JPS59217649A - Coating of optical fiber - Google Patents

Abstract

PURPOSE:To raise coating speed by 2-10 times that of a conventional procedure, by coating optical fiber while passing it through a covering die and vibrating a thermosetting resin packed into the covering die at a specific frequency. CONSTITUTION:A parent material for optical fiber is softened under heating, spun into optical fiber having the desired diameter, the optical fiber is immediately passed through a covering die, and the optical fiber is coated with an uncured thermosetting resin. In the operation, the uncured thermosetting resin is heated in such a way that the cured resin of the uncured thermosetting resin has a curing starting time longer than the retention time of the uncured thermosetting resin in the covering die, and the uncured thermosetting resin is vibrated at 50Hz-5KHz frequency.

Description

[Detailed description of the invention] The present invention relates to a method for high-speed coating of optical fibers.

Currently, glass fibers for optical communications (hereinafter abbreviated as optical fibers) are used in a three-layer coating structure with a core layer coating and a secondary coating for reasons such as transmission loss or handling. The primary coating material and buffer layer coating material include:
Thermosetting resins such as silicone resins or urethane resins are used, but the speed at which fibers can be coated with these resins is low, which is one of the reasons why optical fibers are expensive.

When fiber coating is performed using a thermosetting resin, fluctuations in the coating thickness (hereinafter abbreviated as coating thickness variation) need to be less than a few microns. This is because the transmission loss increases as the variation in coating film thickness increases. When coating a fiber with the thermosetting resin, when the fiber speed exceeds a certain value, the variation in coating thickness increases rapidly, and when the fiber speed is further increased, the fiber is no longer coated at all.

For this reason, the fiber coating speed with thermosetting resin is currently practically 100-7 minutes or less.

In order to reduce the cost of optical fiber, optical core 2
It is necessary to increase the fiber coating speed, that is, the fiber speed at which the coating thickness variations described above begin to increase. However, since the mechanism by which coating film thickness variation increases is not clear, few effective methods have been found to improve the fiber coating speed, and there are only a few optical fiber coating methods that use pressurized dies ( Patent application 1982-'1314
17) is currently being proposed. However, although the pressurized die certainly improves the speed of coating optical fibers, it has the disadvantage that the range of coating thickness that can be controlled by the pressurizing force becomes narrower as the coating speed increases.

The present invention was made in view of the above-mentioned current situation, and its characteristics include vibrating an uncured thermosetting resin material in a frequency range of 50Hz to 5KHz, and vibrating the uncured thermosetting resin material in a coating die. The purpose is to provide a high-speed coating technology for optical fibers that is effective in reducing the cost of optical fibers by heating at a temperature that does not cause curing and by combining these methods.

When coating an optical fiber with a thermosetting resin, when the coating speed, that is, the fiber running speed exceeds a certain value, the variation in coating film thickness increases rapidly, and eventually the fiber is not coated at all. The value of the fiber speed at which this coating film/thickness variation begins to increase (abbreviated as maximum smooth coating speed) is the flow curve (shear rate - The shear stress relationship) is proportional to the value of the shear rate that deviates from the index side (critical shear rate). Therefore, Japanese Patent Application No. 56-95647
211041), it is possible to estimate the maximum smooth coating rate from the value of the critical shear rate, and increasing the maximum smooth coating rate is synonymous with increasing the critical shear rate. .

The present invention provides maximum smooth coating speed and critical shear rate and temperature;
This is based on the results of a detailed study of the relationship with vibration frequency, and according to the present invention, when coating optical fibers using a normal open die, the maximum smooth coating speed can be increased by 2 to 10 times compared to conventional methods. In optical fiber coating using pressurized dies,
The controllable coating thickness range can be expanded by two to three times by applying pressure. The effects of the present invention will be explained in more detail below with reference to Examples. The values in Table 1 () represent relative ratios to Comparative Example 1.

Table 1 summarizes the critical shear rates measured for uncured silicone resins having a viscosity of 7000 cp at 25° C. and a shear rate of 500 sec. The critical shear rate in Table 1 also shows the relative ratio to Comparative Example 1 (25°C without vibration). 1st
It can be seen from the table that the value of critical shear rate increases with heating and excitation. Here, the critical shear rate increases monotonically with temperature, but as the vibration frequency increases, it increases monotonically at first, reaches a maximum value, and then decreases. That is, the vibration frequency that is effective in increasing the critical shear rate is limited to a certain range. The permissible vibration frequency range obtained in this experiment is 50-5 KHz. Note that the value of the optimum vibrational frequency at which the critical shear rate is maximum increases with temperature, and is 25
200Hz at °CX 200~500Hz at 40°C60°
In C, it is 500Hz.

Table 2 1) Heat cure type resin 2) Ultraviolet cure type resin 8) Value at 25°C9 shear rate 5005eC-1 (
4) The coating speed when the coating thickness variation is ±3 μm is measured using a normal open die (nozzle diameter 0.4 mm, nozzle length 2 mm). This is a summary of the results of the fiber coating experiments conducted. The coating film thickness was approximately 50 μm in all cases. Table 2 shows that the maximum smooth coating speed increases with heating and vibration, regardless of which uncured thermosetting resin is used. When silicone was used as the coating agent (Examples 28 and 2)
6) By heating the fiber to 60°C and exciting it at a frequency of 500 Hz, the fiber can be coated at about 2.5 times the speed when not exciting at 25°C (Comparative Example 5.6). I understand.

In Table 2, it was not possible to coat with silicone at temperatures above 60°C. This is because the uncured silicone resin was cured within the coating die.

The silicone used in this experiment had a cure onset time of about 20 minutes at 60°C, while the average residence time of the silicone in the coating die was also about 20 minutes. Therefore, the temperature at which the silicone can be heated is limited to a range where the curing start time of the silicone is equal to or longer than the average residence time in the coating die.

Table 3 1) The range in which the coating film thickness variation is ±3 μm or less at a coating speed of 200 rn/min. The results of the coating experiment are summarized.The coating speed, that is, the fiber running speed, was 200 tn/min.For the pressurized -11° die, the coating thickness can be controlled by adjusting the pressurizing force. However, there is a permissible range for the applied force, and therefore a certain permissible range for the controllable coating film thickness.

Table 3 shows that the controllable range of coating film thickness can be expanded by heating, vibration, or a combination thereof. The effect of heating or vibration, or a combination thereof, on improving this coating thickness control is similar to increasing the critical shear rate or maximum smooth coating rate.

That is, for example, in the case of silicone coating (Example 82)
), by heating to 60°C and shaking at 500 Hz, the control range of the coating film thickness was approximately twice (110 ± 4 μm) as compared with the case without vibration at 25°C (Comparative Example 8,100 ± 25 μm).
5 μm). The upper limit of the heating temperature and the allowable vibration frequency range are also the same as in the case of improving the critical shear rate or the maximum smooth wave M velocity.

As explained above, according to the optical fiber coating method of the present invention, the maximum smooth coating speed can be increased by 2 to 10 times that of conventional optical fiber coating using an ordinary open die. At the same time, in optical core insulating coating using a pressurized die, the controllable coating thickness range can be expanded by two to three times by adjusting the pressurizing force, thereby increasing the production speed of optical fiber cables. This has the advantage that it is possible to manufacture optical fibers with different coating thicknesses, thereby reducing the cost of optical fiber cables.

Patent applicant: Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] L An optical fiber base material is heated and softened to be spun into an optical fiber of a desired diameter, and in the subsequent step, the optical fiber is immediately passed through a coating die and filled into the coating die. In the method of coating the optical fiber with an uncured thermosetting resin, the uncured thermosetting resin is heated for 50 hours.
A method for coating an optical fiber, characterized by vibrating in the range of 7 to 5 KHz. - Spun into an optical fiber of a desired diameter by heating the optical fiber base material, and in the subsequent process, the optical fiber is immediately passed through the coating die, and the uncured thermosetting resin is filled into the coating die. In the method of coating the optical fiber with the uncured thermosetting resin, the curing start time of the uncured thermosetting resin is equal to or longer than the residence time of the uncured thermosetting resin in the coating die. 50 cured products
A method for coating an optical fiber, characterized by vibrating in the range of Hz to 5 KHz. & Spun into an optical fiber of a desired diameter by heating the optical fiber base material, and in the subsequent process, the optical fiber is immediately passed through a pressurizing die for coating, and the thermosetting resin filled in the die is heated. In the method of coating the optical fiber with a cured product, the heat is applied within a range where the curing start time of the uncured thermosetting resin is equal to or longer than the residence time of the uncured thermosetting resin in the coating pressure die. While heating the uncured thermosetting resin, the uncured thermosetting resin was
A method for coating an optical fiber, characterized by vibrating in the range of Hz to 5 KHz.