CN114573858A - Preparation method of multilayer foaming material for electromagnetic shielding - Google Patents
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Abstract
The invention discloses a preparation method of a multilayer foaming material for electromagnetic shielding; according to the invention, a multilayer sheet with good interface binding force is prepared by adopting a simple and convenient way of one-step hot press molding after powder stacking, and then the multilayer foaming material for electromagnetic shielding is prepared by a supercritical gas foaming method; the material has low density and good electromagnetic shielding and absorption capacity, and is a light electromagnetic shielding composite material with excellent overall performance.
Description
Technical Field
The invention relates to the technical field of electromagnetic shielding composite materials, in particular to a preparation method of a foaming material with multiple layers of foam holes.
Background
With the development of new electronic information technology such as 5G and the wide application of various electronic devices, the electromagnetic pollution caused by the technology has become a problem which cannot be ignored. Electromagnetic pollution can not only interfere with the normal use of electronic instruments, but also cause harm to human health. In this context, the demand for high-performance electromagnetic shielding materials is gradually increasing. The application of the conventional shielding material is limited due to the defects of high cost, heavy weight and the like, and the secondary pollution is caused by the shielding mechanism mainly based on reflection, so that the application of the conventional shielding material is limited greatly. The conductive polymer material meets the requirements of emerging communication technology and aerospace equipment on the quality of the material due to the light weight characteristic, so that the conductive polymer material gradually becomes a research hotspot in the field.
The conductivity of the conductive polymer is generally low, and in order to achieve high electromagnetic shielding capability, a large amount of conductive fillers (such as carbon nanotubes, graphene, carbon black, and the like) need to be filled in the polymer matrix to form an adequate conductive network. However, too much conductive filler amplifies the impedance mismatch between the material and the air, so that a large amount of electromagnetic waves are reflected and secondary pollution is caused. How to achieve high electromagnetic shielding absorption at low conductive filler loading is therefore the biggest problem for improving conductive polymers. The construction of a multi-interface structure has been well documented to enhance the electromagnetic wave absorption capability of conductive polymers. The shielding performance of the interfaces between layers in the multilayer conductive polymer can be improved through the attenuation effect of the interfaces, and a plurality of interfaces are also constructed through a cell structure introduced by a foaming method, so that impedance mismatch is favorably reduced, and reflection is reduced. Therefore, the multilayer structure and the cellular structure are organically combined to fully exert the synergistic effect thereof, and the effect of '1 +1> 2' is achieved.
However, the existing multilayer foaming material has the defects of complex preparation process, poor adhesion among layers and the like. For example, patent CN111660641B discloses a method for preparing a multilayer foam for electromagnetic shielding, which comprises loading conductive metal on the surface of fiber and mixing with polymer to obtain conductive fiber-polymer composite material, laminating carbon-based filler-polymer composite material layer by layer onto the conductive fiber-polymer composite material to obtain multilayer composite material, and finally obtaining the polymer electromagnetic shielding composite material with multilayer cellular structure by foaming. However, the method is complex and time-consuming in preparation process, the bonding force between the interfaces of the multilayer composite material prepared by multiple times of hot pressing layer by layer is poor, and gaps and defects are easy to occur between the interfaces after foaming.
Disclosure of Invention
In order to overcome the problem of poor layer-to-layer combination caused by complex preparation process of the existing multilayer foaming material, the invention provides a preparation method of an electromagnetic shielding composite material with multilayer foam holes.
The technical scheme of the invention is as follows:
a method for preparing a multilayer foam material comprises the following steps:
(1) mixing the polymer and the carbon nano filler in a high-speed mixer to obtain carbon nano filler-polymer mixed powder for later use; and preparing a pure polymer powder for use;
the polymer is selected from: at least one of polyethylene, polypropylene, polycarbonate, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyamide, vinyl acetate copolymer, polymethyl methacrylate, polyurethane, polylactic acid, polycaprolactone, polyvinyl alcohol, epoxy resin, melamine formaldehyde resin, silicone resin, polyarylate, acrylate, phenol resin, polyether ether ketone, polysulfone, polyphenylene sulfide, polyimide, preferably polystyrene, polymethyl methacrylate, or polytetrafluoroethylene;
the carbon nanofiller is selected from: at least one of carbon nanotubes, graphene and carbon black, preferably carbon nanotubes;
the mass fraction of the carbon nanofiller in the carbon nanofiller-polymer mixed powder is 3-18%, preferably 6-9%;
the rotating speed of the high-speed mixer is 18000-30000 r/min, and the mixing time is 5-10 min;
(2) stacking the carbon nano filler-polymer mixed powder prepared in the step (1) and pure polymer powder in a mould to form a plurality of layers, and performing hot press molding by using a flat vulcanizing machine to obtain a sheet with a multi-layer structure;
the preferred powder stacking means are: sequentially paving carbon nano filler-polymer mixed powder, pure polymer powder and carbon nano filler-polymer mixed powder from bottom to top, stacking the powder into 3 layers, wherein the paving thickness of each layer of powder is 1.1 mm;
the hot-press molding temperature is 180-200 ℃, the pressure is 8.0-11.0 Mpa, and the hot-press time is 10-15 min;
(3) foaming the sheet with the multilayer structure obtained in the step (2) to obtain the multilayer foaming material;
the foaming treatment is carried out in a supercritical kettle pressure foaming machine, and the specific operation method comprises the following steps:
placing the sheet with the multilayer structure in a supercritical kettle pressure foaming machine, setting the temperature to be 75-95 ℃, introducing supercritical gas after the reaction kettle is closed, keeping the pressure to be 10.8-13.8 MPa, keeping the pressure for 3-4 hours, quickly releasing the pressure for 0.5-1 s, and opening the reaction kettle after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material;
the supercritical gas is one or more of nitrogen, carbon dioxide, helium and argon, preferably CO2、N2One or two of the components are mixed;
the supercritical kettle pressure foaming machine comprises: a reaction kettle and a control system;
the reaction kettle comprises an upper die and a lower die, a reaction cavity is formed in a cavity between the upper die and the lower die, the upper die is provided with an air inlet valve and an air outlet valve, the air inlet valve can control the supercritical gas to enter, the air outlet valve can control the supercritical gas to be discharged, and the pressure relief time is controlled by adjusting the size of an air outlet channel of the air outlet valve; a metal flow guide layer is arranged in the reaction cavity, and is made of foam copper or foam nickel, so that the diffusion of supercritical gas is facilitated;
the control system comprises a pressure maintaining system, the pressure maintaining system is a PCT automatic control system, pressure change in the reaction cavity is monitored in real time through the PCT automatic control system, and the booster pump is controlled to be opened or closed in real time to achieve the purpose of maintaining pressure.
The principle of the invention is as follows:
the carbon nano filler is coated on the surface of the polymer particles in a high-speed mixing mode, and the sheet is prepared by hot-press molding. The carbon nano filler coated with the polymer matrix forms a good conductive network after hot press molding, and the conductivity and the electromagnetic shielding performance of the composite material are well improved. In addition, the conductive network with the similar isolation structure can effectively utilize the filler, so that higher performance can be achieved under lower loading capacity, and the loading capacity of the carbon nano filler is reduced. Meanwhile, the polymer-carbon nano filler multilayer composite material is simply, conveniently and efficiently obtained through the preparation method of powder stacking and one-time hot press molding of the same polymer matrix, the bonding force between layers is good, and interface gaps and defects are not easy to appear between interfaces after foaming.
The invention has the beneficial effects that:
1. according to the invention, by means of high-speed mixing and hot-press molding, a conductive network with an isolation structure is constructed in the polymer-carbon nano filler composite material, and the filler is efficiently utilized, so that higher conductivity is realized under lower filler loading capacity.
2. The preparation method adopted by the invention is simple, convenient and efficient, the process conditions are controllable, and the prepared multilayer foaming material for electromagnetic shielding has stronger bonding force between layers and is not easy to generate gaps and defects.
3. The supercritical foaming technology used in the invention is clean and environment-friendly, and no waste water and waste gas are generated in the production process.
Drawings
FIG. 1 is a SEM image of a section of a foamed material prepared in example 1 of the present invention.
FIG. 2 is a SEM image of a section of a foamed material prepared in example 4 of the invention.
Fig. 3 is a graph comparing the electromagnetic shielding effectiveness of examples 1 to 6 of the present invention.
Fig. 4 is a graph comparing the electromagnetic shielding effectiveness of comparative examples 1 and 2 and example 1 of the present invention.
Detailed Description
The invention will be further described in the following by means of specific embodiments with reference to the attached drawings, to which, however, the scope of protection of the invention is not limited.
The following examples used carbon nanotubes (Nanocyl-7000, Belgium), polystyrene (GP-5250, Ningbo Taiwan).
Example 1: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 4.5g of carbon nano tube and 40.5g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder with the surface coated with 9% of carbon nano tube by mass fraction; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mold in sequence according to the sequence of the carbon nanotube-polystyrene powder, the pure polystyrene powder and the carbon nanotube-polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 85 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Example 2: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 4.5g of carbon nano tube and 40.5g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder with the surface coated with 9% of carbon nano tube by mass fraction; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mold in sequence according to the sequence of the carbon nanotube-polystyrene powder, the carbon nanotube-polystyrene powder and the pure polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 85 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Example 3: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 9g of carbon nano tube and 36g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder coated with 18% of carbon nano tube on the surface; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mould in sequence according to the sequence of the pure polystyrene powder, the carbon nanotube-polystyrene powder and the pure polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 85 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Example 4: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 9g of carbon nano tube and 36g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder coated with 18% of carbon nano tube on the surface; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mould in sequence according to the sequence of the carbon nanotube-polystyrene powder, the pure polystyrene powder and the pure polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 85 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Example 5: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 4.5g of carbon nano tube and 40.5g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder coated with 9% of carbon nano tube on the surface; preparing 6% of carbon nano tube-polystyrene powder and 3% of carbon nano tube-polystyrene powder by the same method;
(2) stacking carbon nanotube-polystyrene powder with different mass fractions in a mold in sequence according to the sequence of 3% of carbon nanotube-polystyrene powder, 6% of carbon nanotube-polystyrene powder and 9% of carbon nanotube-polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 85 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Example 6: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 3g of carbon nano tube and 42g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder coated with 6% of carbon nano tube on the surface; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder with different mass fractions in a mold in sequence according to the sequence of 6% of carbon nanotube-polystyrene powder, 6% of carbon nanotube-polystyrene powder and 6% of carbon nanotube-polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2As supercritical gas, placing the carbon nano tube-polystyrene sheet with the multilayer structure prepared in the step (2) in a supercritical kettle pressure foaming machine, and placing the kettle in advanceThe temperature of the pressure foaming machine is raised to 85 ℃, a sample is put in the pressure foaming machine, the mold is closed, and ScCO is introduced2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Comparative example 1: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 4.5g of carbon nano tube and 40.5g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder with the surface coated with 9% of carbon nano tube by mass fraction; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mold in sequence according to the sequence of the carbon nanotube-polystyrene powder, the pure polystyrene powder and the carbon nanotube-polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 75 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Comparative example 2: a multi-layer foaming material for electromagnetic shielding is prepared by the following steps:
(1) putting 4.5g of carbon nano tube and 40.5g of polystyrene powder into a high-speed mixer, and mixing at 18000r/min for 5min to obtain polystyrene powder with the surface coated with 9% of carbon nano tube by mass fraction; 45g of pure polystyrene powder was prepared in the same manner;
(2) stacking carbon nanotube-polystyrene powder and pure polystyrene powder in a mold in sequence according to the sequence of the carbon nanotube-polystyrene powder, the pure polystyrene powder and the carbon nanotube-polystyrene powder, wherein the laying thickness of each layer of powder is 1.1mm, and performing hot press molding by using a flat vulcanizing machine to obtain a carbon nanotube-polystyrene sheet with a multilayer structure, wherein the hot press temperature is 180 ℃, the pressure is 11MPa, and the hot press time is 10 min;
(3) selection of ScCO2Placing the multilayer-structure carbon nanotube-polystyrene sheet prepared in the step (2) in a supercritical kettle pressure foaming machine as supercritical gas, raising the temperature of the kettle pressure foaming machine to 95 ℃ in advance, placing a sample, closing the mold, and introducing ScCO2And setting the pressure to be 13.8MPa and keeping the pressure for 4 hours, quickly decompressing within 1s, and opening the die after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material for electromagnetic shielding.
Analysis of results
The sectional morphology of the multilayer foaming material for electromagnetic shielding prepared in example 1 is subjected to SEM characterization, and the result is shown in FIG. 1, which shows that the multilayer foaming material prepared by the invention has an obvious interface, good direct compatibility of the interface, and no defect or gap between the interface and the interface.
SEM representation of the section morphology of the multi-layer foaming material for electromagnetic shielding prepared in example 4 is performed, and as shown in FIG. 2, it can be known that the multi-layer foaming material formed by combining cells with different cell sizes and densities can be obtained by adjusting the content of the carbon nanotubes in the carbon nanotube-polystyrene mixture and the arrangement sequence of each layer.
The multi-layer foam material for electromagnetic shielding prepared in examples 1 to 6 was cut into a rectangular parallelepiped of 22.86mm × 10.16mm × 3mm, and the electromagnetic shielding performance of the material was measured using a vector network analyzer (VNA, AV 3672C). The test method is a waveguide method, the test frequency is 8-12.4GHz, and figure 3 shows the electromagnetic shielding effectiveness of each composite material. The design of the multilayer structure and the introduction of the cell structure greatly increase the interfaces in the material, which is beneficial to multiple reflection, absorption and dissipation of electromagnetic waves, and different cell arrangement combinations have different electromagnetic shielding efficiencies, wherein the 9-0-9 structure of example 1 has the best performance, and the shielding efficiency exceeds 20dB, namely 99% of incident electromagnetic waves are shielded by the material.
Considering that the thickness greatly affects the electromagnetic shielding performance of the material, the actual thickness of the foamed sheet is reduced due to the density reduction after foaming, and thus the foam of the same thickness as the unfoamed sample contains less conductive filler. Therefore, the ratio of the shielding effectiveness (shielding effectiveness divided by density) is more suitable as an index for measuring the electromagnetic shielding capability of the foam material. Fig. 4 is a graph comparing the specific electromagnetic shielding effectiveness of comparative examples 1, 2 and example 1. Because the foaming temperature can obviously influence the structure of the foam holes and the integral foaming multiplying power of the foaming material, the samples have different specific electromagnetic shielding efficiencies at different foaming temperatures, and when the foaming temperature is 85 ℃, the prepared multilayer foaming material has the optimal specific shielding efficiency and reaches 49.02dB m3/g。
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (7)
1. A method for preparing a multilayer foamed material, comprising the steps of:
(1) mixing the polymer and the carbon nano filler in a high-speed mixer to obtain carbon nano filler-polymer mixed powder for later use; and preparing a pure polymer powder for use;
the mass fraction of the carbon nanofillers in the carbon nanofiller-polymer mixed powder is 3-18%;
(2) stacking the carbon nano filler-polymer mixed powder prepared in the step (1) and pure polymer powder in a mould to form a plurality of layers, and performing hot press molding by using a flat vulcanizing machine to obtain a sheet with a multi-layer structure;
(3) and (3) foaming the sheet with the multilayer structure obtained in the step (2) to obtain the multilayer foaming material.
2. The process for preparing a multilayer foamed material according to claim 1, wherein in the step (1), the polymer is selected from the group consisting of: at least one of polyethylene, polypropylene, polycarbonate, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyamide, vinyl acetate copolymer, polymethyl methacrylate, polyurethane, polylactic acid, polycaprolactone, polyvinyl alcohol, epoxy resin, melamine formaldehyde resin, silicone resin, polyarylate, acrylate, phenol resin, polyether ether ketone, polysulfone, polyphenylene sulfide, and polyimide.
3. The method for preparing a multi-layered foamed material according to claim 1, wherein in the step (1), the carbon nanofiller is selected from the group consisting of: at least one of carbon nanotubes, graphene and carbon black.
4. The method for preparing a multi-layered foamed material according to claim 1, wherein in the step (1), the rotation speed of the high-speed mixer is 18000 to 30000r/min, and the mixing time is 5 to 10 min.
5. The method for preparing a multi-layered foamed material according to claim 1, wherein in the step (2), the powders are stacked in such a manner that: the carbon nanofiller-polymer mixed powder, the pure polymer powder and the carbon nanofiller-polymer mixed powder were sequentially laid in order from bottom to top, and stacked into 3 layers, each layer of powder having a thickness of 1.1 mm.
6. The method for preparing the multi-layered foamed material according to claim 1, wherein in the step (2), the hot-press molding temperature is 180 to 200 ℃, the pressure is 8.0 to 11.0Mpa, and the hot-press time is 10 to 15 min.
7. The method for preparing a multi-layer foamed material according to claim 1, wherein in the step (3), the foaming process is performed in a supercritical tank foaming machine by the following operation method:
placing the sheet with the multilayer structure in a supercritical kettle pressure foaming machine, setting the temperature to be 75-95 ℃, introducing supercritical gas after the reaction kettle is closed, keeping the pressure to be 10.8-13.8 MPa, keeping the pressure for 3-4 hours, quickly releasing the pressure for 0.5-1 s, and opening the reaction kettle after the pressure in the reaction kettle is completely released to obtain the multilayer foaming material;
the supercritical gas is one or a mixture of nitrogen, carbon dioxide, helium and argon.
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