A high thermal conductivity polyimide composite film and preparation method thereof

Abstract

The present invention relates to a high thermal conductivity polyimide composite film and a preparation method thereof, wherein the polyimide composite microspheres are prepared by plastic polyimide microspheres, a water-soluble polyimide adhesive and a thermal conductive filler and then molded. Compared with the prior art, the polyimide composite film of the present invention has excellent thermal conductivity, while ensuring excellent mechanical properties and high temperature resistance, and can be applied to multiple fields such as electronic appliances and aerospace.

Description

Technical Field

[0001] The invention belongs to the field of polyimide films, and particularly relates to a high thermal conductivity polyimide composite film and a preparation method thereof. Background Art

[0002] As electronic devices and equipment develop towards miniaturization, high performance and high integration, effective heat dissipation has become a major issue affecting the working efficiency and service life of electronic equipment. Polyimide (PI) is widely used in electronic packaging materials due to its excellent mechanical properties, heat resistance, low dielectric properties and chemical stability. However, the thermal conductivity of polyimide with random molecular chain structure itself is low (less than 0.5W / mK), which cannot meet the heat dissipation requirements of microelectronic materials. In order to improve the thermal conductivity of PI, the most commonly used method is to prepare thermally conductive polyimide film by simple physical blending with thermally conductive fillers in polyimide or its precursor polyamic acid solution. However, on the one hand, there is poor interfacial compatibility between the filler and the polymer matrix, which leads to a significant decrease in the mechanical properties of the composite film. On the other hand, the random distribution of the thermally conductive filler and its easy agglomeration make it difficult to form a continuous thermal conductive path when the filler content is low (<30wt%). Therefore, how to efficiently construct a thermal conductive path is one of the keys to preparing a high thermal conductive composite film.

[0003] The commonly used solutions at present are: 1) Surface modification of thermal conductive fillers to increase their interaction with polymers; however, the process is complex and the yield is low, which is not conducive to practical application. 2) In-situ polymerization of polyamic acid to prepare a mixed polymer solution, and then prepare it into a thermal conductive material; however, the mixed polymer solution is prone to aggregation and precipitation during static molding, making the prepared thermal conductive material uneven up and down. 3) Solid-state mixing of polymer powder or microspheres with thermal conductive fillers and then hot pressing molding; however, due to the interface problem between the polymer and the thermal conductive filler, it will also cause the thermal conductive filler to aggregate, thereby affecting the mechanical properties of the composite material. For example, patent CN 113321806 A increases the bonding performance between the polymer and the thermal conductive filler by adding a coupling agent, but the coupling agent contains fatty alkanes with low heat resistance or contains metal elements, which is not conducive to the requirements of the microelectronics field for the temperature resistance and dielectric properties of thermal conductive materials. In patent CN 112266611 A, polyamic acid microspheres are first prepared in aqueous solution, and then composite microspheres are prepared through hydrogen bonding and electrostatic attraction between polyamic acid and filler, and finally high-temperature cyclization is performed to prepare polyimide composite microspheres; polyamic acid may be hydrolyzed in water to reduce the molecular weight, and the morphology of the microspheres may collapse during the high-temperature cyclization process due to the low glass transition temperature of polyamic acid (<200°C). In patent CN106243715 B, a high thermal conductivity composite material is prepared by mechanically mixing a dispersion of boron nitride and a dispersion of polyimide microspheres and then centrifugally molding. Due to the weak interaction between polyimide microspheres and boron nitride, the yield is low when preparing composite microspheres, and the amount of boron nitride retained on the surface of the microspheres is small and uneven, which may make it difficult to form the final thermal conductive path.

[0004] Therefore, there is an urgent need to find a high thermal conductivity composite material with high temperature resistance and excellent mechanical properties. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high thermal conductivity polyimide composite film and a preparation method thereof. The polyimide composite film has excellent thermal conductivity while ensuring excellent mechanical properties and high temperature resistance, and can be used in multiple fields such as electronics and aerospace.

[0006] The invention provides a high thermal conductivity polyimide composite film, which is obtained by preparing polyimide composite microspheres from plastic polyimide microspheres, a water-soluble polyimide adhesive and a thermal conductive filler and then molding the polyimide composite microspheres.

[0007] The plastic polyimide microspheres are obtained by reacting diamine monomer A and anhydride monomer to obtain a plastic polyimide solution, and then dropping an aqueous solution containing a surfactant and stirring.

[0008] The preparation method of the plastic polyimide microspheres is as follows:

[0009] The diamine monomer A and the acid anhydride monomer are reacted in N-methylpyrrolidone (NMP) at low temperature (-5 to 60°C) for 6 to 20 hours, and then reacted at high temperature (150 to 200°C) for 2 to 20 hours, and then cooled to room temperature, and NMP is added to dilute it to a certain solid content (1wt% to 30wt%) to obtain a plastic polyimide solution; an aqueous solution containing a surfactant is slowly added dropwise to the obtained plastic polyimide solution, and plastic polyimide microsphere particles are obtained after filtering, washing and drying.

[0010] The surfactant is a nonionic surfactant, such as polyvinyl alcohol, polyethylene glycol, polyol, block copolyether, etc.

[0011] The added amount of the surfactant accounts for 0% to 30% of the mass of deionized water.

[0012] The volume ratio of the deionized water to the plastic polyimide solution is 1 to 10:1.

[0013] The water-soluble polyimide adhesive is obtained by reacting diamine monomer A, diamine monomer B, anhydride monomer and end-capping agent 4-phenylethynylphthalic anhydride to obtain a polyimide solution, which is dried into powder and then redissolved in an aqueous solution containing an organic base. The viscosity of the water-soluble polyimide adhesive is 1 to 5000 mPa·s.

[0014] The molecular formula of the water-soluble polyimide adhesive is as follows:

[0015]

[0016] The preparation method of the water-soluble polyimide adhesive is as follows:

[0017] The method comprises the following steps: reacting a diamine monomer A, a diamine monomer B, an anhydride monomer and a capping agent 4-phenylethynylphthalic anhydride in a solvent of N-methylpyrrolidone (NMP) at room temperature for 6 to 20 hours, reacting at 180°C for 2 to 24 hours, cooling to room temperature to obtain a polyimide solution with different polymerization degrees (5 to 50), and obtaining polyimide powders with different polymerization degrees after precipitation, washing and drying; and dissolving the polyimide powders with different polymerization degrees in an aqueous solution containing an organic base to obtain a water-soluble polyimide adhesive.

[0018] The molar ratio of the diamine monomer A to the diamine monomer B is (0-9):1.

[0019] The solid content of the polyimide solutions with different polymerization degrees (5 to 50) is 5 wt % to 40 wt %.

[0020] The organic base is one or more of triethylamine, triethanolamine, tripropylamine, tributylamine and tripentylamine; the molar ratio of the diamine monomer B to the organic base is 1:(0.2-20); and the volume ratio of the organic base to water is 1:(1-1000).

[0021] The structure of the diamine monomer A is any one of the following structures:

[0022]

[0023] The structure of the anhydride monomer is any one of the following structures:

[0024]

[0025] The structure of the diamine monomer B is any one of the following structures:

[0026]

[0027] The thermal conductive filler is one or more of boron nitride, aluminum nitride, aluminum oxide, silicon nitride, silicon carbide, zinc oxide, graphite, carbon fiber, carbon nanotube, and graphene, and has a size range of 1 nm to 1 mm.

[0028] The present invention also provides a method for preparing a high thermal conductive polyimide composite film, comprising:

[0029] A water-soluble polyimide adhesive is added to continuously stirred plastic polyimide microsphere particles, and then a thermal conductive filler is added, and after drying, polyimide composite microspheres are obtained; the polyimide composite microspheres are then compression molded to obtain a high thermal conductive polyimide composite film; wherein the mass ratio of the water-soluble polyimide adhesive to the plastic polyimide microsphere particles is 1:(10-1000) (preferably 1:(50-200)); the mass ratio of the thermal conductive filler to the plastic polyimide microsphere particles is 1:(0.5-200).

[0030] The drying temperature is 50-150° C., and the drying time is 6-48 hours.

[0031] The compression molding steps are: placing the polyimide composite microspheres in a mold, heating to 220-320° C., pressurizing 1-1000 MPa, maintaining for 10-120 minutes, then heating to 320-400° C., maintaining for 30-120 minutes, cooling and demolding to obtain a high thermal conductivity polyimide composite film.

[0032] The technical route of the present invention is: (1) Plastic polyimide microspheres are prepared by a one-step method to provide a basis for subsequent hot pressing film formation. 2) In order to enhance the interaction between the thermally conductive filler and the polyimide microspheres, a water-soluble polyimide adhesive is prepared. The water-based adhesive polymer has a suitable viscosity and is a polyimide containing active carboxyl groups in the side chain, which can effectively make the thermally conductive filler evenly bonded to the surface of the polyimide microspheres. (3) In order to enhance the mechanical properties of the composite thermally conductive film, the end of the water-soluble polyimide adhesive contains a cross-linkable phenylethynyl group, which increases the interaction force between different microspheres through a thermal cross-linking reaction during the molding process, thereby increasing the mechanical properties of the composite thermally conductive film.

[0033] Beneficial Effects

[0034] (1) The plastic polyimide microspheres prepared by the present invention, on the one hand, avoid the subsequent high-temperature thermal cyclization process, and on the other hand, provide a basis for the subsequent hot pressing molding of the polyimide composite film.

[0035] (2) The water-soluble polyimide adhesive prepared by the present invention: a) its water-soluble property provides convenience for subsequent solvent removal and is more environmentally friendly; b) the water-soluble polyimide adhesive is a polyimide with an active carboxyl group in the side chain. According to the principle of like-compatibility, when it is added to the plastic polyimide microspheres, it can be uniformly adhered to the surface of the microspheres; c) by controlling the degree of polymerization, solid content, and type of organic base, the water-soluble polyimide adhesive has a suitable viscosity, which is conducive to the uniform adhesion of the thermal conductive filler to the surface of the plastic polyimide microspheres; d) in order to improve the mechanical properties of the composite film, the water-soluble polyimide adhesive used in the present invention contains a cross-linkable phenylethynyl group at its end, so that it increases the interaction force between different microspheres through a thermal cross-linking reaction during the molding process, thereby increasing the mechanical properties of the composite thermal conductive film.

[0036] (3) The present invention does not require special surface chemical modification of the thermally conductive filler, which simplifies the process and is more conducive to mass production.

[0037] (4) The high thermal conductivity polyimide composite film prepared by the present invention has a low preparation temperature, high temperature resistance, and excellent mechanical properties. When the content of thermal conductive filler is very low, a continuous thermal conductive path can be formed, and it can be applied in multiple fields such as electronics and aerospace. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a scanning electron microscope image of the plastic polyimide microspheres in Example 1;

[0039] Figure 2 is a scanning electron microscope image of the plastic polyimide microspheres in Example 4;

[0040] Figure 3 This is a scanning electron microscope image of the polyimide composite microspheres in Example 4;

[0041] Figure 4 This is a scanning electron microscope image of the cross section of the high thermal conductivity polyimide composite film in Example 6. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0043] Example 1

[0044] (1) 0.01 mol (2.9 g) of 1,3-bis(4'-aminophenoxy)benzene (APB) monomer was added to 80 ml of N-methylpyrrolidone (NMP) and stirred until the monomer was completely dissolved, then 0.01 mol (4.4 g) of hexafluorodianhydride (6FDA) was added and stirred for 6 hours, then the temperature was slowly raised to 180° C. and maintained for 8 hours, then cooled to room temperature, 7 g of polyvinyl alcohol and 80 ml of NMP were added to obtain a plastic polyamic acid solution; 400 ml of deionized water was dripped into the above plastic polyamic acid solution at a rotation speed of 6000 rpm, and 6.8 g (yield: 93%) of plastic polyimide microsphere particles were obtained after filtering, washing and drying.

[0045] (2) 1.5 g of 3,5-diaminobenzoic acid (DABA), 2.9 g of APB monomer, 8.4 g of 6FDA monomer and 0.5 g of 4-phenylethynylphthalic anhydride (PEPA) were reacted in 120 ml of NMP at room temperature for 4 hours, and then the temperature was gradually raised to 180° C. and maintained for 8 hours. After cooling, the mixture was precipitated in deionized water, and after washing and drying, a polyimide powder (10.3 g, yield: 84%) with a degree of polymerization of 19 was obtained; and the polyimide powder was redissolved in an aqueous solution of triethylamine (5 g of triethylamine + 50 g of water) to obtain a water-soluble polyimide adhesive with a viscosity of 12 Pa.s.

[0046] (3) 12.5 g of a water-soluble polyimide adhesive was added to 5 g of plastic polyimide microspheres in three times, and the mixture was stirred continuously. 0.5 g of a peeled boron nitride filler was added in three times, and then the mixture was dried in a vacuum at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0047] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 350°C on a vulcanizer, pressurized to 4 MPa and maintained for 1 hour, then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0048] The glass transition temperature of the obtained plastic polyimide microsphere particles is 298°C. The SEM image of the microsphere particles is as follows: Figure 1 As shown, the average particle size is 3 μm. The viscosity of the obtained water-soluble polyimide adhesive is 12 Pa.s. The thermal conductivity of the prepared polyimide / boron nitride composite film is 1.2 W / (mK) and the tensile strength is 140 MPa.

[0049] Example 2

[0050] (1) 12.5 g of the water-soluble polyimide adhesive prepared in Example 1 was added to 5 g of the plastic polyimide microspheres prepared in Example 1 in three times, and the mixture was stirred continuously. 1 g of the exfoliated boron nitride filler was added in three times, and then vacuum dried at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0051] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 350°C on a vulcanizer, pressurized to 4 MPa and maintained for 1 hour, then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0052] The thermal conductivity of the prepared polyimide / boron nitride composite film is 2.4 W / (mK) and the tensile strength is 116 MPa.

[0053] Example 3

[0054] (1) 12.5 g of the water-soluble polyimide adhesive prepared in Example 1 was added to 5 g of the plastic polyimide microspheres prepared in Example 1 in three times, and the mixture was stirred continuously. 1 g of commercial alumina (1 μm) filler was added in three times, and then vacuum dried at 80° C. for 4 hours to obtain polyimide composite microsphere particles.

[0055] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 350°C on a vulcanizer, pressurized to 4 MPa and maintained for 1 hour, then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0056] The thermal conductivity of the prepared polyimide / boron nitride composite film is 1.7 W / (mK) and the tensile strength is 88 MPa.

[0057] Example 4

[0058] (1) 0.01 mol (2.0 g) of 4,4'-diaminodiphenyl ether (ODA) monomer is added to 80 ml of NMP and stirred until the monomer is completely dissolved, then 0.01 mol (5.2 g) of bisphenol A dianhydride (BPADA) is added and stirred for 12 hours, then the temperature is slowly raised to 180° C. and maintained for 10 hours, then cooled to room temperature, 12 g of polyvinyl alcohol and 100 ml of NMP are added to obtain a plastic polyamic acid solution; 500 ml of deionized water is dripped into the above plastic polyamic acid solution at a rotation speed of 8000 rpm, and 6.0 g (yield: 83%) of plastic polyimide microsphere particles are obtained after filtering, washing and drying.

[0059] (2) 1.5 g of 3,5-diaminobenzoic acid (DABA), 2.0 g of ODA monomer, 9.9 g of BPADA monomer and 0.5 g of 4-phenylethynylphthalic anhydride (PEPA) were reacted in 150 ml of NMP at room temperature for 8 hours, and then the temperature was gradually raised to 180° C. and maintained for 12 hours. After cooling, the mixture was precipitated in deionized water, and after washing and drying, a polyimide powder (11.5 g, yield: 83%) with a degree of polymerization of 19 was obtained; and then the polyimide powder was dissolved in an aqueous solution of triethylamine (10 g of triethylamine + 100 g of water) to obtain a water-soluble polyimide adhesive with a viscosity of 374 Pa.s.

[0060] (3) 12.5 g of a water-soluble polyimide adhesive was added to 5 g of plastic polyimide microspheres in three times, stirring continuously, and 1 g of a peeled boron nitride filler was added in three times interspersed, and then vacuum dried at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0061] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 300°C on a vulcanizer, pressurized to 4 MPa and maintained for 1 hour, and then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0062] The glass transition temperature of the obtained plastic polyimide microsphere particles is 223°C. The SEM image of the microsphere particles is as follows: Figure 2 As shown, the average particle size is 2 μm. The viscosity of the obtained water-soluble polyimide adhesive is 8 Pa.s. The prepared polyimide composite microsphere particles are as shown Figure 3 As shown, it can be seen that the boron nitride thermal conductive filler is uniformly adhered to the surface of the polyimide microsphere particles. The thermal conductivity of the prepared polyimide / boron nitride composite film is 2.8W / (mK) and the tensile strength is 124MPa.

[0063] Example 5

[0064] (1) 20 g of the water-soluble polyimide adhesive prepared in Example 4 was added to 5 g of the plastic polyimide microspheres prepared in Example 4 in three times, and the mixture was stirred continuously. 1 g of the exfoliated boron nitride filler was added in three times, and then vacuum dried at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0065] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 300°C on a vulcanizer, pressurized to 2 MPa and maintained for 1 hour, and then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0066] The thermal conductivity of the prepared polyimide / boron nitride composite film is 2.2 W / (mK) and the tensile strength is 147 MPa.

[0067] Example 6

[0068] (1) 20 g of the water-soluble polyimide adhesive prepared in Example 4 was added to 5 g of the plastic polyimide microspheres prepared in Example 4 in three times, and the mixture was stirred continuously. 2 g of the exfoliated boron nitride filler was added in three times, and then vacuum dried at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0069] (4) The prepared polyimide composite microsphere particles are placed between two Kapton films, heated to 320°C on a vulcanizer, pressurized to 2 MPa and maintained for 1 hour, and then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0070] The cross-sectional scanning electron microscopy image of the prepared polyimide / boron nitride composite film is shown in FIG. Figure 4 As shown, it can be seen that although the content of thermal conductive filler is high, the thermal conductive filler and the polyimide matrix are evenly distributed in the prepared composite film without obvious aggregation. The thermal conductivity of the composite thermal conductive film finally prepared is as high as 4.5W / (mK) and the tensile strength is 100MPa.

[0071] Comparative Example 1

[0072] (1) 1 g of the exfoliated boron nitride filler was added to 5 g of plastic polyimide powder in three times, and the mixture was stirred to obtain a composite polyimide powder.

[0073] (2) The composite polyimide powder is placed between two Kapton films, heated to 300°C on a vulcanizer, pressurized to 2 MPa and maintained for 1 hour, and then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0074] The thermal conductivity of the prepared polyimide / boron nitride composite film is 0.5 W / (mK) and the tensile strength is 78 MPa.

[0075] Comparative Example 2

[0076] (1) 0.01 mol (2.0 g) of 4,4'-diaminodiphenyl ether (ODA) monomer was added to 80 ml of NMP and stirred until the monomer was completely dissolved. Then, 0.01 mol (5.2 g) of bisphenol A dianhydride (BPADA) was added and stirred for 12 hours. The temperature was slowly raised to 180° C. and maintained for 10 hours. After cooling to room temperature, 100 ml of NMP was added and the mixture was slowly poured into a large amount of deionized water. After filtering, washing and drying, 6.7 g (yield: 93%) of plastic polyimide powder was obtained.

[0077] (2) 12.5 g of the water-soluble polyimide adhesive synthesized in Example 1 was added to 5 g of plastic polyimide powder in three times, and the mixture was stirred continuously. 1 g of the exfoliated boron nitride filler was added in three times, and then vacuum dried at 80° C. for 6 hours to obtain polyimide composite microsphere particles.

[0078] (4) The prepared polyimide composite powder was placed between two Kapton films, heated to 300°C on a vulcanizer, pressurized to 4 MPa and maintained for 1 hour, and then heated to 370°C and maintained for 1 hour to obtain a polyimide / boron nitride composite film.

[0079] The thermal conductivity of the prepared polyimide / boron nitride composite film is 0.9 W / (mK) and the tensile strength is 96 MPa.

Claims

1. A high thermal conductivity polyimide composite film, characterized in that: The polyimide composite microspheres are prepared by plastic polyamic acid microspheres, water-soluble polyamic acid adhesive and thermal conductive filler and then molded; the plastic polyamic acid microspheres are obtained by reacting diamine monomer A and anhydride monomer to obtain a plastic polyamic acid solution, and then adding an aqueous solution containing a surfactant and stirring; the water-soluble polyamic acid adhesive is obtained by reacting diamine monomer A, diamine monomer B, anhydride monomer and end-capping agent 4-phenylethynylphthalic anhydride to obtain a polyamic acid solution, drying it into powder and then redissolving it in an aqueous solution containing an organic base; Wherein, the structure of the diamine monomer A is any one of the following structures: The structure of the anhydride monomer is any one of the following structures: The structure of the diamine monomer B is any one of the following structures:

2. The composite membrane according to claim 1, characterized in that: The surfactant is a nonionic surfactant.

3. The composite membrane according to claim 2, characterized in that: The organic base is one or more of triethylamine, triethanolamine, tripropylamine, tributylamine and tripentylamine; the molar ratio of the diamine monomer B to the organic base is 1:(0.2-20); and the volume ratio of the organic base to water is 1:(1-1000).

4. The composite membrane according to claim 1, characterized in that: The thermal conductive filler is one or more of boron nitride, aluminum nitride, aluminum oxide, silicon nitride, silicon carbide, zinc oxide, graphite, carbon fiber, carbon nanotube, and graphene.

5. A method for preparing the high thermal conductive polyimide composite film according to claim 1, comprising: A water-soluble polyamic acid adhesive is added to the continuously stirred plastic polyamic acid microsphere particles, and then a thermal conductive filler is added, and after drying, polyimide composite microspheres are obtained; The polyimide composite microspheres are then compression molded to obtain a high thermal conductivity polyimide composite film; wherein the mass ratio of the water-soluble polyimide adhesive to the plastic polyimide microsphere particles is 1:(10-1000); the mass ratio of the thermal conductive filler to the plastic polyimide microsphere particles is 1:(0.5-200).

6. The preparation method according to claim 5, characterized in that: The compression molding steps are: placing the polyimide composite microspheres in a mold, heating to 220-320° C., pressurizing 1-1000 MPa, maintaining for 10-120 minutes, then heating to 320-400° C., maintaining for 30-120 minutes, cooling and demolding to obtain a high thermal conductivity polyimide composite film.

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