JPH02149414A - Production of silica sol - Google Patents

Abstract

PURPOSE:To easily obtain silica sol which is high concn., stable and consists of minimum particles at low cost by mixing an alkali metal silicate aq. soln. with a silicic acid aq. soln. and bringing this mixture into contact with hydrogen type ion exchange fiber to perform ion exchange and heating the produced silica sol at the specified pH and temp. CONSTITUTION:An alkali metal silicate (e.g. sodium silicate) aq. soln. is mixed with a silicic acid aq. soln. A mixing rate is preferably regulated to about >=0.1 pts.wt. SiO2 of the silicic acid aq. soln. for 1 pts.wt. SiO2 of the alkali metal silicate aq. soln. Further SiO2 concn. of the mixture is preferably regulated to about 10-30wt.%. Then this mixture is brought into contact with hydrogen type ion exchange fiber to perform ion exchange. Then high-concn. minimum silica sol is obtained by heating the produced silica sol at 8-10pH at 50-100 deg.C. Obtained silica sol is preferably utilized for a metallic surface treating agent and an adhesive, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing silica sol, and particularly to a method for producing silica sol with extremely small particles having a particle size of 3 to 10 mμ.

Silica sol is an aqueous colloid in which microparticles of 3 to 100 mμ are dispersed in water, and is used as an adhesive and an abrasive material.

It is widely used in various industrial fields as a fiber treatment material, a binder for lost wax casting, etc. Among them, silica sol, which has extremely small particles with a particle size of 3 to 10 mμ, is highly active and is therefore used as a metal surface treatment agent.

Adhesive agent, binder, filler retention agent in paper making process.

It is particularly effective as a fiber treatment agent.

(Prior Art) Known methods for producing silica sol include acid neutralization, ion exchange, electrodialysis, and peptization.

In these methods, it is difficult to directly prepare high-concentration silica sol, and it is usually necessary to concentrate the silica sol to a practical concentration ranging from 2 to 2.

For example, in a normal ion exchange method, an aqueous alkali metal silicate solution with a 5iO7 concentration of 2 to 4 wt% is brought into contact with a hydrogen type ion exchanger to generate a dilute silica sol, and then a dilute silica sol of 20 wt% or more is made available for commercial use. must be concentrated to a silica concentration of

As a concentration method, the so-called evaporation concentration method is generally known, in which water is removed by heating a dilute silica sol, but this method has the disadvantage that the energy and equipment costs for concentration are high. Furthermore, since water evaporates near the boiling point,
The particle size of the silica sol particles increases, and it is generally difficult to obtain a silica sol having a particle size of 10 mμ or less.

On the other hand, a method of concentrating by ultrafiltration is known. For example, in Japanese Patent Application Laid-Open No. 62-7622, there are 5
An aqueous colloidal solution of activated silicic acid with a pH of 2 to 5 and a concentration of 2 to 6 wt% of SiO2 is added to an aqueous alkali metal silicate solution with a concentration of 1.5 to 8 wt% of iO2/M20.
(M represents K or Na, which is an alkali metal atom of the alkali metal silicate) Gradually add while stirring at 30 to 65°C until the molar ratio becomes 20 to 40, then gradually add the acid. Si
A silica sol with O, f1 degree of 20 wt% or more was obtained.

The ultrafiltration method is very advantageous in energy and equipment costs for concentration compared to the evaporation concentration method, and since there is no need to heat during concentration, it is easy to obtain a sol with extremely small particles of 3 to 10 μm. It is. However, even in this method, the concentration of the silica sol initially generated is at most 8 w
t%, and to further reduce the concentration cost,
It is necessary to increase the concentration of the silica sol that is initially generated. Highly concentrated sol without concentration? 1. In this method, a mixture of an alkali metal silicate aqueous solution and silica sol is continuously passed through a hydrogen-type ion exchanger, an alkali metal silicate aqueous solution is mixed with the silica sol that flows out, and this mixture is passed through the ion exchanger. A method has been proposed to obtain a highly concentrated silica sol with a 5in2 concentration of 10 wt% or more by repeatedly circulating it into the body.

For example, in JP-A-47-1713, an aqueous alkali metal silicate solution is added to water circulating at a constant rate, at least initially, and this mixture is continuously transferred to an ion exchanger at a constant rate. The pH of the effluent silica sol is adjusted to 6 to 10 by the aqueous alkali metal silicate solution continuously introduced, and the mixture has a temperature of 60° C. to 100° C.
A method is disclosed for producing a concentrated silica sol by defining the rate of increase in silica concentration until reaching t% and repeating the circulation until the effluent reaches the required silica content.

In such a method, the concentration of the silica sol finally obtained is determined by the concentration and amount of the circulating fluid used at the start of circulation and the concentration and amount of the aqueous alkali metal silicate solution added. However, the concentration and amount of the aqueous alkali metal silicate solution to be added is limited by the exchange capacity of the ion exchanger, so in order to obtain a silica sol with a higher iH degree, the concentration of the circulating fluid must be made as high as possible. It won't happen.

However, if the 5in2 concentration of the alkali metal silicate aqueous solution that can be used at the start is increased, gelation tends to occur, and if it exceeds 4wt%, stable ion exchange becomes difficult. Therefore, if you try to obtain a high-concentration silica sol using the above method, you will start from a low concentration and repeat the circulation to gradually increase the concentration. , which requires complicated operations.

[Problems to be Solved by the Invention] The object of the present invention is to ion-exchange a concentrated aqueous alkali metal silicate solution without precipitation of a gel-like substance,
The object of the present invention is to provide a method that can obtain a highly concentrated silica sol with extremely small particles of 3 to 10 mμ by a simple process that does not require any concentration step or has a low concentration cost.

[Means for Solving the Problems] The gist of the present invention is to provide a method for producing silica sol by contacting an aqueous alkali metal silicate solution with a hydrogen-type ion exchanger. After mixing with an aqueous solution, it is brought into contact with an ion exchanger for ion exchange, and then the generated silica sol is adjusted to pH 8, O ~ 10.
．． This is a method for producing a highly concentrated extremely small silica sol by heating at 0.50 to 100°C, and the details thereof will be explained below.

Examples of the alkali metal silicate used in the present invention include sodium silicate and potassium silicate, but sodium silicate is commonly used.

The aqueous silicic acid solution used in the present invention is an aqueous solution of monosilicic acid, disilicic acid, trisilicic acid, etc. For example, when an alkali metal silicate aqueous solution is brought into contact with a hydrogen type ion exchanger, silicic acid is polymerized. It can be obtained by ion exchange without becoming particulate.

In the present invention, it is essential to mix these alkali metal silicate aqueous solutions and silicic acid aqueous solutions and then perform ion exchange with an ion exchanger.

When ion-exchanging an alkali metal silicate aqueous solution alone without mixing it with a silicic acid aqueous solution, the concentration of Sin is 4.
If it exceeds wt%, gelation may occur during ion exchange even if ion exchange fiber is used as an ion exchanger, and it is not possible to directly ion exchange a concentrated aqueous alkali metal silicate solution to obtain a highly concentrated silica sol. The reason for this is not clear, but by mixing the silicic acid aqueous solution and the alkali metal silicate aqueous solution, the SiO□ concentration increases to 4wt.
%, ion exchange can be performed without gelation.

There are no particular limitations on the method of mixing the alkali metal silicate aqueous solution and the silicic acid aqueous solution. For example, an aqueous silicic acid solution may be added to an aqueous alkali metal silicate solution, or conversely, an aqueous alkali metal silicate solution may be added to an aqueous silicic acid solution. Moreover, there is no problem even if they are mixed continuously.

There is no particular limitation on this mixing ratio, but when obtaining a high concentration silica sol, 5% of the alkali metal silicate aqueous solution
5 in2 of silicic acid aqueous solution per i021ffi amount part
It is preferable to set the amount to 11 parts or more of O.1ff. 5in
In the case of a dilute alkali metal silicate aqueous solution with a S2 concentration of less than 10 wt%, this mixing ratio is not a particular problem;
When attempting to directly obtain a high concentration silica sol with an iO2 concentration of 10 W t 96 or more, 0. If lff is less than 1 m part, the effect of adding the silicic acid aqueous solution will be small, and precipitation or gelation of a gel-like substance may occur in the ion exchange fiber layer.

The 5in2 concentration of the mixture is preferably 10 to 30 wt%. Although it is possible to carry out the method of the present invention with less than 10 wt%, this is not preferred in terms of the gist of the present invention, which is to directly obtain a highly concentrated silica sol. on the other hand,
If it exceeds 30 wt%, gel-like substances will be deposited or gelled in the ion-exchange fiber layer, resulting in crystallization.

Subsequently, the mixture of the alkali metal silicate aqueous solution and silicic acid aqueous solution is passed through the hydrogen type ion exchange fiber.

As ion exchangers, polystyrene resin,
In addition to resinous ion exchangers such as gel-like ion exchange resins in which ion exchange groups are introduced into synthetic resins such as phenol resins and polyacrylic resins and MR type ion exchange resins, inorganic ion exchangers such as zeolites are known. ing. Attempts were made to produce silica sol from a mixed aqueous solution of alkali metal silicate and silicic acid using these ion exchangers, but gel-like substances often precipitated within the ion exchanger or the entire ion exchanger gelled. Yes, 5i02 concentration 10wt
It was difficult to directly obtain a silica sol with a high concentration of more than %.

In several fields, attempts have been made to utilize ion exchange fibers as ion exchangers that have a unique shape compared to conventional ion exchangers. When ion exchange fibers are used in contrast to conventional ion exchangers such as those mentioned above, the reason for this is not clear, but even at high concentrations of SiO□ of 10 wt% or more, precipitation or gelation of gel-like substances occurs. We discovered that ion exchange can be performed without any problems. That is, by bringing a mixture of an aqueous alkali metal silicate solution and an aqueous silicic acid solution having a 5t02a degree of 10 to 30 wt % into contact with an ion exchange fiber, a highly concentrated silica sol can be directly obtained.

The ion exchange method is not particularly limited, but a column method is common. That is, a column is packed with ion exchange fibers, and an aqueous alkali metal silicate solution lCk is added from the top of the column.
and an aqueous silicic acid solution. For example, a mixture of an aqueous alkali metal silicate solution and an aqueous silicic acid solution may be brought into contact with the ion exchange fibers by a batch method.

The solution obtained by flowing out from the column has alkaline components removed by ion exchange and becomes an acidic silicic acid solution, but this acidic silicic acid is directly combined with ifi to form a silica sol. Before the obtained highly concentrated acidic silicic acid aqueous solution becomes a silica sol, the entire amount thereof is mixed with an alkali metal silicate aqueous solution, and then this mixture is brought into contact with ion exchange fibers. This operation may be repeated, or a part of the obtained highly concentrated acidic silicic acid aqueous solution is supplied to the next step, the remainder is mixed with the alkali metal silicate aqueous solution, and this mixture is brought into contact with the ion exchange fiber. The operation may be repeated. Alternatively, as a continuous method, a mixture of an alkali metal silicate aqueous solution and a silicic acid aqueous solution is continuously passed through an ion exchange fiber, and part or all of the acidic silicic acid aqueous solution flowing out is mixed with the alkali metal silicate aqueous solution. However, this mixture can also be continuously circulated through the ion exchange fiber once or multiple times.

After the ion exchange is completed, the acidic silicic acid aqueous solution within the ion exchange fiber layer is separated from the ion exchange fibers and recovered.

Separation methods include, for example, extrusion or suction using water and gas.

In the present invention, the highly concentrated acidic silicic acid obtained by ion exchange directly polymerizes to form a silica sol, but this silica sol is unstable and gels if left as it is at room temperature.

As a result of various studies to stabilize high-concentration silica sol so that it would not gel even during long-term storage, Suimeihiro et al.
0-10. ．． It has been found that silica sol can be stabilized by heating at 0.50 to 100°C. That is, in the present invention, the silica sol produced by polymerization of acidic silicic acid obtained by ion exchange is directly adjusted to pH 8.0 to 10.0.
Heating at 50-100°C is essential.

If the pH is less than 8.0, the silica sol cannot be sufficiently stabilized, and if the pH exceeds 10, a portion of the generated silica sol will dissolve and become silicate ions. pH 8.0-1
There is no particular limitation on the method of adjusting to 0.0. For example, alkali metal silicate, alkali metal hydroxide, alkaline earth metal hydroxide, etc. may be added directly or an aqueous solution thereof may be added, or ammonia gas may be added. may be blown in, or ammonium hydroxide may be added. or.

Alkaline compounds such as Na 2 CO 3 and Na HC 0 3 or aqueous solutions thereof may be added.

The heating temperature needs to be 50 to 100"C. If the temperature is less than 50C, the silica sol cannot be sufficiently stabilized even if the pH is set to 8.0 to 10.0. On the other hand, 100"C
If it exceeds this value, the particle size of the silica sol will increase and it will be difficult to control the particle size to 10 mμ or less.

The heating time is not particularly limited, but 1 to 10 hours is sufficient.

The highly concentrated ultrasmall silica sol obtained in the above manner is
It can be used as a product as it is, or it can be further concentrated if necessary, but as a concentration method, ultrafiltration is preferable in order to maintain a particle size of 3 to 10 mμ. Using an aqueous alkali metal silicate solution as a raw material, a stable silica sol with high concentration and extremely small particles can be obtained without precipitation or gelation of gel-like substances.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, a concentrated aqueous alkali metal silicate solution is ion-exchanged without causing the precipitation of a gel-like substance, and then the generated silica sol is adjusted to pH 8.0 to 10.0. , 50 to 100° C., it is possible to obtain a stable silica sol with high concentration and extremely small particles of 3 to 10 μm by an in-cylinder process that does not require any concentration step or has low concentration cost.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Chibi Co., Ltd. IEF-
While circulating water through a column filled with 3C (0.5 mm cut), a No. 3 sodium silicate aqueous solution containing 7 wt% of SiO2 was gradually added to the circulating water.
A silicic acid aqueous solution with an O2 concentration of 20 wt% was obtained. 610 g of the obtained silicic acid aqueous solution and SiO2 concentration 29.7 wt%
After mixing with 10 g of No. 3 sodium silicate aqueous solution, a portion of the mixture was passed through the same ion exchange fiber-packed column as above to produce an acidic silicic acid aqueous solution. The obtained acidic silicic acid aqueous solution and No. 3 sodium silicate aqueous solution were mixed in a ratio of 1 part SS1021ff of acidic silicic acid to 41 parts by weight of 5i02 of No. 3 sodium silicate aqueous solution. At the same time, the mixture was added to and mixed with the remaining part of the mixture. Subsequently, a portion of the mixture is passed through a column packed with ion exchange fibers. By repeating such mixing and ion exchange operations, a highly concentrated acidic silicic acid aqueous solution having Sto 221, Owt% was obtained. Acidic silicic acid polymerized and immediately became silica sol. 5i0229 to 500g of this silica sol
．． By adding 5.5 g of 7 wt% No. 3 sodium silicate aqueous solution to adjust the pH to 3.5, and then heating at 90°C for 2 hours, S l 0221.5 wt%,...N
A stable silica sol with a200.35 wt% was obtained.

The obtained silica sol was measured by the Sears titration method described in JP-A-62-7622, and the sol particle size was 8.
．． It was 0 mμ.

Example 2 In the same manner as in Example 1, however, 12 g of a 20 W t% NH4OH aqueous solution was added as an alkaline aqueous hI&.
H9,0 and then heated at 80°C for 2 hours.

The obtained silica sol is stable and 5i0220.5w
t%, NH40H0.5wt%.

Further, the particle diameter determined by Sears titration method was 7.0 mμ.

Comparative Example 1 A test was carried out in the same manner as in Example 1, except that an ion exchange resin (Organo ■ product, Anic-Lite IR-124) was used.

During ion exchange, a gel-like substance forms within the ion exchange resin layer.

precipitation was observed.

Comparative Example 2 When a highly concentrated silicic acid aqueous solution obtained in the same manner as in Example 1 was allowed to stand at room temperature without adding an alkaline aqueous solution, it gelled in 24 hours.

Comparative Example 3 In the same manner as in Example 1, except that after heating at 40° C. for 2 hours, the mixture was allowed to stand at room temperature, and gelatinized in 40 hours.

Comparative Example 4 In the same manner as in Example 1, but using an autoclave.
Heated at 50°C for 2 hours. The particle size of the obtained silica sol was 18 mμ.

Claims (1)

[Claims] (1) In a method for producing silica sol by contacting an aqueous alkali metal silicate solution with a hydrogen-type ion exchanger,
After mixing the alkali metal silicate aqueous solution with the silicic acid aqueous solution, it is brought into contact with ion exchange fibers for ion exchange, and then the generated silica sol is adjusted to pH 8.0-10.0, 50-
A method for producing a highly concentrated ultra-small silica sol, which comprises heating at 100°C.