Form-in-place EMI gaskets

• US 20020039658A1
• Filed: 09/12/2001
• Published: 04/04/2002
• Est. Priority Date: 01/20/1995
• Status: Active Grant

• Current Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Original Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Inventors: Kalinoski, John P., Bunyan, Michael H.
• Granted Patent: US 6,635,354 B2
• Time in Patent Office: Days
• US Class Current: 428/450
• CPC Class Codes: B29L 2031/26 Sealing devices, e.g. packaging for pistons or pipe joints
• CPC Class Codes: F16J 15/064 the packing combining the sealing function with other functions
• CPC Class Codes: F16J 15/14 by means of granular or plastic material, or fluid
• CPC Class Codes: H05K 9/0015 Gaskets or seals
• CPC Class Codes: Y10T 428/256 Heavy metal or aluminum or compound thereof
• CPC Class Codes: Y10T 428/31605 Next to free metal
• CPC Class Codes: Y10T 428/31609 Particulate metal or metal compound-containing
• CPC Class Codes: Y10T 428/31696 Including polyene monomers [e.g., butadiene, etc.]
• CPC Class Codes: Y10T 428/31699 Ester, halide or nitrile of addition polymer

Abstract

A form-in-place, electrically-conductive gasket is disclosed. The gasket, foamed, gelled or unfoamed is made of one or more elastomer resins, such as silicone urethane and/or thermoplastic block copolymers and is either filled with a conductive filler and lined onto a desired substrate or lined onto the substrate unfilled and then coated with a conductive outer layer, such as a silver filled elastomer or a conductive flocked layer. A process and system for making the gaskets are also disclosed.

Claims

1. EMI shielding material comprising:

a polymeric thermal addition cure system; and

an electrically-conductive filler,

said material having bulk resistivity of less that about 0.050 ohm cm, and being readily extrudable and remaining so upon storage at room temperature for a period of up to at least one week, butlupon exposure to a temperature of at least 85°

C. for a period of time of at least 30 minutes becoming essentially thermoset.

2. EMI shielding material as in claim 1, the polymeric thermal addition cure system comprising:

a first species having a first functional group;

a second species having a second functional group that is reactive with the first functional group in the presence of a catalyst and heat; and

a catalyst having catalytic action that in the presence of heat catalyzes a reaction between the first and second functional groups,

the electrically-conductive filler inhibiting the catalyst to adversely affect the catalytic activity of the catalyst, and the catalyst being present in an amount sufficient to retain desired catalytic activity.

3. EMI shielding material as in claim 2, packaged as a kit comprising:

a first container containing a first pre-mixed component including the first species, the electrically-conductive filler, and the catalyst;

a second container containing a second pre-mixed component including the first species, the second species, and the electrically-conductive filler; and

a third container containing the catalyst.

4. EMI shielding material as in claim 3, wherein the first species comprises a siloxane polymer including vinyl functional groups, the second species comprises a siloxane cross-linker including reactive hydrides, the electrically-conductive filler comprises a silver-based electrically-conductive filler, and the catalyst comprises a platinum catalyst.

5. EMI shielding material as in claim 1, wherein the electrically-conductive filler is a silver-based filler.

6. EMI shielding material as in claim 2, wherein the first species comprises-a siloxane polymer including vinyl functional croups, and the second species comprises a siloxane cross-linker including reactive hydrides.

7. EMI shielding material as in claim 2, wherein the catalyst is a platinum catalyst.

8. EMI shielding material as in claim 1, the material having a viscosity of from about 100,000 to about 10,000,000 centipoise.

9. EMI shielding material as in claim 1, the material being in the form and shape of a cured EMI shielding gasket having resistance at 25% deflection of less than 10 m ohms, resistance at 50% deflection of less than 5 m ohms, and shielding effectiveness of 10-120 dB at 10 MHz to 12 GHz.

10. EMI shielding material as in claim 1, the material being in the form and shape of a cured EMI shielding gasket having compression set of less than 50% after 30 minutes at 138°

C. when deflected 50% for 22 hours at 85°

C., lap shear greater than 100 psi; and

a shore A hardness of less than 90.

11. EMI shielding material as in claim 1, further comprising a cure inhibitor.

12. An EMI shielding material as in claim 1, further comprising polymeric microspheres.

15. A method as in claim 14, further comprising prior to the extruding step:

forming the polymeric thermal addition cure system by forming a mixture of a first species having a first functional group, a second species having a second functional group that is reactive with the first functional group in the presence of a catalyst and heat, a catalyst that catalyzes a reaction between the first and second functional groups, and the electrically-conductive filler.

16. A method as in claim 15, wherein the forming step comprises:

mixing together;

a first pre-mixed component including the first species, the electrically-conductive filler, and the catalyst; and

a second pre-mixed component including the first species, the second species, and the electrically-conductive filler.

17. A method as in claim 16, further comprising:

prior to mixing together the first and second components, adding additional catalyst to the first pre-mixed component.

18. A method as in claim 15, the catalyst having catalytic action that in the presence of heat catalyzes a reaction between the first and second functional groups, and the electrically-conductive filler inhibiting the catalyst to adversely affect the catalytic activity of the catalyst.

19. A method as in claim 15, wherein the first species comprises a siloxane polymer including vinyl functional groups, the second species comprises a siloxane cross-linker including reactive hydrides, the electrically-conductive filler comprises a silver-based electrically-conductive filler, and the catalyst comprises a platinum catalyst.

20. A method as in claim 14, wherein the electrically-conductive filler is a silver-based filler.

21. A method as in claim 14, wherein the catalyst is a platinum catalyst.

22. A method as in claim 14, the system further comprising a cure inhibitor.

23. A method as in claim 14, the system further comprising polymeric microspheres.

25. The structure of claim 24 wherein the first substrate is an enclosure and the second substrate is a cover for the enclosure.

26. The structure of claim 24 wherein the first and second substrates are formed of an electrically conductive material selected from the group consisting of metals, metal plated plastic, metal/plastic laminate and composites, coated plastisols and combinations thereof.

27. The substrate of claim 24 wherein the gasket is formed of an elastomer resin and is rendered electrically conductive by the incorporation of one or more conductive fillers into the resin.

28. The substrate of claim 24 wherein the gasket is formed of an inner and outer layer, at least the outer layer being electrically conductive.

29. The structure of claim 24 wherein the gasket is formed of an elastomer and one or more electrically conductive fillers.

30. The structure of claim 29, wherein the electrically-conductive filler is selected from the group consisting of noble metals, noble metal-plated noble metals, noble metal-plated non-noble metals, noble metal-plated glass, noble metal-plated plastic, noble metal-plated metal-filled plastic, noble metal-filled plastic, noble metal-plated ceramics, noble-metal plated alumina, noble-metal plated plastic microspheres, noble-metal plated mica, non-noble metal-plated non-noble metals, non-noble metals, non-noble metal plated non-metals, and non-metal materials.

31. The structure of claim 30, wherein the electrically-conductive filler is selected from the group consisting of silver, gold, copper, aluminum, nickel, cobalt, silver-plated gold, silver-plated copper, silver-plated nickel, silver-plated aluminum, silver-plated aluminum core particles, silver-plated glass microspheres, silver-plated copper-filled silicone, silver-plated aluminum-filled silicone, silver-plated copper-filled fluorosilicone, silver-plated aluminum-filled fluorosilicone, silver-filled silicone, silver-filled fluorosilicone, copper-coated iron, nickel-plated copper, nickel plated graphite, carbon black, and graphite.

32. The structure of claim 24 wherein the gasket is formed of silicone-based polymeric material containing one or more electrically conductive fillers.

33. The structure of claim 24 wherein the gasket has a Shore A hardness of from about 5 to about 90, a force/deflection value of from about 0.2 pounds/inch to 15.0 pounds/inch, electrical resistance value of from about 0.005 ohms to 0.1 ohms, a compression set value of from about 5% to 50% and an EMI shielding effectiveness of from about 10-120 dB at a frequency range from about 1 OMHz to about 12 GHz.

35. The substrate of claim 34 wherein the substrate and cover are formed of an electrically conductive material selected from the group consisting of metals, metal plated plastic, metal/plastic laminates and composites, electrically conductive coated plastics, and combinations thereof.

36. The substrate of claim 34 wherein the gasket is formed of an elastomer resin and is rendered electrically conductive by the incorporation of one or more conductive fillers into the resin.

37. The substrate of claim 34 wherein the gasket is formed of an inner and outer layer and wherein at least the outer layer being electrically conductive.

39. The gasket of claim 38 wherein the silicone resin is a silicone-based polymeric material.

51. The method as in claim 14, wherein the polymeric thermal addition cure system and the substrate are essentially free of primer.

52. The method as in claim 14, said extruding step comprising extruding onto a substrate the polymeric thermal addition cure system in the form of a bead having a cross-sectional area of from about 0.0004 in² to about 0.15 in².

53. The method as in claim 14, wherein said heating step is carried out at atmospheric pressure.

13. EMI shielding material comprising:

a hardenable, fluent polymeric thermal addition cure system;

an electrically-conductive filler;

a catalyst having catalytic action that in the presence of heat catalyzes a reaction in the polymeric thermal addition cure system that causes the system to cure and harden,

the electrically-conductive filler inhibiting the catalyst to adversely affect the catalytic activity of the catalyst, and the catalyst being present in an amount sufficient to retain desired catalytic activity.

14. A method of making an EMI shielding gasket, comprising:

extruding onto a substrate a free-form polymeric thermal addition cure system having a viscosity of from about 100,000 to about 10,000,000 centipoise and including an electrically-conductive filler; and

heating the system at a temperature and for a period of time sufficient to cure the system, thereby forming a gasket having bulk resistivity of less that about 0.050 ohm cm.

54. An EMI shielding gasket formed by the process of claim 14.

24. An EMI shielded substrate comprising:

a first electrically conductive substrate;

a second electrically conductive substrate adjacent to the first substrate;

a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the first substrate so as to provide an electrical connection and EMI shielding between the first and second substrates.

34. An EMI shielded substrate comprising:

a substrate having an electrically conductive surface;

a cover for the substrate, the cover having an electrically conductive surface which corresponds to and is in register with the conductive surface of the substrate; and

a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the conductive surface of the substrate or cover so as to provide an electrical connection and EMI shielding between the substrate and cover upon the mating of the cover to the substrate.

38. A form-in-place EMI gasket comprising a composition formed of a silicone resin, one or more conductive fillers, a curing agent for the resin wherein the composition, when mixed and applied to a substrate, will create a form stable, form-in-place gasket capable of providing EMI shielding of from about 10 dB to about 120 dB over a frequency range from 10 MHz to 12 GHz.

40. An EMI gasket comprising a composition formed of;

a first component which is a primary polymer having end groups that are capable of chemically reacting with each other in the presence of moisture to form a derivative polymer having a longer average chain length than said primary polymer;

a second component which is a noncross-linked elastomer that is not substantially chemically reactive with itself or with said first component; and

a third component which is one or more electrically conductive fillers, wherein when said first, said second, said third components are intimately mixed, said composition, when maintained in the absence of moisture and other active hydrogen donor materials, being readily extrudable and otherwise conventionally moldable thermoplastic composition but, upon exposure to moisture, becoming essentially thermoset.

41. The gasket of claim 40 wherein the first component has a polyester backbone and isocyanate or trialkoxysilyl end groups, and the second component is selected from the group consisting of a styrene-isoprene-styrene block polymer, a styrene-butadiene-styrene block polymer, an isoprene homopolymer, a polyvinyl chloride, polyisobutylene, styrene-ethylene-butylene-styrene, or ethylene-propylene rubber and the third component is selected from the group consisting of noble metal fillers;

noble metal-plated noble metals;

noble metal-plated non-noble metals;

noble-metal plated glass, noble metal-plated plastic or noble metal-plated ceramics, noble-metal plated mica;

non-noble metals, non-noble metal-plated non-noble metals; and

non-metal materials such as carbon black and graphite and combinations thereof.

42. A system for forming EMI shielded enclosures comprising:

a support platform;

a compound applicator nozzle located above and in register with the platform;

a supply of electrically conductive compound connected to the applicator nozzle; and

a drive mechanism for moving the nozzle or platform relative to each other in one or more directions of travel.

43. The system of claim 42, further comprising a second drive mechanism.

44. The system of claim 42 further comprising a curing chamber for curing of the compound after application.

45. The system of claim 44 wherein the chamber is selected from the group consisting of hot air ovens, infrared ovens, light chambers, moisture chambers or combinations thereof.

46. The system of claim 42 further comprising a computer for controlling preprogrammed, respective movements of the nozzle relative to the table so as to create a predetermined gasket configuration.

48. The process of claim 47 further comprising, prior to the applying step applying a primer to the substrate.

49. The process of claim 47 wherein the gasketing material is formed of a conductive filled resin, the resin being selected from the group consisting of silicone, urethanes, thermoplastic elastomers and mixtures thereof;

the fillers being selected from the group consisting of noble metal fillers;

carbon black and graphite and combinations thereof; and

the substrate is an electrically conductive material selected from the group consisting of metals, metal composites, metal coated plastics and metal laminates.

50. The process of claim 47 wherein the curing occurs via a curing agent, a cross linking agent, heat, light, moisture or combinations thereof.

47. A process for forming a form-in-place conductive EMI shielding gasket or substrate comprising the steps of:

providing a substrate to be gasketed;

providing a supply of conductive gasket material;

applying the material to the substrate'"'"'s surface in a predetermined pattern; and

curing the material in place upon the substrate.