Graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material, preparation method and application thereof

Abstract

The present application relates to the technical field of heat-conducting interface materials, in particular to a graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material and a preparation method thereof.The graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material is prepared by filling a polyurethane matrix with spherical aluminas of different sizes, and by changing the stacking order of graphene and alumina, a high-performance graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material is obtained (the in-plane thermal conductivity can reach 15.433 W / mK at the highest, and the out-of-plane thermal conductivity can reach 22.433 W / mK at the highest).The graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material prepared by the present application is stable in structure, has excellent flexibility, mechanical properties and certain insulation performance, and has a wide range of application scenarios in the field of electronic devices and the field of smart wear.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-conducting interface materials, in particular to a graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material, a preparation method and application thereof. BACKGROUND

[0002] Nowadays, electronic devices have become an indispensable part of our daily life. With the miniaturization, integration and multi-function of electronic devices, the power density and heat output per unit volume have increased significantly, which will have an adverse effect on the performance and service life if not effectively dissipated. The overheating of microelectronic devices has become a bottleneck restricting the development and application of high-frequency and high-power devices and systems in advanced communication information technology.

[0003] At present, the rapid deployment of 5G technology in the field of electronic consumption puts forward higher requirements and new challenges for more efficient thermal management. The thermal conductivity and other performances of traditional heat-conducting interface materials have been unable to meet the needs of high-power density electronic products and wearable electronic products with increasing demand.

[0004] The heat-conducting interface material prepared by filling traditional heat-conducting fillers often has the phenomenon of filler agglomeration due to the addition of excessive heat-conducting fillers, which affects the effective transmission of heat. The high-performance heat-conducting interface material required at present needs the heat-conducting filler to form a stable, uniform and effective heat-conducting path in the polymer matrix. Under the premise of high thermal conductivity, it also has excellent insulation performance and mechanical properties, and has a long service life, low production cost and large-scale production conditions, which is an important direction for the development of heat-conducting composites. SUMMARY

[0005] The present application is carried out to solve the above problems, and aims to provide a graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material, a preparation method and application thereof, to solve the above technical problems.

[0006] The first aspect of the present application provides a preparation method of a graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material, characterized in that it comprises the following steps:

[0007] S1, preparation of graphene / polyurethane slurry: mixing water-based polyurethane, water-based polymer dispersant and crosslinking agent and adding graphene powder to obtain a first mixed solution, adjusting the viscosity and preliminarily stirring uniformly, and then treating by vacuum degassing and stirring to prepare the graphene / polyurethane slurry;

[0008] S2, preparation of spherical alumina / polyurethane slurry: after ultrasonic treatment of mixing the spherical alumina powder and the dispersant, the aqueous polyurethane and the crosslinking agent are added to obtain a second mixed solution, and the spherical alumina / polyurethane slurry is prepared after uniform mixing, stirring and vacuum degassing treatment;

[0009] S3, preparation of graphene / spherical alumina / polyurethane laminated composite film: the graphene / polyurethane slurry or the spherical alumina / polyurethane slurry prepared in S2 is alternately coated on the polymethyl methacrylate substrate to obtain a graphene / polyurethane slurry layer or a spherical alumina / polyurethane slurry layer, and the next layer is coated after drying treatment of each layer, and the graphene / polyurethane slurry layer or the spherical alumina / polyurethane slurry layer is used as the outermost layer after alternately coating several layers, and then drying treatment is performed, to obtain the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material.

[0010] The graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material with high performance (the in-plane thermal conductivity can reach 15.433 W / mK, and the out-of-plane thermal conductivity can reach 22.433 W / mK) is obtained by filling the polyurethane matrix with the spherical alumina, surrounding the graphene sheets, and forming a unique laminated composite structure film.

[0011] The graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material prepared by the method has stable structure, excellent flexibility, mechanical properties and certain insulation performance.

[0012] The method is simple, controllable, low in cost and easy to scale up, and has wide application scenarios in the field of electronic devices and the field of smart wear.

[0013] In some embodiments of the present application, the mass of the graphene powder added in S1 is 8-15% of the mass of the first mixed solution.

[0014] In the present application, by controlling the mass ratio of the graphene powder, the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material prepared has good mechanical properties and insulation performance.

[0015] In some embodiments of the present application, the mass of the graphene powder added in S1 is 12-15% of the mass of the first mixed solution.

[0016] In some embodiments of the present application, in S1, the cross-linking agent is aziridine, and the adding amount of the water-based polymer dispersant and aziridine is 1-5% of the mass of the first mixed solution; the viscosity is adjusted by adding water and ethanol, and the adding amount of the water and ethanol is 1-9% of the mass of the first mixed solution; the preliminary stirring time is 10-60 min; and the vacuum defoaming stirring time is 5-15 min.

[0017] In some embodiments of the present application, in S2, the mass of the spherical alumina added is 50-60% of the mass of the second mixed solution.

[0018] The present application can weaken the breaking strength of the composite material by adding alumina, and significantly improve the insulation performance and out-of-plane thermal conductivity of the composite material.

[0019] When the mass of the graphene powder added in S1 is 12-15% of the mass of the first mixed solution, and the mass of the spherical alumina added in S2 is 50-60% of the mass of the second mixed solution, the graphene and alumina can form a good synergistic effect, greatly improve the in-plane and out-of-plane thermal conductivity of the composite material, and have good mechanical properties and insulation performance.

[0020] In some embodiments of the present application, in S2, the particle size of the spherical alumina includes 5 μm, 10 μm, 45 μm, and 70 μm, and the adding proportion of the spherical alumina with the particle size of 5 μm, 10 μm, 45 μm, and 70 μm is 1:1-2:1-2:1-3.

[0021] The present application fills the polyurethane matrix with spherical alumina of different sizes, surrounds it with graphene sheets, and forms a unique laminated composite structure film; the large-particle spherical alumina can make the two-dimensional graphene sheets adhere, significantly improve the orientation of the graphene in the vertical direction, and reduce the interfacial thermal resistance between the graphene, alumina, and polyurethane matrix.

[0022] In some embodiments of the present application, in S2, the dispersant is a mixed dispersion liquid of acetone and nano-alumina ethanol, and the adding amount of the dispersant is 3-10% of the mass of the second mixed solution; the cross-linking agent is aziridine, and the adding amount of the aziridine is 1-5% of the mass of the water-based polyurethane; the ultrasonic time is 30-100 min, the mixing and stirring time is 10-60 min, and the vacuum defoaming stirring time is 5-15 min.

[0023] In some embodiments of the present application, in S3, the coating thickness of the graphene / polyurethane slurry layer is 10-40 μm, the coating thickness of the spherical alumina / polyurethane slurry is set to 70-90 μm, the number of coating layers is 3-11 layers, and the total coating thickness is 90-740 μm.

[0024] The present application can adjust the thickness of the film by changing the number of coating layers and the coating thickness, obtain graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface materials with different properties, and can be cut arbitrarily according to actual needs, and is widely applicable.

[0025] The second aspect of the present application provides a graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material prepared according to the preparation method of any one of the first aspect.

[0026] The third aspect of the present application provides an application of the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material according to the second aspect, and the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material is used in the field of high-power electronic devices.

[0027] By implementing the above technical scheme, the present application has the following beneficial effects:

[0028] 1、The present application fills the polyurethane matrix with spherical alumina of different sizes, and forms a unique laminated composite structure film by surrounding with graphene sheets; the large-particle spherical alumina can make the two-dimensional graphene sheets adhere, significantly improve the orientation of graphene in the vertical direction, reduce the interfacial thermal resistance between graphene, alumina and the polyurethane matrix, and obtain a high-performance graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material (the in-plane thermal conductivity can reach 15.433 W / mK, and the out-of-plane thermal conductivity reaches 22.437 W / mK).

[0029] 2、The graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material prepared by the present application has stable structure, excellent flexibility, mechanical properties and certain insulation performance; the thickness of the film can be adjusted by changing the number of coating layers, and the material can be cut arbitrarily according to actual needs, and is widely applicable.

[0030] 3、The present application adopts an alternating and continuous coating technology, which is simple, controllable, low in cost and easy to scale up. DETAILED DESCRIPTION

[0031] Figure 1 A structure schematic diagram of the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material provided by the present application is shown in the figure.

[0032] Figure 2 A preparation method flow chart of the graphene / spherical alumina / polyurethane laminated composite flexible heat-conducting interface material is shown in the figure. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is specifically described below in conjunction with examples and drawings.

[0034] Example 1

[0035] S1, Preparation of graphene / polyurethane slurry: 17 g of water-based polyurethane was weighed, 0.3 g of water-based polymer dispersant and 0.3 g of aziridine crosslinking agent were added and mixed, then 0.6 g of graphene powder was slowly added while stirring, and the initial stirring was performed for 30 min, 1.8 g of ethanol was added at the same time, the viscosity was adjusted, and when the solution had a suitable viscosity, a first mixed solution was obtained. After vacuum degassing and stirring for 10 min, a graphene / polyurethane slurry was prepared for standby;

[0036] S2, Preparation of spherical alumina / polyurethane slurry: 24 g of mixed powder of spherical alumina with particle sizes of 70 μm, 45 μm, 10 μm and 5 μm (3:2:2:1) was weighed, 3.6 g of acetone and nano-alumina ethanol dispersion solution (1:2) was added, and after ultrasonic treatment for 30 min, 20 g of water-based polyurethane and 0.4 g of aziridine crosslinking agent were added and mixed and stirred for 30 min. Finally, a spherical alumina / polyurethane slurry was prepared for standby after vacuum degassing and stirring for 10 min.

[0037] S3, Preparation of graphene / spherical alumina / polyurethane laminated composite film: the prepared slurry was coated on the PMMA substrate by using a battery coating machine, and the graphene / polyurethane slurry was coated first to prepare the graphene layer, and then the spherical alumina / polyurethane slurry was coated to prepare the alumina layer. Each layer after coating was dried in an oven at 50°C for 2 min, and then the next layer was coated on the basis of the previous layer. After 3 layers were alternately coated, they were dried at room temperature for 12 h; trimmed neatly, and the preparation was completed.

[0038] Example 2

[0039] The preparation process is similar to that of Example 1, except that in step S3 of Example 2, the prepared slurry was coated on the PMMA substrate by using a battery coating machine, and the alumina layer was coated first, and then the graphene layer was coated. Each layer after coating was dried in an oven at 50°C for 2 min, and then the next layer was coated on the basis of the previous layer. After 3 layers were alternately coated, they were dried at room temperature for 12 h; trimmed neatly, and the preparation was completed.

[0040] Example 3

[0041] The preparation process is similar to that of Example 1, except that in Example 3, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the graphene layer first and then the aluminum oxide layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0042] Example 4

[0043] The preparation process is similar to that of Example 3, except that in Example 4, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0044] Example 5

[0045] The preparation process is similar to that of Example 1, except that in Example 5, step S1, the ratio of the graphene / polyurethane slurry preparation is changed, and the specific operation of S1 is as follows:

[0046] S1, take 17 g of water-based polyurethane, add 0.3 g of water-based polymer dispersant and 0.3 g of aziridine crosslinking agent, mix, then take 1.6 g of graphene powder, slowly add while stirring, stir for 30 min, add 0.2 g of ethanol and 0.6 g of deionized water, adjust the viscosity, and then vacuum degassing and stirring for 10 min to prepare a graphene / polyurethane slurry.

[0047] The remaining steps are the same as those of Example 1.

[0048] Example 6

[0049] The preparation process is similar to that of Example 5, except that in Example 6, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated. After 3 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0050] Example 7

[0051] The preparation process is similar to that of Example 5, except that in Example 7, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the graphene layer first and then the aluminum oxide layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0052] Example 8

[0053] The preparation process is similar to that of Example 6, except that in Example 8, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0054] Example 9

[0055] The preparation process is similar to that of Example 1, except that in Example 9, step S1, the ratio of the graphene / polyurethane slurry preparation is changed, and the specific operation of S1 is as follows:

[0056] S1, weigh 16 g of water-based polyurethane, add 0.3 g of water-based polymer dispersant and 0.3 g of aziridine crosslinking agent, mix, then weigh 2.4 g of graphene powder, slowly add while stirring, initially stir for 30 min, and then add 1 g of deionized water to adjust the viscosity. When the solution has the appropriate viscosity, a first mixed solution is obtained, which is then vacuum degassed and stirred for 10 min to prepare a graphene / polyurethane slurry for standby.

[0057] The remaining steps are the same as those of Example 1.

[0058] Example 10

[0059] The preparation process is similar to that of Example 9, except that in Example 10, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 3 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0060] Example 11

[0061] The preparation process is similar to that of Example 9, except that in Example 11, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the graphene layer first and then the aluminum oxide layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0062] Example 12

[0063] The preparation process is similar to that of Example 10, except that in Example 12, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 11 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0064] Example 13

[0065] The preparation process is similar to that of Example 1, except that in Example 13, step S1, the ratio of the graphene / polyurethane slurry preparation is changed, and the specific operation of S1 is as follows:

[0066] S1, weigh 15 g of water-based polyurethane, add 0.3 g of water-based polymer dispersant and 0.3 g of aziridine crosslinking agent, mix, then weigh 3 g of graphene powder, slowly add while stirring, initially stir for 30 min, and then add 1.4 g of deionized water to adjust the viscosity. When the solution has the appropriate viscosity, a first mixed solution is obtained, which is then vacuum degassed and stirred for 10 min to prepare a graphene / polyurethane slurry for standby use.

[0067] The remaining steps are the same as those of Example 1.

[0068] Example 14

[0069] The preparation process is similar to that of Example 13, except that in Example 14, step S3, the prepared slurry is alternately coated on the PMMA substrate by using a battery coating machine to coat the aluminum oxide layer first and then the graphene layer, and each coated layer is dried in an oven at 50°C for 2 min, and then the next layer is coated on the basis of the previous layer. After 3 layers are alternately coated, they are dried at room temperature for 12 h; trimmed neatly, and the preparation is completed.

[0070] Example 15

[0071] The preparation process is similar to that of Example 1, except that in Example 15, step S1, the ratio of the graphene / polyurethane slurry preparation is changed, and the specific operation of S1 is as follows:

[0072] S1. Weigh 16g of waterborne polyurethane, add 0.3g of waterborne polymeric dispersant and 0.3g of aziridine crosslinking agent, mix, then weigh 2.4g of graphene powder, add it slowly while stirring, stir for 30 minutes, add 1g of deionized water at the same time to adjust the viscosity, and when the viscosity of the solution is suitable, obtain the first mixture, then vacuum degas and stir for 10 minutes to prepare a graphene / polyurethane slurry for later use.

[0073] The difference lies in step S2 of Example 15, where the amount of spherical alumina mixed powder added is changed. The specific operation of S2 is as follows:

[0074] S2. Preparation of spherical alumina / polyurethane slurry: Weigh 36g of a mixture of 70μm, 45μm, 10μm and 5μm spherical alumina powder (3:2:2:1), add 3.6g of acetone and nano alumina ethanol dispersion (1:2), mix and sonicate for 30min, then add 20g of waterborne polyurethane and 0.4g of aziridine crosslinking agent, mix and stir for 30min, and finally vacuum degas and stir for 10min to prepare spherical alumina / polyurethane slurry for later use.

[0075] The remaining steps are the same as in Example 1.

[0076] Example 16

[0077] The preparation process is similar to that of Example 15, except that in step S3 of Example 16, the prepared slurry is alternately coated onto a PMMA substrate using a battery coating machine, first with an alumina layer and then with a graphene layer. Each layer is dried in an oven at 50°C for 2 minutes, and then another layer is coated on top of that layer. After three layers are alternately coated, the substrate is dried thoroughly at room temperature for 12 hours; then it is neatly cut to complete the preparation.

[0078] Example 17

[0079] The preparation process is similar to that of Example 15, except that in step S3 of Example 17, the prepared slurry is alternately coated onto a PMMA substrate using a battery coating machine, first with a graphene layer and then with an alumina layer. Each layer is dried in an oven at 50°C for 2 minutes, and then another layer is coated on top of that layer. After 11 layers are alternately coated, the substrate is dried thoroughly at room temperature for 12 hours; then it is neatly cut to complete the preparation.

[0080] Example 18

[0081] The preparation process is similar to that of Example 16, except that in step S3 of Example 18, the prepared slurry is alternately coated onto a PMMA substrate using a battery coating machine, first with an alumina layer and then with a graphene layer. Each layer is dried in an oven at 50°C for 2 minutes, and then another layer is coated on top of that layer. After 11 layers are alternately coated, the substrate is dried thoroughly at room temperature for 12 hours; then it is neatly cut to complete the preparation.

[0082] Example 19

[0083] The preparation process is similar to that of Example 15, except that in step S3 of Example 19, the prepared slurry is alternately coated onto a PMMA substrate using a battery coating machine, first with a graphene layer and then with an alumina layer. Each layer is dried in an oven at 50°C for 2 minutes, and then another layer is coated on top of that layer. After coating 5 layers alternately, the substrate is dried thoroughly at room temperature for 12 hours; then it is neatly cut to complete the preparation.

[0084] Example 20

[0085] The preparation process is similar to that of Example 16, except that in step S3 of Example 20, the prepared slurry is alternately coated onto a PMMA substrate using a battery coating machine, first with an alumina layer and then with a graphene layer. Each layer is dried in an oven at 50°C for 2 minutes, and then another layer is coated on top of that layer. After 5 layers are alternately coated, the substrate is dried thoroughly at room temperature for 12 hours; then it is neatly cut to complete the preparation.

[0086] Comparative Example 1

[0087] Similar to Example 15, except that the prepared graphene / polyurethane slurry was first blended with spherical alumina / polyurethane slurry, and then a 5-layer coating was prepared.

[0088] Comparative Example 2

[0089] Similar to Example 15, except that only a 5-layer coating of spherical alumina / polyurethane slurry was prepared.

[0090] Comparative Example 3

[0091] Similar to Example 15, except that only a 5-layer coating of graphene / polyurethane slurry was prepared.

[0092] Performance testing

[0093] The thermally conductive interface materials obtained in Examples 1-20 and Comparative Examples 1-3 were subjected to performance tests. Thermal conductivity was measured using a Netzsch LFA-467 laser thermal conductivity meter, following the ASTM E1461 standard. The thermal conductivity of the materials was tested using circular samples with a diameter of 5.4 mm, repeated three times, and the average value was taken. Breakdown voltage was measured using an electrical strength tester, following the ASTM D149 standard, using circular samples with a diameter of 25 mm. Measurements were taken at 8-10 test points, and the average value was taken. The test results are shown in Table 1.

[0094] Table 1 Performance test results of thermally conductive interface materials

[0095]

[0096] Table 1 shows that the number of layers and thickness of the composite material can be adjusted according to the actual application field to obtain thermally conductive materials with different in-plane or out-of-plane thermal conductivity and insulation properties. From the above examples, it can be seen that as the graphene content increases, the in-plane thermal conductivity of the composite material increases significantly; however, the addition of graphene reduces the insulation effect of the material. When the graphene content increases to 15%, all properties decrease significantly because the excessive content leads to uneven coating and graphene agglomeration. The addition of alumina weakens the fracture strength of the composite material and significantly improves its insulation performance and out-of-plane thermal conductivity. Comparing Comparative Examples 1, 2, and 3 with Examples 15-20, it can be concluded that at this ratio, graphene and alumina form a good synergistic effect, significantly improving both in-plane and out-of-plane thermal conductivity, and exhibiting good mechanical and insulation properties.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene / spherical alumina / polyurethane laminated composite flexible thermally conductive interface material, characterized in that, Includes the following steps: S1. Preparation of graphene / polyurethane slurry: Waterborne polyurethane, waterborne polymer dispersant, crosslinking agent are mixed and graphene powder is added to obtain the first mixture. After adjusting the viscosity and stirring evenly, the graphene / polyurethane slurry is obtained after vacuum degassing and stirring treatment. S2. Preparation of spherical alumina / polyurethane slurry: Spherical alumina powder and dispersant are mixed and ultrasonically treated, then water-based polyurethane and crosslinking agent are added to obtain a second mixture. After mixing and stirring evenly, the mixture is vacuum degassing and stirring to obtain spherical alumina / polyurethane slurry. The particle size of the spherical alumina includes 5μm, 10μm, 45μm, and 70μm, and the addition ratio of spherical alumina with particle sizes of 5μm, 10μm, 45μm, and 70μm is 1:1~2:1~2:1~3. S3. Preparation of graphene / spherical alumina / polyurethane multilayer composite film: Using polymethyl methacrylate as a substrate, graphene layers or spherical alumina layers are prepared by sequentially and alternately coating the polymethyl methacrylate substrate with graphene / polyurethane slurry from S1 or spherical alumina / polyurethane slurry prepared in S2. Each layer is dried after coating before the next layer is coated. After coating several layers alternately, the graphene layer or spherical alumina layer is used as the outermost layer and then dried. After drying, a graphene / spherical alumina / polyurethane multilayer composite flexible thermal conductive interface material is obtained.

2. The preparation method according to claim 1, characterized in that, The mass of graphene powder added to S1 is 8-15% of the mass of the first mixture.

3. The preparation method according to claim 2, characterized in that, The mass of graphene powder added to S1 is 12-15% of the mass of the first mixture.

4. The preparation method according to claim 3, characterized in that, In S1, the crosslinking agent is aziridine, and the amount of aqueous polymeric dispersant and aziridine added is 1-5% of the mass of the first mixture, respectively; the viscosity is adjusted by adding water and ethanol, and the total amount of water and ethanol added is 1-9% of the mass of the first mixture; the initial stirring time is 10-60 min; and the vacuum degassing stirring time is 5-15 min.

5. The preparation method according to claim 1, characterized in that, The mass of spherical alumina added to S2 is 50-60% of the mass of the second mixture.

6. The preparation method according to claim 5, characterized in that, In S2, the dispersant is a mixed dispersion of acetone and nano-alumina ethanol, and the amount of the dispersant added is 3-10% of the mass of the second mixture; the crosslinking agent is aziridine, and the amount of aziridine added is 1-5% of the mass of the waterborne polyurethane; the ultrasonic time is 30-100 min; the mixing and stirring time is 10-60 min; and the vacuum degassing and stirring time is 5-15 min.

7. The preparation method according to claim 1, characterized in that, In step S3, the coating thickness of the graphene / polyurethane slurry layer is 10~40μm, the coating thickness of the spherical alumina / polyurethane slurry is set to 70~90μm, the number of coating layers is 3~11, and the total coating thickness is 90~740μm.

8. A graphene / spherical alumina / polyurethane laminated composite flexible thermal conductive interface material, characterized in that, The graphene / spherical alumina / polyurethane laminated composite flexible thermal conductive interface material is prepared by the method according to any one of claims 1 to 7.

9. An application of the graphene / spherical alumina / polyurethane laminated composite flexible thermally conductive interface material as described in claim 8, characterized in that, The graphene / spherical alumina / polyurethane laminated composite flexible thermally conductive interface material is used in the field of high-power electronic devices.

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