A preparation method of oriented hard carbon fiber and metal composite electromagnetic shielding material

Abstract

The invention discloses a preparation method of an oriented hard carbon fiber and metal composite electromagnetic shielding material, comprising the following steps: step (1): synthesizing a polyamic acid sol to obtain a polyamic acid precursor; step (2): electrospinning the polyamic acid precursor to obtain a polyamic acid fiber membrane; step (3): thermally imidizing the electrospun polyamic acid fiber membrane to obtain a polyimide fiber membrane; step (4): fixing the polyimide fiber membrane on two polished artificial graphite plates and performing a high-temperature carbonization treatment in an argon atmosphere using a vacuum tube furnace; and step (5): plasma magnetron sputtering metal on the polyimide fiber membranes carbonized at different temperatures to obtain a polymer-based electromagnetic shielding composite material. The invention has good controllability and can flexibly control the thickness of the fiber membrane material. In addition, the carbonization treatment of the sample improves its conductivity while also maintaining the excellent flexibility of the polymer-based material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic shielding composite materials, and in particular relates to a method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material. Background Art

[0002] The rapid development of 5G communication technology and the rapid expansion of the Wi-Fi portable device market have led to an excessive concentration of electromagnetic waves in space. These waves can disrupt communication channels across various bands and permeate electronic devices in all aspects of life. Electromagnetic radiation generated by highly integrated circuits can cause malfunctions in surrounding devices and even disrupt the normal operation of the system itself. Therefore, electromagnetic shielding materials are considered essential for dissipating these waves. The main destructive effects of radio interference include transient interference, high-voltage breakdown, and surge shocks. These effects can also have significant impacts on human health, and prolonged exposure to electromagnetic radiation may even induce certain carcinogenic diseases. Therefore, the control and management of electromagnetic radiation has become a critical technical challenge. These issues have prompted researchers to explore and develop electromagnetic shielding materials with a wide range of applications.

[0003] Early electromagnetic shielding materials had the characteristics of high rigidity, high density, easy corrosion and oxidation, which limited the development of their application market. They mainly include metal types (iron, silver, nickel, copper, aluminum, etc.), which have good electromagnetic field and electrostatic field shielding performance; metal surface coating types (electroplating, chemical plating) to form a conductive layer; filled composite types (based on polymer resin) doped with a certain amount of conductive fillers (carbon black, graphene, carbon nanotubes, carbon fiber, etc.); among them, polymer-based electromagnetic shielding composite materials are mainly composed of polymer matrix and conductive and magnetic fillers. They have the characteristics of strong processability, good flexibility and low production cost, but the preparation cost of metal particle fillers is high and there is a problem of poor dispersion.

[0004] Metal-based electromagnetic shielding materials are widely used in the electromagnetic shielding field due to their excellent conductivity, providing efficient reflection loss and good shielding effectiveness. However, these materials often have some drawbacks. Metal-based materials may reduce shielding effectiveness when shielding high-frequency signals due to the skin effect. In certain specific applications, metal shielding materials may not be suitable for environments with special requirements for weight or flexibility. For example, although liquid metal-based materials are cuttable and have high compression resilience, their processability and long-term stability may be affected by their fluidity and surface tension. Therefore, when selecting and applying metal-based electromagnetic shielding materials, it is necessary to comprehensively consider their performance advantages and potential drawbacks. Summary of the Invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing oriented hard carbon fiber and metal composite electromagnetic shielding materials. The preparation method has good controllability, can flexibly control the thickness of the fiber membrane material, and carbonizes the sample to improve its conductivity while maintaining the excellent flexibility of the polymer-based material.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material, comprising the following steps:

[0008] Step (1): synthesizing a polyamic acid sol to obtain a polyamic acid precursor;

[0009] Step (2): electrospinning the polyamic acid precursor to obtain a polyamic acid fiber membrane;

[0010] Step (3): thermally imidizing the electrospun polyamic acid fiber membrane to obtain a polyimide fiber membrane;

[0011] Step (4): fixing the polyimide fiber membrane on two polished artificial graphite plates and performing high-temperature carbonization treatment in an argon atmosphere using a vacuum tube furnace;

[0012] Step (5): Plasma magnetron sputtering of metal is performed on the polyimide fiber membrane carbonized at different temperatures to obtain a polymer-based electromagnetic shielding composite material.

[0013] In the step (1), 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylformamide by in-situ polymerization and ultrasonicated for 5-10 minutes to obtain a diamine dispersion, and then pyromellitic dianhydride is added to the diamine dispersion four times, and shear force is applied and stirred for 2-3 hours to obtain a polyamic acid sol.

[0014] The ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1.02 and dissolved in 35-36 ml of N,N-dimethylformamide;

[0015] The solid content of the polyamic acid sol is 10-15 wt %.

[0016] In the step (2), a 5mL disposable sterile syringe is used to absorb the PI sol, and a 23G stainless steel electrospinning needle is installed. The diameter of the 23G needle spinning fiber is about 1μm, which can provide a large specific surface area and provide abundant attachment sites for subsequent magnetron sputtering of metal ions. The electrospinning machine is set with a speed of 350-400mm / min, a stroke setting of 70-80mm, a receiving speed of 140r / min, a positive voltage of 10.8(±2)kV, a negative voltage of -2.8(±0.5)kV, and electrospinning for 9-10 hours. The polyamide acid fiber membrane prepared according to these parameters is relatively uniform, with no droplets floating near the needle, and the thickness after metal sputtering is similar to that of commercial shielding materials, which can better meet market demand.

[0017] In step (3), the product is dried in a precision high-temperature drying oven at 80°C for 5 hours, and then dried at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0018] In the step (4), a vacuum tube furnace is used to perform high-temperature carbonization at 800° C. to 1400° C. in an argon atmosphere. All samples are kept at the final temperature for 1 hour and then cooled to room temperature.

[0019] In the step (5), magnetron sputtering of metals, copper and gold, is performed on both sides of the hard carbon fiber film carbonized at different temperatures for 180 seconds.

[0020] The specific steps of plasma magnetron sputtering are as follows: (1) Vacuum environment: A high vacuum chamber is required to provide a low-pressure environment for sputtering. (2) Target preparation: The specifications are 50 mm in diameter and 0.2 mm in thickness. (3) Gas introduction: Argon is introduced into the vacuum chamber as the working gas. (4) Sputtering parameter control: The sputtering time and current are controlled to adjust the film growth rate and quality.

[0021] In the polymer-based electromagnetic shielding composite material, the diameter of the polyimide (PI) fiber is 1 μm, pits appear on the surface of the electrospun fiber, and the surface is rough. The rough morphology of the electrospun fiber surface enables the electrostatically spun PI fiber membrane to have good adhesion to the liquid.

[0022] Beneficial effects of the present invention:

[0023] The invention uses electrostatically spun polyimide fiber membrane as a substrate, heat-treats it at different carbonization temperatures, and finally plasma magnetron sputters metal copper and gold to obtain a polymer-based electromagnetic shielding composite material.

[0024] The shielding composite material prepared by the present invention is low-cost, highly flexible, and can withstand bending and folding without damage. It can also shield 99.22% of electromagnetic waves within the 8-12 GHz frequency range. The present invention has potential applications in aerospace and aviation. By utilizing this flexible polymer-based composite material and a production-compatible molding process, it overcomes the limitations of traditional metal-based shielding materials to a certain extent, thus providing new ideas for the development of the electromagnetic shielding field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a preparation flow chart of the present invention.

[0026] Figure 2 These are the Raman spectra of carbonized polyimide materials at different carbonization temperatures.

[0027] Figure 3 Scanning electron microscope image of the oriented hard carbon fiber shielding composite material prepared by the present invention.

[0028] Figure 4 This is the total electromagnetic shielding effectiveness curve of the oriented hard carbon fiber composite material prepared in Example 1.

[0029] Figure 5 This is a graph showing how the absorption shielding effectiveness and reflection shielding effectiveness of the oriented hard carbon fiber composite material prepared in Example 1 vary with frequency.

[0030] Figure 6 Actual pictures of the hard carbon fiber films carbonized at different temperatures prepared by the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0034] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0035] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0036] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0037] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0038] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0039] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0040] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 800 °C in a vacuum tube furnace. The sample was kept at 800 °C for 1 h and then cooled to room temperature.

[0041] (8) Magnetron sputtering of metallic copper was performed on the PI-800 sample.

[0042] Example 2

[0043] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0044] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0045] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0046] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0047] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0048] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0049] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0050] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1000 °C in a vacuum tube furnace. The sample was kept at 1000 °C for 1 h and then cooled to room temperature.

[0051] (8) Plasma magnetron sputtering of metallic copper on PI-1000 sample.

[0052] Example 3

[0053] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0054] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0055] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0056] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0057] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0058] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0059] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0060] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1200 °C in a vacuum tube furnace. The sample was kept at 1200 °C for 1 h and then cooled to room temperature.

[0061] (8) Magnetron sputtering of metallic copper was performed on the PI-1200 sample.

[0062] Example 4

[0063] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0064] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0065] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0066] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0067] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0068] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0069] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0070] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1400 °C in a vacuum tube furnace. The sample was kept at 1400 °C for 1 h and then cooled to room temperature.

[0071] (8) Magnetron sputtering of metallic copper was performed on the PI-1400 sample.

[0072] Figure 2 This is the Raman spectra of electrospun polyimide fiber membrane carbonized at four temperatures: 800℃, 1000℃, 1200℃, and 1400℃. D / I G The change indicates that as the temperature increases, the disordered structure in the PI carbon fiber gradually transforms into a more ordered graphite structure, which can provide a more continuous electron transmission path and increase the conductivity of the material accordingly.

[0073] Example 5

[0074] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0075] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0076] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0077] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0078] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0079] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0080] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0081] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 800 °C in a vacuum tube furnace. The sample was kept at 800 °C for 1 h and then cooled to room temperature.

[0082] (8) Magnetron sputtering of gold was performed on the PI-800 sample.

[0083] Figure 3 (a, b) show SEM images of electrospun polyimide fiber membranes, while (c, d) show SEM images of the membrane after gold plating. Due to the high volatility of the solvent system, the rough morphology of the fiber surface imparts improved wear resistance to the electrospun PI fiber membrane, enhancing interfacial adhesion and acting as a buffer for stress concentration. The fibers, carbonized at 800°C, possess a large specific surface area, providing abundant attachment sites for magnetron sputtering metals.

[0084] The scanning electron microscope images of PI fibers prepared by electrospinning technology in this experiment are attached. Figure 3 The results show that the diameter of the PI fibers can reach approximately 1 μm. The surface of the electrospun fibers exhibits pits. This surface roughness is attributed to the high volatility of the mixed solvent system, which leads to a rapid solidification rate of the sol-spun fibers. The rough surface morphology of the fibers enables the electrospun PI fiber membrane to adhere well to liquids, enhancing the mechanical properties and durability of the composite material.

[0085] Figure 4 This is the shielding effectiveness test of the polyimide system. It can be seen that the total shielding effectiveness of the sample after carbonization gold plating is SE in the 8-12GHz band. T >20dB, can shield about 99.22% of electromagnetic waves.

[0086] Figure 5 It is the absorption shielding effectiveness SE of the PI system sample in the 8-12GHz bandA and reflected shielding effectiveness SE R , in the 8-12GHz band, the SE of the sample A Both higher than SE R About 5-6dB, proving that absorption contributes more to the attenuation of electromagnetic waves.

[0087] Example 6

[0088] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0089] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0090] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0091] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0092] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0093] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0094] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0095] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1000 °C in a vacuum tube furnace. The sample was kept at 1000 °C for 1 h and then cooled to room temperature.

[0096] (8) Magnetron sputtering of gold was performed on the PI-1000 sample.

[0097] Example 7

[0098] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0099] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0100] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0101] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four additional portions, with 0.05 g each time.

[0102] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0103] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0104] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0105] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1200 °C in a vacuum tube furnace. The sample was kept at 1200 °C for 1 h and then cooled to room temperature.

[0106] (8) Magnetron sputtering of gold was performed on the PI-1200 sample.

[0107] Example 8

[0108] A method for preparing an oriented hard carbon fiber and metal composite shielding material comprises the following steps:

[0109] (1) Prepare a polyamic acid (PAA) sol with a solid content of 15%, weigh 3 g of 4-4′-diaminodiphenyl ether (ODA) and 3.28 g of pyromellitic anhydride (PMDA), and place them in an electric blast drying oven for 12 h.

[0110] (2) Take a three-necked flask, add 35.6 mL of N,N-dimethylformamide (DMF) and then add 3 g of ODA. Dissolve it by ultrasonication for 10 min. Stir using a precision power-amplifying electric stirrer, adjust the speed, and place in an ice-water bath.

[0111] (3) Divide 3.28 g of PMDA into four portions. Add 1 g each time to the three-necked flask for the first three times, with an interval of 30 minutes between each addition. Add 0.28 g for the last time and stir for 1 hour. Then add 0.2 g in four more portions, 0.05 g each time.

[0112] (4) Pour the stirred pure PAA sol into a clean 50 mL beaker and place it in a vacuum drying oven for 4-5 hours to remove bubbles in the composite sol.

[0113] (5) PI sol was drawn up using a 5 mL sterile disposable syringe, and a 23G stainless steel electrospinning needle was installed. The electrospinning machine was set up with a speed of 400 mm / min, a stroke setting of 75 mm, a receiving speed of 140 r / min, a positive voltage of 10.8 kV, and a negative voltage of -2.8 kV. Electrospinning was performed for 10 h, with the spin cycle being switched off every 2 h and then on again after a 30-min interval.

[0114] (6) The electrospun polyamic acid fiber membrane was thermally imidized. It was first dried in a vacuum high-temperature drying oven at 80°C for 5 hours, and then treated at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

[0115] (7) The electrospun PI fiber membrane was fixed on two polished artificial graphite plates and carbonized at 1400 °C in a vacuum tube furnace. The sample was kept at 1400 °C for 1 h and then cooled to room temperature.

[0116] (8) Magnetron sputtering of gold was performed on the PI-1400 sample.

[0117] From the attached Figure 6 It can be seen that the polyimide fiber membranes carbonized at four temperatures, 800°C, 1000°C, 1200°C, and 1400°C, all have good flexibility, which helps to reduce the overall weight of the final product and adapt to the shape and size requirements of various products.

[0118] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material, characterized in that: The following steps are included: Step (1): synthesizing a polyamic acid sol to obtain a polyamic acid precursor; Step (2): electrospinning the polyamic acid precursor to obtain a polyamic acid fiber membrane; Step (3): thermally imidizing the electrospun polyamic acid fiber membrane to obtain a polyimide fiber membrane; Step (4): The polyimide fiber membrane is fixed on two polished artificial graphite plates and subjected to high-temperature carbonization treatment in an argon atmosphere using a vacuum tube furnace; Step (5): Plasma magnetron sputtering of metal is performed on the polyimide fiber membrane carbonized at different temperatures to obtain a polymer-based electromagnetic shielding composite material; In step (4), a vacuum tube furnace is used for high-temperature carbonization at 800°C to 1400°C under an argon atmosphere. All samples are kept at the final temperature for 1 hour and then cooled to room temperature. In the step (5), magnetron sputtering of metals, copper and gold, is performed on both sides of the hard carbon fiber film carbonized at different temperatures.

2. The method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material according to claim 1, characterized in that: In the step (1), 4,4'-diaminodiphenyl ether is dissolved in N,N-dimethylformamide by in-situ polymerization and ultrasonicated for 5-10 min to obtain a diamine dispersion, and then pyromellitic dianhydride is added to the diamine dispersion in four portions, and shear force is applied and stirred for 2-3 h to obtain a polyamic acid sol.

3. The method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material according to claim 2, characterized in that: The ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1.02 and dissolved in 35-36 ml of N,N-dimethylformamide; The solid content of the polyamic acid sol is 10-15 wt%.

4. The method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material according to claim 1, characterized in that: In step (2), a 5 mL disposable sterile syringe was used to absorb the PI sol, a 23 G stainless steel electrospinning needle was installed, and the electrospinning machine was set to a speed of 350-400 mm / min, a stroke setting of 70-80 mm, a receiving speed of 140 r / min, a positive voltage of 10.8±2 kV, a negative voltage of -2.8±0.5 kV, and electrospinning for 9-10 hours.

5. The method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material according to claim 1, characterized in that: In step (3), the product is dried in a precision high-temperature drying oven at 80°C for 5 hours, and then dried at 150°C, 200°C, 250°C, 300°C, and 350°C for one hour each before being taken out.

6. The method for preparing an oriented hard carbon fiber and metal composite electromagnetic shielding material according to claim 1, characterized in that: The specific steps of the plasma magnetron sputtering are: (1) Vacuum environment: A high vacuum chamber is required to provide a low-pressure environment for sputtering; (2) Target preparation: specifications are 50 mm in diameter and 0.2 mm in thickness; (3) Gas introduction: Introduce argon into the vacuum chamber as the working gas; (4) Sputtering parameter control: Control the sputtering time and current to adjust the growth rate and quality of the film.

7. A polymer-based electromagnetic shielding composite material prepared according to the method according to any one of claims 1 to 6, characterized in that: In the polymer-based electromagnetic shielding composite material, the diameter of the PI fiber is 1 μm, pits appear on the surface of the electrospun fiber, and the surface is rough. The rough morphology of the fiber surface enables the electrospun PI fiber membrane to have good adhesion to the liquid.

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