JPH05208839A - Production of silica-based porous glass form - Google Patents

Abstract

PURPOSE:To obtain in high yield the subject high-purity glass form of good optical characteristics by a mechanical molding means while suppressing developments of cracks, residual air bubbles, etc. CONSTITUTION:The objective silica-based porous glass form 36 can be obtained by mechanically molding a molding material 35 containing, as the chief stock, silica-based fine glass particles with 0.6-20mum mean diameter. With such appropriate particle size, the above glass form 36 is produced with high productivity and high quality leading to optical fiber matrix of excellent characteristics such as high purity and high mechanical strength, furthermore leading to improvement in the yield of the good-quality products in the subsequent processes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silica-based porous glass body used for producing an optical fiber preform in the field of manufacturing technology relating to optical communication.

[0002]

2. Description of the Related Art In the field of manufacturing technology related to optical communication, when manufacturing a base material for an optical fiber, MCVD method, VA
Although CVD methods such as D method, OVD method and PCVD method have been widely adopted, various powder molding methods using silica powder as a raw material have recently been proposed as a means for manufacturing a base material at a lower cost than these methods. There is.

The powder molding method using silica powder can be roughly classified into dry type and wet type. One of the typical dry powder molding methods is called the MSP method. This MSP method is disclosed in JP-A-60-210539.
It is disclosed in Japanese Patent Laid-Open No. 61-266325. Another one of the dry powder molding methods is a pressure molding method, and this molding method is also disclosed in JP-A-53-48536 and JP-A-6-56.
It is known in, for example, JP-A-3-55132 and JP-A-3-126723. As a wet powder molding method, a sol-gel method using colloidal silica powder as a starting material, that is, a colloidal gel method is well known.
For example, it is disclosed in JP-A-64-18928. Other wet powder molding methods include a centrifugal separation method (JP-A-63-195136), a slip casting method (JP-A-1-56331), an extrusion molding method (JP-A-4-12042), and a slurry. A coating method (Japanese Patent Laid-Open No. 4-124044) and the like can be seen.

The above-mentioned powder molding methods are common in that fine silica particles (fine silica particles) are used. By the way, recent technical literature on the MSP method [Journal of Opt
ical Communi-cation, Vol 10, 1989, No.1, pp 2-5]
Has a specific surface area of 50 to 50 prepared by the flame hydrolysis method.
The use of 350 m ² / g silica powder is described. Further, the above-mentioned Japanese Patent Application Laid-Open No. 6-187242 relating to the colloidal gel method
No. 4-18928 discloses a specific surface area of 5 to 100 m ² /
The technical content of using silica fine particles of g is disclosed. In the example of this publication, the specific surface area is 50 m.
² / g silica fine particles are actually used.

As a method for producing silica powder, a sol-gel method using an alkoxide as a raw material, a flame hydrolysis method using a silicon halide or the like as a raw material, a sodium silicate method, and a method of crushing natural quartz are generally known. , For example,
When a porous glass body for an optical fiber preform is produced by a powder molding method, high-purity silica particles are required as a molding material, so silica powder satisfying such requirements is a sol-gel method or a flame hydrate. Limited to those manufactured by the decomposition method. Furthermore, in the case of a porous glass body using silica powder of the sol-gel method as a molding material, since there are fine pores in the silica particles, it is in the glass that has been vitrified transparently, that is, many bubbles in the optical fiber preform. Remains and does not finish as a good product. From such circumstances, only the silica powder produced by the flame hydrolysis method is effective as a molding material when the porous glass body for an optical fiber is manufactured by the powder molding method.

Silica powder produced by the flame hydrolysis method is manufactured and sold by several domestic and foreign companies such as Degussa (Germany), Cabot (US) and Nippon Aerosil.
Among commercially available silica fine particles, the one having the largest particle diameter is a product “Aerosil OX-50” manufactured by Degussa, which has an average particle diameter of 40 nm and a specific surface area of 50 m ² / g.
Is. In the colloidal gel method of the above patent publication,
5 to 100 m ² / g although mention silica particles having a specific surface area of, if the specific surface area of the silica particles actually made flame hydrolysis method in view that is 50 m ² / g or more, a specific surface area 5 ˜50 m ² / g silica particles are
It can be inferred that it was produced by a method other than the flame hydrolysis method, for example, a natural quartz crushing method.

[0007]

Among the above-mentioned silica powders, the one synthesized through the flame hydrolysis method is the largest one, "Aerosil OX-5 of Degussa".
0 "(average particle size 40 nm, specific surface area 50 m ² / g). When the required porous glass body is powder-molded using such silica powder, various problems occur due to the fine silica powder, so that the yield rate and the productivity of non-defective products decrease. For example, when the dry powder molding method is used, the fluidity of particles is poor, so that the powder filling speed is slowed, the powder filling density is nonuniform, and the porous glass body is nonuniform and brittle. As a result, the productivity of the porous glass body is reduced, and cracks occur in the porous glass body during handling, sintering, etc., and bubbles remain in the sintered glass. Such a problem cannot be solved even by replacing with the wet powder molding method, and in particular, in the case of the wet powder molding method, cracks often occur during drying of the porous glass body.

With respect to silica particles having a specific surface area of 5 to 50 m ² / g, no means for synthesizing the silica particles has been disclosed, and no technical literature has actually confirmed its effectiveness. Even if silica particles having an average particle diameter of 50 nm or more and a specific surface area of 5 to 50 m ² / g are obtained through the natural quartz crushing method, the silica particles do not have homogeneity and contain a large amount of impurities. As a final product,
For example, it is not possible to obtain a high quality optical fiber.

As another technical problem, it is important to highly purify the optical fiber preform so as to satisfy the high transmission characteristics of the optical fiber and wide band. Therefore, the glass for the core has metal impurities of several ppb or less,
It is required or requested that the OH group is several ppm or less, and the glass for cladding is also required to have a considerable degree of purity. Since the silica-based porous glass body produced through the above-mentioned powder molding method contains such impurities, it must be purified to remove metal impurities, OH groups and the like. Usually, this kind of refining is performed by treating the porous glass body in a high temperature Cl ₂ atmosphere, for example, Fe ₂ O ₃ (metal impurities) → FeCl
₃ , such as --OH → HCl, these FeCl
₃ , HCl becomes gaseous and is removed from the porous glass body. However, in such purification, when the pores of the porous glass body formed of silica particles having a small particle size are small, the purified gas (Cl ₂ ) permeates into the porous glass body insufficiently, and Impurity gas (F
Exhaust of eCl ₃ and HCl) also stagnates, so that a high-purity optical fiber preform cannot be obtained. On the other hand, when the silica particles have a large particle diameter, the moldability of the porous glass body is deteriorated and the porous glass body often collapses after molding, which is a problem before air permeability. In the existing powder molding method, technical elucidation and countermeasures for these are not taken, and therefore it is difficult to stably manufacture a high-purity optical fiber preform.

The present invention suppresses the occurrence of the above-mentioned cracks, cracks, residual bubbles, and the like in view of the technical problem in molding a quartz-type porous glass body through a mechanical molding means, and Another object of the present invention is to provide a method capable of producing a high-purity product having good optical characteristics with high yield.

[0011]

In order to achieve the above-mentioned object, the method for producing a silica-based porous glass body according to the present invention comprises silica-based glass fine particles having an average particle size of 0.6 to 20 μm as a main raw material. Is molded mechanically to form a silica-based porous glass body for an optical fiber.

[0012]

In the method of the present invention, fine particles produced through a chemical reaction method such as a flame hydrolysis method, a thermal decomposition method or a high temperature oxidation method, or a treated material thereof is used as a molding material. An example of treating the fine particles is as follows. Usually, the silica-based glass fine particles synthesized by the flame hydrolysis method have an average particle size of 7 to 40 n.
m, a specific surface area of 50 to 380 m ² / g, and homogenized within a range of almost no impurities (excluding additives).
When such glass fine particles are introduced into a high-temperature space and melted, the melted glass fine particles are bonded to each other by association in the high-temperature space, so that the glass particle diameter after the bonding, that is, the silica-based glass powder diameter is before the bonding. Compared with the above, it will be dramatically increased by several tens to several hundreds (example: average particle size of 0.
6 μm to several tens of μm). As another example of the fine particle treatment, there is a method of treating granulated fine particles, as disclosed in JP-A-62-96537. In the case of the method of this known example, fine silica particles having a particle size of 0.05 μm or less are dispersed in water to form a slurry, which has a particle size of 0.5
By finely granulating and firing to 500 μm, silica fine particles having a large particle size can be finished. In addition, a method of making silica fine particles of relatively large diameter by the flame hydrolysis method of silicon tetrachloride and classifying the silica fine particles to extract silica fine particles of large particle size, high-temperature oxidation of metallic silicon powder to obtain silica of large particle size A method of making fine particles is also known.

The silica glass fine particles (powder) used in the method of the present invention have an average particle size of 0.6 to 20 μm.
Since it is m, it has the following characteristics. One of them is that the mutual fluidity of the particles is improved depending on the large particle size, and the other is that the uniform dispersibility in the solvent is increased depending on the large particle size. The solid concentration is increased, and solid-liquid separation is facilitated. When such a silica-based glass fine particle is used, in the dry powder molding method, depending on the above-mentioned fine particle (powder) fluidity, the powder filling speed becomes fast, the powder filling density becomes uniform, and it is uniform. It is possible to mold a porous glass body that does not easily break, and even in the wet powder molding method, depending on the above-mentioned uniform dispersibility in the solvent, high solid concentration in the dispersion, and solid-liquid separability. It is possible to efficiently form a homogeneous and strong porous glass body. Therefore, in both the dry powder molding method and the wet powder molding method, the productivity of the porous glass body is increased, cracks do not occur in the porous glass body in the subsequent process, and bubbles remain in the sintered glass. Not even.

The reason why the silica glass fine particles used in the method of the present invention are limited to those having an average particle size of 0.6 to 20 μm is as follows. That is, among the glass fine particles forming the porous glass body, those having an average particle size of less than 0.6 μm have small pores in the porous glass body, and therefore the purified gas is not purified during purification of the porous glass body. When the permeation is insufficient and the impurity gas is insufficiently exhausted, and the average particle diameter exceeds 20 μm, the formability of the porous glass body is deteriorated and the porous glass body collapses. On the other hand, in the case of the method of the present invention, since the average particle size of the glass fine particles forming the porous glass body is in the range of 0.6 to 20 μm, the purified gas is not sufficiently permeated during the purification, and the exhaust of the impurity gas is insufficient. Does not occur and does not cause moldability during the molding, and therefore a porous glass body that can be finished into a high-purity optical fiber preform can be easily obtained without causing moldability.

The silica glass fine particles used in the method of the present invention may be pure silica or doped silica.
Pure silica is produced through a chemical reaction method such as a flame hydrolysis method, a thermal decomposition method, and a high temperature oxidation method. Usually, SiO ₂ is produced by the flame hydrolysis method, but GeO ₂ , B ₂ O ₃ , P ₂ O ₅ , F is contained in SiO ₂ produced by the flame hydrolysis method.
When a dopant such as is added, a predetermined dopant gas is introduced into the flame together with the silicon halide to produce doped silica. Also in the case of the thermal decomposition method and the high temperature oxidation method, pure silica and / or doped silica is produced by a predetermined reaction using a compound containing metal silicon, an organosilicon compound, silicon halide and / or a dopant. As the silica-based glass fine particles, for example, those disclosed in Japanese Patent Publication No. 47-46274 can be used. In the method of the present invention, as described above, silica-based glass fine particles having an average particle size of 0.6 to 20 μm are used. However, in the dry molding method, in order to improve the fluidity of the fine particles and facilitate the handling thereof, It is desirable to granulate the fine particles by a means such as a spray granulation method before use. Further, it is desirable that the silica glass fine particles used in the method of the present invention have a spherical particle shape. This is because it is possible to avoid the generation of fine pores having poor air permeability when the porous glass body is molded.

When producing an optical fiber preform using such silica glass fine particles as a raw material, first, a porous glass body is produced through a powder molding method, and then the porous glass body is purified and vitrified into a transparent glass. Create a transparent glass body (base material). The transparent glass body produced in this manner is used alone or in combination with another transparent glass body and is heated and drawn to be an optical fiber or other final product.

In the case of the method of the present invention, as a powder molding method for producing a porous glass body, a dry powder molding method such as MSP method, a pressure molding method, a colloidal gel method, a centrifugal separation method and a slip casting method. A wet powder molding method such as an extrusion molding method or a slurry coating method is arbitrarily adopted. The outline of each of these methods is as follows. [MSP Method] The silica-based glass fine particles as a starting material are packed into a mold while being compressed, and in order to coalesce (mold) the silica-based glass particles compressed at the time of filling, the silica-based glass particles are heat-treated and / or pressed to be porous. Create a quality glass body. As a heat treatment means at this time, for example, Japanese Patent Application Laid-Open No. 61-2
The one disclosed in Japanese Patent No. 66325 can be mentioned. Further, as the pressing means, for example, JP-A-60
Examples of those disclosed in Japanese Patent Laid-Open No. -210539 can be given. [Pressure molding method] The silica-based glass fine particles as a starting material are enclosed in a stretchable molding container such as rubber or synthetic resin, and after being placed in the pressure container, the liquid in the pressure container is filled. The molding container is externally pressurized by pressure (hydrostatic pressure) to form a silica-based glass fine particle body that is compression molded in the molding container, that is, a porous glass body. In general, this pressure molding method is an abbreviation for Cold Isostatic Pressing and is called a CIP method. [Colloidal Gel Method] Sol-like silica glass fine particles (starting raw material) dispersed in a solvent are gelled in a container to form a porous glass body. [Centrifugation method] The silica glass fine particles (starting material) suspended in a solvent are put into a hollow molding die and rotated at a high speed. A porous glass body is formed. [Slip casting method] Quartz glass fine particles as a starting material are suspended in a solvent to form a fluid sludge, which is placed in a water-permeable (breathable) mold and water-separated quartz glass fine particles. A body, that is, a porous glass body is formed. [Extrusion Molding Method] A solvent is added to the silica-based glass fine particles as a starting material, and if necessary, a molding aid is also added, and this is put into an extruder to extrude a porous glass body. [Slurry coating method] A silica glass fine particle as a starting material is suspended in a solvent to form a slurry, which is repeatedly coated on the outer peripheral surface of a mandrel to form a porous glass body.

In the above-mentioned powder molding method, a rod-shaped porous glass body or a tubular porous glass body, or a glass rod or glass tube and a porous glass body externally attached to the outer peripheral surface of the glass rod or glass tube. It is possible to make a composite glass body. When using a glass rod, a glass tube, or the like having only the core glass or the core glass and a part of the clad glass, and forming a porous glass body for the clad on the outer peripheral surface of the glass rod, it is a starting material. When the silica-based glass fine particles have an average particle size of less than 0.6 μm, the porous glass body is likely to be damaged, but when the silica-based glass fine particles have an average particle size of 0.6 to 20 μm, the Almost no damage occurs. The rod-shaped porous glass body and the tubular porous glass body are made of core glass and / or clad glass. These are used as the optical fiber preform, either as they are or after being combined with other porous glass bodies or transparent glass bodies after being made transparent.

The above-mentioned porous glass body is purified in a high temperature atmosphere containing Cl ₂ and is transparent vitrified in a high temperature atmosphere containing He. In addition, purification and dehydration may be performed simultaneously.

[0020]

EXAMPLES Specific examples of molding a porous glass body by the method of the present invention and comparative examples thereof will be described. Concrete Example 1 When a porous glass body is produced by a pressure molding method, an elastically deformable tubular molding die (inner diameter 70
(mmφ) and an external container that covers the periphery of the same are used in combination, and a hydrostatic pressure type dry CIP device is used. As a molding material, silica particles having an average particle size of 8 μm (trade name: EXERIKA SE-8: Soda Tokuyama) are used. Manufactured by VAD method was used as a glass rod set at the axial center in the molding space of the cylindrical molding die. A system (core: clad outer diameter ratio = 1: 3) was used. In the first powder filling process, while vibrating the cylindrical molding die in which the glass rod is set, inside the molding space (around the glass rod)
Was filled with the above granulated product. In the next pressure-molding step, pure water was injected into the pressure space between the molding die and the outer container, and the molding die was pressurized with a hydrostatic pressure of 1000 kgf / cm ^2. A porous glass body having an outer diameter of 60 mmφ and an average pore diameter of 4 μm was formed around the glass. After this molding, the composite glass body consisting of the porous glass body and the glass rod is taken out from the molding space, and in order to purify the porous glass body and to make it into a transparent glass,
The following heat treatment was performed using an electric heating furnace. At the time of refining, the atmosphere in the electric heating furnace was formed with helium containing 1% chlorine gas, and the maximum temperature part in the electric heating furnace was set to 1200 ° C.
It was inserted into the furnace at a speed of / min, and the metal impurities were removed from the porous glass body by the heat treatment. In the subsequent vitrification, the inside of the electric heating furnace was switched to a helium-containing atmosphere and the highest temperature part in the electric heating furnace was set to 1600 ° C. to finish the porous glass body into a transparent glass body.
In the case of the optical fiber preform obtained in Example 1, no cracks or bubbles remained, and the content of metal impurities was Na = 0.
022ppm, Fe = 0.012ppm, Cu = 0.0
It was less than 02 ppm and Cr was as small as 0.002 ppm.

Comparative Example 1 When a porous glass body was formed on the outer circumference of a glass rod through the same pressure molding method as in Concrete Example 1, silica fine particles having an average particle diameter of 0.04 μm [trade name: EXCELICA SE-
1: manufactured by Tokuyama Soda Co., Ltd.]
When predetermined molding was carried out in the same manner as above, a porous glass body having an average pore diameter of 0.08 μm was molded around the glass rod. Also in the following, the porous glass body was refined in the same manner as in Example 1 and made into a transparent vitreous material to complete the optical fiber preform. The optical fiber preform obtained in Comparative Example 1 had Na = 0.12 pp.
m, Fe = 5.1 ppm, Cu = 0.034 ppm, C
It is not suitable as a base material of an optical fiber because it contains a large amount of metal impurities, r = 1.6 ppm.

Concrete Example 2 When a pressure molding method is carried out using a molding apparatus similar to that described in Concrete Example 1, V is added to the axial center of the molding space of the cylindrical molding die.
A glass rod for core (having an outer diameter ratio to the clad of 1: 3) manufactured by AD is set, and silica particles having an average particle diameter of 0.6 μm, which is a molding material, are formed around the glass rod [trade name: Admafine]. SO-25R: manufactured by Admatechs Co., Ltd.] and then hydrostatically pressurizing the molding die in the same manner as in Example 1 to give an average pore diameter of 0.2 μm on the outer periphery of the glass rod for core.
The porous glass body for overclad of was molded. Less than,
The composite glass body was taken out from the molding space, and the porous glass body was treated in the same manner as in Example 1 to obtain an optical fiber preform. The optical fiber preform obtained in Example 2 has no cracks or residual bubbles, and has a metal impurity content of Na.
= 0.063 ppm, Fe = 0.049 ppm, Cu =
It was less than 0.005 ppm and Cr was as small as 0.014 ppm.

Concrete Example 3 When a porous glass body is formed on the outer circumference of a glass rod through the same pressure molding method as in Concrete Example 1, silica particles having an average particle diameter of 15 μm (trade name: EXCELICA SE-1) are used as a molding material.
5: manufactured by Tokuyama Soda Co., Ltd.] was used to mold a porous glass body in the same manner as in Specific Example 1, and this was purified and made into transparent glass in the same manner as in Specific Example 1 to give a predetermined light. A fiber preform was obtained. The optical fiber preform obtained in Example 3 was also free from cracks and residual bubbles, and had a metal impurity content of Na =
0.02ppm, Fe = 0.01ppm, Cu = 0.0
It was less than 02 ppm and Cr was as small as 0.002 ppm.

Comparative Example 2 When a porous glass body was formed on the outer periphery of a glass rod through the same pressure molding method as in Concrete Example 1, silica particles having an average particle diameter of 29 μm were used as a molding material (trade name: Elsil: Mitsubishi Metals). Co., Ltd.] was used to form a porous glass body in the same manner as in Example 1. This porous glass body had a considerably low strength after molding, and there was a fear of cracking and collapse. Less than,
When this porous glass body was tried to be refined and made into a transparent vitreous in the same manner as in the previous example, a part of the porous glass body was missing even though it was not particularly impacted during the handling during the refining.

Concrete Example 4 When the porous glass body is molded in Concrete Example 4, the extrusion molding apparatus illustrated in FIGS. 1 and 2 is used, and FIG.
According to the molding steps illustrated in (a) to (e),
An extrusion method is carried out. Regarding Concrete Example 4, first, an outline of the apparatus and steps illustrated in FIGS. 1 to 3 will be described.

In FIG. 1 and FIG. 2, the extrusion head is attached to the tip of the auger cylinder 21 and is arranged on the extension line thereof with respect to the axis of the auger crawl 22. A medium ball 14 having a glass rod passage 11 at its axis is suspended via a suspender 13. The passage 11 of the glass rod and the passage 15 of the molding material in the body 12 of the extrusion head are concentric with each other. The passage 11 may be penetrated or may be closed at one end as shown. The passage 11 penetrating therethrough may be provided so as to extend into the rotation shaft of the middle ball 14 and the rotation shaft of the August crow 22 when the rotation shaft is in contact with the rotation shaft of the August screw 22. In such a case, in order to prevent the molding material from entering the passage 11 of the middle ball 14, the middle ball (non-rotating body) 14 and / or the August crow (rotating body) 2
2 is provided with suitable sealing means. Others, hanging device 13
Is fixed to the body portion 12 via a bolt 16, and the mouthpiece 17 connected to the body portion 12 is configured such that the linear portion 18 and the taper portion 19 constituting the base portion 17 can be disassembled. In FIG. 3, the rod connecting body 31 is a glass rod 32.
A dummy rod 33 and a support rod 34 are connected to both ends of the to produce. In this case, the glass rod 32 for the optical fiber preform
Is made of quartz, and the dummy rods 33 and the support rods 34 connected to both ends (glass welding) are also made of pure quartz or doped quartz. The dummy rod 33 needs to have the same diameter as the glass rod 32, but the support rod 34 may have an outer diameter equal to or larger than that of the glass rod 32.

At the step shown in FIG. 3 (a), the plastic molding material 35 supplied into the passage 15 reaches the tip side of the passage 11 and the tip side of the rod connecting body 31 (dummy). The rod 33) is about to be inserted into the passage 11 of the middle ball 14. At the step shown in FIG. 3B, the rod connecting body 31 is inserted into the passage 11 of the inner ball 14, and the molding material 35 that has been subjected to the extrusion pressure reaches the tip of the die 17. In this state, the molding material 35
Partially covers the outer peripheral surface of the glass rod 32. Figure 3
At the step shown in (c), the molding material 35 that has been subjected to further extrusion pressure is extruded from the tip of the die 17 together with the rod connecting body 31. In this state, the rod connecting body 31 is moving in the direction of escaping from the inside of the passage 11. At the step shown in FIG. 3D, the molding material 3 extruded from the tip of the die 17 and grown to an appropriate length.
5, that is, the porous glass body is cut. In this state, the rod connecting body 31 is completely pulled out from the inside of the passage 11. At the step shown in FIG. 3 (e), the linear portion 18 of the die 17 is removed from the taper portion 19 of the die 17, and the residue 3 of the molding material 35 in the linear portion 18 is removed.
7 is eliminated. Straight part 18 removed in this way
Is again attached to the tapered portion 19 and is ready for the next extrusion molding.

The fourth specific example based on the above contents is implemented in the mode described below. To 100 parts of silica particles having an average particle size of 8 μm, 3 parts of methyl cellulose as a binder,
22 parts of pure water and 0.3 part of a surfactant (trade name SN wet: manufactured by San Nopco) were added, and these were homogeneously kneaded to prepare a plastic molding material. The glass rod for the core has a relative refractive index difference of about 0.3% with respect to quartz and an outer diameter of about 8.5.
mmφ (outer diameter ratio to clad 1: 3), length approx. 300 m
m was used. At one end and the other end of this glass rod for core, a dummy rod having a diameter of about 8.5 mm and a length of about 50 mm,
Support rods each having a diameter of about 25 mm and a length of 15 mm were glass-welded to form a rod connection body. A porous glass body was extrusion-molded by using these plastic molding materials and a rod connecting body according to the extrusion molding method of FIG. In order to finish the porous glass body thus molded into a transparent glass body,
First, the porous glass body is dried at 110 ° C. for 12 hours,
Next, the dried glass body was degreased at 500 ° C. for 15 hours (in air), and then the degreased glass body was heated at 1200 ° C.
After dehydration in an atmosphere of e and Cl ₂ , the dehydrated glass body was subsequently vitrified into a transparent glass in a He atmosphere at 1600 ° C. In the steps so far, the porous glass body and the optical fiber preform were not cracked or warped. The optical fiber preform obtained in Example 4 is drawn by a known heating and drawing means to form a single mode optical fiber having a core diameter of 5 μmφ and an outer diameter of 125 μmφ, and the optical fiber immediately after the drawing is made of an ultraviolet curable resin. A coating layer having an outer diameter of 400 μmφ was formed. The transmission characteristics of this single mode optical fiber were as good as those of the single mode optical fiber of the same specifications obtained from the optical fiber preform based on the vapor phase method.

[0027]

The molding material used in the method of the present invention has an average particle diameter of the silica-based glass fine particles, which is the main raw material, of 0.6-
Since it is suitable to be 20 μm, the fluidity between particles is good,
Depending on the large particle size, the uniform dispersibility in the solvent, the solid concentration in the dispersion increases, and the solid-liquid separation becomes easy. Therefore, when mechanically molding such a molding material to form a silica-based porous glass body, in the dry powder molding method, depending on the above-mentioned particle fluidity, the particle packing speed becomes faster and the particle packing density becomes uniform. In addition, it is possible to mold a porous glass body that is homogeneous and does not easily break, and even in the wet particle molding method, uniform dispersibility in the solvent, high solid concentration in the dispersion, and solid-liquid separability. In this way, a porous glass body with high homogeneity and strength can be efficiently formed. Moreover, the porous glass body thus formed has moderately large pores, and the purified gas does not permeate during purification. Since the exhaust of the impurity gas is not sufficiently insufficient, the optical fiber preform of high purity can be finished. Therefore, according to the method of the present invention, during molding, high characteristics, high purity,
A high-quality porous glass body that can communicate with a high-strength optical fiber preform can be highly produced, and the yield of non-defective products can be improved even in the subsequent process.

[Brief description of drawings]

FIG. 1 is a sectional view of an extrusion molding apparatus used in an embodiment of the method of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view of a main part schematically showing each molding step of a porous glass body by the extrusion molding apparatus illustrated in FIG.

[Explanation of symbols]

 11 Passage for Glass Rod 12 Body of Extrusion Head 14 Middle Ball 15 Passage for Molding Material 17 Base 21 Auger Cylinder 22 Auger Cru 31 Rod Connecting Body 32 Glass Rod 35 Molding Material 36 Porous Glass Body

 ─────────────────────────────────────────────────── ─── Continued front page (72) Ken Yagi Ken 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Takayuki Morikawa 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A silica-based porous glass body for an optical fiber is produced by mechanically molding a molding material containing silica-based glass fine particles having an average particle diameter of 0.6 to 20 μm as a main raw material. A method for manufacturing a quartz-based porous glass body.