Airplane ground electromagnetic protective film based on flaky silver / graphite conductive paste

Abstract

The invention discloses an aircraft ground electromagnetic protective film based on flaky silver / graphite conductive paste, and belongs to the field of aircraft ground protection safeguard.The frequency selective surface is of a two-layer structure, the first layer is a frequency selective surface conductive periodic pattern array coating, and the second layer is a conductive periodic pattern array coating; the periodic pattern array coating prepared by silk-screen printing on the surface of a base material by using the composite conductive paste blended by flaky silver / flaky graphite is used for realizing the filtering effect of in-band high wave transmission and out-of-band reflection shielding of electromagnetic waves in a specific frequency band. And the second layer is a flexible film substrate layer which is a flexible polymer film or a fiber reinforced composite material film thereof and is used as a carrier of the frequency selective surface conductive pattern layer. The airplane ground electromagnetic protective film based on the flaky silver / graphite conductive paste has the characteristics of band-pass wave transmission, flexibility, light weight, low cost and large-area preparation, and has a very good engineering application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of aircraft ground protection and security, and particularly relates to an aircraft ground electromagnetic protection film based on a sheet-shaped silver / graphite conductive paste. BACKGROUND

[0002] When an aircraft is parked on the ground, it is detected by the radar of the other party, and in the case of not exposing its own position and shape, the radar information of the other party needs to be shielded. When the aircraft tests its antenna or radar on the ground, the signal of its own antenna and radar needs to be ensured not to be shielded, and therefore a band-pass frequency selective surface (FSS) material needs to be used to protect the aircraft, so that the filtering function of high wave transmission in a specific electromagnetic frequency band and reflection shielding outside the band can be realized. The traditional frequency selection uses a printed circuit board (PCB) process to prepare the surface material, and the main idea is to first plate a metal film on the surface of a hard substrate such as a polymer material flat plate and a wave-transparent antenna cover, then perform photoetching mask and chemical etching to remove the excess part to leave a conductive array pattern. The prepared FSS material is usually a hard flat plate and has no flexibility, and it is difficult to achieve good coating on the surface of some curved components, which affects the wave transmission rate under oblique incidence. In addition, the PCB preparation method has problems such as high cost, low efficiency, small preparation area, and difficulty in realizing continuous preparation, which seriously limits the engineering application in the field of large-area components (wave-transparent / shielded compatible hangar) and the like.

[0003] In view of the problems of the traditional FSS material that cannot be attached to the curved surface of the component, affects the wave transmission rate under oblique incidence, and the preparation method such as PCB has complex process steps, high cost, small preparation area, and difficulty in realizing continuous manufacturing, the present application discloses an aircraft ground electromagnetic protection film based on a sheet-shaped silver / graphite conductive paste and a preparation method. SUMMARY

[0004] The purpose of the present application is to provide an aircraft ground electromagnetic protection film based on a sheet-shaped silver / graphite conductive paste and a preparation method, which solves the problems of the existing frequency selective surface material that a hard flat plate cannot be attached to the curved surface of the component, affects the wave transmission rate under oblique incidence, and the preparation method such as PCB has complex process steps, high cost, small preparation area, and difficulty in realizing continuous manufacturing.

[0005] To achieve the above-mentioned purpose, the present application proposes the following technical solution:

[0006] An aircraft ground electromagnetic protection film based on a sheet-shaped silver / graphite conductive paste, comprising a two-layer structure, a first layer being a frequency selective surface conductive periodic pattern array layer, and a second layer being a flexible film substrate layer.

[0007] Preferably, in the aircraft ground electromagnetic shielding film based on the flaky silver / graphite conductive paste, the frequency selective surface conductive periodic pattern array layer is a periodic pattern array coating prepared by screen printing of the flaky silver / flaky graphite blended composite conductive paste on the surface of a substrate.

[0008] Preferably, in the aircraft ground electromagnetic shielding film based on the flaky silver / graphite conductive paste, the frequency selective surface conductive periodic pattern array layer is a square conductive pattern array, the periodic unit size is 20-80 mm, the square unit size is 10-60 mm, and the square resistance of the pattern layer is 0.1-50 .

[0009] Preferably, in the aircraft ground electromagnetic shielding film based on the flaky silver / graphite conductive paste, the flaky silver / flaky graphite blended composite conductive paste is a conductive paste prepared by using flaky silver and flaky graphite mixed powder as conductive fillers and using polyurethane, polyimide, polyvinyl alcohol, epoxy resin and the like as a dispersion phase matrix, the flaky silver is micron-level flaky silver powder prepared by a ball milling method, and the flaky graphite is micron-level flaky graphite powder recovered from waste lithium ion battery electrode materials.

[0010] Preferably, in the aircraft ground electromagnetic shielding film based on the flaky silver / graphite conductive paste, the flexible high polymer or fiber reinforced composite material film is a flexible polyimide, polyurethane, polyvinyl alcohol or oxide fiber reinforced composite material film, and the thickness is 0.1-1 mm.

[0011] Based on the same inventive concept, the application further provides a preparation method of an aircraft ground electromagnetic shielding film based on a flaky silver / graphite conductive paste, which comprises the following steps:

[0012] (1) Preparation of flaky silver powder: micron-level flaky silver powder is prepared by a wet ball milling method, micron-level silver powder is used as raw material, a ball milling aid is added into a ball mill together with the micron-level silver powder, and ball milling is completed according to a set ball-to-material ratio, rotation speed and time parameter, then the ball milling mixture is poured out, and micron-level flaky silver powder is obtained after pressure filtration, solution washing and drying;

[0013] (2) Preparation of flaky silver / flaky graphite composite conductive paste: micron-level flaky silver powder prepared in step (1) and micron-level flaky graphite powder recovered from waste lithium ion battery electrode materials are added into a high polymer dispersion phase matrix according to a specified proportion, and slow and continuous stirring is performed until the flaky silver / flaky graphite powder is uniformly dispersed in the high polymer resin matrix, so that a flaky silver / flaky graphite blended composite conductive paste is obtained;

[0014] (3) Flexible FSS screen printing preparation: Flexible FSS is prepared by screen printing method, and flexible polyimide, polyurethane, polyvinyl alcohol or oxide fiber reinforced composite film is used as the printing film substrate. First, the surface of the film substrate is cleaned with alcohol or acetone as a cleaning agent, and the screen printing screen with a hollow square frequency selective surface pattern array is tightly attached to the surface of the film substrate. The composite conductive paste prepared in step (2) is poured on the surface of the screen, and the flat blade is repeatedly coated until the entire pattern area is uniformly coated. The screen is carefully removed, and the film with the array pattern is placed in a drying oven for heating and drying, and then heated and cured to obtain a flexible FSS film material based on the sheet silver / graphite blended conductive paste.

[0015] Preferably, in the above preparation method, the particle size of the micron-sized silver powder in step (1) is 2-20 μm.

[0016] Preferably, in the above preparation method, in step (1), the ball milling aid is n-propanol and propylene glycol, and the ratio of ball milling aid to silver powder is 100-200 mL per 100 g of powder.

[0017] Preferably, in the above preparation method, in step (1), the ball milling parameters are a ball-to-material ratio of 10:1-20:1, a ball milling speed of 300-500 rpm, and a ball milling time of 24-48 h.

[0018] Preferably, in the above preparation method, in step (1), the pressure filtration washing solution is n-propanol and propylene glycol.

[0019] Preferably, in the above preparation method, in step (2), the mixing ratio of micron-sized sheet silver powder and sheet graphite powder is 1:1-1:3.

[0020] Preferably, in the above preparation method, in step (3), the screen printing screen with a hollow square frequency selective surface pattern array has a mesh size of 200-400 mesh.

[0021] Preferably, in the above preparation method, in step (3), the heating and drying process in the drying oven is at a temperature of 40-50℃ for 2-6 h, and the heating and curing temperature is 60-80℃ for 3-6 h.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The aircraft ground electromagnetic protection film based on the sheet silver / graphite conductive paste of the present application is a flexible FSS film, which can be precisely attached to the surface of large curved surface devices such as spherical, conical radar covers, arched inflatable hangars, etc. The problem of affecting the wave transmittance under oblique incidence is solved, which cannot be solved by hard flat plates.

[0024] (2) The aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste of the present application uses flaky silver / flaky graphite blended conductive paste as the conductive coating raw material, and uses the screen printing process with a patterned screen plate as a template to complete the preparation of the FSS material, which greatly improves the preparation efficiency, reduces the preparation cost, and can realize continuous large-area preparation, solving the problems of complex process steps, high cost, small preparation area and difficulty in realizing continuous manufacturing of the traditional FSS material PCB preparation method;

[0025] (3) In the preparation process of the FSS layer of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste of the present application, the flaky graphite powder recovered from the electrode materials of waste lithium ion batteries is used to replace part of the noble metal conductive filler in the preparation process of the conductive paste, and the prepared conductive paste has the outstanding advantages of low cost and green environmental protection, solving the problems of high price and serious environmental pollution after scrap of the traditional noble metal conductive paste. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a decomposition structure schematic diagram of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste of the present application;

[0027] Figure 2 is a block array bandpass frequency selective surface array pattern design scheme and size explanation of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste of the present application;

[0028] Figure 3 is a photo of the flaky silver / flaky graphite blended conductive paste prepared in embodiment 1 of the present application;

[0029] Figure 4 is a photo of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste prepared in embodiment 1 of the present application;

[0030] Figure 5 is the in-band wave permeability test result of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste prepared in embodiment 1 of the present application;

[0031] Figure 6 is the out-of-band shielding effect test result of the aircraft ground electromagnetic protection film based on the flaky silver / graphite conductive paste prepared in embodiment 1 of the present application.

[0032] Legend: 1-Frequency selective surface conductive periodic pattern array layer, 2- Flexible film substrate layer. DETAILED DESCRIPTION

[0033] The application will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only used to explain the application, and the protection scope of the application should include the entire content of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully realize the entire content of the claims of the application.

[0034] Embodiment 1

[0035] A plane ground electromagnetic shielding film structure based on a flaky silver / graphite conductive paste is shown in FIG. 1, which comprises a frequency selective surface conductive periodic pattern array layer 1 and a flexible film substrate layer 2. The frequency selective surface conductive periodic pattern array layer 1 is a square conductive pattern array, the periodic unit size is 72 mm, the square unit size is 60 mm, the square resistance is 10.6 mΩ, and the frequency selective unit size is defined as shown in FIG. 2. The frequency selective surface conductive periodic pattern array layer 1 is printed by a screen printing process using a flaky silver / flaky graphite blended conductive paste / polymer composite conductive paste. The flexible film substrate layer 2 is a polyimide film with a thickness of 1 mm. Figure 1 Figure 2 The preparation method of the plane ground electromagnetic shielding film based on the flaky silver / graphite conductive paste of the embodiment comprises the following steps:

[0036] The preparation method of the plane ground electromagnetic shielding film based on the flaky silver / graphite conductive paste of the embodiment comprises the following steps:

[0037] (1) Preparation of flaky silver powder: silver powder with a particle size distribution range of 10-20 microns is used as raw material, and n-propyl alcohol is used as a ball milling aid. The ball milling parameters are set as a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, and a time of 24 h. After ball milling, the ball milling mixture is poured out, filtered, washed with propylene glycol solution, and dried to obtain flaky silver powder with a particle size of 20-50 microns;

[0038] (2) Preparation of flaky silver / flaky graphite composite conductive paste: micron-sized flaky silver powder prepared in step (1) and micron-sized flaky graphite powder recovered from waste lithium ion battery electrode materials are added to a polyurethane resin matrix at a ratio of 1:3, and slow continuous stirring is performed until the flaky silver / flaky graphite powder is uniformly dispersed in the polymer resin matrix. The obtained flaky silver / flaky graphite blended composite conductive paste is shown in FIG. 3. Figure 3

[0039] ​​(3) Flexible FSS screen printing preparation: Flexible FSS is prepared by screen printing method, using flexible polyimide film as printing film substrate. First, clean the surface of the film substrate with alcohol as cleaning agent. Place the screen printing screen with a hollow square frequency selective surface pattern array on the surface of the film substrate. The screen mesh is 300 meshes. Pour the sheet-shaped silver / sheet-shaped graphite blended conductive paste prepared in step (2) onto the surface of the screen. Repeat the coating with a flat blade until the entire pattern area is evenly coated. Carefully remove the screen. Place the film with the array pattern into a drying oven and heat to 50°C for 2h, and then heat to 80°C for 3h. The flexible FSS film material based on sheet-shaped silver / sheet-shaped graphite blended conductive paste is obtained as shown in FIG. 4. Figure 4

[0040] The performance of the flexible band-pass FSS material prepared in this example was tested. The wave transmission rate was tested by focusing lens method. The average wave transmission rate in the 1.2-1.4 GHz working electromagnetic wave frequency band was 96.2% (see FIG. 5), the shielding effectiveness outside the working frequency band (8~12GHz) was close to -10dB, corresponding to a wave transmission rate of less than 0.1 (see FIG. 6), and it had very good electromagnetic wave shielding effect. Figure 5 Figure 6

[0041] Example 2

[0042] The structure of an aircraft ground electromagnetic protection film based on sheet-shaped silver / graphite conductive paste includes a frequency selective surface conductive periodic pattern array layer and a flexible high polymer film substrate layer. The frequency selective surface conductive periodic pattern array layer is a square conductive pattern array with a periodic unit size of 20mm and a square unit size of 10mm, and a square resistance of 36.5mΩ. It is printed by sheet-shaped silver / sheet-shaped graphite blended conductive paste / high polymer composite conductive paste using a screen printing process. The flexible high polymer composite film substrate is a quartz fiber reinforced polyurethane film with a thickness of 0.3mm.

[0043] The preparation method of an aircraft ground electromagnetic protection film based on sheet-shaped silver / graphite conductive paste of this example includes the following steps:

[0044] (1) Preparation of sheet-shaped silver powder: Silver powder with a particle size distribution range of 2~10 microns is used as raw material, and n-propyl alcohol is used as a ball milling aid. They are added together into a ball mill. The ball milling parameters are set as follows: ball-to-material ratio 20:1, rotation speed 300rpm, and time 48h. After ball milling, the ball milling mixture is poured out, filtered, washed with propylene glycol solution, and dried to obtain sheet-shaped silver powder with a particle size of 5~25 microns.

[0045] ​​​(2) Preparation of flaky silver / flaky graphite composite conductive paste: the micron-sized flaky silver powder prepared in step (1) and the micron-sized flaky graphite powder recovered from the waste lithium ion battery electrode material are added into the polyurethane resin matrix at a ratio of 1:1, and slow continuous stirring is performed until the flaky silver / flaky graphite powder is uniformly dispersed in the polymer resin matrix, to obtain a flaky silver / flaky graphite blended composite conductive paste;

[0046] (3) Preparation of flexible FSS by screen printing: the flexible FSS is prepared by screen printing, and the flexible quartz fiber reinforced polyurethane is used as the printing film substrate. First, the surface of the film substrate is cleaned with acetone as a cleaning agent, and a screen printing screen with a hollow square frequency selective surface pattern array is tightly attached to the surface of the film substrate. The screen printing screen has a mesh size of 200 meshes. The flaky silver / flaky graphite blended composite conductive paste prepared in step (2) is poured onto the surface of the screen, and a flat blade is repeatedly coated until the entire pattern area is uniformly coated. The screen is carefully removed, and the film with the array pattern is placed in a drying oven and heated to 40°C for 6h, and then heated to 60°C for 6h, to obtain a flexible FSS film material based on the flaky silver / flaky graphite blended conductive paste.

[0047] The performance of the flexible band-pass FSS material based on the silver-coated graphite composite conductive paste prepared in this example was tested, and the wave transmittance was tested by the focusing lens method. The average wave transmittance in the 1.2-1.4 GHz working electromagnetic wave frequency band was 89.6% (see FIG. 4), the shielding effectiveness outside the working frequency band (8-10 GHz) was close to -8 dB, corresponding to a wave transmittance of less than 0.16, and the electromagnetic wave shielding effect was significant. Figure 5

[0048] The above description is merely a specific implementation of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.​

Claims

1. An aircraft ground electromagnetic shielding film based on sheet-like silver / graphite conductive paste, characterized in that, It comprises a two-layer structure: the first layer is a frequency-selective surface conductive periodic pattern array layer, and the second layer is a flexible thin film substrate layer; the frequency-selective surface conductive periodic pattern array layer is a periodic pattern array coating prepared by screen printing a composite conductive paste of sheet silver / sheet graphite on the substrate surface, which is used to achieve a filtering effect of high electromagnetic wave transmission and out-of-band reflection shielding; the thin film substrate layer is a flexible polymer or its fiber-reinforced composite film, which serves as a carrier for the frequency-selective surface conductive pattern layer.

2. The aircraft ground electromagnetic shielding film based on sheet-like silver / graphite conductive paste according to claim 1, characterized in that, The frequency-selective surface conductive periodic pattern array layer is a block conductive pattern array, with a periodic unit size of 20~80mm, a block unit size of 10~60mm, and a sheet resistance of 0.1~50. .

3. The aircraft ground electromagnetic shielding film based on sheet-like silver / graphite conductive paste according to claim 1, characterized in that, The composite conductive slurry of flake silver / flake graphite blend is a conductive slurry obtained by using flake silver and flake graphite mixed powder as conductive filler and polyurethane, polyimide, polyvinyl alcohol or epoxy resin as dispersed phase matrix. The flake silver is micron-sized flake silver powder prepared by ball milling, and the flake graphite is micron-sized flake graphite powder obtained by recycling waste lithium-ion battery electrode materials.

4. The aircraft ground electromagnetic shielding film based on sheet-like silver / graphite conductive paste according to claim 1, characterized in that, The flexible polymer or its fiber-reinforced composite film is a flexible polyimide, polyurethane, polyvinyl alcohol or its oxide fiber-reinforced composite film with a thickness of 0.1~1mm.

5. A method for preparing an aircraft ground electromagnetic shielding film based on sheet-like silver / graphite conductive paste as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of flake silver powder: Micron-sized flake silver powder is prepared by wet ball milling. Micron-sized silver powder is used as raw material and added to the ball mill along with ball milling aid. The ball milling is completed according to the set ball-to-material ratio, rotation speed and time parameters. Then the ball milling mixture is poured out, filtered, washed with solution and dried to obtain micron-sized flake silver powder. (2) Preparation of flake silver / flake graphite composite conductive paste: The micron-sized flake silver powder prepared in step (1) and the micron-sized flake graphite powder obtained by recycling waste lithium-ion battery electrode materials are added to the polymer dispersion matrix in a specified ratio and stirred slowly until the flake silver / flake graphite powder is uniformly dispersed in the polymer resin matrix to obtain the flake silver / flake graphite blended composite conductive paste; (3) Flexible FSS screen printing preparation: Flexible FSS is prepared by screen printing. Flexible polyimide, polyurethane, polyvinyl alcohol or its oxide fiber reinforced composite film is used as the printing film substrate. First, the surface of the film substrate is cleaned with alcohol or acetone as a cleaning agent. The screen printing stencil with a hollow square frequency selective surface pattern array is tightly attached to the surface of the film substrate. The composite conductive paste of flake silver / flake graphite blend prepared in step (2) is poured onto the surface of the stencil. The paste is repeatedly scraped with a flat squeegee until it is evenly spread throughout the entire pattern area. The stencil is carefully removed. The film with the array pattern is placed in a drying oven for heating and drying, and then heated and cured to obtain the flexible FSS film material based on the flake silver / flake graphite blend conductive paste.

6. The preparation method according to claim 5, characterized in that, In step (1), the micron-sized silver powder has a particle size of 2~20μm.

7. The preparation method according to claim 5, characterized in that, In step (1), the ball milling aid is n-propanol or propylene glycol, and the ratio of ball milling aid to silver powder is 100-200 mL per 100 g of powder; the ball milling parameters are ball-to-material ratio of 10:1-20:1, ball milling speed of 300-500 rpm, and ball milling time of 24-48 h.

8. The preparation method according to claim 5, characterized in that, In step (1), the pressure filtration washing solution is n-propanol and propylene glycol.

9. The preparation method according to claim 5, characterized in that, In step (2), the mixing ratio of micron-sized flake silver powder and flake graphite powder is 1:1 to 1:

3.

10. The preparation method according to claim 5, characterized in that, In step (3), the mesh count of the screen printing stencil with the hollowed-out square frequency selective surface pattern array is 200~400 mesh; the temperature of the drying process in the drying oven is 40~50℃ and the time is 2~6h; the temperature of the curing process is 60~80℃ and the time is 3~6h.

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