Raychem Limited

Bernadette A Trammell

Ravinder K Oswal

Jeff Shafe

Neville S Batliwalla

Michael C Jones

Gordon McCarty

O James Straley

Electrical devices with improved resistance stability comprise a PTC element comprising a conductive polymer and two electrodes. The conductive polymer composition comprises an organic crystalline polymer and carbon black with a pH of less than 5.0. Particularly preferred conductive polymer compositions comprise carbon blacks which have a pH of less than 5.0, a dry resistivity R.sub.CB and a particle size D in nanometers such that R.sub.CB /D is at most 0.1. Electrical devices of the invention include heaters and circuit protection devices.

Conductive polymer composition

A number of improvements to electrical devices, particularly sheet heaters, comprising conductive polymer compositions, are provided. The preferred heater has the following features (a) it comprises a laminar resistive element and a plurality of electrodes which are so positioned that the predominant direction of current flow is parallel to the faces of the laminar element, (b) it comprises a laminar insulating element adjacent to but not secured to the electrodes and the resistive element; (c) it comprises a metallic foil, which acts as a ground plane and is positioned adjacent the insulating element but is not secured thereto; (d) it comprises a dielectric layer intimately bonded to the resistive element and to the electrodes. The invention also provides an electrical device comprising first and second members having different resistivities, and a thin contact layer of intermediate resistivity positioned between the first and second members.

Devices comprising conductive polymer compositions

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Menlo Park, CA, United States of America

Bernadette A Trammell