CN111002668A

CN111002668A - Artificial graphite composite membrane and preparation method thereof

Info

Publication number: CN111002668A
Application number: CN201911317095.9A
Authority: CN
Inventors: 金亚东; 杨承翰; 王雄伟; 朱正平
Original assignee: Ningbo Solartron Technology Co Ltd
Current assignee: Ningbo Solartron Technology Co Ltd
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2020-04-14
Also published as: WO2021120245A1

Abstract

The invention relates to a preparation method of an artificial graphite composite membrane, which comprises the following steps: dispersing cellulose nanocrystals in a solvent, sequentially adding an aromatic diamine monomer and an aromatic dianhydride monomer, and carrying out polycondensation reaction to obtain a cellulose nanocrystal modified polyamic acid mixture; carrying out chemical imidization treatment on the obtained polyamic acid mixture, removing partial solvent to obtain a gel film, and carrying out biaxial tension and high-temperature treatment to obtain a modified polyimide film; and (3) under an inert atmosphere, treating the obtained modified polyimide film, and graphitizing at a high temperature to obtain the artificial graphite composite film. The invention also provides an artificial graphite composite membrane.

Description

Artificial graphite composite membrane and preparation method thereof

Technical Field

The invention relates to the field of film materials, in particular to an artificial graphite composite film and a preparation method thereof.

Background

With the rapid development of various electronic and electrical devices toward miniaturization, high power, light weight, and integration, the heat generated per unit volume will be significantly increased, and therefore, higher requirements are put on the heat dissipation performance of the devices, especially for 5G electronic communication devices. Compared with the commonly used metal-based or ceramic-based heat dissipation materials, the carbon-based heat dissipation material (such as natural graphite, graphene and carbon nano tubes) has the advantages of high heat conductivity coefficient, light density, low thermal expansion coefficient, good flexibility and the like, and can meet the heat dissipation requirements of future integrated electronic equipment, so that the heat dissipation material is widely researched.

Although the graphite heat dissipation film prepared from graphene or graphene oxide can achieve ultra-high heat conduction performance, the preparation method of the graphite heat dissipation film only stays in a laboratory stage, and the graphite heat dissipation film is difficult to adapt to industrial production. High heat conductivity graphite film (in current industrial production)>1000W·m^-1·K^-1) Mainly prepared by sintering polyimide at high temperature. Although the in-plane thermal conductivity coefficient of the polyimide-based graphite composite film can reach 1000 W.m^-1·K^-1Above, however, the thermal conductivity in the vertical direction is usually low, usually less than 5 W.m^-1·K^-1Therefore, heat is not easy to diffuse rapidly along the vertical direction, and the heat dissipation capability in practical use is greatly limited.

Disclosure of Invention

In view of this, the present invention provides an artificial graphite composite film having a high thermal conductivity in the vertical direction.

A preparation method of an artificial graphite composite membrane comprises the following steps:

dispersing cellulose nanocrystals in a solvent, sequentially adding an aromatic diamine monomer and an aromatic dianhydride monomer, and carrying out polycondensation reaction to obtain a cellulose nanocrystal modified polyamic acid mixture;

carrying out chemical imidization treatment on the obtained polyamic acid mixture, removing partial solvent to obtain a gel film, and carrying out biaxial tension and high-temperature treatment to obtain a modified polyimide film;

and (3) under an inert atmosphere, treating the obtained modified polyimide film, and graphitizing at a high temperature to obtain the artificial graphite composite film.

The present invention also provides an artificial graphite composite membrane comprising graphite wafer structures and rod-like crystalline carbon aggregates located between adjacent graphite wafer structures.

Compared with the prior art, the preparation method of the artificial graphite composite membrane has the advantages that the cellulose nanocrystals are added before the polycondensation reaction for synthesizing the polyamic acid, so that the cellulose nanocrystals can be uniformly dispersed in the polyamic acid and partially participate in the polycondensation reaction to form covalent bond connection with the polyamic acid, promote good interface combination between the cellulose nanocrystals and the polyamic acid, and further reduce interface phonon scattering. Finally, through carbonization and high-temperature graphitization treatment, the doped cellulose nanocrystals are converted into highly crystallized rod-shaped crystalline carbon which is distributed between adjacent graphite wafer structures in an aggregate form and is tightly combined with the graphite wafers, so that phonon scattering of heat transmitted along the vertical direction of the film can be obviously reduced, the heat conductivity coefficients of the film in the in-plane direction and the vertical direction are improved, and the heat conductivity coefficient in the vertical direction can reach 10 W.m^-1·K^-1The above. The artificial graphite composite membrane can play an excellent heat dissipation effect in future integrated and thin electronic equipment and the like, and has important application value.

The preparation method is simple to operate and easy to industrialize.

Drawings

Fig. 1 is a schematic view of the microstructure of the artificial graphite composite membrane according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Referring to fig. 1, the present invention provides an artificial graphite composite membrane including a plurality of graphite wafer structures and rod-shaped crystalline carbon aggregates between the adjacent graphite wafer structures. The rod-shaped crystalline carbon may serve to improve the heat conductivity of the artificial graphite composite membrane in the vertical direction. Specifically, the artificial graphite composite membrane has a thermal conductivity in a direction perpendicular to the surface thereof>10W·m^-1·K^-1。

The invention also provides a preparation method of the artificial graphite composite membrane, which comprises the following steps:

s1, dispersing the cellulose nanocrystals in a solvent, sequentially adding an aromatic diamine monomer and an aromatic dianhydride monomer, and carrying out polycondensation reaction to obtain a polyamide acid mixture modified by the cellulose nanocrystals;

s2, performing chemical imidization treatment on the obtained polyamic acid mixture, removing partial solvent to obtain a gel film, and performing biaxial tension and high-temperature treatment to obtain a modified polyimide film; and

and S3, sequentially carrying out carbonization treatment and high-temperature graphitization treatment on the obtained modified polyimide film in an inert atmosphere to obtain the artificial graphite composite film.

The reason why the cellulose nanocrystals are dispersed in the solvent in advance in step S1 is: the surface of the cellulose nanocrystal is provided with polar functional groups such as hydroxyl, carboxyl or amino, and the like, and the functional groups can partially participate in the reaction in the polycondensation reaction to form covalent bond connection with polyamic acid, so that the cellulose nanocrystal and polyamic acid are firmly combined. Preferably, the functional group is at least one of a hydroxyl group, a carboxyl group and an amino group.

The source of the cellulose nanocrystal is not limited, and the cellulose nanocrystal can be prepared by a TEMPO oxidation method of a crude fiber raw material, comprises one or more of cotton fiber, bamboo fiber, microcrystalline fiber and flax fiber, and is preferably prepared by taking the microcrystalline fiber and the cotton fiber as raw materials. The cellulose nanocrystal is low in manufacturing cost and wide in source. Preferably, the crystallinity of the cellulose nanocrystal is more than 85%, the length is 100nm-200nm, and the diameter is 5nm-20 nm.

The method of dispersing the cellulose nanocrystals in the solvent may be physical blending means such as at least one of magnetic stirring, mechanical stirring, high-speed homogenization, water bath ultrasound, probe ultrasound.

The content of the cellulose nanocrystal in the polyamic acid mixture is 0.4-8.0%. Preferably, the cellulose nanocrystals are contained in the polyamic acid mixture in an amount of 1.0% to 5.0% considering that too little cellulose nanocrystal addition is insufficient to form a sufficiently effective connection between all graphite wafer structures, while excessive cellulose nanocrystal addition increases the spacing between adjacent graphite wafer structures and deteriorates mechanical properties.

The mass ratio of the cellulose nanocrystal to the sum of the aromatic diamine and the aromatic dianhydride monomer is 1 (1-49). Preferably, the mass ratio of the cellulose nanocrystal to the sum of the aromatic diamine and the aromatic dianhydride monomer is 1 (3-19) for the same reason as the above-mentioned preference of the cellulose nanocrystal.

The solvent is organic polar solvent, so that the raw materials can be uniformly dispersed, and specifically can be one of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide and butyl acetate. The aromatic diamine monomer is one of 4,4 '-diaminodiphenyl ether, 1, 4-p-phenylenediamine, 3, 4' -diaminodiphenyl ether and 4, 4-diaminodiphenylmethane. The aromatic dianhydride monomer comprises one of 1,2,4, 5-pyromellitic dianhydride, 3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride, 4,4 ' -benzophenone dianhydride and 3,3 ', 4,4 ' -diphenyl ether tetracarboxylic dianhydride. The molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 1:1-1: 1.05. The temperature of the polycondensation reaction is 2-25 ℃, and the time of the polycondensation reaction is 4-18 hours. In order to make the polyamic acid have a larger molecular weight, it is preferable that the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 1:1 to 1:1.01, the temperature of the polycondensation reaction is 2 ℃ to 5 ℃, and the time of the polycondensation reaction is 6 hours to 8 hours.

It is noted that the aromatic dianhydride monomer is added last, and preferably slowly with mechanical agitation, so that the polycondensation reaction proceeds sufficiently.

In step S2, the step of chemically imidizing the polyamic acid mixture is specifically: and adding a dehydrating agent and a catalyst to the polyamic acid mixture, wherein the catalyst comprises at least one of triethylamine, pyridine, diethyl pyridine and isoquinoline, and the dehydrating agent comprises at least one of acetic anhydride, dicyclohexyl carbodiimide, benzoic anhydride and sodium tert-butoxide. The stretching process can be as follows: and (3) carrying out biaxial stretching at the temperature of 80-140 ℃, wherein the stretching ratio is 1.1-1.9 times, and preferably 1.1-1.5 times. Further, the membrane after biaxial stretching is respectively kept for 5min to 30min at the temperature of 120 ℃ to 200 ℃ and for 5min to 20min at the temperature of 200 ℃ to 350 ℃ under the protection of nitrogen and tension.

In this case, the thickness of the modified polyimide film obtained is 10 μm to 100. mu.m, preferably 30 μm to 100. mu.m.

In step S3, the carbonization process includes a first treatment process and a second treatment process, the first treatment process is performed by maintaining the temperature at 600 ℃ to 1000 ℃ for 0.5 hour to 1.5 hours, and the second treatment process is performed by maintaining the temperature at 1200 ℃ to 1600 ℃ for 0.5 hour to 1.5 hours. Preferably, the carbonization process includes a first treatment process of maintaining the temperature at 800-900 ℃ for 1-1.5 hours and a second treatment process of maintaining the temperature at 1500-1600 ℃ for 0.5-1 hour, considering that too low temperature or too little time may result in a low carbonization degree, and too high temperature or too long time may cause damage to the modified polyimide film.

The high-temperature graphitization process is that heat preservation is carried out for 0.5 to 1.5 hours at 2600 to 3000 ℃ under inert atmosphere. Preferably, the high temperature graphitization process is performed at 2800 deg.C-2850 deg.C for 0.5 hours to 1 hour under an inert atmosphere, considering that too low a temperature or too little time may result in a low graphitization degree of the carbonized film, while too high a temperature or too long a time may cause excessive energy loss or possible damage to the film.

Of course, in practice, the modified polyimide film may be processed by using additional graphite paper as a substrate during carbonization and high-temperature graphitization. The resulting artificial graphite composite membrane may, of course, be subjected to a further calendering step. The role of calendering is: eliminate the gas remained in the film during the sintering process, so that the film structure is more compact and uniform for better application.

The thickness of the artificial graphite composite membrane is 20-60 microns, preferably 20-40 microns.

Hereinafter, the artificial graphite composite membrane and the method for preparing the artificial graphite composite membrane according to the present invention will be described with reference to examples.

Example 1

(1) Adding a certain amount of cellulose nanocrystalline with carboxylated surfaces into N-methyl pyrrolidone, and uniformly dispersing the cellulose nanocrystalline in an organic solvent through water bath ultrasound. Adding 4, 4' -diaminodiphenyl ether into the solution, mechanically stirring to fully dissolve the solution, then reducing the temperature of the system to 5 ℃, gradually adding equal molar amount of pyromellitic dianhydride while stirring, reacting for 6 hours, so that the viscosity of the system is obviously increased, and obtaining a viscous polyamide acid mixture modified by the cellulose nanocrystal. Wherein the mass percentage of the cellulose nanocrystal in the polyamic acid mixture is 1.0%. Since the molar ratios of the aromatic diamine monomer and the aromatic dianhydride monomer are equal, it is assumed that the polycondensation reaction is complete and the polyamic acid mixture has a solids content of about 20 wt%.

(2) Adding acetic anhydride and pyridine to the cellulose nanocrystal-modified polyamic acid mixture obtained in step (1) with mechanical stirring. After being mixed evenly, the air bubbles in the solution are removed by multiple air exhaust and air release in a vacuum oven, and then the film is quickly formed on a flat and clean glass plate by casting. Heating the platform to 50-60 deg.C for 10-20min, and 80-100 deg.C for 10-20min, and volatilizing solvent to obtain non-sticky gel film. Further, the glass plate was peeled off, and the resultant was put into a biaxial stretching jig to be subjected to biaxial stretching treatment, with the stretching ratio being controlled to 1.4. And then placing the film into an oven under the action of tension, and keeping the film at 150 ℃ for 20min and 320 ℃ for 15min to obtain the modified polyimide film.

(3) Cutting the polyimide film doped with the cellulose nanocrystals into a proper size, crossly laminating the polyimide film with graphite paper, applying a certain pressure, putting the polyimide film into a carbonization furnace under the protection of argon, raising the temperature to 800 ℃ according to a program, keeping the temperature for 60min, keeping the temperature at 1500 ℃ for 40min, and then naturally cooling to room temperature to obtain the carbonized film.

(4) And (3) alternately laminating the obtained carbonized film and graphite paper, applying a certain pressure, putting the carbonized film and the graphite paper into a graphitization furnace under the protection of argon, raising the temperature to 2800 ℃ according to a program, keeping the temperature for 40min, naturally cooling the carbonized film to room temperature, and performing calendaring treatment to obtain the final rod-shaped crystal carbon composite artificial graphite composite film.

The in-plane and vertical heat conduction performance of the obtained artificial graphite composite film is tested by a laser flash method heat conduction tester LFA467 of Germany Chineseme corporation, and the test result is as follows: the in-plane and perpendicular thermal conductivities are shown in table 1. The following examples were also tested using this.

Example 2

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the surface-carboxylated cellulose nanocrystal in the polyamic acid mixture in step (1) is 2.0%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 3

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the surface-carboxylated cellulose nanocrystal in the polyamic acid mixture in step (1) is 3.0%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 4

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the cellulose nanocrystal in the polyamic acid mixture in step (1) is 4.0%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 5

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the surface-carboxylated cellulose nanocrystal in the polyamic acid mixture in step (1) is 5.0%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 6

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the surface-carboxylated cellulose nanocrystal in the polyamic acid mixture in step (1) is 0.4%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 7

The same parts of this example as those of example 1 are not repeated, and the difference from example 1 is that the mass percentage of the surface-carboxylated cellulose nanocrystal in the polyamic acid mixture in step (1) is 8.0%. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 8

The same parts of this embodiment as those of embodiment 2 are not repeated, and the difference from embodiment 2 is that the cellulose nanocrystal added in step (1) is a surface-hydroxylated cellulose nanocrystal. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 9

The same parts of this embodiment as those of embodiment 2 are not repeated, and the difference from embodiment 2 is that the cellulose nanocrystal added in step (1) is a surface aminated cellulose nanocrystal. The heat transfer properties of the finally obtained artificial graphite composite membrane are shown in table 1.

Example 10

The same parts of this example as those of example 2 are not repeated, and the difference from example 2 is that the cellulose nanocrystals added in step (1) are surface-esterified cellulose nanocrystals, and the heat conductivity of the finally obtained artificial graphite composite membrane is shown in table 1.

Example 11

The same parts as those in example 2 are not repeated, and the difference from example 2 is that the thickness of the artificial graphite composite film obtained after the calendering in step (4) is 20 μm, and the heat conductivity of the artificial graphite composite film finally obtained is shown in table 1.

Example 12

The same parts as those in example 2 are not repeated, and the difference from example 2 is that the thickness of the artificial graphite composite film obtained after the calendering in step (4) is 40 μm, and the heat conductivity of the artificial graphite composite film finally obtained is shown in table 1.

Example 13

The same parts of this example as those of example 2 are not repeated, and the difference from example 2 is that the thickness of the artificial graphite composite film obtained after the calendering in step (4) is 50 μm, and the heat conductivity of the finally obtained artificial graphite composite film is shown in table 1.

Example 14

The same parts of this example as those of example 2 are not repeated, and the difference from example 2 is that the thickness of the artificial graphite composite film obtained after the calendering in step (4) is 60 μm, and the heat conductivity of the finally obtained artificial graphite composite film is shown in table 1.

In order to better illustrate the advantageous effects of the artificial graphite composite membrane of the present invention, the present invention also provides comparative example 1.

Comparative example 1

The same parts of the comparative example and example 1 are not repeated, and the difference from example 1 is that the cellulose nanocrystals are not added in the step (1), and the heat conduction performance of the finally obtained artificial graphite composite membrane is shown in table 1.

TABLE 1

As can be seen from Table 1, comparing example 2 with examples 8-10, it can be seen that the different modification of the functionalized cellulose nanocrystals provided by the present invention have different enhancing effects on the obtained artificial graphite composite membrane, wherein the effects of carboxyl and hydroxyl are most prominentIt is presumed that the covalent bond is formed better and the bond is tighter with the polyimide. As can be seen from comparison of examples 1 to 7, the content of the cellulose nanocrystals in the polyamic acid mixture was in the range of 1.0 wt% to 5.0 wt%, and the resulting artificial graphite composite film was excellent in thermal conductivity. Comparing example 2 with examples 11 to 14, it can be seen that the artificial graphite composite membrane can realize an in-plane thermal conductivity of more than 1200 W.m in the thickness range of 20 μm to 60 μm^-1·K^-1And a thermal conductivity greater than 10 W.m in the vertical direction^-1·K^-1。

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The preparation method of the artificial graphite composite membrane is characterized by comprising the following steps of:

carrying out chemical imidization treatment on the obtained polyamic acid mixture, removing partial solvent to obtain a gel film, and carrying out biaxial tension and high-temperature treatment to obtain a modified polyimide film; and

and sequentially carrying out carbonization treatment and high-temperature graphitization treatment on the obtained modified polyimide film in an inert atmosphere to obtain the artificial graphite composite film.

2. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the surface of the cellulose nanocrystal has a functional group, and the functional group is at least one of hydroxyl, carboxyl, amino and ester.

3. The preparation method of the artificial graphite composite film according to claim 1, wherein the content of the cellulose nanocrystal in the polyamic acid mixture is 0.4% -8.0%, and the mass ratio of the cellulose nanocrystal to the sum of the aromatic diamine and the aromatic dianhydride monomer is 1 (1-49).

4. The method for preparing the artificial graphite composite membrane according to claim 3, wherein the solvent is one of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, and butyl acetate.

5. The method of preparing the artificial graphite composite film according to claim 1, wherein the aromatic diamine monomer is one of 4,4 ' -diaminodiphenyl ether, 1, 4-p-phenylenediamine, 3,4 ' -diaminodiphenyl ether and 4, 4-diaminodiphenylmethane, and the aromatic dianhydride monomer includes one of 1,2,4, 5-pyromellitic dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -benzophenone dianhydride and 3,3 ', 4,4 ' -diphenylethertetracarboxylic dianhydride.

6. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 1:1 to 1: 1.05.

7. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the temperature of the polycondensation reaction is 2 ℃ to 25 ℃, and the time of the polycondensation reaction is 4 hours to 18 hours.

8. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the carbonization process comprises a first treatment process and a second treatment process, the first treatment process is performed by keeping the temperature at 600-1000 ℃ for 0.5-1.5 hours, and the second treatment process is performed by keeping the temperature at 1200-1600 ℃ for 0.5-1.5 hours.

9. A method for preparing the artificial graphite composite membrane according to claim 1, wherein the thickness of the artificial graphite composite membrane is 20 to 60 μm.

10. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the high temperature graphitization process is heat preservation at 2600 ℃ to 3000 ℃ for 0.5 hour to 1.5 hours under an inert atmosphere.

11. The method for preparing the artificial graphite composite membrane according to claim 1, wherein the chemical imidization treatment of the polyamic acid mixture comprises: and adding a dehydrating agent and a catalyst to the polyamic acid mixture, wherein the catalyst comprises at least one of triethylamine, pyridine, diethyl pyridine and isoquinoline, and the dehydrating agent comprises at least one of acetic anhydride, dicyclohexyl carbodiimide, benzoic anhydride and sodium tert-butoxide.

12. An artificial graphite composite membrane obtained by the production method according to any one of claims 1 to 11, wherein the artificial graphite composite membrane comprises graphite wafer structures and rod-like crystalline carbon aggregates located between adjacent graphite wafer structures.

13. The artificial graphite composite membrane according to claim 12, wherein the artificial graphite composite membrane has a thermal conductivity in a direction perpendicular to a surface thereof>10W·m^-1·K^-1。

14. Use of the artificial graphite composite membrane according to claim 12 in the field of heat conduction.