JP2021170096A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable that can suppress bending of a tension member even when the tension member which is not a steel wire is used.SOLUTION: In a cross section perpendicular to a longer direction of an optical fiber cable 1, a tension member 9 is provided on both sides of a core 4. Specifically, one pair of tension members 9 are provided across the core 4. An outer cover 13 is provided around the core 4. As the tension member 9, a fiber reinforcement plastic (FRP) made of aramid fibers or glass fibers, for example, is used. The adhesion between the tension member 9 and the outer cover 13 is desirably at least 30 N/10 mm and more preferably at least 40 N/10 mm.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber cable having excellent bendability.

As the optical fiber cable, a cable in which a large number of optical fiber core wires and tension members are covered with an outer cover is used.

As such an optical fiber cable, for example, tension members (tensile bodies) having resistance to tension and compression are arranged on both sides of a core made of an optical fiber core wire, and a metal wire (steel wire) is used as the material of the tension member. There are optical fiber cables to which tensile strength fibers (aramid fibers, etc.), FRP, etc. can be applied (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2020-042175

An optical fiber cable as in Patent Document 1 is usually branched as needed, connected to a withdrawal cable, and drawn into a building or the like. Hereinafter, in order to transmit a large amount of information such as long-distance transmission and between data centers at high density as in Patent Document 1, a general ultra-multi-core (for example, 200-core or more) slot cable or slotless cable is used. An optical fiber cable is simply referred to as an optical fiber cable, and in order to distinguish it from this, an optical fiber cable for withdrawal use (for example, an optical fiber cable having a substantially rectangular cross section and a notch formed in the outer cover) is referred to as a drop cable.

Unlike drop cables, such fiber optic cables were typically used outdoors and were never used for pull-in applications. Therefore, it is not assumed that a surge current flows from the outside into the building due to the influence of a lightning strike, and the optical fiber cable itself does not need to be non-inductive. For this reason, steel wires have traditionally been applicable to tension members.

However, in recent years, the application of this cable to a place close to the power line has been considered, and the demand for non-induction has increased. Therefore, glass FRP (Fiber-Reinforced Plastics) or aramid FRP is used for the tension member of this cable. I have been pressed for necessity.

As in Patent Document 1, in a slotless cable, at least two tension members are arranged at positions away from the center of the cable core. Therefore, the optical fiber cable can be bent only in the direction in which the line connecting the two tension members is the center of the bending. On the other hand, if an attempt is made to bend the optical fiber cable in a direction in which the wire connecting the two tension members is not the center of bending, the optical fiber cable rotates, and as a result, the wire connecting the two tension members is bent. The optical fiber cable bends in the direction centered on.

However, when the optical fiber cable is laid in the field, the bending and rotation of the optical fiber cable are hindered, and the optical fiber cable may be bent in a direction that does not bend. In this case, a strong compressive force may be applied to the tension member, but a conventional steel wire can sufficiently withstand such a case.

On the other hand, unlike steel wire, glass FRP, aramid FRP, etc. have a low compressive elastic modulus with respect to a tensile elastic modulus, and have a low resistance when compressed. Therefore, as described above, there is a problem that the tension member buckles and breaks due to being bent in a direction that cannot be originally bent.

On the other hand, if the tension member is made thicker to obtain strength, there is a problem that the diameter of the optical fiber cable becomes thicker and the flexibility of the optical fiber cable deteriorates.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical fiber cable capable of suppressing buckling of a tension member even when a tension member other than a steel wire is used. And.

In order to achieve the above-mentioned object, the present invention covers a core composed of a plurality of optical fiber core wires, tension members provided on both sides of the core in a cross section, the tension member and the optical fiber core wire. The tension member is provided with an outer cover, and the compressive elastic modulus of the tension member is ½ or less of the tensile elastic modulus, and the adhesion between the tension member and the outer cover is 30 N / 10 mm or more. It is an optical fiber cable.

It is desirable that the adhesion between the tension member and the jacket is 40 N / 10 mm or more.

The tension member may be glass FRP or aramid FRP.

According to the present invention, when a tension member having a compressive elastic modulus of 1/2 or less of the tensile elastic modulus is used, the adhesion between the tension member and the jacket is equal to or more than a predetermined value, so that the tension member has a buckling during compression. The occurrence of bending can be suppressed.

In particular, the present invention is particularly effective when the tension member is glass FRP, aramid FRP, or the like.

According to the present invention, it is possible to provide an optical fiber cable capable of suppressing buckling of the tension member even when a tension member other than the steel wire is used.

FIG. 3 is a cross-sectional view of the optical fiber cable 1. The figure which shows the measuring method of the compression strength of a tension member 9. The figure which shows the method of measuring the adhesion force between a tension member 9 and an outer cover 13. (A) is a diagram showing a bending test method of the optical fiber cable 1, and (b) is an enlarged cross-sectional view of portion C of (a).

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the optical fiber cable 1. The optical fiber cable 1 is a slotless cable that does not use a slot, and is composed of a core 4, a tension member 9, a jacket 13, and the like.

The core 4 is formed by twisting a plurality of optical fiber units 5. Further, the optical fiber unit 5 is formed by twisting a plurality of optical fiber core wires 3. The optical fiber core wire 3 is, for example, an intermittently bonded optical fiber tape core wire that is intermittently bonded in the longitudinal direction.

As shown in FIG. 1, a press winding 7 is provided on the outer periphery of the plurality of optical fiber units 5. The presser roll 7 is a tape-shaped member, a non-woven fabric, or the like, and is arranged so as to collectively cover the outer periphery of the plurality of optical fiber units 5 by, for example, vertical winding. That is, the longitudinal direction of the presser winding 7 substantially coincides with the axial direction of the optical fiber cable 1, and the width direction of the presser winding 7 is vertically attached to the outer periphery of the plurality of optical fiber units 5 so as to be the circumferential direction of the optical fiber cable 1. Be rolled up. The presser foot 7 is not always essential, and the presser roll 7 may be included as a core 4.

In the 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. Details of the tension member 9 will be described later. Further, the tear string 11 is provided so as to face each other with the core 4 in the direction substantially orthogonal to the facing direction of the tension member 9.

An outer cover 13 is provided on the outer periphery of the core 4. The tension member 9 and the tear cord 11 are embedded in the outer cover 13. That is, the outer cover 13 is provided so as to cover the core 4 (plurality of optical fiber core wires 3), the tension member 9, and the like. The outer shape of the outer cover 13 is substantially circular. The jacket 13 is, for example, a polyolefin-based resin.

Next, the tension member 9 will be described. The tension member 9 bears the tension of the optical fiber cable 1. As the tension member 9, for example, fiber reinforced plastic (FRP) made of aramid fiber, glass fiber or the like can be used. Such an FRP has a compressive elastic modulus smaller than a tensile elastic modulus. For example, the compressive elastic modulus of the tension member 9 is ½ or less of the tensile elastic modulus.

The tensile elastic modulus of the tension member 9 can be measured by JIS K7161. On the other hand, the compressive elastic modulus of the tension member 9 is measured by the method shown in FIG. First, in a state where the tension member 9 is cut and 20 pieces are bundled, a sample is prepared in which the upper and lower ends are hardened with epoxy resin 15. The distance between the resins 15 is 15 mm (for example, substantially the same as the outer diameter of the bundle of tension members 9). The compressive elastic modulus can be measured from the load and the amount of displacement when this sample is compressed by a testing machine manufactured by Instron (A in the figure).

Further, the adhesion between the tension member 9 and the outer cover 13 is preferably 30 N / 10 mm or more, and more preferably 40 N / 10 mm or more. The adhesion between the tension member 9 and the outer cover 13 can be measured by the method shown in FIG. First, the outer peripheral outer cover 13 of the tension member 9 is removed while leaving a part of the outer cover 13. The length of the remaining outer cover 13 (the length of the tension member 9 in the length direction) is 10 mm.

After that, the tension member 9 is inserted through the die 17 having a hole. The size of the hole of 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 cover 13 left on the outer circumference of the tension member 9. For example, the inner diameter of the hole is about 2.3 mm with respect to the tension member 9 having a diameter of 2 mm.

From the state where the tension member 9 with the outer cover 13 is passed through the die 17, the tension member 9 is pulled out at a speed of 50 mm / min (arrow B in the figure). As a result, the outer cover 13 can be peeled off from the tension member 9 by the die 17. The maximum stress at this time is the adhesion between the tension member 9 and the outer cover 13.

Here, if the adhesion between the tension member 9 and the outer cover 13 is low, the tension member 9 and the outer cover 13 may be peeled off if the internal tension member 9 is bent when the optical fiber cable 1 is bent. At this time, when the optical fiber cable 1 is bent so that a compressive force is applied to one of the tension members 9, the tension member 9 and the outer cover 13 are peeled off, so that the outer cover 13 restrains the tension member 9 from the outer periphery. The force becomes smaller. Therefore, the tension member 9 may buckle.

However, if the tension member 9 and the outer cover 13 are in close contact with each other and the tension member 9 and the outer cover 13 are in close contact with each other, even when a bending force is applied to the tension member 9, the tension member by the outer cover 13 is used. The binding force from the outer circumference of the 9 is high, which suppresses the buckling of the tension member 9. As in the present embodiment, it is particularly effective when a material such as FRP, which has a low compressive elastic modulus with respect to the tensile elastic modulus, is applied to the tension member 9.

Next, a method of manufacturing the optical fiber cable 1 will be described. The optical fiber cable 1 can be manufactured by a manufacturing method substantially the same as that of a normal optical fiber cable, but as described above, it is necessary to increase the adhesion between the tension member 9 and the outer cover 13. In particular, FRP in which glass or aramid fiber is hardened with a thermosetting resin is difficult to increase the adhesion to the outer cover 13 such as low density polyethylene (LDPE).

Therefore, it is desirable to coat the outer circumference of the FRP wire used for the tension member with the same resin as the outer cover 13 in advance. By pushing out the outer cover 13 using the tension member 9 coated with this resin, the adhesion between the tension member 9 and the outer cover 13 can be increased. At this time, it is desirable to raise the extrusion temperature higher than usual. For example, when extruding the outer cover 13 of linear low density polyethylene (LLDPE), the extruding temperature is about 180, but it is desirable that it is about 200 ° C.

Further, in order to increase the adhesion between the tension member 9 and the outer cover 13, it is desirable to preheat the tension member 9 before extrusion. For example, normally, a tension member 9 at room temperature is used, but by preheating to about 60 ° C. (for example, 40 ° C. or higher and extruding temperature or lower), the adhesion at the time of extrusion of the outer cover can be enhanced.

Further, it is desirable to lengthen the time until cooling of the jacket 13 after extrusion coating. For example, the distance to the cooling water tank after normal extrusion coating is about 100 mm, but by increasing this distance to about 500 mm, the fusion time between the tension member 9 and the jacket 13 is secured, and the tension member The adhesion between 9 and the outer cover 13 can be increased. By combining these, it is possible to more reliably obtain the optical fiber cable 1 having a high adhesion between the tension member 9 and the outer cover 13.

As described above, according to the present embodiment, since the adhesion between the tension member 9 and the outer cover 13 is high, even when the compressive elastic modulus of the tension member 9 is smaller than the tensile elastic modulus and the steel wire, even if it is smaller than the tensile elastic modulus and the steel wire. It is possible to suppress buckling of the tension member 9 when it is bent.

The bending test of the optical fiber cable was performed by changing the configuration of the tension member. The optical fiber cable used for evaluation has a cross-sectional shape generally shown in FIG. First, eight optical fibers having a diameter of 250 um were intermittently bonded to prepare an eight-core optical fiber tape core wire. Further, 10 of them were twisted together to form an 80-core optical fiber unit around which a plastic tape having a width of 2 mm was wound.

Twenty-five of these 80-core optical fiber units are supplied, twisted together, water-absorbent non-woven fabric is vertically attached, rolled with a forming jig, and nylon presser thread is wound around them to form a 2000-core core. Created. The core thus prepared, a tension member using FRP having a diameter of 2.0 mm, and a tear string for cutting the outer cover were sheathed in a cylindrical shape with the outer cover material to prepare a cable. The outer cover material was LLDPE. The outer cover thickness was 3.0 mm.

The adhesion was adjusted as follows. In Examples 1 to 4, the outer periphery of the FRP wire was coated with LDPE having a thickness of 0.15 mm before extruding the outer cover, and the thermosetting resin of FRP and polyethylene were brought into close contact with each other in advance. In addition, samples with different adhesions were prepared by adjusting the presence or absence of preheating of the tension member, the extrusion temperature, and the time until cooling after extrusion. On the other hand, Comparative Examples 1 and 2 were manufactured under the conventional conditions.

For each optical fiber cable, the tensile elastic modulus of the tension member was measured by a method according to JIS K 7161, and the compressive elastic modulus was measured by the method shown in FIG. Moreover, the ratio of the obtained tensile elastic modulus and compressive elastic modulus was calculated. Further, the adhesion between the tension member and the jacket was measured by the method shown in FIG.

Two types of bending tests were performed for the optical fiber cable: (1) a bending test without twisting and (2) a bending test with twisting. FIG. 4A is a diagram showing a bending test method.

The optical fiber cable 1 was applied to a mandrel 19 having a diameter of 500 mm, and the optical fiber cable 1 was bent at an angle of 90 degrees. At this time, the optical fiber cable 1 was grasped at a position 30 cm on both sides from the place where the mandrel 19 was applied, and the optical fiber cable 1 was assisted by hand so as not to rotate.

FIG. 4B is an enlarged cross-sectional view of portion C of FIG. 4A. The tension member 9 is arranged so as to come to the mandrel 19 side, and the bending direction of the optical fiber cable 1 is the direction in which the tension member 9 is attached. That is, normally, the bending direction is the direction perpendicular to the bending direction of the optical fiber cable 1.

After bending in this way, the presence or absence of buckling or damage of the tension member 9 was determined based on the presence or absence of damage to the outer cover 13. That is, when buckling of the tension member 9 occurs, the outer cover 13 around the tension member 9 is damaged accordingly, and thus the presence or absence of buckling of the tension member 9 is determined. The outer cover 13 includes a crack in the inner cover 13 of the bend (D in the figure, the outer cover 13 on the core 4 side of the tension member inside the bend) and a crack in the outer cover 13 of the bend (the outer cover 13 of the bend). In the figure, E was confirmed, and the outer cover 13) on the outer peripheral side of the tension member on the outer side of the bend was confirmed.

The above test was evaluated by (1) the case where it was performed without twisting and (2) the case where it was performed with a twist of 180 degrees / m. When twisting was performed, the bending test was performed so that the tension member 9 was located exactly above the mandrel 19. By twisting, the tension member 9 is twisted, so that the evaluation is performed under stricter conditions. The results are shown in Table 1.

As shown in Table 1, when the tension member 9 is a glass FRP, the compressive elastic modulus / tensile modulus is 0.48, and when the tension member 9 is an aramid FRP, the compressive modulus / tensile modulus is It was 0.43.

In Example 1, the adhesion between the tension member 9 and the jacket was 30 N / 10 m. In Example 1, no cracking of the outer cover 13 was confirmed in the bending test of (1). Further, in Example 2, the adhesion between the tension member 9 and the outer cover 13 became 41 N / 10 m by raising the extrusion temperature and further lengthening the time until cooling as compared with Example 1. In Example 2, in addition to the bending test of (1), no cracking of the outer cover was confirmed in the bending test of (2).

Example 3 was manufactured under substantially the same conditions as in Example 1, but the tension member was changed to aramid FRP, but the result was the same as in Example 1. Similarly, Example 4 was produced under substantially the same conditions as in Example 4, but the tension member was changed to aramid FRP, but the same result as in Example 2 was obtained.

On the other hand, in Comparative Examples 1 and 2 manufactured by the conventional manufacturing method, the adhesion between the tension member 9 and the jacket is less than 30 N / 10 m, and both of the bending tests (1) and (2) of the jacket Cracks were confirmed.

From the above, if the adhesion between the tension member 9 and the outer cover is 30 N / 10 m or more, the occurrence of cracks in the bending test of (1) can be suppressed, and the adhesive force between the tension member 9 and the outer cover is high. When it was 40 N / 10 m or more, it was possible to suppress the occurrence of cracks in the bending test (2) in addition to the bending test (1).

Although the embodiment of the present invention has been described above with reference to the attached drawings, the technical scope of the present invention does not depend on the above-described embodiment. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical ideas described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

1 ………… Optical fiber cable 3 ………… Optical fiber core wire 4 ………… Core 5 ………… Optical fiber unit 7 ………… Press winding 9 ………… Tension member 11 ………… Tear string 13 ………… Outside Cover 15 ……… Resin 17 ……… Die 19 ……… Mandrel

Claims (3)

A core consisting of multiple optical fiber cores and
In the cross section, tension members provided on both sides of the core and
An outer cover provided so as to cover the tension member and the optical fiber core wire,
Equipped with
The compressive elastic modulus of the tension member is ½ or less of the tensile elastic modulus.
An optical fiber cable characterized in that the adhesion between the tension member and the jacket is 30 N / 10 mm or more. The optical fiber cable according to claim 1, wherein the adhesion between the tension member and the jacket is 40 N / 10 mm or more. The optical fiber cable according to claim 1 or 2, wherein the tension member is a glass FRP or an aramid FRP.

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