Electric heating – Heating devices – With heater-unit housing – casing – or support means
Patent
1998-02-19
2000-04-25
Hoang, Tu Ba
Electric heating
Heating devices
With heater-unit housing, casing, or support means
219542, H05B 334
Patent
active
060546905
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel electrical heating element in the form of a film or thin sheet with laminated structure, comprising at least one electrically conductive layer and at least one substrate.
2. Discussion of the Background
Electrical heating elements used in household applications, for example, irons, grills, etc. are formed by resistance wires embedded in an insulating ceramic material, itself placed in a metal casing. One drawback of this type of electrical heating element is its thermal inertia. Another drawback is that it is ill-suited to complex contours.
Furthermore, it is thick and the implements which use it are large.
Electrical heating elements are also known which are in the form of sheets having multiple layers; an electrically conductive layer formed by a thin metal film, bonded onto a substrate by means of a hot-melt adhesive layer which is intended to withstand heat. Suitable hot-melt layers are extruded films having a thickness of generally more than 20 .mu.m.
One drawback of this heating element is the low conductivity of the hot-melt film. Furthermore, this low conductivity cannot be improved substantially by incorporating thermally conductive fillers in the extruded layer.
SUMMARY OF THE INVENTION
The invention overcomes the drawbacks which have been mentioned.
It proposes a heating element which is in the form of a thin film and has low thermal inertia, and whose manufacture is simplified.
The heating element according to the invention comprises at least one substrate and at least one electrical resistance layer which adheres to the substrate via a binder formed from a dispersion, solution or powder deposited directly on the substrate.
The binder according to the invention may be selected from dispersions, solutions or powders of at least one polymer (or copolymer) whose melting temperature is greater than the operating temperature of the heating element and which can be deposited on a substrate, if appropriate with a small thickness. The polymer is preferably selected from perfluorinated polymers, in particular perfluoroalkoxyalkane (PFA), MFA and polytetrafluoroethylene (PTFE).
According to one aspect of the invention, a dispersion or solution of at least one of the polymers mentioned above is chosen, it being possible for this dispersion or solution to be, if appropriate, heavily loaded with thermally conductive and electrically insulating fillers, for example, aluminium oxide Al.sub.2 O.sub.3, silicon carbide SiC, mica and glass powder.
The substrate according to the invention which, in particular, fulfils the function of mechanically supporting the heating element, as well as the function of an electrical insulator, may be any kind of sheet, selected according to the application envisaged for the heating element. This sheet may be based on a thermoplastic or thermosetting material or a cellulosic material, or an optionally impregnated glass fabric or web, a fabric or web based on ceramic fibers, or alternatively a sheet that is extruded or rolled out. The thermoplastic or thermosetting material is, in particular, selected from polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PEA), MFA, perfluoro-(ethylene-propylene) (FEP), ethylene-tetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethyleneterephthalate (PET) and polyimide (KAPTON).
The substrate generally has a thickness of between 20 .mu.m and 500 .mu.m or more, if appropriate, depending on the application.
According to one embodiment of the invention, the electrical resistance layer is a film or a thin sheet of an electrically conductive material, in particular one based on a metal such as copper, nickel, aluminium or a metal alloy such as bronze, brass or Constantan.RTM..
With a view, in particular, to improving the adhesion of the metallic conductive thin film, it may, on at least one of its two faces, have a structured surface obtained, for example, by rolling in a calender filled with rollers having structured surfaces, or a rou
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patent: 4725717 (1988-02-01), Harrison
Petit Dominique
Wolki Peter
Hoang Tu Ba
Norton Pampus GmbH
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