A hierarchical aramid electromagnetic shielding sheet and a method of making the same

Abstract

The application provides a hierarchical aramid electromagnetic shielding sheet and a preparation method thereof. The preparation method of the aramid electromagnetic shielding sheet is as follows: firstly, aramid chopped fibers (ACFs), polyphenylene sulfide pulp (PPS) and ferroferric oxide (Fe3O4) are used to prepare an ACFs / PPS / Fe3O4 composite sheet through wet papermaking. Then, chopped carbon fibers (CFs), polyphenylene sulfide pulp and carbon nanotubes (CNT) are used to prepare a CFs / PPS / CNT composite sheet through the same way. The hierarchical aramid electromagnetic shielding sheet is prepared by designing the arrangement mode of the ACFs / PPS / Fe3O4 composite sheet and the CFs / PPS / CNT composite sheet and using the melting and infiltration effect of PPS on ACFs and CFs under high-temperature hot pressing conditions. The method is simple, the prepared aramid electromagnetic shielding sheet has excellent mechanical strength, super high-temperature resistance, flexibility and electromagnetic shielding performance, and can be widely applied in the fields of national defense and military industry, aerospace, 5G telecommunication base materials and electromagnetic shielding.

Description

TECHNICAL FIELD

[0001] The present application relates to high-performance fiber materials, in particular to a hierarchical structure aramid electromagnetic shielding sheet and a preparation method thereof. BACKGROUND

[0002] With the extensive and deep popularization of electronic products, electromagnetic pollution has become a serious social problem. Electromagnetic pollution not only has a great impact on electronic equipment and communication safety, but also affects people's health. For example: in the field of national defense and military industry, electromagnetic attacks on information-based equipment can cause equipment damage or malfunction, which will directly affect the final result of the war; in the health field, electromagnetic radiation can affect the nervous system of human beings, and then make people feel memory loss and loss of appetite, etc. Therefore, it is of great significance to develop materials with excellent electromagnetic shielding performance.

[0003] Among carbon-based materials, carbon fibers are fibers with a carbon content of more than 92% after high-temperature heat treatment of organic fibers in a protective atmosphere. The sp2 hybrid atomic structure between carbon-carbon bonds in the planar hexagonal network endows carbon fibers with excellent mechanical properties, electrical and thermal properties, and extremely high strength-to-weight ratio. Among carbon-based nanomaterials, carbon nanotubes are one-dimensional (1D) materials. Due to their excellent electrical conductivity and larger specific surface area, they are considered to be promising building blocks in carbon fiber paper-based materials. Carbon fibers and carbon nanotubes with excellent electrical conductivity are often considered to be ideal candidates for electromagnetic shielding materials. However, pure carbon fiber and carbon nanotube composites have greater brittleness and lack of flexibility, which greatly limits their application range.

[0004] Among fiber materials, aramid fibers have excellent mechanical properties, high temperature resistance and insulation, and are widely used in aerospace, rail transportation and national defense and military industry. High-performance aramid paper inherits the advantages of aramid fibers and exhibits unique advantages in flexibility and processability. However, aramid sheet is an ideal wave-transparent and insulating material and does not have excellent electromagnetic shielding effect. How to prepare high-performance aramid paper with excellent mechanical strength, high temperature resistance, flame retardance and electromagnetic shielding performance is still a difficult problem.

[0005] In the prior art, loading a metal layer on a sheet by electroplating or chemical plating of metal to impart electromagnetic shielding effect to the material is an effective solution. For example, CN111364283B discloses a silver-plated conductive aramid paper and a preparation method thereof. The method first needs to clean the aramid paper substrate to remove impurities, then needs to treat the aramid paper by plasma to activate the surface of the aramid paper, and finally puts the activated aramid paper into a silver-ammonia solution, and then adds a reducing agent to obtain a silver-plated aramid paper. The aramid paper obtained by the method has certain electrical conductivity and electromagnetic shielding performance. However, the plasma modification of aramid fibers and the reduction of silver-ammonia solution greatly increase the technical difficulty of the preparation process, and at the same time, the interfacial bonding strength between aramid fibers and silver is still a problem. The prior art also discloses an aramid fiber electromagnetic shielding sheet and a preparation method thereof. The method mixes aramid fiber powder and carbon nanotube powder, then coats them on the surface of the substrate film, and then hot-presses to obtain an aramid fiber electromagnetic shielding sheet. The electromagnetic shielding sheet obtained by the method has excellent mechanical properties and electromagnetic shielding performance. However, relying solely on the blending of carbon nanotubes cannot fully utilize their excellent electrical conductivity and electromagnetic shielding performance.

[0006] Through the above analysis, the problems and defects of the prior art are that: after plasma modification of the aramid paper substrate, a metal layer is plated on the surface of the aramid paper by reducing metal oxides to impart electrical conductivity and electromagnetic shielding properties to the aramid paper. However, the complex modification operation and the interface problem between the metal and the paper still need to be considered. In addition, although the addition of conductive nanofillers in aramid paper by physical blending can improve the electrical conductivity and electromagnetic shielding performance of aramid paper to some extent, this method cannot fully utilize the electrical conductivity of conductive nanofillers due to strong interfacial barrier effect. Therefore, the electromagnetic shielding performance of the prepared aramid paper is weak. Based on the defects of the current aramid electromagnetic shielding sheet, it is necessary to improve it. SUMMARY

[0007] In view of the problems of the prior art, the present application provides a preparation method of a hierarchical aramid electromagnetic shielding sheet.

[0008] In one aspect, the present application discloses a preparation method of a hierarchical aramid electromagnetic shielding sheet, comprising:

[0009] Step one, preparation of aramid fiber / polyphenylene sulfide / ferric oxide (ACFs / PPS / Fe3O4) composite sheet;

[0010] Wherein, the aramid fiber is aramid chopped fiber, and the polyphenylene sulfide is polyphenylene sulfide pulp;

[0011] Step two, preparation of chopped carbon fiber / polyphenylene sulfide / carbon nanotube (CFs / PPS / CNT) composite sheet;

[0012] wherein the carbon fiber is short-cut carbon fiber, and the polyphenylene sulfide is polyphenylene sulfide pulp;

[0013] Step three, hierarchical structure compounding of the ACFs / PPS / Fe3O4 composite sheet and the CFs / PPS / CNT composite sheet;

[0014] Step four, hot-pressing treatment of the hierarchical structure composite sheet.

[0015] Further, the step one aramid fiber / polyphenylene sulfide / ferroferric oxide (ACFs / PPS / Fe3O4) composite sheet preparation method comprises:

[0016] Preparation of the ACFs / PPS composite sheet base paper, deposition of the dispersed Fe3O4 solution on the ACFs / PPS composite sheet base paper to obtain the ACFs / PPS / Fe3O4 composite sheet.

[0017] Specifically, the ACFs / PPS / Fe3O4 composite sheet preparation method comprises:

[0018] Weighing aramid short-cut fiber (ACFs), polyphenylene sulfide (PPS) pulp, and ferroferric oxide (Fe3O4);

[0019] Fiber dissociation of the ACFs and the PPS pulp, wherein a fiber dissociator is used for dissociation;

[0020] Adding a dispersant to the dissociated ACFs / PPS mixed fibers, and after stirring, obtaining a uniformly dispersed ACFs / PPS mixed slurry;

[0021] Dissociation of the Fe3O4, wherein a fiber dissociator is used for dissociation of the ferroferric oxide, and a dispersant is added to the dissociated Fe3O4, and after stirring, obtaining a uniformly dispersed Fe3O4 solution;

[0022] Wet papermaking of the uniformly dispersed ACFs / PPS to obtain an ACFs / PPS composite sheet base paper, deposition of the dispersed Fe3O4 solution on the ACFs / PPS composite sheet base paper, drying, and obtaining the ACFs / PPS / Fe3O4 composite sheet.

[0023] Further, the step two CFs / PPS / CNT composite sheet preparation method comprises:

[0024] Wet papermaking of the dispersed CFs / PPS to obtain a CFs / PPS composite sheet base paper, then deposition of the uniformly dispersed CNT solution on the CFs / PPS composite sheet base paper, drying, and obtaining the CFs / PPS / CNT composite sheet;

[0025] Specifically, the preparation method of the CFs / PPS / CNT composite sheet comprises,

[0026] The chopped carbon fibers (CFs), polyphenylene sulfide (PPS) pulp and carbon nanotubes (CNT) are weighed;

[0027] The CFs and PPS pulp are subjected to fiber dissociation, and the fiber dissociation is performed using a fiber dissociator;

[0028] A dispersing agent is added to the dissociated CFs / PPS mixed fibers, and stirring is performed to obtain a uniformly dispersed CFs / PPS mixed slurry;

[0029] The CNT is dissociated, and the dissociation is performed using a fiber dissociator;

[0030] A dispersing agent is added to the dissociated CNT, and stirring is performed to obtain a uniformly dispersed CNT solution;

[0031] The uniformly dispersed CFs / PPS is subjected to wet laying to obtain a CFs / PPS composite sheet base paper, and then the uniformly dispersed CNT solution is deposited on the CFs / PPS composite sheet base paper and dried to obtain a CFs / PPS / CNT composite sheet.

[0032] Further, the step three ACFs / PPS / Fe3O4 composite sheet and the CFs / PPS / CNT composite sheet hierarchical structure composite comprises:

[0033] The CFs / PPS / CNT composite sheet is used as the core layer, and the ACFs / PPS / Fe3O4 composite sheet is used as the outermost layer to obtain a hierarchical structure composite sheet;

[0034] Further, the ACFs / PPS / Fe3O4 composite sheet and the CFs / PPS / CNT composite sheet are stacked layer by layer, and the CFs / PPS / CNT composite sheet is used as the core layer, and the ACFs / PPS / Fe3O4 composite sheet is used as the outermost layer; and the stacking design is not limited to 3 layers, 5 layers, 7 layers and 9 layers.

[0035] Further, the step four hierarchical structure composite sheet heat pressing method comprises:

[0036] Multiple heat pressing is performed using a flat plate vulcanizing machine; preferably three times of heat pressing;

[0037] The temperature of the last heat pressing is higher than that of the previous heat pressing;

[0038] Further, the temperature of the second heat pressing is at least 50 higher than that of the first heat pressing, and the temperature of the third heat pressing is at least 100℃ higher than that of the second heat pressing;

[0039] Specifically, the first-stage hot-pressing process parameters are: temperature 90-110 DEG C, pressure 10-30 MPa, and hot-pressing time 1-5 min.

[0040] The second-stage hot-pressing process parameters are: temperature 160-200 DEG C, pressure 10-30 MPa, and hot-pressing time 1-5 min.

[0041] The third-stage hot-pressing process parameters are: temperature 260-320 DEG C, pressure 10-30 MPa, and hot-pressing time 1-5 min.

[0042] The aramid shielding paper with the structure designed obtains excellent mechanical strength, high-temperature resistance, flame resistance and electromagnetic shielding performance after three-stage hot-pressing.

[0043] Further, the dispersant is a polyethylene oxide and polyacrylamide composition.

[0044] Specifically, the polyethylene oxide and the polyacrylamide are added to water and stirred by a high-speed stirrer to obtain a compound dispersion liquid.

[0045] The concentration of the polyethylene oxide is 0.05 parts / L-0.2 parts / L, and the concentration of the polyacrylamide is 0.01 parts / L-0.1 parts / L.

[0046] Further, the high-speed stirrer has a rotating speed of 2000-5000 r / min and a dissociation time of 10-30 min.

[0047] In another aspect, the application further discloses an aramid electromagnetic shielding sheet prepared by using the method.

[0048] The aramid electromagnetic shielding sheet is applied to the field of electromagnetic equipment.

[0049] The method for preparing the hierarchical aramid electromagnetic shielding sheet has the following beneficial effects compared with the prior art:

[0050] The preparation method of the aramid electromagnetic shielding sheet with a hierarchical structure of the application adopts ACFs, PPS pulp and Fe3O4 to prepare ACFs / PPS / Fe3O4 composite sheet by wet papermaking, specifically, Fe3O4 is attached to the sheet by using the deposition method, and CFs, PPS pulp and CNT are used as raw materials to prepare CFs / PPS / CNT composite sheet by wet papermaking, and the aramid electromagnetic shielding sheet with a hierarchical structure is prepared by using the layer-by-layer stacking method, the sheet uses the CFs / PPS / CNT composite sheet with high conductivity as a separate layer and as a core layer, instead of dispersing the conductive material in the three-dimensional space of the paper in a disorderly manner, the design can fully exert the conductivity of CFs and CNT, and the aramid layer as an outer layer enables the electromagnetic wave to realize multiple internal reflections in the multi-layer aramid electromagnetic shielding sheet, and the electromagnetic shielding performance of the composite sheet is improved. In addition, the aramid electromagnetic shielding sheet contains Fe3O4 with high magnetism and CNT with high conductivity, which greatly improves the electromagnetic shielding efficiency of the aramid electromagnetic shielding sheet.

[0051] The method of the application is simple, does not need to use any organic solvent, is safe and environmentally friendly, and the prepared aramid electromagnetic shielding sheet has a multi-layer structure, the structures are relatively dense, and the interlayer bonding force is strong, which greatly improves the mechanical properties and electromagnetic shielding performance of the aramid electromagnetic shielding sheet. The preparation method of the aramid composite sheet of the application has a multi-layer structure design, which fully exerts the conductivity of carbon fibers and carbon nanotubes and the performance coupling of the magnetic Fe3O4, so that the prepared aramid electromagnetic shielding sheet has excellent mechanical strength, high temperature resistance, flame retardance and electromagnetic shielding performance. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is a structural schematic diagram of a 5-layer aramid electromagnetic shielding sheet provided by an embodiment of the application;

[0053] Figure 2 is a flowchart of the preparation method of the aramid electromagnetic shielding sheet with a hierarchical structure of the application;

[0054] Figure 3 is a flowchart of the preparation method of the ACFs / PPS / Fe3O4 and CFs / PPS / CNT composite sheets of the application;

[0055] Figure 4 is the CFs / PPS / CNT composite sheet (left) and the ACFs / PPS / Fe3O4 composite sheet (right).

[0056] Figure 5 is the CFs / PPS composite sheet (left) and the CFs / PPS / CNT composite sheet (right). DETAILED DESCRIPTION

[0057] In order to more clearly illustrate the technical solutions of the present application, the technical solutions of the present application will be introduced below through specific embodiments and the drawings obtained. Obviously, the specific embodiments and the drawings described below are only specific ways in the scope of the technical solutions of the present application, and do not represent the scope of the present application.

[0058] In order to prepare a high-performance electromagnetic shielding sheet, especially an aramid electromagnetic shielding sheet with hierarchical structure prepared by using high-performance aramid, the preparation method provided by the present application comprises the following steps:

[0059] Step one, preparation of aramid fiber / polyphenylene sulfide / ferroferric oxide (ACFs / PPS / Fe3O4) composite sheet;

[0060] The aramid fiber is aramid chopped fiber, and the polyphenylene sulfide is polyphenylene sulfide pulp.

[0061] The size of the aramid chopped fiber is 3-10 mm, which can be chopped to 5 mm, 6 mm or 8 mm.

[0062] The diameter of the polyphenylene sulfide pulp is about 3-10 pm, and the length is less than 1 mm.

[0063] In the process of wet papermaking, the length of the fiber has an influence on its dispersibility in water. Generally speaking, the longer the fiber, the easier the fiber is to flocculate and entangle in water, resulting in poor dispersibility. Shorter fiber may result in lower paper strength. Therefore, the specification of the fiber has an influence on the performance of the sheet. For electromagnetic shielding sheets, the size specification will affect the adhesion of the shielding material or the conductive material, and further affect the shielding performance.

[0064] For polyphenylene sulfide, polyphenylene sulfide mainly plays a role as a bonding material in the composite material. After the polyphenylene sulfide pulp melts at high temperature, it tightly wraps the surface of the aramid chopped fiber, increases the mechanical properties of the composite sheet, and can stabilize the aramid sheet, ensuring the stability of the structure and content of each component in the composite material, so as to ensure the durability of the material.

[0065] The amount of the aramid fiber, polyphenylene sulfide and ferroferric oxide is (6-10):(2-5):(1-4).

[0066] Preferably, the amount ratio of the aramid fiber, polyphenylene sulfide and ferroferric oxide can be one of 6:5:4, 8:4:2 and 9:4:3.

[0067] The reasonable ratio of the amount of aramid fiber, polyphenylene sulfide and ferroferric oxide can make the ACFs / PPS / Fe3O4 composite sheet have stability and durability in mechanical properties and electromagnetic isolation shielding performance, the application can ensure the void structure of aramid and the uniform and stable fixation of ferroferric oxide for electromagnetic shielding, so that the ferroferric oxide can have a similar layered structure, and the electromagnetic waves can be reflected on one side of the layered structure to achieve the electromagnetic shielding effect.

[0068] Specifically, the step one aramid fiber / polyphenylene sulfide / ferroferric oxide (ACFs / PPS / Fe3O4) composite sheet preparation method comprises:

[0069] The ACFs / PPS composite sheet raw paper is prepared, the dispersed Fe3O4 solution is deposited on the ACFs / PPS composite sheet raw paper, and the ACFs / PPS / Fe3O4 composite sheet is obtained.

[0070] The mass ratio of ACFs, PPS pulp and Fe3O4 in the ACFs / PPS / Fe3O4 composite sheet is (6-10):(2-5):(1-4).

[0071] The amount of aramid fiber and PPS is the key to prepare aramid composite paper, the composite paper prepared by aramid and PPS is the matrix, and Fe3O4 is the filling powder, a small amount of Fe3O4 is added to make the composite paper have certain magnetism, the inorganic metal oxide is used to reflect and interfere with electromagnetic waves, and then the shielding effect is achieved.

[0072] Specifically, the preparation method of the ACFs / PPS / Fe3O4 composite sheet comprises:

[0073] The aramid chopped fiber (ACFs), polyphenylene sulfide (PPS) pulp and ferroferric oxide (Fe3O4) are weighed;

[0074] The ACFs and PPS pulp are subjected to fiber dissociation, wherein a fiber dissociator is used for dissociation;

[0075] The dispersed agent is added to the dissociated ACFs / PPS mixed fiber, and after stirring, the uniformly dispersed ACFs / PPS mixed pulp is obtained;

[0076] The complex dispersing agent of ethylene oxide and anionic polyacrylamide is one of important links for dispersing aramid fiber, if the dispersing agent is not used, the fiber cannot be uniformly dispersed, and the uniformity of the prepared sheet has important influence on the performance of the final product.

[0077] The uniformly dispersed ACFs / PPS mixed fibers make the subsequent prepared composite sheet have more uniform voids, and at the same time can fully play the adhesion of PPS, the composite sheet substrate must ensure a certain void structure, which can provide more fixation sites for the four iron oxide, and ensure the adsorption and adhesion of PPS to the four iron oxide, and more importantly, through the adjustment of this structure, the four iron oxide can tend to form a kind of layered structure, and improve the electromagnetic shielding effect.

[0078] The Fe3O4 is dissociated, wherein the four iron oxide is dissociated by using a fiber dissociator, a dispersing agent is added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution is obtained;

[0079] The uniformly dispersed ACFs / PPS is wet laid to obtain an ACFs / PPS composite sheet base paper, and the uniformly dispersed Fe3O4 solution is deposited on the ACFs / PPS composite sheet base paper, and dried to obtain an ACFs / PPS / Fe3O4 composite sheet.

[0080] The Fe3O4 solution is deposited on the ACFs / PPS composite sheet base paper in order to make the Fe3O4 form a sheet-like structure on the surface of the ACFs / PPS composite sheet base paper, rather than being randomly distributed in the three-dimensional space of the ACFs / PPS composite sheet base paper, which is conducive to fully exerting its excellent magnetic properties.

[0081] The drying is drying the composite sheet in a drying oven at 110-150℃.

[0082] The thickness of the obtained ACFs / PPS / Fe3O4 composite sheet can be realized by controlling the grammage of the composite sheet, and the grammage is generally designed to be 20-40g / m 2 , which can be selected to be 20g / m 2 , 25g / m 2 , 30g / m 2 , 35g / m 2 , or 40g / m 2 .

[0083] Step two, preparation of a short carbon fiber / polyphenylene sulfide / carbon nanotube (CFs / PPS / CNT) composite sheet;

[0084] The carbon fiber is a short carbon fiber, and the polyphenylene sulfide is polyphenylene sulfide pulp.

[0085] The short carbon fiber is 2-12mm, preferably 3mm, 5mm, or 8mm.

[0086] The carbon fiber is used to increase the conductivity, and in the process of preparing the electromagnetic shielding screen, the sheet structure composite with conductivity and shielding property is used, and the multi-layer performance sheet is alternately stacked and compounded, so as to synergistically increase the electromagnetic shielding performance.

[0087] The polyphenylene sulfide pulp has the same bonding effect as the aramid sheet, and after the two layers of raw paper are compounded, hot pressing is performed, and in the hot pressing process, the polyphenylene sulfide in each layer of raw paper is melted, and the carbon fiber, carbon nanotube, aramid fiber, and ferroferric oxide are tightly bonded together.

[0088] The CNT is preferably a 95% pure carbon nanotube, and graphene and Mxene can also be selected. The carbon nanotube is selected here because of its high conductivity and relatively low cost.

[0089] Specifically, the preparation method of the CFs / PPS / CNT composite sheet in step two comprises:

[0090] The dispersed CFs / PPS is wet laid to obtain a CFs / PPS composite sheet raw paper, and then the uniformly dispersed CNT solution is deposited on the CFs / PPS composite sheet raw paper, and dried to obtain a CFs / PPS / CNT composite sheet.

[0091] Specifically, the preparation method of the CFs / PPS / CNT composite sheet comprises,

[0092] The chopped carbon fiber (CFs), polyphenylene sulfide (PPS) pulp, and carbon nanotube (CNT) are weighed;

[0093] The amount is that the mass ratio of CFs, PPS pulp, and CNT is (6-10):(2-5):(1-4).

[0094] Preferably, 0.32 parts of CFs, 0.14 parts of PPS, and 0.18 parts of CNT are used.

[0095] The CFs and PPS pulp are subjected to fiber dissociation, and the fiber dissociation is performed using a fiber dissociator.

[0096] A dispersing agent is added to the dissociated CFs / PPS mixed fibers, and stirring is performed to obtain a uniformly dispersed CFs / PPS mixed slurry.

[0097] The CNT is dissociated, and a fiber dissociator is used for dissociation.

[0098] A dispersing agent is added to the dissociated CNT, and stirring is performed to obtain a uniformly dispersed CNT solution.

[0099] The uniformly dispersed CFs / PPS is wet papermaking to obtain a CFs / PPS composite sheet base paper, and then the uniformly dispersed CNT solution is deposited on the CFs / PPS composite sheet base paper to obtain a CFs / PPS / CNT composite sheet after drying.

[0100] Step three, hierarchical structure composite of ACFs / PPS / Fe3O4 composite sheet and CFs / PPS / CNT composite sheet;

[0101] Further, the step three hierarchical structure composite of ACFs / PPS / Fe3O4 composite sheet and CFs / PPS / CNT composite sheet comprises:

[0102] The CFs / PPS / CNT composite sheet is used as a core layer, and the ACFs / PPS / Fe3O4 composite sheet is used as an outermost layer to obtain a hierarchical structure composite sheet.

[0103] The CFs / PPS / CNT composite sheet is used as a core layer to ensure the flexibility of the final product. It is well known that carbon fibers, carbon nanotubes and polyphenylene sulfide all lack corresponding flexibility and impact strength. Therefore, we put the aramid sheet layer into the outermost layer to improve the comprehensive mechanical properties of the material.

[0104] Further, the ACFs / PPS / Fe3O4 composite sheet and the CFs / PPS / CNT composite sheet are stacked layer by layer, and the CFs / PPS / CNT composite sheet is used as a core layer, and the ACFs / PPS / Fe3O4 composite sheet is used as an outermost layer. It is not limited to a 3-layer, 5-layer, 7-layer and 9-layer design.

[0105] When the 3-layer stack structure is used, the electromagnetic shielding effect is very good, and when the 5-layer stack is used, the total grammage is 100-200g / m 2 At this time, the mechanical properties and electromagnetic shielding effect of the composite sheet can be fully utilized.

[0106] Step four, heat pressing treatment of the hierarchical structure composite sheet.

[0107] Further, the step four heat pressing treatment method of the hierarchical structure composite sheet comprises:

[0108] Multiple heat pressing is adopted by using a flat vulcanizing machine; preferably three times of heat pressing;

[0109] Polyphenylene sulfide is a thermoplastic resin, which can be combined more closely with carbon fibers and aramid fibers after each heat pressing. The temperature is gradually increased because the glass transition temperature of PPS is 85℃. When the temperature is higher than this temperature, PPS will soften and deform, increasing the bonding area between the fibers. Finally, the temperature of the heat pressing is above the melting point of PPS. Only in this way, PPS can better infiltrate the fibers and form a strong interfacial adhesion between the fibers.

[0110] The temperature of the last hot pressing is higher than the temperature of the previous hot pressing;

[0111] Further, the temperature of the second hot pressing is at least 50℃ higher than the temperature of the first hot pressing, and the temperature of the third hot pressing is at least 100℃ higher than the temperature of the second hot pressing;

[0112] And, the temperature of the last hot pressing is higher than the melting point temperature of PPS;

[0113] Specifically, the first-stage hot pressing process parameters are: temperature of 90-110℃, pressure of 10-30MPa, and hot pressing time of 1-5min;

[0114] The second-stage hot pressing process parameters are: temperature of 160-200℃, pressure of 10-30MPa, and hot pressing time of 1-5min;

[0115] The third-stage hot pressing process parameters are: temperature of 260-320℃, pressure of 10-30MPa, and hot pressing time of 1-5min.

[0116] The aramid shielding paper with a designed structure has excellent mechanical strength, high temperature resistance, flame resistance, and electromagnetic shielding performance after three-stage hot pressing.

[0117] Further, the dispersant is a polyoxyethylene and polyacrylamide composition;

[0118] Specifically, the polyoxyethylene and polyacrylamide are added to water and stirred by a high-speed stirrer to obtain a compound dispersion liquid.

[0119] The concentration of the polyoxyethylene is 0.05 parts / L-0.2 parts / L, and the concentration of the polyacrylamide is 0.01 parts / L-0.1 parts / L.

[0120] Further, the high-speed stirrer has a rotating speed of 2000-5000r / min and a dissociation time of 10-30min.

[0121] Further, referring to Figure 1 which is one of the schemes of the composite sheet prepared by the present application, and the sheet has two layers of CFs / PPS / CNT composite sheet as a core layer, and ACFs / PPS / Fe3O4 composite sheet as an outer layer.

[0122] Further, referring to Figure 2 which is a preparation method of a single layer sheet, mainly by wet papermaking to prepare a sheet, and then composite hot pressing to obtain an electromagnetic shielding sheet.

[0123] Example 1

[0124] Effect of blending method on properties of nanoparticles

[0125] The weighed 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.18 parts of Fe3O4, firstly, the ACFs and PPS pulp are placed in a fiber dissociator for fiber dissociation, a compound dispersant is added to the mixed fibers after dissociation, and after stirring, a uniformly dispersed mixed slurry is obtained; then the Fe3O4 is placed in a fiber dissociator for dissociation. Then a dispersant is added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution is obtained. The uniformly dispersed ACFs and PPS mixed fibers are wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution is deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet is obtained.

[0126] Example 2

[0127] The weighed 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.18 parts of Fe3O4, firstly, the ACFs and PPS pulp are placed in a fiber dissociator for fiber dissociation, a compound dispersant is added to the mixed fibers after dissociation, and after stirring, a uniformly dispersed mixed slurry is obtained; then the Fe3O4 is placed in a fiber dissociator for dissociation. Then a dispersant is added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution is obtained. The uniformly dispersed ACFs and PPS mixed fibers are wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution is deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet is obtained.

[0128]

[0129] From the above results, it can be seen that the mixing method of Fe3O4 directly affects the electromagnetic shielding effect of aramid sheet. The electromagnetic shielding performance using simple mixing method is significantly lower than that using deposition method. This may be due to the significant difference in mass between Fe3O4 and aramid fibers and PPS. In the simple blending process, the dispersion is not easy to be uniform, and at the same time, due to the weight difference, it is easy to deposit in the solution during the papermaking process, resulting in less Fe3O4 content in the papermaking; while the deposition method is more similar to the filtration method, Fe3O4 is filled in the gap of the sheet and forms a similar layered structure, thereby improving the electromagnetic shielding performance.

[0130] Example 3

[0131] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.18 parts of CNT are weighed, the CFs and the PPS pulp are first placed in a fiber dissociator for fiber dissociation, a compounded dispersant is added to the mixed fibers of the dissociated ACFs and PPS, and after stirring, a uniformly dispersed mixed pulp is obtained; then the CNT is placed in a fiber dissociator for dissociation. A dispersant is then added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution is obtained. The uniformly dispersed mixed fibers of ACFs and PPS are wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution is deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet is obtained.

[0132] Example 4

[0133] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.18 parts of CNT are weighed, the CFs and the PPS pulp are first placed in a fiber dissociator for fiber dissociation, a compounded dispersant is added to the mixed fibers of the dissociated ACFs and PPS, and after stirring, a uniformly dispersed mixed pulp is obtained; then the CNT is placed in a fiber dissociator for dissociation. A dispersant is then added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution is obtained. The uniformly dispersed mixed fibers of ACFs and PPS are wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution is deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet is obtained.

[0134]

[0135]

[0136] Example 3-4 further verifies the conclusion of Examples 1-2, and the deposition method is obviously better than the blending method in improving the electromagnetic splicing performance.

[0137] Example 5

[0138] 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.18 parts of Fe3O4 are weighed, the ACFs and the PPS pulp are first placed in a fiber dissociator for fiber dissociation, a compounded dispersant is added to the mixed fibers of the dissociated ACFs and PPS, and after stirring, a uniformly dispersed mixed pulp is obtained; then the Fe3O4 is placed in a fiber dissociator for dissociation. A dispersant is then added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution is obtained. The uniformly dispersed mixed fibers of ACFs and PPS are wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution is deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet is obtained.

[0139] Example 6

[0140] The 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.14 parts of Fe3O4 were weighed, the ACFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation, a compound dispersant was added to the mixed fibers after dissociation, and after stirring, a uniformly dispersed mixed slurry was obtained; then the Fe3O4 was placed in a fiber dissociator for dissociation. Then a dispersant was added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution was obtained. The uniformly dispersed ACFs and PPS mixed fibers were wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution was deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet was obtained.

[0141] Example 7

[0142] The 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.14 parts of Fe3O4 were weighed, the ACFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation, a compound dispersant was added to the mixed fibers after dissociation, and after stirring, a uniformly dispersed mixed slurry was obtained; then the Fe3O4 was placed in a fiber dissociator for dissociation. Then a dispersant was added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution was obtained. The uniformly dispersed ACFs and PPS mixed fibers were wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution was deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet was obtained.

[0143] Example 8

[0144] The 0.32 parts of ACFs, 0.14 parts of PPS pulp and 0.14 parts of Fe3O4 were weighed, the ACFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation, a compound dispersant was added to the mixed fibers after dissociation, and after stirring, a uniformly dispersed mixed slurry was obtained; then the Fe3O4 was placed in a fiber dissociator for dissociation. Then a dispersant was added to the dissociated Fe3O4, and after stirring, a uniformly dispersed Fe3O4 solution was obtained. The uniformly dispersed ACFs and PPS mixed fibers were wet laid to obtain an ACFs and PPS composite sheet base paper, and then the uniformly dispersed Fe3O4 solution was deposited on the ACFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet was obtained.

[0145] Specifically, the specific parameters and properties of the composite sheet prepared are as follows

[0146]

[0147]

[0148] Examples 5-8 show the effect of Fe3O4 content on the tensile strength and electromagnetic shielding performance of ACFs / PPS / Fe3O4 composite sheets. It can be found that although the content of Fe3O4 is small, it still has an effect on the mechanical properties. This is mainly because the addition of nanofillers to aramid and polyphenylene sulfide composite materials can cause the interface between aramid and polyphenylene sulfide to weaken, thus changing the mechanical strength.

[0149] Example 9

[0150] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.18 parts of CNT were weighed. The CFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation. A compounded dispersant was added to the dissociated ACFs and PPS mixed fibers, and after stirring, a uniformly dispersed mixed slurry was obtained. Then the CNT was placed in a fiber dissociator for dissociation. A dispersant was then added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution was obtained. The uniformly dispersed CFs and PPS mixed fibers were wet laid to obtain a CFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution was deposited on the CFs and PPS composite sheet base paper. After drying and hot pressing, a composite sheet was obtained.

[0151] Example 10

[0152] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.14 parts of CNT were weighed. The CFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation. A compounded dispersant was added to the dissociated ACFs and PPS mixed fibers, and after stirring, a uniformly dispersed mixed slurry was obtained. Then the CNT was placed in a fiber dissociator for dissociation. A dispersant was then added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution was obtained. The uniformly dispersed CFs and PPS mixed fibers were wet laid to obtain a CFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution was deposited on the CFs and PPS composite sheet base paper. After drying and hot pressing, a composite sheet was obtained.

[0153] Example 11

[0154] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.1 parts of CNT were weighed, the CFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation, a compounded dispersant was added to the mixed fibers of the dissociated ACFs and PPS, and after stirring, a uniformly dispersed mixed pulp was obtained; then the CNT was placed in a fiber dissociator for dissociation. Then a dispersant was added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution was obtained. The uniformly dispersed mixed fibers of CFs and PPS were wet laid to obtain a CFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution was deposited on the CFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet was obtained.

[0155] Example 12

[0156] 0.32 parts of CFs, 0.14 parts of PPS pulp and 0.06 parts of CNT were weighed, the CFs and PPS pulp were first placed in a fiber dissociator for fiber dissociation, a compounded dispersant was added to the mixed fibers of the dissociated ACFs and PPS, and after stirring, a uniformly dispersed mixed pulp was obtained; then the CNT was placed in a fiber dissociator for dissociation. Then a dispersant was added to the dissociated CNT, and after stirring, a uniformly dispersed CNT solution was obtained. The uniformly dispersed mixed fibers of CFs and PPS were wet laid to obtain a CFs and PPS composite sheet base paper, and then the uniformly dispersed CNT solution was deposited on the CFs and PPS composite sheet base paper, and after drying and hot pressing, a composite sheet was obtained.

[0157] Examples 9-12 disclose the preparation of another sheet; CFs, PPS pulp and CNT are weighed, and a CFs / PPS / CNT composite sheet is prepared by the same method as described above.

[0158] Specifically, the specific parameters and properties of the core layer composite sheet prepared are as follows

[0159]

[0160] Examples 9-12 show the effect of carbon nanotube content on the tensile strength and electromagnetic shielding performance of the CFs / PPS / CNT composite sheet.

[0161] In Examples 13-18, aramid electromagnetic shielding sheets with a composite multi-layer structure were prepared, and the specific designs are as follows

[0162]

[0163]

[0164] In Examples 13-18, by selecting different sheet layers and designing different layered structures, the electromagnetic shielding performance of the resulting composite sheet material differs. After three-stage hot pressing, the tensile properties of the aramid electromagnetic shielding sheet material with a three-layer structure are greater than 44.1 MPa, and the electromagnetic shielding effectiveness reaches 81.7 dB. However, it can be seen from the overall results that the electromagnetic shielding effect of the structure with CFs / PPS / CNT composite sheet material as the core layer and ACFs / PPS / Fe3O4 composite sheet material as the outermost layer is obviously better than that with CFs / PPS / CNT composite sheet material as the outer layer.

[0165] Since the third-stage hot pressing temperature plays a crucial role in the performance of the composite sheet material, this is because the melting point of polyphenylene sulfide is close to 285°C. Therefore, in Examples 19-22, the effect of different hot pressing temperatures on the final aramid electromagnetic shielding sheet material is analyzed.

[0166]

[0167]

[0168] As can be seen from the examples, changes in the core layer structure and the outer layer structure material have a greater impact on the ratio effect, and the hot pressing temperature also has a significant impact on the shielding performance.

[0169] Figure 4 The left graph is the CFs / PPS / CNT composite sheet material, which can be seen to be relatively brittle and easy to break; and the right graph is the ACFs / PPS / Fe3O4 composite sheet material.

[0170] Figure 5 The CFs / PPS composite sheet material on the left and the CFs / PPS / CNT composite sheet material on the right differ mainly in whether carbon nanotubes are loaded.

Claims

1. A method of making a hierarchical aramid electromagnetic shielding sheet material, characterized by, The method comprises: Step one, preparation of aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet; Step two, preparation of carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet; Step three, hierarchical structure composite of aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet and carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet; Step four, hot pressing treatment of hierarchical structure composite sheet to obtain the electromagnetic shielding sheet; Wherein, the aramid fiber is aramid short fiber, the polyphenylene sulfide is polyphenylene sulfide pulp; the carbon fiber is short carbon fiber; The preparation method of aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet in step one comprises: Preparation of aramid fiber / polyphenylene sulfide composite sheet base paper, deposition of dispersed ferroferric oxide solution on the aramid fiber / polyphenylene sulfide composite sheet base paper to obtain aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet; Wherein, the aramid fiber / polyphenylene sulfide composite sheet base paper is obtained by wet papermaking; The preparation method of carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet in step two comprises: Wet papermaking is used to obtain carbon fiber / polyphenylene sulfide composite sheet base paper, and uniform dispersion of carbon nanotube solution is deposited on the carbon fiber / polyphenylene sulfide composite sheet base paper to obtain carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet; The hierarchical structure composite of aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet and carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet in step three comprises: At least carbon fiber / polyphenylene sulfide / carbon nanotube composite sheet is used as the core layer, and aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet is used as the outermost layer to obtain the hierarchical structure composite sheet.

2. The preparation method of the hierarchical structure aramid electromagnetic shielding sheet according to claim 1, wherein the hierarchical structure is at least three layers.

3. The preparation method of the hierarchical structure aramid electromagnetic shielding sheet according to claim 2, wherein the hot pressing treatment of the hierarchical structure composite sheet in step four comprises: At least three times of hot pressing is adopted by using a flat vulcanizing machine; The temperature of the last hot pressing is higher than that of the previous hot pressing; The last hot pressing temperature is 260-320℃, the pressure is 10-30MPa, and the hot pressing time is 1-5min; The previous hot pressing temperature is 100-320℃, the pressure is 10-30MPa, and the hot pressing time is 1-5min.

4. The preparation method of the hierarchical structure aramid electromagnetic shielding sheet according to claim 3, wherein the mass ratio of the aramid short fiber, polyphenylene sulfide and ferroferric oxide is (6-10):(2-5):(1-4).

5. The preparation method of the hierarchical structure aramid electromagnetic shielding sheet according to claim 4, wherein the mass ratio of the short carbon fiber, polyphenylene sulfide pulp and carbon nanotube is (6-10):(2-5):(1-4). The size of the aramid short fiber is 3-10mm.

8. The aramid electromagnetic shielding sheet prepared by the preparation method of the hierarchical structure aramid electromagnetic shielding sheet according to any one of claims 1-7. ​ ​ 6. A method of making a hierarchical aramid electromagnetic shielding sheet according to any one of claims 1-5, wherein, The aramid fiber / polyphenylene sulfide / ferroferric oxide composite sheet has a grammage of 20-40 g / m 2 .

7. A method of making a hierarchical aramid electromagnetic shielding sheet according to any one of claims 1-5, wherein, ​ ​ 9. Use of an aramid electromagnetic shielding sheet according to claim 8 on an electromagnetic device.

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