JP2001002411A - Production of aqueous silica sol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aqueous silica sol containing lesser impurities such as alkali metals or multivalent metals, and in particular lesser coagulated gels by adding an alkoxysilane to an acidic aqueous solvent to subject the alkoxysilane to hydrolysis treatment and to form silicic acid monomer and further adding the silicic acid monomer to a basic solvent to subject the silicic acid monomer to polymerization treatment. SOLUTION: This production process comprises adding an alkoxysilane to an acidic aqueous solvent to subject the alkoxysilane to hydrolysis treatment and to form silicic acid monomer and further adding the silicic acid monomer to a basic aqueous solvent to subject the silicic acid monomer to polymerization treatment and to produce the objective aqueous silica sol, wherein: the alcohol formed as a by-product in the hydrolysis treatment is preferably removed in the polymerization treatment; also preferably, the polymerization treatment is performed in such a state that the pH of the system is 8.5 to 11.5, while adjusting the volume of the system so as to be >=95% of the initial volume of the system in this polymerization treatment; as the alkoxysilane, tetraethoxysilane, tetramethoxysilane, methoxytriethoxysilane, or the like, is used; and as the basic aqueous solvent, ethylenediamine, diethylenetriamine, triethylenetetramine, or the like, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity aqueous silica sol containing very few metal impurities, which is useful for the production of semiconductor LSIs, catalyst carriers, fine ceramics, and the like. The present invention relates to a method for producing a high purity aqueous silica sol.

[0002]

2. Description of the Related Art Generally, an aqueous silica sol is produced by heating a silicate monomer obtained by cation exchange of sodium silicate under an alkaline catalyst such as sodium hydroxide to carry out a polymerization reaction. However, even if the generated silica sol is subjected to demetallization and purification again by ion exchange treatment or the like, there is a limit to the removal of impurities, and the production of semiconductor LSIs that do not like inclusion of metal impurities such as alkali metals and polyvalent metals, catalyst In applications such as carriers and fine ceramics, aqueous silica sols could not be used due to adverse effects on product functions due to contamination. For this reason, silica slurry dispersed in water using high-purity finely divided silicon dioxide has been studied. However, there is a problem that long-term storage stability is lacking, for example, because silica particles exist as aggregates and settle. On the other hand, a method for producing an aqueous silica sol using an alkoxysilane as a starting material is disclosed in JP-A-63-74911 and JP-A-6-316407.
No. 6,009,036. In this production method, hydrolysis of a starting material and polymerization of a silicate monomer produced thereby are performed in the same system to obtain an aqueous silica sol. However, in any of the production methods, stable silica sol particles are hardly obtained, and storage stability is affected due to generation of a gel.

[0003]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for producing a stable aqueous silica sol containing extremely few impurities such as alkali metals and polyvalent metals and having a small amount of aggregated gel.

[0004]

That is, according to the present invention, an alkoxysilane is added to an acidic aqueous solvent, a hydrolysis treatment is carried out to obtain a silicate monomer, and the silicate monomer is added to a basic aqueous solvent. In addition to the above, a method for producing an aqueous silica sol characterized by performing a polymerization treatment, and removing alcohol produced as a by-product of hydrolysis during the polymerization treatment. 8.5-11.
The polymerization is performed while adjusting the volume of the system so that the volume of the system does not fall below 95% at the start of the polymerization.

The alkoxysilane used in the present invention is not particularly limited, and any of those which can be conventionally used for producing aqueous silica sol, organic solvent-based silica sol and the like can be used.

[0006]

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(Wherein R ^{1 to} R ⁴ are a branched or straight-chain alkyl group having 1 to 4 carbon atoms which may be the same or different).
Preferred examples include tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methoxytriethoxysilane, and trimethoxyethoxysilane.

[0008] The acidic aqueous solvent (acidic aqueous solvent) to which the alkoxysilane is added is not particularly limited, and a small amount of acid added to water may be used. It is preferable to use various kinds of acids such as inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, and water-soluble organic acids such as formic acid, acetic acid and citric acid. In view of this, inorganic acids are preferred. Of course, it is preferable that the acid has as little impurities as possible.

Although the amount of the acid is not particularly limited,
Generally, the pH of the acidic aqueous solvent may be 2 to 4.

[0010] The ratio of the alkoxysilane to the acidic aqueous solvent is not particularly limited and can be arbitrarily selected as desired. However, if the amount of the alkoxysilane is too small, depending on the final product, the concentration step may take a long time. Since the aqueous silica sol as the final product may be easily aggregated if the amount is too large, for example, the amount of the alkoxysilane may be 5 to 100 parts by weight of the acidic aqueous solvent.
80 parts by weight, preferably 35 to 70 parts by weight.

In the present invention, the above-mentioned alkoxysilane is added to the above-mentioned acidic aqueous solvent to carry out a hydrolysis reaction. The hydrolysis method is not particularly limited and may be in accordance with a conventional method.For example, alkoxysilane was added to an acidic aqueous solvent at room temperature, and the alkoxysilane was hydrophobic. This can be carried out by maintaining the state for about several tens of minutes to several hours. Specifically, what has been in a dispersed state dissolves with the progress of hydrolysis, and thus may be performed until a solution is obtained. Since this hydrolysis reaction is an exothermic reaction, the temperature in the system may rise to about 40 to 50 ° C. in the course of the reaction, but there is no hindrance and the reaction can be carried out as long as it is lower than the boiling point of the solvent. In addition, the reaction can be carried out at a temperature lower than room temperature, but it is not recommended because the reaction time becomes long.

In the hydrolysis reaction step of the present invention, an alcohol corresponding to the alkoxy group of the alkoxysilane is by-produced, and the by-product alcohol is produced during the hydrolysis reaction step or between the hydrolysis reaction step and the polymerization treatment step. When removed from the system, the aqueous silica sol as a final product may be easily aggregated, so that the by-product alcohol is not removed from the system in this step, and is carried over to the polymerization treatment step described below, which is not stable. Is preferred in view of

Next, in the present invention, the silicic acid monomer obtained above is added to a basic aqueous solvent to carry out a polymerization treatment. The basic aqueous solvent (basic aqueous solvent) to which the above-mentioned silicate monomer is added is not particularly limited, and a small amount of a base may be added to water. Water) may be used, and as the base, those conventionally known as alkali catalysts may be used. However, from the viewpoint of reducing metal impurities as much as possible, preferred are, for example, ethylenediamine, diethylenetriamine,
Nitrogen bases such as triethylenetetramine, ammonia and tetramethylammonium hydroxide are preferred.

The amount of the base is not particularly limited, and may be used so that the pH of the basic aqueous solvent is 8.5 to 11.5. When the pH changes during the polymerization process, the pH is maintained in the range of 8.5 to 11.5 by adding an appropriate amount of the above base or adding an appropriate amount of pure water or the above aqueous solvent. Is good.
If the pH is out of the above range in the polymerization treatment step, it is not preferable because the sol is lacking in stability such as formation of a gel. The preferred pH is between 8.9 and 11.1.

The ratio between the basic aqueous solvent and the above-mentioned silicate monomer is not particularly limited. That is, the silicic acid monomer obtained above also contains water, and the alcohol is removed in the course of the polymerization treatment as described later. Therefore, it may be used in such a ratio that the aqueous silica sol concentration as a final product is desired. However, if the amount is too small, a complicated process such as a concentration step is required depending on the final product.If the amount is too large, the aqueous silica sol as the final product may be easily aggregated. 2 to 15% by weight, preferably 3 to 10% by weight.

The method of adding the silicate monomer is not particularly limited, but since the silicate monomer obtained above is acidic, it is necessary to add the silicate monomer dropwise to a basic aqueous solvent to prevent agglomeration. Is preferred in view of However, even if the dripping is too fast, the tendency of agglomeration may appear,
If it is too late, it is inferior in industrialization suitability.
When 180 parts by weight of the silicate monomer having the iO ₂ content is dropped into 120 parts by weight of the basic aqueous solvent, the dropping is preferably performed at a rate of about 2.5 hours to 5 hours.

The conditions of the polymerization treatment step in the present invention are not particularly limited, and may be the same as those in the conventional polymerization treatment step in the step of obtaining an aqueous silica sol. Hereinafter, the temperature may be preferably maintained at 60 ° C to 97 ° C for about 1 to 6 hours.

During this time, it is preferable to remove the alcohol by-produced in the preceding step simultaneously with the polymerization reaction. During this time, a part of the water and the base may be removed simultaneously with the alcohol.However, the water may be less than the amount of water desired as the aqueous silica sol, and may be less than the amount of water desired as the aqueous silica sol. If so, water can be appropriately replenished. Also, the base content decreases,
If it is out of the above pH range, a base can be appropriately replenished.

The polymerization treatment step in the present invention can be carried out even under reduced pressure. Under reduced pressure, the removal of alcohol is easy, but the above-mentioned temperature is required for the polymerization reaction. Since the removal speed of alcohol, water, base and the like is increased and it becomes difficult to adjust the pH and the amount of water, the removal is preferably performed at 400 mmHg or more.

In the polymerization treatment step of the present invention, the capacity of the system tends to decrease due to the evaporation of alcohol and the accompanying evaporation of water and the like, but when the capacity of the system decreases, a gelled product is formed. It is preferable to keep the volume constant by appropriately replenishing water (preferably hot water: further base if the pH is out of the above range). It is preferable to perform the adjustment while adjusting so as not to fall below 95% at the start of the processing.
Although the cause is not clear, it is considered that the evaporation rate at the contact point between the liquid surface and the container surface locally increases, and a gelled substance is generated and adheres to the container surface. Therefore, even if the capacity is within the range of not less than 95% at the start of the polymerization treatment, it is considered that repeating the increase and decrease of the capacity will increase the amount of gelled matter. Good.

The aqueous silica sol obtained according to the present invention comprises:
It can be arbitrarily concentrated by ultrafiltration or the like.

[0022]

The present invention will be further described below with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples. Example 1 45 parts by weight of tetraethoxysilane was added to an acidic aqueous solvent of pH 3.4 in which 4.5 parts by weight of 0.1N hydrochloric acid was dissolved in 71 parts by weight of ion-exchanged water, and the mixture was stirred at room temperature for 55 minutes to obtain S.
A silicate monomer solution having an iO ₂ concentration of 11% by weight was obtained. On the other hand, in a stainless steel reaction tank equipped with a stirrer and a condenser, 130 parts by weight of ion-exchanged water and 0.1% of ethylenediamine were added.
5 parts by weight were dissolved to prepare a basic aqueous solvent having a pH of 11.1. After adjusting the temperature of the basic aqueous solvent to 70 ° C., 100 parts by weight of the above silicate monomer solution was
The mixture was added dropwise over a period of time, and then reacted at 93 ° C. for 3 hours.
The ethanol distilled off during this time was removed, and the SiO ₂ concentration was 4.7% by weight, the pH was 9.0, and the particle diameter was 19.0 nm (BE
T method), sodium 0.2ppm, potassium 0.1pp
m, calcium 0.02 ppm, magnesium 0.02
ppm, aluminum 0.02ppm, iron 0.02pp
m, copper 0.001ppm, nickel 0.0003ppm
Aqueous silica sol was obtained. The aqueous silica sol was concentrated by an ultrafiltration apparatus to obtain an aqueous silica sol having a SiO ₂ concentration of 20.2% by weight, a pH of 8.6 and a particle diameter of 19.2 nm (BET method). The metal components of this silica sol include sodium 0.8 ppm, potassium 0.4 ppm, calcium 0.08 ppm, magnesium 0.1 ppm, aluminum 1.0 ppm, iron 0.1 ppm, and copper 0.006.
ppm and nickel were 0.001 ppm.

Further, the gelation stability was tested as follows. The aqueous silica sol having a SiO ₂ concentration of 4.7% by weight obtained above was applied to a membrane filter (47 mm in inside diameter, 0.5 μm in hole diameter) manufactured by ADVANTEC with a pressure of 0.2 Torr.
Filtered at r. The filtration rate was 12 g / sec, and the generation of gel was extremely small. The aqueous silica sol was placed in a 100 ml glass container and stored in a thermostat (50 ° C.) for 2 months. Observation with the naked eye showed no sedimentation of the gel.

Example 2 An aqueous silica sol was obtained in the same manner as in Example 1 except that hot water was continuously replenished in the polymerization step to keep the volume of the system constant (the change in volume was less than 1%). . Before ultrafiltration and concentration, the SiO ₂ concentration was 4.7% by weight, the pH was 9.1, the particle diameter was 19.9 nm (BET method), and the sodium was 0.1 pp.
m, potassium 0.1ppm, calcium 0.02pp
m, magnesium 0.03 ppm, aluminum 0.2
ppm, iron 0.04 ppm, copper 0.01 ppm, nickel 0.004 ppm, SiO ₂ concentration 2 after ultrafiltration
0.1% by weight, pH 9.1, particle size 20.3 nm (BE
T method), sodium 0.6ppm, potassium 0.4pp
m, calcium 0.08ppm, magnesium 0.1p
pm, aluminum 0.9 ppm, iron 0.1 ppm, copper 0.004 ppm, and nickel 0.001 ppm. When a gelation stability test was performed in the same manner as in Example 1, the filtration rate was 15 g / sec, the generation of gel was extremely small, and the storage stability was not observed after 2 months. Was something.

COMPARATIVE EXAMPLE 1 38 parts by weight of tetraethoxysilane was added dropwise to a basic aqueous solvent having a pH of 11.0 in which 0.7 parts by weight of ethylenediamine was dissolved in 190 parts by weight of ion-exchanged water over 2.5 hours.
The mixture was kept at 2 ° C. for 6 hours, and the hydrolysis of tetraethoxysilane and the polymerization of the resulting silicate monomer were carried out in the same system to obtain an aqueous silica sol. In addition, ethanol by-produced during the reaction was distilled off. The components of the silica sol after the ultrafiltration concentration were as follows: SiO ₂ concentration 20.5% by weight, pH 9.3, particle size 21.3 nm (BET method), sodium 0.8 ppm,
Potassium 0.5 ppm, calcium 0.07 ppm, magnesium 0.1 ppm, aluminum 1.1 ppm,
0.1 ppm iron, 0.005 ppm copper, 0.0 nickel
It was 02 ppm. The filtration rate is 5 g / sec,
Gelation reduced the filtration rate. After storage for 2 months, gel sedimentation was observed.

[0026]

The effect of the present invention is to provide a method for producing a stable aqueous silica sol having a very small amount of impurities such as alkali metals and polyvalent metals and a small amount of aggregated gel.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuru Hanagasaki 7-35 Higashiogu, Arakawa-ku, Tokyo Asahi Denka Kogyo Co., Ltd. F-term (reference) 4G072 AA28 CC01 GG03 HH30 JJ11 JJ13 JJ14 KK03 KK15 LL06 MM01 MM21 PP11 PP17 RR05 RR12 RR15 UU01 UU17 UU30

Claims (4)

[Claims] 1. An alkoxysilane is added to an acidic aqueous solvent and subjected to a hydrolysis treatment to obtain a silicate monomer.
A method for producing an aqueous silica sol, comprising adding the silicate monomer to a basic aqueous solvent and performing a polymerization treatment. 2. The method for producing an aqueous silica sol according to claim 1, wherein alcohol produced as a by-product of the hydrolysis is removed during the polymerization treatment. 3. The polymerization treatment is carried out by adjusting the pH of the system to 8.5-11.
5. The method according to claim 1, wherein the step is performed within a range of 5.
The method for producing an aqueous silica sol according to the above. 4. The aqueous silica sol according to claim 1, wherein the polymerization treatment is carried out while adjusting the volume of the system so as not to be less than 95% at the start of the polymerization treatment. Production method.