EP3438563B1 - Surface heating element, electric surface heating and method for producing a surface heating element - Google Patents

Description

The invention relates to a surface heating element and an electrical surface heating with such a surface heating element. The invention also relates to a method for producing a surface heating element.

Surface heating elements are known from the prior art, in which bodies made of carbon fiber material are heated by supplying electricity. The problem with the known heating elements is the maintenance of reliable electrical contacting of the carbon fiber material in continuous operation, especially at high currents. In this context, this means currents of more than 5 A up to 25 A. Typically, so-called "hotspots" form after a more or less long period of operation, since constant changes in length during the heating process lead to internal stresses and displacements of the conductive crossing points in the surface heating element, which in some cases bring about a gradual degradation of the conductive carbon fiber modification and thus the effectiveness and service life limit the heating element.

In WO 2006/103081 A1 describes a surface heating device with an electrically conductive layer and with electrical leads. In order to provide underfloor heating with a low overall height, which at the same time insulates noise, at least one sound insulation layer is provided. A surface heating element according to the preamble of claim 1 is from WO 2006/103081 A1 known.

A low-voltage heating element in the form of a mechanically resilient flexible layer composite is in EP 0 719 074 A2 described. The heating element is used for flat temperature radiators.

DE 20 2006 007 228 U1 describes an infrared surface heating element which, based on electrically conductive carbon fiber fleece, serves as a multi-layer sandwich for room heating in a high vacuum.

A resistance heating element, in which a special textile fabric subjected to a defined temperature treatment is used as electrical resistance, is out GB 2 285 729 A known.

An object of the present invention is to increase the service life of electrical surface heating systems.

This object is achieved by a surface heating element according to claim 1 or an electrical surface heating according to claim 7 or by a method for producing a surface heating element according to claim 10.

Advantageous embodiments of the invention are specified in the subclaims.

The advantages and configurations explained below in connection with the surface heating element also apply mutatis mutandis to the surface heating according to the invention and vice versa and to the method according to the invention for producing a surface heating element and vice versa.

A basic idea of the invention is to improve the electrical contacting of the contact elements with the base body of the surface heating element by structuring the contact surface of the contact element in such a way that parts of the contact surface, preferably a multiplicity of partial areas of the contact surface, penetrate into the base body, as a result of which the electrical Contact area increases and the contact resistance is reduced. The formation of "hot spots" is thereby avoided and the service life of electrical surface heating systems which use such heating elements is extended.

Another idea (not part of the claimed invention) consists in sealing and fixing the electrical contacting of the contact elements produced with the base body of the surface heating element, by using a protective film or a comparable protective element in order to seal and mechanically fix the contact point. As a result, the electrical connection between these two elements is fixed and secured at the same time, so that even if one of the elements involved or all elements expand or shrink or if the surface heating element needs to change shape, for example due to a specific storage or transport form or due to a certain Application, for example as a heating element of an electrical surface heating, which does not release the electrical contact but instead remains intact unchanged.

Fig. 1

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Längsanordnung der Kontaktelemente,

Fig. 2

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Queranordnung der Kontaktelemente,

Fig. 3

einen Schnitt durch das in Fig. 1 dargestellte Heizelement entlang der Linie III-III,

Fig. 4

einen Schnitt entsprechend Fig. 3 durch ein Heizelement mit vollflächig angebrachter Schutzfolie,

Fig. 5

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Queranordnung der Kontaktelemente und einem Stromfluß quer zu der Faservorzugsrichtung,

Fig. 6

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Queranordnung der Kontaktelemente und einem Stromfluß in Faservorzugsrichtung,

Fig. 7

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Längsanordnung der Kontaktelemente und einem Stromfluß quer zu der Faservorzugsrichtung,

Fig. 8

eine Draufsicht auf die Vorderseite eines Heizelements mit einer Längsanordnung der Kontaktelemente und einem Stromfluß in Faservorzugsrichtung,

Fig. 9

eine Draufsicht auf die Vorderseite eines Heizelements mit drei quer angeordneten Kontaktelementen in einer ersten Anschlußvariante,

Fig. 10

eine Draufsicht auf die Rückseite des Heizelements aus Fig. 9,

Fig. 11

eine Draufsicht auf die Vorderseite eines Heizelements mit drei quer angeordneten Kontaktelementen in einer zweiten Anschlußvariante,

Fig. 12

eine Draufsicht auf die Rückseite des Heizelements aus Fig. 11,

Fig. 13

einen Schnitt durch eine Kontaktfläche,

Fig. 14

eine Draufsicht auf eine strukturierte Kontaktfläche,

Fig. 15

die Komponenten einer Flächenheizung,

Fig. 16

eine Draufsicht auf ein einzelnes Heizelement (stark vereinfacht),

Fig. 17

eine Draufsicht auf einen Heizelementeverbund (stark vereinfacht).

Advantageous embodiments of the invention are explained in more detail below with reference to the drawings using various exemplary embodiments. Here show:

Fig. 1

a plan view of the front of a heating element with a longitudinal arrangement of the contact elements,

Fig. 2

a plan view of the front of a heating element with a transverse arrangement of the contact elements,

Fig. 3

a cut through the in Fig. 1 heating element shown along the line III-III,

Fig. 4

a cut accordingly Fig. 3 by a heating element with protective film applied over the entire surface,

Fig. 5

a plan view of the front of a heating element with a transverse arrangement of the contact elements and a current flow transverse to the fiber preferred direction,

Fig. 6

2 shows a plan view of the front of a heating element with a transverse arrangement of the contact elements and a current flow in the preferred fiber direction,

Fig. 7

a plan view of the front of a heating element with a longitudinal arrangement of the contact elements and a current flow transverse to the preferred fiber direction,

Fig. 8

2 shows a plan view of the front of a heating element with a longitudinal arrangement of the contact elements and a current flow in the preferred fiber direction,

Fig. 9

1 shows a plan view of the front of a heating element with three transversely arranged contact elements in a first connection variant,

Fig. 10

a plan view of the back of the heating element Fig. 9 ,

Fig. 11

a plan view of the front of a heating element with three transversely arranged contact elements in a second connection variant,

Fig. 12

a plan view of the back of the heating element Fig. 11 ,

Fig. 13

a section through a contact surface,

Fig. 14

a plan view of a structured contact surface,

Fig. 15

the components of a surface heating,

Fig. 16

a plan view of a single heating element (greatly simplified),

Fig. 17

a plan view of a heating element assembly (greatly simplified).

The figures do not show the invention to scale, but only schematically and only with its essential components. The same reference numerals correspond to elements of the same or comparable function.

A surface heating element 1 according to the invention comprises a heating resistor, i.e. heatable base body 2 in the form of an electrically conductive, flexible sheet which contains carbon fibers (not shown in detail).

The heating element 1 according to the invention also comprises at least two electrical contact elements 3, 4 which are spaced apart and are connected to the base body 2 in a planar manner. These surface contacts are used to feed electrical current into the base body 2. The contact elements 3, 4 are connected with their contact surfaces 5 to the surface 6 of the base body 2 or are attached to the surface 6 of the base body 2. In particular, the contact elements 3, 4 rest on or on the surface 6 of the base body 2.

The contact surfaces 5 of the contact elements 3, 4 of the heating element 1 according to the invention are designed such that they penetrate into the base body 2. This penetration or intervention preferably does not take place over a large area, but rather selectively, here selectively not in the sense of punctiform, but in the sense of sections or areas. Nevertheless, each individual point of engagement of the base body 2 can be designed as a point-like engagement, caused by a pointed engagement tool. The engagement preferably takes place at a multiplicity of locations on the contact surfaces 5 of the contact elements 3, 4 these points are evenly distributed over the entire contact surface 5.

The base body 2 of the heating element 1 is formed by a flat structure made of fibers. The fabric is either a paper fleece (hereinafter also referred to briefly as paper), more precisely an electrically conductive paper structure with cellulose-containing fibrous materials or other fibers customary for paper production on the one hand and with carbon fibers on the other hand. Or the sheet is a different non-woven fabric, for example a structure made of plastic fibers, e.g. Polyester fibers, mixed fibers or the like, which together with carbon fibers in some way form a nonwoven, i.e. a fiber layer is assembled.

The material of the base body 2 preferably contains 10 to 50% by weight of carbon fibers. Electrically conductive paper is used as an example, as described in DE 10 2013 101 899 A1 is described. Such papers or non-woven fabrics conduct the electrical current and can be contacted in such a way that electrical power can be converted effectively and efficiently into heating by means of low-voltage transformers. According to a particularly preferred embodiment of the invention, the base body 2 contains approximately 35% by weight of carbon fibers and the preferred grammage of the paper is 80 to 150 g / m ² . The material properties of the material used for the base body 2 can preferably be precisely defined, in particular with regard to its electrical conductivity. The carbon fibers used as an electrically conductive component have, for example, a specific electrical resistance of 1.6 x 10 ^-5 Ωm.

In the following it is assumed as an example that the base body 2 consists of a paper fleece.

The carbon fibers are preferably uniformly distributed (dispersed) in the base body 2. The manner in which the nonwovens are produced means that the carbon fibers in the paper structure are oriented anisotropically, usually preferably along the length of the paper web, so that in such cases a defined or uniform fiber direction 7 (“preferred direction”) can be assumed. This results in two different possibilities for contacting, namely on the one hand with a current flow 8 transverse to the preferred fiber orientation 7 and on the other hand with a current flow 8 along the preferred fiber orientation 7. For the "transverse" case, compared to the "longitudinal" -Fall, a higher resistance. In a preferred embodiment of the invention, this is used in a targeted manner.

The base body 2 is preferably designed in such a way that it is flexible or flexible, in particular in such a way that it can be deformed when the heating element 1 is applied in the subsequent surface heating 10, for example can be adapted to the shape of a component to be heated.

The geometry of the base body 2, in particular its length and width, is preferably freely selectable and can be adapted to the particular application. The basic shape of the base body 2 is typically rectangular. In any case, it is a flat structure, ie a flat, in particular flat body, for example in the form of an arch, a plate, a board, a web or a roll.

One side of the flat, i.e. usually at least in the unprocessed initial state of cuboid base body 2 is defined as the front side 11, the opposite side as the rear side 12, it being assumed that the front side 11 is primarily intended to radiate heat radiation, the free area not occupied by contact elements 3, 4 the front 11 thus serves as a heating surface 13. Because of the way in which the heating element 1 works as a resistance heater, the base body 2 heats up continuously, so that the opposite rear side 12 is also heated, even if the contact elements 3, 4 are only electrically connected to the base body 2 on the front side 11. The rear side 12 can therefore also serve as a heating surface 13 or form a heating surface 13.

The base body 2 can be changed in shape as desired, for example cut to size, and / or provided with openings (holes, bores, openings, ...), e.g. for attaching screws or other fastening elements or for adapting to the shape of the component to be heated etc. pp. As long as the contact elements 3, 4 remain intact, the heating element 1 is still functional. In other words, the base body 2 can not only be bent, folded or rolled. The heating surface 13, that is to say typically the surface between the contact elements 3, 4 on the front side 11 of the base body 2 of the heating element 1, can also be shaped asymmetrically, without this affecting the functionality of the heating element 1.

The base body 2 does not necessarily have to be understood as a homogeneous body which consists only of a single material (paper, nonwoven fabric, etc.). The base body 2 can also represent a combination of materials. In particular, the base body 2 can differ from several layers Material built up, provided the core or the essential (predominant) component of the base body 2 consists of carbon fiber-containing material (paper fleece, fiber fleece, etc.) and is suitable for forming a heating resistor, that is, heat can be generated by the material, which is comparatively has low electrical resistance, is traversed by electricity and heats up as a result.

It is particularly advantageous if the material used for the base body 2 is open to diffusion, i.e. moisture can pass through the 2 base body, as is the case e.g. can be useful when using the heating element 1 in a panel heater 10, which is used for dehumidifying masonry.

Modifications to the base material can cause changes in the electrical resistance of the heating element 1. For example, the resistance of the base body 2 can be increased by specifically impregnating the fibers used with plastics or viscous contact adhesives. A low-melting film (not shown), which improves the contacting, can also be provided between the contact elements 3, 4 and the base body 2 as an intermediate layer.

In a preferred embodiment of the invention, the contact elements 3, 4 are formed by foils or tapes. Copper is preferably suitable as the material for the contact elements. The use of other suitable materials is possible.

If the contact elements 3, 4 are not designed as solid conductors or sheets, but as a thin material, in particular as Foils or tapes, for example in the manner of tape electrodes, are easily deformable due to the low material thickness and can therefore be snugly pressed onto the fiber structure of the base body 2.

A flexible or flexible design of the contact elements 3, 4 also ensures that the contact elements 3, 4 can adapt to a changed shape of the base body 2 when the base body 2 deforms, for example bent, during the application of the heating element 1 in the subsequent surface heating 10 , folded or folded.

In comparison to the base body 2, the contact elements 3, 4 have smaller dimensions. As a rule, the contact elements 3, 4 cover only a fraction of the surface 6 of the base body 2 in the contacted state.

The contact elements 3, 4 are preferably connected to the base body 2 simultaneously by means of several types of connection, but in the simplest case by means of an adhesive connection. In other words, the contact elements 3, 4 are glued onto the base body 2. The connection by means of adhesive is very easy to produce, also by means of automated processes. In addition, with a suitable choice of adhesive, adhesive connections are also durable when exposed to high currents.

It is particularly advantageous to use a self-adhesive copper tape, such as is used, for example, to discharge static electricity and shield electromagnetic fields, as contact element 3, 4. In a preferred embodiment of the invention, the adhesive tape comprises a suitable adhesive, for example acrylate adhesive, and a copper foil as a carrier on a paper liner. The copper tape used preferably has a width of 10 to 25 mm.

The connection of the contact elements 3, 4 to the base body 2 can, however, also take place in alternative designs without gluing, for example by fixing the contact elements 3, 4 to the base body 2 by means of mechanical aids. If necessary, such aids can be removed again after the structuring of the contact elements 3, 4 if the contact elements 3, 4 are connected to the base body 2 due to their mechanical engagement.

In connection with the production of the heating element 1, a decision is made not only on the size of the base body 2, but also on the arrangement of the contact elements 3, 4 on the base body 2 in the manner of assembly.

In advantageous embodiments of the invention, the contact elements 3, 4 are arranged on opposite edges or edges of the base body 2. In principle, the contact elements 3, 4 can be arranged longitudinally or transversely on the generally rectangular surface of the base body 2. This has different effects on the distance and the length of the contact elements 3, 4 and for the later passage of current between the contact elements 3, 4 on the one hand and the countless carbon fiber 3 consumers "inside the base body 2 on the other hand.

In this connection, a first fundamental decision must be made with regard to the ratio of length 14 of the contact elements 3, 4 to distance 15 between the contact elements 3, 4 on the front side 11 of the base body 2. In the case of base bodies 2 with sides that are not of equal length, this can be done between a first variant with long contact elements (effective conductor lengths 14) and a small distance 15 between the contact elements 3, 4 (ie the contact elements 3, 4 are arranged on the longer longitudinal sides 16 of the base body 2), as exemplarily in Fig. 1 mapped, and a second variant with short contact elements 3, 4 (effective conductor lengths 14) and a large distance 15 between the contact elements 3, 4 (ie the contact elements 3, 4 are arranged on the shorter narrow sides 17 of the base body 2), how exemplary in Fig. 2 pictured.

In this context, a second fundamental decision must also be made, namely with regard to the arrangement of the contact elements 3, 4 in relation to the preferred direction 7 of the carbon fibers in the base body material. To be more precise, it must be decided whether the current flow 8 takes place in the fiber direction 7 or transverse to the fiber direction 7. This has an influence on the achievable electrical resistance of the heating element 1.

The electrical resistance R important for the heating power of the heating element 1 results according to R = kx A / L, where A is the distance 15 between the contact elements 3, 4 and L the effective length 14 of the contact elements 3, 4 on the base body 2 and k a Represents material constant, which is dependent on the proportion of carbon fibers in the base body material.

In the case of contact elements 3, 4 with a short length 14, which are arranged at a large distance 15 from one another, the current flows through the base body 2 transversely to the fiber direction 7 of the carbon fibers in the base material, as in FIG Fig. 5 shown, there is a first electrical resistance R1.

In the case of contact elements 3, 4 with a short length 14, which are arranged at a large distance 15 from one another, the current flows through the base body 2 in the fiber direction 7 of the carbon fibers in the base material, as in FIG Fig. 6 shown, there is a second electrical resistance R2 <R1.

In the case of contact elements 3, 4 with a large length 14, which are arranged at a short distance 15 from one another, the current flows through the base body 2 transversely to the fiber direction 7 of the carbon fibers in the base material, as in FIG Fig. 7 shown, there is a third electrical resistance R3 << R2.

The current flows through the base body 2 in the case of contact elements 3, 4 of great length 14, which are arranged at a short distance 15 from one another, in the fiber direction 7 of the carbon fibers in the base material, as in FIG Fig. 8 shown, there is a fourth electrical resistance R4 <R3.

Depending on the electrical conductivity or the resistance of the base body 2, taking into account the preferred direction 7 of the carbon fibers and the design and arrangement of the contact elements 3, 4, a defined thermal heating output of the heating element 1 can be achieved.

The aim of the above considerations and selection steps for the preparation or assembly of the heating element 1 is always to achieve the desired heating power (e.g. 300 W) or the desired surface temperatures (e.g. 80 ° C) on the heating surface 13 of the heating element 1 with a low-voltage system, ie To achieve nominal voltages of 12V, preferably 24 to 36V. Despite the fact that comparatively large currents (for example 8 to 12 A) arise, the heating element 1 according to the invention has a comparatively long service life.

With a suitable contact, as described here, it is possible, for example, to generate heat flux densities with transformer powers of preferably 120, 200 to 300 watts, in individual applications also up to 500 or 800 watts, with which, depending on the area size of the base body 2, surface temperatures of preferably 30 to 180 ° C can be achieved.

In the case of particularly narrow base bodies 2, a special arrangement of contact elements 3, 4 and a special connection geometry can be used in preferred embodiments of the invention. This is particularly interesting if the base body 2 has a very uneven aspect ratio, for example if the length of the long side (broad side) 16 to the length of the short side (narrow side) 17 has a ratio of 10: 1. A strongly unequal aspect ratio is understood to mean a value for the ratio between the length of the long side to the length of the transverse side (or vice versa) of at least 5: 1, preferably a value of at least 10: 1 or greater. In these or similar cases, it is provided that three or more contact elements 3, 4, 18 are attached to one side 11 of the base body 2 in such a way that the base body 2 is divided into a plurality of heating resistor segments 21, 22 in its longitudinal direction 19. The contact elements 3, 4, 18 are preferably arranged parallel to one another and parallel to the edges or edges of the transverse sides (narrow sides) 17 of the base body 2.

In other words, the contact elements 3, 4, 18 are not only provided on the edges or edges of the base body 2, but also in the surface of the front and / or rear side 11, 12 of the base body 2, for example by arranging a third contact element in the center 18 on the front 11.

This attachment of additional contact elements 18 results in a preferably uniform segmentation or subdivision of the total area of the base body 2 into several, preferably equally large, smaller areas 21, 22, which leads to a kind of parallel connection for the resistance heating of the heating element 1, which results in several Partial resistances result from which the total resistance of the heating element 1 results.

If the rear supply of the contact elements 3, 4, 18, ie the arrangement of the conductor tracks on the rear 12 of the base body 2, takes place by means of insulating elements 23, both current source connections 24, 25 of the contact elements 3, 4, 18 can be on one and the same side of the base body 2, for example on one of the transverse sides 17, see Figures 9 and 10 respectively. Figures 11 and 12 . However, other positions of the connections 24, 25 or the contact elements 3, 4, 18 are also possible.

In the cases described above, flat electrical insulating elements 23 are used to form an electrically insulating separating layer between the contact elements 3, 4, 18 and the base body 2, namely at those locations where the contact elements 3, 4, 18 are due to the compactness of the heating element 1 are also mounted flat on the base body 2. This is necessary, for example, for returning connecting lines 26 to defined connection points 24, 25 of the heating element 1 on the rear side 12 of the base body 2, without the base body 2 being electrically contacted. The connecting lines 26 which are returned in this way are preferably those which are led around the edges of the base element 2 Contact elements 3, 4, 18, which are also used on the front 11 for contacting the base body 2.

The insulating adhesive tape which is preferably used for this purpose as the insulating element 23 is preferably strongly self-adhesive and has a supple carrier film which is preferably temperature-stable up to approximately 160 ° C.

As in Fig. 10 illustrated, the contact elements 3, 4, 18 placed on the front side 11 on the base body 2 are preferably guided around the edges of the base body 2 onto the rear side 12. There, the contact elements 3, 4, 18 are either returned as connecting lines 26 via the electrical insulating elements 23 to the connection points 24, 25 or the free ends 27 of the contact elements 3, 4, 18 are also there (on the rear side 12) for a short distance directly on the base body 2. This guiding the contact elements 3, 4, 18 down to the rear 12 serves on the one hand as a mechanical securing means, namely to prevent the contact elements 3, 4, 18 from coming loose in the edge region. On the other hand, in particular the free ends 27 on the back 12 can be used to connect further heating elements 1, as may be the case, depending on the particular application, when assembling the surface heating 10 from a plurality of heating elements 1, in particular if there are several heating elements 1 must be placed next to each other and connected to form a composite heating surface that is larger than the heating surface 13 of a single heating element 1.

An important measure for optimizing the function and increasing the service life of the heating element 1 is carried out during the production of the heating element 1. According to the invention, the contact surfaces 5 of FIG Contact elements 3, 4, 18 have a surface structure with a large number of deformations 28, 29 which contribute to establishing a (preferably both mechanical and electrical) connection of the contact elements 3, 4, 18 to the base body 2 by inserting them into the base body 2 penetration. The material properties of the base body 2, in particular its structure as paper or nonwoven and / or the presence of the carbon fibers, enable such an intervention. Depending on the length of the fibers in the fiber structure, there are gaps which, depending on the shape of the fibers, can be filled in different ways. The carbon fibers, which are preferably in the form of pointed needles, only form crossings with free interiors. Instead, the cellulose fibers form a somewhat denser network. The fiber composite as a whole is not compacted and therefore allows the interventions described.

This mechanical penetration of the contact surfaces into the base body 2 serves (at least also, i.e. in addition to an electrically conductive adhesive connection between the contact elements 3, 4, 18 and the base body 2) to produce a particularly safe and permanent electrical contact.

For this purpose, the contact surface 5 of the contact element 3, 4, 18 has bumps pointing in the direction of the base body 2 (in particular elevations and / or depressions of the surface) in order to ensure the best possible mechanical connection between the contact elements 3, 4, 18 when the two components are pressed together and enable body 2. When the contact element 3, 4, 18 is pressed into the base body 2, the base body 2 is deformed.

In a preferred embodiment of the invention, the contact surface 5 is perforated many times or at least provided with a large number of impressions (impression marks) such that the conductor material (for example copper) of the contact element 3, 4, 18 and thus the contact element 3, 4, 18 itself plastically deformed. The deformations 28, 29 are preferably more or less evenly distributed over the entire contact surface 5 of the contact element 3, 4, 18, at least in such a way that there is no deliberately caused accumulation of deformations at specific points on the contact surface 5. The number of deformations 28, 29 is preferably 50 to 100 per square centimeter.

The deformation takes place either with the formation of, for example, funnel-shaped openings 28 or with the formation of (closed) bulges (depressions) 29, see Fig. 13 . Both types of deformations 28, 29 are directed in the direction of the base body 2, preferably in such a way that the closed bulges 29 or the open edges 30 of the openings 28, in particular in the manner of cutting edges, penetrate into the material of the base body 2 and locally and selectively displace and / or deform the carbon fiber material. This takes place in such a way that the contact surface 5 of the contact element 3, 4, 18 conforms particularly closely to the surface 6 of the base body 2, preferably by producing a contact surface 5 which is enlarged compared to a completely flat / flat surface contact. The enlargement of the contact surface 5 results from an expansion of the contact element material occurring during the deformation and / or from the fact that when the cutting edges 30 of the openings 28 penetrate into the base body 2, base material also contacts the side 34 of the contact elements 3 opposite the actual contact surface 5, 4, 18 creates, see Fig. 13 .

In a preferred embodiment of the invention, the contact element 3, 4, 18 is processed, e.g. by means of a needle roller or another processing tool suitable for such material processing (not shown). The structuring of the contact surfaces 5 of the contact elements 3, 4, 18 preferably does not take place by means of a flat roller or the like, as a result of which the nonwoven material of the base body 2 would be inadmissibly compressed. Instead, needling is preferably carried out, a comparatively high pressure being applied to the corresponding punctiform areas of the contact surface 5 to be structured via the thin tips of the individual tool needles. Due to this pressure, the desired deformation of the contact surface 5 takes place. The orientation of the deformations 28, 29 preferably corresponds essentially to the machining direction with which the contact element 3, 4, 18 is machined to produce the deformations 28, 29, or the direction of Applying a suitable processing tool to the contact element 3, 4, 18. The deformations 28, 29 typically extend substantially perpendicular to the surface 6 of the base body 2.

In other words, in accordance with these embodiments of the invention, in addition to the adhesive connection, the contact is made by a "cold" penetration (for example pressing in, cutting or the like) which for this purpose has a suitable surface structure, such as in particular closed bulges 29 and / or open ones Cutting edges 30, provided contact surface 5 of the contact element 3, 4, 18 into the surface 6 of the base body 2 to be contacted, namely preferably in the manner of a "press-in contact", ie the two joining partners are pressed.

The structured surface 5 of the contact element 3, 4, 18 directly attacks individual carbon fibers in the interior of the base body 2 and makes physical contact with them. This increases the number of mechanical and thus electrical contacts of the contact surface 5 with the electrically conductive carbon fibers. A particularly reliable electrical contact produced in this way goes hand in hand with an enlarged electrical contact area and a reduced contact resistance between contact element 3, 4, 18 and base body 2. This contributes to the fact that no "hot spots" arise. This extends the life of the heating element 1.

During the production of the heating element 1, another measure important for optimizing the function and increasing the service life of the heating element 1 is preferably carried out. According to a preferred embodiment of the invention, at least the contact elements 3, 4, 18 and parts of the base body 2 are covered with a number of protective films 32. The protective film 32, if present, also covers the contact elements 3, 4, 18 or connecting lines 26, which are attached to electrical insulating elements 23 and preferably extend on the back of the base body 2. Preferably, the entire heating element 1 with all its components is covered with the protective film 32 covered. As explained in more detail below, however, partial coverage is also possible.

A highly elastic hot-melt film (hot-melt adhesive film) is preferably used as the protective film 32. The film 32 has a very high elasticity, which allows it to fix the contact elements 3, 4, 18 securely to the base body 2 even when the heating element 1 is deformed, for example folded, kinked or rolled. Preferably the protective film 32 is distinguished by a high (positive) elongation, preferably the elongation is more than 500%. Thermoplastic polyurethane films are preferably used. A protective film 32 based on polyether urethanes, for example, which has soft polyether group segments and is distinguished by a comparatively high permeability, has proven particularly suitable. Protective films 32 on a different basis (eg copolyamide or copolyester basis) are also possible.

The protective film 32 is applied when a hot-melt adhesive film is used with the supply of heat, for example in that the film passes through a defined heating region for melting the hot-melt adhesive, and pressure, for example using a roller or the like. Warm air, thermal radiators or heated rollers can be used for this.

It is important that the protective film 32 has a high softening temperature so that it does not melt during normal heating operation. Films 32 with a softening temperature of 140 to 160 ° C. have proven to be particularly suitable.

In one embodiment of the invention, the protective film 32 covers the entire base body 2 on both sides (sealing of the entire base body), see 2, 4 , 9, 10, 11 and 12 . This leads to a particularly high mechanical stability of the heating element 1. In this case, the heating element 1 is particularly well protected against mechanical stress. In addition, the heating element 1 is protected in this case against undesired entry or exit of materials or infiltration with liquids. In particular This type of encapsulation prevents changes in the electrical contacting surfaces between contact elements 3, 4, 18 and base body 2. The entire heating element 1 is then preferably packed liquid-tight.

In an alternative embodiment, the protective film 32 essentially covers only the area of the contact elements 3, 4, 18 and the immediately adjacent areas of the base body 2, see 1 and 3 . As a result, the contact elements 3, 4, 18 are sealed and mechanically fixed in their electrical contact position on the base body 2. In this case, the majority of the surface 6 of the base body 2, in particular the majority of the actual heating surface 13, remains free of protective films.

The thickness of the film 32 is preferably 50 to 200 μm, a small film thickness (for example 50 μm) advantageously being used when the protective film 32 is to be designed to be diffusible, for example in order to allow moisture to pass through in conjunction with a diffusion-open base body 2. On the other hand, particularly thick foils 32 are particularly suitable due to their mechanical stability for applications in which the heating element 1 has to be protected against mechanical loads, such as high pressure cleaning. If the heating element 1 is subjected to particularly high mechanical stress, the layer thickness of the protective film can then be 32 to 1000 μm without the desired flexibility of the heating element 1, as is required, for example, for rolling up, being significantly impaired. The protective film 32 is preferably designed such that it not only protects the base body 2 against mechanical stress, but is also insensitive to chemicals, in particular cleaning agents.

For variants that are open to diffusion, e.g. If water vapor is to diffuse through the heating element 1, for example in the targeted drying of component surfaces which are tempered by means of an electrical surface heating 10 using the heating elements 1 described, a thin protective film 32 preferably comes e.g. with a thickness of 50 μm, which is laminated onto the base body 2 as a type of membrane, or large areas of the heating element 1 are not provided with a protective film 32 at all to ensure a particularly high diffusion performance. However, in this case too, as in the case of a full-surface covering with protective film 32, the contact elements 3, 4, 18 are covered with protective film 32, together with a safety edge 33 on both sides, which is typically approximately 15 mm wide in each case. In both cases, the protective film 32 is used to fix the mechanical connection and thus also to fix the electrical connection of the contact elements 3, 4, 18 to the base body 2, typically in addition to an electrically conductive adhesive connection.

The surface structuring of the contact elements 3, 4, 18, which is carried out for the purpose of improved contacting of the base body 2, is preferably carried out in such a way that the side 34 of the contact element 3, 4, 18 opposite the base body 2 also has a structure which has elevations and / or depressions 28 , 29 includes. These elevations and / or depressions 28, 29 serve to improve the mechanical connection of the protective film 32 to the surface of the contact element 3, 4, 18.

The protective film 32 does not necessarily have to be a film in the actual sense. Any other elastic protective element can serve as protective film 32 in the sense of the invention the main properties of the protective film 32, the sealing of the contact area, in particular the contact surface 5, and the mechanical securing of the electrical contacting are fulfilled.

Since preferably all of the components of the surface heating element 1 involved are designed as layer-forming elements, it is provided according to one embodiment of the invention that the base body 2, the contact elements 3, 4, 18 and possibly the protective films 32 and the insulating elements 23 as (fully or partially laminated layers form a laminate. As already described, the individual components are preferably designed such that the resulting laminate is foldable and / or foldable (e.g. for laying in the window reveal) and / or rollable (e.g. for storage and / or transport). Depending on the application, a piece of the desired length is then cut off from the finished heating element 1, for example as a roll, and installed as part of a heater 10.

The heating element 1 according to the invention is distinguished by the fact that it has a particularly great flexibility in terms of shape, that is, above all, it is particularly flexible, and in particular can also be adapted to irregularly shaped components to be heated. This applies both to the individual components of the heating element 1, in particular the base body 2, the contact elements 3, 4, 18 and the protective films 32 and, if appropriate, the insulating elements 23, and also to the entire heating element 1, in particular when using the Protective film 32 is partially or completely encapsulated into a package.

The heating element 1 according to the invention is preferably manufactured in such a way that a base body 2 serving as a heating resistor in the form of an electrically conductive, flexible sheet-like structure, which contains carbon fibers, with at least two electrical contact elements 3, 4, 18 spaced apart from each other with the base body 2, the contact elements 3, 4, 18 attached to the base body 2 and then the contact surfaces 5 of the contact elements 3, 4, 18 such are changed, in particular changed in shape, that is to say deformed, that they penetrate into the base body 2, more precisely that parts 28, 29, 30 of the contact surface 5 penetrate into the base body 2 at a large number of locations.

The process of structuring the contact surface 5 preferably takes place at the same time as the process of establishing the final mechanical and electrical connection of the contact element 3, 4, 18 with the base body 2 or is identical to this process.

For example, a self-adhesive copper tape 3, 4, 18 is first pre-fixed on an electrically conductive non-woven fabric 2 and pressed onto the non-woven fabric 2 with a suitable pressure roller or the like. Subsequently, micropores 28 are generated on the copper strip 3 with a needle roller or another suitable tool, which enlarge the transition area between the copper strip 3 and the nonwoven fabric 2 for the planned passage of current, thereby optimizing the efficiency of the heating. The microporous surface lines (here in the form of the needled copper tape 3) are then sealed with a highly elastic melting film 32 and mechanically secured in the process. This mechanical securing of the electrical contact serves in particular to ensure that, even when the length of the copper strip 3 changes, it does not lift off the nonwoven fabric 2. Otherwise, the melting film 32 secures the contact, in particular in those cases in which the Heating element 1 is to be wound as a roll or folded and / or folded for the application.

An advantage of the type of production described is that the deformation of the contact element 3, 4, 18 to enlarge the contact area 5, for example the introduction of micropores 28, and the actual contacting of the base body 2 by pressing the contact element 3, 4, 18th be realized by a single common procedural step. This optimizes the manufacturing process for surface heating elements 1.

The invention provides an electrical surface heater 10 which is characterized by the use of at least one of the surface heating elements 1 described. The surface heating 10 also includes a current source 35 (alternating current) that can be connected to the contact elements 3, 4, 18 of the heating element 1, see Fig. 15 . A low-voltage system (transformer) is preferably used as the current source 35. A control unit 36 can be provided for controlling the surface heating 10. In the simplest case, this is an ON / OFF control that takes place via a temperature monitor 37 (sensor), which can be provided, for example, as part of the transformer 35, on the surface of the heating element 1 or in the room in which the surface heater 10 is located. Instead of a temperature sensor or in combination with it, a humidity and / or air pressure sensor can also be used to switch the heater 10. The heating 10 can also be switched on or off simply manually, for which purpose a switch can be provided.

It is particularly advantageous if the heater 10 has a plurality of surface heating elements 1 which are arranged one behind the other or one above the other, ie stacked one on top of the other, so that the radiant heat add up. For heating large areas, a plurality of heating elements 1 can be arranged side by side. Advantageously, adjacent heating elements 1 are then also electrically connected to one another, so that a separate power source, control, etc. is not necessary for each individual heating element 1. The heater 10 can also consist of several heating modules, each heating module comprising one or more surface heating elements 1. The control of the heater 10 can then preferably take place in modules, whereby each heating module can be assigned its own temperature, humidity or air pressure sensor.

The invention provides heating elements 1 with carbon fibers, in which a reliable electrical contacting of the carbon fiber material is ensured in continuous operation even at high currents. These heating elements 1 can be operated with a low-voltage system.

The invention is particularly suitable for heaters 10 in which the heating elements 1 are attached to building structures, such as e.g. are attached to walls and serve to heat the building structure (also as heating), to dry the building structure, to prevent mold or the like from infecting the building structure. Numerous other applications are possible. It is advantageous that the heating is characterized by a very low overall height. It is therefore particularly suitable for cramped installation situations. For example, the heating element 1 to be laid, laminated and provided with electrical connections has a thickness of only 1.5 mm.

A heater 10 has proven to be particularly advantageous, in which thermal insulating elements (not shown) are arranged on the heating element 1 for the purpose of thermal Insulation of one of the two heating surfaces 13 of the base body 2, for example for the insulation of the rear side 12 of the heating element 1. This enables a particularly efficient use of the radiant heat in a defined direction. The combined use of an air cushion film and a reflection layer for directing the radiation heat has proven to be particularly suitable, this combination being arranged on the rear side 12 of the heating element 1.

The embodiments and variants of the invention described above relate primarily, but not exclusively, to the use of low voltage for operating the surface heating element 1.

The heater 10 can advantageously be operated with generally customary transformers, typically with power consumption between 50 and 300 watts. Designed as a low-voltage system and with power consumption of over 300 watts, the heating elements 1, e.g. at a voltage of 12 volts, currents over 25 amps and even with power consumption of over 500 watts at 24 volts, currents over 20 amps are necessary for permanent operation.

It should therefore be pointed out once again that instead of a low-voltage current source (low-voltage current source), a current source 35 fed by a mains voltage can also be used. In particular, an AC mains voltage of 230V can be used at a mains frequency of 50 Hz, as is used in European electricity networks. A transformer, like in Fig. 15 is then not required. Instead, the heater 10 can be connected directly to the power supply, with one still Control unit 36 can take over the control of the surface heating 10.

The use of AC mains voltage has advantages over the use of low voltage. In this way, when the heater 10 is operated on a 230 V / 50 Hz mains voltage system, the increasing fire risk with increasing current strengths can be minimized. An undesirable heat build-up in the areas of the contacting according to the invention between the copper strip and the carbon fibers is avoided, particularly where the contact network is to ensure the actual passage of current.

Even when using the 230Volt / 50Hz mains voltage system, the contacting of the panel heating elements according to the invention is suitable in order to avoid undesirable losses due to the line resistance, which can occur at currents above 20 amperes when contacting panel heating elements that extend over several meters, for example with heating elements in Form of ribbons.

It has proven to be particularly advantageous in the case of supply by AC line voltage that higher surface resistances can be bridged between the contacts with voltages of 230 volts. This allows a particularly flexible design of the geometric shape of the heating elements 1, in particular the use of particularly narrow surface heating elements as "heating surface bands".

With the help of a suitable dimensioning of the electrodes (length and distance of the electrodes), such heating tapes with current strengths between 0.5 and 2.5 amperes and heating powers of 100 to 500 watts and more can be realized. The sink Current strengths to about a tenth compared to a 24 volt low-voltage system, which is particularly advantageous in the case of power consumption of more than 200 to 500 watts and more, because it also protects the copper tape / carbon fiber composite according to the invention from overheating and extends the life of the heating elements 1, by avoiding the creation of "hotspots" even more.

This in Fig. 16 Surface heating element 1 shown is, for example, 300 cm long (length L) and 10 cm wide (width B), so that the aspect ratio of the surface to be heated is 30: 1. The resistance is 99.3 ohms. When operated on a 24 volt low-voltage system, the power is 5.8 watts with a temperature increase of 1.1 ° C. In contrast, when operating on a 230V / 50Hz mains voltage system, the power is 532.7 watts with a temperature increase of 104.5 ° C.

The comparison shows that narrow, with a view to the materials used almost non-metallic heating surface bands with high heat flow density can be realized, which are particularly interesting for applications with possible water contact. The metallic copper content is very low due to the lower current strengths to the total material area, especially in comparison to "metallic" heating systems that generate similar heat flow rates.

It is particularly interesting for universal applicability of the surface heating elements 1 that the heating surface band according to the invention can be dimensioned in the length required for the desired heating output. It is also possible to connect several heating tapes to form a heating element network. By a suitable calculation of the dimensions of the individual heating elements and a suitable one Arrangement of the heating elements or a heating element combination formed therefrom, in particular designed as a series connection of heating segments, corresponding to the desired heatable usable area, the entire application area can be covered with (interconnected) heating elements. Here, as in Fig. 17 shown, not only aspect ratios of the area to be heated of 1: 5, but also aspect ratios of, for example, 1: 1 can be achieved by continuing the series connection accordingly. The total heating output depends, among other things, on the length, width and density of the heating elements of the network.

Fig. 17 shows a simple heating element combination 38 with two heating elements 39, 40 which are connected to one another in a series connection via a cable bridge 41. Advantageously, both connections 24, 25 are provided on the same side of the composite 38, so that line losses due to long connection cables are avoided. In the illustrated example, two segments 39, 40 arranged parallel to one another at a distance A of 10 cm, each with a width B of 10 cm and a length L of 150 cm are connected to one another. With the help of such a heating element assembly consisting of narrow, electrically connected strips, also those application areas can be heated in which, due to their size and / or shape, the use of a single heating element for technical reasons, in particular due to high electrical losses and strong "hotspot" - Education, is not possible.

An arrangement of several, advantageously interconnected, advantageously shaped and dimensioned heating elements in a composite enables a specific application area F, in Fig. 17 indicated by a dash-dotted line, corresponding to the to prove the desired total heating power as densely and / or as regularly as possible.

Reference symbol list

1

Surface heating element

2nd

Basic body

3rd

first contact element

4th

second contact element

5

Contact area

6

surface

7

Preferred direction

8th

Current flow direction

9

(free)

10th

Surface heating

11

front

12

back

13

Heating surface

14

length

15

distance

16

Long side

17th

Narrow side

18th

third contact element

19th

Longitudinal direction

20th

(free)

21

first heating segment

22

second heating segment

23

Insulating element

24th

first power connection

25th

second power connector

26

Connecting cable

27th

Freeers

28

opening

29

deepening

30th

Cutting edge

31

(free)

32

Protective film

33

Security margin

34

Top

35

transformer

36

Control unit

37

sensor

38

Composite

39

Heating element, composite segment

40

Heating element, composite segment

41

Wire bridge

Claims (10)

1. Flat heating element (1),
   comprising a main body (2), which serves as a heating resistor, in the form of an electrically conductive, flexible flat structure which contains carbon fibres,
   comprising at least two electrical contact elements (3, 4, 18), which are connected in a flat manner to the main body (2) at a distance from one another, for feeding electric current into the main body (2),
   wherein the contact areas (5) of the contact elements (3, 4, 18) are formed in such a way that they penetrate the main body (2),
   characterized in that the contact areas (5) of the contact elements (3, 4, 18) have a surface structure with a plurality of deformations (28, 29) which contribute to establishing a connection between the contact elements (3, 4, 18) and the main body (2) by way of penetrating the main body (2).
2. Flat heating element (1) according to Claim 1, characterized in that the main body (2) is formed by a paper or a nonwoven.
3. Flat heating element (1) according to Claim 1 or 2, characterized in that the contact elements (3, 4, 18) are formed by foils or strips.
4. Flat heating element (1) according to one of Claims 1 to 3, characterized in that the main body has a highly uneven aspect ratio and three or more contact elements (3, 4, 18) are mounted on one side (11) of the main body (2) in such a way that the main body (2) is subdivided into a number of heating resistor segments (21, 22) in its longitudinal direction (19).
5. Flat heating element (1) according to one of Claims 1 to 4, characterized in that at least the contact elements (3, 4, 18) and parts of the main body (2) are covered by one or more protective films (32).
6. Flat heating element (1) according to one of Claims 1 to 5, characterized in that at least the main body (2) and the contact elements (3, 4, 18), as layers which are adhesively bonded to one another in a flat manner, form a laminate.
7. Flat electric heater (10) comprising at least one flat heating element (1) according to one of Claims 1 to 6 and comprising a power source (35) which can be connected to the contact elements (3, 4, 18) of the heating element (1).
8. Flat electric heater (10) according to Claim 7, comprising a low-voltage power source (35) or comprising a power source (35) which is fed by a mains voltage.
9. Flat electric heater (10) according to Claim 7 or 8, comprising a plurality of flat heating elements (1) according to one of Claims 1 to 6 which are electrically connected to one another to form a composite heating element.
10. Method for producing a flat heating element (1), in which method a main body (2), which serves as a heating resistor, in the form of an electrically conductive, flexible flat structure which contains carbon fibres, is connected in a flat manner to the main body (2) by way of at least two electrical contact elements (3, 4, 18) at a distance from one another, wherein the contact elements (3, 4, 18) are mounted on the main body (2) and then the contact elements (3, 4, 18), but at least the contact areas (5) of said contact elements, are changed in such a way that they penetrate the main body (2), characterized in that the contact areas (5) of the contact elements (3, 4, 18) have a surface structure with a plurality of deformations (28, 29) which contribute to establishing a connection between the contact elements (3, 4, 18) and the main body (2) by way of penetrating the main body (2).

Images