GB2222912A

GB2222912A - Electromagnetic interference gasket

Info

Publication number: GB2222912A
Application number: GB8920203A
Authority: GB
Inventors: Haruo Shizukuda; Hiroaki Yamaguchi; Yujiro Saitch
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1988-09-16
Filing date: 1989-09-07
Publication date: 1990-03-21
Also published as: KR900005495A; DE3930818A1; GB8920203D0; JPH0283998A

Description

1.

.. r rt r 9 ' e.' 22-2 12 ELECTROMAGNETIC INTERFERENCE GASKET The present invention generally relates to a gasket for shielding movable parts of a container, such as a lid or door for a computer or communications instrumentation, from electromagnetic interference, and more particularly to a gasket in which an elastic member, such as silicon rubber or polyurethane, is covered by a conductive layer of metal.

Electromagnetic gaskets have been adapted for use on moving parts of a container (such as a door for a computer) in order to seal the moving part. The gasket must be sufficiently conductive to shield the container from electromagnetic interference. Moreover, since the position of the gasket is between the container and the lid or door, it receives repeated compression and deformation. Accordingly, the gasket must also have sufficient durability to withstand repeated compression and deformation.

A prior art electromagnetic gasket 7 is shown in Figure 5, in which an elastic member 8 is covered by a layer 9 made of a conductive metal. The outer periphery of elastic member 8 (neoprene or silicon rubber) is surrounded by a knitted layer 9 which is made of conductive, solid wires, such as monel, aluminum or copper plated wire knitted into loops. In order to increase the ability to shield against electromagnetic interference, it is beneficial to increase the conductivity of cover layer 9. That is to say, it is beneficial to increase the density of the knit. In increasing the knit density, however, cover layer 9 becomes hard on account of the rigidity of the conductive solid wire. As a result, although the conductivity of the cover layer increases, the the wire becomes is conformability of the cover layer decreases. Therefore. in the prior art electromagnetic interference gasket, the conductivity and conformability are compromised. In other words, the prior art gasket has inadequate shielding ability and inadequate conformability, and thus has a drawback since the scope of use of the gasket is limited.

Moreover, because the cover layer 8 is a knitting of conductive metal wire formed into loops, entangled as the gasket is compressed, so that an excessive bending deformation is added to a part of the metal wire. As a result, that part of the metal wire is extremely deformed, and often breaks. It would, therefore, be desirable and advantageous to devise a gasket overcoming the above disadvantages.

Accordingly, the primary object of the present invention is to provide an electromagnetic interference gasket which is superior in its capacity to shield against electromagnetic interference and in its conformability, and which has a sufficient durability against repeated compression or bending deformation.

The foregoing objects are achieved in an electromagnetic interference gasket comprising a ropelike elastic member and a cover layer enclosing the elastic member, made of a conductive metal. The cover layer is constructed of a loose plain fabric of a compound metal thread which is made by spirally winding a conductive film on a flexible core. The winding of the conductive film on the core preferably includes a pitch winding which has a gap between adjacent films. It is preferable that the rope-like elastic member be made of silicon rubber and the flexible core be made of glass fibers.

4 1 The novel features of the invention are set forth in the appended claims. The invention itself, however, will best be understood by reference to the accompanying drawings, wherein:

Figure 1 is a perspective view of an electromagnetic interference gasket according to the present invention.

Figure 2 is a perspective view of a compound metal thread forming a conductive metal cover layer of the electromagnetic interference gasket according to the invention.

Figure 3 is a graph showing a result of a comparison experiment concerning the shielding ability against electromagnetic interference between an embodiment of the electromagnetic interference gasket according to the present invention and that of the prior art gasket.

Figure 4A and 4B are elevational views of the cover layer of the electromagnetic interference gasket according to the invention; Figure 4B shows the state after compression and deformation.

Figure 5 is a perspective view of a prior cart electromagnetic interference gasket.

1 An electromagnetic interference gasket 1 shown in Figure 1 comprises a rope-like elastic member 3 and a cover layer 2 made of a conductive metal enclosing elastic member 3. Cover layer 2 is a loose plain fabric having a gap between adjacent threads thereof and is made of a compound metal thread 4 (Figure 2), in which a conductive film 6 is spirally wound around a flexible core 5. The spiral winding of conductive film 6 on core 5 in compound metal thread 4 is, as shown in Figure 2, a winding having a gap between adjacent films, i.e., a pitch winding.

The graph of Figure 3 shows a comparison in results of the shielding ability (attenuation) of the electromagnetic interference gasket of the present invention and a prior art gasket having the same dimension as the inventive gasket. The solid line (designated by reference letter A) represents the present invention, while the dashed line (reference letter B) represents the prior art gasket. The gasket of the present invention tested comprises an elastic member 3 made of silicon rubber having a diameter of 6 millimeters, and a cover layer 2 constructed of a plain fabric of a compound metal thread which comprises a glass fiber which is 150 strand and two

C folded yarn, and a tin plated copper film having a width of 0.32 mm and a thickness of 27 micrometers. The tin plated copper film is wound around the glass fiber with 22 turns per centimeter length of glass fiber. The comparison has been conducted by the KEC method (Kansai Electro-Industry Promotion Center method). As apparent f rorn the graph, the electromagnetic interference gasket of the present invention has superior electromagnetic shielding ability in comparison with the prior art gasket.

In the preferred embodiment, the compound metal thread forming the cover layer is made by spirally winding the conductive metal film around the f lexible core with a gap between adj acent f ilms, i. e., a pitch winding. The compound metal thread thereby has a rich flexibility in comparison with the prior art solid metal wire. Accordingly, even if the density of weave of the cover is increased, the hardening of the cover layer is small and it is possible to maintain the conformability in good state and it is also possible to increase the density of weave of the coverto increase the conductivity of the cover layer. Moreover, because the compound metal thread is a thread in which the conductive metal film

1, &W is made like a coil spring, it has a large durability against the bending deformation in comparison with solid metal wire.

Further, as the cover layer is made by the loose plain fabric having gaps between the threads, the texture of the loose plain f abric of the cover layer can be easily slid in a diamond form when the electromagnetic interference gasket is compressed. As a result, as the bending deformation to be applied to the compound metal thread itself forming the cover layer is reduced, the durability of the electromagnetic interference gasket can be improved. Also, it is possible to improve the conformability.

When silicon rubber is used as the rope-like elastic member and glass fiber is used as the flexible core of the compound metal thread, the electromagnetic interference gasket has a high thermal resistance. Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover such modifications that fall within the true scope of the invention.

Claims

CLAIMS:

is 1. An electromagnetic interference gasket comprising:

rope-like elastic member; and cover layer enclosing said elastic member, said cover layer being constructed of a loose fabric of a compound metal thread formed by spirally winding a conductive film on a flexible core.
2. The electromagnetic interference gasket of Claim 1 wherein the winding of said conductive film on said flexible core includes a pitch winding having a gap.
3. The electromagnetic interference gasket of Claim 1 or 2 wherein said rope-like elastic member is made of silicon rubber and said flexible core is a glass fiber.
4. An electromagnetic interference gasket as claimed in Claim 1 substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings.

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