Preparation method of silicon dioxide for delustering agent

Abstract

The invention discloses a preparation method of silicon dioxide for a delustering agent. Mixing a sodium silicate solution and an organic acid aqueous solution, and carrying out sol-gel reaction to obtain primary silica sol; mixing the primary silica sol with CO2 gas to obtain secondary silica sol; and pressurizing and aging the secondary silica sol, and then centrifuging, washing, drying and crushing to obtain the silicon dioxide for the delustering agent. According to the invention, a sodium silicate diluent and an organic acid aqueous solution are mixed by an acid mixing method to form silica sol, and the silica sol is immediately mixed with carbon dioxide to obtain silicon dioxide with larger specific surface area and pore volume, smaller median particle size and narrower particle size distribution. The silicon dioxide obtained by the invention is better in performance when being used as a delustering agent, and has the advantages of simple process, low production cost and controllable product index range.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of silicon dioxide, in particular to a preparation method of silicon dioxide for a matting agent. BACKGROUND

[0002] Silicon dioxide has good optical properties, and its refractive index is close to that of most resins used in coatings, so that the addition of silicon dioxide to the coatings does not affect the optical properties of the coatings themselves. The addition of silicon dioxide matting agent in the coatings, in the process of forming a paint film by brushing, as the volatilization of the coating solvent decreases, the silicon dioxide particles suspended in the coating system gradually appear on the surface of the paint film, so that the micro surface of the paint film tending to be flat is broken, forming a rough surface with fine concave-convex, when light is projected onto the surface of the paint film added with the matting agent, the specular reflection of light is weakened, and diffuse reflection occurs instead, achieving the matting effect. The matting agent is a high-end market product of silicon dioxide, and has higher requirements for its own indicators. The average particle size and particle size distribution are important indicators of the silicon dioxide for matting. The median particle size (D50) and the particle size distribution directly determine the matting degree of the coating film, the appearance and hand feeling quality of the coating film. The larger the D50 of the matting agent is, the higher the roughness of the paint film surface formed is, the lower the gloss of the paint film is, and the better the matting effect is. However, when the D50 of the silicon dioxide is too large, the surface of the paint film is too rough, which affects the hand feeling and the strength of the paint film surface. If the particle size of the silicon dioxide is too small, the matting effect is affected, and in addition, the viscosity of the coating is increased, which seriously affects the normal use. Therefore, the particle size distribution of the silicon dioxide should be as narrow as possible.

[0003] The specific surface area (BET) and the pore volume reflect the internal pore structure level of the silicon dioxide particles, the larger the specific surface area and the pore volume of the unit mass volume of the silicon dioxide are, the higher the oil absorption value is. The macropore silicon dioxide added as the matting agent into the coating can make the solvent and resin components in the coating more easily enter the pores of the silicon dioxide, thereby improving the compatibility of the matting agent with the coating system and reducing the influence on the refractive properties of the coating resin. The larger the specific surface area and the pore volume of the silicon dioxide of the same mass are, the better the matting effect is. Patent CN101585540A discloses a preparation method of high-pore-volume silicon dioxide, which uses soluble sodium silicate as the raw material, carries out a synthesis reaction under the condition of ammonia water precipitation, ammonium bicarbonate pore expansion and polyethylene glycol surfactant, and combines pressure filtration, washing, organic solvent replacement, pore drying and airflow crushing to prepare the silicon dioxide with a pore volume greater than 2.0 cm 3The high pore volume silica product has high extinction performance, good transparency and high pore volume. However, the use of organic solvent and ammonium bicarbonate makes the process more complicated, the wastewater generated by product washing increases, and the production cost is high. Patent CN102557044A discloses a method for preparing macroporous silica microspheres, which adopts full-sulfurized powder silicone rubber to burn under oxygen condition to prepare macroporous silica microspheres. The energy consumption is high, and the specific surface area and pore volume of the product are not easy to control. In addition, the surface of the silica obtained by burning has no hydroxyl group, which limits the means of surface modification in application. Patent CN102020284A discloses a preparation method of silica, which adopts supercritical / subcritical carbonization reaction coupled with supercritical drying method. The silicide is obtained by reacting sodium silicate aqueous solution with supercritical / subcritical carbon dioxide in a carbonization reactor, and then high-performance silica product is prepared under near room temperature condition by using supercritical drying technology, so as to realize the preparation of high-pore-volume, high-dispersion and high-performance silica product. However, the process condition is harsh, the steps are complicated, the cost is high, and it is not conducive to large-scale production. Therefore, a method for preparing silica with narrow particle size distribution, large specific surface area and large pore volume is needed, which is used as an extinction agent. SUMMARY

[0004] In view of the above prior art, the purpose of the present application is to provide a preparation method of silica for extinction agent. In the present application, sodium silicate dilute solution and organic acid aqueous solution are mixed by mixed acid method, and then mixed with carbon dioxide immediately after forming silica sol, so as to obtain silica with larger specific surface area and pore volume, smaller median particle size and narrower particle size distribution. The silica obtained in the present application has better performance when used as an extinction agent, and has the advantages of simple process, low production cost and controllable product index range.

[0005] To achieve the above purpose, the present application adopts the following technical scheme: In the first aspect of the present application, a preparation method of silica for extinction agent is provided, which comprises the following steps: (1) mixing sodium silicate solution and organic acid aqueous solution to carry out sol-gel reaction, and obtaining primary silica sol; (2) mixing the primary silica sol with CO2 gas to obtain secondary silica sol; (3) pressurizing and aging the secondary silica sol, and then carrying out centrifugation, washing, drying and crushing to obtain silica for extinction agent.

[0006] Preferably, in step (1), the mass concentration of the sodium silicate solution is 10-40%; the organic acid in the organic acid aqueous solution is acetic acid; and the mass concentration of the organic acid aqueous solution is 10-60%. The mixing speed of the sodium silicate solution and the organic acid aqueous solution is 30 g / s.

[0007] Preferably, in step (1), the mass ratio of the sodium silicate solution and the aqueous organic acid solution is 1:1-1.05; the mixing time is 2-10 s; the temperature of the sol-gel reaction is 40-90 DEG C, and the time is 5-60 s.

[0008] Preferably, in step (2), the ratio of the feeding volume flow rate of the primary silica sol to the feeding volume flow rate of CO2 is 8-3:1; and the gas flow rate of CO2 is 360 mL / min.

[0009] Preferably, in step (2), the mixing temperature is 10-30 DEG C, and the pH of the system after mixing is 6-7.

[0010] Preferably, in step (3), the pressure of the pressurized aging is 0.2-0.8 MPa, the time is 1-8 h, and the temperature is 10-90 DEG C.

[0011] Preferably, in step (3), the pressurized aging is that the secondary silica sol is first fed into a pressure tank under liquid, and then the pressurized aging is carried out; and the mass ratio of the pure water in the pressure tank to the secondary silica sol is 0.8-1:1-1.1.

[0012] The second aspect of the present application provides the silica obtained by the preparation method.

[0013] Preferably, the specific surface area of the silica is 100-600 m 2 / g, the pore volume is 1.5-2.2 cm 3 / g, the particle size is 1-20 mu m, and the oil absorption value is 100-400 mL / 100 g.

[0014] The third aspect of the present application provides the use of the silica in preparing a matting product, and the matting product is a matting paint.

[0015] The present application has the following advantages: (1) The present application mixes the sodium silicate dilute solution and the aqueous organic acid solution by the mixed acid method to form primary colloidal particles, and then mixes with CO2 at low temperature to form secondary colloidal particles, so that the silica obtained has large specific surface area and pore volume, high oil absorption value, and concentrated particle size distribution, and has high matting efficiency when used as a matting agent.

[0016] (2) The process flow of the present application is simple and has low energy consumption; after temperature change reaction by the two-stage mixer, the product enters a pressure tank for aging, and then is centrifuged, washed, dried, and crushed to obtain the silica for matting agent, and the process conditions are mild, and the energy consumption cost is low.

[0017] (3) The present application can obtain products with different combinations of oil absorption value, specific surface area, and particle size by adjusting the process parameters, and can be flexibly adjusted according to the actual application requirements of the market. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 : Scanning electron microscope (SEM) image of silica microspheres; Figure 2 : Flow chart of silica preparation process; Figure 3 : Particle size distribution of silica of Example 1; Figure 4 : Particle size distribution of silica of Comparative Example 1; Figure 5 : Particle size distribution of silica of Comparative Example 2; Figure 6 : Particle size distribution of silica of Comparative Example 3; Figure 7 : Particle size distribution of silica of Comparative Example 4; Figure 8 : Particle size distribution of silica of Comparative Example 5; Figure 9 : Particle size distribution of silica of Comparative Example 6; Figure 10 : Test results of different silica matting experiments. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed description is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] As introduced in the background section, the existing preparation method of silica microspheres for matting is complicated, with high energy consumption and high production cost. The specific surface area, pore volume, oil absorption value and particle size distribution of silica used as a matting agent need to be strictly controlled.

[0021] Based on this, the purpose of the present application is to provide a preparation method of silica for light extinction agent. The sodium silicate solution and the organic acid acetic acid are mixed in a mixer to rapidly form a primary silica sol through neutralization reaction. After mixing the primary silica sol with CO2 in a mixer, a part of the carbon dioxide is dissolved in water to form silica from the acid and sodium silicate, and the other part of the insoluble gas produces disturbance in the sol. The disturbance provides a relatively mild and uniform mixing effect, so that the primary colloidal particles are uniformly dispersed. In addition, the bubbles form a relatively uniform liquid film structure in the sol, and the colloidal particles are adsorbed onto the gas-liquid interface of the bubbles, effectively reducing the local agglomeration of the colloidal particles, thereby preventing the formation of larger secondary colloidal particles and being more conducive to controlling the particle size. The process generates primary particles at high temperature, and then the temperature is lowered to make the particles agglomerate. After the temperature is lowered, the Brownian motion of the particles is weakened, and the collision is reduced, so that the pores of the microspheres formed are more loose. In addition, after the temperature is lowered, the viscosity of the reaction solution is high, the movement resistance of the particles is increased, the Brownian motion of the particles is further weakened, and the particles are more likely to form stable and not easy to break particles after agglomeration. The secondary silica sol after secondary mixing and crystallization is fed into a pressure tank for aging under liquid, which also avoids the uneven particle size distribution caused by uneven local mass transfer. In this step, the use of CO2 instead of acetic acid also avoids the presence of orthosilicic acid or different forms of silicon hydroxide in the acetic acid-sodium acetate buffer system, improves the product recovery rate, and is also conducive to a simpler post-processing process. And the pH of the final system should be maintained between 6 and 7, and too large or too small pH will also reduce the specific surface area, pore volume, etc. of the silica microspheres obtained finally. Through the production of silica according to the present application, various grades of products such as high BET high oil absorption value, high BET low oil absorption value, and low BET high oil absorption value can be obtained by controlling the initial acid feeding ratio, different temperatures of each section, and carbon dioxide gas flow.

[0022] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in conjunction with specific examples.

[0023] Description: The present application uses a sodium silicate (Na2O·3.3SiO2) solution with a modulus of 3.3 as a raw material, wherein the mass concentration of SiO2 is 28.05%, and the sodium silicate (Na2O3.3SiO2) solution is purchased from Qingdao Gulf Fine Chemical Co., Ltd. Acetic acid is glacial acetic acid with a purity of >99%; carbon dioxide is industrial grade.

[0024] The test materials used in the examples of the present application are all conventional test materials in the art and can be purchased through commercial channels.

[0025] Example 1: As Figure 2The first-stage mixer water bath external temperature was set to 50°C, and the second-stage mixer water bath external temperature was set to 30°C. 1000 g of sodium silicate (Na2O3·3SiO2) solution was diluted with 580 g of water to obtain a sodium silicate diluent. 400 g of glacial acetic acid and 1200 g of deionized water were mixed to obtain an acetic acid aqueous solution. The sodium silicate diluent and the acetic acid aqueous solution were simultaneously injected into the first-stage mixer at a feeding speed of 30 g / s through a high-pressure liquid feeding pump, and the residence time was about 8 s to obtain a primary silica sol. A carbon dioxide gas flow meter was started in advance at a speed of 360 mL / min, and then the primary silica sol was sent into the second-stage mixer to mix with the carbon dioxide gas to make the pH of the system 6-7, and a secondary silica sol was obtained after mixing. 1700 g of pure water was added to the pressure tank, and the secondary silica sol was fed into the pressure tank under water, and the pressure tank was pressurized to 0.3 MPa, and aged for 2 h. After aging, the reaction solution was centrifuged, and the wet product was washed with deionized water until the conductivity of the washing water was less than 1 ms / cm, and then flash dried, crushed, and 246 g of extinction silica was obtained.

[0026] Comparative Example 1 The difference from Example 1 is that the first-stage mixer water bath external temperature is 30°C.

[0027] Comparative Example 2 The difference from Example 1 is that the gas flow of CO2 is 100 mL / min.

[0028] Comparative Example 3 The difference from Example 1 is that the second-stage mixer water bath external temperature is 60°C.

[0029] Comparative Example 4 The difference from Example 1 is that the acetic acid aqueous solution is replaced by an inorganic acid hydrochloric acid with the same mass concentration and mass. Extinction silica is finally prepared.

[0030] Comparative Example 5 The difference from Example 1 is that the acetic acid aqueous solution is replaced by CO2 with the same mass, and the acetic acid aqueous solution and the primary silica sol are injected into the second-stage mixer at the same speed for mixing. Extinction silica is finally prepared.

[0031] Comparative Example 6 The difference from Example 1 is that the primary silica sol is sent into the second-stage mixer to mix with the carbon dioxide gas to make the pH of the system 5.0.

[0032] The specific surface area, pore volume and pore size of the silica spherule particles prepared in Example 1 and Comparative Examples 1-6 were obtained based on Brunauer-Emmett-Teller (BET) theory through multilayer adsorption isotherm of nitrogen at low temperature (77 K) on the surface of the microspheres; the oil absorption value was measured by dioctyl phthalate (DOP) absorption method; and the particle size distribution of the silica spherule particles was detected by a laser particle size analyzer. The results are shown in Table 1, and the particle size distribution is shown in Figure 3 .

[0033] Table 1 Parameters of silica As can be seen from Table 1, the specific surface area, oil absorption value and pore volume of the silica prepared in Example 1 are the best compared with those of Comparative Examples 1-6, and the particle size distribution of the silica prepared in Example 1 is narrower. The specific surface area, oil absorption value, pore volume and particle size distribution, etc. will all affect the extinction. It is indicated that the extinction of the silica prepared in the application is the best.

[0034] Test Example: Extinction Effect Test The commercially available EVONIK-810 extinction agent (Germany Evonik Industrial Co., Ltd.), the silica prepared in Example 1 and Comparative Examples 1-6 were treated as follows: 10 g of silica was added to 100 mL of ethanol, and 15 wt% of dimethyldichlorosilane based on the silica was added, and heated at 120℃ for 3.5 h to obtain an extinction agent, which was recorded as a control group, an Example 1 group, and Comparative Examples 1-6 groups, respectively. 500 g of commercially available varnish (model A5161, purchased from Qingdao Guanghui Color Decoration Co., Ltd.) was evenly divided into 41 parts, and extinction agents from each group were added, with the mass being 0%, 1%, 2%, 3%, 4% and 5%, respectively. After adding the extinction agent, the varnish was stirred at a speed of 500 rpm to disperse the extinction agent uniformly in the varnish. According to the test method specified in GB / T 9754-1988 “Paint and Varnish Non-metallic Pigment Containing Paint Film 20°, 60° and 85° Mirror Glossiness Determination”, a multi-angle glossiness meter was used to test the surface glossiness of the coating film. The glossiness at 60° was selected, and the extinction test experimental results are shown in Figure 4 The extinction efficiency of the silica prepared in Example 1 is higher than that of Comparative Examples 1-6, and compared with the foreign extinction agent product (EVONIK-810), the extinction efficiency is not inferior, reaching the extinction rate level of the same type of product.

[0035] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing silicon dioxide for matting agent, characterized in that: The following steps are involved: (1) Mixing sodium silicate solution and organic acid aqueous solution to carry out sol-gel reaction to obtain primary silica sol; (2) mixing the primary silica sol and CO2 gas to obtain the secondary silica sol; (3) The secondary silica sol is pressurized and aged, and then centrifuged, washed, dried, and crushed to obtain silica for matting agent.

2. The preparation method according to claim 1, characterized in that In step (1), the mass concentration of the sodium silicate solution is 10-40%; the organic acid in the organic acid aqueous solution is acetic acid; and the mass concentration of the organic acid aqueous solution is 10-60%.

3. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of the sodium silicate solution to the organic acid aqueous solution is 1:1-1.05; the mixing time is 2-10 seconds; the sol-gel reaction temperature is 40-90°C, and the reaction time is 5-60 seconds.

4. The preparation method according to claim 1, characterized in that In step (2), the ratio of the feed volume flow rate of the primary silica sol to the feed volume flow rate of CO2 is 8-3:1; and the gas flow rate of CO2 is 360 mL / min.

5. The preparation method according to claim 1, characterized in that In step (2), the mixing temperature is 10-30° C., and the pH of the system after mixing is 6-7.

6. The preparation method according to claim 1, characterized in that In step (3), the pressure of the pressurized aging is 0.2-0.8 MPa, the time is 1-8 h, and the temperature is 10-90°C.

7. The preparation method according to claim 1, characterized in that In step (3), the pressurized aging is as follows: the secondary silica sol is first fed into a pressure tank through submerged feeding, and then pressurized aging is performed; the mass ratio of pure water to the secondary silica sol in the pressure tank is 0.8~1:1~1.

1.

8. Silicon dioxide obtained by the preparation method according to any one of claims 1 to 7.

9. The silicon dioxide according to claim 8, characterized in that The specific surface area of ​​the silicon dioxide is 100~600m 2 / g, pore volume is 1.5~2.2cm 3 / g, particle size is 1~20μm, and oil absorption value is 100~400mL / 100g.

10. Use of the silicon dioxide according to claim 8 or 9 in the preparation of a matte product, wherein the matte product is a matte coating.

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