Method for making silver filled moldable organopolysiloxane compositions

• US 5,928,570 A
• Filed: 01/22/1998
• Issued: 07/27/1999
• Est. Priority Date: 02/26/1997
• Status: Expired due to Term

• Current Assignee: Specialty Silicone Products Incorporated (Heico Corporation)
• Original Assignee: Specialty Silicone Products Incorporated (Heico Corporation)
• Inventors: Reo, Ned J.
• Primary Examiner(s): Kopec, Mark
• Application Number:
  US09/010,885
• Time in Patent Office: 551 Days
• Field of Search: 252/514, 106/1.19, 528/12, 528/15, 528/32, 264/104
• US Class Current: 252/514
• CPC Class Codes: H01B 1/22 the conductive material comprising metals or alloys
• CPC Class Codes: H05K 9/0083 comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers H05K9/0086 takes precedence

Abstract

A method is provided for blending silver powder with a platinum catalyzed heat curable silicone mixture to make a moldable silicone mixture having an indefinite shelf life. Useful conductive silicone articles, such as EMI shielding, can be made having a volume resistivity (milliohms-cm) value of about 2 or less.

Claims

1. A method for making a moldable silicone composition convertible upon cure to conductive silicone parts having a volume resistivity (milliohms-cm) value of about 2 or less comprising,

(1) incrementally adding silver powder to a one part heat curable silicone fluid mixture while it is being agitated at a rate sufficient to maintain a substantially uniform mixture, and

(2) continuing to incrementally add the silver powder to the resulting silicone fluid- silver powder blend while being agitated until there is obtained a moldable material capable of being injected into a hot mold with pressures up to about 20,000 psi, which injection moldable material comprises by weight, (A) about 60% to about 90% of silver powder having an average diameter of about 0.5 to about 100 micrometers, and (B) about 10% to about 40% of a one part heat curable silicone fluid mixture comprising by weight,

(i) 100 parts of a vinyl containing polydiorganopolysiloxane fluid,

(ii) and 1 to 20 parts of a siloxane hydride fluid, and

(iii) an effective amount of an inhibited platinum catalyst.

2. A method in accordance with claim 1, where the moldable blend of silver powder and one part heat curable silicone fluid mixture is made by blending a mixture comprising silver powder, vinyl containing polydiorganopolysiloxane fluid and inhibited platinum catalyst with a cross linker comprising a siloxane hydride fluid.

3. A method in accordance with claim 1, where the vinyl containing polydiorganopolysiloxane fluid is a vinyl containing poplydimethylsiloxane fluid.

4. A method in accordance with claim 1, where the siloxane hydride fluid is a coupler having terminal dimethylhydrogensiloxy units.

5. A method in accordance with claim 1, where the inhibited platinum catalyst is an inhibited reaction product of chloroplatinic acid and tetramethyldivinyldisiloxane.