CN118562301A - A fireproof heat dissipation insulating sheet and preparation method thereof - Google Patents

Abstract

The present application relates to the technical field of fireproof heat-insulating sheets, and more specifically, to a fireproof heat-dissipating insulating sheet and a preparation method thereof, which is prepared from the following raw materials in parts by weight: 100 parts of vinyl silicone oil, 5-15 parts of hydrogenated silicone oil, 20-30 parts of methyl vinyl silicone resin, 40-60 parts of thermally conductive filler, 6-12 parts of flame retardant, 1-2 parts of catalyst, and 1-2 parts of vulcanizing agent, wherein each part of the thermally conductive filler is obtained by mixing boron nitride, silicon carbide and dispersant in a weight ratio of (10-15): (5-10): 3. The fireproof heat-dissipating insulating sheet prepared by the above formula has good insulation thermal conductivity and flexibility, and the thermal conductivity coefficient can reach above 9.0W/mK. At the same time, the heat-dissipating insulating sheet also has good fire resistance, can be bent at will, and has a wide range of applications.

Description

A fireproof heat dissipation insulating sheet and preparation method thereof

Technical Field

The present application relates to the technical field of fireproof heat-insulating sheets, and more specifically, to a fireproof heat-dissipating insulating sheet and a preparation method thereof.

Background Art

New energy batteries are usually composed of multiple unit battery packs, which are connected in series or/and cross-linked. Two adjacent battery cells are usually separated by insulating heat sinks to avoid short circuits between battery cells and improve the safety performance of new energy batteries.

Traditional insulating heat sinks include rubber insulating heat sinks, thermally conductive silicone insulating heat sinks and ceramic insulating heat sinks. Among them, thermally conductive silicone insulating heat sinks have good insulation and thermal conductivity, can fill the gaps between battery cells, have a certain shock absorption effect, and are more convenient to use than rubber insulating heat sinks and ceramic insulating heat sinks.

However, with the continuous innovation and improvement of battery technology, the energy density of batteries is increasing, the size of batteries is shrinking, and the shapes are changing. The greater the operating power of the battery, the higher the heat dissipated during use and the higher the voltage generated. The thermal conductivity of thermally conductive silicone insulating heat sinks is usually 1.0-5.0W/mK, and its thermal conductivity cannot meet the use of existing batteries. At the same time, the existing thermally conductive silicone insulating heat sinks have a large amount of thermally conductive fillers added, and the amount is generally more than 60%, which greatly reduces its flexibility and is prone to deformation during use, so it needs to be improved.

Summary of the invention

In order to improve the thermal conductivity of thermally conductive silicone insulation and heat dissipation, the present application provides a fireproof heat dissipation insulation sheet and a preparation method thereof.

In the present application, the fireproof heat dissipation insulation sheet is referred to as the heat dissipation insulation sheet for short.

In a first aspect, the present application provides a fireproof heat dissipation insulation sheet, which adopts the following technical solution:

A fireproof heat dissipation insulating sheet is prepared from the following raw materials in parts by weight:

100 parts of vinyl silicone oil

5-15 parts of hydrogen silicone oil

20-30 parts of methyl vinyl silicone resin

Thermally conductive filler 40-60 parts

Flame retardant 6-12 parts

1-2 parts of catalyst

1-2 parts of vulcanizing agent

The thermal conductive filler is obtained by mixing boron nitride, silicon carbide and a dispersant in a weight ratio of (10-15): (5-10): 3.

By adopting the above technical solution, the heat dissipation insulating sheet prepared has good insulation thermal conductivity and flexibility, and the thermal conductivity coefficient can reach above 9.0W/mK. At the same time, the heat dissipation insulating sheet also has good fire resistance and flexibility, and can be bent at will to be suitable for batteries of various shapes.

In this application, by mixing boron nitride, silicon carbide and dispersant in a specific proportion, the thermal conductivity of the fireproof heat dissipation insulation sheet is further improved, and the amount of thermal conductive powder used is reduced. Boron nitride has good thermal conductivity and can greatly improve the thermal conductivity of the heat dissipation insulation sheet, but the use of silicon nitride alone will increase the viscosity of the heat dissipation insulation sheet. At the same time, boron nitride is brittle and easy to break during use, which will affect the flexibility of the heat dissipation insulation sheet; the heat dissipation insulation sheet is to be used in conjunction with the battery, and the existing batteries have a variety of shapes, such as cylindrical, square and soft-pack batteries, so that the insulating heat dissipation sheet needs to be bent during use, and the force at the bend is large, which easily causes the boron nitride to break. Silicon carbide has good toughness, and when used together with boron nitride, the amount of boron nitride can be reduced, and the toughness of the heat dissipation insulation sheet can be improved. At the same time, silicon carbide has good thermal conductivity and insulation performance, which can improve the thermal conductivity and insulation of the heat dissipation insulation sheet. The dispersant allows boron nitride and silicon carbide to be better dispersed in the system, improving the uniformity and stability of the heat dissipation insulation sheet.

Under the action of a catalyst, in this application, methyl vinyl silicone resin undergoes a silylation reaction with -SiH hydrogen-containing silicone oil, vinyl silicone oil undergoes a silylation reaction with -SiH hydrogen-containing silicone oil, and methyl vinyl silicone resin undergoes a silylation reaction with a vinyl silicone oil of a specific structure to form main chains of different lengths and structures, which are then entangled with each other to form a stable three-dimensional network structure, thereby improving the flexibility of the heat dissipation insulation sheet, and the network structure is not easily destroyed during use. In this application, the amount of thermally conductive filler used is less than 50% of the total weight. By evenly distributing the thermally conductive filler in the three-dimensional network structure, a thermally conductive network structure is constructed to improve the thermal conductivity, thereby improving the heat dissipation efficiency. The flame retardant properties of the heat dissipation insulation sheet are further improved by adding a flame retardant. The vulcanizing agent promotes the vulcanization molding of the insulating heat sink, and improves the flexibility, thermal conductivity, and insulation properties of the insulating heat sink.

Preferably, the boron nitride is modified boron nitride, which is prepared by the following preparation method:

A: Put boron nitride in an organic solvent, disperse it evenly, add a coupling agent, stir to react, centrifuge and wash after the reaction is completed to obtain surface-modified boron nitride;

B: adding the surface-modified boron nitride to a mixed solution of ethanol and water, and then ultrasonicating to uniformly disperse the surface-modified boron nitride to form an emulsion, adding an emulsifier and a buffer to the emulsion, and then ultrasonically dispersing it uniformly to obtain a mixed solution;

C: After mixing the mixed solution with vinyl acrylic acid, heat to reflux at 50°C-60°C under nitrogen protection for pre-emulsification, then raise the temperature to 85°C-90°C, and dropwise add an aqueous solution containing an initiator, maintain constant temperature and constant speed stirring for 7-9 hours to obtain a primary product, centrifuge and wash the primary product, and vacuum dry it to obtain modified boron nitride.

By adopting the above technical scheme, the surface of boron nitride is connected with ethylene acrylic acid polymer. Under the action of the polymer, the brittleness of boron nitride is greatly reduced, and the flexibility and thermal conductivity of the heat dissipation insulation sheet are further improved. In this application, the surface of boron nitride is first modified by a coupling agent, which is beneficial to the grafting copolymer on the surface of boron nitride. Then, by using vinyl acrylic acid for emulsion polymerization coating, a vinyl acrylic acid polymer-coated boron nitride is obtained, so that the surface of boron nitride has a protective layer, which can reduce the possibility of easy fragmentation of boron nitride during use, maintain the integrity of the boron nitride structure, and then maintain the thermal conductivity of the insulating heat sink. At the same time, the coating effect of the vinyl acrylic acid polymer greatly reduces the softness of the surface of boron nitride, further improving the flexibility of the insulating heat sink. At the same time, the vinyl acrylic acid polymer can further improve the bonding force between boron nitride and the three-dimensional network structure, improve the structural stability of the heat dissipation insulation sheet, and extend the service life of the heat dissipation insulation sheet.

Preferably, the weight parts of the raw materials used to prepare the modified boron nitride are as follows:

Boron nitride 20-30 parts

50-70 parts of organic solvent

Coupling agent 2.5-3.5 parts

8-18 parts of ethanol

10-20 parts water

Emulsifier 4-5 parts

Buffer 4-5 parts

Vinyl acrylic acid 5-9 parts

Contains 6-10 parts of aqueous solution of initiator.

By adopting the above technical scheme, the weight of the raw materials used to prepare the modified boron nitride is optimized, and the bonding efficiency of boron nitride and vinyl acrylic polymer is further improved, so that the possibility of boron nitride spalling is greatly reduced, thereby improving the flexibility of the insulating heat sink, buffering the force at the bend, and extending the service life of the heat dissipation insulating sheet.

Preferably, the structural formula of the vinyl silicone oil is as follows:

By adopting the above technical solution, the ethylene content in the vinyl silicone oil is increased, which is beneficial to increasing the cross-linking density of the three-dimensional network and further improving the flexibility, insulation and heat dissipation of the heat dissipation insulation sheet.

Preferably, in the vinyl silicone oil, n=50-150, m=60-200.

By adopting the above technical solution, the values of n and m are optimized, so that the vinyl content in the vinyl silicone oil is moderate, which is conducive to cross-linking with methyl vinyl silicone resin and hydrogen-containing silicone oil to form a heat dissipation insulation sheet with good flexibility, and at the same time, it can also improve the flexibility, insulation and heat dissipation of the heat dissipation insulation sheet. The vinyl content in the vinyl silicone oil is relatively high, and the cross-linking points of the spatial network structure after cross-linking are too many, resulting in the heat dissipation insulation sheet being too hard after heating and curing; the vinyl content in the alkenyl silicone oil is low, and the cross-linking points of the spatial network structure after cross-linking are too few, which reduces the strength, insulation and heat dissipation of the heat dissipation insulation sheet.

Preferably, the average particle size of the boron nitride is 30-100 nm, and the average particle size of the silicon carbide is 100-500 nm.

By adopting the above technical solution, the gradation of boron nitride and silicon carbide is further optimized, the thermal conductivity of the composition can be significantly improved, and the spalling of boron nitride during use can be reduced.

Preferably, the ethylene content of the methyl vinyl silicone resin is 0.1-0.5 mol/100g and the molecular weight is 100,000-400,000.

By adopting the above technical scheme, the parameters of methyl vinyl silicone resin are optimized, the efficiency of the silylation reaction between methyl vinyl silicone resin and -SiH hydrogen-containing silicone oil is improved, the formation of a three-dimensional network is promoted, and the flexibility, insulation and thermal conductivity of the heat dissipation insulation sheet are improved.

Preferably, the viscosity of the hydrogen-containing silicone oil at 25° C. is 1000-5000 mPa.s, and the hydrogen content is 0.1-0.4%.

By adopting the above technical scheme, the viscosity and hydrogen content of hydrogenated silicone oil are optimized, the reaction efficiency of the hydrosilylation reaction between methyl vinyl silicone resin and -SiH hydrogenated silicone oil and the hydrosilylation reaction between vinyl silicone oil and -SiH hydrogenated silicone oil is further improved, the crosslinking density is increased, and the flexibility, insulation and thermal conductivity of the heat dissipation insulating sheet are greatly improved.

Preferably, the flame retardant includes at least one of magnesium hydroxide, ammonium polyphosphate, decabromodiphenyl ether, silicone flame retardant, antimony trioxide and aluminum hydroxide. The flame retardant has a good flame retardant effect, and the use of the flame retardant can further improve the fireproof performance of the heat dissipation insulation sheet.

In the second aspect, the present application provides a method for preparing a fireproof heat dissipation insulating sheet for a new energy battery pack, using the following technical solution:

A method for preparing a fireproof heat dissipation insulating sheet for a new energy battery pack comprises the following preparation steps:

S1. According to parts by weight, vinyl silicone oil, hydrogenated silicone oil, methyl vinyl silicone resin, flame retardant and catalyst are mixed to obtain a mixture A, the mixing temperature is 40-50° C., the mixing time is 40-60 min, and the mixing speed is 800-1000 r/min;

S2, mixing mixture A, thermal conductive filler and vulcanizing agent to obtain mixture B, the mixing temperature is 40-50° C., the mixing time is 20-30 min, and the mixing speed is 1000-1200 r/min to obtain mixture B;

S3. Vacuum degassing the mixture B for 20-30 minutes at a vacuum pressure of 0.2-0.4 KPa to form thermally conductive silica gel. S4. Heat the thermally conductive silica gel to 80-100°C for primary vulcanization for 3-6 minutes, then heat it to 110-120°C for secondary vulcanization for 2-4 minutes, cool it down, and then cut it to obtain a fireproof heat dissipation insulating sheet.

By adopting the above technical solution, the prepared fireproof heat dissipation insulating sheet has good insulation thermal conductivity, and the thermal conductivity coefficient can reach above 9.0W/mK. At the same time, the heat dissipation insulating sheet also has good fireproof performance.

In summary, this application has the following beneficial effects:

1. In the present application, a fireproof heat dissipation insulating sheet is prepared by mixing vinyl silicone oil, hydrogen-containing silicone oil, methyl vinyl silicone resin, thermal conductive filler, flame retardant, catalyst and vulcanizing agent, wherein the thermal conductive filler is obtained by mixing boron nitride, silicon carbide and dispersant in a specific proportion. The specific thermal conductive filler is used to improve the thermal conductivity and flexibility of the heat dissipation insulating sheet and reduce the amount of thermal conductive filler added; at the same time, cross-linking occurs between the vinyl silicone oil, hydrogen-containing silicone oil and methyl vinyl silicone resin, which greatly improves the flexibility and insulation of the heat dissipation insulating sheet, so that the heat dissipation insulating sheet can be bent and used at will, and still maintain good thermal conductivity and insulation.

2. In the present application, the boron nitride is modified so that the surface of the boron nitride is bonded with a vinyl acrylic polymer, so that the boron nitride will not spall during use, thereby ensuring the thermal conductivity of the heat dissipation insulating sheet. At the same time, it can also improve the bonding strength between the boron nitride and the three-dimensional network structure, improve the structural stability of the heat dissipation insulating sheet, and extend the service life of the heat dissipation insulating sheet.

DETAILED DESCRIPTION

Example

Example 1

A fireproof heat dissipation insulating sheet is prepared by the following method:

S1, 1000 g of vinyl silicone oil, 50 g of hydrogenated silicone oil, 200 g of methyl vinyl silicone resin, 60 g of flame retardant (decabromodiphenyl ether) and 10 g of catalyst (chloroplatinic acid) were mixed to obtain a mixture A, the mixing temperature was 40° C., the mixing time was 40 min, and the mixing speed was 800 r/min;

S2, mixing mixture A, 400 g of thermal conductive filler (boron nitride) and 10 g of vulcanizing agent (sulfur) to obtain mixture B, the mixing temperature is 40° C., the mixing time is 20 min, and the mixing speed is 1000 r/min to obtain mixture B;

S3, vacuum degassing the mixture B for 20 min at a vacuum pressure of 0.2 KPa to form thermally conductive silica gel;

S4, heat the thermal conductive silicone to 80°C for primary vulcanization for 3 minutes, then heat it to 110°C for secondary vulcanization for 2 minutes, cool it down and cut it to obtain a fireproof heat dissipation insulation sheet.

The structural formula of vinyl silicone oil is as follows:

n=50, m=200

The viscosity of hydrogen-containing silicone oil at 25°C is 1000mpa.s and the hydrogen content is 0.1%.

The ethylene content of methyl vinyl silicone resin is 0.1 mol/100g and the molecular weight is 100,000.

The thermal conductive filler is obtained by mixing 222 g of boron nitride (average particle size of 30 nm), 111 g of silicon carbide (average particle size of 100 nm) and 67 g of dispersant (sodium pyrophosphate) in a weight ratio of 10:5:3.

The difference between Example 2-3 and Example 1 is that the types, amounts and parameters of some raw materials for preparing the fireproof heat dissipation insulation sheet are different. The specific differences are shown in Table 1:

Table 1 Types, amounts and parameters of raw materials for preparing fireproof heat dissipation insulation sheets

In Example 2, the thermal conductive filler is obtained by mixing 273 g of boron nitride (average particle size of 80 nm), 159 g of silicon carbide (average particle size of 300 nm) and 68 g of dispersant (sodium tripolyphosphate) in a weight ratio of 12:7:3.

In Example 3, the thermal conductive filler is obtained by mixing 321 g of boron nitride (average particle size of 100 nm), 214 g of silicon carbide (average particle size of 500 nm) and 64 g of dispersant (sodium hexametaphosphate) in a weight ratio of 15:10:3.

Example 4

A fireproof heat dissipation insulating sheet. The difference between this embodiment and embodiment 1 is that n=50, m=50, and the types, amounts and experimental parameters of other raw materials are consistent with those of embodiment 1.

Example 5

A fireproof heat dissipation insulating sheet. The difference between this embodiment and embodiment 1 is that n=50, m=210, and the types, amounts and experimental parameters of other raw materials are consistent with those of embodiment 1.

Example 6

A fireproof heat dissipation insulating sheet. The difference between this embodiment and embodiment 1 is that n=60, m=50, and the types, amounts and experimental parameters of other raw materials are consistent with those of embodiment 1.

Example 7

A fireproof heat dissipation insulating sheet. The difference between this embodiment and embodiment 1 is that n=40, m=50, and the types, amounts and experimental parameters of other raw materials are consistent with those of embodiment 1.

Example 8

A fireproof heat dissipation insulating sheet, the difference between this embodiment and embodiment 1 is that the boron nitride is modified boron nitride, which is prepared by the following preparation method:

A: Put 250g of boron nitride in 500g of organic solvent (tetrahydrofuran), disperse it evenly, add 25g of coupling agent (γ-methacryloxypropyltrimethoxysilane), stir to react, centrifuge and wash after the reaction is completed, and obtain surface-modified boron nitride;

B: adding the surface-modified boron nitride to a mixed solution of 80 g ethanol and 100 g water, and then ultrasonicating to uniformly disperse the surface-modified boron nitride to form an emulsion, adding 30 g of an emulsifier (peregal-10) and 30 g of a buffer (sodium bicarbonate) to the emulsion, and then ultrasonically dispersing it uniformly to obtain a mixed solution;

C: After mixing the mixed solution with 50 g of vinyl acrylic acid, heat to reflux at 50°C under nitrogen protection for pre-emulsification, then raise the temperature to 85°C, and drop 60 g of an aqueous solution containing an initiator. Keep the temperature and speed constant and stir for 7 hours to obtain a primary product. The primary product is centrifuged and washed, and vacuum dried to obtain modified boron nitride.

The aqueous solution containing the initiator is an ammonium persulfate aqueous solution with a mass fraction of 10%.

The difference between Examples 9-10 and Example 8 is that the types, amounts and parameters of some raw materials for preparing modified boron nitride are different. The specific differences are shown in Table 2:

Table 2 Types, amounts and parameters of raw materials for preparing modified boron nitride

Embodiment 11

A fireproof heat dissipation insulating sheet, the difference between this embodiment and embodiment 1 is that the structural formula of the vinyl silicone oil is as follows:

n=50.

Comparative Example

Comparative Example 1

A fireproof heat dissipation insulating sheet. The difference between this comparative example and Example 1 is that the thermal conductive fillers are all boron nitride, and the types, amounts and experimental parameters of other raw materials are consistent with those of Example 1.

Comparative Example 2

A fireproof heat dissipation insulating sheet. The difference between this comparative example and Example 1 is that the thermal conductive fillers are all silicon carbide, and the types, amounts and experimental parameters of other raw materials are consistent with those of Example 1.

Comparative Example 3

A fireproof heat dissipation insulating sheet. The difference between this comparative example and Example 1 is that methyl vinyl silicone resin is replaced by an equal amount of methyl phenyl silicone resin, and the types, amounts and experimental parameters of other raw materials are consistent with those in Example 1.

The molecular weight of methylphenyl silicone resin is 100,000 and the phenyl content is 20%.

Performance testing

The radial thermal conductivity test, insulation performance test and bending performance test of the fireproof heat dissipation insulation sheet prepared by Examples 1-11 and Comparative Examples 1-3 were conducted.

Detection method/test method

Thermal conductivity: Tested according to national standard GB/T2588-2008, using NETZSCH HY 009 thermal conductivity tester, at 25°C;

Insulation performance test: According to GB/1410-2006; the volume surface resistivity tester LST-121 is used to detect the volume resistance; when testing the volume resistance, the current flows from the heat conductive layer of the heat sink through the heat conductive insulation layer, and the greater the resistance, the better the insulation performance; bending performance test: the fireproof heat dissipation insulation sheet prepared by Examples 1-11 and Comparative Examples 1-3 is repeatedly bent 5000 times, with a bending angle of 90°, and the thermal conductivity and resistance are tested. The smaller the change rate of thermal conductivity and the change rate of resistance, the better the bending performance and flexibility of the heat dissipation insulation sheet. The test data are shown in Table 3:

Table 3 Experimental data of Examples 1-11 and Comparative Examples 1-3

By comparing Example 1 with Comparative Example 1, it can be seen that the thermal conductivity and insulation performance of the heat dissipation insulating sheet can be improved by using boron nitride alone as a thermally conductive filler. However, after the bending performance test, the thermal conductivity and resistance in Comparative Example 1 are greatly reduced, indicating that using boron nitride alone as a thermally conductive filler is not conducive to improving the flexibility of the heat dissipation insulating sheet.

By comparing Example 1 with Comparative Example 2, it can be seen that by using silicon carbide alone as a thermally conductive filler, both the thermal conductivity and the resistance are reduced, and after the bending performance test, both the thermal conductivity and the resistance are reduced, indicating that the use of boron nitride and silicon carbide together can further improve the flexibility, thermal conductivity and insulation of the heat dissipation insulating sheet.

By comparing Example 1 with Comparative Example 3, the thermal conductivity and resistance of Comparative Example 3 are not as good as those of Example 1, and after the bending performance test, the thermal conductivity and resistance are greatly reduced, indicating that in the present application, by adding methyl vinyl silicone resin in combination with other components, the flexibility of the heat dissipation insulating sheet can be further improved, and good thermal conductivity and insulation can be maintained.

Comparing Example 1 with Examples 8-10, the thermal conductivity and resistance in Examples 8-10 are increased, and after repeated bending, the change rate of thermal conductivity and the change rate of resistance in Examples 8-10 are both less than that in Example 1, indicating that the modified boron nitride prepared by the present application can further improve the flexibility, thermal conductivity and insulation of the heat dissipation insulating sheet.

Comparing Example 1 with Example 4-7, after repeated bending, the change rate of thermal conductivity and the change rate of resistance in Example 4-5 are both smaller than those in Example 1; the thermal conductivity and resistance in Example 6-7 are both reduced, and after repeated bending, the change rate of thermal conductivity and the change rate of resistance in Example 6-7 are both smaller than those in Example 1, indicating that the flexibility, thermal conductivity and insulation of the heat dissipation insulating sheet can be further improved by optimizing the values of n and m in the vinyl silicone oil.

Compared with Example 1 and Example 11, the thermal conductivity and resistance in Example 11 are reduced, and after repeated bending, the change rate of thermal conductivity and the change rate of resistance in Example 11 are smaller than those in Example 1, indicating that by using a vinyl silicone oil with a specific structure in combination with other raw materials to prepare the heat dissipation insulating sheet, the flexibility, thermal conductivity and insulation of the heat dissipation insulating sheet can be further improved.

This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed. However, as long as it is within the scope of the claims of the present application, it shall be protected by the patent law.

Claims (10)

1. A fireproof heat dissipation insulating sheet, characterized in that it is prepared from the following raw materials in parts by weight: 100 parts of vinyl silicone oil 5-15 parts of hydrogen silicone oil 20-30 parts of methyl vinyl silicone resin Thermal conductive filler 40-60 parts Flame retardant 6-12 parts 1-2 parts of catalyst 1-2 parts of vulcanizing agent The thermal conductive filler is obtained by mixing boron nitride, silicon carbide and a dispersant in a weight ratio of (10-15): (5-10): 3. 2. A fireproof heat dissipation insulating sheet according to claim 1, characterized in that: the boron nitride is modified boron nitride, which is prepared by the following preparation method: A: Put boron nitride in an organic solvent, disperse it evenly, add a coupling agent, stir to react, centrifuge and wash after the reaction is completed to obtain surface-modified boron nitride; B: adding the surface-modified boron nitride to a mixed solution of ethanol and water, and then ultrasonicating to uniformly disperse the surface-modified boron nitride to form an emulsion, adding an emulsifier and a buffer to the emulsion, and then ultrasonically dispersing it uniformly to obtain a mixed solution; C: After mixing the mixed solution with vinyl acrylic acid, heat to reflux at 50°C-60°C under nitrogen protection for pre-emulsification, then raise the temperature to 85°C-90°C, and dropwise add an aqueous solution containing an initiator, maintain constant temperature and constant speed stirring for 7-9 hours to obtain a primary product, centrifuge and wash the primary product, and vacuum dry it to obtain modified boron nitride. 3. A fireproof heat dissipation insulating sheet according to claim 2, characterized in that the weight parts of the raw materials used to prepare the modified boron nitride are as follows: Boron nitride 20-30 parts 50-70 parts of organic solvent Coupling agent 2.5-3.5 parts 8-18 parts of ethanol 10-20 parts water Emulsifier 4-5 parts Buffer 4-5 parts Vinyl acrylic acid 5-9 parts Contains 6-10 parts of aqueous solution of initiator. 4. A fireproof heat dissipation insulating sheet according to claim 1, characterized in that: the structural formula of the vinyl silicone oil is as follows: 5. A fireproof heat dissipation insulating sheet according to claim 4, characterized in that n=50-150, m=60-200 in the vinyl silicone oil. 6. The fireproof heat dissipation insulating sheet according to claim 1, characterized in that the average particle size of the boron nitride is 30-100 nm, and the average particle size of the silicon carbide is 100-500 nm. 7. A fireproof heat dissipation insulating sheet according to claim 1, characterized in that the ethylene content in the methyl vinyl silicone resin is 0.1-0.5 mol/100g and the molecular weight is 100,000-400,000. 8. A fireproof heat dissipation insulating sheet according to claim 1, characterized in that the viscosity of the hydrogen-containing silicone oil at 25°C is 1000-5000 mPa.s, and the hydrogen content is 0.1-0.4%. 9. A fireproof heat dissipation insulating sheet according to claim 1, characterized in that the flame retardant comprises at least one of magnesium hydroxide, ammonium polyphosphate, decabromodiphenyl ether, silicone flame retardant, ammonium polyphosphate and montmorillonite nanocomposite, antimony trioxide and aluminum hydroxide. 10. A method for preparing a fireproof heat dissipation insulating sheet for a new energy battery pack according to any one of claims 1 to 9, characterized in that it comprises the following preparation steps: S1. According to parts by weight, vinyl silicone oil, hydrogenated silicone oil, methyl vinyl silicone resin, flame retardant and catalyst are mixed to obtain a mixture A, the mixing temperature is 40-50° C., the mixing time is 40-60 min, and the mixing speed is 800-1000 r/min; S2, mixing mixture A, thermal conductive filler and vulcanizing agent to obtain mixture B, the mixing temperature is 40-50° C., the mixing time is 20-30 min, and the mixing speed is 1000-1200 r/min to obtain mixture B; S3, vacuum degassing the mixture B for 20-30 min at a vacuum pressure of 0.2-0.4 KPa to form thermally conductive silica gel; S4. Heat the thermal conductive silicone to 80-100°C for primary vulcanization for 3-6 minutes, then heat to 110-120°C for secondary vulcanization for 2-4 minutes, cool and cut to obtain a fireproof heat dissipation insulation sheet.