Pressure sensitive electro-conductive materials

• US 4,874,549 A
• Filed: 04/26/1988
• Issued: 10/17/1989
• Est. Priority Date: 12/13/1985
• Status: Expired due to Term

• Current Assignee: Pivotech, Inc.
• Original Assignee: Advanced Micro-Matrix Incorporated
• Inventors: Michalchik, Michael
• Primary Examiner(s): Barr, Josephine
• Application Number:
  US07/186,186
• Time in Patent Office: 539 Days
• Field of Search: 252/511, 252/502, 252/510, 524/495, 524/496, 307/119, 338/99, 338/100, 338/113, 338/114, 200/5, 428/241, 428/256, 428/325
• US Class Current: 252/511
• CPC Class Codes: H01B 1/24 the conductive material comprising carbon-silicon compounds, carbon or silicon
• CPC Class Codes: H01C 10/106 on resistive material dispersed in an elastic material H01C10/103 and H01C10/12 take precedence; for electric switches H01H1/029

Abstract

The invention relates to a pressure sensitive electro-conductive material which can be utilized as a pressure sensitive electro-conductive switch or as a variable resistor. The switch comprises two electrodes with a deformable pressure sensitive electro-conductive material sandwiched between the electrodes. The electro-conductive material comprises a deformable elastomeric material impregnated with a plurality of electro-conductive micro-agglomerates of unbound finely divided electro-conductive carbon particles enclosed by a matrix of the elastomeric material and finely divided electro-conductive carbon particles bound together by the elastomeric material.

Claims

1. A process for the preparation of a pressure sensitive electro-conductive material comprising the steps of:

a. Preparing a solvent system comprising water, a water miscible carbon-wetting organic solvent, and a surfactant;

b. Mixing finely divided electro-conductive carbon particles into the solvent system to form a uniform slurry;

c. Maintaining the slurry for a predetermined period of time to obtain substantial wetting of the carbon particles of the solvent system to form a pre-agglomeration composition;

d. Dispersing the pre-agglomeration composition into an aqueous elastomeric composition to form an elastomeric-carbon composition containing electrically conductive micro-agglomerates comprising unbound finely divided electro-conductive carbon particles enclosed by a matrix of elastomeric material and bound finely divided electro-conductive carbon particles; and

e. Drying said elastomeric-carbon composition to obtain the pressure-sensitive electroconductive material.

2. The process of claim 1 wherein the water miscible carbon-wetting organic solvent is miscible in the surfactant and the surfactant is soluble in water.

3. The process according to claim 1 wherein the pH of the solvent system is adjusted to between about 7 and about 10 by the addition of a water soluble volatile base.

4. The process according to claim 1 wherein the water soluble base is selected from the group consisting of ammonium hydroxide and methyl diethanol amine.

5. The process according to claim 1 wherein the finely divided electro-conductive carbon particles have a particle size of from about 15 millimicrons to about 75 millimicrons.

6. The process according to claim 1 wherein the slurry in step c is maintained for a period of 1 to 7 days at ambient temperatures to obtain substantial wetting of the carbon particles.

7. The process according to claim 1 wherein the pH of the aqueous carbon slurry is adjusted to between about 7.0 and about 10.0 by the addition of a volatile base.

8. The process according to claim 1 wherein pH of the elastomeric-carbon composition is adjusted to a value from about 5.0 to about 10.0 by the addition of a water soluble base.

9. The process according to claim 8 wherein the water soluble base is selected form the group consisting of ammonium hydroxide and methyl diethanol amine.

10. The process according to claim 1 wherein the elastomeric composition is an aqueous polyurethane dispersion.

11. The process according to claim 1 wherein the elastomeric-carbon composition is formed into a film and dried to obtain a pressure sensitive electro-conductive material.

12. The process according to claim 10 wherein the film of elastomeric-carbon composition is formed on an electro-conductive substrate.