A shielding material and its preparation method

Abstract

This invention discloses a shielding material and its preparation method. A breakthrough in electromagnetic shielding performance is achieved through synergistic innovation in materials, structure, and process: In terms of material design, copper wire is used as the skeleton, with a graphene layer coated on its surface to form a "metal-carbon" composite fiber. At the structural and process level, an innovative braided structure is adopted, combined with a hot-pressing process, to effectively fill interlayer gaps, eliminate interface defects, and achieve a full-band (1-40GHz) shielding effectiveness SE≥100dB, fundamentally solving the electromagnetic leakage problem caused by poor interlayer contact in traditional metal braided materials.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding material preparation, specifically relating to a shielding material and its preparation method. Background Technology

[0002] In the field of electromagnetic shielding, metallic materials have always occupied a core position due to their fundamental physical advantages: Firstly, metals (such as copper and aluminum) possess ultra-high electrical conductivity (copper: 5.96 × 10⁻⁶). 7 The shielding efficiency (SE) of metals (copper melting point 1085℃, aluminum melting point 660℃) can reach 60-120 dB in a wide frequency range of 1-40 GHz through reflection loss mechanism, especially meeting the stringent attenuation requirements of 5G millimeter wave band (28 / 39 GHz) for high-frequency signals >80 dB. Secondly, the inherent thermal stability of metals (copper melting point 1085℃, aluminum melting point 660℃) allows them to maintain an SE value fluctuation of <3 dB in high-temperature scenarios such as automotive engine compartments (operating temperature 150-200℃) and spacecraft electronics compartments (extreme temperature -180 to 300℃), which is significantly better than conductive polymers (polypyrrole and other heat resistance limits <200℃). Thirdly, through alloy modification (such as tin-plated copper to resist sulfidation, 316L stainless steel to resist chloride ion corrosion) and surface functionalization treatment (nickel / silver plating), metal shielding materials can serve for more than 10 years in harsh environments with humidity >95%RH and salt spray concentration of 5%, effectively protecting precision components such as vehicle radar and shipborne communication equipment from electrochemical corrosion risks. These performance advantages together establish the irreplaceable role of metals in electromagnetic compatibility (EMC) engineering.

[0003] Traditional electromagnetic shielding materials (such as metal foil and conductive coatings) have significant drawbacks due to their reliance on a single metal layer structure. On the one hand, the contradiction between material thickness and shielding effectiveness (SE) is difficult to balance. For example, aluminum foil needs a thickness greater than 50 μm to achieve an SE value of approximately 60 dB, but at this thickness, the material's areal density is as high as 200-300 g / m², making it difficult to meet lightweight requirements. On the other hand, non-woven structures have poor resistance to mechanical fatigue; sprayed conductive layers will crack after 10,000 bends in a folding phone, resulting in an SE attenuation exceeding 15 dB. To overcome these performance bottlenecks, the industry has attempted to use metal wire braided structures. However, pure metal wires (such as copper wire and stainless steel wire) have high hardness (flexural modulus > 110 GPa) and poor ductility, requiring a processing tension of > 5 N / mm², far exceeding the 3 N / mm² tolerance limit of textile equipment. Furthermore, the interlayer peel strength after braiding is < 0.1 MPa, and the porosity is > 30%, making the multi-layer structure prone to slippage and causing electromagnetic wave leakage. These technical bottlenecks severely restrict the application of metal braiding in the field of flexible shielding. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a shielding material and its preparation method. A breakthrough in electromagnetic shielding performance is achieved through synergistic innovation in materials, structure, and process: In material design, copper wire is used as a skeleton, with a graphene layer coated on its surface to form a "metal-carbon" composite fiber. The high conductivity of graphene (sheet resistance <10Ω / sq) significantly suppresses the increase in contact resistance caused by copper wire oxidation, thus improving the overall shielding effectiveness of the composite fiber. Simultaneously, the flexible coating of graphene reduces the bending modulus of the metal fiber, allowing it to withstand knitting processes with a bending radius <1mm without breakage. In terms of structure and process, an innovative braided structure is adopted, combined with a hot-pressing process, to reduce porosity and repair graphene lattice defects, achieving a full-band (1-40GHz) shielding effectiveness SE≥100dB, fundamentally solving the electromagnetic leakage problem caused by poor interlayer contact in traditional metal braiding.

[0005] One of the technical solutions of this invention is to provide a method for preparing a shielding material, the specific steps of which are as follows: (1) Low-oxidation graphene, carbon nanotubes, nickel powder, and silver-plated copper powder are dried, then mixed evenly with polyether polyol and polyester polyol, and then processed by microfluidic technology to obtain slurry A; the oxidation degree of the low-oxidation graphene is 5-15%; (2) Mix slurry A with diisocyanate and react at 70-90℃ for 0.5-1 hour to obtain prepolymer B; (3) Mix diol, diamine, triamine and alkanolamine to obtain mixed chain extender C; (4) The chain extender C is mixed with the prepolymer B and reacted in a screw extruder at a reaction temperature of 180-230℃ to obtain polymer D; (5) Deform the 20-100μm diameter nickel-plated copper wire into spring-shaped or sawtooth-shaped wire E; the deformed nickel-plated copper wire has better elongation, which is helpful for subsequent weaving work; (6) By co-extruding through a die, polymer D is coated onto the surface of E to obtain wire F; (7) Weave 4-8 layers of warp-knitted fabric from the yarn F using a warp knitting machine; (8) High temperature hot pressing to obtain shielding material.

[0006] Furthermore, the mass ratio of the low-oxidation graphene, carbon nanotubes, nickel powder, and silver-plated copper powder is (0.2-1):(1.5-2.5):(8-10):(8-10), the mass ratio of polyether polyol to polyester polyol is (30-60):(40-70), and the mass ratio of low-oxidation graphene to polyether polyol is (0.2-1):(30-60).

[0007] Further, the mass ratio of slurry A to diisocyanate is (90-97):(3-10). Further, the mass ratio of the diol, diamine, triamine, and alkanolamine is (40-60):(30-50):(3-5):(1-2); Furthermore, the mass ratio of the chain extender C to the prepolymer B is 0.5-3.5%. Furthermore, the thickness of polymer D in the wire F is 10-500 μm.

[0008] The second technical solution of the present invention is to provide a shielding material prepared by the above method. The shielding effectiveness SE of this material is ≥100dB across the entire frequency band (1-40GHz).

[0009] The advantages of this invention are: 1. High shielding effectiveness: This material achieves excellent electromagnetic shielding performance through a metal skeleton reinforcement and synergistic shielding mechanism, while the co-extrusion coating process ensures uniform distribution of the shielding material. Regarding the synergistic shielding mechanism, the metallic conductive network (copper, nickel, silver) and carbon-based materials (graphene, carbon nanotubes) form a multi-scale conductive path, achieving broadband electromagnetic shielding through both reflection and absorption. The shielding effectiveness can reach 100dB, covering the requirements from high frequencies to microwave frequencies.

[0010] 2. Excellent Structural Stability: The multi-layered composite structure and mechanical reinforcement design of the material significantly enhance its mechanical stability. The screw extrusion reaction enhances the matrix's resistance to deformation. For mechanical reinforcement, spring-like / serrated metal wires provide elastic support, preventing interlayer delamination; the hot-pressing process further increases the sheet density and imparts high-temperature resistance to the material, while effectively filling interlayer gaps and eliminating interface defects; ensuring its long-term stability under complex working conditions. Attached Figure Description

[0011] Figure 1 The present invention relates to a serrated nickel-plated copper wire.

[0012] Figure 2 The present invention relates to a spring-shaped nickel-plated copper wire.

[0013] Figure 3 This is a physical image of Example 1. Detailed Implementation

[0014] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0015] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0016] The electromagnetic shielding performance described in this invention was tested using the following methods: a logarithmic antenna was used to measure the frequency range from 200 MHz to 1 GHz; a horn antenna was used to measure the frequency range from 1 GHz to 18 GHz; and the radiation was measured using an N5234A vector network. The analyzer records the data; the dynamic test range is measured using a power amplifier; and the final shielding effectiveness level (dB) is measured using frequency modulation technology.

[0017] The embodiments of the present invention will be further described below with reference to several examples.

[0018] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0019] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0020] Example 1 (1) After drying, 1 part by weight of low-oxidation graphene, 1.5 parts by weight of carbon nanotubes, 8 parts by weight of nickel powder and 8 parts by weight of silver-plated copper powder are mixed evenly with 30 parts by weight of polyether polyol and 40 parts by weight of polyester polyol, and then processed by micro-jet process to obtain slurry A. (2) Mix 90 parts by weight of slurry A with 3 parts by weight of diisocyanate and react at 70°C for 0.5 hours to obtain prepolymer B; (3) Mix 40 parts by weight of diol, 30 parts by weight of diamine, 3 parts by weight of triamine and 1 part by weight of alkanolamine to obtain mixed chain extender C; (4) Mix 0.5 parts by weight of chain extender C with 100 parts by weight of prepolymer B and react them in a screw extruder at a reaction temperature of 180°C to obtain polymer D; (5) The 20μm diameter nickel-plated copper wire is deformed into a sawtooth wire E; (6) By co-extruding through a die, polymer D is coated onto the surface of E to obtain wire F with a polymer D thickness of 10 μm; (7) Weave 4 layers of warp-knitted fabric from thread F using a warp knitting machine; (8) The shielding material is obtained by hot pressing at 240℃.

[0021] The shielding material achieved a performance of 100.7 dB.

[0022] Example 2 (1) After drying, 0.2 parts by weight of low-oxidation graphene, 2.5 parts by weight of carbon nanotubes, 10 parts by weight of nickel powder and 10 parts by weight of silver-plated copper powder are mixed evenly with 60 parts by weight of polyether polyol and 70 parts by weight of polyester polyol, and then processed by microfluidic process to obtain slurry A. (2) Mix 97 parts by weight of slurry A with 10 parts by weight of diisocyanate and react at 90°C for 1 hour to obtain prepolymer B; (3) Mix 60 parts by weight of diol, 50 parts by weight of diamine, 5 parts by weight of triamine and 2 parts by weight of alkanolamine to obtain mixed chain extender C; (4) Mix 35 parts by weight of chain extender C with 100 parts by weight of prepolymer B and react them in a screw extruder at a reaction temperature of 230°C to obtain polymer D; (5) Deform a 100μm diameter nickel-plated copper wire into a spring-shaped wire E; (6) By co-extruding through a die, polymer D is coated onto the surface of E to obtain wire F with a polymer D thickness of 500 μm; (7) Weave 8 layers of warp-knitted fabric from thread F using a warp knitting machine; (8) The shielding material is obtained by hot pressing at 300℃.

[0023] The obtained shielding material performance is 102.5dB.

[0024] Table 1 Shielding performance test of Example 2

[0025]

[0026] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a shielding material, characterized in that, It includes the following steps: (1) Low-oxidation graphene, carbon nanotubes, nickel powder, and silver-plated copper powder are dried, then mixed evenly with polyether polyol and polyester polyol, and then processed by microfluidic technology to obtain slurry A; the oxidation degree of the low-oxidation graphene is 5-15%; (2) Mix slurry A with diisocyanate and react at 70-90℃ for 0.5-1 hour to obtain prepolymer B; (3) Mix diol, diamine, triamine and alkanolamine to obtain mixed chain extender C; (4) The chain extender C is mixed with the prepolymer B and reacted in a screw extruder at a reaction temperature of 180-230℃ to obtain polymer D; (5) Deform nickel-plated copper wire with a diameter of 20-100μm into spring-shaped or sawtooth-shaped wire E; (6) By co-extruding through a die, polymer D is coated onto the surface of E to obtain wire F; (7) Weave 4-8 layers of warp-knitted fabric from the yarn F using a warp knitting machine; (8) Hot pressing at 240-300℃ to obtain shielding material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of low-oxidation graphene, carbon nanotubes, nickel powder, and silver-plated copper powder is (0.2-1):(1.5-2.5):(8-10):(8-10), the mass ratio of polyether polyol to polyester polyol is (30-60):(40-70), and the mass ratio of low-oxidation graphene to polyether polyol is (0.2-1):(30-60).

3. The preparation method according to claim 1, characterized in that, The mass ratio of slurry A to diisocyanate is (90-97):(3-10).

4. The preparation method according to claim 1, characterized in that, The mass ratio of the diol, diamine, triamine, and alkanolamine is (40-60):(30-50):(3-5):(1-2).

5. The preparation method according to claim 1, characterized in that, The mass ratio of the chain extender C to the prepolymer B is (0.5-3.5):

100.

6. The preparation method according to claim 1, characterized in that, The thickness of polymer D in the wire F is 10-500 μm.

7. A shielding material prepared by the preparation method according to any one of claims 1-6.

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