JPH0123413B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a silica sol consisting of silica particles having a desired particle size and a narrow particle size distribution by increasing the particle size of silica particles contained in a silica sol. Incidentally, the average particle diameter of silica described in this specification is the surface area S (m ² /g) measured by the methyl red adsorption method converted into a particle diameter d (mμ) based on the following formula. d (mμ) = 2720/S (m ² /g) In addition, the particle size distribution of silica refers to a value measured using an electron microscope. In general, silica sol is manufactured by using alkali metal silicate salts such as sodium silicate, ethyl silicate, silicate chloride, metal silicate, etc. as raw materials, and using techniques such as ion exchange, hydrolysis, and electrodialysis, a dilute aqueous silica sol solution is made once. This dilute aqueous silica sol solution is then concentrated to a concentration that can be sold commercially. The concentration method currently used is the so-called evaporation concentration method in which a dilute aqueous silica sol solution is heated to remove water. On the other hand, an example of concentrating a dilute aqueous silica sol solution using an ultrafiltration method is already known, and an example thereof is disclosed in US Pat. No. 396,926, for example. The average particle diameter of silica particles in the silica sol aqueous solution produced by these methods is generally 10 to 14
mμ, and many have a wide particle size distribution. Such materials are not only unable to sufficiently provide the desired particle size depending on the intended use of the silica sol, but also tend to gel when concentrated to a high concentration due to the small particle size and wide particle size distribution. Another disadvantage is that it tends to become highly viscous. Therefore, a few proposals have been made to increase the particle size by performing high-temperature heat treatment. For example, U.S. Patent No.
No. 2,680,721 proposes a method of rapidly and uniformly heating silica sol while it passes through a tube to increase the size of the particles. However, even with this method, there are problems such as severe scaling inside the pipe and gelation caused by uneven heating due to a decrease in heat exchange power, making it difficult to implement on an industrial scale. Furthermore, the special public service in 1977-
In Publication No. 4639, silica sol is heated at high temperature using an autoclave to increase the silica particle size and narrow the particle size distribution.
The drawback is that the equipment costs are high because it is processed at a high temperature of 300°C. As a result of various studies on industrially advantageous methods for increasing the silica particle size and producing silica sol with a narrow particle size distribution, the present inventors have found that they can smoothly increase the particle size and produce a silica sol with a narrow particle size distribution at an inexpensive price. The present invention was completed by discovering a manufacturing method. That is, in the method of the present invention, an active acidic silica sol aqueous solution is added to an alkaline aqueous solution at a temperature of 70°C or _higher , and the addition rate is ₁ minute per minute. , R is an alkali metal or NH ₄ ), and in order to obtain a stable silica sol aqueous solution, the molar ratio (SiO ₂ /R ₂ O) of NH 4 ) is 10 or less.
It is characterized by being carried out in the presence of 1000 ppm. The active acidic silica sol aqueous solution used in the present invention refers to a very unstable acidic silica sol aqueous solution with a pH of 4 or less, such as an acidic silica sol aqueous solution obtained by reacting an alkali metal silicate with a hydrogen-type cation exchange resin. . The silicic acid (SiO ₂ ) concentration in the acidic silica sol aqueous solution at this time is usually 2 to 10%.
(based on weight, the same applies hereinafter) is normal. In the present invention, a silica sol is obtained by allowing 40 to 1000 ppm of a soluble salt of an alkali metal to be present in an acidic silica sol aqueous solution and/or an alkaline aqueous solution. Soluble salts of alkali metals include lithium, sodium, potassium or cesium hydrochloride;
Preferred examples include sulfuric acid, nitric acid, carbonic acid, phosphoric acid, and aluminate salts, and the soluble salts of alkali metals may be used alone or in the form of multiple salts, and the total amount thereof is preferably 40 to 1000 ppm.
It is more preferably 40 to 500 ppm, preferably 50 ppm or more. If the amount is less than 40 ppm, the catalyst cannot exhibit its effect and only particles with small particle sizes can be obtained. On the other hand, at 1000 ppm or more, it is necessary and sufficient, and even if a larger amount is added, no effect will be produced. The alkali metal soluble salt may be added to the acidic silica sol aqueous solution directly or after being dissolved and diluted with water, or immediately before the acidic silica sol aqueous solution is continuously added to the alkaline aqueous solution. May be mixed. There is an important relationship between the amount of this alkali metal soluble salt, the silicic acid (SiO ₂ ) concentration in the acidic silica sol aqueous solution, and the average particle diameter of silica in the stabilized silica sol aqueous solution. That is, as the concentration of the alkali metal soluble salt increases, the silica particle size in the stabilized silica sol aqueous solution increases. Although it is not clear exactly how the soluble alkali metal salt works, it is thought that it plays an important role as a kind of catalyst in the dehydration condensation of the hydroxyl group of the silanol group of silicic acid. In the present invention, the stabilization tank that converts an acidic silica sol aqueous solution containing an alkali metal soluble salt into a stable silica sol aqueous solution in the presence of an alkali or the like usually includes:
Fill the tank with 1/10 to 1/2 of the aqueous solution and stir thoroughly at a temperature of 70°C or higher. The aqueous solution in the stabilization tank has a molar ratio SiO ₂ /R ₂ O of 0 to 200 and a SiO ₂ concentration of 0 to 200.
40%, and R ₂ O concentration of 0.01 to 1.0% is good. _R2O sources include NaOH, LiOH, KOH, CsOH,
Examples include NH ₄ OH, quaternary alkyl ammonium hydrides, and silicates thereof. Further, an alkali metal soluble salt may be added to the aqueous alkali solution in the stabilizing tank. Furthermore, the stable silica sol aqueous solution obtained by the method of the present invention is placed in a stabilizing tank, and an alkali such as sodium silicate is added to the acidic silica sol aqueous solution containing the alkali metal soluble salt. It can also be added continuously at a molar ratio of ₂ /R ₂ O. Furthermore, when an acidic silica sol aqueous solution containing an alkali metal soluble salt is continuously added to an alkaline aqueous solution, the temperature of the alkali aqueous solution must be kept at 70°C or higher; if it is lower than this, the growth of silica particles will be slow; inappropriate (more preferably
80℃ or higher). In addition, the rate at which the acidic silica sol aqueous solution is continuously added to the alkaline aqueous solution has an important relationship with the silica particle distribution in the stabilized silica sol aqueous solution, and SiO in the acidic silica sol aqueous solution is added per minute to the alkaline aqueous solution. It is necessary to continuously add at a rate such that the molar ratio SiO ₂ /R ₂ O between ₂ and R ₂ O in the alkaline aqueous solution is 10 or less.
More preferably, SiO ₂ /R ₂ O is in the range of 0.1 to 8. If it is less than 0.1, the addition rate is slow, which is industrially disadvantageous and impractical. In addition, if the addition rate exceeds 10, the silicic acid in the acidic silica sol aqueous solution added does not have time to grow into colloidal particles, causing local gelation and sometimes total gelation, which is difficult to achieve in industrial production methods. This not only causes problems, but also increases the particle size distribution of the silica particles in the final stabilized aqueous silica sol solution, which is not suitable for the purpose of the present invention. In this case, SiO ₂ refers only to the silicic acid in the acidic silica sol aqueous solution that is continuously added to the stabilization tank, and does not include the silicic acid content in the aqueous solution that already exists in the stabilization tank. This is because the silicic acid present in the aqueous solution in the stabilization tank is immediately stabilized and grows into colloidal particles. The addition of the acidic silica sol aqueous solution to the stabilizing tank can be stopped at the desired SiO ₂ /R ₂ O molar ratio for the final product, but a molar ratio of 20 to 1000 is preferable, and 40
~500 is more preferred. The silica sol aqueous solution stabilized in the stabilization tank is
Although it is sufficiently stable even if it is cooled as it is, the particle size distribution of the silica particles becomes narrower when it is further heat-treated preferably at a temperature of 70° C. or higher for 0.5 to 4 hours. The silica sol aqueous solution thus obtained is concentrated by a conventional evaporation concentration method or an ultrafiltration method to obtain a silica sol aqueous solution with a controlled particle size according to the present invention. The alkali metal soluble salt contained in the silica sol aqueous solution as a catalyst is small and poses no problem in use, but in some cases it may be treated with an adsorbent such as a hydroxyl group-type anion exchange resin or activated clay. It can also be removed. The present invention provides a silica sol consisting of silica particles having an arbitrary particle size and a narrow particle size distribution by growing the particle size of the silica particles contained in the silica sol in a more industrially and economically advantageous method. The present invention will be explained below with reference to production examples and examples, but the present invention is not limited to these scopes. Production example 1 Sodium silicate JIS No. 3 (Asahi Denka Kogyo Co., Ltd. product,
SiO ₂ 29%, Na ₂ O 9.0%) was diluted with water, SiO ₂ 6.0
%, Na ₂ O 1.86% dilute aqueous solution of sodium silicate was prepared. This diluted sodium silicate aqueous solution was passed through a hydrogen-type cation exchange resin (Albarite IR-120B, manufactured by Organo Co., Ltd.) prepared in advance in a conventional manner to obtain an acidic silica sol aqueous solution containing 6.0% SiO ₂ ( PH2.5). 11.7 g of sodium chloride (special grade) was dissolved in distilled water to obtain a 11.7% aqueous solution of sodium chloride. This is referred to as catalyst aqueous solution I. 0.4 g of catalyst aqueous solution I was added to 400 g of the above acidic silica sol aqueous solution to obtain about 400 g of a catalyst-containing acidic silica sol aqueous solution (SiO ₂ 6.0%, NaCl 117 ppm). 90g of this acidic silica sol aqueous solution containing catalyst
It was added at a rate of 20 g/min for 1 minute into 100 g of a 0.31% Na ₂ O aqueous solution that was sufficiently stirred while maintaining the temperature at °C. Addition takes about 20 minutes, then 90 minutes
℃ for 2 hours and cooled to obtain 500 g of a stable silica sol aqueous solution. Production Example 2 0.2 g of the same catalyst aqueous solution I used in Production Example 1 was added to 400 g of the same acidic silica sol aqueous solution used in Production Example 1 to obtain about 400 g of an acidic silica sol aqueous solution containing a catalyst. 400 g of this catalyst-containing acidic silica sol aqueous solution was added at a rate of 5 g/min to 100 g of a 0.31% Na ₂ O aqueous solution which was being sufficiently stirred while maintaining the temperature at 90°C. The addition took about 80 minutes, and then the mixture was stirred at 90° C. for 1 hour and cooled to obtain 500 g of a stable aqueous silica sol solution. Production Example 3 To 400 g of the same acidic silica sol aqueous solution used in Production Example 1, 0.8 g of the same catalyst aqueous solution I used in Production Example 1 was added to obtain about 400 g of a catalyst-containing acidic silica sol aqueous solution. 400 g of this catalyst-containing acidic silica sol aqueous solution is added to 100 g of a 0.31% Na ₂ O aqueous solution that is sufficiently stirred while keeping the temperature at 90°C.
It was added at a rate of g/min. Addition takes approximately 40 minutes;
Then, the mixture was stirred at 90°C for 1.5 hours and cooled.
500 g of a stable aqueous silica sol solution was obtained. Production Example 4 In Production Example 3, the amount of catalyst aqueous solution I added was 1.2g.
I did everything else the same way. Production Example 5 In Production Example 1, the catalyst aqueous solution was replaced with sodium sulfate.
All treatments were the same except that the 14.2% aqueous solution (hereinafter referred to as catalyst aqueous solution) was used. Production Example 6 In Production Example 1, the catalyst aqueous solution was replaced with potassium chloride.
All treatments were the same except that the 14.9% aqueous solution (hereinafter referred to as catalyst aqueous solution) was used. Production Example 7 Stable colloidal silica obtained in Production Example 3
Add 3.5 g of No. 3 _silica to 96.5 g and put into a stabilizing _tank .
After adjusting 0.4 g of catalyst aqueous solution to 400 g of acidic silica sol aqueous solution, about 400 g of acidic silica sol aqueous solution containing catalyst (SiO ₂ 6.0%,
NaCl (117 ppm) was obtained. 400 g of this catalyst-containing acidic silica sol aqueous solution was mixed with 100 g of an alkaline aqueous solution (SiO ₂ 5.6%,
per minute in Na ₂ O 0.37%, NaCl 180ppm)
Addition was made at a rate of 20 g/min. The addition was completed in about 20 minutes, and then the mixture was stirred and cooled at 90° C. for 2 hours to obtain 500 g of a stable aqueous silica sol solution. Comparative Production Example 1 400 g of the same acidic silica sol aqueous solution used in Production Example 1 was added at a rate of 20 g/min to 100 g of a 0.31% Na ₂ O alkaline aqueous solution that was sufficiently stirred while maintaining the temperature at 90°C. did. The addition was completed in about 20 minutes, and then the mixture was stirred and cooled at 90° C. for 2 hours to obtain 500 g of a stable aqueous silica sol solution. Comparative Production Example 2 500 g of a stable silica sol aqueous solution was obtained by carrying out exactly the same operation as in Production Example 1 except that the amount of catalyst aqueous solution was changed to 0.04 g. Comparative Production Example 3 400g of the catalyst-containing acidic silica sol aqueous solution used in Production Example 1 was sufficiently stirred while being kept at 90°C.
per minute in 100 g of Na ₂ O 0.31% alkaline aqueous solution
Addition was made at a rate of 80 g/min. Because the addition was rapid, the temperature of the alkaline aqueous solution temporarily dropped to 80°C.
In addition, a gelled product of silicic acid was formed locally, but this did not pose a problem for stirring. After the addition was completed, the mixture was stirred at 90° C. for 2 hours and cooled to obtain a stable aqueous silica sol solution. Comparative Production Example 4 400g of the acidic silica sol aqueous solution containing catalyst used in Production Example 1 was sufficiently stirred while being kept at 40℃.
It was added to 100 g of 0.31% Na ₂ O aqueous alkaline solution at a rate of 20 g/min. The addition was completed in about 20 minutes. Thereafter, the entire temperature was raised at a rate of 1° C./min. When the temperature reached 60°C, the whole gelatinized. After stirring for 2 hours, the gel was redissolved. The temperature was then raised to 90°C, stirred at 90°C for 1 hour, and cooled to obtain 500 g of stable silica sol. The above results are shown in Table-1.

[Table] Examples 1 to 7, Comparative Examples 1 to 4 The silica sol aqueous solutions obtained in Production Examples 1 to 7 and Comparative Production Examples 1 to 4 were evaporated and concentrated to 40% SiO ₂ . The results are shown in Table-2. As is clear from Table 2, the method of the present invention yields an aqueous silica sol solution with lower viscosity, larger silica particle size, and narrower particle size distribution than the comparative example.

【table】

Claims (1)

[Scope of Claims] 1. An active acidic silica sol aqueous solution is added to an alkaline aqueous solution at a temperature of 70°C or _higher , and the addition rate is ₁ minute per minute. R is the alkali metal or NH ₄ ) molar ratio (SiO ₂ /R ₂ O)
A method for producing a silica sol, which comprises adding an acidic silica sol aqueous solution in the presence of 40 to 1000 ppm of a soluble salt of an alkali metal, in order to obtain a stable silica sol aqueous solution such that the silica sol is 10 or less. 2. The manufacturing method according to claim 1, wherein the soluble salt of the alkali metal is hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, aluminic acid, or phosphate of lithium, sodium, potassium, or cesium. 3. The manufacturing method according to claim 1, wherein a soluble salt of an alkali metal is added to the acidic silica sol aqueous solution. 4. The manufacturing method according to claim 1, wherein a soluble salt of an alkali metal is added to an aqueous alkaline solution. 5. The manufacturing method according to claim 1, wherein the obtained silica sol aqueous solution is further concentrated. 6. The manufacturing method according to claim 5, wherein the concentration method is an ultrafiltration method or an evaporative concentration method. 7. The manufacturing method according to claim 1, further comprising heat treatment at 70°C or higher for 0.5 to 4 hours.