JPS597655B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber, and spinning methods for obtaining an optical fiber from a base material or raw material are broadly classified into a preform method and a double crucible method.

In the former method, a preform that will become a fiber is fed into a furnace at a certain speed, heated and softened, and the resulting fiber is drawn out. On the other hand, in the latter method, raw materials corresponding to the core and cladding constituting the optical fiber are supplied to a double crucible, and then drawn out and made into a fiber. The present invention relates to a method for applying a plastic material around the fibers obtained by both of these methods immediately after spinning and before contact with other solid materials.

It is said that when a glass material such as an optical fiber is exposed to the outside air after being heat-treated at a high temperature, for example, by spinning paper, microcracks and the like will grow on its surface due to moisture in the outside air.

In this way, an optical fiber with microcracks, etc. grown on its surface will break at a value much lower than the theoretical limit due to stress concentration in these cracks, as known from Griffith's theory, and the breaking strength will be determined by the growth of microcracks. Accordingly, it decreases over time. In particular, this becomes a serious problem when long-term reliability is required, such as in optical communication fibers. In order to prevent the growth of microcracks or a decrease in strength on the surface of an optical fiber, a plastic coat called a primary coat is applied.

The primary coat is a coating that protects the surface of the fiber with a plastic material before the fiber comes into contact with other solid materials immediately after spinning and before microcracks or the like grow on the surface of the fiber.

As the resin used for the primary coat, resins such as epoxy resin, silicone resin, polyester, polyurethane, polybutadiene, polyvinylidene fluoride, modified products thereof, or resin compositions made by mixing two or more of these resins are used.

Hereinafter, spinning by the preform method will be explained using figures. Figure 1 shows the basic configuration of a spinning machine.

Reference numeral 1 designates a base material that becomes a fiber, 2 a spinning furnace, 3 a fiber outer diameter measuring device, 4 a primary coating bed, 5 a baking furnace, 6 a guide roller, and 7 a winder.

As shown in FIG. 1, immediately after spinning, the fiber passes through a coating head 4 filled with resin and is baked in a baking furnace 5. The conventional method shown in FIG. 1 has the following problems.

Since No. 17 fiber is heated and spun at a high temperature of about 500 to 2100°C (depending on the composition of the base material), the fiber itself is also at a high temperature.

When such high temperature fibers are introduced into the coating head, the resin in the coating head decomposes and even burns, making it impossible to obtain a uniform and smooth coating. For this reason, methods have been used to lower the position of the coating head and to reduce the speed of the production line in order to ensure sufficient time for the fiber to cool down. 2. In order to make the obtained fiber outer diameter uniform, outer diameter control is performed by feeding back the measured value by the outer diameter measuring device 3 shown in FIG. 1 to the winding machine 7 (or not the capstan).

In this case, changes in production line speed due to control will cause the temperature of the fiber entering the coating head and the primary coating thickness to change from time to time. As described above, in the conventional method that is not based on the present invention, in addition to the drawback that it is not possible to increase the production line speed to ensure time for the fiber to cool down sufficiently, it is difficult to make the outer diameter of the fiber uniform. There was a problem that the coating thickness changed when controlling the outer diameter.

The present invention is intended to eliminate or improve these drawbacks, and relates to a method of dramatically increasing the production line speed and keeping the primary coat thickness constant while controlling the fiber outer diameter.

Figure 2 shows a schematic diagram of the equipment used to conduct experiments related to fiber cooling, with reference numeral 8 indicating the base material that will become the fiber, 9 indicating the spinning furnace,
10 is a fiber outer diameter measuring device, 11 is a fiber cooling device,
12 is a coating head, 13 is a baking furnace, 14 is a primary coat outer diameter measuring device, 15 is a guide roller, 16
1 is a winding machine, 17 is a gas flow rate adjustment valve, 18 is a gas heater,
19 is a liquefied gas container.

The device shown in FIG. 2 connects the device shown in FIG. A fiber cooling device 11 is added which cools the fiber using low-temperature gas via a filter 17.

Furthermore, a primary coat outer diameter measuring device 14 was attached to measure the outer diameter of the primary coat. While conducting experiments regarding fiber cooling shown in FIG. 2, the following phenomenon was discovered regarding fiber temperature and primary coat outer diameter (thickness).

In other words, the primary coat diameter is decreased by tightening the cooling gas flow rate regulating valve or raising the gas temperature by the gas heater 18, and the primary coat diameter is increased by performing the reverse operation. This phenomenon was discovered.

This phenomenon is explained as follows.

When a relatively high-temperature fiber enters the resin, the viscosity of the resin near the fiber decreases due to the fiber temperature, and the amount of resin adhering to the fiber decreases, resulting in a thinner primary coat. This can easily be explained from the daily experience that when a rod is inserted into a highly viscous liquid and pulled out, a large amount of liquid is pulled up along with the rod, whereas in a liquid with a low viscosity, almost no liquid sticks to it. It can be understood. In this way, by feeding the fiber into the fiber cooling device 11 and adjusting the low temperature gas flow rate or adjusting the low temperature gas temperature, a predetermined primary coat outer diameter (thickness) can be obtained.
can be obtained. It is also possible to perform automatic control to maintain the primary coat outer diameter constant by utilizing the above relationship between the fiber temperature and the primary coat outer diameter.

That is, a motorized valve is used as the low temperature gas flow rate adjustment valve 17 shown in FIG. 2, and the measured value from the primary coat outer diameter measuring device is fed back to the low temperature gas flow rate adjustment motorized valve to make the primary coat outer diameter uniform. is possible.
Yet another method is to apply feedback to the gas heater 1.
8 and may be automatically controlled by the gas temperature. It goes without saying that a method of providing feedback to both the flow rate regulating valve 17 and the gas heater 18 is also effective. By adjusting the temperature of the seven fibers described above and automatically controlling the outer diameter of the primary coat, the outer diameter of the primary coat can be adjusted to the required outer diameter of 165 μm on a fiber with an outer diameter of 150 μm.
On the other hand, a uniform fiber of 165±1 μm could be obtained. In the apparatus shown in FIG. 2, a base material 8 was spun into a glass fiber having a diameter of 150 μm in a spinning furnace 9, and a silicone resin was coated thereon by a coating head 12.
Liquid nitrogen was used as the liquefied gas, and was supplied from the liquefied gas container 19 through the heating device 18 to the cooling device 11 as a low-temperature gas of zero degrees Celsius, and the internal temperature of the cooling device was adjusted by the flow rate of the supplied low-temperature gas. .

By varying the low temperature gas flow rate from 2 to 501/min, the thickness of the silicone resin layer could be varied from 6 to 10 μm. However, when we conducted a similar experiment using air instead of liquid nitrogen, the thickness of the silicone resin layer hardly changed, and when we further increased the amount of air supplied, the outer diameter changed due to line wobbling, and the objective was not achieved. I couldn't do it.

Since this method adjusts or controls the outer diameter of the primary coat by adjusting the fiber temperature, it does not rely on heat curing or ultraviolet curing as a curing method for the primary coat, but instead uses the resin for the primary coat. It can be applied to all methods in which the viscosity of is temperature dependent.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional spinning machine, and FIG. 2 is a schematic diagram of a spinning machine according to the present invention. 1, 8... Base material; 2, 9... Spinning furnace;
3, 10... Outer diameter measuring device; 4, 12...
・Coating head; 5, 13... Baking furnace;
6, 15... Guide roller; 7, 16...
... Winding machine; 11 ... Cooling device; 18 ...
... Gas heater; 19 ... Liquefied gas container.

Claims (1)

[Claims] 1. In the process of introducing an optical fiber immediately after spinning into a cooling device that cools it with low-temperature gas generated by vaporizing liquefied gas before it comes into contact with other solid materials, and applying a plastic layer to the surface of the optical fiber, the cooling device A method for manufacturing an optical fiber, characterized by controlling the thickness of a plastic layer by adjusting temperature.