Preparation method of heat dissipation material based on porous alumina coated hollow glass beads, heat dissipation material and heat dissipation fin

Abstract

The invention relates to the technical field of heat dissipation, in particular to a preparation method of a heat dissipation material based on porous aluminum oxide coated hollow glass beads, the heat dissipation material and a heat dissipation fin. The invention provides a preparation method of a heat dissipation material based on porous alumina coated hollow glass beads. The preparation method comprises the following steps: etching hollow glass beads in an acidic fluoride solution to obtain perforated hollow glass beads; carrying out reaction on the perforated hollow glass beads and an aluminum potassium sulfate solution under a neutral or alkaline condition, carrying out solid-liquid separation, washing by adopting an ammonium salt solution, and then calcining; and dipping the perforated hollow glass beads coated with the porous gamma-type aluminum oxide in a liquid medium. The hollow glass beads are used as a carrier, the porous structure can store a liquid medium, the formed heat dissipation layer liquid medium evaporates at the heated end to absorb heat, steam condenses at the condensation end to release heat, liquid flows back through the pore structure of the microspheres, efficient heat transmission circulation is completed, and the heat dissipation effect is improved.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation technology, specifically to a method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres, as well as the heat dissipation material and heat sink. Background Technology

[0002] With the increasing demand for high-definition, high-color-gamut display panels, the high-resolution screen market has become particularly important. However, as screen resolution increases, the power consumption of integrated circuits (ICs) also increases dramatically, causing temperatures to rise in the IC area. For screen displays, uneven temperature can cause color shifts; for example, in liquid crystal displays (LCDs), color dots in areas with higher temperatures will appear blue-shifted. Therefore, heat dissipation at the IC becomes especially important. Currently, commonly used heat dissipation solutions include using graphite sheet heat dissipation and VC (Vibration Coefficient of Heat) cooling at the bending connections of flexible printed circuit boards (FPCs). Graphite sheet heat dissipation is a commonly used low-cost heat dissipation method, but it is not suitable for instantaneous high heat flux densities (such as exceeding 10W / cm²). 2 For chips with certain properties, their heat dissipation capabilities will reach a bottleneck, making it impossible to effectively remove heat from the heat source.

[0003] For example, Chinese Patent CN105163564B, authorized on July 31, 2018, discloses a graphite heat sink and a liquid crystal display device. The graphite heat sink includes a graphite substrate and a black protective film (PET film) covering the graphite substrate; the liquid crystal display device includes a graphite heat sink, a thermally conductive silicone layer, and a heat source body; the graphite heat sink is combined with the heat source body through the thermally conductive silicone layer to dissipate heat from the heat source body; the graphite substrate has different thicknesses for directional heat conduction.

[0004] VC (Vacuum-Conducting) heatsinks offer extremely high thermal conductivity, but they are far less advantageous than graphite sheets in terms of thickness, manufacturing process, and cost. Furthermore, VC heatsinks are typically rigid flat plates (such as vacuum-sealed copper plates), making them difficult to bend and requiring specific structural designs, which limits their large-area application. In recent years, researchers have been exploring more efficient thermal management solutions, such as two-dimensional materials with higher thermal conductivity (hexagonal boron nitride films and graphene films), but these efforts have largely remained confined to laboratory research.

[0005] Furthermore, while graphite sheets exhibit good thermal conductivity (1500-2000 W / (m•K)) in the planar (XY axis) direction, their thermal conductivity is very poor in the thickness (Z axis) direction. They primarily function to "diffuse" heat rather than "transfer" it. Graphene and hexagonal boron nitride films, both layered structures, suffer from the same problem. Therefore, there is an urgent need for a low-cost thermal management solution that is isotropic, possesses ultra-high thermal conductivity, is lightweight and thin, and can be used in various applications. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres, thereby solving the problem of poor heat dissipation performance of existing heat dissipation materials.

[0007] The second objective of this invention is to provide a heat dissipation material based on porous alumina-coated hollow glass microspheres, thereby solving the problem of poor heat dissipation performance of existing heat dissipation materials.

[0008] The third objective of this invention is to provide a heat sink that solves the problem of poor heat dissipation performance of existing heat sinks.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention for the preparation method of heat dissipation material based on porous alumina-coated hollow glass microspheres is as follows: A method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres includes the following steps: (1) The hollow glass microspheres are etched in an acidic fluoride solution to make the outer wall of the hollow glass microspheres have a channel structure that connects the outside and the inner cavity of the hollow glass microspheres, so as to obtain perforated hollow glass microspheres. (2) Perforated hollow glass microspheres and potassium aluminum sulfate solution are reacted under neutral or alkaline conditions. After the reaction is completed, solid-liquid separation is performed. Ammonium salt solution is used for washing to replace potassium ions with ammonium ions. Then, calcination is performed to obtain porous γ-type alumina-coated perforated hollow glass microspheres. (3) The porous γ-type alumina-coated perforated hollow glass microspheres are vacuum impregnated in a liquid medium, so that the liquid medium enters the inner cavity of the hollow glass microspheres from the pores of the alumina and the through-hole structure of the outer wall of the hollow glass microspheres; the liquid medium is used to carry away heat in an evaporation-condensation cycle.

[0010] This invention improves upon existing technology by providing a method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres. The method involves etching the hollow glass microspheres with an acidic fluoride solution to create a porous structure on the outer wall of the microspheres that connects the external and internal cavities. Under neutral or alkaline conditions, the hydrolysis of potassium aluminum sulfate solution to form Al(OH)3 colloidal precipitates proceeds in the forward direction. Al(OH)3 preferentially adsorbs potassium chloride from the solution. + This process results in Al(OH)3 becoming positively charged, while the etched hollow microspheres become negatively charged. Al(OH)3 is more easily electrostatically attracted and adsorbed onto the surface of the hollow microspheres, resulting in a more uniform coating. Furthermore, K... +With a larger ionic radius, the activated alumina obtained by calcination after ammonium ion replacement has a larger pore volume, which can store more liquid medium. It can be used to form a closed heat dissipation layer. The liquid evaporates and absorbs heat at the heated end, and the vapor condenses and releases heat at the condensing end. The liquid then flows back through the pore structure of the microspheres, completing a highly efficient heat transfer cycle and greatly improving heat dissipation efficiency.

[0011] Preferably, in step (1), the acidic fluoride solution is obtained by dissolving sodium fluoride and hydrochloric acid in water; the mass fraction of sodium fluoride and hydrochloric acid in water is 1.25~3%; the mass of sodium fluoride and hydrochloric acid corresponding to each 50g hollow glass microspheres is 2.5~3g.

[0012] Preferably, in step (2), 150-200g of potassium aluminum sulfate at a concentration of 1.6-2 mol / L is added for every 10-15g of perforated hollow glass microspheres.

[0013] Preferably, in step (2), the reaction temperature is 60~80℃, the pH of the system is 7~9, and the reaction time is 1~2h.

[0014] Preferably, in step (2), the calcination temperature is 450~900℃ and the calcination time is 3~5h.

[0015] Preferably, the porous structure in γ-type alumina has an average pore size of 14-20 nm and a specific surface area of ​​300-400 m². 2 / g.

[0016] Preferably, the liquid medium is selected from one or more of water, alcohol, methanol, and acetone.

[0017] Preferably, the ammonium salt solution is a hot ammonium salt solution with a mass concentration of 3-5% and a temperature of 60-80°C. Since potassium ions are difficult to remove at high temperatures, ammonium salts are chosen for ion exchange, which preserves the larger pores formed by potassium ions while removing ammonium ions at high temperatures.

[0018] The technical solution of the heat dissipation material based on porous alumina-coated hollow glass microspheres of the present invention is as follows: A heat dissipation material based on porous alumina-coated hollow glass microspheres includes hollow glass microspheres and porous γ-type alumina coating the surface of the hollow glass microspheres; the outer wall of the hollow glass microspheres has a channel structure that connects the outside and the inner cavity of the hollow glass microspheres; the inner cavity of the hollow glass microspheres, the channel structure, and the pores of the porous γ-type alumina are all filled with a liquid medium, which is used to remove heat through an evaporation-condensation cycle.

[0019] This invention provides a heat dissipation material based on porous alumina-coated hollow glass microspheres. The hollow glass microspheres are coated with large-pore activated alumina: firstly, the microspheres themselves have deep pores and perforated structures, which can store cooling liquid; secondly, the activated alumina coating, due to its large pores and extremely high porosity, gives the microspheres an exceptionally high specific surface area. Using the perforated hollow glass microspheres as a carrier to store the cooling liquid, a closed heat dissipation layer can be formed. The liquid evaporates at the heated end, absorbing heat, and the vapor condenses at the condensing end, releasing heat. The liquid then flows back through the porous structure of the microspheres, completing a highly efficient heat transfer cycle and significantly improving heat dissipation efficiency.

[0020] The technical solution of the heat sink of the present invention is as follows: A heat sink includes a heat dissipation material layer and a thermally conductive adhesive that wraps around the heat dissipation material layer, with a protective film bonded and fixed to the outside of the thermally conductive adhesive; the heat dissipation material layer includes the heat dissipation material prepared by the method for preparing heat dissipation material based on porous alumina-coated hollow glass microspheres or the heat dissipation material based on porous alumina-coated hollow glass microspheres.

[0021] The heat sink provided by this invention includes a heat dissipation material layer and a protective film encapsulating the heat dissipation material layer. The liquid medium in the hollow glass microspheres encapsulated in the heat dissipation material layer evaporates and absorbs heat at the heated end, and the vapor condenses and releases heat at the condensing end. The liquid then flows back through the porous structure of the microspheres, completing a highly efficient heat transfer cycle and significantly improving heat dissipation efficiency. Due to the highly efficient heat transfer cycle, the thermal conductivity in the X / Y / Z axis directions is excellent, and the overall equivalent thermal conductivity is higher, reaching >4000 W / (m•K), which has a significant advantage, especially in the heat dissipation of high-power heat sources.

[0022] The graphite sheets in graphite heat sinks are brittle and easily torn or damaged, requiring a protective layer or support structure. Once used, the wrinkles cannot be repaired, so they cannot be reused, making repair work difficult and greatly increasing product costs. The heat sink of this invention has a protective film wrapping material to form a closed space, and is filled with hollow glass microspheres with high strength and light weight. While maintaining flexibility, it can still be reused, which can significantly reduce costs.

[0023] Preferably, the thickness of the heat dissipation material layer is 30~200μm. Attached Figure Description

[0024] Figure 1 The image shows the XRD pattern of porous active alumina-coated hollow glass microspheres in Example 1 of this invention. Figure 2 This is a microscopic morphology diagram of porous alumina in hollow glass microspheres coated with porous active alumina according to Example 1 of the present invention. Figure 3This is a microscopic morphology diagram of porous active alumina-coated hollow glass microspheres in Example 1 of the present invention; Figure 4 This is a schematic diagram of the heat sink structure in Embodiment 3 of the present invention; Figure 5 The image shows the microstructure of the porous active alumina-coated hollow glass microspheres in Comparative Example 1. Figure 6 This diagram shows the positional relationship of heat sinks when used for heat dissipation of a mobile phone screen. Figure 7 A schematic diagram of the structure of a commercial graphite heat sink; Figure 8 Thermal image of the display screen without a heatsink attached; Figure 9 Thermal image of a graphite heat sink attached to a display screen; Figure 10 A thermal image of the heat sink of the present invention attached to the display screen; In the attached diagram: 1. PET film; 2. Acrylic adhesive; 3. Heat dissipation material layer; 4. Backing adhesive layer. Detailed Implementation

[0025] The technical concept of the preparation method of the heat dissipation material based on porous alumina-coated hollow glass microspheres provided by the present invention is as follows: Existing technologies use graphite heat sinks, which are easy to bend and can be used for heat dissipation in flexible circuit boards. However, their thermal conductivity varies greatly in the three directions of XYZ. Hexagonal boron nitride films and graphene films have the same problem, resulting in poor heat dissipation.

[0026] This invention utilizes hollow glass microspheres as a carrier. The interconnected pore structure of the inner cavity and outer wall, as well as the porous structure of the alumina coating, can store liquid media. The liquid media in the heat dissipation layer evaporates and absorbs heat at the heated end, while the vapor condenses and releases heat at the condensing end. The liquid then flows back through the porous structure of the microspheres, completing a highly efficient heat transfer cycle. It has ultra-high thermal conductivity in the XYZ axes, significantly improving the heat dissipation effect.

[0027] The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres provided by the present invention includes the following steps: (1) Preparation of perforated hollow glass microspheres: Hollow glass microspheres are etched in an acidic fluoride solution. The hollow glass microspheres are selected from silicate glass microspheres or borosilicate glass microspheres, so that the outer wall of the hollow glass microspheres has a channel structure that connects the outside and the inner cavity of the hollow glass microspheres, thus obtaining perforated hollow glass microspheres.

[0028] In step (1), the acidic fluoride solution is obtained by dissolving sodium fluoride and hydrochloric acid in water; the mass fraction of sodium fluoride and hydrochloric acid in water is 1.25~3%; the mass of sodium fluoride and hydrochloric acid corresponding to each 50g hollow glass microspheres is 2.5~3g.

[0029] In step (1), the etching time is 30~60 min; the etching is carried out under stirring.

[0030] In step (1), after etching is completed, washing is performed until the washing solution is neutral; the solvent used for washing is water.

[0031] In step (1), after washing, drying is carried out at a temperature of 60~100℃ for 2~3 hours. The drying is carried out under vacuum.

[0032] It should be noted that the fluoride mass fraction and reaction time should be strictly controlled to avoid over-crushing and breaking the microspheres.

[0033] (2) Preparation of porous active alumina-coated perforated hollow glass microspheres: Perforated hollow glass microspheres and potassium aluminum sulfate solution were reacted under neutral or alkaline conditions. After the reaction was completed, solid-liquid separation was performed. The microspheres were washed with ammonium salt solution to replace potassium ions with ammonium ions. Then, the microspheres were calcined to obtain porous γ-type alumina-coated perforated hollow glass microspheres. The potassium aluminum sulfate was potassium aluminum sulfate dodecahydrate.

[0034] In step (2), 150-200g of potassium aluminum sulfate at a concentration of 1.6-2 mol / L is added for every 10-15g of perforated hollow glass microspheres.

[0035] In step (2), the reaction temperature is 60~80℃, the pH of the system is 7~9, and the reaction time is 1~2h.

[0036] In step (2), the calcination temperature is 450~900℃ and the calcination time is 3~5h. At this calcination temperature, a porous γ-type alumina coating can be obtained, while removing ammonium ions.

[0037] In step (2), before the reaction, the perforated hollow glass microspheres and potassium aluminum sulfate solution are mixed at room temperature. The mixing is carried out under stirring and the stirring time is 30~60min.

[0038] In step (2), the neutral or alkaline condition is achieved by adding an alkaline solution dropwise to the reaction system; the alkaline solution is a potassium hydroxide solution with a concentration of 2-3 mol / L. The reaction time refers to the time after the alkaline solution has been added.

[0039] In step (2), the ammonium salt solution is a hot ammonium salt solution with a mass concentration of 3-5% and a temperature of 60-80℃. Since potassium ions are not easily removed at high temperatures, ammonium salt is chosen for ion exchange, which preserves the large gaps formed by potassium ions while removing ammonium ions at high temperatures.

[0040] In step (2), the product is dried at 100~110℃ before calcination to remove the residual solvent and moisture after washing, so that it can be further calcined.

[0041] In step (2), the porous activated alumina obtained by calcination is coated with perforated hollow glass microspheres. The average pore size of the porous structure in the γ-type alumina is 14~20 nm, and the specific surface area is 300~400 m². 2 / g. Commercially available hollow glass microspheres can all be coated using the method of this invention.

[0042] (3) Preparation of heat dissipation material: The porous γ-type alumina-coated perforated hollow glass microspheres are vacuum impregnated in a liquid medium to remove the air from the inner cavity of the microspheres. At the same time, the liquid medium enters the inner cavity of the hollow glass microspheres from the pores of the alumina and the through-hole structure of the outer wall of the hollow glass microspheres. The liquid medium is used to carry away heat in an evaporation-condensation cycle.

[0043] In step (3), the liquid medium is selected from one or more of water, alcohol, methanol, and acetone.

[0044] In step (3), the impregnation is carried out under vacuum conditions. The impregnation time is 30~60 minutes.

[0045] The heat dissipation material based on porous alumina-coated hollow glass microspheres provided by the present invention includes hollow glass microspheres and porous γ-type alumina coated on the surface of the hollow glass microspheres; the outer wall of the hollow glass microspheres has a channel structure that connects the outside and the inner cavity of the hollow glass microspheres; the inner cavity of the hollow glass microspheres, the channel structure and the pores of the porous γ-type alumina are all filled with a liquid medium, which is used for evaporation-condensation cycle to remove heat.

[0046] The heat sink of the present invention includes a heat dissipation material layer and a thermally conductive adhesive that wraps the heat dissipation material layer, and a protective film is bonded and fixed to the outside of the thermally conductive adhesive; the heat dissipation material layer includes the heat dissipation material prepared by the method of preparing heat dissipation material based on porous alumina-coated hollow glass microspheres or the heat dissipation material based on porous alumina-coated hollow glass microspheres.

[0047] The method for preparing the heat sink of the present invention includes the following steps: sequentially coating an acrylic adhesive and a heat dissipation material based on porous alumina-coated hollow glass microspheres onto a PET film to form a three-layer structure, wherein the coating amount of the heat dissipation material based on porous alumina-coated hollow glass microspheres is 0.1~0.3 g / cm³. 2 Two identical three-layer heat dissipation materials are stacked opposite each other and pressed together to form a heat sink. The pressing pressure is 5~10 N / cm. 2 .

[0048] The embodiments of the present invention will be further described below with reference to specific examples. Unless otherwise specified, the chemical reagents involved in the following examples are all commercially available conventional products.

[0049] I. Preparation method of heat dissipation material based on porous alumina-coated hollow glass microspheres and specific embodiments of the heat dissipation material of the present invention. Example 1 The preparation method of the heat dissipation material based on porous alumina-coated hollow glass microspheres in this embodiment is as follows: (1) Preparation of perforated hollow glass microspheres: 50g of hollow glass microspheres were added to a mixed solution of NaF and hydrochloric acid, wherein the mass of water was 200g and the mass of NaF and hydrochloric acid was 2.5g. The mixture was mechanically stirred at room temperature for 30min to etch the hollow glass microspheres so that the outer wall of the hollow glass microspheres had a channel structure that connected the outside and the inside of the hollow glass microspheres. The hollow glass microspheres were filtered out and washed three times with deionized water until the pH of the washing solution was 7. The obtained hollow glass microspheres were then vacuum dried at 100℃ for 2 hours to obtain perforated hollow glass microspheres.

[0050] (2) Preparation of porous activated alumina-coated perforated hollow glass microspheres: 150g of potassium aluminum sulfate dodecahydrate solution (1.6mol / L) and 10g of perforated hollow glass microspheres obtained in step (1) were mixed and stirred at room temperature for 30min to ensure uniform mixing; then the temperature was raised to 60℃ and 2 mol / L KOH aqueous solution was slowly added dropwise until the solution pH=7. Stirring was continued for 1.5h. After hydrolysis of potassium aluminum sulfate dodecahydrate solution, Al(OH)3 colloidal particles were formed as precipitates. Al(OH)3 preferentially adsorbed K in the solution. + This process results in Al(OH)3 carrying a positive charge, while the etched hollow glass microspheres carry a negative charge. Al(OH)3 is more easily electrostatically attracted and adsorbed onto the surface of the hollow glass microspheres, resulting in a more uniform coating. The hydrolysis reaction reaches dynamic equilibrium, simultaneously producing H₂. + The pH was adjusted by adding KOH aqueous solution dropwise to promote the hydrolysis reaction and accelerate the hydrolysis efficiency. Afterwards, filtration was performed, followed by vacuum washing with hot ammonium nitrate solution (3%, 60℃). Due to the presence of NH4... + With K+ They have the same charge (+1), but different hydration radii, and NH4 + It may have better binding energy with certain surface sites. High concentrations of NH4 are provided by repeated washing with hot ammonium nitrate solution, utilizing the law of mass action. + NH4 + K is replaced + Remove K + The filtrate was washed, dried at 110℃, and then calcined at 460℃ for 3 hours. + The radius is relatively large, and the pore volume of the activated alumina generated after calcination is relatively large, K + It is not easily volatilized during calcination, so NH4 is used. + Replacement K + Afterward, it is easier to remove, resulting in porous active alumina (γ-type) coated with perforated hollow glass microspheres with large pores.

[0051] XRD analysis can be found in [link to XRD analysis]. Figure 1 The 2θ diffraction angles were 37.33°, 45.78°, and 66.92°, corresponding to the (311), (400), and (440) crystal planes of γ-type alumina, respectively, proving that the obtained alumina was γ-type. The microstructure diagram is shown below. Figure 2-3 As shown, where Figure 2 The microstructure of the porous alumina coating layer is shown, with a clear pore structure on the surface and an average pore size of up to 14 nm (obtained by averaging multiple sites measured by SEM, with a distribution range of 5-30 nm). Figure 3 The microstructure of porous activated alumina-coated perforated hollow glass microspheres is shown. It can be seen that the porous alumina is uniformly coated on the surface of the hollow glass microspheres, with a specific surface area reaching 326 m². 2 / g.

[0052] (3) Preparation of heat dissipation material: Add the porous active alumina coated with perforated hollow glass microspheres from step (2) to water, place it in a vacuum drying oven, and evacuate for 30 minutes to allow the coolant water to enter the inner cavity of the hollow glass microspheres from the large pores of the alumina and the through-hole structure of the outer wall of the hollow glass microspheres, so as to achieve the purpose of filling the pores inside the microspheres with liquid, and filter to obtain heat dissipation material.

[0053] The heat dissipation material prepared in this embodiment is the heat dissipation material based on porous alumina-coated hollow glass microspheres provided by the present invention. It includes hollow glass microspheres and porous γ-type alumina coating the surface of the hollow glass microspheres. The outer wall of the hollow glass microspheres has a channel structure that connects the outside and the inner cavity of the hollow glass microspheres. Water is filled in the inner cavity of the hollow glass microspheres, the channel structure, and the pores of the porous γ-type alumina. The average pore size of the porous structure in the γ-type alumina is 14 nm, and the specific surface area is 326 m². 2 / g.

[0054] Example 2 The preparation method of the heat dissipation material based on porous alumina-coated hollow glass microspheres in this embodiment is as follows: (1) Preparation of perforated hollow glass microspheres: 50g of hollow glass microspheres were added to a mixed solution of NaF and hydrochloric acid, wherein the mass of water was 200g and the mass of NaF and hydrochloric acid was 3g. The mixture was mechanically stirred at room temperature for 30min to etch the hollow glass microspheres so that the outer wall of the hollow glass microspheres had a channel structure that connected the outside and the inner cavity of the hollow glass microspheres. The hollow glass microspheres were filtered out and washed with deionized water 3 times until the pH of the washing solution was 7. The obtained hollow glass microspheres were then vacuum dried at 100℃ for 2 hours to obtain perforated hollow glass microspheres.

[0055] (2) Preparation of porous activated alumina coated perforated hollow glass microspheres: Take 200g of potassium aluminum sulfate dodecahydrate solution (2mol / L) and 15g of perforated hollow glass microspheres obtained in step (1), mix them and stir at room temperature for 30min to make them uniformly mixed; then raise the temperature to stabilize at 80℃, and then slowly add 2 mol / L KOH aqueous solution until the solution pH=9, continue stirring for 1h, then filter, and wash with hot ammonium nitrate solution (3%, 80℃), dry at 110℃ after washing, and then calcine at 900℃ for 5h.

[0056] (3) Preparation of heat dissipation material: The porous active alumina coated with perforated hollow glass microspheres from step (2) is added to alcohol and placed in a vacuum drying oven. Vacuum is drawn for 1 hour so that the cooling liquid alcohol enters the inner cavity of the hollow glass microspheres from the large pores of the alumina and the through-hole structure of the outer wall of the hollow glass microspheres, so as to achieve the purpose of filling the pores inside the microspheres with liquid. The heat dissipation material is obtained by filtration.

[0057] II. Specific Embodiments of the Heatsink of the Present Invention Example 3 A schematic diagram of the heat sink in this embodiment is shown below. Figure 4 As shown, the material includes a heat dissipation material layer 3 and an acrylic adhesive 2 encapsulating the heat dissipation material layer 3. A PET film 1 is bonded to the outer side of the acrylic adhesive 2 away from the heat dissipation material layer 3. The PET film 1 has an adhesive backing layer 4 on the side away from the acrylic adhesive 2. The heat dissipation material layer 3 is formed from the heat dissipation material of Example 1 based on porous alumina-coated hollow glass microspheres. The thickness of the heat dissipation material layer 3 is 30 μm. In other embodiments, the thickness of the heat dissipation material layer 3 is 200 μm.

[0058] The method for preparing the heat sink in this embodiment is as follows: Using PET film as the substrate, the size and shape can be designed according to actual needs. An acrylic adhesive is coated onto the first PET film (covering the entire surface of the PET film). The heat dissipation material based on porous alumina-coated hollow glass microspheres from Example 1 is spread evenly using a scraper coating method (the heat dissipation material obtained after filtration in Example 1 is in a semi-dry, semi-wet state, requiring no other solvents and can be directly scraped; the scraping area is slightly smaller than the acrylic adhesive coating area). The scraping amount is 0.1 g / cm³. 2 A heat dissipation material layer with a thickness of 15 μm was obtained, resulting in a three-layer structure of first PET film - first acrylic adhesive layer - first heat dissipation material layer. The above steps were repeated to obtain another three-layer structure: second PET film - second acrylic adhesive layer - second heat dissipation material layer. The first and second heat dissipation material layers of the two three-layer structures were stacked opposite each other and bonded together to form a heat dissipation material layer. The first and second acrylic adhesive layers were bonded at both ends of the heat dissipation material layer. The acrylic adhesive served to fix the microbeads and seal the edges, forming an acrylic adhesive layer encapsulating the heat dissipation material layer. The edges of the first and second PET films were bonded together. An adhesive backing layer was applied at the position of the second PET film for application to the area requiring heat dissipation. (5 N / cm) 2 The heat sink is obtained by bonding under pressure.

[0059] III. Comparative Example Comparative Example 1 The preparation method of the heat dissipation material based on porous alumina-coated hollow glass microspheres in this comparative example is basically the same as that in Example 1, except that the hot ammonium nitrate solution is replaced with hot water at the same temperature. Figure 5 This section shows the microstructure of the porous alumina coating in the comparative example. The surface coating is dense, due to K... + It cannot be replaced, and the pore volume is significantly reduced.

[0060] Comparative Example 2 The preparation method of the heat dissipation material based on porous alumina-coated hollow glass microspheres in this comparative example is basically the same as that in Example 1. The difference is that step (3) of heat dissipation material preparation is not performed, and the porous active alumina-coated perforated hollow glass microspheres obtained by calcination in step (2) are directly used as heat dissipation material.

[0061] Comparative Example 3 The heat sink in this comparative example is basically the same as that in Example 3, except that the heat dissipation material layer is formed by the heat dissipation material of Comparative Example 1 based on porous alumina-coated hollow glass microspheres.

[0062] Comparative Example 4 The heat sink in this comparative example is basically the same as that in Example 3, except that the heat dissipation material layer is formed by the heat dissipation material of Comparative Example 2 based on porous alumina-coated hollow glass microspheres.

[0063] IV. Experimental Examples This experimental example uses a mobile phone screen as the application object. The heat sink obtained in Example 3 is attached to the FPC of the display screen, as shown in the schematic diagram below. Figure 6 As shown, the red dashed box indicates the location of the heatsink, the orange box indicates the location of the FPC, and the blue rectangle indicates the location of the IC. During device operation, the IC generates heat, and thermal imaging is used to observe the heat dissipation. The liquid medium (water) in the heat dissipation material evaporates and absorbs heat at the heated end near the IC, while the vapor condenses and releases heat at the condensing end away from the IC. Near the IC, due to the evaporation of the liquid medium, the pores in the hollow glass microspheres create a negative pressure. Under this negative pressure and capillary action, the condensed liquid flows back through the porous structure of the hollow glass microspheres, completing an efficient heat transfer cycle.

[0064] The heat sink in Example 3 was replaced with Comparative Example 3, Comparative Example 4, and a commercial graphite heat sink, respectively, to compare the heat dissipation effects. The commercial graphite heat sink comprises an adhesive layer, a PET film, and a graphite layer sequentially bonded together, as shown in the schematic diagram below. Figure 7 As shown.

[0065] Thermal image of the FPC area of ​​the display screen without a heatsink, as shown below Figure 8 As shown, the thermal image of the graphite heat sink is as follows. Figure 9 As shown, the thermal image of the heat sink of Example 3 is as follows. Figure 10 As shown, Figure 8-10 The thermal imaging images show maximum temperatures of 45℃, 42℃, and 37℃, respectively. The heat sink prepared by this invention has a significant cooling effect compared to conventional graphite heat sinks.

[0066] Table 1 lists the thermal conductivity of the heat sinks in the embodiments and comparative examples in different directions. It can be seen that the heat sink of the present invention has a higher thermal conductivity. The equivalent thermal conductivity was measured using the steady-state center heating method. Specifically, a heat source with known heating power is placed on the bottom side of the heat sink, and thermocouples are used to arrange temperature measuring points at equal intervals (distance r) along a straight line from the center to the edge of the upper side of the heat sink (refer to...). Figure 4 ), plot T(r) and r 2 The linear relationship is plotted, and the equivalent thermal conductivity K(eff) = Q / (12.6·t·slope) is derived by using the formula in reverse. Where Q is the heating power, t is the thickness of the heat sink, and slope is the slope of the plotted curve.

[0067] Table 1 Thermal conductivity of heat sinks in different directions

[0068] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres, characterized in that, Includes the following steps: (1) The hollow glass microspheres are etched in an acidic fluoride solution to make the outer wall of the hollow glass microspheres have a channel structure that connects the outside and the inner cavity of the hollow glass microspheres, so as to obtain perforated hollow glass microspheres. (2) Perforated hollow glass microspheres and potassium aluminum sulfate solution are reacted under neutral or alkaline conditions. After the reaction is completed, solid-liquid separation is performed. Ammonium salt solution is used for washing to replace potassium ions with ammonium ions. Then, calcination is performed to obtain porous γ-type alumina-coated perforated hollow glass microspheres. (3) The porous γ-type alumina-coated perforated hollow glass microspheres are vacuum impregnated in a liquid medium, so that the liquid medium enters the inner cavity of the hollow glass microspheres from the pores of the alumina and the through-hole structure of the outer wall of the hollow glass microspheres; the liquid medium is used to carry away heat in an evaporation-condensation cycle.

2. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, In step (1), the acidic fluoride solution is obtained by dissolving sodium fluoride and hydrochloric acid in water; The mass fractions of sodium fluoride and hydrochloric acid in water are both 1.25-3%; the mass of sodium fluoride and hydrochloric acid corresponding to 50g of hollow glass microspheres is 2.5-3g.

3. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, In step (2), 150-200g of potassium aluminum sulfate at a concentration of 1.6-2 mol / L is added for every 10-15g of perforated hollow glass microspheres.

4. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, In step (2), the reaction temperature is 60~80℃, the pH of the system is 7~9, and the reaction time is 1~2h.

5. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, In step (2), the calcination temperature is 450~900℃ and the calcination time is 3~5h.

6. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, The porous structure in γ-alumina has an average pore size of 14–20 nm and a specific surface area of ​​300–400 m². 2 / g.

7. The method for preparing a heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 1, characterized in that, The liquid medium is selected from one or more of water, alcohol, methanol, and acetone.

8. A heat dissipation material based on porous alumina-coated hollow glass microspheres, characterized in that, Including hollow glass microspheres and porous γ-alumina coated on the surface of hollow glass microspheres; The outer wall of the hollow glass microspheres has a channel structure that connects the outside and the inner cavity of the hollow glass microspheres; the inner cavity, channel structure and pores of the porous γ-type alumina of the hollow glass microspheres are all filled with a liquid medium, which is used to remove heat through an evaporation-condensation cycle.

9. A heat sink, characterized in that, It includes a heat dissipation material layer and a thermally conductive adhesive that wraps the heat dissipation material layer, with a protective film bonded and fixed to the outside of the thermally conductive adhesive; the heat dissipation material layer includes the heat dissipation material prepared by the method of preparing heat dissipation material based on porous alumina-coated hollow glass microspheres as described in any one of claims 1-7 or the heat dissipation material based on porous alumina-coated hollow glass microspheres as described in claim 8.

10. The heat sink as described in claim 9, characterized in that, The thickness of the heat dissipation material layer is 30~200μm.

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