Graphene heat-conducting composite powder, coating, preparation method and electronic device

Abstract

The application provides a graphene heat-conducting composite powder, a coating, a preparation method and an electronic device, and the preparation method comprises the following steps: (1) mixing graphene, a metal oxide, polylactic acid and an acid regulator to obtain a mixture; (2) subjecting the mixture to a heating reflux reaction, wherein polylactic acid is subjected to melting, degradation and hydrolysis in the heating reflux reaction to obtain a reaction product; and (3) sequentially subjecting the reaction product to cooling, solid-liquid separation, cleaning and secondary heating to obtain the graphene heat-conducting composite powder, wherein the graphene heat-conducting composite powder comprises graphene, a metal oxide, polylactic acid and degradation and hydrolysis products of polylactic acid. The graphene heat-conducting composite powder prepared by the application has uniformly dispersed graphene and stably existing components, and the heat-conducting effect is improved by combining with titanium suboxide. The heat-dissipating coating prepared from the filler has stable heat-dissipating effect and uniform heat conduction, and is beneficial to the stable heat-dissipating performance of the electronic device.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, and in particular to a graphene thermal conductive composite powder, coating, preparation method, and electronic device. Background Technology

[0002] With the miniaturization and integration of electronic devices, problems such as reduced efficiency and increased energy consumption caused by heat accumulation have become increasingly prominent, and have now become a bottleneck restricting their rapid development.

[0003] Traditional heat dissipation methods for electronic devices involve using fans to increase airflow speed and reduce localized heat accumulation by improving heat diffusion efficiency. However, this method requires additional energy and has drawbacks such as space requirements, making it unsuitable for energy conservation and economic efficiency.

[0004] As a novel heat dissipation method, thermal coatings have gradually become one of the most researched and widely used heat dissipation methods due to their advantages such as ease of preparation, high space utilization, and no need for additional energy consumption. The main research focus of thermal coatings is on composite coatings, whose main components include a polymer substrate and fillers. The polymer substrate primarily functions as corrosion protection, electrical insulation, and as a binder between fillers and between the fillers and the heat dissipation device. The composite fillers are mainly selected based on their heat dissipation function, using materials with high thermal conductivity.

[0005] Graphene has become a hot topic in the research of thermally conductive coating fillers due to its near-blackbody high emissivity and high thermal conductivity (5300 W / m·K). However, the tendency of graphene to agglomerate severely affects its thermal conductivity. To improve the thermal conductivity of graphene, methods such as adding metal powders and inorganic oxides are commonly used to improve its dispersibility and thus enhance heat dissipation. Due to the influence of the mixing process, enhancing the dispersion of graphene by doping with powder requires a long time, and because the density between the doped powder and graphene is relatively high, separation and sedimentation problems easily occur during the mixing process in the polymer. Simple doping is insufficient to achieve the goal of uniformly dispersing graphene.

[0006] Therefore, it is necessary to prepare composite fillers with stable combination of dispersed particles and graphene to improve the dispersion uniformity of graphene and thus improve the thermal conductivity of the composite material. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a graphene thermally conductive composite powder, a coating, a preparation method, and an electronic device. By heating and melting polylactic acid and partially degrading and hydrolyzing it, the originally unstable graphene composite filler is stably and uniformly dispersed in liquid polylactic acid and its degradation and hydrolysis products. Then, rapid cooling is performed to stably solidify the graphene composite filler in polylactic acid and its degradation and hydrolysis products, thereby preparing a graphene thermally conductive composite powder with uniform mixing and stable components. The heat dissipation coating prepared from the graphene thermally conductive composite powder has a stable heat dissipation effect and uniform thermal conductivity, which is beneficial to the stable heat dissipation performance of electronic devices.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing graphene thermally conductive composite powder, the preparation method comprising:

[0010] (1) Mix graphene, metal oxide, polylactic acid and acid regulator to obtain a mixture;

[0011] (2) The mixture is heated and refluxed, during which polylactic acid melts, degrades and hydrolyzes to obtain the reaction product;

[0012] (3) The reaction products are successively cooled, separated into solid and liquid, washed and heated a second time to obtain the graphene thermally conductive composite powder.

[0013] The method for preparing graphene thermally conductive composite powder provided by this invention involves adding an acidic regulator to the mixture. During the subsequent heating and reflux reaction, not only does polylactic acid melt, but it also undergoes partial degradation and hydrolysis. This partial degradation and hydrolysis of polylactic acid improves the overall fluidity of polylactic acid and its degradation and hydrolysis products during the heating and reflux reaction, thereby enhancing the dispersion effect of graphene and metal oxides and effectively preventing graphene agglomeration. Compared to traditional methods that only use polylactic acid, this method improves the dispersion performance of the materials, and the reaction products, after cooling, yield a component-stable graphene thermally conductive composite powder.

[0014] Preferably, the graphene in step (1) is graphene nanoparticles.

[0015] Preferably, the thickness of the graphene nanopowder is 10-30 nm, for example, it can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 18 nm, 20 nm, 25 nm or 30 nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the metal oxide is titanium suboxide.

[0017] The preferred metal oxide in this invention is titanium suboxide. Compared to other metal oxides, titanium suboxide has a porous structure and mature structure control technology. Furthermore, titanium suboxide has high thermal conductivity (10 W / (m·K)) and high and stable emissivity across the entire wavelength range (~0.8). The interaction mechanism between titanium suboxide and graphene in this invention is as follows: high thermal conductivity but easily agglomerated graphene is mixed with porous titanium suboxide. The graphene is dispersed in the pores of titanium suboxide, which is beneficial for uniform dispersion and reduces agglomeration. The network structure of titanium suboxide can also serve as a thermally conductive network, improving the thermal conductivity efficiency of the polymer-based composite material. Moreover, due to the high thermal conductivity of the graphene filling the gaps, the overall thermal conductivity of titanium suboxide is improved.

[0018] Preferably, the particle size of the metal oxide is 350-450 nm, for example, it can be 350 nm, 362 nm, 373 nm, 384 nm, 395 nm, 406 nm, 417 nm, 428 nm, 439 nm or 450 nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the polylactic acid is polylactic acid particles.

[0020] Preferably, the polylactic acid particles have a particle size of 70 to 90 mesh, such as 70 mesh, 73 mesh, 75 mesh, 77 mesh, 79 mesh, 82 mesh, 84 mesh, 86 mesh, 88 mesh or 90 mesh, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the acidity regulator includes acetic acid.

[0022] Preferably, the pH of the acid regulator is 2.5 to 3.5, for example, it can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4 or 3.5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the mass ratio of the sum of the graphene, metal oxide, and polylactic acid to the acidity regulator is 0.8 to 1.2:1, for example, it can be 0.8:1, 0.85:1, 0.89:1, 0.94:1, 0.98:1, 1.03:1, 1.07:1, 1.12:1, 1.16:1, or 1.2:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] It is worth noting that the difficulty of this invention lies in controlling the degree of degradation and hydrolysis of polylactic acid (PLA) during the heating and reflux process. This is because, on the one hand, this invention aims to retain the excellent properties of PLA as a subsequent thermally conductive composite material and to form a solid powder under cooling conditions. Therefore, excessive degradation and hydrolysis of PLA must be avoided. On the other hand, partial degradation and hydrolysis of empty PLA are necessary to improve its mixing uniformity in the molten state, thereby enhancing the dispersion performance of graphene and metal oxides and ensuring the stability of the components in the subsequent graphene thermally conductive composite powder. Since the degree of degradation and hydrolysis during the reaction is difficult to control, this invention preferably controls the pH and dosage of the acidic regulator to ensure the degree of degradation and hydrolysis of PLA, thereby ultimately improving the component stability of the graphene thermally conductive composite powder while simultaneously ensuring the excellent properties of PLA.

[0025] Preferably, the mass ratio of graphene to metal oxide is 1:0.5 to 2, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.5, 1:1.8 or 1:2.0, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the mass ratio of polylactic acid to graphene is 30 to 10:1, for example, it can be 30:1, 28:1, 26:1, 24:1, 22:1, 19:1, 17:1, 15:1, 13:1 or 10:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the mixing in step (1) includes: first mixing graphene, metal oxide and polylactic acid, then ball milling, and then adding an acid regulator.

[0028] In this invention, ball milling followed by the addition of an acidic modifier is preferred for the reaction. After grinding, the particle size affects the surface roughness. According to Kirchhoff's law ε = 1 - R, increasing surface roughness reduces reflectivity, thereby increasing emissivity.

[0029] Preferably, the step of mixing graphene, metal oxide and polylactic acid first includes: first mixing graphene and titanium dioxide, then reducing titanium dioxide to titanium suboxide in a reducing atmosphere, and then adding polylactic acid.

[0030] To prevent titanium suboxide from being further oxidized in air, this invention uses a mixture of titanium dioxide and graphene followed by reduction to form titanium suboxide. Furthermore, the reduction process facilitates the entry of graphene into the pores created by the reduction of titanium dioxide into titanium suboxide, thereby promoting the synergistic thermal conductivity of the two.

[0031] Moreover, the ball milling method can only achieve uniform mixing of powders, and cannot guarantee the uniform dispersion of powder fillers in the binder / diluent system during the subsequent slurry preparation process. This invention first further uniformly solidifies the uniformly mixed graphene and metal oxides in polylactic acid and its degradation and hydrolysis products by melting, and then refines the particles, which is beneficial to improve the uniform distribution of graphene and titanium suboxide.

[0032] Preferably, the reducing atmosphere includes argon.

[0033] Preferably, the temperature range of the heating reflux reaction in step (2) is 140 to 160°C, for example, it can be 140°C, 143°C, 145°C, 147°C, 149°C, 152°C, 154°C, 156°C, 158°C or 160°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the products of polylactic acid degradation and hydrolysis include lactic acid and / or polylactic acid with a low degree of polymerization.

[0035] Preferably, the degree of polymerization of the low-polymer polylactic acid is 2 to 5, for example, it can be 2, 3, 4 or 5.

[0036] Preferably, the duration of the heating reflux reaction is 0.5 to 1.5 h, for example, it can be 0.5 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the cooling in step (3) is cooling to room temperature.

[0038] Preferably, the solid-liquid separation includes filtration.

[0039] Preferably, the cleaning includes ethanol cleaning.

[0040] Preferably, the temperature of the secondary heating is 160 to 180°C, for example, it can be 160°C, 163°C, 165°C, 167°C, 169°C, 172°C, 174°C, 176°C, 178°C or 180°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] The purpose of the secondary heating in this invention is to encapsulate graphene and metal oxides with polylactic acid. Without secondary heating, there will be problems of agglomeration and uneven distribution of graphene and metal oxides during the spraying process.

[0042] Preferably, the holding time for the secondary heating is 0.5 to 1.5 hours, for example, it can be 0.5 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours or 1.5 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the preparation method further includes grinding and sieving sequentially after the secondary heating.

[0044] Preferably, the mesh size of the sieve is 15 to 30 mesh, for example, it can be 15 mesh, 17 mesh, 19 mesh, 20 mesh, 22 mesh, 24 mesh, 25 mesh, 27 mesh, 29 mesh or 30 mesh, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] In a second aspect, the present invention provides a graphene thermally conductive composite powder, the graphene thermally conductive composite powder comprising: graphene, metal oxide, polylactic acid and degradation and hydrolysis products of polylactic acid;

[0046] The polylactic acid and its degradation and hydrolysis products are coated with metal oxides and graphene.

[0047] The graphene thermally conductive composite powder provided by the second aspect of the present invention has a more uniform dispersion and more stable composition due to the presence of polylactic acid degradation and hydrolysis products. Moreover, it adopts a composite of graphene and metal oxides, resulting in high thermal conductivity.

[0048] The present invention does not specifically limit the preparation method of the graphene thermally conductive composite powder described in the second aspect, but preferably uses the preparation method of the graphene thermally conductive composite powder described in the first aspect, which has better thermal conductivity, and the graphene and metal oxide are more uniformly dispersed and the composition is more stable.

[0049] Preferably, the mass ratio of graphene to metal oxide is 1:0.5 to 2, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.5, 1:1.8 or 1:2.0, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable; the mass ratio of polylactic acid and the sum of the mass of polylactic acid degradation and hydrolysis products to graphene is 30 to 10:1, for example, it can be 30:1, 28:1, 26:1, 24:1, 22:1, 19:1, 17:1, 15:1, 13:1 or 10:1, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] Preferably, the particle size of the graphene thermally conductive composite powder is 15-30 mesh.

[0051] Preferably, the metal oxide comprises titanium suboxide.

[0052] Preferably, the degradation and hydrolysis products of the polylactic acid include lactic acid and / or polylactic acid with a low degree of polymerization.

[0053] Thirdly, the present invention provides a method for preparing a graphene thermally conductive coating, wherein the graphene thermally conductive coating is prepared by using the graphene thermally conductive composite powder prepared by the method described in the first aspect, or the graphene thermally conductive coating is prepared by using the graphene thermally conductive composite powder described in the second aspect.

[0054] The graphene thermally conductive coating provided by the third aspect of the present invention has high thermal conductivity and stable composition of each component, which can prevent damage to the heat sink due to local overheating, thereby improving the heat dissipation effect of the heat sink and extending its service life.

[0055] Preferably, the method for preparing the graphene thermally conductive coating includes the following steps:

[0056] (1') A coating is obtained by mixing graphene thermally conductive composite powder, binder and diluent.

[0057] (2') The coating is sprayed onto the substrate and left to stand and the diluent is removed to form a graphene thermally conductive coating.

[0058] Preferably, the graphene thermally conductive composite powder in step (1') accounts for 15% to 30% of the binder, for example, it can be 15%, 17%, 19%, 20%, 22%, 24%, 25%, 27%, 29% or 30%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0059] Preferably, the mass ratio of the adhesive to the diluent is 0.8 to 1.2:2, for example, it can be 0.8:2, 0.82:2, 0.85:2, 0.88:2, 0.9:2, 0.92:2, 0.95:2, 1.0:2, 1.1:2, 1.15:2 or 1.2:2, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] Preferably, the adhesive comprises siloxane.

[0061] Preferably, the diluent comprises ethyl acetate.

[0062] Preferably, the mixing in step (1') is carried out by stirring.

[0063] Preferably, the stirring time is 4 to 6 hours, for example, 4 hours, 4.3 hours, 4.5 hours, 4.7 hours, 4.9 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] Preferably, the stirring speed is 300-500.

[0065] Preferably, the spraying in step (2') includes: spraying the coating described in step (1') onto the substrate using a spray gun.

[0066] Preferably, the substrate is made of aluminum or an aluminum alloy.

[0067] Preferably, the settling time is 4 to 6 hours, for example, it can be 4 hours, 4.3 hours, 4.5 hours, 4.7 hours, 4.9 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] Preferably, the removal of the diluent includes drying.

[0069] Preferably, the drying temperature is 110 to 130°C, for example, it can be 110°C, 113°C, 115°C, 117°C, 119°C, 122°C, 124°C, 126°C, 128°C or 130°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] Preferably, the drying time is 8 to 12 hours, for example, 8 hours, 8.5 hours, 8.9 hours, 9.4 hours, 9.8 hours, 10.3 hours, 10.7 hours, 11.2 hours, 11.6 hours or 12 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] Preferably, the thickness of the graphene thermally conductive coating is 60-80 μm, for example, it can be 60 μm, 63 μm, 65 μm, 67 μm, 69 μm, 72 μm, 74 μm, 76 μm, 78 μm or 80 μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0072] Fourthly, the present invention provides a graphene thermally conductive coating, the graphene thermally conductive coating comprising graphene thermally conductive composite powder and a binder, wherein the graphene thermally conductive composite powder comprises: graphene, metal oxide, polylactic acid and degradation and hydrolysis products of polylactic acid.

[0073] The graphene thermally conductive coating provided in the fourth aspect of the present invention can also be prepared using the graphene thermally conductive composite powder provided in the second aspect or the graphene thermally conductive composite powder prepared in the first aspect, or by the preparation method of the graphene thermally conductive coating provided in the third aspect.

[0074] The graphene thermally conductive coating provided by the fourth aspect of the present invention has high thermal conductivity and stable composition of each component, which can prevent damage to the heat sink due to local overheating, thereby improving the heat dissipation effect of the heat sink and extending its service life.

[0075] Preferably, the mass ratio of graphene to metal oxide is 1:0.5 to 2, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.5, 1:1.8 or 1:2.0, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable; the mass ratio of polylactic acid and the sum of the mass of polylactic acid degradation and hydrolysis products to graphene is 30 to 10:1, for example, it can be 30:1, 28:1, 26:1, 24:1, 22:1, 19:1, 17:1, 15:1, 13:1 or 10:1, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0076] Preferably, the particle size of the graphene thermally conductive composite powder is 15 to 30 mesh, for example, it can be 15 mesh, 16 mesh, 17 mesh, 18 mesh, 19 mesh, 20 mesh, 21 mesh, 22 mesh, 23 mesh, 25 mesh or 30 mesh, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0077] Preferably, the metal oxide comprises titanium suboxide.

[0078] Preferably, the degradation and hydrolysis products of the polylactic acid include lactic acid and / or polylactic acid with a low degree of polymerization.

[0079] Fifthly, the present invention provides an electronic device comprising a graphene thermally conductive coating prepared by the method described in the first aspect, or a graphene thermally conductive coating formed by spraying a coating material as described in the second aspect.

[0080] It is worth noting that electronic device heat sinks often encounter problems such as device damage and power-off protection due to localized overheating. The electronic device provided in the fifth aspect of this invention, due to the graphene thermal conductive coating provided by this invention, has a significantly improved heat dissipation effect, extends its working time, and improves its working efficiency. Applying a composite coating with uniform heat dissipation effect to the surface of the electronic device heat sink can prevent damage to the heat sink due to localized overheating, thereby improving the heat dissipation effect and extending its service life.

[0081] This invention does not limit the type of electronic device or other settings, and can employ any electronic device that requires a thermally conductive coating, as is well known to those skilled in the art.

[0082] Compared with the prior art, the present invention has at least the following beneficial effects:

[0083] (1) The graphene thermally conductive composite powder provided by the present invention has graphene and metal oxides that are uniformly dispersed, the composition is stable, and the overall thermally conductive composite powder has high thermal conductivity and can be uniformly coated on the substrate surface.

[0084] (2) The method for preparing graphene thermally conductive composite powder provided by the present invention can significantly improve the dispersion uniformity of graphene and metal oxide by melting, partial degradation and hydrolysis of polylactic acid, and then cool the graphene and metal oxide to be wrapped inside polylactic acid and its degradation and hydrolysis products, thereby significantly improving the component stability of the thermally conductive composite powder.

[0085] (3) The thermally conductive filler in the graphene thermally conductive coating provided by the present invention is uniformly distributed, the surface coating composition is uniform, and the thermal conductivity is high. After coating the graphene thermally conductive composite powder, the temperature drop percentage reaches more than 12.5%. Attached Figure Description

[0086] Figure 1 This is a schematic diagram of the aluminum alloy substrate provided in Application Example 1 of the present invention and its surface coated with a graphene thermally conductive coating.

[0087] Figure 2 This is a graph showing the temperature change over time of the aluminum alloy and the surface coated with a graphene thermally conductive coating in Application Example 1 of this invention.

[0088] Figure 3 yes Figure 2 Graph showing the change of temperature difference over time. Detailed Implementation

[0089] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0090] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0091] Example 1

[0092] This embodiment provides a method for preparing graphene thermally conductive composite powder, the preparation method comprising the following steps:

[0093] (1) First, graphene (99% purity) with a thickness of 15 nm and titanium dioxide are mixed. Then, titanium dioxide is reduced to titanium suboxide (average particle size of 400 nm) in an argon atmosphere. Then, polylactic acid with a particle size of 80 mesh is added and ball milled at 400 r / min for 4 h. After ball milling, acetic acid with pH 3 is added to obtain a mixture. The mass ratio of graphene to titanium dioxide is 10:10.5, the mass ratio of polylactic acid to graphene is 10:1, and the mass ratio of the sum of the masses of graphene, metal oxide and polylactic acid to the mass ratio of acetic acid is 1:1.

[0094] (2) The mixture is heated to reflux at 150°C for 5 hours. During the heating and reflux reaction, polylactic acid melts, degrades and hydrolyzes to obtain the reaction product.

[0095] (3) The reaction product was successively cooled to room temperature, filtered, washed with 50 ml of ethanol, and the filter cake was collected and heated again at 170°C for 1 hour. Then, it was successively ground and passed through a 20-mesh sieve to obtain the graphene thermally conductive composite powder. Example 2

[0096] This embodiment provides a method for preparing graphene thermally conductive composite powder, the preparation method comprising the following steps:

[0097] (1) First, graphene (99% purity) with a thickness of 20 nm and titanium dioxide were mixed. Then, titanium dioxide was reduced to titanium suboxide (average particle size of 420 nm) in an argon atmosphere. Then, polylactic acid with a particle size of 70 mesh was added and ball milled at 350 r / min for 3 h. After ball milling, acetic acid with pH 2.5 was added to obtain a mixture. The mass ratio of graphene to titanium dioxide was 10:12, the mass ratio of polylactic acid to graphene was 20:1, and the mass ratio of the sum of the masses of graphene, metal oxide and polylactic acid to the mass ratio of acetic acid was 1.2:1.

[0098] (2) The mixture is heated to reflux at 160°C for 0.5 h. During the reflux reaction, polylactic acid melts, degrades, and hydrolyzes to obtain the reaction product.

[0099] (3) The reaction product was cooled to room temperature, filtered, washed with 100ml of ethanol, and the filter cake was collected and heated at 160℃ for 1.5h. Then it was ground and passed through a 15-mesh sieve to obtain the graphene thermally conductive composite powder.

[0100] Example 3

[0101] This embodiment provides a method for preparing graphene thermally conductive composite powder, the preparation method comprising the following steps:

[0102] (1) First, graphene (99% purity) with a thickness of 25 nm and titanium dioxide were mixed. Then, titanium dioxide was reduced to titanium suboxide (average particle size of 350 nm) in a hydrogen atmosphere. Then, polylactic acid with a particle size of 90 mesh was added and ball milled at 450 r / min for 5 h. After ball milling, acetic acid with pH 3.5 was added to obtain a mixture. The mass ratio of graphene to titanium dioxide was 1:0.5, the mass ratio of polylactic acid to graphene was 15:1, and the mass ratio of the sum of the masses of graphene, metal oxide and polylactic acid to acetic acid was 0.8:1.

[0103] (2) The mixture is heated to reflux at 140°C for 1.5 h. During the reflux reaction, polylactic acid melts, degrades, and hydrolyzes to obtain the reaction product.

[0104] (3) The reaction product was cooled to room temperature, filtered, washed with 60 ml of ethanol, and the filter cake was collected and heated at 180°C for 0.5 h. Then it was ground and passed through a 30-mesh sieve to obtain the graphene thermally conductive composite powder.

[0105] Example 4

[0106] This embodiment provides a graphene thermally conductive composite powder. Except for the mass ratio of graphene to titanium dioxide being 50:10.5, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0107] In this embodiment, the graphene content is too high, resulting in uneven graphene dispersion and graphene agglomeration. Consequently, the distribution of graphene and titanium suboxide in the final product is uneven, leading to uneven heat dissipation and poor heat dissipation stability.

[0108] Example 5

[0109] This embodiment provides a graphene thermally conductive composite powder. Except for not reducing titanium dioxide to titanium suboxide, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0110] In this embodiment, titanium dioxide is used, but it is not reduced to titanium suboxide, resulting in a heat dissipation effect that is not as good as in Example 1 after composite.

[0111] Example 6

[0112] This embodiment provides a graphene thermally conductive composite powder. Except for the pH of acetic acid being 5, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0113] In this embodiment, the concentration of acetic acid was relatively low, resulting in poor acid hydrolysis of polylactic acid, poor uniformity of graphene oxide and titanium suboxide distribution, and poorer heat dissipation stability compared to Example 1.

[0114] Example 7

[0115] This embodiment provides a graphene thermally conductive composite powder. Except for the pH of the acetic acid being 2.4, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0116] In this embodiment, the concentration of acetic acid was too high, which led to excessive acid hydrolysis of polylactic acid. It was also difficult to obtain a solid phase after subsequent cooling, making it difficult to prepare graphene thermally conductive composite powder.

[0117] Example 8

[0118] This embodiment provides a graphene thermally conductive composite powder. Except for the ratio of the sum of the masses of graphene, metal oxide, and polylactic acid to acetic acid being 1.5:1, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0119] In this embodiment, the amount of acetic acid was too low, resulting in poor acid hydrolysis of polylactic acid, poor uniformity of graphene oxide and titanium suboxide distribution, and poorer heat dissipation stability compared to Example 1.

[0120] Example 9

[0121] This embodiment provides a graphene thermally conductive composite powder. Except for the ratio of the sum of the masses of graphene, metal oxide, and polylactic acid to acetic acid of 0.6:1, the graphene thermally conductive composite powder is the same as that in Example 1, and will not be described again here.

[0122] In this embodiment, the amount of acetic acid was too high, which led to excessive acid hydrolysis of polylactic acid. It was also difficult to obtain a solid phase after subsequent cooling, making it difficult to prepare graphene thermally conductive composite powder.

[0123] Example 10

[0124] This embodiment provides a graphene thermally conductive composite powder. Except for the fact that the filter cake is directly dried, ground, and sieved without secondary heating, the graphene thermally conductive composite powder is the same as in Embodiment 1, and will not be described again here.

[0125] In this embodiment, secondary heating was not performed, which made it difficult to form polylactic acid-encapsulated graphene and metal oxide products. As a result, particle agglomeration and uneven distribution are likely to occur during the subsequent spraying process.

[0126] Example 11

[0127] This embodiment provides a graphene thermally conductive composite powder. Except for step (1), which does not involve ball milling and directly adds acetic acid, the graphene thermally conductive composite powder is the same as in Example 1, and will not be described again here.

[0128] In this embodiment, ball milling was not performed, resulting in uneven distribution of graphene and titanium suboxide, and poor thermal conductivity of the subsequently coated composite powder.

[0129] Comparative Example 1

[0130] This comparative example provides a graphene thermally conductive composite powder. Except that the graphene thermally conductive composite powder does not contain titanium dioxide and is not reduced, it is otherwise the same as in Example 1, and will not be described again here.

[0131] This comparative example uses only graphene, and the overall composite powder has poorer thermal conductivity compared to Example 1.

[0132] Comparative Example 2

[0133] This comparative example provides a graphene thermally conductive composite powder, which is the same as that in Example 1 except that acetic acid is not added, and will not be described again here.

[0134] The absence of acetic acid in this comparative example resulted in poor acid hydrolysis of polylactic acid, poor uniformity of graphene oxide and titanium suboxide distribution, and poorer heat dissipation stability compared to Example 1.

[0135] Comparative Example 3

[0136] This comparative example provides a graphene thermally conductive composite powder, which is the same as that in Example 1 except that polylactic acid is replaced with paraffin. It will not be described again here.

[0137] In this comparative example, paraffin wax was used for encapsulation and dispersion, which could not achieve the thermal conductivity effect of polylactic acid and graphene working together. As a result, the heat dissipation of the composite powder was not as good as that in Example 1.

[0138] Application Example 1

[0139] This application example provides a method for preparing a graphene thermally conductive coating, the method comprising the following steps:

[0140] (1') The graphene thermally conductive composite powder, binder (siloxane, brand name Dow Corning SYLGARD184) and diluent (ethyl acetate) provided in Example 1 were mixed and stirred at 400 r / min for 5 h. The graphene thermally conductive composite powder accounted for 20% of the binder, and the mass ratio of binder to diluent was 1.0:2 to obtain the coating.

[0141] (2') The coating described in step (1') is sprayed onto the substrate (aluminum alloy 2024) using a spray gun, and the thinner is removed by standing for 5 hours and drying at 120°C for 10 hours in sequence, forming a graphene thermally conductive coating with a thickness of 70 μm.

[0142] The surface diagram of the graphene thermally conductive coating and its original aluminum alloy substrate provided in this application example is shown below. Figure 1 As shown, the left image shows a graphene thermally conductive coating, and the right image shows a graphene thermally conductive coating-free coating. Figure 1 It can be seen that the graphene thermally conductive coating is uniformly applied; the temperature change over time of the aluminum alloy and its surface coated with the graphene thermally conductive coating is shown in the figure below. Figure 2 As shown in the figure, the temperature difference changes over time. Figure 3 As shown, from Figure 3 As can be seen, the graphene thermal conductive coating provided by the present invention is a heat dissipation film with uniform heat dissipation effect, high thermal conductivity and corrosion resistance, which can effectively improve the heat dissipation effect of the substrate material. After coating, the temperature drops from 160℃ to 140℃, about 20℃, and the cooling percentage reaches 12.5%.

[0143] Application Example 2

[0144] This application example provides a method for preparing a graphene thermally conductive coating, the method comprising the following steps:

[0145] (1') The graphene thermally conductive composite powder, binder (siloxane, brand name Dow Corning SYLGARD184) and diluent (ethyl acetate) provided in Example 2 were mixed and stirred at 450 r / min for 4 h. The graphene thermally conductive composite powder accounted for 30% of the binder, and the mass ratio of binder to diluent was 1.2:2 to obtain the coating.

[0146] (2') The coating described in step (1') is sprayed onto the substrate (pure aluminum) using a spray gun, and the diluent is removed by standing for 4 hours and drying at 110°C for 8 hours in sequence, forming a graphene thermally conductive coating with a thickness of 80 μm.

[0147] Application Example 3

[0148] This application example provides a method for preparing a graphene thermally conductive coating, the method comprising the following steps:

[0149] (1') The graphene thermally conductive composite powder, binder (siloxane, brand name Dow Corning SYLGARD184) and diluent (ethyl acetate) provided in Example 3 were mixed and stirred at 500 r / min for 6 h. The graphene thermally conductive composite powder accounted for 15% of the binder, and the mass ratio of binder to diluent was 0.8:2 to obtain the coating.

[0150] (2') The coating described in step (1') is sprayed onto the substrate (aluminum alloy 6061) using a spray gun, and the diluent is removed by standing for 6 hours and drying at 130°C for 12 hours in sequence to form a graphene thermally conductive coating with a thickness of 60 μm.

[0151] Application Examples 4-11 and Comparative Examples 1-3

[0152] Application Examples 4-11 and Comparative Examples 1-3 provide a method for preparing a graphene thermally conductive coating. The method for preparing the graphene thermally conductive coating is the same as that in Application Example 1, except that the graphene thermally conductive composite powder in Examples 4-11 and Comparative Examples 1-3 is used respectively. It will not be described again here.

[0153] The test investigated the temperature change over time of a radiator coated with graphene thermal conductive coating during operation. Three test sites were selected on the surface, and the highest temperature difference between the radiator and the radiator without graphene thermal conductive coating was recorded (i.e., the highest temperature drop in °C). At the same time, the highest surface temperature of the original radiator was recorded, and the percentage temperature drop was calculated (the highest temperature difference divided by the highest temperature of the original radiator).

[0154] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing graphene thermally conductive composite powder, characterized in that, The preparation method includes: (1) Mix graphene, metal oxide, polylactic acid and acid regulator to obtain a mixture; the mixing in step (1) includes: first mixing graphene, metal oxide and polylactic acid, and ball milling, and then adding acid regulator; (2) The mixture is heated and refluxed, during which polylactic acid melts, degrades, and hydrolyzes to obtain the reaction product; (3) The reaction products are successively cooled, separated into solid and liquid, washed and heated a second time to obtain the graphene thermally conductive composite powder; The mass ratio of graphene to metal oxide is 1:0.5~2; The metal oxide is titanium suboxide; The acid regulator includes acetic acid; The pH of the acid regulator is 2.5 to 3.5; the mass ratio of the sum of the mass of graphene, metal oxide and polylactic acid to the mass of the acid regulator is 0.8 to 1.2:

1.

2. The preparation method according to claim 1, characterized in that, The graphene mentioned in step (1) is graphene nanopowder.

3. The preparation method according to claim 2, characterized in that, The thickness of the graphene nanopowder is 10~30nm.

4. The preparation method according to claim 1, characterized in that, The particle size of the metal oxide is 350~450nm.

5. The preparation method according to claim 1, characterized in that, The polylactic acid is polylactic acid particles.

6. The preparation method according to claim 5, characterized in that, The polylactic acid particles have a particle size of 70-90 mesh.

7. The preparation method according to claim 1, characterized in that, The mass ratio of polylactic acid to graphene is 30~10:

1.

8. The preparation method according to claim 1, characterized in that, The process of first mixing graphene, metal oxide, and polylactic acid includes: first mixing graphene and titanium dioxide, then reducing titanium dioxide to titanium suboxide in a reducing atmosphere, and then adding polylactic acid.

9. The preparation method according to claim 8, characterized in that, The reducing atmosphere is argon.

10. The preparation method according to claim 1, characterized in that, The temperature range for the heating reflux reaction in step (2) is 140~160℃.

11. The preparation method according to claim 1, characterized in that, The products of polylactic acid degradation and hydrolysis include lactic acid and / or polylactic acid with a low degree of polymerization.

12. The preparation method according to claim 11, characterized in that, The degree of polymerization of the low-polymer polylactic acid is 2 to 5.

13. The preparation method according to claim 1, characterized in that, The duration of the heating reflux reaction is 0.5~1.5h.

14. The preparation method according to claim 1, characterized in that, The cooling mentioned in step (3) is cooling to room temperature.

15. The preparation method according to claim 1, characterized in that, The solid-liquid separation includes filtration.

16. The preparation method according to claim 1, characterized in that, The cleaning includes ethanol cleaning.

17. The preparation method according to claim 1, characterized in that, The temperature of the secondary heating is 160~180℃.

18. The preparation method according to claim 1, characterized in that, The duration of the secondary heating is 0.5 to 1.5 hours.

19. The preparation method according to claim 1, characterized in that, The preparation method further includes grinding and sieving sequentially after the secondary heating.

20. The preparation method according to claim 19, characterized in that, The sieve mesh size is 15-30 mesh.

21. A graphene thermally conductive composite powder, characterized in that, The graphene thermally conductive composite powder comprises: graphene, metal oxides, polylactic acid, and degradation and hydrolysis products of polylactic acid; The polylactic acid and its degradation and hydrolysis products are coated with metal oxides and graphene. The mass ratio of graphene to metal oxide is 1:0.5~2, and the mass ratio of polylactic acid and the sum of the mass of polylactic acid degradation and hydrolysis products to the mass of graphene is 30~10:

1. The metal oxide includes titanium suboxide.

22. The graphene thermally conductive composite powder according to claim 21, characterized in that, The particle size of the graphene thermally conductive composite powder is 15-30 mesh.

23. The graphene thermally conductive composite powder according to claim 21, characterized in that, The degradation and hydrolysis products of the polylactic acid include lactic acid and / or polylactic acid with a low degree of polymerization.

24. A method for preparing a graphene thermally conductive coating, characterized in that, The graphene thermally conductive coating is prepared by using the graphene thermally conductive composite powder prepared by the method described in any one of claims 1 to 20, or the graphene thermally conductive coating is prepared by using the graphene thermally conductive composite powder prepared by any one of claims 21 to 23.

25. The method for preparing the graphene thermally conductive coating according to claim 24, characterized in that, The preparation method of the graphene thermally conductive coating includes the following steps: (1') A coating is obtained by mixing graphene thermally conductive composite powder, binder and diluent; (2') The coating is sprayed onto the substrate and left to stand and the diluent is removed to form a graphene thermally conductive coating.

26. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The graphene thermally conductive composite powder mentioned in step (1') accounts for 15-30% of the binder.

27. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The mass ratio of the binder to the diluent is 0.8~1.2:

2.

28. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The adhesive includes siloxane.

29. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The diluent includes ethyl acetate.

30. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The mixing described in step (1') is carried out by stirring.

31. The method for preparing the graphene thermally conductive coating according to claim 30, characterized in that, The stirring time is 4-6 hours.

32. The method for preparing the graphene thermally conductive coating according to claim 30, characterized in that, The stirring speed is 300 r / min to 500 r / min.

33. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The spraying in step (2') includes: using a spray gun to spray the coating described in step (1') onto the substrate.

34. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The substrate is made of aluminum or aluminum alloy.

35. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The settling time is 4 to 6 hours.

36. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The removal of the diluent includes drying.

37. The method for preparing the graphene thermally conductive coating according to claim 36, characterized in that, The drying temperature is 110~130℃.

38. The method for preparing the graphene thermally conductive coating according to claim 36, characterized in that, The drying time is 8-12 hours.

39. The method for preparing the graphene thermally conductive coating according to claim 25, characterized in that, The thickness of the graphene thermally conductive coating is 60~80μm.

40. A graphene thermally conductive coating, characterized in that, The graphene thermally conductive coating comprises graphene thermally conductive composite powder and a binder; The graphene thermally conductive composite powder comprises: graphene, metal oxides, polylactic acid, and degradation and hydrolysis products of polylactic acid; the metal oxides include titanium suboxide. The mass ratio of graphene to metal oxide is 1:0.5~2, and the mass ratio of polylactic acid, the sum of the mass of polylactic acid degradation and hydrolysis products to the mass of graphene is 30~10:

1.

41. The coating material of the graphene thermally conductive coating according to claim 40, characterized in that, The particle size of the graphene thermally conductive composite powder is 15-30 mesh.

42. The coating material of graphene thermal conductive coating according to claim 40, characterized in that, The degradation and hydrolysis products of the polylactic acid include lactic acid and / or polylactic acid with a low degree of polymerization.

43. An electronic device, characterized in that, The electronic device comprises a graphene thermally conductive coating prepared by the method of any one of claims 24 to 39, or the electronic device comprises a graphene thermally conductive coating formed by coating spraying of the graphene thermally conductive coating according to any one of claims 40 to 42.

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