Patent Publication Number: US-9842672-B2

Title: LAN cable with PVC cross-filler

Description:
BACKGROUND 
     Field of the Invention 
     This application relates to communication cables. More particularly, this application relates to network cable construction. 
     Description of Related Art 
     Communication cables are broadly grouped into two arrangements, fiber optic cables and metal conductor cables, each of which has its own unique set of construction parameters that affect the quality of the communication signals carried therethrough. 
     Regarding metal conductor cables, one typical arrangement is the LAN (Local Area Network) cable that is usually constructed of four pairs of twisted insulated copper conductors encased within a jacket. Other larger cables may employ ore pairs of conductors. 
     In this typical four pair LAN cable construction, in addition to the outer jacket, each of the eight primary conductors are individually coated with an insulation layer. Among the other components, LAN cables often include a tape or various extruded shapes including cross-fillers to separate the twisted pairs for better NEXT (Near End Cross Talk) performance. 
     In each case, aside from electrical performance considerations, there are certain flammability performance tests that need to be met. One such crucial test is the NFPA (National Fire Protection Association) 262 flame test (or UL 910), which is a standard method of testing for flame travel and smoke generation for testing wires and cables that may be installed in air-handling spaces such as budding ductwork. 
     In this context, FEP (Fluorinated Ethylene Polymer) resin, thanks to its outstanding electrical and flame performance, is a typical material choice for the LAN cable application. Aside from its use as the insulation on the primary conductors of the twisted pairs, FEP is also currently the ideal material choice for tapes or various extruded shapes including cross fillers as it has excellent electrical properties and good flame and smoke performance. 
     Alternative prior art arrangements have used mixtures of LDPE and VLDPE (Low Density and Very Low Density Polyethylene) with significant quantities of flame retardant fillers blended into the polymer composition. Such highly filled LDPE and/or VLDPE olefin blends are used for cross fillers to reduce cost of the LAN cable. However, even when highly filled with flame retardant fillers, such LDPE and VLDPE polymers still exhibit inferior smoke and flame resistance properties relative to the FEP. 
     Other polymers exist such as PVC (Poly-Vinyl Chloride) with fire retardant fillers (e.g. FRPVC), however, prior art constructions do not use PVC for CAT 6 LAN tapes or cross fillers to separate twisted pairs because PVC without plasticizing additives tend to be too rigid for cable applications. When plasticizing additives are incorporated into the PVC, they tend to degrade the electrical properties of the PVC causing too much signal attenuation to be useful in most CAT 6 LAN cable applications. For example, the commonly used plasticizers in PVC insulation for wire and cable arrangements are ester based plasticizers which can have a negative effect on the dissipation factor of the final PVC compound. 
     Generally, there is a dissipation of electrical energy, caused by the presence of dielectric material in close proximity to the wire. The dissipation factor of a dielectric material is a measure of the power loss rate caused by said material. Certain polymers have better (lower) dissipation factors than others. Likewise, the same polymer may exhibit a different dissipation factor depending on different formulations of that polymer (e.g. different additives, flame retardants, processing agents etc incorporated into the polymer). 
     As shown in prior art  FIG. 1 , over various frequency ranges, ester based plasticizers (used at 50 phr in PVC) still result in the PVC exhibiting dissipation loss factors in excess of 0.01 at frequencies between 100 MHz to 500 MHz. 
     OBJECTS AND SUMMARY 
     The present arrangement, overcomes the drawbacks of the prior art arrangements, and employs a PVC cross filler in a LAN cable, where the PVC formulation of fillers and plasticizers is such that the PVC is rendered sufficiently flexible for use as a cross filler, while also simultaneously exhibiting good fire and smoke resistance properties as well as acceptable electrical properties. 
     For example, among other features, the present arrangement employs halogenated phthalates, such as brominated phthalate ester plasticizers, which, at equal loading levels amounts relative to the more common prior art ester based plasticizers, yield PVC formulations with significantly lower dissipation factors. 
     To this end a communications cable includes a jacket and a plurality of twisted pairs, each twisted pair having two insulated conductors twisted around one another. A cross-filler is arranged between the twisted pairs, where the cross filler is constructed of a PVC formulation using a halogenated plasticizer as the primary plasticizer and having a dissipation factor below 0.01 at frequencies between 100 MHz to 500 MHz. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be best understood through the following description and accompanying drawings, wherein: 
         FIG. 1  is a prior art dissipation factor chart of prior art PVC formulations using non-halogenated plasticizers as the primary plasticizers; 
         FIG. 2  shows a LAN cable with a cross-filler according to the present arrangement; and 
         FIG. 3  is a dissipation factor chart comparing prior art PVC formulations using non-halogenated plasticizers as the primary plasticizers to the present PVC formulations using halogenated plasticizers as the primary plasticizers. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment as illustrated in  FIG. 2 , a LAN (Local Area Network) cable  10  is shown, such as a CAT 6 CMP (Plenum) UTP LAN cable (Category 6 250 MHz—Unshielded Twisted Pair). For the purposes of illustration, the salient features of the present arrangement are described in the context of a CAT 6 type LAN cable, however, the invention is not limited in this respect. Other cables that are required to meet certain flame test specifications may also employ the present technology. 
     As shown in  FIG. 2 , LAN cable  10  has a jacket  12  constructed for example from FRPVC (Flame Retardant Poly-Vinyl Chloride). Within jacket  12  there are four twisted pairs  20 . Each twisted pair is formed of two primary conductors  22  twisted around one another. As shown in  FIG. 1  primary conductors  22  are typically made from a copper wire conductor  23  covered with an insulation layer  24 . As noted above, for exemplary purposes, cable  10  is a four pair LAN cable, but it is understood that the salient features of the present arrangement could be used on cables having more or fewer pairs  20 . 
     In the present arrangement, the polymer material used for insulation layers  24  may be made from FEP (Fluorinated Ethylene Polymer), FRPP (Flame Resistant Poly Propylene) or other polymers. Optionally, some of the insulation layers  24  on some of the pairs  20  may be made from a first polymer such as FEP, with other insulation layers  24  on some of the pairs  20  being made from FR olefins such as FRPP in order to balance flame/smoke properties, mechanical properties and costs. It is understood that any selection of insulation material for insulation layers  24  on pairs  20  is within the contemplation of the present invention. 
     For example, in one arrangement, insulation layer  24  on two twisted pairs  20  are made from a flame resistant olefin composition, such as FRPP, and the other two insulation layers  24  on the remaining two twisted pairs  20  are made from FEP. In other examples, all four pairs  20  may be made using FEP;  3  pairs  20  from FEP with one pair  20  using FRPP;  3  pairs  20  from FRPP with one pair  20  using FEP; and all four pairs  20  made using FRPP. 
     Ideally, FEP usage is limited due to its expense, but it is used on at least some of the pairs  20  owing to its superior flame and smoke properties as well as its good electrical properties. The construction of the present cable  10  and other components thereof allow for an advantageous reduction in the number of pairs  20  insulated with FEP, while still maintaining the required plenum and CAT 6 ratings as discussed in more detail below. 
     As illustrated in  FIG. 2 , in addition to the twisted pairs  20 , cable  10  also has a cross filler  30  made from FRPVC. As noted above, in high performance CAT 6 cables, tapes or other extruded shapes such as cross fillers are often required to reduce cross-talk between the different pairs  20  within cable  10 . As noted in the background FEP and highly flame retardant polyolefins have been used in prior art arrangements for making cross-fillers. FRPVC is not typically used because the commonly used non-halogenated plasticizing agents render the FRPVC with poor electrical properties (i.e. high dissipation factors). 
     For the purposes of illustration, cross filler  30  is used to show the dividing element between pairs  20  in cable  10 . However, it is understood that the shape of this divider/cross filler is only for the purposes of illustrating the salient features of the present arrangement. Cross filler  30  may be alternatively formed as a tape of filler/divider or other non-crossed shapes provided is made using the following described formulation. 
     In the present arrangement, and in accordance with one embodiment, cross filler  30  is constructed of PVC using a halogenated ester plasticizer as the primary (in this case only) plasticizer, with the PVC formulation having a dissipation factor lower than 0.01 at frequencies between 100 MHz and 500 MHz as described in more detail below. 
     It is noted that PVC may come in thousands of different formulations, including the basic polymer structure (Molecular Weight), the plasticizers used, the fillers etc. . . . . In accordance with one embodiment, one exemplary PVC formulation is as follows: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 PVC 
                 100.0 
                 phr (phr = parts per 
               
               
                   
                   
                 hundred pounds of resin) 
               
               
                 FRP 45 Brominated DOP 
                 60.0 
                 phr 
               
               
                 Aluminum Trihydrate 
                 50.0 
                 phr 
               
               
                 Huber HPSS (basic zinc molybdate) 
                 10.0 
                 phr 
               
               
                 Antimony Trioxide 
                 2.0 
                 phr 
               
               
                 Ferro RC 641P Ca/Zn Stabilizer 
                 6.0 
                 phr 
               
               
                 Titanium dioxide 
                 0.5 
                 phr 
               
               
                 OPE wax 
                 0.6 
                 phr 
               
               
                   
               
            
           
         
       
     
     From the above description, FRP 45 is the primary plasticizer and can be described chemically as tetrabromo bis(2-ethylhexyl) phthalate. 
     In the above example, Brominated DOP is the only plasticizer used and, at 60 phr to 100 phr PVC resin it is a substantial component, with the remaining components being fire retardant fillers, stabilizers, colorants, processing lubricants, and stabilizers. 
     It is noted that the PVC may be blended with CPVC (Chlorinated PVC) or CPE (chlorinated polyethylene) to achieve additional fire retardant dualities. 
     The above example is intended as one exemplary PVC formulation for cross filler  30 . However, it is understood that modifications can be made provided that the halogenated ester plasticizer remains the primary plasticizer, meaning that the halogenated ester plasticizer is the majority component of the plasticizer(s) in the polymer composition. For example, in other embodiments, the following PVC formulation (range of component parts) may be used: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 PVC 
                 0-100 
                 phr 
                 Resin 
               
               
                 Chlorinated PE 
                 0-100 
                 phr 
                 Resin or plasticizer 
               
               
                   
                   
                   
                 depending on 
               
               
                   
                   
                   
                 chlorine content 
               
               
                 Halogenated Ester Plasticizer 
                 30-150 
                 phr 
                 Plasticizer + FR 
               
               
                 Non-Halogenated Plasticizer 
                 &lt;20 
                 phr 
                 Plasticizer 
               
               
                 Metal Hydrate Flame Retardant(s) 
                 1-300 
                 phr 
                 FR + SS 
               
               
                 Molybdenum FR/SS 
                 0.1-50 
                 phr 
                 FR + SS 
               
               
                 Zinc FR/SS 
                 0.1-50 
                 phr 
                 FR + SS 
               
               
                 Antimony Trioxide 
                 0.1-50 
                 phr 
                 FR 
               
               
                 Stabilizer 
                 0.1-20 
                 phr 
                 Stabilizes 
               
               
                   
                   
                   
                 compound 
               
               
                   
               
               
                 (FR = Flame Retardant - SS = Smoke Suppressant) 
               
            
           
         
       
     
     The halogenated plasticizers may include, but are not limited to: brominated phthalate esters; chlorinated phthalate esters; brominated trimellitate esters; chlorinated trimellitate esters; brominated paraffins; chlorinated paraffins; and chlorinated polyethylene (CPE). 
     The non-halogenated plasticizer may include, but is not limited to phthalate esters, trimellitate esters, pentaerythritol esters, phosphate esters, aliphatic dicarboxylic add esters, sulfonic add esters, sulfamides, citric acid esters, epoxidized fatty add esters, benzoic add esters; and polymeric plasticizers systems containing but not limited to monomers such as adipic add, sebacic add, azeleic add, and commercially available compatible polymers containing acrylate, acetate, nitrile, urethane, or polyether ester functionality. 
     The metal hydrate flame retardant may include, but is not limited to: aluminum trihydrate, boehmite, magnesium dihydroxide, magnesium carbonate, zinc borate, metal hydrates coated with a flame retardant or smoke suppressant; or combinations of two or more metal hydrates. 
     The PVC compound may have smoke suppressants or combinations of smoke suppressants containing one or more of the following elements: Mo, Zn, Sn, Cu, Fe, Si, B, P, C, or N. 
     The above described PVC formulation has excellent flame and smoke performance based on the fillers and halogenated plasticizer as well as good electrical properties to reduce NEXT (Near End Cross Talk) without affecting the cable&#39;s insertion loss performance. 
     Moreover, although the preferred PVC crossfiller formulation in general tends to be stiffer than LDPE, or VLDPE, it is more flexible than crossfillers based on FEP. The final cable  10  manufactured with the above formulation for PVC cross filler  30  exhibits flexibility characteristics similar to those of cables manufactured pith the FR olefin cross fillers. 
     The present arrangement has provided the unexpected result that the use of very high quantities of halogenated ester plasticizers and the near or complete removal of non-halogenated plasticizers actually lead not only to the required fire resistant properties, but also to sufficient flexibility while yielding a dissipation factor value for the PVC formulation below 0.01 at frequencies between 100 MHz and 500 MHz. See for example  FIG. 3  showing a comparison of the dissipation factors of PVC using prior art plasticizers versus brominated phthalate ester (all at 50 phr). 
     To show that the above formulations of PVC are not only good for producing cross filler  30  with good electrical properties they were tested against prior art cross fillers for fire and smoke properties to show that it provides comparable prior flame and smoke properties to FEP and better than other FR olefin formulations (e.g. FRPE, FRPP, etc. . . . ) 
     Turning to test results for the present arrangement, the above described NFPA 262 flame test is applied to cables, such as cable  10 , intended for use within buildings inside of ducts, plenums, or other spaces used for environmental air distribution. Any cable used in these areas must be “plenum rated” in order to be installed without conduit. One such plenum rating test is the NFPA 262 test. In order to pass the NFPA 262 test, these cables must have outstanding resistance to flame spread and generate low levels of smoke during combustion. As noted above, flame spread and smoke generation is directly related to the use of jacketing on cable  10 , and in particular the insulation used on twisted pairs  20 . Because of the need to use low smoke insulation and jacketing materials, these plenum rated cables are the highest in cost of the three major premise data communications cable types specified by the NEC (National Electric Code). 
     The NFPA 262 flame test uses a test apparatus called a Steiner Tunnel. This chamber is 25′ long by 18 inches wide by 12 inches high. An 11.25 inch wide tray is loaded with a single layer of cable, such as cable  10  placed side to side against each other so that the width of the tray is filled. The cable is then exposed to a 300,000 btu flame for 20 minutes. During the course of the test, the flame must not propagate more than 5 feet, the peak smoke must not exceed a value of 0.15 (log Io/I), and the average smoke value must not exceed 0.15 (log Io/I). It is noted that log Io/I refers to the optical density where I is the intensity of light at a specified wavelength λ that has passed through a sample (transmitted light intensity) and I 0  is the intensity of the light before it enters the sample or incident light intensity (or power). If the cable is tested twice and meets all three criteria after each test, it is deemed to have passed the test. 
     To show the effectiveness of cable  10 , cross filler  30  made from the present PVC formulation (using halogenated phthalate ester plasticizer) was tested against a prior art cross filler made from a FR olefin based on a blend of LDPE and VLDPE containing a proprietary flame retardant system with a specific gravity of 1.63. 
     The following table 1 shows the results of the NFPA 262 test: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 NFPA 262 Steiner Tunnel Data FR Olefin Cross filler 
               
               
                 Technology vs present PVC Cross filler composition 
               
               
                 Average of two burns - 0.015″ wall jacket compound 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Flame 
                 Peak 
                 Avg. 
               
               
                   
                   
                 Spread 
                 Smoke 
                 Smoke 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 FR Olefin Technology 
                 4.8′ 
                 0.47 
                 0.13 
               
               
                   
                   
                 New PVC Technology 
                 2.0′ 
                 0.31 
                 0.12 
               
               
                   
                   
                 NFPA 262 Requirements 
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Flame Spread 
                 5.0′ or less 
               
               
                   
                   
                 Peak Smoke 
                 0.50 or less 
               
               
                   
                   
                 Average Smoke 
                 0.15 or less 
               
               
                   
                   
               
            
           
         
       
     
     The above test was performed using the present cable  10  arrangement with a cross filler, using FEP pairs  20  and 2 FRPP pairs  20  with a 15 mil overall jacket of a PVC based plenum rated jacket compound. 
     As seen from the above Table 1, PVC cross filler  30  exhibited improved performance in all test criteria versus a similarly arranged FR olefin cross filler, while being significantly less costly than either an FR olefin cross filler or an FEP cross filler. Such a cross filler  30  may be used in a cable  10 , in place of either FR olefin cross fillers to provide better flame, smoke, or cost performance or in place of FEP cross fillers to save significant costs while maintaining the comparable flame and smoke performance. In fact, because the improved cross filler  30  passes the NFPA standard by such a margin, other exemplary designs of the present cable  10  using only 1 FEP pair  20  or even no FEP pairs  20  (all FRPP) would likely also pass the NFPA 262 fire and smoke standards. 
     While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will 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.