Epoxy resin curing agent, insulating epoxy resin and preparation method thereof

Abstract

The invention belongs to a curing agent structure, and provides an epoxy resin curing agent, an insulating epoxy resin and a preparation method of the insulating epoxy resin in order to solve the technical problems that nanoparticles are easy to agglomerate and non-uniformly dispersed and the electrical performance improvement effect at high temperature is not clear in the existing method for improving the electrical performance of a polymer material at high temperature. Comprising at least two benzene ring structures or at least two non-coplanar rigid alicyclic structures; every two adjacent benzene ring structures or non-coplanar rigid alicyclic structures are connected through methylene, the two sides of the overall structure are each provided with an amino functional group, and electron-withdrawing substituent groups or a plurality of steric hindrance substituent groups are arranged at the ortho-positions of the amino functional groups. The heat stability of the prepared epoxy resin is enhanced by introducing a benzene ring, and good electrical performance can be maintained in a high temperature gradient and large electric field environment by introducing a high electron withdrawing group and a steric hindrance substituent group or using a non-coplanar alicyclic structure with saturated electrons to replace the benzene ring.

Description

Technical Field

[0001] The present application relates to a curing agent structure, and specifically to an epoxy resin curing agent, an insulating epoxy resin and a preparation method thereof. Background Art

[0002] With the focus on carbon emission issues and the rapid development of the renewable energy industry, large-scale energy transmission and utilization are becoming increasingly important, and high voltage direct current (HVDC) transmission technology is of great significance to the development of large-scale energy transmission and utilization. At present, thermosetting polymer-based insulation materials, especially epoxy resin-based insulation materials, are widely used as electrical insulation materials in DC gas-insulated transmission pipelines and switches (GIL, Gas Insulated Transmission Lines, Gas Insulated Metal Enclosed Transmission Lines / GIS, Gas Insulated Switchgear, Gas Insulated Metal Enclosed Switchgear), bushings, solid-state transformers (SSTs, Solid-state Transformers, SSTs), rectifiers and other power equipment and electronic devices due to their excellent mechanical properties, corrosion resistance and electrical properties.

[0003] However, with the increase of voltage level and power density, the resistive consumption of conductors and the heat dissipation inside insulation will cause the working temperature of insulating materials to rise, which requires insulating materials to maintain excellent electrical properties at high temperatures. In addition, under the action of direct current, the electric field is resistive, and the resistivity of epoxy resin is extremely sensitive to temperature changes. Under the action of high temperature and large electric field, it is easy to cause electric field distortion and reduced insulation strength. The glass transition temperature of traditional anhydride-cured epoxy resin is only about 120°C. When the working environment temperature is close to this temperature, its electrical and mechanical properties will drop significantly. Therefore, it is of great significance to develop epoxy resin insulation materials that can still have excellent electrical properties at high temperatures for future energy networks.

[0004] At present, the main methods to improve the electrical properties of polymer materials at high temperatures include nano-doping technology and molecular design. Although nano-doping technology has great potential, it cannot guarantee the uniform dispersion of nanoparticles within the material. If the doping concentration is too high, it will lead to particle agglomeration, which will still hinder its practical application. In addition, molecular design is also an effective method to optimize high-performance polymers. However, this method is still in the experimental stage in designing epoxy resins with high thermal stability and high electrical properties, and the current methods mainly focus on directly improving the electrical insulation properties of polymers. Although the introduction of deep traps can increase the energy required to excite electrons at high temperatures, the dominant factor in the decline of epoxy resin performance is still the molecular thermal motion caused by high temperature. Therefore, it is urgent to find a method to improve the thermal stability and electrical properties of epoxy resin insulating materials. Summary of the invention

[0005] The present application aims to provide an epoxy resin curing agent, an insulating epoxy resin and a preparation method thereof in response to the technical problems that the current methods for improving the electrical properties of polymer materials at high temperatures have the problems of easy agglomeration of nanoparticles, uneven dispersion and unclear effect of improving the electrical properties at high temperatures.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions: In a first aspect, the present application provides an epoxy resin curing agent, comprising: at least two benzene ring structures or at least two non-coplanar rigid alicyclic structures; Two adjacent benzene ring structures or non-coplanar rigid alicyclic structures are connected by methylene groups to form an overall structure; An amino functional group is arranged on both sides of the overall structure, and an electron-withdrawing substituent group or a plurality of steric hindrance substituent groups are arranged at the adjacent position of the amino functional group.

[0007] Further, the electron-withdrawing substituent group is -Cl; The sterically hindered substituent group is -CH3 or -C2H5.

[0008] Further, the epoxy resin curing agent structure includes at least two non-coplanar rigid alicyclic structures; The non-coplanar rigid alicyclic structure is C6H 12 .

[0009] Furthermore, the number of the sterically hindered substituent groups is 1-2.

[0010] In a second aspect, the present application provides a method for preparing an insulating epoxy resin, comprising: Dispersing the epoxy resin curing agent in bisphenol A epoxy resin to obtain a first mixture; adding an alumina filler to the liquid phase mixture to obtain a second mixture; Heating the second mixture to degas the second mixture under vacuum, and then pouring the second mixture into a mold to degas the second mixture under vacuum; After curing and cooling, the insulating epoxy resin finished product is obtained.

[0011] Furthermore, the weight ratio of the epoxy resin curing agent, the bisphenol A epoxy resin and the alumina filler is (10-35):(15-45):(35-65).

[0012] Furthermore, the curing conditions are: Raise the temperature to 120~140 ℃ and continue for 60~120 min; then raise the temperature to 160~180 ℃ and continue for 100~150 min; finally raise the temperature to 180~220 ℃ and continue for 60~120 min.

[0013] Furthermore, the method of dispersing the epoxy resin curing agent in the bisphenol A epoxy resin comprises: The epoxy resin curing agent is melted at 100-120°C, and then the epoxy resin curing agent is stirred and dispersed in the bisphenol A epoxy resin at 100-120°C.

[0014] Furthermore, the second mixture is heated so that the temperature condition for vacuum degassing of the second mixture is 100-140°C.

[0015] In a third aspect, the present application proposes an insulating epoxy resin, which is prepared using the above insulating epoxy resin preparation method.

[0016] Compared with the prior art, this application has the following beneficial effects: The present application proposes an epoxy resin curing agent, which improves the thermal stability of epoxy resin by introducing a diaryl diamine curing agent, and improves the glass transition temperature of epoxy resin by utilizing the rigidity and planar structure of the benzene ring, so that the epoxy resin can maintain its original performance at a higher temperature. By grafting different groups at the ortho position of the amino functional group, the electrical properties of the epoxy resin are improved. By grafting a high electron-withdrawing group at the ortho position of the amino functional group, the π electron density on the benzene ring is reduced by utilizing its adsorption effect on electrons, thereby reducing the conductivity of the epoxy resin. Or by grafting a large steric hindrance group such as methane and ethane at the ortho position of the amino functional group, the steric hindrance effect and distorted conformation generated in the epoxy resin chain are utilized to block the charge transfer between different molecules caused by the conjugation effect of the benzene ring, thereby improving the electrical properties of the epoxy resin. In addition, a non-planar rigid alicyclic structure with saturated electrons is used instead of the benzene ring, and its weak conjugation effect is utilized to reduce the concentration of non-localized electrons, thereby improving the electrical properties of the epoxy resin. By modifying the epoxy resin curing agent using the above method, an insulating epoxy resin having both high thermal stability and high electrical properties can be prepared, thereby solving the problem of insulation failure in high temperature gradient and large electric field environments.

[0017] The present application also proposes a method for preparing an insulating epoxy resin. By introducing a benzene ring, the thermal stability of the epoxy resin obtained is enhanced. By introducing high electron-withdrawing groups and large steric hindrance groups, or using non-coplanar alicyclic structures with saturated electrons to replace the benzene ring, the volume resistivity of the epoxy resin at room temperature and high temperature is significantly improved, and it can maintain good electrical properties in high temperature gradient and large electric field environments.

[0018] The present application also proposes an insulating epoxy resin prepared by the above insulating epoxy resin preparation method, which has all the advantages of the above epoxy resin curing agent and the insulating epoxy resin preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 Fourier transform infrared spectra of bisphenol A epoxy resin (DGEBA) and insulating epoxy resins obtained in Examples 1 to 6 of the present application and comparative examples; Figure 2 The figure is a glass transition temperature diagram of the insulating epoxy resin obtained in Examples 1 to 6 of the present application and the comparative example; Figure 3The DC breakdown strength and shape parameter diagram of the insulating epoxy resin obtained in Examples 1 to 6 of the present application and the comparative example at room temperature; Figure 4 This is a graph showing the volume resistivity results of the insulating epoxy resins obtained in Examples 1 to 6 of the present application and the comparative example at 80°C. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0023] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0024] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invented product is usually placed when used. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0025] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0026] In the description of the embodiments of the present application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0027] With the continuous increase in voltage levels and power density, the problems of conductor resistive consumption and internal heat dissipation of insulation have become increasingly prominent, resulting in a gradual increase in the operating temperature of insulating materials. This requires that insulating materials must be able to maintain excellent electrical properties in high temperature environments. However, under the action of a DC electric field, the electric field is resistive, and the resistivity of epoxy resin is extremely sensitive to temperature changes. High temperature and large electric field environments can easily cause electric field distortion and reduced insulation strength. The glass transition temperature of traditional anhydride-cured epoxy resin is only about 120°C. When the working environment temperature approaches this temperature, its electrical and mechanical properties will be significantly reduced.

[0028] Based on the above situation, the present application proposes an epoxy resin curing agent, an insulating epoxy resin and a preparation method thereof, which will be described in detail below in conjunction with embodiments and drawings.

[0029] First, the present application proposes an epoxy resin curing agent, including two structures: (1) At least two benzene ring structures, two adjacent benzene ring structures are connected by a methylene group to form an overall structure, and the methylene group is set at the 1,4 substitution position of the benzene ring structure. An amino functional group is set on each side of the overall structure, and an electron-withdrawing substituent group or a plurality of steric hindrance substituent groups are set at the ortho position of the amino functional group.

[0030] The two adjacent benzene ring structures are connected by methylene groups, which makes the whole molecule have a certain flexibility, while maintaining the rigidity of the benzene ring. An amino functional group is arranged on each side of the overall structure, which serves as a key part for subsequent curing reaction with epoxy resin. An electron-withdrawing substituent group or a plurality of sterically hindered substituent groups are arranged at the ortho position of the amino functional group, and these substituent groups can affect the electron cloud density and steric hindrance of the amino functional group, thereby affecting its reaction activity with epoxy resin and the performance of the cured product. For the overall structure, due to the presence of the benzene ring structure, this curing agent can have good heat resistance and chemical resistance. The introduction of a high electron-withdrawing group can reduce the electron cloud density on the benzene ring by utilizing its strong adsorption effect on electrons, thereby increasing the resistivity of the material. The introduction of a sterically hindered group can hinder the charge transfer between different molecules and increase the resistivity of the final product.

[0031] (2) at least two non-coplanar rigid alicyclic structures, wherein two adjacent non-coplanar rigid alicyclic structures are connected by a methylene group to form an overall structure, wherein an amino functional group is disposed on each side of the overall structure, and an electron-withdrawing substituent group or a plurality of steric hindrance substituent groups are disposed at the ortho position of the amino functional group.

[0032] The second structure uses a non-planar structure instead of a benzene ring, and reduces the local electron concentration through the weak conjugation effect of the non-planar structure, thereby increasing the resistivity of the final product.

[0033] Some examples of the epoxy resin curing agent include: 1. Includes two benzene ring structures: (1) The electron-withdrawing substituent group uses a high electron-withdrawing group. A high electron-withdrawing group refers to a group with a strong ability to attract electrons, which can significantly reduce the electron cloud density on the benzene ring. It usually has a strong electronegativity and can attract electrons through the inductive effect and conjugation effect. Common high electron-withdrawing groups can be nitro groups, tertiary amine cations, halogen atoms, etc.

[0034] For example, taking a halogen atom: .

[0035] (2) Steric hindrance substituents can be large steric hindrance substituents. Large steric hindrance substituents refer to substituents with a large volume in the molecule. Due to the large volume, they occupy a certain range in space, causing the molecule as a whole to show a certain distortion or deformation, which will affect the spatial orientation, three-dimensional structure and chemical properties of the molecule.

[0036] For example, using -CH3: .

[0037] Using two -CH3: .

[0038] Using -C2H5: .

[0039] Using two -C2H5: .

[0040] 2. Includes two non-coplanar rigid alicyclic structures: The non-coplanar rigid alicyclic structure adopts C6H 12 : .

[0041] The above curing agent structure has enhanced thermal stability of epoxy resin prepared by introducing benzene rings. By introducing high electron-withdrawing groups and large steric hindrance groups or using non-coplanar alicyclic structures with saturated electrons to replace benzene rings, the volume resistivity of epoxy resin at room temperature and high temperature is significantly improved, and it can maintain good electrical properties in high temperature gradient and large electric field environments.

[0042] The present application also proposes a method for preparing an insulating epoxy resin using the above curing agent, which may include: S1, dispersing the epoxy resin curing agent of the present application in bisphenol A epoxy resin to obtain a first mixture.

[0043] S2, adding alumina filler to the liquid mixture to obtain a second mixture.

[0044] Alumina filler can increase the mechanical strength, heat resistance and thermal conductivity of epoxy resin. At the same time, alumina also has good insulation properties and high temperature stability.

[0045] S3, heating the second mixture to degas the second mixture in vacuum, and then pouring the second mixture into a mold for vacuum degassing.

[0046] Degassing under vacuum conditions can remove bubbles from the mixture and improve the density and insulation performance of the finished product. The degassed mixture is poured into a pre-prepared mold and degassed under vacuum conditions to further remove bubbles and ensure that the mixture is evenly distributed in the mold.

[0047] S4, after curing and cooling, a finished insulating epoxy resin product is obtained.

[0048] The temperature and time can also be controlled during the curing process to ensure that the epoxy resin is fully cured. After the curing is completed, the pre-finished product can be taken out of the mold and cooled. After cooling, the insulating epoxy resin finished product can be obtained.

[0049] The following are some examples: Embodiment 1: 4,4'-methylenebis(2-chloroaniline) (MOCA) with two benzene ring structures and a strong electron-withdrawing group -Cl is used as an epoxy resin curing agent, namely:

[0050] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 60 °C for 8 h. 4,4'-methylenebis(2-chloroaniline) (MOCA) was melted at 100 °C, and MOCA was dispersed in bisphenol A epoxy resin at the same temperature under high-speed stirring for 30 min to obtain a first mixture.

[0051] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 120 °C for 30 min. The mold is sprayed with a release agent and preheated to 120 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 10 min. The second mixture contains 10 parts of 4,4'-methylenebis(2-chloroaniline) (MOCA), 15 parts of bisphenol A epoxy resin (DGEBA), and 35 parts of Al2O3 micron base filler.

[0052] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 120 °C and maintained for 60 min, then raised to 160 °C and maintained for 120 min, and finally raised to 180 °C and maintained for 120 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-MOCA.

[0053] Embodiment 2: 4,4'-methylene-bis(2-methylaniline) (MBOT) having two benzene ring structures and a large steric hindrance group -CH3 is used as an epoxy resin curing agent, namely:

[0054] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 80 °C for 6 h. 4,4'-methylene-bis(2-methylaniline) (MBOT) was melted at 110 °C, and MBOT was dispersed in the bisphenol A epoxy resin at the same temperature under high-speed stirring for 35 min to obtain a first mixture.

[0055] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 100 °C for 50 min. The mold is sprayed with a release agent and preheated to 100 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 20 min. The second mixture contains 35 parts of 4,4'-methylene-bis(2-methylaniline) (MBOT), 45 parts of bisphenol A epoxy resin (DGEBA), and 65 parts of Al2O3 micron base filler.

[0056] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 130 °C and maintained for 80 min, then raised to 170 °C for 100 min, and finally raised to 200 °C for 100 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-MBOT.

[0057] Embodiment 3: 4,4-Methylenebis(2,6-dimethylaniline) (MBMDA) having two benzene ring structures and a large steric hindrance group -CH3 is used as an epoxy resin curing agent, namely:

[0058] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 75 °C for 6 h. 4,4-Methylenebis(2,6-dimethylaniline) (MBMDA) was melted at 105 °C, and MBMDA was dispersed in bisphenol A epoxy resin at the same temperature under high-speed stirring for 42 min to obtain a first mixture.

[0059] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 140 °C for 45 min. The mold is sprayed with a release agent and preheated at 140 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 15 min. The second mixture contains 20 parts of 4,4-methylenebis(2,6-dimethylaniline) (MBMDA), 30 parts of bisphenol A epoxy resin (DGEBA), and 50 parts of Al2O3 micron base filler.

[0060] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 120 °C and maintained for 70 min, then raised to 180 °C and maintained for 120 min, and finally raised to 220 °C and maintained for 60 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-MBMDA.

[0061] Embodiment 4: 4,4'-methylenebis(2-ethylaniline) (MOEA) with two benzene ring structures and a large steric hindrance group -C2H5 is used as an epoxy resin curing agent, namely:

[0062] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 80 °C for 7 h. 4,4'-methylenebis(2-ethylaniline) (MOEA) was melted at 115 °C, and MOEA was dispersed in bisphenol A epoxy resin at the same temperature under high-speed stirring for 40 min to obtain a first mixture.

[0063] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 130 °C for 50 min. The mold is sprayed with a release agent and preheated to 130 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 25 min. The second mixture contains 20 parts of 4,4'-methylenebis(2-ethylaniline) (MOEA), 30 parts of bisphenol A epoxy resin (DGEBA), and 50 parts of Al2O3 micron base filler.

[0064] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 140 °C and maintained for 90 min, then raised to 170 °C and maintained for 100 min, and finally raised to 200 °C and maintained for 90 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-MOEA.

[0065] Embodiment 5: 4,4'-methylenebis(2,6-diethylaniline) (MDEA) with two benzene ring structures and a large steric hindrance group -C2H5 is used as an epoxy resin curing agent, namely:

[0066] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 80 °C for 8 h. 4,4'-methylenebis(2,6-diethylaniline) (MDEA) was melted at 120 °C, and MDEA was dispersed in bisphenol A epoxy resin at the same temperature under high-speed stirring for 50 min to obtain a first mixture.

[0067] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 140 °C for 50 min. The mold is sprayed with a release agent and preheated at 140 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 30 min. The second mixture contains 20 parts of 4,4'-methylenebis(2,6-diethylaniline) (MDEA), 30 parts of bisphenol A epoxy resin (DGEBA), and 50 parts of Al2O3 micron base filler.

[0068] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 140 °C and maintained for 120 min, then raised to 180 °C for 150 min, and finally raised to 220 °C for 120 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-MDEA.

[0069] Embodiment 6: Using a non-coplanar saturated alicyclic structure C6H 12 4,4'-Diaminodicyclohexylmethane (PACM) is used as epoxy resin curing agent, namely:

[0070] The preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 60 °C for 6 h. 4,4'-diaminodicyclohexylmethane (PACM) was melted at 100 °C, and PACM was dispersed in bisphenol A epoxy resin at the same temperature with high-speed stirring for 30 min to obtain a first mixture.

[0071] (2) Alumina filler is added to the first mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. The second mixture is heated and stirred, and the second mixture is vacuum degassed at 100 °C for 30 min. The mold is sprayed with a release agent and preheated to 100 °C. Subsequently, the second mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 10 min. The second mixture contains 20 parts of 4,4'-diaminodicyclohexylmethane (PACM), 30 parts of bisphenol A epoxy resin (DGEBA), and 50 parts of Al2O3 micron base filler.

[0072] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 120 °C and maintained for 60 min, then raised to 160 °C and maintained for 100 min, and finally raised to 180 °C and maintained for 60 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-PACM.

[0073] Comparative Example: 4,4'-diaminodiphenylmethane (DDM) is used as epoxy resin curing agent, and the preparation method of insulating epoxy resin is as follows: (1) Bisphenol A epoxy resin (DGEBA) was preheated at 70 °C for 7 h. 4,4'-diaminodiphenylmethane (DDM) was melted at 110 °C and dispersed in the bisphenol A epoxy resin at the same temperature under high-speed stirring for 40 min to obtain a first mixture.

[0074] (2) Alumina filler is added to the liquid phase mixture of epoxy resin curing agent and bisphenol A epoxy resin to obtain a second mixture. Heat and stir, and vacuum degas the second mixture at 120 °C for 40 min. The mold is sprayed with a release agent and preheated to 120 °C. Subsequently, the mixture is poured into the preheated mold and then vacuum degassed at the same temperature for 20 minutes. The second mixture contains 20 parts of 4,4'-diaminodiphenylmethane (DDM), 30 parts of epoxy resin E51, and 50 parts of Al2O3 micron base filler.

[0075] (3) The cross-linking reaction was carried out in a step-by-step heating manner. The curing environment temperature was raised to 130 °C and maintained for 90 min, then raised to 170 °C and maintained for 125 min, and finally raised to 210 °C and maintained for 80 min. After naturally cooling to room temperature, an insulating epoxy resin material with a thickness of about 0.3 mm was taken out from the mold and named EP-DDM.

[0076] Figure 1 The following are Fourier transform infrared spectra of bisphenol A epoxy resin (DGEBA) and insulating epoxy resin obtained in Examples 1 to 6 of the present application and the comparative example. Figure 1 It can be seen that at 915 cm -1 The absorption peak at 3300-3450 cm disappeared, and the characteristic peak associated with the epoxy group disappeared, indicating that the addition reaction between the amine and the epoxy ring has been completed. -1 The NH stretching vibration absorption peak in the range disappears, which also confirms the consumption of the -NH2 functional group in the curing agent.

[0077] Figure 2The figure is a graph of the glass transition temperature of the insulating epoxy resin obtained in Examples 1 to 6 of the present application and the comparative example. For the insulating epoxy resins prepared in Examples 1 to 6 and the comparative example, their glass transition temperatures are much higher than the glass transition temperature of the traditional anhydride-cured epoxy resin (about 120°C), and the glass transition temperature of EP-MBMDA reaches 200°C. It can be seen that the introduction of benzene rings leads to an increase in the glass transition temperature of the resin, and since cyclohexane also has a certain rigidity, the glass transition temperature of EP-PACM is also relatively high.

[0078] Figure 3 The figure shows the DC breakdown strength and shape parameter of the insulating epoxy resin obtained in Examples 1 to 6 of the present application and the comparative example at room temperature. The breakdown field strength is the Weibull breakdown strength. It can be seen that the epoxy resin curing agents containing strong electron-withdrawing groups and large steric hindrance groups all show high electrical properties at room temperature. And for EP-MOEA and EP-MOCA, the breakdown strength exceeds 200 kV / mm, which is higher than the performance of traditional anhydride-cured epoxy resins.

[0079] Figure 4 The volume resistivity results of the insulating epoxy resins obtained in Examples 1 to 6 of the present application and the comparative example at 80°C are shown in FIG. It can be found that the volume resistivity of EP-MOCA and EP-PACM at 80°C exceeds 2.5×10 15 Ω·cm, which is much higher than the performance of traditional anhydride cured epoxy resins. Except for EP-MBOT, the volume resistivity of the insulating epoxy resins prepared in other examples at 80°C is higher than that of EP-DDM, indicating that epoxy resin curing agents containing strong electron-withdrawing groups and large steric hindrance groups, and using non-coplanar saturated alicyclic structures instead of benzene rings, can enable the insulating epoxy resin to maintain a high volume resistivity at high temperatures.

[0080] For current polymer electrolyte materials, their electrical properties and thermal stability are often mutually exclusive, and the increase in temperature often causes the degradation of insulation performance. In order to develop epoxy resins with both high thermal stability and high electrical properties, the present application proposes a modified epoxy resin curing agent and a method for preparing an insulating epoxy resin, as well as an insulating epoxy resin prepared by the method for preparing an insulating epoxy resin. The thermal stability of the epoxy resin is enhanced by introducing a benzene ring. By grafting a high electron-withdrawing group or a large steric hindrance group at the ortho position of the amino functional group on the benzene ring, the π electron concentration on the benzene ring is reduced or the charge transfer between different molecules caused by the conjugation effect of the benzene ring is blocked, thereby improving the electrical properties of the epoxy resin. In addition, the present application also proposes to use a non-planar rigid alicyclic structure with saturated electrons to replace the benzene ring, and use its weak conjugation effect to reduce the concentration of non-localized electrons, thereby improving the electrical properties of the epoxy resin. The epoxy resin curing agent obtained by the above method is used to prepare a high-resistance insulating epoxy resin material. The volume resistivity of the obtained insulating epoxy resin material at room temperature and high temperature is significantly improved, which is of great significance for solving the problem of insulation failure in high temperature gradient and high field strength environment.

[0081] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An epoxy resin curing agent, characterized in that include: at least two benzene ring structures or at least two non-coplanar rigid alicyclic structures; Two adjacent benzene ring structures or non-coplanar rigid alicyclic structures are connected by methylene groups to form an overall structure; An amino functional group is arranged on both sides of the overall structure, and an electron-withdrawing substituent group or a plurality of steric hindrance substituent groups are arranged at the adjacent position of the amino functional group.

2. An epoxy resin curing agent according to claim 1, characterized in that: The electron-withdrawing substituent group is -Cl; The sterically hindered substituent group is -CH3 or -C2H5.

3. An epoxy resin curing agent according to claim 1, characterized in that: The epoxy resin curing agent structure includes at least two non-coplanar rigid alicyclic structures; The non-coplanar rigid alicyclic structure is C6H 12 .

4. The epoxy resin curing agent according to claim 1, characterized in that: The number of the sterically hindered substituent groups is 1-2.

5. A method for preparing an insulating epoxy resin, characterized in that: include: Dispersing the epoxy resin curing agent according to any one of claims 1 to 4 in a bisphenol A epoxy resin to obtain a first mixture; adding an aluminum oxide filler to the liquid phase mixture to obtain a second mixture; Heating the second mixture to degas the second mixture under vacuum, and then pouring the second mixture into a mold to degas the second mixture under vacuum; After curing and cooling, the insulating epoxy resin finished product is obtained.

6. The method for preparing insulating epoxy resin according to claim 5, characterized in that: The weight ratio of epoxy resin curing agent, bisphenol A epoxy resin and alumina filler is (10-35):(15-45):(35-65).

7. The method for preparing insulating epoxy resin according to claim 5, characterized in that: The curing conditions are: Raise the temperature to 120~140 ℃ and continue for 60~120 min; then raise the temperature to 160~180 ℃ and continue for 100~150 min; finally raise the temperature to 180~220 ℃ and continue for 60~120 min.

8. The method for preparing insulating epoxy resin according to claim 5, characterized in that: The method for dispersing the epoxy resin curing agent in the bisphenol A epoxy resin comprises: The epoxy resin curing agent is melted at 100-120°C, and then the epoxy resin curing agent is stirred and dispersed in the bisphenol A epoxy resin at 100-120°C.

9. The method for preparing insulating epoxy resin according to claim 5, characterized in that: The second mixture is heated to make the temperature condition of vacuum degassing of the second mixture be 100-140°C.

10. An insulating epoxy resin, characterized in that: The insulating epoxy resin is prepared by the method for preparing the insulating epoxy resin according to any one of claims 5 to 9.

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