JP2547764B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for producing an optical fiber, more specifically, by heating and melting an optical fiber base material (hereinafter simply referred to as “base material”), The present invention relates to an improvement in a method for producing an optical fiber by coating the surface of a fiber (hereinafter, referred to as "drawn fiber") obtained by drawing from the tip of a base material with a constant tension to form an optical fiber by coating with a resin.

[Conventional technology]

Usually, the optical fiber is manufactured as follows. That is, as shown in FIG. 2, a separately prepared base material 1 is sent into a furnace core tube 3 in a heating furnace 2 and drawn from the tip of the heated and melted base material 1 with a constant tension to obtain a drawn fiber. 4 is passed through a coating die 5 containing a resin solution while being cooled by natural heat dissipation during the drawing process to coat the surface of the drawing fiber 4 with the resin solution.
The optical fiber 7 obtained by baking in a furnace 15 was wound around a drum 8.

The reason why the surface of the wire drawing fiber 4 is coated with the resin when the optical fiber 7 is manufactured is as follows.

That is, since the diameter of the drawn fiber 4 is glass fiber having a diameter of about 100 to 150 μm, it is extremely weak and easily broken by a tensile load of about 100 g.

Further, since the material is glass, unlike metal, it causes brittle fracture, and even small scratches on the fiber surface grow and cause fracture.

Therefore, a method of coating the surface of the drawing fiber with a resin to improve the tensile strength and the bending strength is adopted.

On the other hand, in order to increase the productivity of optical fiber manufacturing, it is necessary to increase the fiber drawing speed. However,
When coating the surface of the drawing fiber with a synthetic resin such as an ultraviolet curable resin, the drawing fiber is drawn from the heated and melted base material, so when the drawing fiber dissipates heat and cools down. However, when it is passed through the coating die 5 in such a state, the coating layer is thermally affected by the drawing fiber, and the resin viscosity around the drawing fiber is excessively reduced, and the dimension of the coating layer is decreased. Will be unstable.

In order to eliminate such a problem, the conventional Japanese Patent Publication Sho 54-
As described in Japanese Patent No. 39496, a gas is blown onto the fiber surface immediately after drawing from the heated and melted base material to cool the fiber. This is shown in FIG.
Reference numeral 6 in the figure represents a cooling gas, and the other reference numerals common to those in FIG. 2 mean the same as those in FIG.

[Problems to be solved by the invention]

By the way, as the fiber drawing speed is increased in order to improve the productivity, the same apparatus has to take a larger amount of heat in the same distance in a shorter time and cool it. In the cooling by spraying gas proposed in the above publication, it is possible to increase the gas flow rate or lower the temperature of the gas, but there is always a limit when the gas temperature is lowered, and the fiber is cooled. If this is done, the gas temperature will gradually rise, and therefore there is only a way to increase the gas flow rate in order to perform cooling that follows the increase in the drawing speed. However, when the gas flow rate is increased, the problem of fiber line blurring occurs.

Further, if it is attempted to increase the amount of heat to be taken by extending the cooling time or distance, the height of the device is increased and the device cost is increased, which is not preferable for the purpose of improving productivity.

The present invention has been made in view of the above circumstances, and even if the drawing speed is increased, the above-mentioned difficulties are solved, effectively without line blurring, and at a low device cost, sufficient cooling is achieved. It is an object of the present invention to provide a method capable of producing a high-quality optical fiber that can be manufactured.

[Means for solving problems]

The present invention is a method of forming an optical fiber by applying a resin coating on the surface of the drawn fiber with a constant tension from the fiber end of the optical fiber base material heated and melted by a heating source, and forming the optical fiber in the method. After passing through the tubular cooling section after passing through the resin-coated fiber, a liquid having a boiling point in a temperature range lower than room temperature is dropped into the tubular cooling section from the upper liquid reservoir of the tubular cooling section to evaporate the liquid. The present invention provides a method for producing an optical fiber, characterized in that the inside of the tubular cooling part is cooled by the heat of vaporization of the gas or the liquid to cool the fiber surface.

As a further preferred embodiment of the present invention, there is mentioned the above method in which the gas evaporated from the liquid in the liquid reservoir in the upper portion of the tubular cooling unit is blown onto the optical fiber before resin coating after leaving the heating source. Further, it is particularly preferable to use liquid nitrogen or liquid argon as the liquid having a boiling point in a temperature range lower than room temperature.

[Operation, Example]

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram for explaining an embodiment of the present invention, in which 1 to 5, 7, 8, and 15 mean the same as in FIGS. 2 and 3. 9 is a liquid having a boiling point in a temperature range lower than room temperature, 10 is a replenishment tank for the liquid 9, and a replenishment pipe 11,
It communicates with the upper liquid reservoir 17 in the tubular cooling section 13 via the valve 12. The tank 10, pipe 11 and valve 12 are
It is kept warm by. A gas outlet 18 is provided at the upper end of the tubular cooling portion 13 extending in the axial direction of the optical fiber, the hollow portion inside the tubular cooling portion 13 is the fiber cooling portion 16, and the liquid receiving portion is at the lower end thereof. 19 are provided. The upper and lower ends of the tubular cooling section 13 and the central portion of the bottom surface of the upper liquid reservoir 17 are provided with passage holes for the drawing fiber 4.
A fine hole is provided on the bottom surface of the fiber cooling unit 16 side of 17. Further, a liquid passage hole 21 is provided near the lower portion of the tubular cooling unit, 20 is an overflow receiving member, and 24 is a liquid removing member.

In order to manufacture an optical fiber according to the present invention, the base material 1 is sent into the furnace core tube 3 heated in the heating furnace 2, and the core tube 3
A constant tension is applied to the front end of the base material 1 which is heated and melted inside to draw in the axial direction, and the fiber 4 is drawn out.

The wire drawing fiber 4 thus drawn out is first fed into the coating die 5 before being fed into the tubular cooling part.
Pass thirteen. In the tubular cooling section 13, the liquid 9 supplied from the tank 10 to the upper liquid reservoir 17 passes through the pores and drops into the fiber cooling section 16, but vaporizes during the drop to generate a cold gas. In addition, the inside of the fiber cooling unit 16 is cooled by the heat of vaporization. The wire drawing fiber 4 is cooled by passing through the inside of the cooled fiber cooling section 16. At this time, the liquid 9 evaporates also in the upper liquid reservoir 17, so that a gas outlet is provided in the upper liquid reservoir 17 as shown in the figure.
The provision of 18 has the effect that the drawing fiber 4 is cooled even before it enters the tubular cooling section 13. Liquid 9
The amount of replenishment from the tank 10 is adjusted by the valve 12 so that all of the liquid 9 evaporates before reaching the liquid receiving portion 19. Further, in order to prevent the collected liquid 9 from overflowing the liquid receiving portion 19 and entering the die 5, the liquid receiving hole 21 is made to enter the overflow receiving portion. Further, since the tubular cooling section 13 is cooled, it is preferable to attach the flange pipe 23 with the heat insulating material 22 interposed therebetween in order to prevent the condensed water in the air from falling into the die 5. Further, it is more effective and preferable to cool the outer surface of the tubular cooling section 13 by keeping it warm or by forming a double structure.

As the liquid having a boiling point in the temperature range lower than room temperature in the present invention, for example, liquid nitrogen (boiling point −195.82 ° C.), liquid argon (boiling point −185.87 ° C.) and the like can be used.

As described above, in the present invention, unlike the conventional method, gas is not passed, and for the purpose of continuously cooling the fiber, a liquid having a boiling point in a temperature range lower than room temperature is continuously evaporated in the tubular cooling section. By doing so, cold gas is generated and the heat of vaporization cools the gas in the tubular cooling section, and the cold gas cools the wire drawing fiber from its surroundings. In other words, heat is exchanged between the hot drawing fiber and the surrounding gas in the tubular cooling section. The ambient gas is warmed by the fiber with the cold vapor of the liquid, but its heat is taken away by evaporating the liquid and can always be kept cold. As a result, the wire drawing fiber can be cooled in the same manner as gas is flowed, and there is no concern about line blurring due to gas flow, and continuous and high-speed cooling can be performed without increasing the size of the device.

〔The invention's effect〕

As is clear from the above description, according to the method for manufacturing an optical fiber of the present invention, the fiber drawn from the heated and melted base material can greatly improve the cooling effect as compared with the case of the conventional method for manufacturing an optical fiber. Not only that, even if the fiber drawing speed is increased, sufficient cooling can be performed without causing line blurring, so that the production efficiency of the optical fiber can be significantly improved.

Furthermore, since the gas generated from the liquid with a low saturation temperature used is filled in the passage of the drawing fiber,
The atmosphere around the fiber can be kept clean, and the optical fiber to be produced has no damage on the surface thereof and can be made to have high strength.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of the present invention. 2 and 3 are schematic configuration diagrams illustrating a conventional method and an improved example thereof.

Claims (3)

(57) [Claims] 1. A method for forming an optical fiber by drawing a fiber from the tip of an optical fiber base material heated and melted by a heating source with a constant tension and applying a resin coating on the surface of the drawn fiber to form an optical fiber. After passing through the inside of the tubular cooling part, the liquid having a boiling point in a temperature range lower than room temperature is dropped into the tubular cooling part from the upper liquid reservoir of the tubular cooling part while passing the fiber before resin coating through the tubular cooling part. A method for producing an optical fiber, characterized in that the fiber surface is cooled by cooling the inside of the tubular cooling section with the heat of vaporization of the vaporized gas or the liquid. 2. The optical fiber according to claim 1, wherein the gas evaporated from the liquid in the liquid reservoir in the upper portion of the tubular cooling section is blown onto the fiber before resin coating after leaving the heating source. Production method. 3. The method for producing an optical fiber according to claim 1 or 2, wherein liquid nitrogen or liquid argon is used as the liquid having a boiling point in a temperature range lower than room temperature.