergistic effect with the AFAs through its own excellent properties.

[0044] During thermal imidization, PAA dehydrates and cyclizes to PI, reducing the number of polar groups. However, under heat treatment, the thermal motion of ANF and PI molecular chains intensifies, potentially leading to a tighter contact at the interface. More importantly, the high temperature may induce minimal chain entanglement or even covalent bonding between the amide bonds on the ANF surface and unreacted carboxyl groups or generated imide rings in the PI precursor, thus forming an "interpenetrating network" or "anchored" structure at the interface. This synergistic effect of chemical and physical processes significantly enhances interfacial bonding. In summary, the beneficial effects of the chemical structure include a transformation from simple physical adsorption to strong hydrogen bonding and potential molecular chain entanglement, resulting in a robust interfacial layer with high energy transfer efficiency.

[0045] Low-viscosity PAA solutions can effectively penetrate and fill the numerous nano / micron-sized pores within the three-dimensional network of aramid nanofibers. After thermal imidization, the original pores are filled with solid polyimide, forming countless "PI bridges" between the ANF fibers, thus strengthening the connections between the nodes of the ANF network. This results in a "skeleton-matrix" composite structure: in this composite system, the aramid nanofibers act as a high-strength skeleton, bearing the main load. The converted polyimide acts as a tough matrix, encapsulating, fixing, and connecting these skeletons, and effectively transferring and dispersing external stress to the high-strength ANF. Ultimately, a dense, continuous, and complete microstructure is formed, with "ANF as the skeleton and PI as the flesh." Transforming the open nanofiber network into a dense nanocomposite material eliminates structural defects and optimizes the stress transmission path.

[0046] The composite insulating paper prepared by this method not only possesses tensile and tear strengths far exceeding those of traditional insulating paper, but also inherits the advantages shared by aramid and polyimide, such as extremely high thermal stability (thermal decomposition temperature >500℃), excellent dielectric strength (>100 kV / mm), and low dielectric constant, fully meeting the stringent material performance requirements of high-end electrical equipment. The process employs a route of first preparing ANF nanopaper as a porous preform, followed by impregnation with PAA and imidization. This process ensures uniform distribution and full filling of PI within the ANF framework, avoiding agglomeration problems that may result from simple blending. By precisely controlling the basis weight of the ANF nanopaper, the concentration of the PAA solution, and the hot-pressing process parameters, the thickness, density, and properties of the final composite paper can be easily adjusted, demonstrating broad adaptability.

[0047] This embodiment also provides an ultra-strong aramid nanocomposite insulating paper. The tensile strength of this aramid nanocomposite insulating paper is 2 to 3 times higher than that of pure aramid nanopaper. This aramid nanocomposite insulating paper can also achieve thinning of the insulating layer and high mechanical properties while ensuring excellent insulation performance.

[0048] The ultra-strong aramid nanocomposite insulating paper prepared in this embodiment can be used as an ultra-thin insulating layer in the field of next-generation highly lightweight and integrated special electrical equipment, such as electrical equipment for 5G communication power systems, rail transit, and new energy vehicles. It can effectively solve the problems of poor active heat dissipation and short service life of electrical equipment due to the low thermal conductivity of insulating paper, realize the miniaturization, integration and weight reduction of equipment, and promote the development of modern compact lightweight electrical insulation equipment towards greater efficiency and reliability.

[0049] Of particular note is that this invention, through the synergistic reinforcement design of the aramid nanofiber framework and the polyimide matrix, achieves both low basis weight and ultrathinness of the insulating paper while ensuring extremely high tensile and dielectric strength. Even at ultra-low basis weights (e.g., below 10 g / m³),2 Under these conditions, its mechanical and electrical properties are still significantly better than those of traditional insulating materials of the same quantitative level, which provides key material support for electrical equipment to further achieve structural weight reduction, space compression and performance improvement.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0051] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A method for preparing a super-strong aramid nanocomposite insulating paper, characterized in that, Includes the following steps: The aqueous dispersion of para-aramid nanofibers was filtered and dried to obtain para-aramid nanopaper. After impregnating para-aramid nanopaper with a polyamic acid solution, the paper is removed and then subjected to gradient temperature drying, thermal imidization, and hot pressing to obtain ultra-strong aramid nanocomposite insulating paper.

2. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 1, characterized in that, The para-aramid nanofiber aqueous dispersion was prepared by the following steps: Para-aramid short-cut fibers, potassium hydroxide, dimethyl sulfoxide and deionized water were mixed to obtain a para-aramid nanofiber dispersion. After high-pressure injection of deionized water into the para-aramid nanofiber dispersion, the mixture is washed with water under vacuum filtration until it becomes gel-like, thus obtaining an aqueous dispersion of para-aramid nanofibers.

3. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 1, characterized in that, The polyamic acid solution is prepared by the following steps: A polyamic acid solution is obtained by mixing polyamic acid resin and N,N-dimethylacetamide.

4. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 1, characterized in that, The immersion time is 10-30 min, and the gradient temperature drying includes: first maintaining the temperature at 30-40 ℃ for 10-20 min, then raising the temperature to 40-60 ℃ and maintaining it for 30-40 min, and finally raising the temperature to 60-80 ℃ and maintaining it for 30-40 min.

5. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 1, characterized in that, The thermal imidization includes heating to 230~255 ℃ in a vacuum environment and holding for 30~60 min.

6. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 1, characterized in that, The hot pressing temperature is 100~200 ℃, the pressure is 10~15 MPa, and the time is 5~10 min.

7. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 3, characterized in that, The concentration of the para-aramid nanofiber aqueous dispersion is 0.05~0.6 mg / mL, the concentration of the polyamic acid solution is 10~60 mg / mL, and the viscosity of the polyamic acid resin is 8000~13000 cp.

8. The method for preparing a super-strong aramid nanocomposite insulating paper according to claim 2, characterized in that, The concentration of the para-aramid nanofiber dispersion is 2~20 mg / mL.

9. A super-strong aramid nanocomposite insulating paper, characterized in that, Obtained by the preparation method according to any one of claims 1 to 8, the tensile strength is 148 to 248 MPa, and the toughness is 1040 to 2430 MJ / m. 3 Its dielectric strength is 90.2~180 kV / mm.

10. The application of the ultra-strong aramid nanocomposite insulating paper as described in claim 9 in the preparation of electrical insulation layers.

Images