Patent Application
20240053559
The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2021-083454, filed May 17, 2021. The contents of this application are incorporated herein by reference in their entirety.
The present invention relates to an optical cable.
PTL 1 discloses a technique of disposing a metal reinforcement sheet inside an outer sheath (external sheath) to protect optical fibers from being bitten by an animal such as a rat or a squirrel.
When an optical cable in which an outer sheath and a reinforcement sheet are adhered together gets twisted, the outer sheath may get damaged so as to crack.
One or more embodiments can suppress damage to an outer sheath.
An optical cable according to one or more embodiments includes: an optical fiber; an outer sheath configured to house the optical fiber; and a tubular reinforcement sheet located between the optical fiber and the outer sheath. In a cross section perpendicular to a length direction, the optical cable includes a first zone in which the reinforcement sheet and the outer sheath are adhered together, and a second zone in which an adhesive strength between the reinforcement sheet and the outer sheath is weaker than the adhesive strength in the first zone (an adhesive strength between the reinforcement sheet and the outer sheath in a first zone is stronger than an adhesive strength between the reinforcement sheet and the outer sheath in a second zone).
Other features of one or more embodiments will become apparent from the following disclosure of the present Description and Drawings.
One or more embodiments can suppress damage to an outer sheath.
At least the following features are disclosed in the Description and Drawings as described below.
Aspect 1 is an optical cable including: an optical fiber; an outer sheath configured to house the optical fiber; and a tubular reinforcement sheet located between the optical fiber and the outer sheath. In a cross section perpendicular to a length direction, the optical cable includes a first zone in which the reinforcement sheet and the outer sheath are adhered together, and a second zone in which an adhesive strength between the reinforcement sheet and the outer sheath is weaker than the adhesive strength in the first zone. With this optical cable, damage to the outer sheath can be suppressed.
Aspect 2 is an optical cable according to Aspect 1, wherein, where a percentage of the second zone with respect to an entire circumference of the reinforcement sheet is defined as A (%) and elongation at break of a resin constituting the outer sheath is defined as B (%), the product of A and B is 500 or greater. Thus, damage to the outer sheath can be suppressed.
Aspect 3 is an optical cable according to Aspect 2, wherein the percentage of the second zone with respect to the entire circumference of the reinforcement sheet is 50% or less. Thus, damage to the outer sheath can be suppressed.
Aspect 4 is an optical cable according to any one of Aspects 1 to 3, wherein the adhesive strength of the second zone is 0.5 N/mm or less. Thus, the outer sheath in the second zone can easily elongate and deform when twisted, and damage to the outer sheath can be suppressed.
Aspect 5 is an optical cable according to any one of Aspects 1 to 4, wherein the second zone is located in a region including an outer end of the reinforcement sheet wrapped in a tubular form. Thus, damage to the outer sheath can easily be suppressed.
Aspect 6 is an optical cable according to Aspect 5, wherein the second zone is located from the outer end toward an overlapping part in which both edges of the reinforcement sheet wrapped in a tubular form overlap one another. Thus, the optical cable can be produced easily.
Aspect 7 is an optical cable according to Aspect 5, wherein the second zone is located in a manner crossing over the outer end in a circumferential direction. Thus, damage to the outer sheath can easily be suppressed.
Aspect 8 is an optical cable according to any one of Aspects 1 to 4, wherein the second zone is located in a non-overlapping part other than the overlapping part in which both edges of the reinforcement sheet wrapped in a tubular form overlap one another, and the outer end of the reinforcement sheet does not coincide with an end of the second zone. Also with this structure, damage to the outer sheath can easily be suppressed.
Aspect 9 is an optical cable according to any one of Aspects 1 to 8, wherein no member other than an adhesive is located between the reinforcement sheet and the outer sheath. This achieves a configuration in which adhesive strength can be adjusted easily.
Aspect 10 is an optical cable according to any one of Aspects 1 to 9, wherein no tension member is embedded in the outer sheath. Thus, damage to the outer sheath can easily be suppressed.
Aspect 11 is an optical cable according to any one of Aspects 1 to 9, wherein a tension member is embedded in the outer sheath, and the tension member is located in a region on a radially outer side of the second zone within the outer sheath. Thus, damage to the outer sheath can easily be suppressed.
The optical cable 1 is a cable configured to house an optical fiber 12. In one or more embodiments, the optical cable 1 includes optical fibers 12, an outer sheath 20, and a reinforcement sheet 30. Herein, the optical cable 1 includes: an inner cable 10 including the optical fibers 12; and a protection tube 3 constituted by the outer sheath 20 and the reinforcement sheet 30.
The inner cable 10 is a cable including the optical fibers 12 and housed within the outer sheath 20. The inner cable 10 illustrated in the figure includes a core 11 and an inner sheath 14. The core 11 includes a plurality of optical fibers 12 and is housed within the inner sheath 14. The core 11 may be constituted by assembling a plurality of optical fibers 12, or may be constituted by one or more optical fiber ribbons, or may be constituted by a single optical fiber. The core 11 may be constituted by wrapping the optical fibers 12 with a sheet-like member (for example, a wrapping tape 13), or by bundling the optical fibers with a string-like member. The inner sheath 14 is a member for covering the core 11. Tension members 15 are embedded in the inner sheath 14. Note, however, that the inner sheath 14 does not have to include a tension member 15. The inner cable 10 illustrated in the figure is a slotless-structure center-tube-type optical cable. Note, however, that the inner cable 10 may be a slotted cable or a loose tube cable.
Further, the optical cable 1 does not have to include the inner cable 10 covered by the inner sheath 14. For example, instead of the inner cable 10, the core 11 may be housed directly within the protection tube 3 (the outer sheath 20 and the reinforcement sheet 30). Note, however, that with a configuration wherein the inner cable 10 covered by the inner sheath 14 is housed inside the outer sheath 20 (and the reinforcement sheet 30), it is possible to suppress damage to the optical fibers 12 when cutting open the outer sheath 20 (and the reinforcement sheet 30) with a tool.
The outer sheath 20 is a member (external sheath) configured to house the optical fibers 12. The outer sheath 20 illustrated in the figure is a member configured to house the inner cable 10 including the optical fibers 12. The outer sheath 20 is configured in a tubular form. The outer sheath 20 is disposed in the outer circumference of the reinforcement sheet 30. For example, the outer sheath 20 is constituted by a resin, such as polyethylene (PE), polyvinyl chloride (PVC), etc. The outer sheath 20 is formed by extrusion-molding a molten resin onto the outer circumference of the reinforcement sheet 30. Note that, in the outer sheath 20 illustrated in the figure, no other member, such as a tension member, is embedded therein. It is, however, possible to embed a tension member inside the outer sheath 20, as will be described further below.
The reinforcement sheet 30 is a sheet-like member located between the optical fibers 12 and the outer sheath 20. The reinforcement sheet 30 is disposed along the inner side of the outer sheath 20 in a state formed into a tubular shape. The outer sheath 20 is disposed on the outer side of the reinforcement sheet 30. The optical fibers 12 (in this example, the inner cable 10) are housed on the inner side of the reinforcement sheet 30. Other members, such as rip cords 23, may be housed on the inner side of the reinforcement sheet 30. Note, however, that no member (such as a rip cord) other than an adhesive is interposed between the reinforcement sheet 30 and the outer sheath 20. Not interposing any member (such as a rip cord) other than an adhesive between the reinforcement sheet 30 and the outer sheath 20 can facilitate adjustment of adhesive strength (described below) between the reinforcement sheet 30 and the outer sheath 20.
The reinforcement sheet 30 is constituted, for example, by a metal sheet. More specifically, the reinforcement sheet 30 is constituted by a sheet made of metal, such as stainless steel, copper, copper alloy, etc. By locating the metal-made reinforcement sheet 30 between the optical fibers 12 and the outer sheath 20, it is possible to protect the optical fibers 12 from getting bitten by an animal such as a rat, a squirrel, etc. Note, however, that the material for the reinforcement sheet 30 is not limited to metal, so long as it is possible to suppress the optical fibers 12 from getting bitten by an animal such as a rat, a squirrel, etc. For example, the material for the reinforcement sheet 30 may be fiber-reinforced plastic (FRP) including carbon fiber, glass fiber, aramid fiber, etc.
The reinforcement sheet 30 is formed by wrapping a sheet-like material in a tubular form. The side surface of the reinforcement sheet 30 wrapped in a tubular form may have bellows-like folds like a corrugated tube. The figures are rendered such that the entire side surface of the reinforcement sheet 30 is in contact with the outer sheath 20, but the entire side surface of the reinforcement sheet 30 does not have to be in contact with the outer sheath 20. For example, in cases where the reinforcement sheet 30 is formed like a corrugated tube, the outer sheath 20 may not enter the valley parts of the bellows-like side surface, and in such cases, portions (the valley parts) of the bellows-like side surface may not be in contact with the inner circumferential surface of the outer sheath 20.
The reinforcement sheet 30 is formed into a spiral shape (tubular shape) by overlapping both edges in the width direction. Both edges of the reinforcement sheet 30 in the circumferential direction overlap one another. In the description below, the part in which both edges of the reinforcement sheet 30 overlap one another is referred to as “overlapping part 31”. A part (region) of the reinforcement sheet 30 on the outer side of the overlapping part 31 is referred to as “outer region 31A”, whereas a part (region) of the reinforcement sheet 30 on the inner side of the overlapping part 31 is referred to as “inner region 31B”. An end (joint) on the outer side of the reinforcement sheet 30 is referred to as “outer end 33”. The outer region 31A includes the outer end 33. A part (region) other than the overlapping part 31 of the reinforcement sheet 30 is referred to as a central region or a non-overlapping part.
It is preferable that, in the overlapping part 31, both edges of the reinforcement sheet 30 (the lower side of the outer region 31A and the upper side of the inner region 31B) are adhered together. In this way, the shape of the reinforcement sheet 30 can be easily retained. Note, however, that both edges of the reinforcement sheet 30 do not have to be adhered together in the overlapping part 31. Both ends of the overlapping part 31 (the lower side of the outer region 31A and the upper side of the inner region 31B) are arranged along the circumferential direction. Compared to a configuration wherein both ends of the overlapping part 31 are standing up (i.e., are arranged along the radial direction), by arranging both ends of the overlapping part 31 along the circumferential direction, the area of the overlapping part 31 can be widened even in the small space within the optical cable 1.
In the comparative example, the outer sheath 20 and the entire zone of the outer circumference of the reinforcement sheet 30 are adhered (joined) together with a predetermined adhesive strength. For example, an adhesive layer (for example, a heat-fusion-type adhesive tape) may be applied in advance to the entire zone of the outer circumferential surface of the reinforcement sheet 30, and the outer sheath 20 (molten resin) may be extruded onto the outer circumference of the reinforcement sheet 30 formed in a tubular shape, to thereby cause the reinforcement sheet 30 and the outer sheath 20 to adhere to one another with a predetermined adhesive strength between the outer sheath 20 and the entire zone of the outer circumference of the reinforcement sheet 30. Note, however, that the adhesive layer cannot be formed on the outer end 33 of the reinforcement sheet 30, and therefore, a part that is not joined (non-adhesion part) will exist between the outer end 33 of the reinforcement sheet 30 and the outer sheath 20.
When the optical cable 1 of the comparative example is twisted, stress that is generated in the outer sheath 20 causes the outer sheath 20 to elongate in the circumferential direction. In the comparative example, the reinforcement sheet 30 and the outer sheath 20 are adhered together over the entire outer circumference of the reinforcement sheet 30 (i.e., the outer sheath 20 is restrained by the reinforcement sheet 30), and therefore, only the outer sheath 20 in the vicinity of the outer end 33 of the reinforcement sheet 30 (i.e., the outer sheath 20 in the vicinity of the non-adhesion part) will elongate and deform in the circumferential direction. Stated differently, in the comparative example, the elongation strain at the time of twisting of the optical cable 1 concentrates at the part indicated by the bold line in
In one or more embodiments, in a cross section perpendicular to the length direction, a first zone 41 and a second zone 42 are located in the circumferential direction between the reinforcement sheet 30 and the outer sheath 20. In
Similar to the comparative example, in the first zone 41, the reinforcement sheet 30 and the outer sheath 20 (first outer sheath 21) are adhered together. The adhesive strength between the reinforcement sheet 30 and the outer sheath 20 (the second outer sheath) in the second zone 42 is weaker than the adhesive strength between the reinforcement sheet 30 and the outer sheath 20 (the first outer sheath) in the first zone 41. Note that, in the second zone 42, the reinforcement sheet 30 and the outer sheath 20 (the second outer sheath) do not have to be adhered together.
As described above, when the optical cable 1 is twisted, stress that is generated in the outer sheath 20 causes the outer sheath 20 to elongate in the circumferential direction. In one or more embodiments, the adhesive strength in the second zone 42 is relatively weak. Therefore, in the second outer sheath 22 (the outer sheath 20 on the outer periphery of the second zone 42; the shaded (stippled) part in the figure), elongating deformation in the circumferential direction is permitted, compared to the first outer sheath 21 (the outer sheath 20 on the outer periphery of the first zone 41). In one or more embodiments, the part that can be subjected to elongating deformation (i.e., the second outer sheath 22; the shaded (stippled) part in the figure) is wider in the circumferential direction than in the comparative example, and thus, elongation strain of the outer sheath 20 can be dispersed. As a result, in one or more embodiments, damage to the outer sheath 20 can be suppressed compared to the comparative example.
The adhesive strength between the reinforcement sheet 30 and the outer sheath 20 can be measured in terms of “peel strength”. More specifically, the adhesive strength is measured as follows. First, a rectangular test piece is prepared by cutting the outer sheath 20 and the reinforcement sheet 30 of the optical cable 1 along the circumferential direction. At one end of the test piece (one end in the circumferential direction), peeling stress is applied so that the reinforcement sheet 30, the outer sheath 20, and the adhesive joint part between the reinforcement sheet 30 and the outer sheath 20 are in a T-peel geometry in a manner that breaking of the adhesive joint part therebetween proceeds in a direction corresponding to the circumferential direction. The peel strength (unit: N/mm) is measured at the time the adhesive joint part between the reinforcement sheet 30 and the outer sheath 20 is broken, and the peel strength is considered as the adhesive strength. In one or more embodiments, the peel strength (unit: N/mm) when the adhesive joint part between the second outer sheath 22 and the reinforcement sheet 30 is broken is weaker than the peel strength when the adhesive joint part between the first outer sheath 21 and the reinforcement sheet 30 is broken.
Note that, preferably, the adhesive strength between the reinforcement sheet 30 and the outer sheath 20 (the second outer sheath 22) in the second zone 42 is 0.5 N/mm or less (described further below). When the adhesive strength between the reinforcement sheet 30 and the outer sheath 20 in the second zone 42 is 0.5 N/mm or less, the reinforcement sheet 30 and the outer sheath 20 will be peeled apart in the second zone 42 at the time of twisting of the optical cable 1, and thus, the outer sheath 20 in the second zone 42 will be able to elongate and deform in the circumferential direction (and as a result, damage to the outer sheath 20 can be suppressed).
The cross section illustrated in
An example of a method for making the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 is as follows. First, a reinforcement sheet 30 having an adhesive layer in advance is prepared. The adhesive layer can be formed on the reinforcement sheet 30 by, for example, attaching a heat-fusion-type adhesive tape to the reinforcement sheet 30. By attaching, to the reinforcement sheet 30, an adhesive tape that is narrower than the width of the reinforcement sheet 30, no adhesive layer is formed in a region corresponding to the second zone 42 of the reinforcement sheet 30. (For example, a region corresponding to the second zone 42 is kept in a state in which no adhesive tape is bonded thereto.) Next, the reinforcement sheet 30 is formed into a tubular shape, and an outer sheath 20 (molten resin) is extrusion-molded onto the outer circumference of the tubular reinforcement sheet 30. The first zone 41 is provided with the adhesive layer in advance, and therefore, in the first zone 41, the heat of the outer sheath 20 (molten resin) at the time of extrusion molding causes the reinforcement sheet 30 and the outer sheath 20 (first outer sheath 21) to adhere to one another via the adhesive layer. Further, the inner region 31B of the overlapping part 31 is also provided with an adhesive layer in advance, and therefore, the heat of the outer sheath 20 (molten resin) at the time of extrusion molding causes both ends of the reinforcement sheet 30 to be adhered together in the overlapping part 31. On the other hand, the second zone 42 does not have an adhesive layer, and therefore, the adhesive strength of the second zone 42 becomes weaker than the adhesive strength of the first zone 41.
Note that it is also possible to make the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 without using an adhesive layer. For example, at the time of extrusion-molding the outer sheath 20 (molten resin) onto the outer circumference of the tubular reinforcement sheet 30, a larger space may be formed between the outer sheath 20 (molten resin) and the reinforcement sheet 30 at the part corresponding to the second zone 42 compared to the part corresponding to the first zone 41, and in this way, it is possible to make the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 without using an adhesive layer. In this case, for example, an extrusion die (a die for determining the shape of the outer sheath 20) of an extruder may be shaped such that a part of the die's inner circumferential surface corresponding to the second zone 42 is formed in an oval-like shape or outwardly-protruding shape, and in this way, a space can be formed between the reinforcement sheet 30 and the outer sheath 20 (molten resin) at the part corresponding to the second zone 42, thus making the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41.
Note, however, that methods for making the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 are not limited to the methods described above (described further below).
In the example illustrated in
In the example illustrated in
In both the first modified example and the second modified example, a first zone 41 and a second zone 42 are located between a reinforcement sheet 30 and an outer sheath 20 in a cross section perpendicular to the length direction. In
In the first modified example illustrated in
In the first modified example illustrated in
Note that, also in the first modified example, it is possible to make the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 by preparing a reinforcement sheet 30 in which no adhesive layer is disposed in a region of the reinforcement sheet 30 corresponding to the second zone 42 (and further forming this reinforcement sheet 30 into a tubular shape and extrusion-molding an outer sheath 20 onto the outer circumference of the tubular reinforcement sheet 30). With this method, however, it is difficult to achieve both the adhesion of both ends of the reinforcement sheet 30 in the overlapping part 31 and the formation of the second zone 42 from the outer end 33 toward the central region side. Therefore, in the first modified example, it is preferable to weaken the adhesive strength of the second zone 42 by pre-heating the adhesive layer after forming the reinforcement sheet 30 into a tubular shape.
In the second modified example illustrated in
In case of the second modified example, it is possible to make the adhesive strength of the second zone 42 weaker than the adhesive strength of the first zone 41 by preparing a reinforcement sheet 30 in which no adhesive layer is disposed in a region corresponding to the second zone 42 (and further forming this reinforcement sheet 30 into a tubular shape and extrusion-molding an outer sheath 20 onto the outer circumference of the tubular reinforcement sheet 30). Further, in case of the second modified example, it is also possible to weaken the adhesive strength of the second zone 42 by pre-heating the adhesive layer after forming the reinforcement sheet 30 into a tubular shape, as in the first modified example.
Also in the second modified example illustrated in
In case of the second modified example illustrated in
In the aforementioned optical cables 1 illustrated in
Optical cables 1 having the structure illustrated in
As shown in Table 1, the percentage of the second zone 42 with respect to the entire circumference of the reinforcement sheet 30 is defined as A (%), and elongation at break of resin constituting the outer sheath 20 is defined as B (%). As described above, since one or more embodiments are based on the premise that the second outer sheath 22 on the outer periphery of the second zone 42 (the shaded (stippled) region in
As shown in Table 1, when the percentage of the second zone 42 was 0%, cracking occurred in the outer sheath 20 during the twist test. The cause of cracking of the outer sheath 20 is thought to be because elongation strain concentrating on a local part of the outer sheath 20 (the part illustrated by the bold line in
When the percentage of the second zone 42 was 3%, cracking occurred in cases where the outer sheath 20 had an elongation at break of 50% and 100%, whereas cracking did not occur in cases where the outer sheath 20 had an elongation at break of 200% or greater. When the percentage of the second zone 42 was 5%, cracking occurred in cases where the outer sheath 20 had an elongation at break of 50%, whereas cracking did not occur in cases where the outer sheath 20 had an elongation at break of 100% or greater. As described above, it was found that, the greater the elongation at break of the resin constituting the outer sheath 20, the more it was possible to suppress the occurrence of cracking of the outer sheath 20 in the twist test.
On the other hand, in cases where the outer sheath 20 had an elongation at break of 50%, cracking occurred in the outer sheath 20 when the percentage of the second zone 42 was 5% or less, whereas cracking did not occur in the outer sheath 20 when the percentage of the second zone 42 was 10% or greater. Further, in cases where the outer sheath 20 had an elongation at break of 100%, cracking occurred in the outer sheath 20 when the percentage of the second zone 42 was 3% or less, whereas cracking did not occur in the outer sheath 20 when the percentage of the second zone 42 was 5% or greater. As described above, it was found that, the greater the percentage of the second zone 42, the more it was possible to suppress the occurrence of cracking of the outer sheath 20 in the twist test.
As described above, it was found that, the greater the elongation at break of the resin constituting the outer sheath 20 and the greater the percentage of the second zone 42, the more it was possible to suppress the occurrence of cracking of the outer sheath 20 in the twist test. From this result, since it is premised that the outer sheath 20 on the outer periphery of the second zone 42 (the shaded (stippled) region in
Further, a plurality of types of optical cables 1 were produced by varying the percentage of the second zone 42 while forming the outer sheath 20 by a resin having an elongation at break of 100%, and each optical cable 1 was subjected to a twist test and tensile test compliant with ICEA S-87-640. In the tensile test, the optical cable 1 was subjected to a tensile load of 2700 N, and presence/absence of abnormalities in the appearance of the optical cable 1 was evaluated. Also in the tensile test, abnormalities in the appearance of the optical cable 1 after the test (herein, cracks in the outer sheath 20) were observed, and examples with no abnormality in the appearance of the optical cable 1 were evaluated as “pass”, whereas examples with an abnormality in the appearance of the optical cable 1 were evaluated as “fail”.
As shown in Table 2, when the percentage of the second zone 42 was 0% and 3%, cracking occurred in the outer sheath 20 in the twist test, whereas when the percentage of the second zone 42 was 5% or greater, cracking did not occur in the outer sheath 20 in the twist test. Here, since the elongation at break was 100% (B=100), it was found that, when the value X (=A×B)—which is the product of the percentage A (%) of the second zone 42 and the elongation at break B (%) of the outer sheath 20 (the second outer sheath)—was 500 or greater, it was possible to suppress the occurrence of cracking of the outer sheath 20 in the twist test, as with the results of the twist test shown in Table 1. On the other hand, when the percentage of the second zone 42 was 60%, cracking occurred in the outer sheath 20 in the tensile test. From this result, it was found that, when the percentage of the second zone 42 is 60% or greater, the zone having a weak adhesive strength occupies more than half the entire circumference, and thus, the structure of the optical cable 1 cannot be retained soundly in the tensile test. Therefore, it is preferable that the percentage of the second zone 42 is 50% or less (less than 60%). Further, if the product of the percentage A (%) of the second zone 42 and the elongation at break B (%) of the outer sheath 20 is 500 or greater and also the percentage of the second zone 42 is 50% or less, it is possible to suppress cracking of the outer sheath both during the twist test and during the tensile test.
Further, a plurality of types of optical cables 1 were produced by varying the adhesive strength (unit: N/mm) of the second zone 42 while keeping the percentage A of the second zone 42 at 10%, and each optical cable 1 was subjected to a twist test compliant with ICEA S-87-640.
As shown in Table 3, in cases where the adhesive strength of the second zone 42 was 1.0 N/mm or greater, cracking occurred in the outer sheath 20 during the twist test. The reason to this is thought to be as follows. In cases where the adhesive strength of the second zone 42 was stronger than a predetermined value, the adhesion between the reinforcement sheet 30 and the outer sheath 20 in the second zone 42 was retained during the twist test (i.e., the reinforcement sheet 30 and the outer sheath 20 in the second zone 42 were not peeled apart) even when the adhesive strength of the second zone 42 was weaker than the adhesive strength of the first zone 41 (for example, even if the adhesive strength of the second zone 42 was about 10% of the adhesive strength of the first zone 41). In this case, the outer sheath 20 of the second zone 42 was inhibited from elongating and deforming in the circumferential direction during the twist test, and as a result, the outer sheath 20 cracked, starting from the outer end 33 of the reinforcement sheet 30. In contrast, as shown in Table 3, in cases where the adhesive strength of the second zone 42 was 0.5 N/mm or less, cracking did not occur in the outer sheath 20 in the twist test. This is thought to be because, in cases where the adhesive strength of the second zone 42 was 0.5 N/mm or less, the reinforcement sheet 30 and the outer sheath 20 (the second outer sheath 22) in the second zone 42 got peeled apart during the twist test, and the second outer sheath 22 elongated and deformed in the circumferential direction. Thus, it is preferable that the adhesive strength between the reinforcement sheet 30 and the outer sheath 20 (the second outer sheath 22) in the second zone 42 is 0.5 N/mm or less.
Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.
For example, in the foregoing embodiments, the reinforcement sheet 30 has an overlapping part 31, but the reinforcement sheet 30 does not have to include an overlapping part 31. For example, the end parts of the reinforcement sheet 30 may be welded together, to form the reinforcement sheet 30 into a tubular shape without including an overlapping part 31. Even with a structure lacking an overlapping part 31, it is effective to include a second zone 42 in which the adhesive strength between the reinforcement sheet 30 and the outer sheath 20 is weaker than the adhesive strength in the first zone 41, in cases where there is a part on which elongation strain is likely to concentrate when the optical cable 1 is twisted (for example, in cases where stress is likely to concentrate on the outer sheath 20 in the vicinity of the welded part of the reinforcement sheet 30 (the outer sheath 20 in the vicinity of the non-adhesion part)).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-083454 | May 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/019022 | 4/27/2022 | WO |
