Coilable and severable heating element
FIELD OF THE INVENTION 
     My present invention relates to a heating element wherein a resistance layer enveloped in an insulating sheath is energizable with a heating current passing through a pair of transversely spaced conductors in contact with that layer. 
     BACKGROUND OF THE INVENTION 
     Resistance layers to be used in such heating elements are conventionally formed from a nonconductive matrix, e.g. of polymeric material, with carbon particles imbedded therein. Such layers may have a certain flexibility permitting bending of the heating elements incorporating them. 
     OBJECT OF THE INVENTION 
     The object of my invention is to provide an improved heating element of this general type, which can be rolled into a coil for storage purposes and from which sections of any desired length can be cut, radiating heat in one direction only. 
     SUMMARY OF THE INVENTION 
     In accordance with my present invention, a flexible tape designed to be used as a heating element includes an elongate carrier of woven cloth impregnated with a flexible, carbon-containing resistance layer in contact with two transversely spaced conductors extending adjacent the longitudinal edges of the carrier over its entire length, this assembly being enveloped in a flat resinous sheath. The tape can be coiled and can also be transversely severed; upon such severance, cutting away parts of the sheath and the carrier exposes terminal portions of the conductors to facilitate their connection to a source of heating current. A flexible heat shield is inserted into the sheath on one side of the carrier and a sheath surface on the same side may be adhesively coated whereby a backing strip of paper can be detachably secured to the tape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which: 
     FIG. 1 is a perspective view of a heat-generating tape according to the present invention; 
     FIG. 2 is a perspective view similar to FIG. 1, showing the tape provided with an adhering paper strip; 
     FIG. 3 is a perspective view of a carbon layer formed on a woven cloth, constituting the core of the tape; 
     FIG. 4 is a perspective view showing a section of the tape of FIG. 1; 
     FIG. 5 is a perspective view of a terminal tape portion partly cut away to expose its electric conductors; 
     FIG. 6 is an enlarged partial perspective view of two juxtaposed heat-generating tapes according to my invention; 
     FIG. 7 is a perspective view similar to FIG. 4 but showing the tape with the paper strip of FIG. 2; and 
     FIG. 8 is a perspective view similar to FIG. 4 but relating to the tape of FIGS. 2 and 7. 
    
    
     SPECIFIC DESCRIPTION 
     FIG. 1 illustrates a heat-generating tape 1 according to the present invention, shown rolled into a coil. Terminal portions 2 of a pair of electric conductors 3, each consisting of a bundle of thin wires, project endwise from the tape. 
     FIG. 2 shows the tape 1 provided with a separable paper strip 11 partially peeled from an adhesive layer 12 on one of its surfaces. 
     The body of the heating element 1 shown in FIGS. 1 and 2 includes an elongate core member 7 which consists of soft tapelike woven cloth 4, e.g. of cotton, impregnated with a carbon-containing flexible resistance layer 5 of conventional composition as shown in FIG. 3. The electric conductors 3 are disposed on the woven cloth 4 in electric contact with the resistance layer 5 and extend along the longitudinal edges of the tape with transverse separation. A thermally insulating member 8, e.g. a glass-fiber layer, is disposed on the lower surface of the woven cloth 4, as seen in FIG. 4, for letting heat radiate only in one direction. Two electrically insulating flexible synthetic-resin layers or foils 9 enclose the core member 7, lead wires 3 and insulating member 8 therebetween, so as to complete the heat-generating tape 1. 
     As seen in FIG. 4, the upper and lower layers 9 of synthetic resin have longitudinal marginal zones merged into edge portions 10 so as to form a flat sheath enclosing the core member 7, the insulating layer 8 and the lead wires 3 therebetween. 
     FIG. 7 shows the adhesive layer 12 of FIG. 2 formed on the outer surface of that synthetic-resin layer 9 which is in contact with the heat-insulating member 8, i.e. on the lower surface of tape 1 as seen in the Figure. The adhesive layer 12 is covered by the separable paper strip 11. This layer advantageously consists of a thermosetting adhesive. 
     Since the coilable heating element 1 according to my invention is made mainly of woven cloth and synthetic-resin layers, the tape 1 can be transversely cut at a selected location with exposure of a terminal portion 2 of each conductor 3 by partially removing the layers 9, the heat shield 8 and the core 7 from the cut edge, as shown in FIGS. 5 and 8. These terminals 2 can be joined to an electric plug (not shown) for connection to a power source (likewise not shown); they could also be used for connection to another geat-generating tape 1. 
     In operation, as an electric current is supplied to the conductive parts 3, 5 of tape 1 through the terminals 2, the resistance layer 5 generates heat. It is possible to use a thermostat (not shown) to hold the tape temperature at a selected level of, for instance, about 70° C. 
     The heat generated by the resistance layer 5 emanates only in the direction opposite the heat-insulating member 8. If the covering synthetic-resin layers 9 are made of a material having a high thermal conductivity, the heat from the resistance layer 5 is transmitted with little heat loss to an object to be heated. Since the synthetic resin forming the layers 9 is electrically insulating, the risk of electric shock is completely eliminated even when the heat-generating tape 1 is energized. 
     In order to heat larger surfaces, e.g. floors and sidewalls of a house (not shown), the heat-generating tape 1 is cut into sections of suitable length which can be juxtaposed side-by-side and electrically interconnected, with the edge portions 10 of the adjacent tape sections overlapping, as shown in FIG. 6. Tapes of the type shown in FIGS. 2, 7 and 8 can be easily secured to a wall or some other object simply by peeling off the separable paper strip 11 and pressing the tape against the object with the adhesive layer 12 facing it. The overlapping of the edge portions 10 of adjacent tape sections, lying substantially on the level of core members 7, avoids any superposition of the woven carriers 4 and their resistance layers 5 while ensuring coverage of the desired area without any gaps. Accordingly, uneven temperature distribution and abnormal temperature rise or excessive heat generation can be prevented. 
     Since the components of my improved heat-generating tape 1 are all flexible, it is possible to wind the tape 1 on a cylindrical conduit such as a water-supply pipe. Thus, the tape 1 can be used for preventing the water in such pipes from freezing and protecting such pipes from resulting rupture. 
     As will be apparent from the foregoing disclosure, the flexible heat-generating tape according to the present invention is readily severable and reconnectible. There are no limitations on the shape and the size of the tape which can be used for heating any residential houses, greenhouses and the like.