Method for manufacturing an optical fiber cable and optical fiber cable

Abstract

The present invention relates to a method for manufacturing an optical fiber cable and an optical fiber cable. The method for manufacturing an optical fiber cable includes: a feeding step of feeding a core portion having a plurality of optical fibers; a winding step of winding a strengthening member around the core portion and forming an overlapping portion in which end portions of the strengthening member overlap with each other in a part of the circumferential direction; and an extrusion molding step of extruding a sheath outside the strengthening member. In the extrusion molding step, a resin constituting the sheath is made to enter at least a part of the overlapping portion.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical fiber cable and an optical fiber cable.

[0002] This application claims the priority of Japanese Patent Application No. 2019-185963 filed on October 9, 2019, and incorporates its content herein by reference. Background Art

[0003] A cable is disclosed in Patent Document 1, which includes an optical fiber core, a reinforcing member disposed to surround the optical fiber core, a filler filled between the optical fiber core and the reinforcing member, and a sheath covering the outside of the reinforcing member.

[0004] In the method for manufacturing this cable, first, a strip-shaped material as a reinforcing member is prepared, and an adhesive is applied to both end portions of the strip-shaped material. Next, the optical fiber core is disposed on the strip-shaped material, and a filler is filled on the strip-shaped material and the optical fiber core. Then, the strip-shaped material and the optical fiber core are passed through a former, whereby both end portions of the strip-shaped material are overlapped to form a reinforcing member. Then, the reinforcing member is introduced and passed through an extrusion forming machine, whereby a sheath is formed by covering the resin on the reinforcing member.

[0005] Patent Document 1: Japanese Patent Laid-Open No. 11-337783

[0006] In the cable of Patent Document 1, since the overlapping portion of the reinforcing member is joined by an adhesive, there is a possibility that a portion with weak adhesive force is generated in the longitudinal direction of the cable. In a portion with weak adhesive force, for example, when the cable is bent, the overlapping portion often opens, and stress is concentrated on the sheath covering this portion, and the sheath may break. Summary of the Invention

[0007] The present invention has been completed in view of such a situation, and an object thereof is to provide a method for manufacturing an optical fiber cable and an optical fiber cable that can suppress the breakage of the sheath.

[0008] In order to solve the above problems, a method for manufacturing an optical fiber cable according to a first embodiment of the present invention includes the following steps: a feeding step of feeding a core portion having a plurality of optical fibers; a winding step of winding a reinforcing member around the core portion and forming an overlapping portion where end portions of the reinforcing member overlap each other in a part in the circumferential direction; and an extrusion molding step of extruding a sheath on the outside of the reinforcing member, and in the extrusion molding step, causing the resin constituting the sheath to enter at least a part of the overlapping portion.

[0009] The optical fiber cable according to the second embodiment of the present invention includes: a core portion having a plurality of optical fibers; a strengthening member surrounding the core portion; and a sheath housing the core portion and the strengthening member, wherein the strengthening member has an overlapping portion where ends thereof overlap in a part of the circumferential direction, and a resin forming the sheath enters at least a part of the overlapping portion.

[0010] According to the above embodiment of the present invention, breakage of the sheath can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a perspective view of the optical fiber cable according to the first embodiment.

[0012] Figure 2 is a cross-sectional view of the optical fiber cable according to the first embodiment.

[0013] Figure 3 is Figure 1 a III-III sectional view.

[0014] Figure 4 is a cross-sectional view before an outer sheath covering Figure 1 the optical fiber cable.

[0015] Figure 5 is a cross-sectional view before an outer sheath covering Figure 1 the optical fiber cable.

[0016] Figure 6 is a view showing a manufacturing method of the optical fiber cable according to the first embodiment.

[0017] Figure 7 is a cross-sectional view of the optical fiber cable according to the first embodiment.

[0018] Figure 8 is a view showing the resistance of the optical fiber cable manufactured by the manufacturing method of the optical fiber cable according to the first embodiment.

[0019] Figure 9 is a cross-sectional view of the optical fiber cable according to the second embodiment.

[0020] Figure 10 is a cross-sectional view before an outer sheath covering the optical fiber cable according to the second embodiment.

[0021] Figure 11 is a cross-sectional view before an outer sheath covering the optical fiber cable according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] (First Embodiment)

[0023] Hereinafter, the structure of the optical fiber cable according to the first embodiment will be described with reference to Figures 1 to 8 the drawings.

[0024] As Figure 1 shown in the figure, the optical fiber cable 1A includes: an inner cable 10 having optical fibers, a strengthening unit (strengthening member) 20, an outer sheath 30, and a pair of first tearing cords 12.

[0025] (Direction definition)

[0026] Here, in the present embodiment, the long side direction of the inner cable 10 is simply referred to as the long side direction, and the central axis of the inner cable 10 is referred to as the central axis O. In addition, a cross section orthogonal to the central axis O is referred to as a cross section. In the cross-sectional view, the direction intersecting the central axis O is referred to as the radial direction, and the direction of rotation around the central axis O is referred to as the circumferential direction.

[0027] The inner cable 10 includes: a core portion 11 having a plurality of optical fibers, a pair of second tearing cords 16, a pair of anti-tension bodies (tension members) 13, and an inner sheath 14. The inner cable 10 may not have the second tearing cords 16.

[0028] The core portion 11 extends in the long side direction. The core portion 11 is formed by gathering a plurality of optical fibers. As the optical fibers constituting the core portion 11, optical fiber wires, optical fiber core wires, optical fiber ribbon core wires, etc. can be used. The plurality of optical fibers constituting the core portion 11 can also be formed by being bundled by a bundling material in a bundled state. The plurality of optical fibers are covered with a pressed roll and a water absorption tape.

[0029] As Figure 2 shown in the figure, in the cross-sectional view, a pair of second tearing cords 16 are buried in the inner sheath 14 so as to sandwich the core portion 11 in the radial direction. The pair of second tearing cords 16 extend in the long side direction. In the cross-sectional view, the pair of second tearing cords 16 are located on a straight line orthogonal to a neutral line L described later and passing through the central axis O. The pair of second tearing cords 16 are in contact with the outer peripheral surface of the core portion 11. As the material of the second tearing cords 16, in addition to cords made of synthetic fibers such as polyester and aramid, cylindrical rods made of PP or nylon can also be used.

[0030] A pair of anti-tension bodies 13 are buried in the inner sheath 14 so as to sandwich the core portion 11 in the radial direction in the cross-sectional view. Each anti-tension body 13 extends in the long side direction. Each anti-tension body 13 can be arranged parallel to the core portion 11 in the long side direction, or can be arranged in a spiral shape with the core portion 11 as the center.

[0031] The anti-tension body 13 functions to protect the optical fibers of the core portion 11 from the tension acting on the optical fiber cable 1A. The material of the anti-tension body 13 is, for example, a metal wire (such as a steel wire), an anti-tension fiber (such as an aramid fiber), FRP, etc. The anti-tension body 13 can be a single wire, or can be a member that bundles a plurality of wire materials or twists them together.

[0032] In a cross-sectional view, the straight line connecting the centers of a pair of tension members 13 is defined as the neutral line L. When the optical fiber cable 1A is bent in a direction perpendicular to the neutral line L ( Figure 2 in the up-and-down direction), the expansion and contraction of the tension members 13 become smaller compared to the case where the optical fiber cable 1A is bent in other directions. Therefore, the optical fiber cable 1A is relatively easy to bend in a direction perpendicular to the neutral line L.

[0033] The inner cable 10 may also include three or more tension members 13. When three or more tension members 13 are arranged at equal intervals in the circumferential direction, the bending directionality of the inner cable 10 becomes smaller, and the optical fiber cable 1A can be more easily handled.

[0034] The inner sheath 14, as Figure 2 shown, covers the core portion 11, a pair of tension members 13, and a pair of second tear ropes 16 together. Resins such as polyethylene (PE) and polyvinyl chloride (PVC) can be used as the material of the inner sheath 14. The inner sheath 14 is formed in a cylindrical shape extending in the longitudinal direction. The inner sheath 14 is formed by extrusion molding or the like.

[0035] The outer sheath 30 houses the inner cable 10, a pair of first tear ropes 12, and the strengthening unit 20.

[0036] The strengthening unit 20 extends in the longitudinal direction and is formed in a cylindrical shape surrounding the inner cable 10. The strengthening unit 20 has a first adhesive film 21 (adhesive layer), a second adhesive film 22, and a strengthening sheet 23.

[0037] Metals such as iron, stainless steel, copper, and copper alloy can be used as the material of the strengthening sheet 23. The material of the strengthening sheet 23 can be appropriately changed. Preferably, the strengthening sheet 23 is, for example, in a strip shape, and is arranged such that the length direction is the same as the longitudinal direction of the inner cable 10. The thickness of the strengthening sheet 23 is, for example, about 0.1 to 0.3 mm. By setting the thickness of the strengthening sheet 23 within this range, it is possible to prevent the optical fiber of the core portion 11 from being damaged by animal gnawing, and it is possible to easily perform the operation of cutting the strengthening sheet 23 using the first tear rope 12.

[0038] In the present embodiment, although the structure in which the strengthening unit 20 includes the first adhesive film 21 and the second adhesive film 22 has been described as an example, the strengthening unit 20 only needs to include at least the first adhesive film 21. When the second adhesive film 22 is further provided in addition to the first adhesive film 21, it is possible to further strengthen the film adhesive force of the overlapping portion 20c (described later) and suppress the rusting of the strengthening sheet 23.

[0039] The reinforcing unit 20 surrounds the inner cable 10 throughout the entire circumference and overlaps at a part in the circumferential direction. In this specification, the part where the first end portion 20a and the second end portion 20b of the reinforcing unit 20 overlap is referred to as the overlapping portion 20c. In the overlapping portion 20c, the first end portion 20a and the second end portion 20b are opposed to each other in the radial direction.

[0040] In the present embodiment, in the cross-sectional view, the entire overlapping portion 20c and the anti-tensile body 13 are arranged at different positions in the circumferential direction.

[0041] The first adhesive film 21 is attached to the surface of the reinforcing sheet 23 facing the outer sheath 30. The second adhesive film 22 is attached to the surface of the reinforcing sheet 23 facing the inner cable 10. As the adhesive for the first adhesive film 21 and the second adhesive film 22, for example, a thermosetting type or a hot melt type adhesive can be used. The material of the adhesive can also be appropriately changed. The first adhesive film 21 has the function of fixing the outer sheath 30 to the reinforcing sheet 23. The second adhesive film 22 may also have the function of fixing the first tearing cord 12 to the reinforcing sheet 23 together with the outer skin 12a of the first tearing cord 12 described later. In the first adhesive film 21 and the second adhesive film 22, the part located between the reinforcing sheets 23 in the overlapping portion 20c has the function of fixing the end portions of the reinforcing sheets 23 to each other by the overlapping portion 20c.

[0042] As Figure 3 shown, the reinforcing unit 20 has a corrugated shape in which the mountain portions 24 protruding radially outward and the valley portions 25 protruding radially inward are alternately formed along the long side direction. In the overlapping portion 20c, the mountain portion 24a of the first end portion 20a and the mountain portion 24b of the second end portion 20b are opposed to each other in the radial direction, and the valley portion 25a of the first end portion 20a and the valley portion 25b of the second end portion 20b are opposed to each other in the radial direction.

[0043] In the overlapping portion 20c, the bonding state of the first end portion 20a and the second end portion 20b bonded by the first adhesive film 21 and the second adhesive film 22 may be uneven in the long side direction. In this specification, the state in which the first end portion 20a and the second end portion 20b are bonded by the adhesive films 21 and 22 with a film adhesive force equal to or greater than a specified film adhesive force is referred to as state S1, and the state in which they are bonded with a film adhesive force smaller than the specified film adhesive force is referred to as state S2. In state S2, for example, as Figure 2 shown, a gap 26 is formed between the first end portion 20a and the second end portion 20b. The "specified film adhesive force" is the force that bonds the first end portion 20a and the second end portion 20b sufficiently strongly through the adhesive films 21 and 22.

[0044] In Figure 3In the example, a part in the long side direction becomes state S1, and the other parts become state S2. In state S2, a gap 26a is formed between the peak portions 24a and 24b, and a gap 26b is formed between the valley portions 25a and 25b. The gap 26 may be formed continuously or discontinuously in the long side direction.

[0045] Here, in the present embodiment, as Figure 2 shown, the resin 30a constituting the outer sheath 30 enters the gap 26 between the first end portion 20a and the second end portion 20b. That is, the outer sheath 30 and the resin 30a that has entered the gap 26 are integrally formed. As Figure 3 shown, the resin 30a enters the gap 26a between the first end portion 20a and the second end portion 20b of the peak portion 24 and the gap 26b between the first end portion 20a and the second end portion 20b of the valley portion 25, respectively.

[0046] The radial dimension M2 of the resin 30a between the valley portions 25a and 25b is thicker than the radial dimension M1 of the resin 30a between the peak portions 24a and 24b.

[0047] Here, in the present embodiment, as Figure 2 shown, if the circumferential width of the resin 30a that has entered the gap 26 is set as W1 and the circumferential width of the overlapping portion 20c is set as W2, then the ratio W1 / W2 of the resin width W1 to the overlapping width W2 is 0.10 or more. The value of W1 / W2 is not particularly limited, but is set to 0.10 or more, whereby the first end portion 20a and the second end portion 20b can be more reliably bonded by the resin 30a.

[0048] The outer sheath 30 is, as Figure 1 shown, formed in a cylindrical shape extending in the long side direction and enters the gap 26 as described above. As the material of the outer sheath 30, resins such as polyethylene (PE) and polyvinyl chloride (PVC) can be used. The outer sheath 30 of the present embodiment is made of a flame-retardant resin (such as (EVA: Ethylene Vinyl Acetate), elastomer, etc.) containing a large amount of flame-retardant filler.

[0049] A pair of first tearing ropes 12, as Figure 1 shown, extend in the long side direction and are disposed between the inner layer cable 10 and the strengthening unit 20. The pair of first tearing ropes 12 are in contact with the outer peripheral surface of the inner sheath 14. The pair of first tearing ropes 12 are in contact with the inner peripheral surface of the strengthening unit 20, that is, the inner surface of the second adhesive film 22. As Figure 2 shown, in a cross-sectional view, the pair of first tearing ropes 12 are located on the neutral line L. As the first tearing ropes 12, ropes formed by twisting synthetic fibers such as polyester and aramid can be used. The optical fiber cable 1A may not have the first tearing ropes 12.

[0050] An outer skin 12a formed of an adhesive resin is provided around the first tearing rope 12. As the material of the outer skin 12a, thermoplastic resins such as polyethylene, its copolymers (such as EVA), etc., polyolefin-based, polyester-based, polyurethane-based, polyamide-based, etc., or adhesive resins such as thermosetting resins, or synthetic rubbers, etc. can be used. Each of the above materials can be used alone as the outer skin 12a. In order to adjust the adhesiveness, tackiness, temperature during heat welding, etc., two or more of the above materials can also be mixed, or modification by introducing functional groups can be carried out.

[0051] In addition, when the reinforcing unit 20 does not have the second adhesive film 22, in order to ensure the adhesiveness between the first tearing rope 12 and the reinforcing piece 23, it is preferable to use a resin containing a functional group as the material of the outer skin 12a. The outer skin 12a can be formed by coating the above-mentioned adhesive resin on the outer periphery of the first tearing rope 12.

[0052] The first tearing rope 12 is used for the operation of tearing the reinforcing piece 23 and the outer sheath 30 (hereinafter, simply referred to as the tearing operation). The first tearing rope 12 is required to have a mechanical strength (such as tensile strength) capable of tearing the reinforcing piece 23 and the outer sheath 30.

[0053] The first tearing rope 12 is as Figure 2 shown, in a cross-sectional view, it is arranged at a position different in the circumferential direction from the overlapping portion 20c of the reinforcing unit 20. Here, when the first tearing rope 12 is arranged at a position overlapping the overlapping portion 20c of the reinforcing unit 20 in the circumferential direction, since the radial thickness of the overlapping portion 20c is relatively thick, the operation of tearing the reinforcing unit 20 by the first tearing rope 12 becomes difficult. In the present embodiment, since the first tearing rope 12 is arranged at a position different in the circumferential direction from the overlapping portion 20c of the reinforcing unit 20, the operability of tearing the reinforcing unit 20 can be improved.

[0054] Moreover, in the present embodiment, in a cross-sectional view, the side edge 23a of the overlapping portion 20c and the first tearing rope 12 are arranged at different positions in the circumferential direction. Thereby, when tearing the reinforcing unit 20, it is possible to prevent the first tearing rope 12 from breaking at the side edge 23a of the overlapping portion 20c and hindering the operation of tearing the reinforcing unit 20.

[0055] (Manufacturing method)

[0056] Next, the manufacturing method of the optical fiber cable 1A of the present embodiment will be described.

[0057] First, prepare the inner cable 10. The inner cable 10 is obtained, for example, by feeding out the core 11 and a pair of tensile members 13 and covering the core 11 and the pair of tensile members 13 with the inner sheath 14 (feeding-out process). The inner cable 10 can also be prepared using other processes, or can be prepared in series with subsequent processes.

[0058] Next, prepare the reinforcing unit 20 with the first adhesive film 21 and the second adhesive film 22 attached to the flat reinforcing sheet 23. Then, process the flat reinforcing unit 20 to form the mountain portion 24 and the valley portion 25. The order of the process of attaching the first adhesive film 21 and the second adhesive film 22 to the reinforcing sheet 23 is not limited to this, and can be changed appropriately.

[0059] Next, longitudinally add two first tearing cords 12 to the reinforcing unit 20. At this time, the two first tearing cords 12 are arranged substantially parallel to each other, and a predetermined interval is provided between the first tearing cords 12.

[0060] Next, wind the reinforcing unit 20 around the inner cable 10 in such a manner that the first end portion 20a and the second end portion 20b of the reinforcing unit 20 overlap in a circumferential part to form the overlapping portion 20c (winding process). As a result, the first end portion 20a and the second end portion 20b are temporarily fixed by the first adhesive film 21 and the second adhesive film 22, and the reinforcing unit 20 becomes a cylindrical shape surrounding the inner cable 10 and extending in the long side direction. In addition, in the winding process, the mountain portions 24 of the first end portion 20a and the second end portion 20b and the valley portions 25 are opposed to each other in the radial direction.

[0061] Next, press the reinforcing unit 20 by opposing rollers (rotating bodies, not shown) so that the first end portion 20a and the second end portion 20b approach each other.

[0062] At this time, in the overlapping portion 20c of the reinforcing unit 20, there are a state S1 where bonding is performed with a film adhesive force equal to or greater than a predetermined film adhesive force, and a state S2 where bonding is performed with a film adhesive force less than the predetermined film adhesive force.

[0063] The state S2 with a film adhesive force less than the predetermined film adhesive force includes, for example, Figure 4 the state S2a shown, and Figure 5 the state S2b shown. In Figure 4 the state S2a shown, the first end portion 20a and the second end portion 20b are in partial contact, and a gap 26 is formed. In Figure 5 the state S2b shown, the first end portion 20a and the second end portion 20b are not in contact, and a gap 26 is formed in the entire circumferential direction of the overlapping portion 20c.

[0064] Next, use Figure 6An extrusion covering device 40 as shown presses and forms the outer sheath 30 (extrusion forming process).

[0065] The extrusion covering device 40 includes a nipple 41 through which the inner cable 10 around which the unit to be strengthened 20 is wound is inserted, and an outer die 42 disposed substantially coaxially outside the nipple 41. The inner cable 10 around which the unit to be strengthened 20 is wound is inserted into the insertion hole 43 of the nipple 41, and molten flame-retardant resin 30a is extruded onto the outer periphery of the unit to be strengthened 20 coming out of the outlet 44 of the nipple 41 from the resin flow path 45 to cover it.

[0066] The resin pressure in the extrusion forming process is set to a pressure obtained in advance such that the ratio W1 / W2 of the resin width W1 to the overlapping width W2 is 0.10 or more. The adjustment of the resin pressure can be performed, for example, by changing the distance N between the front end 41a of the nipple 41 and the front end 42a of the outer die 42. Therefore, the distance N at which W1 / W2 becomes 0.10 or more is calculated in advance through experiments before the start of manufacturing. The resin pressure can also be adjusted by other mechanisms. Other means include, for example, the shapes of the outer die 42 and the nipple 41, the inner diameter of the resin flow path 45, the amount of resin 30a discharged from the extrusion covering device 40, and the temperature setting.

[0067] In the present embodiment, with the distance between the nipple 41 and the outer die 42 being the distance N calculated in advance, the unit to be strengthened 20 is covered with the resin 30a in the set state of the nipple 41 and the outer die 42. In this way, the outer sheath 30 is extrusion formed, and the inner cable 10 and the unit to be strengthened 20 are accommodated in the outer sheath 30.

[0068] In this way, the resin 30a enters the portion (the portion in state S2) where the first end 20a and the second end 20b are bonded with a film adhesion force less than the specified film adhesion force in the overlapping portion 20c. Thus, the Figure 2 optical fiber cable 1A as shown is manufactured.

[0069] In the case of the portion (the portion in state S1) where the first end 20a and the second end 20b in the overlapping portion 20c are in close contact without a gap and are bonded with a specified film adhesion force by the adhesive films 21 and 22, the resin 30a does not enter this portion. That is, even if the resin pressure in the extrusion forming process is constant, due to the difference in the bonding state of the first end 20a and the second end 20b by the adhesive films 21 and 22, there may be a portion where the resin 30a enters and a portion where it does not enter.

[0070] Here, Figure 8 the effects obtained by the present embodiment are described. Figure 8It is a conceptual diagram showing the result of the resin press covering reinforcement unit 20 calculated in advance. In the present embodiment, the resin 30a is made to enter the gap 26, whereby in addition to applying the film adhesion force to the overlapping portion 20c, the restraining force of the first end portion 20a is also applied by the outer sheath 30. Specifically, as Figure 2 and Figure 7 shown, the outer sheath 30 provided on the outer peripheral side of the reinforcement unit 20 and the resin 30a entering the gap 26 are continuously formed. Thereby, the force of the first end portion 20a toward the outer peripheral side of the optical fiber cable 1A can be suppressed when the optical fiber cable 1A is bent. Therefore, in the present embodiment, the resistance to overcome the force that the overlapping portion 20c wants to open when the optical fiber cable 1A is bent becomes the sum of the film adhesion force generated by the adhesive films 21 and 22 and the restraining force generated by the resin 30a.

[0071] Figure 8 The vertical axis of is the resistance, and the horizontal axis is the aforementioned states S1, S2a, and S2b. In Figure 8 , the dashed line represents the film adhesion force before covering the outer sheath 30, and the solid line represents the resistance after covering the outer sheath 30 (that is, the sum of the film adhesion force and the restraining force generated by the resin 30a). Figure 8 The "specified resistance" is the threshold value of the force for suppressing the outer sheath 30 from breaking when the overlapping portion 20c is opened when the optical fiber cable 1A is bent.

[0072] In the state S1, as Figure 8 the solid line shown, the film adhesion force exceeds the specified resistance. That is, in the state S1, the first end portion 20a and the second end portion 20b are bonded strongly enough by the film adhesion force generated by the adhesive films 21 and 22.

[0073] In the state S2b, since the first end portion 20a and the second end portion 20b do not contact each other, the film adhesion force is zero. On the other hand, even if the first end portion 20a and the second end portion 20b do not contact each other, but the resin 30a of the outer sheath 30 enters between the first end portion 20a and the second end portion 20b, a restraining force is also applied to the overlapping portion 20c. In this way, the resin 30a acts as a restraining force, so that in the portion of the state S2b, the resistance is increased to exceed the specified resistance.

[0074] In the state S2a, the first end portion 20a and the second end portion 20b are in partial contact and a gap 26 is formed, so there is a film adhesion force smaller than that in the state S1 ( Figure 8 the dashed line). The resin 30a is made to enter the gap 26, whereby the resin 30a entering the gap 26 acts as a restraining force, and in the portion of the state S2b, the resistance is increased to exceed the specified resistance.

[0075] Thus, it can be understood that in any one of the states S1, S2a, and S2b, the resistance of the overlapping portion 20c is increased to exceed the specified resistance.

[0076] As described above, the manufacturing method of the optical fiber cable 1A according to the present embodiment includes: a feeding step of feeding the core portion 11 of the inner layer cable 10 based on a plurality of optical fibers; a winding step of winding the strengthening unit (strengthening member) 20 around the core portion 11 and forming an overlapping portion 20c in which the end portions 20a and 20b of the strengthening unit 20 overlap with each other in a part of the circumferential direction; and an extrusion molding step of extruding and molding the outer sheath (sheath) 30 outside the strengthening unit 20. Moreover, in the extrusion molding step, the resin 30a constituting the outer sheath 30 is made to enter at least a part of the overlapping portion 20c.

[0077] According to such a manufacturing method, the resin 30a constituting the outer sheath 30 is made to enter the portion of the overlapping portion 20c in the state S2 where the film adhesion force is less than the specified value, whereby an inhibitory force can be applied and the resistance of this portion can be increased. Thus, the resistance of the overlapping portion 20c in the longitudinal direction can be increased to above the specified resistance, so that the phenomenon that the overlapping portion 20c opens when the optical fiber cable 1A is bent can be suppressed. Therefore, the breakage of the outer sheath 30 can be suppressed.

[0078] In addition, the strengthening unit 20 has a corrugated shape in which ridges 24 protruding radially outward and valleys 25 protruding radially inward are alternately formed along the longitudinal direction. In the overlapping portion 20c, the ridges 24 are arranged opposite to each other in the radial direction, and the valleys 25 are arranged opposite to each other in the radial direction. According to this structure, the optical fiber cable 1A can be easily bent. And by setting the strengthening unit 20 to a corrugated shape, the contact area between the strengthening unit 20 and the outer sheath 30 can be increased. Thereby, the film adhesion force between the strengthening unit 20 and the outer sheath 30 can be improved.

[0079] In addition, the resin 30a constituting the outer sheath 30 is formed of a flame-retardant resin. In the case of this structure, since a filler having a relatively low melting point and softening temperature is added to the resin 30a, the strength of the optical fiber cable 1A in a high-temperature environment may become a problem. In a general optical fiber cable, when the resin is a flame-retardant resin, in a high-temperature environment, when the optical fiber cable is bent, the overlapping portion 20c opens and deformation (breakage) occurs. In contrast, in the optical fiber cable 1A of the present embodiment, since the resin 30a constituting the outer sheath 30 is made to enter the overlapping portion 20c of the strengthening unit 20, the force for the overlapping portion 20c to open can be suppressed even in a high-temperature environment. Therefore, even if the resin 30a is a flame-retardant resin, the breakage of the outer sheath 30 can be suppressed.

[0080] In the first embodiment, although the structure in which the reinforcing unit 20 includes the first adhesive film 21 and the second adhesive film 22 has been described as an example, it is sufficient to have at least the first adhesive film 21. Even if there is a portion with low film adhesion force due to the absence of the second adhesive film 22, the portion with weak film adhesion force is provided with a restraining force by the resin 30a, thereby increasing the resistance. Therefore, the second adhesive film 22 can be omitted to achieve cost reduction and the like.

[0081] In addition, in the cross-sectional view, although it has been described that the entire overlapping portion 20c and the anti-tensile body 13 are arranged at different positions in the circumferential direction, the entire overlapping portion 20c and the anti-tensile body 13 may also be arranged at the same position in the circumferential direction.

[0082] In addition, in the present embodiment, before bonding the first end portion 20a and the second end portion 20b with the resin 30a of the outer sheath 30, in the winding process, the first end portion 20a and the second end portion 20b are temporarily fixed at least by the first adhesive film 21. Even when the adhesive strength generated by the first adhesive film 21 is insufficient, since the resin 30a enters the portion with weak film adhesion force, the resistance in the long side direction can be increased to a value above the specified resistance. When temporarily fixing the first end portion 20a and the second end portion 20b, the first adhesive film 21 may not be provided on the entire surface of the reinforcing sheet 23. For example, the first end portion 20a and the second end portion 20b may be temporarily fixed by providing an adhesive only on the overlapping portion 20c.

[0083] (Second Embodiment)

[0084] Next, a second embodiment of the present invention will be described. However, the basic structure is the same as that of the first embodiment. Therefore, the same reference numerals are given to the same structures and their descriptions are omitted, and only the differences will be described.

[0085] In the optical fiber cable 1B of the present embodiment, as Figure 9 shown, the reinforcing unit 20A does not include the first adhesive film 21 and the second adhesive film 22, which is different from the first embodiment. That is, the reinforcing unit (reinforcing member) 20A of the present embodiment corresponds to the reinforcing sheet 23 of the first embodiment.

[0086] Next, a manufacturing method of the optical fiber cable 1B of the present embodiment will be described.

[0087] In the present embodiment, since the reinforcing unit 20A does not include the first adhesive film 21 and the second adhesive film 22, when winding the reinforcing unit 20A having the mountain portion 24 and the valley portion 25 around the inner layer cable 10, the overlapping portion 20c is not fixed or temporarily fixed, and the reinforcing unit 20A surrounds the inner layer cable 10 to form a cylindrical shape extending in the long side direction.

[0088] At this time, in a cross-sectional view, the overlapping portion 20c of the strengthening unit 20A may be in the following states: a state S3a (not shown in the figure) in which the first end portion 20a and the second end portion 20b are in contact without a gap; as Figure 10 shown, a state S3b in which the first end portion 20a and the second end portion 20b are in partial contact and a gap 26 is formed; and as Figure 11 shown, a state S3c in which the first end portion 20a and the second end portion 20b are not in contact and a gap 26 is formed.

[0089] Next, in the same manner as in the first embodiment, the outer sheath 30 is extrusion-molded using the extrusion covering device 40 in a manner that covers the strengthening unit 20A.

[0090] At this time, the relationship between the resin pressure and the bonding strength is obtained in advance, and in the same manner as in the first embodiment, the distance N is calculated so that the value of W1 / W2 is 0.10 or more.

[0091] With the distance between the threaded sleeve 41 and the outer die 42 being N, in a state where the threaded sleeve 41 and the outer die 42 are provided, the strengthening unit 20A is covered with the resin 30a. In order to uniformly maintain the outer diameter dimension of the outer sheath 30 in the longitudinal direction, the resin pressure is maintained substantially uniformly. As a result, the resin 30a evenly enters the overlapping portion 20c in the entire longitudinal direction. In this way, the resin 30a enters Figure 10 the gap 26 in the state S3b shown, and the resin 30a enters Figure 11 the gap 26 in the state S3c shown. In addition, even for the overlapping portion 20c in the state S3a described above, the resin pressure expands between the first end portion 20a and the second end portion 20b, and the resin 30a enters this gap. In this way, in any state, as Figure 9 shown, an outer sheath 30 in which the resin 30a has entered the overlapping portion 20c is formed, and the optical fiber cable 1B is manufactured.

[0092] In the present embodiment, since the strengthening unit 20A does not include the first adhesive film 21 and the second adhesive film 22, the restraining force of the first end portion 20a generated by the outer sheath 30 becomes a resistance to the force that overcomes the tendency of the overlapping portion 20c to open when the optical fiber cable 1A is bent. Even in the optical fiber cable 1B, as in the optical fiber cable 1A of the first embodiment, in any of the states S3a, S3b, and S3c, the resistance is increased to be above the specified resistance.

[0093] As described above, the method for manufacturing the optical fiber cable 1B according to the present embodiment also includes: a feeding step of feeding a core portion 11 having a plurality of optical fibers; a winding step of winding a strengthening unit (strengthening member) 20A around the core portion 11 and forming an overlapping portion 20c in which ends 20a and 20b of the strengthening unit 20A overlap each other in a part of the circumferential direction; and an extrusion molding step of extrusion molding an outer sheath (sheath) 30 on the outside of the strengthening unit 20A. Further, in the extrusion molding step, the resin 30a constituting the outer sheath 30 is made to enter the overlapping portion 20c. Thus, as in the first embodiment, the resistance of the overlapping portion 20c in the longitudinal direction can be increased to a value equal to or greater than a specified resistance, and therefore the phenomenon in which the overlapping portion 20c opens when the optical fiber cable 1B is bent can be suppressed. Accordingly, breakage of the outer sheath 30 can be suppressed.

[0094] Example

[0095] Hereinafter, the above-described embodiment will be described using specific examples. The present invention is not limited to the following examples.

[0096] Evaluation was performed on the optical fiber cable 1A manufactured using the manufacturing method of the first embodiment described above.

[0097] The outer diameter of the inner layer cable 10 was 14.6 mm, the circumferential length of the strengthening unit 20 was 64 mm, the circumferential width W2 of the overlapping portion 20c of the strengthening unit 20 was 10 mm, and the outer diameter of the optical fiber cable 1A was 22.1 mm. EVA was used as the material of the outer sheath 30. As flame retardants, fillers such as metal hydroxides (aluminum hydroxide, magnesium hydroxide) and phosphorus-based flame retardants were added, for example. In order to add fillers such as flame retardants, a base resin having a relatively low melting point and softening temperature, and containing soft EVA, EEA (ethylene-ethyl acrylate copolymer), and elastomer could be used.

[0098] A plurality of samples were prepared in which the value of W1 / W2 was changed by varying the distance between the nipple 41 and the outer die 42 when the outer sheath 30 was extrusion molded under the above conditions. After each sample was left at 70°C for three days, it was investigated whether the outer sheath 30 had broken at the bending diameters φ40D (D: the outer diameter of the optical fiber cable 1A) and φ30D. The above bending diameters were adopted based on the specifications of various optical fiber cables. In addition, regarding the condition of leaving at 70°C for three days, it was set as a condition capable of confirming the reliability of the outer sheath 30 based on a rule of thumb.

[0099] The test results are shown in Table 1.

[0100] [Table 1]

[0101] [Table 1]

[0102]

[0103] As can be seen from Table 1, when the value of the ratio (W1 / W2) of the width W1 of the resin 30a entering the overlapping portion 20c to the width W2 of the overlapping portion 20c is 0.10 or more, the outer sheath 30 does not rupture in either of the bending diameters φ40D and φ30D. Therefore, it can be seen that by setting the value of W1 / W2 to 0.10 or more, the rupture of the outer sheath 30 can be more reliably suppressed.

[0104] Based on this result, it is preferable to press the resin in the extrusion molding process at a pressure obtained in advance so as to satisfy W1 / W2≥0.10.

[0105] The technical scope of the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention.

[0106] For example, in the manufacturing method of the first embodiment, although it has been described that the reinforcing unit 20 has the states S1, S2a, and S2b, it is not necessary to include all of these states. That is, as long as the reinforcing unit 20 includes at least one of the states S2a and S2b, the rupture of the outer sheath 30 can be suppressed, and in a portion where the film adhesion force is weak in the longitudinal direction, a suppressing force is imparted and the resistance increases, so that an effect of improving the reliability of the optical fiber cable 1A can be obtained. Similarly, in the manufacturing method of the second embodiment, the reinforcing unit 20A may not include all of the states S3a, S3b, and S3c, and it is sufficient to include at least one of the states S3a, S3b, and S3c.

[0107] In addition, although the structure in which the mountain portions 24 and the valley portions 25 are alternately formed along the longitudinal direction in the reinforcing units 20 and 20A of the above-described embodiments has been described as an example, the reinforcing unit 20 may not be corrugated. In addition, the corrugated shape of the reinforcing unit 20 is not limited to the above structure. For example, the corrugated shape may also be a structure in which the mountain portions 24 and the valley portions 25 that extend obliquely with respect to the longitudinal direction are alternately formed along the longitudinal direction.

[0108] In the optical fiber cables of the above-described first and second embodiments, although the structure in which the reinforcing unit 20 surrounds the inner layer cable 10 is adopted, it is not limited thereto, and the structure in which the reinforcing unit 20 surrounds the core portion 11 may also be adopted. In the case of this structure, in the above-described first and second embodiments, as long as the inner layer cable 10 is not fed out and only the core portion 11 is fed out, the reinforcing unit 20 can be wound around the core portion 11 in the winding process.

[0109] In addition, in the manufacturing methods of the above first and second embodiments, although the winding process is performed after the formation of the mountain portions 24 and valley portions 25 of the reinforcing unit 20 (20A), it is also possible to use a flat sheet-like reinforcing unit 20 (20A) and form the mountain portions 24 and valley portions 25 after the winding process and before the extrusion molding process.

[0110] In addition, in the above first and second embodiments, although the radial dimension M2 of the resin 30a between the valley portions 25a and 25b is thicker than the radial dimension M1 of the resin 30a between the mountain portions 24a and 24b, it is not limited thereto. That is, it may also be a structure in which the dimension M2 is thinner than the dimension M1, or a structure in which the thickness of the resin 30a is uniform between the mountain portions 24 and the valley portions 25.

[0111] In addition, the resin 30a may also enter at least between the valley portions 25a and 25b between the first end portion 20a and the second end portion 20b of the overlapping portion 20c.

[0112] In addition, the inner cable 10 is not limited to the above structure, and may also be a loose tube, a wrapped tube cable (WTC), or a trough type. In addition, a tensile strength member may be buried in the outer sheath 30. In addition, multiple optical fibers and the inner cable 10 may or may not be covered by a press roll and a water-absorbing tape (sheet) as needed. In addition, it is not limited to the water-absorbing tape (sheet), and other waterproof materials and water-absorbing materials may or may not be provided as needed.

[0113] In addition, in the above embodiments, although the cross-sectional shape of the core portion 11 is circular, the cross-sectional shape of the core portion 11 may also be elliptical, rectangular, etc.

[0114] Description of Reference Numerals

[0115] 1A, 1B... optical fiber cables; 11... core portion; 12... first tearing cord; 20, 20A... reinforcing units (reinforcing members); 20c... overlapping portion; 21... first adhesive film (adhesive layer); 24... mountain portion; 25... valley portion; 30... outer sheath (sheath); 30a... resin.

Claims

1. An optical fiber cable, comprising: A core portion having a plurality of optical fibers; A strengthening member surrounding the core portion; and A sheath housing the core portion and the strengthening member, the strengthening member having an overlapping portion extending in the longitudinal direction of the plurality of optical fibers and having a first end portion and a second end portion overlapping in a part of the circumferential direction, The overlapping portion includes a first long side portion and a second long side portion. The first long side portion is a portion where the local parts of the first end portion and the second end portion are in contact with each other, and a gap in the width of the local part extends only in a part of the overlapping portion in the circumferential direction; the second long side portion is a portion where the first end portion and the second end portion are not in contact with each other, and a gap in the entire width extends in the entire width of the overlapping portion in the circumferential direction, The resin constituting the sheath enters both the gap in the width of the local part and the gap in the entire width.

2. The optical fiber cable according to claim 1, wherein The strengthening member has a corrugated shape in which a mountain portion protruding radially outward and a valley portion protruding radially inward are alternately formed in the longitudinal direction, In the overlapping portion, the mountain portions are arranged opposite to each other in the radial direction, and the valley portions are arranged opposite to each other in the radial direction.

3. The optical fiber cable according to claim 2, wherein The resin enters at least between the valley portions of the overlapping portion.

4. The optical fiber cable according to any one of claims 1 to 3, wherein The sheath is formed of a flame-retardant resin.

5. The optical fiber cable according to any one of claims 1 to 3, wherein When the circumferential width of the overlapping portion is set as W2 and the circumferential width of the resin entering the overlapping portion is set as W1, W1 / W2≥0.10 is satisfied.

6. The optical fiber cable according to any one of claims 1 to 3, further comprising: A tearing cord disposed between the core portion and the strengthening member, In a cross-section, the tearing cord is disposed at a position different from the overlapping portion in the circumferential direction.

7. The optical fiber cable according to any one of claims 1 to 3, wherein An adhesive layer is formed on the surface of the strengthening member facing the sheath.

8. The optical fiber cable according to claim 7, wherein The adhesive layer is formed on the surface of the strengthening member facing radially inward.

9. The optical fiber cable according to any one of claims 1 to 3, wherein The sheath and the resin entering the overlapping portion are formed continuously.

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