process for the manufacture of an electric device, applying this method produced electrical device and self limiting stripverhitter.

摘要

The invention relates to electrical devices comprising an electrode and a conductive polymer composition, preferably a PTC composition, in contact with the electrode. The process of the invention comprises contacting the composition and the electrode while the composition is at a temperature(Tp) above its melting point (Tm) and the electrode is at a temperature (Te) above the melting point of the composition, Tp and Te being the same or different, for a time which is sufficient to reduce the contact resistance between the electrode and the composition but which is not sufficient substantially to reduce the resistivity of the composition, for example, 2 time less than 5 minutes. Preferably both Tp and Te are at least 20.degree.C, especially at least 55.degree.C, above Tm. In a preferred process the composition is melt-extruded over one of more pre-heated electrodes. It has been found that the process of the invention substantially reduces the tendency of the resistance of the device to increase when the device is subject to thermal cycling. The invention is particularly useful in connection with self-regulating heaters, especially strip heaters comprising a pair of stranded wire electrodes embedded in an elongate core of a PTC material comprising carbon black dispersed in a crystalline polymer.