Thermally conductive film preparation method

Abstract

The present invention provides a method for preparing a thermally conductive film, comprising: coating a graphene oxide slurry on a substrate surface, baking to form a graphene oxide film, peeling off the substrate and rolling up the graphene oxide film; performing a thermal reduction treatment on the rolled up graphene oxide film to obtain a graphene film; performing a Joule heat graphitization treatment on the graphene film; and performing a calendering treatment on the graphene film after the Joule heat graphitization treatment to obtain a thermally conductive film. The present invention realizes roll-to-roll production, which can significantly improve production efficiency and reduce production costs.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal conductive films, and in particular relates to a method for preparing a thermal conductive film. Background Art

[0002] In recent years, with the development of 5G mobile terminal equipment, the integration of its core SOC chips has become higher and higher, and the heat generation of chips has become more and more serious. In the process of mobile phone design, the requirements for thermal conductivity and heat dissipation have become higher and higher. Traditional metal foil heat dissipation, natural graphite heat dissipation, and even artificial graphite heat dissipation solutions can no longer meet the needs of high heat flux. Graphene thermal conductive film is a new type of thermal conductive and heat dissipation material developed in recent years. It has the characteristics of high thermal conductivity and high heat flux. It has been well applied in many flagship mobile phones and is expected to solve the thermal management problem of mobile terminal equipment.

[0003] At present, in the production process of graphene thermal conductive film, there are still problems such as low yield rate and sheet production. However, traditional artificial graphite thermal conductive film has basically achieved roll-to-roll production in the production process, with high production efficiency and high yield rate, and its cost is advantageous compared with graphene thermal conductive film. A major constraint on the roll-to-roll production of graphene thermal conductive film is the serious expansion of the material and the decline in the mechanical properties of the material during the heat treatment process. This is because the raw material of graphene thermal conductive film is generally graphene oxide. During the heat treatment process, the violent oxygen loss reaction causes serious expansion of the material. In addition, at present, neither artificial graphite thermal conductive film nor graphene thermal conductive film has achieved roll-to-roll production, which is also an important factor that prevents the production cost of thermal conductive film from continuing to decline. Summary of the invention

[0004] In view of one or more of the problems existing in the prior art, the present invention provides a method for preparing a thermally conductive film, comprising:

[0005] Step S1, coating a graphene oxide slurry on a substrate surface, baking it into a graphene oxide film, and performing substrate peeling and winding of the graphene oxide film;

[0006] Step S2, performing a thermal reduction treatment on the rolled-up graphene oxide film to obtain a graphene film;

[0007] Step S3, performing Joule heat graphitization treatment on the graphene film;

[0008] Step S4, rolling the graphene film after the Joule heat graphitization treatment to obtain a thermally conductive film.

[0009] Optionally, the step S1 includes:

[0010] The graphene oxide slurry is coated on the surface of the substrate by using a coating machine;

[0011] The graphene oxide slurry coated on the surface of the substrate is baked to form a film, and then peeled off from the substrate and rolled up. Preferably, the baking conditions after coating are 50-150°C, and the baking time is 1-60 minutes. The baking temperature of the graphene oxide film cannot be too high to ensure that the surface of the film is dry while there is a certain amount of moisture in the film, so that the film can maintain good flexibility, peelability and rolling characteristics. Preferably, the baking temperature is 60-80°C and the time is 20-40 minutes.

[0012] Optionally, the graphene oxide slurry has a solid content of 1-30 wt % and a viscosity of 1000-100000 cps.

[0013] Optionally, the substrate is a PE (polyethylene) mesh, a PP (polypropylene) filter cloth or a silica gel protective film.

[0014] Optionally, step S2 includes:

[0015] An atmosphere-protected push-plate furnace is used to place the graphene oxide film in the push-plate furnace. Discharging and collecting traction devices are set at the feed inlet and discharge outlet of the push-plate furnace to achieve roll-to-roll discharging and collecting.

[0016] A protective gas is introduced into the push plate furnace. Preferably, the protective gas is high-purity nitrogen or high-purity argon. Further preferably, the oxygen content of the protective gas is controlled below 60 ppm. The low oxygen content ensures that the graphite oxide film is not oxidized during the thermal reduction process.

[0017] Setting the temperature of multiple temperature zones in the push plate furnace and the running speed of the graphene oxide film;

[0018] The graphene oxide film is thermally reduced in multiple temperature ranges of a push plate furnace according to the set running speed of the film to obtain a graphene film.

[0019] Optionally, the step S2 further includes:

[0020] The graphene film is subjected to continuous calendering treatment. Preferably, the pressure in the calendering treatment is 2-20 MPa. During the thermal reduction process, the graphene film expands more severely, resulting in a decrease in the tensile strength of the graphene film. Therefore, it is necessary to improve the tensile strength of the graphene film by calendering to facilitate winding and subsequent graphitization treatment.

[0021] The calendered graphene film is rolled up.

[0022] Optionally, the multiple temperature intervals include a first low temperature zone, a second medium temperature zone and a third high temperature zone, wherein the temperature of the first low temperature zone is set from room temperature to 300°C; the temperature of the second medium temperature zone is set from 300°C to 800°C; the temperature of the third high temperature zone is set from 800°C to 1200°C; preferably, the total length of a temperature interval is 20-100 meters; preferably, the running speed of the graphene film is 0.1-1m / min. In different temperature intervals, the deoxidation and exhaust processes of graphene oxide are different, and the effects on the expansion of the graphene film are different. The severe deoxidation and exhaust processes may cause the graphene film to break into powder.

[0023] Optionally, step S3 includes:

[0024] A Joule heat graphitization zone is set up in a push plate furnace protected by an atmosphere;

[0025] Roll-to-roll feeding and receiving devices are set up in the feeding and discharging areas of the atmosphere-protected push-plate furnace;

[0026] Multiple pairs of rolled graphite electrodes in the form of upper and lower rollers are used to perform continuous Joule heat graphitization treatment on the passing graphene film. Preferably, the Joule heat graphitization temperature is 2400-3100°C, and the running speed of the graphene film is 0.05-1m / min. 2400-3100°C can ensure the graphitization effect. The higher the temperature, the better. The running speed controls the graphitization time, and the slower the speed, the better.

[0027] Optionally, step S3 includes:

[0028] A Joule heat graphitization zone is set up in a push plate furnace protected by an atmosphere;

[0029] Roll-to-roll feeding and receiving devices are set up in the feeding and discharging areas of the atmosphere-protected push-plate furnace;

[0030] The graphene film is semi-continuously treated with Joule heat graphitization using multiple pairs of compacted rolled graphite electrodes. Preferably, the Joule heat graphitization temperature is 2400-3100°C, and the single treatment time is 1-60s. 2400-3100°C can ensure the graphitization effect, and the higher the temperature, the better; the single treatment time controls the graphitization time, and the slower the speed, the better.

[0031] Optionally, step S4 includes:

[0032] The graphene film that has been graphitized by Joule heat is calendered by a vacuum calender or a double-roll calender. Preferably, the calendering pressure is 50-200 MPa to ensure that the graphene thermal conductive film has a density close to that of graphite, improve the mechanical properties, and control the thermal conductivity.

[0033] Optionally, step S4 includes:

[0034] Cutting the rolled graphene film after Joule heat graphitization into sheet graphene films;

[0035] The sheet-type graphene film is calendered using a vacuum calender.

[0036] The present invention adopts graphene oxide slurry, which is coated and then subjected to roll-to-roll reduction in a tunnel-type push-plate furnace protected by inert gas. After calendering, it is graphitized by Joule heat graphitization, and finally roll-to-roll calendering is performed by calendering equipment. Based on this preparation method, roll-to-roll production can be achieved throughout the entire process after optimization, which can significantly improve production efficiency and reduce production costs.

[0037] The present invention starts from the pretreatment of the graphene oxide material after coating, adopts a roll-to-roll heat treatment process to achieve roll-to-roll production of the thermally conductive film, and obtains a graphene film that has undergone high-temperature thermal reduction; and adopts a Joule heat graphitization treatment process to efficiently obtain a graphitized thermally treated graphene film. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding 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:

[0039] Figure 1 It is a schematic diagram of a flow chart of the method for preparing the thermal conductive film of the present invention. DETAILED DESCRIPTION

[0040] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0041] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0042] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0043] Embodiment 1:

[0044] The preparation method of the thermal conductive film comprises:

[0045] 1) coating a graphene oxide slurry on the surface of a PP porous membrane substrate, wherein the solid content of the graphene oxide slurry is 4%, the coating thickness is 1.8 mm, and the viscosity of the graphene oxide slurry is 18000 cps;

[0046] 2) baking the coated graphene oxide film in an IR tunnel furnace at a temperature of 80° C. for 30 minutes, and rolling up after baking, while peeling off the PP porous film substrate;

[0047] 3) placing the baked graphene oxide film into an atmosphere push plate furnace, and using a roll-to-roll unloading and receiving device;

[0048] 4) High-purity nitrogen protective gas is introduced into the push plate furnace, and the oxygen content is controlled at 50ppm at the discharge port and the receiving port, and controlled at 10ppm in the heating zone;

[0049] 5) Multiple temperature zones are set in the push plate furnace. The first low temperature zone has a total length of 100 meters and the temperature is set from 30 to 300°C; the second medium temperature zone has a total length of 80 meters and the temperature is set from 300°C to 800°C; the third high temperature zone has a total length of 60 meters and the temperature is set from 800°C to 1200°C; the graphene oxide film runs at a speed of 0.5m / min;

[0050] 6) Before rolling up, the graphene film is subjected to continuous calendering treatment, the pressure of the calendering process is 10 MPa, and after calendering, the film is rolled up to complete the thermal reduction treatment;

[0051] 7) A Joule heat graphitization zone is set in the atmosphere pusher furnace, and roll-to-roll feeding and receiving devices are set in the feeding zone and the discharging zone of the atmosphere pusher furnace; high-purity nitrogen protective gas is introduced into the pusher furnace, and the oxygen content is controlled at 50ppm at the discharge port and the receiving port, and controlled at 10ppm in the heating zone;

[0052] 8) using a rolled graphite electrode in the form of an upper roller and a lower roller to continuously graphitize the reduced graphene film using Joule heat, wherein the Joule heat graphitization temperature is 2800° C. During the continuous Joule heat graphitization, the graphene film is operated at a speed of 0.3 m / min;

[0053] 9) The graphene film treated with Joule heat graphitization is calendered by a double-roll calender to obtain a thermally conductive film; the calendering pressure is 70 MPa.

[0054] In this embodiment, after the graphitization treatment is completed, the chipping machine is not used for treatment, thereby preventing the defect that the Joule heat temperature of the contact area of ​​the graphite electrode is insufficient to reach the graphitization temperature when the chipping machine is used for treatment.

[0055] Embodiment 2:

[0056] The thermal conductive film preparation method comprises:

[0057] 1) coating a graphene oxide slurry on the surface of a PP porous membrane substrate, wherein the solid content of the graphene oxide slurry is 4%, the coating thickness is 1.8 mm, and the viscosity of the graphene oxide slurry is 18000 cps;

[0058] 2) baking the coated graphene oxide film in an IR tunnel furnace at a temperature of 80° C. for 30 minutes, and rolling up after baking, while peeling off the PP porous film substrate;

[0059] 3) placing the baked graphene oxide film into an atmosphere push plate furnace, and using a roll-to-roll unloading and receiving device;

[0060] 4) High-purity nitrogen protective gas is introduced into the push plate furnace, and the oxygen content is controlled at 50ppm at the discharge port and the receiving port, and controlled at 10ppm in the heating zone;

[0061] 5) Multiple temperature zones are set in the push plate furnace. The first low temperature zone has a total length of 100 meters and the temperature is set from 30 to 300°C; the second medium temperature zone has a total length of 80 meters and the temperature is set from 300°C to 800°C; the third high temperature zone has a total length of 60 meters and the temperature is set from 800°C to 1200°C; the graphene oxide film runs at a speed of 0.3m / min;

[0062] 6) Before rolling up, the graphene film is subjected to continuous calendering treatment, the pressure of the calendering process is 8 MPa, and after calendering, the film is rolled up to complete the thermal reduction treatment;

[0063] 7) A Joule heat graphitization zone is set in the atmosphere pusher furnace, and roll-to-roll feeding and receiving devices are set in the feeding zone and the discharging zone of the atmosphere pusher furnace; high-purity nitrogen protective gas is introduced into the pusher furnace, and the oxygen content is controlled at 50ppm at the discharge port and the receiving port, and controlled at 10ppm in the heating zone;

[0064] 8) The reduced graphene film is subjected to semi-continuous Joule heat graphitization treatment using compressed upper and lower electrodes, the Joule heat graphitization temperature is 2800°C, and the single treatment time is 15 seconds; the graphene film is subjected to semi-continuous movement, and an optical recognition device is used to achieve semi-continuous graphitization on the surface of the film, wherein the graphite electrode is in contact with the graphene film.

[0065] 9) A vacuum calender is used to calender the graphene sheet film that has been graphitized by Joule heat to obtain a thermal conductive film; the calendering pressure is 65 MPa.

[0066] The thermally conductive films of Examples 1 and 2 of the present invention were taken as samples 1 and 2, and the graphene thermally conductive film prepared in the prior art at 2850° C. using a high-temperature graphitization furnace was taken as sample 3 (graphitization treatment was performed at 2850° C. for 10 h using a conventional high-temperature graphitization furnace). The in-plane thermal conductivity of the thermally conductive film was tested, as shown in Table 1 below:

[0067] Table 1

[0068] Sample No. Thickness(μm) <![CDATA[Density (g / cm 3 )]]> Thermal conductivity (W / mK) 1 25 1.82 1180 2 24 1.80 1165 3 25 1.84 1210

[0069] From the above table, it can be seen that the thermal conductivity of the thermal conductive film obtained by the thermal conductive film preparation method of the present invention is slightly different from that of the graphene film prepared by a high-temperature graphitization furnace. The present invention adopts graphene oxide slurry, which is coated and then rolled to roll reduction in a tunnel push plate furnace protected by inert gas. After the first calendering, Joule heat graphitization is used for graphitization treatment, and finally a calendering device is used for the second roll calendering (the first calendering is to improve the mechanical properties and thermal conductivity of the graphene film. In addition to the mechanical properties and thermal conductivity, the second calendering also needs to improve the density. Therefore, the pressure of the second calendering is greater than the pressure of the first calendering). After optimization, roll-to-roll production can be achieved throughout the process, which can significantly improve production efficiency and reduce production costs. Compared with the traditional thermal conductive film preparation process, in the high-temperature graphitization stage, the energy consumed by Joule heat graphitization treatment is only 1 / 4-1 / 2 of the (electricity) energy consumed by vacuum graphitization furnace heat treatment, and the energy consumption has obvious advantages.

[0070] In the existing production process of graphene thermal conductive film, the graphene thermal conductive film cannot be produced in a full roll-to-roll manner during the production process, which is an important factor affecting the production efficiency, production yield and production cost of the graphene thermal conductive film. The present invention starts from the pretreatment of the graphene material end after coating, and adopts a roll-to-roll processing method in the thermal reduction treatment stage of the graphene film, which can achieve high-efficiency, low-cost and high-yield preparation, abandoning the traditional carbonization furnace equipment and sheet processing method, and realizing the roll-to-roll production of the thermal conductive film.

[0071] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a thermally conductive film, characterized in that: include: Step S1, coating a graphene oxide slurry on a substrate surface, baking it into a graphene oxide film, and performing substrate peeling and winding of the graphene oxide film; Step S2, performing a thermal reduction treatment on the rolled-up graphene oxide film to obtain a graphene film; Step S3, performing Joule heat graphitization treatment on the graphene film; Step S4, calendering the graphene film after Joule heat graphitization to obtain a thermally conductive film, wherein the calendering pressure is 50-200 MPa; The step S2 comprises: using an atmosphere-protected push-plate furnace, placing the graphene oxide film in the push-plate furnace, and setting a material discharge and material collection traction device at the feed inlet and the discharge outlet of the push-plate furnace to realize roll-to-roll material discharge and collection; The step S2 further comprises: The graphene film is subjected to continuous calendering treatment, the pressure during the calendering treatment is 2-20 MPa, and the calendered graphene film is rolled up; The step S3 comprises: setting a Joule heat graphitization zone in the atmosphere-protected push plate furnace; setting a roll-to-roll feeding and receiving device in the feeding zone and the discharging zone of the atmosphere-protected push plate furnace; Roll-to-roll production is achieved throughout the entire process.

2. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S1 comprises: The graphene oxide slurry is coated on the surface of the substrate by using a coating machine; The graphene oxide slurry coated on the surface of the substrate is baked to form a film, and then peeled off from the substrate and rolled up.

3. The method for preparing a thermally conductive film according to claim 2, characterized in that: In the step S1, the baking temperature after coating is 50-150° C., and the baking time is 1-60 minutes.

4. The method for preparing a thermally conductive film according to claim 3, characterized in that: In the step S1, the baking temperature is 60-80° C. and the baking time is 20-40 minutes.

5. The method for preparing a thermally conductive film according to claim 1 or 2, characterized in that: The graphene oxide slurry has a solid content of 1-30 wt % and a viscosity of 1000-100000 cps; or / and The substrate is a PE (polyethylene) net, a PP (polypropylene) filter cloth or a silica gel protective film.

6. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S2 comprises: A protective gas is introduced into the push plate furnace; Setting the temperature of multiple temperature zones in the push plate furnace and the running speed of the graphene oxide film; The graphene oxide film is thermally reduced in multiple temperature ranges of a push plate furnace according to the set running speed of the film to obtain a graphene film.

7. The method for preparing a thermally conductive film according to claim 6, characterized in that: The protective gas is high-purity nitrogen or high-purity argon.

8. The method for preparing a thermally conductive film according to claim 7, characterized in that: The oxygen content of the protective gas is controlled below 60 ppm.

9. The method for preparing a thermally conductive film according to claim 6, characterized in that: The multiple temperature intervals include a first low temperature zone, a second medium temperature zone and a third high temperature zone. The first low temperature zone has a temperature set from room temperature to 300°C; the second medium temperature zone has a temperature set from 300°C to 800°C; the third high temperature zone has a temperature set from 800°C to 1200°C.

10. The method for preparing a thermally conductive film according to claim 9, characterized in that: The total length of each of the multiple temperature intervals is 20-100 meters.

11. The method for preparing a thermally conductive film according to claim 10, characterized in that: The graphene oxide film runs at a speed of 0.1-1 m / min.

12. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S3 comprises: Multiple pairs of rolled graphite electrodes in the form of upper and lower rollers are used to perform continuous Joule heat graphitization treatment on the graphene film passing through.

13. The method for preparing a thermally conductive film according to claim 12, characterized in that: The Joule heat graphitization temperature is 2400-3100° C., and the graphene film running speed is 0.05-1 m / min.

14. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S3 comprises: Semi-continuous Joule heat graphitization treatment of graphene film is carried out using multiple pairs of compacted rolled graphite electrodes.

15. The method for preparing a thermally conductive film according to claim 14, characterized in that: The Joule heat graphitization temperature is 2400-3100° C., and the single treatment time is 1-60 s.

16. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S4 comprises: The graphene film that has been graphitized by Joule heat is calendered using a vacuum calender or a double-roll calender.

17. The method for preparing a thermally conductive film according to claim 1, characterized in that: The step S4 comprises: Cutting the rolled graphene film after Joule heat graphitization into sheet graphene films; The sheet-type graphene film is calendered using a vacuum calender.

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