Optical fiber cable and method for manufacturing optical fiber cable

Abstract

This optical fiber cable comprises a cable core, a first sheath, a reinforcing sheet, and a tensile strength body. The cable core includes a plurality of optical fiber cores. The first sheath is disposed around the cable core. The reinforcing sheet is wrapped longitudinally around the first sheath. The tensile strength body is embedded in the first sheath. In a cross section of the cable, the reinforcing sheet is wrapped to form an overlapping portion. In the cross section of the cable, the arc length of the overlapping portion is 7-13 mm. An adhesive is applied between the areas of the reinforcing sheet forming the overlapping portion.

Description

Optical fiber cable and method of manufacturing the same

[0001] This application claims priority from Japanese Patent Application No. 2024-127637, filed on August 2, 2024, and incorporates by reference all of the contents of said application. The present disclosure relates to an optical fiber cable and a method for manufacturing an optical fiber cable.

[0002] Patent Document 1 discloses an optical fiber cable having a reinforcing sheet disposed around the inner sheath.

[0003] Japanese Patent Application Publication No. 2020-106568

[0004] An optical fiber cable according to one embodiment of the present disclosure comprises a cable core including a plurality of optical fiber cores, a first sheath disposed around the cable core, a reinforcing sheet wrapped longitudinally around the first sheath, and a tensile strength member embedded in the first sheath, wherein in the cross section of the cable, the reinforcing sheet is wound so as to form an overlapping portion, the arc length of the overlapping portion being 7 mm or more and 13 mm or less, and adhesive is applied between the reinforcing sheets forming the overlapping portion.

[0005] Fig. 1 is a cross-sectional view of an optical fiber cable according to the present embodiment. Fig. 2 is a schematic diagram of an optical fiber cable manufacturing apparatus according to the present embodiment. Fig. 3 is a cross-sectional view of a coating unit according to the present embodiment, taken along a cross section perpendicular to the axis of the optical fiber cable.

[0006] The provision of a reinforcing sheet makes the optical fiber cable more robust. However, since the optical fiber cable is laid or used in a twisted state, it is desirable that the reinforcing sheet be positioned stably inside the optical fiber cable even if the optical fiber cable is twisted.

[0007] An object of the present disclosure is to provide an optical fiber cable in which a reinforcing sheet is stably arranged inside the optical fiber cable, and a manufacturing method for efficiently manufacturing the above optical fiber cable.

[0008] According to the present disclosure, it is possible to provide an optical fiber cable in which a reinforcing sheet is stably arranged inside the optical fiber cable, and a manufacturing method for efficiently manufacturing the above-mentioned optical fiber cable.

[0009] First, embodiments of the present disclosure will be described below. (1) An optical fiber cable according to one aspect of the present disclosure includes a cable core including a plurality of coated optical fibers, a first sheath provided around the cable core, a reinforcing sheet wound longitudinally around the first sheath, and a tensile strength member embedded in the first sheath, wherein the reinforcing sheet is wound so as to form an overlapping portion in a cross section of the cable, the arc length of the overlapping portion being 7 mm or more and 13 mm or less, and an adhesive is applied between the reinforcing sheets forming the overlapping portion.

[0010] According to the above-described optical fiber cable, the arc length of the overlapping portion is between 7 mm and 13 mm, and adhesive is applied between the reinforcing sheets forming the overlapping portion. If the overlapping portion is too short, the adhesive area of ​​the reinforcing sheet becomes small, and the reinforcing sheet may not be sufficiently adhered, making it difficult for the reinforcing sheet to stabilize inside the optical fiber cable. Furthermore, if the adhesive is applied excessively to the overlapping portion, it may penetrate not only into the overlapping portion but also into the cable core, which may impair the disassembly of the optical fiber cable. If the overlapping portion is too long, areas of the overlapping portion where the adhesive is not applied are created, making the cable core more susceptible to water penetration. By setting the arc length of the overlapping portion to between 7 mm and 13 mm, it becomes easier to apply the adhesive properly to the overlapping portion, allowing the reinforcing sheet to be stably positioned inside the optical fiber cable.

[0011] (2) The optical fiber cable according to (1) above may include a second sheath arranged around the reinforcing sheet, the adhesive may be a thermoplastic adhesive, and the melting point of the second sheath may be lower than the melting point of the adhesive.

[0012] According to the above configuration, the second sheath is formed so as to prevent the solidified adhesive from remelting, and therefore the reinforcing sheet can be more easily arranged in a stable state inside the optical fiber cable.

[0013] (3) In the optical fiber cable according to (2) above, the adhesive may contain ethylene vinyl acetate copolymer as a main component.

[0014] According to the above configuration, since the adhesive contains ethylene vinyl acetate copolymer as a main component, the melting point of the second sheath is likely to be lower than the melting point of the adhesive, and the reinforcing sheets are likely to be firmly bonded to each other.

[0015] (4) The optical fiber cable according to any one of (1) to (3) above may have an outer diameter of 20 mm or more in a cross-sectional view.

[0016] As the outer diameter of an optical fiber cable increases, the amount of distortion due to twisting also increases, making it difficult for the reinforcing sheet to become stable inside the optical fiber cable. With the above configuration, the reinforcing sheet can be easily positioned stably inside the optical fiber cable, even for optical fiber cables with large outer diameters.

[0017] (5) In the optical fiber cable according to any one of (1) to (4) above, the reinforcing sheet may have a thickness of 0.25 mm or more and 0.50 mm or less.

[0018] If the thickness of the reinforcing sheet is less than 0.25 mm, the robustness of the optical fiber cable decreases. If the thickness of the reinforcing sheet exceeds 0.50 mm, the force that the reinforcing sheet wrapped around the first sheath tries to return to its original shape becomes strong, making it difficult to arrange the reinforcing sheet so that the arc length of the overlapping portion is 7 mm to 13 mm. According to the above configuration, the thickness of the reinforcing sheet is 0.25 mm to 0.50 mm, so that both the robustness of the optical fiber cable and the stability of the reinforcing sheet arrangement can be achieved.

[0019] (6) A method for manufacturing an optical fiber cable according to one aspect of the present disclosure is a method for manufacturing an optical fiber cable including a cable core including a plurality of optical fiber cores, a first sheath disposed around the cable core, a reinforcing sheet wrapped longitudinally around the first sheath, and a tensile strength member embedded in the first sheath, wherein the arc length of the overlapping portion where the reinforcing sheet is double-overlapped is 7 mm or more and 13 mm or less, and the method includes applying an adhesive from the outside of the reinforcing sheet while the reinforcing sheet is wrapped longitudinally around the first sheath, thereby allowing the adhesive to penetrate between the reinforcing sheets at the overlapping portion.

[0020] According to the above-described optical fiber cable manufacturing method, the arc length of the overlapping portion is 7 mm or more and 13 mm or less, and adhesive is applied between the reinforcing sheets that form the overlapping portion. This makes it easier to apply an adequate amount of adhesive to the overlapping portion, allowing the reinforcing sheet to be stably positioned inside the optical fiber cable. Furthermore, by applying adhesive from the outside of the reinforcing sheet while it is wrapped longitudinally around the first sheath, there is no need to apply adhesive and then attach it to form the overlapping portion, allowing for more efficient manufacturing of the optical fiber cable.

[0021]

[0023] (Details of the Embodiments of the Present Disclosure) Specific examples of optical fiber cables and manufacturing methods according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0022] Fig. 1 is a cross-sectional view of an optical fiber cable 1. As illustrated in Fig. 1, the optical fiber cable 1 includes a cable core 10, a first sheath 20, a reinforcing sheet 30, and a tensile strength member 50. The optical fiber cable 1 may further include a second sheath 40 and a tear cord 60.

[0023] The cable core 10 includes a plurality of coated optical fibers 11. In this embodiment, an optical fiber ribbon is formed by connecting 12 coated optical fibers 11. Furthermore, an optical fiber unit 12 is formed by twisting six optical fiber ribbons together. The cable core 10 includes six optical fiber units 12. Note that the coated optical fibers 11 may each be in the form of a single fiber, without forming an optical fiber ribbon.

[0024] The optical fiber 11 includes a glass fiber having a core and a cladding, and a resin layer covering the glass fiber. The diameter of the glass fiber is typically about 125 μm. The diameter of the optical fiber 11 is, for example, 180 μm to 220 μm, and is 200 μm in this example.

[0025] The cable core 10 includes a water-absorbent fiber 13 and a holding winding tape 14. The water-absorbent fiber 13 can absorb water that has infiltrated into the inside of the cable core 10. The water-absorbent fiber 13 is, for example, a polyester fiber.

[0026] The holding winding tape 14 is wound so as to cover the six optical fiber units 12 and the water-absorbent fibers 13. For example, the holding winding tape 14 may be a tape of polyethylene terephthalate (PET), or a tape formed by bonding a base material such as PET to a nonwoven fabric. Note that a water-absorbing agent such as water-absorbing powder may be applied to the inside of the holding winding tape 14.

[0027] The first sheath 20 is provided around the cable core 10 and covers the cable core 10. The first sheath 20 can be formed from, for example, polyethylene resin, flame-retardant polyethylene resin, polyvinyl chloride resin, etc. The thickness of the first sheath 20 is, for example, 1.0 mm or more and 2.5 mm or less.

[0028] The reinforcing sheet 30 is provided around the first sheath 20. The reinforcing sheet 30 is wrapped around the first sheath 20 in a longitudinal direction. In the cross section of the optical fiber cable 1, the reinforcing sheet 30 is wrapped so as to form an overlapping portion 31. The arc length L1 of the overlapping portion 31 is a dimension of 7 mm or more and 13 mm or less.

[0029] An adhesive Ad is applied between the reinforcing sheets 30 that form the overlapping portion 31. The adhesive Ad according to this embodiment may be a thermoplastic adhesive that softens when heated. For example, the adhesive Ad may be a hot-melt adhesive. The adhesive Ad may also contain ethylene vinyl acetate copolymer as a main component.

[0030] The reinforcing sheet 30 is made of, for example, steel or hard plastic, and may have a thickness of 0.25 mm or more and 0.50 mm or less.

[0031] The second sheath 40 is provided around the reinforcing sheet 30. The second sheath 40 may be formed from, for example, polyethylene resin, flame-retardant polyethylene resin, polyvinyl chloride resin, etc. The thickness of the second sheath 40 is, for example, 1.0 mm or more and 2.5 mm or less.

[0032] The melting point of the second sheath 40 is desirably lower than the melting point of the adhesive Ad. For example, the melting point of the second sheath 40 is 150° C., and the melting point of the adhesive Ad is 200° C. When the adhesive Ad contains ethylene vinyl acetate copolymer as a main component, the melting point of the second sheath 40 is likely to be lower than the melting point of the adhesive Ad.

[0033] The second sheath 40 defines the outer shape of the optical fiber cable 1. In a cross-sectional view, the outer diameter of the optical fiber cable 1 is 20 mm or more.

[0034] The strength members 50 are embedded in the first sheath 20 and disposed along the cable core 10. The strength members 50 are made of, for example, steel or hard plastic.

[0035] The thickness and material of the reinforcing sheet 30 and the tension members 50 may be adjusted to uniformize the bending rigidity in the circumferential direction of the optical fiber cable 1. The diameter D of the tension members 50 is preferably 0.5 mm or more and 2.0 mm or less.

[0036] There may be provided a plurality of strength members 50. In the optical fiber cable 1 of this embodiment, four strength members 50 are provided in pairs of two. The two strength members 50 of a pair are provided, for example, in close proximity to each other or with at least partial contact.

[0037] The tear cord 60 is used to disassemble the optical fiber cable 1. The tear cord 60 is made of a resin material such as nylon or polyester.

[0038] The tear cord 60 of the optical fiber cable 1 of this embodiment includes two cords: a first tear cord 61 and a second tear cord 62. The first tear cord 61 is embedded in the first sheath 20 so as to contact the cable core 10. The first tear cord 61 is used to tear the first sheath 20. The second tear cord 62 is provided between the first sheath 20 and the reinforcing sheet 30. The second tear cord 62 is used to tear the adhesive Ad applied to the reinforcing sheet 30 and the second sheath 40.

[0039] Next, a method for manufacturing the optical fiber cable 1 will be described. Fig. 2 is a schematic diagram of an apparatus 100 for manufacturing the optical fiber cable 1 according to this embodiment. As illustrated in Fig. 2, the apparatus 100 for manufacturing the optical fiber cable 1 includes a payout section 110, a narrowing section 120, a roller section 130, an adhesive application section 140, and a covering section 150. The cable core 10 covered with the first sheath 20 is transported from left to right on the paper surface through the manufacturing apparatus 100. In the following description, the cable core 10 covered with the first sheath 20 will be referred to as an intermediate molded body M.

[0040] The feeding unit 110 is capable of feeding the reinforcing sheet 30 along the intermediate formed body M. The reinforcing sheet 30 is fed by the feeding unit 110 so as to follow the intermediate formed body M while being rounded.

[0041] The narrowing section 120 deforms the reinforcing sheet 30 so that the reinforcing sheet 30 conforms to the outer periphery of the intermediate formed body M, and enables the reinforcing sheet 30 to be wound longitudinally around the cable core 10. The narrowing section 120 is formed so that the insertion path of the reinforcing sheet 30 gradually narrows. Therefore, the reinforcing sheet 30 is formed so that the outer diameter of the reinforcing sheet 30 gradually decreases, and finally the outer diameter of the reinforcing sheet 30 becomes the finished dimension. In this way, the reinforcing sheet 30 is wound longitudinally around the outer periphery of the intermediate formed body M. Furthermore, an overlapping section 31 is formed during the process in which the reinforcing sheet 30 is narrowed by the narrowing section 120.

[0042] The roller unit 130 guides the intermediate molded body M and the reinforcing sheet 30 to the adhesive application unit 140 while pressing down the reinforcing sheet 30 so that the outer diameter of the reinforcing sheet 30 does not become larger than the finished outer diameter. The roller unit 130 includes a plurality of rollers. The rollers are arranged so that the cable core 10 and the reinforcing sheet 30 come into contact with the rollers in a plurality of directions.

[0043] In the adhesive application section 140, it is possible to apply adhesive Ad between the reinforcing sheets 30 that form the overlapping section 31. The adhesive Ad applied by the adhesive application section 140 bonds the reinforcing sheets 30 that form the overlapping section 31 together by being cooled.

[0044] The covering portion 150 can cover the outer periphery of the reinforcing sheet 30 with the second sheath 40. The covering portion 150 may cover the second sheath 40 by solid extrusion molding, or by draw-down extrusion molding. The covering portion 150 according to this embodiment includes a die 151. Molten resin that forms the second sheath 40 is supplied to the die 151. When the intermediate molded body M around which the reinforcing sheet 30 is wrapped passes through the die 151, the second sheath 40 covers the outer periphery of the reinforcing sheet 30. In this way, the optical fiber cable 1 as illustrated in FIG. 1 is manufactured.

[0045] 3 is a cross-sectional view of the adhesive application unit 140 according to this embodiment, taken along a cross section perpendicular to the axis of the optical fiber cable 1. As illustrated in FIG. 3, the adhesive application unit 140 includes a tank 141. The tank 141 contains molten adhesive Ad. The intermediate molded body M, with the reinforcing sheet 30 wrapped around its outer periphery, passes through the adhesive Ad contained in the tank 141. As a result, the adhesive Ad seeps into the gaps between the reinforcing sheets 30 that form the overlapping portions 31, and the adhesive Ad is applied between the reinforcing sheets 30.

[0046] According to the optical fiber cable 1 of this embodiment, the arc length of the overlapping portion 31 is 7 mm or more and 13 mm or less, and adhesive is applied between the reinforcing sheets 30 that form the overlapping portion 31 .

[0047] If the overlapping portion 31 is too short, the adhesive area of ​​the reinforcing sheet 30 becomes small, and the reinforcing sheet 30 may not be sufficiently adhered, making it difficult for the reinforcing sheet 30 to stabilize inside the optical fiber cable 1. Furthermore, the adhesive Ad may be applied excessively to the overlapping portion 31, penetrating not only the overlapping portion 31 but also the cable core 10. In this case, even if an attempt is made to dismantle the first sheath 20 using the first tearing string 61, the highly viscous adhesive Ad may adhere to the first tearing string 61, making the dismantling operation difficult. This may impair the dismantling ability of the optical fiber cable 1.

[0048] If the overlapping portion 31 is too long, an area where the adhesive Ad is not applied will be formed in the overlapping portion 31, making the cable core 10 more susceptible to water penetration. In particular, since an area where the adhesive Ad is not applied is likely to be formed along the axis of the optical fiber cable 1, water adhering to the reinforcing sheet 30 will flow along the axis of the optical fiber cable 1, which may cause the adhering water to penetrate into the inside of the cable core 10 from a wide area.

[0049] By setting the arc length L1 of the overlapping portion 31 to be 7 mm or more and 13 mm or less, it becomes easier to apply the adhesive Ad at the overlapping portion 31 without excess or deficiency, and the reinforcing sheet 30 can be positioned stably inside the optical fiber cable 1.

[0050] 2 , the second sheath 40 is formed after the adhesive Ad is applied to the reinforcing sheet 30. Therefore, if the melting point of the second sheath 40 is too high, the adhesive Ad applied between the reinforcing sheets 30 may melt, weakening the adhesive strength between the reinforcing sheets 30. According to the optical fiber cable 1 of this embodiment, the melting point of the second sheath 40 is lower than the melting point of the adhesive Ad. Therefore, the second sheath 40 is formed while preventing the viscosity of the adhesive Ad from decreasing, which makes it easier for the reinforcing sheet 30 to be stably positioned inside the optical fiber cable 1.

[0051] Furthermore, according to the manufacturing method of the optical fiber cable 1 in this embodiment, the adhesive Ad is applied from the outside of the reinforcing sheet 30 while the reinforcing sheet 30 is wrapped longitudinally around the first sheath 20. This eliminates the need to peel off part of the overlapping portion 31 of the reinforcing sheet 30, apply the adhesive Ad, and then reattach the reinforcing sheet 30 to form the overlapping portion 31, and therefore the optical fiber cable 1 can be manufactured more efficiently.

[0052] Next, evaluation tests for the optical fiber cable 1 according to this embodiment will be described. The evaluation tests include a post-manufacturing test, a twisting test, and a hydrodynamic test. The post-manufacturing test is a test for evaluating the state of application of adhesive after the optical fiber cable is manufactured. The twisting test is a test for examining the effect of twisting on the optical fiber cable 1 by repeatedly twisting a predetermined length of optical fiber cable 1 through a predetermined angle a predetermined number of times. The hydrodynamic test is a test for continuously contacting the end of a sample with a test length of 3 m with water at a height of 1 m, and measuring whether water leaks from the opposite end of the sample after 24 hours.

[0053] Table 1 shows the results of the evaluation tests. As illustrated in Table 1, the evaluation tests were conducted for each optical fiber cable with an overlap width (i.e., the arc length of the overlap) of 6 mm, 7 mm, 10 mm, 13 mm, and 14 mm. The evaluation tests were also conducted for a 288-fiber optical fiber cable with an outer diameter of 22.0 mm, a 432-fiber optical fiber cable with an outer diameter of 22.5 mm, and an 864-fiber optical fiber cable with an outer diameter of 25.0 mm. Each test result was assigned one of three ratings. Rating A indicates that the optical fiber cable was in good condition in the post-manufacturing test, twisting test, and water run test. Rating B indicates that penetration of adhesive into the cable core was confirmed after at least one of the post-manufacturing test and the twisting test, or that an abnormality such as sheath cracking occurred after the twisting test. Rating C indicates that water was confirmed to have traveled 3 m or more along the axis of the optical fiber cable as a result of the water run test.

[0054]

[0055] As shown in Table 1, when the overlap width was 6 mm, penetration of the adhesive into the interior of the cable core was confirmed after at least one of the post-manufacturing test and the twist test. On the other hand, when the overlap width was 7 mm, 10 mm, and 13 mm, no penetration of the adhesive into the interior of the cable core was confirmed.

[0056] Furthermore, when the overlap width was 14 mm, the water flow test confirmed that water traveled more than 3 m along the axis of the optical fiber cable. On the other hand, when the overlap width was 7 mm, 10 mm, or 13 mm, water did not travel more than 3 m along the axis of the optical fiber cable.

[0057] From the above evaluation test, it is necessary for the arc length L1 of the overlapping portion 31 to be 7 mm or more and 13 mm or less in order to maintain the optical fiber cable in a good condition.

[0058] Although the present disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure.

[0059] REFERENCE SIGNS LIST 1 Optical fiber cable 10 Cable core 11 Optical fiber core 12 Optical fiber unit 13 Water-absorbent fiber 14 Holding and winding tape 20 First sheath 30 Reinforcing sheet 31 Overlapping portion 40 Second sheath 50 Tensile member 60 Tear cord 61 First tear cord 62 Second tear cord 100 Manufacturing device 110 Paying-out portion 120 Narrowing portion 130 Roller portion 140 Adhesive application portion 141 Tank 150 Covering portion Ad Adhesive D Diameter M Intermediate molded body L1 Arc length

Claims

1. An optical fiber cable comprising: a cable core containing a plurality of optical fiber cores; a first sheath disposed around the cable core; a reinforcing sheet wound longitudinally around the first sheath; and a tensile strength member embedded in the first sheath, wherein, in the cross section of the cable, the reinforcing sheet is wound so as to form an overlapping portion, the arc length of the overlapping portion being 7 mm or more and 13 mm or less, and an adhesive is applied between the reinforcing sheets forming the overlapping portion.

2. The optical fiber cable according to claim 1, further comprising a second sheath provided around the reinforcing sheet, the adhesive being a thermoplastic adhesive, and the melting point of the second sheath being lower than the melting point of the adhesive.

3. The optical fiber cable according to claim 2, wherein the adhesive contains ethylene vinyl acetate copolymer as a main component.

4. An optical fiber cable according to any one of claims 1 to 3, having an outer diameter of 20 mm or more in cross section.

5. An optical fiber cable according to any one of claims 1 to 4, wherein the thickness of the reinforcing sheet is 0.25 mm or more and 0.50 mm or less.

6. A method for manufacturing an optical fiber cable comprising: a cable core containing a plurality of optical fiber cores; a first sheath provided around the cable core; a reinforcing sheet wrapped longitudinally around the first sheath; and a tensile strength member embedded in the first sheath, wherein the arc length of an overlapping portion where the reinforcing sheet is double-overlapped is 7 mm or more and 13 mm or less; and the method includes applying an adhesive from the outside of the reinforcing sheet while the reinforcing sheet is wrapped longitudinally around the first sheath, thereby allowing the adhesive to penetrate between the reinforcing sheets at the overlapping portion.

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