JPH02192437A - Coating method for optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention <Industrial Utilization Denominator> The present invention provides an optical fiber manufacturing method for manufacturing an optical fiber that exhibits transmission characteristics comparable to those at room temperature without increasing transmission loss even in an environment of use below 0°C. Relating to a coating method.

<Prior art> Optical fibers that transmit light, such as silica glass fibers, multicomponent glass fibers, and fluoride glass fibers, can be drawn into glass fibers and then immediately coated with a resin coating on the outer periphery. preferable. This is to prevent the fiber surface from being scratched or cracks growing due to exposure to air, thereby preventing the fiber from deteriorating.

As resins for this purpose, thermosetting silicon W resins, ultraviolet curing acrylate resins, etc. are generally used.

FIG. 2 is a diagram illustrating a conventional general method for manufacturing a coated optical fiber, in which an optical fiber base material 1 is heated and melted in a drawing furnace 2 and drawn to form a glass fiber 3, and then a resin coating device 4
After coating the outer periphery of the optical fiber with a coating resin, it is cured in a resin curing device 5 to form a coated optical fiber 6. It is generally believed that if air bubbles are mixed into the coating resin that forms the innermost layer (hereinafter referred to as the primary layer) of the coating formed in this way, a decrease in strength will occur. , Usually, the coating resin is subjected to defoaming treatment before coating. The purpose of the desulfurization treatment is to remove air bubbles present in the resin in the liquid state, and the bubbles are removed by heat treatment or vacuuming, and then the presence or absence of air bubbles is visually checked. After checking, the resin is applied.

<Problem to be solved by the invention> By the way, in 1970, Corning Co., Ltd.
Since the announcement of the development of B/km optical fiber, efforts have been made to reduce the transmission loss of optical fibers, and optical fibers that are comparable to the theoretical limit are now being manufactured. As a result, an increase in transmission loss at low levels, which has not been a problem in the past, has become a problem.

Under such circumstances, an increase in transmission loss in a low-temperature environment has become a problem. That is, there is no problem when used in an environment at room temperature, but when used in an environment below 0° C., for example, there is a problem in that the transmission loss increases, albeit slightly.

SUMMARY OF THE INVENTION In view of these circumstances, the present invention aims to provide an optical fiber coating method capable of obtaining an optical fiber that does not cause an increase in transmission loss even when used in a low-temperature environment.

Means for Solving the Problems> As a result of various studies to achieve the above object, the present inventors have found that ■ When coated optical fibers are manufactured under the same conditions, there is always a certain probability that transmission loss at low temperatures will occur. - If you closely observe an optical fiber that has a large transmission loss at such low temperatures, you will always find minute air bubbles in its coating. - A series of liquid resins such as those mentioned above It has been found that even if a resin is used which has been completely defoamed and has no air bubbles in it, it is inevitable that micro air bubbles will be mixed into the coating.

Then, for example, a resin mixed with a large number of microbubbles with a diameter of 1 to 10 μm was applied around a glass fiber with a diameter of 125 μm, and the optical fiber was cured to form a primary layer and cooled from room temperature to -40°C. When we measured the transmission loss increase at 1.55 μm, it was 1.2 dB/k
On the other hand, an increase in transmission loss at a similar low fi (-40°C) of an optical fiber whose primary layer coating was formed using the resin without any air bubbles was observed. When measured, all five wires were below the measurement limit, so it was found that the increase in transmission loss at low temperatures was due to minute bubbles present in the coating. Furthermore, it is expected that the increase in transmission loss at low temperatures is due to the microbending effect caused by the microbubbles present in the coating, which is caused by the coating material hardening and shrinking at low temperatures. Ru. Furthermore, it was discovered that the factor that causes these microbubbles to occur is dissolved air that exists dissolved in the resin. In other words, air is always dissolved in the resin at a certain concentration.9 Dissolved air is expelled from the resin when the resin cures, but if the amount is too large, it is left behind in the cured resin and forms the microbubbles mentioned above. This causes microbending. Therefore, in order to completely remove air bubbles in the resin coating, it is not sufficient to simply remove the visible air bubbles in the liquid resin as in the past; it is also necessary to take measures to reduce the amount of dissolved air in the resin. must be carried out.

The present invention was made based on such knowledge,
Its structure is based on an optical fiber coating method in which a resin is applied to the surface of a glass fiber drawn in a drawing furnace and cured to form a coating. The method is characterized in that it measures and evaluates the amount of dissolved air, and then performs a process to reduce the amount of dissolved air.

In other words, the primary 1 resin before application is degassed by heating and/or reduced pressure, and the air bubbles are sufficiently degassed even after visual bubbles are removed.Then, the amount of dissolved air is measured, and the curing process is performed. After 7M has been confirmed that the amount will not remain as minute bubbles in the coating when applied, the coating and curing process is performed. On the other hand, if the amount of dissolved air has not decreased,
After degassing, the amount of dissolved air is measured again to confirm that a sufficient amount of dissolved air has been obtained, and then the coating and curing operations are performed.

In addition, to measure the amount of dissolved air in the resin, it is sufficient to measure the amount of oxygen gas, which is contained in a certain proportion in the air and is easy to quantitatively measure. Quantitative analysis can be performed using chemical analysis methods.

In this way, if a defoaming treatment is performed on the resin before application until the amount of dissolved air is reduced, some of the remaining dissolved air will be driven out of the resin during curing, resulting in the presence of microbubbles in the cured resin. There isn't.

Therefore, even if an optical fiber having such a coating is used in a low-temperature environment, no increase in transmission loss occurs.

Example: First, in order to mix air bubbles into the resin used for the primary layer, Primary Tree III was stirred at high speed, and then -
It was set up overnight to remove any visible air bubbles.

This Ia! The fat was defoamed using the following procedure.

First, the resin was left at room temperature for 30 minutes with the pressure reduced to 50111+1Hg in the reaction container, then the pressure inside the container was returned to normal pressure, and the resin was heated to 50°C for 2 hours.
I left it for a while. Various samples were prepared by repeating this defoaming process several times, and the degree of defoaming (dissolved air amount) of each sample was evaluated and the increase in low-temperature transmission loss of the optical fiber using this as a primary layer was measured. The degree of defoaming (dissolved air amount) was evaluated by measuring the amount of dissolved oxygen using gas chromatography as follows.

First, 40 g of each sample resin was weighed into 50 cc screenie vials, and the air in the vials was replaced with nitrogen gas.

At this time, determine the volume of the upper gas phase of the vial. Next, the vial was placed in a constant temperature bath at 100°C and left for 8 hours, after which gas in the upper gas phase was collected and the oxygen concentration in this gas was measured by gas chromatography. Based on this measured oxygen concentration, the amount of dissolved air can be determined using the following formula.

Further, each resin whose dissolved air content was determined in this way was applied to the drawn fiber and cured to produce a coated optical fiber. The increase in transmission loss when these coated optical fibers were cooled from room temperature to -40° C. was measured, and the relationship between the results and the amount of dissolved air is shown in FIG.

As is clear from the results shown in Figure 1, no increase in transmission loss occurs when the amount of dissolved air determined by the method described above is 0.09 m I / g or less, and an increase in transmission loss occurs when it is 0.1 m I / g or more. This was recognized. Therefore, in the measurement and evaluation of the amount of dissolved air as described above, the amount of dissolved air is 9. It was found that an optical fiber without an increase in low-temperature transmission loss can be obtained by coating with a resin having OX10=m j /g or less.

In this way, by measuring and evaluating the amount of dissolved air,
Optical fibers with no increase in low-temperature transmission loss can be reliably obtained, and low molecular weight components in the resin do not evaporate excessively due to excessive defoaming treatment, which is useful from the standpoint of resin quality control. It is.

In addition, since the measurement accuracy of the above-mentioned method of measuring the amount of dissolved oxygen is not affected by the amount of other gases dissolved in the resin, the amount of dissolved air determined by this method can be used to determine the degree of degassing that the resin has undergone. You can know almost exactly what you need.

In addition to the gas chromatography method described above, methods for measuring the amount of dissolved air include, for example, heating and reducing the pressure of a small amount of resin taken out to an extent that the constituent components do not volatilize, and at that time, There are methods to measure the amount of gas.

<Effects of the Invention> As explained above, according to the present invention, it is possible to reliably obtain an optical fiber in which no increase in transmission loss occurs when used in a low-temperature environment.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of dissolved air and the increase in low-temperature transmission loss in Examples, and FIG. 2 is an explanatory diagram showing an example of a method for manufacturing a coated optical fiber. In the drawings, 1 is an optical fiber base material, 2 is a drawing furnace, 3 is a glass fiber, 4 is a resin coating device, 5 is a resin curing device, and 6 is a coated optical fiber.

Claims (1)

[Claims] (1) In an optical fiber coating method in which a coating is formed by coating and curing a resin on the surface of a glass fiber drawn in a drawing furnace, the amount of dissolved air in the resin is measured before coating. A method for coating an optical fiber, characterized by performing a treatment to reduce the amount of dissolved air while evaluating the amount of dissolved air.