Metal fibermat/polymer composite

• US 5,869,412 A
• Filed: 08/22/1991
• Issued: 02/09/1999
• Est. Priority Date: 08/22/1991
• Status: Expired due to Fees

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Lambert, Robert L. Jr., Lundin, David J., Koskenmaki, David C., Calhoun, Clyde D., Yenni, Donald M. Jr.
• Primary Examiner(s): Page, Thurman K.
• Assistant Examiner(s): Shelborne, Kathryne E.
• Application Number:
  US07/748,708
• Time in Patent Office: 2,728 Days
• Field of Search: 428/284, 428/285, 428/903, 174/35
• US Class Current: 442/376
• 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: Y10S 428/903 Microfiber, less than 100 micron diameter
• CPC Class Codes: Y10T 442/654 Including a free metal or alloy constituent

Abstract

A thermoformable add-on EMI shielding sheet comprising a carrier material selected from polymeric films and fibrous webs having the capability of becoming porous when thermoformed, having a metal mat at least partially embedded therein, comprising a plurality of fine, randomly-oriented metal fibers, the carrier material having a softening temperature lower than the highest temperature reached during the thermoforming process.

Claims

1. A thermoformable add-on EMI shielding sheet comprising a carrier material selected from the group consisting of polymeric fibrous webs and sheet materials having the capability of becoming porous during a thermoforming process, said carrier material having a metal mat at least partially embedded therein, said mat comprising a plurality of fine, randomly-oriented metal fibers, said carrier material having a softening temperature and said metal mat having a melting temperature lower than the highest temperature reached during said thermoforming process.

2. A thermoformable add-on EMI shielding sheet according to claim 1 wherein said carrier material is porous prior to said thermoforming process.

3. A thermoformable add-on EMI shielding sheet according to claim 1 wherein said carrier material is a polymeric nonwoven web.

4. A thermoformable add-on EMI shielding sheet according to claim 3 wherein said polymeric nonwoven web comprises blown fibers.

5. A thermoformable add-on EMI shielding sheet according to claim 3 wherein said metal fibers are entangled with said polymeric nonwoven web.

6. A thermoformable add-on EMI shielding sheet according to claim 3 wherein said carrier material comprises at least one polymeric non-woven material selected from the group consisting of polyethylene, ethylene-butyl acrylate copolymers, ethylene-vinyl acetate copolymers, ethylene-methacrylic acid copolymers, thermoplastic polyesters, and mixtures thereof.

7. A thermoformable add-on EMI shielding sheet according to claim 1 wherein said carrier material is nonporous at room temperature, and becomes porous during said thermoforming process.

8. A thermoformable add-on EMI shielding sheet according to claim 1 wherein said carrier material is rendered porous by mechanical means.

9. A thermoformable add-on EMI shielding sheet according to claim 7 wherein said carrier material comprises a polymeric film having mechanically created pores of up to 1 cm in size, said pores being spaced up to 2 cm when measured from center to center.

10. A thermoformable add-on EMI shielding sheet according to claim 1 wherein said metal mat comprises metal fibers selected from the group consisting of tin, lead bismuth, cadmium, indium, gallium, zinc, mixtures thereof, and alloys thereof.

11. A thermoformable article comprising an add-on EMI shielding sheet according to claim 1, and a substrate polymer, said article having a thermoforming temperature higher than said melting onset temperature of said metal fibers.

12. A thermoformable article according to claim 11 wherein the metal fibers of said add-on EMI shielding sheet are entangled with said polymeric nonwoven web.

13. A thermoformable article according to claim 11 comprising a plurality of layers of carrier materials.

14. A thermoformable article according to claim 13 further comprising a plurality of metal mats.

15. A thermoformable article according to claim 11 wherein said substrate polymer is selected from the group consisting of polystyrene, cellulose acetate, cellulose-acetate-butyrate (CAB), cellulose propionate, acrylonitrile-butadiene-styrene polymers, polyethylene, ethylene-butene copolymers, ethylene-vinyl acetate copolymers, polypropylene, and propylene copolymers, poly(methylmethacrylate), methyl methacrylate-acrylonitrile copolymers, acrylic-modified poly(vinyl chloride), polycarbonates, poly(vinyl chloride-co-vinyl acetate), poly(vinyl chloride), polysulfones, polyethersulfones and polyamides.

19. A thermoformable add-on EMI shielding sheet according to claim 10 wherein said metal mat comprises metal fibers selected from the group consisting of alloys of tin, lead, bismuth, cadmium, indium, gallium, and zinc wherein said alloys contain at least one element selected from the group consisting of antimony, aluminum, copper, silver, gold, nickel, cobalt and iron.

16. A thermoformed article comprising a substrate polymer having an EMI shielding layer on a portion thereof, said portion being less than the entire article, said shielding layer having been precut from an add-on EMI shielding sheet, placed atop said substrate polymer, and thermoformed therewith.

17. A thermoformed article made by a method comprising the steps of:

a) providing a polymeric substrate having an area where EMI shielding is desired;

b) preheating said polymeric substrate for sufficient time for it to attain some portion of its thermoforming temperature;

c) forming an article by placing a precut add-on EMI shielding sheet comprising a carrier material, including its metal mat, over said area where EMI shielding is desired;

d) heating said article for a sufficient time for said carrier material to soften and said metal mat to melt and for said article, including the polymeric substrate to reach completely its thermoforming temperature;

e) thermoforming said article into a desired shape.

18. A thermoformed article made by a method comprising the steps of:

a) providing a polymeric substrate having an area where EMI shielding is desired;

b) forming an article by placing a precut add-on EMI shielding sheet comprising a carrier material including its metal mat over said area where EMI shielding is desired;

c) heating said article for a sufficient time for said carrier material to soften and said metal mat to melt and for said article to reach completely its thermoforming temperature;

d) thermoforming said article into a desired shape.