Optical fiber cable and cable core manufacturing method

Abstract

To provide an optical fiber cable which suppresses transmission loss of an optical fiber and has high flame retardancy, and a method for manufacturing the optical fiber cable.SOLUTION: A core part 14 is constituted by twisting a plurality of optical fiber units 5 composed of a plurality of coated optical fibers 3. On the outer periphery of the plurality of optical fiber units 5, a wrapping member 7 is provided. The wrapping member 7 is arranged so as to collectively cover the plurality of optical fiber units 5 by vertical double winding. On the outer periphery of the core part 14 (wrapping member 7), a flame-retardant member 17 is provided. The flame-retardant member 17 is arranged so as to collectively cover the core part 14 by vertical double winding. In the flame-retardant member 17, an overlapping part is formed by winding so that ends are overlapped with each other. The overlapped part of the flame-retardant member 17 is spirally arranged in the longitudinal direction of an optical fiber cable 1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an optical fiber cable that accommodates a plurality of coated optical fibers and a method for manufacturing the cable core. [Background technology]

[0002] With the recent increase in the amount of information transmitted, there is a demand for a higher density of optical fibers in an optical fiber cable and an increased number of optical fibers housed in the cable in order to increase the amount of information transmitted in a single optical fiber cable.

[0003] Such optical fiber cables are used outdoors to connect buildings, and when they are brought indoors, they must be connected to an indoor flame-retardant cable. However, as the number of fibers increases, the connection takes time and costs money, so there is a demand for ultra-high-count flame-retardant cables that can be used both indoors and outdoors.

[0004] As such an optical fiber cable, an optical fiber cable that is given flame retardant properties by using a sheath material containing a flame retardant material has been proposed (Patent Document 1).

[0005] Also, an optical fiber cable has been proposed in which the flame retardant properties are improved by protecting the optical fiber unit using a member such as a tape containing a flame retardant material (Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-148608 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-145017 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method of imparting flame retardancy to the jacket as in Patent Document 1, the jacket must be thickened to improve flame retardancy, which makes it difficult to lay and dismantle the cable.In addition, the need to blend flame retardant material into the entire jacket increases material costs.

[0008] On the other hand, in Patent Document 2, flame retardancy is achieved by wrapping a flame retardant tape around the outer periphery of the slot, but such a tape is usually wrapped longitudinally around the outer periphery of the slot (a method of wrapping the flame retardant tape so that the longitudinal direction of the tape is aligned with the longitudinal direction of the slot). However, when the optical fiber cable burns, it is difficult to prevent the internal optical fiber unit from burning due to openings in the flame retardant tape wrapped longitudinally.

[0009] Another method is to spirally wrap the flame-retardant tape around the core to prevent it from opening (by wrapping the flame-retardant tape in the longitudinal direction at an angle to the circumferential direction of the slot). However, as mentioned above, slotless cables are used to accommodate optical fiber cores at high density, and if the flame-retardant tape is spirally wrapped around the core in this case, the tension will press down on the optical fiber cores inside, causing an increase in transmission loss.

[0010] To prevent the opening of a flame-retardant tape that has been longitudinally wrapped, one method involves winding a linear object such as a thread around the flame-retardant tape after the flame-retardant tape has been wrapped around it. However, because the linear object is wound spirally around the flame-retardant tape, the portion not held down by the linear object is prone to opening due to the restoring force of the flame-retardant tape, potentially exposing the core portion inside. In contrast, shortening the winding pitch of the linear object requires a slower wire speed during manufacturing. Furthermore, as with spiral winding, the tension presses down on the optical fiber core inside, resulting in increased transmission loss.

[0011] While it is possible to prevent the opening by increasing the overlap of the flame-retardant tape, if the overlapping area is raised, it may get caught when passing through the cap used to cover the outer sheath. This requires making the cap larger than necessary and making the cable thicker. Furthermore, increasing the overlapping area increases the amount of linear material used, which leads to increased costs, and also makes it difficult to remove the optical fiber core inside.

[0012] The present invention has been made in view of the above problems, and has as its object to provide an optical fiber cable that suppresses transmission loss of the optical fiber and has high flame retardancy, and a method for manufacturing the optical fiber cable. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the first invention is an optical fiber cable comprising: a cable core having a core portion in which an optical fiber unit consisting of a plurality of optical fiber cores is twisted together; a flame-retardant material wrapped longitudinally around the outer periphery of the core portion; a tension member arranged outside the cable core; and an outer sheath provided around the outer periphery of the cable core and the tension member, wherein the overlapping portion of the flame-retardant material is arranged spirally in the longitudinal direction, and the spiral pitch of the overlapping portion of the flame-retardant material is shorter than the twisting pitch of the optical fiber unit.

[0014] The core portion may be configured by longitudinally wrapping a pressure winding member around the outer periphery of the plurality of optical fiber units, and the flame retardant member may be disposed around the outer periphery of the pressure winding member.

[0015] The holding and wrapping member may be a water-absorbent member.

[0016] The helical pitch of the overlapping portion of the flame-retardant member may be 400 mm or more and 1200 mm or less, and further, the helical pitch of the overlapping portion of the flame-retardant member may be 500 mm or more and 900 mm or less.

[0017] According to the first aspect of the present invention, the cable core around which the flame-retardant member is longitudinally wound is twisted, so that the overlapping portion of the flame-retardant member is arranged helically in the longitudinal direction. This makes it possible to suppress the opening of the overlapping portion. In this case, since the flame-retardant member is not wound helically, the optical fiber core inside is not tightly constricted when the flame-retardant member is wound, and it is also possible to increase the drawing speed.

[0018] In addition, since the twisting pitch of the internal optical fiber units is larger than the twisting pitch of the flame-retardant member, there is no need to twist the optical fiber units excessively, and an increase in transmission loss due to excessive twisting of the optical fiber units can be suppressed. Furthermore, since the helical pitch of the overlapping portion of the flame-retardant member can be shortened while maintaining a long twisting pitch of the optical fiber units, opening of the flame-retardant member can be reliably suppressed.

[0019] Furthermore, if a pressure winding member is provided around the outer periphery of multiple optical fiber units, it becomes easier to form the core portion, and when the core portion is wound around a bobbin or the like, it is possible to prevent the optical fiber units from popping out, etc.

[0020] Furthermore, if the holding wrapping member is a water-absorbent member, waterproofing can be ensured. For example, flame-retardant members usually do not have water-stopping properties, making it difficult to ensure waterproofing, but by overlapping a flame-retardant member and a water-absorbent member, the effects of both can be obtained.

[0021] Furthermore, if the spiral pitch of the overlapping portion of the flame-retardant member is within a predetermined range, it is possible to suppress the opening during combustion and also to suppress an increase in transmission loss due to tightening of the flame-retardant member.

[0022] The second invention is a method for forming a cable by assembling a plurality of optical fibers. Twist together A core part is formed, and a flame-retardant material is wound around the outer periphery of the core part by longitudinal splicing while rotating the unwinding side of the core part and the winding side of the cable core in synchronization with each other with the moving direction of the core part as the rotation axis. The overlapping portion of the flame retardant member is arranged spirally in the longitudinal direction, and the spiral pitch of the overlapping portion of the flame retardant member is shorter than the twisting pitch of the optical fiber unit. The present invention relates to a method for manufacturing a cable core.

[0023] According to the second aspect of the present invention, the flame-retardant member can be efficiently wound spirally around the outer periphery of the core portion without excessively twisting the inner core portion. [Effects of the Invention]

[0024] According to the present invention, an optical fiber cable that suppresses transmission loss of the optical fiber and has high flame retardancy, and a method for manufacturing the optical fiber cable can be provided. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing an optical fiber cable 1. FIG. [Figure 2] FIG. 2 is a diagram showing an intermittently bonded optical fiber core 3. [Figure 3] FIG. 1 is a perspective view showing an optical fiber cable 1. [Figure 4] 3. (a) is a cross-sectional view taken along line AA in FIG. 3, (b) is a cross-sectional view taken along line BB in FIG. 3, and (c) is a cross-sectional view taken along line CC in FIG. [Figure 5] FIG. 2 is a diagram showing a cable core manufacturing apparatus 30a. [Figure 6] 10(a) and 10(b) are diagrams showing a process of longitudinally wrapping the pressure wrapping member 7. FIG. [Figure 7] FIG. 3 is a diagram showing a cable core manufacturing device 30b. [Figure 8] 10(a) and 10(b) are diagrams showing a process of longitudinally wrapping a flame-retardant member 17. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing an optical fiber cable 1. The optical fiber cable 1 is a slotless optical fiber cable that does not use a slot, and is composed of a core 14, a holding winding member 7, a tension member 9, a tear cord 11, an outer jacket 13, a flame-retardant member 17, etc.

[0027] The core portion 14 is made up of a plurality of optical fiber cores 3 and a pressure winding member 7. More specifically, a plurality of optical fiber cores 3 are twisted together to form an optical fiber unit 5, and a plurality of optical fiber units 5 are assembled and wound with a pressure winding member 7 to form the core portion 14. The optical fiber units 5 are bundled together with, for example, a bundling material, and are distinguished from other optical fiber units 5.

[0028] The number of optical fiber units 5 is not limited to the example shown in the figure. Furthermore, the multiple optical fiber cores 3 do not have to be divided into optical fiber units 5. Furthermore, the pressure winding member 7 is not necessarily required, and the core portion 14 may be formed by twisting together multiple optical fiber units 5 each consisting of multiple optical fiber cores 3. In the following explanation, an example will be described in which the core portion 14 is formed by longitudinally winding the pressure winding member 7 around the outer periphery of the multiple optical fiber units 5.

[0029] The optical fiber 3 may be a single-core optical fiber, but is preferably an optical fiber ribbon in which multiple optical fibers are arranged side by side. In this case, it is preferably an intermittently bonded optical fiber ribbon in which adjacent optical fibers are intermittently bonded to each other in the longitudinal direction.

[0030] 2 is a perspective view showing an intermittently bonded optical fiber 3. The optical fiber 3 is formed by arranging a plurality of optical fibers 2a, 2b, 2c, and 2d in parallel and bonding them together. The number of optical fibers constituting the optical fiber 3 is not limited to the example shown in the figure. Furthermore, the optical fiber does not necessarily have to be an intermittently bonded optical fiber ribbon.

[0031] 2, in this embodiment, adjacent optical fibers 2a, 2b, 2c, and 2d are bonded together at adhesive joints 6 at intervals at predetermined intervals in the longitudinal direction of the optical fiber core 3. Furthermore, it is desirable that adjacent adhesive joints 6 in the width direction are arranged so as to be offset from each other in the longitudinal direction of the optical fiber core 3. For example, it is desirable that adjacent adhesive joints 6 are formed so as to be offset by half a pitch in the longitudinal direction of the optical fiber core 3. It is noted that the length and pitch of the adhesive joints 6 are not limited to the example shown in the figure.

[0032] In this way, by arranging the adhesive portions 6 intermittently in the longitudinal direction of the optical fiber core 3, adjacent optical fibers 2a, 2b, 2c, and 2d in the non-adhesive portions can be easily folded (bent) relative to the parallel direction of the optical fibers 2a, 2b, 2c, and 2d.

[0033] A pressure winding member 7 is provided around the outer periphery of the plurality of optical fiber units 5 as needed. The pressure winding member 7 is arranged so as to cover the plurality of optical fiber units 5 collectively by vertical splicing. The pressure winding member 7 is wound so that the ends in the width direction overlap each other, forming an overlapping portion. The pressure winding member 7 may be, for example, a resin tape, but is preferably a water-absorbent material such as a water-absorbent nonwoven fabric. A linear body such as thread may also be wound around the outer periphery of the pressure winding member 7.

[0034] A flame-retardant member 17 is provided on the outer periphery of the core portion 14 (presser winding member 7). The flame-retardant member 17 is arranged so as to cover the entire core portion 14 by vertically wrapping it. The flame-retardant member 17 is wrapped so that its ends overlap, forming an overlapping portion. The core portion 14 with the flame-retardant member 17 wrapped around it constitutes the cable core 15. The flame-retardant member 17 is a sheet-like member to which a flame retardant such as a metal compound is added. A linear object such as thread may be wrapped around the outer periphery of the vertically wrapped flame-retardant member 17.

[0035] A pair of tension members 9 are provided on the outside of the cable core 15 at positions facing each other with the cable core 15 in between. In addition, tear cords 11 are provided in a direction substantially perpendicular to the facing direction of the tension members 9 so as to face each other with the cable core 15 in between.

[0036] Additionally, an outer jacket 13 is provided around the cable core 15, the tear cord 11, and the tension member 9. The outer jacket 13 is a layer for covering and protecting the optical fiber cable 1. The cable core 15, the tear cord 11, and the tension member 9 are all covered by the outer jacket 13. In other words, the tension member 9 and the tear cord 11 are embedded in the outer jacket 13.

[0037] As described above, the holding winding member 7 is wound longitudinally around the outer periphery of the optical fiber unit 5. Therefore, immediately after being wound longitudinally, the overlapping portion of the holding winding member 7 is formed substantially straight in the axial direction of the optical fiber cable 1. Similarly, the flame retardant member 17 is wound longitudinally around the outer periphery of the core portion 14. Therefore, immediately after being wound longitudinally, the overlapping portion of the flame retardant member 17 is formed substantially straight in the axial direction of the optical fiber cable 1.

[0038] Fig. 3 is a perspective view of the optical fiber cable 1, Fig. 4(a) is a cross-sectional view taken along line AA in Fig. 3, Fig. 4(b) is a cross-sectional view taken along line BB in Fig. 3, and Fig. 4(c) is a cross-sectional view taken along line CC in Fig. 3. In the following figures, for simplicity, the optical fiber cores are omitted from the illustration, and only the outline of the optical fiber unit 5 is shown. In Figs. 4(a) to 4(c), only specific optical fiber units 5a are shown hatched.

[0039] 4(a) to 4(c), when the position of the tension member 9 arranged substantially straight in the axial direction of the optical fiber cable 1 is used as a reference, the arrangement of the overlapping portion 21a of the holding winding member 7 and the arrangement of the overlapping portion 21b of the flame retardant member 17 change in the circumferential direction depending on the longitudinal position of the optical fiber cable 1. In other words, the overlapping portion 21a of the holding winding member 7 and the overlapping portion 21b of the flame retardant member 17 are arranged spirally with respect to the longitudinal direction of the optical fiber cable 1.

[0040] 4(a), the overlapping portion 21a of the holding wrapping member 7 and the overlapping portion 21b of the flame-retardant member 17 are positioned at positions offset by exactly 180 degrees. Also, the optical fiber unit 5a is positioned directly below the overlapping portion 21a.

[0041] In contrast, when the arrangement of each portion at predetermined intervals in the longitudinal direction of the optical fiber cable 1 is examined, for example, at the positions shown in Figures 4(b) and 4(c), the overlapping portion 21a and the optical fiber unit 5a are circumferentially offset by an angle θ1, and the overlapping portion 21b is circumferentially offset by an angle θ2. That is, the overlapping portions 21a, 21b and the optical fiber unit 5a are twisted together and arranged in a spiral shape relative to the longitudinal direction of the optical fiber cable 1. In this embodiment, the positions of the overlapping portion 21a and the optical fiber unit 5a are approximately the same. That is, the spiral pitch of the overlapping portion 21a and the twisting pitch of the optical fiber unit 5a are approximately the same.

[0042] Here, θ2 is larger than θ1. That is, the helical pitch of the overlapping portion 21b of the flame-retardant member 17 is shorter than the twisting pitch of the optical fiber unit 5 (the helical pitch of the overlapping portion 21a of the holding winding member 7). The helical pitch of the overlapping portion 21b of the flame-retardant member 17 is preferably 400 mm or more and 1200 mm or less, and more preferably 500 mm or more and 900 mm or less.

[0043] Next, a method for manufacturing the cable core 15 will be described. Fig. 5 is a schematic diagram showing a cable core manufacturing apparatus 30a. First, a plurality of coated optical fibers 3 are twisted together and wrapped with a bundle material to form an optical fiber unit 5, which is then wound around an optical fiber unit supply bobbin 31. The optical fiber units 5 are supplied from the plurality of optical fiber unit supply bobbins 31 and assembled to form the core portion 14. At this time, the plurality of optical fiber units 5 are assembled straight without being twisted together, so the installation position of the optical fiber unit supply bobbin 31 is fixed.

[0044] The assembly of the optical fiber units 5 is sent to the forming device 33 together with the pressure winding member 7. In the forming device 33, the pressure winding member 7 is longitudinally wound around the outer periphery of the assembly of the optical fiber units 5 so as to collectively cover the plurality of optical fiber units 5.

[0045] 6(a) and 6(b) are conceptual diagrams showing the process of longitudinally wrapping the pressure winding member 7 around a plurality of optical fiber units 5. Longitudinal wrapping is a method of wrapping the pressure winding member 7 so that the longitudinal direction of the pressure winding member 7 is aligned with the longitudinal direction of the optical fiber units 5 and a portion of the pressure winding member 7 overlaps in the width direction to cover the optical fiber units 5. As described above, the optical fiber units 5 are gathered together in a straight line in the longitudinal direction, and typically, the overlapping portion 21a of the pressure winding member 7 after longitudinal wrapping is also aligned in a straight line in the longitudinal direction to form the core portion 14.

[0046] As shown in Fig. 5, the core portion 14 that has left the forming device 33 is taken up by the take-up bobbin 35. At this time, in this embodiment, the take-up bobbin 35 is rotatable around the axis of rotation that is the direction of travel of the core portion 14 (arrow D in the figure). By taking up the core portion 14 while rotating the take-up bobbin 35 on the take-up side, the optical fiber unit 5 and the pressure winding member 7 (core portion 14) can be twisted and wound together. Therefore, the optical fiber unit 5 and the overlapping portion 21a of the pressure winding member 7 after longitudinal splicing are twisted together and arranged in a spiral at a predetermined pitch.

[0047] 7 is a schematic diagram showing a cable core manufacturing apparatus 30b. The winding bobbin 35 around which the core portion 14 is wound is used as a core portion supply bobbin 37. The core portion 14 supplied from the core portion supply bobbin 37 is sent to a forming apparatus 41 together with a flame-retardant member 17. In the forming apparatus 41, the flame-retardant member 17 is wound vertically around the core portion 14 so as to cover the entire core portion 14, thereby forming a cable core 15, which is then wound around a winding bobbin 39.

[0048] At this time, the core supply bobbin 37 on which the core portion 14 is unwound and the winding bobbin 39 on which the cable core 15 is wound can rotate synchronously in the same direction at approximately the same speed with the moving direction of the core portion 14 as the rotation axis (arrow E in the figure). In this way, by winding the cable core 15 while rotating the core supply bobbin 37 and the winding bobbin 35, the core portion 14 is not twisted, and only the flame-retardant member 17 can be longitudinally wound around the outer periphery of the core portion 14 while being twisted.

[0049] 8(a) and 8(b) are conceptual diagrams of the process of longitudinally winding flame-retardant material 17 while rotating core portion 14. Fig. 8(a) is a diagram showing the state in which flame-retardant material 17 is being wound around the outer periphery of core portion 14, and Fig. 8(b) is a diagram showing cable core 15 around which flame-retardant material 17 is wound.

[0050] As described above, the overlapping portion 21b formed by longitudinally wrapping the flame-retardant member 17 is arranged spirally in the longitudinal direction of the cable core 15. In this case, the overlapping portion 21b can be formed at a twisting pitch different from the twisting pitch of the core portion 14.

[0051] Thereafter, the cable core 15 wound around the take-up bobbin 39 is supplied to a sheath extruder together with the tension member 9 and the tear cord 11, and the sheath 13 is extruded and coated onto the outer periphery of the cable core 15. In this manner, the optical fiber cable 1 can be manufactured.

[0052] Here, twisting the optical fiber units 5 together can prevent an excessive increase in transmission loss of a specific optical fiber 3 when bending the optical fiber cable 1. Furthermore, since the overlapping portion 21a of the holding and winding member 7 is spiral, it can prevent the optical fiber units 5 and optical fiber 3 inside from being exposed from the overlapping portion 21a when handling the core portion 4.

[0053] On the other hand, if the optical fiber unit 5 is twisted too tightly, the lateral pressure on the optical fiber becomes too great, resulting in increased transmission loss. Also, the spiral pitch of the overlapping portion 21a of the pressure winding member 7 does not need to be excessively short, as long as it is possible to prevent the optical fiber unit 5 (optical fiber 3) inside from protruding during the manufacturing of the cable core 15. For this reason, it is desirable to wind the optical fiber unit 5 and the pressure winding member 7 at a relatively long pitch.

[0054] In contrast, the flame-retardant member 17 needs to have the overlapping portions 21b arranged in a spiral shape at a relatively short pitch to prevent openings or the like from occurring during combustion, such as in the event of a fire. However, as described above, if the twist pitch of the internal optical fiber unit 5 is matched to the spiral pitch of the flame-retardant member 17, transmission loss increases. Therefore, according to this embodiment, only the overlapping portions 21b of the flame-retardant member 17 can be formed at a short pitch without excessively shortening the twist pitch of the internal optical fiber unit 5, thereby making it possible to achieve high flame retardancy while suppressing an increase in transmission loss.

[0055] If necessary, a linear body may be spirally wound around the core portion 14 or the cable core 15. In this case, it is desirable that the twisting direction of the core portion 14 or the cable core 15 and the spiral winding direction of the linear body are opposite to each other. Furthermore, the twisting direction of the optical fiber unit 5 in the cable core manufacturing apparatus 30a and the twisting direction of the core portion 14 and the cable core 15 in the cable core manufacturing apparatus 30b may be opposite to each other. Furthermore, the cable core manufacturing apparatuses 30a and 30b may be integrated. In this case, the forming device 41 may be rotated around the outer periphery of the core portion 14.

[0056] As described above, according to the optical fiber cable 1 of this embodiment, the flame-retardant member 17 is wound not spirally but longitudinally, so that the internal optical fiber 3 is not excessively tightened, thereby suppressing an increase in transmission loss. Furthermore, because the overlapping portion 21b of the flame-retardant member 17 is formed spirally, opening of the flame-retardant member 17 can be suppressed even during combustion.

[0057] Furthermore, the twist pitch of the optical fiber unit 5 can be made longer than that of the flame-retardant member 17, thereby suppressing an increase in transmission loss. Furthermore, by using the holding and winding member 7, it is possible to act as a cushion so that the tightening force of the flame-retardant member 17 is not directly applied to the optical fiber core. Furthermore, if the holding and winding member 7 is made of a water-absorbent material such as a water-absorbent nonwoven fabric, the waterproofness of the optical fiber cable 1 can be improved.

[0058] Furthermore, by rotating the take-up bobbin 35 behind the forming device 33 with the traveling direction of the core portion 14 as the rotation axis, the optical fiber unit 5 and the pressure winding member 7 can be easily twisted together.

[0059] Furthermore, by rotating the core portion supply bobbin 37 and the take-up bobbin 39 in the same direction before and after the forming device 41, with the direction of travel of the core portion 14 as the rotation axis, it is possible to easily arrange only the overlapping portion 21b of the flame-retardant member 17 in a spiral shape without twisting the optical fiber unit 5 inside.

[0060] The present invention is not limited to the optical fiber cable 1 having the cross-sectional shape shown in Fig. 1, and the cross-sectional structure may be different. For example, the optical fiber cable may be a self-supporting type having a support wire portion. [Example]

[0061] The transmission loss and flame retardancy were evaluated by changing the helical pitch of the overlapping portion 21b of the flame-retardant member 17 (simply referred to as the helical pitch of the flame-retardant member 17). The optical fiber cable used had the structure shown in FIG.

[0062] First, 12 optical fibers with a diameter of 200 μm were intermittently bonded to form a 12-fiber ribbon. Twelve of these optical fiber ribbons were twisted together to form a 144-fiber optical fiber unit.

[0063] Forty-eight 144-fiber optical fiber units were supplied and twisted together, and then a pressure winding member was rolled up using a forming jig and longitudinally wrapped so that the overlapping portions formed a spiral with a pitch of 1300 mm. Furthermore, a flame-retardant material was longitudinally wrapped around the pressure winding member. At this time, the overlapping portions of the flame-retardant material were made into a spiral with a specified pitch. A pressure thread was also wrapped around the outer circumference of the flame-retardant material. This produced a cable core with 6,912 fibers.

[0064] The cable core, tension member, and rip cord for ripping the jacket were arranged straight along the length of the cable without twisting, and the jacket was extrusion coated. After sheathing, the cable was cooled to about 20°C in a water bath to create an optical fiber cable. The jacket material was flame-retardant PE.

[0065] The outer diameter of the optical fiber cable was 29.5 mm, and the thickness of the jacket was 4 mm. The tension member used was made of G-FRP (glass fiber reinforced plastic) with a diameter of 2.0 mm.

[0066] The pressure winding member was longitudinally wrapped around the cable core using equipment capable of winding while rotating around the axis of rotation in the direction of cable core flow. The flame-retardant member was longitudinally wrapped around the cable core using equipment capable of unwinding and winding while rotating around the axis of rotation in the direction of cable core flow. In this case, the twist pitch of the flame-retardant member was changed by adjusting the cable core feed speed and the cable core rotation speed.

[0067] The various optical fiber cables thus produced were subjected to various evaluations. The results are shown in Table 1.

[0068] [Table 1]

[0069] In the table, "spiral pitch of pressure winding member" refers to the spiral pitch of the overlapping portion of the pressure winding member, and is the same as the twisting pitch of the optical fiber unit. "Pressure winding structure of flame retardant member" refers to the winding method, i.e., longitudinal splice winding (a method of winding the flame retardant member so that its longitudinal direction is aligned with the longitudinal direction of the core) and spiral winding (a method of winding the flame retardant member so that its longitudinal direction is obliquely wound around the core), and "spiral pitch of flame retardant member" refers to the spiral pitch of the overlapping portion of the flame retardant member.

[0070] The "flame retardant overlap amount" indicates the width of the overlapping portion of the flame retardant material. The "opening of the flame retardant overlapping portion" indicates that when the cable core was held vertically and the holding thread around the outer periphery of the flame retardant material was removed, the flame retardant material did not open and the core was not exposed, and the cable was evaluated as passing (○).

[0071] In the "flammability characteristics" test (UL1666), if the flame height is less than 3.66m and the temperature of the second floor ceiling is 454.4 degrees or less, it is considered a pass (○), and if it does not meet the conditions, it is considered a fail (×). In the "smoke generation characteristics" test (ULST-1), if the total amount of smoke emitted in 20 minutes is 150m 3 or less, and the peak smoke rate is 0.4m 3 Those that did not meet the conditions were deemed to be unsuccessful (×).

[0072] For "transmission loss," a transmission loss of 0.40 dB or less at a wavelength of 1310 nm and a transmission loss of 0.30 dB or less at 1550 nm was deemed a pass (◯), and a failure (×) was deemed to have exceeded either standard.

[0073] Examples 1 to 4 passed the tests for combustion characteristics, smoke generation characteristics, and transmission loss characteristics. On the other hand, in Comparative Example 3, the flame-retardant member was spirally wound, which caused the internal optical fiber unit to be tightly fastened, resulting in a failure in the transmission loss characteristics. In Comparative Example 1, the flame-retardant member was longitudinally wrapped, but as in Comparative Example 3, the spiral pitch of the flame-retardant member was too short, which caused the internal optical fiber unit to be tightly fastened, resulting in a failure in the transmission loss characteristics. In Comparative Example 2, the spiral pitch of the flame-retardant member was too long, which caused the overlapping portion to open up during combustion tests, resulting in a failure in the combustion characteristics and smoke generation characteristics.

[0074] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0075] 1....Optical fiber cable 2a, 2b, 2c, 2d....Optical fiber 3....Optical fiber core 5, 5a....Optical fiber unit 6...Adhesive 7...Pressing and winding member 9...Tension member 11...Tear cord 13……Outer cover 14...Core part 15...Cable core 17...Flame-retardant material 21a, 21b...overlapping portion 30a, 30b... Cable core manufacturing device 31: Optical fiber unit supply bobbin 33, 41...Forming device 35, 39.... Winding bobbin 37...Core supply bobbin

Claims

1. a cable core having a core portion in which a plurality of optical fiber units each consisting of a plurality of coated optical fibers are twisted together, and a flame retardant member wound longitudinally around the outer periphery of the core portion; a tension member disposed outside the cable core; an outer sheath provided on the outer periphery of the cable core and the tension member; Equipped with The overlapping portion of the flame-retardant member is arranged spirally in the longitudinal direction, An optical fiber cable, wherein the helical pitch of the overlapping portion of the flame retardant member is shorter than the twist pitch of the optical fiber units.

2. The optical fiber cable of claim 1, characterized in that the core portion is constructed by vertically wrapping a pressure winding member around the outer periphery of the plurality of optical fiber units, and the flame-retardant member is arranged around the outer periphery of the pressure winding member.

3. 3. The optical fiber cable according to claim 2, wherein the pressure winding member is a water-absorbent material.

4. 4. The optical fiber cable according to claim 1, wherein the helical pitch of the overlapping portion of the flame retardant member is 400 mm or more and 1200 mm or less.

5. 4. The optical fiber cable according to claim 1, wherein the helical pitch of the overlapping portion of the flame-retardant member is 500 mm or more and 900 mm or less.

6. A core portion is formed by assembling and twisting a plurality of optical fiber units together, The unwinding side of the core section and the winding side of the cable core are rotated synchronously with each other around the rotation axis in the moving direction of the core section, and a flame-retardant material is wound around the outer periphery of the core section by longitudinal splicing. The overlapping portion of the flame-retardant member is arranged spirally in the longitudinal direction, The method for manufacturing a cable core, wherein the helical pitch of the overlapping portion of the flame retardant member is shorter than the twisting pitch of the optical fiber unit.

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