A process and apparatus for the continuous production of monodisperse submicron spherical silica

Abstract

The application discloses a process for continuously preparing monodisperse submicron spherical silica, which comprises the following process steps in sequence: hydrolyzing organosilane in an acidic aqueous solution; stirring the prepared hydrolysis solution in an alkaline aqueous solution to prepare a synthesis slurry containing spherical silica; filtering the prepared synthesis slurry through a filter membrane, collecting the slurry with a particle size larger than the membrane holes, and returning the slurry with a particle size smaller than the membrane holes to the alkaline aqueous solution for stirring to continuously grow into spherical silica; drying the collected slurry to obtain a powder; and calcining the dried powder to obtain spherical silica with a uniform particle size, a compact structure and no crystallization water. The application uses water as a medium, does not need organic reagents or emulsifiers, uses a filter membrane for solid-liquid separation when the particle size of the prepared spherical silica meets the requirements, returns small particles to the system for continuous growth, realizes continuous preparation, and the prepared spherical silica is monodisperse.

Description

Technical Field

[0001] This invention relates to a process and apparatus for the continuous preparation of monodisperse submicron spherical silica. Background Technology

[0002] Copper clad laminate (CCL) is a fundamental material in the electronics industry, used to manufacture printed circuit boards (PCBs). It is widely used in electronic products such as computers, communication equipment, and instruments. Spherical silica is one of the main raw materials for CCL. In CCL, spherical silica is mainly used as an inorganic filler to reduce the thermal expansion rate of CCL, improve its heat resistance and moisture resistance, reduce moisture absorption, improve the peel strength of the substrate, and improve the rigidity of the thin CCL substrate and its resistance to cracking from mechanical impact.

[0003] With the continuous development of electronic information technology, PCB substrate materials are rapidly moving towards thinner profiles, especially in HDI (High Density Interconnect) multilayer boards, where the trend towards thinner substrate materials is particularly prominent. Many portable electronic products, striving for thinner, lighter, smaller, and more multifunctional designs, require PCBs with more layers and thinner thicknesses. This places new demands on the spherical silica used in copper-clad laminates: smaller particle size, reaching submicron or even nanometer scale; uniform particle size without large particles; higher purity and better DK (dielectric constant) and DF (dielectric loss factor). Currently, methods for preparing spherical silica micropowder include microemulsion methods, sol-gel methods, and chemical methods.

[0004] Chemical methods are commonly used to prepare high-purity, ultrafine spherical silica powder. Patents CN101891208A and CN109574023A both use organosilicon as the silicon source and ethanol as the solvent to prepare submicron spherical silica. However, these chemical methods require large amounts of organic reagents, resulting in high costs and significant environmental pollution. Patent CN102659123A uses a large amount of organic reagents and emulsifiers to prepare submicron spherical silica via an emulsion method, also involving significant organic reagent use and producing uneven particle size. Furthermore, chemical methods are inefficient, produce small batches, and rely on indirect production, leading to high costs. Therefore, chemically prepared submicron spherical silica powder cannot be widely adopted.

[0005] Patent CN110713192B discloses a method for preparing spherical silica nanoparticle slurry. The preparation process of the spherical silica nanoparticle slurry is carried out in a precipitation aging reactor. The precipitation aging reactor includes a vessel body, a centrifugal mixer at the top, and a liquid distributor at the center of the centrifugal mixer. The lower part of the vessel body is an aging zone. Reactants A and B enter the liquid distributor through pipelines, are uniformly mixed, and then react. The reacted slurry enters the aging zone for aging. While maintaining a certain liquid holdup in the aging zone, the slurry is continuously discharged, forming a continuous production process. The discharged slurry is concentrated by vacuum evaporation to form spherical silica nanoparticle slurry with a particle size between 10 and 200 nm. Although it allows for continuous production and continuous discharge, it uses organic solvents. Summary of the Invention

[0006] The purpose of this invention is to overcome the deficiencies of existing technologies and provide a continuous process for preparing monodisperse submicron spherical silica. This process overcomes the shortcomings and deficiencies of current chemical methods for preparing submicron spherical silica, using water as the medium and eliminating the need for organic reagents or emulsifiers. When the particle size of the prepared spherical silica meets the requirements, solid-liquid separation is achieved using a filtration membrane, with smaller particles returned to the system for continued growth, thus achieving continuous preparation. The prepared spherical silica is monodisperse. This preparation process is highly efficient, low-cost, and environmentally friendly.

[0007] To achieve the above objectives, the technical solution of the present invention is to design a process for the continuous preparation of monodisperse submicron spherical silica, comprising the following sequential process steps: S1: Hydrolyze the organosilane in an acidic aqueous solution; S2: The hydrolysate obtained in step S1 is placed in an alkaline aqueous solution and stirred to prepare a synthetic slurry containing spherical silica. S3: The synthetic slurry obtained in step S2 is filtered and separated through a filter membrane. The slurry with a particle size larger than the membrane pore size is separated and collected, while the slurry with a particle size smaller than the membrane pore size is returned to the alkaline aqueous solution and stirred to continue nucleation and growth into spherical silica. S4: Dry the slurry collected in step S3 into powder; S5: The powder dried in step S4 is calcined to obtain dense, anhydrous, uniformly sized spherical silica. A filtration membrane is used, and the filtered product is a slurry (similar to ultrafiltration). This method overcomes the shortcomings and deficiencies of current chemical methods for preparing submicron spherical silica. Water is used as the medium, eliminating the need for organic reagents or emulsifiers. When the particle size of the prepared spherical silica meets the requirements, solid-liquid separation is achieved using a filtration membrane, with smaller particles returned to the system to continue growth, thus realizing continuous preparation. The prepared spherical silica is monodisperse.

[0008] A further technical solution is to add the amount of hydrolysate to the alkaline aqueous solution in step S2 to the same amount of slurry with particle sizes larger than the membrane pores separated in step S3. This ensures that the amount added and separated in the second device in step S2 is maintained, keeping the system in balance (maintaining the stability of the liquid level in the second device) and ensuring continuous preparation.

[0009] A further technical solution is that, in step S1, the organosilane is slowly added to the hydrolysis tank containing an acidic aqueous solution in the first apparatus. During the addition process, the mixture is continuously stirred to ensure complete hydrolysis of the organosilane. Simultaneously, the hydrolysis tank is circulated and cooled to control the temperature of the hydrolysate. Since the hydrolysis reaction is exothermic, the temperature control of the hydrolysis reaction by circulating and cooling the hydrolysis tank meets the requirements.

[0010] A further technical solution is that, in step S2, the hydrolysate is pumped into a second device containing an alkaline aqueous solution by a metering pump in the first device. During the addition process, the second device is kept stirred, and the hydrolysate nucleates and grows into spherical silica in the alkaline aqueous solution.

[0011] A further technical solution is that, in step S3, the slurry in the second device is pumped into the filter membrane in the third device by a metering pump in the third device for filtration and separation. The flow rates of the metering pumps in the first and third devices are adjusted to ensure that the amount added to the second device and the amount separated in the third device are consistent, thus maintaining system balance. In other words, the amount added to the second device must be consistent with the amount separated in the third device, since the final reduction in the second device is essentially the amount of large-particle slurry separated from the third device. The metering pump in the first device is turned on for a period of time before the metering pump in the third device is turned on (to ensure a certain amount of solution remains in the second device). Maintaining consistency between the amount of hydrolysate added to the second device and the amount of large-particle slurry separated in the third device is crucial to maintaining the balance of the second device (keeping the liquid level stable and preventing overflow).

[0012] A further technical solution is that, in step S1, the organosilane includes the following components or a mixture of the following components: methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, dimethyldimethoxysilane, ethyl silicate, or methyl silicate. The pH value of the acidic aqueous solution is 2-6; The pH adjuster used in acidic aqueous solutions is acetic acid, oxalic acid, nitric acid, hydrochloric acid, or sulfuric acid. The mass ratio of the organosilane to water is 1:(0.5-10). The stirring speed is 50-120 r / min; the temperature of the hydrolysate is controlled at 10-30℃. In step S2, the pH of the alkaline aqueous solution is 10-12; the stirring speed is 50-120 r / min. The pH adjusters used in alkaline aqueous solutions are organic bases such as ammonia, ethylenediamine, dimethylamine, and tetramethylammonium hydroxide. In step S3, the pore size of the filter membrane is 100-1000 nanometers; In step S4, the slurry is dried using a dryer at a temperature of 50-150°C. In step S5, the parts are calcined in a box furnace, tunnel kiln, or roller kiln at a temperature of 500-1200℃ for 3-10 hours.

[0013] A further technical solution is that the dryer is a spray dryer, a vacuum target dryer, or a flash dryer.

[0014] The present invention also provides a technical solution in which a preparation apparatus is involved in the process of continuously preparing monodisperse submicron spherical silica, comprising a first apparatus, a second apparatus and a third apparatus connected in sequence. The first device includes two constant temperature hydrolysis tanks, each equipped with a stirring mechanism; the tank walls of the hydrolysis tanks are equipped with circulating cooling liquid pipelines, and the tank bodies of the hydrolysis tanks are connected to a cooling machine through inlet and outlet pipes, which are also connected to the circulating cooling liquid pipelines; both hydrolysis tanks are connected to a first metering pump. The second device includes an alkaline aqueous solution mixing tank, a stirring mechanism is installed inside the mixing tank, and a first metering pump is connected to the mixing tank. The third apparatus includes a cylindrical body, a filter membrane placed inside the body, and a second metering pump connected to the body. The body is connected to a stirring tank via a third metering pump. The second apparatus utilizes circulating filtration and nucleation growth, resulting in an environmentally friendly, emission-free process. Using two hydrolysis tanks allows for better continuity of preparation. Since hydrolysis takes time, the first hydrolysis tank pumps water into the stirring tank of the second apparatus while the second hydrolysis tank is hydrolyzing. When the solution in the first hydrolysis tank is low, liquid can be added to the first tank while the second hydrolysis tank continues pumping water into the stirring tank. In this case, the hydrolysis in the first tank occurs simultaneously with the pumping of water from the second hydrolysis tank into the stirring tank of the second apparatus.

[0015] The advantages and beneficial effects of this invention are as follows: This method overcomes the shortcomings and limitations of current chemical methods for preparing submicron spherical silica. It uses water as the medium, eliminating the need for organic reagents or emulsifiers. When the prepared spherical silica particle size meets the requirements, solid-liquid separation is achieved using a filtration membrane, with smaller particles returned to the system for continued growth, enabling continuous preparation. The prepared spherical silica is monodisperse. This preparation process is highly efficient, low-cost, and environmentally friendly.

[0016] The second device employs circulating filtration and nucleation growth, resulting in an environmentally friendly, emission-free process. Using two hydrolysis tanks allows for better continuity of preparation. Since hydrolysis takes time, the first hydrolysis tank is pumped into the stirred tank of the second device while the second hydrolysis tank is undergoing hydrolysis. When the solution in the first hydrolysis tank is low, liquid can be added to the first hydrolysis tank while the second hydrolysis tank continues pumping into the stirred tank. In this case, the process becomes simultaneous hydrolysis in the first hydrolysis tank and pumping into the stirred tank of the second device from the second hydrolysis tank. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope image of 300 nm monodisperse spherical silica prepared by a continuous preparation process of monodisperse submicron spherical silica according to the present invention. Figure 2 This is a particle size distribution diagram of spherical silica from Example 1; Figure 3 This is a scanning electron microscope (SEM) image of 500 nm monodisperse spherical silica, which is the second embodiment of the present invention. Figure 4 This is a particle size distribution diagram of spherical silica from Example 2; Figure 5 This is a schematic diagram of the preparation apparatus involved in the continuous preparation process of monodisperse submicron spherical silica of the present invention; In the diagram: 1. First device; 2. Cooling machine; 3. First metering pump; 4. Stirring tank; 5. Second device; 6. Third device; 7. Filter membrane; 8. Second metering pump; 9. Inlet pipe; 10. Outlet pipe; 11. Circulating cooling liquid pipeline; 12. Alkaline aqueous solution stirring tank; 13. Device body. Implementation

[0018] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0019] This invention relates to a process for the continuous preparation of monodisperse submicron spherical silica, the preparation steps of which are as follows: 1. Slowly add organosilanes (such as methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, dimethyldimethoxysilane, ethyl silicate, methyl silicate, or mixtures thereof) to an acidic aqueous solution with pH 2-6 and to the first apparatus 1. (The pH adjuster is acetic acid, oxalic acid, nitric acid, hydrochloric acid, or sulfuric acid.) The ratio of organosilane to water is 1:0.5-10. Stir continuously at 50-120 r / min during the addition process to ensure uniform mixing and complete hydrolysis of the organosilanes. The first apparatus 1 contains a cooling device. The jacket of the stirring tank 4 is cooled by circulating cooling liquid. The cooling liquid is cooled by circulating cooling machine 2. The hydrolysis process releases heat. The temperature of the hydrolysate is controlled at 10-30 degrees Celsius by refrigeration.

[0020] 2. The hydrolysate in the first device 1 is added to the stirring tank device (i.e., the second device 5) through the first metering pump 3. The second device 5 contains an alkaline aqueous solution with a pH of 10-12 (the pH adjuster is an organic base such as ammonia, ethylenediamine, dimethylamine, tetramethylammonium hydroxide, etc.). During the addition process, the stirring speed of the stirring device in the second device 5 is 50-120 r / min. The hydrolysate nucleates and grows into spherical silica in the alkaline aqueous solution.

[0021] 3. Turn on the metering pump in the third device 6 to filter and separate the synthetic slurry in the second device 5 through the filter membrane 7 of the third device 6, which has a pore size of 100-1000 nanometers. The slurry with a particle size larger than the membrane pore size is separated and collected (the large slurry particles are liquid and flow out, so they are collected directly; since this third device, which includes a filter membrane, is similar to an ultrafiltration device, the third device 6 includes a cylindrical device body 13, so the small slurry particles after filtration flow out from one port of the device body. Since this port is connected to the second device, they return to the second device to continue nucleation and growth, while the large slurry particles flow out from the other port of the device body and are collected directly). The slurry with a particle size smaller than the membrane pore size is returned to the stirring tank in the second device 5 to continue growth. Adjust the first metering pump 3 in the first device 1 and the second metering pump 7 in the third device 6 to keep the amount added and the amount separated in the second device 5 (i.e., the amount pumped into the second device 5 from the first metering pump 3 and the amount of slurry particles with a particle size larger than the membrane pore size separated from the third device 6) consistent, and maintain system balance.

[0022] 4. The separated slurry is dried using a dryer, such as a spray dryer, vacuum target dryer, or flash dryer, at a temperature of 50-150 degrees Celsius, until the slurry becomes powder.

[0023] 5. Calcine the dried powder at 500-1200 degrees Celsius for 3-10 hours using a box furnace, tunnel kiln, or roller kiln to obtain dense, water-free, uniformly sized spherical silica.

[0024] like Figure 5 As shown, the preparation apparatus involved in the continuous preparation process of monodisperse submicron spherical silica includes a first apparatus 1, a second apparatus 5, and a third apparatus 6 connected in sequence. The first apparatus 1 includes two constant-temperature hydrolysis tanks (i.e., stirring tanks 4), each equipped with a stirring mechanism. A circulating cooling liquid pipeline 11 is provided inside the tank wall of the hydrolysis tank. The tank body is connected to a cooling machine 2 via an inlet pipe 9 and an outlet pipe 10, both of which are connected to the circulating cooling liquid pipeline 11. Both hydrolysis tanks are connected to a first metering pump 3. The second apparatus 5 includes an alkaline aqueous solution stirring tank 12, which is equipped with a stirring mechanism. The first metering pump 3 is connected to the alkaline aqueous solution stirring tank 12. The third apparatus 6 includes a cylindrical apparatus body 13, a filter membrane 7 placed inside the apparatus body 13, and a second metering pump 8 connected to the apparatus body 13. The apparatus body 13 is connected to the alkaline aqueous solution stirring tank 12 via a connecting pipe (i.e., a pipe that returns small particle slurry to the second apparatus). Example

[0025] The pore size of the filter membrane 7 in the third device 6 is 300 nanometers. Figure 1 and Figure 2 The images shown are scanning electron microscope (SEM) images and particle size distribution diagrams of monodisperse spherical silica in this embodiment. Example

[0026] The pore size of the filter membrane 7 in the third device 6 is 500 nanometers. Figure 3 and Figure 4 The images shown are scanning electron microscope (SEM) images and particle size distribution diagrams of monodisperse spherical silica in this embodiment.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the continuous preparation of monodisperse submicron spherical silica, characterized in that, The process includes the following steps performed sequentially: S1: Hydrolyze the organosilane in an acidic aqueous solution; S2: The hydrolysate obtained in step S1 is placed in an alkaline aqueous solution and stirred to prepare a synthetic slurry containing spherical silica. S3: The synthetic slurry obtained in step S2 is filtered and separated through a filter membrane. The slurry with a particle size larger than the membrane pore size is separated and collected, while the slurry with a particle size smaller than the membrane pore size is returned to the alkaline aqueous solution and stirred to continue nucleation and growth into spherical silica. S4: Dry the slurry collected in step S3 into powder; S5: The powder dried in step S4 is calcined to obtain spherical silica with a dense structure and uniform particle size and no crystal water. The amount of hydrolysate added to the alkaline aqueous solution in step S2 is the same as the amount of slurry with a particle size larger than the membrane pores separated in step S3. In step S1, the organosilane is slowly added to the hydrolysis tank containing an acidic aqueous solution in the first device. During the addition process, the mixture is continuously stirred to ensure that the organosilane is fully hydrolyzed. At the same time, the hydrolysis tank is circulated and cooled to control the temperature of the hydrolysate. In step S2, the hydrolysate is pumped into a second device containing an alkaline aqueous solution by a metering pump in the first device. During the addition process, the second device is kept stirred, and the hydrolysate nucleates and grows into spherical silica in the alkaline aqueous solution. In step S3, the slurry in the second device is pumped into the filter membrane in the third device by the metering pump in the third device for filtration and separation. Adjust the flow rates of the metering pumps in the first and third devices to ensure that the amount added by the second device and the amount separated by the third device are consistent, thus maintaining system balance. The metering pump in the first device is turned on for a period of time before the metering pump in the third device is turned on to ensure that there is a certain amount of solution in the second device, so that the amount of hydrolysate added to the second device is consistent with the amount of large particle slurry separated by the third device.

2. The process for continuous preparation of monodisperse submicron spherical silica according to claim 1, characterized in that, In step S1, the organosilane comprises the following components or a mixture of the following components: methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, dimethyldimethoxysilane, ethyl silicate, or methyl silicate. The pH value of the acidic aqueous solution is 2-6; The pH adjusters used in acidic aqueous solutions are acetic acid, oxalic acid, nitric acid, hydrochloric acid, or sulfuric acid; The mass ratio of the organosilane to water is 1:(0.5-10). The stirring speed is 50-120 r / min; the temperature of the hydrolysate is controlled at 10-30℃. In step S2, the pH of the alkaline aqueous solution is 10-12; the stirring speed is 50-120 r / min. The pH adjusters used in alkaline aqueous solutions are ammonia, ethylenediamine, dimethylamine, and tetramethylammonium hydroxide. In step S3, the pore size of the filter membrane is 100-1000 nanometers; In step S4, the slurry is dried using a dryer at a temperature of 50-150°C. In step S5, a split box furnace, a tunnel kiln, or a roller kiln is used for calcination. The calcination temperature is 500-1200℃, and the calcination time is 3-10h.

3. The process for continuous preparation of monodisperse submicron spherical silica according to claim 2, characterized in that, The dryer can be a spray dryer, a vacuum target dryer, or a flash dryer.

4. The preparation apparatus used in the continuous preparation process of monodisperse submicron spherical silica as described in any one of claims 1 to 3, characterized in that, It includes a first device, a second device, and a third device connected in sequence; The first device includes two constant temperature hydrolysis tanks, each equipped with a stirring mechanism; the tank walls of the hydrolysis tanks are equipped with circulating cooling liquid pipelines, and the tank bodies of the hydrolysis tanks are connected to a cooling machine through inlet and outlet pipes, which are also connected to the circulating cooling liquid pipelines; both hydrolysis tanks are connected to a first metering pump. The second device includes an alkaline aqueous solution stirring tank, a stirring mechanism is installed inside the stirring tank, and a first metering pump is connected to the stirring tank. The third device includes a cylindrical device body, a filter membrane placed inside the device body, a second metering pump connected to the device body, and the device body is connected to the mixing tank through the third metering pump.

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