A polyimide composite coating with both thermal conductivity and electromagnetic shielding functions and its preparation method

Abstract

This invention discloses a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method. The coating is composed of a polyamic acid solution and functional fillers. The polyamic acid solution includes dianhydride, diamine, and an organic solvent, with the weights of each raw material being 10-20 parts dianhydride, 10-20 parts diamine, and 40-60 parts organic solvent. This polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method, constructs a highly efficient and stable dual-functional integrated network, achieving a synergistic improvement in thermal conductivity and electromagnetic shielding performance. By in-situ growing carbon nanotubes on the surface of two-dimensional MXene sheets under multi-metal catalysis, a unique three-dimensional interpenetrating structure is successfully constructed. This structure simultaneously serves as a highly efficient thermal conduction pathway and a conductive or electromagnetic loss network, fundamentally solving the problems of uneven filler dispersion and network discontinuity in traditional methods. It achieves a synergistic multiplication of thermal conductivity and electromagnetic shielding performance with a relatively low filler content.

Description

Technical Field

[0001] This invention relates to the field of multifunctional high-performance polymer coating technology, specifically to a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method. Background Technology

[0002] Polyimide (PI) is a class of special polymer materials with high heat resistance and excellent overall performance, possessing good thermal stability, mechanical properties, dielectric properties, and radiation resistance. Coatings and coatings based on polyimide are commonly used in high-temperature protection, insulation protection, corrosion protection, and surface functionalization of electronic and electrical devices due to their advantages such as high temperature resistance, chemical resistance, aging resistance, and high insulation reliability. With the development of highly integrated, high-power-density electronic equipment and complex electromagnetic environments, coating materials, in addition to maintaining the inherent heat resistance and stability of polyimide, are often required to simultaneously possess electromagnetic shielding and thermal management capabilities to reduce electromagnetic interference and improve heat dissipation and heat dissipation efficiency.

[0003] In the prior art, Chinese Patent Application No. CN114539572B discloses a low thermal conductivity electromagnetic shielding polyimide-based composite material and its preparation method. The preparation method includes: coating a layer of conductive polymer onto hollow glass microspheres (HGM) to obtain core-shell structured low-density conductive hollow glass microspheres@conductive polymer filler; preparing a hollow glass microsphere@conductive polymer / polyamic acid mixed solution using in-situ polymerization; coating the hollow glass microsphere@conductive polymer / polyamic acid mixed solution onto a glass plate, followed by thermal imidization to obtain a hollow glass microsphere@conductive polymer / polyimide low thermal conductivity electromagnetic shielding composite material. The low thermal conductivity electromagnetic shielding polyimide-based composite material prepared by this invention not only achieves excellent electromagnetic shielding performance but also possesses a low thermal conductivity coefficient.

[0004] For example, in the prior art, Chinese patent application number CN115286823B discloses a high thermal conductivity electromagnetic shielding polyimide-based co-carbonized carbon fiber composite material and its preparation method. The method includes: S1, preparation of modified polyimide fiber felt; S2, functionalization and co-carbonization of modified polyimide felt; S3, immersing the three-dimensional co-carbonized carbon fiber felt micro-nano skeleton in step S2 into a high-performance resin to construct a continuous and complete three-dimensional co-carbonized network structure at the micro-nano multi-level scale, thereby obtaining a three-dimensional co-carbonized network resin-based carbon fiber composite material with excellent thermal conductivity, ultra-high electromagnetic shielding, and good mechanical properties. This invention, through the pre-construction of the three-dimensional co-carbonized network, facilitates the bridging of fibers and the formation of a continuous three-dimensional thermally conductive network by fiber welding, reduces the interfacial thermal resistance between fillers, and helps improve the thermal conductivity of the composite material. While the three-dimensional co-carbonized network has good electrical conductivity, the fillers form heterogeneous structures that become polarization centers to jointly enhance the electromagnetic shielding performance of the material.

[0005] Based on the above materials, it can be seen that existing polyimide coatings typically improve conductivity and shielding effectiveness by introducing metal powders, alloy powders, ferromagnetic fillers, conductive polymers, or carbon-based conductive fillers to achieve electromagnetic shielding. However, these fillers generally have shortcomings in polyimide coating systems. Some fillers have high density or poor compatibility with the polyimide matrix, which can easily cause sedimentation, agglomeration, and uneven dispersion, resulting in discontinuous local conductive pathways in the coating and significant fluctuations in shielding performance and stability. Conventional conductive fillers often require high filling amounts to achieve high shielding efficiency, which can significantly increase the viscosity of the coating, leading to poor spray application and potentially causing coating embrittlement, cracking, or decreased adhesion. Traditional electromagnetic shielding coatings focus on improving electrical conductivity but are insufficient in constructing heat conduction paths. The high thermal resistance at the filler or matrix interface makes it difficult to simultaneously meet the requirements of high thermal conductivity and high shielding, especially under high temperature or thermal cycling conditions, where performance degradation is likely to occur.

[0006] Therefore, it is urgent to make technological improvements to the existing methods. Summary of the Invention

[0007] The purpose of this invention is to provide a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method, in order to solve the problems mentioned in the background art, such as discontinuous thermal conductivity pathways, limited shielding effectiveness, insufficient filler dispersion and network stability, and high filler content leading to decreased coating workability and mechanical properties.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, which is composed of a polyamic acid solution and functional fillers; The polyamic acid solution comprises dianhydride, diamine, and organic solvent, and the weight of each raw material is 10-20 parts of dianhydride, 10-20 parts of diamine, and 40-60 parts of organic solvent, and the weight of the functional filler is 10-30 parts.

[0009] Preferably, the dianhydride monomer is a mixture of 4,4'-hexafluoroisopropylidene phthalic anhydride, pyromellitic dianhydride, and biphenyl dianhydride; The diamine monomer is a mixture of 1,4-bis4-amino-2-trifluoromethylphenoxybenzene, 1,4-4-amino-2-trifluoromethylphenoxy-2-3'-methylphenylbenzene and 2,2'-ditrifluoromethyldiaminobiphenyl; The organic solvent is a mixture of N,N-dimethylformamide and N,N-dimethylacetamide.

[0010] Preferably, the functional filler is CoM-CNTs@MXene powder, where M is a doped metal.

[0011] A method for preparing a polyimide composite coating that combines thermal conductivity and electromagnetic shielding functions includes the following steps: Step S1: Functional filler is prepared by acid etching to prepare MXene dispersion, which is then freeze-dried to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salt are dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution are mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution are added sequentially for reaction. After centrifugation and vacuum drying, CoMZIF-67@MXene powder is obtained. CoMZIF-67 enters the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoMZIF-67@MXene powder is placed in a ceramic boat and a carbon source is laid flat below it. The boat is placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoMZIF-67 catalyze the pyrolysis of the carbon source and grow carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridge the MXene sheets and construct a continuous thermally and electrically conductive network, thus obtaining CoM-CNTs@MXene powder. Step S2: Disperse the functional filler in an organic solvent to obtain a dispersion; add diamine to the dispersion under nitrogen protection and stir until dissolved, then add dianhydride to carry out a polycondensation reaction to obtain a polyamic acid composite slurry containing the functional filler; Step S3: Apply the polyamic acid composite slurry to the substrate surface by air spraying. After spraying, place the substrate in a vacuum oven for gradient heating and thermal imide curing to obtain a polyimide composite coating that has both thermal conductivity and electromagnetic shielding functions.

[0012] Preferably, the doped metal salt is a combination of Fe, Ni, Mo, and Cu metal salts; and the carbon source is polyethylene, polypropylene, polystyrene, urea, or melamine.

[0013] Preferably, in the tubular furnace pyrolysis process in step S1, the heating rate is 5℃ / min, and the temperature is maintained at 700℃ for 3 hours, with nitrogen as the inert gas and a flow rate of 50mL / min.

[0014] Preferably, the polycondensation reaction in step S2 is carried out under nitrogen protection and an ice-water bath, and the stirring reaction time is 24-36 hours.

[0015] Preferably, in step S3, the air spraying pressure is 0.45–0.65 MPa, and the output rate is 2–3 mL / min.

[0016] Preferably, the substrate in step S3 is a polymer substrate, a metal substrate, or a ceramic substrate.

[0017] Preferably, the gradient thermal imidization curing process in step S3 is as follows: first, maintaining the temperature at 80–100°C for 2–3 hours; then, maintaining the temperature at 120–150°C for 1–2 hours; then, maintaining the temperature at 200–250°C for 1–2 hours; and finally, maintaining the temperature at 260–300°C for 1–2 hours. Compared with the prior art, the beneficial effects of the present invention are: 1. A highly efficient and stable dual-function integrated network was constructed to achieve a synergistic improvement in thermal conductivity and electromagnetic shielding performance. By growing carbon nanotubes in situ on the surface of two-dimensional MXene sheets under multi-metal catalysis, a unique three-dimensional interpenetrating structure of "CNTs bridging MXene sheets" was successfully constructed. This structure serves as both a highly efficient thermal conduction pathway and a conductive or electromagnetic loss network, fundamentally solving the problems of uneven packing and discontinuous network in traditional systems. It achieves a synergistic multiplication of thermal conductivity and electromagnetic shielding performance at a low packing amount. Furthermore, the multi-metal components in the functional filler form magnetic nanoparticles after thermal decomposition. These magnetic particles combine with highly conductive MXene sheets and CNT networks, enabling the coating to simultaneously possess electrical loss, dielectric loss, and magnetic loss capabilities. This electro-magnetic synergy optimizes the wave impedance matching of the coating, significantly enhances the absorption efficiency of electromagnetic waves, and achieves high-efficiency broadband electromagnetic shielding dominated by absorption. 2. It achieves an excellent balance of comprehensive performance. While improving the thermal conductivity and electromagnetic shielding effectiveness of the coating, it retains the intrinsic advantages of the polyimide matrix to the maximum extent. The resulting coating still maintains excellent thermal stability, good mechanical properties and suitable construction process, thus solving the problems of high filler content leading to a surge in coating viscosity, coating embrittlement and decreased adhesion. Attached Figure Description

[0018] Figure 1 Comparison of XRD spectra of Co-CNTs@MXene, CoNi-CNTs@MXene, CoFe-CNTs@MXene, and CoNiFe-CNTs@MXene of the present invention; Figure 2 The images show a comparison of the SEM morphology of (a) Co-CNTs@MXene, (b) CoNi-CNTs@MXene, (c) CoFe-CNTs@MXene, and (d) CoNiFe-CNTs@MXene of the present invention. Figure 3 The TGA curves of the coating samples obtained in the various embodiments and comparative examples of this invention are shown below. Figure 4 The in-plane thermal conductivity of the coating samples obtained in the various embodiments and comparative examples of this invention; Figure 5The electromagnetic shielding performance curves of the 0.2 mm thick coating samples obtained from various embodiments and comparative examples of the present invention are shown. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-5 This embodiment provides the following technical solution: a polyimide composite coating that combines thermal conductivity and electromagnetic shielding functions. Example 1: The polyamic acid solution comprises dianhydride, diamine, and organic solvent, with each raw material weighing 10-20 parts dianhydride, 10-20 parts diamine, and 40-60 parts organic solvent. The functional filler weighs 10-30 parts. The dianhydride monomer is a mixture of 4,4'-hexafluoroisopropylidene phthalic anhydride, pyromellitic dianhydride, and biphenyl dianhydride. The diamine monomer is a mixture of 1,4-bis(4-amino-2-trifluoromethylphenoxybenzene), 1,4-4-amino-2-trifluoromethylphenoxy-2-3'-methylphenylbenzene, and 2,2'-ditrifluoromethyldiaminobiphenyl. The organic solvent is a mixture of N,N-dimethylformamide and N,N-dimethylacetamide, or a mixture of N-methylpyrrolidone in any proportion. The functional filler is CoM-CNTs@MXene powder, where M is a doped metal. Example 2: Based on Example 1, and referring to... Figures 1-5 The present invention also discloses a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions and its preparation method, as detailed below: Step S1: An MXene dispersion was prepared by acid etching and lyophilized to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salts were dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution were added sequentially for reaction. After centrifugation and vacuum drying, CoMZIF-67@MXene powder was obtained. CoMZIF-67 entered the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoMZIF-67@MXene powder was placed in a ceramic boat and a carbon source was laid flat below it. The boat was placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoMZIF-67 catalyzed the pyrolysis of the carbon source and grew carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridged the MXene sheets and constructed a continuous thermally and electrically conductive network, thus obtaining CoM-CNTs@MXene powder. 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were added to a polytetrafluoroethylene beaker and stirred until completely dissolved. 2 g of Ti3AlC2 was slowly added at 40 °C and the reaction was carried out for 24 h. After the reaction, the resulting slurry was centrifuged and washed, and then MXene dispersion was obtained by hand shaking and ultrasonic exfoliation. The MXene dispersion was freeze-dried for 24–48 h to obtain MXene nanosheets. Then, 2 g of MXene nanosheets, 10 mmol of cobalt nitrate hexahydrate, and 80 mmol of 2-methylimidazole were weighed and dispersed in 50 mL of methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred evenly. 2-methylimidazole solution was added sequentially, and the reaction was continued with stirring for 30 min, followed by aging at room temperature for 24 h. After the reaction, the mixture was centrifuged and vacuum dried to obtain CoZIF-67@MXene powder. Then, 1g of the above CoZIF-67@MXene powder was weighed and placed in a ceramic boat. 5g of carbon source (preferably urea) was laid under the ceramic boat. The boat was then placed in a tube furnace and thermally decomposed under nitrogen protection to obtain Co-CNTs@MXene powder. The heating rate of the tube furnace was 5℃ / min, and the furnace was kept at 700℃ for 3h. The nitrogen flow rate was 50mL / min.

[0021] Step S2: Preparation of composite coating: 3.15g of Co-CNTs@MXene powder was added to 65g of N,N-dimethylacetamide (DMAc), and ultrasonically dispersed for 30min before being transferred to a three-necked flask. Under nitrogen protection and an ice-water bath, 3.2g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 2.4g of 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB) were added to the system, and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropylidene)phthalic anhydride (6FDA) was added all at once, and the polycondensation reaction was continued under ice-water bath conditions for 24h with stirring to obtain a black, viscous polyamic acid composite coating. Step S3: Coating preparation: The above composite coating is sprayed onto the cleaned polyimide substrate surface using air spraying at a pressure of 0.5 MPa and a flow rate of 3 mL / min. After spraying, the substrate is placed in a vacuum oven for gradient temperature thermal imidization curing. The curing procedure is as follows: first, maintain the temperature at 80–100℃ for 2–3 hours; then, maintain the temperature at 120–150℃ for 1–2 hours; then, maintain the temperature at 200–250℃ for 1–2 hours; and finally, maintain the temperature at 260–300℃ for 1–2 hours to obtain the polyimide composite coating.

[0022] Example 3: Unlike Example 2, this invention also discloses a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method, as detailed below: Step S1: An MXene dispersion was prepared by acid etching and lyophilized to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salts were dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution were added sequentially for reaction. After centrifugation and vacuum drying, CoMZIF-67@MXene powder was obtained. CoMZIF-67 entered the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoMZIF-67@MXene powder was placed in a ceramic boat and a carbon source was laid flat below it. The boat was placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoMZIF-67 catalyzed the pyrolysis of the carbon source and grew carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridged the MXene sheets and constructed a continuous thermally and electrically conductive network, thus obtaining CoM-CNTs@MXene powder. 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were added to a polytetrafluoroethylene beaker and stirred until completely dissolved. 2 g of Ti3AlC2 was slowly added at 40 °C and the reaction was allowed to proceed for 24 h. After the reaction, the resulting slurry was centrifuged and washed, and then MXene dispersion was obtained by hand shaking and ultrasonic exfoliation. The MXene dispersion was freeze-dried for 24–48 h to obtain MXene nanosheets. Then, 2 g of MXene nanosheets, 10 mmol of cobalt nitrate hexahydrate, 80 mmol of 2-methylimidazole, and 2.5 mmol of nickel nitrate hexahydrate were weighed and dispersed in 50 mL of methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred until homogeneous. Then, 2-methylimidazole solution was added sequentially, and the reaction was continued with stirring for 30 min, followed by aging at room temperature for 24 h. After the reaction, the mixture was centrifuged and vacuum dried to obtain CoZIF-67@MXene powder. Then, 1g of the above CoZIF-67@MXene powder was weighed and placed in a ceramic boat. 5g of carbon source (preferably urea) was laid under the ceramic boat. The boat was then placed in a tube furnace and thermally decomposed under nitrogen protection to obtain Co-CNTs@MXene powder. The heating rate of the tube furnace was 5℃ / min, and the furnace was kept at 700℃ for 3h. The nitrogen flow rate was 50mL / min.

[0023] Step S2: Preparation of composite coating: 3.15g of Co-CNTs@MXene powder was added to 65g of N,N-dimethylacetamide (DMAc), and ultrasonically dispersed for 30min before being transferred to a three-necked flask. Under nitrogen protection and an ice-water bath, 3.2g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 2.4g of 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB) were added to the system, and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropylidene)phthalic anhydride (6FDA) was added all at once, and the polycondensation reaction was continued under ice-water bath conditions for 24h with stirring to obtain a black, viscous polyamic acid composite coating. Step S3: Coating preparation: The above composite coating is sprayed onto the cleaned polyimide substrate surface using air spraying at a pressure of 0.5 MPa and a flow rate of 3 mL / min. After spraying, the substrate is placed in a vacuum oven for gradient temperature thermal imidization curing. The curing procedure is as follows: first, maintain the temperature at 80–100℃ for 2–3 hours; then, maintain the temperature at 120–150℃ for 1–2 hours; then, maintain the temperature at 200–250℃ for 1–2 hours; and finally, maintain the temperature at 260–300℃ for 1–2 hours to obtain the polyimide composite coating.

[0024] Example 4: Unlike Example 3, this invention also discloses a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method, as detailed below: Step S1: MXene dispersion was prepared by acid etching and lyophilized to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salt were dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution were added sequentially for reaction. The doped metal salt was ferric nitrate nonahydrate. After centrifugation and vacuum drying, CoFe-CNTs@MXene powder was obtained. CoFe-CNTs entered the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoFe-CNTs@MXene powder was placed in a ceramic boat and a carbon source was laid flat below it. The boat was placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoFe-CNTs catalyzed the pyrolysis of the carbon source and grew carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridged the MXene sheets and constructed a continuous thermally and electrically conductive network, thus obtaining CoFe-CNTs@MXene powder. 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were added to a polytetrafluoroethylene beaker and stirred until completely dissolved. 2 g of Ti3AlC2 was slowly added at 40 °C and the reaction was allowed to proceed for 24 h. After the reaction, the resulting slurry was centrifuged and washed, and then MXene dispersion was obtained by hand shaking and ultrasonic exfoliation. The MXene dispersion was freeze-dried for 24–48 h to obtain MXene nanosheets. Then, 2 g of MXene nanosheets, 10 mmol of cobalt nitrate hexahydrate, 80 mmol of 2-methylimidazole, and 2.5 mmol of nickel nitrate hexahydrate were weighed and dispersed in 50 mL of methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred until homogeneous. Then, 2-methylimidazole solution was added sequentially, and the reaction was continued with stirring for 30 min, followed by aging at room temperature for 24 h. After the reaction, the mixture was centrifuged and vacuum dried to obtain CoZIF-67@MXene powder. Then, 1g of the above CoFe-CNTs@MXene powder was weighed and placed in a ceramic boat. 5g of carbon source (preferably urea) was placed under the ceramic boat and placed in a tube furnace for thermal decomposition under nitrogen protection to obtain CoFe-CNTs@MXene powder. The heating rate of the tube furnace was 5℃ / min, and it was kept at 700℃ for 3h with a nitrogen flow rate of 50mL / min.

[0025] Step S2: Preparation of composite coating: 3.15g of CoFe-CNTs@MXene powder was added to 65g of N,N-dimethylacetamide (DMAc), and ultrasonically dispersed for 30min before being transferred to a three-necked flask. Under nitrogen protection and an ice-water bath, 3.2g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 2.4g of 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB) were added to the system, and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropylidene)phthalic anhydride (6FDA) was added all at once, and the polycondensation reaction was continued under ice-water bath conditions for 24h with stirring to obtain a black, viscous polyamic acid composite coating. Step S3: Coating preparation: The above composite coating is sprayed onto the cleaned polyimide substrate surface using air spraying at a pressure of 0.5 MPa and a flow rate of 3 mL / min. After spraying, the substrate is placed in a vacuum oven for gradient temperature thermal imidization curing. The curing procedure is as follows: first, maintain the temperature at 80–100℃ for 2–3 hours; then, maintain the temperature at 120–150℃ for 1–2 hours; then, maintain the temperature at 200–250℃ for 1–2 hours; and finally, maintain the temperature at 260–300℃ for 1–2 hours to obtain the polyimide composite coating.

[0026] Example 5: Unlike Example 3, this invention also discloses a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, and its preparation method, as detailed below: Step S1: MXene dispersion was prepared by acid etching and lyophilized to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salt were dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution were added sequentially for reaction. The doped metal salt was a combination of nickel nitrate hexahydrate and ferric nitrate nonahydrate to obtain CoNiFe-CNTs@MXene powder. CoNiFe-CNTs entered the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoNiFe-CNTs@MXene powder was placed in a ceramic boat and a carbon source was laid flat below it. The boat was placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoNiFe-CNTs catalyzed the pyrolysis of the carbon source and grew carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridged the MXene sheets and constructed a continuous thermally and electrically conductive network, thus obtaining CoNiFe-CNTs@MXene powder. 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were added to a polytetrafluoroethylene beaker and stirred until completely dissolved. 2 g of Ti3AlC2 was slowly added at 40 °C and the reaction was allowed to proceed for 24 h. After the reaction, the resulting slurry was centrifuged and washed, and then MXene dispersion was obtained by hand shaking and ultrasonic exfoliation. The MXene dispersion was freeze-dried for 24–48 h to obtain MXene nanosheets. Then, 2 g of MXene nanosheets, 10 mmol of cobalt nitrate hexahydrate, 80 mmol of 2-methylimidazole, and 2.5 mmol of nickel nitrate hexahydrate were weighed and dispersed in 50 mL of methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution were mixed and stirred until homogeneous. Then, 2-methylimidazole solution was added sequentially, and the reaction was continued with stirring for 30 min, followed by aging at room temperature for 24 h. After the reaction, the mixture was centrifuged and vacuum dried to obtain CoZIF-67@MXene powder. Then, 1g of the above CoNiFe-CNTs@MXene powder was weighed and placed in a ceramic boat. 5g of carbon source (preferably urea) was placed under the ceramic boat and placed in a tube furnace for thermal decomposition under nitrogen protection to obtain CoNiFe-CNTs@MXene powder. The heating rate of the tube furnace was 5℃ / min, and it was kept at 700℃ for 3h. The nitrogen flow rate was 50mL / min.

[0027] Step S2: Preparation of composite coating: 3.15g of CoNiFe-CNTs@MXene powder was added to 65g of N,N-dimethylacetamide (DMAc), and ultrasonically dispersed for 30min before being transferred to a three-necked flask. Under nitrogen protection and an ice-water bath, 3.2g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 2.4g of 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB) were added to the system, and stirred until completely dissolved. Subsequently, 4,4'-(hexafluoroisopropylidene)phthalic anhydride (6FDA) was added all at once, and the polycondensation reaction was continued for 24h under ice-water bath conditions to obtain a black, viscous polyamic acid composite coating. Step S3: Coating preparation: The above composite coating is sprayed onto the cleaned polyimide substrate surface using air spraying at a pressure of 0.5 MPa and a flow rate of 3 mL / min. After spraying, the substrate is placed in a vacuum oven for gradient temperature thermal imidization curing. The curing procedure is as follows: first, maintain the temperature at 80–100℃ for 2–3 hours; then, maintain the temperature at 120–150℃ for 1–2 hours; then, maintain the temperature at 200–250℃ for 1–2 hours; and finally, maintain the temperature at 260–300℃ for 1–2 hours to obtain the polyimide composite coating.

[0028] Comparative Example 1 The comparative example prepares a polyimide coating without functional fillers, and the steps are as follows: 65g of N,N-dimethylacetamide (DMAc) was added to a three-necked flask. Under nitrogen protection and an ice-water bath, 3.2g of 6FAPB and 2.4g of TFMB were added and stirred until completely dissolved. Then, 6FDA was added all at once and the polycondensation reaction was continued under an ice-water bath for 24 hours to obtain a transparent and viscous polyamic acid coating. Pure polyimide coating was prepared using the same spraying and gradient thermal imidization curing procedure as in Example 1.

[0029] Comparative Example 2 The comparative example prepares functional polyimide composite coatings and coating layers using the following steps: (1) Preparation of MXene: 40 mL of hydrochloric acid and 3.2 g of lithium fluoride were added to a polytetrafluoroethylene beaker and stirred until completely dissolved. 2 g of Ti3AlC2 was slowly added at 40 °C and reacted for 24 h. After the reaction was completed, the resulting slurry was centrifuged and washed. Then, MXene dispersion was obtained by hand shaking and ultrasonic exfoliation. The MXene dispersion was placed in a freeze dryer and freeze-dried for 24-48 h to obtain MXene nanosheets.

[0030] (2) Preparation of composite coating: 3.15g of MXene powder was added to 65g of N,N-dimethylacetamide (DMAc), and ultrasonically dispersed for 30min before being transferred to a three-necked flask. Under nitrogen protection and ice-water bath conditions, 3.2g of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 2.4g of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) were added to the system and stirred until completely dissolved. Then, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was added in one go, and the polycondensation reaction was continued under ice-water bath conditions for 24h to obtain a black viscous polyamic acid composite coating.

[0031] (3) Coating preparation: The above composite coating is sprayed onto the cleaned polyimide substrate surface by air spraying. The spraying pressure is 0.5 MPa and the output is 3 mL / min. After spraying, the substrate is placed in a vacuum oven for gradient heating and thermal imidization curing. The curing procedure is as follows: 80-100℃ for 2-3 h; 120-150℃ for 1-2 h; 200-250℃ for 1-2 h; 260-300℃ for 1-2 h; and polyimide composite coating is obtained.

[0032] The above is the entire working process, and all contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0033] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, comprising a polyamic acid solution and functional fillers; Its features are: The polyamic acid solution comprises dianhydride, diamine, and organic solvent, and the weight of each raw material is 10-20 parts of dianhydride, 10-20 parts of diamine, and 40-60 parts of organic solvent, and the weight of the functional filler is 10-30 parts.

2. The polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 1, characterized in that: The dianhydride monomer is a mixture of 4,4'-hexafluoroisopropylidene phthalic anhydride, pyromellitic dianhydride and biphenyl dianhydride; The diamine monomer is a mixture of 1,4-bis4-amino-2-trifluoromethylphenoxybenzene, 1,4-4-amino-2-trifluoromethylphenoxy-2-3'-methylphenylbenzene and 2,2'-ditrifluoromethyldiaminobiphenyl; The organic solvent is a mixture of N,N-dimethylformamide and N,N-dimethylacetamide.

3. The polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 1, characterized in that: The functional filler is CoM-CNTs@MXene powder, where M is a doped metal.

4. A method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions, wherein the coating is applied to the polyimide composite coating with both thermal conductivity and electromagnetic shielding functions as described in claim 3, characterized in that... Includes the following steps: Step S1: Functional filler is prepared by acid etching to prepare MXene dispersion, which is then freeze-dried to obtain MXene nanosheets. MXene nanosheets, cobalt nitrate hexahydrate, 2-methylimidazole, and doped metal salt are dispersed in methanol. The MXene methanol dispersion and cobalt nitrate hexahydrate solution are mixed and stirred evenly. Then, 2-methylimidazole solution and doped metal salt solution are added sequentially for reaction. After centrifugation and vacuum drying, CoMZIF-67@MXene powder is obtained. CoMZIF-67 enters the interlayer of MXene sheets to form an intercalation structure and increase the interlayer spacing. CoMZIF-67@MXene powder is placed in a ceramic boat and a carbon source is laid flat below it. The boat is placed in a tube furnace for thermal pyrolysis under an inert atmosphere. The multi-metal components in CoMZIF-67 catalyze the pyrolysis of the carbon source and grow carbon nanotubes in situ on the MXene surface. The carbon nanotubes bridge the MXene sheets and construct a continuous thermally and electrically conductive network, thus obtaining CoM-CNTs@MXene powder. Step S2: Disperse the functional filler in an organic solvent to obtain a dispersion; add diamine to the dispersion under nitrogen protection and stir until dissolved, then add dianhydride to carry out a polycondensation reaction to obtain a polyamic acid composite slurry containing the functional filler; Step S3: Apply the polyamic acid composite slurry to the substrate surface by air spraying. After spraying, place the substrate in a vacuum oven for gradient heating and thermal imide curing to obtain a polyimide composite coating that has both thermal conductivity and electromagnetic shielding functions.

5. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: The doped metal salt is a combination of the corresponding metal salts of Fe, Ni, Mo, and Cu; the carbon source is polyethylene, polypropylene, polystyrene, urea, or melamine.

6. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: In the tubular furnace pyrolysis process in step S1, the heating rate is 5℃ / min, and the temperature is maintained at 700℃ for 3 hours. The inert gas is nitrogen, and the flow rate is 50mL / min.

7. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: The polycondensation reaction in step S2 is carried out under nitrogen protection and ice-water bath conditions, and the stirring reaction time is 24-36 hours.

8. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: In step S3, the air spraying pressure is 0.45–0.65 MPa, and the output rate is 2–3 mL / min.

9. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: In step S3, the substrate can be a polymer substrate, a metal substrate, or a ceramic substrate.

10. The method for preparing a polyimide composite coating with both thermal conductivity and electromagnetic shielding functions according to claim 4, characterized in that: The gradient thermal imidization curing process in step S3 is as follows: first, keep warm at 80-100℃ for 2-3 hours, then keep warm at 120-150℃ for 1-2 hours; then keep warm at 200-250℃ for 1-2 hours; and finally keep warm at 260-300℃ for 1-2 hours.

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