JP2733863B2 - Method for producing spherical silica - Google Patents

Description

The present invention relates to a method for producing spherical silica.

[Conventional technology]

Conventional methods for producing spherical silica incorporating a spray-drying treatment include: 1) fine spherical particles obtained by spray-drying an aqueous solution of an alkali metal silicate such as sodium silicate; How to get.

(For example, JP-A-60-54914, JP-A-62-128916,
JP-A-62-128917, etc.). 2) A method in which a slurry obtained by dispersing silica powder in water or an organic medium is spray-dried and fired to obtain a spherical silica powder.

(For example, JP-A-61-251509). And so on.

[Problems to be solved by the invention]

Each of the above-mentioned conventional methods for producing spherical silica has the following problems.

The method 1) involves once drying an aqueous solution of an alkali metal silicate, and then returning the aqueous solution to an aqueous system and performing a wet treatment, which wastes a large amount of energy. In addition, this method has a disadvantage that it is difficult to reduce the content of impurities in the obtained spherical silica.

In the method 2), since the silica powder is produced and then spray-dried, the production process is lengthened and energy consumption is large.

An object of the present invention is to provide a method for producing high-purity spherical silica having a low impurity content in a simplified process.

[Means for solving the problem]

The present inventors conducted research to improve the problems of the conventional method, and contacted droplets formed by spraying an aqueous solution of an alkali metal silicate and an aqueous solution of an acid or / and an acid salt into a gas phase. After that, the present inventors have found that the above problem can be solved by treating with an acid-containing liquid and then washing with water, thereby completing the present invention.

The present invention provides an aqueous solution of an alkali metal silicate and an acid or /
A method for producing spherical silica, comprising spraying an aqueous solution of an acidic salt in the gaseous phase, contacting the droplets formed, contacting, collecting, treating with an acid-containing liquid, and washing with water. ”.

 Hereinafter, the present invention will be described.

In the present invention, the term "spherical" refers to a particle having a ratio of a minimum diameter to a maximum diameter of one particle in a range of 1 to 0.5.

In the method of the present invention, an aqueous alkali metal silicate solution used as a raw material has a general formula: M ₂ O · nSiO ₂ (where M is an alkali metal element and n is SiO ₂
Of the alkali metal silicate represented by the following formula (1), and an aqueous solution of a sodium salt, a potassium salt, a lithium salt or the like of silicic acid can be used.

In the method of the present invention, the concentration of SiO ₂ in the aqueous alkali metal silicate solution used as a raw material is usually 5 to 60% by weight.
And preferably in the range of 20 to 50% by weight.
When the SiO ₂ concentration is low, it takes a long time for the droplets of the alkali metal silicate aqueous solution generated by spraying to solidify,
On the other hand, when the SiO ₂ concentration is high, the viscosity of the aqueous solution of the alkali metal silicate increases, and the spraying treatment becomes difficult.

The viscosity of the aqueous alkali metal silicate solution to be sprayed in the method of the present invention is 200 poise or less, preferably 10 poise or less. If the viscosity is too high, spraying becomes difficult and spherical particles cannot be obtained.

Examples of the aqueous solution of an acid sprayed in the method of the present invention include an aqueous solution of an inorganic acid such as sulfuric acid, hydrochloric acid, and nitric acid, and an aqueous solution of an organic acid such as acetic acid and oxalic acid. Carbonated water can also be used. The acid concentration of the acid aqueous solution to be sprayed is in the range of 0.1 to 4N, preferably 0.5 to 3N, more preferably 1 to 2N.

Examples of the aqueous solution of an acidic salt include an aqueous solution of an ammonium salt or an alkali metal hydrogen salt of the acid, wherein the pH of the aqueous solution is 7 or less, preferably 6 or less.
The concentration of the salt is preferably in the range of about 3 to 30% by weight.

Various mechanisms such as a centrifugal system, a two-fluid nozzle system, a pressurized nozzle system, and an ultrasonic system can be used for spraying the alkali metal silicate aqueous solution and the acid or / and acidic salt aqueous solution, respectively. , Preferably centrifugal or 2
A fluid nozzle system is used.

To obtain particles having a large diameter, a pressure nozzle or a dropping nozzle can be used.

The particle size of the droplets and / or gels of the aqueous alkali metal silicate solution obtained by spraying in the method of the present invention is as follows:
It is about 1 μm to 1 mm. Thereby, the particle size is 1-600μ
m spherical silica can be obtained.

In the method of the present invention, in order to obtain spherical silica, the particle size of the aqueous solution of the acid or / and the acidic salt formed by spraying is equivalent to the particle size of the aqueous solution of the alkali metal silicate. Alternatively, it is preferably smaller.

In the method of the present invention, the components of the gas phase for spraying the aqueous solution of the alkali metal silicate and the aqueous solution of the acid or / and the acidic salt are not particularly limited, but air is practically used. An atmosphere of an inert gas such as Ar, He, or nitrogen, a steam atmosphere, or a carbon dioxide gas atmosphere can also be used.

In the method of the present invention, the pressure of the atmosphere in which the aqueous alkali metal silicate solution is sprayed is generally in the range of 0.1 to 100 atm, preferably in the range of 0.9 to 10 atm. The operating temperature is in a range where the aqueous solution of the alkali metal silicate keeps the liquid having the above viscosity, preferably in a range of 10 to 80 ° C.

The droplets and / or gels of the aqueous alkali metal silicate solution produced by spraying and the droplets of the aqueous solution of the acid or / and the acidic salt are collected using a collecting device as an aggregate. In the method of the present invention, as the collecting device, a general collecting device such as a cyclone, a cyclone scrubber, a venturi scrubber, or a wet wall tower can be used.

During the collection process, the droplets of the aqueous alkali metal silicate solution are further gelled, and a suspension containing silica particles is obtained. Silica particles can be obtained from the obtained suspension by ordinary solid-liquid separation operations such as filtration, sedimentation, and centrifugation.

The method of the present invention is not limited by the content of impurities in the spherical silica, but high purity spherical silica having a low impurity content can be obtained depending on the intended use of the spherical silica.

In particular, in the case of spherical silica used as a filler for encapsulants for high-density integrated circuit electronic components; containing alkali metal elements such as Na and K, alkaline earth metal elements such as Mg and Ca, and halogen elements Rate is 1p each
pm or less, and the content of radioactive elements such as U and Th is preferably 1 ppb or less.

Such a high purity spherical silica having a low impurity content,
It can be obtained by treating with the acid-containing solution of the silica particles obtained as described above, followed by washing with water to extract and remove impurities.

Examples of the acid-containing liquid used in the treatment for extracting and removing the impurities include aqueous solutions of inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and carbonic acid, and organic acids such as acetic acid and oxalic acid. The acid concentration of the acid-containing solution is in the range of 0.1 to 4N, preferably 0.5 to 3N, more preferably 1 to 2N.

The processing temperature for extracting and removing impurities is preferably maintained at 20 ° C. or higher, and more preferably 50 ° C. or higher.

If necessary, a chelating agent and / or a peroxide such as hydrogen peroxide may be added to the acid-containing liquid, or a washing treatment with an aqueous solution containing these may be combined. Further, a chelating agent and / or a peroxide such as hydrogen peroxide may be added to the aqueous alkali metal silicate solution in advance.

By the above-mentioned method, it is possible to obtain high-purity spherical silica in which the content of various impurities such as the transition metal elements such as Al, Fe, and Ti is 1 ppm or less.

The silica thus obtained contains a large amount of water and has a large number of pores. Therefore, the silica obtained by the above-mentioned treatment is subjected to a heat treatment as necessary according to the intended use of the spherical silica.

The conditions of the heat treatment differ depending on the use of the spherical silica, and can be appropriately selected.

In order to obtain spherical silica as a filler for a sealing material of an electronic component, heat treatment at a temperature in the range of 1000 to 2200 ° C., preferably firing in a range of 1000 to 1500 ° C. is performed.

By this treatment, water remaining in the silica is removed, the silanol groups present are reduced to about 0.1% by weight or less, the silica particles are made hydrophobic, and the pores of the silica particles are closed to make them fine. The pore volume and the specific surface area are adjusted to change the silica particles into a dense and hardly permeated structure.

In order to obtain spherical silica used as a desiccant, a cosmetic material, a catalyst carrier, a packing material for liquid chromatography, etc., a heat treatment at a temperature in the range of 100 to 50 ° C. is preferable.

As a raw material for glass such as quartz glass or ceramics, spherical silica without heat treatment can be used, or spherical silica with heat treatment can be used.

The heating time ranges from 0.1 seconds to 100 hours, preferably 1 second to 6 hours, more preferably 10 seconds to 3 hours. The combination of high temperature and time as heat treatment conditions can be appropriately selected, and the higher the temperature of heat treatment, the shorter the time.

The atmosphere in which the heat treatment is performed is arbitrary as long as the idea of the present invention is not impaired, and is an inert gas atmosphere such as Ar or He, an oxidizing atmosphere such as air, a reducing atmosphere such as hydrogen, a steam atmosphere, or a silica atmosphere. An atmosphere containing halogen or a halide such as chlorine which can remove impurities effectively can be used. The heat treatment is performed under atmospheric pressure,
It can also be performed under reduced pressure.

The heating source is optional, and electric heating or combustion gas is an economical heat source. In addition, plasma heating and an image furnace can be used.

Note that the heat treatment at a low temperature of about 200 ° C. or lower can also be performed by immersion in water and hydrothermal treatment.

The spherical silica obtained by the heat treatment can be subjected to a crushing / classifying treatment as required.

The average particle size of the spherical silica as a filler for an electronic component sealing material is in the range of 1 to 100 μm, preferably 5 to 40 μm, and more preferably 10 to 30 μm.

The average particle size of spherical silica for quartz glass raw material is
1 to 600 μm, preferably 1 to 300 μm, and more preferably 1 to 20 μm for sintering, hot pressing, auxiliary material for sol-gel method, and 100 to 300 μm for melting such as arc melting and Bernoulli method. is there.

〔The invention's effect〕

By the method of the present invention, high-purity spherical silica having a low impurity content can be produced in a simplified process.

According to the method of the present invention, high-purity spherical silica having a low impurity content such as an alkali (earth) metal, a halogen, a transition metal element, and a radioactive substance and suitable for a sealing material for a high-density integrated circuit electronic component. Can be obtained.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples.

Example-1. A 2N aqueous sulfuric acid solution was fed into a vessel under atmospheric pressure (volume: 30) through each of three two-fluid nozzles at a rate of 40 min / min.
It was supplied at a flow rate of g and sprayed using 10 air per minute as a spray gas. At the same time, a sodium silicate aqueous solution (JIS K1408, No. 3 equivalent; SiO ₂ : 28%, Na
₂ O: 9%) at a flow rate of 10 g / min, spraying into the vessel at a temperature of about 25 ° C. using air at 2 / min as a spraying gas, and applying a sodium silicate aqueous solution and a sulfuric acid aqueous solution. Was contacted.

Using a cyclone, a liquid suit of the aqueous sodium silicate solution and a liquid suit of the gelled product and the sulfuric acid aqueous solution, which flow out through an outlet provided at the lower part of the container, were collected using a cyclone.

The collected aggregate was held at a temperature of about 30 ° C. for about 1 hour with stirring to produce spherical silica.
The formed spherical silica was separated from the aggregate.

15 g of the obtained spherical silica was immersed in 300 g of a 2N aqueous sulfuric acid solution, and the mixture was stirred at a temperature of about 100 ° C. for about 1 hour to extract impurities. Then, washing and filtration with pure water were repeated five times.
It was deoxidized and dehydrated using Nutsche to obtain wet silica.

The wet silica is dried at 150 ° C. for 6 hours using a hot air drier, and the obtained dried silica is placed in a quartz crucible and subjected to a heat treatment at 1250 ° C. for 6 hours using an electric furnace to remove spherical silica. Obtained.

The resulting spherical silica had an average particle size of 22 μm and a specific surface area of 0.6 m ² / g.

The impurity content of this spherical silica is Na0.1ppm, Al0.80p
pm and U was less than 0.1 ppb.

Claims (1)

(57) [Claims] An aqueous solution of an alkali metal silicate and an aqueous solution of an acid or / and an acid salt are each brought into contact with a droplet formed by spraying the aqueous solution into a gas phase, then collected and treated with an acid-containing liquid. And then washing with water.