CN116120610B - Low-thermal-resistance boron nitride heat-conducting gasket and preparation method thereof - Google Patents
Low-thermal-resistance boron nitride heat-conducting gasket and preparation method thereof Download PDFInfo
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- 229910052582 BN Inorganic materials 0.000 title claims abstract description 91
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 title claims abstract description 91
- 238000002360 preparation method Methods 0.000 title claims abstract description 25
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Abstract
The application provides a preparation method of a low-thermal-resistance boron nitride heat-conducting gasket, which comprises the following steps: s1: according to weight portions, uniformly mixing 100 to 200 portions of two-dimensional boron nitride nano-sheets, 200 to 400 portions of organic solvent and 150 to 300 portions of polymer matrix to obtain composite slurry; s2: coating and drying the composite slurry on a bottom film to obtain a composite heat conducting film; s3: laminating the composite heat conducting films, and then hot-pressing to obtain a composite heat conducting block; s4: cutting the composite heat conduction block body into sheets by adopting ultrasonic cutting to obtain the low-thermal-resistance boron nitride heat conduction gasket; wherein the diameter-thickness ratio of the two-dimensional boron nitride nano-sheet is 200-500, and the glass transition temperature of the polymer matrix is-40-20 ℃. The heat-conducting gasket prepared by the preparation method has a special interface bending structure, and can effectively reduce the heat resistance of the heat-conducting gasket. The application also provides a low-thermal-resistance boron nitride heat-conducting gasket.
Description
Technical Field
The application relates to the technical field of heat conduction materials, in particular to a low-thermal-resistance boron nitride heat conduction gasket and a preparation method thereof.
Background
The thermal interface material can be used for coating between a heat dissipation device and a heat generation device, and reduces the contact thermal resistance between the heat dissipation device and the heat generation device because the thermal interface material can ensure the sufficient contact of the interface so as to ensure the effective conduction of heat. The heat-conducting gasket filled with the heat-conducting filler is a typical thermal interface material, and can fill the interface gap, reduce the interface thermal resistance and improve the heat dissipation performance. Currently, common methods for industrially preparing the heat-conducting gasket are a casting knife coating method, an external field orientation method, a laminating cutting method and the like. The cost of the casting and knife coating process is lower, but the performance is limited; the external field orientation method has obvious performance improvement but complicated process flow, and is difficult to adapt to the existing large-scale production; the laminated film cutting method has moderate process flow complexity and preparation cost, and obviously improves the heat conducting property, but the problems of heat resistance increase and the like caused by poor interface contact still exist. Moreover, the prior art mainly considers from raw materials and preparation processes, but does not consider how to carry out structural design on the heat conduction gasket to reduce interface thermal resistance.
Disclosure of Invention
In order to solve the defects in the prior art, the application aims to provide a preparation method of a low-thermal-resistance boron nitride heat-conducting gasket, and the structure of the final heat-conducting gasket is designed by controlling raw materials and specific preparation steps, so that the prepared heat-conducting gasket has a special interface bending structure, and the interface bending structure can effectively reduce the thermal resistance of the heat-conducting gasket.
In addition, the application also provides the low-thermal-resistance heat-conducting gasket prepared by the preparation method.
In order to achieve the above purpose, the application provides a preparation method of a low thermal resistance boron nitride heat conduction gasket, which comprises the following steps:
S1: according to weight portions, uniformly mixing 100 to 200 portions of two-dimensional boron nitride nano-sheets, 200 to 400 portions of organic solvent and 150 to 300 portions of polymer matrix to obtain composite slurry;
s2: coating and drying the composite slurry on a bottom film to obtain a composite heat conducting film;
S3: laminating the composite heat conducting films, and then hot-pressing to obtain a composite heat conducting block;
s4: cutting the composite heat conduction block body into sheets by adopting ultrasonic cutting to obtain the low-thermal-resistance boron nitride heat conduction gasket;
Wherein the diameter-thickness ratio of the two-dimensional boron nitride nano-sheet is 200-500, and the glass transition temperature of the polymer matrix is-40-20 ℃.
In some possible implementations, the polymeric matrix is one of silicone rubber, polyethylene, polyvinyl chloride, phenolic resin, epoxy resin, or acrylic resin.
In some possible implementations, the organic solvent is one of ethyl acetate, isopropanol, or xylene.
In some possible implementations, in step S1, the viscosity of the composite slurry measured using a 4-cup viscometer method is 40-50S.
In some possible implementations, step S1 specifically includes the following steps:
According to parts by weight, stirring 100-200 parts of two-dimensional boron nitride nano-sheets and 200-400 parts of organic solvent by adopting a single-planet homogenizer at a rotating speed of 2000-3000 rpm for 0.5-1 min, and uniformly mixing to obtain two-dimensional boron nitride nano-sheet slurry;
Stirring the two-dimensional boron nitride nano-sheet slurry and 150-300 parts of polymer matrix for 0.5-1 min by adopting a single-planet homogenizer at a rotating speed of 1500-3000 rpm, and uniformly mixing to obtain the composite slurry.
In some possible implementations, step S2 specifically includes:
And uniformly distributing the composite slurry on the polytetrafluoroethylene base film in a thin layer mode by using a coating machine at a knife coating rate of 2-5cm/s and a plate temperature of 25 ℃, and drying at 25 ℃ for 10min, 50 ℃ for 10min and 85 ℃ for 10min in sequence to obtain the composite heat conducting film.
In some possible implementations, the hot pressing in step S3 is performed at a temperature of 60-90 ℃, a pressure of 25-30Mpa, and a time of 20-30min.
In some possible implementations, step S4 specifically includes:
carrying out ultrasonic cutting on the composite material block by adopting an ultrasonic cutter head along the pressure direction parallel to the hot pressing;
wherein the vibration frequency of the ultrasonic tool bit is 20-40kHz, and the cutting rate is 2-10mm/s.
In some possible implementations, the thickness of the low thermal resistance boron nitride heat conduction gasket is 0.1mm at minimum, the machining precision is 0.01mm, and the uniformity of the thickness of the gasket is +/-5%.
The application also provides the low-thermal-resistance boron nitride heat-conducting gasket prepared by the preparation method, and the low-thermal-resistance boron nitride heat-conducting gasket has an interface bending structure.
According to the preparation method of the low-thermal-resistance boron nitride heat-conducting gasket, the two-dimensional boron nitride heat-conducting gasket with the specific ratio of thickness to diameter and the high polymer substrate with the glass transition temperature lower than room temperature are adopted, and the hot pressing and ultrasonic cutting processes are adopted, so that the prepared heat-conducting gasket has a unique interface bending structure, and therefore the low-thermal-resistance performance is achieved. By adjusting the technological parameters, the bending angle of the interface bending structure can be correspondingly adjusted, and the performances of thermal resistance, thermal conductivity, breakdown voltage and the like can be correspondingly adjusted. The thermal conductivity of the prepared low-thermal-resistance boron nitride heat-conducting gasket is more than 15W/mK, the highest thermal conductivity can reach 20.9W/mK, the thermal resistance can be as low as 0.092in 2 K/W, and the breakdown voltage is more than 4.05kV.
Drawings
Fig. 1 is a scanning electron microscope image of the two-dimensional boron nitride nanoplatelet slurry of example 1.
Fig. 2 is a macroscopic optical picture of the low thermal resistance boron nitride thermally conductive pad of example 1.
Fig. 3 is a scanning electron microscope image of the low thermal resistance boron nitride thermal pad of example 1.
Fig. 4 is a scanning electron microscope image of the low thermal resistance boron nitride thermal pad of example 2.
Fig. 5 is a scanning electron microscope image of the low thermal resistance boron nitride thermal pad of example 3.
Fig. 6 is a scanning electron microscope image of the boron nitride heat conductive pad of comparative example 1.
Fig. 7 is a scanning electron microscope image of the boron nitride heat conductive pad of comparative example 2.
Fig. 8 is a scanning electron microscope image of the boron nitride thermally conductive pad of comparative example 3.
Detailed Description
Embodiments of the present invention are described in detail below. The following examples are illustrative only and are not to be construed as limiting the invention.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The application provides a preparation method of a low-thermal-resistance boron nitride heat conduction gasket, which comprises the following steps:
S1: according to weight portions, uniformly mixing 100 to 200 portions of two-dimensional boron nitride nano-sheets, 200 to 400 portions of organic solvent and 150 to 300 portions of polymer matrix to obtain composite slurry;
s2: coating and drying the composite slurry on a bottom film to obtain a composite heat conducting film;
S3: laminating the composite heat conducting films, and then hot-pressing to obtain a composite heat conducting block;
s4: cutting the composite heat conduction block body into sheets by adopting ultrasonic cutting to obtain the low-thermal-resistance boron nitride heat conduction gasket;
Wherein the diameter-thickness ratio of the two-dimensional boron nitride nano-sheet is 200-500, and the glass transition temperature of the polymer matrix is-40-20 ℃.
The applicant finds that, through a great deal of researches, two-dimensional boron nitride nano sheets, organic solvents and polymer matrixes are selected as raw materials, the two-dimensional boron nitride nano sheets, the glass transition temperature of the polymer matrixes and the proportion of the three are controlled to be mixed to obtain composite slurry with proper viscosity, then the composite heat conducting film with the two-dimensional boron nitride filler arranged preferentially along the in-plane orientation is prepared through coating, and then the two-dimensional boron nitride insulating heat conducting gasket is finally prepared through lamination, mould pressing and slicing of the boron nitride film, and has a unique interface bending structure at the interface, wherein the interface bending structure can enable the heat conducting gasket to have low thermal resistance. By adjusting the technological parameters in the preparation method, the bending structure of the interface can be correspondingly adjusted to realize bending of different degrees, and the thermal conductivity and thermal resistance of the corresponding heat conducting gasket are also changed. The heat-conducting gasket prepared by the preparation method has the advantages of simple components, high vertical orientation of the bulk-phase structure filler, contact heat conduction of the filler surface at the interface, good interface filling capability, excellent heat conduction performance and insulating dielectric property of the prepared sample, and realization of rapid preparation and effective cost reduction.
In some embodiments, the polymeric matrix is one of silicone rubber, polyethylene, polyvinyl chloride, phenolic resin, epoxy resin, or acrylic resin.
In some embodiments, the organic solvent is one of ethyl acetate, isopropanol, or xylene.
In some preferred embodiments, step S1 specifically includes:
according to parts by weight, uniformly stirring and mixing 100-200 parts of two-dimensional boron nitride nano-sheets and 200-400 parts of organic solvent to obtain two-dimensional boron nitride nano-sheet slurry; and uniformly stirring and mixing the two-dimensional boron nitride nanosheet slurry with 150-300 parts of polymer matrix to obtain the composite slurry.
Preferably, the stirring process comprises: and (5) using a single-planet homogenizer to stir uniformly at a frequency of 2000-3000 rpm for a period of 0.5-1 min.
In the step S1, the viscosity of the composite slurry measured by a 4-cup viscometer method is 40-50S.
In a specific embodiment, the viscosity can be regulated and controlled to be proper by adding the organic solvent dropwise in a small amount for many times, and a single-planet homogenizer is used for stirring uniformly after each drop. By controlling the proportion of the two-position boron nitride filler in the composite slurry, the composite slurry can be controlled to have proper viscosity, so that the composite heat-conducting film with uniform and controllable thickness, smooth surface and low internal porosity is obtained.
In some preferred embodiments, step S2 specifically includes:
And uniformly distributing the composite slurry on the polytetrafluoroethylene base film in a thin layer mode by using a coating machine at a knife coating rate of 2-5cm/s and a plate temperature of 25 ℃, and drying at 25 ℃ for 10min, 50 ℃ for 10min and 85 ℃ for 10min in sequence to obtain the composite heat conducting film.
Conventional single-step drying methods can cause premature evaporation of the surface solvent, close the escape route for the evaporation of the internal solvent, and become trapped inside the composite film in the form of pores, thereby degrading the properties of the final material. According to the application, the composite heat conducting film is obtained by a gradient drying method at 25 ℃, 50 ℃ and 85 ℃ in sequence, so that the solvent residue can be greatly reduced.
In some preferred embodiments, step S3 specifically includes:
Cutting the composite heat conducting film into proper size, stacking and compacting the film, preheating the film in a hot press at 60-90 deg.c, applying 25-30MPa pressure to the film, maintaining the pressure unchanged and maintaining the temperature for 20-30min to obtain the composite block.
According to the application, the hot pressing temperature, the hot pressing pressure and the hot pressing time are strictly controlled, so that the composite material block can be softened as much as possible to help to remove gas, the interlayer bonding degree is improved, and the excessive softening collapse disorder of the composite material block and the orientation of the two-dimensional boron nitride nano sheet can be avoided.
In some preferred embodiments, step S4 specifically includes:
and (3) unloading the die and cooling at normal temperature, taking out the composite material block from the die, and using ultrasonic cutting equipment along the direction parallel to the hot pressing pressure, wherein the vibration frequency of an ultrasonic tool bit is 20-40kHz, and uniformly cutting at the cutting rate of 2-10mm/s, so that the low-thermal-resistance two-dimensional boron nitride heat-conducting gasket can be obtained.
The low thermal resistance two-dimensional boron nitride heat conduction gasket obtained by ultrasonic cutting has the minimum thickness of 0.1mm, the processing precision of 0.01mm and the thickness uniformity of +/-5%. Compared with the traditional mechanical cutting process, the ultrasonic cutting can effectively reduce the roughness of the processing surface while ensuring the formation of the bending structure of the heat conduction gasket, give higher processing precision and further reduce the thermal resistance. Meanwhile, the processing speed is high, and compared with the traditional machine tool processing, the method has more mass production benefits.
The application also provides the low-thermal-resistance boron nitride heat-conducting gasket prepared by the preparation method, and the prepared heat-conducting gasket has a unique interface bending structure at an interface, and the heat conductivity is more than 10W/mK and can reach 20.9W/mK at most; the thermal resistance can be as low as 0.092in 2 K/W, and the breakdown voltage is more than 4.05kV.
It is understood that the term "aspect ratio" as used herein refers to the ratio of the radial dimension (D 50) to the thickness of the two-dimensional boron nitride nanoplatelets.
The scheme of the present application will be explained below with reference to specific examples and comparative examples. It will be appreciated by those skilled in the art that the following examples are for illustrative purposes only and are not to be construed as limiting the application. The sources of the main materials and equipment used in the specific examples and comparative examples are as follows, and the other reagents, software and instruments not specifically addressed are conventional commercial products or open sources.
Two-dimensional boron nitride nanoplatelets: chengpeng technology Co., buddha;
SH-PSA916 series of silicone rubber adhesive, ji Peng silicon-fluorine materials Co., shenzhen City;
acrylic pressure sensitive adhesive DURO-TAK 380-2954, henkel, germany;
Ultrasonic cutting equipment: ultrasonic rubber cutter G20, shenzhen, inc.
Example 1
A preparation method of a low-thermal-resistance boron nitride heat-conducting gasket comprises the following steps:
S1: 200 parts of ethyl acetate is added into 100 parts of two-dimensional boron nitride nano-sheets (the diameter-thickness ratio D 50 is 500) according to parts by weight, and the mixture is fully stirred by a single-planet homogenizer at a rotation rate of 3000r/min and a rotation time of 0.5min, so as to obtain the two-dimensional boron nitride nano-sheet slurry. 150 parts of organic silicon rubber (glass transition temperature Tg=5℃) is added into the two-dimensional boron nitride nano-sheet slurry, and the mixture is fully stirred by a single-planet homogenizer at a rotation rate of 3000r/min and a rotation time of 0.5min, so as to obtain boron nitride-organic silicon rubber composite slurry; the viscosity of the composite slurry was measured using a paint-4 cup and found to be 40s.
S2: the boron nitride-organic silicon rubber composite slurry is uniformly distributed on the polytetrafluoroethylene base film in a thin layer mode by using a coating machine at a knife coating rate of 2cm/s and a plate temperature of 25 ℃, and is dried for 10min at 25 ℃, dried for 10min at 50 ℃ and dried for 10min at 85 ℃ in sequence to obtain the composite heat conducting film.
S3: taking down the composite heat conducting film, cutting into a proper size by using a utility knife, placing the film into a mould for lamination and uniform compaction, placing the mould into a hot press for full preheating at 80 ℃, applying pressure of 25Mpa to the mould, keeping the pressure unchanged, and preserving heat for 20min to obtain the composite heat conducting block with the two-dimensional boron nitride arranged in priority along the direction perpendicular to the pressure.
S4: taking out the die and cooling at normal temperature, taking out the composite heat conduction block from the die, using ultrasonic cutting equipment along the direction parallel to the applied hot pressing pressure, selecting the vibration frequency of an ultrasonic tool bit to be 30kHz, and uniformly cutting the composite heat conduction block into sheets with the thickness of 1mm at the cutting rate of 5mm/s to obtain the low-thermal-resistance boron nitride heat conduction gasket. Wherein, the processing error of the ultrasonic cutting equipment is less than or equal to 20um, and the surface of the heat conduction gasket is observed to be semi-specular reflection by naked eyes.
Example 2
Example 2 differs from example 1in that:
S1: according to the parts by weight, 300 parts of ethyl acetate is added into 200 parts of two-dimensional boron nitride nano-sheets (the diameter-thickness ratio D 50 is 200), and a single-planet homogenizer is used for fully stirring at the rotation speed of 3000r/min and the rotation time of 0.5min, so as to obtain the two-dimensional boron nitride nano-sheet slurry. Adding 250 parts of organic silicon rubber (with glass transition temperature Tg= -10 ℃) into the two-dimensional boron nitride nano-sheet slurry, and fully stirring at a rotation rate of 3000r/min and a rotation time of 0.5min by using a single-planet homogenizer to obtain boron nitride-organic silicon rubber composite slurry; the viscosity of the composite slurry was measured using a paint-4 cup and found to be 40s.
Example 3
S1: according to the weight portions, 200 portions of ethyl acetate are added into 100 portions of two-dimensional boron nitride nano-sheets (the diameter-thickness ratio D 50 is 300), and a single-planet homogenizer is used for fully stirring at the rotation speed of 3000r/min and the rotation time of 0.5min, so that the two-dimensional boron nitride nano-sheet slurry is obtained. 150 parts of organic silicon rubber (glass transition temperature Tg=20℃) is added into the two-dimensional boron nitride nano-sheet slurry, and the mixture is fully stirred by a single-planet homogenizer at a rotation rate of 1500r/min and a rotation time of 1min, so as to obtain boron nitride-organic silicon rubber composite slurry; the viscosity of the composite slurry was measured using a paint-4 cup and found to be 40s.
S2: the boron nitride-organic silicon rubber composite slurry is uniformly distributed on the polytetrafluoroethylene base film in a thin layer mode by using a coating machine at a knife coating rate of 2cm/s and a plate temperature of 25 ℃, and is dried for 10min at 25 ℃, dried for 10min at 50 ℃ and dried for 10min at 85 ℃ in sequence to obtain the composite heat conducting film.
S3: taking down the composite heat-conducting film, cutting into a proper size by using a utility knife, placing the film into a mould, stacking a plurality of layers, compacting uniformly, placing the mould into a hot press, preheating fully at 70 ℃, applying pressure of 30Mpa to the mould, keeping the pressure unchanged, and preserving heat for 30min to obtain the composite heat-conducting block with the two-dimensional boron nitride arranged in priority along the direction perpendicular to the pressure.
S4: the mold was taken out and cooled at normal temperature, the composite heat conductive block was taken out from the mold, and a sheet having a thickness of 1mm was cut uniformly at a processing rate of 2mm/s using an ultrasonic cutting apparatus with a cutter head vibration frequency of 40kHz in a direction parallel to the direction of the applied hot pressing pressure.
Example 4
Example 4 differs from example 1in that:
the organic solvent adopted in the step S1 is xylene, and the polymer matrix is acrylic pressure-sensitive adhesive (glass transition temperature Tg=5 ℃).
Example 5
Example 5 differs from example 1in that:
and S4, uniformly cutting the composite heat conduction block into sheets with the thickness of 0.1 mm.
Example 6
Example 6 differs from example 1 in that: the cutting rate of the ultrasonic blade in the step S4 is 10mm/S.
Comparative example 1
Comparative example 1 differs from example 1 in that: in the step S1, the diameter-thickness ratio D 50 of the two-dimensional boron nitride nano-sheet is 50.
Comparative example 2
Comparative example 2 is different from example 1 in that: the glass transition temperature of the silicone rubber in step S1 was 40 ℃.
Comparative example 3
Comparative example 3 is different from example 1 in that: the adding part of the two-dimensional boron nitride nano sheet adopted in the step S1 is 300 parts; the viscosity of the composite slurry was measured using a paint-4 cup and found to be 60s.
Comparative example 4
Comparative example 4 differs from example 1 in that: in step S4, a dicing saw is used instead of ultrasonic cutting.
The properties of the boron nitride heat conductive gaskets prepared in examples 1-6 and comparative examples 1-4 were tested as follows:
(1) Thermal conductivity LFA: the test equipment was a relaxation-resistant LFA467, the test specimens were processed into round sheets with a diameter of 25.4mm, and the upper and lower surfaces of the test specimens were required to be parallel and smooth, and the thermal diffusivity of each test specimen was measured. Density was measured using drainage and specific heat capacity was obtained using Differential Scanning Calorimetry (DSC). The thermal conductivity is equal to the product of the thermal diffusion coefficient, the density and the specific heat capacity, and the thermal conductivity value can be obtained through calculation.
(2) Thermal resistance @1mm: the test equipment is a Rake LW9389, a sample is processed into square slices with the side length of 25.4mm, and the upper surface and the lower surface of the sample are required to be parallel and smooth. According to the application, 25/50/75/100 pressure points are selected, and the test time of each pressure point is 15min.
(3) Breakdown voltage: the test equipment was blue LK2672X, the sample size was 30X 30mm X1 mm sheet, the upper and lower surfaces of the sample were required to be parallel and smooth, and each sample was repeatedly tested 3 times to average.
(4) Volume resistivity: the test equipment was Shanghai Telmoguo ZC-90, the sample size was 50X 50mm X1 mm sheet, the upper and lower surfaces of the sample were required to be parallel and smooth, and each sample was repeatedly tested 3 times to average.
The results of performance testing of the boron nitride thermal pads prepared in examples 1-6 and comparative examples 1-4 are shown in Table 1.
Table 1 properties of the boron nitride thermally conductive gaskets in examples 1-6 and comparative examples 1-4
The performance results are analyzed as follows, in conjunction with table 1 and fig. 1-8:
As can be seen from fig. 1 and fig. 2, the two-dimensional boron nitride nanosheet slurry adopted in example 1 has a characteristic stable appearance, and the prepared two-dimensional boron nitride heat-conducting gasket has a smooth and flat surface and controllable size and thickness. As can be seen from fig. 3 to 5, the two-dimensional boron nitride heat-conducting gaskets prepared in examples 1 to 3 each have a unique interface "bending structure", and the bending angles of the interface "bending structure" are correspondingly different according to different specific process parameters. The bending structure with a proper bending angle (30-45 degrees, as shown in fig. 3-5) is helpful to improve interface thermal conductivity, the angle is too small and tends to be horizontally stacked to affect heat dissipation in the vertical direction, and the angle is too large to improve the scattering probability of interface phonons and reduce interface phonon coupling efficiency, so that interface thermal conductivity is deteriorated.
The performance results corresponding to Table 1 show that in examples 1-6, the thermal conductivity of the prepared heat conducting gasket is greater than 15W/mK, up to 20.9W/mK, the thermal resistance can be as low as 0.092in 2 K/W, and the breakdown voltage is greater than 4.05kV by adopting a two-dimensional boron nitride nano-plate with a specific ratio of thickness and a polymer matrix with a specific glass transition temperature, and controlling the proportion of the filler of the two-dimensional boron nitride nano-plate and adopting ultrasonic cutting. The thermal resistance was significantly reduced and the thermal conductivity and breakdown voltage were also improved as compared to comparative examples 1-4. Wherein the thickness was controlled to 0.1mm in example 5, the thermal resistance of the obtained heat conductive gasket was as low as 0.092in 2 K/W while maintaining excellent thermal conductivity and breakdown voltage. In example 6, the cutting rate was increased during ultrasonic cutting, the processing rate was too high, and the interlayer stress of the material was too high, so that the interlayer adhesiveness of the sheet was lowered, and the performance was deteriorated as compared with example 1.
Compared with comparative example 1, the reduction of the diameter-thickness ratio D 50 to 50 will seriously affect the orientation of the two-dimensional boron nitride nanosheets in the process of forming the heat conducting gasket, and the surface of the two-dimensional boron nitride nanosheets will not show an obvious interface "bending structure", and the corresponding heat conductivity and thermal resistance performance are obviously deteriorated.
The glass transition temperature of the silicone rubber in comparative example 2 is too high compared to comparative example 2, so that the processing difficulty is increased during the preparation process and the bending orientation is affected. In fig. 7, there is no interfacial "kink structure", and the corresponding thermal conductivity and thermal resistance properties are significantly deteriorated.
In example 1, the ratio of the two-dimensional boron nitride nanofiller added in comparative example 3 was too large compared with comparative example 3, so that the orientation was deteriorated, corresponding to the interface "bent structure" in fig. 8, but the bending angle was too small, and the interface phonon coupling efficiency was lowered, thereby affecting the interface heat transfer.
Compared with comparative example 4, the processing rate is greatly reduced by adopting the traditional CNC mechanical cutting method, and the obtained sample has larger surface roughness and poorer thickness uniformity, so that the overall performance of the heat-conducting gasket is reduced.
From a comprehensive comparison of examples 1-6 and comparative examples 1-4, it is known that the two-dimensional boron nitride nanoplatelets with specific aspect ratios, the polymer matrix with specific glass transition temperatures, and controlling the proportion of the two-dimensional boron nitride filler and adopting the synergistic effect in ultrasonic cutting, one or more of the two-dimensional boron nitride nanoplatelets are adjusted to affect the performance of the final material. The two-dimensional boron nitride nanosheets with specific ratio of thickness and the high polymer substrate with the glass transition temperature lower than room temperature are basic material requirements for forming a bending structure, and meanwhile, the high polymer substrate with low glass transition temperature has processing friendliness and is convenient for processing treatments such as hot pressing, mechanical cutting and the like. The proper filler-substrate ratio can optimize the shape of the bending structure to further improve the heat conduction performance and regulate the electrical behavior of the heat conduction gasket. Under the optimized parameters, the ultrasonic cutting processing technology forms a bending structure near the processing surface, ensures the high orientation of the internal filler, and shows very promising production efficiency and product yield under the continuous production condition.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention.
Claims (8)
1. The preparation method of the low-thermal-resistance boron nitride heat-conducting gasket is characterized by comprising the following steps of:
S1: according to parts by weight, uniformly mixing 100-200 parts of two-dimensional boron nitride nano-sheets, 200-400 parts of organic solvent and 150-300 parts of polymer matrix to obtain composite slurry, wherein the viscosity of the composite slurry measured by a 4-cup viscometer coating method is 40-50 s, and the polymer matrix is one of organic silicon rubber, polyethylene, acrylic pressure-sensitive adhesive or acrylic resin;
s2: coating and drying the composite slurry on a bottom film to obtain a composite heat conducting film;
S3: laminating the composite heat conducting films, and then hot-pressing to obtain a composite heat conducting block;
s4: cutting the composite heat conduction block body into sheets by adopting ultrasonic cutting to obtain the low-thermal-resistance boron nitride heat conduction gasket;
Wherein the diameter-thickness ratio of the two-dimensional boron nitride nano-sheet is 200-500, and the glass transition temperature of the polymer matrix is-40-20 ℃.
2. The method for preparing the low thermal resistance boron nitride heat conducting gasket according to claim 1, wherein the organic solvent is one of ethyl acetate, isopropanol or xylene.
3. The preparation method according to claim 1, wherein the step S1 specifically comprises the steps of:
According to parts by weight, stirring 100-200 parts of two-dimensional boron nitride nano-sheets and 200-400 parts of organic solvent by adopting a single-planet homogenizer at a rotating speed of 2000-3000 rpm for 0.5-1 min, and uniformly mixing to obtain two-dimensional boron nitride nano-sheet slurry;
Stirring the two-dimensional boron nitride nano-sheet slurry and 150-300 parts of polymer matrix for 0.5-1 min by adopting a single-planet homogenizer at a rotating speed of 1500-3000 rpm, and uniformly mixing to obtain the composite slurry.
4. The preparation method according to claim 1, wherein step S2 specifically comprises:
And uniformly distributing the composite slurry on the polytetrafluoroethylene base film in a thin layer mode by using a coating machine at a knife coating rate of 2-5cm/s and a plate temperature of 25 ℃, and drying at 25 ℃ for 10min, 50 ℃ for 10min and 85 ℃ for 10min in sequence to obtain the composite heat conducting film.
5. The process according to claim 1, wherein the hot pressing in step S3 is carried out at a temperature of 60 to 90℃and a pressure of 25 to 30MPa for a period of 20 to 30 minutes.
6. The method of claim 1, wherein step S4 specifically comprises:
carrying out ultrasonic cutting on the composite material block by adopting an ultrasonic cutter head along the pressure direction parallel to the hot pressing;
wherein the vibration frequency of the ultrasonic tool bit is 20-40kHz, and the cutting rate is 2-10mm/s.
7. The preparation method of claim 6, wherein the low thermal resistance boron nitride heat conduction gasket has a minimum thickness of 0.1mm, a machining precision of 0.01mm and a uniformity of thickness of + -5%.
8. The low thermal resistance boron nitride heat conduction gasket is characterized in that the gasket is prepared by adopting the preparation method according to any one of claims 1-7, and a scanning electron microscope image of the low thermal resistance boron nitride heat conduction gasket shows that the low thermal resistance boron nitride heat conduction gasket has an interface bending structure.
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