JP2836302B2 - Method for manufacturing glass articles - Google Patents

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 more particularly to an optimal method for producing an optical fiber preform or an intermediate product thereof.

[0002]

2. Description of the Related Art A gas phase synthesis method such as a gas phase shafting method (VAD)
Method) or an external method (OVD method), the glass fine particle deposit is transparently vitrified by high-temperature heat treatment in an electric furnace to form a glass article. Heretofore, transparent vitrification has been carried out by a method in which the atmosphere is He or an inert gas containing a trace amount of halogen gas (particularly chlorine) at normal pressure, and traversing and passing through a narrow heating zone. (Zone heating method). Alternatively, a method is adopted in which the glass fine particle deposit is inserted into an electric furnace having a wide heating area so that the entire length of the glass fine particle deposit becomes uniform, and the furnace temperature is gradually increased to make the glass transparent. (Soaking heating method).

[0003] In these methods, at the time of clearing, voids (called bubbles) remain (or later) in the glass article due to gas trapped between the particles of the glass fine particle deposit or gas dissolved during the clearing. (Which may occur during high-temperature machining).
A method for making the film transparent in a vacuum atmosphere or a reduced-pressure atmosphere as described in JP-A-3-201025 has been proposed. In this method, since the atmosphere is under vacuum or reduced pressure, the gas in the glass particle deposit is degassed, and it is expected that no gas remains in the glass.

[0004]

Conventionally, an apparatus for performing a heat treatment in a vacuum or reduced-pressure atmosphere has a structure as shown in FIG. That is, a furnace core tube 12 surrounding the periphery of the glass particle deposit body 11 and a soaking furnace in which a heating heater 13 is provided outside the furnace core tube 12 are arranged in a vacuum vessel 15 with a heat shield 14 interposed therebetween. I have. The vacuum vessel 15 has a structure in which the pressure is reduced and a vacuum atmosphere is generated by a vacuum pump 17 connected to a pipe 16 for deaeration. The glass fine particle stack 11 is made transparent.

[0005] The above-mentioned heating furnace is used to reduce the pressure in a 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 and the glass was made transparent, unexpectedly, bubbles sometimes remained. Further, the outer diameter of the transparentized glass article was not uniform in the longitudinal direction, and the shape became thick at both ends and thin at the middle as shown in FIG. 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 the residual bubbles, and the finished transparent glass article has a uniform outer diameter. It is necessary to.

[0006]

According to the present invention, as a means for solving the above problems, a glass fine particle deposit is synthesized by a vapor phase synthesis method, and the glass fine particle deposit is heat-treated in a vacuum or reduced-pressure atmosphere to be transparent. In the method for producing a glass article by vitrification, as a heat treatment, a first heat treatment at a temperature at which the glass fine particle deposit does not shrink, a first heat treatment,
Second at a temperature higher than the heat treatment of
And a third heat treatment at a temperature for forming a transparent glass. In the present invention, the first heat treatment temperature is 1000 to 1000.
1150 ° C., the second heat treatment temperature is 1250 to 1500
C. and the third heat treatment temperature are particularly preferably performed at 1550 ° C. to 1650 ° C.

[0007]

FIG. 1 is a schematic diagram showing the temperature pattern of the heat treatment according to the present invention. As shown in FIG. 2, a glass fine particle deposit 11 set under vacuum or reduced pressure
Leave in a kept atmosphere at a temperature of 150 ° C. for 30 minutes to 2 hours. Next, raise the furnace temperature to 1250 ° C to 1450 ° C
The mixture is allowed to stand for 30 minutes to 2 hours at the same temperature, 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 particle deposit is performed in a vacuum or reduced pressure atmosphere, and no other gas flows. An inert gas such as He, N ₂ or Ar is used as a purge gas for the purpose of preventing oxidation of metal in the furnace. The furnace pressure should be between 5 and
10 Pa is desirable. The heat treatment is performed at 100 Pa or less, preferably 20 Pa or less. When the temperature becomes high, the pressure increases, but this also becomes almost 100 Pa.

In general, a glass particle deposit synthesized by a gas phase synthesis method has 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 gas phase synthesis. In addition, the way the fine particles are clogged changes. That is, the bulk density (weight per unit deposition including voids: g / cm ³ ) changes. As the particle size during synthesis is smaller and the temperature is higher, the number of pores is smaller, and a hard deposit having a large bulk density can be obtained. It is preferable to use a glass fine particle deposit of the present invention having a density of about 0.1 to 0.9 g / cm ³ . If the density is less than or more than this range, it is too soft and easily cracked, or too hard, and it is difficult to remove gas already taken in,
Air bubbles are likely to remain.

In the VAD method as shown in FIG.
Since a temperature distribution is generated in the flame 52 formed by 1, a bulk density distribution is also generated in the radial direction in the generated glass particle deposit 53. In particular, 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 the particles become smaller,
The gas path narrows. For this reason, even under vacuum or reduced pressure, there is a limit that gas is hardly released. The glass particle deposits melt and coalesce as the ambient temperature rises, and the pores gradually become smaller and finally disappear and become transparent.However, since this transparency proceeds from the outer periphery, after the temperature rises, Even under vacuum, gas does not escape and bubbles remain.

As described above, the glass fine particle deposit gradually contracts, and the manner of contraction depends on how the temperature rises. However, the temperature of the glass fine particle deposit does not always rise uniformly. For example, in the radial direction, the temperature rise at the center portion is slower than at the surface. Further, in the longitudinal direction, the temperature tends to increase at the ends (upper end, lower end) where the heating surface area is large. Therefore, at the upper end and the lower end, heat is relatively easily transmitted to the inside, and contraction is apt to progress. Conversely, the intermediate portion in the longitudinal direction is less likely to shrink than the end portion. Since the shrinkage occurs not only in the radial direction but also in the longitudinal direction, the end portion relatively shrinks in the longitudinal direction, and the outer diameter of the transparent glass article becomes large. Conversely, in the middle part, the shrinkage in the longitudinal direction is small, and the outer diameter tends to be small. Since it is considered that the outer diameter fluctuates in this way, it is necessary to reduce the temperature difference over the entirety and gradually shrink the first heat treatment by maintaining the temperature at a level at which transparency does not proceed rapidly. Therefore, the first heat treatment of the present invention, in which heating is performed at a high temperature that does not cause shrinkage of the glass, that is, at a temperature of 1150 ° C. or less, is required. If the temperature is high, the gas adsorbed on the glass fine particles is also easily released, which is advantageous. Therefore, the temperature is preferably 800 ° C. or more. The reduced pressure or atmosphere at this time is set to 20 Pa or less, preferably 5 to 10 Pa.

1250 ° C. to 1500 as the second heat treatment
When held at ℃, the entire glass fine particle deposit gradually shrinks, so that non-uniformity hardly occurs and a glass article having a uniform outer diameter can be obtained. This heat treatment is performed not only in one stage but also at, for example, 1300 ° C. for 60 minutes,
It is more effective to perform a two-stage process such as holding at 00 for 60 minutes. The pressure or vacuum atmosphere at this time is 100 Pa or less, preferably 20 Pa or less. After the above first and second heat treatments, a uniform glass article can be obtained by heat treatment at a transparent vitrification temperature. The treatment is performed at 100 Pa or less, preferably 20 Pa or less.

Glass particle deposition applying the method of the present invention
Examples of body production methods include the VAD method and the OVD method.
It is. For example, in the VAD method, concentric multi-tube bars are generally used.
Combustion gas such as H as fuel_TwoOr C
H_Four, C_ThreeH₈Such as hydrocarbon gas and supporting gas
O_TwoAlternatively, the air is burned to form a flame,
Gaseous SiCl as glass material_FourOr SiH
Cl_ThreeOr Si (OCH _Three)_FourAlkoxide
By gushing out, H is Nakano refined Buddha_TwoThere is O
O_TwoBy reacting with
Particle SiO_TwoAnd deposit this on the target
By doing so, a glass particle deposit is made. This gala
The fine particle deposits are so that the distance between the burners is constant
To traverse the target relative to the burner
It is made longer to obtain a glass particle deposit. In addition,
As a method for producing the Akira glass fine particle deposit, SiO_TwoFine
Hot or cold fine granular glass powder (0.1-100 μm)
Is a method of compression molding at room temperature to make a porous glass body
Or after being synthesized by each of the above methods,
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 containing
Can be mentioned. The glass fine particle deposit of the present invention
About composition, SiO_TwoWhat is the main component
The deviation is also good, and this can be done by changing the refractive index as described above.
-Punt, for example, GeO_Two, B_TwoO_Three, P_TwoO_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
The glass fine particle deposit in
Consisting of particle deposits only, bending around the periphery rather than the center
Glass microstructure with at least double waveguide structure with low bending ratio
Gas phase synthesis method around particle deposits or glass rods
This composite is a composite of glass
You may. In any case, the same effect can be expected. During ~
In the case of the composite of the core glass rod and the glass particle deposit,
The glass rod in the center part
Doped quartz glass or copper as shown in FIG.
A, the refractive index is higher at the outer periphery than at the center
Having at least a double waveguide structure lowered
It is an intermediate product for optical fibers.

[0013]

【Example】

Comparative Example 1 A glass particle deposit (composition: pure Si) synthesized by the VAD method
O ₂ base material) was clarified in a vacuum atmosphere. The size of the glass particle deposit was φ150 mm × 800 mm. With the configuration 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 held at 1600 ° C. for 30 minutes. Was. As a result, the outer diameter was deformed as shown in FIG. 3, and the maximum diameter was 72 mm, and the minimum part of the middle part was greatly deformed to 64 mm. Regarding the bubbles, bubbles were observed over the entire length in six of the ten sintered pieces, and all of the ten bubbles were present at the upper end.

Example 1 A glass particle deposit (composition: pure SiO ₂ base material) synthesized by the VAD method in the same manner as in the comparative example was made transparent based on the constitution of the present invention. The size of the glass particle deposit is φ150mm ×
The thing of 800 mm was used. Although the outer diameter is slightly different in each case, it can be manufactured with an accuracy within a range of ± 2 mm. This base material was inserted into the furnace of FIG. 2, the pressure in the furnace was reduced to 5 Pa, and heat treatment was performed. Heat treatment temperature is 8 ° up to 1050 ° C
/ Min, hold at 1050 ° C. for 60 minutes, and further 135
The temperature was raised to 0 ° C at a rate of 8 ° / min and maintained at 1350 ° C for 60 minutes.
Finally, the temperature was raised to 1600 ° C. and maintained for 30 minutes, and then lowered. As a result, no bubbles were observed in the obtained glass article over the entire length, and the glass article was a good transparent body. The outer diameter was very uniform at φ68 mm ± 0.5 mm over the entire length.

Embodiment 2 A glass fine particle deposit is synthesized by a VAD method in a configuration as shown in FIG. 5 around a glass rod having a central portion doped with Ge to increase the refractive index and a pure SiO ₂ layer on the outer peripheral portion. Then, a composite was produced. The size of this composite is φ156mm × 8
00 mm. The outer diameter variation was within 1 mm. When this composite was clarified under the same conditions as in Example 1,
No bubbles were observed, and a good outer diameter of φ69 mm ± 0.4 mm was obtained. This glass article was then drawn as an optical fiber preform, and a good optical fiber could be obtained.

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

Comparative Example 3 The same glass fine particle deposit as in Comparative Example 1 was clarified in a vacuum atmosphere. The temperature was raised to 1350 ° C. at a rate of 8 ° C./min.
The temperature was raised to 8 ° C. at a rate of 8 ° C./min, maintained for 30 minutes, and then lowered. In the base material made transparent under these conditions, the outer diameter was kept within 1 mm over the entire length, but bubbles remained over the entire length.

Example 3 The same glass particle deposit as in Example 1 was clarified according to the present invention. The heat treatment temperature was raised to 1050 ° C. at a rate of 8 ° C./min, held at 1050 ° C. for 60 minutes, and further increased to 1350 ° C.
The temperature was raised at 8 ° C./min and maintained for 40 minutes. After this one more
After heating to 450 ° C at 6 ° C / min and holding for 30 minutes,
The temperature was raised to 1600 ° C. at a rate of 8 ° C./min to form a transparent glass.
As a result, the obtained glass article had good transparency over the entire length, and no bubbles were observed. Also, the outer diameter variation was within ± 0.5 mm over the entire length (effective portion), and a high-quality glass article could be obtained. According to the results of the above comparative examples and examples, according to the present invention, it is possible to obtain good glass with improved dimensional accuracy, less variation in the longitudinal direction and radial direction, and no generation of bubbles, etc. You can clearly see that

[0019]

As described above, according to the present invention, since the shrinkage of the glass particle deposit does not progress and the gas can be degassed in a temperature range in which the gas is activated, bubbles are generated in the glass article after being transparentized. Since no shrinkage remains and the shrinkage can be gradually advanced at a temperature at which the glass does not become transparent, uniform shrinkage can be realized and a high quality glass article can be obtained.

[Brief description of the 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 view that illustrates a state of a change in outer diameter in a longitudinal direction of a glass article.

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Glass fine particle deposit 12 Furnace core tube 13 Heater 14 Heat shield 15 Vacuum container 16 Deaeration pipe 17 Vacuum pump 51 Burner for glass fine particle generation 52 Flame 53 Glass fine particle deposit 54 Glass rod

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C03B 8/04 C03B 37/00

Claims (3)

(57) [Claims] 1. A method for producing a glass article by synthesizing a glass particle deposit by a vapor phase synthesis method and heating the glass particle deposit in a vacuum or reduced-pressure atmosphere to produce a glass article. At least three stages 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 not causing vitrification, and a third heat treatment at a temperature at which vitreous vitrification occurs. A method for producing a glass article, comprising performing heat treatment. 2. The first heat treatment temperature is 1000-1150.
2. The method for producing a glass article according to claim 1, wherein the second heat treatment temperature is 1250 to 1500 ° C., and the third heat treatment temperature is 1550 to 1650 ° C. 3. 3. The glass fine particle deposit is further synthesized by a vapor phase synthesis method on the outer periphery of a glass rod having a refractive index lower at the outer periphery than at the center and having at least a double waveguide structure. The method for producing a glass article according to claim 1, wherein the glass article is a composite.