Abstract:
The present invention provides insulation for a wire that comprises a main body configured to cover the wire where the main body has an inner surface that abuts the wire, an outer surface opposite the inner surface, and an insulation cross-sectional area defined between the inner and outer surfaces. A plurality of foamed sections are disposed in the insulation cross-sectional area of the main body. At least one solid section is disposed in the insulation cross-sectional area of the main body, wherein the plurality of foamed sections form at least 45% of the insulation cross-sectional area.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 61/262,366, filed Nov. 18, 2009. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to insulation for wires, particularly wires in twisted pairs of data communication cabling. More specifically, the insulation may have both foamed and solid sections shaped and arranged such that a minimal amount of solid material is used while also providing insulation that resists crushing. 
       BACKGROUND OF THE INVENTION 
       [0003]    Data cables typically include a core of twisted wire pairs with each individual wire being insulated. When foam insulation is used, crushing of the insulation often occurs when the wire pairs are twinned or twisted together which can result in unwanted reduction in conductor-to-conductor spacing. That is because foam is physically weaker in tensile and compressive strength than solid insulation. Also, in current foaming methods, it is often difficult to control foam percentages within the extrusion operation due to a multitude of factors, such as back pressure, melt strength, and catalyst integration. In addition, during normal extrusion processes, such as pressure extrusion, it is not possible to create advantageous shapes on the insulated conductor. That is because pressure extrusion makes adding channels and shapes very difficult around wires. Solid insulation, however, is typically more expensive and often fails flame testing because it generates much more smoke than foamed materials. 
         [0004]    Therefore, a need exists for a wire insulation that is less expensive, passes flame twisting, and also avoids crushing. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, the present invention provides insulation for a wire that comprises a main body configured to cover the wire where the main body has an inner surface that abuts the wire, an outer surface opposite the inner surface, and an insulation cross-sectional area defined between the inner and outer surfaces. A plurality of foamed sections are disposed in the insulation cross-sectional area of the main body. At least one solid section is disposed in the insulation cross-sectional area of the main body, wherein the plurality of foamed sections form at least 45% of the insulation cross-sectional area. 
         [0006]    The present invention also provides insulation for a wire that comprises a main body configured to cover the wire where the main body has an inner surface that abuts the wire, an outer surface opposite the inner surface, and an insulation cross-sectional area defined between the inner and outer surfaces. A plurality of foamed sections are disposed in the insulation cross-sectional area of the main body. At least one solid section is disposed in the insulation cross-sectional area of the main body, wherein the at least one solid section is a center material that substantially covers the circumference of the wire. 
         [0007]    The present invention further provides insulation for a wire that comprises a main body configured to cover the wire where the main body has an inner surface that abuts the wire, an outer surface opposite the inner surface, and an insulation cross-sectional area defined between the inner and outer surfaces. A plurality of foamed sections are disposed in the insulation cross-sectional area of the main body. At least one solid section is disposed in the insulation cross-sectional area of the main body, wherein the at least one solid section is a peripheral material that encompasses substantially the entire insulation cross-sectional area at the outer surface of the main body. 
         [0008]    The present invention also provides a twisted pair of first and second wires that comprises a first insulation that covers the first wire. The first insulation has a main body configured to cover the first wire, the main body has an inner surface that abuts the first wire, and an outer surface is opposite the inner surface. An insulation cross-sectional area is defined between the inner and outer surfaces. A second insulation covers the second wire. The second insulation has a main body configured to cover the second wire, the main body has an inner surface that abuts the second wire, and an outer surface is opposite the inner surface. An insulation cross-sectional area is defined between the inner and outer surfaces. A plurality of foamed sections are disposed in each of the insulation cross-sectional areas of the first and second insulations. At least one solid section is disposed in each of the insulation cross-sectional areas of the first and second insulation. The plurality of foamed sections form at least 45% of the insulation cross-sectional areas of the first and second insulations, respectively. 
         [0009]    Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawing, discloses a preferred embodiment of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing FIGURE, which is a cross-sectional view of insulation covering two wires of a wire pair. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    The insulation in accordance with the present invention mitigates the problems of foam wire insulation and solid wire insulation by leveraging the stronger solid materials in key areas within the insulation. The insulation of the present invention minimizes crushing while also maintaining the highest degree of foaming, thereby reducing costs and improving performance of the data cable for cost, performance, etc. 
         [0012]    Referring to the FIGURE, insulation  100  in accordance with an exemplary embodiment of the present invention covers wires  110  and  112 , respectively. The wires  110  and  112  are preferably twinned to form a twisted wire pair, as is well known in the art of data cabling. The insulation  100  includes a main body with an inner surface  120  that covers the individual wire  110  or  112  and an opposite outer surface  122 . Defined between the inner and outer surfaces  120  and  122  is an insulation cross-sectional area  124 . The cross-sectional area  124  may be about 18.4 mils wide, for example. The insulation  100  preferably has both foamed and unfoamed or solid sections  130  and  140  in the insulation cross-sectional area  124  that run longitudinally with respect to the wires  110  and  112 . For example, the insulation  100  may include a plurality of foamed sections  130  circumferentially arranged around the wire. The foamed sections  130  may be uniformly spaced around the wire with solid sections therebetween. Each foamed section  130  is nearly surrounded by or embedded in the solid section  140 . The dispersed arrangement of the foamed sections  130  defines solid beams  150  consisting of more rigid material running between each of the foamed sections  130  all the way from the inner surface  120  to the outer surface  122  of the insulation  100 . The foamed sections  130  may have a generally triangular cross-sectional shape; however the foamed sections  130  may have any cross-sectional shape including circular. For example, the foamed sections  130  may be about 7.5 mils long and 9 mils wide, for example. The beams  150  act as support structures helping to minimize the crushing of the foamed sections  130  and thus crushing of the insulation. 
         [0013]    In a preferred embodiment, a center material  170  of the insulation  100  is adjacent the inner surface  120  and extends around the circumference of the wire between the inner surface  120  and the foamed sections. The center material  170  is preferably nearly solid or 100% solid, as seen in the FIGURE. The center material  170  may have a width that is about 1 mil in cross-section, for example. That helps eliminate some of the issues that arise from having foam against the wire (irregular bubbles, air pockets, etc) that harm the electrical properties of the data cable. The center material  170  may be thin compared to other solid sections  140  to create a thin solid skin around the wire  110  or  112  as that is all that is needed to protect the electrical properties of the wire, thereby minimizing the use of solid material. Another desired effect of having the material  170  against the wire being all or generally solid is that adhesion to the wire is better compared to that of having only foam against the conductor. 
         [0014]    A peripheral material  180  of the insulation  100  near or closest to the outer surface  122  of the insulation  100  may also be nearly solid or 100% solid. Because the solid material is harder than the foamed material, the peripheral material  180  of the insulation thus has far better compression resistance. By maintaining a mostly solid surface at the peripheral material  180  of the insulation (for example, an area &gt;75% of the insulation&#39;s cross-section), the compression of the foam is greatly reduced as the harder material absorbs the compressive forces on the surface layer  122  of the insulation. Such compressive resistance helps prevent the crushing that happens during the twinning process, especially for foamed materials. Some foamed material  130 , however, may be exposed at portions  132  of the surface layer  122 , as seen in the FIGURE. The portions  132  may be about 1.5 mils wide, for example. That allows for easier tooling and extrusion than if the foamed sections were completely enclosed in the insulation. 
         [0015]    Although the center material  170  and the peripheral material  180  of the insulation are preferably solid, the design of the insulation  100  is such that the foam content is maximized and solid content is minimized while electrical properties are preserved and crushing is reduced. To achieve that, it is preferable that the cross-sectional surface area of the insulation  100  should consist of a minimum 45% foamed sections  130 , for example. With at least 45% foamed sections  130 , the electrical properties of the wire pair are maintained as is the desired crush resistance. Also, ease of manufacture is taken into consideration by having foamed material exposed on the surface. 
         [0016]    Adhesion along the boundaries of the foamed and solid sections  130  and  140  can be maximized in accordance with the present invention to provide better physical strength and tensile properties for the insulation  100 . As shown in the FIGURE, to achieve the surface area requirements as to the percentage of foam, the foamed sections  130  may have a tapered profile. That increases the length or overall size of the boundaries between the foamed and solid sections  130  and  140 . That also helps to increase the adhesion between the sections  130  and  140  as contact between the two is maximized, providing for a physically stronger insulation. 
         [0017]    In accordance with an exemplary embodiment of the present invention, the foamed sections  130  make up 49.5% of the insulation&#39;s cross-sectional area. That percentage could be increased by expanding the width of the foamed sections  130 . The foamed sections  130  may also be expanded at the portions  132  of the surface layer  122  of the insulation  100  while still keeping the surface area over 80% solid. Thus, the design of insulation  100  leverages higher compressive solid material in key areas to protect against crushing and reduced electrical properties. 
         [0018]    Because the insulation  100  contains a high percentage of foam, the fuel load is reduced, thus improving flame and smoke characteristics by creating air pockets where compound once existed. In addition, certain electrical characteristics like dissipation factor, attenuation, and capacitance can be improved by use of a reduced crushed foam insulation and/or a solid insulation. Also, by minimizing the use of solid materials, materials costs are significantly reduced. 
         [0019]    The materials used to make the foamed and solid sections  130  and  140  of the insulation  100  may be the same or different. For example, the foamed and solid sections  130  and  140  may be formed of FEP, HDPE, perfluoromethylvinylether (MFA), Halar, PVC, and other fluropolymers, or resins, such as Polystyrene (PS) or Ethylene Vinyl Acetate (EVA). Moreover, the foamed sections  130  may be foamed either before or after twinning the wires  110  and  112  into a twisted wire pair. 
         [0020]    While a particular embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. For example, although the design of the insulation  100  is preferably the same for both individual wires  110  and  112 , as seen in the FIGURE, the insulation for each wire may be different. That is, the shapes of the foamed and solid sections  130  and  140  for the insulation of the wire  110  may be different than the shapes of the foamed and solid sections  130  and  140  for the insulation of the wire  112 . Also, the percentage of foam and solid material may be different.