Method of making electrical devices comprising conductive polymer compositions
AssigneeRaychem Corporation
InventorsHundi P. Kamath, Jeffrey C. Leder
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Abstract
In order to increase the stability of a device comprising at least one electrode and a conductive polymer composition in contact therewith, the contact resistance between the electrode and the composition should be reduced. This can be achieved by contacting the molten polymer composition with the electrode while the electrode is at a temperature above the melting point of the composition. Preferably, the polymer composition is melt-extruded over the electrode or electrodes, as for example when extruding the composition over a pair of pre-heated stranded wires.
Claims28
A process for the preparation of an electrical device which has improved resistance stability under service conditions, which comprises at least two electrodes, each of said electrodes being in physical and electrical contact with a conductive polymer composition, and in which, when said electrodes are connected to a source of electrical power, current passes between the electrodes through the conductive polymer composition, which process comprises contacting each of said electrodes with conductive polymer composition by
- (1) heating a thermoplastic electrically conductive polymer composition above its melting point;
- (2) heating each electrode, in the absence of the conductive polymer composition, to a temperature above the melting point of the conductive polymer composition;
- (3) (contacting) bringing each electrode which has been heated in step (2), while it is at a temperature above the melting point of the conductive polymer composition, into direct physical contact with the molten conductive polymer composition prepared in step (1);
- and
- (4) cooling each electrode and conductive polymer composition in contact therewith prepared in step (3),
- whereby the contact resistance between each of the electrodes and the conductive polymer in contact therewith is reduced.
A process for the preparation of a self-regulating strip heater having improved resistance stability under service conditions, which process comprises
- (1) heating a thermoplastic electrically conductive polymer composition above its melting point, said conductive polymer composition (a) comprising a crystalline polymer having carbon black dispersed therein, (b) having a volume resistivity at 70.degree. F. of 100 to 50,000 ohm.cm, and (c) exhibiting PTC behavior;
- (2) heating at least two electrodes, in the absence of the conductive polymer composition, to a temperature above the melting point of the conductive polymer composition;
- (3) melt-extruding the molten conductive polymer composition produced in step (1) over the electrodes heated in step (2), each of said electrodes being at a temperature above the melting point of the conductive polymer composition when first contacted by the molten conductive polymer composition, thereby forming an elongate extrudate of the electrically conductive composition with the electrodes embedded therein and in direct physical contact therewith, the electrodes being parallel to each other;
- and
- (4) cooling the extrudate formed in step (3), whereby the contact resistance between each of the electrodes and the conductive polymer in contact therewith is reduced.
Dependencies are inferred from the claim text.