A method for preparing a flexible conductive film with infrared camouflage effect

Abstract

The application discloses a preparation method of a flexible conductive film with infrared camouflage effect, and comprises the following steps: (1) processing a metal mask plate, so that the metal mask plate comprises a hollow area, a grid area and a solid area at the same time; (2) attaching the metal mask plate on a hydrophobic substrate, and performing hydrophilic modification on the hydrophobic substrate to obtain a substrate with different hydrophilic characteristics corresponding to different areas; (3) spraying a dispersion liquid containing conductive nanowires on the surface of the substrate to obtain a conductive network structure with different mesh sizes in different areas of the substrate; and (4) scraping an organic solvent containing a high molecular polymer on the surface of the substrate, and peeling off the flexible conductive film after drying. The film prepared by the method has high transmittance in the visible light band, and can present the image of the substrate covered by the film; in the medium and far infrared band, the infrared emissivity of different blocks of the film is distributed in stages, so that the film has the infrared camouflage effect and can adapt to multi-spectrum compatible stealth.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a flexible conductive film with infrared camouflage effect. BACKGROUND

[0002] With the development of detection technology, the single frequency band camouflage technology has been difficult to cope with the full spectrum detection threat, and the development of multi-spectrum compatible stealth technology is imminent. The transparent conductive film can present the image of the substrate covered thereby, and can also avoid the interference of the visible light camouflage coating on the surface on the infrared characteristics. At present, ITO, AZO and other transparent conductive films have been widely used in infrared camouflage. However, the poor flexibility limits its application in the field of clothing; in addition, the single infrared characteristics of the existing transparent conductive film make it easy to be exposed in a specific environment. SUMMARY

[0003] The purpose of the application is to provide a preparation method of a flexible conductive film with infrared camouflage effect. On the one hand, the film prepared by the method has high transmittance in the visible light band, and can present the image of the substrate covered thereby; on the other hand, in the medium and far infrared band, the infrared emissivity corresponding to different blocks of the film is differentially distributed, so that the film has infrared camouflage effect, and further has the effect of multi-spectrum compatible stealth.

[0004] Technical scheme: The preparation method of the flexible conductive film with infrared camouflage effect comprises the following steps:

[0005] (1) Process the metal mask plate so that the metal mask plate contains a hollow area, a grid area and a solid area at the same time;

[0006] (2) Attach the metal mask plate to the hydrophobic substrate, and perform hydrophilic modification on the hydrophobic substrate to obtain a substrate with different hydrophilic characteristics in different areas;

[0007] (3) Spray a dispersion liquid containing conductive nanowires on the surface of the substrate. Due to the difference in hydrophilicity and liquid drop wetting characteristics between different areas, a conductive network structure with different arrangement modes (different mesh sizes formed by different arrangement modes) of conductive nanowires is obtained in different areas of the substrate;

[0008] (4) Apply an organic solvent containing a high molecular polymer to the surface of the substrate, and after drying, peel off to obtain a flexible conductive film.

[0009] In step (1), the femtosecond laser method is used to process the metal mask plate; in the grid area, the porosity is 36-40%.

[0010] In step (2), the hydrophobic substrate is a glass substrate modified by a silane coupling agent; or the hydrophobic substrate is a PTFE (polytetrafluoroethylene) substrate or a PFA substrate.

[0011] In step (2), the hydrophobic substrate is modified to be hydrophilic, specifically, the hydrophobic substrate with a metal mask plate attached is placed in an oxygen plasma treatment machine for hydrophilic modification.

[0012] The hydrophilic modification is performed in an air, argon or oxygen atmosphere, and the time for the hydrophilic modification is 100-120 s.

[0013] In step (3), the conductive nanowires are silver nanowires or copper nanowires; the diameter of the conductive nanowires is 25-30 nm, and the length is 20-25 μm.

[0014] In step (3), in the dispersion liquid containing the conductive nanowires, the mass concentration of the conductive nanowires is 0.5-1.0 mg / mL; the dispersion liquid is ethanol or isopropanol.

[0015] In step (3), in the spraying process, the spraying rate is 8-9 μL / s, the spraying distance is kept at 10-12 cm, and the aperture of the spray gun used is 0.3-0.35 mm.

[0016] In step (3), on the substrate, the loading amount of the conductive nanowires is 20-100 μg / cm 2 .

[0017] In step (4), the high molecular polymer is cellulose, PDMS or polyurethane; the organic solvent is N,N'-dimethylformamide; the drying temperature is 60-80 ℃, and the drying time is 1.5-2 h, and the drying is used to remove residual solvent.

[0018] The present application makes the liquid droplets on the surface of the substrate show different wetting behaviors by the regional hydrophilic properties of the substrate, thereby generating a conductive network structure with different mesh sizes in different regions, thereby producing different transmission characteristics for different wave bands of electromagnetic waves; wherein the mesh size of the thin film in the hydrophilic region is about several hundred nanometers, and the mesh size in the hydrophobic region is several microns to tens of microns.

[0019] Advantages: Compared with the prior art, the present application has the following obvious advantages: the thin film prepared by the method of the present application has high transmittance in the visible light band and can present the image of the substrate covered by the thin film; in the medium and far infrared wave band, the infrared emissivity of different blocks of the thin film is different, so it has an infrared camouflage effect and can adapt to multi-spectrum compatible stealth; in addition, the thin film also has good flexibility, so it can be well attached to various curved substrates. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Optical photo of the metal mask after processing in Example 1;

[0021] Figure 2 Contact angle image of different areas of the substrate after contact with droplets in Example 1;

[0022] Figure 3 Scanning electron microscope image of silver nanowire conductive network in different areas of the substrate in Example 1;

[0023] Figure 4 Mesh size distribution of different conductive networks in Example 1;

[0024] Figure 5 Image of the film before and after deformation in Example 1;

[0025] Figure 6 Visible light transmittance and infrared emissivity curves of different areas of the film prepared in Example 1;

[0026] Figure 7 Optical and infrared images of the film prepared in Example 1 covering the surface of the camouflage clothing;

[0027] Figure 8 Scanning electron microscope image of silver nanowire conductive network in different areas of the substrate in Example 2;

[0028] Figure 9 Visible light transmittance and infrared emissivity curves of different areas of the film prepared in Example 2. DETAILED DESCRIPTION

[0029] Example 1

[0030] The preparation method of the flexible conductive film with infrared camouflage effect of the present application comprises the following steps:

[0031] (1) The glass substrate is sequentially cleaned with acetone, ethanol and deionized water for 10 min each time to remove residual oil and impurities on the surface of the glass sheet;

[0032] (2) The glass sheet and a sample bottle containing 5 mL of trimethoxy(1H,1H,2H,2H-heptadecafluorodecyl)silane are placed in a glass bottle with a capacity of 500 mL, the glass bottle is sealed, heated to 100℃ and kept for 6 h, and the hydrophobic modified glass substrate is obtained by evaporation coating;

[0033] (3) The metal mask is processed by femtosecond laser, Figure 1An optical image of the processed metal mask in this embodiment is shown in FIG. 1. In the image, region 1 is a hollow region, region 2 is a grid region, in which the size of the square hole is 0.6 mm, the size (width) of the grid between adjacent square holes is 0.4 mm, and the porosity of the grid region is 36%, and region 3 is a solid region.

[0034] (4) The processed metal mask was covered on the hydrophobic substrate to ensure that the two were attached, and then treated in an air environment using an oxygen plasma treatment machine for 120 s to obtain a glass substrate with a regionalized hydrophilic property; Figure 2 An image of the contact angle of the substrate of Example 1 after the different regions were contacted with a liquid drop is shown in FIG. 2. In the hydrophilic region, the liquid drop spread rapidly after contacting the surface of the substrate, and the contact angle decreased from 15° to 4° within 0.9 s. The small contact angle resulted in a small difference in evaporation rate between the center and the edge of the liquid drop, thereby generating a random network. In contrast, the contact angle of the liquid drop in the hydrophobic region decreased slowly from 46° to 32° within 35 s. The large contact angle resulted in a large difference in evaporation rate between the center and the edge of the liquid drop, and the capillary effect was significant, driving the silver nanowires to generate a micro-network structure.

[0035] (5) A silver nanowire-ethanol dispersion solution with a mass concentration of 0.5 mg / mL was sprayed onto the surface of the above glass substrate, in which the diameter of the silver nanowires was 30 nm and the length was 25 μm. The spraying rate was 8 μL / s, the spraying distance was kept at 10 cm, the aperture of the spray gun used was 0.3 mm, and the silver nanowire loading was controlled to be 60 μg / cm by a balance. 2 , Figure 3 An SEM image of the silver nanowire conductive network in the different regions of the substrate of Example 1 is shown in FIG. 3. It can be seen that a conductive network with different pore sizes was successfully prepared on the surface of the substrate. Figure 3 An SEM image of the silver nanowire conductive network in the different regions of the substrate of Example 1 is shown in FIG. 3. It can be seen that a conductive network with different pore sizes was successfully prepared on the surface of the substrate. Figure 4 A pore size distribution graph obtained by ImageJ software is shown in FIG. 4. In the hydrophilic region, the pores were mainly located near 250 nm, while in the hydrophobic region, the pores were concentrated in several microns to tens of microns.

[0036] (6) 5 g of polyurethane pellets were dispersed in 20 mL of N,N’-dimethylformamide, stirred at room temperature for 4 h to ensure that the polyurethane was completely dissolved therein, then left to stand for 10 min to remove residual bubbles therefrom, to obtain a polyurethane solution. The polyurethane solution was blade-coated on the surface of the substrate, placed in a vacuum oven at 80 °C for drying for 2 h to remove residual solvents, and the film was peeled off from the substrate to obtain a flexible conductive film. Figure 5 An optical image of the film after being subjected to various deformations is shown in FIG. 5, which proves that the film has good flexibility.

[0037] Figure 6 Curves of visible light transmittance and infrared emissivity at different regions of the film prepared in Example 1 are shown in FIG. 6. It can be seen that the film has good visible light transmittance and low infrared emissivity. Figure 6It can be seen that the visible light transmittance at 550 nm wavelength is higher than 70% in the presence of the substrate, and the infrared emissivity of the film corresponding to regions 1-3 is 0.27, 0.47 and 0.58, respectively. Figure 7 The optical and infrared images of the film prepared in Example 1 after covering the surface of the camouflage clothing, due to the good visible light transmittance of the film, the film presents the color characteristics similar to the substrate in vision, and presents the typical camouflage pattern under the infrared thermal imager, that is, presents the infrared imaging with different depths, when covering the surface of the human body, can hide the thermal radiation characteristics of the human body itself, and realize infrared camouflage of the human body in various background environments such as city and forest land.

[0038] Example 2

[0039] The preparation method of the flexible conductive film with infrared camouflage effect comprises the following steps:

[0040] (1) The glass substrate is sequentially cleaned by ultrasonic cleaning in acetone, ethanol and deionized water for 10 min, respectively, to remove the residual oil stains and impurities on the surface of the glass sheet;

[0041] (2) The above glass sheet and a sample bottle containing 5 mL of trimethoxy(1H, 1H, 2H, 2H-heptadecafluorodecyl) silane are placed in a glass bottle with a capacity of 500 mL, the glass bottle is sealed, heated to 100℃ and kept for 6h, and the hydrophobic modified glass substrate is obtained by evaporation coating;

[0042] (3) The metal mask plate is processed by femtosecond laser, and the structure of the processed metal mask plate in Example 2 is the same as that in Example 1;

[0043] (4) The processed metal mask plate is covered on the hydrophobic substrate, and the two are adhered, and then treated by oxygen plasma treatment machine in air environment for 120s, to obtain a glass substrate with regional hydrophilic characteristics;

[0044] (5) The silver nanowire-ethanol dispersion solution with a mass concentration of 0.5mg / mL is sprayed on the surface of the above glass substrate, wherein the diameter of the silver nanowire is 30nm, and the length is 25μm; the spraying rate is 8μL / s, the spraying distance is kept at 10cm, the aperture of the used spray gun is 0.3mm, and the silver nanowire loading amount is controlled by the balance to be 40μg / cm 2 , Figure 8 The silver nanowire conductive network structure of different regions in Example 2, compared with Example 1, the density of the random network is reduced, and there is no obvious difference in the micro-network structure;

[0045] (6) 5 g of polyurethane primary particles were dispersed in 20 mL of N,N'-dimethylformamide, stirred at room temperature for 4 h to ensure complete dissolution of the polyurethane therein, and then left to stand for 10 min to remove residual bubbles therefrom, to obtain a polyurethane solution; the polyurethane solution was scraped onto the surface of a substrate, dried in a vacuum oven at 80 °C for 2 h to remove residual solvent, and the film was peeled off the substrate to obtain a flexible conductive film. Figure 9 The visible light transmittance and infrared emissivity curves of different regions of the film prepared in Example 2 showed good visible light transmittance as a whole, and the infrared emissivity of different regions was 0.62 and 0.48, respectively.

[0046] Comparative Example 1

[0047] Comparative Example 1 differed from Example 1 only in that the silver nanowires used had a diameter of 50 nm, and the flexible conductive film prepared had a visible light transmittance at 550 nm of greater than 80% at different regions, and the infrared emissivity was 0.61 and 0.54, respectively. The smaller infrared emissivity contrast was due to the fact that, at the same loading amount, the larger diameter silver lines had a smaller number density, and thus the random network produced larger pores, increasing the transmission of infrared light.

Claims

1. A method for preparing a flexible conductive film having an infrared camouflage effect, characterized in that, The method comprises the following steps: (1) processing a metal mask plate so that the metal mask plate comprises a hollow region, a grid region and a solid region; (2) attaching the metal mask plate to a hydrophobic substrate to modify the hydrophobic substrate to obtain a substrate with different hydrophilic properties in different regions; (3) spraying a dispersion liquid containing conductive nanowires on the surface of the substrate to obtain a conductive network structure with different mesh sizes in different regions of the substrate; (4) coating an organic solvent containing a high polymer on the surface of the substrate, and then peeling off the flexible conductive film after drying.

2. The method of claim 1, wherein: In step (1), the metal mask plate is processed by femtosecond laser; wherein the porosity of the grid region is 36-40%.

3. The method of claim 1, wherein: In step (2), the hydrophobic substrate is a glass substrate modified by a silane coupling agent; or the hydrophobic substrate is a PTFE substrate or a PFA substrate.

4. The method of claim 1, wherein: In step (2), the hydrophobic substrate is modified to be hydrophilic by placing the hydrophobic substrate with the metal mask plate in an oxygen plasma treatment machine.

5. The method of claim 4, wherein: The hydrophilic modification is carried out in an air, argon or oxygen atmosphere, and the time for the hydrophilic modification is 100-120 s.

6. The method of claim 1, wherein: In step (3), the conductive nanowires are silver nanowires or copper nanowires; the diameter of the conductive nanowires is 25-30 nm, and the length is 20-25 μm.

7. The method of claim 1, wherein: In step (3), the mass concentration of the conductive nanowires in the dispersion liquid containing the conductive nanowires is 0.5-1.0 mg / mL; the dispersion liquid is ethanol or isopropanol.

8. The method of claim 1, wherein: In step (3), during the spraying process, the spraying rate is 8-9 μL / s, the spraying distance is kept at 10-12 cm, and the nozzle diameter used is 0.3-0.35 mm.

9. The method of claim 1, wherein: In step (3), the loading amount of the conductive nanowires on the substrate is 20 to 100 μg / cm2 2 .

10. The method of claim 1, wherein: In step (4), the high polymer is cellulose, PDMS or polyurethane; the drying temperature is 60-80 °C, and the drying time is 1.5-2 h.

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