Gas encapsulated dual layer separator for a data communications cable

A data communications cable is disclosed herein. The data communications cable includes a plurality of twisted pairs of conductive wires and a separator between the plurality of twisted pairs of conductive wires. The separator includes an inner member and an outer layer being supported and shaped by the inner member for completely encapsulating at least one gas pocket between the outer layer and the inner member. The outer layer prevents the plurality of twisted pairs of conductive wires from entering the at least one gas pocket.

FIELD OF THE INVENTION

The present invention relates to data communication cabling pair separation. In particular, the present invention relates to a gas-encapsulated dual layer separator for a data communications cable.

BACKGROUND OF THE INVENTION

Conventional data communications cables often include multiple twisted pairs within a protective outer jacket. Typical data cable constructions use pair separation fillers made from solid dielectric materials such as polyolefin and fluoropolymers to provide physical distance (i.e., separation) between the pairs within a cable, thereby reducing crosstalk. In the event a portion of the cable ignites, it is desirable to limit the amount of smoke produced as a result of the melting or burning of the non-conductive portions (e.g., separation filler) of the cable. It is also desirable to prevent or limit the spread of flames along the cable from one portion of the cable to another.

Turning toFIG. 1, a cross-sectional view of a conventional communications cable100showing a star-shaped separator104composed of solid filler material is shown. Cable100includes four twisted pairs of conductive wires102. The twisted pairs102are separated by the conventional “star” shaped filler104which is formed of solid dielectric materials, such as polyolefin and fluoropolymers, to provide physical distance (i.e., separation) between the pairs102within the cable100. An outer jacket106surrounds the twisted pairs102and filler104.

One disadvantage to the use of separation fillers is that typical filler materials, such as fluoropolymers, have poor smoke- and flame-retardant properties. Therefore, the added material of the filler within the cable construction increases the amount of smoke that is emitted as well as the distance that flame travels along a burning cable. In order to mitigate those drawbacks, some manufacturers add flame retardants and smoke suppressants to the polyolefin and fluoropolymer materials used in the conventional fillers. However, smoke suppressants and flame retardants often increase the dielectric constant and dissipative factors of the filler, thereby adversely affecting the electrical properties of the cable construction by increasing the signal loss of the twisted pairs within close proximity to the filler.

As a result, some conventional manufacturers may “foam” the fillers in order to reduce the amount of material, where a foamed filler material is any material that is in a lightweight cellular form resulting from introduction of gas bubbles during manufacture. However, conventional foaming methods can only reduce the amount of material by no more than approximately thirty percent. Another drawback to foamed fillers is that during cable processing or manufacturing, crushing or deformation of the foamed fillers may occur resulting in compacted filler material and less separation between twisted pairs. As a result, foamed fillers often possess an undesirable imbalance between electrical and smoke/flame retardant properties.

Accordingly, in light of the above drawbacks associated with conventional fillers, separators, and cables, there is a need for a separator used in a data communications cable that reduces crosstalk between twisted pairs within the cable while simultaneously improving the flame spread and smoke emission properties of the cable.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an electrical cable assembly that includes a multilayer separator to encapsulate gas within a filler portion. The filler portion includes an inner member (e.g., a rigid inner layer cross bar frame) used to shape an outer layer that completely encapsulates gas within it.

Specifically, objects of the present invention are accomplished by a data communications cable that includes a plurality of twisted pairs of conductive wires and a separator between the plurality of twisted pairs of conductive wires. The separator includes an inner member and an outer layer being supported and shaped by the inner member for completely encapsulating at least one gas pocket between the outer layer and the inner member. The outer layer prevents the plurality of twisted pairs of conductive wires from entering the at least one gas pocket.

With those and other objects, advantages, and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims, and the several drawings attached herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several preferred embodiments of the invention are described for illustrative purposes, it being understood that the invention may be embodied in other forms not specifically shown in the drawings. It is an object of the invention to provide a cable assembly that reduces cross talk between pairs within data communications cables while simultaneously improving the flame spread and smoke emission properties of said cables. That may be accomplished by reducing the amount of filler material used in the data cable construction and replacing the filler with air, which has improved electrical properties.

As seen inFIG. 2, a cross-sectional view of a communications cable200in accordance with an exemplary embodiment of the present invention is shown. The cable200includes a plurality of twisted pairs102being physically separated from one other by a separator204. The separator204extends longitudinally within the cable200to separate the wire pairs102. However, in contrast to the conventional filler104, the separator204includes two layers; an inner member205within an outer layer206. The inner member205is preferably constructed such that it shapes the outer layer206where both the inner and outer layers205and206encapsulate the gas in one or more gas pockets208. Inner member205may comprise one or more segments, for example. In one possible configuration, two segments210and212may be used to form a generally cross bar frame, as shown inFIG. 2. Thus, cable200may include four gas pockets208defined by the inner member205and the outer layer206which provide physical separation between the twisted pairs102. The gas pockets208may be substantially triangular in cross-sectional shape, however, it is appreciated that any suitable cross-sectional shape may be used without departing from the scope of the subject matter described herein. The outer layer206preferably curves at each gas pocket208to a recessed area214for accepting the individual twisted pairs102.

The separator204may be formed of melt processable materials, such as fluoropolymers, foamed or solid polyetherimides (PEI), polyetherimide-siloxane blends and copolymers, polyvinylchorides, polyolefins, polyethylenes, or the like. The separator204may also be formed at least in part by non-melt processable materials, such as PTFE, rubber, glass, silicone, or the like, by a combination of gas (e.g., air) and melt processable materials, such as is achieved with foaming. In one possible embodiment, the inner member205may be comprised of an olefin that is heavily loaded with a flame retardant and which has a higher dielectric constant and heat dissipation factor than an olefin that does not contain such additives. The outer layer206may be comprised of a thin layer of flouropolymer that has a much lower dielectric constant and dissipative factor than the inner member205. That combination allows the cable200to have improved smoke- and flame-retardant properties as compared with single layer or solid fillers, such as filler104of cable100, without degrading its electrical properties.

In the exemplary embodiment shown inFIG. 2, the communications cable200may also comprise a protective outer casing or jacket216for encasing the components of the cable200that are shown inFIG. 2(i.e., at least one twisted wire pair102, the inner member205received in the jacket216, an outer layer206being supported or shaped by the inner member205, and one or more gas pockets208located between the inner member205and the outer layer206). As illustrated inFIG. 2, the segments of inner member205are substantially perpendicular to one other and intersect at a central junction point. The gas pockets208are preferably completely encapsulated between the outer layer206and the inner members205. The gas pockets208provide physical separation between the outer layer206and the portions of the inner segments near the central junction point, whereby the at least one twisted wire pair102is prevented, by the outer layer206, from entering the gas pockets208.

By encapsulating gas within the separator204, the cable200reduces the amount of material used to separate the twisted pairs102as compared with conventional cable separators. It is appreciated that single gasses, such as nitrogen, or mixtures of two or more gasses, such as air, may be encapsulated within the separator204without departing from the scope of the subject matter described herein. Such gasses may be either inert or non-inert (i.e., reactive). They may also be used in foaming of the separator204. By introducing the gas pockets208created by the outer layer206and the inner member205, the cable200reduces crosstalk interference between the twisted pairs102while also improving the smoke/flame performance and the dielectric properties of the cable200. The outer layer206preferably has a shape that pushes the twisted wire pairs102away from the cable's200center and away from each other to reduce interference between the wire pairs102. For example, the outer layer206in combination with inner member205causes the wire pairs102to be positioned radially outwardly by about at least 0.003-0.010 inches more than if the outer layer206and gas pockets208were not employed. Moreover, the cable200achieves the desired pair-to-pair distance using less material than if the dual layer gas-encapsulated separator disclosed herein was not used. For example, the amount of filler material may be reduced by approximately 30-45% using the gas-encapsulated dual layer separator204of cable200. Less material also makes the cable significantly less expensive to manufacture.

Another advantage of cable200is that gas that is encapsulated inside the outer layer206lowers the effective dielectric constant and, therefore, may reduce the signal loss of cable200as compared with cable100.

Yet another advantage of the cable200is that the dual layer separator204may allow a manufacturer to optimize the flame and smoke retardant properties of the cable200. For example, optimization of the layers (i.e., inner member205and outer layer206) may allow the cable200to meet industry standards, such as the National Fire Protection Association (NFPA)262plenum test or the Underwriters Laboratories (UL) 1666 riser test for smoke/flame retardancy, while simultaneously maintaining the desirable electrical properties needed to meet requirements (e.g., insertion loss) for data communications cables.

FIG. 3is a cross-sectional view of a gas-encapsulated dual layer separator304in accordance with an exemplary embodiment of the present invention. Referring toFIG. 3, the separator304includes an inner member305that may be divided into a plurality of segments, with each segment having a terminal end and intersecting at a junction point. For example, in the embodiment shown inFIG. 3, the inner member305may include primary segments308and310which are arranged generally perpendicular to one another in a cross-sectional plane of the cable. The segments308and310may be offset from one another to create gas pockets of different sizes. The segment308includes opposing terminal ends312and the segment310includes opposing terminal ends314. It will be appreciated that while rounded terminal ends312and314are shown, other configurations are possible without departing from the scope of the subject matter described herein. Rounded terminal ends312and314may allow for shaping the outer layer306differently than non-rounded terminal ends, such as are shown inFIG. 2. For example, terminal ends312and314may be shaped so as to provide additional curvature or cradling around each of the twisted pairs102.

The embodiment shown inFIG. 3further includes secondary segments316,318,320, and322for providing additional support for shaping of the outer layer306. By supporting the outer layer306, the size of the gas pockets340may be preserved during manufacturing, shipment, or usage so that the twisted pairs102maintain a proper separation distance and, thus, the cable can maintain its expected electrical and/or burn properties. In the embodiment shown inFIG. 3, the secondary segments316-322are arranged generally perpendicularly to one another in a cross-sectional plane of the cable and angled from the orientation of the primary segments308and310by about forty five degrees. That doubles the number of gas pockets340from four to eight and increases the rigidity of the cable200.

The primary segments308and310and the secondary segments316-322each include a terminal end which is remote from a junction point324of the segments. As mentioned above, the gas pockets340represent the reduction of material to sufficiently space the wire pairs102to reduce interference. The reduction in material reduces manufacturing costs and reduces the amount of combustible material, thereby improving the smoke and flame performance of the cable200.

FIG. 4is a cross-sectional view of still another embodiment of a gas-encapsulated dual layer separator. Unlike the previous embodiments for use in a cable, such as cable200, the separator404is a substantially flat tape with several smaller gas pockets. Referring toFIG. 4, the separator404includes an inner member405that has a primary segment410and a plurality of smaller, secondary segments412which provide support for shaping an outer layer406and creating a plurality of gas pockets408. In this flattened configuration shown inFIG. 4, the number and size of the gas pockets408may be optimized for desired electrical and/or burn characteristics of the cable.

FIG. 5is a cross-sectional view of another gas-encapsulated dual layer separator504and fewer larger gas pockets508in accordance with an exemplary embodiment of the present invention. Referring toFIG. 5, separator504includes an inner member505that has two primary segments510and512, which are joined at junction point514. The primary segments510and512and the junction514may form one piece. As with the embodiments above, the outer layer wraps around the inner member505to form completely enclosed gas pockets508therebetween. Similar to the separator304, the separator504has a substantially flattened shape and is preferably a tape.