Lightweight epoxy resin-based wave-absorbing material and preparation method thereof

Abstract

The invention discloses a light epoxy resin-based wave-absorbing material and a preparation method thereof, and the light epoxy resin-based wave-absorbing material comprises the following components in parts by weight: 100 parts of epoxy resin molding compound, 1-6 parts of conductive filler, 20-40 parts of water-soluble polymer and 1-3 parts of foaming agent. The composition is uniformly dispersed in a ball mill, and the closed-cell foaming material with adjustable density is obtained by chemical foaming. And a Fe3O4 / PEDOT wave-absorbing agent is loaded in the holes in situ, so that a multi-layer structure design of'weak current-magnetism-strong current 'is realized in the integrally uniform foaming material. The epoxy resin-based electromagnetic shielding material has the advantages of low density, high electromagnetic shielding, high wave absorbing efficiency, excellent mechanical properties and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer processing technology, specifically to a lightweight epoxy resin-based microwave absorbing material and its preparation method. Background Technology

[0002] With the rapid development of electronic integration and wireless communication technologies, electromagnetic radiation and interference have become increasingly prominent, seriously affecting the normal operation of electronic equipment and endangering human health. Electromagnetic shielding materials can effectively protect electronic equipment and their environment, preventing electromagnetic information leakage, cutting off electromagnetic wave propagation paths, and suppressing electromagnetic wave radiation and interference. They are one of the effective technical means to solve electromagnetic pollution problems and radar tracking signals. Epoxy resin foam materials have advantages such as good thermal stability, mechanical properties, thermal insulation performance, and lightweight, and are widely used in automobiles, electronic potting, and aircraft components. Adding microwave absorbing agents to epoxy resin and then preparing epoxy resin-based composite foam materials through foaming technology can effectively improve the electromagnetic shielding performance of composite foam materials due to the synergistic effect between the foam cells and the microwave absorbing filler. Ferrites, carbonyl iron, and magnetic metal micropowders, which are mainly responsible for magnetic loss, are the most commonly used microwave absorbing agents. However, their high specific gravity and high filler content increase the density of the corresponding electromagnetic shielding materials, increase processing costs, and deteriorate mechanical properties, greatly limiting their practical applications. Electrically dissipative microwave absorbing agents such as carbon nanotubes, graphene, and two-dimensional transition metal carbides / nitrides (MXene) are also widely used in electromagnetic shielding materials. They can impart good electromagnetic shielding performance to composite materials with relatively low filler content. However, their high conductivity can easily cause impedance mismatch, resulting in the reflection of most electromagnetic waves and secondary pollution. Therefore, when adding microwave absorbing fillers to impart high electromagnetic shielding efficiency to composite foam materials, a high content of microwave absorbing filler is often required. This increases processing difficulty, reduces the mechanical properties of the foam material, and also deteriorates the cell morphology, reduces the foaming ratio, and makes it difficult to simultaneously achieve the requirements of low density, high electromagnetic shielding, high microwave absorption efficiency, and good mechanical properties. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings and provide an epoxy resin-based composite foam material with low density, high electromagnetic shielding, high wave absorption efficiency and excellent mechanical properties, as well as its preparation method.

[0004] To achieve the objective of this invention, the following technical solution is adopted: The present invention discloses a lightweight epoxy resin-based microwave absorbing material, characterized in that, by weight, it comprises 100 parts of epoxy resin molding compound, 1-6 parts of conductive filler, 20-40 parts of water-soluble polymer, and 1-3 parts of foaming agent.

[0005] The above-mentioned epoxy resin molding compound uses bisphenol A type epoxy resin as the base resin and acid anhydride as the curing agent to be mixed into powder. The weight ratio of epoxy resin to curing agent is 100:85.

[0006] The aforementioned conductive particles are one or two of the following: carbon nanofibers, carbon nanotubes, graphene, or carbon nanofibers.

[0007] The aforementioned chemical foaming agent is one or both of N,N'-dinitrospentamethylenetetramine and sodium bicarbonate.

[0008] The aforementioned water-soluble polymer is one of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone.

[0009] A method for preparing a lightweight epoxy resin-based microwave absorbing material, comprising the following steps: (1) foaming and curing molding step: epoxy resin molding compound, conductive filler, water-soluble polymer, and foaming agent are mixed evenly in a ball mill, pressed into tablets, and placed in an oven for foaming at 90°C for 0.5-3 hours, and then cured at 150°C and 200°C for 2 hours respectively to obtain epoxy resin composite foaming material; (2) in-situ loading of poly(3,4-ethylenedioxythiophene / ferric oxide (PEDOT / Fe3O4) microwave absorbing agent in pores: the above steps (1) The composite foaming material is immersed in an aqueous solution of 0.1-1 mol / L trivalent iron compound and soaked at 90°C for 2 h. After taking it out, the sample is placed in a closed container containing 3,4-ethylenedioxythiophene monomer (EDOT) and fumigated with EDOT vapor at 80°C for 0.5-8 h. Then, ammonia water is added to the closed container and the sample is fumigated with ammonia gas at 70°C for 1 h. Finally, the sample is taken out and soaked and washed in a 2 mol / L hydrochloric acid aqueous solution for 4 h. After drying, a lightweight epoxy resin-based microwave absorbing material is obtained.

[0010] The above-mentioned method for preparing a lightweight epoxy resin-based microwave absorbing material, wherein: the density of the epoxy resin composite foaming material in step (1) is 0.08-0.4 g / cm³. 3 The average cell size is 40-100μm, and the cell morphology is closed-cell.

[0011] The above-mentioned method for preparing a lightweight epoxy resin-based microwave absorbing material, wherein: the trivalent iron compound in step (2) is one of FeCl3, iron p-benzenesulfonate, Fe(NO3)3, and Fe2(SO4)3.

[0012] The above-mentioned method for preparing a lightweight epoxy resin-based microwave absorbing material, wherein: in step (2), the trivalent iron salt is preferably FeCl3.

[0013] Compared with existing technologies, this invention has significant advantages: the epoxy resin foam material prepared by this invention is a micron-sized closed-cell material. The hydrophilic polymer in the pore walls acts as a diffusion channel for water and ions. When heated in an iron salt aqueous solution, the volume expansion of the foam material helps open the hydrophilic channels, allowing water and ions to diffuse rapidly into the closed pores. After drying, the pore structure remains essentially unchanged, while the reinforcing effect of the microwave absorber inside the pores improves the mechanical properties of the foam material. The conductive polymer PEDOT and magnetic Fe3O4 particles are simultaneously generated in situ within the closed pores, based on the principle that Fe... 3+ While initiating EDOT polymerization, it is reduced to Fe. 2+ Fe in an alkaline environment 2+ and Fe 3+ The reaction generates Fe3O4, which allows for simple and convenient control of the loading, morphology, and distribution of the two microwave absorbing agents within the pores. Adding a small amount of conductive filler to the foam material creates weakly conductive chains within the pore walls, facilitating the entry of electromagnetic waves into the foam material and reducing electromagnetic wave reflection. The magnetic Fe3O4 and PEDOT loaded inside the pores form a reflection and absorption layer, enhancing the multiple reflections and absorption of electromagnetic waves within the pores. Ultimately, a multi-layered structural design of "weak electrical-magnetic-strong electrical" is achieved within a single, homogeneous foam material, resulting in an epoxy resin-based electromagnetic shielding material with low density, excellent electromagnetic shielding, high absorption efficiency, and superior mechanical properties. Attached Figure Description

[0014] Figure 1 The images shown are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) spectra of the foaming material before and after in-situ loading of the microwave absorbing agent when the FeCl3 concentration is 0.3 mol / L in Example 1. Figure 2 The graph shows the change in electromagnetic shielding efficiency with FeCl3 concentration in Example 1. Figure 3 This is a graph showing the change in electromagnetic shielding efficiency with EDOT fumigation time in Example 2; Figure 4 Here is a scanning electron microscope image of the initial foaming material in Example 3; Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Example 1

[0016] Take 100 parts of epoxy resin molding compound, 1 part of carbon nanotubes, 5 parts of nano carbon black, 30 parts of polyvinylpyrrolidone, and 1 part of foaming agent N,N'-dinitrospentamethylenetetramine. After ball milling and dispersing evenly, compress the mixture into sheets. Place the sheets in an oven and foam at 90℃ for 0.5h. Then, raise the temperature to 150℃ and 200℃ respectively and keep them at these temperatures for 2h each. Allow them to cool naturally to obtain the epoxy resin-based foam material.

[0017] The composite foam material was immersed in FeCl3 aqueous solutions of different concentrations and soaked at 90℃ for 2 hours. After removal, the sample was placed in a sealed container and first fumigated with EDOT steam at 80℃ for 2 hours, followed by fumigation with ammonia at 70℃ for 1 hour. Finally, the sample was removed and immersed in 2mol / L hydrochloric acid aqueous solution for 4 hours and dried to obtain a lightweight epoxy resin-based microwave absorbing material.

[0018] Experimental results: From Figure 1 It can be seen that after loading the microwave absorbing agent, the pore morphology of the material remained basically unchanged, with a layer of PEDOT / Fe3O4 microwave absorbing agent loaded inside the pores. Tests showed that the average pore diameter of the initial sample was 60 μm, and the material density was 0.26 g / cm³. 3 The compressive strength was 4.02 MPa; the average cell diameter of the final sample was 57 μm, and the material density increased slightly to 0.27 g / cm³. 3 The compressive strength increased to 4.67 MPa.

[0019] from Figure 2 It can be seen that as the concentration of FeCl3 aqueous solution increases, the electromagnetic shielding efficiency of the foamed material increases, mainly due to the absorption and loss mechanism of electromagnetic waves. Example 2

[0020] Take 100 parts of epoxy resin molding compound, 6 parts of nano carbon black, 30 parts of polyvinylpyrrolidone, and 1 part of foaming agent N,N'-dinitrospentamethylenetetramine. After ball milling and dispersing evenly, compress the mixture into sheets. Place the sheets in an oven and foam at 90°C for 1 hour. Then, raise the temperature to 150°C and 200°C respectively and keep them at these temperatures for 2 hours to cure. Allow the mixture to cool naturally to obtain the epoxy resin-based foam material.

[0021] The composite foam material was immersed in a 0.5 mol / L FeCl3 aqueous solution at 90°C for 2 hours. After removal, the sample was placed in a sealed container and first fumigated with EDOT steam at 80°C for different times, followed by fumigation with ammonia at 70°C for 1 hour. Finally, the sample was removed and immersed in a 2 mol / L hydrochloric acid aqueous solution for 4 hours and dried to obtain a lightweight epoxy resin-based microwave absorbing material.

[0022] Experimental results: From Figure 3 It can be seen that the electromagnetic shielding efficiency increases with the extension of EDOT fumigation time. Example 3

[0023] Take 100 parts of epoxy resin molding compound, 1 part of graphene, 20 parts of polyvinyl alcohol, 1.5 parts of foaming agent N,N'-dinitrospentamethylenetetramine, and 1.5 parts of sodium bicarbonate. After ball milling and dispersing evenly, compress the mixture into sheets. Place the sheets in an oven and foam at 90℃ for 0.5h. Then, raise the temperature to 150℃ and 200℃ respectively and keep them at these temperatures for 2h each. Allow them to cool naturally to obtain the epoxy resin-based foam material.

[0024] The composite foamed material was immersed in aqueous solutions of FeCl3, iron benzenesulfonate, Fe(NO3)3, and Fe2(SO4)3 at a concentration of 1 mol / L for 2 hours at 90°C. After removal, the sample was placed in a sealed container and fumigated with EDOT steam at 80°C for 3 hours, followed by fumigation with ammonia at 70°C for 1 hour. Finally, the sample was removed and immersed in a 2 mol / L hydrochloric acid aqueous solution for 4 hours. After drying, a lightweight epoxy resin-based microwave absorbing material was obtained.

[0025] Experimental results: such as Figure 4 As shown, the average cell diameter of the initial foamed sample was 70 μm, and the material density was 0.08 g / cm³. 3 Tests showed that the electromagnetic shielding efficiency of the final sample, from highest to lowest, was as follows among the four trivalent iron compounds: FeCl3 > iron benzenesulfonate > Fe(NO3)3 ≈ Fe2(SO4)3. Example 4

[0026] Take 100 parts of epoxy resin molding compound, 6 parts of carbon nanofiber, 20 parts of polyethylene glycol, and 1 part of sodium bicarbonate foaming agent. After ball milling and dispersing evenly, press the mixture into sheets. Place the sheets in an oven and foam at 90℃ for 3 hours. Then, raise the temperature to 150℃ and 200℃ respectively and keep them at these temperatures for 2 hours to cure. Allow them to cool naturally to obtain the epoxy resin-based foam material.

[0027] The composite foam material was immersed in a 0.3 mol / L FeCl3 aqueous solution at 90°C for 2 hours. After removal, the sample was placed in a sealed container and first fumigated with EDOT steam at 80°C for 2 hours, followed by fumigation with ammonia at 70°C for 1 hour. Finally, the sample was removed and immersed in a 2 mol / L hydrochloric acid aqueous solution for 4 hours. After drying, a lightweight epoxy resin-based microwave absorbing material was obtained.

[0028] Tests showed that the initial sample had an average cell diameter of 40 μm and a material density of 0.4 g / cm³. 3 The compressive strength was 16 MPa; the average cell diameter of the final sample was 38 μm, and the material density was 0.42 g / cm³. 3 The compressive strength increased to 18.1 MPa. Example 5

[0029] Take 100 parts of epoxy resin molding compound, 1 part of nano carbon black, 1 part of graphene, 40 parts of polyvinylpyrrolidone, 0.5 parts of foaming agent N,N'-dinitrospentamethylenetetramine, and 1 part of sodium bicarbonate. After ball milling and dispersing evenly, compress the mixture into sheets. Place the sheets in an oven and foam at 90℃ for 3 hours. Then, raise the temperature to 150℃ and 180℃ respectively and keep them at these temperatures for 2 hours to cure. Allow them to cool naturally to obtain the epoxy resin-based foam material.

[0030] The composite foam material was immersed in a 0.5 mol / L FeCl3 aqueous solution at 90°C for 2 hours. After removal, the sample was placed in a sealed container and first fumigated with EDOT steam at 80°C for 5 hours, followed by fumigation with ammonia at 70°C for 1 hour. Finally, the sample was removed and immersed in a 2 mol / L hydrochloric acid aqueous solution for 4 hours. After drying, a lightweight epoxy resin-based microwave absorbing material was obtained.

[0031] In this invention, foaming time, foaming agent content and ratio are the main factors affecting the initial foamed sample pore diameter and material density. The type and content of conductive filler and hydrophilic polymer also affect the material density and pore diameter.

[0032] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, and all such modifications should be included within the scope of protection of this disclosure.

Claims

1. A lightweight epoxy resin-based microwave absorbing material, characterized in that: By weight, it contains 100 parts epoxy resin molding compound, 1-6 parts conductive filler, 20-40 parts water-soluble polymer, and 1-3 parts foaming agent.

2. The lightweight epoxy resin-based microwave absorbing material according to claim 1, characterized in that: The epoxy resin molding compound is made by mixing bisphenol A type epoxy resin as the base resin and acid anhydride as the curing agent into powder, with the weight ratio of epoxy resin to curing agent being 100:

85.

3. The lightweight epoxy resin-based microwave absorbing material according to claim 1, characterized in that: The conductive particles are one or two of the following: carbon black nanoparticles, carbon nanotubes, graphene, or carbon nanofibers.

4. The lightweight epoxy resin-based microwave absorbing material according to claim 1, characterized in that: The chemical foaming agent is one or both of N,N'-dinitrospentamethylenetetramine and sodium bicarbonate.

5. The lightweight epoxy resin-based microwave absorbing material according to claim 1, characterized in that: The water-soluble polymer is one of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone.

6. A method for preparing a lightweight epoxy resin-based microwave absorbing material according to any one of claims 1 to 5, characterized in that... The process includes the following steps: (1) Foaming and curing molding steps: Epoxy resin molding compound, conductive filler, water-soluble polymer, and foaming agent are mixed evenly in a ball mill, pressed into tablets, and placed in an oven to foam at 90°C for 0.5-3 hours. Then, the tablets are cured at 150°C and 200°C for 2 hours respectively to obtain epoxy resin composite foam material; (2) In-situ loading of poly(3,4-ethylenedioxythiophene) / ferric oxide (PEDOT / Fe3O4) microwave absorber in the pores: The composite foam material in step (1) above is loaded into the pores of the foam material. The sample was immersed in an aqueous solution of 0.1-1 mol / L trivalent iron compound at 90°C for 2 hours. After removal, the sample was placed in a sealed container containing 3,4-ethylenedioxythiophene monomer (EDOT) and fumigated with EDOT vapor at 80°C for 0.5-8 hours. Then, ammonia water was added to the sealed container, and the sample was fumigated with ammonia gas at 70°C for 1 hour. Finally, the sample was removed and immersed in a 2 mol / L hydrochloric acid aqueous solution for 4 hours and dried to obtain a lightweight epoxy resin-based microwave absorbing material.

7. The method for preparing a lightweight epoxy resin-based microwave absorbing material according to claim 6, characterized in that: The density of the epoxy resin composite foam material in step (1) is 0.08-0.4 g / cm³. 3 The average cell size is 40-100μm, and the cell morphology is closed-cell.

8. The method for preparing a lightweight epoxy resin-based microwave absorbing material according to claim 6, characterized in that: In step (2), the ferric salt is one of FeCl3, ferric p-benzenesulfonate, Fe(NO3)3, and Fe2(SO4)3.

9. The method for preparing a lightweight epoxy resin-based microwave absorbing material according to claim 6, characterized in that: In step (2), the preferred ferric salt is FeCl3.

Images