JP6442161B2 - Optical cable and optical cable manufacturing method - Google Patents

Description

  The present invention relates to an optical cable and a method for manufacturing the optical cable.

  An optical cable having a two-layer outer sheath (sheath) is known. Patent Document 1 describes that an outer sheath of an optical cable is configured with two layers, and a tension member (strength member) is disposed between an inner sheath (inner layer sheath) and an outer sheath (outer layer sheath). .

JP2013-83830A

  When an optical cable having a two-layer sheath is routed (wired) in a building, only the outer layer sheath may be removed to reduce the diameter (thinner diameter) of the optical cable. However, when a tensile body is disposed at the boundary (interface) between the inner layer sheath and the outer layer sheath as in the optical cable described in Patent Document 1, when the outer layer sheath is removed, the tensile body is exposed to the outside.

  When the strength member is made of, for example, glass-reinforced fiber plastic, if the strength member is exposed to the outside, the strength member comes into contact with water, and the glass fiber may be deteriorated. Further, even when the tensile body is made of a material other than glass, it is not desirable that the tensile body is exposed to the outside (described later).

  When the tensile body is arranged so as to be embedded inside the inner layer sheath having a circular cross section (first reference example described later: see FIG. 4), the tensile body is not exposed to the outside even if the outer layer sheath is removed. However, in this case, the diameter of the optical cable is increased.

  An object of the present invention is to provide an optical cable that does not expose a tensile body when an outer layer sheath is removed while reducing the diameter of the optical cable.

A main invention for achieving the above object is an optical cable comprising an optical fiber unit having a plurality of optical fibers, a sheath for housing the optical fiber unit, and a tensile body embedded in the sheath, The sheath has an inner layer sheath and an outer layer sheath outside the inner layer sheath, and a part of the strength member protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the strength member, The inner layer sheath is covered with a covering portion, and the part of the strength member and the covering portion of the inner layer sheath enter into a recess formed in an inner peripheral surface of the outer layer sheath, and the covering portion The optical cable is characterized in that an interface between the inner layer sheath and the outer layer sheath is formed at the boundary between the concave portion and the concave portion .

  Other characteristics of the present invention will be made clear by the description and drawings described later.

  According to the present invention, it is possible to remove the outer layer sheath without exposing the strength member while reducing the diameter of the optical cable.

FIG. 1A is a cross-sectional view of the optical cable 1. FIG. 1B is an enlarged cross-sectional view of the vicinity of the strength member 6. FIG. 2 is an explanatory view of the intermittently fixed type optical fiber tape 3. FIG. 3A is a process diagram of the manufacturing apparatus for the optical cable 1. FIG. 3B is an explanatory diagram of the nipple 24 and the die 26 of the extruder 22. FIG. 4 is an explanatory diagram of the optical cable 1 of the first reference example. FIG. 5 is an enlarged cross-sectional view of the vicinity of the strength member 6 of the optical cable 1 of the second reference example.

  At least the following matters will be apparent from the description and drawings described below.

An optical cable comprising: an optical fiber unit having a plurality of optical fibers; a sheath accommodating the optical fiber unit; and a tensile body embedded in the sheath, wherein the sheath includes an inner layer sheath and the inner layer sheath And a part of the strength member protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the strength member and is covered with a covering portion of the inner layer sheath. The optical cable is characterized in that the part of the strength member and the covering portion of the inner layer sheath enter a recess formed on the inner peripheral surface of the outer layer sheath.
According to such an optical cable, it is possible to remove the outer layer sheath without exposing the strength member while reducing the diameter of the optical cable.

  The inner layer sheath and the outer layer sheath are preferably formed by coextrusion molding. Thereby, manufacture of an optical cable becomes easy.

  It is desirable that the resin constituting the inner layer sheath is molded in a state where the viscosity of the resin constituting the outer layer sheath is higher. Thereby, manufacture of an optical cable becomes easy.

  The strength member is preferably made of glass fiber reinforced plastic. Even if the outer layer sheath is removed, the deterioration of the strength member can be suppressed, which is particularly effective in this case.

  The strength member is preferably made of a metal wire. Even if the outer sheath is removed, the strength member is insulated, which is particularly effective in this case.

A step of causing the inner layer resin to flow into the nipple side of the flow path of the extruder and causing the outer layer resin to flow into the outside of the inner layer resin in the flow path; an optical fiber unit having a plurality of optical fibers; and a tensile strength The inner layer resin is coated with the outer layer resin immediately after passing through the nipple of the extruder, and then the outer layer resin is coated with the outer layer resin. From the die hole of the extruder, the inner layer resin is coated. A step of pushing an optical cable in which the strength member is embedded in a sheath having an inner layer sheath constituted by and an outer layer sheath constituted by the resin for the outer layer, and a part of the strength member is made of the strength member. It protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity, and is covered with a covering portion of the inner layer sheath. The part of the tensile body and the covering portion of the inner layer sheath Manufacturing method of the optical cable, characterized in that enters the recess formed on the inner peripheral surface of the outer layer sheath becomes apparent.
According to such an optical cable manufacturing method, it is possible to manufacture an optical cable capable of removing the outer sheath without exposing the strength member while reducing the diameter of the optical cable.

=== Optical cable 1 ===
<Configuration>
FIG. 1A is a cross-sectional view of the optical cable 1. FIG. 1B is an enlarged cross-sectional view of the vicinity of the strength member 6.

  The optical cable 1 includes a plurality of optical fibers 3A, a press-wound tape 4, a sheath 10 (outer jacket), a pair of tear strings 5, and a pair of strength members 6. In the following description, an assembly of the plurality of optical fibers 3A and the press-wound tape 4 may be referred to as “optical fiber unit 2”. However, in the case of the optical cable 1 without the press-wound tape 4, the bundle of a plurality of optical fibers 3A may be referred to as “optical fiber unit 2”. The “optical fiber unit 2” may also be referred to as “optical fiber core” or “cable core”.

A bundle of a plurality of optical fibers 3A is formed by collecting a plurality of intermittently fixed optical fiber tapes 3 here.
FIG. 2 is an explanatory view of the intermittently fixed type optical fiber tape 3. The intermittently fixed optical fiber tape 3 is an optical fiber tape 3 in which connecting portions 3B that connect adjacent optical fibers 3A are intermittently arranged in the longitudinal direction and the width direction of the optical fiber 3A.
The intermittently fixed optical fiber tape 3 is composed of three or more optical fibers 3A (optical fiber core wires) arranged in parallel. A plurality of connecting portions 3B that connect two adjacent optical fibers 3A are intermittently arranged two-dimensionally in the longitudinal direction and the width direction. The connecting portion 3B is a portion that connects the two adjacent optical fibers 3A with, for example, an ultraviolet curable resin or a thermoplastic resin. A region other than the connecting portion 3B between the adjacent two optical fibers 3A is a non-connecting portion. In the unconnected portion, the adjacent two optical fibers 3A are not restrained. As a result, the optical fiber tape 3 can be rolled into a cylindrical shape (bundle shape) or folded and stored, and a large number of optical fibers 3A can be stored in the optical cable 1 with high density.

  The plurality of optical fibers 3 </ b> A may not be configured from the intermittently fixed type optical fiber tape 3. For example, instead of the intermittently fixed type optical fiber tape 3, a single-core optical fiber 3A may be used. Further, the bundle of the plurality of optical fibers 3A may be configured by bundling a plurality of optical fiber bundles bundled with a bundle material (identification member). In this case, an optical fiber bundle bundled with a bundle material may be referred to as a “subunit”.

  The presser winding tape 4 is a member that wraps the plurality of optical fibers 3A. As the presser winding tape 4, a polyimide tape, a polyester tape, a polypropylene tape, a polyethylene tape, or the like is used. In addition, a nonwoven fabric can be used as the presser winding tape 4. In this case, the nonwoven fabric used is a tape formed of polyimide, polyester, polypropylene, polyethylene or the like. In addition, the nonwoven fabric may be a material to which water-absorbing powder or the like is attached and applied, or a surface processed for that purpose. The presser winding tape 4 may be a non-woven fabric bonded with a film such as a polyester film.

  The sheath 10 is a member (outer jacket) that covers the optical fiber unit 2 (the plurality of optical fibers 3A and the presser winding tape 4). In this embodiment, the sheath 10 is composed of two layers, an inner layer sheath 11 and an outer layer sheath 12 outside the inner layer sheath 11. Examples of the material of the inner layer sheath 11 and the outer layer sheath 12 include resins such as polyvinyl chloride (PVC), polyethylene (PE), nylon (trademark registered), fluorinated ethylene or polypropylene (PP), and magnesium hydroxide, hydroxide, for example. A polyolefin compound containing a hydrated metal compound such as aluminum as a flame retardant can be appropriately selected and used. Here, medium density polyethylene is used for the inner sheath 11. The outer sheath 12 is made of nylon 6 (registered trademark), which is relatively hard and has high strength, for the purpose of preventing the inner sheath 11 from being damaged by ants.

  The outer shape of the sheath 10 (the outer shape of the outer layer sheath 12) has a circular cross section. Many existing closures, retaining winding grips, and the like are intended for the optical cable 1 having a circular cross section, and therefore can be applied to the optical cable 1 of the present embodiment.

  In the sheath 10, a pair of tear strings 5 and a pair of strength members 6 are embedded. The pair of tear strings 5 are disposed in the sheath 10 so as to sandwich the optical fiber unit 2. The pair of strength members 6 are also arranged in the sheath 10 so as to sandwich the optical fiber unit 2. In other words, the optical fiber unit 2 is sandwiched between the pair of strength members 6.

  The tear string 5 is a string (lip cord) used for tearing the sheath 10. By pulling the tear string 5, the operator tears the sheath 10, peels off the sheath 10, and takes out the optical fiber 3 </ b> A in the optical cable 1. The tear string 5 is vertically attached around the optical fiber unit 2 and is embedded in the sheath 10 (inner layer sheath 11) or disposed between the sheath 10 (inner layer sheath 11) and the optical fiber unit 2. ing. As the tear string 5, for example, a fiber such as polyester, polyimide, or aramid, a fiber assembly, a fiber impregnated with a resin, a fiber strand twisted together, or the like can be used.

The strength member 6 is a member (tension member) that resists the contraction of the sheath 10 and suppresses distortion and bending applied to the optical fiber unit 2 by the contraction of the sheath 10. The strength member 6 is a linear member, and is embedded in the sheath 10 so that the longitudinal direction thereof is along the longitudinal direction (cable direction) of the optical cable 1. As the material of the strength member 6, a non-metallic material or a metallic material can be used. Non-metallic materials include fiber reinforced plastic (FRP) such as glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (KFRP) reinforced with Kevlar (registered trademark), polyethylene fiber reinforced plastic reinforced with polyethylene fiber, etc. Is possible. As the metallic material, a metal wire such as a steel wire can be used. Here, glass fiber reinforced plastic (GFRP) is used for the strength member 6.
When glass fiber reinforced plastic (GFRP), which is a non-metallic material, is used for the tensile body 6, the elastic modulus is smaller than that of the steel wire, so that the glass fiber reinforced is used to obtain the tensile strength required for the optical cable 1. The outer diameter of the strength member 6 made of plastic (GFRP) is larger than that of the strength member 6 made of steel wire. The diameter of the strength member 6 (glass fiber reinforced plastic) of this embodiment is 1.7 mm.

  As shown in FIG. 1A, the strength member 6 is located at the boundary between the inner layer sheath 11 and the outer layer sheath 12 (however, as described later, it is not located at the interface between the inner layer sheath 11 and the outer layer sheath 12). ing. In other words, the tensile body 6 projects outward from the outer peripheral surface of the inner layer sheath 11 excluding the vicinity of the tensile body 6. Hereinafter, the part of the tensile body 6 protruding from the outer peripheral surface of the inner layer sheath 11 excluding the vicinity of the tensile body 6 may be referred to as a “projecting portion 6A” (see FIG. 1B). A concave portion 12A (see FIG. 1B) is formed on the inner peripheral surface of the outer layer sheath 12 excluding the vicinity of the tensile body 6, and the protruding portion 6A of the tensile body 6 enters the concave portion 12A of the outer layer sheath 12.

  As shown in FIG. 1B, the protruding portion 6 </ b> A of the strength member 6 is covered with an inner layer sheath 11. Hereinafter, a portion covering the protruding portion 6A of the strength member 6 may be referred to as a “thin film portion 11A”. For this reason, the protruding portion 6 </ b> A and the thin film portion 11 </ b> A of the strength member 6 protrude outward from the outer peripheral surface of the inner layer sheath 11 except the vicinity of the strength member 6. Further, the protruding portion 6 </ b> A and the thin film portion 11 </ b> A of the strength member 6 enter the recess 12 </ b> A of the outer layer sheath 12.

  Since the protruding portion 6 </ b> A of the strength member 6 is covered with the thin film portion 11 </ b> A, the entire circumference of the strength member 6 is covered with the inner layer sheath 11. For this reason, for example, when the optical cable 1 is routed (wired) in the building, even if the outer sheath 12 is removed to reduce the diameter (thinner diameter), the protruding portion 6A of the strength member 6 does not move to the inner sheath 11 (thin film). Since it is covered with the part 11A), the tension member 6 is not exposed to the outside.

When the strength member 6 is made of glass fiber reinforced plastic (GFRP) as in the present embodiment, the strength member 6 deteriorates (glass deteriorates) if the strength member 6 comes into contact with water. However, in this embodiment, even if the outer layer sheath 12 is removed, the strength member 6 is not exposed to the outside, and therefore, the strength member 6 can be prevented from coming into contact with water.
In addition, when the strength member 6 is formed of a metal wire, if the strength member 6 is exposed to the outside, the strength member 6 is not insulated, which is not desirable. However, if the protrusion 6A of the strength member 6 is covered with the inner layer sheath 11 as in this embodiment, the strength member 6 can be insulated by the thin film portion 11A even if the outer layer sheath 12 is removed.
Further, when the tensile body 6 is made of, for example, KFRP (aramid fiber reinforced plastic), the tensile body 6 is deteriorated when the tensile body 6 is directly irradiated with ultraviolet rays. That is not desirable. However, if the protruding portion 6A of the strength member 6 is covered with the inner layer sheath 11 as in this embodiment, the strength member 6 can be protected from ultraviolet rays by the thin film portion 11A even if the outer layer sheath 12 is removed.

  The strength member 6 of this embodiment is bonded to the inner layer sheath 11. Thereby, the distortion and bending of the optical fiber 3A due to the shrinkage of the sheath 10 due to heat at the time of manufacture (described later), the shrinkage of the sheath 10 due to a change in environmental temperature, and the like can be suppressed. In the present embodiment, since the entire circumference of the strength member 6 is covered with the inner layer sheath 11, the strength member 6 and the inner layer sheath 11 can be easily bonded.

<Method for manufacturing optical cable 1>
FIG. 3A is a process diagram of the manufacturing apparatus for the optical cable 1.
A plurality of (for example, 12) intermittently fixed optical fiber tapes 3 are supplied to the collecting machine 21. A plurality of optical fibers 3 </ b> A twisted into an SZ shape and collected by the collecting machine 21 are wound around the presser winding tape 4 and supplied to the extruder 22. The extruder 22 is supplied with the optical fiber unit 2 (here, the plurality of optical fibers 3A and the presser winding tape 4), the two tear strings 5, and the two strength members 6. The extruder 22 moves the optical fiber unit 2 while feeding the tear string 5 and the tensile body 6 from the respective supply sources, and the sheath 10 (the inner sheath 11 and the outer sheath 12) around the optical fiber unit 2. Cover. In this embodiment, the optical fiber unit 2 is covered with the sheath 10 (inner layer sheath 11 and outer layer sheath 12) having a two-layer structure by coextrusion molding.

FIG. 3B is an explanatory diagram of the nipple 24 and the die 26 of the extruder 22.
The optical fiber unit 2 (the plurality of optical fibers 3A and the presser winding tape 4) supplied to the extruder 22 passes through the first guide hole 24A of the nipple 24 and is guided to the die hole 26A of the die 26. The strength member 6 supplied to the extruder 22 passes through the second guide hole 24 </ b> B of the nipple 24 and is guided to the die hole 26 </ b> A of the die 26. Although not shown, the tear string 5 supplied to the extruder 22 also passes through the nipple 24 and is guided to the die hole 26 </ b> A of the die 26.

  Inside the die 26, a flow path for resin is formed between the nipple 24 and the flow path is filled with resin. The resin for the inner layer constituting the inner layer sheath 11 flows into the nipple 24 side (the inner side of the channel) of the channel. In the figure, the inner layer resin is shown in black. Outer layer resin constituting the outer layer sheath 12 flows into the die 26 side of the channel (outside the channel, outside the inner layer resin in the channel). In the drawing, the resin for the outer layer is shown by hatching in the shade. As shown in FIG. 1A, the pressure in the inner layer resin and the outer layer resin flow path is the boundary between the inner layer sheath 11 and the outer layer sheath 12 (however, as already described, the interface between the inner layer sheath 11 and the outer layer sheath 12). It is adjusted so that the strength member 6 is disposed at the same position.

  Since the outer periphery of the nipple 24 is filled with the inner layer resin, the optical fiber unit 2 (the plurality of optical fibers 3A and the presser winding tape 4) immediately after passing through the first guide hole 24A of the nipple 24 is first used for the inner layer. Touch the resin. Thereafter, the outer side of the inner layer resin is covered with the outer layer resin, and the circular optical cable 1 covered with the sheath 10 is pushed out from the circular die hole 26A.

  Further, the tensile body 6 immediately after passing through the second guide hole 24B of the nipple 24 is also first touched with the inner layer resin because the outer periphery of the nipple 24 is filled with the inner layer resin. Therefore, at this stage, the entire circumference of the strength member 6 is covered with the inner layer resin. Thereafter, a part of the tensile body 6 (projecting portion 6A in FIG. 1B) enters the region of the outer layer resin in the flow path. At this time, the inner layer resin applied to the outer periphery of the strength member 6 is not wiped by the outer layer resin, and a part of the strength member 6 enters the region of the outer layer resin while enclosing the surrounding inner layer resin. Thereby, as shown in FIG. 1B, the protruding portion 6 </ b> A of the strength member 6 is covered with the thin film portion 11 </ b> A of the inner layer sheath 11.

  In this embodiment, the sheath 10 (inner layer sheath 11 and outer layer sheath 12) having a two-layer structure is formed by coextrusion molding. For this reason, since the sheath 10 can be comprised by one extrusion molding, a manufacturing process can be simplified.

  Moreover, in this embodiment, it shape | molds in the state in which the viscosity of resin for inner layers is higher than the viscosity of resin for outer layers. Thus, once the inner layer resin is applied to the outer periphery of the strength member 6, the inner layer resin is less likely to be wiped off by the outer layer resin. Therefore, the protrusion 6 </ b> A of the strength member 6 is covered with the inner layer resin to form a thin film. It becomes easy to form the portion 11A (see FIG. 1B). In addition, as a viscosity of the resin at the time of molding, an index is a melt mass flow rate (MFR: JIS K 7210) at the molding temperature of each layer. By using such molding conditions, the viscosity at the time of molding the inner layer resin is lower than the viscosity at the time of molding the outer layer resin (for example, when the inner layer resin is as low as water), It becomes easy to form the thin film portion 11A.

<First Reference Example>
FIG. 4 is an explanatory diagram of the optical cable 1 of the first reference example. In the first reference example, the inner layer sheath 11 is once formed as shown in the left figure of FIG. 4, and then the outer layer sheath 12 is coated as shown in the right figure to manufacture the optical cable 1. Since the strength member 6 may be damaged after the formation of the inner layer sheath 11 until the formation of the outer layer sheath 12, in the first reference example, the whole strength member 6 is covered with the inner layer sheath 11 having a circular cross section.

  In the first reference example, the strength member 6 is embedded inside an inner layer sheath 11 having a circular cross section, and an outer layer sheath 12 is formed outside the inner layer sheath 11 having a circular cross section. For this reason, the optical cable 1 of the first reference example tends to be thick. On the other hand, in the present embodiment, the protruding portion 6A of the strength member 6 protrudes outward from the outer peripheral surface of the inner layer sheath 11 excluding the vicinity of the strength member 6, and enters the recess 12A of the outer layer sheath 12. For this reason, the optical cable 1 of this embodiment can be reduced in diameter compared with the first reference example shown in FIG.

  Further, in the manufacturing method of the first reference example, the number of steps for coating the resin is increased twice, so that the number of steps is increased as compared with the manufacturing method (coextrusion molding) of the present embodiment.

<Second Reference Example>
FIG. 5 is an enlarged cross-sectional view of the vicinity of the strength member 6 of the optical cable 1 of the second reference example. In the second reference example, the strength member 6 is disposed at the boundary (interface) between the inner layer sheath 11 and the outer layer sheath 12, and the protruding portion 6 </ b> A of the strength member 6 is in contact with the outer layer sheath 12. In the second reference example, the protruding portion 6 </ b> A of the strength member 6 protrudes outward from the outer peripheral surface of the inner layer sheath 11 and enters the recess 12 </ b> A of the outer layer sheath 12. For this reason, the optical cable 1 of the second reference example can be reduced in diameter as compared with the first reference example shown in FIG.

  However, in the second reference example, the protruding portion 6 </ b> A of the strength member 6 is not covered with the inner layer sheath 11 and is in contact with the outer layer sheath 12. For this reason, for example, when the outer layer sheath 12 is removed to reduce the diameter when the optical cable 1 is routed in a building, the tensile body 6 is exposed to the outside. On the other hand, in the present embodiment, even if the outer layer sheath 12 is removed, the protruding portion 6A of the strength member 6 is covered with the inner layer sheath 11 (thin film portion 11A), so that the strength member 6 is not exposed to the outside. It will end.

=== Others ===
The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be modified and improved without departing from the gist thereof, and it goes without saying that the present invention includes equivalents thereof.
<About optical cable 1>
In the above-described embodiment, the tear string 5 and the tensile body 6 are arranged inside the sheath 10, but members different from these may be arranged inside the sheath 10. Further, the tear string 5 may not be provided inside the sheath 10.
In the above-described embodiment, the optical cable 1 has two strength members 6, but the number of strength members 6 is not limited to two. The number of strength members 6 may be one, or three or four or more.
<About sheath 10>
In the above-described embodiment, the sheath 10 has a two-layer structure including the inner layer sheath 11 and the outer layer sheath 12. However, the sheath 10 is not limited to a two-layer structure, and may have a structure of three or more layers. For example, another sheath layer may be formed inside the aforementioned inner layer sheath 11, or another sheath layer may be formed outside the outer layer sheath 12.

1 optical cable, 2 optical fiber unit,
3 optical fiber tape, 3A optical fiber, 3B connecting part,
4 Presser winding tape, 5 tear string,
6 Tensile body, 6A protrusion,
10 sheath (outer coating), 11 inner layer sheath, 11A thin film part,
12 outer layer sheath, 12A recess,
21 collecting machine, 22 extruder,
24 nipple, 24A first guide hole, 24B second guide hole,
26 Dice, 26A Die hole

Claims (9)

An optical fiber unit having a plurality of optical fibers;
A sheath for housing the optical fiber unit;
Strength members embedded in the sheath;
An optical cable comprising:
The sheath has an inner layer sheath and an outer layer sheath outside the inner layer sheath,
A part of the tensile body protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the tensile body, and is covered with a covering portion of the inner layer sheath,
The part of the tensile body and the covering portion of the inner layer sheath enter a recess formed in an inner peripheral surface of the outer layer sheath, and the inner layer sheath and the outer sheath at the boundary between the covering portion and the recess An optical cable characterized in that an outer sheath interface is formed . The optical cable according to claim 1,
The outer layer sheath and the inner layer sheath are separable,
The optical cable, wherein when the outer layer sheath is removed from the inner layer sheath, the tensile body is covered with the covering portion of the inner layer sheath. The optical cable according to claim 1 or 2,
The optical cable, wherein the inner layer sheath and the outer layer sheath are formed by coextrusion molding. The optical cable according to claim 3,
An optical cable characterized in that the viscosity of the resin constituting the inner layer sheath is molded in a state higher than the viscosity of the resin constituting the outer layer sheath. The optical cable according to claim 1,
The optical cable is characterized in that the tensile body is made of glass fiber reinforced plastic. The optical cable according to claim 1,
The optical cable is characterized in that the tensile body is made of a metal wire. A step of causing the inner layer resin to flow into the nipple side of the flow path of the extruder and causing the outer layer resin to flow into the outside of the inner layer resin in the flow path;
After coating an optical fiber unit having a plurality of optical fibers and a tensile body with the inner layer resin immediately after passing through the nipple of the extruder, the outside of the inner layer resin is coated with the outer layer resin, Extruding an optical cable in which the tensile body is embedded in a sheath having an inner layer sheath made of the inner layer resin and an outer layer sheath made of the outer layer resin from a die hole of the extruder;
Have
A part of the tensile body protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the tensile body, and is covered with a covering portion of the inner layer sheath,
The part of the tensile body and the covering portion of the inner layer sheath enter a recess formed in an inner peripheral surface of the outer layer sheath, and the inner layer sheath and the outer sheath at the boundary between the covering portion and the recess An optical cable manufacturing method, wherein an interface of an outer layer sheath is formed . A step of causing the inner layer resin to flow into the nipple side of the flow path of the extruder and causing the outer layer resin to flow into the outside of the inner layer resin in the flow path;
After coating an optical fiber unit having a plurality of optical fibers and a tensile body with the inner layer resin immediately after passing through the nipple of the extruder, the outside of the inner layer resin is coated with the outer layer resin, Extruding an optical cable in which the tensile body is embedded in a sheath having an inner layer sheath made of the inner layer resin and an outer layer sheath made of the outer layer resin from a die hole of the extruder;
Have
A part of the tensile body protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the tensile body, and is covered with a covering portion of the inner layer sheath,
The part of the tensile body and the covering portion of the inner layer sheath enter a recess formed in the inner peripheral surface of the outer layer sheath,
A method of manufacturing an optical cable, comprising: covering the entire periphery of the strength member with the inner layer resin in the flow path of the extruder; and then causing a part of the strength member to enter the region of the outer layer resin. (1) an optical fiber unit having a plurality of optical fibers;
A sheath for housing the optical fiber unit;
Strength members embedded in the sheath;
A step of preparing an optical cable comprising:
The sheath has an inner layer sheath and an outer layer sheath outside the inner layer sheath,
A part of the tensile body protrudes outward from the outer peripheral surface of the inner layer sheath excluding the vicinity of the tensile body, and is covered with a covering portion of the inner layer sheath,
The part of the tensile body and the covering portion of the inner layer sheath enter a recess formed in an inner peripheral surface of the outer layer sheath, and the inner layer sheath and the outer sheath at the boundary between the covering portion and the recess Providing an optical cable configured such that an interface of the outer sheath is formed ;
(2) removing the outer layer sheath from the inner layer sheath of the optical cable, and wiring the optical cable in a state where the tensile body is covered with the covering portion of the inner layer sheath. Wiring method.

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