Preparation method of anisotropic carbon-based electromagnetic shielding composite film

Abstract

The invention relates to a preparation method of an anisotropic carbon-based electromagnetic shielding composite film, and aims to solve the technical problem that an electromagnetic shielding material prepared by an existing method cannot meet bidirectional requirements on electromagnetic protection in current military, medical and other special scenes. The light and efficient absorption and reflection integrated electromagnetic shielding novel material is prepared, under the condition that the filling amount of the non-uniform double-layer structure is low, the high shielding effectiveness is taken into account, and a unique shielding mechanism leading absorption and reflection in different incident directions is achieved. According to the obtained composite film, by means of the forward absorption-shielding-absorption mechanism, under the optimal proportion, the shielding effectiveness mean value of the composite film within the X wave band range reaches 40.3 dB, the forward absorption coefficient and the reverse reflection coefficient are both higher than 0.7, and in different incident directions, the material shows shielding mechanisms dominated by absorption and reflection respectively. The invention relates to the technical field of electromagnetic shielding materials.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave shielding materials, and particularly relates to a preparation method of an anisotropic carbon-based electromagnetic shielding composite film. Background Art

[0002] Electromagnetic technology is a "double-edged sword". In the wave of the second technological revolution, modern communication technologies with electromagnetic waves as carriers have greatly facilitated daily communication. However, with their widespread application, a series of safety and environmental protection problems have followed. It is urgent to pay attention to and solve the problem of electromagnetic pollution. As a key material in the development of electromagnetic shielding technology, the application fields of electromagnetic shielding materials have gradually expanded from the initial military protection and stealth to the range of human electromagnetic safety protection, electromagnetic interference prevention, and information security. Electromagnetic shielding materials can effectively block incident electromagnetic waves and minimize their interference to protected targets, and have become a key technical means to eliminate the negative effects of electromagnetic waves. At the end of the 19th century, metal materials with good electrical conductivity such as copper and aluminum were used as the earliest electromagnetic shielding materials. However, the inherent defects of these metal materials, such as easy corrosion, high cost, high density, poor processing difficulty and flexibility, have restricted their application in frontier intelligent fields such as flexible devices, micro-devices, and aerospace. In view of this, polymer-based composite materials, especially composite materials with carbon materials as conductive fillers, have attracted much attention in recent years due to their advantages such as light weight, corrosion resistance, easy processing, and designability. It is worth noting that in special scenarios such as military radars and medical imaging, there are two-way requirements for electromagnetic protection: the inside of the device needs to efficiently absorb incident electromagnetic waves to prevent signal leakage; the outside of the device needs to suppress the response of internal sensitive components to external electromagnetic interference. This differential demand has given rise to the birth of the concept of multifunctional material design, but existing research has mostly focused on the optimization of single functions, and there is still a lack of systematic research on the anisotropic effects of materials. Summary of the Invention

[0003] In order to solve the technical problem that traditional electromagnetic shielding materials prepared by existing methods cannot meet the two-way requirements for electromagnetic protection in current special scenarios such as military and medical, the present invention further provides a preparation method of an anisotropic carbon-based electromagnetic shielding composite film.

[0004] The technical solution adopted by the present invention to solve the above problems is as follows:

[0005] A preparation method of an anisotropic carbon-based electromagnetic shielding composite film, the method is carried out through the following steps:

[0006] Step 1: Pretreat carbon fibers:

[0007] Place the carbon fibers in a nitrogen environment for heat treatment to remove the gum and grease on the fiber surface, and obtain pretreated carbon fibers;

[0008] The diameter of the carbon fiber is 7 μm, the specific density is 1.8, the tensile strength and Young's modulus are 4.1 GPa and 230 GPa respectively, and the fiber length is 1 mm;

[0009] The temperature of the heat treatment is 400 °C and the time of the heat treatment is 30 min.

[0010] Step 2: Sensitization treatment:

[0011] Disperse the carbon fiber obtained in Step 1 into a sensitizing solution containing stannous chloride, perform ultrasonic treatment and then filter, wash and dry to obtain an intermediate product;

[0012] Furthermore, the sensitizing solution is composed of stannous chloride dihydrate, tin granules, deionized water, and hydrochloric acid with a concentration of 36% mixed in a mass ratio of 3:2:96:4, and the ultrasonic time is 30 min.

[0013] Step 3: Activation treatment:

[0014] Disperse the product obtained in Step 2 into an activation solution containing palladium chloride, perform ultrasonic treatment and then filter, wash and dry to obtain a sensitized and activated carbon fiber;

[0015] The activation solution is composed of palladium chloride, deionized water, and hydrochloric acid with a concentration of 36% mixed in a mass ratio of 0.04:98:2, and the ultrasonic time is 30 min.

[0016] Step 4:

[0017] Electroless copper plating treatment: Disperse the product obtained in Step 3 into an electroless copper plating solution, perform ultrasonic treatment, add sodium hydroxide solution to adjust the pH value, stir at 60 °C for a period of time, and then filter, wash and dry to obtain a red product;

[0018] Furthermore, the electroless copper plating solution is composed of copper sulfate pentahydrate, disodium ethylenediaminetetraacetate, formaldehyde solution, and 2,2'-bipyridine mixed in proportion, where:

[0019] 3.75 g of copper sulfate pentahydrate is dissolved in 50 mL of deionized water, denoted as solution A; 8 g of disodium ethylenediaminetetraacetate and 2,2'-bipyridine are dissolved in 100 mL of deionized water, denoted as solution B; 6.25 mL of formaldehyde with a concentration of 37% is dissolved in 100 mL of deionized water, denoted as solution C: Pour solution A and solution B into solution C in sequence, mix evenly, and perform ultrasonic treatment for 15 min, 30 min, 60 min, and 90 min respectively.

[0020] Furthermore, the concentration of the sodium hydroxide solution is 10 g / L, adjusted to a pH value of 12; the amount of the fiber sample added is 0.5 g, and the reaction time is 1 h.

[0021] Step 5:

[0022] Preparation of the shielding layer composite film: Mix the product obtained in Step 4 with a certain amount of polyethylene powder evenly, put it into a stainless steel mold, and transfer the whole to a flat vulcanizing machine. Conduct hot pressing at 200 °C to prepare the shielding layer composite film;

[0023] Mix the copper-plated carbon fiber obtained in Step 4 with polyethylene powder at a mass ratio of 3:7, add 20 mL of absolute ethanol, stir for 30 min, and then place it in an oven at 100 °C to dry for 24 h to remove the solvent to obtain a mixed powder;

[0024] The conditions for the hot pressing are: hot pressing temperature 200 °C, pressure 15 MPa, and hot pressing time 1 h.

[0025] Step 6. Calcination treatment:

[0026] Place the mesophase carbon microspheres in an inert nitrogen atmosphere for calcination treatment; the calcination treatment temperature is 700 °C, 800 °C, 900 °C, and the time is 6 h.

[0027] Step 7. Preparation of the loss layer composite film:

[0028] Compound the carbon microsphere sample obtained in Step 6 with the polyurethane foam matrix at a mass fraction of 30% by impregnation adsorption method to obtain the loss layer composite film;

[0029] The solvent used in the impregnation adsorption method is aqueous polyurethane emulsion, the thickness of the polyurethane foam used is 2 mm, and the apparent density is 50 kg / m 3 .

[0030] Step 8. Composite film forming:

[0031] Align the shielding layer in Step 5 with the loss layer in Step 6, place it in a flat vulcanizing machine for hot pressing treatment, and cool the product to room temperature to obtain an anisotropic carbon-based electromagnetic shielding composite film.

[0032] The conditions for the hot pressing are: hot pressing temperature 80 °C, pressure 5 MPa, and hot pressing time 0.5 h.

[0033] The beneficial effects of the present invention are:

[0034] 1. The anisotropic carbon-based electromagnetic shielding composite film prepared by the present invention successfully deposits metallic copper on the pretreated carbon fiber through the electroless plating process, significantly improving the conductivity and electromagnetic shielding performance of the shielding layer.

[0035] 2. The anisotropic carbon-based electromagnetic shielding composite film prepared by the present invention successfully adjusts the electromagnetic parameters of the loss layer by controlling the calcination temperature of the mesophase carbon microspheres, making it exhibit excellent electromagnetic loss performance.

[0036] 3. The present invention successfully prepares an anisotropic carbon-based electromagnetic shielding composite film by means of a coating-laminating process. Relying on the positive "absorption-shielding-absorption" mechanism, it achieves excellent bidirectional characteristic electromagnetic shielding performance in the X band and has a broader application prospect in a complex electromagnetic environment.

[0037] 4. The thickness of the anisotropic carbon-based electromagnetic shielding composite film prepared by the present invention is 2.5 mm. It has good adaptability and good resilience performance. The shielding mechanisms mainly include reflection and absorption in different incident directions. The average shielding effectiveness in the range of 8.2 - 12.4 GHz reaches 40.3 dB. In other words, the composite film can shield 99.99% of electromagnetic radiation.

[0038] In summary, the present invention prepares an anisotropic carbon-based electromagnetic shielding composite film. The anisotropic carbon-based electromagnetic shielding composite film obtained through ingenious design presents shielding mechanisms mainly dominated by absorption and reflection in different incident directions, effectively enhancing the protection ability of the material in a complex electromagnetic environment. In addition, the composite film has a low production cost and a simple process, and is suitable for industrial production. Description of the Drawings

[0039] Figure 1 Scanning electron microscope pictures of fibers after different electroless plating times in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 2 - 4, where a, b are CF@Cu-1, c, d are CF@Cu-2, e, f are CF@Cu-3, g, h are CF@Cu-4;

[0040] Figure 2 Comparison of the tensile strength and elongation at break of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 2 - 4;

[0041] Figure 3 Comparison of the conductivity of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 2 - 4;

[0042] Figure 4 Comparison of the electromagnetic shielding effectiveness of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 2 - 4, where a is SE, b is SE A 、c is SE R 、d is the comparison of SE at 10.3 GHz;

[0043] Figure 5For the comparison of the electromagnetic loss performance of different loss layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 5 to 7, where a is C-PUF-1, b is C-PUF-2, c is C-PUF-3, and d is C-PUF-4;

[0044] Figure 6 Figure for the comparison of the bidirectional electromagnetic shielding performance of the anisotropic carbon-based electromagnetic shielding composite film prepared in Example 1, where a is forward incidence (propagating from the loss layer to the shielding layer) and b is reverse incidence (propagating from the shielding layer to the loss layer). Detailed implementation mode

[0045] The following further elaborates the invention in conjunction with specific embodiments. It should be noted that the following embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention. Therefore, although the present specification has described the present invention in detail with reference to the following embodiments, those skilled in the art should understand that the present invention can still be modified or equivalently replaced; and all technical solutions and their improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

[0046] Detailed implementation mode one: A preparation method of an anisotropic carbon-based electromagnetic shielding composite film described in this implementation mode specifically includes the following steps:

[0047] Step one: To remove the gums and oils existing on the fiber surface, the carbon fiber is heat-treated in a nitrogen environment to obtain the pretreated carbon fiber;

[0048] Step two: Disperse the product obtained in step one into a sensitizing solution containing stannous chloride, perform ultrasonic treatment, then filter, wash, and dry to obtain an intermediate product;

[0049] Step three: Disperse the product obtained in step two into an activating solution containing palladium chloride, perform ultrasonic treatment, then filter, wash, and dry to obtain the sensitized and activated carbon fiber;

[0050] Step four: Disperse the product obtained in step three into an electroless copper plating solution, perform ultrasonic treatment, add sodium hydroxide solution to adjust the pH value, stir at 60 °C for a period of time, then filter, wash, and dry to obtain a red product;

[0051] Step five: Mix the product obtained in step four evenly with a certain amount of polyethylene powder, put it into a stainless steel mold, and transfer the whole to a flat vulcanizer for hot pressing at 200 °C to prepare a shielding layer composite film;

[0052] Step six: Calcinate the mesophase carbon microspheres in a nitrogen inert atmosphere;

[0053] Step 7: The carbon microsphere sample obtained in Step 6 is compounded with a polyurethane foam matrix by an impregnation adsorption method (mass fraction is 30 wt%), and a loss layer composite film is prepared;

[0054] Step 8: Align the shielding layer in Step 5 with the loss layer in Step 6, place it in a flat vulcanizing machine for hot pressing treatment, cool the product to room temperature, and finally obtain an anisotropic carbon-based electromagnetic shielding composite film.

[0055] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the diameter of the carbon fiber used in Step 1 is 7 μm, the specific density is 1.8, the tensile strength and Young's modulus are 4.1 GPa and 230 GPa respectively, and the fiber length is 1 mm. Others are the same as Specific Embodiment 1.

[0056] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the pretreatment temperature in Step 1 is 400 °C and the pretreatment time is 30 min. Others are the same as Specific Embodiment 1 or 2.

[0057] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the sensitizing solution in Step 2 is composed of stannous chloride dihydrate, tin granules, deionized water, and hydrochloric acid (concentration 36%) mixed in the ratio of 3 (g): 2 (g): 96 (mL): 4 (mL), and the ultrasonic time is 30 min. Others are the same as any one of Specific Embodiments 1 to 3.

[0058] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the activation solution in Step 3 is composed of palladium chloride, deionized water, and hydrochloric acid (concentration 36%) mixed in the ratio of 0.04 (g): 98 (mL): 2 (mL), and the ultrasonic time is 30 min. Others are the same as any one of Specific Embodiments 1 to 4.

[0059] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that the electroless plating solution in Step 4 is composed of copper sulfate pentahydrate, disodium ethylenediaminetetraacetate, formaldehyde solution, and 2,2'-bipyridine mixed in proportion. Among them, 3.75 g of copper sulfate pentahydrate is dissolved in 50 mL of deionized water, denoted as solution A; 8 g of disodium ethylenediaminetetraacetate and 2,2'-bipyridine are dissolved in 100 mL of deionized water, denoted as solution B; 6.25 mL of formaldehyde (concentration 37%) is dissolved in 100 mL of deionized water, denoted as solution C. Sequentially pour solution A and solution B into solution C, and ultrasonically mix for 30 min to make it uniform. Others are the same as any one of Specific Embodiments 1 to 5.

[0060] Specific Embodiment Seven: The difference between this embodiment and any one of Specific Embodiments One to Six is that: in Step Four, the concentration of the sodium hydroxide solution is 10 g / L, and it is adjusted to a pH value of 12. Others are the same as any one of Specific Embodiments One to Six.

[0061] Specific Embodiment Eight: The difference between this embodiment and any one of Specific Embodiments One to Seven is that: in Step Four, the amount of the fiber sample added is 0.5 g, and the reaction time is 1 h. Others are the same as any one of Specific Embodiments One to Seven.

[0062] Specific Embodiment Nine: The difference between this embodiment and any one of Specific Embodiments One to Eight is that: in Step Five, the mixing method is solution mixing, which is composed of chemically plated carbon fibers, polyethylene powder, and absolute ethanol mixed in a ratio of 3 (g): 7 (g): 20 (mL). Among them, absolute ethanol is the solvent, the mixing time is 30 min, and then it is placed in an oven at 100 °C for 24 h to dry and remove the solvent to obtain the mixed powder. Others are the same as any one of Specific Embodiments One to Eight.

[0063] Specific Embodiment Ten: The difference between this embodiment and any one of Specific Embodiments One to Nine is that: the conditions for hot pressing and forming in Step Five are: hot pressing temperature 200 °C, pressure 15 MPa, and hot pressing time 1 h. Others are the same as any one of Specific Embodiments One to Nine.

[0064] Specific Embodiment Eleven: The difference between this embodiment and any one of Specific Embodiments One to Ten is that: the calcination treatment temperature in Step Six is 700, 800, 900 °C, the time is 6 h, and the original C powder is named C-0 as a comparative sample.

[0065] Specific Embodiment Twelve: The difference between this embodiment and any one of Specific Embodiments One to Eleven is that: the solvent used in the impregnation and adsorption method in Step Seven is a waterborne polyurethane emulsion, the thickness of the polyurethane foam used is 2 mm, and the apparent density is 50 kg / m 3 。

[0066] Specific Embodiment Thirteen: The difference between this embodiment and any one of Specific Embodiments One to Twelve is that: the conditions for hot pressing and forming in Step Eight are: hot pressing temperature 80 °C, pressure 5 MPa, and hot pressing time 0.5 h.

[0067] The following examples are used to verify the beneficial effects of the present invention:

[0068] Example One:

[0069] The preparation method of an anisotropic carbon-based electromagnetic shielding composite film in this example is specifically carried out according to the following steps:

[0070] 1. Place carbon fibers with a diameter of 7 μm, a specific density of 1.8, a tensile strength of 4.1 GPa and a Young's modulus of 230 GPa, and a length of 1 mm in a nitrogen environment at 400 °C for heat treatment for 30 min to obtain pretreated carbon fibers;

[0071] 2. Disperse the product obtained in step 1 into a sensitizing solution prepared by mixing stannous chloride dihydrate, tin granules, deionized water, and hydrochloric acid (concentration 36%) in a ratio of 3 (g): 2 (g): 96 (mL): 4 (mL). After ultrasonic treatment for 30 min, filter, wash, and dry to obtain an intermediate product;

[0072] 3. Disperse the product obtained in step 2 into an activating solution prepared by mixing palladium chloride, deionized water, and hydrochloric acid (concentration 36%) in a ratio of 0.04 (g): 98 (mL): 2 (mL). After ultrasonic treatment for 30 min, filter, wash, and dry to obtain an intermediate product;

[0073] 4. Disperse 0.5 g of the product obtained in step 3 into a chemical plating solution prepared by mixing copper sulfate pentahydrate, disodium ethylenediaminetetraacetate, formaldehyde solution, and 2,2'-bipyridine in a proportional mixture. After ultrasonic mixing for 30 min, add a 10 g / L sodium hydroxide solution to adjust the pH value to 12. After stirring at 60 °C for 60 min, filter, wash, and dry to obtain a red product CF@Cu-3;

[0074] 5. Mix the CF@Cu-3 obtained in step 4 with polyethylene powder and absolute ethanol in a ratio of 3 (g): 7 (g): 20 (mL), where absolute ethanol is the solvent. The mixing time is 30 min. Then place it in an oven at 100 °C for drying for 24 h to remove the solvent. After obtaining the mixed powder, place it in an oven at 100 °C for drying for 24 h. Put the mixed powder into a stainless steel mold and transfer the whole to a flat vulcanizing machine. Carry out hot pressing at a temperature of 200 °C and a pressure of 15 MPa for 1 h to finally obtain a shielding layer CF@Cu-3 / PE;

[0075] 6. Place the mesophase carbon microspheres in a nitrogen inert atmosphere and calcine at 800 °C for 6 h to obtain C-800;

[0076] 7. Disperse the C-800 obtained in step 6 in an aqueous polyurethane emulsion and compound it with a polyurethane foam matrix with a thickness of 2 mm and an apparent density of 50 kg / m 3 by impregnation adsorption method (mass fraction 30 wt%) to prepare a loss layer composite film C-PUF-3;

[0077] VIII. Align the shielding layer in Step 5 with the loss layer in Step 6, place them in a flat vulcanizing machine, and perform hot pressing at a temperature of 80 °C and a pressure of 5 MPa for 0.5 h. Cool the product to room temperature to finally obtain an anisotropic carbon-based electromagnetic shielding composite film.

[0078] Comparative Example 1: The filler used in Step 5 is only pre-treated carbon fiber, and other conditions remain unchanged; the mixing ratio is the same as above, that is, the pre-treated carbon fiber, polyethylene powder, and absolute ethanol are mixed in a ratio of 3 (g): 7 (g): 20 (mL) to prepare the shielding layer 30-CF / PE.

[0079] Comparative Example 2: The chemical plating time in Step 4 is changed to 15 min, and other conditions remain unchanged. That is, after stirring at 60 °C for 15 min, filter, wash, and dry to obtain a red product CF@Cu-1; the mixing ratio is the same as above, that is, CF@Cu-1, polyethylene powder, and absolute ethanol are mixed in a ratio of 3 (g): 7 (g): 20 (mL) to prepare the shielding layer CF@Cu-1 / PE.

[0080] Comparative Example 3: The chemical plating time in Step 4 is changed to 30 min, and other conditions remain unchanged. That is, after stirring at 60 °C for 30 min, filter, wash, and dry to obtain a red product CF@Cu-2; the mixing ratio is the same as above, that is, CF@Cu-2, polyethylene powder, and absolute ethanol are mixed in a ratio of 3 (g): 7 (g): 20 (mL) to prepare the shielding layer CF@Cu-2 / PE.

[0081] Comparative Example 4: The chemical plating time in Step 4 is changed to 90 min, and other conditions remain unchanged. That is, after stirring at 60 °C for 90 min, filter, wash, and dry to obtain a red product CF@Cu-4; the mixing ratio is the same as above, that is, CF@Cu-4, polyethylene powder, and absolute ethanol are mixed in a ratio of 3 (g): 7 (g): 20 (mL) to prepare the shielding layer CF@Cu-4 / PE.

[0082] Comparative Example 5: No calcination treatment is performed in Step 6, denoted as C-0, and other conditions remain unchanged. That is, disperse C-0 in an aqueous polyurethane emulsion and composite it with a polyurethane foam matrix with a thickness of 2 mm and an apparent density of 50 kg / m 3 by the impregnation adsorption method (mass fraction of 30 wt%) to obtain the loss layer composite film C-PUF-1.

[0083] Comparative Example 6: The calcination treatment in Step 6 is 700 °C, denoted as C-700, and other conditions remain unchanged. That is, disperse C-700 in an aqueous polyurethane emulsion and composite it with a polyurethane foam matrix with a thickness of 2 mm and an apparent density of 50 kg / m 3The polyurethane foam matrix is compounded by the impregnation adsorption method (mass fraction of 30 wt%), and the loss layer composite film C-PUF-2 is prepared.

[0084] Comparative Example 7 is that the calcination treatment in Step 6 is 900 °C, denoted as C-900, and other conditions remain unchanged. That is, C-900 is dispersed in the aqueous polyurethane emulsion, and is compounded with a polyurethane foam matrix of 2 mm and an apparent density of 50 kg / m 3 The polyurethane foam matrix is compounded by the impregnation adsorption method (mass fraction of 30 wt%), and the loss layer composite film C-PUF-4 is prepared.

[0085] Figure 1 Figure [ID] is the SEM images of CF@Cu after different electroless plating times in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 2 to 4; through these images, it can be clearly observed that at first the copper layer is thin and unevenly distributed, there are many voids and protrusions, and even de-plating occurs in some local areas; as time goes by, the copper layer gradually becomes more uniform and continuous, and the thickness also increases continuously. After 60 min of electroless copper plating in Example 1, the surface of the coating becomes relatively uniform and dense, and almost no obvious defects can be seen. At this time, the coating thickness is about 1 μm, and there is no cracking or peeling phenomenon, indicating that it has a good combination with the P-CF matrix and can meet certain usage requirements.

[0086] Figure 2 Figure [ID] is a comparison of the tensile strength and elongation at break of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 1 to 4; it can be seen from the figure that electroless plating significantly changes the fracture behavior of the material. As the electroless plating time increases from 0 min (30-CF / PE) to 60 min (CF@Cu-3 / PE), the tensile strength of the composite film increases from 17.18 MPa to 22.85 MPa (an increase of 33.0%), and the elongation at break is about 97.4%. It should be noted that the tensile strength (19.21 MPa) and elongation at break (34.42%) of the CF@Cu-4 / PE composite film decrease, which can be attributed to the fact that too long electroless plating time will cause continuous changes in the plating solution concentration, and the compactness of the copper layer will gradually decrease, which will have a certain impact on the quality of the chemical coating, thus increasing the brittleness of the composite film again.

[0087] Figure 3Comparison of the conductivity of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 1 to 4; it can be seen from the figure that the conductivity of the shielding layer shows a non-linear growth trend with the extension of the electroless plating treatment time, that is, the electrical conductivity is greatly improved in the initial stage. This is because as the electroless plating reaction continues, the copper layer coverage rate on the fiber surface rises rapidly. During this process, a large number of copper particles are continuously deposited and grown on the fiber surface, building a new continuous conductive network to connect more conductive regions, resulting in a synergistic conductive effect; the subsequent slowdown in the increase of conductivity can be attributed to the fact that the growth rate of the electroless plating layer thickness decreases at this time.

[0088] Figure 4 Comparison of the shielding effectiveness of different shielding layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 1 to 4; it can be clearly observed that the introduction of metallic copper has a significant impact on the electromagnetic shielding performance of the composite material. From a macroscopic perspective, the overall trend of the shielding curve is relatively flat, indicating that the shielding performance of the material is stable within the test band and can provide continuous and reliable protection for the external electromagnetic environment. When the electroless plating time increases from 15 min to 90 min, the average shielding effectiveness of the material increases from 26.55 dB to 31.01 dB, 35.48 dB, and 37.60 dB respectively, and the increase rates reach 16.8%, 33.6%, and 41.6% respectively, confirming the decisive role of the integrity of the conductive network in the electromagnetic shielding performance.

[0089] Figure 5 Comparison of the electromagnetic loss performance of different loss layers in the anisotropic carbon-based electromagnetic shielding composite films prepared in Example 1 and Comparative Examples 5 to 7; as can be seen from the figure, with the increase of the calcination temperature of the mesophase carbon microspheres, the thickness corresponding to the peak value of the reflection loss (RL) of the loss layer shows a gradually decreasing trend. C-PUF-3 in Example 1 exhibits more excellent electromagnetic attenuation characteristics, with the strongest reflection loss value of -22.0 dB at 12.19 GHz and the corresponding thickness of 1.7 mm. This phenomenon fully demonstrates that the performance of the loss layer is further optimized at a higher calcination temperature, enabling the material to achieve a more ideal electromagnetic loss effect at a thinner thickness, which is of great significance for the pursuit of thinness and high performance of materials in practical applications.

[0090] Figure 6Comparison diagram of the bidirectional electromagnetic shielding performance of the anisotropic carbon-based electromagnetic shielding composite film prepared in Example 1; as can be seen from the figure, under the condition of forward incidence, a very significant change has occurred in the power distribution of the composite film. Specifically, the value of A has shown a substantial increase, rising from 0.48 to 0.78, forming an absorption-dominated shielding. This data change clearly indicates that introducing a new electromagnetic loss mechanism can effectively enhance the loss ability of the material, and this conclusion is highly consistent with the analysis results in the above text. Under the condition of reverse incidence, its R value has always been stable near 0.80, maintaining a reflection-dominated shielding. This bidirectional but mutually cooperative shielding mechanism further verifies that the "loss-shielding" process induced by the double-layer structure of the composite film is the key mechanism for achieving forward absorption-dominated electromagnetic shielding, providing key data support for in-depth understanding of the electromagnetic shielding characteristics of this material.

[0091] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as the content of the technical solution of the present invention is not departed from, and based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments within the spirit and principles of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of an anisotropic carbon-based electromagnetic shielding composite film, characterized in that The method is carried out through the following steps: Step 1. Pretreatment of carbon fiber: The carbon fiber is heat-treated in a nitrogen environment to remove the gum and grease on the fiber surface, and the pretreated carbon fiber is obtained. Step 2. Sensitization treatment: The carbon fiber obtained in Step 1 is dispersed into a sensitizing solution containing stannous chloride, ultrasonically treated, then filtered, washed, and dried to obtain an intermediate product. Step 3. Activation treatment: The product obtained in Step 2 is dispersed into an activating solution containing palladium chloride, ultrasonically treated, then filtered, washed, and dried to obtain the sensitized and activated carbon fiber. Step 4. Electroless copper plating treatment: The product obtained in Step 3 is dispersed into an electroless copper plating solution, ultrasonically treated, sodium hydroxide solution is added to adjust the pH value, after stirring at 60 °C for a period of time, it is filtered, washed, and dried to obtain a red product. Step 5. Preparation of the shielding layer composite film: The product obtained in Step 4 is mixed evenly with a certain amount of polyethylene powder, put into a stainless steel mold, and the whole is transferred to a flat vulcanizing machine and hot-pressed at 200 °C to prepare the shielding layer composite film. Step 6. Calcination treatment: The mesophase carbon microspheres are calcined in a nitrogen inert atmosphere. Step 7. Preparation of the loss layer composite film: The carbon microsphere sample obtained in Step 6 is compounded with a polyurethane foam matrix at a mass fraction of 30% by impregnation adsorption method to obtain the loss layer composite film. Step 8. Composite film forming: Align the shielding layer in Step 5 with the loss layer in Step 6, place it in a flat vulcanizing machine for hot-pressing treatment, and cool the product to room temperature to obtain the anisotropic carbon-based electromagnetic shielding composite film.

2. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, characterized in that, In Step 1, the diameter of the carbon fiber is 7 μm, the specific density is 1.8, the tensile strength and Young's modulus are 4.1 GPa and 230 GPa respectively, and the fiber length is 1 mm. The temperature of the heat treatment is 400 °C, and the time of the heat treatment is 30 min.

3. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, characterized in that, In Step 2, the sensitizing solution is composed of stannous chloride dihydrate, tin granules, deionized water, and hydrochloric acid with a concentration of 36% mixed in a mass ratio of 3:2:96:4, and the ultrasonic time is 30 min.

4. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, wherein In Step 3, the activating solution is composed of palladium chloride, deionized water, and hydrochloric acid with a concentration of 36% mixed in a mass ratio of 0.04:98:2, and the ultrasonic time is 30 min.

5. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, wherein, In Step 4, the electroless copper plating solution is composed of copper sulfate pentahydrate, disodium ethylenediaminetetraacetate, formaldehyde solution, and 2,2'-bipyridine mixed in proportion, where: 3.75 g of copper sulfate pentahydrate is dissolved in 50 mL of deionized water, denoted as solution A; 8 g of disodium ethylenediaminetetraacetate and 2,2'-bipyridine are dissolved in 100 mL of deionized water, denoted as solution B; 6.25 mL of formaldehyde with a concentration of 37% is dissolved in 100 mL of deionized water, denoted as solution C: Solution A and solution B are poured into solution C in sequence, after mixing evenly, they are ultrasonically treated for 15 min, 30 min, 60 min, and 90 min respectively.

6. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, characterized in that, In Step 4, the concentration of the sodium hydroxide solution is 10 g / L, adjusted to a pH value of 12; the amount of the fiber sample added is 0.5 g, and the reaction time is 1 h.

7. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, wherein, In Step 5, the copper-plated carbon fibers obtained in Step 4 are mixed with polyethylene powder at a mass ratio of 3:7, 20 mL of absolute ethanol is added, and the mixture is stirred for 30 min. Then, it is placed in an oven at 100 °C and dried for 24 h to remove the solvent, obtaining a mixed powder. The conditions for hot pressing are as follows: hot pressing temperature is 200 °C, pressure is 15 MPa, and hot pressing time is 1 h.

8. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, wherein In Step 6, the calcination treatment temperature is 700 °C, 800 °C, 900 °C, and the time is 6 h.

9. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, characterized in that, In Step 7, the solvent used in the impregnation adsorption method is an aqueous polyurethane emulsion, the thickness of the polyurethane foam used is 2 mm, and the apparent density is 50 kg / m 3 .

10. The preparation method of an anisotropic carbon-based electromagnetic shielding composite film according to claim 1, characterized in that, The conditions for hot pressing described in Step 8 are as follows: hot pressing temperature is 80 °C, pressure is 5 MPa, and hot pressing time is 0.5 h.

Images