JPS6191044A - Apparatus for coating optical fiber - Google Patents

Abstract

PURPOSE:To decrease the amount of overflowed liquid flowing reversely in a nipple of an apparatus composed of a nipple and a die, and to improve the appearance of the coating layer, by sucking the overflowed liquid of a coating material in the nipple through a suction hole provided. CONSTITUTION:The objective optical fiber coating apparatus 10 is composed of the nipple 14 passing an optical fiber 12, and the die 18 to apply a coating material 16 to the fiber delivered from the outlet 14a of the nipple 14. A suction hole 20 to suck the overflowed liquid 16a of the coating material 16 is provided in the nipple 24. The amount of the overflowed liquid 16a flowing reversely in the nipple 14 can be decreased and the appearance of the coating layer can be improved by this apparatus 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical fiber coating device for coating an optical fiber formed by drawing an optical fiber preform with a liquid coating material.

(Prior Art) A so-called tapping method is generally used in which an optical fiber base material is softened in a heating furnace and continuously drawn through a drawing die to form an optical fiber, and the optical fiber is passed through an open die and coated. This method has the disadvantage that when the linear speed becomes high, slippage occurs between the optical fiber and the coating material in the die, resulting in intermittent coating or failure to obtain a predetermined coating thickness.

To avoid this, a pressurized coating device has been proposed that forcibly extrudes the coating material in the same direction as the running direction of the optical fiber. This coating device consists of a nipple through which the optical fiber passes, and a tie that is arranged concentrically with the nipple and extrudes a coating material applied to the optical fiber 1- which exits the nipple so as to coat it with a predetermined thickness. but.

In prior art coating devices of this type, depending on the pressurizing conditions, the coating material may flow backwards through the outlet of the nipple, causing overflow and significantly deteriorating the appearance of the coating. That is, when the optical fiber runs at high speed, slipping occurs between the optical fiber and the overflow, causing uneven coating on the surface of the optical fiber as it passes through the outlet of the nipple, and optical fiber with a high temperature of 100°C or more rushing into the overflow, causing the optical fiber to slip. The appearance becomes unstable both because the temperature of the overflow rises near the driving position and because of this.

(Object of the Invention) An object of the present invention is to provide an optical fiber coating device that can obtain a coating with a good appearance even if overflow occurs within the nipple.

(Structure of the Invention) The optical fiber coating device of the present invention is characterized by having a suction port for sucking up the overflow liquid of the coating material in the nipple. According to such a device, even if the coating material moves backward in the nipple and overflows, this overflow liquid is absorbed by the suction [1], so the liquid level of the overflow liquid becomes smaller and the unevenness of the coating is reduced. This does not occur and the appearance of the coating can be improved.

(Example) An example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an optical fiber coating device 10 according to the present invention,
As shown in FIG. 1, this coating device 10 includes a nipple 14 through which the optical fiber 12 passes, and a ## that is placed integrally and concentrically with this nipple 14 and pressurized onto the optical fiber 12 coming out from the outlet of the nipple 14. The die 18 covers the covering material 16 to a predetermined thickness.

A suction port 20 is provided in the nipple 14 close to the nipple outlet 14a for sucking up overflow liquid 16a generated when the coating material 16 therein flows backward from the nipple outlet 14a. In the illustrated embodiment, the suction ports 20 are provided at the tips of a plurality of suction pipes 22 extending along the inner inclined surface of the nipple 14. When such a suction port 20 is provided, the overflow liquid 16a is sucked from the suction port 20, so that the liquid level of the overflow liquid 14a increases. There will be no uneven coating due to

Next, specific examples of the present invention will be described together with comparative examples.

Using a natural fused silica rod with an outer diameter of 25 mm as the optical fiber base material, an optical fiber with an outer diameter of 125#Lm was formed at a drawing temperature of 2100°C, and this optical fiber was formed into a fiber with a nipple exit diameter of 0.4 mm and a die hole diameter of 0.4 mm. Using a 5mm coating device, apply one layer of UV curable resin at a resin pressure of 31Cg/cm”
The coating was carried out at a line speed of 200 m/min. Figure 2 shows the state of nine movements of the outer diameter of the coating when no suction port is provided for the overflow liquid as in the conventional case.As can be seen from this figure, the outer diameter of the coating fluctuates widely and is within the range of ±lOILm. The overflow liquid fills the inside of the nipple and the liquid level reaches 100
mm and was confirmed to overflow from the northern part of the nipple. On the other hand, Figure 3 shows the outer diameter of the coating in the case of the present invention, in which the suction port is arranged so that the overflow liquid is 12 mm, and the overflow liquid is continuously sucked out.The outer diameter is as small as ±27 mm at the maximum. The coating appearance was good.0 The difference between the present invention and the conventional one is the difference in the liquid level of the overflow liquid.The reason why this height difference appears as a difference in the coating appearance is as follows. I think that the. That is, the slippage between the optical fiber and the coating is treated as peeling of the boundary layer from a hydrodynamic point of view, and if peeling occurs, a thin slipstream is created downstream, increasing the shape resistance.

Therefore, when the overflow liquid level is high, the length over which peeling occurs is large, and the optical fiber runs longer in the thin air than when the overflow liquid level is low, which tends to make the optical fiber run unstable, and the resistance increases. As a result, the coating is not uniformly applied.

4 and 5 show other different embodiments of the invention.

In the embodiment of FIG. 4, an overflow liquid suction passage 22' is provided through the wall of the nipple 14, so that in this embodiment the suction port 20 opens at the outlet 14a of the nipple 14. In the embodiment shown in FIG. 5, an overflow liquid suction passage 22' passes through the nipple 14 and the die 18 so as to cross the same, and its suction port 20 opens directly above the outlet 14a of the nipple 14. . In these examples, the liquid level height of the overflow liquid 16a becomes even smaller, so that the coating appearance becomes even better.

(Effects of the Invention) According to the present invention, as described above, there is a practical benefit that the overflow liquid flowing backward through the nipple is reduced, so that the appearance of the coating can be improved.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an optical fiber coating device according to the present invention, and FIGS.
4 and 5 are longitudinal cross-sectional views of main parts of other different embodiments of the present invention. 10---- Optical fiber coating device, 12------
Optical fiber, 14------nipple, 16---
--Covering material, 18--Die, 20-1--Suction port. Figure 1C

Claims (1)

[Claims] An optical fiber coating device comprising a nipple through which an optical fiber passes and a die that coats the optical fiber passing through the nipple with a pressurized coating material to a predetermined thickness, the optical fiber coating device having a suction port for sucking up overflow liquid of the coating material in the nipple. An optical fiber coating device characterized by: