Process for preparation of silica as flow promoter in powder coatings

Abstract

The invention provides a preparation method of silicon dioxide serving as a flow promoter in a powder coating. The preparation method comprises the following steps: synthesizing silicon dioxide by using a precipitation method; washing and filter-pressing to obtain a precipitate; re-dispersing and pulping the silicon dioxide by using pure water; performing drying; performing high-temperature crushing; the synthesis of silicon dioxide comprises the following steps: adding bottom water, and heating to 40-100 DEG C; adding water glass and acid into the bottom water in a parallel flow manner under the conditions of constant temperature and pH value of 5.0-10.0; adjusting the pH value to 2.0-4.0 by using an acid; the specific surface area of the silicon dioxide is 100-500m < 2 > / g; the bulk ratio of the silicon dioxide is not higher than 0.30 g / cm < 3 >; the particle size of the silicon dioxide is not higher than 5.0 microns; the methanol value of the silicon dioxide is higher than 30%; the drying weight loss of the silicon dioxide is not higher than 3.0%. The preparation method of the silicon dioxide serving as the flow promoter in the powder coating is simple in process and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of powder coating additives, and in particular to a preparation method of silica used as a flow aid in powder coatings. Background Art

[0002] Compared with solvent-based coatings, powder coatings have the advantages of no VOC emissions, 100% film formation, low energy consumption, convenient transportation, excellent weather resistance and durability, etc., so they are widely used in the coating industry. The particle size of the particles in the powder coating is in the micron range, and the force between the particles (mainly van der Waals force) is greater than the resistance and the earth's gravity acting on them. Therefore, the particles in the powder coating are extremely easy to agglomerate, resulting in poor fluidity of the coating. For this reason, a small amount of flow aid needs to be added to the powder coating to improve its fluidity. The role of the flow aid is to attach to the surface of the powder particles to separate the particles, thereby increasing the distance between the particles, reducing the probability of particle-to-particle contact, weakening the van der Waals force between the particles, and thus improving the fluidity of the powder coating. The existing flow aids added to powder coatings are as follows. For example, the flow aid mainly composed of fumed silica or hydrophobic fumed silica added to the high heat-resistant powder coating disclosed in US5554681, and the flow aid mainly composed of hydrophobic fumed silica or fumed alumina added to the powder coating resistant to filiform corrosion disclosed in US7723410. Also, the flow aid mainly composed of a mixture of alumina or aluminum hydroxide and fumed silica in the powder coating with triboelectric charging characteristics disclosed in EP300818. However, the preparation costs of the above fumed silica, hydrophobic fumed silica and fumed alumina are relatively high, and the production process is relatively complex. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a preparation method of silica used as a flow aid in powder coatings, with a simple process and low cost.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A preparation method of silica used as a flow aid in powder coatings, comprising the following steps:

[0006] (a) Synthesize silica using the precipitation method;

[0007] (b) Wash with water and filter press to obtain a precipitate;

[0008] (c) Redisperse and slurry the silica with pure water;

[0009] (d) Dry;

[0010] (e) Grind at high temperature;

[0011] Among them, the synthesis of silica in step (a) includes the following steps:

[0012] (a1) Add bottom water (pure water), heat up to 40 - 100 °C, preferably 50 - 80 °C, more preferably 60 - 70 °C;

[0013] (a2) Keep the temperature constant, and add water glass and acid to the bottom water in parallel under the condition of pH value of 5.0 - 10.0, the pH value is preferably 6.0 - 9.0, more preferably 7.0 - 8.0;

[0014] (a3) Adjust the pH to 2.0 - 4.0 with acid, preferably 2.5 - 3.0;

[0015] The specific surface area of the silica is between 100 - 500 m 2 / g, preferably 200 - 400 m 2 / g, more preferably 250 - 300 m 2 / g;

[0016] The bulk density of the silica is not higher than 0.30 g / cm 3 , preferably not higher than 0.20 g / cm 3 , more preferably not higher than 0.15 g / cm 3 ;

[0017] The particle size of the silica is not higher than 5.0 um, preferably not higher than 3.0 um, more preferably not higher than 2.0 um;

[0018] The methanol value of the silica is higher than 30%, preferably higher than 40%, more preferably higher than 50%;

[0019] The drying loss of the silica is not higher than 3.0%, preferably not higher than 2.0%, more preferably not higher than 1.0%.

[0020] Compared with the prior art, the preparation method of silica as a flow aid in powder coatings of the present invention has the following beneficial effects:

[0021] (1) The present invention provides a method for preparing hydrophobic silica by the precipitation method. Compared with the preparation of fumed silica, hydrophobic fumed silica and fumed alumina by the gas phase method, this method has the characteristics of simple process, low cost and equivalent product performance. The silica prepared by this method has an obvious effect on promoting the flow of powder and preventing powder agglomeration. When it is applied to powder coatings, it plays a very important role in improving the powder fluidity, improving the powder fluidization during the coating spraying process and increasing the storage stability of the coating. Moreover, the precipitated silica provided by the present invention can be used as a flow aid and applied to various thermosetting and thermoplastic powder coatings (such as epoxy polyester powder coatings, acrylate powder coatings, polyvinyl chloride powder coatings, polyethylene powder coatings, etc.).

[0022] (2) Since the pH value has a great influence on the properties of the silica synthesized by the precipitation method, different specific surface areas and bulk ratios of silica can be obtained by adjusting the pH value of the reaction solution. In step (a2) of the present invention, silica meeting specific indexes is prepared by reacting sodium silicate and acid under the condition of a pH value of 5.0 - 10.0.

[0023] (3) The specific surface area of silica has an impact on the fluidity of the powder. Silica with a high specific surface area is more likely to adhere to the surface of powder particles, thus effectively reducing the contact between powder particles and improving the fluidity of the coating. However, if the specific surface area of silica is too high, the particle pore size becomes smaller, the bulk ratio increases, and the number of particles of the same amount decreases, which will lead to an increase in the probability of powder particle contact and a deterioration in the fluidity of the coating. The preparation method of the present invention can prepare silica with a suitable specific surface area.

[0024] (4) If the bulk ratio of silica is too high, the number of particles of the same amount decreases, the probability of powder particle contact increases, resulting in an enhanced van der Waals force between particles and a deterioration in the fluidity of the coating. The preparation method of the present invention can prepare silica with a suitable bulk ratio.

[0025] (5) If the particle size of silica is too large, the number of particles per unit amount decreases accordingly, the probability of powder particle contact increases, resulting in an enhanced force between particles and a deterioration in the fluidity of the coating. At the same time, due to the decrease in the fluidity of the coating, it is difficult to disperse the inorganic filler and the organic resin evenly, and their compatibility deteriorates, resulting in a decrease in the flatness of the cured coating film layer and a reduction in the gloss of the film surface. The preparation method of the present invention can prepare silica with a suitable particle size.

[0026] (6) The methanol value can be used to evaluate the hydrophobicity of silica. The larger the methanol value, the stronger the hydrophobicity; the smaller the methanol value, the weaker the hydrophobicity. The hydrophobicity of silica has a great influence on the fluidity of powder coatings (the stronger the hydrophobicity of silica, the better the fluidity of the coating; the weaker the hydrophobicity, the worse the fluidity). In powder coatings, since the resin used contains polar groups such as carboxyl and hydroxyl groups, it is extremely easy to form hydrogen bonds with water molecules in the air, so a water film will be formed on the surface of powder particles. Due to the existence of the water film, under the action of hydrogen bonds, the force between particles will be enhanced, thus deteriorating the fluidity of the coating. In addition, due to the strong surface tension of water molecules between powder particles, it is extremely easy to cause particle aggregation and agglomeration, further deteriorating the fluidity of the coating. After adding the precipitated silica prepared according to the present invention to the powder coating, the surface of the powder particles is not easily formed with a water film because it is coated with hydrophobic silica particles, weakening the force between particles, thus improving the fluidity of the coating.

[0027] (7) The loss on drying is too high. The higher the water content on the surface of silica, the easier it is to form hydrogen bonds with the carboxyl groups, hydroxyl groups, etc. of the organic resin in the coating. At the same time, the surface tension of water is relatively high, which easily causes powder particles to aggregate and form lumps, resulting in poor fluidity of the coating. The loss on drying of the precipitated silica prepared according to the present invention is not higher than 3.0%, thus avoiding the problem of poor fluidity of the coating caused by the aggregation and lumping of powder particles.

[0028] Further, in step (a2), the concentration of the water glass is 5-30%, preferably 15-25%; the modulus of the water glass is 3.0-3.8, preferably 3.3-3.5.

[0029] If the concentration of the water glass is too low, the volume of the water glass required per unit output increases, resulting in a decrease in production capacity; if the concentration of the water glass is too high, the solution is unstable and is likely to precipitate at a relatively low temperature, and the storage is unstable. Therefore, it is necessary to control the concentration of the water glass within a suitable range.

[0030] If the modulus of the water glass is too high, the solution will be unstable and silica will be easily precipitated; if the modulus of the water glass is too low, the amount of acid required will increase correspondingly, resulting in an increase in production cost and a decrease in output. Therefore, it is necessary to select a water glass with a suitable modulus.

[0031] Further, in step (a2), the acid is one or more of citric acid, acetic acid, hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid, and the concentration of the acid is 5-50%, preferably 10-40%, more preferably 20-30%.

[0032] The above acid solutions are common reagents and are easily obtainable. Among them, sulfuric acid is the best; if the concentration of the acid solution is too low, the volume of the acid consumed will increase, resulting in a decrease in production capacity; if the concentration of the acid solution is too high, higher requirements are imposed on the equipment and pipelines, and the loss of the equipment increases. Therefore, it is more appropriate to control the concentration of the acid within 5-50%.

[0033] Further, in step (a2), after the co-current flow ends, the solid content of the suspension is 30-80 g / L, preferably 40-60 g / L.

[0034] If the solid content of the suspension is too low, the batch output will decrease and the cost will increase; if the solid content of the suspension is too high, the bulk ratio will increase and the specific surface area will decrease, which is not conducive to being used as a flow aid in powder coatings.

[0035] Further, in step (c), the solid content of the dispersed slurry is 5-30%, preferably 10-20%.

[0036] If the solid content of the slurry after dispersion is too low, the temperature required for drying increases, the energy consumption increases, and the output decreases; if the solid content of the slurry after dispersion is too high, the viscosity of the suspension increases, the feeding is difficult, and the pipeline is easily blocked. Therefore, it is necessary to redisperse the silica into a slurry with a solid content of 5-30% with pure water.

[0037] Furthermore, in step (d), the drying method can be one of flash drying and spray drying.

[0038] Furthermore, in step (e), the pulverization method can be one of jet milling and flat grinding.

[0039] Furthermore, in step (e), the temperature during pulverization is 100-300 °C, preferably 150-250 °C.

[0040] If the temperature during pulverization is too low, the water content of the pulverized product will be relatively high, which is not conducive to being used as a flow aid in powder coatings; if the temperature during pulverization is too high, the energy consumption increases, and the hydrophobic treatment agent may decompose and become ineffective.

[0041] Furthermore, it further includes step (f), (f) using a hydrophobic treatment agent to perform surface treatment on the silica; or adding a hydrophobic treatment agent in step (a) or step (c) or step (d) or step (e); the dosage of the hydrophobic treatment agent is 2-20%, preferably 3-10%, more preferably 5-8%.

[0042] If the dosage of the hydrophobic treatment agent is too small, the hydrophobicity of the obtained silica is poor, and the fluidity of the powder coating is not good; if the dosage of the hydrophobic treatment agent is too large, the cost increases.

[0043] Furthermore, the hydrophobic treatment agent is one or more of octadecyltrimethoxysilane, cetyltriethoxysilane, dodecyltriethoxysilane, octyltriethoxysilane, polydimethylsiloxane, hexamethyldisilazane, dimethyldichlorosilane, and a self-made hydrophobic treatment agent. Specific embodiments

[0044] The physical and chemical indexes of the precipitated silica in the present invention are measured by the following methods:

[0045] (1) BET specific surface area

[0046] Instrument: TristarIIPlus; the test method refers to GB / T19587-2017.

[0047] (2) Bulk ratio (bulk density)

[0048] The test method refers to DIN EN ISO787.

[0049] (3) Average particle size (D50)

[0050] The instrument is Mastersizer 3000 (MalvernPanalytical). Take a certain amount of the sample according to the requirements of the laser particle size analyzer, add about 400 mL of water (for samples with poor water solubility, add a small amount of anhydrous ethanol first), disperse the sample solution ultrasonically for 15 - 60 s, and measure according to the steps of the laser particle size analyzer. Specifically, refer to the industry standard HG / T 4526 - 2013.

[0051] (4) Methanol value

[0052] Take 0.2 g of surface - modified silica and add it to a beaker containing 50 mL of pure water. Stir with a magnetic stirrer. At this time, the powder floats on the water surface. Add methanol to the beaker through a burette (the dropping port of the burette is inserted into the water). As methanol is added, the amount of silica powder floating on the water surface gradually decreases. When all the hydrophobic silica is completely dissolved in water, record the volume A (mL) of methanol consumed. The methanol value V can be obtained through the following formula:

[0053]

[0054] (5) Loss on drying

[0055] The test method refers to GB 25576 - 2020.

[0056] The precipitated silica obtained in the present invention is evaluated for application in the following way (evaluating its performance in epoxy polyester powder coatings).

[0057] (1) Preparation of powder coating samples

[0058] The composition of the powder coating samples is shown in Table 1. By premixing, melt - extruding polyester resin 6041, epoxy resin E12, accelerator A - 601, barium sulfate, carbon black, and triglycidyl isocyanurate TGIC, and then mixing in different flow aid samples, and then crushing and screening, the crushing particle size is 30.0 ± 0.5 um (D50).

[0059] Table 1 Composition of epoxy polyester powder coatings

[0060] Ingredients Quantity Polyester resin 6041 38.0 Epoxy resin E12 38.0 Accelerator A-601 0.2 Barium sulfate 15.0 Carbon black 1.3 Triglycidyl isocyanurate TGIC 7.0 Flow aid 0.5

[0061] (2) Preparation of films

[0062] Before spraying, the aluminum plate is degreased with alcohol and acetone. The size of the aluminum plate is 88.9 mm * 63.5 mm * 0.8 mm.

[0063] The spraying conditions are controlled the same. The spray gun is a Nordson Surecoat manual electrostatic spray gun, with a voltage of 45 kV and an air pressure of 0.25 MPa.

[0064] The distance between the spray gun and the aluminum plate is 15 cm, the film thickness is basically controlled between 60 and 80 μm, the curing temperature is 200 °C, and the curing time is 10 min.

[0065] (3) Powder fluidity - Angle of repose test

[0066] The fluidity of the powder refers to the degree to which the powder coating is fluidized by air in the fluidized bed. It is an important basis for evaluating the construction performance of the powder coating. The fluidity can be measured by the angle of repose θ. The smaller the angle of repose, the better the fluidity; the larger the angle of repose, the worse the fluidity. The angle of repose test is carried out according to the provisions of GBT16913-2008.

[0067] (4) Gloss (60°)

[0068] It is carried out according to the provisions of GB / T 9754-2007 and tested at 60°.

[0069] Example 1

[0070] Add 150 L of water to a 300 L reaction kettle and heat it up to 60 °C. When the temperature is constant at 60 °C, add 43 Kg of water glass (22%) with a modulus of 3.4 and about 15 Kg of sulfuric acid (30%) simultaneously. During the co-current flow, adjust the flow rate of the acid to control the pH value between 7.0 and 7.5. After the co-current flow ends, adjust the pH value to 2.8 with sulfuric acid. After washing and pressure filtration, redisperse and beat the obtained filter cake with pure water, control the solid content of the slurry to 12%, and add 0.60 Kg of the hydrophobic treatment agent synthesized according to the process of Patent CN115893432 (Synthesis method of hydrophobic treatment agent). Spray dry and grind it to the specified particle size at 160 °C using a jet mill to obtain the finished product of precipitated silica.

[0071] Example 2

[0072] Except that the co-current pH is controlled between 8.0 and 8.5, other processes and reagent dosages are the same as in Example 1.

[0073] Example 3

[0074] Except that the co-current pH value is controlled between 9.0 and 9.5, other processes and reagent dosages are the same as in Example 1.

[0075] Example 4

[0076] Except that the water glass becomes 52 Kg, the sulfuric acid dosage becomes about 18 Kg, and the hydrophobic treatment agent dosage becomes 0.72 Kg, other processes and reagent dosages are the same as in Example 1.

[0077] Example 5

[0078] Except that the sodium silicate becomes 69 Kg, the sulfuric acid dosage becomes about 24 Kg, and the dosage of the hydrophobic treatment agent becomes 0.96 Kg, other processes and reagent dosages are the same as those in Example 1.

[0079] Example 6

[0080] Except that the grinding temperature becomes 120 °C, other processes and reagent dosages are the same as those in Example 1.

[0081] Example 7

[0082] Except that the grinding temperature becomes 230 °C, other processes and reagent dosages are the same as those in Example 1.

[0083] Example 8

[0084] Except that the hydrophobic treatment agent is replaced with octadecyltrimethoxysilane and added before the concurrent flow of sodium silicate and sulfuric acid starts, other processes and reagent dosages are the same as those in Example 1.

[0085] Example 9

[0086] Except that the hydrophobic treatment agent is replaced with hexamethyldisilazane and added in a spraying manner during the grinding process, other processes and reagent dosages are the same as those in Example 1.

[0087] Example 10

[0088] Except that the dosage of the hydrophobic treatment agent becomes 0.40 Kg, other processes and reagent dosages are the same as those in Example 1.

[0089] Example 11

[0090] Except that the dosage of the hydrophobic treatment agent becomes 1.00 Kg, other processes and reagent dosages are the same as those in Example 1.

[0091] Comparative Example 1

[0092] Comparative Example 1 is a blank control, and the powder coating used in Comparative Example 1 is a powder coating without any flow aid.

[0093] Comparative Example 2

[0094] Except that the dosage of the hydrophobic treatment agent becomes 0.00 Kg, other processes and reagent dosages are the same as those in Example 1.

[0095] Comparative Example 3

[0096] The commercial fumed silica AEROSIL R812 (Degussa) is selected as the flow aid. AEROSIL R812 is a hydrophobic product surface-treated with hexamethyldisilazane.

[0097] Comparative Example 4

[0098] Commercial fumed alumina AEROXIDE AluC (Degussa) was selected as the flow aid.

[0099] Table 2 Physical and chemical index data of each sample

[0100]

[0101] Table 3 Application evaluation data of each sample in powder coating

[0102]

[0103]

[0104] Conclusion 1: As shown in Tables 2 and 3, the bulk ratio and specific surface area of the silica obtained in Examples 1 to 3 gradually increase with increasing co-current pH values, while the methanol value changes little, and the hydrophobicity is similar. When used in powder coatings, the increased bulk ratio reduces the number of particles, increasing the probability of powder particle contact, gradually increasing the angle of repose, and deteriorating fluidity. Compared with Comparative Example 1, the addition of hydrophobic silica as a flow aid increases the distance between the powder particles, significantly reduces the angle of repose, and improves the fluidity of the coating. Furthermore, the addition of hydrophobic silica slightly reduces the gloss of the cured film.

[0105] Conclusion 2: It can be seen from Tables 2 and 3 that the larger the hydrophobic silica stacking ratio, the greater the decrease in glossiness of the film after curing, but the difference is not very obvious.

[0106] Conclusion 3: As shown in Tables 2 and 3, as the amount of water glass increases and the co-flow ends, the solid content of the suspensions obtained in Examples 1, 4, and 5 gradually increases, the bulk ratio of the resulting silica increases, and the specific surface area decreases. Since the proportion of hydrophobic additive added is essentially the same, the methanol values are essentially the same, and there is no significant difference in hydrophobicity. When used in powder coatings, the angle of repose gradually increases, and the coating fluidity deteriorates. This is because the bulk ratio of silica increases, the number of particles decreases, the probability of powder particles contacting each other increases, and the coating fluidity deteriorates. At the same time, the specific surface area decreases, making it more difficult for silica to adhere to the surface of the powder particles, further leading to poor fluidity.

[0107] Conclusion 4: As shown in Tables 2 and 3, as the grinding temperature increases, the drying loss of the silica obtained in Examples 6, 1, and 7 gradually decreases, as does the water content, while other indicators do not change significantly. When used in powder coatings, the reduced water content weakens the forces between powder particles, reduces the angle of repose, and improves the coating's fluidity.

[0108] Conclusion 5: As can be seen from Table 2 and Table 3, when different hydrophobic treatment agents are added in different steps, the hydrophobic effects of the silica obtained in Example 8, Example 1, and Example 9 are significantly different. Among them, the hydrophobic effect of octadecyltrimethoxysilane is the worst and the methanol value is the smallest; the hydrophobic effect of hexamethyldisilazane is the best and the methanol value is the largest. When applied to powder coatings, due to the enhanced hydrophobicity of silica, the force between powder particles weakens, the angle of repose becomes smaller, and the fluidity of the coating becomes better.

[0109] Conclusion 6: As can be seen from Table 2 and Table 3, with the increase in the dosage of the hydrophobic treatment agent, the methanol values of the silica obtained in Example 10, Example 1, and Example 11 increase in turn, the hydrophobicity is enhanced, and the drying loss decreases slightly, and there is little difference in other indicators. When applied to powder coatings, the angle of repose decreases and the fluidity becomes better. However, in Comparative Example 2, since no hydrophobic treatment agent was used, the obtained silica has no hydrophobic effect. When applied to powder coatings, it is easy to adsorb water molecules in the air, enhancing the force between powder particles, resulting in poor fluidity of the coating.

[0110] Conclusion 7: As can be seen from Table 3, compared with AEROSIL R812, when the silica obtained in the present invention is used in powder coatings, the angle of repose is similar to it and the fluidity is comparable. After curing, the gloss of the film layer decreases slightly, but the decrease amplitude is basically the same. Compared with R812, the process of the present invention is relatively simple and the cost is low.

[0111] Conclusion 8: As can be seen from Table 3, compared with the commercial fumed alumina AEROXIDE AluC, when the hydrophobic silica obtained in Example 1, Example 7, Example 9, and Example 11 is used in powder coatings, the angle of repose is comparable to it and the fluidity is basically the same. At the same time, compared with Comparative Example 1, the gloss of the film layer decreases after curing, but the decrease amplitude is basically the same. Therefore, the precipitated silica obtained in the present invention can replace AEROXIDE AluC as a flow aid in powder coatings. Compared with AEROXIDE AluC, the process of the present invention is simple, the cost is low, and the performance is comparable to it.

[0112] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing silica as a flow aid in powder coatings, characterized in that, It includes the following steps: (a) Synthesize silica by the precipitation method; (b) Wash with water and filter press to obtain a precipitate; (c) Redisperse and pulp the silica with pure water; (d) Dry; (e) Crush at high temperature; Among them, the synthesis of silica in step (a) includes the following steps: (a1) Add bottom water and heat up to 40 - 100 °C; (a2) Keep the temperature constant and add water glass and acid to the bottom water in parallel flow under the condition of pH value 5.0 - 10.0; (a3) Adjust the pH to 2.0 - 4.0 with acid; The specific surface area of the silica ranges from 100 to 500 m 2 / g; The bulk ratio of the silica is not higher than 0.30 g / cm 3 ; The particle size of the silica is not higher than 5.0 μm; The methanol value of the silica is higher than 30%; The drying loss of the silica is not higher than 3.0%.

2. The preparation method of silica as a flow aid in powder coatings according to claim 1, characterized in that, In step (a2), the concentration of the water glass is 5 - 30%, and the modulus of the water glass is 3.0 - 3.

8.

3. The preparation method of silica used as a flow aid in powder coatings according to claim 1, characterized in that, In step (a2), the acid is one or more of citric acid, acetic acid, hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid, and the concentration of the acid is 5 - 50%.

4. The preparation method of silica used as a flow aid in powder coatings according to claim 1, characterized in that, In step (a2), after the parallel flow ends, the solid content of the suspension is 30 - 80 g / L.

5. The preparation method of silica as a flow aid in powder coatings according to claim 1, characterized in that, In step (c), the solid content of the dispersed slurry is 5 - 30%.

6. The preparation method of silica used as a flow aid in powder coatings according to claim 1, characterized in that, In step (d), the drying method can be one of flash drying and spray drying.

7. The preparation method of silica used as a flow aid in powder coatings according to claim 1, characterized in that, In step (e), the crushing method can be one of jet milling and flat milling.

8. The preparation method of silica used as a flow aid in powder coatings according to claim 1, characterized in that, In step (e), the temperature during crushing is 100 - 300 °C.

9. The preparation method of silica as a flow aid in powder coatings according to claim 1, characterized in that, It also includes step (f), (f) surface-treat the silica with a hydrophobic treatment agent; Or, add a hydrophobic treatment agent in step (a) or step (c) or step (d) or step (e); The dosage of the hydrophobic treatment agent is 2 - 20%.

10. The preparation method of silica used as a flow aid in powder coatings according to claim 9, characterized in that, The hydrophobic treatment agent is one or more of octadecyltrimethoxysilane, cetyltriethoxysilane, dodecyltriethoxysilane, octyltriethoxysilane, polydimethylsiloxane, hexamethyldisilazane, dimethyldichlorosilane, and a self-made hydrophobic treatment agent.

Images