JP7640375B2 - Fiber optic cable - Google Patents

Description

The present invention relates to a slotless type optical fiber cable.

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.

One example of such an optical fiber cable is one 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 the optical fiber unit is then twisted further to form a cable core, which is then covered with an outer jacket containing an embedded tension member.

However, when laying such an optical fiber cable, there is a risk that the cable core may protrude due to shrinkage of the optical fiber cable's sheath after installation. This poses the problem of making it difficult to lay the optical fiber cable properly.

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, two or more winding tapes are arranged between the inner sheath and the outer sheath, and the coefficient of friction between the uppermost winding tape in contact with the outer sheath is greater than the coefficient of friction between the lowermost winding tape in contact with the inner sheath, and between the winding tapes themselves (Patent Document 1).

JP 2007-11019 A

When the outer sheath of an optical fiber cable such as that described in Patent Document 1 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.

However, the optical fiber cable in 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.

The present invention was made in consideration of these problems, and aims to provide an optical fiber cable that can prevent the cable core from protruding from the outer sheath of the optical fiber cable.

In order to achieve the above-mentioned object, the present invention provides an optical fiber 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 sheath 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 pressure winding member wound around the outer periphery of the core portion, and a pressure string that holds down the pressure winding member from the outer periphery , wherein unevenness is formed on the inner surface side of the outer sheath, the unevenness including a first uneven shape formed continuously along the shape of the pressure string, and in an optical fiber cable of a predetermined length, a ratio of an area where the first uneven shape is formed to an inner area of the outer sheath is 0.5% or more and 2.0% or less, and a depth of the first uneven shape is 0.01 mm or more and 0.09 mm or less .

The unevenness may include a second uneven shape to which the uneven shape of the outer surface of the pressing and wrapping member is transferred.

In an optical fiber cable of a given length, the ratio of the area in which the second uneven shape is formed to the inner area of the outer sheath may be 90% or more and 99.5% or less.

It is desirable that the pull-out strength of the cable core is 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.

According to the present invention, an uneven shape is formed on the inner surface of the sheath that covers the cable core, and this uneven shape acts as a resistance to the movement of the cable core in the longitudinal direction of the optical fiber cable, suppressing the protrusion of the cable core from the sheath. In this case, there is no need to make the sheath into multiple layers, and multiple types of winding tapes are also not required, so the number of parts does not increase compared to normal optical fiber cables.

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, which makes it possible to efficiently prevent the cable core from protruding.

In this case, if the ratio of the area where the first uneven shape is formed to the inner area of the outer sheath is 0.5% or more and 2.0% or less, the effect of suppressing the protrusion of the cable core can be obtained more reliably.

In addition, 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, so that the protrusion of the cable core can be efficiently suppressed.

In this case, if the ratio of the area where the second uneven shape is formed to the inner area of the outer sheath is 90% or more and 99.5% or less, the effect of suppressing the protrusion of the cable core can be obtained more reliably.

In addition, by making the unevenness height of the uneven shape 0.01 mm or more, it is possible to efficiently suppress the protrusion of the cable core.

In addition, if the cable core pull-out force is 2.5 kgf or more, the cable core can be more reliably prevented from protruding.

The present invention provides an optical fiber cable that can suppress the cable core from protruding from the outer sheath of the optical fiber cable.

FIG. FIG. FIG. 2A is an enlarged view of part A in FIG. 1 , and FIG. 2B is a developed view of the inner surface of the outer cover 13 .

The following describes an embodiment of the present invention 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 slots, and is composed of a cable core 15, a tension member 9, an outer jacket 13, etc.

The cable core 15 has a generally circular outer shape, and includes a core portion 4 made of multiple optical fiber cores 3, a pressure winding member 7 wound around the outer circumference of the core portion 4, and a pressure string 19 that holds down the pressure winding member 7 from the outer circumference. The core portion 4 is formed by twisting together multiple optical fiber units 5. The optical fiber unit 5 is also formed by twisting together multiple optical fiber cores 3. For example, an intermittently bonded optical fiber ribbon core that is bonded intermittently in the longitudinal direction can be used as the optical fiber cores 3.

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 or nonwoven fabric, and is arranged, for example, by vertical wrapping to cover the outer periphery of the core portion 4 as a whole. In other words, the longitudinal direction of the pressure winding member 7 is approximately aligned with the axial direction of the optical fiber cable 1, and the width direction of the pressure winding member 7 is aligned with the circumferential direction of the optical fiber cable 1, and the pressure winding member 7 is vertically wrapped around the outer periphery of the multiple optical fiber units 5.

Figure 2 is a side view of the cable core 15. As described above, the holding string 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 string 19 is wound around the outer periphery of the holding winding member 7 in a spiral shape in the longitudinal direction.

In a cross-sectional view 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.

An outer sheath 13 is provided around 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, for example, a polyolefin-based resin.

As shown in FIG. 1, a recess 17 corresponding to the thickness of the holding string 19 is 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.

Figure 3 is a diagram showing the outer jacket 13 unfolded and the inner surface of the outer jacket 13. As described above, the inner surface of the outer jacket 13 is formed with recesses 17, which are the first uneven shape. The recesses 17 are formed at a predetermined interval at an angle to the longitudinal direction.

Here, in a given length of optical fiber cable 1, it is desirable that the ratio of the area where the first uneven shape (recess 17) is formed to the inner area of the jacket 13 (length of optical fiber cable 1 × inner circumference of jacket 13) (hereinafter simply referred to as the area ratio of recess 17) is 0.5% or more and 2.0% or less.

The area ratio of the recesses 17 varies, for example, depending on 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 figure, 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.

As mentioned above, the recess 17 is formed at an angle corresponding to the winding angle of the pressure string 19. Therefore, by shortening the winding pitch of the pressure string 19, the area ratio of the recess 17 can be increased. In other words, the area ratio of the recess 17 can be adjusted as appropriate.

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 holding 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.

It is also desirable that the depth of the recess 17 is 0.01 mm or more. If the depth of the recess 17 is 0.01 mm or more, the effect of suppressing longitudinal movement of the cable core can be more reliably obtained.

Next, a method for forming an uneven shape (concave 17) on the inner surface of the jacket 13 will be described. Conventional optical fiber cables do not form the concave 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, so when it is water-cooled immediately after this, the jacket 13 hardens while roughly maintaining the shape formed by the mold. As a result, the inner surface of the jacket 13 becomes approximately smooth.

In contrast, 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 die gradually changes and becomes compatible with the inner shape of the cable core 15. As a result, the slight unevenness of the holding string 19 is transferred to the inner surface of the jacket 13, forming an uneven shape on the inner side of the jacket 13.

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

As described above, the recess 17 can be formed more reliably by pressing the outer jacket 13 firmly against the cable core 15 (holding string 19); however, if the outer jacket 13 is pressed too firmly against the cable core 15, there is a risk of increasing the lateral pressure on the optical fiber core 3 inside. In other words, if the cable core 15 is pressed too firmly by the outer jacket 13, making the depth of the recess 17 on the inner surface of the outer jacket 13 too deep, there is a risk of increasing the lateral pressure on the optical fiber core 3 inside. For this reason, it is desirable that the depth of the recess 17 is, for example, 0.09 mm or less.

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

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

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, the unevenness 21.

Figure 4(b) shows the inner surface of the outer cover 13 in this case when it is unfolded. As described above, a recess 17 is formed in the area corresponding to the holding string 19. In areas other than the recess 17, irregularities 21 are formed over almost the entire surface.

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 the 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.

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

Next, as described above, when extruding the outer jacket 13, for example, the extrusion temperature can be set higher or the time until cooling after extrusion can be lengthened, thereby transferring the uneven shape of the outer surface of the pressure winding member 7 to the inner surface of the outer jacket 13. If extrusion is performed under normal conditions, the outer jacket 13 solidifies before the inner surface of the outer jacket 13 and the pressure winding member 7 come into close contact with each other to form unevenness, and the inner surface of the outer jacket 13 becomes approximately smooth, with almost no unevenness 21 formed. In contrast, if time is allowed to pass between extruding the outer jacket 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 jacket 13.

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.

In addition, the recess 17 formed by the holding string 19 allows the area ratio of the recess 17 to be easily adjusted by winding the holding string 19 (winding pitch, etc.). In addition, the unevenness 21 formed by the holding string winding member 7 allows a high area ratio to be easily ensured.

In the example shown in FIG. 4, both the recess 17 and the unevenness 21 are formed, but as shown in FIG. 3, only the recess 17 may be formed, or only the unevenness 21 may be formed without forming the recess 17. In other words, the uneven shape formed on the inner surface of the outer cover 13 may include a first uneven shape formed continuously along the shape of the holding string 19, or may include a second uneven shape to which the uneven shape of the outer surface of the holding wrap member 7 is transferred.

In this way, the movement of the cable core 15 in the longitudinal direction is suppressed, so the pull-out force of the cable core 15 can be set to 2.5 kgf or more. This makes it possible to suppress the protrusion of the cable core 15. This makes installation work easier.

An optical fiber cable was created, and the pulling force was measured when the cable core was pulled out of the jacket. The cross-sectional shape of the optical fiber cable was a slotless type cable similar to that shown in Figure 1.

First, a core section with 6912 cores was formed. After twisting the core sections together, the nonwoven fabric holding down the winding material was rolled up and wrapped vertically with a forming jig, and a nylon holding string with a width of 2 mm was wrapped around the outer circumference of the holding down winding material to create a cable core. The cable core thus created, a pair of tension members, and a tear string for tearing the jacket were sheathed into a cylindrical shape with the jacket material to create an optical fiber cable.

2 m of the resulting optical fiber cable was cut out, and the outer covering was removed within a range of 10 cm on both ends of the optical fiber cable to expose the cable core. One end was left as it was, and the other end was tied with a string together with the cable core's pressure winding member and pulled in the axial direction, and the pull-out force was measured with a spring scale. A pull-out force of less than 2.5 kgf was deemed a failure (x) because the pull-out force was too small and the core portion was likely to slip out of the pressure winding member, and a pull-out force of 2.5 kgf or more was deemed a pass (o). The results are shown in Table 1.

After completing the measurement of 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 the recesses 17 in the table are recesses formed by the holding string, and the irregularities 21 are the irregular shapes formed by the holding and winding members. Note that 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 areas of 50 mm x 50 mm, and the irregularities are measured for each area at once, and the area where irregularities of 0.01 mm or more existed is defined as the area of the irregularities 21. The maximum irregularity height at this time is defined as the depth of the irregularities 21.

As shown in Table 1, in Examples 1 to 4, in which the inner surface of the outer jacket is uneven, 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 is not uneven, the pull-out force was small and the cable core was rejected.

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-mentioned embodiment. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Reference Signs List 1....Optical fiber cable 3....Optical fiber core 4....Core portion 5....Optical fiber unit 7....Pressing winding member 9....Tension member 11....Tearing string 13....Outer jacket 15....Cable core 17....Recess 19....Pressing string 21....Irregularities

Claims (5)

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 an 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. 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. 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. The optical fiber cable according to claim 1 , wherein the cable core has a pull-out force of 2.5 kgf or more. 3. The optical fiber cable according to claim 2, wherein the depth of the second uneven shape is 0.01 mm or more and 0.05 mm or less.

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