JPS63206321A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To make it possible to form quartz glass tubes free from flow on the inside surface in producing the quartz glass tubes by sol-gel method, by using a material to thermally deform or to change properties by heating as a material to form a hollow part. CONSTITUTION:Sol 3 of pure quartz glass fine particles or sol of quartz glass fine particles containing at least one dopant is cast into space in a cylindrical container 2 coaxially placed in the interior of a material 1 to form a hollow part, the sol 3 is gelatinized and the material 1 to form a hollow part is taken out from the cylindrical container 2 to give a gelatinous cylindrical material 4. Then the gelatinous cylindrical material 4 is dried to give a dried gelatinous cylindrical material 5, which is heated 9a heating furnace 7) at high temperature and made into glass to give a quartz glass tube 6. In the process like this, the material 1 for form a hollow part is made of a material to thermally deform or to change properties by heating, the material 1 to form a hollow part is heated and the material 1 to form a hollow part 1 is released from the gelatinous cylindrical material 4. A thermally shrinkable synthetic resin, a shape memorizing alloy, a thermally melting material, etc., may be used as the material to thermally deform or to change properties by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a quartz-based glass tube using a sol-gel method. More specifically, the present invention relates to a method for manufacturing a quartz-based glass tube that is suitably used as a cladding material for manufacturing optical fibers such as the rod inch cop method.

BACKGROUND OF THE INVENTION In recent years, as optical communications using optical fibers have entered the stage of practical use, research has been increasingly conducted to reduce transmission loss and expand wavelength bands. Optical fibers are obtained by manufacturing a fiber base material by an internal/external CVD method, a VAD method, or the like, and then drawing it into a fiber shape by a wire drawing method or a rod inch cop method. To manufacture optical fiber using the above rod-in-tube method,
A quartz-based glass tube is used to jacket the glass rod that is the core material.

In general, quartz glass is manufactured by hydrolyzing and condensing an organic compound containing silicon.
A sol-gel method is known in which a sol of glass particles is obtained, the sol is gelled, dried, and then vitrified. This method is characterized by high yield and excellent mass productivity. The sol-gel method is also used to manufacture the above-mentioned quartz-based glass tube, and the process is carried out according to the steps shown in FIG.

The sol-gel method will be explained below with reference to Figure 2.
First, as shown in FIG. 2(a), the hollow part forming member 1 is
are arranged coaxially within a cylindrical container 2, and a silica-based glass fine particle sol 3 is injected into a space within the cylindrical container 2. Next, as shown in FIG. 2, et al., the injected sol is gelled to form a gel-like cylinder 4, and then, as shown in FIG. Remove from body 4.

Furthermore, the gel-like cylinder 4 thus obtained is dried,
A dried gel-like cylinder 5 as shown in FIG. 2 (d) is obtained. Next, as shown in FIG. 2(e), the dried gel-like cylinder 5
is taken out from the cylindrical container 2 and heated in an electric furnace 7 such as induction heating to a temperature in the range of 1000° C. to 1400° C. to vitrify it to obtain a glass tube 6.

Problems to be Solved by the Invention In the above method, in order to form the gel into a cylindrical shape,
In the step shown in FIG. 2(C), an operation was performed in which the hollow part forming member 1, which had been placed in advance in the cylindrical container 2, was forcibly pulled out while being in contact with the gel-like cylinder 4. For this reason, for the purpose of preventing scratches caused by friction with the inner surface of the gel-like cylinder 4, a fluorine-based synthetic resin or the like, which has a low affinity with gel, is used for the hollow part forming member l. .

However, even if a material such as a fluorine-based synthetic resin is used, there is a problem in that scratches cannot be avoided on the inner surface of the gel-like cylinder. This scratch on the inner surface of the gel-like cylinder remains on the glass tube after the drying and vitrification process. For this reason, when an optical fiber is manufactured using such a glass tube by the rod-in-tube method, bubbles and the like are generated, especially during vacuum sealing, and the bubbles become light scatterers within the optical fiber, increasing transmission loss. For this reason, there has been a demand for quartz-based glass tubes that are used as materials for the rod-in-tube method, etc., to be of excellent quality with no scratches on the inner surface.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing a quartz-based glass tube without scratches on its inner surface using a sol-gel method.

Means for Solving the Problems As a result of intensive study and research to solve the above-mentioned problems, the inventor of the present invention has developed a method for forming hollow parts by using a thermally deformable or thermally denatured material for the hollow part forming member used in the sol-gel method. We succeeded in developing a method for producing a quartz-based glass tube with no scratches on the inner surface by heating the hollow part forming member to separate it from the gel-like cylinder when the member is taken out of the container.

That is, according to the present invention, a sol of pure silica glass particles or silica-based glass particles containing at least one type of dopant that lowers the refractive index is placed in a cavity in a cylindrical container in which a hollow part forming member is coaxially disposed. After injecting and gelling the sol, the hollow part forming member is taken out from the cylindrical container to obtain a gel-like cylinder, and after drying the gel-like cylinder, it is heated at high temperature to vitrify. The method for manufacturing a quartz-based glass tube includes forming the hollow part forming member with a material that is thermally deformed or thermally denatured, and heating the hollow part forming member to transform the hollow part forming member into a material. A method for manufacturing a quartz-based glass tube is provided, which is characterized in that the tube is separated from a gel-like cylinder.

Function The present invention is a method for manufacturing a glass tube as a material for an optical fiber using a sol-gel method, in which a hollow part forming member is formed of a material that is thermally deformed or thermally denatured, and this hollow part forming member is heated. The feature is that it is separated from the gel-like cylindrical body.

Therefore, in the step of taking out the hollow part forming member from the cylindrical container to obtain a gel-like cylinder, the hollow part forming member deforms and peels off from the gel, or becomes liquid and easily forms a gel-like cylinder. It can be removed from the body and removed from the container in which the hollow part forming member was housed without causing damage to the inner surface of the gel-like cylinder.

Therefore, the optical fiber formed by the rod-in-tube method using the glass tube obtained according to the present invention can eliminate the generation of light scatterers in the core, which has been a problem in the past.

In the method of the present invention, it is necessary to heat the hollow part forming member when taking it out from the cylindrical container, and this heating temperature is a temperature below the boiling point of the sol solvent,
Moreover, it can be determined by the material of the hollow part forming member used. That is, it is sufficient that the temperature is such that the hollow part forming member can be easily pulled out of the gel by deforming or changing the quality of the hollow part forming member.

The material for such a hollow part forming member is required to have properties that allow it to be easily separated from the gel by being thermally deformed or thermally denatured. Examples of such materials include heat-shrinkable synthetic resins, shape memory alloys, and materials that melt when heated. Examples of heat-shrinkable synthetic resins include tetrafluoroethylene.
A hexafluoropropylene copolymer heat-shrinkable tube or the like is suitable.

When using shape memory alloy for hollow part forming member,
For example, a Ni-Ti based shape memory alloy is suitable.

When using a material that melts when heated for the hollow part forming member, paraffin, wax, etc. are suitable, for example.

However, the hollow part forming member used in the method of the present invention is not particularly limited to the above-mentioned materials, and may be any material as long as it has the property of being easily separated from the gel by heating.

The quartz-based glass tube obtained by the present invention is a high-quality quartz glass tube or a quartz-based glass tube doped with other components that can be used not only as a material for optical fibers but also for all kinds of purposes.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

The method for producing a quartz-based glass tube of the present invention is based on the conventional sol-gel method shown in FIG. This process is similar to the manufacturing process of glass tubes, and will be explained below according to the process.

Example 1 An optical fiber base material was manufactured by a sol-gel method using a tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter abbreviated as FEP) heat-shrinkable tube as a member for forming a hollow portion.

First, alkoxide raw material St diluted with ethanol (
A sol for raw material for quartz-based glass tubes was prepared by hydrolyzing OCa Hs) 4, and the sol was poured into an FEP heat-shrinkable tube (
Outer diameter 20mm, wall thickness 0.2mm, length 2501+111
1. (shrinkage start temperature: 45° C.) was injected into the cavity of a cylindrical container (inner diameter: 40 mm, length: 300 mm) arranged coaxially inside.

Next, the sol in the container was gelatinized at room temperature, and the FEP heat-shrinkable tube was shrunk by holding at 50° C. for 1 hour and taken out from the container. At this time, the outer diameter of the FEP heat-shrinkable tube had shrunk by about 5%, and its surface had completely peeled off from the inner surface of the gel-like cylinder, so it could not be easily removed from the gel-like cylinder. Ta.

After drying the obtained gel-like cylinder in a container, the gel-like cylinder was taken out and heated in an electric furnace to vitrify it and reduce the outer diameter to 2.
3III111 Inner diameter 10 ll1m, length 108m
A quartz glass tube of m was obtained. The inner surface of this glass tube was smooth and no scratches were observed.

Next, this quartz glass tube was used as a cladding, and Δ=0.6
A step-index optical fiber was fabricated using a rod-in-tube method using a glass rod doped with 6e having a concentration of 6e as a core.

The transmission loss (λ=1.3μm) of the obtained optical fiber is:
It was 5 dB/km.

Comparative Example 1 A quartz glass tube was obtained in the same manner as in Example 1, except that an FEP tube, which has excellent peelability from gel but does not have heat shrinkability, was used as the hollow part forming member.

Here, in the step of removing the FEP tube from the cylindrical container to obtain the gel-like cylinder, the FEP tube is in contact with the inner surface of the gel-like cylinder, and the gel after the tube is pulled out from the gel-like cylinder is It was confirmed that linear scratches were generated on the inner surface of the cylindrical body. These scratches also remained on the inner surface of the vitrified quartz glass tube.

Further, using this glass tube, a step index type optical fiber was manufactured using the rod-in-tube method in the same manner as in Example 1.

The transmission loss (λ=1.3μm) of the obtained optical fiber was 9
0 dB/km, which was considerably higher than that obtained in Example 1.

Example 2 A quartz glass tube was manufactured in the same manner as in Example 1, except that a member 10 having a shape memory alloy as shown in FIG. 2 was used as the hollow part forming member.

In FIG. 2, the hollow part forming member lO has an inner diameter of 20. Oms
+.

Inside the rubber tube 9 with an outer diameter of 20.5 mm, an outer diameter of 21.0 III
Shape memory alloy bent into IH cylindrical shape 8
is forcibly inserted, and its outer diameter is 21.5 mm. The shape memory alloy 8 in this hollow part forming member 1O is a Ni-Ti based shape memory alloy that undergoes martensitic transformation at a transition point of 45°C, and has the characteristic that the radius of curvature decreases at a temperature above the transition point. .

In the manufacturing process of the glass tube shown in FIG. 2, when the inside of the container was observed immediately after the heat treatment after gelation, it was found that the radius of curvature of the shape memory alloy decreased and the outer diameter of the member 10 decreased to 20.
5u, and since the gel-like cylinder had peeled off from the member 10, it was possible to easily remove the hollow-part forming member 10 without contacting the inner surface of the gel-like cylinder. The inner surface of the gel-like cylinder was smooth and no scratches were observed.

No scratches were observed on the inner surface of the quartz glass tube obtained by vitrifying the gel-like cylinder.

Using the quartz glass tube thus obtained, a step-index optical fiber was manufactured using the rod-in-tube method in the same manner as in Example 1.

The transmission loss (λ=1.3μm) of the obtained optical fiber was 7
It was dB/km.

Example 3 A quartz glass tube was manufactured in the same manner as in Example 1, except that a paraffin rod with a melting point of 45 to 48° C. was used as the hollow part forming member.

In the above manufacturing process, when the inside of the container was observed immediately after the heat treatment after gelation, the surface of the paraffin rod was melted, and the paraffin rod could be easily extracted from the gel-like cylinder.

Moreover, no scratches were observed on the inner surface of the obtained quartz glass tube.

Furthermore, a step index type optical fiber was manufactured using the above glass tube using the rod-in-tube method in the same manner as in Example 1.

The transmission loss (λ=1.3μm) of the obtained optical fiber was 3
It was dB/km.

Example 4 To prepare a sol, alkoxide raw material Si (OC
Example 1 except that 2H3)4 and Si(OC2H5)3F were used as dopants to lower the refractive index.
A glass tube was manufactured in the same manner.

At this time, the amount of F used is F/5i=0.1 (atomic ratio)
And so.

The thus obtained F-doped quartz glass tube has a ratio of Δ=−0.3% (Δ=(n−n s I
o2)/nsi. 2), and no scratches were observed on the inner surface.

Further, using this glass tube, a step index type optical fiber was manufactured using the rod-in-tube method in the same manner as in Example 1.

The transmission loss (λ=1.3μm) of the obtained optical fiber was 4
It was dB/km.

Example 5 To prepare a sol, alkoxide raw material Si (OC
A glass tube was produced in the same manner as in Example 1, except that 2Hs)* and B (n 0 C489) 3 were used as a dopant to lower the refractive index. At this time, the amount of B used was 10 mol/l.

The thus obtained B-doped quartz glass tube has a ratio of Δ=-0.2% (Δ=(n-nsi.2
)/1st. 2), and no scratches were observed on the inner surface.

Further, using this glass tube, a step index type optical fiber was manufactured using the rod-in-tube method in the same manner as in Example 1.

The transmission loss (λ=1.3μm) of the obtained optical fiber was 9
It was dB/km.

In the above example, an FEP heat shrink tube, a tubular member using a shape memory alloy, and a paraffin rod were used as the members for forming the hollow part, but in principle, they cannot be deformed or denatured at a temperature above room temperature and below the boiling point of the sol solvent. Any material can be used as the hollow part forming member as long as the hollow part forming member can be easily removed from the gel-like cylindrical body by using the above-mentioned material. It is not limited to members for use.

As described in detail of the invention, by using a material that can be easily separated from the gel by heat deformation or heat denaturation as the hollow part forming member, a quartz glass tube of excellent quality with no scratches on the inner surface can be produced. Obtainable.

Further, by using the silica-based glass tube manufactured according to the present invention in the rod-in-tube method, the transmission loss of the optical fiber is improved compared to the conventional one.

Therefore, the value of the present invention in the art is extremely high.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a hollow part forming member equipped with a shape memory alloy, which is a specific example of the hollow part forming member used in the method of the present invention, and Fig. 2 shows a quartz-based glass formed by the sol-gel method. It is a figure showing the manufacturing process of a pipe. (Main reference numbers) 1. Hollow part forming member, 2. Cylindrical container, 3. Sol, 4. Gel cylinder, 5. Dry gel cylinder, 6. Glass tube. , 7. Electric furnace, 8. Shape memory alloy, 9. Rubber tube, 10. Hollow part forming member, Patent applicant: Nippon Telegraph and Telephone Corporation Representative, Patent attorney Masahiko Arai 8.・Shape description J1 Kei Alloy 9...Column tube

Claims (7)

[Claims] (1) Injecting a sol of pure silica glass particles or silica-based glass particles containing at least one type of dopant that lowers the refractive index into a cavity in a cylindrical container in which a hollow part forming member is coaxially arranged, After gelling the sol, the hollow part forming member is taken out from the cylindrical container to obtain a gel-like cylinder, and the gel-like cylinder is dried and then heated to a high temperature to vitrify it. In the method for manufacturing a quartz-based glass tube, the hollow part forming member is formed of a material that is thermally deformed or thermally denatured, and the hollow part forming member is heated to separate the hollow part forming member from the gel-like cylindrical body. A method for manufacturing a quartz-based glass tube, characterized by separating the tube. (2) The method for manufacturing a quartz-based glass tube according to claim 1, wherein the thermally deformable material is a heat-shrinkable synthetic resin. (3) The method for manufacturing a quartz-based glass tube according to claim 2, wherein the synthetic resin is a tetrafluoroethylene-hexafluoropropylene copolymer. (4) The method for manufacturing a silica-based glass tube according to claim 1, wherein the hollow portion forming member contains a shape memory alloy. (5) The method for manufacturing a quartz glass tube according to claim 4, wherein the shape memory alloy is a Ni-Ti shape memory alloy. (6) The method for manufacturing a quartz-based glass tube according to claim 1, wherein the thermally denatured material is a material that melts when heated. (7) The method for manufacturing a quartz-based glass tube according to claim 6, wherein the material melted by heating is paraffin.