JP2023109266A - Optical fiber cable - Google Patents

Abstract

To provide an optical fiber cable that is excellent in handleability without lowering manufacturability greatly.SOLUTION: In a cross section vertical to a longitudinal direction of an optical fiber cable 1, a first tension member 9a is provided in a facing portion in a center of a core 5. Also, a plurality of second tension members 9b are disposed in a circumferential direction between the first tension members 9a. The second tension member 9b is lower in tension rigidity (axis rigidity=axis direction force/an amount of displacement in an axial direction) than the first tension member 9a. A sheath 13 is provided so as to cover the core 5 (a plurality of coated optical fibers 3), the first tension member 9a, the second tension member 9b and the like. The shape of the sheath 13 is almost circle. The sheath 13 is, for example, polyolefin-based resin. Herein, the sheath 13 in at least an outer peripheral part of the first tension member 9a is composed of foamed resin 13a.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical fiber cable comprising a plurality of optical fiber core wires.

As an optical fiber cable, one in which a core composed of a large number of optical fiber core wires and a tension member arranged on the outer circumference of the core are covered with a jacket is used (for example, Patent Document 1).

In such an optical fiber cable, since a pair of tension members are arranged at opposing positions centering on the core, it is easy to bend in the direction centered on the straight line connecting the tension members, but bends in other directions. Hateful. 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.

As described above, the optical fiber cable disclosed in Patent Document 1 is very easy to bend in a direction centered on the straight line connecting the tension members. There is a risk of clogging in the pipeline due to bending or undulation of the pipe.

On the other hand, an optical fiber cable has been proposed in which tension members are arranged at opposing positions across a core, and similar tension members are arranged in a direction perpendicular to a line connecting the tension members (Patent Document 2). . That is, an optical fiber cable has been proposed in which tension members are arranged in mutually orthogonal directions with a core interposed therebetween.

Japanese Patent Application Laid-Open No. 2019-109400 JP 2020-204752 A

In the optical fiber cable of Patent Document 2, the tension members are arranged also in the above-described easy-to-bend directions, so the rigidity as a whole is high, making it difficult to bend in any direction. Therefore, it cannot be wound on a small-diameter drum, and excessive packing is required by winding on a drum that is larger than necessary. Also, if the tension member is forced to be wound around a small-diameter drum, the tension member may buckle.

In response to this, the inventors found a method of reducing the adhesion between the tension member and the jacket as a method of suppressing such buckling and further improving bending flexibility. In this way, by reducing the adhesion force between the tension member and the outer cover, for example, when bending in a difficult direction, the tension member and the outer cover can be displaced in the longitudinal direction, making it difficult to bend. is relieved, and buckling of the tension member can be suppressed.

However, in cases where the amount of extruded resin for the jacket is large, such as for an optical fiber cable with a large outer diameter, the resin temperature increases during extrusion molding, and the adhesion between the tension member and the jacket tends to increase. be. On the other hand, if you try to reduce the adhesion between the outer cover and the tension member by lowering the resin temperature, it is necessary to lower the extruder setting temperature or the production line speed, but the resin becomes hard and molding is difficult. There is a problem that it becomes difficult and the production efficiency is lowered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber cable that is easy to handle without greatly lowering manufacturability.

In order to achieve the above object, the present invention provides a core made up of a plurality of optical fiber core wires and a first tension member provided at a portion facing the core in a cross section perpendicular to the longitudinal direction of an optical fiber cable. and a plurality of second tension members arranged between the first tension members in the circumferential direction and having a lower tensile rigidity than the first tension members, the core, the first tension member and the and a jacket provided to cover a second tension member, wherein at least the jacket on the outer peripheral portion of the first tension member is made of foamed resin. .

The outer covering of the outer peripheral portion of the second tension member may be a non-foaming resin.

Foamed resin may be sufficient as the whole of the said outer cover.

It is desirable that the expansion ratio of the foamed resin is 14% or more and 50% or less.

According to the present invention, the first tension member is arranged facing the core, and the second tension member having lower tensile rigidity than the first tension member is arranged between the first tension members in the circumferential direction. By doing so, it is possible to reduce the easiness of bending in the bending direction (hereinafter sometimes simply referred to as "easily bending direction") with the center line of the first tension member in the facing direction as the bending center. Therefore, the rigidity as a whole is increased, and unintended bending of the optical fiber cable can be suppressed.

In addition, compared to the bending direction centered on the center line perpendicular to the facing direction of the first tension member (hereinafter sometimes simply referred to as the "difficult to bend direction"), the direction in which it is easy to bend is relatively Since it is easy to bend, the optical fiber cable can be easily bent when winding it around a drum. In addition, since the bendability in the bendable direction is reduced, excessive bending of the optical fiber cable in this direction can be suppressed.

That is, compared with the optical fiber cable of Patent Document 1, the present invention increases the rigidity in the easy-to-bend direction to make it difficult to bend, and compared with the optical fiber cable of Patent Document 2, the optical fiber cable in the direction that is difficult to bend. On the other hand, the directionality which is relatively easy to bend is intentionally provided. As described above, according to the present invention, the advantages of the conventional optical fiber cables disclosed in Patent Documents 1 and 2 can be achieved by appropriately balancing bendability in directions orthogonal to each other.

In addition, by forming the outer cover covering the outer peripheral portion of the first tension member with foamed resin, even if the resin temperature during extrusion is increased, the adhesion force between the first tension member and the outer cover can be efficiently reduced. be able to. Therefore, the manufacturability is also excellent. In addition, since the adhesion between the first tension member and the jacket is low, when the optical fiber cable is bent, the first tension member and the jacket can be partially displaced. buckling can be suppressed. Therefore, damage to the optical fiber cable can be suppressed when the optical fiber cable is pumped or wound.

In this case, only the outer peripheral portion of the first tension member may be made of foamed resin, and the other portions may be made of non-foamed resin. By doing so, since the outer covering of the portion other than the outer peripheral portion of the first tension member is made of normal non-foamed resin, it is excellent in appearance and secures the strength and wear resistance of the outer covering. be able to.

Moreover, not only the outer peripheral portion of the first tension member, but also the entire jacket can be made of foamed resin. By doing so, the jacket can be made of a single resin material, so that the manufacturability is good and the weight of the optical fiber cable can be reduced.

In addition, by appropriately setting the foaming ratio of the foamed resin covering the first tension member, sufficient protection performance for the inner core is secured while securing the effect of reducing the adhesion force with the first tension member. can do.

ADVANTAGE OF THE INVENTION According to this invention, the optical fiber cable excellent in handleability can be provided, without reducing manufacturability significantly.

Sectional drawing of the optical fiber cable 1. FIG. Sectional drawing of the optical fiber cable 1a. Sectional drawing of the optical fiber cable 1b. Sectional drawing of the optical fiber cable 1c.

(First embodiment)
A first embodiment will be described below 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 5, a first tension member 9a, a second tension member 9b, a jacket 13, and the like.

The core 5 is composed of a plurality of optical fiber core wires 3 . More specifically, a plurality of optical fiber core wires 3 are twisted together to form an optical fiber unit, and a plurality of optical fiber units are further twisted together to form a core 5 . The optical fiber core wire 3 may be, for example, an intermittently bonded optical fiber tape core wire that is intermittently bonded in the longitudinal direction.

As shown in FIG. 1, a pressure winding 7 is provided around the outer periphery of the core 5 (the plurality of optical fibers 3). The press wrap 7 is a tape-like member, nonwoven fabric, or the like, and is arranged so as to collectively cover the outer periphery of the core 5 by, for example, vertical splicing. That is, the presser wrap 7 is longitudinally wound around the outer periphery of the core 5 so that the longitudinal direction of the presser wrap 7 substantially coincides with the axial direction of the optical fiber cable 1 and the width direction of the presser wrap 7 is aligned with the circumferential direction of the optical fiber cable 1 . Note that the presser wrap 7 is not necessarily essential, and the core 5 including the presser wrap 7 may be called.

A first tension member 9a is provided at a portion facing the core 5 in a cross section perpendicular to the longitudinal direction of the optical fiber cable 1 . A plurality of second tension members 9b are arranged between the first tension members 9a in the circumferential direction. The second tension member 9b has lower tensile rigidity (axial rigidity=axial force/axial deformation amount) than the first tension member 9a. For example, the diameter (cross-sectional area) of each first tension member 9a is larger than the diameter (cross-sectional area) of each second tension member 9b.

The first tension member 9 a and the second tension member 9 b bear the tension of the optical fiber cable 1 . The tension of the optical fiber cable 1 is mainly borne by the first tension member 9a, and the tension of the optical fiber cable 1 is auxiliarily borne by the second tension member 9b. Although the material of the first tension member 9a and the second tension member 9b is not particularly limited, for example, fiber reinforced plastic (FRP) made of aramid fiber, glass fiber, or the like can be used. Also, the first tension member 9a and the second tension member 9b may be made of different materials.

In the illustrated example, three second tension members 9b are arranged between the first tension members 9a in the circumferential direction. That is, a total of six second tension members 9b are arranged between the first tension members 9a in the circumferential direction. The total cross-sectional area of the first tension members 9a is preferably larger than the total cross-sectional area of the second tension members 9b. may be larger than the total cross-sectional area of

Also, the second tension member 9b and the first tension member 9a are arranged at substantially equal intervals in the circumferential direction. That is, the first tension members 9a are arranged at intervals of 180°, and the second tension members 9b are arranged at intervals of approximately 45°, and the adjacent first and second tension members 9b are arranged at intervals of about 45°. The number of second tension members 9b is not particularly limited.

A tear string 11 is provided at a circumferential position different from that of the first tension member 9a and the second tension member 9b and facing each other with the core 5 interposed therebetween. A jacket 13 is provided on the outer circumference of the core 5 . The first tension member 9 a , the second tension member 9 b and the tear string 11 are embedded in the jacket 13 . That is, the jacket 13 is provided so as to cover the core 5 (the plurality of optical fiber core wires 3), the first tension member 9a, the second tension member 9b, and the like. The external shape of the outer cover 13 is substantially circular. The jacket 13 is, for example, a polyolefin resin.

Here, at least the jacket 13 in the outer peripheral portion of the first tension member 9a is made of foamed resin 13a. In the illustrated example, the foamed resin 13 a is exposed on the outer surface of the jacket 13 . In addition, the outer cover 13 at the portion other than the first tension member 9a is made of non-foamed resin. That is, the jacket 13 on the outer peripheral portion of the second tension member 9b is made of non-foamed resin. In this way, by arranging the foamed resin 13a only in the necessary parts, the amount of the foaming agent used can be reduced, and the deterioration of the mechanical strength of the outer cover 13 can be minimized.

Such partially foamed resin 13a can be easily formed by two-layer extrusion. For example, by including a foaming agent in the resin to be extruded to the portion corresponding to the foamed resin 13a, the resin can be foamed by heat during extrusion. At this time, even if the linear velocity is increased and the extrusion temperature is increased, the adhesion force with the first tension member 9a can be reduced, so the productivity is also good.

The expansion ratio of the foamed resin is preferably 14% or more and 50% or less. If the foaming ratio is too small, the effect of reducing the adhesion force with the first tension member 9a is small. On the other hand, if the foaming ratio is too large, the mechanical properties of the outer covering will deteriorate, and the durability as a protective layer will deteriorate.

Here, the adhesion between the tension member and the resin tends to decrease as the foaming ratio of the resin increases. That is, the foamed resin 13a has a smaller adhesion force with the tension member than the non-foamed resin. Therefore, in the present embodiment, the adhesion force between the first tension member 9a and the jacket 13 is smaller than the adhesion force between the second tension member 9b and the jacket 13 .

By doing so, when the optical fiber cable 1 is bent in a direction in which it is difficult to bend, the restraining force that the first tension member 9a receives from the jacket 13 can be reduced. can be generated. Therefore, it is possible to suppress the occurrence of buckling of the first tension member 9a. On the other hand, since the second tension member 9b and the outer cover 13 are in close contact with each other, it is possible to suppress loss fluctuation due to expansion and contraction of the outer cover 13 due to changes in the environmental temperature, and stabilize characteristics.

Here, the optical fiber cable 1 is easily bent in a direction (vertical direction in the figure) centered on the center line (the center line A in the figure) parallel to the facing direction of the first tension member 9a. , other directions (for example, the center line B perpendicular to the center line A) are directions that are difficult to bend.

In this case, compared to a conventional optical fiber cable without the second tension member 9b (for example, the optical fiber cable of Patent Document 1), the optical fiber cable 1 has a bendability in the easy-to-bend direction due to the second tension member 9b. reduce (i.e., become less bendable). That is, it is possible to increase the bending rigidity in the easy-to-bend direction.

On the other hand, when compared with an optical fiber cable (for example, the optical fiber cable of Patent Document 2) in which the first tension members 9a are opposed to each other in directions orthogonal to each other to make it difficult to bend in any direction, the optical fiber cable 1 has: There are directions in which it is difficult to bend and directions in which it is easy to bend. That is, the direction in which the bending center is the center line A is relatively easy to bend compared to the other directions, and the direction is easy to bend.

As described above, according to the present embodiment, since the outer cover 13 of the outer periphery of the first tension member 9a is made of the foamed resin 13a, the first tension member 9a and the outer cover 13 (foamed resin 13a) can reduce the adhesion force of Therefore, it is possible to reduce the restraint of the first tension member 9a by the outer cover 13, thereby suppressing the buckling of the first tension member 9a.

In addition, since the second tension member 9b can increase the bending rigidity in the conventional easy-to-bend direction, for example, it is possible to suppress the occurrence of bending of the optical fiber cable during pumping and the occurrence of clogging due to this. . In addition, it is possible to prevent the optical fiber cable from bending beyond the allowable bending radius during laying or the like.

Moreover, when the optical fiber cable is wound around a drum or the like, the optical fiber cable can be bent in an easy-to-bend direction and wound around the drum or the like. In this way, different tension members are used together to increase the bending rigidity in the easy-to-bend direction while leaving the easy-to-bend and hard-to-bend directions, and by optimizing the balance of the ease of bending depending on the direction, handling is improved. It is possible to obtain an optical fiber cable excellent in laying workability.

In addition, since the second tension members 9b are arranged at substantially equal intervals in the circumferential direction, it is possible to smoothly change the directionality of the ease of bending by the second tension members 9b.

The interval (arrangement angle) between the second tension members 9b and the interval (arrangement angle) between the first tension member 9a and the second tension member 9b may not be the same. For example, the second tension members 9b may be unevenly distributed in a direction perpendicular to the facing direction of the first tension members 9a. For example, when arranging three second tension members 9b between each of the first tension members 9a, the arrangement angle between the second tension members 9b is about 30°, and the first tension members 9a and both ends The arrangement angle with the second tension member may be about 60°.

As described above, the further away from the center line A, the greater the effect of improving the bending rigidity in the bending direction with the center line A as the bending center. Therefore, by arranging the second tension members 9b unevenly in the direction perpendicular to the facing direction of the first tension members 9a, the bending rigidity can be efficiently increased in the direction in which the optical fiber cable 1b is easy to bend. can be improved.

(Second embodiment)
Next, a second embodiment will be described. FIG. 2 is a cross-sectional view showing an optical fiber cable 1a according to the second embodiment. In addition, in the following description, the same reference numerals as in FIG. 1 are given to the configurations having the same functions as those of the first embodiment, and overlapping descriptions are omitted.

The optical fiber cable 1a has substantially the same configuration as the optical fiber cable 1, but differs in the form of the first tension member 9a. In the optical fiber cable 1 described above, the two first tension members 9a are arranged one by one at positions facing each other with the core 5 interposed therebetween. are arranged two each at positions opposed to each other with the core 5 interposed therebetween. At this time, all the first tension members 9a are collectively covered with the foamed resin 13a at each position. That is, all the first tension members 9a are in close contact with the foamed resin 13a.

In each part, the first tension member 9a is arranged with a gap in the circumferential direction. In this way, by arranging a plurality of first tension members 9a at positions opposed to each other with the core 5 as the center, the first tension members 9a are arranged so that the first tension members 9a are opposed to each other. They can be arranged at positions shifted from the center line A parallel to the direction.

Also in this case, the cross-sectional area of each first tension member 9a is larger than the cross-sectional area of each second tension member 9b. Furthermore, the cross-sectional area of each first tension member 9a may be larger than the total cross-sectional area of the second tension members 9b. Also in this case, the tensile stiffness of each first tension member 9a is greater than the tensile stiffness of each second tension member 9b. Furthermore, the tensile stiffness of each first tension member 9a may be greater than the total tensile stiffness of the second tension members 9b.

Generally, when a member is bent, the outer side of the bending is subjected to tensile deformation, and the inner side of the bending is subjected to compressive deformation. Therefore, the amount of deformation near the center line is small, and the effect of the structure on the center line on the bending rigidity is small. Therefore, as described above, the direction in which the optical fiber cable 1a is easily bent is the direction in which the center line A in the facing direction of the first tension member 9a is the bending center. That is, by arranging the first tension member 9a on the center line A like the optical fiber cable 1 described above, the improvement in bending rigidity due to the first tension member 9a against bending in this direction can be minimized. It becomes easy to bend in that direction.

On the other hand, in the optical fiber cable 1a, since the first tension member 9a is arranged at a position deviated from the center line A, compared with the optical fiber cable 1, the first tension member 9a has a greater influence on the bending rigidity. . That is, by arranging the first tension member 9a at a position shifted from the center line A, the bending rigidity in the bending direction about the center line A is improved, and the effect of arranging the second tension member 9b is further complemented. can do.

When a plurality of first tension members 9a are arranged in each region, the central position in the circumferential direction is the representative position of the first tension member 9a. For example, when three second tension members 9b are arranged between each of the first tension members 9a, the arrangement angle between (the representative positions of) the first tension members 9a and the second tension members 9b is 45 degrees. °.

According to the second embodiment, effects similar to those of the first embodiment can be obtained. In addition, by arranging a plurality of first tension members 9a at positions facing each other around the core 5 and arranging the first tension members 9a at positions deviated from the center line A, the bending rigidity in the easy-to-bend direction is increased. can be improved. In this embodiment, even when combined with the effect of improving the bending rigidity by the second tension member 9b, the bending rigidity in the bending direction with the center line A as the bending center is Since the bending stiffness in the bending direction is lower than that in the bending direction, this direction remains easy to bend.

If the number of the first tension members 9a arranged at opposing positions is an even number, a straight line connecting the centers of the members in the circumferential direction may be taken as the center line A in the opposing direction. If the number of the first tension members 9a arranged at opposing positions is an odd number, the straight line connecting the central first tension members 9a may be taken as the center line A in the opposing direction. However, when three or more first tension members 9a are arranged in each region, they are arranged at equal intervals.

In this way, when the number of the first tension members 9a arranged at opposite positions is an odd number, the central first tension member 9a is arranged on the center line A, but at least some of the other first tension members 9a are arranged on the center line A. Since the tension members 9a are arranged at positions shifted from the center line A in the facing direction of the first tension members 9a, the same effect can be obtained.

(Third embodiment)
Next, a third embodiment will be described. FIG. 3 is a cross-sectional view showing an optical fiber cable 1b according to the third embodiment. The optical fiber cable 1b has substantially the same configuration as the optical fiber cable 1a, but the arrangement of the foamed resin 13a is different.

In the optical fiber cable 1b, the foamed resin 13a is not exposed on the outer surface of the sheath 13. As shown in FIG. That is, the entire outer surface of the jacket 13 is made of non-foamed resin.

According to the third embodiment, effects similar to those of the first embodiment can be obtained. Moreover, since the foamed resin 13a is not exposed to the outer surface, the appearance is excellent, and damage to the foamed resin 13a can be suppressed.

(Fourth embodiment)
Next, a fourth embodiment will be described. FIG. 4 is a cross-sectional view showing an optical fiber cable 1c according to the fourth embodiment. The optical fiber cable 1c has substantially the same configuration as the optical fiber cable 1a, but the entire sheath 13 is made of foamed resin 13a. In other words, the non-foamed resin is not disposed on the outer cover 13, and the second tension member 9b is also covered with the foamed resin 13a.

According to the fourth embodiment, effects similar to those of the first embodiment can be obtained. Thus, if sufficient durability can be ensured, the entire jacket 13 may be made of the foamed resin 13a. By doing so, manufacturing is facilitated.

Various fiber optic cables with varying jacket configurations were evaluated. The optical fiber cables used for evaluation generally have the cross-sectional configuration shown in FIG. 2 (foamed resin is only in the vicinity of the first tension member) or FIG. 4 (foamed resin is the entire jacket). First, 12 optical fibers with a diameter of 200 μm were intermittently bonded to prepare a 12-core optical fiber ribbon. An optical fiber unit of 144 fibers was constructed by twisting 12 of these optical fiber ribbons.

Forty-eight optical fiber units of 144 fibers were supplied and twisted together, then a pressure winding was vertically attached, rolled with a forming jig, and then a nylon pressure thread was wound to prepare a core of 6912 fibers.

The core thus prepared, the tension member, and the tearing string for tearing the jacket are arranged straight along the length of the cable without being twisted, the jacket is extruded and coated, and after sheathing, it is cooled to about 20°C in a water bath. I made an optical fiber cable. The jacket material was LLDPE. The outer cover is extruded in two layers, and LLDPE containing a sodium bicarbonate-based foaming agent is used for the outer circumference of the first tension member. rice field.

The outer diameter of the optical fiber cable was 29.5 mm, and the thickness of the jacket was 4 mm. Here, as the tension members, there are four first tension members made of G-FRP (glass fiber reinforced resin) with a diameter of 2.0 mm and six members made of K-FRP (aramid fiber reinforced resin) with a diameter of 0.7 mm. A second tension member was used. Two first tension members made of G-FRP with a diameter of 2.0 mm are arranged at opposing positions, and a second tension member made of K-FRP with a diameter of 0.7 mm is placed between the first tension members. placed at equal intervals.

For each of the obtained optical fiber cables, the adhesion force between the tension member and the jacket was measured. The measuring method is as follows. First, a covering piece having a width of 20 mm and a length of 100 mm was cut out, including the first tension member, in the axial direction of the first tension member. Next, a sample was prepared by removing a 45 mm front and rear jacket from the outer periphery of the first tension member while leaving a 10 mm long jacket in the longitudinal direction. The exposed first tension member is passed through a drawing die with a hole of φ2.8 mm, pulled at a tensile speed of 500 mm / min with an Instron type tensile tester, and the maximum stress when it is pulled out is measured between the tension member and the outer cover. of the adhesion force. The adhesion force between the first tension member and the outer cover can be adjusted by setting manufacturing conditions such as the content of the foaming agent (expansion ratio) and the extrusion temperature of the outer cover. Also, the second tension member was passed through a drawing die having a hole of φ1.0 mm in the same manner as the first tension member, and the adhesion force between the tension member and the jacket was measured.

A bending test was performed to evaluate the layability. The bending test was conducted with respect to the bending direction with the center line forming an angle of 90 degrees with respect to the facing direction of the first tension member (the bending direction with the center line B in FIG. 2 as the bending center and the direction that is difficult to bend). Then, bending semicircular mandrels with radii of 600 mm, 300 mm and 200 mm were prepared, and the cable was wound around the mandrels by 180 degrees. At this time, the presence or absence of buckling of the first tension member was confirmed, and the case where no buckling was observed under all conditions was indicated by ○, the case where buckling occurred only under the condition of a radius of 200 mm was indicated by △, and other If buckling occurred under the conditions, it was marked as x.

Also, as an evaluation of temperature characteristics, an increase in transmission loss during a heat cycle test at -30 to 70°C was evaluated. 1000 m of cable is wound around a drum with a barrel diameter of 1400 mm, and the maximum increase in transmission loss with respect to the initial value at a wavelength of 1550 nm is obtained by repeating three cycles of temperature fluctuation in a constant temperature chamber with a temperature holding time of 6 hours and a temperature transfer time of 6 hours. It was measured. As a result, 0.15 dB/km or less was evaluated as ◯.

In addition, as an evaluation of mechanical properties, damage to the jacket during lateral pressure was confirmed. A load of 2200 N was applied to the outer cover having a length of 100 mm. In addition, the loss increase at a wavelength of 1550 nm was evaluated, and the maximum increase in transmission loss with respect to the initial value at a wavelength of 1550 nm was measured. As a result, a value of less than 0.10 dB/km was indicated by ◯, and a value of over 0.10 dB/km was indicated by Δ. Tables 1 and 2 show the results.

From the results, in all of Examples 1 to 8, normal manufacturing conditions (resin temperature of 185° C. or higher during extrusion, line speed of 10 m/min or higher) were used, but the adhesion between the first tension member and the outer cover was was able to be 70 N/10 mm or less. As a result, all of the temperature characteristics were evaluated as ◯, and the installability was evaluated as Δ or higher. In particular, Examples 2 to 8, in which the adhesion force between the first tension member and the outer cover was 50 N/10 mm or less, were evaluated as ◯ in terms of installation performance.

In Example 5, in which the foaming ratio of the foamed resin exceeds 60%, the adhesion between the first tension member and the outer cover is 10 N/10 mm or less, and the increase in loss under lateral pressure is evaluated as Δ. In addition, in Example 8, in which the entire outer cover and the foamed resin are used, the adhesion between the first tension member and the outer cover is 20 N/10 mm or less and the adhesion between the second tension member and the outer cover is 160 N/10 mm or less. The loss increase at the time of lateral pressure was evaluated as △. The other examples 1 to 4 and 6 to 7 also had good mechanical properties.

On the other hand, Comparative Examples 1 and 2 do not use foamed resin, so although there are some differences depending on the manufacturing conditions, the adhesion between the first tension member and the outer cover exceeds 70 N / 10 mm in both cases. Buckling was observed in the resistance, and it was evaluated as ×.

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, 1a, 1b, 1c... Optical fiber cable 3... Optical fiber cable 5... Core 7... Binder wrap 9a... First tension member 9b... Second tension member 11... ……Tear string 13 ……Outer cover 13a ……Foamed resin

Claims (4)

a core composed of a plurality of optical fiber core wires;
a first tension member provided at a portion facing the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable;
a plurality of second tension members disposed between the first tension members in the circumferential direction and having lower tensile rigidity than the first tension members;
a jacket provided to cover the core, the first tension member and the second tension member;
and
An optical fiber cable, wherein at least the jacket on the outer peripheral portion of the first tension member is made of foamed resin. 2. The optical fiber cable according to claim 1, wherein the jacket on the outer circumference of the second tension member is made of non-foamed resin. 2. The optical fiber cable according to claim 1, wherein the entire sheath is made of foamed resin. 4. The optical fiber cable according to any one of claims 1 to 3, wherein the expansion ratio of said foamed resin is 14% or more and 50% or less.

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