EP0719074A2 - Manufacturing method for a flexible, multilayered, mechanically resistant element as low-voltage heating element for planar radiators and flexible planar radiator - Google Patents

Abstract

Flexible, flat, composite heating element is produced by laminating a dielectric textile fabric or mat carrier layer (1) with a load bearing fibre layer (2) comprising electrically conductive fibres, esp. carbon, in random, woven or knitted form, and a covering layer (3) of a dielectric textile. The layers (1,2,3) are needled together. In a process variation the electrically conductive layer (2) is coated or pre-impregnated with plastic before or during application to the carrier layer (1) to maintain fibre position. The heating element is claimed and comprises a carrier layer (1) and a conductive layer (2) mechanically connected to the carrier (1) and comprising electrically conductive, non-metallic fibres whose positions are fixed. An additional load-bearing cover layer (3) may be placed over the conductive layer (2). In both cases current connectors are located at both ends (4,5).

Description

The invention relates to a flexible, flat-shaped component in which electrical energy is converted into thermal energy and which can be used for the energy supply of both flexible and mechanically rigid sheet-like temperature radiators, the surface temperature of which is only slightly, i.e. H. approx. 20 K above the ambient temperature and the heating and warming of rooms, containers, pipes and the like. Ä., As is also provided for the direct heating of people and tears residing in buildings.

The known heating systems converting electrical energy into thermal energy are designed as electrical resistance heaters, the thermal energy of which is generated in metallic conductors, predominantly surfaces of radiators or air or liquids heated as a heat transfer medium. When converting electronic energy into thermal energy, the material of the resistance heating heats up to a high temperature in comparison to the desired room temperature and, unless the heat generated is otherwise transferred to the heat transfer medium, it causes heat radiation from the resistance heating to a few 100 K Resistance heater heated above the ambient temperature, acting as a radiator. Experience has shown that with these heating systems, the surrounding area is heated primarily by forced or free convection. Experience has shown that heat radiation, which is also emitted by a radiator at a high temperature, is perceived as unpleasant and is suppressed or not used to heat the room. For this reason, the efficiency of electrical resistance heating systems is unsatisfactory.

When using non-electric heating systems, by lowering the temperatures of the heat transfer medium, ie by introducing low-temperature heating systems with a corresponding increase in the heating surfaces, considerable reductions in the energy requirements of the heaters have been achieved. Low-temperature air heaters have been developed as effective heating systems. Heating systems with a heat transfer based on convection or those based on the circulation of heated air, however, have the disadvantage of considerable dust pollution for the rooms heated with them. Increased dust concentration in combination with low air humidity, as is common with relatively high air temperatures in rooms heated in this way, lead to physiologically uncomfortable conditions and negative effects on the human respiratory tract.

Disadvantages of this type are largely avoided by radiant heating, provided that the heat is supplied to the rooms to be heated or the body to be heated predominantly by heat radiation and only to a small extent by convection and / or by heat conduction, i. H. by heating bodies in the room via radiation-free heat transfer and heat conduction.

There are a number of proposed solutions for this. As electrical resistance heating, they mainly use strip or wire-shaped resistance heating elements. To convert the heat initially generated into radiation energy z. T. flat radiating bodies, for example films or layers of carbon (soot, graphite), electrically conductive ores, ceramics and. a. used. The achievement of a high degree of efficiency for the conversion of electrical energy into infrared radiation energy is opposed by the excessive electrical energy supply per surface area (greater than 300 W / m 2) and the lack of conditions for a loss-free delivery of the supplied energy in the form of radiation energy. Other solutions assume, also for reasons of avoiding too high temperatures and thus the ignition of combustible materials in the area of heating, that the energy input is too low, for example at 80 W / m 2, which requires an increase in the radiant heating surfaces required and a very good one Insulation of a building presupposes.

According to DE-PS 39 22 465, a heating device embedded in a floor covering has become known, which consists of an electrical resistance heater and is embedded in a radiation body layer. This is formed from a film consisting of a mixture that is granular and powdery Contains coal, granular and powdery electrically conductive ores, granular and powdery, semiconductive ceramic materials, resins, metal oxides, zinc earth and the like. According to this solution, the thermal energy generated by the electrical resistance heating is converted into long-wave infrared radiation in the radiation body layer with the aforementioned composition. The heating device designed according to this teaching for a radiant heater can only be used in plate-shaped radiant heaters, ie in rigid flat structures with a considerable plate thickness. In addition, the production is very costly and the use is limited to new cases, with a large on-site installation required having a disadvantageous effect.

Through the published patent application DE-OS 26 19 466 a flat, prefabricated space heating element supplied with electrical energy is known, in which essentially the same amount of electrical energy is converted into heat at all points of its surface, this having a surface heating conductor. This surface heating conductor has a foil shape after the protection request of this published patent application. The current supply to the surface heating conductor takes place on the opposite sides thereof, along an extended line in each case via strips of metal, preferably copper braid strips, which are fastened by sewing or tacking on the edge of the surface heating conductor to produce an electrical contact with the resistance layer of the surface heating conductor. The flat heating conductor has a carrier fabric made of an insulating material, for example glass fibers, which is impregnated with a composition which contains electrical resistance material and is surrounded on both sides for electrical insulation with a non-conductive, mechanically strong film in an airtight and watertight manner. According to this teaching, the carrier fabric forms the strength structure for an electrically conductive film. Of the Conductive film made of electrical resistance material is created by impregnating the support fabric. As a result of this impregnation by means of a dispersion applied to the fibers of the support fabric, the non-conductive fibers are either covered with an electrical layer or an electrically conductive resistance substance is embedded in a film-like manner between the non-conductive fibers of the support fabric, the fibers of the support fabric itself retaining the character of a non-conductive support fabric.

This solution has the disadvantage that the information formulated in this application in the request for protection as a condition for the expected advantages that the same amount of electrical energy is converted into heat at all points of the surface heater is not realized. The reason for this deficiency lies in the disclosed solution itself. The electrically non-conductive support fabric impregnated with a conductive composition, i.e. the resulting electrically conductive film does not show a constant resistance over the surface distribution. The failure of the solution is due to a moisture sensitivity of the composition, a different application of conductive material on the support fabric and an insufficient elasticity of the coating composite. Furthermore, for electrical insulation of the heating conductor, it is surrounded on both sides with a non-conductive, mechanically firm film in an airtight and watertight manner. This includes the poor elasticity justifies.

Furthermore, a rigid electrical surface heating element is offered on the market, which consists of webs and underneath a floor wear layer, e.g. B. consisting of textile flooring is arranged. These sheet-like heating elements have the same structure as that according to the aforementioned Solution from the published patent application. The shortcomings inherent in this panel heater are the same. In particular, this surface heating element shows that it is inelastic and that the film-like layers, ie the impregnated glass fiber fabric embedded in two outer layers, do not form a composite, have different thermal expansion and therefore cannot have a defined surface heating output.

In addition to the deficiencies described, it is inherent in all two previously described surface heating conductors that laying them is very costly and the surface heating elements are very susceptible to faults, since they cannot be loaded at certain points.

To remedy this deficiency of the surface heating elements described above, a solution has become known in which the coated carrier fabric, which is the actual heating conductor, has been replaced by an electrically conductive plastic. Hostaflon, which is known as heat-resistant from spatial research, was used as the plastic. In addition to the advantages of this material, a surface heating element made of this plastic has the disadvantage that it has a relatively high thickness and the size has a limited surface area of a maximum of approximately 1 m². The installation as underfloor heating is therefore costly and very limited.

Furthermore, it has become known from the literature that, because of the electrical and thermal properties of carbon fiber materials, they are suitable as a heating layer on reinforced plastic components. The principle of resistance heating is applied. Exploitation of the above properties only led to a demonstration model consisting of a plastic plate made of glass fiber reinforced polyester resin, which was designed as a heating plate. For this purpose, a carbon fiber fleece was provided between two rigid plastic layers, the carbon fiber layer being electrically connected at both ends to two brass electrodes. Experiments with such a tabular heating plate have resulted in the same being heated to a temperature of approximately 150 ° C. This use of carbon fiber nonwovens as an ohmic resistor for heating purposes did not go beyond an suggestion for other possible uses, for example because carbon fibers are used in flexible yellow plastic webs the transmission of electrical energy to the fibers of the carbon fiber fleece via brass electrodes has failed and has led to inadmissibly high heating of the contact electrodes in the case of larger flat structures.

The demonstration model of a heating plate shown in this literature reference (magazine "Plastverarbeiter" 1988, p. 18 ff) takes into account the properties of the carbon fleece, namely that the carbon fiber fleece cannot be mechanically loaded by itself. If these fibers are not attached to or embedded in plates made of a solid dielectric and the carbon fibers are thereby fixed in their arrangement relative to one another within the fleece, the carbon fiber fleece loses the positive properties of an ohmic resistance. Experiments have shown that the individual carbon fibers disintegrate within the nonwoven fabric due to the friction of the individual fibers with one another, in particular in the event of changing mechanical loads, and the nonwoven fabric has changed into a powder form. This sensitivity of the carbon fiber fleece to mechanical stresses initially precludes its use as an ohmic resistance in mechanically highly stressed fabrics.

The aim of the invention is to increase the overall efficiency in the conversion of electrical energy into heat radiation energy in the case of sheet-like heating elements for large-area radiation heating devices, and thus to lower the heating costs for the operator, and on the other hand to reduce the costs for installing large-area radiation heating devices in which heating elements are used to reduce, as well as to achieve a uniform temperature distribution over the surface of the heating element for radiant heaters and not to limit the use of the same as web material to pure new buildings, whereby the adaptation to different room contours during assembly must be possible without great effort and the same , used as a heating mat, must adapt well to different surface shapes.

The invention is based on the object of converting an electrical energy into heat energy sheet-like flexible heating element with a defined mechanical strength using fibrous or filament-like carbon modifications and with a resistance value that does not change during use, i. H. with a constant heating output for heat-radiating, largely flexible fabrics, within which the dominant heat equivalent from the electrical energy supplied is largely converted into long-wave infrared radiation and at the same time only a weak heating of the heat-radiating fabric itself by no more than 20 K above that Ambient temperature occurs.

This task was predominantly achieved by a method for producing a mechanically resilient sheet-like composite of layers between a mechanically not resilient fiber web and at least one mechanically resilient Solved textile fabric or nonwoven web, in which according to the invention, according to a planar design of a dielectric textile fabric or nonwoven web, there is a mechanically resilient fiber web consisting of electrically conductive fibers, predominantly carbon fibers or a mixture of carbon fibers and non-conductive fibers, for example glass fibers is applied with a disordered arrangement of fibers with regard to their longitudinal and transverse orientation, in the form of a nonwoven fabric or in an ordered state in the form of a woven, knitted or knitted fabric made of carbon fibers, and these webs or a further dielectric, textile fabric web is subsequently applied to the mechanically electrical fiber web with limited load capacity is applied and these are then mechanically connected to one another, for example by needling.

If this sheet-like layer composite is exposed to a higher, and sometimes a point-like, mechanical load, the mechanically limited loadable, electrically conductive fiber web becomes one in the embodiment of the method proposed according to the invention for fixing the position of the carbon fibers in their crossing or contact points Layer composite partially pre-impregnated or coated with a plastic, the pre-impregnation and / or coating of the electrically conductive non-metallic fibers of the fiber web being carried out by means of a filled or unfilled compact or foamed plastic combination consisting of a polymer. Furthermore, according to a further embodiment of the proposed method, the layer composite consisting of carrier layer, fiber web and cover layer is optionally with an application of a plastisol consisting of PVC paste, a high-solid system (PUR) or with an application of a thermoplastic Condition of the polymer melt and then the carrier layer, the fiber web and the cover layer are combined to form a layer composite by applying a joining force.

According to this method, a sheet-like heating element for a flexible heat-radiating flat structure can be produced, in which electrical energy is converted into thermal energy, the heating element consisting of a sheet-like resistance heater containing non-metallic materials, and according to the invention the sheet-like heating element from a carrier layer and a layer thereon or arranged therein and with this mechanically connected, made of electrically conductive, non-metallic fibers, mechanically limited resilient fiber web and the electrically conductive fiber web is provided on its opposite sides with a power supply device enabling the application of a voltage to the fiber web. The sheet-like heating element consists of a mechanically resilient carrier layer, a mechanically resilient cover layer and an interposed and mechanically connected to these aforementioned layers, made of an electrically conductive, mechanically limited resilient fiber web containing no metallic fibers, each of which has a Applying a voltage to the fiber supply enabling power supply device is provided. The sheet-like heating element consists of a layer composite, preferably mechanically produced by needling, between a dielectric textile carrier layer and an electrically conductive fiber web or from a dielectric, textile carrier layer, an electrically conductive fiber web and a dielectric textile top layer. The mechanically limited loadable fiber web consists of electrically conductive fibers, predominantly carbon fibers, these lying in unordered directions with regard to their longitudinal and transverse orientation and forming a nonwoven fabric.

The mechanically limited loadable fiber web consists of a mixture of electrically conductive fibers, or of electrically conductive and non-conductive fibers, predominantly carbon fibers, or a mixture of carbon fibers and glass fibers or / and / or textile fibers, these fibers with respect to their longitudinal and transverse orientation disorderly directions and form a nonwoven fabric. The mechanically resilient fiber web can consist of electrically conductive fibers, predominantly carbon fibers, which are combined into bundles in which a large number of silk-like carbon threads, so-called carbon fiber filaments, are arranged parallel to one another in their longitudinal direction, these carbon fiber bundles being arranged transversely to them Synthetic fiber threads provided in the longitudinal direction are connected to form a fabric-like flat structure, in which the carbon fiber bundles are attached as so-called warp threads and the synthetic fiber threads as so-called weft threads. The mechanically non-resilient fiber web can consist of a flat fabric woven, knitted or knitted from electrically conductive fibers, predominantly carbon fibers or a mixture of electrically non-conductive fibers and carbon fibers. According to the invention, the fleece consisting of carbon fibers has a defined fleece thickness and a microporous structure with cavities that extend into the fleece thickness.

It has been found that the carbon fiber fleece with a specific fleece thickness and a specific fiber density has a radiation coefficient which is very close to that of the ideal "black body", which does not exist in reality. Provided with a certain microporous structure, there are cavities extending between the carbon fibers of the nonwoven fabric which, according to the definition, correspond in their design to that of a "black box", that is to say they form a "black body" with great approximation and as the cause are to be considered for the high radiation coefficient.

Based on these findings, a carbon fiber fleece was used in accordance with the invention which has the desired high degree of conversion of electrical energy used into radiation energy when the carbon fiber fleece is heated within a temperature range of up to 40 ° C.

Finally, in order to ensure the mechanical strength of the carbon fiber fleece according to a further feature of the invention, the fiber fleece forming the sheet-like flexible heating element was coated on one or both sides with a filled or filler-free compact or foamed polymer, the electrically conductive fibers being wholly or partly penetrated by this polymer composition .

The invention will be explained in more detail using an exemplary embodiment. In the drawing below, a sheet-like heating element constructed according to the invention for a flexible heat-radiating sheet-like structure in which electrical energy is converted into thermal energy is shown in section.

A flat-shaped heating element for a flexible, heat-radiating flat structure, consisting of a mechanically resilient sheet-like composite between a mechanically not resilient, electrically conductive, non-metallic fiber web and at least one mechanically resilient, dielectric, predominantly textile woven, knitted, knitted or nonwoven web formed from a dielectric textile carrier layer 1, an electrically conductive fiber web 2 and a further dielectric textile cover layer 3. The electrically conductive fiber web 2 is on opposite sides 4; 5 with one not provided power supply device for applying a voltage to the electrically conductive fiber web. According to the invention, the layered composite is mechanically joined to form a layered composite by so-called needling according to the principle of producing needle felt. The layered composite produced by this method can be subjected to mechanical loads and can be subjected to further processing in and into sheet-like structures and in this itself can take on a supporting function in combination with other materials.

If this sheet-like layer composite is exposed to a higher, and in some cases a point-like, mechanical load, the mechanically limited loadable, electrically conductive fiber web 2 is closed before or during processing in order to fix the position of the carbon fibers in their crossing or contact points a layer composite partially or completely pre-impregnated or coated with a plastic, the pre-impregnation and / or coating of the electrically conductive non-metallic fibers of the fiber web being carried out by means of a filled or unfilled compact or foamed plastic combination consisting of a polymer, and the carbon fibers are not electrically are isolated from each other, but only coated or a polymer composition is inserted between them, for example. Furthermore, according to a further embodiment of the proposed method, the layer composite consisting of backing layer 1, fiber web 2 and top layer 3 is optionally coated with a plastisol consisting of PVC paste, a high-solid system (PUR) or with a single layer provided in the thermoplastic state of the polymer melt and then the carrier layer 1, the fiber web 2 and the cover layer 3 are combined to form a layer composite using a joining force.

The advantages of this invention are that, on the one hand, a heating element has been developed in which, by using a nonwoven predominantly made of carbon fibers as a radiating fiber web, a high degree of conversion of electrical energy fed into heat radiation when the surface of the fiber web is heated does not exceed a permissible temperature limit of 28 ° C because the structure of this nonwoven comes very close to that of an ideal black body. On the other hand, the method according to the invention ensures that the fiber web used, consisting of carbon fibers, can be subjected to mechanical loads, as a result of which the carbon fiber fleece in the present embodiment can be introduced as a heating element in heat-radiating flexible flat structures.

Claims (13)

Method for producing a mechanically resilient, flexible, sheet-like layer composite between a mechanically non-resilient fiber web and at least one mechanically resilient, predominantly textile fabric or nonwoven web, characterized in that after a sheet-like design, a carrier layer consisting of a dielectric textile fabric or nonwoven web (1 ) a fiber web (2) consisting of electrically conductive fibers, predominantly carbon fibers or a mixture of carbon fibers and non-conductive fibers, for example glass fibers, with a mechanically limited load capacity with a disordered arrangement of fibers with regard to their longitudinal and transverse orientation in the form of a Non-woven fabric or in an ordered state in the form of a woven fabric, knitted fabric or a knitted fabric made of carbon fibers and these webs or another dielectric cover layer (3) consisting of a textile fiber web is then a uf the mechanically limited loadable, electrically conductive fiber web (2) is applied and these needled together and thereby mechanically connected to each other. Method for producing a mechanically resilient, flexible, sheet-like layer composite between a mechanically not resilient fiber web and at least one mechanically resilient, predominantly textile woven or nonwoven web, characterized in that after a planar design, a carrier layer consisting of a dielectric, textile woven or nonwoven web ( 1) on this a mechanically resilient, made of electrically conductive fibers, mainly carbon fibers or a mixture of carbon fibers and non-conductive fibers, for example glass fibers, existing fiber web (2) with a disordered arrangement of fixed fibers with respect to their longitudinal and transverse orientation in Form of a nonwoven fabric or in an ordered state in the form of a woven fabric, knitted fabric or a knitted fabric made of carbon fibers, which before or during the application of a pre-impregnation or coating with a plastic two The position of the carbon fibers has been fixed, and these webs or a further dielectric cover layer (3) consisting of a textile web is then applied to the electrically conductive fiber web (2) which can be mechanically loaded within defined limits and needled with one another and thereby mechanically with one another get connected. A method according to claim 2, characterized in that the electrically conductive fiber web (2) consisting of non-metallic fibers prior to being arranged in a layer composite by means of a filled or unfilled compact or foamed plastic composition, preferably consisting of polymers, for fixing the fibers in position their crossing or contact points while maintaining the electrical contact between the fibers and the flexibility of the fiber web (2) is surface-coated or partially impregnated. Method according to claim 1 or 2 and 3, characterized in that the layer composite, consisting of the carrier layer (1), the fiber web (2) and the cover layer (3), optionally with an application of a plastisol consisting of PVC paste a high-solid system (PUR) or from a thermoplastic polymer melt and then the carrier layer (1), the fibrous web (2) and the cover layer (3) are combined to form a layered composite using a joining force. Sheet-like flexible heating element for a flexible heat-radiating sheet-like structure in which electrical energy is converted into thermal energy and the heating element consists of a sheet-like resistance heater containing non-metallic materials, characterized in that the sheet-like heating element consists of a carrier layer (1) and a layer arranged thereon and with this mechanically connected fiber web (2) consisting of electrically conductive, non-metallic fibers, mechanically limited or with a position-stabilized fiber fixation within defined limits, and the electrically conductive fiber web (2) on its opposite sides (4; 5) with one each the application of a voltage to the fiber web (2) enabling power supply device is provided. Flat-shaped flexible heating element for a flexible, heat-radiating flat structure in which electrical energy is converted into thermal energy and the heating element consists of a flat heating resistor containing non-metallic materials, characterized in that the flat-shaped heating element consists of a mechanically resilient carrier layer (1) and a mechanical one resilient cover layer (3) and a fiber web (1) arranged therebetween and mechanically connected to it, consisting of electrically conductive, non-metallic fibers, mechanically resilient or within defined limits, and the electrically conductive fiber web on its opposite sides (4; 5 ) is each provided with a power supply device which enables a voltage to be applied to the fiber web (2). Sheet-like flexible heating element according to claim 1 or 2 to 6, characterized in that the sheet-like heating element consists of a layered combination mechanically produced by needling between a dielectric textile carrier layer (1) and an electrically conductive fiber web (2) or a dielectric textile carrier layer, an electrically conductive layer Fiber web (2) and a dielectric textile cover layer (3). Sheet-like flexible heating element according to claim 1 or 2 to 7, characterized in that the fiber web (2), which is mechanically limited or can be loaded within defined limits, is made of electrical material conductive fibers, predominantly carbon fibers, which are in their longitudinal and transverse orientation in disordered directions and form a nonwoven fabric. Sheet-like flexible heating element according to claim 1 or 2 to 8, characterized in that the mechanically limited or resilient fiber web (2) consists of a mixture of electrically conductive and electrically non-conductive fibers, predominantly a mixture of carbon fibers and glass fibers or and / or Textile fibers are made, these fibers lying in unordered directions with respect to their longitudinal and transverse orientation and forming a nonwoven fabric. Sheet-like flexible heating element according to claim 1 or 2 to 9, characterized in that the mechanically limited or within certain limits resilient fiber web (2) consists of electrically conductive fibers predominantly carbon fibers, which are combined into bundles in which a large number of silk-like carbon threads, so-called Carbon fiber filaments are arranged parallel to one another in their longitudinal direction, these carbon fiber bundles being connected to a fabric-like flat structure by means of plastic fiber threads provided transversely to their fiber longitudinal direction, in which the carbon fiber bundles are arranged as so-called warp threads and the plastic fiber threads as so-called weft threads. Sheet-like flexible heating element according to claim 1 or 2 to 10, characterized in that the fiber web (2), which is mechanically limited or can be loaded within defined limits, consists either of a nonwoven fabric formed by electrically conductive fibers, predominantly carbon fibers or a mixture of electrically non-conductive fibers and carbon fibers , consists of carbon fiber filaments or a knitted or knitted carbon fiber sheet. Sheet-like flexible heating element according to claim 1 or 2 to 11, characterized in that the fiber fleece consisting of carbon fibers has a defined fleece thickness and a microporous structure with cavities extending into the fleece thickness. Flat flexible heating element according to claim 1 or 2 to 12, characterized in that the non-woven fabric forming the heating element has been coated on one or both sides with a filled or filler-free compact or foamed polymer, the electrically conductive fibers being wholly or partly penetrated by the polymer composition.

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