Optical cable

Abstract

The optical cable according to an embodiment of the present disclosure is for laying thereof in a microduct, the optical cable being provided with an assembly core that accommodates one or more optical fiber cores, and a sheath layer that covers an outer periphery of the assembly core, the density of the sheath layer being 1.0 g / cm3 or less, a main component of the sheath layer being polyethylene, the sheath layer containing silicone, the density of the polyethylene being 0.92 g / cm3 or greater, the weight-average molecular weight of the silicone being 50,000-1,000,000, and the content ratio of the silicone in the sheath layer being 0.5-10 mass%.

Description

optical cable

[0001] This application claims priority to Japanese Patent Application No. 2022-124332, filed on August 3, 2022, and incorporates by reference all of the contents of said Japanese application.

[0002] In addition to the increased speed and volume of information due to the spread of information communications such as the Internet, the construction of optical networks is progressing to accommodate two-way communications and large-capacity communications. In these optical networks, FTTH (Fiber to the Home) has been launched, which provides high-speed communications services by directly connecting telecommunications carriers and individual homes via optical fiber, and the volume of communications is increasing year by year. In response to this, there is a demand for optical cables with smaller diameters and higher densities. For example, Patent Document 1 (JP 2010-8923 A) discloses the structure of an optical cable known as a slotless type.

[0003] JP 2010-8923 A

[0004] An optical cable according to one aspect of the present disclosure is an optical cable to be laid in a microduct, the optical cable including an aggregated core that houses one or more optical fiber cores, and a sheath layer that covers the outer periphery of the aggregated core, and the density of the sheath layer is 1.0 g / cm ３ or less, the main component of the sheath layer is polyethylene, the sheath layer contains silicone, and the density of the polyethylene is 0.92 g / cm ３ The weight average molecular weight of the silicone is 50,000 or more and 1,000,000 or less, and the content of the silicone in the sheath layer is 0.5% by mass or more and 10% by mass or less.

[0005] 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 diagram of a pressure-feeding device used in a microduct pressure-feeding test. Fig. 3 is a schematic cross-sectional view of an optical cable according to another embodiment of the present disclosure. Fig. 4 is a diagram showing an example of an intermittently adhesive optical fiber ribbon housed in an optical cable.

[0006] [Problem to be Solved by the Present Disclosure] A construction method in which a cable is fed into a microduct, which is a small-diameter tubular duct, by air pressure feeding is called the microduct system construction method. As described above, the microduct system construction method makes it possible to quickly install the necessary optical fibers in accordance with the expansion of the optical network, and is an extremely effective means for realizing FTTH. Therefore, there is a demand for optical cables that are suitable for applying this microduct system construction method, particularly in access / drop areas.

[0007] As described above, slotless optical cables are easily lightweight, making them suitable for use as optical cables for compressed air (also known as microduct cables). Such optical cables for compressed air are threaded through a small-diameter duct by supplying air at a predetermined pressure into the duct and pushing the cable through. Therefore, it is desirable for the cable to be able to easily pass through the duct. In particular, the longer the pumping distance, the lower the installation costs, so long-distance air pumping performance is required.

[0008] The present disclosure has been made in light of the above circumstances, and has an object to provide an optical cable that has excellent performance in pumping air into a microduct.

[0009] [Advantages of the Present Disclosure] The optical cable of the present disclosure has excellent performance in pumping air into a microduct.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] An optical cable according to one aspect of the present disclosure is an optical cable to be laid in a microduct, the optical cable including an aggregated core that houses one or more optical fiber cores, and a sheath layer that covers the outer periphery of the aggregated core, and the density of the sheath layer is 1.0 g / cm ３ or less, the main component of the sheath layer is polyethylene, the sheath layer contains silicone, and the density of the polyethylene is 0.92 g / cm ３ The weight average molecular weight of the silicone is 50,000 or more and 1,000,000 or less, and the content of the silicone in the sheath layer is 0.5% by mass or more and 10% by mass or less.

[0012] An optical cable according to another aspect of the present disclosure is an optical cable to be laid in a microduct, the optical cable including an aggregated core that houses one or more optical fiber cores, and a sheath layer that covers an outer periphery of the aggregated core, and the density of the sheath layer is 1.0 g / cm ３ or less, the main component of the sheath layer is polyethylene, the sheath layer contains silicone, and the density of the polyethylene is 0.92 g / cm ３ The above optical cable has a weight average molecular weight of 50,000 or more and 1,000,000 or less, a content of the silicone in the sheath layer of 0.5% by mass or more and 10% by mass or less, and the optical fiber core is an intermittently bonded optical fiber ribbon core.

[0013] The density of the sheath layer of the optical cable used for installation in the microduct is 1.0 g / cm ３ In addition, the sheath layer has a weight of 0.92 g / cm or less, thereby achieving weight reduction. ３ By using polyethylene having a density of 50,000 or more as the main component, good hardness can be obtained. This makes it easier to feed the optical cable into a microduct when pumping air into it. Furthermore, by having the content of silicone having a weight-average molecular weight of 50,000 to 1,000,000 in the sheath layer be 0.5% by mass or more and 10% by mass or less, the surface of the sheath layer has good slipperiness, improving pumpability during air pumping (air pumpability). Therefore, by improving the hardness, surface slipperiness, and weight reduction of the sheath layer, the optical cable can achieve good air pumping performance into a microduct. Here, "main component" refers to the component with the highest content, preferably a content of more than 50% by mass.

[0014] The "weight average molecular weight" is a value calculated in terms of standard polystyrene measured by gel permeation chromatography (GPC). Specifically, the average molecular weight is determined under the following conditions: using tetrahydrofuran as a solvent, using a GPC system (SC-8010 manufactured by Tosoh Corporation), and creating a calibration curve with commercially available standard polystyrene. Flow rate: 1.0 ml / min; Set temperature: 40°C; Column configuration: one Tosoh "TSK guard column MP (xL)" 6.0 mm ID x 4.0 cm column, and two Tosoh "TSK-GELMULTIPORE HXL-M" 7.8 mm ID x 30.0 cm (theoretical plate number: 16,000), for a total of three columns (total theoretical plate number: 32,000); Sample injection volume: 100 μl (sample solution concentration: 1 mg / ml); Solution delivery pressure: 39 kg / cm ２ Detector: RI detector

[0015] The sheath layer may have a modulus of elasticity E1 at 25°C of 250 MPa or more and 2000 MPa or less. When the sheath layer has a modulus of elasticity E1 at 25°C of 250 MPa or more and 2000 MPa or less, the hardness of the sheath layer can be set within a more favorable range, thereby further improving the performance of the optical cable in pumping air into a microduct. The "modulus of elasticity" is a value measured in accordance with the dynamic mechanical property testing method described in JIS-K7244-4 (1999), and is the value of the storage modulus measured using a viscoelasticity measuring device (for example, "DVA-220" manufactured by IT Measurement Control Co., Ltd.) in a tensile mode, in a temperature range of -60°C to 80°C, at a heating rate of 5°C / min, a frequency of 10 Hz, and a strain of 0.05%.

[0016] The sheath layer may have an elastic modulus E2 of 30 MPa or more at 70° C. When the sheath layer has an elastic modulus E2 of 30 MPa or more at 70° C., deformation of the cable during storage at high temperatures can be prevented.

[0017] The product C1×E3 of the sheath layer's linear expansion coefficient C1 from −30° C. to 70° C. and its elastic modulus E3 at −30° C. may be 0.35 MPa / K or less. By setting the product of the sheath layer's linear expansion coefficient and its elastic modulus at low temperatures within the above range, the optical cable can improve the effect of suppressing an increase in transmission loss due to expansion and contraction of the sheath layer after heat cycling. The mechanism behind this is that, since at least one of the linear expansion coefficient and the elastic modulus in the temperature range from low temperature to room temperature or higher is relatively small, the stress that tends to contract the sheath layer at low temperatures is suppressed, thereby suppressing an increase in transmission loss due to contraction. Here, the "linear expansion coefficient" refers to the linear expansion rate measured in accordance with the test method for dynamic mechanical properties described in JIS-K7244-4 (1999), and is a value calculated from the dimensional change of a thin plate with respect to temperature change using a viscoelasticity measuring device (for example, "DVA-220" manufactured by IT Measurement & Control Co., Ltd.) in tension mode, in a temperature range of -60°C to 80°C, under conditions of a heating rate of 5°C / min, a frequency of 10 Hz, and a strain of 0.05%.

[0018] The polyethylene may be high-density polyethylene. When the polyethylene is high-density polyethylene, the hardness of the sheath layer can be further increased, thereby further improving the performance of the optical cable in pumping air into the microduct.

[0019] [Details of the embodiment of the present disclosure] Hereinafter, an optical cable according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0020] <Optical Cable> The optical cable is an optical cable for installation in a microduct and contains 10,000 or fewer optical fiber cores. The optical cable is installed mainly by air pressure feeding in an underground pipe called a microduct. The optical cable includes optical fiber cores and a sheath layer that covers the optical fiber cores. The optical cable also includes an assembled core that houses one or more optical fiber cores and a sheath layer that covers the assembled core.

[0021] Fig. 1 is a schematic cross-sectional view of an optical cable according to an embodiment of the present disclosure. As shown in Fig. 1, the optical cable 10 is a slotless type and includes, for example, an aggregate core 11 that is circular in cross-section, a sheath layer 13 that covers the aggregate core 11, and a tension member 16 and a tear cord 17 that are embedded in the sheath layer 13. Note that the term "circular shape" used here does not mean a circle in the strict sense, but rather means a shape that has a certain width within a range that can be considered circular and that achieves the effects of the present disclosure. The above definition of "circular" applies to all "circular shapes" used in the present disclosure.

[0022] The assembled core 11 of the optical cable 10 houses a plurality of ribbon optical fibers 3 which are bundled together in a circular cross-sectional shape by a water-absorbing tape 12. The ribbon optical fiber 3 has, for example, 12 optical fibers 2. Note that the assembled core 11 can also house, in addition to the ribbon optical fibers 3, a plurality of single-fiber optical fibers 2 bundled together.

[0023] The outside of the water-absorbing tape 12 is covered with a sheath layer 13. In the sheath layer 13, for example, two tension members 6 for maintaining strength in the longitudinal direction and for example, two tear cords 17 for tearing the sheath layer 13 in the cable longitudinal direction are embedded and attached longitudinally during extrusion molding of the sheath layer 13.

[0024] [Tape Fiber] The ribbon fiber 3 is, for example, a bundle of multiple optical fibers 2 covered with a ribbon 1 made of polyester or the like. Known optical fibers can be used as the optical fiber 2. Multiple ribbon fiber 3 may be twisted together to form a unit, and the multiple units may be housed in an assembled state. To achieve high-density packaging of the ribbon fiber 3 within the assembled core 11, the ribbon fiber 3 may be, for example, an intermittently connected type (hereinafter also referred to as an "intermittently bonded type") ribbon fiber. The assembled multiple ribbon fiber 3 may be bundled with a bundling material or the like, or each of the above units may be bundled with a bundling material or the like. In this embodiment, the ribbon fiber 3 is housed within the assembled core 11. However, single-fiber optical fibers 2 may be housed within the assembled core 11 without being in the form of a ribbon fiber 3.

[0025] As described above, the ribbon fiber 3 may be an intermittently bonded optical fiber ribbon fiber housed in an optical cable. The optical cable 30 shown in Fig. 3 is a slotless type and includes, for example, a round core assembly 40 and a sheath layer (hereinafter also referred to as a "cable jacket") 50 formed around the core assembly (hereinafter also referred to as a "cable core") 40. The cable core 40 houses, for example, 150 intermittently bonded optical fiber ribbon fiber 60 (hereinafter also referred to as an "intermittent ribbon fiber"), each having 12 fibers, for a total of 1800 fibers. In the illustrated example, 30 intermittently bonded optical fiber ribbon fiber 60 are bundled together with a loosely wound cord (not shown) or the like to form a unit, and five such units are formed.

[0026] As shown in Fig. 4, the intermittent ribbon fiber 60 is formed by arranging a plurality of optical fibers 61 in a parallel row, with adjacent optical fibers intermittently connected by connecting portions 62 and non-connecting portions 63. Specifically, the example shown in Fig. 4 shows the intermittent ribbon fiber 60 opened in the arrangement direction, and the intermittent ribbon fiber 60 is formed by arranging 12 optical fibers 61 in a parallel row, with every two fibers being intermittently bonded. Note that the intermittent ribbon fiber 60 does not need to have connecting portions 62 and non-connecting portions 63 every two fibers, and may, for example, be intermittently connected by connecting portions 62 and non-connecting portions 63 every other fiber.

[0027] The optical fiber core wires 61 arranged as this intermittent ribbon core wire 60 are what are called optical fiber bare wires, which are glass fibers with a standard outer diameter of 125 μm coated with a coating with an outer diameter of about 250 μm, and then coated with a colored coating. Note that the optical fiber core wires 61 are not limited to this, and may also be small-diameter fibers with a coating outer diameter in the range of 135 μm to 220 μm, for example, about 165 μm or 200 μm. Using small-diameter fibers makes high-density packaging even easier.

[0028] As shown in Figure 3, the cable core 40 is formed by bundling five units, each of which is made up of 30 intermittent ribbon fiber 60, and wrapping them lengthwise or crosswise with a pressure winding tape (hereinafter also referred to as "water-absorbing tape") 41 to form a round shape. The units are twisted together in one direction or by SZ twisting. In this case, the intermittent ribbon fiber 60 can be freely deformed within the cable core 40, which is effective for achieving high density. Note that the above-mentioned intermittent ribbon fiber is incorporated herein by reference in its entirety.

[0029] [Water-Absorbent Tape] The water-absorbent tape 12 is wound, for example, vertically or horizontally, around the entire periphery of the plurality of ribbon fiber 3. The water-absorbent tape 12 is made of a base fabric such as polyester that has been subjected to a water-absorbent treatment by adhering water-absorbent powder to the base fabric.

[0030] [Tear Cord] The tear cord 17 is a cord for tearing the sheath layer 13, and is embedded in the sheath layer 13 along the longitudinal direction of the optical cable 10. In this example, two tear cords 17 are provided. The two tear cords 17 are provided facing each other at approximately the midpoint between adjacent tension members 16. By pulling out the tear cord 17, the sheath layer 13 can be torn in the longitudinal direction, allowing the ribbon fiber 3 to be taken out. The tear cord 17 is made of, for example, a tensile-resistant plastic material (e.g., polyester).

[0031] [Tension Members] The optical cable 10 is provided with two tension members 16 that bear tension to prevent stretching due to its own weight during installation. Each tension member 16 is provided within the sheath layer 13 along the longitudinal direction of the optical cable 10. The tension members 16 are made of wire material that has strength against tension and compression, such as steel wire or fiber reinforced plastics (FRP). The tension members 16 are formed to have a circular cross section.

[0032] The tear cords 17 are provided on a line perpendicular to the line connecting the centers of the two tension members 16, one on each side of the collective core 11. The tear cords 17 are cord-like members with a circular cross section made of a resin material such as polyamide (e.g., nylon) or polyester, and are aligned radially of the collective core 11, for example, on the same straight line.

[0033] [Sheath Layer] The sheath layer 13 is a resin layer that covers the outer periphery of the optical fiber 2. The sheath layer 13 is mainly composed of polyethylene and contains silicone.

[0034] The upper limit of the density of the sheath layer 13 is 1.0 g / cm ３ 0.96 g / cm ３ The density of the sheath layer 13 may be 1.0 g / cm ３ By satisfying the condition of 0.1 mm or less, it is possible to reduce the weight, and therefore the pumping distance within the microduct can be increased.

[0035] The lower limit of the elastic modulus E1 of the sheath layer 13 at 25°C may be 250 MPa or 350 MPa. On the other hand, the upper limit of the elastic modulus E1 of the sheath layer 13 at 25°C may be 2000 MPa or 1850 MPa. If the elastic modulus E1 of the sheath layer 13 at 25°C is less than 250 MPa, the sheath layer 13 may not have sufficient hardness, and the performance of pumping air into the microduct may be reduced. On the other hand, if the elastic modulus E1 of the sheath layer 13 at 25°C exceeds 2000 MPa, the flexibility at room temperature may be reduced, and cracks may occur in the sheath layer during installation.

[0036] The lower limit of the elastic modulus E2 of the sheath layer 13 at 70° C. may be 30 MPa or 40 MPa. If the elastic modulus E2 of the sheath layer 13 at 70° C. is less than 30 MPa, the sheath layer 13 may be deformed during storage at high temperatures. On the other hand, there is no particular limitation on the upper limit of the elastic modulus E2 of the sheath layer 13 at 70° C.

[0037] The lower limit of the elastic modulus E3 of the sheath layer 13 at −30° C. may be 500 MPa or 1000 MPa. On the other hand, the upper limit of the elastic modulus E3 of the sheath layer 13 may be 5000 MPa or 4000 MPa. If the elastic modulus E3 of the sheath layer 13 is less than 500 MPa, the lateral pressure resistance at low temperatures may be insufficient. On the other hand, if the elastic modulus E3 of the sheath layer 13 exceeds 5000 MPa, the flexibility at low temperatures may be reduced, and cracks may occur in the sheath layer 13 during installation.

[0038] The upper limit of the product C1×E3 of the sheath layer 13's linear expansion coefficient C1 from -30°C to 70°C and its elastic modulus E3 at -30°C may be 0.35 [MPa / K] or 0.25 [MPa / K]. By setting the product of the sheath layer 13's linear expansion coefficient and its elastic modulus at low temperatures within the above range, the optical cable can improve the effect of suppressing an increase in transmission loss due to expansion and contraction of the sheath layer after heat cycling. Note that C1×E3 can be adjusted by the type and content of the olefin-based resin, etc.

[0039] The average thickness of the sheath layer 13 is determined appropriately depending on the size, application, etc. of the cable. The lower limit of the average thickness of the sheath layer 13 may be 0.05 mm, 0.5 mm, or 1.0 mm. On the other hand, the upper limit of the average thickness of the sheath layer 13 may be 10 mm, 8 mm, or 5 mm. If the average thickness of the sheath layer 13 is less than 0.05 mm, abrasion resistance may be insufficient. On the other hand, if the average thickness of the sheath layer 13 exceeds 10 mm, space saving during installation may not be achieved. The "average" in the above "average thickness" refers to the average value of thicknesses measured at three arbitrary points.

[0040] (Polyethylene) The sheath layer 13 is primarily composed of polyethylene. Examples of polyethylene include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). The polyethylene may be high-density polyethylene. Using high-density polyethylene can further increase the hardness of the sheath layer, making it easier for the optical cable 10 to pass through the microduct.

[0041] The lower limit of the density of the polyethylene is 0.92 g / cm ３ 0.94 g / cm ３ The upper limit of the density of the polyethylene is 0.98 g / cm ３ 0.96 g / cm ３ The density of the sheath layer 13 may be 0.92 g / cm ３ If the density is smaller than 0.98 g / cm, the sheath layer 13 may not have sufficient hardness, and the performance of pumping air into the microduct may be reduced. ３ If the density exceeds 0.94 g / cm, it is not possible to reduce the weight of the sheath layer 13, and the performance of pumping air into the microduct may be reduced. ３ and the density of high density polyethylene is 0.94 g / cm ３ That's all.

[0042] The lower limit of the polyethylene content in the sheath layer 13 may be 90% by mass or 92% by mass. Meanwhile, the upper limit of the polyethylene content in the resin component may be 99.5% by mass or 98% by mass. If the polyethylene content is less than 90% by mass, the sheath layer 13 may not have sufficient hardness, which may result in a decrease in the performance of pumping air into the microduct. Meanwhile, if the polyethylene content exceeds 99.5% by mass, it may be difficult to improve the slipperiness of the sheath layer 13 by silicone.

[0043] (Silicone) The sheath layer 13 contains silicone as a lubricant. By containing silicone in the sheath layer 13, the coefficient of friction of the sheath layer 13 can be reduced, and the lubricity can be improved. As a result, when the optical cable 10 is compressed air fed through a microduct, friction between the sheath layer 13 and the microduct is reduced, and the pumping distance of the optical cable 10 can be extended.

[0044] The lower limit of the weight-average molecular weight of the silicone may be 50,000 or 70,000. On the other hand, the upper limit of the weight-average molecular weight of the silicone may be 1,000,000 or 800,000. If the weight-average molecular weight of the silicone is less than 50,000, the surface of the sheath layer 13 may not have sufficient slipperiness, which may result in a decrease in the performance of pumping air into the microduct. On the other hand, if the weight-average molecular weight of the silicone is more than 1,000,000, the compatibility with the resin component may decrease.

[0045] The lower limit of the silicone content in the sheath layer 13 may be 0.5% by mass or 1% by mass. On the other hand, the upper limit of the silicone content in the sheath layer 13 may be 10% by mass or 8% by mass. If the silicone content in the sheath layer 13 is less than 0.5% by mass, the surface of the sheath layer 13 may not have sufficient slipperiness, which may result in a decrease in the performance of pumping air into the microduct. On the other hand, if the silicone content in the sheath layer 13 exceeds 10% by mass, the compatibility with the resin component may decrease.

[0046] [Method for Manufacturing Optical Cable] Next, a description will be given of an example of a method for manufacturing the optical cable 10. The method for manufacturing the optical cable 10 includes, for example, a step of producing the ribbon fiber 3 and a step of covering the ribbon fiber 3 with the sheath layer 13.

[0047] In the process of producing the ribbon fiber 3 (tape fiber production process), a plurality of coated optical fibers 2 are held down and wound with a tape to collect the coated optical fibers 2 .

[0048] In the step of covering with the sheath layer 13, the outer periphery of one ribbon optical fiber 3 or an assembly of multiple ribbon optical fiber 3 obtained in the step of producing the ribbon optical fiber 3 is covered with the sheath layer 13. Examples of this covering method include a method of extrusion molding a resin composition for forming a sheath layer that contains polyethylene as a main component and silicone.

[0049] According to the optical cable 10, the sheath layer 13 is made lighter and the hardness and surface smoothness are adjusted within a favorable range, so that the optical cable 10 has excellent performance in pumping air into the microduct.

[0050] [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 of the claims.

[0051] Hereinafter, the present disclosure will be described more specifically with reference to experimental examples, but the present disclosure is not limited to the following experimental examples.

[0052] <Optical Cables No. 1 to No. 15> (1) Preparation of Sheath Layer A composition for forming a sheath layer was prepared according to the formulation shown in Table 1, and the composition for forming a sheath layer was extruded to form tubular sheath layers No. 1 to No. 15 having an average outer diameter of 12.0 mm and an average thickness of 1.5 mm. The composition and density of the composition for forming a sheath layer are shown in Table 1. "-" indicates that the corresponding component was not used.

[0053] (Polyethylene) In Table 1, the polyethylenes used are as follows: (1) HDPE1 (high density polyethylene) "Hi-Zex 5100E" manufactured by Prime Polymer Co., Ltd. Density 0.94 g / cm ３ (2) HDPE2 (high density polyethylene) "Hi-Zex 5000H" manufactured by Prime Polymer Co., Ltd. Density 0.96 g / cm ３ (3) LLDPE (low density polyethylene) "NUCG9121" manufactured by ENEOS NUC Corporation, density 0.92 g / cm ３ (4) VLDPE (very low density polyethylene) "Tafmer DF110" manufactured by Mitsui Chemicals, Inc. Density 0.90 g / cm３

[0054] (Lubricant) (1) High molecular weight silicone 1 Weight average molecular weight 659,000 (2) High molecular weight silicone 2 Weight average molecular weight 71,500 (3) High molecular weight silicone 3 Weight average molecular weight 38,500

[0055] [Evaluation] The sheath layers and optical cables No. 1 to No. 15 were evaluated for the following items.

[0056] (Elastic Modulus) For the sheath layers of optical cables No. 1 to No. 15, the storage modulus was measured in a tensile mode in a temperature range of -60°C to 80°C using a viscoelasticity measuring device ("DVA-220" manufactured by IT Measurement & Control Co., Ltd.) in accordance with the test method for dynamic mechanical properties described in JIS-K7244-4 (1999) under conditions of a heating rate of 5°C / min, a frequency of 10 Hz, and a strain of 0.05%, and from the measured values, the elastic modulus E1 at -25°C, the elastic modulus E2 at 70°C, and the elastic modulus E3 at -30°C were calculated. The results are shown in Table 1.

[0057] (Linear expansion coefficient and product of linear expansion coefficient and elastic modulus at -30°C) In accordance with the dynamic mechanical property testing method described in JIS-K7244-4 (1999), a viscoelasticity measuring device ("DVA-220" manufactured by IT Measurement & Control Co., Ltd.) was used to calculate the linear expansion coefficient C1 from -30°C to 70°C from the dimensional change of the thin plate relative to temperature change under the conditions of tensile mode, temperature range of -60°C to 80°C, heating rate of 5°C / min, frequency of 10 Hz, and strain of 0.05%. Furthermore, the product C1 x E3 of the linear expansion coefficient C1 from -30°C to 70°C and the elastic modulus E3 at -30°C was calculated.

[0058] (Dynamic Friction Coefficient) The dynamic friction coefficient of the sheath layer was measured using the following procedure. First, the sheath layer was produced by extrusion processing only the sheath material. Then, the friction coefficient of the produced sheath layer was measured based on JIS-K7125:1999. When the dynamic friction coefficient is 0.35 or less, the sheath layer surface has good sliding properties, and the air pumpability of the optical cable can be further improved.

[0059] (Air Pumpability of Optical Cables) The pumping distances of optical cables No. 1 to No. 15 were measured using a pumping device 20 shown in FIG. 2 in accordance with the IEC (International Electrotechnical Commission) standard through a microduct pumping test. The pipe 25 had a total length of 1,000 m and was folded back every 100 m. The radius of curvature R (the radius of the circle of curvature centered at P) of the folded portion of the pipe 25 was 40 times the outer diameter of the pipe 25, and the inner diameter of the pipe 25 was 14 mm. Air and each optical cable were fed into the inlet 21 of the pipe 25 and fed out of the outlet 22. The air pressure was set to 1.3 MPa to 1.5 MPa. The air pumpability of the optical cables was evaluated based on the pumping distance of the optical cables, with a two-level rating of A or B. The evaluation criteria for the air pumpability of the optical cables were as follows: A: Good: The pumping distance is 1000 m or more. B: Poor: The pumping distance is less than 1000 m.

[0060] (Presence or absence of die scatter) The presence or absence of die scatter, which is an indicator of productivity, was evaluated according to the following procedure. In extrusion molding, the presence or absence of die scatter remaining in the die was visually confirmed after 500 m of extrusion. If die scatter remains in the die, continuing extrusion may result in the die scatter adhering to the heat-recoverable article, which may cause defects in the heat-recoverable article. For this reason, extrusion molding must be stopped and the die scatter removed. The presence or absence of die scatter was judged according to two levels: A and B. The evaluation criteria for the presence or absence of die scatter were as follows: A: Good: No die scatter remains in the die, and extrusion molding can be continued. B: Poor: Die scatter remains in the die, and extrusion molding must be stopped and the die scatter removed.

[0061] The evaluation results are shown in Table 1.

[0062]

[0063] As shown in Table 1, when the density of the sheath layer is 1.0 g / cm ３ or less, the sheath layer is mainly composed of polyethylene and contains silicone, and the density of the polyethylene is 0.92 g / cm ３In Nos. 1 to 8, in which the weight-average molecular weight of the silicone was 50,000 or more and 1,000,000 or less and the content of the silicone in the sheath layer was 0.5% by mass or more and 10% by mass or less, the coefficient of dynamic friction was low, and the optical cables had good air pumpability and productivity.

[0064] On the other hand, No. 9, whose sheath layer did not contain silicone, had a high coefficient of dynamic friction and the air pumpability of the optical cable was poor. Nos. 10 and 11, whose silicone weight-average molecular weight was less than 50,000, caused die scuffs. The density of the polyethylene was 0.92 g / cm. ３ In No. 12 and No. 13, in which the silicone content in the sheath layer was less than 10% by mass, the optical cables were poor in air pumpability. In No. 14, in which the silicone content in the sheath layer was more than 10% by mass, die scuffs were formed. In No. 15, in which the silicone content in the sheath layer was less than 0.5% by mass, the dynamic friction coefficient was high, and the optical cables were poor in air pumpability.

[0065] The above results demonstrate that the optical cable has good air pumping performance into microducts due to the improved sheath hardness, surface smoothness, and light weight. The optical cable can be suitably used as an optical cable for microducts between data centers where large amounts of information are transmitted.

[0066] REFERENCE SIGNS LIST 1 ribbon 2, 61 optical fiber core 3 ribbon core 10, 30 optical cable 11, 40 assembled core (cable core) 12, 41 water-absorbing tape (pressure winding tape) 13, 50 sheath layer (cable outer jacket) 16, 31 tension member 17, 32 tear cord 20 pressure feeding device 21 inlet 22 outlet 25 pipe 60 intermittent ribbon core 62 connection portion 63 non-connection portion

Claims

1. An optical cable for installation in a microduct, The optical cable includes a core assembly that accommodates one or more optical fibers. a sheath layer covering an outer periphery of the aggregate core; Equipped with The density of the sheath layer is 1.0 g / cm ３ is as follows: The main component of the sheath layer is polyethylene, the sheath layer comprises silicone; The density of the polyethylene is 0.92 g / cm ３ That's all. The weight average molecular weight of the silicone is 50,000 or more and 1,000,000 or less, An optical cable, wherein the content of the silicone in the sheath layer is 0.5% by mass or more and 10% by mass or less.

2. 2. The optical cable according to claim 1, wherein the optical fiber core is accommodated in the bundled core with a water absorbing tape.

3. 3. The optical cable according to claim 2, wherein the optical fibers are bundled in the assembled core in a circular shape in cross section by the water absorbing tape.

4. 4. The optical cable according to claim 1, wherein the optical fiber is an intermittently bonded optical fiber ribbon.

5. 4. The optical cable according to claim 1, wherein the sheath layer has an elastic modulus E1 at 25° C. of 250 MPa or more and 2000 MPa or less.

6. 4. The optical cable according to claim 1, wherein the sheath layer has an elastic modulus E2 at 70° C. of 30 MPa or more.

7. 4. The optical cable according to claim 1, wherein the product C1×E3 of the linear expansion coefficient C1 of the sheath layer from −30° C. to 70° C. and the elastic modulus E3 at −30° C. is 0.35 MPa / K or less.

8. 4. The optical cable according to claim 1, wherein the polyethylene is a high density polyethylene.