Abstract:
A cable shield and method of formation, more specifically, a closure including an adhesive strip on two surfaces, which is dry to the touch and which will adhere to the complementary adhesive strip, but substantially nothing else.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to cable shields and more particularly to a cable shield closed with an adhesive composition. 
     It is known to cover cables that carry electrical signals with RF or electromagnetic (hereinafter collectively “RF”) shields formed, for example, with conductive fabric or foil overwraps that are closed or sealed by various methods. Some methods employ snap buttons, but this can lack permanence and can be lead to leakage between the snap points. Other closures employ zippers, hook and loop closures and rib-in-groove closures. However, such closures also lack sufficient permanence or durability and can lead to unsatisfactory RF shields. 
     It is also known to close cable shields with adhesives. Some adhesive are applied in a liquid state and can be inconvenient to use. Others are covered with release strips, but can be difficult to use if the adhesive coated portion unintentionally contacts the wrong location of the cable shield, or some other object such that repositioning can be difficult and closures having a sloppy appearance, loose or too fight a fit or unsatisfactory shielding can result. 
     Accordingly, it is desirable to provide an improved cable shield and method of closing the cable shield, which overcomes disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     Generally speaking, in accordance with the invention, a cable shield is provided in the form of a sheet having top and bottom surfaces and can include permanent adhesive compositions at edges thereof which can be dry to the touch and which will only bond at the desired location. Adhesives in accordance with preferred embodiments in the invention can also stay unbonded or weakly bonded for sufficiently long periods of time to permit readjustment of the closure, so that the desired fit can be achieved. 
     The shield can be formed as an elongated sheet with a top/inner surface which will wrap around the cable and a bottom, outer surface, which will face outwards from the cable. The adhesive composition can be disposed as a thin strip at least along one edge of the upper surface of the shield, and as a corresponding complementary thin strip on the lower surface, along the opposite edge, so that when the shield is wrapped around the cable, the strips of the adhesive composition can be contacted to each other. The adhesive is advantageously a pressure sensitive type of adhesive, which can be permanent in nature, which can be formed with a mixture of solid particles in sufficient volume or location that the adhesive will be dry to the touch and substantially only bond to another surface containing the same or similar adhesive. Thus, the solid particles can occupy sufficient area of the surface, so that there is substantially no adhesive bonding when the adhesive contacts most materials. However, when a first coat of adhesive contacts a second surface coated with the adhesive, and pressure is applied, sufficient deformation of the adhesive layers is achieved, such that the pressure sensitive adhesive materials from each coating portion come in contact with each other and the two layers bond together. By using electrically conductive solid particles, such as metallic particles, the adhesive bond itself can be made electrically conductive and improve the RF shielding properties of the closure. 
     Accordingly, it is an object of the invention to provide an improved cable shield. 
     Another object of the invention is to provide an improved method of making and closing a cable shield. 
     The invention accordingly comprises the several steps and the relation of one and more of such steps with respect to each of the others, and the article possessing the features, properties, and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the intentional will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference is had to the following description, taking in connection with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a cable shield with a closure, in accordance with preferred embodiments of the invention; 
     FIG. 2 is a cross-sectional view of a cable shield in accordance with preferred embodiments of the invention; and 
     FIG. 3 is a perspective view of the cable shield of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A cable  10  having a cable shield  100  disposed thereover is shown in FIG.  1 . Cable  10  is constructed to transmit an electrical signal. Cable shield  100  is constructed to act as a RF shield, for the purpose of shielding RF emissions from cable  10  or preventing cable  10  from being subjected to RF interference from other sources. 
     Cable shield  100  is formed with an overwrap portion  120  in the form of a sheet elongated in the length direction of the cable and is closed with an adhesive portion  110 . Overwrap  120  can be formed with various known conductive fabrics, foils, or metallized fabrics or elastomers. Adhesive  110  is advantageously a pressure sensitive type of adhesive which is normally dry to the touch, will not adhere to most surfaces, including the surface of overwrap  120  and which will bond to a corresponding complementary adhesive coating when pressure is applied. 
     An open cable shield  200 , constructed in accordance with preferred embodiments of the invention is shown generally in FIGS. 2 and 3, which along with FIG. 1, are not necessarily drawn to scale. Cable shield  200  includes an overwrap portion  220  which includes an upper inner surface  220   b  and a lower, outer surface  220   a.  A strip of adhesive component  210   a  is formed on outer surface  220   a  along edge  221  of overwrap  220  and a matching strip of adhesive component  210   b  is formed on inner surface  220   b  of overwrap  220 , along an edge  222 , opposite edge  221 . In use, edge  221  of overwrap  200  is curved up and around a cable, in the direction of arrow A. Opposite edge  222  is drawn up and around a cable, in the direction of arrow B, such that adhesive strip  210   a  is made to contact adhesive strip  210   b.  In another embodiment of the invention, adhesive strip  210   a  can be formed on inner surface  220   b  of overwrap  220  and adhesive strip  210   b  can be formed on outer surface  220   a,  along edge  222  of overwrap  220 . The adhesive strips can also be formed on both sides along one edge or over the entire surface. It is advantageous, but not mandatory that the two complementary adhesive strips are formed on opposite surfaces of the shield so that the edges of the shield lay flat when the two adhesive strips are contacted. 
     Adhesive  110  is advantageously dry to the touch and will not adhere to most surfaces as a result of, for example, of the inclusion of sufficient solid particles in the adhesive material, so that there is insufficient bonding surface exposed. However, when a coating of the adhesive of a first surface is contacted to a complementary coating of adhesive on a second surface and pressure is applied, there is sufficient deformation of the adhesive layers, such that the pressure sensitive adhesive material from each coating comes in contact and bonds the two layers together. By forming the solid particles from electrically conductive material, such as metal particles, the bond itself can be later conductive. 
     In one embodiment of the invention, the adhesive is provided as two portions which are pressed together to close the shield around a cable. Both of the portions can contain a pressure sensitive adhesive, such as a silicone, acrylic, or rubber composition filled with solid particles. In this manner, adhesive strips can be coated along opposite edges of the shield and such edges will bond to each other, but not the uncoated portion of the shield. In one embodiment of the invention, the uncoated portion of the shield can be coated with release agent, such as various known release agents, to help prevent forming a bond at an undesired location. 
     It is also advantageous to formulate the adhesive to have a suitable time before the bond becomes permanent, to permit adjustments, after the opposing adhesive strips are contacted. A weak, temporary bond is formed when the adhesive strips contact. They may be separated and repositioned. Only after firm pressure is applied will the bond become permanent. 
     Various known pressure sensitive adhesive materials can be used in formulating the adhesive in accordance with the invention. Suitable non-limiting examples of adhesive materials include silicones, acrylics, thermoplastic elastomers, and rubbers. A particularly well suited adhesive is a silicone based adhesive, sold under the tradename Q2 7406 from Dow Corning of Midland, Mich. Additional components may be mixed with the adhesive including curing agents, solvents, coupling agents, and colorants. A particularly well suited coupling agent is an aminosilane coupling agent, sold under the tradename Z6020, by Dow Corning of Midland, Mich. 
     Examples of solvents and diluents include xylene, toluene, and methyl chloroform. A particularly preferred solvent is xylene. 
     Various known powders can be used to formulate adhesive in accordance with the invention, including glass beads, metal particles, metallized particles, and non-metal particles such a graphite. Preferred powders are silver powders and in particular, silver powders sold under the trade designation NX4005, by Engelhard of East Newark, N.J. The particles sizes preferably range from 1 μm to 50 μm. The particles preferably comprise 30% to 70% by volume of the adhesive composition. 
     The width and height of the adhesive strips depend in part on the type, size and use of the closure. For many application, strips 0.1 inch to 2 inches wide and strips 0.002 inch to 0.040 inches high are acceptable. In general, the width of the two complementary strip is substantially equal. 
     Suitable adhesives are described in French patent no. 2698876, the contents of which are incorporated herein by reference. A particularly well suited adhesive is the Dry-Touch Conductive Adhesive sold by Altoflex of France. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the article set forth, without departing from the spirit and the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings, should be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween 
     Particularly, it is too be understood that in said claims, ingredients are compounds recited in the singular are intended to include compatible mixtures of such ingredients wherever the sense permits.