CN118241379A - Preparation method of composite film, composite film and application thereof - Google Patents

Abstract

The embodiment of the application relates to the technical field of polymer-based heat-conducting composite materials, in particular to a preparation method of a composite film, the composite film and application thereof. In the method, BNNS@PDA has better dispersibility in a PI matrix, and is beneficial to improving the thermal conductivity of the composite film. In addition, the composite film is prepared by adopting a method combining in-situ polymerization, electrostatic spinning and compression molding, so that BNNS@PDA is uniformly dispersed and directionally arranged in a PI matrix, and the heat conductivity of the composite film is improved. Meanwhile, the s-CNT with larger length-diameter ratio can be lapped between BNNS@PDA and BNNS@PDA, so that a continuous heat conduction network passage is built in the PI substrate, and the heat conduction coefficient of the composite film is further improved. And the strong viscosity of the polydopamine ensures that the composite film maintains good breakdown strength. The composite film prepared by the method has excellent heat conduction performance and insulating performance; wherein, the heat conductivity coefficient of the composite film can be 0.574W/mK-0.703W/mK, and the volume resistivity can reach more than 10 ¹⁵ Ω & cm.

Description

Preparation method of composite film, composite film and application thereof

Technical Field

The embodiments of the present application relate to the technical field of polymer-based thermally conductive composite materials, and in particular, to a method for preparing a composite film, a composite film and applications thereof.

Background technique

In recent years, as electronic devices have developed rapidly towards high power, integration and multi-function, the operating frequency and assembly density of electronic devices have been increasing, resulting in increasingly serious overheating problems in electronic devices. The large amount of heat generated and accumulated by electronic devices during operation will not only reduce the working efficiency, stability and service life of the devices, but also bring huge safety hazards. Therefore, improving the heat dissipation efficiency of electronic devices is of great significance to promoting the development of the electronics industry and ensuring production safety.

At present, the main method to solve the problem of heat accumulation in electronic devices is to conduct the excess heat in the electronic devices to the external environment through heat dissipation materials. Polymer-based thermal conductive film materials are widely used as heat dissipation materials for electronic devices due to their ultra-high in-plane thermal conductivity and excellent flexibility.

Polyimide (PI) has excellent high temperature resistance, low temperature resistance, chemical corrosion resistance, electrical insulation and dimensional stability, and is often used as the base material of thermally conductive composite films. However, the dispersion of thermally conductive fillers in the PI matrix is poor, which is not conducive to improving the thermal conductivity of PI-based thermally conductive composite materials.

Summary of the invention

In order to further improve the thermal conductivity of PI-based composite materials, the embodiments of the present application provide a method for preparing a composite film, a composite film and its application, which can utilize carboxylated carbon nanotubes and modified boron nitride nanosheets to construct a thermally conductive double network in the PI matrix to improve the thermal conductivity of the composite film.

In order to solve the above technical problems, the embodiments of the present application provide the following technical solutions:

In a first aspect of the present application, a method for preparing a composite film is provided, the method comprising the following steps: preparing a spinning solution, the spinning solution comprising a polyamic acid solution and carboxylated carbon nanotubes and polydopamine-modified boron nitride nanosheets dispersed in the polyamic acid solution; performing electrospinning using the spinning solution to obtain a first fiber felt; performing thermal imidization treatment on the first fiber felt to obtain a second fiber felt; and compression molding the second fiber felt to obtain a composite film; wherein the first fiber felt is used to represent a carboxylated carbon nanotube/polydopamine-modified boron nitride nanosheet/polyamic acid composite fiber felt, and the second fiber felt is used to represent a carboxylated carbon nanotube/polydopamine-modified boron nitride nanosheet/polyimide composite fiber felt.

In the embodiments of the present application, the polydopamine-modified boron nitride nanosheets (BNNS@PDA) have good dispersibility in the PI matrix, which is conducive to increasing the contact area between BNNS@PDA and BNNS@PDA and between BNNS@PDA and PI matrix, thereby reducing the interface defects and heat transfer resistance between the PI matrix and BNNS@PDA, reducing the scattering of phonons during the diffusion process, and improving the thermal conductivity of the composite film. In addition, the composite film is prepared by combining in-situ polymerization, electrospinning and compression molding, which is conducive to the uniform dispersion and directional arrangement of BNNS@PDA in the PI matrix to improve the thermal conductivity of the composite film. At the same time, carboxylated carbon nanotubes (s-CNT) with a large aspect ratio can be overlapped between BNNS@PDA and BNNS@PDA, thereby building a continuous heat conduction network path in the PI matrix, further improving the thermal conductivity of the composite film. In addition, the strong viscosity of polydopamine enables the composite film to maintain good breakdown strength. The composite film prepared by the method has excellent thermal conductivity and insulation properties; wherein the thermal conductivity of the composite film can be 0.574W/mK-0.703W/mK, and the volume resistivity can reach above 10 ¹⁵ Ω·cm.

In some embodiments, the mass of the carboxylated carbon nanotubes accounts for 0.1%-0.5% of the mass of the polyamic acid, and the mass of the polydopamine-modified boron nitride nanosheets accounts for 10% of the mass of the polyamic acid.

In some embodiments, the polydopamine-modified boron nitride nanosheets include: boron nitride nanosheets and polydopamine distributed on the surface of the boron nitride nanosheets, wherein the mass of the polydopamine accounts for 20%-40% of the mass of the boron nitride nanosheets.

In some embodiments, the preparing the spinning solution includes: adding carboxylated carbon nanotubes and polydopamine-modified boron nitride nanosheets into a polyamic acid solution, and then stirring the polyamic acid solution to obtain the spinning solution.

In some embodiments, before configuring the spinning solution, the method further includes: preparing polydopamine-modified boron nitride nanosheets; the preparation of the polydopamine-modified boron nitride nanosheets includes: adding tris(hydroxymethyl)aminomethane to a mixed solution of deionized water and ethanol to prepare a buffer solution, wherein the pH value of the buffer solution is 8.5; after adding the boron nitride nanosheets to the buffer solution, ultrasonically treating the buffer solution; after adding dopamine to the buffer solution, stirring the buffer solution at room temperature, and after the buffer solution becomes gray-black and the reaction product in the buffer solution is precipitated, removing the supernatant to obtain polydopamine-modified boron nitride nanosheets.

In some embodiments, before preparing the spinning solution, the method further includes: preparing polyamic acid; the preparation of polyamic acid includes the following steps: dissolving 4,4'-diaminodiphenyl ether monomer and pyromellitic anhydride monomer in N,N-dimethylformamide under ice-water bath conditions to carry out condensation reaction to obtain polyamic acid; wherein the mass ratio of the 4,4'-diaminodiphenyl ether monomer to the pyromellitic anhydride monomer is 1.15:1.

In some embodiments, the temperature of the compression molding is 290° C. to 320° C., the pressure of the compression molding is 5 MPa to 10 MPa, and the time of the compression molding is 10 min to 15 min.

In some embodiments, the first fiber bond includes carboxylated carbon nanotubes/polydopamine-modified boron nitride nanosheets/polyamic acid composite fibers, and the arrangement of the carboxylated carbon nanotubes/polydopamine-modified boron nitride nanosheets/polyamic acid composite fibers includes a zigzag arrangement.

In the second aspect of the present application, a composite film is also provided. The composite film is prepared according to the method provided in the first aspect.

In the third aspect of the present application, there is also provided an application of a composite film prepared by the method provided in the first aspect in the field of electronic packaging.

It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

FIG1 is a schematic flow diagram of a method for preparing a composite film provided in some embodiments of the present application;

FIG2 is a schematic flow diagram of a method for preparing a composite film according to other embodiments of the present application;

FIG3 is a SEM image of composite films provided in some embodiments and comparative examples of the present application;

FIG4 is a test result of thermal conductivity of composite films provided in some embodiments and comparative examples of the present application, wherein (a) in FIG4 is the thermal conductivity of composite films provided in some embodiments and comparative examples of the present application, and (b) in FIG4 is the improvement rate of thermal conductivity of composite films provided in some embodiments of the present application relative to thermal conductivity of composite films of comparative example 1;

FIG. 5 shows the volume resistivity of composite films provided in some embodiments and comparative examples of the present application.

Detailed ways

The principles and spirit of the present disclosure will be described below with reference to several exemplary embodiments shown in the accompanying drawings. It should be understood that the description of these specific embodiments is only to enable those skilled in the art to better understand and implement the present disclosure, and does not limit the scope of the present disclosure in any way. In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by those of ordinary skill in the art.

As used herein, the term "including" and similar terms should be understood as open inclusion, i.e., "including but not limited to". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc. may refer to different or the same objects, and are only used to distinguish the objects referred to, and do not imply a specific spatial order, temporal order, order of importance, etc. of the objects referred to.

Polymer matrices usually have low intrinsic thermal conductivity. Adding fillers with high thermal conductivity to polymer matrices is a common method to improve their thermal conductivity. For polymer-based thermal conductive composites, interfacial thermal resistance and phonon scattering at the filler/polymer and filler/filler interfaces are the main factors that hinder the further improvement of their thermal conductivity. When the filler content is low, the main factor affecting the thermal conductivity of polymer-based composites is the interfacial thermal resistance of the filler/polymer interface; and when the filler forms a thermally conductive network structure, the main factor affecting the thermal conductivity of polymer-based composites is the interfacial thermal resistance between fillers/fillers. Effective strategies to reduce interfacial thermal resistance include: chemical modification of the filler surface, covalent bond connection between fillers/polymers, polymer layer coating on the filler surface, and the use of high thermal conductivity nanoparticles to construct a "bridge" structure.

In addition to high thermal conductivity, the modern, rapidly developing microelectronics industry has placed high demands on other properties of heat dissipation materials, such as thinness, flatness, resistivity, mechanical properties, and thermal stability. Thin thermal conductive materials can avoid increasing the volume of microelectronic devices; good flatness can reduce the impact of thermal conductive materials on the precision of microelectronic devices; high resistivity can effectively prevent thermal conductive materials from causing short circuits in electronic devices; excellent mechanical properties and thermal stability can enable thermal conductive materials to work stably in various extreme environments. Therefore, it is becoming increasingly important to improve the comprehensive performance of thermal conductive materials.

Based on this, the embodiments of the present application provide a method for preparing a composite film, a composite film and its application, wherein the method uses PI as the matrix material of the composite film, uses carboxylated carbon nanotubes and polydopamine-modified boron nitride nanosheets as fillers, and uses an electrospinning process and a hot pressing process to prepare a composite film with excellent comprehensive performance. In order to facilitate readers to understand the present invention, it is described below in conjunction with specific embodiments.

The present application provides a method for preparing a composite film. For example, FIG1 and FIG2 show a schematic flow chart of the method for preparing a composite film. Referring to FIG1 and FIG2, the method includes the following steps:

Step 11: preparing a spinning solution, wherein the spinning solution includes a polyamic acid solution and carboxylated carbon nanotubes and modified boron nitride nanosheets dispersed in the polyamic acid solution.

In an embodiment of the present application, carboxylated carbon nanotubes (s-CNTs) and polydopamine-modified boron nitride nanosheets (BNNS@PDA) can be dispersed in a polyamic acid (PAA) solution to obtain a spinning solution. For example, s-CNTs, BNNS@PDA and PAA solutions can be mixed first (for example, s-CNTs and BNNS@PDA are added to a PAA solution), and then s-CNTs and BNNS@PDA are evenly dispersed in the PAA solution by stirring to obtain a spinning solution. In some embodiments, a mixture of BNNS@PDA and PAA solution can be prepared first, and then s-CNTs can be added to the mixture of BNNS@PDA and PAA solution in batches. In this embodiment, by adding BNNS@PDA and s-CNTs to a PAA solution and dispersing them evenly, the dispersibility of BNNS@PDA and s-CNTs in the PAA solution can be improved, which helps to prepare a composite film with more uniform performance. In other embodiments, s-CNT and BNNS@PDA may be added to a DMF solution for ultrasonic dispersion, and then the prepared PAA powder may be dissolved in the dispersion and stirred at low temperature to obtain a spinning solution.

In some embodiments, in order to improve the comprehensive properties of the composite film, such as thermal conductivity, insulation and mechanical properties, the mass of s-CNT accounts for 0.1%-0.5% of the mass of PAA, and the mass of BNNS@PDA accounts for 10% of the mass of PAA.

Boron nitride nanosheets (BNNS) are widely used in the field of electronic packaging and insulating materials due to their high thermal conductivity (λ), low dielectric constant (ε) and dielectric loss tangent (tanδ), excellent oxidation resistance and corrosion resistance. However, due to the low solubility, few functional groups and chemical inertness of BNNS, it is difficult to combine well with most polymer matrices. Compared with unmodified boron nitride nanosheets, BNNS@PDA in the embodiments of the present application has better dispersibility. Therefore, using BNNS@PDA as a filler can increase the contact area between fillers and fillers, fillers and PI matrix, reduce the interface defects and heat transfer resistance between the matrix and fillers, reduce the scattering of phonons during diffusion, and thus improve the thermal conductivity of the composite material. In addition, the strong viscosity of polydopamine can also enable the composite film to maintain good breakdown strength.

Specifically, in some embodiments, the step 11 includes the following steps: preparing BNNS@PDA. The preparation method of BNNS@PDA includes the following steps: adding boron nitride nanosheets (BNNS) and dopamine to a mixed solution of tris(hydroxymethylaminomethane) (Tris), deionized water and ethanol, and reacting to obtain BNNS@PDA. BNNS@PDA includes BNNS and PDA distributed on the surface of BNNS; wherein the mass of PDA accounts for 20%-40% of the mass of BNNS.

In some embodiments, the preparation method of BNNS@PDA includes the following specific steps: first, a buffer solution is prepared, which includes a mixed solution of Tris, deionized water and ethanol. For example, Tris powder can be added to a mixed solution of deionized water and ethanol, and Tris can be fully dissolved in the mixed solution of deionized water and ethanol by stirring to obtain a buffer solution. Secondly, BNNS powder is first added to the buffer solution, and the BNNS powder is evenly dispersed in the buffer solution by ultrasonic dispersion, and then dopamine is added. After stirring until the mixed solution is gray-black, it is placed at room temperature for a period of time (or centrifuged), and the supernatant is removed to obtain BNNS@PDA. In some embodiments, the volume ratio of deionized water and ethanol can be 3:1. In order to make the thermal conductivity of the composite film better, the pH value of the buffer solution is 8.5.

In some embodiments, the mass of PDA in BNNS@PDA accounts for 20%-40% of the mass of BNNS.

In the embodiments of the present application, dopamine (DA) is oxidized and self-polymerized under the weak base conditions formed by tris(hydroxymethyl)aminomethane to form polydopamine (PDA) with strong adhesion, and the surface of boron nitride nanosheets (BNNS) is modified by PDA to obtain polydopamine-modified boron nitride nanosheets (BNNS@PDA) with a large number of active groups (-NH and -OH). Surface activation and modification of inorganic filler BNNS can effectively improve the dispersibility of BNNS, thereby increasing the contact area between BNNS@PDA and BNNS@PDA, BNNS@PDA and PI matrix, reducing the interface defects and heat transfer resistance between PI matrix and BNNS@PDA, reducing the scattering of phonons during diffusion, and thus improving the thermal conductivity of the composite film.

In some embodiments, BNNS@PDA needs to be dried before preparing the spinning solution. The specific method of drying can be: drying BNNS@PDA at 60°C~80°C for 12h~24h. Since PAA easily polymerizes and precipitates in water, if the aqueous dispersion of BNNS@PDA is mixed with the PAA solution, PAA will precipitate and reduce the yield of the target product. Therefore, in order to improve the dispersibility of BNNS@PDA in the PAA solution, BNNS@PDA can be added to the PAA solution in the form of dry powder during the preparation of the spinning solution.

In some embodiments, the step 11 includes the following steps: preparing PAA. The method for preparing PAA is as follows: in an ice-water bath, 4,4'-diaminodiphenyl ether monomer and benzene tetracarboxylic anhydride monomer are dissolved in N,N-dimethylformamide for polycondensation to obtain polyamic acid. For example, the method for preparing PAA can be as follows: in an ice-water bath, 4,4'-diaminodiphenyl ether (ODA) monomer is first added to N,N-dimethylformamide (DMF) solution, stirred to completely dissolve the ODA monomer in DMF, and then benzene tetracarboxylic anhydride (PMDA) monomer is added, and stirring is continued until the polymerization reaction is complete to obtain a PAA solution. In order to further improve the thermal conductivity of the composite film, the mass ratio of PMDA monomer to ODA monomer can be specifically 1.15:1.

Specifically, in some embodiments, during the preparation of the PAA solution, PMDA can be added to the DMF in which ODA is dissolved in several batches; after each addition of pyromellitic anhydride, PMDA is stirred to dissolve in DMF and react completely before adding the next batch of PMDA. Specifically, in some embodiments, the weight of PMDA added in each batch does not exceed 0.2 g. By adding PMDA in batches, the heat generated by PMDA during the dissolution process can be effectively reduced, and the self-polymerization process of PMDA can be avoided, thereby reducing the occurrence of side reactions and improving the yield of the target product PAA.

In some embodiments, step 11 specifically includes the following steps: adding ODA to a reaction container, adding DMF under ice water bath conditions, adding PMDA in batches after ODA is completely dissolved, adding BNNS@PDA and s-CNT after all PMDA is added and dissolved, and obtaining a spinning solution after the reactants in the reaction container undergo a condensation reaction.

The s-CNT in the embodiments of the present application can be commercially available s-CNT or homemade s-CNT. The preparation method of s-CNT is a prior art and will not be described in detail in the embodiments of the present application.

Step 12: Perform electrostatic spinning using the spinning solution to obtain a first fiber felt.

Electrospinning is the process of spinning using a spinning solution under high-voltage electrostatic conditions. In some embodiments, during the electrospinning process, the voltage of the high-voltage power supply is 15kV~25kV. Specifically, the spinning solution can be added to an electrospinning instrument for electrospinning, so that the s-CNT/BNNS@PDA/PAA solution is prepared into a s-CNT/BNNS@PDA/PAA composite fiber felt. The electrospinning instrument includes an injection needle with a metal needle. The spinning solution can be loaded into the injection needle, and electrospinning can be performed under the conditions of an applied voltage of 18kV, a collection distance of 15cm, and a flow rate of the spinning solution of 0.017mL/min.

In some embodiments, in the first fiber mat, the arrangement of the s-CNT/BNNS@PDA/PAA composite fibers includes a zigzag arrangement. Compared with other arrangements, such as random arrangement or vertical arrangement, the zigzag arrangement is more conducive to improving the thermal conductivity of the fiber-based material. The thermal conductivity of the composite film prepared using the zigzag-arranged s-CNT/BNNS@PDA/PAA composite fibers is better. Specifically, the s-CNT/BNNS@PDA/PAA composite fibers can be arranged alternately along the bending direction of the first fiber mat. For example, the s-CNT/BNNS@PDA/PAA composite fibers are arranged alternately once for each 1 mL of spinning solution ejected. Electrospinning using the method in this embodiment can enable the spinning solution to be spun continuously, and the s-CNT/BNNS@PDA/PAA composite fibers have a large aspect ratio, good morphology, no bonding phenomenon, and no spindle structure.

In the embodiments of the present application, the composite fiber prepared by the electrospinning process has high porosity, good interconnectivity, micron-level gaps and a large surface-to-volume ratio, and can be used as an excellent material for thermal conductivity of electronic components. The s-CNT/BNNS@PDA/PAA solution is made into s-CNT/BNNS@PDA/PAA composite fiber felt by the electrospinning process, which can effectively improve the uniformity of the distribution of s-CNT and BNNS@PDA in the PI fiber matrix, thereby improving the thermal conductivity of the composite film.

Step 13, performing thermal imidization treatment on the first fiber mat to obtain a second fiber mat;

In this embodiment, the first fiber mat can be subjected to a stepwise thermal imidization treatment in a nitrogen atmosphere using a tubular furnace to obtain a second fiber mat. The heating rate of the thermal imidization treatment is 5°C/min, and the temperature of the thermal imidization treatment is 120°C-250°C.

In some embodiments, the imidization treatment process is as follows: (a) heating the first fiber felt to 120°C at a heating rate of 5°C/min, and then annealing for 1 hour to remove the residual DMF solvent in the first fiber felt; (b) heating the first fiber felt to 200°C at a heating rate of 5°C/min, and then annealing for 1 hour; (c) heating the first fiber felt to 250°C at a heating rate of 5°C/min, and then annealing for 1 hour.

In some embodiments, the step 13 is preceded by the following steps: placing the first fiber felt in a vacuum environment for vacuum treatment. Specifically, the vacuum degree of the vacuum environment is 0.08MPa~0.1MPa, the temperature of the vacuum environment is 60℃~80℃, and the vacuum treatment time is 4h~6h. In this embodiment, the organic solvent in the first fiber felt, such as DMF, can be removed by vacuum treating the first fiber felt. In some embodiments, in order to improve the removal efficiency of the organic solvent, the vacuum degree of the vacuum environment is 0.1MPa, the temperature of the vacuum environment is 60℃, and the vacuum treatment time is 4h.

Step 14: compression molding the second fiber felt to obtain a composite film.

In this embodiment, several layers of the second fiber felt can be molded to obtain a composite film. The shape and size of each layer of the second fiber felt can be prepared according to actual needs; for example, the shape of each layer of the second fiber paper can be square. For example, 2g of the second fiber felt can be weighed, and the second fiber felt can be cut into samples with a size of 20mm×20mm and placed in a mold, and molded on a small flat vulcanizer.

Specifically, in some embodiments, in order to improve the comprehensive performance of the composite film, the temperature of the compression molding is 290° C. to 320° C., the pressure of the compression molding is 5 MPa to 10 MPa, and the time of the compression molding is 10 min to 15 min.

In the embodiments of the present application, the polydopamine modified structure constructed on the boron nitride nanosheet can be effectively bonded with polyimide, effectively improving the dispersibility of the boron nitride nanosheet in the polyimide film; in addition, the polyimide-based composite film is prepared by an electrospinning process, which can further improve the dispersibility of the boron nitride nanosheet in the polyimide film while ensuring the mechanical strength of the polyimide film. At the same time, the method obtains a polydopamine-modified boron nitride nanosheet/polyimide composite fiber thermal conductive film by molding several layers of carboxylated carbon nanotubes/polydopamine-modified boron nitride nanosheets/polyimide composite fiber felt, further effectively improving the mechanical strength of the composite film. The composite film can meet the requirements of electronic devices for its electrical insulation performance, lateral heat transfer performance, high strength and lightweight, and reduce the risk of thermal management failure of electronic devices.

The embodiment of the present application also provides a composite film, namely, a carboxylated carbon nanotube/modified boron nitride nanosheet/polyimide composite film, which is prepared by the method provided in the above method embodiment.

In some embodiments, the thermal conductivity of the carboxylated carbon nanotube/modified boron nitride nanosheet/polyimide composite film is 0.574W/mK-0.703W/mK, and the volume resistivity exceeds 10 ¹⁵ Ω·cm. The composite film has good thermal conductivity and insulation properties.

The present application also provides an application of a composite film prepared by the method provided in the above embodiment in the field of electronic packaging.

The composite film provided in the embodiment of the present application can fill the gap between the heating device and the heat sink or metal base. The flexible characteristics of the composite film enable it to fit on the surface of the heating device, so that heat can be transferred from the heating device (such as PCB, etc.) to the metal housing or heat sink, which is beneficial to improve the heat dissipation efficiency and service life of the heating device. For example, the composite film can be set between the heat dissipation cold plate and the heating chip to transfer the heat generated by the chip to the heat dissipation cold plate, thereby reducing the temperature of the chip.

In the embodiments of the present application, the polydopamine-modified boron nitride nanosheets (BNNS@PDA) have good dispersibility in the PI matrix, which is conducive to increasing the contact area between BNNS@PDA and BNNS@PDA and between BNNS@PDA and PI matrix, thereby reducing the interface defects and heat transfer resistance between the PI matrix and BNNS@PDA, reducing the scattering of phonons during the diffusion process, and improving the thermal conductivity of the composite film. In addition, the composite film is prepared by combining in-situ polymerization, electrospinning and compression molding, which is conducive to the uniform dispersion and directional arrangement of BNNS@PDA in the PI matrix to improve the thermal conductivity of the composite film. At the same time, carboxylated carbon nanotubes (s-CNT) with a large aspect ratio can be overlapped between BNNS@PDA and BNNS@PDA, thereby building a continuous heat conduction network path in the PI matrix, further improving the thermal conductivity of the composite film. In addition, the strong viscosity of polydopamine enables the composite film to maintain good breakdown strength. The composite film prepared by the method has excellent thermal conductivity and insulation properties; wherein the thermal conductivity of the composite film can be 0.574W/mK-0.703W/mK, and the volume resistivity can reach above 10 ¹⁵ Ω·cm.

Several embodiments of the present application are provided below.

Example 1

Step 1: Prepare spinning solution.

1.08g of ODA was added to a three-necked flask; 19g of DMF was added to the three-necked flask under ice-water bath conditions; after ODA was completely dissolved in DMF, 1.244g of PMDA was added to the three-necked flask in batches, and the mass of PMDA added in each batch was 0.15g; after all PMDA was added to the three-necked flask and dissolved, the liquid in the three-necked flask was stirred for 30 minutes by mechanical stirring, and then 0.38g of BNNS@PDA and 0.0076g of s-CNT were added, and stirring was continued for 30 minutes to obtain a mixed solution of s-CNT, BNNS@PDA and PAA, that is, the spinning solution. In the spinning solution, BNNS@PDA accounts for 10% of the mass of PAA, and s-CNT accounts for 0.1% of the mass of PAA; in BNNS@PDA, the mass of PDA accounts for 40% of the mass of BNNS.

Step 2: Using the spinning solution to perform electrostatic spinning to obtain the first fiber felt.

The spinning solution of step 1 is loaded into the injection needle of the electrospinning instrument, and electrospinning is performed under the conditions of an applied voltage of 18 kV, a collection distance of 15 cm, and a flow rate of the spinning solution of 0.017 mL/min, and the first fiber is collected on a drum with a rotation speed of 120 rpm. The humidity of the electrospinning environment is (50 ± 5)%, and the temperature of the electrospinning environment is (25 ± 3) ° C. The inner diameter of the needle tip of the injection needle is 0.41 mm. The fiber collection method is a "zigzag" arrangement.

Step 3: The first fiber mat is subjected to thermal imidization treatment to obtain a second fiber mat.

The first fiber mat was vacuum dried at 60°C for 4 hours, and then placed in a high-temperature oven for thermal imidization treatment under _N2 atmosphere to obtain a second fiber mat. The imidization treatment process specifically includes the following steps: (a) heating the first fiber mat to 120°C at a heating rate of 5°C/min, and then annealing for 1 hour to remove the residual DMF solvent; (b) heating the first fiber mat to 200°C at a heating rate of 5°C/min, and annealing for 1 hour; (c) heating the first fiber mat to 250°C at a heating rate of 5°C/min, and annealing for 1 hour.

Step 4: compression molding the second fiber felt to obtain a composite film.

2g of the second fiber mat was cut into 20mm×20mm samples, loaded into a mold, and molded on a small flat vulcanizer to obtain a composite film. The molding temperature was 320°C, the molding pressure was 10MPa, and the molding time was 10min.

Example 2

The difference between this embodiment and embodiment 1 is that in the spinning solution, the mass of s-CNT accounts for 0.2% of the mass of PAA.

Example 3

The difference between this embodiment and embodiment 1 is that in the spinning solution, the mass of s-CNT accounts for 0.3% of the mass of PAA.

Example 4

The difference between this embodiment and embodiment 1 is that in the spinning solution, the mass of s-CNT accounts for 0.4% of the mass of PAA.

Example 5

The difference between this embodiment and embodiment 1 is that in the spinning solution, the mass of s-CNT accounts for 0.5% of the mass of PAA.

Comparative Example 1

The difference between this embodiment and embodiment 1 is that the spinning solution includes unmodified CNTs and unmodified BNNS; and in the spinning solution, the mass of the unmodified CNTs accounts for 0.3% of the mass of PAA.

The performance test results of Examples 1-5 and Comparative Example 1 are provided below.

FIG3 shows a scanning electron microscope (SEM) image of the composite film provided in Comparative Example 1 and Examples 1-5. Among them, (a) in FIG3 is a SEM image of the composite film provided in Comparative Example 1, and (b)-(f) in FIG3 are SEM images of the composite films provided in Examples 1-5, respectively. As can be seen from (a) in FIG3, unmodified CNT and unmodified BNNS are easy to agglomerate in the PI matrix. As can be seen from (b)-(f) in FIG3, in the composite film prepared using the modified s-CNT and BNNS@PDA, s-CNT and BNNS@PDA are evenly dispersed, and s-CNT is overlapped between BNNS@PDA and BNNS@PDA.

It can be seen from Figure 3 (a) and Figure 3 (d) that when the addition amount of s-CNT and unmodified CNT is the same, the s-CNT in Figure 3 (d) is more evenly dispersed in the PI matrix than the unmodified CNT in Figure 3 (a). This phenomenon is attributed to the formation of covalent bonds between s-CNT and PI chains during the in-situ polymerization process, which promotes the formation of an interface bond between s-CNT and PI matrix.

(a) in FIG4 and Table 1 show the thermal conductivity (λ, in W/mK) of the composite films provided by Comparative Example 1 and Examples 1-5. It can be seen from (a) in FIG4 and Table 1 that as the s-CNT content increases, the thermal conductivity of the composite film is significantly improved. It can be seen from (b) in FIG4 that in the spinning solution, when the mass of s-CNT accounts for 0.5% of the mass of PAA, the thermal conductivity of the composite material is increased by 25.6% relative to Comparative Example 1.

Table I

FIG5 shows the volume resistivity of the composite films provided in Examples 1-5. As can be seen from FIG5, the volume resistivity of the composite films provided in Examples 1-5 is greater than 10 ¹⁵ Ω·cm, far exceeding the volume resistivity (10 ⁹ Ω·cm) required for electrical insulation materials. Therefore, the composite films provided in Examples 1-5 are suitable for the insulation performance requirements of electronic devices.

The thermal conductivity of the thermally conductive filler is much higher than that of the polymer matrix. However, when a single filler is added and the amount of filler is low, gaps often appear between adjacent fillers, making the thermal conductivity path discontinuous, resulting in limited improvement in the thermal conductivity of the material. However, when the amount of filler is too large, the mechanical properties of the material will be reduced. Therefore, the embodiment of the present application compounded the two fillers, s-CNT and BNNS@PDA, while showing good synergy while giving full play to the advantages of the two fillers, forming a more effective thermal conductivity path, and more effectively improving the thermal conductivity efficiency of the composite film even when the amount of filler added is small.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A method of preparing a composite film, the method comprising:

Preparing a spinning solution, wherein the spinning solution comprises a polyamic acid solution, and carboxylated carbon nanotubes and polydopamine modified boron nitride nano-sheets dispersed in the polyamic acid solution;

carrying out electrostatic spinning by using the spinning solution to obtain a first fiber felt;

Performing thermal imidization treatment on the first fiber felt to obtain a second fiber felt;

The second fiber felt is molded to prepare a composite film;

The first fiber felt is used for representing carboxylated carbon nano tube/polydopamine modified boron nitride nano sheet/polyamide acid composite fiber felt, and the second fiber felt is used for representing carboxylated carbon nano tube/polydopamine modified boron nitride nano sheet/polyimide composite fiber felt.

2. The method of claim 1, wherein the carboxylated carbon nanotubes are present in an amount of 0.1% to 0.5% by mass of the polyamic acid, and the polydopamine modified boron nitride nanoplatelets are present in an amount of 10% by mass of the polyamic acid.

3. The method of claim 2, wherein the polydopamine modified boron nitride nanoplatelets comprise: the boron nitride nano-sheet and polydopamine distributed on the surface of the boron nitride nano-sheet, wherein the mass of polydopamine accounts for 20% -40% of the mass of the boron nitride nano-sheet.

4. The method of claim 1, wherein said configuring the dope comprises:

and adding the carboxylated carbon nano tube and the polydopamine modified boron nitride nano sheet into a polyamic acid solution, and stirring the polyamic acid solution to obtain the spinning solution.

5. The method of claim 4, wherein prior to said configuring the dope, the method further comprises: preparing polydopamine modified boron nitride nanosheets;

The preparation of the polydopamine modified boron nitride nanosheets comprises the following steps:

adding tris (hydroxymethyl) aminomethane into a mixed solution of deionized water and ethanol to prepare a buffer solution, wherein the pH value of the buffer solution is 8.5;

adding the boron nitride nanosheets into the buffer solution, and performing ultrasonic treatment on the buffer solution;

And adding dopamine into the buffer solution, stirring the buffer solution at room temperature, and removing supernatant after the buffer solution is gray black and a reaction product in the buffer solution is precipitated to obtain the polydopamine modified boron nitride nanosheets.

6. The method of claim 4, wherein prior to said configuring the dope, the method further comprises: preparing polyamide acid;

The preparation of the polyamic acid comprises the following steps:

under the ice water bath condition, 4' -diaminodiphenyl ether monomer and benzene tetra-acetic anhydride monomer are dissolved in N, N-dimethylformamide for polycondensation reaction to prepare polyamide acid;

Wherein the mass ratio of the 4,4' -diaminodiphenyl ether monomer to the pyromellitic anhydride monomer is 1.15:1.

7. The method according to any one of claims 1 to 6, wherein the temperature of the compression molding is 290 ℃ to 320 ℃, the pressure of the compression molding is 5mpa to 10mpa, and the time of the compression molding is 10min to 15min.

8. The method of any one of claims 1-6, wherein the first fiber bond comprises a carboxylated carbon nanotube/polydopamine modified boron nitride nanoplatelet/polyamic acid composite fiber, and wherein the arrangement of the carboxylated carbon nanotube/polydopamine modified boron nitride nanoplatelet/polyamic acid composite fiber comprises a zig-zag arrangement.

9. A composite film prepared according to the method of any one of claims 1-8.

10. Use of a composite film prepared according to the method of any one of claims 1-8 in the field of electronic packaging.