JPH07196325A - Production of synthetic silica glass - Google Patents

Abstract

PURPOSE:To obtain a silica glass excellent in optical properties suitable for optical materials, by specifically controlling the average particle diameter and specific surface area of the silica particles in a silica sol solution and the agitation rate of the solution in the manufacture by a sol-gel process. CONSTITUTION:Firstly, a silicon alkoxide is hydrolyzed in a basic solution to synthesize a silica sol solution containing silica particleas having <=0.5mum in average diameter and <=50m<2>/g in specific surface area. Second, a silicon alkoxide is dripped into this solution in the presence of an acid catalyst and hydrolyzed to produce a silica sol mixed solution, which is then gelled into a wet gel which is then dried. Subsequently, this dry gel is fired to obtain a transparent synthetic silica glass. In the above process, the silica sol solution and the silica sol mixed solution are put to filtration using filters of <=10mum and <=50mum in mesh, respectively. The processes ranging from the silica sol solution synthesis to the wet gel drying are conducted in a clean room. And, the agitation in preparing the silica sol (mixed) solution is performed at >=50sec<1> of shear rate.

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 synthetic quartz glass, which is suitable for optical materials such as lenses and prisms.

[0002]

2. Description of the Related Art The sol-gel method is known as one of the methods for producing synthetic quartz glass. By this sol-gel method,
As a method for producing high-quality quartz glass, a method in which a silica sol in which a hydrolyzate of silicon alkoxide and silica fine particles are dispersed is filtered and then gelled, the gel is dried to form a dry gel, and then this is fired to vitrify. Is known (Japanese Patent Laid-Open No. 61-26521). Also,
There is also known a method (Japanese Patent Laid-Open No. 62-91428) in which a wet gel preparation step from synthesis of a silica sol solution is performed in a clean room.

[0003]

In the sol-gel method, a silicon alkoxide is hydrolyzed in a basic solution to synthesize a silica sol solution, the pH of the silica sol solution is adjusted to 1 to 2, and the silicon alkoxide is added to cause hydrolysis. After doing
It is usual to adjust the pH to 3 to 5 for gelation, and then dry and calcine to prepare bulk glass. However, in the glass obtained in this way, the bubbles generated when the precursor silica gel is fired remain,
As an optical glass, there have been quality problems.

The cause of the bubbles is considered to be foaming at the time of firing due to liquid components such as alcohol and water remaining in the silica gel. On the other hand, agglomerates of silica particles in the raw material silica sol and foreign substances also cause bubble generation
It was found that when the gel was baked while these were present, bubbles were easily generated.

The liquid component in silica gel can be removed by drying and calcining the gel for a sufficient period of time, which can prevent the formation of bubbles. However, the formation of bubbles due to aggregates of silica particles and foreign substances cannot be prevented even if the gel is dried and fired for a long time, and the reaction from the synthesis of the silica sol solution to the wet gel preparation process is performed in a clean room. However, even if the silica sol solution was filtered, the formation of bubbles could not be effectively prevented.

The present invention provides a method for producing synthetic quartz glass which is useful as various optical materials in the production of synthetic quartz glass using a silicon alkoxide as a raw material by the sol-gel method and has excellent optical characteristics without bubbles. In particular, it is an object of the present invention to provide a method for producing synthetic quartz glass having excellent optical properties as an optical glass material for ultraviolet rays such as lenses for ultraviolet rays such as excimer lasers and prisms.

[0007]

The present invention is to hydrolyze a silicon alkoxide in a basic solution to synthesize a silica sol solution containing silica particles, and to add the silicon alkoxide to the silica sol solution under an acidic catalyst for hydrolysis. To prepare a silica sol mixed solution, then gelate the silica sol mixed solution to prepare a wet gel, and dry the wet gel to obtain a transparent glass body by firing a dry gel to obtain an average particle diameter. Of 0.5 μm or less and a specific surface area of 50 m ² / g or less is used, and the silica sol solution and the silica sol mixed solution are used to obtain pore sizes of 10 μm or less and 50 μm, respectively.
The silica sol solution and the silica sol mixed solution are filtered at a shear rate of 50 s ⁻¹ or more, and the process from the synthesis of the silica sol solution to the drying of the wet gel is performed at least as a class. It is a method for producing synthetic quartz glass, which is performed in a clean room that is dust-free than 10,000.

The silica sol solution in the present invention contains silicon alkoxide in a basic solution and has a shear rate of 50 s.
It is obtained by stirring and hydrolyzing at ^-1 or more, and the average particle diameter of the silica particles in the silica sol solution is 0.5 μm or less and the specific surface area is 50 m ² / g or less. Such a silica sol solution can be preferably obtained as follows. A silicon alkoxide is added dropwise while stirring an alcohol solution containing water and ammonia at concentrations of 5 to 10 mol / l and 1 to 3 mol / l, respectively, under conditions such that the shear rate is 50 s ⁻¹ or more. To synthesize. If the shear rate in stirring is less than 50 s ^-1 , the silica particles aggregate and the yield of the silica particles after filtration decreases. If the average particle size of the silica particles exceeds 0.5 μm, the gel produced will be cracked and glass cannot be produced. Further, in the case of a silica sol solution containing silica particles having a specific surface area of more than 50 m ² / g, the liquid component is likely to remain and the possibility of causing bubbles is increased.

In the present invention, examples of the silicon alkoxide used as a raw material include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like, but tetramethoxysilane is preferable. The upper limit of the amount of silicon alkoxide added is 1 mol per 2 mol of water.
Usually, it is about 1 to 5 mol per 20 mol of water.

Filtration is carried out in order to remove foreign matters, aggregates and the like contained in the silica sol solution, and the filter used for this must have a pore size of 10 μm or less,
It is preferably 1 μm or less. The material of the filter is preferably Teflon, polypropylene, glass or the like, which has no fiber release and no elution component.

An acid is added to the filtered silica sol solution to make it acidic, and the conditions are set under an acidic catalyst and the shear rate is 50.
While stirring at s ^-1 or more, silicon alkoxide is added dropwise to prepare a silica sol mixed solution. Such a silica sol mixed solution can be preferably obtained as follows. The pH is adjusted to 1-2 by adding an acid such as aqueous hydrochloric acid to the silica sol solution, and the shear rate is 50 s ^-1.
Under the above stirring conditions, an appropriate amount of silicon alkoxide,
Preferably, 0.1 to 10 moles of the silicon alkoxide used when synthesizing the silica sol solution is added and hydrolyzed, and then a silica sol mixed solution whose pH is adjusted to 3 to 5 with a basic aqueous solution is prepared. , Dehydration polycondensation of the hydrolyzed silicon alkoxide. At this time, the hydrolyzed silicon alkoxide forms new fine particles,
The silica particles in the silica sol solution are uniformly mixed to form a silica sol mixed solution. A part of the dropped silicon alkoxide may cause silica particles in the raw material silica sol solution to bind nonuniformly to form an aggregate.
In order to prevent this, it is necessary to carry out the reaction under a strong stirring condition at a shear rate or higher, but still some aggregated particles are produced.

The silica sol mixed solution is filtered in order to remove the aggregated particles or foreign substances mixed in during the hydrolysis reaction. At this time, the hydrolyzed silicon alkoxide gradually undergoes dehydration polycondensation, and usually gels in 2 to 4 hours. Therefore, it is necessary to carry out filtration promptly within a time period during which gelation does not occur. Further, if the pH of the silica sol mixed solution exceeds 5, gelation occurs rapidly and filtration cannot be performed. Therefore, it is important to maintain an appropriate pH value in the range of pH 3 to pH 5. .

The filter used for filtering the silica sol mixed solution must have a pore size of 50 μm or less, preferably 10 μm or less. It is preferable that the material of the filter has no fiber release and has a very small amount of eluted components, such as Teflon, polypropylene and glass.

Next, the silica sol mixed solution after filtration is gelated to prepare a wet gel, which is further dried to prepare a dry gel. This can also be performed by a known method, but is preferably performed as follows. The silica sol mixed solution after filtration is cast into a container having a desired shape and allowed to stand at room temperature of 10 to 30 ° C. for gelation to prepare a wet gel. When this wet gel is dried for an appropriate period of time, a dry gel in which the unpolymerized material releases water by a dehydration polycondensation reaction is obtained.

Further, in the steps from the synthesis of these silica sol solutions of the present invention to the production of dry gel, if minute foreign matter such as fine dust or dust from the environment is mixed, it may cause bubbles and the like. Is at least class 10000 (refers to the class according to US Federal Standard 209D, and the number of the class represents the concentration of suspended particles (particles / ft ³ ) of 0.5 μm or more), preferably dust-free than class 1000 Done in a clean room.

The dry gel thus prepared is fired to obtain a transparent glass body, that is, synthetic quartz glass. This firing can also be performed by a known method, but preferably the dry gel is heated stepwise and fired at 1300 to 1800 ° C to obtain a transparent glass body. The glass body can be cut, polished, or the like to obtain an optical material made of synthetic quartz glass.

[0017]

[Function] Aggregation is achieved by performing stirring and filtering of the solution under a specific condition when obtaining a silica sol solution and a silica sol mixed solution, which are raw materials of quartz glass, and performing a process until a dry gel is obtained by a clean room. It is considered that since the presence of foreign matter and foreign substances was reduced, the cause of bubble generation was eliminated, and synthetic quartz glass with excellent optical characteristics could be manufactured.

[0018]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples. Example 1 8 liters of a methanol solution containing 64 mol of water and 12 mol of ammonia was placed in a polypropylene container having a diameter of 30 cm, and a Teflon rotor having a diameter of 15 mm and a length of 100 mm was placed at about 1400 r. p.
m. And rotate at a shear rate of about 70 s ⁻¹ . To this solution under stirring conditions, 8 mol of tetramethoxysilane is added dropwise over about 240 minutes. After that, methanol, ammonia and water are evaporated, and a silica sol solution having a silica content of 35% by weight (average particle size of silica particles: 0.3
μm) is obtained. The silica sol solution was filtered through a polypropylene filter having a pore size of 1.0 μm to obtain a silica content of 30
Water necessary for the gelling reaction is added so that the silica content becomes 30% by weight to obtain a silica sol solution having a silica content of 30% by weight (specific surface area of silica particles: 35 m ² / g).

This silica sol solution was again regenerated with a diameter of 30 cm.
In a polypropylene container made of polypropylene, and using a magnetic stirrer, a rotor made of Teflon having a diameter of 15 mm and a length of 100 mm is about 1400 r. p. m. And rotate at a shear rate of about 70 s ⁻¹ . This stirring was continuously performed during the reaction. 2N hydrochloric acid was added to this to adjust the pH of the solution to 2.0, and then 8 mol of tetramethoxysilane was added for hydrolysis. Furthermore, a 0.2N aqueous ammonia solution was added to adjust the pH to 4.5 to prepare a silica sol mixed solution, which was filtered through a polypropylene filter having a pore size of 10 μm. Approximately 12 kg of the silica sol mixed solution after filtration was cast in a container, gelled in about 3 hours after adjusting the pH, and
A wet gel having a shape of 00 mm × t100 mm was prepared.

The obtained wet gel is heated from room temperature to 200 ° C.
The temperature was gradually raised to and dried for a total of 27 days to obtain a dry gel. This dry gel is fired stepwise at 300 to 1800 ° C. for a total of 26 days to obtain φ200 mm × t50.
A synthetic quartz glass which is a transparent glass body having a size of mm was prepared.
The process from synthesis of silica sol solution to gelation is class 1
00 environment, and the gel was dried in a class 1000 environment. The obtained glass was optically polished, and the air bubbles present in the glass were evaluated by a stereoscopic microscope. The results are shown in Table 1.

Example 2 The silica sol solution was filtered through a polypropylene filter having a pore size of 3.0 μm to give a silica sol mixed solution having a pore size of 30 μm.
Example 1 except that it was filtered through the polypropylene filter of
A synthetic quartz glass was prepared in the same manner as in. The average particle size and specific surface area of the silica particles in the silica sol solution were the same as in Example 1. The obtained synthetic quartz glass was evaluated in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 1 A synthetic quartz glass was prepared in the same manner as in Example 1 except that the silica sol solution was filtered through a polypropylene filter having a pore size of 1.0 μm and the silica sol mixed solution was not filtered. The obtained synthetic quartz glass was evaluated in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 2 A synthetic quartz glass was prepared in the same manner as in Example 1 except that the silica sol solution and the silica sol mixed solution were not filtered. The obtained synthetic quartz glass was evaluated in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 3 A synthetic quartz glass was prepared in the same manner as in Example 1 except that all steps from the synthesis of the silica sol solution to the preparation of the dry gel were carried out in the environment of class 100000. The obtained synthetic quartz glass was evaluated in the same manner as in Example 1 and the results are shown in Table 1.

Comparative Example 4 8 liters of a methanol solution containing 64 moles of water and 12 moles of ammonia was placed in a polypropylene container having a diameter of 30 cm, and a Teflon rotor having a diameter of 15 mm and a length of 100 mm was set to about 600 rpm with a magnetic stirrer. p. m.
And the solution is stirred under the condition that the shear rate is about 30 s ⁻¹ . To this solution under stirring conditions, 8 mol of tetramethoxysilane is added dropwise over about 240 minutes. Then, methanol, ammonia and water were evaporated to prepare a silica sol solution having a silica content of 35% by weight. This silica sol aggregated and formed a precipitate. Water necessary for the gelling reaction was added to this silica sol solution so that the silica content was 30% by weight to obtain a silica sol solution having a silica content of 30% by weight (specific surface area of silica particles: 180 m ² / g).

This silica sol solution was again regenerated with a diameter of 30 cm.
In a polypropylene cylindrical container made of polypropylene, and using a magnetic stirrer, a Teflon rotor having a diameter of 15 mm and a length of 100 mm is about 600 r. p. m. And the mixture is stirred at a shear rate of about 30 s-1. This stirring was continuously performed during the reaction. 2N hydrochloric acid was added to the silica sol solution under this stirring condition to adjust the pH of the solution to 2.0, and then 8 mol of tetramethoxysilane was added to cause hydrolysis. further,
A 0.2N aqueous ammonia solution was added to adjust the pH to 4.5 to prepare a silica sol mixed solution. About 12 kg of this silica sol mixed solution was cast in a container and gelled in about 3 hours after adjusting the pH to prepare a wet gel having a shape of φ400 mm × t100 mm.

The wet gel was gradually heated from room temperature to 200 ° C. and dried for a total of 27 days, and the obtained dry gel body was gradually heated to 300 to 1800 ° C. in a total of 26
It was fired for a day to prepare a synthetic quartz glass of φ200 mm × t50 mm. The steps from the synthesis of the silica sol solution to the gelation were performed in a class 100 environment, and the gel was dried in a class 1000 environment. The obtained glass was optically polished, and the air bubbles present in the glass were evaluated by a stereoscopic microscope. The results are shown in Table 1.

[0028]

[Table 1]

[0029]

According to the present invention, it is possible to produce a synthetic quartz glass having no bubbles and excellent optical characteristics. This synthetic quartz glass is excellent as an optical material for an ultraviolet lens such as an excimer laser and a prism.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hatsushi Inoue 2-18-17 Shimogusa, Suginami-ku, Tokyo (72) Inventor Tetsuhiko Takeuchi 3-3-5 Yamato, Suwa City, Nagano Seiko-Epson Corporation

Claims (1)

[Claims] 1. A step of synthesizing a silica sol solution containing silica particles by hydrolyzing a silicon alkoxide in a basic solution, and adding a silicon alkoxide dropwise to the silica sol solution under an acidic catalyst to hydrolyze to mix the silica sol. From a step of forming a solution, a step of gelling the silica sol mixed solution to form a wet gel, and a step of drying the wet gel to form a dry gel and then firing the dry gel to obtain a transparent glass body. A method for producing synthetic quartz glass, characterized in that the synthetic quartz glass is produced so as to satisfy the following conditions (a) to (d). (A) The average particle size of the silica particles in the silica sol solution is 0.5 μm or less, and the specific surface area is 50 m ² / g or less. (B) Filtering the silica sol solution and the silica sol mixed solution with filters having pore sizes of 10 μm or less and 50 μm or less, respectively. (C) Performing the steps from the synthesis of the silica sol solution to the drying of the wet gel in a clean room that is dust-free at least as high as class 10,000. (D) Stirring at the time of preparing the silica sol solution and the silica sol mixed solution at a shear rate of 50 s ^-1 or more.