Abstract:
The disclosure describes a method of sealing the ends of fabric on a radio frequency interference (RFI) gasket and a description of the gasket made by such method The method used electrically conductive material to cover a foam interior and then sealing the exposed ends of all six sides of the covering, creating a radio frequency interference (RFI) gasket

Description:
[0001]    This application claims priority from Provisional Application No 60/188,409b titled “Sealed End Gasket” filed on Mar. 10, 2000, the disclosure of which incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The invention relates generally to gaskets and more particularly to a method to seal the ends of the fabric in a radio frequency interference (RFI) gasket and the gasket made by such method.  
           [0004]    2. Description of the Prior Art  
           [0005]    Conventional RFI shielding gaskets are formed with an electrically conductive fabric outer covering over a foam interior. Conventional die-cut fabric over foam gaskets typically have an open end in the fabric which can permit RF leakage One way to reduce leakage is by sealing the ends of all six sides. This can be done by creating complex fabric shapes and folding and sealing the complex shape over the foam. This results in high labor costs and reduces output over time It also results in the waste of the electrically conductive fabric.  
           [0006]    Accordingly, it is desirable to provide an improved shielding gaskets with sealed ends which overcomes drawbacks of the prior art  
         SUMMARY OF THE INVENTION  
         [0007]    Generally speaking, in accordance with the invention, a fabric over foam gasket and method of construction are provided. The fabric can be disposed around a foam body, and the ends can be heat sealed or sealed with an adhesive to provide high shielding properties To form gaskets in accordance with the invention, a length of electrically conductive fabric is extended, a foam body is disposed on the fabric with edge portions of the fabric extending sideways beyond the edge of the foam body. The edge portions are then folded over the foam body and joined, such as by heat sealing. The fabric is then cross-cut and the cross-cut ends are sealed, such as by adhesive or heat sealing to provide a foam gasket completely covered with conductive fabric. The cutting and sealing can be accomplished in a single step with a hot knife. The fabric covered foam can then be die cut to the shape of the foam gasket and the outer edges will remain completely covered with the fabric.  
           [0008]    A gasket in accordance with preferred embodiments of the invention preferably comprises an inner supporting structure having a top, a bottom, a pair of sidewalls in the length direction extending from the top to the bottom and a pair of sidewalls in the width direction extending from the top to the bottom and fabric, preferably having conductive properties, covering the top, the bottom, the pair of sides in the width direction and the pair of sides in the length direction. The fabric preferably extends continuously from the top, to the sides in the length direction to the bottom and is sealed at the sides in the width direction and the gasket preferably has electric wave shielding properties.  
           [0009]    A preferred method of forming a gasket in accordance with preferred embodiments of the invention preferably comprises providing a length of fabric preferably having electrically conductive properties having a top surface and a bottom surface and first and second edge regions extending in the length direction and adhesive on a portion of the top surface along at least a first edge region and repeated adhesive stripes extending at least partially from edge to edge on the top surface, perpendicular to the length direction, disposing casket bodies between the repeated adhesive stripes extending in the edge to edge direction between the first and second edge regions; folding the second edge region of the fabric over the top of the gasket body and folding the first edge, which has adhesive on the top surface thereof over the gasket body, such that the adhesive on the top surface of said other side is in contact with what had been the bottom surface of the second edge region; cutting the fabric cross-wise at the adhesive stripes, the cut location intermediate the adhesive stripe; and sealing the adhesive in the cross-wise direction, to provide a fabric covered gasket in which the fabric covers the top, bottom sides in the width direction and sides in the length direction of the gasket body The fabric covered body can then be die cut and the edges will have fabric covering to provide effective shielding capabilities.  
           [0010]    Accordingly, it is an object of the invention to provide an improved RF shielding gasket.  
           [0011]    Another object of the invention is to provide electrically shielding gaskets in a more convenient and simple manner.  
           [0012]    The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and in the article possessing the features, properties and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a fuller understanding of the invention, references had to the following description, taken in connection with the accompanying drawings, in which FIG. 1 is a top plan view of a die cut fabric over foam gasket in accordance with an embodiment of the invention;  
         [0014]    [0014]FIG. 2 is a side view of a die cut fabric over foam gasket in accordance with an embodiment of the invention;  
         [0015]    [0015]FIG. 3 is an end cross sectional view along line  3 - 3  of FIG. 1, of a die cut fabric over foam gasket in accordance with an embodiment of the invention, and  
         [0016]    [0016]FIG. 4 is a top plan view illustrating the manufacture of gaskets in accordance with an embodiment of the invention 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    A die cut fabric over foam gasket in accordance with a preferred embodiment of the invention is shown generally as gasket  100  in FIGS.  1 - 3 . Gasket  100  is formed with a foam inner portion  110  and an electrically conductive fabric  120  disposed around inner foam portion  110 . Gasket  100  also includes ends  130   a  and  130   b  where the fabric has been sealed, as shown most clearly in FIG. 2. Gasket  100  also includes an overlap section  140 , best seen in FIG. 3, where edges of fabric portion  120  overlap and are joined by an adhesive  150   
         [0018]    In a preferred embodiment of the invention, the overall width of gasket  100  is 1.20 inches, the overall length is 12 125 inches, and the thickness is 0.312 inches A rectangular portion 0.606 inches in width is cut out from foam portion  110 , to leave a picture frame shape with 0.312 inch sides. Ends  130   a  and  130   b  are 0.125 inches wide. Shielding up to and in excess of 120 dB @ 1 GHz can be achieved. The gasket is well suited for use at the I/O panel of an electrical device such as a computer.  
         [0019]    Foam portion  110  is preferably formed from any number of urethane or neoprene foams which are well known in the industry. Fabric  120  can be formed from various known types of electrically conductive fabric. For example, fabric in which the individual threads are plated with conductive material, such as silver, where the entire outer surface of the fabric is plated with conductive material, such as a copper/nickel alloy or where some other arrangement is provided so that the fabric has radio frequency interference shielding properties is suitable The adhesives are preferably selected from a wide variety of known adhesives, preferably heat activated adhesives, selected to be compatible with the fabric and foam.  
         [0020]    A preferred non-limiting method of forming end sealed die cut fabric over foam gaskets in accordance with preferred embodiments of the invention is illustrated generally in FIG. 4. A length of fabric  410  having side edges  411   a  and  411   b  is withdrawn from a roll At least one of side edges  411   a  and  411   b , such as side edge  411   a  is preferably pre-coated with an adhesive, such as a heat-activated adhesive  415 . Alternatively, adhesive  415  can be disposed after the fabric is unrolled or on the bottom of the fabric. Fabric  410  also includes repeated cross-stripes (or partial cross-stripes) of adhesive  417  which preferably extend from edge  411   a  to edge  411   b  perpendicular to the length of the fabric  
         [0021]    As fabric  410  travels in the direction of an arrow A, a gasket inner body  420 , preferably formed from foam, is disposed thereon, between repeating adhesive stripes  417 . Edge  411   b  is then folded in the direction of an arrow B so as to cover a portion of gasket inner body  420 . Edge  411   a  is then folded in the direction of an arrow C so as to overlap what had been an underside  411   b ′ of fabric  410  at edge  411   b , with adhesive  415  contacting underside edge  411   b ′ Adhesive  415  is then heat activated. The folding and heat activation can be performed as part of a single step, to yield a length of folded and partially sealed fabric having a plurality of gasket inner bodies  420  enclosed therein.  
         [0022]    After adhesive  415  has sealed edge  411   a  to edge  411   b  fabric  410  is cross-cut at a line  430  to divide the portion of the fabric having adhesive stripe  417  thereon into two portions The cut at line  430  can be performed with a hot knife to simultaneously sever fabric  410  and activate adhesive  417 . It should also be understood that adhesive  417  need not extend completely from edge  411   a  to edge  411   b ′, but only needs to be disposed so as to completely seal the exposed ends of fabric  410  after the cut is made along line  430 .  
         [0023]    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 scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense  
         [0024]    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