Preparation method of silicon dioxide for powder coating

Abstract

The invention discloses a preparation method of silicon dioxide for a powder coating, and belongs to the technical field of precipitation method silicon dioxide preparation, a sodium silicate solution with a specific modulus is selected to be prepared into a proper concentration, and a large amount of silicic acid is generated in the solution in combination with a specific proportion, temperature and early-stage rapid acid adding mode; a large number of uniform primary silicon dioxide particles can be quickly formed, the silicon dioxide particles with high specific surface area and high surface energy are finally separated out, and the growth and aggregation of the silicon dioxide particles are effectively controlled in a manner of slowly adding acid according to a specific proportion and temperature subsequently, so that the silicon dioxide aggregate with uniform particle size is formed; the water-soluble amino acid is added into the silicon dioxide slurry, so that the silicon dioxide particles are endowed with charge property, the finally dried silicon dioxide powder can be directly used in the powder coating, mechanical crushing is not needed again, the energy consumption is reduced, a surfactant is not needed, the influence on the environment in the production process can be avoided, and the method is energy-saving and environment-friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of precipitated silicon dioxide preparation, and particularly relates to a method for preparing silicon dioxide for powder coatings. Background Art

[0002] As an environmentally friendly coating product, in the field of coating, powder coating has the characteristics of no pollution, zero VOCs emission, high recycling rate, simple coating process and high degree of automation;

[0003] Fumed silica or alumina is widely used in powder coatings as a flow aid and anti-caking agent. Fumed silica is generally made of silicon tetrachloride, oxygen and hydrogen, which are generated by reaction at high temperature. Fumed alumina is generally made of aluminum chloride, oxygen and hydrogen, which is generated by sublimating aluminum chloride and burning it in a hydrogen-oxygen flame and hydrolyzing it at high temperature. The final agglomerate particle size of fumed silica and alumina is 4-6μm. The preparation cost of fumed silica and alumina is high, the yield is low, the processing process is complicated and the price is high.

[0004] Precipitated silica, the raw materials are generally sodium silicate (Na2SiO3) and sulfuric acid (H2SO4), which is produced by the acid-base neutralization reaction of sodium silicate and sulfuric acid. The production process of precipitated silica is simple, the process is environmentally friendly, and the price is low. However, the particle size of precipitated silica is relatively large. Although the primary particle size is 3-5nm, after the nucleus growth and agglomeration, the product particle size will reach 20-80μm. The large particle size, small specific surface area, and low surface energy make it difficult to adsorb on the surface of the coating powder, and the powder flow-aiding and anti-caking effects are insufficient;

[0005] The application text with application number CN 202010525799.1 discloses a method for preparing an ultrafine precipitated silica anti-caking agent for powder coatings, the steps of which include: adding sulfuric acid to a sodium silicate aqueous solution to a pH of 5.0-7.0, adding an ionic surfactant to the obtained solution, and simultaneously dripping sodium silicate and sulfuric acid, maintaining the pH value of the reaction process at 5.0-7.0, stopping the dripping of sodium silicate solution after reacting for 35-55 minutes, and continuing to drip sulfuric acid to a pH value of 3.5-4.0, aging for 2 hours, filtering, washing, and obtaining a filter cake, drying after pulping, and crushing with a mechanical grinder to obtain ultrafine precipitated silica. The ultrafine silica prepared by this method has a high specific surface area, rich pore structure, and high surface energy. However, this method requires the use of a surfactant, and the wastewater generated is likely to have a certain impact on the environment. At the same time, the reduction of the silica particle size is achieved by using a mechanical grinding crusher. Although the particle size is reduced, the uniformity of the particle size cannot be guaranteed, resulting in poor particle size uniformity.

[0006] Therefore, it is necessary to develop a precipitated silica that is environmentally friendly, low energy consuming and has uniform particle size. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In order to overcome the shortcomings of the existing technology, a method for preparing silicon dioxide for powder coatings is proposed to solve the problems of the existing technology in which the precipitated silicon dioxide has a large particle size, a small specific surface area, a low surface energy, is difficult to adsorb on the surface of the coating powder, has insufficient flow-aiding and anti-caking effects on the powder, and has high production energy consumption and is easy to pollute the environment.

[0009] (II) Technical solution

[0010] The present invention is achieved through the following technical solution: The present invention proposes a method for preparing silicon dioxide for powder coatings, comprising the following steps:

[0011] S1. Prepare a sodium silicate solution with a modulus of 3.30 to 3.60 into a solution with a concentration of 1.50 to 1.70 mol / L, and place the prepared sodium silicate solution in a storage tank for standby use;

[0012] The modulus of sodium silicate solution is 3.30-3.60, which can regulate the rate and amount of silica generation, affect the formation and growth of silica particles, and make its performance meet the requirements of powder coatings;

[0013] When the modulus is lower than 3.30, the sodium oxide content is high, silicate is generated too quickly, the particles are uneven and easy to agglomerate, the particle size distribution is wide, and the specific surface area is low, which affects the flow-aiding and anti-caking properties of the coating;

[0014] When the modulus is higher than 3.60, the high silica content affects the reaction activity, the generation of silicic acid is slow, the particle growth is incomplete, the yield is low, the surface properties are affected, and it is not conducive to dispersion;

[0015] Formulated into a concentration of 1.50-1.70 mol / L, it can ensure a moderate subsequent reaction rate, facilitate the formation of uniform particles and aggregates, and ensure the performance of product particle size, specific surface area, etc.

[0016] When the concentration is lower than 1.50 mol / L, the subsequent reaction rate will be slow, the cycle will be long, the number and quality of primary particles will be insufficient, the particle size will be uneven, the specific surface area will be small, and the coating application effect will be poor;

[0017] When the concentration is higher than 1.70mol / L, the subsequent reaction will be violent, it is easy to overheat, agglomeration will be aggravated, the particle size will be large and uneven, the specific surface area will be reduced, and the impurities will affect the purity performance;

[0018] S2. Add water and sodium silicate solution into the reactor in a volume ratio of 100:(20-30) in advance: within this ratio range, the initial concentration and fluidity of the reaction can be better controlled to ensure sufficient mixing reaction and adjust the viscosity to avoid uneven concentration affecting the quality;

[0019] When the ratio is higher than this, the initial concentration of the reaction is high, the reaction is violent, the particles are uneven, there are many agglomerations, the particle size is large and uneven, and the dispersion of the coating is affected.

[0020] When the ratio is lower than this, the reaction is slow, the number and quality of particles are insufficient, the yield is low, the specific surface area is small, and the flow-aiding and anti-caking effect is weak;

[0021] Heating to 80-90℃: Within this temperature, appropriate activation energy can be provided, which accelerates the reaction and helps control particle growth and agglomeration, ensuring uniform product particle size, high specific surface area and reasonable energy consumption;

[0022] When the temperature is lower than 80℃, the reaction rate decreases, the particle growth is incomplete, the particle size is small but uneven, the specific surface area is unstable, and the viscosity increases, affecting the quality;

[0023] When the temperature is higher than 90℃, the reaction speeds up, but the particles grow too fast, agglomeration intensifies, the particle size distribution is wide, the specific surface area is small, and many side reactions affect the purity stability and the energy consumption is high.

[0024] Start stirring and quickly add concentrated sulfuric acid. The volume of concentrated sulfuric acid added within 10 to 15 minutes accounts for 50% to 60% of the total volume added. Stop adding sulfuric acid and continue stirring for 10 to 20 minutes: Rapid acid addition promotes the formation of primary particles.

[0025] At this time, adding acid too slowly or in small amounts will result in slow generation of silicate acid, poor primary particles, low specific surface area, and uneven particle size;

[0026] Adding acid too quickly or in large amounts at this time will result in a violent reaction, overheating and agglomeration, and large and uneven particle size;

[0027] S3, maintaining the temperature at 80-90°C, continue to slowly add sulfuric acid, the volume of concentrated sulfuric acid added within 85-95 minutes accounts for 40%-50% of the total volume added, stop adding sulfuric acid when the pH is 3.0-3.5, continue stirring for 10-20 minutes, and prepare silicon dioxide slurry: at this time, slowly add acid to prevent excessive growth and agglomeration;

[0028] If the acid addition time is too short or the amount is insufficient, the particles will not grow completely, the yield will be low, and the particle size will be unstable;

[0029] At this time, adding acid for too long or in too large an amount will cause excessive dissolution and agglomeration of particles, wide particle size distribution, and reduced specific surface area;

[0030] S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding amino acids in a pulping machine to allow the amino acids and the slurry to be fully mixed;

[0031] S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

[0032] Furthermore, the concentration of concentrated sulfuric acid used in steps S2 and S3 is 98%.

[0033] Furthermore, the stirring frequency in step S2 is 300-400 rpm.

[0034] Furthermore, the amino acids obtained in step S4 are common water-soluble amino acids.

[0035] Furthermore, the water-soluble amino acid is glycine, glutamic acid, proline, serine, etc.

[0036] Furthermore, the water-soluble amino acid added in step S4 is 2% to 4% of the theoretical yield of silicon dioxide; within this range, the amino acid can effectively adjust the surface properties of the silicon dioxide particles, giving them a suitable charge, thereby improving their dispersibility and anti-caking properties in the powder coating, while ensuring that the final product has a good uniformity of particle size and does not need to be mechanically crushed again;

[0037] Furthermore, if the amino acid content is less than 2%, the surface properties of the silica particles cannot be fully regulated, resulting in insufficient surface charge of the silica particles, poor dispersion in the powder coating, easy agglomeration, and the uniformity of the product particle size may be affected.

[0038] Furthermore, if the amino acid content is higher than 4%, on the one hand, the production cost will increase, and on the other hand, it is easy to cause too much amino acid to remain in the product, affecting the purity of the product. At the same time, it is also easy to change the surface properties of the silica particles excessively, making it less compatible with the powder coating system, thereby affecting the overall performance of the coating.

[0039] Furthermore, the particle size (D50) of the silicon dioxide powder obtained in step S5 is 4.0 to 6.0 microns, and no mechanical crushing is required again;

[0040] 4.0-6.0 microns meets the application requirements of powder coatings. This particle size has good flow-aiding and anti-caking effects, does not affect other properties of the coating, is conducive to mixing and dispersion in production operations, and ensures the stability and uniformity of the system.

[0041] When it is less than 4.0 microns: the particle size is too small, the surface energy is high, it is easy to agglomerate, the dispersion stability is poor, dust pollution is increased, and the stacking density and fluidity of the coating and the coating process are affected.

[0042] When it is higher than 6.0 microns: the particle size is large and the specific surface area is small, the adsorption capacity is weak, the flow-aiding and anti-caking effect is poor, the paint is easy to agglomerate, and the fluidity is poor, which affects the construction and coating quality.

[0043] (III) Beneficial effects

[0044] One of the above technical solutions has the following advantages or beneficial effects:

[0045] In order to solve the problems that the precipitated silica particles of the prior art are large in size, small in specific surface area, low in surface energy, difficult to be adsorbed on the surface of the coating powder, insufficient in the flow-aiding and anti-caking effects on the powder, high in production energy consumption and easy to pollute the environment, a sodium silicate solution with a specific modulus is selected to be adjusted to a suitable concentration, and a specific ratio, temperature and a method of rapid acid addition in the early stage are combined to produce a large amount of silicic acid in the solution, which is conducive to the rapid formation of a large number of uniform primary silica particles, and finally precipitates silica particles with a high specific surface area and high surface energy, and subsequently, the growth and aggregation of silica particles are effectively controlled by a specific ratio, temperature and a method of slow acid addition to form silica aggregates with uniform particle size, and water-soluble amino acids are added to the silica slurry to give the silica particles electric charge, and finally the dried silica powder can be directly used in the powder coating without mechanical crushing again, reducing energy consumption, and without the use of surfactants, which can avoid the impact on the environment during the production process, and save energy and protect the environment;

[0046] Charged silica particles can improve the fluidity of the coating;

[0047] First, reduce viscosity: the charged silica particles are more evenly dispersed in the paint, reducing agglomeration and accumulation, reducing internal friction, and reducing the viscosity of the paint, which helps to smoothly discharge the paint during spraying, forming a fine and uniform atomization effect, and improving the flatness and uniformity of the coating;

[0048] Secondly, reduce sagging: When the paint is applied on a vertical or inclined surface, gravity can easily cause sagging, while the charged particles enhance the thixotropy of the paint. When it is stationary, the high viscosity prevents sagging. When subjected to shear force, the viscosity decreases for easy operation. After construction, the high viscosity is quickly restored to stabilize the shape, reducing sagging and ensuring uniform coating thickness and appearance quality.

[0049] Charged silica particles also improve the fluidization properties of powder coatings;

[0050] First, promote fluidization: During storage and use, good fluidization performance is key to the uniformity and operability of powder coatings. Charged particles optimize the charge distribution of powders, reduce adhesion and agglomeration, make powders easy to fluidize, and facilitate precise control of transportation, metering and spraying;

[0051] Secondly, uniform powder supply: During electrostatic spraying, well-fluidized powder can be stably and evenly supplied, evenly charged under the electric field of the spray gun and adsorbed on the surface of the workpiece, obtaining a coating with uniform thickness and consistent appearance, improving construction efficiency and quality, and reducing defects caused by uneven fluidization;

[0052] Finally, the charged silica particles can also enhance the adhesion of the coating to the substrate;

[0053] First, electrostatic adsorption: the charged particles form additional electrostatic adsorption between the coating and the substrate, which can improve the initial adhesion and reduce the risk of coating shedding for low surface energy or difficult-to-attach substrates.

[0054] Secondly, it promotes bonding: the charge may promote the chemical reaction between the active groups of the coating and the functional groups of the substrate to form bonds, thereby enhancing the bonding strength, making the coating resist the influence of environmental factors for a long time, maintaining adhesion, extending life, and improving product quality and durability;

[0055] The particle size control of this application is mainly achieved through the following points:

[0056] 1. Rapid acid addition promotes uniform nucleus formation: Rapid acid addition at the beginning produces a large amount of silicic acid, quickly forming a large number of uniform primary silica particles, providing more cores for subsequent growth, making the particle size easy to control in a small and uniform range, reducing the generation of large particles and reducing the need for mechanical crushing;

[0057] 2. Control particle growth and aggregation by slowly adding acid: Slowly add acid to accurately control particle growth and aggregation, avoid excessive agglomeration and fusion, ensure uniform particle size of aggregates, and ensure that the powder particle size meets the requirements after drying without mechanical crushing and adjustment;

[0058] 3. Amino acids have a significant effect on improving the surface properties of particles: adding water-soluble amino acids gives particles charge and enhances dispersion stability. Its interaction with the particle surface inhibits agglomeration during drying, which is conducive to the formation of powders with uniform particle size and good fluidity, without the need to crush and disperse agglomerated particles;

[0059] 4. Close coordination of each step: The parameters such as the modulus, concentration, reaction temperature, solution volume ratio and concentrated sulfuric acid addition rate of the sodium silicate solution are reasonably matched to form an optimized process system. The synergistic effect of each step promotes the formation of silicon dioxide powder with suitable particle size and no need for mechanical crushing. DETAILED DESCRIPTION

[0060] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0061] Here are the steps:

[0062] Embodiment 1

[0063] S1. Take water glass with a modulus of 3.45 and add water to prepare a solution with a concentration of 1.60 mol / L, and place the prepared water glass in a storage tank for standby use;

[0064] S2, add 30m3 of water to a 45m3 reactor, add 7.5m3 of the water glass solution prepared in step S1 to the reactor, heat to 85°C, and quickly add 98% concentrated sulfuric acid by mass to the reactor under stirring at 350 rpm. The flow rate of concentrated sulfuric acid is 1.95m3 / h. Stop adding sulfuric acid after adding for 10min, continue stirring for 15min, and the volume of sulfuric acid added accounts for about 50% of the total volume of sulfuric acid;

[0065] S3, maintaining the temperature at 85°C, continue to slowly add 98% sulfuric acid by mass, the flow rate of concentrated sulfuric acid is 0.22m3 / h, stop adding sulfuric acid when the pH reaches 3.0-3.5, the addition time is about 90min, continue stirring for 20min, and obtain silicon dioxide slurry;

[0066] S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding glycine in a pulping machine to allow the amino acid and the slurry to be fully mixed, the added amount being 2.5% of the theoretical output of silicon dioxide;

[0067] S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

[0068] Embodiment 2

[0069] S1. Take water glass with a modulus of 3.50 and add water to prepare a solution with a concentration of 1.65 mol / L, and place the prepared water glass in a storage tank for standby use;

[0070] S2, add 30m3 of water to a 45m3 reactor, add 7m3 of the water glass solution prepared in step S1 to the reactor, heat to 80°C, and quickly add 98% concentrated sulfuric acid by mass to the reactor under stirring at 300 rpm. The flow rate of concentrated sulfuric acid is 1.38m3 / h. Stop adding sulfuric acid after 15min of addition, continue stirring for 20min, and the volume of sulfuric acid added accounts for about 55% of the total volume of sulfuric acid;

[0071] S3, maintaining the temperature at 80°C, continue to slowly add 98% sulfuric acid by mass, the flow rate of concentrated sulfuric acid is 0.18m3 / h, stop adding sulfuric acid when the pH reaches 3.0-3.5, the addition time is about 95min, continue stirring for 15min, and obtain silicon dioxide slurry;

[0072] S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding glutamine in a pulping machine to allow the amino acid and the slurry to be fully mixed, and the added amount is 3.0% of the theoretical output of silicon dioxide;

[0073] S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

[0074] Embodiment 3

[0075] S1, take water glass with a modulus of 3.60 and add water to prepare a solution with a concentration of 1.50 mol / L, and place the prepared water glass in a storage tank for standby use;

[0076] S2, add 25m3 of water to a 45m3 reactor, add 7.5m3 of the water glass solution prepared in step S1 to the reactor, heat to 90°C, and quickly add 98% concentrated sulfuric acid by mass to the reactor under stirring at 400 rpm. The flow rate of concentrated sulfuric acid is 2.20m3 / h. Stop adding sulfuric acid after adding for 10min, continue stirring for 20min, and the volume of sulfuric acid added accounts for about 60% of the total volume of sulfuric acid;

[0077] S3, maintaining the temperature at 90°C, continue to slowly add 98% sulfuric acid by mass, the flow rate of concentrated sulfuric acid is 0.17m3 / h, stop adding sulfuric acid when the pH reaches 3.0-3.5, the addition time is about 85min, continue stirring for 10min, and obtain silicon dioxide slurry;

[0078] S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding glutamine in a pulping machine so that the amino acid and the slurry can be fully mixed, and the added amount is 2.0% of the theoretical output of silicon dioxide;

[0079] S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

[0080] Embodiment 4

[0081] S1, take water glass with a modulus of 3.30 and add water to prepare a solution with a concentration of 1.55 mol / L, and place the prepared water glass in a storage tank for standby use;

[0082] S2, 45m 3 Add 28m 3 Water, add 8 ml of water glass solution prepared in step S1 into the reactor 3 , the temperature was raised to 88°C, and concentrated sulfuric acid with a mass fraction of 98% was quickly added to the reactor under stirring at 380 rpm. The flow rate of concentrated sulfuric acid was 2.05 m 3 / h, stop adding sulfuric acid after 12 minutes, continue stirring for 18 minutes, the volume of sulfuric acid added accounts for about 58% of the total volume of sulfuric acid;

[0083] S3, maintain the temperature at 88℃, continue to slowly add 98% sulfuric acid, the flow rate of concentrated sulfuric acid is 0.19m 3 / h, stop adding sulfuric acid when the pH reaches 3.0-3.5, the adding time is about 92 minutes, and continue stirring for 16 minutes to obtain silicon dioxide slurry;

[0084] S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding serine in a pulping machine so that the amino acid and the slurry can be fully mixed, and the added amount is 3.5% of the theoretical output of silicon dioxide;

[0085] S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

[0086] Comparative Example 1

[0087] The difference from the first embodiment is that in steps S2 and S3, the concentrated sulfuric acid flow rate is adjusted to 0.4 m3 / h, and the other conditions are the same as those of the first embodiment.

[0088] Comparative Example 2

[0089] The difference from the first embodiment is that the temperature is raised to 70° C. in step S2 , and the other conditions are the same as those of the first embodiment.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that the water-soluble amino acid added in step S4 is 5% of the theoretical yield of silicon dioxide, and the other conditions are the same as Example 1.

[0092] Comparative Example 4

[0093] The difference from Example 1 is that no water-soluble amino acid is added in step S4, and the other conditions are the same as Example 1.

[0094] The test technical indicators of the white carbon black product obtained in the above embodiment are listed in the following table:

[0095]

[0096] It can be seen from the table that the oil absorption value (DBP) of the silica in Examples 1 to 3 of the present invention is 3.0 to 3.2 cm3 / g, the specific surface area (BET) is 325 to 355 m2 / g, and the particle size is 4.5 to 5.6 μm. Compared with the comparative example, the oil absorption value is significantly improved, the particle size is smaller and the uniformity is better. The comprehensive technical indicators of Example 1 are the best, and it is the best example;

[0097] Compared with Example 1, the specific surface area and particle size of Example 2 are increased, and the oil absorption value is reduced, which will lead to poor uniformity, durability, transparency, anti-settling, matting and other properties of the coating, and the appearance is also relatively unsightly, and the powder coating rate and coating viscosity are also reduced;

[0098] Compared with Example 1, the particle size of Example 3 and Comparative Examples 1, 3 and 4 increases, and the specific surface area decreases, which leads to poor uniformity, gloss, fluidity, dispersibility, rheology, adhesion, durability, transparency, anti-settling, matte, appearance, powder coating rate, storage stability and other properties of the coating, and the appearance is also relatively unsightly, and the powder coating rate is also reduced;

[0099] Compared with Example 1, the oil absorption values ​​of Comparative Examples 1 to 4 are also greatly reduced, resulting in greatly reduced viscosity, processing performance and storage stability;

[0100] Compared with Example 1, Example 4 has similar performance, but its particle size is relatively larger, and most of the indicators are lower than Example 1;

[0101] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0102] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing silicon dioxide for powder coatings, characterized in that: The following steps are involved: S1. Prepare a sodium silicate solution with a modulus of 3.30 to 3.60 into a solution with a concentration of 1.50 to 1.70 mol / L, and place the prepared sodium silicate solution in a storage tank for standby use; S2, pre-add water and sodium silicate solution into the reactor in a volume ratio of 100: (20-30), heat to 80-90°C, start stirring, quickly add concentrated sulfuric acid, the volume of concentrated sulfuric acid added within 10-15 minutes accounts for 50%-60% of the total volume added, stop adding sulfuric acid, and continue stirring for 10-20 minutes; S3, maintaining the temperature at 80-90° C., continue to slowly add sulfuric acid, the volume of concentrated sulfuric acid added within 85-95 minutes accounts for 40%-50% of the total volume added, stop adding sulfuric acid when the pH is 3.0-3.5, continue stirring for 10-20 minutes, and obtain silicon dioxide slurry; S4, washing and solid-liquid separation of the silicon dioxide slurry obtained in step S3, adding amino acids in a pulping machine to allow the amino acids and the slurry to be fully mixed; S5. Spray-dry the silicon dioxide slurry obtained in step S4 to obtain silicon dioxide powder.

2. The method for preparing silicon dioxide for powder coating according to claim 1, characterized in that: The concentration of concentrated sulfuric acid used in steps S2 and S3 is 98%.

3. The method for preparing silicon dioxide for powder coating according to claim 1, characterized in that: The stirring frequency in step S2 is 300-400 rpm.

4. The method for preparing silicon dioxide for powder coating according to claim 1, characterized in that: The amino acids obtained in step S4 are common water-soluble amino acids.

5. The method for preparing silicon dioxide for powder coating according to claim 4, characterized in that: The water-soluble amino acid is glycine, glutamic acid, proline or serine.

6. The method for preparing silicon dioxide for powder coating according to claim 1, characterized in that: The water-soluble amino acid added in step S4 is 2% to 4% of the theoretical yield of silicon dioxide.

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