JPH0629157B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline of the Invention] An optical fiber base material is heated, melted and stretched into an optical fiber, passed through a coating die filled with a liquid resin as a coating material, and then the liquid resin is cured by a curing device. In the manufacturing process, the temperature of the liquid resin of the coating material, which is coated near the surface of the optical fiber, is lower than that of the other parts to offset the increase in the optical fiber temperature when the drawing speed is increased. , A method for producing an optical fiber in which the viscosity of the liquid resin in the die is prevented from decreasing near the surface of the optical fiber and the increase in the velocity gradient (shear rate) of the liquid resin near the surface of the optical fiber is suppressed.

[Industrial application field]

The present invention relates to a method for producing an optical fiber, and more particularly to a method for uniformly coating a coating material resin at a high speed in a drawing process.

[Conventional technology]

FIG. 6 shows a drawing for explaining a conventional fiber drawing process. 1 is an optical fiber base material, 2 is a drawing furnace, 3 is an optical fiber, 4 is a liquid resin, 5 is a coating die, 6 is a curing device for curing the coated liquid resin, 7 is a coated optical fiber, and 8 is winding. It is a machine. The optical fiber having high strength is coated with the coating material of the liquid resin 4 such as the silicone resin or the acrylate resin through the coating die 5 immediately after the optical fiber base material 1 is heated and melted and drawn by the manufacturing process as shown in FIG. Then, it is cured by the curing device 6 to obtain a coated optical fiber 7.

With the rapid increase in the demand for optical fibers, low-cost production is required, and it is important for the drawing process to have high productivity, that is, high-speed drawing. However, in the conventional method, the upper limit of the drawing speed (hereinafter referred to as the drawing speed) with which the liquid resin can be coated stably and uniformly is very low. The reason for this is that as the linear velocity increases, it takes a shorter time for the optical fiber to reach the coating die from the heating and melting state, and the temperature of the optical fiber entering the coating die rises.

Fig. 7 shows an example of the measured relationship between the linear velocity and the optical fiber temperature when an optical fiber with an outer diameter of 125 µm is drawn with a distance of 3.5 m between the drawing furnace 2 and the coating die 5 in Fig. 6. Is. As can be seen from this actual measurement example, the linear velocity at which the UV-curable acrylic resin used as the liquid resin for the covering material can be stably coated by the conventional method is about 150 at maximum.
It was m / min. As a method of improving the maximum drawing speed, the optical fiber can be increased by increasing the distance between the conventional drawing furnace and the coating die to increase the natural air-cooling distance, or by lowering the ambient temperature between the drawing furnace and the coating die. The method of lowering the temperature of is taken.

[Problems to be solved by the invention]

The conventional method of increasing the maximum linear velocity has a problem that the equipment price becomes high, the workability is poor, and the manufacturing becomes unstable.

[Means for solving problems]

In order to solve the conventional problems, the present invention heat-melts and stretches an optical fiber base material into an optical fiber, and after passing through a coating die filled with a liquid resin as a coating material, the liquid resin is cured by a curing device. In the manufacturing process of, the step of coating the liquid resin on the optical fiber, the temperature of the liquid resin coated near the surface of the optical fiber,
The method is characterized by including a step of lowering the temperature of the liquid resin coated on the outer peripheral portion.

[Action]

It will be described below that the configuration of the present invention can easily improve the upper limit of the linear velocity at which the optical fiber can be stably coated.

In the conventional optical fiber drawing process of this type, the reason why the coating becomes unstable when the optical fiber temperature rises at a high linear velocity has not been sufficiently clarified at present, but the following theory is considered. ing.

Generally, the higher the temperature is, the lower the viscosity of the liquid resin becomes. Therefore, as shown in FIG. 8, when the temperature of the optical fiber and the liquid resin are the same at low speed, the temperature distribution of the liquid resin in the coating die is small. , The viscosity distribution is constant,
When the linear velocity becomes high and the optical fiber temperature becomes higher than the liquid resin temperature, the liquid resin temperature near the surface of the optical fiber rises, and accordingly, the viscosity of the liquid resin near the surface of the optical fiber decreases. When viscosity distribution occurs in the liquid resin in the coating die,
The flow state of the liquid resin changes greatly, and in the case of a distribution where the liquid resin viscosity near the surface of the optical fiber is reduced at high linear velocity, as shown in Fig. 9, it is closer to the surface of the optical fiber than at low linear velocity. The liquid resin has a large velocity gradient (hereinafter referred to as a shear velocity). If the shear rate exceeds a certain value, the liquid resin slips near the surface of the optical fiber, resulting in non-uniform coating.

In the present invention, only the portion of the liquid resin to be coated near the surface of the optical fiber is coated, and the temperature is made lower than the other portions to offset the increase in the optical fiber temperature at the time of increasing the linear velocity, thereby making the inside of the coating die. This prevents the viscosity of the liquid resin from decreasing near the surface of the optical fiber and suppresses the increase in the shear rate of the liquid resin near the surface of the optical fiber. Embodiments will be described below with reference to the drawings.

〔Example〕

FIG. 1 shows the first step of the liquid resin coating process according to the present invention.
It is a figure explaining the Example of this. 3 is an optical fiber, 4 is a liquid resin, 9 and 10 are a cooler 11 and a heater 12, respectively.
Temperature controller to adjust the temperature to the temperature T ₁ and T _2, 13 denotes inlet of the introduction holes for introducing the optical fiber 3 to 14 Cote queuing die (hereinafter dice referred.) (Hereinafter point called.). Here, the temperatures T ₁ and T ₂ are T ₁ <T ₂ .
In this embodiment, the temperature of the point 13 of the die 14 for introducing the optical fiber 3 is lowered to T _1, and the temperature of the liquid resin 4 supplied from the resin supply device near the surface of the optical fiber 3 is set to T ₁ . The step of lowering and lowering the temperature below the temperature T ₂ of the liquid resin 4 for coating the other portion of the optical fiber 3 led out from the die 14 is used.

FIG. 2 shows the second step of the liquid resin coating process according to the present invention.
It is a figure explaining the Example of this. 3 is an optical fiber, 13 is a point, 4'and 4 "are temperatures T ₁ and T _2, respectively.
In the liquid resin held at, T ₁ <T ₂ , 15 and 16 are dies for coating the liquid resins 4 ′ and 4 ″, respectively.
Separately, liquid resin 4'having a temperature T ₁ and liquid resin 4 "having a temperature T ₂
Is used to lower the temperature of the coating liquid resin in the vicinity of the surface of the optical fiber 3 below the temperature of the coating liquid resin in the outer peripheral portion.

In the case of the first embodiment shown in FIG. 1, as shown in FIG. 3, the temperature distribution of the liquid resin 4 in the die 14 keeps the temperature rise near the optical fiber surface low even during high speed drawing. Therefore, the viscosity does not decrease as compared with the vicinity of the die wall surface (outer peripheral portion), and the liquid resin 4 in the die 14
As shown in FIG. 4, the flow velocity distribution of No. 1 does not cause coating destabilization due to an extremely large shear rate near the surface of the optical fiber even at high speed. It is preferable that the temperature of the liquid resin supplied near the surface of the optical fiber is constant, or it is lowered as the temperature of the optical fiber increases due to the increase in linear velocity. It is desirable that the temperature near the surface of the optical fiber in the die does not always rise above the temperature of other peripheral portions. If the method of changing the temperature of the liquid resin according to the change of the linear velocity, that is, the change of the optical fiber temperature, it is possible to reduce the change of the flow velocity distribution shape of the liquid resin in the die due to the linear velocity. It was confirmed that the speed dependency was small, uniform high-speed coating was possible, practically easy lead-out work was performed, and the amount of defective scraps could be reduced. Next, specific examples will be shown.

Example 1: An optical fiber having an outer diameter of 125 μm was drawn by using a drawing machine having a distance of 3.5 m between a drawing furnace and a coating die, and an ultraviolet curable silicone resin was prepared by the apparatus having the configuration shown in FIG. Coated When the temperature T _{1 of the} point 13 and the temperature T _{2 of the} die 14 of the liquid resin 4 supplied from the resin were all set to the same 30 ° C., the maximum linear velocity for stable coating was about 140 m / min. , Point 1
When the temperature T ₁ of 3 was lowered to 5 ° C, the maximum linear velocity was 21
It increased to 0m / min and 1.5 times. Light fiber 3 at this time
The temperature at the inlet of the die 14 was 50 ° C.

Example 2: An optical fiber having an outer diameter of 125 μm was drawn by the same drawing machine as in Example 1 using the same apparatus as that of Example 1 shown in FIG. 1 and coated with an ultraviolet-curable acrylic resin. . The temperature of the die 14 is set to 50 ° C and the temperature of the point 13 is
According to the point temperature change curve for the linear velocity shown in Fig. 5, when the linear velocity is changed and the linear velocity is 240 m.
A uniform coating was obtained without a large change in outer diameter up to / min. When the temperature at point 13 was kept constant at 50 ° C., uniform coating was impossible at a linear velocity of 180 m / min or higher.

〔The invention's effect〕

As described above, according to the present invention, only the portion of the liquid resin for coating which is coated in the vicinity of the surface of the optical fiber is made lower in temperature than the other outer peripheral portions to offset the increase in the optical fiber temperature at the time of increasing the linear velocity. This prevents the viscosity of the liquid resin in the die from decreasing near the surface of the optical fiber, suppresses the increase in the shear rate of the liquid resin near the surface of the optical fiber, and sets the upper limit of the linear velocity that can stably coat the optical fiber. It can be easily improved and its effect is great.

[Brief description of drawings]

1 and 2 show the first and second aspects of the present invention, respectively.
FIG. 3 is a temperature and viscosity distribution of resin in a die according to the present invention, FIG. 4 is a flow velocity distribution of resin in a die according to the present invention, and FIG. 5 is a specific example of the present invention. A point temperature change curve in Example 2, FIG. 6 is an explanatory drawing of an optical fiber drawing process, FIG. 7 is a relationship between linear velocity and optical fiber temperature, and FIG. 8 is a temperature and viscosity of resin in a die in a conventional method. Distribution, FIG. 9 is a flow velocity distribution of the resin in the die in the conventional method. 1 ... Optical fiber base material, 2 ... Drawing furnace, 3 ... Optical fiber, 4,4 ′, 4 ″ ... Liquid resin, 5 ... Coating die, 6 ... Curing device, 7 ... Coating light Fiber, 8 ...
… Winding machine, 9,10 …… Temperature controller, 11 …… Cooler, 2 …… Heating device, 13 …… Point, 14,15,16 …… Dice

Claims (2)

[Claims] 1. An optical fiber base material is heat-melted and stretched to form an optical fiber, and the optical fiber is introduced from above an introduction hole of a coating die filled with a liquid resin, and the optical fiber of the coating die is An optical fiber for producing a coated optical fiber by leading out an optical fiber in a state in which the liquid resin is coated from a lead-out hole having an inner diameter larger than an outer diameter, and then passing the optical fiber through a curing device for curing the coating material made of the liquid resin. In the manufacturing method of, the step of coating the liquid resin on the optical fiber includes a step of lowering the temperature of the liquid resin coated near the surface of the optical fiber than the temperature of the liquid resin coated on the outer peripheral portion. A method for manufacturing an optical fiber, which is characterized in that 2. The optical fiber according to claim 1, wherein the temperature of the introduction hole for introducing the optical fiber of the coating die is lower than the average temperature of the liquid resin of the coating material. Production method.