JPH05286736A - Production of porous preform for optical fiber - Google Patents

Abstract

PURPOSE:To efficiently obtain a high-strength preform free of bubbles by adding a surfactant to a preform material consisting of a silica powder, a binder and water and extruding the mixture. CONSTITUTION:A granular silica grains having about 8mum average grain diameter, a binder such as methylcellulose, pure water and further a surfactant (e.g. SN wet 366) are mixed to obtain a clad material. Meanwhile, fine silicon particulars having about 0.7mum average diameter, PVA and a surfactant are kneaded to obtain a core material. The core material 52 is supplied to the crosshead 55 of an extruder 5 through a hopper 50, a kneading chamber 53 and a vacuum chamber 54, the clad material 56 is supplied to the crosshead through a hopper 51, a kneading chamber 57 and a vacuum chamber 58, and a core and a clad are formed in the crosshead 55 to obtain a rod powder compact 59, the compact 59 is dried and heated to produce a porous preform for the optical fiber.

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 porous preform for an optical fiber used in the field of optical communication and the like.

[0002]

2. Description of the Related Art Conventionally, a method utilizing extrusion molding has been carried out as a method for producing a porous preform for an optical fiber. The present inventors propose in Japanese Patent Application No. 3-2541212 a method of forming a core part and a clad part at once using a vacuum extrusion molding machine. In this method, in order to impart plasticity to the base material, a silica powder as a main raw material is mixed with a binder and water.

[0003]

Since the above method uses the vacuum extrusion molding machine, air bubbles in the base material are removed when the core portion and the clad portion are formed. The effect is insufficient from the viewpoint of a porous preform for optical fibers. Therefore, molding is performed at a relatively low extrusion molding speed, and the base material is retained in the extruder for as long as possible to promote defoaming. However, even then, the bubbles are not sufficiently removed, and the yield of the base material deteriorates. Further, there is a drawback that mechanical strength is low due to insufficient removal of bubbles.

The present invention has been made in view of the above points, and manufactures a porous preform for optical fibers capable of efficiently obtaining a porous preform having almost no bubbles and exhibiting excellent mechanical strength. The purpose is to provide a method.

[0005]

The present invention is a silica powder,
In a method for producing a porous preform for an optical fiber, in which a preform material composed of a binder and water is extruded to obtain a porous preform, the preform material contains a surfactant. Provided is a method for manufacturing a porous base material.

Here, as the silica powder used as the base material, a high-purity silica powder having an average particle diameter of 100 μm or less, particularly a volume average diameter of 0.1 to 20 μm is preferable. The silica powder preferably has an equiaxed shape, for example, spherical particles for extrusion molding. Further, silica powder to which a dopant is added to adjust the refractive index may be used.

The surfactant used in the present invention is not particularly limited as long as it reduces the interfacial energy between the silica powder particles and water. Considering that it is for a porous base material, a nonionic one is preferable. For example, it is an ethylene oxide type such as polyoxyethylene alkyl ether, and has an HLB (Hydrophile-Lipophi
le Balance) value of 6 to 10 can be used.

The amount of the surfactant added to the plastic material is not particularly limited. For example, when an ethylene oxide-based surfactant such as polyoxyethylene alkyl ether having an HLB value of 6 to 10 is used, 0.01 to 0.5 per 100 parts by weight of silica powder is used. Most preferably, it is parts by weight.

As the extruder, a screw type vacuum extruder, a piston type extruder or the like can be used. When a piston type extruder is used, it is necessary to degas before kneading the base material. Also, between the extrusion screw and the die as an extrusion molding machine,
By using the extruder described in Japanese Patent Application No. 3-218291, which is provided with an auxiliary cylinder for stopping the rotation of the material, the optical and physical properties of the porous base material are synergized by the synergistic effect with the lamination prevention effect. The characteristics are further improved. In this case, as the auxiliary cylinder, one in which the inner surface of the cylinder is roughened to form the resistance portion, or
Cylinders 10, 20, 30, 4 having a shape as shown in FIG.
You may use 0.

The method of the present invention may be applied to the core part or the clad part alone, or may be applied to both the core part and the clad part.

[0011]

In the method for producing a porous base material for an optical fiber according to the present invention, a base material containing a surfactant is used. Therefore, the surfactant lowers the interfacial energy between the silica particles and water. As a result, defoaming from the base material is promoted in extrusion molding. As a result, it is possible to obtain a porous base material having almost no bubbles.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings.

EXAMPLE 100 parts by weight of silica fine particles having an average particle size of 0.7 μm synthesized by the flame hydrolysis method, 36 parts by weight of a 10% solution of PVA (polyvinyl alcohol), and a surfactant SN
0.3 parts by weight of Wet 366 was added, and these were uniformly kneaded to obtain a core material. It should be noted that the silica fine particles should contain 3.5% of GeO ₂ as a dopant for improving the refractive index.
It is contained by weight%.

3 parts by weight of methyl cellulose as a binder to 100 parts by weight of silica particles having an average particle size of 8 μm,
22 parts by weight of pure water was added as a solvent, 0.3 part by weight of SN Wet 366 was further added as a surfactant, and these were uniformly kneaded to obtain a material for the clad part.

The obtained core material and clad material were respectively put into the first hopper 50 and the second hopper 51 of the extrusion molding machine 5 shown in FIG. 5 and extrusion-molded. In the extruder 5, the core material 52 is supplied to the crosshead 55 through the first kneading chamber 53 and the first vacuum chamber 54, and the clad material 56 is fed to the second kneading chamber 57. Through the second vacuum chamber 58 and the crosshead 55.
Is supplied to. A core part and a clad part are formed in the cross head 55 to obtain a rod-shaped powder compact 59. The extrusion rate of the core material is 0.2 kg / h,
The extrusion rate of the material for the clad portion was 40 kg / h.

Next, the obtained powder compact was subjected to 1
It was dried for 2 hours and then degreased in air at 700 ° C. for 4 hours. Furthermore, this is Cl of 1200 ℃
_2. Dehydrated in a He gas atmosphere and made into vitrified glass in a He atmosphere at 1600 ° C. to manufacture a glass preform for optical fibers.

The mechanical strength of the obtained glass preform for optical fibers was investigated. The mechanical strength was measured by subjecting the glass base material for an optical fiber to ordinary wire drawing to obtain an outer diameter of 125.
It was carried out by measuring a 50% value of tensile strength and breaking strength with a single mode fiber of μm. As a result, the mechanical strength was 6.7 kgf, which was equivalent to the mechanical strength of the optical fiber preform obtained by the conventional vapor phase method.

Comparative Example A porous base material was produced in the same manner as in Example except that the surfactant was not added to the material for the clad portion.

When the mechanical strength of the obtained porous base material was examined in the same manner as in the example, the mechanical strength was 1.1 kgf.

In the above-mentioned embodiment, both the core portion and the clad portion are extruded by an extrusion molding machine. For example, as proposed by the applicant in Japanese Patent Application No. 2-244815, Prepare a transparent glass rod manufactured by another method in advance as the part (only the core part may be used, or a part of the clad may be provided around the core part). It goes without saying that the present invention can also be applied to a method of extrusion-molding a clad portion around it.

[0021]

As described above, according to the method for producing a porous preform for optical fibers of the present invention, it is possible to efficiently obtain a preform for optical fibers having almost no bubbles and exhibiting excellent mechanical strength. Is.

[Brief description of drawings]

FIG. 1A is a vertical sectional view showing an auxiliary cylinder of an extrusion molding apparatus that can be used in the method of the present invention. (B) is a cross-sectional view of (A).

FIG. 2A is a longitudinal sectional view showing an auxiliary cylinder of an extrusion molding apparatus that can be used in the method of the present invention. (B) is a cross-sectional view of (A).

FIG. 3A is a vertical sectional view showing an auxiliary cylinder of an extrusion molding apparatus that can be used in the method of the present invention. (B) is a cross-sectional view of (A).

FIG. 4A is a longitudinal sectional view showing an auxiliary cylinder of an extrusion molding apparatus that can be used in the method of the present invention. (B) is a cross-sectional view of (A).

FIG. 5 is an explanatory view showing an extruder used in the method of the present invention.

[Explanation of symbols]

5 ... Extruder, 10, 20, 30, 40 ... Cylinder,
50 ... 1st hopper, 51 ... 2nd hopper, 53 ... 1st
Kneading chamber 54, first vacuum chamber 55, crosshead,
56 ... Material for clad part, 57 ... Second kneading chamber, 58 ...
Second vacuum chamber, 59 ... Powder compact.

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

Claims (1)

[Claims] 1. A method for producing a porous base material for an optical fiber, which comprises extruding a base material composed of silica powder, a binder, and water to obtain a porous base material, wherein the base material contains a surfactant. A method for producing a porous preform for an optical fiber, comprising: