Patent ID: 12235499

DETAILED DESCRIPTION

Various embodiments of an optical fiber cable are provided that is configured to achieve a B2ca-s1a, a1, d0 rating described in EN 13501-6. The optical fiber cable achieves the flame retardance rating through use of a cable sheath comprising a highly-filled, flame retardant composition and, in embodiments, a bedding layer having a composition with an even greater amount of flame retardant filling than the cable sheath. In certain embodiments, the cable includes a single subunit that is capable of carrying up to twelve optical fibers while still being able to be blown through a 3.5 mm or 4 mm duct within a building. The optical fiber cable is able to be blown through such ducts because the diameter of the optical fiber cable is kept to 3 mm or less and because the material from which the cable sheath is made has a low coefficient of friction. Space is conserved in the cable construction to keep the diameter at or below 3 mm by excluding rigid strength elements, such as glass reinforced plastic rods. Such rigid strength elements can be excluded because the material from which the cable sheath is made allows the cable to pass relevant temperature cycling tests without the need for rigid strength elements. Accordingly, in view of the flame retardancy and the ability of the optical fiber cable to be blown through such a narrow duct, the optical fiber cable disclosed herein is particularly suitable for use in indoor applications. In other embodiments, the optical fiber cable includes a plurality of subunits configured to carry, e.g., hundreds of optical fibers, and in such embodiments, the individual subunits contain strengthening yarns disposed therein to facilitate connnectorization of the subunits. These and other aspects and advantages will be discussed in relation to the exemplary embodiments disclosed herein. These embodiments of the optical fiber cable disclosed herein are provided by way of example and not by way of limitation.

FIG.1depicts an embodiment of an optical fiber cable10, particularly for indoor use, that includes a plurality of optical fibers12disposed within a subunit14. The subunit14includes a first interior surface16and a first exterior surface18. The first interior surface16defines a central bore20in which the optical fibers12are disposed. In the embodiment shown in theFIG.1, the optical fibers12are arranged within the bore20in a loose tube configuration (albeit with a relatively low amount of free space with in the subunit14as compared to other embodiments discussed below). In embodiments, the optical fibers12are bare or coated fibers, i.e., they include a core, a cladding surrounding the core, and a coating (optionally including a color-coded ink/pigment layer for identification). In embodiments, the number of optical fibers12in the subunit is from one to twelve optical fibers. In particular embodiments, the number of optical fibers12in the subunit is four, six, eight, or twelve optical fibers12. In embodiments, the optical fiber cable10does not include any water-blocking gels within the bore20, particularly if the optical fiber cable10is used for indoor applications.

The subunit14has a first thickness T1between the first interior surface16and the first exterior surface18. In embodiments, the first thickness T1is from 0.05 to 0.5 mm, particularly about 0.1 mm for the embodiment shown inFIG.1. In embodiments, the subunit14is comprised of a flame retardant compound comprising a mixture of thermoplastic elastomers based on polyolefins (e.g., polyethylene (PE), polypropylene (PP), polybutene, ethylene propylene diene monomer (EPDM) rubber, ethylene propylene rubber (EPR), ethylene vinyl acetate (EVA), ethylene butyl acrylate copolymer (EBA), ethylene methacrylate (EMA)) filled with one or more mineral-based flame retardants (e.g., aluminum trihydrate (ATH), magnesium hydroxide (MDH), or calcium carbonate (CaCO3)). In embodiments, the compound is a blend of PP and a polyolefin or a rubber that is filled with a mixture of MDH and CaCO3. Advantageously, because of the relatively low first thickness T1of the subunit14, the optical fibers12can be used as ripcords to tear open the subunit14during installation. That is, the subunit14can be torn by pulling the optical fibers12against the wall of the subunit14.

Disposed around the subunit14is a yarn layer22comprising a plurality of strengthening yarns24. In embodiments, the strengthening yarns24are wrapped, stranded, or braided around the subunit14so as to take tensile stresses off of the optical fibers12, e.g., when the optical fiber cable10is pulled. In other embodiments, the strengthening yarns24run longitudinally along the length of the subunit14. In embodiments, the yarn layer22is from 0.05 mm to 0.2 mm thick, particularly about 0.1 mm. The yarn layer22is in contact with the exterior surface18of the subunit14. In embodiments, the strengthening yarns24comprise aramid fibers, glass fibers, basalt fibers, or a combination of two or more thereof.

In the embodiment depicted inFIG.1, a cable sheath26is disposed around the yarn layer22. In embodiments, the cable sheath26forms a continuous and contiguous outer layer of the optical fiber cable10along the length of the optical fiber cable10. The cable sheath26includes a second interior surface28and a second exterior surface30that define a second thickness T2therebetween. In embodiments, the second thickness T2is from 0.3 mm to 0.7 mm. Further, in embodiments, the second exterior surface30defines the outermost surface of the optical fiber cable10. As such, the second exterior surface30further defines an outer diameter OD of the optical fiber cable10. In embodiments, the outer diameter OD of the optical fiber cable10is no more than 3 mm, particularly from 2.2 mm to 2.7 mm (depending on fiber count). For example, in embodiments, an optical fiber cable10carrying four optical fibers12has an outer diameter OD of from about 2.2 mm to about 2.4 mm, and in embodiments, an optical fiber cable10carrying twelve optical fibers12has an outer diameter OD of from about 2.6 mm to 2.7 mm.

The cable sheath26of the optical fiber cable10is made of a low-smoke, zero halogen (LSZH) material. In particular, the LSZH material comprises a thermoplastic polymer blend filled with mineral-based flame retardant additives. In an embodiment, the polymer blend of the LSZH material comprises from 35% to 45% by weight of a co-polyester or co-polyether and polyolefins or polyolefin-based elastomers. In such embodiments, the mineral-based flame retardant additives may comprise at least one of aluminum trihydrate (ATH) or magnesium hydroxide (MDH) in an amount of 55% to 68% by weight. Further, the LSZH material may also include other synergistic flame retardant additives such as glass formers or ceramifiers (e.g., zinc borate, zinc molybdate, zinc stannate, etc.), nano-clays (e.g., bentonite, sepiolite, etc.), or mineral fillers (e.g., boehmite, silica, magnesiumoxisulfate, etc.) in the amount of 1.5% to 8% by weight (in addition to 55% to 68% by weight of the mineral-based flame retardant additives). The LSZH material may also include a coupling system, such as a maleic acid anhydride-grafted polyolefin, a vinyl-silane, or an aminosilane, in an amount of 0.5% to 4% by weight. Further, the LSZH material may include thermal stabilizers, antioxidants, and or processing additives in the amount of 0.1% to 1.0% each.

In embodiments, the LSZH material of the cable sheath26exhibits certain mechanical and flame retardant properties. In particular embodiments, the LSZH has a tensile strength of 10 MPa or higher and an elongation at break of at least 180% (both as measured according to IEC 811-1-1). Further, in embodiments, the LSZH material has a Shore A hardness of 90 or lower (as measured according to ISO 7619-1). In embodiments, the LSZH material has a density of at least 1.6 g/cm3. Still further, in embodiments, the storage modulus of the LSZH material in tensile mode at −40° C. is less than 3000 MPa and at −50° C. is less than 3500 MPa. In embodiments, the LSZH material has a brittleness temperature below −50° C. Additionally, in embodiments, the LSZH material exhibits a penetration of less than 2% in a hot pressure test for 6 hours at 80° C. (as measured according to IEC 60811-508). Advantageously, the optical fiber cable10can be cycled between −40° C. and 70° C. without creating substantial change in attenuation (<0.30 dB/km at 1550 nm) of the signal carried by the optical fibers12according to IEC 60794-1-2-F1. Accordingly, rigid strength elements, such as glass-reinforced plastic rods, are not required to prevent such attenuation associated with thermal strain, which means that the diameter of the optical fiber cable10can be reduced by excluding these elements.

With respect to the flame retardant properties, the LSZH material has a limiting oxygen index (LOI) of at least 40% (as measured according to ASTM D 2863 A). Further, in embodiments, a sample of the LSZH material having a length and width of 100 mm and a thickness of 3 mm when tested with 50 kW irradiation exhibits a peak heat release rate (PHRR) of 200 kW/m2or less, a total heat release (THR) of 65 MJ/m2or less, and a smoke production (SEA) of 150 m2/kg or less when measured using a cone calorimeter according to ISO 5660-1.

FIG.2depicts another embodiment of an optical fiber cable10including a bedding layer32disposed between the yarn layer22and the cable sheath26. As shown inFIG.2, the bedding layer32extends circumferentially around the yarn layer22and is in contact with the second interior surface28of the cable sheath26. In embodiments, the bedding layer32has substantially the same thickness as the cable sheath26. In embodiments, the bedding layer32has a third thickness T3of from 0.2 mm to 0.4 mm, and the combined thickness of the bedding layer32and the cable sheath26is thus from 0.3 mm to 0.7 mm. Further, in embodiments, the bedding layer32is substantially comprised of flame retardant fillers with a polymer binding. As such, the bedding layer32has a dough-like consistency and does not impart any substantial mechanical properties to the optical fiber cable. However, the bedding layer32improves flame retardant performance of the optical fiber cable10because some of the cable sheath26is replaced with the bedding layer32, which has more flame retardant material than the cable sheath26. Advantageously, in embodiments, the bedding layer32also reduces the cost to produce the optical fiber cable10because more of the relatively less expensive mineral-based flame retardant additive and less of the relatively more expensive cable sheath compound is used in the optical fiber cable10.

In particular embodiments, the bedding layer32is comprised of 70% to 85% by weight of a mineral-based flame retardant additive, such as aluminum trihydrate or magnesium hydroxide. In embodiments, a portion of the mineral-based flame retardant additive may be substituted with calcium carbonate. The polymer binder of the bedding layer32is comprised of 10% to 30% by weight of a thermoplastic blend of polyolefin elastomers (e.g., EVA, EBA, EMA, EPR, EPDM rubber, and/or styrene-ethylene/butylene-styrene (SEBS)) or polyolefins (e.g., low density polyethylene (LDPE), linear low density polyethylene (LLDPE, and/or polypropylene (PP)). The bedding layer32may also comprise a coupling system, such as a maleic acid anhydride-grafted polyolefin, a vinyl-silane, or an aminosilane, in an amount of 0.5% to 4% by weight. Further, the bedding layer32may include thermal stabilizers, antioxidants, and or processing additives in the amount of 0.1% to 1.0% each. In embodiments, the bedding layer32has a density of 1.7 g/cm3or greater.

Advantageously, the embodiments of the optical fiber cables10described with respect toFIGS.1and2are capable of being routed through a duct having an inner diameter of 3.5 mm to 4 mm (or larger) as may typically be found running through a building interior. In particular, the optical fiber cables10are configured to carry up to twelve optical fibers12while still being able to be blown at least 150 m through a duct having an inner diameter as low as 3.5 mm. An optical fiber cable10constructed according to the foregoing description was blown through a track of duct that was arranged in a spiraling rectangular path having side lengths of 7 m and 3 m with corners having a radius of curvature of 10 mm×5 mm. One rectangular path length was equal to approximately 20 m. Accordingly, in traveling 150 m through the duct, the optical fiber cable10completed 32 turns. The ability to be blown through a duct having an inner diameter as low as 3.5 mm is provided in part by the small outer diameter of the optical fiber cable (3 mm or less) and in part by the low coefficient of friction of the LSZH material (from 0.21 to 0.24) used for the cable sheath.

Additionally, the construction of the optical fiber cable10according to the present disclosure provides other advantages with respect to cable installation. Typically, an optical fiber cable10may be routed (e.g., through a duct as described above) to a splice box where the individual optical fibers12can be spliced for distribution from the splice box. As mentioned, the cable sheath26allows for blowing of the optical fiber cable10through a duct to the splice box while providing flame retardancy along the substantial portion of the length. Once the optical fiber cable10reaches the splice box, the cable sheath26is able to be ring-cut, and at least a length of 1.5 m is able to be pulled off longitudinally over the yarn layer22and subunit14. In this regard, the use of the above-described compounds for the subunit14helps prevent sticking between the cable sheath26and the subunit14such that the length of cable sheath26can be pulled over the subunit14. Within the splice box, the subunit14protects the individual optical fibers12until they reach their splice location (e.g., inside a splice cassette).

Further, the embodiments of the optical fiber cables10described herein achieve a rating of B2ca-s1a, a1, d0 described in EN 13501-6. In order to achieve rating B2ca, the optical fiber cable10must pass the heat release and flame spread requirements of EN50399. Further, to achieve the rating s1a for smoke production, the optical fiber cable10must have a total smoke production of no more than 50 m2and a smoke product rate of no more than 0.25 m2/s as measured according to EN50399 (which corresponds to the “s1” portion of the rating) and must pass the three-meter cube test according to EN 61034-2 with a minimum of 80% light transmission (which corresponds to the “a” portion of the rating). To achieve the rating a1 for acidity, the combusted gasses produced by the individual components of the optical fiber cable10during burn testing must have a conductivity of less than 2.5 μS/mm and a pH of greater than 4.3 according to EN50267-2-3. Finally, in order to achieve a flaming droplets rating of d0, the optical fiber cable10must exhibit no flaming droplets or particles as tested according to EN50399. Embodiments of the optical fiber cables10described herein were able to meet each of these requirements to achieve the rating of B2ca-s1a, a1, do.

FIGS.3and4depict embodiments of optical fiber cables10including multiple subunits14that also are able to achieve a ration of B2ca-s1a, a1, do. Because these optical fiber cables10contain multiple subunits14, the outer diameter OD of the optical fiber cables10is larger than the outer diameter OD of the optical fiber cables10of the embodiments ofFIGS.1and2. For example, the optical fiber cable10depicted inFIG.3includes two subunits14and has an outer diameter OD of 4 mm to 5 mm, and the optical fiber cable10ofFIG.4includes eight subunits14and has an outer diameter of 6.5 mm to 8.5 mm. Other embodiments may include more than eight subunits14and the outer diameter may be correspondingly larger (e.g., up to 20 mm or more).

In embodiments, each of the subunits14ofFIGS.3and4may contain from one to twelve optical fibers12. Exemplary embodiments include, e.g., four, six, eight, or twelve optical fibers12. As compared to the embodiments shown inFIGS.1and2, the subunits14are larger and have a higher wall thickness. In this way, the optical fibers12have more free space within the subunits14ofFIGS.3and4. In particular, the subunits14ofFIGS.3and4have an outer diameter of about 2 mm and a thickness of 0.05 to 0.5 mm. Additionally, in embodiments, the subunits14are made of a flame retardant compound including a mixture of thermoplastic elastomers based on polyolefins (such as PE, PP, polybutene, EPDM rubber, EPR, EVA, EBA, EMA) filled with mineral flame retardant (e.g., ATH, MDH, or CaCO3). In embodiments, the compound is a blend of PP and a polyolefin or a rubber filled with a mixture of MDH and CaCO3.

In embodiments, the subunits14contain and/or are surrounded by the strengthening yarns24. In particular, a plurality of strengthening yarns24may be wrapped around the first exterior surfaces18of the subunits14to keep them bundled in the cable sheath26. In embodiments, one to four strengthening yarns24are helically wrapped around the subunits14to keep them bundled. In such embodiments, the strengthening yarns24may not form a continuous layer (such as yarn layer22ofFIGS.1and2) around the subunits14, and talcum powder may be applied to the first exterior surfaces18of the subunits14to prevent sticking to the cable sheath26. In embodiments, the subunits14include strengthening yarns24within the central bore20to facilitate connectorizing the subunits14(as shown schematically inFIG.3with the diamonds representing strengthening yarns24). During connectorizing, the strengthening yarns24are crimped into the connector to provide tensile strain relief for the optical fibers12. The strengthening yarns24used on the interior and/or exterior of the subunit14may comprise aramid fibers, glass fibers, basalt fibers, or combinations of two or more thereof.

The plurality of subunits14are surrounded with the cable sheath26and, in embodiments, the bedding layer32. The cable sheath26is made from the same LSZH material described above with respect to the embodiments ofFIGS.1and2. Further, in the embodiments in which it is provided, the bedding layer32is the same material as described above with respect toFIG.2. In this way, optical fiber cables10having a higher fiber density are able to be provided with a high degree of flame retardance, particularly achieving the rating of B2ca-s1a, a1, d0 described in EN 13501-6.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article “a” is intended to include one or more than one component or element, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.