CN118373689A - Ultra-high thermal conductivity graphite film and preparation method thereof - Google Patents

Abstract

The invention discloses an ultrahigh heat conduction graphite film and a preparation method thereof, and belongs to the technical field of heat conduction materials. The preparation method of the ultrahigh heat conduction graphite film comprises the following steps: (1) Putting the polyimide film into a high-temperature furnace for pyrolysis treatment; (2) Carbonizing the polyimide film subjected to pyrolysis treatment; (3) Heating the carbonized polyimide film to 2000 ℃ under the protection of inert gas, preserving heat, continuously heating to 2800-3000 ℃ to finish graphitization treatment, and naturally cooling to obtain a carbon foam film; (4) And calendaring the carbon foam film by a calendar to obtain the ultrahigh heat conduction graphite film. According to the invention, the temperature rising rate of the graphitization key section and the growth, development, stacking and orientation of the highest-temperature graphite microcrystal in the heat treatment process are regulated, the interlayer alignment uniformity is improved through proper calendaring parameters, the compact and smooth lamination is ensured, the defects are few, and the graphite film finished product with the ultrahigh heat conductivity is prepared.

Description

Ultra-high thermal conductive graphite film and preparation method thereof

Technical Field

The present invention relates to the technical field of thermal conductive materials, and in particular to an ultra-high thermal conductive graphite film and a preparation method thereof.

Background technique

With the continuous advancement of science and technology, especially the rapid development in aerospace technology, high-end electronics industry, LED chip materials and other fields, the integration of electronic equipment components is getting higher and higher, and the heat consumption and heat flux density generated by them are also showing a substantial increase. This high heat consumption and high heat flux density pose a severe challenge to the stability and reliability of electronic equipment, especially in high-power electronic devices, where heat dissipation has become a key factor restricting their performance improvement and life extension.

In the existing technology, graphite materials have become potential excellent heat dissipation materials due to their unique physical and chemical properties. Graphite is a non-metallic mineral composed of carbon elements, which has extremely high thermal conductivity and electrical conductivity, as well as good thermal stability and chemical stability. Artificial graphite film can be made by carbonizing polyimide (PI) under vacuum conditions at 1200-1300°C and then subjecting it to high-temperature graphitization treatment at 2800-3200°C. The graphite film prepared by this method has excellent thermal conductivity, and the preparation process is relatively simple, with a short cycle and low cost, which greatly promotes the development of graphite as a heat dissipation material. However, in actual preparation, polyimide film may undergo oxidation, cracking and other reactions during high-temperature treatment, resulting in a decrease in the performance of the graphite film; as the thickness of the polyimide film increases, it is easy to produce a graphite film with an uneven structure, thereby affecting the performance of the graphite film; in addition, the microstructures of the polyimide film, such as the crystallinity and orientation, will also affect the thermal conductivity of the graphite film. These problems need to be solved by optimizing the preparation process and parameters.

Summary of the invention

Based on the problems existing in the background technology, the present invention provides an ultra-high thermal conductivity graphite film and a preparation method thereof, by adjusting the heating rate of the key section of graphitization and the growth, development, stacking and orientation of the highest temperature graphite crystallites during the heat treatment process, and improving the uniformity of the interlayer arrangement through appropriate calendering parameters, ensuring that the sheets are tight and flat with few defects, and preparing a finished graphite film with ultra-high thermal conductivity.

The present invention is implemented by the following technical solutions:

The present invention discloses a method for preparing an ultra-high thermal conductive graphite film, comprising the following steps:

(1) placing the polyimide film in a high temperature furnace, heating it to 550-650° C. under vacuum conditions, and maintaining the temperature for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1500-1600° C., maintaining the temperature, and performing carbonization treatment;

(3) heating the carbonized polyimide film to 2000° C. under the protection of an inert gas, maintaining the temperature, and further heating the film to 2800-3000° C. to complete the graphitization treatment, and then cooling the film naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine to obtain an ultra-high thermal conductive graphite film.

Furthermore, in step (1), the thickness of the polyimide film is 38-300 μm.

Furthermore, in step (1), the vacuum condition is to maintain the pressure in the high-temperature furnace below 15 Pa.

Furthermore, in step (1), the temperature is raised to 550-650°C at a rate of 4-8°C/min and maintained for 0.5-1.5h.

Furthermore, in step (2), the temperature is raised to 1500-1600° C. at 3-5° C./min and maintained for 0.5-2 h.

Furthermore, in step (3), the inert gas is nitrogen or argon.

Furthermore, in step (3), the temperature is raised to 2000° C. at 0.5-1° C./min and maintained for 0.5-1 h.

Furthermore, in step (3), the temperature is raised to 2800-3000°C at 2-8°C/min and maintained for 0.2-0.5h.

Furthermore, in step (4), the pressure of the calender is 3-4 MPa.

The invention also discloses an ultra-high thermal conductive graphite film prepared by the method.

Beneficial effects of the present invention:

In the present invention, by adjusting the heating rate of the key graphitization stage and the growth, development, stacking and orientation of the highest temperature graphite crystallites during the heat treatment process, and improving the uniformity of the interlayer arrangement through appropriate calendering parameters, the sheets are ensured to be tight and flat with few defects, and a finished graphite film with ultra-high thermal conductivity is prepared.

In the conventional method of preparing graphite film with polyimide film, the thinner polyimide film is easier to form a uniform and thin graphite film during carbonization and graphitization, and the final graphite film has higher thermal conductivity and lower thermal resistance. As the thickness of the polyimide film increases, stress concentration is easily generated during the preparation process. These stresses will cause cracks or defects in the preparation process of the graphite film, thereby reducing the performance of the graphite film. Therefore, the thickness of the polyimide film used in the preparation of the graphite film is generally controlled within 100μm, and the thickness of the prepared graphite film is within 50μm, which limits the application of the graphite film. This phenomenon can be effectively prevented in the present invention, and a graphite film with a larger thickness and a high level of thermal conductivity can be prepared.

The method for preparing the ultra-high thermal conductive graphite film provided by the present invention has a simple preparation process and is applicable to polyimide films with a thickness of 38-300 μm. The prepared graphite film has high thermal conductivity and good appearance integrity and excellent performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide further explanation of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

FIG1 is a SEM image of the ultrahigh thermal conductive graphite film prepared in Example 1;

FIG2 is a SEM image of the graphite film prepared in Comparative Example 1;

FIG3 is a SEM image of the graphite film prepared in Comparative Example 2;

FIG4 is an appearance diagram of the ultra-high thermal conductive graphite film prepared in Example 1;

FIG5 is an appearance diagram of the graphite film prepared in Comparative Example 1;

FIG6 is an appearance diagram of the graphite film prepared in Comparative Example 2.

Detailed ways

The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

A method for preparing an ultra-high thermal conductive graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 0.5°C/min under nitrogen protection, keeping the temperature for 0.5h, and then heating it to 3000°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Example 2

A method for preparing an ultra-high thermal conductive graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 0.5°C/min under nitrogen protection, keeping the temperature for 0.5h, and then heating it to 2800°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Comparative Example 1

A method for preparing a graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 0.25°C/min under the protection of nitrogen, keeping the temperature for 0.5h, and then heating it to 3000°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Comparative Example 2

A method for preparing a graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 3°C/min under nitrogen protection, keeping the temperature for 0.5h, and then heating it to 3000°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Comparative Example 3

A method for preparing a graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 0.25°C/min under nitrogen protection, keeping the temperature for 0.5h, and then heating it to 2800°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Comparative Example 4

A method for preparing a graphite film comprises the following steps:

(1) placing a 200 μm thick polyimide film in a high temperature furnace, evacuating the furnace to keep the pressure below 15 Pa, heating the film to 600°C at a rate of 6°C/min, and keeping the temperature for 1 hour for pyrolysis treatment;

(2) heating the polyimide film after pyrolysis treatment to 1600°C at a rate of 5°C/min and keeping the temperature for 1 hour to perform carbonization treatment;

(3) heating the carbonized polyimide film to 2000°C at 3°C/min under nitrogen protection, keeping the temperature for 0.5h, and then heating it to 2800°C at 6°C/min, keeping the temperature for 0.5h to complete the graphitization treatment, and cooling it naturally to obtain a carbon foam film;

(4) The carbon foam film is calendered by a calendering machine with a pressure of 3.5 MPa to obtain an ultra-high thermal conductive graphite film.

Test example

The performance of the graphite films prepared in Examples 1-2 and Comparative Examples 1-4 was tested.

Thermal diffusivity test: NETZSCH LFA467 was used to test the thermal diffusivity of graphite film. The test temperature was set at room temperature (25°C), the voltage was 260V, the sampling time was 30ms, the detection area was 14mm, and the test sample size was a disc with a diameter of 2.54cm.

Density test: calculated by weight and size method;

Thermal conductivity: calculated based on thermal diffusivity, density and specific heat capacity (0.85 J/g*K);

The test results are shown in Table 1.

Table 1

It can be seen from the results in Table 1 that the graphite film prepared in Example 1 of the present invention has the best thermal conductivity. Example 2 reduces the maximum temperature of the graphitization treatment to 2800°C on the basis of Example 1, and finds that the thermal diffusion coefficient and thermal conductivity of the graphite film are significantly reduced. The thermal conductivity of graphite mainly depends on its lattice structure and electronic thermal conductivity. At low temperatures, the thermal conductivity of graphite is limited by lattice vibration. The lattice structure of graphite is composed of layered carbon atoms, and the bond structure between layers is weak. When the temperature is low, the vibration of the lattice structure is limited, resulting in low efficiency of heat energy transfer and low thermal conductivity. As the temperature increases, the vibration of the graphite lattice becomes more intense, and the bond structure between layers becomes more active. In this way, the efficiency of heat energy transfer inside the graphite will be improved, and the thermal conductivity will also increase. Comparative Examples 3 and 4 also reduce the maximum temperature of the graphitization treatment to 2800°C on the basis of Comparative Examples 1 and 2, and the thermal diffusion coefficient and thermal conductivity of the prepared graphite film are also reduced.

In Comparative Example 1, based on Example 1, the heating rate of the key section (1600-2000°C) is adjusted to 0.25°C/min. The heating is too slow, resulting in excessive graphitization of the graphite film. The graphite exhibits a mirror-like gloss as a whole, the foaming thickness decreases and the toughness is poor. After calendering, the graphite will have a poor appearance, thereby affecting the thermal conductivity of the graphite film.

In Comparative Example 2, based on Example 1, the heating rate of the key section (1600-2000°C) is adjusted to the conventional 3°C/min. Since a polyimide film with a thickness of 200 μm is used and a conventional heating rate is adopted, a structurally uneven graphite film will be produced, and further calendering by a calendering machine will cause more defects in the graphite film, thereby affecting the thermal conductivity of the graphite film.

Figures 1-3 are SEM images of the graphite films prepared in Example 1 and Comparative Examples 1-2. It can be seen from the figure that the cross section of the graphite film prepared in Example 1 is tight and flat with few defects; the heating rate of the key graphitization section (1600-2000°C) in the preparation process of Comparative Example 1 is 0.25°C/min, and the heating is too slow, resulting in excessive graphitization of the graphite film; the key graphitization section (1600-2000°C) in Comparative Example 2 adopts a conventional heating rate of 3°C/min, and the graphite gaps of the graphite film finally obtained are relatively disordered and have more defects. Figures 4-6 are the appearance pictures of the graphite films prepared in Example 1 and Comparative Examples 1-2, respectively.

Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For ordinary technicians in this field, any modifications, equivalent substitutions, improvements, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims (10)

1. The preparation method of the ultrahigh heat conduction graphite film is characterized by comprising the following steps of:

(1) Placing the polyimide film into a high-temperature furnace, heating to 550-650 ℃ under vacuum condition, preserving heat, and performing pyrolysis treatment;

(2) Continuously heating the polyimide film subjected to pyrolysis treatment to 1500-1600 ℃, preserving heat, and carbonizing;

(3) Heating the carbonized polyimide film to 2000 ℃ under the protection of inert gas, preserving heat, continuously heating to 2800-3000 ℃ to finish graphitization treatment, and naturally cooling to obtain a carbon foam film;

(4) And calendaring the carbon foam film by a calendar to obtain the ultrahigh heat conduction graphite film.

2. The method according to claim 1, wherein the polyimide film in step (1) has a thickness of 38 to 300. Mu.m.

3. The method of claim 1, wherein the vacuum condition in step (1) is to maintain the pressure in the high temperature furnace below 15Pa.

4. The method according to claim 1, wherein in the step (1), the temperature is raised to 550-650 ℃ at 4-8 ℃/min, and the temperature is kept for 0.5-1.5h.

5. The method according to claim 1, wherein in the step (2), the temperature is raised to 1500-1600 ℃ at 3-5 ℃/min, and the temperature is kept for 0.5-2h.

6. The method of claim 1, wherein the inert gas in step (3) is nitrogen or argon.

7. The method according to claim 1, wherein the temperature is raised to 2000 ℃ at 0.5-1 ℃/min in step (3), and the temperature is kept for 0.5-1h.

8. The method according to claim 1, wherein in the step (3), the temperature is raised to 2800-3000 ℃ at 2-8 ℃/min, and the temperature is kept for 0.2-0.5h.

9. The method according to claim 1, wherein the calender in step (4) has a pressure of 3 to 4MPa.

10. An ultra-high thermal conductivity graphite film prepared by the method of any one of claims 1-9.