JPS6251216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing bubble-free, homogeneous and transparent silica glass for optical fibers at a high production rate.

Conventionally, in the manufacturing method of silica glass for optical fibers, especially doped silica glass (see Japanese Patent Application No. 55-126556, etc.), for example, silicon tetrachloride vapor and a dopant such as germanium tetrachloride vapor have been used. Glass-forming raw material gas, together with oxygen and optionally a carrier gas, is held and rotated at both ends, heated with a flame burner, etc., and blown in from the surroundings to undergo flame hydrolysis or thermal oxidation to produce glass particles. In this case, the glass particles are generated by the reaction from the gas phase to the solid phase, so the size of the particles is different from that in the case of flame hydrolysis (1000-1300℃).
500~2000Å, in case of thermal oxidation (1000~1300℃)
It was extremely small, about 100 to 500 Å. On the other hand, in order to produce bubble-free transparent doped silica glass at high speed by feeding glass particles into a flame or plasma flame and melting them, the size of the particles must be 10 to 10.
It is known that about 100 μm is optimal.

Therefore, in the case of glass particles produced by conventional methods, in order to obtain doped silica glass without residual bubbles at a high production rate by melting with flame or plasma flame in the next step and turning it into transparent vitrification (1400-1800°C). In this method, the fine particles are heat-treated (1200-1500°C) to reduce the particle size to 10-100℃ prior to melting and transparent vitrification.
There was a drawback that it was necessary to generate secondary particles of about μm size.

An object of the present invention is to eliminate this drawback and provide a method for producing homogeneous silica glass for optical fibers at a high production rate by producing silica-based glass powder with a large particle size by specific means. .

To summarize the present invention, the method for producing silica glass for optical fibers of the present invention involves hydrolyzing alkyl silicate to produce a sol solution, and spraying the sol solution into a heating zone from a spray nozzle to form silica glass. This method is characterized in that glass powder is produced, and then the glass powder is fed into a flame or plasma flame to melt it and turn it into transparent vitrification.

In the present invention, an alkyl silicate (partial or complete alkyl ester of silicic acid) is used as a glass raw material, and if desired, phosphoric acid is added to this as a dopant material (an additive that changes the refractive index of the glass). A partial or complete alkyl ester of at least one acid selected from the group consisting of , stannic acid, lead acid, zinc acid, boric acid, titanic acid, aluminic acid, and germanic acid can be used in combination.

These alkyl esters typically include tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetramethyl germanate.
Tetraethyl germanoate, tetrapropyl germanoate, tetrabutyl germanoate, etc. can be suitably used, but the present invention is not necessarily limited to these, and partial esters thereof may also be used.

The blending ratio of alkyl silicate and dopant material is determined by the refractive index of the target optical fiber base material,
Can be selected appropriately depending on the type of material,
Not particularly limited.

In the present invention, for example, an alkyl silicate such as the above-mentioned tetramethyl silicate and an alcohol such as methyl alcohol are mixed at a volume ratio of about 1:9, water is added to the mixture for hydrolysis, and a sol-like solution (silica sol) is prepared. This sol-like solution is supplied to the spray nozzle at a rate of about 100 c.c. per minute, and compressed gas of about 2 atmospheres is supplied to the spray nozzle at a rate of about 10 per minute. is sprayed from the tip of a spray nozzle as sol droplets of approximately 70 to 80 μm. At this time, an inert gas such as argon is used as the compressed gas, and the compressed gas pressure is 1 to 1.
It is appropriate to set the pressure to 3 atm, and as the pressure is increased, the diameter of the droplets becomes smaller and the particle size of the silica glass produced becomes smaller. The atmosphere inside the reactor core tube (heating zone) is controlled by inert gas such as argon gas containing 5 mol% or more of ammonia (NH ₄ OH) as a gelling promoter from the atmosphere gas supply port every minute as the atmosphere gas. Supply about 10.

Although ammonia in the atmospheric gas is not necessarily necessary, it is desirable to use it to promote gelation. The higher the concentration of ammonia, the greater the promoting effect, but the above 5 mol% or more is sufficient. or,
The appropriate temperature in the furnace tube (heating zone) is within the range of 100 to 1000℃, but if the temperature is low, water or alkyl esters are likely to remain, reducing the optical properties and mechanical properties (strength) of the product. . On the other hand, too high a temperature is inconvenient. Therefore, it is optimal that the maximum temperature in the furnace tube is about 500°C, thereby making it possible to obtain silica glass powder with a particle size of 20 to 30 μm. Furthermore, if the viscosity of the sol-like solution is high, it is difficult to form a mist during spraying, so it is necessary to keep the viscosity at 10 ³ poise or less.

Furthermore, in the present invention, in order to eliminate the residual water or alkyl ester, etc., it is preferable to heat-treat the produced silica glass powder before melting it to make it transparent vitrified. The heat treatment conditions are
It is appropriate to heat at a temperature of 800 to 1500°C for 30 minutes to 2 hours.

Through the above processing, silica glass powder with a particle size of about 10 to 100 μm can be produced at a high production rate (for example, 500 μm/hour).
~1000g), and the particle size is uniform with no variation, making it possible to obtain particles of the desired particle size.

Next, this silica glass powder is fed into a flame or plasma flame (1400 to 1800°C) blown out from a torch by a known method, and is melted and turned into transparent vitrification to produce a bubble-free homogeneous silica glass base material for optical fiber. Can be manufactured at high speed.

Next, the present invention will be explained with reference to the drawings.

The drawing is a schematic cross-sectional view showing a specific example of the silica glass powder production apparatus according to the present invention, in which reference numeral 1 indicates a gas supply port for pressurizing a sol solution, 2 indicates a sol solution, and 3 indicates a housing for the sol solution. container, 4 is a transport pipe,
5 is a flow rate regulator, 6 is a spray nozzle, 7 is an atmospheric gas supply port, 8 is a compressed gas supply port, 9 is a sol droplet,
10 is a heating element, 11 is a furnace tube, 12 is an exhaust port, 1
3 is a storage container for silica glass powder, and 14 is a silica glass powder.

The sol solution (silica sol liquid) 2 obtained by hydrolyzing the alkyl silicate stored in the sol solution storage container 3 is pressurized by the gas supplied from the pressurizing gas supply port 1, and is passed through the transport pipe 4. is supplied into the spray nozzle 6 through the spray nozzle 6. The supply amount of the sol solution 2 is adjusted by a flow rate regulator 5. Spray nozzle 6
The sol-like solution 2 supplied into the interior is ejected from the tip of the spray nozzle 6, and at the same time becomes atomized by the compressed gas supplied from the compressed gas supply port 8, forming sol droplets 9 (about 10 to 100 μm in size). is formed and gelled in the furnace tube 11 (heating zone) heated by the heating element 10, and the silica glass powder is stored in the storage container 1.
Silica glass powder 14 is obtained in 3. At this time, the gas generated as a result of gelation and the compressed gas ejected from the spray nozzle 6 are exhausted from the exhaust port 12.

The silica glass powder thus produced is melted and made into transparent vitrification by being supplied into a flame blowing out together with oxygen and hydrogen gas, and the silica glass powder produced in this way is melted and made into transparent vitrification by the heat of the flame. Then, silica glass for optical fibers is manufactured (the drawings are omitted).

Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these in any way.

Example 1 Tetramethylsilicate [Si(OCH ₃ ) ₄ ] and methyl alcohol were mixed at a volume ratio of 1:9, and water was added to the mixture for hydrolysis to obtain a sol solution. This sol-like solution was treated by the method shown in the drawing to produce silica glass powder. That is,
This sol-like solution is supplied to the spray nozzle 6 at a rate of 100 c.c. per minute and compressed argon gas at 2 atmospheres at a rate of 10 per minute, respectively, and sol droplets 9 with a size of 70 to 80 μm are released from the tip of the spray nozzle 6. Sprayed. Furthermore, argon gas containing 5 mol% ammonia is supplied as an atmospheric gas from the atmospheric gas supply port 7 at a rate of 10% per minute to maintain the temperature in the furnace core tube 11 (heating zone) at a maximum of approximately
It was maintained at 500°C. As a result, gelled silica glass powder with a particle size of 20 to 30 μm was obtained in the storage container 13.

Then, according to the usual method, oxygen per minute and hydrogen per minute were applied.
10 g of the above silica glass powder was fed per minute into the flame blowing out at 100 °C, and it was melted at a temperature of 1600 to 1800 °C.
Transparent vitrification was performed to obtain silica glass. When the refractive index of this silica glass was measured with an Atsube refractometer, a value of 1.458 was obtained, and no bubbles were observed in the glass, so it could be used satisfactorily as a base material glass for optical fibers.

Example 2 Tetramethyl silicate [Si(OCH ₃ ) ₄ ] and tetramethyl germanate [Ge
(OCH ₃ ) ₄ ] at a volume ratio of 9:1, this mixture and methyl alcohol at a volume ratio of 1:9, water is added to this for hydrolysis, and a sol-like solution is obtained. Obtained. Thereafter, the operation was carried out under the same conditions as in Example 1, and silica glass powder (particle size 20 to 30 μm) containing about 10 mol % of germanium oxide (GeO ₂ ) was obtained.

The melting and transparent vitrification temperature is below 1500~1700℃
Doped silica glass was obtained by the same operation as in Example 1 except for the following. The refractive index of this glass is
The refractive index of the glass was 1.472, which was approximately 1% higher than the refractive index of silica glass (1.458), and there were no bubbles in the glass, which was uniform and could be used satisfactorily as a base glass for optical fibers.

Example 3 Using the same raw materials and operations as Example 1, a particle size of 20~
A gelled silica glass powder of 30 μm was obtained.

Next, the generated silica glass powder was mixed with 1000
A heat treatment was performed at ℃ for about 2 hours to obtain a silica glass powder close to natural quartz with a low content of water and alkyl esters.

Hereinafter, operations were performed under the same conditions as in Example 1, and the refractive index
A transparent silica glass with a value of 1.458 was obtained. No air bubbles were observed in this glass, and it could be used satisfactorily as a base material glass for optical fibers.

As explained above, according to the present invention, silica glass powder can be produced at high speed by producing silica glass powder with a large particle size (10 to 100 μm), and melting this by a conventional method to make it transparent vitrified. or,
In order to generate silica glass powder from a sol-like solution, the doped silica glass produced by adding various dopants has a very homogeneous composition with no bubbles, as both materials are evenly mixed (combined) at the molecular level. It has the advantage of having

[Brief explanation of the drawing]

The drawing is a schematic cross-sectional view showing a specific example of a silica glass powder production apparatus according to the present invention. 1... Gas supply port for pressurizing sol solution, 2...
Sol-like solution, 3... Storage container for sol-like solution, 4...
...Transport pipe, 5...Flow rate regulator, 6...Spray nozzle, 7...Atmospheric gas supply port, 8...Compressed gas supply port, 9...Sol droplet, 10...Heating element, 11...
... Furnace core tube, 12 ... Exhaust port, 13 ... Storage container for silica glass powder, 14 ... Silica glass powder.

Claims (1)

[Claims] 1. Hydrolyze an alkyl silicate to produce a sol solution, spray the sol solution from a spray nozzle into a heating zone to produce silica glass powder, and then spray the glass powder with a flame or A method for producing silica glass for optical fibers, which comprises supplying silica glass to a plasma flame to melt it and turn it into transparent glass. 2 Partial or complete addition of at least one acid selected from the group consisting of phosphoric acid, stannic acid, lead acid, zinc acid, boric acid, titanic acid, aluminic acid and germanic acid as a dopant material to the alkyl silicate before hydrolysis. The method for producing silica glass for optical fibers according to claim 1, wherein alkyl esters are mixed and hydrolyzed. 3. The method for producing silica glass for optical fibers according to claim 1 or 2, wherein the silica glass powder is heat-treated before being melted and turned into transparent vitrification.