Fiber optic cable

Abstract

To provide an optical fiber cable excellent in both laying workability and handling properties.SOLUTION: An optical fiber cable 1 is constituted of a core 5, first tension members 9a, second tension members 9b, a sheath 13 and the like. The core 5 is composed of a plurality of coated optical fibers 3. A press-wrapping 7 is provided on an outer periphery of the core 5 (the plurality of coated optical fibers 3). The first tension members 9a are provided at portions opposed to each other with the core 5 as a center in a cross section perpendicular to a lengthwise direction of the optical fiber cable 1. Furthermore, the plurality of second tension members 9b are disposed between the first tension members 9a in a circumferential direction. The second tension member 9b is lower than the first tension member 9a in a tensile rigidity (shaft rigidity=axial force / axial deformation quantity). Moreover, it is preferable that an adhesion between the first tension members 9a and the sheath 13 is smaller than an adhesion between the second tension members 9b and the sheath 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber cable comprising a plurality of optical fiber cores. [Background technology]

[0002] The optical fiber cable used has a core made up of a large number of optical fiber cores, a tension member disposed around the core, and is covered with an outer jacket (see, for example, Patent Document 1).

[0003] In such optical fiber cables, a pair of tension members are arranged at opposing positions with the core at the center, so that the cable is easy to bend in a direction about the straight line connecting the tension members, but difficult to bend in other directions. In other words, optical fiber cables have a directional tendency to bend. In particular, the cable is most difficult to bend in a direction about the center line perpendicular to the straight line connecting the tension members.

[0004] In response to this, an optical fiber cable has been proposed in which tension members are arranged at opposing positions sandwiching the core, and similar tension members are arranged perpendicular to the line connecting these tension members (Patent Document 2). In other words, an optical fiber cable has been proposed in which tension members are arranged in mutually orthogonal directions sandwiching the core. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-109400 A [Patent Document 2] JP 2020-204752 A Summary of the Invention [Problem to be solved by the invention]

[0006] The optical fiber cable of Patent Document 2 has tension members arranged in the above-mentioned easy-to-bend direction, so it has high overall rigidity and is difficult to bend in either direction. For this reason, it cannot be wound around a small-diameter drum, and winding it around a drum that is larger than necessary requires excessive packaging. Furthermore, if it is forcibly wound around a small-diameter drum, there is a risk that the tension members will buckle. In contrast, if there is an easy-to-bend direction like the optical fiber cable of Patent Document 1, it can be wound around a smaller drum.

[0007] Here, several methods have been proposed for laying such an optical fiber cable in a pipeline. For example, as shown in Fig. 4, there is a method of inserting an optical fiber cable 101 into a pipeline 100 by air pressure feeding. In this method, the optical fiber cable 101 is inserted into the pipeline 100 from a pressure feeding head 105 via a caterpillar (registered trademark)-shaped propulsion unit 103. By feeding the optical fiber cable 101 with the propulsion unit 103 while feeding high-pressure air to the propulsion head 105 (arrow D in the figure), the optical fiber cable 101 can be pressure-fed into the pipeline 100 (arrow C in the figure).

[0008] However, optical fiber cables such as those described in Patent Document 1 are extremely prone to bending in directions around the straight line connecting the tension members as the bending center. If the tip of the optical fiber cable gets caught, for example, at a bent part of the pipeline during pumping, the optical fiber cable may become bent or wavy, causing it to become clogged inside the pipeline.

[0009] In contrast, the optical fiber cable of Patent Document 2 has tension members arranged in the direction in which the optical fiber cable is likely to bend, as mentioned above, so that the optical fiber cable has high overall rigidity and can prevent clogging of the optical fiber cable inside such a conduit.

[0010] On the other hand, there is also a method of inserting the optical fiber cable into the conduit using a towing rope. In this case, a rope for towing the optical fiber cable is laid in the conduit in advance, the optical fiber cable is connected to one end of the towing rope, and the towing rope is pulled from the other end of the conduit, thereby laying the optical fiber cable.

[0011] In such a method, the optical fiber cable may be laid in a plurality of continuous pipelines. In this case, first, as shown in Fig. 5(a), the optical fiber cable 101 is inserted into the first pipeline 100a using the towing rope 107 in the above-mentioned manner (arrow E in the figure). Then, as shown in Fig. 5(b), the optical fiber cable 101 is temporarily taken out of the pipeline (for example, above ground) between the first pipeline 100a and the second pipeline 100b, and the optical fiber cable 101 is taken out in a so-called "figure eight" manner. After the optical fiber cable 1 of a predetermined length is taken out of the first pipeline 100a, the optical fiber cable 101 is inserted into the second pipeline 100b in the same manner as described above.

[0012] However, if the cable is difficult to bend in all directions, as in the case of the optical fiber cable of Patent Document 2, it is difficult to perform this figure-of-eight arrangement. In contrast, if the cable has an easier-to-bend direction than one direction, as in the case of the optical fiber cable of Patent Document 1, it is possible to perform figure-of-eight arrangement, but if the directionality of the ease of bending is strong (i.e., if the bending rigidity in the easier-to-bend direction is too small), there is a risk that the cable will be easily bent below the allowable bending radius in the easier-to-bend direction. For this reason, it is necessary to work carefully so as not to bend below the allowable bending radius, which creates a problem of poor workability. Furthermore, if an attempt is made to bend the cable forcibly, there is a risk that the tension member will buckle.

[0013] As described above, there was no conventional optical fiber cable that was both easy to install and easy to handle (ease of winding onto a drum and ease of handling in a figure-eight configuration).

[0014] The present invention has been made in view of the above problems, and has an object to provide an optical fiber cable that is easy to install and easy to handle. [Means for solving the problem]

[0015] In order to achieve the above-mentioned object, the present invention provides an optical fiber cable comprising a core made of a plurality of optical fiber cores, first tension members provided at locations facing each other with respect to the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable, a plurality of second tension members arranged circumferentially between the first tension members and having a tensile stiffness lower than that of the first tension members, and an outer jacket provided to cover the core, the first tension member and the second tension member, wherein the adhesion force between the first tension member and the outer jacket is 50 N / 10 mm or less. The adhesive force between the second tension member and the outer sheath is greater than the adhesive force between the first tension member and the outer sheath. The optical fiber cable is characterized by the above.

[0016] It is desirable that the adhesive strength between the first tension member and the outer covering is 15N / 10mm or less. Also, it is desirable that the adhesive strength between the second tension member and the outer covering is 300N / 10mm or more.

[0017] The second tension member and the first tension member may be disposed at approximately equal intervals in a circumferential direction.

[0018] The second tension member and the first tension member may not be disposed at equal intervals in the circumferential direction, and the second tension member may be disposed unevenly in a direction perpendicular to the opposing direction of the first tension member.

[0019] A plurality of the first tension members may be arranged in each of the locations facing each other about the core, and at least some of the first tension members may be arranged at positions offset from a center line parallel to the facing direction of the first tension members.

[0020] According to the present invention, by arranging first tension members facing each other around the core and arranging second tension members having lower tensile stiffness than the first tension members between the first tension members in the circumferential direction, it is possible to reduce the ease of bending in the bending direction (hereinafter sometimes simply referred to as the "easy to bend direction") with the center line of the first tension members facing each other as the bending center. This increases the overall stiffness and makes it possible to suppress unintended bending of the optical fiber cable.

[0021] Also, since bending in the easy direction is relatively easier than bending directions centered on a center line perpendicular to the opposing direction of the first tension members (hereinafter sometimes simply referred to as "difficult direction to bend"), the optical fiber cable can be easily bent when winding it around a figure of eight or a drum. Also, since the ease of bending in the easy direction is reduced, excessive bending of the optical fiber cable in this direction can be suppressed.

[0022] That is, the present invention increases the rigidity in the easy bending direction to make it harder to bend compared to the optical fiber cable of Patent Document 1, and intentionally provides a directionality that is relatively easier to bend compared to the hard to bend direction compared to the optical fiber cable of Patent Document 2. In this way, according to the present invention, by appropriately balancing the ease of bending in mutually perpendicular directions, it is possible to achieve both the advantages of the conventional optical fiber cables of Patent Documents 1 and 2.

[0023] Furthermore, by setting the adhesion between the first tension member, which has particularly high tensile stiffness, and the jacket to a predetermined value or less, the restraining force that the first tension member receives from the jacket can be reduced when the optical fiber cable is bent in a direction that makes it difficult to bend, causing a misalignment between the tension member and the jacket, thereby preventing localized strain from being applied to the first tension member and causing buckling, thereby preventing damage to the optical fiber cable when it is being pumped or wound.

[0024] Furthermore, by setting the adhesion between the first tension member and the outer jacket at a predetermined level or less, the first tension member cannot suppress the expansion and contraction of the outer jacket in response to changes in environmental temperature, which raises concerns about loss fluctuations in the optical fiber stored within the jacket. However, by maintaining close adhesion between the second tension member and the outer jacket, the second tension member suppresses the expansion and contraction of the outer jacket, thereby stabilizing the characteristics.

[0025] Furthermore, if the second tension member and the first tension member are disposed at equal intervals in the circumferential direction, the direction of the ease of bending caused by the second tension member can be changed gradually.

[0026] In addition, by disposing the second tension members unevenly in a direction perpendicular to the opposing direction of the first tension members, rather than disposing the second tension members at equal intervals in the circumferential direction, the difference in ease of bending between the easy and difficult directions can be reduced. In other words, the bending rigidity in the easy direction can be easily adjusted by disposing the second tension members.

[0027] In addition, by arranging a plurality of first tension members at each of the opposing portions of the core, and arranging each of the first tension members at a position offset from the center line in the opposing direction, it is possible to reduce the bending ease of the center line of the opposing direction of the first tension members in the bending direction (i.e., the direction in which it is easy to bend), thereby making it possible to reduce the difference in bending ease between the easy and difficult directions. Effect of the Invention

[0028] According to the present invention, an optical fiber cable that is excellent in installation workability and handleability can be provided. [Brief description of the drawings]

[0029] [Figure 1] 1 is a cross-sectional view of an optical fiber cable 1. [Diagram 2]FIG. 2 is a cross-sectional view of the optical fiber cable 1a. [Diagram 3] FIG. 3 is a cross-sectional view of the optical fiber cable 1b. [Figure 4] FIG. 1 is a diagram showing an example of a conventional method for installing an optical fiber cable 101. [Diagram 5] 13(a) and 13(b) are diagrams showing another conventional method for installing an optical fiber cable 101. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] (First embodiment) Hereinafter, an embodiment of the first invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view of an optical fiber cable 1. The optical fiber cable 1 is a slotless type cable that does not use a slot, and is composed of a core 5, a first tension member 9a, a second tension member 9b, an outer jacket 13, etc.

[0031] The core 5 is made of a plurality of optical fiber cores 3. More specifically, the plurality of optical fiber cores 3 are twisted together to form an optical fiber unit, and the plurality of optical fiber units are further twisted together to form the core 5. Note that the optical fiber cores 3 may be, for example, an intermittently bonded optical fiber ribbon core that is bonded intermittently in the longitudinal direction.

[0032] As shown in Fig. 1, a pressure wrap 7 is provided around the outer periphery of the core 5 (plurality of optical fiber cores 3). The pressure wrap 7 is a tape-like member, a nonwoven fabric, or the like, and is arranged, for example, by vertical splicing to cover the outer periphery of the core 5 as a whole. That is, the pressure wrap 7 is vertically spliced ​​around the outer periphery of the core 5 so that 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 the circumferential direction of the optical fiber cable 1. Note that the pressure wrap 7 is not necessarily required, and the pressure wrap 7 may be referred to as the core 5.

[0033] In a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, first tension members 9a are provided at locations facing each other with the core 5 at the center. In addition, a plurality of second tension members 9b are arranged between the first tension members 9a in the circumferential direction. The second tension members 9b have a lower tensile rigidity (axial rigidity = axial force / axial deformation amount) than the first tension members 9a. For example, the diameter (cross-sectional area) of each of the first tension members 9a is larger than the diameter (cross-sectional area) of each of the second tension members 9b.

[0034] The first tension member 9a and the second tension member 9b bear the tension of the optical fiber cable 1. The first tension member 9a mainly bears the tension of the optical fiber cable 1, and the second tension member 9b secondarily bears the tension of the optical fiber cable 1. The material of the first tension member 9a and the second tension member 9b is not particularly limited, and for example, fiber reinforced plastic (FRP) made of aramid fiber, glass fiber, etc. can be used. The first tension member 9a and the second tension member 9b may be made of different materials.

[0035] In the illustrated example, three second tension members 9b are arranged between each pair of first tension members 9a in the circumferential direction. That is, a total of six second tension members 9b are arranged between each pair of first tension members 9a in the circumferential direction. Note that it is preferable that the total cross-sectional area of ​​the first tension members 9a is larger than the total cross-sectional area of ​​the second tension members 9b, and further, the cross-sectional area of ​​each of the first tension members 9a may be larger than the total cross-sectional area of ​​the second tension members 9b.

[0036] The second tension members 9b and the first tension members 9a are arranged at approximately 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 and adjacent first tension members and second tension members 9b are respectively arranged at intervals of approximately 45°. The number of second tension members 9b is not particularly limited.

[0037] Furthermore, a tear cord 11 is provided at a different circumferential position from the first tension member 9a and the second tension member 9b, at a position facing each other with the core 5 in between. Furthermore, an outer jacket 13 is provided on the outer periphery of the core 5. The first tension member 9a, the second tension member 9b and the tear cord 11 are embedded in the outer jacket 13. That is, the outer jacket 13 is provided so as to cover the core 5 (plurality of optical fiber cores 3), the first tension member 9a, the second tension member 9b, etc. The outer shape of the outer jacket 13 is approximately circular. The outer jacket 13 is, for example, a polyolefin-based resin.

[0038] It is preferable that the adhesion force between the first tension member 9a and the outer sheath 13 is smaller than the adhesion force between the second tension member 9b and the outer sheath 13. For example, the adhesion force between the first tension member 9a and the outer sheath 13 is preferably 50 N / 10 mm or less, and more preferably 15 N / 10 mm or less.

[0039] By doing so, when the optical fiber cable 1 is bent in a direction that is difficult to bend, the restraining force that the first tension member 9a receives from the jacket 13 can be reduced, and misalignment can be generated between the tension member and the jacket. This makes it possible to suppress the occurrence of buckling of the first tension member 9a. Meanwhile, because the second tension member 9b and the jacket 13 are in close contact with each other, it is possible to suppress loss fluctuations caused by expansion and contraction of the jacket 13 in response to changes in environmental temperature, and to stabilize characteristics.

[0040] Here, the optical fiber cable 1 is easiest to bend in the direction (up and down in the figure) about the center line (center line A in the figure) parallel to the opposing direction of the first tension member 9a, and is difficult to bend in other directions (for example, center line B perpendicular to center line A).

[0041] In this case, a conventional optical fiber cable without a second tension member (see, for example, Patent Document 1) In comparison with the optical fiber cable 1, the bending stiffness in the easy bending direction is reduced (i.e., it becomes harder to bend) by the second tension member 9b. That is, the bending stiffness in the easy bending direction can be increased.

[0042] On the other hand, compared to an optical fiber cable in which the first tension members 9a are opposed to each other in mutually orthogonal directions to make it difficult to bend in either direction (for example, the optical fiber cable of Patent Document 2), the optical fiber cable 1 has directions in which it is difficult to bend and directions in which it is easy to bend. That is, the optical fiber cable 1 is relatively easier to bend in the direction around the center line A as compared to other directions, and is therefore an easy direction to bend.

[0043] As described above, according to the present embodiment, since the bending rigidity in the conventional direction in which the cable is easily bent can be increased, bending of the optical fiber cable during, for example, pumping and the resulting clogging can be suppressed. Also, when performing figure-of-eight winding, bending of the optical fiber cable beyond the allowable bending radius can be suppressed.

[0044] Furthermore, when winding the optical fiber cable around a drum or the like, the optical fiber cable can be bent in the direction in which it is easiest to bend and then wound around the drum or the like, which prevents the size of the drum or the like from increasing. In this way, by using different tension members in combination, while leaving both the easy-to-bend direction and the hard-to-bend direction, and by improving the bending rigidity in the easy-to-bend direction, it is possible to obtain an optical fiber cable that is easy to handle and easy to install, by appropriately balancing the ease of bending depending on the direction.

[0045] Furthermore, since the second tension members 9b are disposed at approximately equal intervals in the circumferential direction, the direction of the ease of bending caused by the second tension members 9b can be changed gradually.

[0046] 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 the following description, the same reference numerals as in Fig. 1 are used for configurations having the same functions as those in the first embodiment, and duplicated descriptions will be omitted.

[0047] The optical fiber cable 1a has a configuration similar to that of the optical fiber cable 1, but the shape of the first tension member 9a is different. In the optical fiber cable 1 described above, the two first tension members 9a are arranged one on each side of the core 5, but in the optical fiber cable 1a, a total of four first tension members 9a are arranged two on each side of the core 5.

[0048] In each portion, the first tension members 9a are disposed with gaps in the circumferential direction. In this manner, by disposing the multiple first tension members 9a at positions facing each other with the core 5 at the center and spaced apart in the circumferential direction, the first tension members 9a can be disposed at positions shifted from the center line A that is parallel to the facing direction of the first tension members 9a.

[0049] Even in this case, the cross-sectional area of ​​each of the first tension members 9a is larger than the cross-sectional area of ​​each of the second tension members 9b. Furthermore, the cross-sectional area of ​​each of the first tension members 9a may be larger than the total cross-sectional area of ​​the second tension members 9b. Even in this case, the tensile stiffness of each of the first tension members 9a is larger than the tensile stiffness of each of the second tension members 9b. Furthermore, the tensile stiffness of each of the first tension members 9a may be larger than the sum of the tensile stiffnesses of the second tension members 9b.

[0050] Here, normally, when a member is bent, the outside of the bend undergoes tensile deformation and the inside of the bend undergoes compressive deformation, but the bending center line serves as the neutral axis of tension and compression. 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 bending direction with the center line A of the opposing direction of the first tension member 9a as the bending center is the direction in which the optical fiber cable 1a is easy to bend. In other words, by arranging the first tension member 9a on the center line A as in the optical fiber cable 1 described above, it is possible to minimize the improvement in bending rigidity due to the first tension member 9a with respect to bending in this direction, and it becomes easy to bend in that direction.

[0051] On the other hand, in the optical fiber cable 1a, the first tension member 9a is disposed at a position offset from the center line A, and therefore the first tension member 9a has a greater effect on the bending rigidity than the optical fiber cable 1. That is, by disposing the first tension member 9a at a position offset from the center line A, the bending rigidity in the bending direction around the center line A is improved, and the effect of disposing the second tension member 9b can be further complemented.

[0052] When multiple first tension members 9a are arranged in each location, the central position in the circumferential direction is taken as the representative position of the first tension members 9a. For example, when three second tension members 9b are arranged between each of the first tension members 9a, the arrangement angle between the first tension members 9a (representative positions of the first tension members 9a) and the second tension members 9b is 45°.

[0053] According to the second embodiment, it is possible to obtain the same effect as the first embodiment. In addition, by arranging a plurality of first tension members 9a at positions facing each other with respect to the core 5 as the center, and arranging the first tension members 9a at positions shifted from the center line A, it is possible to improve the bending rigidity in the direction in which it is easy to bend. Note that, even in this embodiment, even when combined with the effect of improving the bending rigidity by the second tension members 9b, the bending rigidity in the bending direction about the center line A as the bending center is lower than the bending rigidity in the bending direction about the center line B perpendicular to the center line A as the bending center, so this direction remains the direction in which it is easy to bend.

[0054] If there is an even number of first tension members 9a arranged in each opposing position, the straight line connecting their centers in the circumferential direction should be taken as the opposing direction center line A. If there is an odd number of first tension members 9a arranged in each opposing position, the straight line connecting the central first tension members 9a should be taken as the opposing direction center line A. However, if three or more first tension members 9a are arranged in each location, they should be arranged at equal intervals.

[0055] In this way, when there is an odd number of first tension members 9a arranged in each opposing position, 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 each arranged at a position shifted from the center line A in the opposing direction of the first tension members 9a, thereby obtaining a similar effect.

[0056] (Third embodiment) Next, a third embodiment will be described. Fig. 3 is a cross-sectional view showing an optical fiber cable 1a according to the third embodiment. The optical fiber cable 1b has a configuration substantially similar to that of the optical fiber cable 1a, but the arrangement of the second tension members 9b is different. In the optical fiber cables 1 and 1a described above, the second tension members 9b and the first tension members 9a are arranged at equal intervals in the circumferential direction. For example, when three second tension members 9b are arranged between each of the first tension members 9a, the arrangement angle between the second tension members 9b and the arrangement angle between the first tension member 9a and the second tension members at both ends are both about 45°.

[0057] However, in the optical fiber cable 1b of this embodiment, the second tension members 9b and the first tension members 9a are not arranged at equal intervals, but the second tension members 9b are arranged unevenly in a direction perpendicular to the opposing direction of the first tension members 9a (position F in the figure). For example, when three second tension members 9b are arranged between each of the first tension members 9a, the angle between the second tension members 9b is about 30°, and the angle between the first tension member 9a and the second tension members at both ends is about 60°.

[0058] As described above, the effect of improving the bending rigidity in the bending direction about the center line A increases with increasing distance from the center line A. For this reason, by disposing the second tension members 9b unevenly in a direction perpendicular to the opposing direction of the first tension members 9a, the bending rigidity can be efficiently improved in the direction in which the optical fiber cable 1b is easy to bend.

[0059] According to the third embodiment, it is possible to obtain the same effects as those of the first embodiment. In addition, by disposing the second tension members 9b unevenly in a direction perpendicular to the opposing direction of the first tension members 9a, it is possible to efficiently improve the bending rigidity in the direction in which the optical fiber cable 1b is easily bent.

[0060] Incidentally, in this embodiment, even if the bending rigidity is improved by offsetting the second tension member 9b, the bending rigidity in the bending direction about the center line A is lower than the bending rigidity in the bending direction about the center line B perpendicular to the center line A, and therefore the bending rigidity remains in the direction in which it is easier to bend. EXAMPLES

[0061] Various optical fiber cables with different tension member configurations were evaluated. The optical fiber cables used for the evaluation had a cross-sectional shape generally shown in Figure 2. First, 12 optical fibers with a diameter of 200 μm were intermittently bonded to create a 12-core optical fiber ribbon. These 12 optical fiber ribbons were twisted together and wrapped with a 2 mm wide plastic ribbon to create a 144-core optical fiber unit.

[0062] Forty-eight 144-core optical fiber units were supplied and twisted into four layers in a 2-9-15-22 arrangement from the center. Absorbent nonwoven fabric was then added vertically, the fiber was rolled using a forming jig, and nylon pressure thread was wrapped around it to create a 6,912-core core.

[0063] The core, tension member, and rip string for ripping the jacket were arranged straight along the length of the cable without twisting, and then cylindrically sheathed with jacket material to create an optical fiber cable. Here, the tension members used were four first tension members made of G-FRP (glass fiber reinforced plastic) with a diameter of 2.0 mm, and a given number of second tension members made of K-FRP (aramid fiber reinforced plastic) with a diameter of 0.5 mm.

[0064] The outer jacket material was LLDPE. The outer diameter of the optical fiber cable was 30 mm, and the inner diameter (core outer diameter) was 22 mm. Two first tension members made of φ2.0 mm G-FRP were placed in opposing positions, and two second tension members made of φ0.5 mm K-FRP were placed at equal intervals between the first tension members. By varying the number of second tension members, the possible pumping distance, bending rigidity, and the drum diameter that can be wound with a winding tension of 30 kg were compared.

[0065] The pumping test was carried out using a Gulfstream 400XL from Condux International, with an air pressure of 100 psi and the air being pumped through a 2-inch HDPE duct. A 2000m length of 2-inch duct was prepared, with bending at a radius of R = 2000 mm every 400m. Three tests were carried out, and the one with the shortest pumping distance was adopted as the possible pumping distance.

[0066] The bending stiffness was measured in accordance with IEC 60794-1-21 E17A. The test was performed with a jig interval of 500 mm, a pressure speed of 200 mm / min, and a displacement of 10 mm. The bending stiffness was evaluated in two directions: the bending direction with the opposing direction of the first tension member as the center line (the bending direction with the center line A in Figure 2 as the bending center and the bending direction that is easy to bend) and the bending direction with the center line B perpendicular to this as the bending center (the bending direction that is difficult to bend).

[0067] To determine which drums were suitable for winding, the optical fiber cable was wound around each size drum, and the drum that had a strong rebound when wound and no gaps between the body and the cable was determined to be suitable for winding. The smallest size drum on which the cable could be wound was determined to be the minimum drum diameter that could be used for winding.

[0068] The adhesion between the first tension member and the outer jacket was measured as follows. First, a piece of the outer jacket including the first tension member was cut out with a width of 20 mm and a length of 100 mm in the axial direction of the first tension member. Next, a sample was created by removing 45 mm of the outer jacket from the front and rear of the outer jacket, leaving 10 mm of the outer jacket in the longitudinal direction. The exposed first tension member was passed through a drawing die with a φ2.8 mm hole and pulled at a tensile speed of 500 mm / min with an Instron tensile tester, and the maximum stress when pulled out was taken as the adhesion between the tension member and the outer jacket. The adhesion between the first tension member and the outer jacket can be adjusted by setting the manufacturing conditions such as the extrusion temperature of the outer jacket and the application of a lubricant to the outer periphery of the first tension member. The second tension member was also passed through a drawing die with a φ1.0 mm hole in the same manner as the first tension member, and the adhesion between the tension member and the outer jacket was measured.

[0069] The bending tests were performed by preparing semicircular mandrels with radii of 600 mm and 300 mm and winding the cable 180 degrees around the mandrels in a bending direction centered on a line that forms a 90 degree angle with the facing direction of the first tension member (a bending direction with the bending center at center line B in Figure 2, which is a direction that is difficult to bend).The first tension member was checked for buckling at this time, and those that buckled were marked with an X, and those that did not buckle were marked with an O.

[0070] Additionally, the increase in transmission loss during heat cycle testing from -30 to 70°C was evaluated. 1000m of cable was wound around a drum with a body diameter of 1400mm, and temperature fluctuations were repeated in a thermostatic chamber for 3 cycles with a temperature holding time of 6 hours and a temperature movement time of 6 hours. The maximum increase in transmission loss at a wavelength of 1550nm compared to the initial value was measured. Results of 0.15dB / km or less were marked as ◯, and results exceeding 0.15dB / km were marked as ×. The results are shown in Table 1.

[0071] [Table 1]

[0072] In all of Examples 1 to 3, eight second tension members were arranged (that is, four between each of the first tension members), and the arrangement interval between the first tension members and the second tension members was always 36°.

[0073] On the other hand, in Comparative Example 1, like Example 1, eight second tension members were arranged, and all of the arrangement intervals between the first and second tension members were 36°. In Comparative Example 2, six second tension members were arranged (i.e., three between each pair of first tension members), and all of the arrangement intervals between the first and second tension members were 45° (i.e., the same as in FIG. 2). In Comparative Example 3, four second tension members were arranged (i.e., two between each pair of first tension members), and all of the arrangement intervals between the first and second tension members were 60°.

[0074] The results showed that in Examples 1 to 3 and Comparative Examples 1 to 3, in which the second tension member was added, the bending rigidity increased and pumping of 1000 m or more was possible. In addition, in Examples 1 to 3 and Comparative Examples 1 to 3, it was possible to wind the wire around a drum with a diameter of 1000 mm.

[0075] On the other hand, although the results are omitted, in optical fiber cables that do not have a second tension member, simply increasing the bending rigidity of the optical fiber cable in order to extend the pumpable distance significantly increases the minimum drum diameter that can be wound around it. Also, because the bending rigidity is too large, it is difficult to wind the cable in a figure-eight pattern. In response to this, by using the second tension member to appropriately adjust the bending rigidity in the direction that is easiest to bend, it is possible to achieve both ease of installation and ease of handling.

[0076] The adhesion force between the second tension member and the outer sheath was 300N / 10mm or more, which was higher than the adhesion force between the first tension member and the outer sheath.

[0077] In addition, in Examples 1 to 3 in which the adhesion between the first tension member and the outer jacket is 50 N / 10 mm or less, no buckling of the first tension member was observed in a bending test at a radius of 600 mm. Furthermore, in Examples 1 and 2 in which the adhesion between the first tension member and the outer jacket is 15 N / 10 mm or less, no buckling of the first tension member was observed in a bending test at a radius of 300 mm. Even when the adhesion between the first tension member and the outer jacket is low, the increase in transmission loss during the heat cycle is kept below a specified level due to the adhesion between the second tension member and the outer jacket.

[0078] On the other hand, in all of Comparative Examples 1 to 3, in which the adhesive strength between the first tension member and the jacket exceeded 50 N / 10 mm, buckling of the first tension member was observed in the bending test at a radius of 600 mm.

[0079] Although the embodiment of the present invention has been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the above-described embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0080] 1, 1a, 1b...optical fiber cable 3: Optical fiber core 5. Core 7………Press and roll 9a………First tension member 9b………Second tension member 11...Tear cord 13……Outer cover 100, 100a, 100b……Pipeline 101: Optical fiber cable 103……Promotion Department 105.... Pumping head 107………Towing rope

Claims

1. A core made up of a plurality of optical fiber cores; a first tension member provided at a position 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 a tensile stiffness lower than that of the first tension members; an outer cover provided to cover the core, the first tension member, and the second tension member; Equipped with the adhesion strength between the first tension member and the outer covering is 50 N / 10 mm or less, 2. An optical fiber cable according to claim 1, wherein the adhesion between said second tension member and said outer sheath is greater than the adhesion between said first tension member and said outer sheath.

2. 2. The optical fiber cable according to claim 1, wherein the adhesion strength between the first tension member and the outer sheath is 15 N / 10 mm or less.

3. An optical fiber cable as described in claim 1 or claim 2, characterized in that the adhesion strength between the second tension member and the outer sheath is 300 N / 10 mm or more.

4. 4. The optical fiber cable according to claim 1, wherein the second tension member and the first tension member are arranged at approximately equal intervals in the circumferential direction.

5. 4. The optical fiber cable according to claim 1, wherein the second tension member and the first tension member are not arranged at equal intervals in the circumferential direction, and the second tension member is arranged unevenly in a direction perpendicular to the opposing direction of the first tension member.

6. 6. The optical fiber cable according to claim 1, wherein a plurality of the first tension members are arranged at each of the locations facing each other about the core, and at least some of the first tension members are arranged at positions offset from a center line parallel to the facing direction of the first tension members.

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