CN110540729A - A kind of lightweight high-conductivity shielding material and preparation method thereof - Google Patents

Abstract

the invention discloses a light high-conductivity shielding material and a preparation method thereof. The electric shielding foam composite material comprises a matrix with a foam porous structure, wherein the matrix is made of a high molecular polymer as a framework, conductive fillers are uniformly dispersed in the matrix, and nano silver particles grow in situ on the inner surface and the outer surface of the matrix; the matrix with the foam porous structure is prepared by a template sacrifice method, wherein the template sacrifice method is to mix a mixed organic solution of a high molecular polymer and a conductive filler with a pore-forming agent, remove the organic solvent after mixing uniformly, and then put into water to dissolve and remove the pore-forming agent to obtain the matrix with the foam porous structure. The composite material prepared by the invention has high electromagnetic shielding effectiveness of 60-90dB between 8.2GHz and 12.5GHz, and the density of the material is between 0.1 and 0.16g cm < -1 >, so that the material is light and thin, and can meet the requirements of electronic devices on electromagnetic shielding materials.

Description

A kind of lightweight high-conductivity shielding material and preparation method thereof

technical field

The invention relates to the field of materials, in particular to a lightweight high-conductivity shielding material and a preparation method and application thereof.

Background technique

Lightweight and efficient electromagnetic shielding materials are an important research direction in the field of electromagnetic shielding materials. At present, the commonly used lightweight electromagnetic shielding materials mainly include conductive foam, graphene foam, metal porous material and carbon nanotube composite foam. Conductive foam is prepared by depositing conductive metal particles on the surface of polymer foam skeleton, which has high electromagnetic shielding performance, but the bonding force between the surface metal particles and the surface of polymer foam skeleton is not strong, and it is easy to fall off after repeated deformation. However, graphene foam has disadvantages such as complicated preparation process, high cost, and difficulty in practical application. Metal materials are mostly heavy, not resistant to corrosion, difficult to process, and expensive. Carbon nanotube composite foam has a series of excellent properties, such as electrical conductivity, good mechanical properties (flexibility, elasticity, etc.), high porosity, low density, lipophilicity and hydrophobicity, etc.

Traditional macromolecules are macromolecules connected by covalent bonds. The chemical bonds that make up macromolecules are very stable, and the electrons that form chemical bonds cannot move. There are no very active lone pairs of electrons or very active bonding electrons in the molecule. It is electrically neutral, so polymers have always been regarded as insulating materials. Usually, with the resistivity value of 10 ¹⁰ ohm·cm as the limit, above this limit is an insulating polymer material, and below it is collectively referred to as a conductive polymer material. The electrical conductivity of a material is due to the movement of charged particles present inside the material. These charged particles can be positive or negative ions, or electrons or holes, and are usually called carriers. Carriers move along the direction of the electric field under the action of an external electric field to form a current. The conductivity of a material is related to the number of carriers contained in the substance and its movement speed. The concentration and mobility of carriers are microscopic physical quantities that characterize the conductivity of materials. There are many conductive polymer materials that can be used. Thermoplastic elastomers and thermosetting elastomers are the most common. Among them, thermoplastic elastomer SBS, SIS, SEBS and other polymer matrix materials with the same function have outstanding applications in conductive polymer materials. .

Carbon black is the most common functional reinforcing filler among carbon-based fillers. The smaller the carbon black particles, that is, the more carbon black particles per unit volume of rubber compound, the greater the probability of contact between carbon black particles or the smaller the distance between particles, the smaller the resistance, and the better the conductivity. Among the carbon blacks with the same particle size, the high-structure carbon black has good conductivity, which is due to the fact that the high-structure carbon black has more chain branches, thus forming a conductive channel with more chain branches intertwined. More volatiles or residual tar on the surface of carbon black will form an insulating film on the surface of carbon black and reduce the conductivity of carbon black. Heat treatment of such carbon black in vacuum or inert gas to remove the surface insulating film will improve its conductivity. The greater the surface roughness, the better the conductivity of carbon black, because in the compound with the same amount of carbon black, the probability of contact between rough carbon black particles is greater than that between smooth carbon black particles. Similar conductive fillers include carbon nanofibers, carbon nanotubes, carbon fibers, graphite, graphene, and the like.

Conductive polymer materials have the same electromagnetic shielding performance, and are light in weight, good in toughness, easy to process, easy to adjust conductivity, low in cost, easy to apply on large areas, and convenient in construction. Therefore, it is an ideal electromagnetic shielding material to replace traditional metals, and can be applied to electronic and electrical components such as computers, mobile phones, televisions, computers, and cardiac pacemakers.

At present, the preparation methods of composite conductive polymers mainly include conductive filler composite method, conductive filler lamination composite method, and surface conductive film formation method.

Advantages: light weight (low density), easy molding and processing, electrical conductivity and products can be completed at one time, wide range of resistivity adjustment, low cost, and easy structure adjustment.

Challenges: Stability needs to be improved, and new application areas need to be discovered and developed.

According to the literature, the percolation threshold is an important parameter for the composite conductive polymer filled with carbon-based materials such as carbon black and carbon nanotubes. required electrical conductivity. Under the existing technology, it is very important to control the percolation threshold of conductive polymers.

(1) How to reduce the amount of conductive filler under the premise of improving conductive polymer composite materials;

(2) How to maintain or increase the molding processability, mechanical properties and other properties of conductive polymer composite materials under the premise of increasing the amount of conductive filler to improve the conductivity;

(3) Develop new varieties of conductive polymer composite materials and open up new application fields;

(4) Conductive polymer composite materials are multi-functional. In addition to making them conductive, they also have excellent properties such as flame retardancy, barrier properties, high temperature resistance, corrosion resistance, and friction resistance.

At present, the conductive filler compounding method is the most commonly used method for conductive fillers to be dispersed in composite materials. It uses a polymer as a matrix, and uses a blending method to disperse conductive fillers in it so as to have conductivity. Conductive fillers used in this method include carbon black, carbon fiber, metal fiber, metallized carbon fiber, metal foil, strips and silver-coated glass balls. The conductive filler dispersion composite method has good processing performance and low cost, but its main problems are: (1) The distribution of conductive fillers in the matrix is often uneven, so that the conductivity of the finished product is inconsistent; (2) The bond between the conductive filler and the substrate is generally poor.

Contents of the invention

The present invention adopts the method of mixing materials, uses cheap carbon-based materials as fillers, and uses a series of thermoplastic elastomers such as SBS, SIS, SEBS and other common polymer substrates, which can be melted by heating and solidified by cooling, and the matrix is relatively light. Quality, and there is good adhesion between the matrix and the filler, which can support the main structure of the foam and serve as the skeleton of the foam material, so that the dispersion of the conductive filler in the polymer is relatively uniform. At the same time, the foam-type porous material produced in the experiment has the advantages of stable structure, light weight, corrosion resistance and excellent electrical conductivity.

The invention provides an electrical shielding foam composite material, which comprises a matrix with a foam porous structure made of a high molecular polymer as a skeleton, and conductive fillers are uniformly dispersed in the matrix, and nano-silver is grown in situ on the inner and outer surfaces of the matrix particles.

In the technical scheme of the present invention, the high molecular polymer is selected from styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butadiene-styrene block copolymer ( SEBS), styrene-isoprene-styrene block copolymer (SIS), hydrogenated styrene-isoprene copolymer (SEPS) or a combination of more.

In the technical solution of the present invention, the conductive filler is selected from carbon-based fillers, preferably carbon nanotubes, carbon fibers, carbon nanofibers, graphene, graphite, and carbon black.

In the technical solution of the present invention, the density of the matrix is 0.05-0.1 g cm ^-1 , preferably 0.05-0.08 g cm ^-1 . When the sample density is higher than 0.08g cm ^-1 , the resilience is worse than that of 0.08g cm ^-1 .

In the technical solution of the present invention, the matrix of the foam porous structure is prepared by a template sacrifice method, which refers to mixing a mixed organic solution of a high molecular polymer and a filler with a pore-forming agent, and removing organic solvent, and then dissolved in water to remove the pore-forming agent to obtain a matrix of foam porous structure; the pore-forming agent is a water-soluble inorganic salt or sugar, and the inorganic salt or sugar is in the form of dispersed particles or powder, Preferably, the particle size of the inorganic salt or sugar is 100-3000 μm, preferably in the range of 100-1000 μm, more preferably 100-300 μm.

Wherein, the method for removing the organic solvent is drying, preferably, the drying temperature is lower than 100°C, more preferably lower than 80°C.

In the technical solution of the present invention, the inorganic salt is selected from one or a combination of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

In the technical solution of the present invention, nano-silver is attached to the surface of the substrate by the following method: soak the substrate containing conductive fillers in a silver salt solution, add a reducing agent for in-situ reduction, and grow in-situ on the inner and outer surfaces of the substrate to obtain a nano-silver layer ;

Preferably, described silver salt solution uses ethanol, propanol or butanol as solvent;

Preferably, the silver salt is selected from silver trifluoroacetate, silver nitrate, silver acetate, silver oxide, silver sulfate, silver carbonate, silver formate, silver acetate.

Preferably, the reducing agent is selected from hydrazine hydrate, concentrated sulfuric acid, hydroiodic acid, sodium borohydride.

In the scheme of the present invention, the silver salt solution can make the matrix polymer swell, the silver ions penetrate into the superficial layer and the surface of the polymer matrix, and use hydrazine hydrate to reduce the silver salt on the SBS matrix, so that a thin layer grows on the surface in situ. Thin nano-silver layer, at the same time, the nano-silver particles are embedded in the superficial layer of the polymer matrix SBS. The nano-silver layer prepared by the method of the present invention is evenly distributed, has a good degree of bonding with the matrix, and is not easy to fall off. Under the condition of external force, it can maintain stable conductivity and shielding performance.

In the technical solution of the present invention, the mass ratio between the conductive filler for preparing the matrix and the polymer compound is 1:3-9.

In the technical solution of the present invention, the mass of the silver nano-silver particles accounts for 30-50 wt% of the mass of the electrical shielding foam composite material.

In the technical solution of the present invention, the electric shielding foam composite material has a density of 0.1-0.16 g cm ^-1 .

In the technical solution of the present invention, the EMI SE value of the electric shielding foam composite material is 60-90dB.

In the technical proposal of the present invention, the CB/SBS shielding value of the foam composite material is 5-15dB.

Another aspect of the present invention provides a method for preparing an electric shielding foam composite material, comprising the steps of:

1) Dissolve the high molecular weight polymer and the conductive filler in the organic solvent respectively, and mix evenly,

2) mixing the pore-forming agent with the mixed solution in step 1),

3) removing the solvent therein, and removing the pore-forming agent therein with water, and drying to obtain a foamy matrix containing conductive fillers;

4) Soak the substrate containing the conductive filler in silver salt solution, add a reducing agent for in-situ reduction, grow nano-silver layers in situ on the inner and outer surfaces of the substrate, and dry to obtain an electromagnetic shielding foam composite material.

Beneficial effect

1. Compared with traditional conductive composite metal materials, composite conductive polymer materials have the following advantages: simple preparation, economical, convenient molding and processing, and the electrical and mechanical properties of the material can be adjusted under certain conditions. At the same time, the sample has both polymer specialty.

2. The range of conductive fillers that can be applied to the present invention is wide, and all carbon-based fillers can be used. For example, carbon black (CB) is a spherical filler, isotropic, cheap, and low density. It is currently the largest and most widely used filler. A kind of conductive filler. It can effectively improve the electromagnetic properties of the composite material, reduce the conductive permeation threshold of the composite material, and increase the electromagnetic shielding efficiency. In addition, the conductive filler can also use common carbon-based materials, such as a series of conductive carbon fillers such as carbon nanotubes, carbon fibers, carbon nanofibers, graphene, and graphite.

3. Utilizing the adsorption effect of polymer compounds on silver salts and the large specific surface area of the foamy matrix material, the silver salts are not only reduced in situ on the SBS pore columns, but also allow the growth of nano-silver particles inside the columns. , and then the conductive and shielding properties of the composite material are greatly improved.

4. The experiment uses soluble fillers as porogens to prepare polymer foams with adjustable pore size and pore shape. The fillers can be selected in a wide range. The fillers used are non-toxic and harmless, soluble in water, and have no impact on the environment.

5. The electromagnetic shielding effect of the conductive composite material sample is mainly based on absorption. The overall shielding performance of the foam composite material is improved through the combined effect of the absorption of the carbon material on the electromagnetic wave and the reflection of the metal silver on the electromagnetic wave. The combined effect of the two Complementary to each other, the EMI value of the conductive foam composite material reaches a higher value.

Compared with the existing experimental scheme:

The present invention solves the two problems mentioned above: (1) the distribution of conductive fillers in the matrix is often uneven, so that the conductivity of the finished product is inconsistent; (2) the bonding between the conductive fillers and the matrix is general poor.

The present invention adopts a very simple experimental method. By making foam-type porous material, the conductive filler is evenly dispersed in the matrix. The shape of the sample made in the experiment is regular. In the resistance test, the resistance values of the samples are approximately equal. The conductivity of the solid sample is basically equal everywhere, and the bonding between the conductive filler and the matrix is firm. It has been verified by experiments that it will not separate after ultrasonication in an ultrasonic machine for more than 24 hours. At the same time, a layer of silver is evenly adsorbed on the surface and inside of the polymer composite foam by chemical methods, so that the electrical conductivity is greatly improved, and the magnetic field shielding properties of high-frequency electromagnetic fields at 8.2-12.5GHz are good and the molding processability is good. Also excellent electromagnetic wave shielding material. At the same time, it has low cost of raw materials, light sample weight (density is 0.1-0.16g cm ^-1 ), excellent electrical conductivity (conductivity is 400-700s m ^-1 ), good anti-electromagnetic radiation effect (SE value is 60-90 dB )specialty.

In the present invention, SBS is a styrene-butadiene-styrene block copolymer, and CB is carbon black.

Description of drawings

Figure 1 is the experimental results for verifying sugar cube as a pore-forming agent.

Fig. 2 is a flow chart of the preparation of the electromagnetic shielding foam composite material of the present invention. Among them, (a) is a schematic diagram of the preparation flow chart, (b) is the picture of SBS/CB and SBS/CB/Ag on the stamen, and (c) is the state of SBS/CB/Ag sample after multiple compressions.

Fig. 3 is the compression cycle test result of the present invention, wherein (a) is the SBS/Ag sample, and (b) is the SBS/CB/Ag sample.

Fig. 4 is the SEM figure of CB/SBS composite material, and wherein, a, b, c are the foam (embodiment 1) that adopts the smallest sodium bicarbonate of particle size as pore-forming agent preparation, and d, e, f are that adopt particle size Medium sodium chloride is used as the foam (embodiment 2) prepared by the pore-forming agent, and g, h, and i are the foams (embodiment 3) prepared by adopting the sugar with the largest particle size as the pore-forming agent.

Fig. 5 is the SEM figure of the CB/SBS/Ag composite material that embodiment 6 prepares, and wherein, a, b, c, d are the foam (embodiment 1) that adopts the smallest sodium bicarbonate of particle size as pore-forming agent preparation Carry out the SBS/CB/Ag composite material that silver reduction obtains, e, f, g, h are the foam (embodiment 2) that adopts the medium sodium chloride of particle size to prepare as pore-forming agent to carry out the SBS/CB/Ag that silver reduction obtains Ag composite materials, i, j, k, and l are SBS/CB/Ag composite materials obtained by silver reduction using the foam (Example 3) prepared by using sugar with the largest particle size as a pore-forming agent.

Figure 6 is a picture of the SBS/Ag composite material prepared by the method in the literature, that is, the method of directly adsorbing silver on the surface of SBS, where a is the sample photo, b and c are the scanning electron micrographs of the foam sample, d and e Scanning electron micrographs of the /Ag composite.

Figure 7 shows the electromagnetic shielding value of CB/SBS/Ag samples. Where (a) is the EMI SE value of SBS/CB/Ag formed after silver salt reduction of SBS/CB at different thicknesses, and (b) is SBS/Ag formed after silver salt reduction of SBS and SBS/CB at the same thickness and the EMI SE values of SBS/CB/Ag, (c) is the EMI SE value of SBS/CB/Ag under multiple reductions, (d) is the SEabs and SEref values of SBS/CB/Ag.

Figure 8 is a physical map of the foam.

Fig. 9 is a schematic diagram of material shielding theory.

Figure 10 is a schematic diagram of sodium bicarbonate, sodium chloride and sugar in Examples.

Detailed ways

Embodiment 1 foam sample preparation experiment

Before the experiment, dry the polymer SBS to be used, and place it in an oven at 50-60°C for about 2 hours before use. In the experiment, ethyl acetate was used as the solvent of SBS, and a mixed solution of 20wt% SBS/ethyl acetate was prepared for use. At the same time, conductive filler particles carbon black (CB) were used as carbon-based fillers, and CB was dispersed by ultrasonic dispersion. In the ethyl acetate solution, the proportion is 5wt%. During the experiment, attention should be paid to controlling the concentration. If the concentration is too high, the solution will be too viscous and become gelatinous. Secondly, a fixed ratio of 20wt% SBS/ethyl acetate and 5wt% CB/ethyl acetate solution was used for mixing to form a mixed solution of CB and SBS in ethyl acetate, wherein the ratio of CB to SBS was 1:4, Stir the mixed solution by magnetic force for more than 24 hours, stir evenly, so that the materials are mixed with each other, mix the mixed solution with the crystalline solid of sodium bicarbonate soluble in water as a pore-forming agent through a mixer, and then complete the mixing The solution was transferred to a glass dish, and the glass dish was placed in an oven at 75°C for 24h to remove the ethyl acetate solvent. After the solvent has evaporated, take out the sample, place it in deionized water for a period of time to remove the soluble pore-forming agent, and dry it to form SBS/CB polymer composite foam.

Embodiment 2 Foam sample preparation experiment

The experiment process is similar to that of Example 1, except that the pore-forming agent is replaced by sodium chloride, and the pore diameter ratio 1 of the polymer composite foam of SBS/CB is also larger.

Embodiment 3 foam sample preparation experiment

The experiment process is similar to that of Example 1, except that the pore-forming agent is replaced with coarse sugar for the experiment, and the pore size ratio 2 of the polymer composite foam of SBS/CB is also larger.

Embodiment 4 foam sample preparation experiment

The experiment process is similar to that of Example 1, only the polymer matrix is replaced by SIS, and the polymer composite foam of SIS/CB is also obtained.

Embodiment 5 foam sample preparation experiment

The experiment process is similar to that of Example 1, only the polymer matrix is replaced by SEBS for the experiment, and the SEBS/CB polymer composite foam is also obtained.

Example 6 Composite material sample preparation experiment

Embodiment 1-3 is the experimental process of preparing SBS/CB composite material. Then, the adsorption of nano-silver particles was carried out, and the SBS/CB samples of Examples 1-3 were cut to form a composite foam with a thickness of 20mm*11mm and a thickness of 5mm. Prepare a 10wt% ethanol solution of silver trifluoroacetate, soak the cut foam for 30 minutes, take it out and dry it naturally for 3 hours, prepare a 50wt% aqueous solution of hydrazine hydrate ethanol, put the foam into it for reduction, and the sample is called SBS/CB/Ag composite material. The reaction formula of reducing silver ion with hydrazine hydrate: 2Ag ⁺ +N ₂ H ₄ +2H ₂ O＝2Ag+2NH ₃ OH ⁺ . Through the reduction of hydrazine hydrate, the surface and interior of the foam porous material are covered with a uniform layer of silver. By the quality difference of SBS/CB material and SBS/CB/Ag composite material before the reaction, calculate the 30-40wt% of the quality of SBS/CB/Ag composite material that nano-silver loading is

Reduce the concentration of the ethanol solution of silver trifluoroacetate to 5wt%, and increase the loading of nano-silver by secondary immersion. As can be seen from Figure 7(c), the electromagnetic shielding performance of the sample has been enhanced.

Embodiment 7 effect experiment

Scanning electron microscope analysis was carried out on the sample of the example, and it was found by comparing the results of the scanning electron microscope that the foam samples of Examples 1-3, as the particle size of the pore-forming agent increases, the pore size of the sample is also larger, and the density is also smaller , the smallest density is the pore-forming agent sample with a particle size of 1000-3000 microns, the density can reach 0.05g cm ^-1 , and the density of the sample with a particle size of 50-200 microns sodium bicarbonate is the largest , is 0.1g cm ^-1 . However, if the pore size is too large, the sample will not be easily compressed and the resilience will be poor. The experimental results prove that because the pore size of the sample prepared by using the sodium chloride pore-forming agent is moderate, and the pore diameter is about 100-300 microns, the sodium chloride pore-forming agent has good pore-forming properties and also has resilience properties .

Through the comparison of Example 1, Example 4 and Example 5, it is found that composite foam can be prepared in three kinds of experiments, but the SBS/CB composite material has the best electrical conductivity under the same conditions. It is verified by compression test that the compression of the sample Performance is also better.

Carry out the electromagnetic shielding performance test on the sample, use the vector analyzer to test the electromagnetic shielding performance, and record the data.

In Example 6, it can be seen from the shielding performance experiment that the upper right figure of Figure 7 shows that the EMI SE value of the SBS/Ag foam is much lower than the SE value of the SBS/CB/Ag foam under the same conditions, which proves that after the sample is added with CB, The EMI SE value of the sample is tested by a vector analyzer, and the electromagnetic shielding performance of the sample has been greatly improved.

Carry out a compression test on the sample, and then analyze the resistance of the sample to the compression treatment and the change of the electrical properties. It can be seen from Figure 3 that when the foam sample is compressed, the picture a is the SBS/Ag sample, and the picture b is the SBS/Ag sample. For the SBS/CB/Ag sample, after repeated compression, the electrical properties of the SBS/Ag sample changed. First, when the number of cycles increased, the sample a fluctuated greatly, and the resistance always showed an increasing trend. When adding After CB, a certain conductive network is formed inside the sample, and after adding Ag, the conductivity of the sample SBS/CB/Ag is stronger, so the change of the resistance of the sample after multiple compressions is quite stable, and the electrical performance is excellent.

At the same time, it can be seen from the upper left figure of Figure 7 that the thickness of the sample has an impact on the shielding performance of the sample when the foam sample using sodium chloride pore-forming agent has the same adsorption time of silver. EMI SE can reach a peak value of around 70dB. At the same time, it can be seen from the upper right figure of Figure 7 that the addition of CB also greatly improves the electromagnetic shielding performance of the sample. When two kinds of CB/SBS and pure SBS samples with the same thickness and the same adsorption time, after adsorbing Ag, the composite sample with CB has more excellent electromagnetic shielding performance. Figure 7(c) shows that if the concentration of silver salt is reduced for multiple adsorptions, as the number of times increases, the amount of nano-silver in the sample increases, and the sample has better shielding performance, thus illustrating that the amount of nano-silver is important for electromagnetic shielding. Performance impact is large.

Because the foamed porous material prepared by the method of the present invention has a large specific surface area, good pore dispersion, uniform pore diameter distribution, and interrelationship, and adopts high-conductivity CB particles at the same time, the particle size is very small, and it can be used under magnetic stirring. When it can be distributed in polymer materials such as SBS, the distribution method is relatively uniform. When it is prepared into a foam, the internal nature of the polymer forms a conductive network dominated by conductive materials. The sample has good conductivity and a certain degree of EMI performance. . If a layer of nano-silver particles is further reduced on the surface of the sample, the conductivity of the sample is further improved. The electromagnetic shielding value of the sample at high frequency 8.2GHz-12.5GHz is very high, the highest can reach about 90dB, generally around 60-80dB, it can be seen from Figure 7(d) that the SEabs of the sample is higher than that of SEref, showing Most of the shielding properties of foam composites are absorption losses.

The resistance test is carried out on the top and bottom of the sample surface with a resistance instrument, and the resistance values of the samples are approximately equal. The conductivity of the solid sample is basically equal everywhere, which proves that the conductive filler is distributed evenly in the matrix.

The foam sample was ultrasonically treated with an ultrasonic machine for 24 hours, and the resistance value of the sample before and after ultrasonic testing was tested by a resistance instrument. There was no change, which proved that the connection between the conductive filler and the matrix was tight and not easy to fall off.

Comparative example 1

Using cube sugar used in the prior art as a pore-forming agent, according to the literature, experiments are shown in Figure 1, and the experiments verify the polymer SBS (a, b) and the composite material CB/SBS (b, c, e, f) It is difficult to enter the inside of the sugar cube, and most of them stay on the surface, and the pore size range is relatively limited. The present invention adopts the water-soluble pore forming agent commonly used in the laboratory, such as sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and sugar and baking soda commonly used in life. As a pore-forming agent, it is in a dispersed form, which can better disperse in the matrix material and form connected and uniform pores.

Claims (10)

1. An electric shielding foam composite material, which comprises a matrix of a foam porous structure made of a high molecular polymer as a skeleton, and is uniformly dispersed with a conductive filler inside the matrix, and grows nano-silver particles in situ on the inner and outer surfaces of the matrix; Preferably, the matrix of the foam porous structure is prepared by a template sacrifice method, which refers to mixing a mixed organic solution of a high molecular polymer and a conductive filler with a pore-forming agent, and removing the organic solvent after mixing uniformly, Then put it into water to dissolve and remove the pore-forming agent to obtain the matrix of the foam porous structure; More preferably, the pore-forming agent is a water-soluble inorganic salt or sugar, and the inorganic salt or sugar is in the form of dispersed particles or powder; Most preferably, the particle size of the inorganic salt or sugar is 100-3000 μm. 2. In the technical solution of the present invention, the inorganic salt is selected from one or more combinations of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. 3. The electric shielding foam composite material according to claim 1, the polymer is selected from the group consisting of styrene-butadiene-styrene block copolymer, styrene-ethylene-butadiene-styrene block copolymer One or more combinations of block copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated styrene-isoprene copolymers. 4. The electrical shielding foam composite material according to claim 1, wherein the conductive filler is selected from carbon-based fillers, preferably carbon nanotubes, carbon fibers, carbon nanofibers, graphene, graphite, and carbon black. 5. The electric shielding foam composite material according to claim 1, wherein the density of the electric shielding foam composite material is 0.1-0.16 g cm ⁻¹ . 6. The electrical shielding foam composite material according to claim 1, wherein the EMI SE value of the electrical shielding foam composite material is above 60dB, preferably 60-90dB. 7. The electric shielding foam composite material according to claim 1, the nano-silver is embedded on the surface of the substrate by the following method: the substrate containing the conductive filler is soaked in the silver salt solution, and a reducing agent is added for in-situ reduction, In-situ growth on the inner and outer surfaces of the substrate to obtain a nano-silver layer; Preferably, described silver salt solution uses ethanol, propanol or butanol as solvent; Preferably, the silver salt is selected from silver trifluoroacetate, silver nitrate, silver acetate, silver oxide, silver sulfate, silver carbonate, silver formate, silver acetate; Preferably, the reducing agent is selected from hydrazine hydrate, concentrated sulfuric acid, hydroiodic acid, sodium borohydride. 8. The electrical shielding foam composite material according to claim 1, the mass ratio between the conductive filler of the matrix and the polymer compound is 1:3-9. 9. The electric shielding foam composite material according to claim 1, wherein the mass of the silver nano-silver particles accounts for 30-50wt% of the mass of the electric shielding foam composite material. 10. The preparation method of the electric shielding foam composite material described in claims 1-9, which comprises the steps of: 1) Dissolve the high molecular weight polymer and the conductive filler in the organic solvent respectively, and mix evenly, 2) mixing the pore-forming agent with the mixed solution in step 1), 3) removing the solvent therein, and removing the pore-forming agent therein with water, and drying to obtain a foamy matrix containing conductive fillers; 4) Soak the substrate containing the conductive filler in silver salt solution, add a reducing agent for in-situ reduction, grow nano-silver layers in situ on the inner and outer surfaces of the substrate, and dry to obtain an electromagnetic shielding foam composite material.