JPH0336765B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is suitable as a raw material for synthetic quartz glass,
The present invention relates to a method for efficiently producing high-purity heavy silica. [Technical Background] Since quartz glass has excellent optical properties and low thermal expansion properties, it has come to be used as a filler for semiconductor encapsulants, including substrates for optical fibers. As the quartz glass for such fillers for encapsulants, quartz glass obtained by melting natural silica raw materials such as silica sand has been generally used.
Impurities such as radioactive elements such as uranium and thorium originating from the silica raw material have recently become a problem. In other words, alpha rays such as uranium and thorium contained in quartz glass are used as encapsulant fillers.
Causes IC soft error. Therefore, there has been an increasing demand for high-purity silica raw materials with reduced amounts of such impurities. [Prior Art and Problems] Conventionally, a method of burning silicon halide in a flame has been known as a method for industrially producing high-purity silica. However, the above method has the property that the obtained silica particles are extremely small and bulky. Therefore, quartz glass obtained by melting or sintering this glass generally contains a large amount of bubbles, and has the problem of being difficult to use for the above-mentioned purposes. Furthermore, shrinkage during melting and sintering is very large, and large-capacity equipment is required to produce quartz glass, making it difficult to use as a raw material for industrially obtaining quartz glass. In order to solve the above problem, the present inventors have already proposed a method for producing high-purity heavy silica by bringing water-wetted water-absorbing powder into contact with silicon halide. However, in the above method, the exhaust gas containing hydrogen halide generated by the reaction between the water-absorbing powder and the silicon halide gas, water vapor generated by the reaction heat, carrier gas, etc.
Not only does a part of the water-absorbing powder float and become entrained, resulting in loss, but this powder also adheres to the inner walls of exhaust gas piping, exhaust gas processing equipment, etc. and blocks the piping, etc., resulting in long-term stability. The problem is that it becomes difficult to drive the vehicle. [Means for Solving the Problems] The present inventors have conducted extensive research in order to solve the above problems. As a result, by bringing the water-absorbing powder into contact with silicon halide in the presence of an organic binder, the amount of loss of the water-absorbing powder entrained in the exhaust gas after such contact is significantly reduced, resulting in stable Furthermore, the present invention has been completed by discovering that silica can be produced economically and that high-purity silica can be obtained because the water-soluble polymer can be easily removed by washing or calcination. The present invention is a method for producing silica, which is characterized by bringing water-moistened water-absorbing powder into contact with halogenated silicon in the presence of an organic binder. In the present invention, wetting refers to a state in which the water-absorbing powder supports water within the range that maintains its fluidity as a powder, and generally the water-absorbing powder absorbs water in an amount less than its oil absorption amount. The situation is as follows. In addition, the oil absorption amount is
This refers to the value measured according to JIS6200. In the present invention, the water-absorbing powder used is not particularly limited as long as it has water-absorbing properties, but generally it has an oil absorption of 0.5 cc/g or more, preferably 1 c.c./g or more. is sufficient, and
It is desirable to use a powder containing as few impurities as possible that would have an adverse effect on the use of the resulting silica. Specific examples of such water-absorbing powders include anhydrous silicic acid produced by a dry process called fumed silica, hydrated silicic acid produced by a wet process called white carbon, and silica powder such as silica produced in the reaction described below. In addition, alumina, hydrated aluminum silicate, calcium silicate, etc. can also be used. Furthermore, organic materials such as porous resins that can be removed by firing or the like can also be used. Such water-absorbing powder may be appropriately selected and used depending on the intended use of the obtained silica.
For example, if pure silica is required for the purpose, silica powder may be selected and used. Also,
If the purpose is to produce a multi-component powder, a water-absorbing powder other than silica, such as alumina or zirconia, may be used. The above-mentioned water-absorbing powder generally has a particle size of 1 mm or less, preferably 1 to 100 microns. Examples of the silicon halide used in the present invention include silicon tetrachloride, trichlorosilane, and dichlorosilane, among which silicon tetrachloride is particularly preferred in terms of reactivity and economy. Further, the silicon halide is generally used in a gaseous state, and in this case, the silicon halide may be diluted with an inert gas before use. The organic binder used in the present invention is not particularly limited as long as it exhibits viscosity in the presence of water, but it is preferable to use one that does not contain metals so as not to reduce the purity of silica. Examples of suitable organic binders include water-soluble acrylic resins such as polyacrylamide, water-soluble synthetic resins such as water-soluble alkyd resins, water-soluble melamine resins, water-soluble urea resins, and water-soluble phenolic resins, methylcellulose,
Water-soluble polymers such as natural polymers such as cellulose derivatives such as hydroxyethyl cellulose are preferred because they can be easily removed by washing with water. Among these, water-soluble acrylic resins are particularly preferred in terms of their aggregation effect on water-absorbing powder. In the present invention, the method of contacting the water-absorbing powder with the silicon halide is not particularly limited, and any known method for solid-state reaction may be employed without particular limitation. For example, methods include bringing silicon halide and water-absorbing powder into contact with each other in countercurrent flow, using a fluidized bed, and fluidizing water-absorbing powder in an atmosphere of silicon halide using stirring means such as stirring blades. Common. Among these methods, the method of using a reaction tank with a stirring blade is particularly easy to control the reaction.
This is preferable because the amount of unreacted water in the water-absorbing powder can be controlled. In addition, in the above-mentioned contact method, it is also a preferred embodiment to carry out the contact while replenishing the water that has been reduced by the reaction between the water supported on the water-absorbing powder and the silicon halide. According to this aspect, the particle size of the produced silica can be adjusted as desired. In this case, it is necessary to supply water within a range that can maintain the fluidity of the water-absorbing powder. In the present invention, the contact between the water-absorbing powder and the silicon halide may be carried out continuously or in batches. When carried out continuously, the water-absorbing powder may be supplied continuously or intermittently, but the silica produced as at least a part of the water-absorbing powder may be classified and the fine powder may be supplied to the reaction system. is also possible. In this case, silica may be classified by providing a classifier such as a cyclone outside the reaction apparatus. Further, when the water-absorbing fraction is continuously or intermittently supplied to the reaction system in this way, it is desirable that the water-absorbing powder to be supplied is mixed with the above-mentioned make-up water and supplied in the form of a slurry. In this case, the water in the slurry is immediately absorbed by the water-absorbing powder in the reaction system to maintain a wet state. An important requirement of the present invention is that in the contact between the silicon halide and the water-absorbing powder moistened with water,
The purpose is to have an organic binder present. That is, by making a water-soluble binder exist,
The moist water-absorbing powder can be appropriately condensed, and the phenomenon of these powders floating and being entrained in the exhaust gas can be effectively prevented. If the amount of the above-mentioned organic binder used is too large, it will take time to separate it from the produced silica, and the aggregated particles of the water-absorbing powder will tend to become large and the reactivity will decrease. Also, if the amount of organic binder used is too small,
Water-absorbing powder becomes more likely to float in the exhaust gas. Therefore, the amount of organic binder used is 100 to 5000 ppm, preferably 100 to 5000 ppm based on the water absorbent powder (dry weight).
It is desirable to determine the content within the range of 200 to 4000 ppm. There are no particular restrictions on the method for making the organic binder present when the silicon halide comes into contact with the water-absorbing powder, but in order to make the organic binder uniformly present, it is necessary to use water supported on the water-absorbing powder, or It is desirable to dissolve or disperse the organic binder in the makeup water mentioned above. The organic binder can be easily removed from the silica obtained by the method of the present invention by washing with water and/or firing. [Effect] As understood from the above explanation, according to the method of the present invention, when the silicon halide gas and the water-absorbing powder moistened with water come into contact with each other, the water-absorbing powder suspended in the exhaust gas and entrained is reduced. The amount of powder can be significantly reduced, the powder can be prevented from adhering to exhaust gas piping, exhaust gas processing equipment, etc., and silica can be produced stably over a long period of time. The silica obtained by the method of the present invention can be made into highly pure silica by easily removing the organic binder by washing with water or firing, and can be used as a raw material for optical fibers, fillers for semiconductor encapsulants, etc. In addition to its use as an inorganic powder, it can also be used in known fields without particular restriction. [Examples] Examples are shown below to explain the present invention more specifically, but the present invention is not limited to these Examples. Example 1 2.5 kg of Hyumdrisica (trade name, Rheoroller: manufactured by Tokuyama Soda Co., Ltd.) was stirred with a Henschel mixer, and polyacrylamide-based polymer (trade name, Crylock PA-318: Kurita Water Industries, Ltd.) was added to ion-exchanged water 2.
A wet powder was prepared by adding dropwise a solution containing the following: At that time, the amount of polyacrylamide was 1g,
There were two types of 0.5g. This wet fumed silica powder was placed in a cylindrical stirring tank with an internal capacity of 40°C, and silicon tetrachloride was added at a rate of 270/hr (0°C,
(1atm equivalent), 510ml/510ml of ion-exchanged water from the top of the tank.
It was introduced at a rate of hr and allowed to react for 6 hours. Dust was separated from the exhaust gas using a cyclone and then absorbed into a caustic soda solution. Table 1 shows the amount of polyacrylamide added, the amount of powder collected by the cyclone, and the impurities in the silica obtained by washing the product with an ion exchange membrane and calcining it at 1000° C. for 1 hour.

[Table] By adding 200 ppm of polyacrylamide (0.5 g of polyamide to 2.5 kg of fumed silica), the amount of dust floating in the exhaust gas was reduced by 95%. Furthermore, the amount of impurities in the silica after washing and firing did not change even with the addition of polyacrylamide, and highly pure silica was obtained. Example 2 The same procedure as in Example 1 was carried out except that 2 g and 10 g of methyl cellulose polymer (trade name: Metrose 90SH, manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved instead of the polyacrylamide polymer. Table 2 shows the relationship between the amount of methylcellulose added and the amount of powder collected by the cyclone.

[Table] 800ppm methylcellulose (humid silica)
By adding 2g of methylcellulose to 2.5Kg, the suspended powder in the exhaust gas is reduced by approximately 40% compared to the case without addition, and by adding 4000ppm (10g of methylcellulose to 2.5Kg)
decreased by 80%. In addition, impurities in the silica after washing and firing are U<0.1ppb, Na<2ppm, Cl<4ppm,
High purity silica with Fe<1.5ppm and suitable as an encapsulant filler was obtained.

Claims (1)

[Scope of Claims] 1. A method for producing silica, which comprises contacting a water-absorbing powder moistened with water with a silicon halide in the presence of an organic binder. 2. The method according to claim 1, wherein the water-absorbing powder is silica powder. 3. The method according to claim 1, wherein the silicon halide is silicon tetrachloride. 4 The amount of organic binder added is
The method according to claim 1, wherein the amount is 100 to 4000 ppm. 5. The method according to claim 1, wherein the organic binder is a water-soluble polymer.