EP1088467A1

EP1088467A1 - Electrical resistor heating element

Info

Publication number: EP1088467A1
Application number: EP99929202A
Authority: EP
Inventors: Manfred Elsässer
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-06-15
Filing date: 1999-06-14
Publication date: 2001-04-04
Also published as: CA2335712A1; US6423951B1; DE19826544C1; EA200100036A1; ZA200007358B; AU4609799A; EA002704B1; WO1999066766A1

Abstract

The invention relates to a resistor heating element (1) comprising a resistive sheet layer (2) which contains a resistive material (preferably an electroconductive polymer) and is placed between at least two electroconductive layers (3, 4, 7) shaped as plane electrodes in order to form a sandwich element. Each layer (3, 4, 7) can be connected to a power supply line via contact studs. At least one recess (5) in the first electroconductive layer (3) is shifted relatively to a recess (6) in the second electroconductive layer (4) so that the two recesses (5, 6) (viewed in projection one on top of the other) are placed at a distance from each other. These recesses (5, 6) are located in the border region of the electroconductive layer (3, 4, 7) and at least one contact stud (34) can come into electrical contact and be mechanically connected to the other electroconductive layer (3) in the region of the recess (5) of a first electroconductive layer (4) via the resistive layer (2). Preferably, the contact stud (34) can also be connected to the resistive layer (2), especially through a crimp connection.

Description

ELECTRIC RESISTANCE HEATING ELEMENT

The present invention relates to an electrical resistance heating element according to the preamble of claim 1. Such resistance heating elements are used in many areas, e.g. used in the construction industry as underfloor heating. The conventionally used resistance heating elements, in which the heat is generated by so-called heating wires or heating foils, have the disadvantage that they are sensitive to mechanical stress and, moreover, require a person skilled in the art for precise installation.

US-A-4'801784 describes a self-regulating heating element for the cable accessories and pipe protection industry, which works with surface electrodes and a resistance layer arranged between the surface electrodes. In such a heating element, the surface electrodes are contacted with the power supply lines, for example with rivets. The contacting therefore requires the application of pressure, as a result of which contact between the surface electrodes and thus a short circuit can occur.

Furthermore, from DE-Al-2'856'178 an electric heating mat is known in which heating conductors are laminated or laminated onto a base film. To connect these heating conductors to heating conductors of adjacent heating mats, connection areas are provided in which the heating conductors are exposed and can be connected by solder using a galvanic method or by riveting using a mechanical method. With such a construction, a short circuit is not to be feared since there are no surface electrodes which can come into contact during riveting. However, creating a heating mat of certain dimensions may require connecting a variety of heating mats.

For the use of a resistance heating element, for example as underfloor heating, on the one hand is the uniform heat emission over the surface and on the other hand the simplicity and durability of the installation and the electrical Contacting important. Furthermore, the resistance heating element must be flexible in terms of its dimensions in order to take into account the size of the area to be heated.

It is therefore an object of the present invention to provide a resistance heating element in which contacting can be achieved in a simple manner without the risk of a short circuit or damage to the resistance heating element, which at the same time withstands mechanical loads. Furthermore, the resistance heating element should be able to be manufactured continuously, be flexible in terms of its size, be easy to handle and allow use even in a moist environment.

This object is achieved by a resistance heating element which has the features of the characterizing part of claim 1. Advantageous developments of the invention are described in the dependent claims. For the purposes of this invention, surface electrodes are referred to as electrically conductive layers on which the resistance layer rests and via which the current is supplied.

The resistance heating element according to the invention, which is also referred to as a resistance sandwich, has predetermined contact points on account of the cutouts in the surface electrodes, at each of which a surface electrode can simply be connected to the power line. The contact can be made by pressing at high pressures. In the case of a resistance heating element with two surface electrodes, the tool is attached so that it engages in the recess of a surface electrode and on the other hand encompasses the resistance layer, the further surface electrode and the current supply device or the contact element. Even at high pressures, the contact between the surface electrodes cannot occur due to the recess and Overvoltage is avoided.

When establishing a non-positive or positive connection between the power supply and the surface electrode can also be used in the resistance heating element according to the invention, contact components which contact the surface electrodes in depth. Here, clamps can be used which engage at predetermined points from above and below via electrically conductive contact tongues or teeth in the resistance heating element. The one contact tongue is introduced into the recess of the first surface electrode on one side of the resistance heating element, penetrates the resistance layer and is in contact with the second surface electrode. The second contact tongue contacts the second surface electrode from the other side. The two contact tongues are in turn electrically connected to a power line, for example the phase. Such contacting in the depth of the resistance heating element is only possible with a resistance heating element according to the invention. In conventional resistance heating elements, such a type of contacting would short-circuit the surface electrodes and damage the resistance heating element. In addition to the precise connection of exactly one surface electrode, the type of contacting according to the invention has the advantage that the positive connection between the surface electrode and the power supply can also withstand tensile and shear loads.

A gasket, e.g. in the form of a silicone lip. In the resistance heating element according to the invention, the contact component can be pressed on with the pressure required for sealing. This means that it can also be used in a damp environment.

The resistance heating element according to the invention can easily be produced by conventional lamination processes and, because of the low risk of a short circuit when making contact, can also be contacted and installed by workers with little prior electrical engineering knowledge (e.g. construction workers).

By arranging the cutouts in the edge regions of the electrically conductive layers, each of the two or more layers can be targeted. A protective conductor, a neutral conductor and a layer connected to the phase can thus be arranged in the resistance heating element. Each of these layers can be contacted individually in depth without short-circuiting the electrically conductive layers. Even if contact is made under high pressure, none of the three layers comes into contact with one another and a short circuit is thus effectively prevented.

According to claim 4, several groups of recesses can be provided on the resistance heating element along the edges of the electrically conductive layers, each individual layer each having at least one recess. The distances between the groups of recesses are preferably uniform.

In this embodiment, several contact points are thus available on the edge of the resistance heating element. The number of cutouts provided per group depends on the number of electrically conductive layers that are present in the resistance heating element. The number of recesses per group is preferably one less than the number of layers. Given the large number of contact points, it can be decided on site when installing the resistance heating element which contact point is closest to the power source and should therefore be contacted with it.

In the embodiment according to claim 5, in addition to the contact options in the edge region of the resistance heating element, there are additional contact options in the area. If the resistance heating element is cut and the cut runs through the additional recesses provided in the surface, these can serve as a contact point on the edge after the resistance heating element has been divided. In this embodiment, the resistance heating element can thus be cut into the desired size on site, whereby there are always several contacting options for contacting the individual electrically conductive layers at the edge of the resistance heating element. The spatial spacing of the projection of the individual cutouts provides increased security in order to be able to avoid the contact between the electrically conductive layers or between the contact tongues of the power supply lines. In this preferred embodiment, the contact component, for example a clamp with contact tongues, which generally has a smaller dimension than the cutout, does not have to be positioned exactly in the middle of the cutout of the one electrically conductive layer, but can also engage close to the edge of the cutout as long as it fulfills the condition of claim 2. This additional fuse makes contacting the resistance heating element considerably easier and does not require any precision tools.

The embodiment according to claim 6 has the advantage that when the resistance heating element is cut to the desired size, straight cuts can be made along one of the longitudinal or transverse lines on which the additional recesses are located.

Furthermore, according to claim 7 or 8 by free, i.e. non-conductive areas in places where a short circuit could occur, e.g. in the area of force when contacting, a short circuit and other damage, e.g. by breaking through the tension, counteracted. Any filler material can be selected so that it also has reinforcing or stiffening properties and serves as insulation. As a result, the resistance heating element can be given additional stability in individual areas and the electrically conductive layers can be insulated from one another.

Since the contacting and thus the application of force takes place in the edge area, the omission of resistance mass in this area serves as an additional safeguard. The grid-like extension of such areas along lines in the longitudinal and width directions of the resistance heating element, which preferably correspond to the lines on which the additional cutouts in the surface of the electrically conductive layers are arranged, makes it easier to divide the resistance heating element into smaller pieces because the lines serve as cut edges. In particular in the case of filler material which has stiffening or reinforcing properties, damage to the resistance heating element by compressing the resistance layer at the cut edge can thus be avoided. In addition, the insulating property of the filling material, in particular at the locations of the cutouts where the contact is made, can also counteract a short circuit.

Openings in the electrically conductive layers according to claim 9 or 10, which may for example be in the form of circular holes, allow the resistance heating element to be fixed by conventional fastening means, e.g. Attach nails or screws to the wall or floor. A short circuit via the nail or the screw is prevented through the openings.

Filling material, which preferably has reinforcing or stiffening properties and can serve as insulation, can also act as an attachment in the area of the openings. If the screw or the nail is passed through the resistance layer, which is provided with the filling material at this point, a radial displacement of the screw in the opening, e.g. due to the dead weight of the resistance heating element when fastened to the wall, can be prevented by the filling material.

If the resistance layer comprises a carrier material which is coated with the resistance mass according to claim 11, the elasticity or plasticity of the resistance layer can be adjusted by the suitable choice of the carrier material. In addition, the resistance value of the resistance layer can also be ideally set in such a structure. The more porous the carrier material is chosen, the more resistance mass it can absorb. In addition, the carrier material can be present in a continuous layer, in which only the areas that are to be free of resistance mass, when coated with resistance mass be spared. The production of the resistance layer, which can be done for example by offset printing, is simple and allows a precise arrangement of areas with and areas without resistance mass.

An electrically conductive polymer can easily be applied to a carrier material; at the same time, high electrical heating outputs can be achieved with such a resistance mass. Furthermore, the electrically conductive polymer is flexible so that mechanical stress, e.g. by rolling up the resistance heating element, does not damage the resistance mass and thus leads to undesirable tears in the electrical line in the resistance heating element.

The invention is explained below with reference to the accompanying drawings, in which:

Fig.la: a perspective view of a resistance heating element according to the invention with two surface electrodes;

Fig.lb: top view of the resistance heating element according to the invention according to Fig.la;

2 shows a perspective section of an embodiment of the resistance heating element according to the invention with two surface electrodes and an additional electrically conductive layer;

3 shows a partial section through a resistance heating element according to FIG. 2 with contact component;

4: a plan view of a resistance heating element according to the invention, with two surface electrodes, an additional electrically conductive layer and several cutouts in the surface.

In Fig.la a resistance heating element 1 is shown, in which a resistance layer 2 between two electrical layers (hereinafter also called surface electrodes) 3 and 4 is arranged. A recess 5 is provided on an edge of the surface electrode 3. This is offset from the recess 6, which is arranged in the edge region of the surface electrode 4.

Fig.la is an exploded view of the resistance heating element. The Surface electrodes 3 and 4 are connected to the resistance layer 2, for example by gluing. To contact the resistance heating element shown, a contact component, for example a terminal with contact tongues (see part 34 in FIG. 3), can be attached to the edge of the resistance heating element. As a result, the surface electrode 3 can be connected to a power supply line by engaging in the recess 6. If the contact component is placed in the recess 5, a contact between a power supply line and the surface electrode 4 can be produced.

In Fig.lb the relative position of the recesses 5 and 6 to each other is shown. As can be seen from FIG. 1b, the recesses 5 and 6 do not overlap one another in their projection. The distance between the recesses 5 and 6 is selected such that, on the one hand, an influence of the pressure exerted on the region of a recess when contacting the adjacent recess is avoided and, on the other hand, the connection of the surface electrodes to power lines which are carried in a cable is avoided. is possible.

2 shows a resistance heating element 1 in which three electrically conductive layers (two surface electrodes and a further electrically conductive layer) 3, 4 and 7 are provided. The electrically conductive layer 7 is covered by an insulating layer 8 and separated from the surface electrode 4 by a further insulating layer 9 on the opposite side. The resistance layer 2 is arranged between the surface electrodes 3 and 4, the side of the surface electrode 3 facing away from the resistance layer 2 being covered by a further insulating layer 10.

Each of the electrically conductive layers has a plurality of cutouts in its edge region. The recesses are arranged in groups of two. The pairs of recesses are each arranged in such a way that a recess coincides with a recess of a further electrically conductive layer and is arranged offset to the recesses of the third electrically conductive layer. For example, if the electrically conductive Layer 7 as a protective conductor, the electrically conductive layer 4 as a neutral conductor and the electrically conductive layer 3 as a layer connected to the phase, each of these three electrically conductive layers 3, 4 and 7 can be contacted individually because of the cutouts. For this purpose, the contact to the electrically conductive layer 4 is established by placing the contact component at position A in such a way that it passes through the entire resistance heating element. By applying pressure and introducing contact tongues (not shown here, but see FIG. 3), one tongue can pass through the recess A 'and through the insulating layers 8 and 9 to the electrically conductive layer 4 and contact it. From below, a second contact tongue engages through the cutout A ", the insulating layer 10 and through the resistance layer 2 and thus reaches the underside of the electrically conductive layer 4. Accordingly, the electrically conductive layers 3 can pass through the cutouts B ', B" and electrically conductive layer 7 can be contacted through the recess C and C ".

In the embodiment shown in FIG. 2, the edge region 21 of the resistance layer is provided with an insulating filling material. In this embodiment, the resistance mass is located only in the region of the resistance layer denoted by 22. At the edge of the resistance heating element 1 there is thus a reinforced or stiffened area 1 of the resistance layer 2, which also has insulating properties. Contacting through this resistance layer 2 can therefore take place without voltage drop or without the risk of a short circuit. 2 shows openings 11 in the electrically conductive layers. These openings 11 are circular and are each arranged in the surface of the electrically conductive layers 3, 4 and 7 such that the individual openings 11 of the electrically conductive layers 3, 4 and 7 overlap. A further region 23 is provided on the resistance layer 2 in the region of the openings 11, in which it is free of resistance mass and preferably provided with filler material, which has reinforcing and insulating properties. If a fastening means, for example a screw, is guided through the resistance heating element 1 through the openings 11, then occurs this screw does not come into contact with any of the electrically conductive layers 3, 4 or 7 and is in particular held in the region 23 by the resistance layer 2 provided with insulating material.

3 shows the section through a contact point of the resistance heating element according to FIG. 2 at position B. The contact component 30 comprises two legs 31, 32, each of the legs 31, 32 having a contact tongue 33, 34. The contact tongue 34 is guided under pressure through the insulating layer 8, the recess B 'of the electrically conductive layer 7, the insulating layer 9, the recess B "of the electrically conductive layer 4 and the resistance layer 2 in the region 21. The tip of the contact tongue 34 thus reaches the electrically conductive layer 3 and forms a positive connection therewith The contact tongue 33 extends through the insulating layer 10 and engages in the electrically conductive layer 3. At the other ends, the legs 31, 32 have projections 35, 36, which lie below The contact component 30 is made of an electrically conductive material, for example copper, and an electrical connection is established through the contact with the power line, for example the phase on one side and the electrically conductive layer 3 on the other side. Due to the engagement of the contact tongues in the electrically conductive layer 3, a mechanically firm connection is made at the same time ng achieved. Because of the cutouts in the further electrically conductive layers 4 and 7, through which the contact tongue 34 extends, a direct short circuit of the electrically conductive layers is avoided. Corresponding further contact components are provided offset from the contact component 30, each of which access another power line and connect it to one of the other electrically conductive layers 4 or 7. Such an advantageous type of contacting is only possible with the resistance heating element according to the invention.

4 shows a resistance heating element 1, in which, in addition to the cutouts at the edge, which are designated by I, cutouts II are additionally provided in the surface of the individual electrically conductive layers. These recesses are arranged along lines S. The lines - left

stretch in the longitudinal and width directions of the resistance heating element 1. When dividing such a resistance heating element 1, the lines S can serve as cut edges. As a result, parts of a resistance heating element are made available, each of which itself can serve as a (smaller) resistance heating element and have several contact points in its edge region.

The width of the resistance heating element can vary depending on the area of application. With the heating element according to the invention, however, widths of e.g. 1.5 m can be realized. The lines along which recesses are provided in the surfaces of the individual electrically conductive layers can e.g. be arranged at intervals of 20 cm. Also a finer subdivision of the resistance heating element, i.e. It is possible to provide several lines in the longitudinal and width directions, provided that particularly small resistance heating elements are required on site.

Additional recesses III in the surface can also be arranged so that they extend over the lines S. As a result, when the resistance heating element 1 is divided on each of the resulting resistance heating element parts, there is a contact possibility at the edge.

The thicknesses of the individual layers of the resistance heating element can be selected differently depending on the area of application. For example, the resistance layer has a thickness of 1 mm and the electrically conductive layers and the insulating layers have a smaller thickness, e.g. of only 0.1 mm.

There are preferably three electrically conductive layers in the resistance heating element according to the invention. However, it is also within the scope of the invention to provide more than three electrically conductive layers, the cutouts in the layers being arranged in such a way that when the contact component, for example a contact tongue, engages, it only reaches a single electrically conductive layer. The recesses are therefore always arranged in a heating element according to the invention so that each covers a recess of an electrically conductive layer with a recess provided on one or more further electrically conductive layers, but is offset from a recess of a single other electrically conductive layer.

The cutouts are preferably arranged on the edge of the electrically conductive layer, but can also be at a short distance from the edge in the edge region of the electrically conductive layer. The recesses can have a wide variety of shapes, e.g. be rectangular or round. The shape and size of the cutout in one layer preferably corresponds to the shape and size of the cutouts in the other layers. The cutouts can, for example, have a width or a diameter of 5 mm, preferably 10 mm. The distance between the projection of the recesses, which are arranged in a group, is also 5 mm, preferably 10 mm.

If several groups of recesses are provided along the edge area or along lines in the longitudinal or width direction, the distance between them can be chosen as desired and is e.g. 100 or 50mm.

The insulating layers can consist of known insulating materials, for example polyester. The individual layers of the resistance heating element according to the invention can be connected to one another by conventional methods. The resistance layer can thus be connected to the electrically conductive layers surrounding it by means of an adhesive layer which is previously applied to the electrically conductive layers. The adhesive layer preferably has the same conductance or resistance as the resistance layer. However, it is also within the scope of the invention that the resistance mass provided in the resistance layer also serves as an adhesive. The insulating layers can be connected to one another on the electrically conductive layers by introducing plastic foils, for example polyester foils, between these layers and subsequent thermal treatment. In the regions in which a filler is provided in the resistance layer, the resistance layer is preferably not bonded or connected to the electrically conductive layers which surround it. This interruption of the connection has a great advantage, in particular in the edge regions or along the lines at which the resistance heating element can be cut.

To avoid flashover voltages, the electrically conductive layers are preferably dimensioned such that their edge is a few millimeters behind the resistance layer (see FIG. 2). If the electrically conductive layer is not glued to the resistance layer in this area, the part of the electrically conductive layer which is to be separated in order to avoid flashover voltages can be easily removed by cutting after cutting. This area, which extends over the edge areas and optionally over lines arranged in a grid, is small compared to the overall size of the resistance heating element. For example, the line-shaped areas in which no resistance mass - but possibly filler material - is provided in the resistance layer have a width of approximately 10 mm. The adjacent area of the resistance layer, in which resistance mass is present, on the other hand can e.g. have a width of approx. 100 mm. In the area of the resistance layer covered by filler material or insulating material, temperature compensation takes place over the surface of the electrically conductive layer. As a result, there is no temperature congestion in these areas either.

Due to the small dimensions of the areas in which the resistance layer can be provided with a filling material, the flexibility of the entire resistance heating element is not impaired. It is thus possible to produce resistance heating elements of any size which have filler material in the resistance layer in regions along lines which extend in the longitudinal and width directions. Due to the flexibility of the entire resistance heating element, it can be used as an endless be manufactured. This continuous product can be rolled up on rolls and unrolled as required. Conventional lamination devices are used to produce such a continuous material, in which several layers are processed to form a multilayer structure. The defined cut edges along which the additional recesses provided in the surface are located in the electrically conductive layers, as well as the contact points in the edge region and the positions of the openings in the electrically conductive layers are preferably marked on one of the outer insulating layers. It is thus possible to cut the resistance heating element into the desired size on site and to contact it with the power line. The contacted resistance heating element can then be connected, for example screwed, to the wall or floor at the locations at which openings are provided in the electrically conductive layers.

The resistance heating element according to the invention can be used in a variety of ways, in particular also in a humid environment, due to the contacting possibilities provided by the cutouts in the individual electrically conductive layers. The contact can be made under high pressure, with additional silicone lips at the contact points being able to be used as a seal against water. Furthermore, in the resistance heating element according to the invention, the contacting can take place such that the contact with the electrically conductive layers is deep, i.e. at the position of the respective electrically conductive layer. It is therefore only necessary to seal the entry points of the contact tongues or tabs. The entire remaining surface of the resistance heating element, in particular also the edge of the resistance layer or the electrically conductive layers, can be made watertight by a polyester film which is welded on. At the entry points of the screws, a seal against water ingress is achieved by the screw head, which can optionally also have a silicone lip on the edge.

With the resistance heating element according to the invention, water tightness can thus be achieved, which allows the resistance use heating element also in areas of splash water. Due to the contacting options provided by the cutouts, which enable a high level of security against damage to the resistance heating element, it can be used in low voltage as well as in mains voltage technology.

A suitable resistance layer is selected depending on the area of application. A fiber fabric or a flexible, porous plastic is preferably used as the carrier material of the resistance layer. For example, glass fiber mats or polypropylene nonwovens can be used. The amount of resistance mass that can be absorbed by the resistance layer can be influenced by the porosity or the density of the carrier material.

A plastic, which comprises an electrically conductive polymer, is preferably chosen as the resistance mass. In particular, polymers which are conductive as a result of metal or semimetal atoms which are attached to the polymers can be used as the electrically conductive polymer. Both electrically conductive polymers such as polystyrene, polyvinyl resins, polyacrylic acid derivatives and copolymers thereof, as well as electrically conductive polyamides and their derivatives, polyfluorocarbons, epoxy resins and polyurethanes can be used.

Metal layers can be used as the electrically conductive layers, aluminum foils, in particular, which allow the cutouts and the openings to be punched out, are preferably used. In this embodiment, the resistance mass or the filling material can be applied to the carrier material of the resistance layer using the offset printing process.

However, metal layers of, for example, aluminum, copper, nickel, etc., which have been applied by means of other coating methods known per se, such as, for example, by spraying, sputtering or vapor deposition, can also be used as electrically conductive layers. This has the advantage that the contacting or fastening of the heating sandwich elements is used Structure of the recesses in the conductive layers can be generated in a simple manner using appropriate templates. In particular for metal spraying, the prerequisite is a homogeneous, continuously pore-free resistance layer which prevents short-circuiting between adjacent conductive layers. In this embodiment, the resistance mass itself must be deaerated in a vacuum vessel before coating the carrier layer.

Non-conductive synthetic resin is preferably used as the filler material, the ratio of the electrical conductivity of the filler material to the electrical conductivity of the resistance compound preferably being greater than 1: 5.

Claims

PATENT CLAIMS

1. Electrical resistance heating element (1) with a flat resistance layer (2) which contains a resistance mass - preferably with an electrically conductive polymer - and is arranged between at least two electrically conductive layers (3, 4, 7) designed as surface electrodes, so that The result is a sandwich element, each layer (3, 4, 7) being connectable to a power supply line by means of contact tongues (33, 34) and at least one recess (5) in the first electrically conductive layer (3) opposite a recess (6) the second electrically conductive layer (4) is arranged so that the two recesses (5, 6) - when viewed in projection on one another - are spaced apart, characterized in that the recesses (5, 6) are in the edge region of the electrically conductive layer (3, 4, 7) and at least one contact tongue (34) in the region of the recess (5) of a first electrically conductive layer (4) through the resistance layer (2) can be electrically contacted and mechanically connected to the other electrically conductive layer (3), the contact tongue (34) preferably also being mechanically connectable to the resistance layer (2), in particular by crimping. (Fig.s 1,3)

2. Resistance heating element according to claim 1, characterized in that the distance between two adjacent recesses (5, 6) and / or a contact component (33, 34) from the edge of the relevant recess (5, 6) is chosen to be so large that the resistance the area of the resistance layer (2) in the area in question is at least five times higher than perpendicular to the area.

3. Resistance heating element according to claim 1 or 2, characterized in that it comprises at least one further, electrically conductive layer (7) which is separated by an insulating layer (9) from one of the two electrically conductive layers (4), each of which is electrically conductive layers (3,4,7) each have at least two recesses (A ^' , B'; B ", C; A", C ") and at least one recess (A") of an electrically conductive layer (3) at one point (A) lies on which no recess is arranged in only one (4) of the other electrically conductive layers, so that each power supply line (33, 34) - for example by means of a crimp terminal known per se - can be contacted through the cutouts (A ', A ") with that electrically conductive layer (4) which is in the projection of the relevant cutouts (A'. A ") is not left out. (Fig.2)

4. Resistance heating element according to one of the preceding claims, characterized in that along the edges of the electrically conductive layers (3, 4, 7) several - preferably evenly spaced - groups of recesses are provided. (Fig.4)

5. Resistance heating element according to one of the preceding claims, characterized in that the electrically conductive layers (3,4,7) have additional recesses (II) in the surface, which are arranged so that each electrically conductive layer (3,4,7 ) each has at least one non-recessed point at which the corresponding recesses of the other layers coincide with the additional recesses (II). (Fig.4)

6. Resistance heating element according to claim 5, characterized in that the additional recesses (II) in each case in the surface of the electrically conductive layers (3,4,7) in a grid shape along lines (S) in the longitudinal and / or width direction of the resistance heating element (1) in - preferably evenly spaced - groups are arranged.

7. Resistance heating element according to one of the preceding claims, characterized in that the resistance layer (2) has at least one region (21, 23) which is free of resistance mass and preferably contains a filler material, which in particular is a synthetic resin with at most 20% of the conductivity of the Resistance mass is.

8. Resistance heating element according to claim 7, characterized in that the at least one region (21) extends over the edge region of the resistance layer (2) and / or in a grid-like manner along lines (S) in the longitudinal and / or width direction of the resistance heating element (1) and preferably is not connected to the respectively adjacent electrically conductive layer.

9. Resistance heating element according to claim 7 or 8, characterized in that the electrically conductive layers (3,4,7) each have at least one opening (11) in the surface, which openings (11) with- each other and with the at least one area (23) in the resistance layer (2) which is free of resistance mass, in the projection.

10. Resistance heating element according to one of the preceding claims, characterized in that the resistance layer (2) comprises a carrier material which is coated with the resistance mass.

11. Resistance heating element according to one of claims 5 to 10, characterized in that it is rolled up in a length of at least 10 times, preferably at least 100 times the width and can be rolled off the roll.

12. Resistance heating element according to one of the preceding claims, characterized in that at least one of the outermost electrically conductive layers (3, 7) is covered by an insulating layer (10, 8), on which preferably the position of the recesses underneath (5, 6) ; A, B, C) and / or openings (11, 23) is marked.

13. Resistance heating element according to one of the preceding claims, characterized in that the resistance layer is essentially non-porous, optionally at least one electrically conductive layer being a spray metal layer.

14. A resistance heating element mounted on a substrate according to claims 9 and 12, characterized in that a fastening means, such as e.g. a screw through which openings (11) penetrate into the ground and preferably protect the resistance heating element against splash water by means of an annular seal attached to the underside of its head.