Modified meta-aramid film and preparation method thereof, insulating paper and preparation method thereof

Abstract

The present invention relates to the technical field of insulating paper processing, and specifically to a modified meta-aramid film and its preparation method, as well as insulating paper and its preparation method. The modified meta-aramid film preparation method comprises: uniformly mixing a meta-aramid polymer solution with a high-temperature resistant resin solution, and obtaining the modified meta-aramid film using a film material film-forming method; the high-temperature resistant resin solution comprises a base resin, a curing agent, a high-thermal-conductivity filler, a toughening agent, a accelerator, an initiator, a reactive diluent, and a solvent; the base resin has a glass transition temperature (Tg) of ≥220°C or a long-term temperature resistance of ≥200°C; and the high-thermal-conductivity filler is fluorinated graphene or amino-modified fluorinated graphene. The modified meta-aramid film is used in the processing of insulating paper. The insulating paper has high mechanical strength, excellent insulating properties, low water absorption or moisture regain, strong interlayer bonding, is not easily delaminated, has a uniform thickness, is not easily blistered, and has a simple and efficient preparation process.

Description

Technical Field

[0001] The invention relates to a modified meta-aramid film and a preparation method thereof, insulating paper and a preparation method thereof, and belongs to the technical field of insulating paper processing. Background Art

[0002] Aramid insulation paper has outstanding mechanical strength, insulation properties, and high-temperature resistance. It is widely used as an insulating and protective material in various types of medium- and high-voltage motors, reactors, transformers, and other power equipment, and has a very broad market prospect. With the rapid development of power electronics technology and the gradual increase in the power of motors and transformers, new requirements have been placed on the mechanical strength, insulation performance, temperature resistance, and moisture resistance of traditional insulation materials. Especially in high-frequency working environments, the heat generated by electrical equipment accumulates rapidly. It is urgent to design and prepare paper-based insulation materials with high dielectric strength and high thermal conductivity. These materials can quickly and promptly transfer the heat accumulated in the electrical equipment coils to the heat dissipation device or insulating oil, ensuring the normal operation of the electrical equipment and extending its service life. Therefore, the design and development of insulation materials with high dielectric strength and high thermal conductivity has become the key to the miniaturization, lightweighting, and integration of electrical insulation equipment.

[0003] Existing aramid insulation paper uses meta-aramid fiber as its primary raw material, produced through a wet papermaking and hot-pressing process. However, due to the strong surface inertness of aramid fibers, fibers are difficult to bond to each other. This makes thick, high-weight insulation paper, in particular, subject to low mechanical strength and insulation properties, and prone to delamination, making it unsuitable for practical applications. Furthermore, due to the staggered, non-through pores in aramid paper's microstructure, while its dielectric properties are excellent in dry conditions, they significantly degrade under unusual conditions, such as high humidity or saltwater infiltration, compromising its safety.

[0004] A kind of high dielectric performance composite aramid paper is disclosed in Chinese patent application CN112746522A, propose to be combined into an integral body by the high temperature resistant adhesive layer containing inorganic nano filler between the single-layer aramid paper comprising more than two layers, form composite aramid paper, the composite aramid paper obtained has better breakdown strength and corona resistance.Yet due to the characteristic of aramid fiber surface inertia and two kinds of material interface bonding forces subjected to interface effect are less than, make the bonding force between high temperature resistant adhesive and aramid paper general, cause the various properties of composite aramid paper overall body to be limited (such as dielectric strength is lower).In addition, contain polar group in the resin or the binding agent such as polyimide, epoxy resin that usually adopt in existing open technology, increase the water absorption or moisture regain of aramid paper, can cause the insulation performance in high humidity environment to decline significantly.

[0005] Chinese patent application CN108316056A discloses an aramid paper composited with an aramid nanofiber film and its preparation method. The composite uses an aramid nanofiber (ANF) film as the top and bottom layers, and a core layer made from aramid chopped fibers and aramid pulp or aramid fibrids. The ANF film composited with the aramid paper is post-processed after the three layers are composited. However, relying solely on the compatibility of the aramid fibers to form the three layers, the composite can easily experience loose interfacial bonding and slippage during actual production and processing, resulting in reduced mechanical properties. Furthermore, the lack of other insulating materials results in slightly lower electrical insulation performance.

[0006] Chinese patent application CN111663363A discloses an aramid nanofiber / polyimide composite paper and its preparation method. Aramid nanofibers (ANF) serve as the upper and lower layers of the composite paper, with the middle layer being a composite layer of polyimide (PI) fibrids and mica. After the three are combined, the ANF / PI composite paper is finally obtained through vacuum drying and hot pressing. The introduction of PI fibrids improves the dielectric strength of the aramid paper. However, the inter-fiber bonding in the ANF / PI composite paper described in this patent is weak, and the preparation methods of the aramid nanofibers and PI fibrids are complex, making it difficult to industrialize.

[0007] On the other hand, to improve the thermal conductivity of aramid paper, researchers in this field typically use the following method: adding high-thermal conductive fillers during the aramid paper manufacturing process to improve the thermal conductivity of the paper. Commonly used high-thermal conductive fillers include boron nitride and aluminum nitride. However, these materials have low thermal conductivity, generally less than 50W / mK. Others have introduced graphene and other high-thermal conductive particles into aramid paper. However, graphene's electrical conductivity ultimately reduces the insulation properties of the aramid paper, resulting in poor insulation performance. Therefore, developing aramid paper with high thermal conductivity and excellent insulation properties is of great practical significance. Summary of the Invention

[0008] The present invention addresses the deficiencies in the prior art and provides a modified meta-aramid film and a preparation method thereof, as well as insulating paper and a preparation method thereof. The insulating paper has high thermal conductivity and dielectric strength, high mechanical strength, low water absorption or regain, strong interlayer bonding, is not easy to delaminate, has a simple process and is highly efficient.

[0009] The technical solution of the present invention to solve the above technical problems is as follows: a modified meta-aramid film, wherein the meta-aramid film is prepared from a meta-aramid polymer solution and a high-temperature resistant resin solution;

[0010] The high-temperature resistant resin solution includes a base resin, a curing agent, a high thermal conductivity filler, a toughening agent, a accelerator, an initiator, a reactive diluent and a solvent. The base resin has a glass transition temperature Tg of ≥220°C or a long-term temperature resistance of ≥200°C. The high thermal conductivity filler is fluorinated graphene or amino-modified fluorinated graphene. The base resin contains at least the benzoxazine resin.

[0011] Furthermore, the matrix resin is one or a combination of benzoxazine resin, high heat-resistant epoxy resin, and polyarylate resin containing a phthalazinone structure;

[0012] The toughening agent is any one or a combination of hyperbranched epoxy resin, hyperbranched polyester, hyperbranched unsaturated resin and flexible benzoxazine.

[0013] Preferably, the mass percentage of the benzoxazine resin in the matrix resin is 60% to 100%, and the benzoxazine resin is a daidzein-furfurylamine type benzoxazine resin.

[0014] The modified meta-aramid film described herein exhibits significantly lower thermal shrinkage than pure aramid film, making it more suitable for hot-pressing lamination of the aramid film with aramid paper. Upon curing, the benzoxazine resin in the matrix resin forms numerous hydrogen bonds, forming a "hydrogen-bonded complex" with the meta-aramid in the meta-aramid polymer solution. This significantly improves the dielectric strength of the insulating paper while enhancing its hydrophobicity. The addition of a flexible benzoxazine resin (a di-long-chain benzoxazine synthesized from long-chain phenols and long-chain amines) to the modified meta-aramid film further enhances its flexibility and hydrophobicity.

[0015] Furthermore, the fluorine content of the fluorinated graphene and the amino-modified fluorinated graphene is 35 wt% to 60 wt%, and the sheet diameter is 0.4 to 30 μm.

[0016] Furthermore, the curing agent is one or a combination of aromatic amine curing agents and acid anhydride curing agents.

[0017] Furthermore, the curing agent is one or a combination of 4,4'-diaminodiphenylmethane, diaminodiphenyl sulfone and methyl nadic anhydride;

[0018] The accelerator is aluminum acetylacetonate or cobalt naphthenate;

[0019] The initiator is one or a combination of benzoyl peroxide and dicumyl peroxide;

[0020] The active diluent is one or a combination of 1,4-butanediol diacrylate or diallyl phthalate;

[0021] The solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, dichloromethane, chloroform, N-methylpyrrolidone, ethyl acetate and pyridine.

[0022] Furthermore, the mass ratio of the base resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and reactive diluent is (60-100): (2-5): (8-20): (10-30): (0.1-1): (0.1-1): (2-10);

[0023] The mass concentration of the meta-aramid polymer in the meta-aramid polymer solution is 10% to 35%; the mass concentration of the high-temperature resistant resin in the high-temperature resistant resin solution is 25% to 50%;

[0024] In the mixed solution obtained by uniformly mixing the meta-aramid polymer solution and the high-temperature resistant resin solution, the mass proportion of the high-temperature resistant resin solution is 5% to 50%.

[0025] The present invention also discloses a method for preparing the meta-aramid film: after uniformly mixing a meta-aramid polymer solution with a high-temperature resistant resin solution, the mixture is uniformly coated on a smooth substrate surface, and the solvent is completely volatilized through a multi-stage drying process. The film peeled off from the smooth substrate surface is the modified meta-aramid film;

[0026] The multi-stage drying process is: drying at 50°C to 60°C for 30 to 90 minutes, drying at 70°C to 80°C for 30 to 90 minutes, and then drying at 90°C to 120°C for 0.1 to 12 hours.

[0027] Furthermore, under an inert gas dry environment at a pressure of 14 to 15 kPa, isophthaloyl chloride and meta-phenylenediamine are added to an organic solvent for polymerization reaction, and then a neutralizer is added to neutralize the hydrogen chloride dissolved in the polymerization solution, and the salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution.

[0028] Furthermore, the organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide; and the neutralizing agent is calcium oxide or calcium hydroxide.

[0029] The present invention also discloses an insulating paper, which includes multiple layers, including aramid paper and the modified meta-aramid film. The aramid paper has at least two layers, and the modified meta-aramid film has at least one layer. The modified meta-aramid film is covered between each layer of the aramid paper.

[0030] The present invention also discloses a method for preparing the insulating paper. The method comprises the following steps: covering the modified meta-aramid film between two adjacent layers of aramid paper, and obtaining the insulating paper through a segmented hot pressing process.

[0031] The insulating paper is obtained by a segmented hot pressing process, and the modified meta-aramid film enables each layer of aramid paper to be well combined. In actual production, the corresponding number of layers of insulating paper can be set according to demand.

[0032] Furthermore, the aramid paper is meta-aramid paper or para-aramid paper, which is prepared by mixing aramid chopped fibers, aramid fibrids and amino-modified fluorinated graphene, papermaking, pressing, drying, and then processing with a hot press to obtain meta-aramid paper or para-aramid paper;

[0033] The aramid short fibers are one or both of meta-aramid short fibers and para-aramid short fibers; the aramid fibrids are meta-aramid fibrids, and the beating degree is 35-60°SR.

[0034] In terms of weight, the present invention comprises 35 to 70 parts of aramid short fibers, 30 to 65 parts of aramid fibrids, and 2 to 20 parts of amino-modified fluorinated graphene.

[0035] Furthermore, the staged hot pressing process conditions are: first hot pressing for 4 to 8 hours at a temperature of 130 to 200° C. and a pressure of 4 to 12 MPa; then hot pressing for 0.3 to 3 hours at a temperature of 210 to 300° C. and a pressure of 18 to 35 MPa.

[0036] The beneficial effects of the present invention are:

[0037] (1) Excellent aging and weather resistance

[0038] Polyarylate resin or fluorinated graphene has excellent UV shielding and weather resistance. Compared with traditional aramid paper, the insulating paper of the present invention has better UV resistance and weather resistance, which broadens the application field of aramid insulating paper. In particular, some new motors are designed to operate in a UV environment, which can effectively avoid the problem of aramid paper aging and performance degradation caused by ultraviolet radiation to a certain extent.

[0039] (2) Enhanced internal bonding

[0040] During the preparation of the insulating paper of the present invention, under segmented hot pressing, the meta-aramid polymer and the high-temperature resistant resin in the modified meta-aramid film melt or soften and solidify, and fill the gaps in the aramid paper fibers under high temperature and high pressure, thereby making the modified meta-aramid film and the aramid paper more tightly bonded, greatly enhancing the internal bonding force of the aramid insulating paper, significantly improving the mechanical properties of the aramid insulating paper, and avoiding the occurrence of delamination.

[0041] (3) Excellent moisture resistance

[0042] During the preparation of the insulating paper described in the present invention, the meta-aramid polymer and high-temperature resistant resin in the modified meta-aramid film melt, soften, and solidify under segmented hot pressing. Under high temperature and high pressure, they fill the gaps between the aramid paper fibers, significantly reducing the pores of the insulating paper described in the present invention. Compared to traditional aramid paper, the insulating paper described in the present invention avoids, to a certain extent, the problem of reduced insulation performance caused by the capillary action of water adsorbed in the pores of traditional aramid paper. At the same time, the present invention also avoids the problem of poor moisture resistance caused by simply introducing conventional thermosetting resins (which have poor moisture resistance due to the presence of polar groups).

[0043] At the same time, the benzoxazine resin contained in the modified meta-aramid film forms a large number of hydrogen bonds after curing, forming a "hydrogen bond complex" with the meta-aramid in the modified meta-aramid film, making it have low hygroscopicity and improving the application performance of the insulating paper in special environments, such as the dielectric properties under high humidity conditions.

[0044] (3) Excellent insulation

[0045] During the hot pressing process of the modified meta-aramid film's meta-aramid polymer and the high-temperature resistant resin, the benzoxazine resin contained in the high-temperature resistant resin will solidify to produce many phenolic hydroxyl groups, forming a large number of hydrogen bonds. At the same time, it will also produce hydrogen bonds with the nitrogen or oxygen atoms in the meta-aramid to form a "hydrogen bond complex", which significantly improves the dielectric strength of the modified meta-aramid film, thereby greatly improving the insulation performance of the insulating paper.

[0046] The benzoxazine resin, meta-aramid polymer and high thermal conductivity filler in the insulating paper of the present invention work synergistically, so that the insulating paper has excellent insulation performance and has the advantages of being inherently flame retardant or high temperature resistant.

[0047] (4) Smaller shrinkage

[0048] Compared with pure meta-aramid film, the introduction of benzoxazine resin into the modified meta-aramid film prepared by the present invention greatly reduces the thermal shrinkage during processing, making the production of insulating paper more efficient and convenient, and improving the product qualification rate.

[0049] (5) Excellent thermal conductivity

[0050] The insulating paper of the present invention has a multi-layer structure. The addition of amino-modified fluorinated graphene to aramid paper effectively improves the thermal conductivity of the insulating paper while maintaining excellent insulation performance. Furthermore, the amino-modified fluorinated graphene has excellent dispersibility in water, which facilitates the processing of the aramid paper, preventing the aramid paper's strength from being affected while also improving its thermal conductivity and insulation. Furthermore, the addition of fluorinated graphene or amino-modified fluorinated graphene to a meta-aramid film improves the thermal conductivity and insulation of the modified meta-aramid film. The resulting insulating paper has high strength and excellent thermal conductivity and insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the insulating paper layer structure of Example 1 and Examples 4-9;

[0052] Figure 2 Schematic diagram of the insulating paper layer structure of Example 2-3. DETAILED DESCRIPTION

[0053] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0055] A method for preparing a modified meta-aramid film, comprising: uniformly mixing a meta-aramid polymer solution with a high-temperature resistant resin solution, and obtaining the modified meta-aramid film using a film material film-making method;

[0056] The high-temperature-resistant resin solution includes a base resin, a curing agent, a high-thermal-conductivity filler, a toughening agent, an accelerator, an initiator, a reactive diluent, and a solvent. The base resin has a glass transition temperature (Tg) of 220°C or higher, or a long-term temperature resistance of 200°C or higher. The high-thermal-conductivity filler is fluorinated graphene or amino-modified fluorinated graphene. The base resin contains at least the benzoxazine resin, with the mass percentage of the benzoxazine resin in the base resin being 60% to 100%.

[0057] In an embodiment of the present invention, the matrix resin is one or a combination of benzoxazine resin, high heat-resistant epoxy resin, and polyarylate resin containing a phthalazinone structure;

[0058] The toughening agent is any one or a combination of hyperbranched epoxy resin, hyperbranched polyester, hyperbranched unsaturated resin and flexible benzoxazine.

[0059] The benzoxazine resin is a daidzein-furfurylamine type benzoxazine resin, which is homemade. The preparation method is as follows: first, a certain amount of furfurylamine and paraformaldehyde are added to a toluene solvent, reacted at 50°C for 2 hours, to obtain a uniform milky white mixture; then, a toluene solution containing daidzein is added to the mixture, reacted at 105°C for 8-10 hours, the toluene solvent is removed by vacuum distillation under reduced pressure, and vacuum dried at 70°C for 24 hours to obtain the daidzein-furfurylamine type benzoxazine resin. The molar ratio of furfurylamine, paraformaldehyde, and daidzein required for the reaction is 2:4:1.

[0060] The high heat-resistant epoxy resin is selected from any one or a combination of XY-434L, XY-434, XY-433, ELM-100, and ELM-434.

[0061] XY-434L, XY-434, and XY-433 were purchased from Liaoyang Xinyu Chemical Co., Ltd., and ELM-100 and ELM-434 were purchased from Sumitomo Chemical.

[0062] The polyarylate resin containing a diazolinone structure is homemade. The specific preparation method is as follows: under nitrogen protection, 16 mmol of benzenesulfonyl chloride, 5 ml of pyridine, and 2.6 mmol of N,N-dimethylformamide are added in sequence to a 100 ml three-necked flask equipped with a mechanical stirrer, and the mixture is reacted at room temperature for 30 minutes. A pyridine solution of 5 mmol of 4-[4-(4-aminophenoxy)phenyl]-2-(4-aminophenyl)phthalazin-1-one is added to the reaction system, and the mixture is reacted at room temperature for 10 minutes. The mixture is then heated to 120° C. and reacted for 10 minutes. A pyridine solution of 5 mmol of 4,4'-dihydroxydiphenylpropane is then added dropwise. After the addition is complete, the mixture is kept warm for 3 hours, and the reaction is stopped. The reaction solution is sedimented, washed, and purified to obtain the polyarylate resin containing a diazolinone structure. The reaction equation is:

[0063]

[0064] In the embodiment of the present invention, the hyperbranched epoxy resin is selected from any one or a combination of Hyper E101, Hyper E102, Hyper E103, Hyper E104, HyperPer E201, Hyper Per E202, Hyper Per E203, Hyper Per E204, Hyper E301, 302, 303, 304, Hyper E401, Hyper402, Hyper403, and Hyper404 produced by Suzhou Haibote Resin Technology Co., Ltd.

[0065] The hyperbranched unsaturated resin is any one or a combination of HyPer U102, HUP-101, HUP-102, HUP-103, and HUP-104.

[0066] Among them, HyPer U102 was purchased from Wuhan Hyperbranched Resin Technology Co., Ltd.; HUP 10 series (HUP-101, HUP-102, HUP-103, HUP-104) was purchased from Suzhou Haibote Resin Technology Co., Ltd.

[0067] The flexible benzoxazine is homemade. The phenol used to synthesize the flexible benzoxazine can be any one of cardanol and nonylphenol. The amine can be any one of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine. The aldehyde is paraformaldehyde.

[0068] Using nonylphenol, dodecylamine, and paraformaldehyde as examples, the specific method for preparing a nonylphenol-dodecylamine flexible benzoxazine resin is as follows: In a three-necked flask equipped with a condenser and stirred at 80°C for a period of time, paraformaldehyde is added, and the reaction is continued for a period of time. The temperature is then raised to 110°C and allowed to react for 4 hours to obtain the nonylphenol-dodecylamine flexible benzoxazine resin. The molar ratio of nonylphenol, dodecylamine, and paraformaldehyde required for the reaction is 1:1:2. This method can also be used to prepare other types of flexible benzoxazines, simply by replacing the corresponding phenolic and amine substances.

[0069] In the embodiment of the present invention, the fluorinated graphene (purchased from Xianfeng Nano, fluorine content: 53%-65%, sheet diameter: 4-10 μm) and the amino-modified fluorinated graphene (self-made) have a fluorine content of 35wt%-60wt% and a sheet diameter of 0.4-30 μm.

[0070] The amino-modified fluorinated graphene in the embodiment of the present invention is homemade. The specific preparation method is: grinding and mixing the fluorinated graphene and urea to obtain a mixture, the mass ratio of the fluorinated graphene to the urea is 1:500, and then adding the mixture to a reactor. Under the protection of an inert gas, the mixture is heated to 150° C. and reacted for 4 hours. After cooling, distilled water is added to the reactor, and a black sample is obtained by filtration. Finally, the black sample is washed three times with distilled water and 95% ethanol respectively to obtain the amino-modified fluorinated graphene.

[0071] In the embodiment of the present invention, the curing agent is one or a combination of aromatic amine curing agents and acid anhydride curing agents.

[0072] In an embodiment of the present invention, the curing agent is one or a combination of 4,4'-diaminodiphenylmethane, diaminodiphenyl sulfone and methyl nadic anhydride;

[0073] The accelerator is aluminum acetylacetonate or cobalt naphthenate;

[0074] The initiator is one or a combination of benzoyl peroxide and dicumyl peroxide;

[0075] The active diluent is one or a combination of 1,4-butanediol diacrylate or diallyl phthalate;

[0076] The solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, dichloromethane, chloroform, N-methylpyrrolidone, ethyl acetate and pyridine.

[0077] In an embodiment of the present invention, a meta-aramid polymer solution is uniformly mixed with a high-temperature resistant resin solution, and then uniformly coated on a smooth substrate surface. The solvent is completely evaporated through a multi-stage drying process, and the film peeled off from the smooth substrate surface is the meta-aramid film.

[0078] The multi-stage drying process is: drying at 50°C to 60°C for 30 to 90 minutes, drying at 70°C to 80°C for 30 to 90 minutes, and then drying at 90°C to 120°C for 0.1 to 12 hours.

[0079] In an embodiment of the present invention, a method for preparing a meta-aramid polymer solution is as follows: in an inert gas dry environment at a pressure of 14 to 15 kPa, isophthaloyl chloride and meta-phenylenediamine are added to an organic solvent to carry out a polymerization reaction, and then a neutralizing agent is added to neutralize the hydrogen chloride dissolved in the polymer solution, and the salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymer solution.

[0080] The organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide; and the neutralizing agent is calcium oxide or calcium hydroxide.

[0081] Specifically, in an embodiment of the present invention, m-phenylenediamine is added to an organic solvent in a dry inert gas environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0°C. Stirring is initiated, and isophthaloyl chloride is slowly added. The system is then heated to 60 to 70°C for polymerization. After the reaction is complete, a neutralizing agent is added to neutralize the hydrogen chloride dissolved in the polymerization solution. Salts generated by the neutralization reaction are filtered to remove the salts, thereby obtaining a meta-aramid polymerization solution. The molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:(1 to 1.05).

[0082] In the embodiment of the present invention, the mass ratio of the base resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and reactive diluent is (60-100): (2-5): (8-20): (10-30): (0.1-1): (0.1-1): (2-10);

[0083] The mass concentration of the meta-aramid polymer in the meta-aramid polymer solution is 10% to 35%; the mass concentration of the high-temperature resistant resin in the high-temperature resistant resin solution is 25% to 50%;

[0084] In the mixed solution obtained by uniformly mixing the meta-aramid polymer solution and the high-temperature resistant resin solution, the mass proportion of the high-temperature resistant resin solution is 5% to 50%;

[0085] A method for preparing insulating paper, wherein the insulating paper comprises multiple layers, including aramid paper and a modified meta-aramid film, the aramid paper comprising at least two layers, and the modified meta-aramid film comprising at least one layer. The modified meta-aramid film is coated between each layer of the aramid paper. The insulating paper is obtained by a segmented hot pressing process, and the meta-aramid film enables good bonding between each layer of the aramid paper.

[0086] In an embodiment of the present invention, the aramid paper is meta-aramid paper or para-aramid paper, which is obtained by mixing aramid short fibers, aramid fibrids, and amino-modified fluorinated graphene, papermaking, pressing, drying, and then processing in a hot press. The aramid short fibers are either meta-aramid short fibers or para-aramid short fibers, or both. The aramid fibrids are meta-aramid fibrids, and have a beating degree (SR) of 35 to 60 degrees.

[0087] In terms of weight, the present invention comprises 35 to 70 parts of aramid short fibers, 30 to 65 parts of aramid fibrids, and 2 to 20 parts of amino-modified fluorinated graphene.

[0088] In an embodiment of the present invention, the staged hot pressing process conditions are: first, hot pressing treatment at a temperature of 130-200°C and a pressure of 4-12 MPa for 4-8 hours; then hot pressing treatment at a temperature of 210-300°C and a pressure of 18-35 MPa for 0.3-3 hours.

[0089] Example 1

[0090] (a) Preparation of meta-aramid polymer solution

[0091] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added in a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1. The system is then heated to 60 to 70° C. for polymerization. After the reaction is completed, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 13%.

[0092] (b) Preparation of high temperature resistant resin solution

[0093] The specific raw material composition is as shown in Table 1:

[0094] Table 1 Raw materials of high temperature resistant resin solution of Example 1

[0095]

[0096] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 25%.

[0097] (c) Preparation of modified meta-aramid film

[0098] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring, wherein the mass fraction of the high-temperature resistant resin solution in the mixed solution is 50%.

[0099] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process included drying at 50-60°C for 90 minutes, then at 70-80°C for 30 minutes, and finally at 90-100°C for 30 minutes. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0100] (d) Preparation of meta-aramid paper

[0101] 39 parts of meta-aramid fibrids with a beating degree of 46°SR, 61 parts of meta-aramid short fibers, and 10 parts of amino-modified fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 200°C, a pressure of 10 MPa, and a time of 10 minutes to obtain a thickness of 0.03 mm.

[0102] (e) Preparation of insulating paper

[0103] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0104] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of modified meta-aramid paper prepared in step (d), and a hot press is performed in sections to obtain insulating paper;

[0105] The first hot pressing process was as follows: (1) temperature 150°C, pressure 8 MPa, time 1 hour; (2) temperature 170°C, pressure 10 MPa, time 3 hours; (3) temperature 190°C, pressure 10 MPa, time 1 hour; and the second hot pressing process was as follows: temperature 260°C, pressure 23 MPa, time 0.5 hour. The resulting insulating paper had a thickness of 0.08 mm. The properties are shown in Table 8.

[0106] Example 2

[0107] (a) Preparation of meta-aramid polymer solution

[0108] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent of N,N-dimethylformamide, stirring is started, and isophthaloyl chloride is slowly added, with a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1.05. The system is then heated to 60 to 70° C. for polymerization. After the reaction is completed, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution, and salt generated by the neutralization reaction is filtered out to obtain a m-aramid polymerization solution with a polymer mass concentration of 20%.

[0109] (b) Preparation of high temperature resistant resin solution

[0110] The specific raw material composition is shown in Table 2:

[0111] Table 2 Raw materials of high temperature resistant resin solution of Example 2

[0112]

[0113] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 40%.

[0114] (c) Preparation of modified meta-aramid film

[0115] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring. The mass fraction of the high-temperature resistant resin solution in the mixed solution is 39%.

[0116] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The modified meta-aramid film was then dried through a multi-stage drying process to remove the solvent. The drying process consisted of drying at 50-60°C for 30 minutes, 70-80°C for 90 minutes, and finally at 110-120°C for 2 hours. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0117] (d) Preparation of meta-aramid paper

[0118] 41 parts of meta-aramid fibrids with a beating degree of 40°SR, 59 parts of meta-aramid short fibers, and 8 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 210°C, a pressure of 8 MPa, and a time of 8 minutes to obtain a thickness of 0.03 mm.

[0119] (e) Preparation of insulating paper

[0120] The insulating paper in this embodiment has a 7-layer structure. Figure 2 shown.

[0121] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and the meta-aramid paper prepared in step (d) is formed according to Figure 2 The insulating paper is laminated in a manner and subjected to segmented hot pressing treatment using a hot press;

[0122] The first hot-pressing process was as follows: (1) temperature 140°C, pressure 6 MPa, time 1.5 h; (2) temperature 170°C, pressure 8 MPa, time 2.5 h; (3) temperature 200°C, pressure 10 MPa, time 2 h; and the second hot-pressing process was at 280°C, pressure 25 MPa, time 0.5 h. The resulting insulating paper had a thickness of 0.18 mm. The properties are shown in Table 8.

[0123] Example 3

[0124] (a) Preparation of meta-aramid polymer solution

[0125] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added in a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1. The system is then heated to 60 to 70° C. for polymerization. After the reaction is complete, calcium hydroxide is added as a neutralizing agent to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 30%.

[0126] (b) Preparation of high temperature resistant resin solution

[0127] The specific raw material composition is shown in Table 3:

[0128] Table 3 Raw materials of high temperature resistant resin solution of Example 3

[0129]

[0130] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 50%.

[0131] (c) Preparation of modified meta-aramid film

[0132] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring, wherein the mass fraction of the high-temperature resistant resin solution in the mixed solution is 30%.

[0133] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process consisted of drying at 50-60°C for 90 minutes, then at 70-80°C for 90 minutes, and finally at 100-110°C for 4 hours. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0134] (d) Preparation of meta-aramid paper

[0135] 35 parts of meta-aramid fibrids with a beating degree of 48°SR, 65 parts of meta-aramid short fibers, and 18 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 205°C, a pressure of 8.5 MPa, and a time of 8 minutes to obtain a thickness of 0.08 mm.

[0136] The insulating paper in this embodiment has a seven-layer structure. Figure 2 shown.

[0137] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and the meta-aramid paper prepared in step (d) is formed according to Figure 2 The insulating paper is laminated in a manner and subjected to segmented hot pressing treatment using a hot press;

[0138] The first hot-pressing process was as follows: (1) temperature 130°C, pressure 8 MPa, time 0.5 h; (2) temperature 170°C, pressure 10 MPa, time 1 h; and (3) temperature 190°C, pressure 10 MPa, time 3 h. The second hot-pressing process was as follows: temperature 290°C, pressure 30 MPa, time 0.3 h. The resulting insulating paper had a thickness of 0.38 mm. The properties are shown in Table 8.

[0139] Example 4

[0140] (a) Preparation of meta-aramid polymer solution

[0141] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added in a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1. The system is then heated to 60 to 70° C. for polymerization. After the reaction is completed, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 10%.

[0142] (b) Preparation of high temperature resistant resin solution

[0143] The specific raw material composition is shown in Table 4:

[0144] Table 4 Raw materials of high temperature resistant resin solution of Example 4

[0145]

[0146] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 48%.

[0147] (c) Preparation of modified meta-aramid film

[0148] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and mixed evenly by ultrasound or stirring. The mass fraction of the high-temperature resistant resin solution in the mixed solution is 5%.

[0149] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process included drying at 50-60°C for 60 minutes, then at 70-80°C for 60 minutes, and finally at 90-120°C for 6 hours. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0150] (d) Preparation of meta-aramid paper

[0151] 65 parts of meta-aramid fibrids with a beating degree of 56°SR, 35 parts of meta-aramid short fibers, and 2 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 200°C, a pressure of 10 MPa, and a time of 6 minutes to obtain a thickness of 0.03 mm.

[0152] (e) Preparation of insulating paper

[0153] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0154] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of meta-aramid paper prepared in step (d), and a hot press is used to perform a segmented hot pressing process to obtain insulating paper;

[0155] The first hot-pressing process was as follows: (1) temperature 150°C, pressure 5 MPa, time 2 h; (2) temperature 170°C, pressure 7 MPa, time 3 h; (3) temperature 180°C, pressure 12 MPa, time 2 h; and the second hot-pressing process was as follows: temperature 210°C, pressure 18 MPa, time 3 h. The resulting insulating paper had a thickness of 0.08 mm. The properties are shown in Table 8.

[0156] Example 5

[0157] (a) Preparation of meta-aramid polymer solution

[0158] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added, and the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:1.05. The system is then heated to 60 to 70° C. for polymerization. After the reaction is completed, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 35%.

[0159] (b) Preparation of high temperature resistant resin solution

[0160] The specific raw material composition is shown in Table 5:

[0161] Table 5 Raw materials of high temperature resistant resin solution of Example 5

[0162]

[0163]

[0164] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 45%.

[0165] (c) Preparation of modified meta-aramid film

[0166] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring, wherein the mass fraction of the high-temperature resistant resin solution in the mixed solution is 25%.

[0167] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process consisted of drying at 50-60°C for 60 minutes, then at 70-80°C for 60 minutes, and finally at 100-110°C for 8 hours. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0168] (d) Preparation of meta-aramid paper

[0169] 30 parts of meta-aramid fibrids with a beating degree of 52°SR, 70 parts of meta-aramid short fibers, and 15 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 200°C, a pressure of 10 MPa, and a time of 6 minutes to obtain a thickness of 0.05 mm.

[0170] (e) Preparation of insulating paper

[0171] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0172] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of meta-aramid paper prepared in step (d), and a hot press is used to perform a segmented hot pressing process to obtain insulating paper;

[0173] The first hot-pressing process was as follows: (1) temperature 130°C, pressure 7 MPa, time 1 hour; (2) temperature 170°C, pressure 10 MPa, time 1 hour; (3) temperature 190°C, pressure 10 MPa, time 3 hours; and the second hot-pressing process was as follows: temperature 230°C, pressure 35 MPa, time 1 hour. The resulting insulating paper had a thickness of 0.12 mm. The properties are shown in Table 8.

[0174] Example 6

[0175] (a) Preparation of meta-aramid polymer solution

[0176] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added in a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1. The system is then heated to 60 to 70° C. for polymerization. After the reaction is completed, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 13%.

[0177] (b) Preparation of high temperature resistant resin solution

[0178] The specific raw material composition is shown in Table 6:

[0179] Table 6 Raw materials of high temperature resistant resin solution of Example 6

[0180]

[0181] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 40%.

[0182] (c) Preparation of modified meta-aramid film

[0183] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring. The mass fraction of the high-temperature resistant resin solution in the mixed solution is 15%.

[0184] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process included drying at 50-60°C for 30 minutes, then at 70-80°C for 60 minutes, and finally at 90-120°C for 10 hours. The resulting meta-aramid film had an average thickness of 0.02 mm.

[0185] (d) Preparation of meta-aramid paper

[0186] 40 parts of meta-aramid fibrids with a beating degree of 48°SR, 60 parts of meta-aramid short fibers, and 20 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 210°C, a pressure of 8 MPa, and a time of 6 minutes to obtain a thickness of 0.08 mm.

[0187] (e) Preparation of insulating paper

[0188] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0189] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of meta-aramid paper prepared in step (d), and a hot press is used to perform a segmented hot pressing process to obtain insulating paper;

[0190] The first hot-pressing process was as follows: (1) temperature 140°C, pressure 6 MPa, time 1.5 h; (2) temperature 170°C, pressure 8 MPa, time 2.5 h; (3) temperature 200°C, pressure 10 MPa, time 2 h; and the second hot-pressing process was as follows: temperature 280°C, pressure 30 MPa, time 0.5 h. The resulting insulating paper had a thickness of 0.18 mm. The properties are shown in Table 8.

[0191] Example 7

[0192] (a) Preparation of meta-aramid polymer solution

[0193] In an inert gas dry environment at a pressure of 14 to 15 kPa and at a temperature of -5 to 0° C., m-phenylenediamine is added to an organic solvent, N,N-dimethylacetamide, and stirring is started. Isophthaloyl chloride is slowly added in a molar ratio of m-phenylenediamine to isophthaloyl chloride of 1:1. The system is then heated to 60 to 70° C. for polymerization. After the reaction is complete, calcium oxide is added as a neutralizer to neutralize hydrogen chloride dissolved in the polymerization solution. Salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization solution with a polymer mass concentration of 20%.

[0194] (b) Preparation of high temperature resistant resin solution

[0195] The specific raw material composition is shown in Table 7:

[0196] Table 7 Raw materials of high temperature resistant resin solution of Example 7

[0197]

[0198]

[0199] The matrix resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent are dissolved in a solvent and mixed evenly to prepare a high temperature resistant resin solution with a mass percentage of 35%.

[0200] (c) Preparation of modified meta-aramid film

[0201] The meta-aramid polymer solution in step (a) is mixed with the high-temperature resistant resin solution in step (b), and the mixture is uniformly mixed by ultrasound or stirring. The mass fraction of the high-temperature resistant resin solution in the mixed solution is 35%.

[0202] The mixed solution was applied to smooth tempered glass using a wire rod coating method. The tempered glass plate with the modified meta-aramid film was then subjected to a multi-stage drying process to remove the solvent. The multi-stage drying process included drying at 50-60°C for 30 minutes, then at 70-80°C for 60 minutes, and finally at 90-120°C for 12 hours. The resulting modified meta-aramid film had an average thickness of 0.02 mm.

[0203] (d) Preparation of meta-aramid paper

[0204] 35 parts of meta-aramid fibrids with a beating degree of 47°SR, 65 parts of meta-aramid short fibers, and 20 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain meta-aramid base paper. The resulting meta-aramid paper was then processed in a hot press at 200°C, a pressure of 10 MPa, and a time of 6 minutes to obtain a thickness of 0.03 mm.

[0205] (e) Preparation of insulating paper

[0206] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0207] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of meta-aramid paper prepared in step (d), and a hot press is used to perform a segmented hot pressing process to obtain insulating paper;

[0208] The first hot pressing process was as follows: (1) temperature 150°C, pressure 8 MPa, time 1 hour; (2) temperature 170°C, pressure 10 MPa, time 2 hours; (3) temperature 190°C, pressure 10 MPa, time 1 hour; and the second hot pressing process was as follows: temperature 260°C, pressure 23 MPa, time 0.5 hour. The resulting insulating paper had a thickness of 0.08 mm. The properties are shown in Table 8.

[0209] Example 8

[0210] (a) to (c): Modified meta-aramid films were prepared in the same manner as in Example 1;

[0211] (d) Preparation of para-aramid paper

[0212] 39 parts of meta-aramid fibrids with a beating degree of 48°SR, 61 parts of para-aramid short fibers, and 10 parts of amino-modified fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain para-aramid base paper. The resulting para-aramid paper was then processed in a hot press at 210°C, a pressure of 15 MPa, and a time of 10 minutes to obtain a thickness of 0.03 mm.

[0213] (e) Preparation of insulating paper

[0214] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0215] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of para-aramid paper prepared in step (d), and a hot press is used to perform a segmented hot pressing process to obtain insulating paper;

[0216] The first hot pressing process was as follows: (1) temperature 150°C, pressure 8 MPa, time 1 hour; (2) temperature 170°C, pressure 10 MPa, time 3 hours; (3) temperature 190°C, pressure 10 MPa, time 1 hour; and the second hot pressing process was as follows: temperature 260°C, pressure 23 MPa, time 0.5 hour. The resulting insulating paper had a thickness of 0.08 mm. The properties are shown in Table 8.

[0217] Example 9

[0218] (a) to (c): Modified meta-aramid films were prepared using the same method as in Example 5;

[0219] (d) Preparation of para-aramid paper

[0220] 30 parts of meta-aramid fibrids with a beating degree of 46°SR, 70 parts of para-aramid short fibers, and 15 parts of amino-fluorinated graphene were pulped separately, mixed, sheeted, pressed, and dried to obtain para-aramid base paper. The resulting para-aramid paper was then processed in a hot press at 210°C, a pressure of 15 MPa, and a time of 10 minutes to obtain a thickness of 0.05 mm.

[0221] (e) Preparation of insulating paper

[0222] The insulating paper in this embodiment has a three-layer structure. Figure 1 shown.

[0223] The modified meta-aramid film prepared in step (c) is used as an intermediate layer and is laminated with two sheets of para-aramid paper prepared in step (d), and a hot press is performed in sections to obtain insulating paper;

[0224] The first hot-pressing process was as follows: (1) temperature 130°C, pressure 7 MPa, time 1 hour; (2) temperature 170°C, pressure 10 MPa, time 1 hour; (3) temperature 190°C, pressure 10 MPa, time 3 hours; and the second hot-pressing process was as follows: temperature 230°C, pressure 35 MPa, time 1 hour. The resulting insulating paper had a thickness of 0.12 mm. The properties are shown in Table 8.

[0225] Comparative Example 1

[0226] According to the same method as step (d) of Example 1, meta-aramid paper with a thickness of 0.08 mm was prepared, and the corresponding properties of the prepared meta-aramid paper were tested, as shown in Table 8.

[0227] Comparative Example 2

[0228] A meta-aramid polymer solution was prepared in the same manner as in step (a) of Example 1, and then a modified meta-aramid film (referred to as pure meta-aramid film in this Comparative Example 2) was prepared in the same manner as in step (c) of Example 1. The thickness of the modified meta-aramid film was 0.02 mm. The difference from Example 1 was that no high-temperature resistant resin solution was added during the preparation of the modified meta-aramid film.

[0229] A 0.03 mm thick meta-aramid paper was prepared in the same manner as in step (d) of Example 1. Finally, a 0.08 mm thick insulating paper was prepared in the same manner as in step (e) of Example 1. The properties are shown in Table 8.

[0230] Comparative Example 3

[0231] Insulating paper is prepared according to the same method as in Example 1, except that steps (a) and (c) are not included. The high temperature resistant resin solution prepared in step (b) is sprayed on one side of the meta-aramid paper prepared in step (d), and then dried through a multi-stage drying process. The drying process is: first drying at 50-60°C for 90 minutes, then drying at 70-80°C for 30 minutes, and finally drying at 90-100°C for 30 minutes. Repeat the above spraying steps, control the thickness of the high temperature resistant resin layer to 0.02mm, and then cover it with a layer of meta-aramid paper. The three-layer structure of "meta-aramid paper-high temperature resistant resin-meta-aramid paper" is processed according to the hot pressing process in Example 1. The thickness of the obtained insulating paper is 0.08mm, and the properties are shown in Table 8.

[0232] Comparative Example 4

[0233] Insulating paper was prepared in the same manner as in Example 1, except that no fluorinated graphene was added to the high-temperature resistant resin solution. The properties of the obtained insulating paper are shown in Table 8.

[0234] Comparative Example 5

[0235] Insulating paper was prepared in the same manner as in Example 1, except that amino-modified fluorinated graphene was not added during the preparation of the meta-aramid paper. The properties of the obtained insulating paper are shown in Table 8.

[0236] Comparative Example 6

[0237] Insulating paper was prepared in the same manner as in Example 1, except that no fluorinated graphene was added to the high-temperature resistant resin solution and no amino-modified fluorinated graphene was added to the preparation of the meta-aramid paper. The properties of the obtained insulating paper are shown in Table 8.

[0238] Comparative Example 7

[0239] Insulating paper was prepared in the same manner as in Example 1, except that when preparing the high-temperature resistant resin solution, fluorinated graphene was replaced with boron nitride. The properties of the obtained insulating paper are shown in Table 8.

[0240] Comparative Example 8

[0241] Insulating paper was prepared in the same manner as in Example 1, except that when preparing the high-temperature resistant resin solution, fluorinated graphene was replaced with graphene. The properties of the obtained insulating paper are shown in Table 8.

[0242] Comparative Example 9

[0243] (a) Preparation of meta-aramid polymer solution

[0244] The preparation steps of the meso-aramid polymer solution are the same as those in Example 6.

[0245] (b) Preparation of high temperature resistant resin solution

[0246] The specific raw material composition is the same as that of Example 6, except that 50 parts of daidzein-furfurylamine type benzoxazine resin are replaced with 50 parts of high heat-resistant epoxy resin XY-434.

[0247] Steps (c) to (e) are the same as the preparation steps (c) to (e) in Example 6. The thickness of the obtained aramid composite insulating paper is 0.18 mm, and the properties are shown in Table 8.

[0248] Comparative Example 10

[0249] (a) Preparation of meta-aramid polymer solution

[0250] The preparation steps of the meso-aramid polymer solution are the same as those in Example 1.

[0251] (b) Preparation of high temperature resistant resin solution

[0252] The specific raw material composition is the same as that of Example 1, except that 70 parts of daidzein-furfurylamine type benzoxazine resin are replaced with 70 parts of high heat-resistant epoxy resin XY-434L.

[0253] Steps (c) to (e) are the same as the preparation steps (c) to (e) in Example 1. The thickness of the obtained aramid composite insulating paper is 0.08 mm, and the properties are shown in Table 8.

[0254] Table 8 Insulation paper performance data

[0255]

[0256]

[0257] Note: When the thickness is ≤0.13mm, the tear strength refers to the internal tear strength; when the thickness is greater than 0.13mm, the tear strength refers to the edge tear strength.

[0258] As can be seen from the data in Table 1, the insulating paper prepared using the method of the present invention in Examples 1-9 not only has good mechanical properties, but also has high dielectric strength and good thermal conductivity. In contrast, the insulating paper prepared in Comparative Example 1, which did not include the meta-aramid film, showed significantly reduced thermal conductivity and dielectric strength. The dielectric strength of the insulating paper prepared in Example 1 was increased by 168.4% compared to Comparative Example 1. Furthermore, the tensile strength and interlayer bond strength of the insulating paper prepared in Example 1 were also significantly higher than those in Comparative Example 1. This demonstrates that the meta-aramid film of the present invention can effectively improve the insulating and mechanical properties of insulating paper while also providing excellent thermal conductivity.

[0259] From the comparison of the data of Comparative Example 2 and Example 1, it can be seen that if the high-temperature resistant resin solution is not added during the preparation of the insulating paper, the tensile strength, dielectric strength, and interlayer bonding strength of the prepared insulating paper are significantly reduced. This shows that the addition of the high-temperature resistant resin solution of the present invention is beneficial for making the insulating paper have better insulation performance and mechanical properties. From the comparison of the data of Comparative Example 3 and Example 1, it can be seen that if the meta-aramid polymer solution is not added during the preparation of the insulating paper, the dielectric strength, tensile strength, and interlayer bonding strength of the prepared insulating paper are significantly reduced. From the comparison of the experimental data of Comparative Examples 2-3 and Example 1, it can be clearly seen that only by using the high-temperature resistant resin solution and the meta-aramid polymer to prepare the meta-aramid film and then applying it to the insulating paper can the high-temperature resistant resin-coated aramid paper have excellent insulation performance and mechanical properties. During the preparation of insulating paper, the meta-aramid polymer and high-temperature resistant resin in the modified meta-aramid film melt, soften, or solidify under staged hot pressing, filling the gaps in the aramid paper fibers under high temperature and high pressure. This allows the modified meta-aramid film to bond more tightly to the meta-aramid paper, improving the mechanical properties of the insulating paper, increasing the interlayer bonding strength, and avoiding the occurrence of delamination. At the same time, the pores in the insulating paper can be significantly reduced, avoiding the problem of reduced insulation performance caused by water adsorption due to capillary action in the pores of traditional aramid paper. At the same time, as the high-temperature resistant resin solidifies, benzoxazine forms a "hydrogen bond complex" with the meta-aramid, producing a synergistic effect, thereby improving the overall performance of the insulating paper. Therefore, the meta-aramid polymer and high-temperature resistant resin in the meta-aramid film can play a good synergistic role, improving the overall performance of the insulating paper.

[0260] Comparing the data from Comparative Examples 4, 5, and 6 with Example 1 shows that the addition of fluorinated graphene and amino-modified fluorinated graphene effectively improves the thermal conductivity of the insulating paper while maintaining good insulation and mechanical properties. The fluorinated graphene blends well with the matrix resin in the high-temperature-resistant resin solution, creating a synergistic effect that imparts excellent insulation, thermal conductivity, and mechanical properties to the insulating paper.

[0261] From the data of Comparative Example 7, it can be seen that if the fluorinated graphene is replaced with conventional boron nitride, the thermal conductivity of the insulating paper decreases. This shows that the thermal conductivity of fluorinated graphene is significantly better than that of boron nitride.

[0262] From the data of Comparative Example 8, it can be seen that, based on the certain conductivity of graphene, if fluorinated graphene is replaced with graphene, the dielectric strength of the insulating paper will be significantly reduced, and it will not be able to meet the requirements of areas with higher insulation properties.

[0263] The experimental conditions of Comparative Example 9 and Example 6 are almost the same, and the experimental conditions of Comparative Example 10 and Example 1 are almost the same, except that the base resins in Comparative Examples 9 and 10 do not contain benzoxazine resin. From the data comparison, it can be seen that their dielectric strength is significantly reduced. This is because during the hot pressing process of the modified meta-aramid film, the meta-aramid polymer and the high-temperature resistant resin, the benzoxazine resin contained in the high-temperature resistant resin will solidify to produce many phenolic hydroxyl groups, forming a large number of hydrogen bonds. At the same time, it will also produce hydrogen bonds with nitrogen or oxygen atoms in the meta-aramid to form "hydrogen bond complexes", which greatly improves the dielectric strength of the insulating paper.

[0264] The insulating paper of the present invention not only has good mechanical properties, insulation properties, and thermal conductivity, but also has excellent moisture resistance. To verify the moisture resistance, the insulating papers of Example 1, Example 8, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were placed in an environment with a humidity of 70% to 80% and a temperature of 40°C for 180 days, and the dielectric strength data were measured again. The specific results are shown in Table 9 below.

[0265] Table 9 Moisture-proof performance evaluation

[0266]

[0267]

[0268] Note: Humidity is 70% to 80%, temperature is 40℃.

[0269] The data in Table 9 show that the insulating paper prepared using the method of the present invention in Examples 1 and 8 maintains high dielectric strength after exposure to humidity, meeting insulation performance requirements and being suitable for use in various high-humidity environments. Comparative Examples 1, 2, and 3, however, do not use the method of the present invention to prepare insulating paper. The primary difference from the present invention is that the modified meta-aramid film, meta-aramid polymer solution, or high-temperature-resistant resin solution described herein is not used. Consequently, the resulting insulating paper readily absorbs moisture after exposure to high humidity, ultimately affecting its insulation performance.

[0270] The benzoxazine resin contained in the modified meta-aramid films of Examples 1 and 8 forms numerous hydrogen bonds after curing, forming a "hydrogen bond complex" with the meta-aramid in the modified meta-aramid films. This reduces the hygroscopicity of pure meta-aramid films and improves the dielectric properties of the insulating paper in special environments, such as high humidity. Furthermore, during the preparation of the insulating paper, the meta-aramid polymer and high-temperature resistant resin in the modified meta-aramid films melt or soften under staged hot pressing. Under high temperature and high pressure, they fill the gaps between the aramid paper fibers, significantly reducing the porosity of the insulating paper and avoiding the problem of reduced insulation performance caused by capillary water absorption in the pores of traditional aramid paper. Furthermore, during the preparation process of the insulating paper described herein, the high-temperature resistant resin in the modified meta-aramid film synergizes with the meta-aramid polymer and aramid paper, effectively improving the insulation paper's moisture resistance.

[0271] Furthermore, the modified meta-aramid film described herein exhibits low shrinkage upon heating. This makes hot-press bonding of the aramid paper and the modified meta-aramid film more efficient and convenient during the hot-pressing process for insulating paper production, resulting in a higher yield rate for insulating paper products. The modified meta-aramid film of Example 1 and the pure meta-aramid film of Comparative Example 2 were heat-treated. Specific phenomena and shrinkage data are shown in Table 10.

[0272] Table 10 Determination of thermal shrinkage

[0273]

[0274] It can be seen from the data in Table 10 that the modified meta-aramid film prepared by the method of the present invention has smaller heat shrinkage and is more conducive to the preparation of insulating paper.

[0275] In summary, the modified meta-aramid film described in the present invention can be used in insulating paper to effectively improve the dielectric strength, thermal conductivity, moisture resistance and mechanical properties of the insulating paper. The insulating paper described in the present invention can provide higher dielectric protection performance for large motors, reactors, transformers and other equipment, thereby extending the service life of the motor, reducing maintenance costs and improving production efficiency.

[0276] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0277] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A modified meta-aramid film, characterized in that: The meta-aramid film is made from a meta-aramid polymer solution and a high-temperature resistant resin solution; The high-temperature resistant resin solution comprises a base resin, a curing agent, a high thermal conductivity filler, a toughening agent, an accelerator, an initiator, a reactive diluent, and a solvent. The base resin has a glass transition temperature Tg of ≥220°C or a long-term temperature resistance of ≥200°C. The high thermal conductivity filler is fluorinated graphene or amino-modified fluorinated graphene. The base resin contains at least the benzoxazine resin. The mass percentage of the benzoxazine resin in the matrix resin is 60% to 100%; The mass concentration of the meta-aramid polymer in the meta-aramid polymer solution is 10% to 35%; the mass concentration of the high-temperature resistant resin in the high-temperature resistant resin solution is 25% to 50%; In the mixed solution obtained by uniformly mixing the meta-aramid polymer solution and the high-temperature resistant resin solution, the mass proportion of the high-temperature resistant resin solution is 5% to 50%.

2. The modified meta-aramid film according to claim 1, characterized in that: The matrix resin is one or a combination of benzoxazine resin, high heat-resistant epoxy resin, and polyarylate resin containing a diazinone structure; the matrix resin contains at least the benzoxazine resin; The toughening agent is any one or a combination of hyperbranched epoxy resin, hyperbranched polyester, hyperbranched unsaturated resin and flexible benzoxazine.

3. The modified meta-aramid film according to claim 1, characterized in that: The benzoxazine resin is a daidzein-furfurylamine type benzoxazine resin.

4. The modified meta-aramid film according to claim 1, characterized in that: The curing agent is one or a combination of aromatic amine curing agents and acid anhydride curing agents; The accelerator is aluminum acetylacetonate or cobalt naphthenate; The initiator is one or a combination of benzoyl peroxide and dicumyl peroxide; The active diluent is one or a combination of 1,4-butanediol diacrylate or diallyl phthalate; The solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, dichloromethane, chloroform, N-methylpyrrolidone, ethyl acetate, and pyridine; The mass ratio of the base resin, curing agent, high thermal conductive filler, toughening agent, accelerator, initiator and active diluent is (60-100): (2-5): (8-20): (10-30): (0.1-1): (0.1-1): (2-10).

5. A method for preparing the modified meta-aramid film according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: uniformly mixing meta-aramid polymer solution and high-temperature resistant resin solution, and obtaining the modified meta-aramid film by a film material film making method.

6. The method for preparing a modified meta-aramid film according to claim 5, characterized in that: After uniformly mixing the meta-aramid polymer solution and the high-temperature resistant resin solution, the mixture is evenly coated on the smooth surface of a substrate, and the solvent is completely evaporated through a multi-stage drying process. The film peeled off from the smooth surface of the substrate is the modified meta-aramid film; The multi-stage drying process is: drying at 50°C to 60°C for 30 to 90 minutes, drying at 70°C to 80°C for 30 to 90 minutes, and then drying at 90°C to 120°C for 0.1 to 12 hours.

7. The method for preparing a modified meta-aramid film according to claim 5, characterized in that: In an inert gas dry environment at a pressure of 14 to 15 kPa, isophthaloyl chloride and meta-phenylenediamine are added to an organic solvent for polymerization reaction, and then a neutralizing agent is added, and salt generated by the neutralization reaction is filtered out to obtain a meta-aramid polymerization liquid; The organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide; and the neutralizing agent is calcium oxide or calcium hydroxide.

8. An insulating paper, characterized in that: The insulating paper comprises multiple layers, comprising aramid paper and the modified meta-aramid film according to any one of claims 1 to 4 or the modified meta-aramid film prepared by the method for preparing a modified meta-aramid film according to any one of claims 5 to 7, the aramid paper comprising at least two layers, the modified meta-aramid film comprising at least one layer, and the modified meta-aramid film being coated between each layer of the aramid paper; The aramid paper is meta-aramid paper or para-aramid paper, which is prepared by mixing aramid chopped fibers, aramid fibrils and amino-modified fluorinated graphene, papermaking, pressing, drying, and then being processed by a hot press to obtain the meta-aramid paper or para-aramid paper.

9. A method for preparing insulating paper according to claim 8, characterized in that: The preparation method comprises the following steps: covering the modified meta-aramid film between two adjacent layers of aramid paper, and obtaining the insulating paper through a segmented hot pressing process.

10. The method for preparing insulating paper according to claim 9, characterized in that: The aramid short-cut fibers are one or both of meta-aramid short-cut fibers and para-aramid short-cut fibers; the aramid fibrids are meta-aramid fibrids with a beating degree of 35 to 60. · SR; According to parts by weight, 35-70 parts of aramid short fibers, 30-65 parts of aramid fibrids, and 2-20 parts of amino-modified fluorinated graphene; The staged hot pressing process conditions are: first hot pressing for 4 to 8 hours at a temperature of 130 to 200° C. and a pressure of 4 to 12 MPa; then hot pressing for 0.3 to 3 hours at a temperature of 210 to 300° C. and a pressure of 18 to 35 MPa.

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