JPH09142828A - Production of highly pure sandy synthetic silica, and production of highly pure synthetic quartz glass molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce highly pure sandy synthetic silica having the same or higher purity as that produced by an oxyhydrogen flame medium method. SOLUTION: This method for producing the highly pure sandy synthetic silica by a liquid phase reaction comprises producing a gel from the solution or dispersion of a raw material, drying the gel and calcining the dried gel. Therein, the dried gel is fed into the calcination process followed to the drying process through a flexible cylinder having a binding or unbinding means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing sandy synthetic silica for producing high-purity silica glass products suitable for semiconductor-related fields such as optical fibers, silicon single crystal pulling crucibles, and LSI encapsulating materials.

In recent years, glass products used in the fields of optical communication, semiconductor industry, etc. have undergone extremely strict control regarding the purity. In order to obtain such high-purity glass, conventionally, it was produced by melting sand-like natural quartz powder (so-called sand) obtained by crushing natural quartz. Even if it is of good quality, it contains various metal impurities and was not sufficiently satisfactory in terms of purity and uniformity. Therefore, as a means to improve the purity, the soot generated by decomposing silicon tetrachloride in an oxyhydrogen flame is made to adhere and grow on the substrate, and the obtained soot mass is heated to make it transparent and block quartz. Obtain glass and crush this block to obtain synthetic sandy silica,
There is an oxyhydrogen soot method, and since it is a gas phase reaction, it is possible to prevent impurities from mixing in. However, this method has a drawback that it requires a lot of energy and the manufacturing cost is high. On the other hand, an organic metal compound such as a metal alkoxide is used as a raw material to generate a sol, which is gelled and further dried,
It has been proposed to manufacture synthetic quartz glass by a so-called sol-gel method in which glass is obtained through steps such as firing, crushing, and melting, and this method is inexpensive because it is a liquid phase reaction.

[0003]

However, the sol
In the gel method, it is possible to obtain quartz glass with a high degree of purity by using raw materials that have been purified by means such as distillation, but since it is in contact with the container consistently from the raw material stage, it is possible to completely eliminate impurities. In particular, not only sandy synthetic silica obtained by calcination but also dry gel obtained by drying by heating at about 100 ° C. prior to calcination is very hard (in Vickers hardness, stainless steel). However, since impurities are easily mixed from the inner wall of a series of reactors such as a container and a pipe by the transfer between each step, it was not possible to sufficiently meet the purpose that requires high purity. Therefore, there has been a demand for a method of obtaining a synthetic quartz glass having a high purity equal to or higher than that of the oxyhydrogen flame soot method even by an inexpensive liquid phase reaction.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, by carrying out a manufacturing process in a specific arrangement, an extremely high-purity sandy synthetic silica can be obtained by a liquid phase reaction. The inventors have found what can be obtained and have reached the present invention. That is, an object of the present invention is to obtain a high-purity sandy synthetic silica, and such an object is a gelling step of obtaining a gel from a raw material solution or dispersion, and a drying step of drying the gel to obtain a dried gel. And a baking step of baking the dry gel, the dry gel is used in a method for producing a sandy synthetic silica by a liquid phase reaction, and the dry gel is provided at a lower part of the drying step through a tube having a binding / unbinding means. It is achieved by a method for producing high-purity sandy synthetic silica, which is characterized by being subjected to a calcination step in.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The gelation step in the present invention is a step of obtaining silica gel from a raw material solution or dispersion. As a raw material, a silicon alkoxide, a salt, a silicon compound such as an oxide is hydrolyzed to give a silica sol, and a hydrolysis method using this as silica gel, and fumed silica or the like dispersed in water to give a silica sol, which is further The two main methods are a colloidal dispersion method using silica gel, but the present invention is not limited to these methods and can be applied as long as it is a step of forming a gel from a liquid phase. However, of these, the hydrolysis method is more preferable. This is because in the case of the colloidal dispersion method, the production of fumed silica itself requires high temperatures, and trace amounts of metal oxides, etc. may evaporate from refractory materials such as bricks on the furnace wall during production, and may be mixed in as impurities. This is because problems may occur, the physical properties of the obtained gel are slightly inferior to those obtained by the hydrolysis method, and the yield of the obtained sandy synthetic silica is reduced.

Of the hydrolysis methods, it is most preferable to use silicon alkoxide as a raw material. This is because the by-product is only alcohol, so that there is no problem of corrosion of the container and the like, and it can be easily distilled off, which is preferable. When obtaining a silicon alkoxide, a method of reacting metal silicon with an alcohol, a method of reacting a silicon halide such as silicon tetrachloride with an alcohol,
There are a method of reacting a silicon hydroxide or an oxide with an alcohol, a transesterification, an alcohol exchange reaction, a method by a reaction of an alkylsilicon hydride and a ketone, and the like, which can be appropriately selected depending on conditions, purposes, etc. In particular, the method of reacting metal silicon with alcohol is
It is suitable without problems such as corrosion of containers due to generation of chlorine and the like and separation and recovery of other by-products.

The type of silicon alkoxide has 1 to 1 carbon atoms.
The alkoxy group of 4, that is, a methoxy group, an ethoxy group, a propoxy group, a butoxy group and the like can be mentioned, and among these, a methoxy group or an ethoxy group is preferable. Further, the number is preferably 2 or more, and a monomer or an oligomer can be used.

Specific examples thereof include tetramethoxysilane, dimethoxydimethylsilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Among them, tetramethoxy having no alkyl group directly bonded to a silicon atom. The use of silane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, etc. is more preferable because it can prevent the generation of black foreign matter in the obtained sandy synthetic silica.

The hydrolysis reaction is carried out by reacting an alkoxide with water according to a known method. On this occasion,
If necessary, compatible alcohols and ethers,
You may mix organic solvents, such as ketones. As alcohol, methanol, ethanol, propanol, etc.,
Examples of ethers include diethyl ether, and examples of ketones include acetone.

However, when the alkoxy group bonded to the alkoxide is liberated as alcohol as the hydrolysis reaction proceeds, the reaction solution becomes in a uniform state before gelling, that is, the alkoxy group having a high hydrolysis rate. In the case of a raw material having (for example, a methoxy group),
It can be operated without any problems without adding alcohol.

Examples of the catalyst include acids such as hydrochloric acid, acetic acid, hydrofluoric acid and sulfuric acid, and alkali such as aqueous ammonia. The water used for hydrolysis is required to keep the target sandy synthetic silica in high purity because the amount of impurities that accompany the water used and brought into the reaction solution should be minimized. It is preferable to use ultrapure water or the like.

The amount of water added is not particularly limited as long as the hydrolysis reaction proceeds, but in practice, it is often added in excess of the theoretically required amount, and the time required for gelation and coarse In order to adjust the time required for pulverization to an appropriate range, the molar ratio of alkoxide to water is 1: 2 to 1:10,
Desirably 1: 3 to 1: 8, and particularly desirably 1: 4 to
It is practical that the range is 1: 7. If the amount of water is extremely large, not only does gelation take a long time, but even if gelation occurs, it takes time for the gel to reach the hardness suitable for the crushing process, and in some cases unless excess water is evaporated. In addition to this, other disadvantages such as the time required for the drying process to be described later occur. On the other hand, if the amount of water is too small, the hydrolysis does not proceed sufficiently, so that gelation is not sufficiently performed.

The hydrolysis reaction is almost completed after the time when a uniform solution of alkoxide and water is formed. After completion of the hydrolysis reaction, the solution is allowed to stand still until it gels and is integrated. The conditions of the hydrolysis reaction and gelation differ depending on the raw materials used, but are generally about 20 minutes to 10 hours at a temperature of 20 to 80 ° C. and under a normal pressure condition. To gel the hydrolyzate, you can obtain the gel immediately by heating, but it will gel in several hours even if left at room temperature, so adjust the gelling time by adjusting the degree of heating. can do.

The gel obtained is subjected to a drying process. The drying method is generally heating at 100 to 200 ° C. in a vacuum or an inert gas. It is also possible to use a method such as supplying steam to the outer jacket of the container. For example, a rotation heating method (a method of rolling heating in a tubular body, Japanese Patent Application No. 344741/1992).
2), a method of stirring with a rotary stirrer such as a conical dryer (Japanese Patent Application No. 5-126266), a method of removing the volatile components by reducing the pressure in the reaction tank, etc., which may be appropriately selected according to the conditions and purposes. Good. It is also possible to carry out post-treatment drying, such as washing the gel with an aqueous solvent and then drying, washing the container with alkali and then drying (Japanese Patent Application No. 5-126262).

The drying step is preferably carried out below the gelling step. The lower part means a position at a lower altitude, and as long as this is the case, it may be anywhere. That is, the drying process is performed just below the portion where the gelation process is performed, or diagonally below. In such a position, no power is required, and the gel can naturally move to the drying step by gravity. Preferably,
Of these, the effect most suitable for the purpose of the present invention can be obtained directly under the portion where the gelation step is performed. For example, if the dryer is arranged directly below the hopper provided in the lower part of the reaction tank, and the reaction product is directly charged into the dryer, it will not be contaminated along the way.

A crushing step may be performed before the drying step. Alternatively, the pulverization step may be performed after the drying step. It is also possible to carry out full-scale drying after preliminary drying and pulverization, or coarse pulverization and then drying and pulverization again. Generally, crushing in a wet gel state before drying is soft and easy to crush, requires less impact, and contains less impurities. When pulverizing after drying, the pulverizing step is preferably performed in the lower part of the drying step. In the case of crushing and then drying, the drying step is preferably performed at the lower part of the crushing step. The crushing method is a known method, for example, a method in which a gel is roughly crushed and then dried or fed to a granulator or a crusher with a commercially available screen or an undried coarsely crushed gel, and a vertically rotatable seal is used. Although a method of crushing the gel by rotating the container after performing the gelation step in the mold type rotary container (Japanese Patent Laid-Open No. 5-201717), etc., can be adopted, but directly below the hopper at the bottom of the reaction tank. It is even more effective if a rotary crusher with a nylon screen is attached and the gel passing through this is put directly into the dryer.

The firing process is carried out by a conventional method in the range of 1000 to 13
It can be performed at 00 ° C. Baking with a rigid moving device (JP-A-5-17123), oxygen concentration 30v
It is also possible to reduce the amount of black foreign matter by making it ol% or more. The firing step is preferably performed below the drying step. In this case, it is preferable that the dried gel is subjected to a firing step in the lower part of the drying step through a tube having flexibility and having a binding / unbundling means. Here, the flexible tube having a binding / unbunching means is a woven cloth, a non-woven cloth, a woven cloth coated with polytetrafluoroethylene (“Teflon”, a trademark), various coating cloths, rubber, etc. The tube is made of a flexible material. As long as it has flexibility and has a strength that is industrially sufficiently practical even after repeated deformation by binding and unbinding operations described later,
The material is not particularly limited. However, it is necessary that the amount of impurities mixed in is negligible even when the dried gel or the sandy synthetic silica passes through it. The bundling / unbundling means included in the cylinder is a means for controlling the amount of objects passing through the cylinder by squeezing or releasing the cylinder. The easiest way is to pass a linear object such as a lasso or string through the circumference of the cylinder and pull the linear object from the outside to bind the cylinders together to stop the passage of objects inside the cylinder, or The cylinder can be released by loosening to maximize the passage amount of the object in the cylinder.

However, although the binding / unbunching means has an extremely simple structure, the arm force required for pulling the linear object is large and stable operation is difficult. Therefore, industrially, as shown in FIGS. 1 and 2, the string 22 that connects the tube 20 to the frame 21 and connects two or more points (A, B, C ... H) around the frame 21 is By operating the handle 23 set in the groove provided in the frame 21, binding of the cylinder 20
If the structure for performing the debinding operation is used, stable operation is possible even with a small torque, and there are no obstacles in the cylinder, which is the passageway for gel and sandy synthetic silica. The body does not come into contact with any part that may contain impurities due to contact with metal parts such as casing,
It is suitable. 1 and 2 are views showing a state of a cylinder having a binding / unbundling means at the time of bundling and at the time of bundling, respectively. In FIG. 2, the string 22 is in a state along the frame 21 to unbundle the tube 20. Further, the cylinder having the bundling / unbundling means having such a structure is easy and reliable to operate, has a simple structure, requires few constituent parts, is lightweight, and is easily mounted. In the present invention, the use of a cylinder having such flexibility and a binding / unbundling means makes it possible to stably and easily supply the dried gel to the firing step. Supplying dried and high-hardness dry gel containing almost no water to the firing process using an ordinary flow rate control device such as a ball valve, or an ordinary powder feeder such as a rotary feeder or a table feeder. Due to the contact between the powder contact part of the machine and the gel, the material of the powder contact part of the feeder is likely to be mixed as an impurity. In addition, a fine dry gel having high hardness and being easily rubbed into the powder contacting part, so that the flow rate may not be easily adjusted. When the above-mentioned cylinder having flexibility and having a binding / unbunching means is used, these difficulties are not caused, and further simplification and weight reduction of the entire apparatus can be achieved at the same time, which is desirable. When classifying a dry gel prior to firing, a tube having flexibility and a binding / unbundling means is provided in the lower part of the drying step, and the dry gel passing through the tube is supplied to a classifier. If only the dry gel having the optimum particle size distribution obtained by the classification is further dropped at the lower part, such as a structure in which it is directly thrown into the baking furnace, if the baking step is performed at the lower part of the drying step, the classification device It is possible to easily and appropriately supply the gel of the above and the supply of the classified gel to the firing step, which is the same as the above, through the tube having the above-mentioned flexibility and binding / unbundling means. Becomes
If the entire process is installed as a vertically long building, it is possible to easily proceed from the gelation process to the firing process from the upper part to the lower part. At this time, if a water tank used as raw material or for washing is also installed at the upper part of the building, it is not necessary to carry it by the rotator each time it is used, and it is possible to prevent impurities from entering from the shaft of the rotator. .

[0019]

EXAMPLES FIGS. 3, 4 and 5 show an example of a three-dimensional configuration for the production method of the present invention. As shown in FIG. 3, tetramethoxysilane 11 and water 12 are supplied to the reaction tank 1,
A gelation process by a hydrolysis reaction is performed. At this time, the reaction can be carried out while heating by passing hot water 13 or the like through the jacket of the reaction tank. The produced gel is transferred to the lower hopper 2a by gravity and further supplied to the lower crusher 8 by gravity. At this time, if the flow control device 7 is provided, the supply amount of gel can be adjusted appropriately. The flow rate control device 7 can also be operated by the motor 6 or the like. The gel crushed by the crusher 8 is transferred to the lower hopper 2b by gravity, and when an appropriate amount is collected, the lower dryer 3
Is transferred by gravity to the drying process. By installing a jacket 9 in the dryer and passing water vapor 15 etc.,
It can be dried. In addition, it is also possible to perform drying by evacuating the dryer 14. The obtained dry gel is transferred by gravity to the hopper 2c located below.
Here, an appropriate amount of dry gel is supplied to the sieving means such as the vibrating screen 4 through the flexible tube 18a having the binding / unbunching means below the hopper 2c. Only the dry gel having a desired particle size obtained by this sieving is dropped into the crucible 5 by gravity, and if a calcination step is performed, sieving of the obtained sandy synthetic silica is not required, It can also be a product. In addition, if the crucible 5 is installed on the carriage 10 and is movable, a plurality of crucibles are provided and firing is performed alternately, so that the efficiency can be further improved. The firing can be performed while blowing the dry air 16.

As another example of the present invention, as shown in FIG. 4, the gel obtained by the gelation step in the reaction tank 1 is continuously dried without being transferred from the reaction tank 1 to obtain a gel. After the dried gel is transferred to the hopper 2, it is passed directly through the vibrating screen 4, and a suitable amount of gel is heated by a heater 19 or the like through a cylinder 18b having flexibility and binding / unbundling means in a rotary kiln 17. It is also possible to drop by gravity to perform a firing step, and the obtained sandy synthetic silica can be taken out and packaged in an appropriate amount from a lower portion of the rotary kiln through a cylinder 18c having a binding / unbundling means.

Further, as shown in FIG. 5, the gel obtained by the gelling step in the reaction tank 1 is dropped from the hopper 2a into the vibrating fluidized dryer 3a, and the gel is obtained through the drying step here. The dried gel is further pulverized by the pulverizer 8 at the lower portion, and the pulverized dried gel is supplied to the sieving machine in an appropriate amount through a cylinder 18d having flexibility and having binding / unbunching means, and after sieving, the rotary kiln 17 The sandy synthetic silica thus obtained may be dropped into the rotary kiln and taken out from the lower part of the rotary kiln for packaging.

[0022]

INDUSTRIAL APPLICABILITY As described above, a series of operations can be efficiently performed by using a specific cylinder for supplying the dried gel to the classification step, the firing step, and taking out the sandy synthetic silica obtained by firing. Moreover, the obtained sandy synthetic silica can be kept in high purity. Furthermore, by adopting a configuration in which the drying step is performed in the lower part of the gelling step, and the baking step of baking the dried gel is further performed in the lower part, a belt feeder, a bucket feeder, a chain feeder, which are usually used,
Since it is possible to perform from the gelation process to the firing process without horizontal or upward movement by a transport machine such as a screw feeder, it is possible to obtain highly pure sandy synthetic silica with high efficiency. be able to. Not only sandy synthetic silica but also its precursor, dry gel, is much harder than general powder and granules (the Vickers hardness is higher than that of SUS), and friction with the inner wall of the device is severe and the inner wall component Are easily mixed as impurities, and it is also difficult to prevent the mixing of impurities from the precursors of silica gel, which is the precursor thereof, in the transportation process using a transport machine, various valves, supply parts to various devices such as feeders, and flow control parts. In some cases, the sandy synthetic silica or the dried gel may bite into the valve portion, making it difficult to open and close, which is an obstacle to high-purity applications. Therefore, by using the unique structure and the specific cylinder of the present invention, it is possible to extremely easily and effectively prevent the mixing of impurities, and at the same time, achieve a great energy saving, and the sandy synthetic silica from the gelation reaction. It is significant that the effect of shortening the time required for all the steps until collection can be achieved.

[Brief description of the drawings]

FIG. 1 is a view showing a state of a cylinder having flexibility and having a binding / unbinding means which can be used in the present invention, at the time of binding.

FIG. 2 is a diagram showing a state of a tube having flexibility and having a binding / unbinding means, which can be used in the present invention, at the time of unbundling.

FIG. 3 is a diagram showing an example of a three-dimensional configuration for the production method of the present invention.

FIG. 4 is a diagram showing an example of a three-dimensional configuration for the production method of the present invention.

FIG. 5 is a diagram showing an example of a three-dimensional configuration for the production method of the present invention.

[Explanation of symbols]

 1 Reaction Tank 2 Hopper 3 Dryer 5 Crucible 17 Rotary Kiln 20 Tube 22 String 21 Waku

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tana 邉 ▼ Yasuo 2-5-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Chemical Co., Ltd. New Business Development Office

Claims (8)

[Claims] 1. A sandy synthetic silica by a liquid phase reaction, which comprises a gelling step of obtaining a gel from a raw material solution or dispersion, a drying step of drying the gel to give a dried gel, and a baking step of firing the dried gel. In the manufacturing method of, the dry gel,
A method for producing high-purity sandy synthetic silica, characterized by being subjected to a firing step in the lower part of a drying step through a tube having flexibility and having a binding / unbundling means. 2. A sandy synthetic silica by a liquid phase reaction, which comprises a gelling step of obtaining a gel from a raw material solution or dispersion, a drying step of drying the gel to obtain a dried gel, and a firing step of firing the dried gel. In the manufacturing method of, the dry gel,
A method for producing high-purity sandy synthetic silica, characterized by being supplied to a classifying device through a cylinder having flexibility and having a binding / unbundling means, and further being subjected to a firing step at a lower part of a drying step. . 3. A sandy synthetic silica by a liquid phase reaction, which comprises a gelling step of obtaining a gel from a raw material solution or dispersion, a drying step of drying the gel to give a dried gel, and a baking step of firing the dried gel. 2. The method for producing high-purity sandy synthetic silica according to claim 1, wherein the sandy synthetic silica that has undergone the firing step is taken out through a tube having flexibility and having a binding / unbundling means. 4. The method for producing high-purity sandy synthetic silica according to claim 1, wherein a drying step is performed below the gelling step. 5. A flexible cylinder having a binding / unbundling means is made of a polytetrafluoroethylene-coated woven fabric or rubber, and any one of claims 1 to 4 is characterized in that A method for producing the high-purity sandy synthetic silica described. 6. The binding / unbinding means is one or two or more linear objects which are provided outside the cylinder and pass through two or more points on the circumference of the cylinder. 6. The method for producing the high-purity sandy synthetic silica according to any one of to 5. 7. A high-purity sandy synthetic silica according to claim 1, wherein a gel obtained by hydrolyzing an alkoxysilane obtained by reacting alcohol with metallic silicon is used. Manufacturing method. 8. A method for producing a high-purity synthetic quartz glass molding, which comprises melting the high-purity sandy synthetic silica obtained by the production method according to any one of claims 1 to 7.