Sub-micron spherical modified silica micropowder and preparation method thereof

Abstract

This invention belongs to the field of silicon micropowder technology, and specifically discloses a submicron spherical modified silicon micropowder and its preparation method, including the following steps: (1) silicon micropowder pretreatment; (2) aminosilane gradient pH grafting; (3) plasma pretreatment and boron nitride coating; (4) post-treatment; The submicron spherical modified silicon micropowder prepared by this invention has achieved a breakthrough improvement in comprehensive performance, and can effectively reduce the internal porosity of composite materials; the thermal decomposition initiation temperature reaches above 428℃, and the mass retention rate at 800℃ exceeds 97.5%, meeting the high-temperature resistance requirements of high-end electronic materials; the oil absorption value is as low as 0.30-0.32mL / g, and the viscosity of the slurry dispersed in epoxy resin is only 820-850mPa·s, which greatly improves the compatibility with organic matrix and processing fluidity.

Description

Technical Field

[0001] This application relates to the field of silicon micropowder technology, specifically to a submicron spherical modified silicon micropowder and its preparation method. Background Technology

[0002] In high-end manufacturing fields such as electronic information, semiconductor packaging, and copper-clad laminates, submicron spherical silicon powder has become a core inorganic filler for improving the overall performance of materials due to its high insulation, low coefficient of thermal expansion, and excellent filling properties. As electronic devices develop towards miniaturization and high density, the performance requirements for silicon powder are becoming increasingly stringent, requiring not only precise particle size control but also good dispersibility, thermal stability, and compatibility with organic matrices.

[0003] In existing technologies, the application of silicon micropowder faces numerous unresolved issues. The native surface of silicon micropowder contains metallic impurities and hydroxyl contaminants. Insufficient pretreatment can obscure the active sites for the treatment reaction, thus affecting the bonding strength with the resin matrix and making the composite material prone to voids and cracking. To address these technical problems, there is an urgent need to develop a preparation method with strong process synergy and stable modification effects to obtain submicron spherical modified silicon micropowder with excellent comprehensive properties, meeting the needs of high-end manufacturing fields. Summary of the Invention

[0004] In view of this, the purpose of this invention is to overcome the shortcomings of the prior art by proposing a submicron spherical modified silicon powder and its preparation method to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing submicron spherical modified silica powder, comprising the following steps: (1) Pretreatment of silicon micro powder: Submicron spherical silicon micro powder is added to a 3-5% dilute hydrochloric acid solution and stirred for 1-2 hours at 40-50℃±0.5℃ and 200-300r / min. After washing with deionized water until neutral and washing with anhydrous ethanol 2-3 times, it is dried at 80-100℃ and vacuum degree -0.08~-0.1MPa for 2-3 hours to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent and ultrasonically dispersed for 30-40 min at 150-200W and 20-40kHz to form a suspension; 3-5% of the mass of the pretreated silica powder was added to the compound aminosilane, the pH was first adjusted to 7-7.5 by adding sodium bicarbonate solution, and stirred at a constant temperature for 1 h, then the pH was adjusted to 8-9 by adding sodium carbonate solution, and stirred for 2-3 h at 60-70℃ to obtain the grafted modified silica powder; (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micropowder was placed in a plasma device and pretreated for 6-10 min under an argon atmosphere, a power of 80-120 W and a discharge gap of 2-5 mm. The pretreated grafted modified silicon micropowder was returned to the reaction system, and 1-2% of polyethylene glycol by weight of the pretreated silicon micropowder was added. The mixture was stirred and dispersed at 300-400 r / min for 20-30 min. The nano boron nitride powder pretreated with ethanol-water mixed solvent was added at a rate of 0.1-0.2 g / min. The temperature was raised to 80-90 °C and stirred and reacted under a nitrogen atmosphere for 2-3 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) is filtered, washed with anhydrous ethanol for 1-2 hours by Soxhlet extraction, vacuum dried, and then pulverized by air jet to obtain submicron spherical modified silica powder with a particle size of 0.1-1 μm. As a further technical solution, in step (1), the liquid-solid ratio of dilute hydrochloric acid solution to submicron spherical silicon powder is 10-15:1 (mL / g).

[0006] As a further technical solution, the volume ratio of ethanol to water in the ethanol-water mixed solvent is 3:1.

[0007] As a further technical solution, in step (2), the mass concentration of sodium bicarbonate solution is 5-8%, and the mass concentration of sodium carbonate solution is 8-12%.

[0008] As a further technical solution, in step (3), the pretreatment process of nano boron nitride is as follows: add nano boron nitride powder to a γ-aminopropyltriethoxysilane ethanol solution with a mass fraction of 2-3%, disperse ultrasonically for 20 min, stir and react at 60℃ for 1 h, filter and dry for later use.

[0009] As a further technical solution, in step (3), the polyethylene glycol is PEG-1000.

[0010] As a further technical solution, in step (4), the vacuum drying is performed at 90-110℃ and a vacuum of -0.08 to -0.1MPa for 3-4 hours.

[0011] 8. The preparation method according to claim 1, characterized in that, in step (4), the air intake pressure of the air jet mill is 0.6-0.8 MPa and the speed of the classifier wheel is 20000-30000 r / min.

[0012] As a further technical solution, in step (4), the feed rate of the air jet mill is 10-20 g / min.

[0013] The preparation method described above yields submicron spherical modified silicon powder.

[0014] Compared with the prior art, the present invention has the following beneficial effects: In this invention, the silicon micropowder pretreatment step involves immersion in a dilute hydrochloric acid solution followed by multi-stage washing and drying. This effectively removes metallic impurities and residual hydroxyl contaminants from the silicon micropowder surface, significantly improving surface cleanliness and providing sufficient and uniform active sites for subsequent grafting reactions. This solves the problem of low grafting efficiency caused by impurities obscuring active centers. The aminosilane gradient pH grafting process first adjusts the pH to 7-7.5 with sodium bicarbonate, allowing the compounded aminosilane to fully hydrolyze and form stable silanol intermediates. Then, it adjusts the pH to 8-9 with sodium carbonate to promote the condensation reaction between silanol and hydroxyl groups on the silicon micropowder surface. This method avoids the drawbacks of incomplete silane hydrolysis or excessive cross-linking, achieving uniform grafting of aminosilane onto the silicon micropowder surface and effectively improving the oleophilic and hydrophobic properties of the silicon micropowder. Plasma pretreatment, conducted under an argon atmosphere, involves bombarding the surface of grafted modified silica powder with high-energy particles. This introduces a large number of active free radicals and functional groups, significantly enhancing surface reactivity and laying the foundation for a robust bond in the boron nitride coating. Simultaneously, it refines the surface microstructure and further optimizes particle dispersibility. After pretreatment with γ-aminopropyltriethoxysilane, nano-boron nitride introduces amino functional groups to its surface, forming chemical bonds with the plasma-activated silica powder. This solves the problems of poor dispersion and weak coating caused by the inertness of the boron nitride surface, fully leveraging its high heat resistance. Furthermore, the addition of PEG-1000 prevents particle agglomeration through steric hindrance, further improving the system's dispersion stability.

[0015] The various process steps of this invention form a complete synergistic system encompassing pretreatment, grafting, activation, coating, and post-treatment. The clean surface obtained after pretreatment of the silica powder with dilute hydrochloric acid allows the gradient-pH-grafted aminosilanes to more uniformly cover the particle surface, forming a dense organic transition layer. The amino groups on this transition layer synergistically enhance the binding strength with modified boron nitride, preventing the coating layer from detaching during subsequent processing or use. Simultaneously, the dispersing effect of PEG-1000 complements the coating modification of boron nitride, preventing particle agglomeration during modification and constructing a high-temperature resistant network through the lamellar structure of boron nitride, thus simultaneously improving thermal stability and dispersibility. The Soxhlet extraction in the post-treatment stage thoroughly removes unreacted modifiers, while vacuum drying and controlled airflow pulverization ensure a relatively concentrated particle size range, further optimizing particle filling performance. This multi-step synergistic effect effectively solves problems such as uneven grafting, weak coating, and poor dispersibility in existing technologies, achieving a comprehensive performance improvement.

[0016] The submicron spherical modified silica powder prepared by this invention achieves a breakthrough improvement in comprehensive performance, effectively reducing the internal porosity of composite materials; the thermal decomposition initiation temperature reaches above 428℃, and the mass retention rate at 800℃ exceeds 97.5%, meeting the high-temperature resistance requirements of high-end electronic materials; the oil absorption value is as low as 0.30-0.32mL / g, and the viscosity of the slurry dispersed in epoxy resin is only 820-850mPa・s, which greatly improves the compatibility with organic matrices and processing fluidity. Detailed Implementation

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0018] This invention provides a method for preparing submicron spherical modified silica powder, comprising the following steps: (1) Pretreatment of silicon micro powder: Submicron spherical silicon micro powder is added to a 3-5% dilute hydrochloric acid solution and stirred for 1-2 hours at 40-50℃±0.5℃ and 200-300r / min. After washing with deionized water until neutral and washing with anhydrous ethanol 2-3 times, it is dried at 80-100℃ and vacuum degree -0.08~-0.1MPa for 2-3 hours to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent and ultrasonically dispersed for 30-40 min at 150-200W and 20-40kHz to form a suspension; 3-5% of the mass of the pretreated silica powder was added to the compound aminosilane, the pH was first adjusted to 7-7.5 by adding sodium bicarbonate solution, and stirred at a constant temperature for 1 h, then the pH was adjusted to 8-9 by adding sodium carbonate solution, and stirred for 2-3 h at 60-70℃ to obtain the grafted modified silica powder; (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micropowder was placed in a plasma device and pretreated for 6-10 min under an argon atmosphere, a power of 80-120 W and a discharge gap of 2-5 mm. The pretreated grafted modified silicon micropowder was returned to the reaction system, and 1-2% of polyethylene glycol by weight of the pretreated silicon micropowder was added. The mixture was stirred and dispersed at 300-400 r / min for 20-30 min. The nano boron nitride powder pretreated with ethanol-water mixed solvent was added at a rate of 0.1-0.2 g / min. The temperature was raised to 80-90 °C and stirred and reacted under a nitrogen atmosphere for 2-3 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) is filtered, washed with anhydrous ethanol for 1-2 hours by Soxhlet extraction, dried under vacuum, and then pulverized by air jet to obtain submicron spherical modified silica powder with a particle size of 0.1-1 μm.

[0019] In this invention, the submicron spherical silicon powder can be any commercially available product known to those skilled in the art, without any special restrictions.

[0020] In this invention, the liquid-solid ratio of the dilute hydrochloric acid solution to the submicron spherical silicon powder in step (1) is preferably 10-15:1 (mL / g). This liquid-solid ratio range can ensure that the dilute hydrochloric acid solution is in full contact with the submicron spherical silicon powder and effectively remove impurities from the surface of the silicon powder.

[0021] In this invention, the volume ratio of ethanol to water in the ethanol-water mixed solvent is fixed at 3:1. This ratio of mixed solvent can provide a suitable reaction environment for each reaction step and ensure the smooth progress of the reaction.

[0022] In this invention, the mass concentration of sodium bicarbonate solution in step (2) is preferably 5-8%, and the mass concentration of sodium carbonate solution is preferably 8-12%. The acid-base solution within this concentration range can accurately adjust the pH value of the reaction system and meet the requirements of gradient pH grafting reaction.

[0023] In this invention, the preferred pretreatment process for boron nanonitride in step (3) is as follows: add boron nanonitride powder to a γ-aminopropyltriethoxysilane ethanol solution with a mass fraction of 2-3%, disperse ultrasonically for 20 min, stir and react at 60°C for 1 h, filter and dry for later use; the boron nanonitride powder after this pretreatment can better combine with the grafted modified silicon micro powder and improve the coating effect.

[0024] In this invention, in step (3), polyethylene glycol is fixed as PEG-1000. PEG-1000 has a suitable molecular weight and can play a good role in dispersion and bridging in the reaction system, promoting the uniform coating of boron nitride.

[0025] In this invention, the vacuum drying conditions in step (4) are preferably 90-110℃ and vacuum degree -0.08 to -0.1MPa for 3-4 hours. These drying conditions can quickly remove moisture and residual solvent from the reaction product without affecting the performance of the modified silicon micropowder.

[0026] In this invention, the air inlet pressure of the air jet mill in step (4) is preferably 0.6-0.8 MPa, the speed of the classifier wheel is preferably 20000-30000 r / min, and the feed rate is preferably 10-20 g / min. This set of air jet milling parameters can pulverize the dried product to the target particle size range and ensure that the product particle size distribution is uniform.

[0027] The preparation method provided by this invention removes impurities through silicon micropowder pretreatment, improves surface activity through aminosilane gradient pH grafting, enhances performance through plasma pretreatment and boron nitride coating, and ensures product quality through post-treatment. The synergistic effect of each step results in submicron spherical modified silicon micropowder with excellent performance, and the preparation process is stable and controllable, making it suitable for industrial production.

[0028] To further illustrate the present invention, the following detailed description is provided through the examples and comparative examples.

[0029] In the following embodiments and comparative examples of the present invention: the submicron spherical silica powder used is a commercially available conventional product; the compounded aminosilane used is a commercially available conventional product; the γ-aminopropyltriethoxysilane used is a commercially available conventional product; the PEG-1000 used is a commercially available conventional product; and the nano boron nitride powder used is a commercially available conventional product.

[0030] Example 1: (1) Pretreatment of silicon micro powder: Take an appropriate amount of submicron spherical silicon micro powder, add a 3% mass concentration of dilute hydrochloric acid solution, the liquid-solid ratio of dilute hydrochloric acid solution to submicron spherical silicon micro powder is 10:1 (mL / g), stir for 1h at 40℃±0.5℃ and 200r / min, then wash with deionized water until neutral, and then wash twice with anhydrous ethanol. Place the washed silicon micro powder in an environment of 80℃ and vacuum degree -0.08MPa for 2h to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent (ethanol to water volume ratio 3:1) and ultrasonically dispersed for 30 min at 150 W and 20 kHz to form a suspension; 3% of the mass of the pretreated silica powder was added to the compound aminosilane, and 5% sodium bicarbonate solution was added to adjust the pH to 7. The mixture was stirred at a constant temperature for 1 h, and then 8% sodium carbonate solution was added to adjust the pH to 8. The mixture was stirred at 60 °C for 2 h to obtain the grafted modified silica powder. (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micro powder was placed in a plasma device and pretreated for 6 min under an argon atmosphere, a power of 80 W and a discharge gap of 2 mm. The pretreated grafted modified silicon micro powder was returned to the reaction system, and 1% of the pretreated silicon micro powder was added to PEG-1000. The mixture was stirred and dispersed at 300 r / min for 20 min. At a rate of 0.1 g / min, nano boron nitride powder pretreated with ethanol-water mixed solvent was added (the pretreatment process of nano boron nitride: nano boron nitride powder was added to 2% of γ-aminopropyltriethoxysilane ethanol solution, ultrasonically dispersed for 20 min, stirred and reacted at 60 °C for 1 h, filtered and dried for later use). The temperature was raised to 80 °C and stirred and reacted under a nitrogen atmosphere for 2 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) was filtered, washed with anhydrous ethanol for 1 h by Soxhlet extraction, dried at 90℃ and vacuum degree -0.08MPa for 3 h, and then subjected to air jet milling with an air pressure of 0.6MPa, a classifier speed of 20000r / min and a feed rate of 10g / min to obtain submicron spherical modified silica powder with a particle size of 0.1-1μm.

[0031] Example 2: (1) Pretreatment of silicon micro powder: Take an appropriate amount of submicron spherical silicon micro powder, add a 4% mass concentration of dilute hydrochloric acid solution, the liquid-solid ratio of dilute hydrochloric acid solution to submicron spherical silicon micro powder is 12:1 (mL / g), stir for 1.5h at 45℃±0.5℃ and 250r / min, then wash with deionized water until neutral, and then wash twice with anhydrous ethanol. Place the washed silicon micro powder in an environment of 90℃ and vacuum degree -0.09MPa for 2.5h to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent (ethanol to water volume ratio 3:1) and ultrasonically dispersed for 35 min at 180 W and 30 kHz to form a suspension; 4% of the mass of the pretreated silica powder was added to the compound aminosilane, and the pH was adjusted to 7.2 by adding 6% sodium bicarbonate solution. The mixture was stirred at a constant temperature for 1 h, and then the pH was adjusted to 8.5 by adding 10% sodium carbonate solution. The mixture was stirred at 65 °C for 2.5 h to obtain the grafted modified silica powder. (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micro powder was placed in a plasma device and pretreated for 8 min under an argon atmosphere, a power of 100 W and a discharge gap of 3 mm. The pretreated grafted modified silicon micro powder was returned to the reaction system, and 1.5% of the pretreated silicon micro powder was added to PEG-1000. The mixture was stirred and dispersed at 350 r / min for 25 min. The nano boron nitride powder pretreated with ethanol-water mixed solvent was added at a rate of 0.15 g / min (the pretreatment process of nano boron nitride is: the nano boron nitride powder is added to 2.5% of γ-aminopropyltriethoxysilane ethanol solution, ultrasonically dispersed for 20 min, stirred and reacted at 60 °C for 1 h, filtered and dried for later use). The temperature was raised to 85 °C and stirred and reacted under a nitrogen atmosphere for 2.5 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) was filtered, washed with anhydrous ethanol for 1.5 h by Soxhlet extraction, dried at 100 °C and vacuum degree -0.09 MPa for 3.5 h, and then subjected to air jet milling with an air pressure of 0.7 MPa, a classifier speed of 25000 r / min and a feed rate of 15 g / min to obtain submicron spherical modified silica powder with a particle size of 0.1-1 μm.

[0032] Example 3: (1) Pretreatment of silicon micro powder: Take an appropriate amount of submicron spherical silicon micro powder, add a 5% mass concentration of dilute hydrochloric acid solution, the liquid-solid ratio of dilute hydrochloric acid solution to submicron spherical silicon micro powder is 15:1 (mL / g), stir for 2h at 50℃±0.5℃ and 300r / min, then wash with deionized water until neutral, and then wash with anhydrous ethanol 3 times. Place the washed silicon micro powder in an environment of 100℃ and vacuum degree -0.1MPa for 3h to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent (ethanol to water volume ratio 3:1) and ultrasonically dispersed for 40 min at 200 W and 40 kHz to form a suspension; 5% of the mass of the pretreated silica powder was added to the compound aminosilane, and 8% sodium bicarbonate solution was added to adjust the pH to 7.5. The mixture was stirred at a constant temperature for 1 h, and then 12% sodium carbonate solution was added to adjust the pH to 9. The mixture was stirred at 70 °C for 3 h to obtain the grafted modified silica powder. (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micro powder was placed in a plasma device and pretreated for 10 min under an argon atmosphere, a power of 120 W and a discharge gap of 5 mm. The pretreated grafted modified silicon micro powder was returned to the reaction system, and 2% of the pretreated silicon micro powder was added to PEG-1000. The mixture was stirred and dispersed at 400 r / min for 30 min. The nano boron nitride powder pretreated with ethanol-water mixed solvent was added at a rate of 0.2 g / min (the pretreatment process of nano boron nitride: the nano boron nitride powder was added to a 3% mass fraction of γ-aminopropyltriethoxysilane ethanol solution, ultrasonically dispersed for 20 min, stirred and reacted at 60 °C for 1 h, filtered and dried for later use). The temperature was raised to 90 °C and stirred and reacted under a nitrogen atmosphere for 3 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) was filtered, washed with anhydrous ethanol for 2 hours by Soxhlet extraction, dried at 110℃ and vacuum degree -0.1MPa for 4 hours, and then subjected to air jet milling with an air pressure of 0.8MPa, a classifier speed of 30000r / min and a feed rate of 20g / min to obtain submicron spherical modified silica powder with a particle size of 0.1-1μm.

[0033] Comparative Example 1: The preparation method provided in Example 2 is adopted, except that: in step (1), the dilute hydrochloric acid solution soaking and subsequent washing and drying treatment are not carried out, and submicron spherical silicon powder is directly used for the reaction in step (2).

[0034] Comparative Example 2: The preparation method provided in Example 2 is used, except that: in step (2), the gradient pH adjustment method is not used, and a sodium carbonate solution with a mass concentration of 10% is directly added to adjust the pH to 8.5, and the mixture is stirred at a constant temperature for 3.5 hours.

[0035] Comparative Example 3: The preparation method provided in Example 2 is used, except that plasma pretreatment is not performed in step (3).

[0036] Comparative Example 4: The preparation method provided in Example 2 is used, except that no nano boron nitride powder is added in step (3).

[0037] test: Experiment 1: Thermal stability test; Thermogravimetric analysis (TGA) was used to test the thermal stability of the products from each example and comparative example. Test conditions: nitrogen atmosphere, heating rate 10℃ / min, test temperature range 25-800℃. The mass retention rate of the samples at different temperatures was recorded. The temperature corresponding to 5% mass loss (T5%) was taken as the thermal decomposition initiation temperature, and the mass retention rate at 800℃ was used as the thermal stability evaluation index. The results are as follows: Table 1

[0038] As can be seen from Table 1, the T5% of the products in Examples 1-3 are all between 428-435℃, and the mass retention rate at 800℃ is all between 97.5-97.8%, indicating that the submicron spherical modified silicon powder prepared by the present invention has excellent thermal stability. Comparative Example 1 did not undergo silicon micropowder pretreatment, and residual surface impurities accelerated the thermal decomposition process, resulting in a T5% of 395℃ and a mass retention rate of only 95.2% at 800℃. Comparative Example 2 did not use gradient pH grafting, and the aminosilane grafting was insufficient, resulting in poor surface modification of silicon micropowder and limited improvement in thermal stability. Its T5% was 410℃, and the mass retention rate at 800℃ was 96.3%. Comparative Example 3 did not undergo plasma pretreatment, and the bond between the grafted modified silicon micropowder and boron nitride was not strong enough, making it prone to peeling at high temperatures. This resulted in a T5% of 405℃ and a mass retention rate of 96.0% at 800℃. Comparative Example 4 did not add nano boron nitride powder, lacking the high-temperature protection of boron nitride. It had the worst thermal stability, with a T5% of only 388℃ and a mass retention rate of 94.8% at 800℃.

[0039] Experiment 2: Oil absorption value and dispersibility test; Oil absorption value test: The linseed oil method was used. 5g of sample was accurately weighed and placed in a glass mortar. Linseed oil was added drop by drop while grinding continuously until the sample formed a uniform mass that did not stick to the inner wall of the mortar. The volume of linseed oil consumed was recorded and the oil absorption value (mL / g) was calculated.

[0040] Dispersibility test: The sample was added to epoxy resin at a mass fraction of 5% and dispersed in a high-speed disperser at 3000 r / min for 30 min to prepare a slurry. The viscosity of the slurry was tested using a rotational rheometer. The lower the viscosity, the better the dispersibility of the sample in epoxy resin. The test temperature was 25℃ and the shear rate was 10 s. -1 The results are as follows: Table 2

[0041] As can be seen from Table 2, the oil absorption value and dispersibility test results show that the oil absorption values ​​of the products in Examples 1-3 are all between 0.30-0.32 mL / g, and the corresponding slurry viscosity is between 820-850 mPa·s. This indicates that the submicron spherical modified silica powder prepared in this invention has a low oil absorption value and good dispersibility in epoxy resin. Comparative Example 1, without pretreatment of the silica powder, resulted in increased surface impurities, leading to increased particle specific surface area and surface activity defects. This resulted in an oil absorption value of 0.45 mL / g and a slurry viscosity of 1280 mPa·s, indicating poor dispersibility. Comparative Example 2, without gradient pH grafting, had uneven aminosilane grafting, resulting in an imbalance between the oleophilic and hydrophilic properties of the silica powder surface. The oil absorption value was 0.39 mL / g, and the slurry viscosity was 1050 mPa·s, indicating poorer dispersibility than the examples. Comparative Example 3, without plasma pretreatment, had insufficient coating bonding between the grafted modified silica powder and boron nitride, resulting in insufficient particle surface smoothness. The oil absorption value was 0.37 mL / g, and the slurry viscosity was 980 mPa·s, indicating a certain decrease in dispersibility. Comparative Example 4, without the addition of nano-boron nitride powder, lacked boron nitride modification on the silica powder surface, resulting in high surface energy and easy agglomeration. This led to an oil absorption value as high as 0.48 mL / g and a slurry viscosity of 1350 mPa·s, indicating the worst dispersibility.

[0042] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing a submicron spherical modified silica powder, characterized by comprising the steps of: Includes the following steps: ​ (1) Pretreatment of silicon micro powder: Submicron spherical silicon micro powder is added to a 3-5% dilute hydrochloric acid solution and stirred for 1-2 hours at 40-50℃±0.5℃ and 200-300r / min. After washing with deionized water until neutral and washing with anhydrous ethanol 2-3 times, it is dried at 80-100℃ and vacuum degree -0.08~-0.1MPa for 2-3 hours to obtain pretreated silicon micro powder; (2) Gradient pH grafting of aminosilane: The pretreated silica powder was added to an ethanol-water mixed solvent and ultrasonically dispersed for 30-40 min at 150-200W and 20-40kHz to form a suspension; 3-5% of the mass of the pretreated silica powder was added to the compound aminosilane, the pH was first adjusted to 7-7.5 by adding sodium bicarbonate solution, and stirred at a constant temperature for 1 h, then the pH was adjusted to 8-9 by adding sodium carbonate solution, and stirred for 2-3 h at 60-70℃ to obtain the grafted modified silica powder; (3) Plasma pretreatment and boron nitride coating: The grafted modified silicon micropowder was placed in a plasma device and pretreated for 6-10 min under an argon atmosphere, a power of 80-120 W and a discharge gap of 2-5 mm. The pretreated grafted modified silicon micropowder was returned to the reaction system, and 1-2% of polyethylene glycol by weight of the pretreated silicon micropowder was added. The mixture was stirred and dispersed at 300-400 r / min for 20-30 min. The nano boron nitride powder pretreated with ethanol-water mixed solvent was added at a rate of 0.1-0.2 g / min. The temperature was raised to 80-90 °C and stirred and reacted under a nitrogen atmosphere for 2-3 h to obtain the reaction product. (4) Post-processing: The reaction product of step (3) is filtered, washed with anhydrous ethanol for 1-2 hours by Soxhlet extraction, dried under vacuum, and then pulverized by air jet to obtain submicron spherical modified silica powder with a particle size of 0.1-1 μm.

2. The production method according to claim 1, characterized by, In step (1), the liquid-solid ratio of the dilute hydrochloric acid solution to the submicron spherical silica powder is 10-15:1 (mL / g).

3. The preparation method according to claim 1, characterized in that, The volume ratio of ethanol to water in an ethanol-water mixed solvent is 3:

1.

4. The method of claim 1, wherein, In step (2), the mass concentration of sodium bicarbonate solution is 5-8%, and the mass concentration of sodium carbonate solution is 8-12%.

5. The preparation method according to claim 4, characterized in that, In step (3), the pretreatment process of nano boron nitride is as follows: add nano boron nitride powder to a γ-aminopropyltriethoxysilane ethanol solution with a mass fraction of 2-3%, disperse ultrasonically for 20 min, stir and react at 60℃ for 1 h, filter and dry for later use.

6. The method of claim 1, wherein, In step (3), the polyethylene glycol is PEG-1000.

7. The preparation method according to claim 1, characterized in that, In step (4), vacuum drying is performed at 90-110℃ and a vacuum of -0.08 to -0.1MPa for 3-4 hours.

8. The method of claim 1, wherein, In step (4), the inlet pressure of the airflow pulverizer is 0.6-0.8 MPa and the speed of the classifier wheel is 20000-30000 r / min.

9. The method of claim 1, wherein, In step (4), the feed rate of the air jet mill is 10-20 g / min.

10. Submicron spherical modified silica powder is obtained by the preparation method according to any one of claims 1-9.

Images