JP2024044184A - fiber optic cable - Google Patents

Abstract

[Problem] To provide an optical fiber cable with high waterproof properties. [Solution] The optical fiber cable 1 is a slotless type optical fiber cable that does not use a slot rod, and is composed of a core portion 15, a pressure winding member 7, a tension member 9, a tear string 11, an outer jacket 13, etc. The pressure winding member 7 is arranged on the outer periphery of the core portion 15. The tension member 9 and the tear string 11 are collectively covered on the outer periphery of the core portion 15 (pressure winding member 7) by an outer jacket 13 made of resin. A groove 19 is provided on the inner surface of the outer jacket 13. A water-absorbent member 21 is arranged inside the groove 19. [Selected Figure] Figure 1

Description

The present invention relates to an optical fiber cable that accommodates a plurality of optical fiber cores.

With the increase in the amount of information in recent years, in order to increase the amount of information transmitted through a single optical fiber cable, it is desirable to store optical fibers in an optical fiber cable at a high density and increase the number of optical fibers stored in the cable. ing.

Since these optical fiber cables are installed underground, they are required to have waterproof properties that prevent water or seawater from running far along the cable from the location of the flooding, even if water or seawater floods into the cable.

As such a waterproof optical fiber cable, for example, an optical fiber cable having a structure in which a water-absorbing nonwoven fabric is wrapped around a fiber unit has been proposed (for example, Patent Document 1). Further, there have been proposed bundle materials in which water-absorbing particles are attached, and optical fibers in which water-absorbing powder is directly attached (Patent Documents 2 and 3).

Patent No. 6598813 JP 2015-215448 A Japanese Patent Application Publication No. 2001-343566

Even when absorbent nonwoven fabric is used as a core press wrap as in Patent Document 1, it is difficult to prevent water from seeping between the flame-retardant material and the outer sheath if a flame-retardant material is placed on the outer periphery. However, wrapping more absorbent nonwoven fabric around the flame-retardant material increases the outer diameter of the cable.

Furthermore, even when a flame-retardant member is not used, an optical cable with a slotless structure is used as a super multi-core cable in which a large number of optical fibers are mounted within a cable of limited size. In such a slotless cable, if too much pressure is applied from the outer periphery of the presser wrap when extruding the jacket, the lateral pressure on the core will increase, causing an increase in transmission loss. For this reason, as in so-called cylinder extrusion, the outer jacket may be extruded to prevent too much pressure from being applied to the core. In such a case, a clearance is formed between the water-absorbing nonwoven fabric and the outer covering, which becomes a factor in deteriorating waterproof properties.

In addition, in the method of applying water-absorbing powder to the core (flame-retardant material, etc.) when pushing out the jacket, the water-absorbing powder falls off due to contact between the nozzle and the core when pushing out the jacket, making it difficult to stably apply the desired amount of water-absorbing powder. Also, if the diameter of the nozzle is increased to prevent contact between the nozzle and the core, the problem of the cable diameter also increases.

The present invention was made in consideration of these problems, and aims to provide an optical fiber cable with high waterproof properties.

In order to achieve the above-mentioned object, the present invention includes: a core portion made of a plurality of optical fiber cores; a presser winding member disposed on the outer periphery of the core portion; and an outer sheath provided on the outer periphery of the presser winder member. The optical fiber cable is characterized in that a groove is provided on the inner surface of the jacket, and a water-absorbing member is disposed in the groove.

In a cross section perpendicular to the longitudinal direction of the optical fiber cable, the total cross-sectional area of the grooves may be 0.6% or more and 2.4% or less of the inner cross-sectional area of the jacket excluding the grooves. desirable.

A flame retardant member may be disposed on the outer periphery of the pressure winding member, and the jacket may be disposed on the outer periphery of the flame retardant member.

The grooves may be arranged in an S-shape or SZ-shape in the longitudinal direction.

According to the present invention, by forming a groove on the inner surface of the jacket and disposing a water-absorbent material in the groove, it is possible to suppress water leakage in the gap between the inner surface of the jacket and the core. In addition, by forming a groove, even if the jacket is pushed out after applying the water-absorbent material during the manufacture of the optical fiber cable, the water-absorbent material can be held in the groove without falling off.

In particular, by making the total cross-sectional area of the grooves in a cross section perpendicular to the longitudinal direction of the optical fiber cable 0.6% to 2.4% of the inner cross-sectional area of the jacket not including the grooves, it is possible to achieve both a sufficient water-stopping effect and the protective effect of the jacket.

Further, flame retardance can be improved by arranging a flame retardant member around the outer periphery of the pressing member. At this time, the water-absorbing member can suppress water running through the gap between the flame-retardant member and the outer cover.

In addition, by arranging the grooves in an S-shape or SZ-shape in the longitudinal direction, water leakage in the longitudinal direction on the inner surface of the outer jacket can be more reliably suppressed.

According to the present invention, an optical fiber cable having high waterproof properties can be provided.

1 is a sectional view showing an optical fiber cable 1. FIG. FIG. 2 is a cross-sectional view showing the optical fiber cable 1a. FIG. 3 is a sectional view showing an optical fiber cable 1b.

The first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical fiber cable 1. The optical fiber cable 1 is a slotless type optical fiber cable that does not use a slot rod, and is composed of a core portion 15, a pressure winding member 7, a tension member 9, a tear string 11, an outer jacket 13, etc.

The core portion 15 is made up of a plurality of optical fiber cores 3. More specifically, a plurality of optical fiber cores 3 are twisted together to form an optical fiber unit 5, and a plurality of optical fiber units 5 are assembled to form the core portion 15. The optical fiber units 5 are bundled together, for example, by a bundling material, and are distinguished from other optical fiber units 5.

The number of optical fiber units 5 is not limited to the example shown in the figure. Furthermore, the multiple optical fiber cores 3 do not have to be divided into optical fiber units 5. In other words, the core portion 15 may be formed by twisting together multiple optical fiber cores 3.

Although the optical fiber coated wire 3 may be a single-core optical fiber coated wire, it is preferably an optical fiber ribbon coated wire in which a plurality of single-core optical fiber coated wires are arranged side by side. In this case, it is desirable to use an intermittently bonded optical fiber ribbon in which adjacent optical fibers are bonded intermittently in the longitudinal direction.

A pressure winding member 7 is placed on the outer periphery of the core portion 15. In the illustrated example, the pressure winding member 7 is wound vertically around the outer periphery of the multiple optical fiber units 5. Vertical winding is a method of winding the pressure winding member 7 so that the longitudinal direction of the pressure winding member 7 is aligned with the longitudinal direction of the core portion 15 and a portion of the pressure winding member 7 overlaps in the width direction to collectively cover the multiple optical fiber cores 3 (optical fiber units 5).

The holding and wrapping member 7 may be, for example, a resin tape, but is preferably a water-absorbent material such as a water-absorbent nonwoven fabric. A linear body such as thread may also be wound around the outer periphery of the holding and wrapping member 7. Note that the holding and wrapping member 7 may also be referred to as the core portion.

A pair of tension members 9 are provided on the outside of the core 15, facing each other across the core 15. The tension members 9 are members that bear the tension of the optical fiber cable 1, and although there is no particular limit to the material, for example, fiber-reinforced plastic (FRP) made of aramid fiber, glass fiber, etc. can be used. The number of tension members 9 is not limited to the example shown in the figure.

A tear cord 11 is provided on the outside of the pressure winding member 7 at a different circumferential position from the tension member 9, facing the core portion 15. The outer periphery of the core portion 15 (pressure winding member 7) is covered collectively with the tension member 9 and the tear cord 11 by a resin outer jacket 13. The outer jacket 13 can be easily torn by the tear cord 11.

Next, details of the outer cover 13 will be explained. A groove 19 is provided on the inner surface of the jacket 13. The groove 19 opens on the inner surface side (the core portion 15 side) of the outer sheath 13 and has a predetermined space. More specifically, the bottom of the groove 19 (on the outer peripheral side of the cable) is formed into a gently curved shape. By doing so, it is possible to suppress the occurrence of cracks or the like in the outer sheath 13 from the bottom of the groove 19. In the illustrated example, a plurality of grooves 19 are arranged at regular intervals in the circumferential direction, but the number of grooves 19 is not particularly limited.

Note that the groove 19 may be formed straight in the longitudinal direction of the optical fiber cable 1, but the groove 19 may be arranged in an S shape or an SZ shape with respect to the longitudinal direction. Here, arranging the grooves 19 in an S-shape means arranging the grooves 19 such that the formation position of the grooves 19 in the circumferential direction changes in a constant direction with respect to the longitudinal direction. That is, the groove 19 is formed in a spiral shape in a certain direction.

Also, arranging the grooves 19 in an SZ pattern means that the circumferential formation position of the grooves 19 is changed relative to the longitudinal direction, but in one section, the grooves are arranged spirally in one direction, and in another section, the grooves are arranged spirally in the other direction, so that the spiral direction of the spiral is alternated at a predetermined interval.

A water absorbing member 21 is arranged inside the groove 19 . The water-absorbing member 21 is in the form of a powder, and can be made of, for example, water-absorbing resin powder using Na polyacrylate. The water-absorbing member 21 is a member that swells when it absorbs water.

Here, unlike slot-type cables, in slotless cables, if too much pressure is applied when pushing out the outer sheath to the outer periphery of the core part 15 (pressing and winding member 7), the lateral pressure against the optical fiber inside the core will increase. . In particular, in order to achieve higher density in recent years, technology using small diameter optical fibers has been advanced, and the lateral pressure caused by extrusion of the outer jacket has a large effect on increasing transmission loss.

For this reason, as described above, when manufacturing a slotless cable, the outer sheath may be extruded into a cylindrical shape to prevent too much pressure from being applied to the core portion 15. For this reason, the outer sheath 13 does not come into close contact with the core portion 15 (presser winding member 7), and a slight clearance is formed. The size of the clearance (clearance cross-sectional area) between the core portion 15 (press winding member 7) and the outer sheath 13 that occurs at this time tends to be within a substantially constant range with respect to the inner diameter of the outer sheath 13.

Therefore, in the present embodiment, in a cross section perpendicular to the longitudinal direction of the optical fiber cable 1, the total cross-sectional area of the grooves 19 (the sum of the cross-sectional areas of all grooves 19) is calculated as It is desirable to set it to 0.6% or more and 2.4% or less of the internal cross-sectional area. Here, the inner cross-sectional area of the outer sheath 13 that does not include the groove 19 is D ² × using the inner diameter D of the outer sheath 13 in FIG. It is expressed as π/4.

By setting the total cross-sectional area of the grooves 19 (that is, the total amount of the water-absorbing member 21) to 0.6% or more of the inner cross-sectional area of the outer sheath 13, which does not include the grooves 19, water can enter and the water-absorbing member 21 expands, it is possible to block at least a part of the path of water in the clearance, thereby achieving the effect of suppressing further water running.

On the other hand, if the total cross-sectional area of the groove 19 (that is, the total amount of the water-absorbing member 21) exceeds 2.4% of the inner cross-sectional area of the outer cover 13, the amount of the water-absorbing member 21 is too large, resulting in increased cost and expansion. It is also a cause of increased lateral pressure. Furthermore, if the groove 19 becomes too large, the thickness of the outer sheath 13 at the relevant portion becomes thinner, and the protective effect of the outer sheath 13 also becomes smaller. Therefore, the total cross-sectional area of the grooves 19 is desirably 0.6% or more and 2.4% or less of the inner cross-sectional area of the outer cover 13 excluding the grooves 19.

Note that, as described above, the amount of the water-absorbing member 21 can also be set depending on the clearance between the core portion 15 (pressing winding member 7) and the outer sheath 13. For example, the total cross-sectional area of the grooves 19 (the sum of the cross-sectional areas of all the grooves 19) can be calculated as It may be 8% or more and 33% or less of the area). Note that the clearance cross-sectional area that does not include the groove 19 is calculated from the outer diameter d of the structure disposed inside the outer sheath 13 (in this embodiment, the pressing winding member 7) and the above-mentioned inner diameter D of the outer sheath 13. It is expressed as ² ×π/4−d ² ×π/4.

The upper limit of the above range is due to the fact that the expansion ratio of the general water-absorbent member 21 due to water absorption is about 4 times. For example, when the water-absorbent member 21 in the groove 19 expands to 4 times the general expansion, if the cross-sectional area of the expanded water-absorbent member 21 protruding from the groove 19 (3 times the total cross-sectional area of the groove) exceeds the clearance cross-sectional area, there is a risk of an increase in lateral pressure due to expansion. On the other hand, the lower limit of the above range is due to the fact that if the expansion of the water-absorbent member 21 (the water-absorbent member 21 expanding and protruding from the groove 19) can block about 1/4 of the entire clearance, a minimum water run-in suppression effect can be obtained. As mentioned above, the clearance cross-sectional area is often within a certain range relative to the cross-sectional area inside the outer jacket, so the above range is considered to roughly overlap with the range in which the total cross-sectional area of the groove 19 is 0.6% or more and 2.4% or less of the cross-sectional area inside the outer jacket 13.

Next, a method for manufacturing the optical fiber cable 1 will be explained. First, the optical fiber unit 5 is constructed by twisting a plurality of optical fiber cores 3 together in advance and wrapping a bundle material around them. The core portion 15 is formed by supplying optical fiber units 5 from a plurality of optical fiber unit supply bobbins and assembling them.

The assembly of the plurality of optical fiber units 5 is sent to a forming device together with a pressing member 7, and a pressing member 7 is applied around the outer periphery of the assembly of optical fiber units 5 so as to cover the plurality of optical fiber units 5 all at once. is attached vertically. Thereafter, a powdery water absorbing member 21 is applied to the entire outer periphery of the pressure winding member 7.

The core part 15, on which the pressure winding member 7 is wrapped and the water-absorbent member 21 is applied, is fed together with the tension member 9 and the tear string 11 to an extruder for the outer sheath 13, which extrudes the outer sheath 13 onto the outer circumference of the core part 15. At this time, the outer sheath 13 is extruded by pipe extrusion so that a clearance is formed between the pressure winding member 7 and the outer sheath 13.

The grooves 19 are formed by the shape of the cap when the jacket 13 is extruded. At this time, the cap or the core portion 15 supplied to the cap can be rotated around the feed direction as an axis to form the grooves 19 in an S or SZ shape. After the jacket 13 is extruded, it is water-cooled to produce the optical fiber cable 1.

As described above, according to the optical fiber cable 1 of the present embodiment, since the concave groove 19 is formed on the inner surface of the outer sheath 13, when coating the outer sheath 13 with the water-absorbing member 21, the cap is used to absorb water. The water absorbent member 21 can be held without all of the absorbent member 21 falling off. In addition, since there is no need to adhere the water-absorbing member 21 to the outer periphery of the core part using an adhesive, there is no need for an adhesive application and curing process, which simplifies the process and increases the outer diameter of the cable due to the adhesive layer. This can be suppressed.

In addition, since a water-absorbent member 21 can be placed inside the groove 19, even if a clearance occurs between the inner surface of the outer jacket 13 and the core portion 15 (pressure winding member 7), the water-stopping property can be improved without increasing the outer diameter of the cable.

In addition, by forming the grooves 19 in an S-shape or SZ-shape in the longitudinal direction, the circumferential arrangement of the grooves 19 can be changed in the longitudinal direction, thereby improving the effect of suppressing water leakage in the longitudinal direction of the optical fiber cable.

Next, the 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 that perform the same functions as the first embodiment, and duplicated descriptions will be omitted.

The optical fiber cable 1a has substantially the same configuration as the optical fiber cable 1, but differs in that a flame retardant member 17 is used. The flame retardant member 17 is wound around the outer periphery of the presser wrapping member 7, for example, by vertical wrapping. That is, the outer sheath 13 is arranged around the outer periphery of the flame retardant member 17. Although the material of the flame retardant member 17 is not particularly limited, it is, for example, a sheet-like member in which a flame retardant such as a metal hydrate is added to an inorganic fiber sheet and is integrated with a binder.

By arranging the flame-retardant member 17 on the outer periphery of the core portion 15 (pressure winding member 7), higher flame retardant performance can be obtained. On the other hand, the flame-retardant member 17 does not have water absorption properties. As mentioned above, water-absorbent nonwoven fabrics can be used for the pressurizing winding member 7, but if the flame-retardant member 17 is arranged on the outer periphery of the pressurizing winding member 7, the water absorption properties of the pressurizing winding member 7 cannot be utilized for the clearance on the inner surface side of the outer jacket 13. On the other hand, there is a method of further wrapping a water-absorbent member on the outer periphery of the flame-retardant member 17, but this method is not desirable because it increases the outer diameter of the cable.

On the other hand, in this embodiment, since the water-absorbing member 21 is disposed inside the groove 19 on the outer circumferential side of the flame-retardant member 17, there is a clearance between the outer surface of the flame-retardant member 17 and the inner surface of the jacket 13. Even if the water absorbent member 21 is formed, water running can be suppressed by the water absorbing member 21.

According to the second embodiment, effects similar to those of the first embodiment can be obtained. Further, the present invention is particularly effective when the flame retardant member 17 is used and the pressure winding member 7 is not exposed on the inner surface side of the outer sheath 13, as in this embodiment.

Next, the third embodiment will be described. FIG. 3 is a cross-sectional view showing an optical fiber cable 1b according to the third embodiment. The optical fiber cable 1b has a configuration substantially similar to that of the optical fiber cable 1a, but differs in that the tear string 11 is disposed in the recessed groove 19.

In this case, it is preferable that the groove 19 is formed straight in the longitudinal direction of the optical fiber cable 1. It is also preferable that the total cross-sectional area of the groove 19 mentioned above is the cross-sectional area of the tear cord 11 minus that of the tear cord 11. In the illustrated example, both of the pair of tear cords 11 are disposed inside the groove 19, but only one of them may be disposed inside.

According to the third embodiment, the same effect as the second embodiment can be obtained. In addition, by arranging the tear cord 11 in the recessed groove 19, the thickness of the outer jacket 13 to be torn by the tear cord 11 can be made thinner. This makes the tearing operation easier.

Various types of optical fiber cables were prototyped and their waterproofing properties were evaluated. The optical fiber cables used for the evaluation had a cross-sectional shape generally shown in Figure 1 or Figure 2. First, 12 optical fibers were intermittently bonded to create a 12-core optical fiber ribbon. 12 of these optical fiber ribbons were twisted together to form a 144-core optical fiber unit. 48 144-core optical fiber units were supplied and twisted together, and then a pressure winding member made of water-absorbent nonwoven fabric was attached vertically and rolled with a forming jig to create a 6,912-core core. Note that a flame-retardant member was also wrapped vertically around the outer periphery of some of the cores (pressure winding members).

A water-absorbing resin powder using sodium polyacrylate was applied to the core thus prepared. A core coated with water-absorbing powder, a tension member, and a tearing string for tearing the outer sheath were arranged along the length of the cable, and the outer sheath was extruded into a cylindrical shape using a mouthpiece capable of forming grooves. Note that the groove was formed straight in the longitudinal direction. Thereafter, it was cooled to 20° C. by water cooling to produce an optical fiber cable.

Here, two tension members made of G-FRP (glass fiber reinforced resin) with a diameter of 2.0 mm were used as the tension members. In addition, the outer covering material was made of flame-retardant PE. The outer diameter of the optical fiber cable was 29 to 30 mm, and the jacket thickness was 2.5 mm.

A plurality of types of optical fiber cables of Examples 1 to 4 were prepared by changing the presence or absence of a flame-retardant member and the size and number of grooves. The form of each optical fiber cable is shown in Table 1.

Comparative Example 1 differs from Example 2 in that no grooves are formed on the inner surface of the outer sheath. In Comparative Example 1, water-absorbent resin powder is also applied before the outer sheath is extruded. In Comparative Example 2, instead of applying water-absorbent resin powder, an external pressing wrap member made of water-absorbent nonwoven fabric is wrapped vertically around the outer periphery of the flame-retardant member. In other words, neither Comparative Example 1 nor Comparative Example 2 has grooves formed on the inner surface of the outer sheath.

The waterproof properties were evaluated as follows. A 40 m optical fiber cable as a test specimen with both end faces exposed was placed horizontally, a hollow container for injecting water was connected to one end, and water was poured into the hollow container. Note that the water head length, which is the height from the center of the optical fiber cable to the water surface of the hollow container, was 1 m. This state was maintained for 10 days, and those with no water leakage from the other end were marked as ○, and those with water leakage were marked as ×. It should be noted that both tap water and seawater were evaluated, and those that were rated ○ in both cases were given a rating of ○ for waterproofing.

The outer diameter was determined based on the optical fiber cable wrapped with a flame-retardant member, and 30 mm or less was rated as ○, and 31 mm or more was rated as x. In addition, if both the waterproof judgment and the outer diameter were ○, the overall judgment was ○, and if either one was ○, the overall judgment was ○.

Examples 1 to 4, in which grooves were formed on the inner surface of the outer cover and water-absorbing resin powder was applied before extrusion of the outer cover, all received an overall evaluation of ○. In Examples 1 to 4, the total cross-sectional area of the groove/internal cross-sectional area of the jacket was within the range of 0.6% to 2.4%.

On the other hand, in Comparative Example 1, in which the water-absorbing resin powder was applied without grooves and the outer cover was extruded, the water-absorbing resin powder fell off when the outer cover was extruded, making it difficult to ensure sufficient water absorption performance. could not. In addition, in Comparative Example 2, in which a water-absorbing pressing member was placed around the outer periphery of the flame-retardant member instead of applying water-absorbing resin powder, water absorption was secured, but the outer diameter became large, and the outer diameter evaluation became ×.

The product passed both the flammability test specified in UL1666 and the smoke generation test specified in ULST-1.

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 embodiments described above. It is clear that those skilled in the art can come up with various changes or modifications within the scope of the technical idea stated in the claims, and these naturally fall within the technical scope of the present invention. It is understood that it belongs.

1, 1a, 1b... Optical fiber cable 3... Optical fiber core 5... Optical fiber unit 7... Presser winding member 9... Tension member 11... Tear string 13... Outer jacket 15... Core portion 17... Flame retardant member 19... Groove 21... Water absorbing member

Claims (4)

A core portion consisting of a plurality of optical fiber cores,
a pressing member disposed around the outer periphery of the core portion;
an outer cover provided on the outer periphery of the presser winding member;
Equipped with
An optical fiber cable, characterized in that a groove is provided on the inner surface of the jacket, and a water-absorbing member is disposed in the groove. The optical fiber cable according to claim 1, characterized in that in a cross section perpendicular to the longitudinal direction of the optical fiber cable, the total cross-sectional area of the grooves is 0.6% or more and 2.4% or less of the inner cross-sectional area of the jacket not including the grooves. The optical fiber cable according to claim 1, characterized in that a flame-retardant material is arranged on the outer periphery of the pressure winding member, and the outer jacket is arranged on the outer periphery of the flame-retardant material. The optical fiber cable according to claim 1, characterized in that the grooves are arranged in an S-shape or SZ-shape in the longitudinal direction.

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