Patent Description:
Communication networks are used to transport a variety of signals such as voice, video, data transmission, and the like. Traditional communication networks use copper wires in cables for transporting information and data. However, copper cables have drawbacks because they are large, heavy, and can only transmit a relatively limited amount of data. On the other hand, an optical waveguide is capable of transmitting an extremely large amount of bandwidth compared with a copper conductor. Moreover, an optical waveguide cable is much lighter and smaller compared with a copper cable having the same bandwidth capacity.

Consequently, optical waveguide cables replaced most of the copper cables in long-haul communication network links, thereby providing greater bandwidth capacity for long-haul links. However, many of these long-haul links have bandwidth capacity that is not being used. This is due in part to communication networks that use copper cables for distribution and/or drop links on the subscriber side of the central office. In other words, subscribers have a limited amount of available bandwidth due to the constraints of copper cables in the communication network. Stated another way, the copper cables are a bottleneck that inhibit the subscriber from utilizing the relatively high-bandwidth capacity of the long-hauls links.

As optical waveguides are deployed deeper into communication networks, subscribers will have access to increased bandwidth. But there are certain obstacles that make it challenging and/or expensive to route optical waveguides/ optical cables deeper into the communication network, i.e., closer to the subscriber. Optical cables are mainly provided with inflammable plastic materials that easily propagate and transfer the fire from a source of the fire to other areas within a building.

The European Construction Regulation (CPR) which became operational in <NUM> regulates the fire and smoke behaviour of permanently installed indoor cables within the European market. In order to fulfil the new CPR requirements, high performing materials with low smoke and heat release are needed in indoor cable designs. The traditional cable materials need to be replaced with high performing halogen-free flame-retardant options. However, the change of the manufacturing steps to replace the traditional cable materials with a high performance flame-retardant material could be very costly and complex, especially when the whole cable design needs to be changed in the cable development process.

Fire-resistant optical communication cables comprising a multi-layered sheath surrounding a cable core are shown in <CIT>, <CIT>, and <CIT>. <CIT> and <CIT> show a fiber optic cable having a cable jacket and a bedding compound filling interstices between buffer tubes, wherein the cable jacket and the bedding compound include a flame-retardant material.

There is a need to provide an optical fiber cable that has excellent fire protection properties and can be manufactured without complex manufacturing steps.

An embodiment of an optical fiber cable with improved cable fiber performance that may be manufactured with traditional extrusion methods is specified in claim <NUM>.

Nowadays materials providing a high fire protection performance are available on the market.

The inventors found that the use of one single material layer for a cable jacket of an optical fiber cable is in most cases still not enough to protect the optical cable in an efficient way against cable fire and prevent the fire from propagating along the cable. The proposed optical fiber cable design uses several materials assembled as a multilayer in a cable jacket of an optical cable. The inventors found that the combination of two or more layers of flame-retardant materials, possibly also having a different mode of action regarding fire protection mechanisms, for example intumescent-acting materials or materials forming a charring layer in case of a fire, enables to achieve higher fire protection performance of an optical cable than a single material layer used for the cable jacket.

The optical fiber cable has a multilayered jacket made of two or more layers of flame-retardant materials to be used as an outer sheath of the optical fiber cable. In particular, the multilayered embodiment of the cable jacket may be used in indoor and outdoor cable applications. The multilayered structure of the cable jacket gives <NUM>% halogen-free, non-corrosive, high flame retardant protection. The two or more different materials are assembled in a multilayered thin sheath of the optical cable comprising different flame-retardant additives and mechanisms. The different flame-retardant additives included in a base material of the various layers of the cable jacket may include intumescent-acting materials, mineral fillers, phosphorous and/or nitrogen gas phase active materials, materials to provide an inorganic barrier protection or other highly filled materials.

The multilayered cable jacket has the advantage of tailoring the fire protection performance of the different material layers and thus the fire protection properties of the whole cable by selecting an appropriate base resin material and flame-retardant mechanism.

Moreover, different flame-retardant mechanisms may be combined in one layer of material or in different layers of the multilayered cable jacket. The effectiveness of the fire protection system of the optical cable can be tailored by changing or varying the thickness of each layer of the cable jacket and/or the concentration of the flame-retardant additives in the compound used for the various layers. The optical fiber cable comprising the multilayered structure of the cable jacket shows significantly improved fire protection performances, wherein the use of toxic products, solvents or additives is avoided.

The different layers of the cable jacket may be easily applied on the cable core without changing the inner cable structure. In particular, the multilayered cable jacket may be prepared and processed with traditional extrusion methods. The different layers of the cable jacket, each with a different flame-retardant mechanism can, for example, be co-extruded in one step or in several steps on the cable core of the optical fiber cable, for example an indoor cable design. According to an alternative manufacturing method, a tandem extrusion process may be used to prepare the multilayered structure of the cable jacket.

Additional features and advantages are set forth in the detailed description that follows and in part will be readily apparent to those skilled in the art from the description or recognized by practising the embodiments as described in the written description and claims hereof, as well as the appended drawings.

The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of the specification. The drawings illustrate one or more embodiments, and together with the detailed description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures in which.

Reference is now made in detail to various embodiments of an optical fiber cable, examples of which are partly illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessary to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure. The claims as set forth below are incorporated into and constitute part of this detailed description.

<FIG> shows an optical fiber cable <NUM> having a high fire protection performance. The optical fiber cable <NUM> may be used as an indoor or outdoor optical fiber cable.

The optical fiber cable <NUM> comprises a cable core <NUM> including at least one optical transmission element <NUM> to transfer light. The optical cable further comprises a cable jacket <NUM> surrounding the cable core <NUM>. The cable jacket <NUM> is embodied as a multilayered structure having a first sheath layer <NUM> and at least a second sheath layer <NUM>. The at least one second sheath layer <NUM> is surrounded by the first sheath layer <NUM>. The material of the first sheath layer <NUM> and the material of the at least one second sheath layer <NUM> is halogen-free. The material of the first sheath layer <NUM> and the material of the at least one second sheath layer <NUM> have a different flame-retardant additive providing different flame-retardant mechanisms. Ripcords <NUM> in or adjoining the jacket <NUM> may be provided to facilitate opening the jacket.

The cable jacket <NUM> may optionally comprise a layer <NUM> which is disposed on the first sheath layer <NUM> to facilitate a blowing-in process of the optical fiber cable <NUM> in an empty duct. The layer <NUM> may be the outermost layer of the cable jacket. The layer <NUM> may include an antistatic agent to reduce friction between the cable jacket and the duct into which the cable is blown, thereby enhancing blowability.

The cable comprises a halogen-free multi-component layered structured material to be used as a jacketing application. The multilayered cable jacket <NUM> may be applied onto the cable core <NUM> by an extrusion process, for example a co-extrusion process or a tandem extrusion process. To limit the process complexity, the number of layers of the cable jacket <NUM> may be limited to two or three. However, providing the cable jacket <NUM> with a larger number of layers is possible.

According to a possible embodiment of the optical fiber cable, the material of the sheath layer <NUM> may include a first flame-retardant additive of at least one of an intumescent-acting material and a filler material and a gas-phase active material and a condensed-phase active material. The material of the at least one second sheath layer <NUM> may include a second flame-retardant additive of at least another one of the intumescent-acting material and the mineral filler and the gas-phase active material and the condensed-phase active material.

The condensed-phase active material may be configured to provide an inorganic barrier protection for the cable in the case of a cable fire. The condensed-phase active material may induce some char or residue formation. Possible materials for the condensed-phase active material are clay, nanocomposite, inorganic fillers, siloxane or combinations thereof.

The gas-phase active material may be a phosphorous and/or nitrogen-based material. The main mechanism of flame retardation in the gas phase involves inert gas dilution and chemical quenching of active radicals. The dilution effect refers to the release of non-combustible vapors during combustion, diluting the oxygen supply to the flame or diluting the fuel concentration to below the flammability limit.

The material of the first sheath layer <NUM> may include a mixture of a polymer-based resin and a polymer-filler coupling system and processing additives and the first flame-retardant additive. The material of the at least one second sheath layer <NUM> may include a mixture of a polymer-based resin and a polymer-filler coupling system and processing additives and the second flame-retardant additive.

The flame-retardant system may either be a system based on a (hydrated) mineral filler, for example a metal hydrate filler and/or a metal hydroxide filler and/or a metal oxide hydroxide filler and/or combinations thereof, or an intumescent system. According to a possible embodiment of the optical fiber cable <NUM>, the first flame-retardant additive in the first sheath layer <NUM> may include the intumescent-acting material. According to a possible embodiment, the density of the intumescent-acting material is lower than <NUM>/cm<NUM>. The second flame-retardant additive may be included in the second sheath layer <NUM> and may include the mineral filler. The density of the mineral-based flame-retardant compound can be above <NUM>/cm<NUM> due to the filler. According to a possible embodiment of the optical fiber cable <NUM>, a loading of the mineral filler in the material mixture of the second sheath layer <NUM> is between <NUM> and <NUM> wt%.

The intumescent-acting material may include a phosphorous-nitrogen combination or ammonium polyphosphate (APP) or intumescent graphite or triazine or combinations thereof. Aluminium-tri-hydroxide (ATH) or magnesium-di-hydroxide (MDH) may be used as possible metal hydrate filler materials or metal hydroxide filler materials. Boehmite (AMH) may be used a possible metal hydroxide filler material. Metal oxide hydroxide filler materials decompose at higher temperature compared to the corresponding hydroxides. Thus, by using metal hydroxides and/or metal oxide hydroxide, the decomposition temperature of the mineral filler can be controlled.

In addition, the intumescent-acting material and/or the mineral filler may include at least one synergist. Examples are zinc borate, bromide, siloxanes, nanoclays or POS (Polyorganosiloxane). The synergists can be used to further improve the fire protection performance of the optical cable.

According to a possible embodiment of the optical fiber cable <NUM>, the polymer-based resin may be configured as a mixture of polyolefins and polyolefin-based copolymers. The polyolefins may include low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). The polyolefin-based copolymer may include ethylene-vinyl acetate (EVA) or ethylene-butyl acetate (EBA) or ethylene-methacrylic acid (EMA) or octane branched polyolefins or butane branched polyolefins.

According to a possible embodiment of the optical fiber cable <NUM>, the polymer-filler coupling system may include grafted polymers, like low-density polyethylene (LDPE), ethylene-vinyl acetate (EVA), etc., with at least one of maleic-acid-anhydride and a maleic-acid-terpolymer or silane-peroxide grafting.

According to a further embodiment of the optical fiber cable <NUM>, the processing additives are lubricants like metal soaps, fatty acids or siloxane-based organics.

According to a further embodiment of the optical fiber cable <NUM>, the first sheath layer <NUM> and the at least one second sheath layer <NUM> may respectively include stabilizers for heat aging and UV radiation. Stabilization for heat aging and UV radiation may be realized by phenolic or phosphorous based antioxidants and hindered amine light stabilizers (HALS).

According to a possible embodiment, the first sheath layer <NUM> is the outermost layer of the jacket <NUM>. The second sheath layer <NUM> may be a layer which directly surrounds the core section <NUM>, for example the buffer tubes <NUM> of the optical transmission elements <NUM>. In any case, the at least one second sheath layer <NUM> is arranged closer to the cable core <NUM> than the first sheath layer <NUM>.

The intumescent-acting material is preferably included in the first sheath layer <NUM>, i.e. the outer sheath layer on top of the multilayered structure of the cable jacket <NUM>, in order to efficiently react in the case of a cable fire by quickly forming an insulating barrier, protecting the cable from the fire and delaying the combustion process of the underlying materials and sheaths.

The number and thickness of each single layer of the multilayered cable jacket <NUM> can be varied according to the performances that need to be achieved. According to a possible embodiment of the optical fiber cable <NUM>, the first, outer sheath layer <NUM> has a thickness of between <NUM> to <NUM>. The second sheath layer <NUM> may have a thickness of between <NUM> to <NUM>.

According to a possible embodiment of the optical fiber cable <NUM>, the material mixture of the first sheath layer <NUM> may include a polypropylene-copolymer based material and the intumescent-acting material. The material mixture of the second sheath layer <NUM> may include a polymer combination of equal ratios of ethylene-vinyl acetate and octane branched linear low-density polyethylene and low-density polyethylene, for example each approximately <NUM>%. The material mixture may further comprise a mineral filler of magnesium-di-hydroxide with a synergist of zinc borate. In particular, the flame-retardant system may be comprised of <NUM>% of magnesium-di-hydroxide with <NUM>% zinc borate synergist. The material mixture of the second sheath layer <NUM> may further include a polymer-filler coupling of vinyl-tri-methoxy-silane (VTMS).

The intumescent-acting material may have an oxygen index of between <NUM> to <NUM>% determined according to ASTM D-<NUM> test method, and a vertical flame rating (<NUM>/<NUM>'' thick specimens) of V-<NUM> according to UL-<NUM> test method. The mineral filler may have a specific gravity of between <NUM> to <NUM> determined according to test method ASTM D-<NUM>, an oxygen index (LOI) of between <NUM> to <NUM> % determined according to test method ASTM D-<NUM>, and a vertical flame rating (<NUM>/<NUM>" thick specimens) of V-<NUM> determined according to test method UL-<NUM>.

According to the embodiment of the optical fiber cable shown in <FIG>, the cable core <NUM> may comprise a plurality of the at least one optical transmission element <NUM> and a strength member <NUM>. Each of the optical transmission elements <NUM> includes a plurality of optical fibers <NUM>. The optical transmission elements <NUM> further comprise a respective buffer tube <NUM> which surrounds the plurality of the optical fibers <NUM>. The optical transmission elements <NUM> are placed around the strength member <NUM>. The strength member <NUM> may be configured as a dielectric strength member, for example an up-jacketed glass-reinforced composite rod. In other embodiments, the strength member <NUM> may be, or may include, a steel rod, a stranded steel, tensile yarn or fibers, for example bundled aramid, or other strengthening materials.

The optical transmission elements <NUM> may be stranded around the strength member <NUM> in a pattern of stranding including reversals in lay direction of the optical transmission elements. The optical transmission elements <NUM> may be stranded in a repeating reverse-oscillatory pattern, such as so-called SZ stranding or other stranding patterns, for example helical. In other contemplated embodiments, the optical transmission elements <NUM> may be non-stranded. The optical transmission elements are bound together around the strength member <NUM> by a film or binder <NUM>.

<FIG> shows a first embodiment of an optical fiber cable <NUM> comprising a cable core <NUM> including optical transmission elements <NUM>, and a cable jacket <NUM> surrounding the cable core <NUM>. The cable jacket <NUM> is embodied as the multilayered structure having the first sheath layer <NUM> and the at least one second sheath layer <NUM>. The cable may optionally comprise the layer <NUM>. Regarding the material composition and the properties of the first sheath layer <NUM> and the optional layer <NUM>, reference is made to the explanations of <FIG>.

The at least one second sheath layer <NUM> comprises a bedding layer <NUM> and an intermediate layer <NUM>. The intermediate layer <NUM> is comparable with the at least one second sheath layer <NUM>, as described with reference to <FIG>. Regarding the properties and material composition of the intermediate layer <NUM> reference is made to the description of the at least one second sheath layer <NUM> of <FIG>. In comparison to the embodiment of the optical fiber cable <NUM> shown in <FIG>, the cable jacket <NUM> of the optical fiber cable <NUM> additionally comprises the bedding layer <NUM>. The bedding layer <NUM> comprises a polymer based resin including a mineral filler. The bedding layer <NUM> is placed in gaps <NUM> between the optical transmission elements <NUM>.

The polymer based resin may be configured as a mixture of polyolefins and polyolefin based copolymers. The polyolefins may include low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). The polyolefin based copolymer may include ethylene-vinyl acetate (EVA) or ethylene butylacetate (EBA) or ethylene methacrylic acid (EMA) or octane branched polyolefins or butane branched polyolefins or or ethylene vinyl acetate copolymer (EVM) or ethylene propylene diene monomer rubber (EPDM) or ethylene propylene rubber (EPR). Regarding the bedding layer <NUM> soft polymers like EVM or EPDM or EPR are the preferred materials.

The mineral filler of the bedding layer <NUM> may be configured as a system based on a metal hydrate filler like aluminum-tri-hydroxide (ATH) or magnesium-di-hydroxide (MDH) or boehmite. The material of the bedding layer <NUM> may include the metal hydrate filler, for example aluminum-tri-hydroxide (ATH) or magnesium-di-hydroxide (MDH). The bedding layer <NUM> may be configured as a higher filled material than the second sheath layer <NUM>. According to a possible embodiment of the optical fiber cable <NUM>, a loading of the mineral filler in the bedding compound <NUM> is between <NUM> and <NUM> wt%. Regarding the bedding layer <NUM>, very soft polymers like above-mentioned EVM or EPDM or EPR in combination with very high amount of the filler material are preferred.

<FIG> shows a second embodiment of an optical fiber cable <NUM> comprising the first sheath layer <NUM> and the at least one second sheath layer <NUM>. The fiber cable may optionally comprise the layer <NUM>. Regarding the material composition and properties of the first sheath layer <NUM> and the optional layer <NUM>, reference is made to the description of the first sheath layer <NUM> of the embodiment of the optical fiber cable <NUM> shown in <FIG>.

In contrast to the embodiment of the optical fiber cable <NUM> of <FIG>, the at least one second sheath layer <NUM> is configured as a bedding layer. The plurality of the optical transmission elements <NUM> is embedded in the bedding layer. The bedding layer is placed in gaps <NUM> between the plurality of the at least one optical transmission element <NUM>. As illustrated in <FIG>, the bedding layer may also have a portion being arranged above the optical transmission elements <NUM>, i.e. above the buffer tubes <NUM>. Regarding the composition and properties of the at least one second layer <NUM>, reference is made to the description of the bedding layer <NUM> of the embodiment of the optical fiber cable <NUM> shown in <FIG>.

The embodiments of the optical fiber cables <NUM>, <NUM> and <NUM> comprise respective optical transmission elements <NUM> being configured as buffered optical fibers, i.e. the optical fibers <NUM> are surrounded by a buffer tube <NUM>, and the optical fibers <NUM> are loosely arranged within the buffer tubes <NUM>. <FIG> and <FIG> show different embodiments of an optical fiber cable <NUM> and <NUM>, wherein the optical transmission elements <NUM> are configured as tight buffered optical fibers. The optical fiber cables <NUM> and <NUM> may preferably be used as indoor optical cables.

<FIG> shows an optical fiber cable <NUM> comprising a plurality of optical transmission elements <NUM> being arranged in a cable core <NUM> of the optical fiber cable <NUM>. The optical transmission elements <NUM> are configured as tight buffered optical fibers. Each of the optical transmission elements comprises a plurality of optical fibers <NUM> being surrounded by a respective buffer tube <NUM>. The cable core <NUM> and the optical transmission elements <NUM> are surrounded by a reinforcing element <NUM> which may be configured as an aramid yarn. The cable core <NUM> is further surrounded by a cable jacket <NUM> being embodied as the multilayered structure. The multilayered structure of the cable jacket <NUM> comprises the first sheath <NUM> and the at least one second sheath layer <NUM>. The cable jacket <NUM> may optionally comprise the layer <NUM> to facilitate a blowing-in process of the optical fiber cable in an empty duct. Regarding the composition and properties of the first sheath layer <NUM> and the at least one second sheath layer <NUM> and the optinal layer <NUM>, reference is made to the description of the optical fiber cable <NUM> of <FIG>.

<FIG> shows an optical fiber cable <NUM> having a cable core <NUM> including optical transmission elements being configured as tight buffered optical fibers. The optical transmission elements/tight buffered optical fibers <NUM> respectively include an optical fiber <NUM> being surrounded by the buffer tube <NUM>. The cable core <NUM> may comprise a first and at least a second layer of the optical transmission elements <NUM>. According to the embodiment of the optical fiber cable <NUM>, a first, inner layer of optical transmission elements <NUM> is arranged around the strength member <NUM>, and a second, outer layer of the optical transmission elements <NUM> is arranged around the first inner layer of the optical transmission elements. The inner and the outer layer of the optical transmission elements <NUM> may be separated by a reinforcing element <NUM>. Another reinforcing element <NUM> may be arranged around the outer layer of the optical transmission elements <NUM> to separate the cable jacket <NUM> from the cable core <NUM>.

The cable jacket <NUM> which surrounds the cable core <NUM> comprises the multilayered structure having the first sheath layer <NUM> and the at least one second sheath layer <NUM>. The cable jacket <NUM> may optionally comprise the low-friction layer <NUM> to facilitate a blowing-in process of the optical fiber cable in an empty conduit. Regarding the material composition and properties of the first sheath layer <NUM> and the at least one second sheath layer <NUM> and the optional layer <NUM>, reference is made to the description of the optical fiber cable <NUM> of <FIG>.

In order to prove the feasibility and effectiveness of the described approach to improve the materials' and cables' fire protection performances, low smoke halogen-free commercially available materials, having different kinds of flame retardant action mode, were selected. Among the selected materials are intumescent options like Halguard series <NUM> and mineral-filled materials like Halguard <NUM>, both from Teknor Apex. Halguard <NUM> has a specific gravity of <NUM>, an oxygen index of <NUM>%, and a vertical flame rating V-<NUM> (<NUM>/<NUM>" thick specimens). Halguard <NUM> is a polyprophylene-copolymer based material including an intumescent system and may be used for the first, outer sheath layer <NUM>. Halguard <NUM> may be used for the second sheath layer <NUM>.

In the following a preliminary feasibility test for assessment of the fire protection performance of a multilayered structure based on Halguard <NUM> and Halguard <NUM> is described. The tested multilayered structure <NUM> shown in <FIG> comprises a first layer <NUM> made of Halguard <NUM> representing the first sheath layer <NUM>, and a second layer <NUM> made of Halguard <NUM> representing the second sheath layer <NUM>.

In order to manufacture the stacked multilayered structure <NUM> the single materials of Halguard <NUM> and Halguard <NUM> were first pressed separately at a defined thickness and then hot-pressed together to achieve a total thickness of <NUM>. The hot-pressing process was conducted for each layer separately, with a thickness based on the aimed design. Pressing was performed in a uniaxial heated press with plate temperatures of <NUM>. The compounds of Halguard <NUM> and Halguard <NUM> in pellet shape were placed in a tooling frame with a certain thickness between the plates and molten at low pressure to release all potential volatiles.

After <NUM> minutes the pressure was increased to a higher load for five minutes. Each of the two samples based on Halguard <NUM> and Halguard <NUM> were then cooled between water-cooled copper plates and taken off the frame. The first layer <NUM> and the second layer <NUM> were stacked in a frame with a height of <NUM> and pressed at <NUM> for <NUM> minutes to create the multilayer sample design <NUM> shown in <FIG>. After cooling, a final sample size of <NUM> x <NUM> x <NUM> was achieved by die-cutting the <NUM> x <NUM> size.

The fire behavior of the multilayered structure was tested under forced flame conditions according to cone calorimeter measurements (ISO <NUM>) by using square specimens (<NUM> × <NUM> x <NUM>) horizontally fixed on a sample holder. The irradiation used was <NUM> kWm-<NUM>. When exposed to elevated temperature, each single layer <NUM> and <NUM> in the multilayered structure <NUM> started burning separately, first the layer <NUM> on the top, i.e. the surface directly exposed to the cone heater, and later the layer <NUM> underneath. In the case of an intumescent layer on the top, which may serve as a sacrificial layer, the material started foaming and expanding its volume during the combustion process. Only once the first layer <NUM> was completely combusted and converted to black char did the second layer <NUM> undergo ignition and start the combustion process as well. At the end of the fire test, the original multilayered structure can still be identified in the fire residue.

Among the several tested multilayered configurations, according to cone calorimeter measurements, the multilayer structures of Halguard <NUM> : Halguard <NUM> (<NUM>:<NUM>) mm (i.e. the layer <NUM> of Halguard <NUM> having a thickness of <NUM> and the layer <NUM> of Halguard <NUM> having a thickness of <NUM>) and Halguard <NUM> : Halguard <NUM> (<NUM>:<NUM>) mm (i.e. the layer <NUM> of Halguard <NUM> having a thickness of <NUM> and the layer <NUM> of Halguard <NUM> having a thickness of <NUM>) and Halguard <NUM>:Halguard <NUM> (<NUM>:<NUM>) mm (i.e. both of the layer <NUM> of Halguard <NUM> and the layer <NUM> of Halguard <NUM> having a thickness of <NUM>) show better fire properties than the pure single materials. In particular, compared to the single materials alone (i.e. Halguard <NUM> and Halguard <NUM>, separately tested by cone calorimeter with a total plaque thickness of <NUM>), the three mentioned multilayered structures exhibited better heat release performances.

The shape of respective heat release curves for the multilayered structures shows a clear double peak behaviour which indicates that each single layer <NUM> and <NUM>, <NUM> and <NUM> respectively, burns almost separately. Once the most exposed layer <NUM> or <NUM> is consumed, the underlying layer <NUM> or <NUM> ignites and starts burning.

That results overall in a longer/slower burner process that may have impact when applying these multilayered structures as jacket material in a real cable design. The proposed multilayered structure for the cable jacket hence enables to delay and slow down the cable combustion, delaying the fire and heat from reaching the cable core.

The proposed multi-layered structures for a cable jacket <NUM> of an optical fiber cable show better fire protection performances compared to pure separate materials and also to blended materials. A multilayered structure of a cable jacket improves the fire performance of a fiber optical cable as well as when tested according to the European standard EN <NUM>, when applied as a jacket material.

Claim 1:
An optical fiber cable with improved fire protection performance, comprising:
- a cable core (<NUM>) including at least one optical transmission element (<NUM>) to transfer light,
- a cable jacket (<NUM>) surrounding the cable core (<NUM>),
- wherein the cable jacket (<NUM>) is embodied as a multilayered structure having a first sheath layer (<NUM>) and one or more second sheath layers (<NUM>) surrounded by the first sheath layer (<NUM>),
- wherein the material of the first sheath layer (<NUM>) and the material of the one or more second sheath layers (<NUM>) are halogen free,
- wherein the material of the first sheath layer (<NUM>) and the material of the one or more second sheath layers (<NUM>) each have a different flame retardant additive providing different flame retardant mechanisms,
- wherein the cable core (<NUM>) comprises a plurality of the at least one optical transmission element (<NUM>) and a strength member (<NUM>), wherein each of the optical transmission elements (<NUM>) includes a plurality of optical fibers (<NUM>) surrounded by a buffer tube (<NUM>), wherein the optical transmission elements (<NUM>) are placed around the strength member (<NUM>),
- wherein at least one second sheath layer (<NUM>) is configured as a bedding layer,
- wherein the plurality of the at least one optical transmission element (<NUM>) is embedded in the bedding layer so that the bedding layer is placed in gaps (<NUM>) between the plurality of the at least one optical transmission element (<NUM>),
characterized in that
the material of the first sheath layer (<NUM>) includes a first flame retardant additive of an intumescent-acting material, and
the material of the one or more second sheath layers (<NUM>) includes a second flame retardant additive which is a polymer based resin including a mineral filler.