Fiber optic cable

Abstract

To provide an optical fiber cable that has excellent handling properties and can suppress an increase in transmission loss.SOLUTION: In a cross-sectional view vertical to the longitudinal direction of an optical fiber cable 1, tension members 9 are provided in both the sides of a core 4. Specifically, the pair of tension members 9 is provided in opposing positions while sandwiching the core 4. A covering 13 is provided in an outer periphery of the core 4. The covering 13 is provided so as to cover the core 4, the tension members 9, and the like. Adhesion force of the tension members 9 and the covering 13 is preferably maintained even after the tension members 9 and the covering 13 relatively deviate in the longitudinal direction. The adhesion force of the tension members 9 and the covering 13 is also preferably equal to or more than 200 N / 300 mm and equal to or less than 1200 N / 300 mm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber cable having a tension member. [Background technology]

[0002] An optical fiber cable is used in which a large number of optical fiber cores and tension members are covered with an outer sheath.

[0003] Such optical fiber cables include, for example, optical fiber cables in which tension members (tensile strength bodies) having resistance to tension and compression are arranged on both sides of a core made of optical fiber core wire, and the materials for the tension members can be metal wires (such as steel wires), tensile strength fibers (such as aramid fibers), FRP, etc. (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-042175 A Summary of the Invention [Problem to be solved by the invention]

[0005] In an optical fiber cable such as that described in Patent Document 1, a pair of tension members are arranged at opposing positions with the core at the center, so that the cable is easy to bend in a direction about the straight line connecting the tension members as the bending center, but is difficult to bend in other directions. In other words, optical fiber cables have a directional property of bending ease. In particular, the cable is most difficult to bend in a direction about the bending center line that is perpendicular to the straight line connecting the tension members.

[0006] On the other hand, when laying such optical fiber cables in a pipeline, the general method is to first lay a rope to tow the optical fiber cable, connect the optical fiber cable to the towing rope, and lay the cable in the pipeline by pulling the towing rope. When laying optical fiber cables in multiple consecutive pipelines through manholes, etc., the optical fiber cable may be passed through the first pipeline, then brought out onto the ground at the manhole between the first and second pipelines, in a so-called figure-eight arrangement, and then passed through the second pipeline.

[0007] However, when performing such a figure-of-eight configuration, if the optical fiber cable has a strong directional tendency to bend easily, it becomes difficult to perform the figure-of-eight configuration. For example, there is a risk that the optical fiber cable may be locally twisted, or that the tension member may buckle if the optical fiber cable is forcibly bent in a direction that makes it difficult to bend.

[0008] Even if the tension member does not buckle, if the adhesion between the tension member and the jacket is peeled off, it becomes impossible to suppress the longitudinal displacement between the tension member and the jacket. For this reason, when the optical fiber cable expands or contracts due to a change in the environmental temperature, the difference in the linear expansion coefficient between the tension member and the jacket may cause a large longitudinal displacement between the tension member and the jacket, causing the optical fiber inside the jacket to bend, which may result in an increase in loss.

[0009] The present invention has been made in consideration of such problems, and has an object to provide an optical fiber cable that is easy to handle and capable of suppressing an increase in transmission loss. [Means for solving the problem]

[0010] To achieve the above-mentioned objectives BooksThe invention is an optical fiber cable comprising a core consisting of a plurality of optical fiber strands, tension members arranged at opposing positions on either side of the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable, and an outer sheath arranged to cover the core and the tension member, wherein the adhesion force between the tension member and the outer sheath is within the range of 600 N / 300 mm or more and 1200 N / 300 mm or less, and the adhesion force between the tension member and the outer sheath remains within the above range even after the tension member and the outer sheath are shifted relative to each other in the longitudinal direction.

[0011] The adhesion between the tension member and the outer sheath 60 It may be in the range of 0N / 300mm or more and 1000N / 300mm or less.

[0012] It is preferable that the tension member and the outer covering are not bonded to each other.

[0014] According to the present invention, since the adhesion force between the tension member and the outer sheath is 200N / 300mm or more and 1200N / 300mm or less, the adhesion between the tension member and the outer sheath is maintained even during, for example, temperature changes, and since the tension member and the outer sheath can shift in the longitudinal direction when bending in a direction in which bending is difficult, the difficulty in bending is alleviated and buckling of the tension member can be suppressed. Furthermore, since the adhesion force between the tension member and the outer sheath remains within the above range even after the tension member and the outer sheath shift relatively in the longitudinal direction, the tension member can suppress the expansion and contraction of the outer sheath during subsequent temperature changes, etc.

[0015] This effect can be obtained more efficiently when the adhesive strength between the tension member and the outer sheath is 250N / 300mm or more and 1000N / 300mm or less.

[0016] Furthermore, in order to obtain such an effect, it is desirable that the tension member and the outer sheath are not adhered to each other, and by disposing a resin having tackiness between the tension member and the outer sheath, the adhesion between the tension member and the outer sheath can be reliably maintained even after the tension member and the outer sheath are shifted relative to each other in the longitudinal direction. Effect of the Invention

[0017] According to the present invention, it is possible to provide an optical fiber cable that is easy to handle and capable of suppressing an increase in transmission loss. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of an optical fiber cable 1. [Diagram 2] An enlarged view of the vicinity of the tension member 9. [Diagram 3] 4 is a diagram showing a method for measuring the adhesion between a tension member 9 and an outer covering 13. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view of an optical fiber cable 1. The optical fiber cable 1 is a slotless type cable that does not use a slot, and is composed of a core 4, a tension member 9, an outer jacket 13, etc.

[0020] The core 4 is formed by twisting together a plurality of optical fiber units 5. Moreover, the optical fiber unit 5 is formed by twisting together a plurality of optical fiber core wires 3. The optical fiber core wires 3 are, for example, intermittently bonded optical fiber ribbon core wires that are bonded intermittently in the longitudinal direction.

[0021] 1, a pressure wrap 7 is provided around the outer periphery of the multiple optical fiber units 5. The pressure wrap 7 is a tape-like member, a nonwoven fabric, or the like, and is arranged so as to collectively cover the outer periphery of the multiple optical fiber units 5 by, for example, vertical splicing. That is, the pressure wrap 7 is vertically spliced ​​around the outer periphery of the multiple optical fiber units 5 so that the longitudinal direction of the pressure wrap 7 approximately coincides with the axial direction of the optical fiber cable 1, and the width direction of the pressure wrap 7 is the circumferential direction of the optical fiber cable 1. Note that the pressure wrap 7 is not necessarily required, and the pressure wrap 7 may be referred to as the core 4.

[0022] In a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 1, tension members 9 are provided on both sides of the core 4. That is, a pair of tension members 9 are provided at positions facing each other with the core 4 in between. Also, tear cords 11 are provided in a direction approximately perpendicular to the facing direction of the tension members 9 so as to face each other with the core 4 in between. There are no particular restrictions on the material of the tension members 9, but the present invention is more effective when a material such as FRP having a low compressive elastic modulus relative to the tensile elastic modulus is used.

[0023] An outer sheath 13 is provided on the outer periphery of the core 4. The tension members 9 and the tear cord 11 are embedded in the outer sheath 13. In other words, the outer sheath 13 is provided so as to cover the core 4, the tension members 9, etc. The outer shape of the outer sheath 13 is approximately circular. The outer sheath 13 is made of, for example, a polyolefin-based resin.

[0024] Next, we will explain the adhesion between the tension member 9 and the outer sheath 13. It is desirable that the adhesion between the tension member 9 and the outer sheath 13 remains within a predetermined range even after the tension member 9 and the outer sheath 13 are relatively misaligned in the longitudinal direction. In other words, it is desirable that the tension member 9 and the outer sheath 13 are not bonded to each other.

[0025] 2 is an enlarged view of the tension member 9. The tension member 9 is covered with a coating resin 15. That is, the coating resin 15 is disposed between the tension member 9 and the outer sheath 13. The coating resin 15 is, for example, a resin such as urethane acrylate having tackiness (adhesiveness).

[0026] If the coating resin 15 has tackiness, the tension member 9 and the outer sheath 13 will adhere to each other due to the tackiness of the coating resin 15. Therefore, compared to when the tension member 9 and the outer sheath 13 are joined with an adhesive, even if the tension member 9 and the outer sheath 13 are peeled off once, the adhesion can be ensured by bringing the tension member 9 and the outer sheath 13 into contact with each other again.

[0027] For example, in Fig. 1, when the optical fiber cable 1 is bent around the center line of the tension members 9 in the opposing direction (straight line A in the figure) as the bending center (hereinafter, this direction may be referred to as bending in the easy bending direction), the optical fiber cable 1 can be bent easily. On the other hand, when the bending center is center line B perpendicular to center line A, the optical fiber cable 1 becomes relatively difficult to bend (hereinafter, this direction may be referred to as bending in the difficult bending direction). In this case, a compressive force is applied to the tension members 9 located particularly on the inner periphery of the bend, which may cause buckling.

[0028] In contrast, if the tension member 9 and the outer sheath 13 are not glued together but are only attached by tackiness, when a force greater than a certain level is applied, the tension member 9 and the outer sheath 13 will shift from each other, releasing part of the stress. This improves bending in the difficult-to-bend direction, and buckling of the tension member 9 can be suppressed.

[0029] If the tension member 9 and the jacket 13 are allowed to slip out of alignment too easily, the tension member 9 will not be able to suppress expansion and contraction of the jacket 13 etc. when the environmental temperature changes, and the expansion and contraction of the jacket will place stress on the core 4, which may increase transmission loss. For this reason, in this embodiment, the adhesion between the tension member 9 and the jacket 13 is preferably within the range of 200N / 300mm to 1200N / 300mm, and more preferably within the range of 250N / 300mm to 1000N / 300mm.

[0030] The adhesion between the tension member 9 and the sheath 13 can be measured by the method shown in Fig. 3. First, the optical fiber cable is cut to a predetermined length, and the sheath at both ends is completely removed from the sheath 13 around the tension member 9, leaving behind a piece of sheath 20 mm wide and 300 mm long. In other words, the tension members 9 at both ends are exposed.

[0031] After that, the exposed tension member 9 is inserted into a die 17 having a hole. The size of the hole in the die 17 is slightly larger than the outer diameter of the tension member 9 so that the tension member 9 can pass through without resistance, and smaller than the size of the outer sheath 13 left on the outer periphery of the tension member 9. For example, for a tension member 9 with a diameter of 2 mm, the inner diameter of the hole is set to about 2.6 mm.

[0032] The tension member 9 with the outer sheath 13 is passed through the die 17, and then pulled out at a speed of 500 mm / min by an Instron type tensile testing machine (arrow C in the figure). This allows the outer sheath 13 to be peeled off from the tension member 9 by the die 17. The maximum stress at this time is the adhesion force between the tension member 9 and the outer sheath 13. In other words, the load when the tension member 9 is displaced relative to the outer sheath 13 is the adhesion force.

[0033] In addition, after the tension member 9 has shifted relative to the outer sheath 13, if the withdrawal of the load is stopped (the pulling force is removed) and then withdrawal of the tension member 9 is started again at the same speed, the load at which the tension member 9 again shifts in position relative to the outer sheath 13 is defined as the adhesion force between the tension member 9 and the outer sheath 13 after they have shifted relative to each other in the longitudinal direction.

[0034] As described above, when the tension member 9 and the outer jacket 13 are in close contact with each other due to tackiness, the same adhesion force as the initial adhesion force can be ensured even when the tension member 9 is pulled out and then pulled out again. In other words, the adhesion force can be maintained even after the tension member 9 and the outer jacket 13 are displaced in the longitudinal direction.

[0035] As described above, according to this embodiment, the tension member 9 and the outer sheath 13 are in close contact with each other without being bonded, and the adhesion force is equal to or less than a predetermined value. Therefore, for example, when bending in a direction in which bending is difficult (a direction in which the center line B in FIG. 1 is the bending center), the tension member 9 and the outer sheath 13 can be misaligned, making it easier to bend in this direction and suppressing buckling.

[0036] Furthermore, even if the tension member 9 and the jacket 13 are once peeled off and shifted in the longitudinal direction, a predetermined level of adhesion can be ensured in that state. In this way, because the tension member 9 and the jacket 13 always have a predetermined level of adhesion, it is possible to prevent the tension member 9 and the jacket 13 from shifting in the longitudinal direction due to the difference in the linear expansion coefficients of the tension member 9 and the jacket 13 when the optical fiber cable 1 expands or contracts due to changes in the environmental temperature. Therefore, the tension member 9 can suppress the expansion and contraction of the jacket 13, and suppress an increase in loss in the optical fiber inside. EXAMPLES

[0037] Bending tests were conducted on optical fiber cables by changing the adhesion force between the tension member and the jacket. The optical fiber cable used for the evaluation had a cross-sectional shape roughly as shown in Figure 1. First, 12 optical fibers with a diameter of 200 um were intermittently bonded to create a 12-core optical fiber ribbon. These were then twisted together and wrapped with a 2 mm wide plastic ribbon to create a 144-core optical fiber unit.

[0038] Forty-eight of these 144-core optical fiber units were supplied, twisted together in four layers in a 2-9-15-22 arrangement, then absorbent nonwoven fabric was attached vertically, rolled up with a forming jig, and nylon pressure thread was wrapped around it to create a 6,912-core core. The core thus created, a tension member made of φ2.0mm G-FRP (glass fiber reinforced plastic), and a ripping string for ripping the outer jacket were arranged in a straight line without being twisted, and then sheathed into a cylindrical shape with the outer jacket to create an optical fiber cable. LLDPE was used as the jacket material, and the outer diameter of the jacket was 29mm, and the inner diameter was 22mm.

[0039] Before extruding the jacket of the optical fiber cable, the outer circumference of the G-FRP was covered with urethane acrylate resin having tackiness. Note that urethane acrylate resin has no thermoplasticity and does not melt when the jacket is extruded, but its tackiness allows the jacket to adhere to the tension member 9. Note that the adhesion force, which will be described later, was adjusted by changing the type of urethane acrylate used (tackiness) and the jacket thickness.

[0040] For comparison, an optical fiber cable was created in which the outer circumference of the G-FRP was covered with a thermoplastic resin (low-density polyethylene) as an adhesive. In this case, part of the thermoplastic resin melted when the jacket was extruded, and it bonded firmly to the jacket. As a further comparison, an optical fiber cable was created in which the jacket and tension member were adhered to each other only by the adhesive force generated when the jacket was extruded, without using any adhesive.

[0041] For each of the obtained optical fiber cables, the adhesion between the tension member and the jacket was measured before and after bending deformation. First, the adhesion between the tension member and the jacket was measured before bending deformation in the direction that is difficult to bend (before bending deformation was performed around line B in Figure 1). The adhesion was measured using the method shown in Figure 3.

[0042] Next, the adhesion between the tension member and the jacket was measured after bending the optical fiber cable in a direction that is difficult to bend (after the tension member and jacket were relatively misaligned in the longitudinal direction). The measurement method was to first cut a 2m length of optical fiber cable and wrap the center part 180 degrees around a φ600mm mandrel in a direction that is difficult to bend. Next, the optical fiber cable was straightened out, and the adhesion between the tension member and jacket was measured using the same procedure as before bending deformation.

[0043] In addition, each optical fiber cable was bundled in a figure of eight and its bendability was evaluated. The bendability evaluation method was to first bundle a 200m long optical fiber cable in a figure of eight with a minor axis of about 1m, and check whether localized twisting occurred. For example, if the difference between the ease of bending in the direction that is difficult to bend and the ease of bending in the direction that is easy to bend becomes large, twisting is more likely to occur when the cable is bundled in a figure of eight.

[0044] We also evaluated whether the tension member buckled after bending it in a direction that is difficult to bend. First, we cut out a 5m length of optical fiber cable and wrapped the center part 180 degrees around a φ600mm mandrel in a direction that is difficult to bend, and then visually checked whether the tension member buckled.

[0045] In addition, after bending the cable in a direction that is difficult to bend, a heat cycle test was performed to evaluate the increase in transmission loss during the heat cycle. The evaluation method was as follows: first, while rewinding a 1,000m length of optical fiber cable, the cable was wound 180 degrees around a φ600mm mandrel in the direction that is difficult to bend at 10 locations every 100m, and then straightened out.

[0046] All optical fiber cables were rewound onto a drum with a body diameter of 1400 mm, then placed in a thermostatic chamber and subjected to three cycles of heat cycles from -30°C to 70°C, with a temperature holding time of 6 hours and a temperature transfer time of 6 hours. During this heat cycle test, the maximum increase in transmission loss at a wavelength of 1550 nm was measured relative to the initial value (before the heat cycle began). The results are shown in Table 1.

[0047] [Table 1]

[0048] "Coating layer" in the table indicates the type of resin that coats the outer circumference of the tension member and whether it has tackiness or not. "TM adhesion" is the force that pulls the tension member out of the outer coating, measured before and after bending in the direction that makes it difficult to bend, using the method shown in Figure 3.

[0049] In addition, the "Local twist during the figure-eight take" in the table indicates whether or not there was a local twist when the figure-eight take was made, with 0 occurrences of local twists being marked "O", 1-2 occurrences being marked "△", and 3 or more occurrences being marked "X".

[0050] In addition, "TM buckling after bending" in the table indicates whether or not the tension member buckled after being bent in a direction that makes it difficult to bend, with "O" indicating no buckling and "X" indicating buckling.

[0051] In addition, in the table, for "Increase in transmission loss during heat cycle after bending", a maximum increase in transmission loss during the heat cycle compared to the transmission loss before the heat cycle described above of less than 0.10 dB / km is marked as "Good", a maximum increase in transmission loss of 0.10 to 0.15 dB / km is marked as "Good", and a maximum increase in transmission loss exceeding 0.15 dB / km is marked as "Poor".

[0052] From the results, in all of Examples 1 to 5 in which a coating layer having tackiness was disposed between the tension member and the sheath, there was no significant difference in the adhesion between the tension member and the sheath before and after bending. More specifically, in all of Examples 1 to 5, the adhesion after bending was 96.5% or more of the adhesion before bending. In addition, in Examples 1 to 5, the adhesion between the tension member and the sheath was in the range of 200N / 300mm to 1200N / 300mm both before and after bending, and the local twist during the figure-eight take, the buckling of the tension member after bending, and the increase in transmission loss during the heat cycle were all rated as △ or higher. In particular, in Examples 2 to 4 in which the adhesion of the tension member was 250N / 300mm to 1000N / 300mm both before and after bending, the above evaluations were all rated as ◯.

[0053] On the other hand, in Comparative Example 1, which does not have a coating layer on the outer periphery of the tension member, the adhesion between the tension member and the outer sheath was weak, resulting in a large increase in transmission loss during heat cycles. In Comparative Example 2, which used an adhesive, the adhesion between the tension member and the outer sheath before bending was too strong, resulting in localized twisting when making a figure eight and buckling of the tension member after bending. In Comparative Example 2, once it was bent in a direction that was difficult to bend, the adhesion between the tension member and the outer sheath came off, and the adhesion of the tension member after bending was greatly reduced. This resulted in a large increase in transmission loss during heat cycles.

[0054] Although the embodiment of the present invention has been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the above-described embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0055] 1: Optical fiber cable 3: Optical fiber core 4. Core 5: Optical fiber unit 7………Press and roll 9...Tension member 11...Tear cord 13……Outer cover 15....Coating resin 17………Dice

Claims

1. A core made up of a plurality of optical fiber cores; tension members provided at positions facing each other across the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable; an outer cover provided to cover the core and the tension member; Equipped with An optical fiber cable characterized in that the adhesion force between the tension member and the outer sheath is within the range of 600 N / 300 mm or more and 1200 N / 300 mm or less, and that the adhesion force between the tension member and the outer sheath remains within the above range even after the tension member and the outer sheath are relatively shifted in the longitudinal direction.

2. 2. The optical fiber cable according to claim 1, wherein the adhesion strength between the tension member and the outer sheath is within a range of 600 N / 300 mm to 1000 N / 300 mm.

3. 3. The optical fiber cable according to claim 1, wherein the tension member and the outer jacket are not bonded to each other.

Images