Method for manufacturing electro-magnetic shield having multiple polymeric layers of differing fill compositions

• US 5,714,102 A
• Filed: 04/20/1995
• Issued: 02/03/1998
• Est. Priority Date: 01/02/1992
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Highum, Edward Allan, Mueller, Alfred Wilhelm, Nash, Thomas William, Stadler, Ewald Emil Gottlob, Thorvilson, Scott Marvin
• Primary Examiner(s): Ortiz, Angela Y.
• Application Number:
  US08/425,271
• Time in Patent Office: 1,020 Days
• Field of Search: 264/332, 264/109, 264/272.19, 264/105, 264/255, 264/328.8
• US Class Current: 264/105
• CPC Class Codes: B29C 45/0013 using fillers dispersed in the moulding material, e.g. metal particles
• CPC Class Codes: B29C 45/1642 having a "sandwich" structure B29C45/1603 takes precedence
• CPC Class Codes: B29C 70/882 partly or totally electrically conductive, e.g. for EMI shielding conductive floors or floor coverings H05F3/025; EMI shielding in general H05K9/00
• CPC Class Codes: B29K 2105/16 Fillers
• CPC Class Codes: B32B 2262/106 Carbon fibres, e.g. graphite fibres
• CPC Class Codes: B32B 2270/00 Resin or rubber layer containing a blend of at least two different polymers
• CPC Class Codes: B32B 2307/202 Conductive
• CPC Class Codes: B32B 2307/208 Magnetic, paramagnetic
• CPC Class Codes: B32B 2307/212 Electromagnetic interference shielding
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/18 characterised by the use of special additives
• CPC Class Codes: B32B 27/302 comprising aromatic vinyl (co)polymers, e.g. styrenic (co)polymers
• CPC Class Codes: B32B 27/365 comprising polycarbonates
• CPC Class Codes: B32B 5/00 Layered products characterised by the non- homogeneity or physical structure , i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
• CPC Class Codes: B32B 7/02 Physical, chemical or physicochemical properties
• CPC Class Codes: H05K 9/0088 comprising a plurality of shielding layers; combining different shielding material structure
• CPC Class Codes: Y10T 428/1359 Three or more layers [continuous layer]

Abstract

An enclosure for an electronic device forms a barrier to electro-magnetic radiation. A typical cross-section of the enclosure comprises three parallel layers. The outer and inner surface layers are of a polymeric base material in which is suspended an electrically conductive fill material, giving the surface layers relatively high electrical conductivity. The middle layer is of a polymeric base material, in which is suspended fill material having high magnetic permeability, giving the middle layer relatively high magnetic permeability. In the preferred embodiment, the enclosure is constructed using a co-injection molding process. Nickel-coated graphite (high conductivity) in a polymeric base is injected into a mold from the outer co-injection nozzle, while carbonyl iron powder (high permeability) in a polymeric base is injected into the mold from the inner co-injection nozzle. The resultant molded structure contains the three layers described above, yet can be made inexpensively in a single co-injection molding operation. The enclosure may comprise multiple co-injection molded pieces, which are attached together by any of various conventional means.

Claims

1. A method for manufacturing a multiple layer electro-magnetic shielding structure, comprising the steps of:

providing an injection mold of suitable shape for said structure;

loading an electrically conductive fill material suspended in a polymeric base material in a hopper for an outer nozzle of a co-injection molding press;

loading a magnetically permeable fill material suspended in a polymeric base material in a hopper for an inner nozzle of a co-injection molding press;

forming said structure by injecting into said injection mold with said outer nozzle said electrically conductive fill material suspended in a polymeric base material thus forming outer layers of the structure, concurrently with injecting into said injection mold with said inner nozzle said magnetically permeable fill material suspended in a polymeric base, thus forming an inner layer of the structure.

2. The method of claim 1, wherein said magnetically permeable fill material comprises carbonyl iron powder.

3. The method of claim 1, wherein said electrically conductive fill material comprises nickel-coated graphite fibers.

4. The method of claim 1, wherein said polymeric base materials each comprises a blend of ABS and polycarbonate.