Abstract:
A cable that comprises a core that has at least one conductor, a dielectric barrier layer that surrounds the core, and a conductive shield that surrounds the core. The dielectric barrier layer is formed of a substantially non-flammable material and is devoid of fluoropolymers.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/578,614, filed on Dec. 21, 2011. This application may relate to commonly owned currently pending U.S. application Ser. No. 13/707,077, filed on Dec. 6, 2012, entitled Cable With Non-Flammable Component, the subject matter of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a cable having a barrier layer formed of a substantially non-flammable material. More specifically, the barrier layer of non-flammable material is provided between the shield and core of the cable. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional communication cables for both riser and plenum applications typically include a number of insulated conductors that are bundled together or twisted together into pairs and surrounded by an outer jacket. Crosstalk or interference often occurs because of electromagnetic coupling between the conductors within the cable or other components in the cable, thereby degrading the cable&#39;s electrical performance. 
         [0004]    Barriers are often used, particularly in plenum applications, to isolate the pairs of conductors, thereby reducing interference. Such barriers are normally made of polyester (PET) or fluoropolymers like FEP to meet industry standards, such as the requirements of NFPA 262 in the case of plenum cables. However, materials like polyester typically emit too much smoke which limits the amount of separation from the shielding. Flouropolymers like FEP tend to drip in the burn chamber. When these materials drip and hit the floor of the burn chamber, they smoke. Such smoke is undesirable, particularly in the plenum applications, and makes it more difficult to meet the industry requirements. Moreover, fluoropolymers are typically halogenated and release toxic halogens when burned. Also, fluoropolymers are typically more expensive due to material costs and high demand. 
         [0005]    Therefore, a need exists for a cable barrier that meets industry standard burn requirements and that is less toxic, melts less, and is less expensive. 
       SUMMARY OF THE INVENTION 
       [0006]    Accordingly, the present invention provides a cable that comprises a core that has at least one conductor, a dielectric barrier layer that surrounds the core, and a conductive shield that surrounds the core. The dielectric barrier layer is formed of a substantially non-flammable material and is devoid of fluoropolymers. 
         [0007]    The present invention may also provide a cable that comprises a core that includes a plurality of twisted pairs of conductors and a separator that separates the plurality of twisted pairs of conductors. A dielectric barrier layer surrounds the core and is formed of a substantially non-flammable, low smoke, zero halogen material and is devoid of fluoropolymers. A conductive shield surrounds the dielectric barrier layer and an outer jacket surrounds the conductive shield. 
         [0008]    Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawing, discloses a preferred embodiment of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying Figure which is a cross-sectional view of a cable according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    Referring to the Figure, the present invention relates to a cable  10  that has an improved electrical performance because it incorporates a substantially non-flammable barrier layer  20 . The barrier layer  20  surrounds a core  30  of conductors  32  of the cable  10  and separates the core  30  from a conductive shield  40  of the cable. The conductors  32  may be twisted into pairs and separated by a separator component  50 , as seen in the Figure. The separator component  50  may be formed with any shape which accomplishes the desired separation properties. The shield  40  may be any conventional shield layer either continuously conductive or a discontinuous layer comprised of conductive segments. An outer jacket  60  may surround the core  20 , barrier layer  30  and the shield  40 . The outer jacket  60  may be formed of any conventional insulation, such as PVC. 
         [0011]    The barrier layer  20  is preferably formed of a material that is substantially non-flammable, and more preferably a material that is low-smoke and zero halogen (LSZH) to reduce the toxicity of the cable when burned. Zero halogen means the material is non-halogenated and/or total ppm of accidental trace halogens as defined by applicable industry standards for zero halogen materials. 
         [0012]    Exemplary non-flammable materials of the barrier layer  20  include fiberglass, individual glass fibers bunched together, fiberglass yarns, fiberglass strands, fiberglass rovings, chopped fiberglass, woven fiberglass tapes or sheets, and the like. Those materials are desirable because they have optimal burn properties while also allowing the barrier layer to maintain flexibility. Other suitable non-flammable materials can also be employed, such as basalt fibers, yarns, woven tapes, high temperature ceramic oxide fibers, yarns and woven tapes, other ceramic mica tapes, and the like. Those materials are desirable because of their high temperature performance in cable applications. The barrier layer  20  may be coated with a flame retardant material, that is preferably LSZH, to further aid the burn performance of the barrier layer  20  and the cable  10 . 
         [0013]    Additionally, the barrier layer  20  is preferably substantially devoid of any fluoroploymers, thereby significantly reducing material in the barrier layer that drips and smokes in the burn chamber. That improves the smoke performance in the plenum cable burn testing, for example, per NFPA 262. 
         [0014]    The present invention allows for the cable core  30  to be separated from the shield  40  by a non-flammable barrier layer, such as an inorganic fiberglass tape for example, that has a suitable dielectric constant. That helps improve the attenuation performance of the cable  10  by providing spacing between the twisted pairs of conductors  32  in the core  30  and the shield  40  as well as providing a dielectric barrier between the core  30  and the shield  40 . In addition, the present invention also aids in improving the burn and smoke performance of the cable by removing fluoropolymers from the cable construction which drip and smoke compared to the fiberglass material which will not melt or drip. Furthermore, halogenated materials are preferably removed from the cable which reduces the toxicity of the cable. 
         [0015]    While a particular embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.