Manufacturing method of optical fiber cable

Abstract

The invention relates to a method for manufacturing an optical fiber cable and an optical fiber cable. This method for manufacturing an optical fiber cable comprises: a feeding step for feeding a core having a plurality of optical fibers; a winding step in which the reinforcing members are wound around the core portion and an overlapping portion in which the end portions of the reinforcing members partially overlap each other in the circumferential direction is formed; and an extrusion molding step in which a sheath is extrusion-molded on the outside of the reinforcing member, and in the extrusion molding step, a resin constituting the sheath enters at least a portion of the overlapping portion.

Description

[0001] This application is a divisional application of an application filed on August 11, 2020, with application number 202080058684.4, and invention name “Manufacturing method of optical fiber cable and optical fiber cable”. Technical Field

[0002] The present invention relates to a method for manufacturing an optical fiber cable and an optical fiber cable.

[0003] This application claims priority from Japanese Patent Application No. 2019-185963 filed on October 9, 2019, the contents of which are incorporated herein by reference. Background Art

[0004] Patent Document 1 discloses an optical fiber cable including an optical fiber core, a reinforcement member disposed to surround the optical fiber core, a filler filled between the optical fiber core and the reinforcement member, and a sheath covering the outer side of the reinforcement member.

[0005] This optical cable manufacturing method first prepares a ribbon material serving as a reinforcement member and applies adhesive to both ends of the ribbon material. Next, optical fibers are placed on the ribbon material and filled with filler. The ribbon material and optical fibers are then passed through a former, where the ends of the ribbon material overlap to form the reinforcement member. The reinforcement member is then introduced into an extruder, where it is coated with resin to form a sheath.

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 11-337783

[0007] In the optical cable of Patent Document 1, the overlapping portions of the reinforcement members are bonded with adhesive, which may create weak adhesion areas along the longitudinal direction of the optical cable. In such weak adhesion areas, the overlapping portions may break apart when the optical cable is bent, for example. This can cause stress to concentrate on the sheath covering these areas, potentially causing the sheath to rupture. Summary of the Invention

[0008] The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a method for manufacturing an optical fiber cable and an optical fiber cable capable of suppressing breakage of a sheath.

[0009] In order to solve the above-mentioned problems, the manufacturing method of the optical fiber cable of the first embodiment of the present invention has the following steps: a feeding step of feeding out a core having multiple optical fibers; a winding step of winding a reinforcing component on the above-mentioned core to form an overlapping portion in which the ends of the above-mentioned reinforcing component overlap with each other in a part of the circumferential direction; and an extrusion molding step of extruding a sheath on the outside of the above-mentioned reinforcing component, and in the above-mentioned extrusion molding step, causing the resin constituting the above-mentioned sheath to enter at least a part of the above-mentioned overlapping portion.

[0010] The optical fiber cable of the second embodiment of the present invention comprises: a core portion having a plurality of optical fibers; a reinforcement member surrounding the core portion; and a sheath housing the core portion and the reinforcement member, wherein the reinforcement member has an overlapping portion whose ends overlap with each other in a portion of the circumferential direction, and the resin constituting the sheath enters at least a portion of the overlapping portion.

[0011] According to the above-described embodiment of the present invention, breakage of the sheath can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a perspective view of the optical fiber cable according to the first embodiment.

[0013] Figure 2 It is a cross-sectional view of the optical fiber cable according to the first embodiment.

[0014] Figure 3 yes Figure 1 Section III-III view.

[0015] Figure 4 is covered Figure 1 A cross-sectional view of the front of the outer jacket of a fiber optic cable.

[0016] Figure 5 is covered Figure 1 A cross-sectional view of the front of the outer jacket of a fiber optic cable.

[0017] Figure 6 It is a diagram showing a method for manufacturing an optical fiber cable according to the first embodiment.

[0018] Figure 7 It is a cross-sectional view of the optical fiber cable according to the first embodiment.

[0019] Figure 8 This is a graph showing the resistance of the optical fiber cable manufactured by the method for manufacturing the optical fiber cable according to the first embodiment.

[0020] Figure 9 It is a cross-sectional view of an optical fiber cable according to a second embodiment.

[0021] Figure 10 This is a cross-sectional view of the optical fiber cable before being covered with the outer sheath according to the second embodiment.

[0022] Figure 11 This is a cross-sectional view of the optical fiber cable before being covered with the outer sheath according to the second embodiment. DETAILED DESCRIPTION

[0023] (First embodiment)

[0024] Below, refer to Figures 1 to 8 The structure of the optical fiber cable according to the first embodiment will be described.

[0025] like Figure 1 As shown, the optical fiber cable 1A includes an inner layer cable 10 having an optical fiber, a reinforcement unit (reinforcement member) 20 , an outer sheath 30 , and a pair of first rip cords 12 .

[0026] (Direction definition)

[0027] In this embodiment, the longitudinal direction of the inner layer cable 10 is simply referred to as the longitudinal direction, and the central axis of the inner layer cable 10 is referred to as the central axis O. Furthermore, a cross section perpendicular to the central axis O is referred to as a transverse cross section. In a transverse cross-sectional view, the direction intersecting the central axis O is referred to as a radial direction, and the direction rotating around the central axis O is referred to as a circumferential direction.

[0028] The inner layer cable 10 includes a core 11 having a plurality of optical fibers, a pair of second tear cords 16, a tension-resistant body (tension member) 13, and an inner sheath 14. The inner layer cable 10 may not include the second tear cord 16.

[0029] The core 11 extends longitudinally. It is formed by assembling multiple optical fibers. The optical fibers constituting the core 11 can be optical fiber wires, optical fiber cores, optical fiber ribbons, or the like. The multiple optical fibers constituting the core 11 can also be bundled together with a bundling material to form an optical fiber unit. The multiple optical fibers are rolled and covered with a water-absorbing tape.

[0030] like Figure 2 As shown, a pair of second rip cords 16 are embedded in the inner sheath 14 so as to radially clamp the core 11 in a cross-sectional view. The pair of second rip cords 16 extend in the longitudinal direction. In a cross-sectional view, the pair of second rip cords 16 are located on a straight line that is orthogonal to a neutral line L (described later) and passes through the central axis O. The pair of second rip cords 16 are in contact with the outer peripheral surface of the core 11. The second rip cords 16 can be made of a rope made of synthetic fibers such as polyester and aramid, or a cylindrical rod made of PP or nylon.

[0031] A pair of tensile members 13 are embedded in the inner sheath 14 so as to sandwich the core 11 in the radial direction in a cross-sectional view. Each tensile member 13 extends in the longitudinal direction. Each tensile member 13 can be arranged parallel to the core 11 in the longitudinal direction, or can be arranged in a spiral shape centered on the core 11.

[0032] The tension member 13 protects the optical fibers in the core 11 from the tension acting on the optical fiber cable 1A. Examples of materials for the tension member 13 include metal wire (steel wire, etc.), tension-resistant fiber (aramid fiber, etc.), and FRP. The tension member 13 can be a single wire or a bundle of multiple wires, twisted together.

[0033] In the cross-sectional view, the straight line connecting the centers of the tension members 13 is called the neutral line L. Figure 2 When the optical fiber cable 1A is bent in the vertical direction (in the vertical direction), the expansion and contraction of the tension member 13 is smaller than when the optical fiber cable 1A is bent in other directions. Therefore, the optical fiber cable 1A is relatively easy to bend in the direction perpendicular to the neutral line L.

[0034] The inner layer cable 10 may include three or more tension members 13. When three or more tension members 13 are arranged at equal intervals in the circumferential direction, the inner layer cable 10 has less directivity in bending, making it easier to handle the optical fiber cable 1A.

[0035] Inner sheath 14 as Figure 2 As shown, the inner sheath 14 covers the core 11, a pair of tensile members 13, and a pair of second tear cords 16. Resins such as polyethylene (PE) and polyvinyl chloride (PVC) can be used as the material for the inner sheath 14. The inner sheath 14 is formed into a cylindrical shape extending in the longitudinal direction. The inner sheath 14 is formed by extrusion molding or the like.

[0036] The outer sheath 30 houses the inner cable 10 , a pair of first ripcords 12 , and the reinforcement unit 20 .

[0037] The reinforcing unit 20 extends in the longitudinal direction and is formed in a cylindrical shape surrounding the inner layer cable 10. The reinforcing unit 20 includes a first adhesive film 21 (adhesive layer), a second adhesive film 22, and a reinforcing sheet 23.

[0038] The reinforcement sheet 23 can be made of a metal such as iron, stainless steel, copper, or a copper alloy. The material of the reinforcement sheet 23 can be changed as appropriate. Preferably, the reinforcement sheet 23 is, for example, in the form of a strip, with its length aligned with the longitudinal direction of the inner cable 10. The thickness of the reinforcement sheet 23 is, for example, approximately 0.1 to 0.3 mm. Setting the thickness of the reinforcement sheet 23 within this range prevents damage to the optical fibers of the core 11 due to gnawing by animals and facilitates the operation of cutting the reinforcement sheet 23 using the first tear cord 12.

[0039] In this embodiment, although the structure in which the reinforcing unit 20 includes the first adhesive film 21 and the second adhesive film 22 is described as an example, the reinforcing unit 20 only needs to include the first adhesive film 21. When the second adhesive film 22 is provided in addition to the first adhesive film 21, the film adhesion strength of the overlapping portion 20c (described later) can be further enhanced and rusting of the reinforcing sheet 23 can be suppressed.

[0040] The reinforcing element 20 surrounds the inner cable 10 entirely and overlaps it at a portion of the circumference. In this specification, the portion where the first end 20a and the second end 20b of the reinforcing element 20 overlap is referred to as the overlapping portion 20c. In the overlapping portion 20c, the first end 20a and the second end 20b are radially opposed to each other.

[0041] In the present embodiment, in a cross-sectional view, the entire overlapping portion 20 c is arranged at a position different from that of the tensile member 13 in the circumferential direction.

[0042] 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 adhesive or a hot melt adhesive can be used. The material of the adhesive can also be changed appropriately. The first adhesive film 21 has the function of fixing the outer sheath 30 to the reinforcing sheet 23. The second adhesive film 22 can also have the function of fixing the first tear cord 12 to the reinforcing sheet 23 together with the outer skin 12a of the first tear cord 12 described later. In the first adhesive film 21 and the second adhesive film 22, the portion located between the reinforcing sheets 23 in the overlapping portion 20c has the function of fixing the ends of the reinforcing sheets 23 to each other using the overlapping portion 20c.

[0043] like Figure 3 As shown, the reinforcing element 20 has a corrugated shape with peaks 24 protruding radially outward and valleys 25 protruding radially inwardly formed alternately along the longitudinal direction. In the overlapping portion 20c, the peaks 24a of the first end portion 20a and the peaks 24b of the second end portion 20b are arranged radially opposite each other, and the valleys 25a of the first end portion 20a and the valleys 25b of the second end portion 20b are arranged radially opposite each other.

[0044] In the overlapping portion 20c, the bonding state between the first end portion 20a and the second end portion 20b bonded by the first adhesive film 21 and the second adhesive film 22 is sometimes uneven in the longitudinal 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 bonding force greater than a predetermined film bonding force is referred to as state S1, and the state in which the first end portion 20a and the second end portion 20b are bonded with a film bonding force less than the predetermined film bonding force is referred to as state S2. In state S2, for example, Figure 2 As shown, a gap 26 is formed between the first end portion 20a and the second end portion 20b. The "predetermined film bonding force" is a force that allows the adhesive films 21 and 22 to bond the first end portion 20a and the second end portion 20b sufficiently strongly.

[0045] exist Figure 3In the example shown in FIG. 1 , a portion of the longitudinal direction is in state S1, while the remaining portion is in state S2. In state S2, gaps 26a are formed between peaks 24a and 24b, and gaps 26b are formed between valleys 25a and 25b. Gaps 26a may be formed continuously in the longitudinal direction or discontinuously.

[0046] Here in this embodiment, as Figure 2 As shown in FIG. 2 , 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 entering the gap 26 are formed integrally. Figure 3 As shown, the resin 30 a enters the gap 26 a between the first end 20 a and the second end 20 b of the mountain portion 24 and the gap 26 b between the first end 20 a and the second end 20 b of the valley portion 25 .

[0047] A radial dimension M2 of the resin 30a between the valley portions 25a and 25b is thicker than a radial dimension M1 of the resin 30a between the peak portions 24a and 24b.

[0048] Here in this embodiment, as Figure 2 As shown in FIG. 2 , if the circumferential width of the resin 30a that enters the gap 26 is W1 and the circumferential width of the overlapping portion 20c is W2, then the ratio W1 / W2 of the resin width W1 to the overlapping width W2 is 0.10 or greater. While the value of W1 / W2 is not particularly limited, setting it to 0.10 or greater allows the first end portion 20a and the second end portion 20b to be more reliably bonded together by the resin 30a.

[0049] The outer sheath 30 is as follows Figure 1 As shown, the outer sheath 30 is formed into a cylindrical shape extending in the longitudinal direction and, as described above, enters the gap 26. Resins such as polyethylene (PE) and polyvinyl chloride (PVC) can be used as the material for the outer sheath 30. In this embodiment, the outer sheath 30 is made of a flame-retardant resin (EVA: Ethylene Vinyl Acetate, elastomer, etc.) containing a large amount of flame-retardant filler.

[0050] A pair of first tear cords 12 such as Figure 1 As shown, the pair of first tear cords 12 extend along the longitudinal direction and are disposed between the inner cable 10 and the reinforcement unit 20. The pair of first tear cords 12 are in contact with the outer peripheral surface of the inner sheath 14. The pair of first tear cords 12 are in contact with the inner peripheral surface of the reinforcement unit 20, that is, the inner surface of the second adhesive film 22. Figure 2 As shown, the pair of first tear cords 12 are located on the neutral line L in a cross-sectional view. A twisted string of synthetic fibers such as polyester and aramid can be used as the first tear cord 12. The optical fiber cable 1A does not need to have the first tear cord 12.

[0051] A sheath 12a made of an adhesive resin is provided around the first tear cord 12. Sheath 12a can be made of a thermoplastic resin such as polyethylene or its copolymers (e.g., EVA), a polyolefin-based resin, a polyester-based resin, a polyurethane-based resin, or a polyamide-based resin, or an adhesive resin such as a thermosetting resin, or synthetic rubber. Sheath 12a can be made of any of the above materials alone, or two or more of these materials can be mixed or modified by introducing functional groups to adjust adhesiveness, viscosity, and the temperature during heat fusion.

[0052] Furthermore, when the reinforcing unit 20 does not include the second adhesive film 22, a resin containing a functional group is preferably used as the material for the outer skin 12a to ensure adhesion between the first tear cord 12 and the reinforcing sheet 23. The outer skin 12a can be formed by coating the outer circumference of the first tear cord 12 with the adhesive resin.

[0053] The first tear cord 12 is used in the operation of tearing the reinforcing sheet 23 and the outer sheath 30 (hereinafter referred to as the tearing operation). The first tear cord 12 is required to have a mechanical strength (eg, tensile strength) sufficient to tear the reinforcing sheet 23 and the outer sheath 30 .

[0054] The first tear cord 12 is as Figure 2 As shown in the cross-sectional view, it is arranged at a position different from the overlapping portion 20c of the reinforcing unit 20 in the circumferential direction. Here, when the first rip cord 12 is arranged at a position overlapping with the overlapping portion 20c of the reinforcing unit 20 in the circumferential direction, the radial thickness of the overlapping portion 20c is large, making it difficult to tear the reinforcing unit 20 with the first rip cord 12. In this embodiment, the first rip cord 12 is arranged at a position different from the overlapping portion 20c of the reinforcing unit 20 in the circumferential direction, thereby improving the operability of tearing the reinforcing unit 20.

[0055] Furthermore, in this embodiment, in a cross-sectional view, the side edge 23a of the overlapping portion 20c and the first tear cord 12 are arranged at different positions in the circumferential direction. This prevents the first tear cord 12 from breaking at the side edge 23a of the overlapping portion 20c and hindering the operation of the tearing reinforcement unit 20 when the reinforcement unit 20 is torn.

[0056] (Manufacturing Method)

[0057] Next, a method for manufacturing the optical fiber cable 1A according to the present embodiment will be described.

[0058] First, the inner layer cable 10 is prepared. The inner layer cable 10 is obtained by, for example, feeding out a core 11 and a pair of tensile members 13, and then covering the core 11 and the pair of tensile members 13 with an inner sheath 14 (feeding out step). The inner layer cable 10 can also be prepared in a separate step or in series with a subsequent step.

[0059] Next, a reinforcing unit 20 is prepared, in which the first adhesive film 21 and the second adhesive film 22 are attached to a flat reinforcing sheet 23. The flat reinforcing unit 20 is then processed to form peaks 24 and valleys 25. The order of attaching the first adhesive film 21 and the second adhesive film 22 to the reinforcing sheet 23 is not limited to this order and may be modified as appropriate.

[0060] Next, two first tear cords 12 are added longitudinally to the reinforcement unit 20. At this time, the two first tear cords 12 are arranged substantially parallel to each other, and a predetermined interval is provided between the first tear cords 12.

[0061] Next, the reinforcing element 20 is wound around the inner cable 10 (a winding step) to form an overlapping portion 20c where the first end 20a and the second end 20b of the reinforcing element 20 partially overlap in the circumferential direction. This temporarily secures the first end 20a and the second end 20b with the first adhesive film 21 and the second adhesive film 22, and the reinforcing element 20 assumes a cylindrical shape that surrounds the inner cable 10 and extends longitudinally. Furthermore, during the winding step, the peaks 24 and valleys 25 of the first and second end portions 20a, 20b are aligned radially opposite each other.

[0062] Next, the reinforcing unit 20 is pressed by rollers (rotating bodies, not shown) that are arranged opposite to each other so that the first end portion 20 a and the second end portion 20 b come close to each other.

[0063] At this time, the overlapping portion 20 c of the reinforcing unit 20 has a state S1 in which the film is bonded with a predetermined film adhesive force or more, and a state S2 in which the film is bonded with a film adhesive force less than the predetermined film adhesive force.

[0064] The state S2 of less than the predetermined film adhesion strength includes, for example, Figure 4 State S2a shown, and Figure 5 State S2b is shown. Figure 4 In the state S2a shown, the first end portion 20a is partially in contact with the second end portion 20b, forming a gap 26. Figure 5 In the illustrated state S2b, the first end portion 20a and the second end portion 20b are not in contact with each other, and a gap 26 is formed throughout the entire circumferential direction of the overlapping portion 20c.

[0065] Next, in order to cover the reinforcement unit 20, use Figure 6The extrusion covering device 40 shown here extrudes the outer sheath 30 (extrusion molding step).

[0066] The extrusion coating device 40 includes a nipple 41 through which the inner cable 10 surrounded by the reinforcement unit 20 is inserted, and an outer mold 42 provided approximately coaxially with the outer side of the nipple 41. The inner cable 10 surrounded by the reinforcement unit 20 is inserted through the insertion hole 43 of the nipple 41, and the molten flame-retardant resin 30a is extruded from the resin flow path 45 onto the outer periphery of the reinforcement unit 20 emerging from the outlet 44 of the nipple 41 to coat the outer periphery.

[0067] The resin pressure during the extrusion molding process is set to a predetermined pressure such that the ratio W1 / W2 of the resin width W1 to the overlap width W2 is 0.10 or greater. The resin pressure can be adjusted, for example, by varying 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 that achieves W1 / W2 of 0.10 or greater is pre-calculated through experiments before manufacturing begins. Other mechanisms can also be used to adjust the resin pressure. Examples of other means include the shapes of the outer die 42 and nipple 41, the inner diameter of the resin flow path 45, the amount of resin 30a discharged from the extrusion coating device 40, and temperature settings.

[0068] In this embodiment, the nipple 41 and the outer mold 42 are arranged so that the distance between them is the pre-calculated distance N, and then the reinforcing element 20 is covered with the resin 30a. In this way, the outer sheath 30 is extruded, and the inner layer cable 10 and the reinforcing element 20 are housed within the outer sheath 30.

[0069] Thus, the resin 30a enters the portion of the overlapping portion 20c where the first end portion 20a and the second end portion 20b are bonded with a film adhesive force smaller than a predetermined film adhesive force (the portion in state S2). Figure 2 Fiber optic cable 1A is shown.

[0070] In the case of the portion of the overlapping portion 20c where the first end portion 20a and the second end portion 20b are in close contact without a gap and bonded together with a predetermined film bonding strength by the adhesive films 21 and 22 (the portion in state S1), the resin 30a does not enter this portion. In other words, even if the resin pressure during the extrusion molding process is constant, the bonding state between the first end portion 20a and the second end portion 20b by the adhesive films 21 and 22 may vary, resulting in portions where the resin 30a enters and portions where it does not.

[0071] Here, use Figure 8 The effects obtained by this embodiment will be described. Figure 8This is a conceptual diagram showing the result of covering the reinforcing unit 20 with a pre-calculated resin pressure. In this embodiment, the resin 30a is allowed to enter the gap 26, thereby applying a film adhesive force to the overlapping portion 20c and also applying a restraining force by the outer sheath 30 to restrain the first end portion 20a. Specifically, as Figure 2 as well as Figure 7 As shown, the outer sheath 30 provided on the outer periphery of the reinforcement unit 20 and the resin 30a that enters the gap 26 are continuously formed. This suppresses the force that pushes the first end portion 20a toward the outer periphery of the optical fiber cable 1A when the optical fiber cable 1A is bent. Therefore, in this embodiment, the resistance against the force that attempts to open the overlapping portion 20c when the optical fiber cable 1A is bent is the sum of the film adhesion force generated by the adhesive films 21 and 22 and the restraining force generated by the resin 30a.

[0072] Figure 8 The vertical axis is resistance, and the horizontal axis is the aforementioned state S1, state S2a, and state S2b. Figure 8 In FIG. 5 , the dotted line indicates the film adhesive force before covering with the outer sheath 30 , and the solid line indicates the resistance after covering with the outer sheath 30 (ie, the sum of the film adhesive force and the restraining force by the resin 30 a ). Figure 8 The “predetermined resistance” is a threshold value of force for suppressing the overlapped portion 20 c from opening and causing the outer sheath 30 to rupture when the optical fiber cable 1A is bent.

[0073] In state S1, if Figure 8 As shown by the solid line, the film adhesive force exceeds the predetermined resistance. That is, in state S1, the first end portion 20a and the second end portion 20b are sufficiently strongly bonded together by the film adhesive force generated by the adhesive films 21 and 22.

[0074] In state S2b, since the first end 20a and the second end 20b are not in contact, the film adhesion force is zero. On the other hand, even though the first end 20a and the second end 20b are not in contact, the resin 30a of the outer sheath 30 enters between the first and second end portions 20a, 20b, exerting a restraining force on the overlapping portion 20c. This restraining force exerted by the resin 30a increases the resistance in state S2b to a value exceeding the specified resistance.

[0075] In the state S2a, the first end portion 20a and the second end portion 20b are partially in contact with each other and a gap 26 is formed, so there is a film adhesive force ( Figure 8 The resin 30a is caused to enter the gap 26. The resin 30a that has entered the gap 26 acts as a restraining force, and the resistance is increased to exceed the predetermined resistance at the portion of state S2b.

[0076] Thus, it can be seen that in any of the states S1, S2a, and S2b, the resistance of the overlapping portion 20c increases to exceed the predetermined resistance.

[0077] As described above, the method for manufacturing the optical fiber cable 1A of this embodiment includes: a feeding step of feeding the core 11, which is the inner layer cable 10 composed of multiple optical fibers; a winding step of winding the reinforcement element (reinforcement member) 20 around the core 11 to form an overlapping portion 20c in which the ends 20a and 20b of the reinforcement element 20 partially overlap each other in the circumferential direction; and an extrusion molding step of extruding the outer sheath (jacket) 30 onto the outer side of the reinforcement element 20. Furthermore, in the extrusion molding step, the resin 30a constituting the outer sheath 30 is allowed to enter at least a portion of the overlapping portion 20c.

[0078] According to this manufacturing method, the resin 30a constituting the outer sheath 30 is allowed to enter the portion of the overlapping portion 20c where the film adhesion strength is less than the predetermined state S2, thereby applying a restraining force and increasing the resistance of this portion. This increases the resistance of the overlapping portion 20c in the longitudinal direction to above the predetermined resistance, thereby preventing the overlapping portion 20c from opening when the optical fiber cable 1A is bent. Consequently, rupture of the outer sheath 30 can be suppressed.

[0079] Furthermore, the reinforcement element 20 has a corrugated shape, with peaks 24 protruding radially outward and valleys 25 protruding radially inward alternately formed along its longitudinal direction. In the overlapping portion 20c, the peaks 24 are radially opposed to each other, and the valleys 25 are radially opposed to each other. This structure facilitates bending of the optical fiber cable 1A. Furthermore, the corrugated shape of the reinforcement element 20 increases the contact area between the reinforcement element 20 and the outer sheath 30. This improves the film adhesion between the reinforcement element 20 and the outer sheath 30.

[0080] In addition, the resin 30a constituting the outer sheath 30 is formed of a flame-retardant resin. In the case of this structure, since fillers with relatively low melting points and softening temperatures are added to the resin 30a, the strength of the optical fiber cable 1A in a high-temperature environment may be reduced, which may become a problem. In general optical fiber cables, when the resin is a flame-retardant resin, when the optical fiber cable is bent in a high-temperature environment, the overlapping portion 20c opens and deforms (ruptures). In contrast, in the optical fiber cable 1A of this embodiment, since the resin 30a constituting the outer sheath 30 is allowed to enter the overlapping portion 20c of the reinforcement unit 20, the force that forces 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 rupture of the outer sheath 30 can be suppressed.

[0081] While the first embodiment illustrates a structure in which the reinforcing unit 20 includes both the first adhesive film 21 and the second adhesive film 22, at least the first adhesive film 21 is sufficient. Without the second adhesive film 22, even if there are areas with low film adhesion, the resin 30a exerts a suppressive force on these areas, increasing the resistance. Therefore, the second adhesive film 22 can be omitted, leading to cost reductions.

[0082] In the cross-sectional view, although the entire overlapping portion 20 c and the tensile member 13 are described as being arranged at different positions in the circumferential direction, the entire overlapping portion 20 c and the tensile member 13 may be arranged at the same position in the circumferential direction.

[0083] Furthermore, in this embodiment, before the first end portion 20a and the second end portion 20b are bonded together using the resin 30a of the outer sheath 30, the first end portion 20a and the second end portion 20b are temporarily secured together during the winding process using at least the first adhesive film 21. Even if the bonding strength provided by the first adhesive film 21 is insufficient, the resin 30a penetrates into the weaker portions of the film, thereby increasing the resistance in the longitudinal direction to a level above a predetermined resistance. When temporarily securing the first end portion 20a and the second end portion 20b, the first adhesive film 21 need not be applied across the entire surface of the reinforcing sheet 23. For example, adhesive may be applied only to the overlapping portion 20c to secure the first end portion 20a and the second end portion 20b.

[0084] (Second embodiment)

[0085] 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 description is omitted. Only the differences will be described.

[0086] In the optical fiber cable 1B of this embodiment, as Figure 9 As shown, the reinforcing unit 20A is different from the first embodiment in that it does not include the first adhesive film 21 and the second adhesive film 22. That is, the reinforcing unit (reinforcing member) 20A of this embodiment corresponds to the reinforcing sheet 23 of the first embodiment.

[0087] Next, a method for manufacturing the optical fiber cable 1B according to this embodiment will be described.

[0088] In this embodiment, since the reinforcing unit 20A does not have the first adhesive film 21 and the second adhesive film 22, when the reinforcing unit 20A having the mountain portion 24 and the valley portion 25 is wound on 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 and becomes a tube extending along the long side direction.

[0089] At this time, the overlapping portion 20c of the reinforcing unit 20A may be in the following state in the cross-sectional view, that is, the state S3a (omitted from the figure) in which the first end portion 20a and the second end portion 20b are in contact with each other without a gap; Figure 10 As shown, the first end portion 20a is partially in contact with the second end portion 20b, and a gap 26 is formed in the state S3b; and Figure 11 As shown, the first end portion 20a and the second end portion 20b are not in contact with each other and a gap 26 is formed in a state S3c.

[0090] Next, the outer sheath 30 is extruded using the extrusion covering device 40 in the same manner as in the first embodiment so as to cover the reinforcing unit 20A.

[0091] At this time, the relationship between the resin pressure and the adhesive strength is determined in advance, and the distance N is calculated so that the value of W1 / W2 becomes 0.10 or more, similarly to the first embodiment.

[0092] With the nipple 41 and the outer mold 42 positioned so that the distance between them is N, the reinforcing unit 20A is covered with the resin 30a. To maintain the outer diameter of the outer sheath 30 uniformly along the longitudinal direction, the resin pressure is maintained substantially uniform. As a result, the resin 30a enters the overlapping portion 20c uniformly along the entire longitudinal direction. Figure 10 In the state S3b shown, the resin 30a enters the gap 26. Figure 11 In addition, even in the overlapping portion 20c in the aforementioned state S3a, the resin 30a enters the gap between the first end portion 20a and the second end portion 20b by the resin pressure expansion. Figure 9 As shown, the forming resin 30a is introduced into the outer sheath 30 of the overlapping portion 20c, and the optical fiber cable 1B is manufactured.

[0093] In this embodiment, since the reinforcing element 20A lacks the first adhesive film 21 and the second adhesive film 22, the restraining force exerted by the outer sheath 30 on the first end portion 20a acts as a resistance force against the force exerted by the overlapping portion 20c to open when the optical fiber cable 1A is bent. Similarly to the optical fiber cable 1A of the first embodiment, in the optical fiber cable 1B, the resistance force is increased to a predetermined value or higher in any of the states S3a, S3b, and S3c.

[0094] As described above, the manufacturing method of the optical fiber cable 1B of this embodiment also includes: a feeding step for feeding the core 11 having multiple optical fibers; a winding step for winding the reinforcement unit (reinforcement component) 20A around the core 11 to form an overlapping portion 20c in which the ends 20a and 20b of the reinforcement unit 20A partially overlap each other in the circumferential direction; and an extrusion molding step for extruding the outer sheath (sheath) 30 onto the outside of the reinforcement unit 20A. Furthermore, during the extrusion molding step, the resin 30a constituting the outer sheath 30 is allowed to enter the overlapping portion 20c. As in the first embodiment, this increases the resistance of the overlapping portion 20c in the longitudinal direction to a predetermined resistance or higher, thereby preventing the overlapping portion 20c from opening when the optical fiber cable 1B is bent. Consequently, rupture of the outer sheath 30 can be suppressed.

[0095] Example

[0096] The above-mentioned embodiment will be described below using specific examples. However, the present invention is not limited to the following examples.

[0097] The optical fiber cable 1A manufactured using the manufacturing method of the above-described first embodiment was evaluated.

[0098] The outer diameter of the inner cable 10 is 14.6 mm, the circumferential length of the reinforcement unit 20 is 64 mm, the circumferential width W2 of the overlapping portion 20 c of the reinforcement unit 20 is 10 mm, and the outer diameter of the optical fiber cable 1A is 22.1 mm. EVA is used as the material for the outer sheath 30. Fillers such as metal hydroxides (aluminum hydroxide, magnesium hydroxide) and phosphorus-based flame retardants are added as flame retardants. In order to add fillers such as flame retardants, a base resin such as EVA, EEA (ethylene-ethyl acrylate copolymer), and an elastomer with a relatively low melting point and softening temperature can be used.

[0099] Under the above conditions, multiple samples were prepared in which the distance between the nipple 41 and the outer die 42 during extrusion molding of the outer sheath 30 was varied, thereby changing the value of W1 / W2. After aging each sample at 70°C for three days, the presence of cracks in the outer sheath 30 with bend diameters of φ40D (D: the outer diameter of the optical fiber cable 1A) and φ30D was examined. These bend diameters were adopted based on the specifications of various optical fiber cables. Furthermore, the three-day aging condition at 70°C was established based on empirical evidence to confirm the reliability of the outer sheath 30.

[0100] Table 1 shows the test results.

[0101] [Table 1]

[0102] [Table 1]

[0103]

[0104] As shown in Table 1, when 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 greater, the outer sheath 30 does not break at either the bending diameters φ40D or φ30D. Therefore, it can be seen that setting the W1 / W2 ratio to 0.10 or greater can more reliably suppress breakage of the outer sheath 30.

[0105] Based on this result, it is preferable that the resin pressure in the extrusion molding step be set to a pressure determined in advance so as to satisfy W1 / W2≥0.10.

[0106] The technical scope of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the spirit of the present invention.

[0107] For example, in the manufacturing method of the first embodiment, although the reinforcement unit 20 is described as having states S1, S2a, and S2b, it need not include all of these states. Specifically, as long as the reinforcement unit 20 includes at least one of states S2a and S2b, rupture of the outer sheath 30 can be suppressed. Furthermore, a suppressive force is imparted to portions of the longitudinal direction where film adhesion is weak, increasing resistance and thereby improving the reliability of the optical fiber cable 1A. Similarly, in the manufacturing method of the second embodiment, the reinforcement unit 20A need not include all of states S3a, S3b, and S3c; it only needs to include at least one of states S3a, S3b, and S3c.

[0108] Furthermore, while the reinforcing units 20 and 20A of the above embodiments have been described as having alternately formed peaks 24 and valleys 25 along the longitudinal direction, the reinforcing units 20 do not necessarily need to be corrugated. Furthermore, the corrugated shape of the reinforcing units 20 is not limited to the above-described structure. For example, the corrugated shape may alternatively have alternately formed peaks 24 and valleys 25 extending obliquely with respect to the longitudinal direction.

[0109] In the optical fiber cables of the first and second embodiments described above, the reinforcing element 20 is configured to surround the inner cable 10. However, the present invention is not limited thereto, and the reinforcing element 20 may be configured to surround the core 11. In this configuration, in the first and second embodiments described above, as long as only the core 11 is fed out without feeding out the inner cable 10, the reinforcing element 20 may be wound around the core 11 during the winding process.

[0110] In addition, in the manufacturing methods of the above-mentioned first and second embodiments, although the winding process is performed after the peaks 24 and valleys 25 of the reinforcing unit 20 (20A) are formed, a flat sheet-shaped reinforcing unit 20 (20A) can also be used to form the peaks 24 and valleys 25 after the winding process and before the extrusion molding process.

[0111] Furthermore, in the first and second embodiments described above, the radial dimension M2 of the resin 30a between the valleys 25a and 25b is thicker than the radial dimension M1 of the resin 30a between the peaks 24a and 24b. However, this is not limiting. Specifically, the dimension M2 may be thinner than the dimension M1, and the thickness of the resin 30a may be uniform between the peaks 24 and the valleys 25.

[0112] Furthermore, the resin 30 a may enter at least between the valley portions 25 a and 25 b between the first end portion 20 a and the second end portion 20 b of the overlapping portion 20 c.

[0113] Furthermore, the inner cable 10 is not limited to the above-described structure and may also be a loose tube, wrapped tube cable (WTC), or a trough-type cable. Furthermore, the tension member may be embedded in the outer sheath 30. Furthermore, the multiple optical fibers and inner cable 10 may be covered with a press roll or a water-absorbing tape (sheet) or may not be covered, as needed. Furthermore, the inner cable 10 is not limited to a water-absorbing tape (sheet) and may or may not be provided with other waterproof materials or water-absorbing materials as needed.

[0114] In addition, in each of the above-described embodiments, the cross-sectional shape of the core portion 11 is circular, but the cross-sectional shape of the core portion 11 may be elliptical, rectangular, or the like.

[0115] Description of Reference Signs

[0116] 1A, 1B…optical fiber cable; 11…core; 12…first tear cord; 20, 20A…reinforcement unit (reinforcement component); 20c…overlapping portion; 21…first adhesive film (adhesive layer); 24…mountain portion; 25…valley portion; 30…outer sheath (sheath); 30a…resin.

Claims

1. A method for manufacturing an optical fiber cable, comprising the following steps: a feeding step of feeding out a core having a plurality of optical fibers; a winding step of winding a reinforcing member around the core portion to form an overlapping portion extending along the longitudinal direction of the plurality of optical fibers and having ends of the reinforcing member partially overlap each other in the circumferential direction; and In the extrusion molding process, the sheath is extruded and molded on the outside of the above-mentioned reinforcement component. In the extrusion molding step, the resin constituting the sheath is allowed to enter at least a portion of the overlapping portion. The resin is allowed to enter the overlapping portion where the portion is bonded with an adhesive force smaller than a predetermined adhesive force.

2. The method for manufacturing an optical fiber cable according to claim 1, wherein: When the circumferential width of the overlapping portion is represented by W2 and the circumferential width of the resin entering the overlapping portion is represented by W1, W1 / W2≧0.10 is satisfied.

3. The method for manufacturing an optical fiber cable according to claim 2, wherein: The resin pressure in the extrusion molding step is set to a pressure determined in advance so as to satisfy W1 / W2≥0.

10.

4. The method for manufacturing an optical fiber cable according to any one of claims 1 to 3, wherein: In the winding step, the overlapping portion is temporarily fixed by an adhesive.

5. The method for manufacturing an optical fiber cable according to any one of claims 1 to 3, wherein: In the extrusion molding step, the resin pressure of the resin constituting the sheath is adjusted so that the resin enters at least a portion of the overlapping portion.

6. The method for manufacturing an optical fiber cable according to any one of claims 1 to 3, wherein: The resin inserted into the overlapping portion is formed integrally with the resin.

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