Meta-aramid composite paper with double-layer structure as well as preparation method and application of meta-aramid composite paper

Abstract

The invention belongs to the technical field of high-performance fiber composite materials, and particularly relates to meta-aramid composite paper with a double-layer structure as well as a preparation method and application of the meta-aramid composite paper. According to the preparation method of the meta-aramid composite paper with the double-layer structure, provided by the invention, a layer of nAl2O3 / PMIA-F composite film is constructed on the surface of the meta-aramid paper, so that the breakdown strength of the meta-aramid paper can be improved, and high tearing strength and high mechanical strength of the meta-aramid paper can be maintained; meanwhile, the preparation method also has the advantages of controllable cost and simple and efficient process, solves the problem of tear strength reduction caused by coating the surface of meta-aramid paper with conventional slurry, and can provide basic material support for upgrading and updating of a novel power system; wide application prospects are realized in the fields of ultrahigh-voltage equipment, high-insulation equipment, aviation power systems and the like.

Description

Technical Field

[0001] This invention belongs to the field of high-performance fiber composite materials technology, specifically relating to a bilayer meta-aramid composite paper, its preparation method, and its application. Background Technology

[0002] Meta-aramid insulating paper is a special fiber insulating paper and lightweight structural material prepared by wet forming and hot pressing of a certain proportion of meta-aramid short fibers and meta-aramid pulp. It has been widely used in electrical insulation, high-temperature filtration materials, high-temperature protective clothing, and radar antennas. In the structure of aramid insulating paper, chopped fibers act as the skeleton material, uniformly dispersed in the paper, determining the paper's physical strength and mechanical properties; aramid pulp acts as a filler and binder, forming the paper structure through bonding the chopped fibers and self-adhesion, giving aramid paper excellent insulation properties.

[0003] In recent years, with the rapid development of electrification of rail transit and urban subways and light rail in my country, as well as the iterative upgrading of ultra-high voltage technology, the demand for meta-aramid fiber paper with higher breakdown strength has been increasing. However, domestically produced meta-aramid paper still lags significantly behind DuPont's Nomex series insulating paper in terms of insulation performance. Therefore, improving the insulation performance of domestically produced meta-aramid paper is imperative to meet the development needs of high-end electrical equipment and rail transit in my country. Furthermore, the breakdown strength of domestically produced meta-aramid paper is currently lower than that of DuPont's Nomex T410 meta-aramid paper. Since meta-aramid paper is a blend of meta-aramid short fibers and meta-aramid pulp, its surface porosity and roughness are relatively high, making it prone to localized electrical breakdown. Therefore, effectively reducing the surface porosity and roughness of meta-aramid paper is a key issue in improving its breakdown strength.

[0004] To improve the breakdown strength of meta-aramid paper, researchers have conducted extensive studies. Patent application CN116926982A describes a method of electrospinning para-aramid microfibers (nano to submicron) onto the surface of meta-aramid base paper, forming a network structure. While this network structure optimizes the tensile strength of the meta-aramid paper, it significantly increases the surface roughness of the composite paper, hindering its breakdown strength improvement. Patent application CN108316056A describes a three-layer meta-aramid composite paper structure with meta-aramid paper as the core layer and aramid nanofiber layers as the upper and lower layers. However, this method involves separately preparing the meta-aramid paper and aramid nanofiber layers, drying them, and then hot-pressing them together, resulting in poor interfacial bonding performance. Meanwhile, the addition of cationic polyacrylamide increases the number of internal charge carriers, which is detrimental to improving the breakdown strength. Therefore, the highest breakdown strength of the meta-aramid composite paper prepared by this method is only 29.2 MV / m. In the patent application with publication number CN119352329A, meta-aramid paper is impregnated in a mixture containing organic solvent, adhesive, and co-solvent to form a dense layer by dissolving the meta-aramid short fibers and meta-aramid pulp on the surface of the paper. Although the dense layer reduces the porosity of the meta-aramid paper surface, its breakdown strength is not significantly improved. In addition, tear resistance is an important application performance of meta-aramid paper. The dissolution of meta-aramid short fibers and meta-aramid pulp will reduce the tear resistance of the meta-aramid paper. This method does not take into account its impact on tear resistance.

[0005] To address the aforementioned problems, the technical problem that this invention urgently needs to solve is how to develop a simple and convenient meta-aramid composite paper with high breakdown strength and high tear resistance to meet the upgrading needs of new power systems and rail transit. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide a method for preparing a double-layer meta-aramid composite paper. This invention constructs an nAl2O3 / PMIA-F composite film on the surface of meta-aramid paper, which not only improves the breakdown strength of the meta-aramid paper but also maintains its high tear strength and high mechanical strength. Furthermore, the preparation method of this invention has the advantages of controllable cost, simple and efficient process, and solves the problem of reduced tear strength caused by coating the surface of meta-aramid paper with conventional slurry. This provides fundamental material support for the upgrading of new power systems.

[0007] The present invention also aims to provide a bilayer meta-aramid composite paper prepared by the above preparation method, which has both excellent breakdown strength and tear resistance.

[0008] The present invention also aims to provide applications of the bilayer meta-aramid composite paper prepared by the above preparation method.

[0009] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution: A method for preparing a bilayer meta-aramid composite paper includes the following steps: (1) 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, m-phenylenediamine, and isophthaloyl chloride were subjected to a polycondensation reaction in a solvent to obtain a PMIA-F polymer slurry; aluminum oxide nanoparticles were ultrasonically dispersed in a solvent to obtain an nAl2O3 dispersion; the PMIA-F polymer slurry and the nAl2O3 dispersion were mixed to obtain an nAl2O3 / PMIA-F composite slurry; (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto the substrate and then dried to obtain an nAl2O3 / PMIA-F composite wet film; (3) The meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and then pressure is applied to the surface of the meta-aramid paper for pre-pressing treatment. Then, drying and hot pressing treatment are performed in sequence to obtain the double-layer structure meta-aramid composite paper.

[0010] As a preferred embodiment, in step (1), the molar ratio of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, m-phenylenediamine, and isophthaloyl chloride is (0.05~0.2):(0.8~0.95):1; the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. In this step, the modification of the polycondensation process of m-phenylenediamine and isophthaloyl chloride by 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl is beneficial to further improve the breakdown strength and tear resistance of the material.

[0011] As a preferred option, in step (1), the temperature of the polycondensation reaction is -12 to -8°C and the time is 1 to 4 hours.

[0012] As a further preferred embodiment, the polycondensation reaction is further followed by a neutralization reaction with alkali and a degassing treatment.

[0013] As a preferred embodiment, in step (1), the PMIA-F polymer slurry is a slurry of modified poly(m-phenylene isophthalamide); the concentration of modified poly(m-phenylene isophthalamide) in the PMIA-F polymer slurry is 18~20wt%; the concentration of aluminum oxide nanoparticles in the nAl2O3 dispersion is 0.02~15wt%; the mass ratio of the PMIA-F polymer slurry to the nAl2O3 dispersion is (0.25~1):1; the concentration of modified poly(m-phenylene isophthalamide) in the nAl2O3 / PMIA-F composite slurry is 10~14wt%, and the concentration of aluminum oxide nanoparticles is 0.1~5wt%.

[0014] As a preferred embodiment, in step (2), the substrate is a glass plate or a stainless steel plate, more preferably a glass plate. The drying temperature is 60~100℃, and the time is 30~100s. In this step, by controlling the drying process, most of the solvent in the composite slurry is removed, while maintaining the viscosity of the nAl2O3 / PMIA-F composite wet film, thereby ensuring the composite effect of the composite wet film and the meta-aramid paper.

[0015] As a preferred embodiment, in step (3), the thickness of the meta-aramid paper is 40~60 μm. More preferably, the basis weight of the meta-aramid paper is 30~50 g / m³. 2 .

[0016] In step (3), to ensure the adhesion between the nAl2O3 / PMIA-F composite wet film and the meta-aramid paper, pressure is first uniformly applied to the surface of the meta-aramid paper, followed by drying and hot pressing to obtain a double-layer meta-aramid composite paper. As a preferred embodiment, in step (3), the pressure of the pre-pressing treatment is 5~40 g / cm³. 2 The drying process takes 1-3 hours; the drying temperature is 60-100℃ and the drying time is 3-10 hours; the hot pressing treatment takes 150-220℃, 5-15 MPa and 10-20 minutes.

[0017] The second aspect of this invention is the following technical solution: A bilayer meta-aramid composite paper prepared by the preparation method described above, the bilayer meta-aramid composite paper comprising an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0018] As a preferred embodiment, the thickness of the nAl2O3 / PMIA-F composite film is 2~20μm; the thickness of the bilayer meta-aramid composite paper is 42~80μm.

[0019] The third aspect of this invention is the following technical solution: An application of a bilayer meta-aramid composite paper prepared by the method described above, specifically in high-voltage insulating materials for power systems.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least the following: (i) To address the shortcomings of traditional processes that directly coat the slurry onto the surface of meta-aramid paper, such as the dissolution of aramid paper and a significant decrease in tear resistance, the present invention provides a method for preparing a double-layer meta-aramid composite paper. First, an nAl2O3 / PMIA-F composite slurry is coated onto a substrate and heated to concentrate it, thereby removing most of the solvent from the composite slurry while maintaining the viscosity of the composite wet film. Then, meta-aramid paper is loaded onto the surface of the high-concentration nAl2O3 / PMIA-F composite wet film, and a certain pressure is applied to enhance the adhesion between the meta-aramid paper and the nAl2O3 / PMIA-F composite wet film. Finally, the double-layer meta-aramid composite paper is obtained by hot pressing.

[0021] The preparation method described above in this invention is simple, operates under mild conditions, and effectively meets the needs of large-scale production. In particular, the preparation process of this invention, by forming an nAl₂O₃ / PMIA-F composite film on the surface of meta-aramid paper, helps to reduce the surface roughness of the meta-aramid paper, inhibits electron accumulation on the surface, and hinders the growth of electrical trees. Simultaneously, the high-concentration nAl₂O₃ / PMIA-F composite slurry can penetrate into the pores of the meta-aramid paper during the composite process, reducing the porosity of the meta-aramid while improving its tear resistance. Therefore, this invention, by combining the concentrated nAl₂O₃ / PMIA-F composite slurry with meta-aramid paper, effectively reduces the porosity and surface roughness of the meta-aramid paper, while simultaneously improving tensile strength, tear resistance, and breakdown strength.

[0022] Furthermore, due to the similarity between the chemical structure of meta-aramid and PMIA-F, the interaction between the two layers ensures high adhesion and strong interaction. Meanwhile, the wide-bandgap nAl2O3 nanoparticles can suppress electron transitions and migrations, reducing the leakage current density within the composite paper and synergistically improving the material's performance. Moreover, the concentration heat treatment after coating the nAl2O3 / PMIA-F composite slurry onto the substrate helps reduce the solvent content in the nAl2O3 / PMIA-F slurry, minimizing the solvent's dissolution and corrosion of the meta-aramid paper structure, thus contributing to maintaining high tensile strength and tear resistance.

[0023] (II) The bilayer meta-aramid composite paper provided by this invention is a novel bilayer meta-aramid composite paper constructed by loading meta-aramid paper onto the surface of an nAl2O3 / PMIA-F composite film. This invention, by combining the nAl2O3 / PMIA-F composite film with meta-aramid paper, helps to reduce the surface roughness and porosity of the meta-aramid paper. The PMIA-F molecular structure contains strong electron-withdrawing groups, which can effectively suppress the formation of leakage current under the action of an electric field. Simultaneously, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl can disrupt the π-π conjugated structure in the PMIA molecular structure. Therefore, modified poly(m-phenylene isophthalamide) (PMIA-F) has superior insulation properties compared to unmodified poly(m-phenylene isophthalamide) (PMIA); while nAl2O3 has a high bandgap and excellent thermal conductivity. Therefore, combining nAl2O3 / PMIA-F composite film with meta-aramid paper helps to construct meta-aramid composite insulating paper with higher breakdown strength.

[0024] Tests have confirmed that the double-layer meta-aramid composite paper of the present invention has high tensile strength, high tear strength, high breakdown strength and low surface roughness, which can meet the application requirements of extreme environments such as ultra-high voltage equipment, high insulation equipment and aviation power systems, and has broad application prospects and economic value. Attached Figure Description

[0025] Figure 1 The infrared spectra of PMIA-F, meta-aramid paper, and nAl2O3 in this invention are shown. Figure 2 The images show the SEM surface morphology of the meta-aramid paper raw material of the present invention and the bilayer meta-aramid composite paper prepared in Example 4. Detailed Implementation

[0026] The technical solutions and effects of the present invention will be clearly and completely described below with reference to specific embodiments and experimental examples. However, those skilled in the art should understand that the embodiments are only used to illustrate the technical solutions of the present invention and should not be regarded as limiting the scope of protection of the present invention.

[0027] Unless otherwise stated, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. Furthermore, the terms "comprising," "including," "having," "containing," etc., as used herein are open-ended, meaning they include but are not limited to.

[0028] In the following embodiments, the raw materials used are sourced from Aladdin Reagent (Shanghai) Co., Ltd.: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, m-phenylenediamine, and isophthaloyl chloride. The meta-aramid paper used in this invention is from Chaomisi New Materials Co., Ltd., with a basis weight of 38±2 g / m³. 2 In other embodiments, meta-aramid paper can also be prepared by blending meta-aramid pulp and meta-aramid short fibers; this invention does not impose any particular limitation on this method. The alumina nanoparticles (nAl2O3) used below have a particle size of 50±5 nm. Unless otherwise specified, other raw materials are commercially available and commonly used in the art.

[0029] Example 1

[0030] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0031] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.005 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.095 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -12 °C for 1.5 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for another 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 18 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 0.225 wt%. Subsequently, 24g of the above-prepared nAl2O3 dispersion was added to 30g of PMIA-F slurry, and stirred at 600r / min for 6h to obtain an nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 10wt% and the content of nAl2O3 was 0.1wt%.

[0032] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 60°C for 100s to obtain an nAl2O3 / PMIA-F composite wet film.

[0033] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 5 g / cm layer is uniformly applied to the surface of the meta-aramid paper. 2The pressure was applied for 3 hours, followed by drying at 60°C for 3 hours, and finally hot-pressed at 5 MPa pressure and 150°C for 20 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0034] Example 2

[0035] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0036] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.01 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.09 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -10 °C for 2 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 20 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 4 wt%. Subsequently, 30g of the above-prepared nAl2O3 dispersion was added to 30g of PMIA-F slurry, and stirred at 600r / min for 8h to obtain an nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 10wt% and the content of nAl2O3 was 2wt%.

[0037] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 60°C for 100s to obtain an nAl2O3 / PMIA-F composite wet film.

[0038] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 10 g / cm layer is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 2.5 hours, followed by drying at 80°C for 5 hours, and finally hot-pressed at 7 MPa pressure and 160°C for 18 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0039] Example 3

[0040] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0041] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.015 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.085 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -9 °C for 2.5 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for another 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 18 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 15 wt%. Subsequently, 15g of the above-prepared nAl2O3 dispersion was added to 30g of PMIA-F slurry, and stirred at 600r / min for 10h to obtain an nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 12wt% and the content of nAl2O3 was 5wt%.

[0042] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 100°C for 30s to obtain an nAl2O3 / PMIA-F composite wet film.

[0043] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 20 g / cm³ coating is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 2 hours, followed by drying at 80°C for 5 hours, and finally hot-pressed at 8 MPa pressure and 180°C for 16 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0044] Example 4

[0045] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0046] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.08 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -10 °C for 3 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 18 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 13.5 wt%. Subsequently, 8.6 g of the nAl2O3 dispersion prepared above was added to 30 g of PMIA-F slurry, and stirred at 600 r / min for 12 h to obtain nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 14 wt% and the content of nAl2O3 was 3 wt%.

[0047] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 80°C for 60s to obtain an nAl2O3 / PMIA-F composite wet film.

[0048] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 25 g / cm² coating is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 1.5 hours, followed by drying at 80°C for 8 hours, and finally hot-pressed at 10 MPa pressure and 210°C for 14 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0049] Example 5

[0050] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0051] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.08 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -10 °C for 3 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 18 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 13.5 wt%. Subsequently, 8.6 g of the prepared nAl2O3 dispersion was added to 30 g of PMIA-F slurry, and stirred at 600 r / min for 6 h to obtain an nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 14 wt%, and the content of nAl2O3 was 3 wt%.

[0052] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 60°C for 100s to obtain an nAl2O3 / PMIA-F composite wet film.

[0053] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 40 g / cm³ coating is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 1 hour, followed by drying at 100°C for 10 hours, and finally hot-pressed at 12 MPa pressure and 200°C for 12 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0054] Example 6

[0055] This embodiment provides a bilayer meta-aramid composite paper, including an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; the lower surface layer is meta-aramid paper.

[0056] The bilayer meta-aramid composite paper of this embodiment is prepared by a method including the following steps: (1) 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.08 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -10 °C for 1.5 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for another 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 19 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 10.6 wt%. Subsequently, 27g of the nAl2O3 dispersion prepared above was added to 30g of PMIA-F slurry, and stirred at 600r / min for 6h to obtain nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 10wt% and the content of nAl2O3 was 5wt%.

[0057] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto a substrate (glass plate) and dried at 80°C for 60s to obtain an nAl2O3 / PMIA-F composite wet film.

[0058] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and a 20 g / cm³ coating is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 2 hours, followed by drying at 80°C for 10 hours, and finally hot-pressed at 15 MPa pressure and 220°C for 10 minutes to obtain the double-layer meta-aramid composite paper of this embodiment.

[0059] Comparative Example 1 This comparative example provides a meta-aramid paper with a thickness of 50 μm, without any treatment.

[0060] Comparative Example 2 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4, the only difference being that nAl2O3 is omitted. The specific preparation method includes the following steps: (1) Dissolve 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.08 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride in N,N-dimethylacetamide and react at -10 °C for 3 h. Then add 0.1 mol of calcium hydroxide to neutralize the hydrogen chloride generated during the reaction and continue stirring for 0.5 h. Then let stand at 60 °C for 24 h to remove bubbles and obtain a PMIA-F slurry with a solid content of 18 wt%. Then add 8.6 g of N,N-dimethylacetamide to 30 g of PMIA-F slurry with a solid content of 18 wt% and stir at 600 r / min for 12 h to obtain a PMIA-F slurry with a solid content of 14 wt%.

[0061] (2) The PMIA-F slurry (14wt%) obtained in step (1) is coated onto the substrate (glass plate) and dried at 80°C for 60s to obtain a PMIA-F wet film.

[0062] (3) Lay a 50 μm thick meta-aramid paper flat on the surface of the PMIA-F wet film obtained in step (2), and apply 25 g / cm² of the film evenly to the surface of the meta-aramid paper. 2 The pressure was applied for 1.5 hours, followed by drying at 80°C for 8 hours, and finally hot-pressed at 10 MPa pressure and 210°C for 14 minutes to obtain the bilayer meta-aramid composite paper of the comparative example.

[0063] Comparative Example 3 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4, the only difference being the omission of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The specific preparation method includes the following steps: (1) Dissolve m-phenylenediamine (0.1 mol) and isophthaloyl chloride (0.1 mol) in N,N-dimethylacetamide and react at -10℃ for 3 h. Then add 0.1 mol of calcium hydroxide to neutralize the hydrogen chloride generated during the reaction. Continue stirring for 0.5 h and then let stand at 60℃ for 24 h to remove bubbles, to obtain a PMIA slurry with a solid content of 18 wt%. Separately, disperse nAl2O3 nanoparticles in N,N-dimethylacetamide and sonicate to obtain an nAl2O3 dispersion with a concentration of 13.5 wt%. Subsequently, 8.6 g of the nAl2O3 dispersion prepared above was added to 30 g of PMIA slurry, and stirred at 600 r / min for 12 h to obtain nAl2O3 / PMIA composite slurry. In the nAl2O3 / PMIA composite slurry, the solid content of PMIA was 14 wt% and the content of nAl2O3 was 3 wt%.

[0064] (2) The nAl2O3 / PMIA composite slurry obtained in step (1) is coated onto the substrate (glass plate) and dried at 80°C for 60s to obtain an nAl2O3 / PMIA composite wet film.

[0065] (3) A 50 μm thick meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA composite wet film obtained in step (2), and a 25 g / cm³ coating is uniformly applied to the surface of the meta-aramid paper. 2 The pressure was applied for 1.5 hours, followed by drying at 80°C for 8 hours, and finally hot-pressed at 10 MPa pressure and 210°C for 14 minutes to obtain the bilayer meta-aramid composite paper of the comparative example.

[0066] Comparative Example 4 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4, the only difference being that the pre-compression treatment is omitted in step (3) (i.e. the pressure applied to the surface of the aramid paper is 0 g / cm). 2 (Let stand for 2 hours), other reaction conditions are the same as in Example 4.

[0067] Comparative Example 5 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4. The only difference is that the solid content of the PMIA-F slurry prepared in step (1) is adjusted so that the solid content of PMIA-F in the nAl2O3 / PMIA-F composite slurry prepared in step (1) is 8wt% and the content of nAl2O3 is 3wt%. Other reaction conditions are the same as those in Example 4.

[0068] Comparative Example 6 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4. The only difference is that the solid content of the PMIA-F slurry prepared in step (1) is adjusted so that the solid content of PMIA-F in the nAl2O3 / PMIA-F composite slurry prepared in step (1) is 25wt% and the content of nAl2O3 is 3wt%. Other reaction conditions are the same as those in Example 4.

[0069] Comparative Example 7 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4, the only difference being that: step (2) involves coating the nAl2O3 / PMIA-F composite slurry obtained in step (1) onto a substrate (glass plate) and drying it at 80°C for 150s, while other reaction conditions are the same as in Example 4. The results showed that nAl2O3 / PMIA-F had dried into a dry film and could not adhere to the meta-aramid paper.

[0070] Comparative Example 8 This comparative example provides a bilayer meta-aramid composite paper, the preparation method of which is basically the same as that of Example 4. The only difference between the two is that the hot pressing step in step (3) is omitted, and the other reaction conditions are the same as those of Example 4.

[0071] Comparative Example 9 This comparative example provides a bilayer meta-aramid composite paper, which is prepared using a direct coating method. The specific preparation method includes the following steps: (1) 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 0.08 mol of m-phenylenediamine and 0.1 mol of isophthaloyl chloride were dissolved in N,N-dimethylacetamide and reacted at -10 °C for 3 h. Then 0.1 mol of calcium hydroxide was added to neutralize the hydrogen chloride generated during the reaction. The mixture was stirred for 0.5 h and then allowed to stand at 60 °C for 24 h to remove bubbles, resulting in a PMIA-F slurry with a solid content of 18 wt%. In addition, nAl2O3 nanoparticles were dispersed in N,N-dimethylacetamide and sonicated to obtain a nAl2O3 dispersion with a concentration of 13.5 wt%. Subsequently, 8.6 g of the nAl2O3 dispersion prepared above was added to 30 g of PMIA-F slurry, and stirred at 600 r / min for 12 h to obtain nAl2O3 / PMIA-F composite slurry. In the nAl2O3 / PMIA-F composite slurry, the solid content of PMIA-F was 14 wt% and the content of nAl2O3 was 3 wt%.

[0072] (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is directly coated onto the surface of meta-aramid paper with a thickness of 50 μm, then dried at 80 °C for 8 h, and finally hot-pressed at 10 MPa pressure and 210 °C for 14 min to obtain the bilayer structure meta-aramid composite paper of the comparative example.

[0073] Comparative Example 10 This comparative example provides a 50 μm thick nAl2O3 / PMIA-F film. Specifically, the nAl2O3 / PMIA-F composite slurry (PMIA-F solid content is 14 wt% and nAl2O3 content is 3 wt%) prepared in step (1) of Example 4 is coated onto a glass plate and then dried at 100°C for 24 h to obtain the nAl2O3 / PMIA-F film.

[0074] Experimental Example 1: Structural Characterization 1.1 Infrared Spectroscopy Analysis The structures of PMIA-F, meta-aramid paper, and nAl2O3 involved in Examples 1-4 were characterized using infrared spectroscopy, and the resulting infrared spectra are shown below. Figure 1 As shown. Figure 1In the diagram, the left image shows the infrared spectra of PMIA-F and meta-aramid paper, and the right image shows the infrared spectrum of nAl2O3. In the left image, for ease of description of the PMIA-F prepared in Examples 1-4, they are named PMIA-F-5, PMIA-F-10, PMIA-F-15, and PMIA-F-20 according to the molar content of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, respectively, representing 0.0095 mol, 0.01 mol, 0.015 mol, and 0.02 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

[0075] Depend on Figure 1 As shown in the left figure, with the increase of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl content, at 1123 cm⁻¹... -1 The presence of a characteristic absorption peak of trifluoromethyl (-CF3) indicates that the present invention successfully prepared the polymer PMIA-F (i.e., modified poly(m-phenylene isophthalamide)) using a ternary copolymerization method. Figure 1 The right figure shows the infrared spectrum of nAl2O3, where 710 cm⁻¹... -1 The peak at this location is a characteristic peak of Al-O-Al.

[0076] 1.2 Scanning electron microscopy analysis The surface morphology of meta-aramid paper raw material and the bilayer meta-aramid composite paper prepared in Example 4 was analyzed using scanning electron microscopy (SEM). The obtained SEM images are shown below. Figure 2 As shown. Figure 2 In the diagram, the area below the dashed line shows the morphology of the meta-aramid paper raw material, while the area above the dashed line shows the morphology of the double-layer meta-aramid composite paper of this invention.

[0077] Depend on Figure 2 As can be seen, meta-aramid short fibers, meta-aramid pulp, and surface pores are clearly visible on the surface of untreated meta-aramid paper. However, in the bilayer meta-aramid composite paper prepared in this invention, the meta-aramid short fibers are covered by an nAl2O3 / PMIA-F film, resulting in a denser and smoother surface with significantly reduced surface roughness.

[0078] Experiment Example 2: Performance Testing The samples prepared in Examples 1-6 and Comparative Examples 1-10 were tested for maximum breakdown strength, tensile strength, tear resistance index, and the thickness of each layer. The maximum breakdown strength was tested according to GB / T 1408.1-2022; the tensile strength was tested according to GB / T 34004-2023; and the tear resistance index was tested according to GB / T 16578.1-2008. The performance test results for each material are shown in Table 1.

[0079] Table 1. Performance test results of each sample

[0080] As shown in Table 1, the double-layer meta-aramid composite paper prepared by the present invention can comprehensively improve the breakdown strength, tear resistance and tensile strength of meta-aramid paper compared with comparative examples 1 to 10, and has broad application prospects in ultra-high voltage equipment, high insulation equipment, aviation power system and other fields.

[0081] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the protection scope of the present invention.

Claims

1. A method for preparing a double-layer meta-aramid composite paper, characterized in that, Includes the following steps: (1) 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, m-phenylenediamine, and isophthaloyl chloride were subjected to a polycondensation reaction in a solvent to obtain a PMIA-F polymer slurry; aluminum oxide nanoparticles were ultrasonically dispersed in a solvent to obtain an nAl2O3 dispersion; the PMIA-F polymer slurry and the nAl2O3 dispersion were mixed to obtain an nAl2O3 / PMIA-F composite slurry; (2) The nAl2O3 / PMIA-F composite slurry obtained in step (1) is coated onto the substrate and then dried to obtain an nAl2O3 / PMIA-F composite wet film; (3) The meta-aramid paper is laid flat on the surface of the nAl2O3 / PMIA-F composite wet film obtained in step (2), and then pressure is applied to the surface of the meta-aramid paper for pre-pressing treatment. Then, drying and hot pressing treatment are performed in sequence to obtain the double-layer structure meta-aramid composite paper.

2. The method for preparing the double-layer meta-aramid composite paper according to claim 1, characterized in that, In step (1), the molar ratio of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, m-phenylenediamine and isophthaloyl chloride is (0.05~0.2):(0.8~0.95):1; the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

3. The method for preparing the double-layer meta-aramid composite paper according to claim 1, characterized in that, In step (1), the temperature of the polycondensation reaction is -12 to -8°C, and the time is 1 to 4 hours.

4. The method for preparing the double-layer meta-aramid composite paper according to claim 1, characterized in that, In step (1), the PMIA-F polymer slurry is a slurry of modified poly(m-phenylene isophthalamide); the concentration of modified poly(m-phenylene isophthalamide) in the PMIA-F polymer slurry is 18~20wt%; the concentration of aluminum oxide nanoparticles in the nAl2O3 dispersion is 0.02~15wt%; the mass ratio of the PMIA-F polymer slurry to the nAl2O3 dispersion is (0.25~1):1; the concentration of modified poly(m-phenylene isophthalamide) in the nAl2O3 / PMIA-F composite slurry is 10~14wt%, and the concentration of aluminum oxide nanoparticles is 0.1~5wt%.

5. The method for preparing a double-layer meta-aramid composite paper according to any one of claims 1 to 4, characterized in that, In step (2), the substrate is a glass plate or a stainless steel plate; the drying temperature is 60~100℃ and the time is 30~100s.

6. The method for preparing a double-layer meta-aramid composite paper according to any one of claims 1 to 4, characterized in that, In step (3), the thickness of the meta-aramid paper is 40~60μm.

7. The method for preparing a double-layer meta-aramid composite paper according to any one of claims 1 to 4, characterized in that, In step (3), the pressure of the pre-compression treatment is 5~40 g / cm³. 2 The drying process takes 1-3 hours; the drying temperature is 60-100℃ and the drying time is 3-10 hours; the hot pressing treatment takes 150-220℃, 5-15 MPa and 10-20 minutes.

8. A bilayer meta-aramid composite paper prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The bilayer meta-aramid composite paper includes an upper surface layer and a lower surface layer; the upper surface layer is an nAl2O3 / PMIA-F composite film; and the lower surface layer is meta-aramid paper.

9. The double-layer meta-aramid composite paper according to claim 8, characterized in that, The thickness of the nAl2O3 / PMIA-F composite film is 2~20μm; the thickness of the bilayer meta-aramid composite paper is 42~80μm.

10. An application of a bilayer meta-aramid composite paper prepared by the preparation method according to any one of claims 1 to 7, characterized in that, Applications in high-voltage insulation materials for power systems.

Images