Electric heating – Heating devices – With heating unit structure
Patent
1991-07-24
1993-07-20
Reynolds, Bruce A.
Electric heating
Heating devices
With heating unit structure
219528, 219549, 338211, H05B 308, H05B 334, H01C 306
Patent
active
052295826
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a flexible heating element comprising a flexible sheet substrate, a layer of an electrically conductive material for generating heat on conduction of an electric current and supply means for applying an electric current to the conductive material.
Such heating elements can be used in applications such as ceiling heating, underfloor heating, wooden/metal panel heating, motor vehicle mirror and car seat heating, and a wide range of horticultural and agricultural applications.
A problem which arises in connection with heating elements of this kind is that of ensuring good electrical contact between the supply means and the layer of electrically conductive material, that is, low resistance between the supply and conductive layer.
United Kingdom Patent 1,087,794 proposes the use of an electrode strip with pre-cut tabs which pierce both the conductive layer and the substrate. United Kingdom Patent 1,333,086 also describes a similar arrangement in which the foil electrode strips are secured to the substrate by means of a plurality of eyelets. Both of these products, however, are subject to the disadvantage that piercing of the substrate weakens it considerably and the heating element is liable to tearing.
United Kingdom Patent 1,191,847 discloses the use of a conductive adhesive to secure the supply electrodes to the conductive layer but this does not always provide the good contact necessary.
Accordingly, the flexible heating element of the invention is characterised in that the supply means includes at least one electrode having an embossed surface, the embossed surface of the electrode being bonded to the conductive material by means of thermoplastic polymeric based adhesive. Preferably, protruberances on the embossed surface make physical contact with the conductive material.
With an arrangement in accordance with the invention, a reliable low resistance connection can be effected between a power supply and the conductive material.
An embodiment of the invention will now be described by way of example with reference to accompanying drawings, in which:
FIG. 1 is a perspective view showing a length of a flexible heating element stored in a roll, and partially unrolled.
FIG. 2 is a plan view of the edge region of the flexible heating element shown in FIG. 1;
FIG. 3 is a sectional view along the line II--II of FIG. 2; and
FIG. 4 is a sectional view similar to FIG. 3, but showing an alternative arrangement in the heating element.
Referring to FIGS. 1, 2, and 3, a flexible heating element 10 includes a rectangular flexible sheet substrate 12 of an electrically insulating material. The material used for the substrate will depend on the requirements for the intended application of the heating element, for example on overall thickness, operating temperature and the nature of the application environment. In the present embodiment, the operating temperature is intended to be less than 100.degree. C., and the substrate material used is polyethylene terephthalate. The substrate thickness is approximately 75 .mu.m. The heating element is sufficiently flexible that it can be stored in a roll, as in FIG. 1.
The substrate 12 carries a layer of an electrically conductive material 14. When an electric current is passed through the conductive material 14, heat is produced owing to the predetermined resistance of the conductive material. The conductive material 14 is a thermoplastic polymer based material, utilising a blend of conductive and non-conductive constituents. The ratio of the conductive and non-conductive constituents used determines the resistivity of the conductive material 14, and hence partly determines the output power of the heating element. The conductive constituent contains a mixture of carbon black and graphite to provide the conductive property.
Depending on the application for which the heating element is intended, the layer of conductive material 14 may be formed as a continuous layer substantially covering the surface of the substrate 12, or it may be formed as a predeterm
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patent: 4818823 (1989-04-01), Bradley
Reynolds Bruce A.
Switzer Michael D.
Thermaflex Limited
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