JP7800293B2 - Optical cable slot and optical cable - Google Patents

Description

This disclosure relates to a slot for an optical cable and an optical cable.

Optical cable slots with multiple grooves on their outer periphery are known. Each groove in this optical cable slot accommodates a single optical fiber core or a ribbon core made up of multiple optical fiber cores bundled together with a coating.

Slots for optical cables are typically formed by profile extrusion molding using a resin composition such as polyethylene. Optical cable slots have multiple ribs erected on the outer periphery in a spiral or SZ pattern in the axial direction, with two adjacent ribs forming side walls that form a groove.

Such slots for optical cables have been devised using polyethylene, which exhibits excellent surface smoothness and dimensional stability (see Patent Document 1).

Japanese Patent Application Publication No. 7-333476

An optical cable slot according to one aspect of the present disclosure contains a resin with a flexural modulus of elasticity of 1000 MPa or greater, and has multiple ribs spirally arranged in the axial direction on its outer peripheral surface, with the ratio h1/t of the average height h1 of the ribs to the average thickness t being 4 or greater, the ribs having multiple slits extending in the axial direction from the outer edge in the longitudinal direction, and the ratio h2/h1 of the average depth h2 of the slits to the average height h1 of the ribs being 0.5 or greater and 0.8 or less.

FIG. 1 is a schematic cross-sectional view of an optical cable according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of an optical cable slot according to one embodiment of the present disclosure. FIG. 3 is a schematic partial perspective view of a rib. FIG. 4 is a schematic partial view of a slot for explaining the average height of a rib. FIG. 5 is a schematic partial diagram of a rib in a plan view.

[Problem to be solved by the present disclosure]
Optical cables are subject to external bending during cable routing, so they require crushing strength to withstand such bending. Furthermore, optical cables used in data centers and other applications are required to transmit large amounts of data, so they must pack as many optical fibers as possible into a given diameter of optical cable to increase density. However, when polyethylene, which has traditionally been used as a material for optical cable slots, is used, the crushing strength of the optical cable ribs is insufficient when the ribs are thinned to increase optical fiber density. On the other hand, using a high-strength material for optical cable slots reduces flexibility, which creates the problem of rib undulations occurring more easily when the optical cable is bent.

This disclosure was made based on the above circumstances, and aims to provide an optical cable slot that is thin-walled but has excellent crushing strength and is equipped with ribs that can suppress undulation when the optical cable is bent.

[Effects of the present disclosure]
The optical cable slot of the present disclosure allows for a thinner rib, and is excellent in the crush strength of the rib and in the suppression of undulations when the optical cable is bent.

Description of the embodiments of the present disclosure
First, embodiments of the present disclosure will be listed and described.

An optical cable slot according to one aspect of the present disclosure contains a resin with a flexural modulus of elasticity of 1000 MPa or greater, and has multiple ribs spirally arranged in the axial direction on its outer peripheral surface, with the ratio h1/t of the average height h1 of the ribs to the average thickness t being 4 or greater, the ribs having multiple slits extending in the axial direction from the outer edge in the longitudinal direction, and the ratio h2/h1 of the average depth h2 of the slits to the average height h1 of the ribs being 0.5 or greater and 0.8 or less.

The optical cable slot (hereinafter simply referred to as the slot) contains a resin with a flexural modulus of 1000 MPa or greater, thereby providing excellent crushing strength against bending. Furthermore, by setting the ratio h1/t (the average height h1 of the rib of the optical cable slot) to the average thickness t at 4 or greater, the rib can be thinned. Furthermore, by having the rib have multiple slits extending axially from the longitudinal outer edge, and by setting the ratio h2/h1 (the average depth h2 of the slits to the average height h1 of the rib) at 0.5 or greater and 0.8 or less, the rib can be given appropriate elasticity while maintaining its crushing strength. Therefore, the optical cable slot not only allows for thinning of the rib, but also provides excellent rib crushing strength and suppresses undulation when the optical cable is bent. Here, "flexural modulus" refers to a value measured in accordance with JIS-K-7171 (2016). In this disclosure, the "average" in "average thickness" refers to the average value of thicknesses measured at three random locations. The same applies to the "average height," "average width," and "average depth" described below. In this disclosure, "thin-walled" means that the ratio h1/t of the average height h1 to the average thickness t is 4 or greater.

It is preferable that the twist pitch of the rib be 600 mm or more and 1600 mm or less. By having a twist pitch of 600 mm or more and 1600 mm or less, the crush strength of the rib can be maintained while improving the effect of suppressing undulation during bending. "Rib twist pitch" refers to the axial spacing at which the ribs 2 are twisted spirally and are positioned at the same radial position in the cross section of the optical cable slot.

It is preferable that the average width of the slits is 0.1 mm or more and 20 mm or less. By having the average width of the slits be 0.1 mm or more and 20 mm or less, the crush strength of the rib can be maintained while improving the effect of suppressing undulations when bending.

It is preferable that the rib has at least one slit per pitch. By having the rib have at least one slit per pitch, the crush strength of the rib can be maintained while improving the effect of suppressing undulation during bending.

An optical cable according to another aspect of the present disclosure comprises the slot, a tension member embedded in the center of the slot, an optical fiber disposed between adjacent ribs, and an outer jacket covering the slot and the optical fiber.

This optical cable is equipped with the optical cable slot disclosed herein, which allows for the thinning of the ribs in the optical cable slot, while also improving the crush strength of the ribs and suppressing undulation when the optical cable is bent.

[Details of the embodiment of the present disclosure]
Hereinafter, an optical cable slot and an optical cable according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

<Optical cable>
As shown in FIG. 1, the optical cable 11 includes an optical cable slot (hereinafter also referred to as a slot) 2 having a plurality of ribs 21, a tension member 1 embedded in the center of the slot 2, an optical fiber 4 arranged between adjacent ribs 21, and an outer jacket 5 covering the slot 2 and the optical fiber 4.

The optical cable 11 may further include an adhesive layer that bonds the tension member 1 to the optical cable slot, with the tension member 1 being embedded in the optical cable slot 2 via the adhesive layer. The adhesive layer is primarily made of an adhesive that bonds the tension member 1 to the optical cable slot 2. There are no particular restrictions on the adhesive used, as long as it can bond the tension member 1 to the optical cable slot 2, and thermoplastic resins such as polyethylene can be used. The "major component" refers to the component with the highest content, for example, a component that accounts for 50% or more by mass of the total mass of the adhesive layer.

<Optical cable slot>
The optical cable slot 2 according to one embodiment of the present disclosure has a tension member 1 embedded in the center and multiple ribs spiraling in the axial direction on the outer circumferential surface. The optical cable slot 2 has multiple ribs 21 protruding from the circumferential surface of a main body 24. The central axis of the main body 24 coincides with the central axis of the tension member 1.

The optical cable slot 2 contains a resin with a flexural modulus of 1000 MPa or more. If the flexural modulus of the optical cable slot 2 is lower than the lower limit, the optical cable 11 may not be able to deform sufficiently. There is no particular upper limit to the flexural modulus of the optical cable slot 2, but it is, for example, 2500 MPa.

Examples of resins with a flexural modulus of 1000 MPa or greater that can be used to form the optical cable slot 2 include polyethylene and polypropylene. Of these, polypropylene or high-density polyethylene is preferred from the perspective of increasing the crushing strength of the rib 21.

The lower limit of the resin content in the optical cable slot 2 with a flexural modulus of 1000 MPa or greater is preferably 60% by mass, more preferably 70% by mass, and even more preferably 75% by mass. If the resin content is less than 50% by mass, the crush strength of the optical cable slot 2 and the effect of suppressing undulation during bending may not be sufficiently achieved.

The optical cable slot 2 may contain other components in addition to the resin having a modulus of 1000 MPa or more. Examples of other components include resins other than the resin having a modulus of 1000 MPa or more, and various additives. The upper limit of the content of other components is preferably 5% by mass, more preferably 1% by mass, and even more preferably it is substantially free of other components.

The optical cable slot 2 has a groove formed by the surfaces of adjacent ribs 21, and the optical fiber 4 is arranged in this groove. Figure 2 shows an example in which there are eight optical cable slot 2 grooves. As shown in Figure 3, the optical cable slot 2 grooves are formed in a spiral shape. Also, as shown in Figure 3, the optical cable slot 2 grooves are formed in a spiral shape. Furthermore, the shape of the groove formed by adjacent ribs 21 in a cross-sectional view can be, for example, V-shaped, rectangular, U-shaped, or fan-shaped. As shown in Figure 2, in this embodiment, the groove shape is fan-shaped.

(rib)
The ribs 21 have a shape that protrudes from the peripheral surface of the main body of the slot 2. The ribs 21 are provided spirally in the axial direction on the outer peripheral surface. Each rib 21 is strip-shaped and is formed integrally with the main body 24 such that its inner edge in the longitudinal direction is joined to the main body 24 in a spiral shape. Each rib 21 is strip-shaped and is formed integrally with the main body 24 such that its inner edge in the longitudinal direction is joined to the main body 24 in a spiral shape.

The grooves of the slots 2 are formed between adjacent ribs 21, separating them from the grooves of other optical cable slots 2. In other words, the grooves of the optical cable slots 2 are grooves between adjacent ribs 21. The optical fibers 4 are placed in the grooves formed between adjacent ribs 21.

The twist pitch of the rib is preferably 600 mm or more and 1600 mm or less, and more preferably 600 mm or more and 800 mm or less. By having a twist pitch of 600 mm or more and 1600 mm or less, the crush strength of the rib can be maintained while improving the effect of suppressing undulation during bending.

The average height h1 of the ribs 21 is preferably 5 mm or more and 30 mm or less, and more preferably 6 mm or more and 25 mm or less. By setting the average height h1 of the ribs 21 to 5 mm or more and 30 mm or less, the crush strength of the ribs 21 can be maintained while improving the effect of suppressing undulation during bending.

The "average height h1 of the ribs 21" refers to the average value of the height measured using the following procedure. Figure 4 is a schematic partial diagram of a slot 2 to explain the average height h1 of the ribs 21. As shown in Figure 4, first, a straight line is set connecting two points L1 and L2 located at the lowest points of adjacent grooves via any rib 21. Then, when this straight line is set as the base, the average height h1 is determined as the average height of the perpendicular lines connecting the base and the apex of the rib 21.

The average thickness t of the rib 21 is preferably 0.5 mm or more and 5.0 mm or less, and more preferably 0.5 mm or more and 3 mm or less. By setting the average thickness t of the rib 21 to 0.5 mm or more and 3 mm or less, the crush strength of the rib 21 can be maintained while improving the effect of suppressing undulation during bending.

The ratio h1/t of the average height h1 to the average thickness t of the rib 21 is 4 or greater, and preferably 5 or greater. By making the ratio h1/t of the average height h1 to the average thickness t of the rib 21 4 or greater, the rib 21 can be made thinner. By making the rib 21 thinner, optical fibers can be accommodated at a higher density.

(slit)
The rib has a plurality of slits 25 extending in the axial direction from the outer edge in the longitudinal direction. The plurality of slits 25 are arranged at intervals in the longitudinal direction of the rib 21. The slits 25 open on the outer edge side in the longitudinal direction, and as shown in Fig. 4, the slits 25 extend inward substantially perpendicularly from the outer edge in the longitudinal direction of the rib 21 in a plan view.

The ratio h2/h1 of the average depth h2 of the slits 25 to the average height h1 of the ribs 21 is 0.5 or greater and 0.8 or less, and preferably 0.6 or greater and 0.8 or less. By setting the ratio h2/h1 of the average depth h2 of the slits 25 to the average height h1 of the ribs 21 to 0.5 or greater and 0.8 or less, it is possible to impart appropriate elasticity while maintaining the crushing strength of the ribs.

It is preferable that the rib 21 have at least one slit per pitch, and more preferably four or more slits per pitch. By having the rib 21 have at least one slit per pitch, the crush strength of the rib 21 can be maintained while improving the effect of suppressing undulation during bending.

The average width w1 of the slits 25 is preferably 0.1 mm or more and 20 mm or less, and more preferably 2 mm or more and 18 mm or less. By setting the average width w1 of the slits 25 to 0.1 mm or more and 20 mm or less, the crush strength of the rib can be maintained while improving the effect of suppressing undulation during bending.

(tension member)
The optical fiber 11 has a tension member 1 disposed in the center to bear tension and prevent it from stretching due to its own weight during installation. If the optical fiber slot and the tension member are not firmly bonded, they may shift during installation, causing only the optical fiber slot to stretch, putting tension on the optical fiber and potentially causing transmission loss or breakage. The tension member 1 can be, for example, a metal single wire or twisted wire, or a linear body made of organic or inorganic fiber.

(optical fiber)
A known optical fiber can be used as the optical fiber 4. For example, a ribbon core wire in which a plurality of optical fiber core wires are bundled with a coating can be suitably used, but a single optical fiber core wire can also be used. When a ribbon core wire is used as the optical fiber 4, the optical cable 11 becomes a so-called tape slot type optical cable.

(outer covering)
The jacket 5 is a resin layer that covers the outer periphery of the optical cable slot 2 and the optical fiber 4. There are no particular limitations on the main component of the jacket 5, and polyethylene or the like is used, for example. The jacket 5 may have a multi-layer structure having multiple types of layers.

[Optical cable manufacturing method]
Next, an example of a method for manufacturing the optical cable will be described. The method for manufacturing the optical cable includes, for example, a step of manufacturing a slot for the optical cable, a step of assembling the optical cables, and a step of covering the outer jacket.

In the process for manufacturing an optical cable slot (optical cable slot manufacturing process), the optical cable slot is formed, for example, by profile extrusion of the resin composition that constitutes the optical cable slot. Specifically, the tension member and heated resin composition are extruded through a die to form the optical cable slot that covers the tension member. By rotating the die during extrusion, multiple ribs are erected spirally in the axial direction on the outer circumferential surface of the optical cable slot.

In addition, optical cable slots can be manufactured not only by extrusion molding, but also by injection molding, compression molding, etc. A cutting machine presses blades against the resulting slot at regular intervals from the outer longitudinal edge of the rib toward the axial direction to form slits. The depth and width of the slits can be adjusted by changing the length and thickness of the blades pressed against them.

In the process of assembling the optical cables (assembly process), the optical fibers are inserted into the grooves of the optical cable slots formed in the optical cable slot manufacturing process and then pressed and wound to assemble the optical cables.

The jacketing process involves covering the outer periphery of the assembly of optical fiber and slot for optical cable obtained in the assembly process with a jacket. This covering method can be, for example, extrusion molding.

This optical cable slot allows for a thinner rib, which increases the optical fiber capacity, while also improving the rib's crush strength and suppressing undulation when the optical cable is bent.

This optical cable is equipped with the optical cable slot of the present disclosure, which allows for the thinning of the ribs in the optical cable slot, while also improving the crush strength of the ribs and suppressing undulation when the optical cable is bent.

Other Embodiments
The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to the following examples.

<Test No. 4 to Test No. 6>
A slot was molded using 100 parts by mass of polypropylene (Novatec PP EA9FTD, manufactured by Japan Polypropylene) with a flexural modulus of 1800 MPa as the forming material, and the slot was coated on the outer circumferential surface of the metal tension member.

The flexural modulus of the resin used to make the slots was measured using a tensile tester in accordance with JIS-K-7171 (2016).

The slots were fabricated by heating the resin to 180°C and extrusion-molding it. The rib shape had an average rib height h1 of 24 mm, an average rib thickness t of 3 mm (thin-walled type), and a ratio of average rib height to average rib thickness h1/t of 8. The spiral slot shape was unidirectionally twisted, with one pitch (twist pitch) of 600 mm. The ribs had slits with an average slit depth h2, a ratio h2/h1 of average slit depth h2 to average rib height h1, an average slit width w1, and the number of slits per pitch as shown in Table 1.

<Test No. 3>
The slot was molded in the same manner as in Test No. 4, except that no slits were formed in the ribs of the slot, and the outer peripheral surface of the tension member was covered.

<Test No. 2>
The slot was formed in the same manner as in Test No. 4, except that 100 parts by mass of polyethylene ("Nipolon L F13" manufactured by Tosoh Corporation) with a flexural modulus of 800 MPa was used as the slot forming material, and a slit was not formed in the slot, and the slot was coated on the outer peripheral surface of the tension member.

<Test No. 1>
The slot was molded in the same manner as in Test No. 2, except that the rib shape of the slot was such that the average rib height h1 was 24 mm, the average rib thickness t was 8 mm (conventional type), and the ratio h1/t of the average rib height to the average rib thickness was 3, and the slot was coated on the outer peripheral surface of the tension member.

<Evaluation>
The test specimens No. 1 to No. 6, which were equipped with the fabricated tension members and slots, were evaluated as follows. The results are shown in Table 1.

(Swell evaluation)
The optical cable slot was wound in two layers around a drum with a radius of 10D (D: diameter of the optical cable slot) mm with a tension of 500 N, and then the presence or absence of undulations in the ribs was visually confirmed. If undulations were observed in the ribs, the product was deemed to have failed.

(Crushing strength test)
Two 100mm square stainless steel plates with an average thickness of 10mm were placed above and below the slot, and a load was applied using a compression testing machine. The load at which the rib deformed was taken as the crushing strength, with a grade of A (pass) being given for 2200N or more, and a grade of B (fail) being given for less than 2200N.

(Opportunity of optical fiber in the cable)
Regarding the density of the optical fibers within the cable, the optical fiber occupancy rate was determined by dividing the total cross-sectional area of all the optical fibers contained in the space surrounded by the two ribs and the outer sheath by the cross-sectional area of the space surrounded by the two ribs and the outer sheath, and an occupancy rate of 0.4 or more was rated A, and an occupancy rate of less than 0.4 was rated B.

As shown in Table 1, Tests No. 4, No. 6, and No. 7, in which the resin material had a flexural modulus of 1000 MPa or greater, the ratio h1/t (the ratio of the average slit rib height h1 to the average rib thickness t) was 4 or greater, and the ratio h2/h1 (the ratio of the average slit depth h2 to the average rib height h1) was 0.5 or greater and 0.8 or less, exhibited excellent rib crush strength, and no rib waviness was observed in an evaluation of the rib waviness after winding around a drum. Tests No. 4, No. 6, and No. 7 demonstrate improved optical fiber density while maintaining the same crush strength as Test No. 1, a conventional reference example with thick ribs (h1/t less than 4) and a resin material with a flexural modulus of 800 MPa.

On the other hand, in Test No. 2, in which the rib of Reference Example Test No. 1 was thinned, the flexural modulus of the resin material was 800 MP, and there was no slit, no undulation occurred in the rib when wrapped, but the crushing strength of the rib was poor. In Test No. 3, in which the rib was thinned, the flexural modulus of the resin material was 900 MP, and there was no slit, there was undulation in the rib when wrapped, and the crushing strength was poor.
Furthermore, as shown in Test No. 5, even when the flexural modulus of the resin material was 1000 MPa or more, if the thin-walled rib did not have a slit, undulation occurred when the rib was wound. Furthermore, as shown in Test No. 8, even when the thin-walled rib had a slit and the flexural modulus of the resin material was 1000 MPa or more, if the h2/h1 ratio was less than 0.5, undulation occurred when the rib was wound. In Test No. 9, where the h2/h1 ratio exceeded 0.8, the rib's crush strength was poor.

These results demonstrate that the optical cable slot allows for thinner ribs, has high crushing strength, and is effective in suppressing rib undulation when the optical cable is bent.

By thinning the ribs, the optical cable slots can accommodate more optical fibers, while also improving the crushing strength of the ribs and suppressing undulations when the optical cable is bent. Therefore, optical cables equipped with the optical cable slots can be ideally used for cabling between data centers or data center floors, where large volumes of information are transmitted.

REFERENCE SIGNS LIST 1 tension member 2 optical cable slot 4 optical fiber 5 jacket 11 optical cable 21 rib 22 slot center 24 slot body 25 slit

Claims (5)

Contains a resin having a flexural modulus of 1000 MPa or more,
a main body; and a plurality of ribs spirally provided on an outer circumferential surface of the main body in a direction along the central axis of the main body ;
a ratio h1/t of an average height h1 of the rib from the central axis toward the apex of the rib to an average thickness t of the rib in a cross section perpendicular to the central axis is 4 or more;
the rib has a plurality of slits extending from its longitudinal outer edge toward the central axis ;
A slot for optical cable, wherein the ratio h2/h1 of the average depth h2 of the slit from the longitudinal outer edge of the slit toward the central axis to the average height h1 of the rib is 0.5 or more and 0.8 or less. The optical cable slot of claim 1, wherein the twist pitch of the rib is 600 mm or more and 1600 mm or less. The optical cable slot of claim 1 or 2, wherein the average width of the slit is 0.1 mm or more and 20 mm or less. The optical cable slot of claim 1 or 2, wherein the rib has at least one slit per pitch. The optical cable slot according to claim 1 or 2;
a tension member embedded in the center of the slot;
an optical fiber disposed between adjacent said ribs;
an outer jacket covering the slot and the optical fiber.