JPS5928882B2 - Optical fiber coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating optical fibers.

Currently, optical fibers are in the stage of being gradually put into practical use, but when actually using a thin and weak optical fiber core, it is necessary to provide the surrounding area with functions as an optical fiber and to provide various protections. It is coated with plastic and is used in the same shape as a general communication cable.

The plastic coating provided around the core varies depending on whether the core fiber is made of glass or plastic and also on the purpose of use, but in summary, it reduces mechanical stress on the optical fiber. These include providing a buffering effect, preventing water molecules from adhering to optical fibers, increasing mechanical strength, and providing heat and chemical resistance. By the way, when various coatings are provided around optical fibers for the above-mentioned purpose, although various methods are used as in the case of conventional electric cables, they often rely on the melt extrusion effect.

However, in that case, if the melting point of the plastic material coated on the outside is higher than the melting point of the plastic material present on the inside, the low melting point plastic material present on the inside will be affected by the heat during the melt extrusion process. , melting, deformation, expansion, foaming, etc. occur, and the function of the optical fiber and the dimensions and functions of the optical cable are lost. Therefore, the inventors of the present invention have conducted various studies to solve the problems associated with melt extrusion of optical fibers as described above, and have achieved this goal.

That is, in the case where a plastic fiber or a plastic-coated glass fiber is coated with another plastic having a higher melting point than the plastic by melt extrusion, the fiber to be coated is first coated by melt extrusion. A method of coating an optical fiber is characterized in that the fiber is surrounded by a porous material having a higher melting point than the plastic to be coated, and then the enclosed plastic is melt-extruded and coated with the high melting point plastic. The optical fiber coated in the present invention is a plastic fiber 1 or a glass fiber 3 coated with a plastic coating 2, the former being typified by an acrylic fiber, and the latter being, for example, a glass fiber coated with silicone resin, fluoride, etc. It is coated with vinylidene resin, epoxy resin, urethane resin, etc.

The outer diameter of the former is thicker than the latter, usually about 1.0 mm, and the latter is usually about 0.15 mm, and on top of that, the overall outer diameter of the resin as described above varies depending on the purpose. 0.
It is coated so that about 4 columns are covered. Next, the plastic fiber 1 or the glass fiber 3 with the plastic coating 2 is coated with a porous material 4. This porous material 4 is a commercially available porous material having various independent or continuous pores. The selection criterion for the porous material 4 is that it has a melting point higher than that of the plastic to which it is coated on the outside by melt extrusion and its processing temperature. Therefore, plastics that meet this standard are generally resins with relatively high melting points, such as polyvinylidene fluoride, ethylene/
Tetrafluoroethylene copolymer, tetrafluoroethylene/hexafluoropropylene copolymer, tetrafluoroethylene polymer, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, polyvinyl chloride, nylon, polyethylene, polyethylene Examples include terephthalate. Among these, preferred are porous materials of crystalline polymers having continuous pores obtained by a stretching method, for example,
This is a stretched porous ethylene tetrafluoride sheet described in Publication No. 91. In order to surround the fiber 1 with this porous material 4, the porous material 4 may be cut into a tape shape, and this may be carried out by vertically wrapping or wrapping the tape around the fiber 1. Further, instead of surrounding it with a tape-like material, it is also possible to cover it with the above-mentioned resin containing a foaming agent by extrusion or coating to cause foaming. Thus porous material 4
The coated fiber is then passed through an extruder to coat the outside thereof with a coating 5 of a plastic having a higher melting point than the plastic coated on the plastic or glass fiber. will be administered. The thicker the coating 5, the more heat it contains per unit volume, which makes the plastic coated on the inner plastic fiber or glass fiber more susceptible to thermal effects. Therefore, in such a case,
The thickness of the coating 5 can be determined so that the thermal denaturation of the inner plastic material is within permissible limits, or it can be applied in several thin coats. According to the present invention as described above, due to the heat insulating (heat shielding) effect of the porous material layer 4 formed in advance to surround the outer periphery of the fiber, the plastic material for forming the fiber, which has a relatively low melting point, is removed. is prevented from being denatured by heat during melt extrusion processing of the outer jacket (jacket) 5.

Since the porous material layer 4 is made of a material having a higher melting point than the outer covering 5, the porous material layer 4 itself does not melt due to the heat during processing of the outer covering 5, and its porous structure is maintained. , and porous materials have good heat insulation properties due to internal pores, so it is possible to make the porous material layer 4 thinner and economical without significantly increasing the outer diameter of the entire optical fiber cable including the outer sheath 5. Therefore, it becomes possible to mass-produce high-quality optical fiber cables. The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto.

Example: A stretched porous 4-tetrafluoroethylene (PTFE) tape 4 manufactured by the method described in Japanese Patent Publication No. 18991/1983 was wrapped around an acrylic fiber 1 (trade name: Esca) having a diameter of 0.95 mm. It was wound so that the thickness was 0.4 m7IL.

Next, two acrylic fibers covered with the porous material obtained in this way were placed in parallel and passed through the crosshead of the extruder, and around the 0.5m7IL thick ethylene/
A tetrafluoroethylene copolymer (ETFE) resin coating 5 was provided to obtain a two-core parallel acrylic fiber cable as shown in FIG. When the coating 5 and porous material 4 of the cable thus obtained were peeled off and the surface of the acrylic fiber was inspected, there was no change in appearance and no change in optical properties was observed.

This is because the softening temperature of acrylic is 70 to 80°C and the extrusion temperature of ETFE (about 350°C).
This shows that porous PTFE has an excellent heat insulating effect. For comparison, when an acrylic fiber was coated with ETFE in the same manner as above except that the porous PTFE layer 4 was not provided, the acrylic fiber melted and deformed and completely lost its function as an optical fiber cable. Ta.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a plastic fiber coated by the method of the present invention, FIG. 2 is a cross-sectional view of a plastic-coated glass fiber fiber coated by the method of the present invention, and FIG. Figure 3 is a cross-sectional view of a two-core parallel acrylic fiber cable manufactured in accordance with an example. 1 is a plastic fiber, 2 is a plastic coating,
3 is a glass fiber, 4 is a porous material, and 5 is a plastic coating made by melt extrusion.

Claims (1)

[Claims] 1. When a plastic fiber or a plastic-coated glass fiber is coated with another plastic having a higher melting point than the plastic by melt extrusion, the plastic to be coated by melt extrusion first covers the fiber to be coated. 1. A method of coating an optical fiber, comprising surrounding the fiber with a porous material having a melting point higher than that of the fiber, and then melt-extruding the plastic with the high melting point onto the surrounded fiber.