JPH05213636A - Method for coating optical fiber - Google Patents

Abstract

PURPOSE:To improve the fiber forming linear velocity by applying an UV curing resin around an optical fiber and then keeping the optical fiber at a specified temp. by the multiple UV lamps from the second lamp onward to cure the resin. CONSTITUTION:An optical fiber preform 2 is melted and spun at a specified rate by a heating furnace 1 to form an optical fiber, and the optical fiber 3 is passed through a cooler 4 and cooled to 50-80 deg.C. The optical fiber 3 is then passed through a first coating die 5 contg. an UV curing resin soln. and coated with a primer layer. The coated optical fiber is then passed through a first UV lamp device 7 and cooled by gaseous N2 and H2 from nozzles 11 and 12, and the primer layer is cured to obtain a coated optical fiber 6. The coated optical fiber 6 is then passed through a second coating die 9 contg. an UV curing resin at 50-80 deg.C to coat the coated optical fiber 6 with a secondary layer and then passed through a second UV lamp device 10, and hence the secondary layer is cured to obtain a coated optical fiber 8 which is wound on a receiving roll 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a resin coating on an optical fiber, and more particularly to a method for forming a resin coating capable of increasing the spinning linear velocity of an optical fiber.

[0002]

2. Description of the Related Art An optical fiber bare wire formed by drawing an optical fiber preform in a heating furnace is a very thin fiber having an outer diameter of about 100 to 150 μm, and therefore is very weak unless coated.
It breaks with a tensile load of about 100 g. This is because glass, unlike metal, is a material that exhibits brittle fracture, so if microscopic defects grow on the surface of bare optical fiber and local stress concentration occurs in that area, it will cause fracture. Is. Therefore, for the purpose of protecting the surface of the bare optical fiber, improving tensile strength and bending strength, and making it easier to handle, it is widely practiced to coat the bare optical fiber with a resin.

The coating is roughly classified into a primary coating made of a resin such as silicone or urethane for strengthening the optical fiber, and a nylon or polyethylene coated on the primary coating for easy handling. There is a second coating.
Furthermore, the primary coating is usually made up of two layers, and the inner layer (primary layer) uses a modified silicone resin having a large refractive index for absorbing light leaked from the clad. Resin is often used. Ordinary silicone resin or the like is used for the outer layer (secondary layer), but recently, UV curable resin is also often used.

These coatings are carried out after drawing the optical fiber preform in a heating furnace to form a bare optical fiber. In the drawing of the optical fiber preform, sufficient care has been taken to prevent microscopic scratches on the surface of the bare optical fiber, but it is impossible to eliminate all surface defects.
It is necessary to coat the surface of the bare optical fiber as quickly as possible so that minute defects do not become large in response to moisture in the air.

Therefore, in the manufacture of optical fibers,
Following wire drawing, primary coating is performed in the same process. That is, in order to form a resin coating of a UV curable resin on an optical fiber, the optical fiber is placed in a drawing furnace, a bare optical fiber having a predetermined diameter is drawn, and then the optical fiber outer peripheral surface is directly passed through a coating die. A method of applying a UV curable resin and irradiating the applied resin with UV to cure the resin is repeated twice and then wound.

On the other hand, in order to reduce the manufacturing cost of the optical fiber, it is necessary to increase the spinning linear velocity. However, if the spinning linear velocity is increased, the coating material curing step time is shortened. The degree of cure is insufficient. Therefore, it is necessary to connect a plurality of UV lamps for curing the coating material (multi-lighting).

[0007]

However, a sufficient degree of curing of the coating material cannot be obtained by simply increasing the number of UV lamps. FIG. 2 shows the relationship between the spinning linear velocity of the optical fiber and the degree of curing of the coating material when the number of UV lamps is 2 (white circles) or 4 (black circles). It can be seen that when the spinning linear velocity of the optical fiber is doubled, even if the number of UV lamps is doubled, the same degree of curing degree of the coating material cannot be obtained.

As described above, the reason why the curing degree of the coating material is low even when using a multi-lamp UV lamp is that the curing of the UV resin is an exothermic reaction. It was thought that the temperature would rise. Therefore, the present inventor investigated the relationship between the fiber temperature at the entrance of the second UV lamp and the Young's modulus of the coating material. As a result, UV lamp 2
It was found that the incoming line temperature after the eyes should be 80 ° C. or lower.

The present invention has been made in view of the above circumstances, and provides a method for controlling the incoming line temperature of the second and subsequent UV lamps to be 80 ° C. or lower.

[0010]

The method for forming a coating according to the present invention, in addition to nitrogen gas, which is usually introduced as an inert gas into a UV lamp used in a coating material curing step, has a high thermal conductivity. The introduction of gas as a cooling gas was taken as a means for solving the above problems.

[0011]

The present invention will be described in detail below. FIG. 1 is a schematic configuration diagram showing an example of the manufacturing apparatus of the present invention. In the figure, reference numeral 1 is a heating furnace for heating and melting the optical fiber preform 2. Below the heating furnace 1, a cooling device 4 for cooling the bare optical fiber 3 is provided. Further, below the optical fiber bare wire 3 cooled by the cooling device 4, the first coating die 5 for applying the UV resin as the primary layer and the applied primary layer are cured,
First UV lamp device 7 for obtaining optical fiber strand 6
Is provided. Subsequently, a second coating die 9 for coating the secondary layer in the same manner to form the optical fiber core wire 8
And a second UV lamp device 10 is provided.

First and second UV lamp devices 7, 10
Each has a multi-lamp structure in which a plurality of UV lamps are arranged in a row along the traveling direction of the optical fiber. Further, in this UV lamp device, in addition to the nozzle 11 for introducing the nitrogen gas, a plurality of nozzles 12 for introducing the cooling gas are provided so as to surround the optical fiber, whereby the optical fiber is used after the second lamp. The surface temperature of the coating material can be kept low. Further, in order to monitor the surface temperature of the optical fiber with the second UV lamp, the second UV lamp is provided with a temperature measuring device (not shown) using infrared rays.
Further, a take-up roll 13 is provided below these.

To manufacture an optical fiber using the manufacturing apparatus as shown in FIG. 1, the following steps are performed. First, the optical fiber preform 2 is prepared, and this is heated in the heating furnace 1 to 500 to 80
The bare optical fiber 3 is formed by melt spinning at a speed of 0 m / min, and the bare optical fiber 3 is inserted into the cooling device 4 to reach 50 to 80 ° C. Next, the cooled optical fiber bare wire 3 is inserted through the first coating die 5 in which the UV resin solution serving as the primary layer at 40 to 60 ° C. is stored, and the primary layer is provided on the surface of the bare optical fiber 3. Coating the first UV lamp device 7
And the primary layer on the surface is cured to form the optical fiber element wire 6. Then, the cooled optical fiber element wire 6 is inserted into the second coating die 9 in which the UV resin solution serving as the secondary layer at 40 to 60 ° C. is stored, and the secondary layer is formed on the surface of the optical fiber element wire 6. Second UV coating
It is inserted into the lamp device 10, the secondary layer on the surface is cured to form the optical fiber core wire 8, and the optical fiber core wire 8 is wound by a take-up roll 13.

In the present invention, the UV lamp devices 7 and 10 described above are used.
Nitrogen gas is introduced from the nozzle 11 and cooling gas is introduced from the nozzle 12 into the respective UV lamps. Then, while adjusting these flow rates, the entry temperature after the second UV lamp is set to 80 ° C. or lower, preferably 20 to 50 ° C. The flow rate of the cooling gas is preferably as low as possible. This is because when the amount of the cooling gas is increased, the fluctuation of the coat diameter due to the line deviation becomes large and the variation of the lateral pressure characteristic of the optical fiber core becomes large. If the cooling gas used has a high thermal conductivity, a sufficient cooling effect can be obtained even at a low flow rate. Therefore, as the cooling gas, an inert gas having a high thermal conductivity such as helium is preferable. .

Example 1 A SM type optical fiber base material was melt-spun to obtain a bare SM type optical fiber having an outer diameter of 125 μm. At the same time, as a primary layer and a secondary layer, a urethane acrylate-based UV curable resin is coated to give an outer diameter of 2
An optical fiber core of 50 μm was obtained. At this time, the second UV lamp device 10 for curing the secondary layer is set to 4 lamps, and the flow rate from the nozzle 11 is set to 5 in the UV lamps.
Nitrogen gas at a rate of 1 l / min and helium gas at a flow rate of 5 l / min were introduced from the nozzle 12. Then, the spinning linear velocity of the optical fiber was changed to a standard linear velocity of 150 m / min and 2 times, 4 times and 8 times the standard linear velocity, and the Young's modulus of each secondary material was examined. The results are indicated by triangles in FIG.

(Comparative Example 1) In Example 1, the second U
The secondary layer was cured without introducing helium gas into the four UV lamps of the V lamp device 10. Others were the same as in Example 1. The results are shown by black circles in FIG. (Comparative Example 2) In Example 1, the number of the second UV lamp device 10 was changed to two, and the secondary layer was cured without introducing helium gas into the UV lamp. Others are Example 1
It carried out similarly to. The results are shown by white circles in FIG. From the results of FIG. 2, the Young's modulus of the secondary layer of the optical fiber obtained by introducing the helium gas and curing the helium gas obtained in Example 1 (4 lamps) was found to be a comparative example even if the spinning linear velocity was doubled from the standard. The value of Young's modulus at the same level as the value at the standard spinning linear velocity of 2 (2 lights) was shown.

(Example 2) In Example 1, the spinning linear velocity of the optical fiber and the type and flow rate of the gas introduced into the UV lamp were changed to change the incoming temperature of the optical fiber.
Others were the same as in Example 1. The result is shown in FIG. From the results of FIG. 3, in any case, when the fiber temperature at the second light inlet exceeded 80 ° C., the Young's modulus of the secondary layer was decreased. From this result, it was confirmed that the incoming line temperature after the second UV lamp should be 80 ° C. or lower.

In all of the above examples, the cooling gas is introduced into the UV lamp for curing the secondary layer, but even if the cooling gas is introduced into the UV lamp for curing the primary layer. The same effect can be obtained.

[0019]

As described above, according to the coating forming method of the present invention, after the UV curable resin is applied to the outer peripheral surface of the optical fiber, the UV curable resin is cured by using the UV lamp device of multiple lights, In addition, the surface temperature of the optical fiber in the second and subsequent UV lamps of the above-mentioned multi-lamp UV lamp device is maintained at 80 ° C. or lower by introducing the cooling gas. Therefore, since the curing reaction of the UV curable resin in the second and subsequent UV lamps is promoted, the degree of curing of the coating material can be improved, and an optical fiber having excellent lateral pressure characteristics and reliability can be manufactured.
It is also an effective method for increasing the spinning linear velocity.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber manufacturing apparatus of the present invention.

FIG. 2 is a graph showing the relationship between the spinning linear velocity of the optical fiber and the Young's modulus of the secondary layer in the optical fibers obtained in Example 1 of the present invention and Comparative Examples 1 and 2.

FIG. 3 is a graph showing the relationship between the optical fiber temperature at the second entrance of the UV lamp and the Young's modulus of the secondary layer, which was obtained in Example 2.

[Explanation of symbols]

3 ... Bare optical fiber 5 ... Primary layer coating die, 7 ... Primary layer curing UV lamp 9 ... Secondary layer coating die, 10 ... Secondary layer curing UV lamp

Claims (1)

[Claims] 1. A coating forming method for forming a coating made of a UV curable resin on an optical fiber, wherein a UV curable resin is applied to an outer peripheral surface of a bare optical fiber and then UV cured by using a multi-lamp UV lamp device. The coating of the optical fiber, characterized in that the mold resin is cured and the surface temperature of the optical fiber of the second and subsequent UV lamps of the multi-lamp UV lamp device is maintained at 80 ° C. or lower by introducing a cooling gas. Forming method.