US20040055777A1 - Communication wire - Google Patents

Abstract

The present invention relates to an improved insulated conductor with allow dielectric constant and reduced materials costs. Apparatuses methods of manufacturing the improved insulated conductors are also disclosed.

Description

FIELD OF THE INVENTION
• The present invention relates to an improved wire and methods of making the same.[0001]
BACKGROUND OF THE INVENTION
• One method of transmitting data and other signals is by using twisted pairs. A twisted pair includes at least one pair of insulated conductors twisted about one another to form a two conductor pair. A number of methods known in the art may be employed to arrange and configure the twisted pairs into various high-performance transmission cable arrangements. Once the twisted pairs are configured into the desired “core,” a plastic jacket is typically extruded over them to maintain their configuration and to function as a protective layer. When more than one twisted pair group is bundled together, the combination is referred to as a multi-pair cable.[0002]
• In cabling arrangements where the conductors within the wires of the twisted pairs are stranded, two different, but interactive sets of twists can be present in the cable configuration. First, there is the twist of the wires that make up the twisted pair. Second, within each individual wire of the twisted pair, there is the twist of the wire strands that form the conductor. Taken in combination, both sets of twists have an interrelated effect on the data signal being transmitted through the twisted pairs.[0003]
• With multi-pair cables, the signals generated at one end of the cable should ideally arrive at the same time at the opposite end even if they travel along different twisted pair wires. Measured in nanoseconds, the timing difference in signal transmissions between the twisted wire pairs within a cable in response to a generated signal is commonly referred to as “delay skew.” Problems arise when the delay skew of the signal transmitted by one twisted pair and another is too large and the device receiving the signal is not able to properly reassemble the signal. Such a delay skew results in transmission errors or lost data.[0004]
• Moreover, as the throughput of data is increased in high-speed data communication applications, delay skew problems can become increasingly magnified. Even the delay in properly reassembling a transmitted signal because of signal skew will significantly and adversely affect signal throughput. Thus, as more complex systems with needs for increased data transmission rates are deployed in networks, a need for improved data transmission has developed. Such complex, higher-speed systems require multi-pair cables with stronger signals, and minimized delay skew.[0005]
• The dielectric constant (DK) of the insulation affects signal throughput and attenuation values of the wire. That is, the signal throughput increases as the DK decreases and attenuation decreases as DK decreases. Together, a lower DK means a stronger signal arrives more quickly and with less distortion. Thus, a wire with a DK that is lower (approaching 1) is always favored over an insulated conductor with a higher DK, e.g. greater than 2.[0006]
• In twisted pair applications, the DK of the insulation affects the delay skew of the twisted pair. Generally accepted delay skew, according to EIA/TIA 568-A-1, is that both signals should arrive within 45 nanoseconds (ns) of each other, based on 100 meters of cable. A delay skew of this magnitude is problematic when high frequency signals (greater than 100 MHz) are being transmitted. At these frequencies, a delay skew of less than 20 ns is considered superior and has yet to be achieved in practice.[0007]
• In addition, previously, the only way to affect the delay skew in a particular twisted pair or multi-pair cable was to adjust the lay length or degree of twist of the insulated conductors. This in turn required a redesign of the insulated conductor, including changing the diameter of the conductor and the thickness of the insulation to maintain suitable electrical properties, e.g. impedance and attenuation.[0008]
• Another area of concern in the wire and cable field is how the wire performs in a fire. The National Fire Prevention Association (NFPA) set standards for how materials used in residential and commercial building burn. These tests generally measure the amount of smoke given off, the smoke density, rate of flame spread and/or the amount of heat generated by burning the insulated conductor. Successfully completing these tests is an aspect of creating wiring that is considered safe under modern fire codes. As consumers become more aware, successful completion of these tests will also be a selling point.[0009]
• Known materials for use in the insulation of wires, such as fluoropolymers, have desirable electrical properties such as low DK. But fluoropolymers are comparatively expensive. Other compounds are less expensive but do not minimize DK, and thus delay skew, to same extent as fluoropolymers. Furthermore, non-fluorinated polymers propagate flame and generate smoke to a greater extent than fluoropolymers and thus are less desirable material to use in constructing wires.[0010]
• Thus, there is a need for a wire that addresses the limitations of the prior art to effectively minimize delay skew and provide high rates of transmission while also being cost effective and clean burning.[0011]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 shows a perspective, stepped cut away view of a wire according to the present invention.[0012]
• FIG. 2 shows a cross-section of a wire according to the present invention.[0013]
• FIG. 3 shows a cross-section of another wire according to the present invention.[0014]
• FIG. 4 shows a perspective view of an extrusion tip for manufacturing a wire according to the present invention.[0015]
• FIG. 5 shows a perspective view of another extrusion tip for manufacturing a wire according to the present invention.[0016]
DESCRIPTION OF THE PREFERRED EMBODIMENT
• The wire of the present invention is designed to have a minimized dielectric constant (DK). A minimized DK has several significant effects on the electrical properties of the wire. Signal throughput is increased while signal attenuation is decreased. In addition, delay skew in twisted pair applications is minimized. The minimized DK is achieved through the utilization of an improved insulated conductor as described below.[0017]
• A[0018]wire10 of the present invention has aconductor12 surrounded by aprimary insulation14, as shown in FIG. 1.Insulation14 includes at least onechannel16 that runs the length of the conductor. Multiple channels may be circumferentially disposed aboutconductor12. The multiple channels are separated from each other bylegs18 of insulation. Theindividual wires10 may be twisted together to form a twisted pair. Twisted pairs, in turn, may be twisted together to form a multi-pair cable. Any plural number of twisted pairs may be utilized in a cable. Alternately, the channeled insulation may be used in coaxial, fiber optic or other styles of cables. Anouter jacket20 is optionally utilized inwire10. Also, an outer jacket may be used to cover a twisted pair or a cable. Additional layers of secondary, un-channeled insulation may be utilized either surrounding the conductor or at other locations within the wire. In addition, twisted-pairs or cables may utilize shielding.
• The cross-section of one aspect of the present invention is seen in FIG. 2. The[0019]wire10 includes aconductor12 surrounded by aninsulation14. Theinsulation14 includes a plurality ofchannels16 disposed circumferentially about theconductor12 that are separated from each other bylegs18.Channels16 may have one side bounded by an outerperipheral surface19 of theconductor12.Channels16 of this aspect generally have a cross-sectional shape that is rectangular.
• The cross-section of another aspect of the present invention is seen in FIG. 3. The[0020]insulation14′ includes a plurality ofchannels16′ that differ in shape from thechannels16 of the previous aspect. Specifically, thechannels16′ have curved walls with a flat top. Like the previous aspect, thechannels16′ are circumferentially disposed about theconductor12 and are separated bylegs18′. Also in this aspect, theinsulation14′ may include a second plurality ofchannels22. The second plurality ofchannels22 may be surrounded on all sides by theinsulation14′. Thechannels16′ and22 are preferably used in combination with each other.
• The channeled insulation protects both the conductor and the signal being transmitted thereon. The composition of the[0021]insulation14,14′ is important because the DK of the chosen insulation will affect the electrical properties of theoverall wire10. Theinsulation14,14′ is preferably an extruded polymer layer that is formed with a plurality ofchannels16,16′ separated by interveninglegs18,18′ of insulation.Channels22 are also preferably formed in the extruded polymer layer.
• Any of the conventional polymers used in wire and cable manufacturing may be employed in the[0022]insulation14,14′, such as, for example, a polyolefin or a fluoropolymer. Some polyolefins that may be used include polyethylene and polypropylene. However, when the cable is to be placed into a service environment where good flame resistance and low smoke generation characteristics are required, it may be desirable to use a fluoropolymer as the insulation for one or more of the conductors included in a twisted pair or cable. In addition, fluoropolymers are preferred when superior physical properties, such as tensile strength or elongation, are required or when superior electrical properties, such as low DK or attenuation, are required. While foamed polymers may be used, a solid polymer is preferred because the physical properties are superior and the required blowing agent can be eliminated.
• As important as the chemical make up of the[0023]insulation14,14′ are the structural features of theinsulation14,14′. Thechannels16,16′ and22 in the insulation generally have a structure where the length of the channel is longer than the width, depth or diameter of the channel. Thechannels16,16′ and22 are such that they create a pocket in the insulation that runs from one end of the conductor to the other end of the conductor. Thechannels16,16′ and22 are preferably parallel to an axis defined by theconductor12.
• Air is preferably used in the channels; however, materials other than air may be utilized. For example, other gases may be used as well as other polymers. The[0024]channels16,16′ and22 are distinguished from other insulation types that may contain air. For example, channeled insulation differs from foamed insulation, which has closed-cell air pockets within the insulation. The present invention also differs from other types of insulation that are pinched against the conductor to form air pockets, like beads on a string. Whatever material is selected for inclusion in the channels, it is preferably selected to have a DK that differs from the DK of the surrounding insulation.
• Preferably, the[0025]legs18,18′ of theinsulation14,14′ abut the outerperipheral surface19 of theconductor12. In this way, the outerperipheral surface19 of theconductor12 forms one face of the channel, as seen in FIGS.1-3. At high frequencies, the signal travels at or near the surface of theconductor12. By placing air at the surface of theconductor12, the signal can travel through a material that has a DK of 1, that is, air. Thus, the area that thelegs18,18′ of theinsulation14,14′ occupy on the outerperipheral surface19 of theconductor12 is preferably minimized. This may be accomplished by maximizing the cross-sectional area of thechannels16,16′, and consequently minimizing the size oflegs18,18′, utilized in theinsulation14,14′. Also, the shape of thechannels16,16′ may be selected to minimize thelegs18,18′ contact area with theconductor12.
• A good example of these two concepts used in combination is seen in FIG. 3, where[0026]channels16′ with curved walls are utilized. The walls curve out to give channels an almost trapezoidal shape. The almosttrapezoidal channels16′ have larger cross-sectional areas than generallyrectangular channels16. Furthermore, the curve walls of adjacent channels cooperate to minimize the size of theleg18′ that abuts the outerperipheral surface19 of theconductor12.
• Furthermore, the area that the[0027]legs18,18′ of theinsulation14 occupy on the outerperipheral surface19 of theconductor12 can be minimized by reducing the number ofchannels16,16′ utilized. For example instead of the sixchannels16,16′ illustrated in FIGS.2-3, five or four channels may be used.
• The[0028]channels22 also minimize the overall DK of theinsulation14′ by including air in theinsulation14′. Furthermore, thechannels22 can be utilized without compromising the physical integrity of thewire10.
• The cross-sectional area of the channels should be selected to maintain the physical integrity of wire. Namely, it is preferred that any one channel not have a cross-sectional area greater than about 30% of the cross-sectional area of the insulation.[0029]
• Through the use of the[0030]wire10 with channeledinsulation14,14′, a delay skew of less than 20 ns is easily achieved in twisted pair or multi-pair cable applications, with a delay skew of 15 ns preferred. A delay skew of as small as 5 ns is possible if other parameters, e.g. lay length and conductor size, are also selected to minimize delay skew.
• Also, the lowered DK of the[0031]insulation14,14′ is advantageous when used in combination with a cable jacket. Typically, jacketed plenum cables use a fire resistant PVC (FRPVC) for the outer jacket. FRPVC has a relatively high DK that negatively affects the impedance and attenuation values of the jacketed cable, but it is inexpensive. Theinsulation14,14′, with its low DK, helps to offset the negative effects of the FRPVC jacket. Practically, a jacketed cable can be given the impedance and attenuation values more like an un-jacketed cable.
• Indeed, the low DK provided by the[0032]insulation14,14′ also increases the signal speed on the conductor, which, in turn, increases the signal throughput. Signal throughput of at least 450 ns for 100 meters of twisted pair is obtained, while signal speeds of about 400 ns are possible. As signal speeds increase, however, the delay skew must be minimized to prevent errors in data transmission from occurring.
• Furthermore, since the DK of the channeled insulation is proportional to the cross-sectional area of the channels, the signal speed in a twisted pair is also proportional to the cross-sectional area of the channels and thus easily adjustable. The lay length, conductor diameter, and the insulator thickness need not be changed. Rather, the cross-sectional area of the channels can be adjusted to obtain the desired signal speed in balance with other physical and electrical properties of the twisted pair. This is particularly useful in a multi-pair cable. The delay skew of the cable may be thought of as the difference in signal speed between the fastest twisted pair and the slowest twisted pair. By increasing the cross-sectional area of the channels in the insulation of the slowest twist pair, its signal speed can be increased and thus more closely matched to the signal speed of the fastest twisted pair. The closer the match, the smaller the delay skew.[0033]
• Besides the desirable effects on the electrical properties of the[0034]wire10, theinsulation14,14′ has economic and fire prevention benefits as well. Thechannels16,16′ and22 in theinsulation14,14′ reduce the materials cost of manufacturing thewire10. The amount of insulation material used for theinsulation14,14′ is significantly reduced compared to non-channeled insulation and the cost of the filler gas is free. Stated alternately, more length of theinsulation14,14′ can be manufactured from a predetermined amount of starting material when compared to non-channeled insulation. The number and cross-sectional area of thechannels16,16′ and22 will ultimately determine the size of the reduction in material costs.
• The reduction in the amount of material used in the[0035]insulation14,14′ also reduces the fuel load of thewire10.Insulation14,14′ gives off fewer decomposition by-products because it has comparatively less insulation material per unit length. With a decreased fuel load, the amount of smoke given off and the rate of flame spread and the amount of heat generated during burning are all significantly decreased and the likelihood of passing the pertinent fire safety codes, such as NFPA 255, 259 and 262, is significantly increased. A comparison of the amount of smoke given off and the rate of flame spread may be accomplished through subjecting the wire to be compared to a UL 910 Steiner Tunnel burn test. The Steiner Tunnel burn test serves as the basis for the NFPA 255 and 262 standards. In every case, a wire with channeled insulation where the channels contain air will produce at least 10% less smoke then wire with un-channeled insulation. Likewise, the rate of flame spread will be at least 10% less than that of un-channeled insulation.
• A preferred embodiment of the present invention is a[0036]wire10 withinsulation14,14′ made of fluoropolymers where the insulation is less than about 0.010 in thick, while the insulated conductor has a diameter of less than about 0.042 in. Also, the overall DK of the wire is preferably less than about 2.0, while the channels have a cross-sectional are of at least 2.0×10⁻⁵in². Such a wire would have the electrical properties advantages of a reduced DK provided by both the fluoropolymer and the air, while also having reduced material costs and reduced fuel loads compared to known non-channeled insulated conductors.
• Examples of some[0037]acceptable conductors12 include solid conductors and several conductors twisted together. Theconductors12 may be made of copper, aluminum, copper-clad steel and plated copper. It has been found that copper is the optimal conductor material. In addition, the conductor may be glass or plastic fiber, such that fiber optic cable is produced.
• The[0038]outer jacket20 may be formed over the twisted wire pairs and as can a foil shield by any conventional process. Examples of some of the more common processes that may be used to form the outer jacket include injection molding and extrusion molding. Preferably, the jacket is comprised of a plastic material, such as fluoropolymers, polyvinyl chloride (PVC), or a PVC equivalent that is suitable for communication cable use.
• The present invention also includes methods and apparatuses for manufacturing wires with channeled insulation. The insulation is preferably extruded onto the conductor using conventional extrusion processes, although other manufacturing processes are suitable. In a typical insulation extrusion apparatus, the insulation material is in a plastic state, not fully solid and not fully liquid, when it reaches the crosshead of the extruder. The crosshead includes a tip that defines the interior diameter and physical features of the extruded insulation. The crosshead also includes a die that defines the exterior diameter of the extruded insulation. Together the tip and die help place the insulation material around the conductor. Known tip and die combinations have only provided an insulation material with a relatively uniform thickness at a cross-section with a tip that is an unadulterated cylinder. The goal of known tip and die combinations is to provide insulation with a uniform and consistent thickness. In the present invention, the tip provides insulation with interior physical features; for example, channels. The die, on the other hand, will provide an insulation relatively constant exterior diameter. Together, the tip and die combination of the present invention provides an insulation that has several thicknesses.[0039]
• The[0040]insulation14 shown in FIG. 2 is achieved through the use of anextrusion tip30 as depicted in FIG. 4. Thetip30 includes abore32 through which the conductor may be fed during the extrusion process. Aland34 on thetip30 includes a number ofgrooves36. In the extrusion process, thetip30, in combination with the die, fashions theinsulation14 that then may be applied to theconductor12. Specifically, in this embodiment, thegrooves36 of theland34 create thelegs18 of theinsulation14 such that thelegs18 contact the conductor12 (or a layer of an un-channeled insulation). Theprominences38 between thegrooves36 on theland34 effectively block the insulation material, thus creating thechannels16 in the insulation material as it is extruded.
• The[0041]insulation14′ shown in FIG. 3 is achieved through the use of an extrusion tip as depicted in FIG. 5. Thetip30′ includes abore32 through which the conductor may be fed during the extrusion process. Like the tip of FIG. 4, theland34 of thetip30′ includes a number ofgrooves36′ separated byprominences38′. In this embodiment, thegrooves36′ are concave, while theprominences38′ are flat topped. Together, thegrooves36′ andprominences38′ of theland34 formconvex legs18′ and flat-toppedchannels16′ of the insulation. In addition, thetip30′ also includes a number ofrods40 spaced from theland34. Therods40 act similar to theprominences38′ and effectively block the insulation material, thus creatinglong channels22 surrounded byinsulation14′, as seen in FIG. 3.
• While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.[0042]

Claims (32)

What is claimed is:

1. A wire comprising:

a conductor extending along a longitudinal axis, an insulation surrounding the conductor and at least one channel in the insulation extending generally along the longitudinal axis to form an insulated conductor.

2. The wire ofclaim 1, wherein the insulated conductor has an overall dielectric constant of less than 2.0.

3. The wire ofclaim 1, wherein the channel contains a material that has a dielectric constant that differs from a dielectric constant of the insulation.

4. The wire ofclaim 3, wherein the channel contains air.

5. The wire ofclaim 1, wherein the insulation includes a plurality of channels.

6. The wire ofclaim 5, wherein no one of the plurality of channels has a cross-sectional area greater than about 30% of a cross-sectional areas of the insulation.

7. The wire ofclaim 1, wherein an outer peripheral surface of the conductor forms one side of the at least one channel.

8. The wire ofclaim 1, wherein the insulation fully surrounds the at least one channel.

9. The wire ofclaim 1, wherein an outer peripheral surface of the conductor forms one side of at least a first channel and the insulation fully surrounds at least a second separate channel.

10. The wire ofclaim 1, wherein the at least one channel has a cross-sectional area of at least 2.0×10⁻⁵in².

11. The wire ofclaim 1, further comprising an outer jacket surrounding the insulation.

12. The wire ofclaim 1, wherein the insulated conductor has a diameter of less than about 0.042 in.

13. The wire ofclaim 12, wherein the insulation has a thickness of less than about 0.010 in.

14. The wire ofclaim 1, wherein two insulated conductors are twisted together to form a twisted pair.

15. The wire ofclaim 14, wherein the delay skew is no greater than 15 ns between the insulated conductors.

16. The wire ofclaim 14, further including a plurality of twisted pairs.

17. The wire ofclaim 16, further comprising an outer jacket surrounding the twisted pairs.

18. The wire ofclaim 16, wherein each twisted pair includes a shield.

19. The wire ofclaim 16, wherein the delay skew is no greater than 15 ns between individual twisted pairs.

20. The wire ofclaim 1, wherein the conductor is solid copper.

21. The wire ofclaim 1, further comprising a secondary insulation surrounding the conductor.

22. The wire ofclaim 1, wherein the insulated conductor passes a test selected from the group consisting of NFPA 255, NFPA 259, NFPA 262 or combinations thereof.

23. The wire ofclaim 22, wherein the insulated conductor passes all of NFPA 255, NFPA 259 and NFPA 262.

24. The wire ofclaim 1, wherein the insulated conductor generates at least 10% less smoke when burned according to a UL 910 Steiner Tunnel test when compared to an insulated conductor without channels in its insulation.

25. The wire ofclaim 1, wherein the insulated conductor spreads flame at a rate at least 10% slower when burned according to a UL 910 Steiner Tunnel test when compared to an insulated conductor without channels in its insulation.

26. An insulation for a wire comprising:

an elongated body of a polymeric material having a bore adapted to house a conductor, wherein at least one channel is located in the elongated body.

27. The insulation ofclaim 26, wherein the channel has a cross-sectional area of at least 2.0×10⁻⁵in².

28. The insulation ofclaim 26, wherein the at least one channel is open to the bore.

29. The insulation ofclaim 26, wherein the at least one channel is surrounded by the thermoplastic material.

30. An insulated conductor comprising:

a conductor having a length; and

an insulation surrounding the conductor and having substantially the same length as the conductor,

wherein the insulation includes at least one channel that extends generally the length of the conductor.

31. A wire with a minimized delay skew, comprising:

a first twisted pair having a first signal speed and having a channel in its insulation with a first predetermined cross-sectional area; and

a second twisted pair having a second signal speed and having a channel in its insulation with a second predetermined cross-sectional area,

wherein each cross-sectional area is selected to match the first signal speed to the second signal speed.

32. The wire ofclaim 30, wherein the first signal speed differs from the second signal speed by less than about 15 ns.

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