JP2023020683A - Optical fiber cable - Google Patents

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

The present invention relates to an optical fiber cable with tension members.

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

As such an optical fiber cable, for example, tension members (strength members) having strength against 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. etc.), tensile strength fiber (such as aramid fiber), FRP, etc. are applicable (for example, Patent Document 1).

JP 2020-042175 A

In the optical fiber cable disclosed in Patent Document 1, since a pair of tension members are arranged at positions facing each other centering on the core, it is easy to bend in a direction centered on a straight line connecting the tension members, and in other directions. difficult to bend. In other words, the optical fiber cable has directionality of bendability. In particular, it is most difficult to bend in a direction in which the bending center is the center line perpendicular to the straight line connecting the tension members.

On the other hand, when laying such an optical fiber cable in a conduit, a rope for towing the optical fiber cable is laid in advance, the optical fiber cable is connected to the tow rope, and the tow rope is pulled to pull the cable inside the conduit. Laying method is common. When laying optical fiber cables in a series of conduits through manholes, etc., after passing the optical fiber cable through the first conduit, open the manhole between the first and second conduits. In some cases, the optical fiber cable is put out on the ground once, followed by a so-called figure of eight, and then passed through a second conduit.

However, when performing such a figure-of-eight alignment, if the directionality of the bendability of the optical fiber cable is strong, it becomes difficult to perform the figure-of-eight alignment. For example, the optical fiber cable may be locally twisted, or the tension member may buckle if the optical fiber cable is forcibly bent in a direction in which it is difficult to bend.

Further, even if the tension member does not buckle, if the tight contact between the tension member and the outer cover is broken, the longitudinal displacement between the tension member and the outer cover cannot be suppressed. For this reason, when the optical fiber cable expands and contracts due to a change in environmental temperature, the tension member and the jacket are largely displaced in the longitudinal direction due to the difference in linear expansion coefficient between the tension member and the jacket. Bending may occur, resulting in increased loss.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber cable which is excellent in handleability and capable of suppressing an increase in transmission loss.

In order to achieve the object described above, the present invention provides a core made of a plurality of optical fibers, tension members provided at positions facing each other across the core in a cross section perpendicular to the longitudinal direction of an optical fiber cable, and a core and an outer cover provided to cover the tension member, wherein the adhesion force between the tension member and the outer cover is within a range of 200 N/300 mm or more and 1200 N/300 mm or less, and the tension member and the The optical fiber cable is characterized in that the adhesion force between the tension member and the jacket is within the range even after the jacket and the jacket are displaced relative to each other in the longitudinal direction.

The adhesion force between the tension member and the outer cover may be within a range of 250 N/300 mm or more and 1000 N/300 mm or less.

It is desirable that the tension member and the jacket are not adhered.

A urethane acrylate resin having tackiness may be arranged between the tension member and the jacket.

According to the present invention, the adhesion force between the tension member and the jacket is 200 N/300 mm or more and 1200 N/300 mm or less. When bending in a difficult direction, the tension member and the jacket can be displaced in the longitudinal direction, so that the difficulty of bending can be alleviated and the buckling of the tension member can be suppressed. In addition, even after the tension member and the outer cover are relatively displaced in the longitudinal direction, the adhesion force between the tension member and the outer cover is within the above range. It is possible to suppress the expansion and contraction of the cover.

Such an effect can be obtained more efficiently when the adhesion force between the tension member and the jacket is 250 N/300 mm or more and 1000 N/300 mm or less.

In order to obtain such an effect, it is desirable that the tension member and the jacket are not adhered to each other. Even after the member and the outer cover are displaced relative to each other in the longitudinal direction, the adhesion force between the tension member and the outer cover can be reliably maintained.

ADVANTAGE OF THE INVENTION According to this invention, the optical fiber cable which is excellent in handleability and can suppress the increase in transmission loss can be provided.

Sectional drawing of the optical fiber cable 1. FIG. FIG. 4 is an enlarged view of the vicinity of the tension member 9; FIG. 5 is a diagram showing a method of measuring the adhesion force between the tension member 9 and the jacket 13;

Hereinafter, embodiments 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. FIG. The optical fiber cable 1 is a slotless type cable that does not use slots, 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 together. Further, the optical fiber unit 5 is formed by twisting a plurality of optical fiber core wires 3 together. The optical fiber cable 3 is, for example, an intermittently bonded optical fiber tape cable that is intermittently bonded in the longitudinal direction.

As shown in FIG. 1, a pressure wrap 7 is provided around the outer periphery of the plurality of optical fiber units 5 . The pressing wrap 7 is a tape-like member, a non-woven fabric, or the like, and is arranged so as to collectively cover the outer circumferences of the plurality of optical fiber units 5 by, for example, vertical wrapping. That is, the longitudinal direction of the pressure wrap 7 substantially coincides with the axial direction of the optical fiber cable 1 , and the width direction of the pressure wrap 7 is aligned with the circumferential direction of the optical fiber cable 1 . be wound. Note that the presser wrap 7 is not necessarily essential, and the core 4 including the presser wrap 7 may be called.

Tension members 9 are provided on both sides of the core 4 in a cross-sectional view perpendicular to the longitudinal direction of the optical fiber cable 1 . That is, a pair of tension members 9 are provided at positions facing each other with the core 4 interposed therebetween. In addition, a tear string 11 is provided so as to face each other with the core 4 interposed therebetween in a direction substantially perpendicular to the facing direction of the tension member 9 . The material of the tension member 9 is not particularly limited, but the present invention is more effective when using a material such as FRP having a low compressive modulus relative to the tensile modulus.

A jacket 13 is provided on the outer circumference of the core 4 . The tension member 9 and tear string 11 are embedded in the jacket 13 . That is, the jacket 13 is provided so as to cover the core 4, the tension member 9, and the like. The external shape of the outer cover 13 is substantially circular. The jacket 13 is, for example, a polyolefin resin.

Next, the adhesion force between the tension member 9 and the jacket 13 will be described. It is desirable that the adhesion force between the tension member 9 and the outer cover 13 is within a predetermined range even after the tension member 9 and the outer cover 13 are displaced relative to each other in the longitudinal direction. That is, it is desirable that the tension member 9 and the jacket 13 are not adhered.

2 is an enlarged view of the tension member 9. FIG. The tension member 9 is covered with a covering resin 15 . That is, a covering resin 15 is arranged between the tension member 9 and the jacket 13 . The coating resin 15 is, for example, a tacky (adhesive) resin such as urethane acrylate.

If the coating resin 15 has tackiness, the tension member 9 and the outer cover 13 are brought into close contact with each other due to the tackiness of the coating resin 15 . Therefore, compared to the case where the tension member 9 and the outer cover 13 are bonded with an adhesive, even if the tension member 9 and the outer cover 13 are once peeled off, the tension member 9 and the outer cover 13 are brought into contact with each other again. Adhesion can be ensured.

For example, in FIG. 1, when the optical fiber cable 1 is bent with the center line (straight line A in the drawing) of the tension members 9 facing each other as the center of bending (hereinafter, this direction may be referred to as bending in an easy-to-bend direction). , the optical fiber cable 1 can be easily bent. On the other hand, if the center line B orthogonal to the center line A is set as the bending center, the optical fiber cable 1 becomes relatively difficult to bend (hereinafter, this direction may be referred to as bending in a direction that is difficult to bend). At this time, compressive force is applied to the tension member 9 located particularly on the inner peripheral side of the bend, and there is a risk of buckling.

On the other hand, if the tension member 9 and the outer cover 13 are not adhered to each other but are in close contact with each other due to tackiness, the tension member 9 and the outer cover 13 will be displaced from each other when a force exceeding a predetermined level is applied. to release some of the stress. For this reason, the bendability in directions in which it is difficult to bend is improved, and buckling of the tension member 9 can be suppressed.

If the tension member 9 and the outer cover 13 are too easily displaced, the tension member 9 cannot suppress the expansion and contraction of the outer cover 13 and the like when the environmental temperature changes. The expansion and contraction of the core 4 applies stress to the core 4, which may increase the transmission loss. For this reason, in the present embodiment, the adhesion between the tension member 9 and the jacket 13 is preferably in the range of 200 N/300 mm or more and 1200 N/300 mm or less, and is in the range of 250 N/300 mm or more and 1000 N/300 mm or less. is even more desirable.

The adhesion force between the tension member 9 and the jacket 13 can be measured by the method shown in FIG. First, the optical fiber cable is cut to a predetermined length, and the outer covering 13 around the tension member 9 is entirely removed from the front and rear ends, leaving a covering piece having a width of 20 mm and a length of 300 mm. That is, the tension members 9 at the front and rear ends are exposed.

After that, the exposed tension member 9 is inserted through a 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 to the extent that the tension member 9 can pass through without resistance, and is smaller than the size of the jacket 13 left on the outer periphery of the tension member 9 . For example, the inner diameter of the hole is set to about 2.6 mm for the tension member 9 having a diameter of 2 mm.

After the tension member 9 with the jacket 13 passed through the die 17, the tension member 9 is pulled out at a speed of 500 mm/min using an Instron type tensile tester (arrow C 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 defined as the adhesion force between the tension member 9 and the jacket 13 . That is, the load when the tension member 9 is displaced relative to the outer cover 13 is defined as the adhesion force.

After the tension member 9 is displaced with respect to the outer cover 13, the pullout of the load is once stopped (the pullout force is eliminated), and when the pullout of the tension member 9 is started again at the same speed, the tension member 9 is pulled out again. However, the load when the tension member 9 and the outer cover 13 are relatively displaced in the longitudinal direction is the load when the tension member 9 and the outer cover 13 are relatively displaced in the longitudinal direction. power.

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

As described above, according to the present embodiment, the tension member 9 and the outer cover 13 are in close contact with each other without adhesion, and the adhesion strength is equal to or less than a predetermined value. Therefore, when the tension member 9 is bent in a direction that is difficult to bend (a direction centered on the center line B in FIG. 1), the tension member 9 and the jacket 13 can be displaced. bending can be suppressed.

Further, even if the tension member 9 and the outer cover 13 are once peeled off and shifted in the longitudinal direction, it is possible to secure a predetermined or more adhesion force in that state. In this way, since the adhesion force is always greater than or equal to a predetermined value, when the optical fiber cable 1 expands and contracts due to changes in the environmental temperature, the difference in coefficient of linear expansion between the tension member 9 and the outer cover 13 causes the tension member 9 and the outer cover 13 to close together. can be suppressed from shifting in the longitudinal direction. Therefore, the tension member 9 can suppress the expansion and contraction of the jacket 13, thereby suppressing an increase in loss of the internal optical fiber.

A bending test of the optical fiber cable was conducted by changing the adhesion force between the tension member and the jacket. The optical fiber cable used for evaluation has a cross-sectional configuration shown in FIG. First, 12 optical fibers with a diameter of 200 μm were intermittently bonded to prepare a 12-core optical fiber ribbon. Also, 12 fibers were twisted together and wrapped with a plastic tape having a width of 2 mm to form a 144-core optical fiber unit.

48 of these 144-core optical fiber units are supplied, twisted together in 4 layers in a 2-9-15-22 arrangement, vertically attached with water-absorbent nonwoven fabric, rounded with a forming jig, and then made of nylon. of presser thread was wound to prepare a core of 6912 fibers. The core created in this way, the tension member using G-FRP (glass fiber reinforced plastic) of φ2.0mm, and the tear string that cuts the outer cover are arranged in a straight line without being twisted together and attached to the outer cover. An optical fiber cable was produced by sheathing it in a cylindrical shape. LLDPE was used as the jacket material, and the jacket had an outer diameter of 29 mm and an inner diameter of 22 mm.

For the optical fiber cable, the outer circumference of the G-FRP was coated with a tacky urethane acrylate resin before the jacket was extruded. Since the urethane acrylate resin does not have thermoplasticity, it does not melt when the outer cover is extruded. By changing the type (tackiness) of the urethane acrylate used, the thickness of the coating, and the like, the adhesion force, which will be described later, was adjusted.

For comparison, an optical fiber cable was prepared by coating the outer periphery of G-FRP with a thermoplastic resin (low-density polyethylene) as an adhesive. In this case, the thermoplastic resin partially melted when the outer cover was extrusion-coated, and firmly adhered to the outer cover. Further, for comparison, an optical fiber cable was produced in which the jacket and the tension member were brought into close contact only by the adhesion force when the jacket was extruded, without using any adhesive.

For each of the obtained optical fiber cables, the adhesion force between the tension member and the sheath was measured before and after bending deformation. First, the adhesion force between the tension member and the jacket was measured before bending deformation in the direction in which it is difficult to bend (before bending deformation around straight line B in FIG. 1). In addition, the method shown in FIG. 3 was used as the method for measuring the adhesion force.

Next, after bending the optical fiber cable in a direction in which it is difficult to bend (after the tension member and the outer cover are relatively displaced in the longitudinal direction), the adhesion force between the tension member and the outer cover was measured. As for the measurement method, first, an optical fiber cable of 2 m was cut out, and the central part was wound around a mandrel of φ600 mm by 180 degrees in a direction in which it is difficult to bend. Next, the optical fiber cable was straightened, and the adhesion force between the tension member and the jacket was measured in the same procedure as before bending deformation.

Also, each optical fiber cable was subjected to a so-called figure-of-eight pattern to evaluate its bendability. As a bendability evaluation method, first, an optical fiber cable having a length of 200 m was bundled into a figure-eight shape with a short diameter of about 1 m, and the occurrence of local twisting was confirmed at this time. For example, if there is a large difference between the ease of bending in a direction that is difficult to bend and the ease of bending in a direction that is easy to bend, twisting is likely to occur during the figure-of-eight cut.

In addition, the presence or absence of buckling of the tension member after bending in a direction that is difficult to bend was evaluated. First, an optical fiber cable of 5 m was cut out, and the central portion was wound around a mandrel of φ600 mm by 180 degrees in a direction in which it is difficult to bend.

In addition, after bending in a direction that is difficult to bend, a heat cycle test was performed to evaluate an increase in transmission loss during the heat cycle. As an evaluation method, first, while rewinding an optical fiber cable of 1000 m, it was wound around a mandrel of φ600 mm at 10 points every 100 m in a direction in which it is difficult to bend, and then stretched straight.

After all the optical fiber cables were wound around a drum with a barrel diameter of 1400 mm, they were placed in a constant temperature bath and subjected to a heat cycle of -30°C to 70°C with a temperature holding time of 6 hours and a temperature transfer time of 6 hours for 3 times. cycle repeated. During this heat cycle test, the maximum increase in transmission loss at a wavelength of 1550 nm relative to the initial value (before the start of the heat cycle) was measured. Table 1 shows the results.

The "coating layer" in the table indicates the type of resin that coats the outer periphery of the tension member and the presence or absence of tackiness. Also, the "TM adhesive strength" is the pull-out force of the tension member from the outer cover, measured before and after bending in the direction in which it is difficult to bend, by the method shown in FIG.

In addition, "local twist when drawing the figure of eight" in the table indicates the presence or absence of a local twist when drawing the figure of eight. Those that occurred 1 or 2 times were rated as "△", and those that occurred 3 or more times were rated as "x".

In addition, "TM buckling after bending" in the table indicates the presence or absence of buckling of the tension member after bending in a direction that is difficult to bend. Those that occurred were marked with "x".

In addition, "Increase in transmission loss during heat cycle after bending" in the table indicates that the maximum increase in transmission loss during heat cycle relative to the transmission loss before heat cycle is less than 0.10 dB/km. A value of 0.10 to 0.15 dB/km was rated as “Δ”, and a value exceeding 0.15 dB/km was rated as “x”.

As a result, there was no significant difference in adhesion between the tension member and the outer cover before and after bending in any of Examples 1 to 5, in which a coating layer having tackiness was arranged between the tension member and the outer cover. . 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, both before and after bending, the adhesion between the tension member and the outer cover is within the range of 200 N/300 mm or more and 1200 N/300 mm or less. Both the buckling of the tension member after bending and the increase in transmission loss during the heat cycle were evaluated as Δ or higher. In particular, Examples 2 to 4, in which the adhesion force of the tension member was 250 N/300 mm or more and 1000 N/300 mm or less both before and after bending, were all evaluated as ◯.

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 jacket is small, resulting in a large increase in transmission loss during the heat cycle. In addition, in Comparative Example 2 using an adhesive, the adhesion between the tension member and the jacket before bending was too strong, so local twisting occurred when the figure-of-eight was taken and the tension member buckled after bending. . Further, in Comparative Example 2, once bending in a direction in which it is difficult to bend, the adhesion between the tension member and the outer cover was separated, and the adhesion of the tension member after bending was greatly reduced. For this reason, the increase in transmission loss during the heat cycle increased.

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 influenced by the above-described embodiments. It is obvious that a person skilled in the art can conceive various modifications or modifications within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. be understood to belong to

1 Optical fiber cable 3 Optical fiber cable 4 Core 5 Optical fiber unit 7 Presser wrap 9 Tension member 11 Tear string 13 Outside Cover 15 …… Coating resin 17 …… Die

Claims (4)

a core composed of a plurality of optical fiber core wires;
a tension member provided at a portion facing 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;
and
The adhesion force between the tension member and the outer cover is within the range of 200 N/300 mm or more and 1200 N/300 mm or less, and the tension member and the outer cover remain even after the tension member and the outer cover are relatively displaced in the longitudinal direction. An optical fiber cable, wherein the adhesion force to the jacket is within the above range. 2. The optical fiber cable according to claim 1, wherein the adhesion force between said tension member and said jacket is in the range of 250 N/300 mm or more and 1000 N/300 mm or less. 3. The optical fiber cable according to claim 1, wherein the tension member and the jacket are not adhered. 4. The optical fiber cable according to any one of claims 1 to 3, wherein a urethane acrylate resin having tackiness is arranged between the tension member and the jacket.

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