Method of making an electrical device comprising a conductive polymer composition

• US 5,181,006 A
• Filed: 12/11/1991
• Issued: 01/19/1993
• Est. Priority Date: 09/20/1988
• Status: Expired due to Term

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Raychem Limited (TE Connectivity Limited)
• Inventors: McCarty, Gordon, Straley, O. James, Shafe, Jeff, Oswal, Ravinder K., Dharia, Amitkumar N.
• Primary Examiner(s): LUSIGNAN, MICHAEL R
• Application Number:
  US07/805,212
• Time in Patent Office: 405 Days
• Field of Search: 252/511, 260/DIG. 38, 427/256, 427/287, 427/58, 338/22 R, 338/22 SD
• US Class Current: 338/22.00R
• CPC Class Codes: H01C 7/027 consisting of conducting or semi-conducting material dispersed in a non-conductive organic material
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics

Abstract

A polymer thick film ink which exhibits PTC behavior comprising an organic polymer which is crystalline, an active solvent suitable for dissolving the polymer, and carbon black which has a pH of less than 4.0. The ink is particularly useful in producing electrical devices such as heaters and circuit protection devices.

Claims

1. A method for producing an electrical device which comprises a conductive polymer which exhibits PTC behavior, said method comprising

(1) mixing (a) carbon black which has a pH of less than 4.0, (b) an organic polymer which has a crystallinity of at least 5% and a melting point T_m, and (c) an active solvent for the polymer;

(2) allowing the polymer to dissolve in the solvent to form an ink;

(3) applying the ink to a substrate to form a resistive element which, when cured, will exhibit PTC behavior; and

(4) curing the ink by heating at a temperature T_c for a time sufficient to remove the solvent.

2. A method according to claim 1 which further comprises crosslinking the ink after step (4).

3. A method according to claim 1 wherein the carbon black and polymer are melt-mixed and pelletized prior to mixing with the solvent.

4. A method according to claim 1 wherein T_c is greater than T_m.

16. A method according to claim 1 wherein the carbon black has a pH of less than 3.0.

17. A method according to claim 1 wherein the active solvent is suitable for dissolving the polymer at room temperature.

18. A method according to claim 1 which further includes crosslinking the ink during step (4).

5. An electrical device which comprises

(1) a first electrode,

(2) a second electrode, and

(3) a resistive element which exhibits PTC behavior and which is supported by a substrate and which has been prepared by

(a) mixing (i) carbon black which has a pH of less than 4.0, (ii) an organic polymer which has a crystallinity of at least 5% and a melting point T_m, and (iii) an active solvent for the polymer;

(b) allowing the polymer to dissolve in the solvent to form an ink;

applying the ink to the substrate to form the resistive element which, when cured, will exhibit PTC behavior; and

(d) curing the ink by heating at a temperature T_c for a time sufficient to remove the solvent,

the first and the second electrodes being connectable to a source of electrical power to pass current between the electrodes.

6. An electrical device according to claim 5 which is a heater.

7. An electrical device according to claim 5 wherein the resistive element has a thickness of at least 0.001 inch.

8. An electrical device according to claim 5 which is a circuit protection device.

9. A device according to claim 6 which is a mirror heater.

10. A device according to claim 5 wherein the substrate is flexible.

11. A device according to claim 10 wherein the substrate is a polymer.

12. A device according to claim 11 wherein the substrate is polyester.

13. A device according to claim 5 wherein the carbon black has a pH of less than 3.0.

14. A device according to claim 5 wherein the carbon black has been oxidized.

15. A device according to claim 5 wherein the resistive element has been crosslinked.