Fiber optic cable

Abstract

To provide an optical fiber cable capable of suppressing projection of a cable core from a sheath of an optical fiber cable.SOLUTION: A cable core 15 has a nearly circular outer shape and includes: a core part 4 composed of a plurality of coated optical fibers 3; a press-wrapping member 7 wound on an outer periphery of the core part 4; and a pressing string 19 for pressing the press-wrapping member 7 from an outer periphery thereof. Tension members 9 are provided on both sides of the cable core 15 in a sectional view perpendicular to a lengthwise direction of the cable core 15. A sheath 13 is provided to cover the cable core 15, the tension members 9, and the like. An inner surface of the sheath 13 is not smooth, and irregularities are formed on an inner surface side of the sheath 13.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a slotless optical fiber cable. [Background technology]

[0002] In recent years, rapid advances in cloud computing technology have made it possible to process larger volumes of information, and there is a strong demand for higher density optical fiber cables connecting data centers (DCs) that process this information.

[0003] An example of such an optical fiber cable is an optical fiber cable in which an optical fiber unit is formed by twisting together intermittent ribbon cores, which are advantageous for increasing the density of optical fibers, and this optical fiber unit is further twisted to form a cable core, which is then covered with an outer jacket in which a tension member is embedded.

[0004] However, when such an optical fiber cable is laid, there is a risk that the cable core may protrude due to shrinkage of the optical fiber cable jacket after laying, which makes it difficult to lay the optical fiber cable properly.

[0005] In response to this, an optical fiber cable has been proposed in which the optical fiber core is covered with an outer jacket consisting of an inner sheath and an outer sheath, and two or more winding tapes are arranged between the inner sheath and the outer sheath, so that the coefficient of friction between the top winding tape in contact with the outer sheath is greater than the coefficient of friction between the bottom winding tape in contact with the inner sheath, and between the winding tapes themselves (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-11019 Summary of the Invention [Problem to be solved by the invention]

[0007] In an optical fiber cable such as that described in Patent Document 1, when the outer sheath attempts to shrink, wrinkles are generated in the winding tape that is not in contact with the outer sheath, which acts to increase the frictional force between the outer sheath and the winding tape that is in contact with it with a large frictional force, thereby suppressing the protrusion of the inner sheath.

[0008] However, the optical fiber cable of Patent Document 1 requires a double-layered sheath and two types of winding tape with different friction coefficients, which increases the number of parts and complicates the process, resulting in increased manufacturing costs.

[0009] The present invention has been made in view of the above problems, and has an object to provide an optical fiber cable that can suppress the cable core from protruding from the outer sheath of the optical fiber cable. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the present invention provides a cable comprising a cable core, tension members provided on both sides of the cable core in a cross section perpendicular to the longitudinal direction of the cable core, and an outer jacket provided to cover the tension members and the cable core, wherein the cable core has a core portion consisting of a plurality of optical fiber cores, a holding winding member wound around the outer periphery of the core portion, and a holding string that holds down the holding winding member from the outer periphery, and the inner surface of the outer jacket has unevenness. The concave-convex shape includes a first concave-convex shape formed continuously along the shape of the holding string, and in a predetermined length of the optical fiber cable, the ratio of the area where the first concave-convex shape is formed to the inner area of ​​the jacket is 0.5% or more and 2.0% or less, and the depth of the first concave-convex shape is 0.01 mm or more and 0.09 mm or less. The optical fiber cable is characterized by the above.

[0013] The concave-convex shape may include a second concave-convex shape that is a transfer of the concave-convex shape of the outer surface of the holding wrapping member.

[0014] In an optical fiber cable of a predetermined length, the ratio of the area where the second uneven shape is formed to the inner area of ​​the jacket may be 90% or more and 99.5% or less.

[0016] It is desirable that the cable core has a pull-out force of 2.5 kgf or more. It is desirable that the depth of the second uneven shape be 0.01 mm or more and 0.05 mm or less.

[0017] According to the present invention, the inner surface of the sheath that covers the cable core is formed with a concave-convex shape, which acts as a resistance to the movement of the cable core in the longitudinal direction of the optical fiber cable, thereby preventing the cable core from protruding from the sheath. In this case, there is no need for multiple layers of the sheath, and there is no need for multiple types of winding tape, so the number of parts does not increase compared to a normal optical fiber cable.

[0018] For example, if the first uneven shape is formed continuously along the shape of the holding string, the uneven shape can be easily formed, and the uneven shape can be formed spirally in the longitudinal direction, thereby efficiently suppressing the protrusion of the cable core.

[0019] In this case, if the ratio of the area where the first uneven shape is formed to the inner area of ​​the jacket is 0.5% or more and 2.0% or less, the effect of suppressing the cable core from protruding can be more reliably obtained.

[0020] Furthermore, if the second uneven shape is formed by transferring the uneven shape of the outer surface of the pressure winding member, the uneven shape can be easily formed and can be formed over a wide area, thereby efficiently suppressing the protrusion of the cable core.

[0021] In this case, if the ratio of the area where the second uneven shape is formed to the inner area of ​​the jacket is 90% or more and 99.5% or less, the effect of suppressing the cable core from protruding can be more reliably obtained.

[0022] Furthermore, by setting the height of the unevenness of the uneven shape to 0.01 mm or more, it is possible to efficiently obtain the effect of suppressing the protrusion of the cable core.

[0023] Furthermore, if the cable core pull-out force is 2.5 kgf or more, protrusion of the cable core can be more reliably prevented. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an optical fiber cable that can suppress the cable core from protruding from the outer sheath of the optical fiber cable. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view of an optical fiber cable 1. FIG. [Figure 2] FIG. [Figure 3] 1 is a development view of the inner surface of the outer cover 13. [Figure 4] 1A is an enlarged view of part A in FIG. 1, and FIG. 1B is a developed view of the inner surface of the outer jacket 13. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view of an optical fiber cable 1. The optical fiber cable 1 is a slotless cable that does not use a slot, and is composed of a cable core 15, a tension member 9, an outer jacket 13, etc.

[0027] The cable core 15 has a substantially circular outer shape and includes a core portion 4 made up of a plurality of optical fiber cores 3, a pressure winding member 7 wound around the outer periphery of the core portion 4, and a pressure string 19 that holds the pressure winding member 7 from the outer periphery. The core portion 4 is formed by twisting together a plurality of optical fiber units 5. The optical fiber unit 5 is also formed by twisting together a plurality of optical fiber cores 3. The optical fiber cores 3 can be, for example, intermittently bonded optical fiber ribbons that are bonded intermittently in the longitudinal direction.

[0028] A pressure winding member 7 is wound around the outer periphery of the core portion 4. The pressure winding member 7 is a tape-like member, a nonwoven fabric, or the like, and is arranged, for example, by longitudinal wrapping to collectively cover the outer periphery of the core portion 4. That is, the pressure winding member 7 is longitudinally wrapped around the outer periphery of the plurality of optical fiber units 5 so that the longitudinal direction of the pressure winding member 7 substantially coincides with the axial direction of the optical fiber cable 1 and the width direction of the pressure winding member 7 coincides with the circumferential direction of the optical fiber cable 1.

[0029] 2 is a side view of the cable core 15. As described above, the holding cord 19 is wound around the outer periphery of the holding winding member 7 to prevent the opening of the overlapping portion of the holding winding member 7. The holding cord 19 is wound around the outer periphery of the holding winding member 7 in a spiral shape in the longitudinal direction.

[0030] In a cross section perpendicular to the longitudinal direction of the cable core 15, tension members 9 are provided on both sides of the cable core 15. That is, a pair of tension members 9 are provided at positions facing each other with the cable core 15 in between. In addition, tear cords 11 are provided in a direction approximately perpendicular to the facing direction of the tension members 9 so as to face each other with the cable core 15 in between.

[0031] An outer sheath 13 is provided on the outer periphery of the cable core 15. The tension members 9 and the tear cord 11 are embedded in the outer sheath 13. In other words, the outer sheath 13 is provided so as to cover the cable core 15, the tension members 9, etc. The outer shape of the outer sheath 13 is approximately circular. The outer sheath 13 is made of, for example, a polyolefin-based resin.

[0032] 1, recesses 17 corresponding to the thickness of the holding string 19 are formed on the inner surface of the outer cover 13. In other words, the inner surface of the outer cover 13 is not smooth, and unevenness is formed on the inner surface side of the outer cover 13.

[0033] 3 is a diagram showing the outer jacket 13 unfolded and illustrating the inner surface of the outer jacket 13. As described above, recesses 17, which are the first uneven shape, are formed on the inner surface of the outer jacket 13. The recesses 17 are formed at predetermined intervals diagonally relative to the longitudinal direction.

[0034] Here, in an optical fiber cable 1 of a predetermined length, it is desirable that the ratio of the area where the first uneven shape (depression 17) is formed to the inner area of ​​the outer sheath 13 (length of the optical fiber cable 1 x inner circumference length of the outer sheath 13) (hereinafter simply referred to as the area ratio of the depression 17) be 0.5% or more and 2.0% or less.

[0035] The area ratio of the recesses 17 varies depending on, for example, the width and angle (pitch) of the recesses 17. For example, when the angle of the recesses 17 (the angle relative to the direction perpendicular to the longitudinal direction (the vertical direction in the drawing, which is the circumferential direction of the cable core)) becomes smaller, the pitch of the recesses 17 relative to the longitudinal direction becomes shorter, and this increases the area ratio of the recesses 17. Also, when the angle of the recesses 17 becomes larger, the pitch of the recesses 17 relative to the longitudinal direction becomes longer, and this decreases the area ratio of the recesses 17.

[0036] As described above, the recesses 17 are formed at an angle corresponding to the winding angle of the pressure cord 19. Therefore, by shortening the winding pitch of the pressure cord 19, the area ratio of the recesses 17 can be increased. In other words, the area ratio of the recesses 17 can be adjusted appropriately.

[0037] In this case, if the area ratio of the recesses 17 is less than 0.5%, the effect of the recesses 17 is small. On the other hand, if the area ratio of the recesses 17 exceeds 2.0%, as mentioned above, the winding pitch of the pressure string becomes small, which deteriorates manufacturability. For this reason, it is desirable that the area ratio of the recesses 17 be 0.5% or more and 2.0% or less.

[0038] Furthermore, it is desirable that the depth of recess 17 is 0.01 mm or more. If the depth of recess 17 is 0.01 mm or more, the effect of suppressing longitudinal movement of the cable core can be more reliably obtained.

[0039] Next, a method for forming the uneven shape (recesses 17) on the inner surface of the jacket 13 will be described. Conventional optical fiber cables do not form recesses 17 as shown in FIG. 3, even when a holding string 19 is used. For example, immediately after the jacket 13 is extrusion-molded, both the inner and outer surfaces are smooth and approximately circular. Therefore, when the jacket 13 is water-cooled immediately after this, the jacket 13 hardens while substantially maintaining the shape formed by the mold. As a result, the inner surface of the jacket 13 becomes approximately smooth.

[0040] In contrast to this, for example, if the extrusion temperature of the jacket 13 is set higher and the time from extrusion to cooling in a water bath is lengthened, the shape formed by the mold gradually deforms and conforms to the inner shape of the cable core 15. As a result, the slight unevenness of the holding cord 19 is transferred to the inner surface of the jacket 13, and an uneven shape can be formed on the inner surface side of the jacket 13.

[0041] The uneven shape may be formed by other methods. For example, the inner diameter of the die used to extrude the outer jacket 13 may be designed in advance to be smaller than the outer diameter of the cable core 15, and the outer jacket 13 may be pressed against the holding cord 19 to transfer the uneven shape. In this way, the method of forming the uneven shape is not limited to the above-mentioned method, and is not particularly limited.

[0042] As described above, the recess 17 can be formed more reliably by strongly pressing the jacket 13 against the cable core 15 (holding cord 19), but if the jacket 13 is pressed too strongly against the cable core 15, there is a risk of increasing the lateral pressure on the internal optical fiber 3. In other words, if the cable core 15 is pressed too strongly by the jacket 13, and the depth of the recess 17 on the inner surface of the jacket 13 is made too deep, there is a risk of increasing the lateral pressure on the internal optical fiber 3. For this reason, it is desirable that the depth of the recess 17 be, for example, 0.09 mm or less.

[0043] Furthermore, if the holding cord 19 is thin and has a substantially circular cross section, the holding cord 19 will be embedded inside the outer sheath 13 when the outer sheath 13 is extruded, similar to the tear cord 11, making it difficult to form an uneven shape on the inner surface of the outer sheath 13. As a result, there is almost no increase in the friction force between the cable core 15 and the outer sheath 13. For this reason, it is desirable that the holding cord 19 be a tape-like member having a certain width (for example, about 2 mm).

[0044] As described above, by forming the first uneven shape (spiral recess 17) on the inner surface side of outer sheath 13, the friction between cable core 15 and outer sheath 13 increases, and protrusion of cable core 15 can be suppressed.

[0045] The uneven shape formed on the inner surface of the outer jacket 13 is not limited to the recesses 17. Fig. 4(a) is an enlarged conceptual diagram of part A in Fig. 1. When a material having an uneven surface rather than a smooth surface, such as a nonwoven fabric, is used as the holding and wrapping member 7, the uneven shape of the outer surface of the holding and wrapping member 7 is transferred to the outer jacket 13, forming the second uneven shape, i.e., the unevenness 21.

[0046] 4(b) is a diagram showing the inner surface of the unfolded outer cover 13 in this case. As described above, recesses 17 are formed in the areas corresponding to the holding strings 19. In areas other than the recesses 17, irregularities 21 are formed over almost the entire surface.

[0047] In addition, in a given length of optical fiber cable 1, the ratio of the area where the second uneven shape (unevenness 21) is formed to the inner area of ​​jacket 13 (hereinafter simply referred to as the area ratio of unevenness 21) is preferably 90% or more and 99.5% or less. If the area ratio of unevenness 21 is too small, the effect of unevenness 21 will be reduced.

[0048] As a method for forming the unevenness 21, a member having an uneven surface, such as a nonwoven fabric, is used as the pressure winding member 7. Note that any member having an uneven surface other than a nonwoven fabric may be used. First, the cable core 15 is formed using such a pressure winding member 7 having an uneven surface.

[0049] Next, as described above, when extruding the outer covering 13, the uneven shape of the outer surface of the pressure winding member 7 can be transferred to the inner surface of the outer covering 13, for example, by setting a higher extrusion temperature or by extending the time until cooling after extrusion. If extrusion is performed under normal conditions, the outer covering 13 solidifies before the inner surface of the outer covering 13 and the pressure winding member 7 come into close contact with each other to form unevenness, making the inner surface of the outer covering 13 approximately smooth and hardly forming unevenness 21. In contrast, if time is allowed to pass between extruding the outer covering 13 and hardening, the surface of the pressure winding member 7, which was once crushed, returns to its original shape due to its elasticity, and unevenness 21 can be formed on the inner surface of the outer covering 13.

[0050] As described above, according to this embodiment, by forming an uneven shape on the inner surface of the outer sheath 13, the frictional force between the outer sheath 13 and the cable core 15 is increased, and longitudinal movement of the cable core 15 relative to the outer sheath 13 can be suppressed.

[0051] Furthermore, the recesses 17 formed by the pressure string 19 make it possible to easily adjust the area ratio of the recesses 17 by changing the winding method (winding pitch, etc.) of the pressure string 19. Furthermore, the irregularities 21 formed by the pressure winding member 7 make it easy to ensure a high area ratio.

[0052] 4 shows an example in which both recesses 17 and irregularities 21 are formed, but as shown in FIG. 3, only recesses 17 may be formed, or only irregularities 21 may be formed without recesses 17. That is, the irregular shape formed on the inner surface of outer cover 13 may include a first irregular shape formed continuously along the shape of pressure cord 19, or may include a second irregular shape formed by transferring the irregular shape of the outer surface of pressure winding member 7.

[0053] In this way, the movement of the cable core 15 in the longitudinal direction is suppressed, so that the pull-out force of the cable core 15 can be set to 2.5 kgf or more. In this way, the protrusion of the cable core 15 can be suppressed, which makes the installation work easier. [Example]

[0054] An optical fiber cable was fabricated, and the pull-out force when the cable core was pulled out from the jacket was measured. The cross-sectional shape of the optical fiber cable was a slotless cable similar to that shown in Figure 1.

[0055] First, a 6912-fiber core was formed. After twisting the cores together, a nonwoven fabric holding and wrapping material was rolled up and wrapped lengthwise using a forming jig, and a 2mm-wide nylon holding cord was wrapped around the outer circumference of the holding and wrapping material to create a cable core. The cable core thus created, a pair of tension members, and a rip cord for slicing the outer jacket were sheathed into a cylindrical shape with the jacket material to create an optical fiber cable.

[0056] Two meters of the resulting optical fiber cable were cut, and 10 cm of the outer jacket was removed from both ends of the optical fiber cable to expose the cable core. One end was left as is, while the other end was tied with string together with the cable core and pressure winding member and pulled in the axial direction, and the pull-out force was measured using a spring balance. A pull-out force of less than 2.5 kgf was deemed a failure (×) because the pull-out force was too small and the core portion was likely to slip out of the pressure winding member, while a pull-out force of 2.5 kgf or more was deemed a pass (◯). The results are shown in Table 1.

[0057] [Table 1]

[0058] After measuring the pull-out force, the entire sheath of the optical fiber cable was removed, and the depth and area ratio of the irregularities on the inner surface of the sheath were measured. Note that in the table, depressions 17 are depressions formed by the holding string, and depressions 21 are the irregularities formed by the holding winding member. The area ratio of the irregularities 21 can be measured for the inner surface of the sheath using a laser microscope equipped with a white light interferometer. For example, the inner surface of the sheath is divided into 50 mm x 50 mm areas, and the irregularities are measured for each area at once. The area where irregularities of 0.01 mm or more existed was defined as the area of ​​the irregularities 21. The maximum irregularity height at this time was defined as the depth of the irregularities 21.

[0059] As shown in Table 1, in Examples 1 to 4, in which the inner surface of the outer jacket had an uneven shape, the pull-out force of the cable core was 2.5 kgf or more. In contrast, in Comparative Example 1, in which the inner surface of the outer jacket did not have an uneven shape, the pull-out force was small and the cable core was rejected.

[0060] 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 limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0061] 1....Optical fiber cable 3....Optical fiber core 4....Core part 5....Optical fiber unit 7...Pressing and winding member 9...Tension member 11...Tear cord 13……Outer cover 15...Cable core 17...Concave 19....Pressing cord 21……Unevenness

Claims

1. A cable core; tension members provided on both sides of the cable core in a cross section perpendicular to the longitudinal direction of the cable core; an outer sheath provided to cover the tension member and the cable core; Equipped with The cable core includes a core portion including a plurality of optical fiber cores, a pressure winding member wound around the outer periphery of the core portion, and a pressure string for holding the pressure winding member from the outer periphery, The inner surface of the outer jacket is formed with projections and recesses, The unevenness includes a first uneven shape formed continuously along the shape of the pressing string, In a given length of the optical fiber cable, a ratio of an area where the first uneven shape is formed to an inner area of ​​the jacket is 0.5% or more and 2.0% or less, An optical fiber cable, characterized in that the depth of the first uneven shape is 0.01 mm or more and 0.09 mm or less.

2. 2. The optical fiber cable according to claim 1, wherein the unevenness includes a second uneven shape formed by transferring the uneven shape of the outer surface of the pressure winding member.

3. 3. The optical fiber cable according to claim 2, wherein the ratio of the area where the second uneven shape is formed to the inner area of ​​the jacket is 90% or more in a given length of the optical fiber cable.

4. 4. The optical fiber cable according to claim 1, wherein the cable core has a pull-out force of 2.5 kgf or more.

5. An optical fiber cable as described in claim 2, characterized in that the depth of the second uneven shape is 0.01 mm or more and 0.05 mm or less.

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