Method of forming metal fiber mat/polymer composite

• US 5,226,210 A
• Filed: 01/21/1992
• Issued: 07/13/1993
• Est. Priority Date: 01/23/1989
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Tucker, Pamela S., Koskenmaki, David C., Calhoun, Clyde D., Lambert, Robert L. Jr.
• Primary Examiner(s): Arbes, Carl J.
• Application Number:
  US07/823,151
• Time in Patent Office: 539 Days
• Field of Search: 29/527.5, 29/527.1, 428/594, 428/608, 428/626, 428/138, 428/256, 428/373, 174/35 MS
• US Class Current: 29/527.5
• CPC Class Codes: B29C 70/086 and with one or more layers of pure plastics material, e.g. foam layers applying a non-preformed coating, e.g. a gel-coat, B29C37/0025; with foam blocks B29C70/86
• CPC Class Codes: B29C 70/088 and with one or more layers of non-plastics material or non-specified material, e.g. supports
• CPC Class Codes: B29C 70/12 using fibres of short length, e.g. in the form of a mat non-woven fabrics per se D04H1/00
• CPC Class Codes: B29C 70/508 and first forming a mat composed of short fibres
• CPC Class Codes: B29C 70/885 with incorporated metallic wires, nets, films or plates as lost heating elements B29C35/0272, B29C61/0625
• CPC Class Codes: B29K 2105/12 of short lengths, e.g. chopped filaments, staple fibres or bristles
• CPC Class Codes: B29K 2305/00 Use of metals, their alloys or their compounds, as reinforcement
• CPC Class Codes: B29K 2705/00 Use of metals, their alloys or their compounds, for preformed parts, e.g. for inserts
• CPC Class Codes: B29K 2995/0005 Conductive
• CPC Class Codes: B32B 15/02 Layer formed of wires, e.g. mesh
• CPC Class Codes: H01B 1/22 the conductive material comprising metals or alloys
• CPC Class Codes: H05K 9/009 comprising electro-conductive fibres, e.g. metal fibres, carbon fibres, metallised textile fibres, electro-conductive mesh, woven, non-woven mat, fleece, cross-linked
• CPC Class Codes: Y10T 29/49988 Metal casting
• CPC Class Codes: Y10T 428/12347 Plural layers discontinuously bonded [e.g., spot-weld, mechanical fastener, etc.]
• CPC Class Codes: Y10T 428/12444 Embodying fibers interengaged or between layers [e.g., paper, etc.]
• CPC Class Codes: Y10T 428/12583 Component contains compound of adjacent metal
• CPC Class Codes: Y10T 442/655 Metal or metal-coated strand or fiber material

Abstract

The present invention provides a metal/polymer composite comprising a polymeric substrate and a sintered mat of randomly-oriented metal fibers embedded therein, the fibers having a substantially circular cross-section and a diameter of about 10 to 200 μm. The polymeric substrate is typically a thin, flexible sheet-like material having a pair of planar surfaces. The polymeric substrate is preferably thermoformable. If thermoformability is desired the metal will have a melting point of less than the thermoforming temperature of the polymeric substrate. The thermoformable metal/polymer composite of the present invention may be stretched to at least 20%, and often can be stretched at least 200% of its original dimensions, at least in certain regions, without loss of electrical continuity or EMI shielding properties. The present invention also provides a method of making a metal/polymer composite and a sintered mat of randomly-oriented metal fibers.

Claims

1. A method of forming a metal/polymer composite comprising the steps of:

(a) providing a polymeric substrate; and

(b) squirting at least one fine stream of a molten metal from at least one orifice into an atmosphere;

(c) solidifying said at least one stream as a plurality of metal strands in the atmosphere above said substrate;

(d) collecting said solidified metal strands on the substrate as a loose mat of a randomly intersecting pattern of metal strands; and

(e) simultaneously embedding the loose mat into the substrate and sintering the strands of metal together at the points of intersection by passing the substrate and mat between heated rollers under pressure at a temperature less than the melting temperature of said metal.

2. The method of claim 1 wherein said molten metal is squirted from said at least one orifice at a pressure greater than P_c.

3. The method of claim 1 wherein said substrate is a thermoformable polymer and said metal having a melting point of less than the thermoforming temperature of said polymeric substrate.

4. The method of claim 1 wherein said strands have a diameter of about 25-100 μ

m.

5. The method of claim 4 wherein said strands have a diameter of about 25-100 μ

m.

6. The method of claim 1 wherein said metal is selected from the group consisting of tin, lead, bismuth, cadmium, indium, gallium, mixtures thereof and alloys of said metals containing one or more metals selected from the group consisting of zinc, aluminum, copper, silver, gold, nickel, cobalt, and iron.

7. The method of claim 1 further including the step of thermoforming said composite.

8. The method of claim 7 wherein said composite is stretched in certain regions at least 20% in one direction during thermoforming without losing substantial electromagnetic shielding properties.

9. The method of claim 7 wherein said composite is stretched in certain regions at least 20% in more than one direction during thermoforming without losing substantial electromagnetic shielding properties.

10. A method of forming a metal/polymer composite comprising the steps of:

(a) squirting at least one fine stream of a molten metal from at least one orifice into an atmosphere;

(b) solidifying said at least one stream as a plurality of metal strands in the atmosphere above the substrate;

(c) collecting said solidified metal strands on a support forming a loose mat of a randomly intersecting pattern of metal strands;

(d) passing said loose mat between two heated rollers at a temperature which is less than the melting temperature of the metal thereby sintering the strands of metal together at points of intersection to form a sintered mat; and

(e) laminating said sintered mat to a polymeric substrate at a temperature below the melting temperature of said metal.

11. The method of claim 10 wherein said substrate is thermoformable, said metal having a melting point of less than the thermoforming temperature of said polymeric substrate.