JPH0776117B2 - Optical fiber coating method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber coating method, and more particularly, to an optical fiber drawn by applying a certain tension to the tip of a heat-softened optical fiber preform (hereinafter referred to as An improved coating method for coating the surface of a drawn optical fiber with a resin layer.

<Technical background> When manufacturing an optical fiber from an optical fiber preform,
As shown in the drawing, while heating and softening the optical fiber preform 1 in the heating furnace 2, tension is applied to the tip of the optical fiber preform 1 to draw it, and the drawn fiber 3 is passed through the resin liquid tank 4 to apply the resin liquid to the surface, Subsequently, it is sent to a curing oven 5, the applied resin liquid is cured, and a coated optical fiber (hereinafter referred to as “coated fiber”) 6 thus obtained is manufactured, and then wound on a winding bobbin 8 via a capstan 7. I was trying to take it. Moreover, in such a manufacturing process, the diameters of the drawn fiber 3 and the coated fiber 6 are monitored by the laser outer diameter monitors 9 and 10, respectively, and the drawing speed of the drawn fiber 3 is adjusted so that a constant outer diameter can be obtained. I was adjusting it.

On the other hand, since the degree of cure of the resin layer of the coated fiber 6 is directly related to the transmission characteristics, mechanical strength, long-term reliability, etc. of the final optical fiber, the degree of cure is measured in the manufacture of the optical fiber. There is a need.

Young's modulus is usually adopted as a measure of the degree of curing. Conventionally, to measure the Young's modulus of the resin coating layer of an optical fiber,
The Young's modulus was measured by taking out the resin coating layer from the coated fiber.

<Problems to be Solved by the Invention> However, since the Young's modulus of the resin coating layer of the conventional coated fiber described above is measured for the resin coating layer peeled from the coated fiber, a uniform thickness is maintained when peeling. It was difficult to take it out in the state, and the measurement error was large.

In addition, it takes a long time for measurement, and it is impossible to measure the Young's modulus of the resin coating layer in the state of forming the coated fiber because the drawn fiber is coated with the resin liquid and cannot be measured in the cured state. There was an inconvenience.

The present invention was made in an effort to eliminate the drawback of manufacturing an optical fiber in such a state that the conventional grasp of the Young's modulus in the optical fiber coating is unsatisfactory. An object of the present invention is to provide an optical fiber coating method capable of measuring the ratio sufficiently accurately and measuring without taking out the resin coating layer from the coated fiber.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the coating method of the optical fiber of the present invention is applied with a drawn fiber resin liquid obtained by drawing from a heat-softened optical fiber preform, In an optical fiber coating method that cures to produce a coated fiber, the outer diameter of the coated fiber applied to the drawn fiber before and after the resin solution cures is monitored, and the outer diameter ratio before and after the resin solution cures is kept constant. It is characterized by drawing while drawing.

<Operation> As described above, since the outer diameter of the coated fiber before and after the resin liquid applied to the drawn fiber is cured is monitored, and the drawing is performed while maintaining the ratio to be constant, the coated resin liquid layer Curing shrinkage x (%) is Becomes Here, R is the outer diameter of the applied resin liquid layer before curing, r is the outer diameter of the resin after curing, and a is the wire diameter of the drawn fiber.

It is known that the cure shrinkage rate x is proportional to the degree of cure of the resin, and thus the determination of the cure shrinkage rate means the determination of the degree of cure of the resin. Then, the curing shrinkage ratio can be obtained from the outer diameter of the resin liquid coating layer of the drawn fiber before and after the curing according to the above-mentioned formula (1). These values can be obtained by a laser outer diameter measuring device, and the measurement accuracy is
Since it is as high as 0.2 μm and there is no need to remove the resin coating layer because of non-destructive analysis, the cure shrinkage, that is, the degree of cure, can be obtained quickly and highly accurately during the coating process.

Further, when the curing shrinkage rate of the resin liquid, that is, the degree of curing changes, the deviation signal is immediately sent to the capstan, and for example, by adjusting the total irradiation light amount to the coated fiber per unit area, An optical fiber having a coating layer with a constant Young's modulus can be manufactured.

<Examples> Next, typical examples of the present invention will be described.

FIG. 1 is a schematic configuration diagram of a coating device used for carrying out the optical fiber coating method of the embodiment. The difference from the conventional coating device (see FIG. 5) is that the resin liquid layer 4 and the curing furnace 5 are different from each other. A laser outer diameter measuring device 11 for measuring the outer diameter of the resin liquid layer coated on the drawn fiber 3 before curing is provided between the two.

The curing furnace 5 used in this embodiment is an ultraviolet irradiation furnace, and the power of irradiation light can be adjusted by electric power supplied from a power source (not shown). The resin in the resin liquid tank 4 contains an acrylate resin that is cured by irradiation with ultraviolet rays, and has a structure that adheres to the surface of the drawn fiber 3 when the drawn fiber 3 passes through the tank.

If the relationship between the Young's modulus change amount of the coated fiber before and after the curing of the acrylate resin coated on the surface of the drawn fiber 3 and the curing shrinkage rate is shown in this example, the characteristic diagram as shown in FIG. 2 can be obtained.

From the characteristic curve in Fig. 2, the Young's modulus change amount and the curing shrinkage before and after curing the resin liquid coating layer are in a proportional relationship, and an increase in shrinkage of 1% corresponds to an increase in Young's modulus of approximately 5 kg / mm ^2. I understand.

Further, the relationship between the cure shrinkage and the change amount of the coating diameter is as shown in FIG. 3, and when the cure shrinkage is increased by 1%, the coating diameter is reduced by about 1 μm. Therefore, it was found that a decrease in coating diameter of 1 μm corresponds to an increase in Young's modulus of 5 kg / mm ² .

In this embodiment, the Young's modulus of the resin coating is 1 kg / mm by using a laser outer diameter monitor with a measurement accuracy of 0.2 μm.
It was found that up to ² can be measured with high accuracy.

Next, if the relationship between the Young's modulus of the resin coating layer and the amount of UV irradiation light on the coating resin liquid layer is shown, the relationship shown in Fig. 4 is established, and both are in a proportional relationship, increasing the Young's modulus of 1 kg / mm ^2. It was found that the irradiation light amount of about ² mJ / cm ² should be increased in order to make it. In fact, when the Young's modulus of the coating increased by 1 kg / mm ² , the Young's modulus decreased by ² mJ / cm ^{2 and}
kg / mm ² decreased. At this time, as a method of reducing the irradiation light amount, it was used that the total irradiation light amount per unit area was inversely proportional to the linear velocity of the optical fiber. The irradiation light amount per unit area used in ordinary coating is
Since it is approximately 100 mJ / cm ² , the irradiation light amount of ² mJ / cm ² can be reduced by 0.98 times, and the linear velocity of the optical fiber can be increased by 1.02 times in order to reduce the irradiation light amount. In fact
As a result of feeding back the rotation speed of the capstan and increasing the drawing speed by 1.02 times, it became possible to lower the Young's modulus of the coating by 1 kg / mm ² .

<Invention and Effect> As is clear from the above description, according to the optical fiber coating method of the present invention, the degree of cure can be measured quickly and accurately during the resin coating operation on the drawn fiber. By adjusting the amount of irradiation light to and the drawing speed, it is possible to always provide a coating having a constant degree of curing.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical fiber coating apparatus which is actually used in the optical fiber coating method of the present invention, and FIG. 2 is a Young's modulus change amount vs. curing shrinkage rate of a resin liquid coating layer applied to the surface of a drawn fiber. FIG. 3 is a characteristic diagram showing the relationship between the outer diameter change amount of the coated fiber and the curing shrinkage ratio, and FIG. 4 is a change of the total irradiation light amount to the resin liquid coating layer of the coated fiber versus the Young's modulus. FIG. 5 is a characteristic diagram showing the relationship between the amounts, and FIG. 5 is a schematic configuration diagram of a coating device used in a conventional optical fiber coating method. In the figure, 1 ... Optical fiber base material, 2 ... Heating furnace, 3 ... Drawing fiber, 4 ... Resin solution tank, 5 ... Infrared (or ultraviolet) irradiation device, 6 ... Coated fiber, 7 ... Capstan, 8 ... Winding bobbin, 9, 10, 11 ... Laser outer diameter measuring instrument.

Claims (2)

[Claims] 1. A method for coating an optical fiber, which comprises applying a resin solution to a drawn fiber obtained by drawing from a heat-softened optical fiber preform and curing it to produce a coated fiber. A method for coating an optical fiber, which comprises monitoring the outer diameters of the coated fiber before and after curing and drawing the fiber while keeping the outer diameter ratio before and after curing the resin liquid constant. 2. The outer diameter ratio before and after curing the resin liquid is made constant by adjusting the resin liquid curing speed and / or the drawing speed of the drawn fiber. Optical fiber coating method.