JPS62153149A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To improve the upper limit of a linear velocity for stably coating an optical fiber, by reducing the temperature of a liquid resin to be coated in the vicinity of the surface of the optical fiber below the temperature of the liquid resin to be coated on the outer peripheral part. CONSTITUTION:A preform for an optical fiber is melt drawn while heating to give the optical fiber 4, which is then introduced from above an inlet port of a coating die 14 filled with a liquid resin 4 filled therein to lead the optical fiber 3 in a state coated with the liquid resin 4 from an outlet port having a larger diameter than the outside diameter of the optical fiber 3 of the coating die 14 and passed through a curing device to produce the aimed coated optical fiber 3. A cooler 11 and temperature controller 9 are provided on the inlet side of the coating die 14 and a heater 12 and temperature controller 10 are provided on the outlet side thereof to reduce the temperature (T1) of the liquid resin 4 to be coated in the vicinity of the surface of the optical fiber 3 below the temperature (T2) of the liquid resin 4 to be coated on the outer peripheral part thereof.

Description

[Detailed Description of the Invention] [Summary of the Invention] An optical fiber base material is heated, melted and drawn to form 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 only the part of the liquid resin that is coated near the surface of the optical fiber is lowered than that of the other parts, thereby offsetting the rise in the temperature of the optical fiber when the drawing speed increases. A method for manufacturing an optical fiber that prevents the viscosity of the liquid resin in the die from decreasing near the surface of the optical fiber and suppresses an increase in the velocity gradient (shear rate) of the liquid resin near the surface of the optical fiber.

[Industrial application field]

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

[Conventional technology]

Fig. 6 shows a diagram explaining the conventional optical 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, and 6 is a coating. A curing device for curing the liquid resin, 7 is a coated optical fiber, and 8 is a winder. A high-strength optical fiber is produced by coating the optical fiber base material 1 with a coating material of liquid resin 4 such as silicone resin or acrylate resin through a coating die 5 immediately after heating and melting and drawing the optical fiber base material 1 through the manufacturing process shown in FIG. Then, it is cured by a curing device 6 to obtain a coated optical fiber 7.

With the rapid increase in demand for optical fibers, low-cost production is required, and high productivity, that is, high-speed drawing, is also important in the drawing process. However, in conventional methods, the drawing speed (hereinafter referred to as "line speed") at which the liquid resin can be coated stably and uniformly has always been low. The reason for this is that as the linear speed increases, the time for the optical fiber to reach the coating die from a heated and molten state becomes shorter, and the temperature of the optical fiber entering the coating die increases.

Figure 7 shows the relationship between the drawing speed and the optical fiber temperature when an optical fiber with an outer diameter of 125 μm was drawn with a distance of 3.5 m between the drawing furnace 2 and the coating die 5 in Figure 6. This is an example. As can be seen from this actual measurement example, in the conventional method, the maximum linear speed at which the ultraviolet curing acrylic resin used as the liquid resin of the coating material could be stably coated was about 150 m/min. Conventional methods to increase this maximum drawing speed include widening the distance between the drawing furnace and coating die, increasing the natural air cooling distance, or lowering the ambient temperature between the drawing furnace and the coating die. Measures are being taken to lower the temperature of

[Problem that the invention seeks to solve]

Conventional methods for increasing the maximum linear speed have problems such as high equipment costs, poor workability, and unstable manufacturing.

[Means for solving problems]

In order to solve the conventional problems, the present invention heat-melts and draws an optical fiber base material to form an optical fiber, passes it through a coating die filled with liquid resin as a coating material, and then hardens the liquid resin using a curing device. In the manufacturing process of coating an optical fiber with liquid resin, the temperature of the liquid resin coated near the surface of the optical fiber is
It is characterized by including a step of lowering the temperature to a temperature lower than that of the liquid resin coated on the outer periphery.

[For production]

The following describes how the configuration of the present invention can easily increase the upper limit of the linear velocity that can be stably coated onto an optical fiber.

In the conventional optical fiber drawing process of this type, the reason why the coating becomes unstable when the optical fiber temperature rises at high drawing speeds has not yet been fully elucidated, but the following theories can be considered: ing.

In general, the viscosity of liquid resin decreases as the temperature increases, so if the temperature of the optical fiber and liquid resin match at low speeds, as shown in Figure 8, the temperature distribution of the liquid resin in the coating die Although 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 optical fiber surface increases, and therefore the liquid resin viscosity near the optical fiber surface decreases. When a viscosity distribution occurs in the liquid resin in the coating die, the flow state of the liquid resin changes significantly.At high linear speeds, if the viscosity of the liquid resin near the surface of the optical fiber has a reduced distribution,
As shown in Figure 9, the velocity gradient (hereinafter referred to as shear velocity) of the liquid resin near the surface of the optical fiber is higher than that at low linear speeds.
becomes larger.

When this shear rate exceeds a certain value, sliding of the liquid resin occurs near the surface of the optical fiber, resulting in non-uniform coating.

The present invention lowers the temperature of only the part of the liquid resin to be coated near the surface of the optical fiber compared to other parts to offset the rise in temperature of the optical fiber when the linear speed increases, thereby making it possible to reduce the temperature inside the coating die. This prevents the viscosity of the liquid resin from decreasing near the surface of the optical fiber, and suppresses an increase in the shear rate of the liquid resin near the surface of the optical fiber. Examples will be described below based on the drawings.

〔Example〕

Figure 1 shows the first step of the liquid resin coating process according to the present invention.
It is a figure explaining an example of. 3 is an optical fiber; 4 is a liquid resin; 9 and 10 are temperature controllers that adjust the temperatures of the cooler 11 and the heater 12 to temperatures T and T2, respectively;
Reference numeral 13 indicates an introduction port (hereinafter referred to as a point) of an introduction hole through which the optical fiber 3 is introduced into a coating die 14 (hereinafter referred to as a die).

Here, the temperatures T and L are T+ < T2. In this embodiment, the point 13 of the die 14 where the optical fiber 3 is introduced is
The temperature of the liquid resin 4 supplied from the resin supply device near the surface of the optical fiber 3 is lowered to T1.
A process is used in which the temperature is lowered to lower than the temperature T2 of the liquid resin 4 that coats the other portion of the optical fiber 3 led out from the die 14.

Figure 2 shows the second stage of the liquid resin coating process according to the present invention.
It is a figure explaining an example of. 3 is an optical fiber, 13 is a point, 4' and 4# are liquid resins whose temperature is maintained at T and T2, respectively.
indicate dies for coating liquid resins 4' and 4'', respectively. In this embodiment, liquid resin 4' at temperature T and liquid resin 4'' at temperature T are separately applied near the surface and outer periphery of optical fiber 3. A process is used in which the temperature of the coating liquid resin near the surface of the optical fiber 3 is lower than the temperature of the coating liquid resin at the outer circumference.

In the case of the first embodiment shown in FIG. 1, the temperature distribution of the liquid resin 4 in the die 14 is such that the rise in temperature near the surface of the optical fiber is kept low even during high-speed drawing, as shown in FIG. Therefore, the viscosity does not decrease compared to the vicinity of the die wall surface (outer circumference), and the flow velocity distribution of the liquid resin 4 inside the die 14 does not change to light even at high speeds, as shown in Fig. 4. No coating instability occurs due to extremely high shear rates near the fiber surface. It is preferable that the temperature of the liquid resin supplied near the surface of the optical fiber be kept constant or lowered as the temperature of the optical fiber increases due to the increase in linear velocity. Further, it is desirable that the temperature near the surface of the optical fiber within the die does not rise above the temperature of other surrounding areas. By changing the temperature of the liquid resin according to changes in the linear velocity, that is, changes in the optical fiber temperature, it is possible to reduce the change in the flow velocity distribution shape of the liquid resin in the die due to the linear velocity. sex is small;
It has been confirmed that this method has remarkable effects, such as enabling uniform high-speed coating, making the cutting work easier in practice, and reducing the amount of defective scraps. Next, specific examples will be shown.

Example 1: An optical fiber μ having an outer diameter of 125 μm was drawn using a wire drawing machine with a distance of 3.5 m between the drawing furnace and the coating die, and ultraviolet rays were applied using the apparatus shown in FIG. Coated with hardening silicone resin. Liquid resin 4 supplied from the resin supply resin is heated to temperature T at point 13 and die 1
When the temperature T2 in step 4 was all set to the same 30°C, the maximum linear speed that could be stably coated was approximately 140 m/m i
However, when the temperature T1 at point H3 was lowered to 5°C, the maximum linear speed was 210 m/min.
It rose 1.5 times. At this time, the temperature at the introduction port of the optical fiber 3 to the die 14 was 50°C.

Example 2: An optical fiber with an outer diameter of 125 μm was drawn using the same drawing machine as in Example 1 and the same configuration shown in FIG. 1 as in Example 1, and coated with an ultraviolet curable acrylic resin. . The temperature of the die 14 was set to 50°C, and the temperature at the point 13 was changed as the linear speed increased according to the point temperature change curve with respect to the linear speed shown in FIG.
A uniform coating was obtained with no large change in outer diameter up to 40 m/min. If the temperature at point 13 is kept constant at 50°C, the linear velocity is 180 m/m i
Uniform coating was impossible at n or more.

〔Effect of the invention〕

As described above, the present invention reduces the temperature of only the portion of the coating liquid resin coated near the surface of the optical fiber than the other peripheral portion, thereby offsetting the increase in the temperature of the optical fiber when the linear speed is increased. This prevents the viscosity of the liquid resin in the die from decreasing near the optical fiber surface, suppresses the increase in shear rate of the liquid resin near the optical fiber surface, and sets the upper limit of the linear speed at which the optical fiber can be stably coated. It can be easily improved and the effect is great.

[Brief explanation of drawings]

1 and 2 are the first and second embodiments of the present invention, respectively.
Fig. 3 shows the temperature and viscosity distribution of the resin in the die in the present invention, Fig. 4 shows the flow velocity distribution of the resin in the die in the present invention, and Fig. 5 shows a specific example of the present invention. Point temperature change curve in Example 2, Figure 6 is an explanatory diagram of the optical fiber drawing process, Figure 7 is the relationship between the drawing speed and optical fiber temperature, and Figure 8 is the temperature and viscosity of the resin in the die in the conventional method. Figure 9 shows the 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...
Coated optical fiber, 8... Winder, 9.10... Temperature controller, 11... Cooler, 2... Heater, 13... Point, 14.15.16... die patent applicant
Sumitomo Electric Industries Co., Ltd. Agent Patent Attorney Hisashi Tamamushi 5 Parts Illustrations explaining the main parts of the process of the first embodiment of the present invention 1 Fig. Illustrations explaining the main parts of the steps of the second embodiment of the invention 2 Fig. Optical fiber Surface Die wall surface Figure 3 Figure 4 Explanation of optical fiber drawing process Figure 6 Figure 7 Figure 8

Claims (2)

[Claims] (1) An optical fiber base material is heated and melted and drawn to form an optical fiber, and the optical fiber is introduced from above the introduction hole of a coating die filled with liquid resin, and the outer diameter of the optical fiber of the coating die is Manufacture of an optical fiber in which a coated optical fiber is manufactured by leading out the optical fiber coated with the liquid resin from a lead-out hole having a larger inner diameter and then passing it through a curing device that hardens the coating material made of the liquid resin. In the method, the step of coating the optical fiber with a liquid resin includes the step of making the temperature of the liquid resin coated near the surface of the optical fiber lower than the temperature of the liquid resin coated on the outer periphery. Characteristic optical fiber manufacturing method. (2) The method for manufacturing an optical fiber according to claim 1, characterized in that the temperature of the introduction hole of the coating die into which the optical fiber is introduced is lower than the average temperature of the liquid resin of the coating material. .