Composite heat-conducting film and preparation method and application thereof

Abstract

The application discloses a composite heat-conducting film and a preparation method and application thereof, wherein carbon nanotube dispersion liquid is added into aramid nanofiber water dispersion liquid to prepare a modified dispersion liquid, then the modified dispersion liquid is compounded with graphene dispersion liquid, and finally the composite heat-conducting film is prepared through filtration, drying and heat treatment. The method introduces aramid nanofiber to prepare the modified dispersion liquid of ANF / CNT, and then the modified dispersion liquid is compounded with graphene dispersion liquid. The interaction between ANF, CNT and GO can be utilized to solve the problems of poor dispersibility of CNT in GO and poor mechanical property of the film. According to the performance of the composite heat-conducting film, the composite heat-conducting film can be applied to the heat dissipation field of electronic products such as smart phones, tablet computers, LED and TV, and the miniaturization, thinness and lightness of the electronic products can be realized.

Description

Technical Field

[0001] This invention relates to a composite thermally conductive film, its preparation method, and its application, specifically to a composite thermally conductive film of modified carbon nanotubes and graphene, its preparation method, and its application, belonging to the field of thermally conductive composite materials. Background Technology

[0002] With the continuous advancement of science and technology, the development of microelectronic integration and assembly technology, and the widespread application of high power density devices, the size of components has been greatly reduced. Electronic instruments and equipment are developing towards integration, miniaturization, and high density. Flexible thin films with high thermal conductivity have attracted widespread attention in modern electronic thermal management.

[0003] Traditional heat dissipation materials mainly rely on metals, such as silver, copper, and aluminum. However, the inherent properties of metals, such as high density and poor corrosion resistance, have severely limited their application in heat dissipation materials. Carbon materials, due to their advantages such as light weight, corrosion resistance, good mechanical properties, excellent thermal conductivity, and low coefficient of thermal expansion, are considered to be high thermal conductivity materials with great development potential. Among them, graphene oxide (GO) and carbon nanotubes (CNTs) have attracted much attention since their discovery.

[0004] Graphene oxide (GO) serves as a precursor material for the synthesis of graphene. The numerous hydrophilic groups (-COOH, -OH, etc.) on the GO surface enable it to remain stable in most solvents without agglomeration. However, compared to graphene, the introduction of oxygen-containing groups to some extent disrupts its structural integrity, and these doping sites also become locations for phonon and electron scattering, thus significantly reducing its electrical and thermal conductivity and limiting the effective utilization of its thermoelectric properties.

[0005] Carbon nanotubes (CNTs) can be viewed as graphene or graphene sheets rolled up, with both ends covered by hemispherical fullerene molecules. Based on the number of graphene layers constituting the CNT rolls, they can be classified into multi-walled carbon nanotubes, double-walled carbon nanotubes, and single-walled carbon nanotubes. The primary thermal conductivity of carbon nanotubes (CNTs) is lattice vibration phonon conduction, resulting in extremely high thermal conductivity. Single-walled carbon nanotubes can achieve a thermal conductivity of up to 3900 W / (m·K), while multi-walled carbon nanotubes have a thermal conductivity of 3500 W / (m·K). By combining graphene films with carbon nanotubes, pure carbon composite films can be obtained. In these films, the carbon nanotubes compensate for the grain boundary defects of graphene, fully leveraging the advantages of both materials to improve the mechanical properties and thermal conductivity of the film.

[0006] In the invention patent with publication number CN111154461A, a directional assembly method is used. First, an aqueous solution of graphene oxide and a water-soluble metal salt are mixed. Then, the mixture is slowly cooled until water molecules crystallize into ice, and then freeze-dried to obtain directionally assembled graphene oxide. After reduction, directionally assembled graphene loaded with metal nanoparticles is obtained. This method can combine graphene and carbon nanotubes into a three-dimensional network structure to form a composite thermally conductive film. However, this method has a complex process, high energy consumption, and is not easy to scale up.

[0007] In the invention patent with publication number CN103725263A, graphene and carbon nanotubes are thoroughly mixed by stirring and ultrasonic dispersion. Then, under hydrothermal or solvothermal conditions, the graphene and carbon nanotubes are allowed to react fully. After the reaction is complete and the solvent is removed, a graphene-carbon nanotube composite material with an entangled network structure is obtained. This method is simple to operate, low in cost, and has significant commercial application value. However, the overall performance of GO / CNT composite films with added CNTs in existing technologies has not reached the ideal value; mechanical and heat resistance properties cannot be simultaneously achieved. The addition of CNTs has not significantly improved the vertical planar thermal conductivity of graphene because the dispersion of CNTs in the graphene matrix is ​​poor, and the connection between CNTs and graphene sheets remains weak. For graphene, its two-dimensional structure and huge specific surface area make it difficult to disperse and prone to agglomeration. This agglomeration is irreversible and will greatly affect the thermal conductivity of graphene. For carbon nanotubes, due to their high aspect ratio and large surface area, there are large van der Waals forces between the tubes, making them almost insoluble. They also become entangled and cross-linked, resulting in strong agglomeration and entanglement. Therefore, to effectively improve the overall performance of carbon nanotube and graphene composites, solving their dispersibility is the primary task in preparing high-performance composite materials. Summary of the Invention

[0008] To address the technical shortcomings of current methods for preparing high-performance composite materials using graphene and carbon nanotubes, this invention provides a novel method for preparing a composite thermally conductive film. This method involves introducing aramid nanofibers to prepare a modified ANF / CNT dispersion, which is then composited with a graphene dispersion. Utilizing the interactions between ANF, CNTs, and carbon nanotubes (GO), this method not only solves the problems of poor CNT dispersibility in GO and the poor mechanical properties of the film, but also provides the composite thermally conductive film obtained by this method.

[0009] Furthermore, based on the performance of the composite thermal conductive film, the present invention can be applied to the heat dissipation of electronic products such as smartphones, tablets, LEDs, and TVs, achieving the goals of miniaturization, thinning, and lightweighting.

[0010] This invention is achieved through the following technical solution: a method for preparing a composite thermally conductive film, comprising adding a carbon nanotube dispersion to an aramid nanofiber aqueous dispersion to obtain a modified dispersion, then combining it with a graphene dispersion, followed by filtration, drying, and heat treatment to obtain the final product.

[0011] Aramid fibers and KOH were mixed with dimethyl sulfoxide in a mass ratio of 1:1 to 1:2 and stirred to form an ANF / DMSO solution. Water was then added to the ANF / DMSO solution in a volume ratio of 1:1 to 4:1 and stirred to obtain an ANF / DMSO / H2O solution. After filtration, washing with water, and homogenization, the aramid nanofiber aqueous dispersion was obtained.

[0012] The carbon nanotube dispersion is prepared by mixing and dispersing 0.005-0.05 parts of carbon nanotube powder, 0.005-0.1 parts of dispersant, 0.005-0.1 parts of stabilizer, and 1 part of water by weight. The stabilizer is selected from one or more of the following: high molecular weight stabilizers DNA / RNA, cellulose and its derivatives, and sodium carboxymethyl cellulose.

[0013] Graphene oxide is added to water, and the mass concentration of graphene oxide is controlled at 0.005~1%. After stirring, the graphene dispersion is obtained.

[0014] The aramid nanofiber aqueous dispersion and the carbon nanotube dispersion are mixed at a volume ratio of 1:1 to 1:2; the modified dispersion and the graphene dispersion are compounded at a volume ratio of 2.5:50 to 50:100.

[0015] The mass ratio of water added to the ANF / DMSO solution to the solvent in the solution is 1:1 to 1:50.

[0016] The aramid fiber has a length of 1~13μm.

[0017] The carbon nanotube powder has a length of 5 μm or more.

[0018] The dispersant is selected from one or more of the following compounds of formula (1): TNRDIS, Disponer 983, FA 196, FX 9086, sodium glycocholate and its derivatives, sodium glycodeoxycholate and its derivatives, sodium chenodeoxycholate and its derivatives, sodium taurocholate and its derivatives, sodium deoxycholate and its derivatives, polyvinylpyrrolidone and its derivatives, polyvinylcaprolactam and its derivatives, polyvinylacetamide and its derivatives, and sodium dodecylbenzenesulfonate.

[0019] (1)

[0020] Wherein, R1 is -OH, -ONa, -NH3C2O2Na, -NHCH2COOH, -N2H8C4SO4Na or -NH5C2SO3Na, and R2 is -H, -OH, halogen, -OCH3, -OCH2CH3 or an ester group with 2-8 carbon atoms.

[0021] The heat treatment process includes: heating to 500℃ and holding for 2 hours, then heating to 1000℃ and holding for 2 hours.

[0022] The composite thermal conductive film prepared by the above method has a thermal conductivity of 4.5~4.8 W / m*k or higher at 25℃.

[0023] Density: 1.2~1.3 g / cm³ 3 ;

[0024] Tensile strength: 60~65 MPa;

[0025] Electrical conductivity: 11~12.5 S / cm.

[0026] The aforementioned composite thermally conductive film is used in the manufacture of heat dissipation components for electronic devices, such as smartphones, tablets, LEDs, and TVs.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) In order to solve the problems of poor dispersion and mechanical properties of existing GO / CNT composite films, the present invention provides a method for preparing composite films by modifying carbon nanotubes with aramid fibers and then reacting them with graphene. In this method, the strong π-π interaction between aramid fibers and GO and CNT can be utilized to further connect and bridge between composite film materials to form a longitudinal bridging reinforcement network, thereby better solving the problems of poor dispersion of CNT in GO and poor mechanical properties of the film. At the same time, after heat treatment and reduction, aramid fibers can be transformed into a graphite-like structure to repair the structural defects of graphene and carbon nanotubes, construct a more complete heat conduction path, reduce interfacial phonon scattering, and improve thermal conductivity.

[0029] (2) In this invention, aramid fiber is used as an additive material, which can be used to improve the interaction between graphene and carbon nanotubes in the preparation of composite films. At the same time, aramid fiber also has excellent mechanical and chemical properties, and can significantly enhance the mechanical properties of the material.

[0030] (3) In this invention, modified carbon nanotubes are prepared by mixing aramid nanofiber aqueous dispersion and carbon nanotube dispersion. The entire modification system uses water as a solvent. Similarly, the graphene oxide dispersion also uses water as a solvent. The raw materials are non-toxic, easy to obtain, and have low cost.

[0031] In summary, this invention solves a series of comprehensive performance problems of GO and CNT in the preparation of composite films by introducing aramid fibers, and realizes the preparation of film products with high thermal conductivity and excellent mechanical properties. It also has the advantages of simple preparation process, safe raw materials and low cost. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the preparation process of the GO / CNT / ANF thin film.

[0033] Figure 2 The image shows the cross-sectional morphology of the GO / CNT / ANF thin film of Example 1 (left: 10 μm, right: 5 μm).

[0034] Figure 3 The cross-sectional morphology of the GO / CNT film in Comparative Example 2 is shown (left: 10 μm, right: 5 μm).

[0035] Figure 4 The cross-sectional morphology of the ANF / CNT film in Comparative Example 3 is shown (left: 10 μm, right: 5 μm). Detailed Implementation

[0036] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0037] Example 1: GO / CNT / ANF thin film

[0038] Preparation of carbon nanotube dispersion: 0.5g of carbon nanotube powder (greater than 5μm) was added to 100ml of deionized water, followed by 0.25g of compound (2), 0.25g of sodium deoxycholate, 0.25g of DNA, and 0.25g of cellulose. After mixing, the mixture was dispersed by ball milling to obtain the CNT dispersion. In other possible embodiments, various methods such as ultrasonication, three-roll milling, Dyno-milling, stirring, and extrusion can be used to replace ball milling in order to achieve a good dispersion effect.

[0039] (2)

[0040] Graphene oxide dispersion: Graphene oxide was added to deionized water, and the mass concentration of graphene oxide was controlled at 0.005%. After magnetic stirring for 2 hours, GO dispersion was obtained.

[0041] Preparation of aramid nanofiber aqueous dispersion: 1g of aramid (PPTA) fiber (1~13μm) and 1.5g of KOH were added to 500ml of dimethyl sulfoxide, followed by 20ml of deionized water. The mixture was then magnetically stirred for 4h to form an ANF / DMSO solution. Deionized water was then added to the ANF / DMSO solution at a volume ratio of 4:1, and the mixture was magnetically stirred for 1h. The solution was then washed multiple times with deionized water under vacuum filtration to remove excess KOH and DMSO. Finally, the solution was homogenized at 20000rpm using a homogenizer to obtain the ANF aqueous dispersion.

[0042] See Figure 1 The process described involves mixing an ANF aqueous dispersion with an equal volume of CNT dispersion, homogenizing the mixture using a homogenizer at 10,000 rpm to obtain a CNT / ANF solution. The CNT / ANF solution and GO dispersion are then mixed at a 50%:50% volume ratio and magnetically stirred for 4 hours to prepare a homogeneous GO / CNT / ANF-50% solution. The prepared solution is then vacuum filtered and dried in a 70°C oven to form a GO / CNT / ANF film.

[0043] Example 2: GO / CNT / ANF thin film

[0044] The only difference between this embodiment and Example 1 in preparing the GO / CNT / ANF film is the process for preparing the carbon nanotube dispersion, as detailed below:

[0045] Preparation of carbon nanotube dispersion: 2.0g of carbon nanotube powder (greater than 5μm) was added to 100ml of deionized water, and then 0.5g of compound (3), 0.5g of polyvinylpyrrolidone, 0.5g of DNA and 0.5g of cellulose were added. After mixing, the mixture was dispersed by ball milling to obtain the CNT dispersion.

[0046] (3)

[0047] Example 3: GO / CNT / ANF thin film

[0048] The only difference between this embodiment and Example 1 in preparing the GO / CNT / ANF film is the process for preparing the graphene oxide dispersion, as detailed below:

[0049] Graphene oxide dispersion: Graphene oxide was added to deionized water, and the mass concentration of graphene oxide was controlled at 0.05%. After magnetic stirring for 2 hours, GO dispersion was obtained.

[0050] Example 4: GO / CNT / ANF thin film

[0051] The only difference between this embodiment and Example 1 in preparing the GO / CNT / ANF film is the process for preparing the aramid nanofiber aqueous dispersion, as detailed below:

[0052] Preparation of aramid nanofiber aqueous dispersion: 1g of aramid (PPTA) fiber (1~13μm) and 1.5g of KOH were added to 500ml of dimethyl sulfoxide, followed by 100ml of deionized water. The mixture was then magnetically stirred for 6h to form an ANF / DMSO solution. Deionized water was then added to the ANF / DMSO solution at a volume ratio of 1:1, and the mixture was magnetically stirred for 2h. The solution was then washed multiple times with deionized water under vacuum filtration to remove excess KOH and DMSO. Finally, the solution was homogenized at 20000rpm using a homogenizer to obtain the ANF aqueous dispersion.

[0053] Example 5: GO / CNT / ANF thin film

[0054] The only difference between this embodiment and Example 1 in preparing the GO / CNT / ANF film is the mixing process of the dispersion, as detailed below:

[0055] An ANF aqueous dispersion was mixed with an equal volume of a CNT dispersion and homogenized using a homogenizer at 15,000 rpm to obtain a CNT / ANF solution. The CNT / ANF solution and a GO dispersion were then mixed at a volume ratio of 15%:85% and magnetically stirred for 4 hours to obtain a homogeneous GO / CNT / ANF-15% solution. The prepared solution was then vacuum filtered and dried in a 70°C oven to form a GO / CNT / ANF film.

[0056] Comparative Example 1: GO / CNT / ANF Thin Film

[0057] The GO / CNT / ANF film was prepared in the same manner as in Example 1, except that the ANF aqueous dispersion and the CNT dispersion were mixed at a volume ratio of 15%:85%, and the CNT / ANF solution and the GO dispersion were mixed at a volume ratio of 25%:75%.

[0058] Comparative Example 2: GO / CNT Thin Film

[0059] Carbon nanotube dispersions (CNT dispersions) and graphene oxide dispersions (GO dispersions) were prepared using the same method as in Example 1.

[0060] A homogeneous GO / CNT-15% solution was prepared by mixing CNT and GO dispersions at a mass ratio of 15:85 and stirring magnetically for 4 hours. The prepared solution was then vacuum filtered and dried in a 70°C oven to form a GO / CNT film.

[0061] Comparative Example 3: ANF / CNT Thin Film

[0062] Carbon nanotube dispersion (CNT dispersion) was prepared in the same manner as in Example 1, and aramid nanofiber aqueous dispersion (ANF aqueous dispersion) was prepared in the same manner as in Example 2.

[0063] An ANF aqueous dispersion was mixed with an equal volume of a CNT dispersion and homogenized using a homogenizer at 10,000 rpm to obtain a CNT / ANF solution. The prepared solution was then vacuum filtered and dried in an oven at 70°C to form an ANF / CNT film.

[0064] The GO / CNT / ANF films prepared in Example 1 and Comparative Example 1 were respectively immersed in 100 ml of 25 mg / ml L-ascorbic acid solution and reduced in an 80°C water bath for 30 min. The films were then removed, washed several times with deionized water, and air-dried. Subsequently, the films underwent hot-press reduction treatment. The temperature of the upper and lower plates of the double-plate hot press was set to 200°C. After preheating, the film samples were sequentially covered with transparent PI sheets on both sides, labeled, and clamped in a steel plate. The samples were then fed into the hot press at a pressure of 10 MPa. After 15 min, the samples were removed, yielding sample A and comparative sample I.

[0065] The GO / CNT film and ANF / CNT film prepared in Comparative Examples 2 and 3 were subjected to hot-press reduction treatment. The temperature of the upper and lower plates of the double-plate hot press was set to 200℃. After preheating, the film samples were wrapped with transparent PI sheets on both sides in sequence. After marking the names, they were clamped in steel plates and sent into the hot press. The pressure was set to 10MPa. After 15 minutes, the samples were taken out to obtain Comparative Sample II and Comparative Sample III.

[0066] The above-mentioned sample A, and control samples I, II, and III were tested as follows:

[0067] (1) Thin film morphology test

[0068] Observations were performed using field emission scanning electron microscopy (FE-SEM) (Inspect-F, FEI, Finland) at an accelerating voltage of 15 kV. Results are shown below. Figure 2 (Sample A) Figure 3 (Comparative sample II) and Figure 4 (Comparative sample III).

[0069] in, Figure 2 The thin film material shown has a good layered structure, in which rGO flakes are parallel to the film plane, and ANFs and CNTs appear between the rGO flakes to form a good network structure.

[0070] Figure 3 The cross-sectional morphology of the GO film shown is a stacked layered structure with some voids between the graphene oxide layers. Carbon nanotubes are loaded on the surface of the graphene oxide and form a network structure between the graphene layers, effectively filling the air pores between the graphene layers, but the filling network does not form a dense connection.

[0071] Figure 4 The tightly interwoven ANF / CNT network shown can distribute stress evenly on the frame, improving mechanical properties, but it lacks a layered support structure.

[0072] (2) Thermal conductivity test

[0073] The thermal diffusivity α of the thin film was measured using an LFA467. The specific heat capacity Cp of the sample was tested using DSC. The sample density ρ was measured using Archimedes' principle: first, the weight m1 of the sample in air was measured; then, the sample was placed in an ethanol solution, and the weight m2 of the sample in the ethanol solution was measured. The measurement environment was 25℃, and the ethanol density was 0.79 g / cm³. The density can be calculated using the following formula:

[0074] The thermal conductivity of the thin film is calculated as λ = α * ρ * Cp.

[0075] (3) Mechanical property testing

[0076] The mechanical properties of the thin film were tested using an INSTRON universal testing machine from the United States. Each group of samples was tested three times and the average value was calculated.

[0077] The performance parameters tested are shown in Table 1.

[0078] Table 1

[0079]

[0080] As shown in Table 1 above, the method of the present invention can prepare composite thermally conductive films with low conductivity and high tensile strength, meeting the specific performance index system required for heat dissipation components of electronic devices. Comparative Example 1, by changing the mixing volume ratio of the dispersion, can prepare films with comparable density and thermal conductivity, but its mechanical properties are significantly reduced, while its conductivity increases. This may be due to the deterioration of the dispersion performance of aramid fibers in graphene. Comparative Example 2 shows the preparation process of GO / CNT films. Due to the introduction of graphene materials, its thermal conductivity can reach 48.4939 W / m*k, but its mechanical properties are poor, while its conductivity is high. Comparative Example 3 shows the preparation process of ANF / CNT films. Due to the introduction of aramid fibers, the mechanical properties of the film are enhanced, and its conductivity increases significantly.

[0081] In summary, the present invention provides a thin film with a specific performance index system, which enables the thermal conductivity, tensile strength and electrical conductivity of the thin film to meet the specific index range. Since the performance of the thin films of Comparative Examples 1 to 3 cannot meet the index system, they are not suitable for use in heat dissipation components of electronic devices.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method of making a composite heat-conductive film, characterized by: The carbon nanotube dispersion liquid is prepared by mixing 0.005-0.05 parts of carbon nanotube powder, 0.005-0.1 parts of a dispersant, 0.005-0.1 parts of a stabilizer and 1 part of water in terms of mass fraction, wherein the dispersant is one or more selected from the group consisting of a compound of formula (1), TNRDIS, Disponer 983, FA 196, FX 9086, polyvinylpyrrolidone and derivatives thereof, polyvinylcaprolactam and derivatives thereof, polyvinylacetamide and derivatives thereof, and sodium dodecylbenzenesulfonate, R1 is -OH, -ONa, -NH3C2O2Na, -NHCH2COOH, -N2H8C4SO4Na or -NH5C2SO3Na, and R2 is -H, -OH, halogen, -OCH3, -OCH2CH3 or an ester group with 2-8 carbon atoms. The graphene dispersion liquid is prepared by adding graphene oxide into water to control the mass concentration of the graphene oxide to be 0.005-1%, and then stirring, （1） The performance indicators of the composite heat-conducting film satisfy the following conditions: The thermal conductivity at 25℃ is 4.5-4.8 W / m·k or above; The tensile strength is 60-65 MPa; The electrical conductivity is 11-12.5 S / cm. Density: 1.2-1.3 g / cm 3 ; The mass ratio of the water added into the ANF / DMSO solution to the solvent in the solution is 1:1-1:

50. The size length of the aramid fiber is 1-13 μm.

2. The method of claim 1, wherein: The length of the carbon nanotube powder is 5 μm or above.

3. The method of claim 1, wherein: The stabilizer is one or more selected from the group consisting of high-molecular stabilizers DNA / RNA, cellulose and derivatives thereof, and sodium carboxymethylcellulose.

4. The method of claim 1, wherein: The heat treatment process comprises: heating to 500℃ for 2 h, and then heating to 1000℃ for 2 h.

5. The method of claim 1, wherein: The composite heat-conducting film is prepared by using the preparation method of any one of claims 1-6.

6. The method of claim 1, wherein:

8. Use of the composite heat-conducting film according to claim 7 in preparing a heat-dissipating component of an electronic device.

7. A composite heat conducting film, characterized by: ​ ​

Images