CN114957786A - Asymmetric electromagnetic shielding composite material, preparation method thereof and electromagnetic shielding device - Google Patents
Asymmetric electromagnetic shielding composite material, preparation method thereof and electromagnetic shielding device Download PDFInfo
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Abstract
The invention relates to the technical field of functional materials, in particular to an electromagnetic shielding composite material with an asymmetric structure, a preparation method thereof and an electromagnetic shielding device. The invention firstly introduces a porous structure into a matrix through a gas foaming technology, then coats a conductive metal electromagnetic shielding layer on one side of the surface of the matrix to form an asymmetric structure, takes the porous polymer matrix as a wave-absorbing foam layer, and combines the reflection action of the conductive metal shielding layer on electromagnetic waves to ensure that the electromagnetic waves undergo the processes of 'low reflection-absorption-reflection-reabsorption' when entering from one side of the wave-absorbing foam; meanwhile, the invention adopts a foaming process method of dipping at low temperature and high pressure and then processing by high-temperature supercritical gas to form a uniform cellular structure in the base material, so that electromagnetic waves entering the material are reflected and scattered for many times to further prolong the attenuation path of the electromagnetic waves, and the prepared composite material has extremely low reflection characteristic and ultrahigh electromagnetic shielding performance and can be applied to the fields of electronic communication equipment, aerospace, medical care, health care and the like.
Description
Technical Field
The invention relates to the technical field of functional materials, in particular to an electromagnetic shielding composite material with an asymmetric structure, a preparation method thereof and an electromagnetic shielding device.
Background
With the rapid development of the electronic information industry and the wide use of integrated and high-power electronic equipment, the problem of electromagnetic radiation pollution is increasingly serious, which not only influences the normal operation of precise instruments and equipment, but also threatens the human health. Therefore, the development of high-performance electromagnetic shielding materials is significant for protecting against electromagnetic hazards. Meanwhile, in the fields of electromagnetic protection such as information communication, aerospace, war industry, civil use and the like, a light electromagnetic shielding material is needed to reduce energy consumption, and a light high-performance electromagnetic shielding composite material is urgently needed in the future.
The performance of conventional shielding materials depends primarily on the perfection and conductivity of the conductive network. To obtain good conductivity, it is often necessary to add high levels of conductive fillers (e.g., graphene, carbon nanotubes, carbon black, metals, etc.). The conductive fillers can not only cause impedance mismatch between the surface of the composite material and air, but also cause a large amount of incident electromagnetic waves to be reflected (more than 90%), thereby causing serious secondary electromagnetic radiation pollution. In order to tune the contradiction between high shielding performance and low reflection characteristics, the studied method comprises the step of constructing a porous structure in the composite material, but the existing porous structure needs complex preparation processes such as freeze drying, chemical foaming, expanded microsphere foaming and the like, and has the problems of expensive equipment, environmental pollution, high material cost and the like. Therefore, the development of a lightweight polymer electromagnetic shielding material with both low reflection characteristics and high shielding performance, the simplification of the process flow, and the realization of low-cost standardized preparation become technical problems to be solved at present.
Disclosure of Invention
In order to overcome the defects of the prior art, one of the objectives of the present invention is to provide a method for preparing an electromagnetic shielding composite material with an asymmetric structure, wherein a supercritical fluid is dipped at a low temperature and is foamed with a high-temperature supercritical fluid to form a uniform cell structure, so that the composite material has a low reflection performance.
The invention also aims to provide an electromagnetic shielding composite material with an asymmetric structure, which is prepared by adopting the preparation method, and the internal porous structure and the surface metal layer have synergistic effect, so that the composite material has excellent electromagnetic shielding performance.
Meanwhile, the invention also provides an electromagnetic shielding device which is prepared by adopting the electromagnetic shielding composite material with the asymmetric structure.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of an electromagnetic shielding composite material with an asymmetric structure comprises the steps of firstly preparing a magnetic conductive polymer matrix, and then carrying out foaming treatment on the magnetic conductive polymer matrix; wherein the foaming treatment comprises the steps of firstly, carrying out low-temperature pressure maintaining impregnation on the magnetic conductive polymer matrix in supercritical fluid, quickly foaming by the supercritical fluid at a foaming temperature after pressure relief, and preparing the porous structure polymer matrix; coating a conductive metal electromagnetic shielding layer on the surface of one side of a porous polymer matrix; wherein the pressure of the low-temperature pressure-maintaining impregnation is greater than the foaming pressure.
Optionally, the magnetic conductive polymer matrix is prepared by compounding conductive filler, magnetic particles and high molecular polymer; the mass proportion of the conductive filler, the magnetic particles and the high molecular polymer is 1: 1: 100.
by way of illustration, in some embodiments of the invention, the conductive filler is carbon fiber, carbon nanotubes, graphene, carbon nanofibers, graphite nanoplatelets, graphite, carbon black, or fullerene; further preferably carbon nanotubes; the magnetic particles are reduced graphene oxide loaded ferroferric oxide; the high molecular polymer is polypropylene, polyethylene, polylactic acid, silicon rubber, thermoplastic polystyrene elastomer, thermoplastic polyolefin elastomer, thermoplastic copolyester elastomer, thermoplastic polyamide elastomer or thermoplastic polyurethane elastomer; further preferred is a thermoplastic polyurethane elastomer.
Preferably, the pressure of the low-temperature pressure-maintaining impregnation is 20Mpa, the temperature is 40 ℃, and the pressure-maintaining time is 2 hours; the pressure relief rate is 5 MPa/s.
Further preferably, the specific process of rapidly foaming with the supercritical fluid at the foaming temperature after pressure relief comprises, after pressure maintaining, dipping and pressure relief, rapidly taking out the sample, placing the sample into a reaction kettle with the internal temperature reaching the foaming temperature, introducing the preheated supercritical fluid, and pressure relief after pressure maintaining for a certain time.
Further preferably, the foaming temperature is 100 ℃; the temperature of the preheated supercritical fluid is 90 ℃; keeping the pressure for 10 min; the pressure relief rate is 5 MPa/s.
It should be noted that the supercritical fluid can be any foaming gas known in the art, and the type of the foaming gas does not affect the properties of the prepared composite material, and the supercritical fluid can be selected from nitrogen, air, helium, argon, petroleum ether, methane, ethane, propane, butane, pentane, hexane, heptane, n-pentane, n-hexane, n-heptane, dichloromethane or trichlorofluoromethane, for example.
Optionally, the preparation method of the magnetic conductive polymer matrix comprises adding the conductive filler into the magnetic particle organic solvent dispersion, adding the high molecular polymer particles, heating to a dissolving temperature, stirring and mixing uniformly, pouring into excessive deionized water for flocculent precipitation, taking out, drying to remove the organic solvent, and performing hot press molding to obtain the magnetic conductive polymer matrix;
the preparation method comprises the steps of slowly adding ferric chloride hexahydrate into graphene organic solvent dispersion liquid, stirring and mixing uniformly, adding NaOH and hydrazine hydrate, heating for reaction, cooling to room temperature to obtain graphene-loaded ferroferric oxide composite particle dispersion liquid, washing with water and ethanol alternately, and drying to obtain reduced graphene oxide-loaded ferroferric oxide composite particle powder.
The organic solvent used in the above production method is selected from ethanol, methanol, isopropanol, ethylene glycol, acetone, hexane, pentane, heptane, octane, aniline, butanone, chloroform, dimethylamine, N-heptanol, tetrahydrofuran, benzene, toluene, xylene, ethylbenzene, butyl acetate, chloroform, formic acid, dimethyl sulfoxide, chlorobenzene, dichlorobenzene, dichloromethane, trichloroethylene, N-methylpyrrolidone, or the like.
Optionally, the conductive metal electromagnetic shielding layer is a conductive silver layer; the thickness is 30 mm; the thickness of the porous structured polymer matrix was 2 mm.
An electromagnetic shielding composite material with an asymmetric structure is prepared by the preparation method. The composite material can be used for manufacturing electromagnetic shielding devices applied to the fields of electronic communication equipment, aerospace, medical care and the like.
The electromagnetic shielding composite material with the asymmetric structure, provided by the invention, is characterized in that firstly, a porous structure is introduced into a magnetic conductive polymer matrix through a gas foaming technology, then a conductive metal electromagnetic shielding layer is coated on one side of the surface of the matrix to form the asymmetric structure, the porous polymer matrix is used as a wave absorbing layer, and then the conductive metal electromagnetic shielding layer on one side of the surface is combined, so that electromagnetic waves undergo the processes of low reflection, absorption, reflection and reabsorption when being incident from one side of wave absorbing foam; according to the invention, by optimizing the foaming process of the magnetic conductive polymer matrix, a uniform cell structure is formed in the magnetic conductive polymer matrix, the reflection of the material to electromagnetic waves is reduced, and meanwhile, the multiple reflection and scattering of electromagnetic waves by the cell interface prolong the attenuation path of the electromagnetic waves, so that the prepared composite material has low reflection characteristics and high electromagnetic shielding performance, and can be applied to the fields of electronic communication equipment, aerospace, medical care and the like. The principle comprises the following steps:
(1) low reflection principle: after low-temperature high-pressure impregnation, the magnetic conductive polymer matrix is quickly foamed under the conditions of foaming temperature and pressure, and a preheated supercritical fluid is introduced at the preferable foaming temperature, so that a uniform cell structure is introduced into the magnetic conductive polymer matrix, impedance matching is increased, and more electromagnetic waves enter the material instead of being reflected. Meanwhile, multiple reflection and scattering of electromagnetic waves are increased, the transmission path of the electromagnetic waves is prolonged, and the absorption of the electromagnetic waves is enhanced, so that the composite material is endowed with a low-reflection characteristic;
(2) principle of high electromagnetic shielding performance: due to the composition of the compact conductive metal electromagnetic shielding layer, the composite material with the asymmetric structure based on the wave-absorbing foam is constructed, so that the transmission path of electromagnetic waves is prolonged through the processes of low reflection, absorption, reflection and reabsorption when the electromagnetic waves enter from one side of the wave-absorbing foam, the absorption of the electromagnetic waves is enhanced, and the composite foam is endowed with excellent electromagnetic shielding performance.
The preparation method provided by the invention is simple, feasible, low in cost and suitable for large-scale production.
Drawings
Fig. 1 is a schematic overall flow chart of a method for preparing an electromagnetic shielding composite material with an asymmetric structure according to an embodiment of the present invention;
fig. 2 is a scanning electron microscope image of the reduced graphene oxide-supported ferroferric oxide composite particle prepared in example 1 of the present invention;
FIG. 3 is a scanning electron microscope cross-sectional view of the composite material for electromagnetic shielding with an asymmetric structure prepared in example 1 of the present invention;
FIG. 4 is a graph showing a comparison of the reflection power coefficients in the X band before and after foaming of the magnetic conductive polymer matrices prepared in example 1, comparative example 1 and comparative example 2 according to the present invention; wherein (a) is before foaming; (b) after foaming;
FIG. 5 shows electromagnetic shielding performance (SSE) before and after foaming of magnetic conductive polymer matrices prepared in example 1, comparative example 1 and comparative example 2 of the present invention T ) A comparison graph of the absorption power coefficient A, the transmission power coefficient T and the reflection power coefficient R; wherein (a) is before foaming; (b) after foaming;
FIG. 6 shows absorption efficiency (SE) of the asymmetric-structure electromagnetic shielding composite materials prepared in example 1, comparative example 1 and comparative example 2 of the present invention in X-band A ) Total electromagnetic Shielding Effectiveness (SE) T ) Reflective Shielding Effectiveness (SE) R ) Comparing the images; wherein (a) is an average value; (b) for different frequency absorption efficiency (SE) A ) And total electromagnetic Shielding Effectiveness (SE) T ) A variation graph; (c) shielding effectiveness for different frequency reflections (SE) R ) BecomeChanging a curve chart;
FIG. 7 is a graph comparing the reflection power (R), the absorption power (A) and the transmission power (T) in the X band of the composite materials for electromagnetic shielding with asymmetric structure prepared in example 1, comparative example 1 and comparative example 2 of the present invention; wherein (a) is an average value; (b) a graph of reflected power (R) variation for different frequencies; (c) a graph of variation of absorbed power (a) and transmitted power (T) for different frequencies;
FIG. 8 is an absorption efficiency (SE) in X band of the asymmetric-structure electro-magnetic shielding composite material prepared according to the preparation process provided in comparative example 3 A ) Total electromagnetic Shielding Effectiveness (SE) T ) Reflective Shielding Effectiveness (SE) R ) Mean values are compared to the figure.
Detailed Description
The technical solution of the present invention will be described in detail by specific examples.
The overall flow of the preparation method of the electromagnetic shielding composite material with the asymmetric structure provided by the following embodiment is shown in fig. 1.
Example 1
The embodiment provides an electromagnetic shielding composite material with an asymmetric structure, and the preparation method comprises the following specific operation steps:
s1, preparing reduced graphene oxide loaded ferroferric oxide composite particles:
0.28g of graphene is added into 140ml of ethylene glycol and is uniformly dispersed by ultrasonic treatment for 30min, then 2.7g of ferric chloride hexahydrate is slowly added under the condition of mechanical stirring, and 2g of NaOH and 10ml of hydrazine hydrate are added after uniform stirring. Then, putting the uniformly mixed solution into a reaction kettle, standing at 200 ℃ for 12 hours, and naturally cooling to room temperature to obtain reduced graphene oxide loaded ferroferric oxide composite particle dispersion liquid; washing the dispersion liquid with deionized water and ethanol alternately and centrifugally for five times, and drying in an oven at 80 ℃ to obtain reduced graphene oxide-loaded ferroferric oxide composite particle powder, wherein a scanning electron microscope image of the reduced graphene oxide-loaded ferroferric oxide composite particle as shown in fig. 2 shows that the reduced graphene oxide-loaded ferroferric oxide composite particle prepared by the embodiment is free of agglomeration and is uniformly dispersed;
s2, preparing a magnetic conductive polymer matrix:
ultrasonically dispersing 0.15g of carbon nano tube and 0.15g of reduced graphene oxide-loaded ferroferric oxide composite particle powder prepared in the step S1 in 200ml of N-N dimethylformamide, adding 15g of polyurethane particles, stirring for 4 hours at 60 ℃, pouring the mixed solution into excessive deionized water, performing flocculation precipitation, taking out, drying for 8 hours in an oven at 80 ℃ to remove the solvent, and then performing hot press molding on the dried composite material through a vacuum auxiliary hot press to obtain the carbon nano tube/graphene-loaded ferroferric oxide/polyurethane composite material serving as a magnetic conductive polymer matrix and marked as S-T/C1/MG;
s3, preparing the electromagnetic shielding composite material with the asymmetric structure:
placing the carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite material prepared in the step S2 into a 40 ℃ high-pressure reaction kettle, injecting 20MPa carbon dioxide gas, keeping the pressure for 2 hours, then releasing the pressure to normal pressure at the speed of 5MPa/S, quickly taking out a sample, placing the sample into another reaction kettle with the temperature of 100 ℃, introducing 8MPa carbon dioxide heated to 90 ℃, and after 10 minutes, quickly releasing the pressure at the speed of 5MPa/S to obtain carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite foam, wherein the thickness of the carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite foam is about 2mm and is marked as F-T/C1/MG; and then coating a layer of conductive silver adhesive on one side of the composite foam by using a scraper, putting the composite foam into an oven at 80 ℃ for 10min to solidify the composite foam, setting the distance between the scraper and the surface of the composite foam to be 30mm, and preparing the carbon nano tube/graphene-loaded ferroferric oxide/polyurethane composite foam with an asymmetric structure, wherein the carbon nano tube/graphene-loaded ferroferric oxide/polyurethane composite foam is marked as F-T/C1/MG-Ag, and as shown in a cross-sectional scanning electron microscope image of F-T/C1/MG-Ag in figure 3, the inner part of the composite foam is shown to have a uniform and compact porous structure, and the surface of the composite foam is uniformly covered with a conductive silver layer.
Comparative example 1
The embodiment provides an electromagnetic shielding composite material with an asymmetric structure, and the preparation method is different from that of embodiment 1 in that 0.3g of carbon nanotubes are added in step S2, and the prepared magnetic conductive polymer matrix is marked as S-T/C2/MG; the carbon nano tube/graphene-loaded ferroferric oxide/polyurethane composite foam is 2mm thick and marked as F-T/C2/MG; the carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite foam with the asymmetric structure is marked as F-T/C2/MG-Ag.
Comparative example 2
The embodiment provides an electromagnetic shielding composite material with an asymmetric structure, and the preparation method is different from that of embodiment 1 in that 0.45g of carbon nanotubes are added in step S2, and the prepared magnetic conductive polymer matrix is marked as S-T/C3/MG; the carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite foam is 2mm thick and marked as F-T/C3/MG; the carbon nano tube/graphene loaded ferroferric oxide/polyurethane composite foam with the asymmetric structure is marked as F-T/C3/MG-Ag.
Comparative example 3
The preparation process of the electromagnetic shielding composite material with the asymmetric structure comprises the steps of putting the carbon nanotube/graphene-loaded ferroferric oxide/polyurethane composite material prepared in the step S2 in the embodiment 1 into a reaction kettle at the temperature of 100 ℃, introducing 8Mpa of carbon dioxide, keeping the pressure for 2 hours, and then rapidly relieving the pressure at the speed of 5Mpa/S to obtain carbon nanotube/graphene-loaded ferroferric oxide/polyurethane composite foam, wherein the thickness of the carbon nanotube/graphene-loaded ferroferric oxide/polyurethane composite foam is controlled to be 2 mm. And finally, coating a layer of conductive silver adhesive on one side of the composite foam, putting the composite foam into an oven at 80 ℃ for 10min to be cured, setting the distance between a scraper and the surface of the composite foam to be 30mm, and preparing the carbon nano tube/graphene-loaded ferroferric oxide/polyurethane composite foam with the asymmetric structure, wherein the label is F-T/C1/MG-Ag-N.
The amount of carbon nanotubes in step S2 is adjusted according to the same method as in comparative example 1 and comparative example 2, and then the asymmetric-structure carbon nanotube/graphene-supported ferroferric oxide/polyurethane composite foam is prepared according to the same preparation process as in comparative example 3, and respectively marked as F-T/C2/MG-Ag-N and F-T/C3/MG-Ag-N.
Test examples Performance verification
1. The reflection power coefficients R of the magnetic conductive polymer substrates prepared in example 1, comparative example 1, and comparative example 2 at the X band before and after foaming were measured by an electromagnetic shielding tester, and the results are shown in fig. 4; absorption power coefficient a, transmission power coefficient T, average reflection power coefficient R, as shown in fig. 5;
the results shown in FIGS. 4 and 5 indicate that the following carbon nanotubes are presentThe increase in the amount of the solid before foaming in example 1, comparative example 1 and comparative example 2 has a reflection power coefficient R of: 0.46, 0.61, 0.68; the reflection power coefficients R of the porous foam after foaming are respectively as follows: 0.23, 0.36, 0.42; the absorption power coefficient A of the solid before foaming is respectively as follows: 0.49, 0.38, 0.32; the absorption power coefficients A of the foamed porous foam are respectively as follows: 0.46, 0.48, 0.51; the characteristic shielding properties of the foamed solid are respectively as follows: 11.9, 19.2, 23.9dB cm 3 g -1 (ii) a The characteristic shielding properties of the foamed foam are respectively as follows: 13.2, 21.8, 26.3dB cm 3 g -1 (ii) a In the whole X wave band, the reflection power coefficients of the solid sample before foaming under different carbon nano tube contents are all larger than the reflection power coefficient of the sample after foaming, which shows that the reflection of the composite material to electromagnetic waves is reduced in the foaming process; with the increase of the content of the carbon nano tube, the R value of the reflection power coefficient of the solid sample before foaming is larger than the R value of the reflection power coefficient of the sample after foaming, and the characteristic electromagnetic shielding performance after foaming is obviously improved, which shows that the reflection of the composite material to electromagnetic waves is obviously reduced in the foaming process, and the shielding performance of the composite material is improved.
3. The absorption efficiency (SE) of the asymmetric-structure electromagnetic shielding composite materials prepared in example 1, comparative example 1 and comparative example 2 in the X wave band was measured and calculated by using an electromagnetic shielding tester A ) Total electromagnetic Shielding Effectiveness (SE) T ) Reflective Shielding Effectiveness (SE) R ) As shown in fig. 6, as the amount of the carbon nanotubes increases, the absorption efficiency SE of the electromagnetic shielding composite materials of asymmetric structures prepared in example 1, comparative example 1 and comparative example 2 was increased A 88.9dB, 95dB and 102.7dB respectively; total shielding effectiveness SE T 89.2dB,95.5dB and 103.5dB respectively; average reflective shielding effectiveness SE of X-band R 0.24dB, 0.5dB and 0.83dB respectively; average reflective Shielding Effectiveness (SE) of the electromagnetic shielding composite material with the asymmetric structure in the whole X wave band R ) Absorption efficiency (SE) A ) And total electromagnetic Shielding Effectiveness (SE) T ) All increased with increasing carbon nanotube content, indicating increased reflection of electromagnetic waves, and SE A Curve almost equal to SE T Overlap, representing total shielding performance SE T Is mainly due to absorption loss SE A The increase proves that the composite material prepared by the invention realizes an electromagnetic shielding mechanism mainly based on absorption loss by a specific porous structure.
4. The reflection power (R), the absorption power (a), and the transmission power (T) of the asymmetric-structure electromagnetic shielding composite materials prepared in example 1, comparative example 1, and comparative example 2 in the X band were measured and calculated using an electromagnetic shielding tester, and as shown in fig. 7, the average reflection power coefficient (R) of the asymmetric-structure composite foams prepared in example 1, comparative example 1, and comparative example 2 was as follows as the amount of the carbon nanotubes was increased: 0.05, 0.11, 0.17, the values of the absorbed power coefficient (a) are respectively: 0.95, 0.89, 0.83, T values are: 2.73545X 10 -9 ，3.76084×10 -10 ，9.41558×10 -11 (ii) a In the whole X wave band, the reflection power coefficient R of the electromagnetic shielding composite material with the asymmetric structure prepared in the embodiment 1, the comparative example 1 and the comparative example 2 is improved along with the increase of the content of the carbon nano tube, the absorption power coefficient A and the transmission power coefficient T are both reduced along with the increase of the content of the carbon nano tube, but due to the design of the asymmetric structure, the R value keeps an extremely low level in the whole X wave band range; when the mass of the carbon nano tube in example 1 is 1% of the mass of the polyurethane and the asymmetric structure composite foam is at 10.9GHz, the minimum peak value of the reflection power coefficient R is 0.001, and the maximum peak value of the absorption power coefficient A is 0.999, which shows that 99.9% of electromagnetic waves are absorbed.
5. The absorption efficiency (SE) of the asymmetric-structure electromagnetic shielding composite material prepared according to the preparation process described in comparative example 3 in the X band was measured and calculated using an electromagnetic shielding tester A ) Total electromagnetic Shielding Effectiveness (SE) T ) Reflective Shielding Effectiveness (SE) R ) As shown in FIG. 8, with the increase of the amount of the carbon nanotubes, the absorption efficiency SE of the prepared electromagnetic shielding composite material with asymmetric structure A 77.9dB, 81.5dB and 84.1dB respectively; total shielding effectiveness SE T Respectively 80.3dB,85.6dB and 91.3 dB; average reflective shielding effectiveness SE of X-band R 2.4dB, 4.1dB and 7.2dB, and the electromagnetic shielding performance of the composite materials prepared in comparative example 1, comparative example 1 and comparative example 2 is greatly reduced after the treatment process of low-temperature high-pressure impregnation is omitted.
In summary, the following steps: the mass proportion of the conductive filler, the magnetic particles and the high molecular polymer is 1: 1: 100 has high electromagnetic shielding performance of 89.2dB and reflection power coefficient as low as 0.05, and reflection efficiency SE R The power absorption coefficient A is only 0.24dB and reaches up to 0.95. Indicating that 99.9999999% of the electromagnetic waves are shielded and only 0.5% of the electromagnetic waves are reflected. Further, at 10.9GHz, the minimum reflected power coefficient R value was as low as 0.001, indicating that only 0.1% of the electromagnetic waves were reflected. The electromagnetic shielding composite material with the asymmetric structure prepared by the invention has the characteristics of low reflection and high electromagnetic shielding performance, and can be applied to the fields of electronic communication equipment, aerospace, medical care and the like.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A preparation method of an electromagnetic shielding composite material with an asymmetric structure is characterized by comprising the steps of firstly preparing a magnetic conductive polymer matrix, and then carrying out foaming treatment on the magnetic conductive polymer matrix; wherein the foaming treatment comprises that firstly, the magnetic conductive polymer matrix is dipped in supercritical fluid at low temperature and pressure maintaining, and the supercritical fluid is used for foaming rapidly at foaming temperature after pressure relief to prepare the polymer matrix with porous structure; coating a conductive metal electromagnetic shielding layer on the surface of one side of a porous polymer matrix; wherein the pressure of the low-temperature pressure-maintaining impregnation is greater than or equal to the foaming pressure.
2. The method for preparing an electromagnetically shielding composite material with an asymmetric structure as claimed in claim 1, wherein said magnetic conductive polymer matrix is prepared by compounding conductive filler, magnetic particles, and high molecular polymer; the mass proportion of the conductive filler, the magnetic particles and the high molecular polymer is 1: 1: 100.
3. the method for preparing an electromagnetically shielding composite material having an asymmetric structure according to claim 2, wherein the conductive filler is carbon fiber, carbon nanotube, graphene, carbon nanofiber, graphite nanoplatelet, graphite, carbon black or fullerene; the magnetic particles are reduced graphene oxide loaded ferroferric oxide; the high molecular polymer is polypropylene, polyethylene, polylactic acid, silicon rubber, thermoplastic polystyrene elastomer, thermoplastic polyolefin elastomer, thermoplastic copolyester elastomer, thermoplastic polyamide elastomer or thermoplastic polyurethane elastomer.
4. The method for preparing an electromagnetically shielding composite material having an asymmetric structure according to claim 3, wherein the pressure of the low-temperature pressure-maintaining impregnation is 20Mpa, the temperature is 40 ℃, and the pressure-maintaining time is 2 hours; the pressure relief rate is 5 MPa/s.
5. The method for preparing an electromagnetically shielding composite material having an asymmetric structure as claimed in claim 4, wherein the specific process of rapidly foaming at a foaming temperature with a supercritical fluid after pressure relief comprises maintaining pressure, immersing and pressure relief, rapidly taking out a sample, placing the sample in a reaction kettle whose internal temperature reaches the foaming temperature, introducing a preheated supercritical fluid, and maintaining the pressure for a certain period of time.
6. The method for preparing an electromagnetically shielding composite material having an asymmetric structure as claimed in claim 5, wherein the foaming temperature is 100 ℃; the temperature of the preheated supercritical fluid is 90 ℃; keeping the pressure for 10 min; the pressure relief rate is 5 MPa/s.
7. The method for preparing an electromagnetically shielding composite material with an asymmetric structure as claimed in any one of claims 2 to 6, wherein the method for preparing the magnetically conductive polymer matrix comprises adding the conductive filler into the dispersion of the organic solvent of magnetic particles, adding the high molecular polymer particles, heating to a melting temperature, stirring, mixing, pouring into an excessive amount of deionized water, precipitating to obtain a flocculent precipitate, drying to remove the organic solvent, and hot-pressing to obtain the magnetically conductive polymer matrix.
8. The method for preparing the asymmetric-structure electromagnetic shielding composite material as claimed in any one of claims 2 to 6, wherein the conductive metal electromagnetic shielding layer is a conductive silver layer; the thickness is 30 mm; the thickness of the porous structured polymer matrix was 2 mm.
9. An electromagnetic shielding composite material with an asymmetric structure, which is prepared by the preparation method of any one of claims 1 to 8.
10. An electromagnetic shielding device, characterized in that it is made of the asymmetric electromagnetic shielding composite material as claimed in claim 9.
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