JPH10338549A - Method for coating optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for coating an optical fiber by which the fiber is drawn while being stably coated. SOLUTION: The method for coating an optical fiber consists in coating the optical fiber 3 drawn from an optical fiber preform 1 with a resin to form a primary coated fiber 3a and then coating the primary coated fiber 3a with a resin to form a secondary coated fiber 3b. In this case, the primary coated fiber 3a is heated by a heater 9, then the secondary coated fiber 3b is formed, and the diameter of the secondary coat is controlled by the heating temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for coating an optical fiber.

[0002]

2. Description of the Related Art A conventional method of coating an optical fiber with a UV-curable resin will be described with reference to FIG. In the drawing, 1 is an optical fiber preform, 2 is a drawing furnace, 3 is an optical fiber, 4a and 4b are supplied to a cooling device, 5a and 5b are supplied to a resin coating device, and 6a and 6b are supplied to a resin coating device 5a and 5b. Ultraviolet curing resin, 7a and 7b are resin curing devices, and 8 is a winding machine. In FIG. 3, an optical fiber 3 drawn by a drawing furnace 2 passes through a cooling device 4a. This cooling device 4a
Is for cooling the high-temperature optical fiber 3 immediately after drawing to a temperature at which the resin can be covered with a resin, and is, for example, composed of a cooling tube in which He gas having good heat conductivity flows. The optical fiber 3 is coated with a resin for primary coating which serves as a buffer layer against external force by a resin coating device 5a. The primary coating diameter of the primary coated fiber 3a is adjusted by adjusting the temperature of the optical fiber 3 entering the coating device 5a by the cooling device 4a, or by adjusting the temperatures of the coating device 5a and the ultraviolet curable resin 6a. Will be Specifically, H of the cooling device 4a
e To increase the gas amount to lower the temperature of the optical fiber 3, or to raise the temperature of the coating device 5a and the ultraviolet curable resin 6a (in other words, to reduce the degree of the temperature drop of the optical fiber during the primary coating). Thereby, the primary coating diameter can be increased. Further, the amount of He gas is reduced to reduce the degree of temperature decrease of the optical fiber by the cooling device 4a, or to lower the temperature of the coating device 5a and the ultraviolet curable resin 6a (in other words, the temperature of the optical fiber at the time of primary coating). The primary coating diameter can be reduced by increasing the temperature drop). The primary coating fiber 3a is coated with a secondary coating resin by a secondary coating resin coating device 5b. When the primary coating layer is cured by the resin curing device 7a, the reaction heat of the ultraviolet curing resin 6a and the radiation heat from the resin curing device 7a increase the temperature of the primary coating fiber 3a. The coating diameter is adjusted by controlling the degree to which the temperature of the primary coated fiber 3a is cooled using the cooling device 4b, and controlling the temperatures of the resin coating device 5b for secondary coating and the ultraviolet curable resin 6b.

[0003]

In the optical fiber manufacturing process, with the rapid increase in demand in recent years, it is desired to improve the productivity by increasing the drawing speed. However, when the drawing speed is increased, there is a problem that the fluctuation of the resin coating diameter of the optical fiber rapidly increases at a certain drawing speed or the resin cannot be coated.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems. An optical fiber drawn from an optical fiber preform is provided with a primary coating, and then the optical fiber having the primary coating is provided. In the method of coating an optical fiber for applying a secondary coating to the optical fiber, the secondary coating is applied to the optical fiber which has been subjected to the primary coating while heating the optical fiber, and the coating diameter of the secondary coating is controlled by the heating temperature. It is characterized by the following.

[0005] When the drawing speed is increased, the fluctuation of the resin coating diameter of the optical fiber at a certain drawing speed sharply increases or the resin cannot be coated. This is considered to be because the shear rate of the resin exceeds the critical shear rate, the flow of the resin in the die becomes unstable, and stable coating cannot be performed. Therefore, in order to perform resin coating at a high speed, it is sufficient that the shear rate of the resin does not exceed the critical shear rate even in high-speed drawing.
Here, the critical shear rate of the resin is specific to the resin. It means a shearing speed at which the drawing speed is increased and the shearing speed is increased, and the resin viscosity is reduced. By the way, the shear rate η of the resin is given by the following equation in high-speed drawing. η∝V / Rf / log (Rd / Rf) (1) Here, V: drawing speed Rf: radius of optical fiber Rd: radius of die hole From equation (1), even if drawing speed V is increased, Shear rate η
In order to prevent the critical shear rate from being exceeded by reducing the increase in the diameter, the radius Rd of the die hole should be increased. The present invention has been made based on such a background. As described above, if the die hole radius Rd is increased, the shear rate η does not exceed the critical shear rate even when the drawing rate V is increased, and good resin coating can be performed. However, when the diameter of the die hole is increased, the diameter of the resin coating also increases. Therefore, it is necessary to control the diameter of the resin coating so as not to increase.
Therefore, as in the present invention, when the secondary coating is applied to the primary-coated optical fiber in a positively heated state, the temperature drop of the primary-coated fiber can be increased during the secondary coating, so that the coating diameter is reduced. It can be controlled small.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the figure, the same parts as those described with reference to FIG. 3 are designated by the same reference numerals. (Embodiment 1) FIG. 1 shows an apparatus used in an embodiment of an optical fiber coating method according to the present invention. The apparatus of this embodiment is characterized by a primary coating resin curing apparatus 7a and a secondary coating resin curing apparatus 7a. The point is that the heating device 9 is provided between the heating device 9 and the resin coating device 5b. The method for coating the optical fiber of the present embodiment is as follows. 1) First, an outer diameter of 125 μm drawn from the optical fiber preform 1
m of the optical fiber 3 is passed through the coating device 5a to apply the primary coating resin, and then is passed through the resin curing device 7a to have an outer diameter of 19 mm.
A primary coated fiber 3a of 0 μm is formed. 2) Next, the primary coated fiber 3a is 300 mm in length.
Is heated by a heating device 9 using an infrared lamp, and the secondary coated fiber 3 is passed through a secondary coating device 5b and a resin curing device 7b having a die hole diameter of φ0.30 mm and a resin temperature of 40 ° C.
b is formed. At this time, the heating device 9 changes the internal temperature in the range from room temperature to 1000 ° C. by adjusting the lamp output, and controls the temperature of the primary coated fiber 3a entering the secondary coating device 5b. The lamp output of the heating device 9 was adjusted by such a method so that the outer diameter of the secondary coated fiber 3b became a specified value (245 μm to 250 μm), and the secondary coating was performed.
Even if the drawing speed was increased to 1200 m / min, a good secondary coating could be applied. In the present embodiment, the heating device 9 may use a UV lamp instead of the infrared lamp.

(Embodiment 2) This embodiment is different from Embodiment 1 in that the lamp output of the heating device 9 is adjusted to keep the internal temperature at a constant temperature of about 600 ° C. By changing the distance from the device 5b, the secondary coating device 5b
The temperature of the primary coated fiber 3a to be entered is adjusted. Also in the present embodiment, 1200 m / mi as in the first embodiment.
By increasing the drawing speed to n, a good secondary coating could be applied.

(Embodiment 3) FIG. 2 is a partial explanatory view of an apparatus used in a third embodiment, and shows a heating device 19.
Parts other than the heating device 19 are the same as those in FIG. In the present embodiment, the heating device 19 is a device for flowing He gas heated to about 150 ° C. by the heater 19c into the cylinder 19b heated to about 100 ° C. by the resistance heater or the heater 19a of the high-frequency induction coil. In this heating device 19,
The temperature of the primary coated fiber 3a can be adjusted by adjusting the amount of He gas or the temperature of He gas. Also in the present embodiment, similar to the first embodiment, the drawing speed was increased to 1200 m / min, and a good secondary coating could be applied.

In the case where the secondary coating is performed by the secondary coating device 5b having the hole diameter of the die of φ0.28 mm by the apparatus shown in FIG. In order to apply the next coating, the drawing speed is set to 1000 m / mi.
n or less.

[0010]

According to the present invention, there is an excellent effect that high-speed drawing can be performed while performing stable coating.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus used for an embodiment of an optical fiber coating method according to the present invention.

FIG. 2 is a partial explanatory view of an apparatus used in another embodiment.

FIG. 3 is an explanatory view of a conventional optical fiber coating method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber preform 2 Drawing furnace 3 Optical fiber 3a Primary coating fiber 3b Secondary coating fiber 4a, 4b Cooling device 5a, 5b Resin coating device 6a, 6b Ultraviolet curing resin 7a, 7b Resin curing device 8 Winding machine 9 , 19 Heating device 19a Heater 19b Tube 19c Heater

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Sakata 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd.

Claims (1)

[Claims] An optical fiber coating method comprising: applying a primary coating to an optical fiber drawn from an optical fiber preform; and then applying a secondary coating to the optical fiber provided with the primary coating.
A method for coating an optical fiber, comprising: applying a secondary coating while heating an optical fiber to which a primary coating has been applied, and controlling a coating diameter of the secondary coating by the heating temperature.