Wave-absorbing honeycomb sheet and preparation and application thereof

Abstract

The application discloses a wave-absorbing honeycomb sheet, which comprises a wave-absorbing honeycomb and a functional adhesive film, wherein the honeycomb wall of the wave-absorbing honeycomb penetrates the functional adhesive film, and the ratio of the distance between the lower surface of the functional adhesive film and the lower edge of the honeycomb wall of the wave-absorbing honeycomb to the thickness of the wave-absorbing honeycomb is 1-3:25. The application further discloses a method for preparing the wave-absorbing honeycomb sheet. The honeycomb composite material comprising the wave-absorbing honeycomb sheet provided by the application can maximize the wave-absorbing performance of the whole honeycomb composite material while not affecting the connection reliability between the wave-absorbing honeycomb and the bottom panel in the case that the functional adhesive film is inserted between the wave-absorbing honeycomb and the bottom panel.

Description

Technical Field

[0001] This invention relates to a microwave absorbing honeycomb sheet, its preparation, and its application. Background Technology

[0002] In modern manufacturing, the application of honeycomb composite materials is becoming increasingly widespread, leading to greater functional demands for microwave absorbing honeycomb composites. Often, functional adhesive layers need to be inserted between the honeycomb and the panel or skin material. Besides replacing ordinary honeycomb with microwave absorbing honeycomb, a magnetic microwave absorbing adhesive layer is also needed between the honeycomb and the bottom panel to improve low-frequency performance. However, magnetic microwave absorbing adhesive films have very high absorbent content, resulting in poor interlayer strength and toughness. This layup method can damage the interfacial strength of the honeycomb sandwich composite material, reducing the structural stability of the product.

[0003] In the fabrication of honeycomb composite materials, it is often necessary to insert other functional materials or films between the bottom panel and the honeycomb. For example, due to process limitations and bandwidth requirements, carbon-based materials are often used as absorbers in absorbing honeycomb materials, which tend to perform poorly at low frequencies, especially in the P-band. In existing technologies, to address low-frequency requirements, a low-frequency magnetic functional film 2 is often inserted at the bottom of the honeycomb material, between the bottom panel 3 and the honeycomb material 1, for use as a honeycomb composite material. Its structure is as follows: Figure 1 Low-frequency magnetic functional adhesive film 2 often has a large absorbent content, poor film toughness, and low interlayer tear strength. After molding using existing processes, the connection strength between the honeycomb and the bottom panel decreases, reducing structural reliability. Currently, a common process is to use the high pressure conditions during autoclaving to press the honeycomb wall 4 into the low-frequency magnetic functional adhesive film 2, increasing the interfacial bonding strength (the bonding method is as follows). Figure 2 However, it will still disrupt the original climbing structure of the structural adhesive film formed on the honeycomb wall through the siphon effect of the adhesive and the surface wetting effect of the adhesive. Figure 3 This can damage the bonding strength of the honeycomb, because the bonding surface between the honeycomb and other materials is not a complete and continuous plane, but a line-to-plane connection. Only this climbing microstructure within the wall can guarantee the bonding strength between the honeycomb and other planes. Summary of the Invention

[0004] In view of the above problems, this invention, taking absorbing honeycomb and magnetic adhesive film as examples, proposes a process route and an optimal adhesive film embedding ratio. This allows for the insertion of other functional adhesive films between the honeycomb and the bottom panel during the preparation of the honeycomb composite material, without affecting the connection reliability between the honeycomb and the bottom panel, while maximizing the overall absorbing performance of the honeycomb material. The process flow diagram of the proposed process scheme is shown below. Figure 4 .

[0005] Reference Figure 4 Under the functional adhesive film 6, foam 7 is laid, and pressure is applied in the pressure application direction 8 to fill the functional adhesive film 6 into the microwave absorbing honeycomb holes. After removing the foam 7, the honeycomb wall 4 of the microwave absorbing honeycomb in the obtained microwave absorbing honeycomb sheet can extend out of the functional adhesive film 6, so that when the microwave absorbing honeycomb sheet is connected to the bottom panel, the connection can continue to maintain the original bonding mode between the honeycomb wall and the panel prepreg, that is, forming an adhesive slope to ensure stable bonding.

[0006] As one aspect of the present invention, a microwave absorbing honeycomb sheet is provided, comprising a microwave absorbing honeycomb and a functional adhesive film, wherein the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film, and the ratio of the distance from the lower surface of the functional adhesive film to the lower edge of the honeycomb wall of the microwave absorbing honeycomb to the thickness of the microwave absorbing honeycomb is 1-3:25.

[0007] In a feasible specific implementation, the ratio of the thickness of the functional adhesive film to the thickness of the microwave absorbing honeycomb is 1-2:25.

[0008] In a feasible specific implementation, the ratio of the distance from the upper surface of the functional adhesive film to the upper edge of the cell wall of the absorbing honeycomb to the thickness of the absorbing honeycomb is 21-23:25.

[0009] In a feasible specific implementation, the functional adhesive film is a low-frequency magnetic adhesive film.

[0010] As another aspect of the present invention, a method for preparing a microwave absorbing honeycomb sheet is provided, the method comprising:

[0011] First, the press, the microwave-absorbing honeycomb, and the foam are fully preheated, and the functional adhesive film is preheated to a softened state. The foam, the functional adhesive film, and the microwave-absorbing honeycomb are then laid out sequentially in the press. Pressure is applied, and the lower edge of the honeycomb wall of the microwave-absorbing honeycomb penetrates the functional adhesive film and extends into the foam. The ratio of the distance from the lower surface of the functional adhesive film to the lower edge of the honeycomb wall to the thickness of the microwave-absorbing honeycomb is 1-3:25. The material is then cooled, and the foam is removed to obtain the microwave-absorbing honeycomb sheet.

[0012] In a feasible specific implementation, the functional adhesive film in the above method is a low-frequency magnetic adhesive film.

[0013] In a feasible specific implementation, the ratio of the thickness of the functional adhesive film to the thickness of the microwave absorbing honeycomb in the above method is 1-2:25.

[0014] In a feasible specific implementation, in the above method, the ratio of the distance between the upper surface of the functional adhesive film and the upper edge of the cell wall of the absorbing cell to the thickness of the absorbing cell is 21-23:25.

[0015] As another aspect of the invention, a honeycomb composite material is provided, wherein the aforementioned microwave absorbing honeycomb sheet is bonded to a bottom panel using an adhesive.

[0016] As another aspect of the present invention, the application of the above-mentioned honeycomb composite material in microwave absorbing devices is involved.

[0017] The absorbing honeycomb sheet and honeycomb composite material and their preparation method provided by this invention can maximize the structural strength and the absorbing performance of the material, ensuring that the structural connection strength and original broadband absorption performance of the absorbing honeycomb material can be taken into account at the same time, while giving full play to the low-frequency absorption performance brought by the magnetic film layer, and improving the stealth performance of the material structure to meet design requirements. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a schematic diagram of a honeycomb composite material structure in the prior art;

[0020] Figure 2 This is a schematic diagram of the bonding method of honeycomb composite materials in the prior art;

[0021] Figure 3 This is a schematic diagram of a structural adhesive film climbing structure formed by honeycomb composite materials in the absence of magnetic adhesive film in the prior art.

[0022] Figure 4 A schematic diagram of the process for preparing the microwave absorbing honeycomb sheet provided by the present invention;

[0023] Figure 5 The reflectance curves for Examples 1-3 are shown below;

[0024] Figure 6 The reflectance curves are for Example 1, Example 3, and Comparative Example 1;

[0025] Figure 7 The reflectance curves for Examples 3-5 are shown below.

[0026] Figure 8 The reflectance curves for Examples 6-9 are shown below;

[0027] Wherein: 1 is the honeycomb material; 2 is the low-frequency magnetic functional adhesive film; 3 is the bottom panel; 4 is the honeycomb wall of the wave-absorbing honeycomb; 5 is the climbing structure of the structural adhesive film; 6 is the functional adhesive film; 7 is the foam; 8 is the direction of pressure application. Detailed Implementation

[0028] In the embodiments and comparative examples of this invention:

[0029] The broadband 25mm thick absorbing honeycomb is obtained using honeycomb material AXND-2.75-4.8 (produced by Aoxing Yabo) through an impregnation process. The impregnation slurry used in the impregnation process consists of: isopropanol (Beijing Chemical), phenolic resin (Lighthouse brand F30-13 phenolic resin), and carbon black (5000 mesh, produced by Huifeng Chemical). The preparation steps are as follows: The isopropanol, phenolic resin, and carbon black are dispersed using a high-speed disperser to form the impregnation solution; the honeycomb material is uniformly impregnated in the impregnation solution, dried at 70 degrees Celsius, and then cured in a 180-degree Celsius oven for 1-2 hours to obtain the broadband 25mm thick absorbing honeycomb.

[0030] The raw materials used in the preparation of the 1mm thick low-frequency medium-temperature epoxy magnetic film include: bisphenol A epoxy resin E51, produced by Guangzhou Dongjun Chemical Co., Ltd.; and carbonyl iron powder JC-Fe-1, a metallic carbonyl iron powder produced by Junchen Metal. The preparation process is as follows: 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) are added to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixture with curing agent. Then, the carbonyl iron powder is added at a mass ratio of 63:37 (carbonyl iron powder: the bisphenol A epoxy resin mixture with curing agent), and mixed evenly to obtain a well-mixed resin. Then, a coating operation is performed: the well-mixed resin is added to a coating roller, which is tightly attached to a fixed wheel. The coating machine is started, and the well-mixed resin is coated onto continuous release paper to obtain a resin film, with the resin film thickness controlled at 0.2mm. Five layers of resin film were stacked at room temperature, placed in a vacuum bag, and vacuumed at 70 degrees Celsius for 20 minutes to obtain the 1 mm thick low-frequency medium-temperature epoxy magnetic film.

[0031] The raw materials used in the preparation of the 2mm thick low-frequency medium-temperature epoxy magnetic film include: bisphenol A epoxy resin E51, produced by Guangzhou Dongjun Chemical Co., Ltd.; and carbonyl iron powder JC-Fe-1, a metallic carbonyl iron powder produced by Junchen Metal. The preparation process is as follows: 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) are added to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixture with curing agent. Then, the carbonyl iron powder is added at a mass ratio of 63:37 (carbonyl iron powder: the bisphenol A epoxy resin mixture with curing agent), and mixed evenly to obtain a well-mixed resin. Then, a coating operation is performed: the well-mixed resin is added to a coating roller, which is tightly attached to a fixed wheel. The coating machine is started, and the well-mixed resin is coated onto a continuous release paper to obtain a resin film. The thickness of the resin film is controlled to be 0.2mm. Ten layers of adhesive film were stacked at room temperature, placed in a vacuum bag, and vacuumed at 70 degrees Celsius for 20 minutes to obtain the 2mm thick low-frequency medium-temperature epoxy magnetic adhesive film.

[0032] The raw materials used in the preparation of the adhesive include: bisphenol A epoxy resin, specifically bisphenol A epoxy resin E51, produced by Guangzhou Dongjun Chemical Co., Ltd. The preparation process is as follows: 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) are added to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixture with curing agent; then, a coating operation is performed: the bisphenol A epoxy resin mixture with curing agent is added to a coating roller, the roller is tightly attached to a fixed wheel, the coating machine is started, and the bisphenol A epoxy resin mixture with curing agent is coated onto a continuous release paper to obtain a pure resin film. The thickness of the pure resin film is controlled to be 0.1 mm to obtain the adhesive.

[0033] The bottom panel is a composite material board formed by curing carbon fiber prepreg, specifically a T700 carbon fiber board produced by Shanghai Lishuo Composite Materials.

[0034] The method for testing the reflectivity of the honeycomb composite materials prepared in the examples and comparative examples is the bow-shaped method: the honeycomb composite material to be tested is cut into 300mm*300mm pieces and placed on a metal plate. During the wave absorption performance test, the transmitting antenna excites the honeycomb composite material, and the reflected signal is picked up by the receiving antenna. By comparing the reflected signals with and without the honeycomb composite material, the reflectivity of the honeycomb composite material, i.e., its wave absorption performance, can be calculated.

[0035] The absorbing honeycomb described in Examples 1-5 are all broadband 25mm thick absorbing honeycomb, and the functional adhesive films are all 1mm thick low-frequency medium-temperature epoxy magnetic adhesive films, all with a size of 300*300mm.

[0036] Example 1:

[0037] The microwave absorbing honeycomb and a smooth, clean metal base plate are preheated to 90°C, and the press is preheated to 100°C on both sides. The functional adhesive film is preheated to 90°C in an oven to soften it. The metal base plate, functional adhesive film, and microwave absorbing honeycomb are laid out sequentially in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Under pressure of 0.3 MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and comes into contact with the metal base plate. That is, the distance between the bottom surface of the functional adhesive film and the bottom edge of the honeycomb wall of the microwave absorbing honeycomb is 0. After holding for 1 minute, the material is allowed to cool naturally to room temperature. The metal base plate is then removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film. The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-1-0). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 5 and Figure 6 And Table 1.

[0038] Example 2:

[0039] The microwave absorbing honeycomb and foam were preheated to 90℃. The selected foam was rigid PMI foam board with a density of 60 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Pressure is applied, and under a pressure of 0.3MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and penetrates 1mm into the foam. After holding for 1 minute, it is allowed to cool naturally to room temperature, and the foam is removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0040] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 23:1:1.

[0041] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-1-1). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 5 And Table 1.

[0042] Example 3:

[0043] The microwave absorbing honeycomb and foam were preheated to 90℃. The selected foam was rigid PMI foam board with a density of 50 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Under pressure of 0.4MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and extends 2mm into the foam. After holding for 1 minute, it is allowed to cool naturally to room temperature, and the foam is removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0044] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 22:1:2.

[0045] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-1-2). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 5 and Figure 6 And Table 1.

[0046] Example 4:

[0047] The absorbing honeycomb and foam were preheated to 80℃. The selected foam was rigid PMI foam board with a density of 50 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid out in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Pressure is applied at 0.5MPa, and after 30 seconds, the pressure is reduced to 0.3MPa. The honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and extends 3mm into the foam. After holding for 1 minute, it is allowed to cool naturally to 50°C. The foam is then removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0048] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 21:1:3.

[0049] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-1-3). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 7 And Table 1.

[0050] Example 5:

[0051] The microwave absorbing honeycomb and foam were preheated to 80℃. The selected foam was rigid PMI foam board with a density of 50 kg / m³. 3The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid out in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Pressure is applied at 0.5MPa, and then the pressure is reduced to 0.3MPa. The honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and extends 7mm into the foam. After holding for 1 minute, it is allowed to cool naturally to 50°C. The foam is then removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0052] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 17:1:7.

[0053] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-1-7). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 7 And Table 1.

[0054] In Examples 6-9, the absorbing honeycomb cells used are all broadband 25mm thick absorbing honeycomb cells, and the functional films are all 2mm thick low-frequency medium-temperature epoxy magnetic films, each 300*300mm in size. Film packing experiments were conducted.

[0055] Example 6:

[0056] The microwave absorbing honeycomb and a smooth, clean metal base plate are preheated to 90°C, and the press is preheated to 100°C on both sides. The functional adhesive film is preheated to 90°C in an oven to soften it. The metal base plate, functional adhesive film, and microwave absorbing honeycomb are laid out sequentially in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Under pressure of 0.3 MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and comes into contact with the metal base plate. That is, the distance between the bottom surface of the functional adhesive film and the bottom edge of the honeycomb wall of the microwave absorbing honeycomb is 0. After holding for 1 minute, the material is allowed to cool naturally to room temperature. The metal base plate is then removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film. The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-2-0). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 8 And Table 1.

[0057] Example 7:

[0058] The absorbing honeycomb and foam were preheated to 90℃. The selected foam was rigid PMI foam board with a density of 70 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Pressure is applied, and under a pressure of 0.3MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and penetrates 1mm into the foam. After holding for 1 minute, it is allowed to cool naturally to room temperature, and the foam is removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0059] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 22:2:1.

[0060] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-2-1). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 8 And Table 1.

[0061] Example 8:

[0062] The absorbing honeycomb and foam were preheated to 90℃. The selected foam was rigid PMI foam board with a density of 70 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Under pressure of 0.4MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and extends 2mm into the foam. After holding for 1 minute, it is allowed to cool naturally to room temperature, and the foam is removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0063] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 21:2:2.

[0064] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was slowly cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-2-2). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 8 And Table 1.

[0065] Example 9:

[0066] The absorbing honeycomb and foam were preheated to 90℃. The selected foam was rigid PMI foam board with a density of 70 kg / m³. 3 The press is preheated to 100°C on both sides, and the functional adhesive film is preheated to 90°C in an oven to soften it. Foam, functional adhesive film and microwave absorbing honeycomb are laid in sequence in the press, with the microwave absorbing honeycomb aligned on top of the functional adhesive film. Under pressure of 0.4MPa, the honeycomb wall of the microwave absorbing honeycomb penetrates the functional adhesive film and extends 8mm into the foam. After holding for 1 minute, it is allowed to cool naturally to room temperature, and the foam is removed to obtain a microwave absorbing honeycomb sheet, which is filled with a magnetic adhesive film.

[0067] In the aforementioned microwave absorbing honeycomb sheet, the distance from the upper surface of the functional adhesive film to the upper edge of the honeycomb wall of the microwave absorbing honeycomb is ( Figure 4 Section A): Functional film thickness ( Figure 4 Section B): The distance from the lower surface of the functional adhesive film to the lower edge of the cell wall of the absorbing cell ( Figure 4 (Section C) = 15:2:8.

[0068] The microwave-absorbing honeycomb sheet was placed entirely in an oven and heated to 130°C for 1 hour, then heated to 180°C and held for another hour to complete curing. Afterward, it was cooled to room temperature, and then adhesive was used to bond the microwave-absorbing honeycomb sheet to the bottom panel to obtain a honeycomb composite material (numbered 25-2-8). The reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 8 And Table 1.

[0069] Comparative Example 1:

[0070] The absorbing cell described in this comparative example is a broadband 25mm thick absorbing cell.

[0071] The absorbing honeycomb cells were bonded to the bottom panel using adhesive to obtain a honeycomb composite material (numbered 25-0-0); the reflectivity of this honeycomb composite material was tested. The results are shown below. Figure 6 And Table 1.

[0072] correspond Figure 5-8The test data is numbered and named according to the following rule: XX-TD, where XX represents the thickness of the selected absorbing cell, T represents the thickness of the selected functional adhesive film, and D represents the embedding thickness of the functional adhesive film in the absorbing cell, that is, the height of the bottom surface of the functional adhesive film from the bottom surface of the absorbing cell. When T is 0, it represents an absorbing cell without using magnetic adhesive film.

[0073] The reflectivity data at the 1 GHz frequency point in Examples 1-9 and the comparative examples are shown in Table 1.

[0074] Table 1

[0075]

[0076] Based on the data in Table 1, Figure 5-8 Analysis:

[0077] By comparing the reflectance curves of Examples 1-5 and Comparative Example 1, we can obtain:

[0078] like Figure 6 Comparing the reflectivity curves of 25-1-0 and 25-0-0, it can be seen that the functional film affects the low-frequency absorption performance of the honeycomb composite material, and the absorption performance of 25-1-0 is significantly better than that of 25-0-0.

[0079] like Figure 5-7 Comparing the reflectivity curves of 25-1-0, 25-1-1, 25-1-2, and 25-1-3, it can be seen that when the burial depth is 1, 2, and 3 mm, the wave absorption performance of Examples 2-4 is similar to that of Example 1 (25-1-0), which can be considered as retaining structural strength and meeting the stealth design requirements. Comparing the reflectivity curves of 25-1-1, 25-1-2, 25-1-3, and 25-1-7, it can be seen that the wave absorption performance of Example 5 (25-1-7) is significantly worse. Due to the excessive burial depth of the film, the performance of the honeycomb cannot be fully utilized, and the film forms the main reflective layer. As a result, although the performance is improved below 2 GHz, the performance in the subsequent frequency bands drops significantly.

[0080] By comparing the reflectance curves of Examples 6-9, we can obtain:

[0081] like Figure 8 Comparing the reflectance curves of 25-2-0, 25-2-1, and 25-2-2, it can be seen that the reflectance curves of the honeycomb composite materials in Examples 7-8 are similar. It can be considered that the wave absorption performance of the honeycomb composite materials with functional film pressed into the core by 1mm and 2mm is almost the same as that of Example 6 (25-2-0). Comparing the reflectance curve of 25-2-8, it can be seen that the reflectance of 25-2-8 (Example 9) is generally higher, and its wave absorption performance is significantly inferior to that of Example 6 (25-2-0), Example 7 (25-2-1), and Example 8 (25-2-2).

[0082] In Examples 1-9, Examples 2, 3, 4, 7, and 8 can retain structural strength and wave absorption performance. The wave-absorbing honeycomb sheets of Examples 2, 3, 4, 7, and 8 include wave-absorbing honeycombs and functional adhesive films. The functional adhesive film fills the pores of the wave-absorbing honeycomb, and the honeycomb walls of the wave-absorbing honeycomb extend beyond the magnetic adhesive film. The ratio of the height of the extension to the thickness of the wave-absorbing honeycomb is 1-3:25. The ratio of the thickness of the functional adhesive film to the thickness of the wave-absorbing honeycomb is 1-2:25. The ratio of the height of the wave-absorbing honeycomb on the functional adhesive film to the thickness of the wave-absorbing honeycomb in the wave-absorbing honeycomb sheet is 21-23:25.

[0083] Based on comparisons of different embodiments and experience from actual production experiments, it can be concluded that when using a 1-2mm magnetic adhesive film to enhance the structure of the microwave-absorbing honeycomb composite material, embedding the functional adhesive film inside the microwave-absorbing honeycomb material according to the proportions described in this invention can simultaneously meet the requirements of microwave absorption performance and leave sufficient length to ensure the bonding strength between the microwave-absorbing honeycomb material and the bottom panel material, thereby achieving the overall structure's microwave absorption performance and structural strength requirements. Furthermore, using rigid foam as an auxiliary material to push the adhesive film into the honeycomb saves on the cost of manufacturing precision molds for pushing the adhesive film in. On the other hand, commercially available honeycomb materials often have irregular hexagonal pores, and ordinary precision-machined molds can cause damage to the honeycomb and difficulties in demolding during actual use. Using rigid foam instead of molds increases the tolerance for honeycomb irregularities and also makes it easier to apply the process to honeycomb materials with other pore shapes and sizes.

Claims

1. A microwave absorbing honeycomb sheet, characterized in that, The device includes an absorbing honeycomb and a functional adhesive film, wherein the honeycomb wall of the absorbing honeycomb penetrates the functional adhesive film, and the ratio of the distance from the lower surface of the functional adhesive film to the lower edge of the honeycomb wall of the absorbing honeycomb to the thickness of the absorbing honeycomb is 1:25; the ratio of the thickness of the functional adhesive film to the thickness of the absorbing honeycomb is 1-2:

25.

2. The microwave absorbing honeycomb sheet according to claim 1, characterized in that, The ratio of the distance from the upper surface of the functional adhesive film to the upper edge of the cell wall of the microwave absorbing honeycomb to the thickness of the microwave absorbing honeycomb is 21-23:

25.

3. The microwave absorbing honeycomb sheet according to any one of claims 1-2, characterized in that, The functional adhesive film is a low-frequency magnetic adhesive film.

4. A method for preparing microwave absorbing honeycomb sheets, characterized in that, The method includes: First, the press, the microwave-absorbing honeycomb, and the foam are fully preheated, and the functional adhesive film is preheated to a softened state. Then, the foam, the functional adhesive film, and the microwave-absorbing honeycomb are sequentially laid in the press. Pressure is applied, causing the lower edge of the honeycomb wall of the microwave-absorbing honeycomb to penetrate the functional adhesive film and extend into the foam. The ratio of the distance from the lower surface of the functional adhesive film to the lower edge of the honeycomb wall to the thickness of the microwave-absorbing honeycomb is 1:

25. After cooling, the foam is removed, yielding a microwave-absorbing honeycomb sheet. The ratio of the thickness of the functional adhesive film to the thickness of the microwave absorbing honeycomb is 1-2:

25.

5. The method of claim 4, characterized in that, The functional adhesive film is a low-frequency magnetic adhesive film.

6. The method of claim 4, characterized in that, The ratio of the distance from the upper surface of the functional adhesive film to the upper edge of the cell wall of the microwave absorbing honeycomb to the thickness of the microwave absorbing honeycomb is 21-23:

25.

7. A honeycomb composite material, characterized in that, The absorbing honeycomb sheet according to any one of claims 1-3 or the absorbing honeycomb sheet prepared by any one of claims 4-6 is bonded to the bottom panel using an adhesive.

8. The application of the honeycomb composite material of claim 7 in a microwave absorbing device.

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