Carrier-free multifunctional master batch with insulating, heat-conducting and flame-retardant properties as well as preparation method and application of carrier-free multifunctional master batch

Abstract

The invention discloses an insulating, heat-conducting and flame-retardant carrier-free multifunctional master batch as well as a preparation method and application thereof. The multifunctional master batch is prepared from the following raw materials: modified hexagonal boron nitride, aluminum oxide with a core-shell structure, a flame retardant, an antioxidant, a processing aid and a binder. The surface of the modified hexagonal boron nitride is modified by tri (dioctylpyrophosphoryloxy) titanate, the aluminum oxide with the core-shell structure is coated by silicon dioxide, and the aluminum oxide is alpha crystal form aluminum oxide. And the flame retardant is diethyl aluminum hypophosphite and melamine polyphosphate. The preparation method of the multifunctional master batch comprises the steps of cold pressing, crushing and drying. The multifunctional master batch can be applied to modification of polymer composite materials such as PA66, PA6 and PBT, and can comprehensively improve the electrical insulation, heat conduction and flame retardant properties of the polymer composite materials.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and in particular to a multifunctional masterbatch for modifying polymer composite materials. Specifically, it relates to a multifunctional masterbatch that does not require a traditional polymer carrier and possesses excellent insulation, thermal conductivity and flame retardant properties, as well as its preparation method and application. Background Technology

[0002] The rapid development of industries such as electronics, 5G communications, and new energy vehicles has placed extremely high demands on the comprehensive performance of polymer materials. Many applications (such as LED heat sinks, battery pack housings, and integrated circuit packaging) require materials to simultaneously possess good thermal conductivity to dissipate heat, excellent electrical insulation to ensure safe use, and reliable flame retardancy to prevent fire risks.

[0003] Currently, the main method for imparting the aforementioned functions to polymer materials is to blend functional fillers into the matrix resin (such as nylon, polyester, polycarbonate, polypropylene, polyethylene, etc.). For example, alumina and boron nitride are used for thermal conductivity and insulation, while magnesium hydroxide and aluminum hydroxide are used for flame retardancy. However, directly adding powdered fillers has many drawbacks: 1) The filler has a high density and is prone to sedimentation, leading to uneven blending; 2) A very high filler content (usually >60wt%) is required to form an effective thermal conductivity and flame retardancy network, which severely degrades the material's processing flowability and mechanical properties; 3) At high filler content, the filler is prone to agglomeration and is difficult to disperse, affecting the final performance.

[0004] Traditional solutions involve using masterbatches, which pre-mix high-concentration fillers with carrier resin and then granulate. However, the introduction of carrier resin leads to a dilution effect, meaning that the filler concentration is reduced as the masterbatch contains a certain proportion of carrier resin. Furthermore, carrier resins are not compatible with all substrates, potentially degrading the composite material's performance. Additionally, carrier resins themselves are not thermally conductive, non-flame-retardant, and even have poor insulation properties, becoming a performance bottleneck. Carrier-free masterbatches, on the other hand, do not suffer from the dilution effect of carriers, have a low addition ratio, are broadly applicable to various resin matrices, have low granulation temperatures, reducing energy consumption, and avoid the thermal decomposition of flame retardants. Invention patent CN116554580A, "A carrier-free composite flame retardant masterbatch and its preparation method and application," provides a carrier-free composite flame retardant masterbatch, mainly composed of ultrafine magnesium hydroxide, antimony trioxide, and a silane coupling agent. When applied to PVC (SG-5), it effectively blocks fires in both the early and late stages of combustion and has good smoke suppression effects. However, this masterbatch has a single function, only providing flame retardancy. Invention patent CN111703042A, "A method for preparing a carrier-free plastic filler masterbatch and its product", provides a method for preparing masterbatch using attapulgite as a binder. The prepared masterbatch is easily dispersed in plastic, and attapulgite can also strengthen and toughen plastic. However, the main purpose of this masterbatch is to improve the strength and flame retardancy of plastic, without addressing the flame retardancy, electrical insulation and thermal conductivity of plastic.

[0005] With the rapid development of emerging industries, it has become an urgent need to develop a carrier-free masterbatch that combines insulation, thermal conductivity, and flame retardancy, and apply it to the field of high-performance composite materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties, as well as its preparation method and application. The masterbatch itself does not contain resin carriers (such as PA6, PP, etc.) that are traditionally added in large quantities for dilution and easy processing. The amount of binder used is very small and is only used to bond other components. The content of functional fillers is extremely high.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: The present invention provides a carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardant properties, which is made from the following raw materials in parts by weight: 20-45 parts modified hexagonal boron nitride, 20-45 parts silica-coated alumina, 30-45 parts flame retardant, 1-2 parts antioxidant, 0-3 parts processing aid and 1-5 parts binder.

[0008] Preferably, the method for preparing the modified hexagonal boron nitride includes the following steps: a1. Place hexagonal boron nitride in a vacuum drying oven, evacuate, and dry at 120-150℃ for 3-6 hours to obtain dried hexagonal boron nitride; a2. Tris(dioctylpyrophosphoryloxy)titanate is added to a mixed solvent of toluene and xylene to prepare a titanate modified solution, wherein the mass concentration of tris(dioctylpyrophosphoryloxy)titanate is 0.5-2.0%; the titanate modified solution is mixed with dried hexagonal boron nitride, heated under reflux for 6-8 hours, and the solid and liquid are separated, the solid being the treated hexagonal boron nitride; a3. The treated hexagonal boron nitride was washed alternately with toluene and ethanol 1-3 times, and then dried under vacuum to obtain modified hexagonal boron nitride.

[0009] In step a3 above, the vacuum drying temperature is preferably 50-75℃.

[0010] Preferably, the method for preparing the silica-coated alumina includes the following steps: b1. Take α-Al2O3 and calcine it in a muffle furnace at 480-580℃ for 1.5-3 hours to obtain calcined α-Al2O3; mix tetraethyl orthosilicate, ethanol and water, and adjust the pH to 9.5-10.5 with ammonia to obtain modified gel. b2. Disperse the calcined α-Al2O3 into ethanol by mechanical stirring, with a mass ratio of α-Al2O3 to ethanol of 3-5:90-100, and then sonicate for 20-60 minutes to obtain a mixture of α-Al2O3 and ethanol. b3. Under stirring conditions, the modified gel is added to a mixture of α-Al2O3 and ethanol, wherein the volume ratio of the modified gel to the α-Al2O3 and ethanol mixture is 1:0.1-3.5, and the reaction is carried out at 35-55℃ for 0.8-2 hours; then the same amount of modified gel is added again, and the reaction is continued at 35-55℃ for 1.5-3 hours. After the reaction is completed, the solid and liquid are separated, and the solid is the treated alumina. b4. The treated alumina is washed 1-3 times with anhydrous ethanol, vacuum dried at 70-95℃, and then calcined in a muffle furnace at 480-580℃ for 1.5-3 hours to obtain silica-coated alumina.

[0011] More preferably, in step b1, the molar ratio of ethyl silicate, ethanol, and water is 1:2-5:2-5.

[0012] In step b4, the heating rate of the muffle furnace is 2-5℃ / min.

[0013] In step b1 above, the concentration of ammonia water is preferably 0.3-0.6 mol / L.

[0014] The silica-coated alumina prepared by the above method is a core-shell structure alumina (α-Al₂O₃@SiO₂). The shell is silica, and the core is α-Al₂O₃.

[0015] The modified hexagonal boron nitride primarily functions as an electrical insulator, while the silica-coated alumina primarily functions as a thermal conductor. Although hexagonal boron nitride itself has good thermal conductivity, and α-Al₂O₃ also possesses certain electrical insulation properties, it is difficult for a single filler to simultaneously meet the requirements of good electrical insulation and high thermal conductivity. Typically, multiple fillers need to be blended, but this increases the total amount of filler added, and a large amount of filler can reduce the strength and toughness of the polymer-based composite material. This invention satisfies the multifunctional requirements by blending hexagonal boron nitride and α-Al₂O₃, and improves the efficiency of the blended filler, achieving performance requirements with a smaller amount of filler. Al₂O₃ is the most commonly used thermally conductive filler, and while it has good insulation properties, it is lower than that of hexagonal boron nitride. Silica-coating modification of Al₂O₃ can improve dielectric strength and arc resistance, while also reducing the interfacial thermal resistance between α-Al₂O₃ and the resin matrix, thus optimizing the thermal conduction path. Unlike α-Al₂O₃, hexagonal boron nitride has excellent insulation properties but lower thermal conductivity. Surface treatment of hexagonal boron nitride with titanate can significantly improve its thermal conductivity and also reduce its volume resistivity to below 10 Ω·cm. 16 Ω·cm threshold.

[0016] The flame retardant is aluminum diethyl phosphite (ADP) and melamine polyphosphate (MPP), with a mass ratio of aluminum diethyl phosphite to melamine polyphosphate of 1:0-1.

[0017] Among common nitrogen- and phosphorus-containing flame retardants, ADP has good heat resistance and is not easily decomposed, making it suitable for use in flame retardant systems for engineering plastics. ADP is also considered an environmentally friendly flame retardant. However, ADP's market price is higher than other flame retardants. Therefore, this invention uses MPP to replace part of ADP, reducing the cost of masterbatch materials and allowing its use in composite materials processed at low temperatures. This invention incorporates a compound flame retardant of ADP and MPP, which can be successfully integrated with a specific insulating and thermally conductive filler system containing hexagonal boron nitride and α-Al₂O₃ in a carrier-free masterbatch, achieving a balance of performance. Halogenated flame retardants have good flame retardant effects, effectively slowing down the combustion rate and reducing the probability of fire accidents. However, this invention does not use halogenated flame retardants, mainly because they release acidic substances such as hydrogen halides during aging, which can corrode metal components in electronic devices. In addition, red phosphorus is not used in this invention because it is easily oxidized. In a high-humidity environment, it will slowly release phosphoric acid, which will corrode metal parts. In particular, it will have a great negative impact on the leakage of weak electrical components and the insulation of high-voltage components. Moreover, red phosphorus is usually red or black and cannot be used in composite materials where color is required.

[0018] Preferably, the antioxidant is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) and tris[2,4-di-tert-butylphenyl] phosphite (antioxidant 168), wherein the mass ratio of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to tris[2,4-di-tert-butylphenyl] phosphite is 1-5:1-5; And / or, the processing aid is pentaerythritol stearate (PETS) and anti-glass fiber exposure agent TAF, with a mass ratio of pentaerythritol stearate to anti-glass fiber exposure agent TAF of 1-3:1-3. The above processing aid mainly plays a lubricating role.

[0019] Preferably, the adhesive is polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG).

[0020] Compared to other binders, these two have higher decomposition temperatures, making them particularly suitable for composite materials using engineering plastics and specialty engineering plastics as the matrix.

[0021] The second aspect of this invention provides a method for preparing the carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties described above, comprising the following steps: S1. Add the modified hexagonal boron nitride, silica-coated alumina, flame retardant, antioxidant, processing aid, and binder to a high-speed mixer, start the high-speed mixer, and mix evenly to obtain the tableting material; S2. The tableting material is fed into a tablet press and pressed into shape to obtain a sheet-like preform; S3. Remove the sheet-like blank, crush and screen it to obtain molding masterbatch with the required particle size; the particle size range of the molding masterbatch is 1mm-5mm; S4. Dry the molding masterbatch at 80-120℃ for 2-4 hours to obtain a carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties.

[0022] The preparation method described above is simple, cost-controllable, and easy to industrialize.

[0023] The third aspect of this invention provides the application of the carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties described above in the preparation of polymer composite materials with electrical insulation, thermal conductivity and flame retardancy properties.

[0024] Preferably, the carrier-free multifunctional masterbatch with insulating, thermally conductive, and flame-retardant properties is added at an amount of 1-45 wt% to the polymer composite material with electrically insulating, thermally conductive, and flame-retardant properties. Compared with the prior art, the advantages of the present invention are as follows: (1) Applying modified hexagonal boron nitride and silica-coated alumina to the same masterbatch and filling it into polymer materials can improve both the electrical insulation and thermal conductivity of the materials. Surface modification of h-NB with titanate coupling agents can improve the interfacial bonding force with the resin matrix, which is also beneficial for improving the mechanical properties of the composite material. Coating α-Al2O3 with silica can improve the dielectric strength and arc resistance of α-Al2O3, while also reducing the interfacial thermal resistance between α-Al2O3 and the resin matrix, thus optimizing the heat conduction path. These advantages are not present in unmodified h-NB and alumina.

[0025] (2) The present invention introduces a suitable flame retardant combination of aluminum diethyl phosphite (ADP) and melamine polyphosphate, which can be successfully integrated with a specific insulating and thermally conductive filler system containing hexagonal boron nitride and α-Al2O3 in carrier-free masterbatch. When applied to polymer materials, it can comprehensively and stably exert the insulating, thermally conductive and flame retardant properties.

[0026] (3) In terms of process, this invention does not use a traditional resin carrier, but only a small amount of binder. Combined with dry compression process, it maximizes efficiency, reduces the use of fillers, lowers the quality of masterbatch, and reduces transportation costs. Combined with dry compression process, it can be carried out at room temperature, which is green and environmentally friendly. At the same time, it avoids the damage to the molecular structure of heat-sensitive flame retardant caused by high temperature processing, thus protecting the flame retardant. Through unique dry binder and optimized compression parameters, the masterbatch produced has high strength, is not easy to pulverize, and can be quickly dispersed in downstream processing. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] Example 1

[0029] A carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties is made from the following raw materials in parts by weight: 25 parts modified hexagonal boron nitride, 35 parts silica-coated alumina, 33 parts ADP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl] phosphite, 1.4 parts PETS, 1.4 parts TAF, and 3 parts PVP.

[0030] Comparative Example 1 A carrier-free multifunctional masterbatch is made from the following raw materials in parts by weight: 25 parts modified hexagonal boron nitride, 35 parts α-Al2O3, 33 parts ADP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl] phosphite, 1.4 parts PETS, 1.4 parts TAF, and 3 parts PVP.

[0031] Example 2

[0032] A carrier-free multifunctional masterbatch with insulating, thermally conductive, and flame-retardant properties is made from the following raw materials in parts by weight: 30 parts modified hexagonal boron nitride, 25 parts silica-coated alumina, 28 parts ADP, 10 parts MPP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl]phosphite, 1.4 parts PETS, 1.4 parts TAF, and 3 parts PEG.

[0033] Comparative Example 2 A carrier-free multifunctional masterbatch is made from the following raw materials in parts by weight: 30 parts hexagonal boron nitride, 25 parts silica-coated alumina, 28 parts ADP, 10 parts MPP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl]phosphite, 1.4 parts PETS, 1.4 parts TAF, and 3 parts PEG.

[0034] Example 3

[0035] A carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties is made from the following raw materials in parts by weight: 40 parts modified hexagonal boron nitride, 23 parts silica-coated alumina, 15 parts ADP, 15 parts MPP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl]phosphite, 1.4 parts PETS, 1.4 parts TAF, 2 parts PVP, and 1 part PEG.

[0036] Comparative Example 3 A carrier-free multifunctional masterbatch is made from the following raw materials in parts by weight: 40 parts hexagonal boron nitride, 23 parts α-Al2O3, 15 parts ADP, 15 parts MPP, 0.6 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 0.6 parts tris[2,4-di-tert-butylphenyl]phosphite, 1.4 parts PETS, 1.4 parts TAF, 2 parts PVP, and 1 part PEG.

[0037] In the above embodiments and comparative examples, the preparation method of modified hexagonal boron nitride includes the following steps: a1. Place 300gH-BN (powder, 325 mesh) in a vacuum drying oven, evacuate, and dry at 120°C for 4 hours to obtain dried hexagonal boron nitride; dissolve tris(dioctylpyrophosphoryloxy)titanate in a mixed solvent of toluene and xylene (1 / 1, wt / wt) to prepare a 1% solution to obtain a titanate modified solution; then transfer the titanate modified solution to a heating reflux apparatus, add the dried hexagonal boron nitride, and heat under reflux for 7 hours; remove the solvent using a separatory funnel to obtain the treated hexagonal boron nitride; a3. Wash the treated hexagonal boron nitride three times alternately with toluene and ethanol, and place it in a vacuum oven to dry under vacuum at 60°C for 12 hours to obtain modified hexagonal boron nitride.

[0038] In the above embodiments and comparative examples, the preparation method of silica-coated alumina includes the following steps: b1. Take 300g of α-Al₂O₃ (powder, specific surface area 210m²) 2 / g) is placed in a muffle furnace and calcined at 500℃ for 2 hours to obtain calcined α-Al2O3; ethyl silicate, ethanol and water are mixed in a molar ratio of 1:4:4, and the pH is adjusted to 9.5-10.5 with 0.5mol / L ammonia water to obtain modified gel; b2. 50g of calcined α-Al2O3 is weighed and added to 950ml of anhydrous ethanol. Mechanical stirring is started to disperse it evenly, and then ultrasonic treatment is performed for 30min to obtain a mixture of α-Al2O3 and ethanol; b3. Under stirring conditions, 300ml of modified gel is added to the mixture. Add a mixture of α-Al₂O₃ and ethanol to the hydrogel, heat to 40°C and react for 1 hour. Then add 300 ml of tetraethyl orthosilicate / ethanol / hydrogel, heat to 40°C and continue the reaction for 2 hours. After the reaction is complete, centrifuge to separate and collect the solid, which is the treated alumina. b4. Wash the treated alumina three times with 100 ml of anhydrous ethanol each time. Place it in a vacuum oven and dry it at 80°C for 1 hour. Transfer it to a muffle furnace and heat to 500°C for 2 hours, with a heating rate of 3°C / min, to obtain silica-coated alumina.

[0039] The masterbatch preparation methods of the above embodiments and comparative examples include the following steps: S1. Weigh each component according to the listed formula, then add them together to a high-speed mixer. Start the high-speed mixer at 300 rpm for 30 minutes to obtain the tableting material. S2. Feed the tableting material into a tablet press and compress it at room temperature to obtain a sheet-like preform with a thickness of 2 mm. S3. Take out the sheet-like preform, crush it with a pulverizer, and then sieve it to collect particles with a particle size between 2 mm and 4 mm to obtain the molding masterbatch with the required particle size. S4. Dry the molding masterbatch in a forced-air drying oven at 100°C for 3 hours to obtain a carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties.

[0040] The masterbatches from the above examples and comparative examples were applied to the preparation of nylon 66, nylon 6, and PBT. Specific formulations are shown in the following application examples: Application Example 1 A polymer composite material is made from the following raw materials in parts by weight: 60 parts of nylon 66 resin, 10 parts of chopped glass fiber, and 30 parts of carrier-free masterbatch from Example 1.

[0041] Application Comparative Example 1 A polymer composite material is made from the following raw materials in parts by weight: 60 parts of nylon 66 resin, 10 parts of chopped glass fiber, and 30 parts of carrier-free masterbatch from Comparative Example 1.

[0042] Application Example 2 A polymer composite material is made from the following raw materials in parts by weight: 60 parts of nylon 6 resin and 40 parts of carrier-free masterbatch from Example 2.

[0043] Application Comparative Example 2 A polymer composite material is made from the following raw materials in parts by weight: 60 parts of nylon 6 resin and 40 parts of carrier-free masterbatch from Comparative Example 2.

[0044] Application Example 3 A polymer composite material is made from the following raw materials in parts by weight: 60 parts PBT resin and 40 parts carrier-free masterbatch from Example 3.

[0045] Application Comparative Example 3 A polymer composite material is made from the following raw materials in parts by weight: 60 parts of PBT resin and 40 parts of carrier-free masterbatch from Comparative Example 3.

[0046] The mechanical properties, impact properties, flame retardant properties, melt flowability, and insulation properties of the polymer composite materials used in Application Examples 1-3 and Comparative Examples 1-3 were determined using the following methods: Tensile strength was determined according to national standard GB / T 1040.1-2025, with a tensile rate of 50 mm / min.

[0047] Impact strength was determined according to national standard GB / T 1843-2008, using a cantilever beam with a V-notch.

[0048] The flame retardant rating is determined according to UL94 standard.

[0049] The MFR (Mel Flow Index) test conditions are as follows: for PA66-based composites, 275℃ and 5kg; for PA6-based composites, 235℃ and 2.16kg; and for PBT-based composites, 265℃ and 5kg. The measurement results are shown in Table 1.

[0050] Table 1. Test results of polymer composite materials that combine electrical insulation, thermal conductivity, and flame retardancy.

[0051] The above examples and comparative examples show that modifying h-BN and coating α-Al2O3 with it can achieve beneficial effects in preparing carrier-free multifunctional masterbatches.

[0052] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A carrier-free multifunctional masterbatch possessing insulation, thermal conductivity, and flame retardant properties, characterized in that, It is made from the following raw materials in parts by weight: 20-45 parts modified hexagonal boron nitride, 20-45 parts silica-coated alumina, 30-45 parts flame retardant, 1-2 parts antioxidant, 0-3 parts processing aid, and 1-5 parts binder.

2. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 1, characterized in that, The method for preparing the modified hexagonal boron nitride includes the following steps: a1. Place hexagonal boron nitride in a vacuum drying oven, evacuate, and dry at 120-150℃ for 3-6 hours to obtain dried hexagonal boron nitride; a2. Tris(dioctylpyrophosphoryloxy)titanate is added to a mixed solvent of toluene and xylene to prepare a titanate modified solution, wherein the mass concentration of tris(dioctylpyrophosphoryloxy)titanate is 0.5-2.0%; the titanate modified solution is mixed with dried hexagonal boron nitride, heated under reflux for 6-8 hours, and the solid and liquid are separated, the solid being the treated hexagonal boron nitride; a3. The treated hexagonal boron nitride was washed alternately with toluene and ethanol 1-3 times, and then dried under vacuum to obtain modified hexagonal boron nitride.

3. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 1, characterized in that, The method for preparing silica-coated alumina includes the following steps: b1. Take α-Al2O3 and calcine it in a muffle furnace at 480-580℃ for 1.5-3 hours to obtain calcined α-Al2O3; mix tetraethyl orthosilicate, ethanol and water, and adjust the pH to 9.5-10.5 with ammonia to obtain modified gel. b2. Disperse the calcined α-Al2O3 into ethanol by mechanical stirring, with a mass ratio of α-Al2O3 to ethanol of 3-5:90-100, and then sonicate for 20-60 minutes to obtain a mixture of α-Al2O3 and ethanol. b3. Under stirring conditions, the modified gel is added to a mixture of α-Al2O3 and ethanol, wherein the volume ratio of the modified gel to the α-Al2O3 and ethanol mixture is 1:0.1-3.5, and the reaction is carried out at 35-55℃ for 0.8-2 hours; then the same amount of modified gel is added again, and the reaction is continued at 35-55℃ for 1.5-3 hours. After the reaction is completed, the solid and liquid are separated, and the solid is the treated alumina. b4. The treated alumina is washed 1-3 times with anhydrous ethanol, vacuum dried at 70-95℃, and then calcined in a muffle furnace at 480-580℃ for 1.5-3 hours to obtain silica-coated alumina.

4. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 3, characterized in that, In step b1, the molar ratio of ethyl silicate, ethanol, and water is 1:2-5:2-5; In step b4, the heating rate of the muffle furnace is 2-5℃ / min.

5. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 1, characterized in that, The flame retardant is aluminum diethyl phosphite and melamine polyphosphate, with a mass ratio of aluminum diethyl phosphite to melamine polyphosphate of 1:0-1.

6. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 1, characterized in that, The antioxidant is a mixture of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris[2,4-di-tert-butylphenyl] phosphite, wherein the mass ratio of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to tris[2,4-di-tert-butylphenyl] phosphite is 1-5:1-5; And / or, the processing aid is pentaerythritol stearate and anti-glass fiber exposure agent TAF, and the mass ratio of pentaerythritol stearate to anti-glass fiber exposure agent TAF is 1-3:1-3.

7. The carrier-free multifunctional masterbatch with insulation, thermal conductivity, and flame retardant properties according to claim 1, characterized in that, The adhesive is polyvinylpyrrolidone or polyethylene glycol.

8. The method for preparing a carrier-free multifunctional masterbatch with insulating, thermally conductive, and flame-retardant properties according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Add the modified hexagonal boron nitride, silica-coated alumina, flame retardant, antioxidant, processing aid, and binder to a high-speed mixer, start the high-speed mixer, and mix evenly to obtain the tableting material; S2. The tableting material is fed into a tablet press and pressed into shape to obtain a sheet-like preform; S3. Remove the sheet-like blank, crush and screen it to obtain molding masterbatch with the required particle size; the particle size range of the molding masterbatch is 1mm-5mm; S4. Dry the molding masterbatch at 80-120℃ for 2-4 hours to obtain a carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties.

9. The application of the carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties as described in any one of claims 1-7 in the preparation of polymer composite materials with electrical insulation, thermal conductivity and flame retardancy properties.

10. The application according to claim 9, characterized in that, The amount of carrier-free multifunctional masterbatch with insulation, thermal conductivity and flame retardancy properties added to polymer composite materials with electrical insulation, thermal conductivity and flame retardancy properties is 1-45wt%.

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