JPH03223107A - Preparation of spherical silica - Google Patents

Abstract

PURPOSE:To prepare highly pure spherical silica having a low impurity content in simplified processes by spraying an alkali metal silicate salt aqueous solution in a gaseous phase, capturing the produced fine particles in an acid-containing solution in a water-containing state, treating the prepared spherical silica gel with an acid-containing solution and subsequently washing the silica gel with water. CONSTITUTION:The aqueous solution of an alkali metal silicate salt such as the Na salt or K salt of silicic acid in a concentration of usually 20-60wt.% is sprayed in a gaseous phase comprising air, etc., by a centrifugal method, a two fluid nozzle method, etc. The pressure of the atmosphere to be sprayed therein is usually 0.1-100 atmospheres, especially 0.9-10 atmospheres, and the operation temperature is preferably 10-80 deg.C. The produced fine particles are captured in an acid-containing solution containing an inorganic acid or organic acid in the water-containing state. The prepared gelled silica particles are separated from the suspension solution by a method such as filtration, precipitation or centrifugation and washed with water to provide the objective highly pure spherical silica.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing spherical silica.

[Conventional technology]

Conventionally, methods for producing spherical silica incorporating spray drying include: 1) Fine spherical particles obtained by spray drying an aqueous solution of an alkali metal silicate such as sodium silicate are treated with an acid aqueous solution to produce fine spherical silica. How to get it.

(For example, JP-A-60-54914, JP-A-62-1
No. 28916, Japanese Unexamined Patent Publication No. 128917/1984, 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 spherical silica powder.

(For example, JP-A-61-251509, etc.).

etc. have been proposed.

[Problem to be solved by the invention]

The above-mentioned conventional methods for producing spherical silica each have the following problems.

Method 1) involves drying the aqueous solution of alkali metal silicate and then returning it to the aqueous system for wet treatment, which wastes a lot of energy. Furthermore, this method has the disadvantage that it is difficult to reduce the impurity content in the obtained spherical silica.

In method 2), the silica powder is spray-dried after being produced, which lengthens the production process and consumes a large amount of energy.

An object of the present invention is to provide a method for producing highly pure spherical silica with a low impurity content through a simplified process.

[Means to solve the problem]

According to the research conducted by the present inventors, the lower the water content of the fine particles obtained by spray drying in the method 1) above, the lower the impurity content in the glue obtained by treating with an acid aqueous solution. In addition, if the fine particles obtained by spraying in method 1) have a high moisture content, the generated particles may adhere to each other or inside the device, causing the problem. It was learned that it was not possible to obtain the spherical silica that was the object of the invention.

The present inventors conducted research to improve the problems of the conventional method, and collected fine particles generated by spraying an aqueous alkali metal silicate solution into the gas phase with an acid-containing liquid in a state containing water.
The present invention was completed based on the knowledge that the above problem can be solved by treating the obtained spherical silica gel with an acid-containing liquid and then washing it with water.

The present invention is based on the following method: ``fine particles generated by spraying an aqueous alkali metal silicate solution into a gas phase are collected in a water-containing state with an acid-containing liquid, and then the obtained spherical silica gel is treated with the acid-containing liquid. ``A method for producing spherical silica, which is characterized by washing with water after washing.''

The present invention will be explained below.

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

In the method of the present invention, the aqueous alkali metal silicate solution used as a raw material has the general formula; MtO・n SiO□(
(where M is an alkali metal element, n is the number of moles of 5iOi and is 0.5 to 5), and an aqueous solution of a sodium salt, potassium salt, or lithium salt of silicic acid is used. be able to.

In the method of the present invention, the alkali metal silicate concentration in the aqueous alkali metal silicate solution used as a raw material is usually in the range of 20 to 60% by weight, preferably 30 to 55% by weight.
% by weight. When the alkali metal silicate concentration is low, it takes a long time for the aqueous alkali metal silicate solution droplets formed by spraying to solidify, whereas when the alkali metal silicate concentration is high, the alkali The viscosity of the aqueous metal silicate solution increases, making spraying difficult.

The viscosity of the aqueous alkali metal silicate solution 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 it becomes difficult to obtain spherical particles.

Methods for spraying aqueous alkali metal silicate solutions include centrifugal, 2fL nozzle, and pressure nozzle.

Various mechanisms such as an ultrasonic type can be used, and preferably a centrifugal type or a two-fluid nozzle type is used.

In the method of the present invention, the particle size of the spherical gel of silica that is collected by the droplets of the aqueous alkali metal silicate solution obtained by spraying and the acid-containing liquid is approximately 1 μm −1
It is about m. Thereby, spherical silica having a particle size in the range of 1 to 600 μm can be obtained.

In the method of the present invention, there are no particular restrictions on the constituents of the gas phase in which the aqueous alkali metal silicate solution is sprayed, but air is practically used.* A r + He + inert gas atmosphere such as nitrogen, water vapor The atmosphere may also be a carbon dioxide gas atmosphere.

In the method of the present invention, the pressure of the atmosphere in which the aqueous alkali metal silicate solution is sprayed is usually in the range of 0.1 to 100 atm, preferably in the range of 0.9 to 10 atm. Further, the operating temperature is set within a range in which the aqueous alkali metal silicate solution maintains a liquid state with the above-mentioned viscosity, preferably within a range of 10 to 80''C.

In the method of the present invention, the acid-containing liquid used to collect fine particles generated by spraying an aqueous alkali metal silicate solution into the gas phase includes sulfuric acid and hydrochloric acid.

Examples include aqueous solutions of inorganic acids such as nitric acid, and organic acids such as acetic acid and oxalic acid, and carbonated water can also be used.

The acid concentration of the acid-containing liquid is 0.1 to 4 normal, preferably 0.1 to 4 normal.
It is in the range of 5 to 3 normal, more preferably 1 to 2 normal.

If the acid concentration of the acid-containing liquid is high, it will be difficult to extract and remove impurities from the obtained silica, while if the acid concentration is low, the dissolution loss of the silicic acid component will be large.

In the method of the invention, the water content of the spray product of the aqueous alkali metal silicate solution collected in the acid-containing liquid is preferably greater than 40% by weight, and more preferably greater than 44% by weight.

The moisture content is expressed as the percentage weight loss of the sprayed product (dry product) when the sprayed product is dried at a temperature of 180'C for 6 hours.

Fine particles generated by spraying an aqueous alkali metal silicate solution into a gas phase can be collected using a method for collecting fine particles, such as a sedimentation type, a collision type, or an aerosol. In the method of the present invention, a conventional collection device such as a cyclone scrubber, a Hentury Scrach wet wall tower, a wet scrubber, or a trel can be used.

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

Although the method of the present invention is not limited by the impurity content in the spherical silica, it is possible to obtain high purity spherical silica with a low impurity content depending on the intended use of the spherical warping force.

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

Such high-purity spherical silica with a low impurity content can be obtained by treating the silica particles obtained as described above with an acid-containing liquid and then washing with water to extract and remove impurities.

Acid-containing liquids used in the process to extract and remove impurities include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and carbonic acid;
Examples include aqueous solutions of organic acids such as acetic acid and oxalic acid. The acid concentration of the acid-containing liquid is in the range of 01-4N, preferably 0.5-3N, more preferably 1-2N.

The processing temperature when extracting and removing impurities is 20°C or higher,
Preferably, the temperature is maintained at 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 cleaning treatment using an aqueous solution containing these may be combined. Furthermore, a chelating agent and/or a peroxide such as hydrogen peroxide may be added in advance to the aqueous alkali metal silicate solution.

By the above method, it is possible to obtain high-purity spherical silica having a content of various impurities such as the aforementioned transition metal elements such as AI, Fe, and Ti, all of which are 1 ppa+ or less.

Since the silica thus obtained contains a large amount of water and has a large number of pores, the silica obtained by the above treatment is heat-treated as necessary depending on the intended use of the spherical silica.

Heat treatment conditions vary depending on the use of the spherical silica.
It can be selected as appropriate.

When obtaining spherical silica as a filler for encapsulants of electronic components, heat treatment is performed at a temperature in the range of 1000 to 2200'C, preferably firing in the range of 1000 to 1500'C.

This treatment removes moisture remaining in the silica,
Furthermore, the silica particles are made hydrophobic by reducing the existing silanol groups to about 1% by weight or less, and the pores of the silica particles are closed to adjust the pore volume and specific surface area. Changes the structure to a dense one that is difficult for moisture to penetrate.

When obtaining spherical silica for use in drying agents, cosmetic raw materials, catalyst supports, liquid chromatography fillers, etc.
Heat treatment at a temperature in the range of 100 to 1050'c is preferable.

As a raw material for glass such as quartz glass or ceramic fuchs, spherical silica that is not subjected to heat treatment can be used, or spherical silica that has been subjected to heat treatment can also be used.

The heating time is 0.1 seconds to 100 hours, preferably 1 second to 6 hours.
The time is more preferably in the range of 10 seconds to 3 hours. The combination of temperature and time as heat treatment conditions can be selected as appropriate; the higher the heat treatment temperature is, the shorter the time can be.

The atmosphere in which the heat treatment is carried out is arbitrary as long as it does not impair the idea of the present invention, and may be an inert gas atmosphere such as Ar or He, an oxidizing atmosphere such as air, a reducing atmosphere such as hydrogen, a water vapor atmosphere, or an atmosphere containing silica. An atmosphere containing a halogen or halide, such as chlorine, can be used to effectively remove impurities. The heat treatment is performed under atmospheric pressure, but can also be performed under reduced pressure.

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

Note that the heat treatment at a low temperature of about 200'C or less can also be performed by immersing it in water and hydrothermal treatment.

The spherical silica obtained by heat treatment can be subjected to crushing and classification treatment, if necessary.

The average particle diameter of spherical silica as a filler for 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 as a raw material for quartz glass is 1
~600 μm, preferably 1 to 300 tt m, more preferably 1 to 20 μm for sintering, hot pressing, sol-gel method auxiliary materials, etc., and 100 to 300 μm for melting such as arc melting, Bertie method, etc. is within the range of

[Effects of the Invention] According to the method of the present invention, highly pure spherical silica with a low impurity content can be produced in a simplified process.

By the method of the present invention, alkali (earth 111i) metals.

It is possible to obtain high-purity spherical silica, which has a low content of impurities such as halogens, transition metal elements, and radioactive substances, and is passed through a filler for encapsulants of high-density integrated circuit electronic components.

〔Example〕

The present invention will be explained below with reference to Examples and Comparative Examples. Note that "%" indicates "% by weight". Moreover, the moisture content on each side is a value on a dry matter basis.

Example - 1° Air at a temperature of 60° C. was supplied at a rate of 30 per minute as a conveying gas into a container in which a wet wall was formed by flowing 6 kg of a 10% sulfuric acid aqueous solution per hour onto the inner wall.

In this container, a sodium silicate aqueous solution having a viscosity of 140 centipoise at a temperature of 20°C (JIS 1408°3
Equivalent product; 5iOz: 30%, NatO: 1
0%3 moisture content: 60%) was supplied through a two-fluid nozzle at a flow rate of 10 g/min, and atomized using air at 17 N/min as the atomizing gas.

Droplets of the aqueous sodium silicate solution and aggregates of the gelled product and the aqueous sulfuric acid solution that were generated by spraying and flowing out from the outlet at the bottom of the container were collected using a cyclone.

The collected aggregate was heated to a temperature of 100° while stirring.
By holding at C for about 1 hour, spherical silica was produced. The produced spherical silica was separated from the aggregate.

The spherical silica obtained from 3 kg of the above aggregate was treated with sulfur 6I1
It was immersed in 1 kg of a 10% aqueous solution and stirred at a temperature of 100° C. for about 1 hour to extract impurities, then washed with pure water to deoxidize, and then filtered to obtain wet silica.

This wet silica was dried at a temperature of 180°C for 6 hours, and the obtained dry silica was placed in a quartz crucible and heated using an electric furnace at a temperature of 180°C.
A heat treatment was performed at 250° C. for 4 hours to obtain spherical silica.

The obtained spherical silica had an average particle diameter of 22 μm and a specific surface area of 0.9 po/g.

The impurity content of this spherical silica is NaO, 2ppm
.

Al was 1ρpI11, and U was 0.1 ppb or less.

Comparative Example 1 A sodium silicate aqueous solution was sprayed in the same manner as in Example 1, except that the sulfuric acid aqueous solution was not poured onto the inner wall of the container and no wet wall was formed.

Under these conditions, most of the sprayed product of the sodium silicate aqueous solution adhered to the inside of the container, and only a small amount of aggregated particles were collected by the cyclone provided at the outlet of the container.

The moisture content of the collected material was 45%.

Comparative Example-2゜Into a container similar to Example-1, air at a temperature of 80°C was pumped at 3001°C per minute. supplied. However, the sulfuric acid aqueous solution was not poured onto the inner wall to prevent the formation of a wet wall.

A sodium silicate aqueous solution was sprayed into this container in the same manner as in Example-1.

Even under these conditions, a large amount of sodium silicate adhered to the inside of the container, and the yield of sodium silicate collected by the cyclone provided at the outlet of the container was 3%.

The moisture content of the collected material was 22%.

Comparative Example = 3: Air at a temperature of 100° C. was supplied at a rate of 300 f/min into a container similar to Example-1. However, the sulfuric acid aqueous solution was not poured onto the inner wall to prevent the formation of a wet wall.

A sodium silicate aqueous solution was sprayed into this container in the same manner as in Example-1.

Under these conditions, a large amount of water dissipated from the droplets of the aqueous sodium silicate solution produced by spraying, and spherical particles of sodium silicate with a water content of 11% were collected by a cyclone provided at the outlet of the container. However, even under these conditions, a large amount of sodium silicate adhered to the inside of the container, and the yield of sodium silicate spherical particles collected by the cyclone was 21%.

2.9 kg of a 10% aqueous sulfuric acid solution was added to 130 g of the obtained sodium silicate particles, and the mixture was stirred at a temperature of about 100'C for about 1 hour to produce silica.

Separate the generated silica and add 1k of fresh 10% sulfuric acid aqueous solution.
g, and then treated in the same manner as in Example 1 to obtain spherical silica.

The obtained spherical silica had an average particle diameter of 24 μm and a specific surface area of 0.9 bo/g.

The impurity content of this spherical silica is Na 10pp...A
l 5 pρ-, and U was 2 ppb.

Claims (1)

[Claims] 1) Fine particles generated by spraying an aqueous alkali metal silicate solution into the gas phase are collected with an acid-containing liquid in a water-containing state,
A method for producing spherical silica, which comprises treating the obtained spherical silica gel with an acid-containing liquid and then washing it with water.