Abstract:
A communications cable is provided having a jacket and a plurality of twisted pair, each twisted pair having two insulated conductors twisted around one another. The insulation on the insulated twisted conductors is foamed polysulfone.

Description:
FIELD OF THE INVENTION 
       [0001]    The present arrangement relates to LAN cables. More particularly, the present arrangement relates to LAN cables that employ polysulfone insulation. 
       BACKGROUND 
       [0002]    Communication cables come in wide variety of shapes and sizes depending on the application. One type of communication cable is the LAN cable or Local Area Network cable common in the computer industry. Such cables typically include one or more twisted pairs of cables, one or more additional components such as separators, shields, drain wires etc . . . and a jacket around the components. LAN cables can come in many sizes based on the pair count, but for the purposes of illustration the present application, the present examples use the common 4-pair LAN cable used for network communication such as the one pictured in prior art  FIG. 1  (shown with optional cross-filler). 
         [0003]    When constructing the cables careful attention is paid to the construction of each component in order to not only maintain the desired electrical characteristics but also to meet the various mechanical and fire safety standards. For example, LAN cables need to meet certain electrical characteristics such as those set forth in the CAT 5, CAT 5e, CAT 6, etc . . . (setting for example allowable insertion loss, return loss and crosstalk requirements for 100 ohm impedance cable) based on the TIA 568C.2 industry standard. 
         [0004]    While meeting those electrical standards, these same LAN cables also need to meet certain physical requirements such as cold bend, insulation elongation, and tensile requirements as set forth in the UL 444 industry standard. 
         [0005]    Moreover, LAN cables also need to meet fire and smoke tests such as those outlined in NFPA 262/UL 910, UL1666 and UL1685 depending on listing type. 
         [0006]    In order to meet these requirements, regarding the insulation used on the twisted pairs, LAN cable producers often use FEP (Fluorinated Ethylene Propylene) because it not only has excellent electrical properties but also has both good mechanical properties and fame/smoke resistance. However, FEP is expensive and it is halogenated and there is generally a desire to reduce harmful halogens in cables owing to environmental and health concerns. 
         [0007]    In order to avoid the use of FEP some prior art solutions use fire/smoke resistant PE (Polyethylene), PP (Polypropylene), and PVC (Poly Vinyl Chloride) for the pair insulation because they are less expensive than FEP. However, these polymers require fillers and modifications to enhance their smoke/fire resistance properties that negatively affects their mechanical properties and their electrical properties are likewise not as good as FEP. 
         [0008]    Other prior art solutions, including U.S. Patent Publication No. 2014/0262427, have used foamed non-halogenated polymers including polysulfone in LAN cables for its improved fire and smoke properties. In these solutions the polymer is foamed to improve smoke and flame spread. In this solution, in some options the polymer is polysulfone but it is employed as a separator (and not on the primary pair insulation). 
       OBJECTS AND SUMMARY 
       [0009]    The present arrangement improves on the prior art by providing a LAN cable that employs foamed polysulfone for use as insulation on the twisted pairs in LAN cable. The foamed polysulfone of the present arrangement has good fire resistance properties and simultaneously has good mechanical properties. 
         [0010]    Polysulfone (non-foamed) is known to have good fire resistance properties but it is roughly as expensive as FEP and it tends to be stiff preventing its effective use as LAN pair insulation. The present arrangement employs a formulation for foamed polysulfone that makes it a suitable replacement for FEP as LAN pair insulation to provide comparable electrical and mechanical characteristics compared to FEP but at a lesser cost. 
         [0011]    To this end the present arrangement provides for a communications cable having a jacket and a plurality of twisted pair, each twisted pair having two insulated conductors twisted around one another. The insulation on the insulated twisted conductors is foamed polysulfone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention can be best understood through the following description and accompanying drawings, wherein: 
           [0013]      FIG. 1  illustrates a prior art LAN cable; 
           [0014]      FIG. 2  illustrates a LAN cable according to one embodiment; and 
           [0015]      FIG. 3  illustrates a LAN cable according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The present arrangement as illustrated for example in  FIG. 2  is directed to a LAN cable  10  having a jacket  12 , four twisted pairs of conductors (pairs)  14  and optional separator  16 . Each of twisted pairs  14  are made from two twisted conductors  20 , each of which has an insulation  22  thereon, It is understood that such components are exemplary and are in no way intended to limit the scope of the present invention. Cable  10  may have more or less than four (4) twisted pairs  14 . Additionally, cable  10  may have additional components (not shown) such shielding, ground w res, binders etc . . . The construction of jacket  12  may be made from flame retardant polymers typically used in LAN cable construction such as FRPVC (Flame Retardant Poly Vinyl Chloride) or other flame retardant polyolefins. 
         [0017]    In the present arrangement, insulation  22  on each of conductors  20  are made from foamed polysulfone. In the present example conductors  20  are preferably 24 awg to 22 awg copper conductors. Insulation  22  preferably has a thickness ranging from 0.006″ to 0.015″ and is made from a foamed polysulfone. It is noted that higher void percentages improve electrical results and reduce costs, however decrease crush resistance and increase scrap, so a balance is required for each cable design. In the present arrangement a void percentage in the foamed polysulfone of about 20% to 50% is used depending on the desired physical requirements. 
         [0018]    Applicants note that insulation  22  differs from crossfillers such as optional cross filler/separator  16  in several ways. One of the largest differences is that the effective dielectric of insulation  22  is critical to make cable  10  perform as intended due to the proximity of insulation  22  to conductors  20 . A cross filler and the material selection thereof may have some effect on the overall cable performance. However due to its location which is farther from conductors  20 , the material section effect is greatly diminished. 
         [0019]    In the present instance where insulation  22  is foamed polysulfone, the effective dielectric can be altered by changing the foaming %, the thickness of insulation  22 , the shape of insulation  22 , as well as additives mixed into the material. The present arrangement contemplates the use of foamed polysulfone as insulation  22  on conductors  20  with the correct balance of the above variables needed for cable  10  to achieve the performance criteria listed in TIA 568C.2 industry standard as discussed in more detail below. In addition, such factors for the dimensions and material/void % for insulation  22  are selected so survive the cabling (twisting of insulated conductors  20  into twisted pairs), including but not limited to the correct blend of foam void %, wall thickness and insulation material combinations. 
         [0020]    In such an arrangement, when insulation  22  is foamed, it allows the reduction of the diameter of insulation  22  when compared to prior art solid insulations between 0.008″ to 0.020″ in wall thickness. This helps in several areas, including less material usage, smaller cable size, and reduced cost. In addition, by using foamed polysulfone for insulation  22 , pairs  14  exhibit very good flame and smoke properties and because of this, the wall thickness of jacket  12  can likewise be reduced while still providing acceptable margins in the UL 262 flame test. 
         [0021]    In another embodiment as shown in  FIG. 3 , a cable  100  is shown having a jacket  112 , four twisted pairs of conductors (pairs)  114  and optional separator  116 . As with  FIG. 2  above, each of twisted pairs  114  are made from two twisted conductors  120 , each of which has an insulation  122  thereon. However, in the arrangement of  FIG. 3 , insulation  122  is divided into a first inner layer  122   a  and a second outer layer  122   b.    
         [0022]    In a first arrangement, inner layer  122   a  is made from a solid PEI, PVC, Polyolefin, etc . . . material, typically a polymer which has a low dielectric constant and which is good for electrical performance and ideally with good with flame retardant properties. Outer layer  122   b  is then made from foamed Polysulfone (PSU). 
         [0023]    In such an arrangement the polysulfone outer layer  122   b  will generally be of the same material type as in the example shown above in  FIG. 2 . However, it is possible that the void percentage in the foam can be increased due to inner layer  122   a  being used as a support structure. 
         [0024]    In one exemplary embodiment, the thicknesses of layers  122   a  and  122   b  may depend on the cable design and electrical criteria. However, in one exemplary design, the ratio of thicknesses is 20%/80% and vice versa. Generally the thickness of inner layer  122   a  Is about 0.004″ to 0.008″ and the thickness of outer layer  122   b  is about 0.004″ to 0.008.″ Such a dual layer insulation  122   a / 122   b  should be slightly smaller than its solid counter part due to the foaming of the insulation allows a reduction in OD(outside diameter) of the cable while still achieving the same electrical results. 
         [0025]    In the case of using polyolefins as solid material for inner layer  122   a  and foamed polysulfone as outer layer  122   b,  the polyolefin can provide good electrical properties and increased crush resistance at a low cost for inner layer  122   a,  without have to worry about its poor flame performance. Adding a foamed polysulfone insulation as second layer  122   b  serves as a barrier the fire test and thus should allow acceptable margins in both electrical and fire testing. 
         [0026]    Moreover, two layers of insulation  122   a  and  122   b  allow the cable designer to customize cable  100  for particular applications, For example to provide good electrical properties for a cable inner layer  122   a  can have a low dielectric constant and dissipation factor, but does not need to have good flame resistance. In turn the flame resistance can be accomplished by outer layer  122   b  which in turn does not need to have good electrical properties in general, but can have good flame and smoke properties, Another advantage of this arrangement is to reduce costs. Typically materials which have good flame; smoke and electrical properties (like FEP) are very costly. Using layered insulation allows lower cost materials to be used where their benefits can be maximized. 
         [0027]    In another embodiment, it is possible to invert the materials and use foam Polysulfone as the inner layer  122   a  and other material on the outer layer  122   b  such as the above described polyolefins. 
         [0028]    While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.