COMMUNICATION CABLES CONTAINING FIRE RESISTANT FIBERS
REFERENCE TO RELATED APPLICATION This application claims priority from U.S. Provisional Patent Application Number 60/305,458, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to voice, video and data communication cables. More particularly, the invention relates to communication cables containing ripcords and binders. Even more particularly, this invention relates to communications cables containing ripcords and binders made with fire resistant fibers.
BACKGROUND OF THE INVENTION
Communication cables are generally used to transmit a variety of signals, including voice, video, and data signals. Each cable includes single or multiple strands of a transmission media (e.g., copper wire) coated with an insulating material. The strands of the transmission media signals are generally contained within a hollow core of a tubular jacket. The insulating material, often called the primary insulation, confines the signals to the transmission media during transmission. Although the jacket can be electrically insulating, its main purpose is to provide mechanical and environmental protection. Conventional materials used for the insulation and jacketing include thermoplastic polymers. These polymers are solid at normal temperatures and pressures, but can soften and flow upon application of higher heat and/or higher pressure. Examples of thermoplastic polymers include polyethylene, polypropylene, and polyvinyl chloride. These polymers often contain additives to improve flame resistance. Other examples of thermoplastic polymers include inherently flame- resistant polymers, such as ethylene chlorotrifluoroethylene copolymer (ECTFE) and fluorinated ethylene- 1-propylene copolymer (FEP).
The communication cable may also include elongated binders and ripcords. Binders hold together cable components during and after manufacturing, and often contain a tape, cord, or thread that is wrapped around the cable components. Ripcords are used to split the jacketing axially, thereby exposing the cable components whenever access inside the jacket is needed. Ripcords are usually single or multi- strand filaments that are embedded in the jacket or disposed within the jacket core. Conventional binders and ripcords are usually made of synthetic fibers, such as polyester fiber and Composite (aramid) fiber. h addition to exhibiting many other characteristics, it is often necessary that communication cables exhibit fire resistance. When installed in existing buildings, communication cables are often routed through the ductwork of the building's air exchange system. Such cables are called plenum cables. To reduce the risk of fire propagating through the building's ductwork, safety codes often require that plenum cables meet standards for low smoke generation and low flame spread. Communication cables installed in vertical shafts connecting different floors of a building are known as riser cables. As with plenum cables, safety codes often require that riser cables satisfy certain standards for flame propagation. To minimize flame spread and smoke generation, cable manufacturers have often focused on the composition and structure of the primary insulation and jacket materials. For example, cable manufacturers have employed fire resistant materials, such as FEP, as the material for the primary insulation and jacketing. As well, cable manufacturers have added inert fillers or introduced pockets of air (voids) in the primary insulation and jacketing material in an effort to reduce fuel load and hence decrease smoke generation and flame spread.
Unfortunately, such efforts have produced other disadvantages. For example, FEP is significantly more expensive than PVC and polyethylene, polypropylene or other polyolefins. As well, the presence of voids in the primary insulation or jacket often can reduce the strength and durability of the cable. SUMMARY OF THE INVENTION The invention provides a communication cable for transmitting various communication signals. The cable comprises an outer jacket and a transmission media contained within the outer jacket. The communication cable can include a binder that is disposed within the outer jacket and is made of a glass fiber. The binder is wrapped about the transmission media and can extend along the length of the cable. The communication cable can also contain a ripcord that is made of a glass fiber. The ripcord is disposed on the inside of the jacket wall. The glass fiber — typically in the form of rovings — allows the communication cable to limit the amount of flame spread and smoke generation, while exhibiting the necessary transmission characteristics.
The invention includes a communication cable containing a jacket defining a core, a transmission media disposed within the core, and a binder constraining the transmission media where the binder comprises a fire resistant fiber. The invention also includes a communication cable containing a jacket defining a core, a transmission media disposed within the core, and a ripcord disposed within or adjacent the jacket where the ripcord comprises a fire resistant fiber. The invention further includes a communication cable containing a jacket defining a core, a transmission media disposed within the core, a ripcord disposed within or adjacent the jacket with the ripcord comprising a fire resistant fiber, and a binder constraining the transmission media with the binder comprising a fire resistant fiber. The invention still further includes a communication cable containing a jacket defining a core, a transmission media disposed within the core, a ripcord disposed within or adjacent the jacket with the ripcord comprising a glass fiber, and a binder constraining the transmission media with the binder comprising a glass fiber. The invention also includes communication systems containing such cables.
The invention includes a method for making a communication cable by providing a transmission media, providing a binder around the transmission media where the binder comprising a fire resistant fiber, and providing a jacket around the transmission media and the binder. The invention also includes a method of making a communication cable by providing a transmission media, and then providing a jacket around the transmission media where the jacket has a ripcord located within or adjacent the jacket and the ripcord comprises a fire resistant fiber. The invention further includes a method of making a communication cable by providing a transmission media, providing a binder around the transmission media where the binder comprising a fire resistant fiber, and providing a jacket around the transmission media and the binder where the jacket has a ripcord located within or adjacent the jacket and the ripcord comprises a fire resistant fiber.
The invention includes a method for communicating by first, providing a cable containing a jacket defining a core, a transmission media disposed within the core, and a binder constraining the transmission media, wherein the binder comprises a fire resistant fiber, and then second, transmitting a signal over the cable. The invention also includes a method for communicating by first, providing a cable containing a jacket defining a core, a transmission media disposed within the core, and a ripcord disposed within or adjacent the jacket, wherein the ripcord comprises a fire resistant fiber, and then second, transmitting a signal over the cable. The invention further includes a method for communicating by first, providing a cable containing a jacket defining a core, a transmission media disposed within the core with a binder constraining the transmission media, and a ripcord disposed within or adjacent the jacket, wherein the binder and the ripcord comprise a fire resistant fiber, and then second, transmitting a signal over the cable.
BRIEF DESCRIPTION OF THE DRAWINGS Figures 1- 2 are views of several aspects of the communication cables and methods for making and using the same according to the invention, in which:
Fig. 1 shows a perspective side view of a cable in one aspect of the invention; and
Fig. 2 shows a cross-sectional view of the cable through section line 2-2 of Fig. 1.
Figures 1-2 illustrate specific aspects of the invention and are a part of the specification. Together with the following description, the Figures demonstrate and explain the principles of the invention and are views of only particular — rather than complete — portions of the invention. DETAILED DESCRIPTION OF THE INVENTION
The following description provides specific details in order to provide a thorough understanding of the invention. The skilled artisan, however, would understand that the invention can be practiced without employing these specific details. Indeed, the present invention can be practiced by modifying the illustrated system and method and can be used in conjunction with apparatus and techniques conventionally used in the industry. For example, the invention is described below for unshielded twisted pair (UTP) cable, but could be modified for any other communications cable using a binder and/or a ripcord such as fiber optic cable where the insulated pairs of wires of the UTP cable would be replaced by tightly buffered fiber or fiber subunits bundled together.
As noted above, the invention generally comprises using fire resistant fibers in binders and ripcords of communication cables. Any communication cable known in the art that contains a binder and ripcord can be employed in the invention. In one aspect of the invention, a UTP communication cable is used.
Fig. 1 and Fig. 2 show, respectively, a perspective side view and a cross- sectional view of one aspect of one UTP communication cable 10. The UTP cable 10 includes the transmission medium (e.g., four twisted pairs 12 of insulated wires 14) contained within a core 16 of a cable jacket 18 or outer covering. The cable is substantially rectangular, cylindrical, or tubular in shape.
The communication cable 10 may contain fewer or greater numbers of twisted pairs 12 depending on the end us of the cable. Cables containing up to 4200 pairs are currently standard in the communications industry. Four twisted pairs are illustrated in the invention because four pair cables are currently the most common number of pairs used in plenums.
Each of the insulated wires 14 within the twisted pair 12 comprises a conductor 20. Typically, the conductor is a single or multi-strand copper filament that is coated with an electrically insulating material 22, often called the primary insulation. The conductor can be made of any electrically conducting material, but is conventionally made of copper or a copper alloy. The primary insulation confines the electrical signals to the conductor 20 during signal transmission. The jacket 18 is also electrically insulating, even though its main purpose is to provide mechanical and environmental protection. Thus, the cable jacket 18 and the primary insulation 22 can be fabricated from a wide variety of materials serving this function, including uncurable, thremoset, and thermoplastic polymers. Examples of thermoplastics polymers include polyvinyl chloride (PVC) and various polyolefins, such as polyethylene, polypropylene, and the like. If necessary, the thermoplastic polymer can contain compatible fire retardant fillers that minimize smoke generation and flame spread, such as phosphonate compounds. Examples of other useful thermoplastics include inherently flame-resistant polymers, such as ethylene chlorotrifluoroethylene copolymer (ECTFE) and fluorinated ethylene- 1-propylene copolymer (FEP).
In the invention, the communication cable 10 includes a binder and/or a ripcord. The binder serves to contain the transmission medium along part or all of the length of the communication cable, h the aspect of the invention illustrated in Fig. 1 and Fig 2, the binder 24 is helically wrapped about the twisted pairs 12 and holds the twisted pairs 12 together in the desired configuration. While the figures show a helical winding, other configurations confining the transmission medium — such as longitudinal or counter helical — can be employed in the invention. The communication cable of the invention may also contain a ripcord. The ripcord serves to provide access to the core of the communication cable by separating the jacket. For example, as illustrated in the Figures, one can grasp an end 30 of the ripcord 26 and pull it outward away from an outer surface 32 of the jacket 18, thereby splitting the jacket 18 and exposing the core 16. Any configuration for the ripcord that achieves this function can be employed in the invention. For example, as illustrated in the Figures, the ripcord 26 can be disposed along the length of the cable 10 adjacent to an inner surface 28 that defines the core 16 of the jacket 18. Like the binder, the ripcord can extend along part or all of the length of the communication cable. In another aspect of the invention, the ripcord is not located adjacent the jacket, but is embedded therein. The binder 24 and the ripcord 26 can comprise a fire-retarding or fire-reducing (fire resistant or FR) fiber. The FR fibers help the binder and the ripcord resist combustion of the communication cable, as well as the related functions described herein. Any fiber known in the art serving that function can be employed in the invention. Examples of FR fibers include certain composite fibers, ceramic fibers, glass fibers, and combinations thereof. In one aspect of the invention, glass fibers are used because because of the superior performance of glass fibers. Glass fibers reduce the fuel load and hold the core of the cable together, preventing or reducing penetration of the flame into the core. In one aspect of the invention, the binder and the ripcord contain FR fibers as well as the materials conventionally used in the binder and ripcord such as polyester and aramid materials. In other words, the binder and the ripcord are made of hybrid materials containing the conventional material as well as the FR fibers. In the aspect of the invention using glass fibers, the hybrid material could contain from about 1 vol% glass fibers to about 99 vol% glass fibers. Preferably, the hybrid material could contain about 5 to about 95 vol% glass fibers.
In one aspect of the invention, the binder and/or the ripcord are made of glass fiber rovings, which comprise one or more strands of continuous glass fibers. Glass fiber rovings can be characterized by their filament diameter and linear yarn density and are primarily used as reinforcements in polymer composites. The individual glass fibers of rovings can be coated with a sizing, which protects the glass fiber during processing and helps integrate the glass fiber into a particular polymer.
Generally, any glass fiber roving can be used in the binder 24 or the ripcord 26 provided it has the necessary strength to serve the functions described above. In one aspect of the invention, the glass fibers may have filament diameters ranging from about 3 microns to about 125 microns and linear yarn densities ranging from about 200 g/km to about 2000 g/km. Useful glass fiber rovings can be obtained from numerous manufacturers, including Owens Corning, Neptco, PPG Industries, Saint Gobain, and Johns Manville. As well, the glass fiber roving (as well as the FR fiber) used for the binder 24 and the ripcord 26 can be the same or different. The communication cable 10 shown in Fig. 1 and Fig. 2 employs a separate binder 24 and ripcord 26. In other aspects of the invention, the communication cable may include a glass fiber binder 24, but may lack a glass fiber ripcord or may use a conventional polyester ripcord. Similarly, the communication cable may include a glass fiber ripcord 26, but may lack a glass fiber binder or may use a conventional polyester binder. In still other aspects of the invention, the communication cable may use a single glass fiber roving as both the binder and the ripcord. In addition to glass fiber rovings, the cable may instead employ flexible, woven glass fiber tapes, glass fiber scrims, and other glass fiber forms. Communication cables 10 that utilize FR fiber for the binder 24 or the ripcord
26 are made in substantially the same way as communication cables that employ polyester or aramid fibers for the binders and ripcords. However, since FR fiber will not burn, communication cables 10 like those shown in Fig. 1 and Fig. 2 will demonstrate lower flame spread and generate less smoke than similar cables made using polyester or aramid fibers.
The following non-limiting examples illustrate the invention.
EXAMPLE A 25-pair UTP Category 5 cable was prepared using a binder made of glass fiber roving. The glass fiber roving had a nominal filament diameter of 19 microns and a nominal linear yarn density of 850 g/km. The binder was applied using a binding head as a helical wrap around the 25 twisted pairs so that the binder made a full turn around the cable axis about every 100 mm. All of the twisted pairs were made from 24 AWG solid copper wire (0.51 mm outer diameter) and were insulated with FEP polymer obtained from DuPont under the trade name TEFLON. The outer diameter of each insulated wire was approximately 0.91 mm. The twisted pairs were enclosed within a jacket made from ETCFE, which was obtained from Ausimont under the trade name HALAR. The nominal inner and outer diameters of the cable jacket were approximately 11 mm and 12 mm, respectively. The cable was tested in accordance with EIA/TIA 568-A, and was found to satisfy electrical requirements for Category 5 UTP cable, hi addition, the cable was tested by Underwriters Laboratory, which determined that the cable satisfied smoke generation and flame spread requirements set forth in UL 910-1998. An otherwise identical cable made with a polyester binder was also tested by Underwriters Laboratory, but did not meet the smoke generation requirement set forth in UL 910- 1998.
Having described these aspects of the invention, it is understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description, as many apparent variations thereof are possible without departing from the spirit or scope thereof.