Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1997-02-20
2001-04-03
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S305500, C428S317900, C428S318400, C428S319300, C428S320200, C428S325000, C428S327000, C428S328000, C428S406000, C428S421000, C428S422000, C428S447000
Reexamination Certificate
active
06210789
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an improved, electrically conductive polytetrafluoroethylene article.
BACKGROUND OF THE INVENTION
Electromagnetic interference (EMI) has been defined as undesired conducted or radiated electrical disturbances from an electrical or electronic apparatus, including transients, which can interfere with the operation of other electrical or electronic apparatus. Such disturbances can occur anywhere in the electromagnetic spectrum. Radio frequency interference (RFI) is often used interchangeably with electromagnetic interference, although it is more properly restricted to the radio frequency portion of the electromagnetic spectrum, usually defined as between 10 kilohertz (kHz) and 100 gigahertz (GHz).
A shield is defined as a metallic or otherwise electrically conductive configuration inserted between a source of EMI/RFI and a desired area of protection. Such a shield may be provided to prevent electromagnetic energy from radiating from a source. Additionally, such a shield may prevent electromagnetic energy from entering a shielded system. As a practical matter, such shields normally take the form of an electrically conductive housing which is electrically grounded. The energy of the EMI/RFI is thereby dissipated harmlessly to ground.
Necessarily, most housings for electrical equipment are provided with access panels, hatches, doors or removable covers. Gaps which form between the panels, hatches, doors or removable covers provide an undesired opportunity for electromagnetic energy to leak into the shielded system. Such gaps also interfere with electrical current running along the surfaces of a housing. For example, if a gap is encountered, the impedance of the gap is such that electromagnetic energy may radiate from an opposed side of the gap, much like a slot antenna.
Various configurations of gaskets have been developed over the years to close the gaps of such shields and to effect the least possible disturbance of the ground conduction currents. Each seeks to establish as continuous as possible electrically conductive path across the gap(s). However, there are inevitable compromises between: the ability of the gasket to smoothly and thoroughly engage and conform to the surface of the housing adjacent the gaps; the conductive capacity of the gasket; the ease of mounting the gasket; and the cost of manufacturing and installing the gasket.
Presently, many electronic devices, such as but not limited to, pocket pagers, cellular phones, laptop computers and wireless local area networks (LANS) are constructed using metallized plastic injection molded housings which are not manufactured to exact tolerances. Therefore, gaps form about the seams of an individual housing. Typically, in such devices mating housing members incorporate a snap-together method of closure, or in other instances, a limited number of light gauge screws are utilized to provide housing closure. Accordingly, most electronic devices having metallized plastic injected molded housings do not require substantial closure force to assemble a respective housing. Any shielded gasket which is incorporated into such electronic devices must be deformable or extremely conductive under a low compression force.
Conventionally, conductive particle filled silicone elastomers have been utilized as conductive gaskets to reduce EMI and RFI. However, such materials tend to be relatively hard (e.g. Shore A hardness of about 60 or greater). Because of their hardness, conductive particle filled silicone elastomers are not well suited for use as a gasket in a device having a housing which is assembled with a substantially low closure force. Additionally, conductive particle filled silicone elastomers are difficult to manipulate when die cut into a thin gasket.
Other EMI/RFI shielding gaskets have been proposed which incorporate a conductive fabric or mesh which surrounds a soft, conformable foam material. Examples of such gaskets are disclosed in U.S. Pat. Nos. 5,028,739; 5,115,104; 4,857,668; 5,045,635; 5,105,056; 5,202,526; and 5,294,270. Although the gaskets disclosed in the foregoing U.S. patents may be deformable under a low compression force, these gaskets do not have continuous conductivity throughout the material. Therefore, these gasket materials cannot be die cut into arbitrary shapes to function as an EMI/RFI gasket.
Seemingly, what the prior art lacks is an improved electrically conductive material which is extremely conductive under a low compressive load, and which is conformable and continuously conductive throughout the structure of the material such that the material is operable, in one application, to provide EMI shielding, in a frequency range from about 10 MHz to about 20 GHz, when used as a gasket between conductive seams.
SUMMARY OF THE INVENTION
The present invention relates to an electrically conductive composite article. The electrically conductive composite article is defined by a main body having a predetermined shape. The main body consists of a polytetrafluoroethylene material and a plurality of electrically conductive particles. Disposed within the main body is an elastomer material. The electrically conductive composite article of the present invention is permanently and continuously electrically conductive throughout its entire structure.
The electrically conductive particles may be selected from a group consisting of: metal powder, metal bead, metal fiber, metal flake, metal coated fiber, metal coated metals, metal coated ceramics, metal coated glass bubbles, metal coated glass beads, and metal coated mica flakes.
Suitable elastomer materials include but are not limited to: silicone elastomers, silicone rubbers, fluorosilicone elastomers, fluorocarbon elastomers, perfluoro elastomers, fluoroelastomers, polyurethane, or ethylene/propylene (EPDM).
It is, therefore, a purpose of the present invention to provide an improved, continuously electrically conductive polytetrafluoroethylene article for use in a variety of applications requiring a flexible and continuously electrically conductive material throughout the entire structure of the article.
It is also a purpose of the present invention to provide an improved electrically conductive material for use as an EMI shielding gasket.
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Chen Vivian
W. L. Gore & Associates, Inc.
Wheatcraft Allan M.
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