Article having heating elements comprising conductive polymers capable of dimensional change

DETAILED DESCRIPTION I have now discovered that if a laminar conductive polymer member is sandwiched between a pair of laminar flexible electrodes, and suitable apertures are formed in the resulting laminate, it is possible to obtain an easily expandable and/or contractable product having greatly improved electrical characteristics.
DETAILED DESCRIPTION OF THE INVENTION Thus in its first aspect, the invention provides a heating element which comprises: (A) a laminar member composed of a material which comprises an organic polymer and electrically conductive particles dispersed in the polymer in amount sufficient to render the member electrically conductive; and (B) a pair of laminar flexible electrodes which (i) are connected (directly or indirectly) to opposite faces of said laminar member; (ii) are substantially parallel to said laminar member; and (iii) are adapted to be connected to an external source of power to cause current to pass through said laminar member; said laminar member and laminar electrodes having a plurality of apertures through the thickness thereof, the apertures being of a size, shape and distribution which permit at least one of the dimensions of the element in the plane thereof to be changed by a change in the shape of the apertures.
Preferably at least one of the planar dimensions of the element can be changed at the melting point of the polymer (and preferably at some lower temperature, e.
g.
25.
degree.
or 50.
degree.
C.
) by a percentage which is at least 30%, without complete rupture of the electrode at any point, the dimensional change being accomodated by a change in the shape of the apertures.
It is to be understood that the said dimensional change may be an increase as a result of stretching, or a decrease as a result of compression, or both (i.
e.
an element which can be stretched by X% and compressed by Y% in the same dimension, where X+Y is at least 30).
The term "without complete rupture of the electrode at any point" means that each electrode maintains an electrical pathway completely surrounding each aperture; thus the electrode may tear partially but not completely at any point