JP2012041227A - Method for producing porous glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high quality porous glass preform free from cracking without flickering a flame from an oxyhydrogen flame burner.SOLUTION: The method for producing a porous glass preform 11 comprises subjecting a glass raw material blown off from an oxyhydrogen flame burner 17 to flame hydrolysis at the inside 15a of a vessel 15, and depositing formed porous glass 11 on a starting member 13, wherein a flow rate of a seal gas is controlled so that the total amount of the gaseous glass raw material, a combustible gas, a combustion supporting gas and the seal gas each supplied to the oxyhydrogen flame burner 17 is made constant during porous glass deposition, and the inside 15a of the vessel 15 is kept under a constant negative pressure.

Description

  The present invention relates to a method for producing a porous glass base material in which a glass raw material is ejected from an oxyhydrogen flame burner and flame-hydrolyzed in a reaction vessel, and the produced porous glass is deposited on a starting member. It is related with the manufacturing method of the porous glass base material which can suppress the fluctuation | variation of the pressure of this and can aim at the improvement of a product yield.

  As a method for producing a silica porous glass base material by the VAD method, gaseous glass raw material, hydrogen gas, oxygen gas and inert gas are supplied to a burner, and a silica particle is produced by a flame hydrolysis reaction in a reaction vessel. A method for producing a silica porous glass base material in which the silica fine particles are attached to and deposited on a starting member made of quartz or the like is known. In this production method, in the flame hydrolysis reaction of the gaseous glass raw material, high temperature gas containing unattached silica fine particles composed of water, hydrogen chloride, unreacted glass raw material, other nitrogen, etc. is generated. The material is manufactured inside a reaction vessel that is isolated from the outside. High-temperature exhaust gas is generated in the reaction vessel by the flame hydrolysis reaction, and the method of exhausting this exhaust gas greatly affects the physical properties and productivity of the silica porous glass base material.

  For example, in a method for producing a porous silica base material disclosed in Patent Document 1, a secondary gas (clean air) is fed into a container and exhaust gas generated during flame hydrolysis is exhausted. In this manufacturing method, by exhausting a certain amount of the exhaust gas flow rate 7.5 to 15 times in terms of the standard state of the total gas flow rate supplied to the burner, the base material due to the reattachment of silica fine particles when the exhaust gas flow rate is small Suppression of cracks and delamination due to instantaneous base material temperature changes caused by cracks on the sides and flame disturbance when the exhaust gas flow rate is large, reproducibility and stability of synthesis in the production of silica porous base material, and synthesis The yield is improved.

JP-A-5-155630

However, the problem of cracking during the production of the porous glass base material remains a problem. In other words, as in the above manufacturing method, exhausting exhaust gas at a constant amount can be expected to have some effect, but due to fluctuations in the flow rate that occurs when adjusting the exhaust amount, and fluctuations in the amount of clean air introduced due to exhaust at that time This is because the burner flame is disturbed.
In addition, when porous glass is deposited, it is necessary to keep the inside of the container at a negative pressure so that the glass raw material does not leak to the outside. On the other hand, the flow rate of the raw material / oxyhydrogen supplied to the burner is the same as that of the glass base material. It is necessary to increase the amount according to the growth of the base material diameter. For this reason, if the conditions of clean air and exhaust pressure are kept constant during deposition, the initial pressure will be in a high negative pressure state. If the negative pressure is too high, outside air will easily enter the device. , Dust adheres and the frequency of defective parts increases. As a countermeasure in this case, as in the above manufacturing method, it is possible to make the pressure constant by controlling the flow rate of clean air entering the apparatus, but if the flow rate of clean air is changed, Disturbance is likely to occur. Further, when the air flow rate is increased, the porous glass base material is cooled, and the base material may be cracked. On the other hand, it is difficult to strictly control the flow rate of clean air according to the adjustment of the exhaust amount, and the equipment cost also increases. Further, if clean air temperature control is performed as a countermeasure against cracking of the base material due to temperature change, the equipment cost will be further increased.

  The present invention has been made in view of the above circumstances, and its purpose is to produce a high-quality porous glass base material that does not break without disturbing the flame of the oxyhydrogen flame burner, and achieves low product yield. The object is to provide a method for producing a good porous glass base material.

The above object of the present invention is achieved by the following configuration.
(1) In the method for producing a porous glass base material, in which a glass raw material is ejected from an oxyhydrogen flame burner, flame is hydrolyzed inside the container, and the generated porous glass is deposited on a starting member, the oxyhydrogen flame burner The flow rate of the sealing gas is controlled so that the total amount of the glass raw material gas, the flammable gas, the auxiliary combustion gas, and the sealing gas supplied to the gas is constant during the porous glass deposition, and the pressure inside the container is constant. A method for producing a porous glass base material, wherein the negative pressure is set to a negative pressure.

  According to this method for producing a porous glass base material, the pressure inside the container is reduced by reducing the inert gas flowing in the burner or the seal gas that is nitrogen gas as the raw material gas increases from the initial stage of production. Can be kept constant. Since the flow rate of clean air to be put into the container is not controlled as in the prior art, flame disturbance (changes in conditions accompanying the flow rate variation of clean air) does not occur. In addition, since it is not necessary to add an adjustment function to clean air supply and exhaust as in the prior art, it is possible to reduce equipment costs.

(2) In the method for producing a porous glass base material according to (1),
A multi-tube burner is used as the oxyhydrogen flame burner, the seal gas is flowed from a plurality of layers of the multi-tube burner, and the flow rate of the seal gas in the outer layer of the multi-tube burner during the porous glass deposition The method for producing a porous glass base material, wherein the change is made larger than the change in the flow rate of the seal gas in the inner layer of the multi-tube burner.

  According to this method for manufacturing a porous glass base material, cracking of the base material can be further prevented by changing the seal gas flow rate in the multiple tube burner during the manufacture of the porous glass toward the outer layer. This is because by suppressing the flow rate of the inner sealing gas, it is not necessary to lower the central flame temperature important for deposition, and the amount of sealing gas can be increased without affecting the quality.

  According to the method for producing a porous glass base material of the present invention, the internal pressure of the reaction vessel is adjusted by the seal gas flow rate supplied to the oxyhydrogen flame burner, so that the internal pressure is kept constant without changing the clean air conditions. It is possible to maintain a high quality porous glass base material that does not disturb the flame of the oxyhydrogen flame burner, is low-cost, and does not crack.

It is the side view which represented notionally the manufacturing apparatus of the porous glass base material which enforces the manufacturing method which concerns on this invention. It is a front view of an example of the oxyhydrogen flame burner which enforces the manufacturing method concerning the present invention. It is the graph showing the correlation with the raw material gas flow volume in a comparative example, a seal gas flow volume, and an apparatus internal / external pressure difference, (A) shows the comparative example 1, (B) shows the comparative example 2. FIG. It is the graph showing the correlation with the raw material gas flow volume in an Example, a seal gas flow volume, and the internal / external differential pressure | voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view conceptually showing a porous glass base material manufacturing apparatus for carrying out the manufacturing method according to the present invention.
The manufacturing apparatus 100 for the porous glass base material 11 generates fine glass particles generated by a flame hydrolysis reaction from a reaction vessel 15 that houses a rotating starting member 13, a glass raw material gas, a combustible gas, and an auxiliary combustible gas. An oxyhydrogen flame burner 17 sprayed toward the starting member 13, lifting means (not shown) for lifting and lowering the starting member 13, and clean air supply for supplying clean air 19, which is a cleaning gas, into the reaction vessel 15 And a device (clean air generator) 21.

  A through hole (not shown) is provided on the upper wall of the reaction vessel 15, and the starting member 13 is disposed so as to pass through the through hole in the vertical direction. The starting member 13 is rotated while being gripped by the rotary chuck 23 at the upper end, and is moved up and down by the lifting means. By pulling up the starting member 13 along the axial direction while rotating the starting member 13, glass particulates are deposited on the starting member 13 in the axial direction to manufacture the porous glass base material 11. That is, the manufacturing apparatus 100 for the porous glass base material 11 has an apparatus configuration for manufacturing the porous glass base material 11 by a VAD (Vapor-phase Axial Deposition) method.

  The reaction vessel 15 is provided with an exhaust port 27 on the side opposite to the air supply port 25 of the clean air 19 with the starting member 13 interposed therebetween. An exhaust line (not shown) is connected to the exhaust port 27, and the exhaust line is configured to efficiently exhaust air from the air supply port 25 in order to prevent soot from adhering to the inner wall of the container. In the present embodiment, the supply amount of the clean air 19 supplied from the clean air supply device 21 is constant. Further, the exhaust amount exhausted from the exhaust line via the exhaust port 27 is also constant.

The oxyhydrogen flame burner 17 is used for manufacturing a porous glass base material, and H ₂ gas is used as a flammable gas, O ₂ gas is used as a combustion gas, N ₂ gas, or an inert gas such as Ar gas. As a carrier gas or seal gas, glass fine particles generated by the hydrolysis reaction of flame with various source gases such as SiCl ₄ and GeCl ₄ as a dopant are ejected toward the starting member 13 installed at the deposition reference point. Deposit.

FIG. 2 is a front view of an example of an oxyhydrogen flame burner (eight tubes) for carrying out the manufacturing method according to the present invention.
The oxyhydrogen flame burner 17 includes a burner body provided with a plurality of gas introduction paths 17a to 71h for various source gases, and a plurality of gases (not shown) connected to the gas introduction paths 17a to 17h of the burner body. And a supply branch pipe. In the burner body, a plurality of quartz tubes 29, 31, 33, 35, 37, 39, 41, and 43 having different diameters are concentrically fitted to each other, and adjacent quartz tubes are arranged on the outer periphery of the inner quartz tube. A base end portion of the outer quartz tube is welded to a concentric multiple tube structure.

The multi-tube burner forms a flame with a plurality of kinds of source gases at the tip of a burner body having a concentric multi-tube structure. In the example of FIG. 2, the inner three quartz tubes 29, 31, 33 that form the first flame are the tips of the outer five quartz tubes 35, 37, 39, 41, 43 that form the second flame. This constitutes an 8-pipe double-flame burner that is further retracted.
The multi-tube burner is not limited to the above-mentioned 8-fold double flame burner, but may be other multi-tube burners such as a 12-fold tube burner that forms a triple flame and a 16-fold tube burner that forms a quadruple flame. it can.

A gas supply device (not shown) is connected to a gas supply branch tube (not shown) connected to each gas introduction path 17a to 17h, and the gas supply apparatus supplies the gas supplied to each gas introduction path 17a to 17h. Can be adjusted with high accuracy. As an example of this embodiment, the gas inlet passage 17a is supplied with SiCl ₄ and H _2, 17b is H ₂ is supplied to, N ₂ (or Ar) is supplied to 17c, the 17d O ₂ is supplied, N ₂ (or Ar) is supplied to 17e, H ₂ is supplied to 17f, N ₂ (or Ar) is supplied to 17g, and O ₂ is supplied to 17h. In the configuration of the manufacturing apparatus 100, the supply amount of N ₂ (or Ar), which is a seal gas supplied to the gas introduction paths 17c, 17e, and 17g, can be adjusted with high accuracy.

  In the manufacturing apparatus 100, the flow rate of the raw material / oxyhydrogen supplied to the oxyhydrogen flame burner 17 is increased because the base material diameter of the porous glass base material 11 is increased compared to the initial stage. On the other hand, the flow rate of the seal gas is controlled to be decreased by the increased amount of the raw material / oxyhydrogen.

  Further, the seal gas flowing from the plurality of layers (gas introduction passages 17c, 17e, 17g) of the oxyhydrogen flame burner 17 is sealed in the outer layer 17g according to the growth of the base material diameter of the porous glass base material 11. It is desirable to make the change in the gas flow rate larger than the change in the flow rate of the sealing gas in the inner layers 17c and 17e.

Next, the manufacturing method of the porous glass preform | base_material by the manufacturing apparatus 100 of the said structure is demonstrated.
In the production of the porous glass base material 11, glass raw material is ejected from the oxyhydrogen flame burner 17, flame hydrolysis is performed inside the reaction vessel 15, and the produced porous glass is deposited on the starting member 13 to form the porous glass. The base material 11 is manufactured. In the present invention, the seal gas is supplied so that the total amount of the glass raw material gas, the combustible gas, the auxiliary combustible gas, and the seal gas supplied to the oxyhydrogen flame burner 17 during the production is constant during the deposition of the porous glass. The flow rate is controlled so that the pressure inside the reaction vessel 15 becomes a constant negative pressure.

  In the present embodiment, the supply amount of the clean air 19 is constant as described above. On the other hand, the flow rate of the raw material / oxyhydrogen supplied to the oxyhydrogen flame burner 17 is increased according to the growth of the base material diameter of the porous glass base material 11. That is, in the manufacturing apparatus 100, the flow rate of the seal gas is gradually controlled to decrease as the flow rate of the raw material / oxyhydrogen is increased. Accordingly, the conditions of clean air and exhaust pressure are kept constant during deposition, and the pressure fluctuation caused by the increase of the raw material / oxyhydrogen is canceled by the flow control (decrease) of the seal gas. As a result, the operation is performed so that the differential pressure between the inside 15a and the outside of the reaction vessel 15 is kept constant during the manufacturing process from the start of deposition to the end of deposition.

  The flow rate of the seal gas flowing from the plurality of layers of the oxyhydrogen flame burner 17 is controlled so that the change in the flow rate of the outer layer 17g is larger than the change in the flow rate of the inner layers 17c and 17e. As a result, the flow rate of the inner seal gas can be suppressed, the central flame temperature important for deposition can be prevented from being lowered, and the amount of the seal gas can be increased without affecting the quality.

  Thus, in this production method, the pressure in the interior 15a of the reaction vessel 15 can be kept constant by reducing the seal gas as the raw material gas increases from the initial stage of production. Since the flow rate of clean air to be introduced into the reaction vessel 15 is not controlled as in the prior art, flame disturbance (changes in conditions associated with fluctuations in the flow rate of clean air) does not occur. In addition, since it is not necessary to add an adjustment function to clean air supply and exhaust as in the prior art, it is possible to reduce equipment costs. Further, by changing the seal gas flow rate in the multiple tube burner during the production of porous glass toward the outer layer, the flame can be made more stable and the base material can be further prevented from cracking.

  Therefore, according to the method for manufacturing the porous glass preform 11 according to the present embodiment, the pressure of the inside 15a of the reaction vessel 15 is adjusted by the flow rate of the seal gas supplied to the oxyhydrogen flame burner 17, so the condition of clean air is set. Without changing, the internal pressure can be kept constant, the flame of the oxyhydrogen flame burner 17 is not disturbed, and a high-quality porous glass base material 11 that does not crack can be manufactured.

  In addition, since the amount of seal gas is increased at the initial stage of manufacture, compared to the conventional method, it is possible to avoid a negative pressure more than necessary at the initial stage of manufacture, reducing the risk of inflow of outside air, and high quality without cracking. A porous glass base material 11 can be manufactured.

Next, an example in which a porous glass base material was actually manufactured with the same configuration as the above-described embodiment, and a comparative example in which a porous glass base material was actually manufactured with a constant supply amount of seal gas as before The results of evaluating the above will be described.
FIG. 3A is a graph showing the correlation among the raw material gas flow rate, the seal gas flow rate, and the internal / external differential pressure in Comparative Example 1, and FIG. 3B is the raw material gas flow rate, the seal gas flow rate, and the internal / external pressure in Comparative Example 2. FIG. 4 is a graph showing the correlation between the raw material gas flow rate, the seal gas flow rate, and the internal / external differential pressure in Example 1 and Example 2.
As shown in FIGS. 3 (A) and 3 (B), in Comparative Examples 1 and 2, the supply amount of Ar gas, which is a seal gas, was constant. The flow rate of the raw material and oxyhydrogen was gradually increased from the start to time t and then kept constant. In Comparative Example 1 in FIG. 3A, the flow rate of the raw material / oxyhydrogen was gradually increased, so that the pressure difference between the inside and outside of the apparatus gradually decreased from the start to time t, and then became constant. In Comparative Example 2 in FIG. 3B, the amount of clean air was adjusted while the flow rate of the raw material / oxyhydrogen increased, so the pressure difference inside and outside the apparatus became constant from the start to the end.

  As shown in FIG. 4, in the first and second embodiments, the supply amount of the Ar gas, which is the seal gas, is gradually reduced from the start to the time t so as to cancel the increase in the flow rate of the raw material / oxyhydrogen. And then constant. The flow rate of the raw material and oxyhydrogen was gradually increased from the start to time t and then kept constant. The pressure difference between the inside and outside of the apparatus was constant from the start to the end.

  In Comparative Example 1, Comparative Example 2, Example 1 and Example 2, each flow rate of raw materials and oxyhydrogen gas from the start of production to the end of production, the flow rate of Ar gas in the third and fifth layers, Ar gas in the seventh layer Table 1, Table 2, Table 3, and Table 4 show the total flow rate, the total flow rate of all the gases, the total flow rate of the raw materials and oxyhydrogen gas, the total flow rate of Ar gas, and the internal / external pressure difference.

  In each of N = 100 porous glass base materials according to the comparative examples and examples manufactured under the conditions in Tables 1 to 4, the number of internal abnormal points and the crack occurrence rate of the porous glass base material were examined. The results are shown in Table 5.

Comparative Example 1
When the sealing gas supplied to the oxyhydrogen flame burner was set at a constant flow rate, many abnormal points were generated inside the porous glass base material corresponding to the initial stage of production.
Comparative Example 2
When the amount of clean air supplied into the manufacturing apparatus was increased in the initial stage of manufacturing the porous glass base material, the pressure fluctuation in the manufacturing apparatus could be suppressed, but the porous glass base material was cooled. The cracking frequency of the porous glass base material, which seems to have increased, increased to 1.5%.

Example 1
When the pressure inside the production equipment is maintained by controlling the flow rate of the seal gas so that the total amount of raw material, hydrogen, and seal gas supplied to the oxyhydrogen flame burner is constant during production, there are many abnormalities at the initial stage of production. The problem has been resolved.
Example 2
When maintaining the pressure inside the production equipment by controlling the flow rate of the seal gas so that the total amount of raw material, hydrogen, and seal gas supplied to the oxyhydrogen flame burner is constant during production, the flow rate of the seal gas is increased toward the outside of the burner. As a result, the problem of many abnormal points at the initial stage of manufacturing was solved, and the frequency of cracking of the porous glass base material during the manufacturing was improved to 0.5%.

  In the above embodiment, the method for producing a porous glass base material by the VAD method has been described. However, the production method according to the present invention includes a burner for synthesizing glass fine particles and a rod-like shape rotating around an axis. An OVD method in which glass particles are deposited on the starting material by relatively reciprocating the starting material, a burner row composed of a plurality of glass particle synthesizing burners, and a rod-shaped starting material that rotates around an axis. The range in which the glass particles synthesized by each burner are deposited so as to cover a part of the length direction of the starting member and the glass particles are deposited by the adjacent burner continuously is reciprocated relatively. It can be similarly employed in a method for producing a porous glass base material (MMD method; multi-burner multilayer attaching method) for forming one glass fine particle deposit.

11 Porous glass base material 13 Starting member 15 Reaction vessel 15a Inside 17 Oxyhydrogen flame burner 29, 31, 33, 35, 37, 39, 41, 43 Tube

Claims (2)

In a method for producing a porous glass base material, in which a glass raw material is jetted from an oxyhydrogen flame burner, flame hydrolyzed inside a container, and the generated porous glass is deposited on a starting member.
The flow rate of the sealing gas is controlled so that the total amount of the glass raw material gas, the flammable gas, the auxiliary combustion gas, and the sealing gas supplied to the oxyhydrogen flame burner is constant during the porous glass deposition, A method for producing a porous glass base material, characterized in that the internal pressure becomes a constant negative pressure. In the manufacturing method of the porous glass base material of Claim 1,
A multi-tube burner is used as the oxyhydrogen flame burner, the seal gas is flowed from a plurality of layers of the multi-tube burner, and the flow rate of the seal gas in the outer layer of the multi-tube burner during the porous glass deposition The method for producing a porous glass base material, wherein the change is made larger than the change in the flow rate of the seal gas in the inner layer of the multi-tube burner.

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