JP2021110820A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable that has excellent tearing working efficiency of a covering made of plural layers and can suppress deterioration of handling properties and an increase in loss.SOLUTION: A winding member 5 is disposed in an outer periphery of a cable core 15. A covering 13 made of resin is provided in an outer periphery of the winding member 5. The covering 13 is a layer for covering and protecting an optical fiber cable 1. The covering 13 is made of plural layers having an inner layer sheath 7a, and an outer layer sheath 7b formed in an outer periphery of the inner layer sheath 7a. A first tearing string 11a is disposed between the winding member 5 and the inner layer sheath 7a. A second tearing string 11b is disposed between the inner layer sheath 7a and the outer layer sheath 7b. In this case, in the optical fiber cable 1, extraction force of the inner layer sheath 7a (and the cable core 15 or the like inside the inner layer sheath 7a) in a state in which the outer layer sheath 7b is fixed is equal to or more than 18 N/10 m.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber cable capable of satisfying different characteristics such as strength and flame retardancy.

With the increase in the amount of information in recent years, various optical fiber cables accommodating a plurality of optical fiber core wires have been proposed. In such an optical fiber cable, in order to satisfy a plurality of characteristics required for an optical fiber cable such as strength and flame retardancy, a case where a plurality of layers of outer covering materials having different characteristics are sheathed on the outer circumference of the cable core. There is. For example, a high-strength resin that can withstand lateral pressure and impact is used for the inner layer sheath, and a flame-retardant resin is used for the outer layer sheath.

In such an optical fiber cable, for example, the outer cover has a two-layer structure of an inner layer sheath and an outer layer sheath, and an adhesive resin layer is provided between the layers in order to prevent only the outer layer sheath from extending and breaking when an external force is applied. An optical fiber cable in which a two-layer sheath is bonded by sandwiching the cable has been proposed (Patent Document 1).

Further, in order to improve the recyclability of the outer cover after use, an optical fiber cable capable of easily separating the inner layer sheath and the outer layer sheath has been proposed (Patent Document 2).

Japanese Unexamined Patent Publication No. 09-102220 Japanese Unexamined Patent Publication No. 2005-99445

However, in an optical fiber cable as in Patent Document 1, since the inner layer sheath and the outer layer sheath are adhered to each other and cannot be peeled off, it is necessary to tear the two layers together with a tear string. However, such tearing requires a large force, which imposes a heavy burden on the operator and makes it difficult to take out the internal optical fiber core wire. Further, since it is necessary to provide an adhesive layer between the two layers, it causes an increase in the outer diameter and weight of the cable.

On the other hand, as in Patent Document 2, workability can be improved by providing a tear string on both the inside of the inner layer sheath and the inside of the outer layer sheath and tearing the tear string layer by layer using the tear string. For example, first tear the outer sheath with the outer lace, open the crevice by hand and remove the outer sheath to expose the inner sheath, then tear the inner sheath with the inner lace and open the crevice by hand. By removing the inner layer sheath, the inner core can be taken out.

As described above, as a method of improving the peelability between the inner layer sheath and the outer layer sheath, for example, there is a method of providing a peeling layer such as a presser winding between the inner layer sheath and the outer layer sheath. However, by adding a member such as a presser winding, the number of members to be removed during the laying work increases, so that the work efficiency is lowered. Further, the outer diameter of the optical fiber cable is increased, the laying space is increased, and the weight of the optical fiber cable is increased, so that there is a problem that it is difficult to handle the optical fiber cable.

Further, as in Patent Document 2, if an attempt is made to improve the peelability between the inner layer sheath and the outer layer sheath, as described in Patent Document 1, only the outer layer sheath may be stretched and broken when an external force is applied. .. For example, when laying a slot-type cable with a tension member placed in the core or a slotless cable with a tension member placed inside the inner layer sheath, if the outer layer sheath is gripped and tension is applied, only the outer layer sheath that does not include the tension member will be applied. It may stretch and plastically deform, leading to the worst fracture.

On the contrary, in the case of a slotless cable in which a tension member is provided in the outer layer sheath, the outer layer sheath integrated with the tension member made of metal or FRP is limited in shrinkage at low temperature, but the resin constituting the outer cover. Since polyethylene is generally a material having a large coefficient of thermal expansion, the inner layer sheath contracts freely. As a result, the optical fiber core wire in the core in contact with the inner layer sheath may be compressed, resulting in an increase in loss.

The present invention has been made in view of such a problem, and provides an optical fiber cable having excellent tearing workability of a coating composed of a plurality of layers and capable of suppressing deterioration of handleability and increase in loss. With the goal.

In order to achieve the above-mentioned object, the present invention comprises a cable core composed of a plurality of optical fiber core wires, a presser foot wound arranged on the outer periphery of the cable core, and an outer cover arranged on the outer periphery of the presser foot winding. The outer cover is composed of a plurality of layers having an inner layer sheath and an outer layer sheath formed on the outer periphery of the inner layer sheath, and the inner layer sheath and the outer layer sheath are in contact with each other without heat fusion, and the presser foot is provided. A first tear cord is arranged between the winding and the inner layer sheath, a second tear cord is arranged between the inner layer sheath and the outer layer sheath, and the outer layer sheath is fixed from the inner layer sheath. It is an optical fiber cable characterized in that the pulling force when pulling out the inside is 18 N / 10 m or more.

The surface roughness Ra of the outer surface of the inner layer sheath is preferably 0.5 μm or more, and more preferably the surface roughness Ra of the outer surface of the inner layer sheath is 0.9 μm or more.

It is desirable that the MFR of the outer layer sheath is 0.10 g / 10 minutes or more.

The shore D hardness of the inner layer sheath is preferably 38 or more, more preferably the shore D hardness of the inner layer sheath is 50 or more, and further preferably the shore D hardness of the inner layer sheath is 68 or more.

It is desirable that the softening temperature of the inner layer sheath is 25 degrees or more higher than the softening temperature of the outer layer sheath.

It is desirable that the peeling force when a 90-degree peeling test is performed from the inner layer sheath by making notches in the longitudinal direction at positions 180 degrees apart from each other of the outer layer sheath and grasping only the outer layer sheath is 30 N or less. ..

The cable core may have a groove formed in the S direction or the SZ direction, a slot having a tension member inside, and the optical fiber core wire housed in the groove.

The cable core is composed of an optical fiber unit in which a plurality of the optical fiber core wires are bundled, and a tension member may be provided inside the inner layer sheath.

The cable core is composed of an optical fiber unit in which a plurality of the optical fiber core wires are bundled, and a tension member may be provided inside the outer layer sheath.

According to the present invention, the outer cover can have different characteristics by forming the outer cover into a plurality of layers. At this time, the inner layer sheath and the outer layer sheath are not heat-sealed, and each layer can be separately torn and removed with a tear string, so that the work is easy.

Further, since the pulling force of the inner layer sheath from the outer layer sheath is 18 N / 10 m or more, slippage or displacement between the inner layer sheath and the outer layer sheath is small during laying or heat cycle, and a tension member is arranged inside the outer layer sheath. Even if it is not present, the elongation and breakage of the outer layer sheath can be suppressed. Similarly, even when the tension member is not arranged inside the inner layer sheath, the compression of the optical fiber inside the inner layer sheath can be suppressed, and the accompanying increase in transmission loss can be suppressed.

As described above, as a method of increasing the pulling force, by setting the surface roughness of the outer surface of the inner layer sheath to a predetermined value or more, the unevenness of the surfaces of the inner layer sheath and the outer layer sheath mesh with each other to improve the pulling force. can.

Further, if the melt flow rate of the outer layer sheath is 0.10 g / 10 minutes or more, when the resin of the outer layer sheath is extruded to the outer peripheral surface of the fine irregularities on the outer surface of the inner layer sheath, the resin enters the fine irregularities. It is easy and the unevenness of the inner layer sheath and the outer layer sheath can be efficiently meshed.

Further, by setting the shore D hardness of the inner layer sheath to a predetermined value or higher, when a force from the outer layer sheath is received, the deformation of the unevenness on the surface of the inner layer sheath is small, so that the pulling force can be maintained more efficiently. can.

Further, if the softening temperature of the inner layer sheath is 25 degrees or more higher than the softening temperature of the outer layer sheath, heat fusion between the two can be prevented more reliably.

Further, even if the slip between the inner layer sheath and the outer layer sheath in the longitudinal direction of the optical fiber cable is suppressed, if the peeling force when the outer layer sheath is peeled 90 degrees from the inner layer sheath is less than a predetermined value, the outer cover is removed. The work of taking out the internal optical fiber core wire is easy.

As such an optical fiber cable, it can be applied to a slot type optical fiber cable, and can also be applied to a slotless type optical fiber cable. Further, in the case of the slotless type optical fiber cable, the same effect can be obtained regardless of whether the tension member is arranged in the outer layer sheath or the inner layer sheath.

According to the present invention, it is possible to provide an optical fiber cable having excellent tearing workability of a jacket composed of a plurality of layers and capable of suppressing deterioration of handleability and increase in loss.

(A) is a cross-sectional view showing the optical fiber cable 1, and (b) is an enlarged conceptual view of the vicinity of the interface between the inner layer sheath 7a and the outer layer sheath 7b of the optical fiber cable 1. The figure which shows the measuring method of a pull-out force. (A) and (b) are diagrams showing a method of measuring a peeling force. The cross-sectional view which shows the optical fiber cable 1a. The cross-sectional view which shows the optical fiber cable 1b. The figure which shows the relationship between the pull-out force and the pull-in amount of the inner layer at the time of laying. The figure which shows the relationship between the pull-out force and the maximum loss increase amount at the time of laying.

(First Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an optical fiber cable 1. The optical fiber cable 1 is a slot type optical fiber cable. The optical fiber cable 1 is composed of a cable core 15, a tension member 9, tear cords 11a and 11b, a slot 17, a jacket 13, and the like.

The cable core 15 is composed of a plurality of optical fiber core wires 3 housed in the slot 17. The slot 17 is made of a flexible resin. A groove 19 is formed in the longitudinal direction of the slot 17 in the S direction or the SZ direction. The plurality of optical fiber core wires 3 are housed in the groove 19. Further, a tension member 9 is provided at substantially the center inside the slot 17. The tension member 9 is, for example, a steel wire. The shape, number of arrangements, and depth of the grooves 19 are not limited to the illustrated examples.

The optical fiber core wire 3 may be a single-core optical fiber core wire, but it is desirable that the optical fiber core wire 3 is an optical fiber tape core wire in which a plurality of optical fiber core wires are provided. In this case, it is desirable to use an intermittently bonded optical fiber tape core wire in which adjacent optical fibers are intermittently bonded to each other in the longitudinal direction.

A presser winding member 5 is arranged on the outer circumference of the cable core 15. The presser winding member 5 is arranged so as to collectively cover the cable core 15 by vertical wrapping so that the ends thereof overlap each other, for example. For example, a resin tape, a water-absorbent non-woven fabric, or the like can be applied to the presser winding member 5. Further, a coarse winding string (not shown) is spirally wound around the outer circumference of the presser winding member 5.

A resin outer cover 13 is provided on the outer periphery of the presser winding member 5. The outer cover 13 is a layer for covering and protecting the optical fiber cable 1. The outer cover 13 is composed of a plurality of layers having an inner layer sheath 7a and an outer layer sheath 7b formed on the outer periphery of the inner layer sheath 7a. The inner layer sheath 7a and the outer layer sheath 7b are in direct contact with each other without heat fusion.

The inner layer sheath 7a and the outer layer sheath 7b may be the same resin, but it is desirable that the inner layer sheath 7a and the outer layer sheath 7b are resins having different characteristics. For example, the inner layer sheath 7a has higher strength than the outer layer sheath 7b, and the outer layer sheath 7b has excellent flame retardancy with respect to the inner layer sheath 7a. The details of the inner layer sheath 7a and the outer layer sheath 7b will be described later.

A first tear cord 11a is arranged between the presser winding member 5 and the inner layer sheath 7a. Further, a second tear string 11b is arranged between the inner layer sheath 7a and the outer layer sheath 7b. A pair of tear cords 11a and 11b are arranged respectively, and the pair of tear cords are arranged at positions 180 degrees apart from each other. In this way, the cable core 15 and the tear cords 11a and 11b are collectively covered with the outer cover 13.

Here, in the optical fiber cable 1, the pulling force of the inner layer sheath 7a (and the cable core 15 inside the inner layer sheath 7a, etc.) in the state where the outer layer sheath 7b is fixed is 18 N / 10 m or more. The pull-out force is an index indicating the degree of integration of the inner layer sheath 7a and the outer layer sheath 7b.

FIG. 2 is a diagram showing a method for measuring a pulling force in the present invention. To measure the pulling force, first prepare a 10.2 m optical fiber cable 1 and remove only the 0.1 m outer layer sheath 7b of each terminal. Next, the vicinity of both ends of the outer layer sheath 7b is fixed by the fixing portions 23. The fixing portion 23 may be fixed by using, for example, tape or the like so that the optical fiber cable 1 does not move.

Next, the internal structures of the inner layer sheath 7a and the inner layer sheath 7a are pulled out together from one end side (arrow A in the figure). The tensile force is gradually increased, and the load at the time when the inner layer sheath 7a moves with respect to the outer layer sheath 7b at the opposite end is used as the pulling force. That is, in the present invention, in the optical fiber cable 1 having a length of 10 m, the inner layer sheath 7a does not move with respect to the outer layer sheath 7b with a tensile force of less than 18 N, and the inner layer sheath 7a and the outer layer sheath 7b slip or shift. Is unlikely to occur.

Further, in the optical fiber cable 1, it is desirable that the peeling force of the inner layer sheath 7a with respect to the outer layer sheath 7b is 30 N or less. The peeling force is an index indicating the ease of peeling the outer layer sheath 7b from the inner layer sheath 7a.

FIG. 3 is a diagram showing a method for measuring a peeling force in the present invention. First, as shown in FIG. 3A, an optical fiber cable 1 is prepared, and cuts 25 are made in the longitudinal direction at positions 180 degrees apart from each other on the outer layer sheath 7b. Next, as shown in FIG. 3B, only the outer layer sheath 7b is grasped at the end of the cable, the outer layer sheath 7b is pulled from the inner layer sheath 7a in the direction of 90 degrees, and the load at the time of this 90 degree peeling test is applied. Measure. At this time, the force required for peeling the outer layer sheath 7b from the inner layer sheath 7a is defined as the peeling force. That is, by setting the peeling force of the outer layer sheath 7b from the inner layer sheath 7a to 30 N or less, the outer layer sheath 7b can be easily peeled off.

Here, as described above, by strongly joining the inner layer sheath 7a and the outer layer sheath 7b by heat fusion or adhesion or the like, the pulling force of the inner layer sheath 7a from the outer layer sheath 7b can be increased. Therefore, it is possible to suppress slippage and slippage between the inner layer sheath 7a and the outer layer sheath 7b in the longitudinal direction during laying or thermal cycle. On the other hand, if the two are strongly joined in this way, the peeling force between the two becomes large, which makes the peeling work difficult.

On the other hand, the present invention reduces the peeling force by increasing the pulling force of the inner layer sheath 7a from the outer layer sheath 7b without performing heat fusion or the like. As for this method, as shown in FIG. 1, it is desirable to increase the unevenness of the outer surface (interface with the outer layer sheath 7b) of the inner layer sheath 7a. In order to increase the pulling force, the unevenness (surface roughness) of the outer surface of the inner layer sheath 7a may be large in the cross section of the optical fiber cable 1 in the longitudinal direction.

As an index of the size of the unevenness of the outer surface of the inner layer sheath 7a in the longitudinal direction, it is desirable that the surface roughness Ra of the inner layer sheath 7a in the longitudinal direction is 0.5 μm or more, and more preferably 0.9 μm. That is all. The surface roughness 7a of the inner layer sheath 7a can be measured by, for example, a non-contact surface roughness meter in a state where the outer layer sheath 7b is peeled off and the outer surface of the inner layer sheath 7a is exposed. At this time, the outer layer sheath 7b and the inner layer sheath 7a are not separated by heat fusion or adhesion, and a part of the outer layer sheath 7b remains on the outer surface of the inner layer sheath 7a, or a part of the inner layer sheath 7a is the outer layer sheath 7b. It is a condition that it does not remain on the inner surface of.

By increasing the unevenness (surface roughness) between the inner layer sheath 7a and the outer layer sheath 7b in this way, the pulling force in the longitudinal direction can be increased and the peeling force in the 90 degree direction can be increased. It can be suppressed. Therefore, it is possible to improve the peelability of the outer layer sheath 7b while suppressing the displacement of the inner layer sheath 7a and the outer layer sheath 7b in the longitudinal direction.

As a method of increasing the surface roughness of the outer surface of the inner layer sheath 7a in this way, when the inner layer sheath 7a is extruded, the friction between the die surface and the molten resin is increased in the extrusion head to increase the inner layer sheath. The surface roughness of 7a can be roughened. Specifically, there are methods such as intentionally increasing the linear velocity, lowering the resin temperature, or lowering the die temperature with respect to the normal manufacturing conditions.

For example, as described above, when the linear velocity is increased, the resin fluctuates due to a phenomenon called melt fracture, and an uneven shape is formed on the surface. Normally, it is not desirable that the surface roughness after extrusion becomes rough. Therefore, since the extrusion conditions are set so that the surface is as smooth as possible, the above-mentioned phenomenon can be avoided. However, in the present invention, unevenness can be formed on the surface of the inner layer sheath 7a by intentionally setting the extrusion conditions so that the surface roughness becomes coarser than that of the conventional one.

In addition to this, for example, by blending particles having an average particle size of 1 μm or more into the inner layer resin, the surface of the inner layer sheath 7a can be roughened. In this case, for example, talc (phyllosilicate mineral), carbon black, metal hydroxide (magnesium hydroxide, aluminum hydroxide) and the like can be applied to the particles, and the average particle size is specified by, for example, laser diffraction. .. Further, if the average particle size is too large, large irregularities are generated on the inside (core side), and there is a problem that the convex portion presses the core wire to increase the loss. Therefore, the average particle size is 1 mm or less, which is more desirable. Is preferably 500 μm or less.

Further, when the surface roughness of the surface of the inner layer sheath 7a is roughened, it is desirable that the outer layer sheath 7b has an uneven shape that follows the unevenness of the inner layer sheath 7a. That is, it is desirable that the resin of the outer layer sheath 7b surely flows into the surface recess of the inner layer sheath 7a and meshes with each other. For this purpose, it is desirable that the melt flow rate (MFR) of the resin of the outer layer sheath 7b specified by JIS K6922-2 is 0.10 g / 10 minutes or more. By increasing the fluidity of the outer layer sheath 7b in this way, when the outer layer sheath 7b is extruded, the molten resin adheres in a shape corresponding to the uneven shape of the inner layer sheath 7a surface, and the pulling force can be increased.

Further, it is desirable that the softening temperature of the inner layer sheath 7a is 25 degrees or more higher than the softening temperature of the outer layer sheath 7b. This is to prevent the inner layer sheath 7a from softening and heat-sealing when the outer layer sheath 7b is extruded.

Further, the shore D hardness of the inner layer sheath 7a is preferably 38 or more, more preferably the shore D hardness of the inner layer sheath 7a is 50 or more, and further preferably the shore D hardness of the inner layer sheath 7a is 63 or more. be. As the hardness of the inner layer sheath 7a becomes higher, the uneven shape of the inner layer sheath 7a is less likely to be deformed with respect to the tensile force on the outer layer sheath 7b, and the uneven shape is maintained, so that a higher pulling force can be obtained.

Next, a method of removing the outer cover of the optical fiber cable 1 will be described. First, in a part of the optical fiber cable 1, a cutter or the like is used to make a notch in the length direction only in the outer layer sheath 7b (up to the interface with the inner layer sheath 7a). Next, the outer layer sheath 7b can be removed by grasping the tear string 11a on the surface of the inner layer sheath 7a, tearing it in the longitudinal direction, and peeling the outer layer sheath 7b from the inner layer sheath 7a.

Next, the inner layer sheath 7a is also cut with a cutter or the like to a length of about several cm, and only the inner layer sheath 7a (up to the interface with the presser winding member 5) is cut in the length direction. Next, the inner layer sheath 7a can be removed by grasping the tear string 11b on the surface of the presser winding member 5, tearing it in the longitudinal direction, and peeling the inner layer sheath 7a from the presser winding member 5. At this time, by using two tear strings 11a and 11b respectively, the outer cover after tearing is divided into two left and right, and it is easy to remove. The cutter may cut the outer layer sheath 7b and the inner layer sheath 7a at the same time.

As described above, according to the optical fiber cable 1 of the present embodiment, since the pull-out force of the inner layer sheath 7a is high, the inner layer sheath 7a protrudes from the outer layer sheath 7b at the time of laying or temperature change in the longitudinal direction. It is hard to slip and has good handleability. Further, since the outer layer sheath 7b and the inner layer sheath 7a are not heat-sealed, even if the pulling force is increased, the peeling force between the two can be reduced, and the workability for removing the outer cover is also good.

Further, in order to make the surface roughness of the inner layer sheath 7a rough, a special mold or the like is not required, and for example, it can be easily manufactured by setting the manufacturing conditions so that so-called melt fracture occurs.

At this time, if the MFR of the outer layer sheath 7b is equal to or higher than a predetermined value, the resin of the outer layer sheath 7b can be surely made to follow the uneven shape of the surface of the inner layer sheath 7a when the outer layer sheath 7b is extruded, and a higher pulling force can be more reliably obtained. Can be secured.

Further, by setting the inner layer sheath 7a to a hardness equal to or higher than a predetermined value, deformation of the inner layer sheath 7a is suppressed and the uneven shape is maintained, so that a high pulling force can be ensured.

(Second Embodiment)
Next, the second embodiment will be described. FIG. 4 is a cross-sectional view of the optical fiber cable 1a. In the following description, the same configurations as those of the optical fiber cable 1 are designated by the same reference numerals as those in FIG. 1 and the like, and duplicate description will be omitted.

The optical fiber cable 1a is a slotless type optical fiber cable, unlike the slot type optical fiber cable 1. The cable core 15a of the optical fiber cable 1a is composed of an optical fiber unit 21 in which a plurality of optical fiber core wires 3 are bundled. More specifically, a plurality of optical fiber core wires 3 are twisted together to form an optical fiber unit 21, and the plurality of optical fiber units 21 are assembled to form a cable core 15. Each optical fiber unit 21 is bundled with, for example, a bundle material to distinguish it from other optical fiber units 21.

A presser winding member 5 is wound around the outer circumference of the cable core 15a. An inner layer sheath 7a is arranged on the outer circumference of the presser winding member 5, and an outer layer sheath 7b is arranged on the outer circumference of the inner layer sheath 7a. Inside the inner layer sheath 7a, a pair of tension members 9 are provided at positions facing each other with the cable core 15 interposed therebetween. Further, a pair of tear cords 11a are provided on the outer circumference of the presser winding member 5 so as to face each other with the cable core 15 sandwiched in a direction substantially orthogonal to the facing direction of the tension member 9. Further, on the outer peripheral side of the inner layer sheath 7a, a pair of tear cords 11b are provided at the outer peripheral positions of the pair of tear cords 11a.

According to the second embodiment, the same effect as that of the first embodiment can be obtained. In particular, since the tension member 9 is arranged inside the inner layer sheath 7a, only the outer layer sheath 7b that does not include the tension member 9 may be stretched, but the pulling force of the inner layer sheath 7a from the outer layer sheath 7b is large. Even when a tensile external force is applied to the outer layer sheath 7b, the inner layer sheath 7a and the outer layer sheath 7b are prevented from slipping and shifting in the longitudinal direction. As described above, the present invention can also be applied to a slotless type optical fiber cable.

(Third Embodiment)
Next, a third embodiment will be described. FIG. 5 is a cross-sectional view of the optical fiber cable 1b. The optical fiber cable 1b has almost the same configuration as the optical fiber cable 1a, but the arrangement of the tension members 9 is different.

Unlike the optical fiber cable 1a, the optical fiber cable 1b is provided with a tension member 9 inside the outer layer sheath 7b. That is, inside the outer layer sheath 7b, a pair of tension members 9 are provided at positions facing each other with the cable core 15 interposed therebetween. Further, a pair of tear cords 11a and 11b are provided on the outer circumference of the presser winding member 5 and the outer circumference of the inner layer sheath 7a so as to face each other with the cable core 15 sandwiched in a direction substantially orthogonal to the facing direction of the tension member 9. Be done.

According to the third embodiment, the same effect as that of the first embodiment can be obtained. In particular, since the tension member 9 is arranged inside the outer layer sheath 7b, the inner layer sheath 7a that does not include the tension member 9 may shrink at a low temperature, but the pulling force of the inner layer sheath 7a from the outer layer sheath 7b is large. Therefore, even when a contraction force is applied to the inner layer sheath 7a, the inner layer sheath 7a and the outer layer sheath 7b are prevented from slipping and shifting in the longitudinal direction. As described above, the present invention is applicable to various types of optical fiber cables, and is also applicable to, for example, self-supporting optical fiber cables.

Various optical fiber cables are manufactured by changing the resin and extrusion conditions, and the "pulling force", "removability of the jacket", "pull-in amount of the jacket" and "loss fluctuation during the thermal cycle" are evaluated. did.

(Pulling force)
The pull-out force was evaluated by the method shown in FIG.

(Coat removal property)
The outer layer sheath 7b and the inner layer sheath 7a were torn in order using the tear strings 11a and 11b, the outer layer sheath 7b and the inner layer sheath 7a could be torn, and the outer layer sheath 7b and the inner layer sheath 7a could be removed to take out the cable core. Those were accepted as "○". On the other hand, if the outer layer sheath 7b or the inner layer sheath 7a is hard and cannot be torn, if the tear strings 11a and 11b are broken and the work cannot be continued, or if a notch is made with a cutter, the inner layer sheath 7a and the outer layer sheath 7b are stuck together. Those in which the surface of the inner layer sheath 7a could not be exposed and the tear string 11b could not be taken out were marked as "x".

(Amount of pull-in of outer cover)
In order to simulate the actual laying environment, a trough with a length of 30 m was arranged in a straight line, a wire was stretched in advance in the trough, and a 30 m optical fiber cable wound in a figure eight was arranged at the trough entrance. Next, a cable grip was attached to the end of the optical fiber cable and connected to the wire, and the wire was pulled from the trough outlet side to pass the optical fiber cable over the entire length of the trough. After passing the wire, the cable grip was removed, and the displacement between the outer layer sheath 7b and the inner layer sheath 7a (the displacement in the longitudinal direction at the end) was measured as the pull-in amount of the inner layer sheath 7a.

When the outer layer sheath 7b and the inner layer sheath 7a slide easily, tension is concentrated on the outer layer sheath 7b at the time of wire passage, so that the outer layer sheath 7b tends to stretch. As a result, when the elongation of the outer layer sheath 7b exceeds the elastic limit, the elongation of the outer layer sheath 7b remains even after the tension is released, and the inner layer sheath 7a is pulled in. The practically permissible pull-in amount was set to 50 mm, those less than that were evaluated as "○", and those more than that were evaluated as "×". In particular, when the pull-in amount was 0, it was evaluated as “⊚”.

(Loss fluctuation during thermal cycle)
A thermal cycle test of −20 ° → + 60 ° → −20 ° → ... Was performed for 3 cycles, and the maximum loss increase at that time was measured. Those within 0.1 dB / km, which have no practical problem, were rated as “◯”, and those exceeding 0.1 dB / km were rated as rejected “x”. In particular, those with a loss increase of 0.02 dB / km or less were marked with “⊚”.

The evaluation results of the slot type optical fiber cable shown in FIG. 1 are shown in Table 1, the evaluation results of the optical fiber cable 1a shown in FIG. 3 are shown in Table 2, and the evaluation results of the optical fiber cable 1b shown in FIG. 4 are shown. Is shown in Table 3. Further, the relationship between the pulling force and the pulling amount of the inner layer obtained from the results of Tables 1 and 2 is shown in FIG. 6, and the relationship between the pulling force and the maximum loss increase obtained from the results of Table 3 is shown in FIG. Indicated.

In Table 1, when the pull-out force was 18 N / 10 m or more, the pull-in amount of the inner layer sheath 7a was less than 50 mm, which was acceptable. In particular, when the pull-out force was 34 N / 10 m or more, the pull-in amount of the inner layer sheath 7a was 0 mm.

Further, the larger the surface roughness Ra value of the surface of the inner layer sheath 7a, the smaller the pull-in amount. When the MFR of the resin of the outer layer sheath is 0.10 g / 10 minutes, the Ra value is 0.50 μm or more and the pull-in amount is small. Was passed. On the other hand, when the MFR of the resin of the outer layer sheath was 0.06 g / 10 minutes, the pulling force was less than 18 N / 10 m even if the Ra value was 0.50 μm or more. Further, even when the MFR of the resin of the outer layer sheath was 0.06 g / 10 minutes, the pulling force was 18 N / 10 m or more when the Ra value was 0.90 μm or more.

Further, when the samples having the same Ra value were compared, the larger the Shore D hardness, the larger the pulling force tended to be. In particular, when the shore D hardness exceeds 50, the retracted amount of the inner layer sheath becomes 0 mm, which is a very good result. As described above, the larger the shore D hardness, the smaller the pull-in amount of the inner layer sheath can be reduced even if the Ra value is small, and when the shore D hardness exceeds 63, the pull-in amount of the inner layer sheath is more reliably reduced. be able to.

Similarly, in Table 2, when the pull-out force was 22 N / 10 m or more, the pull-in amount of the inner layer was less than 50 mm, which was acceptable. Further, as in Table 1, the larger the Ra value on the surface of the inner layer sheath 7a, the smaller the retracted amount of the inner layer sheath, and when the MFR of the resin of the outer layer sheath is 0.10 g / 10 minutes, the Ra value is high. The pull-in amount was acceptable at 0.50 μm or more. On the other hand, when the MFR of the resin of the outer layer sheath was 0.06 g / 10 minutes, the pulling force was less than 22 N / 10 m even if the Ra value was 0.50 μm or more.

Further, as in Table 1, when the samples having the same Ra value were compared, the larger the Shore D hardness, the larger the pulling force tended to be. In particular, when the shore D hardness exceeds 50, the retracted amount of the inner layer sheath becomes 0 mm, which is a very good result.

From the above results, as shown in FIG. 6, when the pull-out force was 18 N / 10 m or more, the pull-in amount of the inner layer was less than 50 mm.

Further, in Table 3, when the pull-out force was 20 N / 10 m or more, the maximum value of the loss increase during the thermal cycle was 0.10 dB / km or less, which was acceptable. Further, the larger the Ra value on the surface of the inner layer sheath 7a, the smaller the maximum loss increase amount. When the MFR of the resin of the outer layer sheath is 0.10 g / 10 minutes, the Ra value is 0.51 μm or more and the thermal cycle is performed. The maximum loss increase in the test passed. On the other hand, when the MFR of the resin of the outer layer sheath was 0.06 g / 10 minutes, the maximum loss increase amount in the thermal cycle test was rejected even if the Ra value was 0.50 μm or more.

Further, when comparing samples with similar Ra values, the larger the shore D hardness, the smaller the maximum loss increase, and especially when the shore D hardness exceeds 50, the loss increase during the thermal cycle is 0.02 dB / km. The results were very good. The increase in loss all occurred at low temperatures.

From the above, as shown in FIG. 7, when the pulling force is 20 N / 10 m or more, the maximum value of the loss increase during the thermal cycle is 0.10 dB / km or less.

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 idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

1, 1a, 1b ………… Optical fiber cable 3 ………… Optical fiber core wire 5 ………… Press winding member 7a ………… Inner layer sheath 7b ………… Outer layer sheath 9 ………… Tension members 11a, 11b ………… Tear string 13 ………… Cover 15, 15a ………… Cable core 17 ………… Slot 19 ………… Groove 21 ………… Optical fiber unit 23 ………… Fixed part 25 ………… Notch

Claims (12)

A cable core consisting of multiple optical fiber cores and
With the presser foot wound arranged on the outer circumference of the cable core,
The outer cover arranged on the outer circumference of the presser foot and
Equipped with
The jacket is composed of a plurality of layers having an inner layer sheath and an outer layer sheath formed on the outer periphery of the inner layer sheath, and the inner layer sheath and the outer layer sheath are in contact with each other without heat fusion.
A first tear cord is placed between the presser winding and the inner layer sheath, and a second tear cord is placed between the inner layer sheath and the outer layer sheath.
An optical fiber cable having a pulling force of 18 N / 10 m or more when pulling out the inside of the inner layer sheath with the outer layer sheath fixed. The optical fiber cable according to claim 1, wherein the surface roughness Ra of the outer surface of the inner layer sheath is 0.5 μm or more. The optical fiber cable according to claim 1, wherein the surface roughness Ra of the outer surface of the inner layer sheath is 0.9 μm or more. The optical fiber cable according to any one of claims 1 to 3, wherein the melt flow rate of the outer layer sheath is 0.10 g / 10 minutes or more. The optical fiber cable according to any one of claims 1 to 4, wherein the inner layer sheath has a shore D hardness of 38 or more. The optical fiber cable according to any one of claims 1 to 4, wherein the inner layer sheath has a shore D hardness of 50 or more. The optical fiber cable according to any one of claims 1 to 4, wherein the inner layer sheath has a shore D hardness of 63 or more. The optical fiber cable according to any one of claims 1 to 7, wherein the softening temperature of the inner layer sheath is 25 degrees or more higher than the softening temperature of the outer layer sheath. The outer layer sheaths are notched at positions 180 degrees apart from each other in the longitudinal direction, and when only the outer layer sheath is grasped and a 90 degree peeling test is performed from the inner layer sheath, the peeling force is 30 N or less. The optical fiber cable according to any one of claims 1 to 8. According to claim 1, the cable core has a groove formed in the S direction or the SZ direction, and comprises a slot having a tension member inside and the optical fiber core wire accommodated in the groove. The optical fiber cable according to any one of claims 9. The cable core according to any one of claims 1 to 9, wherein the cable core includes an optical fiber unit in which a plurality of the optical fiber core wires are bundled, and a tension member is provided inside the inner layer sheath. Fiber optic cable. The cable core according to any one of claims 1 to 9, wherein the cable core comprises an optical fiber unit in which a plurality of the optical fiber core wires are bundled, and a tension member is provided inside the outer layer sheath. Fiber optic cable.

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