JP2003054957A - Method for manufacturing porous glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a porous glass preform by which inflow of outdoor air in a reaction vessel and an anterior chamber of the reaction vessel can be prevented by comparatively simple device constitution and there is no fear of generating flame turbulence. SOLUTION: A burner for synthesizing a glass fine particle is arranged near a starting rod in the reaction vessel and glass fine particles are deposited around the staring rod by relatively moving the starting rod or the burner while rotating the starting rod. The method for manufacturing the porous glass preform is characterized in that the glass fine particles are deposited while holding inner pressure in the anterior chamber of the reaction vessel which is provided via a partitioning member at a side before a growing side top end of the glass fine particles deposited layer in the reaction vessel at a level being equal to or higher than external pressure.

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 a porous glass base material in which glass particles are deposited around a starting rod.

[0002]

2. Description of the Related Art As a method for producing a porous glass preform which is a precursor material for an optical fiber preform or the like, a burner for synthesizing fine glass particles is arranged near a starting rod supported in a reaction vessel, There is a method of producing a porous glass preform by depositing glass fine particles around the starting rod while forming a glass fine particle deposition layer while relatively moving the starting rod or the burner while rotating the rod.

FIG. 2 is an explanatory view schematically showing the manufacturing process of the porous glass base material, in which 21 is a starting rod and 22 is a starting rod.
Is a glass particle deposition layer, 23 is a porous glass base material, 24
Is a reaction vessel, 25 is an exhaust pipe, 26 is a reaction vessel front chamber, 27
Is a burner (burner for synthesizing glass particles), and 28 is a flow of glass particles. A raw material gas such as SiCl ₄ , a fuel gas such as hydrogen and oxygen, and an inert gas as a seal gas are supplied to a burner 27 installed in the reaction vessel 24 to synthesize glass particles. A porous glass base material is manufactured by depositing the glass particles around the starting rod 21 to form a glass particle deposition layer.

In such a method, when dust adheres to the starting rod, the dust remains as foreign matter in the porous glass preform, and the transmission characteristics of the optical fiber manufactured by the porous glass preform are measured. It causes problems such as deterioration and deterioration of strength. Further, in the above manufacturing method, the gas and the like after the combustion in the reaction container is exhausted from the exhaust pipe by the blower, and the inside of the reaction container is usually at a negative pressure. Therefore, in the case of the gap between the burner and the exhaust pipe where it is attached to the reaction vessel, the gap between the reaction vessel and the reaction vessel front chamber, and when the reaction vessel and the reaction vessel front chamber are formed integrally. Even if there is a long-term use, outside air flows in from the cracks that tend to occur at the boundary between the reaction vessel and the reaction chamber front chamber, etc., and dust from the outside is mixed in, and the porous glass matrix is disturbed by flame disturbance. There have been problems such as fluctuations in material profile and glass fine particles adhering to the inside of the container re-suspending and adhering to the glass fine particle deposition layer.

Various methods have been proposed to solve these problems. For example, Japanese Unexamined Patent Application Publication No. 2000-16829 discloses a starting base metal set in a chamber by blowing a flame of a burner onto the starting base metal. In a method of manufacturing an optical fiber preform in which glass particles are deposited in the axial direction, in order to prevent external air from flowing through the gaps in the chamber to disturb the flame and to prevent unadhered particles in the chamber from rising and mixing in the deposition layer, A method is disclosed in which the whole is surrounded by an outer container and the pressure in this container is set to a negative pressure that is about the same as that in the chamber or a negative pressure that is slightly lower than that in the chamber.

Further, in the reaction vessel, a burner is arranged near the starting member, and glass particles are deposited around the starting member while moving the rotating starting member burner relatively to produce a porous glass preform. In the method, a clean gas (inert gas or air) is blown to a starting member in a reaction container front chamber provided in front of a growth side of a glass particulate deposit in the reaction container to remove dust adhering to the surface of the starting member ( JP-A-2000-109329),
Furthermore, a method of purging the surface of the starting member in the reaction vessel with an inert gas to maintain a clean atmosphere (Japanese Patent Publication No. 6-600).
No. 23), etc. are also proposed.

[0007]

In any of the methods proposed in the above publications, the internal gas is exhausted by the exhaust pipe attached to the reaction vessel, so that the internal pressure of the reaction vessel or the reaction vessel front chamber is It is a negative pressure environment. In a negative pressure environment, outside air containing dust flows into the reaction container body or the connection part with the reaction chamber anterior chamber, parts mounting part, etc. from the gap caused by deterioration over time, and the flame is disturbed or the rod surface is disturbed. There is a possibility that dust will adhere. According to the method of the above-mentioned JP 2000-16829 A,
It is considered to be effective because the reaction vessel is doubled to prevent the outside air from flowing into the inner reaction vessel, but with the increase in size of the reaction vessel, the device itself that encloses it also becomes large and large-scale. There is a problem that it ends up.

The present invention solves the above problems of the prior art, prevents the inflow of outside air into the reaction vessel and the reaction chamber front chamber, and prevents dust from adhering to the starting rod with a relatively simple device configuration. It is an object of the present invention to provide a method for producing a porous glass base material, which is capable of producing a porous glass base material and which is free from the risk of flame disturbance.

[0009]

The present invention adopts the following constitutions (1) to (11) as means for solving the above problems. (1) A burner for synthesizing glass particles is arranged in the vicinity of a starting rod in a reaction container, and while the starting rod is being rotated, the starting rod or burner is relatively moved to deposit glass particles around the starting rod. In the method for producing a porous glass preform, on the growth side tip front side of the glass particle deposition layer of the reaction vessel, the internal pressure of the reaction vessel front chamber provided via a partition member, the same as the external pressure or it A method for producing a porous glass preform, which comprises depositing glass particles while maintaining the temperature higher than that. (2) The method for producing a porous glass preform according to the above (1), characterized in that the internal pressure in the reaction chamber front chamber is maintained at 0 to 50 Pa higher than the external pressure. (3) The method for producing a porous glass preform according to (2), characterized in that the internal pressure in the reaction chamber front chamber is maintained so as to be 1 to 10 Pa higher than the external pressure.

(4) Clean air in the reaction chamber front chamber,
By introducing an inert gas or a mixed gas thereof, the internal pressure in the reaction chamber front chamber is kept equal to or higher than the external pressure, and the above (1) to (3) are provided. Any one of the methods for producing a porous glass preform. (5) The flow rate of the gas introduced into the reaction chamber front chamber is 1
The method for producing a porous glass preform according to the above (4), which is at least 100 liters / minute.

(6) The above-mentioned (1) to (5) are characterized in that a mechanism for allowing the gas in the reaction chamber front chamber to flow out is provided in the vicinity of the boundary between the reaction chamber front chamber and the reaction container. 1. A method for producing a porous glass preform according to any one of 1. (7) The porous glass according to any one of (1) to (6), wherein the atmosphere in the reaction chamber front chamber has a number of particles having a size of 0.3 μm or more of 1000 or less per CF. Base material manufacturing method. (8) The method for producing a porous glass preform according to the above (7), wherein the atmosphere in the reaction chamber front chamber is such that the number of particles having a size of 0.5 μm or more is 50 or less per 1 CF.

(9) The method for producing a porous glass preform according to the above (8), wherein the atmosphere in the reaction chamber front chamber has 10 or less particles having a size of 1 μm or more per CF. (10) The method for producing a porous glass preform according to the above (9), wherein the atmosphere in the reaction chamber front chamber has a number of particles having a size of 2 μm or more of 5 or less per CF. (11) The method for producing a porous glass preform according to the above (10), wherein the atmosphere in the reaction chamber front chamber has a number of particles having a size of 5 μm or more of 1 or less per 1 CF.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view schematically showing an example of an apparatus for carrying out the method of the present invention. In FIG. 1, 1 is a starting rod, 2 is a glass particle deposition layer, 3 is a porous glass base material, 4 is a burner, 5 is a reaction vessel, 6 is a front chamber, 7 is a connecting portion, 8 is a partition member, and 9 is an exhaust. A pipe, 10 is a clean gas introduction pipe, 11 is a clean gas generator, 12 is a flow controller, 13 is a pressure gauge, 14 is a ventilation window, and 15 is a flow of glass particles.

A raw material gas such as silicon tetrachloride, a fuel gas such as hydrogen and oxygen, and an inert gas as a seal gas are supplied to a burner 4 installed in a reaction vessel 5 to synthesize glass fine particles. The porous glass base material 3 is manufactured by depositing the glass particles around the starting rod 1 to form the glass particle deposition layer 2. The flow 13 of the glass fine particles emitted from the burner 4 reaches the vicinity of the growth-side tip of the glass fine particle deposition layer 2, and the glass particulate deposition layer 2 is coaxial with the outer circumference of the starting rod 1 by pulling the starting rod 1 upward. Grow axially. In this example, the position of the burner 4 is fixed and the starting rod 1 is moved upward, but the position of the starting rod is fixed and the burner is moved.

A reaction chamber front chamber 6 into which the starting rod 1 is inserted is provided in front of the growth side tip of the glass particle deposition layer 2. The interior of the reaction container 5 and the interior of the front chamber 6 are partitioned by a partition member 8, and the starting rod 1 is pulled up from the front chamber 6 side to the reaction container 5 side through a through hole of the partition member 8. A clean gas introduction pipe 10 is attached to the front chamber 6 so that the clean gas can be introduced from the clean gas generator 11 through the flow rate controller 12. Since the greatest object of the present invention is to prevent dust from adhering to the surface of the starting rod 1, it is effective to prevent dust from adhering to the front chamber 6, which is an area where the surface of the starting rod 1 is exposed. Is.

In the method of the present invention, the reaction chamber front chamber 6 is used during the deposition of the glass particles in order to achieve the above object.
Glass fine particles are deposited while maintaining the internal pressure equal to or higher than the external pressure. As a result, the gap between the mounting portion of the burner 4 and the exhaust pipe 9 to the reaction container 5, the gap near the connecting portion 7 between the reaction container 5 and the reaction container front chamber 6, and the reaction container 5 and the reaction container front chamber 6 Even when the and are integrally formed, outside air flows in from the cracks generated at the boundary between the reaction vessel and the reaction chamber front chamber, etc. during long-term use, preventing dust from entering from the outside. be able to. Further, it is possible to eliminate the inconvenience that the glass particles inside the reaction container float and enter the front chamber and adhere to the starting rod.

The pressure difference between the inside of the front chamber 6 and the outside is 0 to 50 Pa.
Is preferred. If the internal pressure is high, it is effective in reducing the amount of dust, but if it is too high, the influence on the gas flow in the reaction vessel 5 becomes large, and the deposition efficiency of the glass particles is reduced. Therefore, it is more preferable that the pressure difference between the outside and the outside is 1 to 10 Pa, since there is almost no influence on the inside of the reaction vessel 5. In the normal case, the pressure inside the reaction vessel 5 is a negative pressure of -10 to -50 Pa with respect to the outside.
That is, the relationship between the pressure inside the reaction chamber and the pressure inside the reaction chamber is as follows.

As a means for keeping the internal pressure in the reaction chamber front chamber 6 equal to or higher than the external pressure, a clean gas introducing pipe 10 is attached to the front chamber 6 to clean gas, for example, clean. A suitable method is to introduce air or an inert gas such as nitrogen, helium, or argon. The introduction amount of the clean gas is largely influenced by the size of the apparatus and the airtight state of the antechamber 6 (size and number of existing gaps and cracks), but it cannot be said unconditionally, but it is preferable to set it to 100 l / min or more. .

Since a large amount of clean gas is introduced as described above, it is preferable to use clean air from which dust has been removed by a high performance filter as the clean gas from the viewpoint of cost and environment. As a high-performance filter for clean air, HEPA filter (High-Efficiency Particle Air
A filter called "filter" (collection efficiency of particles with a size of 0.3 μm or more is 99.9% or more) is generally used. A clean air generator that generates clean air by unitizing this high-performance filter and fan. (CAG)
Since it is widely marketed, it is easy to use such a device as the clean gas generator 11, and the device can be constructed at low cost.

The clean gas introduced into the front chamber 6 enters the reaction vessel 5 and is exhausted from the exhaust pipe 9 together with the combustion gas. Therefore, when the amount of introduced clean gas increases, the amount of gas flowing into the reaction container 5 increases, which disturbs the flow 15 of the glass particles and affects the gas flow in the reaction container 5 to change the deposition conditions. There is a fear. As a measure against this,
It is preferable to provide a mechanism in the vicinity of the boundary between the reaction container 5 and the front chamber 6 so that the gas in the front chamber 6 flows to the outside. In the example of FIG. 1, as such a mechanism, the connecting portion 7 is provided with the ventilation window 14 capable of adjusting the size of the opening. As a result, the clean gas introduced into the front chamber 6 can be released to the outside, and the influence on the gas flow in the reaction vessel 5 can be minimized. Further, it is also effective to install a partition member 8 whose opening area can be freely changed at the connecting portion 7 between the reaction container 5 and the front chamber 6.

In order to prevent the generation of air bubbles inside the porous glass base material and the inclusion of foreign matter, it is preferable to maintain the inside of the front chamber 6 in an atmosphere with a small number of dusts. According to the examination results of the present inventors,
The amount of dust in the front chamber 6 is 1 CF (cubic feet: 28.3
The number of particles having a size (particle diameter) of 0.3 μm or more is preferably 1000 or less, more preferably 0.5 or more and 50 or less, and further preferably 1 or more. No more than 5, more preferably no more than 2 μm, more preferably no more than 5 μ
It has been found that it is effective to set the number of m or more to 1 or less. The number of dusts was measured by detecting the intensity of scattered light from the particles using a commercially available particle counter for clean rooms (manufactured by Met One, Inc .: small multifunction laser particle counter, model 237B).

[0022]

Example 1 Example 1 is performed by using the apparatus having the configuration shown in FIG.
A production test of a porous glass base material was conducted. In front chamber 6, 0.
10 pieces / m of dust with a size of 3 μm or more³Clean below
0.5m air ³Supply at a flow rate of / min, and intake air from the exhaust pipe 9
Pressure, size of gap between partition member 8 and starting rod 1
By adjusting the size of the opening of the ventilation window 14,
Therefore, the pressure inside the reaction vessel 5 is set to 20 Pa lower than the outside.
Was determined (differential pressure with the outside −20 Pa). In addition, in the front chamber 6
Increase the pressure by 5 Pa from the outside (differential pressure from the outside + 5 P
a), the porous glass base material 3 was produced. Anterior chamber at this time
The number of dust in 6 per 1CF (28.3 liters)
500 of 0.3 μm or more, 0.5 μm or more
20 pieces, 3 pieces of 1 μm or more, 2 pieces of 2 μm or more
Was 0. As a result, the obtained porous glass mother
It is a good product with almost no air bubbles or foreign matter mixed in the material 3.
Had quality.

(Comparative Example 1) A production test of a porous glass preform was conducted in the same manner as in Example 1 except that the introduction of clean air was stopped. At this time, the pressure inside the reaction vessel 5 is set to 20
When the pressure was set to be lower than Pa, the pressure difference between the pressure inside the front chamber 6 and the outside was −5 Pa. At this time, the number of dusts in the front chamber 6 is 0. per 1 CF (28.3 liters).
The number of particles of 3 μm or more was 4000, the number of particles of 0.5 μm or more was 200, the number of 1 μm or more was 15, the number of 2 μm or more was 7, and the number of 5 μm or more was 2. As a result, it was confirmed that air bubbles and foreign matter were mixed into the obtained porous glass base material 3.

[0024]

EFFECTS OF THE INVENTION According to the present invention, the gap between the parts mounting portion to the reaction container, the gap near the connecting portion between the reaction container and the reaction chamber front chamber, and the reaction with the reaction container during long-term use It is possible to prevent external dust from entering the front chamber due to inflow of outside air from a crack or the like generated at a boundary with the front chamber of the container. Further, it is possible to prevent the glass fine particles inside the reaction vessel from floating and being mixed into the front chamber and adhering to the starting rod. Further, there is no problem such as fluctuation of the porous glass base material profile due to turbulence of flame, re-suspension of glass particles adhered inside the container and adhesion to the glass particle deposition layer.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is an explanatory view schematically showing an example of a manufacturing process of a porous glass base material according to a conventional technique.

[Explanation of symbols]

1 Starting Rod 2 Glass Fine Particle Deposited Layer 3 Porous Glass Base Material 4 Burner 5 Reaction Vessel 6 Anterior Chamber 7 Connection Part 8 Partition Member 9 Exhaust Pipe 10 Clean Gas Introducing Pipe 11 Clean Gas Generator 12 Flow Regulator 13
Pressure gauge 14 Ventilation window 15 Flow of glass particles 21 Starting rod 22 Glass particle deposition layer 2
3 Porous glass base material 24 Burner 25 Exhaust pipe 26 Front chamber 2
7 Burner 28 Flow of fine glass particles

Continued front page    (72) Inventor Shinji Nakahara             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 4G014 AH14                 4G021 EA01 EA02 EB18

Claims (11)

[Claims] 1. A glass fine particle synthesizing burner is arranged in the vicinity of a starting rod in a reaction vessel, and while the starting rod is being rotated, the starting rod or burner is relatively moved and glass fine particles are provided around the starting rod. In the method for producing a porous glass base material to be deposited, in the front side of the growth side tip of the glass particulate deposition layer of the reaction vessel, the internal pressure in the reaction vessel front chamber provided via a partition member is the same as the external pressure. Alternatively, a method for producing a porous glass base material, which comprises depositing glass fine particles while maintaining the temperature higher than that. 2. The method for producing a porous glass preform according to claim 1, wherein the internal pressure in the reaction chamber front chamber is maintained so as to be higher than the external pressure by 0 to 50 Pa. 3. The method for producing a porous glass preform according to claim 2, wherein the internal pressure in the reaction chamber front chamber is maintained to be higher than the external pressure by 1 to 10 Pa. 4. The internal pressure of the reaction chamber is kept at the same as or higher than the external pressure by introducing clean air, an inert gas, or a mixed gas thereof into the reaction chamber. The method according to claim 1, wherein
4. The method for producing a porous glass preform according to any one of 3 above. 5. The method for producing a porous glass preform according to claim 4, wherein the flow rate of the gas introduced into the reaction chamber front chamber is 100 liters / minute or more. 6. A mechanism for allowing gas in the reaction chamber front chamber to flow to the outside in the vicinity of a boundary between the reaction chamber front chamber and the reaction container. The method for producing a porous glass preform according to item. 7. The atmosphere in the reaction chamber front chamber is
The number of particles with a size of 0.3 μm or more is 1000 per 1CF
The method for producing a porous glass preform according to any one of claims 1 to 6, wherein the number is less than or equal to one. 8. The atmosphere in the reaction chamber front chamber is
The method for producing a porous glass preform according to claim 7, wherein the number of particles having a size of 0.5 μm or more is 50 or less per 1 CF. 9. The atmosphere in the reaction chamber front chamber is
9. The method for producing a porous glass preform according to claim 8, wherein the number of particles having a size of 1 μm or more is 10 or less per 1 CF. 10. The method for producing a porous glass preform according to claim 9, wherein the atmosphere in the reaction chamber front chamber is such that the number of particles having a size of 2 μm or more is 5 or less per 1 CF. 11. The method for producing a porous glass preform according to claim 10, wherein the atmosphere in the reaction chamber front chamber has one or less particles having a size of 5 μm or more per 1 CF.