CN112492865B - Electromagnetic shielding foam and preparation method and application thereof - Google Patents
Electromagnetic shielding foam and preparation method and application thereof Download PDFInfo
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- CN112492865B CN112492865B CN202011348239.XA CN202011348239A CN112492865B CN 112492865 B CN112492865 B CN 112492865B CN 202011348239 A CN202011348239 A CN 202011348239A CN 112492865 B CN112492865 B CN 112492865B
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- 239000006260 foam Substances 0.000 title claims abstract description 128
- 238000002360 preparation method Methods 0.000 title abstract description 29
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 169
- 239000002041 carbon nanotube Substances 0.000 claims abstract description 166
- 229910021393 carbon nanotube Inorganic materials 0.000 claims abstract description 166
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 150
- 229910052709 silver Inorganic materials 0.000 claims abstract description 144
- 239000004332 silver Substances 0.000 claims abstract description 144
- 210000001787 dendrite Anatomy 0.000 claims abstract description 140
- 229920005570 flexible polymer Polymers 0.000 claims abstract description 27
- 238000004108 freeze drying Methods 0.000 claims abstract description 22
- 239000000463 material Substances 0.000 claims abstract description 12
- 230000005855 radiation Effects 0.000 claims abstract description 8
- 239000002994 raw material Substances 0.000 claims abstract description 8
- 239000002002 slurry Substances 0.000 claims description 124
- 229920000642 polymer Polymers 0.000 claims description 47
- 239000004433 Thermoplastic polyurethane Substances 0.000 claims description 46
- 229920002803 thermoplastic polyurethane Polymers 0.000 claims description 46
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 45
- 239000000725 suspension Substances 0.000 claims description 32
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 238000006116 polymerization reaction Methods 0.000 claims description 28
- 238000000034 method Methods 0.000 claims description 24
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims description 23
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims description 23
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims description 23
- RYHBNJHYFVUHQT-UHFFFAOYSA-N 1,4-Dioxane Chemical group C1COCCO1 RYHBNJHYFVUHQT-UHFFFAOYSA-N 0.000 claims description 21
- 239000002861 polymer material Substances 0.000 claims description 19
- 238000005245 sintering Methods 0.000 claims description 16
- 239000007788 liquid Substances 0.000 claims description 14
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 13
- 229910052802 copper Inorganic materials 0.000 claims description 13
- 239000010949 copper Substances 0.000 claims description 13
- 239000002904 solvent Substances 0.000 claims description 13
- 239000002109 single walled nanotube Substances 0.000 claims description 12
- 239000007787 solid Substances 0.000 claims description 11
- 238000009736 wetting Methods 0.000 claims description 11
- 229920000468 styrene butadiene styrene block copolymer Polymers 0.000 claims description 10
- 230000006835 compression Effects 0.000 claims description 7
- 238000007906 compression Methods 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 239000002048 multi walled nanotube Substances 0.000 claims description 6
- 239000002086 nanomaterial Substances 0.000 claims description 5
- 238000005266 casting Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 239000000412 dendrimer Substances 0.000 claims description 4
- 229920000736 dendritic polymer Polymers 0.000 claims description 4
- 229920006132 styrene block copolymer Polymers 0.000 claims description 4
- -1 styrene-ethylene-propylene-styrene Chemical class 0.000 claims description 4
- 229920000346 polystyrene-polyisoprene block-polystyrene Polymers 0.000 claims description 3
- 238000007711 solidification Methods 0.000 claims description 3
- 230000008023 solidification Effects 0.000 claims description 3
- 239000011231 conductive filler Substances 0.000 abstract description 7
- 238000005516 engineering process Methods 0.000 abstract description 5
- 239000011159 matrix material Substances 0.000 abstract description 3
- 239000011347 resin Substances 0.000 abstract description 3
- 229920005989 resin Polymers 0.000 abstract description 3
- 238000009833 condensation Methods 0.000 abstract description 2
- 230000005494 condensation Effects 0.000 abstract description 2
- 239000000243 solution Substances 0.000 description 56
- 238000001035 drying Methods 0.000 description 23
- 239000011259 mixed solution Substances 0.000 description 17
- 239000002131 composite material Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 8
- AVXURJPOCDRRFD-UHFFFAOYSA-N Hydroxylamine Chemical compound ON AVXURJPOCDRRFD-UHFFFAOYSA-N 0.000 description 4
- 238000011049 filling Methods 0.000 description 4
- 229910001961 silver nitrate Inorganic materials 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 125000004122 cyclic group Chemical group 0.000 description 3
- 239000006261 foam material Substances 0.000 description 3
- 239000002071 nanotube Substances 0.000 description 3
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 239000002390 adhesive tape Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 210000004027 cell Anatomy 0.000 description 1
- 238000012669 compression test Methods 0.000 description 1
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- SZVJSHCCFOBDDC-UHFFFAOYSA-N ferrosoferric oxide Chemical compound O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
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- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
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- B32B5/18—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by features of a layer of foamed material
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
- B32B5/32—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed at least two layers being foamed and next to each other
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
- H05K9/0083—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
- H05K9/0088—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising a plurality of shielding layers; combining different shielding material structure
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
- H05K9/009—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising electro-conductive fibres, e.g. metal fibres, carbon fibres, metallised textile fibres, electro-conductive mesh, woven, non-woven mat, fleece, cross-linked
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2250/00—Layers arrangement
- B32B2250/03—3 layers
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- B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
- B32B2262/10—Inorganic fibres
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- B32B2266/00—Composition of foam
- B32B2266/02—Organic
- B32B2266/0214—Materials belonging to B32B27/00
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- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
- B32B2307/212—Electromagnetic interference shielding
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- C—CHEMISTRY; METALLURGY
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/048—Elimination of a frozen liquid phase
- C08J2201/0482—Elimination of a frozen liquid phase the liquid phase being organic
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2353/00—Characterised by the use of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/02—Elements
- C08K3/04—Carbon
- C08K3/041—Carbon nanotubes
Abstract
The invention provides electromagnetic shielding foam, a preparation method and application thereof. The electromagnetic shielding foam is prepared from the following raw materials: three-dimensional fractal silver dendrites, carbon nanotubes, and flexible polymeric materials. The invention selects fractal silver powder and carbon nano tubes with three-dimensional radiation growth as conductive filler, takes flexible polymer as resin matrix, and combines the technologies of layer-by-layer pouring condensation and freeze drying to prepare the layered foam with conductive gradient. The electromagnetic shielding foam has the characteristics of low reflection, high shielding and compressibility, and is particularly suitable for electromagnetic shielding of electronic equipment and devices at a closed position.
Description
Technical Field
The invention belongs to the field of electromagnetic shielding material processing, and particularly relates to electromagnetic shielding foam and a preparation method and application thereof.
Background
In recent years, as electronic devices and apparatuses are advanced to high frequency and high speed, problems of electromagnetic leakage and electromagnetic interference are also becoming serious. The blocking between the protected body and the electromagnetic wave radiation source by using the electromagnetic shielding material is a simple and effective method for solving electromagnetic wave leakage or electromagnetic wave interference in engineering practice. The areas where electromagnetic wave leakage occurs and electromagnetic interference is generated to the receptor mainly occur at the closed positions of the equipment, and electromagnetic shielding is mainly carried out on the areas by adopting modes of plugging conductive adhesive tapes, conductive foam (foam) and the like. Meanwhile, in order to maintain stable electromagnetic shielding effect for a long time, these shielding materials should also have good compression properties. At present, the electromagnetic shielding materials mainly adopt a method for improving the conductivity of the materials to ensure that the materials obtain good electromagnetic shielding performance, but the shielding materials reflect a large amount of electromagnetic waves due to the fact that the impedance mismatch degree between air and the surfaces of the materials is increased, so that secondary pollution of the electromagnetic waves generated by built-in electronic circuits and components is very easy to influence the normal operation of electronic equipment.
CN111138836a discloses a flexible electromagnetic shielding composite material and a preparation method thereof. The flexible electromagnetic shielding composite material is prepared from the following components in parts by weight: 25-50 parts of three-dimensional fractal silver dendrite; 50-75 parts of flexible polymer material; the three-dimensional fractal silver dendrite refers to silver powder with a three-dimensional radial primary fractal structure, a micro-nano scale secondary fractal structure and a micro-nano scale tertiary fractal structure. Under the condition of filling rate of 25-50wt%, electromagnetic shielding effectiveness is 40-80dB, shielding effectiveness is 30-70dB under 20% tensile strain, and shielding effectiveness per unit thickness is up to 400-1500dB mm -1 Can be widely applied to the field of flexible electromagnetic shielding. The electromagnetic shielding effectiveness of the flexible electromagnetic shielding composite material remains to be improved.
CN109591391a discloses a foam material with low reflection and high shielding gradient structure and a preparation method thereof. The graphene-supported ferroferric oxide nanoparticle foam with an orientation cell structure and a carbon nanotube foam are prepared respectively by a liquid nitrogen freeze-drying method, a tetragonal needle-shaped zinc oxide whisker nanoparticle silver-supported film is prepared by blending, pouring and drying, and finally the three are compounded by an adhesive to obtain the electromagnetic shielding foam with a gradient lamellar structure, so that the conductivity and the electromagnetic shielding performance of the composite foam material are obviously improved under the condition of effectively reducing electromagnetic wave reflection. The electromagnetic shielding effectiveness of the foam material is still to be improved and the rebound resilience performance is poor.
Therefore, it is particularly important to develop a novel electromagnetic shielding foam which is high in shielding, low in reflection and compressible.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide electromagnetic shielding foam and a preparation method and application thereof, in particular to low-reflection high-shielding compressible electromagnetic shielding foam and a preparation method and application thereof.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides an electromagnetic shielding foam, the electromagnetic shielding foam comprising: three-dimensional fractal silver dendrites, carbon nanotubes, and flexible polymeric materials.
The invention selects fractal silver powder (three-dimensional fractal silver dendrite) with three-dimensional radiation growth and carbon nano tubes as conductive filler, uses flexible polymer as resin matrix, and combines the technologies of layer-by-layer pouring condensation and freeze drying to prepare the layered foam with conductive gradient. By reasonably constructing the conductive network, electromagnetic wave reflection is greatly reduced, and excellent shielding efficiency is obtained. When electromagnetic waves propagate to the layered foam along the positive conductive gradient direction, the reflection of electromagnetic waves at the interface is greatly reduced, the incident waves are continuously reflected and absorbed in the foam, the paths of the reflected waves acting on the inner wall of the foam are also continuously increased along with the increase of the incident depth, and as a result, most of the incident waves are consumed in the foam, so that the foam simultaneously has excellent electromagnetic shielding efficiency and very low reflection coefficient, and the electromagnetic shielding performance of the foam is very excellent.
The fractal tissue with abundant three-dimensional fractal silver dendrites increases the interaction sites of the conductive network and electromagnetic waves; the nano structure with clean fractal structure enables silver dendrites to be sintered at a lower temperature, metallurgical bonding is achieved, and the conductivity of the composite material is improved. The carbon nanotube is selected as another conductive filling phase, mainly for the purpose of facilitating control of the conductive gradient so as to reduce reflection of electromagnetic waves and increase absorption of electromagnetic waves. Meanwhile, the lower seepage threshold value can improve the proportion of the resin binding phase, so that the lamellar foam has good compression performance.
Preferably, the electromagnetic shielding foam is prepared from the following raw materials in parts by weight: 5.8-12.4 parts of three-dimensional fractal silver dendrite, 4.0-6.0 parts of carbon nano tube and 81.6-90.2 parts of flexible polymer material.
According to the invention, by reasonably constructing the conductive network, the shielding effectiveness is greatly improved, the consumption of the conductive filler is greatly reduced, and the filling rates of the three-dimensional fractal silver dendrites and the carbon nano tubes in the foam are only 5.8-12.4 parts and 4.0-6.0 parts respectively, so that the preparation cost of the foam is low, and the economic value is high.
In the preparation raw materials of the electromagnetic shielding foam, the weight parts of the three-dimensional fractal silver dendrites are 5.8-12.4 parts, and can be 5.8 parts, 6.0 parts, 6.5 parts, 7.0 parts, 7.5 parts, 8.0 parts, 8.5 parts, 9.0 parts, 9.5 parts, 10.0 parts, 10.5 parts, 11.0 parts, 11.5 parts, 12 parts, 12.4 parts and the like.
In the raw materials for preparing the electromagnetic shielding foam, the weight parts of the carbon nano tubes are 4.0-6.0 parts, for example, 4.0 parts, 4.2 parts, 4.4 parts, 4.6 parts, 4.8 parts, 5.0 parts, 5.2 parts, 5.4 parts, 5.6 parts, 5.8 parts, 6.0 parts and the like.
In the preparation raw materials of the electromagnetic shielding foam, the weight parts of the flexible polymer materials are 81.6-90.2 parts, for example, 81.6 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts, 89 parts, 90 parts, 90.2 parts and the like.
Preferably, the three-dimensional fractal silver dendrite refers to silver powder with a first-level fractal structure which shows three-dimensional radiation growth and rich nano structures at the tips of second-level and third-level fractal tissues.
The three-dimensional fractal silver dendrite is prepared by using hydroxylamine reduction silver nitrate technology, and has the characteristics of three-dimensional radiation, abundant fractal tissues and clean surfaces. The morphology of three-dimensional radiation in the composite material enables silver dendrites to occupy more free space, so that the composite material obtains a lower seepage threshold; the abundant fractal tissues increase the interaction sites of the conductive network and the electromagnetic wave; the nano structure with clean fractal structure enables silver dendrites to be sintered at a lower temperature, metallurgical bonding is achieved, and the conductivity of the composite material is improved. Therefore, the three-dimensional fractal silver dendrite is very suitable for preparing a low-filling high-conductivity composite material and is applied to high-efficiency electromagnetic shielding.
Preferably, the three-dimensional fractal silver dendrite is prepared by mixing silver nitrate solution and hydroxylamine in a molar ratio of 1:4-1:16, wherein the first-level fractal structure shows three-dimensional radiation growth, and silver powder with abundant nano structures is arranged at the tips of the second-level fractal structure and the third-level fractal structure.
Preferably, the carbon nanotubes are selected from single-walled carbon nanotubes (SWCNTs) and/or multi-walled carbon nanotubes (MWCNTs).
Preferably, the flexible polymeric material is selected from any one or a combination of at least two of Thermoplastic Polyurethane (TPU), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-butylene-styrene block copolymer (SEBS) or styrene-isoprene-styrene block copolymer (SIS).
Preferably, the electromagnetic shielding foam comprises, in order from bottom to top: the three-dimensional fractal silver dendrite polymer layer, the first carbon nanotube polymer layer, the second carbon nanotube polymer layer and the third carbon nanotube polymer layer.
Preferably, the content of carbon nanotubes in the first carbon nanotube polymer layer > the content of carbon nanotubes in the second carbon nanotube polymer layer > the content of carbon nanotubes in the third carbon nanotube polymer layer.
According to the invention, three-dimensional fractal silver dendrite is selected as a conductive filler at the bottommost layer in the layered foam, carbon nano tubes are selected as conductive fillers at the second layer to the fourth layer, flexible polymers are selected as polymer matrixes of each layer, and the layered foam with a conductive gradient is prepared by pouring, condensing and combining a freeze drying technology layer by layer. The foam has the characteristics of low reflection, high shielding and compressibility, and is particularly suitable for electromagnetic shielding of electronic equipment and devices at a closed position.
Preferably, the difference between the carbon nanotube content in the first carbon nanotube polymer layer and the second carbon nanotube polymer layer is 2.0-4.0%, for example, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, etc.
Preferably, the difference between the carbon nanotube content in the second carbon nanotube polymer layer and the third carbon nanotube polymer layer is 2.0-4.0%, for example, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, etc.
Preferably, the shielding effectiveness of the electromagnetic shielding foam is 60-100dB, and may be 60dB, 65dB, 70dB, 75dB, 80dB, 82dB, 84dB, 86dB, 88dB, 90dB, 92dB, 94dB, 96dB, 98dB, 100dB, etc., for example.
The electromagnetic shielding foam preferably has a reflectance of 0.15 or less, and may be, for example, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.08, 0.07, 0.06, 0.05, or the like.
Preferably, the electromagnetic shielding foam has a thickness of 2.0-4.0mm, for example, 2.0mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3.0mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4.0mm, etc.
Preferably, the maximum compressive strain of the electromagnetic shielding foam is 50% or less, and may be, for example, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or the like.
Preferably, after 100 cycles of compression, the resilience of the electromagnetic shielding foam is 85% or more, for example, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or less, and the electromagnetic shielding effectiveness is changed to a value of 10dB or less, for example, 10dB, 9dB, 8dB, 7dB, 6dB, 5dB, 4dB, 3dB, 2dB, 1dB or less.
In a second aspect, the present invention provides a method for producing the electromagnetic shielding foam according to the first aspect, the method comprising the steps of:
(1) Preparing three-dimensional fractal silver dendrite into three-dimensional fractal silver dendrite suspension; dispersing carbon nanotubes in a solution of a flexible polymer material, and preparing to obtain carbon nanotube slurry;
(2) Casting and sintering the three-dimensional fractal silver dendrite suspension obtained in the step (1), and wetting by adopting a solution of a flexible polymer material to form a three-dimensional fractal silver dendrite polymer layer;
(3) And (3) pouring the carbon nano tube slurry obtained in the step (1) above the three-dimensional fractal silver dendrite polymer layer obtained in the step (2), and freeze-drying after solidification to obtain the electromagnetic shielding foam.
Preferably, the three-dimensional fractal silver dendrite suspension comprises three-dimensional fractal silver dendrite, polyvinylpyrrolidone (PVP) and an alcohol solvent.
Preferably, in the three-dimensional fractal silver dendrite suspension in the step (1), the solid content of the three-dimensional fractal silver dendrite is 1.0-2.0%, for example, may be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc.
Preferably, in the three-dimensional fractal silver dendrite suspension, the addition amount of polyvinylpyrrolidone accounts for 0.1-1.0% of the mass of the three-dimensional fractal silver dendrite, and may be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.
Preferably, in the three-dimensional fractal silver dendrite suspension, the alcohol solvent is selected from ethanol.
Preferably, in the step (1), the flexible polymer material and the solvent are included in the solution of the flexible polymer material in a mass ratio of (4-6): 100, for example, 4:100, 4.2:100, 4.4:100, 4.6:100, 4.8:100, 5:100, 5.2:100, 5.4:100, 5.6:100, 5.8:100, 6:100, etc.
Preferably, the solvent is 1, 4-dioxane.
Preferably, in step (1), three carbon nanotube slurries having different concentration gradients are configured, including: a first carbon nanotube slurry having an absolute mass fraction of 7.5-9.0wt% (e.g., may be 7.5wt%, 7.6wt%, 7.8wt%, 8.0wt%, 8.2wt%, 8.4wt%, 8.6wt%, 8.8wt%, 9.0wt%, etc.), a second carbon nanotube slurry having an absolute mass fraction of 5.0-7.0wt% (e.g., may be 5.0wt%, 5.2wt%, 5.4wt%, 5.6wt%, 5.8wt%, 6.0wt%, 6.2wt%, 6.4wt%, 6.6wt%, 6.8wt%, 7.0wt%, etc.), and a third carbon nanotube slurry having an absolute mass fraction of 3.0-4.5wt% (e.g., may be 3.0wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, 4.0wt%, 4.5.5 wt%, etc.).
In the invention, carbon nanotubes with different masses are dispersed in a flexible polymer solution to prepare carbon nanotube slurries with different concentration gradients. Wherein, "oven dry mass fraction" refers to [ mass of carbon nanotubes/(mass of carbon nanotubes+mass of flexible polymer) ] x 100%.
Preferably, in the step (2), the sintering temperature is 150-180 ℃, for example, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, 175 ℃, 180 ℃ and the like, and the sintering time is 1.0-2.0h, for example, 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h and the like.
Preferably, in the step (2), the mass ratio of the three-dimensional fractal silver dendrite suspension to the solution of the flexible polymer material is (5-8): 1, for example, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, etc.
Preferably, in the step (2), the flexible polymer material and the solvent are included in the solution of the flexible polymer material in a mass ratio of (4-6): 100, for example, 4:100, 4.2:100, 4.4:100, 4.6:100, 4.8:100, 5:100, 5.2:100, 5.4:100, 5.6:100, 5.8:100, 6:100, etc.
In the invention, the step (2) specifically comprises the following steps: pouring three-dimensional fractal silver dendrite suspension with certain quality into a groove with a horizontal bottom, naturally drying to volatilize a solvent to form a silver dendrite layer, transferring the groove into an oven, sintering for 1.0-2.0h at 150-180 ℃, and finally wetting the silver dendrite layer with a small amount of flexible polymer solution to form the three-dimensional fractal silver dendrite polymer layer.
Preferably, the solvent is 1, 4-dioxane.
Preferably, in the step (3), the concrete steps of pouring are as follows: pouring the carbon nano tube slurry obtained in the step (1) into a groove containing the three-dimensional fractal silver dendritic polymer layer, standing, and cooling and solidifying.
Preferably, in the step (3), the concrete steps of pouring are as follows: pouring the first carbon nano tube slurry into a groove containing the three-dimensional fractal silver dendritic polymer layer, standing for 5-20min (for example, 5min, 6min, 8min, 10min, 12min, 14min, 16min, 18min, 20min and the like), and then standing the groove on a copper table cooled by liquid nitrogen for cooling and solidifying to form a first carbon nano tube polymerization layer; and then the second carbon nano tube slurry and the third carbon nano tube slurry are sequentially poured and condensed by adopting the same method.
In the invention, carbon nano tube/polymer slurry with certain concentration and quality is slowly poured into a groove containing silver dendrite/flexible polymer layer, the slurry is fully leveled and further wets the silver dendrite layer by standing, and then the groove is placed on a copper table cooled by liquid nitrogen, so that the slurry of the first layer is just solidified. Next, the same mass but smaller concentration of carbon nanotube/polymer slurry was slowly poured into the coagulum, and the second, third layer slurry was just coagulated in the same manner. According to the invention, the carbon nano tube/polymer solidification layer with negative conductivity gradient can be formed by casting and condensing layer by layer and reducing the concentration of the slurry.
Preferably, in the step (3), the temperature of the freeze-drying is-60 to-40 ℃, for example, -40 ℃, -45 ℃, -50 ℃, -55 ℃, -60 ℃ and the like, and the pressure of the freeze-drying is 40 to 60Pa, for example, 40Pa, 45Pa, 50Pa, 55Pa, 60Pa and the like.
Preferably, in step (3), the freeze-drying time is 2-3 days.
In a third aspect, the present invention provides the use of an electromagnetic shielding foam as described in the second aspect for the manufacture of an electronic device.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, three-dimensional fractal silver dendrites and carbon nanotubes are used as conductive fillers, and flexible polymer materials are used as matrix materials, so that a conductive network is reasonably constructed, electromagnetic wave reflection is greatly reduced, and excellent shielding efficiency is obtained;
(2) The invention greatly reduces the consumption of two conductive fillers, namely three-dimensional fractal silver dendrite and carbon nano tube in the electromagnetic shielding foam, and has low preparation cost and high economic value;
(3) The three-dimensional fractal silver dendrite raw material is easy to prepare and store, and the method for preparing the layered foam is simple and feasible, so that the popularization and the application of the technology are facilitated;
(4) The shielding effectiveness of the electromagnetic shielding foam is 60-100dB, the reflection coefficient is below 0.25, and the thickness is 2.0-4.5mm; under the condition that the maximum compressive strain is 20-50%, after 100 times of cyclic compression, the rebound rate is above 85%, and the variation value of electromagnetic shielding effectiveness is below 10 dB.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
The sources of the components in the following examples are shown below: three-dimensional fractal silver dendrites (homemade), SWCNTs (Shenzhen Bay Co., diameter: 6-14nm, length: 20-75 μm), MWCNTs (manufacturer: ala Ding Gongsi, inner diameter: 3-5nm, outer diameter: 8-15nm, length: 50 μm), TPU (manufacturer: basoff, brand 85A), SBS (manufacturer: china petrochemical Co., brand 75A), SEBS (manufacturer: china petrochemical Co., brand 80A).
The three-dimensional fractal silver dendrite is prepared in a laboratory, specifically, is obtained by adopting a method of reducing silver nitrate solution by hydroxylamine at room temperature, wherein the molar concentration ratio of the silver nitrate to the hydroxylamine solution is 1:4, and the reaction solution is mixed at equal flow rate (5 mL/min) under the shaking condition. After the reaction is finished, washing with deionized water and alcohol for 3 times respectively, and then drying in a freeze dryer to obtain the three-dimensional fractal silver dendrite powder.
Example 1
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
the SWCNTs are ultrasonically dispersed in TPU solution, and three carbon nanotube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 9.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 3.0wt% of third carbon nanotube slurry, wherein TPU solution is mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 5.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 150 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 6.5g of first carbon nano tube slurry with the absolute dry mass fraction of 9.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 6.5g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 6.5g of third carbon nano tube slurry with the absolute dry mass fraction of 3.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 2
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 1.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
The MWCNT is dispersed in SBS solution in an ultrasonic way, and three carbon nano tube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 7.5wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 4.5wt% of third carbon nanotube slurry, wherein SBS solution is mixed solution of SBS and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 8.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 160 ℃ for 1.5h, and finally wetting the silver dendrite layer with 1.0g of SBS solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the SBS solution is a mixed solution of SBS and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 6.0g of first carbon nano tube slurry with absolute dry mass fraction of 7.5wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 6.0g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 6.0g of third carbon nano tube slurry with absolute dry mass fraction of 4.5wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 3
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
the SWCNTs are ultrasonically dispersed in TPU solution, and three carbon nanotube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 8.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 4.0wt% of third carbon nanotube slurry, wherein TPU solution is mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 6.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 170 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 7.0g of first carbon nano tube slurry with the absolute dry mass fraction of 8.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then 7.0g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% is poured into the condensate, and is solidified in the same way, so as to form a second carbon nano tube polymerization layer; then 7.0g of third carbon nano tube slurry with absolute dry mass fraction of 4.0wt% is poured into the condensate, and solidified in the same way, so as to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 4
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
The MWCNT is dispersed in SEBS solution in an ultrasonic way, and three carbon nano tube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 8.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 5.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 3.0wt% of third carbon nanotube slurry, wherein SEBS solution is mixed solution of SEBS and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 7.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 170 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of SEBS solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the SEBS solution is a mixed solution of SEBS and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 5.5g of first carbon nano tube slurry with the absolute dry mass fraction of 8.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 5.5g of second carbon nano tube slurry with an absolute dry mass fraction of 5.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 5.5g of third carbon nano tube slurry with the absolute dry mass fraction of 3.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 5
This example provides an electromagnetic shielding foam differing from example 1 only in that the first carbon nanotube slurry has an absolute dry mass fraction of 9.0wt%, the second carbon nanotube slurry has an absolute dry mass fraction of 8.0wt%, the third carbon nanotube slurry has an absolute dry mass fraction of 1.0wt%, and the other steps are the same as in example 1.
Example 6
This example provides an electromagnetic shielding foam differing from example 1 only in that the first carbon nanotube slurry has a dry mass fraction of 9.0wt%, the second carbon nanotube slurry has a dry mass fraction of 5.0wt%, the third carbon nanotube slurry has a dry mass fraction of 4.0wt%, and the other steps are the same as in example 1.
Example 7
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites; the SWCNT is dispersed in TPU solution by ultrasonic, and two carbon nano tube slurries with different concentration gradients are prepared: the absolute dry mass fraction of the first carbon nano tube slurry is 9.0wt% and the absolute dry mass fraction of the second carbon nano tube slurry is 6.0wt%, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 5.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 150 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 10g of first carbon nano tube slurry with the absolute dry mass fraction of 9.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 10g of second carbon nano tube slurry with absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 8
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites; dispersing SWCNT (SWCNT) in TPU (thermoplastic polyurethane) solution in an ultrasonic manner to obtain carbon nano tube slurry with the absolute dry mass fraction of 9.0wt%, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane with the mass ratio of 5:100;
(2) Pouring 5.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 150 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 6.5g of nano tube slurry with absolute dry mass fraction of 9.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 6.5g of nanotube slurry with an absolute dry mass fraction of 9.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nanotube polymerization layer; then pouring 6.5g of nanotube slurry with an absolute dry mass fraction of 9.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nanotube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 9
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
the SWCNTs are ultrasonically dispersed in TPU solution, and three carbon nanotube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 9.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 3.0wt% of third carbon nanotube slurry, wherein TPU solution is mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 2.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 150 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 8.0g of first carbon nano tube slurry with the absolute dry mass fraction of 9.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 8.0g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 8.0g of third carbon nano tube slurry with the absolute dry mass fraction of 3.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Example 10
The embodiment provides an electromagnetic shielding foam, and the preparation method of the electromagnetic shielding foam comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
The SWCNTs are ultrasonically dispersed in TPU solution, and three carbon nanotube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 9.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 3.0wt% of third carbon nanotube slurry, wherein TPU solution is mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 10.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, transferring the groove into an oven, sintering at 150 ℃ for 1.0h, and finally wetting the silver dendrite layer with 1.0g of TPU solution to form a three-dimensional fractal silver dendrite polymer layer, wherein the TPU solution is a mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(3) Slowly pouring 5.0g of first carbon nano tube slurry with the absolute dry mass fraction of 9.0wt% into a groove containing a three-dimensional fractal silver dendrite polymer layer, standing for 10min to enable the slurry to be fully leveled and further wet the silver dendrite layer, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 5.0g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the second carbon nano tube slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 5.0g of third carbon nano tube slurry with absolute dry mass fraction of 3.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Comparative example 1
The comparative example provides an electromagnetic shielding foam, the preparation method of which comprises the following steps:
(1) The SWCNTs are ultrasonically dispersed in TPU solution, and three carbon nanotube slurries with different concentration gradients are prepared: the preparation method comprises the following steps of (1) performing absolute dry mass fraction of 9.0wt% of first carbon nanotube slurry, absolute dry mass fraction of 6.0wt% of second carbon nanotube slurry and absolute dry mass fraction of 3.0wt% of third carbon nanotube slurry, wherein TPU solution is mixed solution of TPU and 1, 4-dioxane in a mass ratio of 5:100;
(2) Pouring 6.5g of first carbon nano tube slurry with the absolute dry mass fraction of 9.0wt% into a groove with the bottom horizontal and the diameter of 72mm, standing for 10min to enable the slurry to be fully leveled, and then standing the groove on a copper table cooled by liquid nitrogen to enable the slurry to be just solidified to form a first carbon nano tube polymerization layer; then pouring 6.5g of second carbon nano tube slurry with the absolute dry mass fraction of 6.0wt% into the condensate, and solidifying the slurry in the same way to form a second carbon nano tube polymerization layer; then pouring 6.5g of third carbon nano tube slurry with the absolute dry mass fraction of 3.0wt% into the condensate, and solidifying the slurry in the same way to form a third carbon nano tube polymerization layer; and (3) placing the groove containing the condensate in a freeze dryer, freeze drying the sample at 50Pa at-50 ℃ for 2 days, taking out and stripping after drying is finished, and obtaining the electromagnetic shielding foam.
Comparative example 2
The comparative example provides an electromagnetic shielding foam, the preparation method of which comprises the following steps:
(1) Dispersing three-dimensional fractal silver dendrites in an ethanol solution containing PVP, and preparing to obtain three-dimensional fractal silver dendrite suspension with solid content of 2.0wt%, wherein the addition amount of PVP is 0.5% of the mass of the three-dimensional fractal silver dendrites;
(2) Pouring 5.0g of three-dimensional fractal silver dendrite suspension into a groove with the bottom level and the diameter of 72mm, naturally drying to volatilize ethanol to form a silver dendrite layer, then transferring the groove into an oven, sintering at 150 ℃ for 1.0h, pouring 20.0g of TPU solution (5:100) into the silver dendrite layer, standing for 10min to enable the TPU solution to be fully leveled and further moisten the silver dendrite layer, standing the groove on a copper table cooled by liquid nitrogen to be condensed, finally placing the groove containing condensate into a freeze dryer, freeze drying a sample at 50Pa below-50 ℃, drying for 2 days, taking out after drying, and stripping to obtain the contrast electromagnetic shielding foam.
Performance testing
The electromagnetic shielding foams provided in examples 1 to 10 and comparative examples 1 to 2 above were each tested for each property, as follows: wherein, shielding effectiveness: waveguide method, vector network analyzer (model E5071C); reflection coefficient: calculating the measured S parameter by a waveguide method; thickness: a thickness gauge; maximum compressive strain: setting on a cyclic stretcher (Shenzhen regel instruments Co., ltd.); 100 cycle compression test: the test was carried out on a cyclic stretcher (Shenzhen regel instruments Co., ltd.).
The specific test results are shown in table 1 below:
TABLE 1
As shown in the test data of Table 1, the electromagnetic shielding foam of the invention has shielding effectiveness of 60-100dB, reflection coefficient of below 0.25 and thickness of 2.0-4.5mm; after 100 cycles of compression under the maximum compression strain of 20-50%, the rebound resilience of the electromagnetic shielding foam is still above 85%, and the variation value of electromagnetic shielding effectiveness is below 10 dB. The invention is fully demonstrated that the electromagnetic wave reflection is greatly reduced and excellent shielding efficiency is obtained through reasonably constructing the conductive network. When electromagnetic waves propagate to the layered foam along the positive conductive gradient direction, the reflection of electromagnetic waves at the interface is greatly reduced, the incident waves are continuously reflected and absorbed inside the foam, and along with the increase of the incident depth, the paths of the reflected waves inside the foam and the action of the inner walls of the foam are also continuously increased, so that most of the incident waves are consumed inside the foam. The data show that the foam simultaneously achieves excellent electromagnetic shielding effectiveness and a very low reflection coefficient. The electromagnetic shielding performance of the foam is excellent.
As can be seen from the comparison of comparative example 1, when the electromagnetic shielding foam contains no three-dimensional fractal silver dendrite and only contains carbon nanotubes, the shielding effectiveness of the electromagnetic shielding foam is greatly reduced due to the lack of a high-conductivity three-dimensional fractal silver dendrite/flexible polymer layer; as is clear from the comparison of comparative example 2, the electromagnetic shielding foam only contains three-dimensional fractal silver dendrites, and when no carbon nanotubes are present, the shielding effectiveness of the electromagnetic shielding foam is improved as compared with that of comparative example 1, but the reflection coefficient of the electromagnetic shielding foam is remarkably improved because the reflected waves cannot be consumed inside the electromagnetic shielding foam.
The applicant states that the electromagnetic shielding foam and the method of making and using it are illustrated by the above examples, but the invention is not limited to, i.e. it is not meant that the invention must be practiced in dependence on the above examples. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.
Claims (28)
1. The electromagnetic shielding foam is characterized by comprising the following raw materials in parts by weight: 5.8-12.4 parts of three-dimensional fractal silver dendrite, 4.0-6.0 parts of carbon nano tube and 81.6-90.2 parts of flexible polymer material;
the electromagnetic shielding foam sequentially comprises the following components from bottom to top: the three-dimensional fractal silver dendrite polymer layer, the first carbon nanotube polymer layer, the second carbon nanotube polymer layer and the third carbon nanotube polymer layer;
the content of the carbon nano tube in the first carbon nano tube polymer layer is more than the content of the carbon nano tube in the second carbon nano tube polymer layer is more than the content of the carbon nano tube in the third carbon nano tube polymer layer.
2. The electromagnetic shielding foam of claim 1, wherein the three-dimensional fractal silver dendrite means that a first-level fractal structure shows three-dimensional radiation growth, and silver powder with abundant nano structures is arranged at the tip of a second-level fractal structure and a third-level fractal structure.
3. The electromagnetic shielding foam of claim 1, wherein the carbon nanotubes are selected from single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
4. The electromagnetic shielding foam of claim 1, wherein the flexible polymeric material is selected from any one or a combination of at least two of thermoplastic polyurethane, styrene-butadiene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, or styrene-isoprene-styrene block copolymer.
5. The electromagnetic shielding foam of claim 1, wherein a difference between the carbon nanotube content in the first carbon nanotube polymer layer and the second carbon nanotube polymer layer is 2.0-4.0%.
6. The electromagnetic shielding foam of claim 1, wherein the difference between the carbon nanotube content in the second carbon nanotube polymer layer and the third carbon nanotube polymer layer is 2.0-4.0%.
7. The electromagnetic shielding foam of claim 1, wherein the electromagnetic shielding foam has a shielding effectiveness of 60-100 dB.
8. The electromagnetic shielding foam of claim 1, wherein the electromagnetic shielding foam has a reflectance of 0.15 or less.
9. The electromagnetic shielding foam of claim 1, wherein the electromagnetic shielding foam has a thickness of 2.0-4.0 mm.
10. The electromagnetic shielding foam of claim 1, wherein the electromagnetic shielding foam has a maximum compressive strain of 50% or less.
11. The electromagnetic shielding foam of claim 1, wherein the electromagnetic shielding foam has a rebound resilience of 85% or more and an electromagnetic shielding effectiveness variation of 10 dB or less after 100 cycles of compression.
12. The method for producing an electromagnetic shielding foam according to any one of claims 1 to 11, characterized in that the method for producing comprises the steps of:
step 1: preparing three-dimensional fractal silver dendrite into three-dimensional fractal silver dendrite suspension; dispersing carbon nanotubes in a solution of a flexible polymer material, and preparing to obtain carbon nanotube slurry;
step 2: pouring and sintering the three-dimensional fractal silver dendrite suspension obtained in the step 1, and wetting by adopting a solution of a flexible polymer material to form a three-dimensional fractal silver dendrite polymer layer;
Step 3: and (3) pouring the carbon nanotube slurry obtained in the step (1) above the three-dimensional fractal silver dendrite polymer layer obtained in the step (2), and freeze-drying after solidification to obtain the electromagnetic shielding foam.
13. The method for preparing the electromagnetic shielding foam according to claim 12, wherein in the step 1, the three-dimensional fractal silver dendrite suspension comprises three-dimensional fractal silver dendrite, polyvinylpyrrolidone and an alcohol solvent.
14. The method for preparing an electromagnetic shielding foam according to claim 13, wherein in the step 1, the solid content of the three-dimensional fractal silver dendrite is 1.0-2.0%.
15. The method for preparing the electromagnetic shielding foam according to claim 13, wherein the addition amount of the polyvinylpyrrolidone in the three-dimensional fractal silver dendrite suspension is 0.1-1.0% of the mass of the three-dimensional fractal silver dendrite.
16. The method of producing an electromagnetic shielding foam according to claim 13, wherein the alcohol solvent is selected from ethanol in the three-dimensional fractal silver dendrite suspension.
17. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 1, the flexible polymer material and the solvent are included in a solution of the flexible polymer material in a mass ratio of (4-6): 100.
18. The method of producing an electromagnetic shielding foam according to claim 17, wherein the solvent is 1, 4-dioxane.
19. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 1, three carbon nanotube slurries having different concentration gradients are prepared, comprising: the first carbon nano tube slurry with the absolute dry mass fraction of 7.5-9.0wt%, the second carbon nano tube slurry with the absolute dry mass fraction of 5.0-7.0wt% and the third carbon nano tube slurry with the absolute dry mass fraction of 3.0-4.5 wt%.
20. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 2, the sintering temperature is 150-180 ℃ and the sintering time is 1.0-2.0. 2.0 h.
21. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 2, the mass ratio of the three-dimensional fractal silver dendrite suspension to the solution of the flexible polymer material is (5-8): 1.
22. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 2, the flexible polymer material and the solvent are included in a solution of the flexible polymer material in a mass ratio of (4-6): 100.
23. The method of preparing an electromagnetic shielding foam according to claim 22, wherein the solvent is 1, 4-dioxane.
24. The method for preparing electromagnetic shielding foam according to claim 12, wherein in step 3, the concrete steps of casting are: pouring the carbon nano tube slurry obtained in the step 1 into a groove containing the three-dimensional fractal silver dendritic polymer layer, standing, and cooling and solidifying.
25. The method for preparing electromagnetic shielding foam according to claim 24, wherein in step 3, the concrete steps of casting are: pouring the first carbon nano tube slurry into a groove containing a three-dimensional fractal silver dendritic polymer layer, standing for 5-20 min, and then standing the groove on a copper table cooled by liquid nitrogen for cooling and solidifying to form a first carbon nano tube polymerization layer; and then the second carbon nano tube slurry and the third carbon nano tube slurry are sequentially poured and condensed by adopting the same method.
26. The method for producing an electromagnetic shielding foam according to claim 12, wherein in the step 3, the temperature of the freeze-drying is-60 to-40 ℃, and the pressure of the freeze-drying is 40-60 Pa.
27. The method of producing an electromagnetic shielding foam according to claim 12, wherein in step 3, the time of freeze-drying is 2 to 3 days.
28. Use of an electromagnetic shielding foam according to any of claims 1-11 for the manufacture of an electronic device.
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