JPS60180911A - High-purity silica and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture industrially high purity silica in the form of fine powder by converting an aqueous alkali silicate soln. into gel, purifying the resulting silica gel with a volatile acid, dehydrating it under heating, and spouting the dehydrated silica powder into a flame to carry out melting treatment. CONSTITUTION:An aqueous alkali silicate soln. of high purity such as an aqueous sodium silicate soln. prepd. by dissolving crystalline sodium silicate is brought into contact with an ion exchange resin to form acidic silica sol, and this sol is converted into gel by adding an aqueous ammonia soln. Said alkali silicate soln. may be directly converted into gel by neutralization with an acid such as sulfuric acid. Impurities such as radioactive substances are removed from the precipitated silica gel with an acid which is volatilized by the following heat treatment such as nitric acid or hydrochloric acid to purify the silica gel. The resulting silica hydrate is dehydrated under heating by spraying or other method, and the dehydrated silica powder is spouted into a flame at >=about 3,000 deg.C such as an oxyhydrogen flame. The powder is made spherical by melting to obtain high purity silica contg. <=10ppb radioactive substances and having 1- 100mum average particle size and >=80% degree of melting. The electric conductivity of boiling water passed through the silica to carry out leaching or extraction is <=100muS/ cm.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to high purity silica and a method for producing the same. More specifically, the present invention relates to high-purity silica that can be applied to fillers such as resins, adhesives, abrasives, substrates, package materials, etc. used in special fields requiring high purity such as electronic materials, and a method for producing the same.

Conventionally, silica has been widely used as a reinforcing filler for rubbers, resins, etc., and recently, with the development of electronic technology, there has been an increasing demand for higher purity silica for use. For example, when used as a packaging material for LSI or VLSI, the presence of even a trace amount of α-radiators, especially uranium, thorium, etc. in the packaging material or resin causes α-particles to be released with radioactive decay. It penetrates into the IC chip and generates a large amount of electron-hole pairs near the storage nodes of dynamic RAM and COD, which is likely to cause soft errors, so the selection of materials for fillers, substrates, etc. is important. Others such as sodium, potassium,
metals such as calcium, electrolytes such as sulfates, chlorides,
High purity silica free of impurities such as other soluble substances is desirable.

Traditionally, silica, which has been used as a filler in general-purpose resins and rubber, is mainly obtained through neutralization reaction with alkali silicate and acid, gas phase reaction, and hydrolysis of silicate ester, silicon tetrachloride, etc. However, silica made from inexpensive alkali silicate has problems in terms of purity, and silica produced by hydrolysis of silica or silicate ester through gas phase reactions is expensive. The emergence of silica that is compatible with the above uses in terms of purity and economic efficiency has been awaited. Conventionally known wet-process silica, for example, wet-process silica powder obtained by neutralizing reaction with alkali silicate and fermentation, contains salts in the mother liquor and colloids of impurity components in the silica precipitate produced. In order to remove these substances, large amounts of washing water and acid solutions are required, which is not only extremely inefficient, but also cannot be completely removed, making it impossible to supply high-purity silica especially for electronic materials. was.

On the other hand, as a method for producing high-purity silica from an aqueous alkali silicate solution, it is known to generate a silica sol using an ion exchange resin and then recover it as precipitated silica (Japanese Patent Publication No. 3B-9415, Japanese Patent Publication No. 3B-1999). -18
315, Japanese Patent Publication No. 37-4304), both methods have poor sedimentation and filterability of the silica precipitate, so not only does it take a lot of time to wash the filtration, but the water content of the filter cake also decreases. is extremely large, and it is not only impossible to sufficiently separate and remove contaminant impurities from the obtained silica, but also unsuitable for obtaining a single granular melt.

On the other hand, a method has recently been proposed for producing high-purity fused granular silica by subjecting finely pulverized natural high-purity silica to flame treatment. (Japanese Unexamined Patent Publication No. 58-145813) However, since the raw material is a natural product, it depends on the production area in terms of purity, and if it is always supplied uniformly, it is not necessarily consistent with industrial standards. Yes, it's difficult.

In view of the current situation, the present inventors conducted extensive research in order to industrially advantageously obtain high-purity silica from an aqueous alkali silicate solution, and as a result, completed the present invention.

That is, the present invention provides silica obtained from an aqueous alkali silicate solution, in which the radioactive substance is 10 ppb or less, and the electric conductivity at 25°C of the extracted water obtained by boiling and leaching the silica is 10.
01LS/cm or less, and the average particle size is 1 to 100
The present invention is a high-purity silica that falls within the range of JLII and has a degree of melting of 80% or more, and a method for producing the same.

The present invention will be explained in detail below.

The first feature of the high-purity silica according to the present invention is that an aqueous alkali silicate solution prepared as a starting material is used.

Therefore, unlike conventional products, it is not a processed or purified product of natural products, and it is different from silica prepared by hydrolyzing silicon tetrachloride or the like, a so-called dry method.

In other words, it is obtained from wet process silica, and its second characteristic is that the electrical conductivity of the extracted water obtained by boiling and leaching the silica with radioactive substances of 10 ppb or less is 100 JLS/c.
■It is a high purity silica with the following.

Radioactive substances are mainly uranium, but also include chemical substances such as thorium that emit alpha rays, which are high-density ionizing radiation, and the total amount of metal is 10 ppb or less based on activation analysis. The content is preferably 5 ppb or less, and if it exceeds 10 ppb, when used as a resin encapsulant filler for highly integrated ICs, LSIs, and VLSIs (7), it is preferable because it may cause soft errors due to the radiation described above. do not have.

Also, the electrical conductivity of the extracted water from which silica is boiled and leached is 10.
0 p, S/c+s or less, preferably 10 ILS/c
6 or less, and this value is attributable to the ionic impurities contained in the silica. For example, ionic impurities such as alkaline content and chloride ions are approximately 10 p as Na20 and i.
pm or less, preferably 5 ppm or less, and when the electrical conductivity exceeds 100 S/C, when used as a resin sealant filled with silica, the release of ionic substances may cause problems in ICs, LSIs, and VLSIs. This is undesirable because it tends to cause corrosion to lead wires, lead frames, etc.

The electrical conductivity of the extracted water is a value measured by making the silica into a 10% by weight slurry with pure water, boiling it for 8 hours while stirring, and then cooling the extracted solution at 25° C. as a sample.

Next, as a third characteristic, it is desirable that the average particle diameter is in the range of 1 to 100 μm. In the present invention, when particle size is meant, it is based on a particle size distribution measurement method based on the Coulter counter method5, and the average particle size refers to the volume median diameter (
R50), and its value is in the range of 1 to 100 degrees.

This particle size varies greatly depending on the product's use and manufacturing method, but it is generally within the above range, especially when R50 is 10 to 50.
It is preferable that the average particle size is within the range of JL.
If it exceeds QQ JL I+, it is not preferable because uniformity in the resin cannot be maintained and workability during resin sealing may be poor.

Further, another feature of the silica product according to the present invention is that it is composed of fused granules having a degree of melting of 80% or more. If the degree of melting is less than 80%, hydroxyl groups or moisture may be adsorbed due to the activity of the silica surface, resulting in deterioration of the sealant properties, which is not preferable.

Whether or not silica particles are melted can be easily determined by, for example, observation using a stereomicroscope; melted particles are recognized as transparent glass particles, and unfused particles are recognized as white opaque particles.

Therefore, in the present invention, the degree of melting (MR) is expressed by the following formula: % It is desirable that the field of view of the microscope is at least two fields, and that at least 50 or more particles can be detected in one field of view. Incidentally, particles that are observed to be molten on the outside and have a slight unmelted portion in the core are included in the range of molten particles.

High-purity fused silica particles having the above characteristics are a new substance, and are particularly suitable as fillers for resin compounds for IC packages.

Next, such high-purity fused silica particles can be produced industrially by the following method.

That is, a first step of gelling an aqueous alkali silicate solution to precipitate silica gel, a second step of purifying the silica gel with a volatile acid to obtain hydrated silica, and heating and dehydrating the hydrated silica to obtain dehydrated silica. This method of producing high-purity silica is characterized by comprising a third step and a fourth step of injecting the dehydrated silica into a flame and melting it. Each step will be explained below.

Milk finishing process 1 Many proposals have been made for this process as a so-called wet method for producing silica, and in most cases it can be said to be a known method.

In the present invention, this step can be roughly divided into two modes. One method is to bring an aqueous alkali silicate solution into contact with a cation exchange resin to produce an acidic silica sol, and then gel the silica sol as a silica precipitate. This is the case where silica gel is obtained directly by a neutralization reaction with an acid such as hydrochloric acid.

First, the case of obtaining silica gel via silica sol will be described. The method of producing silica sol from an aqueous alkali silicate solution is known, and the sol is produced according to a conventional method.
A solution diluted to a concentration of around 100% by weight is used. In ion exchange operations, it is common to pass the solution to be treated through a column packed with ion exchange resin, but other methods, such as a batch method in which the ion exchange resin and aqueous alkali silicate solution are directly mixed, are also possible. .

The aqueous alkali silicate solution is brought into contact with an ion exchange resin to separate and remove almost all of the alkali metals or alkaline earth metals to obtain an acidic sol.

In this case, in the present invention, the contact treatment is performed once or multiple times using the same or different ion exchange resin and/or chelate resin as desired, depending on the liquid nature of the aqueous alkali silicate solution or the use of the silica. can do.

Normally, when high-purity silica is desired, it is preferable to generate a sol by sequentially treating with a cation exchange resin in an acid form, an anion exchange resin in a hydroxyl form, and a cation exchange resin. .

This acidic sol was recovered from P) 11.8 to 3.0, and the particle size of the silica particles constituting the sol is less than 511 JL, making it an extremely active sol. It should be avoided to leave it for a long time because it will solidify into a gel-like state.

Although the impurities present in the ionic state in the raw material solution are substantially removed by the production of silica sol using such an ion exchange resin, in order to remove impurity ions more completely,
If necessary, a chelate resin may be used in combination with an ion exchange resin for contact treatment.

In this way, the purified acidic sol of silica colloid is precipitated and recovered as hydrous silica, but in this case, incorrect precipitation conditions will not only reduce the purity of the silica but also cause operational troubles. The conditions for silica precipitation are extremely important.

Therefore, in the present invention, the sol prepared by adding 0.5 mol or less, preferably 0.2 to 0.5 mol of aqueous ammonia per mol of 5i021 to the above acidic sol to make it weakly alkaline, and an aqueous ammonium salt solution are stirred. Silica precipitates are precipitated by reacting under weakly alkaline conditions where pn is always 10.5 or less.

In this case, even if p)l during the reaction is too high, or even if it is neutral to acidic, it is not possible to obtain a good precipitation, which is convenient for the present invention. For example, if most of the reaction is acidic or Translucent agar-like (silica) when carried out in neutral
This results in a precipitate with a high moisture content and poor filterability. Such a precipitate is not only extremely difficult to wash, but also shrinks during drying and baking, causing cracks and becoming a hard lump that cannot be easily crushed, significantly interfering with subsequent operations. Furthermore, if the reaction is carried out in a strongly alkaline environment, the amount of ammonia that evaporates will increase, resulting in a poor working environment and the resulting silica will become very fine particles, making it difficult to filter and having poor sedimentation properties.

The sol and the ammonium salt aqueous solution can be mixed together individually or by adding the sol into the ammonium salt aqueous solution, but the latter is generally better, but the reverse addition, That is, addition of aqueous ammonium salt solutions into the sol should be avoided.

The concentration of the ammonium salt aqueous solution varies depending on the type of salt, but is usually 5 to 20% by weight, preferably 7 to 13% by weight.
Good.

If the ammonium salt concentration is outside the above range, part or most of the precipitated silica will become transparent agar-like silica or become a bulky precipitate, resulting in a marked deterioration in filtration performance, and the water content will be extremely low. This may make subsequent collection operations difficult or make it impossible to control product particle size.

The amount of the ammonium salt aqueous solution charged in advance into the reactor varies depending on incidental conditions such as the addition rate of the silica sol to be added, the silica concentration, the concentration of the ammonium salt aqueous solution, and the desired particle size of the product, but it is at least 115 times the amount of the silica sol to be added.
More than a certain amount is necessary.

Suitable ammonium salts used as coagulants for silica include salts that decompose and volatilize upon heating, such as ammonium chloride, ammonium carbonate, and ammonium nitrate.

There is no particular reason to limit the temperature at which silica is precipitated, and it may be at room temperature or at elevated temperature, but it is necessary to sufficiently control the pi of the reaction system, and it should always be kept in a mildly alkaline state. It is preferable to precipitate.

The hydrous silica precipitate thus obtained has extremely good filterability and can be separated from the mother liquor by filtration.

Next, a method for directly obtaining silica using an aqueous alkali silicate solution and an acid such as sulfuric acid is known, as is the method for producing silica sol using an ion exchange resin.
No., Special Publication No. 51-25235, Special Publication No. 56-2172
An example of an excellent industrial production method is a method of adding acid in portions such as No. 8, but it is not limited to this method.

However, with this direct method, the content of radioactive M substances and alkalis, which are impurities in the silica, varies widely depending on the precipitation conditions of silica precipitate based on neutralization. In such cases, it is preferable to form a silica precipitate through contact with an ion exchange resin to form a silica sol.

Note that it is preferable that the alkaline silicate aqueous solution used be sufficiently purified in view of its purpose.For example, it is preferable to remove fine particles in advance using a pre-coat filter, microfilter, ultrafiltration, etc. as well as a general filter. good.

In particular, an aqueous aqueous solution of an alkali silicate prepared by dissolving crystalline substances such as alkali metasilicate and alkali sesquisilicate can significantly reduce radioactive impurities. Less silica can be obtained. As such an aqueous alkali silicate solution, a sodium silicate aqueous solution prepared by dissolving crystalline sodium silicate is preferable.

Eaves 1 This step purifies the precipitated silica gel obtained in the previous step, that is, removes ionic impurities such as radioactive substances, alkaline earth metal salts, and alkali metal salts remaining in the silica gel. Therefore, this step can be said to be an essential step for obtaining high purity silica by the wet method.

In the previous step, when a well-purified alkali silicate aqueous solution is used as a starting material and precipitated silica gel is recovered through silica sol using an ion exchange resin, impurities such as radioactive substances can be removed from the silica to a fairly high level. However, it is not necessarily satisfactory as a filler for a resin sealant that requires high performance. However, when this precipitated silica gel is thoroughly mixed with a volatile acid and washed, not only radioactive substances but also alkaline earth metal salts, alkali metal salts, and trace impurities such as iron and aluminum compounds can be removed. It becomes possible.

In other words, this process is a purification process of precipitated silica gel using a volatile acid, and by employing this process, it can be said that a path has been opened for preparing high-purity silica from wet process silica, which is completely comparable to dry process silica.

The term "volatile acid" as used herein refers to an acid that is completely volatilized by heating in the next third or fourth step, preferably nitric acid, hydrochloric acid, or the like.

Further, precipitated silica gel means a silica gel that is easily separated from the mother liquor by filtration or has good filtration property due to the precipitation of silica obtained by the method of the first step.

The operation is to add acid to a slurry concentration of 1 to 40% by weight as 5i02 so that the acid concentration is 0.1N or more, preferably 0.5N or more, and thoroughly mix it at room temperature or heating. . This operation is not limited to one time, but may be performed multiple times, two or more times, or continuously, as appropriate.

Thus, purified hydrated silica is substantially free of impurities and often has a concentration of u:t PPb per 5i02.
Below, Th: 10ppb or less, Na: 10pp
m or less, Fe: 5 ppm or less, Cfl: 10 ppm
It has the following high purity.

Kamelko I This step can be said to be a granulation step in which hydrous silica is dehydrated in order to obtain a granulated product that is easy to handle in the next fourth step.

There is no particular reason to limit this step as long as the dehydration process yields granules with a certain degree of fluidity, but industrially, for example, spray drying of a hydrous silica slurry, or the slurry or filter cake is used. There are two modes in which the material is dried using a desired drying device and then pulverized.

In the present invention, it is preferable to granulate the material by fluidized drying, such as spray drying, except for the energy cost. The reason for this is that since the silica particles have good fluidity, they can be easily supplied to the heating part in the next process, and since there is no need for any pulverization process other than drying, contamination with impurities can be avoided as much as possible. Note that the dehydrated silica obtained by this heat dehydration treatment usually needs to have a water content of 15% by weight or less. The reason for this is that if it exceeds 15% by weight, not only will it be impossible to obtain fluid powder particles, but also the thermal load on the particles will increase as the flame temperature decreases in the subsequent melting process, making it difficult to achieve melting. It depends on the difficult ζ.

Unlike conventional silica powder, this process is an essential process along with the second process as a filler for the sealant, and it essentially involves melting the dehydrated silica powder obtained in the previous process. . This melting operation involves melting and spheroidizing dehydrated silica particles by continuously supplying dehydrated silica particles to a predetermined flame section, such as an oxygen-hydrogen flame, an oxygen-acetylene flame, an oxygen-propane flame, or a plasma flame. This flame melting operation itself is a long-known technique for melting inorganic powders. Therefore, in order to flame-melt and mold silica particles with a primary particle size of 200 μm or less, particularly around 20 μm, to obtain spherical or elliptical fused silica with an average particle size of 1 to 100 μL. Requires moderate flame conditions. That is, when fuel gas is used, the flame temperature must be at least 3000°C or higher, the flame length must be at least 2000°C, and the flame length must be 30 cm or more. In the case of an oxygen-fuel gas type burner that can be used for this purpose, oxygen is injected from the inside of the burner, fuel gas is injected from a number of holes on the outside, and dehydrated silica is preferably injected along with the oxygen gas. In this case, the temperature of the arc part is significantly higher than that in the oxygen-fuel gas system, so it can be processed without problems unless the amount of powder injected is excessive. The silica obtained in this way has a melting degree of 80% or more even though the contact time in the high-temperature part is shorter than that of the silica, and becomes substantially molten glass-like transparent spherical to elliptical particles. This results in particles with extremely good fluidity.

The fused silica particles thus obtained can be collected with a cyclone after being cooled with a gas stream, if necessary, or wet-collected with water, etc., to obtain the high-purity silica product according to the present invention.

As described above, the method of the present invention makes it possible to industrially advantageously produce high-purity fused silica particles as a filler for sealants that require high performance, rather than wet silica using an aqueous alkali silicate solution as a starting material. It is possible to supply in large quantities.

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

Example 1 Commercially available No. 3 sodium silicate aqueous solution (5i0228.8% by weight)
, Na20θ, 4% by weight, u 100P per 5i02
Pb (containing 240 ppb of Th per 5i02) was diluted with water to obtain a diluted sodium silicate aqueous solution containing 24% by weight of 5i02.

This was treated with a cation exchange resin (Amberlite IR-120B, manufactured by Organo Co., Ltd.) that had been regenerated with sulfuric acid according to a conventional method to obtain an aqueous silica sol solution with a pH of 2.2.

While stirring 30 g of a 10.5% by weight aqueous solution of ammonium nitrate at room temperature, 50 g of an alkali silica sol solution made by adding ammonia to the pH 10.5 was added to the silica sol aqueous solution over 3 hours to coagulate and precipitate to form precipitated silica gel. The obtained 0 was then filtered and washed by displacement, and then redispersed in ion-exchanged water to a 5i02 concentration of 8% by weight. Nitric acid was added to the solution to give an IN/31 concentration, and the mixture was stirred at 95°C for 3 hours. Processed. This was purified by filtering and washing with water to obtain a cake of purified silica gel with a water content of 78% by weight.This cake of purified silica gel was dispersed in water for 15 minutes.
After forming a silica gel suspension of % by weight, it was spray-dried using a production minor type spray dryer manufactured by Ashizawa Waniro. The processing conditions were an inlet temperature of 340°C, an outlet temperature of 120°C, an electric heat source, and an atmospheric air flow rate of 5.
．． It was done at 7m3/win. The particle shape of the silica particles collected in the cyclone is as shown in Figure 1.
It is an aggregate of fine silica particles with a water content of 4.0% or less, estimated from the weight loss after heating at 800°C for 80 minutes.
It was 3% by weight.

The thus obtained dehydrated silica powder with good fluidity was subjected to flame melting treatment to obtain the fused silica powder shown in FIG.

The flame melting device has an oxygen nozzle in the center, from which oxygen and dehydrated silica are spouted, and a ring-shaped fuel gas nozzle surrounding the oxygen nozzle on the outside, from which fuel gas is spouted. Furthermore, a gas burner was used which was provided with an oxygen jet hole and a fuel gas hole on the outside. Fuel gas is
Using acetylene, its flow rate is 5 Nm'/H1 oxygen flow rate 5
Nm3/H and feed rate of dehydrated silica particles 5 Kg/
The dehydrated silica was melted with H. The length of the flame that could be seen with the naked eye was about 40 centimeters. Figure 2 shows the shape of the particles of fused silica collected by a cyclone after passing through the water-cooled combustion chamber □.The degree of fusion is approximately 80%, and the physical properties of the fused silica are average when measured. The particle size is 204m, and the amount of impurities is Na201.5ppm.
, ci not detected, υ0.4ppb or less, Th4±2PPb
And the electric conductivity of the extracted water was 6#LS/Cm.

Example 2 Adding caustic soda and water to No. 3 sodium silicate solution
0214.13% by weight and Na2017.3% by weight aqueous solution. This was slowly stirred at 50°C to obtain sodium metasilicate nonahydrate. This was separated from the mother liquor, dissolved again in water, and subjected to the same series of treatments as in Example 1 to obtain a 5i02 concentration of 4% by weight.

The recovered fused silica has a particle shape similar to that of Example 1, with a spherical fused silica having a degree of fusion of approximately 88%, and its physical properties include an average particle diameter of 181 Lm, and an impurity content of Na202.
, Oppm, C1 not detected, υO, '4PPb or less, Th
O, 7 ppb or less and electrical conductivity of extracted water 5 final S/
cm or less.

Example 3 In the same manner as in Example 2, a 4% by weight 5i02-containing sodium metasilicate aqueous solution and 4% by weight sulfuric acid were simultaneously added at pH 9 to produce silica gel. After filtering and washing with water, I
It was dispersed in an aqueous N-hydrochloric acid solution so that the 5i02 concentration was 10% by weight. This was stirred at 95°C for 3 hours and then filtered. After performing this pickling operation three times, it was washed with water to obtain a 20% by weight 5i02 slurry.

As a result of spray drying this slurry and flame treatment using propane flame in the same manner as in Example 1, spherical fused silica with a degree of melting of 83% was obtained, and its physical properties were as follows:
is, and the impurity content is Na204.5ppm,
cu not detected, U2±i Ppb, Th7±2 PPb
and the electrical conductivity of the extracted water was 8.5 #LS/C Peng.

[Brief explanation of the drawing]

FIG. 1 is a 1000x micrograph showing the particle structure of the silica particles subjected to dehydration treatment in Example 1, and FIG. 2 is a silica product particle according to the present invention obtained by melting the silica particles shown in FIG. 250x micrograph showing the structure. Applicant Nihon Kagaku Kogyo Co., Ltd. Agent Yutaka 1) Yoshio

Claims (1)

[Claims] l) Silica obtained from an aqueous alkali silicate solution,
The radioactive substance is 10 ppb or less, and the electric conductivity of the extracted water obtained by boiling and leaching the silica is 100 pS,/cm or less,
High purity silica having an average particle diameter in the range of 1-100 gm and a degree of melting of 80% or more. 2) A first step of gelling an aqueous alkali silicate solution to precipitate silica gel, a second step of purifying the silica gel with a volatile acid to obtain hydrated silica, and heating and dehydrating the hydrated silica to obtain dehydrated silica. A method for producing high-purity silica, comprising a third step and a fourth step of injecting the dehydrated silica into a flame and melting it. 3) The method for producing high-purity silica according to claim 2, wherein the alkaline silicate aqueous solution is a sodium silicate aqueous solution prepared by dissolving crystalline sodium silicate. 4) The method for producing high-purity silica according to claim 2, characterized in that an aqueous alkali silicate solution is brought into contact with an ion exchange resin to produce an acidic silica sol. 5) The method for producing high-purity silica according to claim 2, wherein an aqueous alkali silicate solution is neutralized with an acid to form a gel. 6) The method for producing high-purity silica according to claim 2, which comprises spray-drying and heat-treating hydrated silica.