Lightweight wave-absorbing composite material based on epoxy foaming system and preparation method thereof

Abstract

The application discloses a kind of light wave-absorbing composite material based on epoxy foaming system and preparation method, raw material includes by weight portion: epoxy resin 40~70 portions, foaming agent 1~15 portions, curing agent 10~30 portions, wave-absorbing agent 5~40 portions;The light wave-absorbing composite material has along open porous foam structure and hollow tubular microstructure inside.This application has the beneficial effect: this application has prepared the epoxy foam matrix with open porous or hollow tubular structure under normal temperature and pressure or mild conditions by breathing pattern method or solid carbon dioxide foaming method, process is simple, good compatibility, avoid the shortcomings of traditional supercritical foaming equipment complex, harsh conditions.This application constructs porous microstructure, realizes material light weight at the same time, significantly improves the impedance matching characteristics of material, reduces the surface reflection of electromagnetic wave, and enhances absorption loss by increasing electromagnetic wave internal propagation path.

Description

Technical Field

[0001] This invention relates to the technical field of functional composite materials, specifically to a lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method. Background Technology

[0002] With the rapid development of electronic communication, wireless communication, and radar technology, electromagnetic interference and radar detection problems are becoming increasingly prominent. Absorbing materials can effectively absorb and attenuate incident electromagnetic waves, and have significant application value in military stealth technology and civilian electromagnetic protection. An ideal absorbing material needs to meet the comprehensive requirements of being thin, wide-bandwidth, lightweight, and strong—that is, thin, with a wide absorption bandwidth, light weight, and strong absorption capacity.

[0003] Epoxy resins are ideal matrices for preparing microwave absorbing composites due to their low density, good processability, stable physicochemical properties, and excellent adhesion. However, traditional epoxy-based microwave absorbing materials suffer from problems such as high density, thick coatings, poor mechanical properties, and poor compatibility between the matrix and the absorbing agent. In existing technologies, supercritical carbon dioxide or nitrogen foaming processes are often used to reduce material density, but these processes generally suffer from drawbacks such as complex equipment, harsh process conditions, and poor compatibility with different absorbing agents, limiting their industrial application.

[0004] Therefore, developing an epoxy-based composite material that is simple to process, has good compatibility, is lightweight, and has excellent microwave absorption properties is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] Purpose of the invention: To provide a lightweight microwave absorbing composite material based on an epoxy foam system to solve the above-mentioned problems existing in the prior art.

[0006] Technical solution: A lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method, wherein the raw materials include, by weight: 40-70 parts epoxy resin, 1-15 parts foaming agent, 10-30 parts curing agent, and 5-40 parts microwave absorbing agent; the lightweight microwave absorbing composite material has an open porous foam structure and a hollow tubular microstructure inside.

[0007] Preferably, the foaming agent is composed of one or two of chemical foaming agents and physical foaming agents; the physical foaming agent is one or a mixture of two or more of solid carbon dioxide, supercritical carbon dioxide and nitrogen; the chemical foaming agent includes azodicarbonamide and polymethylhydrosiloxane.

[0008] Preferably, the microwave absorbing agent is composed of one or both of dielectric loss type microwave absorbing agents and magnetic loss type microwave absorbing agents; the dielectric loss type microwave absorbing agent is a carbon-based material, which is selected from one or more of carbon fiber, graphene, carbon nanotubes, and conductive carbon black; the magnetic loss type microwave absorbing agent includes one or more of ferrite, carbonyl iron powder, and nickel-zinc ferrite.

[0009] Preferably, the epoxy resin is a bisphenol A type epoxy resin; and the curing agent is an amine curing agent.

[0010] Preferably, the lightweight microwave absorbing composite material has a density of 0.05~0.6 g / cm³, a porosity of 50%~95%, and an electromagnetic wave reflection loss value of ≤-10 dB in the frequency range of 2~18 GHz.

[0011] A method for preparing a lightweight microwave absorbing composite material based on an epoxy foaming system as described in any one of claims 1 to 5, characterized in that it comprises the following steps: S1. Epoxy resin, foaming agent, microwave absorber and part of the curing agent are mixed in the pre-curing stage and dispersed by mechanical stirring or ultrasonication to make the components uniformly dispersed to obtain a mixture. S2. The mixture is pre-cured in a nitrogen or vacuum environment at 50~80℃ to form a gel-state preform with a preliminary cross-linked network. S3. Using the breathing pattern method or solid carbon dioxide foaming method, a precisely controlled microporous or hollow tubular structure is formed in the gel-state preform. S4. The product obtained in S3 is subjected to secondary curing at 60~120℃ to completely crosslink the epoxy resin, thereby obtaining the lightweight microwave absorbing composite material.

[0012] Preferably, the breathing pattern method specifically includes: The gel-state preform described in S2 is placed in a humid airflow environment with a humidity of 60% to 90%. By controlling the ambient temperature and gas flow rate, water vapor is condensed on the surface of the preform to form an orderly arranged water droplet template. After drying, the water droplets are removed to obtain a foam matrix with a regular porous structure.

[0013] Preferably, the solid carbon dioxide foaming method specifically includes: The gel-state preform is placed in a high-pressure carbon dioxide environment and subjected to saturation absorption at 25~50℃ and 4~8 MPa. Then, the pressure is rapidly released, allowing the dissolved carbon dioxide to nucleate and grow in the epoxy resin, forming a uniform microporous foam structure.

[0014] Preferably, the gel-state preform obtained in S2 is preheated before proceeding to S3, and the preheating temperature is 40~60℃ for 10~30 minutes.

[0015] The lightweight microwave absorbing composite material is used in the preparation of stealth coatings for aerospace vehicles, electromagnetic shielding materials for electronic equipment, or microwave absorbing protective layers for building curtain walls.

[0016] The beneficial effects of the present invention are as follows: The present invention prepares an epoxy foam matrix with an open porous or hollow tubular structure under normal temperature and pressure or mild conditions by means of a breathing pattern method or a solid carbon dioxide foaming method. The process is simple and has good compatibility, avoiding the disadvantages of traditional supercritical foaming equipment being complex and having harsh conditions.

[0017] This invention achieves material lightweighting by constructing a porous microstructure, significantly improves the impedance matching characteristics of the material, reduces surface reflection of electromagnetic waves, and enhances absorption loss by increasing the internal propagation path of electromagnetic waves.

[0018] This invention achieves a synergistic enhancement effect of wide bandwidth and high absorption by compounding a carbon-based dielectric loss absorbing agent with a magnetic absorbing agent, thus meeting the comprehensive requirements of thinness, width, lightness, and strength.

[0019] The composite material obtained by this invention has excellent wave absorption performance, low density and good mechanical properties, and has broad application prospects in both military and civilian fields. Attached Figure Description

[0020] Figure 1 Scanning electron microscope (SEM) image of the lightweight microwave absorbing composite material prepared according to the present invention; Figure 2 The reflection loss curves of the lightweight microwave absorbing composite material prepared for this invention in the frequency range of 2~18 GHz. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The performance tests of this invention include: Density determination: The density of the composite material was determined by the water displacement method according to ASTM D792 standard.

[0023] Microscopic morphology analysis: The cross-sectional morphology and pore structure of the composite material were observed using a scanning electron microscope.

[0024] Wave absorption performance measurement: The complex permittivity and complex permeability of the composite material in the frequency range of 2~18GHz were tested using a vector network analyzer by coaxial method or waveguide method, and the reflection loss was calculated according to transmission line theory.

[0025] Compressive strength determination: The compressive strength of the composite material was tested in accordance with GB / T 8813-2020 standard. Example

[0026] As attached Figure 1-2 As shown in this embodiment, a lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method are disclosed. The raw materials include, by weight, 60 parts of epoxy resin; 5 parts of polymethylhydrosiloxane; 20 parts of polyetheramine D-230; 10 parts of multi-walled carbon nanotubes; and 5 parts of nickel-zinc ferrite.

[0027] The preparation method is as follows: S1. One-time blending: Epoxy resin, polymethylhydrosiloxane, multi-walled carbon nanotubes and nickel-zinc ferrite are mechanically stirred at 40°C for 30 minutes, then polyetheramine D-230 is added, and stirring is continued for 10 minutes. Ultrasonic dispersion is then carried out for 15 minutes to obtain a uniform mixture.

[0028] S2. Pre-curing: After degassing the mixture under vacuum, pour it into a mold and pre-cur it at 60°C for 2 hours to obtain a gel-state preform.

[0029] S3. Microstructure forming: Using the breathing pattern method, the gel-state preform is placed in a constant temperature and humidity chamber with a humidity of 80% and treated with a humid airflow for 1 hour to allow water vapor to condense and form an ordered water droplet template. Then, it is dried in a vacuum drying oven at 50℃ to remove the water droplets and obtain a porous structure preform.

[0030] S4. Secondary curing: The porous preform is cured at 100°C for 3 hours to fully crosslink the epoxy resin and obtain a lightweight microwave absorbing composite material.

[0031] The lightweight microwave absorbing composite material prepared in this embodiment was subjected to various tests, and its density was 0.28 g / cm³. 3 It has a porosity of 78%, an optimal reflection loss of -32.5 dB, an effective absorption bandwidth of less than -10 dB up to 4.2 GHz, and a compressive strength of 8.5 MPa. Example

[0032] This embodiment is basically the same as embodiment 1, except that the solid carbon dioxide foaming method is used in step S3: the pre-cured gel-state preform is placed in a high-pressure autoclave, carbon dioxide is introduced to a pressure of 5 MPa and a temperature of 30°C, and saturated absorption is carried out for 4 hours. Then the pressure is quickly released to allow carbon dioxide to nucleate and foam, and a microporous foam preform is obtained.

[0033] The lightweight microwave absorbing composite material prepared in this embodiment was subjected to various tests. It had a density of 0.21 g / cm3, a porosity of 84%, an optimal reflection loss of -28.6 dB, an effective absorption bandwidth of less than -10 dB up to 3.8 GHz, and a compressive strength of 6.2 MPa.

[0034] Comparative Example 1: This comparative example is basically the same as Example 1, except that no foaming agent is added and the microstructure shaping in step S3 is not performed. Instead, a second curing is performed directly to obtain a non-porous epoxy / wave-absorbing composite material.

[0035] The lightweight microwave absorbing composite material prepared in this embodiment was subjected to various tests. It had a density of 1.15 g / cm3, a porosity of 5%, an optimal reflection loss of -15.2 dB, an effective absorption bandwidth of less than -10 dB up to 1.5 GHz, and a compressive strength of 45.0 MPa.

[0036] The test data of the lightweight microwave absorbing composite materials obtained in Examples 1 and 2 and Comparative Example 1 are summarized in Table 1 below: Table 1 Comparison of Performance Test Results

[0037] As shown in Table 1, the lightweight microwave absorbing composite materials prepared in Examples 1 and 2 of this invention significantly reduce density to 0.2-0.3 g / cm³ by introducing a porous structure, achieving remarkable weight reduction. Simultaneously, the porous structure improves impedance matching, making it easier for electromagnetic waves to penetrate and be absorbed within the material. The optimal reflection loss and effective absorption bandwidth are significantly better than those of the non-porous comparative example 1. Specifically, Example 1, using the breathing pattern method, obtained a more regular pore structure and superior microwave absorption performance; Example 2, using the solid carbon dioxide foaming method, achieved higher porosity and lower density. Although the introduction of the porous structure leads to a slight decrease in compressive strength compared to solid materials, the resulting foam materials still possess good mechanical integrity, meeting the requirements for lightweight microwave absorbing coatings.

[0038] The preferred embodiments have been shown and described, but should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method, characterized in that: The raw materials include, by weight: 40-70 parts epoxy resin, 1-15 parts foaming agent, 10-30 parts curing agent, and 5-40 parts microwave absorbing agent; the lightweight microwave absorbing composite material has an open porous foam structure and a hollow tubular microstructure inside.

2. The lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method according to claim 1, characterized in that: The foaming agent is one or two of chemical foaming agents and physical foaming agents; the physical foaming agent is one or a mixture of two or more of solid carbon dioxide, supercritical carbon dioxide and nitrogen; the chemical foaming agent includes azodicarbonamide and polymethylhydrosiloxane.

3. The lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method according to claim 2, characterized in that: The microwave absorbing agent is composed of one or both of dielectric loss type microwave absorbing agents and magnetic loss type microwave absorbing agents; the dielectric loss type microwave absorbing agent is a carbon-based material, which is selected from one or more of carbon fiber, graphene, carbon nanotubes, and conductive carbon black; the magnetic loss type microwave absorbing agent includes one or more of ferrite, carbonyl iron powder, and nickel-zinc ferrite.

4. The lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method according to claim 3, characterized in that: The epoxy resin is a bisphenol A type epoxy resin; the curing agent is an amine curing agent.

5. The lightweight microwave absorbing composite material based on an epoxy foaming system and its preparation method according to claim 4, characterized in that: The lightweight microwave absorbing composite material has a density of 0.05~0.6 g / cm³, a porosity of 50%~95%, and an electromagnetic wave reflection loss value of ≤-10 dB in the frequency range of 2~18 GHz.

6. A method for preparing a lightweight microwave absorbing composite material based on an epoxy foaming system as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Epoxy resin, foaming agent, microwave absorber and part of the curing agent are mixed in the pre-curing stage and dispersed by mechanical stirring or ultrasonication to make the components uniformly dispersed to obtain a mixture. S2. The mixture is pre-cured in a nitrogen or vacuum environment at 50~80℃ to form a gel-state preform with a preliminary cross-linked network. S3. Using the breathing pattern method or solid carbon dioxide foaming method, a precisely controlled microporous or hollow tubular structure is formed in the gel-state preform. S4. The product obtained in S3 is subjected to secondary curing at 60~120℃ to completely crosslink the epoxy resin, thereby obtaining the lightweight microwave absorbing composite material.

7. The method for preparing the lightweight microwave absorbing composite material based on the epoxy foaming system according to claim 6, characterized in that: The breathing pattern method specifically includes: The gel-state preform described in S2 is placed in a humid airflow environment with a humidity of 60% to 90%. By controlling the ambient temperature and gas flow rate, water vapor is condensed on the surface of the preform to form an orderly arranged water droplet template. After drying, the water droplets are removed to obtain a foam matrix with a regular porous structure.

8. The method for preparing the lightweight microwave absorbing composite material based on the epoxy foaming system according to claim 7, characterized in that: The solid carbon dioxide foaming method specifically includes: The gel-state preform is placed in a high-pressure carbon dioxide environment and subjected to saturation absorption at 25~50℃ and 4~8 MPa. Then, the pressure is rapidly released, allowing the dissolved carbon dioxide to nucleate and grow in the epoxy resin, forming a uniform microporous foam structure.

9. The method for preparing the lightweight microwave absorbing composite material based on the epoxy foaming system according to claim 8, characterized in that: Before proceeding to S3, the gel-state preform obtained in S2 undergoes a preheating treatment at a temperature of 40-60°C for 10-30 minutes.

10. The lightweight microwave absorbing composite material as described in any one of claims 1-5 is used in the preparation of stealth coatings for aerospace vehicles, electromagnetic shielding materials for electronic equipment, or microwave absorbing protective layers for building curtain walls.

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