Multi-layer epoxy composite coating capable of preventing electromagnetic radiation

Abstract

The invention discloses an anti-electromagnetic radiation multi-layer epoxy composite coating which is arranged from a protected object side to an electromagnetic radiation source side. The composite material sequentially comprises a first layer of high pure copper composite material layer, a second layer of conductive fiber cloth and cobalt powder composite material layer, a third layer of cobalt alloy powder composite material layer, a fourth layer of cobalt alloy powder composite material layer, a fifth layer of carbon nanotube composite material layer, a sixth layer of carbon nanotube composite material layer and a seventh layer of carbon nanotube composite material layer, the eighth layer is a carbon nanotube composite material layer; the ninth layer is a dielectric material layer; each layer of material takes a polymer dielectric material as a matrix; the conductivity, wave impedance, absorption and scattering characteristics of each layer are gradually reduced from the protection object side to the electromagnetic radiation source side. The multilayer epoxy composite coating provided by the invention has a relatively wide electromagnetic protection frequency range, and the electromagnetic radiation shielding effectiveness is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic protection, and particularly to a multi-layer composite coating for electromagnetic radiation (EMR) protection made of polymers with different compositions. Background Art

[0002] Radio products include radio transmitting devices, radio receiving devices, digital device system components, antennas, and deep space communication systems, as well as radio equipment in industries such as the aviation industry and the instrumentation manufacturing industry. The electromagnetic radiation generated by electronic devices is becoming increasingly serious. Electromagnetic radiation poses potential hazards to human health. Long-term exposure to a high electromagnetic radiation environment may increase the risk of certain health problems. Electromagnetic radiation can also interfere with the normal operation of electronic devices, resulting in problems such as signal distortion, increased error rate, and interference with wireless communication devices. Especially in the high-frequency band, the interference of electromagnetic radiation on devices is more significant. Therefore, using an electromagnetic radiation protection coating can reduce the risk to human health and ensure the normal operation of electronic devices.

[0003] Ukrainian Patent UA114444 (U). IPC: C09D5 / 30 (2006.01), C09D131 / 00 (2017.01) discloses a composite material for electromagnetic radiation protection, which is made of a polymer-based composite material containing dispersed carbon fillers, colloidal graphite, and dispersed transition metal oxides. In addition, this material has sufficient adhesive strength and moisture resistance, and is low in cost and easy to manufacture. However, the disadvantage of this coating is its low protection ability against electromagnetic waves (EMV) in the frequency range of 30 MHz to 30 GHz and low shielding efficiency. When the frequency reaches the industrial frequency of 5 - 70 kHz, the electromagnetic radiation shielding efficiency is further reduced. This disadvantage greatly limits the use of the coating in a wide range of electromagnetic radiation frequencies.

[0004] Ukrainian Patent UA39729 (A). 7 / H01Q17 / 00 discloses a shielding coating made of a wire fabric containing components for absorbing and dissipating EMR. The wire fabric contains carbon black powder, graphite, ferrite, metal, or a mixture thereof, which are uniformly distributed in the material in the form of a wire fabric. The ratio of the EMR-absorbing and -scattering material to the dielectric material in the wire fabric is 1:1, and the proportion of the EMR-absorbing and -scattering electromagnetic wave material can also be 70%. The disadvantage of this shielding coating is its low protection against electromagnetic radiation in the radar range. In the frequency range of 1 - 100 kHz, this coating cannot provide effective protection either.

[0005] Ukrainian Patent UA93293 (C2), IPC: (January 2017) H05K9 / 00 (2017.01), H01Q17 / 00. An electromagnetic wave absorbing coating is disclosed, which is composed of multi-layer materials with different electrical properties. These layers are made of conductive and dielectric materials with a thickness less than the skin depth. The conductivity and thickness of each layer decrease as the distance from the product surface increases, and the layer closest to the product surface has the highest conductivity. The disadvantage of this coating is its relatively low level of electromagnetic radiation protection in the frequency range of 1 - 100 kHz. At the same time, this coating will produce an electromagnetic wave reflection effect at ultra-high frequency radiation frequencies, thus significantly reducing the shielding characteristics in a wide frequency range of electromagnetic radiation.

[0006] Therefore, it is necessary to develop a radiation protection coating with good shielding characteristics in a wide frequency range. Summary of the Invention

[0007] The main objective of the present invention is to develop a multi-layer composite coating composed of polymer layers with different electrical properties. These coatings contain dispersed fillers, enabling them to reduce the impact of electromagnetic radiation on the human body and electronic devices in a wider frequency range. It is characterized in that a multi-layer coating is formed, and each polymer layer exhibits different electrical properties due to the different functionalities of the additives. This multi-layer composite coating can attenuate electromagnetic radiation by 25 - 30 dB, effectively reducing the impact of electromagnetic radiation on the human body and the performance of radio products, such as radio transmitting and receiving devices, components of digital device systems and antennas, as well as radio equipment in industries such as deep space communication, the aviation industry, and instrument manufacturing.

[0008] The technical solution adopted by the present invention is:

[0009] A multi-layer epoxy composite coating for preventing electromagnetic radiation, from the side of the protected object to the side of the electromagnetic radiation source, successively includes a first layer of high-purity copper composite material layer, a second layer of conductive fiber cloth and cobalt powder composite material layer, a third layer of cobalt alloy powder composite material layer, a fourth layer of cobalt alloy powder composite material layer, a fifth layer of carbon nanotube composite material layer, a sixth layer of carbon nanotube composite material layer, a seventh layer of carbon nanotube composite material layer, an eighth layer of carbon nanotube composite material layer, and a ninth layer of dielectric material layer; each layer of material is based on a polymer dielectric material; from the side of the protected object to the side of the electromagnetic radiation source, the conductivity, wave impedance, absorption, and scattering characteristics of each layer gradually decrease. The ninth layer of dielectric material layer close to the electromagnetic radiation source is made of a dielectric material, and its wave impedance is equal to or close to the wave impedance of the external environment.

[0010] Furthermore, each layer of the multi-layer epoxy composite coating is based on a polymer dielectric material, and the matrix includes epoxy resin and polyethylene polyamine, and the mass ratio of epoxy resin to polyethylene polyamine is 95 - 100:10 - 12.

[0011] The epoxy resin is preferably polypropylene oxide bisphenol A resin, such as CYD128, SYD128, ED-20, etc.

[0012] Furthermore, the first high-purity copper composite layer comprises a matrix and high-purity copper powder; the thickness of the first high-purity copper composite layer is 150 - 200 μm.

[0013] Furthermore, the mass ratio of the matrix to the high-purity copper powder is 100:100 - 105.

[0014] When the weight ratio of the high-purity copper powder is greater than 105, due to the limitation of the coating preparation technology, pores will be generated in the composite material, which will have a negative impact on the performance of the entire coating.

[0015] The thickness of the first high-purity copper composite layer is 150 - 200 μm. When the thickness is less than 150 μm, the continuity of the filler in this layer cannot be guaranteed. When the thickness is greater than 200 μm, it will increase the weight and total thickness of the coating.

[0016] The particle size of the high-purity copper powder is 1.5 - 2.0 μm. When the particle size is less than 1.5 μm, the copper powder will agglomerate in the epoxy resin; when the particle size is greater than 2.0 μm, the copper powder will cause local heating due to the induced current.

[0017] The second conductive fiber cloth and cobalt powder composite layer is formed by impregnating the conductive fiber cloth in the cobalt powder composite material, and the cobalt powder composite material comprises a matrix and cobalt powder;

[0018] The particle size of the cobalt powder is generally 1 - 2 μm.

[0019] Furthermore, the mass ratio of the matrix to the cobalt powder is 100:100 - 115; that is, 100 - 115 parts by weight of cobalt powder are added as the impregnating material for every 100 parts by weight of the matrix. When the weight ratio of the cobalt powder is less than 100, sufficient shielding effect cannot be provided. When the weight parts of the cobalt powder are greater than 115, the distribution of the cobalt powder in the composite material will be uneven, and it cannot ensure a good impregnating effect for the carbon fiber cloth.

[0020] The thickness of the conductive fiber cloth and cobalt powder composite layer is 1300 - 1350 μm.

[0021] When the thickness is less than 1300 μm, the impregnated composite material may be discontinuous, and it cannot ensure the formation of a continuous and uniform coating according to the given composition ratio; when the thickness is greater than 1350 μm, it will cause uneven coating thickness, weight increase, and will not improve its shielding efficiency.

[0022] The conductive fiber cloth is generally a conductive carbon fiber cloth, and more preferably a copper plating layer is provided on the surface of the carbon fiber cloth, or a copper plating layer and a nickel plating layer are sequentially provided on the surface of the carbon fiber cloth.

[0023] Preferably, the copper plating layer is disposed on the surface of the carbon fiber cloth facing the electromagnetic radiation source side, that is, the copper plating layer is disposed on the surface of the carbon fiber cloth facing the third cobalt alloy powder composite layer. No copper plating layer or nickel plating layer is provided on the surface of the carbon fiber cloth facing the protected object side or facing the second conductive fiber cloth and cobalt powder composite layer.

[0024] Further, the conductive fiber cloth is preferably a carbon fiber cloth with a copper plating layer and a nickel plating layer sequentially disposed on the surface facing the electromagnetic radiation source side.

[0025] A copper plating layer with a thickness of 800-900 μm is provided on the surface of the carbon fiber cloth. When the thickness of the copper plating layer is less than 800 μm, the shielding effect will decrease sharply. When the thickness exceeds 900 μm, it will increase the weight of the second layer and the plating thickness will be uneven. In order to prevent copper oxidation, a nickel plating layer with a thickness of 1-3 μm is preferably provided on the surface of the copper plating layer. When the thickness of the nickel plating layer is less than 1 μm, effective anti-oxidation protection cannot be provided due to insufficient continuity. When the thickness of the nickel plating layer exceeds 3 μm, it will not only not improve the protection effect, but also increase the immersion time of the plating layer, resulting in additional energy consumption.

[0026] The third cobalt alloy powder composite layer and the fourth cobalt alloy powder composite layer respectively include a matrix and cobalt alloy powder. The thickness of the third cobalt alloy powder composite layer is 200-230 μm; the thickness of the fourth cobalt alloy powder composite layer is 150-200 μm.

[0027] The composition of the cobalt alloy powder is 65-72% Co, 10-15% Fe, 5-10% Si, 5-10% Ni, 2-5% C;

[0028] In a preferred embodiment, the composition of the cobalt alloy powder is 71.2% Co, 12.2% Fe, 7.3% Si, 6.1% Ni, 3.2% C.

[0029] The particle size of the cobalt alloy powder is 15-20 μm. When the particle size is less than 15 μm, the processing conditions will deteriorate and a uniformly distributed coating cannot be formed; when the particle size is greater than 20 μm, the temperature will rise under the action of electromagnetic radiation, thereby reducing the reliability of the entire coating.

[0030] In the third cobalt alloy powder composite layer, the mass ratio of the matrix to the cobalt alloy powder is 100:100-105. When the amount of the cobalt alloy powder is less than 100, the electromagnetic wave scattering will be reduced; when it is greater than 105, the uniformity of the coating will deteriorate.

[0031] The thickness of the third cobalt alloy powder composite layer is 200 - 230 μm. If the thickness is less than 200 μm, it cannot ensure sufficient absorption of electromagnetic waves in this layer; if the thickness exceeds 230 μm, the layer thickness will be uneven and the electromagnetic radiation shielding effect cannot be improved.

[0032] In the fourth cobalt alloy powder composite layer, the mass ratio of the matrix to the cobalt alloy powder is 100:50 - 52. When the amount of cobalt alloy powder is less than 50, the penetration of electromagnetic radiation through this layer will be reduced; when the amount is greater than 52, the reflection of electromagnetic waves will increase, thus reducing the penetration of electromagnetic waves through this layer.

[0033] The thickness of the fourth cobalt alloy powder composite layer is 150 - 200 μm. When the thickness is less than 150 μm, the absorption effect of the electromagnetic field will be reduced; when the thickness exceeds 200 μm, the reflection of electromagnetic waves will increase, which is not conducive to electromagnetic shielding.

[0034] The fifth carbon nanotube composite layer, the sixth carbon nanotube composite layer, the seventh carbon nanotube composite layer, and the eighth carbon nanotube composite layer each include a matrix and carbon nanotubes. The thickness of each layer is different and the weight ratio of the carbon nanotubes as fillers is different.

[0035] The wave impedance of the fifth carbon nanotube composite layer, the sixth carbon nanotube composite layer, the seventh carbon nanotube composite layer, and the eighth carbon nanotube composite layer gradually decreases in turn until the ninth layer is a dielectric coating.

[0036] The thickness of the fifth carbon nanotube composite layer is 200 - 230 μm. When the layer thickness is less than 200 μm, the scattering of electromagnetic radiation will be significantly reduced; when it exceeds 230 μm, the non-uniformity of the thickness will increase, thus enhancing the reflection of electromagnetic waves, which is not conducive to anti-electromagnetic radiation.

[0037] In the fifth carbon nanotube composite layer, the mass ratio of the matrix to the carbon nanotubes is 100:8 - 10. When the weight ratio of the carbon nanotubes is less than 8, the absorption and scattering of electromagnetic radiation will be reduced; when the weight ratio of the carbon nanotubes is greater than 10, the uniformity of the coating will deteriorate.

[0038] Preferably, ethanol can also be added to the fifth carbon nanotube composite layer, and the mass ratio of the matrix, carbon nanotubes, and ethanol is 100:8 - 10:8 - 12. When the weight ratio of ethanol is less than 8 parts, the compatibility of the components in the coating deteriorates and pores are likely to form in the coating. When the weight ratio of ethanol is greater than 12 parts, the uniformity in the coating thickness direction deteriorates, and the absorption and dissipation of electromagnetic radiation will be reduced.

[0039] The thickness of the sixth carbon nanotube composite layer is 200 - 230 μm. When the layer thickness is less than 200 μm, the absorption of electromagnetic radiation by this layer will be reduced; while a thickness exceeding 230 μm will deteriorate the thickness uniformity, thus increasing the effect of electromagnetic wave reflection.

[0040] In the sixth carbon nanotube composite layer, the mass ratio of the matrix to the carbon nanotubes is 100:6 - 8. Carbon nanotube fillers with a weight ratio less than 6 will increase the possibility of electromagnetic radiation penetration and reduce the absorption and scattering of electromagnetic waves. Carbon nanotube fillers with a weight ratio greater than 8 will deteriorate the processability of the composite due to the formation of pores.

[0041] The thickness of the seventh carbon nanotube composite layer is 150 - 200 μm. When the thickness is less than 150 μm, the absorption of electromagnetic radiation by this layer will be reduced; when the thickness exceeds 200 μm, the thickness non-uniformity will increase, making the electromagnetic wave reflection effect worse.

[0042] In the seventh carbon nanotube composite layer, the mass ratio of the matrix to the carbon nanotubes is 100:2.5 - 3. Carbon nanotube fillers with a weight ratio less than 2.5 will increase the possibility of electromagnetic radiation penetration and reduce the absorption and scattering of electromagnetic waves. Carbon nanotube fillers with a weight ratio exceeding 3 will affect the synchronization of the wave impedance and resistance with the sixth layer. It should be noted that within the specific weight ratio range of 2.5 - 3.0, a clear boundary can be ensured between the sixth and seventh layers, which will contribute to the scattering of electromagnetic radiation.

[0043] The thickness of the eighth carbon nanotube composite layer is 150 - 200 μm. When the thickness is less than 150 μm, the absorption of electromagnetic radiation will be reduced; when the thickness exceeds 200 μm, the thickness non-uniformity will increase, making the electromagnetic wave reflection effect worse.

[0044] In the eighth carbon nanotube composite layer, the mass ratio of the matrix to the carbon nanotubes is 100:1 - 1.3. Carbon nanotube fillers with a weight ratio less than 1 will increase the possibility of electromagnetic radiation penetration and reduce the absorption and scattering of electromagnetic waves. Carbon nanotube fillers with a weight ratio exceeding 1.3 will affect the synchronization of the wave impedance and resistance with the seventh layer. It should be noted that within the specific weight ratio range of 1 - 1.3, a clear boundary can be ensured between the seventh and eighth layers, which will contribute to the absorption and scattering of electromagnetic radiation.

[0045] The ninth dielectric material layer includes a matrix, and the matrix includes epoxy resin and polyethylene polyamine, and the mass ratio of epoxy resin to polyethylene polyamine is 95 - 100:10 - 12.

[0046] The thickness of the ninth dielectric material layer is 120 - 150 μm. Due to the interaction between the electromagnetic radiation and the eighth layer, a ninth dielectric material layer with a thickness less than 120 μm will not be able to achieve an equal wave impedance with the external environment. When its thickness is greater than 150 μm, it will not significantly improve the consistency of the wave impedance with the external environment.

[0047] In the present invention, the multi-layer epoxy composite coating comprises a dielectric layer, a conductive layer, and coatings with different electrical properties. To expand the frequency range of the protected electromagnetic radiation, different functional additives are contained in different coatings. Since the interaction mechanism of each layer of material with the EMR is different, the shielding function in a wider frequency range will be significantly improved.

[0048] The present invention also provides the application of the multi-layer epoxy composite coating for electromagnetic radiation protection in electromagnetic shielding protection.

[0049] The present invention also provides the application of the multi-layer epoxy composite coating for electromagnetic radiation protection in the frequency range of 1 kHz - 3000 MHz in electromagnetic shielding protection.

[0050] The multi-layer epoxy composite coating of the present invention has good electromagnetic shielding protection effect in the frequency range of 1 kHz - 3000 MHz.

[0051] Each layer of the multi-layer epoxy composite coating has different electromagnetic characteristics. From the side of the protected object to the side of the electromagnetic radiation source, the conductivity, absorption, and scattering characteristics of the coating decrease, so that electromagnetic waves are scattered and absorbed when passing through the interlayer interface.

[0052] In each layer, a polymer dielectric material is used as the matrix, and the main component in the matrix is epoxy resin. Poly(propylene oxide) bisphenol A resin has excellent mechanical, corrosion-resistant, and adhesion properties, so it is used to prepare various functional coatings, such as electromagnetic radiation protection materials. In the multi-layer epoxy composite coating, poly(propylene oxide) bisphenol A resin is used as a binder, and polyethylene polyamine is added to the binder as the matrix of each layer of shielding material, which can be easily coated on complex surfaces to form a coating.

[0053] In the multi-layer epoxy composite coating, the surface layer close to the electromagnetic radiation source is made of a dielectric material, and its wave impedance is equal to or close to the wave impedance of the external environment (referring to the environment between the electromagnetic radiation source and the coating surface), which can significantly reduce the reflection of electromagnetic waves on the material surface and create conditions for the absorption and scattering of electromagnetic waves when interacting with the subsequent coating (the coating close to the protected object).

[0054] In each layer of the materials of the present invention, the weight ratio of the filler needs to be within a specified range; otherwise, electromagnetic waves cannot achieve shielding through mutual cancellation in each layer. The selected coating material has good absorption characteristics, which can significantly reduce the integral effect of its reflection. The coating design principle proposed by the present invention provides shielding by absorbing electromagnetic radiation energy. In the proposed multi-layer coating, due to the different selective absorption characteristics of each layer of material with respect to the environment, the integral effect of its reflection is significantly reduced. The design principle of this product is to ensure the shielding effect by absorbing electromagnetic radiation energy. In the proposed multi-layer coating, the absorption of electromagnetic waves occurs due to multiple re-reflections of electromagnetic waves between different layers inside the coating, and the electromagnetic waves are absorbed due to the repeated reflections of electromagnetic waves between different layers inside the coating. It should be noted that the energy absorption of electromagnetic radiation occurs due to dielectric, magnetic, and conduction losses, thereby significantly improving the shielding efficiency. The present invention can have better electromagnetic shielding function in a wider frequency range.

[0055] The multi-layer epoxy composite coating provided by the present invention broadens the electromagnetic protection frequency range and improves the electromagnetic radiation shielding efficiency at the same time. The multi-layer epoxy composite coating designed by the present invention takes into account the matching of the shielding surface wave impedance with the wave impedance of the electromagnetic radiation propagation environment. The matching of the absorption characteristics of each layer of material (including the surface layer in contact with the surrounding environment) in the coating significantly improves the shielding energy efficiency of the product. Brief Description of the Drawings

[0056] The multi-layer epoxy composite coating of the present invention and its shielding efficiency test principle are described by the following drawings and schematic diagrams.

[0057] Figure 1 is a schematic structural diagram of the multi-layer epoxy composite coating, Figure 1 in which, 1 - the first high-purity copper composite material layer; 2 - the second conductive fiber cloth and cobalt powder composite material layer; 3 - the third cobalt alloy powder composite material layer; 4 - the fourth cobalt alloy powder composite material layer; 5 - the fifth carbon nanotube composite material layer; 6 - the sixth carbon nanotube composite material layer; 7 - the seventh carbon nanotube composite material layer; 8 - the eighth carbon nanotube composite material layer; 9 - the ninth dielectric material layer.

[0058] Figure 2 is a flange coaxial method test device for testing the shielding efficiency in the frequency range of 1 - 70 kHz, Figure 2 in which, 1 - DX-160 gaussmeter; 2 - signal amplifier; 3 - signal generator; 4 - oscilloscope; 5 - Helmholtz coil.

[0059] Figure 3 is a photo of the Helmholtz coil and a schematic diagram of the magnetic field line distribution, where figure (b) is the photo of the Helmholtz coil, and figure (a) is the schematic diagram of the magnetic field line distribution in the Helmholtz coil of figure (b).

[0060] Figure 4 Photos of the 0.1 mm cobalt plate reference sample and the detection experiment photos, where Figure (a) is the photo of the 0.1 mm cobalt plate reference sample; Figure (b) is the photo of the placement position of the reference sample in Figure (a) in the Helmholtz coil.

[0061] Figure 5 Photo of the probe placed in the Helmholtz coil.

[0062] Figure 6 Schematic diagram of the magnetic field change of the shielding coating samples of different sizes.

[0063] Figure 7 Schematic diagram of the signal generator / spectrum analyzer test system, where 1 - signal generator; 2 - attenuator; 3 - sample; 4 - flange coaxial device; 5 - spectrum analyzer.

[0064] Figure 8 Test sample for testing the shielding effectiveness of the coating, where Figure (a) is the reference sample; Figure (b) is the loaded sample.

[0065] Figure 9 Test configuration diagram of the shielding chamber method (0.6 m window). In the figure, 1 - transmitting device; 2 - transmitting antenna; 3 - test sample; 4 - receiving antenna; 5 - receiving device. Specific implementation mode

[0066] The technical solution of the present invention will be further described below with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0067] Embodiment 1

[0068] Starting from the layer close to the protected object, the components, thickness and weight ratio of each layer in the multi-layer epoxy composite coating are as shown in Table 1 below:

[0069] Table 1 Thickness and weight component ratio of the multi-layer epoxy composite coating

[0070]

[0071] The matrix is a mixture of CYD128 and polyethylene polyamine with a mass ratio of 100:11.

[0072] The specific experimental steps are as follows:

[0073] The coating test in the first stage ( Figures 1-7 ) is carried out in the frequency range of 1 - 70 kHz. In order to test the effect of the protective coating ( Figure 1 ) in shielding electromagnetic radiation, a uniform magnetic field needs to be created. In order to obtain a magnetic field of up to 0.1 T, coils with current are usually used. A solenoid or a Helmholtz coil can obtain a highly uniform magnetic field (Figure 2 )。The Helmholtz coil system consists of two identical coils fixed coaxially and connected in series, and the distance between their centers is equal to their average radius ( Figure 3 ). The region of quasi-uniform electromagnetic field is located inside the coils ( Figure 3 、 Figure 4 Figure (b)). The placement of the probe for measuring the electromagnetic field strength and the reference sample of a 0.1-mm-thick cobalt plate in the Helmholtz coils are shown respectively as Figure 5 、 Figure 4 shown.

[0074] Using a 0.1-mm-thick cobalt plate shielding material as the reference sample, the unit for measuring the magnetic field strength is Gs

[0075] (Gauss), the measurement frequency range is 1 - 70 kHz, and the measurement interval is 5 kHz. The schematic diagram, the placement of the sample, and the test schematic diagram are shown as Figures 1-6 shown. The test results are shown in Table 2.

[0076] G1 - The magnetic field strength without the cobalt sample is 15 Gs.

[0077] G2 - The magnetic field strength when the cobalt sample is installed

[0078] Table 2 Test results of the magnetic field strength without the 0.1-mm cobalt plate sample and with the 0.1-mm cobalt plate sample placed.

[0079]

[0080] Using carbon fiber cloth samples with copper plating layers of different thicknesses on the surface for testing the magnetic field strength, the unit for measuring the magnetic field strength is Gs. The measurement frequency range is 1 - 60 kHz, and the measurement intervals are 1 kHz and 5 kHz.

[0081] The original value of the electromagnetic field strength is 20 Gs. Only one side of the carbon fiber cloth is copper-plated, and the copper-plated surface faces the radiation source, while the surface without the copper plating layer faces the protected object side.

[0082] Table 3 shows the test results of the magnetic field strength of copper-plated carbon fiber cloth samples with different thicknesses. No.1 - The copper plating layer thickness is 0.7 mm, the resistance is 0.6 - 0.7 Ohm, and it needs to be plated in the electrolyte for 6 h. No.2 - The copper plating layer thickness is 0.8 mm, the resistance is 0.1 Ohm, and it needs to be plated in the electrolyte for 15 h. No.3 - The copper thickness is 0.8 - 0.9 mm

[0083] (The plating is not very uniform, and the thickness distribution is about 0.8 - 0.9 mm), the resistance is 0.1 Ohm, and it needs to be plated in the electrolyte for 20 h.

[0084] Table 3 Test results of the magnetic field strength of copper-plated carbon fiber cloth samples.

[0085]

[0086] As can be seen from the results in Table 3, the copper plating layer with a thickness of 800 - 900 μm has a good shielding effect. When the thickness of the copper plating layer is less than 800 μm (such as in Experiment No. 1), the shielding effect will decrease sharply. When the thickness exceeds 900 μm, it will increase the weight of the second layer and the plating thickness will also be uneven.

[0087] To prevent copper oxidation, the present invention preferably further provides a nickel plating layer with a thickness of 1 - 3 μm on the surface of the copper plating layer. When the thickness of the nickel plating layer is less than 1 μm, effective anti-oxidation protection cannot be provided due to insufficient continuity. When the thickness of the nickel plating layer exceeds 3 μm, it will not only not improve the protection effect, but also increase the immersion time of the plating layer, resulting in additional energy consumption.

[0088] Thus, a composite coating was developed based on the proposed copper-nickel plated conductive carbon fiber cloth. The components, thicknesses, and weight ratios of each layer in the multi-layer epoxy composite coating are shown in Table 1. Next, the electromagnetic radiation shielding coating prepared above was tested for shielding effectiveness according to the ASMT D4935-18 standard (national standard GB / T30142-2013).

[0089] The shielding effectiveness of the multi-layer epoxy composite coating of the invention was tested using a test device developed by the Paton Welding Institute of the National Academy of Sciences of Ukraine. The measurement intervals are 5 kHz in the frequency range of 1 - 70 kHz, and 30 MHz, 80 MHz, 150 MHz, 300 MHz, 450 MHz, 915 MHz, 1000 MHz, 1500 MHz, 1800 MHz, 2450 MHz, 3000 MHz respectively in the frequency range of 30 - 3000 MHz.

[0090] In the measurement within each electromagnetic radiation frequency range, the distance between the antenna and the shielding material is: 0.3 m (10 - 30 kHz), 0.6 m (1 - 18 GHz), 1.0 m (30 - 1000 MHz), 0.3 m (18 - 40 GHz). It should be noted that the tested frequency range covers all types of antennas.

[0091] The test results of electromagnetic shielding effectiveness in the frequency range of 1 - 70 kHz show that: when using a 0.1 mm cobalt plate reference sample, a monotonic increase in shielding effectiveness up to 2.30 dB can be observed; when using a carbon fiber cloth without a copper plating layer, there is no increase in shielding effectiveness; while when using conductive carbon fibers coated with a copper plating layer with a thickness of 0.8 - 0.9 mm on the surface, the shielding effectiveness is improved. The electromagnetic field strength after shielding decreases monotonically and attenuates to 7.63 dB at 70 kHz. In the multi-layer epoxy composite coating of the present application, the second layer of conductive fiber cloth and cobalt powder composite material layer contains conductive carbon fibers coated with a copper plating layer with a thickness of 0.8 - 0.9 mm on the surface. Therefore, it can be expected that the multi-layer epoxy composite coating has better or at least comparable electromagnetic shielding effectiveness in the frequency range of 1 - 70 kHz.

[0092] The multi-layer epoxy composite coating also has excellent shielding effectiveness in the relatively high frequency range of 30 - 3000 MHz. Table 4 shows the test results of the composite coating according to the GB / T 30142 - 2013 standard, and the results show that the shielding effectiveness of the multi-layer epoxy composite coating has increased several times.

[0093] Table 4 Test results of electromagnetic shielding effectiveness (SE) in the frequency range of 30 - 3000 MHz

[0094]

[0095] The multi-layer coating developed in the present invention significantly reduces the integral effect of its reflection due to the different selective absorption characteristics of its various layer materials with respect to the environment. The design principle of this product is to ensure the shielding effect by absorbing electromagnetic radiation energy. In the proposed multi-layer coating, the absorption of electromagnetic waves occurs due to multiple re-reflections of electromagnetic waves between different layers inside the coating. The absorption of electromagnetic radiation source energy occurs due to dielectric, magnetic, and conduction losses, which significantly improves the shielding efficiency.

[0096] The design of the multi-layer shielding coating of the present invention takes into account the matching of the shielding surface wave impedance with the wave impedance of the electromagnetic radiation propagation environment. The matching of the absorption characteristics of the materials of each layer in the coating (including the layer in contact with the surrounding environment) significantly improves the shielding characteristics of the product. The developed coating includes a copper-nickel plated conductive carbon fiber cloth. The nickel layer on the surface of the copper plating layer has two functions: nickel increases the reflection within the material of this layer and prevents the oxidation of copper. The materials of different layers contain nano-sized components and fillers as well as high-purity particles close to the nano-size, which are used to study the interaction with electromagnetic radiation. The frequency range is extended by alternating layers of electromagnetic radiation absorption, scattering, and reflection. Using a dielectric material to make the wave resistance value of the surface layer close to the wave resistance value of the external environment will significantly reduce the reflection of the entire coating to electromagnetic radiation. The absorption and dissipation of electromagnetic energy are achieved at the boundaries between layers with different reflection coefficients. It should be noted that the interaction between electromagnetic energy and dispersed filler particles with high conductivity is observed, which further expands the frequency range of electromagnetic radiation shielding.

Claims

1. A multi-layer epoxy composite coating for anti-electromagnetic radiation, characterized in that The multilayer epoxy composite coating includes, from the side of the protected object to the side of the electromagnetic radiation source, a first layer of high-purity copper composite material layer, a second layer of conductive fiber cloth and cobalt powder composite material layer, a third layer of cobalt alloy powder composite material layer, a fourth layer of cobalt alloy powder composite material layer, a fifth layer of carbon nanotube composite material layer, a sixth layer of carbon nanotube composite material layer, a seventh layer of carbon nanotube composite material layer, an eighth layer of carbon nanotube composite material layer, and a ninth layer of dielectric material layer in sequence; each layer of material is based on a polymer dielectric material; from the side of the protected object to the side of the electromagnetic radiation source, the conductivity, wave impedance, absorption and scattering characteristics of each layer gradually decrease.

2. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 1, characterized in that Each layer of the multi-layer epoxy composite coating is based on a polymer dielectric material, the base material comprises epoxy resin and polyethylene polyamine, and the mass ratio of epoxy resin to polyethylene polyamine is 95-100:10-12.

3. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 1, characterized in that The first layer of high-purity copper composite material layer includes a matrix and high-purity copper powder; the thickness of the first layer of high-purity copper composite material layer is 150-200 μm; the mass ratio of the matrix and the high-purity copper powder is 100:100-105; the particle size of the high-purity copper powder is 1.5-2.0 μm.

4. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 1, characterized in that The second layer of conductive fiber cloth and cobalt powder composite material is formed by dipping the conductive fiber cloth into the cobalt powder composite material, wherein the cobalt powder composite material comprises a matrix and cobalt powder; the particle size of the cobalt powder is 1 to 2 μm; The mass ratio of the matrix to the cobalt powder is 100:100-115; The conductive fiber cloth is a carbon fiber cloth having a copper-plated layer and a nickel-plated layer sequentially arranged on the surface facing the electromagnetic radiation source, the copper-plated layer has a thickness of 800 to 900 μm, and the nickel-plated layer has a thickness of 1 to 3 μm; The thickness of the second layer of the conductive fiber cloth and cobalt powder composite material is 1300-1350 μm.

5. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 1, characterized in that The third layer of cobalt alloy powder composite material layer and the fourth layer of cobalt alloy powder composite material layer respectively include a matrix and cobalt alloy powder, the thickness of the third layer of cobalt alloy powder composite material layer is 200-230 μm; the thickness of the fourth layer of cobalt alloy powder composite material layer is 150-200 μm; The cobalt alloy powder comprises the following components in mass fraction: 65~72% Co, 10~15% Fe, 5~10% Si, 5~10% Ni, 2~5% C; The particle size of the cobalt alloy powder is 15 to 20 μm; In the third layer of cobalt alloy powder composite material layer, the mass ratio of matrix to cobalt alloy powder is 100:100-105; In the fourth cobalt alloy powder composite material layer, the mass ratio of the matrix to the cobalt alloy powder is 100:50-52.

6. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 1, characterized in that The fifth carbon nanotube composite material layer, the sixth carbon nanotube composite material layer, the seventh carbon nanotube composite material layer and the eighth carbon nanotube composite material layer respectively include a matrix and carbon nanotubes, and the wave impedances of the fifth carbon nanotube composite material layer, the sixth carbon nanotube composite material layer, the seventh carbon nanotube composite material layer and the eighth carbon nanotube composite material layer gradually decrease.

7. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 6, characterized in that The thickness of the fifth carbon nanotube composite material layer is 200-230 μm; the thickness of the sixth carbon nanotube composite material layer is 200-230 μm; the thickness of the seventh carbon nanotube composite material layer is 150-200 μm; The eighth carbon nanotube composite material layer has a thickness of 150-200 μm.

8. The multi-layer epoxy composite coating for electromagnetic radiation protection according to claim 6, characterized in that In the fifth carbon nanotube composite material layer, the mass ratio of the matrix to the carbon nanotube is 100:8-10; ethanol is also added to the fifth carbon nanotube composite material layer, and the mass ratio of the matrix to the carbon nanotube to the ethanol is 100:8-10:8-12; In the sixth carbon nanotube composite material layer, the mass ratio of the matrix to the carbon nanotube is 100:6-8; In the seventh carbon nanotube composite material layer, the mass ratio of the matrix to the carbon nanotube is 100:2.5-3; In the eighth carbon nanotube composite material layer, the mass ratio of the matrix to the carbon nanotubes is 100:1-1.

3.

9. The multi-layer epoxy composite coating for electromagnetic radiation protection as claimed in claim 1, characterized in that The ninth dielectric material layer includes a matrix, which includes epoxy resin and polyethylene polyamine, and the mass ratio of epoxy resin to polyethylene polyamine is 95-100:10-12; the thickness of the ninth dielectric material layer is 120-150μm; the wave impedance of the ninth dielectric material layer is equal to or close to the wave impedance of the external environment.

10. Use of the multi-layer epoxy composite coating for electromagnetic radiation protection according to any one of claims 1 to 9 in electromagnetic shielding protection.

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