fiber optic cable

Abstract

To provide an optical fiber cable light in weight and excellent in handling properties.SOLUTION: A plurality of coated optical fibers 3 are twisted together, so that an optical fiber unit 6 is formed, and the plurality of optical fiber units 6 are further twisted together, so that a core 5 is formed. Tension members 9 are provided on portions opposed to each other with the core 5 as a center, on an outer periphery of the core 5 in a cross section perpendicular to a lengthwise direction of an optical fiber cable 1. A sheath 13 is provided so as to cover the core 5 (the plurality of coated optical fibers 3) and the tension members 9. An outer shape of the sheath 13 is substantially circular, where the sheath 13 is formed of one layer of a foamed resin made of high-density polyethylene.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] An optical fiber cable is used that has a core made up of many optical fiber strands, a tension member arranged around the core, and an outer jacket (see, for example, Patent Document 1). In such an optical fiber cable, a pair of tension members are arranged in positions facing each other with the core at the center.

[0003] Also, an optical fiber cable has been proposed in which tension members are arranged at positions facing each other across 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]

[0004] [Patent Document 1] Patent Publication No. 2021-157062 [Patent Document 2] Japanese Patent Publication No. 2020-204752 Summary of the Invention [Problem to be solved by the invention]

[0005] In optical fiber cables, the tension members are embedded in the jacket. Therefore, in order to increase the strength of the jacket around the tension members against external pressures such as lateral pressure and impacts, it is necessary to thicken the jacket around the tension members. For example, it has been necessary to make the jacket thicker than the outer diameter of the tension members.

[0006] In particular, slotless optical fiber cables have a soft core because the optical fiber core inside is not protected by a high-strength component such as a slotted rod or tube. Therefore, when external pressure, such as lateral pressure or impact, is applied to the optical fiber cable, the jacket easily deforms, leading to increased optical fiber loss. For this reason, a sufficient jacket thickness is required, even in areas other than the tension member. For this reason, a jacket thickness of approximately 3 to 5 mm is typically used, which results in the jacket taking up the majority of the weight of the optical fiber cable, resulting in the issue of heavy cable weight.

[0007] On the other hand, if the jacket is too thick, there is a risk that the string will break when trying to tear the jacket, making it impossible to tear the jacket. For this reason, soft materials such as linear low-density polyethylene (LLDPE) or low-density polyethylene (LDPE) are generally used for the jacket. However, even with this, when trying to tear the jacket at low temperatures (for example, -10°C), the load required to tear it increases, making it difficult to work with.

[0008] The present invention has been made in view of the above problems, and has as its object to provide an optical fiber cable that is lightweight and easy to handle. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the present invention provides an optical fiber cable comprising a core formed by twisting together optical fiber units consisting of a plurality of optical fiber cores, tension members provided at positions facing each other around the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable, and an outer jacket provided to cover the core and the tension member, wherein the outer jacket is made of a single layer of foamed resin made of high-density polyethylene.

[0010] The foamed resin may have a volume ratio of bubbles of 29% or more and 61% or less.

[0011] The Young's modulus of the outer jacket may be 810 MPa or more and 1170 MPa or less. The air bubble volume ratio of the outer jacket near the interface between the outer jacket and the tension member or near the interface between the outer jacket and the core may be lower than the air bubble volume ratio of other portions. The air bubble volume ratio of the outer covering near the interface between the outer covering and the tension member or near the interface between the outer covering and the core may be 5% lower than that of other portions.

[0012] According to the present invention, the outer jacket is lightweight because it is made of foamed resin. Furthermore, by using high-density polyethylene for the outer jacket, which has not been used much in the past due to its tearability and flexibility, the base resin can compensate for the loss of strength that occurs when foamed resin is used. Furthermore, because the outer jacket is a single layer (rather than multiple layers, such as laminated layers of different resins), it is easy to manufacture and has good tearability.

[0013] For example, conventional jackets made of low-density polyethylene have the problem of increased weight as mentioned above, but foaming low-density polyethylene does not provide sufficient strength against lateral pressure, etc.

[0014] On the other hand, high-density polyethylene is harder than low-density polyethylene, which means that it is less easy to tear and less flexible to handle. However, by foaming high-density polyethylene, it is possible to achieve a lightweight structure while still maintaining adequate strength and ease of handling.

[0015] In particular, if the volume fraction of bubbles in the foamed resin is 29% or more and 61% or less, the tearability is good and an increase in loss due to lateral pressure can be efficiently suppressed.

[0016] Furthermore, if the Young's modulus of the jacket is 810 MPa or more and 1170 MPa or less, the above-mentioned effects can be obtained more reliably. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an optical fiber cable that is lightweight and easy to handle. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of an optical fiber cable 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] The first embodiment will be described below 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 core 5, a tension member 9, a tear cord 11, an outer jacket 13, etc.

[0020] The core 5 is made up 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 6, and the plurality of optical fiber units 6 are further twisted together to form the core 5. The optical fiber cores 3 may be, for example, intermittently bonded optical fiber ribbons that are bonded intermittently in the longitudinal direction.

[0021] As shown in Fig. 1, a pressure wrap 7 is provided around the core 5 (plurality of coated optical fibers 3). The pressure wrap 7 is a tape-like member, a nonwoven fabric, or the like, and is arranged to cover the entire outer periphery of the core 5 by, for example, vertical splicing. 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 also be referred to as the core 5.

[0022] In a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, tension members 9 are provided on the outer periphery of the core 5 at positions facing each other with the core 5 at the center. The tension members 9 are components that bear the tension of the optical fiber cable 1.

[0023] In the illustrated example, four pairs (eight in total) of tension members 9 are arranged facing each other with the core 5 at the center. By arranging multiple pairs of tension members 9 at regular intervals in this way, the required tension can be distributed among many tension members, allowing the diameter of each tension member to be reduced. For this reason, it is desirable to arrange multiple pairs (three or more pairs) of tension members 9 at equal intervals.

[0024] The material of the tension members 9 is not particularly limited, but for example, fiber reinforced plastic (FRP) made of aramid fiber, glass fiber, or the like can be used.

[0025] In addition, tear cords 11 are provided at circumferential positions different from those of the tension members 9, but at positions facing each other across the core 5. An outer jacket 13 is provided on the outer periphery of the core 5. The tension members 9 and the tear cords 11 are embedded in the outer jacket 13. In other words, the outer jacket 13 is provided so as to cover the core 5 (plurality of coated optical fibers 3), the tension members 9, etc. The outer shape of the outer jacket 13 is approximately circular.

[0026] Here, the outer jacket 13 is made of a single layer of foamed resin made of high-density polyethylene. Here, the fact that the outer jacket 13 is a single layer means that there are no different types (differences in materials, differences between foamed and non-foamed sections, etc.) and that the entire jacket has a substantially uniform configuration. In other words, the outer jacket 13 is made substantially entirely of foam. Therefore, so-called two-layer extrusion or the like is not required.

[0027] The volume ratio of the bubbles in the foamed resin (foaming rate) is preferably between 29% and 61%. If the bubble volume ratio is too small, the weight reduction effect is small. If the bubble volume ratio is too large, the loss due to lateral pressure increases significantly. The bubble volume ratio of the outer sheath 13 can be calculated from the ratio of the specific gravity of the base resin (high-density polyethylene) of the outer sheath 13 to the specific gravity of the outer sheath 13 (foamed resin).

[0028] As mentioned above, the jacket 13 is formed in one layer, and the bubbles are distributed almost uniformly throughout the jacket 13, but it is also possible to form areas with fewer bubbles in certain areas. For example, the amount of bubbles may be slightly reduced at the interface with the tension members 9 or at the interface with the core 5. This allows the jacket 13 to be more securely attached to the core 5 or tension members 9.

[0029] For example, the volume fraction of bubbles near the interface of the core 5 and the tension member 9 may be set to be about 5% lower than that of other parts. The local amount of bubbles can be calculated from the area ratio of the resin part to the bubble part when observing the cross section of each part.

[0030] In this way, to form a distribution with a small amount of bubbles in some areas, the time between extruding the outer covering and water cooling can be adjusted. Normally, allowing sufficient cooling time results in a roughly uniform bubble distribution. However, by slightly shortening the time from resin extrusion to cooling, the resin is cooled slightly by the temperature of the core 5 and tension members 9 when the resin is extruded, which can delay the foaming in some areas. Therefore, by starting cooling slightly earlier than when the bubble distribution becomes uniform, the bubble distribution described above can be formed.

[0031] On the other hand, if the time from resin extrusion to cooling is too short, sufficient foaming will not occur. For this reason, it is desirable to cool the jacket 13 at a timing that allows an appropriate amount of bubbles to be generated throughout the jacket 13, while delaying the generation of bubbles near the interfaces of the tension members 9, etc.

[0032] The Young's modulus of the outer jacket is preferably 810 MPa or more and 1170 MPa or less. If the Young's modulus is too low, loss due to lateral pressure increases. If the Young's modulus is too high, the jacket is less tearable with a tear cord and less flexible.

[0033] As described above, according to this embodiment, the outer jacket 13 is made of foamed resin, which is lightweight and easy to tear with a tear cord. Furthermore, because the outer jacket 13 is made of high-density polyethylene, even foamed resin can suppress an increase in loss due to lateral pressure.

[0034] In particular, by appropriately setting the foaming ratio, it is possible to improve the tearability with a tear string and to suppress an increase in loss due to lateral pressure. [Example]

[0035] We evaluated various optical fiber cables with different jacket configurations. First, we intermittently glued twelve 200um diameter ITU-T G.657.A1 compliant optical fibers together to create a 12-fiber intermittent ribbon. Six of these were bundled together and wrapped in a 2mm wide plastic ribbon to create a 72-fiber unit.

[0036] Next, eight 72-fiber units were supplied and twisted together, and then absorbent nonwoven fabric was attached lengthwise. The resulting core was rolled up in a forming jig and then wrapped with nylon pressure thread to create a 576-fiber core. The outer jacket material was extruded cylindrically around the outer periphery of the core, eight 1.0mm diameter glass FRP tension members, and a ripping string for ripping the jacket. After sheathing, the cable was cooled to approximately 20°C in a water bath to create an optical fiber cable.

[0037] The outer sheath material was made from a base material of linear low-density polyethylene or high-density polyethylene mixed with a sodium bicarbonate foaming agent, and the foaming rate was changed by adjusting the mixing ratio and the extruder temperature setting. The thickness of the outer sheath was 3.5 mm. The tear-off string was made from 830 dtex x 3-ply twisted polyester yarn.

[0038] Various optical fiber cables were created by changing the base material of the jacket and the foaming ratio (volume ratio of air bubbles to resin).The cable weight, jacket tearability, and lateral pressure strength of the obtained optical fiber cables were compared.

[0039] The sheath tearability was evaluated by leaving the cable in a thermostatic chamber at -10°C for at least one hour, and then tearing the sheath in the chamber. In this evaluation, a cable in which the string broke when torn 1m was given an X rating, a cable in which the string broke when torn 1m was given an △ rating, a cable in which the tear force was 20kg or more and the sheath was torn without breaking the string, although workability was poor, a ◯ rating was given, a cable in which the string broke but the sheath was torn with a tear force of 15kg or more but less than 20kg, although workability was poor, and a ◎ rating was given, and a cable in which the string broke easily, but the string did not break, with a tear force of less than 15kg.

[0040] The lateral pressure strength was judged by the maximum increase in loss of the optical fiber when a lateral pressure of 2200 N / 100 mm was applied. Loss increase values ​​of 0.10 dB or more were evaluated as ×, 0.05 dB or more but less than 0.10 dB as △, 0.02 dB or more but less than 0.05 dB as ○, and less than 0.02 dB as ◎. The results are shown in Tables 1 to 3.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] The results showed that the cable weight was 150 kg / km or less for all of Examples 1 to 10. The sheath tearability was rated as fair or better, and the loss increase under lateral pressure was also fair or better. Furthermore, Examples 2 to 4 and 7 to 9, which had foaming rates (bubble volume fractions) of 29% to 61%, were good, with the sheath tearability and loss increase under lateral pressure both rated as good or better.

[0045] On the other hand, Comparative Examples 1, 3, and 4 were heavy, weighing over 165 kg / km, because the outer jacket was not made of foamed resin. Also, Comparative Example 2 used conventional linear low-density polyethylene as the base resin for the outer jacket, so the increase in loss during lateral pressure was evaluated as "poor."

[0046] In addition, in Comparative Example 3, high density polyethylene was used for the outer jacket, and therefore the tearability of the outer jacket was evaluated as "Poor."

[0047] Similarly, in Comparative Example 4, high density polyethylene was used for the outer jacket, and therefore the tearability of the outer jacket was evaluated as "Poor."

[0048] 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]

[0049] 1....Optical fiber cable 3....Optical fiber core 5...Core 7. Press down 9...Tension member 11...Tear cord 13……Outer cover

Claims

1. a core formed by twisting together optical fiber units each consisting of a plurality of optical fiber cores; tension members provided at positions facing each other across the core in a cross section perpendicular to the longitudinal direction of the optical fiber cable; an outer covering provided to cover the core and the tension member; Equipped with An optical fiber cable characterized in that the outer jacket is made of a single layer of foamed resin made of high-density polyethylene.

2. 2. The optical fiber cable according to claim 1, wherein the volume ratio of bubbles in the foamed resin is 29% or more and 61% or less.

3. 2. The optical fiber cable according to claim 1, wherein the Young's modulus of the base material of the jacket is 810 MPa or more and 1170 MPa or less.

4. An optical fiber cable as described in claim 1, characterized in that the bubble volume fraction of the outer sheath near the interface between the outer sheath and the tension member, or near the interface between the outer sheath and the core, is lower than the bubble volume fraction of other parts.

5. An optical fiber cable as described in claim 4, characterized in that the bubble volume ratio of the outer sheath near the interface between the outer sheath and the tension member or near the interface between the outer sheath and the core is 5% lower than in other areas.

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