JPS59113403A - High strength optical fiber unit - Google Patents

Abstract

PURPOSE:To obtain high strength without requiring a central tension member by forming a coating layer of a thermoplastic resin molecularly oriented by stretching it in the longitudinal direction in a speed not below a specified shear rate, on the outside of a press winding tape for tying plural optical fiber strands in a bundle. CONSTITUTION:Plural glass fiber strands 1, e.g. five strands as illustrated in the figure, are bundled by tying them with a press winding tape 6 without using a conventional center tension member. A coating layer (unit pipe) 3' is formed on the outside of the tape 6 by extruding a modified polyester obtained by substituting a part of polyethylene terephthalate for p-hydroxybenzoic acid, or the like polyester, and stretching it in a speed of >= about 10<3>/sec melt shear rate with the nozzle of an extruder head. As a result, an optical fiber unit having sufficiently high strength is obtained without requiring the central tension member 2, such as a steel wire and the central tension member of optical fiber, and hence reduction of the diameter of an optical cable is made possible and it may be made suitable for its protection from thunder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber unit used for optical communications.

When the original fiber is used for communication, the fiber is cored and further made into a cable in order to prevent a decrease in fiber strength, to suppress an increase in transmission loss, and to facilitate handling. As optical fiber communications enter the stage of practical use, economicalization and reduction in diameter of optical fiber cables become important.

FIG. 1 is a cross-sectional view of an example of a conventional optical fiber cable, where l is a glass fiber 'Afg2, 2' unit center tension member, 3 is a unit pipe, 4 is a cable center tension member, and 5 is a cable jacket. be.

First, a plurality of fiber strands primarily coated with silicone resin or epoxy acrylate resin are twisted around a unit tension member made of 20 steel wires,
The optical fiber is then covered with a plastic tube (unit pipe 8) made of thermoplastic resin such as nylon.
Make an Iba unit.

Next, this unit is twisted around the circumference of a cable center tension member 4 made of steel wire, etc., and coated with a thermoplastic resin (cable jacket 5) such as polyethylene to form a multicore high-density optical fiber cable. Made.

As is clear from FIG. 1, tensile strength members are used in both the cable and the unit. These tension members have an elastic modulus (several GPa or less) and a linear expansion coefficient (of the order of 1 O-'°C-1) of the thermoplastic resin that is the material of the unit pipe 3 and cable jacket 5, but are similar to those of glass fiber. elastic modulus (approximately 70 GPa), linear expansion 'a
<'1k (10-7°c-": t-p--). The cable tension member 4 mainly has the role of compensating for the low elastic modulus of thermoplastic resin, and The central tension member 2 plays the role of compensating for the high coefficient of linear expansion of the thermoplastic resin. It is essential to use tension members for both the cable and the cable, which has drawbacks in terms of economy and reduction in diameter.

In order to eliminate these drawbacks, the present invention gathers optical fiber strands of multiple ratios together with a pressure-wrapping tape, and on the outside thereof, molecules are oriented in the longitudinal direction of the fiber at a melting shear rate of approximately 1 OSec or more. It is characterized by using a thermoplastic resin with a low modulus of elasticity and a low coefficient of linear expansion as the unit pipe, and its purpose is to omit the central tension member of the unit and to make the optical fiber cable more economical and smaller in diameter.

The present invention will be described below based on Examples.

FIG. 2 is a cross-sectional view of the optical fiber unit according to the present invention, where l is a glass fiber wire, 3' is a unit pipe which has a high elastic modulus and low coefficient of linear expansion due to fused spun Fr orientation, and 6 is a fiber This is a tape for holding and wrapping strands of wire together. The unit pipe 8' is a feature of the present invention, and in this embodiment, polyethylene terephthalate (PE) is used as the unit pipe material.
Modified P in which part of T) is substituted with p-hydroxybenzoic acid
E'I' is used. The fact that the modified PE'I' etc. is subjected to shear stress at the nozzle of the extruder head, resulting in highly oriented molecular orientation in the longitudinal direction of the pipe, has already been reported by the present inventors in the "Method for Manufacturing Optical Fiber Corded Wire" (1981). (Patent application filed on December 9th). The modified PET subjected to a shear rate of approximately 108 Sec-1 or higher at the nozzle of the extruder head has an elastic modulus of approximately 10 GPa or higher and a linear expansion coefficient of 1 O.
-6°C-1 or less.

As described above, since the unit pipe itself has a high modulus of elasticity and a low coefficient of linear expansion, the tension member 2 used in the optical fiber unit of 071 is no longer necessary.1. It has a simple structure and can be made low-cost and small in diameter. Furthermore, if the diameter is the same as before, a larger number of fiber wires can be accommodated in the unit pipe, achieving higher density. The unexploded ErJJ (D optical fiber unit) is a so-called non-metallic optical fiber unit that does not include the conventional unit central tension member 2 made of steel wire or the like.

Therefore, it is ideal as an optical fiber unit for non-metallic optical fiber cables, especially when lightning protection is required.

The thermoplastic resin used as the unit pipe in the present invention is a polymer that exhibits a liquid crystal state in a molten state (thermotropic liquid crystal), or a polymer that exhibits a liquid crystal state (tQt) in the flow direction under high temperature and flow conditions, even if it does not clearly exhibit a liquid crystal state. Can it be used if it is a polymer with a high degree of molecular orientation? Examples include, but are not limited to, polymers containing chemical structures capable of forming liquid crystals in their side chains or engraftments, flexible polymers such as polyphosphazene, polydiethyl, and siloxane, or blends of these polymers and other polymers. Things can be given. Note that the thermotropic liquid crystal referred to herein is a polymer that has crystal anisotropy and liquid fluidity before melting and becoming a liquid, as is generally known.

As explained above, the optical fiber unit according to the present invention does not require a separate center tension member because the unit pipe itself serves as a tensile strength member, and is an optical fiber unit for non-metallic use. Compared to conventional optical fiber units, this optical fiber unit has the following advantages: it is more economical, it can be made smaller in diameter, and it is suitable as an optical fiber unit for lightning protection.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an example of a conventional optical fiber cable, and FIG. 2 is a sectional view of an optical fiber unit according to the present invention. l...Glass fiber wire 2...Unit center tension member 8...Unit vibe 4...Cable center tension member 5...Cable jacket 6...Pressure winding tape 3'...piece Unit vibe according to the invention. Patent applicant: Nippon Telegraph and Telephone Public Corporation Figure 1 Figure 2

Claims (1)

[Claims] Lm several optical fiber strands, a presser-wrapping tape that gathers these optical fiber strands together, and molecular orientation in the direction of the fiber padlock on the outside of the presser-wrap tape at a melting shear rate of approximately 108 seconds or more. A high-strength optical fiber unit characterized by having a coating layer made of a thermoplastic resin.