JP4993811B2 - Modified sol-gel silica particles and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to novel modified sol-gel silica particles. Specifically, it is a sol-gel method silica particle whose fluidity is remarkably improved. In particular, the spherical particle provides a modified sol-gel method silica particle useful as a spacer for liquid crystal.
[0002]
[Prior art]
The sol-gel method silica particles are produced by hydrolyzing an alkyl silicate in the presence of a hydrolysis catalyst in an aqueous solvent containing alcohol and drying the generated silica particles.
[0003]
According to the above method, spherical and monodisperse sol-gel method silica particles are easily obtained, and such sol-gel method silica particles are suitably used for applications as spacers for liquid crystals. In the above applications, the sol-gel method silica particles are preferably spherical silica particles having a particle size of 1 μm or more and high monodispersity with uniform particle sizes.
[0004]
As a method for producing such sol-gel method silica particles, for example, in JP-A-4-240112, JP-A-4-21515, JP-A-8-337413, JP-A-10-203820, etc. A specific manufacturing method has been proposed.
[0005]
The above-mentioned conventional sol-gel method for producing silica particles is generally a technique for specifying various conditions for producing silica particles. The produced silica particles are separated from a solvent and dried, and optionally fired. Thus, sol-gel silica particles are obtained.
[0006]
However, among the silica particles obtained by the sol-gel method, those having a particle diameter in the submicron to several μm range have room for improvement in fluidity.
[0007]
That is, the above sol-gel silica particles are often suspended in a hopper supplied to a spreader in a spacer application or it is difficult to spray a certain amount from a spray nozzle. Further, not only spherical particles but also sol-gel silica particles having poor fluidity have a problem of poor dispersibility in resins or the like even when used as a filler for resins, for example.
[0008]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide modified sol-gel silica particles having excellent fluidity.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have made extensive studies to solve the above problems. As a result, the sol-gel method obtained by subjecting the sol-gel method silica particles obtained by a known method to a specific ratio based on the infrared spectrum based on hydrogen-bonded silanol groups and isolated silanol groups It has been found that silica particles exhibit extremely high fluidity, and the present invention has been completed.
[0010]
The reformed sol - gel method silica particles are have you in infrared spectrum measured in diffuse reflection method, the peak area based on the silanol groups hydrogen bond with peak area (A1) based on the isolated silanol group (A2) The modified sol-gel method silica particles having a ratio (A1 / A2) of 0.03 or more. The present invention, the reformer sol - a manufacturing method of gel method silica particles, i.e., the sol in the presence of (I) ammonia - give silica cake (1) comprising silica particles gel method, the silica cake (1) A silica cake (2) in which the solvent is replaced with alcohol by washing with ammonia after washing with alcohol and then with another alcohol washing, and the silica cake (2) is heated at 100 to 200 ° C., (II) A silica cake (3) containing silica particles is obtained by a sol-gel method. After the silica cake (3) is pickled to obtain a silica cake (4), the silica cake (4) is immersed in aqueous ammonia, followed by alcohol. A silica cake (5) in which the solvent is substituted with alcohol by washing is obtained, and the production method of heating the silica cake (5) at 100 to 200 ° C., and III) A silica cake (3) containing silica particles is obtained by a sol-gel method, and the silica cake (3) is pickled to obtain a silica cake (4), and then the silica cake (4) is added in the presence of ammonia gas. It is the manufacturing method heated at -200 degreeC.
[0011]
In the present invention, the measurement of the infrared spectrum by the diffuse reflection method is performed when a mixture of KBr powder and silica particles in a mortar is poured into a cup-shaped container and infrared light is diffusely reflected on the sample surface. This is a method for measuring the absorption spectrum.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the silica particles according to the present invention will be described in detail.
[0013]
This onset Ming sol - manufacturing method of gel method silica particles, a method of hydrolysis and polycondensation of alkyl silicate in an aqueous solvent is used without any particular limitation.
[0014]
The alkyl silicate can be represented by the general formula Si (OR) ₄ . In formula, R is a C1-C7 alkyl group, Preferably it is a C1-C4 alkyl group. Examples of such alkyl silicates include methyl silicate (tetramethoxysilane), ethyl silicate (tetraethoxysilane), propyl silicate (tetrapropoxysilane), and butyl silicate (tetrabutoxysilane).
[0015]
As the aqueous solvent, an alcohol aqueous solution is preferable in order to obtain spherical sol-gel silica particles having high monodispersibility. As the alcohol, monoalcohols such as methanol, ethanol, isopropyl alcohol and butanol may be used alone or in admixture of two or more, and polyhydric alcohols such as ethylene glycol and glycerin may be added to the above. May be.
[0016]
Furthermore, it is preferable that an alkali is present in the aqueous solvent as a hydrolysis catalyst. As the alkali, ammonia, potassium hydroxide, sodium hydroxide, various amines, and the like are used, and among them, ammonia is preferably used.
[0017]
The hydrolysis reaction is performed by adding an alkyl silicate to an aqueous solvent for hydrolysis and polycondensation to produce a gel.
[0018]
In this case, the gel body can be obtained in the form of particles or a lump by adjusting the type of the aqueous solvent, reaction conditions, and the like. These conditions can be appropriately selected from known conditions.
[0019]
And the sol-gel method silica obtained as a lump can be made into sol-gel method silica particles by pulverizing this.
[0020]
Among the sol-gel method silica particles obtained as described above, those to which the method of the present invention is suitably applied have a lower limit of the average particle diameter of 0.01 μm, preferably 0.1 μm, and particularly preferably 0.8. The upper limit of the average particle diameter is 100 μm, preferably 30 μm, especially 20 μm.
[0021]
In addition, in the use of spacer silica, silica particles having a standard deviation value of 30% or less, preferably 20% or less, more preferably 10% or less are particularly suitable as an index representing monodispersity.
[0022]
The modified sol-gel method silica particles of the present invention are characterized by the peak area (A1) based on isolated silanol groups in the infrared spectrum measured by the diffuse reflection method in the silica particles obtained by the sol-gel method. The ratio (A1 / A2) of the peak areas (A2) based on hydrogen-bonded silanol groups is 0.03 or more, preferably 0.05 or more, more preferably 0.05 to 0.5, and still more preferably 0.00. It is in being adjusted to 1-0.4.
[0023]
The peak based on the isolated silanol group herein, a peak having a peak top at a wavenumber ^{3740cm -1 ~3760cm} -1, and the peak based on the silanol groups hydrogen bond, a peak at a wavenumber of ^{3640cm -1 ~3680cm} -1 It is a peak with a top.
[0024]
The infrared spectrum by diffuse reflection is measured by the following method, for example.
[0025]
In the background, the KBr powder crushed in a mortar is ground into a cup-shaped measuring container, set in a device, and an absorption spectrum is measured when infrared light is diffusely reflected on the sample surface. For the sample, after the silica particles are dried at 700 ° C. for 10 hours, the silica particles and the KBr powder are mixed well in a mortar, and then put into a cup-shaped measuring container and measured in the same manner as the background.
[0026]
A1 and A2 are values obtained by the following method. That is, if it demonstrates according to FIG. 1 which shows a typical spectrum, the peak area (A1) based on an isolated silanol group will be based on the straight line which connects two points of wave numbers 3720cm < ^-1 > (B1) and 3760cm < ^-1 > (B2). As the peak area between B1 and B2. The peak area (A2) based on the hydrogen-bonded silanol group is the peak area between B3 and B4 when the straight line connecting the two points of wave numbers 3500 cm ⁻¹ (B3) and 3790 cm ⁻¹ (B4) is used as the baseline. It is obtained as a value (A3−A1) obtained by subtracting A1 from (A3).
[0027]
The peak area indicated by A1 indicates the relative amount of isolated silanol groups present on the surface of the sol-gel method silica particles, and the peak area indicated by A2 indicates the hydrogen-bonded silanol groups present on the surface of the particles. The relative amounts are shown respectively.
[0028]
Conventional sol-gel silica particles generally have a low A1 / A2 ratio and cannot satisfy the above range of the present invention. The conventional sol-gel method silica particles having such a low ratio have poor fluidity.
[0029]
On the other hand, the modified sol-gel method silica particles of the present invention exhibit extremely excellent fluidity by increasing the ratio of the isolated silanol groups when the ratio is equal to or higher than the specific value.
[0030]
In the present invention, in order to obtain an infrared spectroscopic spectrum by the diffuse reflection method with good reproducibility, as a pretreatment for measurement, it is heated and dried in air at 700 ° C. for 10 hours and adsorbed on silica particles. An operation for removing moisture is performed.
[0031]
In addition, the said heat drying is performed in order to measure the infrared spectroscopy spectrum of a sol-gel method silica particle. Therefore, the sol-gel method silica particles satisfying the scope of the present invention in such measurement show good fluidity both before and after heat drying. Sol-gel silica particles.
[0032]
The method for producing the modified sol-gel method silica particles of the present invention is not particularly limited. A suitable production method includes a method in which sol-gel silica particles are heated in a gas at a temperature of 100 ° C. or higher in the presence of ammonia.
[0033]
Conventionally, when heat treatment is performed in the presence of ammonia, an irritating odor is generated and harmful, so when drying sol-gel silica particles, after washing with pure water or removing ammonia with an evaporator, The method of heating was common.
[0034]
However, the present inventors have industrially advantageously used the modified sol-gel of the present invention by a method of heat-treating sol-gel silica particles in a gas at a temperature of 100 ° C. or higher in the presence of ammonia. It was found that method silica particles were obtained.
[0035]
If the temperature of the heat treatment is less than 100 ° C., it takes too much time. Moreover, although the upper limit of this heat processing temperature is less than the decomposition temperature of ammonia, 300 degreeC and especially 200 degreeC are suitable from economical efficiency.
[0036]
As said gas, air is used from economical efficiency. The concentration of ammonia in the gas is not particularly limited, but is preferably 10 ppm or more, and preferably 100 ppm or more. On the other hand, since ammonia is harmful, there is a danger at high concentrations. Accordingly, a range of 10% by weight or less, preferably 1% by weight or less, and more preferably 1000 ppm or less is preferred.
[0037]
The above heat treatment time is suitably in the range of 10 minutes to several days, preferably in the range of 1 hour to 24 hours.
[0038]
The following method is mentioned as a suitable aspect which heat-processes said sol-gel method silica particle at the temperature of 100-200 degreeC in the atmosphere of ammonia.
(1) A method of heat-treating dried sol-gel silica particles at a temperature of 100 to 200 ° C. in an ammonia gas atmosphere.
(2) A method in which, after producing sol-gel silica particles in the presence of ammonia, the particles are washed with alcohol under conditions where the ammonia remains, and then heated at 100 to 200 ° C.
(3) A method in which the sol-gel method silica particles are pickled and then immersed in aqueous ammonia, followed by washing with alcohol and then heat treatment at 100 to 200 ° C.
[0039]
The methods (1) to (3) may be performed alone or in combination as necessary.
[0040]
In addition, about the method of said (2) and (3), since the silica particle manufactured by these methods contains ammonia in the inside of a silica particle, ammonia gas is generated from the inside of silica at the time of heat processing, As in (1), heat treatment is performed in an ammonia gas atmosphere.
[0041]
As the alcohol used in the final washing, an alcohol having a low boiling point such as methanol, ethanol, isopropyl alcohol or the like can be used. Of these, methanol that is easy to dry is particularly preferred. In order to remove alcohol from the silica particles, methods such as filtration and centrifugation can be used, but air drying may be used.
[0042]
A commercially available drier or the like can be used for the heat treatment, but when drying, it is preferable to cover the container so that the inside of the container becomes an ammonia atmosphere.
[0043]
Among the modified sol-gel method silica particles of the present invention, spherical particles can be suitably used as spacers for liquid crystals. That is, the present invention can be obtained by heat-treating sol-gel silica particles having a high monodispersity produced by hydrolyzing an alkyl silicate in a solvent of ammonia and alcohol in an ammonia atmosphere. The modified sol-gel method silica particles can be provided as a practically extremely useful spacer for liquid crystal having low cohesion and high fluidity.
[0044]
By the way, the modified sol-gel method silica particles of the present invention are characterized by low cohesiveness and high fluidity. As an indicator of this property, as will be described in detail later, the remaining amount on the screen when sieving using a sieve can be used as an indicator of fluidity.
[0045]
The modified sol-gel method silica particles of the present invention can achieve a residual amount on the sieve of 40% or less, preferably 30% or less, more preferably 20% or less.
[0046]
【Effect of the invention】
As described above, the modified sol-gel method silica particles of the present invention have extremely high fluidity, and particularly when used as a spacer for liquid crystal, the cohesiveness is suppressed and the fluidity is high. The supply to the spreading surface is very smooth and useful.
[0047]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
(Measurement method of infrared spectrum)
The infrared spectral spectrum by diffuse reflection was measured by the following method. As a measuring device, a Fourier transform infrared spectroscopic measuring device manufactured by Bio-Rad was used. As for the background, KBr powder pulverized in a mortar was ground into a cup-shaped measurement container and set in an apparatus, and an absorption spectrum was measured when infrared light was diffusely reflected on the sample surface. The sample was dried at 700 ° C. for 10 hours, and then mixed with 20 mg of silica particles and 180 mg of KBr powder in a mortar, and put into a cup-shaped measuring container and measured in the same manner as the background.
[0048]
A1 and A2 were determined by the above method.
(Evaluation method for fluidity)
The fluidity of the particles was evaluated using a vibrating sieve. That is, 1 g of particles was put on a sieve (made of stainless steel) having an opening of 75 μm, and the residual amount (% by weight) on the sieve after sieving with a vibrating sieve for 1 minute at a frequency of 60 Hz and an amplitude of 1 mm was measured. . When the cohesiveness of the particles is weak (dispersibility is good) and the fluidity is good, the remaining amount on the sieve is small.
[0049]
Example 1
(1) 400 g and 100 g of isopropyl alcohol and aqueous ammonia (25% by weight) were charged in a glass reaction vessel (internal volume 5 L) equipped with a stirrer, and mixed well to prepare a reaction solution. Next, 5 g of ethyl silicate (Kanto Chemical Co., Ltd., product name: tetraethoxysilane, purity: 3N) was added while maintaining the temperature of the reaction solution at 30 ° C., and stirred for 30 minutes to generate core particles. Next, ethyl silicate (Si (OEt) ₄ , Colcoat Co., Ltd., product name: ethyl silicate 28) was fed at a rate of 8.3 g / min, and aqueous ammonia (25 wt%) was fed at a rate of 2.7 g / min. Separately, it was simultaneously dropped into the reaction solution. The dropping was finished 4 hours after the start of dropping, and 2,000 g of ethyl silicate and 640 g of aqueous ammonia were dropped. After further stirring for 1 hour, the solution in the system was taken out, transferred to a 5 L beaker and allowed to stand. After the particles settled, the supernatant was separated to obtain a silica cake (referred to as silica cake A).
[0050]
(2) After adding 2 L of methanol to the silica cake A and stirring, the particles were allowed to settle by allowing to stand. After discarding the supernatant, 2 L of 1% aqueous ammonia was added and stirred for 1 hour.
[0051]
Further, the washing operation with 1% ammonia water was performed once and the washing operation with methanol was performed three times to replace the solvent with methanol, and the produced silica cake was taken out (referred to as silica cake B). Silica cake B was put into a glass beaker while thoroughly unraveling the silica cake, covered with a lid, put in a dryer at 150 ° C. for 24 hours and dried to obtain silica particles (referred to as dry silica particles B).
[0052]
(3) When the dried silica particles B were observed with an electron microscope, they were found to be spherical silica particles having a high monodispersity with a uniform particle diameter of about 2.1 μm. Further, there were no aggregated particles that particularly required pulverization or crushing treatment, and the fluidity was evaluated. As a result, the remaining amount on the sieve was 16% by weight.
[0053]
As a result of measuring the infrared spectroscopic spectrum after heat-treating the dried silica particles B in an electric furnace at 700 ° C. for 10 hours in the air, the peak area of the isolated silanol group (A1) and the peak area of the silanol group hydrogen-bonded ( The ratio (A1 / A2) of A2) was 0.06. The silica particles after the above heat treatment did not have aggregates, and the remaining amount on the sieve was 18% by weight.
[0054]
Example 2
(1) The operation of (1) was performed in the same manner as in Example 1, and 140 g of the extracted silica cake A, 400 g of methanol, and 400 g of isopropyl alcohol were placed in a glass reaction vessel equipped with a stirrer (internal volume 5 L) and stirred. Ammonia water (25% by weight) 160 g was added and maintained at 40 ° C.
[0055]
Subsequently, ethyl silicate was simultaneously dropped into the reaction solution separately at a rate of 3.3 g / min and aqueous ammonia (25 wt%) was separately added at a rate of 2.9 g / min. The dropping was finished 4 hours after the start of dropping, and 800 g of ethyl silicate and 700 g of aqueous ammonia were dropped. After further stirring for 1 hour, the solution in the system was taken out, transferred to a 5 L beaker and allowed to stand. After the particles settled, the supernatant was separated to obtain silica cake (referred to as silica cake C).
[0056]
Using this silica cake C, the same operation was repeated to obtain a silica cake (referred to as silica cake D).
[0057]
(2) Thereafter, 2 L of methanol was added to the silica cake D, stirred, and allowed to stand to precipitate particles, and the supernatant was separated. Next, the particles were filtered, and 2 L of 1% aqueous ammonia was added and stirred for 10 minutes. (This is silica slurry D)
Further, the washing operation with 1% aqueous ammonia was performed once and the washing operation with methanol was performed three times to replace the solvent with methanol, and the produced silica cake was taken out (referred to as silica cake E). The silica cake E was put into a glass beaker while thoroughly undissolved, covered with a lid gently, put in a dryer at 150 ° C. for 24 hours and dried to obtain silica particles (referred to as dry silica particles E).
[0058]
(3) When the dried silica particles E were observed with an electron microscope, they were found to be highly monodispersed silica having a uniform particle size of about 6.3 μm. Further, there were no aggregated particles that particularly required pulverization or crushing treatment, and the fluidity was evaluated.
[0059]
As a result of measuring the infrared spectroscopic spectrum after heat-treating the dried silica particles E in air at 700 ° C. for 10 hours, A1 / A2 was 0.09. There was no agglomerate after the heat treatment, and the remaining amount on the sieve was 15% by weight.
[0060]
Comparative Example 1
Silica cake D was obtained in the same manner as in Example 2 (1). 2 L of methanol was added to this silica cake D, stirred, and allowed to stand to precipitate particles, and the supernatant was separated. Next, the particles were filtered, 2 L of pure water was added, and the mixture was stirred for 10 minutes. (This state is referred to as silica slurry F) The obtained silica slurry F was applied to an evaporator to remove ammonia and methanol in the slurry. Thereafter, the supernatant liquid was removed, the silica cake was taken out, put into a dryer at 150 ° C. for 24 hours and dried to obtain silica particles (referred to as dry silica particles F).
[0061]
Aggregated particles of about 0.5 mm were observed in the obtained silica particles F, and the fluidity was evaluated. As a result, the remaining amount on the sieve was 60%.
[0062]
In addition, as a result of measuring the infrared spectrum after silica particles F were heat-treated in an electric furnace at 700 ° C. for 10 hours in the air, no peak of isolated silanol groups was observed, and the A1 / A2 ratio was almost zero. It was. The remaining amount on the screen after the heat treatment was 80% by weight.
[0063]
Example 3
(1) Silica cake E was obtained in the same manner as in Example 2.
[0064]
Subsequently, the silica cake was dispersed in pure water, and solid-liquid separation was performed using a centrifuge. After discarding the supernatant, 2 L of pure water and about 0.1 L of 60 wt% nitric acid were added to 100 g of silica and stirred for 12 hours. Thereafter, decantation was repeated with pure water until the pH exceeded 6.
[0065]
(2) Subsequently, 1% by weight of ammonia water was added to the silica cake and stirred for 24 hours. The solvent was replaced with methanol by repeating decantation with methanol twice, and the produced silica cake was taken out (referred to as silica cake G).
[0066]
(3) While thoroughly unraveling the silica cake G, it was placed in a glass beaker, covered gently and placed in a dryer at 150 ° C. for 24 hours for drying (referred to as dry silica particles G).
[0067]
The obtained dried silica particles G had no agglomerated particles that particularly needed to be crushed or crushed, and when the fluidity was evaluated, the remaining amount on the sieve was 7%. Moreover, as a result of measuring the infrared spectroscopy spectrum after heat-processing the dry silica particle G for 10 hours in the 700 degreeC electric furnace in the air, A1 / A2 ratio was 0.16. Even after the heat treatment, the remaining amount on the sieve was 10% by weight.
[0068]
Comparative Example 2
After performing the operation of (1) in the same manner as in Example 3, a silica cake was obtained in the same manner as in Example 3 except that pure water was used instead of ammonia water in the process of (2) (referred to as silica cake H). ).
[0069]
The obtained silica cake H was subjected to the same operation as (3) of Example 3 to obtain dry silica particles (referred to as dry silica particles H).
[0070]
Aggregated particles of about 0.5 mm were observed in the obtained dried silica particles H, and when the fluidity was evaluated, the residual amount on the sieve was 75% by weight.
[0071]
Moreover, as a result of measuring the infrared spectrum after the dry silica particles H were heat-treated in an electric furnace at 700 ° C. for 10 hours in the air, the peak of the isolated silanol group was not observed, and the A1 / A2 ratio was almost zero. there were. Even after the heat treatment, the remaining amount on the sieve was 68% by weight.
[0072]
Example 4
After performing the operation (1) in the same manner as in Example 3, a silica cake was obtained in the same manner as in Example 3 except that pure water was used instead of ammonia water in the process (2) (referred to as silica cake H). ).
[0073]
The obtained silica cake H was put into a heating tube made of quartz glass capable of gas purge, and heated at 150 ° C. for 2 hours while introducing ammonia gas to obtain dry silica particles (referred to as dry silica particles I).
[0074]
The obtained dried silica particles I did not have any agglomerated particles that particularly needed to be crushed or crushed, and the fluidity was evaluated. As a result, the remaining amount on the sieve was 15%. Moreover, as a result of measuring the infrared-spectroscopy spectrum after heat-processing the dry silica particle I for 10 hours in the 700 degreeC electric furnace in the air, A1 / A2 ratio was 0.12. Even after the heat treatment, the remaining amount on the sieve was 18% by weight.
[0075]
From Examples 1 to 4 and Comparative Examples 1 and 2, it was found that the heat treatment in the presence of ammonia increases the A1 / A2 ratio and improves the fluidity of the silica particles.
[Brief description of the drawings]
[Fig. 1] Infrared spectrum by diffuse reflection of silica particles

Claims (4)

A silica cake (1) containing silica particles is obtained by a sol-gel method in the presence of ammonia, and the silica cake (1) is washed with alcohol and then with aqueous ammonia, and then the solvent is replaced with alcohol by washing with alcohol again. Silica group (2) is obtained, and the silica cake (2) is heated at 100 to 200 ° C. In the infrared spectrum measured by the diffuse reflection method, the silanol group hydrogen bonded to the peak area (A1) based on the isolated silanol group A method for producing sol-gel method silica particles in which the ratio (A1 / A2) of the peak area (A2) based on the above is 0.03 or more . A silica cake (3) containing silica particles is obtained by a sol-gel method. After the silica cake (3) is pickled to obtain a silica cake (4), the silica cake (4) is immersed in aqueous ammonia, followed by alcohol. The silica cake (5) in which the solvent is substituted with alcohol is obtained by washing, and the silica cake (5) is heated at 100 to 200 ° C. In the infrared spectrum measured by the diffuse reflection method, the peak area based on the isolated silanol group A method for producing sol-gel silica particles, wherein the ratio (A1 / A2) of the peak area (A2) based on (A1) and hydrogen-bonded silanol groups is 0.03 or more . A silica cake (3) containing silica particles is obtained by a sol-gel method, the silica cake (3) is pickled to obtain a silica cake (4), and then the silica cake (4) is added in the presence of ammonia gas in the presence of 100 to 200. In the infrared spectroscopic spectrum measured by the diffuse reflection method heated at ° C., the ratio (A1 / A2) of the peak area (A1) based on the isolated silanol group to the peak area (A2) based on the hydrogen-bonded silanol group is 0. A method for producing sol-gel method silica particles of 0.03 or more . In the infrared spectroscopic spectrum measured by the diffuse reflection method, the ratio (A1 / A2) of the peak area (A1) based on the isolated silanol group to the peak area (A2) based on the hydrogen-bonded silanol group is 0.03 or more. The method according to any one of claims 1 to 3, wherein the sol-gel silica particles are spherical.

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