Hollow silica microspheres and their preparation method

Abstract

This invention discloses a hollow silica microsphere and its preparation method. The preparation method includes mixing a template sphere solution with an alkaline catalyst to obtain solution A, and separately mixing the template sphere solution with a silicon source to obtain solution B. After heating solutions A and B, they are pumped into the two inlet pipes of a three-way pipe through a metering pump, so that they collide and mix at the confluence of the three-way pipe and flow out through the outlet pipe. The outflowing product is aged, ultra-fine and gradient calcined to obtain hollow silica microspheres. The hollow silica microspheres prepared by this invention are monodisperse microspheres.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic powder materials technology, specifically to a hollow silica microsphere and its preparation method. Background Technology

[0002] Hollow silica microspheres, ranging in size from nanometers to micrometers, possess a hollow cavity structure. Therefore, compared to solid spherical silicon, they exhibit lower density and unique mechanical, optical, and electrical physical properties, leading to significant application value. Especially in the integrated circuit packaging and copper-clad laminate (CCL) industries, hollow silica serves as a key raw material, not only reducing costs but also lowering the coefficient of thermal expansion and improving substrate modulus and heat resistance. However, damage to hollow silica microspheres directly degrades their performance in applications. For example, damage increases density and specific surface area, leading to increased dielectric constant, severe thickening, difficulty in good dispersion in resins, reduced peel strength, lower glass transition temperature, and increased losses when used as fillers in CCLs.

[0003] Therefore, providing completely monodisperse, unbroken hollow silica microspheres is particularly crucial for applications.

[0004] However, for a long time, the production of micron-sized hollow silica microspheres has not been achieved due to challenges such as complex preparation processes, long cycles, numerous process control points, and limitations in equipment technology. The traditional template method combined with a batch reactor is currently the most widely used technical solution. However, during the scale-up process, it is subject to the scale-up effect, resulting in problems such as low mass and heat transfer efficiency, uncontrollable reaction process, and easy agglomeration. Especially in the stage of coating silica on the surface of the template spheres, hard agglomeration is very likely to occur. Even if the microspheres are separated by ultrafine means at the later stage, the breakage rate of hollow microspheres will increase. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a hollow silica microsphere and its preparation method, so as to prepare completely monodisperse, unbroken hollow silica microspheres.

[0006] To achieve the above-mentioned objectives, the present invention proposes the following technical solution: a method for preparing hollow silica microspheres, comprising the following steps:

[0007] S1. Mix the template ball solution with the alkaline catalyst to obtain solution A;

[0008] S2. Separately, mix the template ball solution with the silicon source to obtain solution B;

[0009] S3. After heating the A solution and the B solution, pump them into the two inlet pipes of the three-way pipe through a metering pump, control the flow rate and inflow time of the A solution and the B solution, so that they collide and mix at the confluence of the three-way pipe and flow out through the outlet pipe.

[0010] S4. After aging, ultrafine and gradient calcination of the effluent, monodisperse, undamaged hollow silica microspheres are obtained.

[0011] Preferably, the method for preparing the template sphere solution includes:

[0012] S11. Mix and stir 1-6% by mass of polyvinylpyrrolidone, 5-25% by mass of styrene, 0.2-1.2% by mass of azobisisobutyronitrile, 0.01-10% by mass of cationic comonomer acryloyloxyethyltrimethylammonium chloride, water and ethanol.

[0013] S12. The obtained uniformly mixed solution is purged with nitrogen gas for 10-30 minutes, heated to 50-80℃ and stirred continuously for 10-30 hours to obtain the template ball dispersion.

[0014] Preferably, the alkaline catalyst is selected from one or more of ammonia, sodium hydroxide, dodecylamine, and isopropylamine.

[0015] Preferably, after the template ball solution and the alkaline catalyst are mixed in S1, the pH of solution A is 7.5-11.

[0016] Preferably, the silicon source is selected from one or both of alkylsilanes and alkoxysilanes.

[0017] Preferably, the template ball solutions in S1 and S2 are each half-volume template ball solutions, and the ratio of silicon source to total template ball solution is 0.08 to 0.3:1.

[0018] Preferably, in step S3, the heating temperature of solution A and solution B is 25-70℃, the flow rate ratio of the metering pump is the volume ratio of solution A to solution B, and the mixing reaction time is 0.5-30 min.

[0019] Preferably, the gradient calcination includes first heating the dried product to 350-700℃ at a rate of 0.1-0.5℃ / min and holding it at that temperature for 2-6 hours, and then heating it to 800-1100℃ at a rate of 1-3℃ / min and holding it at that temperature for 2-6 hours.

[0020] The three-way pipe in S3 includes two inlet pipes for adding solution A and solution B, a confluence of the two inlet pipes, and an outlet pipe connected to the confluence. Solution A and solution B rapidly mix and collide at the confluence, and the product of the collision reaction flows out through the outlet pipe. The present invention is not limited to the specific structure of the three-way pipe and the metering pump.

[0021] Preferably, the aging temperature is 25-70℃, the aging time is 2-24h, and the ultrafine method is air jet milling with an air pressure of 0.1-0.7MPa.

[0022] Preferably, the preparation method of the present invention further includes washing and drying treatment before ultrafine processing.

[0023] The present invention also proposes a hollow silica microsphere, which is prepared by the preparation method of the present invention.

[0024] Preferably, the median particle size of the hollow silica microspheres is 0.3-5 μm, and the breakage rate is ≤3%.

[0025] Unlike the synthesis of solid silica spheres, the process of coating template spheres with a silica shell is prone to agglomeration and adhesion. This means that two or more template spheres may interlock, sharing a single shell interface. When the template spheres are subsequently removed and the interlocked hollow spheres are separated using ultrafine methods, numerous holes are created. The method of this invention solves this hole problem, resulting in completely monodisperse, unbroken hollow silica microspheres. A key factor is the use of a rapid liquid-liquid impaction method via a three-way pipe, which enhances mass transfer. The spheres move relative to each other during impact, overcoming the static state between spheres in the reactor (agglomeration mainly occurs because two or more adjacent spheres move together in the system, remaining relatively stationary, and their SiOH surfaces easily condense and bond together. Relative movement between spheres largely avoids this phenomenon). Furthermore, the silicon source is unlikely to contact and form interlocks with adjacent, relatively moving template spheres during hydrolysis and condensation on the template sphere surface.

[0026] Furthermore, the template ball solution of the present invention not only provides template balls for coating, but can also serve as a diluent to carry alkaline catalysts and silicon sources to obtain solutions A and B. Due to the principle of "like dissolves like," solutions A and B are more easily mixed uniformly in the pipeline, further solving the agglomeration problem. In a preferred embodiment of the present invention, since the template ball solution is evenly distributed in solutions A and B, the flow rate difference between the two liquids can be made similar, allowing them to mix in the expected proportion and avoiding the effects of counteracting.

[0027] Furthermore, the present invention performs ultrafine treatment before calcination to break up the soft agglomerates generated during the drying process, ensuring that the material remains loose before calcination and avoiding caking and sticking after calcination.

[0028] Furthermore, according to TGA test data analysis, the organic matter inside silica needs to be expelled through the mesopores in the surface shell generated during the self-assembly of silica particles at a lower thermal decomposition temperature and a slower heating rate. After expulsion, the mesopores and loose particle stacking structure in the surface shell are densified through higher temperatures. Therefore, the gradient calcination method used in the preferred embodiment of the present invention is beneficial for densifying the microsphere shell, improving the compressive strength of the microspheres, and reducing the specific surface area.

[0029] The method of this invention has wide applicability; different silicon sources and different catalysts can be combined by adjusting the flow rate and reaction time. Attached Figure Description

[0030] Figure 1 This is a SEM image of the hollow silica microspheres obtained in Example 1 of the present invention;

[0031] Figure 2 This is a particle size distribution diagram of the hollow silica microspheres obtained in Example 1 of the present invention.

[0032] Figure 3 This is a SEM image of the hollow silica microspheres obtained in Example 2 of the present invention;

[0033] Figure 4 This is a SEM image of the hollow silica microspheres obtained in Example 3 of the present invention;

[0034] Figure 5 This is a SEM image of the hollow silica microspheres obtained in Example 4 of the present invention;

[0035] Figure 6 This is a SEM image of the hollow silica microspheres obtained in Example 5 of the present invention;

[0036] Figure 7 This is a SEM image of the hollow silica microspheres obtained in Comparative Example 6 of this invention. Detailed Implementation

[0037] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0038] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated ingredients or components without excluding other ingredients or other components.

[0039] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0040] Example 1

[0041] Step 1.1: Mix half of the synthesized template ball solution with ammonia in a mixing tank for 30 minutes and heat to 50°C to obtain solution A. After adding ammonia, the pH of solution A is 10.3.

[0042] Step 1.2: Mix half of the synthesized template ball solution with tetraethyl silicate in a mixing tank for 30 min and heat to 50°C to obtain solution B. The ratio of tetraethyl silicate to total template ball solution is 0.15:1.

[0043] Step 1.3: Pump solution A and solution B into the two narrow inlet pipes of the three-way pipe using two metering pumps. The flow rate of the two metering pumps is set according to the volume ratio of solution A to solution B. The mixture is mixed and reacted for 0.5 minutes before flowing out.

[0044] Step 1.4: Aging was carried out in an aging tank with stirring for 4 hours at an aging temperature of 50℃. The synthesized product was washed by plate and frame filter press, dried at 70℃, and then ultrafine-processed under a gas flow pressure of 0.2MPa. The final ultrafine product was first heated to 400℃ at a rate of 0.3℃ / min and held for 5 hours, then heated to 1050℃ at a rate of 1.5℃ / min and held for 4 hours to obtain monodisperse, non-destructible hollow silica microspheres.

[0045] The scanning electron microscope (SEM) images of the above monodisperse, unbreakable hollow silica microspheres are shown below. Figure 1 As shown, from Figure 1 As can be seen, the obtained hollow silica microspheres are spherical and have a uniform particle size distribution, and are combined with Figure 2 As shown, the hollow silica microspheres exhibit a single peak with a median particle size D50 of 0.869 μm; the test showed a breakage rate of 2.8%, indicating that the hollow spheres have an extremely low breakage rate.

[0046] Example 2

[0047] The preparation process of this embodiment is exactly the same as that of Embodiment 1 above, except that: the amount of ammonia added is changed, and the pH of solution A is 9.5 after the ammonia is added; the amount of tetraethyl silicate added is changed, and the ratio of tetraethyl silicate to total template ball solution is 0.2:1.

[0048] like Figure 3As shown, the prepared monodisperse, unbroken hollow silica microspheres are spherical with complete shape and uniform particle size distribution, with a median particle size D50 of 1.113 μm; the test showed that the breakage rate was 1%, indicating that the breakage rate of the hollow spheres was extremely low.

[0049] Example 3

[0050] The preparation process of this embodiment is exactly the same as that of Embodiment 1 above, except that: the amount of ammonia added is changed, and the pH of solution A is 11 after the ammonia is added; the amount of tetraethyl silicate added is changed, and the ratio of tetraethyl silicate to total template ball solution is 0.08:1; and the mixing reaction time is adjusted to 1 min.

[0051] like Figure 4 As shown, the obtained monodisperse, unbroken hollow silica microspheres have slight depressions, but the particle size distribution is uniform, with a median particle size D50 of 0.927 μm; the test showed a breakage rate of 2.5%, indicating that the breakage rate of the above hollow spheres is extremely low.

[0052] Example 4

[0053] The preparation process of this embodiment is exactly the same as that of Embodiment 1 above, except that: the alkaline catalyst is replaced with sodium hydroxide, and the pH of solution A is 11 after the addition of sodium hydroxide; the silicon source is replaced with methyltrimethoxysilane, the ratio of methyltrimethoxysilane to total template sphere solution is 0.25:1, and the mixing reaction time is adjusted to 3 min.

[0054] like Figure 5 As shown, the monodisperse, unbreakable hollow silica microspheres prepared in this embodiment, after grinding tests, exhibited intact spherical shape, uniform particle size distribution, median particle size D50 = 1.23 μm, and relatively thick microsphere walls (145.2 nm as indicated in the figure), thus providing sufficient strength. The tested breakage rate was 1%, indicating an extremely low breakage rate for the hollow microspheres.

[0055] Example 5

[0056] The preparation process of this embodiment is exactly the same as that of Embodiment 1 above, except that the heating temperature of solution A and solution B is 25°C, the mixing reaction time is 1 min, and the aging temperature is 25°C.

[0057] like Figure 6 As shown, the obtained hollow silica microspheres are spherical and have a uniform particle size distribution, with a median particle size D50 of 1.053 μm; the test showed that the breakage rate was 2%, indicating that the breakage rate of the hollow spheres was extremely low.

[0058] Comparative Example 6

[0059] The difference between this embodiment and Embodiment 1 is that: solution A and solution B are mixed and reacted in a reaction vessel, and the dried product is not subjected to ultrafine treatment.

[0060] Step 6.1: The synthesized template ball solution and ammonia water are stirred and mixed in a reaction vessel for 30 minutes and heated to 50°C to obtain solution A. After adding ammonia water, the pH of solution A is 10.3.

[0061] Step 6.2: Tetraethyl silicate is used as solution B. While stirring, solution B is added to solution A. The mixture is reacted in a reactor at 50°C for 4 hours to obtain the synthesized product. The ratio of tetraethyl silicate to template ball solution is 0.15:1.

[0062] Step 6.3: The synthesized product is washed by plate and frame filter press, dried at 70℃, then heated to 400℃ at 0.5℃ / min and held for 5h, and then heated to 1050℃ at 1.5℃ / min and held for 4h to obtain hollow silica microspheres.

[0063] Scanning electron microscope image of the obtained hollow silica microspheres is shown below. Figure 7 As shown, the hollow silica microspheres obtained were severely aggregated, and there were many holes caused by the separation of the hard agglomerates formed by the adhesion. The breakage rate reached 30%.

[0064] The description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for producing hollow silica microspheres, characterized by, The method comprises the following steps: S1. mixing a template ball solution with an alkaline catalyst to obtain an A solution; S2. mixing another template ball solution with a silicon source to obtain a B solution; S3. after heating the A solution and the B solution, pumping them into two inlet pipes of a three-way pipe through metering pumps respectively, controlling the flow rate and flow time of the A solution and the B solution, so that they are mixed by colliding at the convergence of the three-way pipe, and then flowing out through an outlet pipe; S4. obtaining monodisperse, non-broken hollow silica microspheres after aging, superfine treatment and gradient calcination of the outflow product.

2. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: The preparation method of the template ball solution comprises: S11. mixing 1-6% of polyvinylpyrrolidone by mass percentage, 5-25% of styrene by mass percentage, 0.2-1.2% of azobisisobutyronitrile by mass percentage, 0.01-10% of cationic comonomer acryloyloxyethyl trimethyl ammonium chloride by mass percentage, water and ethanol, and stirring; S12. after the obtained mixed uniform solution is passed through nitrogen, the solution is heated and continuously stirred for a certain time to obtain a template ball solution.

3. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: The alkaline catalyst is selected from one or more of ammonia, sodium hydroxide, dodecylamine and isopropylamine.

4. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: After the template ball solution in S1 is mixed with the alkaline catalyst, the PH value of the A solution is 7.5-11.

5. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: The silicon source is selected from one or both of alkylsilane and alkoxysilane.

6. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: The template ball solution in S1 and S2 is half of the template ball solution respectively, and the mass ratio of the silicon source to the total template ball solution is 0.08-0.3:

1.

7. The method for preparing hollow silica microspheres according to claim 1, characterized in that, In S3, the heating temperature of the A solution and the B solution is 25-70℃, and the mixing reaction time is 0.5-30 min.

8. The method of claim 1, wherein the hollow silica microspheres are prepared by the steps of: The gradient calcination comprises first heating the dried product to 350-700℃ at a rate of 0.1-0.5℃ / min and maintaining the temperature for 2-6h, and then heating to 800-1100℃ at a rate of 1-3℃ / min and maintaining the temperature for 2-6h.

9. The method for preparing hollow silica microspheres according to claim 1, characterized in that, The aging temperature is 25-70℃, and the aging time is 2-24h. The superfine method is airflow milling superfine, and the airflow pressure is 0.1-0.7MPa.

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