High-concentration water-dispersible heat-conducting coating based on two-dimensional boron nitride as well as preparation method and application thereof

Abstract

The invention discloses a high-concentration water-dispersible heat-conducting coating based on two-dimensional boron nitride as well as a preparation method and application thereof. The method comprises the following steps: preparing a boron nitride water mixed solution and a dispersant water solution; a dispersing agent in the dispersing agent aqueous solution is polyether P123 or polyvinylpyrrolidone (PVP); adding the dispersant aqueous solution into the boron nitride-water mixed solution to prepare a boron nitride aqueous dispersion; and adding the diluted polyimide aqueous solution into the boron nitride aqueous dispersion to prepare the water-dispersible heat-conducting coating based on the two-dimensional boron nitride. According to application requirements, the low-concentration and even high-concentration boron nitride water-based stable coating can be prepared through process regulation and control, so that a composite material with the corresponding boron nitride content can be controlled, and the coating is suitable for the application fields of glass, paper-based materials, plastics, metals and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal conductive coating technology, and specifically relates to a high-concentration water-dispersed thermal conductive coating based on two-dimensional boron nitride, and a preparation method and application thereof. Background Art

[0002] As electronic devices continue to develop towards miniaturization, high integration and high power, the heat generated by the equipment will accumulate rapidly. For example, high-power solid-state lasers will generate a lot of heat during operation. If this heat cannot be dissipated in a timely and effective manner, it will lead to a decline in the performance of the laser, damage to the device, or even explosion and fire; the heat generated by the operation of the high-frequency circuit substrate causes it to expand in length, width and thickness, increase the stress at the connection, and affect the normal and stable operation of the substrate; the battery will generate heat during the charging and discharging process. If it cannot be discharged in time, the battery temperature will rise, the internal chemical reaction rate will change, and the performance of the electrode material will be affected, resulting in a decrease in battery capacity, a decrease in charging and discharging efficiency, and a shortened battery life or a reduced use time. In addition, high temperature will accelerate the aging and decomposition of the chemical substances inside the battery, damage the electrode material, reduce the battery cycle life, affect the overall performance and life of the battery pack, and require frequent battery replacement. In addition, heat accumulation may cause thermal runaway, causing the battery to bulge, smoke, or even explode and catch fire, posing a serious threat to personal and property safety. Therefore, how to prevent the local temperature of the equipment from being too high, how to effectively transfer the generated heat, reduce the loss of heat to the equipment, ensure the normal operation of the equipment and extend its service life, heat dissipation has become a key issue in device design.

[0003] Efficient thermal conductive materials are essential for improving the heat dissipation performance of electronic devices. Among the commonly used thermal conductive materials, metal materials and carbon materials have high thermal conductivity, but the dielectric constant or dielectric loss is high; the thermal conductivity of traditional ceramic materials is insufficient and it is difficult to meet high power requirements. The thermal conductivity of silicon carbide, silicon nitride, and aluminum nitride can reach 200W·m -1 ·K -1 , but the dielectric constant is high. None of these three types of materials can simultaneously meet the requirements of high thermal conductivity and low dielectric properties, thus limiting their application in devices that require low dielectric constant and high thermal conductivity. The thermal conductivity of two-dimensional boron nitride nanosheets can reach 700W·m -1 ·K -1, meanwhile, it has excellent dielectric properties, and its decomposition temperature is close to 3000 degrees. In an air atmosphere, its dielectric properties can remain stable at 900 degrees. Moreover, compared with other types of boron nitride, two-dimensional boron nitride has excellent in-plane thermal conductivity, and its thermal conductivity is higher. This is because the propagation of phonons in the two-dimensional structure is smoother, and phonon scattering is relatively less, which can effectively conduct heat in the plane. The high in-plane thermal conductivity makes two-dimensional boron nitride have important application value in the fields of heat dissipation and thermal management of electronic devices. It can be used to prepare high-performance heat dissipation materials, improve the heat dissipation efficiency of electronic devices, reduce the device temperature, and extend the service life. In addition, two-dimensional boron nitride has a low coefficient of thermal expansion. When the temperature changes, its size changes relatively little, enabling it to better match the matrix material when compounded with other materials, reducing stress and deformation caused by thermal expansion differences, and improving the stability and reliability of the composite material. Furthermore, two-dimensional boron nitride is a wide-bandgap semiconductor material with good insulation properties, and its insulation performance is superior to other boron nitride materials in some aspects. This makes two-dimensional boron nitride an ideal insulating layer material in electronic devices, which can effectively isolate charges, prevent current leakage, and improve the performance and stability of the device. Generally speaking, two-dimensional boron nitride is a new type of thermal conductive filler with excellent dielectric and thermal conductivity properties.

[0004] The crystal structure of boron nitride is formed by the alternating arrangement of boron atoms and nitrogen atoms, forming a hexagonal lattice structure similar to that. Because their atomic arrangement does not support the formation of stable hydrogen bonds between water molecules and its surface, this structure results in the hydrophobicity of the boron nitride surface. Due to the hydrophobicity of the boron nitride surface and water being a polar solvent, the mismatch of their surface energies may cause boron nitride to be difficult to disperse uniformly in water. The hydrophobicity of boron nitride itself makes it tend to aggregate and form agglomerates or clusters in water rather than being uniformly dispersed, affecting its uniform distribution in the composite substrate and resulting in uneven overall heat conduction of the composite material. Moreover, when the boron nitride coating is applied to the surface of the substrate and dried, due to the brittleness of boron nitride, the binding force between boron nitride and the substrate is weak, and the coating is prone to powdering, and even the coating may crack and peel off in large pieces.

[0005] At present, the studied boron nitride is dispersed evenly in some organic solvents or functionalized boron nitride with hydrophilic properties is prepared through modification. The existing well-dispersed boron nitride mixed solution is an organic solvent system. However, since the organic solvent is used as the dispersion solvent for boron nitride, it will cause environmental pollution during the preparation of composite materials. Moreover, some organic solvents have volatile gases, which are prone to combine with oxygen, leading to flammable safety problems. And the defects existing in the modified boron nitride will damage the original thermal conductivity to a certain extent. Therefore, the boron nitride dispersion liquids prepared by these processes cannot be used for industrial production of thermal conductive composite materials. In addition, the concentration of the boron nitride aqueous dispersion introduced in current patents is relatively low. For example, in the patent "Preparation Method and Process of a Hydroxyl-Modified Boron Nitride Nanosheet Dispersion Liquid", the highest concentration of the boron nitride nanosheet aqueous dispersion liquid with excellent stability prepared is 5 mg / ml; in the patent "Boron Nitride Dispersant, Method for Liquid Phase Exfoliating Two-Dimensional Boron Nitride Nanosheets and Their Applications", the concentration of the boron nitride dispersion liquid is ≤10 mg / mL. The low-concentration and stable boron nitride aqueous dispersion liquid cannot be efficiently used in fields such as coating. To meet the demand for high-concentration boron nitride aqueous dispersion liquid in some fields, it is necessary to prepare a stable high-concentration boron nitride aqueous dispersion liquid. At the same time, to enhance the binding force between boron nitrides and between boron nitride and the coating substrate, a suitable adhesive needs to be selected. The active groups in the molecular structure of polyimide enable it to have good bonding effects on various materials such as metals, ceramics, glass, plastics, and fibers. Polyimide has a very high glass transition temperature and decomposition temperature, and can maintain stable physical and chemical properties in a high-temperature environment, and can be used at a temperature of 200 - 300 °C for a long time. Therefore, in a high-temperature environment, the polyimide adhesive can still maintain good bonding performance. In addition, polyimide has good insulation properties, relatively high tensile strength and modulus, low dielectric constant, and small dielectric loss. It can effectively isolate current, prevent electric leakage and short circuit, and can withstand a large external force, playing the role of a binder while enhancing the material strength. Due to these advantages, on the one hand, as a boron nitride adhesive, it can solve the problem of boron nitride powder falling off, and on the other hand, it can enhance the strength of the composite material. Polyimide is a very good choice. Summary of the Invention

[0006] The present invention provides a water-dispersible thermal conductive coating based on two-dimensional boron nitride and a preparation method thereof, aiming to solve the technical problems of high-concentration uniform dispersion of boron nitride in water and the ability of this coating to serve as a "thermal conductive glue" to enhance the bonding force between the boron nitride thermal conductive filler and the substrate. The present invention uses an aqueous solution of polyether P123 (polyvinylpyrrolidone PVP) to treat hexagonal boron nitride nanosheets with high thermal conductivity and low dielectric constant, and prepares a boron nitride aqueous dispersion with good dispersibility. At the same time, a polyimide aqueous solution with high-temperature stability, excellent mechanical properties, good chemical stability, dielectric properties, wear resistance and heat resistance is used to prepare a stable water-dispersible thermal conductive coating based on two-dimensional boron nitride according to a certain ratio. The present invention can solve the problems of uneven distribution of boron nitride in water and brittleness of the boron nitride coating at present. Replacing the organic solvent system with an aqueous system can avoid the safety problems caused by the flammability of the organic system and its inapplicability to industrial coating. By controlling the dosage of polyimide, the addition of the polyimide aqueous solution is used as an adhesive for boron nitride nanosheets without affecting the thermal conductivity of boron nitride, strengthening the bonding force between boron nitride nanosheets and between boron nitride nanosheets and the coated substrate, promoting the coherent construction of the boron nitride thermal conduction network, and avoiding the powder falling and coating cracking phenomena of the boron nitride coating due to brittleness. The present invention does not use complex modification processes and does not damage the thermal conductivity of boron nitride. A stable thermal conductive boron nitride coating is developed and produced through a simple production process, providing an aqueous-phase thermal conductive coating for the industrial preparation of thermal conductive composites, which can promote the development and upgrading of thermal conductive insulating composites, further solve the heat dissipation problem, ensure the normal operation of products in the electronic device insulation industry and extend their service life.

[0007] The object of the present invention is achieved by at least one of the following technical solutions.

[0008] A preparation method of a water-dispersible thermal conductive coating based on two-dimensional boron nitride includes the following steps:

[0009] S1. Prepare a boron nitride water mixture and an aqueous dispersant solution; the dispersant in the aqueous dispersant solution is polyether P123 or polyvinylpyrrolidone PVP;

[0010] S2. Add the aqueous dispersant solution to the boron nitride water mixture to prepare a boron nitride aqueous dispersion;

[0011] S3. Add the diluted polyimide aqueous solution to the boron nitride aqueous dispersion to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

[0012] Further, in the above method, in step S1, through multiple water washings, the isopropanol solvent in the boron nitride nanosheet and isopropanol mixed dispersion is removed. After centrifugation, the boron nitride precipitate is added to water and stirred into a paste to obtain a boron nitride nanosheet aqueous dispersion. The concentration of the boron nitride water mixture is: 1 wt% - 50 wt%.

[0013] Further, in the above method, in step S1, the crystal form of the boron nitride nanosheet is a hexagonal crystal structure and presents a flaky structure.

[0014] Further, in the above method, in step S1, the preparation method of the dispersant aqueous solution is: dissolving white crystalline powder polyether P123 or white powder polyvinylpyrrolidone PVP in water to obtain a polyether P123 or polyvinylpyrrolidone PVP aqueous solution; the concentration of the polyether P123 or polyvinylpyrrolidone PVP aqueous solution is: 1 wt% - 90 wt%.

[0015] Further, in the above method, in step S2, the addition amount between the dispersant aqueous solution and the boron nitride water mixture satisfies: the dispersant accounts for 1 wt% - 30 wt% of boron nitride.

[0016] Further, in the above method, in step S3, the mass percentage concentration of the polyimide aqueous solution is 0.5% - 10%, preferably 10%.

[0017] A water-dispersible thermal conductive coating based on two-dimensional boron nitride, the water-dispersible thermal conductive coating is composed of boron nitride, polyimide, a dispersant and water, wherein boron nitride accounts for 1% - 40% of the total mass of the thermal conductive coating, the mass of polyimide is 10% - 60% of that of boron nitride, and the mass of the dispersant is 1 wt% - 30% of that of boron nitride; the dispersant is polyether P123 or polyvinylpyrrolidone PVP.

[0018] The water-dispersible thermal conductive coating based on two-dimensional boron nitride in the present invention is applied to fields such as glass, paper-based materials, plastics and metals.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) The present invention can prepare a water-based stable coating of boron nitride with low concentration or even high concentration through process-adjustable control according to application requirements, so as to control the composite material with the corresponding boron nitride content to be applicable to application fields such as glass, paper-based materials, plastics and metals;

[0021] (2) The coating prepared by the present invention can adjust the polyimide content to prepare a coating with high bonding strength to the coated substrate, so that the coating forms a thermal conductive coating with high surface peel strength after drying on various substrates. Currently, tested by GBT 22837-2008 "Determination of surface strength (wax bar method)", when the prepared thermal conductive coating is coated on the glass surface and dried into a film, its adhesion corresponds to a 13A wax bar, and the adhesion is relatively high. Detailed implementation manners

[0022] To make the objectives, contents and advantages of the present invention clearer, the following combines examples to further describe in detail the specific implementation manners of the present invention.

[0023] Example 1

[0024] This example presents a water-dispersible thermal conductive coating based on two-dimensional boron nitride and its preparation method. The preparation method includes the following steps:

[0025] S1. Through multiple water washings, the isopropanol solvent in the mixed dispersion of hexagonal boron nitride nanosheets and isopropanol is removed. After centrifugation at 6000 r / min, the boron nitride precipitate is added to water and stirred into a paste to obtain a boron nitride-water mixed solution; the white crystalline powder polyether P123 is dissolved in water to obtain an aqueous polyether P123 solution.

[0026] S2. The aqueous polyether P123 solution is added to the boron nitride-water mixed solution to prepare a boron nitride water dispersion; the addition amount of polyether P123 accounts for 5% of the absolute dry weight of boron nitride.

[0027] S3. The diluted 10% aqueous polyimide solution is added to the boron nitride water dispersion. The mass of polyimide is 40% of the absolute dry weight of boron nitride. Stir with a stirrer for 15 min to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

[0028] Table 1 shows the Zeta potential and particle size data of a common boron nitride aqueous coating and the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example. It can be seen from the table that the Zeta potential of the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example is 46 mV, and the average particle size of boron nitride decreases from 10.5 μm to 3.0 μm. The boron nitride aggregates are dispersed, and the dispersion stability of this water-dispersible thermal conductive coating is good.

[0029] Table 1 Zeta potential of boron nitride aqueous resin and coating and particle size

[0030] Sample (without adjustment p H situation) Average particle size ( μ m) Zeta (mV)

[0031] Boron nitride-water mixed solution 10.5 20.9

[0032] Water-dispersible Thermal Conductive Coating of Boron Nitride 3.0 46

[0033] Example 2

[0034] This example presents a water-dispersible thermal conductive coating based on two-dimensional boron nitride and its preparation method. The preparation method includes the following steps:

[0035] S1. Through multiple water washes, the isopropanol solvent in the mixed dispersion of hexagonal boron nitride nanosheets and isopropanol is removed. After centrifugation at 6000 r / min, the boron nitride precipitate is added to water and stirred into a paste to obtain a water mixture of boron nitride nanosheets; the white crystalline powder polyether P123 is dissolved in water to obtain an aqueous polyether P123 solution;

[0036] S2. The aqueous polyether P123 solution is added to the water mixture of boron nitride to prepare a water-dispersible boron nitride solution; the addition amount of polyether P123 accounts for 4% of the absolute dry weight of boron nitride;

[0037] S3. The diluted 10% aqueous polyimide solution is added to the water-dispersible boron nitride solution. The mass of polyimide is 40% of the absolute dry weight of boron nitride, and it is stirred with a stirrer for 15 min to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

[0038] Example 3

[0039] S1. Through multiple water washes, the isopropanol solvent in the mixed dispersion of hexagonal boron nitride nanosheets and isopropanol is removed. After centrifugation at 6000 r / min, the boron nitride nanosheet precipitate is added to water and stirred into a paste to obtain a water dispersion of boron nitride nanosheets; the white powder polyvinylpyrrolidone PVP is dissolved in water to obtain an aqueous polyvinylpyrrolidone solution;

[0040] S2. The aqueous polyvinylpyrrolidone solution is added to the water mixture of boron nitride to prepare a water-dispersible boron nitride solution; the addition amount of polyvinylpyrrolidone accounts for 4% of the absolute dry weight of boron nitride;

[0041] S3. The diluted 10% aqueous polyimide solution is added to the water-dispersible boron nitride solution. The mass of polyimide is 30% of the absolute dry weight of boron nitride, and it is stirred with a stirrer for 15 min to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

[0042] Table 2 shows the Zeta potential and particle size data of the ordinary boron nitride aqueous coating and the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example. It can be seen from the table that the Zeta potential of the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example is 52.1 mV, and the particle size is reduced to 2.0 μm, indicating that the water-dispersible thermal conductive coating has good dispersion stability.

[0043] Table 2 Zeta potential and particle size of boron nitride aqueous resin and coating

[0044]

[0045] Example 4

[0046] S1. Through multiple water washings, the isopropanol solvent in the mixed dispersion of hexagonal boron nitride nanosheets and isopropanol is removed. After centrifugation at 6000 r / min, the boron nitride nanosheet precipitate is added to water and stirred into a paste to obtain a boron nitride-water mixed solution; the white powder polyvinylpyrrolidone PVP is dissolved in water to obtain an aqueous polyvinylpyrrolidone solution.

[0047] S2. The aqueous polyvinylpyrrolidone solution is added to the boron nitride-water mixed solution to prepare a boron nitride water dispersion; the addition amount of polyvinylpyrrolidone accounts for 4% of the absolute dry weight of boron nitride.

[0048] S3. The diluted 10% aqueous polyimide solution is added to the boron nitride water dispersion. The mass of polyimide is 40% of the absolute dry weight of boron nitride. Stir with a stirrer for 15 min to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

[0049] Table 3 shows the Zeta potential and particle size data of the ordinary boron nitride aqueous coating and the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example. It can be seen from the table that the Zeta potential of the water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared in this example is 54.4 mV, and the particle size is reduced to 1.8 μm, indicating that the water-dispersible thermal conductive coating has good dispersion stability.

[0050] Table 3 Zeta potential and particle size of boron nitride aqueous resin and coating

[0051]

[0052] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a high-concentration aqueous dispersion heat-conducting coating based on two-dimensional boron nitride, characterized in that, It includes the following steps: S1. Prepare a boron nitride water mixture and a dispersant aqueous solution; the dispersant in the dispersant aqueous solution is polyether P123 or polyvinylpyrrolidone PVP; S2. Add the dispersant aqueous solution to the boron nitride water mixture to prepare a boron nitride aqueous dispersion; S3. Add the diluted polyimide aqueous solution to the boron nitride aqueous dispersion to prepare a water-dispersible thermal conductive coating based on two-dimensional boron nitride.

2. The preparation method of a high-concentration aqueous dispersion thermal conductive coating based on two-dimensional boron nitride according to claim 1, characterized in that In step S1, the method for preparing the boron nitride water mixture is as follows: through multiple water washings, remove the isopropanol solvent in the boron nitride nanosheet and isopropanol mixed dispersion, and after centrifugation, add the boron nitride sheet precipitate to water and stir into a paste to obtain the boron nitride water mixture; the concentration of the boron nitride water mixture is: 1 wt% - 50 wt%.

3. The preparation method of a high-concentration aqueous dispersion heat-conducting coating based on two-dimensional boron nitride according to claim 1, wherein, In step S1, the crystal form of the boron nitride nanosheets is a hexagonal crystal structure and presents a flaky structure.

4. The preparation method of a high-concentration aqueous dispersion heat-conducting coating based on two-dimensional boron nitride according to claim 1, characterized in that, In step S1, the method for preparing the dispersant aqueous solution is as follows: dissolve the white crystalline powder polyether P123 or the white powder polyvinylpyrrolidone PVP in water to obtain a polyether P123 or polyvinylpyrrolidone PVP aqueous solution; the concentration of the polyether P123 or polyvinylpyrrolidone PVP aqueous solution is: 1 wt% - 90 wt%.

5. The preparation method of a high-concentration water-dispersible thermal conductive coating based on two-dimensional boron nitride as claimed in claim 1, wherein In step S2, the addition amount between the dispersant aqueous solution and the boron nitride water mixture satisfies that the dispersant accounts for 1 wt% - 30 wt% of boron nitride.

6. The preparation method of a high-concentration aqueous dispersion heat-conducting coating based on two-dimensional boron nitride according to claim 1, wherein In step S3, the mass percentage concentration of the polyimide aqueous solution is 0.5% - 10%.

7. The preparation method of a high-concentration aqueous dispersion thermal conductive coating based on two-dimensional boron nitride as claimed in claim 1, characterized in that, In step S3, the mass percentage concentration of the polyimide aqueous solution is 10%.

8. A high-concentration water-dispersible thermal conductive coating based on two-dimensional boron nitride prepared by the preparation method according to any one of claims 1 to 7.

9. The water-dispersible thermal conductive coating based on two-dimensional boron nitride according to claim 8, wherein, The water-dispersible thermal conductive coating is composed of boron nitride, polyimide, a dispersant and water, wherein boron nitride accounts for 1% - 40% of the total mass of the thermal conductive coating, the mass of polyimide is 10% - 60% of that of boron nitride, and the mass of the dispersant is 1 wt% - 30% of that of boron nitride; the dispersant is polyether P123 or polyvinylpyrrolidone PVP.

10. The water-dispersible thermal conductive coating based on two-dimensional boron nitride according to claim 8 or 9 is applied to the fields of glass, paper-based materials, plastics and metals.

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