JPH0529618B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing an optical fiber cable having an extruded coating layer made of a tetrafluoroethylene/ethylene copolymer. [Technical background of the invention and its problems] Conventionally, optical fiber cables for nuclear reactors or overhead ground wires have been coated with a buffer made of silicone resin, polyurethane-acrylate resin, or epoxy resin on the outside of the optical fiber wire. A structure in which a layer is provided and a secondary coating layer is provided thereon for mechanical protection is known. Traditionally, nylon has been mainly used as the material constituting the secondary coating layer in such optical fiber cables, but as the field of use for this type of optical fiber cable expands, flame retardancy and heat resistance have also improved. For example, in optical fiber cables for nuclear power applications, OF composite optical fiber cables, etc., materials with various excellent properties such as flame retardancy and heat resistance are required as materials constituting the secondary coating layer or cable sheath. Fluororesins with In particular, among fluororesins, tetrafluoroethylene-ethylene copolymer (hereinafter referred to as ETFE) is among the fluororesins that generally have poor processability, but it has excellent processability and has flame retardant and heat resistance. Optical fiber cables coated with extruded ETFE are attracting attention due to their excellent properties.
Suitable conditions for extrusion molding ETFE, that is, extrusion conditions that minimize the increase in optical transmission loss, have not yet been established, and the problem has been that quality varies and reliability is poor. This is because fluorocarbon resins, including ETFE,
Because it has higher crystallinity and density than other nylons, etc., the molding shrinkage after extrusion coating varies greatly depending on the extrusion conditions, which is thought to have a large effect on optical transmission loss. [Object of the Invention] The present invention has been made in response to the above-mentioned conventional circumstances, and it is an object of the present invention to provide a method for manufacturing an optical fiber cable in which there is almost no increase in optical transmission loss due to extrusion coating of ETFE. [Summary of the Invention] That is, the present invention provides, when providing an extrusion coating layer made of ETFE on the outer periphery of one or more optical fiber strands, molten ETFE is applied to the outer periphery of the optical fiber strand at a drawing ratio of 20 or less. After extrusion coating with
This is a method for manufacturing an optical fiber cable, which is characterized by immediate quenching. Note that the withdrawal ratio here is
It is the value obtained by dividing the hole diameter of the forming die by the finished diameter. 1 and 2 show an example of the structure of an optical fiber cable manufactured by the method of the present invention. In FIG. 1, reference numeral 1 indicates an optical fiber strand, and this optical fiber 1 consists of a central core 2 made of quartz glass or the like with a small refractive index, and a core 2 coated on the outside with a higher refractive index. It is composed of a cladding 3 made of quartz glass or the like. On the outside of the optical fiber wire 1 having such a structure, there is a two-layer structure made of silicone resin, epoxy acrylate resin, urethane acrylate resin, or butadiene acrylate resin, etc.
A buffer layer 4 with a thickness of about 150 μm is provided,
A secondary coating layer 5 made of ETFE is provided on the outside. Fig. 2 shows an optical fiber cable used for composite overhead ground wires, etc. Six optical fiber wires 1 are gathered around a steel wire 6 at its center, leaving a gap 7 on the outside. A sheath layer 8 made of ETFE is provided. Hereinafter, the method of the present invention will be explained by taking as an example the production of an optical fiber cable shown in FIG. First, the above-mentioned buffer layer 4 is provided on the outside of the optical fiber wire 1, and then molten ETFE is extruded and coated thereon at a drawing ratio of 20 or less, and then immediately passed through water at about 20°C to extrude coat it. Quench the layer. Note that ETFE includes, for example, Neofron.
ETFE (Daikin Industries, Ltd. product name), Aflon
COP (product name of Asahi Glass Co., Ltd.) etc. are used. According to such a manufacturing method, the molding shrinkage of ETFE extruded at high temperature after extrusion is minimized, so that an optical fiber cable having excellent coating loss characteristics can be obtained. The experiments and experimental results that led to setting the extrusion conditions for ETFE as described above will be explained below. First, the transmission loss is 2.42 and 2.56 dB/Km (λp
Aphron COP-88A was placed on two types of 125 μm diameter silica glass fibers (=0.86 μm) at a temperature of 280 μm.
~330℃, speed 23~24m/min, draw ratio 20 or 50
After coating by extrusion, an ETFE coated optical fiber with a diameter of 900 μm was manufactured by continuously cooling (air cooling) in air at room temperature. When the draw ratio was 20, the increase in optical transmission loss Δα was 1.11 and 0.92 dB, respectively. /Km
(λp=0.86μm), indicating good coating loss characteristics. Next, ETFE-coated optical fibers were manufactured in the same manner as above, with the draw ratio limited to 20 and the cooling method changed to the following three methods, and the optical transmission loss thereof was measured. Cooling methods include air cooling (slow cooling), hot cooling (cooling with 80℃ hot water),
There are three methods: water cooling (quenching with room temperature water at 20°C). The results show that when the cooling method is water cooling, Δα is
It showed good coating loss characteristics of 0.04 and 0.06 dB/Km (λp=0.86 μm). The table summarizes the above experimental results.

[Table] Experiment 1 All cooling was done by air cooling.
Experiment 2 The withdrawal amount is 20.
Regarding the above results, first of all, the reason why there is a large difference in loss characteristics due to the difference in drawdown ratio is because ETFE has a higher density than other nylons and has a higher melting temperature, so the molding shrinkage immediately after extrusion is extremely large. it is conceivable that. In addition, in the cooling method, it is thought that the crystallization of highly crystalline ETFE is minimized by rapid cooling, and as a result, molding shrinkage is suppressed and loss characteristics are improved. [Examples of the invention] Examples of the invention will be described below. Example Diameter 125μm, transmission loss 2.4dB/Km (λp=
After applying molten XE14-907 (trade name of silicone resin manufactured by Toshiba Silicone Co., Ltd.) onto a silica glass fiber wire of 0.86μm), OF-
111 (trade name of silicone resin manufactured by Shin-Etsu Silicone Co., Ltd.) was applied to produce a primary coated optical fiber with a diameter of 400 μm. Then apply Afron COP-88A on top of it at a temperature of 280
After extrusion under the extrusion conditions of ~330°C, speed of 50 m/min, and draw down ratio of 20, it was immediately (within 1 second) cooled by passing it through room temperature water at 20°C for 15 seconds to obtain an optical fiber cable with a diameter of 900 μm ( (having the structure shown in FIG. 1). When we investigated the coating loss characteristics of the obtained optical fiber cable, we found that Δα=0.04dB/Km
(λp=0.86μm), showing good characteristics. [Effects of the Invention] As is clear from the above explanation, according to the method of the present invention, molding shrinkage during extrusion coating of ETFE can be minimized, so a highly reliable optical fiber with excellent coating loss resistance can be produced. You can get the cable.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of an optical fiber cable manufactured by the method of the present invention, and FIG.
The figure is a sectional view showing the structure of another embodiment. DESCRIPTION OF SYMBOLS 1... Optical fiber wire, 2... Core, 3... Clad, 4... Buffer layer, 5... Secondary coating layer, 6...
...Steel wire, 7...Void, 8...Sheath layer.

Claims (1)

[Scope of Claims] 1. When providing an extrusion coating layer made of a tetrafluoroethylene/ethylene copolymer on the outer periphery of one or more optical fiber strands, molten tetrafluoroethylene is applied to the outer periphery of the optical fiber strand. A method for manufacturing an optical fiber cable, which comprises extrusion coating an ethylene/ethylene copolymer at a drawdown ratio of 20 or less, and then immediately rapidly cooling it. 2. The method for manufacturing an optical fiber cable according to claim 1, wherein the quenching is performed by bringing the extruded coating layer into contact with cooling water within 1 second after extrusion.