Corrosion-resistant, form-in-place EMI shielding gasket

• US 5,910,524 A
• Filed: 10/06/1997
• Issued: 06/08/1999
• Est. Priority Date: 01/20/1995
• Status: Expired due to Term

• Current Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Original Assignee: Parker-Hannifin Corporation
• Inventors: Kalinoski, John P.
• Primary Examiner(s): Marquis, Melvyn I.
• Application Number:
  US08/944,897
• Time in Patent Office: 610 Days
• Field of Search: 524/440, 523/215, 521/82, 427/387, 428/447, 264/40.3, 264/40.7, 264/40.1
• US Class Current: 523/215
• 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 428/31663 As siloxane, silicone or silane

Abstract

An electrically-conductive, corrosion-resistant EMI shielding gasket having an EMI shielding effectiveness of at least about 80 dB at between about 10 MHz and 10 GHz. The gasket is formed-in-place on a surface of a substrate as applied to such surface in a form-stable bead of a fluent polymeric reaction system and cured thereon under substantially atmospheric pressure. The reaction system has a strip volume resistivity of from about 500-1000 mΩ-cm and is admixture of: (a) an elastomeric resin binder component; and (b) an electrically-conductive filler component of nickel-coated graphite particles. The substrate surface may be that of a housing or other enclosure for electronic components.

Claims

1. A one-part, fluent polymeric reaction system which may be applied as a form-stable bead to a surface of a substrate and cured by thermal-addition thereon under substantially atmospheric pressure to form a corrosion-resistant, electrically-conductive, elastomeric EMI shielding gasket having an EMI shielding effectiveness of at least about 80 dB substantially over a frequency range of between about 10 MHz and about 10 GHz, said reaction system having a strip volume resistivity of from about 500-1000 mΩ

-cm and comprising an admixture of;

(a) a silicone resin binder component including a first functional group;

(b) a cross-linking agent component including a second functional group reactive with said first functional group of said binder component;

(c) a metallic catalyst component effective to catalyze the reaction of said first and second functional groups; and

(d) an electrically-conductive filler component comprising nickel-coated graphite particles.

2. The reaction system of claim 1 further comprising one or more additives selected from the group consisting of fumed silica, crystalline silica, glass or polymeric microballoons, and mixtures thereof.

3. The reaction system of claim 1 wherein said catalyst component is a platinum catalyst.

4. The reaction system of claim 1 wherein said filler component comprises, by weight of said filler, between about 60-70% nickel.

5. The reaction system of claim 1 wherein said filler component has a particle size of from about 0.25-75 μ

m.

6. The reaction system of claim 1 which comprises, by weight of components (a)-(d), from about 50-60% of said filler.

7. The reaction system of claim 1 wherein said first functional groups are vinyl functional groups and said second functional groups are hydride functional groups.

8. The reaction system of claim 7 wherein said binder component is a vinyl-functional siloxane polymer, and said cross-linking agent component includes a hydride-functional siloxane.

9. The reaction system of claim 1 wherein said filler component consists essentially of nickel-coated graphite particles.

10. An electrically-conductive, corrosion-resistant EMI shielding gasket having an EMI shielding effectiveness of at least about 80 dB substantially over a frequency range of between about 10 MHz and about 10 GHz which is formed-in-place on a surface of a substrate as applied to said surface in a form-stable bead of a fluent polymeric reaction system and cured thereon under substantially atmospheric pressure, said reaction system having a strip volume resistivity of from about 500-1000 mΩ

-cm and comprising an admixture of;

(a) an elastomeric resin binder component; and

(b) an electrically-conductive filler component comprising nickel-coated graphite particles.

11. The shielding gasket of claim 10 having a Shore A hardness of less than about 60, a force/deflection value of less than about 2.6 kN/m (15 psi), a compression set of less than about 50%, and a closure force of less than about 1 N/cm (5 lb_f /in).

12. The shielding gasket of claim 10 wherein said bead has a cross-sectional area of less than about 10 mm² (0.015 in²).

13. The shielding gasket of claim 10 wherein said reaction system further comprises one or more additives selected from the group consisting of fumed silica, crystalline silica, glass or polymeric microballoons, and mixtures thereof.

14. The shielding gasket of claim 10 wherein said filler component comprises, by weight of said filler, between about 60-70% nickel.

15. The shielding gasket of claim 10 wherein said filler component has a particle size of from about 0.25-75 μ

m.

16. The shielding gasket of claim 10 wherein said resin binder component includes a first functional group and wherein said reaction system further comprises:

(c) a cross-linking agent component including a second functional group reactive with said first functional group of said binder component; and

(d) a metallic catalyst component effective to catalyze the reaction of said first and second functional groups.

17. The shielding gasket of claim 16 wherein said catalyst component is a platinum catalyst.

18. The shielding gasket of claim 16 which comprises, by weight of components (a)-(d), from about 50-60% of said filler component.

19. The shielding gasket of claim 16 wherein said first functional groups are vinyl functional groups and said second functional groups are hydride functional groups.

20. The shielding gasket of claim 19 wherein said binder component is a vinyl-functional siloxane polymer, and said cross-linking agent component includes a hydride-functional siloxane.

21. The shielding gasket of claim 10 wherein said filler component consists essentially of nickel-coated graphite particles.

22. A method of forming an electrically-conductive, corrosion-resistant elastomeric EMI shielding gasket in situ on a surface of a substrate, said gasket having an EMI shielding effectiveness of at least about 80 substantially over a frequency range of between about 10 MHz and about 10 GHz, and said method comprising the steps of:

(a) providing a fluent, polymeric reaction mixture having a strip volume resistivity of from about 500-1000 mΩ

-cm and comprising;

(i) an elastomeric resin binder component; and

(ii) an electrically-conductive filler component comprising nickel-coated graphite particles;

(b) applying a bead of said reaction mixture to the surface of the substrate; and

(c) curing said reaction mixture under substantially atmospheric pressure to form said gasket on the surface of the substrate.

23. The method of claim 22 wherein said gasket of step (c) has a Shore A hardness of less than about 60, a force/deflection value of less than about 2.6 kN/m (15 psi), a compression set less than about 50%, and a closure force of less than about 1 N/cm (5 lb_f /in).

24. The method of claim 22 wherein said bead of step (b) has a cross-sectional area of less than about 10 mm² (0.015 in²).

25. The method of claim 22 wherein said reaction mixture of step (a) further comprises one or more additives selected from the group consisting of fumed silica, crystalline silica, glass or polymeric microballoons, and mixtures thereof.

26. The method of claim 22 wherein the filler component (ii) of said reaction mixture of step (a) comprises, by weight of said filler, between about 60-70% nickel.

27. The method of claim 22 wherein the filler component (ii) of said reaction mixture of step (a) has a particle size of from about 0.25-75 μ

m.

28. The method of claim 22 wherein the resin binder component (i) of said reaction mixture of step (a) includes a first functional group and wherein said reaction mixture further comprises:

(iii) a cross-linking agent component including a second functional group reactive with said first functional group of said binder component; and

(iv) a metallic catalyst component effective to catalyze the reaction of said first and second functional groups.

29. The method of claim 28 wherein said catalyst component is a platinum catalyst.

30. The method of claim 28 wherein said reaction mixture is cured in step (c) by heating said bead to a predefined cure temperature.

31. The method of claim 28 wherein said reaction mixture comprises, by weight of components (i)-(iv), from about 50-60% of said filler.

32. The method of claim 28 wherein said first functional groups are vinyl functional groups and said second functional groups are hydride functional groups.

33. The method of claim 32 wherein said binder component is a vinyl-functional siloxane polymer, and said cross-linking agent component includes a hydride-functional siloxane.

34. The method of claim 22 wherein the surface of the substrate is unprimed.

35. The shielding gasket of claim 22 wherein the resin binder component (ii) of said reaction mixture of step (a) consists essentially of nickel-coated graphite particles.

36. The EMI shielding gasket formed by the method of claim 22.