JP7780974B2 - Optical fiber cable and cable core manufacturing method - Google Patents

Description

The present invention relates to an optical fiber cable containing multiple optical fiber cores and a method for manufacturing the cable core.

With the increase in the amount of information being transmitted in recent years, there is a demand for optical fibers to be packed densely into optical fiber cables and for the number of optical fibers to be increased in order to increase the amount of information transmitted through a single optical fiber cable.

Such optical fiber cables are used outdoors to connect buildings, and when bringing them indoors, they need to be connected to an indoor flame-retardant cable. However, as the number of cores increases, the time and cost required for connection increases, so there is a demand for ultra-high-core flame-retardant cables that can be used both indoors and outdoors.

One such optical fiber cable proposed is one that has flame-retardant properties achieved by using a sheath material containing a flame-retardant material (Patent Document 1).

Furthermore, optical fiber cables have been proposed that improve flame retardancy by protecting the optical fiber unit using components such as tape containing flame retardant materials (Patent Document 2).

JP 2013-148608 A Japanese Patent Application Laid-Open No. 2004-145017

Methods such as those described in Patent Document 1, which make the outer sheath flame-retardant, require the outer sheath to be thicker in order to improve flame retardancy, which makes the cable easier to install and dismantle. Furthermore, since the entire outer sheath must be blended with flame-retardant material, material costs also increase.

Meanwhile, in Patent Document 2, flame retardancy is achieved by wrapping flame retardant tape around the outer periphery of the slot, but such tape is typically wrapped longitudinally around the outer periphery of the slot (a method of wrapping the flame retardant tape so that its longitudinal direction is aligned with the longitudinal direction of the slot). However, when the optical fiber cable burns, the openings in the flame retardant tape that is wrapped longitudinally make it difficult to prevent the optical fiber unit inside from burning.

Another method is to spirally wrap the flame-retardant tape around the core to prevent it from opening up (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 high-density optical fiber cores, and in this case, if the flame-retardant tape is spirally wrapped around the core, the tension will press down on the optical fiber cores inside, resulting in increased transmission loss.

In order to prevent vertically wrapped flame-retardant tape from opening, one method is to wrap a linear object such as thread around the flame-retardant tape after wrapping it. However, because the linear object is wrapped spirally around the flame-retardant tape, the restoring force of the flame-retardant tape can easily cause the portions not held down by the linear object to open, exposing the internal core. In contrast, shortening the winding pitch of the linear object requires a slower line speed during manufacturing, and, as with spiral winding, the tension presses down on the optical fiber core inside, resulting in increased transmission loss.

In addition, while it is possible to prevent the opening from opening by increasing the overlap of the flame-retardant tape, if the overlapping area is raised, there is a risk that it will get caught when passing through the base plate used to cover the outer sheath. This means that the base plate must be made larger than necessary, making the cable thicker. Furthermore, increasing the overlapping area increases the amount of linear material used, which is a factor in increasing costs, and also makes it difficult to remove the optical fiber core inside.

The present invention was made in consideration of these problems, and aims to provide an optical fiber cable and a method for manufacturing an optical fiber cable that reduces optical fiber transmission loss and has high flame retardancy.

To achieve the above-mentioned objective, the first invention is an optical fiber cable comprising: a cable core having a core portion in which optical fiber units consisting of multiple optical fiber cores are twisted together; a flame-retardant material wrapped longitudinally around the outer periphery of the core portion; a tension member arranged on the outside of the cable core; and an outer jacket arranged on 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 units.

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.

The holding and wrapping member may be a water-absorbent material.

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.

According to the first invention, the cable core around which the flame-retardant material is wound longitudinally is twisted, so that the overlapping portion of the flame-retardant material is arranged helically in the longitudinal direction. This makes it possible to suppress the opening of the overlapping portion. In this case, because the flame-retardant material is not wound helically, the optical fiber core inside is not tightly constricted when the flame-retardant material is wound, making it possible to increase the winding speed.

In addition, because the twisting pitch of the internal optical fiber unit is larger than the twisting pitch of the flame-retardant member, there is no need to twist the optical fiber unit excessively, which reduces the increase in transmission loss that would otherwise result from excessive twisting of the optical fiber unit. Furthermore, because 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 unit, opening of the flame-retardant member can be reliably reduced.

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.

Furthermore, if the holding wrapping material is a water-absorbent material, waterproofing can be ensured. For example, flame-retardant materials usually do not have water-stopping properties, making it difficult to ensure waterproofing, but by layering a flame-retardant material and a water-absorbent material, the effects of both can be achieved.

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

The second invention is a method for manufacturing a cable core, characterized in that a core portion is formed by gathering and twisting together multiple optical fiber cores, and the unwinding side of the core portion and the winding side of the cable core are rotated synchronously with the traveling direction of the core portion as the rotation axis, while a flame-retardant material is wound longitudinally around the outer periphery of the core portion, 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.

According to the second invention, the flame-retardant material can be efficiently wound spirally around the outer periphery of the core portion without excessively twisting the inner core portion.

The present invention provides an optical fiber cable and a method for manufacturing an optical fiber cable that suppresses optical fiber transmission loss and has high flame retardancy.

FIG. 1 is a cross-sectional view showing an optical fiber cable 1. FIG. 2 is a diagram showing an intermittently adhesive type optical fiber core 3. FIG. 1 is a perspective view showing an optical fiber cable 1. 4A is a cross-sectional view taken along line AA in FIG. 3, FIG. 4B is a cross-sectional view taken along line BB in FIG. 3, and FIG. 4C is a cross-sectional view taken along line CC in FIG. FIG. 3 is a diagram showing a cable core manufacturing apparatus 30a. 10A and 10B are diagrams showing a process of longitudinally wrapping the pressure wrapping member 7. FIG. FIG. 3 is a diagram showing a cable core manufacturing device 30b. 10A and 10B are diagrams showing a process of longitudinally wrapping a flame-retardant member 17. FIG.

Embodiments of the present invention will now be described with reference to the drawings. Figure 1 shows an optical fiber cable 1. The optical fiber cable 1 is a slotless optical fiber cable that does not use slots, and is composed of a core 14, a pressure winding member 7, a tension member 9, a tear cord 11, an outer jacket 13, a flame-retardant member 17, etc.

The core portion 14 consists of multiple optical fiber cores 3 and a pressure winding member 7. More specifically, multiple optical fiber cores 3 are twisted together to form an optical fiber unit 5, and multiple optical fiber units 5 are then gathered together and wrapped around the pressure winding member 7 to form the core portion 14. The optical fiber units 5 are bundled together, for example, with a bundling material, and are distinguished from other optical fiber units 5.

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 multiple optical fiber units 5.

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

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

As shown in Figure 2, in this embodiment, adjacent optical fibers 2a, 2b, 2c, and 2d are intermittently bonded together at adhesive joints 6 at predetermined intervals along the longitudinal direction of the optical fiber core 3. Furthermore, it is desirable that adjacent adhesive joints 6 in the width direction are offset from each other along the longitudinal direction of the optical fiber core 3. For example, it is desirable that adjacent adhesive joints 6 are formed with an offset of half a pitch along the longitudinal direction of the optical fiber core 3. Note that the length and pitch of the adhesive joints 6 are not limited to the example shown.

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 can be easily folded (bent) relative to each other in the parallel direction of the optical fibers 2a, 2b, 2c, and 2d in the non-adhesive portions.

A pressure winding member 7 is provided around the outer periphery of the multiple optical fiber units 5 as needed. The pressure winding member 7 is arranged so as to cover the multiple optical fiber units 5 collectively by vertically wrapping them. The pressure winding member 7 is wound so that the ends in the width direction overlap, 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 object such as thread may also be wound around the outer periphery of the pressure winding member 7.

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 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 has been added. A linear object such as thread may be wrapped around the outer periphery of the vertically wrapped flame-retardant member 17.

A pair of tension members 9 are provided on the outside of the cable core 15, facing each other across the cable core 15. In addition, tear cords 11 are provided in a direction approximately perpendicular to the direction in which the tension members 9 face each other, facing each other across the cable core 15.

An outer jacket 13 is also provided around the cable core 15, tear cord 11, and tension member 9. The outer jacket 13 is a layer that covers and protects the optical fiber cable 1. The cable core 15, tear cord 11, and tension member 9 are all covered by the outer jacket 13. In other words, the tension member 9 and tear cord 11 are embedded in the outer jacket 13.

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.

Figure 3 is a perspective view of the optical fiber cable 1, Figure 4(a) is a cross-sectional view taken along line A-A in Figure 3, Figure 4(b) is a cross-sectional view taken along line B-B in Figure 3, and Figure 4(c) is a cross-sectional view taken along line C-C in Figure 3. For simplicity, in the following figures, the optical fiber core is omitted from the illustration, and only the outline of the optical fiber unit 5 is shown. Also, in Figures 4(a) to 4(c), only specific optical fiber units 5a are shown hatched.

As shown in Figures 4(a) to 4(c), when the position of the tension member 9, which is arranged approximately 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 pressure winding member 7 and the arrangement of the overlapping portion 21b of the flame retardant member 17 change circumferentially depending on the longitudinal position of the optical fiber cable 1. In other words, the overlapping portion 21a of the pressure winding member 7 and the overlapping portion 21b of the flame retardant member 17 are arranged spirally relative to the longitudinal direction of the optical fiber cable 1.

For example, in the state shown in Figure 4(a), the overlapping portion 21a of the pressure winding member 7 and the overlapping portion 21b of the flame-retardant member 17 are positioned exactly 180 degrees apart. Furthermore, the optical fiber unit 5a is positioned directly below the overlapping portion 21a.

In contrast, when looking at the arrangement of each part at predetermined intervals along the length of the optical fiber cable 1, for example, at the positions shown in Figures 4(b) and 4(c), the overlapping part 21a and the optical fiber unit 5a are circumferentially offset by angle θ1, and the overlapping part 21b is circumferentially offset by angle θ2. In other words, the overlapping parts 21a, 21b and the optical fiber unit 5a are twisted together and arranged in a spiral shape relative to the length of the optical fiber cable 1. In this embodiment, the positions of the overlapping part 21a and the optical fiber unit 5a are approximately the same. In other words, the helical pitch of the overlapping part 21a and the twisting pitch of the optical fiber unit 5a are approximately the same.

Here, θ2 is greater 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 pressure 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.

Next, a method for manufacturing the cable core 15 will be described. Figure 5 is a schematic diagram showing a cable core manufacturing device 30a. First, a plurality of optical fiber cores 3 are twisted together and wrapped with bundling material to form an optical fiber unit 5, which is then wound around an optical fiber unit supply bobbin 31. The core portion 14 is formed by supplying and assembling optical fiber units 5 from the plurality of optical fiber unit supply bobbins 31. At this time, the plurality of optical fiber units 5 are assembled straight without being twisted, so the installation position of the optical fiber unit supply bobbin 31 is fixed.

The assembly of multiple 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 wound vertically around the outer periphery of the assembly of optical fiber units 5 so as to cover the multiple optical fiber units 5 collectively.

Figures 6(a) and 6(b) are conceptual diagrams showing the process of longitudinally wrapping a pressure winding member 7 around multiple optical fiber units 5. Longitudinal wrapping is a method of wrapping the pressure winding member 7 so that its longitudinal direction is aligned with the longitudinal direction of the optical fiber units 5 and that a portion of the pressure winding member 7 overlaps in the width direction, covering the optical fiber units 5. As mentioned 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.

As shown in Figure 5, the core portion 14 that leaves the forming device 33 is wound by the take-up bobbin 35. 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 winding the core portion 14 while rotating the take-up bobbin 35 on the winding side, the optical fiber unit 5 and the pressure winding member 7 (core portion 14) can be twisted and wound together. As a result, the optical fiber unit 5 and the overlapping portion 21a of the pressure winding member 7 after longitudinal winding are twisted together and arranged in a spiral at a predetermined pitch.

Figure 7 is a schematic diagram showing a cable core manufacturing device 30b. The take-up bobbin 35 on 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 device 41 together with a flame-retardant material 17. In the forming device 41, the flame-retardant material 17 is wound vertically around the core portion 14 to cover it collectively, forming a cable core 15, which is then wound onto a take-up bobbin 39.

At this time, the core supply bobbin 37, which is the unwinding side of the core 14, and the winding bobbin 39, which is the winding side of the cable core 15, can rotate synchronously in the same direction at approximately the same speed, with the direction of travel of the core 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 14 is not twisted, and only the flame-retardant material 17 can be twisted and wound longitudinally around the outer periphery of the core 14.

Figures 8(a) and 8(b) are conceptual diagrams of the process of longitudinally wrapping the flame-retardant material 17 around the core portion 14 while rotating it. Figure 8(a) shows the state in which the flame-retardant material 17 is being wrapped around the outer periphery of the core portion 14, and Figure 8(b) shows the cable core 15 with the flame-retardant material 17 wrapped around it.

As mentioned above, the overlapping portion 21b formed by longitudinally wrapping the flame-retardant material 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 pitch different from the twisting pitch of the core portion 14.

Then, the cable core 15 wound around the take-up bobbin 39 is fed to the sheath extruder together with the tension member 9 and tear string 11, and the sheath 13 is extruded onto the outer periphery of the cable core 15. In this way, the optical fiber cable 1 can be manufactured.

By twisting the optical fiber units 5 together, it is possible to prevent an excessive increase in transmission loss of a particular optical fiber core 3 when the optical fiber cable 1 is bent. Furthermore, because the overlapping portion 21a of the pressure winding member 7 is spiral, it is possible to prevent the internal optical fiber units 5 and optical fiber core 3 from being exposed through the overlapping portion 21a when handling the core portion 4.

On the other hand, if the optical fiber unit 5 is twisted too tightly, the lateral pressure on the optical fiber core will become too great, resulting in increased transmission loss. Furthermore, the spiral pitch of the overlapping portion 21a of the pressure winding member 7 does not need to be excessively short, as it is sufficient to prevent the optical fiber unit 5 (optical fiber core 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 pressure winding member 7 at a relatively long pitch.

In contrast, the flame-retardant member 17 must have overlapping portions 21b arranged in a spiral at a relatively short pitch to prevent openings or other problems from occurring during combustion, such as in a fire. However, as mentioned above, matching the twist pitch of the internal optical fiber unit 5 to the spiral pitch of the flame-retardant member 17 results in increased transmission loss. 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 achieving high flame retardancy while suppressing increases in transmission loss.

If necessary, a linear body may be spirally wound around the core portion 14 or cable core 15. In this case, it is desirable that the twisting direction of the core portion 14 or cable core 15 and the spiral winding direction of the linear body are opposite. Furthermore, the twisting direction of the optical fiber unit 5 in the cable core manufacturing device 30a may be opposite to the twisting direction of the core portion 14 and cable core 15 in the cable core manufacturing device 30b. Furthermore, the cable core manufacturing devices 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.

As described above, with the optical fiber cable 1 of this embodiment, the flame-retardant member 17 is wound vertically rather than spirally, so the optical fiber core 3 inside is not overly tightened, and an increase in transmission loss can be suppressed. Furthermore, because the overlapping portion 21b of the flame-retardant member 17 is formed in a spiral shape, opening of the flame-retardant member 17 can be suppressed even during combustion.

Furthermore, the twist pitch of the optical fiber unit 5 can be made longer than that of the flame-retardant member 17, thereby suppressing increases in transmission loss. Furthermore, by using the holding and winding member 7, it can also act as a cushion to prevent the tightening force of the flame-retardant member 17 from being 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.

Furthermore, by rotating the winding bobbin 35 behind the forming device 33 with the direction of travel of the core portion 14 as its rotation axis, the optical fiber unit 5 and the pressure winding member 7 can be easily twisted together.

Furthermore, by rotating the core 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 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.

Note that the present invention is not limited to the optical fiber cable 1 having the cross-sectional shape shown in Figure 1, and the cross-sectional structure may be different. For example, it may be a self-supporting optical fiber cable having a support wire portion.

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) was varied to evaluate transmission loss and flame retardancy. The optical fiber cable used had the structure shown in Figure 1.

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

After supplying and twisting 48 144-core optical fiber units, the pressure winding member was rolled using a forming jig and longitudinally wrapped so that the overlapping portions formed a spiral with a 1300 mm pitch. Furthermore, a flame-retardant member was longitudinally wrapped around the pressure winding member. At this time, the overlapping portions of the flame-retardant member were made into a spiral with a specified pitch. A pressure thread was also wrapped around the outer circumference of the flame-retardant member. This resulted in the creation of a 6912-core cable core.

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

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

The pressure winding member was longitudinally wrapped using equipment capable of winding while rotating around the direction of the cable core flow as the axis of rotation. The flame-retardant member was longitudinally wrapped using equipment capable of unwinding and winding while rotating around the direction of the cable core flow as the axis of rotation. The twist pitch of the flame-retardant member was changed by adjusting the cable core feed speed and the cable core rotation speed.

Various evaluations were carried out on the various optical fiber cables created in this way. The results are shown in Table 1.

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. "Flame-retardant member pressure winding structure" refers to the winding method: 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 circumferential direction of the core), and "spiral pitch of flame-retardant member" refers to the spiral pitch of the overlapping portion of the flame-retardant member.

"Flame retardant overlap amount" refers to the width of the overlapping portion of the flame retardant material, and "flame retardant overlap opening" refers to the cable core being held vertically and the retaining threads around the flame retardant material being removed. If the flame retardant material did not open and the core was not exposed, the cable was rated as passing (○).

For "flammability characteristics," in the flammability test (UL1666), a product was rated as passing (○) if the flame height was less than 3.66 m and the temperature of the second-floor ceiling was 454.4°C or less, while products that did not meet the conditions were rated as failing (×). For "smoke generation characteristics," in the smoke generation test (ULST-1), a product was rated as passing (○) if the total amount of smoke emitted in 20 minutes was 150 ^m3 or less and the peak smoke rate was 0.4 ^m3 /s or less, while products that did not meet the conditions were rated as failing (×).

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

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 tightened the internal optical fiber unit too much, resulting in a failure in the transmission loss characteristics. In Comparative Example 1, the flame-retardant member was wrapped vertically, but like Comparative Example 3, the spiral pitch of the flame-retardant member was too short, which tightened the internal optical fiber unit too much, 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 overlap to open up during combustion tests, resulting in a failure in the combustion and smoke generation characteristics.

Although the embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that a person skilled in the art could conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1....Optical fiber cables 2a, 2b, 2c, 2d....Optical fiber 3....Optical fiber core wires 5, 5a....Optical fiber unit 6....Adhesive 7....Pressure winding member 9....Tension member 11....Tear string 13....Outer jacket 14....Core portion 15....Cable core 17....Flame retardant member 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 portion supply bobbin

Claims (6)

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. The optical fiber cable of claim 1, characterized in that the core portion is constructed by longitudinally wrapping a pressure winding member around the outer periphery of the plurality of optical fiber units, and the flame-retardant member is disposed around the outer periphery of the pressure winding member. The optical fiber cable according to claim 2, characterized in that the pressure winding member is a water-absorbent material. An optical fiber cable as described in any one of claims 1 to 3, characterized in that the spiral pitch of the overlapping portion of the flame-retardant member is 400 mm or more and 1200 mm or less. An optical fiber cable as described in any one of claims 1 to 3, characterized in that the spiral pitch of the overlapping portion of the flame-retardant member is 500 mm or more and 900 mm or less. 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 .