EP0304595A1 - Electric heating device - Google Patents

Abstract

In the case of an electrical heating unit (1), at least one heating circuit of the heating resistor (2) is arranged as a coated or printed conductor track and thus via an adhesive connection (16) on a carrier (3) made of a high-temperature-resistant, synthetic paper and with its bare side facing away from it Side fastened directly to the associated receiving side (11) of the body (10) to be heated by means of a full-surface adhesive connection (13). The adhesive connection (13) is expedient by an adhesive layer (14) made of a silicone resin adhesive or the like which is at most a few tenths of a millimeter thick. or a self-adhesive layer is formed, which has approximately the same temperature resistance as the carrier (3) to compensate for stress. At least one heating circuit can be switched via a mechanical temperature switch with high switching hysteresis.

Description

The invention relates to an electrical heating unit for a body to be heated with a support and an electrical heating resistor arranged, for example, in the form of a flat layer.

Attempts have already been made to arrange the heating resistor between polyamide parts in such heating units and thus to attach them to the plate to be heated as a multilayer unit. However, it has been shown that this structure involves a relatively cumbersome processing and does not always withstand the stresses that occur, in particular the stresses caused by heat, to a sufficient degree. However, these and other designs also frequently have the disadvantage that they are only suitable for relatively low limit temperatures of, for example, up to 80 ° C. or slightly above are suitable, in particular between the heating resistor and the plate to be heated, there is a prefabricated plastic part which affects both the temperature resistance of the composite with the heating plate as well as the thermal coupling of the heating resistor and the compactness of the entire heating unit.

The invention has for its object to provide an electric heating unit of the type mentioned, which ensures an easy installation of the heating resistor in the heating unit with a simple structure and high temperature resistance.

To solve this problem it is provided that the heating unit has at least one flat support with at least one heating resistor. It is particularly advantageous if the carrier is at least partially formed by a paper-like substrate which, when coated, forms a unit with at least one heating resistor. In contrast to an etched heating conductor, a much higher temperature resistance can be ensured in spite of simpler production in such an arrangement, and the heating resistor can also be applied in the manner of a thick layer in a substantially greater material thickness, so that higher heating outputs can also be achieved. The heating resistor can also be arranged between two identical or similar carrier layers of the same or different thickness.

The electric heating unit can be used for a wide variety of bodies to be heated, for example for flat bodies such as heating plates, mirror plates or mirror glasses and the like. At least one heating resistor with the associated carrier expediently forms a self-contained structural unit in the form of a heating device, the carrier having the flat-layer heating resistor on one Receiving side and the heating resistor forms a heating resistor surface facing away from this receiving side, which can form a bare exposed metal surface in the associated unit before the heating device is installed. It is particularly advantageous if the heating device has, on its side associated with the heating resistor surface, an adhesive connection which is provided at least over part of the surface for direct connection to a counter surface intended for holding the heating device, either directly through a surface of the body to be heated or, in certain cases , can also be formed by a surface facing away from it. The heating resistor surface is then only covered by this counter surface or by the adhesive connection at the latest after assembly and is therefore protected or electrically insulated. Depending on the requirements, the adhesive connection can also be provided over the entire surface so that it covers both the entire heating resistor surface and the associated surface of the carrier.

The adhesive connection can optionally be formed by an adhesive layer that hardens only when the heating resistor is fastened, for example previously applied plastically or liquid, so that after connecting the heating resistor and to the heating body, only this single adhesive connection layer is provided between these parts. In a preferred embodiment, the adhesive connection is formed by an adhesive layer, which can have a relatively small layer thickness of, for example, at most the thickness of the heating resistor or less, although a layer thickness which is greater than the thickness of the heating resistor can also be advantageous for some areas of application.

It is conceivable to use a two-component adhesive as the adhesive layer. In any case, it is advantageous if the adhesive connection maintains a certain permanent elasticity, so that Tensions in the connection between the heating device and the body to be heated are constantly compensated for by themselves without damage.

A silicone or silicone resin adhesive is particularly suitable as a bonding layer. In the case of such adhesives, the solidification takes place by means of a chemical reaction with atmospheric moisture, small amounts of acetic acid being released as the degradation product. In order to achieve the highest possible temperature resistance of over 200 ° C, it is advantageous to anneal the adhesive layer after the complete curing at a slowly increasing temperature. The heating device according to the invention is, in particular in such an embodiment, stable against permanent temperatures of above 100 ° C. to at least 150 ° C., and brief peak loads of up to approximately 300 ° C. are possible. It is particularly advantageous if the adhesive, in flowable viscosity, is applied directly to the heating resistor and to a sub-film which may carry it, since then very thin layers and a very uniform distribution can be achieved. For example, the adhesive known under the trademark PACTAN can be used as an adhesive, or an adhesive that connects in a tension-compensating manner, has good sealing properties, maintains elasticity, elasticity and notch resistance even at high and low temperatures, against water, water vapor, dilute acids, alkalis and Salt solutions are resistant, aging-resistant and embrittlement-free and also have good electrical insulating properties and finally have a low volume shrinkage of preferably less than 5% when solidifying.

A particularly advantageous development of the subject matter of the invention is that the adhesive connection is formed by a preferably layer-like or film-like, prefabricated self-adhesive layer which is effective on both sides or on all sides which, for example, can be a transparent acrylate layer with a thickness of the order of 0.13 mm. Such an adhesive layer, which can be provided on each side with an easily removable protective cover, for example made of siliconized paper, can have a heat resistance well above 100 °, for example up to at least 130 ° C, and can be easily attached to the outer contour adjust the heater or its support or the body to be heated by cutting.

The heating resistor can also be attached with its surface facing away from the body to be heated by means of an adhesive connection to a suitable carrier, in particular the above-mentioned back or bottom film, or can form a self-contained, inseparable structural unit through this adhesive connection with the carrier.

A very advantageous and secure connection can also result from the fact that the heating resistor is produced by coating, such as, for example, printing on the associated receiving side, so that the adhesion arising from the pressure alone forms the adhesive connection. If the heating resistor is not printed directly on the body to be heated, it expediently forms a printed unit with the carrier, which can then be very easily attached to the body to be heated via the first-mentioned adhesive connection. In the other case, a bottom film would expediently have to be attached as a cover for the heating resistor after the heating resistor had been printed on. After application as a layer, the heating resistor can be stabilized or hardened in an advantageous manner, for example, by baking it into the carrier at a temperature of the order of 200 ° C.

A particularly advantageous development of the subject matter of the invention consists in that at least the receiving side of the body to be heated consists of electrically insulating material, a ceramic material, in particular a glass-ceramic material, having proven to be particularly advantageous and the body to be heated usefully over its entire cross section or its entire panel thickness consists of one layer made of the same material, although a two- or multi-layer structure of the body itself, depending on the use, is also conceivable. The heating plate according to the invention is particularly suitable for flat warming plates in the household area, but also for curved designs, such as may be required on containers. An advantageous application is also to prevent the fogging of mirrors by the heating unit or to keep the outside mirrors free of ice.

In a further embodiment of the invention, a material made of a high-temperature-resistant plastic, in particular a polymer, is proposed for the carrier, which can preferably be produced from individual particles in the manner of a synthetic paper, for example on a conventional paper machine, from a slurry. If this raw material is heavily compressed, for example by calendering at high temperature, the result is a very tough, tensile and tear-resistant, flame-retardant, self-extinguishing, non-melting and flexible film with a high permanent temperature resistance of almost the same values of the adhesive bond or only slightly lower Values with very good dielectric properties, low shrinkage at elevated temperatures, high tightness and very good chemical resistance to common solvents, resins and oils. The permanent temperature resistance can reach up to about 220 ° C and so on Similar to the adhesive of the adhesive connection, resistance to over 300 ° C can also be given in the case of brief peak loads.

The favorable values mentioned can be achieved in a particularly simple manner at low production costs if the carrier consists of an aromatic polyamide, as is known, for example, under the name aramid. Furthermore, it is advantageous if elongate or flat particles in the manner of fibers or flakes are used to produce the carrier, a particularly advantageous composite being obtained if not only uniform particles, but for example both flakes and fibers are mixed together. It is also conceivable to construct the carrier from two or more identical or different layers in the manner of a laminate as a composite body, it being possible, for example, to arrange a further film layer made of a homogeneous material, for example polyester, between two film layers of the type mentioned. For example, the paper known under the trademark NOMEX from DUPONT or the paper known under the trademark PRETEX from Faserprodukte GmbH Lahnstein can be used. In this respect, a paper-like material is also conceivable in which long-fiber cellulose fibers mixed with polyamide fibers are used in combination with synthetic binders of the class acrylic acid ester copolymers. The surface structure forming the support can be provided with a one- or both-sided top coat.

• Fig. 1 eine elektrische Heizvorrichtung einer erfindungsgemäßen Heizeinheit in Ansicht;
• Fig. 2 einen Schnitt durch die Heizvorrichtung gemäß Fig. 1;
• Fig. 3 einen Ausschnitt der Fig. 2 in vergrößer­ter Darstellung sowie im Verbund mit einem zu beheizenden Körper der Heizeinheit;
• Fig. 4 eine weitere Ausführungsform einer Heizein­heit in Ansicht;
• Fig. 5 einen Ausschnitt der Heizeinheit gemäß Fig. 4 in wesentlich vergrößertem Querschnitt;
• Fig. 6 eine weitere Ausführungsform einer Heiz­einheit in Vorderansicht, jedoch ohne zu be­heizenden Körper;
• Fig. 7 einen Ausschnitt der Heizeinheit nach Fig. 6 in wesentlich vergrößertem Querschnitt und
• Fig. 8 einen Ausschnitt der Fig. 7 in wesentlich vergrößerter Darstellung.

These and further features of preferred developments of the invention are evident from the claims and also from the description and the drawings, the individual features being realized individually or in groups in the form of sub-combination in one embodiment of the invention and in other fields, and can represent advantageous and protectable designs, for which protection is claimed here. An embodiment of the invention is shown in the drawings and is explained in more detail below. The drawings show:

• 1 shows an electric heating device of a heating unit according to the invention in view;
• FIG. 2 shows a section through the heating device according to FIG. 1;
• 3 shows a detail of FIG. 2 in an enlarged representation and in conjunction with a body of the heating unit to be heated;
• 4 shows a further embodiment of a heating unit in view;
• FIG. 5 shows a detail of the heating unit according to FIG. 4 in a substantially enlarged cross section;
• 6 shows a further embodiment of a heating unit in a front view, but without a body to be heated;
• Fig. 7 shows a detail of the heating unit of FIG. 6 in a substantially enlarged cross section and
• Fig. 8 shows a detail of Fig. 7 in a substantially enlarged view.

1 to 3, a heating unit 1 is shown by way of example with a heating device for a power of approximately 70 W under a voltage of approximately 220 V, which are designed for a continuous operating temperature of approximately 130 ° C. can and has edge dimensions of less than 1 m. In the illustrated embodiment, the heating device 1 is oblong rectangular in view with a longer edge dimension which, for example, is approximately twice as large as the smaller edge dimension, for example approximately 30 cm.

The heating device has a flat-layer heating resistor 2, which has a thickness of less than 1 mm, or the thickness of which may be of the order of a tenth of a millimeter. The heating resistor 2 is expediently formed from a metal and / or graphite-containing paste, in particular a polymer paste, and is laid in a meandering manner in such a way that a large number of sections 4 of equal length lying next to one another and with a small spacing are formed, which are parallel to the longitudinal edges of the heating device, the two outermost sections 4 being at a distance from the associated longitudinal edges of a carrier 3 which is approximately two to three times greater than the distance between adjacent sections 4. The heating resistor 3 expediently consists of a polymer paste which is applied to the carrier 3 in the manner of a printing process and thus forms a printed, electrical conductor track. The two ends of this conductor track are adjacent and laid parallel to each other parallel to a narrow edge of the carrier 3 and form areally enlarged connection ends 5 on the same side of the carrier 3 on which the remaining heating resistor 2 is also located.

The carrier 3 is formed by a paper-like synthetic film of substantially less than 1 mm in thickness, which together with the heating resistor 2 can have a total thickness of only a few tenths of a millimeter, for example approximately or less than three to five tenths of a millimeter. On the associated side of this carrier 3, the heating resistor 2 with its associated surface 15 lying essentially in one plane or surface is connected via an adhesive connection 16 applied, which is formed directly by adhesion between the metallic surface 15 and the associated side of the carrier 3 without additional adhesive. In order to achieve particularly favorable properties, the heating resistor 2 can consist of a silver polymer paste or a mixture of a silver and a graphite polymer paste.

The other, parallel to the surface 15 and also essentially continuous in one plane or surface lying metallic surface 12 of the heating resistor 2 is free or bare before the arrangement on the body 10 to be heated, so that the heating device before assembly only needs to exist two layers, of which the heating resistor 2 forms a boundary layer. With this surface 12 and without gaps with the parts of the associated surface of the carrier 3 that are exposed between the sections 4 of the heating resistor 2, the heating device is then permanently or permanently attached to the associated, smooth or flat receiving side of the body 10 to be heated by means of an adhesive connection 13 .

This adhesive connection 13 is expediently produced using a separate adhesive in the form of an adhesive layer 14, the thickness of which may be approximately in the order of the total thickness of the heating device, the thickness of which is therefore only slightly larger or smaller than or approximately the same as the thickness of the heating resistor 2 itself can be. To produce the adhesive connection, the film heating element or the heating device is expediently coated on the associated side printed with the conductor track and over its entire extent, after which it can be mounted by applying it to the dry, untreated receiving side 11 of the body 10. After application, pressing can be done by smoothing, rolling, flat pressure or the like. be made. If an adhesive that cures under atmospheric humidity is used, this is expediently used in applied a layer thickness of about three tenths of a millimeter and ensured that, despite the relatively good tightness of the carrier 3, the air humidity has a relatively uniform access to the hardening adhesive layer 14.

To support this reaction process and to ensure that any air pockets between the heating device and the body 10 to be heated can escape completely, the carrier 3 has a plurality of openings 9 which are expediently arranged such that they only penetrate the carrier 3 in such areas , in which the heating resistor 2 is not. The openings 9 are therefore expediently designed as slots lying parallel to the sections 4 and between these sections 4, the longitudinal boundaries of which are expediently located at a short distance from the associated heating resistor sections 4. After the adhesive layer 14 has hardened, these openings 9 can be sealed by the adhesive layer 14 in such a way that the adjacent sections 4 of the heating resistor 2 are covered in the manner of a seal.

The edges 17, which are approximately the same width in the area of the connecting ends 5 as in the area of the longitudinal edges and on the edge opposite the connecting ends 5, are adhered to the receiving side 11 of the up to their edge edges protruding beyond the heating resistor 2 fixed heating body 10 and thus form an all-round, ring seal-like closure, which is expediently set back relative to the associated outer edges of the body 10 to be heated. As a result, the heating resistor is permanently sealed in a watertight manner by embedding to the outside and is partially embedded directly in the adhesive layer 14 and is thus also advantageously secured against leakage currents.

At the directly adjacent or opposite connection ends 5 of the heating resistor 2, connecting lines 6 are connected at one end. These connecting lines 6, which are expediently made of highly flexible material and can be formed, for example, by copper strands, are supplied from the side of the carrier 3 facing away from the heating resistor 2 and pass through this and the heating resistor 2 or its connecting ends 5 in the region of openings whose width is greater than the cross section of the connecting lines 6. At these ends of the connecting lines 6, connecting heads 7 are provided, which completely fill the openings mentioned in the connecting ends 5 and the carrier 3, consist of electrically highly conductive material, for example solder material, and are essentially flush or flush with the surface 12 of the heating resistor 2 complete so that they reach at most up to this surface 12. But it is also conceivable that the respective connecting head 7 protrudes like a rivet head by a fraction of a millimeter or a tenth of a millimeter above the surface, in particular at most by the thickness of the adhesive layer 16, so that this part can also be embedded in the adhesive layer 14. In any case, there is a direct adhesive connection of the connecting head 7 or of its associated end face with the adhesive layer 14, so that the connecting head 7 is also fixed by the adhesive connection 13 directly opposite the receiving side 11 of the body 10 to be heated and a high mechanical strength against Tensile loads on the connecting line 6 is guaranteed. The connecting head 7, which can have an approximately twice the diameter compared to the connecting line 6, expediently protrudes slightly beyond the side of the carrier 3 remote from the heating resistor 2.

The respective connecting line 6 is expediently provided with a flexible insulation 18, which however begins only at a certain distance from the carrier 3 or the connecting head 7, so that a short, exposed section of the connecting line 6 is provided between the insulation 18 and the carrier 3 is. The insulation can be formed by using a siliconized copper braid. At the free ends of the connecting lines 6, connecting members 8 are provided, for example in the form of plug sleeves, so that the heating device can be easily and electrically connected by plug connections.

In FIGS. 4 to 7, the same reference numerals are used for corresponding parts as in the other figures, but each with different letter indices.

In the case of the embodiment according to FIGS. 4 and 5, the heating unit represents a wall mirror for a wet or sanitary room, in which, as in the case of a bathroom, for example, the mirror can be exposed to such a high level of humidity that it always tends to fog up . The mirror glass forming the body 10a to be heated is arranged in a frame-like base body 20 made of plastic or a similar material with electrically insulating properties, which covers the entire surface of the body 10a on the back and also encompasses it closed on the outer edge over the circumference. In this case, in which the electrical safety also plays an essential role in the event of a break in the body 10a, the carrier 17a is expediently arranged as an additional electrical safety protective layer between the heating resistor 2a and the body 10a. Therefore, the heating device with the heating resistor 2a remote from the body 10a is advantageously attached directly to a plate-shaped back part of the base body 20. At least the whole, the heating resistor stood 2a receiving surface of the carrier 3a can be covered with a thin self-adhesive layer or in particular with a similar or the same layer as the carrier, gapless and moisture-proof so that the heating resistor 2a completely in the manner of a sandwich construction between the carrier 3a and the whole area adhesive layer 30 is embedded.

In the case shown, the heating device is fastened to the base body 20 with an adhesive connection 19 which is separate from the heating resistor 2a at a distance or outside the heated field and which, although it can be formed by a full-surface adhesive or self-adhesive layer, is expediently so by individual, small-area and spaced, thicker adhesive connections 19 is formed so that the associated sides can always be exposed to ventilation. The adhesive connections 19 are, for example, four individual pieces of self-adhesive layers lying in the corner regions of the body 10a or an imaginary square, one side directly on the side of the carrier 3a associated with the heating resistor 2a or on the additional layer 30 and the other side directly can be adhesively attached to the front of the base body 20. As a result, the adhesive connections 19 also act in the manner of spacers, by means of which a gap 9a is kept free for ventilation between the remaining carrier 3a and the front of the base body 20. The circumferential edges of the body 10a also lie at a gap distance from the base body 20, which results in a chimney-like air flow or circulation along the rear of the heating unit. Due to the described configuration, the body 10a is fastened to the base body 20 exclusively by its connection to the heating device or to the carrier 3a, so that separate fastening members connecting the body 10a directly to the base body 20 are not required.

In the embodiment according to FIGS. 6 to 8, the heated object or the heating unit 1b represents a car exterior mirror, which is designed to be heatable in particular for the purpose of rapid deicing, the heating in this case using low current of, for example, 12 to 24 volt voltage is to be operated.

The heating device, which consists of at least one heating resistor 2b, carrier 3b and self-adhesive layer 19b and is considerably thinner than the mirror glass 10b, is arranged between the mirror glass 10b and a base plate 20b receiving the latter, which in turn is adjustable in a mirror housing for mirror adjustment. The heating resistor 2b is located on the side of the carrier 3b facing the mirror glass 10b, on the side thereof remote from which the self-adhesive layer 19b is arranged. The adhesive connection 13b to the mirror glass 10b is produced by means of a self-adhesive layer 14b, which is first applied to the mirror glass 10b or to the mirroring layer provided on the rear side and, in this respect, represents a prefabricated structural unit with the mirror glass 10b. On its side facing away from the mirror glass 10b, the self-adhesive layer 14b is initially covered with a protective film 28. After removal of this protective film 28, the heating device with the surface 12b of the heating resistor 2b is attached to the self-adhesive layer 14b and thus to the mirror glass 10b. A protective film 29, which initially covers the self-adhesive layer 19b on the side facing away from the carrier 3b, can also be removed, after which the self-adhesive layer 19b is adhesively connected to the base plate 20b and then the base plate 20b with the mirror glass 10b and the heating device is a self-contained assembly unit forms. In the center, the base plate 20b has a large-area, approximately circular opening extending approximately to its longitudinal edges, in the edge region of which there is a ring of fastening elements projecting beyond the rear side which is provided in the form of, for example, one-piece snap members formed with the base plate. The self-adhesive layer 19b is also expediently provided with an opening in this area.

In the exemplary embodiment shown, the heating resistor 2b forms at least two separately or essentially independently switchable heating circuits 21, 22, each of which is distributed substantially uniformly over the entire surface of the heating device or of the mirror glass 10b in that the two heating circuits are laid in a meandering manner one inside the other are. A heating circuit 21 with a higher or the highest heating output of over 25 or 30 watts, in particular of about 35 watts, is formed by a band-shaped, meandering coating, the bandwidth of which is significantly larger than that of the other heating circuit 22 of lower output. The heating circuit 21 runs in two mutually parallel meandering sections directly adjacent to the mutually opposite longitudinal edges of the mirror glass 10b, while the heating circuit 22 engages in the mutually facing meandering openings of these two meandering sections likewise with two mutually parallel meandering sections and thereby slightly from the mentioned longitudinal edges of the mirror glass 10b has a greater distance.

The ends of the two heating circuits 21, 22, which are produced by a one-piece coating in a single operation, merge in pairs adjacent to a narrow side of the mirror glass 10b to form common connection ends 5b. An electrical connection element 8b is electrically conductively connected to these connection ends 5b by a mechanical connection, namely by a rivet 7b. The shaft of the rivet 7b passes through the carrier 3b and the associated connecting end 5b and has a layer-like flat disk-shaped rivet on the side of the heating resistor 2b facing away from the carrier 3b head with a thickness that can be of the order of one to a few tenths of a millimeter and is expediently pressed into the connection end 5b or the carrier 3b in such a way that its surface facing away from the heating resistor 2b is at least almost in the plane of the associated surface of the rest Heating resistor 2b is. The other, substantially thicker rivet head rests on the side of a leg of the angular connecting element 8b facing away from the carrier 3b, this leg being able to be supported over the entire surface on the side of the carrier 3b facing away from the heating resistor 2b. The other leg of the connecting member 8b projecting towards the rear over the carrier 3b forms an electrical plug in the form of a flat tongue which passes through an opening in the base plate 20b which is adapted to it and on the rear side of which is exposed for detachable connection to the mating connector of a connecting line.

In a heating circuit, namely expediently in the heating circuit 21 of higher power, a temperature switch 25 is interposed according to the invention, which, in contrast to a PTC temperature monitor, can have a significantly higher temperature resistance especially when it is used as a mechanical switch, for example as a bimetal Snap disc thermostat is designed. This temperature switch 25 is fastened within the aforementioned opening in the self-adhesive layer 19b on the back of the carrier 3b with a flat adhesive connection 27 and has, for example, a flat housing, rectangular in view, which is only supported by the carrier 3b lying parallel to it, so that the temperature switch 25 forms a structural unit with the heating device. Adjacent to the connection ends 5b, the heating circuit 21 is interrupted, so that it forms two further, spaced-apart ends which can be connected to the temperature switch 25 via two short and essentially straight connection wires provided with insulating jackets. The only at the back of the Carrier 3b, essentially straight and V-shaped, relatively short connecting wires 26 can also be mechanically supporting parts for securing the temperature switch 25 with respect to the carrier 3b.

Each of the further connection ends of the heating circuit 21 is expediently penetrated by an electrical connection member, which can be designed as a rivet, in particular as a hollow rivet, and whose rivet head lying on the surface 12b of the heating resistor is expediently formed and sunk as described with reference to the rivet heads of the connection ends 5b is arranged. The end of the associated connecting wire 26 is expediently fastened to the other rivet head with a soldering head 24.

After switching on the heating with the aid of, for example, a manually operated switch, the two heating circuits 21, 22 are first operated in parallel, so that a heating output of more than 35 watts, for example between about 40 to 45 or more watts, results. The temperature switch 25 is adjusted so that it opens at a temperature between approximately 30 and 50 ° C., preferably approximately 40 ° C., and thus switches off the heating circuit 21, while the heating circuit 22 continues to operate with a so-called steady-state power. This steady-state power is expediently below half the total power or power of the heating circuit 21, namely, for example, between approximately 7.5 and 11 watts. The switching hysteresis of the temperature switch 25 is relatively high, namely above 15 to 25 ° C, preferably around 30 ° C, so that the temperature switch 25 only switches on again when it cools down to a temperature above freezing point, but relatively close to it , where a switch-on temperature in the order of 10 ° C has proven to be expedient. As a rule, however, this temperature is maintained by the steady-state performance below the usually occurring outside temperatures hold so that the temperature switch 25 does not turn on again, but the heating circuit 21 is only switched on when the exterior mirror has cooled below about 10 ° C after a long time and therefore in a short time, namely within a few minutes to be kept by the heating circuit 22 Operating temperature should be heated. It has been shown that this heating and thus a complete defrosting of the mirror can be achieved in about seven minutes or even less by the inventive design. This is possible in particular because the carrier has a temperature resistance up to about 200 ° C, the temperature switch has a temperature resistance well above 100 ° C and the adhesive bonds have temperature strengths up to about 130 ° C or are functionally heat-resistant up to these temperatures.

Claims (11)

1. Electric heating unit for a body to be heated (10, 10a, 10b), characterized in that it has a flat carrier (3, 3a, 3b) and at least one heating resistor (2, 2a, 2b) arranged thereon. 2. Heating unit according to claim 1, characterized in that the carrier (3, 3a, 3b) is at least partially formed by a paper-like substrate which forms a unit with at least one heating resistor (2, 2a, 2b) by coating. 3. Heating unit, in particular according to claim 1 or 2, characterized in that a heating device is provided with a receiving side (11) provided on the carrier (3) for the flat-layer electrical heating resistor (2) which has a heating resistor surface (12 ) and that the electric heating device has on its side associated with the heating resistor surface (12) an at least partially provided adhesive connection (13) for direct connection to a mating surface intended for holding the heating device, preferably at least one adhesive connection (13) at least partly by an adhesive layer (14) such as an adhesive that cures under atmospheric humidity, or a silicone resin adhesive of at least about 0.1 mm and at most 0.8 mm, in particular less than 0.5 mm thick and / or at least one adhesive connection by one to at least one about 130 ° C heat-resistant self-adhesive layer (14b, 19b), especially one Acrylic layer of at least 1/10 mm thick is formed. 4. Heating unit, in particular according to one of the preceding claims, characterized in that the heating resistor (2) on one or both sides, in particular on its side facing away from the body (10) to be heated, from the carrier (3), such as a film, is made of electrically insulating material, that in particular the carrier (3) in its areas adjacent to the sections (4) of the heating resistor (2) with an adhesive connection, in particular with the same adhesive connection (13) as the heating resistor (2), directly on the counter surface (11) is to be fastened and that preferably the heating device is provided with an adhesive connection (13) provided on the heating resistor surface (12), in particular essentially over the entire surface of the support (3) and the heating resistor (2) the body to be heated (10), such as a heating plate, is fastened, the heating resistor (2) preferably being a prefabricated structural unit with the carrier (3) and in particular with electrical connecting lines (6) of the heating resistor (2) penetrating them or fastened by rivets ) forms and this assembly as a whole is to be fastened to the body (10) to be heated via the adhesive connection (13). 5. Heating unit, in particular according to one of the preceding claims, characterized in that the carrier (3) within its outer boundaries, in particular approximately uniformly distributed over its surface, has openings (9) which are preferably adjacent to the sections (4) of the heating resistor ( 2) are, in particular formed by slots which are provided parallel to and between adjacent sections (4) of the heating resistor (2). 6. Heating unit, in particular according to one of the preceding claims, characterized in that the heating resistor (2) to form an adhesive bond (13 or 16) as with its associated surface (12 or 15) formed by coating applied or printed layer, is connected in particular as a printed conductor to the carrier (3), and that the heating resistor (2) is preferably formed from a metal-containing paste, in particular a polymer paste, such as a silver polymer paste, or from the mixture of a silver and a graphite polymer paste stabilized by heat treatment, in particular baked at a temperature in the order of 200 ° C. or solidified in its connection with the carrier (3, 3a, 3b). 7. Heating unit, in particular according to one of the preceding claims, characterized in that at least the receiving side (11) of the body to be heated (10) consists of electrically insulating material, preferably of a ceramic material such as glass ceramic, preferably the body to be heated (10) consists essentially of the same material over its entire thickness and in particular forms an at least three-layer composite panel with at least one adhesive layer (14), the heating resistor (2) and the carrier (3). 8. Heating unit, in particular according to one of the preceding claims, characterized in that the carrier (3) at least partially made of non-melting, high-temperature-resistant plastic, in particular of an aromatic polymer such as aramid and / or at least partially made of a paper-like material, in particular by a compressed mixture of fibers, flakes or the like. is formed, preferably long-fiber cellulose fibers mixed with polyamide fibers in combination with synthetic binders of the class acrylic ester copolymers and top coat on both sides of the support are provided. 9. Heating unit, in particular according to one of the preceding claims, characterized in that the heating device with from the body to be heated (10a), in particular a mirror, turned heating resistor (2a), preferably outside of the heated field with arranged in the manner of spacers, partial area Adhesive connections (19) are provided for fastening, which are provided in particular on the side of the carrier (3a) facing away from the body (10a) to be heated. 10. Heating unit, in particular according to one of the preceding claims, characterized in that, for example. For heating an outside mirror, the heating resistor (2b) has at least two heating circuits (21, 22), in particular different nominal power, at least one of which can be switched independently of the other , preferably at least one heating resistor, in particular the heating circuit (21) having a higher nominal output, can be switched via a temperature switch (25), such as a bimetal snap disk thermostat, with preferably high switching hysteresis or above 15 to 25 ° C, and the temperature switch (25 ) is attached in particular to the side of the carrier (3b) facing away from the heating resistor (2b) with an adhesive connection (26) or the like. 11. Heating unit, in particular according to one of the preceding claims, characterized in that the body to be heated, in particular the mirror glass (10b) of a car mirror, with an adhesive connection (19b) provided on the heating device on a base body (20b), such as a mirror holder, to be fastened.

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