Areal Heating Element

Abstract

An areal heating element is disclosed in which the resistive portion is established by a polyester fleece contacting metal tapes as current lead-ins. The arrangement is lined with insulation layers, e.g., fiber fleeces or plastic sheets. The latter arrangement can be clad in a grounded metal foil. The insulating layers are bonded to the polyester fleece and to the tapes by adhesive or through heat sealing.

Description

The present invention relates to a flexible, electrical areal heating element which includes a resistive means for converting electrical energy to thermal energy and which further includes a source of electric current for connection to the resistive means by means of appropriate lead-in for providing electric power to the resistive portion.

Stationary areal heating systems are known for heating interior rooms as well as for providing outdoor, open area heating. The areal heating elements in such systems usually comprise resistance wires arranged to form mats. Current supplied to the wires is converted therein to thermal energy. The individual wires are usually covered with a heat-resistive insulation comprised of rubber or a suitable plastic. Other known areal heating elements are clothlike mats comprised of plastic thread or metallic wires interwoven with bare or insulated heating conductors. Such cloth-type areal heating elements are usually used for installation in nonstationary surface heaters.

These two types of partially flexible-partially inflexible heating mats have a number of deficiencies. First of all, the temperature distribution is not uniform as there are relatively high temperatures, locally concentrated in the vicinity of the conductors and comparatively low temperatures prevail in the region between adjacent but spaced apart heating conductors. Moreover, such mats or cloths are rather complicated to make, require manual labor to a considerable extent and are therefore rather expensive.

These mats or cloths are usually operated at similar voltages, namely from the mains, but difficulties arise if it is desired to provide such cloths or mats so as to furnish different heating powers per unit area or even to trim and to adjust them accordingly. This is particularly so because in essence variable parameters are the distance between the conductors in the mat or cloth, the length of the conductor, or the construction thereof. Additionally, of course, the heating conductors must be provided with lead-in and connecting wires which have to remain cold, particularly in case provisions are to be made for normal manual plug-in.

In other types of areal heating heaters which are also known as wall-heating mats, looped conductors are embedded in a foam plastic, whereby temperature equalizing metal foils are positioned inbetween the heating conductors. Again, the manufacturing of such conductors, and the contacting of the individual looping heating elements forming the heating surface and which are individually connected in parallel, is rather complicated, It is a particular disadvantage or these types of areal heaters that they have relatively large installation height.

Furthermore, metal foils have become known which are slotted or provided with indentations or longitudinal recesses so that in between two longitudinally extending outer strips, loop-shaped conductors are established which, upon application of voltage, are heated in the desired manner. Again, the manufacturing of such areal heaters is rather time consuming and there is the additional disadvantage that actually there are provided alternating zones of high and low temperatures. Furthermore, these heating foils have rather low mechanical strength and, therefore, break easily which in turn increases the danger of short circuiting. Finally, there is the difficulty that different heating output per unit area can be obtained only by changing the cutting or stamping tools.

Still another type of heating element is known in which a cloth is woven from textile or glass fibers which have been made electrically conductive by spraying on a thin carbon or graphite layer. The resulting thin layer conductivity is instrumental to obtain the desired conversion of electricity in thermal energy. However, the weaving of such a cloth is very slow and the cost of making such a heating element is rather high accordingly. Moreover, the electric contact making with the sprayed-on conductive layer is complicated to obtain and still not certain and durable, particularly in case of flexing.

It is a principle object of the invention to provide an areal heating element obviating the deficiencies outlined above and which has such layer thickness which is so low that the heating element can be actually provided underneath wallpaper without being clearly visible. It is another object of the present invention to provide an areal heating element which inherently includes broad surface contact between current lead-in and resistance element. It is a further object of the present invention to provide an areal heating element in which flexibility is not the result of trade-off with certainty of contact making. It is a still further object of the present invention to provide an areal heating element which does not require weaving of metalized fibers, wires or the like.

In accordance with present inventions the heating element provided in accordance with the preferred embodiment employs an electrically conductive, polyester fleece as resistive heating element. Metal tapes are placed on the fleece in flat surface contact therewith and at a distance from each other to serve as lead-in conductors. Polyester fleece and metallic tape are completely covered by electrically insulating layers. In the preferred embodiment these layers are comprised of fiber fleeces (or a single, folded-over fiber fleece) having an adhesive layer on their sides facing polyester fleece and tape to provide secure connection between all the various parts outlined above.

The polyester fleece is to be very thin to be highly flexible, but still has good mechanical strength, and it retains its shape in spite of a very small value in thickness. The electric resistivity of such a fleece is rather constant over a large temperature range. One can make such a fleece even at large lengths without difficulties. Firm connection and, therefore, positive contact making between polyester fleece and metal tapes is primarily obtained through the fiber fleece adhering to a metal tape as well as to the polyester fleece at both sides (edges) of the tape thus urging the latter to the former. The fiber fleece may, for example, be bonded to the polyester fleece by concurrent application of heat and mechanical pressure.

In order to improve the contact making between fleece and metal tape, it may be advisable to provide the construction with the following particular features. The metal tapes may be provided with apertures. These apertures may in particular be located somewhat excentrically, closer to that edge of the tape facing the other tape across the polyester fleece. The adhesive layer on the fiber fleece contacts the polyester fleece through the apertures and provides for additional positioning of metal tape relative to and in contact with the polyester fleece.

The heating element in accordance with the invention can be improved further in that at least on one side of the outer insulating fleece or sheet there is provided a metal foil which, in turn, in connected to a grounded contact, for example, of the mains. The advantage of this feature is protection against danger from severe damage to the heating element; for example, if a nail pierces the several layers, the nail makes contact with that foil and is in effect grounded. Particular protection is afforded here to the person wielding the hammer.

This metal foil may preferably be made of aluminum in accordance with an additional aspect of the invention, and as it is connected to the ground terminal of the mains it grounds all contacting, conductive objects, including a piercing nail. Of course conventional protective circuit means may be used in addition in circuit connection with the areal heating element operating preferably on a selective basis to stop current flow through the particular damaged element in order to avoid large leakage currents into that element as extensive damage or even fire may result, for example, from local excessive heating.

A further improvement of the inventive concept will be as follows. In lieu of a fiber fleece or fleeces a plastic sheet or foil is provided carrying on one side a heat-sealing layer prior to assembly. For example, the plastic, insulating foil could be a polyester foil having a polyethylene layer to be used for bonding the insulating foil to the heating element proper. As a heat-sealing layer one can also use a copolymer of polytetrafluoroethylene-perfluoropropylene on a polyimid foil as insulating sheet. Such an arrangement has the advantage that the plastic or foil as suggested has considerably mechanical strength, is voltage proofed, for regular AC as well as DC and has a very low-water vapor permeability. Therefore, such an areal heating element can be handled roughly during the installation. Also, it establishes a heating element which can be used for heating highly humid rooms.

Foil layering of the heating element in accordance with this aspect of the invention, has the further advantage in that upon mounting the heating element, for example, to a wall, regular wallpaper glue can be used even though it contains a rather large amount of water. Moisture will not penetrate into the electrically conductive polyester fleece so that damage to the latter does not have to be expected. The foil structure guarantees in addition that the element maintains its shape and can be wound on a roll. The quality and certainty of contact making between metal tapes and polyester fleece is also improved in view of the high-bonding strength of heat sealing.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIG. 1 illustrates an elevational view of an areal heating element in accordance with the preferred embodiment of the present invention.

FIG. 2 illustrates a cross section along lines 2--2 in FIG. 1, however, with grossly exaggerated representation of thickness dimensions to facilitate illustration thereof.

FIG. 2a is a detail of a modified arrangement.

FIGS. 3 and 4 show elevations of further embodiments of heating elements in accordance with the present invention; and

FIGS. 5 and 6 show cross sections through heating elements in accordance with two additional embodiments of the present invention.

Turning now to the detailed description of the drawings, in FIGS. 1 and 2 there is illustrated a polyester fleece 1 to be used as resistive element for an areal heater and in which conversion of electrical energy to thermal energy takes place. Along the long sides of fleece 1 there are provided two metallic tapes 2 and 3. Edges of fleece 1 and outer edges of tapes 2 and 3, respectively, are vertically aligned, as can be seen in FIG. 2. Preferably these metallic tapes are made of copper and have dimensions that on one hand the thickness of the heating element as a whole is not noticeably increased and in addition, they are sufficiently thick so that current flow through them does not cause heating to any significant degree.

Fleece 1 is covered on both sides with fiber fleeces 4 and 5, fiber fleece 4 particularly covering also the conducting tapes 2 and 3 on that particular side. The inner sides of the fiber fleeces 4 and 5 are provided with an adhesive layer permitting direct bonding to polyester fleece 1 and metal tapes 2 and 3 were in surface contact. As can be seen in particular in FIG. 2, fiber fleeces 4 and 5 have overhanging portions along the edges of fleece 1. The adhesive layers on fleeces 4 and 5 thus bond them together, providing an all-around enclosure for fleece 1.

FIG. 1 illustrates, furthermore, one end of this elongated areal heating element, and one can see that tapes 2 and 3 project beyond that edge of fleece for providing lead-ins for connection to a suitable conductor through which voltage is applied to and between conductors 2 and 3. Of course, additional layers could be provided on top of the fiber fleeces, transparent or opaque foil or layers, etc. It should also be mentioned that the fiber fleece layers or at least one thereof may itself be made of transparent or translucent material which facilitates control and inspection of the quality of contact making particularly between metallic tapes 2 and 3 and polyester fleece 1.

FIG. 2a illustrates another feature of the invention, the metal tape 12 used here as current lead-in for the heating element, has asymmetrically positioned apertures 13. Aperture 13 is closer to the edge facing away from the tape edge which is flush with the edge of fleece 1 along which tape 12 extends.

Generally, it should be mentioned that the metal tapes are maintained in position by being bonded to fleece 5. Moreover, fleece 5 is bonded to fleece 1, particularly also along the portion adjacent the tapes but not covered by them. Additionally, fleece 5 is bonded to fleece 4 along the edge of the tapes, respectively flush with the edges of fleece 1. Here, the fleece grips somewhat around the tapes. Additionally, the tapes are position-arrested in that the fleece grips through the aperture and is bonded to fleece 1 were exposed through the apertures. This gripping-through is not illustrated in FIG. 2, because of the exaggerated thickness dimensions. It is emphasized that in reality the apertures in the tapes 2 and 3 are considerably wider than the tapes are thick.

It is of significance that the areal heating element of the type illustrated has a very small layer thickness which is instrumental in obtaining large versatility of employment. Also, the heating power per unit area or other parameters are readily adjustable. For a chosen areal heating power, the particular distance between the conductors 2 and 3 is predetermined. The entire heating element can now be as long as desired to obtain a particular overall heating output.

Particular areas of employment are, for example, installation as ceiling or wall heaters underneath even thin wallpaper, whereby the transition between, for example, a central wall zone provided with such elements, and a marginal or corner zone of the wall without heater underneath, is in fact hardly noticeable. The novel heating element can also be employed as floor heater and can particularly be installed under parquet layers or vinyl and other plastic type of floor covers, or even underneath wall-to-wall carpeting. Heaters in accordance with the invention are not limited to employment as large area covers, instead, one can make such areal heating elements part of small mats; one can even use this type of heating element in and for hot plates. It should be mentioned finally that for most areas of employment conventional and commonly used adhesives can be used to provide the adhesive layer on the fiber fleeces 4 and 5.

FIG. 3 illustrates another embodiment of the invention. For example, in certain long polyester fleeces having not too small a width and having a wider than normal width one can provide more than two metallic tapes; also more than two metallic tapes may be required as lead-ins in case two areal elements of different heating power are to be provided next to each other. FIG. 3 illustrates such an embodiment.

There are shown three metallic tapes, 2, 3 and 6. Tapes 2 and 6 are arranged essentially as are tapes 2 and 3 in FIG. 1, along the long edges of fleece 1, but possibly at a larger distance from each other. Tape 3 is provided here between tapes 2 and 6, dividing the total heating area into zones A and B. The arrangement is somewhat asymmetrical, i.e., the distance between tapes 2 and 3 is larger than between tapes 3 and 6, area A being larger than area B.

TApe 3 is, for example, connected to a return reference or ground terminal and similar voltages are applied to conductors 2 and 6. As the distance between tapes 2 and 3 is larger than between the tapes 3 and 6 and if the polyester fleece 1 has uniform thickness, area A is heated less than area B. One can, therefore, see that in a rather simple manner, i.e., by providing an asymmetrical tape conduction arrangement on the areal heating power can readily be controlled particularly as far as ratio of heating powers of two different areas is concerned.

FIG. 4 illustrates another special case in which the two metallic conductor tapes, again denoted here with 2 and 3 on fleece 1 are not equidistantly spaced, they do not run parallel to each other but have an acute angle between them. Voltage applied to the two conductors 2 and 3 is similar along the fleece, but Region D is heated more on a per unit area basis than Region C with stepless, gradual increase of heating power from C to D. One can see that a gradient of developed heat per unit area is obtained and heating increases continuously from top to bottom in the drawing.

Turning now to the embodiment shown in FIG. 5, there is again illustrated the polyester fleece 1 with metal tapes 2 and 3 for providing current to flow through fleece 1. Also, and as in the embodiments described above, polyester fleece and metallic tapes are clad by a pair of fiber fleeces 4 and 5 bonded together along the margin of fleece 1 by means of an adhesive layer. In this particular embodiment and in accordance with the general principles outlined in the introduction there are provided additional metallic foils for lining the sheet arrangement as described thus far. There is in particular illustrated a lower foil 7 and an upper foil 8. However, this may actually be one and the same foil folded over at the end of the heating element. The metal foil or foils are preferably made of aluminum.

In principle, of course, it may be sufficient to provide such a metal foil on one side of the arrangement only. However, in this case it would be critical how to place the heating element, as the side provided with that metal foil should be the side not facing the wall, floor, ceiling, or other support element to which the heating element is to be attached. This selection rule, of course, can be dispensed with in case both sides of the arrangement are lined with metal foil as illustrated.

The purpose of the metal foil cover is to provide for flat grounding of the heating element as a whole. The metal foil or foils is/are, of course, insulated from thermoconduction 1. In order to properly ground the foil or foils 7, 8, they make contact with a metal tape 11, serving as the lead-in for a connection between foil or foils and ground. Tape 11 is a thin metal tape preferably of the same type used to supply current to fleece 1. Generally it is of advantage if tape 11 is positioned approximately halfway in between the two tapes 2 and 3.

Foils 7 and 8 are bonded to the heating element construction, particularly to the outer surfaces of insulating layers 4 and 5 by means of conventional glue or adhesive, or a foil for heat sealing, for example, a thin polyethylene foil, may be provided between the grounded metal foil on one hand and the fiber fleeces on the other hand. The polyethylene foil is caused to melt by application of external mechanical pressure at an elevated temperature. Upon melting and resolidification the metal foil(s) are bonded to the fiber fleeces.

The thickness of the areal heating element as a whole is only insignificantly increased by the two additional layers of metal foil and the latter should be very thin so that the flexibility of the heating element is not impeded. Flexibility is desirable as, for example, a long sheet of such heating element may be wound on spools or rolls for facilitating transportation. Therefore, it is repeated here, that also in FIG. 5 the dimensions representing thickness of the heating element and other several foils, layers and fleeces are quite exaggerated.

FIG. 6 illustrates an example of another embodiment of the invention. Again reference numeral 1 refers to the polyester fleece and electric current is provided to and across the polyester fleece by the two metallic tapes 2 and 3. Polyester fleece and metallic tapes are clad in insulating lining provided here by two plastic foils 14 and 15 each of which having on one side a heat-sealing layer. The heat-sealing layers are respectively denoted with reference numerals 9 and 10. The heat-sealing layers face polyester fleece 1, but since foils 14 and 15 reach beyond fleece 1 along the margin thereof, heat-sealing layers 9 and 10 are in direct engagement along the margin of fleece 1. Metal foils 7 and 8 are provided above plastic foils 14 and 15, respectively.

The metal tapes 2 and 3 themselves make good contact with the polyester fleece in all of the embodiments, but due to their flexibility they are also highly suitable for connecting to other current supply elements. For this it is merely necessary to bend over the ends of the metallic tape projecting from the heating element. The thus resulting loops or eyes receive the connecting wires or the like. Tapes and connecting wires are secured to each other, for example, by means of hollow rivets.

The invention is not limited to the embodiment described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

Claims

I claim:

1. Flexible electric areal heating element comprising:

a thin electrically conductive polyester fleece having two opposed flat sides and serving as resistive heating element;

at least a pair of electrically conductive tapes each having two flat sides, one flat side of each tape being in direct flat surface-to-surface contact with the fleece the tapes having perforations also in contact with the fleece, the tapes being disposed on the fleece in spaced apart relationship from each other;

insulating layers lining the fleece and tapes, on both flat sides of the fleece; and

adhesive layer means between said fleece and said insulating layers bonding the insulating layers to the fleece particularly along the tapes and through the perforations and bonding one of the insulating layers to the respective other flat sides of the tapes for position-arresting the tapes to the fleece, for maintaining contact making engagement between the respective one flat sides of the tapes and the fleece.

2. Flexible heating element as in claim 1, the insulating layers are provided as fiber fleeces.

3. Flexible heating element as in claim 1, the metal tapes being made of bare copper.

4. Flexible heating element as in claim 1, the metal tapes being perforated.

5. Flexible heating element as in claim 4, the perforations being excentric to the centerline of the tape, closer to the edge of the tape facing the other tape across the fleece.

6. Flexible electric areal heating element as in claim 1, the tapes being flush with long side margins of the fleece.

7. Flexible electric heating element as in claim 1, the tapes running parallel to each other.

8. Flexible electric heating element as in claim 1, the tapes having an angle to each other.

9. Flexible electric heating element as in claim 1, there being a metal foil on the outer side of at least one of the insulating layers, the metal foil being grounded.

10. Flexible electric heating element as in claim 9, there being a third metal tape attached to the metal foil in contact therewith to establish grounding of the foil.

11. Flexible electric heating element as in claim 10, the third tape being centrally positioned in relation to the two tapes in contact with the fleece.

12. Flexible electric heating element as in claim 9, the foil being made of aluminum.

13. Flexible electric heating element as in claim 9, there being a heat-sealing layer interposed between the foil and the one-insulating layer.

14. Flexible electric heating element as in claim 1, the insulating sheets made of plastic and provided with heat-sealing layers for bonding to the fleece and the tapes. 15. Flexible electric heating element as in claim 14, the heat plastic sheets being made of polyester, the heat-sealing

layer comprising polyethylene. 16. Flexible electric heating element as in claim 14, the plastic sheets being made of polyimid, the heat-sealing layer comprising a copolymer of polytetrafluoroethylene-perfluoropropylen.

7. Flexible electric heating element as in claim 1, the tapes projecting beyond the fleece for connection to connecting wires, the tapes being

flexible to permit folding over for riveting. 18. Flexible electric heating element as in claim 1, there being a plurality of tapes on the

fleece, in excess of two. 19. Flexible electric heating element as in claim 18, the tapes being asymmetrically arranged relative to each other so that the distances between the tapes of different pairs of neighboring tapes differ.