JPH0524854A - Production of glass article - Google Patents

Abstract

PURPOSE:To provide a process most suitable especially for the production of a preform for optical fiber or its intermediate product. CONSTITUTION:A deposited glass soot is synthesized by a vapor-phase synthesis and heat-treated in vacuum or in an atmosphere having reduced pressure to convert the soot into transparent glass and obtain a glass article. In the above process, the heat-treatment is carried out in at least three steps comprising the 1st heat-treatment at a temperature not to cause the shrinkage of the deposited glass soot, the 2nd heat-treatment at a temperature higher than the 1st heat-treatment temperature but not cause the conversion of the soot to transparent glass and the 3rd heat-treatment at a temperature to convert the soot into transparent glass. Since the deposited glass soot uniformly shrinks by the present heat-treatment, a high-quality glass article having small outer diameter unevenness and free from residual bubble, etc., can be produced.

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 high-quality glass article, and particularly to a method for producing an optical fiber preform or an intermediate product thereof.

[0002]

2. Description of the Related Art A vapor phase synthesis method, for example, a method with a vapor phase axis (VAD
Method) or an externally added method (OVD method), the fine glass particle deposit is subjected to high-temperature heat treatment in an electric furnace to be vitrified into a glass article. Heretofore, transparent vitrification has been carried out by using He or an inert gas containing a small amount of halogen gas (especially chlorine) as an atmosphere at atmospheric pressure, and traversing a narrow heating zone to make it transparent. (Zone heating method). Alternatively, a method is adopted in which the glass particle deposit is inserted into an electric furnace having a wide heating area so that the entire length of the glass particle deposit becomes uniform, and the temperature of the furnace is gradually raised to make it transparent. (Soaking and heating method).

[0003] In these methods, pores (referred to as bubbles) remain (or later) in the glass article due to the gas trapped between the particles of the glass particulate deposit or the gas dissolved during the clearing during the transparentization. However, in recent years, there is a problem in that
There is proposed a method of making transparent in a vacuum atmosphere or a reduced pressure atmosphere as described in JP-A-3-201025. In this method, since the atmosphere is under vacuum or under reduced pressure, the gas in the glass particulate deposit is degassed, and it is expected that the gas will not remain in the glass.

[0004]

Conventionally, an apparatus for heat treatment in a vacuum or reduced pressure atmosphere has a structure as shown in FIG. That is, the furnace core tube 12 surrounding the glass particulate deposit body 11 and the soaking furnace in which the heater 13 for heating is installed outside the furnace core tube 12 are arranged inside the vacuum container 15 with the heat shield 14 interposed therebetween. There is. The vacuum container 15 has a structure in which a vacuum pump 17 connected to a degassing pipe 16 reduces the pressure and creates a vacuum atmosphere. In this state, the heater temperature is raised to insert the furnace core tube 12. The glass particulate deposit 11 that is present is made transparent.

[0005] Using the heating furnace, under reduced pressure and vacuum atmosphere,
As an example of the heat treatment according to the conventional method, when the temperature was raised to the clearing temperature (usually 1550 ° C. to 1650 ° C.) under the temperature conditions shown in FIG. 6 to make the material transparent, unexpectedly, there were some cases where bubbles remained. Further, the outer diameter of the transparent glass article was not uniform in the longitudinal direction, and as shown in FIG. 3, the glass article had a shape in which both ends were thick and the middle part was thin. In order to produce a high-quality glass article using the heating rod obtained by this method, it is necessary to stably reduce or eliminate residual air bubbles, and the finished transparent glass article has a uniform outer diameter. It is necessary to.

[0006]

As means for solving the above-mentioned problems, the present invention is transparent by synthesizing glass particulate deposits by a gas phase synthesis method and heating the glass particulate deposits in a vacuum or reduced pressure atmosphere. In the method for producing a glass article by vitrification, the first heat treatment at a temperature at which the glass particle deposit does not shrink as the heat treatment,
Second at a temperature higher than the heat treatment of
And at least three stages of the third heat treatment at the temperature of vitrification. In the present invention, the first heat treatment temperature is 1000 to
1150 ° C., second heat treatment temperature is 1250 to 1500
C. and the third heat treatment temperature are particularly preferably 1550.degree. C. to 1650.degree.

[0007]

FIG. 1 shows a schematic view of the temperature pattern of the heat treatment of the present invention. As shown in FIG. 2, the glass fine particle deposits 11 set under vacuum or reduced pressure are first set to 1100-1.
Leave in a maintained atmosphere at a temperature of 150 ° C. for 30 minutes to 2 hours. Next, the furnace temperature is raised to 1250 ° C to 1450 ° C.
It is left to stand for 30 minutes to 2 hours at a temperature between the above, and then the temperature is raised to the clearing temperature to make it transparent. The clearing temperature is usually in the range of 1550 to 1650 ° C. In the present invention, the heat treatment of the glass particulate deposit is performed in a vacuum or a reduced pressure atmosphere, and no other gas is introduced. An inert gas such as He, N ₂ or Ar is used as a purge gas for the purpose of preventing the metal in the furnace from being oxidized. Before the temperature rise, the furnace pressure is 5
10 Pa is desirable. The heat treatment is performed at 100 Pa or less, preferably 20 Pa or less. The pressure rises at high temperature, but it is almost 100 Pa.

Generally, the glass fine particle deposits synthesized by the vapor phase synthesis method have a structure in which fine particles of 0.1 to 0.5 μm are filled, but the filling state differs depending on the conditions of the vapor phase synthesis. , The way the particles are clogged will change. That is, the bulk density (weight per unit deposit including pores: g / cm ³ ) changes. The smaller the particles during synthesis and the higher the temperature, the smaller the number of vacancies and the harder the deposit with a higher bulk density can be obtained. As the glass particle deposit of the present invention, it is preferable to use one having a density of about 0.1 to 0.9 g / cm ³ . If the density is below this range or exceeds this range, it is too soft and easily cracks, or too hard, and it is difficult to remove the gas that has already been taken in,
Air bubbles tend to remain.

In the VAD method as shown in FIG. 5, the burner 5
Since a temperature distribution is generated in the flame 52 formed by No. 1, a bulk density distribution can be formed in the radial direction in the generated glass particle deposit body 53. Especially in the case of a large-diameter deposit, a large difference in bulk density may occur. As the bulk density increases, the pores surrounded by particles become smaller,
The gas passage becomes narrow. Therefore, there is a limit that the gas is difficult to escape even under vacuum or reduced pressure. The glass particle deposit melts and coalesces as the ambient temperature rises, and the pores gradually become smaller, and finally the pores disappear and become transparent. The gas does not escape even under vacuum, and bubbles remain.

As described above, the glass particulate deposit gradually shrinks, but the shrinking method depends on how the temperature rises. However, the temperature of the glass particle deposit does not rise uniformly, and the temperature rise in the central portion becomes slower in the radial direction than in the surface, for example. Further, in the longitudinal direction, the temperature tends to rise at the ends (upper end and lower end) having a large heating surface area. Therefore, at the upper end and the lower end, heat is relatively easily transferred to the inside, and contraction is likely to proceed. On the contrary, the intermediate portion in the longitudinal direction is less likely to contract than the end portion. Since the contraction not only contracts in the radial direction but also in the longitudinal direction, the end part relatively contracts in the longitudinal direction, and the outer diameter of the glass article after being transparent becomes large. On the contrary, in the middle portion, the contraction in the longitudinal direction is small, and the outer diameter is likely to be thin. Since it is considered that the outer diameter fluctuates in this way, it is necessary for the first heat treatment to reduce the temperature difference over the whole by gradually maintaining the temperature at a temperature at which the clearing does not proceed rapidly. Therefore, the first heat treatment of the present invention in which the glass is heated at a high temperature at which shrinkage does not occur, that is, at a temperature of 1150 ° C. or lower is required. It is advantageous to set the temperature to a high temperature because the gas adsorbed on the glass fine particles can easily escape, so that the temperature is preferably 800 ° C. or higher. The pressure reduction or atmosphere at this time is 20 Pa or less, and preferably 5 to 10 Pa.

As the second heat treatment, 1250 ° C. to 1500 ° C.
When kept at 0 ° C., the entire glass particle deposit gradually shrinks, so that nonuniformity hardly occurs and a glass article having a uniform outer diameter can be obtained. This heat treatment is carried out not only in one step but also at, for example, 1300 ° C. for 60 minutes, then
It is more effective to perform a two-step process such as holding at 00 for 60 minutes. At this time, the pressure reduction or vacuum atmosphere is 100 Pa or less, preferably 20 Pa or less. A uniform glass article can be obtained by heat-treating at the transparent vitrification temperature after the above first and second heat treatments. 100 Pa or less, preferably 20 Pa or less.

Glass particulate deposition applying the method of the present invention
Examples of the body manufacturing method include the VAD method and the OVD method.
Be done. For example, in the VAD method, generally, a concentric multi-tube bar is used.
The combustion gas, for example H as fuel₂Or C
H_Four, C₃H₈As a hydrocarbon gas such as
O₂Alternatively, when air is burned to form a flame,
Gaseous SiCl as a glass raw material_FourOr SiH
Cl₃Or Si (OCH ₃)_FourSuch as alkoxide
H, which is a refined Buddha in flame Nakano,₂There is O
O overflowed₂By reacting with
Particle SiO₂Generated and deposited on the target
By doing so, a glass particulate deposit is produced. This gala
As for the fine particle deposit, the distance of the burner should be constant.
To traverse the target relative to the burner
It is made longer and a glass particle deposit is obtained. Also,
As a method of manufacturing the glass particle deposit of Ming,₂Fine
Heat fine granular glass powder (0.1-100 μm)
Is a method of compression molding at room temperature to form a porous glass body,
Alternatively, after synthesizing by the above methods, rare earth elements or
Immersion or heat treatment of the dopant that changes the refractive index
Various known means such as a method for forming a porous glass body
Can be mentioned. The glass particulate deposit of the present invention
Regarding composition, SiO₂If the main component is
The deviation is good, and this is the reason why the refractive index changes as described above.
-Puntes such as GeO₂, B₂O₃, P₂O_FiveOr
F added, rare earth elements such as Er, Nd, etc.
It may contain various additives such as doped ones.
Basically, any porous glass body may be used. The present invention
As a glass particle deposit in
Consists only of particle deposits, bending at the outer periphery rather than at the center
A glass microstructure with at least double waveguide structure with low bending rate
Vapor-phase synthesis method on the periphery of particle deposit or glass rod
Is a composite of glass particle deposits.
May be. In any case, the same effect can be expected. During ~
In the case of a composite of core glass rod-glass particulate deposit,
The glass rod in the center is made of pure silica glass with trace impurities.
Doped quartz glass, or
A, the refractive index in the outer peripheral part is higher than that in the central part with clad.
Such as having a lowered at least double waveguide structure
It is an intermediate product for optical fiber.

[0013]

【Example】

Comparative Example 1 Glass fine particle deposited body synthesized by VAD method (composition: pure Si
The O ₂ matrix was made transparent in a vacuum atmosphere. The size of the glass particulate deposit was φ150 mm × 800 mm. With the structure shown in FIG. 2, the pressure inside the furnace was reduced to 5 Pa using a vacuum pump, the temperature was raised to 1600 ° C. at 8 ° / min, and the temperature was maintained at 1600 ° C. for 30 minutes, then taken out from the furnace after cooling. It was As a result, the outer diameter was deformed as shown in FIG. 3, and the maximum diameter was 72 mm, and the minimum intermediate portion was 64 mm. Regarding bubbles, bubbles were seen over the entire length in 6 out of 10 sintered, and bubbles were present in all 10 at the upper end.

Example 1 A glass fine particle deposit (composition: pure SiO ₂ base material) synthesized by the VAD method as in the comparative example was made transparent based on the constitution of the present invention. The size of the glass particle deposit is φ150 mm ×
The thing of 800 mm was used. The outer diameter was slightly different for each, but could be manufactured with an accuracy within a range of ± 2 mm. This base material was inserted into the furnace shown in FIG. 2, the furnace pressure was reduced to 5 Pa, and heat treatment was performed. Heat treatment temperature is 8 ° up to 1050 ° C
The temperature is raised at a rate of 1 / min and held at 1050 ° C for 60 minutes, then 135
Raise the temperature to 0 ° C at 8 ° / min and hold at 1350 ° C for 60 minutes,
Finally, the temperature was raised to 1600 ° C., held for 30 minutes, and then lowered. As a result, the obtained glass article was a good transparent body with no bubbles observed over the entire length. The outer diameter was φ68 mm ± 0.5 mm, which was very uniform over the entire length.

Example 2 A glass fine particle deposit was synthesized by a VAD method around a glass rod having a central portion doped with Ge to have a high refractive index and having a pure SiO ₂ layer on the outer peripheral portion, by the VAD method. Then, a composite was manufactured. The size of this composite is φ156mm × 8
It became 00 mm. The outer diameter variation was within 1 mm. When this composite was made transparent under the same conditions as in Example 1,
No bubbles were observed, and the outer diameter was as good as φ69 mm ± 0.4 mm. This glass article was then drawn as a preform for an optical fiber, and a good optical fiber could be obtained.

Comparative Example 2 The same glass particle deposit as in Comparative Example 1 was made transparent in a vacuum atmosphere. The temperature condition was that the temperature was raised to 1050 ° C. at 8 ° C./min, held at 1050 ° C. for 60 minutes, and then 1600
The temperature was raised up to 8 ° C./min and kept for 30 minutes, and then lowered. The base material made transparent under these conditions had good transparency, but the outer diameter varied, and the maximum outer diameter was 73 mm and the minimum outer diameter of the intermediate portion was 64 mm.

Comparative Example 3 The same glass particle deposit as in Comparative Example 1 was made transparent in a vacuum atmosphere. The temperature condition was that the temperature was raised up to 1350 ° C. at 8 ° C./min, held at 1350 ° C. for 60 minutes, and then 1600 ° C.
The temperature was raised up to 8 ° C./min and kept for 30 minutes, and then lowered. Although the outer diameter of the base material made transparent under these conditions was within 1 mm variation over the entire length, air bubbles remained over the entire length.

Example 3 The same glass particle deposit as in Example 1 was made transparent according to the present invention. The heat treatment temperature is raised to 1050 ° C at a rate of 8 ° C / min, and the temperature is kept at 1050 ° C for 60 minutes, and then 1350 ° C.
Furthermore, the temperature was raised at 8 ° C./min and held for 40 minutes. 1 more after this
After heating up to 450 ° C at 6 ° C / min and holding for 30 minutes,
The temperature was raised to 1600 ° C. at 8 ° C./minute to form a transparent glass.
As a result, the obtained glass article had good transparency over the entire length and no bubbles were observed. Further, the outer diameter variation was suppressed within ± 0.5 mm over the entire length (effective portion), and a high quality glass article could be obtained. Looking at the results of the above comparative examples and examples, according to the present invention, it is possible to obtain a good glass with improved dimensional accuracy and less fluctuation in the longitudinal direction and radial direction and generation of bubbles etc. It is clear that you can do it.

[0019]

As described above, according to the present invention, since the glass particulate deposit can be degassed within the temperature range in which the shrinkage does not proceed and the gas is activated, air bubbles remain in the glass article after being transparentized. Since the shrinkage can be gradually promoted at a temperature at which the glass does not remain and the glass does not become transparent, uniform shrinkage can be realized and a high quality glass article can be obtained.

[Brief description of drawings]

FIG. 1 is a temperature pattern diagram showing a heat treatment of the present invention.

FIG. 2 is a schematic diagram illustrating a transparentizing device under vacuum or reduced pressure.

FIG. 3 is a schematic diagram showing how the outer diameter of a glass article fluctuates in the longitudinal direction.

FIG. 4 is a diagram showing a refractive index distribution in a glass rod used for a glass rod-glass fine particle deposit composite body.

FIG. 5 is a schematic view showing the synthesis of a glass fine particle deposit by the VAD method.

FIG. 6 is a temperature pattern diagram of a conventional heat treatment.

[Explanation of symbols]

11 Glass particle deposit 12 Furnace core tube 13 heater 14 Heat shield 15 Vacuum container 16 Degassing piping 17 Vacuum pump 51 Burner for producing fine glass particles 52 flame 53 Glass particulate deposit 54 glass rod

Claims (3)

[Claims] 1. A method for producing a glass article by synthesizing a glass fine particle deposit by a gas phase synthesis method and heating the glass particulate deposit to heat the glass in a vacuum or a reduced pressure atmosphere to produce a glass article. At least three steps of a first heat treatment at a temperature at which the fine particle deposit does not shrink, a second heat treatment at a temperature higher than the first heat treatment and at which transparent vitrification does not occur, and a third heat treatment at a temperature at which transparent vitrification occurs A method for manufacturing a glass article, which comprises performing a heat treatment. 2. The first heat treatment temperature is 1000 to 1150.
C., the second heat treatment temperature is 1250 to 1500.degree. C., and the third heat treatment temperature is 1550.degree. C. to 1650.degree. 3. The glass particle deposit is further synthesized by a vapor phase synthesis method on the outer periphery of a glass rod having a waveguide structure in which the refractive index is lower in the outer peripheral portion than in the central portion and has at least double waveguide structure. It is a composite, The manufacturing method of the glass article of Claim 1 or 2 characterized by the above-mentioned.