Polyimide-based high-thermal-conductivity graphite film as well as preparation method and application thereof

Abstract

The invention relates to a polyimide-based high-thermal-conductivity graphite film and a preparation method and application thereof.The preparation method comprises the following preparation steps that S1, a diamine monomer, a dianhydride monomer and calcium phosphate react in a polar solvent, and a polyamide acid solution is obtained; s2, the polyamide acid solution obtained in the step S1 is subjected to film casting and imidization treatment, and a polyimide film is prepared; and S3, carbonizing and graphitizing the polyimide film obtained in the step S2 to obtain the polyimide-based high-thermal-conductivity graphite film. Compared with the prior art, the method has the advantages that calcium phosphate promotes molecular orientation in a polyamide film plane, ordered arrangement and accumulation of a graphite microcrystalline structure are facilitated during carbonization and graphitization, the graphitization degree is improved, lattice defects are reduced, the heat conductivity coefficient of the prepared polyimide-based graphite film is high, and the heat-conducting property can reach 1800 W / m.K.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, and in particular to a polyimide-based high thermal conductivity graphite film and a preparation method and application thereof. Background Art

[0002] As a functional polymer material with good comprehensive performance, polyimide has the characteristics of heat resistance, low temperature resistance, radiation resistance, flame retardancy and non-toxicity, excellent mechanical properties, dimensional stability, chemical stability and biological stability. Due to its special structure and high carbon content of nearly 69%, polyimide is also used as an excellent carbon precursor to prepare graphite film materials.

[0003] Graphite film generally needs to have the characteristics of light weight, high thermal conductivity, low density, and cuttability. It has a broad application space in the electronic products market and the future development prospects of the industry are bright.

[0004] Currently, common methods for preparing graphite films include vapor deposition, redox graphene, and polyimide heat treatment. The vapor deposition method has defects such as strict experimental conditions and can only be temporarily limited to small-scale preparation in the laboratory. The redox graphene method has defects such as destruction of the electronic structure in the graphite film. Compared with the former two, polyimide heat treatment has the advantages of simple preparation process and no large amount of waste liquid generated. However, it also has the defect of insufficient improvement in the thermal conductivity of the graphite film. The present invention is aimed at improving this defect. Summary of the invention

[0005] The purpose of the present invention is to provide a polyimide-based high thermal conductivity graphite film and a preparation method and application thereof in order to overcome the defect that the thermal conductivity of the graphite film in the prior art is not sufficiently improved.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a polyimide (PI)-based high thermal conductivity graphite film, comprising the following steps:

[0008] S1, reacting a diamine monomer, a dianhydride monomer, and calcium phosphate in a polar solvent to obtain a polyamic acid (PAA) solution;

[0009] S2, performing film casting and imidization treatment on the polyamic acid solution obtained in step S1 to obtain a polyimide film;

[0010] S3, subjecting the polyimide film obtained in step S2 to carbonization and graphitization to obtain a polyimide-based high thermal conductivity graphite film.

[0011] In some specific embodiments, in step S1, the amount of calcium phosphate added is 0.1-5 wt % of the total mass of dianhydride and diamine;

[0012] The total mass of dianhydride and diamine accounts for 8-20wt% of the mass of the polyamic acid solution, wherein the mass ratio of dianhydride to diamine is (10.1-1.02):1.

[0013] In some specific embodiments, in step S1, the diamine monomer is selected from any one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, diaminodiphenyl sulfone and its derivatives, diaminobenzophenone and its derivatives.

[0014] In some specific embodiments, in step S1, the dianhydride monomer is selected from any one of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenylmethane dianhydride compounds, ketone-containing carbonyl dianhydride compounds and diphenyl ether dianhydride.

[0015] In some specific embodiments, in step S1, the polar solvent is selected from any one of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

[0016] In some specific embodiments, in step S1, the reaction temperature is 0-60°C, and the reaction time is 3-4h.

[0017] In some specific embodiments, in step S2, the temperature of the imidization treatment is 220-350°C.

[0018] In some specific embodiments, in step S3, the carbonization treatment is carried out under an inert atmosphere at a heating rate gradient of 1-15°C / min from room temperature to 1000°C, and the holding time of each gradient is 30-60 min.

[0019] In some specific embodiments, in step S3, the carbonization treatment is to increase the temperature from room temperature to 400°C at a rate of 12°C / min over 30 minutes under an inert atmosphere; then increase the temperature to 480°C at a rate of 2°C / min and keep it warm for 30 minutes; then increase the temperature to 600°C at a rate of 1°C / min and keep it warm for 60 minutes; continue to increase the temperature to 800°C at a rate of 1°C / min and keep it warm for 30 minutes; then increase the temperature to 1000°C at a rate of 5°C / min and keep it warm for 30 minutes; finally, decrease the temperature to 800°C at a rate of 5°C / min, and then naturally cool to room temperature.

[0020] In some specific embodiments, in step S3, the graphitization treatment is to heat the temperature from room temperature to 2800° C. at a heating rate of 5° C. / min under an inert atmosphere and keep the temperature for 30 minutes.

[0021] The second technical solution of the present invention is to provide a polyimide-based high thermal conductivity graphite film, which is obtained based on the preparation method described in one of the above technical solutions.

[0022] The third technical solution of the present invention is to provide an application of the polyimide-based high thermal conductivity graphite film as described in the second technical solution above, wherein the polyimide-based high thermal conductivity graphite film is used as a heat dissipation material.

[0023] In some specific embodiments, in electronic devices, such as integrated circuits and microprocessors, the polyimide-based high thermal conductivity graphite film can be used as an efficient heat dissipation material to help quickly conduct and dissipate the generated heat and maintain stable operation of the device;

[0024] In industrial processing, such as metal smelting, heat treatment, etc., the polyimide-based high thermal conductivity graphite film can be used as a heat dissipation layer for high-temperature process equipment to improve the stability and service life of the equipment;

[0025] In thermoelectric conversion devices, such as thermocouples and thermoelectric generators, the polyimide-based high thermal conductivity graphite film can be used to improve heat conduction efficiency and enhance the performance of thermoelectric conversion.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the present invention, calcium phosphate promotes the molecular orientation within the polyamide film surface, which is beneficial to the orderly arrangement and accumulation of graphite microcrystalline structures during carbonization and graphitization, improves the degree of graphitization, and reduces lattice defects. Therefore, the polyamide film prepared by the present invention is more suitable as a base film for preparing graphite film than traditional polyamide films.

[0028] (2) The preparation process provided by the present invention is simple to operate, the preparation process is highly practical, the production efficiency is high, and it is easy to realize industrial production. In addition, the thermal conductivity of the prepared polyimide-based graphite film is high, and the thermal conductivity can reach 1800W / m·K. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The stress-strain curve of PI film with different calcium phosphate addition amounts.

[0030] Figure 2 SEM images of PI-based graphite films with different calcium phosphate additions: (a, d) surface and cross-section of graphite film without calcium phosphate; (b, c) surface of graphite film with 0.7% calcium phosphate addition; (e, f) cross-section of graphite film with 0.7% calcium phosphate addition. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] In the following examples and comparative examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0033] Embodiment 1:

[0034] (1) Add 123g of N,N-dimethylacetamide to a reaction vessel, then add 0.5wt% calcium phosphate (0.135g) and stir for 10 minutes. Then add 12.79g of 4,4'-diaminodiphenyl ether and stir at a speed of 300r / min (stir at this rate during the polymerization process) until 4,4'-diaminodiphenyl ether is completely dissolved. Then add 14.21g of pyromellitic anhydride in three times, and stir the solution in an oil bath at 60°C for 3 to 4 hours to obtain a polyamic acid solution with a total mass of 18wt% (total mass of 4,4'-diaminodiphenyl ether and pyromellitic anhydride).

[0035] (2) The polyamic acid solution in (1) is coated on a support plate, and then kept at 80°C, 120°C, and 160°C for 30 minutes to volatilize the solvent. The temperature is then continued to rise, and kept at 220°C, 260°C, and 300°C for 10 minutes to fully imidize, and then cooled to room temperature to obtain a polyimide film.

[0036] (3) The polyimide film in (2) is subjected to carbonization treatment. In a nitrogen atmosphere, the temperature is raised from room temperature to 400°C at 12°C / min over 30 minutes; then the temperature is raised to 480°C at 2°C / min and kept at this temperature for 30 minutes; then the temperature is raised to 600°C at 1°C / min and kept at this temperature for 60 minutes; then the temperature is raised to 800°C at 1°C / min and kept at this temperature for 30 minutes; then the temperature is raised to 1000°C at 5°C / min and kept at this temperature for 30 minutes; finally, the temperature is lowered to 800°C at 5°C / min, and then naturally cooled to room temperature and taken out to obtain a carbon film.

[0037] (4) The carbon film in (3) is graphitized by heating from room temperature to 2800°C at a rate of 5°C / min in an argon atmosphere, maintaining the temperature for 30 minutes, and finally naturally cooling to room temperature to obtain a graphite film.

[0038] Embodiment 2:

[0039] Compared with Example 1, most of the conditions are the same, and the only difference is that the "60°C oil bath condition" in step (1) is adjusted to "0°C ice bath condition".

[0040] Embodiment 3:

[0041] Compared with Example 1, most of the conditions are the same, and the only difference is that the "60°C oil bath condition" in step (1) is adjusted to "25°C room temperature condition".

[0042] Embodiment 4:

[0043] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.1wt% calcium phosphate".

[0044] Embodiment 5:

[0045] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.3wt% calcium phosphate".

[0046] Embodiment 6:

[0047] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.7wt% calcium phosphate".

[0048] Embodiment 7:

[0049] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.9wt% calcium phosphate".

[0050] Embodiment 8:

[0051] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "1.2wt% calcium phosphate".

[0052] Embodiment 9:

[0053] Compared with Example 1, most of the steps are the same, except that the "N,N-dimethylacetamide" in step (1) is adjusted to an equal mass of "N,N-dimethylformamide".

[0054] Embodiment 10:

[0055] Compared with Example 1, most of the components are the same, except that the "4,4'-diaminodiphenyl ether" in step (1) is adjusted to an equal mass of "p-phenylenediamine".

[0056] Embodiment 11:

[0057] Compared with Example 1, most of the components are the same, except that the "pyromellitic dianhydride" in step (1) is adjusted to an equal mass of "biphenyltetracarboxylic dianhydride".

[0058] Embodiment 12:

[0059] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.4wt% calcium phosphate".

[0060] Embodiment 13:

[0061] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.6wt% calcium phosphate".

[0062] Embodiment 14:

[0063] Compared with Example 1, most of them are the same, and the only difference is that the "0.5wt% calcium phosphate" in step (1) is adjusted to "0.8wt% calcium phosphate".

[0064] Comparative Example 1:

[0065] Compared with Example 1, most of them are the same, and the only difference is that calcium phosphate is omitted.

[0066] Comparative Example 2:

[0067] Compared with Example 6, most of the steps are the same, except that calcium phosphate is replaced by isoquinoline of the same mass.

[0068] The performance of the polyimide-based graphite films prepared in the above Examples 1-11 and the samples prepared in Comparative Examples 1 and 2 was tested. The results are shown in Table 1.

[0069] Table 1 Performance results

[0070]

[0071] It can be seen from Comparative Example 1 that the addition of calcium phosphate greatly improves the thermal conductivity of the graphite film. It can be seen from Comparative Example 2 that the addition of isoquinoline improves the thermal conductivity of the graphite film to a certain extent, but the effect is not as significant as that of calcium phosphate.

[0072] The polyimide-based graphite films prepared in the above-mentioned Examples 1, 6, 7, 12, 13, and 14 were subjected to stress-strain analysis. The film samples were cut into strips with a width of 3 cm and a length of 10 cm. Three samples of each were prepared for tensile testing. During the test, the tensile speed of the film was set to 50 mm / min.

[0073] like Figure 1As shown, as the amount of calcium phosphate added increases from 0.4wt% to 0.9wt%, the tensile strength corresponding to each PI film shows a trend of first increasing and then decreasing, reaching a maximum value of 121MPa when the amount of calcium phosphate added is 0.7wt%. The internal molecular structure of the PI films with different amounts of calcium phosphate added is almost the same, and the different tensile strengths of the PI films may be caused by the differences in the aggregated structures of the films. When the amount of calcium phosphate added is 0.7%, the tensile strength of the PI film is 1.68 times that of the sample without calcium phosphate added (72.07MPa, Comparative Example 1), indicating that the addition of a small amount of calcium phosphate promotes the imidization transformation of the PAA solution during the imidization process, and the molecular chain mobility is reduced, so that the internal molecular chains of the prepared PI film are arranged more regularly and neatly, with a high in-plane orientation degree, so the corresponding PI film has better mechanical properties. However, excessive calcium phosphate will affect the bonding force between PI molecular chains, causing the mechanical properties of the film to decline.

[0074] Figure 2 The SEM images of the surface and cross section of the PI-based graphite film prepared by graphitization at 2800°C. Figure 2 As can be seen in (a), the sample without calcium phosphate addition (Comparative Example 1) has impurities and unevenness on the surface. Figure 2 As shown in (b, c), the surface of the PI-based graphite film prepared by adding 0.7wt% calcium phosphate is relatively flat and smooth, indicating that the addition of calcium phosphate promotes the orderly arrangement of molecular chains in the film. Figure 2 It can be seen from (df) that the cross-section of each graphite film is a layered structure. Figure 2 (d) shows that the cross-sectional layered structure has obvious gaps, which affects the heat transfer. Figure 2 The cross-sectional layered structure shown in (ef) is denser and more ordered, which will reduce the scattering of phonons and improve thermal conductivity. This shows that adding calcium phosphate and adjusting the amount of addition can help prepare a highly oriented, dense and defect-free high thermal conductivity graphite film.

[0075] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide-based high thermal conductivity graphite film, characterized in that: The steps include: S1, reacting a diamine monomer, a dianhydride monomer, and calcium phosphate in a polar solvent to obtain a polyamic acid solution; S2, performing film casting and imidization treatment on the polyamic acid solution obtained in step S1 to obtain a polyimide film; S3, subjecting the polyimide film obtained in step S2 to carbonization and graphitization to obtain a polyimide-based high thermal conductivity graphite film.

2. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S1, the amount of calcium phosphate added is 0.1-5 wt% of the total mass of dianhydride and diamine; The total mass of dianhydride and diamine accounts for 8-20wt% of the mass of the polyamic acid solution, wherein the mass ratio of dianhydride to diamine is (1.01-1.02):

1.

3. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S1, the diamine monomer is selected from any one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, diaminodiphenyl sulfone and its derivatives, and diaminobenzophenone and its derivatives.

4. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S1, the dianhydride monomer is selected from any one of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenylmethane dianhydride compounds, ketone-containing carbonyl dianhydride compounds and diphenyl ether dianhydride.

5. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S1, the polar solvent is selected from any one of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

6. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S1, the reaction temperature is 0-60°C and the reaction time is 3-12h; In step S2, the temperature of the imidization treatment is 220-350°C.

7. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 1, characterized in that: In step S3, the carbonization treatment is carried out under an inert atmosphere, with a heating rate gradient of 1-15°C / min from room temperature to 1000°C, and the holding time of each gradient is 0-60min; The graphitization treatment was carried out under an inert atmosphere by heating from room temperature to 2800°C at a heating rate of 5°C / min and keeping the temperature for 30 min.

8. The method for preparing a polyimide-based high thermal conductivity graphite film according to claim 7, characterized in that: In step S3, the carbonization treatment is carried out under an inert atmosphere, heating from room temperature to 400°C at a rate of 12°C / min over 30 minutes; then heating to 480°C at a rate of 2°C / min and keeping warm for 30 minutes; then heating to 600°C at a rate of 1°C / min and keeping warm for 60 minutes; continuing to heat to 800°C at a rate of 1°C / min and keeping warm for 30 minutes; then heating to 1000°C at a rate of 5°C / min and keeping warm for 30 minutes; finally cooling to 800°C at a rate of 5°C / min, and then naturally cooling to room temperature.

9. A polyimide-based high thermal conductivity graphite film, characterized in that: Obtained based on the preparation method according to any one of claims 1 to 8.

10. A polyimide-based high thermal conductivity graphite film as claimed in claim 9, characterized in that: The polyimide-based high thermal conductivity graphite film is used as a heat dissipation material.

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