A flexible thermal management composite film with oriented graphene and its preparation method

Abstract

This invention relates to a flexible thermal management composite film with oriented graphene and its preparation method, belonging to the field of heat dissipation technology. The flexible thermal management composite film with oriented graphene includes a graphene thermally conductive layer and a thermally conductive silicone rubber layer. The thermally conductive silicone rubber layer is made of thermally conductive silicone with a thermal conductivity of 3–8 W / m·K. The graphene thermally conductive layer is a thermally conductive unit formed by the oriented alignment of graphene materials. Graphene is combined with conductive silicone, and graphene oxide is dispersed using a good solvent. High-speed shearing action is provided to the graphene oxide dispersion through coating, spraying, and printing, thereby causing the graphene oxide sheets to align during the coating process, forming a layered film structure. A slit-type heated rolling technique provides good flowability of the silicone rubber and ensures the oriented alignment of the graphene oxide within it. Finally, a secondary vulcanization process efficiently forms a flexible thermal management composite film with controllable structure and high thermal conductivity.

Description

Technical Field

[0001] This invention relates to a flexible thermal management composite film with oriented graphene and its preparation method, belonging to the field of heat dissipation technology. Background Technology

[0002] With the rapid development of electronic and electrical integration technology and battery assembly technology, electronic components, logic circuits, and battery modules are gradually upgrading towards multi-core, high-performance, and high-power directions. The continuous pursuit of thinner, smaller, and faster-responding devices leads to a rapid accumulation of heat during operation, resulting in a significant decrease in reliability. Research shows that for every 2°C increase in temperature of electronic components, their reliability decreases by approximately 10%; for temperatures above 70°C, the reliability decreases by 5%; and for every 10°C increase, the failure rate increases exponentially by an order of magnitude. Therefore, it is essential to use highly thermally conductive interface / thermal conductive composite functional materials to effectively remove the heat generated by electronic devices, thereby ensuring the normal operation of electronic components and guaranteeing the product's lifespan and quality reliability. In power batteries, areas such as the battery pack's BMS system and terminals are prone to heat accumulation. Conversely, in cold regions / low-temperature environments, battery packs experience slow charging, low capacity, and reduced range due to cabin heating, resulting in a poor user experience. More seriously, lithium ions are prone to forming lithium dendrites that pierce the separator, leading to spontaneous combustion and affecting safety performance. Furthermore, prolonged use at low temperatures can cause batteries to be "permanently frozen." Therefore, it is possible to effectively dissipate the locally generated heat and use it for auxiliary heating of other areas of the battery pack, which can achieve the dual purpose of heat equalization and control of the battery pack system temperature.

[0003] The typical two-dimensional crystal structure of graphene can greatly reduce the adverse effects of phonon boundary scattering at grain boundaries and endow it with the phonon diffusion mode unique to low-dimensional systems, achieving a thermal conductivity of up to 5300 W / (m·K), even overturning Fourier's law (q = -K·ΔT) in its thermal conductivity mechanism. Its two-dimensional geometry, strong coupling with the matrix material, and low cost make graphene an ideal filler for interface materials. Haddon and Coworkers et al. composited graphene sheets with epoxy resin, achieving a thermal conductivity of 6.45 W / (m·K) (filler volume f = 25%). Patent CN105131607B prepared a three-dimensional carbon material composite thermally conductive silicone using modification technology, achieving a maximum thermal conductivity of 8.7 W / m·K through multiple contact mechanisms at points, lines, and surfaces. However, due to the two-dimensional nature of graphene, while its in-plane thermal conductivity is high, it is essentially powerless to improve its longitudinal thermal conductivity. Simply using conventional dispersion techniques to randomly align graphene within silicone rubber is insufficient to effectively utilize its high thermal conductivity. However, combining graphene with conductive silicone and using techniques to orient the graphene sheets perpendicular to the silicone rubber axis, fully leveraging the high thermal conductivity of the graphene surface, could potentially improve its thermal conductivity. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a flexible thermal management composite film with oriented graphene and its preparation method.

[0005] To achieve the above objectives, the present invention employs the following technical solutions:

[0006] A flexible thermal management composite film with oriented graphene includes a graphene thermally conductive layer and a thermally conductive silicone rubber layer; the thermally conductive silicone rubber layer is made of thermally conductive silicone with a thermal conductivity of 3-8 W / m·K; the graphene thermally conductive layer is a thermally conductive unit formed by oriented graphene material.

[0007] To achieve the oriented alignment of graphene and its efficient dispersion in silicone rubber, this invention provides, on the one hand, a method for modifying and dispersing graphene oxide in a good solvent system; on the other hand, it provides a mechanical slit extrusion technique to achieve the orientation of graphene oxide in a silicone rubber system.

[0008] A method for preparing a flexible thermal management composite film with oriented graphene includes the following steps:

[0009] Step 1: Disperse graphene oxide in an appropriate amount of good solvent to form a stable graphene oxide dispersion.

[0010] Step 2: Press the thermally conductive silicone rubber layer into a film with a thickness of 5-20 μm as needed;

[0011] Step 3: The graphene oxide dispersion from Step 1 is coated or printed onto the thermally conductive silicone rubber layer to form a graphene oxide coating with a thickness of 6 to 15 micrometers. After drying, a graphene oxide / thermally conductive silicone rubber composite material is obtained.

[0012] Step 4: Continue to process the thermally conductive silicone rubber layer according to the method in Step 2. Adhere the processed thermally conductive silicone rubber layer to the surface of the graphene oxide / thermally conductive silicone rubber composite material obtained in Step 3 and close to the graphene oxide side. Then form the second layer of graphene oxide / thermally conductive silicone rubber composite material according to the method in Step 3. Repeat the above steps 3 to 4 times to form a layer-by-layer assembled graphene oxide / thermally conductive silicone rubber composite material.

[0013] Step 5: Fold the graphene oxide / thermal conductive silicone rubber composite material assembled layer by layer in step 4 into 3 to 4 layers, and repeatedly fold and roll it 5 to 15 times through a slit-type heat-tracing roller press to form a thermal conductive silicone rubber composite material containing graphene oxide sheet orientation.

[0014] Step 6: Add an appropriate amount of crosslinking agent to the thermally conductive silicone rubber composite material containing graphene oxide sheet orientation, fold it according to actual needs, and then place it at a perpendicular angle to the vulcanizing machine plate according to the folding direction, and perform secondary vulcanization molding on the vulcanizing agent to obtain a flexible thermal management composite film with graphene orientation.

[0015] Furthermore, in step 1, a good solvent refers to a solvent that can simultaneously dissolve uncured silicone rubber and disperse graphene oxide, and the good solvent is one of n-hexane, n-heptane, petroleum ether, or xylene.

[0016] Furthermore, in step 1, the graphene oxide sheet has a diameter of 3–10 μm and a thickness of 1–5 layers.

[0017] Furthermore, the gap between the two rollers of the slit-type heated roller press is 0.5–10 μm, and the heating temperature is 80–200 °C.

[0018] Furthermore, the crosslinking agent is any one of methyl hydrogen silicone oil, condensation-type two-component silicone rubber, and methyltriacetoxysilane.

[0019] Furthermore, the secondary vulcanization molding includes two vulcanization processes, wherein the first vulcanization temperature is 170-180℃ and the second vulcanization temperature is 210-240℃.

[0020] Furthermore, the graphene oxide sheets have a diameter of 5–10 μm and a thickness of 2–3 layers.

[0021] Furthermore, the gap between the two rollers of the slit-type heat-tracing roller press is 0.5 to 3 μm, and the heat tracing temperature is 150 to 160°C.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention provides a flexible thermal management composite film with oriented graphene and its preparation method, which has the following advantages: (1) The good solvent dispersion technology for graphene oxide ensures a good contact interface between the graphene oxide dispersion and silicone rubber; (2) Coating, spraying, printing and other processes provide high-speed shearing action for the graphene oxide dispersion, thereby causing the graphene oxide sheets to orient during the coating process and forming a sheet-overlapping film structure; (3) The slit-type heated rolling technology can provide good fluidity of silicone rubber and oriented orientation of graphene oxide inside it; (4) The secondary vulcanization process, on the one hand, effectively removes the gas generated by heat processing under low-temperature vulcanization conditions, and on the other hand, high-temperature secondary vulcanization can realize the simultaneous vulcanization of silicone rubber and the synchronous reduction of graphene oxide, efficiently forming a flexible thermal management composite film with oriented graphene. This flexible thermal management composite film with oriented graphene has the characteristics of controllable structure and high thermal conductivity, and can be widely used in devices with high heat dissipation requirements such as smartphones, tablets, ultra-thin laptops, 5G high-power communications, and high-power electrical appliances. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the fabrication process of the flexible thermal management composite film with oriented graphene according to the present invention.

[0025] Figure 2 This is a schematic diagram of the graphene oxide / thermal conductive silicone rubber composite structure.

[0026] Figure 3 A schematic diagram of a flexible thermal management composite film structure with graphene orientation;

[0027] Among them: 1. Graphene oxide dispersion, 2. Graphene oxide coating, 3. Thermally conductive silicone rubber layer, 4. Multi-layer folded graphene oxide / thermally conductive silicone rubber composite material, 5. Slit-type heat-tracing roller pressing device, 6. Thermally conductive silicone rubber composite material containing oriented graphene oxide sheets, 7. Vulcanized plate, 8. Vertically oriented graphene. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] Figure 1 This is a schematic diagram illustrating the fabrication process of the flexible thermal management composite film with oriented graphene according to the present invention. The specific fabrication method includes the following steps:

[0031] First, 3g of graphene oxide with a diameter of 3 micrometers and a thickness of 2 layers was dispersed in 100mL of n-hexane solvent to form a stable graphene oxide dispersion. Second, a thermally conductive silicone rubber layer with a thermal conductivity of 8W / m·K was pressed into a film with a thickness of 15μm. Then, the above-mentioned graphene oxide dispersion with a thickness of 10 micrometers was coated onto one side of the thermally conductive silicone rubber layer by a coating method and dried to obtain a graphene oxide / thermally conductive silicone rubber composite material (e.g., ...). Figure 2 (As shown); Continue processing the thermally conductive silicone rubber layer according to the above method, attach the processed thermally conductive silicone rubber layer to the surface of the graphene oxide / thermally conductive silicone rubber composite material and close to the graphene oxide side, and then form a second layer of graphene oxide / thermally conductive silicone rubber composite material in the above manner. Repeat this process 3 to 4 times to form a layer-by-layer assembled graphene oxide / thermally conductive silicone rubber composite material; Next, fold the above composite material into 3 layers, and pass it through a slit-type heat-traced roller press with a heat tracing temperature of 120°C and a gap of 5 micrometers. Repeat the folding and rolling process 15 times to form a thermally conductive silicone rubber composite material containing graphene oxide sheet orientation; Finally, add an appropriate amount of methyl hydrogen silicone oil to the thermally conductive silicone rubber composite material containing graphene oxide sheet orientation, fold 30 layers, and then place it at a perpendicular angle to the vulcanizing machine plate according to the folding direction. Vulcanize it on the vulcanizing agent. The first vulcanization temperature is 170°C and the vulcanization time is 3 hours; the second vulcanization temperature is 230°C and the vulcanization time is 2 hours, thereby obtaining a flexible thermal management composite film with graphene orientation (e.g. Figure 3 (As shown). According to the ASTM D5470 heat flow method, its thermal conductivity was measured to be 13.2 W / m·K.

[0032] Example 2

[0033] First, a graphene-hexane dispersion with a sheet diameter of 8 μm and a thickness of 1 layer and a concentration of 10 mg / mL was prepared. Second, a thermally conductive silicone rubber layer with a thermal conductivity of 3 W / m·K was pressed into a film with a thickness of 8 μm. Then, the aforementioned graphene-hexane dispersion with a thickness of 5 μm was coated onto one side of the thermally conductive silicone rubber layer and dried to obtain a graphene oxide / thermally conductive silicone rubber composite material. The thermally conductive silicone rubber layer was then treated according to the above method and bonded to the surface of the graphene oxide / thermally conductive silicone rubber composite material, closer to the graphene oxide side. A second layer of graphene oxide / thermally conductive silicone rubber composite material was then formed in the same manner. This process was repeated 3–4 times to form a layer-by-layer assembled graphene oxide / thermally conductive silicone rubber composite material. A graphene / thermally conductive silicone rubber composite material was prepared. Next, the composite material was folded into four layers and repeatedly folded and rolled five times using a slit-type heated roller press with a heat tracing temperature of 80°C and a gap of 10 micrometers to form a thermally conductive silicone rubber composite material containing graphene oxide sheets oriented. Finally, an appropriate amount of condensation-type two-component silicone rubber (RTV-2) crosslinking agent was added to the thermally conductive silicone rubber composite material containing graphene oxide sheets oriented. The mixture was folded 20 times and then placed perpendicular to the vulcanizing machine plate according to the folding direction. Vulcanization was performed on the vulcanizing agent. The first vulcanization temperature was 180°C, and the vulcanization time was 3 hours; the second vulcanization temperature was 240°C, and the vulcanization time was 2 hours, thus obtaining a flexible thermal management composite film with graphene oriented alignment. According to the ASTM D5470 heat flow method, its thermal conductivity was measured to be 6.49 W / m·K.

[0034] Example 3

[0035] First, a graphene-hexane dispersion with a sheet diameter of 10 μm and a thickness of 2 layers (15 mg / mL) was prepared. Second, a thermally conductive silicone rubber layer with a thermal conductivity of 6 W / m·K was pressed into a film with a thickness of 5 μm. Then, the aforementioned graphene oxide with a thickness of 5 μm was coated onto one side of the thermally conductive silicone rubber layer and dried to obtain a graphene oxide / thermally conductive silicone rubber composite material. The thermally conductive silicone rubber layer was then treated according to the above method and bonded to the surface of the graphene oxide / thermally conductive silicone rubber composite material, closer to the graphene oxide. A second layer of graphene oxide / thermally conductive silicone rubber composite material was then formed in the same manner. This process was repeated 3–4 times to form a layer-by-layer assembly. A graphene oxide / thermal conductive silicone rubber composite material was prepared. Next, the composite material was folded into four layers and repeatedly folded and rolled 10 times using a slit-type heated roller press with a heat tracing temperature of 150°C and a gap of 0.5 micrometers to form a thermally conductive silicone rubber composite material containing graphene oxide sheets with an oriented structure. Finally, an appropriate amount of methyltriacetoxysilane was added to the graphene oxide-oriented thermally conductive silicone rubber composite material, which was then folded 50 times. The folded material was then placed perpendicular to the vulcanizing machine plate and vulcanized on a vulcanizing agent. The first vulcanization temperature was 180°C for 4 hours, and the second vulcanization temperature was 240°C for 3 hours, thus obtaining a flexible thermal management composite film with graphene oriented alignment. Its thermal conductivity was measured to be 35.96 W / m·K according to the ASTM D5470 heat flow method.

[0036] Example 4

[0037] First, a graphene-hexane dispersion with a sheet diameter of 6 μm and a thickness of 3 layers and a concentration of 8 mg / mL was prepared. Second, a thermally conductive silicone rubber layer with a thermal conductivity of 5 W / m·K was pressed into a film with a thickness of 20 μm. Then, the aforementioned graphene-hexane dispersion with a thickness of 15 μm was coated onto one side of the thermally conductive silicone rubber layer and dried to obtain a graphene oxide / thermally conductive silicone rubber composite material. The thermally conductive silicone rubber layer was then treated according to the above method and adhered to the surface of the graphene oxide / thermally conductive silicone rubber composite material, closer to the graphene oxide side. A second layer of graphene oxide / thermally conductive silicone rubber composite material was then formed in the same manner. This process was repeated 3–4 times to form a composite material. A layer-by-layer graphene oxide / thermal conductive silicone rubber composite material was assembled. Next, the composite material was folded into three layers and repeatedly folded and rolled eight times using a slit-type heated roller press with a heat tracing temperature of 100°C and a gap of 8 micrometers to form a thermally conductive silicone rubber composite material containing graphene oxide sheets with an orientation. Finally, an appropriate amount of methyltriacetoxysilane was added to the graphene oxide-oriented thermally conductive silicone rubber composite material, and it was folded 20 times. Then, it was placed perpendicular to the vulcanizing machine plate with the folding direction and vulcanized on a vulcanizing agent. The first vulcanization temperature was 175°C, and the vulcanization time was 2 hours; the second vulcanization temperature was 220°C, and the vulcanization time was 2 hours, thus obtaining a flexible thermal management composite film with graphene orientation. Its thermal conductivity was measured to be 15.41 W / m·K according to the ASTM D5470 heat flow method.

[0038] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A method for preparing a flexible thermal management composite film with oriented graphene, characterized in that, Includes the following steps: Step 1: Disperse graphene oxide in an appropriate amount of good solvent to form a stable graphene oxide dispersion. Step 2: Press the thermally conductive silicone rubber layer into a film with a thickness of 5-20 μm as needed; Step 3: The graphene oxide dispersion from Step 1 is coated onto the thermally conductive silicone rubber layer to a thickness of 6-15 micrometers to form a graphene oxide coating. After drying, a graphene oxide / thermally conductive silicone rubber composite material is obtained. Step 4: Continue to process the thermally conductive silicone rubber layer according to the method in Step 2. Adhere the processed thermally conductive silicone rubber layer to the surface of the graphene oxide / thermally conductive silicone rubber composite material obtained in Step 3 and close to the graphene oxide side. Then form the second layer of graphene oxide / thermally conductive silicone rubber composite material according to the method in Step 3. Repeat the above steps 3 to 4 times to form a layer-by-layer assembled graphene oxide / thermally conductive silicone rubber composite material. Step 5: Fold the graphene oxide / thermal conductive silicone rubber composite material assembled layer by layer in step 4 into 3 to 4 layers, and repeat the folding and rolling 5 to 15 times through a slit-type heat-tracing roller press to form a thermal conductive silicone rubber composite material containing graphene oxide sheet orientation. Step 6: Add an appropriate amount of crosslinking agent to the thermally conductive silicone rubber composite material containing graphene oxide sheet orientation, fold it according to actual needs, and then place it at a perpendicular angle to the vulcanizing machine plate according to the folding direction, and perform secondary vulcanization molding on the vulcanizing machine to obtain a flexible thermal management composite film with graphene orientation. The graphene-oriented flexible thermal management composite film includes a graphene thermally conductive layer and a thermally conductive silicone rubber layer; the thermally conductive silicone rubber layer is made of thermally conductive silicone with a thermal conductivity of 3-8 W / m·K; the graphene thermally conductive layer is a thermally conductive unit formed by the oriented arrangement of graphene materials. In step 1, a good solvent refers to a solvent that can simultaneously dissolve uncured silicone rubber and disperse graphene oxide. The good solvent is one of n-hexane, n-heptane, petroleum ether, or xylene.

2. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 1, characterized in that, In step 1, the graphene oxide sheets have a diameter of 3–10 μm and a thickness of 1–5 layers.

3. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 1, characterized in that, The gap between the two rollers of the slit-type heat-tracing roller press is 0.5 to 10 μm, and the heat tracing temperature is 80 to 200℃.

4. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 1, characterized in that, The crosslinking agent is any one of methyl hydrogen silicone oil, condensation-type two-component silicone rubber, and methyltriacetoxysilane.

5. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 1, characterized in that, The secondary vulcanization molding includes two vulcanization processes, wherein the first vulcanization temperature is 170-180℃ and the second vulcanization temperature is 210-240℃.

6. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 2, characterized in that, The graphene oxide sheets have a diameter of 5–10 μm and a thickness of 2–3 layers.

7. The method for preparing a flexible thermal management composite film with oriented graphene according to claim 3, characterized in that, The gap between the two rollers of the slit-type heat-tracing roller press is 0.5 to 3 μm, and the heat tracing temperature is 150 to 160℃.

Images