CN114620734B - Preparation method of micron silica gel with low dielectric constant and low dielectric loss - Google Patents
Preparation method of micron silica gel with low dielectric constant and low dielectric loss Download PDFInfo
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Abstract
The amorphous micron spherical silica particles with the core-shell structure and the certain internal pore channels of the micron silica gel comprise the following steps: (1) preparing silica sol slurry by a sol-gel method; (2) The silica sol slurry is formed by a spray drying method to obtain micron spherical particles; (3) The micron spherical particles and TEOS are subjected to hydrolysis-polymerization reaction to form sol solution; (4) And aging, washing, drying, roasting and hydrophobically modifying the sol solution to obtain the micron silica gel. The prepared micron silica gel has high strength and purity, particularly reduces the dielectric constant of the micron silica gel filler due to the space provided by the internally rich closed pore canal, has the advantages of strong hydrophobicity, low density, good fluidity, high insulativity, acid and alkali resistance and the like, can reduce the dielectric loss of a copper-clad plate, has the dielectric constant of 2.8-3.2 in the high-frequency (10 GHz) range, and can completely replace the inorganic oxide filler of the existing copper-clad plate.
Description
Technical Field
The invention relates to a preparation method of a micron silica gel material with low dielectric constant and low dielectric loss, belonging to the technical field of chemistry.
Background
The silicon dioxide is used as an inorganic nonmetallic material, has stable chemical property, no toxicity and no pollution to the environment. The high-temperature-resistant and low-expansion insulating material has good temperature resistance, acid and alkali corrosion resistance, high insulation and low expansion performance, and is widely applied to the fields of chemical industry, electronics, integrated circuits and the like.
With the continuous development of the electronic and electric industries, the sizes of electronic and electric equipment and elements thereof are smaller and the power is larger, in order to improve the transmission rate of signals or energy, reduce line loss and interference between signals or energy among different lines, the dielectric constant and dielectric loss of copper-clad Plate (PCB) materials are required to be reduced, and a method is generally adopted in which inorganic powder filler is added into the copper-clad plate to improve the mechanical, size and electrical performance of the cured resin so as to obtain the copper-clad plate with low dielectric constant; common inorganic fillers known in nature include aluminum oxide, aluminum hydroxide, magnesium hydroxide, zeolite, wollastonite, silicon oxide, magnesium oxide, calcium carbonate, calcium silicate, clay and the like, and the dielectric constants of the materials are all more than 4, so that the performance requirements of the high-frequency high-speed copper-clad plate cannot be met.
Aiming at the application requirements of a PCB dielectric layer, the micrometer silica microsphere filler mainly comprises the dimensions, the dimension distribution, the morphology, the surface properties, the structure, the purity and the like of particles, and the indexes are the synthesis difficulties of filler materials. In addition, how to control the production cost of the synthetic material, batch reproducibility, and especially consistency after large scale up is critical to industrialization and to form core competitiveness.
The invention provides for the kinetics of growth by surrounding micron silica particles; physical structural characteristics of silicon oxide; the key problems of the regulation and control characteristics of hydroxyl groups on the surface of the micron silicon oxide are that the micron silica gel is improved by a chemical method, and the micron silica gel is mainly realized through the following processes: firstly, high-purity spherical micron silica gel is obtained, then the high-purity spherical micron silica gel is chemically grown to form core-shell silica spherical powder with an internal porous structure, the low dielectric constant of the core-shell silica spherical powder is reduced by utilizing pore channels and pore volume in the core-shell silica spherical powder, and finally the hydrophobicity is modified, so that the fluidity of an inorganic filler can be improved by controllable micron spherical particle size on the premise of meeting the low dielectric constant, the strength of the inorganic filler can be improved by the controllable micron spherical particle size, the water absorption rate of the inorganic filler can be improved by the surface hydrophobicity modification, the particle size controllable preparation of the filler can be met by taking the micron silica gel as a copper-clad plate filler, the chemical property is stable, the insulativity and the thermal conductivity are improved, and the overall dielectric constant of the copper-clad plate can be reduced by ultra-strong hydrophobicity and lower dielectric constant.
The currently internationally available micron fillers are basically monopoly in the united states, japan, etc., greatly limiting the multipurpose use of 5G. Thus, the preparation of porous, small particle size microsilica sphere fillers has become a critical task for 5G technology PCB dielectric layers.
CN111471321a discloses a preparation method of porous light silica filler, comprising the following preparation steps: (1) pulping and cleaning; (2) freeze concentration; (3) drying and calcining; (4) crushing and grading; (5) high-temperature spraying and burning; (6) flotation classification. The prepared material has the advantages of high strength far higher than hollow materials such as hollow glass beads and the like, spherical morphology, high energy efficiency and limited productivity by using a traditional quartz fusion method, and the prepared material can obtain a required size range only by floatation classification and has low sphericity.
US20030096692A1 discloses a dense lead-free glass ceramic having a low dielectric constant and low dielectric loss for use in the manufacture of high frequency ceramic devices, the composition being amorphous and crystalline SiO2 and other inorganic oxides such as Al 2 O 3 ，BaO，Sb 2 O 3 ，V 2 O 5 ，CoO，MgO，B 2 O 3 ，Nb 2 O 5 At least one oxide of SrO and ZnO, the dielectric constant of the dense glass ceramic at 20MHz is 4.2-4.6, loss tangent (tan degree)<0.0025, the material of the invention can not meet the requirements of high-frequency high-speed copper clad laminate in the current stage 5G communication, and has complex components, poor fluidity and high manufacturing cost.
Disclosure of Invention
The invention is based on the requirements of miniaturization, light weight and thin type of 5G technology, and the micrometer silica filler with 30-50um in the market at present is difficult to meet the requirements, and the development of the silica filler with small particle size, small dielectric constant and small dielectric loss and the preparation route thereof are urgently needed. The invention surrounds the relation of the organization structure, the surface property and the dielectric property of the micron silicon oxide, and obtains controllable preparation technical routes of physical and chemical properties such as the dimension, the morphology, the structure, the property and the like of the micron silicon oxide, thereby realizing the stability preparation of the micron silicon oxide with low dielectric property and low loss property.
In order to achieve the above object, the present invention provides the following technical solutions:
1. preparation of high purity wet gel solution by sol-gel method
The water glass and inorganic acid are reacted and synthesized according to certain conditions, and the silica wet gel solution with certain granularity is formed through aging, solid-liquid separation, high-speed grinding and dispersion, then the silica powder is added into the silica wet gel sol, and then the acid and the organic amine are added and fully mixed to form silica sol slurry. The key technology of the scheme is how to control the microstructure of sol in synthesis, the addition of inorganic acid determines the microscopic scale of the final product, and proper conditions are key for molding. The water glass is commercial water glass, and the modulus is 3.0-3.3; the acid is one or more of inorganic acid such as hydrochloric acid, nitric acid, phosphoric acid and the like, and the molar ratio of the addition amount to the water glass is 1-3:1; the mass ratio of the added silicon oxide powder to the whole slurry is 10-30%, and the particle size of the silicon oxide powder is preferably 0.1-2 mu m; the organic amine is mainly one or more of ethylenediamine, ethanolamine, triethylenediamine, diethylenetriamine and hexamethylenetetramine, and the addition amount is that the mol ratio of SiO2 to the organic amine in the slurry system is 1:0.05-0.2.
2. Control of the scale range of micron spherical particles by spray drying
Spray granulating and forming the silica sol slurry, and controlling the size and the shape of the micron spherical particles by adjusting parameters, wherein the preparation scale range of the micron silica is as follows: d50 =1-50 μm, D100<25 μm, D90/D10<3.0; preferably d50=2-10 μm, d100<15 μm, D90/D10<2.0; the shape of the micron silicon oxide is spherical, and the sphericity rate is more than or equal to 98 percent. The spray drying atomization forming mode can be a disc atomizer, a single-nozzle atomizer or a double-fluid atomizer, the forming temperature is 150-200 ℃, the final dimension control of the micron silica gel is realized by adjusting parameters of the atomizer and configuring slurry, the slurry with different solid contents has great influence on the micron silica gel product, the internal structure of the micron silica gel is ensured to be complete and the pore volume is required to be as large as possible under the condition of meeting the requirement of D50, and a high-strength micron silica gel particle with rich pore channels is provided for subsequent products.
3. The micron spherical particles are hydrolyzed and polymerized with TEOS to form sol solution
Adding the preferable micron spherical particles obtained in the step (2) and 2-5 wt% of ammonia water solution into a reaction container, dissolving TEOS into ethanol, adding water, stirring to form solution A, slowly adding the solution A into the reaction container to form solution B with solid and liquid phases, and stirring fully. Wherein, micron spherical silicon oxide particles are used as a core, tetraethoxysilane is used as a shell silicon source, ammonia water is used as a catalyst, alcohols are used as solvents, and aging is carried out at the temperature of 40-80 ℃ to enable the outer layers of the spherical particles to uniformly grow into nano silica gel layers with certain thickness, thus forming a solution. Factors such as ammonia water consumption, TEOS consumption and reaction time have great influence on the morphology and physical parameters of the silica microspheres, PH control is required to be accurate in alkaline environment, uniform growth of the obtained micron silica gel shell can be ensured only by fully stirring, and the TEOS consumption is not excessive, so that agglomeration phenomenon among particles is prevented.
4. Ageing, vacuum drying, roasting, and hydrophobically modifying to obtain the micrometer silica gel filler
Firstly, aging the sol solution at 50-80 ℃ for 12-24hr, washing the sol solution with alcohol aqueous solution, wherein alcohol/water=1-3:1, then vacuum drying at 20-60 ℃, and roasting at 500-750 ℃ to obtain xerogel particles. And then carrying out surface modification on the xerogel particles by using one or two of TMCS and HMDS, wherein the preferable reaction temperature is 150-180 ℃, so that Si-OH groups are changed into Si-R groups, and the strong-hydrophobicity micron silica gel material is obtained.
The technological concept of the present invention is to control the size of the outer shape particle of micron silica gel product via spray drying, control the microscopic pore canal structure and the volume of the inner space of the particle via sol-gel process, to utilize the hydrolysis polymerization of TEOS to grow nanometer silica layer in the shell layer of the microsphere to seal the pore canal, and to modify the surface hydrophobicity of the microsphere via HMDS.
The preparation method of the micron silica gel comprises the following steps:
(1) Preparing silica sol slurry by a sol-gel method;
(2) The silica sol slurry is formed by a spray drying method to obtain micron spherical particles;
(3) The micron spherical particles and TEOS are subjected to hydrolysis-polymerization reaction to form sol solution;
(4) And aging, washing, drying, roasting and hydrophobically modifying the sol solution to obtain the micron silica gel.
Optionally, step (1) comprises the steps of:
after sol-gel reaction and aging, solid-liquid separation and dispersion are carried out on the mixture containing water glass and inorganic acid to form silica gel, then silica powder is added into the silica gel sol, and then inorganic acid and organic amine are added and fully mixed to form the silica sol slurry.
Optionally, the modulus of the water glass is between 3.0 and 3.3;
the inorganic acid is at least one of hydrochloric acid, nitric acid and phosphoric acid;
preferably, the molar ratio of the inorganic acid to the water glass is 1-3:1, a step of; the silicon oxide powder accounts for 10-30% of the mass of the silica sol slurry;
preferably, the silica powder has a particle size of 0.1 to 2 μm;
preferably, the organic amine is at least one selected from ethylenediamine, ethanolamine, triethylenediamine, diethylenetriamine and hexamethylenetetramine;
preferably, the moles of the organic amine are relative to the SiO in the slurry system 2 And the ratio of the total mole number of the organic amine is 1:0.05-0.2.
Optionally, in the step (2),
the scale range of the micrometer spherical particles: d50 =1-50 μm, D100<25 μm, D90/D10<3.0;
optionally, the micrometer-sized spherical particles have a range of dimensions: d50 =2-10 μm, D100<15 μm, D90/D10<2.0.
Optionally, the shape of the micron silicon oxide is spherical, and the sphericity rate is more than or equal to 98 percent.
Optionally, in the step (2),
the spray drying method is characterized in that the spray forming mode is selected from a high-speed disc atomizer, a single-nozzle atomizer or a double-fluid atomizer.
Optionally, the molding temperature is 150-200 ℃.
Optionally, step (3) comprises the steps of:
taking the micron spherical particles as a core, taking tetraethoxysilane as a shell silicon source, taking ammonia water as a catalyst, taking alcohols as a solvent, adding a surfactant, and aging at the temperature of 40-80 ℃ to enable the outer layers of the micron spherical particles to uniformly grow a nanometer silica gel layer, so as to form a sol solution.
Optionally, step (3) comprises the steps of: (3-1) mixing the micron spherical particles with D50=2-10 μm, D100<15 μm and D90/D10<2.0 obtained in the step (2) with 2-5% wt ammonia water solution, and adding a surfactant to obtain a first solution;
(3-2) obtaining a second solution comprising TEOS, ethanol, water, and a surfactant.
(3-3) mixing the first solution and the second solution to form the sol solution of both solid and liquid phases;
optionally, in step (3-1), the mass ratio of the micron spherical particles, 2-5% wt ammonia water solution and surfactant is 1:10-50:0.01-0.1;
in step (3-2), the mass ratio of TEOS to ethanol is 1:1-10, preferably 1:5-10.
Optionally, the surfactant is at least one selected from cetyltrimethylammonium bromide, dodecyltrimethylammonium chloride and octadecyl aminotrimethylammonium chloride.
Optionally, step (4) comprises the steps of:
aging the sol solution obtained in the step (3), washing, drying and roasting to obtain xerogel particles; and then carrying out surface hydrophobic modification on the xerogel particles by using one or two of TMCS and HMDS to obtain the micron silica gel.
Optionally, the washed solvent is an aqueous alcohol solution.
Optionally, in the alcohol aqueous solution, alcohol/water=1-3:1.
Optionally, the aging temperature is 50-80 ℃ and the aging time is 12-24hr.
Optionally, the drying is vacuum drying; the vacuum drying temperature is 20-60deg.C, and drying time is 12-36hr.
Optionally, the firing temperature is 500-800 ℃.
Alternatively, siO 2 The molar ratio of the catalyst to HMDS is 5-10:1.
Alternatively, the reaction temperature of the surface hydrophobic modification is 150-180 ℃.
Alternatively, the microsilica has a bulk specific gravity of 0.48-0.6g/cm 3 ；
Xx of the micron silica gel is xx-xx;
the water absorption rate of the micron silica gel is 0.45-0.6;
the dielectric constant of the micron silica gel at 10GHz is 2.92-3.11;
the particle size D50 of the micron silica gel is 5.73-9.98 mu m;
the specific surface area of the micron silica gel is 13.5-31.5m 2 /g。
In this application, "TEOS" refers to ethyl orthosilicate. "HMDS" refers to hexamethyldisilazane. "TMCS" refers to trimethylchlorosilane.
In the present application, "D50" means an average diameter corresponding to 50% of the cumulative distribution, "D100" means an average diameter corresponding to 50% of the calculated distribution, and "D90/D10" means a width coefficient reflecting the particle diameter distribution.
The beneficial effects that this application can produce include:
1) The micron silica gel prepared by the invention is amorphous silica with a core-shell structure and a certain internal pore canal, and has high strength and small density.
2) The surface of the micron silica gel prepared by the invention is modified by hydrophobicity, si-OH groups are changed into Si-R groups, the water absorption rate is low, and the fluidity is strong.
3) The micron silica gel prepared by the method is simple in preparation method, low in energy consumption and easy to realize industrialization.
4) The micron silica gel prepared by the invention can enable the porous silica micron spherical particle shell layer to grow a solid nanometer silica gel layer with a certain thickness, and an amorphous silica spherical particle filler with a closed pore structure as an outer shell layer is formed. The strong hydrophobic material micron silica gel prepared by the method has higher strength and purity than the conventional inorganic filler, particularly the space provided by the internal abundant closed pore canal, reduces the dielectric constant of the micron silica gel filler, is particularly suitable for being used as the inorganic silica filler of the copper-clad plate, has the advantages of strong hydrophobicity, low density, good fluidity, high insulativity, acid and alkali resistance and the like, can reduce the dielectric loss of the copper-clad plate, has the dielectric constant of 2.8-3.2 in the high-frequency (10 GHz) range, and can completely replace the inorganic oxide filler of the existing copper-clad plate.
Drawings
FIG. 1 is a flow chart of a process for preparing the silica gel with a micron size.
FIG. 2 is an SEM image of the product of example 1 of the present invention.
FIG. 3 is an SEM image of the product of example 3 of the present invention.
Detailed Description
The present application is described in detail below with reference to examples, but the present application is not limited to these examples.
Unless otherwise indicated, both the starting materials and the catalysts in the examples of the present application were purchased commercially.
The analytical method in the examples of the present application is as follows:
morphology analysis was performed using JSM-7800F.
Example 1
The preparation method of the micron silica gel with low dielectric constant and low dielectric loss comprises the following steps:
(1) Mixing 1250ml of water glass with the modulus of 3.3 and 3750ml of water, adding 2800ml of 1mol/L nitric acid at the temperature of 55 ℃, fully stirring, aging for 12 hours, washing with water, filtering, separating, and then grinding and dispersing at high speed to form a wet sol solution; 2000g of silica powder with an average particle size of 2 μm and 500g of hexamethylenetetramine are added into the wet sol solution and mixed thoroughly to form silica gel sol.
(2) Spray drying and granulating the sol obtained in the step (1), selecting a disc type atomizer with the rotating speed of 20000r/min, the temperature of an atomizing cavity of 150 ℃, selecting micron particles with D50=2-10 mu m after cyclone separation, putting the micron particles into a drying dish, and introducing inert gas to replace the air in the cavity of the particles for later use.
(3) 200g of the 2-10 mu m spherical particles obtained in the step (2) are added into 600ml of 2%wt ammonia water solution, the temperature is controlled at 60 ℃, and the solution B is formed by fully stirring; dissolving 100ml TEOS in 1000ml ethanol solution, adding cetyl trimethyl ammonium bromide as surfactant to form solution A, slowly adding A into solution B, aging at 80deg.C for 12hr.
(4) Repeatedly washing the solution in the step (3) with methanol water solution (1:1) to neutrality, vacuum filtering, vacuum drying at 20deg.C for 24hr, taking out, and roasting at 600deg.C for 12hr with quartz boat to obtain xerogel particles. Adding 50ml HMDS into 100g xerogel, placing into a hydrothermal reaction kettle, replacing air, vacuumizing, heating to 150 ℃ for reaction for 12hr.
Example 2:
the preparation method of the micron silica gel with low dielectric constant and low dielectric loss comprises the following steps:
(1) Mixing 1500ml of water glass with the modulus of 3.0 and 3500ml of water, adding 3000ml of 1mol/L nitric acid at the temperature of 50 ℃, fully stirring, aging for 12hr, washing with water, filtering, separating, grinding at high speed, and dispersing to form a wet sol solution; 2400g of silicon oxide powder with the particle size of 0.5 mu m and 800g of hexamethylenetetramine are taken and added into the wet sol solution to be fully mixed to form silica gel sol.
(2) Spray drying and granulating the sol obtained in the step (1), selecting a disc type atomizer with the rotating speed of 20000r/min, the temperature of an atomizing cavity of 200 ℃, selecting micron particles with D50=2-10 mu m after cyclone separation, putting the micron particles into a drying dish, and introducing inert gas to replace the air in the cavity of the particles for later use.
(3) 200g of the 2-10 mu m spherical particles obtained in the step (2) are added into 600ml of 2%wt ammonia water solution, the temperature is controlled at 50 ℃, and the solution B is formed by fully stirring; dissolving 100ml TEOS in 500ml ethanol solution, adding hexadecyl trimethyl ammonium bromide as surfactant to form solution A, slowly adding A into solution B, aging at 80deg.C for 24hr.
(4) Repeatedly washing the solution in the step (3) with methanol water solution (1:1) to neutrality, vacuum filtering, vacuum drying at 30deg.C for 12hr, taking out, and roasting at 750deg.C for 6hr to obtain xerogel particles. Adding 50ml HMDS into 100g xerogel, placing into a hydrothermal reaction kettle, replacing air, vacuumizing, heating to 150 ℃ for reaction for 24hr.
Example 3
The preparation method of the micron silica gel with low dielectric constant and low dielectric loss comprises the following steps:
(1) Mixing 2000ml of water glass with the modulus of 3.3 and 3000ml of water, adding 3200ml of 1mol/L nitric acid at the temperature of 80 ℃, fully stirring, aging for 24 hours, washing with water, filtering, separating, and then grinding and dispersing at high speed to form a wet sol solution; 2400g of silicon oxide powder with the diameter of 0.1 mu m and 800g of hexamethylenetetramine are taken and added into the wet sol solution to be fully mixed to form silica gel sol.
(2) Spray drying and granulating the sol obtained in the step (1), selecting a disc type atomizer at a rotating speed of 17500r/min, selecting micron particles with D50=5-10 mu m after cyclone separation at a atomizing cavity temperature of 180 ℃, putting the micron particles into a drying dish, and introducing inert gas to replace the air in the cavity of the particles for later use.
(3) 120g of the 5-10 mu m spherical particles obtained in the step (2) are added into 200ml of 5%wt ammonia water solution, the temperature is controlled at 50 ℃, and the solution B is formed by fully stirring; dissolving 100ml TEOS in 500ml ethanol solution, adding hexadecyl trimethyl ammonium bromide as surfactant to form solution A, slowly adding A into solution B, aging at 80deg.C for 24hr.
(4) Repeatedly washing the solution in the step (3) with methanol water solution (1:1) to neutrality, vacuum filtering, vacuum drying at 50deg.C for 12hr, taking out, and roasting at 750deg.C for 6hr to obtain xerogel particles. Adding 50ml HMDS into 100g xerogel, placing into a hydrothermal reaction kettle, replacing air, vacuumizing, heating to 180 ℃ for reaction for 12hr.
Example 4
The preparation method of the micron silica gel with low dielectric constant and low dielectric loss comprises the following steps:
(1) Mixing 1250ml of water glass with the modulus of 3.3 and 3750ml of water, adding 2800ml of 1mol/L nitric acid at the temperature of 55 ℃, fully stirring, aging for 12 hours, washing with water, filtering, separating, and then grinding and dispersing at high speed to form a wet sol solution; 2000kg of 1 μm silicon oxide powder and 500kg of hexamethylenetetramine were added to the wet sol solution and mixed thoroughly to form a silica gel sol.
(2) Spray drying and granulating the sol obtained in the step (1), selecting a disc type atomizer with the rotating speed of 20000r/min, the temperature of an atomizing cavity of 170 ℃, selecting micron particles with D50=2-10 mu m after cyclone separation, putting the micron particles into a drying dish, and introducing inert gas to replace the air in the cavity of the particles for later use.
(3) 200g of the 2-10 mu m spherical particles obtained in the step (2) are added into 600ml of 2%wt ammonia water solution, the temperature is controlled at 50 ℃, and the solution B is formed by fully stirring; dissolving 100ml TEOS in 500ml ethanol solution, adding hexadecyl trimethyl ammonium bromide as surfactant to form solution A, slowly adding A into solution B, aging at 80deg.C for 24hr.
(4) Repeatedly washing the solution in the step (3) with methanol water solution (1:1) to neutrality, vacuum filtering, vacuum drying at 60deg.C for 24hr, taking out, and roasting at 500 deg.C for 12hr to obtain xerogel particles. Adding 200ml HMDS into 100g xerogel, placing into a hydrothermal reaction kettle, replacing air, vacuumizing, heating to 180 ℃ for reaction for 24hr.
Example 5
The materials prepared in examples 1-4 were subjected to morphology testing, the test results are shown in fig. 2 and 3, and as can be seen in fig. 3, the overall particle diameter distribution is concentrated, the overall sphericity is high, and the surface is smooth; as can be seen from fig. 2, the shell-core structure is obvious, the inside is rich porous structure, and the outer layer is compact shell structure; other examples produced materials with morphology similar to that of figure 3.
Examples 1-4 materials were tested for dielectric constant at 10GHz using the prepared microsilica as filler
1) And (3) a glue mixing process: 5A glue, solid content 65%, filler content 20%, big glue GT247.7s.
2) And (3) gluing: the table-jia 2116 cloth is set,
3) And (3) pressing plates: 8 x 2116, 35 mu plain copper foil, 190/90 procedure
Examples 1-4 characterization data sheets
The foregoing description is only a few examples of the present application and is not intended to limit the present application in any way, and although the present application is disclosed in the preferred examples, it is not intended to limit the present application, and any person skilled in the art may make some changes or modifications to the disclosed technology without departing from the scope of the technical solution of the present application, and the technical solution is equivalent to the equivalent embodiments.
Claims (15)
1. The preparation method of the micron silica gel is characterized by comprising the following steps of:
(1) Preparing silica sol slurry by a sol-gel method;
(2) The silica sol slurry is formed by a spray drying method to obtain micron spherical particles;
(3) The micron spherical particles and TEOS are subjected to hydrolysis-polymerization reaction to form sol solution;
(4) Aging, washing, drying, roasting and hydrophobically modifying the sol solution to obtain the micron silica gel;
step (1) comprises the steps of:
performing sol-gel reaction and aging on a mixture containing water glass and inorganic acid, performing solid-liquid separation, dispersing to form silica gel, adding silica powder into the silica gel sol, and then adding inorganic acid and organic amine to be fully mixed to form the silica sol slurry;
the mol ratio of the inorganic acid to the water glass is 1-3:1, a step of; the silicon oxide powder accounts for 10-30% of the mass of the silica sol slurry;
the scale range of the micrometer spherical particles: d50 =2-10 μm, D100<15 μm, D90/D10<2.0;
step (3) comprises the following steps:
taking the micron spherical particles as a core, taking tetraethoxysilane as a shell silicon source, taking ammonia water as a catalyst, taking alcohols as a solvent, adding a surfactant, and aging at the temperature of 40-80 ℃ to enable the outer layers of the micron spherical particles to uniformly grow a nanometer silica gel layer, so as to form a sol solution;
step (3) comprises the following steps:
(3-1) mixing the micron spherical particles with D50=2-10 μm, D100<15 μm and D90/D10<2.0 obtained in the step (2) with 2-5% wt ammonia water solution, and adding a surfactant to obtain a first solution;
(3-2) obtaining a second solution containing TEOS, ethanol;
(3-3) mixing the first solution and the second solution to form the sol solution of both solid and liquid phases;
in the step (3-1), the mass ratio of the micron spherical particles, 2-5% wt of ammonia water solution and the surfactant is 1:10-50:0.01-0.1;
in the step (3-2), the mass ratio of TEOS to ethanol is 1:1-10;
step (4) comprises the following steps:
aging the sol solution obtained in the step (3), washing, drying and roasting to obtain xerogel particles; then mixing the xerogel particles with HMDS to carry out surface hydrophobic modification to obtain the micron silica gel;
the micrometer silica gel has bulk specific gravity of 0.48-0.6g/cm 3 ；
The water absorption rate of the micron silica gel is 0.45-0.6;
the dielectric constant of the micron silica gel at 10GHz is 2.92-3.11;
the particle size D50 of the micron silica gel is 5.73-9.98 mu m;
the specific surface area of the micron silica gel is 13.5-31.5m 2 /g。
2. The method according to claim 1, wherein,
the modulus of the water glass is 3.0-3.3;
the inorganic acid is at least one selected from hydrochloric acid, nitric acid and phosphoric acid.
3. The method of claim 1, wherein the silica powder has a particle size of 0.1 to 2 μm.
4. The method according to claim 1, wherein the organic amine is at least one selected from ethylenediamine, ethanolamine, triethylenediamine, diethylenetriamine, and hexamethylenetetramine.
5. The method according to claim 1, wherein the molar number of the organic amine is equal to the SiO in the slurry system 2 And the ratio of the total mole number of the organic amine is 1:0.05-0.2.
6. The method according to claim 1, wherein the sphericity of the micron spherical particles is not less than 98%.
7. The process according to claim 1, wherein in step (2),
the spray drying method is characterized in that the spray forming mode is selected from a high-speed disc atomizer, a single-nozzle atomizer or a double-fluid atomizer.
8. The method of claim 1, wherein the molding temperature is 150-200 ℃.
9. The method according to claim 1, wherein in the step (3-2), the mass ratio of TEOS to ethanol is 1:5-10.
10. The method according to claim 1, wherein the surfactant is at least one selected from cetyltrimethylammonium bromide, dodecyltrimethylammonium chloride and octadecyl-aminotrimethylammonium chloride.
11. The method according to claim 1, wherein the washed solvent is an aqueous alcohol solution.
12. The method according to claim 1, wherein the aging temperature is 50 to 80 ℃ and the aging time is 12 to 24hr.
13. The method of claim 1, wherein the drying is vacuum drying; the vacuum drying temperature is 20-60deg.C, and drying time is 12-36hr.
14. The method of claim 1, wherein the firing temperature is 500-800 ℃.
15. The method of claim 1, wherein the surface hydrophobically modified reaction temperature is 150-180 ℃.
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