JPS63151648A - Production of coated optical fiber - Google Patents

Abstract

PURPOSE:To obtain a coated optical fiber having plural coating layers and having excellent screening resistance and temperature characteristics, by using an ultraviolet-curable resin as a material for the inner coating layer, irradiating the resin with ultraviolet radiation in an atmosphere having a specific oxygen concentration and directly applying an outer coating layer to the cured resin layer. CONSTITUTION:In the production of a coated optical fiber having plural coating layers, the inner coating layer and the outer coating layer which are necessary to be mutually bonded are formed by the following method. An ultraviolet- curable resin is used as a material for the inner coating layer and the curing of the layer is carried out in an atmosphere having an oxygen concentration of >=5% to form the inner coating layer. The outer coating layer is directly formed on the inner coating layer. An ultraviolet-curable resin, a thermosetting resin or a thermoplastic resin may be used as a material for the outer coating layer and, above all, the use of an ultraviolet-curable resin is especially preferable to form a crosslinking between the inner and the outer layers and increase the bonding strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of manufacturing a coated optical fiber having multiple layers of coating.

[Prior art and its problems]

As shown in Fig. 1, a typical structure of a silica-based coated optical fiber for communications is as follows: an optical fiber 1 with an outer diameter of 125 μm consisting of a core and a cladding has an outer diameter of 200 μm with a soft ultraviolet curing resin as a buffer layer. A soft coating 2 of ~300 .mu.m is formed, and a hard coating 3 of 250 to 500 .mu.m in outer diameter is formed thereon as a protective layer using a hard ultraviolet curable resin. In other words, the coating structure consists of a soft coating (Young's modulus I Kg/mm" or less) and a hard coating (Young's modulus 10 Kg/mm" or less).
/ms1 or more) is common.

The soft coating equalizes the variations in molding when forming the hard coating on the outside, and in combination with the hard coating, it prevents micro-bends that occur in the optical fiber due to external forces such as lateral pressure and thermal stress due to temperature changes. This functions to prevent an increase in transmission loss. The hard coating also serves to prevent deterioration of the optical fiber due to screening of the coated optical fiber, particularly high strain screening of 1% or more.

In order to improve the screening resistance, temperature characteristics, etc. of optical fibers with such a double-layer coating structure, the adhesion state at the interface between the soft coating and the hard coating is an important point.
For example, regarding screening resistance, it is necessary that the interface between the two be sufficiently adhered, and regarding temperature characteristics, uniformity of the adhesion state of the interface in the longitudinal direction is important. .

In addition to this, the state of adhesion between coating layers in coated optical fibers may pose a problem. For example, as shown in FIG. 2, a colored layer 5 made of ultraviolet curing ink or thermosetting ink may be formed on the coated optical fiber 4 as shown in FIG. 1 for identification purposes. Good adhesion between the hard coating 3 and the colored layer 5 is required. Furthermore, as shown in FIG. 3, a tape-shaped multicore coated optical fiber 8 is prepared by arranging a plurality of coated optical fibers 4 as shown in FIG. 1 and sequentially forming a soft common coating 6 and a hard common coating 7 thereon. The adhesion state between the soft common coating 6 and the hard common coating 7 greatly affects the temperature characteristics and the removability of the common coating.

As described above, in coated optical fibers, there is a demand for sufficient and uniform adhesion of the inner layer side coating and the outer layer side coating, but a practical means for adhering them has not yet been found. Using an adhesive to bond the inner and outer coatings not only complicates the manufacturing process but is also disadvantageous in terms of cost.

[Means for solving problems and their effects]

The present invention provides a method for manufacturing a coated optical fiber that solves the problems of the prior art as described above. When forming the inner and outer coatings that need to be bonded to each other, an ultraviolet curable resin is used as the material for the inner coating, and the ultraviolet rays used to coat and cure the resin are oxygen-free. The method is characterized in that the inner coating is formed in an atmosphere having a concentration of 5% or more, and the outer coating is directly formed thereon.

As mentioned above, if UV curable resin is coated and cured by UV irradiation in an atmosphere with an oxygen concentration of 5% or more, a coating that is cured inside but has an uncured surface can be obtained. It will be done. This is because oxygen activated by ultraviolet rays traps radicals on the coated surface and stops the polymerization reaction.
This is thought to be because only the surface remains unreacted. Therefore, when this layer is used as an inner layer coating and an outer layer coating is formed thereon, the unreacted portions react and bond with the outer layer coating, resulting in a good adhesive state. The reason why the oxygen concentration is set to 5% or more is that if it is lower than this, the surface will be hardened and the surface will not be in an unreacted state.

The material for the inner layer side coating may be any resin (ethylenically unsaturated compound) that radically polymerizes with ultraviolet light that activates oxygen. Typical examples include ultraviolet curable urethane acrylate resin, epoxy acrylate resin, and silicone acrylate. resin, polybutadiene acrylate resin, etc.

In addition, as the outer layer side coating, ultraviolet curable resin, thermosetting resin, thermoplastic resin (nylon), etc. can be used.
It is particularly preferable to use ultraviolet curable resin, because if ultraviolet curable resin is used for the outer layer coating,
This is because when it is cured by ultraviolet irradiation, the unreacted portion of the coating surface on the inner layer side undergoes radical polymerization at the same time, forming a crosslink between the inner and outer layers, thereby strengthening the adhesion.

〔Example〕

As shown in Figure 4, an optical fiber with an outer diameter of 125 μm (core diameter 50 μm, Δ-1%
, GI type) 1 is drawn at a linear speed of 100 m/min, and the optical fiber 1 is passed through a coating bag N12 to coat a soft ultraviolet curable urethane acrylate resin (Young's modulus after curing is 0.
1Kg/mm") to have an outer diameter of 200 μm, it is passed through an ultraviolet irradiation device 13 equipped with a 120W/am metal halide lamp to irradiate it with ultraviolet light, and at the same time passes through an optical fiber inside the device 13. 1517 ml of air was flowed into the cylinder from the bottom to the top, and the coated ultraviolet curable urethane acrylate resin was cured in an air atmosphere (oxygen concentration 21%) to form a soft coating 2.

Next, it was passed through the coating device 14 and coated with a hard ultraviolet curable urethane acrylate resin (Young's modulus after curing is 50 g/III) so that the outer diameter was 250 μm, and then coated with the same 120 W/III coating as above. Ultraviolet rays are irradiated through an ultraviolet irradiation device 15 equipped with a cm metal halide lamp, and at the same time, 1517w1n of nitrogen is flowed from bottom to top into the cylinder in which the optical fiber is passed in the device 13, and the coated ultraviolet curable urethane acrylate resin is coated with ultraviolet rays. harden,
A hard coating 3 was formed.

As a result of performing 1% screening on 15 km of the coated optical fiber manufactured as described above, there was no disconnection. Furthermore, to look at the temperature characteristics of IKm bundled samples, we measured the transmission loss at -40°C and found that it was 0.
The loss increased by 0.05 dB/Km or less.

Table 1 below shows the results of similar experiments conducted by changing the curing atmosphere when forming the soft coating and keeping the other conditions the same.

In Comparative Example 1 with an oxygen concentration of 4% in Table 1, the soft coating and hard coating were adhered to some extent, and there was one disconnection at 715 during 1% screening, but the adhesion was unstable and the longitudinal Due to the non-uniformity in the direction, an increase in loss of 0.3 dB/Im was observed at -40°C. In addition, in Comparative Example 2 with an oxygen concentration of 2%, the soft coating and hard coating were not bonded, and the shrinkage stress at low temperatures was equalized by the sliding between the two coatings.
The loss increase at −40° C. was 0.05 dB/Ks or less, which was good. However, in the 1% screening, disconnections occurred 9 times/15 km because there was no adhesion between the two coatings. On the other hand, in Examples 1 and 2 where the oxygen concentration was 5% or more, the soft coating and the hard coating were sufficiently and uniformly bonded, and excellent screening resistance and temperature characteristics were obtained.

In the above embodiment, a case was explained in which a coated optical fiber having a two-layer coating structure was manufactured. However, the present invention is not limited to this. For example, when manufacturing a coated optical fiber as shown in FIG. The first layer of soft coating 2 was formed in the same manner as in the above example, and the second layer of hard coating 3 was also formed using ultraviolet curable resin with an oxygen concentration of 5%.
By curing in the above atmosphere, the adhesiveness between the hard coating 3 and the colored layer 5 can be improved. Further, when manufacturing a tape-shaped multi-core coated optical fiber as shown in Fig. 3, when forming the soft common coating 6, an ultraviolet curable resin is used and cured in an atmosphere with an oxygen concentration of 5% or more. If so, the adhesiveness between it and the hard common coating 7 can be improved.

〔Effect of the invention〕

As explained above, according to the present invention, in a method for manufacturing a coated optical fiber having multiple layers of coating, the inner layer coating and the outer layer coating, which need to be bonded to each other, can be bonded together without using an adhesive or the like. This makes it possible to achieve sufficient and uniform adhesion by the extremely simple means of adjusting the oxygen concentration during ultraviolet irradiation, which greatly contributes to improving the performance of coated optical fibers.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views showing various types of coated optical fibers, and FIG. 4 is an explanatory view showing an embodiment in which a coated optical fiber as shown in FIG. 1 is manufactured by the method of the present invention. 1-Optical fiber, 2-Soft coating, 3-Hard coating, 4-Coated optical fiber, 1)-Heating furnace, 12/14-Dice, 1
3.15 ~ Ultraviolet irradiation equipment. Figure 1 Figure 2 Figure 3 Figure 4

Claims (4)

[Claims] (1) In a method for manufacturing a coated optical fiber having a plurality of coating layers, when forming an inner coating and an outer coating that need to be bonded to each other among the plurality of coating layers, the material of the inner coating is Using an ultraviolet curable resin, the inner layer coating is formed by irradiating ultraviolet rays when coating and curing it in an atmosphere with an oxygen concentration of 5% or more, and the outer layer coating is directly formed thereon. A method of manufacturing a coated optical fiber characterized by: (2) The manufacturing method according to claim 1, comprising:
Both the inner layer side coating and the outer layer side coating are made of a resin that is cured by a radical polymerization reaction. (3) The manufacturing method according to claim 2, comprising:
The inner coating is made of ultraviolet curable urethane acrylate resin. (4) The manufacturing method according to claim 1 or 3, characterized in that the outer layer coating is made of an ultraviolet curable resin, a thermosetting resin, or a thermoplastic resin.