Preparation method of infrared transparent broadband electromagnetic shielding material

Abstract

The invention discloses a preparation method of an infrared transparent broadband electromagnetic shielding material, which comprises the following steps: S1, base material surface treatment: selecting a base material with infrared light transmittance greater than 85%, spin-coating an infrared transparent high-molecular polymer on the surface of the clean base material, and curing to form an adhesive force enhancement layer with the thickness of 2-10 [mu] m; s2, designing a grid pattern; s3, printing a first layer of conductive grid; s4, grounding protection and a covering layer; s5, printing a second layer of conductive grid; s6, packaging is carried out; a fine grid structure is formed through the 3D printing technology, the balance of high light transmission of an infrared band and high shielding effectiveness of a broadband band is achieved, it is ensured that a working system normally operates in a complex electromagnetic environment, the infrared stealth capacity is achieved, uniform distribution of light is ensured through the irregular design of grid patterns, and the detection and surveying and mapping effects are not affected; through the double-layer structure, the number of printing layers is optimally designed, and the slurry material cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding materials, and specifically to a preparation method of an infrared transparent broadband electromagnetic shielding material. Background Art

[0002] With the development of high-frequency and integrated electronic devices, electromagnetic shielding materials are required to have high shielding efficiency in a wide frequency band and meet the high light transmittance requirements in the infrared band to achieve the compatibility of optoelectronic systems, such as infrared windows and optical detectors. However, the existing technologies have the following limitations:

[0003] Traditional transparent conductive materials represented by indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) have high light transmittance and conductivity in the visible and near-infrared bands of 380 - 1500 nm, but their light transmittance in the infrared band decreases significantly, and they have problems such as high brittleness, poor flexibility, and narrow frequency band shielding range, making it difficult to meet the composite requirements of broadband electromagnetic shielding and infrared stealth; Regular metal grids prepared by photolithography or nanoimprinting processes, such as square wave and hexagonal structures, can improve the light transmittance by reducing the line width, but the regular periodic structure is prone to cause optical diffraction effects, resulting in infrared imaging distortion; and the thickness of a single metal layer is limited, and there is limited room for improving the shielding efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an infrared transparent broadband electromagnetic shielding material to solve the problems proposed in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of an infrared transparent broadband electromagnetic shielding material, comprising the following steps:

[0006] S1: Substrate surface treatment: Select a substrate with an infrared transmittance greater than 85%, spin-coat an infrared transparent polymer on the clean substrate surface, and form an adhesion enhancement layer with a thickness of 2 - 10 μm after curing;

[0007] S2: Mesh pattern design: Input an irregular mesh pattern, the area ratio of the mesh unit is greater than 80%, and the line width of the mesh boundary is 1 - 5 μm, and optimize through the fractal algorithm to avoid diffraction of the periodic structure;

[0008] S3: Printing of the first layer of conductive mesh: Use copper-based conductive paste, and form the first layer of metal mesh by 3D printing layer by layer, the single-layer line width is 1 - 5 μm, and sinter and cure at 200 - 400 °C after printing;

[0009] S4: Grounding protection and covering layer: Perform local mask protection on the grounding end of the metal mesh, and coat an infrared transparent polymer on the non-protected area, and cure to form a dielectric covering layer with a thickness of 50 - 250 μm;

[0010] S5: Printing of the second-layer conductive grid: Repeat steps S2 - S3 to form a second-layer metal grid on the covering layer. The two-layer grid materials can be designed differently.

[0011] S6: Encapsulation: Encapsulate the overall structure through an infrared-transparent adhesive layer.

[0012] Preferably, the substrate is made of one of chalcogenide optical glass, modified PC, PS, PVC or PMMA resin, and its infrared light transmission band covers 2 - 20 μm.

[0013] Preferably, the infrared-transparent polymer is polyurethane acrylate, cycloolefin copolymer or fluorinated polyimide. The spin coating speed is 1000 - 3000 rpm, and the curing is carried out by ultraviolet light irradiation or thermal curing.

[0014] Preferably, the irregular grid pattern is generated by the Voronoi algorithm. The dispersion degree of the side length of the grid unit is 10% - 50%, the included angle between adjacent grids is 30° - 150°, and the density of the grid line intersection points is not more than 5 per mm 2 .

[0015] Preferably, the conductive paste includes the following components: conductive metal powder, copper powder with a particle size of 50 - 500 nm, accounting for 70 - 90 wt%; binder, thermosetting epoxy resin, accounting for 5 - 15 wt%; dispersant, polyvinylpyrrolidone, accounting for 1 - 5 wt%; solvent, ethylene glycol or terpineol, accounting for 4 - 6 wt%.

[0016] Preferably, the sintering and curing adopt a stepwise temperature rising process. In the first stage, keep the temperature at 80 - 120 °C for 10 - 30 min to remove the solvent; in the second stage, keep the temperature at 200 - 300 °C for 20 - 60 min to complete the resin crosslinking; in the third stage, keep the temperature at 350 - 400 °C for 5 - 15 min to achieve the melting and connection of metal particles.

[0017] Preferably, the material of the dielectric covering layer is silicone gel, and its dielectric constant is not more than 3.0.

[0018] Preferably, the material difference between the second-layer metal grid and the first-layer metal grid is that the first layer is silver-based paste and the second layer is copper-based paste.

[0019] Preferably, the infrared-transparent adhesive layer is a silica gel film filled with zinc sulfide. The refractive index of the infrared-transparent adhesive layer matches that of the substrate and the covering layer, and the surface roughness is not more than 50 nm.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The present invention selects a substrate with an infrared transmittance greater than 85%, uses an infrared transparent polymer as an adhesion enhancement layer, and optimizes the design of the metal grid, so that the material has a high transmittance in the 2-20 μm infrared band. In particular, the chalcogenide optical glass has a transmittance greater than 90% in the 8-12 μm infrared window, meeting the requirements of infrared stealth and light-transmitting observation.

[0022] 2. Through the design of a double-layer heterostructure metal grid, the present invention achieves electromagnetic shielding effectiveness in the full frequency band of 1-40 GHz, effectively overcoming the problems of low transmittance in the infrared band and narrow shielding frequency band of traditional ITO / FTO materials. By using a flexible resin substrate and an infrared transparent polymer, the flexibility and bending resistance of the material are improved, and at the same time, the brittleness problem of traditional ITO / FTO materials is avoided. Through the design of an irregular grid pattern and the optimization of the fractal algorithm, the diffraction effect caused by the regular periodic structure is avoided, the infrared imaging distortion is reduced, and the imaging quality is improved.

[0023] 3. By adjusting the grid line width and the proportion of the grid unit area, the present invention realizes maintaining good electrical conductivity continuity and low resistance while keeping a high transmittance, solving the problem that a single reduction in line width leads to an increase in resistance. The metal grid is prepared by 3D printing technology to improve production efficiency and product consistency. At the same time, the stepwise temperature rise curing process ensures solvent volatilization, resin cross-linking, and metal particle melting and connection, avoiding the substrate deformation caused by traditional high-temperature sintering. By locally masking and protecting the grounded end of the metal grid, the pollution of subsequent coating processes is avoided, ensuring the stability of the shielding effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the grounding protection and non-protection area of the present invention.

[0025] Figure 2 It is an architecture diagram of the double-layer conductive grid of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Please refer to Figures 1 to 2 , the present invention provides a technical solution: a preparation method of an infrared transparent broadband electromagnetic shielding material, including the following steps:

[0028] S1: Substrate surface treatment: Select a substrate with an infrared transmittance greater than 85%, spin-coat an infrared transparent polymer on the clean substrate surface, and form an adhesion enhancement layer with a thickness of 2 - 10 μm after curing.

[0029] The substrate is made of one of chalcogenide optical glass, modified PC, PS, PVC or PMMA resin, and its infrared transmission band covers 2 - 20 μm. The chalcogenide optical glass has an infrared transmittance greater than 90% in the 8 - 12 μm infrared window. The modified PC reduces infrared absorption by introducing fluorinated groups, breaking through the transmittance bottleneck of traditional ITO / FTO materials in the infrared band.

[0030] The infrared transparent polymer is polyurethane acrylate, cycloolefin copolymer or fluorinated polyimide. The spin-coating speed is 1000 - 3000 rpm, and the curing is carried out by ultraviolet light irradiation or thermal curing.

[0031] Increase the substrate surface dyne value to 40 - 60 dyn / cm to avoid the peeling problem of the subsequent metal grid caused by insufficient substrate surface energy, especially suitable for flexible resin substrates.

[0032] S2: Grid pattern design: Input an irregular grid pattern, the grid unit area ratio is greater than 80%, and the grid boundary line width is 1 - 5 μm. Optimize through the fractal algorithm to avoid periodic structure diffraction.

[0033] The irregular grid pattern is generated by the Voronoi algorithm. The Voronoi algorithm is a computational geometry algorithm used to divide a plane into several regions. Each region contains a set of given points called seed points, and the distance from any point in the region to the corresponding seed point of the region is closer than the distance to other seed points.

[0034] The grid unit side length dispersion is 10% - 50%, the adjacent grid included angle is 30° - 150°, and the grid line intersection point density is not more than 5 per mm 2 , breaking the periodic structure of traditional regular grids such as square waves and hexagons to avoid infrared imaging distortion.

[0035] By having a mesh area ratio of not less than 80% and a line width of 1 - 5 μm, an infrared transmittance of not less than 75% is achieved while maintaining electrical conductivity continuity, overcoming the contradiction of increased resistance caused by simply reducing the line width.

[0036] S3: Printing of the first layer of conductive grid: Use copper-based conductive paste, and form the first layer of metal grid by 3D printing layer by layer. The single-layer line width is 1 - 5 μm. After printing, sinter and cure at 200 - 400 °C to form a low-resistance metal grid, breaking through the shielding efficiency limit of a single thin layer.

[0037] The conductive paste comprises the following components: conductive metal powder, copper powder with a particle size of 50 - 500 nm, accounting for 70 - 90 wt%; binder, thermosetting epoxy resin, accounting for 5 - 15 wt%; dispersant, polyvinylpyrrolidone, accounting for 1 - 5 wt%; solvent, ethylene glycol or terpineol, accounting for 4 - 6 wt%.

[0038] The copper powder has a gradient particle size distribution, and the solvent evaporation rate matches the sintering temperature to avoid bubble defects.

[0039] The sintering and curing adopt a step - wise temperature - rising process. In the first stage, it is kept at 80 - 120 °C for 10 - 30 min to remove the solvent; in the second stage, it is kept at 200 - 300 °C for 20 - 60 min to complete the resin cross - linking; in the third stage, it is kept at 350 - 400 °C for 5 - 15 min to achieve the melting and connection of metal particles.

[0040] The step - wise temperature - rising curing ensures the solvent evaporation, resin cross - linking and the melting and connection of metal particles, and avoids the deformation of the substrate caused by traditional high - temperature sintering.

[0041] S4: Grounding protection and coating: Locally mask - protect the grounding end of the metal grid, and coat an infrared - transparent polymer on the non - protected area, and cure to form a dielectric coating layer with a thickness of 50 - 250 μm;

[0042] The material of the dielectric coating layer is silicone gel, its dielectric constant is not greater than 3.0, and nano - SiO2 is added to the silicone gel to adjust the dielectric constant and reduce the high - frequency loss; The doctor - blade coating method is adopted, and the gel leveling time is controlled to be 10 - 30 s to avoid uneven coating layer thickness.

[0043] Coating 50 - 250 μm of silicone gel expands the electromagnetic wave absorption frequency band through the dielectric - layer / metal - layer coupling effect, locally mask - protects the grounding end, and avoids pollution in subsequent coating processes.

[0044] S5: Printing the second - layer conductive grid: Repeat steps S2 - S3 to form the second - layer metal grid on the coating layer, and the two - layer grid materials can be designed differently;

[0045] The material difference between the second - layer metal grid and the first - layer metal grid is that the first layer is a silver - based paste and the second layer is a copper - based paste. 0.5 wt% of graphene is incorporated into the silver paste to improve the shielding efficiency in the high - frequency band; 1 wt% of Ni coating is added to the copper paste to prevent oxidation, and the 1 - 40 GHz full - band shielding efficiency is achieved through the double - layer heterostructure.

[0046] S6: Encapsulation: Encapsulate the overall structure through an infrared - transparent adhesive layer.

[0047] The infrared - transparent adhesive layer is a silica gel film filled with zinc sulfide. The refractive index of the infrared - transparent adhesive layer matches that of the substrate and the coating layer, and its surface roughness is not greater than 50 nm.

[0048] In summary, by selecting a substrate with an infrared transmittance greater than 85% and using an infrared transparent polymer as the adhesion enhancement layer, and optimizing the design of the metal grid, the material has a high transmittance in the 2-20 μm infrared band. In particular, the chalcogenide optical glass has a transmittance greater than 90% in the 8-12 μm infrared window, meeting the requirements of infrared stealth and light-transmitting observation. Through the design of a double-layer heterostructure metal grid, the electromagnetic shielding effectiveness in the full frequency band of 1-40 GHz is achieved, effectively overcoming the problems of low transmittance in the infrared band and narrow shielding frequency band of traditional ITO / FTO materials. By using a flexible resin substrate and an infrared transparent polymer, the flexibility and bending resistance of the material are improved, while avoiding the brittleness problem of traditional ITO / FTO materials. Through the design of an irregular grid pattern and the optimization of the fractal algorithm, the diffraction effect caused by the regular periodic structure is avoided, reducing the infrared imaging distortion and improving the imaging quality. By adjusting the grid line width and the proportion of the grid unit area, while maintaining a high transmittance, good electrical conductivity continuity and low resistance are maintained, solving the problem of increased resistance caused by simply reducing the line width. The metal grid is prepared by 3D printing technology, improving the production efficiency and product consistency. At the same time, the stepwise temperature rise curing process ensures the volatilization of the solvent, the cross-linking of the resin and the melting and connection of the metal particles, avoiding the deformation of the substrate caused by traditional high-temperature sintering. By locally masking and protecting the grounding end of the metal grid, the pollution of the subsequent coating process is avoided, ensuring the stability of the shielding effect.

[0049] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of an infrared transparent broadband electromagnetic shielding material, characterized in that: It includes the following steps: S1: Substrate surface treatment: Select a substrate with an infrared transmittance greater than 85%, spin-coat an infrared transparent polymer on the clean substrate surface, and form an adhesion enhancement layer with a thickness of 2 - 10 μm after curing; S2: Mesh pattern design: Input an irregular mesh pattern, the area ratio of the mesh unit is greater than 80%, and the width of the mesh boundary line is 1 - 5 μm. Optimize through the fractal algorithm to avoid periodic structure diffraction; S3: First-layer conductive mesh printing: Use copper-based conductive paste, and form the first-layer metal mesh by 3D printing layer by layer. The single-layer line width is 1 - 5 μm, and after printing, sinter and cure at 200 - 400 °C; S4: Grounding protection and covering layer: Locally mask and protect the grounding end of the metal mesh, and coat an infrared transparent polymer on the non-protected area, and cure to form a dielectric covering layer with a thickness of 50 - 250 μm; S5: Second-layer conductive mesh printing: Repeat steps S2 - S3 to form the second-layer metal mesh on the covering layer, and the two-layer mesh materials can be designed differently; S6: Encapsulation: Encapsulate the overall structure through an infrared transparent adhesive layer.

2. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The substrate is one of chalcogenide optical glass, modified PC, PS, PVC or PMMA resin, and its infrared transmission band covers 2 - 20 μm.

3. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The infrared transparent polymer is polyurethane acrylate, cycloolefin copolymer or fluorinated polyimide, the spin-coating speed is 1000 - 3000 rpm, and the curing is carried out by ultraviolet light irradiation or thermal curing.

4. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The irregular grid pattern is generated by the Voronoi algorithm, the dispersion of the side length of the grid cells is 10%-50%, the included angle between adjacent grids is 30°-150°, and the density of the grid line intersection points is not greater than 5 / mm 2 .

5. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The conductive paste includes the following components: conductive metal powder, copper powder with a particle size of 50 - 500 nm, accounting for 70 - 90 wt%; binder, thermosetting epoxy resin, accounting for 5 - 15 wt%; Dispersant, polyvinylpyrrolidone, accounting for 1 - 5 wt%; solvent, ethylene glycol or terpineol, accounting for 4 - 6 wt%.

6. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The sintering and curing adopts a stepwise heating process. In the first stage, keep the temperature at 80 - 120 °C for 10 - 30 min to remove the solvent; in the second stage, keep the temperature at 200 - 300 °C for 20 - 60 min to complete resin cross-linking; In the third stage, keep the temperature at 350 - 400 °C for 5 - 15 min to achieve the melting and connection of metal particles.

7. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, wherein: The material of the dielectric covering layer is silicone gel, and its dielectric constant is not greater than 3.

0.

8. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, wherein: The difference in materials between the second-layer metal mesh and the first-layer metal mesh is that the first layer is silver-based paste and the second layer is copper-based paste.

9. The preparation method of an infrared transparent broadband electromagnetic shielding material according to claim 1, characterized in that: The infrared transparent adhesive layer is a silicone film filled with zinc sulfide. The refractive index of the infrared transparent adhesive layer matches that of the substrate and the covering layer, and the surface roughness is not greater than 50 nm.

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