Optical fiber cable

Abstract

The present disclosure makes it possible to provide a slotless optical fiber cable having excellent impact resistance and lateral pressure resistance.　An optical fiber cable (1) is a slotless optical fiber cable comprising a plurality of optical fiber cores, a sheath (40) covering the plurality of optical fiber cores, and a plurality of tension members (50) embedded in the sheath (40). The sheath (40) contains both high-density polyethylene and linear low-density polyethylene, and the inner sheath thickness of the tension member (50) is 0.1 mm or more.

Description

fiber optic cable

[0001] This application claims priority to Japanese Patent Application No. 2024-100380, filed on June 21, 2024, and incorporates the entire contents of said application by reference. The present disclosure relates to an optical fiber cable.

[0002] Patent Document 1 discloses a slotless optical fiber cable.

[0003] International Publication No. 2018 / 174004

[0004] An optical fiber cable according to one embodiment of the present disclosure is a slotless optical fiber cable comprising a plurality of optical fiber cores, a sheath covering the plurality of optical fiber cores, and a plurality of tension members embedded in the sheath, wherein the sheath contains both high-density polyethylene and linear low-density polyethylene, and the inner sheath thickness of the tension members is 0.1 mm or more.

[0005] 1 is a cross-sectional view of an optical fiber cable according to an embodiment of the present disclosure.

[0006] With the spread of information communications such as the Internet, the speed of communication has increased and the amount of information has increased, resulting in a demand for thinner and higher-density optical fiber cables. Slotless optical fiber cables, which do not have slots, are easily made thinner and more dense. On the other hand, optical fiber cables are also required to have excellent impact resistance and lateral pressure resistance. However, it has been difficult to manufacture optical fiber cables that have excellent impact resistance and lateral pressure resistance while also meeting the demand for thinner diameters.

[0007] According to the present disclosure, a slotless optical fiber cable having excellent impact resistance and lateral pressure resistance can be provided.

[0008] First, embodiments of the present disclosure will be described below. (1) An optical fiber cable according to one embodiment of the present disclosure is a slotless optical fiber cable including a plurality of optical fiber cores, a sheath covering the plurality of optical fiber cores, and a plurality of tension members embedded in the sheath, wherein the sheath contains both high-density polyethylene and linear low-density polyethylene, and the inner sheath thickness of the tension members is 0.1 mm or more.

[0009] By having the sheath contain both high-density polyethylene and linear low-density polyethylene and the inner sheath thickness of the tension member being 0.1 mm or more, it is possible to achieve both good hardness and toughness, resulting in an optical fiber cable with excellent impact resistance and lateral pressure resistance.

[0010] (2) In the above (1), the proportion of the high-density polyethylene contained in the sheath may be 50% by mass or more and 70% by mass or less, and the proportion of the linear low-density polyethylene contained in the sheath may be 30% by mass or more and 50% by mass or less. When the blending ratio of the polyethylene contained in the sheath is within the above range, the balance between the hardness and toughness of the sheath is better, and an optical fiber cable having even more excellent impact resistance and lateral pressure resistance can be obtained.

[0011] (3) In the above (1) or (2), the sheath may have a tensile strength of 19.2 MPa or more, a tensile elongation of 618% or more, and a low-temperature shrinkage force of less than 14.3 MPa at −40° C. When the tensile properties and low-temperature properties of the sheath are within the above ranges, the sheath has a better balance between hardness and toughness, and an optical fiber cable having even more excellent impact resistance and lateral pressure resistance can be obtained.

[0012] (4) In any of (1) to (3) above, the distance between adjacent tension members may be 0.1 mm or more. If the distance between adjacent tension members is sufficiently large, the resin can properly penetrate between the tension members, which tends to improve the adhesion between the tension members and the sheath.

[0013] [Details of the embodiments of the present disclosure] Specific examples of the optical fiber cable of the present disclosure will be described below with reference to the drawings. Note that the present invention 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.

[0014] FIG. 1 is a cross-sectional view of an optical fiber cable according to an embodiment of the present disclosure. As shown in FIG. 1 , the optical fiber cable 1 includes multiple optical fiber units 10, a sheath 40, and a tension member 50. The optical fiber cable 1 may include at least one of a water-absorbing yarn 20, a pressure winding 30, and a tear cord 60, any combination thereof, or all of them. The optical fiber cable 1 is a slotless optical fiber cable that does not have a slot. Note that FIG. 1 is a diagram that schematically illustrates the cable structure and is not intended to show the specific arrangement or dimensions of each component. For example, the optical fiber units 10 and the water-absorbing yarn 20 may be housed inside the pressure winding 30 so that the gap around the optical fiber units 10 and the water-absorbing yarn 20 is smaller.

[0015] Each optical fiber unit 10 includes a plurality of optical fiber cores. The optical fiber unit 10 may include an optical fiber ribbon in which a plurality of optical fiber cores are intermittently connected. The optical fiber unit 10 is formed by bundling and twisting a plurality of optical fiber cores or optical fiber ribbons. Each of the optical fiber ribbons included in the optical fiber unit 10 may be in a rounded shape in cross section. Furthermore, a plurality of optical fiber cores or optical fiber ribbons may be bundled together so that the outer shape of each optical fiber unit 10 is round in cross section.

[0016] The water-absorbing yarn 20 is an example of a water-absorbing material. In this embodiment, as shown in Figure 1, two water-absorbing yarns are arranged at the center of the cross section of the optical fiber cable 1. The water-absorbing yarn 20 may be wound around the optical fiber unit 10.

[0017] The pressure wrap 30 wraps the optical fiber units 10. The pressure wrap 30 may be a tape of nonwoven fabric or a laminate of a base material such as polyethylene terephthalate (PET) and nonwoven fabric. The pressure wrap 30 may be given the function of a water-absorbing material by using a water-absorbing powder or the like. When the pressure wrap 30 functions as a water-absorbing material, the water-absorbing yarn 20 does not need to be disposed.

[0018] The sheath 40 is formed of a resin material and covers the multiple optical fiber units 10 and the tension winding 30. In the optical fiber cable 1 of this embodiment, the sheath 40 contains both high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). That is, the sheath 40 is formed of a resin material obtained by blending high-density polyethylene and linear low-density polyethylene. "High-density polyethylene" has a density of 0.942 g / cm ３ "Linear low-density polyethylene" refers to a polyethylene homopolymer or polyethylene copolymer having a density of 0.910 g / cm or higher. ３ 0.925g / cm or more ３ means a linear polyethylene copolymer which is:

[0019] The tension members 50 are embedded in the sheath 40 and are bonded to the sheath 40 with an adhesive such as ethylene acrylic acid resin (EAA). The tension members 50 prevent excessive tension from being applied to the optical fiber core when tension is applied to the optical fiber cable 1. The tension members 50 are formed of, for example, steel wire or fiber reinforced plastic (FRP). The optical fiber cable 1 includes a plurality of tension members 50. The plurality of tension members 50 are typically arranged so as to be point symmetrical in the cross section of the cable.

[0020] In this specification, the portion of the sheath 40 located inside the tension member 50 in the cross-sectional view of the optical fiber cable 1 shown in Figure 1 is referred to as the sheath inner wall 41. The thickness T of the thinnest portion of the sheath inner wall 41 is referred to as the inner sheath thickness T1 of the tension member 50. In the optical fiber cable 1, the inner sheath thickness T1 of the tension member 50 is 0.1 mm or more. There is no particular upper limit to the inner sheath thickness T1, but from the perspective of reducing the diameter of the cable, the inner sheath thickness T1 may be 0.5 mm or less, 0.3 mm or less, or 0.2 mm or less. If the tension member 50 and the sheath 40 are bonded together with an adhesive, the inner sheath thickness T1 includes the thickness of the adhesive portion.

[0021] The tear cord 60 is used to tear the sheath 40 and extract the optical fiber unit 10 therein. In the optical fiber cable 1 shown in Fig. 1, two tear cords 60 are arranged symmetrically with respect to the center of the cable, but the number and arrangement of the tear cords 60 are not particularly limited.

[0022] Meanwhile, there is a demand for thinner optical fiber cables. One possible means for achieving this is to thin the sheath. However, if the inner sheath thickness T1 of the tension member 50 in the cross-sectional view of the optical fiber cable 1 shown in FIG. 1 is excessively small, the sheath inner wall 41 may crack when an impact is applied to the optical fiber cable 1. In other words, if the inner sheath thickness T1 is small, the impact resistance of the optical fiber cable 1 is likely to decrease.

[0023] In particular, when the sheath is made of high-density polyethylene, which has relatively low toughness, impact resistance is more likely to decrease. For example, when the sheath is made only of high-density polyethylene and the inner sheath thickness of the tension member is 0.2 mm or less, cracks are likely to occur in the inner wall of the sheath when the cable is subjected to an impact. To prevent cracks in the inner wall of the sheath, the inner sheath thickness of the tension member must be sufficiently large, but if the inner sheath thickness is large, it becomes difficult to reduce the diameter of the optical fiber cable. Furthermore, because high-density polyethylene has a strong shrinkage force at low temperatures, if the sheath is made only of high-density polyethylene, the sheath will shrink in low-temperature environments, leading to increased transmission loss.

[0024] On the other hand, optical fiber cables are required to have excellent resistance to lateral pressure. If the sheath is made only of a relatively soft resin material such as low-density polyethylene, the optical fiber cable will be crushed when lateral pressure is applied, leading to increased transmission loss. From this perspective, optical fiber cables that are sufficiently resistant to both impact and lateral pressure are desired.

[0025] In the optical fiber cable 1 according to this embodiment, the sheath 40 contains both high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). This configuration provides the sheath 40 with both hardness and toughness. Therefore, even if the inner sheath thickness T1 of the tension member 50 is set to a relatively small value of 0.1 mm or more, the sheath inner wall 41 will not crack when subjected to an impact. Furthermore, even when lateral pressure is applied, the optical fiber cable 1 will not collapse, and transmission loss will not increase significantly.

[0026] Furthermore, adhesives such as ethylene-acrylic acid resin have better adhesion to linear low-density polyethylene than to high-density polyethylene. Therefore, compared to a sheath made only of high-density polyethylene, the sheath 40 in this embodiment has better adhesion to the tension member 50, reducing distortion of the sheath 40 when lateral pressure or impact is applied. Furthermore, because the sheath 40 contains linear low-density polyethylene, shrinkage of the sheath 40 in low-temperature environments can be made relatively small, reducing increases in transmission loss in low-temperature environments.

[0027] The proportion of high-density polyethylene contained in the sheath 40 may be 50% by mass or more and 70% by mass or less, or 50% by mass or more and 60% by mass or less. The proportion of linear low-density polyethylene contained in the sheath 40 may be 30% by mass or more and 50% by mass or less, or 40% by mass or more and 50% by mass or less. When the proportions of high-density polyethylene and linear low-density polyethylene are within the above ranges, excellent tensile strength and tensile elongation are achieved, and the impact resistance and lateral pressure resistance of the optical fiber cable 1 are further improved. The sheath 40 may be made only of high-density polyethylene and linear low-density polyethylene.

[0028] The tensile strength of the sheath 40 may be 19.2 MPa or more, or may be 19.2 MPa or more and less than 29.4 MPa. The tensile strength is measured by the method described in JIS K 7161:2014, for example.

[0029] The tensile elongation of the sheath 40 may be 500% or more, or may be 618% or more. The upper limit of the tensile elongation of the sheath 40 is not particularly limited, but is, for example, 800% or less. The tensile elongation is the ratio of the length of the test specimen at break to the length of the test specimen before the test, for example, in the method described in JIS K 7161:2014.

[0030] The low-temperature shrinkage force of the sheath 40 at -40°C may be less than 14.3 MPa, greater than 10.7 MPa and less than 14.3 MPa, or greater than 10.7 MPa and 12.5 MPa or less. The low-temperature shrinkage force at -40°C is measured, for example, as follows: A test specimen having a length of 100 mm, a width of 25 mm, and a height of 1 mm is attached to grippers at two points 20 mm apart along the length of the test specimen. After being set at room temperature (25°C) so that the stress in the grippers is zero, the specimen is cooled to -40°C at a rate of 0.25°C / min, and the force generated between the grippers due to the shrinkage of the test specimen at the time when the temperature reaches -40°C is measured. The force generated between the grippers at -40°C divided by the cross-sectional area perpendicular to the direction along the length of the test specimen is defined as the low-temperature shrinkage force at -40°C.

[0031] The distance D between adjacent tension members 50 may be 0.1 mm or more. If the distance D between adjacent tension members 50 is 0.1 mm or more, the resin can properly penetrate between the tension members 50, which makes it easier to improve the adhesion between the tension members 50 and the sheath 40.

[0032] Next, the optical fiber cable of the present disclosure will be described more specifically with reference to examples, but the present disclosure is not limited to these examples.

[0033] (Fabrication of Optical Fiber Cable) Example 1 A 432-fiber slotless optical fiber cable having the cross-sectional structure shown schematically in Figure 1 was fabricated. The fabricated optical fiber cable had an outer diameter of 14.0 mm, a core diameter (inner diameter) of 9.0 mm, and a sheath thickness of 2.5 mm. The inner sheath thickness of the tension member was 0.3 mm. In Example 1, the sheath was formed using a resin material containing 50% by mass of high-density polyethylene and 50% by mass of linear low-density polyethylene.

[0034] <Examples 2 to 4> An optical fiber cable of Example 2 was produced under the same conditions as Example 1, except that the mass ratio of the resin material forming the sheath was changed to 70 mass% high-density polyethylene and 30 mass% linear low-density polyethylene. An optical fiber cable of Example 3 was produced under the same conditions as Example 1, except that the resin material forming the sheath was changed to 100 mass% high-density polyethylene. An optical fiber cable of Example 4 was produced under the same conditions as Example 1, except that the resin material forming the sheath was changed to 100 mass% linear low-density polyethylene.

[0035] (Evaluation) The tensile strength, tensile elongation, and -40°C low-temperature shrinkage force of the resin material forming the sheath of each of the optical fiber cables of Examples 1 to 4 were measured. In addition, an impact test, a lateral pressure test, and an evaluation of low-temperature loss at -40°C were performed on the produced optical fiber cables. The physical properties of the resin material and the evaluation results of the optical fiber cables of each example are shown in Table 1. The tensile strength and tensile elongation of the resin material were measured based on the method described in JIS K 7161:2014. The measurement of -40°C low-temperature shrinkage force, as well as the impact test and lateral pressure test, were performed according to the following procedures.

[0036] <-40°C Low-Temperature Shrinkage Force> A test piece of resin material measuring 100 mm in length, 25 mm in width, and 1 mm in height was attached to grippers at two points 20 mm apart along the length of the test piece. After being set at room temperature of 25°C so that the stress of the grippers was zero, the test piece was cooled to -40°C at a rate of 0.25°C / min, and the force generated between the grippers due to the shrinkage of the test piece at the time when the temperature reached -40°C was measured. The force generated between the grippers at -40°C divided by the cross-sectional area perpendicular to the direction along the length of the test piece was taken as the low-temperature shrinkage force at -40°C.

[0037] <Impact test> An optical fiber cable was placed on a horizontal surface with the tension member at the top, and a weight with a mass of 0.45 kg and a circular impact surface with a diameter of 10 mm was dropped twice from a height of 1 m onto the same location on the optical fiber cable. The impact energy from the weight drop was 4.4 N·m. The cable was then split, and the presence or absence of cracks on the inner wall of the sheath was visually determined and evaluated according to the following criteria: A: no cracks, B: slight cracks, C: cracks

[0038] <Lateral Pressure Test> A flat plate was pressed against the side of the optical fiber cable, and a load of 220 N / cm was applied for 1 minute, followed by a load of 110 N / cm for 10 minutes. The transmission loss of the optical fiber cable was then measured with a load of 110 N / cm applied. The increase in transmission loss from the value before the load was applied was rated as A, with an increase of 0.15 dB / km or less, and an increase of more than 0.15 dB / km was rated as C.

[0039]

[0040] Examples 1 and 2 are working examples, and Examples 3 and 4 are comparative examples. As shown in Table 1, the optical fiber cables having sheaths containing both high-density polyethylene and linear low-density polyethylene were excellent in both impact resistance and lateral pressure resistance. Examples 1 and 2 also had good low-temperature properties.

[0041] 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 any number, position, shape, etc. suitable for implementing the present disclosure. Furthermore, it should be understood that at least one configuration or feature described in each embodiment and example can be combined with other embodiments and examples, or can be modified in various ways.

[0042] REFERENCE SIGNS LIST 1 Optical fiber cable 10 Optical fiber unit 20 Water-absorbing yarn 30 Pressure winding 40 Sheath 41 Inner wall of sheath 50 Tension member 60 Tear cord

Claims

1. A slotless optical fiber cable comprising: a plurality of optical fiber cores; a sheath covering the plurality of optical fiber cores; and a plurality of tension members embedded in the sheath, wherein the sheath contains both high-density polyethylene and linear low-density polyethylene, and the inner sheath thickness of the tension members is 0.1 mm or more.

2. An optical fiber cable as described in claim 1, wherein the proportion of said high-density polyethylene contained in said sheath is 50% by mass or more and 70% by mass or less, and the proportion of said linear low-density polyethylene contained in said sheath is 30% by mass or more and 50% by mass or less.

3. An optical fiber cable according to claim 1 or 2, wherein the sheath has a tensile strength of 19.2 MPa or more, a tensile elongation of 618% or more, and a low-temperature shrinkage force at -40°C of less than 14.3 MPa.

4. An optical fiber cable according to any one of claims 1 to 3, wherein the distance between adjacent tension members is 0.1 mm or more.

Images