High-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film and preparation method thereof

Abstract

This invention discloses a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film and its preparation method. The preparation method includes: reacting a first mixed reaction system containing a diamine monomer, a salt-forming reagent, and a dianhydride monomer to obtain an aqueous polyamic acid salt; uniformly mixing a polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion with the aqueous polyamic acid salt to form an aqueous polyamic acid salt / carbon nanotube dispersion; applying the aqueous polyamic acid salt / carbon nanotube dispersion onto a substrate, followed by thermal imidization treatment to obtain the high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film. The preparation method provided by this invention is simple, safe, and environmentally friendly, suitable for industrial application. The final composite film maintains good mechanical properties and high-temperature electromagnetic shielding performance even with high carbon nanotube content, which is beneficial for its application in extreme environments.

Description

Technical Field

[0001] This invention belongs to the field of polyimide nanocomposite film preparation technology, and particularly relates to a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film and its green preparation method. Background Technology

[0002] The rapid development of electronics and communication technologies has placed higher demands on electromagnetic shielding materials. Ultra-thin, flexible, high-strength, and heat-resistant electromagnetic shielding materials are indispensable in many fields, including aerospace, electronics, and small wearable electronic products. Traditional metallic materials (Ag, Cu, Fe) are limited by their high density and are susceptible to corrosion. More importantly, the electrical properties of metallic and alloy nanomaterials decrease with increasing temperature, leading to a reduction in their electromagnetic wave shielding capabilities. Simultaneously, the susceptibility to corrosion, high density, and poor flexibility of metallic materials also limit their practical applications in specific fields. Furthermore, magnetic materials such as iron oxide and cobalt oxide can achieve efficient attenuation of electromagnetic waves, but their use under high-temperature conditions is limited by their Curie temperature.

[0003] It is worth noting that carbon nanotubes possess excellent electrical conductivity, high mechanical strength, and large-scale production capabilities, showing great potential in the development of electromagnetic shielding materials. The electrical conductivity of a single carbon nanotube can reach 1×10⁻⁶. 8 S / m, mechanical strength exceeding 1×10 5 MPa. The preparation of conductive polymers for electromagnetic shielding by combining them with polymers possessing good processability has attracted considerable attention. However, the performance of traditional macroscopic carbon nanotube films is far inferior to that of single carbon nanotubes, mainly because the loose and disordered arrangement of carbon nanotubes in the film inhibits the improvement of carbon nanotube film performance. Polyimide materials typically exhibit excellent mechanical properties at high and low temperatures (-200~300℃), and have great application potential in the field of electromagnetic shielding materials.

[0004] The good dispersibility of fillers in the polymer matrix determines the overall performance of the composite membrane. Some researchers have used a mixture of polyamic acid and MXene to prepare high-performance conductive composite membranes. For example, Chinese patent CN752331159A discloses a method for synthesizing polyamic acid, a polyimide precursor, in an organic solvent such as N,N-dimethylacetamide (DMAc), and then reacting it with triethylamine and water to prepare an aqueous solution of polyamic acid, which is then uniformly mixed with MXene to finally prepare a polyimide / MXene composite membrane for electromagnetic shielding. However, when the mass of MXene accounts for 60 wt% of the total mass of the polyimide composite system, the strength of the composite membrane has dropped to about 80 MPa, and the electromagnetic shielding performance of the composite membrane is about 28 dB.

[0005] However, while high levels of conductive fillers (>30 wt%) impart excellent electrical conductivity to polymers, they often lead to a sharp decline in the mechanical properties of the polymer matrix. Therefore, the preparation of flexible, high-strength, and high-temperature-resistant polyimide composite films with high-conductivity fillers is of great significance for electromagnetic shielding in harsh environments. Summary of the Invention

[0006] The main objective of this invention is to provide a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film and its green preparation method, so as to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0008] This invention provides a method for preparing a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film, comprising:

[0009] A first mixed reaction system containing a diamine monomer, a salt-forming agent, and a dianhydride monomer is reacted to obtain an aqueous polyamic acid salt.

[0010] A polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion is mixed evenly with an aqueous polyamic acid salt to form an aqueous polyamic acid salt / carbon nanotube dispersion.

[0011] The aqueous polyamic acid salt / carbon nanotube dispersion was applied to a substrate and then subjected to thermal imidization treatment to obtain a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film.

[0012] In some embodiments, the process conditions for the thermal imidization treatment include: a gradient heating treatment at 100–450°C for 0.5–2 hours under nitrogen or vacuum conditions.

[0013] In some embodiments, the preparation method includes:

[0014] The aqueous polyamic acid salt / carbon nanotube dispersion was cast onto a substrate and the solvent was removed by heating to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0015] The aqueous polyamic acid salt / carbon nanotube composite film was heated to complete the thermal imidization treatment and remove polyvinylpyrrolidone to obtain a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film.

[0016] Furthermore, embodiments of the present invention also provide a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared by the aforementioned preparation method.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0018] 1) The entire preparation process provided by this invention uses water as a solvent, avoiding the large-scale use of organic solvents. The preparation method is simple and environmentally friendly, and suitable for industrial promotion.

[0019] 2) The polyvinylpyrrolidone-modified carbon nanotube slurry used in this invention exhibits excellent compatibility with the polyimide precursor polyamic acid salt aqueous solution, avoiding problems such as the decrease in mechanical properties caused by the agglomeration of conductive fillers, and achieving excellent mechanical properties and electromagnetic shielding performance under extremely high carbon nanotube content loading (66.7wt%).

[0020] 3) The aqueous polyimide / carbon nanotube composite electromagnetic shielding film finally prepared by this invention exhibits excellent mechanical properties (tensile strength of about 68-284 MPa) and electromagnetic shielding effectiveness of up to about 51 dB. It remains stable under high temperature conditions (350 °C) and even improves electromagnetic shielding effectiveness by 1.5 dB compared with room temperature. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings obtained from these drawings without creative effort still fall within the scope of the present invention.

[0022] Figure 1 The above is the 1H NMR spectrum of the aqueous polyamic acid salt obtained in Example 1 of this invention;

[0023] Figure 2 The particle size distribution diagrams are of the aqueous polyamic acid salt / PVP / CNT dispersions obtained in Examples 1, 2, 3, and 4 of this invention.

[0024] Figure 3 This is a cross-sectional scanning electron microscope image of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film obtained in Example 2 of the present invention.

[0025] Figure 4 The stress-strain curves of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding films obtained in Examples 1, 2, 3, 4, 5, and 6 of this invention are shown.

[0026] Figure 5 This is a scatter plot of the X-band electromagnetic shielding effectiveness of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film obtained in Example 1 of the present invention. Detailed Implementation

[0027] Traditional conductive polymer composites used as electromagnetic shielding materials often require high levels of conductive filler to achieve high electromagnetic shielding effectiveness. However, high filler content often leads to agglomeration and other phenomena, resulting in a sharp decline in mechanical properties. Through long-term research and extensive practical application, the inventors of this case aim to solve the balance between the mechanical properties and electromagnetic shielding performance of composite materials with high filler content, thereby improving overall performance to meet the needs of practical applications.

[0028] This invention synthesizes a series of aqueous polyimides. Excitingly, the polyvinylpyrrolidone-modified carbon nanotube slurry exhibits excellent compatibility with aqueous polyamic acid salt precursors, particularly due to the cationic-π interactions and electrostatic interactions between the imidazole salt series aqueous polyamic acid salts and carbon nanotubes. This facilitates the stability of the mixed dispersion and avoids problems such as decreased mechanical properties caused by the agglomeration of conductive fillers, ultimately achieving a high carbon nanotube loading (66.7 wt%). The resulting aqueous polyimide / carbon nanotube composite film exhibits excellent mechanical and electromagnetic shielding properties.

[0029] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0030] One aspect of the present invention provides a method for preparing a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film (also referred to as "waterborne polyimide (WPI)-based flexible electromagnetic shielding composite film"), comprising:

[0031] A first mixed reaction system containing a diamine monomer, a salt-forming agent, and a dianhydride monomer is reacted to obtain an aqueous polyamic acid salt.

[0032] A polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion is mixed evenly with an aqueous polyamic acid salt to form an aqueous polyamic acid salt / carbon nanotube dispersion.

[0033] The aqueous polyamic acid salt / carbon nanotube dispersion was applied to a substrate and then subjected to thermal imidization treatment to obtain a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film.

[0034] In some embodiments, the diamine monomer may include (p-phenylenediamine) (4,4′-diaminodiphenyl ether), Any one or more combinations of (2,2-dimethylbenzidine), but not limited to these.

[0035] In some embodiments, the dianhydride monomer is (3,3′,4,4-Biphenyltetracarboxylic acid dianhydride).

[0036] In some embodiments, the salt-forming reagent is an alkaline salt-forming reagent, for example preferably it can be... (triethylamine) (1,2-Dimethylimidazole) Any one or more combinations of (imidazole) and other similar ingredients, but not limited to these.

[0037] In some embodiments, the molar ratio of the diamine monomer to the dianhydride monomer is 0.98:1 to 1:1.

[0038] In some embodiments, the molar ratio of the dianhydride monomer to the salt-forming agent is 1:2 to 1:5.

[0039] In some embodiments, the preparation method includes: mixing a diamine monomer with deoxygenated water, adding a salt-forming reagent to assist in the rapid dissolution of the diamine monomer, then adding a dianhydride monomer, stirring and mixing evenly, and reacting to obtain an aqueous polyamic acid salt solution.

[0040] Furthermore, the stirring speed is controlled at 100–300 rpm.

[0041] Furthermore, the ratio of the diamine monomer to water is (0.01–0.05) mol: (50–200) mL.

[0042] Furthermore, the viscosity of the aqueous polyamic acid salt solution is 40,000 to 100,000 cP.

[0043] In some embodiments, the reaction is carried out under a protective atmosphere (such as nitrogen atmosphere), the reaction temperature is set to 25–80°C, and the reaction time is 6–12 h.

[0044] In some embodiments, the preparation method includes: modifying carbon nanotubes with polyvinylpyrrolidone to obtain a polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion.

[0045] In some embodiments, the preparation method includes: mixing a polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion and an aqueous polyamic acid salt, followed by ultrasonication and stirring to obtain a uniformly mixed aqueous polyamic acid salt / carbon nanotube dispersion.

[0046] Furthermore, the diameter of the carbon nanotubes is 5–50 nm.

[0047] In some more preferred embodiments, the mass ratio of polyvinylpyrrolidone to carbon nanotubes is 1:4 to 1:9.

[0048] In some preferred embodiments, the carbon nanotube aqueous dispersion is modified with polyvinylpyrrolidone, wherein the mass ratio of the aqueous polyamic acid salt to the carbon nanotubes is 10:1 to 1:5.

[0049] In some more preferred embodiments, the solid content of the aqueous polyamic acid salt / carbon nanotube dispersion is 20-60 mg / mL, preferably 20-50 mg / mL.

[0050] In some more preferred embodiments, the temperature of the ultrasound is 20–30°C, the duration of the ultrasound is 0.5–2 hours, and the power of the ultrasound is 100–500 kHz.

[0051] In some more preferred embodiments, the stirring speed is 300-600 rpm and the stirring time is 12-36 h.

[0052] In some embodiments, the preparation method specifically includes:

[0053] The aqueous polyamic acid salt / carbon nanotube dispersion was cast onto a substrate and the solvent was removed by heating to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0054] The aqueous polyamic acid salt / carbon nanotube composite film was heated to complete the thermal imidization treatment and remove polyvinylpyrrolidone to obtain a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film.

[0055] Furthermore, the heating temperature is 50–80°C, and the heating time is 1–3 hours.

[0056] Furthermore, the substrate includes, but is not limited to, a glass plate.

[0057] In some embodiments, the process conditions for the thermal imidization treatment of the aqueous polyimide / carbon nanotube composite film include: a gradient heating treatment at 100–450°C for 0.5–2 hours under nitrogen or vacuum conditions.

[0058] In some preferred embodiments, the thermal imidization treatment of the aqueous polyimide / carbon nanotube composite film is a gradient heating treatment under nitrogen protection, specifically: first, heating to 100-120°C and holding for 1-2 hours, then heating to 150-170°C and holding for 1-2 hours, then heating to 200-220°C and holding for 1-2 hours, then heating to 250-270°C and holding for 1-2 hours, then heating to 300-320°C and holding for 0.5-2 hours, and finally heating to 350-450°C to dehydrate the polyamic acid and form an imide ring, followed by a cyclization treatment of 0.5-2 hours.

[0059] In some specific implementations, the preparation method of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film mainly includes:

[0060] In a green aqueous solvent, aqueous polyamic acid salts (WPAAS) were prepared using 4,4′-diaminodiphenyl ether (ODA) and p-phenylenediamine (PDA) as diamines, 3,3′,4,4-biphenyltetracarboxylic acid dianhydride (BPDA) as dianhydride, and 1,2-dimethylimidazolium (DMZ), triethylamine (TEA), or imidazole (IM) as salt-forming agents. The obtained aqueous polyamic acid salts were uniformly mixed with an aqueous slurry of multi-walled carbon nanotubes (MWCNTs). Due to the presence of hydrogen bonds and cation-π, π-π interactions between the polyamic acid salts and the aqueous carbon nanotube slurry, the mixed solution system exhibited excellent dispersibility. Finally, a high-strength, high-electromagnetic-shielding aqueous polyimide / carbon nanotube composite electromagnetic shielding film was prepared through simple solution casting and thermal imidization.

[0061] In some more specific embodiments, the preparation method of the high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film includes the following steps:

[0062] (1) Add diamine monomer and deoxygenated deionized water to a three-necked flask, and add alkaline salt-forming reagent to help the diamine monomer dissolve quickly. Then add dianhydride monomer to react and obtain an aqueous polyamic acid salt solution.

[0063] (2) Mix the polyvinylpyrrolidone (PVP) modified multi-walled carbon nanotube aqueous dispersion with the aqueous polyamic acid salt solution obtained in step (1), and sonicate and stir to obtain a uniformly mixed aqueous polyamic acid salt / carbon nanotube dispersion.

[0064] (3) The aqueous polyamic acid salt / carbon nanotube dispersion obtained in step (2) is poured onto a clean glass plate of 5×10cm and heated in an oven to remove the solvent water, thereby obtaining an aqueous polyamic acid salt / carbon nanotube composite film.

[0065] (4) The obtained polyamic acid salt / carbon nanotube composite film is heated to 350-450℃ in an oven to complete thermal imidization and remove polyvinylpyrrolidone, and finally a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film is obtained.

[0066] Furthermore, in step (2), the ultrasonic duration of the aqueous polyamic acid salt / carbon nanotube dispersion is 20-30℃, the ultrasonic time is 0.5-2h, the ultrasonic power is 100-500kHz, the stirring speed is 300-600rpm, and the stirring time is 12-36h.

[0067] Furthermore, in step (3), the waterborne polyamic acid salt / carbon nanotube composite film is treated in an oven at a temperature of 50–80°C for 1–3 hours.

[0068] In some preferred embodiments, a method for preparing a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film specifically includes the following steps:

[0069] (1) In an oxygen-free aqueous solvent, diamine monomer and a salt-forming agent are added to assist dissolution, resulting in a completely dissolved diamine monomer solution. Then, dianhydride monomer is added to react with it to obtain a high-viscosity aqueous polyamic acid salt solution (40,000–100,000 cP). The molar ratio of diamine monomer to dianhydride monomer is 0.98:1 to 1:1, the molar ratio of dianhydride monomer to alkaline salt-forming reagent is 1:2 to 1:5, and the ratio of diamine monomer to solvent is (0.01–0.05) mol to (50–200) mL.

[0070] (2) The aqueous polyamic acid salt solution obtained in step (1) is mixed with the polyvinylpyrrolidone-modified carbon nanotube aqueous slurry and dispersed uniformly by ultrasonication and stirring. The aqueous polyamic acid salt / carbon nanotube dispersion is poured onto a clean glass plate and heated in an oven to remove the solvent water, thereby obtaining an aqueous polyamic acid salt / carbon nanotube composite film. The mass ratio of polyvinylpyrrolidone to carbon nanotubes is determined to be 1:9 to 1:4. The mass ratio of aqueous polyamic acid salt to carbon nanotubes is 10:1 to 1:5, and the solid content of the aqueous polyamic acid salt / carbon nanotube dispersion is 20 to 50 mg / ml.

[0071] (3) The polyamic acid salt / carbon nanotube film obtained in step (2) is subjected to a gradient heating treatment at 100-450℃ in an oven for 0.5-2h to complete the thermal imidization treatment, thereby obtaining a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film.

[0072] Furthermore, the preparation processes in steps (1) and (2) are all deionized water solvents, which avoids the large-scale use of organic solvents. The entire preparation process is simple, safe, and environmentally friendly, and is suitable for industrial promotion.

[0073] In summary, this invention uses water as a solvent, avoiding the extensive use of organic solvents. The preparation method is simple and environmentally friendly, suitable for industrial application, and has significant implications for both scientific research and practical application of polyimide-based composite electromagnetic shielding materials. The polyvinylpyrrolidone-modified carbon nanotube slurry exhibits excellent compatibility with the polyimide precursor polyamic acid salt aqueous solution, avoiding problems such as decreased mechanical properties caused by the agglomeration of conductive fillers, and achieving an extremely high carbon nanotube content loading (66.7 wt%).

[0074] Another aspect of the present invention provides a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared by the aforementioned preparation method, which achieves an extremely high carbon nanotube content loading (66.7 wt%).

[0075] Furthermore, the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film has a thickness of 20–350 μm, a tensile strength of 68–284 MPa, and an electromagnetic shielding effectiveness of up to 51 dB.

[0076] Furthermore, the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared by this invention exhibits excellent mechanical properties (tensile strength of approximately 68-284 MPa) and an electromagnetic shielding effectiveness of up to 51 dB. More importantly, the electromagnetic shielding performance of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film remains stable under high-temperature conditions (350 °C), and even shows an improvement of 1.5 dB in electromagnetic shielding effectiveness compared to room temperature.

[0077] In summary, the composite membrane finally prepared by this invention can still maintain good mechanical properties and high-temperature electromagnetic shielding performance even with high carbon nanotube content, which is beneficial for its application in extreme environments.

[0078] To further understand the present invention, the aqueous polyimide / carbon nanotube composite electromagnetic shielding film provided by the present invention will be described in detail below with reference to embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0079] Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention were all purchased commercially.

[0080] The polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion used in the following examples is prepared by modifying carbon nanotubes with polyvinylpyrrolidone. Specifically, the process includes mixing the polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion with an aqueous polyamic acid salt, followed by ultrasonication and stirring to obtain a uniformly mixed aqueous polyamic acid salt / carbon nanotube dispersion. The carbon nanotubes have a diameter of 5–50 μm, and the mass ratio of polyvinylpyrrolidone to carbon nanotubes is 1:4 to 1:9.

[0081] Example 1

[0082] (1) First, measure about 150 mL of deionized water and add it to a 250 mL three-necked flask. Under nitrogen purging, heat the flask to 80 °C to remove oxygen from the deionized water. Set aside for later use.

[0083] (2) At room temperature and under nitrogen purging, p-phenylenediamine (3.0279 g, 0.028 mol) and 1,2-dimethylimidazole (6.3 mL, 0.07 mol) were added to 101 mL of the above-mentioned deionized water, and the reaction was carried out for 0.5 h until the p-phenylenediamine monomer was completely dissolved. Then, the dianhydride monomer 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride (8.2376 g, 0.028 mol) was added, and the temperature was raised to 70 °C and reacted for 12 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0084] (3) The polyamic acid salt aqueous solution (2.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (4.00 g, 5 wt%) (the mass ratio of polyvinylpyrrolidone to carbon nanotubes is 1:5) were added to 4.00 g of deionized water, and the mixture was ultrasonicated and stirred to prepare a uniformly mixed dispersion with a solid content of 3 wt% and an average particle size of 224 nm. The ultrasonication temperature was 25 °C, the ultrasonication time was 1 h, and the ultrasonication power was 300 kHz. The stirring speed was 500 rpm, and the stirring time was 24 h. The above dispersion was poured onto a glass plate with a size of 5 x 10 cm. Finally, the mixture was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain a polyamic acid salt / carbon nanotube composite film.

[0085] (4) The polyamic acid salt / carbon nanotube composite film obtained in step (3) above is treated at 100℃, 150℃, 200℃, 250℃, 300℃ and 350℃ for 1h, 1h, 1h, 1h, 0.5h and 0.5h respectively to obtain a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film.

[0086] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment maintains excellent mechanical properties even with a carbon nanotube content of 66.7 wt%. Its tensile strength reaches approximately 174 MPa, and its modulus reaches approximately 6.8 GPa. With a composite film thickness ranging from 0.02 to 0.35 mm, the corresponding electromagnetic shielding performance ranges from 23 to 51 dB, all meeting the requirements for commercial applications (>20 dB). Furthermore, this composite electromagnetic shielding film maintains stable electromagnetic shielding performance under high-temperature conditions.

[0087] Figure 1 The above is the 1H NMR spectrum of the 1,2-dimethylimidazolium salt-terminated polyamic acid salt prepared in this embodiment. Figure 1 It can be seen that the corresponding polyimide precursor salt solution was synthesized. The particle size distribution of the aqueous polyamic acid salt / PVP / CNT dispersion is as follows. Figure 2 As shown.

[0088] Figure 4The stress-strain curve of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment is shown.

[0089] Figure 5 The electromagnetic shielding performance of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment in the 8.2-12.4GHz (X-band) range was measured. When the film thickness increased from 0.02mm to 0.35mm, the electromagnetic shielding effectiveness increased from 23dB to 51dB.

[0090] Example 2

[0091] (1) The process is consistent with step (1) in Example 1.

[0092] (2) The process is consistent with step (2) in Example 1.

[0093] (3) The polyamic acid salt aqueous solution (2.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (2.00 g, 5 wt%) were added to 2.67 g of deionized water to prepare a uniformly mixed dispersion with a solid content of 3 wt% and an average particle size of 211 nm. The dispersion was then cast onto a 5 x 10 cm glass plate. Finally, the film was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0094] (4) is consistent with step (4) in Example 1.

[0095] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment maintains excellent mechanical properties even with a carbon nanotube content of 50 wt%, achieving a tensile strength of 212 MPa. The corresponding electromagnetic shielding performance reaches a maximum of 26.3 dB at a film thickness of 0.03 mm. Furthermore, this composite film maintains stable electromagnetic shielding performance at a high temperature of 350°C, with the electromagnetic shielding effectiveness increasing to 27.8 dB.

[0096] The particle size distribution of the aqueous polyamic acid salt / PVP / CNT dispersion prepared in this embodiment is as follows: Figure 2 As shown.

[0097] Figure 3 This is a cross-sectional scanning electron microscope image of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment. Figure 3 The carbon nanotubes are uniformly dispersed in the polymer matrix without obvious agglomeration, which also makes the composite electromagnetic shielding film exhibit excellent mechanical properties.

[0098] Figure 4The stress-strain curve of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment is shown.

[0099] Example 3

[0100] (1) The process is consistent with step (1) in Example 1.

[0101] (2) The process is consistent with step (2) in Example 1.

[0102] (3) The polyamic acid salt aqueous solution (4.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (0.40 g, 5 wt%) were added to 2.93 g of deionized water to prepare a uniformly mixed dispersion with a solid content of 3 wt% and an average particle size of 249 nm. The dispersion was then cast onto a 5 x 10 cm glass plate. Finally, the film was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0103] (4) is consistent with step (4) in Example 1.

[0104] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment exhibits excellent mechanical properties with a carbon nanotube content of 9.1 wt%, a tensile strength of up to 284 MPa, and a corresponding electromagnetic shielding performance of up to 4.3 dB with a film thickness of 0.03 mm.

[0105] Example 4

[0106] (1) The process is consistent with step (1) in Example 1.

[0107] (2) The process is consistent with step (2) in Example 1.

[0108] (3) The polyamic acid salt aqueous solution (2.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (10.00 g, 5 wt%) were added to 8.00 g of deionized water to prepare a uniformly mixed dispersion with a solid content of 3 wt% and an average particle size of 370 nm. The dispersion was then cast onto a 5 x 10 cm glass plate. Finally, the film was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0109] (4) is consistent with step (4) in Example 1.

[0110] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment has a tensile strength of approximately 68 MPa when the carbon nanotube content is 83.3 wt%, and the corresponding electromagnetic shielding performance can reach up to 36.1 dB when the film thickness is 0.032 mm.

[0111] Example 5

[0112] (1) The process is consistent with step (1) in Example 1.

[0113] (2) At room temperature and under nitrogen purging, 5.6066 g (0.028 mol) of 4,4′-diaminodiphenyl ether and 6.3 ml (0.07 mol) of 1,2-dimethylimidazole were added to 124 ml of the above-mentioned deionized water, and the reaction was allowed to proceed for 0.5 h until the 4,4′-diaminodiphenyl ether was completely dissolved. Then, the dianhydride monomer 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (8.2376 g, 0.028 mol) was added, and the temperature was raised to 70 °C and reacted for 12 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0114] (3) is consistent with step (3) in Example 2.

[0115] (4) is consistent with step (4) in Example 1.

[0116] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment achieves a tensile strength of 126 MPa when the carbon nanotube content is 50 wt%, while the tensile strength of the pure waterborne polyimide film is 134 MPa, a decrease of only about 6.0%. Simultaneously, the electromagnetic shielding effectiveness reaches 33 dB when the film thickness is approximately 0.035 mm.

[0117] Figure 3 The stress-strain curve of the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment shows that when the carbon nanotube content is greater than 50 wt%, the high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film still exhibits excellent mechanical properties.

[0118] Example 6

[0119] (1) The process is consistent with step (1) in Example 1.

[0120] (2) At room temperature and under nitrogen purging, p-phenylenediamine (3.0279 g, 0.028 mol) and triethylamine (19.5 ml, 0.14 mol) were added to 101 ml of the above-mentioned deionized water, and the reaction was allowed to proceed for 0.5 h until the p-phenylenediamine monomer was completely dissolved. Then, the dianhydride monomer 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride (8.2376 g, 0.028 mol) was added, and the temperature was raised to 25 °C and reacted for 12 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0121] (3) The polyamic acid salt aqueous solution (4.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (2.00 g, 5 wt%) (the ratio of polyvinylpyrrolidone to carbon nanotubes is 1:4) were added to 4.00 g of deionized water to prepare a uniformly mixed dispersion with a solid content of 3 wt%. The dispersion was then cast onto a glass plate with a size of 5 x 10 cm. Finally, the mixture was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0122] (4) is consistent with step (4) in Example 1.

[0123] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment can achieve a tensile strength of 169 MPa when the carbon nanotube mass ratio is 33.3 wt%, and an electromagnetic shielding effectiveness of 22 dB when the film thickness is about 0.035 mm.

[0124] Example 7

[0125] (1) The process is consistent with step (1) in Example 1.

[0126] (2) At room temperature and under nitrogen purging, p-phenylenediamine (3.0279 g, 0.028 mol) and imidazole (4.77 g, 0.07 mol) were added to 101 ml of the above-mentioned deionized water, and the reaction was allowed to proceed for 0.5 h until the p-phenylenediamine monomer was completely dissolved. Then, dianhydride monomer 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride (8.2376 g, 0.028 mol) was added, and the temperature was raised to 70 °C and reacted for 12 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0127] (3) The polyamic acid salt aqueous solution (4.00 g, 5 wt%) obtained in step (2) and the polyvinylpyrrolidone modified carbon nanotube slurry (2.00 g, 5 wt%) were added to 4.00 g of deionized water to prepare a uniformly mixed dispersion with a solid content of 3 wt%. The dispersion was then cast onto a glass plate with a size of 5 x 10 cm. Finally, the mixture was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0128] (4) is consistent with step (4) in Example 1.

[0129] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment can achieve an electromagnetic shielding effectiveness of 23dB when the carbon nanotube mass ratio is 33.3wt% and the film thickness is about 0.03mm.

[0130] Example 8

[0131] The only difference between this embodiment and Embodiment 1 is that:

[0132] In step (2), the molar ratio of p-phenylenediamine to 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride is 0.98:1, and the molar ratio of 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride to 1,2-dimethylimidazole is 1:2. The ratio of p-phenylenediamine to deionized water is 0.01 mol:50 mL. The mixture is heated to 60 °C and reacted for 10 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0133] In step (3), the mass ratio of the aqueous polyamic acid salt to the carbon nanotubes is 10:1. The ultrasonic temperature is 20°C, the ultrasonic time is 2 hours, and the ultrasonic power is 100 kHz. The stirring speed is 300 rpm, and the stirring time is 36 hours.

[0134] In step (4), the polyamic acid salt / carbon nanotube composite film is treated at 120℃, 170℃, 220℃, 270℃, 320℃, and 450℃ for 2h, 2h, 2h, 2h, 2h, and 2h respectively to obtain a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film.

[0135] Example 9

[0136] The only difference between this embodiment and Embodiment 1 is that:

[0137] In step (2), the molar ratio of p-phenylenediamine to 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride is 0.99:1, and the molar ratio of 3,3′,4,4'-biphenyltetracarboxylic acid dianhydride to 1,2-dimethylimidazole is 1:3. The ratio of p-phenylenediamine to deionized water is 0.05 mol:200 mL. The reaction is carried out at 80 °C for 6 h to obtain a high-viscosity polyamic acid salt aqueous solution.

[0138] In step (3), the mass ratio of the aqueous polyamic acid salt to the carbon nanotubes is 1:5. The ultrasonic temperature is 30°C, the ultrasonic time is 0.5 h, and the ultrasonic power is 500 kHz. The stirring speed is 600 rpm, and the stirring time is 12 h.

[0139] Example 10

[0140] The only difference between this embodiment and Embodiment 1 is that:

[0141] The polyvinylpyrrolidone-modified carbon nanotube slurry (4.00 g, 5 wt%) in step (3) has a polyvinylpyrrolidone to carbon nanotube mass ratio of 1:9. The prepared uniformly mixed dispersion with a solid content of 3 wt% was poured onto a 5 x 10 cm glass plate. Finally, it was heat-treated in an oven at 50℃, 60℃, 70℃, and 80℃ for 2 h, 2 h, 2 h, and 2 h respectively to obtain an aqueous polyamic acid salt / carbon nanotube composite film.

[0142] The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared in this embodiment has a tensile strength of approximately 161 MPa when the carbon nanotube content is 66.7 wt%, and the corresponding electromagnetic shielding performance can reach up to 25.8 dB when the film thickness is 0.033 mm, thus achieving both high tensile strength and electromagnetic shielding effectiveness.

[0143] Comparative Example 1

[0144] CN752331159A discloses a method for synthesizing polyamic acid, a polyimide precursor, in an organic solvent such as N,N-dimethylacetamide (DMAc), followed by reacting it with triethylamine and water to prepare an aqueous solution of polyamic acid, which is then uniformly mixed with MXene to ultimately prepare a polyimide / MXene composite film for electromagnetic shielding. However, when MXene accounts for 60 wt% of the total mass of the polyimide composite system, the strength of the composite film is only 80 MPa, and the elongation at break is <2%. The mechanical properties of the composite film decrease significantly at higher MXene contents. Furthermore, the electromagnetic shielding effectiveness of this composite film is approximately 28 dB. Notably, the preparation of the polyamic acid aqueous solution in this method is cumbersome and involves the use of a large amount of organic solvent.

[0145] In this invention, when the carbon nanotube filler content is relatively high (66.7 wt%), the mechanical strength of the aqueous polyimide / carbon nanotube composite film can reach 174 MPa, while also imparting good electromagnetic shielding performance (23-51 dB). Furthermore, this invention is carried out entirely in an aqueous solution, avoiding the use of large amounts of organic solvents, making it suitable for industrial application.

[0146] Comparative Example 2

[0147] (1) First, about 55 mL of N-methylpyrrolidone was added to a 100 mL three-necked flask. Under nitrogen purging at room temperature, p-phenylenediamine (2.6494 g, 0.0245 mol) was added to the organic solvent until the p-phenylenediamine monomer was completely dissolved. Then, dianhydride monomer 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (7.3600 g, 0.025 mol) was added and reacted for 12 h to obtain a high-viscosity polyamic acid (PAA) solution.

[0148] (2) Mix the polyamic acid organic solution (2.00 g, 5 wt%) obtained in step (1) and the polyvinylpyrrolidone modified carbon nanotube organic solvent dispersion evenly and dilute to a solid content of 3 wt%.

[0149] (3) The polyamic acid / carbon nanotube organic solvent dispersion obtained in step (2) is poured onto a glass plate with a size of 5x10cm. Finally, it is heat-treated in an oven at 50℃, 60℃, 70℃ and 80℃ for 2h, 2h, 2h and 2h respectively to obtain a polyamic acid / polyvinylpyrrolidone / carbon nanotube composite film.

[0150] (4) is consistent with step (4) in Example 1.

[0151] In this comparative example, the mechanical properties of the polyimide / carbon nanotube composite electromagnetic shielding film prepared based on an organic solvent system deteriorated significantly when the carbon nanotube content was 50 wt%. The tensile strength was only 67 MPa, which was much lower than the 212 MPa of the waterborne polyimide / carbon nanotube composite film with the same carbon nanotube content (50 wt%). When the composite film thickness was ~0.035 mm, the corresponding electromagnetic shielding performance was 24.8 dB, which was lower than the 26.3 dB of the waterborne polyimide / carbon nanotube composite film.

[0152] Comparative Example 3

[0153] (1) The process is consistent with step (1) in Example 1.

[0154] (2) The process is consistent with step (2) in Example 1.

[0155] (3) The polyamic acid salt aqueous solution (4.00 g, 5 wt%) obtained in step (2) and carbon nanotube powder (0.20 g, added to 9.10 g of deionized water) were added to prepare a uniformly mixed dispersion with a solid content of 3 wt%. The dispersion was then cast onto a glass plate with a size of 5 x 10 cm. Finally, the mixture was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain a polyamic acid salt / carbon nanotube composite film.

[0156] (4) is consistent with step (4) in Example 1.

[0157] (5) Aqueous polyimide / carbon nanotube composite films prepared directly from polyamic acid salts and carbon nanotube powder exhibited decreased mechanical properties at a carbon nanotube content of 50 wt%, with a tensile strength of only 151 MPa and a corresponding elastic modulus of 6.3 GPa. When the composite film thickness was 0.032 mm, the corresponding electromagnetic shielding performance reached approximately 23 dB, which also meets the requirements for commercial applications (>20 dB). However, at the same carbon nanotube content (50 wt%), compared to the PVP-modified composite film with a tensile strength of 212 MPa, the mechanical properties decreased significantly, and the electromagnetic shielding effectiveness decreased by approximately 3.3 dB.

[0158] Comparative Example 4

[0159] (1) The process is consistent with step (1) in Example 1.

[0160] (2) The process is consistent with step (2) in Example 1.

[0161] (3) is consistent with step (3) in Example 1.

[0162] The aqueous polyamic acid salt / carbon nanotube composite electromagnetic shielding film prepared in this comparative example exhibits poor mechanical properties with a carbon nanotube content of 9.1 wt% (a mass ratio of polyamic acid salt to carbon nanotubes of 10:1), achieving a tensile strength of only 32 MPa. However, the composite film after cyclization treatment achieves an average tensile strength of 284 MPa, indicating that the absence of imidization has a significant impact on the mechanical properties of the composite film.

[0163] Comparative Example 5

[0164] (1) A polyvinylpyrrolidone / carbon nanotube aqueous dispersion (4.00 g, 5 wt%) was added to 2.67 g of deionized water and dispersed evenly to prepare a carbon nanotube dispersion with a solid content of 3 wt% and an average particle size of 313 nm. The dispersion was then cast onto a 5 x 10 cm glass plate. Finally, the dispersion was heat-treated in an oven at 50 °C, 60 °C, 70 °C, and 80 °C for 2 h, 2 h, 2 h, and 2 h, respectively, to obtain a polyvinylpyrrolidone / carbon nanotube composite film.

[0165] (2) The polyvinylpyrrolidone / carbon nanotube composite film obtained in step (3) above was treated at 100℃, 150℃, 200℃, 250℃, 300℃ and 350℃ for 1h, 1h, 1h, 0.5h and 0.5h respectively to obtain carbon nanotube composite film.

[0166] (3) The carbon nanotube film finally prepared is extremely brittle, with a sharp decline in mechanical properties, and a tensile strength of only 30 MPa. Figure 4 As shown, it cannot meet the needs of practical applications.

[0167] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0168] Obviously, the embodiments of the present invention shown above are only intended to illustrate the principles of the invention and not to limit its implementation. Those skilled in the art can make other modifications or alterations to the present invention based on the above description. While it is impossible to exhaustively list all embodiments, any obviously deducible changes to the technical solutions are still protected by this invention.

Claims

1. A method for preparing a high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film, characterized in that, include: The diamine monomer and deoxygenated water are mixed, and a salt-forming reagent is added to assist in the dissolution of the diamine monomer. Then, the dianhydride monomer is added and stirred until homogeneous. The mixture is then reacted to obtain an aqueous polyamic acid salt solution. Carbon nanotubes were modified with polyvinylpyrrolidone to obtain a polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion; the diameter of the carbon nanotubes was 5~50 nm, and the mass ratio of polyvinylpyrrolidone to carbon nanotubes was 1:4~1:

9. A polyvinylpyrrolidone-modified carbon nanotube aqueous dispersion and an aqueous polyamic acid salt were mixed, ultrasonicated, and stirred a second time to obtain a uniformly mixed aqueous polyamic acid salt / carbon nanotube dispersion; the mass ratio of the aqueous polyamic acid salt to the carbon nanotubes was 10:1 to 1:5, and the solid content of the aqueous polyamic acid salt / carbon nanotube dispersion was 20 to 60 mg / mL. The aqueous polyamic acid salt / carbon nanotube dispersion was cast onto a substrate and the solvent was removed by heating to obtain an aqueous polyamic acid salt / carbon nanotube composite film. The aqueous polyamic acid salt / carbon nanotube composite film was heated to complete the thermal imidization treatment and remove polyvinylpyrrolidone to obtain a high-performance aqueous polyimide / carbon nanotube composite electromagnetic shielding film. The diamine monomer is selected from , , The dianhydride monomer is any one or more combinations thereof. The salt-forming reagent is selected from... , , The diamine monomer and the dianhydride monomer are any one or more of the following; the molar ratio of the diamine monomer to the dianhydride monomer is 0.98:1 to 1:1, and the molar ratio of the dianhydride monomer to the salt-forming reagent is 1:2 to 1:

5.

2. The preparation method according to claim 1, characterized in that: The first stirring speed is 100~300 rpm.

3. The preparation method according to claim 1, characterized in that: The ratio of the diamine monomer to water is (0.01~0.05) mol: (50~200) mL.

4. The preparation method according to claim 1, characterized in that: The viscosity of the aqueous polyamic acid salt solution is 40,000~100,000 cP.

5. The preparation method according to claim 1, characterized in that: The reaction is carried out under a protective atmosphere at a temperature of 25-80°C for 6-12 hours.

6. The preparation method according to claim 1, characterized in that: The solid content of the aqueous polyamic acid salt / carbon nanotube dispersion is 20~50 mg / mL.

7. The preparation method according to claim 1, characterized in that: The ultrasound temperature is 20~30℃, the ultrasound duration is 0.5~2h, and the ultrasound power is 100~500kHz.

8. The preparation method according to claim 1, characterized in that: The second stirring speed is 300~600 rpm, and the second stirring time is 12~36 h.

9. The preparation method according to claim 1, characterized in that, The process conditions for the thermal imidization treatment include: heating at a gradient temperature of 100~450℃ for 0.5~2h under nitrogen or vacuum conditions.

10. The preparation method according to claim 1, characterized in that: The temperature for removing the solvent by heating is 50~80℃, and the time is 1~3h.

11. The preparation method according to claim 1, characterized in that: The substrate is a glass plate.

12. The preparation method according to claim 1, characterized in that, The process conditions for the thermal imidization treatment include: first, heating to 100~120℃ and holding for 1~2 hours, then heating to 150~170℃ and holding for 1~2 hours, then heating to 200~220℃ and holding for 1~2 hours, then heating to 250~270℃ and holding for 1~2 hours, then heating to 300~320℃ and holding for 0.5~2 hours, and finally heating to 350~450℃ to dehydrate the polyamic acid and form an imide ring, followed by cyclization treatment for 0.5~2 hours.

13. A high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film prepared by the preparation method according to any one of claims 1-12, characterized in that: The high-performance waterborne polyimide / carbon nanotube composite electromagnetic shielding film has a thickness of 20~350 µm, a tensile strength of 68~284 MPa, and an electromagnetic shielding effectiveness of up to 51 dB.

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