JPH05201736A - Production of porous parent material for quartz glass - Google Patents

Abstract

PURPOSE:To easily and stably produce a porous base material of high quality. CONSTITUTION:Slurry 31 in which quartz glass fine powder is dispersed in solvent is cast into a quartz based tubular porous molding 41 to make a porous layer 32 in the porous molding 41. Thereby, since the prescribed slurry 31 is cast in the tubular porous molding 41 to make the porous layer 32 in the porous molding 41, a quartz glass porous base material of high quality is easily and stably 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 porous base materials such as silica-based optical fibers used in the fields of communication and optics and silica-based optical fibers for optical amplification.

[0002]

2. Description of the Related Art In the fields of communication and optics, a slurry casting method has been adopted as one means for producing an optical fiber preform.

This sludge pouring method is disclosed, for example, in JP-A-64
As disclosed in Japanese Laid-Open Patent Publication No. 56331, first, a silica-based fine powder glass raw material is dispersed in pure water to form a slurry, and then the slurry is poured into a molding die to be dehydrated. A porous glass body is formed from a fine powder glass raw material, and then the porous body is dried and made into a transparent glass.

In the case of such a slurry casting method, a high quality porous body can be produced in high quantity with simple equipment, but it is not possible to form a waveguide structure by itself. Therefore,
There is no technical suggestion for this in the known examples of the slurry casting method, although this method itself needs to be improved or intervention of other means is required.

As a countermeasure, a method of manufacturing a porous base material by an extrusion molding method has been proposed. In the case of such an extrusion molding method, each predetermined molding material having plasticity is supplied into the extrusion molding device, and a porous glass base material having a porous body for a core and a porous body for a clad is extruded and formed. Therefore, a good quality porous glass preform can be obtained all at once with economical equipment and a simple process, and in the subsequent process, the porous preform is dried and made into transparent glass. Therefore, in the case of the extrusion molding method, it can be seen that it is considerably effective as a means for producing a quartz-based porous base material.

[0006]

However, even in the case of the extrusion molding method, there are still technical problems caused by the preparation of the molding material as described below.

In general, a material for extruding a porous base material is added with a binder in order to impart plasticity to the silica-based glass fine powder which is a main raw material. The organic components and metallic impurities contained in the binder are removed by subjecting the molded porous base material to degreasing and refining treatments, but if these treatments are not performed completely, impurities will remain in the base material. To do. In particular, in the case of the core porous body that is the main part of the base material, since the above-mentioned process gas does not reach the inside sufficiently because it is covered with the clad porous body, impurities tend to remain. Becomes Therefore, when the porous base material is wholly synthesized through the extrusion molding method and finished into an optical fiber, variations in the characteristics of the optical fiber beyond the allowable value may occur, and the yield of non-defective products may be reduced. ..

Of course, a molding material in which only pure water is added to the silica-based glass fine powder and no binder is used has been considered, but such a molding material is much inferior in moldability to a material using a binder, For example, the base material is distorted due to a poor material flow during molding, or cracks are generated in the base material when the material is in a disproportionate state.

In view of such technical problems, the present invention aims to provide a method capable of easily and stably producing a high-quality porous base material.

[0010]

In order to achieve the intended purpose, a method for producing a porous base material for quartz-based glass according to the present invention uses a silica-based glass fine powder as a main raw material, and It is characterized in that it is cast into a tubular porous molded body made of glass powder to form another porous layer in the tubular porous molded body. The following examples are used as the slurry in the present invention. One is that silica particles are dispersed in pure water, and the other is that part or all of pure water imparts an element and / or functionality for controlling the refractive index. Those in which silica particles are dispersed in a solvent substituted with a solution containing an element, and yet another is a compound containing the element for controlling the refractive index and / or an element for imparting functionality. A compound containing
The silica particles are dispersed in pure water. One other than these is that the powder obtained by calcining and crushing a predetermined gel-like substance is dispersed in pure water. The gel-like material in this case is obtained by hydrolyzing the alkoxide of silicon in a solution containing an element for controlling the refractive index and / or an element for imparting functionality.

[0011]

The tubular porous molded article in the present invention serves as a glass for clad and can be produced by an extrusion molding method, a hydrostatic molding method, a slurry casting method and the like. When a tubular porous molded article is produced by, for example, an extrusion molding method, there is no problem even if the molding material contains a binder for maintaining plasticity. One of the reasons is that since the porous molded body has a self-evident tubular shape, the processing gas penetrates well into the wall thickness of the tube in the process of removing organic components, metal impurities, etc. This is because it will be removed. Another reason is that even if impurities remain in the porous molded body, this tube itself is for cladding, and it almost affects the characteristics of the final product such as an optical fiber (core). Because there is no. Furthermore, in the case of using the porous molded body by the hydrostatic molding method or the slurry casting method, even if these are manufactured from a molding material containing a binder, there is no problem as in the above case.

The slurry used in the present invention is for making core glass. This slurry consists of a slurry in which silica-based fine glass powder, which is the main raw material, is dispersed in a solvent, and since no binder is added to this slurry,
Does not contain harmful organic components or metallic impurities.

When the above-mentioned sludge is cast into a tubular porous compact, the water content in the slurry (slurry) is removed by the capillarity (water absorption or dehydration) of the porous compact and the silica-based glass fine powder is removed. The distance between them gradually becomes smaller, and finally, the silica-based glass fine powders are entangled with each other to form a porous layer. In the case of the porous base material for quartz glass thus produced, the step of forming the porous molded body for cladding and the step of forming the porous layer for core are independent from each other. It is possible to obtain the base material with the required waveguide structure by selecting the material for the high-quality molded body and the porous layer and making these glass characteristics, for example, the refractive index different, and further selecting such material. By adding a specific rare earth element in (1), the base material of the optical fiber for optical amplification can be obtained.

[0014]

1 and 2, a method of manufacturing a porous preform for quartz glass according to the present invention is schematically shown together with an apparatus used for the method. In FIG. 1 and FIG. 2, the pipe support 11 is provided with a recess 12 on the upper surface, and the discharge port 22 of the slurry supply system 21 is arranged above the recess 12.

The pipe support 11 is made of a hard material having a water draining effect such as water absorbency and dewatering property. As an example of this, continuous pores made of synthetic resin or synthetic quartz fine powder (fumed silica) are used. A container having a can be mentioned.

The sludge supply system 21 is such that a pipe is connected to a sludge tank (not shown), and a pump (or a screw conveyor), a flow meter, a valve, etc. are provided at appropriate places in the pipe, and the sludge is supplied in the tank. Is housed.

The slurry 31 shown in FIGS. 1 and 2 is made of silica glass fine powder as a main raw material and dispersed in a solvent to form a slurry, which forms a porous layer 32 described later. It is used to The slurry 31 is, for example,
Silica particles (= SiO ₂ powder) are dispersed in pure water. In the slurry 31, a refractive index controlling element (Ge,
P, Ti, Al, etc.) and / or a function-imparting element (rare earth, etc.) can also be contained. In such a case, the slurry 31 is prepared as follows. As an example, a solution in which a part or all of pure water is replaced with a solution such as acetate, nitrate, or alkoxide containing the above elements is prepared, and silica particles are dispersed in the solvent.
As another example, silica particles and particles for controlling the refractive index (GeO ₂ , P ₂ O ₅ , TiO ₂ , Al ₂ O _{3 and the} like) and / or functionalization particles (Er ₂ O ₃ and other rare earth oxides). Compound powder such as) is dispersed in pure water. As another example, the refractive index controlling elements (Ge, P,
(Ti, Al, etc.) and / or a function-imparting element (rare earth, etc.) is used to hydrolyze the alkoxide of silicon to form a gel, and the gel is calcined and crushed. Disperse in pure water. Sludge 31
It is desirable that the particle diameter of the powder inside is larger than the pore diameter of the porous molded body 41 in order to prevent the diffusion to the porous molded body 41 side.

The porous molded body 41 shown in FIGS. 1 and 2 is also made of quartz, and in the case of this porous molded body 41, as an example, a molding material having plasticity is put into an extrusion molding machine, and the extrusion molded product is obtained. Obtained by drying or by drying and degreasing. The molding material in this case is obtained by adding a molding aid or a molding aid containing pure water to the SiO ₂ powder, which is the main raw material, and then kneading the mixture homogeneously. Plasticity is imparted by such preparation. .. As a molding aid,
Organic substances such as polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and glycerin are appropriately adopted. As for the molding material of the porous molded body 41, SiO ₂ as a main raw material, B ₂ O ₃ , and F are used as additives for controlling the refractive index.
Compounds such as As a means for adding these compounds, a method of mixing with a powder, a method of adding with a solution such as an acetate, a nitrate, and an alkoxide, and a method of synthesizing a silica powder to which a compound is added through a gas phase method are adopted. To be done. Examples of the molding machine for the porous molded body 41 include a vacuum extruder having a prime mover equipped with a transmission means, a primary kneading chamber having a hopper, a vacuum chamber, and a secondary kneading chamber which are sequentially connected. In addition, the porous molded body 41 may be molded mainly by a known or well-known hydrostatic molding method or sludge casting method.

1 and 2, when the porous layer 32 is formed in the porous molded body 41, first, the porous molded body 41 is set up in the recess 12 of the pipe support 11, and then,
A predetermined amount of slurry 31 is injected into the porous molded body 41 from the discharge port 22 of the slurry supply system 21. When the time elapses in this way, the water content in the slurry 31 is reduced to the porous molded body 41.
The porous layer 32 is formed in the porous molded body 41 because the porous layer 32 penetrates and is discharged to the outside.

The thus prepared porous base material for quartz glass is placed in a dryer to dry the porous layer 32 and the porous molded body 41. As the dryer used at this time, a cylindrical electric furnace having an electric heater, a cylindrical infrared heater having an infrared heater, a warm air dryer having an electric heater and a blower, the heater and suction Examples thereof include a vacuum dryer equipped with a system.

The dried porous base material is dehydrated and transparent glass by a known or well-known means, for example,
A quartz glass base material for optical fibers.

Specific examples 1 to 3 of the method of the present invention based on the matters described with reference to FIGS. 1 and 2 will be described below.

Example 1 To 100 parts of silica fine particles having an average particle size of 8 μm, 3 parts of methyl cellulose as a binder and 22 parts of pure water were added, and 0.3 part of a surfactant (SN wet 366: manufactured by San Nopco) was added. Then, these were uniformly kneaded to prepare a plastic molding material for the porous molded body 41. This molding material is applied to a vacuum extrusion molding machine to have an outer diameter of 65 mmφ and an inner diameter of 4 m.
A porous molded body 41 having mφ and a length of about 500 mm was extruded. The porous molded body 41 thus obtained was dried at 110 ° C. and further degreased in air at 500 ° C. for 4 hours. Porous molded article 41 after these treatments
Has a pore diameter of about 1.2 μm.

Average particle size 4 μm synthesized by flame hydrolysis method
100 parts of silica fine particles (however, including GeO ₂ with 3.5 wt% dopant for increasing the refractive index), 30 parts of pure water
Parts were added, and these were uniformly stirred to prepare a slurry 31.

The sludge 31 is poured into the porous molded body 41 which is held in a vertical state through the pipe support tool 11 and about 6
When left standing for a time, the water content of the sludge 31 was removed, and the porous layer 32 having a contracted volume was formed on the porous molded body 41.

After that, the porous layer 32 and the porous molded body 41 are formed.
Are dried at 110 ° C. and dehydrated (120
Cl _{2 at} 0 ° C., He atmosphere) and transparent vitrification (160
He atmosphere (0 ° C.) was used to obtain a silica-based glass preform for an optical fiber.

Further, thereafter, the above-mentioned base material is drawn by a well-known heat drawing method to form a Sinkk mode type optical fiber having an outer diameter of 125 μmφ, and an outer diameter made of an ultraviolet curable resin is provided on the outer circumference of the optical fiber immediately after the drawing. A coating layer of 400 μmφ was applied. The transmission characteristics of the coated optical fiber of the specific example 1 are equal to or higher than those of the optical fiber obtained by mainly using the conventional full-synthesis VAD method.

SPECIFIC EXAMPLE 2 The porous molded body 41 was produced in the same manner as in the specific example 1, and the slurry 31 was pure silica fine particles having an average particle diameter of 4 μm and erbium powder synthesized by the flame hydrolysis method. 100 parts of mixed powder with (Er ₂ O ₃ ) was added with 30 parts of pure water
Parts were added and they were prepared by homogeneous stirring.

Thereafter, in the same manner as in Example 1, the slurry 3 was used.
1 was cast into the porous molded body 41, and then dehydrated and transparent vitrified in the same procedure as in Example 1 to obtain a silica-based optical fiber preform for optical amplification.

With respect to such an optical fiber preform, an optical fiber for optical amplification was prepared by drawing the optical fiber by the above-mentioned heating and drawing method, and its optical amplification characteristics were measured.
It was confirmed to be effective for optical amplification in the 55 μm band.

Concrete Example 3 The porous molded body 41 was prepared in the same manner as in Concrete Example 1, and the slurry 31 was prepared as follows. When an aqueous solution of erbium chloride (ErCl ₃ ) is added to an ethanol solution of tetraethoxysilane (TEOS) to hydrolyze them with catalytic ammonia, fumed silica (surface area 100 m ²
/ G) was also added, and the silica gel containing Er was obtained by such hydrolysis. The silica gel thus obtained was dried at 70 ° C. and then heated to 700 ° C. in air or in O ₂ to remove excess organic matter, and subsequently, dried in air at 8 ° C.
It was heated to 00 ° C. and calcined. Further, the silica gel after calcination was pulverized to form a powder, 30 parts of pure water was added to 100 parts of the powder, and these were homogeneously stirred to prepare a slurry 31.

Thereafter, in the same manner as in Example 1, the slurry 3 was used.
1 was cast into the porous molded body 41, and then dehydrated and transparent vitrified in the same procedure as in Example 1 to obtain a silica-based optical fiber preform for optical amplification. It has been confirmed that the optical fiber for optical amplification obtained from such an optical fiber preform is also effective for optical amplification in the wavelength band of 1.55 μm, as in Example 2.

[0033]

According to the method for producing a porous preform for quartz glass according to the present invention, a predetermined sludge is cast into a tubular porous molded body to form a porous layer in the porous molded body. Therefore, a high-quality porous base material can be manufactured easily and stably.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the method of the present invention.

FIG. 2 is a plan view schematically showing an embodiment of the method of the present invention.

[Explanation of symbols]

 11 Pipe Support Tool 12 Recess of Pipe Support Tool 21 Sludge Supply System 22 Discharge Port of Sludge Supply System 31 Sludge 32 Porous Layer 41 Tubular Porous Molded Body

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuaki Yoshida 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (5)

[Claims] 1. A sludge containing quartz glass fine powder as a main raw material is cast into a tubular porous compact made of quartz glass powder to form another porous layer in the tubular porous compact. A method for producing a porous base material for quartz glass, which is characterized in that 2. The method for producing a porous base material for silica glass according to claim 1, wherein silica particles dispersed in pure water are used as a slurry. 3. A solvent in which pure water is partially or wholly replaced with a solution containing an element for controlling the refractive index and / or an element for imparting functionality, and silica particles are contained in the solvent. The method for producing a porous preform for quartz glass according to claim 1, wherein a material in which is dispersed is used as a slurry. 4. A slurry containing a compound containing an element for controlling a refractive index and / or a compound containing an element for imparting functionality and silica particles dispersed in pure water is used as a slurry. The method for producing a porous base material for quartz glass according to claim 1. 5. A gel-like material obtained by hydrolyzing alkoxide of silicon in a solution containing an element for controlling a refractive index and / or an element for imparting functionality is calcined and ground to obtain a powder. The method for producing a porous base material for silica glass according to claim 1, wherein the powder is dispersed in pure water and used as a slurry.